title: PNPLA3 has retinyl-palmitate lipase activity in human hepatic stellate cells.
abstract: 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.
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Carlo
authors.initials: C
authors.lastname: Pirazzi
authors.affiliation: Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Valenti
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy.
authors.forename: Benedetta Maria
authors.initials: BM
authors.lastname: Motta
authors.affiliation: Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden Department BEST (Biologia, Ecologia, Scienze Della Terra), Unit of Biochemistry and Molecular Biotechnology, University of Calabria, Arcavacata di Rende, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Pingitore
authors.affiliation: Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Hedfalk
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and Department of Medical and Surgical Sciences, Clinical Nutrition Unit, University Magna Graecia of Catanzaro, Catanzaro, Italy.
authors.forename: Rosellina Margherita
authors.initials: RM
authors.lastname: Mancina
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Maria Antonella
authors.initials: MA
authors.lastname: Burza
authors.affiliation: Department BEST (Biologia, Ecologia, Scienze Della Terra), Unit of Biochemistry and Molecular Biotechnology, University of Calabria, Arcavacata di Rende, Italy.
authors.forename: Cesare
authors.initials: C
authors.lastname: Indiveri
authors.affiliation: Department of Medical and Surgical Sciences, Clinical Nutrition Unit, University Magna Graecia of Catanzaro, Catanzaro, Italy.
authors.forename: Yvelise
authors.initials: Y
authors.lastname: Ferro
authors.affiliation: Department of Medical and Surgical Sciences, Clinical Nutrition Unit, University Magna Graecia of Catanzaro, Catanzaro, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Montalcini
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Cristina
authors.initials: C
authors.lastname: Maglio
authors.affiliation: Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Dongiovanni
authors.affiliation: Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Fargion
authors.affiliation: Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy.
authors.forename: Raffaela
authors.initials: R
authors.lastname: Rametta
authors.affiliation: Department of Medical and Surgical Sciences, Clinical Nutrition Unit, University Magna Graecia of Catanzaro, Catanzaro, Italy.
authors.forename: Arturo
authors.initials: A
authors.lastname: Pujia
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Linda
authors.initials: L
authors.lastname: Andersson
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Saswati
authors.initials: S
authors.lastname: Ghosal
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Malin
authors.initials: M
authors.lastname: Levin
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Olov
authors.initials: O
authors.lastname: Wiklund
authors.affiliation: Department of Pediatrics, LA Biomedical Research Institute at Harbor-UCLA, 1124 W. Carson Street, HH1, Torrance, CA 90502, USA.
authors.forename: Michelina
authors.initials: M
authors.lastname: Iacovino
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and.
authors.forename: Jan
authors.initials: J
authors.lastname: Borén
authors.affiliation: Department of Molecular and Clinical Medicine, Institute of Medicine, Sahlgrenska Center for Cardiovascular and Metabolic Research, Wallenberg Laboratory and Department of Medical and Surgical Sciences, Clinical Nutrition Unit, University Magna Graecia of Catanzaro, Catanzaro, Italy stefano.romeo@wlab.gu.se.
authors.forename: Stefano
authors.initials: S
authors.lastname: Romeo
mesh_terms: D000328:Adult; D004224:Diterpenes; D005260:Female; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D055166:Hepatic Stellate Cells / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology; D008049:Lipase / Q000235:genetics* / Q000378:metabolism; D066292:Lipid Droplets / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008875:Middle Aged; D009154:Mutation; D065626:Non-alcoholic Fatty Liver Disease / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D019308:Palmitic Acid / Q000378:metabolism; D061251:Primary Cell Culture; D054839:Retinol-Binding Proteins, Plasma / Q000235:genetics / Q000378:metabolism; D000084562:Retinyl Esters; D014801:Vitamin A / Q000031:analogs & derivatives* / Q000378:metabolism; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent
chemical_list: D004224:Diterpenes; D007328:Insulin; D008049:Lipase; D008565:Membrane Proteins; D019308:Palmitic Acid; D054839:Retinol-Binding Proteins, Plasma; D000084562:Retinyl Esters; D014801:Vitamin A; C101326:RBP4 protein, human; C014794:retinol palmitate; C533682:PNPLA3 protein, human; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent