A hallmark of schizophrenia pathophysiology is the dysfunction of cortical inhibitory GABA neurons expressing parvalbumin, which are essential for coordinating neuronal synchrony during various sensory and cognitive tasks. The high metabolic requirements of these fast-spiking cells may render them susceptible to redox dysregulation and oxidative stress. Using mice carrying a genetic redox imbalance, we demonstrate that extracellular perineuronal nets, which constitute a specialized polyanionic matrix enwrapping most of these interneurons as they mature, play a critical role in the protection against oxidative stress. These nets limit the effect of genetically impaired antioxidant systems and/or excessive reactive oxygen species produced by severe environmental insults. We observe an inverse relationship between the robustness of the perineuronal nets around parvalbumin cells and the degree of intracellular oxidative stress they display. Enzymatic degradation of the perineuronal nets renders mature parvalbumin cells and fast rhythmic neuronal synchrony more susceptible to oxidative stress. In parallel, parvalbumin cells enwrapped with mature perineuronal nets are better protected than immature parvalbumin cells surrounded by less-condensed perineuronal nets. Although the perineuronal nets act as a protective shield, they are also themselves sensitive to excess oxidative stress. The protection might therefore reflect a balance between the oxidative burden on perineuronal net degradation and the capacity of the system to maintain the nets. Abnormal perineuronal nets, as observed in the postmortem patient brain, may thus underlie the vulnerability and functional impairment of pivotal inhibitory circuits in schizophrenia.critical period | extracellular matrix | glutamate cysteine ligase | glutathione | neuronal synchronization F ast-spiking interneurons expressing parvalbumin (PV) constitute a subpopulation of GABA cells that control the output of principal neurons and are necessary for fast rhythmic neuronal synchrony, facilitating information processing during cognitive tasks (1, 2). To coordinate the activity of neuronal assemblies, PV cells are interconnected by both chemical and electrical synapses, have the capacity to fire at high frequency without adaptation, and selectively position inhibitory synaptic terminals onto the cell body and axon initial segment of their target neurons. Fast-spiking properties consequently impose high metabolic demand and increased mitochondrial density, which renders PV cells, but not other interneurons such as calretinin and calbindin cells, particularly sensitive to oxidative stress (3). For instance, ketamine induces superoxide overproduction that strongly impairs PV cells (i.e., loss of normal phenotype including PV immunoreactivity but without cell death) (4, 5). Moreover, severe environmental stressors produce oxidative stress in the brain and impair PV cells (6)(7)(8). Postmortem studies reveal PV-cell anomalies in individuals with schizophrenia or bipolar disorder (9-11). ...

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Schizophrenia is a complex multifactorial brain disorder with a genetic component. Convergent evidence has implicated oxidative stress and glutathione (GSH) deficits in the pathogenesis of this disease. The aim of the present study was to test whether schizophrenia is associated with a deficit of GSH synthesis. Cultured skin fibroblasts from schizophrenia patients and control subjects were challenged with oxidative stress, and parameters of the ratelimiting enzyme for the GSH synthesis, the glutamate cysteine ligase (GCL), were measured. Stressed cells of patients had a 26% (P ‫؍‬ 0.002) decreased GCL activity as compared with controls. This reduction correlated with a 29% (P < 0.001) decreased protein expression of the catalytic GCL subunit (GCLC). Genetic analysis of a trinucleotide repeat (TNR) polymorphism in the GCLC gene showed a significant association with schizophrenia in two independent case-control studies. The most common TNR genotype 7/7 was more frequent in controls [odds ratio (OR) ‫؍‬ 0.6, P ‫؍‬ 0.003], whereas the rarest TNR genotype 8/8 was three times more frequent in patients (OR ‫؍‬ 3.0, P ‫؍‬ 0.007). Moreover, subjects with disease-associated genotypes had lower GCLC protein expression (P ‫؍‬ 0.017), GCL activity (P ‫؍‬ 0.037), and GSH contents (P ‫؍‬ 0.004) than subjects with genotypes that were more frequent in controls. Taken together, the study provides genetic and functional evidence that an impaired capacity to synthesize GSH under conditions of oxidative stress is a vulnerability factor for schizophrenia.genetic association ͉ glutamate cysteine ligase ͉ oxidative stress ͉ GAG trinucleotide repeat polymorphism ͉ skin fibroblasts

Parvalbumin inhibitory interneurons (PVIs) are crucial for maintaining proper excitatory/inhibitory balance and high-frequency neuronal synchronization. Their activity supports critical developmental trajectories, sensory and cognitive processing, and social behavior. Despite heterogeneity in the etiology across schizophrenia and autism spectrum disorder, PVI circuits are altered in these psychiatric disorders. Identifying mechanism(s) underlying PVI deficits is essential to establish treatments targeting in particular cognition. On the basis of published and new data, we propose oxidative stress as a common pathological mechanism leading to PVI impairment in schizophrenia and some forms of autism. A series of animal models carrying genetic and/or environmental risks relevant to diverse etiological aspects of these disorders show PVI deficits to be all accompanied by oxidative stress in the anterior cingulate cortex. Specifically, oxidative stress is negatively correlated with the integrity of PVIs and the extracellular perineuronal net enwrapping these interneurons. Oxidative stress may result from dysregulation of systems typically affected in schizophrenia, including glutamatergic, dopaminergic, immune and antioxidant signaling. As convergent end point, redox dysregulation has successfully been targeted to protect PVIs with antioxidants/redox regulators across several animal models. This opens up new perspectives for the use of antioxidant treatments to be applied to at-risk individuals, in close temporal proximity to environmental impacts known to induce oxidative stress.

A key feature of memory processes is to link different input signals by association and to preserve this coupling at the level of synaptic connections. Late-phase long-term potentiation (L-LTP), a form of synaptic plasticity thought to encode long-term memory, requires gene transcription and protein synthesis. In this study, we report that a recently cloned coactivator of cAMP-response elementbinding protein (CREB), called transducer of regulated CREB activity 1 (TORC1), contributes to this process by sensing the coincidence of calcium and cAMP signals in neurons and by converting it into a transcriptional response that leads to the synthesis of factors required for enhanced synaptic transmission. We provide evidence that TORC1 is involved in L-LTP maintenance at the Schaffer collateral-CA1 synapses in the hippocampus.BDNF ͉ calcineurin ͉ cAMP-response element-binding protein ͉ long-term potentiation ͉ memory T ransducers of regulated cAMP-response element-binding protein (CREB) activity (TORCs) are newly discovered coactivators that dramatically increase CREB's transcriptional activity independently of CREB Ser-133 phosphorylation (1, 2). Recently, it has been shown that TORC2 functions as a pancreatic coincidence detector. In insulinoma cells, glucose and gut hormones, via respective activation of L-type calcium channels and the cAMP pathway, synergistically promote the dephosphorylation and the concomitant nuclear translocation of TORC2 (3). In the brain, encoding and storing associative memories requires detection of the coincidence of different input signals and translation of these associations into changes in the number, structure, or function of synapses. Therefore, it appears that short-lived coincidences result in the transcriptional activation of genes encoding factors required for enhanced synaptic transmission. TORCs present two features that neurons could use to create an association: they can detect the coincidence of the two most important second messengers, calcium and cAMP, and they are potent coactivators of CREB, a transcription factor known to drive the expression of genes underlying synaptic plasticity, late-phase long-term potentiation (L-LTP), learning, and memory (4-7).CREB-dependent promoters have been generally thought to respond to various intracellular and extracellular cues by the stimulus-dependent phosphorylation of CREB at Ser-133 and resultant recruitment of the coactivator CREB binding protein (CBP) (5,6,8,9). Modification of CREB at this site often mirrors the activation of neurons, leading to the idea that the expression of plasticity-related genes relies on CREB/CBP interaction. However, some studies revealing a discrepancy between CREB phosphorylation and CREB-mediated gene transcription have challenged this model. For instance, monocular deprivation induces LacZ expression in the visual cortex of cAMP-response element (CRE)-LacZ transgenic mice (10), whereas phosphorylation of CREB at Ser-133 remains static (11). Similarly, the mechanism underlying CREB activation during L...

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Accumulating evidence points to altered GABAergic parvalbumin-expressing interneurons and impaired myelin/axonal integrity in schizophrenia. Both findings could be due to abnormal neurodevelopmental trajectories, affecting local neuronal networks and long-range synchrony and leading to cognitive deficits. In this review, we present data from animal models demonstrating that redox dysregulation, neuroinflammation and/or NMDAR hypofunction (as observed in patients) impairs the normal development of both parvalbumin interneurons and oligodendrocytes. These observations suggest that a dysregulation of the redox, neuroimmune, and glutamatergic systems due to genetic and early-life environmental risk factors could contribute to the anomalies of parvalbumin interneurons and white matter in schizophrenia, ultimately impacting cognition, social competence, and affective behavior via abnormal function of micro- and macrocircuits. Moreover, we propose that the redox, neuroimmune, and glutamatergic systems form a “central hub” where an imbalance within any of these “hub” systems leads to similar anomalies of parvalbumin interneurons and oligodendrocytes due to the tight and reciprocal interactions that exist among these systems. A combination of vulnerabilities for a dysregulation within more than one of these systems may be particularly deleterious. For these reasons, molecules, such as N-acetylcysteine, that possess antioxidant and anti-inflammatory properties and can also regulate glutamatergic transmission are promising tools for prevention in ultra-high risk patients or for early intervention therapy during the first stages of the disease.

Elevated oxidative stress and alteration in antioxidant systems, including glutathione (GSH) decrease, are observed in schizophrenia. Genetic and functional data indicate that impaired GSH synthesis represents a susceptibility factor for the disorder. Here, we show that a genetically compromised GSH synthesis affects the morphological and functional integrity of hippocampal parvalbumin-immunoreactive (PV-IR) interneurons, known to be affected in schizophrenia. A GSH deficit causes a selective decrease of PV-IR interneurons in CA3 and dendate gyrus (DG) of the ventral but not dorsal hippocampus and a concomitant reduction of ␤/␥ oscillations. Impairment of PV-IR interneurons emerges at the end of adolescence/early adulthood as oxidative stress increases or cumulates selectively in CA3 and DG of the ventral hippocampus. Such redox dysregulation alters stress and emotion-related behaviors but leaves spatial abilities intact, indicating functional disruption of the ventral but not dorsal hippocampus. Thus, a GSH deficit affects PV-IR interneuron's integrity and neuronal synchrony in a region-and time-specific manner, leading to behavioral phenotypes related to psychiatric disorders.