ANGPTL3 Downregulation Increases Intracellular Lipids by Reducing Energy Utilization.

BACKGROUND: ANGPTL3 (angiopoietin-like protein 3) is a circulating protein with a key role in maintaining lipoprotein homeostasis. A monoclonal antibody against ANGPTL3 is an approved and well-tolerated treatment to reduce lipoproteins in familial hypercholesterolemia homozygotes. However, the reduction of hepatic ANGPTL3 synthesis using an antisense oligonucleotide unexpectedly resulted in a dose-dependent increase in liver lipid content and circulating transaminases, resulting in the termination of the clinical trial. Meanwhile, the use of silencing RNAs remains an area of active investigation. Our study sought to investigate whether intracellular downregulation of ANGPTL3 may lead to a primary increase in neutral lipids within the hepatocyte. METHODS: We downregulated ANGPTL3 by silencing RNA in primary human hepatocytes 3-dimensional spheroids, HepG2/LX-2 3-dimensional spheroids, and in HepG2, Hep3B2, and Huh7 cultured in 2 dimensions. RESULTS: ANGPTL3 downregulation increased neutral lipids in all models investigated. Interestingly, ANGPTL3 induced lower intracellular deiodinase type 1 protein levels resulting in a reduction in beta-oxidation and causing an increase in triglycerides stored in lipid droplets. CONCLUSIONS: In conclusion, intracellular ANGPTL3 downregulation by silencing RNA led to an increase in triglycerides content due to a reduction in energy substrate utilization resembling a primary intracellular hepatocyte hypothyroidism.

Mitochondrial amidoxime-reducing component 1 p.Ala165Thr increases protein degradation mediated by the proteasome.

OBJECTIVE: Metabolic dysfunction-associated steatotic liver disease (MASLD) is a global health concern with no effective and specific drug treatment available. The rs2642438 minor allele in mitochondrial amidoxime-reducing component 1 (MARC1) results in an aminoacidic substitution (p.Ala165Thr) and associates with protection against MASLD. However, the mechanisms behind this protective effect are unknown. In this study, we examined the consequences of this aminoacidic substitution on protein stability and subcellular localization. METHODS: We overexpressed the human MARC1 A165 (wild-type) or 165T (mutant) in vivo in mice and in vitro in human hepatoma cells (HepG2 and HuH-7), generated several mutants at position 165 by in situ mutagenesis and then examined protein levels. We also generated HepG2 cells stably overexpressing MARC1 A165 or 165T to test the effect of this substitution on MARC1 subcellular localization. RESULTS: MARC1 165T overexpression resulted in lower protein levels than A165 both in vivo and in vitro. Similarly, any mutant at position 165 showed lower protein levels compared to the wild-type protein. We showed that the 165T mutant protein is polyubiquitinated and its degradation is accelerated through lysine-48 ubiquitin-mediated proteasomal degradation. We also showed that the 165T substitution does not affect the MARC1 subcellular localization. CONCLUSIONS: This study shows that alanine at position 165 in MARC1 is crucial for protein stability, and the threonine substitution at this position leads to a hypomorphic protein variant due to lower protein levels. Our result supports the notion that lowering hepatic MARC1 protein level may be a successful therapeutic strategy for treating MASLD.

Generation and validation of a classification model to diagnose familial hypercholesterolaemia in adults.

BACKGROUND AND AIMS: The early diagnosis of familial hypercholesterolaemia is associated with a significant reduction in cardiovascular disease (CVD) risk. While the recent use of statistical and machine learning algorithms has shown promising results in comparison with traditional clinical criteria, when applied to screening of potential FH cases in large cohorts, most studies in this field are developed using a single cohort of patients, which may hamper the application of such algorithms to other populations. In the current study, a logistic regression (LR) based algorithm was developed combining observations from three different national FH cohorts, from Portugal, Brazil and Sweden. Independent samples from these cohorts were then used to test the model, as well as an external dataset from Italy. METHODS: The area under the receiver operating characteristics (AUROC) and precision-recall (AUPRC) curves was used to assess the discriminatory ability among the different samples. Comparisons between the LR model and Dutch Lipid Clinic Network (DLCN) clinical criteria were performed by means of McNemar tests, and by the calculation of several operating characteristics. RESULTS: AUROC and AUPRC values were generally higher for all testing sets when compared to the training set. Compared with DLCN criteria, a significantly higher number of correctly classified observations were identified for the Brazilian (p < 0.01), Swedish (p < 0.01), and Italian testing sets (p < 0.01). Higher accuracy (Acc), G mean and F1 score values were also observed for all testing sets. CONCLUSIONS: Compared to DLCN criteria, the LR model revealed improved ability to correctly classify observations, and was able to retain a similar number of FH cases, with less false positive retention. Generalization of the LR model was very good across all testing samples, suggesting it can be an effective screening tool if applied to different populations.

Rare ATG7 genetic variants predispose patients to severe fatty liver disease.

BACKGROUND & AIMS: Non-alcoholic fatty liver disease (NAFLD) is the leading cause of liver disorders and has a strong heritable component. The aim of this study was to identify new loci that contribute to severe NAFLD by examining rare variants. METHODS: We performed whole-exome sequencing in individuals with NAFLD and advanced fibrosis or hepatocellular carcinoma (n = 301) and examined the enrichment of likely pathogenic rare variants vs. the general population. This was followed by validation at the gene level. RESULTS: In patients with severe NAFLD, we observed an enrichment of the p.P426L variant (rs143545741 C>T; odds ratio [OR] 5.26, 95% CI 2.1-12.6; p = 0.003) of autophagy-related 7 (ATG7), which we characterized as a loss-of-function, vs. the general population, and an enrichment in rare variants affecting the catalytic domain (OR 13.9; 95% CI 1.9-612; p = 0.002). In the UK Biobank cohort, loss-of-function ATG7 variants increased the risk of cirrhosis and hepatocellular carcinoma (OR 3.30; 95% CI 1.1-7.5 and OR 12.30, 95% CI 2.6-36, respectively; p <0.001 for both). The low-frequency loss-of-function p.V471A variant (rs36117895 T>C) was also associated with severe NAFLD in the clinical cohort (OR 1.7; 95% CI 1.2-2.5; p = 0.003), predisposed to hepatocellular ballooning (p = 0.007) evolving to fibrosis in the Liver biopsy cohort (n = 2,268), and was associated with liver injury in the UK Biobank (aspartate aminotransferase levels, p <0.001), with a larger effect in severely obese individuals in whom it was linked to hepatocellular carcinoma (p = 0.009). ATG7 protein localized to periportal hepatocytes, particularly in the presence of ballooning. In the Liver Transcriptomic cohort (n = 125), ATG7 expression correlated with suppression of the TNFα pathway, which was conversely upregulated in p.V471A carriers. CONCLUSIONS: We identified rare and low-frequency ATG7 loss-of-function variants that promote NAFLD progression by impairing autophagy and facilitating ballooning and inflammation. LAY SUMMARY: We found that rare mutations in a gene called autophagy-related 7 (ATG7) increase the risk of developing severe liver disease in individuals with dysmetabolism. These mutations cause an alteration in protein function and impairment of self-renewal of cellular content, leading to liver damage and inflammation.

PSD3 downregulation confers protection against fatty liver disease.

Fatty liver disease (FLD) is a growing health issue with burdening unmet clinical needs. FLD has a genetic component but, despite the common variants already identified, there is still a missing heritability component. Using a candidate gene approach, we identify a locus (rs71519934) at the Pleckstrin and Sec7 domain-containing 3 (PSD3) gene resulting in a leucine to threonine substitution at position 186 of the protein (L186T) that reduces susceptibility to the entire spectrum of FLD in individuals at risk. PSD3 downregulation by short interfering RNA reduces intracellular lipid content in primary human hepatocytes cultured in two and three dimensions, and in human and rodent hepatoma cells. Consistent with this, Psd3 downregulation by antisense oligonucleotides in vivo protects against FLD in mice fed a non-alcoholic steatohepatitis-inducing diet. Thus, translating these results to humans, PSD3 downregulation might be a future therapeutic option for treating FLD.

PCSK7 gene variation bridges atherogenic dyslipidemia with hepatic inflammation in NAFLD patients.

Dyslipidemia and altered iron metabolism are typical features of nonalcoholic fatty liver disease (NAFLD). Proprotein convertase subtilisin/kexin type 7 (PCSK7) gene variation has been associated with circulating lipids and liver damage during iron overload. The aim of this study was to examine the impact of the PCSK7 rs236918 variant on NAFLD-related traits in 1,801 individuals from the Liver Biopsy Cohort (LBC), 500,000 from the UK Biobank Cohort (UKBBC), and 4,580 from the Dallas Heart Study (DHS). The minor PCSK7 rs236918 C allele was associated with higher triglycerides, aminotransferases, and hepatic inflammation in the LBC (P < 0.05) and with hypercholesterolemia and liver disease in the UKBBC. In the DHS, PCSK7 missense variants were associated with circulating lipids. PCSK7 was expressed in hepatocytes and its hepatic expression correlated with that of lipogenic genes (P < 0.05). The rs236918 C allele was associated with upregulation of a new "intra-PCSK7" long noncoding RNA predicted to interact with the protein, higher hepatic and circulating PCSK7 protein (P < 0.01), which correlated with triglycerides (P = 0.04). In HepG2 cells, PCSK7 deletion reduced lipogenesis, fat accumulation, inflammation, transforming growth factor ß pathway activation, and fibrogenesis. In conclusion, PCSK7 gene variation is associated with dyslipidemia and more severe liver disease in high risk individuals, likely by modulating PCSK7 expression/activity.

Protein phosphatase 1 regulatory subunit 3B gene variation protects against hepatic fat accumulation and fibrosis in individuals at high risk of nonalcoholic fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) is a major cause of liver damage and has a strong genetic component. The rs4841132 G>A variant, modulating the expression of protein phosphatase 1 regulatory subunit 3B (PPP1R3B), which is involved in glycogen synthesis, has been reported to reduce the risk of NAFLD but at the same time may favor liver disease by facilitating glycogen accumulation. The aim of this study was to assess the impact of rs4841132 on development of histologic steatosis and fibrosis in 1,388 European individuals in a liver biopsy cohort, on NAFLD hepatocellular carcinoma in a cross-sectional Italian cohort (n = 132 cases), and on liver disease at the population level in the United Kingdom Biobank cohort. We investigated the underlying mechanism by examining the impact of the variant on gene expression profiles. In the liver biopsy cohort, the rs4841132 minor A allele was associated with protection against steatosis (odds ratio [OR], 0.63; 95% confidence interval [CI], 0.42-0.95; P = 0.03) and clinically significant fibrosis (OR, 0.35; 95% CI, 0.14-0.87; P = 0.02) and with reduced circulating cholesterol (P = 0.02). This translated into protection against hepatocellular carcinoma development (OR, 0.22; 95% CI, 0.07-0.70; P = 0.01). At the population level, the rs4841132 variation was not associated with nonalcoholic or nonviral diseases of the liver but was associated with lower cholesterol (P = 1.7 × 10-8). In individuals with obesity, the A allele protecting against steatosis was associated with increased PPP1R3B messenger RNA expression and activation of lipid oxidation and with down-regulation of pathways related to lipid metabolism, inflammation, and cell cycle. Conclusion: The rs4841132 A allele is associated with protection against hepatic steatosis and fibrosis in individuals at high risk of NAFLD but not in the general population and against dyslipidemia. The mechanism may be related to modulation of PPP1R3B expression and hepatic lipid metabolism. (Hepatology Communications 2018;2:666-675).

Deregulation of SGK1 in Ulcerative Colitis: A Paradoxical Relationship Between Immune Cells and Colonic Epithelial Cells.

BACKGROUND: Inflammatory bowel disease (IBD) is due to the interaction of genetic and environmental factors that trigger an unbalanced immune response ultimately resulting in the peculiar inflammatory reaction. Experimental models of IBD point to a role of T-cell-derived cytokines (Th17) and to SGK1 as mediator of the Th17 switch. We hypothesize that SGK1, a salt inducible kinase, directs lymphocytic behavior and tissue damage. METHODS: Eleven controls and 32 ulcerative colitis (UC) patients were randomized according to endoscopic Mayo score. Mucosal biopsies from different intestinal tracts were analyzed by immunohistochemistry and quantitative real-time polymerase chain reaction to check the expression of disease markers including SGK1. Peripheral blood mononuclear cells (PBMCs) from patients and controls were analyzed by fluorescence-activated cell sorting. Finally, an in vitro cell model was developed to test the hypothesis. RESULTS: SGK1 mRNA and protein expression in lesional areas of UC patients were lower than in normal peri-lesional areas of the same patients and in normal tissues of healthy controls. SGK1 expression was increased in PBMCs from UC patients, particularly in the CD4+ cell population, enriched in Th17 cells. IL17/IL13 was increased in patients and correlated with SGK1 expression. Genetically engineered Jurkat cells confirmed the effect of SGK1 overexpression on viability of RKO cells. CONCLUSIONS: These observations suggest a pathogenic mechanism whereby SGK1 overexpression in CD4+ T cells induces the secretion of the inflammatory cytokines IL17 and IL13, which downregulate the expression of SGK1 in target tissues. Our data suggest a novel hypothesis in the pathogenesis of UC, integrating colonic epithelial cells and lymphocytes.

An Integrated Understanding of the Rapid Metabolic Benefits of a Carbohydrate-Restricted Diet on Hepatic Steatosis in Humans.

A carbohydrate-restricted diet is a widely recommended intervention for non-alcoholic fatty liver disease (NAFLD), but a systematic perspective on the multiple benefits of this diet is lacking. Here, we performed a short-term intervention with an isocaloric low-carbohydrate diet with increased protein content in obese subjects with NAFLD and characterized the resulting alterations in metabolism and the gut microbiota using a multi-omics approach. We observed rapid and dramatic reductions of liver fat and other cardiometabolic risk factors paralleled by (1) marked decreases in hepatic de novo lipogenesis; (2) large increases in serum ß-hydroxybutyrate concentrations, reflecting increased mitochondrial ß-oxidation; and (3) rapid increases in folate-producing Streptococcus and serum folate concentrations. Liver transcriptomic analysis on biopsy samples from a second cohort revealed downregulation of the fatty acid synthesis pathway and upregulation of folate-mediated one-carbon metabolism and fatty acid oxidation pathways. Our results highlight the potential of exploring diet-microbiota interactions for treating NAFLD.

PNPLA3 I148M Variant Influences Circulating Retinol in Adults with Nonalcoholic Fatty Liver Disease or Obesity.

BACKGROUND: Retinol is a lipid-soluble essential nutrient that is stored as retinyl esters in lipid droplets of hepatic stellate cells. Patatin-like phospholipase domain-containing 3 (PNPLA3), through its retinyl-palmitate lipase activity, releases retinol from lipid droplets in hepatic stellate cells in vitro and ex vivo. We have shown that the genetic variant I148M (rs738409) reduces the PNPLA3 retinyl-palmitate lipase activity. OBJECTIVE: The aim of the present genetic association study was to test whether overweight/obese carriers of the PNPLA3 148M mutant allele had lower circulating concentrations of retinol than individuals who are homozygous for the 148I allele. METHODS: PNPLA3 I148M (rs738409) was genotyped by Taqman assay in 76 overweight/obese individuals [BMI (kg/m(2)) ≥25; mean ± SD age: 59.7 ± 11.4 y; male gender: 70%] with a histologic diagnosis of nonalcoholic fatty liver disease (NAFLD; namely the Milan NAFLD cohort) and in 413 obese men (BMI ≥30; mean ± SD age: 57.1 ± 4.9 y) from the α-Tocopherol, ß-Carotene Cancer Prevention (ATBC) Study. Serum concentrations of retinol and α-tocopherol were measured by HPLC in both cohorts. ß-Carotene concentrations in the ATBC study were measured by using HPLC. RESULTS: The PNPLA3 148M mutant allele was associated with lower fasting circulating concentrations of retinol (ß = -0.289, P = 0.03) in adults with NAFLD (Milan NAFLD cohort). The PNPLA3 148M mutant allele was also associated with lower fasting circulating concentrations of retinol in adults with a BMI ≥30 (ATBC study; ß = -0.043, P = 0.04). CONCLUSION: We showed for the first time, to our knowledge, that carriers of the PNPLA3 148M allele with either fatty liver plus obesity or obesity alone have lower fasting circulating retinol concentrations.