The PNPLA3 Ile148Met interacts with overweight and dietary intakes on fasting triglyceride levels

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

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

No association of NAFLD-related polymorphisms in PNPLA3 and TM6SF2 with all-cause and cardiovascular mortality in an Austrian population study

BACKGROUND AND AIMS

Single-nucleotide-polymorphisms in PNPLA3-rs738409 and the TM6SF2-rs58542926, associated with metabolic-dysfunction-associated fatty liver disease (MAFLD), have been discussed as potentially protective for cardiovascular diseases. Therefore, we aimed to study the associations of PNPLA3/TM6SF2 variants with MAFLD and cardiovascular risk in a population-based sample of asymptomatic patients.

METHODS

The study cohort comprised 1742 patients of European decent aged 45-80 years from a registry study undergoing screening colonoscopy for colorectal cancer between 2010 and 2014. SCORE2 and Framingham risk score calculated to assess cardiovascular risk. Data on survival were obtained from the national death registry RESULTS: Half of included patients were male (52%, 59 ± 10 years), 819 (47%) carried PNPLA3‑G and 278 (16%) TM6SF2-T-alleles. MAFLD (PNPLA3‑G-allele: 46% vs. 41%, p = 0.041; TM6SF2‑T-allele: 54% vs. 42%, p < 0.001) was more frequent in patients harbouring risk alleles with both showing independent associations with MAFLD on multivariable binary logistic regression analysis. While median Framingham risk score was lower in PNPLA3‑G-allele carriers (10 vs. 8, p = 0.011), SCORE2 and established cardiovascular diseases were similar across carriers vs. non-carriers of the respective risk-alleles. During a median follow-up of 9.1 years, neither PNPLA3‑G-allele nor TM6SF2‑T-allele was associated with overall nor with cardiovascular mortality.

CONCLUSION

Carriage of PNPLA3/TM6SF2 risk alleles could not be identified as significant factor for all-cause or cardiovascular mortality in asymptomatic middle-aged individuals undergoing screening colonoscopy.

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.

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.

What do we know about nutrient-based strategies targeting molecular mechanisms associated with obesity-related fatty liver disease?

Obesity is a risk factor for developing nonalcoholic fatty liver disease (NAFLD), and the associated molecular mechanisms could be targeted with nutrient-based strategies. Therefore, it is necessary to review the current mechanisms to propose further treatments. Obesity facilitates the onset of insulin resistance, lipidic abnormalities, hepatic fat accumulation, lipid peroxidation, mitochondrial dysfunction, excessive reactive oxygen species (ROS) production, and inflammation, all related to further steatosis progression and fibrosis. Microbiota alterations can also influence liver disease by the translocation of pathogenic bacteria, energy extraction from short chain fatty acids (SCFAs), intestinal suppression of the expression of fasting-induced adipose factor (FIAF), reduction of bile acids, and altered choline metabolism. There are also genetic polymorphisms in metabolic proteins that predispose to a higher risk of liver diseases, such as those found in the patatin-like phospholipase domain-containing 3 (PNPLA3), transmembrane 6 superfamily member 2 (TM6SF2), membrane-bound O-acyltransferase domain-containing 7 (MBOAT7) or also known as lysophosphatidylinositol acyltransferase 1 (LPIAT1), transmembrane channel-like 4 genes (TMC4), fat mass and obesity-associated protein (FTO), the b Klotho (KLB) and carboxylesterase (CES1). No clear dietary guidelines target all mechanisms related to NAFLD development and progression. However, energy and carbohydrate intake restriction, regular physical exercise, supplementation of antioxidants, and restoration of gut microbiota seem to have beneficial effects on the new proposed features of NAFLD.

Genome-wide association analysis of serum alanine and aspartate aminotransferase, and the modifying effects of BMI in 388k European individuals

Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are biomarkers for liver health. Here we report the largest genome-wide association analysis to date of serum ALT and AST levels in over 388k people of European ancestry from UK biobank and DiscovEHR. Eleven million imputed markers with a minor allele frequency (MAF) ≥ 0.5% were analyzed. Overall, 300 ALT and 336 AST independent genome-wide significant associations were identified. Among them, 81 ALT and 61 AST associations are reported for the first time. Genome-wide interaction study identified 9 ALT and 12 AST independent associations significantly modified by body mass index (BMI), including several previously reported potential liver disease therapeutic targets, for example, PNPLA3, HSD17B13, and MARC1. While further work is necessary to understand the effect of ALT and AST-associated variants on liver disease, the weighted burden of significant BMI-modified signals is significantly associated with liver disease outcomes. In summary, this study identifies genetic associations which offer an important step forward in understanding the genetic architecture of serum ALT and AST levels. Significant interactions between BMI and genetic loci not only highlight the important role of adiposity in liver damage but also shed light on the genetic etiology of liver disease in obese individuals.

Assessing Interactions between PNPLA3 and Dietary Intake on Liver Steatosis in Mexican-Origin Adults

Mexican-origin (MO) adults have among the highest rates of nonalcoholic fatty liver disease (NAFLD) placing them at increased risk of liver cancer. Evidence suggests that a single nucleotide polymorphism (SNP) in the PNPLA3 gene, rs738409, increases the risk and progression of NAFLD and may modify the relationship between certain dietary factors and liver steatosis. The purpose of this study was to identify whether interactions exist between specific dietary factors and rs738409 genotype status among MO adults in relation to levels of liver steatosis. We analyzed cross-sectional data from a sample of 288 MO adults. Participants completed at least two 24-h dietary recalls. Multiple linear regression was performed assuming an additive genetic model to test the main effects of several dietary variables on levels of hepatic steatosis, adjusting for covariates. To test for effect modification, the product of the genotype and the dietary variable was included as a covariate in the model. No significant association between dietary intake and level of hepatic steatosis was observed, nor any significant gene-diet interactions. Our findings suggest that dietary intake may have the same magnitude of protective or deleterious effect even among MO adults with high genetic risk for NAFLD and NAFLD progression.

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.

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.

Toward Genetic Prediction of Nonalcoholic Fatty Liver Disease Trajectories: PNPLA3 and Beyond

Nonalcoholic fatty liver disease (NAFLD) is on the verge of becoming the leading cause of liver disease. NAFLD develops at the interface between environmental factors and inherited predisposition. Genome-wide association studies, followed by exome-wide analyses, led to identification of genetic risk variants (eg, PNPLA3, TM6SF2, and SERPINA1) and key pathways involved in fatty liver disease pathobiology. Functional studies improved our understanding of these genetic factors and the molecular mechanisms underlying the trajectories from fat accumulation to fibrosis, cirrhosis, and cancer over time. Here, we summarize key NAFLD risk genes and illustrate their interactions in a 3-dimensional "risk space." Although NAFLD genomics sometimes appears to be "lost in translation," we envision clinical utility in trial design, outcome prediction, and NAFLD surveillance.

Gene-environment interactions due to quantile-specific heritability of triglyceride and VLDL concentrations

"Quantile-dependent expressivity" is a dependence of genetic effects on whether the phenotype (e.g., triglycerides) is high or low relative to its distribution in the population. Quantile-specific offspring-parent regression slopes (βOP) were estimated by quantile regression for 6227 offspring-parent pairs. Quantile-specific heritability (h2), estimated by 2βOP/(1 + rspouse), decreased 0.0047 ± 0.0007 (P = 2.9 × 10-14) for each one-percent decrement in fasting triglyceride concentrations, i.e., h2 ± SE were: 0.428 ± 0.059, 0.230 ± 0.030, 0.111 ± 0.015, 0.050 ± 0.016, and 0.033 ± 0.010 at the 90th, 75th, 50th, 25th, and 10th percentiles of the triglyceride distribution, respectively. Consistent with quantile-dependent expressivity, 11 drug studies report smaller genotype differences at lower (post-treatment) than higher (pre-treatment) triglyceride concentrations. This meant genotype-specific triglyceride changes could not move in parallel when triglycerides were decreased pharmacologically, so that subtracting pre-treatment from post-treatment triglyceride levels necessarily created a greater triglyceride decrease for the genotype with a higher pre-treatment value (purported precision-medicine genetic markers). In addition, sixty-five purported gene-environment interactions were found to be potentially attributable to triglyceride's quantile-dependent expressivity, including gene-adiposity (APOA5, APOB, APOE, GCKR, IRS-1, LPL, MTHFR, PCSK9, PNPLA3, PPARγ2), gene-exercise (APOA1, APOA2, LPL), gene-diet (APOA5, APOE, INSIG2, LPL, MYB, NXPH1, PER2, TNFA), gene-alcohol (ALDH2, APOA5, APOC3, CETP, LPL), gene-smoking (APOC3, CYBA, LPL, USF1), gene-pregnancy (LPL), and gene-insulin resistance interactions (APOE, LPL).

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.

A genome-wide search for gene-by-obesity interaction loci of dyslipidemia in Koreans shows diverse genetic risk alleles

Dyslipidemia is a well-established risk factor for CVD. Studies suggest that similar fat accumulation in a given population might result in different levels of dyslipidemia risk among individuals; for example, despite similar or leaner body composition compared with Caucasians, Asians of Korean descent experience a higher prevalence of dyslipidemia. These variations imply a possible role of gene-obesity interactions on lipid profiles. Genome-wide association studies have identified more than 500 loci regulating plasma lipids, but the interaction structure between genes and obesity traits remains unclear. We hypothesized that some loci modify the effects of obesity on dyslipidemia risk and analyzed extensive gene-environment interactions (G×Es) at genome-wide levels to search for replicated gene-obesity interactive SNPs. In four Korean cohorts (n = 18,025), we identified and replicated 20 gene-obesity interactions, including novel variants (SCN1A and SLC12A8) and known lipid-associated variants (APOA5, BUD13, ZNF259, and HMGCR). When we estimated the additional heritability of dyslipidemia by considering G×Es, the gain was substantial for triglycerides (TGs) but mild for LDL cholesterol (LDL-C) and total cholesterol (Total-C); the interaction explained up to 18.7% of TG, 2.4% of LDL-C, and 1.9% of Total-C heritability associated with waist-hip ratio. Our findings suggest that some individuals are prone to develop abnormal lipid profiles, particularly with regard to TGs, even with slight increases in obesity indices; ethnic diversities in the risk alleles might partly explain the differential dyslipidemia risk between populations. Research about these interacting variables may facilitate knowledge-based approaches to personalize health guidelines according to individual genetic profiles.

Insulin Resistance Exacerbates Genetic Predisposition to Nonalcoholic Fatty Liver Disease in Individuals Without Diabetes

The accumulation of excess fat in the liver (hepatic steatosis) in the absence of heavy alcohol consumption causes nonalcoholic fatty liver disease (NAFLD), which has become a global epidemic. Identifying metabolic risk factors that interact with the genetic risk of NAFLD is important for reducing disease burden. We tested whether serum glucose, insulin, insulin resistance, triglyceride (TG), low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, body mass index (BMI), and waist-to-hip ratio adjusted for BMI interact with genetic variants in or near the patatin-like phospholipase domain containing 3 (PNPLA3) gene, the glucokinase regulatory protein (GCKR) gene, the neurocan/transmembrane 6 superfamily member 2 (NCAN/TM6SF2) gene, and the lysophospholipase-like 1 (LYPLAL1) gene to exacerbate hepatic steatosis, estimated by liver attenuation. We performed association analyses in 10 population-based cohorts separately and then meta-analyzed results in up to 14,751 individuals (11,870 of European ancestry and 2,881 of African ancestry). We found that PNPLA3-rs738409 significantly interacted with insulin, insulin resistance, BMI, glucose, and TG to increase hepatic steatosis in nondiabetic individuals carrying the G allele. Additionally, GCKR-rs780094 significantly interacted with insulin, insulin resistance, and TG. Conditional analyses using the two largest European ancestry cohorts in the study showed that insulin levels accounted for most of the interaction of PNPLA3-rs738409 with BMI, glucose, and TG in nondiabetic individuals. Insulin, PNPLA3-rs738409, and their interaction accounted for at least 8% of the variance in hepatic steatosis in these two cohorts. Conclusion: Insulin resistance, either directly or through the resultant elevated insulin levels, more than other metabolic traits, appears to amplify the PNPLA3-rs738409-G genetic risk for hepatic steatosis. Improving insulin resistance in nondiabetic individuals carrying PNPLA3-rs738409-G may preferentially decrease hepatic steatosis.

Dissociation of Fatty Liver and Insulin Resistance in I148M PNPLA3 Carriers: Differences in Diacylglycerol (DAG) FA18:1 Lipid Species as a Possible Explanation

Fatty liver is tightly associated with insulin resistance and the development of type 2 diabetes. I148M variant in patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene is associated with high liver fat but normal insulin sensitivity. The underlying mechanism of the disassociation between high liver fat but normal insulin sensitivity remains obscure. We investigated the effect of I148M variant on hepatic lipidome of subjects with or without fatty liver, using the Lipidyzer method. Liver samples of four groups of subjects consisting of normal liver fat with wild-type PNPLA3 allele (group 1); normal liver fat with variant PNPLA3 allele (group 2); high liver fat with wild-type PNPLA3 allele (group 3); high liver fat with variant PNPLA3 allele (group 4); were analyzed. When high liver fat to normal liver fat groups were compared, wild-type carriers (group 3 vs. group 1) showed similar lipid changes compared to I148M PNPLA3 carriers (group 4 vs. group 2). On the other hand, in wild-type carriers, increased liver fat significantly elevated the proportion of specific DAGs (diacylglycerols), mostly DAG (FA18:1) which, however, remained unchanged in I148M PNPLA3 carriers. Since DAG (FA18:1) has been implicated in hepatic insulin resistance, the unaltered proportion of DAG (FA18:1) in I148M PNPLA3 carriers with fatty liver may explain the normal insulin sensitivity in these subjects.

AQP3 is regulated by PPARγ and JNK in hepatic stellate cells carrying PNPLA3 I148M

Aquaglyceroporins (AQPs) allow the movement of glycerol that is required for triglyceride formation in hepatic stellate cells (HSC), as key cellular source of fibrogenesis in the liver. The genetic polymorphism I148M of the patatin-like phospholipase domain-containing 3 (PNPLA3) is associated with hepatic steatosis and its progression to steatohepatitis (NASH), fibrosis and cancer. We aimed to explore the role of AQP3 for HSC activation and unveil its potential interactions with PNPLA3. HSC were isolated from human liver, experiments were performed in primary HSC and human HSC line LX2. AQP3 was the only aquaglyceroporin present in HSC and its expression decreased during activation. The PPARγ agonist, rosiglitazone, recovered AQP3 expression also in PNPLA3 I148M carrying HSC. When PNPLA3 was silenced, AQP3 expression increased. In liver sections from patients with NASH, the decreased amount of AQP3 was proportional to the severity of fibrosis and presence of the PNPLA3 I148M variant. In PNPLA3 I148M cells, the blockade of JNK pathway upregulated AQP3 in synergism with PPARγ. In conclusion, we demonstrated profound reduction of AQP3 in HSC carrying the PNPLA3 I148M variant in parallel to decreased PPARγ activation, which could be rescued by rosiglitazone and blockade of JNK.

PNPLA3 rs1010023 Predisposes Chronic Hepatitis B to Hepatic Steatosis but Improves Insulin Resistance and Glucose Metabolism

PNPLA3 polymorphisms serve as the genetic basis of hepatic steatosis in normal population and lead to dysregulated glucose metabolism. Whether it underlies the hepatic steatosis and glucose homeostasis in chronic hepatitis B patients remains uncertain. Here, we investigated the PNPLA3 polymorphisms in biopsy-proven chronic hepatitis B patients with (CHB+HS group, n = 52) or without hepatic steatosis (CHB group, n = 47) and non-CHB subjects with (HS group, n = 37) or without hepatic steatosis (normal group, n = 45). When compared to the TT genotype, C-allele at PNPLA3 rs1010023 (CC and TC genotypes) conferred higher risk to hepatic steatosis in chronic hepatitis B patients (odds ratio (OR) = 1.768, 95% confidence interval (CI): 1.027-3.105; P = 0.045) independent of age, gender, and body mass index. In contrast to their role in hepatic steatosis, CC and TC genotypes of PNPLA3 rs1010023 were correlated to significant improvement of homeostasis model assessment index (HOMA-IR) as compared to TT genotype in the CHB+HS group. Downregulated fasting blood glucose also characterized the CHB+HS patients with C-allele at PNPLA3 rs1010023 (CC/TC versus TT: 4.81 ± 0.92 mmol/L versus 5.86 ± 2.11 mmol/L, P = 0.02). These findings suggest that PNPLA3 rs1010023 may predispose chronic hepatitis B patients to hepatic steatosis but protects them from glucose dysregulation by attenuating insulin resistance.

Erratum to: The PNPLA3 Ile148Met interacts with overweight and dietary intakes on fasting triglyceride levels

[This corrects the article DOI: 10.1007/s12263-014-0388-4.].

PNPLA3 gene in liver diseases

Genome-wide association studies (GWAS) in the field of liver diseases have revealed previously unknown pathogenic loci and generated new biological hypotheses. In 2008, a GWAS performed in a population-based sample study, where hepatic liver fat content was measured by magnetic spectroscopy, showed a strong association between a variant (rs738409 C>G p.I148M) in the patatin-like phospholipase domain containing 3 (PNPLA3) gene and nonalcoholic fatty liver disease. Further replication studies have shown robust associations between PNPLA3 and steatosis, fibrosis/cirrhosis, and hepatocellular carcinoma on a background of metabolic, alcoholic, and viral insults. The PNPLA3 protein has lipase activity towards triglycerides in hepatocytes and retinyl esters in hepatic stellate cells. The I148M substitution leads to a loss of function promoting triglyceride accumulation in hepatocytes. Although PNPLA3 function has been extensively studied, the molecular mechanisms leading to hepatic fibrosis and carcinogenesis remain unclear. This unsuspected association has highlighted the fact that liver fat metabolism may have a major impact on the pathophysiology of liver diseases. Conversely, alone, this locus may have limited predictive value with regard to liver disease outcomes in clinical practice. Additional studies at the genome-wide level will be required to identify new variants associated with liver damage and cancer to explain a greater proportion of the heritability of these phenotypes. Thus, incorporating PNPLA3 and other genetic variants in combination with clinical data will allow for the development of tailored predictive models. This attractive approach should be evaluated in prospective cohorts.

Do Genetic Factors Modify the Relationship Between Obesity and Hypertriglyceridemia?

Background—

Obesity is a major risk factor for dyslipidemia, but this relationship is highly variable. Recently published data from 2 Danish cohorts suggest that genetic factors may underlie some of this variability.

Methods and Results—

We tested whether established triglyceride-associated loci modify the relationship of body mass index (BMI) and triglyceride concentrations in 2 Swedish cohorts (the Gene–Lifestyle Interactions and Complex Traits Involved in Elevated Disease Risk [GLACIER Study; N=4312] and the Malmö Diet and Cancer Study [N=5352]). The genetic loci were amalgamated into a weighted genetic risk score (WGRS TG ) by summing the triglyceride-elevating alleles (weighted by their established marginal effects) for all loci. Both BMI and the WGRS TG were strongly associated with triglyceride concentrations in GLACIER, with each additional BMI unit (kg/m 2 ) associated with 2.8% ( P =8.4×10 –84 ) higher triglyceride concentration and each additional WGRS TG unit with 2% ( P =7.6×10 –48 ) higher triglyceride concentration. Each unit of the WGRS TG was associated with 1.5% higher triglyceride concentrations in normal weight and 2.4% higher concentrations in overweight/obese participants ( P interaction =0.056). Meta-analyses of results from the Swedish cohorts yielded a statistically significant WGRS TG ×BMI interaction effect ( P interaction =6.0×10 –4 ), which was strengthened by including data from the Danish cohorts ( P interaction =6.5×10 –7 ). In the meta-analysis of the Swedish cohorts, nominal evidence of a 3-way interaction (WGRS TG ×BMI×sex) was observed ( P interaction =0.03), where the WGRS TG ×BMI interaction was only statistically significant in females. Using protein–protein interaction network analyses, we identified molecular interactions and pathways elucidating the metabolic relationships between BMI and triglyceride-associated loci.

Conclusions—

Our findings provide evidence that body fatness accentuates the effects of genetic susceptibility variants in hypertriglyceridemia, effects that are most evident in females.

PNPLA3 I148M Variant Influences Circulating Retinol in Adults with Nonalcoholic Fatty Liver Disease or Obesity

BACKGROUND

Retinol is a lipid-soluble essential nutrient that is stored as retinyl esters in lipid droplets of hepatic stellate cells. Patatin-like phospholipase domain-containing 3 (PNPLA3), through its retinyl-palmitate lipase activity, releases retinol from lipid droplets in hepatic stellate cells in vitro and ex vivo. We have shown that the genetic variant I148M (rs738409) reduces the PNPLA3 retinyl-palmitate lipase activity.

OBJECTIVE

The aim of the present genetic association study was to test whether overweight/obese carriers of the PNPLA3 148M mutant allele had lower circulating concentrations of retinol than individuals who are homozygous for the 148I allele.

METHODS

PNPLA3 I148M (rs738409) was genotyped by Taqman assay in 76 overweight/obese individuals [BMI (kg/m(2)) ≥25; mean ± SD age: 59.7 ± 11.4 y; male gender: 70%] with a histologic diagnosis of nonalcoholic fatty liver disease (NAFLD; namely the Milan NAFLD cohort) and in 413 obese men (BMI ≥30; mean ± SD age: 57.1 ± 4.9 y) from the α-Tocopherol, β-Carotene Cancer Prevention (ATBC) Study. Serum concentrations of retinol and α-tocopherol were measured by HPLC in both cohorts. β-Carotene concentrations in the ATBC study were measured by using HPLC.

RESULTS

The PNPLA3 148M mutant allele was associated with lower fasting circulating concentrations of retinol (β = -0.289, P = 0.03) in adults with NAFLD (Milan NAFLD cohort). The PNPLA3 148M mutant allele was also associated with lower fasting circulating concentrations of retinol in adults with a BMI ≥30 (ATBC study; β = -0.043, P = 0.04).

CONCLUSION

We showed for the first time, to our knowledge, that carriers of the PNPLA3 148M allele with either fatty liver plus obesity or obesity alone have lower fasting circulating retinol concentrations.

Patatin-like phospholipase 3 (rs738409) gene polymorphism is associated with increased liver enzymes in obese adolescents and metabolic syndrome in all ages

BACKGROUND

Obesity is associated with non-alcoholic fatty liver disease (NAFLD), and the patatin-like phospholipase 3 (PNPLA3) rs738409 (Ile148Met, C>G) gene polymorphism is one of the most important genetic determinants of NAFLD. Carriers have been reported to better respond to lifestyle modification.

AIM

To investigate the effect of rs738409 on overweight/obese adolescents and adults with and without metabolic syndrome (MetS).

METHODS

Two hundred and eighty-eight overweight/obese and 209 normal weight participants of the STYJOBS/EDECTA cohort (NCT00482924) were analysed for PNPLA3 genotypes.

RESULTS

Compared to overweight/obese without MetS, in overweight/obese study participants with MetS, the presence of the G allele (148Met) was significantly higher (CC: 5.0% vs. 9.2%, Spearman's correlation, 0.12; P = 0.038). Persons with CG (heterozygote for the risk allele) and with GG (homozygote for the risk allele) genotypes showed significantly higher ALT levels than those with CC genotypes. Even young individuals aged below 20 years had significantly increased ALT levels if they were homozygote with the G allele.

CONCLUSIONS

The PNPLA3 rs738409 polymorphism is associated already in youths with increased ALT, and is more frequent in obese with MetS of all ages. Hence, overweight/obese rs738409 carriers should be identified early in life and treated with a rigorous life style intervention.

Composite prognostic models across the non-alcoholic fatty liver disease spectrum: Clinical application in developing countries

Heterogeneity in clinical presentation, histological severity, prognosis and therapeutic outcomes characteristic of non-alcoholic fatty liver disease (NAFLD) necessitates the development of scientifically sound classification schemes to assist clinicians in stratifying patients into meaningful prognostic subgroups. The need for replacement of invasive liver biopsies as the standard method whereby NAFLD is diagnosed, graded and staged with biomarkers of histological severity injury led to the development of composite prognostic models as potentially viable surrogate alternatives. In the present article, we review existing scoring systems used to (1) confirm the presence of undiagnosed hepatosteatosis; (2) distinguish between simple steatosis and NASH; and (3) predict advanced hepatic fibrosis, with particular emphasis on the role of NAFLD as an independent cardio-metabolic risk factor. In addition, the incorporation of functional genomic markers and application of emerging imaging technologies are discussed as a means to improve the diagnostic accuracy and predictive performance of promising composite models found to be most appropriate for widespread clinical adoption.

Altered hepatic gene expression in nonalcoholic fatty liver disease is associated with lower hepatic n-3 and n-6 polyunsaturated fatty acids

In nonalcoholic fatty liver disease, hepatic gene expression and fatty acid (FA) composition have been reported independently, but a comprehensive gene expression profiling in relation to FA composition is lacking. The aim was to assess this relationship. In a cross-sectional study, hepatic gene expression (Illumina Microarray) was first compared among 20 patients with simple steatosis (SS), 19 with nonalcoholic steatohepatitis (NASH), and 24 healthy controls. The FA composition in hepatic total lipids was compared between SS and NASH, and associations between gene expression and FAs were examined. Gene expression differed mainly between healthy controls and patients (SS and NASH), including genes related to unsaturated FA metabolism. Twenty-two genes were differentially expressed between NASH and SS; most of them correlated with disease severity and related more to cancer progression than to lipid metabolism. Biologically active long-chain polyunsaturated FAs (PUFAs; eicosapentaenoic acid + docosahexaenoic acid, arachidonic acid) in hepatic total lipids were lower in NASH than in SS. This may be related to overexpression of FADS1, FADS2, and PNPLA3. The degree and direction of correlations between PUFAs and gene expression were different among SS and NASH, which may suggest that low PUFA content in NASH modulates gene expression in a different way compared with SS or, alternatively, that gene expression influences PUFA content differently depending on disease severity (SS versus NASH).

CONCLUSION

Well-defined subjects with either healthy liver, SS, or NASH showed distinct hepatic gene expression profiles including genes involved in unsaturated FA metabolism. In patients with NASH, hepatic PUFAs were lower and associations with gene expression were different compared to SS.

Isoleucine-to-methionine substitution at residue 148 variant of PNPLA3 gene and metabolic outcomes in gestational diabetes

BACKGROUND

A single nucleotide polymorphism (SNP) of the patatin-like phospholipase-3 (PNPLA3)/adiponutrin gene (rs738409 C>G) is strongly associated with nonalcoholic fatty liver disease; to our knowledge, no data are available on the impact of this PNPLA3 SNP on liver and metabolic outcomes during pregnancy in patients with gestational diabetes (GD).

OBJECTIVE

We evaluated the impact of the PNPLA3 rs738409 SNP on liver enzymes, metabolic indexes, and maternal and neonatal outcomes in 200 GD patients enrolled in a lifestyle intervention.

DESIGN

In a randomized trial with a 2 × 2 factorial design, exercise significantly improved maternal and neonatal outcomes in GD patients. Effects of the G allele on metabolic and liver indexes and maternal and neonatal outcomes were evaluated in these patients.

RESULTS

At the end of the trial, fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) values were significantly lower and liver enzymes significantly higher in PNPLA3 G-allele carriers. In a multiple regression model, the G allele was associated directly with aspartate aminotransferase (β = 2.60; 95% CI: 0.99, 4.20), alanine aminotransferase (β = 3.70; 95% CI: 1.78, 5.62), and γ-glutamyl transferase (β = 3.70; 95% CI: 0.80, 6.60) and inversely with insulin (β = -2.01; 95% CI: -3.24, -0.78) and HOMA-IR (β = -0.39; -0.64, -0.14) values at the end of the trial. In a multiple logistic regression model, the G allele was associated directly with risk of developing liver enzyme elevation during pregnancy (OR: 4.21; 95% CI: 1.78, 9.97) and inversely with the birth of large-for-gestational-age newborns (OR: 0.19; 95% CI: 0.06, 0.62). No diet × genotype or exercise × genotype interaction was shown.

CONCLUSION

The PNPLA3 SNP rs738409 G allele was associated with risk of mildly elevated transaminases in GD independent of a lifestyle intervention and despite a significant reduction in insulin resistance and risk of macrosomic offspring. This trial was registered at clinicaltrials.gov as NCT01506310.

Personalizing care for nonalcoholic fatty liver disease patients: what are the research priorities?

Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease whose prevalence has reached global epidemic proportions, not only in adults but also in children. From a clinical point of view, NAFLD stems a myriad of challenges to physicians, researchers and patients. In this study, we revise the current knowledge and recent insights on NAFLD pathogenesis and diagnosis in the context of a personalized perspective with special focus on the following issues: noninvasive biomarkers for the evaluation of disease severity and progression, lifestyle-related patients' recommendations, risk prediction of disease by genetic testing, management of NAFLD-associated comorbidities and patient-oriented therapeutic intervention strategies.