Bronchial Epithelial Calcium Metabolism Impairment in Smokers and Chronic Obstructive Pulmonary Disease. Decreased ORAI3 Signaling.

The airway epithelium represents a fragile environmental interface potentially disturbed by cigarette smoke (CS), the major risk factor for developing chronic obstructive pulmonary disease (COPD). CS leads to bronchial epithelial damage on ciliated, goblet, and club cells, which could involve calcium (Ca²⁺) signaling. Ca²⁺ is a key messenger involved in virtually all fundamental physiological functions, including mucus and cytokine secretion, cilia beating, and epithelial repair. In this study, we analyzed Ca²⁺ signaling in air-liquid interface-reconstituted bronchial epithelium from control subjects and smokers (with and without COPD). We further aimed to determine how smoking impaired Ca²⁺ signaling. First, we showed that the endoplasmic reticulum (ER) depletion of Ca²⁺ stores was decreased in patients with COPD and that the Ca²⁺ influx was decreased in epithelial cells from smokers (regardless of COPD status). In addition, acute CS exposure led to a decrease in ER Ca²⁺ release, significant in smoker subjects, and to a decrease in Ca²⁺ influx only in control subjects. Furthermore, the differential expression of 55 genes involved in Ca²⁺ signaling highlighted that only ORAI3 expression was significantly altered in smokers (regardless of COPD status). Finally, we incubated epithelial cells with an ORAI antagonist (GSK-7975A). GSK-7975A altered Ca²⁺ influx and ciliary beating, but not mucus and cytokine secretion or epithelial repair, in control subjects. Our data suggest that Ca²⁺ signaling is impaired in smoker epithelia (regardless of COPD status) and involves ORAI3. Moreover, ORAI3 is additionally involved in ciliary beating.

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