JNK signaling plays an important role in the effects of TNF-alpha and IL-1 beta on in vitro osteoblastic differentiation of cultured human periosteal-derived cells

Abstract

The purpose of this study was to examine the effects of TNF-alpha and IL-1 beta on in vitro osteoblastic differentiation of cultured human periosteal-derived cells. To examine the effects of TNF-alpha and IL-1 beta on in vitro osteoblastic differentiation of cultured human periosteal-derived cells, the cells cultured in the osteogenic induction medium were treated with 0.1-10 ng/ml TNF-alpha and 0.01-1 ng/ml IL-1 beta. TNF-alpha and IL-1 beta enhanced the alkaline phosphatase (ALP) activity and alizarin red S staining in cultured human periosteal-derived cells. However, these cytokines did not stimulate the Runt-related transcription factor (Runx) 2 activity and osteocalcin secretion. The ALP activity was decreased in the periosteal-derived cells pretreated with mitogen activated protein kinase (MAPK) inhibitors and then treated with TNF-alpha or IL-1 beta. Among the periosteal-derived cells pretreated with MAPK inhibitors, the ALP activity was markedly decreased in the cells pretreated with SP 600125, the specific inhibitor of C-Jun N-terminal kinase (JNK). The periosteal-derived cells treated with TNF-alpha and IL-1 beta showed an increase in extracellular signal-regulated kinase (ERK) and JNK phosphorylation. Among the ERK and JNK phosphorylation, JNK phosphorylation was strongly observed in the cells. These results suggest that TNF-alpha and IL-1 beta increased the in vitro osteoblastic differentiation of cultured human periosteal-derived cells by enhancing the ALP activity and mineralization process, but not by Runx2 activation. The functional role of TNF-alpha and IL-1 beta in increasing the ALP activity and mineralization of periosteal-derived cells primarily depends on the JNK signaling among the MAPK pathways.