Bcl-2, an inhibitor of apoptosis, is expressed in LPS-induced metaplastic goblet cells of rat airways. The present study investigated expression of Bcl-2 in airway mucous cells of persons with cystic fibrosis and tested in rats and mice whether its expression is responsible for sustaining metaplastic mucous cells. A significantly higher percentage of mucous cells expressed Bcl-2 in humans with cystic fibrosis compared with control subjects with no disease or subjects with other diseases. In LPS-instilled F344/N rats, the percentage of Bcl-2-positive mucous cells was decreased to background levels before the resolution of goblet cell metaplasia. Furthermore, intraperitoneal injection of rats with antisense oligonucleotides significantly reduced Bcl-2 expression and goblet cell metaplasia in nasal and pulmonary airway epithelia in rats. In contrast, sustained expression of Bcl-2 in transgenic mice by a metallothionein promoter caused increased LPS-induced goblet cell metaplasia over 8 days compared with wild-type mice. These studies demonstrate that Bcl-2 expression sustains goblet cell metaplasia in various species, that epithelial cell numbers are directly linked to the regulation of the numbers of goblet cells, and that downregulating Bcl-2 expression reduces goblet cell metaplasia.

Environmental toxins, infection, and allergens lead to a transient mucous cell hyperplasia (MCH) in airway epithelia; however, the mechanisms for reducing mucous cell numbers during recovery are largely unknown. This study investigated Bcl-2 expression in mucous cells induced by a neutrophilic or eosinophilic inflammatory response. Brown Norway rats intratracheally instilled with lipopolysaccharide (LPS) showed an inflammatory response characterized primarily by neutrophils. Secreted mucin was increased fourfold at 1 day, and the number of mucous cells was increased fivefold 2, 3, and 4 days post-LPS instillation compared with those in noninstilled rats. None of the mucous cells in non- or saline-instilled control animals expressed Bcl-2, whereas 20-30% of mucous cells were Bcl-2 positive 1 and 2 days post-LPS instillation. Brown Norway rats immunized and challenged with ovalbumin (OVA) for 2, 4, and 6 days showed an inflammatory response characterized primarily by eosinophils. Secreted mucin increased fivefold, and mucous cell number increased fivefold after 4 and 6 days of OVA exposure compared with water-immunized control rats challenged with OVA aerosols. Approximately 10-25% of mucous cells were Bcl-2 positive in OVA-immunized and -challenged rats. These data demonstrate Bcl-2 expression in hyperplastic mucous cells of Brown Norway rats regardless of the type of inflammatory response and indicate that apoptotic mechanisms may be involved in the resolution of MCHs.

Allergic airway responses cause proliferation of epithelial cells and mucus cell metaplasia (MCM), and the resolution of MCM involves reduction of cell numbers. The role of inflammation and apoptosis on this process was investigated in P-selectin +/+ and −/− mice sensitized and challenged with OVA by analyzing the expression and the role of regulators of apoptosis in metaplastic mucus cells. No differences were observed in MCM at 5 days of allergen exposure between +/+ and −/− mice, despite reduced IL-13 levels in −/− mice. Although IL-4 levels were similar in both −/− and +/+ mice, IL-13 and IL-5 levels had decreased and IFN-γ levels were increased earlier in −/− compared with +/+ mice. MCM levels were decreased 4-fold at 7 days of allergen exposure in −/− mice and at 15 days in +/+ mice. The percentage of Bax-expressing mucus cells increased significantly at 7 days in −/− mice and at 10 days in +/+ mice. The Bax-positive mucus cells exhibited caspase-specific cleavage of cytokeratin 18. IFN-γ caused Bax expression in IL-13-induced MCM in microdissected airway cultures. MCM remained significantly elevated in Bax −/− mice following 15 days of allergen exposure compared with +/+ mice, while the number of eosinophils was reduced in both Bax +/+ and −/− mice at 15 days. Together, these data demonstrate that reduced IL-13 levels were sufficient to elicit maximum MCM, that IFN-γ induces Bax in metaplastic mucus cells, and that Bax plays a critical role in the resolution of MCM, but not in the resolution of eosinophils.