Circular RNA circ_0000020 promotes osteogenic differentiation to reduce osteoporosis via sponging microRNA miR-142-5p to up-regulate Bone Morphogenetic Protein BMP2

This study was designed to study functions of Circ_0000020 during osteogenic differentiation. First, we used RT-qPCR to detect the expression of Circ_0000020, miR-142-5p and osteogenesis-related genes, whereas western blot analysis detected the expression of osteogenesis markers after the osteogenic differentiation of primary BMSCs isolated from rats. Alkaline phosphatase (ALP) activity and alizarin red Sstaining validated osteoblast phenotypes. Flow cytometry was used to detect cell apoptosis. Sh-Circ_0000020 was used to study the function of Circ_0000020 in osteogenic differentiation of BMSCs. Luciferase assay and RNA immunoprecipitation were used to validate the interaction between Circ_0000020 and miR-142-5p, and BMP2 and miR-142-5p. Co-transfection of miR-142-5p and sh-Circ_0000020 was used to verify the downstream signaling pathway. Circ_0000020 expression was up-regulated during osteogenic differentiation, whereas miR-142-5p expression was significantly decreased. Silencing Circ_0000020 inhibited osteogenic differentiation and promoted apoptosis, and inhibited ALP activity and mineralization ability. Moreover, Circ_0000020 interacts directly with miR-142-5p which binds to the BMP2 3ʹUTR and inhibits its expression. Additionally, co-transfection of miR-142-5p inhibitors and sh-Circ_0000020 rescued down-regulated BMP2, increased the expression osteogenesis-related gene expressions, and thereby rescued the inhibition of osteogenic differentiation induced by Circ_0000020 silencing. Furthermore, co-transfection of miR-142-5p inhibitors and sh-Circ_0000020 reversed Circ_0000020 silencing-induced downregulation of p-Smad1/5/8, Runx2, and Osterix protein levels. Circ_0000020 regulates BMP2 expression through sponging miR-142-5p as ceRNA, thereby positively regulating BMSCs osteogenic differentiation through Circ_0000020/miR-142-5p/BMP2/SMAD-dependent signaling pathway.