冬眠是许多小型和大型哺乳动物物种在冬季期间生存的代谢抑制期。由于潜在的细胞和分子机制尚未完全了解,我们的研究旨在确定骨骼肌肌球蛋白及其代谢效率在冬眠期间是否发生改变,以优化能量利用。我们从小型冬眠动物中分离出肌肉纤维,三叶草和Eliomysquercinus和较大的冬眠者,Ursusarctos和Ursusamericanus.然后,我们与X射线衍射一起进行了加载的Mant-ATP追踪实验,以测量静息肌球蛋白动力学及其ATP需求。并行,我们进行了多种蛋白质组学分析.我们的结果显示冬眠期间U.arctos和U.americanus的肌球蛋白结构得到保留,而在I.Tridecemlineatus和E.quercinus,在torpor期间肌球蛋白代谢状态的变化意外地导致更高水平的II型能量消耗,在环境实验室温度(20°C)下快速抽搐的肌肉纤维。在8°C(接近暴躁动物的体温)重复加载的Mant-ATP追踪实验后,我们发现,与活跃期相比,Ⅱ型肌纤维肌球蛋白ATP消耗减少了77-107%.此外,我们观察到Myh2在torpor期间过度磷酸化。预测可以稳定肌球蛋白分子。这可能是一种潜在的分子机制,可以缓解因寒冷暴露而导致的与肌球蛋白相关的骨骼肌能量消耗增加。总之,我们证明静息肌球蛋白在冬眠的哺乳动物中发生了改变,有助于骨骼肌ATP消耗的显著变化。此外,我们观察到,它在响应冷暴露时进一步改变,并强调肌球蛋白是骨骼肌非颤抖产热的潜在原因。
许多动物使用冬眠作为生存严冬的策略。在这个休眠期间,非活动状态,动物减少或限制身体过程,比如心率和体温,尽量减少他们的能源使用。为了在冬眠期间保存能量,动物可以使用不同的方法。例如,花园睡鼠经历极低的核心温度(低至4-8oC)的周期性状态;而欧亚棕熊则看到温和的温度下降(低至23-25oC)。冬眠期间变化的重要器官是骨骼肌。骨骼肌通常消耗大量的能量,占身体质量的50%左右。为了生存,冬眠的动物必须改变它们的骨骼肌如何使用能量。传统上,活性肌球蛋白——一种在肌肉中发现的帮助肌肉收缩的蛋白质——被认为是骨骼肌消耗大部分能量的原因。但是,最近,当肌肉放松时,静息肌球蛋白也被发现使用能量。刘易斯等人。研究了冬眠期间肌球蛋白和骨骼肌能量使用的变化,以及它们是否会影响冬眠动物的新陈代谢。刘易斯等人。评估松鼠肌肉样本中肌球蛋白的变化,冬眠和活动期间的休眠和熊。实验表明,松鼠和睡鼠(冬眠期间温度降至4-8oC)的静息肌球蛋白发生变化,但熊却没有。进一步的分析显示,从非冬眠肌肉到4-8oC的冷却样品增加了静息肌球蛋白的能量使用,从而产生热量。然而,在将冬眠肌肉样本冷却至4-8oC后,未发现能量消耗增加。这表明静息肌球蛋白在凉爽的温度下产生热量-冬眠动物中关闭的机制可以使它们冷却体温。这些发现揭示了动物在冬眠期间如何保存能量的关键见解。此外,结果表明,肌球蛋白调节骨骼肌的能量使用,这表明肌球蛋白可能是代谢性疾病的潜在药物靶标,比如肥胖。
Hibernation is a period of metabolic suppression utilized by many small and large mammal species to survive during winter periods. As the underlying cellular and molecular mechanisms remain incompletely understood, our study aimed to determine whether skeletal muscle myosin and its metabolic efficiency undergo alterations during hibernation to optimize energy utilization. We isolated muscle fibers from small hibernators, Ictidomys tridecemlineatus and Eliomys quercinus and larger hibernators, Ursus arctos and Ursus americanus. We then conducted loaded Mant-ATP chase experiments alongside X-ray diffraction to measure resting myosin dynamics and its ATP demand. In parallel, we performed multiple proteomics analyses. Our results showed a preservation of myosin structure in U. arctos and U. americanus during hibernation, whilst in I. tridecemlineatus and E. quercinus, changes in myosin metabolic states during torpor unexpectedly led to higher levels in energy expenditure of type II, fast-twitch muscle fibers at ambient lab temperatures (20 °C). Upon repeating loaded Mant-ATP chase experiments at 8 °C (near the body temperature of torpid animals), we found that myosin ATP consumption in type II muscle fibers was reduced by 77-107% during torpor compared to active periods. Additionally, we observed Myh2 hyper-phosphorylation during torpor in I. tridecemilineatus, which was predicted to stabilize the myosin molecule. This may act as a potential molecular mechanism mitigating myosin-associated increases in skeletal muscle energy expenditure during periods of torpor in response to cold exposure. Altogether, we demonstrate that resting myosin is altered in hibernating mammals, contributing to significant changes to the ATP consumption of skeletal muscle. Additionally, we observe that it is further altered in response to cold exposure and highlight myosin as a potentially contributor to skeletal muscle non-shivering thermogenesis.
Many animals use hibernation as a tactic to survive harsh winters. During this dormant, inactive state, animals reduce or limit body processes, such as heart rate and body temperature, to minimise their energy use. To conserve energy during hibernation, animals can use different approaches. For example, garden dormice undergo periodic states of extremely low core temperatures (down to 4–8oC); whereas Eurasian brown bears see milder temperature drops (down to 23–25oC). An important organ that changes during hibernation is skeletal muscle. Skeletal muscle typically uses large amounts of energy, making up around 50% of body mass. To survive, hibernating animals must change how their skeletal muscle uses energy. Traditionally, active myosin – a protein found in muscles that helps muscles to contract – was thought to be responsible for most of the energy use by skeletal muscle. But, more recently, resting myosin has also been found to use energy when muscles are relaxed. Lewis et al. studied myosin and skeletal muscle energy use changes during hibernation and whether they could impact the metabolism of hibernating animals. Lewis et al. assessed myosin changes in muscle samples from squirrels, dormice and bears during hibernation and during activity. Experiments showed changes in resting myosin in squirrels and dormice (whose temperature drops to 4–8oC during hibernation) but not in bears. Further analysis revealed that cooling samples from non-hibernating muscle to 4–8oC increased energy use in resting myosin, thereby generating heat. However, no increase in energy use was found after cooling hibernating muscle samples to 4–8oC. This suggest that resting myosin generates heat at cool temperatures – a mechanism that is switched off in hibernating animals to allow them to cool their body temperature. These findings reveal key insights into how animals conserve energy during hibernation. In addition, the results show that myosin regulates energy use in skeletal muscles, which indicates myosin may be a potential drug target in metabolic diseases, such as obesity.