Bariatric surgery appears to be markedly more efficient than usual care in the prevention of type 2 diabetes in obese persons. (Funded by the Swedish Research Council and others; ClinicalTrials.gov number, NCT01479452.).

Retinoids are micronutrients that are stored as retinyl esters in the retina and hepatic stellate cells (HSCs). HSCs are key players in fibrogenesis in chronic liver diseases. The enzyme responsible for hydrolysis and release of retinyl esters from HSCs is unknown and the relationship between retinoid metabolism and liver disease remains unclear. We hypothesize that the patatin-like phospholipase domain-containing 3 (PNPLA3) protein is involved in retinol metabolism in HSCs. We tested our hypothesis both in primary human HSCs and in a human cohort of subjects with non-alcoholic fatty liver disease (N = 146). Here we show that PNPLA3 is highly expressed in human HSCs. Its expression is regulated by retinol availability and insulin, and increased PNPLA3 expression results in reduced lipid droplet content. PNPLA3 promotes extracellular release of retinol from HSCs in response to insulin. We also show that purified wild-type PNPLA3 hydrolyzes retinyl palmitate into retinol and palmitic acid. Conversely, this enzymatic activity is markedly reduced with purified PNPLA3 148M, a common mutation robustly associated with liver fibrosis and hepatocellular carcinoma development. We also find the PNPLA3 I148M genotype to be an independent (P = 0.009 in a multivariate analysis) determinant of circulating retinol-binding protein 4, a reliable proxy for retinol levels in humans. This study identifies PNPLA3 as a lipase responsible for retinyl-palmitate hydrolysis in HSCs in humans. Importantly, this indicates a potential novel link between HSCs, retinoid metabolism and PNPLA3 in determining the susceptibility to chronic liver disease.

No abstract

The patatin-like phospholipase domain containing 3 (PNPLA3, also called adiponutrin, ADPN) is a membrane-bound protein highly expressed in the liver. The genetic variant I148M (rs738409) was found to be associated with progression of chronic liver disease. We aimed to establish a protein purification protocol in a yeast system (Pichia pastoris) and to examine the human PNPLA3 enzymatic activity, substrate specificity and the I148M mutation effect. hPNPLA3 148I wild type and 148M mutant cDNA were cloned into P. pastoris expression vectors. Yeast cells were grown in 3L fermentors. PNPLA3 protein was purified from membrane fractions by Ni-affinity chromatography. Enzymatic activity was assessed using radiolabeled substrates. Both 148I wild type and 148M mutant proteins are localized to the membrane. The wild type protein shows a predominant lipase activity with mild lysophosphatidic acid acyl transferase activity (LPAAT) and the I148M mutation results in a loss of function of both these activities. Our data show that PNPLA3 has a predominant lipase activity and I148M mutation results in a loss of function.

Nonalcoholic fatty liver disease (NAFLD) is the most common form of liver disease, and 10% to 20% of NAFLD patients progress to nonalcoholic steatohepatitis (NASH). The molecular pathways controlling progression to NAFLD/NASH remain poorly understood. We recently identified serine/threonine protein kinase 25 (STK25) as a regulator of whole-body insulin and glucose homeostasis. This study investigates the role of STK25 in liver lipid accumulation and NASH. Stk25 transgenic mice challenged with a high-fat diet displayed a dramatic increase in liver steatosis and hepatic insulin resistance compared to wild-type siblings. Focal fibrosis, hepatocellular damage, and inflammation were readily seen in transgenic but not wild-type livers. Transgenic livers displayed reduced b-oxidation and triacylglycerol secretion, while lipid uptake and synthesis remained unchanged. STK25 was associated with lipid droplets, colocalizing with the main hepatic lipid droplet-coating protein adipose differentiation-related protein, the level of which was increased 3.8 6 0.7-fold in transgenic livers (P < 0.01), while a key hepatic lipase, adipose triacylglycerol lipase, was translocated from the lipid droplets surface to the cytoplasm, providing the likely mechanism underlying the effect of STK25. In summary, STK25 is a lipid dropletassociated protein that promotes NAFLD through control of lipid release from the droplets for b-oxidation and triacylglycerol secretion. STK25 also drives pathogenesis of NASH.-Amrutkar, M., Cansby, E., Nuñez-Durán, E., Pirazzi, C., Ståhlman, M., Stenfeldt, E., Smith, U., Borén, J., Mahlapuu, M. Protein kinase STK25 regulates hepatic lipid partitioning and progression of liver steatosis and NASH. FASEB J. 29, 1564-1576 (2015). www.fasebj.orgTHE METABOLIC SYNDROME is a cluster of abnormalities including abdominal obesity, insulin resistance, glucose intolerance, and dyslipidemia. Recently, attention has focused on the excessive accumulation of triacylglycerols (TAG) in lipid droplets within the liver as part of this metabolic syndrome. The development of nonalcoholic fatty liver disease (NAFLD) is strongly associated with the metabolic syndrome: approximately 90% of patients with NAFLD have more than one feature of metabolic syndrome (1), and NAFLD is consistently associated with obesity (60-95%), type 2 diabetes (28-55%), and dyslipidemia (27-92%) (2). Furthermore, recent evidence suggests that lipid accumulation in the liver is not merely a consequence of metabolic syndrome, but rather that NAFLD exacerbates hepatic and systemic insulin resistance and actively contributes to the pathogenesis of metabolic syndrome (3).Approximately 10 to 20% of patients with NAFLD progress to nonalcoholic steatohepatitis (NASH), which is characterized by inflammation, fibrosis, and cellular damage in the liver in addition to fatty infiltration. Patients with NASH are at high risk of developing cirrhosis, liver failure, and hepatocellular carcinoma (3). More than a decade ago, Day and James (4) presented the so-called 2-...

OBJECTIVEObese individuals with type 2 diabetes have an increased risk of cardiovascular disease. The effect of bariatric surgery on cardiovascular events in obese individuals with type 2 diabetes remains to be determined. The Swedish Obese Subjects (SOS) study is a prospective, controlled intervention study that examines the effects of bariatric surgery on hard end points. The aim of the present study was to examine the effect of bariatric surgery on cardiovascular events in the SOS study participants with type 2 diabetes.RESEARCH DESIGN AND METHODSAll SOS study participants with type 2 diabetes at baseline were included in the analyses (n = 345 in the surgery group and n = 262 in the control group). Mean follow-up was 13.3 years (interquartile range 10.2–16.4) for all cardiovascular events.RESULTSBariatric surgery was associated with a reduced myocardial infarction incidence (38 events among the 345 subjects in the surgery group vs. 43 events among the 262 subjects in the control group; log-rank P = 0.017; adjusted hazard ratio [HR] 0.56 [95% CI 0.34–0.93]; P = 0.025). No effect of bariatric surgery was observed on stroke incidence (34 events among the 345 subjects in the surgery group vs. 24 events among the 262 subjects in the control group; log-rank P = 0.852; adjusted HR 0.73 [0.41–1.30]; P = 0.29). The effect of surgery in reducing myocardial infarction incidence was stronger in individuals with higher serum total cholesterol and triglycerides at baseline (interaction P value = 0.02 for both traits). BMI (interaction P value = 0.12) was not related to the surgery outcome.CONCLUSIONSBariatric surgery reduces the incidence of myocardial infarction in obese individuals with type 2 diabetes. Preoperative BMI should be integrated with metabolic parameters to maximize the benefits of bariatric surgery.

BackgroundObesity is highly associated with elevated serum triglycerides, hepatic steatosis and type 2 diabetes (T2D). The I148M (rs738409) genetic variant of patatin-like phospholipase domain-containing 3 gene (PNPLA3) is known to modulate hepatic triglyceride accumulation, leading to steatosis. No association between PNPLA3 I148M genotype and T2D in Europeans has been reported. Aim of this study is to examine the relationship between PNPLA3 I148M genotypes and serum triglycerides, insulin resistance and T2D susceptibility by testing a gene-environment interaction model with severe obesity.Methods and Findings PNPLA3 I148M was genotyped in a large obese cohort, the SOS study (n = 3,473) and in the Go-DARTS (n = 15,448), a T2D case-control study. Metabolic parameters were examined across the PNPLA3 I148M genotypes in participants of the SOS study at baseline and at 2- and 10-year follow up after bariatric surgery or conventional therapy. The associations with metabolic parameters were validated in the Go-DARTS study. Serum triglycerides were found to be lower in the PNPLA3 148M carriers from the SOS study at baseline and from the Go-DARTS T2D cohort. An increased risk for T2D conferred by the 148M allele was found in the SOS study (O.R. 1.09, 95% C.I. 1.01-1.39, P = 0.040) and in severely obese individuals in the Go-DARTS study (O.R. 1.37, 95% C.I. 1.13-1.66, P = 0.001). The 148M allele was no longer associated with insulin resistance or T2D after bariatric surgery in the SOS study and no association with the 148M allele was observed in the less obese (BMI<35) individuals in the Go-DARTS study (P for interaction  = 0.002). This provides evidence for the obesity interaction with I48M allele and T2D risk in a large-scale cross-sectional and a prospective interventional study.ConclusionsSeverely obese individuals carrying the PNPLA3 148M allele have lower serum triglyceride levels, are more insulin resistant and more susceptible to T2D. This study supports the hypothesis that obesity-driven hepatic lipid accumulation may contribute to T2D susceptibility.

No abstract