In this study, we begin to investigate the underlying mechanism of leptin-induced vascular calcification. We found that treatment of cultured bovine aortic smooth muscle cells (BASMCs) with leptin (0.5-4 mu g/ml) induced osteoblast differentiation in a dose-dependent manner. Furthermore, we found that leptin significantly increased the mRNA expression of osteopontin and bone sialoprotein, while down-regulating matrix gla protein (MOP) expression in BASMCs. Key factors implicated in osteoblast differentiation, including members of the Wnt signaling pathway, were examined. Exposure to leptin enhanced phosphorylation of GSK-3 beta on serine-9 thereby inhibiting activity and promoting the nuclear accumulation of p-catenin. Transfection of BASMCs with an adenovirus that expressed constitutively active GSK-3 beta (Ad-GSK-3 beta S9A) resulted in a >2-fold increase in GSK-3 beta activity and a significant decrease in leptin-induced alkaline phosphatase (ALP) activity. In addition, qRT-PCR analysis showed that GSK-3 beta activation resulted in a significant decrease in the expression of osteopontin and bone sialoprotein, but a marked increase in MGP mRNA expression. When taken together, our results suggest a mechanism by which leptin promotes osteoblast differentiation and vascular calcification in vivo. (C) 2012 Elsevier Inc. All rights reserved.