Proteome profile of telencephalon associates attenuated neurogenesis with chronic stress induced mood disorder phenotypes in zebrafish model.

Debilitating mental illness like depression and related mood disorders is due to the disruption in circuitry that controls emotion, motivation, and reward, characterized by disparate phenotypes like decrease in socialization, motivation, threshold for threat apprehension, etc. Chronic stress is a major factor in the etiology of these disorders. Here, using a chronic unpredictable stress (CUS) paradigm the characterization of an array of mood disorder phenotypes in adult zebrafish, in comparison to normal control unstressed fish, was achieved using a battery of behavioral assays including novel ones comprising social interaction test, feed approach test, threat response test and novel tank test. For the predictive validity of the model for mood disorders, the mitigative role of a slow (imipramine) and fast (ketamine) acting antidepressant was assessed. The molecular changes associated with CUS-induced mood disorder phenotype was investigated utilizing a high throughput method called isobaric tag for relative and absolute quantification (iTRAQ) in telencephalon, the region critically associated with the processing of emotional information in the fish brain. Out of 222 proteins identified to be significantly altered, 58 were differentially expressed across the stress and antidepressant-treatment groups at more than one fold (in log2) change. Of these proteins, some were implicated in earlier studies on mood disorders such as CABP1, PER2, mTOR, etc. The enrichment of altered proteins by Ingenuity Pathway Analysis (IPA) led us to mTOR and opioid signaling pathways, the top canonical pathways affected in the fish telencephalon. Interestingly, most of the pathways affected converge at the one controlling cell proliferation thus indicating altered neurogenesis, which was validated using immunohistochemistry for cell proliferation markers BrdU, SOX2, and BLBP. The study concludes that molecules that regulate telencephalon neural progenitor cell proliferation or neurogenesis are crucially involved in chronic stress-induced mood disorders by affecting the circuitry that controls emotion and reward.