Novel actions of neurosteroids on GABA (A) receptor trafficking

神经活性类固醇（NAS），如别孕烯醇酮（ALLO），通过调节行为发挥核心作用。 其有效的抗焦虑、抗惊厥、镇静和催眠作用。因此，在水平上的修改 NAS会导致焦虑、自闭症谱系障碍、抑郁、癫痫和经前综合征。 经典地，NAS被认为通过快速增强神经元抑制来起作用，所述神经元抑制是通过以下方式进行的： γ-氨基丁酸A型受体（GABAARs）的活性。除了它们的变构作用外，我们还有 最近表明，NASs通过蛋白激酶C依赖性机制发挥作用， 包括β3亚基（S408/9）中丝氨酸408和409的残基，这是一个增加GABAAR数量的过程 导致GABA能抑制功效的持续增加。虽然我们 已经表明NASs不直接激活PKC，而PKC是NASs导致 GABAAR亚基的磷酸化是未知的。研究表明，除了积极的变构作用外， 调节GABAAR，NAS可直接激活膜孕酮受体（mPR）; G蛋白 偶联受体调节PKC信号。然而，没有关于mPR所起作用的信息 调节GABAAR活性。同样，持续的mPR介导的 NAS的促代谢作用仍然未被探索。为了解决这些问题，我们创造了小鼠， β3亚基中的S408/9已突变为丙氨酸，预测这些突变会降低β 3亚基的表达。 NASs对GABAAR功能的促代谢作用。使用这些工具的初步研究使我们能够 提出了一个中心假设，将在这里进行测试; NAS激活mPR，以增强 β3亚基中包括S408/9在内的残基上GABAAR的磷酸化， 是其抗惊厥功效的基础。相比之下，它们的抗焦虑功效是通过变构介导的。 增强GABAAR活性，这是一个依赖于α2亚基中Q241的过程。我们的实验将 重点实现以下目标。 目标1.为了验证NAS诱导GABA能持续作用的能力， 抑制作用依赖于β3亚基中的S408/9A。 目标2.检验NAS的抗焦虑和抗惊厥疗效依赖于 在β3亚基中的S408/9上。 目标3：为了检验NAS通过GABAAR介导其代谢效应的假设， 激活mPR。 总的来说，我们的建议将确定NAS发挥其治疗作用的分子机制。 这些信息可能有助于开发新的治疗策略，以减轻焦虑的负担， 自闭症谱系障碍、抑郁症、癫痫和经前综合征。

Neuroactive steroids (NASs) such as allopregnanolone (ALLO) play a central role in regulating behavior via their potent anxiolytic, anticonvulsant, sedative, and hypnotic actions. Accordingly, modifications in the levels of NASs contribute to anxiety, autism spectrum disorders, depression, epilepsy, and premenstrual syndrome. Classically, NASs are thought to act by rapidly boosting neuronal inhibition by positive allosteric modulation of the activity of γ-aminobutyric acid type A receptors (GABAARs). In addition to their allosteric actions, we have recently shown that NASs act via a protein kinase C-dependent mechanism to enhance the phosphorylation of residues including Serine’s 408 and 409 in the β3 subunit (S408/9), a process that increases GABAAR number on the plasma membrane leading to a sustained increase in the efficacy of GABAergic inhibition. Although we have shown that NASs do not directly activate PKC, the mechanism by which NASs lead to changes in phosphorylation of GABAAR subunits are unknown. It is emerging that in addition to their positive allosteric modulation of GABAARs, NASs can directly activate membrane progesterone receptors (mPRs); G-protein coupled receptors that regulate PKC signaling. However, no information is available on the role that mPRs play in regulating GABAAR activity. Likewise, the behavioral significance of the sustained mPR-mediated metabotropic actions of NASs remains unexplored. To address these issues we have created mice in which S408/9 in the β3 subunit have been mutated to alanines, mutations that are predicted to reduce the metabotropic actions of NASs on GABAAR function. Preliminary studies using these tools have allowed us to formulate a central hypothesis that will be tested here; NASs activate mPRs to enhance the phosphorylation of GABAARs on residues including S408/9 in the β3 subunit, a mechanism that underlies their anticonvulsant efficacy. In contrast, their anxiolytic efficacy is mediated via allosteric potentiation of GABAAR activity, a process dependent upon Q241 in the α2 subunit. Our experiments will focus on the following aims. Aim 1. To test the hypothesis that the ability of NAS to induce sustained effects on GABAergic inhibition is dependent upon S408/9A in the β3 subunit. Aim 2. To test the hypothesis that the anxiolytic, and anticonvulsant efficacy of NASs is dependent upon S408/9 in the β3 subunit. Aim 3. To test the hypothesis that NASs mediate their metabotropic effects on GABAARs via the activation of mPRs. Collectively, our proposal will identify the molecular mechanisms by which NAS exert their therapeutic actions. This information may aid the development of new therapeutic strategies to alleviate the burdens of anxiety, autism spectrum disorders, depression, epilepsy, and premenstrual syndrome.