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.