Localization of TIMP-3 mRNA expression to the retinal pigment epithelium

Purpose. Mutations in the TIMP-3 (tissue inhibitor of metalloproteinases-3) gene have been found in patients with Sorsby's fundus dystrophy, an autosomal dominant condition characterized by early onset choroidal neovascularization and severe visual loss. In this study we evaluated the pattern of expression of TIMP-3 in the normal eye. Methods. In situ hybridization was performed on frozen sections of albino mouse eyes using riboprobes generated to the 3′ untranslated region of TIMP-3. In addition, reverse transcription-polymerase chain reaction (RT-PCR) was undertaken on cultured human retinal pigment epithelium (RPE) and freshly isolated human and bovine RPE. Results. TIMP-3 mRNA expression was strongly detected by in situ hybridization in the RPE and to a minor extent in the ciliary epithelium, but not at any other site within the mouse eye. RT-PCR analysis detected TIMP-3 expression in human RPE cells cultured from two different donors and in freshly isolated human and bovine RPE. Currently, we are using northern analysis to evaluate the modulation of TIMP-3 expression in cultured human RPE cells under the influence of various angiogenic stimuli and growth factors. Conclusion. Expression of TIMP-3 in the RPE is consistent with the recent demonstration of TIMP-3 mutations in Sorsby's patients. The similarities between Sorsby's fundus dystrophy and age-related macular degeneration (AMD) highlight the importance of understanding TIMP-3 function in the RPE and evaluating its possible involvement in AMD. Unlike many of the recently described genes which cause human retinal disease, TIMP-3 is preferentially expressed in the RPE of the normal eye, as opposed to the photoreceptors.