Gianmarco Latte

Glutamatergic Postsynaptic Density Protein Dysfunctions in Synaptic Plasticity and Dendritic Spines Morphology: Relevance to Schizophrenia and Other Behavioral Disorders Pathophysiology, and Implications for Novel Therapeutic Approaches

Emerging researches point to a relevant role of postsynaptic density (PSD) proteins, such as PSD-95, Homer, Shank, and DISC-1, in the pathophysiology of schizophrenia and autism spectrum disorders. The PSD is a thickness, detectable at electronic microscopy, localized at the postsynaptic membrane of glutamatergic synapses, and made by scaffolding proteins, receptors, and effector proteins; it is considered a structural and functional crossroad where multiple neurotransmitter systems converge, including the dopaminergic, serotonergic, and glutamatergic ones, which are all implicated in the pathophysiology of psychosis. Decreased PSD-95 protein levels have been reported in postmortem brains of schizophrenia patients. Variants of Homer1, a key PSD protein for glutamate signaling, have been associated with schizophrenia symptoms severity and therapeutic response. Mutations in Shank gene have been recognized in autism spectrum disorder patients, as well as reported to be associated to behaviors reminiscent of schizophrenia symptoms when expressed in genetically engineered mice. Here, we provide a critical appraisal of PSD proteins role in the pathophysiology of schizophrenia and autism spectrum disorders. Then, we discuss how antipsychotics may affect PSD proteins in brain regions relevant to psychosis pathophysiology, possibly by controlling synaptic plasticity and dendritic spine rearrangements through the modulation of glutamate-related targets. We finally provide a framework that may explain how PSD proteins might be useful candidates to develop new therapeutic approaches for schizophrenia and related disorders in which there is a need for new biological treatments, especially against some symptom domains, such as negative symptoms, that are poorly affected by current antipsychotics.

Differential cognitive performances between schizophrenic responders and non-responders to antipsychotics: Correlation with course of the illness, psychopathology, attitude to the treatment and antipsychotics doses

Multiple lines of evidence demonstrate that schizophrenia patients may perform worse than normal controls in several cognitive tasks. However, little is known on putative differences in cognitive functioning between schizophrenia patients responding to antipsychotics and those resistant to the treatment. In this cross-sectional study, 63 subjects (41 schizophrenia and schizoaffective patients and 22 age and sex-matched controls) were enrolled. Patients were divided in resistant (TRS, n=19) and non-resistant to pharmacological treatment (non-TRS, n=22) according to the American Psychiatric Association (APA) criteria for treatment resistance. The Brief Assessment of Cognition in Schizophrenia (BACS) was administered to patients and controls. The following rating scales were administered to schizophrenia patients: the Positive and Negative Syndrome Scale (PANSS), the Drug Attitude Inventory (DAI) and the Subjective Well-being under Neuroleptics (SWN). Statistically significant differences among non-TRS patients, TRS ones, and controls were detected at the BACS. TRS patients performed significantly worse than non-TRS ones on Verbal Memory task, exhibited higher PANSS total and subscales scores and were prescribed higher antipsychotic doses. Poorer performances at the BACS significantly correlated with more severe negative symptoms in TRS but not in non-TRS patients. These results may suggest that TRS patients suffer from a form of the disease with prominent cognitive impairment possibly related to negative symptoms.

Treatment resistant schizophrenia is associated with the worst community functioning among severely-ill highly-disabling psychiatric conditions and is the most relevant predictor of poorer achievements in functional milestones

The aim of this work was to compare achievements in milestones of community functioning in highly disabling psychiatric conditions, including treatment resistant schizophrenia (TRS), schizophrenia (responsive to antipsychotics), bipolar disorder, and anxiety/depressive diseases. Also, we investigated the predictors of community functioning outcomes across several domains. Among consecutive patients screened, 188 met inclusion criteria and 118 ultimately entered the study. Diagnosis of TRS was made by stringent criteria, including historic and perspective evaluations and excluding potential confounding factors. Achievements in functional milestones of everyday living were recorded. Performances in discrete cognitive tasks were assessed. The Positive and Negative Syndrome Scale, the Personal and Social Performance Scale, the Drug Attitude Inventory-10, and the Quality of Life Enjoyment and Satisfaction Questionnaire were administered. TRS patients showed the highest impairment in community functioning among diagnostic groups. TRS was found to have more severe psychopathology, more impaired cognitive functioning, and poorer psychosocial adjustment compared to all the other groups. In the whole sample, the main predictors of community functioning were the diagnostic group (with TRS diagnosis associated with worst functioning) and achievements in the other functional milestones. In psychotic patients, however, the main predictors of community functioning were clinical and psychopathological variables. These results may support the hypothesis that TRS represents a separate schizophrenia subtype, with its own neurobiology, psychopathology and clinical course. Our results identify a group of modifiable predictors to be addressed to prevent community disability.

Progressive recruitment of cortical and striatal regions by inducible postsynaptic density transcripts after increasing doses of antipsychotics with different receptor profiles: insights for psychosis treatment.

Antipsychotics may modulate the transcription of multiple gene programs, including those belonging to postsynaptic density (PSD) network, within cortical and subcortical brain regions. Understanding which brain region is activated progressively by increasing doses of antipsychotics and how their different receptor profiles may impact such an activation could be relevant to better correlate the mechanism of action of antipsychotics both with their efficacy and side effects. We analyzed the differential topography of PSD transcripts by incremental doses of two antipsychotics: haloperidol, the prototypical first generation antipsychotic with prevalent dopamine D2 receptors antagonism, and asenapine, a second generation antipsychotic characterized by multiple receptors occupancy. We investigated the expression of PSD genes involved in synaptic plasticity and previously demonstrated to be modulated by antipsychotics: Homer1a, and its related interacting constitutive genes Homer1b/c and PSD95, as well as Arc, C-fos and Zif-268, also known to be induced by antipsychotics administration. We found that increasing acute doses of haloperidol induced immediate-early genes (IEGs) expression in different striatal areas, which were progressively recruited by incremental doses with a dorsal-to-ventral gradient of expression. Conversely, increasing acute asenapine doses progressively de-recruited IEGs expression in cortical areas and increased striatal genes signal intensity. These effects were mirrored by a progressive reduction in locomotor animal activity by haloperidol, and an opposite increase by asenapine. Thus, we demonstrated for the first time that antipsychotics may progressively recruit PSD-related IEGs expression in cortical and subcortical areas when administered at incremental doses and these effects may reflect a fine-tuned dose-dependent modulation of the PSD.

Dopamine transporter (DAT) genetic hypofunction in mice produces alterations consistent with ADHD but not schizophrenia or bipolar disorder

ADHD, schizophrenia and bipolar disorder are psychiatric diseases with a strong genetic component which share dopaminergic alterations. Dopamine transporter (DAT) genetics might be potentially implicated in all these disorders. However, in contrast to DAT absence, the effects of DAT hypofunction especially in developmental trajectories have been scarcely addressed. Thus, we comprehensively studied DAT hypofunctional mice (DAT+/-) from adolescence to adulthood to disentangle DAT-dependent alterations in the development of psychiatric-relevant phenotypes. From pre-adolescence onward, DAT+/- displayed a hyperactive phenotype, while responses to external stimuli and sensorimotor gating abilities were unaltered. General cognitive impairments in adolescent DAT+/- were partially ameliorated during adulthood in males but not in females. Despite this, attentional and impulsivity deficits were evident in DAT+/- adult males. At the molecular level, DAT+/- mice showed a reduced expression of Homer1a in the prefrontal cortex, while other brain regions as well as Arc and Homer1b expression were mostly unaffected. Amphetamine treatments reverted DAT+/- hyperactivity and rescued cognitive deficits. Moreover, amphetamine shifted DAT-dependent Homer1a altered expression from prefrontal cortex to striatal regions. These behavioral and molecular phenotypes indicate that a genetic-driven DAT hypofunction alters neurodevelopmental trajectories consistent with ADHD, but not with schizophrenia and bipolar disorders.

Regulation of postsynaptic plasticity genes' expression and topography by sustained dopamine perturbation and modulation by acute memantine: Relevance to schizophrenia

A relevant role for dopamine-glutamate interaction has been reported in the pathophysiology and treatment of psychoses. Dopamine and glutamate may interact at multiple levels, including the glutamatergic postsynaptic density (PSD), an electron-dense thickening that has gained recent attention as a switchboard of dopamine-glutamate interactions and for its role in synaptic plasticity. Recently, glutamate-based strategies, such as memantine add-on to antipsychotics, have been proposed for refractory symptoms of schizophrenia, e.g. cognitive impairment. Both antipsychotics and memantine regulate PSD transcripts but sparse information is available on memantines effects under dopamine perturbation. We tested gene expression changes of the Homer1 and PSD-95 PSD proteins in models of sustained dopamine perturbation, i.e. subchronic treatment by: a) GBR-12909, a dopamine receptor indirect agonist; b) haloperidol, a D2R antagonist; c) SCH-23390, a dopamine D1 receptor (D1R) antagonist; and d) SCH-23390+haloperidol. On the last day of treatment, rats were acutely treated with vehicle or memantine. The Homer1a immediate-early gene was significantly induced by haloperidol and by haloperidol+SCH-23390. The gene was not induced by SCH-23390 per se or by GBR-12909. Expression of the constitutive genes Homer1b/c and PSD-95 was less affected by these dopaminergic paradigms. Acute memantine administration significantly increased Homer1a expression by the dopaminergic compounds used herein. Both haloperidol and haloperidol+SCH-23390 shifted Homer1a/Homer1b/c ratio of expression toward Homer1a. This pattern was sharpened by acute memantine. Dopaminergic compounds and acute memantine also differentially affected topographic distribution of gene expression and coordinated expression of Homer1a among cortical-subcortical regions. These results indicate that dopaminergic perturbations may affect glutamatergic signaling in different directions. Memantine may help partially revert dopamine-mediated glutamatergic dysfunctions.

The Glucocorticoid Analog Dexamethasone Alters the Expression and the Distribution of Dopamine Receptors and Enkephalin within Cortico- Subcortical Regions

In humans, glucocorticoid excess may cause neuropsychiatric symptoms, including psychosis and cognitive impairment, and glucocorticoid signaling hyperactivation may sensitize to substance of abuse. The aim of this work was to evaluate whether exposure to glucocorticoid excess triggers molecular changes in dopaminergic and opioidergic systems within relevant forebrain areas. We acutely exposed Sprague-Dawley rats to dexamethasone, a glucocorticoid analog, or vehicle and evaluated the mRNA expression of dopamine D1 and D2 receptors and enkephalin within the cortex, the striatum, and the midbrain. Dexamethasone reduced mRNA expression of D1 receptor and enkephalin in the cortex. In the striatum, dexamethasone reduced the expression of D1 receptor mRNA, but not that of D2 receptor and enkephalin. No significant changes in D2 receptor mRNA expression were observed in the midbrain. Basal distribution of D1 and D2 receptor mRNA showed a clear-cut striatal/cortical gradient, while this distribution was less obvious for enkephalin mRNA. Dexamethasone increased the cortico-striatal separation in terms of D1 and D2 receptor mRNA expression. These molecular changes may represent adaptive mechanisms to dexamethasone-induced potentiation of dopaminergic and opioidergic transmission, mostly in cortical areas.

Postsynaptic density protein transcripts are differentially modulated by minocycline alone or in add-on to haloperidol: Implications for treatment resistant schizophrenia.

In this study, we investigated whether minocycline, a second-generation tetracycline proposed as an add-on to antipsychotics in treatment-resistant schizophrenia (TRS), may affect the expression of Homer and Arc postsynaptic density (PSD) transcripts, implicated in synaptic regulation. Minocycline was administered alone or with haloperidol in rats exposed or not to ketamine, mimicking acute glutamatergic psychosis or naturalistic conditions, respectively. Arc expression was significantly reduced by minocycline compared with controls. Minocycline in combination with haloperidol also significantly reduced Arc expression compared with both controls and haloperidol alone. Moreover, haloperidol/minocycline combination significantly affected Arc expression in cortical regions, while haloperidol alone was ineffective on cortical gene expression. These results suggest that minocycline may strongly affect the expression of Arc as mediated by haloperidol, both in terms of quantitative levels and of topography of haloperidol-related expression. It is noteworthy that no significant pre-treatment effect was found, suggesting that pre-exposure to ketamine did not grossly affect gene expression. Minocycline was not found to significantly affect haloperidol-related Homer1a expression. No significant changes in Homer1b/c expression were observed. These results are consistent with previous observations that minocycline may modulate postsynaptic glutamatergic transmission, affecting distinct downstream pathways initiated by N-methyl-D-aspartate (NMDA) receptor modulation, i.e. Arc-mediated but not Homer1a-mediated pathways.

The expression of genes involved in glucose metabolism is affected by N-methyl-D-aspartate receptor antagonism: a putative link between metabolism and an animal model of psychosis.

Psychosis has been associated with glucose metabolism impairment. Here, we explored the gene expression of hexokinase 1 (Hk1) and glucose transporter 3 (GLUT3) after the administration of a subanesthetic or a subconvulsant dose of ketamine in rats, considered to provide an animal model of psychosis. Indeed, Hk1 and GLUT3 are crucially involved in the glucose utilization in brain tissues and have also been implicated in the pathophysiology of psychosis. Quantitative brain imaging of transcripts was used to evaluate Hk1 and GLUT3 mRNA in rat brain regions related to ketamine‐induced behavioral abnormalities. Hk1 transcript was significantly increased by 50 mg/kg ketamine in cortical and subcortical areas, whereas 12 mg/kg ketamine affected Hk1 expression in the auditory cortex only. GLUT3 expression was increased by 12 mg/kg ketamine in the frontal cortex and decreased by 50 mg/kg ketamine in subcortical areas. The results show that Hk1 and GLUT3 are extensively and differentially affected by ketamine dose, supporting the view that glucose metabolism and psychosis may be causally related and suggesting that these molecules may play a role in the pathophysiology of ketamine‐induced behavioral abnormalities.

Immediate-Early Genes Modulation by Antipsychotics: Translational Implications for a Putative Gateway to Drug-Induced Long-Term Brain Changes

An increasing amount of research aims at recognizing the molecular mechanisms involved in long-lasting brain architectural changes induced by antipsychotic treatments. Although both structural and functional modifications have been identified following acute antipsychotic administration in humans, currently there is scarce knowledge on the enduring consequences of these acute changes. New insights in immediate-early genes (IEGs) modulation following acute or chronic antipsychotic administration may help to fill the gap between primary molecular response and putative long-term changes. Moreover, a critical appraisal of the spatial and temporal patterns of IEGs expression may shed light on the functional “signature” of antipsychotics, such as the propensity to induce motor side effects, the potential neurobiological mechanisms underlying the differences between antipsychotics beyond D2 dopamine receptor affinity, as well as the relevant effects of brain region-specificity in their mechanisms of action. The interest for brain IEGs modulation after antipsychotic treatments has been revitalized by breakthrough findings such as the role of early genes in schizophrenia pathophysiology, the involvement of IEGs in epigenetic mechanisms relevant for cognition, and in neuronal mapping by means of IEGs expression profiling. Here we critically review the evidence on the differential modulation of IEGs by antipsychotics, highlighting the association between IEGs expression and neuroplasticity changes in brain regions impacted by antipsychotics, trying to elucidate the molecular mechanisms underpinning the effects of this class of drugs on psychotic, cognitive and behavioral symptoms.