title: Equine insulin receptor and insulin-like growth factor-1 receptor expression in digital lamellar tissue and insulin target tissues.
abstract: BACKGROUND
  Hyperinsulinaemia is implicated in the pathogenesis of endocrinopathic laminitis. Insulin can bind to different receptors: two insulin receptor isoforms (InsR-A and InsR-B), insulin-like growth factor-1 receptor (IGF-1R) and InsR/IGF-1R hybrid receptor (Hybrid). Currently, mRNA expression of these receptors in equine tissues and the influence of body type and dietary carbohydrate intake on expression of these receptors is not known.
  
  
  OBJECTIVE
  The study objectives were to characterise InsR-A, InsR-B, IGF-1R and Hybrid expression in lamellar tissue (LT) and insulin responsive tissues from horses and examine the effect of dietary nonstructural carbohydrate (NSC) on mRNA expression of these receptors in LT, skeletal muscle, liver and two adipose tissue (AT) depots of lean and obese ponies.
  
  
  METHODS
  In vivo experiment.
  
  
  METHODS
  Lamellar tissue samples were evaluated by quantitative reverse transcription polymerase chain reaction (RT-qPCR) for receptor mRNA expression (n = 8) and immunoblotting for protein expression (n = 3). Archived LT, skeletal muscle, liver and AT from lean and obese mixed-breed ponies fed either a low (~7% NSC as dry matter; 5 lean, 5 obese) or high NSC diet (~42% NSC as dry matter; 6 lean, 6 obese) for 7 days were evaluated by RT-qPCR to determine the effect of body condition and diet on expression of the receptors in different tissues. Significance was set at P≤0.05.
  
  
  RESULTS
  Lamellar tissue expresses both InsR isoforms, IGF-1R and Hybrid. LT IGF-1R gene expression was greater than either InsR isoform and InsR-A expression was greater than InsR-B (P≤0.05). Obesity significantly lowered IGF-1R, InsR-A and InsR-B mRNA expression in LT and InsR-A in tailhead AT. High NSC diet lowered expression of all three receptor types in liver; IGF-1R and InsR-A in LT and InsR-A in tailhead AT.
  
  
  CONCLUSIONS
  Lamellar tissue expresses IGF-1R, InsR isoforms and Hybrids. The functional characteristics of these receptors and their role in endocrinopathic laminitis warrants further investigation.
authors.affiliation: Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, USA.
authors.forename: A
authors.initials: A
authors.lastname: Kullmann
authors.affiliation: Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Weber
authors.affiliation: Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Bishop
authors.affiliation: Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: Roux
authors.affiliation: Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, USA.
authors.forename: B
authors.initials: B
authors.lastname: Norby
authors.affiliation: Department of Veterinary Clinical Sciences, The Ohio State University, Columbus, USA.
authors.forename: T A
authors.initials: TA
authors.lastname: Burns
authors.affiliation: Department of Pathobiology and Diagnostic Investigation, Michigan State University, East Lansing, USA.
authors.forename: L J
authors.initials: LJ
authors.lastname: McCutcheon
authors.affiliation: Department of Veterinary Clinical Sciences, The Ohio State University, Columbus, USA.
authors.forename: J K
authors.initials: JK
authors.lastname: Belknap
authors.affiliation: Department of Large Animal Clinical Sciences, Michigan State University, East Lansing, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Geor
mesh_terms: D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D004032:Diet / Q000662:veterinary; D004040:Dietary Carbohydrates / Q000009:adverse effects; D005534:Foot Diseases / Q000662:veterinary; D005786:Gene Expression Regulation / Q000502:physiology; D006734:Horse Diseases / Q000378:metabolism*; D006736:Horses; D007328:Insulin / Q000378:metabolism*; D009765:Obesity / Q000139:chemically induced / Q000378:metabolism / Q000662:veterinary*; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*
chemical_list: D004040:Dietary Carbohydrates; D007328:Insulin; D020033:Protein Isoforms; D012333:RNA, Messenger; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin
keywords: horse; hybrid receptors; hyperinsulinaemia; laminitis