Abstract 17142: Deficiency of Smooth Muscle ADAR1 Exacerbates Vascular Remodeling and Pulmonary Hypertension

Background: Adenosine deaminase acting on RNA 1 (ADAR1) catalyzes the conversion of adenosine (A) to inosine (I) in double-stranded RNA, 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 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: Total RNAs from IPAH PASMCs (N=3) and healthy control (N=3) were deep sequenced by RNA-seq and determined the fraction of reads with a ‘G’ nucleotide editing sites using RADAR database. A transgenic line ADAR1 ^SMC-KO was generated by knocking down ADAR1 selectively in αSMA+ cells, followed by 3 weeks of hypoxia. PKR inhibitor Imoxin was used to treat ADAR1 ^SMC-KO .

Results: SMC layers of human IPAH tissues expressed reduced levels of ADAR1. Moreover, IPAH PASMCs displayed decreased mRNA and protein levels of ADAR1, along with reduced editing sites compared to healthy PASMCs (Fig.1A). The knockdown of ADAR1 in PASMCs resulted in the activation of the MDA5-PKR-IFNβ signaling pathway. Compared with controls in vivo , hypoxic ADAR1 ^SMC-KO mice developed severe PH, as evidenced by excessive vascular remodeling in distal arterioles (Fig.1B) and increased vascular leakage resulting in elevated right ventricular systolic pressure (37 vs 23 mmHg) and right ventricular hypertrophy by Fulton Index (46 vs. control 20%) (Fig.1C). The immunofluorescence staining showed higher expression of IFNβ and increased recruitment of inflammatory immune cells. Imoxin treatment prevented PH & RVH.

Conclusions: The deficiency of ADAR1 leads to the activation of IFNβ thus contributing to the pathological processes observed in PAH. Inhibiting PKR activity could attenuate the aberrant IFNβ activation and potentially serve as a new therapeutic strategy to treat PAH.