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Marmugi A, Ducheix S, Lasserre F, Polizzi A, Paris A, Priymenko N, Bertrand-Michel J, Pineau T, Guillou H, Martin PGP, Mselli-Lakhal L. Low doses of bisphenol A induce gene expression related to lipid synthesis and trigger triglyceride accumulation in adult mouse liver. Hepatology 2012; 55:395-407. [PMID: 21932408 DOI: 10.1002/hep.24685] [Citation(s) in RCA: 216] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Accepted: 08/31/2011] [Indexed: 12/11/2022]
Abstract
UNLABELLED Changes in lifestyle are suspected to have strongly influenced the current obesity epidemic. Based on recent experimental, clinical, and epidemiological work, it has been proposed that some food contaminants may exert damaging effects on endocrine and metabolic functions, thereby promoting obesity and associated metabolic diseases such as nonalcoholic fatty liver disease (NAFLD). In this work, we investigated the effect of one suspicious food contaminant, bisphenol A (BPA), in vivo. We used a transcriptomic approach in male CD1 mice exposed for 28 days to different doses of BPA (0, 5, 50, 500, and 5,000 μg/kg/day) through food contamination. Data analysis revealed a specific impact of low doses of BPA on the hepatic transcriptome, more particularly on genes involved in lipid synthesis. Strikingly, the effect of BPA on the expression of de novo lipogenesis followed a nonmonotonic dose-response curve, with more important effects at lower doses than at the higher dose. In addition to lipogenic enzymes (Acc, Fasn, Scd1), the expression of transcription factors such as liver X Receptor, the sterol regulatory element binding protein-1c, and the carbohydrate responsive element binding protein that govern the expression of lipogenic genes also followed a nonmonotonic dose-response curve in response to BPA. Consistent with an increased fatty acid biosynthesis, determination of fat in the liver showed an accumulation of cholesteryl esters and of triglycerides. CONCLUSION Our work suggests that exposure to low BPA doses may influence de novo fatty acid synthesis through increased expression of lipogenic genes, thereby contributing to hepatic steatosis. Exposure to such contaminants should be carefully examined in the etiology of metabolic diseases such as NAFLD and nonalcoholic steatohepatitis.
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Affiliation(s)
- Alice Marmugi
- INRA, TOXALIM (Research Centre in Food Toxicology), Toulouse, France
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Abstract
Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common cause of pediatric liver disease in the developed world. Children have a form of NAFLD that is pathologically distinct from adults. Although NAFLD remains a pathologic diagnosis, biomarkers and imaging studies hold promise as noninvasive means of both establishing the diagnosis and following the disease course. Significant advancements have recently been made in genetics, pathophysiology, and the treatment of NAFLD. The purpose of this article is to provide a clinically relevant review of pediatric NAFLD with an emphasis on recent developments in the field.
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253
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Hernaez R. Genetic factors associated with the presence and progression of nonalcoholic fatty liver disease: a narrative review. GASTROENTEROLOGIA Y HEPATOLOGIA 2011; 35:32-41. [PMID: 22093607 DOI: 10.1016/j.gastrohep.2011.08.002] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 08/04/2011] [Indexed: 12/25/2022]
Abstract
Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. Whereas insulin resistance and obesity are considered major risk factors for the development and progression of NAFLD, the genetic underpinnings are unclear. Before 2008, candidate gene studies based on prior knowledge of pathophysiology of fatty liver yielded conflicting results. In 2008, Romeo et al. published the first genome wide association study and reported the strongest genetic signal for the presence of fatty liver (PNPLA3, patatin-like phospholipase domain containing 3; rs738409). Since then, two additional genome wide scans were published and identified 9 additional genetic variants. Whereas these results shed light into the understanding of the genetics of NAFLD, most of associations have not been replicated in independent samples and, therefore, remain undetermined the significance of these findings. This review aims to summarize the understanding of genetic epidemiology of NAFLD and highlights the gaps in knowledge.
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Affiliation(s)
- Ruben Hernaez
- Department of Medicine, The Johns Hopkins School of Medicine, Baltimore, MD 21287, USA.
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Trépo E, Franchimont D, Moreno C. Association ofPNPLA3(rs738409 C>G) with liver damage in liver diseases: one step closer to personalized medicine? Per Med 2011; 8:595-597. [DOI: 10.2217/pme.11.66] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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256
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Coleman RA, Mashek DG. Mammalian triacylglycerol metabolism: synthesis, lipolysis, and signaling. Chem Rev 2011; 111:6359-86. [PMID: 21627334 PMCID: PMC3181269 DOI: 10.1021/cr100404w] [Citation(s) in RCA: 206] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Rosalind A Coleman
- Department of Nutrition, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
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257
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Trépo E, Gustot T, Degré D, Lemmers A, Verset L, Demetter P, Ouziel R, Quertinmont E, Vercruysse V, Amininejad L, Deltenre P, Le Moine O, Devière J, Franchimont D, Moreno C. Common polymorphism in the PNPLA3/adiponutrin gene confers higher risk of cirrhosis and liver damage in alcoholic liver disease. J Hepatol 2011; 55:906-12. [PMID: 21334404 DOI: 10.1016/j.jhep.2011.01.028] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Revised: 12/20/2010] [Accepted: 01/06/2011] [Indexed: 12/14/2022]
Abstract
BACKGROUND & AIMS A recent genome-wide association study identified genetic polymorphism (rs738409 C>G) in the PNPLA3/adiponutrin gene associated with liver steatosis. This variant has also been linked to increased risk of alcoholic liver disease (ALD) and cirrhosis in Mestizo Mexicans with excessive alcohol intake. Our aim was to study the influence of this polymorphism on European Caucasian patients with histologically suggestive ALD. METHODS Three-hundred-and-twenty-eight healthy controls and 330 ALD patients, among whom 265 had cirrhosis, were genotyped for the rs738409 polymorphism. We studied the impact of rs738409 on clinical and biological parameters, together with histological staging of steatosis and fibrosis. PNPLA3 messenger RNA (mRNA) levels were measured by quantitative real-time PCR according to the patient's phenotype. RESULTS The G-allele was significantly more frequent in ALD patients than in controls (odds ratio [OR] = 1.54, 95% confidence interval [CI] = 1.12-2.11 p = 0.008) and was, among ALD patients, significantly associated with steatosis (p = 0.048), fibrosis (p = 0.001), and greater risk of cirrhosis (p = 0.001). In multivariate analysis, rs738409 remained the strongest independent factor associated with risk of cirrhosis (OR = 2.08; 95% CI = 1.15-3.77; p = 0.02). Furthermore, the PNPLA3 mRNA liver expression level was significantly lower in patients with more advanced fibrosis (p = 0.03) and negatively correlated with the hepatic venous pressure gradient (r = -0.41, p = 0.006). CONCLUSIONS In European Caucasians, the rs738409 variant is associated with increased risk of ALD, liver damage, and cirrhosis. Further prospective studies are required to confirm these results and to evaluate the potential of PNPLA3 as both a predictor and a therapeutic target in ALD.
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Affiliation(s)
- Eric Trépo
- Department of Gastroenterology, Hepatopancreatology and Digestive Oncology, Erasme Hospital, Université Libre de Bruxelles, Brussels, Belgium
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Cold exposure down-regulates adiponutrin/PNPLA3 mRNA expression and affects its nutritional regulation in adipose tissues of lean and obese Zucker rats. Br J Nutr 2011; 107:1283-95. [PMID: 21914237 DOI: 10.1017/s000711451100434x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Adiponutrin/PNPLA3 is a protein highly produced in adipose tissue whose expression is under tight nutritional regulation. It possesses lipogenic/lipolytic capacity and, although adiponutrin polymorphisms are related to obesity, its physiological role is not clear. To help clarify its role, we studied the effect of acute cold exposure on adiponutrin mRNA expression in different adipose tissues of lean/obese Zucker rats subjected to feeding/fasting/refeeding. The effect of cold on the expression of key lipogenic enzymes and on uncoupling protein-1 (UCP1) was evaluated in selected adipose depots. Adiponutrin mRNA levels were also determined in the adipose tissue of isoprenaline-treated rats and in cultured adipocytes treated with noradrenaline, isoprenaline and a selective β3-adrenoceptor (AR) agonist. Adiponutrin expression was strongly down-regulated by cold in the different adipose depots in lean animals, while this down-regulation was impaired in obese rats. Adiponutrin pattern of expression in response to cold correlated positively with that of the lipogenic enzymes and negatively with UCP1 expression. Acute intraperitoneal administration of isoprenaline also produced a decrease in adiponutrin expression in adipose tissue. In vitro data suggest that adiponutrin's inhibitory effect could be mediated, at least in part, by the sympathetic system via β1/β2-AR. In addition, improvement in metabolic parameters related to obesity in cold-exposed animals was related to an improvement in adiponutrin nutritional regulation. Thus, cold inhibition of adiponutrin expression in adipose tissue (which correlates with the response of lipogenic enzymes) supports a physiological role for this protein in lipogenesis. Moreover, alterations in adiponutrin expression and regulation in adipose tissue are related to obesity.
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259
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Di Rosa M, Malaguarnera L. Genetic variants in candidate genes influencing NAFLD progression. J Mol Med (Berl) 2011; 90:105-18. [PMID: 21894552 DOI: 10.1007/s00109-011-0803-x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Revised: 08/08/2011] [Accepted: 08/08/2011] [Indexed: 12/17/2022]
Abstract
Nonalcoholic fatty liver disease (NAFLD) is a metabolic disorder including simple steatosis and nonalcoholic steatohepatitis (NASH). Advanced stages of NASH result ultimately in fibrosis, cirrhosis, and hepatocarcinoma. A diagnosis of NASH entails an increased risk of both liver-related and cardiovascular mortality as worsening of the metabolic syndrome. Because of its escalation, many investigations have been performed to elucidate the pathophysiologic origins of the disease progression. Human epidemiologic studies describing polymorphisms in a number of genes involved in metabolic dysfunctions have contributed to clarify the causes leading to the disease evolution. In this review, we attempt to outline critically the most recently identified genetic variants in NAFLD patients to identify possible risk factors promoting the progression of the disease. The evaluation of altered genotypes together with other clinical variables may facilitate the clinical management of these patients.
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Affiliation(s)
- Michelino Di Rosa
- Department of Biomedical Sciences, University of Catania, Via Androne, 83, 95124 Catania, Italy
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260
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Falleti E, Fabris C, Cmet S, Cussigh A, Bitetto D, Fontanini E, Fornasiere E, Bignulin S, Fumolo E, Bignulin E, Pirisi M, Toniutto P. PNPLA3 rs738409C/G polymorphism in cirrhosis: relationship with the aetiology of liver disease and hepatocellular carcinoma occurrence. Liver Int 2011; 31:1137-43. [PMID: 21745286 DOI: 10.1111/j.1478-3231.2011.02534.x] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/13/2023]
Abstract
BACKGROUND AND AIM The PNPLA3 rs738409 C>G polymorphism has been found to be strongly associated with non-alcoholic fatty liver disease and with alcoholic liver disease. Whether the PNPLA3 rs738409 polymorphism could be a risk factor for the development of hepatocellular carcinoma (HCC) in cirrhosis patients is unknown. METHODS This study included 483 (344 males) consecutive Italian patients of Caucasian ethnicity affected by cirrhosis, of whom 279 had undergone transplantation for end-stage liver disease while 204 had been referred to our liver and transplant unit for the diagnosis of cirrhosis. The aetiologies were hepatitis C virus=209, hepatitis B virus=76, alcohol=166, metabolic=32. Ile148Met rs738409 transversion was genotyped using an restriction fragment length polymorphism-based assay. RESULTS The genotype frequencies of the rs738409 polymorphism were distributed differently in patients with cirrhosis C/C=168, C/G=220, G/G=95 vs controls C/C=218, C/G=175, G/G=35 (P<0.0001). Among cirrhotics, the G allele was over-represented in alcoholic/metabolic (0.505) vs viral (0.368, P<0.001) liver disease. Patients with cirrhosis complicated by HCC were more likely to be G/G homozygotes (38/141) than the remaining patients (57/342, P<0.02). At multivariate analysis, the PNPLA3 rs738409 polymorphism was confirmed to be an independent predictor of HCC occurrence (odds ratio 1.76, 95% confidence interval 1.06-2.92, P<0.05). HCC rates increased from 13/116 (11.2%; female C/(*) carriers), to 97/295 (32.9%; male C/(*) carriers and female G/G homozygotes), to 31/72 (43.1%; male G/G homozygotes) (P<0.0001). CONCLUSIONS The PNPLA3 rs738409 C>G polymorphism is associated with cirrhosis. In synergy with gender, this polymorphism is a strong predictor of HCC occurrence among patients with cirrhosis.
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Affiliation(s)
- Edmondo Falleti
- Department of Medical Sciences Experimental and Clinical, University of Udine, Udine, Italy
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261
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Huang Y, Cohen JC, Hobbs HH. Expression and characterization of a PNPLA3 protein isoform (I148M) associated with nonalcoholic fatty liver disease. J Biol Chem 2011; 286:37085-93. [PMID: 21878620 PMCID: PMC3199456 DOI: 10.1074/jbc.m111.290114] [Citation(s) in RCA: 212] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
A genetic variant of PNPLA3 (patatin-like phospholipase domain-containing 3; PNPLA3-I148M), a serine protease of unknown function, is associated with accumulation of triacylglycerol (TAG) in the liver. To determine the biological substrates of PNPLA3 and the effect of the I148M substitution on enzymatic activity and substrate specificity, we purified and characterized recombinant human PNPLA3 and PNPLA3-I148M. Maximal hydrolytic activity of PNPLA3 was observed against the three major glycerolipids, TAG, diacylglycerol, and monoacylglycerol, with a strong preference for oleic acid as the acyl moiety. Substitution of methionine for isoleucine at position 148 markedly decreased the V(max) of the enzyme for glycerolipids but had only a modest effect on the K(m). Purified PNPLA3 also catalyzed the hydrolysis of oleoyl-CoA, but the V(max) was 100-fold lower for oleoyl-CoA than for triolein. The thioesterase activity required the catalytic serine but was only modestly decreased by the I148M substitution. The enzyme had little or no hydrolytic activity against the other lipid substrates tested, including phospholipids, cholesteryl ester, and retinyl esters. Neither the wild-type nor mutant enzyme catalyzed transfer of oleic acid from oleoyl-CoA to glycerophosphate, lysophosphatidic acid, or diacylglycerol, suggesting that the enzyme does not promote de novo TAG synthesis. Taken together, our results are consistent with the notion that PNPLA3 plays a role in the hydrolysis of glycerolipids and that the I148M substitution causes a loss of function, although we cannot exclude the possibility that the enzyme has additional substrates or activities.
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Affiliation(s)
- Yongcheng Huang
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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262
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Anstee QM, Daly AK, Day CP. Genetic modifiers of non-alcoholic fatty liver disease progression. Biochim Biophys Acta Mol Basis Dis 2011; 1812:1557-66. [PMID: 21840395 DOI: 10.1016/j.bbadis.2011.07.017] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2011] [Revised: 07/28/2011] [Accepted: 07/29/2011] [Indexed: 12/11/2022]
Abstract
Non-alcoholic fatty liver disease (NAFLD) is now recognised as the most common cause of liver dysfunction worldwide. However, whilst the majority of individuals who exhibit features of the metabolic syndrome including obesity and insulin resistance will develop steatosis, only a minority progress to steatohepatitis, fibrosis and cirrhosis. Subtle inter-patient genetic variations and environment interact to determine disease phenotype and influence progression. A decade after the sequencing of the human genome, the comprehensive study of genomic variation offers new insights into the modifier genes, pathogenic mechanisms and is beginning to suggest novel therapeutic targets. We review the current status of the field with particular focus on advances from recent genome-wide association studies.
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Affiliation(s)
- Quentin M Anstee
- Liver Research Group, Instiutte of Cellular Medicine, Teh Medical School, Newcastle University, Framlington Place, Newcaltle-upon-Type, NE2 4HHK, UK
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263
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Krawczyk M, Grünhage F, Zimmer V, Lammert F. Variant adiponutrin (PNPLA3) represents a common fibrosis risk gene: non-invasive elastography-based study in chronic liver disease. J Hepatol 2011; 55:299-306. [PMID: 21168459 DOI: 10.1016/j.jhep.2010.10.042] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/24/2010] [Revised: 10/17/2010] [Accepted: 10/25/2010] [Indexed: 12/12/2022]
Abstract
BACKGROUND & AIMS Recent genome-wide association studies have identified the variant p.I148M of the adiponutrin gene PNPLA3 as a risk factor for developing severe forms of non-alcoholic and alcoholic liver diseases. The risk allele confers an increased risk for fatty liver disease and elevated serum aminotransferase activities reflecting liver injury. In the current elastography-based study, we investigate variant adiponutrin as genetic determinant of liver fibrosis, the hallmark of all chronic liver diseases. METHODS In this observational cross-sectional study, we staged 899 patients with different chronic liver diseases non-invasively by transient elastography (Fibroscan) and genotyped them for variant adiponutrin (rs738409) by PCR-based assays. A subgroup of 229 patients consented to percutaneous liver biopsy, validating the accuracy of elastography in staging fibrosis (ρ=0.743, p<0.01). RESULTS Carriers of distinct p.I148M adiponutrin genotypes display significant (p=0.017) differences in liver stiffness determined by elastography. In particular, individuals carrying the allele [G] are at higher risk of developing liver cirrhosis defined by stiffness values ≥13.0kPa (OR=1.56, p=0.005). Of note, the PNPLA3 risk variant advances fibrosis in the total cohort as well as in the subgroups of patients with viral hepatitis and non-viral liver diseases and contributes 16% of the total cirrhosis risk. CONCLUSIONS The adiponutrin risk variant is a common genetic determinant of progressive liver fibrosis. Our results underpin non-invasive follow-up for individuals with chronic liver disease at-risk for developing advanced fibrosis and cirrhosis.
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Affiliation(s)
- Marcin Krawczyk
- Department of Medicine II, Saarland University Hospital, Homburg, Germany
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Affiliation(s)
- Norbert Stefan
- Department of Internal Medicine IV, Division of Endocrinology, Diabetology, Vascular Medicine, Nephrology and Clinical Chemistry, University of Tübingen, Tübingen, Germany.
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265
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Qiao A, Liang J, Ke Y, Li C, Cui Y, Shen L, Zhang H, Cui A, Liu X, Liu C, Chen Y, Zhu Y, Guan Y, Fang F, Chang Y. Mouse patatin-like phospholipase domain-containing 3 influences systemic lipid and glucose homeostasis. Hepatology 2011; 54:509-21. [PMID: 21547936 DOI: 10.1002/hep.24402] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2011] [Accepted: 04/20/2011] [Indexed: 12/11/2022]
Abstract
UNLABELLED Human patatin-like phospholipase domain-containing 3 (PNPLA3) is associated with increased liver fat content and liver injury. Here, we show that nutritional status regulates PNPLA3 gene expression in the mouse liver. Sterol response element binding protein-1 (SREBP-1) activated PNPLA3 gene transcription via sterol regulatory elements (SREs) mapped to the promoter region. Chromatin immunoprecipitation and electrophoretic mobility shift assays confirmed that SREBP-1 proteins bound to the identified SREs. Furthermore, SREBP-1c mediated the insulin and liver X receptor agonist TO901317-dependent induction of PNPLA3 gene expression in hepatocytes. Adenovirus-mediated overexpression of mouse PNPLA3 increased intracellular triglyceride content in primary hepatocytes, and knockdown of PNPLA3 suppressed the ability of SREBP-1c to stimulate lipid accumulation in hepatocytes. Finally, the overexpression of PNPLA3 in mouse liver increased the serum triglyceride level and impaired glucose tolerance; in contrast, the knockdown of PNPLA3 in db/db mouse liver improved glucose tolerance. CONCLUSION Our data suggest that mouse PNPLA3, which is a lipogenic gene directly targeted by SREBP-1, promotes lipogenesis in primary hepatocytes and influences systemic lipid and glucose metabolism.
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Affiliation(s)
- Aijun Qiao
- National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
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266
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Dubuquoy C, Robichon C, Lasnier F, Langlois C, Dugail I, Foufelle F, Girard J, Burnol AF, Postic C, Moldes M. Distinct regulation of adiponutrin/PNPLA3 gene expression by the transcription factors ChREBP and SREBP1c in mouse and human hepatocytes. J Hepatol 2011; 55:145-53. [PMID: 21145868 DOI: 10.1016/j.jhep.2010.10.024] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2010] [Revised: 09/30/2010] [Accepted: 10/19/2010] [Indexed: 02/08/2023]
Abstract
BACKGROUND & AIMS The adiponutrin/PNPLA3 (patatin-like phospholipase domain-containing protein 3) variant I148M has recently emerged as an important marker of human fatty liver disease. In order to understand the role of the adiponutrin/PNPLA3 protein, we investigated the regulation of its expression in both human and mouse hepatocytes. METHODS Adiponutrin/PNPLA3 and lipogenic enzyme expression was determined by real-time PCR analysis in a wide panel of analysis in vivo in the mouse liver and in vitro in murine hepatocytes and human hepatocyte cell lines infected with ChREBP or SREBP1c-expressing adenoviruses. RESULTS We show that in the mouse liver, adiponutrin/PNPLA3 gene expression is under the direct transcriptional control of ChREBP (carbohydrate-response element-binding protein) and SREBP1c (sterol regulatory element binding protein1c) in response to glucose and insulin, respectively. In silico analysis revealed the presence of a ChoRE (carbohydrate response element) and of a SRE (sterol response element) binding site on the mouse adiponutrin/PNPLA3 gene promoter. Point mutation analysis in reporter gene assays identified the functional response of these two binding sites in the mouse adiponutrin/PNPLA3 promoter. In contrast, in human immortalized hepatocytes and in HepG2 hepatoma cells, only SREBP1c was able to induce adiponutrin/PNPLA3 expression, whereas ChREBP was unable to modulate its expression. CONCLUSIONS All together, our results suggest that adiponutrin/PNPLA3 is regulated by two key factors of the glycolytic and lipogenic pathways, raising the question of its implication in the metabolism of carbohydrates and lipids.
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Trépo E, Pradat P, Potthoff A, Momozawa Y, Quertinmont E, Gustot T, Lemmers A, Berthillon P, Amininejad L, Chevallier M, Schlué J, Kreipe H, Devière J, Manns M, Trépo C, Sninsky J, Wedemeyer H, Franchimont D, Moreno C. Impact of patatin-like phospholipase-3 (rs738409 C>G) polymorphism on fibrosis progression and steatosis in chronic hepatitis C. Hepatology 2011; 54:60-9. [PMID: 21488075 DOI: 10.1002/hep.24350] [Citation(s) in RCA: 152] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
UNLABELLED Only 20% of patients with chronic hepatitis C (CHC) will develop cirrhosis, and fibrosis progression remains highly unpredictable. A recent genome-wide association study identified a genetic variant in the patatin-like phospholipase-3 (PNPLA3) gene (rs738409 C>G) associated with steatosis that was further demonstrated to influence severity of fibrosis in nonalcoholic fatty liver disease. The aim of this study was to assess the impact of this polymorphism on histological liver damage and response to antiviral therapy in CHC. We recruited 537 Caucasian CHC patients from three European centers (Brussels, Belgium [n = 229]; Hannover, Germany [n = 171]; Lyon, France [n = 137]); these patients were centrally genotyped for the PNPLA3 (rs738409 C>G) polymorphism. We studied the influence of rs738409 and other variants in the PNPLA3 region on steatosis and fibrosis assessed both in a cross-sectional and longitudinal manner. Seven other variants previously associated with fibrosis progression were included. Finally, we explored the impact of rs738409 on response to standard antiviral therapy using the interferon lambda 3 (IL28B) [rs12979860 C>T] variant both as a comparator and as a positive control. After adjustment for age, sex, body mass index, alcohol consumption, and diabetes, rs738409 mutant G allele homozygote carriers remained at higher risk for steatosis (odds ratio [OR] 2.55, 95% confidence interval [CI] 1.08-6.03, P = 0.034), fibrosis (OR 3.13, 95% CI 1.50-6.51, P = 0.002), and fibrosis progression (OR 2.64, 95% CI 1.22-5.67, P = 0.013). Conversely, rs738409 was not independently associated with treatment failure (OR 1.07, 95% CI 0.46-2.49, P = 0.875) and did not influence clinical or biological variables. CONCLUSION The PNPLA3 (rs738409 C>G) polymorphism favors steatosis and fibrosis progression in CHC. This polymorphism may represent a valuable genetic predictor and a potential therapeutic target in CHC liver damage.
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Affiliation(s)
- Eric Trépo
- Department of Gastroenterology, Hepatopancreatology, and Digestive Oncology, Erasme Hospital, Brussels, Belgium
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268
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Abstract
Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem that affects one-third of adults and an increasing number of children in developed countries. The disease begins with the aberrant accumulation of triglyceride in the liver, which in some individuals elicits an inflammatory response that can progress to cirrhosis and liver cancer. Although NAFLD is strongly associated with obesity and insulin resistance, its pathogenesis remains poorly understood, and therapeutic options are limited. Here, we discuss recent mechanistic insights into NAFLD, focusing primarily on those that have emerged from human genetic and metabolic studies.
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Affiliation(s)
- Jonathan C. Cohen
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390–9046, USA
| | - Jay D. Horton
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390–9046, USA
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390–9046, USA
| | - Helen H. Hobbs
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390–9046, USA
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390–9046, USA
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390–9046, USA
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Li DY, Lin LJ, Zheng CQ. Advances in understanding the role of PNPLA3 in the pathogenesis of non-alcoholic fatty liver disease. Shijie Huaren Xiaohua Zazhi 2011; 19:1796-1801. [DOI: 10.11569/wcjd.v19.i17.1796] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The incidence of non-alcoholic fatty liver disease (NAFLD) is rising worldwide. Investigation of genes involved in the pathogenesis of NAFLD is significant for replenishing treatment scheme and improving prognosis. Multiple studies have established a correlation between patatin-like phospholipase domain-containing 3 (PNPLA3) gene mutation and the pathogenesis of NAFLD, suggesting that PNPLA3 may affect lipid metabolism. However, the precise mechanism remains to be elucidated. Some researchers believed that PNPLA3 as a patatin-like protein might have triglyceride hydrolysis activity and therefore affect fat metabolism in the liver, while some others thought that PNPLA3 mutation might interfere with the lipid transfer process. In this paper, we give an overview of the PNPLA3 gene and its expression, and explore the correlation between PNPLA3 gene mutation and the pathogenesis of NAFLD.
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Abstract
Liver X receptors (LXRs) are cholesterol-sensing nuclear receptors that are not only key regulators of lipid metabolism and transport but also suppress inflammatory signaling in macrophages through a unique mechanism of transrepression. In this brief review, we focus on the regulatory actions of LXR primarily in macrophages responding to a proatherogenic environment. LXR potentially interferes with atherosclerosis by 2 different agonist-dependent signaling pathways. The first is through promoting reverse cholesterol transportby directly activating genes of cellular cholesterol export. The second is through a general inhibitory action on proinflammatory genes where sumo-modified and agonist-bound LXR recruits negative coregulatory proteins to nuclear factor κB at immune response gene promoters through protein-protein interactions. The antiinflammatory actions of LXR may be a direct response to the proinflammatory actions recently proposed for cholesterol on inflammasome activity in the vessel wall.
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Affiliation(s)
- Seung-Soon Im
- Metabolic Signaling and Disease Program, Diabetes and Obesity Research Center, Sanford-Burnham Medical Research Institute, Lake Nona, Orlando, FL, USA
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271
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Sookoian S, Pirola CJ. Meta-analysis of the influence of I148M variant of patatin-like phospholipase domain containing 3 gene (PNPLA3) on the susceptibility and histological severity of nonalcoholic fatty liver disease. Hepatology 2011; 53:1883-94. [PMID: 21381068 DOI: 10.1002/hep.24283] [Citation(s) in RCA: 697] [Impact Index Per Article: 53.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2010] [Accepted: 02/21/2011] [Indexed: 12/12/2022]
Abstract
UNLABELLED Our objective was to estimate the strength of the effect of the I148M (rs738409 C/G) patatin-like phospholipase domain containing 3 (PNPLA3) variant on nonalcoholic fatty liver (NAFLD) and disease severity across different populations. We performed a systematic review by a meta-analysis; literature searches identified 16 studies. Our results showed that rs738409 exerted a strong influence not only on liver fat accumulation (GG homozygous showed 73% higher lipid fat content when compared with CC ones, data from 2,937 subjects; P < 1 × 10(-9) ), but also on the susceptibility of a more aggressive disease (GG homozygous had 3.24-fold greater risk of higher necroinflammatory scores and 3.2-fold greater risk of developing fibrosis when compared with CC homozygous; P < 1 × 10(-9) ; data from 1,739 and 2,251 individuals, respectively). Nonalcoholic steatohepatitis (NASH) was more frequently observed in GG than CC homozygous (odds ratio [OR] 3.488, 95% confidence interval [CI] 1.859-6.545, random model; P < 2 × 10(-4) ; data from 2,124 patients). Evaluation of the risk associated with heterozygosity for the variant suggests that the additive genetic model best explains the effect of rs738409 on the susceptibility to develop NAFLD. Nevertheless, carrying two G alleles does not seem to increase the risk of severe histological features. Meta-regression showed a negative correlation between male sex and the effect of rs738409 on liver fat content (slope: -2.45 ± 1.04; P < 0.02). The rs738409 GG genotype versus the CC genotype was associated with a 28% increase in serum alanine aminotransferase levels. CONCLUSION By summarizing the amount of evidence, this study provided unequivocal evidence of rs738409 as a strong modifier of the natural history of NAFLD in different populations around the world.
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Affiliation(s)
- Silvia Sookoian
- Department of Clinical and Molecular Hepatology, Institute of Medical Research A Lanari-IDIM, University of Buenos Aires-National-Council of Scientific and Technological Research (CONICET), Ciudad Autónoma de Buenos Aires, Argentina.
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272
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Tateno C, Kataoka M, Utoh R, Tachibana A, Itamoto T, Asahara T, Miya F, Tsunoda T, Yoshizato K. Growth hormone-dependent pathogenesis of human hepatic steatosis in a novel mouse model bearing a human hepatocyte-repopulated liver. Endocrinology 2011; 152:1479-91. [PMID: 21303949 DOI: 10.1210/en.2010-0953] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Clinical studies have shown a close association between nonalcoholic fatty liver disease and adult-onset GH deficiency, but the relevant molecular mechanisms are still unclear. No mouse model has been suitable to study the etiological relationship of human nonalcoholic fatty liver disease and human adult-onset GH deficiency under conditions similar to the human liver in vivo. We generated human (h-)hepatocyte chimeric mice with livers that were predominantly repopulated with h-hepatocytes in a h-GH-deficient state. The chimeric mouse liver was mostly repopulated with h-hepatocytes about 50 d after transplantation and spontaneously became fatty in the h-hepatocyte regions after about 70 d. Infusion of the chimeric mouse with h-GH drastically decreased steatosis, showing the direct cause of h-GH deficiency in the generation of hepatic steatosis. Using microarray profiles aided by real-time quantitative RT-PCR, comparison between h-hepatocytes from h-GH-untreated and -treated mice identified 14 GH-up-regulated and four GH-down-regulated genes, including IGF-I, SOCS2, NNMT, IGFLS, P4AH1, SLC16A1, SRD5A1, FADS1, and AKR1B10, respectively. These GH-up- and -down-regulated genes were expressed in the chimeric mouse liver at lower and higher levels than in human livers, respectively. Treatment of the chimeric mice with h-GH ameliorated their altered expression. h-Hepatocytes were separated from chimeric mouse livers for testing in vitro effects of h-GH or h-IGF-I on gene expression, and results showed that GH directly regulated the expression of IGF-I, SOCS2, NNMT, IGFALS, P4AH1, FADS1, and AKR1B10. In conclusion, the chimeric mouse is a novel h-GH-deficient animal model for studying in vivo h-GH-dependent human liver dysfunctions.
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Affiliation(s)
- Chise Tateno
- Yoshizato Project, Hiroshima Prefectural Institute of Industrial Science and Technology, Cooperative Link of Unique Science and Technology for Economy Revitalization, Higashihirosima, Hiroshima 739-0046, Japan
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273
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Riegler B, Besenboeck C, Bauer R, Nimpf J, Schneider WJ. Enzymes involved in hepatic acylglycerol metabolism in the chicken. Biochem Biophys Res Commun 2011; 406:257-61. [PMID: 21316342 DOI: 10.1016/j.bbrc.2011.02.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Accepted: 02/06/2011] [Indexed: 11/17/2022]
Abstract
In laying hens, massive hepatic mobilization of fatty acids is required for the synthesis of oocyte-targeted very-low density lipoproteins (VLDL). The current study aims at identification of enzymes that hydrolyze hepatic acylglycerol stores regulated in a fashion compatible with supporting enhanced VLDL synthesis. We show that unlike mammals, chickens express adipose triglyceride lipase (ATGL) also in liver, where it is upregulated by fasting, while the enzyme patatin-like phospholipase domain-containing lipase 3 (PNPLA3) is suppressed. For the first time in any system, we show that hepatic arylacetamide deacetylase (AADA) is upregulated by fasting, and that its affinity for an insoluble carboxylester substrate is compatible with an in-vivo function similar to that of ATGL. Unknown heretofore, hepatic expression of chicken AADA is estrogen-responsive, and is induced to the same degree as the stimulation of VLDL-production by estrogen. These observations support roles of chicken ATGL, PNPLA3, and AADA in acylglycerol metabolism related to the high rates of VLDL synthesis that are essential for reproduction.
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Affiliation(s)
- Barbara Riegler
- Department of Medical Biochemistry, Medical University Vienna, Max F. Perutz Laboratories, A-1030 Vienna, Austria
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274
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Basantani MK, Sitnick MT, Cai L, Brenner DS, Gardner NP, Li JZ, Schoiswohl G, Yang K, Kumari M, Gross RW, Zechner R, Kershaw EE. Pnpla3/Adiponutrin deficiency in mice does not contribute to fatty liver disease or metabolic syndrome. J Lipid Res 2011; 52:318-29. [PMID: 21068004 PMCID: PMC3023552 DOI: 10.1194/jlr.m011205] [Citation(s) in RCA: 180] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Revised: 11/02/2010] [Indexed: 12/11/2022] Open
Abstract
PNPLA3 (adiponutrin, calcium-independent phospholipase A(2) epsilon [iPLA(2)ε]) is an adipose-enriched, nutritionally regulated protein that belongs to the patatin-like phospholipase domain containing (PNPLA) family of lipid metabolizing proteins. Genetic variations in the human PNPLA3 gene (i.e., the rs738409 I148M allele) has been strongly and repeatedly associated with fatty liver disease. Although human PNPLA3 has triacylglycerol (TAG) hydrolase and transacylase activities in vitro, its in vivo function and physiological relevance remain controversial. The objective of this study was to determine the metabolic consequences of global targeted deletion of the Pnpla3 gene in mice. We found that Pnpla3 mRNA expression is altered in adipose tissue and liver in response to acute and chronic nutritional challenges. However, global targeted deletion of the Pnpla3 gene in mice did not affect TAG hydrolysis, nor did it influence energy/glucose/lipid homoeostasis or hepatic steatosis/injury. Experimental interventions designed to increase Pnpla3 expression (refeeding, high-sucrose diet, diet-induced obesity, and liver X receptor agonism) likewise failed to reveal differences in the above-mentioned metabolic phenotypes. Expression of the Pnpla3 paralog, Pnpla5, was increased in adipose tissue but not in liver of Pnpla3-deficient mice, but compensatory regulation of genes involved in TAG metabolism was not identified. Together these data argue against a role for Pnpla3 loss-of-function in fatty liver disease or metabolic syndrome in mice.
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Affiliation(s)
- Mahesh K. Basantani
- Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Mitch T. Sitnick
- Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Lingzhi Cai
- Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh, Pittsburgh, PA
| | - Daniel S. Brenner
- Division of Endocrinology and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA
| | - Noah P. Gardner
- Division of Endocrinology and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA
| | - John Zhong Li
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX
| | | | - Kui Yang
- Division of Bioorganic Chemistry and Molecular Pharmacology, Department of Medicine, Washington University School of Medicine, St. Louis, MO
| | - Manju Kumari
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | - Richard W. Gross
- Division of Bioorganic Chemistry and Molecular Pharmacology, Department of Medicine, Washington University School of Medicine, St. Louis, MO
| | - Rudolf Zechner
- Institute of Molecular Biosciences, University of Graz, Graz, Austria
| | - Erin E. Kershaw
- Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh, Pittsburgh, PA
- Division of Endocrinology and Metabolism, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, MA
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275
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Hooper AJ, Adams LA, Burnett JR. Genetic determinants of hepatic steatosis in man. J Lipid Res 2011; 52:593-617. [PMID: 21245030 DOI: 10.1194/jlr.r008896] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Hepatic steatosis is one of the most common liver disorders in the general population. The main cause of hepatic steatosis is nonalcoholic fatty liver disease (NAFLD), representing the hepatic component of the metabolic syndrome, which is characterized by type 2 diabetes, obesity, and dyslipidemia. Insulin resistance and excess adiposity are considered to play key roles in the pathogenesis of NAFLD. Although the risk factors for NAFLD are well established, the genetic basis of hepatic steatosis is largely unknown. Here we review recent progress on genomic variants and their association with hepatic steatosis and discuss the potential impact of these genetic studies on clinical practice. Identifying the genetic determinants of hepatic steatosis will lead to a better understanding of the pathogenesis and progression of NAFLD.
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Affiliation(s)
- Amanda J Hooper
- Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital, Perth, Australia
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276
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Murakami M, Taketomi Y, Miki Y, Sato H, Hirabayashi T, Yamamoto K. Recent progress in phospholipase A₂ research: from cells to animals to humans. Prog Lipid Res 2010; 50:152-92. [PMID: 21185866 DOI: 10.1016/j.plipres.2010.12.001] [Citation(s) in RCA: 368] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mammalian genomes encode genes for more than 30 phospholipase A₂s (PLA₂s) or related enzymes, which are subdivided into several classes including low-molecular-weight secreted PLA₂s (sPLA₂s), Ca²+-dependent cytosolic PLA₂s (cPLA₂s), Ca²+-independent PLA₂s (iPLA₂s), platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA₂s, and a recently identified adipose-specific PLA. Of these, the intracellular cPLA₂ and iPLA₂ families and the extracellular sPLA₂ family are recognized as the "big three". From a general viewpoint, cPLA₂α (the prototypic cPLA₂ plays a major role in the initiation of arachidonic acid metabolism, the iPLA₂ family contributes to membrane homeostasis and energy metabolism, and the sPLA₂ family affects various biological events by modulating the extracellular phospholipid milieus. The cPLA₂ family evolved along with eicosanoid receptors when vertebrates first appeared, whereas the diverse branching of the iPLA₂ and sPLA₂ families during earlier eukaryote development suggests that they play fundamental roles in life-related processes. During the past decade, data concerning the unexplored roles of various PLA₂ enzymes in pathophysiology have emerged on the basis of studies using knockout and transgenic mice, the use of specific inhibitors, and information obtained from analysis of human diseases caused by mutations in PLA₂ genes. This review focuses on current understanding of the emerging biological functions of PLA₂s and related enzymes.
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Affiliation(s)
- Makoto Murakami
- Lipid Metabolism Project, The Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan.
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277
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Goran MI, Walker R, Le KA, Mahurkar S, Vikman S, Davis JN, Spruijt-Metz D, Weigensberg MJ, Allayee H. Effects of PNPLA3 on liver fat and metabolic profile in Hispanic children and adolescents. Diabetes 2010; 59:3127-30. [PMID: 20852027 PMCID: PMC2992774 DOI: 10.2337/db10-0554] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
OBJECTIVE A genome-wide study of adults identified a variant of PNPLA3 (rs738409) associated with ∼twofold higher liver fat. The purpose of this study was to examine the influence of PNPLA3 genotype on liver fat and other related metabolic outcomes in obese Hispanic children and adolescents. RESEARCH DESIGN AND METHODS Three hundred and twenty-seven Hispanics aged 8-18 years were genotyped for rs738409. One hundred and eighty-eight subjects had measures of visceral (VAT) and subcutaneous (SAT) adipose tissue volume and hepatic (HFF) and pancreatic (PFF) fat fraction by magnetic resonance imaging. One hundred and thirty-nine subjects did not have HFF measures but had extensive measures of insulin sensitivity and fasting lipids. RESULTS Liver fat in GG subjects was 1.7 and 2.4 times higher than GC and CC (11.1 ± 0.8% in GG vs. 6.6 ± 0.7% in GC and 4.7 ± 0.9% in CC; P < 0.0001), and this effect was observed even in the youngest children (8-10 years of age). The variant was not associated with VAT, SAT, PFF, or insulin sensitivity or other glucose/insulin indexes. However, Hispanic children carrying the GG genotype had significantly lower HDL cholesterol (40.9 ± 10.9 in CC vs. 37.0 ± 8.3 in CG vs. 35.7 ± 7.4 in GG; P = 0.03) and a tendency toward lower free fatty acid levels (P = 0.06). CONCLUSIONS These results provide new evidence that the effect of the PNPLA3 variant is apparent in Hispanic children and adolescents, is unique to fat deposition in liver as compared with other ectopic depots examined, and is associated with lower HDL cholesterol.
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Affiliation(s)
- Michael I Goran
- Department of Preventive Medicine, Childhood Obesity Research Center, University of Southern California, Los Angeles, California, USA.
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278
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Davis JN, Lê KA, Walker RW, Vikman S, Spruijt-Metz D, Weigensberg MJ, Allayee H, Goran MI. Increased hepatic fat in overweight Hispanic youth influenced by interaction between genetic variation in PNPLA3 and high dietary carbohydrate and sugar consumption. Am J Clin Nutr 2010; 92:1522-7. [PMID: 20962157 PMCID: PMC2980971 DOI: 10.3945/ajcn.2010.30185] [Citation(s) in RCA: 151] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Recently, a genetic variant (rs738409; C→G) of the PNPLA3 gene was identified to be associated with increased hepatic fat deposition, and the effect was more pronounced in Hispanics. Animal models have also shown that PNPLA3 expression can be regulated by dietary carbohydrate. OBJECTIVE The aim of this study was to examine whether the influence of PNPLA3 genotype on hepatic fat is modulated by dietary factors in Hispanic children. DESIGN PNPLA3 was genotyped in 153 Hispanic children (75% female, ages 8-18 y) by using the TaqMan method. Dietary intake was assessed by using three 24-h dietary recalls or diet records. Visceral adipose tissue (VAT), subcutaneous abdominal adipose tissue (SAAT), and hepatic fat fraction (HFF) were assessed in multiple abdominal slices by magnetic resonance imaging. Analysis of covariance was used to assess the diet × genotype interaction in liver fat, with the following a priori covariates: sex, age, energy, VAT, and SAAT. RESULTS HFF was influenced by a significant interaction between genotype and diet (genotype × carbohydrate, P = 0.04; genotype × total sugar, P = 0.01). HFF was positively related to carbohydrate (r = 0.31, P = 0.04) and total sugar (r = 0.34, P = 0.02) intakes but only in the GG group, independent of covariates. Dietary variables were not related to HFF in the CC or CG group or to other fat depots in all genotype groups. CONCLUSIONS These findings suggest that Hispanic children carrying the GG genotype are susceptible to increased hepatic fat when dietary carbohydrate intake, specifically sugar, is high. Specific dietary interventions based on genetic predisposition in this population may lead to more effective therapeutic outcomes for fatty liver. This trial was registered at clinicaltrials.gov as NCT00697580, 195-1642394A1, and NCT00693511.
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Affiliation(s)
- Jaimie N Davis
- Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA.
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279
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Lass A, Zimmermann R, Oberer M, Zechner R. Lipolysis - a highly regulated multi-enzyme complex mediates the catabolism of cellular fat stores. Prog Lipid Res 2010; 50:14-27. [PMID: 21087632 PMCID: PMC3031774 DOI: 10.1016/j.plipres.2010.10.004] [Citation(s) in RCA: 454] [Impact Index Per Article: 32.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Revised: 10/12/2010] [Accepted: 10/13/2010] [Indexed: 12/17/2022]
Abstract
Lipolysis is the biochemical pathway responsible for the catabolism of triacylglycerol (TAG) stored in cellular lipid droplets. The hydrolytic cleavage of TAG generates non-esterified fatty acids, which are subsequently used as energy substrates, essential precursors for lipid and membrane synthesis, or mediators in cell signaling processes. Consistent with its central importance in lipid and energy homeostasis, lipolysis occurs in essentially all tissues and cell types, it is most abundant, however, in white and brown adipose tissue. Over the last 5years, important enzymes and regulatory protein factors involved in lipolysis have been identified. These include an essential TAG hydrolase named adipose triglyceride lipase (ATGL) [annotated as patatin-like phospholipase domain-containing protein A2], the ATGL activator comparative gene identification-58 [annotated as α/β hydrolase containing protein 5], and the ATGL inhibitor G0/G1 switch gene 2. Together with the established hormone-sensitive lipase [annotated as lipase E] and monoglyceride lipase, these proteins constitute the basic "lipolytic machinery". Additionally, a large number of hormonal signaling pathways and lipid droplet-associated protein factors regulate substrate access and the activity of the "lipolysome". This review summarizes the current knowledge concerning the enzymes and regulatory processes governing lipolysis of fat stores in adipose and non-adipose tissues. Special emphasis will be given to ATGL, its regulation, and physiological function.
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Affiliation(s)
- Achim Lass
- Institute of Molecular Biosciences, University of Graz, 8010 Graz, Austria
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280
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Basantani MK, Sitnick MT, Cai L, Brenner DS, Gardner NP, Li JZ, Schoiswohl G, Yang K, Kumari M, Gross RW, Zechner R, Kershaw EE. Pnpla3/Adiponutrin deficiency in mice does not contribute to fatty liver disease or metabolic syndrome. J Lipid Res 2010. [PMID: 21068004 DOI: 10.1194/jlr.m01120] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
PNPLA3 (adiponutrin, calcium-independent phospholipase A(2) epsilon [iPLA(2)ε]) is an adipose-enriched, nutritionally regulated protein that belongs to the patatin-like phospholipase domain containing (PNPLA) family of lipid metabolizing proteins. Genetic variations in the human PNPLA3 gene (i.e., the rs738409 I148M allele) has been strongly and repeatedly associated with fatty liver disease. Although human PNPLA3 has triacylglycerol (TAG) hydrolase and transacylase activities in vitro, its in vivo function and physiological relevance remain controversial. The objective of this study was to determine the metabolic consequences of global targeted deletion of the Pnpla3 gene in mice. We found that Pnpla3 mRNA expression is altered in adipose tissue and liver in response to acute and chronic nutritional challenges. However, global targeted deletion of the Pnpla3 gene in mice did not affect TAG hydrolysis, nor did it influence energy/glucose/lipid homoeostasis or hepatic steatosis/injury. Experimental interventions designed to increase Pnpla3 expression (refeeding, high-sucrose diet, diet-induced obesity, and liver X receptor agonism) likewise failed to reveal differences in the above-mentioned metabolic phenotypes. Expression of the Pnpla3 paralog, Pnpla5, was increased in adipose tissue but not in liver of Pnpla3-deficient mice, but compensatory regulation of genes involved in TAG metabolism was not identified. Together these data argue against a role for Pnpla3 loss-of-function in fatty liver disease or metabolic syndrome in mice.
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Affiliation(s)
- Mahesh K Basantani
- Division of Endocrinology and Metabolism, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
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281
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Rae-Whitcombe SM, Kennedy D, Voyles M, Thompson MP. Regulation of the promoter region of the human adiponutrin/PNPLA3 gene by glucose and insulin. Biochem Biophys Res Commun 2010; 402:767-72. [PMID: 21036152 DOI: 10.1016/j.bbrc.2010.10.106] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Accepted: 10/22/2010] [Indexed: 12/29/2022]
Abstract
The adiponutrin/PNPLA3 gene is highly expressed in adipose tissue and liver. Its expression is down-regulated by fasting and rapidly induced by refeeding a high carbohydrate diet. We aimed to determine whether the promoter region of adiponutrin is regulated by glucose and insulin. Endogenous adiponutrin mRNA was increased in mouse 3T3-L1 and human SGBS adipocytes and in human HepG2 cells cultured in 25 mM glucose compared to absence of glucose. A 3100 bp 5'-upstream region of the human adiponutrin gene was cloned into a luciferase reporter plasmid and used in transient transfection studies. Promoter activity was up-regulated by 25 mM glucose, 4.7-fold in HepG2 cells and 2-fold in CHO cells. The effect was shown in CHO cells to be concentration dependent and to depend on glucose metabolism as a non-metabolisable analogue was without effect. In CHO cells constitutively expressing human insulin receptor (CHO-IR), there was a concentration dependent increase of promoter activity by insulin in the presence of glucose. Cotransfection with an expression plasmid for upstream stimulatory factor 2 (USF2), increased promoter activity 1.6-fold in CHO-IR cells. The combined effect of insulin and USF2 (2.3-fold) was greater than the individual effects. Cotransfection of carbohydrate-response element binding protein did not elicit any induction of promoter activity. These results point to potential mechanisms for the observed in vivo nutritional regulation of adiponutrin expression and its up-regulation in fatty liver and by obesity.
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282
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Valenti L, Alisi A, Galmozzi E, Bartuli A, Del Menico B, Alterio A, Dongiovanni P, Fargion S, Nobili V. I148M patatin-like phospholipase domain-containing 3 gene variant and severity of pediatric nonalcoholic fatty liver disease. Hepatology 2010; 52:1274-80. [PMID: 20648474 DOI: 10.1002/hep.23823] [Citation(s) in RCA: 218] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
UNLABELLED Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver disease in children. Genetic variability, which is a main player in NAFLD, is especially characterized by polymorphisms in genes involved in the development and progression of the disease to nonalcoholic steatohepatitis (NASH). Recently, the rs738409 C>G adiponutrin/patatin-like phospholipase domain-containing 3 (PNPLA3) polymorphism, which encodes the I148M protein variant in the catalytic domain, has been associated with severe steatosis, NASH, and liver fibrosis in adults. In this study, we investigated the association between the rs738409 PNPLA3 gene polymorphism and NAFLD in 149 consecutive children and adolescents (age = 6-13 years) with biopsy-proven NAFLD. We analyzed the rs738409 polymorphism by a 5'-nuclease TaqMan assay and assessed its association with NASH: 41% of the subjects with NAFLD showed heterozygosity and 15% showed homozygosity for the at-risk G allele. The rs738409 genotype did not influence the body mass, adiposity, lipid levels, or insulin resistance and was not associated with alanine aminotransferase levels. Interestingly, the rs738409 G allele was strongly associated with the severity of steatosis (P < 0.0001), the presence of NASH (P < 0.0001), hepatocellular ballooning (P < 0.0001), lobular inflammation (P < 0.0001), and the presence of fibrosis (P = 0.01) independently of confounders. Individuals carrying two minor G alleles almost always had severe steatosis and NASH, heterozygotes were at intermediate risk, and patients negative for G alleles had milder and often uncomplicated steatosis. CONCLUSION The PNPLA3 rs738409 polymorphism is associated with steatosis severity, hepatocellular ballooning, lobular inflammation, and perivenular fibrosis in pediatric NAFLD.
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Affiliation(s)
- Luca Valenti
- Department of Internal Medicine, Università degli Studi, Ospedale Maggiore Policlinico (Ca' Granda) Istituto di Ricovero e Cura a Carattere Scientifico, Milan, Italy
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283
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Rakhshandehroo M, Knoch B, Müller M, Kersten S. Peroxisome proliferator-activated receptor alpha target genes. PPAR Res 2010; 2010:612089. [PMID: 20936127 PMCID: PMC2948931 DOI: 10.1155/2010/612089] [Citation(s) in RCA: 532] [Impact Index Per Article: 38.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Accepted: 08/09/2010] [Indexed: 12/11/2022] Open
Abstract
The peroxisome proliferator-activated receptor alpha (PPARα) is a ligand-activated transcription factor involved in the regulation of a variety of processes, ranging from inflammation and immunity to nutrient metabolism and energy homeostasis. PPARα serves as a molecular target for hypolipidemic fibrates drugs which bind the receptor with high affinity. Furthermore, PPARα binds and is activated by numerous fatty acids and fatty acid-derived compounds. PPARα governs biological processes by altering the expression of a large number of target genes. Accordingly, the specific role of PPARα is directly related to the biological function of its target genes. Here, we present an overview of the involvement of PPARα in lipid metabolism and other pathways through a detailed analysis of the different known or putative PPARα target genes. The emphasis is on gene regulation by PPARα in liver although many of the results likely apply to other organs and tissues as well.
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Affiliation(s)
- Maryam Rakhshandehroo
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
| | - Bianca Knoch
- Food, Metabolism & Microbiology, Food & Textiles Group, AgResearch, Palmerston North 4442, New Zealand
- Institute of Food, Nutrition & Human Health, Massey University, Tennent Drive, Palmerston North 4442, New Zealand
| | - Michael Müller
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
| | - Sander Kersten
- Nutrition, Metabolism and Genomics Group, Division of Human Nutrition, Wageningen University, Bomenweg 2, 6703 HD Wageningen, The Netherlands
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284
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Chen W, Chang B, Li L, Chan L. Patatin-like phospholipase domain-containing 3/adiponutrin deficiency in mice is not associated with fatty liver disease. Hepatology 2010; 52:1134-42. [PMID: 20648554 PMCID: PMC2932863 DOI: 10.1002/hep.23812] [Citation(s) in RCA: 187] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
UNLABELLED PNPLA3 (adiponutrin), a novel patatin-like phospholipase domain-containing enzyme, is expressed at high level in fat, but also in other tissues including liver. Polymorphisms in PNPLA3 have been linked to obesity and insulin sensitivity. Notably, a nonsynonymous variant rs738409(G) allele of the PNPLA3 gene was found to be strongly associated with both nonalcoholic and alcoholic fatty liver disease. We have generated Pnpla3(-/-) mice by gene targeting. Loss of Pnpla3 has no effect on body weight or composition, adipose mass, or development, whether the mice were fed regular chow or high-fat diet or bred into the genetic obese Lep(ob/ob) background. Plasma and liver triglyceride content and plasma aspartate aminotransferase and alanine aminotransferase levels were not different between Pnpla3(+/+) and Pnpla3(-/-) mice while they were on regular chow, fed three different fatty liver-inducing diets, or after they were bred into Lep(ob/ob) background. Hepatic Pnpla5 messenger RNA (mRNA) levels were similar in wild-type and Pnpla3(-/-) mice, although adipose Pnpla5 mRNA level was increased in Pnpla3(-/-) mice. A high-sucrose lipogenic diet stimulated hepatic Pnpla3 and Pnpla5 mRNA levels to a similar degree, but it did not affect adipose or liver triglyceride lipase (ATGL, known also as Pnpla2) mRNA in Pnpla3(+/+) and Pnpla3(-/-) mice. Finally, Pnpla3(+/+) and Pnpla3(-/-) mice displayed similar glucose tolerance and insulin tolerance tests while on regular chow or three different fatty liver-inducing diets. CONCLUSION Loss of Pnpla3 does not cause fatty liver, liver enzyme elevation, or insulin resistance in mice.
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Affiliation(s)
- Weiqin Chen
- Diabetes and Endocrinology Research Center (DERC), Section of Diabetes and Endocrinology, Departments of Medicine, Molecular & Cellular Biology and Biochemistry & Molecular Biology, Baylor College of Medicine, Houston, Texas, USA
| | - Benny Chang
- Diabetes and Endocrinology Research Center (DERC), Section of Diabetes and Endocrinology, Departments of Medicine, Molecular & Cellular Biology and Biochemistry & Molecular Biology, Baylor College of Medicine, Houston, Texas, USA
| | - Lan Li
- Diabetes and Endocrinology Research Center (DERC), Section of Diabetes and Endocrinology, Departments of Medicine, Molecular & Cellular Biology and Biochemistry & Molecular Biology, Baylor College of Medicine, Houston, Texas, USA
| | - Lawrence Chan
- Diabetes and Endocrinology Research Center (DERC), Section of Diabetes and Endocrinology, Departments of Medicine, Molecular & Cellular Biology and Biochemistry & Molecular Biology, Baylor College of Medicine, Houston, Texas, USA, St. Luke’s Episcopal Hospital, Houston, Texas, USA,Contact Information: Lawrence Chan, Diabetes and Endocrinology Research Center R614, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA. Tel: 713-798-4478, Fax: 713-798-8764,
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285
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Koutsari C, Lazaridis KN. Emerging genes associated with the progression of nonalcoholic fatty liver disease. Hepatology 2010; 52:807-10. [PMID: 20812353 DOI: 10.1002/hep.23869] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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