Abstract Body (Do not enter title and authors here): Background:
Pulmonary arterial hypertension (PAH) is a progressive cardiopulmonary disorder characterized by elevated pulmonary arterial pressure, vascular remodeling, and right ventricular failure. Dysregulation of bone morphogenetic protein (BMP) and TGF-β signaling, including both canonical and non-canonical pathways, is central to PAH pathogenesis. The innate immune adaptor TIFA (TRAF-interacting protein with FHA domain) facilitates non-canonical TGF-β signaling by promoting TRAF6 oligomerization and K63-linked ubiquitination, but its contribution to pulmonary vascular remodeling remains undefined.
Methods:
TIFA expression, Thr9 phosphorylation, and TRAF6 oligomerization were assessed in pulmonary endothelial cells (ECs) from idiopathic PAH (IPAH) patients. Functional assays in human ECs examined the effects of TIFA overexpression or mutation (T9A) on TRAF6 activation and downstream signaling. BRCC3, a K63-specific deubiquitinase, was evaluated for its ability to deubiquitinate TIFA at Lys76 and Lys93. In vivo relevance was tested using TIFA knockout (KO), T9A knock-in, TIFA transgenic, and EC-specific BRCC3 KO mice exposed to chronic hypoxia/SU5416 to induce pulmonary hypertension.
Results:
IPAH pulmonary ECs displayed elevated TIFA expression, Thr9 phosphorylation, and TRAF6 oligomerization, alongside reduced BRCC3 levels. TIFA overexpression induced non-canonical TGF-β signaling and EC dysfunction in a Thr9-dependent manner, whereas BRCC3 overexpression reversed these effects via TIFA deubiquitination at Lys76 and Lys93. In vivo, TIFA deletion or T9A knock-in alleviated experimental PH, while EC-BRCC3 KO exacerbated disease severity. Notably, adenoviral delivery of a non-ubiquitatable TIFA mutant (K76/93R) in EC-BRCC3 KO mice rescued PH phenotypes and reduced inflammatory signaling.
Conclusions:
TIFA–TRAF6–mediated non-canonical TGF-β signaling drives endothelial dysfunction and pulmonary vascular remodeling in PAH. BRCC3 acts as an endogenous negative regulator by deubiquitinating TIFA and curbing TRAF6 activation. Modulating this axis may represent a promising strategy to counteract innate immune–driven vascular remodeling in PAH.