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Dr. Andrew Tsin

Dr. Andrew Tsin



Research Profile


Research Interests

The focus of our Vision Research Laboratory is to understand the biochemical and cellular/molecular events in the eye related to normal visual functions and to abnormal/disease conditions.

A major emphasis of our laboratory is to investigate the mechanism of pigment regeneration in the cone visual system. Upon light adaptation, cone pigments are bleached to initiate electrical signals in the cone photoreceptors. These signals are then transmitted by neurons to the brain for color visual perception. In order to sustain such visual function, cone pigment must be regenerated in-situ but the underlying mechanism of this cone pigment regeneration is not known. Using animals models, the kinetics of cone pigment bleaching and regeneration are studied in details using biochemical methods. The cellular mechanisms of cone pigment regeneration are also studied using Muller cells and retinal pigment epithelial cells in culture. Specifically, we focus on the abilities of these cells to esterify, isomerize and oxidize the vitamin A (retinoid) chromophore of cone visual pigments.

An additional emphasis of our vision research laboratory is to learn how hyperglycemia and/or insulin induce vascular endothelial growth factor (VEGF) secretion by retinal cells. Retinal pigment epithelial cells, retinal pericytes, and endothelial cells are maintained in culture. Growth factors such as VEGF, transforming growth factor (TGF), and bone morphological proteins (BMP) are assayed for protein end-product using ELISA. The expression of these proteins is measured by RNA protection assays. We are particularly interested in the effect of BMP-4, TGB-β, and PEDF on the secretion of VEGF by retinal cells. Our long term goal is to learn how cytokines mediate angiogenesis leading to diabetic retinopathy or age-related macular degeneration.

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