Integrative Muscle Metabolism Laboratory, Department of Health, Human Performance and Recreation, University of Arkansas, Fayetteville, AR, United States of America; Laboratory for Functional Optical Imaging and Spectroscopy, Department of Biomedical Engineering, University of Arkansas, Fayetteville, AR, United States of America.
Exercise Muscle Biology Laboratory, Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, AR, United States of America.
Exp Gerontol. 2019 Jul 1;121:62-70. doi: 10.1016/j.exger.2019.03.009. Epub 2019 Mar 27.
Being both advanced in age and obese each contribute to cardiac hypertrophy in a unique manner. Electron transport complexes I and IV are implicated in deficient electron transport during cardiomyopathies and contain the majority of protein subunits that are transcribed and translated by machinery localized within the mitochondria.
To assess myocardial mt-mRNA translation factors in relation to mitochondrial content and mtDNA-encoded protein using a mouse model of aged obesity and to test the relationship of mt-mRNA translation initiation factor 2 (mtIF2) to oxidative capacity and the cellular oxidation-reduction (redox) state in cardiomyocytes.
Male C56BL/6 J mice fed lean or high fat diet were aged to either ~3 months or ~22 months, the heart was excised and analyzed using immunoblot and qPCR to assess differences in mitochondrial mRNA translation machinery. Using H9c2 cardiomyocytes, mtIF2 was knocked-down and oxidative metabolic characteristics assessed including oxidation/reduction state, bioenergetic flux, and hypoxic resistance was tested.
Aged, obese mouse hearts were ~40% larger than young, lean controls and contained ~50% less mtIF2 protein alongside ~25-50% lower content of Cytb, a protein encoded by mtDNA. Reducing the level of mtIF2 by shRNA is associated with ~15-20% lower content of OXPHOS complex I and IV, ~30% lower optical redox ratio, ~40% oxygen reserve capacity, and ~20% less cell survival following hypoxia.
We present evidence of altered mt-mRNA translation during cardiac hypertrophy in aged obesity. We build on these results by demonstrating the necessity of mtIF2 in maintaining oxidative characteristics of cardiac muscle cells.
年龄增长和肥胖都会以独特的方式导致心肌肥大。电子传递复合物 I 和 IV 与心肌病中的电子传递缺陷有关，并且包含大多数由定位于线粒体内部的机器转录和翻译的蛋白质亚基。
使用年龄肥胖的小鼠模型评估与线粒体含量和 mtDNA 编码蛋白相关的心肌 mt-mRNA 翻译因子，并测试 mt-mRNA 翻译起始因子 2 (mtIF2) 与氧化能力以及心肌细胞中细胞氧化还原 (redox) 状态的关系。
雄性 C56BL/6J 小鼠喂食低脂或高脂饮食，分别老化至约 3 个月或约 22 个月，取出心脏，使用免疫印迹和 qPCR 分析评估线粒体 mRNA 翻译机制的差异。使用 H9c2 心肌细胞，敲低 mtIF2，并评估氧化代谢特征，包括氧化/还原状态、生物能量通量和缺氧抗性。
与年轻、低脂对照组相比，年老、肥胖的小鼠心脏大约大 40%，并且 mtIF2 蛋白含量降低约 50%，同时 Cytb（一种由 mtDNA 编码的蛋白质）含量降低约 25-50%。通过 shRNA 降低 mtIF2 的水平与 OXPHOS 复合物 I 和 IV 的含量降低约 15-20%、光氧化还原比降低约 30%、氧储备能力降低约 40%以及缺氧后细胞存活率降低约 20%有关。
我们提出了在年龄肥胖引起的心肌肥大过程中改变 mt-mRNA 翻译的证据。我们通过证明 mtIF2 在维持心肌细胞的氧化特性方面的必要性，进一步证实了这些结果。
