Molecular Basis Of Aberrant Signal Pathways For Mood Regulation In The Prefrontal Cortex Of Depressed Patients

Mood disorder is a debilitating disorder of altered mood regulation that affects about17%of the population at some point in life, resulting in serious personal, social and economic burdens. Structural and functional alterations in the dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) have been consistently reported in mood disorders and on the other hand, antidepressant treatment would attenuate or reverse such abnormalities. However, the possible underlying biological mechanism for such abnormalities in the prefrontal cortex is not fully understood yet. In the present study, we used quantitative real-time PCR to determine the mRNA levels of crucial genes involved in mood regulation in the grey matter isolated from postmortem ACC and DLPFC of patients with mood disorder and of well-matched controls. Both patients with bipolar disorder (BPD) and major depressive disorder (MDD) are included in the mood disorder group. Immunohistochemistry in the ACC of several interested targets with alterations in mRNA levels was performed. In addition, cell cultures and molecular biology techniques for investigating possible molecular mechnisms were conducted. The main findings are as follows.1) mRNA levels of the important elements of retinoid signaling were significantly reduced in the postmortem DLPFC/ACC from patients with mood disorder. Decreased mRNA levels of BDNF and TrkB isoforms were also found. A positive correlation between mRNA levels of retinoic acid receptor a (RARa) and TrkB was found in the ACC of control subjects but not of patients with mood disorder, suggesting the interaction between them was affected. Last, immunohistochemistry of RARa and TrkB showed both receptors are localized in the same neuron in the ACC, and chromatin immunoprecipitation assay and dual luciferase reporter gene assay showed that RARa was able to bind to and transactivate the TrkB promoter via a putative retinoic acid response element within the TrkB promoter.2) Transcript level of mineralocorticoid receptor (MR) were significantly decreased, while the ratios of glucocorticoid receptor (GR) α to MR mRNA levels were increased in the ACC/DLPFC in the mood disorder group. After the correlation between the expression of these DLPFC genes and their earlier measured expression in the paraventricular nucleus (PVN) of the same subjects was determined, significant inverse correlations were found for MR mRNA levels and for GRα/MR ratios in the DLPFC and PVN. It is suggested that the prefrontal cortex could inhibit the response of hypothalamic-pituitary-adrenal (HPA) axis to stress. The change of MR transcript level in the prefrontal cortex and PVN may explain the hyperactivity of HPA-axis and contribute to the pathophysiology of mood disorders.3) In the ACC of MDD patients, a significant decrease was observed in the mRNA level of cytochrome P45017A1(CYP17A1, synthesizing C19ketosteroids) and a significant increase in that of hydroxysteroid sulfotransferase2A (SULT2A, catalizing the sulphate conjugation of dehydroepiandrosterone (DHEA)), suggesting alterations in DHEA and its sulfate metabolite DHEA-S levels. Immunohistochemistry showed expression of SULT2A and CYP17A1in both neurons and glia-cells in human ACC and semiquantification of immunohistochemistry showed lower CYP17A1positive cell number in the patients with MDD. Furthermore, in the DLPFC, a significant increase in SULT2A and11β-hydroxysteroid dehydrogenase1(HSD11B1, reducing cortisone to the active hormone cortisol) mRNA level was observed in the MDD patients. Higher mRNA level of steroidogenic acute regulatory protein (StAR, facilitating the shuttle of cholesterol through the intermembrane space) was found in the BPD patients.4) A significant increase of glial fibrillary acidic protein α (GFAPα) mRNA level was found in the ACC of subjects with BPD as compared to their matched controls. In addition, a significant reduction in mRNA levels of proteolipid protein (PLP) and GFAPδ were found in the ACC of patiens with MDD. Interestingly, a significant lower GFAPα mRNA level were observed during daytime (10:01-22:00h) compared to that during nighttime (22:01-10:00h) in the DLPFC of control subjects, which was also confirmed in an additional control group with more subjects. Such GFAPa mRNA day-night fluctuation was not present in mood disorder group. Immunocytochemistry of GFAP in the ACC showed that the optical density of GFAP+signal was increased, while the percentage of surface area covered by GFAP+signal decreased in the ACC of BPD patients, indicating that there might be a retraction of GFAP processes in BPD patients.To conclude, our results provide evidence for a selective dsyregulation of several mood-related molecules in the DLPFC/ACC of patients with mood disorder and thus offer molecular neuropathological evidence for the development of depression.