ALKBH4 Promotes Osteogenesis via Epigenetic Regulation of BMP2-Wnt/β-Catenin Signaling in Cervical Spine OPLL

DNA N6-methyladenine (6 mA) has recently been recognized as a novel epigenetic modification, with ALKBH4 identified as a specific demethylase. However, the role of ALKBH4 and DNA 6 mA in the pathogenesis of ossification of the posterior longitudinal ligament (OPLL) remains unclear. Tissue samples from OPLL patients and normal posterior longitudinal ligaments were collected, and ligament fibroblastic cells (LFCs) were isolated from OPLL tissues using primary culture. The expression and functional relevance of ALKBH4 in OPLL were investigated through reverse transcription quantitative polymerase chain reaction and western blot analyses. Osteogenic potential was further assessed using alizarin red S staining and alkaline phosphatase activity assays. Methylation status was evaluated by enzyme-linked immunosorbent assay and chromatin immunoprecipitation. Furthermore, the regulatory role of ALKBH4 in LFC ossification was investigated through the bone morphogenetic protein 2 (BMP2) and Wnt/β-catenin pathways. ALKBH4 expression was significantly elevated in both OPLL tissues and LFCs, whereas global 6 mA levels and BMP2-associated 6 mA were reduced. Overexpression of ALKBH4 promoted the ossification of LFCs, while its knockdown suppressed osteogenesis. ALKBH4-mediated DNA demethylation at the 6 mA site facilitated Yin Yang 1 (YY1) binding to the BMP2 promoter, enhancing BMP2 transcription and driving ossification. Silencing of BMP2, Wnt/β-catenin, or YY1 attenuated the pro-ossification effects of ALKBH4. Furthermore, the mutation that affects the action of ALKBH4 at the 6 mA site fails to induce the osteogenic effect of LFC. These findings demonstrate that ALKBH4 regulates OPLL progression by modulating BMP2 and Wnt/β-catenin signaling and by promoting BMP2 transcription through site-specific demethylation in human OPLL tissues and primary LFCs. ALKBH4 may therefore represent a promising therapeutic target for the management of OPLL.