Accumulation of airway mucus in cystic fibrosis

Modulation of MUC7 mucin expression by exogenous factors in airway cells in vitro and in vivo

The human MUC7 gene encodes a low-molecular-mass mucin that participates in the maintenance of healthy epithelium in the oral cavity, and possibly in respiratory tracts, by promoting the clearance of various bacteria. We examined whether MUC7 gene is expressed in primary normal human tracheobronchial epithelial cells and whether the expression is modulated by exogenous factors. By assessing MUC7 transcripts, we found that the MUC7 gene was induced by culturing the normal human tracheobronchial epithelial cells at the air-liquid interface, in which the cells were well differentiated. When the cells were treated with a panel of cytokines (IL-1beta, IL-4, IL-13, and TNF-alpha), epidermal growth factor, or a bacterial product (Pseudomonas aeruginosa lipopolysaccharide [LPS]), MUC7 transcripts and glycoprotein products were increased 1.7- to 3.2-fold. The effect of LPS on MUC7 gene expression was also studied in the airway tissues of MUC7 gene transgenic mice. In the in vitro cultured trachea and lung explants, the LPS-treated tissues showed over 2-fold increased levels of MUC7 mRNA compared with the untreated specimens. These results were confirmed by in vivo studies using the lungs and tracheas harvested from the transgenic mice irritated by LPS through the tracheal instillation. By immunohistochemistry, MUC7 glycoprotein was localized in tracheal submucosa within the serous cells. Upon LPS stimulation, the overexpressed MUC7 remains confined to the serous glands. In the lungs, MUC7 seems to be expressed within the respiratory epithelium at the level of the bronchioles. Upon stimulation with LPS, it seems to be overexpressed within the same cells and within the stromal tissue.

Circulating markers to assess nutritional therapy in cystic fibrosis

Cystic fibrosis (CF) is the most commonly occurring lethal autosomal recessive disorder. The gene defect causes defective sodium and chloride transport across epithelial cells of the respiratory, hepatobiliary, gastrointestinal and reproductive tracts, resulting in thick mucus secretions. In the respiratory tract, mucus traps bacteria, causing repeated lung infections, progressive bronchiectasis and eventual death due to respiratory failure. In the gastrointestinal tract, mucus prevents pancreatic enzymes reaching the gut, leading to nutrient malabsorption. Careful nutritional management has a dramatic effect on growth and survival rates in CF. Appropriate nutritional support includes pancreatic enzyme replacement therapy, a high-fat/high-energy diet and essential nutrient supplementation, specifically fat-soluble vitamins and essential fatty acids (EFA). Long-term studies are required to examine the effects of nutritional interventions on key clinical outcomes in CF, such as the rate of decline of lung function. The use of circulating markers to assess the influence of nutritional therapy allows short-term intervention studies to predict the potential for clinical improvements. This article provides an overview of the biomarkers useful in the prediction of the efficacy of nutritional therapy on improvements in quality and quantity of life in CF.

Physiology and pathology of tracheobronchial glands

The tracheobronchial glands, composed of mucous and serous secretory cells, provide a mucin-rich, antimicrobial-rich secretion for the conducting airways. The secretory processes of these cells are under complex neurohumoral control. Several diseases demonstrate considerable increases in the volume of secretory glands, the amount of glandular secretions or the character of the secretory product. The role of the tracheobronchial glands in the pathophysiology of chronic bronchitis, asthma and cystic fibrosis is discussed.

Role of CFTR in airway disease

Role of CFTR in Airway Disease. Physiol. Rev. 79, Suppl.: S215-S255, 1999. - Cystic fibrosis (CF) is caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), which accounts for the cAMP-regulated chloride conductance of airway epithelial cells. Lung disease is the chief cause of morbidity and mortality in CF patients. This review focuses on mechanisms whereby the deletion or impairment of CFTR chloride channel function produces lung disease. It examines the major themes of the channel hypothesis of CF, which involve impaired regulation of airway surface fluid volume or composition. Available evidence indicates that the effect of CFTR deletion alters physiological functions of both surface and submucosal gland epithelia. At the airway surface, deletion of CFTR causes hyperabsorption of sodium chloride and a reduction in the periciliary salt and water content, which impairs mucociliary clearance. In submucosal glands, loss of CFTR-mediated salt and water secretion compromises the clearance of mucins and a variety of defense substances onto the airway surface. Impaired mucociliary clearance, together with CFTR-related changes in the airway surface microenvironment, leads to a progressive cycle of infection, inflammation, and declining lung function. Here, we provide the details of this pathophysiological cascade in the hope that its understanding will promote the development of new therapies for CF.