Long-Term Cigarette Smoke Exposure in a Mouse Model of Ciliated Epithelial Cell Function

Abstract

Exposure to cigarette smoke is associated with airway epithelial mucus cell hyperplasia and a decrease in cilia and ciliated cells. Few models have addressed the long-term effects of chronic cigarette smoke exposure on ciliated epithelial cells. Our previous in vitro studies showed that cigarette smoke decreases ciliary beat frequency (CBF) via the activation of protein kinase C (PKC). We hypothesized that chronic cigarette smoke exposure in an in vivo model would decrease airway epithelial cell ciliary beating in a PKCdependent manner. We exposed C57BL/6 mice to whole-body cigarette smoke 2 hours/day, 5 days/week for up to 1 year. Tracheal epithelial cell CBF and the number of motile cells were measured after necropsy in cut tracheal rings, using high-speed digital video microscopy. Tracheal epithelial PKC was assayed according to direct kinase activity. At 6 weeks and 3 months of smoke exposure, the baseline CBF was slightly elevated (z 1 Hz) versus control mice, with no change in b-agonist-stimulated CBF between control mice and cigarette smoke-exposed mice. By 6 months of smoke exposure, the baseline CBF was significantly decreased (2-3 Hz) versus control mice, and a b-agonist failed to stimulate increased CBF. The loss of b-agonist-increased CBF continued at 9 months and 12 months of smoke exposure, and the baseline CBF was significantly decreased to less than one third of the control rate. In addition to CBF, ciliated cell numbers significantly decreased in response to smoke over time, with a significant loss of tracheal ciliated cells occurring between 6 and 12 months. In parallel with the slowing of CBF, significant PKC activation from cytosol to the membrane of tracheal epithelial cells was detected in mice exposed to smoke for 6-12 months.

FOXJ1 Prevents Cilia Growth Inhibition by Cigarette Smoke in Human Airway Epithelium In Vitro

“…A variety of studies have assessed the mechanisms by which cigarette smoke inhibits ciliary beat frequency (11)(12)(13)(14)(15)(16)(17). For example, cigarette smoke extract (CSE)-induced oxidative stress and intracellular reactive oxygen species generation cause loss of the ciliated phenotype, suggesting that oxidative stress may play a major role in the CSE-induced effects on ciliogenesis (12).…”

Particulate Matter in Cigarette Smoke Increases Ciliary Axoneme Beating Through Mechanical Stimulation

“…In vivo studies with ciliated epithelium similarly demonstrate a transient, but significant increase in baseline CBF in mice exposed to CS and cigarette smoke extract (CSE). (7,8) An initial and rapid increase in MCC was also observed in rats exposed to unfiltered CS. (9) Other studies, however, show significant decreases in CBF with exposure to CS.…”

“…Because in vitro studies have been inconclusive on whether CSE exposure results in CBF stimulation or inhibition (7)(8)(9)11,21) we assayed CBF in a cell-free preparation of ciliary axonemes exposed to CSE. Given the high incidence of pulmonary disease in tobacco users, we hypothesized that CSE would alter CBF in a cell-free axoneme model.…”

Innate Immunity of Airway Epithelium and COPD

“…In addition, respiratory epithelial cells exposed to cigarette smoke extract or condensate showed 70% less cilia and shorter cilia compared to control cells ). Mice exposed to cigarette smoke although showed slight increase in ciliary beat frequency at 6 weeks and 3 months, it was significantly reduced at 6 months and these mice also showed significant loss of tracheal ciliated cells (Simet et al, 2010). Decreased number of cilia, reduced ciliary function combined with hypersecretion of mucin, increased viscoelasticity of secreted mucus in COPD patients can lead to airways obstruction and promote persistence of trapped pathogens in the airways Voynow et al, 2006).…”