Inter-tissue networks between the basal forebrain, hippocampus, and prefrontal cortex in a model for depression caused by disturbed sleep.

Disturbances in sleep are encountered in the majority of patients with depressive disorder. To elucidate the molecular mechanisms behind this relationship, we examined gene expression changes in a rodent model for disturbed sleep and depression. The animals were treated with daily injections of clomipramine to affect their sleep during early infancy. This early interference with sleep is known to induce depression-like behavior in adult animals. After 2 weeks of treatment, the change in gene expression was examined using the Affymetrix Rat 230.2 chip. We studied the gene expression in the basal forebrain, hippocampus, and frontal cortex and combined the results to reveal the otherwise indissectible networks between and around the tissues. The major disrupted pathways between the three brain areas were related to synaptic transmission, regulation of translation, and ubiquitinylation. The involved pathways were within the cellular components of the axons, growth cones, melanosomes, and pigment granules. A network analysis allowing for additional interactors, in the form of chemicals or gene products, revealed a disturbed communicational network between the different brain areas. This disturbed network is centered around serotonin, Mn(II), and Rhoa. The findings elucidate inter-tissue pathways and networks in the brain that are involved in sleep and mood regulation. The findings are of uttermost interest, some are quite predictable and obvious, but some are novel or have only been proposed by rare theoretical speculations (such as the melanosome and Mn(II) involvement). Equally important as the findings are the methods described in this article. In this study, we present two novel simple ways to perform system biological analysis based on gene expression array data. We used two already existing tools in a new way, and by careful planning of the input data, managed to extrapolate intricate hidden inter-tissue networks to build a molecular picture of disease.

Gene expression patterns in a rodent model for depression.

Disturbances in sleep are encountered in the majority of patients with depression. To elucidate the possible molecular mechanisms behind this relationship we examined gene expression changes in a rodent model for depression and disturbed sleep. Animals were treated with daily injections of clomipramine in their early infancy, after which gene expression in basal forebrain was examined using Affymetrix Rat 230.2 chips. We tested the levels of both single transcripts and involved pathways, and searched for common nominators (i.e. transcription factors) that could explain these changes. We identified 72 differentially expressed gene transcripts, many of which are involved in epigenetic regulation, such as DNMT2. Analysis of functional pathways revealed statistically significant changes of the biological process of synaptic transmission, the cellular compartment of the synapse and the molecular function of GABA signalling, showing that transcripts with altered expression are functionally related. Finally, promoter analysis of the differentially expressed genes showed a clear enrichment of binding sites for the transcription factor CREB1, a molecule also involved in epigenetic regulation (cAMP response element-binding protein induces histone modifications). These results indicate that CREB1 may constitute one of the major links between disturbed sleep and mood. The results also highlight the molecular mechanisms in the murine clomipramine model, previously shown to be a valid model for depression.

Environmental stress affects DNA methylation of a CpG rich promoter region of serotonin transporter gene in a nurse cohort.

BACKGROUND: Shift-working nurses are exposed to a stressful work environment, which puts them at an increased risk for burnout and depression. We explored the effect of environmental stress on serotonin transporter gene (SLC6A4) promoter methylation among nurses from high and low work stress environments. METHODOLOGY: Using bisulfite sequencing, we investigated the methylation status of five CpG residues of a CpG-rich region in the promoter of SLC6A4 by comparing female shift working nurses from a high work stress environment (n = 24) to low work stress environment (n = 25). We also analyzed the association of 5-HTTLPR polymorphism at 5' end of SLC6A4. Work stress was assessed by the Karasek's Model and possible signs of burnout or depression were measured by the Maslach Burnout Index General Survey and Beck Depression Index. Methylation levels were assessed by bisulfite sequencing of DNA extracted from peripheral blood leucocytes. Restriction enzyme treatment followed by standard PCR was used to identify 5-HTTLPR genotypes. PRINCIPAL FINDINGS: We found that nurses in the high stress environment had significantly lower promoter methylation levels at all five CpG residues compared to nurses in the low stress environment (p<0.01). There was no significant interaction of 5-HTTLPR genotype and work stress with methylation (p = 0.58). In unadjusted (bivariate) analysis, burnout was not significantly associated to methylation levels. However, when mutually adjusted for both, burnout and work stress were significant contributors (p = 0.038 and p<0.0001 respectively) to methylation levels. CONCLUSIONS: Our findings show that environmental stress is concurrent with decreased methylation of the SLC6A4 promoter. This may lead to increased transcriptional activity of the gene, increased reuptake of serotonin from synaptic clefts, and termination of the activity of serotonin. This could present a possible coping mechanism for environmental stress in humans that could eventually increase risk for disturbed functional capability and experience of depressed mood in long-term stress.