下丘脑饥饿信号通路在热量限制抗肝脏衰老中的作用研究

Calorie restriction (CR) is one of the few known environmental manipulations that increases the lifespan and health span of animals, and reverses many of the signs of ageing at the level of tissues/organs. Recent work in non-human primates and the first human trial of CR (CALERIE) provide strong indications that CR will also be effective in humans. Reducing caloric input in modern society is however difficult to achieve, and it has several negative side effects including perpetual hunger, a drop in body temperature and reduced libido. There has been considerable effort therefore directed at understanding the mechanism by which CR exerts its beneficial effects in the hope that it may be possible to capture these benefits divorced from the side effects. Previous work by the PI has shown that CR results in major changes in the levels of circulating hormones that interact with the hunger signaling pathways in the hypothalamus. These changes are associated (correlation) with a change in the transcripome of the liver which includes anti-aging impacts in twelve key pathways that have been implicated in the aging process. These include mTOR signaling, insulin/IGF-1 signalling, sirtuin signaling, p53 and cancer signaling and oxidative stress pathways. The hypothesis being tested in the current proposal is that these changes in hunger signaling are the critical switch that activates the beneficial effects of CR. To demonstrate causality in the correlative associations emerging from our pilot work we propose to examine the responses of mice with genetic ablation of three key genes in the hunger signaling pathway. These are neuropeptide Y (NPY), Agouti regulated peptide (AgRP) and the melanocortin 3 receptor (MC3R) where the gene products of AgRP and pro-opiomelanocortin (POMC) genes intersect. The key responses will be the activity of the aging related pathways in the liver where we have previously shown an anti-aging impact of CR. The main output from this work will be an understanding of the causal links between the brain response to CR and the critical organ level responses that underpin the anti-aging effect of this environmental manipulation.

热量限制（CR）是为数不多的能延长动物寿命和健康寿命，在组织/器官水平逆转多种衰老信号通路的环境手段之一，对非人灵长类动物和人类也有效。但在现代社会实现CR很难，且CR还有多种副作用包括持续饥饿感，低体温和低性欲。因此有很多研究旨在了解CR的作用机制，探索发挥其有利作用而避免其副作用的可能性。申请人的前期研究发现，CR引起血清中多种能与下丘脑饥饿信号通路互作的激素水平发生变化，而这与肝脏转录组的变化有关，包括对mTOR，胰岛素/IGF-1，sirtuin，p53和氧化胁迫通路等12种涉及衰老过程的信号通路的抗衰老作用。本项目拟验证饥饿信号通路的变化是否是激活CR有利作用的关键开关。为阐明前期发现的相关性的因果关系，计划采用饥饿信号通路中3个关键信号NPY，AgRP和MC3R的缺失型小鼠，检验其肝脏中衰老相关通路的活性。本项目将促进了解CR抗衰老作用中脑与关键器官水平变化的的因果关系。

本项目中，我们使用UCP1 KO小鼠研究了UCP1蛋白在冷暴露效应中的作用。首先，我们探索了微生物组与低温反应之间的潜在联系，结果表明，微生物组缺失的小鼠对冷暴露的反应减弱，并最终鉴定出微生物合成的丁酸盐与冷暴露激活BAT有关（Cell Reports, 2019）。该结果为我们提示了两个研究方向：1）观察BAT及其他组织的具体反应。基于稳定同位素示踪技术，我们采用13C标记的葡萄糖分别检测了室温（23℃）和冷暴露（4℃）下不同组织水平的葡萄糖吸收率，结果发现，野生型小鼠冷暴露后BAT对葡萄糖摄取率高于室温小鼠的BAT。而在UCP1（-/-）小鼠中，无论在冷暴露还是室温下，BAT对葡萄糖的摄取量都高于野生型小鼠。用13C-葡萄糖注射小鼠后分析呼气中13C丰度，结果表明，冷暴露下无论UCP1状态如何，葡萄糖的代谢速率都比室温下快得多。皮下注射葡萄糖耐量试验的结果也印证了上述结果，即无论是否存在UCP1蛋白，冷暴露后葡萄糖的清除速率都更快。总结了两个实验的结果，我们的研究表明，冷暴露对葡萄糖稳态的调节过程是不依赖于UCP1的。由于与肠道菌群的联系，我们还探索了肠道菌群随限食（CR）强度发生的变化，而CR已知能逆转衰老。结果发现，肠道菌群在不同的CR强度下差异巨大，并最终提出了关于CR调节寿命过程中作用机制的新假说，即“打扫橱柜”假设（已投稿）。