TIMP3 expression in the human retina and choroid

Purpose. Extracellular matrix homeostasis is dependent in part upon a family of matrix metalloproteinases and their specific tissue inhibitors, the TIMPs. Recently, gene defects in TIMP3 have been identified in the affected individuals of several families exhibiting Sorsby's fundus dystrophy (SFD). Little information is available regarding TIMP3 function or even its existence in the retina or choroid. Methods. We evaluated the levels and expression of TIMP1, 2 and 3 mRNA and protein in human retina and choroid and by human RPE, choroidal microcapillary pericytes and endothelial cells in culture. We used western immunoblots, reverse zymography, reverse transcription-polymerase chain reaction (RT-PCR), northerns and immunohistochemistry. Results. TIMP3 mRNA and protein are expressed by RPE and choroidal endothelium. TIMP3 protein is localized to extracellular matrix, while TIMP1 and 2 are found in culture medium. Changes in TIMP1, 2 and 3 mRNA and protein levels were evaluated after treatment with a phorbol mitogen or bFGF. Immunohistochemistry shows dense, specifically localized TIMP3 immunostaining in Bruch's membrane and some choroidal vascular basememt membranes. In contrast, immunostaining for TIMP1 is absent and for TIMP2 is much lighter and more generally localized in Bruch's membrane. Conclusions. These results suggest that retinal TIMP3 expression is tissue- and cell type-specific and partially explain, why mutations in this protein could produce SFD.