Expression and activity of matrix metalloproteinase-2 and -9 in experimental granulation tissue

The restoration of functional connective tissue is a major goal of the wound healing process which is probably affected by matrix-modifying enzymes. To evaluate the spatial and temporal expression of matrix metalloproteinases (MMP) MMP-2 and MMP-9 and to study the regulation of MMP-2 in wound healing, subcutaneously implanted viscose cellulose sponges in rats were used to induce granulation tissue formation for up to 3 months. MMP-2 mRNA expression was seen throughout the experiment and it was highest after 2 months. MMP-9 gene expression was low between days 8-21 and increased after 4 weeks of granulation tissue formation. Membrane-type 1 MMP (MT1-MMP) mRNA was upregulated early and tissue inhibitor 2 of MMP (TIMP-2) mRNA later during wound healing. In in situ hybridization the expression of MMP-2 mRNA was seen mostly in fibroblast-like cells and MMP-9 mRNA in macrophage-like cells. MMP-9 immunoreactivity was detected in the polymorphonuclear leukocytes and macrophage-like cells on days 3-8. MMP-9 proteolytic activity was observed only on days 3-8. The active form of the MMP-2 increased up to day 14, whereafter it remained at a constant level, whereas latent MMP-2 did not show any apparent changes during the experimental period. We conclude that MMP-2 is important during the prolonged remodelling phase, whereas the gelatinolytic activity of MMP-9 was demonstrated only in early wound healing, and the MMP-9 gene is upregulated when the granulation tissue matures.