Inhibition of RUNX1 slows the progression of pulmonary hypertension by targeting CBX5

Pulmonary artery smooth muscle cell (PASMC) dysfunction is the central pathogenic mechanism in pulmonary hypertension (PH). This study explored the mechanism of action of RUNX1, a potential therapeutic target for PH, in PASMCs. A PH mouse model was used to investigate the impacts of RUNX1 knockdown on hemodynamics, right ventricular hypertrophy (RVH), and pulmonary artery remodeling (hematoxylin–eosin H&E staining). Isolated PASMCs were transfected with RUNX1- or chromobox 5 (CBX5)-related vectors and then subjected to cell function assays. Immunoprecipitation was used to detect molecular binding and ubiquitination. RUNX1 knockdown reduced right ventricular systolic pressure (RVSP), RVH, and pulmonary artery remodeling in mice with PH. Knockdown of RUNX1 or CBX5 suppressed proliferation, invasion, and migration and stimulated apoptosis in PASMCs under hypoxia. RUNX1 enhanced ubiquitin-specific protease 15 (USP15) promoter activity. USP15 bound to CBX5 and reduced CBX5 ubiquitination, thereby promoting CBX5 expression. CBX5 overexpression promoted the proliferation and movement of hypoxic PASMCs with reduced RUNX1 expression and decreased their apoptosis. In conclusion, RUNX1 knockdown inhibits USP15 transcription to promote the ubiquitination and degradation of CBX5, thereby alleviating PH in mice and reducing hypoxia-induced PASMC dysfunction.