Cold exposure-induced asthma exacerbation through airway epithelial
barrier disruption in mice
Abstract
Background: Cold exposure can trigger asthma attacks. However,
the underlying mechanism is yet to be elucidated. We hypothesize that
low temperature reduces occludin expression and compromises airway
epithelial barrier function, which, in turn, results in asthma
exacerbation. Methods: We examined occludin expression in
Beas-2B cells exposed to either 29 °C or 37 °C. The following drugs were
administered prior to cold treatment: MG132 (a proteasome inhibitor),
cycloheximide (a protein synthesis inhibitor), HC-067047 plus GSK2193874
(transient receptor potential vanilloid 4 [TRPV4] antagonists), or
C4-ceramide (an SGK1 activator). siNedd4-2 was transfected into Beas-2B
cells to investigate the role of Nedd4-2 in mediating cold-induced
occludin instability. In animal experiments, we treated ovalbumin
(OVA)-induced asthmatic mice with either a thermoneutral temperature of
30 °C or repeated cold stress (10 °C, 6 h/day) for 2 weeks. Either
GSK2193874 or C4-ceramide was administered during the cold treatment.
After a final OVA challenge, pulmonary permeability, serum IgE levels,
and lung inflammation were assessed. Results: Treatment at 29
°C for 1−9 h significantly reduced Beas-2B cell occludin expression,
which was rescued upon treatment with MG132, HC-067047 plus GSK2193874,
C4-ceramide, or the Nedd4-2 knockdown. Notably, low temperatures
affected occludin stability through SGK1/Nedd4-2-dependent proteolysis.
In vivo analyses revealed that repeated cold exposure compromised
the airway epithelial barrier function and exacerbated lung inflammation
in mice, which was partially attenuated by the GSK2193874 or C4-ceramide
injection. Conclusions: We identified a new mechanism
underlying cold-induced asthma exacerbation that may involve
SGK1/Nedd4-2-mediated occludin proteolysis, resulting in epithelial
barrier dysfunction.