Airway obstruction correlates with collagenase-2 (MMP-8) expression and activation in bronchial asthma

Matrix metalloproteinases (MMPs) contribute to extracellular matrix and basement membrane degradation in asthma. The present study analyzed molecular forms and degree of activation and expression of MMP-8 in bronchoalveolar lavage fluid (BALF), BALF cells, and bronchial tissue specimens from 14 steroid-naive asthma patients, 13 uncontrolled severe asthma patients, 13 controlled asthma patients, and 14 healthy subjects by Western immunoblotting, immunohistochemistry, and in situ hybridization. Immunohistochemistry and in situ hybridization revealed a prominent MMP-8 immunoreactivity in submucosal inflammatory, glandular, and shed, but not in intact bronchial epithelial cells of asthma patients. In BALF cytospins, both MMP-8 protein and mRNA expression were observed in epithelial cells, macrophages, and polymorphonuclear leukocytes (PMNs). MMP-8 was present in BALFs asthma patients in complex, pro- and active PMN-type, and pro- and active non-PMN-type forms. BALF MMP-8 was significantly converted to active form only in BALFs from steroid-naive and uncontrolled severe asthma patients, but not in BALFs from well-controlled asthma patients or healthy controls. A significant inverse correlation between BALF MMP-8 levels and FEV1 (r = -0.283, p = 0.04), and BALF activated MMP-8 forms and FEV1 (r = -0.427, p = 0.001) was detected. Overall, these data suggest that MMP-8 and its activation has an important role in the airway destruction, healing, remodeling, and treatment response in asthma.