EGR1 mediates METTL3/m6A/CHI3L1 to promote osteoclastogenesis in osteoporosis

Objective: To investigate EGR1-mediated METTL3/m6A/CHI3L1 axis in osteoporosis. Methods: Ovariectomy (OVX) was performed on mice to induce osteoporosis, followed by & mu;-CT scanning of femurs, histological staining, immunohistochemistry analysis of MMP9 and NFATc1, and ELISA of serum BGP, ALP, Ca, and CTX-I. The isolated mouse bone marrow mononuclear macrophages (BMMs) were differentiated into osteoclasts under cytokine stimulation. TRAP staining was performed to quantify osteoclasts. The levels of Nfatc1, c-Fos, Acp5, and Ctsk in osteoclasts, m6A level, and the relationships among EGR1, METTL3, and CHI3L1 were analyzed. Results: The EGR1/METTL3/CHI3L1 levels and m6A level were upregulated in osteoporotic mice and the derived BMMs. EGR1 was a transcription factor of METTL3. METTL3 promoted the post-transcriptional regulation of CHI3L1 by increasing m6A methylation. EGR1 downregulation reduced BMMs-differentiated osteoclasts and alleviated OVX-induced osteoporosis by regulating the METTL3/m6A/CHI3L1 axis. Conclusion: EGR1 promotes METTL3 transcription and increases m6A-modified CHI3L1 level, thereby stimulating osteoclast differentiation and osteoporosis development.