Hepatocyte mARC1 promotes fatty liver disease.

Background & Aims: Non-alcoholic fatty liver disease (NAFLD) has a prevalence of ∼25% worldwide, with significant public health consequences yet few effective treatments. Human genetics can help elucidate novel biology and identify targets for new therapeutics. Genetic variants in mitochondrial amidoxime-reducing component 1 (MTARC1) have been associated with NAFLD and liver-related mortality; however, its pathophysiological role and the cell type(s) mediating these effects remain unclear. We aimed to investigate how MTARC1 exerts its effects on NAFLD by integrating human genetics with in vitro and in vivo studies of mARC1 knockdown. Methods: Analyses including multi-trait colocalisation and Mendelian randomisation were used to assess the genetic associations of MTARC1. In addition, we established an in vitro long-term primary human hepatocyte model with metabolic readouts and used the Gubra Amylin NASH (GAN)-diet non-alcoholic steatohepatitis mouse model treated with hepatocyte-specific N-acetylgalactosamine (GalNAc)-siRNA to understand the in vivo impacts of MTARC1. Results: We showed that genetic variants within the MTARC1 locus are associated with liver enzymes, liver fat, plasma lipids, and body composition, and these associations are attributable to the same causal variant (p.A165T, rs2642438 G>A), suggesting a shared mechanism. We demonstrated that increased MTARC1 mRNA had an adverse effect on these traits using Mendelian randomisation, implying therapeutic inhibition of mARC1 could be beneficial. In vitro mARC1 knockdown decreased lipid accumulation and increased triglyceride secretion, and in vivo GalNAc-siRNA-mediated knockdown of mARC1 lowered hepatic but increased plasma triglycerides. We found alterations in pathways regulating lipid metabolism and decreased secretion of 3-hydroxybutyrate upon mARC1 knockdown in vitro and in vivo. Conclusions: Collectively, our findings from human genetics, and in vitro and in vivo hepatocyte-specific mARC1 knockdown support the potential efficacy of hepatocyte-specific targeting of mARC1 for treatment of NAFLD. Impact and implications: We report that genetically predicted increases in MTARC1 mRNA associate with poor liver health. Furthermore, knockdown of mARC1 reduces hepatic steatosis in primary human hepatocytes and a murine NASH model. Together, these findings further underscore the therapeutic potential of targeting hepatocyte MTARC1 for NAFLD.

MLX plays a key role in lipid and glucose metabolism in humans: Evidence from in vitro and in vivo studies.

BACKGROUND AND AIM: Enhanced hepatic de novo lipogenesis (DNL) has been proposed as an underlying mechanism for the development of NAFLD and insulin resistance. Max-like protein factor X (MLX) acts as a heterodimer binding partner for glucose sensing transcription factors and inhibition of MLX or downstream targets has been shown to alleviate intrahepatic triglyceride (IHTG) accumulation in mice. However, its effect on insulin sensitivity remains unclear. As human data is lacking, the aim of the present work was to investigate the role of MLX in regulating lipid and glucose metabolism in primary human hepatocytes (PHH) and in healthy participants with and without MLX polymorphisms. METHODS: PHH were transfected with non-targeting or MLX siRNA to assess the effect of MLX knockdown on lipid and glucose metabolism, insulin signalling and the hepatocellular transcriptome. A targeted association analysis on imputed genotype data for MLX on healthy individuals was undertaken to assess associations between specific MLX SNPs (rs665268, rs632758 and rs1474040), plasma biochemistry, IHTG content, DNL and gluconeogenesis. RESULTS: MLX knockdown in PHH altered lipid metabolism (decreased DNL (p < 0.05), increased fatty acid oxidation and ketogenesis (p < 0.05), and reduced lipid accumulation (p < 0.001)). Additionally, MLX knockdown increased glycolysis, lactate secretion and glucose production (p < 0.001) and insulin-stimulated pAKT levels (p < 0.01) as assessed by transcriptomic, steady-state and dynamic measurements. Consistent with the in vitro data, individuals with the rs1474040-A and rs632758-C variants had lower fasting plasma insulin (p < 0.05 and p < 0.01, respectively) and TG (p < 0.05 and p < 0.01, respectively). Although there was no difference in IHTG or gluconeogenesis, individuals with rs632758 SNP had notably lower hepatic DNL (p < 0.01). CONCLUSION: We have demonstrated using human in vitro and in vivo models that MLX inhibition favored lipid catabolism over anabolism and increased glucose production, despite increased glycolysis and phosphorylation of Akt, suggesting a metabolic mechanism that involves futile cycling.