Vesicular signalling and immune modulation as hedonic fingerprints: proteomic profiling in the chronic mild stress depression model

Connecting Dots between Mitochondrial Dysfunction and Depression

Mitochondria are the prime source of cellular energy, and are also responsible for important processes such as oxidative stress, apoptosis and Ca2+ homeostasis. Depression is a psychiatric disease characterized by alteration in the metabolism, neurotransmission and neuroplasticity. In this manuscript, we summarize the recent evidence linking mitochondrial dysfunction to the pathophysiology of depression. Impaired expression of mitochondria-related genes, damage to mitochondrial membrane proteins and lipids, disruption of the electron transport chain, higher oxidative stress, neuroinflammation and apoptosis are all observed in preclinical models of depression and most of these parameters can be altered in the brain of patients with depression. A deeper knowledge of the depression pathophysiology and the identification of phenotypes and biomarkers with respect to mitochondrial dysfunction are needed to help early diagnosis and the development of new treatment strategies for this devastating disorder.

Tianeptine modulates synaptic vesicle dynamics and favors synaptic mitochondria processes in socially isolated rats

Deregulation of synaptic function and neurotransmission has been linked with the development of major depression disorder (MDD). Tianeptine (Tian) has been used as antidepressant with anxiolytic properties and recently as a nootropic to improve cognitive performance, but its mechanism of action is unknown. We conducted a proteomic study on the hippocampal synaptosomal fractions of adult male Wistar rats exposed to chronic social isolation (CSIS, 6 weeks), an animal model of depression and after chronic Tian treatment in controls (nootropic effect) and CSIS-exposed rats (lasting 3 weeks of 6-week CSIS) (therapeutic effect). Increased expression of Syn1 and Camk2-related neurotransmission, vesicle transport and energy processes in Tian-treated controls were found. CSIS led to upregulation of proteins associated with actin cytoskeleton, signaling transduction and glucose metabolism. In CSIS rats, Tian up-regulated proteins involved in mitochondrial energy production, mitochondrial transport and dynamics, antioxidative defense and glutamate clearance, while attenuating the CSIS-increased glycolytic pathway and cytoskeleton organization proteins expression and decreased the expression of proteins involved in V-ATPase and vesicle endocytosis. Our overall findings revealed that synaptic vesicle dynamics, specifically exocytosis, and mitochondria-related energy processes might be key biological pathways modulated by the effective nootropic and antidepressant treatment with Tian and be a potential target for therapeutic efficacy of the stress-related mood disorders.

The Roles of Peroxiredoxin 6 in Brain Diseases

Peroxiredoxin 6 (PRDX6), the only mammalian 1-Cys member of the peroxiredoxins (PRDXs) family, has multiple functions of glutathione peroxidase (Gpx) activity, acidic calcium-independent phospholipase (aiPLA2) activity, and lysophosphatidylcholine acyl transferase (LPCAT) activity. It has been documented to be involved in redox homeostasis, phospholipid turnover, glycolipid metabolism, and cellular signaling. Here, we reviewed the characteristics of the available Prdx6 genetic mouse models and the research progresses made with regard to PRDX6 in neuropsychiatric disorders, including neurodegenerative diseases, brain aging, stroke, neurotrauma, gliomas, major depressive disorder, drug addiction, post-traumatic stress disorder, and schizophrenia. The present review highlights the important roles of PRDX6 in neuropsychiatric disorders and may provide novel insights for the development of effective pharmacological treatments and genetic therapies.

Hippocampal synaptoproteomic changes of susceptibility and resilience of male rats to chronic social isolation

The susceptibility of an individual to chronic social isolation (CSIS) stress may cause major depression (MD) whereby some individuals are resistant to the stress. Recent studies relate MD with altered expression of synaptic proteins in specific brain regions. To explore the neurobiological underpinnings and identify candidate biomarkers of susceptibility or resilience to CSIS, a comparative proteomic approach was used to map hippocampal synaptic protein alterations of rats exposed to 6 weeks of CSIS, an animal model of depression. This model generates two stress-response phenotypes: CSIS-sensitive (depressive-like behaviour) and CSIS-resilience assessed by means of sucrose preference and forced swim tests. Our aim was to characterize the synaptoproteome changes representative of potential long-term changes in protein expression underlying susceptibility or resilience to stress. Proteomic data showed increased expression of glycolytic enzymes, the energy-related mitochondrial proteins, actin cytoskeleton, signalling transduction and synaptic transmission proteins in CSIS-sensitive rats. Protein levels of glutamate-related enzymes such as glutamate dehydrogenase and glutamine synthetase were also increased. CSIS-resilient rats showed similar proteome changes, however with a weaker increase compared to CSIS-sensitive rats. The main difference was observed in the level of protein expression of vesicle-mediated transport proteins. Nonetheless, only few proteins were uniquely up-regulated in the CSIS-resilient rats, whereby Cytochrome b-c1 complex subunit 2, mitochondrial (Uqcrc2) and Voltage-dependent anion-selective channel protein 1 (Vdac1) were uniquely down-regulated. Identified altered activated pathways and potential protein biomarkers may help us better understand the molecular mechanisms underlying synaptic neurotransmission in MD or resilience, crucial for development of new therapeutics.

Proinflammatory Cytokines and Oxidative Stress Decrease the Transport of Dopamine Precursor Tyrosine in Human Fibroblasts

BACKGROUND

Proinflammatory cytokines and oxidative stress responses have been extensively implicated in the pathophysiology of neuropsychiatric disorders over the past 2 decades. Moreover, disturbed transport of the dopamine precursor (i.e., the amino acid tyrosine) has been demonstrated, in different studies, across fibroblast cell membranes obtained from neuropsychiatric patients. However, the role and influences of proinflammatory cytokines and oxidative stress, and the reasons for disturbed tyrosine transport in neuropsychiatric disorders, are still not evaluated.

AIMS

The present study aimed to assess the role of proinflammatory cytokines and oxidative stress, indicated in many neuropsychiatric disorders, in tyrosine transportation, by using human skin-derived fibroblasts.

METHODS

Fibroblasts obtained from a healthy control were used in this study. Fibroblasts were treated with proinflammatory cytokines (IL-1β, IFN-γ, IL-6, TNF-α), their combinations, and oxidative stress, optimized for concentrations and incubation time, to analyze the uptake of 14C-tyrosine compared to untreated controls.

RESULTS AND CONCLUSION

This study demonstrates that proinflammatory cytokines and oxidative stress decrease the transport of tyrosine (47% and 33%, respectively), which can alter dopamine synthesis. The functionality of the tyrosine transporter could be a new potential biomarker to target for discovering new drugs to counteract the effects of proinflammatory cytokines and oxidative stress in the pathophysiology of neuropsychiatric disorders.

Long-Term Stress Disrupts the Structural and Functional Integrity of GABAergic Neuronal Networks in the Medial Prefrontal Cortex of Rats

Clinical and experimental data suggest that fronto-cortical GABAergic deficits contribute to the pathophysiology of major depressive disorder (MDD). To further test this hypothesis, we used a well characterized rat model for depression and examined the effect of stress on GABAergic neuron numbers and GABA-mediated synaptic transmission in the medial prefrontal cortex (mPFC) of rats. Adult male Wistar rats were subjected to 9-weeks of chronic mild stress (CMS) and based on their hedonic-anhedonic behavior they were behaviorally phenotyped as being stress-susceptible (anhedonic) or stress-resilient. Post mortem quantitative histopathology was used to examine the effect of stress on parvalbumin (PV)-, calretinin- (CR), calbindin- (CB), cholecystokinin- (CCK), somatostatin-(SST) and neuropeptide Y-positive (NPY+) GABAergic neuron numbers in all cortical subareas of the mPFC (anterior cingulate (Cg1), prelimbic (PrL) and infralimbic (IL) cortexes). In vitro, whole-cell patch-clamp recordings from layer II–III pyramidal neurons of the ventral mPFC was used to examine GABAergic neurotransmission. The cognitive performance of the animals was assessed in a hippocampal-prefrontal-cortical circuit dependent learning task. Stress exposure reduced the number of CCK-, CR- and PV-positive GABAergic neurons in the mPFC, most prominently in the IL cortex. Interestingly, in the stress-resilient animals, we found higher number of neuropeptide Y-positive neurons in the entire mPFC. The electrophysiological analysis revealed reduced frequencies of spontaneous and miniature IPSCs in the anhedonic rats and decreased release probability of perisomatic-targeting GABAergic synapses and alterations in GABA_B receptor mediated signaling. In turn, pyramidal neurons showed higher excitability. Anhedonic rats were also significantly impaired in the object-place paired-associate learning task. These data demonstrate that long-term stress results in functional and structural deficits of prefrontal GABAergic networks. Our findings support the concept that fronto-limbic GABAergic dysfunctions may contribute to emotional and cognitive symptoms of MDD.

Synaptic proteomics as a means to identify the molecular basis of mental illness: Are we getting there?

Synapses are centrally involved in many brain disorders, particularly in psychiatric and neurodevelopmental ones. However, our current understanding of the proteomic alterations affecting synaptic performance in the majority of mental illnesses is limited. As a result, novel pharmacotherapies with improved neurological efficacy have been scarce over the past decades. The main goal of synaptic proteomics in the context of mental illnesses is to identify dysregulated molecular mechanisms underlying these conditions. Here we reviewed and performed a meta-analysis of previous neuroproteomic research to identify proteins that may be consistently dysregulated in one or several mental disorders. Notably, we found very few proteins reproducibly altered among independent experiments for any given condition or between conditions, indicating that we are still far from identifying key pathophysiological mechanisms of mental illness. We suggest that future research in the field will require higher levels of standardization and larger-scale experiments to address the challenge posed by biological and methodological variability. We strongly believe that more resources should be placed in this field as the need to identify the molecular roots of mental illnesses is highly pressing.

The effect of rat strain and stress exposure on performance in touchscreen tasks

Patients suffering from depression-associated cognitive impairments often recover incompletely after remission from the core symptoms of depression (lack of energy, depressed mood and anhedonia). This study aimed to set the basis for clinically relevant testing of cognitive impairments in a preclinical model of depression. Hence, we used the chronic mild stress (CMS) model of depression, which provokes the core symptom of anhedonia in a fraction of the stress exposed animals, while others remain resilient, and assessed the entire CMS groups' cognitive performance on the touchscreen operant platform. Specifically, we applied the pairwise discrimination (PD) and reversal task including a retention phase on Wistar and Long Evans controls and CMS exposed Long Evans rats. We observed differences between the albino Wistar and the pigmented Long Evans strain regarding performance in the PD and reversal task as well as in memory consolidation. CMS exposure did not alter learning and memory in the PD and reversal task, even though it altered affective behaviours in the elevated plus-maze and open field test. This is likely due to the heterogeneity of the CMS group, in which stress exposure elicited the expected range of phenotypes from anhedonic-like to resilient shown with the sucrose consumption test. Thus, our study suggests that pigmented rat strains, such as Long Evans, are superior to albino rats in the vision-based touchscreen studies. Furthermore, we propose investigation of the CMS subgroups in more complex, hippocampus-dependent tasks to refine a translational preclinical model of depression-induced cognitive impairments. Hence, this study increased awareness of strain-specific differences in touchscreen performance and added to the literature regarding the sensitivity of the PD and reversal task to stress-induced cognitive alterations.

Differential Peripheral Proteomic Biosignature of Fluoxetine Response in a Mouse Model of Anxiety/Depression

The incorporation of peripheral biomarkers in the treatment of major depressive disorders (MDD) could improve the efficiency of treatments and increase remission rate. Peripheral blood mononuclear cells (PBMCs) represent an attractive biological substrate allowing the identification of a drug response signature. Using a proteomic approach with high-resolution mass spectrometry, the present study aimed to identify a biosignature of antidepressant response (fluoxetine, a Selective Serotonin Reuptake Inhibitor) in PBMCs in a mouse model of anxiety/depression. Following determination of an emotionality score, using complementary behavioral analysis of anxiety/depression across three different tests (Elevated Plus Maze, Novelty Suppressed Feeding, Splash Test), we showed that a 4-week corticosterone treatment (35 μg/ml, CORT model) in C57BL/6NTac male mice induced an anxiety/depressive-like behavior. Then, chronic fluoxetine treatment (18 mg/kg/day for 28 days in the drinking water) reduced corticosterone-induced increase in emotional behavior. However, among 46 fluoxetine-treated mice, only 30 of them presented a 50% decrease in emotionality score, defining fluoxetine responders (CORT/Flx-R). To determine a peripheral biological signature of fluoxetine response, proteomic analysis was performed from PBMCs isolated from the “most” affected corticosterone/vehicle (CORT/V), corticosterone/fluoxetine responders and non-responders (CORT/Flx-NR) animals. In comparison to CORT/V, a total of 263 proteins were differently expressed after fluoxetine exposure. Expression profile of these proteins showed a strong similarity between CORT/Flx-R and CORT/Flx-NR (R = 0.827, p < 1e^-7). Direct comparison of CORT/Flx-R and CORT/Flx-NR groups revealed 100 differently expressed proteins, representing a combination of markers associated either with the maintenance of animals in a refractory state, or associated with behavioral improvement. Finally, 19 proteins showed a differential direction of expression between CORT/Flx-R and CORT/Flx-NR that drove them away from the CORT-treated profile. Among them, eight upregulated proteins (RPN2, HSPA9, NPTN, AP2B1, UQCRC2, RACK-1, TOLLIP) and one downregulated protein, TLN2, were previously associated with MDD or antidepressant drug response in the literature. Future preclinical studies will be required to validate whether proteomic changes observed in PBMCs from CORT/Flx-R mice mirror biological changes in brain tissues.

Tau Deletion Prevents Stress-Induced Dendritic Atrophy in Prefrontal Cortex: Role of Synaptic Mitochondria

Tau protein in dendrites and synapses has been recently implicated in synaptic degeneration and neuronal malfunction. Chronic stress, a well-known inducer of neuronal/synaptic atrophy, triggers hyperphosphorylation of Tau protein and cognitive deficits. However, the cause-effect relationship between these events remains to be established. To test the involvement of Tau in stress-induced impairments of cognition, we investigated the impact of stress on cognitive behavior, neuronal structure, and the synaptic proteome in the prefrontal cortex (PFC) of Tau knock-out (Tau-KO) and wild-type (WT) mice. Whereas exposure to chronic stress resulted in atrophy of apical dendrites and spine loss in PFC neurons as well as significant impairments in working memory in WT mice, such changes were absent in Tau-KO animals. Quantitative proteomic analysis of PFC synaptosomal fractions, combined with transmission electron microscopy analysis, suggested a prominent role for mitochondria in the regulation of the effects of stress. Specifically, chronically stressed animals exhibit Tau-dependent alterations in the levels of proteins involved in mitochondrial transport and oxidative phosphorylation as well as in the synaptic localization of mitochondria in PFC. These findings provide evidence for a causal role of Tau in mediating stress-elicited neuronal atrophy and cognitive impairment and indicate that Tau may exert its effects through synaptic mitochondria.

MicroRNA Profiling in the Medial and Lateral Habenula of Rats Exposed to the Learned Helplessness Paradigm: Candidate Biomarkers for Susceptibility and Resilience to Inescapable Shock

Depression is a highly heterogeneous disorder presumably caused by a combination of several factors ultimately causing the pathological condition. The genetic liability model of depression is likely to be of polygenic heterogeneity. miRNAs can regulate multiple genes simultaneously and therefore are candidates that align with this model. The habenula has been linked to depression in both clinical and animal studies, shifting interest towards this region as a neural substrate in depression. The goal of the present study was to search for alterations in miRNA expression levels in the medial and lateral habenula of rats exposed to the learned helplessness (LH) rat model of depression. Ten miRNAs showed significant alterations associating with their response to the LH paradigm. Of these, six and four miRNAs were significantly regulated in the MHb and LHb, respectively. In the MHb we identified miR-490, miR-291a-3p, MiR-467a, miR-216a, miR-18b, and miR-302a. In the LHb miR-543, miR-367, miR-467c, and miR-760-5p were significantly regulated. A target gene analysis showed that several of the target genes are involved in MAPK signaling, neutrophin signaling, and ErbB signaling, indicating that neurotransmission is affected in the habenula as a consequence of exposure to the LH paradigm.

What Have Mass Spectrometry-Based Proteomics and Metabolomics (Not) Taught Us about Psychiatric Disorders?

Understanding the molecular causes and finding appropriate therapies for psychiatric disorders are challenging tasks for research; -omics technologies are used to elucidate the molecular mechanisms underlying brain dysfunction in a hypothesis-free manner. In this review, we will focus on mass spectrometry-based proteomics and metabolomics and address how these approaches have contributed to our understanding of psychiatric disorders. Specifically, we will discuss what we have learned from mass spectrometry-based proteomics and metabolomics studies in rodent models and human cohorts, outline current limitations and discuss the potential of these methods for future applications in psychiatry.

The ups and downs of modelling mood disorders in rodents

The wide spectrum of disruptions that characterizes major depressive disorder (MDD) and bipolar disorder (BD) highlights the difficulties researchers are posed with as they try to mimic these disorders in the laboratory. Nonetheless, numerous attempts have been made to create rodent models of mood disorders or at least models of the symptoms of MDD and BD. Present antidepressants are all descendants of the serendipitous findings in the 1950s that the monoamine oxidase inhibitor iproniazid and the tricyclic antidepressant imipramine were effective antidepressants. Thus, the need for improved animal models to provide insights into the neuropathology underlying the disease is critical. Such information is in turn crucial for identifying new antidepressants and mood stabilisers. Currently, there is a shift away from traditional animal models to more focused research dealing with an endophenotype-style approach, genetic models, and incorporation of new findings from human neuroimaging and genetic studies. Such approaches are opening up more tractable avenues for understanding the neurobiological and genetic bases of these disorders. Further, such models promise to yield better translational animal models and hence more fruitful therapeutic targets. This overview focuses on such animal models and tests and how they can be used to assess MDD and BD in rodents.

Targeting dynamic interplay among disordered domains or endophenotypes to understand complex neuropsychiatric disorders: Translational lessons from preclinical models

Contemporary biological psychiatry uses clinical and experimental (animal) models to increase our understanding of brain pathogenesis. Modeling psychiatric disorders is currently performed by targeting various key neurobehavioral clusters of phenotypic traits (domains), including affective, cognitive, social, motor and reward. Analyses of such domains and their 'smaller units' - individual endophenotypes - are critical for the study of complex brain disorders and their neural underpinnings. The spectrum nature of brain disorders and the importance of pathogenetic linkage among various disordered domains or endophenotypes have also been recognized as an important strategic direction of translational research. Here, we discuss cross-domain analyses of animal models, and focus on their value for mimicking the clinical overlap between disordered neurobehavioral domains in humans. Based on recent experimental evidence, we argue that understanding of brain pathogenesis requires modeling the clinically relevant inter-relationships between various individual endophenotypes (or their domains).

The contribution of proteomic studies in humans, animal models, and after antidepressant treatments to investigate the molecular neurobiology of major depression

The neurobiological basis of major depressive disorder (MDD) is only partially understood. The proposed hypotheses postulate dysregulations of monoaminergic and other neurotransmitter pathways, impaired stress responses, insufficient neurogenetic and neurotrophic processes generating maladaptive neuroplasticity, inappropriate inflammatory and metabolic responses. Proteomic approaches can provide useful contributions to the investigation of the molecular neurobiology of MDD due to their open-ended nature. Studies performed in brain regions of MDD patients which had received antidepressant (AD) treatment showed that affected proteins mainly belonged to energy pathways, transport of molecules, signaling, and synaptic transmission. Studies performed in animal models offer the advantage of more controlled experimental conditions at the expense of potential loss in relevance. The design of proteomic investigations included experiments carried out in MDD models, in naive animals treated with ADs, and in animal models subjected to AD treatments. A comparison of results suggested an overlap of several modulated pathways between MDD patients and animal models. Examples include the regulation of energy metabolism, especially oxidative phosphorylation and glycolysis, signal transduction pathways, including calcium-calmodulin kinase II, synaptic proteins, and cytoskeletal proteins. Nevertheless, the paucity of studies performed in human brains requires additional studies to confirm the correspondence.

Proteomics, metabolomics, and protein interactomics in the characterization of the molecular features of major depressive disorder

Omics technologies emerged as complementary strategies to genomics in the attempt to understand human illnesses. In general, proteomics technologies emerged earlier than those of metabolomics for major depressive disorder (MDD) research, but both are driven by the identification of proteins and/or metabolites that can delineate a comprehensive characterization of MDD's molecular mechanisms, as well as lead to the identification of biomarker candidates of all types—prognosis, diagnosis, treatment, and patient stratification. Also, one can explore protein and metabolite interactomes in order to pinpoint additional molecules associated with the disease that had not been picked up initially. Here, results and methodological aspects of MDD research using proteomics, metabolomics, and protein interactomics are reviewed, focusing on human samples.

Novel therapeutic targets in depression and anxiety: antioxidants as a candidate treatment

There is growing evidence that the imbalance between oxidative stress and the antioxidant defense system may be associated with the development neuropsychiatric disorders, such as depression and anxiety. Major depression and anxiety are presently correlated with a lowered total antioxidant state and by an activated oxidative stress (OS) pathway. The classical antidepressants may produce therapeutic effects other than regulation of monoamines by increasing the antioxidant levels and normalizing the damage caused by OS processes. This chapter provides an overview of recent work on oxidative stress markers in the animal models of depression and anxiety, as well as patients with the aforementioned mood disorders. It is well documented that antioxidants can remove the reactive oxygen species (ROS) and reactive nitrogen species (RNS) through scavenging radicals and suppressing the OS pathway, which further protect against neuronal damage caused oxidative or nitrosative stress sources in the brain, hopefully resulting in remission of depression or anxiety symptoms. The functional understanding of the relationship between oxidative stress and depression and anxiety may pave the way for discovery of novel targets for treatment of neuropsychiatric disorders.

Molecular profiling of the lateral habenula in a rat model of depression

Objective

This study systematically investigated the effect of chronic mild stress and response to antidepressant treatment in the lateral habenula at the whole genome level.

Methods

Rat whole genome expression chips (Affymetrix) were used to detect gene expression regulations in the lateral habenula of rats subjected to chronic mild stress (mild stressors exchanged twice a day for 8 weeks). Some rats received antidepressant treatment during fifth to eights week of CMS. The lateral habenula gene expression profile was studied through the gene ontology and signal pathway analyses using bioinformatics. Real-time quantitative polymerase chain reaction (RT-PCR) was used to verify the microarray results and determine the expression of the Fcrla, Eif3k, Sec3l1, Ubr5, Abca8a, Ankrd49, Cyp2j10, Frs3, Syn2, and Znf503 genes in the lateral habenula tissue.

Results

In particular we found that stress and antidepressant treatment affected intracellular cascades like growth factor receptor signaling, G-protein-coupled receptor signaling, and Wnt signaling – processes involved in the neuroplastic changes observed during the progression of depression and antidepressant treatment.

Conclusion

The present study suggests an important role of the lateral habenula in the development of depression-like conditions and correlates to previous studies demonstrating a significant role of the lateral habenula in depressive-like conditions and antidepressant treatment.

Chronic mild stress for modeling anhedonia

Major depressive disorder is a complex disease implicating many brain circuitries. The clinical symptomatology is inconsistent and heterogenous and the pathogenesis is a complicated interplay of genetic and environmental factors. The episodic and recurrent nature of the disease, as well as the fact that several symptoms are only verbally expressed, make it challenging to establish valid and legitimate animal models of this disease. The purpose of this review is to provide some background knowledge and overview of valid rodent models of depression with an emphasis on our own experience with a chronic mild stress model in modeling of anhedonia and cognitive impairments associated with depression. In a final concluding remark, a 'dying-forward' hypothesis, for development of depression, is suggested on the basis of mainly our own data on a hippocampal pathology.

Towards translational rodent models of depression

Rodent models of depression have been developed in an effort to identify novel antidepressant compounds and to further our understanding of the pathophysiology of depression. Various rodent models of depression and antidepressant-like behaviour are currently used but, clearly, none of these current models fully recapitulate all features of depression. Moreover, these models have not resulted in the development of novel non-monoaminergic-based antidepressants with clinical efficacy. Thus, a refinement of the current models of depression is required. The present review outlines the most commonly used models of depression and antidepressant drug-like activity and suggests several factors that should be considered when refining these models.