Inhibition of adipose triglyceride lipase alleviates non-alcoholic steatohepatitis in diabetic mice via impaired PPARa signalling favouring hydrophilic bile acid composition
Inhibition of adipocyte triglyceride lipase (ATGL/PNPLA2) activity in insulin resistance and non-alcoholic fatty liver disease is an attractive therapeutic target. This study evaluated the impact of Atglistatin-mediated ATGL inhibition on non-alcoholic steatohepatitis (NASH) development in diabetic and hyperlipidaemic mice. Streptozotocin-injected male mice were fed an HFD to induce NASH. We analysed liver histology, hepatic lipid content, immunohistochemistry, RNA sequencing, and serum biochemistry. Mechanistically, we treated Caco2 cells, human primary ileum-derived organoids, and HepG2 ATGL KD cells with the novel human ATGL inhibitor NG-497 and WY14643.  Atglistatin reduced body and liver weights, total liver lipid content, and improved blood sugar levels consistent with improved liver enzymes, histological liver injury, and NAFLD activity scores. Mechanistically, Atglistatin reduced Cpt1a and Abca1, suggesting impaired Ppara signalling that favours hydrophilic bile acids (BA) synthesis since Cyp7a1, Cyp27a1, and Cyp2c70 were increased while Cyp8b1 was reduced. Accordingly, Intestinal lipid transporters, Abca1 and Cd36, were reduced, consistent with the reduction of liver TAG species, mostly linoleic acids. We used human-specific ATGL inhibitor NG-497 to validate the mouse findings. The NG-497-treated human primary ileum organoids and Caco2 cells showed reduced ATGL, ABCA1, FATP5, CD36, and MTTP. PPARa signalling was impaired in the ileum organoids and HepG2 treated with NG-497 and in HepG2 ATGL KD since PPARa, CPT1a, AOX, ABCA1, and CYP8B1 were reduced, and CYP7A1 increased. Inhibition of ATGL activity reduces the availability of ligands for Ppara activation leading to impaired Ppara signalling, which translate into hydrophilic BA that interferes with dietary lipid absorption, improving metabolic disturbances. The validation with the NG-497 should open a new clinical avenue for NAFLD clinical trial and treatment. Overall design: The STAM mouse was established by subcutaneously injecting 200 µg streptozotocin in 2-days-old male mice and feeding a HFD supplemented with Atglistatin (STAM + ATGLi) or without Atglistatin (STAM) after 4 weeks of age for further 4 weeks. Control mice (noSTZ + NC) were fed chow diet and neither receive STZ nor Atglistatin.