New insights into the mechanism of microvascular rarefaction via endothelial-mesenchymal transition in steroid-induced osteonecrosis of femoral head.

This study aimed to investigate the potential role of endothelial-to-mesenchymal transition (EndMT) in steroid-induced osteonecrosis of the femoral head (SONFH), evaluate its association with microvascular rarefaction and tissue damage, and preliminarily explore whether glucocorticoid-induced oxidative stress may be involved in this process. A combination of single-cell RNA sequencing (scRNA-seq), in vitro experiments, and animal models were employed. scRNA-seq was performed on SONFH cystic lesions to identify endothelial subpopulations and trace developmental trajectories. In vitro, human umbilical vein endothelial cells (HUVECs) were treated with methylprednisolone and antioxidant (N-acetylcysteine) intervention to assess EndMT features and endothelial function. In vivo, a glucocorticoid-induced SONFH mouse model was established with or without antioxidant intervention to evaluate changes in microvascular density, EndMT occurrence, and oxidative stress levels. scRNA-seq analysis revealed endothelial subpopulations with EndMT-like features in the cystic areas of SONFH. In vitro experiments demonstrated that glucocorticoid treatment downregulated endothelial markers and upregulated mesenchymal markers in HUVECs, accompanied by impaired angiogenic function, and antioxidant therapy improves these conditions. In vivo, glucocorticoid administration led to significant microvascular rarefaction and increased EndMT marker expression in the femoral head, along with elevated oxidative stress; these changes were partially alleviated by antioxidant treatment. This study is the first to identify a potential involvement of EndMT in the pathogenesis of SONFH, highlighting its close association with microvascular rarefaction. Targeting EndMT and its upstream regulators, such as oxidative stress, may offer novel strategies for the early intervention and treatment of SONFH.