I148M Variant Research Articles

Impact of PNPLA3 I148M on Clinical Outcomes in Patients With MASLD.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a heterogenous clinical and histopathological entity, where multiple metabolic co-factors are intertwined with high interindividual variability. The impact and severity of each factor (including obesity and type 2 diabetes) define a systemic dysmetabolism that can lead to either advanced liver disease and its complication (including hepatocellular carcinoma and clinical events related to portal hypertension) or extrahepatic events: incident cardiovascular disease, chronic kidney disease and extrahepatic cancers. The balance between environmental factors and genetic susceptibility has unique implications in MASLD: the intermittent injury of metabolic co-factors, their fluctuation over time and their specific management, are counterbalanced by the presence of gene variants that can significantly impact the disease at multiple levels. The I148M variant in the PNPLA3 gene is the most investigated genetic susceptibility that induces a more severe steatohepatitis, enhanced fibrogenesis and can shape the incidence of long-term clinical events regardless of, or worsened by, other metabolic risk factors. In this review, we will summarise the updated evidence on the natural history of MASLD accounting for classical metabolic risk factors, the role of PNPLA3 in clinical sub-phenotyping (e.g., 'lean MASLD'), impact on disease severity and fibrosis progression, as well as its role for prognostication, alone or in combination with non-invasive tools into polygenic risk scores.

Role of PNPLA3 in Hepatic Stellate Cells and Hepatic Cellular Crosstalk.

Since its discovery, the patatin-like phospholipase domain containing 3 (PNPLA3) (rs738409 C>G p.I148M) variant has been studied extensively to unravel its molecular function. Although several studies proved a causal relationship between the PNPLA3 I148M variant and MASLD development and particularly fibrosis, the pathological mechanisms promoting this phenotype have not yet been fully clarified. We summarise the latest data regarding the PNPLA3 I148M variant in hepatic stellate cells (HSCs) activation and macrophage biology or the path to inflammation-induced fibrosis. Elegant but contradictory studies have ascribed PNPLA3 a hydrolase or an acyltransferase function. The PNPLA3 I148M results in hepatic lipid accumulation, which predisposes the hepatocyte to lipotoxicity and lipo-apoptosis, producing DAMPs, cytokines and chemokines leading to recruitment and activation of macrophages and HSCs, propagating fibrosis. Recent studies showed that the PNPLA3 I148M variant alters HSCs biology via attenuation of PPARγ, AP-1, LXRα and TGFβ activity and signalling. The advent of refined techniques in isolating HSCs has made PNPLA3's direct role in HSCs for liver fibrosis development more apparent. However, many other mechanisms still need detailed investigations.

Sex-specific effects of PNPLA3 I148M.

Metabolic dysfunction-associated steatotic liver disease (MASLD, previously termed NAFLD, nonalcoholic fatty liver disease) is a complex multifactorial disease showing generally higher prevalence and severity in men than in women. With respect to women, men are also more prone to develop metabolic dysfunction-associated steatohepatitis, fibrosis and liver-related complications. Several genetic, hormonal, environmental and lifestyle factors may contribute to sex differences in MASLD development, progression and outcomes. However, after menopause, the sex-specific prevalence of MASLD shows an opposite trend between men and women, pointing to the relevance of oestrogen signalling in the sexual dimorphism of MASLD. The patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene, that encodes a triacylglycerol lipase that plays a crucial role in lipid metabolism, has emerged as a key player in the pathogenesis of MASLD, with the I148M variant being strongly associated with increased liver fat content and disease severity. Recent advances indicate that carrying the PNPLA3 I148M variant can be a risk factor for MASLD especially for women. To elucidate the molecular mechanisms underlying the sex-specific role of PNPLA3 I148M in the development of MASLD, several invitro, exvivo and invivo models have been developed.

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.

The health care experience of adults with metabolic dysfunction-associated steatohepatitis and influence of PNPLA3: A qualitative study.

Metabolic dysfunction-associated steatohepatitis (MASH) is a progressive form of metabolic dysfunction-associated steatotic liver disease, for which there is limited information about patient experience, including the patient journey. In this study, we conducted interviews with patients with MASH to qualitatively evaluate the patient journey and help elucidate the experiences of this patient population. We also investigated if the patatin-like phospholipase domain-containing protein 3 (PNPLA3) I148M variant (non-Hispanic) or being of Hispanic ethnicity may influence patient experiences because these 2 subgroups develop advanced liver disease more frequently than other patient groups. One-to-one interviews were conducted with 28 adults (with PNPLA3 I148M genetic variant, n = 10; Hispanic, n = 8) living in the United States who had been diagnosed with MASH with liver fibrosis. Patients were asked open-ended questions about their experiences before, at, and after their diagnosis. The data collected found that patients experienced a long process of misdiagnoses before their diagnosis of MASH, a lack of clear information provided by clinicians, and limited accessibility to support groups. Hispanic patients reported "impact on family/friends" (75%) and "fear of disease progression" (75%) more frequently than the other patient cohorts interviewed. This is the first report of "fear of progression" in patients with MASH. No patients who were White and had the PNPLA3 I148M variant reported nausea/vomiting, in contrast to other patient cohorts. This qualitative study identified key aspects of the patient journey that are important for clinical providers and medical teams to recognize. We also propose a new algorithm that could be developed to help screen relatives of patients who are found to carry the PNPLA3 I148M variant.

A genome-first approach to variants in MLXIPL and their association with hepatic steatosis and plasma lipids.

Common variants of the max-like protein X (MLX)-interacting protein-like (MLXIPL) gene, encoding the transcription factor carbohydrate-responsive element-binding protein, have been shown to be associated with plasma triglyceride levels. However, the role of these variants in steatotic liver disease (SLD) is unclear. We used a genome-first approach to analyze a variety of metabolic phenotypes and clinical outcomes associated with a common missense variant in MLXIPL, Gln241His, in 2 large biobanks: the UK Biobank and the Penn Medicine Biobank. Carriers of MLXIPL Gln241His were associated with significantly lower serum levels of triglycerides, apolipoprotein-B, gamma-glutamyl transferase, and alkaline phosphatase. Additionally, MLXIPL Gln241His carriers were associated with significantly higher serum levels of HDL cholesterol and alanine aminotransferase. Carriers homozygous for MLXIPL Gln241His showed a higher risk of SLD in 2 unrelated cohorts. Carriers of MLXIPL Gln241His were especially more likely to be diagnosed with SLD if they were female, obese, and/or also carried the PNPLA3 I148M variant. Furthermore, the heterozygous carriage of MLXIPL Gln241His was associated with significantly higher all-cause, liver-related, and cardiovascular mortality rates. Nuclear magnetic resonance metabolomics data indicated that carriage of MLXIPL Gln241His was significantly associated with lower serum levels of VLDL and increased serum levels of HDL cholesterol. Analyses of the MLXIPL Gln241His polymorphism showed a significant association with a higher risk of SLD diagnosis and elevated serum alanine aminotransferase as well as significantly lower serum triglycerides and apolipoprotein-B levels. MLXIPL might, therefore, be a potential pharmacological target for the treatment of SLD and hyperlipidemia, notably for patients at risk. More mechanistic studies are needed to better understand the role of MLXIPL Gln241His on lipid metabolism and steatosis development.

Comparison of wild-type and high-risk PNPLA3 variants in a human biomimetic liver microphysiology system for metabolic dysfunction-associated steatotic liver disease precision therapy.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a worldwide health epidemic with a global occurrence of approximately 30%. The pathogenesis of MASLD is a complex, multisystem disorder driven by multiple factors, including genetics, lifestyle, and the environment. Patient heterogeneity presents challenges in developing MASLD therapeutics, creating patient cohorts for clinical trials, and optimizing therapeutic strategies for specific patient cohorts. Implementing pre-clinical experimental models for drug development creates a significant challenge as simple in vitro systems and animal models do not fully recapitulate critical steps in the pathogenesis and the complexity of MASLD progression. To address this, we implemented a precision medicine strategy that couples the use of our liver acinus microphysiology system (LAMPS) constructed with patient-derived primary cells. We investigated the MASLD-associated genetic variant patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs738409 (I148M variant) in primary hepatocytes as it is associated with MASLD progression. We constructed the LAMPS with genotyped wild-type and variant PNPLA3 hepatocytes, together with key non-parenchymal cells, and quantified the reproducibility of the model. We altered media components to mimic blood chemistries, including insulin, glucose, free fatty acids, and immune-activating molecules to reflect normal fasting (NF), early metabolic syndrome (EMS), and late metabolic syndrome (LMS) conditions. Finally, we investigated the response to treatment with resmetirom, an approved drug for metabolic syndrome-associated steatohepatitis (MASH), the progressive form of MASLD. This study, using primary cells, serves as a benchmark for studies using "patient biomimetic twins" constructed with patient induced pluripotent stem cell (iPSC)-derived liver cells using a panel of reproducible metrics. We observed increased steatosis, immune activation, stellate cell activation, and secretion of pro-fibrotic markers in the PNPLA3 GG variant compared to the wild-type CC LAMPS, consistent with the clinical characterization of this variant. We also observed greater resmetirom efficacy in the PNPLA3 wild-type CC LAMPS compared to the GG variant in multiple MASLD metrics, including steatosis, stellate cell activation, and the secretion of pro-fibrotic markers. In conclusion, our study demonstrates the capability of the LAMPS platform for the development of MASLD precision therapeutics, enrichment of patient cohorts for clinical trials, and optimization of therapeutic strategies for patient subgroups with different clinical traits and disease stages.

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.

WED-418 - The PNPLA3 I148M variant aggravates inflammation through dysfunctional LXR and PPAR gamma signalling in macrophages

WED-418 - The PNPLA3 I148M variant aggravates inflammation through dysfunctional LXR and PPAR gamma signalling in macrophages

PNPLA3 allele frequency has no impact on biliary bile acid composition or disease course in patients with primary sclerosing cholangitis.

Primary sclerosing cholangitis (PSC) is a chronic inflammatory disease that leads to bile duct strictures, cholestasis, and biliary cirrhosis. PNPLA3 (patatin-like phospholipase domain containing 3), regulates cellular lipid synthesis by converting lysophosphatidic acid into phosphatidic acid. Isoleucine mutation to methionine at position 148 (I148M) causes a loss of this function. Only two studies, with contradictory results, have evaluated the role of PNPLA3 in PSC. The rs738409(G) variant of PNPLA3 has been associated with an increased risk for transplantation in male patients with dominant strictures (DS). The study aimed to evaluate the PNPLA3 allele frequency effect on the clinical outcomes, progression, and prognosis of PSC. Furthermore, we analyzed the impact of PNPLA3 on phospholipid and bile acid composition to evaluate the effect of the PNPLA3 status on UDCA response. We recruited 560 patients prospectively and collected clinical and laboratory data as well as liver histology and imaging findings. PNPLA3 (CC, CG, GG) alleles were analyzed with TaqManTM. We also analyzed bile acids (BA), cholesterol and phospholipids and individual BA from a sample aspirated during endoscopic retrograde cholangiography (ERC). Among the recruited patients, 58.4%, 35.7% and 5.9% had the wild (CC), heterozygous (CG) and homozygous (GG) alleles, respectively. The PNPLA3 haplotype did not impact bile composition or individual BA. In addition, we found no differences in age at diagnosis, disease progression, liver fibrosis or survival between the cohorts. The PNPLA3 I148M variant had no significant impact on on bile composition, including UDCA content, clinical outcomes, progression of liver fibrosis, hepatobiliary cancer risk, liver transplantation, or overall survival.

Synergistic Associations of PNPLA3 I148M Variant, Alcohol Intake, and Obesity With Risk of Cirrhosis, Hepatocellular Carcinoma, and Mortality

Alcohol drinking and obesity are associated with an increased risk of cirrhosis and hepatocellular carcinoma (HCC), but the risk is not uniform among people with these risk factors. Genetic variants, such as I148M in the patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene, may play an important role in modulating cirrhosis and HCC risk. To investigate the joint associations of the PNPLA3 I148M variant, alcohol intake, and obesity with the risk of cirrhosis, HCC, and liver disease-related mortality. This prospective cohort study analyzed 414 209 participants enrolled in the UK Biobank study from March 2006 to December 2010. Participants had no previous diagnosis of cirrhosis and HCC and were followed up through March 2021. Self-reported alcohol intake (nonexcessive vs excessive), obesity (body mass index ≥30 [calculated as weight in kilograms divided by height in meters squared]), and PNPLA3 I148M variant status (noncarrier, heterozygous carrier, or homozygous carrier) from initial assessment. The primary outcomes were incident cirrhosis and HCC cases and liver disease-related death ascertained from inpatient hospitalization records and death registry. The risks were calculated by Cox proportional hazards regression models. A total of 414 209 participants (mean [SD] age, 56.3 [8.09] years; 218 567 women [52.8%]; 389 452 White race and ethnicity [94.0%]) were included. Of these participants, 2398 participants (0.6%) developed cirrhosis (5.07 [95% CI, 4.87-5.28] cases per 100 person-years), 323 (0.1%) developed HCC (0.68 [95% CI, 0.61-0.76] cases per 100 person-years), and 878 (0.2%) died from a liver disease-related cause (1.76 [95% CI, 1.64-1.88] cases per 100 person-years) during a median follow-up of 10.9 years. Synergistic interactions between the PNPLA3 I148M variant, obesity, and alcohol intake were associated with the risk of cirrhosis, HCC, and liver disease-related mortality. The risk of cirrhosis increased supramultiplicatively (adjusted hazard ratio [aHR], 17.52; 95% CI, 12.84-23.90) in individuals with obesity, with excessive drinking, and who were homozygous carriers compared with those with no obesity, with nonexcessive drinking, and who were noncarriers. Supramultiplicative associations between the 3 factors and risks of HCC were found in individuals with 3 risk factors (aHR, 30.13; 95% CI, 16.51-54.98) and liver disease-related mortality (aHR, 21.82; 95% CI, 13.78-34.56). The PNPLA3 I148M variant status significantly differentiated the risk of cirrhosis, HCC, and liver disease-related mortality in persons with excessive drinking and obesity. This study found synergistic associations of the PNPLA3 I148M variant, excessive alcohol intake, and obesity with increased risk of cirrhosis, HCC, and liver disease-related death in the general population. The PNPLA3 I148M variant status may help refine the risk stratification for liver disease in persons with excessive drinking and obesity who may need early preventive measures.

IL-6/STAT3 axis dictates the PNPLA3-mediated susceptibility to non-alcoholic fatty liver disease

A number of genetic polymorphisms have been associated with susceptibility to or protection against non-alcoholic fatty liver disease (NAFLD), but the underlying mechanisms remain unknown. Here, we focused on the rs738409C>G single nucleotide polymorphism (SNP), which produces the I148M variant of patatin-like phospholipase domain-containing protein 3 (PNPLA3) and is strongly associated with NAFLD. To enable mechanistic dissection, we developed a human pluripotent stem cell (hPSC)-derived multicellular liver culture by incorporating hPSC-derived hepatocytes, hepatic stellate cells, and macrophages. We first applied this liver culture to model NAFLD by utilising a lipotoxic milieu reflecting the circulating levels of disease risk factors in affected individuals. We then created an isogenic pair of liver cultures differing only at rs738049 and compared NAFLD phenotype development. Our hPSC-derived liver culture recapitulated many key characteristics of NAFLD development and progression including lipid accumulation and oxidative stress, inflammatory response, and stellate cell activation. Under the lipotoxic conditions, the I148M variant caused the enhanced development of NAFLD phenotypes. These differences were associated with elevated IL-6/signal transducer and activator of transcription 3 (STAT3) activity in liver cultures, consistent with transcriptomic data of liver biopsies from individuals carrying the rs738409 SNP. Dampening IL-6/STAT3 activity alleviated the I148M-mediated susceptibility to NAFLD, whereas boosting it in wild-type liver cultures enhanced NAFLD development. Finally, we attributed this elevated IL-6/STAT3 activity in liver cultures carrying the rs738409 SNP to increased NF-κB activity. Our study thus reveals a potential causal link between elevated IL-6/STAT3 activity and 148M-mediated susceptibility to NAFLD. An increasing number of genetic variants manifest in non-alcoholic fatty liver disease (NAFLD) development and progression; however, the underlying mechanisms remain elusive. To study these variants in human-relevant systems, we developed an induced pluripotent stem cell-derived multicellular liver culture and focused on a common genetic variant (i.e. rs738409 in PNPLA3). Our findings not only provide mechanistic insight, but also a potential therapeutic strategy for NAFLD driven by this genetic variant in PNPLA3. Our liver culture is therefore a useful platform for exploring genetic variants in NAFLD development.

SAT008 - Transcriptomic analysis confirms that PNPLA3 I148M variant is associated with impaired mitochondrial function and antioxidant response in 3D cultured human hepatic stellate cells and liver tissue of patients with NAFLD

SAT008 - Transcriptomic analysis confirms that PNPLA3 I148M variant is associated with impaired mitochondrial function and antioxidant response in 3D cultured human hepatic stellate cells and liver tissue of patients with NAFLD

SAT052 - The PNPLA3 I148M variant increases intrahepatic lipolysis and beta oxidation and decreases de novo lipogenesis and hepatic mitochondrial function in humans

SAT052 - The PNPLA3 I148M variant increases intrahepatic lipolysis and beta oxidation and decreases de novo lipogenesis and hepatic mitochondrial function in humans

I148M variant of PNPLA3-gene is not associated with metabolic syndrome in patients with NAFLD in the Indian ethnicity

BackgroundNon-alcoholic fatty liver disease (NAFLD) is now considered to precede the development of diabetes and metabolic syndrome (MetS) overriding the earlier notion of NAFLD being the hepatic manifestation of MetS. Studies identified variants conferring enhanced susceptibility to MetS predominantly in lipid metabolism related genes. A variant I148M in PNPLA3 is replicated across ethnicities for its role in NAFLD, however its association with MetS is conflicting. We performed this study to explore its association with MetS. MethodsThis is a retro-prospective study that recruited 502 individuals with/without NAFLD based on fatty infiltration (B-type ultrasonography). Demographic/anthropometric data, blood samples were collected. Genotyping was carried out by PCR and direct sequencing. Student's t-test was used for continuous variables. Chi-square test was used to test the association of the variant with MetS. The strength of association was explored by using Odds ratio (95% CI). Multiple logistic regression was used to identify independent predictor variables for metabolic syndrome. ResultsOf the 502 that comrised the study group, data pertaining (MetS) to 476 were used for further analysis. The mean age of controls (n = 121) and patients with NAFLD (n = 355) were 38.7 ± 12.3; 37.8 ± 9.4 years respectively. A significant difference in the anthropometric and levels of liver enzymes were noted between the groups with higher levels in patients. Association of I148M variant in PNPLA3 gene conferring a 2.29-fold risk of fatty infiltration in the variant carriers was noted. Further, of the 355 with NAFLD, 152 (42.82%) were found to have MetS. There was no association (p = 0.9) of the I148M in PNPLA3 gene with MetS. None of the variables were associated with metabolic syndrome between wild and variant carriers. ConclusionAlthough a sizeable number of patients with NAFLD had metabolic syndrome, I148M- PNPLA3 variant was not associated with MetS. However, the I148M variant conferred enhanced susceptibility to fatty infiltration.

The PNPLA3 variant I148M reveals protective effects toward hepatocellular carcinoma in mice via restoration of omega-3 polyunsaturated fats

Alcohol consumption and high caloric diet are leading causes of progressive fatty liver disease. Genetic variant rs738409 in patatin-like phospholipase domain-containing protein 3 (PNPLA3 rs738409 C>G) has been repeatedly described as one of the major risk loci for alcoholic liver cirrhosis (ALC) and hepatocellular carcinoma (HCC) in humans, however, the mechanism behind this association is incompletely understood. We generated mice carrying the rs738409 variant (PNPLA3 I148M) in order to detect genotype–phenotype relationships in mice upon chow and alcohol-high fat/high sugar diet (EtOH/WD). We could clearly demonstrate that the presence of rs738409 per se is sufficient to induce spontaneous development of steatosis after 1 year in mice on a chow diet, whereas in the setting of unhealthy diet feeding, PNPLA3 I148M did not affect hepatic inflammation or fibrosis, but induced a striking lipid remodeling, microvesicular steatosis and protected from HCC formation. Using shot gun lipidomics, we detected a striking restoration of reduced long chain-polyunsaturated fatty acids (LC-PUFA)-containing TGs, docosapentaenoic acid (C22:5 n3) and omega-3-derived eicosanoids (5-HEPE, 20-HEPE, 19,20-EDP, 21-HDHA) in PNPLA3 I148M mice upon EtOH/WD. At the molecular level, PNPLA3 I148M modulated enzymes for fatty acid and TG transport and metabolism. These findings suggest (dietary) lipids as an important and independent driver of hepatic tumorigenesis. Genetic variant in PNPLA3 exerted protective effects in mice, conflicting with findings in humans. Species-related differences in physiology and metabolism should be taken into account when modeling unhealthy human lifestyle, as genetic mouse models may not always allow for translation of insight gained in humans.

Advances in pediatric non-alcoholic fatty liver disease: From genetics to lipidomics.

As a result of the obesity epidemic, non-alcoholic fatty liver disease (NAFLD) represents a global medical concern in childhood with a closely related increased cardiometabolic risk. Knowledge on NAFLD pathophysiology has been largely expanded over the last decades. Besides the well-known key NAFLD genes (including the I148M variant of the PNPLA3 gene, the E167K allele of the TM6SF2, the GCKR gene, the MBOAT7-TMC4 rs641738 variant, and the rs72613567:TA variant in the HSD17B13 gene), an intriguing pathogenic role has also been demonstrated for the gut microbiota. More interestingly, evidence has added new factors involved in the “multiple hits” theory. In particular, omics determinants have been highlighted as potential innovative markers for NAFLD diagnosis and treatment. In fact, different branches of omics including metabolomics, lipidomics (in particular sphingolipids and ceramides), transcriptomics (including micro RNAs), epigenomics (such as DNA methylation), proteomics, and glycomics represent the most attractive pathogenic elements in NAFLD development, by providing insightful perspectives in this field. In this perspective, we aimed to provide a comprehensive overview of NAFLD pathophysiology in children, from the oldest pathogenic elements (including genetics) to the newest intriguing perspectives (such as omics branches).

PNPLA3 I148M Polymorphism Influences Renal Function in Children With Obesity and Prediabetes

Nonalcoholic fatty liver disease negatively impacts on renal function with the contribution of the I148M variant in the patatin-like phospholipase-containing domain 3 (PNPLA3) gene. We hypothesized that children with prediabetes present with a lower estimated glomerular filtration rate (eGFR) than those with normal glucose tolerance (NGT) and that the 148M PNPLA3 allele could play a worsening role. We aimed evaluating the influence of the I148M PNPLA3 polymorphism on the relationship between the eGFR and prediabetes in children with obesity. One thousand thirty-six children underwent to complete assessment and were genotyped for the I148M PNPLA3 polymorphism. Patients with prediabetes showed lower eGFR levels (171.03±40.32 vs. 190.80±41.71mL/min/1.73m2; P=.001) and higher prevalence of nonalcoholic fatty liver disease (80% vs. 59%; P=.003) than those with NGT. Children with prediabetes showed lower eGFR levels than those with NGT (150.97±14.56 vs. 192.88±40.09; P<.0001) among carriers of the PNPLA3 148M allele. This was not confirmed among patients homozygous for the PNPLA3 I148 allele. A general linear model for eGFR variance confirmed an inverse and significant association of the eGFR with prediabetes in patients carrying the 148M PNPLA3 allele but not in patients homozygous for the PNPLA3 I148 allele. Prediabetes negatively affects renal function in children with obesity. This effect is heightened in patients carrying the PNPLA3 148M allele.

Clinically silent LINE 1 insertion in the PNPLA3 gene may impede genotyping of the p.I148M variant

The patatin-like phospholipase domain containing 3 (PNPLA3) gene (viz. its I148M variant) is one of the key players in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We have identified a novel insertion/deletion variant of 1114 bp, localized in the second intron of the PNPLA3 gene, which corresponds to the 3′ terminal sequence of the long-interspersed element (LINE-1). DNA analysis of 122 NAFLD patients and 167 control subjects as well as RNA analysis of 19 liver biopsies revealed that the novel variant is very common (frequency = 0.41), fully linked to the clinically important I148M variant, and clinically silent. Although the LINE-1 insertion does not seem to have any biological effect, it can impede genotyping of the I148M variant. If insertion prevents the attachment of the diagnostic primer, then the non-insertion allele will be selectively amplified; and thus the frequency of the 148M "risk" allele will be significantly overestimated due to the complete linkage of the LINE-1 insertion and the 148I allele of the PNPLA3 gene. Therefore, our findings underline the importance of careful design and consistent documentation of the methodology, including primer sequences. Critical revisions of the results of some studies that have already been reported may therefore be needed.

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

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. We used isogenic hiPSC lines with either a knockout (PNPLA3KO ) of the PNPLA3 gene or with the I148M variant (PNPLA3I148M ) 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. PNPLA3KO 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 PNPLA3KO cells to be more susceptible to ethanol-induced and methotrexate-induced toxicity. The PNPLA3I148M cells exhibited an intermediate phenotype between the wild-type and PNPLA3KO cells. Together, these results indicate that the I148M variant induces a loss of function predisposing to steatosis and increased susceptibility to hepatotoxins.