title: ENU mutagenesis identifies mice with morbid obesity and severe hyperinsulinemia caused by a novel mutation in leptin.
abstract: BACKGROUND
  Obesity is a multifactorial disease that arises from complex interactions between genetic predisposition and environmental factors. Leptin is central to the regulation of energy metabolism and control of body weight in mammals.
  
  
  RESULTS
  To better recapitulate the complexity of human obesity syndrome, we applied N-ethyl-N-nitrosourea (ENU) mutagenesis in combination with a set of metabolic assays in screening mice for obesity. Mapping revealed linkage to the chromosome 6 within a region containing mouse Leptin gene. Sequencing on the candidate genes identified a novel T-to-A mutation in the third exon of Leptin gene, which translates to a V145E amino acid exchange in the leptin propeptide. Homozygous Leptin(145E/145E) mutant mice exhibited morbid obesity, accompanied by adipose hypertrophy, energy imbalance, and liver steatosis. This was further associated with severe insulin resistance, hyperinsulinemia, dyslipidemia, and hyperleptinemia, characteristics of human obesity syndrome. Hypothalamic leptin actions in inhibition of orexigenic peptides NPY and AgRP and induction of SOCS1 and SOCS3 were attenuated in Leptin(145E/145E) mice. Administration of exogenous wild-type leptin attenuated hyperphagia and body weight increase in Leptin(145E/145E) mice. However, mutant V145E leptin coimmunoprecipitated with leptin receptor, suggesting that the V145E mutation does not affect the binding of leptin to its receptor. Molecular modeling predicted that the mutated residue would form hydrogen bond with the adjacent residues, potentially affecting the structure and formation of an active complex with leptin receptor within that region.
  
  
  CONCLUSIONS
  Thus, our evolutionary, structural, and in vivo metabolic information suggests the residue 145 as of special function significance. The mouse model harboring leptin V145E mutation will provide new information on the current understanding of leptin biology and novel mouse model for the study of human obesity syndrome.
authors.affiliation: Institute of Brain Science, School of Medicine, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Chen-Jee
authors.initials: CJ
authors.lastname: Hong
authors.forename: Pei-Jane
authors.initials: PJ
authors.lastname: Tsai
authors.forename: Chih-Ya
authors.initials: CY
authors.lastname: Cheng
authors.forename: Chuan-Kai
authors.initials: CK
authors.lastname: Chou
authors.forename: Huei-Fen
authors.initials: HF
authors.lastname: Jheng
authors.forename: You-Chung
authors.initials: YC
authors.lastname: Chuang
authors.forename: Chia-Ning
authors.initials: CN
authors.lastname: Yang
authors.forename: Ya-Tzu
authors.initials: YT
authors.lastname: Lin
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Hsu
authors.forename: Irene H
authors.initials: IH
authors.lastname: Cheng
authors.forename: Shiow-Yi
authors.initials: SY
authors.lastname: Chen
authors.forename: Shih-Jen
authors.initials: SJ
authors.lastname: Tsai
authors.forename: Ying-Jay
authors.initials: YJ
authors.lastname: Liou
authors.forename: Yau-Sheng
authors.initials: YS
authors.lastname: Tsai
mesh_terms: D000818:Animals; D001835:Body Weight; D005038:Ethylnitrosourea; D019143:Evolution, Molecular; D005091:Exons; D020022:Genetic Predisposition to Disease; D006720:Homozygote; D006801:Humans; D006946:Hyperinsulinism / Q000235:genetics*; D020738:Leptin / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D016296:Mutagenesis; D009154:Mutation; D009767:Obesity, Morbid / Q000235:genetics*; D054411:Receptors, Leptin / Q000235:genetics
chemical_list: D020738:Leptin; D054411:Receptors, Leptin; D005038:Ethylnitrosourea