Patatin-like phospholipase domain-containing 3 (PNPLA3) I148M (rs738409) affects hepatic VLDL secretion in humans and in vitro

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.

Liver lipid droplet cholesterol content is a key determinant of metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) represents a progressive form of steatotic liver disease which increases the risk for fibrosis and advanced liver disease. The accumulation of discrete species of bioactive lipids has been postulated to activate signaling pathways that promote inflammation and fibrosis. However, the key pathogenic lipid species is a matter of debate. We explored candidates using various dietary, molecular, and genetic models. Mice fed a choline-deficient L-amino acid-defined high-fat diet (CDAHFD) developed steatohepatitis and manifested early markers of liver fibrosis associated with increased cholesterol content in liver lipid droplets within 5 d without any changes in total liver cholesterol content. Treating mice with antisense oligonucleotides against Coenzyme A synthase (Coasy) or treatment with bempedoic acid or atorvastatin decreased liver lipid droplet cholesterol content and prevented CDAHFD-induced MASH and the fibrotic response. All these salutary effects were abrogated with dietary cholesterol supplementation. Analysis of human liver samples demonstrated that cholesterol in liver lipid droplets was increased in humans with MASH and liver fibrosis and was higher in PNPLA3 I148M (variants rs738409) than in HSD17B13 variants (rs72613567). Together, these data identify cholesterol in liver lipid droplets as a critical mediator of MASH and demonstrate that Coenzyme A synthase knockdown and bempedoic acid are therapeutic approaches to reduce liver lipid droplet cholesterol content and thereby prevent the development of MASH and liver fibrosis.

Genomic approaches to explore susceptibility and pathogenesis of alcohol use disorder and alcohol-associated liver disease

Excessive alcohol use is a major risk factor for the development of an alcohol use disorder (AUD) and contributes to a wide variety of other medical illnesses, including alcohol-associated liver disease (ALD). Both AUD and ALD are complex and causally interrelated diseases, and multiple factors other than alcohol consumption are implicated in the disease pathogenesis. While the underlying pathophysiology of AUD and ALD is complex, there is substantial evidence for a genetic susceptibility of both diseases. Current genome-wide association studies indicate that the genes associated with clinical AUD only poorly overlap with the genes identified for heavy drinking and, in turn, neither overlap with the genes identified for ALD. Uncovering the main genetic factors will enable us to identify molecular drivers underlying the pathogenesis, discover potential targets for therapy, and implement patient care early in disease progression. In this review, we described multiple genomic approaches and their implications to investigate the susceptibility and pathogenesis of both AUD and ALD. We concluded our review with a discussion of the knowledge gaps and future research on genomic studies in these 2 diseases.

Experimental Models to Investigate PNPLA3 in Liver Steatosis

Patatin-like phospholipase domain-containing 3 (PNPLA3) was the first gene identified through genome-wide association studies to be linked to hepatic fat accumulation. A missense variant, encoding the PNPLA3-148M allele, has since been shown to increase the risk for the full spectrum of steatotic liver disease (SLD), from simple steatosis to steatohepatitis, cirrhosis, and hepatocellular carcinoma. Despite extensive validation of this association and ongoing research into its pathogenic role, the precise mechanisms by which PNPLA3-148M contributes to the progression of SLD remain poorly understood. In this review, we evaluate preclinical in vitro and in vivo models used to investigate PNPLA3 and its involvement in SLD, with particular emphasis on metabolic dysfunction-associated steatotic liver disease. We assess the strengths and limitations of these models, as well as the challenges arising from species differences in PNPLA3 expression and function between human and murine systems.

Cellular communication networks in fibrosis: Insights from the MASLD pig model

BACKGROUND

This research aims to reveal the cellular cross talk in fibrosis liver using transgenic pigs (TG) expressing humanized risk genes (PNPLA3I148M-GIPRdn-hIAPP) as a metabolic dysfunction-associated steatotic liver disease (MASLD) model.

METHODS AND RESULTS

The study uses single-nucleus sequencing to reveal the differentiation and interaction characteristics of various cell populations in the liver during the development of MASLD. After 6 months of high-fat, high-sucrose diet induction, the model pigs exhibited obvious liver pathological features, including fat deposition, inflammatory cell aggregation, fibrosis, and blocked insulin signaling pathways, similar to PNPLA3 rs738409 C>G carriers. Single-nucleus RNA sequencing showed that pigs share a high correlation with human hepatic cell types and zonation. HSCs in TG pigs are more activated, showing enhancing fibrosis-related pathways and declining retinol metabolism. Pseudo-trajectory analysis revealed that over 90% of macrophages in TG liver differentiated to Fate 1 (CD68hi) with higher expression of major histocompatibility complex-II molecules, proinflammatory cytokines, phagosomes, and lysosomal-related genes. Active cell interactions were found between HSCs, endothelial cells, and Fate1 macrophages. Ligand and receptor interactions, including FGF23-FGFR, PDGFs-PDGFRs, EFNA1-EPHRs, and CXCL12-CXCR4/CXCR7, were predicted to involve in hepatic fibrosis in model pigs.

CONCLUSIONS

The transgenic pig model of MASLD exhibits liver pathological features consistent with patients with MASLD. Our data supplemented the mechanism by which PNPLA3 mutations lead to hepatic steatosis, depicted a detailed atlas of hepatic profibrosis cellular network, and provided a reliable large animal model and data reference for MASLD drug development and precision treatment.

PNPLA3 Polymorphism Is Inversely Correlated with Aortic Stiffness in Patients with Metabolic Dysfunction-Associated Steatotic Liver Disease Without Fibrosis

Metabolic dysfunction-associated steatotic liver disease (MASLD) corresponds to the condition of increased hepatic fat levels, which is the leading cause of hepatic failure and carcinoma. It is also an independent risk factor for cardiovascular disease (CVD) and mortality. MASLD can be due to obesity with insulin resistance and/or genetic predisposition, i.e., polymorphism in the patatin-like phospholipase domain-containing 3 (PNPLA3) gene. PNPLA3 polymorphism has been associated with increased hepatic fat levels, fibrosis, cirrhosis, and hepatocellular carcinoma, while its association with CVD remains to be fully understood. The aim of the current study was to examine whether the vascular phenotype of patients with MASLD differed between carriers and noncarriers of the PNPLA3 polymorphism. Adult patients with MASLD underwent clinical assessment, PNPLA3 genotyping, arterial tonometry for aortic stiffness measurement, and ultrasound examination of carotid arteries. In total, 117 patients with MASLD and no fibrosis (median hepatic stiffness was 4.71 kPa) were recruited. Carriers of the PNPLA3 polymorphism were younger and exhibited higher levels of ALT and APRI, as compared to wild-type subjects. On the other hand, carriers of the PNPLA3 polymorphism had not only a better metabolic profile (i.e., lower glucose and glycated hemoglobin) but also lower blood pressure, carotid intima-media thickness (IMT), and cardiovascular risk. In addition, PNPLA3 polymorphism was negatively correlated with aortic stiffness, which is a marker of arteriolosclerosis and vascular ageing. Our data are consistent with previous observations that in case of genetically-driven MASLD, there is an inverse association with common predictors of CVD. Our data support the view that the main contributors to CVD risk in patients with MASLD remain conventional cardiometabolic risk factors (i.e., age, glucose) that are more likely to be found in metabolic syndrome-related MASLD rather than genetically-driven MASLD, at least in the first stages of the disease.

Role of PNPLA3 in Hepatic Stellate Cells and Hepatic Cellular Crosstalk

AIMS

Since its discovery, the patatin-like phospholipase domain containing 3 (PNPLA3) (rs738409 C>G p.I148M) variant has been studied extensively to unravel its molecular function. Although several studies proved a causal relationship between the PNPLA3 I148M variant and MASLD development and particularly fibrosis, the pathological mechanisms promoting this phenotype have not yet been fully clarified.

METHODS

We summarise the latest data regarding the PNPLA3 I148M variant in hepatic stellate cells (HSCs) activation and macrophage biology or the path to inflammation-induced fibrosis.

RESULTS

Elegant but contradictory studies have ascribed PNPLA3 a hydrolase or an acyltransferase function. The PNPLA3 I148M results in hepatic lipid accumulation, which predisposes the hepatocyte to lipotoxicity and lipo-apoptosis, producing DAMPs, cytokines and chemokines leading to recruitment and activation of macrophages and HSCs, propagating fibrosis. Recent studies showed that the PNPLA3 I148M variant alters HSCs biology via attenuation of PPARγ, AP-1, LXRα and TGFβ activity and signalling.

CONCLUSIONS

The advent of refined techniques in isolating HSCs has made PNPLA3's direct role in HSCs for liver fibrosis development more apparent. However, many other mechanisms still need detailed investigations.

Post-hoc analysis of the tofogliflozin post-marketing surveillance study (J-STEP/LT): Tofogliflozin improves liver function in type 2 diabetes patients regardless of BMI

AIMS/INTRODUCTION

Patients with type 2 diabetes are at high risk of developing steatotic liver disease (SLD). Weight loss has proven effective in treating metabolic dysfunction-associated steatotic liver disease (MASLD) in obese patients with type 2 diabetes, with sodium-glucose cotransporter 2 (SGLT2) inhibitors showing promising results. However, lean MASLD is more prevalent in Japan, necessitating alternative approaches to body weight reduction.

MATERIALS AND METHODS

We used the J-STEP/LT dataset including up to 3-year treatment data to analyze the effects of the SGLT2 inhibitor tofogliflozin on liver function and treatment safety and conducted a subgroup analysis based on body mass index (BMI; kg/m2, <20, 20-<23, 23-<25, 25-<30, and ≥30).

RESULTS

This study included 4,208 participants. Tofogliflozin significantly reduced alanine aminotransferase (ALT) levels in participants with baseline ALT levels >30 U/L across all BMI groups, with median changes of -12, -16, -13, -15, and -15 U/L, respectively (P = 0.9291 for trends). However, median changes in body weight with tofogliflozin were -2.00, -2.75, -2.00, -3.00, and -3.80 kg, respectively (P < 0.0001 for trends), with no significant weight loss observed in the BMI <20 group. ALT levels were also significantly decreased in participants who did not lose weight. Safety assessments according to BMI and age categories revealed no clear differences in the frequency of adverse events.

CONCLUSIONS

Tofogliflozin reduced ALT levels without substantial body weight reduction among lean participants. These findings suggest that SGLT2 inhibitors may be a viable treatment option for non-obese patients with type 2 diabetes and SLD.

Liver lipid droplet cholesterol content is a key determinant of metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) represents a progressive form of steatotic liver disease which increases the risk for fibrosis and advanced liver disease. The accumulation of discrete species of bioactive lipids has been postulated to activate signaling pathways that promote inflammation and fibrosis. However, the key pathogenic lipid species is a matter of debate. We explored candidates using various dietary, molecular, and genetic models. Mice fed a choline-deficient L-amino acid-defined high-fat diet (CDAHFD) developed steatohepatitis and manifested early markers of liver fibrosis associated with increased cholesterol content in liver lipid droplets within 5 days without any changes in total liver cholesterol content. Treating mice with antisense oligonucleotides (ASOs) against Coenzyme A synthase (Cosay) or treatment with bempedoic acid or atorvastatin decreased liver lipid droplet cholesterol content and prevented CDAHFD-induced MASH and the fibrotic response. All these salutary effects were abrogated with dietary cholesterol supplementation. Analysis of human liver samples demonstrated that cholesterol in liver lipid droplets was increased in humans with MASH and liver fibrosis and was higher in PNPLA3 I148M (variants rs738409) than in HSD17B13 variants (rs72613567). Together, these data identify cholesterol in liver lipid droplets as a critical mediator of MASH and demonstrate that COASY knockdown and bempedoic acid are novel therapeutic approaches to reduce liver lipid droplet cholesterol content and thereby prevent the development of MASH and liver fibrosis.

Significance Statement

Metabolic dysfunction-associated steatohepatitis (MASH) is a progressive liver disease linked to fibrosis. The role of specific lipid species in its pathogenesis remains debated. Using dietary, molecular, and genetic models, we found that mice on a choline-deficient, high-fat diet (CDAHFD) developed steatohepatitis and early fibrosis, marked by increased cholesterol in liver lipid droplets within five days. Targeting COASY with antisense oligonucleotides or treating with bempedoic acid or atorvastatin reduced lipid droplet cholesterol and prevented MASH. However, dietary cholesterol supplementation negated these effects. Human liver samples confirmed elevated lipid droplet cholesterol in MASH and fibrosis, especially in PNPLA3 I148M carriers. These findings highlight cholesterol reduction as a potential MASH therapy.

The lack of apoA-I in apoE-KO mice affects the liver transcriptome

BACKGROUND AND AIMS

Liver is the major organ involved in apoA-I synthesis and HDL-C turnover, but the impact of apoA-I/HDL on hepatic transcriptome has never been investigated before. In the present study, a transcriptomic analysis by high-throughput RNA-seq was conducted in the liver of atherosclerosis-prone mice, with the aim of identifying new genes/pathways modulated by apoA-I/HDL with a potential effect on atherosclerosis development.

METHODS AND RESULTS

Eight-week-old apoE knockout (apoEKO) mice lacking apoA-I/HDL (DKO) and with physiological levels of apoA-I/HDL (DKO/hA-I) were fed either a standard rodent diet (SRD) or a Western diet (WD) for 22 weeks. After both dietary treatments, DKO mice were characterized by lower cholesterol levels, but increased atherosclerosis development, compared to DKO/hA-I mice. The liver transcriptome of DKO and DKO/hA-I mice fed SRD diverged in a relatively small number of genes, suggestive of a greater activation of the PPAR signaling pathway and the retinoid metabolism pathway in DKO/hA-I mice. Following WD, transcriptomic analysis highlighted in both genotypes an upregulated expression of immune/inflammatory genes and a reduced activation of the retinoid metabolism. The evaluation of the hepatic response of the two genotypes to the dietary switch from SRD to WD revealed strong divergences in genes involved in metabolic pathways only in the presence of apoA-I/HDL, with reduced endogenous sterol biosynthesis and glutathione metabolism, together with increased glucose metabolism.

CONCLUSION

The presence or absence of apoA-I expression differently alters hepatic pathways involved not only in cholesterol metabolism, but also in those of glutathione and glucose metabolism.

PNPLA3 in Alcohol-Related Liver Disease

The discovery of PNPLA3 as a genetic risk factor for liver disease has transformed our understanding of the pathogenesis of alcohol-related liver disease (ALD). The recent reclassification of fatty liver disease as steatotic liver disease (SLD), introducing metabolic dysfunction and alcohol-related liver disease (MetALD), has highlighted how genetic and environmental factors synergistically drive liver damage. The PNPLA3 rs738409 variant stands as a paradigmatic example of gene-environment interaction, where its effect on liver disease is dramatically amplified by alcohol consumption, obesity and type 2 diabetes. Understanding these interactions has revealed novel pathogenic mechanisms. The robust genetic evidence and a growing understanding of molecular mechanisms have made PNPLA3 an attractive therapeutic target. Several compounds targeting PNPLA3 are now in clinical development. While initial trials have focused on metabolic dysfunction-associated SLD, the recognition that almost all individuals with excessive alcohol consumption have metabolic comorbidities provides an unprecedented opportunity to evaluate these genetically informed therapies in MetALD. In this review, we examine the role of PNPLA3 in ALD, focusing on gene-environment interactions and therapeutic implications in the context of the new disease classification framework.

Liver metabolism in human MASLD: A review of recent advancements using human tissue metabolomics

Global incidence of Metabolic dysfunction-Associated Steatotic Liver Disease (MASLD) is on the rise while treatments remain elusive. MASLD is a disease of dysregulated systemic and hepatic metabolism. Current understanding of disease pathophysiology as it relates to metabolome changes largely comes from studies on animal models and human plasma. However, human tissue data are crucial for transitioning from mechanisms to clinical therapies. The close relationship between MASLD and comorbidities like obesity, type 2 diabetes and dyslipidemia make it difficult to determine the contribution from liver disease itself. Here, we review recent metabolomics studies in liver tissue from human MASLD patients, which have predominately focused on lipid metabolism, but also include bile acid, tricarboxylic acid (TCA) cycle, and branched chain amino acid (BCAA) metabolism. Several clinical trials are underway to target various of these lipid-related pathways in MASLD. Although only the β-selective thyroid hormone receptor agonist resmetirom has so far been approved for use, many metabolism-targeting pharmaceuticals show promising results for halting disease progression, if not promoting outright reversal. Ultimately, the scarcity of human tissue data and the variability of confounding factors, like obesity, within and between cohorts are impediments to the pathophysiological understanding required for efficient development of metabolic treatments.

Diverting hepatic lipid fluxes with lifestyles revision and pharmacological interventions as a strategy to tackle steatotic liver disease (SLD) and hepatocellular carcinoma (HCC)

Steatotic liver disease (SLD) and Hepatocellular Carcinoma (HCC) are characterised by a substantial rewiring of lipid fluxes caused by systemic metabolic unbalances and/or disrupted intracellular metabolic pathways. SLD is a direct consequence of the interaction between genetic predisposition and a chronic positive energy balance affecting whole-body energy homeostasis and the function of metabolically-competent organs. In this review, we discuss how the impairment of the cross-talk between peripheral organs and the liver stalls glucose and lipid metabolism, leading to unbalances in hepatic lipid fluxes that promote hepatic fat accumulation. We also describe how prolonged metabolic stress builds up toxic lipid species in the liver, and how lipotoxicity and metabolic disturbances drive disease progression by promoting a chronic activation of wound healing, leading to fibrosis and HCC. Last, we provide a critical overview of current state of the art (pre-clinical and clinical evidence) regarding mechanisms of action and therapeutic efficacy of candidate SLD treatment options, and their potential to interfere with SLD/HCC pathophysiology by diverting lipids away from the liver therefore improving metabolic health.

Partitioned polygenic risk scores identify distinct types of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is characterized by an excess of lipids, mainly triglycerides, in the liver and components of the metabolic syndrome, which can lead to cirrhosis and liver cancer. While there is solid epidemiological evidence that MASLD clusters with cardiometabolic disease, several leading genetic risk factors for MASLD do not increase the risk of cardiovascular disease, suggesting no causal relationship between MASLD and cardiometabolic derangement. In this work, we leveraged measurements of visceral adiposity identifying 27 previously unknown genetic loci associated with MASLD (n = 36,394), six replicated in four independent cohorts (n = 3,903). Next, we generated two partitioned polygenic risk scores based on the presence of lipoprotein retention in the liver. The two polygenic risk scores suggest the presence of at least two distinct types of MASLD, one confined to the liver resulting in a more aggressive liver disease and one that is systemic and results in a higher risk of cardiometabolic disease. These findings shed light on the heterogeneity of MASLD and have the potential to improve the prediction of clinical trajectories and inform precision medicine approaches.

A genome-wide association analysis reveals new pathogenic pathways in gout

Gout is a chronic disease that is caused by an innate immune response to deposited monosodium urate crystals in the setting of hyperuricemia. Here, we provide insights into the molecular mechanism of the poorly understood inflammatory component of gout from a genome-wide association study (GWAS) of 2.6 million people, including 120,295 people with prevalent gout. We detected 377 loci and 410 genetically independent signals (149 previously unreported loci in urate and gout). An additional 65 loci with signals in urate (from a GWAS of 630,117 individuals) but not gout were identified. A prioritization scheme identified candidate genes in the inflammatory process of gout, including genes involved in epigenetic remodeling, cell osmolarity and regulation of NOD-like receptor protein 3 (NLRP3) inflammasome activity. Mendelian randomization analysis provided evidence for a causal role of clonal hematopoiesis of indeterminate potential in gout. Our study identifies candidate genes and molecular processes in the inflammatory pathogenesis of gout suitable for follow-up studies.

Impact of non-alcoholic fatty liver disease and fibrosis on mortality and kidney outcomes in patients with type 2 diabetes and chronic kidney disease: A multi-cohort longitudinal study

AIM

To evaluate the impact of non-alcoholic fatty liver disease (NAFLD) presence and fibrosis risk on adverse outcomes in patients with type 2 diabetes and chronic kidney disease.

METHODS

Data were sourced from two longitudinal cohorts: 1172 patients from the National Health and Nutrition Examination Survey (NHANES) and 326 patients from the kidney biopsy cohort at the West China Hospital of Sichuan University. Cox regression estimated hazard ratios (HRs) for NAFLD and liver fibrosis concerning adverse clinical outcomes. Subsequently, a two-sample Mendelian randomization study using genome-wide association study statistics explored NAFLD's potential causal link to cardio-cerebrovascular events.

RESULTS

In the NHANES cohort, NAFLD stood as an independent risk factor for various outcomes: overall mortality [HR 1.53 (95% confidence interval, CI 1.21-1.95)], mortality because of cardio-cerebrovascular diseases [HR 1.63 (95% CI 1.12-2.37)], heart disease [HR 1.58 (95% CI 1.00-2.49)], and cerebrovascular disease [HR 3.95 (95% CI 1.48-10.55)]. Notably, advanced liver fibrosis, identified by a fibrosis-4 (FIB-4) score >2.67, exhibited associations with overall mortality, cardio-cerebrovascular disease mortality and heart disease mortality. Within the kidney biopsy cohort, NAFLD correlated with future end-stage kidney disease [ESKD; HR 2.17 (95% CI 1.41-3.34)], while elevated FIB-4 or NAFLD Fibrosis Scores predicted future ESKD, following full adjustment. Liver fibrosis was positively correlated with renal interstitial fibrosis and tubular atrophy in biopsies. Further Mendelian randomization analysis supported a causal relationship between NAFLD and cardio-cerebrovascular events.

CONCLUSIONS

In patients with type 2 diabetes and chronic kidney disease, the NAFLD presence and elevated FIB-4 scores link to heightened mortality risk and ESKD susceptibility. Moreover, NAFLD shows a causal relationship with cardio-cerebrovascular events.

Hepatic glucokinase regulatory protein and carbohydrate response element binding protein attenuation reduce de novo lipogenesis but do not mitigate intrahepatic triglyceride accumulation in Aldob deficiency

OBJECTIVE

Stable isotope studies have shown that hepatic de novo lipogenesis (DNL) plays an important role in the pathogenesis of intrahepatic lipid (IHL) deposition. Furthermore, previous research has demonstrated that fructose 1-phosphate (F1P) not only serves as a substrate for DNL, but also acts as a signalling metabolite that stimulates DNL from glucose. The aim of this study was to elucidate the mediators of F1P-stimulated DNL, with special focus on two key regulators of intrahepatic glucose metabolism, i.e., glucokinase regulatory protein (GKRP) and carbohydrate response element binding protein (ChREBP).

METHODS

Aldolase B deficient mice (Aldob-/-), characterized by hepatocellular F1P accumulation, enhanced DNL, and hepatic steatosis, were either crossed with GKRP deficient mice (Gckr-/-) or treated with short hairpin RNAs directed against hepatic ChREBP.

RESULTS

Aldob-/- mice showed higher rates of de novo palmitate synthesis from glucose when compared to wildtype mice (p < 0.001). Gckr knockout reduced de novo palmitate synthesis in Aldob-/- mice (p = 0.017), without affecting the hepatic mRNA expression of enzymes involved in DNL. In contrast, hepatic ChREBP knockdown normalized the hepatic mRNA expression levels of enzymes involved in DNL and reduced fractional DNL in Aldob-/- mice (p < 0.05). Of interest, despite downregulation of DNL in response to Gckr and ChREBP attenuation, no reduction in intrahepatic triglyceride levels was observed.

CONCLUSIONS

Both GKRP and ChREBP mediate F1P-stimulated DNL in aldolase B deficient mice. Further studies are needed to unravel the role of GKRP and hepatic ChREBP in regulating IHL accumulation in aldolase B deficiency.

A co-ordinated transcriptional programme in the maternal liver supplies long chain polyunsaturated fatty acids to the conceptus using phospholipids

The long and very long chain polyunsaturated fatty acids (LC-PUFAs) are preferentially transported by the mother to the fetus. Failure to supply LC-PUFAs is strongly linked with stillbirth, fetal growth restriction, and impaired neurodevelopmental outcomes. However, dietary supplementation during pregnancy is unable to simply reverse these outcomes, suggesting imperfectly understood interactions between dietary fatty acid intake and the molecular mechanisms of maternal supply. Here we employ a comprehensive approach combining untargeted and targeted lipidomics with transcriptional profiling of maternal and fetal tissues in mouse pregnancy. Comparison of wild-type mice with genetic models of impaired lipid metabolism allows us to describe maternal hepatic adaptations required to provide LC-PUFAs to the developing fetus. A late pregnancy-specific, selective activation of the Liver X Receptor signalling pathway dramatically increases maternal supply of LC-PUFAs within circulating phospholipids. Crucially, genetic ablation of this pathway in the mother reduces LC-PUFA accumulation by the fetus, specifically of docosahexaenoic acid (DHA), a critical nutrient for brain development.

Exploring the Role of Bempedoic Acid in Metabolic Dysfunction Associated Steatotic Liver Disease: Actual Evidence and Future Perspectives

Metabolic dysfunction-associated steatotic liver disease (MASLD) involves excessive lipid accumulation in hepatocytes, impacting global healthcare due to its high prevalence and risk of progression to severe liver conditions. Its pathogenesis involves genetic, metabolic, and inflammatory factors, with cardiovascular events as the leading cause of mortality. This review examines the role of lipid-lowering therapies in MASLD, with a particular focus on bempedoic acid, a recently approved cholesterol-lowering agent for hypercholesterolemia and high cardiovascular-risk patients. It explores its potential in liver disease by modulating lipid metabolism and inflammatory pathways based on the most recent studies available. Bempedoic acid inhibits ATP-citrate lyase, reducing cholesterol and fatty acid synthesis while activating AMP-activated protein kinase to suppress gluconeogenesis and lipogenesis. Animal studies indicate its efficacy in reducing hepatic steatosis, inflammation, and fibrosis. Bempedoic acid holds promise as a therapeutic for MASLD, offering dual benefits in lipid metabolism and inflammation. Further clinical trials are required to confirm its efficacy and safety in MASLD patients, potentially addressing the multifaceted nature of this disease.

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.

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.

The fatty liver disease-causing protein PNPLA3-I148M alters lipid droplet-Golgi dynamics

Nonalcoholic fatty liver disease, recently renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a progressive metabolic disorder that begins with aberrant triglyceride accumulation in the liver and can lead to cirrhosis and cancer. A common variant in the gene PNPLA3, encoding the protein PNPLA3-I148M, is the strongest known genetic risk factor for MASLD. Despite its discovery 20 y ago, the function of PNPLA3, and now the role of PNPLA3-I148M, remain unclear. In this study, we sought to dissect the biogenesis of PNPLA3 and PNPLA3-I148M and characterize changes induced by endogenous expression of the disease-causing variant. Contrary to bioinformatic predictions and prior studies with overexpressed proteins, we demonstrate here that PNPLA3 and PNPLA3-I148M are not endoplasmic reticulum-resident transmembrane proteins. To identify their intracellular associations, we generated a paired set of isogenic human hepatoma cells expressing PNPLA3 and PNPLA3-I148M at endogenous levels. Both proteins were enriched in lipid droplet, Golgi, and endosomal fractions. Purified PNPLA3 and PNPLA3-I148M proteins associated with phosphoinositides commonly found in these compartments. Despite a similar fractionation pattern as the wild-type variant, PNPLA3-I148M induced morphological changes in the Golgi apparatus, including increased lipid droplet-Golgi contact sites, which were also observed in I148M-expressing primary human patient hepatocytes. In addition to lipid droplet accumulation, PNPLA3-I148M expression caused significant proteomic and transcriptomic changes that resembled all stages of liver disease. Cumulatively, we validate an endogenous human cellular system for investigating PNPLA3-I148M biology and identify the Golgi apparatus as a central hub of PNPLA3-I148M-driven cellular change.

Partitioned polygenic risk scores identify distinct types of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) encompasses an excess of triglycerides in the liver, which can lead to cirrhosis and liver cancer. While there is solid epidemiological evidence of MASLD coexisting with cardiometabolic disease, several leading genetic risk factors for MASLD do not increase the risk of cardiovascular disease, suggesting no causal relationship between MASLD and cardiometabolic derangement. In this work, we leveraged measurements of visceral adiposity and identified 27 novel genetic loci associated with MASLD. Among these loci, we replicated 6 in several independent cohorts. Next, we generated two partitioned polygenic risk scores (PRS) based on the mechanism of genetic association with MASLD encompassing intra-hepatic lipoprotein retention. The two PRS suggest the presence of at least two distinct types of MASLD, one confined to the liver resulting in a more aggressive liver disease and one that is systemic and results in a higher risk of cardiometabolic disease.

Association of liver fibrosis with extrahepatic cancer in steatotic liver disease patients with PNPLA3 I148M GG genotype

The impacts of patatin-like phospholipase domain-containing protein 3 (PNPLA3) I148M-rs738409, methylenetetrahydrofolate reductase (MTHFR) Ala222Val-rs1801133, and aldehyde dehydrogenase 2 (ALDH2) Glu504Lys-rs671 on the outcomes of Taiwanese patients with steatotic liver disease (SLD) have remained elusive. An 8-year prospective cohort study of patients with (n = 546) and without (n = 580) SLD (controls) was undertaken in a Taiwanese tertiary care center. The 546 SLD patients comprised 306 (56.0%) men and 240 (44.0%) women with mean ages of 53.3 and 56.4 years, respectively. Compared with the controls, SLD patients had an increased frequency of the PNPLA3 I148M-rs738409 GG genotype (25.5 vs. 5.9%, p = 0.001). Among the SLD patients, 236 (43.1%) suffered cardiovascular events, 52 (9.5%) showed extrahepatic cancers, 13 (2.38%) experienced hepatic events, including hepatocellular carcinoma (n = 3, 0.5%) and liver cirrhosis (n = 8, 1.47%), and none died. The Fibrosis-4 (FIB-4) scores were associated with extrahepatic cancer (hazard ratio [HR] 1.325; 95% confidence interval [CI], 1.038-1.691) and cirrhosis development (HR 1.532; 95% CI, 1.055-2.224), and the PNPLA3 I148M-rs738409 G allele (β = 0.158, 95% CI, 0.054-0.325) was associated with the FIB-4 score. Stratified analyses showed that the impact of the FIB-4 score on extrahepatic cancer development was evident only in SLD patients with the PNPLA3 I148M-rs738409 GG genotype (HR 1.543; 95% CI, 1.195-1.993) and not in patients with the GC or CC genotype. Moreover, the ALDH2 Glu504Lys-rs671 G allele had a dose-dependent effect on alcoholism, and the MTHFR and ALDH2 genotypes were not significantly associated with SLD patient outcomes. In conclusion, special vigilance should be exercised for emerging extrahepatic cancer in SLD patients with the PNPLA3 I148M-rs738409 GG genotype and high FIB-4 scores.

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.

Metabolic dysfunction-associated steatotic liver disease and the heart

The prevalence and severity of metabolic dysfunction-associated steatotic liver disease (MASLD) are increasing. Physicians who treat patients with MASLD may acknowledge the strong coincidence with cardiometabolic disease, including atherosclerotic cardiovascular disease (asCVD). This raises questions on co-occurrence, causality, and the need for screening and multidisciplinary care for MASLD in patients with asCVD, and vice versa. Here, we review the interrelations of MASLD and heart disease and formulate answers to these matters. Epidemiological studies scoring proxies for atherosclerosis and actual cardiovascular events indicate increased atherosclerosis in patients with MASLD, yet no increased risk of asCVD mortality. MASLD and asCVD share common drivers: obesity, insulin resistance and type 2 diabetes mellitus (T2DM), smoking, hypertension, and sleep apnea syndrome. In addition, Mendelian randomization studies support that MASLD may cause atherosclerosis through mixed hyperlipidemia, while such evidence is lacking for liver-derived procoagulant factors. In the more advanced fibrotic stages, MASLD may contribute to heart failure with preserved ejection fraction by reduced filling of the right ventricle, which may induce fatigue upon exertion, often mentioned by patients with MASLD. Some evidence points to an association between MASLD and cardiac arrhythmias. Regarding treatment and given the strong co-occurrence of MASLD and asCVD, pharmacotherapy in development for advanced stages of MASLD would ideally also reduce cardiovascular events, as has been demonstrated for T2DM treatments. Given the common drivers, potential causal factors and especially given the increased rate of cardiovascular events, comprehensive cardiometabolic risk management is warranted in patients with MASLD, preferably in a multidisciplinary approach.

Engineered human hepatocyte organoids enable CRISPR-based target discovery and drug screening for steatosis

The lack of registered drugs for nonalcoholic fatty liver disease (NAFLD) is partly due to the paucity of human-relevant models for target discovery and compound screening. Here we use human fetal hepatocyte organoids to model the first stage of NAFLD, steatosis, representing three different triggers: free fatty acid loading, interindividual genetic variability (PNPLA3 I148M) and monogenic lipid disorders (APOB and MTTP mutations). Screening of drug candidates revealed compounds effective at resolving steatosis. Mechanistic evaluation of effective drugs uncovered repression of de novo lipogenesis as the convergent molecular pathway. We present FatTracer, a CRISPR screening platform to identify steatosis modulators and putative targets using APOB-/- and MTTP-/- organoids. From a screen targeting 35 genes implicated in lipid metabolism and/or NAFLD risk, FADS2 (fatty acid desaturase 2) emerged as an important determinant of hepatic steatosis. Enhancement of FADS2 expression increases polyunsaturated fatty acid abundancy which, in turn, reduces de novo lipogenesis. These organoid models facilitate study of steatosis etiology and drug targets.

The fatty liver disease-causing protein PNPLA3-I148M alters lipid droplet-Golgi dynamics

Non-alcoholic fatty liver disease (NAFLD), recently renamed metabolic dysfunction-associated steatotic liver disease (MASLD), is a progressive metabolic disorder that begins with aberrant triglyceride accumulation in the liver and can lead to cirrhosis and cancer. A common variant in the gene PNPLA3, encoding the protein PNPLA3-I148M, is the strongest known genetic risk factor for MASLD to date. Despite its discovery twenty years ago, the function of PNPLA3, and now the role of PNPLA3-I148M, remain unclear. In this study, we sought to dissect the biogenesis of PNPLA3 and PNPLA3-I148M and characterize changes induced by endogenous expression of the disease-causing variant. Contrary to bioinformatic predictions and prior studies with overexpressed proteins, we demonstrate here that PNPLA3 and PNPLA3-I148M are not endoplasmic reticulum-resident transmembrane proteins. To identify their intracellular associations, we generated a paired set of isogenic human hepatoma cells expressing PNPLA3 and PNPLA3-I148M at endogenous levels. Both proteins were enriched in lipid droplet, Golgi, and endosomal fractions. Purified PNPLA3 and PNPLA3-I148M proteins associated with phosphoinositides commonly found in these compartments. Despite a similar fractionation pattern as the wild-type variant, PNPLA3-I148M induced morphological changes in the Golgi apparatus, including increased lipid droplet-Golgi contact sites, which were also observed in I148M-expressing primary human patient hepatocytes. In addition to lipid droplet accumulation, PNPLA3-I148M expression caused significant proteomic and transcriptomic changes that resembled all stages of liver disease. Cumulatively, we validate an endogenous human cellular system for investigating PNPLA3-I148M biology and identify the Golgi apparatus as a central hub of PNPLA3-I148M-driven cellular change.

Cardiovascular Implications of Metabolic Dysfunction-Associated Fatty Liver Disease

Both nonalcoholic fatty liver disease (NAFLD) and metabolic dysfunction-associated fatty liver disease (MAFLD) have been associated with incident cardiovascular disease (CVD), independent of confounders. Causality has recently been inferred by Mendelian randomization studies. Although these findings have contributed to current guidelines that recommend screening for and treatment of cardiovascular risk factors, it not yet clear how to position NAFLD/MAFLD in cardiovascular risk estimation scores and, consequently, which treatment targets should be used. This review aims to provide practical tools as well as suggestions for further research in order to effectively prevent CVD events in patients with NAFLD/MAFLD.

Genetic Predictors of Comorbid Course of COVID-19 and MAFLD: A Comprehensive Analysis

Metabolic-associated fatty liver disease (MAFLD) and its potential impact on the severity of COVID-19 have gained significant attention during the pandemic. This review aimed to explore the genetic determinants associated with MAFLD, previously recognized as non-alcoholic fatty liver disease (NAFLD), and their potential influence on COVID-19 outcomes. Various genetic polymorphisms, including PNPLA3 (rs738409), GCKR (rs780094), TM6SF2 (rs58542926), and LYPLAL1 (rs12137855), have been investigated in relation to MAFLD susceptibility and progression. Genome-wide association studies and meta-analyses have revealed associations between these genetic variants and MAFLD risk, as well as their effects on lipid metabolism, glucose regulation, and liver function. Furthermore, emerging evidence suggests a possible connection between these MAFLD-associated polymorphisms and the severity of COVID-19. Studies exploring the association between indicated genetic variants and COVID-19 outcomes have shown conflicting results. Some studies observed a potential protective effect of certain variants against severe COVID-19, while others reported no significant associations. This review highlights the importance of understanding the genetic determinants of MAFLD and its potential implications for COVID-19 outcomes. Further research is needed to elucidate the precise mechanisms linking these genetic variants to disease severity and to develop gene profiling tools for the early prediction of COVID-19 outcomes. If confirmed as determinants of disease severity, these genetic polymorphisms could aid in the identification of high-risk individuals and in improving the management of COVID-19.

Metabolic liver cancer: associations of rare and common germline variants in one-carbon metabolism and DNA methylation genes

Animal studies implicate one-carbon metabolism and DNA methylation genes in hepatocellular carcinoma (HCC) development in the setting of metabolic perturbations. Using human samples, we investigated the associations between common and rare variants in these closely related biochemical pathways and risk for metabolic HCC development in a multicenter international study. We performed targeted exome sequencing of 64 genes among 556 metabolic HCC cases and 643 cancer-free controls with metabolic conditions. Multivariable logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs), adjusting for multiple comparisons. Gene-burden tests were used for rare variant associations. Analyses were performed in the overall sample and among non-Hispanic whites. The results show that among non-Hispanic whites, presence of rare functional variants in ABCC2 was associated with 7-fold higher risk of metabolic HCC (OR = 6.92, 95% CI: 2.38-20.15, P = 0.0004), and this association remained significant when analyses were restricted to functional rare variants observed in ≥2 participants (cases 3.2% versus controls 0.0%, P = 1.02 × 10-5). In the overall multiethnic sample, presence of rare functional variants in ABCC2 was nominally associated with metabolic HCC (OR = 3.60, 95% CI: 1.52-8.58, P = 0.004), with similar nominal association when analyses were restricted to functional rare variants observed in ≥2 participants (cases 2.9% versus controls 0.2%, P = 0.006). A common variant in PNPLA3 (rs738409[G]) was associated with higher HCC risk in the overall sample (P = 6.36 × 10-6) and in non-Hispanic whites (P = 0.0002). Our findings indicate that rare functional variants in ABCC2 are associated with susceptibility to metabolic HCC in non-Hispanic whites. PNPLA3-rs738409 is also associated with metabolic HCC risk.

Identification and characterisation of a rare MTTP variant underlying hereditary non-alcoholic fatty liver disease

Background & Aims

Non-alcoholic fatty liver disease (NAFLD) is a complex trait with an estimated prevalence of 25% globally. We aimed to identify the genetic variant underlying a four-generation family with progressive NAFLD leading to cirrhosis, decompensation, and development of hepatocellular carcinoma in the absence of common risk factors such as obesity and type 2 diabetes.

Methods

Exome sequencing and genome comparisons were used to identify the likely causal variant. We extensively characterised the clinical phenotype and post-prandial metabolic responses of family members with the identified novel variant in comparison with healthy non-carriers and wild-type patients with NAFLD. Variant-expressing hepatocyte-like cells (HLCs) were derived from human-induced pluripotent stem cells generated from homozygous donor skin fibroblasts and restored to wild-type using CRISPR-Cas9. The phenotype was assessed using imaging, targeted RNA analysis, and molecular expression arrays.

Results

We identified a rare causal variant c.1691T>C p.I564T (rs745447480) in MTTP, encoding microsomal triglyceride transfer protein (MTP), associated with progressive NAFLD, unrelated to metabolic syndrome and without characteristic features of abetalipoproteinaemia. HLCs derived from a homozygote donor had significantly lower MTP activity and lower lipoprotein ApoB secretion than wild-type cells, while having similar levels of MTP mRNA and protein. Cytoplasmic triglyceride accumulation in HLCs triggered endoplasmic reticulum stress, secretion of pro-inflammatory mediators, and production of reactive oxygen species.

Conclusions

We have identified and characterised a rare causal variant in MTTP, and homozygosity for MTTP p.I564T is associated with progressive NAFLD without any other manifestations of abetalipoproteinaemia. Our findings provide insights into mechanisms driving progressive NAFLD.

Impact and Implications

A rare genetic variant in the gene MTTP has been identified as responsible for the development of severe non-alcoholic fatty liver disease in a four-generation family with no typical disease risk factors. A cell line culture created harbouring this variant gene was characterised to understand how this genetic variation leads to a defect in liver cells, which results in accumulation of fat and processes that promote disease. This is now a useful model for studying the disease pathways and to discover new ways to treat common types of fatty liver disease.

Triglyceride-Rich Lipoprotein Metabolism: Key Regulators of Their Flux

The residual risk for arteriosclerotic cardiovascular disease after optimal statin treatment may amount to 50% and is the consequence of both immunological and lipid disturbances. Regarding the lipid disturbances, the role of triglyceride-rich lipoproteins (TRLs) and their remnants has come to the forefront in the past decade. Triglycerides (TGs) stand as markers of the remnants of the catabolism of TRLs that tend to contain twice as much cholesterol as compared to LDL. The accumulation of circulating TRLs and their partially lipolyzed derivatives, known as "remnants", is caused mainly by ineffective triglyceride catabolism. These cholesterol-enriched remnant particles are hypothesized to contribute to atherogenesis. The aim of the present narrative review is to briefly summarize the main pathways of TRL metabolism, bringing to the forefront the newly discovered role of apolipoproteins, the key physiological function of lipoprotein lipase and its main regulators, the importance of the fluxes of these particles in the post-prandial period, their catabolic rates and the role of apo CIII and angiopoietin-like proteins in the partition of TRLs during the fast-fed cycle. Finally, we provide a succinct summary of the new and old therapeutic armamentarium and the outcomes of key current trials with a final outlook on the different methodological approaches to measuring TRL remnants, still in search of the gold standard.

Evaluating the role of non-alcoholic fatty liver disease in cardiovascular diseases and type 2 diabetes: a Mendelian randomization study in Europeans and East Asians

BACKGROUND

Whether non-alcoholic fatty liver disease (NAFLD) causes cardiovascular disease (CVD) and type 2 diabetes (T2D) is unclear and possible differences between ethnicities have not been thoroughly explored. We used Mendelian randomization (MR) to assess the role of NAFLD in CVD and T2D risk in Europeans and East Asians.

METHODS

We conducted a MR study using genetic predictors of alanine aminotransferase (ALT), liability to NAFLD, aspartate transaminase (AST), liver magnetic resonance imaging corrected T1 and proton density fat fraction and combined them with genome-wide association studies (GWAS) summary statistics of CVD, T2D and glycaemic traits (sample size ranging from 14 400 to 977 320). Inverse-variance weighted analysis was used to assess the effect of NAFLD in these outcomes, with sensitivity analyses and replication in FinnGen. We conducted analyses in East Asians using ethnicity-specific genetic predictors of ALT and AST, and the respective outcome GWAS summary statistics.

RESULTS

In Europeans, higher ALT was associated with higher T2D risk (odds ratio: 1.77 per standard deviation, 95% CI 1.5 to 2.08), with similar results for other exposures, across sensitivity analyses and in FinnGen. Although NAFLD proxies were related to higher coronary artery disease (CAD) and stroke risk, sensitivity analyses suggested possible bias by horizontal pleiotropy. In East Asians, higher ALT was possibly associated with higher T2D risk, and ALT and AST were inversely associated with CAD.

CONCLUSIONS

NAFLD likely increases the risk of T2D in Europeans and East Asians. Potential differential effects on CAD between Europeans and East Asians require further investigation.

Patatin-like phospholipase domain-containing 3 gene (PNPLA3) polymorphic (rs738409) single nucleotide polymorphisms and susceptibility to nonalcoholic fatty liver disease: A meta-analysis of twenty studies

BACKGROUND

To investigate the correlation between rs738409 polymorphism of patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene (encoding I148m) and genetic susceptibility to nonalcoholic fatty liver disease (NAFLD).

METHODS

Web of Science, Embase, PubMed, Cochrane Library, China National Knowledge Infrastructure, Wanfang Data Knowledge Service Platform databases were subjected to study retrieving, from the earliest records to November 2022. International databases were searched using the key words (PNPLA3 gene or PNPLA3 polymorphism or patatin-like phospholipase domain-containing pro-tein3) and (nonalcoholic fatty liver disease or NAFLD or nonalcoholic steatohepatitis) and their possible combination. There was no limitation to language. Ethnicity and country restrictions were not applied. Hardy-Weinberg equilibrium about the genotype frequencies of rs738,409 polymorphism in group of controls was assessed using a chi-square goodness-of-fit test (P > .05). A chi-square-based Q test was applied to assess heterogeneity among studies. The random-effect model (DerSimonian-Laird method) was used when a probability value of P < .10, I2 > 50%. If not, the fixed-effect model (Mantel-Haenszel method) was adopted. The current meta-analysis was done by using STATA 16.0.

RESULTS

Twenty studies are selected for this meta-analysis, which includes totally 3240 patients in the treatment group and 5210 patients in the control group. These studies demonstrated a significant increased association between rs738,409 and NAFLD under 5 models: allelic contrast (odds ratio [OR] = 1.98, 95% confidence interval [CI] = 1.65-2.37, Pheterogeneity = 0.000, Z = 7.346, P = .000), homozygote comparison (OR = 3.59, 95% CI = 2.56-5.04, Pheterogeneity = 0.000, Z = 7.416, P = .000), heterozygote comparison (OR = 1.93, 95% CI = 1.63-2.30, Pheterogeneity = 0.002, Z = 7.507, P = .000), the dominant allele model (OR = 2.33, 95% CI = 1.89-2.88, Pheterogeneity = 0.000, Z = 7.856, P = .000), and the recessive allele model (OR = 2.56, 95% CI = 1.96-3.35, Pheterogeneity = 0.000, Z = 6.850, P = .000). Subgroup analysis shows that the rs738,409 polymorphism of PNPLA3 gene in Caucasians and those with a sample size of < 300 is significantly associated with the susceptibility to nonalcoholic fatty liver. Sensitivity analysis shows that the results of meta-analysis are stable.

CONCLUSION

PNPLA3 rs738,409 may play a significant role in increasing risk of NAFLD.

Relationship between NAFLD and coronary artery disease: A Mendelian randomization study

BACKGROUND AND AIMS

There is an ongoing debate on whether NAFLD is an active contributor or an innocent bystander in the pathogenesis of coronary artery disease (CAD). The aim of the present study was to assess the causal relationship between NAFLD and CAD.

APPROACH AND RESULTS

We performed two-sample Mendelian randomization (MR) analyses using summary-level data to assess the association between genetically predicted NAFLD (i.e., chronically elevated serum alanine aminotransferase levels [cALT], imaging-based and biopsy-confirmed NAFLD) and risk of CAD. Analyses were repeated after exclusion of NAFLD susceptibility genes that are associated with impaired VLDL secretion.Inverse-variance weighted MR analyses showed a statistically significant association between genetically predicted cALT and risk of CAD (OR: 1.116, 95% CI: 1.039, 1.199), but not for the other NAFLD-related traits (OR: 1.046, 95% CI: 0.764, 1.433 and OR: 1.014, 95% CI: 0.968, 1.062 for imaging-based and biopsy-confirmed NAFLD, respectively). MR-Egger regression revealed a statistically significant intercept, indicative of directional pleiotropy, for all traits. Repeat analyses after exclusion of genes associated with impaired VLDL secretion showed consistent associations between genetically predicted NAFLD and CAD for all traits (i.e., cALT [OR: 1.203, 95% CI: 1.113, 1.300]), imaging-based (OR: 2.149, 95% CI: 1.276, 3.620) and biopsy-confirmed NAFLD (OR: 1.113, 95% CI: 1.041, 1.189), which persisted when more stringent biopsy-confirmed NAFLD criteria were used (OR: 1.154, 95% CI: 1.043, 1.278) or when more stringent MR methods were applied. MR-Egger regression did not show a statistically significant intercept.

CONCLUSION

The two-sample MR analyses showed a robust association between genetically predicted NAFLD and CAD after exclusion of genetic variants that are implicated in impaired VLDL secretion.

Genetic Polymorphisms and Diversity in Nonalcoholic Fatty Liver Disease (NAFLD): A Mini Review

Nonalcoholic fatty liver disease (NAFLD) is a common liver disease with a wide spectrum of liver conditions ranging from hepatic steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma. The prevalence of NAFLD varies across populations, and different ethnicities have specific risks for the disease. NAFLD is a multi-factorial disease where the genetics, metabolic, and environmental factors interplay and modulate the disease's development and progression. Several genetic polymorphisms have been identified and are associated with the disease risk. This mini-review discussed the NAFLD's genetic polymorphisms and focusing on the differences in the findings between the populations (diversity), including of those reports that did not show any significant association. The challenges of genetic diversity are also summarized. Understanding the genetic contribution of NAFLD will allow for better diagnosis and management explicitly tailored for the various populations.

PNPLA3(I148M) Inhibits Lipolysis by Perilipin-5-Dependent Competition with ATGL

The single nucleotide polymorphism I148M of the lipase patatin-like phospholipase domain containing 3 (PNPLA3) is associated with an unfavorable prognosis in alcoholic and non-alcoholic steatohepatitis (ASH, NASH), with progression to liver cirrhosis and development of hepatocellular carcinoma. In this study, we investigated the mechanistic interaction of PNPLA3 with lipid droplet (LD)-associated proteins of the perilipin family, which serve as gatekeepers for LD degradation. In a collective of 106 NASH, ASH and control liver samples, immunohistochemical analyses revealed increased ballooning, inflammation and fibrosis, as well as an accumulation of PNPLA3-perilipin 5 complexes on larger LDs in patients homo- and heterozygous for PNPLA3(I148M). Co-immunoprecipitation demonstrated an interaction of PNPLA3 with perilipin 5 and the key enzyme of lipolysis, adipose triglyceride lipase (ATGL). Localization studies in cell cultures and human liver showed colocalization of perilipin 5, ATGL and PNPLA3. Moreover, the lipolytic activity of ATGL was negatively regulated by PNPLA3 and perilipin 5, whereas perilipin 1 displaced PNPLA3 from the ATGL complex. Furthermore, ballooned hepatocytes, the hallmark of steatohepatitis, were positive for PNPLA3 and perilipins 2 and 5, but showed decreased perilipin 1 expression with respect to neighboured hepatocytes. In summary, PNPLA3- and ATGL-driven lipolysis is significantly regulated by perilipin 1 and 5 in steatohepatitis.

Association between de novo lipogenesis susceptibility genes and coronary artery disease

BACKGROUND AND AIMS

Coronary artery disease (CAD) is the principal cause of death in individuals with non-alcoholic fatty liver disease (NAFLD). The aim of this study was to use genetic epidemiology to study the association between de novo lipogenesis (DNL), one of the major pathways leading to NAFLD, and CAD risk.

METHODS AND RESULTS

DNL susceptibility genes were used as instruments and selected using three approaches: 1) genes that are associated with both high serum triglycerides and low sex hormone-binding globulin, both downstream consequences of DNL (unbiased approach), 2) genes that have a known role in DNL (biased approach), and 3) genes that have been associated with serum fatty acids, used as a proxy of DNL. Gene-CAD effect estimates were retrieved from the meta-analysis of CARDIoGRAM and the UK Biobank (∼76014 cases and ∼264785 controls). Effect estimates were clustered using a fixed-effects meta-analysis. Twenty-two DNL susceptibility genes were identified by the unbiased approach, nine genes by the biased approach and seven genes were associated with plasma fatty acids. Clustering of genes selected in the unbiased and biased approach showed a statistically significant association with CAD (OR:1.016, 95%CI:1.012; 1.020 and OR:1.013, 95%CI:1.007; 1.020, respectively), while clustering of fatty acid genes did not (OR:1.004, 95%CI:0.996-1.011). Subsequent exclusion of potential influential outliers did reveal a statistically significant association (OR:1.009, 95%CI:1.000; 1.018).

CONCLUSIONS

DNL susceptibility genes are associated with an increased risk of CAD. These findings suggest that DNL may be involved in the pathogenesis of CAD and favor further development of strategies that target NAFLD through DNL.

Associations of PNPLA3 rs738409 Polymorphism with Plasma Lipid Levels: A Systematic Review and Meta-Analysis

Accumulating evidence has shown that the rs738409 polymorphism of patatin-like phospholipase domain-containing 3 (PNPLA3) is associated with non-alcoholic fatty liver disease (NAFLD). Since NAFLD has been reported to be associated with lipid metabolism, this study is conducted to explore whether the rs738409 polymorphism of PNPLA3 was associated with lipid levels. By searching PubMed and the Cochrane database from May 31, 2020, to June 30, 2021. Sixty-three studies (81 003 subjects) were included for the analysis. The consistent findings for the associations of rs738409 polymorphism with lipid levels were the significantly decreased triglycerides (TG) (SMD=-0.04, 95% CI=-0.07 to -0.01, p=0.02) and total cholesterol (TC) (SMD=-0.03, 95% CI=-0.05 to -0.01, p<0.01) levels. Subgroup analysis indicated that the associations of rs738409 polymorphism with TG and TC levels were stronger in Caucasians, obesity patients, and adult subjects than in Asians, T2DM patients, and children subjects. The rs738409 polymorphism of PNPLA3 was associated with lower TG and TC levels in Caucasians, obese and adult subjects, which may contribute to the reduced coronary artery disease (CAD) risk between PNPLA3 rs738409 polymorphism and CAD.

Recent advances in lean NAFLD

As the predominant type of chronic liver disease, the growing prevalence of nonalcoholic fatty liver disease (NAFLD) has become a concern worldwide. Although obesity plays the most pivotal role in NAFLD, approximately 10-20% of individuals with NAFLD who are not overweight or obese (BMI < 25 kg/m2, or BMI < 23 kg/m2 in Asians) have "lean NAFLD." Lean individuals with NAFLD have a lower prevalence of diabetes, hypertension, hypertriglyceridemia, central obesity, and metabolic syndrome than nonlean individuals with NAFLD, but higher fibrosis scores and rates of cardiovascular morbidity and all-cause mortality in advanced stages. The pathophysiological mechanisms of lean NAFLD remain poorly understood. Studies have shown that lean NAFLD is more correlated with factors such as environmental, genetic susceptibility, and epigenetic regulation. This review will examine the way in which the research progress and characteristic of lean NAFLD, and explore the function of epigenetic modification to provide the basis for the clinical treatment and diagnosis of lean NAFLD.

PNPLA3 and TM6SF2 genetic variants and hepatic fibrosis and cirrhosis in Pakistani chronic hepatitis C patients: a genetic association study

Background

The present study investigates if common missense functional variants p.I148M and p.E167K in PNPLA3 and TM6SF2 genes, respectively, associate with development of hepatic fibrosis and cirrhosis in a geographically novel cohort of Pakistani chronic hepatitis C (CHC) patients.

Methods

In total, 502 Pakistani CHC patients [242 males, median age 40 years, 220 with significant hepatic fibrosis, including 114 with cirrhosis] were genotyped for PNPLA3 and TM6SF2 variants using TaqMan genotyping assays. Associations between genotypes, biochemical and clinical parameters were evaluated.

Results

Genotypic distributions for PNPLA3 and TM6SF2 polymorphisms conformed to Hardy–Weinberg equilibrium and did not associate with fibrosis grades ≥ F2 or cirrhosis in any of the genetic models tested (all p =  > 0.05). PNPLA3 and TM6SF2 variants did not modulate baseline characteristics and serum markers of liver injury in CHC patients. Similarly, increasing number of risk alleles of PNPLA3 and TM6SF2 polymorphisms had no trend effect on serum liver enzyme activities or proportion of CHC patients with significant or advanced fibrosis or cirrhosis (p =  > 0.05). The same trend of no association with hepatic fibrosis or cirrhosis persisted in the multivariate logistic regression models adjusting for age, gender, body mass index and HCV viral load (p =  > 0.05).

Conclusions

PNPLA3 and TM6SF2 variants do not appear to modulate development of hepatic fibrosis or cirrhosis in present CHC patients of Pakistani origin, and may be of more relevance in liver pathology involving abnormalities in hepatic fat accumulation. These results also reflect the divergent associations observed for different genetic modifiers of hepatic fibrosis and cirrhosis in distinct ethnicities.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-022-02469-6.

Genetic variants associated with metabolic dysfunction-associated fatty liver disease in western China

INTRODUCTION

We aimed to confirm the association between some single nucleotide polymorphisms (SNPs) and metabolic dysfunction-associated fatty liver disease (MAFLD) in western China.

METHODS

A total of 286 cases and 250 healthy controls were enrolled in our study. All samples were genotyped for patatin-like phospholipase domain containing 3 (PNPLA3) rs738409, transmembrane 6 superfamily member 2 (TM6SF2) rs58542926, membrane-bound O-acyltransferase domain containing 7 (MBOAT7) rs641738, glucokinase regulator (GCKR) rs1260326 and rs780094, and GATA zinc finger domain containing 2A (GATAD2A) rs4808199. Using logistic regression analysis, we evaluated the association between MAFLD and each SNP under different models. Multiple linear regression was used to find the association between SNPs and laboratory characteristics. Multifactor dimensionality reduction was applied to test SNP-SNP interactions.

RESULTS

The recessive model and additive model of PNPLA3 rs738409 variant were related to MAFLD (odds ratio [OR] = 1.791 and 1.377, respectively, p = 0.038 and 0.027, respectively). However, after Benjamini-Hochberg adjustment for multiple tests, all associations were no longer statistically significant. PNPLA3 rs738409 correlated with AST levels. GCKR rs780094 and rs1260326 negatively correlated with serum glucose but positively correlated with triglycerides in MAFLD. Based on MDR analysis, the best single-locus and multilocus models for MAFLD risk were rs738409 and six-locus models, respectively.

CONCLUSIONS

In the Han population in western China, no association was found between these SNPs and the risk of MAFLD. PNPLA3 rs738409 was associated with aspartate aminotransferase levels in MAFLD patients. GCKR variants were associated with increased triglyceride levels and reduced serum fasting glucose in patients with MAFLD.

KHK, PNPLA3 and PPAR as Novel Targets for the Anti-Steatotic Action of Bempedoic Acid

Bempedoic acid (BemA) is an ATP-citrate lyase (ACLY) inhibitor used to treat hypercholesterolemia. We studied the anti-steatotic effect of BemA, and the mechanisms involved, in a model of fatty liver in female rats obtained through the administration of a high-fat diet supplemented with liquid fructose (HFHFr) for three months. In the third month, a group of rats was treated with BemA (30 mg/kg/day) by gavage. Plasma analytes, liver histology, adiposity, and the expression of key genes controlling fatty acid metabolism were determined, and PPAR agonism was explored by using luciferase reporter assays. Our results showed that, compared to HFHFr, BemA-treated rats exhibited lower body weight, higher liver/body weight, and reduced hepatic steatosis. In addition to ACLY inhibition, we found three novel mechanisms that could account for the anti-steatotic effect: (1) reduction of liver ketohexokinase, leading to lower fructose intake and reduced de novo lipogenesis; (2) increased expression of patatin-like phospholipase domain-containing protein 3, a protein related to the export of liver triglycerides to blood; and (3) PPARα agonist activity, leading to increased hepatic fatty acid β-oxidation. In conclusion, BemA may represent a novel approach to treat hepatic steatosis, and therefore to avoid progression to advanced stages of non-alcoholic fatty liver disease.

Postprandial Plasma Lipidomics Reveal Specific Alteration of Hepatic-derived Diacylglycerols in Nonalcoholic Fatty Liver Disease

BACKGROUND & AIMS

Hepatic energy metabolism is a dynamic process modulated by multiple stimuli. In nonalcoholic fatty liver disease (NAFLD), human studies typically focus on the static fasting state. We hypothesized that unique postprandial alterations in hepatic lipid metabolism are present in NAFLD.

METHODS

In a prospective clinical study, 37 patients with NAFLD and 10 healthy control subjects ingested a standardized liquid meal with pre- and postprandial blood sampling. Postprandial plasma lipid kinetics were characterized at the molecular lipid species level by untargeted lipidomics, cluster analysis, and lipid particle isolation, then confirmed in a mouse model.

RESULTS

There was a specific increase of multiple plasma diacylglycerol (DAG) species at 4 hours postprandially in patients with NAFLD but not in controls. This was replicated in a nonalcoholic steatohepatitis mouse model, where postprandial DAGs increased in plasma and concomitantly decreased in the liver. The increase in plasma DAGs appears early in the disease course, is dissociated from NAFLD severity and obesity, and correlates with postprandial insulin levels. Immunocapture isolation of very low density lipoprotein in human samples and stable isotope tracer studies in mice revealed that elevated postprandial plasma DAGs reflect hepatic secretion of endogenous, rather than meal-derived lipids.

CONCLUSIONS

We identified a selective insulin-related increase in hepatic secretion of endogenously derived DAGs after a mixed meal as a unique feature of NAFLD. DAGs are known to be lipotoxic and associated with atherosclerosis. Although it is still unknown whether the increased exposure to hepatic DAGs contributes to extrahepatic manifestations and cardiovascular risk in NAFLD, our study highlights the importance of extending NAFLD research beyond the fasting state.

Association of metabolic dysfunction-associated fatty liver disease with kidney disease

Non-alcoholic fatty liver disease (NAFLD) is characterized by the accumulation of fat in more than 5% of hepatocytes in the absence of excessive alcohol consumption and other secondary causes of hepatic steatosis. In 2020, the more inclusive term metabolic (dysfunction)-associated fatty liver disease (MAFLD) - defined by broader diagnostic criteria - was proposed to replace the term NAFLD. The new terminology and revised definition better emphasize the pathogenic role of metabolic dysfunction and uses a set of definitive, inclusive criteria for diagnosis. Diagnosis of MAFLD is based on evidence of hepatic steatosis (as assessed by liver biopsy, imaging techniques or blood biomarkers and scores) in persons who are overweight or obese and have type 2 diabetes mellitus or metabolic dysregulation, regardless of the coexistence of other liver diseases or excessive alcohol consumption. The known association between NAFLD and chronic kidney disease (CKD) and our understanding that CKD can occur as a consequence of metabolic dysfunction suggests that individuals with MAFLD - who by definition have fatty liver and metabolic comorbidities - are at increased risk of CKD. In this Perspective article, we discuss the clinical associations between MAFLD and CKD, the pathophysiological mechanisms by which MAFLD may increase the risk of CKD and the potential drug treatments that may benefit both conditions.

NAFLD-related gene polymorphisms and all-cause and cause-specific mortality in an Asian population: the Shanghai Changfeng Study

BACKGROUND

The PNPLA3 and TM6SF2 gene variants have been found to cause NAFLD with a favourable cardiovascular risk profile.

AIMS

To investigate the effects of the NAFLD risk alleles on the all-cause and cause-specific mortality in 5581 Chinese adults.

METHODS

The genome-wide genotypes were detected using a genotyping array and serum lipoprotein profiles were examined using 1H NMR platform. Liver fat content (LFC) was measured using a quantitative ultrasound method. The vital status was determined using official registration data.

RESULTS

Genome-wide association analysis showed that a series of variants in PNPLA3 were associated with LFC, including rs738409 C>G variant (P = 8.6 × 10-7 ). Further analyses validated the associations of TM6SF2 rs58542926 C>T and MBOAT7 rs641738 C>T variants with NAFLD. During 29 425.1 person-years of follow-up, the overall mortality was 816 per 100 000 person-years, where 299 deaths were attributable to cardiovascular disease and 85 to liver disease. The PNPLA3 rs738409 C>G variant was independently associated with increased liver-specific mortality (P for trend = 0.034) but reduced cardiovascular mortality (P for trend = 0.047). A composite genetic-predisposition score of PNPLA3, TM6SF2, and MBOAT7 risk alleles presented similar opposite effects on liver-specific and cardiovascular mortality. Moreover, interactions of the NAFLD risk alleles with adiposity for liver-specific mortality were found (Pinteraction  < 0.05). The reduced serum VLDL1 concentration was responsible for the increased liver-specific mortality related to NAFLD risk alleles.

CONCLUSION

The PNPLA3 rs738409 C>G variant and its combination with TM6SF2 rs58542926 C>T and MBOAT7 rs641738 C>T variants increase liver-specific mortality but reduce cardiovascular mortality in overweight/obese Chinese.

Effects of PNPLA3 I148M on hepatic lipid and very-low-density lipoprotein metabolism in humans

BACKGROUND

The phospholipase domain-containing 3 gene (PNPLA3)-148M variant is associated with liver steatosis but its influence on the metabolism of triglyceride-rich lipoproteins remains unclear. Here, we investigated the kinetics of large, triglyceride-rich very-low-density lipoprotein (VLDL), (VLDL₁ ), and smaller VLDL₂ in homozygotes for the PNPLA3-148M variant.

METHODS AND RESULTS

The kinetics of apolipoprotein (apo) B100 (apoB100) and triglyceride in VLDL subfractions were analysed in nine subjects homozygous for PNPLA3-148M and nine subjects homozygous for PNPLA3-148I (controls). Liver fat was >3-fold higher in the 148M subjects. Production rates for apoB100 and triglyceride in VLDL₁ did not differ significantly between the two groups. Likewise, production rates for VLDL₂ -apoB100 and -triglyceride, and fractional clearance rates for both apoB100 and triglyceride in VLDL₁ and VLDL₂ , were not significantly different.

CONCLUSIONS

Despite the higher liver fat content in PNPLA3 148M homozygotes, there was no increase in VLDL production. Equally, VLDL production was maintained at normal levels despite the putative impairment in cytosolic lipid hydrolysis in these subjects.

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.