Regulatory and functional pathways mediating the control of central osmotic defences by hypothalamic transcription factor CREB3L1

哺乳动物有机体的体液处于不断流动的状态。即使在没有脱水、出血或饥饿等挑战的情况下，由于正常的、强制性的肾脏排泄功能以及呼吸和排汗过程，盐和水也不断丢失。人体有两种机制来控制水和盐的消耗和排泄，以保持健康所需的最佳身体内容。第一种机制是由大脑的下丘脑产生一种叫做“精氨酸加压素”(AVP)的荷尔蒙，这种荷尔蒙告诉肾脏节约水分。第二种机制是行为机制，涉及口渴和食盐的本能，这些本能在情感上驱使生物体纠正其液体平衡。这些机制可能会出错，导致健康状况不佳。例如，在住院的老年患者中，相当大比例的患者明显存在液体平衡障碍，脱水是老年人发病和死亡的常见原因。AVP是一种由相应的AVP基因编码的多肽激素。当动物脱水时，AVP从下丘脑释放出来，因此需要制造更多的AVP。25年前，我们发现AVP基因的表达因此被激活，更多的信使RNA(MRNA)由该基因产生，这一过程被称为“转录”。正是AVP mRNA将基因编码的信息带到细胞质中。在这里，信使核糖核酸中的信息被“翻译”成蛋白质。然而，到目前为止，涉及的确切分子机制仍然不清楚。使用可以同时描述所有基因表达的方法，我们发现了另一个基因，称为CREB3L1，它在脱水后在下丘脑中表达增加。CREB3L1是一种特殊的蛋白质(“转录因子”)，控制目标基因的表达。我们发现CREB3L1在AVP神经元中表达，并与AVP基因的启动子区域结合，从而驱动其表达。我们现在的目标是破译CREB3L1影响下丘脑基因表达的详细分子机制，从而调节控制盐分和水分动态平衡的关键激素过程。我们将：*找出哪些信号告诉下丘脑在脱水后增加CREB3L1的表达。*找出哪些其他蛋白质与CREB3L1结合，这将告诉我们调节CREB3L1的上游因素，以及CREB3L1可能通过其发挥作用的下游效应器。*找出AVP细胞中受CREB3L1调控的其他基因。*确定CREB3L1如何在全球范围内影响下丘脑神经肽的形成。*开展研究，告诉我们CREB3L1的生理作用，它与之相互作用的蛋白质，以及它调节的基因。重要的是，这些实验将在整个生物体的生理完整性中进行。这些独特的研究将告诉我们转录因子蛋白影响大脑中基因表达从而调节生理稳定性的机制。

The bodily fluids of the mammalian organism are in a constant state of flux. Even in the absence of challenges such as dehydration, haemorrhage or starvation, salt and water are constantly being lost as a consequence of normal, obligatory renal excretory functions, and by the processes of respiration and perspiration. The body has two mechanisms that function to control the consumption and the excretion of water and salt, in order to maintain the optimal bodily content required for good health. The first mechanism involves the production, by a part of the brain called the hypothalamus, of a hormone called "arginine vasopressin" (AVP) that tells the kidney to conserve water. The second mechanism is behavioural, and involves the instincts of thirst and salt appetite that emotionally drive the organism to correct its fluid balance. These mechanisms can go wrong resulting in ill-health. For example, disorders of fluid balance are evident in a substantial proportion of elderly patients admitted to hospital, and dehydration is a frequent cause of morbidity and mortality in old people. AVP is a peptide hormone that is encoded by the corresponding AVP gene. When an animal becomes dehydrated, AVP is released from the hypothalamus and there is thus a need to make more. Twenty five years ago, we showed that the expression of the AVP gene is hence activated, and more messenger RNA (mRNA) is made from the gene, a process known as "transcription". It is the AVP mRNA that take the information coded by the gene to the cytoplasm of the cell. Here, the information in the mRNA is "translated" into protein. However, the exact molecular mechanisms involved have remained elusive, until now. Using methods that allow us to simultaneously describe the expression of all genes, we identified another gene, called CREB3L1, as being increased in expression in the hypothalamus following dehydration. CREB3L1 is a specialised protein (a "transcription factor") that controls the expression of target genes. We showed that CREB3L1 is expressed in AVP neurones, binds to the promoter region of the AVP gene, and hence drives its expression. Our aims are now to decipher the detailed molecular mechanisms by which CREB3L1 affects gene expression in the hypothalamus, and hence regulates the crucial hormonal processes that govern salt and water homeostasis. We will:*work out which signals tell the hypothalamus to increase the expression of CREB3L1 following dehydration.*find out what other proteins are bound to CREB3L1, which will tell us about upstream factors that regulate CREB3L1, and downstream effectors through which CREB3L1 might exerts its action. *find out what other genes in the AVP cell are regulated by CREB3L1. *determine how CREB3L1 globally affects the elaboration of neuropeptides in the hypothalamus. *embark upon studies that will tell us about the physiological roles of CREB3L1, the proteins that it interacts with and the genes that it regulates. Importantly, these experiments will take place in the physiological integrity of the whole organism. These unique studies will tell us about the mechanisms by which transcription factor protein affects gene expression in the brain, and hence mediates physiological stability.