Deficiency of Smooth Muscle ADAR1 RNA Editing Exacerbates Vascular Remodeling and Pulmonary Hypertension [pul51_RNA-seq]

Adenosine deaminase acting on RNA 1 (ADAR1) catalyzes the conversion of adenosine (A) to inosine (I) in double-stranded RNA (dsRNA), which is critical to prevent auto-inflammatory responses mediated by activation of the type I interferon (IFN) signaling. Here, we define the role of ADAR1-dependent RNA editing in interferon-β(IFNβ) activation and pulmonary artery smooth muscle cell (PASMC) remodeling in pulmonary arterial hypertension (PAH), a devastating disease leading to right heart failure and premature death. Methods: RNA editing levels were analyzed in human pulmonary artery smooth muscle cells (PASMCs) from idiopathic PAH (IPAH) patients versus healthy controls. A conditional transgenic line ADAR1SMC-KO was generated by knocking out ADAR1 selectively in α-smooth muscle actin-positive cells, followed by hypoxic exposure to induce PH. Results: PASMCs from IPAH patients displayed decreased levels of ADAR1 mRNA and protein, accompanied by reduced A-to-I editing compared to healthy PASMCs. ADAR1 knockdown in PASMCs upregulated MDA5, PKR, IFN-β and IFN-Stimulated Genes (ISGs). Compared with controls in vivo, hypoxic ADAR1SMC-KO mice developed severe PH, as evidenced by excessive vascular remodeling in distal arterioles and increased vascular leakage resulting in elevated right ventricular systolic pressure and right ventricular hypertrophy. Mechanistically, IFNβ signaling in ADAR1SMC-KO lungs induced the recruitment of inflammatory cells, including macrophages, which in turn enhanced PASMC proliferation and muscularization. Correspondingly, pharmacological treatment with PKR kinase inhibitor Imoxin decreased IFNβ thus attenuating the hypoxia-induced PH phenotype of ADAR1SMC-KO mice. Conclusions: ADAR1-dependent A-to-I RNA editing tempers IFN signaling in PASMCs. Pathologic reduction of ADAR1 in SMCs increased IFNβ activity, macrophage recruitment, and worsened PH, thus demonstrating a direct detrimental role of vascular innate immune responses in PH. Targeting PKR could be the new therapeutic strategy aimed at treating PAH.