Project description:Background and Aims Non-alcoholic fatty liver disease (NAFLD) has a prevalence of ~25% worldwide, with significant public health consequences yet has few effective treatments. Human genetics can help elucidate novel biology and identify targets of 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 colocalization and Mendelian randomization 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 GAN diet NASH mouse model treated with hepatocyte specific GalNAc-siRNA to understand the in vivo impacts of MTARC1. Results We show that genetic variants within the MTARC1 locus are associated with liver enzymes, liver fat, plasma lipids and body composition and these associations are due 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 Randomization, 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.
Project description: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 of 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 colocalization and mendelian randomization 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 GAN-diet NASH mouse model treated with hepatocyte specific GalNAc-siRNA to understand the in vivo impacts of MTARC1. Results: We show that genetic variants within the MTARC1 locus are associated with liver enzymes, liver fat, plasma lipids and body composition and these associations are due 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 Randomization, 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.
Project description:Backgruound and aims: Loss of hepatocyte identity is associated with impaired liver function in alcohol-related hepatitis (AH). However, the mechanisms and the impact of hepatocyte reprogramming in liver disease are poorly understood. Here we show that both hepatocytes expressing KRT7 (hepatobiliary (HB) cells) and ductular reaction cells were increased in decompensated cirrhotic patients and AH, but only HB cells correlated with poor liver function, reduced liver synthetic capacity and poor outcome. Transcriptomic analysis of microdissected HB cells revealed the expression of biliary-specific genes and a mild reduction of hepatocyte metabolism. Functional analysis identified pathways involved in hepatocyte reprogramming together with inflammatory, stemness and cancer gene programs. In this context, CXCR4 pathway was highly enriched in HB cells, and CXCR4 correlated with disease severity and reduced expression of hepatocyte transcription factors and albumin. Mechanistically, TGFβ induced the expression of CXCR4 in primary hepatocytes, and its ligand CXCL12 promoted hepatocyte reprogramming. Liver overexpression of CXCR4 in chronic liver injury decreased hepatocyte gene expression and promoted liver injury. Pharmacological inhibition of CXCR4 reverted hepatocyte loss of identity and reduced ductular reaction and fibrosis progression. Conclusions: This study shows the association of hepatocyte reprogramming with disease progression and poor outcome in AH. Moreover, we identify CXCR4 as a driver of hepatocyte reprogramming as well as a potential therapeutic target in chronic liver injury.
Project description:Thrombospondin 1 (TSP1) is a multifunctional matricellular protein. Previously we have shown that TSP1 plays an important role in obesity-associated metabolic complications including inflammation, insulin resistance, cardiovascular and renal disease. However, its contribution to obesity-associated non-alcoholic fatty liver disease (NAFLD) or non-alcoholic steatohepatitis (NASH) remains largely unknown and is determined in this study. High fat diet or AMLN diet-induced obese and insulin resistant NAFLD/NASH mouse models were utilized. In addition, tissue specific TSP1 knockout mice were utilized to determine the contribution of different cellular sources of obesity-induced TSP1 to NAFLD/NASH development. The data demonstrated that liver TSP1 levels were increased in experimental obese and insulin resistant NAFLD/NASH mouse models as well as in human obese NASH patients. Moreover, TSP1 deletion in hepatocyte or adipocytes did not protect mice from diet-induced NAFLD/NASH. However, myeloid/macrophage-specific TSP1 deletion protected mice against obesity-associated liver injury, accompanied by reduced liver inflammation and fibrosis. Importantly, this protection is independent of the levels of obesity and hepatic steatosis. Mechanistically, through an autocrine effect, macrophage-derived TSP1 suppressed SMPDL3B expression in liver, which amplified liver pro-inflammatory signaling (TLR4 signal pathway) and promoted NAFLD progression. Together, out data suggest that macrophage-derived TSP1 is a significant contributor to obesity-associated NAFLD/NASH development and progression and may serve as a therapeutic target for this disease.