urocortin: a protective peptide that targets both the myocardium and vasculature

Review

Urocortin: a protective peptide that targets boththe myocardium and vasculature

Sean M. Davidson, Derek M. Yellon

The Hatter Cardiovascular Institute, University College London Hospital and Medical School,

67 Chenies Mews, London WC1E 6HX, United Kingdom

Correspondence: Derek M. Yellon, e-mail: [email protected]

Abstract:

The urocortins are a family of endogenously produced peptide hormones that show great promise as potential drugs for the treatmentof heart disease. They can increase contractility and cardiac output without causing changes in mean arterial blood pressure. As ex-pected, the receptor for these peptides is present in cardiomyocytes, and they can bind and protect these cells from simulatedischemia and reperfusion in vitro. The receptor is present, however, in much higher density in the endothelial cells that form a con-tinuous lining of the coronary vasculature. Functionally, the urocortin peptides have been shown to have potent local vasodilatory ef-fects, and may affect other aspects of vascular function. In this review, we will attempt to distinguish the “cardio” from the“vascular” effects of urocortin and its homologues, including the archetypal family member, corticotrophin releasing hormone.

Key words: urocortin, heart, heart failure, cardiomyocytes, endothelial cells

Abbreviations: Ang II – angiotensin II, CRH – corticotrophinreleasing hormone, CRH-R – CRH receptor, iPLA2 – Ca2+-in-dependent phospholipase A2, MABP – mean arterial bloodpressure, MAPK – mitogen activated protein kinase, NO – ni-tric oxide, NOS – nitric oxide synthase), PKA – cAMP-dependent protein kinase A, PI3K – phosphoinositide 3-kinase,Ucn – urocortin

Introduction

Urocortin (Ucn 1) is an endogenously produced pep-tide hormone that shows great promise as a potentialdrug for the treatment of heart disease. It is able to in-crease cardiac output, cardiac contractility and heartrate with only small increases or even decreases inmean arterial pressure and systemic vascular resis-

tance (reviewed in [20]). However, in order to opti-mize its therapeutic efficacy, it is important tounderstand its pharmacology and to have a basic un-derstanding of its mechanism/s of action. In particu-lar, since its receptors are present in various organs, itis useful to be able to separate out local effects fromsystemic or centrally mediated effects. Furthermore,target tissues such as the heart contain numerous celltypes that might additionally mediate some of the ef-fects of urocortin and its homologues. Since endothe-lial dysfunction contributes to the development ofheart failure [7], an optimal therapeutic agent forheart disease might be anticipated to improve endo-thelial function, as well as myocyte function. Here,we review the known cardiovascular effects of uro-cortin, and discuss how some of these effects are dueto direct interaction with cardiomyocytes, while oth-ers appear to be mediated via the endothelium.

172 Pharmacological Reports, 2009, 61, 172–182

Pharmacological Reports

2009, 61, 172–182

ISSN 1734-1140

Copyright © 2009

by Institute of Pharmacology

Polish Academy of Sciences

Pharmacological Reports, 2009, 61, 172–182 173

Urocortin: a cardioprotective peptideSean M. Davidson and Derek M. Yellon

Tab. 1. Sequence alignment of human CRH family peptides

Sequences were aligned using ClustalW2 then highlighted using Boxshade 3.21, which shades conserved residues according to whether theyare completely conserved (black), or similar (grey)

Tab. 2. The distribution of the CRH peptides (A), and CRH receptors (B), in the heart

A

LocalizationPeptide

CRH Ucn 1 Ucn 2/SRP Ucn 3/SCP

Heart � human mRNA [47]

� human protein [47]

� human mRNA [47]



� mouse mRNA[15]

� human mRNA & protein[38]

� mouse mRNA [52]

� human mRNA (weak) [38]



Myocytes � rat neonatal mRNA [56]

� rat neonatal mRNA [9]

� rat neonatal mRNA [55]

� rat mRNA [6]

� neonatal mouse mRNA[55]

� rat mRNA [6]

Fibroblasts � rat neonatal mRNA [55] � neonatal mouse mRNA[55]

Endothelial cells � human protein [37] � rat protein [40] � human endocardiumprotein [73]

Smooth muscle cells � rat protein [40]

B

LocalizationReceptor

CRH-R1 CRH-R21 CRH-R2� CRH-R2�

Heart � human mRNA [47] � human mRNA [47] � human mRNA LA2 [47]

Myocytes � neonatal mouse mRNA[55]

� human binding activity[79]



Fibroblasts � neonatal mouse mRNA[55]



Endothelial cells � human mRNA & protein[78]

� human binding activity[79]

Smooth muscle cells

Localization has been determined for mRNA or protein, or receptor binding activity as indicated.� = detected, � = not detected. Blank panelsindicate no data available. 1 CRH-R2 splice variant was not determined in these studies. 2 LA = left atrium only

Urocortin belongs to a family of hormones that arehighly evolutionarily conserved (Tab. 1) [26]. Corti-cotrophin releasing hormone (CRH), the archetypalmember of this peptide family, is expressed primarilyin the brain, where it has an important role in regulat-ing thermogenesis and energy homeostasis [26, 55]. Itis unlikely to have major direct effects on the heartsince it is not expressed there locally, and its plasmaconcentration is very low. However, there are nowthree known mammalian paralogues of CRH that aredetectable in plasma – these are called urocortin(Ucn 1), urocortin 2 (Ucn 2, also called stresscopin-related peptide or SRP)[39] and urocortin 3 (Ucn 3,also called stresscopin or SCP) [39]. The term “uro-cortin”, when used here, refers to all of the paralogues– Ucn 1, Ucn 2 and Ucn 3.

There are two receptors that can bind CRH, CRH-R1and CRH-R2. Both belong to the G-protein coupled,seven transmembrane domain receptor family (GPCR),and couple to multiple signal transduction pathwaysincluding those involving cAMP/PKA, MAPK,NO/cGMP, and calcium channels (reviewed in [37]).Both receptors are expressed in the brain, though onlyCRH-R2 is detected in the heart. In cell-based assays,Ucn 1 can bind and activate both receptors, though it ismore potent than CRH at activating CRH-R2 [73]. Ucn2 and Ucn 3, however, activate only CRH-R2 and notCRH-R1 [39, 50] – they therefore represent therapeu-tic agents with potential cardiac-specificity. They arealso highly potent, and increase cAMP levels in cellsexpressing CRH-R2 with an EC50 of 10–9 – 10–10 M[39, 50, 73], although in some studies, Ucn 2 is lesspotent [39]. There are two splice variants of CRH-R2– which may have different expression patterns [46] –however, binding studies indicate they have verysimilar binding affinities [39, 50].

The CRH peptides are widely expressed in the brain,although their level of expression is variable andmainly restricted to neurons in certain regions [26].Ucn 1 and Ucn 2 are widely expressed in the cardio-vascular system as well as other tissues, particularlyadrenals, placenta, endometrium, the immune systemand the digestive system (reviewed in [26]). There maybe some species-specific differences in expression,since no Ucn 2 mRNA was detected in mouse heart byRNAse protection assay [16], despite strong levelshaving been detected by RT-PCR of human heart sam-ples [39] (Tab. 2). On the other hand, this may bea matter of sensitivity since RT-PCR was able to detectUcn 2 expression in isolated rat neonatal cardiomyo-

cytes [9]. Similarly, although Ucn 3 mRNA was notdetected in the mouse heart [50] or isolated neonatalrat cardiomyocytes [9], it was detectable in humanheart samples by RT-PCR [39], corresponding to ap-proximately 0.74–1.15 pmol/g wet weight Ucn 3 pro-tein when measured by radioimmunoassay [69].

Since unmodified urocortin peptides have a rea-sonably long half-life in plasma, circulating urocortinmay be more relevant to cardiovascular regulation. Innormal sheep, arterial plasma Ucn 1 measures 15.2 ±0.5 pM and this increases with heart failure to 19.1 ±1.6 pM, though it appears to be secreted not by theheart, but by other organs such as the liver and kidney[15]. In contrast, Ucn 1 in tail vein blood rose fromundetectable levels to ~8 pM following sublethal car-diac ischemia and reperfusion in rats [47]. Experi-ments with isolated perfused rat hearts indicate thatsome of this Ucn 1 originates from the heart itself[47], suggesting that acute ischemia might induce lo-cal release. An increase in plasma Ucn 1 levels hasalso been observed, from ~19 pM in normal humanmales to ~50 pM in those with systolic heart failure[52]. In another study, ~11 pM plasma Ucn 1 wasmeasured in humans with stable congestive cardiacfailure [24]. Ucn 2 has been detected in healthy hu-man plasma at 90 pM (95% CI 50–170 pM) [21], in-creasing to 230 pM (95% CI 40–420 pM) in heart fail-ure patients [22]. Only one study has reported theplasma concentration of Ucn 3, which was 52 ± 16 pMin healthy human subjects [69].

In considering the effect of Ucn on the heart, it isimportant to bear in mind that Ucn may potentiallyhave effects independently even from the myocar-dium or vasculature. For example, injection of CRHor Ucn 3 into the brain has been shown to modulatecardiovascular function by increasing plasma cate-cholamines [17]. However, when administered to ratsintravenously, the same dose had no effect on meanarterial blood pressure or heart rate [17]. Using directmeasurements of cardiac efferent sympathetic neuralactivity in conscious sheep, bolus intravenous admini-stration of 2.5 �g to 100 �g Ucn 1 was found to re-duce cardiac sympathetic nerve activity, independ-ently of effects on hemodynamic parameters, includ-ing heart rate, mean arterial pressure and cardiacoutput, and with no changes in plasma norepinephrineor epinephrine levels [14]. These doses raised circu-lating levels of peptide to approximately 50 and 250 pMin the low-dose group and to approximately 1200 and5000 pM, i.e., to pathophysiological and pharmacol-


ogical ranges, respectively, at higher doses. On theother hand, Ucn 1 is also able to induce increases incardiac output, heart rate and cardiac contractility inthe absence of an intact autonomic nervous system,i.e.: in sheep subjected to ganglionic blockade withhexamethonium [57]. These responses must be coor-dinated by CRH receptors present in cells of the heart.

Which cell types express the CRH

receptor in the heart?

Most of the above studies examining tissue expres-sion levels of CRH receptor have used whole tissuesamples containing blood vessels, fibroblasts, and po-tentially even hematopoietic cells, etc. Other analyseshave revealed that expression is cell-type restricted(Tab. 2). For example, in one experiment comparingcultured neonatal rat myocytes with cardiac fibro-blasts, quantitative RT-PCR revealed CRH-R2� ex-pression predominantly in the myocytes, but not fi-broblasts [53]. However, by in situ hybridization,a much higher level of CHR-R2 mRNA was localizedto the arterioles within the myocardium than in thecardiomyocytes themselves [58]. Similarly, high lev-els of CRH-R2� protein have been detected in the rataortic vascular endothelium [44] and CRH-R2 was

detected in human coronary artery and microvascularendothelial cells [74] as well as the endothelium ofvarious other vascular beds [12, 26]. Indeed, ~80% ofthe specific binding of radio-labeled CRH to rabbitaortas was localized to the endothelial layer [19].

In a particularly informative experiment, sectionsof human left ventricle were incubated with [125I]-antisauvagine – a truncated form of the amphibianCRH-R agonist “sauvagine”, a receptor antagonistthat binds with up to 1000-fold selectivity for CRH-R2 [75]. This experiment revealed that the density ofCRH-R2 receptors was actually ~5.7 fold greater insmall intramyocardial blood vessels of human LV (di-ameters < 200 �m), than in cardiomyocytes (Fig. 1)[75]. The overall receptor binding density was ofa similar order to that of other cardiovascular recep-tors such as the AT1 receptor (~1 fmol/mg protein)[75]. This illustrates the potential significance of theendothelial effects of CRH-R2 ligands.

Which cells express the CRH family

peptides in the heart?

Given that CRH peptides are found in the blood, andthat the highest levels of the receptor may be in thecardiac vasculature, it is possible that urocortins act



Fig. 1. Distribution of the CRH receptor in human left ventricle as determined by binding of 0.2 nM [125I]antisauvagine 30 to a tissue section.(A) Total binding and (B) nonspecific binding [75]. CA, coronary artery; IMB, intramyocardial blood vessel; M, myocardium. Reprinted with per-mission from Macmillan Publishers Ltd.: British Journal of Pharmacology, 143 (2004) 508–514, copyright (2004)

primarily as systemically produced hormones that caninfluence cardiac function. However, there is also thepossibility of locally restricted regulation by urocortinif it is indeed produced by cells in the heart. There-fore, it is important to establish which cells in theheart might actually produce the CRH peptides in theheart (Tab. 2). The above-cited study comparing cul-tured neonatal rat cardiac fibroblasts and neonatal car-diac cardiomyocytes detected Ucn 1 mRNA in bothcell types by quantitative RT-PCR [53]. Ucn 1 immu-noreactivity was detected in the myocytes of humanhearts, with a significantly increased intensity ofstaining in failing hearts [53]. Strong Ucn 1 immuno-reactivity has also been localized to the endotheliallayer of coronary arteries and microvessels in rats andhumans, though it was not present in smooth musclecells [38, 40]. Immunoreactivity for Ucn 2 was identi-fied in the mouse myocardium, particularly in theatrium, and not in a large coronary blood vessel, butthe low magnification of the published image makes itimpossible to determine whether the microvessels ex-pressed Ucn 2 [39]. Immunoreactivity for Ucn 3 hasbeen identified in human cardiomyocytes, but not inendocardium or pericardial adipocytes [69].

Evidence from in vitro studies suggests that cardiacfibroblasts may also be able to secrete Ucn 1 [41], butthe question remains as to whether this Ucn is free toenter into the circulation, or whether it instead acts lo-cally on cells expressing CRH-R2. It is not knownwhether the Ucn 1 observed in the perfusate of isolatedrat hearts originates from endothelial cells or myo-cytes. In other vascular beds such as human umbilicalveins, the endothelium appears to be capable of releas-ing CRH peptides [68]. Indeed, expression and releaseof Ucn 1 from human endothelial cells was increasedby treatment with pitavastatin, and serum Ucn 1 levelsin healthy male volunteers increased from 11.0 ± 6.5 to16.4 ± 7.3 ng/ml after treatment with pitavastatin(2 mg/day) for 4 weeks [38]. Treatment with 10 nMUcn 1 suppressed angiotensin II-induced ROS in iso-lated endothelial cells [38], suggesting that Ucn maymediate part of the pleiotropic effects of statins.

The effects of CRH ligands on cardiac

myocytes

CRH-related peptides have potent inotropic and lusi-tropic effects on the hearts of rats and sheep [5, 56,

70] caused by activation of the CRH-R2 receptor [5,18], and independent of �-adrenergic receptors [5].This appears to be due to direct activation of CRH-R2in cardiomyocytes, since Ucn 2 has the same effect onisolated cardiomyocytes via CRH-R2-mediated sti-mulation of PKA, with an EC50 of 10.7 nM, a similarpotency to that observed in vivo [78].

Each of the CRH peptides have been shown tohave potent cardioprotective properties both in vivo

and in vitro in the isolated perfused rat heart, and theycan also directly protect isolated cardiomyocytes fromsimulated ischemia and reperfusion injury [9, 10, 47,54, 71]. This must involve the rapid activation of pro-tective signaling pathway/s, since protection can alsobe achieved by administration of Ucn peptides duringthe early minutes of reperfusion [65], when myocytedamage is believed to rapidly accrue [35]. Indeed, in-hibition of either the PI3K/Akt [9, 11] or ERK1/2MAPK [67] signaling kinase pathways at reperfusioneliminates the protection afforded by Ucn peptides(reviewed in [20, 48]). These pathways have been col-lectively identified as the “reperfusion injury salvagekinase (RISK)” pathways [34, 67], and evidence sug-gests they underlie most, if not all, acute cardioprotec-tive mechanisms [35].

Incubation of isolated myocytes with Ucn peptidesalso induces a hypertrophic response, namely an in-crease in secretion of atrial natriuretic peptide (ANP)and brain natriuretic peptide (BNP), as well as an in-crease in protein synthesis activity [13, 42, 43, 64].This appears to involve the PI3K/Akt but not theERK1/2 MAPK pathway [13] and is also blunted bythe PKA inhibitor, H-89 [43].

If circulating Ucn peptides are to influence cardiacfunction by directly binding receptors on cardiomyo-cytes in the intact heart, one question which remainsto be addressed is how readily Ucn can cross the con-tinual, non-fenestrated endothelial layer which linesthe cardiac vasculature. In mice, intravenously in-jected Ucn 1 does not enter the brain, presumably be-cause of the blood-brain-barrier, which may be con-sidered as an impermeable barrier formed by peri-cytes, astrocytes and endothelial cells [8]. Duringhyperglycemia or in the presence of leptin, however,Ucn binds CRH-R2 and is transported unidirection-ally across the endothelial cells of the blood-brain-barrier (reviewed in [55]). It is not known if a similarmechanism exists to regulate access of Ucn to the car-diac parenchyma. There is strong evidence, however,that Ucn can bind to cardiac endothelial cells and


modulate vascular tone and function, as described inthe following section.

The effect of CRH ligands on vascular

tension

Intravenous administration of Ucn 1 causes a strong andsustained vasodilatory response in mice, which is absentin those lacking CRH-R2 [3, 18, 73]. These mice alsohave elevated resting mean arterial blood pressure(MABP) [18], suggesting that basal systemic vasculartone is influenced by CRH-R2. This led to the proposalthat CRH peptides have distinct roles in the brain and inthe body; intracerebrovascular CRH stimulates nora-drenergic sympathetic nervous outflow, increasing meanarterial pressure and regional blood flow appropriate forthe “fight-or-flight” response [1, 27], whereas peripheralCRH-R2 signals restore homeostasis during the recov-ery phase of the stress response [18].

In contrast to the effects noted in rodents, however,hypotensive effects have only been detected in mon-keys and in humans at the highest doses of CRH used[36, 72], perhaps because lower effective plasma con-centrations were obtained in these studies. Similarly,in humans, no in vivo hemodynamic effects of Ucn 1were observed following intravenous administration[23, 24], despite hemodynamic effects having beenobserved with Ucn 1 in sheep [56, 61]. Even in sheep,the hemodynamic effects of Ucn 1 are augmented inheart failure compared to healthy sheep [61], raisingthe possibility that various factors (i.e.: species, healthstatus, effective plasma concentration), contribute tothe heterogeneity in responses. Further evidence thatthe systemic, homeostatic regulatory system involv-ing CRH-R2 is more highly activated during diseasecomes from experiments in which sheep were injectedwith an antagonist of the CRH receptors. In thosewith experimental heart failure there was an increasein MABP, but in healthy sheep the increase was non-significant (though the trend remained) [62].

More consistent results have been obtained afteradministration of Ucn 2, which decreased MABP bothin normal sheep and humans, and in those with heartfailure [21, 22, 59]. Interestingly, it was suggested inthe human study that the decrease in blood pressuremay have contributed to the increase in cardiac outputby reducing afterload, though it was not possible todistinguish this possibility from any direct inotropic

effect that Ucn 2 may have on the heart [21]. It seemsquite likely that some of the changes in vascular ten-sion may be confounded by several variables, includ-ing changes in cardiac contractile activity. For exam-ple, the tachycardia observed in rats injected withUcn 1 or Ucn 2 is due to autonomic nervous activa-tion, mainly through baroreflex mechanisms [30].

The vascular effects of Ucn peptides may be spe-cific or localized to particular organs. For example,the immediate hypotensive response to CRH peptidesis believed to be due mainly to vasodilation of mesen-teric arteries [49]. A number of studies have evaluatedthe direct vasorelaxant properties of Ucn in isolatedorgans. The CRH-induced vasorelaxation of isolatedrat mesenteric resistance arteries was originally foundto be endothelial-independent [49], though a later studyrevealed a second component to the response whichwas endothelial-dependent and involved eNOS [6].

To some extent, whether Ucn-mediated vasorelaxa-tion is mediated by the endothelium via nitric oxide re-lease or by direct actions on smooth muscle may de-pend on the tissue of origin. For example, Ucn 1-me-diated vasodilation requires intact endothelium inuterine arteries [45], but not in rat isolated basilar arter-ies [66]. With respect to the heart, CRF, Ucn 1 and Ucn2 have all been shown to cause direct coronary arteryvasodilation [31, 32, 40, 70]. In pigs, coronary vasodi-lation in response to Ucn 2 was found to be NOS-de-pendent [31], strongly suggesting the involvement ofthe endothelium. Nitric oxide was also required for thesustained increase in coronary flow in the isolated per-fused working rat heart model exposed to CRH, al-though there seems to be an additional nitric oxide-independent component [32]. Similarly, Ucn 1 – medi-ated vasodilation of rat coronary arteries appears tohave both an endothelial-dependent and an endothelial-independent component [40, 70]. The endothelium-dependent component has an IC50 of 2.5 nM and ismediated by endothelial nitric oxide and subsequentactivation of Ba2+-sensitive K+ channels, while theendothelium-independent component has an IC50 of16.5 nM and is cyclic GMP-dependent [40, 79].

Other vascular effects of CRH ligands

In addition to causing coronary vasorelaxation itself,Ucn 1 protects coronary endothelial function againstthe damage of ischemia-reperfusion, preserving vaso-



relaxation in response to acetylcholine [28, 29]. Endo-thelial survival in response to ischemia and reperfu-sion is also improved by Ucn 1 treatment, with lowerlevels of apoptosis detected in the isolated perfused ratheart after co-immunostaining with antibodies againstactive caspase 3 and von Willebrand factor [65].

It has been suggested that Ucn may also have somedetrimental effects on the endothelium [76], however,the evidence is mixed and may be species-specific.Yang et al. measured elevated activity of angiotensinconverting enzyme (ACE) in the tissue of rats admin-istered Ucn 1 intravenously and in aortic endothelialcells treated with Ucn 1 [76, 77]. This would be ex-pected to increase the levels of bioactive Ang II,which is vasoconstrictive and prothrombotic. On theother hand, serum ACE levels were decreased in thesame rats [77]. In sheep with experimental heart fail-ure, endogenous urocortins reduce vascular tone andrenin-aldosterone/endothelin activity [62], and ad-ministration of Ucn 1 strongly decreased plasmaAng II levels [61]. Elevated Ang II levels were de-tected in healthy humans injected intravenously withUcn 2 but only at high doses (i.e.: bolus of 100 �g at-taining plasma Ucn 2 levels of nearly 500 pM) [21].The effect of Ucn 2 on Ang II levels in heart failurepatients cannot be determined from published experi-ments since the majority of these patients were receiv-ing ACE inhibitors [22, 23].

There is accumulating evidence that Ucn peptidescan modulate the immune response via binding recep-tors of both type CRH-R1 and CRH-R2 that have beenidentified in monocytes, macrophages and T lympho-cytes [26] (reviewed in [2]). Given that some of thesecell types also express CRH peptides, it is possible thatthey might have detrimental, pro-inflammatory effectson the endothelium, for example increasing the perme-ability of the brain microvessel endothelial layer in theblood-brain barrier [25]. On the other hand, peripheralinjection of urocortins has been shown to decreaseedema in rat paws exposed to heat [39].

Urocortins may also have more profound, long-termeffects on the vasculature, although this has not yetbeen extensively investigated. Ligands of CRH-R2may confer tonic inhibition of vascularization sincemice lacking CRH-R2 develop profound postnatal hy-pervascularization [4]. Treatment with CRH-R2 ago-nists can also inhibit capillary formation by endothelialcells in vitro [4], and also strikingly inhibits the growthand vascularization of some tumors in vivo [33].

In summary, urocortins appear to have varied andpowerful regulatory effects on vascular and endothe-

lial survival, proliferation and function, though manyquestions remain to be addressed in this area. For ex-ample, would the cardioprotective benefits of long-term treatment with Ucn in heart failure be out-weighed by its apparent anti-angiogenic properties?

Therapeutic potential

In view of the highly favorable effects on the heart,CRH peptides have been proposed as pharmacologi-cal agents for the treatment of heart disease. Studiesare underway to test the potential utility of CRH pep-tide for anxiety-related disorders, but the urocortinsare viewed as having greater potential in treating car-diovascular disease. Indeed, phase I clinical studiesusing Ucn 2 have already been performed, with phaseII studies being planned. A recent study of experimen-tal heart failure found that co-treatment with Ucn 2was more beneficial than treatment with an ACE in-hibitor alone [63]. Since each of the urocortins is be-lieved to activate the same receptor, potential differ-ences in therapeutic efficacy are likely to lie in theirslightly different pharmacokinetic profiles. The half-life of Ucn 1 has been determined to be 52 min [24] or54 ± 3 min [23], compared to a half-life of Ucn 2 inhealthy humans of 10.1 min [22]. Ucn 3 appears tohave a more rapid onset of action and a shorter dura-tion of action [60].

Ucn may have additional protective qualities in-cluding antioxidative properties. For example, treat-ment of obese db/db mice with Ucn 1 decreased gly-cation and malondialdehyde levels, ameliorating dia-betic nephropathy without affecting blood glucose orinsulin, though the mechanism is unknown [51].Similarly, levels of oxidative stress caused by ische-mia and reperfusion injury in isolated rat hearts wasdramatically reduced by Ucn treatment, which trans-lated into significantly decreased size of infarct [71].As mentioned, Ucn has also been observed to de-crease Ang II-stimulated ROS production [38].

Conclusion

Since the original discovery of the central role ofCRH in brain function, the known roles for the other


members of the family – the urocortins – have ex-panded throughout the other organs of the body. Thisseparation of roles is perhaps not so surprising whenone appreciates the fact that the urocortins are actu-ally more similar in sequence to each other and to uro-tensin – a protein in fish with roles in systemic ho-meostasis – than to CRH [73]. Even within a singleorgan, the variable expression of CRH-R2 across dif-ferent cell types suggests multiple roles for itsligands. For example, whereas in vitro studies candemonstrate the efficacy of urocortins in protectingagainst ischemia and reperfusion injury in cardiomyo-cytes, this does not exclude the possibility that theyalso protect the function of coronary vasculature, ashas been determined in studies using isolated perfusedhearts. The relative importance of these activities inthe intact heart is difficult to determine. AlthoughCRH-R2 is around five times more abundant on thesurface of endothelial cells than on cardiomyocytes,suggesting a more prominent role for urocortin in thecoronary vasculature, perhaps its abundance there ac-tually reflects a role in the specific transport of uro-cortin across the endothelial layer to the cardiomyo-cytes, as has been demonstrated in the brain. Certainlythe inotropic effects of intravenously administeredurocortins indicate a direct role for urocortin on car-diomyocytes in vivo, yet the involvement of CRH-R2ligands in inhibiting neovascularization also indicatesthey have powerful roles in regulating angiogenesis.It is likely, it will not be possible to selectively acti-vate the receptors in just one organ or cell type, there-fore it is important to understand the range of effectsthat urocortin has in each of them. There seem to besome species-specific differences in this regard. Pro-misingly, however, the majority of the effects ex-plored thus far appear to be beneficial in terms of hu-man therapy, although longer term studies in humansremain to be performed.

Acknowledgments:

SD acknowledges funding from the Medical Research Council.

DY acknowledges funding from the British Heart Foundation.

References:

1. Abdelrahman AM, Lin LS, Pang CC: Influence of uro-cortin and corticotropin releasing factor on venous tonein conscious rats. Eur J Pharmacol, 2005, 510, 107–111.

2. Baigent SM: Peripheral corticotropin-releasing hormoneand urocortin in the control of the immune response.Peptides, 2001, 22, 809–820.

3. Bale TL, Contarino A, Smith GW, Chan R, Gold LH,Sawchenko PE, Koob GF et al.: Mice deficient forcorticotropin-releasing hormone receptor-2 displayanxiety-like behaviour and are hypersensitive to stress.Nat Genet, 2000, 24, 410–414.

4. Bale TL, Giordano FJ, Hickey RP, Huang Y, Nath AK,Peterson KL, Vale WW, Lee KF: Corticotropin-releasingfactor receptor 2 is a tonic suppressor of vascularization.Proc Natl Acad Sci USA, 2002, 99, 7734–7749.

5. Bale TL, Hoshijima M, Gu Y, Dalton N, Anderson KR,Lee KF, Rivier J et al.: The cardiovascular physiologicactions of urocortin II: acute effects in murine heart fail-ure. Proc Natl Acad Sci USA, 2004, 101, 3697–3702.

6. Barker DM, Corder R: Studies of the role ofendothelium-dependent nitric oxide release in the sus-tained vasodilator effects of corticotrophin releasing fac-tor and sauvagine. Br J Pharmacol, 1999, 126, 317–325.

7. Bauersachs J, Widder JD: Endothelial dysfunction inheart failure. Pharmacol Rep, 2008, 60, 119–226.

8. Bernacki J, Dobrowolska A, Nierwiñska K, Ma³ecki A:Physiology and pharmacological role of the blood-brainbarrier. Pharmacol Rep, 2008, 60, 600–622.

9. Brar BK, Jonassen AK, Egorina EM, Chen A, Negro A,Perrin MH, Mjos OD et al.: Urocortin-II and urocortin-IIIare cardioprotective against ischemia reperfusion injury:an essential endogenous cardioprotective role for corti-cotropin releasing factor receptor type 2 in the murineheart. Endocrinology, 2004, 145, 24–35.

10. Brar BK, Jonassen AK, Stephanou A, Santilli G,Railson J, Knight RA, Yellon DM, Latchman DS:Urocortin protects against ischemic and reperfusioninjury via a MAPK-dependent pathway. J Biol Chem,2000, 275, 8508–8514.

11. Brar BK, Stephanou A, Knight R, Latchman DS:Activation of protein kinase B/Akt by urocortin is essen-tial for its ability to protect cardiac cells against hypoxia/reoxygenation-induced cell death. J Mol Cell Cardiol,2002, 34, 483–492.

12. Cantarella G, Lempereur L, Lombardo G, Chiarenza A,Pafumi C, Zappala G, Bernardini R: Divergent effects ofcorticotropin releasing hormone on endothelial cell nitricoxide synthase are associated with different expressionof CRH type 1 and 2 receptors. Br J Pharmacol, 2001,134, 837–844.

13. Chanalaris A, Lawrence KM, Townsend PA, Davidson S,Jamshidi Y, Stephanou A, Knight RD et al.: Hypertro-phic effects of urocortin homologous peptides are medi-ated via activation of the Akt pathway. Biochem BiophysRes Commun, 2005, 328, 442–448.

14. Charles CJ, Jardine DL, Nicholls MG, Rademaker MT,Richards AM: Urocortin 1 exhibits potent inhibition ofcardiac sympathetic nerve activity in conscious sheep.J Hypertens, 2008, 26, 53–60.

15. Charles CJ, Rademaker MT, Richards AM, Yandle TG:Plasma urocortin 1 in sheep: regional sampling and ef-fects of experimental heart failure. Peptides, 2006, 27,1801–1805.



16. Chen A, Blount A, Vaughan J, Brar B, Vale W:Urocortin II gene is highly expressed in mouse skinand skeletal muscle tissues: localization, basal expres-sion in corticotropin-releasing factor receptor (CRFR)1- and CRFR2-null mice, and regulation by glucocorti-coids. Endocrinology, 2004, 145, 2445–2457.

17. Chu CP, Qiu DL, Kato K, Kunitake T, Watanabe S,Yu NS, Nakazato M, Kannan H: Central stresscopinmodulates cardiovascular function through the adrenalmedulla in conscious rats. Regul Pept, 2004, 119, 53–59.

18. Coste SC, Kesterson RA, Heldwein KA, Stevens SL,Heard AD, Hollis JH, Murray SE et al.: Abnormal adap-tations to stress and impaired cardiovascular function inmice lacking corticotropin-releasing hormone receptor-2.Nat Genet, 2000, 24, 403–409.

19. Dashwood MR, Andrews HE, Wei ET: Binding of[125I]Tyr-corticotropin-releasing factor to rabbit aortais reduced by removal of the endothelium. Eur J Pharma-col, 1987, 135, 111–112.

20. Davidson SM, Rybka AE, Townsend PA: The powerfulcardioprotective effects of urocortin and the corticotropinreleasing hormone (CRH) family. Biochem Pharmacol,2009, 77, 141–150.

21. Davis ME, Pemberton CJ, Yandle TG, Fisher SF, Lainch-bury JG, Frampton CM, Rademaker MT, Richards AM:Urocortin 2 infusion in healthy humans: hemodynamic,neurohormonal, and renal responses. J Am Coll Cardiol,2007, 49, 461–471.

22. Davis ME, Pemberton CJ, Yandle TG, Fisher SF, Lainch-bury JG, Frampton CM, Rademaker MT, Richards AM:Urocortin 2 infusion in human heart failure. Eur Heart J,2007, 28, 2589–2597.

23. Davis ME, Pemberton CJ, Yandle TG, Lainchbury JG,Rademaker MT, Nicholls MG, Frampton CM, RichardsAM: Effect of urocortin 1 infusion in humans with stablecongestive cardiac failure. Clin Sci (Lond), 2005, 109,381–388.

24. Davis ME, Pemberton CJ, Yandle TG, Lainchbury JG,Rademaker MT, Nicholls MG, Frampton CM, RichardsAM: Urocortin-1 infusion in normal humans. J Clin En-docrinol Metab, 2004, 89, 1402–1409.

25. Esposito P, Basu S, Letourneau R, Jacobson S, Theoha-rides TC: Corticotropin-releasing factor (CRF) can di-rectly affect brain microvessel endothelial cells. BrainRes, 2003, 968, 192–198.

26. Fekete EM, Zorrilla EP: Physiology, pharmacology, andtherapeutic relevance of urocortins in mammals: ancientCRF paralogs. Front Neuroendocrinol, 2007, 28, 1–27.

27. Fisher LA, Jessen G, Brown MR: Corticotropin-releas-ing factor (CRF): mechanism to elevate mean arterialpressure and heart rate. Regul Pept, 1983, 5, 153–161.

28. Garcia-Villalon AL, Amezquita YM, Monge L, Fernan-dez N, Climent B, Sanchez A, Dieguez G: Mechanismsof the protective effects of urocortin on coronary endo-thelial function during ischemia-reperfusion in rat iso-lated hearts. Br J Pharmacol, 2005, 145, 490–494.

29. Garcia-Villalon AL, Sanz E, Monge L, Fernandez N,Climent B, Dieguez G: Urocortin protects coronaryendothelial function during ischemia-reperfusion:a brief communication. Exp Biol Med (Maywood),2004, 229, 118–120.

30. Gardiner SM, March JE, Kemp PA, Bennett T: A com-parison between the cardiovascular actions of urocortin 1and urocortin 2 (stresscopin-related peptide) in consciousrats. J Pharmacol Exp Ther, 2007, 321, 221–226.

31. Grossini E, Molinari C, Mary DA, Marino P, Vacca G:The effect of urocortin II administration on the coronarycirculation and cardiac function in the anaesthetized pigis nitric-oxide-dependent. Eur J Pharmacol, 2008, 578,242–248.

32. Grunt M, Glaser J, Schmidhuber H, Pauschinger P,Born J: Effects of corticotropin-releasing factor onisolated rat heart activity. Am J Physiol, 1993, 264,H1124–H1129.

33. Hao Z, Huang Y, Cleman J, Jovin IS, Vale WW, Bale TL,Giordano FJ: Urocortin2 inhibits tumor growth via ef-fects on vascularization and cell proliferation. Proc NatlAcad Sci USA, 2008, 105, 3939–3944.

34. Hausenloy DJ, Yellon DM: New directions for protectingthe heart against ischaemia-reperfusion injury: targetingthe Reperfusion Injury Salvage Kinase (RISK)-pathway.Cardiovasc Res, 2004, 61, 448–460.

35. Hausenloy DJ, Yellon DM: Survival kinases in ischemicpreconditioning and postconditioning. Cardiovasc Res,2006, 70, 240–253.

36. Hermus AR, Pieters GF, Willemsen JJ, Ross HA, SmalsAG, Benraad TJ, Kloppenborg PW: Hypotensive effectsof ovine and human corticotrophin-releasing factors inman. Eur J Clin Pharmacol, 1987, 31, 531–534.

37. Hillhouse EW, Grammatopoulos DK: The molecularmechanisms underlying the regulation of the biologicalactivity of corticotropin-releasing hormone receptors:implications for physiology and pathophysiology.Endocr Rev, 2006, 27, 260–286.

38. Honjo T, Inoue N, Shiraki R, Kobayashi S, Otsui K,Takahashi M, Hirata K et al.: Endothelial urocortin haspotent antioxidative properties and is upregulated byinflammatory cytokines and pitavastatin. J Vasc Res,2006, 43, 131–138.

39. Hsu SY, Hsueh AJ: Human stresscopin and stresscopin-related peptide are selective ligands for the type 2corticotropin-releasing hormone receptor. Nat Med,2001, 7, 605–611.

40. Huang Y, Chan FL, Lau CW, Tsang SY, He GW, ChenZY, Yao X: Urocortin-induced endothelium-dependentrelaxation of rat coronary artery: role of nitric oxide andK+ channels. Br J Pharmacol, 2002, 135, 1467–1476.

41. Ikeda K, Tojo K, Oki Y, Nakao K: Urocortin has cell-proliferative effects on cardiac non-myocytes. Life Sci,2002, 71, 1929–1938.

42. Ikeda K, Tojo K, Otsubo C, Udagawa T, Hosoya T,Tajima N, Nakao K, Kawamura M: Effects of urocortinII on neonatal rat cardiac myocytes and non-myocytes.Peptides, 2005, 26, 2473–2481.

43. Ikeda K, Tojo K, Sato S, Ebisawa T, Tokudome G,Hosoya T, Harada M et al.: Urocortin, a newly identifiedcorticotropin-releasing factor-related mammalian pep-tide, stimulates atrial natriuretic peptide and brainnatriuretic peptide secretions from neonatal rat cardio-myocytes. Biochem Biophys Res Commun, 1998, 250,298–304.


44. Jain V, Longo M, Ali M, Saade GR, Chwalisz K,Garfield RE: Expression of receptors for corticotropin-releasing factor in the vasculature of pregnant rats.J Soc Gynecol Investig, 2000, 7, 153–160.

45. Jain V, Vedernikov YP, Saade GR, Chwalisz K,Garfield RE: Endothelium-dependent and -independentmechanisms of vasorelaxation by corticotropin-releasingfactor in pregnant rat uterine artery. J Pharmacol ExpTher, 1999, 288, 407–413.

46. Kimura Y, Takahashi K, Totsune K, Muramatsu Y,Kaneko C, Darnel AD, Suzuki T et al.: Expression ofurocortin and corticotropin-releasing factor receptorsubtypes in the human heart. J Clin Endocrinol Metab,2002, 87, 340–346.

47. Knight RA, Chen-Scarabelli C, Yuan Z, McCauley RB,Di RJ, Scarabelli GM, Townsend PA et al.: Cardiac re-lease of urocortin precedes the occurrence of irreversiblemyocardial damage in the rat heart exposed to ische-mia/reperfusion injury. FEBS Lett, 2008, 582, 984–990.

48. Lawrence KM, Latchman DS: The Urocortins: mecha-nisms of cardioprotection and therapeutic potential.Mini Rev Med Chem, 2006, 6, 1119–1126.

49. Lei S, Richter R, Bienert M, Mulvany MJ: Relaxing ac-tions of corticotropin-releasing factor on rat resistancearteries. Br J Pharmacol, 1993, 108, 941–947.

50. Lewis K, Li C, Perrin MH, Blount A, Kunitake K,Donaldson C, Vaughan J et al.: Identification of uro-cortin III, an additional member of the corticotropin-releasing factor (CRF) family with high affinity forthe CRF2 receptor. Proc Natl Acad Sci USA, 2001, 98,7570–7575.

51. Li X, Hu J, Zhang R, Sun X, Zhang Q, Guan X, Chen Jet al.: Urocortin ameliorates diabetic nephropathy inobese db/db mice. Br J Pharmacol, 2008, 154, 1025–1034.

52. Ng LL, Loke IW, O’Brien RJ, Squire IB, Davies JE:Plasma urocortin in human systolic heart failure. ClinSci (Lond), 2004, 106, 383–388.

53. Nishikimi T, Miyata A, Horio T, Yoshihara F, Nagaya N,Takishita S, Yutani C et al.: Urocortin, a member of thecorticotropin-releasing factor family, in normal and dis-eased heart. Am J Physiol Heart Circ Physiol, 2000, 279,H3031–H3039.

54. Okosi A, Brar BK, Chan M, D’Souza L, Smith E,Stephanou A, Latchman DS et al.: Expression and pro-tective effects of urocortin in cardiac myocytes. Neuro-peptides, 1998, 32, 167–171.

55. Pan W, Kastin AJ: Urocortin and the brain. Prog Neuro-biol, 2008, 84, 148–156.

56. Parkes DG, Vaughan J, Rivier J, Vale W, May CN:Cardiac inotropic actions of urocortin in conscioussheep. Am J Physiol Heart Circ Physiol, 1997, 272,H2115–H2122.

57. Parkes DG, Weisinger RS, May CN: Cardiovascular ac-tions of CRH and urocortin: an update. Peptides, 2001,22, 821–827.

58. Perrin M, Donaldson C, Chen R, Blount A, Berggren T,Bilezikjian L, Sawchenko P, Vale W: Identification ofa second corticotropin-releasing factor receptor gene andcharacterization of a cDNA expressed in heart. Proc NatlAcad Sci USA, 1995, 92, 2969–2973.

59. Rademaker MT, Cameron VA, Charles CJ, Richards AM:Integrated hemodynamic, hormonal, and renal actions ofurocortin 2 in normal and paced sheep: beneficial effectsin heart failure. Circulation, 2005, 112, 3624–3632.

60. Rademaker MT, Cameron VA, Charles CJ, RichardsAM: Urocortin 3: haemodynamic, hormonal, and renaleffects in experimental heart failure. Eur Heart J, 2006,27, 2088–2098.

61. Rademaker MT, Charles CJ, Espiner EA, Fisher S,Frampton CM, Kirkpatrick CM, Lainchbury JG et al.:Beneficial hemodynamic, endocrine, and renal effects ofurocortin in experimental heart failure: comparison withnormal sheep. J Am Coll Cardiol, 2002, 40, 1495–1505.

62. Rademaker MT, Charles CJ, Espiner EA, Frampton CM,Lainchbury JG, Richards AM: Endogenous urocortinsreduce vascular tone and renin-aldosterone/endothelinactivity in experimental heart failure. Eur Heart J, 2005,26, 2046–2054.

63. Rademaker MT, Charles CJ, Nicholls MG, Richards AM:Urocortin 2 combined with angiotensin-converting en-zyme inhibition in experimental heart failure. Clin Sci(Lond), 2008, 114, 635–642.

64. Railson JE, Liao Z, Brar BK, Buddle JC, Pennica D,Stephanou A, Latchman DS: Cardiotrophin-1 andurocortin cause protection by the same pathway andhypertrophy via distinct pathways in cardiac myocytes.Cytokine, 2002, 17, 243–253.

65. Scarabelli TM, Pasini E, Stephanou A, Comini L,Curello S, Raddino R, Ferrari R et al.: Urocortin pro-motes hemodynamic and bioenergetic recovery and im-proves cell survival in the isolated rat heart exposed toischemia/reperfusion. J Am Coll Cardiol, 2002, 40,155–161.

66. Schilling L, Kanzler C, Schmiedek P, Ehrenreich H:Characterization of the relaxant action of urocortin,a new peptide related to corticotropin-releasing factor inthe rat isolated basilar artery. Br J Pharmacol, 1998, 125,1164–1171.

67. Schulman D, Latchman DS, Yellon DM: Urocortin pro-tects the heart from reperfusion injury via upregulationof p42/p44 MAPK signaling pathway. Am J PhysiolHeart Circ Physiol, 2002, 283, H1481–H1488.

68. Simoncini T, Apa R, Reis FM, Miceli F, Stomati M,Driul L, Lanzone A et al.: Human umbilical vein endo-thelial cells: a new source and potential target forcorticotropin-releasing factor. J Clin Endocrinol Metab,1999, 84, 2802–2806.

69. Takahashi K, Totsune K, Murakami O, Saruta M,Nakabayashi M, Suzuki T, Sasano H, Shibahara S:Expression of urocortin III/stresscopin in human heartand kidney. J Clin Endocrinol Metab, 2004, 89,1897–1903.

70. Terui K, Higashiyama A, Horiba N, Furukawa KI,Motomura S, Suda T: Coronary vasodilation and positiveinotropism by urocortin in the isolated rat heart. J Endo-crinol, 2001, 169, 177–183.

71. Townsend PA, Davidson SM, Clarke SJ, Khaliulin I,Carroll CJ, Scarabelli TM, Knight RA et al.: Urocortinprevents mitochondrial permeability transition in re-sponse to reperfusion injury indirectly by reducing



oxidative stress. Am J Physiol Heart Circ Physiol,2007, 293, H928–H938.

72. Udelsman R, Gallucci WT, Bacher J, Loriaux DL,Chrousos GP: Hemodynamic effects of corticotropinreleasing hormone in the anesthetized cynomolgusmonkey. Peptides, 1986, 7, 465–471.

73. Vaughan J, Donaldson C, Bittencourt J, Perrin MH,Lewis K, Sutton S, Chan R et al.: Urocortin, a mammal-ian neuropeptide related to fish urotensin I and tocorticotropin-releasing factor. Nature, 1995, 378,287–292.

74. Wilbert-Lampen U, Trapp A, Modrzik M, Fiedler B,Straube F, Plasse A: Effects of corticotropin-releasinghormone (CRH) on endothelin-1 and NO release, medi-ated by CRH receptor subtype R2: a potential link be-tween stress and endothelial dysfunction? J PsychosomRes, 2006, 61, 453–460.

75. Wiley KE, Davenport AP: CRF2 receptors are highlyexpressed in the human cardiovascular system and theircognate ligands urocortins 2 and 3 are potent vasodila-tors. Br J Pharmacol, 2004, 143, 508–514.

76. Yang C, Xu Y, Li S: Urocortin: a beneficial or detrimen-tal agent to endothelium? Biochem Biophys Res Com-mun, 2008, 371, 345–349.

77. Yang C, Xu Y, Mendez T, Wang F, Yang Q, Li S: Effectsof intravenous urocortin on angiotensin-converting en-zyme in rats. Vascul Pharmacol, 2006, 44, 238–246.

78. Yang LZ, Kockskamper J, Heinzel FR, Hauber M,Walther S, Spiess J, Pieske B: Urocortin II enhancescontractility in rabbit ventricular myocytes via CRF(2)receptor-mediated stimulation of protein kinase A.Cardiovasc Res, 2006, 69, 402–411.

79. Yao X, He GW, Chan FL, Lau CW, Tsang SY, Chen ZY,Huang Y: Endothelium-dependent and -independentcoronary relaxation induced by urocortin. J Card Surg,2002, 17, 347–349.

Received:

December 18, 2008; in revised form: January 22, 2009.


urocortin: a protective peptide that targets both the myocardium and vasculature

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