Neurosteroid Modulation of GABA(A) Receptors

描述（由申请人提供）：癫痫是一种使人衰弱的疾病，影响1-2%的人口。抗惊厥药物治疗是治疗的选择，然而约30%的癫痫对药物治疗难以治愈，需要手术切除脑组织。此外，抗惊厥药物非特异性地降低整个大脑的神经元兴奋性，导致镇静和嗜睡作为副作用。因此，持续需要开发新的抗癫痫药物。拟议研究的总体目标是通过研究一类新的抗惊厥药物神经类固醇的机制来帮助开发新的抗癫痫药物疗法。神经类固醇在大脑中合成，通过调节GABAA受体（大脑中主要的抑制性神经递质受体）来调节神经元的兴奋性。在临床试验中，合成神经类固醇已被证明是有效的抗癫痫药物，甚至可以治疗其他耐药性癫痫。此外，神经类固醇有可能被设计成具有更大的特异性，以减少副作用。将采取两种方法来更好地理解GABAA受体的神经类固醇调节。首先，为了获得神经类固醇机制的基本见解，我们将研究一个简单的、具有良好特征的类固醇-受体相互作用：硫酸孕烯醇酮（PS）对秀丽隐杆线虫UNC-49受体的抑制作用。快速配体交换方法将用于表征UNC-49的PS调制机制，并确定关键残基如何作为PS调制的效应器。由于UNC-49是高度保守的GABAA受体同源物，本研究结果将适用于理解人类神经类固醇调节。其次，将利用UNC-49独特的药理学性质进行结构域交换实验，直接鉴定人类GABAA受体中神经类固醇调节的重要残基。这两种方法的结果将增加对内源性神经类固醇如何调节癫痫易感性的理解，并将有助于设计新的抗癫痫药物。

DESCRIPTION (provided by applicant): Epilepsy is a debilitating disease that affects 1-2% of the population. Anticonvulsant drug therapy is the treatment of choice, however about 30% of epilepsies are intractable to drug therapy, and necessitate surgical removal of brain tissue. In addition, anticonvulsant drugs reduce neuronal excitability non-specifically throughout the brain, leading to sedation and somnolence as side effects. Thus, there is an ongoing need to develop new anti-epileptic drugs. The overall goals of the proposed research are to help develop new anti-epileptic drug therapies by investigating the mechanisms of a new class of anticonvulsant drugs, the neurosteroids. Neurosteroids are synthesized in the brain, and regulate neuronal excitability by modulating GABAA receptors (the major inhibitory neurotransmitter receptors in the brain). Synthetic neurosteroids have proven to be effective anti-epileptic drugs in clinical trials, even against otherwise drug resistant epilepsies. Moreover, neurosteroids can potentially be engineered for greater specificity, to reduce side-effects. Two approaches will be taken to better understand neurosteroid modulation of GABAA receptors. First, to gain fundamental insights into neurosteroid mechanisms, a simple, well-characterized steroid-receptor interaction will be studied: The inhibition of the C. elegans UNC-49 receptor by pregnenolone sulfate (PS). Rapid ligand exchange methods will be used to characterize the mechanism of PS modulation of UNC-49, and to determine how the key residues act as effectors of PS modulation. Results of this study will be applicable to understanding neurosteroid modulation in humans because UNC-49 is a highly conserved GABAA receptor homologue. Second, the unique pharmacological properties of UNC-49 will be exploited in domain swap experiments to directly identify residues important for neurosteroid modulation in human GABAA receptors. The results of both approaches will increase understanding of how endogenous neurosteroids regulate seizure susceptibility, and will aid the design of new anti-epileptic drugs.