Lane H E, Burns T A, Hegedus O C, Watts M R, Weber P S, Woltman K A, Geor R J, McCutcheon L J, Eades S C, Mathes L E, Belknap J K
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University, Columbus, Ohio, USA.
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA.
Equine Vet J. 2017 Sep;49(5):643-654. doi: 10.1111/evj.12663. Epub 2017 Mar 2.
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.
To use a dietary challenge model (DCM) and a euglycaemic-hyperinsulinaemic clamp (EHC) model to assess lamellar growth factor-related signalling.
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.
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.
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).
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.
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.
胰岛素调节异常、肥胖以及高非结构性碳水化合物（NSC）草料暴露是马属动物代谢综合征相关蹄叶炎（EMSAL）的危险因素；有人提出，EMSAL中高全身胰岛素浓度可通过激活胰岛素样生长因子-1受体诱导蹄叶细胞调节异常。
使用饮食挑战模型（DCM）和正常血糖-高胰岛素钳夹（EHC）模型评估蹄叶生长因子相关信号传导。
在两个模型中评估生长因子相关信号传导中重要的信号蛋白的蹄叶磷酸化（P）-蛋白浓度：1）低或高NSC饮食的瘦型和肥胖型小马；2）使用标准赛马的EHC模型。
根据身体状况分层的小马（瘦型[LN，n = 11]和肥胖型[OB，n = 11]）接受低NSC饮食（LO，LN LO和OB LO组每组n = 5）或高NSC饮食（HI，LN HI和OB HI组每组n = 6）7天。对于EHC模型，给马输注胰岛素（持续速率输注[6 mIU/kg体重/分钟]联合50%葡萄糖，EHC组，n = 8）或生理盐水（0.57 mL/kg体重/小时，CON组，n = 8）48小时。采用免疫印迹法评估两个模型的蹄叶样本中PI3K/Akt/mTORC1和Ras/ERK途径成员的活化/磷酸化蛋白和总蛋白浓度。
在DCM中，OB HI小马的蹄叶P-（Ser 240/244）RPS6增加（与OB LO相比，P<0.05）；第7天基础血清胰岛素浓度与P-p70S6K和P-（Ser 240/244）RPS6的蹄叶浓度之间存在正相关（P<0.05；r>0.5）。在EHC模型中，EHC组的蹄叶P-Akt、P-p70S6K、P-ERK 1/2、P-p90RSK以及P-（Ser 235/236）和P-（Ser 240/244）RPS6浓度均增加（与CON相比，P<0.05）。
本研究的主要局限性在于DCM研究中每组动物数量较少，以及许多动物未发生蹄叶炎，因为这不是任何一项研究的终点。
这些结果支持进一步研究mTORC1/RPS6信号传导作为EMSAL潜在治疗靶点。总结内容有中文版本 - 见补充信息。
