Wound fluids from saline solution‐ and Staphylococcus aureus peptidoglycan‐inoculated sponges induce expression of matrix metalloproteinase 13 messenger ribonucleic acid by cultured rat fibroblasts

Abstract

Polyvinyl alcohol sponges inoculated with Staphylococcus aureus peptidoglycan induce an accelerated wound healing response when implanted subcutaneously in rats. S. aureus peptidoglycan leads to a marked increase (50%) in reparative tissue collagen (as measured by hydroxyproline) by 4 days. However, this effect drops by 7 days and by 14 days; hydroxyproline levels are similar in sponges inoculated with S. aureus peptidoglycan or saline solution. These data suggest a very active early remodeling process in S. aureus peptidoglycan sponge reparative tissue. Consistent with this observation, we had found that steady-state levels of matrix metalloproteinase-13 mRNA were higher and persisted longer in S. aureus peptidoglycan sponge reparative tissue than in controls. We hypothesized that S. aureus peptidoglycan might induce a change in reparative tissue fibroblast phenotype or modify the character of the wound fluid. Fibroblasts obtained from saline solution- and S. aureus peptidoglycan-inoculated sponges 4 days after subcutaneous implantation and cultured in Eagle's minimal essential medium supplemented with 10% fetal calf serum were similar with respect to morphologic features, proliferation, and expression of pro alpha1 (I) and alpha1 (III) collagens and tissue inhibitor of metalloproteinase-1 mRNA by Northern blot analysis. Neither cell type expressed matrix metalloproteinase-13 mRNA. No changes in the above parameters were detected when such fibroblasts were cultured for 24 hours in the presence of 0.5 mg of S. aureus peptidoglycan per 10 ml of medium or with fluid obtained from control sponges cultured for 12 hours with phosphate-buffered saline solution. Wound fluids extracted with Eagle's minimal essential medium by homogenization of saline solution- and S. aureus peptidoglycan-inoculated sponges implanted subcutaneously for 12 hours did not affect the proliferation of the fibroblasts. However, the extracts had a profound effect on the cellular expression of tissue inhibitor of metalloproteinase-1, matrix metalloproteinase-13, and pro alpha1 (I) collagen mRNA. Specifically, expression of matrix metalloproteinase-13 mRNA was induced, expression of pro alpha1 (I) collagen mRNA was reduced by 70%, and expression of tissue inhibitor of metalloproteinase-1 mRNA was increased by 150%. These changes were the same irrespective of whether the wound fluid was obtained from saline solution- or S. aureus peptidoglycan-inoculated sponges. Fluid obtained from S. aureus peptidoglycan-inoculated sponges, which contain a greater inflammatory exudate than saline solution-inoculated sponges do, is enriched in matrix metalloproteinase-13 mRNA-inducing activity. The nature of the factor(s) that induces matrix metalloproteinase-13 mRNA expression is not known. However, preliminary data suggest that the matrix metalloproteinase-13-inducing factor(s) is heterogeneous with regard to size and is temperature sensitive and trypsin resistant.