Molecular, genetic and pathological evidence suggests that deficits in GABAergic parvalbumin-positive interneurons contribute to schizophrenia pathophysiology through alterations in the brain's ...excitation-inhibition balance that result in impaired behaviour and cognition. Although the factors that trigger these deficits are diverse, there is increasing evidence that they converge on a common pathological hub that involves NMDA receptor hypofunction and oxidative stress. These factors have been separately linked to schizophrenia pathogenesis, but evidence now suggests that they are mechanistically interdependent and contribute to a common schizophrenia-associated pathology.
•Early detection and intervention, improving prognosis, require mechanistic biomarkers.•Mechanism-based biomarkers allow patient stratification, disease monitoring and treatment.•Oxidative stress: ...hub on which genetic & environmental risks converge during development.•OxS interaction with dysfunction of dopamine, NMDAR, mitochondria and inflammation.•Parvalbumine GABA interneurons, gamma oscillations, critical for cognition.•miR-137 and COX6A2: markers of parvalbumin microcircuit impairments.
Early detection and intervention in schizophrenia, improving prognosis, requires mechanism-based biomarkers that capture circuitry dysfunction, allowing optimized patient stratification, disease monitoring and treatment.
Dr. Do's translational research, bridging basic neuroscience and clinical psychiatry, tackles an urgent need to develop effective treatments that target mechanisms underlying cognitive deficits, a critical dimension of schizophrenia, currently not well treated. By adopting a reverse translation of validated circuitry relevant human endpoints, her research brought new insights in mechanism-based biomarker guided treatment of patients in early stages of psychosis. She showed that oxidative stress/redox dysregulation, in reciprocal interaction with dopamine imbalance, NMDAR hypofunction, neuroinflammation and mitochondrial bioenergetic dysfunction, may represent a "hub" on which both genetic and environmental risk factors converge during neurodevelopment. This leads to impairments of structural and functional connectivity in microcircuits, involving impaired parvalbumin fast-spiking GABA neurons, and macrocircuits, impacting myelination of fiber tracts, at the basis of neural synchronization abnormalities, as well as sensory and cognitive deficits. These unique insights led to successful proof-of-concept clinical trials, targeting oxidative stress through antioxidant-based strategies in patients at various disease stages, paving the way for precision medicine in psychiatry.
Converging evidence implicates redox dysregulation as a pathological mechanism driving the emergence of psychosis. Increased oxidative damage and decreased capacity of intracellular redox modulatory ...systems are consistent findings in persons with schizophrenia as well as in persons at clinical high risk who subsequently developed frank psychosis. Levels of glutathione, a key regulator of cellular redox status, are reduced in the medial prefrontal cortex, striatum, and thalamus in schizophrenia. In humans with schizophrenia and in rodent models recapitulating various features of schizophrenia, redox dysregulation is linked to reductions of parvalbumin containing gamma-aminobutyric acid (GABA) interneurons and volumes of their perineuronal nets, white matter abnormalities, and microglia activation. Importantly, the activity of transcription factors, kinases, and phosphatases regulating diverse aspects of neurodevelopment and synaptic plasticity varies according to cellular redox state. Molecules regulating interneuron function under redox control include NMDA receptor subunits GluN1 and GluN2A as well as KEAP1 (regulator of transcription factor NRF2). In a rodent schizophrenia model characterized by impaired glutathione synthesis, the Gclm knockout mouse, oxidative stress activated MMP9 (matrix metalloprotease 9) via its redox-responsive regulatory sites, causing a cascade of molecular events leading to microglia activation, perineural net degradation, and impaired NMDA receptor function. Molecular pathways under redox control are implicated in the etiopathology of schizophrenia and are attractive drug targets for individualized drug therapy trials in the contexts of prevention and treatment of psychosis.
Schizophrenia is a neurodevelopmental disorder reflecting a convergence of genetic risk and early life stress. The slow progression to first psychotic episode represents both a window of ...vulnerability as well as opportunity for therapeutic intervention. Here, we consider recent neurobiological insight into the cellular and molecular components of developmental critical periods and their vulnerability to redox dysregulation. In particular, the consistent loss of parvalbumin-positive interneuron (PVI) function and their surrounding perineuronal nets (PNNs) as well as myelination in patient brains is consistent with a delayed or extended period of circuit instability. This linkage to critical period triggers (PVI) and brakes (PNN, myelin) implicates mistimed trajectories of brain development in mental illness. Strategically introduced antioxidant treatment or later reinforcement of molecular brakes may then offer a novel prophylactic psychiatry.
Alzheimer's disease (AD) is characterized by the accumulation of the tau protein in neurons, neurodegeneration and memory loss. However, the role of non-neuronal cells in this chain of events remains ...unclear. In the present study, we found accumulation of tau in hilar astrocytes of the dentate gyrus of individuals with AD. In mice, the overexpression of 3R tau specifically in hilar astrocytes of the dentate gyrus altered mitochondrial dynamics and function. In turn, these changes led to a reduction of adult neurogenesis, parvalbumin-expressing neurons, inhibitory synapses and hilar gamma oscillations, which were accompanied by impaired spatial memory performances. Together, these results indicate that the loss of tau homeostasis in hilar astrocytes of the dentate gyrus is sufficient to induce AD-like symptoms, through the impairment of the neuronal network. These results are important for our understanding of disease mechanisms and underline the crucial role of astrocytes in hippocampal function.
The recent discovery that collision of ribosomes triggers quality control and stress responses in eukaryotes has shifted the perspective of the field. Collided eukaryotic ribosomes adopt a unique ...structure, acting as a ubiquitin signaling platform for various response factors. While several of the signals that determine which downstream pathways are activated have been uncovered, we are only beginning to learn how the specificity for the activation of each process is achieved during collisions. This review will summarize those findings and how ribosome-associated factors act as molecular sentinels, linking aberrations in translation to the overall cellular state. Insights into how cells respond to ribosome collision events will provide greater understanding of the role of the ribosome in the maintenance of cellular homeostasis.
Collision of ribosomes is the key event for quality control processes and other stress response pathways during translation.The collided di-ribosome adopts a unique structure that acts as a signaling platform for various factors.Differential ubiquitination of ribosomal proteins determines which pathways are activated and the fate of the ribosome.Ribosome quality control and the integrated stress response appear to antagonize one another’s activation.Ribosome collisions are utilized to trigger global reprogramming of gene expression in response to stress.
Ubiquitin (Ub) conjugation is a critical signalling process in eukaryotic cells. The precise regulation of deubiquitination is an important component of this signalling cascade. Here, we discuss how ...USP7 (or Herpes-Associated Ubiquitin-Specific Protease, HAUSP), one of the most abundant deubiquitinating enzymes, is regulated by complex formation with regulatory proteins and targets.
Full activity of USP7 requires that its C-terminal Ub-like domains fold back onto the catalytic domain, to allow the remodelling of the active site to a catalytically competent state by the very C-terminal peptide. This regulatory mode can be modulated by complex formation with other proteins.
USP7 is found in a large number of relatively stable complexes with different possible functions. Complex formation can provide recruitment of a target, bring in an E3 Ub ligase, or modulate the activation of the deubiquitinating enzyme activity. These complexes make up potential cellular “switches”, using their (de)ubiquitination ability to switch pathways on or off upon cellular signals. Here, we summarize what is known for USP7 complexes, focussing on the prevalence of E3 Ub ligases and how complex formation can affect Ub switches.
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•USP7 activity is regulated by itself and interacting proteins.•Many of the USP7 interacting proteins are E3 ubiquitin ligases.•E3/USP7 complexes can form cellular switches.
Abnormal development can lead to deficits in adult brain function, a trajectory likely underlying adolescent-onset psychiatric conditions such as schizophrenia. Developmental manipulations yielding ...adult deficits in rodents provide an opportunity to explore mechanisms involved in a delayed emergence of anomalies driven by developmental alterations. Here we assessed whether oxidative stress during presymptomatic stages causes adult anomalies in rats with a neonatal ventral hippocampal lesion, a developmental rodent model useful for schizophrenia research. Juvenile and adolescent treatment with the antioxidant N-acetyl cysteine prevented the reduction of prefrontal parvalbumin interneuron activity observed in this model, as well as electrophysiological and behavioral deficits relevant to schizophrenia. Adolescent treatment with the glutathione peroxidase mimic ebselen also reversed behavioral deficits in this animal model. These findings suggest that presymptomatic oxidative stress yields abnormal adult brain function in a developmentally compromised brain, and highlight redox modulation as a potential target for early intervention.
•Presymptomatic antioxidant treatment prevents loss of parvalbumin in NVHL rats•Antioxidant treatment prevents altered prefrontal electrophysiology in NVHL rats•Prepulse inhibition deficits are prevented by antioxidants
Cabungcal et al. show that antioxidant treatment during juvenile and adolescent stages prevents the onset of electrophysiological and behavioral deficits in a developmental model for schizophrenia. The reversal of adolescent-onset deficits suggests redox modulation is a potential target for early intervention.
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.
Background A hallmark of the pathophysiology of schizophrenia is a dysfunction of parvalbumin-expressing fast-spiking interneurons, which are essential for the coordination of neuronal synchrony ...during sensory and cognitive processing. Oxidative stress as observed in schizophrenia affects parvalbumin interneurons. However, it is unknown whether the deleterious effect of oxidative stress is particularly prevalent during specific developmental time windows. Methods We used mice with impaired synthesis of glutathione ( Gclm knockout KO mice) to investigate the effect of redox dysregulation and additional insults applied at various periods of postnatal development on maturation and long-term integrity of parvalbumin interneurons in the anterior cingulate cortex. Results A redox dysregulation, as in Gclm KO mice, renders parvalbumin interneurons but not calbindin or calretinin interneurons vulnerable and prone to exhibit oxidative stress. A glutathione deficit delays maturation of parvalbumin interneurons, including their perineuronal net. Moreover, an additional oxidative challenge in preweaning or pubertal but not in young adult Gclm KO mice reduces the number of parvalbumin-immunoreactive interneurons. This effect persists into adulthood and can be prevented with the antioxidant N -acetylcysteine. Conclusions In Gclm KO mice, early-life insults inducing oxidative stress are detrimental to immature parvalbumin interneurons and have long-term consequences. In analogy, individuals carrying genetic risks to redox dysregulation would be potentially vulnerable to early-life environmental insults, during the maturation of parvalbumin interneurons. Our data support the need to develop novel therapeutic approaches based on antioxidant and redox regulator compounds such as N -acetylcysteine, which could be used preventively in young at-risk subjects.
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