Targeting ADAR1-mediated RNA editing inhibits hepatic stellate cell activation and liver fibrosis by enhancing HSC-intrinsic innate immunity.

Abstract

The pathogenesis of liver fibrosis centres on the activation of hepatic stellate cells (HSCs). Adenosine-to-inosine RNA editing, primarily catalysed by adenosine deaminase acting on RNA1 (ADAR1), is the most prevalent post-transcriptional modification that increases transcriptome diversity. This study aims to elucidate the role of ADAR1-imposed RNA editome in HSC activation and to determine the therapeutic potential of targeting ADAR1 for liver fibrosis. ADAR1 expression was measured in fibrotic human and mouse livers, as well as in primary human and mouse HSCs. Adar1 loss-of-function effect was evaluated in <i>Adar1^f/f</i> /<i>Cre-ER</i>, <i>Adar1^△HSC</i> and <i>Adar1^i△HSC</i> mice, whereas viral infection with Ad-Adar1 was employed in gain-of-function studies. <i>Adar1^△HSCIfih1^-/--</i> and <i>Adar1^△HSCIfnar^△HSC</i> mice were used for mechanistic studies. An ADAR1 inhibitor and HSC-selective RNAi were used for therapeutic evaluations. ADAR1 is decreased in human and mouse fibrotic livers and activated HSCs. HSC-specific ablation or pharmacological inhibition of ADAR1 ameliorated HSC activation and liver fibrosis. In contrast, forced expression of ADAR1, but not its editing-deficient mutant, exacerbated HSC activation. Mechanistically, ADAR1 ablation accumulated double-stranded RNA and activated HSC-intrinsic innate immunity in a melanoma differentiation-associated gene 5-dependent manner. Interferon-β was identified as a key antifibrotic effector via the activation of the JAK1/2 pathway. RNA editome analysis revealed the <i>Col3a1</i> 3' UTR as a novel ADAR1 editing target, leading to increased collagen production. ADAR1-imposed RNA editome suppresses HSC-intrinsic innate immunity and promotes collagen production, leading to aggravated HSC activation and liver fibrosis. Targeting ADAR1 with its pharmacological inhibitor or HSC-selective RNAi shows great promise in treating liver fibrosis.