The rs2294918 E434K variant modulates patatin-like phospholipase domain-containing 3 expression and liver damage

PNPLA3(148M) is a gain-of-function mutation that promotes hepatic steatosis by inhibiting ATGL-mediated triglyceride hydrolysis

BACKGROUND & AIMS

PNPLA3(148M) (patatin-like phospholipase domain-containing protein 3) is the most impactful genetic risk factor for steatotic liver disease (SLD). A key unresolved issue is whether PNPLA3(148M) confers a loss- or gain-of-function. Here we test the hypothesis that PNPLA3 causes steatosis by sequestering ABHD5 (α/β hydrolase domain containing protein 5), the cofactor of ATGL (adipose TG lipase), thus limiting mobilization of hepatic triglyceride (TG).

METHODS

We quantified and compared the physical interactions between ABHD5 and PNPLA3/ATGL in cultured hepatocytes using NanoBiT complementation assays and immunocytochemistry. Recombinant proteins purified from human cells were used to compare TG hydrolytic activities of PNPLA3 and ATGL in the presence or absence of ABHD5. Adenoviruses and adeno-associated viruses were used to express PNPLA3 in liver-specific Atgl-/- mice and to express ABHD5 in livers of Pnpla3M/M mice, respectively.

RESULTS

ABHD5 interacted preferentially with PNPLA3 relative to ATGL in cultured hepatocytes. No differences were seen in the strength of the interactions between ABHD5 with PNPLA3(WT) and PNPLA3(148M). In contrast to prior findings, we found that PNPLA3, like ATGL, is activated by ABHD5 in in vitro assays using purified proteins. PNPLA3(148M)-associated inhibition of TG hydrolysis required that ATGL be expressed and that PNPLA3 be located on LDs. Finally, overexpression of ABHD5 reversed the hepatic steatosis in Pnpla3M/M mice.

CONCLUSIONS

These findings support the premise that PNPLA3(148M) is a gain-of-function mutation that promotes hepatic steatosis by accumulating on LDs and inhibiting ATGL-mediated lipolysis in an ABHD5-dependent manner. Our results predict that reducing, rather that increasing, PNPLA3 expression will be the best strategy to treat PNPLA3(148M)-associated SLD.

IMPACT AND IMPLICATIONS

Steatotic liver disease (SLD) is a common complex disorder associated with both environmental and genetic risk factors. PNPLA3(148M) is the most impactful genetic risk factor for SLD and yet its pathogenic mechanism remains controversial. Here we provide evidence that PNPLA3(148M) promotes triglyceride (TG) accumulation by sequestering ABHD5, thus limiting its availability to activate ATGL. Although the substitution of methionine for isoleucine reduces the TG hydrolase activity of PNPLA3, the loss of enzymatic function is not directly related to the steatotic effect of the variant. It is the resulting accumulation of PNPLA3 on LDs that confers a gain-of-function by interfering with ATGL-mediated TG hydrolysis. These findings have implications for the design of potential PNPLA3(148M)-based therapies. Reducing, rather than increasing, PNPLA3 levels is predicted to reverse steatosis in susceptible individuals.

Prevalence and Determinants of Liver Disease in Relatives of Italian Patients With Advanced MASLD

BACKGROUND & AIMS

Metabolic dysfunction associated steatotic liver disease (MASLD) has a strong genetic component. The aim of this study was to examine noninvasively the prevalence of MASLD and of advanced fibrosis in relatives of patients with advanced MASLD and the risk factors for liver involvement, with a focus on the contribution of common genetic risk variants.

METHODS

We prospectively enrolled 98 consecutive probands with advanced fibrosis and/or hepatocellular carcinoma caused by MASLD and 160 nontwin first-degree relatives noninvasively screened for MASLD and advanced fibrosis at 4 Italian centers. We evaluated common genetic determinants and polygenic risk scores of liver disease.

RESULTS

Among relatives, prevalence of MASLD was 56.8% overall, whereas advanced fibrosis was observed in 14.4%. At multivariable analysis in relatives, MASLD was associated with body mass index (odds ratio [OR], 1.31 [1.18-1.46]) and tended to be associated with diabetes (OR, 5.21 [0.97-28.10]), alcohol intake (OR, 1.32 [0.98-1.78]), and with female sex (OR, 0.54 [0.23-1.15]), whereas advanced fibrosis was associated with diabetes (OR, 3.13 [1.16-8.45]) and nearly with body mass index (OR, 1.09 [1.00-1.19]). Despite that the PNPLA3 risk variant was enriched in probands (P = .003) and overtransmitted to relatives with MASLD (P = .045), evaluation of genetic risk variants and polygenic risk scores was not useful to guide noninvasive screening of advanced fibrosis in relatives.

CONCLUSIONS

We confirmed that about 1 in 7 relatives of patients with advanced MASLD has advanced fibrosis, supporting clinical recommendations to perform family screening in this setting. Genetic risk variants contributed to liver disease within families but did not meaningfully improve fibrosis risk stratification.

Global Epidemiological Impact of PNPLA3 I148M on Liver Disease

The prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) has increased exponentially over the past three decades, in parallel with the global rise in obesity and type 2 diabetes. It is currently the most common cause of liver-related morbidity and mortality. Although obesity has been identified as a key factor in the increased prevalence of MASLD, individual differences in susceptibility are significantly influenced by genetic factors. PNPLA3 I148M (rs738409 C>G) is the variant with the greatest impact on the risk of developing progressive MASLD and likely other forms of steatotic liver disease. This variant is prevalent across the globe, with the risk allele (G) frequency exhibiting considerable variation. Here, we review the contribution of PNPLA3 I148M to global burden and regional differences in MASLD prevalence, focusing on recent evidence emerging from population-based sequencing studies and prevalence assessments. We calculated the population attributable fraction (PAF) as a means of quantifying the impact of the variant on MASLD. Furthermore, we employ quantitative trait locus (QTL) analysis to ascertain the associations between rs738409 and a range of phenotypic traits. This analysis suggests that these QTLs may underpin pleiotropic effects on extrahepatic traits. Finally, we outline potential avenues for further research and identify key areas for investigation in future studies.

LNCHC directly binds and regulates YBX1 stability to ameliorate metabolic dysfunction-associated steatotic liver disease progression

BACKGROUND AND AIMS

Metabolic dysfunction-associated steatotic liver disease (MASLD) represents the foremost cause of chronic liver disease, yet its underlying mechanisms remain elusive. Our group previously discovered a novel long non-coding RNA (lncRNA) in rats, termed lncHC and its human counterpart, LNCHC. This study aimed to explore the role of LNCHC in the progression of MASLD.

METHODS

RNA-binding proteins bound to LNCHC were searched by mass spectrometry. The target genes of LNCHC and Y-Box binding protein 1 (YBX1) were identified by RNA-seq. MASLD animal models were utilised to examine the roles of LNCHC, YBX1 and patatin-like phospholipase domain containing 3 (PNPLA3) in MASLD progression.

RESULTS

Here, we identified LNCHC as a native restrainer during MASLD development. Notably, LNCHC directly binds YBX1 and prevents protein ubiquitination. Up-regulation of YBX1 then stabilises PNPLA3 mRNA to alleviate lipid accumulation in hepatocytes. Furthermore, both cell and animal studies demonstrate that LNCHC, YBX1 and PNPLA3 function to improve hepatocyte lipid accumulation and exacerbate metabolic dysfunction-associated steatohepatitis development.

CONCLUSIONS

In summary, our findings unveil a novel LNCHC functionality in regulating YBX1 and PNPLA3 mRNA stability during MASLD development, providing new avenues in MASLD treatment.

Exploring the role of genetic variations in NAFLD: implications for disease pathogenesis and precision medicine approaches

Non-alcoholic fatty liver disease (NAFLD) is one of the leading causes of chronic liver diseases, affecting more than one-quarter of people worldwide. Hepatic steatosis can progress to more severe forms of NAFLD, including NASH and cirrhosis. It also may develop secondary diseases such as diabetes and cardiovascular disease. Genetic and environmental factors regulate NAFLD incidence and progression, making it a complex disease. The contribution of various environmental risk factors, such as type 2 diabetes, obesity, hyperlipidemia, diet, and sedentary lifestyle, to the exacerbation of liver injury is highly understood. Nevertheless, the underlying mechanisms of genetic variations in the NAFLD occurrence or its deterioration still need to be clarified. Hence, understanding the genetic susceptibility to NAFLD is essential for controlling the course of the disease. The current review discusses genetics' role in the pathological pathways of NAFLD, including lipid and glucose metabolism, insulin resistance, cellular stresses, and immune responses. Additionally, it explains the role of the genetic components in the induction and progression of NAFLD in lean individuals. Finally, it highlights the utility of genetic knowledge in precision medicine for the early diagnosis and treatment of NAFLD patients.

The variability of PNPLA3 gene as a potential marker of cold adaptation in Yakuts

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases. It has been reported that specific variants of patatin-like phospholipase domain-containing 3 (PNPLA3) gene, notably SNPs rs738409 and rs2294918 are associated with high risks of liver disease. PNPLA3 rs738409 polymorphism is the main determinant of fatty liver and affects development and progression of NAFLD. rs2294918 is another SNP localised in PNPLA3 gene, it is associated with reduced expression of the PNPLA3 protein, lowering the effect of the rs738409:G variant on predisposition to steatosis and liver damage. The frequencies of alleles, genotypes, haplotypes and diplotypes (combinations of genotypes at two loci) of polymorphic variants of the PNPLA3 gene (rs2294918 and rs738409) were studied in the cohort of Yakuts (n = 150) living in the Republic of Sakha (Yakutia). Genotyping of PNPLA3 (rs738409 and rs2294918) was performed by PCR-PDRF method. The single nucleotide polymorphism rs738409 (I148M) of the PNPLA3 gene in the Yakut population is characterised by a high frequency of the risk allele G (72%). Analysis of the distribution frequency of the rs2294918 polymorphism genotypes showed that the allele G was predominant in 89.3% of individuals of the studied group of Yakuts. In this study, we identified two major diplotypes [GG][GG] and [CG][GG]. The high frequency of the mutant rs738409: G variant in Yakuts may be an adaptation of the organism to low temperatures. The study of the adiponutringene may be an important key to understanding the mechanisms of adaptation to low temperatures and metabolic processes in the indigenous population of the North.

Therapeutic opportunities for the treatment of NASH with genetically validated targets

The identification of genetic variants associated with fatty liver disease (FLD) from genome-wide association studies started in 2008 when single nucleotide polymorphisms in PNPLA3, the gene encoding patatin-like phospholipase domain-containing 3, were found to be associated with altered hepatic fat content. Since then, several genetic variants associated with protection from, or an increased risk of, FLD have been identified. The identification of these variants has provided insight into the metabolic pathways that cause FLD and enabled the identification of potential therapeutic targets. In this mini-review, we will examine the therapeutic opportunities derived from genetically validated targets in FLD, including oligonucleotide-based therapies targeting PNPLA3 and HSD17B13 that are currently being evaluated in clinical trials for the treatment of NASH (non-alcoholic steatohepatitis).

Nonalcoholic Fatty Liver Disease and Chronic Kidney Disease Cross Talk

Nonalcoholic fatty liver disease is a multisystem condition with effects beyond the liver. The identification of chronic kidney disease as an independent mediator of nonalcoholic fatty liver disease or associated entity with shared cardiometabolic risk factors remains controversial and continues to draw scientific interest. With increasing prevalence of nonalcoholic fatty liver disease and lack of Food and Drug Administration approved therapies, these shared cardiometabolic risk factors have drawn significant attention. In this article, we review shared pathophysiological mechanisms between nonalcoholic fatty liver disease and chronic kidney disease along with current treatment strategies that might be useful for both disease processes.

Genomic analyses of hair from Ludwig van Beethoven

Ludwig van Beethoven (1770-1827) remains among the most influential and popular classical music composers. Health problems significantly impacted his career as a composer and pianist, including progressive hearing loss, recurring gastrointestinal complaints, and liver disease. In 1802, Beethoven requested that following his death, his disease be described and made public. Medical biographers have since proposed numerous hypotheses, including many substantially heritable conditions. Here we attempt a genomic analysis of Beethoven in order to elucidate potential underlying genetic and infectious causes of his illnesses. We incorporated improvements in ancient DNA methods into existing protocols for ancient hair samples, enabling the sequencing of high-coverage genomes from small quantities of historical hair. We analyzed eight independently sourced locks of hair attributed to Beethoven, five of which originated from a single European male. We deemed these matching samples to be almost certainly authentic and sequenced Beethoven's genome to 24-fold genomic coverage. Although we could not identify a genetic explanation for Beethoven's hearing disorder or gastrointestinal problems, we found that Beethoven had a genetic predisposition for liver disease. Metagenomic analyses revealed furthermore that Beethoven had a hepatitis B infection during at least the months prior to his death. Together with the genetic predisposition and his broadly accepted alcohol consumption, these present plausible explanations for Beethoven's severe liver disease, which culminated in his death. Unexpectedly, an analysis of Y chromosomes sequenced from five living members of the Van Beethoven patrilineage revealed the occurrence of an extra-pair paternity event in Ludwig van Beethoven's patrilineal ancestry.

Association between Serum Uric Acid and Liver Enzymes in Adults Aged 20 Years and Older in the United States: NHANES 2005-2012

Although the relationship between serum uric acid (SUA) and nonalcoholic fatty liver disease has been widely reported, the relationship between SUA and liver enzymes has rarely been reported. The purpose of this study was to evaluate the association of SUA levels with alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in populations aged 20 years and older in the United States. We analyzed 7165 individuals aged 20 years and older from the National Health and Nutrition Examination Survey (NHANES) in the United States. Weighted multiple linear regression models were used to analyze the relationship between SUA and ALT and AST. A generalized additive model and a smooth curve fitting were used to observe the linear relationship. SUA was positively correlated with ALT and AST. In addition, the overall increasing trend of ALT and SUA was observed across the SUA quartile groups. In the stratified analysis by sex and race, the SUA levels in male, female, Mexican American, and Non-Hispanic White individuals, and those of another race, were positively correlated with ALT and AST. However, the SUA levels in Non-Hispanic Black individuals had a nonlinear relationship with ALT and AST. In individuals aged 20 years and older in the United States (excluding Non-Hispanic Black individuals), SUA levels were positively associated with ALT and AST. Therefore, with a rise in SUA levels, liver function should be monitored or intervened with in people aged 20 years and older in the United States.

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.

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.

A case of NASH with genetic predisposition successfully treated with an SGLT2 inhibitor: a possible involvement of mitochondrial dysfunction

Summary

In this study, we herein describe a 47-year-old Japanese woman who manifested inheritable non-alcoholic steatohepatitis (NASH) and severe dyslipidemia. Interestingly, her NASH progression was ameliorated by treatment with a sodium-glucose co-transporter 2 (SGLT2) inhibitor. This inheritability prompted us to comprehensively decode her genomic information using whole-exome sequencing. We found the well-established I148M mutation in PNPLA3 as well as mutations in LGALS3 and PEMT for her NASH. Mutations in GCKR may contribute to both NASH and dyslipidemia. We further mined gene mutations potentially responsible for her manifestations that led to the identification of a novel M188fs mutation in MUL1 that may be causally associated with her mitochondrial dysfunction. Our case may provide some clues to better understand this spectrum of disease as well as the rationale for selecting medications.

Learning points

While the PNPLA3 I148M mutation is well-established, accumulation of other mutations may accelerate susceptibility to non-alcoholic steatohepatitis (NASH). NASH and dyslipidemia may be intertwined biochemically and genetically through several key genes. SGLT2 inhibitors emerge as promising treatment for NASH albeit with interindividual variation in efficacy. Genetic background may explain the mechanisms behind the variation. A novel dysfunctional mutation in MUL1 may lead to metabolic inflexibilities through impaired mitochondrial dynamics and function.

En masse organoid phenotyping informs metabolic-associated genetic susceptibility to NASH

Genotype-phenotype associations for common diseases are often compounded by pleiotropy and metabolic state. Here, we devised a pooled human organoid-panel of steatohepatitis to investigate the impact of metabolic status on genotype-phenotype association. En masse population-based phenotypic analysis under insulin insensitive conditions predicted key non-alcoholic steatohepatitis (NASH)-genetic factors including the glucokinase regulatory protein (GCKR)-rs1260326:C>T. Analysis of NASH clinical cohorts revealed that GCKR-rs1260326-T allele elevates disease severity only under diabetic state but protects from fibrosis under non-diabetic states. Transcriptomic, metabolomic, and pharmacological analyses indicate significant mitochondrial dysfunction incurred by GCKR-rs1260326, which was not reversed with metformin. Uncoupling oxidative mechanisms mitigated mitochondrial dysfunction and permitted adaptation to increased fatty acid supply while protecting against oxidant stress, forming a basis for future therapeutic approaches for diabetic NASH. Thus, "in-a-dish" genotype-phenotype association strategies disentangle the opposing roles of metabolic-associated gene variant functions and offer a rich mechanistic, diagnostic, and therapeutic inference toolbox toward precision hepatology. VIDEO ABSTRACT.

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.

Hepatic patatin-like phospholipase domain-containing 3 levels are increased in I148M risk allele carriers and correlate with NAFLD in humans

In nonalcoholic fatty liver disease (NAFLD) the patatin‐like phospholipase domain‐containing 3 (PNPLA3) rs738409 variant is a contributor. In mice, the Pnpla3 148M variant accumulates on lipid droplets and probably leads to sequestration of a lipase cofactor leading to impaired mobilization of triglycerides. To advance our understanding of the localization and abundance of PNPLA3 protein in humans, we used liver biopsies from patients with NAFLD to investigate the link to NAFLD and the PNPLA3 148M genotype. We experimentally qualified an antibody against human PNPLA3. Hepatic PNPLA3 protein fractional area and localization were determined by immunohistochemistry in biopsies from a well‐characterized NAFLD cohort of 67 patients. Potential differences in hepatic PNPLA3 protein levels among patients related to degree of steatosis, lobular inflammation, ballooning, and fibrosis, and PNPLA3 I148M gene variants were assessed. Immunohistochemistry staining in biopsies from patients with NAFLD showed that hepatic PNPLA3 protein was predominantly localized to the membranes of small and large lipid droplets in hepatocytes. PNPLA3 protein levels correlated strongly with steatosis grade (p = 0.000027) and were also significantly higher in patients with lobular inflammation (p = 0.009), ballooning (p = 0.022), and significant fibrosis (stage 2–4, p = 0.014). In addition, PNPLA3 levels were higher in PNPLA3 rs738409 148M (CG, GG) risk allele carriers compared to 148I (CC) nonrisk allele carriers (p = 0.0029). Conclusion: PNPLA3 protein levels were associated with increased hepatic lipid content and disease severity in patients with NAFLD and were higher in PNPLA3 rs738409 (148M) risk allele carriers. Our hypothesis that increased hepatic levels of PNPLA3 may be part of the pathophysiological mechanism of NAFLD is supported.

The Role of Insulin Resistance in Fueling NAFLD Pathogenesis: From Molecular Mechanisms to Clinical Implications

Non-alcoholic fatty liver disease (NAFLD) represents a predominant hepatopathy that is rapidly becoming the most common cause of hepatocellular carcinoma worldwide. The close association with metabolic syndrome’s extrahepatic components has suggested the nature of the systemic metabolic-related disorder based on the interplay between genetic, nutritional, and environmental factors, creating a complex network of yet-unclarified pathogenetic mechanisms in which the role of insulin resistance (IR) could be crucial. This review detailed the clinical and pathogenetic evidence involved in the NAFLD–IR relationship, presenting both the classic and more innovative models. In particular, we focused on the reciprocal effects of IR, oxidative stress, and systemic inflammation on insulin-sensitivity disruption in critical regions such as the hepatic and the adipose tissue, while considering the impact of genetics/epigenetics on the regulation of IR mechanisms as well as nutrients on specific insulin-related gene expression (nutrigenetics and nutrigenomics). In addition, we discussed the emerging capability of the gut microbiota to interfere with physiological signaling of the hormonal pathways responsible for maintaining metabolic homeostasis and by inducing an abnormal activation of the immune system. The translation of these novel findings into clinical practice could promote the expansion of accurate diagnostic/prognostic stratification tools and tailored pharmacological approaches.

The association between rs1260326 with the risk of NAFLD and the mediation effect of triglyceride on NAFLD in the elderly Chinese Han population

Background: Accumulated studies have pointed out the striking association between variants in or near APOC3, GCKR, PNPLA3, and nonalcoholic fatty liver disease (NAFLD) at various ages from multiple ethnic groups. This association remained unclear in the Chinese Han elderly population, and whether this relationship correlated to any clinical parameters was also unclear.

Objectives: This study aims to decipher the complex relevance between gene polymorphisms, clinical parameters, and NAFLD by association study and mediation analysis.

Methods: Eight SNPs (rs2854116, rs2854117, rs780093, rs780094, rs1260362, rs738409, rs2294918, and rs2281135) within APOC3, GCKR, and PNPLA3 were genotyped using the MassARRAY® platform in a large Chinese Han sample comprising of 733 elderly NAFLD patients and 824 age- and ethnic-matched controls. Association and mediation analysis were employed by R.

Results: The genotypic frequencies of rs1260326 and rs780094 were significantly different between NAFLD and control (rs1260326: P=0.004, P_corr=0.020, OR [95%CI]= 0.69 [0.54-0.89]; rs780094: P=0.005, P_corr=0.025, OR [95%CI]= 0.70 [0.55-0.90]). Particularly, an increased triglyceride level was observed in carriers of rs1260326 T allele (1.94±1.19 mmol/L) compared with non-carriers (1.73±1.05 mmol/L).no significant results were observed in rs780094. Notably, triglyceride levels had considerably indirect impacts on association between NAFLD and rs1260326 (β =0.01, 95% CI: 0.01–0.02), indicating that 12.7% of the association of NAFLD with rs1260326 was mediated by triglyceride levels.

Conclusions: Our results identified a prominent relationship between GCKR rs1260326 and NAFLD, and highlighted the mediated effect of triglyceride levels on the that association in the Chinese Han elderly.

Hepatocellular carcinoma in patients with metabolic dysfunction-associated fatty liver disease: Can we stratify at-risk populations?

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a new nomenclature recently proposed by a panel of international experts so that the entity is defined based on positive criteria and linked to pathogenesis, replacing the traditional non-alcoholic fatty liver disease (NAFLD), a definition based on exclusion criteria. NAFLD/MAFLD is currently the most common form of chronic liver disease worldwide and is a growing risk factor for development of hepatocellular carcinoma (HCC). It is estimated than 25% of the global population have NAFLD and is projected to increase in the next years. Major Scientific Societies agree that surveillance for HCC should be indicated in patients with NAFLD/ MAFLD and cirrhosis but differ in non-cirrhotic patients (including those with advanced fibrosis). Several studies have shown that the annual incidence rate of HCC in NAFLD-cirrhosis is greater than 1%, thus surveillance for HCC is cost-effective. Risk factors that increase HCC incidence in these patients are male gender, older age, presence of diabetes and any degree of alcohol consumption. In non-cirrhotic patients, the incidence of HCC is much lower and variable, being a great challenge to stratify the risk of HCC in this group. Furthermore, large epidemiological studies based on the general population have shown that diabetes and obesity significantly increase risk of HCC. Some genetic variants may also play a role modifying the HCC occurrence among patients with NAFLD. The purpose of this review is to discuss the epidemiology, clinical and genetic risk factors that may influence the risk of HCC in NAFLD/MAFLD patients and propose screening strategy to translate into better patient care.

Waitlist mortality and transplant free survival in Hispanic patients listed for liver transplant using the UNOS database

INTRODUCTION AND OBJECTIVES

After the implementation of "Share 35", several concerns arose such as the potential to increase travel distance, costs, and decreased liver availability. These elements could have a negative impact on waitlist outcomes among ethnic minorities. We aimed to determine waitlist survival after the implementation of the Share 35 policy in non-Hispanic white and Hispanic patients.

MATERIALS AND METHODS

We identified non-Hispanic whites and Hispanics who were listed for liver transplantation from June 18th, 2013 to June 18, 2018. We excluded pediatric patients, patients with acute hepatic necrosis, re-transplants, multiorgan transplant, living donor, and exception cases. The primary outcome was death or removal from the waitlist due to clinical deterioration. We used competing risk analysis to compare waitlist survival between the two groups.

RESULTS

There were 23,340 non-Hispanic whites and 4938 Hispanics listed for transplant. On competing risk analysis, Hispanic patients had a higher risk of being removed from the waitlist for death or clinical deterioration compared to their counterpart (SHR 1.23, 95% CI 1.13-1.34; P < 0.001).

CONCLUSION

After the implementation of Share 35, disparities are still present and continue to negatively impact outcomes in minority populations especially Hispanic patients.

PNPLA3 as a therapeutic target for fatty liver disease: the evidence to date

INTRODUCTION

An interaction between metabolic triggers and inherited predisposition underpins the development and progression of non alcoholic fatty liver disease (NAFLD) and fatty liver disease in general. Among the specific NAFLD risk variants, PNPLA3 rs738409 C>G, encoding for the p.I148M protein variant, accounts for the largest fraction of liver disease heritability and is being intensively scrutinized. It promotes intrahepatic lipid accumulation and is associated with lipotoxicity and the more severe phenotypes, including fibrosis and carcinogenesis. Therefore, PNPLA3 appears as an appealing therapeutic target to counter NAFLD progression.

AREAS COVERED

The scope of this review is to briefly describe the PNPLA3 gene and protein function before discussing therapeutic approaches for fatty liver aiming at this target. Literature review was carried out searching through PubMed and clinicaltrials.gov website and focusing on the most recent works and reviews.

EXPERT OPINION

The main therapeutic strategies under development for NAFLD have shown variable efficacy and side-effects likely due to disease heterogeneity and lack of engagement of the main pathogenic drivers of liver disease. To overcome these limitations, new strategies are becoming available for targeting PNPLA3 p.I148M, responsible for a large fraction of disease susceptibility.

Metabolic Associated Fatty Liver Disease in Children-From Atomistic to Holistic

Non-alcoholic fatty liver disease has become the most common chronic liver disease in children due to the alarmingly increasing incidence of pediatric obesity. It is well-documented that MAFLD prevalence is directly related to an incremental increase in BMI. The multiple hits theory was designed for providing insights regarding the pathogenesis of steatohepatitis and fibrosis in MAFLD. Recent evidence suggested that the microbiome is a crucial contributor in the pathogenesis of MAFLD. Aside from obesity, the most common risk factors for pediatric MAFLD include male gender, low-birth weight, family history of obesity, MAFLD, insulin resistance, type 2 diabetes mellitus, obstructive sleep apnea, and polycystic ovarium syndrome. Usually, pediatric patients with MAFLD have nonspecific symptoms consisting of fatigue, malaise, or diffuse abdominal pain. A wide spectrum of biomarkers was proposed for the diagnosis of MAFLD and NASH, as well as for quantifying the degree of fibrosis, but liver biopsy remains the key diagnostic and staging tool. Nevertheless, elastography-based methods present promising results in this age group as potential non-invasive replacers for liver biopsy. Despite the lack of current guidelines regarding MAFLD treatment in children, lifestyle intervention was proven to be crucial in the management of these patients.

Genetics Is of the Essence to Face NAFLD

Nonalcoholic fatty liver disease (NAFLD) is the commonest cause of chronic liver disease worldwide. It is closely related to obesity, insulin resistance (IR) and dyslipidemia so much so it is considered the hepatic manifestation of the Metabolic Syndrome. The NAFLD spectrum extends from simple steatosis to nonalcoholic steatohepatitis (NASH), a clinical condition which may progress up to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). NAFLD is a complex disease whose pathogenesis is shaped by both environmental and genetic factors. In the last two decades, several heritable modifications in genes influencing hepatic lipid remodeling, and mitochondrial oxidative status have been emerged as predictors of progressive hepatic damage. Among them, the patatin-like phospholipase domain-containing 3 (PNPLA3) p.I148M, the Transmembrane 6 superfamily member 2 (TM6SF2) p.E167K and the rs641738 membrane bound-o-acyltransferase domain-containing 7 (MBOAT7) polymorphisms are considered the most robust modifiers of NAFLD. However, a forefront frontier in the study of NAFLD heritability is to postulate score-based strategy, building polygenic risk scores (PRS), which aggregate the most relevant genetic determinants of NAFLD and biochemical parameters, with the purpose to foresee patients with greater risk of severe NAFLD, guaranteeing the most highly predictive value, the best diagnostic accuracy and the more precise individualized therapy.

Nonalcoholic fatty liver disease (NAFLD) from pathogenesis to treatment concepts in humans

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) comprises hepatic alterations with increased lipid accumulation (steatosis) without or with inflammation (nonalcoholic steatohepatitis, NASH) and/or fibrosis in the absence of other causes of liver disease. NAFLD is developing as a burgeoning health challenge, mainly due to the worldwide obesity and diabetes epidemics.

SCOPE OF REVIEW

This review summarizes the knowledge on the pathogenesis underlying NAFLD by focusing on studies in humans and on hypercaloric nutrition, including effects of saturated fat and fructose, as well as adipose tissue dysfunction, leading to hepatic lipotoxicity, abnormal mitochondrial function, and oxidative stress, and highlights intestinal dysbiosis. These mechanisms are discussed in the context of current treatments targeting metabolic pathways and the results of related clinical trials.

MAJOR CONCLUSIONS

Recent studies have provided evidence that certain conditions, for example, the severe insulin-resistant diabetes (SIRD) subgroup (cluster) and the presence of an increasing number of gene variants, seem to predispose for excessive risk of NAFLD and its accelerated progression. Recent clinical trials have been frequently unsuccessful in halting or preventing NAFLD progression, perhaps partly due to including unselected cohorts in later stages of NAFLD. On the basis of this literature review, this study proposed screening in individuals with the highest genetic or acquired risk of disease progression, for example, the SIRD subgroup, and developing treatment concepts targeting the earliest pathophysiolgical alterations, namely, adipocyte dysfunction and insulin resistance.

Non-Alcoholic Fatty Liver Disease: Metabolic, Genetic, Epigenetic and Environmental Risk Factors

Non-alcoholic fatty liver disease (NAFLD) is one of the most frequent causes of chronic liver disease in the Western world, probably due to the growing prevalence of obesity, metabolic diseases, and exposure to some environmental agents. In certain patients, simple hepatic steatosis can progress to non-alcoholic steatohepatitis (NASH), which can sometimes lead to liver cirrhosis and its complications including hepatocellular carcinoma. Understanding the mechanisms that cause the progression of NAFLD to NASH is crucial to be able to control the advancement of the disease. The main hypothesis considers that it is due to multiple factors that act together on genetically predisposed subjects to suffer from NAFLD including insulin resistance, nutritional factors, gut microbiota, and genetic and epigenetic factors. In this article, we will discuss the epidemiology of NAFLD, and we overview several topics that influence the development of the disease from simple steatosis to liver cirrhosis and its possible complications.

Genetic predisposition similarities between NASH and ASH: Identification of new therapeutic targets

Fatty liver disease can be triggered by a combination of excess alcohol, dysmetabolism and other environmental cues, which can lead to steatohepatitis and can evolve to acute/chronic liver failure and hepatocellular carcinoma, especially in the presence of shared inherited determinants. The recent identification of the genetic causes of steatohepatitis is revealing new avenues for more effective risk stratification. Discovery of the mechanisms underpinning the detrimental effect of causal mutations has led to some breakthroughs in the comprehension of the pathophysiology of steatohepatitis. Thanks to this approach, hepatocellular fat accumulation, altered lipid droplet remodelling and lipotoxicity have now taken centre stage, while the role of adiposity and gut-liver axis alterations have been independently validated. This process could ignite a virtuous research cycle that, starting from human genomics, through omics approaches, molecular genetics and disease models, may lead to the development of new therapeutics targeted to patients at higher risk. Herein, we also review how this knowledge has been applied to: a) the study of the main PNPLA3 I148M risk variant, up to the stage of the first in-human therapeutic trials; b) highlight a role of MBOAT7 downregulation and lysophosphatidyl-inositol in steatohepatitis; c) identify IL-32 as a candidate mediator linking lipotoxicity to inflammation and liver disease. Although this precision medicine drug discovery pipeline is mainly being applied to non-alcoholic steatohepatitis, there is hope that successful products could be repurposed to treat alcohol-related liver disease as well.

RORα regulates hepatic lipolysis by inducing transcriptional expression of PNPLA3 in mice

Nonalcoholic fatty liver diseases (NAFLDs) are characterized by excessive triacylglycerol (TAG) accumulation in the liver which contributes to hepatocyte dysfunction, inflammation, and fibrosis. Patatin-like phospholipase domain-containing 3 (PNPLA3; also known as adiponutrin) has emerged as an important enzyme leading to hepatic TAG hydrolysis. Because the I148M substitution in the PNPLA3 gene markedly reduces hepatic TAG hydrolase activity, this genetic variation is strongly associated with increased hepatic TAG in the full spectrum of NAFLDs. The Retinoic acid-related orphan receptor α (RORα) regulates various target genes related to lipid metabolism. Here, we investigated the role of RORα on PNPLA3-mediated hepatic lipid hydrolysis. With blockade of lipid esterification and β-oxidation, RORα enhanced TAG hydrolysis, resulting in increased free glycerol levels. We found a putative RORα response element on the upstream of PNPLA3 gene that was activated by RORα. Furthermore, the inhibitory action of cJUN on the RORα/PNPLA3 axis was enhanced under lipid stress and contributed to hepatic lipid accumulation. In summary, we showed for the first time that RORα activates the transcription of PNPLA3, which suggests that RORα and its ligands represent potential precision therapeutic approaches for NAFLDs.

Mechanisms of Non-Alcoholic Fatty Liver Disease in the Metabolic Syndrome. A Narrative Review

Non-alcoholic fatty liver disease (NAFLD) and metabolic syndrome (MS) are two different entities sharing common clinical and physio-pathological features, with insulin resistance (IR) as the most relevant. Large evidence leads to consider it as a risk factor for cardiovascular disease, regardless of age, sex, smoking habit, cholesterolemia, and other elements of MS. Therapeutic strategies remain still unclear, but lifestyle modifications (diet, physical exercise, and weight loss) determine an improvement in IR, MS, and both clinical and histologic liver picture. NAFLD and IR are bidirectionally correlated and, consequently, the development of pre-diabetes and diabetes is the most direct consequence at the extrahepatic level. In turn, type 2 diabetes is a well-known risk factor for multiorgan damage, including an involvement of cardiovascular system, kidney and peripheral nervous system. The increased MS incidence worldwide, above all due to changes in diet and lifestyle, is associated with an equally significant increase in NAFLD, with a subsequent rise in both morbidity and mortality due to both metabolic, hepatic and cardiovascular diseases. Therefore, the slowdown in the increase of the "bad company" constituted by MS and NAFLD, with all the consequent direct and indirect costs, represents one of the main challenges for the National Health Systems.

Genetic Contribution to Non-alcoholic Fatty Liver Disease and Prognostic Implications

PURPOSE OF REVIEW

Non-alcoholic fatty liver disease (NAFLD) is a major and increasing health burden, with the potential to overwhelm hepatology services. However, only a minority of patients develop advanced liver disease. The challenge is early identification of patients at risk of progression. This review aims to summarize current knowledge on the genetic predisposition to NAFLD, and its implications for prognostication and risk stratification.

RECENT FINDINGS

PNPLA3-I148M is the most robustly associated genetic variant with NAFLD. Recently, variants in TM6SF2, MBOAT7, GCKR and HSD17B13 have also been implicated. NAFLD is a complex disease, and any one genetic variant alone is insufficient for risk stratification, but combining multiple genetic variants with other parameters is a promising strategy. It is anticipated that, in the near future, analysis of data from large-scale prospective cohorts will reveal NAFLD subtypes and enable the development of prognostic models. This will facilitate risk stratification of patients, enabling optimisation of resources to effectively manage the NAFLD epidemic.

Genetic and epigenetic disease modifiers: non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD)

Inter-individual and inter-ethnic differences and difference in the severity and progression of liver disease among patients with non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) suggests the involvement of genetic and epigenetic factors in their pathogenesis. This article reviews the genetic and epigenetic modifiers in patients with NAFLD and ALD. Evidence regarding the genetic and epigenetic disease modifiers of NAFLD and ALD was reviewed by searching the available literature. Both genome wide association studies (GWAS) and candidate gene studies pertaining to the pathogenesis in both diseases were included. Clinical implications of the available information are also discussed. Several studies have shown association of both NAFLD and ALD with I148M PNPLA3 variant. In addition to the higher prevalence of hepatic steatosis, the I148M PNPLA3 variant is also associated with severity of liver disease and risk of hepatocellular carcinoma (HCC). TM6SF2 is the other genetic variant shown to be significantly associated with hepatic steatosis and cirrhosis in patients with NAFLD and ALD. The Membrane bound O-acyltransferase domain-containing 7 (MBOAT7) genetic variant is also associated with both NAFLD and ALD. In addition to these mutations, several variants related to the genes involved in glucose metabolism, insulin resistance, lipid metabolism, oxidative stress, inflammatory pathways, fibrosis have also been shown to be the disease modifiers in patients with NAFLD and ALD. Epigenetics involving several micro RNAs and DNA methylation could also modify the disease course in NAFLD and ALD. In conclusion the available literature suggests that genetics and epigenetics are involved in the pathogenesis of NAFLD and ALD which may affect the disease prevalence, severity and response to treatment in these patients.

Gene-Environmental Interactions as Metabolic Drivers of Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) has emerged as a leading cause of chronic liver disease worldwide in the past few decades as a consequence of the global obesity epidemic and is associated with significant morbidity and mortality. NAFLD is closely associated with components of the metabolic syndrome, type 2 diabetes mellitus and cardiovascular disease, suggesting a plausible metabolic mechanistic basis. Metabolic inflexibility is considered a nidus for NAFLD pathogenesis, causing lipotoxicity, mitochondrial dysfunction and cellular stress leading to inflammation, apoptosis and fibrogenesis, thus mediating disease progression into nonalcoholic steatohepatitis (NASH) and ultimately cirrhosis. In this review, we describe they key metabolic drivers that contribute to development of NAFLD and NASH, and we explain how NASH is a metabolic disease. Understanding the metabolic basis of NASH is crucial for the prevention and treatment of this disease.

Discovery and Targeting of the Signaling Controls of PNPLA3 to Effectively Reduce Transcription, Expression, and Function in Pre-Clinical NAFLD/NASH Settings

Non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) are emerging worldwide epidemics, projected to become the leading cause of liver transplants. The strongest genetic risk factor for NAFLD/NASH susceptibility and progression is a single-nucleotide polymorphism (SNP) in the patatin-like phospholipase domain-containing 3 gene (PNPLA3), rs738409, encoding the missense mutation I148M. This aminoacidic substitution interferes with the normal remodeling of lipid droplets in hepatocytes. It is also thought to play a key role in promoting liver fibrosis by inhibiting the release of retinol from hepatic stellate cells. Reducing PNPLA3 levels in individuals homozygous for 148M may be an effective treatment for the entire spectrum of NAFLD, based on gene dosage analysis in the human population, as well as the protective effect of another naturally occurring SNP (rs2294918) in PNPLA3 which, when co-inherited, reduces PNPLA3 mRNA levels to 50% and counteracts disease risk. By screening a clinical compound library targeting specific signaling pathways active in primary human hepatocytes, we identified momelotinib, a drug evaluated in clinical trials to treat myelofibrosis, as a potent down-regulator of PNPLA3 expression, across all genotypes. We found that momelotinib treatment yielded >80% reduction in PNPLA3 mRNA in human primary hepatocytes and stellate cells, as well as in vivo via acute and chronic treatment of WT mice. Using a human multilineage 3D spheroid model of NASH homozygous for the PNPLA3 mutant protein, we additionally show that it decreases PNPLA3 mRNA as well as intracellular lipid content. Furthermore, we show that the effects on PNPLA3 coincide with changes in chromatin accessibility within regulatory regions of the PNPLA3 locus, consistent with inhibition occurring at the level of transcription. In addition to its primary reported targets, the JAK kinases, momelotinib inhibits several non-JAK kinases, including ACVR1. Using a combination of targeted siRNA knockdowns and signaling pathway perturbations, we show that momelotinib reduces the expression of the PNPLA3 gene largely through the inhibition of BMP signaling rather than the JAK/STAT pathway. Overall, our work identified momelotinib as a potential NASH therapeutic and uncovered previously unrecognized connections between signaling pathways and PNPLA3. These pathways may be exploited by drug modalities to “tune down” the level of gene expression, and therefore offer a potential therapeutic benefit to a high at-risk subset of NAFLD/NASH patients.

Nonalcoholic fatty liver disease and type 2 diabetes: pathophysiological mechanisms shared between the two faces of the same coin

The pathophysiological mechanisms underlying the close relationship between nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) are multiple, complex and only partially known. The purpose of this paper was to review the current knowledge of these mechanisms in a unified manner. Subjects with NAFLD and T2DM have established insulin resistance (IR), which exacerbates the two comorbidities. IR worsens NAFLD by increasing the accumulation of free fatty acids (FFAs) in the liver. This occurs due to an increase in the influx of FFAs from peripheral adipose tissue by the activation of hormone-sensitive lipase. In addition, there is de novo increased lipogenesis, a transcription factor, the sterols regulatory element-binding transcription factor 1c (SREBP-1c), which activates the expression of several genes strongly promotes lipogenesis by the liver and facilitate storage of triglycerides. Lipids accumulation in the liver induces a chronic stress in the endoplasmic reticulum of the hepatocytes. Genome-wide association studies have identified genetic variants associated with NAFLD severity, but unrelated to IR. In particular, the alteration of patatin-like phospholipase domain-containing protein 3 contributes to the susceptibility to NAFLD. Furthermore, the lipotoxicity of ceramides and diacylglycerol, well known in T2DM, triggers a chronic inflammatory process favoring the progression from hepatic steatosis to steatohepatitis. Reactive oxygen species produced by mitochondrial dysfunction trigger both liver inflammation and beta-cells damage, promoting the progression of both NAFLD and T2DM. The close association between NAFLD and T2DM is bidirectional, as T2DM may trigger both NAFLD onset and its progression, but NAFLD itself may contribute to the development of IR and T2DM. Future studies on the mechanisms will have to deepen the knowledge of the interaction between the two pathologies and should allow the identification of new therapeutic targets for the treatment of NAFLD, currently substantially absent.

[Non-alcoholic fatty liver disease and type 2 diabetes mellitus: issues of the liver fibrosis diagnostics]

AIM

To evaluate the frequency of liver fibrosis progression to stage 34 among patients with non-alcoholic fatty liver disease (NAFLD), type 2 diabetes and obesity, to identify predictors of severe liver fibrosis, to propose an algorithm for diagnosing fibrosis in this category of patients.

MATERIALS AND METHODS

160 patients with NAFLD, type 2 diabetes mellitus (DM) and obesity and 50 patients with NAFLD without diabetes were comprehensively examined. Patients underwent laboratory examination (clinical blood test, biochemical analysis, immunoglobulins G, M, autoantibody assay, coagulogram), liver ultrasound. All patients underwent determination of the liver fibrosis stage by two methods: the serological test FibroMax and indirect ultrasound elastometry of the liver; 40 patients underwent a liver biopsy. Statistical data processing was performed using the programming language and statistical calculations R: we used correlation analysis, multiple logistic regression method, one-way analysis of variance, multi-factor analysis, the Kruskal-Wallis method, and comparison of the number of patients using the Fisher test.

RESULTS

DM is a risk factor for the liver fibrosis progression in patients with NAFLD. Significant markers of severe fibrosis in this category of patients are increased levels of GGTP, haptoglobin and alpha-2-macroglobulin, lower platelet and prothrombin levels. Obesity and isolated steatosis without steatohepatitis are not markers of severe liver fibrosis at present, but obesity can be considered a risk factor for the progression of fibrosis in the future.

CONCLUSION

All patients with NAFLD in combination with diabetes need screening to detect advanced liver fibrosis: it is advisable to determine the levels of GGTP, haptoglobin and alpha-2-macroglobulin.

Disruption of the ERLIN-TM6SF2-APOB complex destabilizes APOB and contributes to non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disorder characterized by excess lipid accumulation in the liver without significant consumption of alcohol. The transmembrane 6 superfamily member 2 (TM6SF2) E167K missense variant strongly associates with NAFLD in humans. The E167K mutation destabilizes TM6SF2, resulting in hepatic lipid accumulation and low serum lipid levels. However, the molecular mechanism by which TM6SF2 regulates lipid metabolism remains unclear. By using tandem affinity purification in combination with mass spectrometry, we found that apolipoprotein B (APOB), ER lipid raft protein (ERLIN) 1 and 2 were TM6SF2-interacting proteins. ERLINs and TM6SF2 mutually bound and stabilized each other. TM6SF2 bound and stabilized APOB via two luminal loops. ERLINs did not interact with APOB directly but still increased APOB stability through stabilizing TM6SF2. This APOB stabilization was hampered by the E167K mutation that reduced the protein expression of TM6SF2. In mice, knockout of Tm6sf2 and knockdown of Tm6sf2 or Erlins decreased hepatic APOB protein level, causing lipid accumulation in the liver and lowering lipid levels in the serum. We conclude that defective APOB stabilization, as a result of ERLINs or TM6SF2 deficiency or E167K mutation, is a key factor contributing to NAFLD.

Non-alcoholic fatty liver disease (NAFLD) is a very common liver disorder that occurs in people who do not drink too much alcohol. It initiates from extra fat storage in the liver and can advance to hepatitis, fibrosis, liver failure and liver cancer. NAFLD is often associated with other health problems such as obesity, diabetes, and hyperlipidemia. The TM6SF2 gene variant is a strong risk factor for NAFLD in humans. However, the mechanism by which loss of TM6SF2 protein causes NAFLD is unclear. Here, we demonstrate that TM6SF2 forms a complex with ERLINs and APOB. ERLINs and TM6SF2 stabilize each other, and TM6SF2 stabilizes APOB. In mice, ablating the expression of ERLINs or TM6SF2 lowers APOB protein level, causing lipid accumulation in the liver while decreasing lipid levels in the blood. These phenotypes resemble the symptoms of NAFLD patients carrying TM6SF2 mutations. We conclude that TM6SF2 promotes APOB stability via complex formation and that defective APOB stabilization is one of the underlying causes of NAFLD.

Genetic Pathways in Nonalcoholic Fatty Liver Disease: Insights From Systems Biology

Nonalcoholic fatty liver disease (NAFLD) represents a burgeoning worldwide epidemic whose etiology reflects multiple interactions between environmental and genetic factors. Here, we review the major pathways and dominant genetic modifiers known to be relevant players in human NAFLD and which may determine key components of the heritability of distinctive disease traits including steatosis and fibrosis. In addition, we have employed general assumptions which are based on known genetic factors in NAFLD to build a systems biology prediction model that includes functional enrichment. This prediction model highlights additional complementary pathways that represent plausible intersecting signaling networks that we define here as an NAFLD-Reactome. We review the evidence connecting variants in each of the major known genetic modifiers (variants in patatin-like phospholipase domain containing 3, transmembrane 6 superfamily member 2, membrane-bound O-acyltransferase domain containing 7, glucokinase regulator, and hydroxysteroid 17-beta dehydrogenase 13) to NAFLD and expand the associated underlying mechanisms using functional enrichment predictions, based on both preclinical and cell-based experimental findings. These major candidate gene variants function in distinct pathways, including substrate delivery for de novo lipogenesis; mitochondrial energy use; lipid droplet assembly, lipolytic catabolism, and fatty acid compartmentalization; and very low-density lipoprotein assembly and secretion. The NAFLD-Reactome model expands these pathways and allows for hypothesis testing, as well as serving as a discovery platform for druggable targets across multiple pathways that promote NAFLD development and influence several progressive outcomes. In conclusion, we summarize the strengths and weaknesses of studies implicating selected variants in the pathophysiology of NAFLD and highlight opportunities for future clinical research and pharmacologic intervention, as well as the implications for clinical practice.

Update on NAFLD genetics: From new variants to the clinic

Non-alcoholic fatty liver disease (NAFLD) is the leading cause of liver diseases in high-income countries and the burden of NAFLD is increasing at an alarming rate. The risk of developing NAFLD and related complications is highly variable among individuals and is determined by environmental and genetic factors. Genome-wide association studies have uncovered robust and reproducible associations between variations in genes such as PNPLA3, TM6SF2, MBOAT7, GCKR, HSD17B13 and the natural history of NAFLD. These findings have provided compelling new insights into the biology of NAFLD and highlighted potentially attractive pharmaceutical targets. More recently the development of polygenic risk scores, which have shown promising results for the clinical risk prediction of other complex traits (such as cardiovascular disease and breast cancer), have provided new impetus for the clinical validation of genetic variants in NAFLD risk stratification. Herein, we review current knowledge on the genetic architecture of NAFLD, including gene-environment interactions, and discuss the implications for disease pathobiology, drug discovery and risk prediction. We particularly focus on the potential clinical translation of recent genetic advances, discussing methodological hurdles that must be overcome before these discoveries can be implemented in everyday practice.

Effect of the patatin-like phospholipase domain containing 3 gene (PNPLA3) I148M polymorphism on the risk and severity of nonalcoholic fatty liver disease and metabolic syndromes: A meta-analysis of paediatric and adolescent individuals

BACKGROUND

The effect of the patatin-like phospholipase domain containing 3 gene (PNPLA3) I148M polymorphism on the risk and severity of paediatric and adolescent nonalcoholic fatty liver disease (NAFLD) remains inconclusive.

OBJECTIVES

We aimed to estimate the effect of this polymorphism not only on early-onset NAFLD risk and severity but also on metabolic syndromes susceptibility.

METHODS

A systematic literature search was performed to identify relevant datasets. The odds ratio of the dichotomic variables and the standardized mean difference of quantitative variables with corresponding 95% confidence intervals were calculated to assess the strength of the associations.

RESULTS

Twenty-seven studies comprising 10 070 subjects were eligible. The summary effect showed that this polymorphism increased susceptibility to NAFLD development. Furthermore, it also indicated that nonalcoholic steatohepatitis (NASH) was more frequently observed in G allele carriers among paediatric and adolescent NAFLD patients. Moreover, the meta-analysis suggested that the variant was significantly associated with elevated liver damage indexes, including serum alanine transaminase, aspartate transaminase, gamma-glutamyltransferase concentrations, and liver fat content. However, the summary estimates for insulin resistance, lipid metabolism, and adiposity showed no significant associations.

CONCLUSIONS

The PNPLA3 I148M polymorphism is associated with elevated early-onset NAFLD risk, severity, and liver damage but not with related metabolic syndromes.

Review article: the emerging role of genetics in precision medicine for patients with non-alcoholic steatohepatitis

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is a severe form of non-alcoholic fatty liver disease (NAFLD) characterised by liver fat accumulation, inflammation and progressive fibrosis. Emerging data indicate that genetic susceptibility increases risks of NAFLD, NASH and NASH-related cirrhosis.

AIMS

To review NASH genetics and discuss the potential for precision medicine approaches to treatment.

METHOD

PubMed search and inclusion of relevant literature.

RESULTS

Single-nucleotide polymorphisms in PNPLA3, TM6SF2, GCKR, MBOAT7 and HSD17B13 are clearly associated with NASH development or progression. These genetic variants are common and have moderate-to-large effect sizes for development of NAFLD, NASH and hepatocellular carcinoma (HCC). The genes play roles in lipid remodelling in lipid droplets, hepatic very low-density lipoprotein (VLDL) secretion and de novo lipogenesis. The PNPLA3 I148M variant (rs738409) has large effects, with approximately twofold increased odds of NAFLD and threefold increased odds of NASH and HCC per allele. Obesity interacts with PNPLA3 I148M to elevate liver fat content and increase rates of NASH. Although the isoleucine-to-methionine substitution at amino acid position 148 of the PNPLA3 enzyme inactivates its lipid remodelling activity, the effect of PNPLA3 I148M results from trans-repression of another lipase (ATGL/PNPLA2) by sequestration of a shared cofactor (CGI-58/ABHD5), leading to decreased hepatic lipolysis and VLDL secretion. In homozygous Pnpla3 I148M knock-in rodent models of NAFLD, targeted PNPLA3 mRNA knockdown reduces hepatic steatosis, inflammation and fibrosis.

CONCLUSION

The emerging genetic and molecular understanding of NASH paves the way for novel interventions, including precision medicines that can modulate the activity of specific genes associated with NASH.

Validation of PNPLA3 polymorphisms as risk factor for NAFLD and liver fibrosis in an admixed population

INTRODUCTION AND AIM

Studies have shown that two polymorphisms were associated with steatosis and progression of non-alcoholic fatty liver disease (NAFLD) in different populations: the Patatin-like Phospholipase Domain Containing 3 (PNPLA3) and Transmembrane 6 Superfamily Member 2 (TM6SF2). However, the frequency and significance of these polymorphisms in an admixed population, i.e., Brazilian, is unknown. Therefore, we aimed to evaluate them in healthy subjects in comparison to patients with NAFLD.

MATERIAL AND METHODS

This was a multicenter cross-sectional study in 248 patients with biopsy-proven NAFLD and in 134 healthy controls from two tertiary centers in Brazil. PNPLA3 (rs738409 c.444C>G) and TM6SF2 (rs58542926 c.449C>T) polymorphisms were evaluated.

RESULTS

In controls, the frequencies of PNPLA3 CC and CG+GG were 49.25% and 50.74%, respectively; in NAFLD patients, this was 31.05% and 68.88% (p=0.0044, 95% CI 1.037-2.977). PNPLA3 GG subjects had an increased risk (3.29-fold) of having NAFLD when compared to CC subjects (p=0.0044, 95% CI 1.504-7.225). In patients with nonalcoholic steatohepatitis (NASH), PNPLA3 GG compared to CC was associated with higher AST levels [38.4±25.3 versus 36.7±40.1IU/L, p=0.0395)] and with the presence of liver fibrosis (≥F2 fibrosis, p=0.0272). TM6SF2 polymorphisms were not in Hardy-Weinberg equilibrium in our NAFLD group precluding further analysis.

CONCLUSION

We demonstrated for the first time that PNPLA3 CG+GG increase the risk of NAFLD among Brazilian subjects. Moreover, PNPLA3 GG was associated with liver enzyme elevation and fibrosis in NASH patients.

PNPLA3 I148M gene variant and chronic kidney disease in type 2 diabetic patients with NAFLD: Clinical and experimental findings

BACKGROUND AND AIMS

Emerging evidence suggests an association between patatin-like phospholipase domain-containing protein-3 (PNPLA3) rs738409 (I148M protein variant) and risk of chronic kidney disease (CKD), but the mechanisms underpinning this association are poorly understood.

METHODS

We studied 157 patients with type 2 diabetes (T2DM) who underwent ultrasonography and vibration-controlled transient elastography for diagnosing nonalcoholic fatty liver disease (NAFLD). CKD was defined as estimated glomerular filtration rate (e-GFR) <60 mL/min/1.73 m² and/or abnormal albuminuria. We surveyed PNPLA3 mRNA expression in human tissues, using the liver as a positive control, and also measured PNPLA3 mRNA and protein expression levels in human cell lines represented in the kidney and the liver.

RESULTS

In all, 112 patients had NAFLD and 43 had CKD. Patients homozygous for the I148M variant (n = 11) had lower e-GFR levels (60.6 ± 11.7 vs 77.8 ± 15.9 vs 83.5 ± 16.5 mL/min/1.73 m² , P = .0001) and higher prevalence of CKD (63.6% vs 24.2% vs 25.0%, P = .028), compared to those with I/M (n = 66) and I/I (n = 80) PNPLA3 genotype. The association of I148M homozygosity with lower e-GFR levels (P < .0001) and higher risk of CKD (adjusted-odds ratio 6.65; 95% CI 1.65-26.8, P = .008) was independent of liver disease severity (as detected by liver stiffness ≥7kPa) and other risk factors. PNPLA3 mRNA expression was greatest in liver and renal cortex, and podocytes showed high PNPLA3 mRNA and protein levels, comparable to that of hepatocytes and hepatic stellate cells respectively.

CONCLUSIONS

The PNPLA3 I148M variant was associated with CKD, independently of common renal risk factors and severity of NAFLD PNPLA3 expression levels were particularly high in renal podocytes.

Risk of Kidney Dysfunction IN Nafld

Background:

The timely identification of traditional and non-traditional precursors and risk factors for chronic kidney disease (CKD) (a common systemic disease defined as a decreased kidney function documented by reduced glomerular filtration rate, or markers of kidney damage, or both) is relevant in clinical practice, as CKD increases the risk of end-stage renal disease and other serious comorbidities. A possible relationship between non-alcoholic fatty liver disease (NAFLD) (which is to date the most common chronic disease worldwide) and CKD has recently gained significant attention of researchers.

Methods :

A systematic literature search using appropriate keywords was made in order to identify relevant articles that have investigated the association between NAFLD and CKD.

Results:

Several observational studies and meta-analyses have reported the existence of an independent association between NAFLD and risk of CKD in patients with and without diabetes. However, whilst the association between NAFLD and risk of prevalent CKD is strong across various patient populations, whether NAFLD is independently associated with the development and progression of CKD is still debatable. Moreover, emerging evidence now suggests a potential association between patatin-like phospholipase domain-containing protein-3 (PNPLA3) rs738409 genotype (the most important genetic variant associated to NAFLD) and decreasing kidney function, independent of NAFLD.

Conclusions :

Convincing evidence now indicates that CKD is increased among patients with NAFLD. For this reason, patients with NAFLD should be regularly monitored for renal function and, on the other hand , NAFLD should be considered in all patients with CKD, especially if they are obese or have type 2 diabetes.

Nutrition and Genetics in NAFLD: The Perfect Binomium

Nonalcoholic fatty liver disease (NAFLD) represents a global healthcare burden since it is epidemiologically related to obesity, type 2 diabetes (T2D) and Metabolic Syndrome (MetS). It embraces a wide spectrum of hepatic injuries, which include simple steatosis, nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis and hepatocellular carcinoma (HCC). The susceptibility to develop NAFLD is highly variable and it is influenced by several cues including environmental (i.e., dietary habits and physical activity) and inherited (i.e., genetic/epigenetic) risk factors. Nonetheless, even intestinal microbiota and its by-products play a crucial role in NAFLD pathophysiology. The interaction of dietary exposure with the genome is referred to as 'nutritional genomics,' which encompasses both 'nutrigenetics' and 'nutriepigenomics.' It is focused on revealing the biological mechanisms that entail both the acute and persistent genome-nutrient interactions that influence health and it may represent a promising field of study to improve both clinical and health nutrition practices. Thus, the premise of this review is to discuss the relevance of personalized nutritional advices as a novel therapeutic approach in NAFLD tailored management.

Assessment of Genetic Aspects of Non-alcoholic Fatty Liver and Premature Cardiovascular Events

Recent evidence has demonstrated a strong interplay and multifaceted relationship between non-alcoholic fatty liver disease (NAFLD) and cardiovascular disease (CVD). CVD is the major cause of death in patients with NAFLD. NAFLD also has strong associations with diabetes and metabolic syndrome. In this comprehensive review, we aimed to overview the primary environmental and genetic risk factors of NAFLD, and CVD and also focus on the genetic aspects of these two disorders. NAFLD and CVD are both heterogeneous diseases with common genetic and molecular pathways. We have searched for the latest published articles regarding this matter and tried to provide an overview of recent insights into the genetic aspects of NAFLD and CVD. The common genetic and molecular pathways involved in NAFLD and CVD are insulin resistance (IR), subclinical inflammation, oxidative stress, and atherogenic dyslipidemia. According to an investigation, the exact associations between genomic characteristics of NAFLD and CVD and casual relationships are not fully determined. Different gene polymorphisms have been identified as the genetic components of the NAFLDCVD association. Some of the most documented ones of these gene polymorphisms are patatin-like phospholipase domain-containing protein 3 (PNPLA3), transmembrane 6 superfamily member 2 (TM6SF2), hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13), adiponectin-encoding gene (ADIPOQ), apolipoprotein C3 (APOC3), peroxisome proliferator-activated receptors (PPAR), leptin receptor (LEPR), sterol regulatory element-binding proteins (SREBP), tumor necrosis factor-alpha (TNF-α), microsomal triglyceride transfer protein (MTTP), manganese superoxide dismutase (MnSOD), membrane-bound O-acyltransferase domain-containing 7 (MBOAT7), and mutation in DYRK1B that substitutes cysteine for arginine at position 102 in kinase-like domain. Further cohort studies with a significant sample size using advanced genomic assessments and next-generation sequencing techniques are needed to shed more light on genetic associations between NAFLD and CVD.

Genetic Risk Factors and Disease Modifiers of Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease is strongly associated with obesity and the metabolic syndrome, but genetic factors also contribute to disease susceptibility. Human genetic studies have identified several common genetic variants contributing to nonalcoholic fatty liver disease initiation and progression. These findings have provided new insights into the pathogenesis of nonalcoholic fatty liver disease and opened up new avenues for the development of therapeutic interventions. In this review, we summarize the current state of knowledge about the genetic determinants of nonalcoholic fatty liver disease, focusing on the most robustly validated genetic risk factors and on recently discovered modifiers of disease progression.

Leveraging Human Genetics to Identify Potential New Treatments for Fatty Liver Disease

Fatty liver disease (FLD), including its more severe pathologies, namely steatohepatitis, hepatocarcinoma, and cirrhosis, is the most common cause of chronic liver disease worldwide and is projected to become the leading cause of hepatocellular carcinoma and end-stage liver disease. FLD is heterogeneous with multiple etiologies and diverse histological phenotypes, so therapies will ultimately need to be individualized for relevant targets. Inherited factors contribute to FLD, and most of the genetic variation influencing liver disease development and progression is derived from genes involved in lipid biology, including PNPLA3, TM6SF2, GCKR, MBOAT7, and HSD17B13. From this point of view, we focus in this perspective on how human molecular genetics of FLD have highlighted defects in hepatic lipid handling as a major common mechanism of its pathology and how this insight could be leveraged to treat and prevent its more serious complications.

Nonalcoholic Fatty Liver Disease in Adults: Current Concepts in Etiology, Outcomes, and Management

Nonalcoholic fatty liver disease (NAFLD) is a spectrum of disease, extending from simple steatosis to inflammation and fibrosis with a significant risk for the development of cirrhosis. It is highly prevalent and is associated with significant adverse outcomes both through liver-specific morbidity and mortality but, perhaps more important, through adverse cardiovascular and metabolic outcomes. It is closely associated with type 2 diabetes and obesity, and both of these conditions drive progressive disease toward the more advanced stages. The mechanisms that govern hepatic lipid accumulation and the predisposition to inflammation and fibrosis are still not fully understood but reflect a complex interplay between metabolic target tissues including adipose and skeletal muscle, and immune and inflammatory cells. The ability to make an accurate assessment of disease stage (that relates to clinical outcome) can also be challenging. While liver biopsy is still regarded as the gold-standard investigative tool, there is an extensive literature on the search for novel noninvasive biomarkers and imaging modalities that aim to accurately reflect the stage of underlying disease. Finally, although no therapies are currently licensed for the treatment of NAFLD, there are interventions that appear to have proven efficacy in randomized controlled trials as well as an extensive emerging therapeutic landscape of new agents that target many of the fundamental pathophysiological processes that drive NAFLD. It is highly likely that over the next few years, new treatments with a specific license for the treatment of NAFLD will become available.

Severity of Nonalcoholic Fatty Liver Disease in Type 2 Diabetes Mellitus: Relationship between Nongenetic Factors and PNPLA3/HSD17B13 Polymorphisms

BACKGROUND

The prevalence of nonalcoholic fatty liver disease (NAFLD) in patients with type 2 diabetes mellitus (T2DM) is high, though its severity is often underestimated. Our aim is to provide an estimate of the prevalence of severe NAFLD in T2DM and identify its major predictors.

METHODS

T2DM patients (n=328) not previously known to have NAFLD underwent clinical assessment, transient elastography with measure of liver stiffness (LS) and controlled attenuation parameter (CAP), and genotyping for patatin like phospholipase domain containing 3 (PNPLA3) and 17β-hydroxysteroid-dehydrogenase type 13 (HSD17B13).

RESULTS

Median LS was 6.1 kPa (4.9 to 8.6). More than one-fourth patients had advanced liver disease, defined as LS ≥7.9 kPa (n=94/238, 29%), and had a higher body mass index (BMI) than those with a LS <7.9 kPa. Carriage of the G allele in the PNPLA3 gene was associated with higher LS, being 5.9 kPa (4.7 to 7.7) in C/C homozygotes, 6.1 kPa (5.2 to 8.7) in C/G heterozygotes, and 6.8 kPa (5.8 to 9.2) in G/G homozygotes (P=0.01). This trend was absent in patients with ≥1 mutated HSD17B13 allele. In a multiple linear regression model, BMI and PNPLA3 genotype predicted LS, while age, gender, disease duration, and glycosylated hemoglobin did not fit into the model. None of these variables was confirmed to be predictive among carriers of at least one HSD17B13 mutated allele. There was no association between CAP and polymorphisms of PNPLA3 or HSD17B13.

CONCLUSION

Advanced NAFLD is common among T2DM patients. LS is predicted by both BMI and PNPLA3 polymorphism, the effect of the latter being modulated by mutated HSD17B13.