Perineuronal nets protect fast-spiking interneurons against oxidative stress

Abstract

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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