Glimepiride induces proliferation and differentiation of rat osteoblasts via the PI3-kinase/Akt pathway

Glimepiride is a third-generation sulfonylurea agent and is widely used in the treatment of type 2 diabetes mellitus. In addition to the stimulatory effects on pancreatic insulin secretion, glimepiride has also been reported to have extrapancreatic functions including activation of PI3 kinase (PI3K) and Akt in rat adipocytes and skeletal muscle. PI3-kinase and Akt are important signaling molecules in the regulation of proliferation and differentiation in various cells. This study investigated the actions of glimepiride in rat osteoblasts and the role of PI3K/Akt pathway. Cell proliferation was determined by measuring absorbance at 550 nm. Supernatant assay was used for measuring alkaline phosphatase activity. Western blot analysis was used for determining collagen I, insulin receptor substrate-1/2, PI3K/Akt, and endothelial nitric oxide synthase expression. We found that glimepiride significantly enhanced proliferation and differentiation of osteoblasts and led to activation of several key signaling molecules including insulin receptor substrate-1/2, PI3K/Akt, and endothelial nitric oxide synthase. Furthermore, a specific inhibitor of PI3K abolished the stimulatory effects of glimepiride on proliferation and differentiation. Taken together, these observations provide concrete evidence that glimepiride activates the PI3K/Akt pathway; and this activation is likely required for glimepiride to stimulate proliferation and differentiation of rat osteoblasts.