title: Patatin-like phospholipase domain-containing 3 (PNPLA3) I148M (rs738409) affects hepatic VLDL secretion in humans and in vitro.
abstract: OBJECTIVE
  The robust association between non-alcoholic fatty liver disease (NAFLD) and the genetic variant I148M (rs738409) in PNPLA3 has been widely replicated. The aim of this study was to investigate the effect of the PNPLA3 I148M mutation on: (1) hepatic secretion of very low density lipoproteins (VLDL) in humans; and (2) secretion of apolipoprotein B (apoB) from McA-RH 7777 cells, which secrete VLDL-sized apoB-containing lipoproteins.
  
  
  METHODS
  VLDL kinetics was analyzed after a bolus infusion of stable isotopes in 55 overweight/obese men genotyped for the PNPLA3 I148M variant. Intracellular lipid content, apoB secretion and glycerolipid metabolism were studied in McA-RH 7777 cells overexpressing the human 148I wild type or 148M mutant PNPLA3 protein.
  
  
  RESULTS
  In humans, carriers of the PNPLA3 148M allele had increased liver fat compared to 148I homozygotes, and kinetic analysis showed a relatively lower secretion of the large, triglyceride-rich VLDL (VLDL(1)) in 148M carriers vs. 148I homozygotes for the same amount of liver fat. McA-RH 7777 cells overexpressing the 148M mutant protein showed a higher intracellular triglyceride content with a lower apoB secretion and fatty acid efflux, compared to cells overexpressing the 148I wild type protein. The responses with 148M matched those observed in cells expressing the empty vector, indicating that the mutation results in loss of function.
  
  
  CONCLUSIONS
  We have shown that PNPLA3 affects the secretion of apoB-containing lipoproteins both in humans and in vitro and that the 148M protein is a loss-of-function mutation. We propose that PNPLA3 148M promotes intracellular lipid accumulation in the liver by reducing the lipidation of VLDL.
authors.affiliation: Sahlgrenska Center for Cardiovascular and Metabolic Research/Wallenberg Laboratory, Department of Molecular and Clinical Medicine, University of Gothenburg, Sweden.
authors.forename: Carlo
authors.initials: C
authors.lastname: Pirazzi
authors.forename: Martin
authors.initials: M
authors.lastname: Adiels
authors.forename: Maria Antonella
authors.initials: MA
authors.lastname: Burza
authors.forename: Rosellina Margherita
authors.initials: RM
authors.lastname: Mancina
authors.forename: Malin
authors.initials: M
authors.lastname: Levin
authors.forename: Marcus
authors.initials: M
authors.lastname: Ståhlman
authors.forename: Marja-Riitta
authors.initials: MR
authors.lastname: Taskinen
authors.forename: Marju
authors.initials: M
authors.lastname: Orho-Melander
authors.forename: Jeanna
authors.initials: J
authors.lastname: Perman
authors.forename: Arturo
authors.initials: A
authors.lastname: Pujia
authors.forename: Linda
authors.initials: L
authors.lastname: Andersson
authors.forename: Cristina
authors.initials: C
authors.lastname: Maglio
authors.forename: Tiziana
authors.initials: T
authors.lastname: Montalcini
authors.forename: Olov
authors.initials: O
authors.lastname: Wiklund
authors.forename: Jan
authors.initials: J
authors.lastname: Borén
authors.forename: Stefano
authors.initials: S
authors.lastname: Romeo
mesh_terms: D000328:Adult; D000818:Animals; D001055:Apolipoproteins B / Q000378:metabolism; D002478:Cells, Cultured; D005838:Genotype; D006801:Humans; D008049:Lipase / Q000235:genetics* / Q000502:physiology; D050356:Lipid Metabolism; D008079:Lipoproteins, VLDL / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics* / Q000502:physiology; D008875:Middle Aged; D051381:Rats; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent
chemical_list: D001055:Apolipoproteins B; D008049:Lipase; D008079:Lipoproteins, VLDL; D008565:Membrane Proteins; C533682:PNPLA3 protein, human; D000217:Acyltransferases; D054512:Phospholipases A2, Calcium-Independent