MICA Cryo-chronobiology: how do cold-inducible chaperones maintain neural clock function under brain temperature fluctuation?

生物钟是生命的基础，使我们适应环境中可预测的变化。这些时钟的中断发生在几种大脑疾病中，包括痴呆症--这是英国的一种主要死亡原因。了解时钟是如何工作的意味着我们可以控制它们；这是一种解决我们一些最复杂的全球健康挑战的新策略。在分子水平上，反馈环支持整个身体细胞功能的日常“昼夜节律”。这些节律的24小时循环对温度变化具有抵抗力，确保细胞时钟在不同的体温下不会加速或减慢。然而，值得注意的是，细胞时钟与体温的每日变化同步，这意味着它们必须感知并对温度变化做出反应。这种发条的“温度悖论”仍然没有得到解释，尤其是对大脑来说，因为神经细胞的活动会导致大脑温度的快速变化。那么，是什么让我们的脑细胞时钟在大脑温度变化时保持强劲运转呢？昼夜节律和对寒冷的反应是在整个进化过程中保留下来的关键细胞功能。冷诱导伴侣(CICs)是一种在低温下高度活跃的蛋白质；它们在通常会停止蛋白质生产的条件下保护关键细胞蛋白质的制造。CICS通过与从我们每个细胞中的DNA转录的消息绑定来实现这一点，以便这些消息可以被翻译成对细胞生存至关重要的蛋白质，包括发条组件。CIC活动也以昼夜节律的方式循环，对每日体温的变化做出反应。我认为CIC-Clock蛋白的相互作用对脑细胞的计时至关重要。我将测试在大脑温度变化时，这些相互作用是否需要维持脑细胞时钟功能。来自脑损伤患者的数据显示，与体温一样，人类大脑温度以24小时节律循环。然而，大脑和体温是不一样的，我们需要知道健康的大脑发生了什么。与爱丁堡成像公司合作，我将使用一种非侵入性的MRI扫描技术来绘制健康志愿者一天中不同时间的大脑温度图。与此同时，我将使用无线电发射器远程监测小鼠的大脑温度周期。这些实验将建立正常的人脑温度范围，并分离昼夜节律和睡眠-觉醒周期对脑温节律的影响。然后，剑桥的实验将确定在模拟脑温周期下，CIC和时钟蛋白干扰对脑细胞昼夜节律的影响。脑细胞时钟将通过在从人类干细胞培养的脑细胞中用发光记者标记CIC和时钟蛋白来表征。这将使实时监测CIC和Clock蛋白在不同温度下的几天内以及它们之间的过渡期间的循环丰度成为可能。然后，CIC和时钟蛋白将被操纵，使它们被困在细胞的不同部分，不能再相互作用。这种“陷阱”将是完全可逆的，这样CIC与时钟的相互作用可以在温度变化期间打开或关闭，以查看这对时钟功能有什么影响。最后，无线电发射器实验将在携带CIC和时钟蛋白基因突变的小鼠身上重复进行。这项工作将为在痴呆和其他慢性脑部疾病的人类细胞模型中调节CIC-时钟相互作用奠定基础。我预测，增强CIC活动将保护和恢复脆弱脑细胞的时钟功能。这一结果可能最终导致一系列昼夜节律被打乱的疾病的新疗法，以及在现代世界管理我们的“昼夜健康”的新方法。

Biological clocks are fundamental to life, adapting us to predictable changes in our environment. Disruption of these clocks occurs in several brain disorders including dementia - a leading cause of death in the UK. Understanding how clocks work means that we can control them; a fresh strategy to tackle some of our most complex global health challenges.At the molecular level, feedback loops support daily 'circadian' rhythms in cell function throughout the body. The 24-hour cycle of these rhythms is resistant to temperature variation, ensuring that cellular clocks do not speed up or slow down at different body temperatures. Remarkably however, cellular clocks synchronize to daily changes in body temperature, which means they must sense and respond to temperature shift. This 'temperature paradox' of the clockwork remains unexplained, especially for the brain where nerve cell activity produces rapid changes in brain temperature. What then keeps our brain cell clocks ticking robustly as brain temperature changes?Circadian rhythms and responses to cold are critical cellular functions that have been retained throughout evolution. Cold-inducible chaperones (CICs) are highly active proteins at cold temperatures; they safeguard the manufacture of key cellular proteins under conditions that would normally halt protein production. CICs do this by binding to messages transcribed from the DNA in each of our cells so that these messages can be translated into proteins that are critical for cell survival, including components of the clockwork. CIC activity also cycles in a circadian manner, responding to daily changes in body temperature. I propose that CIC-clock protein interactions are critical to timekeeping in brain cells. I will test whether these interactions are required to maintain brain cell clock function as brain temperature changes.Data from patients with brain injury show that, like body temperature, human brain temperature cycles with a 24-hour rhythm. However, brain and body temperature are not the same, and we need to know what happens in the healthy brain. In collaboration with Edinburgh Imaging, I will use a non-invasive MRI scan technique to map brain temperature in healthy volunteers at different times of the day. In parallel, I will monitor brain temperature cycles in mice remotely using radio transmitters. These experiments will establish normal human brain temperature ranges, and separate the effects of circadian and sleep-wake cycles on brain temperature rhythms.Experiments in Cambridge will then determine the impact of CIC versus clock protein disruption on brain cell circadian rhythms under simulated brain temperature cycles. The brain cell clock will be characterized 'in a dish' by tagging CIC and clock proteins with luminescent reporters in brain cells grown from human stem cells. This will make it possible to monitor the cyclic abundance of CIC and clock proteins in real time over several days at different temperatures, and during transitions between them. CIC and clock proteins will then be manipulated so that they are trapped in different parts of the cell and can no longer interact with each other. This 'trapping' will be entirely reversible such that CIC-clock interactions can be switched on or off during temperature shifts, to see what effect this has on clock function. Finally, radio transmitter experiments will be repeated in mice carrying genetic mutations in CIC and clock proteins. This work will establish a basis for modulating CIC-clock interactions in human cellular models of dementia and other chronic brain disorders. I predict that boosting CIC activity will protect and restore clock function in vulnerable brain cells. The results could ultimately lead to new treatments for a range of disorders in which circadian rhythms are disrupted, and also new ways to manage our 'circadian health' in the modern world.