In Vitro Culture of Microdissected Rat Nasal Airway Tissues

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Abstract
The surface epithelium lining the nasal airways is a potential target for inhaled contaminants such as ozone, endotoxin, formaldehyde, tobacco smoke, and organic dusts. The epithelial response to injury may depend on the toxicant, the type of epithelium, the severity of the injury, and the presence of inflammatory cells and their secreted products. To study mechanisms of toxicant-induced epithelial injury and repair, in the absence of cellular inflammation or other systemic effects, we have developed a culture system to maintain morphologically distinct nasal airway epithelium in vitro. Microdissected maxilloturbinates and proximal nasal septa of male F344/N rats were cultured at an air-liquid interface for up to 14 d in supplemented serum-free medium. Maxilloturbinates are lined by nonciliated cuboidal nasal transitional epithelium (NTE) with few or no mucous cells. The proximal nasal septum is lined by a mucociliary respiratory epithelium (RE) that normally contains numerous mucous cells. Preservation of the normal RE and NTE phenotype in culture was assessed by light and electron microscopy, and analysis of an airway mucin gene (rMuc-5AC) messenger RNA (mRNA). Both RE and NTE retained normal cell morphology for 14 d in culture (DIC). After 14 DIC there were 20% fewer RE cells in the septa (equal loss of ciliated and mucous cells) and 25% more NTE cells in the maxilloturbinates (increased number of basal cells). Compared with the RE, the NTE expressed consistently low levels of rMuc-5AC mRNA and had little to no histochemically detectable intraepithelial mucosubstances (IM) after 0, 3, 7, or 14 DIC. The amount of stored IM and the steady-state levels of rMuc-5AC mRNA in the RE decreased with time in culture. In summary, this culture system can maintain fully differentiated secretory and nonsecretory rat airway epithelia in vitro for up to 14 d. This study was an essential first step in developing a system to study the pathogenesis of toxicant-induced airway epithelial injury and mechanisms of cellular repair and adaptation in the absence of cellular inflammation and other systemic influences.