Proteome analysis of the thalamus and cerebrospinal fluid reveals glycolysis dysfunction and potential biomarkers candidates for schizophrenia

Recent advances in quantitative neuroproteomics

The field of proteomics is undergoing rapid development in a number of different areas including improvements in mass spectrometric platforms, peptide identification algorithms and bioinformatics. In particular, new and/or improved approaches have established robust methods that not only allow for in-depth and accurate peptide and protein identification and modification, but also allow for sensitive measurement of relative or absolute quantitation. These methods are beginning to be applied to the area of neuroproteomics, but the central nervous system poses many specific challenges in terms of quantitative proteomics, given the large number of different neuronal cell types that are intermixed and that exhibit distinct patterns of gene and protein expression. This review highlights the recent advances that have been made in quantitative neuroproteomics, with a focus on work published over the last five years that applies emerging methods to normal brain function as well as to various neuropsychiatric disorders including schizophrenia and drug addiction as well as of neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. While older methods such as two-dimensional polyacrylamide electrophoresis continued to be used, a variety of more in-depth MS-based approaches including both label (ICAT, iTRAQ, TMT, SILAC, SILAM), label-free (label-free, MRM, SWATH) and absolute quantification methods, are rapidly being applied to neurobiological investigations of normal and diseased brain tissue as well as of cerebrospinal fluid (CSF). While the biological implications of many of these studies remain to be clearly established, that there is a clear need for standardization of experimental design and data analysis, and that the analysis of protein changes in specific neuronal cell types in the central nervous system remains a serious challenge, it appears that the quality and depth of the more recent quantitative proteomics studies is beginning to shed light on a number of aspects of neuroscience that relates to normal brain function as well as of the changes in protein expression and regulation that occurs in neuropsychiatric and neurodegenerative disorders.

Schizophrenia: metabolic aspects of aetiology, diagnosis and future treatment strategies

Despite decades of research, the pathophysiology and aetiology of schizophrenia remains incompletely understood. The disorder is frequently accompanied by metabolic symptoms including dyslipidaemia, hyperinsulinaemia, type 2 diabetes and obesity. These symptoms are a common side effect of currently available antipsychotic medications. However, reports of metabolic dysfunction in schizophrenia predate the antipsychotic era and have also been observed in first onset patients prior to antipsychotic treatment. Here, we review the evidence for abnormalities in metabolism in schizophrenia patients, both in the central nervous system and periphery. Molecular analysis of post mortem brain tissue has pointed towards alterations in glucose metabolism and insulin signalling pathways, and blood-based molecular profiling analyses have demonstrated hyperinsulinaemia and abnormalities in secretion of insulin and co-released factors at first presentation of symptoms. Nonetheless, such features are not observed for all subjects with the disorder and not all individuals with such abnormalities suffer the symptoms of schizophrenia. One interpretation of these data is the presence of an underlying metabolic vulnerability in a subset of individuals which interacts with environmental or genetic factors to produce the overt symptoms of the disorder. Further investigation of metabolic aspects of schizophrenia may prove critical for diagnosis, improvement of existing treatment based on patient stratification/personalised medicine strategies and development of novel antipsychotic agents.

Gene expression analysis reveals schizophrenia-associated dysregulation of immune pathways in peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMCs) represent an accessible tissue source for gene expression profiling in schizophrenia that could provide insight into the molecular basis of the disorder. This study used the Illumina HT_12 microarray platform and quantitative real time PCR (QPCR) to perform mRNA expression profiling on 114 patients with schizophrenia or schizoaffective disorder and 80 non-psychiatric controls from the Australian Schizophrenia Research Bank (ASRB). Differential expression analysis revealed altered expression of 164 genes (59 up-regulated and 105 down-regulated) in the PBMCs from patients with schizophrenia compared to controls. Bioinformatic analysis indicated significant enrichment of differentially expressed genes known to be involved or associated with immune function and regulating the immune response. The differential expression of 6 genes, EIF2C2 (Ago 2), MEF2D, EVL, PI3, S100A12 and DEFA4 was confirmed by QPCR. Genome-wide expression analysis of PBMCs from individuals with schizophrenia was characterized by the alteration of genes with immune system function, supporting the hypothesis that the disorder has a significant immunological component in its etiology.

Chronic phencyclidine increases synapsin-1 and synaptic adaptation proteins in the medial prefrontal cortex

Phencyclidine (PCP) mimics many aspects of schizophrenia, yet the underlying mechanism of neurochemical adaptation for PCP is unknown. We therefore used proteomics to study changes in the medial prefrontal cortex in animals with PCP-induced behavioural deficits. Male Wistar rats were injected with saline or 5 mg/kg phencyclidine for 5 days followed by two days of washout. Spontaneous alternation behaviour was tested in a Y-maze and then proteins were extracted from the medial prefrontal cortex. 2D-DIGE analysis followed by spot picking and protein identification with mass spectrometry then provided a list of differentially expressed proteins. Treatment with 5 mg/kg phencyclidine decreased the percentage of correct alternations in the Y-maze compared to saline-treated controls. Proteomics analysis of the medial prefrontal cortex found upregulation of 6 proteins (synapsin-1, Dpysl3, Aco2, Fscn1, Tuba1c, and Mapk1) and downregulation of 11 (Bin1, Dpysl2, Sugt1, ApoE, Psme1, ERp29, Pgam1, Uchl1, Ndufv2, Pcmt1, and Vdac1). A trend to upregulation was observed for Gnb4 and Capza2, while downregulation trends were noted for alpha-enolase and Fh. Many of the hits in this study concur with recent postmortem data from schizophrenic patients and this further validates the use of phencyclidine in preclinical translational research.

Identification of protein biomarkers in human serum using iTRAQ and shotgun mass spectrometry

Blood serum is one of the easiest accessible sources of biomarkers and its proteome presents a significant parcel of immune system proteins. These proteins can provide not only biological explanation but also diagnostic and drug response answers independently of the type of disease or condition in question. Shotgun mass spectrometry has profoundly contributed to proteome analysis and is presently considered as an indispensible tool in the field of biomarker discovery. In addition, the multiplexing potential of isotopic labeling techniques such as iTRAQ can increase statistical relevance and accuracy of proteomic data through the simultaneous analysis of different biological samples. Here, we describe a complete protocol using iTRAQ in a shotgun proteomics workflow along with data analysis steps, customized for the challenges associated with the serum proteome.

Gene expression of peripheral blood lymphocytes may discriminate patients with schizophrenia from controls

To identify a classifier in schizophrenia, blood gene expression profiling was applied to patients with schizophrenia under different treatments and to controls. Expression of six genes discriminated patients with sensitivity of 89.3% and specificity of 90%, supporting the use of peripheral blood as biological material for diagnosis in schizophrenia.

Striatal development involves a switch in gene expression networks, followed by a myelination event: implications for neuropsychiatric disease

Because abnormal development of striatal neurons is thought to be the part of pathology underlying major psychiatric illnesses, we studied the expression pattern of genes involved in striatal development and of genes comprising key striatal-specific pathways, during an active striatal maturation period, the first two postnatal weeks in rat. This period parallels human striatal development during the second trimester, when prenatal stress is though to lead to increased risk for neuropsychiatric disorders. To identify genes involved in this developmental process, we used subtractive hybridization, followed by quantitative real-time PCR, which allowed us to characterize the developmental expression of over 60 genes, many not previously known to play a role in neuromaturation. Of these 12 were novel transcripts, which did not match known genes, but which showed strict developmental expression and may play a role in striatal neurodevelopment. An additional 89 genes were identified as strong candidates for involvement in this neurodevelopmental process. We show that during the first two postnatal weeks in rat, an early gene expression network, still lacking key striatal-specific signaling pathways, is downregulated and replaced by a mature gene expression network, containing key striatal-specific genes including the dopamine D1 and D2 receptors, conferring to these neurons their functional identity. Therefore, before this developmental switch, striatal neurons lack many of their key phenotypic characteristics. This maturation process is followed by a striking rise in expression of myelination genes, indicating a striatal-specific myelination event. Such strictly controlled developmental program has the potential to be a point of susceptibility to disruption by external factors. Indeed, this period is known to be a susceptibility period in both humans and rats.

Análise proteômica da esquizofrenia

Valioso conhecimento a respeito de esquizofrenia tem sido gerado recentemente para decifrar sua patobiologia e revelar biomarcadores. Entretanto, esforços ainda são necessários, especialmente se levarmos em conta que essa debilitante desordem mental afeta aproximadamente 30 milhões de pessoas ao redor do mundo. Considerando que esquizofrenia é resultado de uma complexa interação entre fatores ambientais, função genética alterada e expressão proteica diferencial sistemática, a proteômica é provavelmente uma ferramenta adequada ao estudo dessa desordem. Aqui sintetizamos os principais achados em estudos proteômicos e posteriores direções a serem tomadas de forma a melhor compreender a bioquímica da esquizofrenia, bem como revelar biomarcadores.

Altered functional protein networks in the prefrontal cortex and amygdala of victims of suicide

Probing molecular brain mechanisms related to increased suicide risk is an important issue in biological psychiatry research. Gene expression studies on post mortem brains indicate extensive changes prior to a successful suicide attempt; however, proteomic studies are scarce. Thus, we performed a DIGE proteomic analysis of post mortem tissue samples from the prefrontal cortex and amygdala of suicide victims to identify protein changes and biomarker candidates of suicide. Among our matched spots we found 46 and 16 significant differences in the prefrontal cortex and amygdala, respectively; by using the industry standard t test and 1.3 fold change as cut off for significance. Because of the risk of false discoveries (FDR) in these data, we also made FDR adjustment by calculating the q-values for all the t tests performed and by using 0.06 and 0.4 as alpha thresholds we reduced the number of significant spots to 27 and 9 respectively. From these we identified 59 proteins in the cortex and 11 proteins in the amygdala. These proteins are related to biological functions and structures such as metabolism, the redox system, the cytoskeleton, synaptic function, and proteolysis. Thirteen of these proteins (CBR1, DPYSL2, EFHD2, FKBP4, GFAP, GLUL, HSPA8, NEFL, NEFM, PGAM1, PRDX6, SELENBP1 and VIM,) have already been suggested to be biomarkers of psychiatric disorders at protein or genome level. We also pointed out 9 proteins that changed in both the amygdala and the cortex, and from these, GFAP, INA, NEFL, NEFM and TUBA1 are interacting cytoskeletal proteins that have a functional connection to glutamate, GABA, and serotonin receptors. Moreover, ACTB, CTSD and GFAP displayed opposite changes in the two examined brain structures that might be a suitable characteristic for brain imaging studies. The opposite changes of ACTB, CTSD and GFAP in the two brain structures were validated by western blot analysis.

Myelination and oxidative stress alterations in the cerebellum of the G72/G30 transgenic schizophrenia mouse model

G72/G30 is a primate-specific locus that has been repeatedly implicated as a risk factor in genetic studies of schizophrenia. The function of the longest G72 splice variant (LG72 protein) encoded by this locus is not fully understood. To investigate the role of the LG72 protein in vivo, we have generated transgenic (G72Tg) mice carrying the G72/G30 locus that exhibit schizophrenia-like symptoms. We investigated protein expression alterations in the cerebella of G72Tg compared to wild type (WT) mice using a proteomics approach based on in vivo(15)N metabolic labeling and quantitative mass spectrometry (MS). Our data revealed expression level differences of proteins involved in myelin-related processes, oxidative stress and mitochondrial function. Furthermore, in silico pathway analyses suggested common regulators and targets for the observed protein alterations. Our work sheds light on the functional role of the LG72 protein and pinpoints molecular correlates of schizophrenia-like behavior.

The association of white matter volume in psychotic disorders with genotypic variation in NRG1, MOG and CNP: a voxel-based analysis in affected individuals and their unaffected relatives

We investigated the role of variation in putative psychosis genes coding for elements of the white matter system by examining the contribution of genotypic variation in three single-nucleotide polymorphisms (SNPs) neuregulin 1 (NRG1) SNP8NRG221533, myelin oligodendrocytes glycoprotein (MOG) rs2857766 and CNP (rs2070106) and one haplotype HAP(ICE) (deCODE) to white matter volume in patients with psychotic disorder and their unaffected relatives. Structural magnetic resonance imaging and blood samples for genotyping were collected on 189 participants including patients with schizophrenia (SZ) or bipolar I disorder (BDI), unaffected first-degree relatives of these patients and healthy volunteers. The association of genotypic variation with white matter volume was assessed using voxel-based morphometry in SPM5. The NRG1 SNP and the HAP(ICE) haplotype were associated with abnormal white matter volume in the BDI group in the fornix, cingulum and parahippocampal gyrus circuit. In SZ the NRG1 SNP risk allele was associated with lower white matter volume in the uncinate fasciculus (UF), right inferior longitudinal fasciculus and the anterior limb of the internal capsule. Healthy G-homozygotes of the MOG SNP had greater white matter volume in areas of the brainstem and cerebellum; this relationship was absent in those with a psychotic disorder and the unaffected relatives groups. The CNP SNP did not contribute to white matter volume variation in the diagnostic groups studied. Variation in the genes coding for structural and protective components of myelin are implicated in abnormal white matter volume in the emotion circuitry of the cingulum, fornix, parahippocampal gyrus and UF in psychotic disorders.

Bridging the gap between the immune and glutamate hypotheses of schizophrenia and major depression: Potential role of glial NMDA receptor modulators and impaired blood-brain barrier integrity

OBJECTIVES

Previous studies have suggested that the pathogenesis of schizophrenia and major depression involves an altered peripheral immune system. It is not clear, however, whether such changes are associated with corresponding neuroinflammatory responses and disturbances of neurotransmission.

METHODS

This paper reviews the current state of knowledge about the involvement of immune alterations in schizophrenia and major depression and a possible link to disturbances of glutamatergic transmission.

RESULTS

Inflammatory endogenous modulators of the NMDA receptor, the kynurenine pathway metabolites, are potential candidates for such a link. Studies of the blood and cerebrospinal fluid have suggested a schizophrenia-related upregulation of the NMDA receptor antagonist kynurenic acid in astrocytes, analogous to the ketamine psychosis model. Conversely, it has been proposed that there is depression-related microglial synthesis of the NMDA receptor agonist quinolinic acid, which is consistent with the observation that ketamine has therapeutic effects in major depression. Few publications have studied NMDA receptor modulating kynurenines in the brain, however.

CONCLUSIONS

Future research on the cerebral cell-type specific distribution of kynurenine metabolites and their brain-regional concentration imbalances will be required to connect peripheral immune changes, the hypotheses of blood-brain barrier dysfunction and glial pathology with concepts of altered neurotransmission in schizophrenia and major depression.

Gene Expression Profiling of Tuberculous Meningitis Co-infected with HIV

Tuberculous meningitis (TBM) is a fatal form of Mycobacterium tuberculosis infection of the central nervous system (CNS). The similarities in the clinical and radiological findings in TBM cases with or without HIV make the diagnosis very challenging. Identification of genes, which are differentially expressed in brain tissues of HIV positive and HIV negative TBM patients, would enable better understanding of the molecular aspects of the infection and would also serve as an initial platform to evaluate potential biomarkers. Here, we report the identification of 796 differentially regulated genes in brain tissues of TBM patients co-infected with HIV using oligonucleotide DNA microarrays. We also performed immunohistochemical validation and confirmed the abundance of four gene products-glial fibrillary acidic protein (GFAP), serpin peptidase inhibitor, clade A member 3 (SERPINA3), thymidine phosphorylase (TYMP/ECGF1) and heat shock 70 kDa protein 8 (HSPA8). Our study paves the way for understanding the mechanism of TBM in HIV positive patients and for further validation of potential disease biomarkers.

Association of genetic copy number variations at 11 q14.2 with brain regional volume differences in an alcohol use disorder population

This study investigates the relationship between genetic copy number variations and brain volume differences in an alcohol use disorder (AUD) population. We hypothesized that copy number variations may influence subject's risk for alcohol use disorders through variations in regional gray and white matter brain volumes. Since genetic influences upon behavior are the result of many complicated interactions we focus on differences in brain volume as a putative intermediate phenotype between genetic variation and behavior. Copy number variation, alcohol use assessments and brain structural magnetic resonance images from 283 subjects, 199 male and 84 females who were enrolled in two AUD studies were obtained and analyzed using a combination of the Freesurfer image analysis suite and independent component analysis. Because brain volume varies by age we compared participant's volume variation with that derived from a control cohort of 75 subjects. In addition we also regressed out the possible brain volume changes induced by long term alcohol consumption. Small cerebral cortex, cerebellar and caudate along with large cerebral white matter and 5th ventricle volumes are shown to be significantly associated with increased AUD severity. When these volume variations are compared with control subject volumes; the variations seen in subjects with AUD are markedly different from normal aging effects. CNVs at 11 q14.2 are marginally (p < 0.05 uncorrected) correlated with such brain volume variations and the correlation holds true after controlling for long-term alcohol consumption; deletion carriers have smaller cerebral cortex, cerebellar, caudate and larger cerebral white matter and 5th ventricle volumes than insertion carriers or subjects with no variation in this region. Similarly, deletion carriers also demonstrate higher AUD severity scores than insertion carriers or subjects with no variation. The results presented here suggest that copy number variation and in particular the variation at chromosome 11 q14.2 may have an impact in brain volume variation, potentially influencing AUD behavior.

Cerebrospinal fluid biomarker candidates of schizophrenia: where do we stand?

Here, we review the cerebrospinal fluid (CSF) candidate markers with regard to their clinical relevance as potential surrogates for disease activity, prognosis assessment, and predictors of treatment response. We searched different online databases such as MEDLINE and EMBASE for studies on schizophrenia and CSF. Initial studies on cerebrospinal fluid in patients with schizophrenia revealed increased brain-blood barrier permeability with elevated total protein content, increased CSF-to-serum ratio for albumin, and intrathecal production of immunoglobulins in subgroups of patients. Analyses of metabolites in CSF suggest alterations within glutamatergic neurotransmission as well as monoamine and cannabinoid metabolism. Decreased levels of brain-derived neurotrophic factor and nerve growth factor in CSF of first-episode patients with schizophrenia reported in recent studies point to a dysregulation of neuroprotective and neurodevelopmental processes. Still, these findings must be considered as non-specific. A more profound characterization of the particular psychopathological profiles, the investigation of patients in the prodromal phase or within the first episode of schizophrenia promoting longitudinal investigations, implementation of different approaches of proteomics, and rigorous adherence to standard procedures based on international CSF guidelines are necessary to improve the quality of CSF studies in schizophrenia, paving the way for identification of syndrome-specific biomarker candidates.

Regulation of munc18-1 and syntaxin-1A interactive partners in schizophrenia prefrontal cortex: down-regulation of munc18-1a isoform and 75 kDa SNARE complex after antipsychotic treatment

Munc18-1 and syntaxin-1 are crucial interacting molecules for synaptic membrane fusion and neurotransmitter release. Contrasting abnormalities of several proteins of the exocytotic machinery, including the formation of SNARE (synaptobrevin, SNAP-25 and syntaxin-1) complexes, have been reported in schizophrenia. This study quantified in the dorsolateral prefrontal cortex (PFC, Brodmann area 9) the immunocontent of munc18-1a/b isoforms, syntaxin-1A, other presynaptic proteins (synaptotagmin, synaptophysin), and SNARE complexes, as well as the effects of psychoactive drug exposure, in schizophrenia (SZ, n=24), non-schizophrenia suicide (SD, n=13) and major depression (MD, n=15) subjects compared to matched controls (n=39). SZ was associated with normal expression of munc18-1a/b and increased syntaxin-1A (+44%). The presence of antipsychotic drugs reduced the basal content of munc18-1a isoform (-23%) and synaptobrevin (-32%), and modestly reduced that of up-regulated syntaxin-1A (-16%). Munc18-1a and syntaxin-1A protein expression correlated positively in controls but showed a markedly opposite pattern in SZ, regardless of antipsychotic treatment. Thus, the ratio of syntaxin-1A to munc18-1a showed a net increase in SZ (+53/114%). The SNARE complex (75 kDa) was found unaltered in antipsychotic-free and reduced (-28%) in antipsychotic-treated SZ subjects. None of these abnormalities were observed in SD and MD subjects, unexposed or exposed to psychoactive drugs. The results reveal some exocytotic dysfunctions in SZ that are probably related to an imbalance of the interaction between munc18-1a and SNARE (mainly syntaxin-1A) complex. Moreover, antipsychotic drug treatment is associated with lower content of key proteins of the exocytotic machinery, which could result in a destabilization/impairment of neurosecretion.

Increased stress reactivity is associated with reduced hippocampal activity and neuronal integrity along with changes in energy metabolism

Patients suffering from major depression have repeatedly been reported to have dysregulations in hypothalamus-pituitary-adrenal (HPA) axis activity along with deficits in cognitive processes related to hippocampal and prefrontal cortex (PFC) malfunction. Here, we utilized three mouse lines selectively bred for high (HR), intermediate, or low (LR) stress reactivity, determined by the corticosterone response to a psychological stressor, probing the behavioral and functional consequences of increased vs. decreased HPA axis reactivity on the hippocampus and PFC. We assessed performance in hippocampus- and PFC-dependent tasks and determined the volume, basal activity, and neuronal integrity of the hippocampus and PFC using in vivo manganese-enhanced magnetic resonance imaging and proton magnetic resonance spectroscopy. The hippocampal proteomes of HR and LR mice were also compared using two-dimensional gel electrophoresis and mass spectrometry. HR mice were found to have deficits in the performance of hippocampus- and PFC-dependent tests and showed decreased N-acetylaspartate levels in the right dorsal hippocampus and PFC. In addition, the basal activity of the hippocampus, as assessed by manganese-enhanced magnetic resonance imaging, was reduced in HR mice. The three mouse lines, however, did not differ in hippocampal volume. Proteomic analysis identified several proteins that were differentially expressed in HR and LR mice. In accordance with the notion that N-acetylaspartate levels, in part, reflect dysfunctional mitochondrial metabolism, these proteins were found to be involved in energy metabolism pathways. Thus, our results provide further support for the involvement of a dysregulated HPA axis and mitochondrial dysfunction in the etiology and pathophysiology of affective disorders.

Proteomic approaches to unravel the complexity of schizophrenia

Schizophrenia is a debilitating mental disorder that affects approximately 30 million people worldwide. The development and progression of this disease is now thought to be precipitated through a complex interaction between altered gene function and environmental factors. Proteomic analyses have been applied extensively over the past 10 years in studies of several tissues from schizophrenic patients, resulting in increased insight into the affected molecular pathways. In addition, these proteomic approaches have led to the identification of a set of molecular biomarker assays as the first blood-based test to aid in the diagnosis of schizophrenia. Here, we discuss the main outcome of these investigations and suggest a practical means of integrating and translating the findings between the brain and peripheral blood to increase our understanding of schizophrenia pathophysiology.

Differential expression of HINT1 in schizophrenia brain tissue

Recent findings in the literature suggest a relation between histidine triad nucleotide-binding protein-1 (HINT1) and psychiatric disorders such as major depression, anxiety, and schizophrenia, although its physiological roles are not completely comprehended. Using Western blot, we compared HINT1 protein expression in the postmortem dorsolateral prefrontal cortex and thalamus of schizophrenia patients and healthy controls for contributing to elucidate the role of HINT1 in schizophrenia pathophysiology. HINT1 was found to be downregulated in the dorsolateral prefrontal cortex and upregulated in the thalamus. Our results combined to previous studies in human samples and preclinical models support the notion that HINT1 must be more explored as a potential target for psychiatric disorders.

Identification of proteomic signatures associated with depression and psychotic depression in post-mortem brains from major depression patients

Major depressive disorder (MDD) is a leading cause of disability worldwide and results tragically in the loss of almost one million lives in Western societies every year. This is due to poor understanding of the disease pathophysiology and lack of empirical medical tests for accurate diagnosis or for guiding antidepressant treatment strategies. Here, we have used shotgun proteomics in the analysis of post-mortem dorsolateral prefrontal cortex brain tissue from 24 MDD patients and 12 matched controls. Brain proteomes were pre-fractionated by gel electrophoresis and further analyzed by shotgun data-independent label-free liquid chromatography-mass spectrometry. This led to identification of distinct proteome fingerprints between MDD and control subjects. Some of these differences were validated by Western blot or selected reaction monitoring mass spectrometry. This included proteins associated with energy metabolism and synaptic function and we also found changes in the histidine triad nucleotide-binding protein 1 (HINT1), which has been implicated recently in regulation of mood and behavior. We also found differential proteome profiles in MDD with (n=11) and without (n=12) psychosis. Interestingly, the psychosis fingerprint showed a marked overlap to changes seen in the brain proteome of schizophrenia patients. These findings suggest that it may be possible to contribute to the disease understanding by distinguishing different subtypes of MDD based on distinct brain proteomic profiles.

Proteomics as a tool for understanding schizophrenia

Schizophrenia is likely to be a multifactorial disorder, consequence of alterations in gene and protein expression since the neurodevelopment that together to environmental factors will trigger the establishment of the disease. In the post-genomic era, proteomics has emerged as a promising strategy for revealing disease and treatment biomarkers as well as a tool for the comprehension of the mechanisms of schizophrenia pathobiology. Here, there is a discussion of the potential pathways and structures that are compromised in schizophrenia according to proteomic findings while studying five distinct brain regions of post-mortem tissue from schizophrenia patients and controls. Proteins involved in energy metabolism, calcium homeostasis, myelinization, and cytoskeleton have been recurrently found to be differentially expressed in schizophrenia brains. These findings may encourage new studies on the understanding of schizophrenia biochemical pathways and even new potential drug targets.

Biomarkers in development of psychotropic drugs

Biomarkers have been receiving increasing attention, especially in the field of psychiatry. In contrast to the availability of potent therapeutic tools including pharmacotherapy, psychotherapy, and biological therapies, unmet needs remain in terms of onset of action, stability of response, and further improvement of the clinical course. Biomarkers are objectively measured characteristics which serve as indicators of the causes of illnesses, their clinical course, and modification by treatment. There exist a variety of markers: laboratory markers which comprise the determination of genetic and epigenetic markers, neurotransmitters, hormones, cytokines, neuropeptides, enzymes, and others as single measures; electrophysiological markers which usually comprise electroencephalography (EEG) measures, and in particular sleep EEG and evoked potentials, magnetic encephalography, electrocardiogram, facial electromyography, skin conductance, and others; brain imaging techniques such as cranial computed tomography, magnetic resonance imaging, functional MRl, magnetic resonance spectroscopy, positron emission tomography, and single photon emission computed tomography; and behavioral approaches such as cue exposure and challenge tests which can be used to induce especially emotional processes in anxiety and depression. Examples for each of these domains are provided in this review. With a view to developing more individually tailored therapeutic strategies, the characterization of patients and the courses of different types of treatment will become even more important in the future.

Differential effects of prenatal stress in 5-Htt deficient mice: towards molecular mechanisms of gene × environment interactions

Prenatal stress (PS) has been shown to influence the development of the fetal brain and to increase the risk for the development of psychiatric disorders in later life. Furthermore, the variation of human serotonin transporter (5-HTT, SLC6A4) gene was suggested to exert a modulating effect on the association between early life stress and the risk for depression. In the present study, we used a 5-Htt×PS paradigm to investigate whether the effects of PS are dependent on the 5-Htt genotype. For this purpose, the effects of PS on cognition, anxiety- and depression-related behavior were examined using a maternal restraint stress paradigm of PS in C57BL6 wild-type (WT) and heterozygous 5-Htt deficient (5-Htt +/-) mice. Additionally, in female offspring, a genome-wide hippocampal gene expression profiling was performed using the Affymetrix GeneChip® Mouse Genome 430 2.0 Array. 5-Htt +/- offspring showed enhanced memory performance and signs of reduced anxiety as compared to WT offspring. In contrast, exposure of 5-Htt +/- mice to PS was associated with increased depressive-like behavior, an effect that tended to be more pronounced in female offspring. Further, 5-Htt genotype, PS and their interaction differentially affected the expression of numerous genes and related pathways within the female hippocampus. Specifically, MAPK and neurotrophin signaling were regulated by both the 5-Htt +/- genotype and PS exposure, whereas cytokine and Wnt signaling were affected in a 5-Htt genotype×PS manner, indicating a gene×environment interaction at the molecular level. In conclusion, our data suggest that although the 5-Htt +/- genotype shows clear adaptive capacity, 5-Htt +/- mice--particularly females--at the same time appear to be more vulnerable to developmental stress exposure when compared to WT offspring. Moreover, hippocampal gene expression profiles suggest that distinct molecular mechanisms mediate the behavioral effects of the 5-Htt genotype, PS exposure, and their interaction.

Progress in defining the biological causes of schizophrenia

Schizophrenia is a common mental illness resulting from a complex interplay of genetic and environmental risk factors. Establishing its primary molecular and cellular aetiopathologies has proved difficult. However, this is a vital step towards the rational development of useful disease biomarkers and new therapeutic strategies. The advent and large-scale application of genomic, transcriptomic, proteomic and metabolomic technologies are generating data sets required to achieve this goal. This discovery phase, typified by its objective and hypothesis-free approach, is described in the first part of the review. The accumulating biological information, when viewed as a whole, reveals a number of biological process and subcellular locations that contribute to schizophrenia causation. The data also show that each technique targets different aspects of central nervous system function in the disease state. In the second part of the review, key schizophrenia candidate genes are discussed more fully. Two higher-order processes - adult neurogenesis and inflammation - that appear to have pathological relevance are also described in detail. Finally, three areas where progress would have a large impact on schizophrenia biology are discussed: deducing the causes of schizophrenia in the individual, explaining the phenomenon of cross-disorder risk factors, and distinguishing causative disease factors from those that are reactive or compensatory.

The disulfide proteome and other reactive cysteine proteomes: analysis and functional significance

Ten years ago, proteomics techniques designed for large-scale investigations of redox-sensitive proteins started to emerge. The proteomes, defined as sets of proteins containing reactive cysteines that undergo oxidative post-translational modifications, have had a particular impact on research concerning the redox regulation of cellular processes. These proteomes, which are hereafter termed "disulfide proteomes," have been studied in nearly all kingdoms of life, including animals, plants, fungi, and bacteria. Disulfide proteomics has been applied to the identification of proteins modified by reactive oxygen and nitrogen species under stress conditions. Other studies involving disulfide proteomics have addressed the functions of thioredoxins and glutaredoxins. Hence, there is a steadily growing number of proteins containing reactive cysteines, which are probable targets for redox regulation. The disulfide proteomes have provided evidence that entire pathways, such as glycolysis, the tricarboxylic acid cycle, and the Calvin-Benson cycle, are controlled by mechanisms involving changes in the cysteine redox state of each enzyme implicated. Synthesis and degradation of proteins are processes highly represented in disulfide proteomes and additional biochemical data have established some mechanisms for their redox regulation. Thus, combined with biochemistry and genetics, disulfide proteomics has a significant potential to contribute to new discoveries on redox regulation and signaling.

Proteome analyses of cultured astrocytes treated with MK-801 and clozapine: similarities with schizophrenia

On the basis of impaired glutamatergic transmission and the potential role of astrocytes in schizophrenia, we treated cultured astrocytes with MK-801, an NMDA-receptor antagonist, to investigate whether the resulting proteome changes are similar to those we found in our earlier proteome analysis of schizophrenia human brain tissue as well as to better comprehend the role of astrocytes in the disorder. Indeed, there are similarities. Furthermore, to verify the efficacy of clozapine and its effect over the proteome, we treated MK-801-treated astrocytes with clozapine. Interestingly, clozapine reversed protein changes induced by MK-801. The treatment of cell cultures with neural transmission agonists and antagonists might provide useful insights about psychiatric disorders.

General overview: biomarkers in neuroscience research

Biomarkers are in demand for disease diagnosis, treatment response monitoring, and development of novel therapeutics. Biomarker discovery in neuroscience is challenging due to absence of robust molecular correlates and the interpatient heterogeneity that characterizes neuropsychiatric disorders. Because of the complexity of these disorders, a panel of biomarkers derived from different platforms will be required to precisely reflect disease-related alterations. Animal models of psychiatric phenotypes as well as -omics and imaging methodologies are important tools for biomarker discovery. However, the limitations of current research concerning sample handling and collection, candidate biomarker validation, and a lack of interdisciplinary approaches need to be addressed. Ultimately, the coordinated effort of relevant stakeholders including researchers, physicians, and funding organizations together with standardization initiatives will be vital to overcome the present challenges and to advance personalized health care using sensitive and specific biomarkers.

Proteomic technologies for biomarker studies in psychiatry: advances and needs

In the postgenome era, proteomics has arisen as a promising tool for more complete comprehension of diseases and for biomarker discovery. Some of these objectives have already been partly achieved for illnesses such as cancer. In the case of psychiatric conditions, however, proteomic advances have had a less profound impact. Here, we outline the necessity of improving and applying proteomic methods for biomarker discovery and validation in the field of psychiatric disorders. While proteomic-based applications in neurosciences have increased in accuracy and sensitivity over the past 10 years, the development of orthogonal validation technologies has fallen behind. These issues are discussed along with the importance of integrating systems biology approaches and combining proteomics with other research approaches. The future development of such technologies may put proteomics closer to clinical applications in psychiatry.

The role of proteomics in depression research

Depression is a severe neuropsychiatric disorder affecting approximately 10% of the world population. Despite this, the molecular mechanisms underlying the disorder are still not understood. Novel technologies such as proteomic-based platforms are beginning to offer new insights into this devastating illness, beyond those provided by the standard targeted methodologies. Here, we will show the potential of proteome analyses as a tool to elucidate the pathophysiological mechanisms of depression as well as the discovery of potential diagnostic, therapeutic and disease course biomarkers.