Let-7c Regulates Proliferation and Osteodifferentiation of Human Adipose-derived Mesenchymal Stem Cells Under Oxidative Stress by Targeting SCD-1

Osteoporosis is a progressive bone disease characterized by decreased bone mass and density, which usually parallels a reduced antioxidative capacity and increased reactive oxygen species formation. Adipose-derived mesenchymal stem cells (ADMSCs), a population of self-renewing multipotent cells, are a well-recognized source of potential bone precursors with significant clinical potential for tissue regeneration. We previously showed that overexpressing stearoyl-CoA desaturase 1 (SCD-1) promotes osteogenic differentiation of mesenchymal stem cells. Micro-RNAs (miRNAs) are noncoding RNAs recently recognized to play key roles in many developmental processes, and miRNA let-7c is downregulated during osteoinduction. We found that let-7c was upregulated in the serum of patients with postmenopausal osteoporosis compared with healthy controls. Levels of let-7c during osteogenic differentiation of ADMSCs were examined under oxidative stress in vitro and found to be upregulated. Overexpression of let-7c inhibited osteogenic differentiation, whereas inhibition of let-7c function promoted this process, evidenced by increased expression of osteoblast-specific genes, alkaline phosphatase activity, and matrix mineralization. The luciferase reporter assay was used to validate SCD-1 as a target of let-7c. Further experiments showed that silencing of SCD-1 significantly attenuated the effect of let-7c inhibitor on osteoblast markers, providing strong evidence that let-7c modulates osteogenic differentiation by targeting SCD-1. Inhibition of let-7c promoted the translocation of β-catenin into nuclei, thus activating Wnt/β-catenin signaling. Collectively, these data suggest that let-7c is induced under oxidative stress conditions and in osteoporosis, reducing SCD-1 protein levels, switching off Wnt/β-catenin signaling, and inhibiting osteogenic differentiation. Thus, let-7c may be a potential therapeutic target in the treatment of osteoporosis and especially postmenopausal osteoporosis.