Asmase Regulates autophagy and lysosomal membrane permeabilization and its inhibition prevents early stage nonalcoholic steatohepatitis

Abstract

Background & Aims: Acid sphingomyelinase (ASMase) is activated in nonalcoholic steatohepatitis (NASH). However, ASMase's contribution to NASH is poorly understood and limited to hepatic steatosis and glucose metabolism. Here we examined ASMase's role in high fat diet (HFD)-induced NASH. Methods: Autophagy, endoplasmic reticulum (ER) stress and lysosomal membrane permeabilization (LMP) were determined in ASMase-/- mice fed HFD. The impact of pharmacological ASMase inhibition on NASH was analyzed in wild type mice fed HFD. Results: ASMase deficiency determined resistance to HFD or methionine and choline deficient diet-mediated hepatic steatosis. ASMase-/- mice were resistant to HFD-induced hepatic ER stress, but sensitive to tunicamycin-mediated ER stress and steatosis, indicating selectivity in the resistance of ASMase-/- mice to ER stress. Autophagic flux determined in the presence of rapamycin and/or chloroquine was lower in primary mouse hepatocytes (PMH) from ASMase-/- mice and accompanied by increased p62 levels, suggesting autophagic impairment. Moreover, autophagy suppression by chloroquine and brefeldinA caused ER stress in PMH from ASMase+/+ mice but not ASMase-/- mice. ASMase-/- PMH exhibited increased lysosomal cholesterol loading, decreased LMP and apoptosis resistance induced by O-methyl-serine dodecylamide hydrochloride or palmitic acid, effects that were reversed by decreasing cholesterol levels by the oxysterol 25-hydroxycholesterol. In vivo pharmacological ASMase inhibition by amitriptyline, a widely used tricyclic antidepressant, protected wild type mice against HFD- induced hepatic steatosis, fibrosis, and liver damage, effects indicative of early-stage NASH. Conclusions: These findings underscore a critical role for ASMase in diet-induced NASH and suggest the potential of amitriptyline as a treatment for patients with NASH.