Liver Pyruvate Kinase Promotes NAFLD/NASH in both Mice and Humans in a Sex-Specific Manner

ABSTRACT BACKGROUND AND AIMS The etiology of non-alcoholic fatty liver disease (NAFLD) is poorly understood, with males and certain populations exhibiting markedly increased susceptibility. Using a systems genetics approach, involving multi-omic analysis of ∼100 diverse inbred strains of mice, we recently identified several candidate genes driving NAFLD. We investigated the role of one of these, liver pyruvate kinase (L-PK or Pklr) in NAFLD using patient samples and mouse models. METHODS We examined L-PK expression in mice of both sexes and in a cohort of bariatric surgery patients. We used liver-specific loss- and gain-of-function strategies in independent animal models of diet-induced steatosis and fibrosis. Following treatment, we measured several metabolic phenotypes, including obesity, insulin resistance, dyslipidemia, liver steatosis and fibrosis. Liver tissues were used for gene expression and immunoblotting, and liver mitochondria bioenergetics was characterized. RESULTS In both mice and humans, L-PK expression is upregulated in males via testosterone and is strongly associated with NAFLD severity. In a steatosis model, L-PK silencing in male mice improved glucose tolerance, insulin sensitivity and lactate/pyruvate tolerance compared to controls. Further, these animals had reduced plasma cholesterol levels and intrahepatic triglyceride accumulation. Conversely, L-PK overexpression in male mice resulted in augmented disease phenotypes. In contrast, female mice overexpressing L-PK were unaffected. Mechanistically, L-PK altered mitochondrial pyruvate flux and its incorporation into citrate and this, in turn, increased liver triglycerides via upregulated de novo lipogenesis and increased PNPLA3 levels accompanied by mitochondrial dysfunction. Also, L-PK increased plasma cholesterol levels via increased PCSK9 levels. L-PK silencing, on the other hand, reduced de novo lipogenesis, PNPLA3 and PCSK9 levels and improved mitochondrial function. Finally, in fibrosis model, we demonstrate that L-PK silencing in male mice reduced both liver steatosis and fibrosis, accompanied by reduced de novo lipogenesis and improved mitochondrial function. CONCLUSION L-PK acts in a male-specific manner in the development of liver steatosis and fibrosis. Given that NAFLD/NASH exhibit sexual dimorphism, our results have important implications for the development of personalized therapeutics.