Tissue inhibitor of metalloproteinase (TIMP)-3 can inhibit neovascularization, a key event in the progression of diabetic retinopathy. We examined the influences of modified LDL on retinal pericyte expression of TIMP-3 compared with other TIMPs and matrix metalloproteinases (MMPs) since low-density lipoproteins (LDLs) modified by oxidation/glycation are implicated in diabetic vascular complications. Quiescent human retinal pericytes were exposed for 24 hours to native LDL (N-LDL), glycated LDL (G-LDL), and heavily oxidized-glycated LDL (HOG-LDL). TIMP and MMP expression were assessed at the level of mRNA (meta-analysis of microarray data, quantitative PCR) and protein (immunoblotting, ELISA). By microarray analysis, TIMP-1, -2, -3, and -4 and MMP-1, -2, -11, -14, and -25 expression was detected, but only TIMP-3 mRNA showed a differential response, being expressed at significantly lower levels in response to HOG-LDL versus N-LDL, and this was confirmed by quantitative PCR and immunoblotting of cell/matrix proteins. In contrast to TIMP-3 in cells, analyses of secreted TIMP-1, TIMP-2, MMP-1, and collagenase activity indicated no changes in their production in response to modified LDL. Combined N-LDL and HOG-LDL treatment restored TIMP-3 mRNA expression to levels comparable to N-LDL alone. We conclude that among the TIMPs and MMPs expressed in retinal pericytes, expression of TIMP-3 is uniquely regulated by HOG-LDL. Reduced TIMP-3 expression may be implicated in neovascularization in diabetic retinopathy.
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