title: The osteogenic or adipogenic lineage commitment of human mesenchymal stem cells is determined by protein kinase C delta.
abstract: BACKGROUND
  Mesenchymal stem cells (MSCs) have the potential to differentiate into specialized cell lineages such as osteoblasts and adipocytes in vitro. There exists a reciprocal relationship between osteogenic and adipogenic differentiation of MSCs that an osteogenic phenotype occurs at the expense of an adipogenic phenotype and vice versa, which in turn influence one another's phenotype through negative feedback loops. Thus, it is important to understand what signaling molecules modulate the lineage commitment of MSCs. Protein kinase C (PKC) plays a central role in cellular signal transduction for mediating diverse biological functions, and dysregulation of PKC activity is involved in various metabolic diseases including cancer, diabetes, and heart disease. Although the role of individual PKC isoforms has been investigated in various fields, the potential role of PKC in bone metabolism is not completely understood. In this study, we investigated the potential role of PKCδ in osteogenic lineage commitment of human bone marrow-derived mesenchymal stem cells (hBMSCs).
  
  
  RESULTS
  We observed that expression and phosphorylation of PKCδ were increased during osteogenic differentiation of hBMSCs. Pharmacological inhibition and genetic ablation of PKCδ in hBMSCs resulted in a significant attenuation of osteogenic differentiation as evidenced by reduced ALP activity and ECM mineralization, as well as down-regulation of the expression of osteoblast-specific genes. These effects were also accompanied by induction of adipogenic differentiation and up-regulation of the expression of adipocyte-specific genes involved in lipid synthesis in osteogenic induction of hBMSCs. Additionally, the activation of AMPK, which is a key cellular energy sensor, induced osteogenesis of hBMSCs. However, the inhibition of AMPK activity by compound C did not affect the activation of PKCδ at all, indicating that there is no direct correlation between AMPK and PKCδ in osteogenesis of hBMSCs.
  
  
  CONCLUSIONS
  These results suggest that PKCδ is a critical regulator for the balance between osteogenesis and adipogenesis of hBMSCs and thus has a potential novel therapeutic target for the treatment of metabolic bone diseases.
authors.forename: Sooho
authors.initials: S
authors.lastname: Lee
authors.forename: Hee-Yeon
authors.initials: HY
authors.lastname: Cho
authors.forename: Hang Thi Thuy
authors.initials: HT
authors.lastname: Bui
authors.forename: Dongchul
authors.initials: D
authors.lastname: Kang
mesh_terms: D017667:Adipocytes / Q000378:metabolism; D050156:Adipogenesis; D002454:Cell Differentiation; D019070:Cell Lineage; D002478:Cells, Cultured; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000201:enzymology*; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D010012:Osteogenesis; D051745:Protein Kinase C-delta / Q000378:metabolism*
chemical_list: D051745:Protein Kinase C-delta