Abstract
Chronic physical restraint stress increases oxidative stress in the brain, and dysregulation of oxidative stress can be one of the causes of major depressive disorder. To understand the underlying mechanisms, we undertook a systematic proteomic analysis of hippocampus in a chronic restraint stress mouse model of depression. Combining two-dimensional gel electrophoresis (2D-PAGE) for protein separation with nanoUPLC-ESI-q-TOF tandem mass spectrometry, we identified sixty-three protein spots that changed in the hippocampus of mice subjected to chronic restraint stress. We identified and classified the proteins that changed after chronic stress, into three groups respectively functioning in neural plasticity, metabolic processes and protein aggregation. Of these, 5 proteins including ubiquitin C-terminal hydrolase L1 (UCH-L1), dihydropyrimidinase-related protein 2 (DPYL2), haloacid dehalogenase-like hydrolase domain-containing protein 2 (HDHD2), actin-related protein 2/3 complex subunit 5 (ARPC5) and peroxiredoxin-2 (PRDX2), showed pI shifts attributable to post-translational modifications. Further analysis indicated that UCH-L1 underwent differential oxidations of 2 cysteine residues following chronic stress. We investigated whether the oxidized form of UCH-L1 plays a role in stressed hippocampus, by comparing the effects of UCH-L1 and its Cys mutants on hippocampal cell line HT-22 in response to oxidative stress. This study demonstrated that UCH-L1 wild-type and cysteine to aspartic acid mutants, but not its cysteine to serine mutants, afforded neuroprotective effects against oxidative stress; there were no discernible differences between wild-type UCH-L1 and its mutants in the absence of oxidative stress. These findings suggest that cysteine oxidative modifications of UCH-L1 in the hippocampus play key roles in neuroprotection against oxidative stress caused in major depressive disorder.
Highlights
Major depressive disorder (MDD)1 in human is a life-threatening mood disorder, accompanied, in addition to persistent depression, by lethargy, and memory impairment among other symptoms
Upon further analysis based on their known biological functions using text-mining approach (Table I and Fig. 2A) and protein interaction network analysis (STRING version 10.0; http://string-db.org/) with additional clustering methods (Fig. 2B), we found that proteins functioning in synaptic plasticity, neurite outgrowth and neuronal morphology (20.6%) were the most enriched, followed by proteins related to protein metabolic process (15.9%), protein aggregation, neurodegenerative diseases (7.9%), neural differentiation (7.9%), intracellular protein transport, vesicle mediated transport (7.9%), antiapoptotic role (6.3%), reactive oxygen species generation (6.3%), calcium-dependent regulation of neural plasticity (6.3%), carbohydrate metabolic processes (6.3%), haloacid dehalogenase (HAD)-type phosphatases (4.8%), extracellular antioxidant defenses (3.2%), generation of precursor metabolites and energy (3.2%), neuronal migration, cell motility (1.6%), and vitamin metabolic processes (1.6%)
In this study employing 2D-PAGE and MS analysis, we identified 63 proteins that changed in the hippocampus of chronic restraint stress mouse model of major depressive disorder (MDD)
Summary
Major depressive disorder (MDD)1 in human is a life-threatening mood disorder, accompanied, in addition to persistent depression, by lethargy, and memory impairment among other symptoms. In the present study, using 2D-PAGE-based proteomic analysis, we identified sixty-three stress-responsive proteins in the hippocampus of chronic restraint stress mouse model and found the most significant changes in UCH-L1.
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