Airborne particulate matter increases MUC5AC expression by downregulating Claudin-1 expression in human airway cells

Area of Science:

• Immunology
• Cell Biology
• Respiratory Medicine

Background:

• CLB2.0, a component of particulate matter, is known to induce airway inflammation.
• Cytokines and chemokines play critical roles in regulating inflammatory responses in the airways.

Purpose of the Study:

• To elucidate the molecular mechanisms by which CLB2.0 induces airway inflammation.
• To investigate the role of interleukin-6 (IL-6), reactive oxygen species (ROS), and ERK1/2 mitogen-activated protein kinase (MAPK) pathway in CLB2.0-mediated responses.
• To examine the impact of CLB2.0 on tight junction proteins, specifically claudin-1, and mucin expression (MUC5AC and MUC1).

Main Methods:

• Cell culture experiments to assess cytokine and chemokine secretion.
• Western blotting and quantitative PCR to measure protein and gene expression of mucins and tight junction proteins.
• Measurement of ROS production using fluorescent probes.
• Pharmacological inhibition of ROS and MAPK pathways.

Main Results:

• CLB2.0 induced the secretion of IL-6, which upregulated MUC5AC and MUC1 expression.
• CLB2.0 inhibited claudin-1 expression; overexpression of claudin-1 decreased MUC5AC but increased MUC1 expression.
• IL-6 secretion was dependent on ROS, and N-acetylcysteine (ROS scavenger) inhibited IL-6 and MUC5AC expression while increasing MUC1 expression.
• CLB2.0 activated ERK1/2 MAPK via a ROS-dependent pathway. ERK1/2 activation downregulated claudin-1 and MUC1 but increased MUC5AC expression.

Conclusions:

• CLB2.0-induced ERK1/2 activation acts as a switch regulating airway inflammation through a ROS-dependent pathway.
• Secreted IL-6, via ROS-mediated downregulation of claudin-1, influences MUC5AC and MUC1 expression to maintain airway mucus homeostasis.