RXRa Modulates Hepatic Stellate Cell Activation and Liver Fibrosis by Targeting CaMKKß-AMPKa Axis

Hepatic stellate cells (HSCs) represent a dominant fibrogenic cell population in the liver, whose activation is a key event in the development and progression of hepatic fibrosis. We report here that retinoid X receptor-alpha (RXRa), a unique member of the nuclear receptor superfamily, is a critical modulator of HSC activation and liver fibrosis through its regulation of calcium/calmodulin-dependent protein kinase kinase ß (CaMKKß)-mediated activation of AMP-activated protein kinase-alpha (AMPKa). K-80003, which binds RXRa by a unique mechanism, effectively inhibits the activation, proliferation and migration of HSCs and inhibits liver fibrosis in the CCl4 and AMLN animal models by AMPKa activation, which promotes mitophagy in HSCs. Mechanistically, K-80003 activation of AMPKa requires its induction of RXRa formation of condensates with CaMKKß and AMPKa via a two-phase mechanism. The formation of RXRa condensates is mediated by the N-terminal intrinsically disorder region of RXRa and is dependent on its phosphorylation by CaMKKß. Our results therefore unravel an important RXRa-CaMKKß-AMPKa axis in the modulation of HSC activation through phase separation and identify K-80003 as a potent inhibitor of HSC activation and liver fibrosis by targeting the axis. Overall design: Primary mouse hepatic stellate cells (mHSCs) isolated from mice were treated with TGF-ß and K-80003 and divided into three groups: Control, TGF-beta, and TGF-beta-K-80003, with 2 replicates in each group.