Deficiency of Smooth Muscle ADAR1 Exacerbates Vascular Remodeling and Pulmonary Hypertension.

BACKGROUND ADAR1 (adenosine deaminase acting on RNA 1) catalyzes the conversion of adenosine to inosine in double-stranded RNAs, which is critical to prevent autoinflammatory responses mediated by activation of the type I IFN (interferon) signaling. We define the role of ADAR1-dependent RNA editing in IFNβ activation and pulmonary artery smooth muscle cell remodeling in pulmonary arterial hypertension, a devastating disease leading to right heart failure and death. METHODS RNA editing levels were analyzed in pulmonary arterial smooth muscle cells from idiopathic pulmonary arterial hypertension patients versus healthy controls. A conditional transgenic model, Adar1SMC-KO, was generated by knocking out Adar1 selectively in α-SMA (smooth muscle actin)-expressing cells, followed by 3 weeks of hypoxic exposure to induce PH. RESULTS Pulmonary arterial smooth muscle cells from patients with idiopathic pulmonary arterial hypertension displayed decreased levels of ADAR1 mRNA and isoform p150 protein, accompanied by accumulated double-stranded RNA compared with healthy pulmonary arterial smooth muscle cells. ADAR1 knockdown in pulmonary arterial smooth muscle cells upregulated MDA5 (melanoma differentiation-associated protein 5), PKR (protein kinase R), IFNβ, and IFN-stimulated genes. Compared with controls in vivo, hypoxic Adar1SMC-KO mice developed severe PH, as evidenced by excessive vascular remodeling in distal arterioles and increased endothelium leakage, resulting in elevated right ventricular systolic pressure and right ventricular hypertrophy. Mechanistically, Ifnβ signaling in Adar1SMC-KO induced the recruitment of macrophages, enhancing pulmonary artery muscularization. Pharmacological treatment with PKR-relevant inhibitor 2BAct decreased Ifnβ and macrophages, thus attenuating PH in hypoxic Adar1SMC-KO mice. CONCLUSIONS Our study describes a fundamental molecular mechanism underlying the progression of PH. We highlight the detrimental role of innate immune responses, where smooth muscle cell and context-specific RNA editing, along with the sensing of double-stranded RNA, mediate disease progression and excessive vascular remodeling. This finding suggests that targeting PKR could be the new therapeutic strategy for treating pulmonary arterial hypertension.