Matrix metalloproteinases and aggrecanase - Their role in disorders of thehuman intervertebral disc

Study Design. A comprehensive immunohistochemical study of matrix metallopr oteinase activity in discs from patients with different disc diseases. Objectives. To identify individual matrix metalloproteinase enzymes that co uld contribute to the degeneration of the matrix of the intervertebral disc , to identify the cells that produce matrix metalloproteinases (for example , the endogenous disc cells or invading cells associated with vascularisati on), and to determine if "aggrecanase" contributes to degradation of proteo glycans in disc disorders. Summary of Background Data. Matrix disorganization and loss of substance ar e the most common findings in degenerate discs, and proteinase enzyme activ ity is one means of causing these changes. Methods. Forty-nine discs from 46 patients with degenerative disc disease, posterior anular tears, spondylolisthesis, or disc herniation were studied immunohistochemically to determine the presence of matrix metalloproteinase s 1, 2, 3, 7, 8, 9 and 13, tissue metalloproteinases 1 and 2, and proteogly can degradation products generated by either matrix metalloproteinases or a ggrecanase activity, In addition, insitu zymography was used to confirm mat rix metalloproteinase activity. Results. The most extensive staining was seen for matrix metalloproteinases 1, 2, 3, and 9, with 91%, 71%1 65%, and 72% of samples having some immunop ositivity for the respective antibodies. In contrast, staining for matrix m etalloproteinases 7 and 8 was much less (38% for both). Tissue inhibitor of metalloproteinases 1 and 2 were expressed in 34% and 79% of specimens, res pectively. Matrix metalloproteinases were found particularly in cell cluste rs and blood vessels of degenerate discs, with staining correlating positiv ely with macroscopic degenerative grade. For all of the enzymes, there was most staining in the herniation specimens and least in the autopsy samples. The opposite was true of staining for the matrix metalloproteinases inhibi tor, tissue inhibitor of metalloproteinases 2, with most found in the autop sy specimens. Enzyme activity was confirmed by in situ zymography and stain ing for matrix metalloproteinase degradation products of proteoglycans. In addition, there was staining with antibodies demonstrating aggrecanase degr adation products. Conclusions. Matrix metalloproteinase activity is more prevalent in herniat ed discs than in other disc disorders studied, although matrix metalloprote inases may have been more common earlier in the disease progression. Matrix metalloproteinases can be produced by invading blood vessels and associate d cells, as well as by indige- nous disc cells. Aggrecanase activity, altho ugh present in some samples, was not as obvious as that of matrix met allop roteinases. In addition to altered matrix metalloproteinase production; the re appears to be a change in the balance between enzymes and,endogenous inh ibitors, tissue inhibitors of metalloproteinases. This study highlights spe cific matrix metalloproteinases that might be most efficient to target in d eveloping therapeutics for minimizing degradation df the extracellular matr ix of the disc.