A Functional Anatomic Defect of the Cystic Fibrosis Airway

Abstract

Rationale: The mechanisms underlying cystic fibrosis (CF) lung disease pathogenesis are unknown.Objectives: To establish mechanisms linking anion transport with the functional microanatomy, we evaluated normal and CF piglet trachea as well as adult swine trachea in the presence of selective anion inhibitors.Methods: We investigated airway functional microanatomy using microoptical coherence tomography, a new imaging modality that concurrently quantifies multiple functional parameters of airway epithelium in a colocalized fashion.Measurements and Main Results: Tracheal explants from wild-type swine demonstrated a direct link between periciliary liquid (PCL) hydration and mucociliary transport (MCT) rates, a relationship frequently invoked but never experimentally confirmed. However, in CF airways this relationship was completely disrupted, with greater PCL depths associated with slowest transport rates. This disrupted relationship was recapitulated by selectively inhibiting bicarbonate transport in vitro and ex vivo. CF mucus exhibited increased viscosity in situ due to the absence of bicarbonate transport, explaining defective MCT that occurs even in the presence of adequate PCL hydration.Conclusions: An inherent defect in CF airway surface liquid contributes to delayed MCT beyond that caused by airway dehydration alone and identifies a fundamental mechanism underlying the pathogenesis of CF lung disease in the absence of antecedent infection or inflammation.

In vivo imaging of airway cilia and mucus clearance with micro-optical coherence tomography

“…The velocity of mucus transport in this sequence was also measured to be 71 ± 28 µm/s. These values were in accordance with previous results derived from ex vivo swine trachea [10,11,13]. Fig.…”

“…More recently, we have utilized µOCT for in vitro imaging of the airway surface, including the cilia [10][11][12][13][14]. Cilia are microscopic organelles that line respiratory epithelia and beat repeatedly in a sweeping motion to clear mucus from the airways.…”

Development of an airway mucus defect in the cystic fibrosis rat

“…Although male rats of both genotypes grow larger than females of the same age, there was no detectable sex-related difference in histomorphometry. To assess the function of tracheal submucosal glands and the effect of their secretions on the airway surface at 1, 3, and 6 months of age, tracheae were imaged under μOCT as previously described (22,24,26,34) and the airway surface liquid (ASL) depth was measured before and after cholinergic stimulation with acetylcholine ( Figure 2A). Comparison of ASL depths of KO rats to those of their age-matched WT littermates showed that ASL depths were diminished in both basal and stimulated conditions, from weaning until at least 6 months of age (WT 1 month 22.9 ± 4.6 μm, 6 months 43.6 ± 12.5 μm vs. KO 1 month 6.9 ± 0.7 μm, 6 month 19.5 ± 4.8 μm; P < 0.05 at all ages, Figure 2, B and C).…”

“…In vivo studies of the CF mucus abnormality have been limited, as the CF mouse models do not accurately replicate the muco-obstructive lung disease characteristic of human patients with CF (17,18). While significant insights have arisen from the CF pig and ferret models (19)(20)(21)(22)(23)(24), particularly regarding mucus secretion and release at the onset of disease (13,25), these models are less amenable for longitudinal studies to characterize how CF pathogenesis ensues over time. These limitations have led us to develop a Cftr -/-rat (here referred to as the CFTR…”

Relationships among CFTR expression, HCO 3 − secretion, and host defense may inform gene- and cell-based cystic fibrosis therapies

“…A limitation of this study is that loss of CFTR may influence the function of other cell types and structures, including submucosal glands (31,55), airway smooth muscle (56), cartilage (57,58), and myeloid-derived cells (59). Impairment of their function might also contribute to the pathogenesis of CF airway disease.…”