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

Molecular changes in hippocampal energy metabolism in mice selectively bred for extremes in stress reactivity: Relevance of mitochondrial dysfunction for affective disorders

Affective disorders, such as major depression, are frequently associated with metabolic disturbances involving mitochondria. Although dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis is known to alter energy metabolism, the precise mechanisms linking stress and metabolic disturbances are not sufficiently understood. We used a mouse model of affective disorders to investigate the impact of a genetic predisposition for extremes in stress reactivity on behavioural and metabolic phenotypes as well as energy metabolism. Adult males of three independent mouse lines selectively bred for high, intermediate or low HPA axis reactivity were tested for exploratory and locomotor activity as well as stress-coping behaviour. Additionally, basal and stress-induced plasma corticosterone levels, body weight, food intake and body composition were measured. At the molecular level, the hippocampal transcriptome was analysed using microarray, serial analysis of gene expression and qRT-PCR. Finally, mitochondrial DNA copy number, damages and mitochondrial respiration were assessed. We found clear effects of the differential stress reactivity on the behavioural, morphometric and metabolic measures. Remarkably, the hyperactive behavioural and neuroendocrine stress-coping style of high-reactivity mice was associated with significant changes in the expression of an extended list of genes involved in energy metabolism and several mitochondrial functions. Yet, only minor changes were found in mitochondrial DNA copy number, damages and respiration. Thus, our findings support a prominent role of glucocorticoids in shaping the major endophenotypes of the stress reactivity mouse model and contribute towards understanding the important role of HPA axis dysregulation and changes in energy metabolism in the pathophysiology of affective disorders

Connecting Anxiety and Genomic Copy Number Variation: A Genome-Wide Analysis in CD-1 Mice.

Genomic copy number variants (CNVs) have been implicated in multiple psychiatric disorders, but not much is known about their influence on anxiety disorders specifically. Using next-generation sequencing (NGS) and two additional array-based genotyping approaches, we detected CNVs in a mouse model consisting of two inbred mouse lines showing high (HAB) and low (LAB) anxiety-related behavior, respectively. An influence of CNVs on gene expression in the central (CeA) and basolateral (BLA) amygdala, paraventricular nucleus (PVN), and cingulate cortex (Cg) was shown by a two-proportion Z-test (p = 1.6 x 10-31), with a positive correlation in the CeA (p = 0.0062), PVN (p = 0.0046) and Cg (p = 0.0114), indicating a contribution of CNVs to the genetic predisposition to trait anxiety in the specific context of HAB/LAB mice. In order to confirm anxiety-relevant CNVs and corresponding genes in a second mouse model, we further examined CD-1 outbred mice. We revealed the distribution of CNVs by genotyping 64 CD 1 individuals using a high-density genotyping array (Jackson Laboratory). 78 genes within those CNVs were identified to show nominally significant association (48 genes), or a statistical trend in their association (30 genes) with the time animals spent on the open arms of the elevated plus-maze (EPM). Fifteen of them were considered promising candidate genes of anxiety-related behavior as we could show a significant overlap (permutation test, p = 0.0051) with genes within HAB/LAB CNVs. Thus, here we provide what is to our knowledge the first extensive catalogue of CNVs in CD-1 mice and potential corresponding candidate genes linked to anxiety-related behavior in mice

Protein coding genes in genomic regions of CNVs detected in HAB/LAB and CD-1 mice.

<p>All genes listed overlap both CNVs in HAB/LAB mice detected with aCGH, JaxMDGA and NGS, and CNVs in CD-1 mice which were best associated with the time the animals spent on the open arm of the EPM (nominal <i>p</i>-value < 0.1).</p><p>Protein coding genes in genomic regions of CNVs detected in HAB/LAB and CD-1 mice.</p

Distribution of CNVs in CD-1 mice.

<p>Chromosomes are indicated by grey horizontal lines. Start points of CNVs are marked by dots and lines are drawn to the end points. Due to limitations in resolution, a small CNV might appear as dot only. CNVs highlighted in blue or red were associated with anxiety-related behavior (time on the open arm of the EPM) with a nominal <i>p</i>-value less than 0.1 or 0.05, respectively.</p

Association of copy number with anxiety-related behavior in CD-1 mice.

<p>Exemplarily, data of three associations resulting in nominal <i>p</i>-values reaching significance (<i>p</i> < 0.05), a trend (<i>p</i> < 0.1), and not reaching significance (<i>p</i> > 0.05), respectively, are shown. Each dot represents data of a single animal (N = 64). The relative copy number is represented by the mean normalized intensities of JaxMDGA probes within the respective CNV. <b>(A)</b> CNV no. 498; <i>P</i>_nom = 0.0009; regression line: y = 0.0091x + 9.4389. <b>(B)</b> CNV no. 164; <i>P</i>_nom = 0.0554; regression line: y = 0.0061x + 10.201. <b>(C)</b> CNV no. 453; <i>P</i>_nom = 0.9791; regression line: y = 0.0008x + 9.6225.</p

Genomic positions of CNVs on chromosome 3.

<p>The chromosome is indicated by a thick horizontal line (grey). Depending on the detection method, CNVs in HAB/LAB mice are depicted in orange (aCGH), dark red (JaxMDGA) and red (NGS), respectively. Data displayed above the grey line represent a copy number gain in HAB vs. LAB animals, data below a copy number loss. Data printed on the grey line show CNVs in 64 CD-1 mice, with those highlighted in color that could be associated with anxiety-related behavior (time on the open arm of EPM) with a nominal <i>p</i>-value less than 0.1 (light blue) or less than 0.05 (blue). Start points of CNVs are marked by dots and lines are drawn to the end points.</p