Effects of Insulin and IGF-1 on Osteoblast Differentiation and Mineralization

Introduction: insulin and the insulin-like growth factor 1 (IGF-1) are genetically related polypeptides that have similar tertiary structures and substantial amino acid identity. Like the cognate peptides, the insulin and IGF-1 receptors are cognate tyrosine kinase receptors which share the same signaling pathway in cells. The function and its underlying mechanism of insulin and IGF-1 in osteoblast differentiation have not been well defined. Objective: The purpose of this study was to characterize the role of insulin and IGF-1 in osteoblasts and examine the underlying mechanism of their functions. Methods: Primary osteoblasts were isolated from the calvaria of newborn C57B6 mouse and differentiated in the osteogenic medium supplemented with 50 µg/ml L-ascorbic acid and 5 mM ß-glycerol phosphate with insulin (10nM), IGF-1(10nM), or PBS control for twenty-one days totally. The medium was changed every two days. Alkaline phosphatase (ALP) and von Kossa staining was performed at day 7, 14 and day 14, 21. Western blotting for detecting the major molecules in the insulin/IGF-1 pathway was performed at day 7 and 14. Results: Both ALP and von Kossa staining were significantly increased by addition of insulin whereas decreased by addition of IGF-1 compared to the control. Western blotting showed that insulin induced phosphorylation of Akt and GSK3-ß and inhibited phosphorylation of ß-catenin compared with the control. In contrast, IGF-1 inhibited phosphorylation of Akt and GSK3-ß and enhanced phosphorylation of ß-catenin compared with the control. Both insulin and IGF-1 had no impact on Erk phosphorylation. Conclusions: These results suggest that insulin can promote the osteoblast differentiation and mineralization in vitro in contrast to IGF-1. And insulin and IGF-1 regulate the primary osteoblast differentiation through Akt-GSK3-ß-catenin pathway.