In asthma, goblet cell numbers are increased within the airway epithelium, 
perpetuating the production of mucus that is more difficult to clear and results 
in airway mucus plugging. Notch1, Notch2, or Notch3, or a combination of these 
has been shown to influence the differentiation of airway epithelial cells. How 
the expression of specific Notch isoforms differs in fully differentiated adult 
asthmatic epithelium and whether Notch influences mucin production after 
differentiation is currently unknown. We aimed to quantify different Notch 
isoforms in the airway epithelium of individuals with severe asthma and to 
examine the impact of Notch signaling on mucin MUC5AC. Human lung sections and 
primary bronchial epithelial cells from individuals with and without asthma were 
used in this study. Primary bronchial epithelial cells were differentiated at 
the air-liquid interface for 28 days. Notch isoform expression was analyzed by 
Taqman quantitative PCR. Immunohistochemistry was used to localize and quantify 
Notch isoforms in human airway sections. Notch signaling was inhibited in vitro 
using dibenzazepine or Notch3-specific siRNA, followed by analysis of MUC5AC. 
NOTCH3 was highly expressed in asthmatic airway epithelium compared with 
nonasthmatic epithelium. Dibenzazepine significantly reduced MUC5AC production 
in air-liquid interface cultures of primary bronchial epithelial cells 
concomitantly with suppression of NOTCH3 intracellular domain protein. Specific 
knockdown using NOTCH3 siRNA recapitulated the dibenzazepine-induced reduction 
in MUC5AC. We demonstrate that NOTCH3 is a regulator of MUC5AC production. 
Increased NOTCH3 signaling in the asthmatic airway epithelium may therefore be 
an underlying driver of excess MUC5AC production.