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），然后激活下丘脑-垂体-肾上腺（HPA）轴的新信息，HPA轴是一种进化上保守的稳态调节器。我们的重点是这种炎症诱导的反应，前列腺素（PG）E2，这是通过环氧合酶（考克斯）途径产生的关键介质。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 2（一种考克斯的诱导型同工酶）的从头诱导。COX 2衍生的PGE 2反过来在大脑中起作用以引起反应。然而，COX 2的诱导是缓慢的，它已经变得越来越清楚，COX 1，组成型同工酶，是至关重要的HPA轴反应的早期发作。这表明PGE 2合成的双相模式，并提出了一个问题：“COX 1介导的PGE 2合成的早期上升信号是什么？”此外，无论是通过COX 1还是COX 2产生，目前还不清楚PGE 2如何引起HPA轴反应。研究表明，PGE受体的两种亚型，即EP 1和EP 3，参与HPA轴反应。不同的EP亚型是否与COX 1和COX 2衍生的PGE 2作用相关还有待研究。 假设：多种考克斯和EP受体亚型以时间互补的方式驱动HPA轴反应。 长期目标：阐明PGE 2的双相合成和作用的机制，主要关注（了解较少）COX 1和HPA轴反应的早期发作。 为了解决快速PGE 2合成的“组成型”COX 1，我们将使用电生理方法在大脑切片，包含HPA轴的命令神经元。我们将评估PGE 2依赖的兴奋的命令神经元作为读出的快速PGE 2合成。我们还将阐明参与PGE 2作用的特定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PGE 2合成中的作用。 2)阐明哪些EP受体亚型，以及它们如何介导PGE 2对HPA轴命令神经元的兴奋作用。 3)确定COX 1和COX 2衍生的PGE 2是否作用于不同的EP受体亚型。 我们的研究计划的成功将建立PGE 2功能的双相模式的基础，并填补了我们对HPA轴反应早发性的理解的差距。这一发现的意义在于，“冗余”（多种同工酶和受体）有助于系统的最佳功能（早发性和延迟持续的HPA轴输出）。我们的研究计划还将提供系统生物学和最先进技术（例如膜片钳电生理学和光遗传学）的丰富培训环境。

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).