Goblet cell
hyperplasia in the superficial airway epithelia is a signature pathological feature of
chronic bronchitis and
cystic fibrosis. In these chronic inflammatory airway diseases,
neutrophil elastase (NE) is found in high concentrations in the epithelial lining fluid. NE has been reported to trigger
mucin secretion and increase
mucin gene expression in vitro. We hypothesized that chronic NE exposure to murine airways in vivo would induce goblet cell
metaplasia. Human NE (50 microg) or PBS saline was aspirated intratracheally by male Balb/c (6 wk of age) mice on days 1, 4, and 7. On days 8, 11, and 14, lung tissues for histology and bronchoalveolar lavage (BAL) samples for cell counts and
cytokine levels were obtained. NE induced Muc5ac
mRNA and
protein expression and goblet cell
metaplasia on days 8, 11, and 14. These cellular changes were the result of proteolytic activity, since the addition of an
elastase inhibitor, methoxysuccinyl
Ala-Ala-Pro-Val chloromethylketone (AAPV-CMK), blocked NE-induced Muc5ac expression and goblet cell
metaplasia. NE significantly increased keratinocyte-derived
chemokine and
IL-5 in BAL and increased lung tissue
inflammation and BAL leukocyte counts. The addition of AAPV-CMK reduced these measures of
inflammation to control levels. These experiments suggest that NE proteolytic activity initiates an inflammatory process leading to goblet cell
metaplasia.