Impact of psychosocial stress on airway inflammation and its mechanism in a murine model of allergic asthma.

BACKGROUND: It has already been recognized that psychosocial stress evokes asthma exacerbation; however, the mechanism of how stress gets inside the body is not clear. This study aimed to observe the impact of psychosocial stress on airway inflammation and its mechanism in the ovalbumin-induced asthmatic mice combined with social disruption stress.

METHODS: Thirty-six male BALB/c mice were randomly divided into: control group, asthma group (ovalbumin-induced), asthma plus social disruption stress group (SDR), and SDR group. The open field video tracking system was used to assess animal behaviors. The invasive pulmonary resistance (RL) and dynamic lung compliance (cdyn) test system from Buxco was applied to detect pulmonary function. The enzyme-linked immunosorbent assay (ELISA) was utilized to determine OVA-IgE, T-helper type 2 (Th2) cytokines (IL-4, IL-5, IL-13) and corticosterone in mouse serum, the Th2 cytokines (IL-4, IL-5, IL-13, IL-6, TNF-α) in bronchoalveolar lavage fluid (BALF), and IL-6 and TNF-α levels in the supernatant of splenocytes cultured in vitro. Hematoxylin-eosin (H&E) staining was used to assess airway inflammation in lung histology. The cell count kit-8 assay (CCK-8) was applied to evaluate the inhibitory effect of corticosterone on splenocyte proliferation induced by lipopolysaccharide (LPS). Real time-PCR and Western blotting were utilized to determine glucocorticoid receptor (GR) mRNA and GR protein expression in lungs.

RESULTS: The open field test showed that combined allergen exposure and repeated stress significantly shortened the time the mice spent in the center of the open field (P < 0.01), increased ambulatory activity (P < 0.01) and the count of fecal boli (P < 0.01), but deceased vertical activity (P < 0.01). Results from pulmonary function demonstrated that airway hyperresponsiveness (AHR) was enhanced by psychosocial stress compared with allergy exposure alone. The ELISA results showed that cytokines in serum and BALF were significantly increased (P < 0.05). Moreover, the lung histology showed that infiltrated inflammatory cells were significantly increased in the asthma-SDR group compared with the asthma group (P < 0.05). Interestingly, serum corticosterone was remarkably raised by psychosocial stress (P < 0.05). In addition, the inhibitory effect of corticosterone on IL-6 and TNF-α in LPS-stimulated splenocyte cultures in vitro was diminished in the asthma-SDR group compared to the asthma group. The CCK-8 test revealed that the inhibition effect of corticosterone on splenocyte proliferation induced by LPS was significantly impaired in the SDR and asthma-SDR groups, while no significant effect was observed in the control and asthma groups. Furthermore, expression of GR mRNA and GR protein were significantly reduced in the lung tissues of the asthma-SDR group (P < 0.05).

CONCLUSIONS: Social disruption stress can promote anxiety behavior, activate the hypothalamic-pituitary-adrenal (HPA) axis, increase AHR and inflammation, and also impair glucocorticoid sensitivity and its function in a murine model of asthma. The down-regulation of GR expression induced by social disruption stress is in part associated with glucocorticoid insensitivity, which leads to asthma exacerbation.