IL-8 Inhibits Isoproterenol-Stimulated Ciliary Beat Frequency in Bovine Bronchial Epithelial Cells

Abstract

Mucociliary clearance is a critical host defense that protects the lung. The mechanisms by which mucociliary function is altered by inflammation are poorly defined. Chronic exposure to cigarette smoke decreases ciliary beating and interferes with proper airway clearance. Bronchoalveolar lavage (BAL) fluid from smokers and ex-smokers has increased amounts of IL-8, which has played a critical role in airway inflammation. We hypothesized that IL-8 might interfere with stimulated ciliary beating in airway epithelium. To test this hypothesis, we stimulated bovine ciliated bronchial epithelial cells (BBECs) with a known activator of ciliary beat frequency (CBF), isoproterenol (ISO; 100 μM), in the presence or absence of IL-8 (100 pg/mL). We measured CBF digitally using the Sisson-Ammons Video Analysis (SAVA) system. CBF increased in untreated cells exposed to ISO (~3 Hz) over baseline. In contrast, cells pre-incubated with IL-8 failed to respond to ISO. Pretreatment with IL-8 also blocked ISO-stimulated cAMP-dependent kinase (PKA) activation, which is known to control ISO-stimulated CBF. In addition, IL-8 pretreated cells revealed a marked decrease in PKA activity when cells were stimulated with forskolin (FSK; 10 μM). Cells were assayed specifically for cAMP-phosphodiesterase (PDE) activity. ISO-stimulated cells demonstrated an increase in PDE activity as compared to control. Pretreatment with IL-8 had no effect on ISO-stimulated PDE activity. Collectively, these data suggest that IL-8 appears to mediate its effect at the level of adenylyl cyclase. It is also possible that IL-8 may not only act as a chemotactic agent, but also as a potential autocrine/paracrine inhibitor of PKA-mediated stimulation of ciliary motility. In conclusion, IL-8 inhibits beta-agonist dependent ciliostimulation and such inhibition of stimulated ciliary activity may contribute to the impaired mucociliary clearance seen in airway diseases. Furthermore, since IL-8 levels are increased in the airway of cigarette smokers, it is likely they may be more resistant to the cilio and muco-ciliostimulating effects of beta-agonists.