H E Lane1, T A Burns1, O C Hegedus1, M R Watts1, P S Weber2, K A Woltman2, R J Geor2, L J McCutcheon2, S C Eades3, L E Mathes1,4, J K Belknap1. 1. Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University, Columbus, Ohio, USA. 2. Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA. 3. Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA. 4. Department of Veterinary Biosciences, College of Veterinary Medicine, Ohio State University, Columbus, Ohio, USA.
Abstract
BACKGROUND: Insulin dysregulation, obesity, and exposure to high-nonstructural carbohydrate (NSC) forage are risk factors for equine metabolic syndrome-associated laminitis (EMSAL); high systemic insulin concentrations in EMSAL are proposed to induce cellular dysregulation in the digital lamellae through activation of the insulin-like growth factor-1 receptor. OBJECTIVES: To use a dietary challenge model (DCM) and a euglycaemic-hyperinsulinaemic clamp (EHC) model to assess lamellar growth factor-related signalling. STUDY DESIGN: Lamellar phospho (P)-protein concentrations of signalling proteins important in growth factor-related signalling were assessed in 2 models: 1) lean and obese ponies on a low- or high-NSC diet; and 2) EHC model using Standardbred horses. METHODS: Ponies stratified for body condition (lean [LN, n = 11] and obese [OB, n = 11]) were exposed to a low-NSC diet (LO, n = 5 per group for LN LO and OB LO) or a high NSC diet (HI, n = 6 per group for LN HI and OB HI groups) for 7 days. For the EHC model, horses were administered insulin (constant rate infusion [6 mIU/kg bwt/min] combined with 50% dextrose, EHC group, n = 8)] or saline (0.57 mL/kg bwt/h, CON group, n = 8) for 48 h. Immunoblotting was employed to assess concentrations of activated/phosphorylated and total protein for members of the PI3K/Akt/mTORC1 and Ras/ERK pathways in lamellar samples from both models. RESULTS: In the DCM, lamellar P-(Ser 240/244) RPS6 was increased in OB HI ponies (vs. OB LO, P<0.05); positive correlations existed (P<0.05; r>0.5) between Day 7 basal serum insulin concentrations and lamellar concentrations of P-p70S6K and P-(Ser 240/244) RPS6. In the EHC model, lamellar concentrations of P-Akt, P-p70S6K, P-ERK 1/2, P-p90RSK, and both P-(Ser 235/236) and P-(Ser 240/244) RPS6 were increased in the EHC group (vs. CON, P<0.05). MAIN LIMITATIONS: The primary limitations of this study are the small number of animals per group in the DCM study, and the fact that many animals did not develop laminitis as that was not the endpoint of either study. CONCLUSIONS: These results support further investigation of mTORC1/RPS6 signalling as a potential therapeutic target(s) in EMSAL. The Summary is available in Chinese - see Supporting Information.
BACKGROUND: Insulin dysregulation, obesity, and exposure to high-nonstructural carbohydrate (NSC) forage are risk factors for equine metabolic syndrome-associated laminitis (EMSAL); high systemic insulin concentrations in EMSAL are proposed to induce cellular dysregulation in the digital lamellae through activation of the insulin-like growth factor-1 receptor. OBJECTIVES: To use a dietary challenge model (DCM) and a euglycaemic-hyperinsulinaemic clamp (EHC) model to assess lamellar growth factor-related signalling. STUDY DESIGN: Lamellar phospho (P)-protein concentrations of signalling proteins important in growth factor-related signalling were assessed in 2 models: 1) lean and obese ponies on a low- or high-NSC diet; and 2) EHC model using Standardbred horses. METHODS: Ponies stratified for body condition (lean [LN, n = 11] and obese [OB, n = 11]) were exposed to a low-NSC diet (LO, n = 5 per group for LN LO and OB LO) or a high NSC diet (HI, n = 6 per group for LN HI and OB HI groups) for 7 days. For the EHC model, horses were administered insulin (constant rate infusion [6 mIU/kg bwt/min] combined with 50% dextrose, EHC group, n = 8)] or saline (0.57 mL/kg bwt/h, CON group, n = 8) for 48 h. Immunoblotting was employed to assess concentrations of activated/phosphorylated and total protein for members of the PI3K/Akt/mTORC1 and Ras/ERK pathways in lamellar samples from both models. RESULTS: In the DCM, lamellar P-(Ser 240/244) RPS6 was increased in OB HI ponies (vs. OB LO, P<0.05); positive correlations existed (P<0.05; r>0.5) between Day 7 basal serum insulin concentrations and lamellar concentrations of P-p70S6K and P-(Ser 240/244) RPS6. In the EHC model, lamellar concentrations of P-Akt, P-p70S6K, P-ERK 1/2, P-p90RSK, and both P-(Ser 235/236) and P-(Ser 240/244) RPS6 were increased in the EHC group (vs. CON, P<0.05). MAIN LIMITATIONS: The primary limitations of this study are the small number of animals per group in the DCM study, and the fact that many animals did not develop laminitis as that was not the endpoint of either study. CONCLUSIONS: These results support further investigation of mTORC1/RPS6 signalling as a potential therapeutic target(s) in EMSAL. The Summary is available in Chinese - see Supporting Information.
Authors: Simon M Stokes; Teresa A Burns; Mauria R Watts; François-René Bertin; Darko Stefanovski; Carlos E Medina-Torres; James K Belknap; Andrew W van Eps Journal: J Vet Intern Med Date: 2020-06-25 Impact factor: 3.333
Authors: Mauria R Watts; Olivia C Hegedus; Susan C Eades; James K Belknap; Teresa A Burns Journal: J Vet Intern Med Date: 2019-03-25 Impact factor: 3.333
Authors: Alexandra Meier; Melody de Laat; Christopher Pollitt; Donald Walsh; James McGree; Dania B Reiche; Marcella von Salis-Soglio; Luke Wells-Smith; Ulrich Mengeler; Daniel Mesa Salas; Susanne Droegemueller; Martin N Sillence Journal: PeerJ Date: 2019-06-07 Impact factor: 2.984
Authors: Andy E Durham; Nicholas Frank; Cathy M McGowan; Nicola J Menzies-Gow; Ellen Roelfsema; Ingrid Vervuert; Karsten Feige; Kerstin Fey Journal: J Vet Intern Med Date: 2019-02-06 Impact factor: 3.333