SP1-stimulated miR-545-3p inhibits osteogenesis via targeting LRP5-activated Wnt/beta-catenin signaling.

Recently, the emerging role of microRNAs (miRNAs) has been identified in osteogenesis and the development of osteoporosis. Here, we found that miR-545-3p was decreased with the progression of osteogenic differentiation of MC3T3-E1 cells. Gain-of-function assay elucidated that ectopic expression of miR-545-3p led to abolishment on the levels of osteogenic differentiation markers including OC, ALP and Runx2, as well as increase on the expression of SOST, a negative regulator of osteogenic differentiation. Meanwhile, we explained that the inhibitory role of miR-545-3p in the proliferation of differentiated MC3T3-E1 cells was attributed to its induction on apoptosis. Furthermore, the mechanistic investigations validated that miR-545-3p inactivated Wnt/β-catenin signaling pathway by post-transcriptionally silencing LRP5. Importantly, we verified that miR-545-3p-confined osteogenic differentiation was mediated by the inhibition of LRP5-dependent Wnt/β-catenin pathway. Furthermore, it was identified that miR-545-3p downregulation in osteogenic differentiation was due to the positive transcriptional regulation by SP1, an osteoporosis-promoting transcription factor that was proved to be lessened along with osteoblastic differentiation. Jointly, this study elaborated that the SP1-modulated miR-545-3p functions as an osteogenesis-inhibitory factor through targeting LRP5 to inactivate Wnt/β-catenin signaling. Remarkably, strategies targeting miR-545-3p might be an innovative idea for the therapy of patients with osteoporosis.