Cigarette Smoke Extract Induces MUC5AC Expression Through the ROS/ IP3R/Ca²⁺ Pathway in Calu-3 Cells

Chronic obstructive pulmonary disease (COPD) is caused by exposure to noxious external particles, air pollution, and the inhalation of cigarette smoke. Airway mucus hypersecretion particularly mucin5AC (MUC5AC), is a crucial pathological feature of COPD and is associated with its initiation and progression. In this study, we aimed to investigate the effects of cigarette smoke extract (CSE) on MUC5AC expression, particularly the mechanisms by which reactive oxygen species (ROS) induce MUC5AC expression.

The effects of CSE on the expression of MUC5AC and mucin5B (MUC5B) were investigated in vitro in Calu-3 cells. MUC5AC and MUC5B expression levels were measured using quantitative reverse transcription-polymerase chain reaction (qRT-PCR), immunofluorescence staining, and enzyme-linked immunosorbent assay (ELISA). Total cellular levels of ROS and Ca²⁺ were determined using DCFH-DA and Fluo-4 AM. Subsequently, the expression levels of IP3R, IRE1α, p-IRE1α and XBP1s were measured by Western blotting. Gene silencing was achieved by using small-interfering RNAs.

Our findings revealed that exposure to CSE increased MUC5AC levels and upregulated ROS, IP3R/Ca²⁺ and unfolded protein response (UPR)-associated factors. In addition, knockdown of IP3R using siRNA decreased CSE-induced Ca²⁺ production, UPR-associated factors, and MUC5AC expression. Furthermore, 10 mM N-acetyl-l-cysteine (NAC) treatment suppressed the effects of CSE, including ROS generation, IP3R/ Ca²⁺, UPR activation, and MUC5AC overexpression.

Our results suggest that ROS regulates CSE-induced UPR and MUC5AC overexpression through IP3R/ Ca²⁺ signaling. Additionally, we identified NAC as a promising therapeutic agent for mitigating CSE-induced MUC5AC overexpression.