The study on the effect of depression on breast cancer incidence through IDO/kynurenine pathway.

Abstract

e13569 Background: Psychosocial factors have been considered as the most common causes for women with breast cancer. However, it remains unclear whether mental stress can influence cancer incidence and progression. This study aims to investigate the relationship between them and the potential molecular mechanism. Methods: Depression model was established by restricting MMTV-PyMT mice in a 50ml-fixator for 4 h per day for 21 consecutive days. Behavioral tests including light-dark box test, open-field test and force swimming test were performed. Then blood, brain and mammary samples were collected at the indicated time points. ELISA was used to detect the concentration of neurotransmitters serotonin, epinephrine and norepinephrine and inflammatory factors IL-6, TNF-a and IL-1β in brain tissue and serum. Real-time quantitative qPCR and western blot were used to detect indoleamine 2, 3-dioxygenase (IDO) expression. The level of tryptophan was measured by high performance liquid chromatography(HPLC). Flow cytometry was used to evaluate the exhaustion of CD8+ T cells. Besides, the correlation between IDO expression detected by immunohistochemistry and the severity of mammary tumors was analyzed in the tumor specimens. Results: We observed that chronic stress caused depression-like behaviors, abnormal secretion of neurotransmitters serotonin, epinephrine and norepinephrine and promoted the development of breast cancer in MMTV-PyMT mice. Depression elevated the secretion of inflammatory factors IL-6, TNF-a and IL-1β in brain tissue and serum, which upregulated the expression of IDO and decreased the level of tryptophan in mice. Furthermore, T cells are sensitive to low tryptophan concentration, so elevated IDO expression suppressed and exhausted CD8+ T cells, ultimately promoting cancer incidence. Administration of xiaoyao pill (a well-known Chinese herbal formula for treating depression) or IDO inhibitor reversed the depression-like behaviors in mice and slowed the development of breast cancer. At the same time, the analysis of clinical samples showed that depression identified by Hamilton Depression Scale(HAMD) and IDO expression in mammary tumor tissues were positively correlated with the severity of mammary tumors. Conclusions: Altogether, our results suggest that depression can promote tumor immune privilege and cancer occurrence through inducing upregulated IDO expression.