Hepatocyte Pparg knockout and restored Bhmt expression reduce liver steatosis in male mice with diet-induced MASH

Abstract

Metabolic dysfunction-associated liver disease (MASLD) is characterized by the accumulation of triglycerides in hepatocytes and can progress to metabolic dysfunction-associated steatohepatitis (MASH) with inflammation, hepatocyte ballooning, and fibrosis. MASLD is associated with increased plasma homocysteine levels. Homocysteine is an amino acid generated by the S-adenosylmethionine-dependent transmethylation pathway of the methionine cycle, and it is remethylated to methionine by the betaine-homocysteine S-methyltransferase (BHMT) in hepatocytes. Mice fed a high-fat, cholesterol, and fructose (HFCF) diet develop MASLD and MASH associated with increased peroxisome proliferator-activated receptor γ (PPARγ, Pparg) expression and homocysteine levels, and decreased hepatic Bhmt expression. Here, we sought to determine whether the hepatocyte-specific knockout of Pparg (PpargΛHep) or restoration of Bhmt expression in hepatocytes (BhmtHep) in mice with HFCF-induced MASH reduce MASLD progression. To this end, adult male Pparg-floxed mice were fed an HFCF diet for 20 weeks to induce MASH. Then, we generated PpargΛHep and/or BhmtHep mice using an adeno-associated virus encoding Cre recombinase or Bhmt in hepatocytes, respectively. HFCF diet-induced MASH increased hepatic Pparg expression and reduced Bhmt expression. 8 weeks after the induction of PpargΛHep, hepatic Bhmt expression was increased, and both MASH severity and homocysteine levels decreased. The restoration of hepatocyte BHMT in BhmtHep (Pparg-intact) mice reduced hepatic triglyceride and homocysteine levels, which were associated with reduced expression of the steatogenic genes Cidea and Cidec. Overall, our results indicate a protective role for BHMT in hepatocytes of mice with MASH, even in mice expressing Pparg in hepatocytes.