ROAD MAPS TO GLAUCOMATOUS NEURODEGENERATION BY LABEL-FREE QUANTITATIVE PROTEOMICS

Purpose: There is a scarcity in reports on the molecular cross-talks occurring between the retina and optic nerve in glaucoma. Menopausal hormone deficiency also has been considered a risk factor of glaucomatous neurodegeneration hitherto without plausible mechanistic origins. To address these gaps of knowledge, we designed a global proteomics-based analysis of rat retina and optic nerve to gain a detailed understanding of IOP-associated alterations occurring at the protein level upon estrogen deprivation. Methods: Tissues were obtained through collaboration from rats in which one eye was subjected to routine IOP elevation by sclerosing the episcleral vein with hypertonic saline. Proteins from target tissues were extracted and analyzed separately for mass spectrometry-based proteomics using label-free quantification. Differentially expressed proteins were mapped to protein interaction networks and biological processes through Ingenuity Pathway Analysis (IPA?). Results: Our mass discovery-driven proteomic analysis covered nearly 1900 proteins in the rat retina and optic nerves. Regulated proteins triggered by increased IOP showed both distinct and similar functions between the retina and the optic nerve. The most interesting regulation we observed was the inhibition of signaling mechanisms involved in growth and proliferation, such as semaphorin signaling in neurons, and clathrin-mediated endocytosis responsible for maintaining cell morphology, regulating uptake of nutrients and synaptogenesis. Conclusion: Our study has provided the first global insight into alterations occurring at the molecular level and involving protein networks with associated biological processes upon glaucomatous neurodegeneration of the retina and optic nerve in response to elevated IOP.