Park, Juyoung1, Shi, Songtao2, Chen, Chider2
1University of Pennsylvania School of Dental Medicine, Department of Orthodontics
2University of Pennsylvania School of Dental Medicine, Department of Oral & Maxillofacial Surgery/Pharmacology
The success of stem cell-based regeneration depends on how to obtain and expand holoclonogenic stem cells, characterized by higher growth potential and long-term self-renewal capacity. In early stage of life, stem cells are highly active for tissue formation and organismal growth, but during adult reproductive phase, this growth is suppressed, and stem cells evolve to maintain tissue homeostasis and repair. This transition involves a shift in cellular metabolic program to accommodate to the tissue- and stage-specific stem cell function. However, the distinct metabolic program of stem cells at perinatal stage compared to that of somatic stem cells has yet fully elucidated.Methods
We used molecular biological analysis approaches, including quantitative PCR, Western blot, flow cytometry, inductive differentiation, immunofluorescence and histochemical staining, and colorimetric and respirometry assays to analyze cell metabolism, proliferation and function. Histomorphometric analysis including microCT, histochemical and immunohistochemical staining using transgenic mouse model were performed to examine craniofacial skeletal development of metabolically compromised mice.Results
Mandibular-derived mesenchymal stem cells (MMSCs) from newborn and adult mice employ distinct metabolic programs reflective of their functional requirements. Newborn MMSCs relied highly on oxidative phosphorylation (OxPhos) and generated more ATP to satisfy bioenergetic requirement for rapid proliferation, whereas adult MMSCs showed less reliance on OxPhos, reduced ATP generation, and slower proliferation rate. In line with this, newborn MMSCs had higher CFU-F, proliferation rate, and multilineage differentiation capacity in vitro than adult MMSCs. The cellular metabolism unique to each cell type was intrinsically regulated by the level of pluripotency genes, specifically Oct4 which is expressed higher in newborn MMSCs than adult MMSCs. Moreover, Oct4 expression positively correlated with expression of Pgc1-⍺, the master regulator of mitochondrial biogenesis, explicating OxPhos dependent metabolic program of newborn MMSCs. Loss of Pgc1-⍺ in the developing craniofacial skeleton caused depauperate skeletal phenotypes with overall undersized, hypostotic tissues.Conclusion
These findings explain functional difference between MMSCs from different stages of life in the context of metabolism and its genetic regulation. The role for Pgc1-⍺ and cognate cellular metabolic program in stem cell status and function, and the regulatory mechanisms flicking this metabolic switch would have great significance in understanding stem cell evolution processes.