Ossification of the Posterior Longitudinal Ligament (OPLL) is a degenerative hyperostosis disease characterized by the transformation of the soft and elastic vertebral ligament into bone, resulting in limited spinal mobility and nerve compression. Employing both bulk and single-cell RNA sequencing, we elucidate the molecular characteristics, cellular components, and their evolution during the OPLL process at a single-cell resolution, and validate these findings in clinical samples. This study also uncovers the capability of ligament stem cells to exhibit endothelial cell-like phenotypes in vitro and in vivo. Notably, our study identifies LOXL2 as a key regulator in this process. Through gain-and loss-of-function studies, we elucidate the role of LOXL2 in the endothelial-like differentiation of ligament cells. It acts via the HIF1A pathway, promoting the secretion of downstream VEGFA and PDGF-BB. This function is not related to the enzymatic activity of LOXL2. Furthermore, we identify sorafenib, a broad-spectrum tyrosine kinase inhibitor, as an effective suppressor of LOXL2-mediated vascular morphogenesis. By disrupting the coupling between vascularization and osteogenesis, sorafenib demonstrates significant inhibition of OPLL progression in both BMP-induced and enpp1 deficiency-induced animal models while having no discernible effect on normal bone mass. These findings underscore the potential of sorafenib as a therapeutic intervention for OPLL.

后纵韧带骨化（OPLL）是一种退行性骨质增生疾病，其特征是柔软而有弹性的椎体韧带转变为骨骼，导致脊柱活动受限和神经受压。采用批量和单细胞 RNA 测序，我们以单细胞分辨率阐明了 OPLL 过程中的分子特征、细胞成分及其进化，并在临床样本中验证了这些发现。这项研究还揭示了韧带干细胞在体外和体内表现出内皮细胞样表型的能力。值得注意的是，我们的研究确定 LOXL2 是这一过程中的关键调节因子。通过功能获得和丧失的研究，我们阐明了 LOXL2 在韧带细胞内皮样分化中的作用。它通过 HIF1A 途径发挥作用，促进下游 VEGFA 和 PDGF-BB 的分泌。该功能与 LOXL2 的酶活性无关。此外，我们确定索拉非尼（一种广谱酪氨酸激酶抑制剂）是 LOXL2 介导的血管形态发生的有效抑制剂。通过破坏血管形成和成骨之间的耦合，索拉非尼在 BMP 诱导和enpp1缺乏诱导的动物模型中显示出对 OPLL 进展的显着抑制，同时对正常骨量没有明显影响。这些发现强调了索拉非尼作为 OPLL 治疗干预的潜力。