Actin polymerization is reduced in the anterior cingulate cortex of elderly patients with schizophrenia

Structural and biochemical alterations in dendritic spines as key mechanisms for severe mental illnesses

Severe mental illnesses (SMI) collectively affect approximately 20% of the global population, as estimated by the World Health Organization (WHO). Despite having diverse etiologies, clinical symptoms, and pharmacotherapies, these diseases share a common pathophysiological characteristic: the misconnection of brain areas involved in reality perception, executive control, and cognition, including the corticolimbic system. Dendritic spines play a crucial role in excitatory neurotransmission within the central nervous system. These small structures exhibit remarkable plasticity, regulated by factors such as neurotransmitter tone, neurotrophic factors, and innate immunity-related molecules, and other mechanisms - all of which are associated with the pathophysiology of SMI. However, studying dendritic spine mechanisms in both healthy and pathological conditions in patients is fraught with technical limitations. This is where animal models related to these diseases become indispensable. They have played a pivotal role in elucidating the significance of dendritic spines in SMI. In this review, the information regarding the potential role of dendritic spines in SMI was summarized, drawing from clinical and animal model reports. Also, the implications of targeting dendritic spine-related molecules for SMI treatment were explored. Specifically, our focus is on major depressive disorder and the neurodevelopmental disorders schizophrenia and autism spectrum disorder. Abundant clinical and basic research has studied the functional and structural plasticity of dendritic spines in these diseases, along with potential pharmacological targets that modulate the dynamics of these structures. These targets may be associated with the clinical efficacy of the pharmacotherapy.

Protein Succinylation and Malonylation as Potential Biomarkers in Schizophrenia

Two protein post-translational modifications, lysine succinylation and malonylation, are implicated in protein regulation, glycolysis, and energy metabolism. The precursors of these modifications, succinyl-CoA and malonyl-CoA, are key players in central metabolic processes. Both modification profiles have been proven to be responsive to metabolic stimuli, such as hypoxia. As mitochondrial dysfunction and metabolic dysregulation are implicated in schizophrenia and other psychiatric illnesses, these modification profiles have the potential to reveal yet another layer of protein regulation and can furthermore represent targets for biomarkers that are indicative of disease as well as its progression and treatment. In this work, data from shotgun mass spectrometry-based quantitative proteomics were compiled and analyzed to probe the succinylome and malonylome of postmortem brain tissue from patients with schizophrenia against controls and the human oligodendrocyte precursor cell line MO3.13 with the dizocilpine chemical model for schizophrenia, three antipsychotics, and co-treatments. Several changes in the succinylome and malonylome were seen in these comparisons, revealing these modifications to be a largely under-studied yet important form of protein regulation with broad potential applications.

Neurons: The Interplay between Cytoskeleton, Ion Channels/Transporters and Mitochondria

Neurons are permanent cells whose key feature is information transmission via chemical and electrical signals. Therefore, a finely tuned homeostasis is necessary to maintain function and preserve neuronal lifelong survival. The cytoskeleton, and in particular microtubules, are far from being inert actors in the maintenance of this complex cellular equilibrium, and they participate in the mobilization of molecular cargos and organelles, thus influencing neuronal migration, neuritis growth and synaptic transmission. Notably, alterations of cytoskeletal dynamics have been linked to alterations of neuronal excitability. In this review, we discuss the characteristics of the neuronal cytoskeleton and provide insights into alterations of this component leading to human diseases, addressing how these might affect excitability/synaptic activity, as well as neuronal functioning. We also provide an overview of the microscopic approaches to visualize and assess the cytoskeleton, with a specific focus on mitochondrial trafficking.

mTOR kinase activity disrupts a phosphorylation signaling network in schizophrenia brain

The AKT-mTOR signaling transduction pathway plays an important role in neurodevelopment and synaptic plasticity. mTOR is a serine/threonine kinase that modulates signals from multiple neurotransmitters and phosphorylates specific proteins to regulate protein synthesis and cytoskeletal organization. There is substantial evidence demonstrating abnormalities in AKT expression and activity in different schizophrenia (SZ) models. However, direct evidence for dysregulated mTOR kinase activity and its consequences on downstream effector proteins in SZ pathophysiology is lacking. Recently, we reported reduced phosphorylation of mTOR at an activating site and abnormal mTOR complex formation in the SZ dorsolateral prefrontal cortex (DLPFC). Here, we expand on our hypothesis of disrupted mTOR signaling in the SZ brain and studied the expression and activity of downstream effector proteins of mTOR complexes and the kinase activity profiles of SZ subjects. We found that S6RP phosphorylation, downstream of mTOR complex I, is reduced, whereas PKCα phosphorylation, downstream of mTOR complex II, is increased in SZ DLPFC. In rats chronically treated with haloperidol, we showed that S6RP phosphorylation is increased in the rat frontal cortex, suggesting a potential novel mechanism of action for antipsychotics. We also demonstrated key differences in kinase signaling networks between SZ and comparison subjects for both males and females using kinome peptide arrays. We further investigated the role of mTOR kinase activity by inhibiting it with rapamycin in postmortem tissue and compared the impact of mTOR inhibition in SZ and comparison subjects using kinome arrays. We found that SZ subjects are globally more sensitive to rapamycin treatment and AMP-activated protein kinase (AMPK) contributes to this differential kinase activity. Together, our findings provide new insights into the role of mTOR as a master regulator of kinase activity in SZ and suggest potential targets for therapeutic intervention.

Lower levels of tubulin alpha 1b in the frontal pole in schizophrenia supports a role for changed cytoskeletal dynamics in the aetiology of the disorder

Our transcriptomic study suggested there were markedly lower levels of tubulin alpha 1b (TUBA1B) expression in BA 10, but not BA 9, from patients with schizophrenia. We now use Western blotting to compare levels of TUBA1B protein in BA 9 and 10 from patients with schizophrenia and BA 10 from patients with mood disorders to controls as well as in the frontal cortex from rats after treatment with haloperidol, chlorpromazine or vehicle for 28 days. Levels of TUBA1B were significantly lower (- 18.6%) in BA 10, but not BA 9, from patients with schizophrenia. Levels of TUBA1B did not differ significantly from controls in BA 10 from patients with mood disorders or in the cortex of rats after antipsychotic drug treatments. Levels of TUBA1B were significantly lower (- 30%) in BA 10 from patients with schizophrenia who were not being treated with antipsychotic drugs close to death compared to those who were treated close to death. These data suggest that lower levels of TUBA1B, a cytoskeletal protein, in BA 10 from patients with schizophrenia are not a simple drug effect and therefore add to the hypothesis that a breakdown in cytoskeletal homoeostasis may be contributing to the genesis of the symptoms of the disorder.

Neuronal Cytoskeleton in Intellectual Disability: From Systems Biology and Modeling to Therapeutic Opportunities

Intellectual disability (ID) is a pathological condition characterized by limited intellectual functioning and adaptive behaviors. It affects 1–3% of the worldwide population, and no pharmacological therapies are currently available. More than 1000 genes have been found mutated in ID patients pointing out that, despite the common phenotype, the genetic bases are highly heterogeneous and apparently unrelated. Bibliomic analysis reveals that ID genes converge onto a few biological modules, including cytoskeleton dynamics, whose regulation depends on Rho GTPases transduction. Genetic variants exert their effects at different levels in a hierarchical arrangement, starting from the molecular level and moving toward higher levels of organization, i.e., cell compartment and functions, circuits, cognition, and behavior. Thus, cytoskeleton alterations that have an impact on cell processes such as neuronal migration, neuritogenesis, and synaptic plasticity rebound on the overall establishment of an effective network and consequently on the cognitive phenotype. Systems biology (SB) approaches are more focused on the overall interconnected network rather than on individual genes, thus encouraging the design of therapies that aim to correct common dysregulated biological processes. This review summarizes current knowledge about cytoskeleton control in neurons and its relevance for the ID pathogenesis, exploiting in silico modeling and translating the implications of those findings into biomedical research.

Maternal Exposure to Di-(2-ethylhexyl) Phthalate Impairs Hippocampal Synaptic Plasticity in Male Offspring: Involvement of Damage to Dendritic Spine Development

Exposure to di-(2-ethylhexyl) phthalate (DEHP), a widely used kind of plasticizer, can result in neurodevelopment impairments and learning and memory disorders. We studied the effects and possible mechanisms of maternal DEHP treatment on hippocampal synaptic plasticity in offspring. Pregnant Wistar rats were randomly divided into four groups and received 0, 30, 300, 750 (mg/kg)/d DEHP by gavage from gestational day (GD) 0 to postnatal day (PN) 21. Our data showed that DEHP exposure impaired hippocampal synaptic plasticity, damaged synaptic ultrastructure, and decreased synaptic protein levels in male pups. Furthermore, DEHP decreased the density of dendritic spines, affected F-actin polymerization, and downregulated the Rac1/PAK/LIMK1/cofilin signaling pathway in male offspring. However, the alterations in the hippocampi of female offspring were not observed. These results illustrate that maternal DEHP exposure could impair hippocampal synaptic plasticity by affecting synaptic structure and dendritic spine development in male offspring, which may be attributed to altered cytoskeleton construction induced by downregulation of the Rac1/PAK/LIMK1/cofilin signaling pathway.

Ubiquitin-proteasome system, lipid metabolism and DNA damage repair are triggered by antipsychotic medication in human oligodendrocytes: implications in schizophrenia

Schizophrenia is a chronic, severe and disabling psychiatric disorder, whose treatment is based on psychosocial interventions and the use of antipsychotic drugs. While the effects of these drugs are well elucidated in neuronal cells, they are still not so clear in oligodendrocytes, which play a vital role in schizophrenia. Thus, we aimed to characterize biochemical profiles by proteomic analyses of human oligodendrocytes (MO3.13) which were matured using a protocol we developed and treated with either haloperidol (a typical antipsychotic), clozapine (an atypical antipsychotic) or a clozapine + D-serine co-treatment, which has emerged lately as an alternative type of treatment. This was accomplished by employing shotgun proteomics, using nanoESI-LC-MS/MS label-free quantitation. Proteomic analysis revealed biochemical pathways commonly affected by all tested antipsychotics were mainly associated to ubiquitination, proteasome degradation, lipid metabolism and DNA damage repair. Clozapine and haloperidol treatments also affected proteins involved with the actin cytoskeleton and with EIF2 signaling. In turn, metabolic processes, especially the metabolism of nitrogenous compounds, were a predominant target of modulation of clozapine + D-serine treatment. In this context, we seek to contribute to the understanding of the biochemical and molecular mechanisms involved in the action of antipsychotics on oligodendrocytes, along with their possible implications in schizophrenia.

Downregulated AKT-mTOR signaling pathway proteins in dorsolateral prefrontal cortex in Schizophrenia

Abnormal neurotransmission is central to schizophrenia (SZ). Alterations across multiple neurotransmitter systems in SZ suggest that this illness may be associated with dysregulation of core intracellular processes such as signaling pathways that underlie the regulation and integration of these systems. The AKT-mTOR signaling cascade has been implicated in SZ by gene association, postmortem brain and animal studies. AKT and mTOR are serine/threonine kinases which play important roles in cell growth, proliferation, survival, and differentiation. Both AKT and mTOR require phosphorylation at specific sites for their complete activation. mTOR forms two functionally distinct multiprotein complexes, mTOR Complex 1 (mTORC1) and Complex 2 (mTORC2). mTORC1 mediates ribosome biogenesis, protein translation, and autophagy, whereas mTORC2 contributes to actin dynamics. Altered protein synthesis and actin dynamics can lead to an abnormal neuronal morphology resulting in deficits in learning and memory. Currently, there is a lack of direct evidence to support the hypothesis of disrupted mTOR signaling in SZ, and we have addressed this by characterizing this signaling pathway in SZ brain. We found a reduction in AKT and mTOR protein expression and/or phosphorylation state in dorsolateral prefrontal cortex (DLPFC) from 22 pairs of SZ and matched comparison subjects. We also found reduced protein expression of GβL, a subunit protein common to both mTOR complexes. We further investigated mTOR complex-specific subunit composition and phosphorylation state, and found abnormal mTOR expression in both complexes in SZ DLPFC. These findings provide evidence that proteins associated with the AKT-mTOR signaling cascade are downregulated in SZ DLPFC.

Post-translational protein modifications in schizophrenia

Research investigating the pathophysiology of schizophrenia has not yet precisely defined the molecular phenotype of this disorder. Many studies have investigated cellular dysfunction by examining expression levels of molecular targets in postmortem patient brain; however, inconsistencies between transcript and protein measures in schizophrenia are common in the field and represent a challenge to the identification of a unified model of schizophrenia pathogenesis. In humans, >4800 unique proteins are expressed, and the majority of these are modified by glycans and/or lipids. Estimates indicate ~70% of all eukaryotic proteins are modified by at least one type of glycosylation, while nearly 20% of all proteins are known to be lipid-modified. Protein post-translational modification (PTM) by glycosylation and lipidation rely on the spatiotemporal colocalization of enzyme, substrate, and glycan or lipid donor molecule and do not require an upstream “blueprint” or specialized processing machinery for synthesis. Glycan and lipid PTMs can thus facilitate cellular adaptation to environmental signals more rapidly than changes of gene or protein expression, and can significantly impact the localization, function, and interactions of modified substrates, though relatively few studies in schizophrenia have evaluated the PTM status of target proteins. A growing body of literature reports glycosylation and lipidation abnormalities in schizophrenia brain as well as in patient peripheral fluids. In this review, we explain the functional significance of key glycan and lipid PTMs and summarize current findings associated with abnormal glycosylation and lipidation in this illness.

The difference in serum proteomes in schizophrenia and bipolar disorder

BACKGROUND

Purpose of study is revealing significant differences in serum proteomes in schizophrenia and bipolar disorder (BD).

RESULTS

Quantitative mass-spectrometry based proteomic analysis was used to quantify proteins in the blood serum samples after the depletion of six major blood proteins. Comparison of proteome profiles of different groups revealed 27 proteins being specific for schizophrenia, and 18 - for BD. Protein set in schizophrenia was mostly associated with immune response, cell communication, cell growth and maintenance, protein metabolism and regulation of nucleic acid metabolism. Protein set in BD was mostly associated with immune response, regulating transport processes across cell membrane and cell communication, development of neurons and oligodendrocytes and cell growth. Concentrations of ankyrin repeat domain-containing protein 12 (ANKRD12) and cadherin 5 in serum samples were determined by ELISA. Significant difference between three groups was revealed in ANKRD12 concentration (p = 0.02), with maximum elevation of ANKRD12 concentration (median level) in schizophrenia followed by BD. Cadherin 5 concentration differed significantly (p = 0.035) between schizophrenic patients with prevailing positive symptoms (4.78 [2.71, 7.12] ng/ml) and those with prevailing negative symptoms (1.86 [0.001, 4.11] ng/ml).

CONCLUSIONS

Our results are presumably useful for discovering the new pathways involved in endogenous psychotic disorders.

New insights on synaptic dysfunction in neuropsychiatric disorders

Growing evidence implicates synaptic proteins in the pathogenesis of neuropsychiatric disorders such as autism spectrum disorder (ASD), intellectual disability (ID) and schizophrenia. In fact, mutations in genes encoding synaptic proteins are enriched and overlap among different conditions highlighting the complex and pleiotropic nature of these disorders. In this review, we discuss recently described candidate genes that affect excitatory synapse function and result in changes in spine number and morphology. Spine pathology has been observed in several animal models of disease and in human brain post-mortem samples from ID, ASD, and schizophrenia patients. Recent data point to convergent mechanisms, such as dysregulation of the actin cytoskeleton and dysfunction of microglia synaptic remodeling, underlying dendritic spine dysgenesis. Interestingly, the reversion of important pathologic features, including spine abnormalities, has been observed in adult animal models of neuropsychiatric disorders, suggesting that therapies may not be restricted to a specific developmental window. Shedding light on the specific mechanisms impacted in neuropsychiatric disorders will undeniably contribute to the development of more directed and personalized therapies.

Plasticity of Spine Structure: Local Signaling, Translation and Cytoskeletal Reorganization

Dendritic spines are small protrusive structures on dendritic surfaces, and function as postsynaptic compartments for excitatory synapses. Plasticity of spine structure is associated with many forms of long-term neuronal plasticity, learning and memory. Inside these small dendritic compartments, biochemical states and protein-protein interactions are dynamically modulated by synaptic activity, leading to the regulation of protein synthesis and reorganization of cytoskeletal architecture. This in turn causes plasticity of structure and function of the spine. Technical advances in monitoring molecular behaviors in single dendritic spines have revealed that each signaling pathway is differently regulated across multiple spatiotemporal domains. The spatial pattern of signaling activity expands from a single spine to the nearby dendritic area, dendritic branch and the nucleus, regulating different cellular events at each spatial scale. Temporally, biochemical events are typically triggered by short Ca²⁺ pulses (~10–100 ms). However, these signals can then trigger activation of downstream protein cascades that can last from milliseconds to hours. Recent imaging studies provide many insights into the biochemical processes governing signaling events of molecular assemblies at different spatial localizations. Here, we highlight recent findings of signaling dynamics during synaptic plasticity and discuss their roles in long-term structural plasticity of dendritic spines.