Konhilas John P, Widegren Ulrika, Allen David L, Paul Angelika C, Cleary Allison, Leinwand Leslie A
Dept. of Molecular, Cellular, and Developmental Biology, Univ. of Colorado, Campus Box 347, Boulder, CO 80309-0347, USA.
Am J Physiol Heart Circ Physiol. 2005 Jul;289(1):H455-65. doi: 10.1152/ajpheart.00085.2005. Epub 2005 Feb 25.
Voluntary cage wheel exercise has been used extensively to determine the physiological adaptation of cardiac and skeletal muscle in mice. In this study, we tested the effect of different loading conditions on voluntary cage wheel performance and muscle adaptation. Male C57Bl/6 mice were exposed to a cage wheel with no-resistance (NR), low-resistance (LR), or high-resistance (HR) loads for 7 wk. Power output was elevated (3-fold) under increased loading (LR and HR) conditions compared with unloaded (NR) exercise training. Only unloaded (NR) exercise induced an increase in heart mass, whereas only loaded (LR and HR) exercise training induced an increase in skeletal (soleus) muscle mass. Moreover, unloaded and loaded exercise training had a differential impact on the cross-sectional area of muscle fibers, depending on the type of myosin heavy chain expressed by each fiber. The biochemical adaptation of the heart was characterized by a decrease in genes associated with pathological (but not physiological) cardiac hypertrophy and a decrease in calcineurin expression in all exercise groups. In addition, transcriptional activity of myocyte enhancer factor-2 (MEF-2) was significantly decreased in the hearts of the LR group as determined by a MEF-2-dependent transgene driving the expression of beta-galactosidase. Phosphorylation of glycogen synthase kinase-3beta, protein kinase B (Akt), and p70 S6 kinase was increased only in the hearts of the NR group, consistent with the significant increase in cardiac mass. In conclusion, unloaded and loaded cage wheel exercise have a differential impact on cage wheel performance and muscle (cardiac and skeletal) adaptation.
自愿式笼轮运动已被广泛用于确定小鼠心脏和骨骼肌的生理适应性。在本研究中，我们测试了不同负荷条件对自愿式笼轮运动表现和肌肉适应性的影响。将雄性C57Bl/6小鼠置于无阻力（NR）、低阻力（LR）或高阻力（HR）负荷的笼轮中7周。与无负荷（NR）运动训练相比，在增加负荷（LR和HR）条件下，功率输出提高了（3倍）。只有无负荷（NR）运动导致心脏质量增加，而只有有负荷（LR和HR）运动训练导致骨骼肌（比目鱼肌）质量增加。此外，无负荷和有负荷运动训练对肌纤维横截面积有不同影响，这取决于每条纤维所表达的肌球蛋白重链类型。心脏的生化适应性表现为与病理性（而非生理性）心肌肥大相关的基因减少，且所有运动组中钙调神经磷酸酶表达均降低。此外，通过驱动β-半乳糖苷酶表达的MEF-2依赖性转基因测定，LR组心脏中肌细胞增强因子2（MEF-2）的转录活性显著降低。糖原合酶激酶-3β、蛋白激酶B（Akt）和p70 S6激酶的磷酸化仅在NR组心脏中增加，这与心脏质量的显著增加一致。总之，无负荷和有负荷的笼轮运动对笼轮运动表现和肌肉（心脏和骨骼肌）适应性有不同影响。
