||Adiponectin, a relatively abundant plasma protein secreted by adipocytes, exhibits various biological functions. Low plasma adiponectin levels are known to cause insulin resistance and metabolic syndrome. We previously demonstrated the expression of adiponectin receptors (AdipoR1 and AdipoR2) in osteoblasts, indicating that adiponectin may affect bone metabolism. In this study, we investigated gene expression in osteoblasts which showed suppressed receptor expression due to small interfering RNA (siRNA), to elucidate the influences of the failure of adiponectin action on bone metabolism.
Two days after transfecting siRNA against adiponectin receptors (siRNA-AdipoR), murine pro-osteoblastic cells were stimulated with ascorbic acid and β-glycerophosphate to induce osteoblast differentiation. The mRNA expression level was measured using real-time quantitative RT-PCR two days after stimulation.
Ascorbic acid and β-glycerophosphate-dependent induction of BMP-2 and osteocalcin were significantly suppressed by siRNA-AdipoR2 compared with non-silencing siRNA controls. Both mRNA expression levels of BMP-2 and osteocalcin were correlated with that of AdipoR2, while there was no correlation of osteoblast differentiation markers with AdipoR1; therefore, the failure of adiponectin action may suppress the progression of osteoblast differentiation and bone formation.