Chronic nicotine administration restores brain region specific upregulation of oxytocin receptor binding levels in a G72 mouse model of schizophrenia.

Nicotine dependence and schizophrenia are two mental health disorders with remarkably high comorbidity. Cigarette smoking is particularly prevalent amongst schizophrenic patients and it is hypothesised to comprise a form of self-medication for relieving cognitive deficits in these patients. Emerging evidence suggests a role of the neurohypophysial peptide oxytocin in the modulation of drug addiction, as well as schizophrenia symptomology; however, the underlying mechanism remains unclear. Therefore, we sought to investigate the effects of chronic nicotine administration on oxytocin receptor (OTR) binding in the brain of a transgenic mouse model of schizophrenia that carries a bacterial artificial chromosome of the human G72/G30 locus (G72Tg). Female wild-type (WT) and heterozygous G72 transgenic CD-1 mice were treated with a chronic nicotine regimen (24 mg/kg/day, osmotic minipumps for 14 days) and quantitative autoradiographic mapping of oxytocin receptors was carried out in brains of these animals. OTR binding levels were higher in the cingulate cortex (CgCx), nucleus accumbens (Acb), and central amygdala (CeA) of saline treated G72Tg mice compared to WT control mice. Chronic nicotine administration reversed this upregulation in the CgCx and CeA. Interestingly, chronic nicotine administration induced an increase in OTR binding in the CeA of solely WT mice. These results indicate that nicotine administration normalises the dysregulated central oxytocinergic system of this mouse model of schizophrenia and may contribute towards nicotine's ability to modulate cognitive deficits which are common symptoms of schizophrenia.

Altered glyoxalase 1 expression in psychiatric disorders: cause or consequence?

Glyoxalase 1 is an enzyme, shown to protect against dicarbonyl glycation and the formation of advanced glycation end products. Recent findings suggest glyoxalase 1 as a molecular marker of psychiatric disorders. In clinical studies aberrant expression of glyoxalase 1 was shown to be involved in major depression, panic disorders and schizophrenia. In mouse models glyoxalase 1 was identified as a molecular marker of trait anxiety. However, anxiety-related behaviour in mice was inconsistently reported to correlate with elevated or reduced expression of glyoxalase 1. As yet, those findings were considered contradicting and the contribution of glyoxalase 1 to the aetiology of psychiatric disorders remained elusive. This review summarizes recent clinical and animal studies. In order to unravel the role of glyoxalase 1 in mental disease, findings are discussed with a particular focus on dicarbonyl substrate concentration. Prevailing the impact of dicarbonyl substrates on anxiety-related behaviour over the influence of glyoxalase 1 expression may consolidate findings that have been considered inconsistent. Taken together, this report suggests that physiological concentration of dicarbonyl compounds may differentiate a remedy from a poison.

Proteomic and metabolomic profiling of a trait anxiety mouse model implicate affected pathways.

Depression and anxiety disorders affect a great number of people worldwide. Whereas singular factors have been associated with the pathogenesis of psychiatric disorders, growing evidence emphasizes the significance of dysfunctional neural circuits and signaling pathways. Hence, a systems biology approach is required to get a better understanding of psychiatric phenotypes such as depression and anxiety. Furthermore, the availability of biomarkers for these disorders is critical for improved diagnosis and monitoring treatment response. In the present study, a mouse model presenting with robust high versus low anxiety phenotypes was subjected to thorough molecular biomarker and pathway discovery analyses. Reference animals were metabolically labeled with the stable (15)N isotope allowing an accurate comparison of protein expression levels between the high anxiety-related behavior versus low anxiety-related behavior mouse lines using quantitative mass spectrometry. Plasma metabolomic analyses identified a number of small molecule biomarkers characteristic for the anxiety phenotype with particular focus on myo-inositol and glutamate as well as the intermediates involved in the tricarboxylic acid cycle. In silico analyses suggested pathways and subnetworks as relevant for the anxiety phenotype. Our data demonstrate that the high anxiety-related behavior and low anxiety-related behavior mouse model is a valuable tool for anxiety disorder drug discovery efforts.

Methylglyoxal-mediated anxiolysis involves increased protein modification and elevated expression of glyoxalase 1 in the brain.

Methylglyoxal (MG) is a highly reactive metabolite that forms adducts with basic amino acid side chains in proteins. MG is degraded by glyoxalase1 (GLO1), an enzyme shown to be differentially expressed in several mouse models of anxiety-related behavior. As yet, molecular mechanisms by which altered GLO1 expression influences emotionality have not been elucidated. Here we report that both MG concentration and protein modification are altered in brain tissue of a mouse model for trait anxiety, with elevated levels in low anxiety-related behavior relative to high anxiety-related behavior animals. Accordingly, repeated intracerebroventricular injections of MG mediated anxiolysis in inbred high anxiety-related behavior and outbred CD1 mice. We found that anxiolytic-like properties of MG were independent of GLO1 expression. In contrast, antidepressant-like properties of intracerebroventricular MG were suppressed in CD1 mice carrying extra copies of the GLO1 gene. Moreover, MG treatment increased expression of GLO1 only in CD1 mice that did not have extra copies of GLO1. Taken together, these results suggest that the MG levels in brain are negatively correlated with anxiety. Thereby, we identified a novel molecular mechanism for anxiety-related behavior in mice that may help to elucidate genesis of psychiatric disorders in humans.

The glycolytic metabolite methylglyoxal induces changes in vigilance by generating low-amplitude non-REM sleep.

Methylglyoxal (MG), an essential by-product of glycolysis, is a highly reactive endogenous α-oxoaldehyde. Although high levels of MG are cytotoxic, physiological doses of MG were shown to reduce anxiety-related behavior through selective activation of γ-aminobutyric acid type A (GABAA) receptors. Because the latter play a major role in sleep induction, this study examined the potential of MG to regulate sleep. Specifically, we assessed how MG influences sleep-wake behavior in CD1 mice that received intracerebroventricular injections of either vehicle or 0.7 µmol MG at onset of darkness. We used electroencephalogram (EEG) and electromyogram (EMG) recordings to monitor changes in vigilance states, sleep architecture and the EEG spectrum, for 24 h after receipt of injections. Administration of MG rapidly induced non-rapid eye movement sleep (NREMS) and, concomitantly, decreased wakefulness and suppressed EEG delta power during NREMS. In addition, MG robustly enhanced the amount and number of episodes of an unclassified state of vigilance in which EMG, as well as EEG delta and theta power, were very low. MG did not affect overall rapid eye movement sleep (REMS) in a given 24-h period, but significantly reduced the power of theta activity during REMS. Our results provide the first evidence that MG can exert sleep-promoting properties by triggering low-amplitude NREMS.

Proteomics and metabolomics analysis of a trait anxiety mouse model reveals divergent mitochondrial pathways.

BACKGROUND: Although anxiety disorders are the most prevalent psychiatric disorders, no molecular biomarkers exist for their premorbid diagnosis, accurate patient subcategorization, or treatment efficacy prediction. To unravel the neurobiological underpinnings and identify candidate biomarkers and affected pathways for anxiety disorders, we interrogated the mouse model of high anxiety-related behavior (HAB), normal anxiety-related behavior (NAB), and low anxiety-related behavior (LAB) employing a quantitative proteomics and metabolomics discovery approach. METHODS: We compared the cingulate cortex synaptosome proteomes of HAB and LAB mice by in vivo (15)N metabolic labeling and mass spectrometry and quantified the cingulate cortex metabolomes of HAB/NAB/LAB mice. The combined data sets were used to identify divergent protein and metabolite networks by in silico pathway analysis. Selected differentially expressed proteins and affected pathways were validated with immunochemical and enzymatic assays. RESULTS: Altered levels of up to 300 proteins and metabolites were found between HAB and LAB mice. Our data reveal alterations in energy metabolism, mitochondrial import and transport, oxidative stress, and neurotransmission, implicating a previously nonhighlighted role of mitochondria in modulating anxiety-related behavior. CONCLUSIONS: Our results offer insights toward a molecular network of anxiety pathophysiology with a focus on mitochondrial contribution and provide the basis for pinpointing affected pathways in anxiety-related behavior.

Profiling trait anxiety: transcriptome analysis reveals cathepsin B (Ctsb) as a novel candidate gene for emotionality in mice.

Behavioral endophenotypes are determined by a multitude of counteracting but precisely balanced molecular and physiological mechanisms. In this study, we aim to identify potential novel molecular targets that contribute to the multigenic trait "anxiety". We used microarrays to investigate the gene expression profiles of different brain regions within the limbic system of mice which were selectively bred for either high (HAB) or low (LAB) anxiety-related behavior, and also show signs of comorbid depression-like behavior. We identified and confirmed sex-independent differences in the basal expression of 13 candidate genes, using tissue from the entire brain, including coronin 7 (Coro7), cathepsin B (Ctsb), muscleblind-like 1 (Mbnl1), metallothionein 1 (Mt1), solute carrier family 25 member 17 (Slc25a17), tribbles homolog 2 (Trib2), zinc finger protein 672 (Zfp672), syntaxin 3 (Stx3), ATP-binding cassette, sub-family A member 2 (Abca2), ectonucleotide pyrophosphatase/phosphodiesterase 5 (Enpp5), high mobility group nucleosomal binding domain 3 (Hmgn3) and pyruvate dehydrogenase beta (Pdhb). Additionally, we confirmed brain region-specific differences in the expression of synaptotagmin 4 (Syt4).Our identification of about 90 polymorphisms in Ctsb suggested that this gene might play a critical role in shaping our mouse model's behavioral endophenotypes. Indeed, the assessment of anxiety-related and depression-like behaviors of Ctsb knock-out mice revealed an increase in depression-like behavior in females. Altogether, our results suggest that Ctsb has significant effects on emotionality, irrespective of the tested mouse strain, making it a promising target for future pharmacotherapy.

Stable isotope metabolic labeling with a novel N-enriched bacteria diet for improved proteomic analyses of mouse models for psychopathologies.

The identification of differentially regulated proteins in animal models of psychiatric diseases is essential for a comprehensive analysis of associated psychopathological processes. Mass spectrometry is the most relevant method for analyzing differences in protein expression of tissue and body fluid proteomes. However, standardization of sample handling and sample-to-sample variability are problematic. Stable isotope metabolic labeling of a proteome represents the gold standard for quantitative mass spectrometry analysis. The simultaneous processing of a mixture of labeled and unlabeled samples allows a sensitive and accurate comparative analysis between the respective proteomes. Here, we describe a cost-effective feeding protocol based on a newly developed (15)N bacteria diet based on Ralstonia eutropha protein, which was applied to a mouse model for trait anxiety. Tissue from (15)N-labeled vs. (14)N-unlabeled mice was examined by mass spectrometry and differences in the expression of glyoxalase-1 (GLO1) and histidine triad nucleotide binding protein 2 (Hint2) proteins were correlated with the animals' psychopathological behaviors for methodological validation and proof of concept, respectively. Additionally, phenotyping unraveled an antidepressant-like effect of the incorporation of the stable isotope (15)N into the proteome of highly anxious mice. This novel phenomenon is of considerable relevance to the metabolic labeling method and could provide an opportunity for the discovery of candidate proteins involved in depression-like behavior. The newly developed (15)N bacteria diet provides researchers a novel tool to discover disease-relevant protein expression differences in mouse models using quantitative mass spectrometry.

{gamma}-Protocadherins, presenilin-mediated release of C-terminal fragment promotes locus expression.

gamma-Protocadherins (gamma-pcdhs) are type I membrane-spanning glycoproteins, widely expressed in the mammal and required for survival. These cell adhesion molecules are expressed from a complex locus comprising 22 functional variable exons arranged in tandem, each encoding extracellular, transmembrane and intracellular sequence, and three exons for an invariant C-terminal domain (gamma-ICD). However, the signaling mechanisms that lie downstream of gamma-pcdhs have not been elucidated. Here we report that gamma-pcdhs are subject to presenilin-dependent intramembrane cleavage (PS-IP), accompanied by shedding of the extracellular domain. The cleaved intracellular domain (gamma-ICD) translocates to the cell nucleus and was detected in subsets of cortical neurons. Notably, gene-targeted mice lacking functional gamma-ICD sequence showed severely reduced gamma-pcdh mRNA levels and neonatal lethality. Most importantly, inhibition of gamma-secretase decreased gamma-pcdh locus expression. Luciferase reporter assays demonstrated that gamma-pcdh promoter activity is increased by gamma-ICD. These results reveal an intracellular signaling mechanism for gamma-pcdhs and identify a novel vital target for the gamma-secretase complex.