Dietary and genetic disruption of hepatic methionine metabolism induce acid sphingomyelinase to promote steatohepatitis

Alcoholic (ASH) and nonalcoholic. (NASH).steatohepatitis are advanced.stages.of.fatty.liver.disease.Methionine adenosyltransferase 1A (MAT1A) plays a key role in hepatic methionine metabolism and germline Mat1a deletion in mice promotes NASH. Acid sphingomyelinase (ASMase) triggers hepatocellular apoptosis and liver fibrosis and has been shown to downregulate MAT1A expression in the context of fulminant liver failure. Given the role of ASMase in steatohepatitis development, we investigated the status of ASMase in Mat1a-/- mice and the regulation of ASMase by SAM/SAH. Consistent with its role in NASH, Mat1a-/- mice fed a choline-deficient (CD) diet exhibited macrosteatosis, inflammation, fibrosis and liver injury as well as reduced total and mitochondrial GSH levels. Our data uncovered an increased basal expression and activity of ASMase but not neutral SMase in Mat1a-/- mice, which further increased upon CD feeding. Interestingly, adenovirus-mediated shRNA expression targeting ASMase reduced ASMase activity and protected Mat1a-/- mice against CD diet-induced NASH. Similar results were observed in CD fed Mat1a-/- mice by pharmacological inhibition of ASMase with amitriptyline. Moreover, Mat1a/ASMase double knockout mice were resistant to CD-induced NASH. ASMase knockdown protected wild type mice against NASH induced by feeding a diet deficient in methionine and choline. Furthermore, Mat1a-/- mice developed acute-on-chronic ASH and this outcome was ameliorated by amitriptyline treatment. In vitro data in primary mouse hepatocytes revealed that decreased SAM/SAH ratio increased ASMase mRNA level and activity. MAT1A and ASMase mRNA levels exhibited an inverse correlation in liver samples from patients with ASH and NASH. Thus, disruption of methionine metabolism sensitizes to steatohepatitis by ASMase activation via decreased SAM/SAH. These findings imply that MAT1A deletion and ASMase activation engage in a self-sustained loop of relevance for steatohepatitis.This project has received funding from the European Horizon’s research and innovation programme HORIZON-HLTH-2022- STAYHLTH-02 under agreement No 101095679. We acknowledge the support from grants PID2019-111669RB, and PID2020-115055RB-I00 from Plan Nacional de I + D funded by the Agencia Estatal de Investigacion ´ (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER) and from the CIBEREHD; the center grant P50AA011999 Southern California Research Center for ALPD and Cirrhosis funded by NIAAA/NIH; as well as support from AGAUR of the Generalitat de Catalunya SGR-2017-1112, European Cooperation in Science & Technology (COST) ACTION CA17112 Prospective European Drug-Induced Liver Injury Network, the “ER stress-mitochondrial cholesterol axis in obesity-associated insulin resistance and comorbidities”-Ayudas FUNDACION BBVA, the Red Nacional 2018-102799-T de Enfermedades Metabolicas ´ y Cancer ´ and the Project 201916/31 Contribution of mitochondrial oxysterol and bile acid metabolism to liver carcinogenesis 2019 by Fundacio ´ Marato TV3