Patatin-like Phospholipase Domain-containing 3 I148M Research Articles

Patatin-like phospholipase domain-containing 3 I148M affects liver steatosis in patients with chronic hepatitis B

Steatosis is a common histopathological feature of chronic hepatitis B (CHB) and has been associated with severity of liver disease. Recently, the rs738409 I148M patatin-like phospholipase domain-containing 3 (PNPLA3) polymorphism has been demonstrated to influence steatosis susceptibility and fibrosis progression in patients with different liver diseases, but no data are yet available for CHB. The aim of this study was to evaluate whether PNPLA3 I148M influences steatosis susceptibility in a large series of patients with CHB. We enrolled 235 treatment-naïve CHB patients consecutively examined by percutaneous liver biopsy. In ≥2-cm-long liver tissue cores, steatosis and fibrosis were staged by Kleiner and METAVIR scores, respectively. The I148M polymorphism was determined by Taqman assays. Steatosis was present in 146 (62%) patients, of whom 24 (10%) had severe (>33% of hepatocytes) steatosis. Steatosis was independently associated with age (odds ratio [OR]: 2.67; confidence interval [CI]: 1.50-4.92; for age ≥50 years), body mass index (BMI; OR, 2.84; CI, 1.30-6.76; for BMI ≥27.5 kg/m(2) ), diabetes or impaired fasting glucose (OR, 4.45; CI, 1.10-30.0), and PNPLA3 148M allele (OR, 1.62; CI, 1.00-7.00; for each 148M allele). Independent predictors of severe steatosis were BMI (OR, 3.60; CI, 1.39-9.22; for BMI ≥27.5 kg/m(2) ) and PNPLA3 148M allele (OR, 6.03; CI, 1.23-5.0; for each 148M allele). PNPLA3 148M alleles were associated with a progressive increase in severe steatosis in patients with acquired cofactors, such severe overweight and a history of alcohol intake (P = 0.005). In CHB patients, the PNPLA3 I148M polymorphism influences susceptibility to steatosis and, in particular, when associated with severe overweight and alcohol intake, severe steatosis.

PNPLA3 I148M polymorphism and progressive liver disease

The 148 Isoleucine to Methionine protein variant (I148M) of patatin-like phospholipase domain-containing 3 (PNPLA3), a protein is expressed in the liver and is involved in lipid metabolism, has recently been identified as a major determinant of liver fat content. Several studies confirmed that the I148M variant predisposes towards the full spectrum of liver damage associated with fatty liver: from simple steatosis to steatohepatitis and progressive fibrosis. Furthermore, the I148M variant represents a major determinant of progression of alcohol related steatohepatitis to cirrhosis, and to influence fibrogenesis and related clinical outcomes in chronic hepatitis C virus hepatitis, and possibly chronic hepatitis B virus hepatitis, hereditary hemochromatosis and primary sclerosing cholangitis. All in all, studies suggest that the I148M polymorphism may represent a general modifier of fibrogenesis in liver diseases. Remarkably, the effect of the I148M variant on fibrosis was independent of that on hepatic steatosis and inflammation, suggesting that it may affect both the quantity and quality of hepatic lipids and the biology of non-parenchymal liver cells besides hepatocytes, directly promoting fibrogenesis. Therefore, PNPLA3 is a key player in liver disease progression. Assessment of the I148M polymorphism will possibly inform clinical practice in the future, whereas the determination of the effect of the 148M variant will reveal mechanisms involved in hepatic fibrogenesis.

PNPLA3 I148M (rs738409) genetic variant is associated with hepatocellular carcinoma in obese individuals

BackgroundObesity is a risk factor for cancer, including hepatocellular carcinoma. Patatin-like phospholipase domain-containing 3 (PNPLA3) I148M (rs738409) genetic variant has been associated with hepatocellular carcinoma (HCC) in individuals with chronic alcohol abuse or hepatic viral infection. In the present study we examined the association between the PNPLA3 I148M genetic variant and hepatocellular carcinoma in obese individuals from the Swedish Obese Subjects cohort (n=4047). MethodsWe performed a matched, prospective, controlled, interventional trial, investigating the effect of bariatric surgery (surgery group) compared to conventional treatment (control group) for obesity. ResultsA total of 9 events were observed in the 15-year median follow up (5 in the control group and 4 in the surgery group). A significantly higher incidence of hepatocellular carcinoma in PNPLA3 148M allele carriers was found in obese individuals in the control group (log-rank P-value=0.001), but not in the surgery group (log-rank P-value=0.783). Consistently, an increased risk (for each PNPLA3 148M allele, hazard ratio: 5.9; 95% confidence interval 1.5–23.8; P-value=0.013) of developing hepatocellular carcinoma was observed only in the control group. ConclusionThe current study is the first prospective report showing the association of the PNPLA3 I148M genetic variant and hepatocellular carcinoma in severely obese individuals.

PNPLA3 is regulated by glucose in human hepatocytes, and its I148M mutant slows down triglyceride hydrolysis

Liver fat is increased in carriers of the minor G allele in rs738409 (I148M amino acid substitution) in patatin-like phospholipase domain-containing 3 (PNPLA3)/adiponutrin. We studied transcriptional regulation of PNPLA3 in immortalized human hepatocytes (IHH) and human hepatoma cells (HuH7) and the impact of PNPLA3 I148M mutant on hepatocyte triglyceride metabolism. Studies in IHH showed that silencing of the carbohydrate response element-binding protein (ChREBP) abolished induction of PNPLA3 mRNA by glucose. Glucose-dependent binding of ChREBP to a newly identified carbohydrate response element in the PNPLA3 promoter was demonstrated by chromatin immunoprecipitation. Adenoviral overexpression of mouse ChREBP in IHH failed to induce PNPLA3 mRNA. [(3)H]acetate or [(3)H]oleate incorporation with 1-h pulse labeling or 18-h [(3)H]oleate labeling in HuH7 cells showed no effect of PNPLA3 I148M on triglyceride (TG) synthesis in the absence of free fatty acid (FFA) loading. Increased [(3)H]oleate accumulation into triglycerides in I148M-expressing cells was observed after 18 h of labeling in the presence of 200 μM FFA-albumin complexes. This was accompanied by increased PNPLA3 protein levels. The rate of hydrolysis of [(3)H]TG during lipid depletion was decreased significantly by PNPLA3 I148M. Our results suggest that PNPLA3 is regulated in human hepatocytes by glucose via ChREBP. PNPLA3 I148M enhances cellular accumulation of [(3)H]TG in the presence of excess FFA, which is known to stabilize PNPLA3 protein. These data do not exclude an effect of PNPLA3 I148M on hepatocyte lipogenesis but show that the mutant increases the stability of triglycerides.