The molecular circadian clock of eosinophils: a potential therapeutic target for asthma.

Asthma is a chronic inflammatory airway disease exhibiting time-of-day variability in symptoms and severity. Eosinophils, pivotal players and biomarkers in asthma, are regulated by the molecular circadian clock. This study aimed to investigate the impact of the molecular circadian clock on eosinophil effector function and its potential as a diagnostic biomarker and therapeutic target. We monitored clock proteins by flow cytometry in peripheral blood eosinophils from participants with mild asthma over a 24-h period. The observed decreased protein levels were confirmed in a cohort of patients with moderate asthma. To assess the interaction between inflammation and the molecular circadian clock, eosinophils were stimulated with patients' sera, inflammatory mediators, and clock-modulating ligands. The therapeutic potential of the inverse retinoic acid receptor-related-related orphan receptor (ROR) agonist SR1001 was evaluated in vitro and in a murine model of allergen-induced airway inflammation. Altered protein levels of circadian locomotor output cycles kaput (CLOCK), Brain and muscle Arnt-like protein-1 (BMAL1), REV-ERBs, and RORs in eosinophils from participants with asthma reflected the disease severity and allergy status of the patients. Mimicking an inflammatory environment in vitro resulted in similar changes. Blocking C-C chemokine receptor type 3 (CCR3)/ERK and epidermal growth factor receptor (EGFR) signaling with an inverse ROR agonist SR1001 reset the molecular circadian clock in eosinophils and exhibited anti-inflammatory effects by inhibiting eosinophil migration in vitro. In addition, we confirmed the therapeutic potential of the clock-modulating SR1001, bronchoprotective effects in two in vivo models. This study suggests that clock proteins could serve as therapeutic targets in asthma. Pharmacological inhibition of ROR signaling demonstrated significant anti-inflammatory and bronchoprotective properties, indicating its potential as a novel treatment strategy for asthma and other eosinophilic diseases.NEW & NOTEWORTHY Our findings highlight the role of the circadian system as an immunomodulatory regulator, biomarker, and therapeutic target in chronic inflammatory diseases. The observed inflammation-driven downregulation of the molecular circadian clock may also represent a key mechanism that triggers the switch from homeostatic to pro-inflammatory eosinophils. Furthermore, we demonstrate for the first time that pharmacologic inhibition of ROR resets the molecular circadian clock and induces anti-inflammatory and lung-protective effects without disrupting circadian rhythms.