Inhibition of JNK and ERK pathways by SP600125- and U0126-enhanced osteogenic differentiation of bone marrow stromal cells

Abstract

Bone marrow stromal cells (BMSCs) can undergo osteogenesis when treated with an osteogenic stimulus, which makes them a potential cell source for bone tissue engineering. MAPK signaling pathways involved in osteogenesis have shown opposing effects. The aim of this study was to characterize the MAPK signaling pathways involved in the osteogenic differentiation of BMSCs. Cells were treated or non-treated with osteogenic differentiation medium (ODM) and specific inhibitors of JNK, ERK, p38. Cell proliferation, alkaline phosphatase (ALP) activity, calcium content, expression levels of osteogenic markers and mineralization were measured to assess osteogenic differentiation of BMSCs. ALP activity, calcium content, expression of ALP, osteopontin and osteocalcin, and calcium deposition were significantly enhanced by blocking the JNK or ERK pathway with SP600125 and U0126, respectively but they were strongly down-regulated by inhibiting the p38 pathway with SB203580, indicating that SP600125 and U0126 enhanced osteogenic differentiation of BMSCs, whereas SB203580 suppressed osteogenic differentiation of BMSCs. In addition, 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. These findings suggest that the MAPK signaling pathways play a regulatory role in osteogenesis, in which, JNK and ERK pathways are repressors of osteogenesis, whereas p38 pathway is an enhancer of osteogenesis of BMSCs. A cross-talk between ERK and p38 signaling pathways in BMSCs by their specific inhibitors was observed. SP600125 and U0126 may be good candidates for promoting osteogenesis during bone formation.