Possible role of arginase 1 positive microglia on depressive/anxiety-like behaviors in atopic dermatitis mouse model.

Atopic dermatitis (AD) and mood disorder comorbidities are typical, but the exact mechanism underlying their interplay has not been clarified. In this study, we aimed to identify the possible mechanisms of anxiety/depressive-like behaviors observed in AD, focusing on microglia. AD was induced by Dermatophagoides farinae body extract (Dfb) in NC/Nga mice and anxiety/depressive-like behaviors were analyzed by behavioral assessments such as open field test (OFT), tail suspension test (TST), sucrose preference test (SPT), and social interaction. As clinical symptoms of AD induced, anxiety/depressive-like behaviors were increased in the OFT and TST and serum glucocorticoid was elevated. AD mice showed an increased mRNA expression of interleukin-4 (IL-4) in lymph nodes but decreased arginase 1 (Arg1) mRNA expression without a change of IL-4 in the hippocampus. In addition, AD mice showed microglia with a shortened branch of de-ramified form and astrocytes with longer processes and decreased branching in the hippocampus, especially in the dentate gyrus (DG). The immunofluorescence study of the DG confirmed that Arg1 reduction was associated with microglia, but not astrocytes. Furthermore, glucocorticoid receptor reduction, increased 5-HT1AR, reduced phosphorylated cAMP response element-binding protein (pCREB), and brain-derived neurotrophic factor (BDNF) expression were identified in the hippocampus of AD mice. Notably, an immunofluorescence study confirmed that pCREB was decreased in the DG of AD mice. Collectively, our data suggest that the reduced Arg1 positive microglia might contribute to anxiety/depressive-like behaviors via pCREB/BDNF reduction in AD.