Structural and Functional Alterations of Interneurons in Models of Schizophrenia

描述(申请人提供)：精神分裂症与表达钙结合蛋白小白蛋白(PV)的皮质中间神经元亚群中GABA合成减少有关。这些抑制性中间神经元表现出快速的尖峰特性，并以兴奋性锥体神经元的体周区域和轴突起始段为靶点，从而能够精确地控制它们的尖峰时序。精神分裂症患者肢体周围抑制的缺陷可能导致快速皮质网络同步和高级认知加工的障碍，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包裹其胞体和初级突起的细胞外基质分子的致密聚集体，出现为神经周围神经网络(PNN)。这些PNN的形成和降解是活动依赖的，但它们在精神分裂症中的功能和调节仍不清楚。我们的假设是：1)精神分裂症的PV中间神经元可塑性与PNNS的结构重构有关；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：他莫昔芬诱导显性负DISC1 C末端片段(DISC1-cc)在1-CaMKII表达的神经元中的表达和在前脑GABA能中间神经元(Ppp1r2-Cre x NR1loxP/loxP小鼠)中选择性地敲除NMDA受体。在固定组织中使用受激辐射耗竭(STED)超分辨显微镜(纳米显微镜)检测PV中间神经元传入终末周围的PNN的超微结构。精神分裂症患者皮质PV中间神经元抑制输出的缺陷被认为导致兴奋性锥体神经元的过度活动和低同步性，并导致认知功能障碍。PV中间神经元也表现出紧密的相互连接，但这种相互抑制的可能病理生理学仍未被探索。来自PV中间神经元的体外膜片钳记录将阐明这些相互作用的GABA能信号的多种模式和内在膜特性在精神分裂症小鼠模型中是如何被改变的。我们认为，PV中间神经元周围PNN的重塑以及隔区化突触和突触外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。了解精神分裂症患者GABA能抑制的多个方面是如何受到干扰的，对于合理设计GABA能治疗药物是至关重要的。此外，阐明PNNS在PV中间神经元功能和功能障碍中的特殊作用将启发针对PNN降解的蛋白酶的新的治疗策略。 公共卫生相关性：精神分裂症是一种令人衰弱的精神疾病，影响着约240万美国人，占世界成年人口的约1%。这种综合征被认为是通过大脑发育过程中多种遗传和环境因素的相互作用而产生的，导致多巴胺能、谷氨酸能、GABA能和胆碱能神经递质系统持续功能障碍直到成年。目前治疗精神分裂症的单胺类药物在治疗阳性症状方面最有效，包括幻觉和/或妄想。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的影响。有研究表明，精神分裂症患者的认知功能障碍可能与皮质GABA能传递障碍有更密切的联系。解决这种功能障碍的潜力很大，因为GABAA受体在亚基组成上表现出高度的异质性，这反映在不同细胞类型和大脑区域的不同表达模式上，并为选择性药物调节提供了机会。然而，GABA能疗法的合理设计需要更详细地理解GABA受体介导的信号的多个方面的功能失衡是如何导致精神分裂症症状的。

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.