TRAF6 mediates vascular remodeling via endoplasmic reticulum stress-mitophagy in hypoxic pulmonary hypertension

Hypoxia-induced pulmonary hypertension (HPH) is a cardiopulmonary disease marked by pulmonary vascular remodeling and elevated resistance in the pulmonary arteries. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a key mediator in the pathophysiology of multiple diseases, yet its functional involvement in HPH remains poorly understood.

We first examined TRAF6 expression and localization in lung tissues from HPH patients and experimental mouse models using Western blotting and immunofluorescence. Adeno-associated virus 9 (AAV9) with the SM22α promoter was used to achieve spatially restricted silencing of TRAF6 in vascular smooth muscle cells in vivo. Subsequently, hypoxic human pulmonary arterial smooth muscle cells (HPASMCs) were subjected in vitro to EdU proliferation assays, Transwell migration assays, Annexin V-FITC/PI apoptosis detection, electron microscopy, immunofluorescence, flow cytometry, qPCR, and Western blotting to evaluate TRAF6's effects on phenotypic modulation and mitophagy.

TRAF6 was significantly overexpressed in both human HPH tissues and experimental HPH mouse models. Inhibition of TRAF6 attenuated hypoxia-induced phenotypic switching of HPASMCs in vitro, while in vivo TRAF6 silencing ameliorated pulmonary vascular remodeling and right ventricular hypertrophy. Mechanistically, TRAF6 knockdown suppressed mitochondrial dysfunction and excessive mitophagy in HPASMCs under hypoxia. Notably, hypoxia upregulated TRAF6 expression in the endoplasmic reticulum (ER), where it selectively activated the IRE1/XBP1 signaling axis during ER stress. Crucially, inhibition of the IRE1α/XBP1s pathway partially reversed TRAF6-mediated regulation of mitophagy, proliferation, migration, and apoptosis resistance in HPASMCs.

Our findings demonstrate that TRAF6 exacerbates endoplasmic reticulum stress and dysregulates mitophagy, thereby driving pathological HPASMC proliferation and migration during HPH progression. TRAF6 inhibition presents a potential therapeutic intervention against the pathological vascular remodeling in HPH.