Exome-wide association study identifies a TM6SF2 variant that confers susceptibility to nonalcoholic fatty liver disease

Association of MAFLD with end-stage kidney disease: a prospective study of 337,783 UK Biobank participants

INTRODUCTION

Metabolic dysfunction-associated fatty liver (MAFLD) has been found to be associated with the prevalence of chronic kidney disease (CKD). However, it is unknown whether MAFLD is associated with CKD development and the incidence of end-stage kidney disease (ESKD). We aimed to clarify the association between MAFLD and incident ESKD in the prospective UK Biobank cohort.

METHODS

We analyzed the data of 337,783 UK Biobank participants and relative risks for the ESKD were calculated by using the Cox regression analysis.

RESULTS

Among 337,783 participants over a median duration of 12.8 years follow-up, a total of 618 ESKD cases were diagnosed. Participants with MAFLD were twice likely to develop ESKD (hazard ratio [HR] 2.03, 95% confidence interval [CI] 1.68-2.46, p < 0.001). The association of MAFLD with ESKD risk remained significant in both non-CKD and CKD participants. Our results also showed that there were graded associations between liver fibrosis scores and the risk of ESKD in MAFLD cases. Compared to non-MAFLD individuals, the adjusted HRs for incident ESKD in MAFLD patients with increasing levels of NAFLD fibrosis score were 1.23 (95% CI 0.96-1.58), 2.45 (1.98-3.03) and 7.67 (5.48-10.73), respectively. Furthermore, the risking alleles of PNPLA3 rs738409, TM6SF2 rs58542926, GCKR rs1260326 and MBOAT7 rs641738 amplified the MAFLD effect on ESKD risk. In conclusion, MAFLD is associated with incident ESKD.

CONCLUSION

MAFLD may help identify the subjects at high risk of ESKD development and MAFLD interventions should be encouraged to slow down CKD progression.

Plasma Metabolite Signatures in Male Carriers of Genetic Variants Associated with Non-Alcoholic Fatty Liver Disease

Both genetic and non-genetic factors are important in the pathophysiology of non-alcoholic fatty liver disease (NAFLD). The aim of our study was to identify novel metabolites and pathways associated with NAFLD by including both genetic and non-genetic factors in statistical analyses. We genotyped six genetic variants in the PNPLA3, TM6SF2, MBOAT7, GCKR, PPP1R3B, and HSD17B13 genes reported to be associated with NAFLD. Non-targeted metabolomic profiling was performed from plasma samples. We applied a previously validated fatty liver index to identify participants with NAFLD. First, we associated the six genetic variants with 1098 metabolites in 2 339 men without NAFLD to determine the effects of the genetic variants on metabolites, and then in 2 535 men with NAFLD to determine the joint effects of genetic variants and non-genetic factors on metabolites. We identified several novel metabolites and metabolic pathways, especially for PNPLA3, GCKR, and PPP1R38 variants relevant to the pathophysiology of NAFLD. Importantly, we showed that each genetic variant for NAFLD had a specific metabolite signature. The plasma metabolite signature was unique for each genetic variant, suggesting that several metabolites and different pathways are involved in the risk of NAFLD. The FLI index reliably identifies metabolites for NAFLD in large population-based studies.

Different effects of low muscle mass on the risk of non-alcoholic fatty liver disease and hepatic fibrosis in a prospective cohort

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) and sarcopenia share insulin resistance as a common pathophysiology and have overlapping clinical manifestation of metabolic derangement; hence, it is difficult to differentiate the independent effect of sarcopenia on the development of NAFLD from concomitant metabolic disorders. Using a community-based prospective cohort study, the contributions of low muscle mass and genetic risk factors to the development of NAFLD and NAFLD-related hepatic fibrosis were investigated in the Korean population.

METHODS

This prospective community-based cohort study included 40-70-year-old adults, followed up biennially from 2001-2002 to 2017-2018. NAFLD was defined as a hepatic steatosis index of ≥36, and hepatic fibrosis was defined based on the fibrosis-4 index. Sex-specific quartiles of body mass index (BMI)-adjusted muscle mass were calculated (muscle mass/BMI), and low muscle mass was defined as the lowest quartile (Q1). Cox proportional hazard models for incident NAFLD or hepatic fibrosis incorporating age, sex, BMI of ≥25 kg/m² , metabolic syndrome and PNPLA3 and TM6SF2 risk alleles were used to assess the independent determinants for incident NAFLD and hepatic fibrosis among individuals with NAFLD at baseline.

RESULTS

Among the 4038 participants without NAFLD at baseline (mean age, 51.5 ± 8.8 years), 920 (22.8%) developed NAFLD during the 12-year follow-up period. As muscle mass decreased, the risk of NAFLD increased even after adjustment for age, sex, obesity, metabolic syndrome and PNPLA3 and TM6SF2 risk alleles [hazard ratio (HR) per quartile, 1.18, 95% confidence interval (CI), 1.11-1.27, P < 0.001]. TM6SF2 also affected the risk of NAFLD development [HR 1.19, (95% CI, 1.00-1.40), P = 0.044]. Of the 1176 patients with NAFLD but without hepatic fibrosis at baseline, the incident of hepatic fibrosis was found in 51.8%, 44.7%, 42.6% and 41.0% in Q1, Q2, Q3 and Q4 of BMI-adjusted muscle mass, respectively, during the follow-up period (P for trend = 0.006). However, this trend lost its statistical significance when adjusted for confounders. The PNPLA3 risk variant, but not the TM6SF2 genotype, was an independent risk factor for developing hepatic fibrosis among patients with NAFLD (HR 1.17, 95% CI 1.04-1.32, P = 0.010).

CONCLUSIONS

Both lower muscle mass index and genetic risk variants are important contributors to the development of NAFLD. In patients already diagnosed with NAFLD, however, PNPLA3 confers a greater risk for hepatic fibrosis progression than lower muscle mass.

Genetic variation in TERT modifies the risk of hepatocellular carcinoma in alcohol-related cirrhosis: results from a genome-wide case-control study

OBJECTIVE

Hepatocellular carcinoma (HCC) often develops in patients with alcohol-related cirrhosis at an annual risk of up to 2.5%. Some host genetic risk factors have been identified but do not account for the majority of the variance in occurrence. This study aimed to identify novel susceptibility loci for the development of HCC in people with alcohol related cirrhosis.

DESIGN

Patients with alcohol-related cirrhosis and HCC (cases: n=1214) and controls without HCC (n=1866), recruited from Germany, Austria, Switzerland, Italy and the UK, were included in a two-stage genome-wide association study using a case-control design. A validation cohort of 1520 people misusing alcohol but with no evidence of liver disease was included to control for possible association effects with alcohol misuse. Genotyping was performed using the InfiniumGlobal Screening Array (V.24v2, Illumina) and the OmniExpress Array (V.24v1-0a, Illumina).

RESULTS

Associations with variants rs738409 in PNPLA3 and rs58542926 in TM6SF2 previously associated with an increased risk of HCC in patients with alcohol-related cirrhosis were confirmed at genome-wide significance. A novel locus rs2242652(A) in TERT (telomerase reverse transcriptase) was also associated with a decreased risk of HCC, in the combined meta-analysis, at genome-wide significance (p=6.41×10-9, OR=0.61 (95% CI 0.52 to 0.70). This protective association remained significant after correction for sex, age, body mass index and type 2 diabetes (p=7.94×10-5, OR=0.63 (95% CI 0.50 to 0.79). Carriage of rs2242652(A) in TERT was associated with an increased leucocyte telomere length (p=2.12×10-44).

CONCLUSION

This study identifies rs2242652 in TERT as a novel protective factor for HCC in patients with alcohol-related cirrhosis.

Comparison between obese and non-obese nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver conditions that are characterized by excess accumulation of fat in the liver, and is diagnosed after exclusion of significant alcohol intake and other causes of chronic liver disease. In the majority of cases, NAFLD is associated with overnutrition and obesity, although it may be also found in lean or non-obese individuals. It has been estimated that 19.2% of NAFLD patients are lean and 40.8% are non-obese. The proportion of patients with more severe liver disease and the incidence of all-cause mortality, liver-related mortality, and cardiovascular mortality among non-obese and obese NAFLD patients varies across studies and may be confounded by selection bias, underestimation of alcohol intake, and unaccounted weight changes over time. Genetic factors may have a greater effect towards the development of NAFLD in lean or non-obese individuals, but the effect may be less pronounced in the presence of strong environmental factors, such as poor dietary choices and a sedentary lifestyle, as body mass index increases in the obese state. Overall, non-invasive tests, such as the Fibrosis-4 index, NAFLD fibrosis score, and liver stiffness measurement, perform better in lean or non-obese patients compared to obese patients. Lifestyle intervention works in non-obese patients, and less amount of weight loss may be required to achieve similar results compared to obese patients. Pharmacological therapy in non-obese NAFLD patients may require special consideration and a different approach compared to obese patients.

Genetics in non-alcoholic fatty liver disease: The role of risk alleles through the lens of immune response

The knowledge on the genetic component of non-alcoholic fatty liver disease (NAFLD) has grown exponentially over the last 10 to 15 years. This review summarizes the current evidence and the latest developments in the genetics of NAFLD and non-alcoholic steatohepatitis (NASH) from the immune system's perspective. Activation of innate and or adaptive immune response is an essential driver of NAFLD disease severity and progression. Lipid and immune pathways are crucial in the pathophysiology of NAFLD and NASH. Here, we highlight novel applications of genomic techniques, including single-cell sequencing and the genetics of gene expression, to elucidate the potential involvement of NAFLD/NASH-risk alleles in modulating immune system cells. Together, our focus is to provide an overview of the potential involvement of the NAFLD/NASH-related risk variants in mediating the immune-driven liver disease severity and diverse systemic pleiotropic effects.

Clinical features and metabolic complications for non-alcoholic fatty liver disease (NAFLD) in youth with obesity

Pediatric obesity has become in the last forty years the most common metabolic disease in children and adolescents affecting about 25% of the pediatric population in the western world. As obesity worsens, a whole-body insulin resistance (IR) occurs. This phenomenon is more pronounced during adolescence, when youth experience a high degree of insulin resistance due the production of growth hormone. As IR progresses, the blunted control of insulin on adipose tissue lipolysis causes an increased flux of fatty acids with FFA deposition in ectopic tissues and organs such as the liver, leading to the development of NAFLD. In this brief review, we will discuss the clinical implications of IR and NAFLD in the context of pediatric obesity. We will review the pathogenesis and the link between these two entities, the major pathophysiologic underpinnings, including the role of genetics and metagenomics, how these two entities lead to the development of type 2 diabetes, and which are the therapeutic options for NAFLD in youth.

MAFLD and Celiac Disease in Children

Celiac disease (CD) is an immune-mediated systemic disorder elicited by the ingestion of gluten whose clinical presentation ranges from the asymptomatic form to clinical patterns characterized by multiple systemic involvement. Although CD is a disease more frequently diagnosed in patients with symptoms of malabsorption such as diarrhea, steatorrhea, weight loss, or failure to thrive, the raised rate of overweight and obesity among general pediatric and adult populations has increased the possibility to diagnose celiac disease in obese patients as well. Consequently, it is not difficult to also find obesity-related disorders in patients with CD, including "metabolic associated fatty liver disease" (MAFLD). The exact mechanisms linking these two conditions are not yet known. The going assumption is that a gluten-free diet (GFD) plays a pivotal role in determining an altered metabolic profile because of the elevated content of sugars, proteins, saturated fats, and complex carbohydrates, and the higher glycemic index of gluten-free products than gluten-contained foods, predisposing individuals to the development of insulin resistance. However, recent evidence supports the hypothesis that alterations in one of the components of the so-called "gut-liver axis" might contribute to the increased afflux of toxic substances to the liver triggering the liver fat accumulation and to the subsequent hepatocellular damage. The aim of this paper was to describe the actual knowledge about the factors implicated in the pathogenesis of hepatic steatosis in pediatric patients with CD. The presented review allows us to conclude that the serological evaluations for CD with anti-transglutaminase antibodies, should be a part of the general workup in the asymptomatic patients with "non-alcoholic fatty liver disease" (NAFLD) when metabolic risk factors are not evident, and in the patients with steatohepatitis when other causes of liver disease are excluded.

Glutathione: Pharmacological aspects and implications for clinical use in non-alcoholic fatty liver disease

Glutathione is a tripeptide synthesized at cytosolic level, that exists in cells in a reduced form (thiol-reduced-GSH-) and in an oxidized form (disulfide-oxidized). The antioxidant function of GSH has led to speculation about its therapeutic role in numerous chronic diseases characterized by altered redox balance and reduced GSH levels, including, for instance, neurodegenerative disorders, cancer, and chronic liver diseases. Among these latter, non-alcoholic fatty liver disease (NAFLD), characterized by lipid accumulation in hepatocytes, in the absence of alcohol abuse or other steatogenic factors, is one of the most prevalent. The umbrella term NAFLD includes the pure liver fat accumulation, the so-called hepatic steatosis or non-alcoholic fatty liver, and the progressive form with inflammation, also known as non-alcoholic steatohepatitis, which is related to the increase in oxidative stress and reactive oxygen species, eventually leading to liver fibrosis. Although the pathogenetic role of oxidative stress in these diseases is well established, there is still limited evidence on the therapeutic role of GSH in such conditions. Hence, the aim of this review is to depict the current molecular and pharmacological knowledge on glutathione, focusing on the available studies related to its therapeutic activity in 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.

Fatty liver disease in children (MAFLD/PeFLD Type 2): unique classification considerations and challenges

In children, fatty liver disease is a group of disorders that often overlaps with inherited metabolic disorders (IMDs), which requires prompt diagnosis and specific management. Metabolic dysfunction-associated fatty liver disease (MAFLD) or, formerly, non-alcoholic fatty liver disease (NAFLD) is the hepatic component of a multisystemic disease that requires a positive criteria in metabolic dysfunction for diagnosis. However, in children, the diagnosis of MAFLD is one of the exclusions of an IMD [paediatric fatty liver disease (PeFLD) type 1] including the possibility that an IMD can be identified in the future following investigations that may be negative at the time. Therefore, while children with fatty liver with metabolic dysfunction could be classified as MAFLD (PeFLD type 2) and managed that way, those who do not fulfil the criteria for metabolic dysfunction should be considered separately bearing in mind the possibility of identifying a yet undiagnosed IMD (PeFLD type 3). This concept is ever more important in a world where MAFLD is the most common cause of liver disease in children and adolescents in whom about 7% are affected. The disease is only partially understood, and awareness is still lacking outside hepatology and gastroenterology. Despite its increasing pervasiveness, the management is far from a one-size-fits-all. Increasing complexities around the genetic, epigenetic, non-invasive modalities of assessment, psychosocial impacts, therapeutics, and natural history of the disease have meant that an individualised approach is required. This is where the challenge lies so that children with fatty liver are considered on their own merits. The purpose of this review is to give a clinical perspective of fatty liver disease in children with relevance to metabolic dysfunction.

Review article: the role of HSD17B13 on global epidemiology, natural history, pathogenesis and treatment of NAFLD

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) occurs in around a quarter of the global population and is one of the leading causes of chronic liver disease. The phenotypic manifestation and the severity of NAFLD are influenced by an interplay of environmental and genetic factors. Recently, several inactivating variants in the novel 17-Beta hydroxysteroid dehydrogenase 13 (HSD17B13) gene have been found to be associated with a reduced risk of chronic liver diseases, including NAFLD.

AIMS

To review the existing literature on the epidemiology of HSD17B13 and discuss its role in the natural history, disease pathogenesis and treatment of NAFLD.

METHODS

We extensively searched relevant literature in PubMed, Google Scholar, clinicaltrials.gov and the reference list of articles included in the review.

RESULTS

HSD17B13 is a liver-specific, lipid droplet (LD)-associated protein that has enzymatic pathways involving steroids, pro-inflammatory lipid mediators and retinol. The estimated prevalence of the best characterised HSD17B13 variant (rs72613567) ranges from 5% in Africa to 34% in East Asia. Loss-of-function variants in HSD17B13 are protective against the progression of NAFLD from simple steatosis to non-alcoholic steatohepatitis (NASH), liver fibrosis, cirrhosis and hepatocellular carcinoma. Emerging data from mechanistic and preclinical studies with RNA interference (RNAi) and small molecule agents indicate that inhibiting HSD17B13 activity may prevent NAFLD progression.

CONCLUSIONS

The loss-of-function polymorphisms of the newly identified HSD17B13 gene mitigate the progression of NAFLD. It is important to understand the exact mechanism by which these variants exert a protective effect and implement the gathered knowledge in the treatment of NAFLD.

MAFLD: a multisystem disease

Nonalcoholic fatty liver disease (NAFLD), affecting about 25% of general population and more than 50% of dysmetabolic patients, is an emerging cause of chronic liver disease and its complications. Recently, an international consensus of experts proposed to rename this disease as 'Metabolic dysfunction-Associated Fatty Liver Disease' (MAFLD) to focus on the bidirectional interplay between fatty liver and metabolic alterations and to stress the need of assessing fatty liver independently from alcohol consumption and other coexisting causes of liver disease. The peculiarity of NAFLD/MAFLD lies in the presence of a higher risk of not only - as expected - liver-related events but also of extrahepatic events, mostly cardiovascular and cancers. Available evidence suggests that these associations are not only the expression of sharing the same risk factors but shed light about the ability of NAFLD/MAFLD and particularly of its progressive form - nonalcoholic/metabolic dysfunction-associated steatohepatitis - to act as an independent risk factor via promotion of atherogenic dyslipidemia and a proinflammatory, profibrogenic, and procoagulant systemic environment. The present review summarizes available epidemiological and clinical evidence supporting the concept of NAFLD/MAFLD as a multisystemic disease, and highlights potential explanatory mechanisms underlying the association between NAFLD/MAFLD and extrahepatic disorders.

The association of non-alcoholic fatty liver disease between parents and adolescent children

BACKGROUND

Data reporting the heritability of non-alcoholic fatty liver disease (NAFLD) are highly variable.

AIMS

To investigate the association of NAFLD between parents and their adolescent children using a nationwide, population-based cohort.

METHODS

We analysed 1737 families with both parents and adolescent children aged 12-18 who participated in Korean National Health and Nutrition Examination Surveys (KNHANES) between 2010 and 2019. NAFLD was defined by body mass index and elevated alanine aminotransferase levels in children and by the hepatic steatosis index in parents.

RESULTS

The prevalence of NAFLD in adolescent children with either parent with NAFLD was higher than that in those without a parent with NAFLD (10.2% vs. 3.1%, p < 0.001). In a model fully adjusted for demographic, nutritional, behavioural and metabolic risk factors, children with either parent with NAFLD had a higher odds ratio (OR) for NAFLD (OR = 1.75, 95% CI: 1.02-3.00) than those without a parent with NAFLD. Compared to those without a parent with NAFLD, the fully adjusted ORs of NAFLD in children with paternal NAFLD, maternal NAFLD and NAFLD in both parents were 1.80 (95% CI: 1.01-3.20), 2.21 (95% CI: 1.11-4.42) and 2.60 (95% CI: 1.03-6.54), respectively.

CONCLUSION

Adolescent children with a parent with NAFLD were at increased risk of NAFLD; risk was higher when both parents had NAFLD. Further studies are needed to explore the benefit of NAFLD screening in children who have a parent with NAFLD.

Pathogenesis and treatment of non-alcoholic steatohepatitis and its fibrosis

The initial presentation of non-alcoholic steatohepatitis (NASH) is hepatic steatosis. The dysfunction of lipid metabolism within hepatocytes caused by genetic factors, diet, and insulin resistance causes lipid accumulation. Lipotoxicity, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum stress would further contribute to hepatocyte injury and death, leading to inflammation and immune dysfunction in the liver. During the healing process, the accumulation of an excessive amount of fibrosis might occur while healing. During the development of NASH and liver fibrosis, the gut-liver axis, adipose-liver axis, and renin-angiotensin system (RAS) may be dysregulated and impaired. Translocation of bacteria or its end-products entering the liver could activate hepatocytes, Kupffer cells, and hepatic stellate cells, exacerbating hepatic steatosis, inflammation, and fibrosis. Bile acids regulate glucose and lipid metabolism through Farnesoid X receptors in the liver and intestine. Increased adipose tissue-derived non-esterified fatty acids would aggravate hepatic steatosis. Increased leptin also plays a role in hepatic fibrogenesis, and decreased adiponectin may contribute to hepatic insulin resistance. Moreover, dysregulation of peroxisome proliferator-activated receptors in the liver, adipose, and muscle tissues may impair lipid metabolism. In addition, the RAS may contribute to hepatic fatty acid metabolism, inflammation, and fibrosis. The treatment includes lifestyle modification, pharmacological therapy, and non-pharmacological therapy. Currently, weight reduction by lifestyle modification or surgery is the most effective therapy. However, vitamin E, pioglitazone, and obeticholic acid have also been suggested. In this review, we will introduce some new clinical trials and experimental therapies for the treatment of NASH and related fibrosis.

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.

Exome-wide association analysis of CT imaging-derived hepatic fat in a medical biobank

Nonalcoholic fatty liver disease is common and highly heritable. Genetic studies of hepatic fat have not sufficiently addressed non-European and rare variants. In a medical biobank, we quantitate hepatic fat from clinical computed tomography (CT) scans via deep learning in 10,283 participants with whole-exome sequences available. We conduct exome-wide associations of single variants and rare predicted loss-of-function (pLOF) variants with CT-based hepatic fat and perform cross-modality replication in the UK Biobank (UKB) by linking whole-exome sequences to MRI-based hepatic fat. We confirm single variants previously associated with hepatic fat and identify several additional variants, including two (FGD5 H600Y and CITED2 S198_G199del) that replicated in UKB. A burden of rare pLOF variants in LMF2 is associated with increased hepatic fat and replicates in UKB. Quantitative phenotypes generated from clinical imaging studies and intersected with genomic data in medical biobanks have the potential to identify molecular pathways associated with human traits and disease.

Epidemiologic, Genetic, Pathogenic, Metabolic, Epigenetic Aspects Involved in NASH-HCC: Current Therapeutic Strategies

Hepatocellular carcinoma (HCC) is the most common primary liver cancer and is the sixth most frequent cancer in the world, being the third cause of cancer-related deaths. Nonalcoholic steatohepatitis (NASH) is characterized by fatty infiltration, oxidative stress and necroinflammation of the liver, with or without fibrosis, which can progress to advanced liver fibrosis, cirrhosis and HCC. Obesity, metabolic syndrome, insulin resistance, and diabetes exacerbates the course of NASH, which elevate the risk of HCC. The growing prevalence of obesity are related with increasing incidence of NASH, which may play a growing role in HCC epidemiology worldwide. In addition, HCC initiation and progression is driven by reprogramming of metabolism, which indicates growing appreciation of metabolism in the pathogenesis of this disease. Although no specific preventive pharmacological treatments have recommended for NASH, dietary restriction and exercise are recommended. This review focuses on the molecular connections between HCC and NASH, including genetic and risk factors, highlighting the metabolic reprogramming and aberrant epigenetic alterations in the development of HCC in NASH. Current therapeutic aspects of NASH/HCC are also reviewed.

Genetic and Diet-Induced Animal Models for Non-Alcoholic Fatty Liver Disease (NAFLD) Research

A rapidly increasing incidence of non-alcoholic fatty liver disease (NAFLD) is noted worldwide due to the adoption of western-type lifestyles and eating habits. This makes the understanding of the molecular mechanisms that drive the pathogenesis of this chronic disease and the development of newly approved treatments of utmost necessity. Animal models are indispensable tools for achieving these ends. Although the ideal mouse model for human NAFLD does not exist yet, several models have arisen with the combination of dietary interventions, genetic manipulations and/or administration of chemical substances. Herein, we present the most common mouse models used in the research of NAFLD, either for the whole disease spectrum or for a particular disease stage (e.g., non-alcoholic steatohepatitis). We also discuss the advantages and disadvantages of each model, along with the challenges facing the researchers who aim to develop and use animal models for translational research in NAFLD. Based on these characteristics and the specific study aims/needs, researchers should select the most appropriate model with caution when translating results from animal to human.

MTARC1 and HSD17B13 Variants Have Protective Effects on Non-Alcoholic Fatty Liver Disease in Patients Undergoing Bariatric Surgery

The severity of hepatic steatosis is modulated by genetic variants, such as patatin-like phospholipase domain containing 3 (PNPLA3) rs738409, transmembrane 6 superfamily member 2 (TM6SF2) rs58542926, and membrane-bound O-acyltransferase domain containing 7 (MBOAT7) rs641738. Recently, mitochondrial amidoxime reducing component 1 (MTARC1) rs2642438 and hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13) rs72613567 polymorphisms were shown to have protective effects on liver diseases. Here, we evaluate these variants in patients undergoing bariatric surgery. A total of 165 patients who underwent laparoscopic sleeve gastrectomy and intraoperative liver biopsies and 314 controls were prospectively recruited. Genotyping was performed using TaqMan assays. Overall, 70.3% of operated patients presented with hepatic steatosis. NASH (non-alcoholic steatohepatitis) was detected in 28.5% of patients; none had cirrhosis. The increment of liver fibrosis stage was associated with decreasing frequency of the MTARC1 minor allele (p = 0.03). In multivariate analysis MTARC1 was an independent protective factor against fibrosis ≥ 1b (OR = 0.52, p = 0.03) and ≥ 1c (OR = 0.51, p = 0.04). The PNPLA3 risk allele was associated with increased hepatic steatosis, fibrosis, and NASH (OR = 2.22, p = 0.04). The HSD17B13 polymorphism was protective against liver injury as reflected by lower AST (p = 0.04) and ALT (p = 0.03) activities. The TM6SF2 polymorphism was associated with increased ALT (p = 0.04). In conclusion, hepatic steatosis is common among patients scheduled for bariatric surgery, but the MTARC1 and HSD17B13 polymorphisms lower liver injury in these individuals.

Molecular Screening via Sanger Sequencing of the Genetic Variants in Non-Alcoholic Fatty Liver Disease Subjects in the Saudi Population: A Hospital-Based Study

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, along with steatosis and non-alcoholic steatohepatitis (NASH), and is associated with cirrhosis and hepatocellular carcinoma. Candidate gene and genome-wide association studies have validated the relationships between NAFLD, NASH, PNPLA3, TM6SF2, and HFE. The present study utilized five polymorphisms in three genes: PNPLA3 (I148M and K434E) TM6SF2 (E167K), and HFE (H63D and C282Y), based on undocumented case−control studies in the Saudi Arabian population. A total of 95 patients with NAFLD and 78 non-NAFLD subjects were recruited. Genomic DNA was isolated, and polymerase chain reaction and Sanger sequencing were performed using specific primers for the I148M, K434E, E167K, H63D, and C282Y. NAFLD subjects were older when compared to controls and showed the significant association (p = 0.0001). Non-significant association was found between gender (p = 0.26). However, both weight and BMI were found to be associated. Hardy−Weinberg equilibrium analysis confirmed that H63D, I148M, and K434E polymorphisms were associated. Genotype analysis showed only K434E variant was associated with NAFLD and non-NAFLD (OR-2.16; 95% CI: 1.08−4.31; p = 0.02). However, other polymorphisms performed with NAFLD and NASH were not associated (p > 0.05), and similar analysis was found when ANOVA was performed (p > 0.05). In conclusion, we confirmed that K434E polymorphism showed a positive association in the Saudi population.

Effect of common genetic variants on the risk of cirrhosis in non-alcoholic fatty liver disease during 20 years of follow-up

BACKGROUND AND AIMS

Several genotypes associate with a worse histopathological profile in patients with non-alcoholic fatty liver disease (NAFLD). Whether genotypes impact long-term outcomes is unclear. We investigated the importance of PNPLA3, TM6SF2, MBOAT7 and GCKR genotype for the development of severe outcomes in NAFLD.

METHOD

DNA samples were collected from 546 patients with NAFLD. Advanced fibrosis was diagnosed by liver biopsy or elastography. Non-alcoholic steatohepatitis (NASH) was histologically defined. Additionally, 5396 controls matched for age, sex and municipality were identified from population-based registers. Events of severe liver disease and all-cause mortality were collected from national registries. Hazard ratios (HRs) adjusted for age, sex, body mass index and type 2 diabetes were estimated with Cox regression.

RESULTS

In NAFLD, the G/G genotype of PNPLA3 was associated with a higher prevalence of NASH at baseline (odds ratio [OR] 3.67, 95% CI = 1.66-8.08), but not with advanced fibrosis (OR 1.81, 95% CI = 0.79-4.14). After up to 40 years of follow-up, the PNPLA3 G/G genotype was associated with a higher rate of severe liver disease (adjusted hazard ratio [aHR] 2.27, 95% CI = 1.15-4.47) compared with the C/C variant. NAFLD patients developed cirrhosis at a higher rate than controls (aHR 9.00, 95% CI = 6.85-11.83). The PNPLA3 G/G genotype accentuated this rate (aHR 23.32, 95% = CI 9.14-59.47). Overall mortality was not affected by any genetic variant.

CONCLUSION

The PNPLA3 G/G genotype is associated with an increased rate of cirrhosis in NAFLD. Our results suggest that assessment of the PNPLA3 genotype is of clinical relevance in patients with NAFLD to individualize monitoring and therapeutic strategies.

Non-alcoholic fatty liver disease establishment and progression: genetics and epigenetics as relevant modulators of the pathology

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) results from metabolic dysfunctions that affect more than one-third of the world population. Over the last decades, scientific investigations have clarified many details on the pathology establishment and development; however, effective therapeutics approaches are still evasive. In addition, studies demonstrated that NAFLD establishment and progression are related to several etiologies. Recently, genetics and epigenetics backgrounds have emerged as relevant elements to the pathology onset, and, hence, deserve deep investigation to clarify molecular details on NAFLD signaling, which may be correlated with population behavior. Thus, to minimize the global problem, public health and public policies should take advantage of studies on NAFLD over the next following decades.

METHODS

In this context, we have performed a selective literature review focusing on biochemistry of lipid metabolism, genetics, epigenetics, and the ethnicity as strong elements that drive NAFLD establishment.

RESULTS

Considering the etiological agents that acts on NAFLD development and progression, the genetics and the epigenetics emerged as relevant factors. Genetics acts as a powerful element in the establishment and progression of the NAFLD. Over the last decades, details concerning genes and their polymorphisms, as well as epigenetics, have been considered relevant elements in the systems biology of diseases, and their effects on NAFLD should be considered in-depth, as well as the ethnicity, clarifying whether people are susceptible to liver diseases. Moreover, the endemicity and social problems of hepatic disfunction are far to be solved, which require a combined effort of various sectors of society.

CONCLUSION

Hence, the elements presented and discussed in this short review demonstrated their relevance to the physiological control of NAFLD, opening perspectives for research to develop new strategy to treat fatty liver diseases.

Dietary Recommendations for the Management of Non-alcoholic Fatty Liver Disease (NAFLD): A Nutritional Geometry Perspective

Diet could be both culprit and solution of NAFLD. Dietary modifications have been associated with histological features improvement in NAFLD. The Western diet was related to a greater risk of disease progression while the Mediterranean diet (MD) could promote regression of histological lesions. Modifications in the nutrient composition seems to have lesser impact on NAFLD than dietary modifications. An intrinsic interaction between nutrients in the diet support a specific effect not seen when added separately. Dietary modifications should focus on promoting weight loss but also look for patterns that are able to promote histological improvement. Although several micronutrients' deficit has been related to NAFLD progression, prescribing these micronutrients' supplementation did not reach a positive impact. However, an enriching diet with specific nutrients could be useful, like olive oil supplemented in MD. Geometry of nutrition defines a framework to better understand the interaction between nutrients, foods, and dietetic pattern in the model of diseases and how we could approach taking into consideration the interaction between meals and disease features. After analyzing baseline diet and histological lesions, we could calculate the distance to optimal diet and to promote changes in lifestyle to reach all these goals. A standard MD menu would be recommended.

Multiomics study of nonalcoholic fatty liver disease

Nonalcoholic fatty liver (NAFL) and its sequelae are growing health problems. We performed a genome-wide association study of NAFL, cirrhosis and hepatocellular carcinoma, and integrated the findings with expression and proteomic data. For NAFL, we utilized 9,491 clinical cases and proton density fat fraction extracted from 36,116 liver magnetic resonance images. We identified 18 sequence variants associated with NAFL and 4 with cirrhosis, and found rare, protective, predicted loss-of-function variants in MTARC1 and GPAM, underscoring them as potential drug targets. We leveraged messenger RNA expression, splicing and predicted coding effects to identify 16 putative causal genes, of which many are implicated in lipid metabolism. We analyzed levels of 4,907 plasma proteins in 35,559 Icelanders and 1,459 proteins in 47,151 UK Biobank participants, identifying multiple proteins involved in disease pathogenesis. We show that proteomics can discriminate between NAFL and cirrhosis. The present study provides insights into the development of noninvasive evaluation of NAFL and new therapeutic options.

Shared Mechanisms between Cardiovascular Disease and NAFLD

The burden of nonalcoholic fatty liver disease (NAFLD) is rising globally. Cardiovascular disease is the leading cause of death in patients with NAFLD. Nearly half of individuals with NAFLD have coronary heart disease, and more than a third have carotid artery atherosclerosis. Individuals with NAFLD are at a substantially higher risk of fatal and nonfatal cardiovascular events. NAFLD and cardiovascular disease share multiple common disease mechanisms, such as systemic inflammation, insulin resistance, genetic risk variants, and gut microbial dysbiosis. In this review, we discuss the epidemiology of cardiovascular disease in NAFLD, and highlight common risk factors. In addition, we examine recent advances evaluating the shared disease mechanisms between NAFLD and cardiovascular disease. In conclusion, multidisciplinary collaborations are required to further our understanding of the complex relationship between NAFLD and cardiovascular disease and potentially identify therapeutic targets.

Pathological Connections between Nonalcoholic Fatty Liver Disease and Chronic Kidney Disease

Background

Nonalcoholic fatty liver disease and chronic kidney disease are major public health issues worldwide. The clinical burden of nonalcoholic fatty liver disease is not only confined to liver-related morbidity and mortality, but it also includes the burden of chronic extrahepatic complications. It is well known that liver and kidney are strictly interconnected in physiological and pathological conditions.

Summary

Mounting evidence indicates a strong association between nonalcoholic fatty liver disease and chronic kidney disease, independent of the identified cardiorenal risk factors. The presence and severity of nonalcoholic fatty liver disease are related to the developmental stage and risk of chronic kidney disease. And chronic kidney disease progression also contributes to nonalcoholic fatty liver disease development. Nonalcoholic fatty liver disease and chronic kidney disease mutually contribute to disease progression through pathological links. Shared pathogenic mechanisms also exist between nonalcoholic fatty liver disease and chronic kidney disease, including pyroptosis and ferroptosis. Additionally, the use of combined liver-kidney transplantation has increased exponentially in recent years.

Key Messages

This review focuses on the emerging pathological mechanisms linking nonalcoholic fatty liver disease and chronic kidney disease and shared pathogenic mechanisms to find novel targeted therapies and retard the progression of both disease processes.

Update on genetics and epigenetics in metabolic associated fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is becoming the most frequent chronic liver disease worldwide. Metabolic (dysfunction) associated fatty liver disease (MAFLD) is suggested to replace the nomenclature of NAFLD. For individuals with metabolic dysfunction, multiple NAFLD-related factors also contribute to the development and progression of MAFLD including genetics and epigenetics. The application of genome-wide association study (GWAS) and exome-wide association study (EWAS) uncovers single-nucleotide polymorphisms (SNPs) in MAFLD. In addition to the classic SNPs in PNPLA3, TM6SF2, and GCKR, some new SNPs have been found recently to contribute to the pathogenesis of liver steatosis. Epigenetic factors involving DNA methylation, histone modifications, non-coding RNAs regulations, and RNA methylation also play a critical role in MAFLD. DNA methylation is the most reported epigenetic modification. Developing a non-invasion biomarker to distinguish metabolic steatohepatitis (MASH) or liver fibrosis is ongoing. In this review, we summarized and discussed the latest progress in genetic and epigenetic factors of NAFLD/MAFLD, in order to provide potential clues for MAFLD treatment.

Non-alcoholic fatty liver disease is not a causal risk factor for psoriasis: A Mendelian randomization study of 108,835 individuals

Background

Psoriasis is observationally associated with a higher risk of non-alcoholic fatty liver disease (NAFLD); however, the causal relationship between the two diseases remains unclear.

Objective

We hypothesized that individuals with NAFLD or elevated liver fat content have higher risk of psoriasis and that NAFLD is a causal risk factor for psoriasis. We tested this using a Mendelian randomization approach.

Methods

We included 108,835 individuals from the Danish general population, including 1,277 individuals with psoriasis and 802 individuals with NAFLD according to ICD codes. To estimate liver fat content, a subset of the participants (N = 7,416) also had a CT scan performed. First, we tested whether a diagnosis of NAFLD or elevated liver fat content was observationally associated with risk of psoriasis. Subsequently, we used the genetic variants PNPLA3 and TM6SF2, both strongly associated with NAFLD and high liver fat content, to test whether NAFLD was causally associated with increased risk of psoriasis.

Results

Observationally, individuals with vs. without a diagnosis of NAFLD had higher risk of psoriasis with an odds ratio of 2.03 (95% confidence interval 1.28-3.21). The risk of psoriasis increased in a stepwise manner with increasing liver fat content with an odds ratio of 5.00 (2.63-9.46) in individuals in the highest quartile of liver fat content compared to individuals in the lowest quartile. In genetic analyses, PNPLA3 and TM6SF2 were both associated with increased risk of NAFLD but not with increased risk of psoriasis.

Conclusion

Observationally, a diagnosis of NAFLD or elevated liver fat content was associated with higher risk of psoriasis. However, using genetic variants as a proxy for NAFLD, we did not find evidence of a causal relationship between NAFLD and psoriasis. Thus, the observational association between NAFLD and psoriasis is presumably a result of shared confounding factors or reverse causation.

The role of PCSK9 in NAFLD/NASH and therapeutic implications of PCSK9 inhibition

INTRODUCTION

There are inconsistent findings regarding the effect of lipid-lowering agents on nonalcoholic fatty liver disease (NAFLD). Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) is an important player in cholesterol homeostasis and intracellular lipogenesis, and PCSK9 inhibitors (PCSK9-i) have been found to be efficient for pharmacological management of hyperlipidemia.

AREAS COVERED

Whether PCSK9 (itself) or PCSK9-i affects NAFLD is still disputed. To address this question, we review published preclinical and clinical studies providing evidence for the role of PCSK9 in and the effect of PCSK9-I on the development and pathogenesis of NAFLD.

EXPERT OPINION

The current evidence from a landscape of preclinical and clinical studies examining the role of PCSK9 in NAFLD shows controversial results. Preclinical studies indicate that PCSK9 associates with NAFLD and nonalcoholic steatohepatitis (NASH) progression in opposite directions. In humans, it has been concluded that the severity of hepatic steatosis affects the correlation between circulating PCSK9 and liver fat content in humans, with a possible impact of circulating PCSK9 in the early stages of NAFLD, but not in the late stages. However, data from clinical trials with PCSK9-i reassure to the safety of these agents, although real-life long-term evidence is needed.

Metabolic subtypes of patients with NAFLD exhibit distinctive cardiovascular risk profiles

BACKGROUND AND AIMS

We previously identified subsets of patients with NAFLD with different metabolic phenotypes. Here we align metabolomic signatures with cardiovascular disease (CVD) and genetic risk factors.

APPROACH AND RESULTS

We analyzed serum metabolome from 1154 individuals with biopsy-proven NAFLD, and from four mouse models of NAFLD with impaired VLDL-triglyceride (TG) secretion, and one with normal VLDL-TG secretion. We identified three metabolic subtypes: A (47%), B (27%), and C (26%). Subtype A phenocopied the metabolome of mice with impaired VLDL-TG secretion; subtype C phenocopied the metabolome of mice with normal VLDL-TG; and subtype B showed an intermediate signature. The percent of patients with NASH and fibrosis was comparable among subtypes, although subtypes B and C exhibited higher liver enzymes. Serum VLDL-TG levels and secretion rate were lower among subtype A compared with subtypes B and C. Subtype A VLDL-TG and VLDL-apolipoprotein B concentrations were independent of steatosis, whereas subtypes B and C showed an association with these parameters. Serum TG, cholesterol, VLDL, small dense LDL5,6 , and remnant lipoprotein cholesterol were lower among subtype A compared with subtypes B and C. The 10-year high risk of CVD, measured with the Framingham risk score, and the frequency of patatin-like phospholipase domain-containing protein 3 NAFLD risk allele were lower in subtype A.

CONCLUSIONS

Metabolomic signatures identify three NAFLD subgroups, independent of histological disease severity. These signatures align with known CVD and genetic risk factors, with subtype A exhibiting a lower CVD risk profile. This may account for the variation in hepatic versus cardiovascular outcomes, offering clinically relevant risk stratification.

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.

Contribution of a genetic risk score to ethnic differences in fatty liver disease

BACKGROUND AND AIMS

Susceptibility to fatty liver disease (FLD) varies among individuals and between racial/ethnic groups. Several genetic variants influence FLD risk, but whether these variants explain racial/ethnic differences in FLD prevalence is unclear. We examined the contribution of genetic risk factors to racial/ethnic-specific differences in FLD.

METHODS

A case-control study comparing FLD patients (n = 1194) and population-based controls (n = 3120) was performed. Patient characteristics, FLD risk variants (PNPLA3-rs738409 + rs6006460, TM6SF2-rs58542926, HSD17B13-rs80182459 + rs72613567, MBOAT7/TMC4-rs641738, and GCKR-rs1260326) and a multi-locus genetic risk score (GRS) were examined. The odds of FLD for individuals with different risk factor burdens were determined.

RESULTS

Hispanics and Whites were over-represented (56% vs. 38% and 36% vs. 29% respectively) and Blacks under-represented (5% vs. 23%) among FLD patients, compared to the population from which controls were selected (p < .001). Among cases and controls, Blacks had a lower and Hispanics a greater, net number of risk alleles than Whites (p < .001). GRS was associated with increased odds of FLD (OR_Q5vsQ1  = 8.72 [95% CI = 5.97-13.0], p = 9.8 × 10^-28 ), with the association being stronger in Hispanics (OR_Q5vsQ1  = 14.8 [8.3-27.1]) than Blacks (OR_Q5vsQ1  = 3.7 [1.5-11.5], P-interaction = 0.002). After accounting for GRS, the odds of FLD between Hispanics and Whites did not differ significantly (OR = 1.06 [0.87-1.28], p = .58), whereas Blacks retained much lower odds of FLD (OR = 0.21, [0.15-0.30], p < .001).

CONCLUSIONS

Blacks had a lower and Hispanics a greater FLD risk allele burden than Whites. These differences contributed to, but did not fully explain, racial/ethnic differences in FLD prevalence. Identification of additional factors protecting Blacks from FLD may provide new targets for prevention and treatment of FLD.

The impact of polymorphism in PNPLA3 and TM6SF2 genes on the susceptibility and survival of hepatitis C-related hepatocellular carcinoma

Background

Genetic variants of Patatin-like phospholipase domain-containing protein 3 (PNPLA3) and transmembrane 6 superfamily member 2 (TM6SF2) genes have been reported with the development of hepatocellular carcinoma (HCC). This study aims to explore the role of The PNPLA3 rs738409 and TM6SF2 rs58542926 single-nucleotide polymorphisms (SNPs) on the incidence and survival of HCV-induced HCC in Egyptians.

Methods and results

This case-control study included (120) HCC and (144) hepatitis C virus (HCV) patients. Baseline clinical, laboratory, tumor characteristics data, HCC recurrence, and overall survival were collected. PNPLA3 rs738409 and TM6SF2 rs58542926 polymorphism were detected by TaqMan allelic discrimination assay. We found that HCC patients were significantly older with male predominance. A significant difference between the TT genotypes of TM6SF2 frequency was observed in HCC compared with HCV patients. Moreover, the T allele of TM6SF2 distributions revealed a significant contribution to the different stages of HCC (p=0.03). Both PNPLA3 rs738409 and TM6SF2 rs58542926 variants showed a significant relation with treatment response according to the modified RECIST criteria. Age and diabetes mellitus were the independent factors associated with the development of HCC by multivariate regression analysis.

Conclusions

TM6SF2 rs58542926 polymorphism, not PNPLA3 rs738409, could be implicated in the development of HCV-induced HCC and its progression.

Myeloid TM6SF2 Deficiency Inhibits Atherosclerosis

Genetic variants in transmembrane 6 superfamily member 2 (TM6SF2), such as E167K, are associated with atherosclerotic cardiovascular disease (ASCVD). Chronic inflammation and lipid-laden macrophage foam cell formation are the central pathogeneses in the development of atherosclerosis. This study was undertaken to illustrate the biological function of TM6SF2 in macrophages and its role during atherosclerosis development. We generated myeloid cell-specific Tm6sf2 knockout mice on ApoE-deficient background (LysM Cre+/Tm6sf2fl/fl/ApoE-/-, TM6 mKO) with littermate LysM Cre-/Tm6sf2fl/fl/ApoE-/- (Control) mice as controls. Mice were fed a Western diet for 12 weeks to induce atherosclerosis. Myeloid Tm6sf2 deficiency inhibited atherosclerosis and decreased foam cells in the plaques without changing the plasma lipid profile. RNA sequencing of bone marrow-derived macrophages (BMDMs) from TM6 mKO mice demonstrated the downregulation of genes associated with inflammation, cholesterol uptake, and endoplasmic reticulum (ER) stress. TM6SF2 was upregulated by oxidized low-density lipoprotein (oxLDL) in macrophages. Silencing TM6SF2 in THP-1-derived macrophages and Tm6sf2 deficiency in BMDMs reduced inflammatory responses and ER stress and attenuated cholesterol uptake and foam cell formation, while the overexpression of TM6SF2 showed opposite effects. In conclusion, myeloid TM6SF2 deficiency inhibits atherosclerosis development and is a potential therapeutic target for the treatment of atherogenesis.

Human hepatocyte PNPLA3-148M exacerbates rapid non-alcoholic fatty liver disease development in chimeric mice

Advanced non-alcoholic fatty liver disease (NAFLD) is a rapidly emerging global health problem associated with pre-disposing genetic polymorphisms, most strikingly an isoleucine to methionine substitution in patatin-like phospholipase domain-containing protein 3 (PNPLA3-I148M). Here, we study how human hepatocytes with PNPLA3 148I and 148M variants engrafted in the livers of broadly immunodeficient chimeric mice respond to hypercaloric diets. As early as four weeks, mice developed dyslipidemia, impaired glucose tolerance, and steatosis with ballooning degeneration selectively in the human graft, followed by pericellular fibrosis after eight weeks of hypercaloric feeding. Hepatocytes with the PNPLA3-148M variant, either from a homozygous 148M donor or overexpressed in a 148I donor background, developed microvesicular and severe steatosis with frequent ballooning degeneration, resulting in more active steatohepatitis than 148I hepatocytes. We conclude that PNPLA3-148M in human hepatocytes exacerbates NAFLD. These models will facilitate mechanistic studies into human genetic variant contributions to advanced fatty liver diseases.

Mouse models of nonalcoholic fatty liver disease (NAFLD): pathomechanisms and pharmacotherapies

The prevalence of non-alcoholic fatty liver disease (NAFLD) increases year by year, and as a consequence, NAFLD has become one of the most prevalent liver diseases worldwide. Unfortunately, no pharmacotherapies for NAFLD have been approved by the United States Food and Drug Administration despite promising pre-clinical benefits; this situation highlights the urgent need to explore new therapeutic targets for NAFLD and for the discovery of effective therapeutic drugs. The mouse is one of the most commonly used models to study human disease and develop novel pharmacotherapies due to its small size, low-cost and ease in genetic engineering. Different mouse models are used to simulate various stages of NAFLD induced by dietary and/or genetic intervention. In this review, we summarize the newly described patho-mechanisms of NAFLD and review the preclinical mouse models of NAFLD (based on the method of induction) and appraises the use of these models in anti-NAFLD drug discovery. This article will provide a useful resource for researchers to select the appropriate model for research based on the research question being addressed.

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.

Non-invasive diagnosis and staging of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is considered to be the hepatic manifestation of the metabolic syndrome and is characterized by ectopic accumulation of triglycerides in the cytoplasm of hepatocytes, i.e., steatosis. NAFLD has become the most common chronic liver disease, with an estimated global prevalence of 25%. Although the majority of NAFLD patients will never experience liver-related complications, the progressive potential of NAFLD is indisputable, with 5-10% of subjects progressing to cirrhosis, end-stage liver disease, or hepatocellular carcinoma. NAFLD patients with advanced fibrosis are at the highest risk of developing cardiovascular and cirrhosis-related complications. Liver biopsy has hitherto been considered the reference method for evaluation of hepatic steatosis and fibrosis stage. Given the limitations of biopsy for widescale screening, non-invasive tests (NITs) for assessment of steatosis and fibrosis stage, including serum-based algorithms and ultrasound- and magnetic resonance-based methods, will play an increasing role in the management of NAFLD patients. This comprehensive review presents the advantages and limitations of NITs for identification of steatosis and advanced fibrosis in NAFLD. The clinical implications of using NITs to identify and manage NAFLD patients are also discussed.

The effects of seaweed supplementation consumption for improvement of liver injury in patients with non-alcoholic fatty liver disease: a systematic review

Seaweed is a food that is widely consumed by Asian people and has many health benefits, including lipid and glycemic reduction, but the effect of seaweed on non-alcoholic fatty liver disease (NAFLD) has not been widely discussed. This study aims to compare the effect of seaweed consumption on improving liver injury in NAFLD patients. The primary outcome is the change of liver enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], alkaline phosphatase [ALP], and g-glutamyl transferase [GGT]), while the secondary outcome includes body weight, waist circumstance, body mass index (BMI), lipid profile, insulin level, and insulin sensitivity and any related metabolic indicators. There was significant liver improvement in the intervention group, but some parameters from secondary outcomes showed no significant effect. Further studies with larger and heterogeneous populations are still needed to confirm the effectiveness of seaweed supplementation in NAFLD patients.

Heterogeneity of non-alcoholic fatty liver disease (NAFLD): Implication for cardiovascular risk stratification

NAFLD is currently considered the most common liver disease worldwide and mounting data support its strong link with atherosclerotic cardiovascular disease (ASCVD). This association is important as cardiovascular disease (CVD) is generally recognized as the leading cause of death in individuals with NAFLD. However, NAFLD represents a heterogeneous condition showing a wide spectrum of clinical and pathophysiological sub-phenotypes with different adverse outcomes ranging from ASCVD to liver damage progression. The contribution to NAFLD pathogenesis of different environmental, metabolic, and genetic factors underlies this heterogeneity. The more frequent phenotype of NAFLD patients is associated with metabolic dysfunctions such as obesity and insulin-resistant syndrome and this has been recently named as Metabolic Associated Fatty Liver disease (MAFLD). However, NAFLD is encountered also in subjects without insulin resistance and metabolic alterations and in whom genetic factors play a major role. It has been suggested that these individuals are at risk of liver disease progression but not of cardiovascular complications. Separating metabolic from genetic factors could be useful in disentangling the intricate relationship between NAFLD and atherosclerosis. In the present review, we aim to address the epidemic of NAFLD, its epidemiologically association with ASCVD complications and the overall mechanisms involved in the pathophysiology of atherosclerotic vascular damage in NAFLD patients. Finally, we will revise the potential role of genetics in identifying disease subtyping and predicting individualised CVD risk.

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.

Effect of cofactors on NAFLD/NASH and MAFLD. A paradigm illustrating the pathomechanics of organ dysfunction

Primary nonalcoholic fatty liver disease (NAFLD) is bi-directionally associated with the metabolic syndrome and its constitutive features ("factors": impaired glucose disposal, visceral obesity, arterial hypertension, and dyslipidemia). Secondary NAFLD occurs due to endocrinologic disturbances or other cofactors. This nosography tends to be outdated by the novel definition of metabolic associated fatty liver disease (MAFLD). Irrespective of nomenclature, this condition exhibits a remarkable pathogenic heterogeneity with unpredictable clinical outcomes which are heavily influenced by liver histology changes. Genetics and epigenetics, lifestyle habits [including diet and physical (in)activity] and immunity/infection appear to be major cofactors that modulate NAFLD/MAFLD outcomes, including organ dysfunction owing to liver cirrhosis and hepatocellular carcinoma, type 2 diabetes, chronic kidney disease, heart failure, and sarcopenia. The identification of cofactors for organ dysfunction that may help understand disease heterogeneity and reliably support inherently personalized medicine approaches is a research priority, thus paving the way for innovative treatment strategies.

The genetic interactions between non-alcoholic fatty liver disease and cardiovascular diseases

The ongoing debate on whether non-alcoholic fatty liver disease (NAFLD) is an active contributor or an innocent bystander in the development of cardiovascular disease (CVD) has sparked interests in understanding the common mediators between the two biologically distinct entities. This comprehensive review identifies and curates genetic studies of NAFLD overlapping with CVD, and describes the colinear as well as opposing correlations between genetic associations for the two diseases. Here, CVD described in relation to NAFLD are coronary artery disease, cardiomyopathy and atrial fibrillation. Unique findings of this review included certain NAFLD susceptibility genes that possessed cardioprotective properties. Moreover, the complex interactions of genetic and environmental risk factors shed light on the disparity in genetic influence on NAFLD and its incident CVD. This serves to unravel NAFLD-mediated pathways in order to reduce CVD events, and helps identify targeted treatment strategies, develop polygenic risk scores to improve risk prediction and personalise disease prevention.

Genetics of Type 2 Diabetes: Past, Present, and Future

Diabetes has reached epidemic proportions worldwide. Currently, approximately 537 million adults (20–79 years) have diabetes, and the total number of people with diabetes is continuously increasing. Diabetes includes several subtypes. About 80% of all cases of diabetes are type 2 diabetes (T2D). T2D is a polygenic disease with an inheritance ranging from 30 to 70%. Genetic and environment/lifestyle factors, especially obesity and sedentary lifestyle, increase the risk of T2D. In this review, we discuss how studies on the genetics of diabetes started, how they expanded when genome-wide association studies and exome and whole-genome sequencing became available, and the current challenges in genetic studies of diabetes. T2D is heterogeneous with respect to clinical presentation, disease course, and response to treatment, and has several subgroups which differ in pathophysiology and risk of micro- and macrovascular complications. Currently, genetic studies of T2D focus on these subgroups to find the best diagnoses and treatments for these patients according to the principles of precision medicine.