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C.J. Whiting, D.J. Rak, Jr, B.S. McKay; Neurotrophic Factor Secretion by Pigmenting RPE . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2297.
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Purpose: Ocular Albinism, a disease characterized by the loss of pigmentation in the RPE, causes abnormal sensory retina development. Since pigmentation occurs in the RPE and not in the neurosensory retina, neurotrophic factors are likely expressed there during the process of pigmentation. The lack of expression of the proteins tyrosinase or OA1 can each cause ocular albinism, suggesting that either may be involved in RPE control over aspects of retinal development. This experiment investigates the role of pigmentation, tyrosinase, and OA1 in promoting retinal neuron growth and survival. Methods: Test Media: Cultures of RPE and COS cells were used to test for secretion of neurotrophic factors. Conditioned media was collected from cells actively pigmenting (RPE), and cells were transfected to express either Tyrosinase or OA1 (COS). Neuronal Cell Culture: Neurons from the eyes of E16 rats were cultured and test or control media was applied on Days 4 and 8. A minimum of 3 fields per experimental group were analyzed between days 6 and 12. Test analysis was used to determine the significance of differences in cell survival among the various groups. Results: Media from pigmenting RPE had a significant effect on the number of neurons surviving between Days 6 and 9 when compared to parallel neuron cultures given control RPE conditioned media obtained from nonpigmenting cultures. There was no significant difference between the number of neurons surviving between Days 6 and 12 given conditioned medium from COS cells transfected to express tyrosinase when compared paired COS control cultures. There was a significant difference in the number of neurons surviving between Days 7 and 9 when treated with conditioned medium from COS transfected to express OA1 compared to paired control cultures. Conclusions: Our experiment examines whether paracrine neurotrophic factors are released by RPE cells during pigment production. Conditioned medium collected from RPE cells actively producing pigment increased retinal neuron survival. We also examined the potential roles of two proteins that function in pigment production, tyrosinase and OA1. Medium from COS cells transfected to express tyrosinase had no effect on neuronal survival, but medium from COS expressing OA1 had a significant impact on neuronal survival. OA1 may be part of the RPE pathway lost in albinism important for retinal development.
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