Cellular clocks in hyperoxia effects on [Ca^{2 þ} ]_i regulation in developing human airway smooth muscle

Supplemental O₂ (hyperoxia) is necessary for preterm infant survival but is associated with development of bronchial airway hyperreactivity and childhood asthma. Understanding early mechanisms that link hyperoxia to altered airway structure and function are key to developing advanced therapies. We previously showed that even moderate hyperoxia (50% O₂) enhances intracellular calcium ([Ca^2þ]_i) and proliferation of human fetal airway smooth muscle (fASM), thereby facilitating bronchoconstriction and remodeling. Here, we introduce cellular clock biology as a novel mechanism linking early oxygen exposure to airway biology. Peripheral, intracellular clocks are a network of transcription-translation feedback loops that produce circadian oscillations with downstream targets highly relevant to airway function and asthma. Premature infants suffer circadian disruption whereas entrainment strategies improve outcomes, highlighting the need to understand relationships between clocks and developing airways. We hypothesized that hyperoxia impacts clock function in fASM and that the clock can be leveraged to attenuate deleterious effects of O₂ on the developing airway. We report that human fASM express core clock machinery (PER1, PER2, CRY1, ARNTL/BMAL1, CLOCK) that is responsive to dexamethasone (Dex) and altered by O₂. Disruption of the clock via siRNA-mediated PER1 or ARNTL knockdown alters store-operated calcium entry (SOCE) and [Ca^2þ]_i response to histamine in hyperoxia. Effects of O₂ on [Ca^2þ]_i are rescued by driving expression of clock proteins, via effects on the Ca^2þ channels IP₃R and Orai1. These data reveal a functional fASM clock that modulates [Ca^2þ]_i regulation, particularly in hyperoxia. Harnessing clock biology may be a novel therapeutic consideration for neonatal airway diseases following prematurity.