Expression of BMP-2 and Ets1 in BMP-2-stimulated mouse pre-osteoblast differentiation is regulated by microRNA-370

MicroRNAs (miRs) regulate several biological functions such as cell growth, cell differentiation, and carcinogenesis, by binding to the 3'-untranslated regions (3'-UTR) of specific target genes, in order to repress translation or promote degradation of the transcribed mRNAs. In the present study, using microRNA array and in silico analyses, we found that miR-370 regulates the expression of bone morphogenetic protein-2 (BMP-2) and V-ets Erythroblastosis Virus E26 Oncogene Homolog 1 (Ets1) in BMP-2-stimulated murine pre-osteoblast MC3T3-E1 cell differentiation. The enforced expression of mature miR-370 in MC3T3-E1 cells or primary osteoblast cells remarkably attenuated BMP-2-induced pre-osteoblast differentiation. To ascertain the mechanisms underlying the regulation of osteoblast differentiation by miR-370, we hypothesized a BMP-2-Ets1-PTHrP feed-forward loop regulatory mechanism.     

Adenovirus-mediated transfer of siRNA against Runx2/Cbfa1 inhibits the formation of heterotopic ossification in animal model

The heterotopic ossification of muscles, tendons, and ligaments is a common problem faced by orthopaedic surgeons. Runx2/Cbfa1 plays an essential role during the osteoblast differentiation and is considered as a molecular switch in osteoblast biology. RNA interference technology is a powerful tool for silencing endogenous or exogenous genes in mammalian cells. In this study, we investigated the effect of Runx2/Cbfa1-specific siRNA on osteoblast differentiation and mineralization in osteoblastic cells, and then constructed adenovirus containing siRNA against Runx2/Cbfa1 (Ad-Runx2-siRNA) to inhibit the formation of heterotopic ossification induced by BMP4, demineralized bone matrix, and trauma in animal model. Our results showed that the Runx2/Cbfa1-specific siRNA could inhibit the expression of Runx2/Cbfa1 at the level of mRNA and protein. Analysis of the expression of osteoblast maturation genes including type I collagen, osteopontin, bone sialoprotein, and osteocalcin, alkaline phosphatase activity, and matrix mineralization (von kossa) revealed that osteoblast differentiation was inhibited in cultured primary mouse osteoblasts transduced with Ad-Runx2-siRNA. Furthermore, adenovirus-mediated transfer of siRNA against Runx2/Cbfa1 could inhibit the formation of heterotopic ossification induced by BMP4, demineralized bone matrix, and trauma in animal model. It is likely that the inhibition of Runx2/Cbfa1 by RNAi could be developed as a powerful approach to prevent or treat heterotopic ossification.