title: Muscle-derived angiopoietin-like protein 4 is induced by fatty acids via peroxisome proliferator-activated receptor (PPAR)-delta and is of metabolic relevance in humans.
abstract: OBJECTIVE
  Long-chain fatty acids (LCFAs) contribute to metabolic homeostasis in part via gene regulation. This study's objective was to identify novel LCFA target genes in human skeletal muscle cells (myotubes).
  
  
  METHODS
  In vitro methods included culture and treatment of human myotubes and C2C12 cells, gene array analysis, real-time RT-PCR, Western blotting, ELISA, chromatin immunoprecipitation, and RNA interference. Human subjects (two cohorts) were characterized by oral glucose tolerance test, hyperinsulinemic-euglycemic clamp, magnetic resonance imaging and spectroscopy, and standard blood analyses (glucose, insulin, C-peptide, and plasma lipids).
  
  
  RESULTS
  We show here that ANGPTL4 (encoding angiopoietin-like protein 4) represents a prominent LCFA-responsive gene in human myotubes. LCFA activated peroxisome proliferator-activated receptor (PPAR)-delta, but not PPAR-alpha or -gamma, and pharmacological activation of PPAR-delta markedly induced ANGPTL4 production and secretion. In C2C12 myocytes, knockdown of PPARD, but not of PPARG, blocked LCFA-mediated ANGPTL4 induction, and LCFA treatment resulted in PPAR-delta recruitment to the ANGPTL4 gene. In addition, pharmacological PPAR-delta activation induced LIPE (encoding hormone-sensitive lipase), and this response crucially depended on ANGPTL4, as revealed by ANGPTL4 knockdown. In a human cohort of 108 thoroughly phenotyped subjects, plasma ANGPTL4 positively correlated with fasting nonesterified fatty acids (P = 0.0036) and adipose tissue lipolysis (P = 0.0012). Moreover, in 38 myotube donors, plasma ANGPTL4 levels and adipose tissue lipolysis in vivo were reflected by basal myotube ANGPTL4 expression in vitro (P = 0.02, both).
  
  
  CONCLUSIONS
  ANGPTL4 is produced by human myotubes in response to LCFA via PPAR-delta, and muscle-derived ANGPTL4 seems to be of systemic relevance in humans.
authors.affiliation: Department of Internal Medicine, Division of Endocrinology, Diabetology, Angiology, Nephrology, and Clinical Chemistry, Eberhard-Karls-University Tübingen, Tübingen, Germany. harald.staiger@med.uni-tuebingen.de
authors.forename: Harald
authors.initials: H
authors.lastname: Staiger
authors.forename: Carina
authors.initials: C
authors.lastname: Haas
authors.forename: Jürgen
authors.initials: J
authors.lastname: Machann
authors.forename: Roman
authors.initials: R
authors.lastname: Werner
authors.forename: Melanie
authors.initials: M
authors.lastname: Weisser
authors.forename: Fritz
authors.initials: F
authors.lastname: Schick
authors.forename: Fausto
authors.initials: F
authors.lastname: Machicao
authors.forename: Norbert
authors.initials: N
authors.lastname: Stefan
authors.forename: Andreas
authors.initials: A
authors.lastname: Fritsche
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Häring
mesh_terms: D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins / Q000235:genetics*; D001786:Blood Glucose / Q000378:metabolism; D002096:C-Peptide / Q000097:blood; D005786:Gene Expression Regulation / Q000187:drug effects; D015309:Glucose Clamp Technique; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood; D019787:Linoleic Acid / Q000494:pharmacology; D008055:Lipids / Q000097:blood; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000201:enzymology / Q000502:physiology*; D020411:Oligonucleotide Array Sequence Analysis; D047493:PPAR alpha / Q000502:physiology; D047494:PPAR delta / Q000235:genetics / Q000502:physiology*; D019308:Palmitic Acid / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics
chemical_list: C474772:ANGPTL4 protein, human; D000075803:Angiopoietin-Like Protein 4; D042682:Angiopoietins; D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D008055:Lipids; D047493:PPAR alpha; D047494:PPAR delta; D012333:RNA, Messenger; D019308:Palmitic Acid; D019787:Linoleic Acid