Corticosterone Metabolism Locally Regulates Glucocorticoid Exposure in Brain

 描述(申请人提供)：糖皮质激素(CORT)是生理、行为和认知的重要媒介。皮质醇受体在脊椎动物的大脑中表达，并在调节这些反应中发挥关键作用；然而，局部控制皮质醇水平是必要的，因为过度暴露可能是有害的，导致神经元死亡和神经发生的抑制(Miresu和Gould，2006；Sapolsky等人，1985)。大脑实现这种控制的一种方式是通过皮质醇代谢酶11β羟基类固醇脱氢酶1(11βHSD1)和2(11βHSD2)的作用，它们分别重新激活和去激活皮质醇。虽然成年啮齿动物的大脑似乎丰富地表达11βHSD1，但不表达11βHSD2(Holmes等人，2006年)，而鸣禽的大脑表达类型2，先前的研究表明，这种表达可能与大脑皮质中产生的区域差异和大脑对应激影响的缓冲有关(Katz等人，2010年；Rensel等人，2014年)。此外，尚不清楚啮齿动物模型是否准确地代表了支配人类皮质醇暴露的神经内分泌系统；因此，需要替代模型。这项拟议的研究有两个具体目标：首先，该研究将检验这样一个假设，即皮质醇代谢酶11βhsd1和11βhsd2协同作用，动态调节不同大脑区域的皮质醇水平，并限制血液进入大脑的波动。实验将评估这两种酶在鸣禽大脑中的区域分布，然后利用体外测试来建立对CORT反应的酶活性和特异性。此外，11βHSD抑制剂的体内微透析和反透析将在海马区进行，以评估11βHSD 2型作为缓冲来自外周的皮质醇升高的功能效果。先前的研究发现，雄性鸣禽侧脑室区域(VZ)的神经发生被皮质醇减少，但雌性没有，这表明雌性更大的皮质醇失活可能具有神经保护作用(Katz等人，2008年)。这项研究的第二个具体目标将检验11个βHSD对这种性别差异负有责任的假设。包含外侧VZ的大脑部分将暴露在CORT中，并使用或不使用11βHSD抑制剂，BrdU标记将被量化。因此，在多个组织水平(体外和体内)进行的实验，以及对皮质醇的mRNA、酶活性和直接神经测量的测量，将确定大脑中局部皮质醇暴露的控制机制的本质。这项研究有可能揭示皮质醇调节的新机制，并为以糖皮质激素过量和调节失调为特征的人类疾病的未来治疗提供信息。

 DESCRIPTION (provided by applicant): Glucocorticoids (CORT) are essential mediators of physiology, behavior, and cognition. CORT receptors are expressed in the vertebrate brain and play a key role in mediating these responses; however, local control over CORT levels is necessary because over-exposure can be detrimental, leading to neuronal death and inhibition of neurogenesis (Mirescu and Gould, 2006; Sapolsky et al., 1985). One way the brain may achieve this control is through the actions of CORT-metabolizing enzymes 11β hydroxysteroid dehydrogenase types 1 (11β HSD1) and 2 (11β HSD2), which re-activate and de-activate CORT, respectively. While the adult rodent brain appears to abundantly express 11β HSD1 but not 11β HSD2 (Holmes et al., 2006), the songbird brain expresses type 2 and previous research has shown that this expression may be responsible for producing a regional difference in brain CORT and a buffering of the brain from the effects of stress (Katz et al., 2010; Rensel et al., 2014). In addition, it is unclear whether the rodent model is an accurate representation of the neuroendocrine system governing CORT exposure in humans; therefore there is a need for alternative models. The proposed research has two specific aims: first, the research will test the hypothesis that the CORT-metabolizing enzymes 11β HSD1 and 11β HSD2 act in concert to dynamically regulate CORT levels in discrete brain regions and limit fluctuations in blood from reaching the brain. Experiments will assess the regional distribution of both enzymes in the songbird brain, then utilize in vitro assays to establish enzyme activity and specificity in response to CORT. In addition, in vivo microdialysis and retrodialysis of an 11β HSD inhibitor will be employed in the hippocampus to assess the functional effects of 11β HSD type 2 as a buffer against CORT elevation coming from the periphery. Previous research found that neurogenesis in the songbird lateral ventricular zone (VZ) is reduced by CORT in males but not females, suggesting greater CORT inactivation in females that may be neuroprotective (Katz et al., 2008). The second specific aim of this research will test the hypothesis that the 11β HSDs are responsible for this sex difference. Sections of brain containing the lateral VZ will be exposed to CORT with or without an 11β HSD inhibitor and BrdU labeling will be quantified. Thus, experiments conducted at multiple levels of organization (both in vitro and in vivo) as well as measures of mRNA, enzyme activity, and direct neural measures of CORT will establish the nature of the mechanisms controlling local CORT exposure in brain. This research has the potential to uncover novel mechanisms of CORT regulation and inform development of future treatments for human disease characterized by glucocorticoid excess and dysregulation.