DISCRETE EXPRESSION AND DISTRIBUTION PATTERN OF TIMP-3 IN THE HUMAN RETINA AND CHOROID

Purpose. Extracellular matrix homeostasis is dependent in part upon a family of matrix metalloproteinases and their specific inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). Recently, gene defec ts in TIMP-3 have been identified in the affected individuals of sever al families with Sorsby's fundus dystrophy (SFD). Very little informat ion is available regarding TIMP-3 function or even its existence in th e retina or choroid. Methods. We used reverse transcription-polymerase chain reaction and Northern analysis to evaluate the expression of TI MP mRNA and Western immunoblots to evaluate TIMP protein produced by s elect cells of the human retina and choroid. We also used these method s and immunohistochemistry to localize the TIMPs in the retina and cho roid. Results. TIMP-3 transcripts are found in cultured human retinal pigment epithelium (RPE), choroidal microcapillary endothelium and per icytes. RPE cells also express and secrete TIMP-3 protein, which is lo calized to the extracellular matrix and is not found in culture medium ; TIMP-1 and -2 are found almost exclusively in the medium. Immunohist ochemistry of human retina/choroid sections shows pronounced TIMP-3 im munostaining in Bruch's membrane, particularly near the surface of the RPE and endothelial cells, presumably in their basement membranes, wi th minimal staining in other portions of the retina. Immunostaining fo r TIMP-1 is absent and for TIMP-2 is much less prevalent, but detectab le in Bruch's membrane. Conclusions. TIMP-1, -2 and -3 exhibit distinc tive expression patterns in the retina and choroid. This distribution and expression pattern partially explains why TIMP-3 mutations result in SFD, rather than other retinal pathologies, such as those associate d with proliferative diabetic retinopathy.