Regulation of mesenchymal stem cell chondrogenesis by glucose through protein kinase C/transforming growth factor signaling

Abstract

Effective induction of human mesenchymal stem cell (hMSC) differentiation for regenerative medicine applications remains a great challenge. While much research has studied hMSC activity during differentiation, it is unclear whether pre-differentiation culture can modulate differentiation capacity. We investigate the effect of glucose concentration in pre-differentiation/expansion culture on modulating chondrogenic capacity of hMSCs, and explore the underlying molecular mechanism. The extent of chondrogenesis of hMSCs previously cultured with different concentrations of glucose was evaluated. Transforming growth factor-beta (TGF-β) signaling molecules and protein kinase C (PKC) were analyzed to identify the role of these molecules in the regulation of glucose on chondrogenesis. In addition, hMSCs in high-glucose expansion culture were treated with the PKC inhibitor to modulate the activity of PKC and TGF-β signaling molecules. High-glucose maintained hMSCs were less chondrogenic than low-glucose maintained cells upon receiving differentiation signals. Interestingly, we found that high-glucose culture increased the phosphorylation of PKC and expression of type II TGF-β receptor (TGFβRII) in pre-differentiation hMSCs. However, low-glucose maintained hMSCs became more responsive to chondrogenic induction with increased PKC activation and TGFβRII expression than high-glucose maintained hMSCs during differentiation. Inhibiting the PKC activity of high-glucose maintained hMSCs during expansion culture upregulated the TGFβRII expression of chondrogenic cell pellets, and enhanced chondrogenesis. Our findings demonstrate the effect of glucose concentration on regulating the chondrogenic capability of pre-differentiation hMSCs, and provide insight into the mechanism of how glucose concentration regulates PKC and TGF-β signaling molecules to prime pre-differentiation hMSCs for subsequent chondrogenesis.