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

调节动态平衡的神经机制必须有效地感知扰动并迅速做出反应。NSERC的这项研究计划将提供有关大脑如何感知上升的警告信号(例如外周炎症)的新信息，然后激活下丘脑-垂体-肾上腺(HPA)轴，这是一种进化上保守的动态平衡调节器。我们的重点是这种炎症诱导反应的关键介质-前列腺素(PG)E2，它是通过环氧合酶(COX)途径产生的。已有的观点认为，循环中的细胞因子(即上升的炎症信号)导致COX2在大脑中从头开始诱导，COX2是COX的一种可诱导的同工酶。COX2衍生的PGE2反过来在大脑中起作用，引发反应。然而，COX2的诱导是缓慢的；越来越清楚的是，COX1是一种结构性同工酶，对于HPA轴反应的早期发生至关重要。这指向了PGE2合成的两相模式，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是如何引起HPA轴反应的还不清楚。研究表明，PGE受体的两个亚型，即EP1和EP3参与了HPA轴的反应。不同的EP亚型是否与COX1和COX2衍生的PGE2作用偶联仍有待研究。*假设：多种COX和EP受体亚型以时间互补的方式工作以驱动HPA轴的反应。*长期目标：通过主要关注(较少了解的)COX1和HPA轴反应的早期开始，阐明PGE2双相合成和作用的机制。*为了解决COX1的快速合成PGE2的问题，我们将在包含HPA轴指挥神经元的脑片上使用电生理学方法。我们将评估命令神经元对PGE2的依赖兴奋，以此作为快速合成PGE2的读数。我们还将阐明参与PGE2作用的特定EP亚型。*短期目标：*1)研究上升神经输入(去甲肾上腺素)在诱导COX1介导的PGE2合成中的作用。*2)阐明哪些EP受体亚型，以及它们如何介导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。*我们的研究计划的成功将为PGE2功能的双相模式奠定基础，并填补我们对HPA轴反应早发的认识空白。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(早发性和延迟性持续的HPA轴输出)。我们的研究计划还将提供丰富的系统生物学和最新技术(如膜片钳、电生理学和光遗传学)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).