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The PNPLA3 p.I148M, TM6SF2 p.E167K, and MBOAT7 rs641738 variants represent genetic risk factors for nonalcoholic fatty liver disease (NAFLD). Here we investigate if these polymorphisms modulate both steatosis and fibrosis in patients with NAFLD. We recruited 515 patients with NAFLD (age 16–88 years, 280 female patients). Liver biopsies were performed in 320 patients. PCR-based assays were used to genotype the PNPLA3, TM6SF2, and MBOAT7 variants. Carriers of the PNPLA3 and TM6SF2 risk alleles showed increased serum aspartate aminotransferase and alanine transaminase activities (P < 0.05). The PNPLA3 genotype was associated with steatosis grades S2–S3 (P < 0.001) and fibrosis stages F2–F4 (P < 0.001). The TM6SF2 genotype was associated with steatosis (P = 0.003) but not with fibrosis (P > 0.05). The MBOAT7 variant was solely associated with increased fibrosis (P = 0.046). In the multivariate model, variants PNPLA3 (P = 0.004) and TM6SF2 (P = 0.038) were associated with steatosis. Fibrosis stages were affected by the PNPLA3 (P = 0.042) and MBOAT7 (P = 0.021) but not by the TM6SF2 polymorphism (P > 0.05). The PNPLA3, TM6SF2, and MBOAT7 variants are associated with increased liver injury. The TM6SF2 variant seems to modulate predominantly hepatic fat accumulation, whereas the MBOAT7 polymorphism is linked to fibrosis. The PNPLA3 polymorphism confers risk of both increased steatosis and fibrosis.

Patatin-like phospholipase domain containing proteins (PNPLAs) play diverse roles in lipid metabolism. In this review, we focus on the enzymatic properties and predicted 3D structures of PNPLA1-5. PNPLA2-4 exert both catabolic and anabolic functions. Whereas PNPLA1 is predominantly expressed in the epidermis and involved in sphingolipid biosynthesis, PNPLA2 and 4 are ubiquitously expressed and exhibit several enzymatic activities, including hydrolysis and transacylation of various (glycero-)lipid species. This review summarizes known biological roles for PNPLA-mediated hydrolysis and transacylation reactions and highlights open questions concerning their physiological function., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

The identification of genetic variants associated with fatty liver disease (FLD) from genome-wide association studies started in 2008 when single nucleotide polymorphisms in PNPLA3, the gene encoding patatin-like phospholipase domain-containing 3, were found to be associated with altered hepatic fat content. Since then, several genetic variants associated with protection from, or an increased risk of, FLD have been identified. The identification of these variants has provided insight into the metabolic pathways that cause FLD and enabled the identification of potential therapeutic targets. In this mini-review, we will examine the therapeutic opportunities derived from genetically validated targets in FLD, including oligonucleotide-based therapies targeting PNPLA3 and HSD17B13 that are currently being evaluated in clinical trials for the treatment of NASH (non-alcoholic steatohepatitis)., (Copyright © 2023. Published by Elsevier B.V.)

The I148M substitution in patatin-like phospholipase domain containing 3 (PNPLA3I148M) determines a genetic form of nonalcoholic fatty liver disease. To elucidate the mode of PNPLA3 action in human hepatocytes, we studied effects of WT PNPLA3 (PNPLA3WT) and PNPLA3I148M on HuH7 cell lipidome after [13C]glycerol labeling, cellular turnover of oleic acid labeled with 17 deuterium atoms ([D17]oleic acid) in triacylglycerols (TAGs), and subcellular distribution of the protein variants. PNPLA3I148M induced a net accumulation of unlabeled TAGs, but not newly synthesized total [13C]TAGs. Principal component analysis (PCA) revealed that both PNPLA3WT and PNPLA3I148M induced a relative enrichment of TAGs with saturated FAs or MUFAs, with concurrent enrichment of polyunsaturated phosphatidylcholines. PNPLA3WT associated in PCA with newly synthesized [13C]TAGs, particularly 52:1 and 50:1, while PNPLA3I148M associated with similar preexisting TAGs. PNPLA3WT overexpression resulted in increased [D17]oleic acid labeling of TAGs during 24 h, and after longer incubations their turnover was accelerated, effects not detected with PNPLA3I148M. PNPLA3I148M localized more extensively to lipid droplets (LDs) than PNPLA3WT, suggesting that the substitution alters distribution of PNPLA3 between LDs and endoplasmic reticulum/cytosol. This study reveals a function of PNPLA3 in FA-selective TAG remodeling, resulting in increased TAG saturation. A defect in TAG remodeling activity likely contributes to the TAG accumulation observed in cells expressing PNPLA3I148M.

Several publications have described biological roles for human patatin-like phospholipases (PNPLAs) in the regulation of adipocyte differentiation. Here, we report on the characterization and expression profiling of 10 human PNPLAs. A variety of bioinformatics approaches were used to identify and characterize all PNPLAs encoded by the human genome. The genes described represent a divergent family, most with a highly conserved ortholog in several mammalian species. In silico characterization predicts that two of the genes function as integral membrane proteins and are regulated by cAMP/cGMP. A structurally guided protein alignment of the patatin-like domain identifies a number of conserved residues in all family members. Quantitative PCR was used to determine the expression profile of each family member. Affymetrix-based profiling of a human preadipocyte cell line identified several members that are differentially regulated during cell differentiation. Cumulative data suggest that patatin-like genes normally expressed at very low levels are induced in response to environmental signals. Given the observed conservation of the patatin fold and lipase motif in all human PNPLAs, a single nomenclature to describe the PNPLA family is proposed.

The human genome expresses nine patatin-like phospholipase domain containing proteins (PNPLA1–9). Members of this family share a protein domain discovered initially in patatin, the most abundant protein of the potato tuber. Patatin is a lipid hydrolase with an unusual folding topology that differs from classical lipases. Mammalian PNPLAs include lipid hydrolases with specificities for diverse substrates such as triacylglycerols, phospholipids, and retinol esters. Analysis of induced mutant mouse models and the clinical phenotype of patients with mutations revealed important insights into the physiological role of several members of the PNPLA family. This review aims to summarize current knowledge of PNPLA proteins and to document their emerging importance in lipid and energy homeostasis.

Background and Aims: Liver steatosis is one of the side effects of chemotherapy. The PNPLA3 p.I148M, TM6SF2 p.E167K and MBOAT7 p.G17E variants represent genetic determinants for progressive liver diseases. Here, we investigate their association with chemotherapy-associated steatosis., Patients and Methods: Prospectively, we recruited 87 patients undergoing systemic chemotherapy for gastrointestinal cancers. Hepatic fat (controlled attenuation parameter, CAP) and liver stiffness (LSM) were measured non-invasively before the initiation of chemotherapy (T0) and after at least two (T1) and four cycles (T2). Genetic variants were genotyped using allelic discrimination assays., Results: In the final dataset (n = 60) patients demonstrated the following CAP values: T0 - 215.0 ± 55.7 dB/m, T1 - 223.3 ± 53.6 dB/m, T2 - 223.4 ± 56.7 dB/m, consistent with mild steatosis. Initial CAP correlated with BMI (P < 0.01) and serum triglyceride concentrations (P = 0.03). Whereas at T0 none of the variants was associated with CAP or LSM, carriers of the prosteatotic PNPLA3 p.148M allele showed significantly (P = 0.008) higher steatosis at T1 as compared to patients carrying the homozygous wild-type genotype [II]., Conclusions: Our preliminary results show that patients carrying the PNPLA3 p.I148 M risk allele might be prone to hepatic fat accumulation during chemotherapy. Further studies are be needed to validate the clinical value of these findings., (Copyright © 2019 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.)

The aim of this study was to evaluate the potential use of the I148M/PNPLA3 (rs738409) gene polymorphism as a susceptibility marker for premature coronary artery disease (pCAD) and/or cardiovascular risk factors in Mexican type 2 diabetes mellitus patients (T2DM). The polymorphism was genotyped by 5' exonuclease TaqMan assays in a group of 2572 subjects (1103 with pCAD and 1469 healthy controls) belonging to the Genetics of Atherosclerotic Disease (GEA) Mexican Study. Anthropometric and biochemical measurements were performed in all individuals. The association between the I148M/PNPLA3 (rs738409) gene polymorphism with pCAD and other metabolic and cardiovascular risk factors was evaluated using logistic regression analysis under different statistical approaches including dominant, recessive, heterozygous, additive, and co-dominant models. The polymorphism was not associated with pCAD in the whole group of participants, however, when patients and controls were divided into those with and without T2DM, under additive model, the polymorphism was associated with the presence of pCAD only in patients with T2DM (OR=1.20, 95% CI: 1.01-1.42, P add =0.042). On the other hand, under several models adjusted for age, gender, body mass index and T2DM, the polymorphism was associated with increased risk of fatty liver and elevated levels of alanine transaminase (ALT) in the whole group of pCAD patients and controls. In the control group, the polymorphism was associated with insulin resistance and coronary artery calcification (CAC) score≥10 under several models. The results suggest that the I148M/PNPLA3 (rs738409) polymorphism is associated with the presence of pCAD in T2DM patients and with some cardiometabolic parameters. The association detected with CAC in the control group indicates that this polymorphism could be a marker for subclinical atherosclerosis., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

The PNPLA3 p.I148M, TM6SF2 p.E167K, and MBOAT7 rs641738 variants represent genetic risk factors for nonalcoholic fatty liver disease (NAFLD). Here we investigate if these polymorphisms modulate both steatosis and fibrosis in patients with NAFLD. We recruited 515 patients with NAFLD (age 16-88 years, 280 female patients). Liver biopsies were performed in 320 patients. PCR-based assays were used to genotype the PNPLA3, TM6SF2, and MBOAT7 variants. Carriers of the PNPLA3 and TM6SF2 risk alleles showed increased serum aspartate aminotransferase and alanine transaminase activities (P < 0.05). The PNPLA3 genotype was associated with steatosis grades S2-S3 (P < 0.001) and fibrosis stages F2-F4 (P < 0.001). The TM6SF2 genotype was associated with steatosis (P = 0.003) but not with fibrosis (P > 0.05). The MBOAT7 variant was solely associated with increased fibrosis (P = 0.046). In the multivariate model, variants PNPLA3 (P = 0.004) and TM6SF2 (P = 0.038) were associated with steatosis. Fibrosis stages were affected by the PNPLA3 (P = 0.042) and MBOAT7 (P = 0.021) but not by the TM6SF2 polymorphism (P > 0.05). The PNPLA3, TM6SF2, and MBOAT7 variants are associated with increased liver injury. The TM6SF2 variant seems to modulate predominantly hepatic fat accumulation, whereas the MBOAT7 polymorphism is linked to fibrosis. The PNPLA3 polymorphism confers risk of both increased steatosis and fibrosis., (Copyright © 2017 by the American Society for Biochemistry and Molecular Biology, Inc.)

Background: Obesity is the major trigger of nonalcoholic fatty liver disease (NAFLD). NAFLD is further favored by the patatin-like phospholipase domain-containing 3 (PNPLA3) p.I148M, transmembrane 6 superfamily member 2 (TM6SF2) p.E167K, and membrane-bound O-acyltransferase domain containing 7 (MBOAT7) rs641738 variants., Objectives: To investigate the relationship between the PNPLA3, TM6SF2, and MBOAT7 genotypes and the outcomes of bariatric surgery., Setting: University hospital., Methods: Prospectively we monitored 84 obese individuals (body mass index 35-64 kg/m 2 ) scheduled for bariatric surgery. The PNPLA3 p.I148M, TM6SF2 p.E167K, and MBOAT7 rs641738 variants were genotyped using restriction fragment length polymorphism analysis and TaqMan assays. Hepatic steatosis was determined before surgery using analysis of liver biopsy samples and a novel magnetic resonance imaging-based equation. One year later, steatosis was reevaluated by magnetic resonance imaging., Results: The presence of the PNPLA3 allle [M] was associated with increased hepatic triglyceride content (P = .03), steatosis detected by magnetic resonance imaging (P = 0.04), and decreased serum glucose concentrations (P = .04). Neither variant TM6SF2 nor MBOAT7 increased hepatic steatosis (all P>.05); however, the MBOAT7 polymorphism was associated with increased triglyceride, total cholesterol, low density lipoprotein, and serum glucose levels (all P<.05). Patients carrying the prosteatotic PNPLA3 allele [M] lost more weight (P<.01) and liver fat (P = .04) one year after surgery, as compared to individuals having the common genotype. The PNPLA3 genotype and initial grade of steatosis, but not the TM6SF2 or MBOAT7 variants, were independent predictors of NAFLD improvement (P = .03 and P<.01, respectively)., Conclusion: In obese patients, the presence of the PNPLA3 p.I148M allele might be associated with greater improvement of hepatic steatosis after bariatric surgery in comparison to carriers of PNPLA3 wild-type alleles., (Copyright © 2016 American Society for Bariatric Surgery. Published by Elsevier Inc. All rights reserved.)

The interest in adiponutrin stems from adiponutrin variant I148M, which is strongly associated to non-alcoholic fatty liver disease. Adiponutrin has to date been considered to be solely an intracellular protein, with a role in lipid metabolism in liver and adipose tissue. However, a physiologically relevant role for adiponutrin has not been found. The aim of this study was to investigate the presence of adiponutrin in human plasma, a new facet of adiponutrin research. We demonstrate that adiponutrin is present in plasma as disulfide-bond dependent multimers, estimated to circulate at a concentration of 1.25-4 nM. Experiments reveal that adiponutrin is released from HepG2 cells in the presence of oleate. The presence of adiponutrin in plasma makes it accessible for clinical investigations and use as a potential biomarker for metabolic disease., (Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.)

The I148M substitution in patatin-like phospholipase domain containing 3 (PNPLA3(I148M)) determines a genetic form of nonalcoholic fatty liver disease. To elucidate the mode of PNPLA3 action in human hepatocytes, we studied effects of WT PNPLA3 (PNPLA3(WT)) and PNPLA3(I148M) on HuH7 cell lipidome after [(13)C]glycerol labeling, cellular turnover of oleic acid labeled with 17 deuterium atoms ([D17]oleic acid) in triacylglycerols (TAGs), and subcellular distribution of the protein variants. PNPLA3(I148M) induced a net accumulation of unlabeled TAGs, but not newly synthesized total [(13)C]TAGs. Principal component analysis (PCA) revealed that both PNPLA3(WT) and PNPLA3(I148M) induced a relative enrichment of TAGs with saturated FAs or MUFAs, with concurrent enrichment of polyunsaturated phosphatidylcholines. PNPLA3(WT) associated in PCA with newly synthesized [(13)C]TAGs, particularly 52:1 and 50:1, while PNPLA3(I148M) associated with similar preexisting TAGs. PNPLA3(WT) overexpression resulted in increased [D17]oleic acid labeling of TAGs during 24 h, and after longer incubations their turnover was accelerated, effects not detected with PNPLA3(I148M). PNPLA3(I148M) localized more extensively to lipid droplets (LDs) than PNPLA3(WT), suggesting that the substitution alters distribution of PNPLA3 between LDs and endoplasmic reticulum/cytosol. This study reveals a function of PNPLA3 in FA-selective TAG remodeling, resulting in increased TAG saturation. A defect in TAG remodeling activity likely contributes to the TAG accumulation observed in cells expressing PNPLA3(I148M).