The major objective of the proposed study of signals and second messengers in retinal pigment epithelium (RPE) is to understand the pathways and mechanisms that regulate phagocytosis of photoreceptor outer segments. The applicant has previously found that phagocytosis of rod outer segments (ROS) triggers the expression of some early response genes (nur-77, zif-268, and c-fos) as well as consequent appearance of DNA-binding proteins (NUR-77, ZIF-268, AP1, AP2). This induction is specific because other early response genes (COX-2, NFKB) are unchanged, latex bead phagocytosis does not modify early response genes, and early response genes are not changed in RCS rat cells that were fed ROS. Two hypotheses are proposed: (1) that ROS phagocytosis triggers the activation of specific transcription factors and that lipid messengers are the modulators of these events, with the specific messengers to be examined including prostaglandin D2 (PGD2), which is an autocrine regulator of RPE function through modulation of the early response gene nur-77, and platelet-activating factor (PAF), which is a modulator of other early response genes triggered by ROS phagocytosis; and (2) that under physiological conditions, prostaglandin synthase (COX-2) stimulation by growth factors generates prostaglandin messengers for cell functions whereas under pathological conditions (e.g., retinal light damage), COX-2 may be overexpressed and may participate in photoreceptor cell death. Biochemical, cell biological and molecular biological approaches as well as in vivo and in vitro cell cultures are used to test these hypotheses. The knowledge obtained about alterations in RPE cell signaling and gene transcription, especially as a function of age, may allow the eventual design of drugs for the prevention and treatment of age-related macular degeneration and other degenerative retinal diseases.
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