Biphasic contribution of prostaglandin E2 to the hypothalamic-pituitary-adrenal axis

调节体内平衡的神经机制必须有效地感知扰动并迅速作出反应。这个NSERC的研究项目将提供关于大脑如何感知上升的警告信号（例如外周炎症），然后激活下丘脑-垂体-肾上腺（HPA）轴的新信息，HPA轴是一个进化上保守的体内平衡调节器。我们的重点是炎症诱导反应的一个关键介质，前列腺素（PG）E2，它是通过环氧化酶（COX）途径产生的。已确立的观点是，循环细胞因子（即上升的炎症信号）导致大脑中COX的诱导同工酶COX2的重新诱导。cox2衍生的PGE2反过来在大脑中起作用，引发反应。但COX2诱导缓慢；越来越清楚的是，COX1是一种组成型同工酶，对HPA轴反应的早期发病至关重要。这指出了PGE2合成的双相模式，并提出了一个问题“cox1介导的PGE2合成的早期上升信号是什么？”此外，无论是通过COX1还是COX2产生，PGE2如何引发HPA轴反应尚不清楚。研究表明，PGE受体的两种亚型EP1和EP3参与HPA轴反应。不同的EP亚型是否与COX1-和cox -衍生的PGE2作用耦合还有待研究。******假设：多种COX和EP受体亚型以暂时补充的方式工作，以驱动HPA轴反应。******长期目标：通过主要关注（尚不清楚的）COX1和HPA轴反应的早期发作来阐明PGE2双相合成和作用的机制。******为了解决由“组成型”COX1快速合成PGE2的问题，我们将在包含HPA轴指令神经元的脑切片中使用电生理方法。我们将评估指令神经元的PGE2依赖性兴奋作为快速PGE2合成的读数。我们还将阐明与PGE2作用有关的特定EP亚型。******短期目标：***1)研究上行神经输入（去甲肾上腺素）在诱导cox - 1介导的PGE2合成中的作用。***2)阐明EP受体亚型及其如何介导PGE2对HPA轴命令神经元的兴奋作用。***3)确定COX1-和cox2衍生的PGE2是否作用于不同的EP受体亚型。******本研究项目的成功将为PGE2功能的双相模式奠定基础，填补我们对HPA轴反应早发性认识的空白。这一发现的意义在于“冗余”（多个同工酶和受体）有助于系统的最佳功能（早发和延迟持续的HPA轴输出）。我们的研究项目还将为系统生物学和最新技术（如膜片钳电生理学和光遗传学）提供丰富的培训环境。

The neural mechanisms that regulate homeostasis must effectively sense perturbations and respond rapidly. This NSERC research program will provide new information about how the brain senses ascending warning signals (e.g. peripheral inflammation), and then activates the hypothalamic-pituitary-adrenal (HPA) axis, an evolutionarily conserved regulator of homeostasis. Our focus is on a key mediator of this inflammation-induced response, prostaglandin (PG)E2, which is produced through the cyclooxygenase (COX) pathway. The established view is that circulating cytokines (i.e. ascending inflammation signals) cause de novo induction of COX2, an inducible isozyme of COX, in the brain. The COX2-derived PGE2 in turn acts in the brain to elicit the response. However, COX2 induction is slow; it has become increasingly clear that COX1, a constitutive isozyme, is crucial for the early-onset of HPA axis response. This points to a biphasic mode of PGE2 synthesis and raises a question `what are the early ascending signals for the COX1-mediated PGE2 synthesis?' Furthermore, whether produced through COX1 or COX2, it is unclear how PGE2 elicits the HPA axis response. It has been shown that two subtypes of PGE receptor, namely EP1 and EP3, contribute to the HPA axis response. It remains to be examined whether distinct EP subtypes are coupled to COX1- and COX2-derived PGE2 actions. ******Hypothesis: Multiple COX and EP receptor subtypes work in temporally supplementary manners to drive the HPA axis response.******Long-term goal: to clarify the mechanisms underlying the biphasic synthesis and actions of PGE2 by primarily focusing on (less understood) COX1 and early onset of the HPA axis response.******In order to resolve the rapid PGE2 synthesis by `constitutive' COX1, we will use electrophysiological approaches in brain slices that contain the command neurons of the HPA axis. We will assess PGE2-dependent excitation of the command neurons as a readout for the rapid PGE2 synthesis. We will also clarify specific EP subtypes involved in PGE2 actions.******Short-term goals:***1) To examine the role of ascending neural inputs (noradrenaline) in eliciting COX1-mediated PGE2 synthesis.***2) To clarify which EP receptor subtypes, and how they mediate the excitatory actions of PGE2 on the HPA axis command neurons. ***3) To determine whether COX1- and COX2-derived PGE2 act on distinct EP receptor subtypes.******The success of our research program will establish the basis for the biphasic mode of PGE2 function and fill the gap in our understanding of the early-onset of HPA axis response. The significance of this finding is that `redundancy' (multiple isozymes and receptors) is instrumental for an optimal functioning of the system (the early-onset and delayed-sustained HPA axis outputs). Our research program will also provide a rich training environment in system biology and state of the art techniques (e.g patch clamp electrophysiology and optogenetics).