Overexpression of miR-182 inhibits ossification of ligamentum flavum cells by targeting NAMPT

Ossification of the ligamentum flavum (OLF) is a debilitating disease resulting from the development of ectopic bone formation, which leads to the compression of the spinal cord. Nicotinamide phosphoribosyltransferase (NAMPT) was found to be upregulated and microRNA-182 (miR-182) was downregulated in OLF tissue. We investigated the effects of NAMPT and miR-182 expression in OLF cells and the influence on proteins associated with osteogenic differentiation. MiR-182 overexpression inhibited NAMPT, RUNX2, OCN and OPN mRNA and protein expression in OLF cells. Alkaline phosphatase (ALP) assay and Alizarin red staining confirmed reduced levels of osteogenic differentiation and mineralized nodule formation. Knockdown of NAMPT and the NAMPT inhibitor FK866 also inhibits RUNX2, OCN and OPN mRNA expression and protein levels, whereas over expression of NAMPT promotes the expression of RUNX2, OCN and OPN and the generation of bone nodules. Dual-luciferase reporter assays revealed that miR-182 directly targets NAMPT and downregulates its expression. Transfection of OLF cells with miR-182 downregulated NAMPT and suppressed the regulation of RUNX2, OCN, and OPN by NAMPT overexpression. Overall, these data demonstrate that miR-182 suppresses OLF by down regulating NAMPT.