Production and activation of matrix metalloproteinase-2 in proliferative diabetic retinopathy

PURPOSE. To investigate the matrix metalloproteinase (MMP) species and their activation associated with the pathogenesis of proliferative diabetic retinopathy (PDR). METHODS. Sandwich enzyme immunoassays were used to measure concentrations of MMP-1, -2, -3, -7, -8, -9, and -13 in vitreous samples from patients with PDR and nondiabetic vitreoretinal diseases. To evaluate activation ratios of the zymogen of MMP-2 (proMMP-2) and -9 (proMMP-9) in the vitreous samples and fibrovascular tissues, gelatin zymography was performed. Production and tissue localization of MMP-2, membrane type 1-MMP (MT1-MMP), tissue inhibitor of metalloproteinases (TIMP)-2, and MMP-9 in the fibrovascular tissues were examined by immunohistochemistry. mRNA expression of MT1-MMP in the tissues was determined by reverse transcription-polymerase chain reaction (RT-PCR). RESULTS. Among the seven different MMPs examined in the vitreous samples, only the levels of MMP-2 and -9 were significantly higher in the PDR samples than in the control. However, activation ratios of proMMP-2 (10.6% +/- 11.8%) and proMMP-9 (2.5% +/- 5.1%) in PDR vitreous samples were low and not significantly different from those of the control. In contrast, high activation ratios of proMMP-2 (54.3% +/- 13.6%) and notable activation of proMMP-9 (19.5% +/- 7.8%) were observed in the fibrovascular tissues. Immunohistochemical study demonstrated the localization of MMP-2 and -9 in the endothelial cells and glial cells of the fibrovascular tissues. MMP-2 was colocalized with MT1-MMP and TIMP-2, which are an activator and an activation-enhancing factor, respectively, for proMMP-2. RT-PCR analysis indicated the gene expression of MT1-MMP in the tissues. CONCLUSIONS. These data demonstrate that proMMP-2 is efficiently activated in the fibrovascular tissues of PDR, probably through interaction with MT1-MMP and TIMP-2, and suggest the possibility that the activity of MMP-2 and MT1-MMP is involved in the formation of the fibrovascular tissues.