Leukocytes, particularly mononuclear phagocytes (Mphi), are key participants of common blinding retinal diseases in the United States. Descriptive studies have identified Mphi, apoptosis, chemokines, and growth factors in diseases, including proliferative diabetic retinopathy, proliferative vitreoretinopathy, and age-related macular degeneration (AMD). Epidemiologic studies of AMD also implicate reactive oxygen metabolites (ROM) as a causative factor. However, a hypothesis unifying these agents in a pathogenetic mechanism responsible for the initiation and propagation of AMD lesions has not been proposed. We hypothesize a novel mechanism in which cellular adhesion molecule (CAM)-dependent RPE-Mphi adhesion induces rapid intracellular release of Ca++ waves and subsequent ROM accumulation that promote RPE apoptosis, chemokine elaboration, and growth factor production. Validation of this hypothesis by the proposed studies will illuminate how in AMD lesions, specific CAM-mediated, RPE-Mphi binding, normally forbidden at the blood-retina barrier, results in prompt Ca++ and ROM signaling. Using a novel ultra high-speed microscopy and specific inhibitors we will demonstrate that Ca++ waves travel along the contiguous RPE cell monolayer for great distances, leading to ROM accumulation. Ca++ and ROM signaling will be shown to be required for initiation of RPE signal specific-apoptosis, chemokine elaboration, and growth factor production. We will show that the principal chemokine to be induced by this mechanism is MCP-1, the most potent of Mphi chemoattractants and activators, while the principal growth factor produced is VEGF, the most potent angiogenic agent. Using laser capture microdissection, contiguous RPE cells receiving Ca++ and ROM signaling and nearby unsignaled cells will be separately assessed by RT-PCR. This will allow comparison of genes induced by direct Ca++ and ROM signaling to those induced in nearby unsignaled cells whose gene expression may be altered by ambient mediators secreted by Ca++ and ROM-signaled cells. We will use DNA microarrays to screen for genes induced or inhibited by CAM-dependent RPE-Mphi binding. Corresponding proteins, including complement components, serum-derived clotting factors, and ROM antioxidant enzymes will be assessed for their ability to modulate RPE-Mphi responses. Using a confluence of new technologies and a robust tissue culture model for AMD, our studies will reveal and characterize a pathogenic mechanism that explains relationships of agents implicated in AMD as well as never before shown processes that may initiate and propagate AMD lesions. This new knowledge is likely to lead to advances in therapy, which may stem or prevent AMD.
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