Alterations Of Oxytocin System In Depression:Relation With Androgen

Backgrounds:Oxytocin(OXT),synthesized in the hypothalamic paraventricular nucleus(PVN)may act both as a hormone and a neurotransmitter/neuromodulator.OXT is presumed to play an important role in central regulations for pro-social behaviors,and anti-stress responses,the mechanism behind which is,however,still unclear.Changes in peripheral plasma OXT levels were reported in depression,with contradictory results.In addition,in many neiuropsychiatric disorders(including depression),OXT and testosterone levels show opposite changes,the reason of which was unknown.Oxytocin receptor(OXTR)is essential for the effects of OXT.It remains to be elucidated whether and how OXT and OXTR participate in the pathogenesis of depression and whether androgen directly regulates the human OXT expression.In order to reveal the alternations of brain OXT in depression and to explore the possible mechanism of testosterone regulating OXT gene expression,we investigated the OXT expression in the hypothalamic PVN of depression patients and the co-locolization of OXT and androgen receptor(AR)in OXT-expressing neurons.Next,we identified the androgen response element(ARE)in human OXT gene promoter,and examined the molecular mechanism that androgen regulates human OXT gene expression.We also measured the changes in cerebrospinal fluid(CSF)testosterone levels,and we determined the OXTR mRNA and AR mRNA expression in the anterior cortex(ACC)and the dorsolateral prefrontal cortex(DLPFC)in depression,since ACC and DLPFC are not only the important projection areas of OXT,but also crucially involved in mood regulation and depression.Methods:(1)The changes of OXT expression in the hypothalamic PVN in depression were studied by immunocytochemistry(ICC)and image analysis.The co-locolization of OXT-expressing neurons and AR in the PVN was detected by double-labelling ICC.(2)The effect of testosterone on the endogenous OXT expression in human neuroblastoma cells SK-N-SH was detected by immunofluorescence and real-time quantitative PCR.The existence of ARE in human OXT gene promoter region was identified by electrophoretic mobility shift assay and immunoprecipitation reaction.(3)The CSF-testosterone levels were detected by enzyme-linked immunosorbent assay.(4)The expression of OXTR mRNA and AR mRNA in the ACC and DLPFC regions were detected by real-time fluorescence quantitative PCR.Correlations among the parameters were also analyzed.Results:(1)The expression of PVN OXT-immunoreactivity was significantly increased(p=0.027)in depression patients compared with the controls.There was AR co-expressed in the OXT-expressing neurons in the hypothalamic PVN,mainly in the nucleus.(2)Human neuroblastoma cells SK-N-SH express endogenous OXT and AR.The OXT expression was significantly decreased after estrogen receptor antagonist and testosterone treatment(p = 0.05).Testosterone can interact through AR with ARE found in the human OXT gene promoter and decreases OXT promoter luciferase reporter activity(p = 0.02).(3)Compared with the control group,CSF levels of testosterone did not change significantly in depression.In addition,CSF-testosterone levels showed positive correlations with age in female depression patients(r = 0.610,p = 0.046),and in patients with major depressive disorder(MDD)(r = 0.550,p = 0.042),while this correlation did not show in male depression nor in bipolar disorder(BD)patients.(4)No significant differences were found in the OXTR mRNA and AR mRNA expression in the ACC and DLPFC between depression and control groups.In the male control group,there was a significant positive correlation between the expression of AR mRNA and age both in the ACC(r = 0.703,p = 0.034)and in the DLPFC(r = 0.657,p = 0.02),and there was a significant positive correlation between the AR mRNA and OXTR mRNA in the ACC(r =0.810,p=0.008)which did not exist in the DLPFC of male controls.In addition,neither the female control group nor the whole depression group showed any correlation between AR mRNA and OXTR mRNA in ACC or DLPFC.BD patients,however,showed such correlation in the ACC(r = 0.971,p = 0.000)and a trend of correlation in the DLPFC(r = 0.682,p = 0.092),respectively.Moreover,male controls showed significantly lower AR mRNA(p = 0.032)and OXTR mRNA(p =0.007)"in the DLPFC compared with female controls,which needs to be confirmed,due to the small size of the subgroups(male =9,female = 3).Conclusion:The OXT expression in the hypothalamic PVN of depression patients was significantly increased.Androgen can directly inhibit human OXT gene expression by binding to ARE in OXT gene promoter through AR.CSF-testosterone and peripheral testosterone levels may be two relatively independent compartments,and CSF-testosterone levels could be different from those in different brain regions.OXT system activity and its interaction with androgen involving in the pathogenesis of depression are sex-,brain region-,and subtype of depression-related,which need attention for studies and warrant further study to elucidate the mechanisms behind.