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尖峰特性，并以兴奋性锥体神经元的周围结构域和轴突初始段为靶点，从而能够精确控制其尖峰时间。在精神分裂症中，这种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损伤，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，它们包裹着它们的体细胞和初级突起，表现为神经元周围网（pnn）。这些pnn的形成和降解是活性依赖的，但它们在精神分裂症中的功能和调节尚不清楚。我们的假设是：1)精神分裂症患者PV中间神经元的可塑性与pnn的结构重塑有关；2)PV中间神经元间互抑功能障碍可能继发于pnn结构改变，是精神分裂症患者gaba能缺陷的关键组成部分。我们将使用两种最近表征的精神分裂症转基因小鼠模型：在表达1-CaMKII的神经元中，他莫昔芬诱导显性阴性DISC1 c -末端片段（DISC1-cc）的表达，以及在前脑gaba能中间神经元中选择性敲除NMDA受体（Ppp1r2-Cre x NR1loxP/loxP小鼠）。在固定组织中，利用受激发射损耗（STED）超分辨率显微镜（纳米显微镜）测定PV中间神经元传入末端周围pnn的超微结构。精神分裂症患者皮层PV中间神经元抑制输出的缺失被认为会导致兴奋性锥体神经元的过度活跃和低同步性，并导致认知功能的缺陷。PV中间神经元也表现出密集的相互连接，但这种相互抑制的可能病理生理机制尚不清楚。来自PV中间神经元的膜片钳记录将阐明在精神分裂症小鼠模型中，这些相互的gaba能信号传导和内在膜特性的多种模式是如何被改变的。我们认为，PV中间神经元周围pnn的重塑，以及区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。理解精神分裂症中gaba能抑制的多个方面是如何受到干扰的，对于合理设计gaba能疗法至关重要。此外，阐明PNN在PV中间神经元功能和功能障碍中的特殊作用，将激发针对PNN降解蛋白酶的新治疗策略。

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.