αb crystallin is apically secreted within exosomes by polarized human retinal pigment epithelium and provides neuroprotection to adjacent cellsαb晶状体蛋白分泌是水液内极化人类视网膜色素上皮细胞并提供神经保护邻近细胞.pdf

aB Crystallin Is Apically Secreted within Exosomes by Polarized Human Retinal Pigment Epithelium and Provides Neuroprotection to Adjacent Cells 1. 1,2. 1 1 1 Parameswaran G. Sreekumar , Ram Kannan , Mizuki Kitamura , Christine Spee , Ernesto Barron , Stephen J. Ryan1,2, David R. Hinton1,2,3* 1 Arnold and Mabel Beckman Macular Research Center, Doheny Eye Institute, Los Angeles, California, United States of America, 2 Department of Ophthalmology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States of America, 3 Department of Pathology, Keck School of Medicine of the University of Southern California, Los Angeles, California, United States of America Abstract aB Crystallin is a chaperone protein with anti-apoptotic and anti-inflammatory functions and has been identified as a biomarker in age-related macular degeneration. The purpose of this study was to determine whether aB crystallin is secreted from retinal pigment epithelial (RPE) cells, the mechanism of this secretory pathway and to determine whether extracellular aB crystallin can be taken up by adjacent retinal cells and provide protection from oxidant stress. We used human RPE cells to establish that aB crystallin is secreted by a non-classical pathway that involves exosomes. Evidence for the release of exosomes by RPE and localization of aB crystallin within the exosomes was achieved by immunoblot, immunofluorescence, and electron microscopic analyses. Inhibition of lipid rafts or exosomes significantly reduced aB crystallin secretion, while inhibitors of classic secretory pathways had no effect. In highly polarized RPE monolayers, aB