Matrix metalloproteinase-9 delays wound healing in a murine wound model

Background. Metalloproteinase-9 (MMP-9) is a type IV collagenase found at elevated levels in chronic wounds. As wounds heal, MMP-9 diminishes. In this study, we investigated whether MMP-9 directly contributes to chronic wound pathogenesis. Methods. Recombinant proMMP-9 was prepared using immortalized keratinocytes transduced by a lentivirus. ProMMP-9 was Purified from cell culture media and activated using 4-aminophenylmercuric acetate. Active MMP-9 was then suspended in xanthan gum to a concentration paralleling that found in human chronic wounds. Two, Parallel 6-mm, punch biopsies were made on the backs of C57BL mice. Wounds were treated daily with MMP-9 or vehicle. Wound areas were measured and tissues examined by densitometry, real-time RT-PCR, histology, and immunohistochemistry at days 7, 10, and 12. Results. Exogenous MMP-9, at the level found within chronic wounds, delayed. wound healing in this animal model. By 7 days, wounds in the MMP-9-injected group were 12% larger than control wounds (P = .008). By day 12 wounds in the MMP-9-injected group were 25% larger than those of the control group (P = .03). Histologic examination shows that high levels of active MMP-9-impaired epithelial migrating tongues (P = .0008). Moreover, consistent with elevated MMP-9, the collagen IV in the leading edge of the epithelial tongue was diminished. Conclusion. MMP-9 appears to directly delay wound healing. Our data suggests that this may occur through interference with re-epithelialization. We propose that MMP-9 interferes with the basement membrane protein structure, which in turn impedes keratinocyte migration, attachment, and the reestablishment of the epidermis. (Surgery 2010;147:295-302.)