Absence of Gene Predisposes Mice to Mild Social Isolation - Chronic Stress, Leading to Depression-Like Phenotype Associated With Differential Expression of Synaptic Proteins.

We earlier reported that the male mice lacking the gene () showed mild anxiety, better memory retention, and up-regulation of synaptic proteins in the hippocampus. With increasing evidences from parallel studies in our laboratory about the possible role of in stress response, we investigated its role in brain. We observed that transcript gets up-regulated in the hippocampus of the wild-type mice exposed to stress. To further dissect its function, we analyzed the behavioral and molecular phenotypes of mice when subjected to mild chronic psychological stress, namely; mild (attenuated) social isolation. We employed iTRAQ based quantitative proteomics, real time PCR and western blotting to investigate molecular changes. Three weeks of social isolation predisposed mice to anhedonia, heightened anxiety-measured by Open field test (OFT), increased behavior despair- measured by Forced swim test (FST) and reduced dendritic branching along with decreased spine density of hippocampal CA1 neurons as compared to wild-type counterparts. This depression-like-phenotype was however ameliorated when treated with anti-depressant imipramine. Molecular analysis revealed that out of 1002 quantified proteins [1% False discovery rate (FDR), at-least two unique peptides], strikingly, a significant proportion of synaptic proteins including, SYN1, CAMK2A, and RAB3A were down-regulated in the socially isolated mice as compared to its wild-type counterparts. This was in contrast to the elevated levels of these proteins in non-stressed mutants as compared to the controls. We hypothesized that a de-regulated transcription factor upstream of the synaptic genes might be responsible for the observed phenotype. Indeed, in the socially isolated mice, there was an up-regulation of GATA1 - a transcription factor that negatively regulates synaptic genes and has been associated with Major Depression (MD) in humans. The present study demonstrates significant genotype × enviornment interaction for gene as shown by the reversal in the expression levels of several synaptic proteins in the mutant vis-à-vis wild-type mouse when exposed to social isolation stress.