Differential expression and localization of human tissue inhibitors of metalloproteinases in proliferative diabetic retinopathy

The differential expression of TIMPs in PDR suggests that among the 4 TIMPs, TIMP-1 and TIMP-4 may be possible biomarkers of disease activity.

Vitreous samples from 38 PDR and 21 nondiabetic control patients and epiretinal membranes from 14 patients with PDR and 10 patients with proliferative vitreoretinopathy (PVR) were studied by enzyme-linked immunosorbent assay, Western blot analysis and immunohistochemistry.

Tissue inhibitors of metalloproteinases (TIMPs) block the catalysis by matrix metalloproteinases (MMPs) and have additional biologic activities, including regulation of cell growth and differentiation, apoptosis, angiogenesis and oncogenesis. We investigated the expression levels of all the four human TIMPs and correlated these levels with those of MMP-9 and vascular endothelial growth factor (VEGF) in proliferative diabetic retinopathy (PDR).

Tissue inhibitor of metalloproteinases-1, TIMP-4, MMP-9 and VEGF levels were significantly higher in vitreous samples from PDR patients than in nondiabetic controls (p < 0.0001 for all comparisons), whereas TIMP-2 and TIMP-3 levels did not differ significantly. TIMP-1, TIMP-4, MMP-9 and VEGF levels in PDR with active neovascularization were significantly higher than those in inactive PDR (p < 0.0001, 0.001, 0.013, 0.004, respectively). Significant positive correlations existed between levels of TIMP-1 and levels of TIMP-4 (r = 0.37; p = 0.004), MMP-9 (r = 0.65; p < 0.0001) and VEGF (r = 0.59; p < 0.0001), between levels of TIMP-4 and levels of MMP-9 (r = 0.61; p < 0.0001) and VEGF (r = 0.62; p < 0.0001) and between levels of MMP-9 and VEGF (r = 0.62; p < 0.0001). TIMP-1 and TIMP-3 were expressed in vascular endothelial cells in PDR epiretinal membranes and in myofibroblasts and leucocytes in PDR and PVR epiretinal membranes.