title: Differential pre-mRNA splicing regulates Nnat isoforms in the hypothalamus after gastric bypass surgery in mice.
abstract: BACKGROUND
  Neuronatin (NNAT) is an endoplasmic reticulum proteolipid implicated in intracellular signalling. Nnat is highly-expressed in the hypothalamus, where it is acutely regulated by nutrients and leptin. Nnat pre-mRNA is differentially spliced to create Nnat-α and -β isoforms. Genetic variation of NNAT is associated with severe obesity. Currently, little is known about the long-term regulation of Nnat.
  
  
  METHODS
  Expression of Nnat isoforms were examined in the hypothalamus of mice in response to acute fast/feed, chronic caloric restriction, diet-induced obesity and modified gastric bypass surgery. Nnat expression was assessed in the central nervous system and gastrointestinal tissues. RTqPCR was used to determine isoform-specific expression of Nnat mRNA.
  
  
  RESULTS
  Hypothalamic expression of both Nnat isoforms was comparably decreased by overnight and 24-h fasting. Nnat expression was unaltered in diet-induced obesity, or subsequent switch to a calorie restricted diet. Nnat isoforms showed differential expression in the hypothalamus but not brainstem after bypass surgery. Hypothalamic Nnat-β expression was significantly reduced after bypass compared with sham surgery (P = 0.003), and was positively correlated with post-operative weight-loss (R(2) = 0.38, P = 0.01). In contrast, Nnat-α expression was not suppressed after bypass surgery (P = 0.19), and expression did not correlate with reduction in weight after surgery (R(2) = 0.06, P = 0.34). Hypothalamic expression of Nnat-β correlated weakly with circulating leptin, but neither isoform correlated with fasting gut hormone levels post- surgery. Nnat expression was detected in brainstem, brown-adipose tissue, stomach and small intestine.
  
  
  CONCLUSIONS
  Nnat expression in hypothalamus is regulated by short-term nutrient availability, but unaltered by diet-induced obesity or calorie restriction. While Nnat isoforms in the hypothalamus are co-ordinately regulated by acute nutrient supply, after modified gastric bypass surgery Nnat isoforms show differential expression. These results raise the possibility that in the radically altered nutrient and hormonal milieu created by bypass surgery, resultant differential splicing of Nnat pre-mRNA may contribute to weight-loss.
authors.affiliation: Centre for Obesity Research, Rayne Institute, Department of Medicine, University College London, London, United Kingdom.
authors.forename: William R
authors.initials: WR
authors.lastname: Scott
authors.forename: Cigdem
authors.initials: C
authors.lastname: Gelegen
authors.forename: Keval
authors.initials: K
authors.lastname: Chandarana
authors.forename: Efthimia
authors.initials: E
authors.lastname: Karra
authors.forename: Ahmed
authors.initials: A
authors.lastname: Yousseif
authors.forename: Chloé
authors.initials: C
authors.lastname: Amouyal
authors.forename: Agharul I
authors.initials: AI
authors.lastname: Choudhury
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Andreelli
authors.forename: Dominic J
authors.initials: DJ
authors.lastname: Withers
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Batterham
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D031204:Caloric Restriction; D015390:Gastric Bypass; D041981:Gastrointestinal Tract / Q000378:metabolism; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000502:physiology*; D007031:Hypothalamus / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009765:Obesity / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D012326:RNA Splicing / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C490239:Nnat protein, mouse; D020033:Protein Isoforms