The Role of Hydrogen Sulfide in the Hypoxia Tolerance of Hibernators

冬眠是哺乳动物的一种极端生理状态。小型冬眠动物，如地松鼠，通过陷入深度麻木来度过冬天，在这种情况下，重要的生理频率和新陈代谢急剧下降，体温显著下降。在整个冬眠过程中，麻木会被周期性的唤醒所打断，在这个过程中，动物会重新温暖到夏季的正常体温，并恢复身体功能。作为这种戏剧性循环的一部分，冬眠者自然会经历血液流量减少和组织氧气供应枯竭(缺氧)。这种血液供应中断和由此导致的缺氧对包括人类在内的非冬眠者可能是致命的。通过研究冬眠的地面松鼠如何在大脑等关键组织中度过低氧水平，这个项目扩大了我们对所有哺乳动物细胞能量产生策略的理解，并可能突出与大脑低氧状况相关的治疗新途径，如中风。具体地说，研究人员检查了一条假设为感知低氧条件的信号通路，并启动了抑制细胞能量产生的反应。为了评估这一信号通路在自然冬眠中的功能，研究人员检查了13只线沙鼠的新陈代谢和耐低氧能力，并比较了哺乳动物之间的关键基因序列。该项目还进一步推动了NSF培养新一代科学家和向公众提供科学发现的目标：该项目包括培训本科生和博士后研究员，以及通过社区卫生改善中心和公共动物园进行公众宣传。小体冬眠者的众多生理奥秘之一是他们对严重缺氧的显著耐受性，这种耐受性发生在从深度麻木中唤醒的复温过程中。该项目的目标是确定在正常情况下对缺氧敏感的组织(如大脑)中支持冬眠地松鼠耐缺氧的机制。在小鼠等不耐缺氧的物种中，损伤或致命的缺氧是通过气体递质硫化氢(H2S)的急剧增加而在大脑中介导的，硫化氢抑制了电子传递链。该项目使用体内、体外和硅胶方法来检验这样一种假设，即深度冬眠者的脑细胞能够代谢硫化氢，这种与生俱来的能力是他们在严重缺氧事件中存活的基础。这项研究解决了13只地松鼠(Ictidomys Tridecemlineatus)大脑的三个特定目标。第一个目的是确定沙鼠对吸入硫化氢的季节性反应，并与大鼠进行比较。第二个目的是跟踪缺氧暴露期间线粒体和神经元中硫化氢的产生和代谢。第三个也是最后一个目的是评估啮齿动物谱系中硫化氢产生和代谢的关键基因的选择压力。预计拟议的研究将促进我们对冬眠者耐受脑缺氧的生化和生理适应的了解。

Hibernation is an extreme physiological condition among mammals. Small hibernators, such as ground squirrels, survive the winter by falling into deep bouts of torpor, in which vital physiological rates and metabolism are reduced dramatically and body temperature drops significantly. Torpor is punctuated throughout hibernation by periodic arousals, in which animals re-warm to normal summer body temperatures, and restore body functions. As part of this dramatic cycling, hibernators naturally experience reduced blood flow and depleted oxygen supply (hypoxia) to tissues. Such disruptions in blood supply and resulting hypoxia can be lethal to non-hibernators, including humans. By examining how hibernating ground squirrels survive low oxygen levels in critical tissues such as the brain, this project expands our understanding of strategies for cellular energy production in all mammals, and may highlight new avenues for therapies associated with low oxygen conditions in the brain, such as stroke. Specifically, the investigators examine a signaling pathway hypothesized to sense low oxygen conditions and initiate a response that suppresses cellular energy production. To evaluate the function of this signaling pathway in a natural hibernator, the investigators examine metabolism and hypoxia tolerance in 13-lined ground squirrels, and compare the sequences of key genes among mammals. The project also furthers the NSF goals of training new generations of scientists and making scientific discoveries available to the general public: the project includes training of undergraduate students and a postdoctoral researcher, and public outreach via a center for community health improvement and a public zoo. One of the many physiological mysteries of small-bodied hibernators is their marked tolerance to severe hypoxia, which occurs during rewarming arousal from deep torpor bouts. The goal of this project is to identify mechanisms that support hypoxia tolerance of hibernating ground squirrels in normally hypoxia-sensitive tissues such as the brain. In non-hypoxia tolerant species like mice, damaging or lethal hypoxia is mediated in the brain by an acute increase in the gasotransmitter hydrogen sulfide (H2S), which inhibits the electron transport chain. This project uses in vivo, in vitro and in silico approaches to examine the hypothesis that the brain cells of deep hibernators are able to metabolize H2S, and that this innate ability underlies their survival of severe hypoxic events. This study addresses three specific objectives in the brain of 13-lined ground squirrels (Ictidomys tridecemlineatus). The first aims serves to determine the seasonal responsiveness of ground squirrels to inhaled H2S, in comparison to rats. The second aim serves to track H2S production and metabolism during hypoxia exposure in isolated mitochondria and neurons. The third and last aim serves to evaluate selective pressures on the key genes of H2S production and metabolism within the rodent lineage. It is expected that the proposed studies will advance our knowledge of the biochemical and physiological adaptations that allow hibernators to tolerate cerebral hypoxia.