Dental Stem Cells

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Dental Stem Cells
Reviewed by Terrell F. Pannkuk, D.D.S. M.Sc.D
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Mesenchymal Stem Cells Derived from Dental
Tissues vs. Those from Other Sources Their
Biology and Role in Regenerative Medicine
This presentation is an outline derived from the
following article

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

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Stem Cells Derived
from Dental Tissues

• Mesenchymal Stem Cells (MSCs)
• 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

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Other Lineages Possibly Derived from Bone Marrow
Mesenchymal Stem Cells

• Myogenic
• Neurogenic
• Tenogenic

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Dental Tissue MSCs

• Human Pulp Tissue (DPSCs, 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

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Dental Stem Cell Lineages

• Osteo/Odontogenic
• Adipogenic
• Neurogenic
• Dental Stem cells appear to be more committed to
  odontogenic paths than BMMSCs

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BMMSCs

• Colony Forming Unit Fibroblasts (CFU-Fs)
• Self Renewal (like hematopoietic lines)
• 30-50 PDs (population doublings)
• Cell Surface Markers
• Heterogeneity supports stromal hierarchy of
  differentiation
• Minor proportion involved with extensive
  proliferation

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Dental MSCs

• Dental 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.

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Isolation of Dental Pulp Stem Cells

• Enzymatically isolated and seeded onto dentin to
  promote Odontoblast-like cells.
• Multilineage differentiation of hDPSC
  subpopulations
• Adipogenic
• Neurogenic
• Osteogenic
• Chondrogenic
• Myogenic

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Ectopic Formation of Dentin-Pulp-like Complex

• Transplanted DPSCs mixed with hydroxyapatite/tric
  alcium 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

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SHED (Exfoliated Deciduous Teeth SCs)

• Fast proliferation
• Greater PD (population doubling)
• Sphere like cluster formation (cultured
  neurogenic medium
• Also termed immature stem cells)
• Unable to regenerate a complete dentin-pulp
  complex in vivo
• Unlike DPSCs can differentiate into bone forming
  cells.

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SCAP ( Apical Papilla SCs)

• Odontogenic differentiation
• Adipogenic differentiation

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DPSCs vs. SCAP

• Apical papilla is a precursor to radicular pulp
• Earlier line of stem/progenator cells (SCAP)
• SCAPs superior source of stem cells

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PDLSCs (periodontal ligament scs)

• Form cementoblasts and osteoblasts
• Homeostasis and regeneration of perio tissues
• Cementum-PDL structure unique from BMMSCs and
  DPSCs

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DFPCs (Dental Follicle Precursor Cells)

• Periodontium, cementum, PDL, alveolar bone
  precursors
• Source impacted third molars

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Dental MSCs vs. BMMSCs

• Gene Expression 4000 known human genes
• Cooperative regulation of genes for cell
  signaling, cell communication, or metabolism
• BMMSCs only form bone tissue in mice
• DPSC chondrogenic potential is weak
• BMMSCs have stronger adipogenic potential than
  both DPSCs and SCAP
• Neurogenicity in dental stem cells more potent
  than BMMSCs (probably due to neural crest origin)

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MSC Niche

• Specialized microenvironment needed to maintain
  stem cells in their multipotent state.
  (Schofield, 1978)
• Considered a fixed compartment
• Regulate proliferation
• Control fate of stem cell progeny
• Prevent 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

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MSC Homing

• MSCs in human blood is low under steady state
  conditions
• Ex Vivo expanded MSCs injected into the blood
  stream have a limited capacity to home into
  various tissues and organs.
• Injected Ex Vivo-expanded BMMSCs through
  intravenous infusion lodge mainly in lungs,
  smaller amounts in liver, heart, spleen, and
  damaged areas of the brain.
• No evidence that BMMSCs migrate to orofacial
  /dental organs

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Immunomodulation of MSCs

• Allogenic MSCs are well tolerated by the
  recipient hosts (Xenografts do not take).
• MSCs have an immunosuppressive effect
• Preliminary study shows interferon may act to
  differentiate MSCs into osteoblasts
• Inflammatory reactions against scaffold materials
  and serum components lead to the production of
  cytokines

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Dental MSC-Based Therapy for
Regenerative Medicine

• SCAP and PDLSCs 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.

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Obstacles to Tooth Regeneration

• Abnormal (small) tooth size
• Lack of consistent root formation
• Incomplete eruption into functional occlusion.

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Regeneration of Perio Defects with PDLSCs

• PDGF (platelet derived growth factor)
• IGF (insulin derived growth factor)
• PRP (platelet rich plasma)
• Cell based regenerative therapy
• Ex vivo expanded autologous BMMSCs 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 PDL
• PDLSCs may be an ideal source to regenerate PDL
  (Liu et al., 2008)

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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
  DPSCs SHED and SCAP, more sophisticated
  regenerative investigation has occurred (Huang et
  al., 2006, 2008 Murray et al., 2007 Prescott et
  al., 2008)

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Modern Pulp Regeneration

• SHED 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 MSCs residing in
  the periapical tissue and BMMSCs 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)

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Modern Pulp Regeneration (cont.)

• More realistically the known characteristics of
  PDLSCs, DPSCs, and SCAP suggest that it is
  unlikely that odontoblasts can be derived from
  PDL or periapical bone.
• When BMMSCs and DPSCs are transplanted into the
  subcutaneous space of immunocompromised mice they
  form BM-like and Dentin-pulp like complexes
  respectively (Gronthos et al., 2000)
• DPSCs have shown osteogenic potential but there
  is no evidence showing BMMSCs can give rise to
  functional odontoblasts and dentin.

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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
  MSCs may suppress recipient host short and long
  term immunorejection.
• Controlling and preventing ex vivo expanded MSCs
  from transformation . Adipose derived MSCs
  lost genetic stability over time and are prone to
  tumor formation (Rubio et al., 2005)