Dental Stem Cells

Reviewed by Terrell F. Pannkuk, D.D.S. M.Sc.D

Mesenchymal Stem Cells Derived from Dental Tissues vs. Those from Other Sources: Their Biology and Role in Regenerative Medicine

G. T. –J. Huang, S. Gronthos, and S. Shi, J Dent Res 88 (9): 792-806, 2009

This presentation is an outline derived from the following article:

Stem Cells Derived from Dental TissuesMesenchymal Stem Cells (MSC’s)

Sources: Bone Marrow (Friedenstein et al, 1976; Caplan,

1991; Prockop, 1997; Pittenger et al, 1999; Gronthos et al, 2003)

Adipose Tissue/Umbilical Cord (Mareschi et al, 2001; Zuk et al, 2001)

Lineages: Osteogenic Chondrogenic Adipogenic

Other Lineages Possibly Derived from Bone Marrow Mesenchymal Stem Cells

MyogenicNeurogenic

Tenogenic

Dental Tissue MSC’s Human Pulp Tissue (DPSC’s, post-natal dental pulp stem

cells) Gronthos et al, 2000

Exfoliated Deciduous Teeth (SHED) Miura et al, 2003

Periodontal Ligament (PDLSC) Seo et al, 2004

Apical Papilla (SCAP) Sonoyama et al, 2006, 2008

Dental Follicle Precursors (DFPC) Morsczeck et al, 2005

Dental Stem Cell LineagesOsteo/Odontogenic

Adipogenic

Neurogenic

*Dental Stem cells appear to be more committed to odontogenic paths than BMMSC’s

BMMSC’sColony Forming Unit Fibroblasts (CFU-F’s)Self Renewal (like hematopoietic lines)30-50 PD’s (population doublings)Cell Surface MarkersHeterogeneity supports stromal hierarchy of

differentiationMinor proportion involved with extensive

proliferation

Dental MSC’sDental tissues are specialized tissues that do

not undergo continuous remodeling as shown in bony tissues

Dental mesenchyme is termed ‘ectomesenchyme’ due to its earlier interaction with the neural crest.

Isolation of Dental Pulp Stem CellsEnzymatically isolated and seeded onto

dentin to promote “Odontoblast-like” cells.

Multilineage differentiation of hDPSC subpopulations:AdipogenicNeurogenicOsteogenicChondrogenicMyogenic

Ectopic Formation of Dentin-Pulp-like Complex

Transplanted DPSC’s mixed with hydroxyapatite/tricalcium phosphate (HA/TCP) forms ectopic pulp-dentin like tissue complexes in immunocompromised mice.(Gronthos et al., 2000; Batouli et al., 2003)

Odontoblast-like cells express sialophosphoprotein (DSPP), producing dentinal tubules similar to natural dentin

SHED (Exfoliated Deciduous Teeth SC’s)Fast proliferationGreater PD (population doubling)Sphere like cluster formation (cultured

neurogenic mediumAlso termed “immature stem cells)Unable to regenerate a complete dentin-pulp

complex in vivoUnlike DPSC’s can differentiate into bone

forming cells.

SCAP ( Apical Papilla SC’s) Odontogenic differentiationAdipogenic differentiation

DPSC’s vs. SCAPApical papilla is a precursor to radicular pulpEarlier line of stem/progenator cells (SCAP)SCAP’s superior source of stem cells

PDLSC’s (periodontal ligament sc’s)Form cementoblasts and osteoblastsHomeostasis and regeneration of perio

tissuesCementum-PDL structure unique from

BMMSC’s and DPSC’s

DFPC’s (Dental Follicle Precursor Cells)

Periodontium, cementum, PDL, alveolar bone precursors

Source: impacted third molars

Dental MSC’s vs. BMMSC’s Gene Expression: 4000 known human genesCooperative regulation of genes for cell

signaling, cell communication, or metabolismBMMSC’s only form bone tissue in miceDPSC chondrogenic potential is weakBMMSC’s have stronger adipogenic potential

than both DPSC’s and SCAPNeurogenicity in dental stem cells more

potent than BMMSC’s (probably due to neural crest origin)

MSC NicheSpecialized microenvironment needed to

maintain stem cells in their multipotent state. (Schofield, 1978)

Considered a fixed compartment:Regulate proliferationControl fate of stem cell progenyPrevent exhaustion and death of stem cells(Scadden, 2006; Jones and Wagers, 2008)

• BMMSC niche-perivascular area of bone marrow

• DPSC niche-perivascular and perineural sheath areas

MSC HomingMSC’s in human blood is low under steady

state conditionsEx Vivo expanded MSC’s injected into the

blood stream have a limited capacity to home into various tissues and organs.

Injected Ex Vivo-expanded BMMSC’s through intravenous infusion lodge mainly in lungs, smaller amounts in liver, heart, spleen, and damaged areas of the brain.

No evidence that BMMSC’s migrate to orofacial /dental organs

Immunomodulation of MSC’s Allogenic MSC’s are well tolerated by the

recipient hosts (Xenografts do not take).MSC’s have an immunosuppressive effectPreliminary study shows interferon may act

to differentiate MSC’s into osteoblastsInflammatory reactions against scaffold

materials and serum components lead to the production of cytokines

Dental MSC-Based Therapy for Regenerative MedicineSCAP and PDLSC’s for Bio-root Engineering

Single cells from dog tooth buds at the bell stage seeded onto scaffolds and transplanted back into sockets resulted in some dentin structure regeneration with no enamel or root formation (Honda et al., 2006)

Kuo et al., 2007 used pigs, expanded ex vivo expansion of bud cells from bell stage and observed some root structures along with periodontium.

Obstacles to Tooth Regeneration

Abnormal (small) tooth size

Lack of consistent root formation

Incomplete eruption into functional occlusion.

Regeneration of Perio Defects with PDLSC’s

PDGF (platelet derived growth factor)IGF (insulin derived growth factor)PRP (platelet rich plasma)Cell based regenerative therapy:

Ex vivo expanded autologous BMMSC’s facilitated repair of perio defects (Yamada et al., 2006)

PDL regeneration is as important as bone regeneration otherwise ankylosis ensues

rhBMP-2 therapy does not regenerate PDLPDLSC’s may be an ideal source to regenerate PDL

(Liu et al., 2008)

Pulp Tissue Engineering/Regeneration

Early attempts (Myers and Fountain, 1974) allowed a blood clot to form in the canal but only connective tissue formed.

More recently pulp cells grown on polyglycolic acid (PGA) formed pulp-like tissue in vitro and in vivo (Gu et al., 1996; Moony et al., 1996, and Burma et al., 1999)

Since the isolation and characterization of DPSC’s SHED and SCAP, more sophisticated regenerative investigation has occurred (Huang et al., 2006, 2008; Murray et al., 2007; Prescott et al., 2008)

Modern Pulp RegenerationSHED seeded onto synthetic scaffolds seated

into pulp chamber space formed odontoblast-like cells that located against the existing dentin surface. (not orthotopic) (Cordeiro et al., 2008)

Speculation: undifferentiated MSC’s residing in the periapical tissue and BMMSC’s in the alveolar bone of the jaws can be introduced into the root canal space and via blood clots to allow for pulp tissue regeneration and formation of odontoblasts (Myers and Fountain, 1974)

Modern Pulp Regeneration (cont.)More realistically: the known characteristics of

PDLSC’s, DPSC’s, and SCAP suggest that it is unlikely that odontoblasts can be derived from PDL or periapical bone.

When BMMSC’s and DPSC’s are transplanted into the subcutaneous space of immunocompromised mice they form BM-like and Dentin-pulp like complexes respectively (Gronthos et al., 2000)

DPSC’s have shown osteogenic potential but there is no evidence showing BMMSC’s can give rise to functional odontoblasts and dentin.

The Future: Need to understand mechanisms of self-renewal and regulate

stem cell growth to generate sufficient numbers

Need to overcome regulation of differentiation into specific tissue production, specialized extracellular matrices (bone, dentin, cartilage, and tendon). The production of the extracellular matrix and its maturation into specialized tissues involves a sequential activation of cascades of signals.

Need to understand the interactions between stem cells and the immune system. Allogenic dental MSC’s may suppress recipient host short and long term immunorejection.

Controlling and preventing ex vivo expanded MSC’s from transformation . Adipose –derived MSC’s lost genetic stability over time and are prone to tumor formation (Rubio et al., 2005)