Protease dysregulation: Role in neutrophilic inflammation in cystic fibrosis

Abstract

Cystic fibrosis (CF) is a lethal disorder characterized by abnormal epithelial ion transport; this disorder is characterized by an ongoing airway remodeling and neutrophilic inflammation. Much of the airway remodeling is due to activation of a group of enzymes known as proteases; human neutrophil elastase (HNE) is a prominent protease found in the CF airway. While specific cytokines/chemokines are well-known for their role in the inflammation seen in CF, it is unknown how the protease-rich environment in CF lung disease influences airway inflammation. Recently, our group has characterized a novel collagen-derived fragment, proline-glycine-proline (PGP), which causes neutrophil influx through mechanisms similar to interleukin-8 (IL-8) in an experimental model of airway inflammation. However, the role of this peptide in clinical disease and the mechanism of PGP generation are unknown. In the current work, we first examine the protease signature seen in airway secretions from CF individuals, determining notable increases in members of the matrix metalloprotease (MMP) family. One member of this family, MMP-9, has increased activity in CF. The importance of increased MMP-9 activity in airway inflammation is reinforced in a murine model of F. tularensis infection in which MMP-9 deficiency leads to decreased airway neutrophilia; PGP, which was elevated in MMP-9+/+ mice, were significantly diminished in MMP-9 knockout mice. Administration of MMP-9 or MMP-8, in concert with prolyl endopeptidase (PE), is capable of generating PGP in mice. In addition, sputum from CF individuals is also capable of generating PGP from intact collagen ex vivo. The use of specific inhibitors can significantly attenuate PGP generation both in vivo and ex vivo. Finally, we demonstrate that PGP is elevated in CF patients compared to normal controls. In addition to these findings, we also show that MMP-9 also is capable of cleaving IL-8 in vitro, leading to the generation of a new, more potent IL-8 species. These studies underscore the importance of MMP-9 in airway inflammation seen in CF lung disease; indeed, as many of these proteases are found in other conditions with ongoing inflammation and extracellular remodeling, it is possible that these findings may be more generalized to chronic neutrophilic inflammatory conditions.