Background and objective: Bone marrow-derived multipotent mesenchymal stem cells (BM-MSCs) can differentiate into osteoblasts via signal transduction pathways that cause nuclear responses. The extracellular signal-regulated kinase (ERK) and p38 signaling pathways control a variety of important cellular events, especially, cell proliferation, differentiation and apoptosis. The aim of this study was to elucidate the role of ERK and p38 signaling pathways involved in the osteogenic differentiation of BM-MSCs.
Methods: BM-MSCs were treated or non-treated with osteogenic differentiation medium (ODM) and specific inhibitors of ERK and p38. Cell proliferation, alkaline phosphatase (ALP) activity, calcium content, expression levels of osteogenic markers and mineralization were measured to assess osteogenic differentiation of BM-MSCs.
Results: ALP activity, calcium content, expression of ALP, osteopontin and osteocalcin, and calcium deposition were significantly enhanced by blocking the ERK pathway with U0126, but they were strongly down-regulated by inhibiting the p38 pathway with SB203580, indicating that U0126 enhanced osteogenic differentiation of BM-MSCs, whereas SB203580 suppressed osteogenic differentiation of BM-MSCs. Interestingly, Western Blot and immunofluorescent analysis showed that treatment with the p38 inhibitor resulted in an increase in the activated form of ERK, whereas treatment with the ERK inhibitor resulted in an increase in the activated form of p38.
Conclusions: These findings suggest that the ERK pathway is repressors of osteogenesis, whereas p38 pathway is an enhancer of osteogenesis of BM-MSCs via the cross-talk between ERK and p38 signaling pathways in BM-MSCs. Inhibition of ERK signaling pathway by U0126 may be useful for promoting osteogenesis during bone formation.
