Glucocorticoid regulates parkin expression in mouse frontal cortex: Implications in schizophrenia

Stress and glucocorticoid hormones, which are released into the circulation following stressful experiences, have been shown to contribute significantly to the manifestation of various psychiatric illnesses including schizophrenia and depression. Studies in rodents have reported dose and time dependent effects of glucocorticoids on the expression of proteins related to neuroplasticity. However, the mechanism(s) involved in the regulation of proteins by glucocorticoids are not clear. Ubiquitin ligases play important role in degradation, trafficking and stabilization of proteins. The present study investigated the effect of glucocorticoid on ubiquitin-proteasome system in mouse frontal cortex. A significant increase in mRNA and protein levels of parkin, an E3 ubiquitin ligase was found in cultured mouse primary cortical neurons following corticosterone treatment. An increase in parkin levels was also found in mouse frontal cortex in vivo following acute dexamethasone treatment. However, chronic treatment with corticosterone did not change parkin protein levels in mouse frontal cortex. Studies using postmortem brain samples from schizophrenia and control subjects indicated a significant increase in parkin protein levels in frontal cortex of schizophrenia subjects suggesting a response to increased stress conditions in schizophrenia. These findings suggest a possible role of parkin in the pathophysiology of stress-related psychiatric disorders.