Bone Abstracts

MicroRNAs (miRNAs) are small non-coding RNAs that have emerged as critical post-transcriptional regulators of gene expression. There is increasing evidence that miRNAs play an important role in osteoblast commitment and differentiation. The main aim of this study was to identify and characterize novel microRNAs regulating osteoblast functions. We report the role of mmu-miR-1187 in osteoblast differentiation and the mode by which it regulates osteogenesis. MicroRNA profiling of calvarial osteoblasts revealed that mmu-miR-1187 was ~8.5 fold down regulated in response to Med treatment. This data was further validated by qRT-PCR in calvarial osteoblasts. Over-expression of mmu-miR-1187 inhibited osteoblast differentiation, whereas inhibition of mmu-miR-1187 function promoted osteoblast differentiation and mineralization. Target prediction analysis tools and experimental validation by luciferase 3′ UTR reporter assay identified BMPRII as a direct target of mmu-miR-1187. Over expression of mmu-miR-1187 in osteoblasts led to down regulation of BMP-2 induced and cdc42 mediated actin cytoskeletal organization. All these results were reversed on transfection with anti-miR-1187. Additionally, after visualizing actin with TRITC-conjugated phalloidin, it was revealed that over expression of anti-miR-1187 resulted in increased actin polymerization and cortical protrusions formation. Invivo experiments revealed that on injecting miR-1187 subcutaneously in 1–2 days old Balb/c pups inhibited osteoblast differentiation, whereas inhibition of mmu-miR-1187 function promoted osteoblast differentiation in Balb/c calvaria. Our data suggests that binding of mmu-miR-1187 represses BMPRII thus inhibiting BMP2 signalling pathway which is required to activate cdc42 and phosphorylate LIMK1. LIMK1 is not able to inactivate cofilin which is an actin depolymerizing factor. mmu-miR-1187 may thus be inhibiting osteoblast functions by suppressing actin polymerization. Our findings suggest that therapeutic approaches targeting mmu-miR-1187 for enhancing osteoblast functions may be useful.

Disclosure: The authors declared no competing interests.