Airway mucin glycoproteins (MUC)

Airway mucin glycoproteins are large, heavily O-glycosylated proteins that serve as the primary structural components of the mucus layer lining the respiratory tract [1.4.1, 1.4.5]. In healthy lungs, the gel-forming mucins MUC5B and MUC5AC are secreted to form a viscoelastic blanket that traps inhaled pathogens, toxins, and debris, allowing them to be cleared by ciliary action [1.3.1, 1.5.3]. However, in chronic muco-obstructive diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis, the overproduction and hypersecretion of these mucins lead to the formation of thick, adhesive mucus plugs that obstruct the airways and promote chronic infection and inflammation [1.1.1, 1.3.3]. Pharmacological interventions target these mucins to restore effective clearance and reduce airway obstruction. Traditional mucolytics, such as N-acetylcysteine, act by breaking the disulfide bonds that link mucin monomers, thereby reducing the viscosity of the mucus gel [1.5.3, 1.5.4]. Emerging therapies focus on more specific targets, such as inhibiting the signaling pathways that drive mucin overproduction or blocking the proteins involved in the rapid exocytosis of mucin granules [1.4.2, 1.4.3]. While these treatments are essential for managing severe respiratory symptoms, they must be used cautiously to avoid inducing bronchospasm or excessively depleting MUC5B, which is critical for maintaining baseline lung sterility and defense [1.3.1, 1.5.1].

Other names

MUC5ACMUC5BMucin-5ACMucin-5BGel-forming mucinsSecreted mucinsAirway mucus glycoproteinsMucins in airway/alveolar lining fluidAlveolar lining fluid mucins

Mucoactive agents target airway mucins through several distinct pathways: 1) Thiol-disulfide exchange, where drugs like N-acetylcysteine and erdosteine break the disulfide cross-links between mucin monomers to reduce gel viscosity [1.5.3, 1.5.4]; 2) Mucoregulatory action, which involves inhibiting the synthesis of mucins (e.g., MUC5AC) by targeting signaling pathways such as EGFR or using glucocorticoids [1.4.1, 1.4.4]; 3) Inhibition of mucin secretion, where experimental agents like Bio-11006 or SP9 block the MARCKS protein or synaptotagmin-2 to prevent the rapid release of mucin granules [1.4.1, 1.4.2]; 4) Osmotic hydration, where hypertonic saline or mannitol increases the water content of the airway surface liquid to facilitate clearance [1.1.1, 1.4.5]; and 5) Enzymatic degradation of extracellular DNA, which reduces the tenacity of purulent mucus (e.g., dornase alfa) [1.5.1, 1.5.3].