RXRα Modulates Hepatic Stellate Cell Activation and Liver Fibrosis by Targeting CaMKKβ-AMPKα 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 (RXRα), 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 β (CaMKKβ)-mediated activation of AMP-activated protein kinase-alpha (AMPKα). K-80003, which binds RXRα 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 AMPKα activation, which promotes mitophagy in HSCs. Mechanistically, K-80003 activation of AMPKα requires its induction of RXRα formation of condensates with CaMKKβ and AMPKα via a two-phase mechanism. The formation of RXRα condensates is mediated by the N-terminal intrinsically disorder region of RXRα and is dependent on its phosphorylation by CaMKKβ. Our results therefore unravel an important RXRα-CaMKKβ-AMPKα 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.