Department of Integrative Physiology, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-Ku, Hiroshima, 734-8553, Japan.
Department of Physical Therapy, School of Rehabilitation Sciences, Health Sciences University of Hokkaido, Hokkaido, Japan.
Sci Rep. 2022 Nov 16;12(1):19723. doi: 10.1038/s41598-022-24251-0.
Hibernating animals exhibit an unexplained physiological characteristic of skeletal muscles being atrophy resistance, in which case muscle mass and strength remain almost unchanged both before and after hibernation. In this study, we examined the alterations in the regulatory systems of protein and energy metabolism in the skeletal muscles of Asiatic black bears during hibernation. Skeletal muscle samples (vastus lateralis muscle) were collected from identical individuals (n = 8) during the active (July) and hibernating (February) periods, while histochemical and biochemical analyses were performed. We observed no significant alterations in body weight, muscle fiber size, and fiber type composition during the active and hibernating periods, indicating that the skeletal muscles of bears are very well preserved during hibernation. In hibernating bear skeletal muscles, both regulatory pathways of muscle protein synthesis (Akt/mechanistic target of rapamycin and mitogen-activated protein kinase systems) and proteolysis (ubiquitin-proteasome and autophagy systems) were down-regulated. Gene expression levels of factors regulating oxidative metabolism were also decreased in hibernating bear skeletal muscles. This is likely an adaptive strategy to minimize the energy wasting of amino acids and lipids during hibernation, which is accompanied by a prolonged period of disuse and starvation.
冬眠动物表现出一种未被解释的生理特征,即骨骼肌肉具有抗萎缩性,在这种情况下,肌肉质量和力量在冬眠前后几乎保持不变。在这项研究中,我们研究了亚洲黑熊在冬眠期间骨骼肌肉中蛋白质和能量代谢调节系统的变化。在活跃期(7 月)和冬眠期(2 月),从相同个体(n=8)采集了骨骼肌样本(股外侧肌),同时进行了组织化学和生化分析。我们观察到在活跃期和冬眠期,体重、肌肉纤维大小和纤维类型组成没有明显变化,这表明熊的骨骼肌在冬眠期间得到了很好的保护。在冬眠熊的骨骼肌中,肌肉蛋白合成的调节途径(Akt/雷帕霉素靶蛋白和丝裂原激活蛋白激酶系统)和蛋白水解(泛素-蛋白酶体和自噬系统)都被下调。调节氧化代谢的因子的基因表达水平在冬眠熊的骨骼肌中也降低了。这可能是一种适应策略,以最小化冬眠期间氨基酸和脂质的能量浪费,冬眠伴随着长时间的不用和饥饿。