Mahmassani Ziad S, McKenzie Alec I, Petrocelli Jonathan J, de Hart Naomi M, Fix Dennis K, Kelly Joshua J, Baird Lisa M, Howard Michael T, Drummond Micah J
Department of Physical Therapy and Athletic Training, University of Utah, Salt Lake City, USA.
Department of Nutrition and Integrative Physiology, University of Utah, Salt Lake City, USA.
J Gerontol A Biol Sci Med Sci. 2021 Nov 15;76(12):2112-2121. doi: 10.1093/gerona/glab077.
Periods of inactivity experienced by older adults induce nutrient anabolic resistance creating a cascade of skeletal muscle transcriptional and translational aberrations contributing to muscle dysfunction. The purpose of this study was to identify how inactivity alters leucine-stimulated translation of molecules and pathways within the skeletal muscle of older adults. We performed ribosomal profiling alongside RNA sequencing from skeletal muscle biopsies taken from older adults (n = 8; ~72 years; 6 F/2 M) in response to a leucine bolus before (Active) and after (Reduced Activity) 2 weeks of reduced physical activity. At both visits, muscle biopsies were taken at baseline, 60 minutes (early response), and 180 minutes (late response) after leucine ingestion. Previously identified inactivity-related gene transcription changes (PFKFB3, GADD45A, NMRK2) were heightened by leucine with corresponding changes in translation. In contrast, leucine also stimulated translational efficiency of several transcripts in a manner not explained by corresponding changes in mRNA abundance ("uncoupled translation"). Inactivity eliminated this uncoupled translational response for several transcripts, and reduced the translation of most mRNAs encoding for ribosomal proteins. Ingenuity Pathway Analysis identified discordant circadian translation and transcription as a result of inactivity such as translation changes to PER2 and PER3 despite unchanged transcription. We demonstrate inactivity alters leucine-stimulated "uncoupled translation" of ribosomal proteins and circadian regulators otherwise not detectable by traditional RNA sequencing. Innovative techniques such as ribosomal profiling continues to further our understanding of how physical activity mediates translational regulation, and will set a path toward therapies that can restore optimal protein synthesis on the transcript-specific level to combat negative consequences of inactivity on aging muscle.
老年人经历的不活动期会引发营养合成代谢抵抗，从而导致一系列骨骼肌转录和翻译异常，进而造成肌肉功能障碍。本研究的目的是确定不活动如何改变老年人骨骼肌中亮氨酸刺激的分子翻译和信号通路。我们对8名老年人（年龄约72岁；6名女性/2名男性）进行了核糖体分析，并结合骨骼肌活检样本进行RNA测序，这些老年人在进行2周的体力活动减少之前（活跃状态）和之后（活动减少状态）接受了亮氨酸推注。在两次就诊时，均在摄入亮氨酸后的基线、60分钟（早期反应）和180分钟（晚期反应）采集肌肉活检样本。先前确定的与不活动相关的基因转录变化（PFKFB3、GADD45A、NMRK2）在亮氨酸作用下增强，同时翻译也发生相应变化。相比之下，亮氨酸还以一种无法用mRNA丰度的相应变化来解释的方式刺激了几种转录本的翻译效率（“非耦合翻译”）。不活动消除了几种转录本的这种非耦合翻译反应，并减少了大多数编码核糖体蛋白的mRNA的翻译。通路分析识别出不活动导致昼夜节律翻译和转录不一致，例如尽管转录未改变，但PER2和PER3的翻译发生了变化。我们证明，不活动会改变亮氨酸刺激的核糖体蛋白和昼夜节律调节因子的“非耦合翻译”，而传统RNA测序无法检测到这种变化。核糖体分析等创新技术不断加深我们对体力活动如何介导翻译调控的理解，并将为开发能够在转录本特异性水平恢复最佳蛋白质合成的疗法指明道路，以对抗不活动对衰老肌肉产生的负面影响。
