In contrast to the above findings that suggest decreased NOTCH3 signalling may contribute to the development of airway epithelial remodelling associated with CS exposure and COPD, our recent study demonstrated that in vitro CS exposure activates NOTCH3 signalling to promote development of GCMH in both non-smoker and COPD airway epithelial cells (Ref. Here, NOTCH3 is linked to chronic obstructive pulmonary disease.