Adiponectin increases BMP-2 expression in osteoblasts via AdipoR receptor signaling pathway

Adiponectin is a protein hormone secreted predominantly by differentiated adipocytes and involved in energy homeostasis. Bone morphogenetic protein (BMP) plays important roles in osteoblastic differentiation and bone formation. However, the effects of adiponectin on BMPs expression in cultured osteoblasts are largely unknown. Here we found that adiponectin increased mRNA expression of BMP-2 but not other BMPs in cultured osteoblastic cells. Stimulation of osteoblasts with adiponectin also increased protein levels of BMP-2 by Western blot and ELISA assay. Adiponectin-mediated BMP-2 expression was attenuated by 5'-AMP-activated protein kinase (AMPK) small interference RNA and AMPK inhibitor (araA and compound C). Activations of p38 and NF-kappaB pathways after adiponectin treatment were demonstrated, and adiponectin-induced expression of BMP-2 was inhibited by the specific inhibitor and mutant of p38 and NF-kappaB cascades. Taken together, our results provide evidence that adiponectin enhances BMP-2 expression in osteoblastic cells, and AdipoR1 receptor, AMPK, p38 and NF-kappaB signaling pathways may be involved in increasing BMP-2 expression by adiponectin.