MiR-103a: A Novel Mechano-sensitive MicroRNA Inhibits Bone Formation Through Targeting Runx2

ObjectivesEmerging evidence indicates that microRNAs(miRNAs)play essential roles in regulating osteoblastogenesis and bone formation.However,the role of miRNA in osteoblast mechanotransduction remains to be defined.In this study,we aimed to investigate if miRNAs regulate mechanical stimulation-triggered osteoblast differentiation and bone formation through modulation of Runx2,the master transcription factor for osteogenesis.MethodsWe first investigated the role of mechanical loading both in a mouse model and in osteoblasts culture system and the outcomes clearly demonstrated that mechanical stimuli can regulate osteogenesis and bone formation both in vivo and in vitro.ResultsUsing bioinformatic analyses and subsequently confirmed by quantitative Real-Time PCR(q RT-PCR),we identified miR-103 a as a novel mechano-sensitive miRNA in human preosteoblast cell lines.Both miR-103 a and its host gene PANK3 were downregulated during cyclic mechanical stretch-induced(CMS,8% elongation,0.5 Hz)osteoblast differentiation,whereas Runx2 protein expression was upregulated.Overexpression of miR-103 a significantly decreased Runx2 protein level and inhibition of miR-103 a increased Runx2 protein level,suggesting that miR-103 a acts as an endogenous attenuator of Runx2 in osteoblasts.Mutation of putative miR-103 a binding sites in Runx2 m RNA abolishes miR-103a-mediated repression of the Runx2 3'UTR luciferase reporter activity,suggesting that miR-103a binds to Runx2 3'UTR.Osteoblast marker genes profiling and osteogenic phenotype assays demonstrated that miR-103a negatively correlates with CMS-induced osteogenesis.Further,the perturbation of miR-103a also has a significant effect on osteoblast activity and matrix mineralization.More importantly,we found an inhibitory role of miR-103a in regulating bone formation in hindlimb unloading mice,and pretreatment with antagomir-103a partly rescued the osteoporosis caused by mechanical unloading.ConclusionTaken together,our data suggest that miR-103 a is the first identified mechano-sensitive miRNA that regulates osteoblast differentiation via directly targeting Runx2,and therapeutic inhibition of miR-103 a may be an efficient anabolic strategy for skeletal disorders caused by pathological mechanical loading.