Vascular receptor autoantibodies in pulmonary arterial hypertension associated with systemic sclerosis

Rationale: Systemic sclerosis (SSc)-associated pulmonary arterial hypertension (PAH) portends worse outcome than other forms of PAH. Vasoconstrictive and vascular remodeling actions of endothelin (ET) 1 and angiotensin (Ang) II via endothelin receptor type A (ET_AR) and Ang receptor type-1 (AT₁R) activation are implicated in PAH pathogenesis. Objectives: We hypothesized that stimulating autoantibodies (Abs) targeting and activating AT₁R and ET_AR may contribute to SSc-PAH pathogenesis, and tested their functional and biomarker relevance. Methods: Anti-AT₁R and -ET_AR Abs were detected by ELISA in different cohorts of patients and tested in vitro and in an animal model for their pathophysiological effects. Measurements and Main Results: The Abs were significantly higher and more prevalent in patients with SSc-PAH (n = 81) and connective tissue disease-associated PAH (n = 110) compared with other forms of PAH/pulmonary hypertension (n = 106). High anti- AT₁R and anti-ET_AR Abs predicted development of SSc-PAH and SSc-PAH-related mortality in a prospective analysis. Both Abs increased endothelial cytosolic Ca²⁺ concentrations in isolated perfused rat lungs, which could be blocked by respective specific receptor antagonists. Ab-mediated stimulation of intralobar pulmonary rat artery ring segments increased vasoconstrictive responses to Ang II and ET-1, and implicated cross-talk between both pathways demonstrated by reciprocal blockade with respective antagonists. Transfer of SSc-IgG containing both autoantibodies into healthy C57BL/6J mice led to more abundant vascular and airway α-smooth muscle actin expression and inflammatory pulmonary vasculopathy. Conclusions: Anti-AT₁R and -ET_AR Abs are more frequent in SSc-PAH/connective tissue disease-PAH compared with other forms of pulmonary hypertension, and serve as predictive and prognostic biomarkers in SSc-PAH. Both antibodies may contribute to SSc-PAH via increased vascular endothelial reactivity and induction of pulmonary vasculopathy.