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Insulin Resistance and the Polycystic OvarySyndrome Revisited: An Update on Mechanisms

and Implications

Evanthia Diamanti-Kandarakis and Andrea Dunaif

Medical School, University of Athens (E.D.-K.), Athens GR-14578, Greece; and Northwestern University FeinbergSchool of Medicine (A.D.), Chicago, Illinois 60611-3008

Polycystic ovary syndrome (PCOS) is now recognized as an important metabolic as well as reproductivedisorder conferring substantially increased risk for type 2 diabetes. Affected women have marked insulinresistance, independent of obesity. This article summarizes the state of the science since we last reviewedthe field in the Endocrine Reviews in 1997. There is general agreement that obese women with PCOS areinsulin resistant, but some groups of lean affected women may have normal insulin sensitivity. There is apost-binding defect in receptor signaling likely due to increased receptor and insulin receptor substrate-1serine phosphorylation that selectively affects metabolic but not mitogenic pathways in classic insulintarget tissues and in the ovary. Constitutive activation of serine kinases in the MAPK-ERK pathway maycontribute to resistance to insulins metabolic actions in skeletal muscle. Insulin functions as a co-gonad-otropin through its cognate receptor to modulate ovarian steroidogenesis. Genetic disruption of insulinsignaling in the brain has indicated that this pathway is important for ovulation and body weight regu-lation. These insights have been directly translated into a novel therapy for PCOS with insulin-sensitizingdrugs. Furthermore, androgens contributeto insulin resistance in PCOS.PCOS may alsohave developmentalorigins dueto androgen exposure at critical periods or to intrauterinegrowth restriction.PCOSis a complexgenetic disease, and first-degree relatives have reproductive and metabolic phenotypes. Several PCOSgenetic susceptibility loci have been mapped and replicated. Some of the same susceptibility genes con-tribute to disease risk in Chinese and European PCOS populations, suggesting that PCOS is an ancient trait.(Endocrine Reviews 33: 9811030, 2012)

I. Background and Historical PerspectiveA. Reproduction and metabolismB. Experiments of naturerare syndromes of extreme

insulin resistance and hyperandrogenismC. Insulin resistance and PCOS

II. PCOS Reproductive PhenotypeA. Clinical featuresB. Biochemical profileC. Polycystic ovaries

III. Diagnostic Criteria for PCOSA. Development of diagnostic criteria for PCOSB. National Institutes of ChildHealth and Human De-

velopment (NICHD)C. RotterdamD. Androgen Excess Society (AES)E. Impact of diagnostic criteria on PCOS phenotypesF. Epidemiology

IV. PCOS Metabolic PhenotypeA. Glucose toleranceB. Insulin resistance

C. Other metabolic actions of insulin in PCOSD. Mitogenic actions of insulin in PCOSE. Insulin secretion in PCOSF. Insulin clearance in PCOSG. Obesity and PCOS

V. Mechanisms for the Association of Insulin Resistanceand PCOSA. Insulin as a reproductive hormoneB. Metabolic actions of androgensC. Genetic susceptibility to PCOSD. Developmental origins of PCOS

VI. Implications and Future Directions

ISSN Print 0163-769X ISSN Online 1945-7189Printed in U.S.A.Copyright 2012 by The Endocrine Societydoi: 10.1210/er.2011-1034 Received August 8, 2011. Accepted July 9, 2012.First Published Online October 12, 2012

Abbreviations: AIRg, Acute insulin response to glucose; BMI, body mass index; CI, confi-dence interval; CNS, central nervous system; DHEA, dehydroepiandrosterone; DHEAS,DHEAsulfate; DI,disposition index; eIF2B, eukaryotic initiationfactor2B; FSIGT, frequentlysamplediv glucosetolerance test; GLUT, glucosetransporter;GnRHa,GnRHanalog;GSK3,glycogen synthase kinase-3; GWAS, genome-wide association studies; IGT, impaired glu-cose tolerance; IMGD, insulin-mediated glucose disposal; IRS, insulin receptor substrate;ISD, insulin-sensitizing drug; MEK, MAPK kinase; MRI, magnetic resonance imaging;mTOR, mammalian target of rapamycin; OGTT, oralglucosetolerance test; OR,odds ratio;PCO, polycystic ovaries; PCOS, polycystic ovary syndrome; PI3-K, phosphatidylinositol 3-kinase; PKB, protein kinase B; PKC, protein kinase C; PTEN, phosphatase and tensionhomolog deleted on chromosome 10; PTP1B, protein tyrosine phosphatase 1B; Shc, srchomolog and collagen homolog; SNP, single nucleotide polymorphism; T, testosterone;TCF7L2, transcription factor 7-like 2 (gene); T2D, type 2 diabetes; TDT, transmission dis-equilibrium test; TZD, thiazolidinedione.

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I. Background and Historical Perspective

A. Reproduction and metabolism

The pathways linking reproductive function with met-abolic cues are evolutionarily conserved traits thatare present in Caenorhabditis elegans and Drosophila (1,

2). The reproductive features of polycystic ovary syn-drome (PCOS) were noted by Hippocrates in the fifth cen-tury B.C. (3). The observation that signs of androgen ex-cess were coupled with metabolic abnormalities, such asincreased visceral fat, dates back to at least the 18th cen-tury. In 1765, Morgagni (4) reported detailed anatomicinvestigations in various conditions. He described a 74-yr-old woman with severe obesity and android aspect(valde obesa et virili aspectu). In 1921, Achard and Thiers(5) reported the coexistence of diabetes mellitus with clin-ical signs of androgen excess in a postmenopausal wom-

anthe so-called Achard-Thiers syndrome or diabe-tes of the bearded women (diabete des femmes a barbe). Jean Vague (6) from the University of Marseille intro-duced the term android obesity to define the abdominalfataccumulation,which is thetypicalmalepattern ofbodyfat distribution, and started to explore the concept thatthis type of body adiposity was associated with increaseddiabetes and cardiovascular disease risk. Elegant studiesby Kissebah etal . (7) documented that women with upperbody obesity were insulin resistant.Thesewomen also hadincreased androgen production rates (8).

B. Experiments of naturerare syndromes of extremeinsulin resistance and hyperandrogenism

In the 1970s, several rare syndromes of extreme insulinresistance, acanthosis nigricans, and hyperandrogenismwere described (9). The molecular mechanisms of insulinresistance in these syndromes involved reduced insulinbinding to its receptor or defective receptor autophos-phorylation due to insulin receptor mutations (Type Asyndrome, Rabson-Mendenhall syndrome, Donohuesyndrome, or leprechaunism) or insulin receptor auto-antibodies (type B syndrome) (1012). The phenotyp-ically distinct disorders of familial lipodystrophy andextreme insulin resistance were also noted to be asso-ciated with signs and symptoms of hyperandrogenism(1215). The common feature of these syndromes wasprofound hyperinsulinemia, which suggested for thefirst time that insulin might directly stimulate testos-terone (T) production (9, 11).

C. Insulin resistance and PCOSThe original description of enlarged, smooth polycystic

ovaries (PCO) is credited to Chereau in 1844 (16). In the19th century, ovarian wedge resection became a recom-

mended therapy (17), although Stein and Leventhal (18)first reported that the clinical features of menstrual regu-larityand infertility could be improved by removal of por-tions of both ovaries. As a result, the constellation of en-larged, sclerocystic ovaries frequently associated withhirsutism, menstrual irregularity, obesity, and infertilitybecame known as the Stein-Leventhal syndrome (17, 19).In recent decades, PCOS has become the preferred termi-nology(17, 20). Until the 1980s,PCOS remained a poorlyunderstood reproductive disorder (17, 19). In 1980, Bur-ghen et al . (21) reported that women with PCOS had in-creased insulin responses during oral glucose tolerancetesting that were not accounted for by obesity. Further-more, women with typical PCOS had acanthosis nigri-cans,raisingthepossibility thattheywere insulin resistant,similar to women with the rare syndromes of extreme in-sulin resistance (22, 23). These observations launched anew field of study on the mechanisms for the associationbetween insulin resistance and PCOS (Fig. 1).

II. PCOS Reproductive Phenotype (Fig. 2)

A. Clinical featuresApproximately 60% of women with PCOS are hirsute,

the most common clinical sign of hyperandrogenemia(24). Acne andandrogenic alopecia areother clinical signsof hyperandrogenemia (2532). Acanthosis nigricans is a

skin lesion characterized clinically by velvety, papilloma-tous, brownish-black, hyperkeratotic plaques, typicallyon the intertriginous surfaces and neck. However, acan-thosis nigricans is diagnosed definitively by histologicalexamination of the skin showing hyperkeratosis and pap-illomatosis, frequently with hyperpigmentation (33). It isevident on clinicalexamination in a substantialpercentageofobesewomenwithPCOSaswellasinsomeleanaffectedwomen. However, it is present in the majority of obesewomen with PCOS and in obese control women by his-tologicalexamination(33).Many lean women with PCOSalso show histological evidence of acanthosis nigricans(33). Its severity is directly correlated with the degree of insulin resistance (33, 34).

Oligomenorrhea is defined as menstrual cycles that arelonger than 35 d (usually fewer than eight cycles per year)and is a sign of anovulatory cycles (35). However, regularmenstrual cycles do not exclude chronic anovulation, es-pecially in women with clinical signs of androgen excess(24). Twenty to 50% of women with clinical hyperandro-genism and apparent eumenorrhea may have anovulationas documented by consecutive luteal serum progesteronelevels in the follicular range (24). Therefore, ovulationshould be assessed by measuring serum progesterone con-

982 Diamanti-Kandarakis and Dunaif Insulin Resistance and PCOS Endocrine Reviews, December 2012, 33(6):9811030



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centration duringthelutealphase of themenstrualcycle inwomen with regular menses and androgenic signs orsymptoms (24).

B. Biochemical profile

1. Sex hormones

Hyperandrogenemia is the biochemical hallmark of PCOS (24). Elevated circulating androgen levels are ob-served in 8090% of women with oligomenorrhea (24,36). Elevated levels of free T account for the vast majorityof abnormal findings in the laboratory examination (24,37). This finding reflects the fact that SHBG levels aretypicallydecreasedinPCOSduetotheeffectsofT(38)andinsulin (39) to decrease hepatic production of SHBG.

The measurement of total and free T levels is con-strained by theavailableassay methods. Assaysfor total Tlack precision and sensitivity in the female T range, in-cluding T levels typical of PCOS (40, 41). The accuratemeasurement of free T by equilibrium dialysis is techni-cally challenging and costly, whereas direct measurementof free T is inaccurate (41, 42). Measurements of total T byRIA or liquid chromatography-mass spectrometry in a spe-cialized endocrine laboratoryarecurrently thebestavailablemethodologies(43).Free andbiologically available T canbecalculated from the concentrations of total T, SHBG, andalbumin by using the affinity constants of T for these mole-cules (42).In practice,albumin isoftennotmeasured,andanassumed normal value is used in the calculation.

Whether the concurrent measurement of androstene-dione increases thediagnosisof hyperandrogenemia is un-

clear (24, 37). Approximately 25% of womenwith PCOS will have elevated levels of dehy-droepiandrosterone sulfate (DHEAS) (24),which may be the sole abnormality in circulat-ing androgens in approximately 10% of thesewomen (24).

Although the ovaries are the main sourceof increased androgens in PCOS (44), adre-nal androgen excess is a common feature of the syndrome (24, 45). The prevalence of ad-renal androgen excess is approximately20% among white women and 30% amongblack women with PCOS using age- and race-adjusted normative values for circulatingDHEASlevels(24,45).WomenwithPCOSdem-onstrate increased secretion of adrenocorticalprecursor steroids basally and in response to

ACTH stimulation including pregnenolone, 17-hydroxypregnenolone, dehydroepiandrosterone(DHEA), androstenedione, 11-deoxycortisol,and possibly cortisol (45, 46).

Estradiol levels areconstantly in the early tomidfollicularrangewithout the normal midcycle increases(47, 48). Estrone levels are increased (47) because of ex-traglandular aromatization of increased circulating an-drostenedione levels (49). The decreased SHBG levels typ-ical of PCOS result in increased non-SHBG bound orbioavailable estradiol as well as T levels (38, 50, 51).

2. GonadotropinsAlthough PCOS is considered a part of the spectrum of

normogonadotropic normoestrogenic anovulation (35),serum LH concentrations and the LH to FSH ratio arefrequently elevated in affected women (52). FSHlevels arenormal to slightly suppressed and do not increase tothreshold levels required during the early follicular phaseof the menstrual cycle to stimulate normal follicular mat-uration (53). However, gonadotropin levels have neverbeen included in any of the diagnostic criteria for PCOSbecause the characteristic derangements can escape detec-tion on random blood samples because of the pulsatilenature of LH release (24, 5456). Furthermore, LH levelsmay be lower in obese women with PCOS and may de-crease after an ovulatory cycle in oligo-ovulatory affectedwomen (56, 57).

C. Polycystic ovariesPCO are characterized by an increase in antral follicles

andovarianstromaas well as by thecacell hyperplasiaandovarian cortical thickening (55, 58). Careful histologicalexamination of PCO has revealed an excess of growingfollicles, the number ofwhich is2- to3-fold thatofnormal

Figure 1.

Figure 1. A new fieldPCOS and insulin resistance. The first article reporting anassociation between PCOS and hyperinsulinemia was published in 1980 (21). There areapproximately 103,000 citations in a Web of Science (Thomson Reuters, New York, NY)

Citation Report for 19802011 on the topics of PCOS or hyperandrogenism andhyperinsulinemia, insulin resistance, glucose intolerance, or diabetes mellitus. The annualcitations have increased steadily from 1 in 1980 to approximately 12,000 in 2011. Thisfigure was created from the Web of Science Citation Report.




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ovaries (58). A more recent study of ovarian cortical bi-opsies from normaland PCOS women (59) confirmedthisobservation, finding that the number of small, preantralfollicles, both primordial and primary follicles, was sub-stantially increased in anovulatory PCO compared withnormal ovaries. In both ovulatory and anovulatory PCO,the proportion of early growing (primary) follicles is sig-nificantly increased, with a reciprocal decrease in the pro-portion of primordialfolliclescompared withnormal ova-ries (59). These differences are particularly striking inanovulatory PCO (59). There is decreased atresia of fol-licles from PCO in culture compared with those from nor-mal ovaries (60). Markers of cell proliferation are signif-icantly increased in granulosacellsfromanovulatory PCO(61). Thus, it now appears that the gonadotropin-inde-pendent development of preantral follicles is disorderedinPCOS (62). The excess of follicles could result from ac-celerated follicle growth and/or prolonged survival of small follicles in comparison to follicles from normal ova-ries (59, 60, 62).

Theca cells from PCO secrete more androgens, ba-sally and in response to LH and insulin (63), due toconstitutive increases in the activity of multiple steroid-

ogenic enzymes in these cells (64). Thus,enhanced ovarian androgen production inPCOS results from the combined effects of intrinsically increased thecal androgen secre-tion and increased responsiveness to trophichormone stimulation. Whereas the increasesin androgen production are found in thecacells isolated from ovulatory as well as an-ovulatory women with PCOS (63), granu-losa cell steroidogenesis differs by ovulatorystatus (62, 65). Granulosa cells from ovula-tory women with PCO are similar in terms of responses to FSH and estradiol production tothose from normal women (65, 66). In con-trast, granulosa cells isolated from somesmall-to-medium sized antral follicles ob-tained from anovulatory women with PCO

showed increased estradiol production in re-sponse to FSH and premature responsivenessto LH (65, 66). These abnormalities maycontribute to the arrest of follicular develop-ment. However, the arrest of antral follicledevelopment in the otherwise normal folliclepopulation is most likely accounted for bylower circulatingFSH levels because FSH ad-ministration can produce normal follicularmaturation and ovulation (62, 67, 68).

III. Diagnostic Criteria for PCOS (Table 1)

A. Development of diagnostic criteria for PCOSAll of the diagnostic criteria for PCOS (24, 54, 6971)

have been based on expert opinion, the lowest level of evidence (7275). None of these criteria were based on aformal consensusprocess (75, 76). In theUnited States, theNational Institutes of Health (NIH) Consensus Develop-ment Program, administered by the Office of Medical Ap-plications of Research, which has recently become part of the Office of Disease Prevention (http://consensus.nih.gov/), is a widely accepted consensus process (77, 78).

Figure 2.

Figure 2. Pathophysiology of the PCOS reproductive phenotype. There isincreased frequency of pulsatile GnRH release that selectively increases LHsecretion. LH stimulates ovarian theca cell T production. T is incompletelyaromatized by the adjacent granulosa cells because of relative FSH deficiency.There are also constitutive increases in the activity of multiple steroidogenicenzymes in polycystic ovaries contributing to increased androgen production.Increased adrenal androgen production may also be present in PCOS. T acts inthe periphery to produce signs of androgen excess, such as hirsutism, acne, andalopecia. T and androstenedione can also be aromatized extragonadally toestradiol and estrone, respectively, resulting in unopposed estrogen action onthe endometrium. T feeds back on the hypothalamus to decrease the sensitivityto the normal feedback effects of estradiol and progesterone to slow GnRH pulsefrequency. This figure is used with the permission of Andrea Dunaif.

TABLE 1. Diagnostic criteria for PCOS

CriteriaNICHD (54) Both hyperandrogenism and chronic anovulationRotterdam (69, 70) Two of the following: hyperandrogenism, chronic

anovulation, and PCOAndrogen Excess

Society (24, 71)Hyperandrogenism plus ovarian dysfunction

indicated by oligoanovulationand/or PCO

All criteria require exclusion of other disorders: hyperprolactinemia, nonclassiccongenital adrenal 21-hydroxylase deficiency, thyroid dysfunction, androgen-secreting neoplasms, and Cushings syndrome.




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These conferences have a court model where there is apresentation of evidence to a panel that functions as a jury(http://consensus.nih.gov/FAQs.htm#whatistheCDP).The panel is made up of individuals who are experts intheir own fields but are not closely aligned with the sub-ject. Thus, these Consensus Development Conferencespermit an independent assessment of the issues in the fieldby an unbiased panel. An NIH conference on PCOS usingthis court model will be held in December 2012.

B. National Institutes of Child Health and HumanDevelopment (NICHD)

After a series of landmark studies in the 1980s identi-fying insulin resistance as a cardinal feature of the syn-drome (21, 34, 79 81), the metabolic sequelae of the dis-order began to be appreciated. This renaissance of interestin PCOS created a need for a better working definition of

the syndrome; an issue of that was addressed at the 1990NICHD Conference on PCOS (20). This conferencewas ameeting of experts who discussed various features of thesyndrome. Participants were asked to vote on potentialdiagnostic features (Table 2); those receiving the mostvotes, hyperandrogenism and chronic anovulation, withthe exclusion of secondary causes, became what areknown as the NICHD or NIH criteria (54) and are oftenand inaccurately referred to as consensus criteria. TheNICHD criteria did not include ovarian morphology be-cause of the lack of specificity of this finding (54). It wasclear at that time that 2030% of women with regularmensesandnoandrogenic symptomshadPCO on ovarianultrasound examination (82). Many of these women didhave elevated circulating T and/or LH levels (82). Fur-thermore, almost 10% of women with PCOS defined byNICHD criteria did not have PCO (83).

C. RotterdamIn Europe, ovarian imaging was used for the diagnosis

PCOS (27, 84, 85). Moreover, with the widespread use of assisted reproductive technologies, it became evident thatwomen with PCO, even those who were reproductivelynormal, were hyperresponsive to exogenous gonadotro-

pin stimulation and thus at risk for ovarian hyperstimu-lation syndrome (8688). Accordingly, defining ovarianmorphology became an essential component of infertilitymanagement (88). In 2003, another conference on diag-nostic criteria was convened in Rotterdam (70). Despitebeing identified as a consensusconference, the recommen-dations were also based on expert opinion rather than aformal consensus process.

Theresultof theconference wasthat polycystic ovarianmorphology on ultrasound examination was added to theNICHD diagnostic criteria (70). The Rotterdam criteria(69, 70) for the diagnosis of PCOS required the presenceof two of the following findings, after the exclusion of disorders of the pituitary, ovary, or adrenals that couldpresent in a manner similar to PCOS: 1) hyperandro-genism (clinical or biochemical); 2) chronic anovulation;and 3) PCO (Table 1). These criteria have extended thediagnosis to include two new groups of affected women:1) PCO and hyperandrogenism without chronic anovula-tion; and 2) PCO and chronic anovulation without hy-perandrogenism (71) (Fig. 3).

D. Androgen Excess Society (AES)The Rotterdam Criteria do not discriminate between

the cardinal features of PCOS, placing equal diagnosticimportance on PCO, chronic anovulation, and hyperan-drogenism (24, 71). In 2006, an expert panel of the AESrecommended criteria that hyperandrogenism be consid-

ered as an essential component of PCOS (71). These cri-teria require the combination of biochemical or clinicalhyperandrogenism with chronic anovulation or PCO (24,71)(Table 1).Nevertheless, theseAEScriteriaincludedtheadditional phenotypeof hyperandrogenism, ovulatorycy-cles and PCO (71) (Table 3).

E. Impact of diagnostic criteria on PCOSphenotypes (Table 3)

Even before Rotterdam, studies (34, 89) had suggestedthat these additional subgroups differed metabolicallyfrom the group with classic PCOS identified by theNICHD criteria (Fig. 4). Women with ovulatory cyclesand hyperandrogenemia (34) or PCO (89) had normalinsulin sensitivity. Furthermore, ovarian morphology didnot correlate with the severity of symptoms in PCOS (90,91). The hyperandrogenic woman with PCO but docu-mentednormal ovulationwas recognizedasa distinctphe-notype of PCOS by both the Rotterdam criteria and theAES criteria (24, 70, 71) (Table 3). It has been suggestedthat this ovulatory form of PCOS may represent a transi-tional, intermediate stage between normality and theclassic anovulatory form of PCOS. Women with this phe-notype are often leaner than those with classic PCOS (92

TABLE 2. Percentage of participants agreeing onvarious criteria at 1990 NICHD PCOS conference (54)

Definite or probable PossibleHyperandrogenemia, 64% Insulin resistance, 69%Exclusion of other etiologies, 60% Perimenarchal onset, 62%Exclusion of CAH, 59% Elevated LH/FSH, 55%Menstrual dysfunction, 52% PCO by ultrasound, 52%Clinical hyperandrogenism, 48% Clinical hyperandrogenism, 52%

Menstrual dysfunction, 45%

CAH, Congenital adrenal hyperplasia.




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94). In addition,theyhavemilder metabolicabnormalitiesor may even be metabolically normal (92, 95103). ThisPCOS group may potentially convert to classic PCOS un-der the influenceof environmental factors like weightgain(104).However,therehave been no longitudinalstudies tofollowthe natural courseof women with ovulatoryPCOS.

The anovulatory woman with normal androgen levelsand PCO is a second distinct phenotype of PCOS accord-ing to the Rotterdamcriteria (24, 71) (Table3). Women inthis group most often have normal insulin sensitivity (97100). Women with ovulatory cycles and PCO but no hy-perandrogenismdo notfulfillNICHD, Rotterdam, or AEScriteria for PCOS (Table 3). However, these groups of nonhyperandrogenic women with PCO may have subtleendocrine aberrations, like higher LH and lower SHBGlevels (82, 92, 97, 99). Moreover, they may have hyperan-drogenic responses to GnRH analog(GnRHa) testing, de-spitenormalandrogen levelsat baseline (95, 105).Women

with isolated PCO are at increased risk to de-velop ovarian hyperstimulation during ovula-tion induction, analogous to women with hy-perandrogenic forms of PCOS (88). PCOfromovulatorywomen do have abnormalities in fol-liculogenesis (62) and constitutive increases inthecacell androgenproduction (62, 63). Takentogether, these findings suggest that PCO haveconstitutive increases in androgen biosynthesisandresponsiveness to gonadotropins in theab-sence of ovulatory disturbances (62, 106).

However, a follow-up study of eumenor-rheic women with the isolated PCO has shownthat this ultrasound finding is unstable and ir-reproducible across the reproductive period(91). Women with PCO at baseline did notdemonstrate any tendency to develop PCOS

during the follow-up arguing against the hy-pothesis that PCO could represent an early,preclinical stage in the natural continuum of PCOS (91). The prevalence of PCO is also age-related and decreases in frequency with in-creasing age (103). There appears to be a ge-netic susceptibility to PCO because they arehighly heritable in affected sister pairs (107).

F. EpidemiologyPCOS is now recognized as one of the most common

endocrinopathies in women of reproductive age with aprevalence of 410% for the NICHD defined form (108111). These prevalence estimates for PCOS using theNICHD criteria are remarkably consistent across racialand ethnic groups (108, 109, 111113). This observationsuggests that PCOS is an ancient evolutionary trait thatwas present before humans migrated out of Africa. Therecent confirmation in European PCOS cohorts (114,115) of two gene loci identified in a genome-wide associ-ation of Han Chinese women with PCOS (116) supportsthis hypothesis (the genetics of PCOS is discussed later inSection V.C. ). There is, however, variation in the pheno-types of PCOS in many ethnic/racial groups, such as Lati-nas (117,118),African-Americans (119), Icelanders(120)SriLankans (93),Koreans (121),and Chinese (100).How-ever, a recent study comparing Black and White womenwith PCOS found no differences in reproductive featuresand mild differences in metabolic features (119).

PCOS is the most common cause of normogonado-tropic anovulation, accounting for 5591% of the entireWorldHealth Organization-II (WHO-II)cohort (35).Theprevalence of PCOS is higher using the 2003 Rotterdamcriteria because it includes additional phenotypes (70)(Table 3). The Rotterdam-PCOS group was 1.5 times

Figure 3.

Figure 3. Features of PCOS. The diagnostic criteria for PCOS (Table 1) include two ormore of these features: hyperandrogenism ( blue circle), anovulation ( pink circle),and PCO ( green circle ), resulting in several PCOS phenotypes depending on thediagnostic criteria applied (Table 3). This figure is used with the permission of AndreaDunaif.

TABLE 3. PCOS phenotypes according to diagnosticcriteria applied

HA andAnov

HA andPCO

Anov andPCO HA PCO Anov

NICHD Rotterdam AES

HA, Hyperandrogenism; Anov, chronic anovulation.




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larger than the group classified as NICHD PCOS amongwomen with normogonadotropic anovulation (35). Al-though PCOS is commonly associated with obesity, thereis no evidence that the prevalence of PCOS is increasingwith the increasing prevalence of obesity (122).

IV. PCOS Metabolic Phenotype

A. Glucose tolerance (Fig. 5)Despite the fact that hyperinsulinemia reflecting some

degreeof peripheralinsulin resistance waswell recognizedin PCOS by the mid 1980s, glucose tolerance was notsystematically investigated until 1987 (49). This study re-ported that obese women with PCOS had significantlyincreased glucose levels during an oral glucose tolerancetest (OGTT) compared with age- and weight-comparablereproductively normal control women. However, obeseovulatory hyperandrogenemic women had OGTT-glucose responses similar to control women, suggestingthat derangements in glucose homeostasis were a featureof the anovulatory PCOS phenotype ( i.e., NICHD criteriaPCOS) rather than hyperandrogenemia per se. Twentypercent of the obese women with PCOS met criteria forimpaired glucose tolerance (IGT) or type 2 diabetes (T2D)(34). Conversely, there were no significant differences inOGTT- glucose responses in lean women with PCOS com-

pared withage-andweight-comparablereproductively normal control women.This study also suggested that metabolicfeatures varied by PCOS phenotype, afinding that has been confirmed with in-vestigation of the Rotterdam PCOS phe-notypes (discussed in Section III.E. andreviewed in Ref. 101): women withNICHD PCOS are at the greatest meta-bolic risk. Accordingly, differing diag-nostic criteria for PCOS will affect theresults of metabolic investigations. Themajority of the studies assessing glucosetolerance and insulin resistance haveused theNICHD criteria forthediagno-sis of PCOS.

The prevalence of IGT and T2D in

U.S. women with PCOS has been as-sessed in three large cross-sectionalstudies in racially and ethnically di-verse cohorts (123125) (Fig. 5). Theprevalence was 2335% for IGT and410% for T2D in these studies. Fur-thermore, prevalence rates of IGT andT2D did not change in a subgroupanalysis limited to non-Hispanic white

women (123). The prevalence rate of IGT in PCOS was3-fold higher than the population prevalence rate in

women of similar age from the National Health and Nu-trition Survey (NHANES) II and twice the prevalence ratein age- and weight-comparable reproductively normalcontrol women (123). The prevalence rate of undiagnosedT2D was 7.5- to 10-fold higher than the prevalence rate inNHANES II women of similar age (123, 124); none of thecontrol women had T2D. Moreover, these studies likely un-derestimated the prevalence of diabetes mellitus in PCOSbecause they excludedwomen with diagnosed type 1 or type2 diabetes (123125).

Dysglycemia (fasting glucose 100 mg/dl, and/or 2-hpostchallenge glucose 140 mg/dl)was mainlyevident inpost-glucosechallenge glucose levels(Fig.6), andthe prev-alence of dysglycemia increased with body mass index(BMI),being highest in obese affected women ( i.e.,BMI30 kg/m 2 ) (123, 125). However, even lean women withPCOS had increased rates of IGT and T2D (123). A first-degree relative with T2D increased risk for dysglycemia(123, 125). The majority of women in these studies werein their third andfourthdecadesof life; however, theprev-alence rates of IGT and T2D were similarly increased inU.S. adolescents with PCOS (126).

Prevalence rates of dysglycemia are elevated in non-U.S. women with PCOS but not to the same magnitude as

Figure 4.

Figure 4. Insulin responses basally and after a 40 g/m2

oral glucose load in obese and leanPCOS women ( black circles), ovulatory hyperandrogenic (HA) women ( gray circles), and age-and weight-comparable ovulatory control women ( white circles ). Insulin responses aresignificantly increased only in PCOS women ( P 0.001 obese PCOS vs. obese HA and obesecontrol; P 0.01 lean PCOS vs. lean HA and control), suggesting that hyperinsulinemia is aunique feature of PCOS and not hyperandrogenic states in general. [Adapted from A. Dunaifet al. : Characterization of groups of hyperandrogenic women with acanthosis nigricans,impaired glucose tolerance, and/or hyperinsulinemia. J Clin Endocrinol Metab 65:499507,1987 (34), with permission. The Endocrine Society.]




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those in U.S. women with PCOS. The prevalence rates of IGT and T2D were 15.7 and 2.5%, respectively, whichwas higher than the estimated rates in the general popu-lation in an Italian PCOS cohort (127). A telephone in-terview study of Dutch women with PCOS found a sig-nificant increase in diagnosed T2D compared withpopulationprevalenceestimates(128). Another Europeanstudy(129)didnotshowincreasedprevalenceratesofIGTand T2D in women with NICHD PCOS from Spain com-pared with age-, BMI-, and ethnicity-comparable controlwomen. The reasons for these discrepant findings, apartfor racial/ethnic differences, are unclear. Although theprevalence of obesity is higher and its severity is greater inU.S. PCOS populations (123, 124), such differences alonecannot account for differing rates of dysglycemia, whichpersist between European and U.S. PCOS cohorts in com-parable BMI categories (123, 127, 129). Other factors,such as diet (130, 131) and race/ethnicity (118, 132), maycontribute to higher prevalence rates of dysglycemiaamong U.S. women with PCOS.

A recent meta-analysis (133) reviewed more than 2000studies of glucose tolerance in PCOS from which only 30full-text studies were assessed for the final analysis. The

increased prevalence of IGT and T2D inwomen with PCOS compared with womenwithout PCOS, in both BMI- and non-BMI-matched studies, was confirmed. In the meta-analysis, the odds ratios (OR) and confidenceintervals (CI) were significantly increased:IGTOR, 2.48; 95% CI, 1.633.77; BMI-matched studies, OR, 2.54; 95% CI, 1.444.47; and T2DOR, 4.43; 95% CI, 4.064.82; BMI-matched studies, OR, 4.00; 95%CI, 1.978.10. This meta-analysis confirmsthat the risk for IGT and T2D is increased inPCOS. PCOS is now recognized as a diabetesrisk factor by the American Diabetes Associa-tion (134). Nevertheless, the magnitude of riskis unclear because most studies have beencross-sectional, relatively small, and lacking

concurrently studied control women (135).Furthermore, differences in diagnostic criteriafor PCOS, race/ethnicity, and BMI have led tovariable risk estimates among PCOS cohorts(133, 135).

Large cross-sectional and prospective pop-ulation-based studies are needed to accuratelyestimate the magnitude of T2D risk in PCOS.A recent prospective study in an Italian PCOScohort confirmed an increased risk for T2D(594).However,some insights canbe provided

by prospective cohort studies that have usedself-reported menstrual irregularity (136,137) and/or hir-sutism (138) as surrogate markers for PCOS. Among re-productive-age women with oligomenorrhea, as many as90%mayhave PCOS,dependingon thediagnosticcriteriaapplied (35, 36,139,140).Furthermore,womenwith self-reported oligomenorrheaand/or hirsutismhavereproduc-tive and metabolic features of PCOS (138, 141), particu-larly those with both clinical findings (141). In PimaIndians (136) and in the Nurses Health Study II (137), therisk for T2D was significantly increased in women withmenstrual irregularity. In the Nurses Health Study (137),a multivariate analysis adjusting for multiple confound-ers, including BMI at age 18, race, physical activity, first-degree relative with diabetes, smoking, and oral contra-ceptive use, found the relative risk for diabetes was 1.82(95% CI, 1.352.44) in women with long or irregularmenstrual cycles at ages 1822 yr. The risk was increasedby obesity but remained significant in lean women withirregular menses (137). This association was not con-firmed in a relatively small U.S. prospective cohort study(142), but it was supported in a more recent and largerDutch study (143). Several studies in postmenopausalwomen with a history of PCOS and/or PCO are consistent

Figure 5.

Figure 5. Prevalence of glucose intolerance and T2D in PCOS. The prevalence of IGTand T2D in four large multiethnic PCOS cohorts is substantially increased. The trueprevalence of diabetes was likely underestimated in these studies because diagnosed

women with type 1 or type 2 diabetes were not included in the cohorts. NGT,Normal glucose tolerance.* [The University of Chicago data were reported by D. A.Ehrmann et al. : Prevalence of impaired glucose tolerance and diabetes in womenwith polycystic ovary syndrome. Diabetes Care 22:141146, 1999 (124), withpermission. American Diabetes Association.** The Penn State University and Mt.Sinai data were reported by R. S. Legro et al. : Prevalence and predictors of risk fortype 2 diabetes mellitus and impaired glucose tolerance in polycystic ovarysyndrome: a prospective, controlled study in 254 affected women. J Clin Endocrinol Metab 84:165169, 1999 (123), with permission. The Endocrine Society.*** TheRezulin (troglitazone) Collaborative Group data were reported by R. Azziz et al. :Troglitazone improves ovulation and hirsutism in the polycystic ovary syndrome: amulticenter, double blind, placebo-controlled trial. J Clin Endocrinol Metab 86:16261632, 2001 (392), with permission. The Endocrine Society.] The figure is used withthe permission of David Ehrmann.




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with an ongoing increased risk for T2D (144148). Thesedata suggest that PCOS increases the risk for T2D acrossa womans lifespan.

There have been very few follow-up studies to assessconversion rates from normal glucose tolerance to IGTand from IGT to T2D. The conversion rate from normalto IGT or from IGT to T2D in PCOS has been estimatedto range from 2.5 to 3.6% annually over a period of 38yr (133, 149152). These conversion rates are lower thanin the general population of individuals with IGT whoconvert to T2D at rates of approximately 7% annually(153155). This discrepancy likely represents an under-estimate in conversion rates in PCOS because the studieshave been limited by small sample size (133, 149 152).

Women with PCOS most commonly have postprandialdysglycemia (123,125),which reflects peripheral,primar-ily skeletal muscle, insulin resistance (156) rather thanfasting dysglycemia (Fig. 6), which reflects increased en-dogenous glucose production (156). Therefore, 2-h post-challenge glucose values are optimal for the diagnosis of

IGT and T2D in PCOS (123, 125, 135) and theAES position statement (157) has recom-mended screening of all women with PCOSwith a 75-g OGTT. The optimal time periodfor repeat OGTT is uncertain. A hemoglobinA1c value between 5.7 and 6.4% has been rec-ommended by the American Diabetes Associ-ation (158) for predicting increased diabetesrisk. A recent study (159) that assessed theutil-ity of hemoglobin A1c to detect IGT anddiabetes in PCOS found that this test had lowsensitivity when compared with OGTT assess-ment of glucose tolerance. This discrepancy indiagnostic accuracy may be because affectedwomen have mainly post-glucose challengerather than fasting dysglycemia (123, 125).

B. Insulin resistance1. Insulin action in vivo

Insulin acts to regulate glucose homeosta-sis by stimulating glucose uptake by insulin-responsive target tissues, adipocytes, andskeletaland cardiac muscle, as well as by sup-pressing hepatic glucose production (160,161). Insulin also suppresses lipolysis, result-ing in a decrease in circulating free fatty acidlevels(162), which may mediate the actionof insulin on hepatic glucose production (163

165). Insulin resistance has traditionallybeen defined as a decreased ability of insulinto mediate these metabolic actions on glu-cose uptake, glucose production, and/or li-

polysis, resulting in a requirement for increasedamounts of insulin to achieve a given metabolic action(166). Accordingly, insulin resistance is characterizedby increased circulating insulin levels, basally and inresponse to a glucose load, if pancreatic -cell functionis intact (166, 167). Insulin has other metabolic as wellas mitogenic and reproductive actions (discussed in Sec-

tions IV.D. and V.A. and in Refs. 12, 168, and 169), butit is unknown whether isolated defects in these path-ways would provoke compensatory hyperinsulinemia.

The gold standard for assessing metabolic insulinresistance in vivo is the hyperinsulinemic, euglycemic glu-cose clamp technique (167, 170). This technique quanti-tatively assesses insulin action on whole-body glucose up-take by infusing a desired dose of insulin and maintainingeuglycemia using a variable glucose infusion where therate is adjusted based on frequent arterialized blood glu-cose determinations and a negative feedback principle(167, 170). At steady state, the amount of glucose that is

Figure 6.

Figure 6. Fasting and post-challenge dysglycemia in PCOS. The individual fasting and2-h post-75 g oral glucose challenge glucose data from 254 women with PCOS areshown. The dotted vertical line is the fasting glucose threshold for impaired fastingglucose (100 mg/dl), the dashed vertical line is the fasting glucose threshold fordiabetes (T2D) (126 mg/dl), the dotted horizontal line is the post-challenge glucosethreshold for IGT (140 mg/dl), and the horizontal dashed line is the post-challengeglucose threshold (200 mg/dl) for T2D, according to the American DiabetesAssociation criteria (158). Most women with PCOS have post-challenge rather thanfasting dysglycemia. NGT, Normal glucose tolerance. [Adapted from R. S. Legro et

al.: Prevalence and predictors of risk for type 2 diabetes mellitus and impairedglucose tolerance in polycystic ovary syndrome: a prospective, controlled study in254 affected women. J Clin Endocrinol Metab 84:165169, 1999 (123), withpermission. The Endocrine Society.]




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infused equals the amount of glucose taken up by the pe-ripheral tissues, and it can be used as a measure of periph-eral sensitivity to insulin, known as insulin-mediated glu-cose disposal (IMGD) or M (167, 170). In lean, normalindividuals, skeletal muscle accounts for about 85% of IMGD (160).As fatmass increases, it accounts fora largeramountof IMGD (160).Endogenous glucose production,which reflects both hepatic and renal glucose production(167, 170172), can be determined by the infusion of iso-topically labeled glucose at baseline and during the eugly-cemic clamp (173, 174). The suppression of hepatic glu-cose production can be assessed by determining thedecrease in endogenous glucose production in response toinsulin (173, 174).

Whole-body insulin sensitivity can also be accuratelymeasured in subjects without diabetes using the frequentlysampled iv glucose tolerance test (FSIGT) with minimal

model analysis(167).Theminimal model determinesinsulinsensitivity (sensitivity index), which reflects insulin action tostimulate glucose uptake as well as to suppress glucose pro-duction (167). The acute insulin response to glucose (AIRg)is also determined from the FSIGT data. The disposition in-dex(DI), theproductofAIRgand insulin sensitivity, assessesinsulin secretion in the context of insulin sensitivity and is arobust parameter of pancreatic -cell function (161, 175)that will be discussed in Section IV.E . It is possible to modelhepatic glucose production with the administration of iso-topically labeled glucose during the FSIGT (176, 177), but

this measurement is rarely performed because the tracer isexpensive and themodel is complex. The standardFSIGT issubstantially easier and less expensive to perform than theclamp, although it is still an investigational procedure thatrequires frequent blood sampling.

The FSIGT provides quantitative, reproducible mea-surements of insulin sensitivity in individuals withoutT2D; in patients with diabetes, it may not be possible todifferentiate between very low insulin sensitivity values(178, 179). The FSIGT also provides a simultaneous as-sessment of insulin secretion (161, 178). The euglycemicclampprovides a quantitative, reproducible measurementof insulin action across a spectrum of insulin sensitivitiesand can be used in patients with T2D (167, 170). Endog-enous, primarily hepatic, glucose production can also beassessed duringthe clamp(170,178).Themeasurementof insulin secretion requires a separate,hyperglycemic clampstudy (170, 178, 180). The glucose clamp procedure re-quireshighly trained personnel and specializedequipment(167, 170). It is also substantially more expensive to per-form than the FSIGT (167).

Because of the complexity and expense of the clampand the FSIGT, there has been a desire to use fastingparameters of glucose homeostasis as surrogate mea-

sures of insulin resistance. These measures include ho-meostatic model assessment (181), fasting glucose:in-sulin ratio (182), and quantitative insulin sensitivitycheck index (183). They are all based on fasting glucoseand insulin levels and essentially provide identical in-formation (184). Fasting glucose levels reflect endoge-nous glucose production (156), an index of hepaticrather than peripheral insulin action(156).Fasting insulinlevels reflect not only insulin sensitivity but also insulinsecretion and clearance (184). Accordingly, fasting insu-lin levels will not provide accurate information on insulinsensitivity in individuals with -cell dysfunction (184).OGTT-derived parameters of insulin action have alsobeen shown to be insensitive to large changes in insulinsensitivity (184). Although fasting measures (185) andOGTT-derived parameters (186) may correlate withclamp or FSIGT measures of insulin sensitivity, they lack

precisionforquantitativelymeasuring insulin resistanceinthe general population (184). These measures have beenfound to be similarly imprecise for the assessment of in-sulin sensitivity in women with PCOS (187).

PCOS women have an increased prevalence of obesity(19, 122, 188), and women with upper as opposed tolower body obesity have an increased frequency of hy-perandrogenism (189). Androgens can also increase vis-ceral fat mass in women (190). Muscle is the major site of insulin-mediated glucose use (160), and androgens canincrease muscle mass (191). Thus, potential changes in

lean body (primarily muscle) and fat mass as well as in fatdistribution should be considered to accurately assess in-sulin action in PCOS(81,192). In1989 (81), itwas shownthat IMGD measured by euglycemic clamp was signifi-cantlyand substantially decreased ( 3540%) in womenwith PCOS compared with age- and body composition-comparable reproductively normal control women (81,192) (Fig. 7). The decrease in IMGD in PCOS was of asimilar magnitude to that reported in T2D (160) (Fig. 7).Furthermore, IMGD was significantly decreased per ki-logram of fat free, primarily muscle, mass (160). IMGDwas also significantly decreased in lean PCOS women, allof whom had normal glucose tolerance.

Body fat topography, upper compared with lowerbody, can affect insulin sensitivity (7), with increases inupper body and visceral fat being associated with de-creased insulin sensitivity (7, 193). The study of Dunaif et al . (81) did not control for this parameter, and some sub-sequent studies have suggested that increases in upperbody obesity, assessed by waistandhipmeasurements andadipocyte size, are associated with insulin resistance inPCOS (192, 194197). However, visceral fat mass accu-rately quantified by magnetic resonance imaging (MRI)(197,198) or bycomputerizedtomography (199)does not




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differ in women with PCOS compared with BMI-matchedcontrol women. Thus, the study of PCOS and controlwomen of comparable BMI appears to be sufficient tocontrol for the confounding effects of obesity as well as of fat distribution on insulin sensitivity.

Insulin has concentration-dependent saturable actionsthat can be examined in vivo using sequential multipleinsulin dose euglycemic clamp studies (200). The concen-tration required for a half-maximal (ED 50 ) response de-fines insulin sensitivity and usually reflects insulin recep-tor binding or phosphorylation, whereas the maximalbiological effect is defined as insulin responsiveness andusually reflects postreceptor events, for example, translo-cationof theGLUT4 glucose transporter forIMGD (166).Dose-responsestudies have indicatedthat theED 50 insulinfor glucose uptake was significantly increased and thatmaximal rates of IMGD were significantly decreased inlean and in obese women with PCOS women (192) (Fig.8). It appears, however, that body fat has a more pro-nounced negative effect on insulin sensitivity in womenwith PCOS (201, 202). Basal endogenous glucose produc-tion and the ED 50 insulin for suppression of endogenousglucose production were significantly increased only inobese PCOS women (81, 192) (Fig. 8). This synergisticnegative effect of obesity and PCOS on endogenous glu-cose production is an important factor in the pathogenesisof glucose intolerance (34, 81, 123, 192).

Many subsequent studies using euglycemic glucoseclampsor FSIGTshave confirmedthat women with PCOS

have profound resistance to the actionof insulin to stimulate glucose uptake(for example, see Refs. 201 and 203209). There is general consensus thatobese women with PCOS are insulinresistant (24). However, several stud-ies have failed to demonstrate insulinresistance in lean women with PCOS(for example, see Refs. 205, 210, and211) using the highly sensitive eugly-cemic glucose clamp technique. Someof these conflicting results can be ac-counted for by differences in the diag-nostic criteria for PCOS that resultedin the inclusion of women with ovu-latory cycles and hyperandrogenismwho have minimal to absent evidence

for insulin resistance (see discussionin Section III.E. of diagnostic criteriaand Refs. 34, 89, 96, 98, and 101).However, it is also possible that racial/ ethnicdifferences in insulin action (118,132) or environmental factors such as

diet (130, 131) contributed to these discrepant findings.Attempts to quantitate the prevalence of insulin resis-

tance in PCOS are limited by the methods used to deter-mine insulin sensitivity. Prevalence rates of insulin resis-tance have been reported from 44 to 70% (187, 212216)

using surrogate markers, which lack sensitivity and spec-ificity (184, 187). Even when insulin resistance is assessedusing the euglycemic glucose clamp, it is clear that somewomen with PCOS have normal insulin sensitivity (81)(Fig. 9). Thus, defects in insulin action on glucose metab-olism are not a universal feature of the syndrome. Indeed,two of the PCOS phenotypes identified with the Rotter-damcriteria (Table 3)hyperandrogenism andPCOwithovulatory cycles, and anovulation and PCO without hy-perandrogenismhave modest (217) or absent (99) evi-dence for insulin resistance using surrogatemarkers. Nev-

ertheless, it remains possible that there is increasedsensitivity to the reproductive actions of insulin in PCOSbecause hyperandrogenismand anovulation improve dur-ing metformin treatment in women with PCOS withoutevidence for insulin resistance (218). Alternatively, theseimprovements may be related to a direct action of met-formin on steroidogenesis (219).

2. Cellular and molecular mechanisms of insulinresistance (Fig. 10)a. Molecular mechanisms of insulin action. Insulin has multi-ple cellular actions beyond the regulation of glucose up-take (220). It hasother anabolic effects to increase storage

Figure 7.

Figure 7. Decreased IMGD in PCOS. IMGD at steady-state insulin levels of 100 U/ml issignificantly decreased by 3540% in women with PCOS ( gray bars ), independent of obesity,compared with age- and weight-matched control women (NL, open bars ). This decrease issimilar in magnitude to that reported in T2D ( open bars ) (160). This figure is used with thepermission of Andrea Dunaif.




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of lipidsand proteinsas wellas topromote cellgrowthanddifferentiation (220). Insulin acts on cells by binding to itscell surface receptor (221, 222). The insulin receptor is aheterotetramer made up of two , dimers linked by disul-fide bonds (223). Each , dimer is the product of one gene(224, 225). The -subunit is extracellular and contains theligand-binding domain; it also inhibits the intrinsic kinaseactivity of the -subunit(220, 222). The -subunitspans themembrane, and the cytoplasmic portion contains intrinsicproteintyrosinekinase activity,which is activated furtherby

ligand-mediated autophosphorylation(226). The insulin receptor shares sub-stantial structural homology the IGF-Ireceptorandtheinsulin-relatedreceptor(220). The , dimer of the insulin re-ceptorcanassemblewith similar dimersof the IGF-I receptor or insulin-relatedreceptor to formhybrid receptors(227).

Ligand binding induces autophos-phorylation of the insulin receptor onspecific tyrosine residuesand further ac-tivation of its intrinsic kinase activity(228230). The activated insulin recep-tor then tyrosine-phosphorylates intra-cellular substrates,suchas insulinrecep-tor substrates (IRS) 14, src homologand collagen homolog (Shc), and APS

[adapter protein with a PH and homol-ogy 2 (SH2) domain], to initiate signaltransduction (222, 231, 232). The IRSare phosphorylated on specific motifs,andthesephosphorylatedsites thenbindsignalingmolecules,such astheSH2 do-main of phosphatidylinositol 3-kinase(PI3-K) or the adaptor molecule, Nck(220,222, 233), leading to activation of downstream signaling pathways.

Insulinstimulatesglucoseuptakebyin-

creasing the translocation of the insulin-responsive glucose transporter, GLUT4,from intracellular vesicles to the cell sur-face (222,232).This pathway ismediatedby activation of PI3-K, which then phos-phorylates membrane phospholipids andphosphatidylinositol 4,5-bisphosphate,leadingtoactivationofthe3-phosphoino-sitide-dependent protein kinases (PDK-1and PDK-2) (220, 232). These kinasesactivate the serine/threonine kinasesAkt/protein kinase B (PKB) and atypicalproteinkinase C and , (PKC / ).Akt/ PKB transmits the signal by phosphory-

lation of its 160-kDa substrate, AS160 (220, 232). Both of these pathwaysstimulate the translocation of GLUT4 to thecell surface (220, 232). Glycogen synthase activity is consti-tutively inhibited via phosphorylation by glycogen synthasekinase-3 (GSK3) (220, 232). Activation of Akt/PKB also re-sults intheserinephosphorylationand inactivationofGSK3,allowing glycogen synthaseactivity to increaseandresultingin glycogen synthesis (220, 232, 234).

Insulinstimulatescellgrowth anddifferentiationthroughthe MAPK-ERK (220, 232) pathway (220, 235). This path-

Figure 8.

Figure 8. Insulin action in isolated sc adipocytes and in vivo. The dose-response of insulin-stimulated glucose uptake was determined in isolated sc adipocytes in vitro and in vivo duringsequential multiple insulin dose euglycemic glucose clamp studies. Maximal rates of glucoseuptake (insulin responsiveness) in isolated sc adipocytes are depicted in vitro (A, left ) and invivo, which reflects primarily skeletal muscle glucose uptake (B, left ). Rates of postabsorptiveendogenous glucose production (EGP) (C, left ) and its suppression by insulin were alsoassessed during the euglycemic glucose clamp study. The ED 50 insulin (insulin sensitivity) forstimulation of glucose uptake and suppression of EGP are depicted in the graphs on the right (A, sc adipocytes in vitro; B, in vivo; C, EGP). Women with PCOS, gray bars ; normal controlwomen (NL), open bars . A two-way ANOVA with PCOS and obesity as factors was applied:*, P 0.01 PCOS groups vs. NL groups; , P 0.05 obese groups vs. lean groups; , P 0.01 obese groups vs. lean groups; , P 0.001 obese groups vs. lean groups; , P 0.05interaction PCOS and obesity. [Adapted from data published in A. Dunaif et al. : Evidence fordistinctive and intrinsic defects in insulin action in polycystic ovary syndrome. Diabetes41:12571266, 1992 (192), with permission. American Diabetes Association.]




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way is activated by insulin receptor-mediated phosphoryla-tion of Shc or IRS, leading to association with Grb2 andSon-of-sevenless resulting in Ras activation (220). This acti-vationstimulates a cascadeof serine/threonine kinase result-ing in the stepwise stimulation of Raf, MAPK kinase (MEK)andMAPK-ERK1/2.ERK1/2translocatestothenucleusandphosphorylates transcription factors to initiate cell growthand differentiation (220). This so-called mitogenic pathwaycan be disrupted without affecting the metabolic actions of insulin and vice versa (220, 236238). As a result, insulinresistance can be selective and affect only metabolic but notmitogenicpathwaysofinsulinaction(236,239,240).Insulinregulates protein synthesis and degradation via mammaliantarget of rapamycin (mTOR) (220), which is activated viaPI3-K. The mTOR pathway is also important in nutrientsensing (241). Insulin-stimulated inhibition of GSK3 viaPI3-KandAkt/PKB also results in dephosphorylation of eu-karyotic initiation factor 2B (eIF2B) activating protein syn-thesis (234).

The insulin signal can be terminated by dephosphor-ylation of proximal signaling molecules. Multiple ty-

rosine phosphatases, such as protein tyrosinephosphatase 1B (PTP1B), can dephosphory-late the insulin receptor to terminate the in-sulin signal (220, 232). Phosphatase and ten-sion homolog deleted on chromosome 10(PTEN), a lipid phosphatase, decreases PI3-Ksignaling by dephosphorylating lipid signal-ing molecules (232, 242, 243). Serine phos-phorylation of the insulin receptor and IRScan also inhibit insulin signaling (220, 244246). It has been postulated that PKC-medi-ated serine phosphorylation of the insulin re-ceptor is important in the pathogenesis of hyperglycemia-induced insulin resistance(246248) and that the mechanism of TNF-

-mediated insulin resistance is serine phos-phorylation of IRS-1 (249). Furthermore, it

has been suggested that a number of serine/ threonine kinases in the insulin signalingpathway, such as PI3-K, Akt/PKB and GSK3,can serine phosphorylate the insulin receptorand/orIRS-1 to attenuatesignalingproviding afeedback mechanism to terminate insulin ac-tion (220, 246).

b. Molecular defects in PCOS (Fig. 11). The cellu-larandmolecularmechanismsof insulin actionin PCOS have been characterized in cultured

skin fibroblasts, which are not classic insulintarget tissues (222). Defects in fibroblast insu-lin action that persist in cells that have beenremoved from the in vivo environment for

many passages suggest that the changes are the resultof mu-tations in genes regulating these pathways (10, 250). Con-sistent with this hypothesis, decreases in insulin receptorbinding or autophosphorylation in cultured skin fibroblastshave reflectedmutationsin theinsulin receptor gene inpatientswith the syndromes of extreme insulin resistance (10, 12).

Insulin action has also been examined in the classicinsulin target tissues for glucose uptake, adipocytes andskeletal muscle (160, 222). The size of sc adipocytesisolated from both lean and obese women with PCOSwas increased (192, 197). Insulin receptor numberand/or receptoraffinity was similar to control women inisolated sc adipocytes (192, 251). However, decreasedinsulin receptor -subunit abundance has been reportedin homogenates of omental adipose tissue from womenwith PCOS (252). The most striking and consistent de-fect in adipocyte insulin action in PCOS was a markedincrease in the ED 50 for insulin-mediated glucose up-take (192, 206, 251), indicating a decrease in insulinsensitivity, when compared with isolated adipocytes

Figure 9.

Figure 9. Fasting and dynamic measures of insulin resistance. Fasting measure ofinsulin sensitivity, the glucose:insulin ratio (185) and insulin levels are shown in thetop graphs . Dynamic measures of insulin sensitivity, the euglycemic glucose clampdetermined IMGD, and sensitivity index (SI) assessed by minimal model analysis ofFSIGT are shown in the bottom graphs . For all measures of insulin action, there isconsiderable overlap between control ( open triangles ) and PCOS ( gray circles)women. The data have been previously published (81, 185, 301) and were adaptedfor use in this figure, which is used with the permission of Andrea Dunaif.




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from appropriately weight-comparable reproductivelynormal control women (Fig. 8). The decrease in insulinsensitivity suggested that there was a defect in insulinreceptor binding or phosphorylation (166).

Most studieshavealso found lessstriking, butsignificant,decreases in maximal rates of insulin-stimulated glucosetransport (192, 253), insulinresponsiveness,suggestinga de-crease in post-receptor events (192,251) (Fig. 8).Significantdecreases in the abundance of GLUT4 glucose transportersin sc adipocytes from women with PCOS most likely ac-countedforthedecreasein insulinresponsiveness(252,254).However, a recent study (206) failed to find decreases ininsulinresponsivenessorGLUT4abundanceinscadipocytesisolated from womenwith PCOS, despite the fact the eugly-

cemic clamp studies in these PCOS subjects showed de-creased insulin responsiveness for IMGD consistent with apostbinding defect in insulin action. The reasons for thesediscrepant results in isolated sc adipocytes are unclear becauseboth studies used the same diagnostic criteria (NICHD) forPCOSandcontainedcontrolwomenofcomparable BMI(206,254). Similar defects in adipocyte insulin action have been re-ported inT2D and inobesity but are ameliorated bycontrol of hyperglycemia and hyperinsulinemia as well as by weight-reduction, suggesting acquired rather than intrinsic defects(255257).In contrast, inPCOSsuchdefects canoccur intheabsenceofobesityandglucoseintolerance(192,254).More-over, these abnormalities are not significantly correlatedwith sex hormone levels (55, 117).

Figure 10.

Figure 10. Insulin receptor signaling pathways. The insulin receptor is a heterotetramer consisting of two , dimers linked by disulfide bonds. The-subunit contains the ligand binding domain, and the -subunit contains a ligand-activated tyrosine kinase. Tyrosine autophosphorylation

increases the receptors intrinsic tyrosine kinase activity, whereas serine phosphorylation inhibits it. The tyrosine-phosphorylated insulin receptorphosphorylates intracellular substrates, such as IRS 14, Shc, and APS, initiating signal transduction pathways mediating the pleiotropic actions ofinsulin. The major pathway for the metabolic actions of insulin is mediated through activation of PI3-K and Akt/PKB, resulting in the translocation

for the insulin responsive glucose transporter, GLUT4, from intracellular vesicles to the plasma membrane. Insulin activation of PI3-K and Akt/PKBalso leads to serine phosphorylation of GSK3, resulting in inhibition of its kinase activity. The inhibition of GSK3 results in dephosphorylation ofglycogen synthase increasing glycogen synthesis. The Ras-ERK/MAPK pathway regulates gene expression. Insulin modulates protein synthesis anddegradation via mTOR, which is activated via PI3-K and Akt/PKB. The mTOR pathway is also important in nutrient sensing. Insulin-stimulatedinhibition of GSK3 via PI3-K and Akt/PKB also results in dephosphorylation of eIF2B increasing protein synthesis. Insulin signaling can beterminated by dephosphorylation of the receptor by tyrosine phosphatases, such as PTP1B, or dephosphorylation of PI3-K by PTEN. Serinephosphorylation of the insulin receptor and IRSs can also decrease insulin signaling and may be mediated by serine kinases in the insulin signalingpathway providing a feedback mechanism to terminate insulin action. There is a post-binding defect in insulin signaling in PCOS affectingmetabolic but not mitogenic pathways (see Fig. 11 for details). The signaling steps that are compromised in PCOS are circled with a dotted line .Signaling steps downstream of these abnormalities may also be compromised. SOS, Son-of-sevenless. This figure is used with the permission ofAndrea Dunaif.




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There have been no differences in abundance of down-

stream signaling proteins, IRS-1, Akt/PKB 1/2, PKC , c-Cbl-associated protein, or cbl or in activation of Akt/PKBat maximal insulin doses in PCOS adipocytes (206).How-ever, one study suggested abnormalities in the phosphor-ylation of GSK3 , which is a substrate for Akt/PKB, inPCOS adipocytes (253). These studies are constrained bythe fact that signaling protein abundance and basal phos-phorylation may be unaltered, but insulin-stimulated ac-tivation may still be defective in insulin-resistant states(220). Studies using maximally stimulating doses of insu-linmay fail todetectalterationsin insulin sensitivity (232).Akt/PKB activation may be normal despite substantial in-sulin resistance(232,258).Furthermore, downstreamsig-naling events may be decreased if there are defects in sig-naling at the level of the insulin receptor (220).

Insulinreceptorfunction in PCOSwas investigated inreceptors isolated from cultured skin fibroblasts. Con-sistent with findings in isolated adipocytes (192, 251),there was no change in insulin binding or receptor af-finity compared with control women (69). However,insulin receptor basal autophosphorylation was mark-edly increased with minimal further insulin-stimulated au-tophosphorylation in receptors isolated from approxi-mately 50%of PCOSfibroblasts (259). Insulin-dependent

receptor tyrosine autophosphoryla-tion was significantly decreased (259,260). Insulin-independent receptor ser-ine phosphorylation was markedly in-creased (259), and thesereceptorshad re-duced intrinsic tyrosine kinaseactivity, suggesting that serine phos-phorylation inhibited normal recep-tor signaling (259). Although fibro-blasts are not a classic insulin targettissue for glucose uptake, insulin re-ceptors isolated from skeletal musclebiopsies from women with PCOS hadsimilar abnormalities in phosphoryla-tion, suggesting that this defect wasphysiologically relevant (259).

Isolating insulin receptors from ly-

sates of PCOS skin fibroblasts by im-munopurification before insulin-stim-ulated autophosphorylation correctedconstitutive increases in receptor ser-ine phosphorylation (259). Further-more, mixing lysates from PCOS skinfibroblasts with purified human insu-lin receptors resulted in increased re-ceptor serine phosphorylation (259).Taken together, these findings sug-

gested that a serine kinase extrinsic to the insulin receptor

was responsible for the abnormal pattern of receptorphosphorylation (259). These findings were supported byan independent group of investigators (260) who con-firmed significant decreases in PCOS skin fibroblast insu-lin receptor autophosphorylation. Furthermore, theydemonstrated that decreased receptor autophosphoryla-tion could be corrected immunocapture of the insulin re-ceptorbefore insulin stimulation,consistent with thepres-ence of a factor extrinsic to the receptor as the cause of thedefect (260). Most importantly, serine kinase inhibitorscorrected the phosphorylation defect, supporting the roleof a serine kinase extrinsic to the insulin receptor as thecause of decreased receptor autophosphorylation (260).

This defect in the early steps of the insulin signalingpathway may cause the insulin resistance in a subpopula-tion of women with PCOS (Fig. 11). Increased insulin-independent serine phosphorylation in PCOS insulin re-ceptors appears to be a unique disorder of insulin actionbecause other insulin-resistant states, such as obesity,T2D, Type A syndrome, and leprechaunism, do not ex-hibit this abnormality (222, 255, 259). In approximately50% of PCOS women, insulin receptor phosphorylationin receptors isolated from skin fibroblasts was similar tocontrol women (259), despite the fact that these women

Figure 11.

Figure 11. Insulin signaling defects in PCOS. There is a post-binding defect in insulin signalingin PCOS resulting in marked decreases in insulin sensitivity (see Fig. 8). There is a more modestdefect in insulin responsiveness. The signaling defect is due to serine phosphorylation of theinsulin receptor and IRS-1 secondary to intracellular serine kinases. This results in decreasedinsulin-mediated activation of PI3-K and resistance to the metabolic actions of insulin. There isconstitutive activation of kinases in the ERK/MAPK mitogenic pathway in PCOS, and thesekinases contribute to inhibitory serine phosphorylation of IRS-1 in PCOS skeletal muscle. Serinephosphorylation of P450c17 increases its activity, and it has been postulated that the samekinase may inhibit insulin signaling and increase androgen production in PCOS. S-S, Disulfidebond; Y, tyrosine; S, serine; P, phosphate. This figure is used with the permission of AndreaDunaif.




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hadcomparable severityof insulin resistanceas that foundin affected women with abnormal insulin receptor phos-phorylation. This observation suggests that a defectdownstream of insulin receptor phosphorylation, such asphosphorylation of IRS-1 or activation of PI3-K, was re-sponsible for insulin resistance in some PCOS women(220, 222, 259).

Studies of insulin signaling in vivo have shown a sig-nificant decrease in insulin-mediated IRS-1-associatedPI3-Kactivation in serial skeletal muscle biopsiesobtainedduring a euglycemic clamp study in association with de-creased IMGD in women with PCOS (261). The abun-dance of the insulin receptor, IRS-1, and the p85 subunitof PI3-K was unchanged, consistent with an abnormalityin insulin receptor and/or post-receptor phosphorylationevents (261). The abundance of IRS-2 was increased, sug-gesting a changeto compensate fordecreasedsignalingvia

IRS-1 (261). Analogous to in vitro studies, the signalingchanges occurred rapidly and were evident in biopsies at15- and 30-min time points during each insulin dose, butthe changes had returned to baseline by 90 min of eachinfusion (261). This study confirmed that there is a phys-iologically relevant defect in rapid insulin receptor-medi-ated signaling in the major insulin target tissue for IMGD,skeletal muscle.

Hjlund et al . (262), however, did not find differences ininsulin-stimulatedIRS-1-associatedPI3-Kactivity inskeletalmuscle biopsies taken after 3 h of insulin infusion, despite

significant decreases in IMGD in women with PCOS. Nev-ertheless, this finding is consistent with the time course of these signaling changes determined in the previous study of Dunaif et al . (261). These authors did find signaling abnor-malities in the activation of Akt/PKB and its downstreamtarget for GLUT4 translocation, AS160(262) (Fig. 10). Thedecrease in insulin receptor-mediated IRS-1 phosphoryla-tion and PI3-K activation identified in PCOS skeletal muscle(263)couldaccountforthesechangesbecausethesesignalingevents are downstream in thepathway of insulin-stimulatedglucose uptake (232) (Fig. 10). In contrast, Ciaraldi et al .(206) failed to find changes inAkt/PKB activation inskeletalmuscle biopsiesfromPCOSwomentakenafter3 h of insulininfusion, despite significant decreases in IMGD in affectedwomen. However, theyusedmaximallystimulating doses of insulin, whereas Hjlund et al . (262) used physiologicaldoses of insulin. Accordingly, changes in the sensitivity of Akt/PKB activation to insulin could have escaped detectionin the Ciaraldi study (206).

It is possible to isolate myoblasts from human skeletalmuscle biopsies, culture these cells in vitro , and differen-tiate them into myotubes (264266). This culture systemhas been used to investigate whether the defects in in-sulin action in PCOS skeletal muscle are the result of the

in vivo hormonal environment or reflect intrinsic ab-normalities (206, 267269). Cultured myotubes fromwomen with PCOS had a distinctive phenotype: despitesimilar population doublings, they had an increase inmarkers of differentiation compared with myotubesfrom control women (267). Insulin action findings inPCOS myotubes have been conflicting. Corbould et al .(267) found that basal and insulin-stimulated glucosetransport was increased in PCOS compared with con-trol myotubes, but the increments in glucose transportwere similar in both groups. GLUT1 abundance wasincreased in PCOS myotubes and correlated with theincreases in basal, non-insulin-mediated glucose trans-port, whereas GLUT4 abundance was unchanged inPCOS compared with control myotubes (267). In con-trast, Ciaraldi et al . (206) found that both basal and max-imal insulin-stimulated glucose transport were decreased

in another study of PCOS myotubes. PCOS myotubeGLUT4 abundance did not differ in PCOS and controlmyotubes in this study (206). Eriksen et al . (269, 270)found no significant changes in glucose transport in PCOSmyotubes,although there wasa trend towardhigherbasalrates of glucose transport in PCOS myotubes. Insulin ac-tion on other metabolic parameters, such as glycogen syn-thesis and lipid uptake, also did not differ in PCOS com-pared with control myotubes (270).

The most comprehensive study of insulin signaling inPCOS myotubes by Corbould et al . (267) found no dif-

ferences in insulin receptor -subunit abundance or ty-rosine phosphorylation. However, the abundance of IRS-1 was increased in PCOS myotubes. When normal-ized for IRS-1 abundance, PI3-K activity was decreasedin PCOS myotubes. Furthermore, phosphorylation of the IRS-1 inhibitory serine 312 was increased in PCOSmyotubes. IRS-2-associated PI3-K activity was also de-creased in PCOS myotubes. These findings suggest thatthere are intrinsic abnormalities in insulin signaling inPCOS myotubes, despite the fact that glucose transportis not compromised (267). It is possible that these ab-normalities confer increased susceptibility to circulat-ing factors that induce insulin resistance, such as freefatty acids or TNF- (267).

Ciaraldi et al . (206) found no changes in IRS-1, Akt/ PKB 1/2, PKC , c-Cbl-associated protein, or cbl proteinexpression in PCOS myotubes, analogous to their find-ings in skeletal muscle biopsies. They only examinedactivation of Akt/PKB at maximal insulin doses and didnot detect any changes in PCOS compared with controlmyotubes, despite the fact that this group reported de-creased basal and insulin-stimulated glucose transportin these PCOS myotubes (206). Activation of PI3-K wasnot examined, and as discussed in this Section, de-




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creases in the sensitivity of Akt/PKB activation by in-sulin could have escaped detection by the use of onlymaximally stimulating doses of insulin (232).

In addition to insulin signaling defects, it has also beensuggested that mitochondrial dysfunction may contributeto insulin resistance in PCOS skeletal muscle. In T2D,decreased numbers of skeletal muscle mitochondria havebeenreported (271). Skeletalmuscle biopsies fromwomenwith PCOS have shown decreased expression of genes in-volved in mitochondrial oxidative metabolism (272). Fur-thermore, pioglitazone-mediated improvements in insulinsensitivity were associated with increased expression of genes involved in mitochondrial phosphorylation path-ways in these affected women (273). However, there wereno differences in mitochondrial number or function incultured myotubes from women with PCOS (269). Thesefindings suggest that changes in mitochondrial oxidativegene expression in PCOS skeletal musclearenota primarydefect.

C. Other metabolic actions of insulin in PCOSThere have been limited studies of insulin action lipid

homeostasis in PCOS. Fasting free fatty acid levels havebeen increased (274) or unchanged (262) in obese womenwith PCOS compared with control women of similarweight. There has been decreased insulin-mediated sup-pression of lipid oxidation during euglycemic clamp stud-ies in obese women with PCOS (262). However, lipid up-

take and oxidation did not differ from control in PCOSmyotubes (270).Alterations in catecholamine regulation of lipolysis

have been reported in PCOS. There was decreased sensi-tivity to catecholamine-stimulated lipolysis in adipocytesisolated from the sc fat depot of lean women with PCOS,which may favor increased fat cell size (275). In contrast,adipocytes isolated from the visceral fat depot of leanwomen with PCOS had increased catecholamine-stimu-lated lipolysis (276). The cellular mechanisms of this de-fect,alterations inprotein kinaseA subunit expression and

decreases in hormone sensitive lipase, differed from thosein visceral adipocytes in subjects with the metabolic syn-drome (276). This increase in catecholamine-stimulatedlipolysis may contribute to hepatic insulin resistance byincreasing portal free fatty acid delivery to the liver (163).Insulin action to suppress lipolysis was similar in visceraladipocytes from lean women with PCOS and controlwomen (276). There are no reports of insulin action onprotein turnover in PCOS.

D. Mitogenic actions of insulin in PCOSInsulins mitogenic actions on cell growth and differ-

entiation can be regulated by the MAPK-ERK 1/2 path-

way independently of insulins metabolic action (220)(Fig. 10). The metabolic pathway can be disrupted with-out altering the mitogenic pathway (220). Such so-calledselective insulin resistance has been found in cultured skinfibroblasts from patients with extreme insulin resistance(236).A similar selectivedefectin insulin actionwas foundinculturedskin fibroblasts from womenwith PCOS (277).Both insulin- and IGF-I-stimulated glycogen synthesiswere significantly decreased in PCOSfibroblasts, whereasthymidine incorporation was similar to that in controlfibroblasts (277).

Euglycemic clamp studies in subjects with T2D havedemonstrated decreased metabolic signaling via PI3-Kwith preserved mitogenic signaling via MAPK-ERK1/2 inskeletal muscle biopsies (240). In skeletal muscle biopsiesfrom women with PCOS, MAPK-ERK1/2 was constitu-tivelyactivated (268).This alteration persisted in cultured

PCOS myotubes where MAPK-ERK1/2 was activated ba-sally and in response to insulin, whereas MEK activationwas increased only in response to insulin (268). The ac-tivity of p21 Ras was significantly decreased, and theabundance of Raf-1 was increased, suggesting that thealteration of signaling began at this molecule. Pharmaco-logical inhibition of MEK1/2 inhibited MAPK-ERK1/2activation, reduced IRS-1 serine 312 phosphorylation,and enhanced IRS-1-associated PI3-K activation (268).These findings suggested that activation of MAPK-ERK1/2 contributed to serine phosphorylation of IRS-1

and diminished metabolic signaling in PCOS myotubes.MAPK-ERK1/2maybe a serinekinase contributing to theincreased serine phosphorylation of IRS-1 and, perhaps,the insulin receptor in PCOS (55, 259, 268), althoughmyotube insulin receptor serine phosphorylation was notdirectly examined. Furthermore, these findings suggestthat a primary activation of mitogenic signaling pathwaysproduces metabolic insulin resistance by serine phosphor-ylating proximal metabolic signaling molecules, such asIRS-1 (268) (Fig. 11).

A recent study in skeletal muscle biopsies fromwomen with PCOS confirmed the constitutive activa-tion of MAPK-ERK1/2 (278). This study also reportedthat insulin-stimulated activation of MAPK-ERK1/2was decreased in PCOS skeletal muscle biopsies. How-ever, the biopsies were performed 1520 min after abolus dose of insulin, which is cleared rapidly (279), aspart of an insulin tolerance test rather than during thecontinuous infusion of insulin as part of a euglycemicclamp study. The clearance of insulin is also altered ininsulin-resistant states (279, 280). Therefore, differ-ences in the kinetics of the insulin bolus in PCOS com-pared with control women could have confounded theresults. Moreover, a counterregulatory hormone re-




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sponse due to insulin-induced hypoglycemia could alsoconfound the results (281). Nevertheless, the findingsare consistent with the hypothesis that constitutive ac-tivation of MAPK-ERK1/2 impairs metabolic signalingin PCOS via serine phosphorylation of IRS-1.

In summary, the major defect in insulin action inPCOS is a post-binding defect in the early steps of in-sulin signal transduction (Figs. 10 and 11). This defectis present in the two main target tissues for insulin-stimulated glucose uptake: adipocytes (192, 251) andskeletal muscle (259, 263). Furthermore, in at leastsome tissues, such as skin fibroblasts (277) and ovariangranulosa-lutein cells (see in Section V.A. and Ref. 282),insulin resistance in PCOS is selective, affecting meta-bolic but not other actions of insulin (Figs. 10 and 11).However, both metabolic and mitogenic pathways maybe compromised in PCOS skeletal muscle (278).

The post-binding defect in insulin signaling appears tobe secondary to increased inhibitory serine phosphoryla-tion of the insulin receptor and IRS-1. Our group (259)and Li et al . (260) have provided evidence that autophos-phorylation can be normalized after immunopurificationof the insulin receptor. This observation suggests that akinaseextrinsicto theinsulin receptorcauses theincreasedreceptor serine phosphorylation. This hypothesis is sup-portedbythefindingofLi etal .(260)thatdecreasedPCOSskin fibroblast insulin receptor autophosphorylation canbe ameliorated by serinekinaseinhibitors. Inskeletalmus-

cle, two groups (268, 278) have shown that kinases in theMAPK-ERK1/2 mitogenic pathway are constitutively ac-tivated. The activation of these kinases contributes to ser-ine phosphorylation of IRS-1 and inhibition of metabolicsignaling (268). Two studies suggest that metabolic insu-lin resistance does not persist in cultured myotubes fromwomen with PCOS (267, 270), whereas another (206) hasfoundpersistentdefects in glucose uptake. However, someof the abnormalities in insulin signalingarepresent in pas-saged myotubes, suggesting the interaction of the in vivoenvironment with intrinsic defects to produce insulin re-sistance in vivo (267).

In 1995, Miller and colleagues (283) reported that ser-ine phosphorylation of human cytochrome P450c17, akey regulatory enzyme for ovarian and adrenal androgenbiosynthesis with both 17 -hydroxylase and C17, 20lyase activities, increases its C17,20 lyase activity (283).Thus, this posttranslational modification could result inincreased androgen production (283). This observationled to thehypothesis that thesame factor that serine-phos-phorylates the insulin receptor causing insulin resistancealso serine-phosphorylates P450c17 causing hyperandro-genism. Accordingly,some cases of PCOS could be causedby an activating mutation in a serine kinase (283285)

resulting in both hyperandrogenism and insulin resistance(Fig. 11).

There has been considerable interest in identifying acommon kinase that could cause serine phosphorylationaffectinginsulin signalingandsteroidogenesis. A screen of serine kinases in an adrenal cell line did not find evidencethat MAPK-ERK1/2 increases P450c17 activity (286).Conversely, this pathway may inhibit P450c17 in thecacells (see in Section V.A. and Ref. 287). In adrenal cells, aRho-associated, coiled-coil containing protein kinase 1was identified as a potential factor regulating the phos-phorylation of P450c17 (286).This kinasecanalso serine-phosphorylate IRS-1 and inhibit insulin signaling (288).However, attempts to prove that the same kinase can ser-ine-phosphorylate P450c17 and the insulin receptor bytransfecting P450c17 into skin fibroblasts from womenwi

pcos and insulin

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