A feed-forward loop amplifies nutritional regulation of PNPLA3. Proc Natl Acad Sci U S A. 2010;107:7892-7897. [PMID: 20385813 DOI: 10.1073/pnas.1003585107]

NAFLD (MASLD)/NASH (MASH): Does It Bother to Label at All? A Comprehensive Narrative Review

Nonalcoholic fatty liver disease (NAFLD), or metabolic dysfunction-associated steatotic liver disease (MASLD), is a liver condition that is linked to overweight, obesity, diabetes mellitus, and metabolic syndrome. Nonalcoholic steatohepatitis (NASH), or metabolic dysfunction-associated steatohepatitis (MASH), is a form of NAFLD/MASLD that progresses over time. While steatosis is a prominent histological characteristic and recognizable grossly and microscopically, liver biopsies of individuals with NASH/MASH may exhibit several other abnormalities, such as mononuclear inflammation in the portal and lobular regions, hepatocellular damage characterized by ballooning and programmed cell death (apoptosis), misfolded hepatocytic protein inclusions (Mallory-Denk bodies, MDBs), megamitochondria as hyaline inclusions, and fibrosis. Ballooning hepatocellular damage remains the defining feature of NASH/MASH. The fibrosis pattern is characterized by the initial expression of perisinusoidal fibrosis ("chicken wire") and fibrosis surrounding the central veins. Children may have an alternative form of progressive NAFLD/MASLD characterized by steatosis, inflammation, and fibrosis, mainly in Rappaport zone 1 of the liver acinus. To identify, synthesize, and analyze the scientific knowledge produced regarding the implications of using a score for evaluating NAFLD/MASLD in a comprehensive narrative review. The search for articles was conducted between 1 January 2000 and 31 December 2023, on the PubMed/MEDLINE, Scopus, Web of Science, and Cochrane databases. This search was complemented by a gray search, including internet browsers (e.g., Google) and textbooks. The following research question guided the study: "What are the basic data on using a score for evaluating NAFLD/MASLD?" All stages of the selection process were carried out by the single author. Of the 1783 articles found, 75 were included in the sample for analysis, which was implemented with an additional 25 articles from references and gray literature. The studies analyzed indicated the beneficial effects of scoring liver biopsies. Although similarity between alcoholic steatohepatitis (ASH) and NASH/MASH occurs, some patterns of hepatocellular damage seen in alcoholic disease of the liver do not happen in NASH/MASH, including cholestatic featuring steatohepatitis, alcoholic foamy degeneration, and sclerosing predominant hyaline necrosis. Generally, neutrophilic-rich cellular infiltrates, prominent hyaline inclusions and MDBs, cholestasis, and obvious pericellular sinusoidal fibrosis should favor the diagnosis of alcohol-induced hepatocellular injury over NASH/MASH. Multiple grading and staging methods are available for implementation in investigations and clinical trials, each possessing merits and drawbacks. The systems primarily used are the Brunt, the NASH CRN (NASH Clinical Research Network), and the SAF (steatosis, activity, and fibrosis) systems. Clinical investigations have utilized several approaches to link laboratory and demographic observations with histology findings with optimal platforms for clinical trials of rapidly commercialized drugs. It is promising that machine learning procedures (artificial intelligence) may be critical for developing new platforms to evaluate the benefits of current and future drug formulations.

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

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

Exploring the impact of the PNPLA3 I148M variant on primary human hepatic stellate cells using 3D extracellular matrix models

BACKGROUND & AIMS

The PNPLA3 rs738409 C>G (encoding for I148M) variant is a risk locus for the fibrogenic progression of chronic liver diseases, a process driven by hepatic stellate cells (HSCs). We investigated how the PNPLA3 I148M variant affects HSC biology using transcriptomic data and validated findings in 3D-culture models.

METHODS

RNA sequencing was performed on 2D-cultured primary human HSCs and liver biopsies of individuals with obesity, genotyped for the PNPLA3 I148M variant. Data were validated in wild-type (WT) or PNPLA3 I148M variant-carrying HSCs cultured on 3D extracellular matrix (ECM) scaffolds from human healthy and cirrhotic livers, with/without TGFB1 or cytosporone B (Csn-B) treatment.

RESULTS

Transcriptomic analyses of liver biopsies and HSCs highlighted shared PNPLA3 I148M-driven dysregulated pathways related to mitochondrial function, antioxidant response, ECM remodelling and TGFB1 signalling. Analogous pathways were dysregulated in WT/PNPLA3-I148M HSCs cultured in 3D liver scaffolds. Mitochondrial dysfunction in PNPLA3-I148M cells was linked to respiratory chain complex IV insufficiency. Antioxidant capacity was lower in PNPLA3-I148M HSCs, while reactive oxygen species secretion was increased in PNPLA3-I148M HSCs and higher in bioengineered cirrhotic vs. healthy scaffolds. TGFB1 signalling followed the same trend. In PNPLA3-I148M cells, expression and activation of the endogenous TGFB1 inhibitor NR4A1 were decreased: treatment with the Csn-B agonist increased total NR4A1 in HSCs cultured in healthy but not in cirrhotic 3D scaffolds. NR4A1 regulation by TGFB1/Csn-B was linked to Akt signalling in PNPLA3-WT HSCs and to Erk signalling in PNPLA3-I148M HSCs.

CONCLUSION

HSCs carrying the PNPLA3 I148M variant have impaired mitochondrial function, antioxidant responses, and increased TGFB1 signalling, which dampens antifibrotic NR4A1 activity. These features are exacerbated by cirrhotic ECM, highlighting the dual impact of the PNPLA3 I148M variant and the fibrotic microenvironment in progressive chronic liver diseases.

IMPACT AND IMPLICATIONS

Hepatic stellate cells (HSCs) play a key role in the fibrogenic process associated with chronic liver disease. The PNPLA3 genetic mutation has been linked with increased risk of fibrogenesis, but its role in HSCs requires further investigation. Here, by using comparative transcriptomics and a novel 3D in vitro model, we demonstrate the impact of the PNPLA3 genetic mutation on primary human HSCs' behaviour, and we show that it affects the cell's mitochondrial function and antioxidant response, as well as the antifibrotic gene NR4A1. Our publicly available transcriptomic data, 3D platform and our findings on NR4A1 could facilitate the discovery of targets to develop more effective treatments for chronic liver diseases.

PNPLA3 fatty liver allele was fixed in Neanderthals and segregates neutrally in humans

OBJECTIVE

Fat deposition is modulated by environmental factors and genetic predisposition. Genome-wide association studies identified PNPLA3 p.I148M (rs738409) as a common variant that increases risk of developing liver steatosis. When and how this variant evolved in humans has not been studied to date.

DESIGN

Here we analyse ancient DNA to track the history of this allele throughout human history. In total, 6444 published ancient (modern humans, Neanderthal, Denisovan) and 3943 published present day genomes were used for analysis after extracting genotype calls for PNPLA3 p.I148M. To quantify changes through time, logistic and, by grouping individuals according to geography and age, linear regression analyses were performed.

RESULTS

We find that archaic human individuals (Neanderthal, Denisovan) exclusively carried a fixed PNPLA3 risk allele, whereas allele frequencies in modern human populations range from very low in Africa to >50% in Mesoamerica. Over the last 15 000 years, distributions of ancestral and derived alleles roughly match the present day distribution. Logistic regression analyses did not yield signals of natural selection during the last 10 000 years.

CONCLUSION

Archaic human individuals exclusively carried a fixed PNPLA3 allele associated with fatty liver, whereas allele frequencies in modern human populations are variable even in the oldest samples. Our observation might underscore the advantage of fat storage in cold climate and particularly for Neanderthal under ice age conditions. The absent signals of natural selection during modern human history does not support the thrifty gene hypothesis in case of PNPLA3 p.I148M.

Genetics of liver disease in adults

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

Natural compounds proposed for the management of non-alcoholic fatty liver disease

Although non-alcoholic fatty liver disease (NAFLD) presents as an intricate condition characterized by a growing prevalence, the often-recommended lifestyle interventions mostly lack high-level evidence of efficacy and there are currently no effective drugs proposed for this indication. The present review delves into NAFLD pathology, its diverse underlying physiopathological mechanisms and the available in vitro, in vivo, and clinical evidence regarding the use of natural compounds for its management, through three pivotal targets (oxidative stress, cellular inflammation, and insulin resistance). The promising perspectives that natural compounds offer for NAFLD management underscore the need for additional clinical and lifestyle intervention trials. Encouraging further research will contribute to establishing more robust evidence and practical recommendations tailored to patients with varying NAFLD grades.

DGAT2 inhibition blocks SREBP-1 cleavage and improves hepatic steatosis by increasing phosphatidylethanolamine in the ER

Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step of triglyceride (TG) synthesis. DGAT2 deletion in mice lowers liver TGs, and DGAT2 inhibitors are under investigation for the treatment of fatty liver disease. Here, we show that DGAT2 inhibition also suppressed SREBP-1 cleavage, reduced fatty acid synthesis, and lowered TG accumulation and secretion from liver. DGAT2 inhibition increased phosphatidylethanolamine (PE) levels in the endoplasmic reticulum (ER) and inhibited SREBP-1 cleavage, while DGAT2 overexpression lowered ER PE concentrations and increased SREBP-1 cleavage in vivo. ER enrichment with PE blocked SREBP-1 cleavage independent of Insigs, which are ER proteins that normally retain SREBPs in the ER. Thus, inhibition of DGAT2 shunted diacylglycerol into phospholipid synthesis, increasing the PE content of the ER, resulting in reduced SREBP-1 cleavage and less hepatic steatosis. This study reveals a new mechanism that regulates SREBP-1 activation and lipogenesis that is independent of sterols and SREBP-2 in liver.

Divergent role of Mitochondrial Amidoxime Reducing Component 1 (MARC1) in human and mouse

Recent human genome-wide association studies have identified common missense variants in MARC1, p.Ala165Thr and p.Met187Lys, associated with lower hepatic fat, reduction in liver enzymes and protection from most causes of cirrhosis. Using an exome-wide association study we recapitulated earlier MARC1 p.Ala165Thr and p.Met187Lys findings in 540,000 individuals from five ancestry groups. We also discovered novel rare putative loss of function variants in MARC1 with a phenotype similar to MARC1 p.Ala165Thr/p.Met187Lys variants. In vitro studies of recombinant human MARC1 protein revealed Ala165Thr substitution causes protein instability and aberrant localization in hepatic cells, suggesting MARC1 inhibition or deletion may lead to hepatoprotection. Following this hypothesis, we generated Marc1 knockout mice and evaluated the effect of Marc1 deletion on liver phenotype. Unexpectedly, our study found that whole-body Marc1 deficiency in mouse is not protective against hepatic triglyceride accumulation, liver inflammation or fibrosis. In attempts to explain the lack of the observed phenotype, we discovered that Marc1 plays only a minor role in mouse liver while its paralogue Marc2 is the main Marc family enzyme in mice. Our findings highlight the major difference in MARC1 physiological function between human and mouse.

The ubiquitin E3 ligase BFAR promotes degradation of PNPLA3

A missense variant in patatin-like phospholipase domain-containing protein 3 [PNPLA3(I148M)] is the most impactful genetic risk factor for fatty liver disease (FLD). We previously showed that PNPLA3 is ubiquitylated and subsequently degraded by proteasomes and autophagosomes and that the PNPLA3(148M) variant interferes with this process. To define the machinery responsible for PNPLA3 turnover, we used small interfering (si)RNAs to inactivate components of the ubiquitin proteasome system. Inactivation of bifunctional apoptosis regulator (BFAR), a membrane-bound E3 ubiquitin ligase, reproducibly increased PNPLA3 levels in two lines of cultured hepatocytes. Conversely, overexpression of BFAR decreased levels of endogenous PNPLA3 in HuH7 cells. BFAR and PNPLA3 co-immunoprecipitated when co-expressed in cells. BFAR promoted ubiquitylation of PNPLA3 in vitro in a reconstitution assay using purified, epitope-tagged recombinant proteins. To confirm that BFAR targets PNPLA3, we inactivated Bfar in mice. Levels of PNPLA3 protein were increased twofold in hepatic lipid droplets of Bfar-/- mice with no associated increase in PNPLA3 mRNA levels. Taken together these data are consistent with a model in which BFAR plays a role in the post-translational degradation of PNPLA3. The identification of BFAR provides a potential target to enhance PNPLA3 turnover and prevent FLD.

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

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

Modifiable lifestyle factors, genetic and acquired risk, and the risk of severe liver disease in the UK Biobank cohort: (Lifestyle factors and SLD)

BACKGROUND

Lifestyle intervention is important for the treatment of liver diseases.

AIMS

To clarify the association of healthy lifestyle with severe liver disease (SLD) and assessed whether genetic susceptibility and acquired fibrosis risk can modify the association.

METHODS

We included 417,986 UK Biobank participants who were free of SLD at baseline. Information on seven modifiable lifestyle factors was collected through a baseline questionnaire. SLD was defined as a medical diagnosis of cirrhosis, hepatocellular carcinoma or liver failure. Cox proportional hazards models were used to evaluate the association between healthy lifestyle factors and risk of incident SLD. The polygenic risk score (PRS) and fibrosis-4 index (FIB-4) were calculated and set as an interaction term.

RESULTS

During a median follow-up of 12.6 years, 4542 fatal and non-fatal SLD incidents were identified. A higher overall lifestyle score was associated with a significantly lower SLD risk (Ptrend <0.001). An increment of 1-point lifestyle score combined with a 1-SD increment in FIB-4 or PRS was associated with an additional reduction of 3% or 2% in SLD risk.

CONCLUSIONS

In European individuals, a healthy lifestyle is associated with a lower risk of incident SLD, which is more pronounced among individuals with a higher genetic and fibrosis risk.

The PNPLA3 I148M variant increases ketogenesis and decreases hepatic de novo lipogenesis and mitochondrial function in humans

The PNPLA3 I148M variant is the major genetic risk factor for all stages of fatty liver disease, but the underlying pathophysiology remains unclear. We studied the effect of this variant on hepatic metabolism in homozygous carriers and non-carriers under multiple physiological conditions with state-of-the-art stable isotope techniques. After an overnight fast, carriers had higher plasma β-hydroxybutyrate concentrations and lower hepatic de novo lipogenesis (DNL) compared to non-carriers. After a mixed meal, fatty acids were channeled toward ketogenesis in carriers, which was associated with an increase in hepatic mitochondrial redox state. During a ketogenic diet, carriers manifested increased rates of intrahepatic lipolysis, increased plasma β-hydroxybutyrate concentrations, and decreased rates of hepatic mitochondrial citrate synthase flux. These studies demonstrate that homozygous PNPLA3 I148M carriers have hepatic mitochondrial dysfunction leading to reduced DNL and channeling of carbons to ketogenesis. These findings have implications for understanding why the PNPLA3 variant predisposes to progressive liver disease.

A nutrigenetic precision approach for the management of non-alcoholic fatty liver disease

BACKGROUND & AIMS

The Patatin-like phospholipase domain-containing 3 (PNPLA3) rs738409 single nucleotide polymorphism (SNP) is one of the major genetic determinant of non-alcoholic fatty liver disease (NAFLD) and is strongly regulated by changes in energy balance and dietary factors. We aimed to investigate the association between the PNPLA3 rs738409 SNP, nutrient intake and NAFLD severity.

METHOD

PNPLA3-rs738409 SNP was genotyped in 181 patients with NAFLD who completed the EPIC Food Frequency Questionnaire. Liver steatosis was evaluated by Controlled Attenuation Parameter (CAP) (Fibroscan®530, Echosens). According to the established cut-off, a CAP value ≥ 300 dB/m was used to identify severe steatosis (S3). An independent group of 46 biopsy-proven NAFLD subjects was used as validation cohort.

RESULTS

Overall, median age was 53 years (range 44; 62) and 60.2% of patients were male. Most subjects (56.3%) had S3 and showed increased liver stiffness (p < 0.001), AST (p = 0.003) and ALT levels (p < 0.001) compared to those with CAP<300 dB/m. At logistic regression analyses we found that the interaction between carbohydrates intake and the carriers of the PNPLA3 G risk allele was significantly associated with S3 (p = 0.001). The same result was confirmed in the validation cohort, were the interaction between high carbohydrate intake (48%) and PNPLA3 SNP was significantly associated with steatosis ≥33% (p = 0.038).

CONCLUSION

The intake of greater than or equal to 48% carbohydrate in NAFLD patients carriers of the CG/GG allele of PNPLA3 rs738409 may increase the risk of significant steatosis.

Loss of KDM6B epigenetically confers resistance to lipotoxicity in nonalcoholic fatty liver disease-related HCC

BACKGROUND

NAFLD caused by abnormalities in hepatic lipid metabolism is associated with an increased risk of developing HCC. The molecular mechanisms underlying the progression of NAFLD-related HCC are not fully understood. We investigated the molecular mechanism and role of KDM6B downregulation in NAFLD-related HCC after the KDM6B gene was identified using microarray analysis as commonly downregulated in mouse NAFLD-related HCC and human nonhepatitis B and nonhepatitis C viral-HCC.

METHODS

The 5-hydroxymethylcytosine levels of KDM6B in HCC cells were determined using glycosylated hydroxymethyl-sensitive PCR. Microarray and chromatin immunoprecipitation analyses using KDM6B-knockout (KO) cells were used to identify KDM6B target genes. Lipotoxicity was assessed using a palmitate-treated cell proliferation assay. Immunohistochemistry was used to evaluate KDM6B expression in human HCC tissues.

RESULTS

KDM6B expression levels in HCC cells correlated with the 5-hydroxymethylcytosine levels in the KDM6B gene body region. Gene set enrichment analysis revealed that the lipid metabolism pathway was suppressed in KDM6B-KO cells. KDM6B-KO cells acquired resistance to lipotoxicity (p < 0.01) and downregulated the expression of G0S2, an adipose triglyceride lipase/patatin like phospholipase domain containing 2 (ATGL/PNPLA2) inhibitor, through increased histone H3 lysine-27 trimethylation levels. G0S2 knockdown in KDM6B-expressed HCC cells conferred lipotoxicity resistance, whereas ATGL/PNPLA2 inhibition in the KDM6B-KO cells reduced these effects. Immunohistochemistry revealed that KDM6B expression was decreased in human NAFLD-related HCC tissues (p < 0.001), which was significantly associated with decreased G0S2 expression (p = 0.032).

CONCLUSIONS

KDM6B-disrupted HCC acquires resistance to lipotoxicity via ATGL/PNPLA2 activation caused by epigenetic downregulation of G0S2 expression. Reduced KDM6B and G0S2 expression levels are common in NAFLD-related HCC. Targeting the KDM6B-G0S2-ATGL/PNPLA2 pathway may be a useful therapeutic strategy for NAFLD-related HCC.

Substrate-Specific Function of PNPLA3 Facilitates Hepatic VLDL-Triglyceride Secretion During Stimulated Lipogenesis

The I148M variant of PNPLA3 is strongly linked to hepatic steatosis. Evidence suggests a gain-of-function role for the I148M mutant as an ATGL inhibitor, leaving the physiological relevance of wild-type PNPLA3 undefined. Here we show that PNPLA3 selectively degrades triglycerides (TGs) enriched in polyunsaturated fatty acids (PUFAs) independently of ATGL in cultured cells and mice. Lipidomics and metabolite tracing analyses demonstrated that PNPLA3 mobilizes PUFAs from intracellular TGs for phospholipid desaturation, supporting hepatic secretion of TG-rich lipoproteins. Consequently, mice with liver-specific knockout or acute knockdown of PNPLA3 both exhibited aggravated liver steatosis and concomitant decreases in plasma VLDL-TG, phenotypes that manifest only under lipogenic conditions. I148M-knockin mice similarly displayed impaired hepatic TG secretion during lipogenic stimulation. Our results highlight a specific context whereby PNPLA3 facilitates the balance between hepatic TG storage and secretion and suggest the potential contributions of I148M variant loss-of-function to the development of hepatic steatosis in humans.

Summary Statement

We define the physiological role of wild type PNPLA3 in maintaining hepatic VLDL-TG secretion.

Predictive risk markers in alcoholism

The medical disorders of alcoholism rank among the leading public health problems worldwide and the need for predictive and prognostic risk markers for assessing alcohol use disorders (AUD) has been widely acknowledged. Early-phase detection of problem drinking and associated tissue toxicity are important prerequisites for timely initiations of appropriate treatments and improving patient's committing to the objective of reducing drinking. Recent advances in clinical chemistry have provided novel approaches for a specific detection of heavy drinking through assays of unique ethanol metabolites, phosphatidylethanol (PEth) or ethyl glucuronide (EtG). Carbohydrate-deficient transferrin (CDT) measurements can be used to indicate severe alcohol problems. Hazardous drinking frequently manifests as heavy episodic drinking or in combinations with other unfavorable lifestyle factors, such as smoking, physical inactivity, poor diet or adiposity, which aggravate the metabolic consequences of alcohol intake in a supra-additive manner. Such interactions are also reflected in multiple disease outcomes and distinct abnormalities in biomarkers of liver function, inflammation and oxidative stress. Use of predictive biomarkers either alone or as part of specifically designed biological algorithms helps to predict both hepatic and extrahepatic morbidity in individuals with such risk factors. Novel approaches for assessing progression of fibrosis, a major determinant of prognosis in AUD, have also been made available. Predictive algorithms based on the combined use of biomarkers and clinical observations may prove to have a major impact on clinical decisions to detect AUD in early pre-symptomatic stages, stratify patients according to their substantially different disease risks and predict individual responses to treatment.

Advances in our understanding of the molecular heterogeneity of fatty liver disease: toward informed treatment decision making

INTRODUCTION

nonalcoholic fatty liver disease (NAFLD) is a complex disorder resulting from intricate relationships with diverse cardiometabolic risk factors and environmental factors. NAFLD may result in severe chronic liver damage and potentially declining liver function.

AREAS COVERED

Accumulated knowledge over the last decade indicates that the disease trajectory presents substantial heterogeneity. In addition, overlapping features with the diseases of the metabolic syndrome, combined with heterogeneity in disease mechanisms, further complicates NAFLD diagnosis and prognosis, and hampers progress in biomarker and pharmacological discoveries. Here, we explore solving the heterogeneous clinical landscape of NAFLD by cluster analysis of molecular signatures that serve as a proxy for disease stratification into molecular sub-types. First, we collected information on NAFLD and metabolic syndrome-associated protein-coding genes by data mining the literature. Next, we performed pathways enrichment and cluster analyses to decipher and dissect the different patterns of phenotypic heterogeneity. Our approach showed unique biological pathways for every clinical subtype/group, namely NAFLD + obesity, NAFLD + arterial hypertension, NAFLD + dyslipidemia, and NAFLD + type 2 diabetes.

EXPERT OPINION

Patients with NAFLD may be benefited by a better understanding of the disease biology, which involves 'dissection' of the molecular sub-phenotypes that drive the disease progression.

TM6SF2-rs58542926 Genetic Variant Modifies the Protective Effect of a "Prudent" Dietary Pattern on Serum Triglyceride Levels

The epidemic prevalence of non-alcoholic fatty liver disease (NAFLD), despite extensive research in the field, underlines the importance of focusing on personalized therapeutic approaches. However, nutrigenetic effects on NAFLD are poorly investigated. To this end, we aimed to explore potential gene-dietary pattern interactions in a NAFLD case-control study. The disease was diagnosed with liver ultrasound and blood collection was performed after an overnight fast. Adherence to four a posteriori, data-driven, dietary patterns was used to investigate interactions with PNPLA3-rs738409, TM6SF2-rs58542926, MBOAT7-rs641738, and GCKR-rs738409 in disease and related traits. IBM SPSS Statistics/v21.0 and Plink/v1.07 were used for statistical analyses. The sample consisted of 351 Caucasian individuals. PNPLA3-rs738409 was positively associated with disease odds (OR = 1.575, p = 0.012) and GCKR-rs738409 with lnC-reactive protein (CRP) (beta = 0.098, p = 0.003) and Fatty Liver Index (FLI) levels (beta = 5.011, p = 0.007). The protective effect of a "Prudent" dietary pattern on serum triglyceride (TG) levels in this sample was significantly modified by TM6SF2-rs58542926 (pinteraction = 0.007). TM6SF2-rs58542926 carriers may not benefit from a diet rich in unsaturated fatty acids and carbohydrates in regard to TG levels, a commonly elevated feature in NAFLD patients.

Nutritional Genomics in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a common chronic condition associated with genetic and environmental factors in which fat abnormally accumulates in the liver. NAFLD is epidemiologically associated with obesity, type 2 diabetes, and dyslipidemia. Environmental factors, such as physical inactivity and an unbalanced diet, interact with genetic factors, such as epigenetic mechanisms and polymorphisms for the genesis and development of the condition. Different genetic polymorphisms seem to be involved in this context, including variants in PNPLA3, TM6SF2, PEMT, and CHDH genes, playing a role in the disease's susceptibility, development, and severity. From carbohydrate intake and weight loss to omega-3 supplementation and caloric restriction, different dietary and nutritional factors appear to be involved in controlling the onset and progression of NAFLD conditions influencing metabolism, gene, and protein expression. The polygenic risk score represents a sum of trait-associated alleles carried by an individual and seems to be associated with NAFLD outcomes depending on the dietary context. Understanding the exact extent to which lifestyle interventions and genetic predispositions can play a role in the prevention and management of NAFLD can be crucial for the establishment of a personalized and integrative approach to patients.

The I148M PNPLA3 variant mitigates niacin beneficial effects: How the genetic screening in non-alcoholic fatty liver disease patients gains value

Background

The PNPLA3 p.I148M impact on fat accumulation can be modulated by nutrients. Niacin (Vitamin B3) reduced triglycerides synthesis in in vitro and in vivo NAFLD models.

Objectives

In this study, we aimed to investigate the niacin-I148M polymorphism crosstalk in NAFLD patients and examine niacin's beneficial effect in reducing fat by exploiting hepatoma cells with different PNPLA3 genotype.

Design

We enrolled 172 (Discovery cohort) and 358 (Validation cohort) patients with non-invasive and histological diagnosis of NAFLD, respectively. Dietary niacin was collected from food diary, while its serum levels were quantified by ELISA. Hepatic expression of genes related to NAD metabolism was evaluated by RNAseq in bariatric NAFLD patients (n = 183; Transcriptomic cohort). Hep3B (148I/I) and HepG2 (148M/M) cells were silenced (siHep3B) or overexpressed (HepG2^I148+ ) for PNPLA3, respectively.

Results

In the Discovery cohort, dietary niacin was significantly reduced in patients with steatosis ≥ 2 and in I148M carriers. Serum niacin was lower in subjects carrying the G at risk allele and negatively correlated with obesity. The latter result was confirmed in the Validation cohort. At multivariate analysis, the I148M polymorphism was independently associated with serum niacin, supporting that it may be directly involved in the modulation of its availability. siHep3B cells showed an impaired NAD biosynthesis comparable to HepG2 cells which led to lower niacin efficacy in clearing fat, supporting a required functional protein to guarantee its effectiveness. Conversely, the restoration of PNPLA3 Wt protein in HepG2^I148+ cells recovered the NAD pathway and improved niacin efficacy. Finally, niacin inhibited de novo lipogenesis through the ERK1/2/AMPK/SIRT1 pathway, with the consequent SREBP1-driven PNPLA3 reduction only in Hep3B and HepG2^I148M+ cells.

Conclusions

We demonstrated a niacin-PNPLA3 I148M interaction in NAFLD patients which possibly pave the way to vitamin B3 supplementation in those with a predisposing genetic background.

γ-Linolenic Acid-Rich Oil- and Fish Oil-Induced Alterations of Hepatic Lipogenesis, Fatty Acid Oxidation, and Adipose Tissue mRNA Expression in Obese KK-A y Mice

The physiological activity of γ-linolenic acid (GLA)-rich evening primrose oil and eicosapentaenoic and doxosahexaenoic acids-rich fish oil, which affect hepatic fatty acid oxidation and synthesis, and adipose tissue mRNA expression were compared in diabetic obese KK-A ^y mice. The mice were fed diets containing 100 g/kg of either palm oil (saturated fat), GLA oil, or fish oil for 21 days. These oils, compared with palm oil, greatly increased the activity and mRNA levels of hepatic fatty acid oxidation enzymes. These oils also increased the carnitine concentrations and mRNA levels of carnitine transporter (solute carrier family 22, member 5) in the liver. In general, these effects were comparable between GLA and fish oils. In contrast, GLA and fish oils, compared with palm oil, reduced the activity and mRNA levels of the proteins related to hepatic lipogenesis, except for those of malic enzyme. The reducing effect was stronger for fish oil than for GLA oil. These changes were accompanied by reductions in the triacylglycerol levels in the serum and liver. The reduction in the liver was stronger for fish oil than for GLA oil. These oils also reduced epididymal adipose tissue weight accompanied by a reduction in the mRNA levels of several proteins that regulate adipocyte functions; these effects were stronger for fish oil than for GLA oil. These oils were also effective in reducing serum glucose levels. Therefore, both fish oil and GLA-rich oil were effective at ameliorating metabolic disorders related to obesity and diabetes mellitus.

Mapping transcriptional heterogeneity and metabolic networks in fatty livers at single-cell resolution

Non-alcoholic fatty liver disease is a heterogeneous disease with unclear underlying molecular mechanisms. Here, we perform single-cell RNA sequencing of hepatocytes and hepatic non-parenchymal cells to map the lipid signatures in mice with non-alcoholic fatty liver disease (NAFLD). We uncover previously unidentified clusters of hepatocytes characterized by either high or low srebp1 expression. Surprisingly, the canonical lipid synthesis driver Srebp1 is not predictive of hepatic lipid accumulation, suggestive of other drivers of lipid metabolism. By combining transcriptional data at single-cell resolution with computational network analyses, we find that NAFLD is associated with high constitutive androstane receptor (CAR) expression. Mechanistically, CAR interacts with four functional modules: cholesterol homeostasis, bile acid metabolism, fatty acid metabolism, and estrogen response. Nuclear expression of CAR positively correlates with steatohepatitis in human livers. These findings demonstrate significant cellular differences in lipid signatures and identify functional networks linked to hepatic steatosis in mice and humans.

Discovery of an insulin-induced gene binding compound that ameliorates nonalcoholic steatohepatitis by inhibiting sterol regulatory element-binding protein-mediated lipogenesis

BACKGROUND AND AIMS

NASH is associated with high levels of cholesterol and triglyceride (TG) in the liver; however, there is still no approved pharmacological therapy. Synthesis of cholesterol and TG is controlled by sterol regulatory element-binding protein (SREBP), which is found to be abnormally activated in NASH patients. We aim to discover small molecules for treating NASH by inhibiting the SREBP pathway.

APPROACH AND RESULTS

Here, we identify a potent SREBP inhibitor, 25-hydroxylanosterol (25-HL). 25-HL binds to insulin-induced gene (INSIG) proteins, stimulates the interaction between INSIG and SCAP, and retains them in the endoplasmic reticulum, thereby suppressing SREBP activation and inhibiting lipogenesis. In NASH mouse models, 25-HL lowers levels of cholesterol and TG in serum and the liver, enhances energy expenditure to prevent obesity, and improves insulin sensitivity. 25-HL dramatically ameliorates hepatic steatosis, inflammation, ballooning, and fibrosis through down-regulating the expression of lipogenic genes. Furthermore, 25-HL exhibits both prophylactic and therapeutic efficacies of alleviating NASH and atherosclerosis in amylin liver NASH model diet-treated Ldlr^-/- mice, and reduces the formation of cholesterol crystals and associated crown-like structures of Kupffer cells. Notably, 25-HL lowers lipid contents in serum and the liver to a greater extent than lovastatin or obeticholic acid. 25-HL shows a good safety and pharmacokinetics profile.

CONCLUSIONS

This study provides the proof of concept that inhibiting SREBP activation by targeting INSIG to lower lipids could be a promising strategy for treating NASH. It suggests the translational potential of 25-HL in human NASH and demonstrates the critical role of SREBP-controlled lipogenesis in the progression of NASH by pharmacological inhibition.

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.

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.

SIRT1 mediates nutritional regulation of SREBP-1c-driven hepatic PNPLA3 transcription via modulation of H3k9 acetylation

Background

Patatin-like phospholipase domain containing 3 (PNPLA3) is the main nonalcoholic fatty liver disease (NAFLD) susceptibility. Its expression is regulated tightly by nutritional and energy status, but the mechanism of epigenetic regulation of PNPLA3 gene by nutritional dietary factors has not been reported. Here, we investigated the effect and mechanism of Sirtuin 1 (SIRT1) regulated H3K9 deacetylation on PNPLA3 transcriptional expression in vivo and in vitro.

Methods

Mouse models of fasting/re-feeding transition and nonalcoholic fatty liver induced by high Sucrose diet were constructed; and HepG2 cells were treated with serum- and glucose-free medium or exposed to high glucose and high insulin, to generate fasting and high-glucose-induced lipid deposition cell states. Enrichment levels of histone H3K9 acetylation and sterol responsive element binding protein-1c (SREBP-1c) at the PNPLA3 promoter were observed by ChIP-qPCR. PNPLA3 gene expression was detected by real-time PCR; SIRT1 protein expression was detected by western blot. And lipid deposition was detected by Oil Red O.

Results

H3K9ac levels at SRE regions of PNPLA3 promoter were found to be decreased in mice during fasting and increase during refeeding, and increased in mice with NAFLD induced by high-sucrose diet. The change pattern of PNPLA3 promoter H3K9Ac physiologically (fasting/refeeding) and pathologically was consistent with that of PNPLA3 gene expression, but opposite to that of SIRT1 protein expression. In HepG2 cells, overexpression of SIRT1 inhibited high-glucose induced hyper-acetylation of H3K9 at PNPLA3 promoter, and silent expression of SIRT1 suppressed fasting-induced hypo-acetylation of H3K9. Overexpression of SIRT1 prevented basal and SREBP-1c-driven PNPLA3 gene expression and also prevented the endogenous binding of SREBP-1c to PNPLA3.

Conclusions

We first preliminarily revealed SIRT1 may regulate PNPLA3 gene expression by affecting SREBP-1-driven transcription via acetylation modification of H3K9.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41021-022-00246-1.

A Genetic and Metabolic Staging System for Predicting the Outcome of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is an emerging cause of liver-related events (LREs). Here, we have assessed the ability of a composite score based on clinical features, metabolic comorbidities, and genetic variants to predict LREs. A total of 546 consecutive patients with NAFLD were recruited and stratified according to the fibrosis-4 (FIB-4) index. LREs were defined as occurrence of hepatocellular carcinoma or hepatic decompensation. Cox regression multivariate analysis was used to identify baseline variables associated with LREs. The UK Biobank was used as the validation cohort, and severe liver disease (incidence of cirrhosis, decompensated liver disease, hepatocellular carcinoma, and/or liver transplantation) was used as the outcome. LREs were experienced by 58 patients, only one of whom was in the cohort of patients with a FIB-4 score < 1.3. Multivariate Cox regression analysis of 229 patients with a FIB-4 score ≥ 1.3 highlighted clinical variables independently associated with the development of LREs, including older age, low platelet count, low albumin, low high-density lipoprotein cholesterol, certain genetic factors, and interactions between genetic factors and sex or diabetes. The area under the curve (AUC) for the model was 0.87 at 1, 3, and 5 years. Our novel Genetic and Metabolic Staging (GEMS) scoring system was derived from the Cox model linear predictor, ranked from 0 to 10, and categorized into five classes (0-5, 5-6, 6-7, 7-8, and 8-10). The risk of LREs increased from 4% in patients in the best class (GEMS score 0-5) to 91% in the worst (GEMS score 8-10). GEMS score was associated with incident severe liver disease in the study population (hazard ratio, 1.56; 95% confidence interval, 1.48-1.65; P < 0.001) as well as in the UK Biobank cohort where AUCs for prediction of severe liver disease at 1, 3, and 5 years were 0.70, 0.69, and 0.67, respectively. Conclusion: The novel GEMS scoring system has an adequate ability to predict the outcome of patients with NAFLD.

Metabolic dysfunction-associated fatty liver disease and the risk of 24 specific cancers

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a significant health issue closely associated with multiple metabolic dysfunctions. The association between MAFLD and cancer risk is yet unknown.

METHODS

UK Biobank study participants were diagnosed for the presence of MAFLD at baseline. A multivariable Cox regression model was performed to examine the associations of MAFLD with incident events in 24 specific cancers.

RESULTS

We included 352,911 individuals (37.2% with MAFLD), among whom 23,345 developed cancers. Compared with non-MAFLD, MAFLD was significantly associated with 10 of the 24 examined cancers, including corpus uteri (hazard ratio [HR] = 2.36, 95% CI 1.99-2.80), gallbladder (2.20, 1.14-4.23), liver (1.81, 1.43-2.28), kidney (1.77, 1.49-2.11), thyroid (1.69, 1.20-2.38), esophagus (1.48, 1.25-1.76), pancreas (1.31, 1.10-1.56), bladder (1.26, 1.11-1.43), breast (1.19, 1.11-1.27), and colorectal and anus cancers (1.14, 1.06-1.23). The associations of MAFLD with liver, esophageal, pancreatic, colorectal and anal and bladder cancers and malignant melanoma were strengthened in males, and associations with kidney, thyroid, and lung cancers were increased in females. The associations of MAFLD with the risk of liver, kidney, and thyroid cancers remained significant after further adjusting for the waist circumference or body mass index and the number of metabolic syndrome components based on the main models. The risk-increasing allele of PNPLA3 rs738409 significantly amplified the association of MAFLD with the risk of liver and kidney cancers.

CONCLUSION

MAFLD is associated with an increased risk of a set of cancers, but the effect substantially varies by site. MAFLD deserves higher priority in the current scheme of cancer prevention.

Interaction between Lifestyle Changes and PNPLA3 Genotype in NAFLD Patients during the COVID-19 Lockdown

The coronavirus disease 2019 (COVID-19) lockdown dramatically changed people’s lifestyles. Diet, physical activity, and the PNPLA3 gene are known risk factors for non-alcoholic fatty liver disease (NAFLD). Aim: To evaluate changes in metabolic and hepatic disease in NAFLD patients after the COVID-19 lockdown. Three hundred and fifty seven NAFLD patients were enrolled, all previously instructed to follow a Mediterranean diet (MD). Anthropometric, metabolic, and laboratory data were collected before the COVID-19 lockdown in Italy and 6 months apart, along with ultrasound (US) steatosis grading and information about adherence to MD and physical activity (PA). In 188 patients, PNPLA3 genotyping was performed. After the lockdown, 48% of patients gained weight, while 16% had a worsened steatosis grade. Weight gain was associated with poor adherence to MD (p = 0.005), reduced PA (p = 0.03), and increased prevalence of PNPLA3 GG (p = 0.04). At multivariate analysis (corrected for age, sex, MD, PA, and PNPLA3 GG), only PNPLA3 remained independently associated with weight gain (p = 0.04), which was also associated with worsened glycemia (p = 0.002) and transaminases (p = 0.02). During lockdown, due to a dramatic change in lifestyles, half of our cohort of NAFLD patients gained weight, with a worsening of metabolic and hepatologic features. Interestingly, the PNPLA3 GG genotype nullified the effect of lifestyle and emerged as an independent risk factor for weight gain, opening new perspectives in NAFLD patient care.

Responsiveness of PNPLA3 and lipid-related transcription factors is dependent upon fatty acid profile in primary bovine hepatocytes

Knockdown of patatin-like phospholipase domain-containing protein 3 (PNPLA3) increased triglycerides (TG) in primary bovine hepatocytes, suggesting that PNPLA3 plays a causal role in hepatic TG clearing. In vivo, PNPLA3 abundance across the periparturient period is inversely related to hepatic TG accumulation and circulating fatty acid (FA) concentrations. The purpose of this research was to determine if PNPLA3, as well as other lipases, transcription factors, or FA-mediated genes, are regulated by FA mimicking liver lipid accumulation (ACCUM) and liver lipid clearing (RECOV) or singular FA physiologically found in dairy cows at 0.5 mM of circulating RECOV (iRECOV). Abundance of PNPLA3 tended to decrease with ACCUM and increased quadratically with RECOV (P ≤ 0.10), differing from PNPLA3 expression, but consistent with previous in vivo research. Adipose TG lipase abundance, but not other lipase abundances, was quadratically responsive to both ACCUM and RECOV (P ≤ 0.005). Abundance of PNPLA3 and SREBP1c and expression of LXRA responded similarly to iRECOV, with C18:0 tending to decrease abundance (P ≤ 0.07). Results indicate that bovine PNPLA3 is translationally regulated by FA and although a LXRA-SREBP1c pathway mediation is possible, the mechanism warrants further investigation.

Nonalcoholic Fatty Liver Disease (NAFLD) Name Change: Requiem or Reveille?

Nonalcoholic fatty liver disease (NAFLD) affects about a quarter of the world's population and poses a major health and economic burden globally. Recently, there have been hasty attempts to rename NAFLD to metabolic-associated fatty liver disease (MAFLD) despite the fact that there is no scientific rationale for this. Quest for a "positive criterion" to diagnose the disease and destigmatizing the disease have been the main reasons put forth for the name change. A close scrutiny of the pathogenesis of NAFLD would make it clear that NAFLD is a heterogeneous disorder, involving different pathogenic mechanisms of which metabolic dysfunction-driven hepatic steatosis is only one. Replacing NAFLD with MAFLD would neither enhance the legitimacy of clinical practice and clinical trials, nor improve clinical care or move NAFLD research forward. Rather than changing the nomenclature without a strong scientific backing to support such a change, efforts should be directed at understanding NAFLD pathogenesis across diverse populations and ethnicities which could potentially help develop newer therapeutic options.

Progressive Liver Fibrosis in Non-Alcoholic Fatty Liver Disease

Non-alcoholic steatohepatitis (NASH) is a chronic and progressive form of non-alcoholic fatty liver disease. Its global incidence is increasing and makes NASH an epidemic and a public health threat. Non-alcoholic fatty liver disease is associated with major morbidity and mortality, with a heavy burden on quality of life and liver transplant requirements. Due to repeated insults to the liver, patients are at risk for developing hepatocellular carcinoma. The progression of NASH was initially defined according to a two-hit model involving an initial development of steatosis, followed by a process of lipid peroxidation and inflammation. In contrast, current evidence proposes a “multi-hit” or “multi-parallel hit” model that includes multiple pathways promoting progressive fibrosis and oncogenesis. This model includes multiple cellular, genetic, immunological, metabolic, and endocrine pathways leading to hepatocellular carcinoma development, underscoring the complexity of this disease.

Interaction Between Alcohol Consumption and PNPLA3 Variant in the Prevalence of Hepatic Steatosis in the US Population

BACKGROUND & AIMS

To our knowledge, the interaction between alcohol consumption and PNPLA3 genotype on hepatic steatosis has not been explored in a representative sample. To examine the interaction between alcohol consumption and PNPLA3 genotype on hepatic steatosis in the US adult population.

METHODS

Cross-sectional study of 4,674 adult participants of the Third National Health and Nutrition Examination Survey, Phase 2 (1991-1994) with data on PNPLA3 genotype, self-reported alcohol consumption, ultrasound-defined hepatic steatosis and socio-demographic characteristics.

RESULTS

In 1991-1994 in the U.S. population, the weighted allele frequency of the G (risk) allele of the rs738409 at PNPLA3 was 25.4%. We confirmed both a J shaped association between alcohol consumption and hepatic steatosis among those with the CC genotype of PNPLA3, and a higher prevalence of hepatic steatosis among those with PNPLA3 gene G variant. We found evidence of an interaction of PNPLA3 G allele presence on the association between moderate alcohol consumption and hepatic steatosis on both the multiplicative (relative prevalence ratio [RPR]=1.95, 95% confidence interval [CI] 1.04-3.65) and additive scales (relative excess risk due to interaction=0.49, 95% CI 0.13-0.85). Compared to never drinkers, moderate alcohol drinking was associated with a 48% decreased risk of hepatic steatosis only among those without PNPLA3 G allele (PR=0.52, 95% CI 0.26-1.05), with no association among those with at least one copy of the PNPLA3 G allele (PR=1.02, 95% CI 0.68-1.54).

CONCLUSIONS

Our results suggest that a highly common and strong genetic susceptibility to liver disease is modifiable by the level of alcohol consumption. Keeping alcohol consumption low may offset genetic predisposition to liver disease.

Modeling PNPLA3-Associated NAFLD Using Human-Induced Pluripotent Stem Cells

BACKGROUND AND AIMS

NAFLD is a growing public health burden. However, the pathogenesis of NAFLD has not yet been fully elucidated, and the importance of genetic factors has only recently been appreciated. Genomic studies have revealed a strong association between NAFLD progression and the I148M variant in patatin-like phospholipase domain-containing protein 3 (PNPLA3). Nonetheless, very little is known about the mechanisms by which this gene and its variants can influence disease development. To investigate these mechanisms, we have developed an in vitro model that takes advantage of the unique properties of human-induced pluripotent stem cells (hiPSCs) and the CRISPR/CAS9 gene editing technology.

APPROACH AND RESULTS

We used isogenic hiPSC lines with either a knockout (PNPLA3^KO ) of the PNPLA3 gene or with the I148M variant (PNPLA3^I148M ) to model PNPLA3-associated NAFLD. The resulting hiPSCs were differentiated into hepatocytes, treated with either unsaturated or saturated free fatty acids to induce NAFLD-like phenotypes, and characterized by various functional, transcriptomic, and lipidomic assays. PNPLA3^KO hepatocytes showed higher lipid accumulation as well as an altered pattern of response to lipid-induced stress. Interestingly, loss of PNPLA3 also caused a reduction in xenobiotic metabolism and predisposed PNPLA3^KO cells to be more susceptible to ethanol-induced and methotrexate-induced toxicity. The PNPLA3^I148M cells exhibited an intermediate phenotype between the wild-type and PNPLA3^KO cells.

CONCLUSIONS

Together, these results indicate that the I148M variant induces a loss of function predisposing to steatosis and increased susceptibility to hepatotoxins.

Main Risk Factors of Type 2 Diabetes Mellitus with Nonalcoholic Fatty Liver Disease and Hepatocellular Carcinoma

Type 2 diabetes mellitus (T2DM) with nonalcoholic fatty liver disease (NAFLD) is a pathological metabolic disease characterized by high ketone lipid based on abnormal lipid metabolism. Compared with patients with single T2DM or NAFLD, T2DM complicated with NAFLD has more complicated pathogenic factors and pathological processes. Hepatocellular carcinoma (HCC), the leading malignancy arising from cirrhosis, is the second most lethal cancer globally. The purpose of this study was to clarify the main risk factors of T2DM with NAFLD and HCC. There are many challenges in the diagnosis and treatment of T2DM patients with NAFLD and HCC. The current gold standard is to adjust treatment strategy, optimize metabolic control, and improve liver phenotype. It is necessary to identify further the risk factors driving the progression of T2DM with NAFLD and HCC and evaluate new therapeutic targets, in addition to exploring the syndromic forms of T2DM combined with NAFLD and providing a theoretical basis for early prevention, diagnosis, and treatment of the disease using traditional Chinese medicine (TCM).

Associations of Nutrient Intake Changes During Childhood with Adolescent Hepatic Fat: The Exploring Perinatal Outcomes Among CHildren Study

OBJECTIVE

To examine associations of dietary changes from childhood to adolescence with adolescent hepatic fat and whether the PNPLA3 rs738409 risk allele, a strong genetic risk factor for hepatic fat, modifies associations.

STUDY DESIGN

Data were from 358 participants in the Exploring Perinatal Outcomes among CHildren (EPOCH) study, a longitudinal cohort in Colorado. Diet was assessed by food frequency questionnaire in childhood (approximately 10 years of age) and adolescence (approximately 16 years of age) and converted to nutrient densities. Hepatic fat was assessed in adolescence by magnetic resonance imaging. Linear regression was used to test associations of dietary changes from childhood to adolescence with adolescent hepatic fat.

RESULTS

Increases in fiber, vegetable protein, and polyunsaturated fat intake from childhood to adolescence were associated with lower adolescent hepatic fat, and increases in animal protein were associated with higher hepatic fat (β per 5-unit increase on log-hepatic fat: -0.12 [95% CI, -0.21 to -0.02] for ▵fiber; -0.26 [95% CI, -0.45 to -0.07] for ▵vegetable protein; -0.18 [95% CI, -0.35 to -0.02] for ▵polyunsaturated fat; 0.13 [95% CI, 0.04-0.22] for ▵animal protein). There was evidence of effect modification by PNPLA3 variant, whereby inverse associations of ▵fiber and ▵vegetable protein and positive associations of ▵saturated fat with adolescent hepatic fat were stronger in risk allele carriers. Most conclusions were similar after adjusting for obesity in adolescence, but associations of ▵saturated fat with hepatic fat were attenuated toward the null.

CONCLUSIONS

Our results suggest that nutrient intake changes between childhood and adolescence, particularly decreases in fiber and vegetable protein and increases in saturated fat intake, interact with the PNPLA3 variant to predict higher hepatic fat in adolescence, and may be targets for reducing hepatic fat in high-risk youth.

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.

Research progress, challenges and perspectives on PNPLA3 and its variants in Liver Diseases

The human patatin-like phospholipase domain-containing 3 gene (PNPLA3) is highly expressed in liver and adipose tissue and encodes a transmembrane polypeptide chain containing 481 amino acids. The I148M variant of PNPLA3 is a single nucleotide polymorphism, which is related to a variety of liver and cardiovascular diseases and their complications (such as non-alcoholic fatty liver disease, liver fibrosis, coronary artery disease). This review mainly describes the pathophysiological effects of PNPLA3 and its variants, and their roles in the progression of liver disease and its complications.

Lipid Droplet-Associated Factors, PNPLA3, TM6SF2, and HSD17B Proteins in Hepatopancreatobiliary Cancer

Simple Summary

Aberrant lipid synthesis and reprogrammed lipid metabolism are both associated with the development and progression of pancreatic and liver cancer. Most cells store fatty acids in the form of triacylglycerols in lipid droplets. Lipid droplets are intracellular organelles that not only store neutral lipids, but also play roles as molecular messengers and signaling factors. Some cancer cells accumulate massive amount of lipid droplets. Lipid droplets and lipid droplet-associated factors are further implicated to mediate proliferation, invasion, metastasis, as well as chemotherapy resistance in several types of cancer. This review dissected recent findings on the role of several lipid droplet-associated factors, patatin-like phospholipase domain-containing 3 (PNPLA3), Transmembrane 6 superfamily member 2 (TM6SF2), and 17β-hydroxysteroid dehydrogenase (HSD17B) 11 and 13 as well as their genetic variations in hepatopancreatobiliary diseases, especially cancer.

Abstract

Pancreatic and liver cancer are leading causes of cancer deaths, and by 2030, they are projected to become the second and the third deadliest cancer respectively. Cancer metabolism, especially lipid metabolism, plays an important role in progression and metastasis of many types of cancer, including pancreatic and liver cancer. Lipid droplets are intracellular organelles that store neutral lipids, but also act as molecular messengers, and signaling factors. It is becoming increasingly evident that alterations in the regulation of lipid droplets and their associated factors influence the risk of developing not only metabolic disease but also fibrosis and cancer. In the current review article, we summarized recent findings concerning the roles of lipid droplet-associated factors, patatin-like phospholipase domain-containing 3, Transmembrane 6 superfamily member 2, and 17β-hydroxysteroid dehydrogenase 11 and 13 as well as genetic variants in pancreatic and hepatic diseases. A better understanding of cancer type- and cell type-specific roles of lipid droplet-associated factors is important for establishing new therapeutic options in the future.

Metabolic drivers of non-alcoholic fatty liver disease

BACKGROUND

The incidence of non-alcoholic fatty liver disease (NAFLD) is rapidly increasing worldwide parallel to the global obesity epidemic. NAFLD encompasses a range of liver pathologies and most often originates from metabolically driven accumulation of fat in the liver, or non-alcoholic fatty liver (NAFL). In a subset of NAFL patients, the disease can progress to non-alcoholic steatohepatitis (NASH), which is a more severe form of liver disease characterized by hepatocyte injury, inflammation, and fibrosis. Significant progress has been made over the past decade in our understanding of NASH pathogenesis, but gaps remain in our mechanistic knowledge of the precise metabolic triggers for disease worsening.

SCOPE OF REVIEW

The transition from NAFL to NASH likely involves a complex constellation of multiple factors intrinsic and extrinsic to the liver. This review focuses on early metabolic events in the establishment of NAFL and initial stages of NASH. We discuss the association of NAFL with obesity as well as the role of adipose tissue in disease progression and highlight early metabolic drivers implicated in the pathological transition from hepatic fat accumulation to steatohepatitis.

MAJOR CONCLUSIONS

The close association of NAFL with features of metabolic syndrome highlight plausible mechanistic roles for adipose tissue health and the release of lipotoxic lipids, hepatic de novo lipogenesis (DNL), and disruption of the intestinal barrier in not only the initial establishment of hepatic steatosis, but also in mediating disease progression. Human genetic variants linked to NASH risk to date are heavily biased toward genes involved in the regulation of lipid metabolism, providing compelling support for the hypothesis that NASH is fundamentally a metabolic disease.

Fasting increases 18:2-containing phosphatidylcholines to complement the decrease in 22:6-containing phosphatidylcholines in mouse skeletal muscle

Fasting stimulates catabolic reactions in skeletal muscle to survive nutrient deprivation. Cellular phospholipids have large structural diversity due to various polar-heads and acyl-chains that affect many cellular functions. Skeletal muscle phospholipid profiles have been suggested to be associated with muscle adaptations to nutritional and environmental status. However, the effect of fasting on skeletal muscle phospholipid profiles remains unknown. Here, we analyzed phospholipids using liquid chromatography mass spectrometry. We determined that fasting resulted in a decrease in 22:6-containing phosphatidylcholines (PCs) (22:6-PCs) and an increase in 18:2-containing PCs (18:2-PCs). The fasting-induced increase in 18:2-PCs was sufficient to complement 22:6-PCs loss, resulting in the maintenance of the total amount of polyunsaturated fatty acid (PUFA)-containing PCs. Similar phospholipid alterations occurred in insulin-deficient mice, which indicate that these observed phospholipid perturbations were characteristic of catabolic skeletal muscle. In lysophosphatidic acid acyltransferase 3-knockout muscles that mostly lack 22:6-PCs, other PUFA-containing PCs, mainly 18:2-PCs, accumulated. This suggests a compensatory mechanism for skeletal muscles to maintain PUFA-containing PCs.

Identification and Optimization of a Minor Allele-Specific Small Interfering RNA to Prevent PNPLA3 I148M-Driven Nonalcoholic Fatty Liver Disease

Human genome wide association studies confirm the association of the rs738409 single nucleotide polymorphism (SNP) in the gene encoding protein patatin like phospholipase domain containing 3 (PNPLA3) with nonalcoholic fatty liver disease (NAFLD); the presence of the resulting mutant PNPLA3 I148M protein is a driver of nonalcoholic steatohepatitis (NASH). While Pnpla3-deficient mice do not display an adverse phenotype, the safety of knocking down endogenous wild type PNPLA3 in humans remains unknown. To expand the scope of a potential targeted NAFLD therapeutic to both homozygous and heterozygous PNPLA3 rs738409 populations, we sought to identify a minor allele-specific small interfering RNA (siRNA). Limiting our search to SNP-spanning triggers, a series of chemically modified siRNA were tested in vitro for activity and selectivity toward PNPLA3 rs738409 mRNA. Conjugation of the siRNA to a triantennary N-acetylgalactosamine (GalNAc) ligand enabled in vivo screening using adeno-associated virus to overexpress human PNPLA3^I148M versus human PNPLA3^I148I in mouse livers. Structure-activity relationship optimization yielded potent and minor allele-specific compounds that achieved high levels of mRNA and protein knockdown of human PNPLA3^I148M but not PNPLA3^I148I. Testing of the minor allele-specific siRNA in PNPLA3^I148M-expressing mice fed a NASH-inducing diet prevented PNPLA3^I148M-driven disease phenotypes, thus demonstrating the potential of a precision medicine approach to treating NAFLD.

Adipokines in patients with hypertensive disease with obesity in the dynamics of combined antihypertensive therapy

Hypertensive disease today is one of the most common cardiovascular diseases, as well as the most common disease associated with obesity. Evaluation of the level of adipokines, namely adiponutrin and galanin, depending on the degree and duration of hypertension, the degree of obesity and their correction against the background of combined antihypertensive therapy is relevant for further understanding of this comorbidity and improvement of the early diagnostics. 127 people were examined, including 107 patients with hypertension of degree 1–3 and 20 healthy persons. Of the patients included in the study, the adiponutrin and the galanin levels were determined in 58 patients, out of which 22 were prescribed different regimens of combined antihypertensive therapy. To determine the level of adiponutrin and galanin, an enzyme-linked immunosorbent assay was used. A significant increase was found in the blood serum of the examined adipokines in comparison with the control group: the galanin level was 4.8 times higher than in the control group, the adiponutrin level in patients with this comorbid pathology was 3.3 times higher than that in the control group. The galanin level is most pronounced in patients with hypertension of degree 3 and obesity of degree 3, which is confirmed by the presence of a direct correlation with systolic, diastolic and pulse blood pressure, very low density lipoprotein cholesterol. The adiponutrin level in the blood serum increased correspondingly to the increase in body mass index: in patients with obesity of degree 3 it was 15.8 times higher than this indicator in patients with normal body weight, 8.8 times higher than in patients with overweight, 6.1 times higher than in patients with obesity of degree 1 and 2.5 times higher than in patients with obesity of degree 2. The levels of the studied adipokines in patients differed also relative to the duration of hypertension. There was a 1.8-, 5.1-, 5.2-fold increase (respectively, ≤5, 6–10, >10 years) of the galanin content in the blood serum compared to the control group. Also an increase of the serum adiponutrin level was noted in comparison with the control group. Against the background of combined antihypertensive therapy, we observed favourable dynamics of galanin and adiponutrin. It is important to conduct further studies to assess the activity of galanin and adiponutrin with a longer follow-up period in wider populations.

Nonalcohol fatty liver disease: balancing supply and utilization of triglycerides

PURPOSE OF REVIEW

Nonalcoholic fatty liver disease (NAFLD) is defined as the abnormal accumulation of lipids in the liver, called hepatic steatosis, which occurs most often as a concomitant of the metabolic syndrome. Its incidence has surged significantly in recent decades concomitant with the obesity pandemic and increasing consumption of refined carbohydrates and saturated fats. This makes a review of the origins of NAFLD timely and relevant.

RECENT FINDINGS

This disorder, which shares histologic markers found in alcoholic fatty liver disease, was named NAFLD to distinguish it from the latter. Recently, however, the term metabolic-associated fatty liver disease (MAFLD) has been suggested as a refinement of NAFLD that should highlight the central, etiologic role of insulin resistance, obesity, and diabetes mellitus. The complexity of the pathways involved in the regulation of hepatic triglyceride synthesis and utilization have become obvious over the past 10 years, including the recent identification of monogenic causes of metabolic-associated fatty liver disease. These include PNPLA3, transmembrane 6 superfamily member 2, GCKR, membrane-bound O-acyltransferase 7 suggest targets for new therapies for hepatic steatosis.

SUMMARY

The current review can serve as a guide to the complex pathways involved in the maintenance of hepatic triglyceride levels as well as an introduction to the most recent discoveries, including those of key genes that have provided opportunities for new and novel therapeutics.

Nutrigenomics and Nutrigenetics in Metabolic- (Dysfunction) Associated Fatty Liver Disease: Novel Insights and Future Perspectives

Metabolic- (dysfunction) associated fatty liver disease (MAFLD) represents the predominant hepatopathy and one of the most important systemic, metabolic-related disorders all over the world associated with severe medical and socio-economic repercussions due to its growing prevalence, clinical course (steatohepatitis and/or hepatocellular-carcinoma), and related extra-hepatic comorbidities. To date, no specific medications for the treatment of this condition exist, and the most valid recommendation for patients remains lifestyle change. MAFLD has been associated with metabolic syndrome; its development and progression are widely influenced by the interplay between genetic, environmental, and nutritional factors. Nutrigenetics and nutrigenomics findings suggest nutrition’s capability, by acting on the individual genetic background and modifying the specific epigenetic expression as well, to influence patients’ clinical outcome. Besides, immunity response is emerging as pivotal in this multifactorial scenario, suggesting the interaction between diet, genetics, and immunity as another tangled network that needs to be explored. The present review describes the genetic background contribution to MAFLD onset and worsening, its possibility to be influenced by nutritional habits, and the interplay between nutrients and immunity as one of the most promising research fields of the future in this context.

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.

PNPLA3 Genotype, Arachidonic Acid Intake, and Unsaturated Fat Intake Influences Liver Fibrosis in Hispanic Youth with Obesity

Non-alcoholic fatty liver disease impacts 15.2% of Hispanic adolescents and can progress to a build-up of scared tissue called liver fibrosis. If diagnosed early, liver fibrosis may be reversible, so it is necessary to understand risk factors. The aims of this study in 59 Hispanic adolescents with obesity were to: (1) identify potential biological predictors of liver fibrosis and dietary components that influence liver fibrosis, and (2) determine if the association between dietary components and liver fibrosis differs by PNPLA3 genotype, which is highly prevalent in Hispanic adolescents and associated with elevated liver fat. We examined liver fat and fibrosis, genotyped for PNPLA3 gene, and assessed diet via 24-h diet recalls. The prevalence of increased fibrosis was 20.9% greater in males, whereas participants with the GG genotype showed 23.7% greater prevalence. Arachidonic acid was associated with liver fibrosis after accounting for sex, genotype, and liver fat (β = 0.072, p = 0.033). Intakes of several dietary types of unsaturated fat have different associations with liver fibrosis by PNPLA3 genotype after accounting for sex, caloric intake, and liver fat. These included monounsaturated fat (βCC/CG = -0.0007, βGG = 0.03, p-value = 0.004), polyunsaturated fat (βCC/CG = -0.01, βGG = 0.02, p-value = 0.01), and omega-6 (βCC/CG = -0.0102, βGG = 0.028, p-value = 0.01). Results from this study suggest that reduction of arachidonic acid and polyunsaturated fatty acid intake might be important for the prevention of non-alcoholic fatty liver disease progression, especially among those with PNPLA3 risk alleles.

Impact of the Association Between PNPLA3 Genetic Variation and Dietary Intake on the Risk of Significant Fibrosis in Patients With NAFLD

INTRODUCTION

This study explored the relationship between patatin-like phospholipase domain-containing 3 gene (PNPLA3 rs738409), nutrient intake, and liver histology severity in patients with nonalcoholic fatty liver disease (NAFLD).

METHODS

PNPLA3-rs738409 variant was genotyped in 452 non-Hispanic whites with histologically confirmed NAFLD who completed Food Frequency Questionnaire within 6 months of their liver biopsy. The fibrosis severity on liver histology was the outcome of interest.

RESULTS

The distribution of PNPLA3 genotypes was CC: 28%, CG: 46%, and GG: 25%. High-carbohydrate (% of energy/d) intake was positively associated (adjusted [Adj] odds ratio [OR]: 1.03, P < 0.01), whereas higher n-3 polyunsaturated fatty acids (n-3 PUFAs) (g/d) (Adj. OR: 0.17, P < 0.01), isoflavones (mg/d) (Adj. OR: 0.74, P = 0.049), methionine (mg/d) (Adj. OR: 0.32, P < 0.01), and choline (mg/d) (Adj. OR: 0.32, P < 0.01) intakes were inversely associated with increased risk of significant fibrosis (stage of fibrosis ≥2). By using an additive model of inheritance, our moderation analysis showed that PNPLA3 rs738409 significantly modulates the relationship between carbohydrate (%), n-3 PUFAs, total isoflavones, methionine, and choline intakes and fibrosis severity in a dose-dependent, genotype manner. These dietary factors tended to have a larger and significant effect on fibrosis severity among rs738409 G-allele carriers. Associations between significant fibrosis and carbohydrates (Adj. OR: 1.04, P = 0.019), n-3 PUFAs (Adj. OR: 0.16, P < 0.01), isoflavones (Adj. OR: 0.65, P = 0.025), methionine (Adj. OR: 0.30, P < 0.01), and total choline (Adj. OR: 0.29, P < 0.01) intakes remained significant only among rs738409 G-allele carriers.

DISCUSSION

This gene-diet interaction study suggests that PNPLA3 rs738409 G-allele might modulate the effect of specific dietary nutrients on risk of fibrosis in patients with NAFLD.