miR-873-5p targets mitochondrialGNMT-Complex II interface contributing tonon-alcoholic fatty liver disease

Objective:Non-alcoholic fatty liver disease (NAFLD) is a complex pathology in which several dysfunctions, including alterations in metabolicpathways, mitochondrial functionality and unbalanced lipid import/export, lead to lipid accumulation and progression to inflammation andfibrosis.The enzyme glycine N-methyltransferase (GNMT), the most important enzyme implicated in S-adenosylmethionine catabolism in the liver, isdownregulated during NAFLD progression. We have studied the mechanism involved in GNMT downregulation by its repressor microRNA miR-873-5p and the metabolic pathways affected in NAFLD as well as the benefit of recovery GNMT expression.Methods:miR-873-5p and GNMT expression were evaluated in liver biopsies of NAFLD/NASH patients. Differentin vitroandin vivoNAFLD murinemodels were used to assess miR-873-5p/GNMT involvement in fatty liver progression through targeting of the miR-873-5p as NAFLD therapy.Results:We describe a new function of GNMT as an essential regulator of Complex II activity in the electron transport chain in the mitochondria.In NAFLD, GNMT expression is controlled by miR-873-5p in the hepatocytes, leading to disruptions in mitochondrial functionality in a preclinicalmurine non-alcoholic steatohepatitis (NASH) model. Upregulation of miR-873-5p is shown in the liver of NAFLD/NASH patients, correlating withhepatic GNMT depletion. Importantly, NASH therapies based on anti-miR-873-5p resolve lipid accumulation, inflammation andfibrosis byenhancing fatty acidb-oxidation in the mitochondria. Therefore, miR-873-5p inhibitor emerges as a potential tool for NASH treatment.Conclusion:GNMT participates in the regulation of metabolic pathways and mitochondrial functionality through the regulation of Complex II activityin the electron transport chain. In NAFLD, GNMT is repressed by miR-873-5p and its targeting arises as a valuable therapeutic option for treatment.