Downregulation of METTL14 improves postmenopausal osteoporosis via IGF2BP1 dependent posttranscriptional silencing of SMAD1

Osteoporosis (OP) tends to occur in postmenopausal women, making them prone to fractures. N6-methyladenosine (m6A) methylation plays a crucial role in OP. Herein, we aimed to explore the effects of METTL14 on osteogenesis and the underlying mechanism. Osteogenic differentiation was assessed through osteoblast markers expression, cell proliferation, ALP activity, and mineralization, which were detected by qRT-PCR, CCK-8, EdU assay, ALP staining assay, and ARS staining assay, respectively. Osteoporosis was evaluated in OVX mice using qRT-PCR, microcomputed tomography, and H&E staining assay. The levels of METTL14 and SMAD1 were measured using qRT-PCR and western blot, and their interaction was assessed using RIP and luciferase reporter assay. M6A methylation was analyzed using the Me-RIP assay. The results indicated that m6A, METTL14, and SMAD1 levels were downregulated in patients with OP and OVX mice, and upregulated in osteogenic BMSCs. Knockdown of METTL14 suppressed osteogenesis of BMSCs and reduced bone mass of OVX mice. Moreover, silencing of METTL14 positively related to SMAD1 and inhibited m6A modification of SMAD1 by suppressing its stability. IGF2BP1 was identified as the methylation reader, and which knockdown reversed the upregulation induced by SMAD1. Overexpression of SMAD1 reversed the suppression of osteogenic differentiation induced by METTL14 knockdown. In conclusion, interference with METTL14 inhibited osteogenic differentiation of BSMCs by m6A modification of SMAD1 in an IGFBP1 manner, suggesting that METTL14 might be a novel approach for improving osteoporosis.