Photodynamic action of proflavine on coliphage T3. I. Kinetics of inactivation. J Virol. 1971;7:314-318. [PMID: 24927523 DOI: 10.1073/pnas.1323785111]

VLDL lipidomics reveals hepatocellular lipidome changes in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

The production of VLDL is one of the primary mechanisms through which liver cells regulate intracellular lipid homeostasis. We hypothesize that the disease characteristics of metabolic dysfunction-associated steatotic liver disease (MASLD) differentially impact VLDL lipid composition. This study comprehensively examines the relationship between VLDL-lipidome and MASLD histology and disease-associated genetics, aiming to define MASLD-related VLDL changes.

METHODS

We performed untargeted lipidomics on serum VLDL particles in a cohort of biopsy-proven MASLD patients to examine the relationship between VLDL-lipidome and MASLD disease features as well as MASLD-related genetic variants.

RESULTS

Among 1514 detected lipid species in VLDL, triglyceride (TG), phosphatidylcholine (PC), and ceramide (Cer) were the top classes. Moderate to severe hepatic steatosis was associated an increase in VLDL-TG, especially those with palmitic acid (C16:0). A unified acyl chain distribution analysis revealed that steatosis was associated with increases in TGs with saturated and monounsaturated fatty acyl chains, but decreases in polyunsaturated fatty acyl chains, a pattern that was not mirrored in acyl chains from VLDL-PC or VLDL-Cer. Lobular inflammation was associated with reductions in lipids with polyunsaturated acyl chains, particularly docosahexaenoic acid (C22:6). Meanwhile, patients with advanced liver fibrosis (stages 3-4) had reductions in VLDL-TGs with both saturated and polyunsaturated acyl chains and overall enrichment in Cer species. Furthermore, MASLD-associated genetic variants in PNPLA3, TM6SF2, GPAM, HSD17B13, and MTARC1 demonstrated distinct VLDL-lipidomic signatures in keeping with their biology in lipoprotein metabolism.

CONCLUSIONS

Hepatic steatosis and liver fibrosis in MASLD are associated with distinct VLDL-lipidomic signatures, respectively. This relationship is further modified by MASLD-genetics, suggesting a differential impact of pathogenic features on hepatocellular lipid homeostasis.

Polygenic Risk Score for Metabolic Dysfunction-Associated Steatotic Liver Disease and Steatohepatitis: A Narrative Review

Metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH) are spreading worldwide as the most critical causes of cirrhosis and hepatocellular carcinoma (HCC). Thus, improving the screening and managing strategies for patients with MASLD or MASH is necessary. A traditional non-systemic review provided this narrative. Genetic variations associated with the development of MASLD and MASH, such as PNPLA3, TM6SF2, GCKR, MBOAT7, MERTK, and HSD17B13, were initially reviewed. PNPLA3 genetic variants appeared to be strongly associated with the increased pathogenesis of MASLD, MASH, cirrhosis, and HCC. We also reviewed the useful polygenic risk score (PRS) for the development of MASLD, MASH, their related cirrhosis, and the occurrence of HCC. PRSs appeared to be better predictors of MASLD, MASH, the development of cirrhosis, and the occurrence of HCC in patients with MASLD or MASH than any single-nucleotide polymorphisms. RNA interference and antisense nucleotides against the genetic variations of PNPLA3 and HSD17B13 are also being developed. Multidisciplinary collaboration and cooperation involving hepatologists, geneticists, pharmacologists, and pathologists should resolve complicated problems in MASLD and MASH. This narrative review highlights the importance of the genetic susceptibility and PRS as predictive markers and personalized medicine for patients with MASLD or MASH in the future.

Clearance of Hepatitis C Viremia During Direct-Acting Antiviral Therapy Leads to Rapid Changes in Lipid and Lipoprotein Metabolism

BACKGROUND AND AIMS

Chronic hepatitis C virus (HCV) infection is associated with hypolipidemia. HCV eradication may, therefore, result in hyperlipidemia and increase cardiovascular disease (CVD) risk. We investigated the impact of HCV eradication on serum lipid and lipoprotein profiles and CVD risk during and following direct-acting antiviral (DAA) therapy.

APPROACH AND RESULTS

We retrospectively analysed stored sera and plasma from 60 DAA-naïve patients, genotypes 1-4, treated with 12 weeks of sofosbuvir-velpatasvir. Serum lipids, apolipoproteins (apo), and a systemic inflammatory marker, GlycA, were measured serially beginning early on treatment and off treatment. Additionally, NMR LipoProfile analysis was performed on plasma samples. Expression of genes regulating lipid metabolism was assessed from paired liver biopsies obtained before and on treatment. Linear mixed models were used to examine changes in lipid and inflammatory markers; Framingham and ASCVD CVD risk scores were assessed before and after treatment. Decline in HCV viremia was associated with a rapid, significant increase in TChol, HDL-C, LDL-C, ApoA-1 and ApoB, and GlycA, improvement in ALT, hepatic inflammation, and steatosis but no change in glycemic control (HOMA-IR and HbA1c). Increase in TChol, LDL-C, and ApoB was associated with an increased SREBP1expression. Both ASCVD and Framingham risk scores were significantly increased at week 24 post treatment after adjusting for age (p < 0.0001).

CONCLUSION

Serum lipids and lipoproteins rapidly increase with inhibition of viral replication during DAA therapy, an effect that may be mediated by genes affecting hepatic de novo lipogenesis. Based on lipid changes, HCV eradication may increase CVD risk, but this needs to be investigated prospectively.

Mechanistic evaluation of Jiu Wei Qing Zhi Gao in non-alcoholic fatty liver disease: insights from network Pharmacology and experimental validation

CONTEXT

Jiu Wei Qing Zhi Gao (JWQZG), a traditional Chinese medicine (TCM) formulation, is widely utilized in China for managing non-alcoholic fatty liver disease (NAFLD).

OBJECTIVE

This study aimed to elucidate the therapeutic mechanisms of JWQZG in the management of NAFLD.

MATERIALS AND METHODS

Network pharmacology was employed to predict the potential mechanisms of JWQZG in NAFLD management. In vivo experiments were conducted using C57BL/6J mice fed a high-fat diet (HFD) for 16 weeks, followed by treatment with JWQZG at three dosages (1.85, 3.7, and 7.4 g/kg/day) or metformin (150 mg/kg/day) for 8 weeks. In vitro studies utilized HepG2 cells exposed to 0.5 mM palmitic acid (PA) for 24 h to establish an NAFLD model, followed by exposure to JWQZG-containing serum at three concentrations for an additional 24 h. Western blot analysis was used to analyze the expression levels of key signaling pathway components.

RESULTS

Results of network pharmacology analysis identified the insulin signaling pathway as a potential mediator of the protective effects of JWQZG in NAFLD. Treatment with JWQZG markedly reduced hepatic steatosis and improved insulin resistance. This was accompanied by enhanced expression of key components in the insulin signaling pathway, including insulin receptor substrate 1 (IRS1), phosphorylated PI3K (p-PI3K), phosphorylated AKT (p-AKT), and phosphorylated GSK3β (p-GSK3β), compared to the NAFLD model group.

CONCLUSIONS

These findings provide robust evidence supporting the therapeutic potential of JWQZG in NAFLD and its modulation of the insulin signaling pathway. Furthermore, the study offers valuable insights for the discovery of anti-NAFLD compounds derived from TCM formulations.

Genetic Risk Phenotypes for Type 2 Diabetes Differ with Ancestry in US Adults with Diabetes and Overweight/Obesity

BACKGROUND

Type 2 diabetes (T2D) risk is higher among non-Hispanic black (NHB) and Hispanic individuals, for reasons that are unclear.

AIMS

With this cross-sectional study, we tested the hypothesis that racial disparities in T2D prevalence can be partially traced to heterogeneity in etiology, as indicated by genetic subtypes that reflect distinct T2D phenotypes.

METHODS

Using a diverse sample of 361 US adults with T2D (69.5% women; 34.1% NHB; 13.9% Hispanic), we derived genetic risk scores (GRS) representing five distinct T2D pathophysiological pathways from 94 loci: β-cell, proinsulin, obesity, lipodystrophy, and liver/lipid. Genetic predisposition for insulin resistance (IR) was also assessed using a 52-SNP IR risk score.

RESULTS

The β-cell and proinsulin scores (as median [IQR]) were higher among NHB participants relative to NHW and Hispanics (β-cell GRS [NHB, 0.842(0.784-0.887) vs. NHW, 0.762(0.702-0.835) and Hispanic, 0.772(0.717-0.848)]); proinsulin GRS (NHB, 1.006[0.973-1.070] vs. NHW, 0.969[0.853-1.044] and Hispanic, 0.976[0.901-1.048]), whereas the liver/lipid and 52-SNP IR scores were higher in both NHB and Hispanic participants versus NHW (liver/lipid GRS [NHB, 1.09(0.78-1.18) and Hispanic, 0.895(0.736-1.227) vs. NHW, 0.794(0.666-1.157)]); 52-SNP IR GRS (NHB, 0.0095[0.009-0.010] and Hispanic, 0.0096 [0.0092-0.0101] vs. NHW, 0.0090[0.0084-0.0095]).

CONCLUSIONS

Impaired β-cell function may underlie T2D etiology more profoundly in NHB, whereas hepatic dysfunction, lipid metabolism abnormalities, and genetic IR contribute to T2D etiology to a greater degree in both NHB and Hispanics. Further validation of these findings may form the basis for a personalized medicine approach to prevention and treatment of T2D.

Exome-wide association analysis identifies novel risk loci for alcohol-associated hepatitis

BACKGROUND AND AIMS

Alcohol-associated hepatitis (AH) is a clinically severe, acute disease that afflicts only a fraction of patients with alcohol use disorder. Genomic studies of alcohol-associated cirrhosis (AC) have identified several genes of large effect, but the genetic and environmental factors that lead to AH and AC, and their degree of genetic overlap, remain largely unknown. This study aims to identify genes and genetic variations that contribute to the development of AH.

APPROACH AND RESULTS

Exome-sequencing of patients with AH (N=784) and heavy drinking controls (N=951) identified an exome-wide significant association for AH at patalin-like phospholipase domain containing 3, as previously observed for AC in genome-wide association study, although with a much lower effect size. Single nucleotide polymorphisms (SNPs) of large effect size at inducible T cell costimulatory ligand ( ICOSLG ) (Chr 21) and TOX4/RAB2B (Chr 14) were also exome-wide significant. ICOSLG encodes a co-stimulatory signal for T-cell proliferation and cytokine secretion and induces B-cell proliferation and differentiation. TOX high mobility group box family member 4 ( TOX4 ) was previously implicated in diabetes and immune system function. Other genes previously implicated in AC did not strongly contribute to AH, and the only prominently implicated (but not exome-wide significant) gene overlapping with alcohol use disorder was alcohol dehydrogenase 1B ( ADH1B ). Polygenic signals for AH were observed in both common and rare variant analysis and identified genes with roles associated with inflammation.

CONCLUSIONS

This study has identified 2 new genes of high effect size with a previously unknown contribution to alcohol-associated liver disease and highlights both the overlap in etiology between liver diseases and the unique origins of AH.

Human genetics of metabolic dysfunction-associated steatotic liver disease: from variants to cause to precision treatment

Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterized by increased hepatic steatosis with cardiometabolic disease and is a leading cause of advanced liver disease. We review here the genetic basis of MASLD. The genetic variants most consistently associated with hepatic steatosis implicate genes involved in lipoprotein input or output, glucose metabolism, adiposity/fat distribution, insulin resistance, or mitochondrial/ER biology. The distinct mechanisms by which these variants promote hepatic steatosis result in distinct effects on cardiometabolic disease that may be best suited to precision medicine. Recent work on gene-environment interactions has shown that genetic risk is not fixed and may be exacerbated or attenuated by modifiable (diet, exercise, alcohol intake) and nonmodifiable environmental risk factors. Some steatosis-associated variants, notably those in patatin-like phospholipase domain-containing 3 (PNPLA3) and transmembrane 6 superfamily member 2 (TM6SF2), are associated with risk of developing adverse liver-related outcomes and provide information beyond clinical risk stratification tools, especially in individuals at intermediate to high risk for disease. Future work to better characterize disease heterogeneity by combining genetics with clinical risk factors to holistically predict risk and develop therapies based on genetic risk is required.

Role of genetic variants and DNA methylation of lipid metabolism-related genes in metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD), is one of the most common chronic liver diseases, which encompasses a spectrum of diseases, from metabolic dysfunction-associated steatotic liver (MASL) to metabolic dysfunction-associated steatohepatitis (MASH), and may ultimately progress to MASH-related cirrhosis and hepatocellular carcinoma (HCC). MASLD is a complex disease that is influenced by genetic and environmental factors. Dysregulation of hepatic lipid metabolism plays a crucial role in the development and progression of MASLD. Therefore, the focus of this review is to discuss the links between the genetic variants and DNA methylation of lipid metabolism-related genes and MASLD pathogenesis. We first summarize the interplay between MASLD and the disturbance of hepatic lipid metabolism. Next, we focus on reviewing the role of hepatic lipid related gene loci in the onset and progression of MASLD. We summarize the existing literature around the single nucleotide polymorphisms (SNPs) associated with MASLD identified by genome-wide association studies (GWAS) and candidate gene analyses. Moreover, based on recent evidence from human and animal studies, we further discussed the regulatory function and associated mechanisms of changes in DNA methylation levels in the occurrence and progression of MASLD, with a particular emphasis on its regulatory role of lipid metabolism-related genes in MASLD and MASH. Furthermore, we review the alterations of hepatic DNA and blood DNA methylation levels associated with lipid metabolism-related genes in MASLD and MASH patients. Finally, we introduce potential value of the genetic variants and DNA methylation profiles of lipid metabolism-related genes in developing novel prognostic biomarkers and therapeutic targets for MASLD, intending to provide references for the future studies of MASLD.

Hepatic TM6SF2 activates antitumour immunity to suppress metabolic dysfunction-associated steatotic liver disease-related hepatocellular carcinoma and boosts immunotherapy

BACKGROUND

Transmembrane 6 superfamily member 2 (TM6SF2) has a protective role against metabolic dysfunction-associated steatotic liver disease (MASLD).

OBJECTIVE

We aim to investigate the mechanistic role and therapeutic potential of hepatic TM6SF2 in MASLD-related hepatocellular carcinoma (HCC).

DESIGN

Hepatocyte-specific Tm6sf2 knockout (Tm6sf2 ∆hep) mice were fed with high-fat/high-cholesterol (HFHC) diet or diethylnitrosamine plus HFHC diet to induce MASLD-HCC. TM6SF2 function was also evaluated in orthotopic MASLD-HCC mice. Human MASLD-HCC specimens were included to evaluate clinical significance.

RESULTS

TM6SF2 was downregulated in tumours compared with adjacent normal tissues from MASLD-HCC patients. Hepatocyte-specific Tm6sf2 knockout exacerbated tumour formation in mice with diet-induced or diet-induced and carcinogen-induced MASLD-HCC. The tumour-promoting effect of Tm6sf2 knockout was verified in orthotopic MASLD-HCC mice, while mice bearing Tm6sf2-overexpressing tumours had opposite phenotypes. We observed the reduction of interferon-gamma (IFN-γ)+CD8+ T cells in the tumours of Tm6sf2 ∆hep mice and orthotopic Tm6sf2 knockout mice, while the tumour-suppressive effect of Tm6sf2 was abolished after depleting CD8+ T cells. The correlation between TM6SF2 and CD8+ T cells was confirmed in human MASLD-HCC tissues, inferring that TM6SF2 could promote antitumour immunity. Mechanistically, TM6SF2 directly bound to IKKβ and inhibited NF-κB signalling pathway to reduce interleukin (IL)-6 secretion, thereby activating cytotoxic CD8+ T cells. IL-6 neutralisation abolished the tumour-promoting and immunosuppressive effects of Tm6sf2 knockout in mice. Moreover, introducing Tm6sf2 by adenovirus improved immunotherapy response against MASLD-HCC in mice.

CONCLUSION

Hepatic TM6SF2 protects against MASLD-HCC and activates cytotoxic CD8+ T cells via NF-κB-IL-6 axis. TM6SF2 is a promising strategy for sensitising MASLD-HCC to immunotherapy.

Proximity proteomics reveals a mechanism of fatty acid transfer at lipid droplet-mitochondria- endoplasmic reticulum contact sites

Membrane contact sites between organelles are critical for the transfer of biomolecules. Lipid droplets store fatty acids and form contacts with mitochondria, which regulate fatty acid oxidation and adenosine triphosphate production. Protein compartmentalization at lipid droplet-mitochondria contact sites and their effects on biological processes are poorly described. Using proximity-dependent biotinylation methods, we identify 71 proteins at lipid droplet-mitochondria contact sites, including a multimeric complex containing extended synaptotagmin (ESYT) 1, ESYT2, and VAMP Associated Protein B and C (VAPB). High resolution imaging confirms localization of this complex at the interface of lipid droplet-mitochondria-endoplasmic reticulum where it likely transfers fatty acids to enable β-oxidation. Deletion of ESYT1, ESYT2 or VAPB limits lipid droplet-derived fatty acid oxidation, resulting in depletion of tricarboxylic acid cycle metabolites, remodeling of the cellular lipidome, and induction of lipotoxic stress. These findings were recapitulated in Esyt1 and Esyt2 deficient mice. Our study uncovers a fundamental mechanism that is required for lipid droplet-derived fatty acid oxidation and cellular lipid homeostasis, with implications for metabolic diseases and survival.

The biogenesis and transport of triglyceride-rich lipoproteins

Triglyceride-rich lipoproteins (TRLs) play essential roles in human health and disease by transporting bulk lipids into the circulation. This review summarizes the fundamental mechanisms and diverse factors governing lipoprotein production, secretion, and regulation. Emphasizing the broader implications for human health, we outline the intricate landscape of lipoprotein research and highlight the potential coordination between the biogenesis and transport of TRLs in physiology, particularly the unexpected coupling of metabolic enzymes and transport machineries. Challenges and opportunities in lipoprotein biology with respect to inherited diseases and viral infections are also discussed. Further characterization of the biogenesis and transport of TRLs will advance both basic research in lipid biology and translational medicine for metabolic diseases.

Walking the VLDL tightrope in cardiometabolic diseases

Very-low-density lipoprotein (VLDL), a triglyceride-rich lipoprotein secreted by hepatocytes, is pivotal for supplying peripheral tissues with fatty acids for energy production. As if walking on a tightrope, perturbations in the balance of VLDL metabolism contribute to cardiometabolic dysfunction, promoting pathologies such as cardiovascular disease (CVD) or metabolic dysfunction-associated steatotic liver disease (MASLD). Despite the advent of lipid-lowering therapies, including statins and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors, risks for cardiovascular events persist. With limitations to currently available CVD therapeutics and no US Food and Drug Administration (FDA)-approved treatment for MASLD, this review summarizes the current understanding of VLDL metabolism that sheds light on novel therapeutic avenues to pursue for cardiometabolic disorders.

Precision medicine and nucleotide-based therapeutics to treat steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a complex multifactorial disease and becoming the leading cause of liver-related morbidity and mortality. MASLD spans from isolated steatosis to metabolic dysfunction-associated steatohepatitis (MASH), that may progress to cirrhosis and hepatocellular carcinoma (HCC). Genetic, metabolic, and environmental factors strongly contribute to the heterogeneity of MASLD. Lifestyle intervention and weight loss represent a viable treatment for MASLD. Moreover, Resmetirom, a thyroid hormone beta receptor agonist, has recently been approved for MASLD treatment. However, most individuals treated did not respond to this therapeutic, suggesting the need for a more tailored approach to treat MASLD. Oligonucleotide-based therapies, namely small-interfering RNA (siRNA) and antisense oligonucleotide (ASO), have been recently developed to tackle MASLD by reducing the expression of genes influencing MASH progression, such as PNPLA3 and HSD17B13. Here, we review the latest progress made in the synthesis and development of oligonucleotide-based agents targeting genetic determinants of MASH.

Identification of Interactive Genetic Loci Linked to Insulin Resistance in Metabolic Syndrome-An Update

Metabolic syndrome is a metabolic disorder characterized by hypertension, dyslipidemia, impaired glucose tolerance, and abdominal obesity. Impaired insulin action or insulin resistance initiates metabolic syndrome. The prevalence of insulin resistance is increasing all over the world. Insulin resistance results in the defective metabolism of carbohydrates and lipids, in addition to low-grade chronic inflammation. Insulin resistance is associated with metabolic syndrome, which is a risk factor for a number of pathological conditions, such as Type 2 diabetes (T2D), cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD), and polycystic ovarian syndrome (PCOS). Genome-wide association studies have increased our understanding of many loci linked to these diseases and others. In this review, we discuss insulin resistance and its contribution to metabolic syndrome and these diseases. We also discuss the genetic loci associated with them. Genetic testing is invaluable in the identification and stratification of susceptible populations and/or individuals. After susceptible individuals and/or populations have been identified via genetic testing or screening, lifestyle modifications such as regular exercise, weight loss, a healthy diet, and smoking cessation can reduce or prevent metabolic syndrome and its associated pathologies.

Deep metabolic phenotyping of humans with protein-altering variants in TM6SF2 using a genome-first approach

Background & Aim

An unbiased genome-first approach can expand the molecular understanding of specific genes in disease-agnostic biobanks for deeper phenotyping. TM6SF2 represents a good candidate for this approach due to its known association with steatotic liver disease (SLD).

Methods

We screened participants with whole-exome sequences in the Penn Medicine Biobank (PMBB, n >40,000) and the UK Biobank (UKB, n >200,000) for protein-altering variants in TM6SF2 and evaluated their association with liver phenotypes and clinical outcomes.

Results

Missense variants in TM6SF2 (E167K, L156P, P216L) were associated with an increased risk of clinically diagnosed and imaging-proven steatosis, independent of the PNPLA3 I48M risk allele and hepatitis B/C (p <0.001). E167K homozygotes had significantly increased risk of SLD (odds ratio [OR] 5.38, p <0.001), steatohepatitis (OR 5.76, p <0.05) and hepatocellular carcinoma (OR 11.22, p <0.0001), while heterozygous carriers of L156P and P216L were also at an increased risk of steatohepatitis. In addition, carriers of E167K are at a 3-fold increased risk of at-risk MASH (OR 2.75, p <0.001). CT-derived liver fat scores were higher in E167K and L156P in an allele-dose manner (p <0.05). This corresponded with the UKB nuclear magnetic resonance-derived lipidomic analyses (n = 105,348), revealing all carriers to exhibit lower total cholesterol, triglycerides and total choline. In silico predictions suggested that these missense variants cause structural disruptions in the EXPERA domain, leading to reduced protein function. This hypothesis was supported by the association of rare loss-of-function variants in TM6SF2 with an increased risk of SLD (OR 4.9, p <0.05), primarily driven by a novel rare stop-gain variant (W35X) with the same directionality.

Conclusion

The functional genetic study of protein-altering variants provides insights on the association between loss of TM6SF2 function and SLD and provides the basis for future mechanistic studies.

Impact and implications

The genome-first approach expands insights into genetic risk factors for steatotic liver disease with TM6SF2 being a focal point due to its known association with plasma lipid traits. Our findings validated the association of two missense variants (E167K and L156P) with increased risk of hepatic steatosis on CT and MRI scans, as well as the risk of clinically diagnosed hepatocellular carcinoma independent of the common PNPLA3 I48M risk variant. Notably, we also identified a predicted deleterious missense variant (P216L) linked to steatotic risk and demonstrated that an aggregated gene burden of rare putative loss-of-function variants was associated with the risk of hepatic steatosis. Combined, this study sets the stage for future mechanistic investigations into the functional consequences of TM6SF2 variants in metabolic dysfunction-associated steatotic liver disease.

Unraveling Mechanisms of Genetic Risks in Metabolic Dysfunction-Associated Steatotic Liver Diseases: A Pathway to Precision Medicine

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing global health problem, affecting ∼1 billion people. This condition is well established to have a heritable component with strong familial clustering. With the extraordinary breakthroughs in genetic research techniques coupled with their application to large-scale biobanks, the field of genetics in MASLD has expanded rapidly. In this review, we summarize evidence regarding genetic predisposition to MASLD drawn from family and twin studies. Significantly, we delve into detailed genetic variations associated with diverse pathogenic mechanisms driving MASLD. We highlight the interplay between these genetic variants and their connections with metabolic factors, the gut microbiome, and metabolites, which collectively influence MASLD progression. These discoveries are paving the way for precise medicine, including noninvasive diagnostics and therapies. The promising landscape of novel genetically informed drug targets such as RNA interference is explored. Many of these therapies are currently under clinical validation, raising hopes for more effective MASLD treatment.

Recent advances in MASLD genetics: Insights into disease mechanisms and the next frontiers in clinical application

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease in the world and a growing cause of liver-related morbidity and mortality. Yet, at the same time, our understanding of the pathophysiology and genetic underpinnings of this increasingly common yet heterogeneous disease has increased dramatically over the last 2 decades, with the potential to lead to meaningful clinical interventions for patients. We have now seen the first pharmacologic therapy approved for the treatment of MASLD, and multiple other potential treatments are currently under investigation-including gene-targeted RNA therapies that directly extend from advances in MASLD genetics. Here we review recent advances in MASLD genetics, some of the key pathophysiologic insights that human genetics has provided, and the ways in which human genetics may inform our clinical practice in the field of MASLD in the near future.

Intestinal TM6SF2 protects against metabolic dysfunction-associated steatohepatitis through the gut-liver axis

Transmembrane-6 superfamily member 2 (TM6SF2) regulates hepatic fat metabolism and is associated with metabolic dysfunction-associated steatohepatitis (MASH). TM6SF2 genetic variants are associated with steatotic liver disease. The pathogenesis of MASH involves genetic factors and gut microbiota alteration, yet the role of host-microbe interactions in MASH development remains unclear. Here, we discover that mice with intestinal epithelial cell-specific knockout of Tm6sf2 (Tm6sf2ΔIEC) develop MASH, accompanied by impaired intestinal barrier and microbial dysbiosis. Transplanting stools from Tm6sf2ΔIEC mice induces steatohepatitis in germ-free recipient mice, whereas MASH is alleviated in Tm6sf2ΔIEC mice co-housed with wild-type mice. Mechanistically, Tm6sf2-deficient intestinal cells secrete more free fatty acids by interacting with fatty acid-binding protein 5 to induce intestinal barrier dysfunction, enrichment of pathobionts, and elevation of lysophosphatidic acid (LPA) levels. LPA is translocated from the gut to the liver, contributing to lipid accumulation and inflammation. Pharmacological inhibition of the LPA receptor suppresses MASH in both Tm6sf2ΔIEC and wild-type mice. Hence, modulating microbiota or blocking the LPA receptor is a potential therapeutic strategy in TM6SF2 deficiency-induced MASH.

PNPLA3 as a driver of steatotic liver disease: navigating from pathobiology to the clinics via epidemiology

Steatotic liver disease (SLD), particularly metabolic dysfunction-associated SLD, represents a significant public health concern worldwide. Among the various factors implicated in the development and progression of this condition, the patatin-like phospholipase domain-containing protein 3 (PNPLA3 ) gene has emerged as a critical player. Variants of PNPLA3 are associated with altered lipid metabolism, leading to increased hepatic fat accumulation and subsequent inflammation and fibrosis. Understanding the role of PNPLA3 not only enhances our comprehension of the pathomechanisms driving SLD but also informs potential therapeutic strategies. The molecular mechanisms through which PNPLA3 variants contribute to lipid dysregulation and hepatocyte injury in SLD are critically discussed in the present review article. We extensively analyze clinical cohorts and population-based studies underpinning the association between PNPLA3 polymorphisms and the risk of developing SLD, and its liver-related and protean extrahepatic outcomes, in concert with other risk modifiers, notably including age, sex, and ethnicity in adults and children. We also discuss the increasingly recognized role played by the PNPLA3 gene in liver transplantation, autoimmune hepatitis, and acquired immunodeficiency syndrome. Finally, we examine the clinical implications of PNPLA3 diagnostics regarding risk stratification and targeted therapies for patients affected by SLD in the context of precision medicine approaches.

Combination of risk alleles of PNPLA3, TM6SF2, and HSD17B13 of donors can predict recurrence of steatotic liver disease after liver transplantation

AIMS

This study aimed to identify the genetic risk factors from donors or recipients that contribute to postliver transplantation (LT) steatotic liver disease (SLD), focusing on the genetic risk score (GRS) based on single nucleotide polymorphisms (SNPs) in SLD patients.

METHODS

This retrospective study included 55 Japanese SLD recipients and their respective donors. Genotyping of PNPLA3, TM6SF2, and HSD17B13 was undertaken, and the combined GRS was calculated. The relationship between the GRS and the incidence of posttransplant SLD was also evaluated.

RESULTS

The SLD recipients had a high prevalence of post-LT graft steatosis/steatohepatitis (76.4% and 58.2%, respectively). Although the recipients had a high frequency of risk alleles, there was no relationship between the number of risk alleles for each SNP and the incidence of posttransplant SLD. In contrast, an increased number of risk alleles for any SNP in the donor was correlated with high incidence rates of both post-LT steatosis and steatohepatitis. A multivariable analysis showed that a high donor GRS was an independent risk factor for graft steatosis (odds ratio 8.77; 95% CI, 1.94-52.94; p = 0.009). Similarly, a high donor GRS was an independent risk factor (odds ratio 6.76; 95% CI, 1.84-30.78; p = 0.007) for post-LT graft steatohepatitis.

CONCLUSIONS

Donor risk alleles of PNPLA3, TM6SF2, and HSD17B13, rather than recipient risk alleles, have been implicated in the development of posttransplant SLD. The combination of these donor risk alleles into a GRS could predict the development of posttransplant SLD.

Gut microbes, diet, and genetics as drivers of metabolic liver disease: a narrative review outlining implications for precision medicine

Metabolic dysfunction-associated steatotic liver disease (MASLD) is rapidly increasing in prevalence, impacting over a third of the global population. The advanced form of MASLD, Metabolic dysfunction-associated steatohepatitis (MASH), is on track to become the number one indication for liver transplant. FDA-approved pharmacological agents are limited for MASH, despite over 400 ongoing clinical trials, with only a single drug (resmetirom) currently on the market. This is likely due to the heterogeneous nature of disease pathophysiology, which involves interactions between highly individualized genetic and environmental factors. To apply precision medicine approaches that overcome interpersonal variability, in-depth insights into interactions between genetics, nutrition, and the gut microbiome are needed, given that each have emerged as dynamic contributors to MASLD and MASH pathogenesis. Here, we discuss the associations and molecular underpinnings of several of these factors individually and outline their interactions in the context of both patient-based studies and preclinical animal model systems. Finally, we highlight gaps in knowledge that will require further investigation to aid in successfully implementing precision medicine to prevent and alleviate MASLD and MASH.

TM6SF2 -rs58542926 Genotype Has Opposing Effects on Incidence of Hepatic and Cardiac Events in a Community Cohort

INTRODUCTION

TM6SF2 -rs58542926-T is associated with increased cirrhosis and modestly decreased coronary artery disease prevalence. However, relative effects of TM6SF2 genotype on major adverse cardiovascular events (MACE) vs liver-related events (LRE) are not known.

METHODS

We used the UK Biobank, a prospective cohort with genetic and inpatient diagnosis data. The primary predictor was TM6SF2 -rs58542926 genotype, and the primary outcomes were MACE and LRE. Effects were reported as subhazard ratios (sHRs) and 10-year cumulative incidence by Fine-Gray competing risk analyses.

RESULTS

More than 430,000 individuals met inclusion criteria. TM6SF2 -rs58542926-TT genotype (vs CC) was associated with higher incidence of LRE (adjusted sHR 3.16, 95% confidence interval 1.86-5.37) and lower incidence of MACE (adjusted sHR for TT vs CC genotype 0.76, 95% confidence interval 0.63-0.91). In individuals with fibrosis-4 (FIB4) < 1.3, 1.3-2.67, and > 2.67, 10-year LRE incidence in TM6SF2 -rs58542926-TT vs CC individuals was 0.08% vs 0.06% ( P > 0.05), 0.81% vs 0.20% ( P < 0.0001), and 10.5% vs 3.4% ( P = 0.00094), respectively. The corresponding values for MACE were 3.8% vs 5.1% ( P = 0.032), 6.4% vs 8.2% ( P = 0.040), and 17.1% vs 12.4% ( P > 0.05). The absolute decrease in MACE with rs58542926-TT (vs CC) genotype exceeded the absolute increase in LRE in all groups but FIB4 > 2.67. Associations of TM6SF2 genotype with LRE/MACE were significant in men but not women. TM6SF2 -rs58542926-T allele was also associated with increased hepatic steatosis and corrected T1 time by magnetic resonance imaging, with greater effect sizes in men than women.

DISCUSSION

TM6SF2 genotype has opposite effects on LRE vs MACE incidence, and absolute effects on MACE were greater except in those with highest FIB4 scores. Effects were strongest in men. These findings clarify implications of TM6SF2 genotype based on personalized clinical risk.

Interaction Between PNPLA3 and SIRT5 Genetic Variants in Association with Liver Fibrosis Severity in Patients with Metabolic Dysfunction-Associated Steatotic Liver Disease

BACKGROUND/OBJECTIVES

This study evaluated the association between polymorphisms in the PNPLA3, TM6SF2, HSD17B13, and SIRT5 genes and the severity of fibrosis and steatosis in metabolic dysfunction-associated steatotic liver disease (MASLD).

METHODS

Fibrosis and steatosis were assessed by MRE and MRI-PDFF, respectively. The polymorphisms were determined by allelic discrimination in blood samples.

RESULTS

204 patients aged 57.0 ± 13.5 years were included. Sixty-two (30.4%) patients had significant fibrosis (≥F2). Among F2-F4 fibrosis, the PNPLA3 rs738409 GG genotype was significantly higher than the CC + CG genotypes (44.9% vs. 21.4%, p = 0.001). The SIRT5 rs12216101 GG vs. TT + TG genotypes also exhibited a similar trend (64.3% vs. 27.9%, p = 0.012). In multivariate analysis, the PNPLA3 GG genotype (OR = 3.48, 95%CI: 1.50-8.06; p = 0.004) and SIRT5 rs12216101 GG genotype (OR = 5.43, 95%CI: 1.32-22.33; p = 0.019) were independently associated with F2-F4 fibrosis. Additionally, the proportion of patients with F2-F4 fibrosis significantly increased with the number of combined risk genotypes. Among S2-S3 steatosis, the prevalence of HSD17B13 AG + GG genotypes was higher than that of the AA genotype (37.5% vs. 23.9%, p = 0.048) and independently associated with moderate/severe steatosis in multivariate analysis (OR = 2.26, 95%CI: 1.14-4.49; p = 0.020).

CONCLUSIONS

Our data indicate that the PNPLA3 and SIRT5 polymorphisms were independently and additively linked to significant fibrosis, while the HSD17B13 polymorphism was associated with increased steatosis in Thai populations. These data might emphasize the importance of genetic variants in progressive MASLD.

Inhibition of Cellular Factor TM6SF2 Suppresses Secretion Pathways of Hepatitis B, Hepatitis C, and Hepatitis D Viruses

Chronic viral hepatitis is caused by hepatitis B virus (HBV), hepatitis C virus (HCV), or hepatitis D virus (HDV). Despite different replication strategies, all of these viruses rely on secretion through the host endoplasmic reticulum-Golgi pathway, providing potential host targets for antiviral therapy. Knockdown of transmembrane 6 superfamily member 2 (TM6SF2) in virus cell culture models reduced secretion of infectious HCV virions, HDV virions, and HBV subviral particles. Moreover, in a cohort of people with hepatitis B, a TM6SF2 polymorphism (rs58542926 CT/TT, which causes protein misfolding and reduced TM6SF2 in the liver) correlated with lower concentrations of subviral particles in blood, complementing our previous work showing decreased HCV viral load in people with this polymorphism. In conclusion, the host protein TM6SF2 plays a key role in secretion of HBV, HCV, and HDV, providing the potential for novel pan-viral agents to treat people with chronic viral hepatitis.

Molecular Regulation and Therapeutic Targeting of VLDL Production in Cardiometabolic Disease

There exists a complex relationship between steatotic liver disease (SLD) and atherosclerotic cardiovascular disease (CVD). CVD is a leading cause of morbidity and mortality among individuals with SLD, particularly those with metabolic dysfunction-associated SLD (MASLD), a significant proportion of whom also exhibit features of insulin resistance. Recent evidence supports an expanded role of very low-density lipoprotein (VLDL) in the pathogenesis of CVD in patients, both with and without associated metabolic dysfunction. VLDL represents the major vehicle for exporting neutral lipid from hepatocytes, with each particle containing one molecule of apolipoproteinB100 (APOB100). VLDL production becomes dysregulated under conditions characteristic of MASLD including steatosis and insulin resistance. Insulin resistance not only affects VLDL production but also mediates the pathogenesis of atherosclerotic CVD. VLDL assembly and secretion therefore represents an important pathway in the setting of cardiometabolic disease and offers several candidates for therapeutic targeting, particularly in metabolically complex patients with MASLD at increased risk of atherosclerotic CVD. Here we review the clinical significance as well as the translational and therapeutic potential of key regulatory steps impacting VLDL initiation, maturation, secretion, catabolism, and clearance.

Drivers of cardiovascular disease in metabolic dysfunction-associated steatotic liver disease: the threats of oxidative stress

Non-alcoholic fatty liver disease (NAFLD), now known as metabolic-associated steatotic liver disease (MASLD), is the most common liver disease worldwide, with a prevalence of 38%. In these patients, cardiovascular disease (CVD) is the number one cause of mortality rather than liver disease. Liver abnormalities per se due to MASLD contribute to risk factors such as dyslipidemia and obesity and increase CVD incidents. In this review we discuss hepatic pathophysiological changes the liver of MASLD leading to cardiovascular risks, including liver sinusoidal endothelial cells, insulin resistance, and oxidative stress with a focus on glutathione metabolism and function. In an era where there is an increasingly robust recognition of what causes CVD, such as the factors included by the American Heart Association in the recently developed PREVENT equation, the inclusion of liver disease may open doors to how we approach treatment for MASLD patients who are at risk of CVD.

TM6SF2 E167K variant decreases PNPLA3-mediated PUFA transfer to promote hepatic steatosis and injury in MASLD

BACKGROUNDS/AIMS

Transmembrane 6 superfamily member 2 (TM6SF2) E167K variant is closely associated with the occurrence and development of metabolic dysfunction-associated steatotic liver disease (MASLD). However, the role and mechanism of TM6SF2 E167K variant during MASLD progression are not yet fully understood.

METHODS

The Tm6sf2167K knock-in (KI) mice were subjected to high-fat diet (HFD). Hepatic lipid levels of Tm6sf2167K KI mice were detected by lipidomics analysis. Thin-layer chromatography (TLC) was used to measure the newly synthesized triglyceride (TG) and phosphatidylcholine (PC).

RESULTS

The TM6SF2 E167K variant significantly aggravated hepatic steatosis and injury in HFD-induced mice. Decreased polyunsaturated PC level and increased polyunsaturated TG level were found in liver tissue of HFD-induced Tm6sf2167K KI mice. Mechanistic studies demonstrated that the TM6SF2 E167K variant increased the interaction between TM6SF2 and PNPLA3, and impaired PNPLA3-mediated transfer of polyunsaturated fatty acids (PUFAs) from TG to PC. The TM6SF2 E167K variant increased the level of fatty acid-induced malondialdehyde and reactive oxygen species, and decreased fatty acid-downregulated cell membrane fluidity. Additionally, the TM6SF2 E167K variant decreased the level of hepatic PC containing C18:3, and dietary supplementation of PC containing C18:3 significantly attenuated the TM6SF2 E167K-induced hepatic steatosis and injury in HFD-fed mice.

CONCLUSION

The TM6SF2 E167K variant could promote its interaction with PNPLA3 and inhibit PNPLA3-mediated transfer of PUFAs from TG to PC, resulting in the hepatic steatosis and injury during MASLD progression. PC containing C18:3 could act as a potential therapeutic supplement for MASLD patients carrying the TM6SF2 E167K variant.

A sexually dimorphic hepatic cycle of periportal VLDL generation and subsequent pericentral VLDLR-mediated re-uptake

Recent single-cell transcriptomes revealed spatiotemporal programmes of liver function on the sublobular scale. However, how sexual dimorphism affected this space-time logic remained poorly understood. We addressed this by performing scRNA-seq in the mouse liver, which revealed that sex, space and time together markedly influence xenobiotic detoxification and lipoprotein metabolism. The very low density lipoprotein receptor (VLDLR) exhibits a pericentral expression pattern, with significantly higher mRNA and protein levels in female mice. Conversely, VLDL assembly is periportally biased, suggesting a sexually dimorphic hepatic cycle of periportal formation and pericentral uptake of VLDL. In humans, VLDLR expression is also pericentral, with higher mRNA and protein levels in premenopausal women compared to similarly aged men. Individuals with low hepatic VLDLR expression show a high prevalence of atherosis in the coronary artery already at an early age and an increased incidence of heart attack.

Metabolic-associated fatty liver disease and pregnancy complications: new challenges and clinical perspectives

The term metabolic-associated fatty liver disease (MAFLD), with a global prevalence estimated at 38.77%, has gradually replaced the traditional concept of non-alcoholic fatty liver disease (NAFLD). Compared to the general population, the incidence of MAFLD is notably higher among pregnant women, posing potential risks to both maternal and neonatal health. This review summarizes the latest research on MAFLD, focusing on its association with pregnancy complications. Additionally, it provides a comparative analysis with previous studies on NAFLD, presenting a comprehensive perspective for clinical management. Findings suggest that pregnant women with MAFLD face a higher risk of gestational hypertension and cesarean delivery compared to those with NAFLD, while the risk for gestational diabetes mellitus remains similar between the two conditions. Additionally, MAFLD is associated with an increased likelihood of delivering large-for-gestational-age infants and heightened risks of preterm birth and low birth weight. Current treatment strategies for MAFLD focus on lifestyle modifications, such as dietary adjustments and increased physical activity. However, there is an urgent need for the development of safe and effective pharmacological treatments, particularly tailored toward pregnant women. Future research should delve deeper into the causal relationships between MAFLD and pregnancy complications and explore optimal therapeutic approaches to improve outcomes for mothers and their infants.

A suite of genome-engineered hepatic cells provides novel insights into the spatiotemporal metabolism of apolipoprotein B and apolipoprotein B-containing lipoprotein secretion

AIMS

Apolipoprotein B (APOB)-containing very LDL (VLDL) production, secretion, and clearance by hepatocytes is a central determinant of hepatic and circulating lipid levels. Impairment of any of the aforementioned processes is associated with the development of multiple diseases. Despite the discovery of genes and processes that govern hepatic VLDL metabolism, our understanding of the different mechanistic steps involved is far from complete. An impediment to these studies is the lack of tractable hepatocyte-based systems to interrogate and follow APOB in cells, which the current study addresses.

METHODS AND RESULTS

To facilitate the cellular study of VLDL metabolism, we generated human hepatic HepG2 and Huh-7 cell lines in which CRISPR/Cas9-based genome engineering was used to introduce the fluorescent protein mNeonGreen into the APOB gene locus. This results in the production of APOB100-mNeon that localizes predominantly to the endoplasmic reticulum (ER) and Golgi by immunofluorescence and electron microscopy imaging. The production and secretion of APOB100-mNeon can be quantitatively followed in medium over time and results in the production of lipoproteins that are taken up via the LDL receptor pathway. Importantly, the production and secretion of APOB-mNeon is sensitive to established pharmacological and physiological treatments and to genetic modifiers known to influence VLDL production in humans. As a showcase, we used HepG2-APOBmNeon cells to interrogate ER-associated degradation of APOB. The use of a dedicated sgRNA library targeting all established membrane-associated ER-resident E3 ubiquitin ligases led to the identification of SYNV1 as the E3 responsible for the degradation of poorly lipidated APOB in HepG2 cells.

CONCLUSIONS

In summary, the engineered cells reported here allow the study of hepatic VLDL assembly and secretion and facilitate spatiotemporal interrogation induced by pharmacologic and genetic perturbations.

Human-induced pluripotent stem cell-based hepatic modeling of lipid metabolism-associated TM6SF2-E167K variant

BACKGROUND AND AIMS

TM6SF2 rs58542926 (E167K) is related to an increased prevalence of metabolic dysfunction-associated steatotic liver disease. Conflicting mouse study results highlight the need for a human model to understand this mutation's impact. This study aims to create and characterize a reliable human in vitro model to mimic the effects of the TM6SF2-E167K mutation for future studies.

APPROACH AND RESULTS

We used gene editing on human-induced pluripotent stem cells from a healthy individual to create cells with the TM6SF2-E167K mutation. After hepatocyte-directed differentiation, we observed decreased TM6SF2 protein expression, increased intracellular lipid droplets, and total cholesterol, in addition to reduced VLDL secretion. Transcriptomics revealed the upregulation of genes involved in lipid, fatty acid, and cholesterol transport, flux, and oxidation. Global lipidomics showed increased lipid classes associated with endoplasmic reticulum (ER) stress, mitochondrial dysfunction, apoptosis, and lipid metabolism. In addition, the TM6SF2-E167K mutation conferred a proinflammatory phenotype with signs of mitochondria and ER stress. Importantly, by facilitating protein folding within the ER of hepatocytes carrying TM6SF2-E167K mutation, VLDL secretion and ER stress markers improved.

CONCLUSIONS

Our findings indicate that induced hepatocytes generated from human-induced pluripotent stem cells carrying the TM6SF2-E167K recapitulate the effects observed in human hepatocytes from individuals with the TM6SF2 mutation. This study characterizes an in vitro model that can be used as a platform to identify potential clinical targets and highlights the therapeutic potential of targeting protein misfolding to alleviate ER stress and mitigate the detrimental effects of the TM6SF2-E167K mutation on hepatic lipid metabolism.

Team players in the pathogenesis of metabolic dysfunctions-associated steatotic liver disease: The basis of development of pharmacotherapy

Nutrient metabolism is regulated by several factors. Social determinants of health with or without genetics are the primary regulator of metabolism, and an unhealthy lifestyle affects all modulators and mediators, leading to the adaptation and finally to the exhaustion of cellular functions. Hepatic steatosis is defined by presence of fat in more than 5% of hepatocytes. In hepatocytes, fat is stored as triglycerides in lipid droplet. Hepatic steatosis results from a combination of multiple intracellular processes. In a healthy individual nutrient metabolism is regulated at several steps. It ranges from the selection of nutrients in a grocery store to the last step of consumption of ATP as an energy or as a building block of a cell as structural component. Several hormones, peptides, and genes have been described that participate in nutrient metabolism. Several enzymes participate in each nutrient metabolism as described above from ingestion to generation of ATP. As of now several publications have revealed very intricate regulation of nutrient metabolism, where most of the regulatory factors are tied to each other bidirectionally, making it difficult to comprehend chronological sequence of events. Insulin hormone is the primary regulator of all nutrients' metabolism both in prandial and fasting states. Insulin exerts its effects directly and indirectly on enzymes involved in the three main cellular function processes; metabolic, inflammation and repair, and cell growth and regeneration. Final regulators that control the enzymatic functions through stimulation or suppression of a cell are nuclear receptors in especially farnesoid X receptor and peroxisome proliferator-activated receptor/RXR ligands, adiponectin, leptin, and adiponutrin. Insulin hormone has direct effect on these final modulators. Whereas blood glucose level, serum lipids, incretin hormones, bile acids in conjunction with microbiota are intermediary modulators which are controlled by lifestyle. The purpose of this review is to overview the key players in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) that help us understand the disease natural course, risk stratification, role of lifestyle and pharmacotherapy in each individual patient with MASLD to achieve personalized care and target the practice of precision medicine. PubMed and Google Scholar databases were used to identify publication related to metabolism of carbohydrate and fat in states of health and disease states; MASLD, cardiovascular disease and cancer. More than 1000 publications including original research and review papers were reviewed.

Increased Genetic Risk for β-Cell Failure Is Associated With β-Cell Function Decline in People With Prediabetes

Partitioned polygenic scores (pPS) have been developed to capture pathophysiologic processes underlying type 2 diabetes (T2D). We investigated the association of T2D pPS with diabetes-related traits and T2D incidence in the Diabetes Prevention Program. We generated five T2D pPS (β-cell, proinsulin, liver/lipid, obesity, lipodystrophy) in 2,647 participants randomized to intensive lifestyle, metformin, or placebo arms. Associations were tested with general linear models and Cox regression with adjustment for age, sex, and principal components. Sensitivity analyses included adjustment for BMI. Higher β-cell pPS was associated with lower insulinogenic index and corrected insulin response at 1-year follow-up with adjustment for baseline measures (effect per pPS SD -0.04, P = 9.6 × 10-7, and -8.45 μU/mg, P = 5.6 × 10-6, respectively) and with increased diabetes incidence with adjustment for BMI at nominal significance (hazard ratio 1.10 per SD, P = 0.035). The liver/lipid pPS was associated with reduced 1-year baseline-adjusted triglyceride levels (effect per SD -4.37, P = 0.001). There was no significant interaction between T2D pPS and randomized groups. The remaining pPS were associated with baseline measures only. We conclude that despite interventions for diabetes prevention, participants with a high genetic burden of the β-cell cluster pPS had worsening in measures of β-cell function.

ARTICLE HIGHLIGHTS

Altered lipid metabolism and the development of metabolic-associated fatty liver disease

PURPOSE OF REVIEW

An increasing amount of research has underscored the significant role of lipoproteins in the pathogenesis of metabolic-associated fatty liver disease (MAFLD). This comprehensive review examines the intricate relationship between lipoprotein abnormalities and the development of MAFLD.

RECENT FINDINGS

Atherogenic dyslipidemia seen in insulin resistance states play a significant role in initiating and exacerbating hepatic lipid accumulation. There are also specific genetic factors ( PNPLA3 , TM6SF2 , MBOAT7 , HSD17B13 , GCKR- P446L) and transcription factors (SREBP-2, FXR, and LXR9) that increase susceptibility to both lipoprotein disorders and MAFLD. Most monogenic primary lipid disorders do not cause hepatic steatosis unless accompanied by metabolic stress. Hepatic steatosis occurs in the presence of secondary systemic metabolic stress in conjunction with predisposing environmental factors that lead to insulin resistance. Identifying specific aberrant lipoprotein metabolic factors promoting hepatic fat accumulation and subsequently exacerbating steatohepatitis will shed light on potential targets for therapeutic interventions.

SUMMARY

The clinical implications of interconnection between genetic factors and an insulin resistant environment that predisposes MAFLD is many fold. Potential therapeutic strategies in preventing or mitigating MAFLD progression include lifestyle modifications, pharmacological interventions, and emerging therapies targeting aberrant lipoprotein metabolism.

Dysfunctional VLDL metabolism in MASLD

Lipidomics has unveiled the intricate human lipidome, emphasizing the extensive diversity within lipid classes in mammalian tissues critical for cellular functions. This diversity poses a challenge in maintaining a delicate balance between adaptability to recurring physiological changes and overall stability. Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD), linked to factors such as obesity and diabetes, stems from a compromise in the structural and functional stability of the liver within the complexities of lipid metabolism. This compromise inaccurately senses an increase in energy status, such as during fasting-feeding cycles or an upsurge in lipogenesis. Serum lipidomic studies have delineated three distinct metabolic phenotypes, or "metabotypes" in MASLD. MASLD-A is characterized by lower very low-density lipoprotein (VLDL) secretion and triglyceride (TG) levels, associated with a reduced risk of cardiovascular disease (CVD). In contrast, MASLD-C exhibits increased VLDL secretion and TG levels, correlating with elevated CVD risk. An intermediate subtype, with a blend of features, is designated as the MASLD-B metabotype. In this perspective, we examine into recent findings that show the multifaceted regulation of VLDL secretion by S-adenosylmethionine, the primary cellular methyl donor. Furthermore, we explore the differential CVD and hepatic cancer risk across MASLD metabotypes and discuss the context and potential paths forward to gear the findings from genetic studies towards a better understanding of the observed heterogeneity in MASLD.

Review article: Hepatic steatosis and its associations with acute and chronic liver diseases

BACKGROUND

Hepatic steatosis is a common finding in liver histopathology and the hallmark of metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), whose global prevalence is rising.

AIMS

To review the histopathology of hepatic steatosis and its mechanisms of development and to identify common and rare disease associations.

METHODS

We reviewed literature on the basic science of lipid droplet (LD) biology and clinical research on acute and chronic liver diseases associated with hepatic steatosis using the PubMed database.

RESULTS

A variety of genetic and environmental factors contribute to the development of chronic hepatic steatosis or steatotic liver disease, which typically appears macrovesicular. Microvesicular steatosis is associated with acute mitochondrial dysfunction and liver failure. Fat metabolic processes in hepatocytes whose dysregulation leads to the development of steatosis include secretion of lipoprotein particles, uptake of remnant lipoprotein particles or free fatty acids from blood, de novo lipogenesis, oxidation of fatty acids, lipolysis and lipophagy. Hepatic insulin resistance is a key feature of MASLD. Seipin is a polyfunctional protein that facilitates LD biogenesis. Assembly of hepatitis C virus takes place on LD surfaces. LDs make important, functional contact with the endoplasmic reticulum and other organelles.

CONCLUSIONS

Diverse liver pathologies are associated with hepatic steatosis, with MASLD being the most important contributor. The biogenesis and dynamics of LDs in hepatocytes are complex and warrant further investigation. Organellar interfaces permit co-regulation of lipid metabolism to match generation of potentially toxic lipid species with their LD depot storage.

PNPLA3 is a triglyceride lipase that mobilizes polyunsaturated fatty acids to facilitate hepatic secretion of large-sized very low-density lipoprotein

The I148M variant of PNPLA3 is closely associated with hepatic steatosis. Recent evidence indicates that the I148M mutant functions as an inhibitor of PNPLA2/ATGL-mediated lipolysis, leaving the role of wild-type PNPLA3 undefined. Despite showing a triglyceride hydrolase activity in vitro, PNPLA3 has yet to be established as a lipase in vivo. Here, we show that PNPLA3 preferentially hydrolyzes polyunsaturated triglycerides, mobilizing polyunsaturated fatty acids for phospholipid desaturation and enhancing hepatic secretion of triglyceride-rich lipoproteins. Under lipogenic conditions, mice with liver-specific knockout or acute knockdown of PNPLA3 exhibit aggravated liver steatosis and reduced plasma VLDL-triglyceride levels. Similarly, I148M-knockin mice show decreased hepatic triglyceride secretion during lipogenic stimulation. Our results highlight a specific context whereby the wild-type PNPLA3 facilitates the balance between hepatic triglyceride storage and secretion, and suggest the potential contribution of a loss-of-function by the I148M variant to the development of fatty liver disease in humans.

Basic and translational evidence supporting the role of TM6SF2 in VLDL metabolism

PURPOSE OF REVIEW

Transmembrane 6 superfamily member 2 ( TM6SF2 ) gene was identified through exome-wide studies in 2014. A genetic variant from glutamic acid to lysine substitution at amino acid position 167 (NM_001001524.3:c.499G> A) (p.Gln167Lys/p.E167K, rs58542926) was discovered (p.E167K) to be highly associated with increased hepatic fat content and reduced levels of plasma triglycerides and LDL cholesterol. In this review, we focus on the discovery of TM6SF2 and its role in VLDL secretion pathways. Human data suggest TM6SF2 is linked to hepatic steatosis and cardiovascular disease (CVD), hence understanding its metabolic pathways is of high scientific interest.

RECENT FINDINGS

Since its discovery, completed research studies in cell, rodent and human models have defined the role of TM6SF2 and its links to human disease. TM6SF2 resides in the endoplasmic reticulum (ER) and the ER-Golgi interface and helps with the lipidation of nascent VLDL, the main carrier of triglycerides from the liver to the periphery. Consistent results from cells and rodents indicated that the secretion of triglycerides is reduced in carriers of the p.E167K variant or when hepatic TM6SF2 is deleted. However, data for secretion of APOB, the main protein of VLDL particles responsible for triglycerides transport, are inconsistent.

SUMMARY

The identification of genetic variants that are highly associated with human disease presentation should be followed by the validation and investigation into the pathways that regulate disease mechanisms. In this review, we highlight the role of TM6SF2 and its role in processing of liver triglycerides.

Metabolic dysfunction-associated steatotic liver disease heterogeneity: Need of subtyping

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a widespread global disease with significant health burden. Unhealthy lifestyle, obesity, diabetes mellitus (DM), insulin resistance, and genetics have been implicated in the pathogenesis of MASLD. A significant degree of heterogeneity exists among each of above-mentioned risk factors. Heterogeneity of these risk factors translates into the heterogeneity of MASLD. On the other hand, MASLD can itself lead to insulin resistance and DM. Such heterogeneity makes it difficult to assess the natural course of an individual with MASLD in clinical practice. At present MASLD is considered as one disease despite the variability of etiopathogenic processes, and we lack the consensus definitions of unique subtypes of MASLD. In this review, pathogenic processes of MASLD are discussed and a need of subtyping is recommended.

Exploring the impact of lipid droplets on the evolution and progress of hepatocarcinoma

Over the past 10 years, the biological role of lipid droplets (LDs) has gained significant attention in the context of both physiological and pathological conditions. Considerable progress has been made in elucidating key aspects of these organelles, yet much remains to be accomplished to fully comprehend the myriad functions they serve in the progression of hepatic tumors. Our current perception is that LDs are complex and active structures managed by a distinct set of cellular processes. This understanding represents a significant paradigm shift from earlier perspectives. In this review, we aim to recapitulate the function of LDs within the liver, highlighting their pivotal role in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) (Hsu and Loomba, 2024) and their contribution to the progression towards more advanced pathological stages up to hepatocellular carcinoma (HC) (Farese and Walther, 2009). We are aware of the molecular complexity and changes occurring in the neoplastic evolution of the liver. Our attempt, however, is to summarize the most important and recent roles of LDs across both healthy and all pathological liver states, up to hepatocarcinoma. For more detailed insights, we direct readers to some of the many excellent reviews already available in the literature (Gluchowski et al., 2017; Hu et al., 2020; Seebacher et al., 2020; Paul et al., 2022).

The Relationship between Pathogenesis and Possible Treatments for the MASLD-Cirrhosis Spectrum

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a term that entails a broad spectrum of conditions that vary in severity. Its development is influenced by multiple factors such as environment, microbiome, comorbidities, and genetic factors. MASLD is closely related to metabolic syndrome as it is caused by an alteration in the metabolism of fatty acids due to the accumulation of lipids because of an imbalance between its absorption and elimination in the liver. Its progression to fibrosis is due to a constant flow of fatty acids through the mitochondria and the inability of the liver to slow down this metabolic load, which generates oxidative stress and lipid peroxidation, triggering cell death. The development and progression of MASLD are closely related to unhealthy lifestyle habits, and nutritional epigenetic and genetic mechanisms have also been implicated. Currently, lifestyle modification is the first-line treatment for MASLD and nonalcoholic steatohepatitis; weight loss of ≥10% produces resolution of steatohepatitis and fibrosis regression. In many patients, body weight reduction cannot be achieved; therefore, pharmacological treatment should be offered in particular populations.

Genetics of liver disease in adults

Chronic liver disease stands as a significant global health problem with an estimated 2 million annual deaths across the globe. Combining the use of next-generation sequencing technologies with evolving knowledge in the interpretation of genetic variation across the human genome is propelling our understanding, diagnosis, and management of both rare and common liver diseases. Here, we review the contribution of risk and protective alleles to common forms of liver disease, the rising number of monogenic diseases affecting the liver, and the role of somatic genetic variants in the onset and progression of oncological and non-oncological liver diseases. The incorporation of genomic information in the diagnosis and management of patients with liver disease is driving the beginning of a new era of genomics-informed clinical hepatology practice, facilitating personalized medicine, and improving patient care.

Novel insights into metabolic-associated steatotic liver disease preclinical models

Metabolic-associated steatotic liver disease (MASLD) encompasses a wide spectrum of metabolic conditions associated with an excess of fat accumulation in the liver, ranging from simple hepatic steatosis to cirrhosis and hepatocellular carcinoma. Finding appropriate tools to study its development and progression is essential to address essential unmet therapeutic and staging needs. This review discusses advantages and shortcomings of different dietary, chemical and genetic factors that can be used to mimic this disease and its progression in mice from a hepatic and metabolic point of view. Also, this review will highlight some additional factors and considerations that could have a strong impact on the outcomes of our model to end up providing recommendations and a checklist to facilitate the selection of the appropriate MASLD preclinical model based on clinical aims.

Integrated traditional Chinese and Western medicine in the prevention and treatment of non-alcoholic fatty liver disease: future directions and strategies

Traditional Chinese medicine (TCM) has been widely used for several centuries for metabolic diseases, including non-alcoholic fatty liver disease (NAFLD). At present, NAFLD has become the most prevalent form of chronic liver disease worldwide and can progress to non-alcoholic steatohepatitis (NASH), cirrhosis, and even hepatocellular carcinoma. However, there is still a lack of effective treatment strategies in Western medicine. The development of NAFLD is driven by multiple mechanisms, including genetic factors, insulin resistance, lipotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, inflammation, gut microbiota dysbiosis, and adipose tissue dysfunction. Currently, certain drugs, including insulin sensitizers, statins, vitamin E, ursodeoxycholic acid and betaine, are proven to be beneficial for the clinical treatment of NAFLD. Due to its complex pathogenesis, personalized medicine that integrates various mechanisms may provide better benefits to patients with NAFLD. The holistic view and syndrome differentiation of TCM have advantages in treating NAFLD, which are similar to the principles of personalized medicine. In TCM, NAFLD is primarily classified into five types based on clinical experience. It is located in the liver and is closely related to spleen and kidney functions. However, due to the multi-component characteristics of traditional Chinese medicine, its application in the treatment of NAFLD has been considerably limited. In this review, we summarize the advances in the pathogenesis and treatment of NAFLD, drawn from both the Western medicine and TCM perspectives. We highlight that Chinese and Western medicine have complementary advantages and should receive increased attention in the prevention and treatment of NAFLD.

Comprehensive genetic study of the insulin resistance marker TG:HDL-C in the UK Biobank

Insulin resistance (IR) is a well-established risk factor for metabolic disease. The ratio of triglycerides to high-density lipoprotein cholesterol (TG:HDL-C) is a surrogate marker of IR. We conducted a genome-wide association study of the TG:HDL-C ratio in 402,398 Europeans within the UK Biobank. We identified 369 independent SNPs, of which 114 had a false discovery rate-adjusted P value < 0.05 in other genome-wide studies of IR making them high-confidence IR-associated loci. Seventy-two of these 114 loci have not been previously associated with IR. These 114 loci cluster into five groups upon phenome-wide analysis and are enriched for candidate genes important in insulin signaling, adipocyte physiology and protein metabolism. We created a polygenic-risk score from the high-confidence IR-associated loci using 51,550 European individuals in the Michigan Genomics Initiative. We identified associations with diabetes, hyperglyceridemia, hypertension, nonalcoholic fatty liver disease and ischemic heart disease. Collectively, this study provides insight into the genes, pathways, tissues and subtypes critical in IR.

Liver fibrosis in NAFLD/NASH: from pathophysiology towards diagnostic and therapeutic strategies

Liver fibrosis, as an excess deposition of extracellular matrix (ECM) components, results from chronic liver injury as well as persistent activation of inflammatory response and of fibrogenesis. Liver fibrosis is a major determinant for chronic liver disease (CLD) progression and in the last two decades our understanding on the major molecular and cellular mechanisms underlying the fibrogenic progression of CLD has dramatically improved, boosting pre-clinical studies and clinical trials designed to find novel therapeutic approaches. From these studies several critical concepts have emerged, starting to reveal the complexity of the pro-fibrotic microenvironment which involves very complex, dynamic and interrelated interactions between different hepatic and extrahepatic cell populations. This review will offer first a recapitulation of established and novel pathophysiological basic principles and concepts by intentionally focus the attention on NAFLD/NASH, a metabolic-related form of CLD with a high impact on the general population and emerging as a leading cause of CLD worldwide. NAFLD/NASH-related pro-inflammatory and profibrogenic mechanisms will be analysed as well as novel information on cells, mediators and signalling pathways which have taken advantage from novel methodological approaches and techniques (single cell genomics, imaging mass cytometry, novel in vitro two- and three-dimensional models, etc.). We will next offer an overview on recent advancement in diagnostic and prognostic tools, including serum biomarkers and polygenic scores, to support the analysis of liver biopsies. Finally, this review will provide an analysis of current and emerging therapies for the treatment of NAFLD/NASH patients.

VLDL Biogenesis and Secretion: It Takes a Village

The production and secretion of VLDLs (very-low-density lipoproteins) by hepatocytes has a direct impact on liver fat content, as well as the concentrations of cholesterol and triglycerides in the circulation and thus affects both liver and cardiovascular health, respectively. Importantly, insulin resistance, excess caloric intake, and lack of physical activity are associated with overproduction of VLDL, hepatic steatosis, and increased plasma levels of atherogenic lipoproteins. Cholesterol and triglycerides in remnant particles generated by VLDL lipolysis are risk factors for atherosclerotic cardiovascular disease and have garnered increasing attention over the last few decades. Presently, however, increased risk of atherosclerosis is not the only concern when considering today's cardiometabolic patients, as they often also experience hepatic steatosis, a prevalent disorder that can progress to steatohepatitis and cirrhosis. This duality of metabolic risk highlights the importance of understanding the molecular regulation of the biogenesis of VLDL, the lipoprotein that transports triglycerides and cholesterol out of the liver. Fortunately, there has been a resurgence of interest in the intracellular assembly, trafficking, degradation, and secretion of VLDL by hepatocytes, which has led to many exciting new molecular insights that are the topic of this review. Increasing our understanding of the biology of this pathway will aid to the identification of novel therapeutic targets to improve both the cardiovascular and the hepatic health of cardiometabolic patients. This review focuses, for the first time, on this duality.

The Intersection of Genetic Factors, Aberrant Nutrient Metabolism and Oxidative Stress in the Progression of Cardiometabolic Disease

Cardiometabolic disease (CMD), which encompasses metabolic-associated fatty liver disease (MAFLD), chronic kidney disease (CKD) and cardiovascular disease (CVD), has been increasing considerably in the past 50 years. CMD is a complex disease that can be influenced by genetics and environmental factors such as diet. With the increased reliance on processed foods containing saturated fats, fructose and cholesterol, a mechanistic understanding of how these molecules cause metabolic disease is required. A major pathway by which excessive nutrients contribute to CMD is through oxidative stress. In this review, we discuss how oxidative stress can drive CMD and the role of aberrant nutrient metabolism and genetic risk factors and how they potentially interact to promote progression of MAFLD, CVD and CKD. This review will focus on genetic mutations that are known to alter nutrient metabolism. We discuss the major genetic risk factors for MAFLD, which include Patatin-like phospholipase domain-containing protein 3 (PNPLA3), Membrane Bound O-Acyltransferase Domain Containing 7 (MBOAT7) and Transmembrane 6 Superfamily Member 2 (TM6SF2). In addition, mutations that prevent nutrient uptake cause hypercholesterolemia that contributes to CVD. We also discuss the mechanisms by which MAFLD, CKD and CVD are mutually associated with one another. In addition, some of the genetic risk factors which are associated with MAFLD and CVD are also associated with CKD, while some genetic risk factors seem to dissociate one disease from the other. Through a better understanding of the causative effect of genetic mutations in CMD and how aberrant nutrient metabolism intersects with our genetics, novel therapies and precision approaches can be developed for treating CMD.