RAB25/GCN1 Signaling Promotes ER Stress to Mediate Alcohol-associated Liver Disease Progression.

Background/aims: Endoplasmic reticulum (ER) stress in hepatocytes plays a causative role in alcohol-associated liver disease (ALD). The incomplete inhibition of ER stress by targeting canonical ER stress sensor proteins suggests the existence of noncanonical ER stress pathways in ALD pathology. This study aimed to delineate the role of RAB25 in ALD and its regulatory mechanism in noncanonical ER stress pathways.

Methods: RAB25 activation was examined in liver samples from ALD patients and ethanol-fed mice. The interaction between RAB25 and GCN1 was confirmed through mass spectrometry and co-immunoprecipitation (Co-IP) assays in vitro. The role of RAB25/GCN1 in promoting noncanonical ER stress in ALD was assessed both in vitro and in vivo.

Results: RAB25 expression was upregulated and specifically accumulated on the endoplasmic reticulum in ALD. Mass spectrometry and Co-IP assays confirmed that RAB25 interacts with GCN1, thereby activating a noncanonical ER stress pathway that facilitates ALD progression. Further analysis revealed that RAB25 interaction with GCN1 inhibits K33-ubiquitination-mediated degradation of GCN1, promotes GCN2 phosphorylation, and subsequently activates ATF4-mediated ER stress. This activation modulates lipid metabolism, mitochondrial function, and inflammation, thereby facilitating ALD progression. Knockdown of RAB25 in hepatocytes inhibited ER stress activation and mitigated associated mitochondrial dysfunction, excessive lipid synthesis, and the exaggerated inflammatory response in an ALD model.

Conclusions: Our findings demonstrate a causal role for RAB25-GCN1 signaling in activating the ER stress pathway, which contributes to ALD progression. This pathway may provide a proof-of-concept target for treating ALD and associated metabolic disorders.