Acute HDM exposure shows time-of-day and sex-based differences in the severity of lung inflammation and circadian clock disruption.

BACKGROUND: Asthma is a chronic inflammatory disease that shows a time-of-day response to variations in symptoms/severity. However, how the lung circadian clock influences time-of-day response and sex-based differences in house dust mite (HDM)-induced airway inflammation and remodeling has not been thoroughly investigated.

OBJECTIVE: We sought to determine whether acute HDM exposure in wild-type mice shows time-of-day response and sex-based differences in allergic airway inflammation and circadian clock disruption in the lungs.

METHODS: Wild-type (C57BL/6J) and Rev-erbα knockout (KO) mice were exposed to either PBS or HDM (for 10 days) intranasally at Zeitgeber time (ZT0: 6 am; ZT12: 6 pm) and euthanized 48 hours after the last exposure. Acute HDM-induced time-of-day response and sex-based differences in lung inflammation, gated cytokines/chemokines, humoral and hormonal responses, and circadian clock gene expression were analyzed.

RESULTS: Acute HDM-exposed mice showed a time-of-day response and sex-based differences in exaggerated lung inflammation (inflammatory eosinophils and interstitial macrophages) at ZT12 when compared with ZT0. HDM-exposed female mice showed increased inflammatory response at ZT12, but HDM-exposed male mice showed comparatively lower inflammation with no time-of-day response. HDM-exposed female and male mice showed augmented IgE levels at ZT12 when compared with ZT0. Myeloid innate immunity panel, cytokines/chemokines, and mucin genes showed a time-of-day gating response at ZT0 and ZT12 in the HDM group. In addition, HDM exposure altered the expression of circadian clock genes in the lung, which was evident in female mice at ZT12. Overall, female mice showed significant time-of-day responses to all these parameters compared with male mice. Rev-erbα KO mice exposed to acute HDM showed exaggerated lung inflammation associated with increased IgE and proinflammatory cytokines in bronchoalveolar lavage fluid. Interestingly, HDM exposure causes reduced expression of clock genes in flow-sorted resident eosinophils but not alveolar macrophages. Acute HDM exposure reduced the nocturnal locomotor activity in mice 5 days post-HDM exposure until day 10.

CONCLUSIONS: This study shows a time-of-day response to acute HDM exposure and sex-based differences in the severity of lung inflammation and humoral immune response associated with circadian clock disruption. Our findings support the use of separate female and male mice cohorts for preclinical studies to understand the molecular heterogeneity in asthma pathophysiology.