1Military Nutrition Division, U.S. Army Research Institute of Environmental Medicine, 15 Kansas Street, Building 42, Natick, MA 01760, USA.
FASEB J. 2013 Dec;27(12):5104-11. doi: 10.1096/fj.13-239228. Epub 2013 Aug 21.
This study was undertaken to characterize the ubiquitin proteasome system (UPS) response to varied dietary protein intake, energy deficit (ED), and consumption of a mixed meal. A randomized, controlled trial of 39 adults consuming protein at 0.8 (recommended dietary allowance [RDA]), 1.6 (2×-RDA), or 2.4 (3×-RDA) g · kg(-1) · d(-1) for 31 d. A 10-d weight maintenance (WM) period was followed by 21 d of 40% ED. Ubiquitin (Ub)-mediated proteolysis and associated gene expression were assessed in the postabsorptive (fasted) and postprandial (fed; 480 kcal, 20 g protein) states after WM and ED by using muscle biopsies, fluorescence-based assays, immunoblot analysis, and real-time qRT-PCR. In the assessment of UPS responses to varied protein intakes, ED, and feeding, the RDA, WM, and fasted measures served as appropriate controls. ED resulted in the up-regulation of UPS-associated gene expression, as mRNA expression of the atrogenes muscle RING finger-1 (MuRF1) and atrogin-1 were 1.2- and 1.3-fold higher (P<0.05) for ED than for WM. However, mixed-meal consumption attenuated UPS-mediated proteolysis, independent of energy status or dietary protein, as the activities of the 26S proteasome subunits β1, β2, and β5 were lower (P<0.05) for fed than for fasted. Muscle protein ubiquitylation was also 45% lower (P<0.05) for fed than for fasted, regardless of dietary protein and energy manipulations. Independent of habitual protein intake and despite increased MuRF1 and atrogin-1 mRNA expression during ED, consuming a protein-containing mixed meal attenuates Ub-mediated proteolysis.
本研究旨在描述不同膳食蛋白质摄入量、能量不足（ED）和混合餐摄入对泛素蛋白酶体系统（UPS）的影响。一项随机对照试验纳入 39 名成年人，他们连续 31 天摄入 0.8（推荐膳食允许量 [RDA]）、1.6（2×RDA）或 2.4（3×RDA）g·kg-1·d-1的蛋白质。在 10 天的维持体重（WM）期后，进行 21 天 40%ED。在 WM 和 ED 后，通过肌肉活检、荧光测定、免疫印迹分析和实时 qRT-PCR，评估吸收后（空腹）和餐后（进食；480 千卡，20 克蛋白质）状态下 Ub 介导的蛋白水解和相关基因表达。在评估 UPS 对不同蛋白质摄入量、ED 和喂养的反应时，RDA、WM 和空腹测量值作为适当的对照。ED 导致 UPS 相关基因表达上调，因为 ED 时肌肉 RING 指蛋白 1（MuRF1）和 Atrogin-1 的 atrogenes mRNA 表达分别比 WM 高 1.2-1.3 倍（P<0.05）。然而，混合餐摄入独立于能量状态或膳食蛋白质，降低了 UPS 介导的蛋白水解，因为 26S 蛋白酶体亚基β1、β2 和β5 的活性（P<0.05）在进食时比空腹时低。肌肉蛋白泛素化也比空腹时低 45%（P<0.05），无论膳食蛋白质和能量如何变化。独立于习惯性蛋白质摄入，尽管 ED 期间 MuRF1 和 Atrogin-1 mRNA 表达增加，摄入含蛋白质的混合餐会减弱 Ub 介导的蛋白水解。
