title: Functional relevance of genes implicated by obesity genome-wide association study signals for human adipocyte biology.
abstract: OBJECTIVE
  Genome-wide association studies (GWAS) have identified numerous single-nucleotide polymorphisms associated with obesity, consequently implying a role in adipocyte biology for many closely residing genes. We investigated the functional relevance of such genes in human adipocytes.
  
  
  METHODS
  We selected eight genes (BDNF, MAF, MTCH2, NEGR1, NPC1, PTER, SH2B1 and TMEM18) from obesity GWAS and analysed their effect in human adipogenesis using small interfering (si)RNA-mediated knockdown, their regulation by metabolic agents in adipocytes and pre-adipocytes, and gene expression in paired samples of human fat biopsies (68 non-obese, 165 obese) by quantitative real-time PCR.
  
  
  RESULTS
  We show a two- to threefold upregulation of MAF, MTCH2 and NEGR1 and a two- to fourfold downregulation of BDNF and PTER during adipogenesis. Knockdown of BDNF (mean ± SEM; 83.8 ± 4.7% of control; p = 0.0002), MTCH2 (72.7 ± 9.5%; p = 0.0006), NEGR1 (70.2 ± 5.7%; p < 0.0001) and TMEM18 (70.8 ± 6.1%; p < 0.0001) significantly inhibited adipocyte maturation, while knockdown of the other proteins had no effect. Insulin slightly induced MAF (1.65-fold; p = 0.0009) and MTCH2 (1.72-fold; p < 0.0001), while it suppressed BDNF (59.6%; p = 0.0009), NEGR1 (58.0%; p = 0.0085) and TMEM18 (69.3%; p = 0.0377) in adipocytes. The synthetic glucocorticoid dexamethasone suppressed MAF (45.7%; p = 0.0022), BDNF (66.6%; p = 0.0012) and TMEM18 (63.5%; p = 0.0181), but induced NEGR1 (3.2-fold; p = 0.0117) expression. Furthermore, MTCH2, NEGR1 and TMEM18 were differentially expressed in subcutaneous and visceral adipose tissue. TMEM18 expression was decreased in the adipose tissue of obese patients, and negatively correlated with anthropometric variables and adipocyte size.
  
  
  CONCLUSIONS
  Our results imply a regulatory role for TMEM18, BDNF, MTCH2 and NEGR1 in adipocyte differentiation and biology. In addition, we show a variation of MAF expression during adipogenesis, while NPC1, PTER and SH2B1 were not regulated.
authors.affiliation: Center for Pediatric Research, Hospital for Children & Adolescents, Department of Women's and Child Health, University of Leipzig, Liebigstraße 21, Leipzig, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Bernhard
authors.forename: K
authors.initials: K
authors.lastname: Landgraf
authors.forename: N
authors.initials: N
authors.lastname: Klöting
authors.forename: A
authors.initials: A
authors.lastname: Berthold
authors.forename: P
authors.initials: P
authors.lastname: Büttner
authors.forename: D
authors.initials: D
authors.lastname: Friebe
authors.forename: W
authors.initials: W
authors.lastname: Kiess
authors.forename: P
authors.initials: P
authors.lastname: Kovacs
authors.forename: M
authors.initials: M
authors.lastname: Blüher
authors.forename: A
authors.initials: A
authors.lastname: Körner
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics; D017667:Adipocytes / Q000378:metabolism*; D000273:Adipose Tissue / Q000378:metabolism; D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics; D005260:Female; D058851:GPI-Linked Proteins / Q000235:genetics; D055106:Genome-Wide Association Study / Q000379:methods*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D033681:Mitochondrial Membrane Transport Proteins / Q000235:genetics; D000077296:Niemann-Pick C1 Protein; D009765:Obesity / Q000235:genetics*; D051257:Proto-Oncogene Proteins c-maf / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D019208:Brain-Derived Neurotrophic Factor; D002352:Carrier Proteins; D015816:Cell Adhesion Molecules, Neuronal; D058851:GPI-Linked Proteins; D047908:Intracellular Signaling Peptides and Proteins; C495607:MAF protein, human; C502207:MTCH2 protein, human; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D033681:Mitochondrial Membrane Transport Proteins; C485559:NEGR1 protein, human; C106881:NPC1 protein, human; D000077296:Niemann-Pick C1 Protein; C484578:PTER protein, human; D051257:Proto-Oncogene Proteins c-maf; C518910:SH2B1 protein, human; C530715:TMEM18 protein, human