Structural and Functional Alterations of Interneurons in Models of Schizophrenia

描述（由申请人提供）：精神分裂症与表达钙结合蛋白小清蛋白（PV）的皮质中间神经元亚群中GABA合成减少相关。这些抑制性中间神经元显示出快速尖峰特性，并靶向兴奋性锥体神经元的体周域和轴突起始段，从而能够精确控制其尖峰时间。精神分裂症患者这种躯体周围抑制的缺陷可能导致快速皮层网络同步和高级认知处理的损害，这是这种致残性精神障碍的关键特征。皮质PV中间神经元的另一个显著特征是细胞外基质分子的密集聚集体，其包裹它们的胞体和初级突起，表现为神经元周网（PNN）。这些PNN的形成和降解是活性依赖性的，但它们在精神分裂症中的功能和调节仍然未知。我们的假设是：1）精神分裂症中PV中间神经元的可塑性与PNNs的结构重塑有关，2）PV中间神经元之间的相互抑制功能障碍，可能继发于PNNs结构的改变，是精神分裂症中GABA能缺陷的关键组成部分。我们将使用两个最近表征的精神分裂症转基因小鼠模型：他莫昔芬诱导表达的显性阴性DISC 1 C-末端片段（DISC 1-cc）在1-CaMKII表达神经元和选择性敲除NMDA受体前脑GABA能中间神经元（Ppp 1 r2-Cre x NR 1 loxP/loxP小鼠）。PV中间神经元上的传入末梢周围的PNN的超微结构将使用固定组织中的受激发射损耗（STED）超分辨率显微镜（纳米镜）来确定。精神分裂症中皮质PV中间神经元的抑制性输出的缺陷被认为导致兴奋性锥体神经元的过度活跃和同步性减退，并导致认知功能的缺陷。PV中间神经元也显示出密集的相互连接，但这种相互抑制的可能病理生理学仍未被探索。PV中间神经元的膜片钳记录将阐明这些相互GABA能信号传导和内在膜特性的多种模式在精神分裂症小鼠模型中是如何改变的。我们认为PV中间神经元周围PNNs的重塑以及分隔化的突触和突触外GABA能信号通路的侵蚀是精神分裂症皮质网络去抑制的关键组成部分。了解GABA能抑制的多个方面在精神分裂症中是如何受到干扰的，对于GABA能治疗的合理设计至关重要。此外，阐明PNN在PV中间神经元的功能和功能障碍中的特殊作用，应该激发新的治疗策略，靶向负责PNN降解的蛋白酶。 精神分裂症是一种使人衰弱的精神障碍，影响约240万美国人，约占世界成年人口的1%。这种综合征被认为是在大脑发育过程中通过多种遗传和环境因素的相互作用而产生的，导致多巴胺能、多巴胺能、GABA能和胆碱能神经递质系统持续功能障碍直至成年。目前用于精神分裂症的单胺能治疗在治疗阳性症状（包括幻觉和/或妄想）方面是最有效的。然而，这种抗精神病药物对阴性症状和认知障碍的负担几乎没有改善，这可能对患者的长期社会和职业能力产生最大影响。有研究表明，精神分裂症的认知功能障碍可能与皮质GABA能传递缺陷有更密切的联系。解决这种功能障碍有很大的潜力，因为GABAA受体在亚基组成中显示出高度的异质性，这反映在跨细胞类型和脑区域的不同表达模式中，并赋予选择性药理学调节的机会。然而，GABA能治疗的合理设计需要更详细地了解GABAA受体介导的信号传导的多个方面的功能失衡如何导致精神分裂症症状。

DESCRIPTION (provided by applicant): Schizophrenia is associated with a reduction in GABA synthesis in a subpopulation of cortical interneurons that express the calcium-binding protein, parvalbumin (PV). These inhibitory interneurons display fast-spiking properties and target the perisomatic domain and axon initial segment of excitatory pyramidal neurons, thus enabling exquisite control over their spike timing. A deficit in such perisomatic inhibition in schizophrenia is likely to contribute to the impairments of fast cortical network synchronization and higher cognitive processing, which are key features of this disabling mental disorder. Another distinguishing characteristic of cortical PV interneurons are the dense aggregates of extracellular matrix molecules that ensheath their somata and primary processes, appearing as perineuronal nets (PNNs). The formation and degradation of these PNNs are activity-dependent, but their function and modulation in schizophrenia remain unknown. Our hypotheses are that 1) PV interneuron plasticity in schizophrenia is related to structural remodeling of PNNs, and 2) dysfunction of reciprocal inhibition between PV interneurons, possibly secondary to the altered structure of PNNs, is a key component of GABAergic deficits in schizophrenia. We will use two recently characterized transgenic mouse models of schizophrenia: the tamoxifen-inducible expression of the dominant-negative DISC1 C-terminal fragment (DISC1-cc) in 1-CaMKII expressing neurons and the selective knockout of NMDA receptors in forebrain GABAergic interneurons (Ppp1r2-Cre x NR1loxP/loxP mice). The ultrastructure of PNNs surrounding afferent terminals on PV interneurons will be determined using stimulated emission depletion (STED) super-resolution microscopy (nanoscopy) in fixed tissue. A deficiency in the inhibitory output of cortical PV interneurons in schizophrenia is thought to lead to hyperactivity and hyposynchrony of excitatory pyramidal neurons, and contribute to deficits in cognitive function. PV interneurons also show dense reciprocal connectivity, but the possible pathophysiology of such mutual inhibition remains unexplored. Patch-clamp recordings from PV interneurons in vitro will elucidate how these multiple modes of reciprocal GABAergic signaling and intrinsic membrane properties are modified in mouse models of schizophrenia. We propose that remodeling of the PNNs surrounding PV interneurons, and the erosion of compartmentalized synaptic and extrasynaptic GABAergic signaling pathways are critical components of the cortical network disinhibition in schizophrenia. Understanding how the multiple facets of GABAergic inhibition are disturbed in schizophrenia is essential for the rational design of GABAergic therapeutics. Moreover, elucidating the particular role of PNNs in both the function and dysfunction of PV interneurons should inspire new treatment strategies targeting the proteases responsible for PNN degradation. PUBLIC HEALTH RELEVANCE: Schizophrenia is a debilitating mental disorder that affects ~2.4 million Americans, and ~1% of the world's adult population. This syndrome is thought to arise through an interaction of multiple genetic and environmental factors during brain development, leading to a persistent dysfunction of dopaminergic, glutamatergic, GABAergic and cholinergic neurotransmitter systems into adulthood. Current monoaminergic treatments for schizophrenia are most effective in treating positive symptoms, comprising hallucinations and/or delusions. However, such antipsychotics yield little amelioration of the burden of negative symptoms and cognitive impairments, which may have the greatest impact on patients' long-term social and occupational abilities. It has been suggested that cognitive dysfunction in schizophrenia might be more intimately linked with deficits in cortical GABAergic transmission. There is great potential for addressing such dysfunction, as GABAA receptors display a high degree of heterogeneity in subunit composition, which is reflected in distinct patterns of expression across cell types and brain regions, and confers the opportunity for selective pharmacological modulation. The rational design of GABAergic therapeutics, though, will require a more detailed understanding of how functional imbalances in the multiple facets of GABAA receptor-mediated signaling contribute to schizophrenic symptoms.