Cleavage of denatured natural collagen type II by neutrophil gelatinase B reveals enzyme specificity, post-translational modifications in the substrate, and the formation of remnant epitopes in rheumatoid arthritis
During acute inflammation, leukocytes release proteolytic enzymes including matrix metalloproteinases (MMPs), but the physiopathological mechanisms and consequences of this process are not yet fully understood. Neutrophils, the predominant leukocyte type, produce neutrophil collagenase (MMP-8) and gelatinase B (MMP-9) but not the tissue inhibitors of MMPs. After stimulation, these cells also activate MMPs chemically. In arthritic diseases, neutrophils undergo great chemoattraction to the synovium, are activated by interleukin-8, and are stimulated to release gelatinase B in vivo. Production levels and net activities of gelatinase B were found to be absent in degenerative osteoarthritis but significantly increased in rheumatoid arthritis. The cleavage sites in cartilage type II collagen by gelatinase B were determined by a combination of reverse phase high-performance liquid chromatography, Edman degradation, and mass spectrometry analysis. The analysis revealed the site specificity of proline and lysine hydroxylations and O-linked glycosylation, the cleavage specificities by gelatinase B, and the preferential absence and presence of post-translational modifications at P2' and P5', respectively. Furthermore, gelatinase B leaves the immunodominant peptides intact, which are known from studies with (autoreactive) T cells. Lysine hydroxylation was detected at a critical position for T-cell activation. These data lend support to the thesis that extracellular proteolysis and other post-translational modifications of antigenic peptides may be critical in the establishment and perpetuation of autoimmune processes.