Department of Animal Sciences, University of Illinois, Urbana, IL.
Animal Medicine Department, Beni-Suef University, Beni-Suef, Egypt.
J Anim Sci. 2019 Apr 29;97(5):2181-2187. doi: 10.1093/jas/skz080.
Residual feed intake (RFI) is a widely used measure of feed efficiency in cattle. Although the precise biologic mechanisms associated with improved feed efficiency are not well-known, most-efficient steers (i.e., with low RFI coefficient) downregulate abundance of proteins controlling protein degradation in skeletal muscle. Whether cellular mechanisms controlling protein turnover in ruminal tissue differ by RFI classification is unknown. The aim was to investigate associations between RFI and signaling through the mechanistic target of rapamycin (MTOR) and ubiquitin-proteasome pathways in ruminal epithelium. One hundred and forty-nine Red Angus cattle were allocated to 3 contemporary groups according to sex and herd origin. Animals were offered a finishing diet for 70 d to calculate the RFI coefficient for each. Within each group, the 2 most-efficient (n = 6) and least-efficient animals (n = 6) were selected. Compared with least-efficient animals, the most-efficient animals consumed less feed (P < 0.05; 18.36 vs. 23.39 kg/d DMI). At day 70, plasma samples were collected for insulin concentration analysis. Ruminal epithelium was collected immediately after slaughter to determine abundance and phosphorylation status of 29 proteins associated with MTOR, ubiquitin-proteasome, insulin signaling, and glucose and amino acid transport. Among the proteins involved in cellular protein synthesis, most-efficient animals had lower (P ≤ 0.05) abundance of MTOR, p-MTOR, RPS6KB1, EIF2A, EEF2K, AKT1, and RPS6KB1, whereas MAPK3 tended (P = 0.07) to be lower. In contrast, abundance of p-EEF2K, p-EEF2K:EEF2K, and p-EIF2A:EIF2A in most-efficient animals was greater (P ≤ 0.05). Among proteins catalyzing steps required for protein degradation, the abundance of UBA1, NEDD4, and STUB1 was lower (P ≤ 0.05) and MDM2 tended (P = 0.06) to be lower in most-efficient cattle. Plasma insulin and ruminal epithelium insulin signaling proteins did not differ (P > 0.05) between RFI groups. However, abundance of the insulin-responsive glucose transporter SLC2A4 and the amino acid transporters SLC1A3 and SLC1A5 also was lower (P ≤ 0.05) in most-efficient cattle. Overall, the data indicate that differences in signaling mechanisms controlling protein turnover and nutrient transport in ruminal epithelium are components of feed efficiency in beef cattle.
残留采食量（RFI）是衡量牛饲料效率的常用指标。尽管与提高饲料效率相关的确切生物学机制尚不清楚，但效率最高的牛（即 RFI 系数较低的牛）下调了控制骨骼肌中蛋白质降解的蛋白质的丰度。尚不清楚控制瘤胃组织中蛋白质周转的细胞机制是否因 RFI 分类而不同。本研究旨在调查 RFI 与机械靶标雷帕霉素（MTOR）和泛素-蛋白酶体途径之间的信号转导之间的相关性在瘤胃上皮细胞中。将 149 头红安格斯牛根据性别和畜群来源分配到 3 个当代组中。动物接受育肥日粮 70 d 以计算每个动物的 RFI 系数。在每个组内，选择 2 头最有效的（n = 6）和最无效的动物（n = 6）。与最无效的动物相比，最有效的动物消耗的饲料较少（P < 0.05；18.36 与 23.39 kg/d DMI）。在第 70 天，采集血浆样品以分析胰岛素浓度。宰后立即采集瘤胃上皮细胞以确定与 MTOR、泛素-蛋白酶体、胰岛素信号转导以及葡萄糖和氨基酸转运相关的 29 种蛋白质的丰度和磷酸化状态。在参与细胞蛋白质合成的蛋白质中，最有效的动物的 MTOR、p-MTOR、RPS6KB1、EIF2A、EEF2K、AKT1 和 RPS6KB1 的丰度较低（P ≤ 0.05），而 MAPK3 则趋于较低（P = 0.07）。相反，最有效的动物中 p-EEF2K、p-EEF2K:EEF2K 和 p-EIF2A:EIF2A 的丰度更高（P ≤ 0.05）。在催化蛋白质降解所需步骤的蛋白质中，UBA1、NEDD4 和 STUB1 的丰度较低（P ≤ 0.05），而 MDM2 的丰度较低（P = 0.06）最有效的牛。RFI 组之间的血浆胰岛素和瘤胃上皮细胞胰岛素信号转导蛋白无差异（P > 0.05）。然而，胰岛素反应性葡萄糖转运蛋白 SLC2A4 和氨基酸转运蛋白 SLC1A3 和 SLC1A5 的丰度也较低（P ≤ 0.05）在最有效的牛中。总的来说，数据表明，控制瘤胃上皮细胞中蛋白质周转和营养物质转运的信号转导机制的差异是肉牛饲料效率的组成部分。
