Identification of novel microRNA inhibiting actin cytoskeletal rearrangement thereby suppressing osteoblast differentiation

We report the role of mir-1187 in regulation of osteoblast functions. over-expression of mir-1187 inhibited osteoblast differentiation. target prediction analysis tools and experimental validation by luciferase 3′ utr reporter assay identified bmpr-ii and arhgef-9 as direct targets of mir-1187. arhgef-9 activates cdc42 which has a major role in actin reorganization. bmp-2 also induces actin polymerization. role of mir-1187 in actin reorganization was determined by western blotting, immunofluorescence, and in vivo gene silencing studies. reduced protein levels of bmpr-ii, activated cdc42, and downstream signaling molecules were observed in mir-1187-transfected osteoblasts. mir-1187 over-expression resulted in decreased actin polymerization. additionally, p-cofilin, which does not bind f-actin, was decreased in mir-1187-transfected cells. these results were corroborated by administration of bmpr-ii exogenously in mir-1187-transfected osteoblasts. silencing of mir-1187 in neonatal mice mitigated all the inhibitory effects of mir-1187 on actin cytoskeletal rearrangement. importantly, in vivo treatment of mir-1187 inhibitor to ovariectomized balb/c mice led to significant improvement in trabecular bone microarchitecture. overall, mir-1187 functions as a negative regulator of osteogenesis by repressing bmpr-ii and arhgef-9 expression thus suppressing non-smad bmp2/cdc42 signaling pathway and inhibiting actin reorganization. mir-1187 functions as a negative regulator of osteogenesis by repressing bmpr-ii expression, which in turn, suppresses non-smad bmp2/cdc42 signaling pathway, thus inhibiting actin cytoskeletal rearrangement. silencing of mir-1187 significantly improves trabecular bone microarchitecture. as mir-1187 exerts a negative regulatory role in osteoblasts function, hence, we propose that therapeutic approaches targeting mir-1187 could be useful in enhancing the bone formation and treatment of pathological conditions of bone loss.