Cell-type specific GABA signaling is required for newborn neuron incorporation

描述(由申请人提供)： 可以说，创伤性脑损伤是影响退伍军人的最重要的神经问题，会导致顽固性癫痫和令人衰弱的认知缺陷等破坏性问题。虽然最初的损伤对决定最终结果很重要，但这些问题中的许多直到几年后才显现出来。这些延迟的后遗症被认为是由于病理可塑性，包括细胞死亡、轴突发芽和蛋白质表达的变化。最近，成人神经发生的研究已经成为一种很有前途的方法，为深入了解脑损伤的机制和潜在的治疗方法提供了帮助。移植的胚胎间神经元已在许多神经疾病的动物模型中用于改善症状，脑损伤后内源性神经发生得到显著增强。然而，这些新生神经元中的许多在形态和功能上都非常异常，实际上可能导致脑损伤后的病理变化。我们理解损伤后病理可塑性的一个关键漏洞是理解指导新生神经元如何结合到正常成人神经回路中的信号。GABA受体(GABA受体)是指导神经元增殖、迁移和突触整合的重要形态发生分子。GABAR是一种异五聚体蛋白质复合体，通常含有2 1、2 2和单个3或4亚单位蛋白质。1亚基异构体(11-6)的同一性是GABAR功能的关键决定因素，能够在GABAR的动力学性质和药理敏感性方面产生深刻的差异。虽然含有GABAR的11个是成熟神经元突触抑制的主要介质，但从14个到12个，3个到11个主要的GABA能信号在胚胎神经元和成年新生神经元中都有非常一致的发现。在成人脑损伤后，也经常遇到类似的表达程序跟随已经建立的神经元。虽然GABA通常会引起抑制性反应，但在这一过渡时期，GABAR的激活会产生去极化反应，使GABA成为一种强大的形态原。去极化GABA的扰动会导致神经元的异常成熟，这严重依赖于细胞类型(中间神经元与主细胞)和相关的发育阶段。虽然GABAR的功能很明显地依赖于亚单位的组合，但在神经元整合过程中特定的GABAR表达模式的重要性仍然知之甚少。为了阐明特定的GABAR亚基组合的作用，我们将表征GABAR亚基亚基异构体表达的随时间的演变，以及主要表达的GABAR的生物物理性质。最后，我们将使用急性脑片记录结合组织后形态和免疫细胞化学分析，将GABA能信号的变化作为细胞类型和成熟状态的函数进行关联。最重要的假设是，具有独特生物物理性质的特定GABAR亚单位亚型的表达以细胞类型特定的方式与神经元成熟在空间和时间上锁定，以有效地介导整合到功能回路中所需的GABA能信号的演变角色。我们的龙 学期目标是了解这一系统在脑损伤后如何病理重现，并利用这些信息开发特定的药物治疗方法来预防和治疗脑损伤的慢性神经后遗症。

DESCRIPTION (provided by applicant): Traumatic brain injury is arguably the most significant neurological problem affecting our Veterans, leading to such devastating problems as refractory epilepsy and debilitating cognitive deficits. While the initial injury is important in determining eventual outcome, many of these problems do not manifest themselves until several years later. These delayed sequelae are thought to be due to pathological plasticity, including cell death, axonal sprouting, and changes in protein expression. Recently, the study of adult neurogenesis has emerged as a promising approach to provide both insight into the mechanisms of and potential treatment for brain injury. Transplanted embryonic interneurons have been used to ameliorate symptoms in a number of animal models of neurological disorders, and endogenous neurogenesis is robustly enhanced following brain injury. However, many of these newborn neurons are morphologically and functionally very abnormal, and may actually contribute to pathological changes following brain injury. A key hole in our understanding of pathological postinjury plasticity is an understanding o the signals directing how newborn neurons become incorporated into normal adult circuits. GABAA Receptors (GABARs) are particularly crucial morphogenic molecules directing neuronal proliferation, migration and synaptic integration. GABARs are heteropentameric protein complexes, typically containing 2 1, 2 2 and either a single 3 or 4 subunit protein. The identity o the 1 subunit isoform (11-6) is a key determinant of GABAR function, capable of producing profound differences in the kinetic properties and pharmacological sensitivity of GABARs. While 11 containing GABARs are the primary mediators of synaptic inhibition in mature neurons, there is a progression from 14 to 12,3 to 11 predominant GABAergic signaling that is an extraordinarily consistent finding in both embryonic neurons, as well as newborn neurons of the adult. A similar program of expression has also frequently encountered following already established neurons following adult brain injury. While GABA generally evokes inhibitory responses, activation of GABARs during this transitional period produces depolarizing responses, allowing GABA to serve as a powerful morphogen. Perturbations of depolarizing GABA cause aberrant neuronal maturation that depends critically on the cell type (interneuron vs principal cell) and developmental stage in question. While it is clear that GABAR function depends critically on the subunit combination, the significance of specific GABAR expression patterns during neuronal incorporation remain very poorly understood. In order to elucidate the role of specific GABAR subunit combinations, we will characterize the time-dependent evolution of GABAR subunit isoform expression, as well as the biophysical properties of the predominant GABARs being expressed. Finally acute brain slice recording with post-hoc morphological and immunocytochemical analysis will be used to correlate the changes in GABAergic signaling as a function of cell-type and maturational state. The overarching hypothesis is that the expression of specific GABAR subunit isoforms with unique biophysical properties are spatially and temporally locked with neuronal maturation in a cell-type specific manner to effectively mediate the evolving roles of GABAergic signaling required for incorporation into functional circuits. Our long term goal is to understand how this system becomes pathologically recapitulated following brain injury, and use this information to develop specific pharmacological treatments to prevent and treat the chronic neurological sequelae of brain injury.