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Modulation of hepatocyte sialylation drives spontaneous fatty liver disease and inflammation.

ABSTRACT: Circulatory protein glycosylation is a biomarker of multiple disease and inflammatory states and has been applied in the clinic for liver dysfunction, heart disease and diabetes. With the notable exception of antibodies, the liver produces most of the circulatory glycoproteins, including the acute phase proteins released as a function of the inflammatory response. Among these proteins is ?-galactoside ?2,6-sialyltransferase (ST6Gal1), an enzyme required for ?2,6-linked sialylation of glycoproteins. Here, we describe a hepatocyte-specific conditional knockout of ST6Gal1 (H-cKO) using albumin promoter-driven Cre-lox recombination. We confirm the loss of circulatory glycoprotein ?2,6 sialylation and note no obvious dysfunction or pathology in young H-cKO mice, yet these mice show robust changes in plasma glycoprotein fucosylation, branching and the abundance of bisecting GlcNAc and marked changes in a number of metabolic pathways. As H-cKO mice aged, they spontaneously developed fatty liver disease characterized by the buildup of fat droplets in the liver, inflammatory cytokine production and a shift in liver leukocyte phenotype away from anti-inflammatory Kupffer cells and towards proinflammatory M1 macrophages. These findings connect hepatocyte and circulatory glycoprotein sialylation to the regulation of metabolism and inflammation, potentially identifying the glycome as a new target for liver-driven disease.

SUBMITTER: Oswald DM

PROVIDER: S-EPMC7175972 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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Modulation of hepatocyte sialylation drives spontaneous fatty liver disease and inflammation.

Oswald Douglas M DM Jones Mark B MB Cobb Brian A BA

Glycobiology 20200401 5

Circulatory protein glycosylation is a biomarker of multiple disease and inflammatory states and has been applied in the clinic for liver dysfunction, heart disease and diabetes. With the notable exception of antibodies, the liver produces most of the circulatory glycoproteins, including the acute phase proteins released as a function of the inflammatory response. Among these proteins is β-galactoside α2,6-sialyltransferase (ST6Gal1), an enzyme required for α2,6-linked sialylation of glycoprotei ...[more]

PMID: 31742330

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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:BACKGROUNDAn increase in intrahepatic triglyceride (IHTG) is the hallmark feature of nonalcoholic fatty liver disease (NAFLD) and is decreased by weight loss. Hepatic de novo lipogenesis (DNL) contributes to steatosis in individuals with NAFLD. The physiological factors that stimulate hepatic DNL and the effect of weight loss on hepatic DNL are not clear.METHODSHepatic DNL, 24-hour integrated plasma insulin and glucose concentrations, and both liver and whole-body insulin sensitivity were determined in individuals who were lean (n = 14), obese with normal IHTG content (n = 26), or obese with NAFLD (n = 27). Hepatic DNL was assessed using the deuterated water method corrected for the potential confounding contribution of adipose tissue DNL. Liver and whole-body insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp procedure in conjunction with glucose tracer infusion. Six subjects in the obese-NAFLD group were also evaluated before and after a diet-induced weight loss of 10%.RESULTSThe contribution of hepatic DNL to IHTG-palmitate was 11%, 19%, and 38% in the lean, obese, and obese-NAFLD groups, respectively. Hepatic DNL was inversely correlated with hepatic and whole-body insulin sensitivity, but directly correlated with 24-hour plasma glucose and insulin concentrations. Weight loss decreased IHTG content, in conjunction with a decrease in hepatic DNL and 24-hour plasma glucose and insulin concentrations.CONCLUSIONSThese data suggest hepatic DNL is an important regulator of IHTG content and that increases in circulating glucose and insulin stimulate hepatic DNL in individuals with NAFLD. Weight loss decreased IHTG content, at least in part, by decreasing hepatic DNL.TRIAL REGISTRATIONClinicalTrials.gov NCT02706262.FUNDINGThis study was supported by NIH grants DK56341 (Nutrition Obesity Research Center), DK20579 (Diabetes Research Center), DK52574 (Digestive Disease Research Center), and RR024992 (Clinical and Translational Science Award), and by grants from the Academy of Nutrition and Dietetics Foundation, the College of Natural Resources of UCB, and the Pershing Square Foundation.

Dataset Information

Modulation of hepatocyte sialylation drives spontaneous fatty liver disease and inflammation.

Publications

Modulation of hepatocyte sialylation drives spontaneous fatty liver disease and inflammation.

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