597-P: Retinol Binding Protein 3 in Diabetic Retinopathy: Mechanisms of Protective Activity
Authors: YOKOMIZO HISASHI , PARK KYOUNGMIN , CLERMONT ALLEN , MAEDA YASUTAKA , FICKWEILER WARD , ISHIKADO ATSUSHI , LI QIAN , WANG CHIH-HAO , POBER DAVID M. , WU I-HSIEN , KEENAN HILLARY A. , AIELLO LLOYD P. , SUN JENNIFER K. , KING GEORGE L. 
Published: June 2019

The Joslin Medalist study reported that after having type 1 diabetes (T1D) for &gt; 50 years, over 35% of Medalists exhibit no to mild diabetic retinopathy (DR) independent of glycemic control, suggesting presence of endogenous protective factors against DR. Proteomic analysis of Medalist retina and vitreous found that Retinol Binding Protein 3 (RBP3), secreted by photoreceptors, is elevated in individuals protected from DR. This finding was confirmed by RBP3 ELISA of replicate vitreous samples from Medalists and other T1D and T2D individuals. In contrast, vitreous VEGF concentrations increased with DR severity. Thus, elevated ratios of intravitreous RBP3/VEGF correlated with lack of progression to advanced DR. Intervention and prevention studies overexpressing RBP3 in retina/photoreceptors of nondiabetic and diabetic animals inhibited VEGF actions and normalized diabetes-induced retinal capillary permeability, neuro-retinal dysfunctions, expressions of VEGF and IL-6, and formation of acellular capillaries. Mechanistically, physiological levels of recombinant RBP3 (10-100nM), but not RBP4 or FGF, inhibited the increased in VEGFR2 tyrosine phosphorylation, hyperglycemia-induced expression of pro-inflammatory cytokines (VEGF and IL-6), and migration of retinal endothelial cells and Müller cells. RBP3, but not RBP4, physically bound to VEGFR2 in cross linkage studies. At physiological levels, RBP3 significantly inhibited glucose uptake into retinal endothelial and Müller cells, and subsequently decreased expression of VEGF and IL-6. These results suggest novel actions for RBP3 to slow glucose uptake in retinal cells and inhibit VEGF actions, thereby preventing, delaying and even arresting diabetes-induced neuro- and vascular retinal dysfunction, inflammatory abnormalities and DR pathologies. These findings strongly support therapeutic potential of RBP3 in DR.

Disclosure
H. Yokomizo: None. K. Park: None. A. Clermont: Consultant; Self; KalVista Pharmaceuticals, Inc. Y. Maeda: Research Support; Self; Abbott, Arkray, Inc. Speaker's Bureau; Self; Abbott, Arkray, Inc., Astellas Pharma Inc., AstraZeneca, Daiichi Sankyo Company, Limited, Eli Lilly and Company, Kissei Pharmaceutical Co., Ltd., Kyowa Hakko Kirin Co., Ltd., Mitsubishi Tanabe Pharma Corporation, Novartis Pharmaceuticals Corporation, Novo Nordisk Inc., Sanofi, Sumitomo Dainippon Pharma Co., Ltd., Taisho Toyama Pharmaceutical Co., Ltd., Terumo Medical Corporation. W. Fickweiler: None. A. Ishikado: Employee; Self; SunStar Inc. Employee; Spouse/Partner; SunStar Inc. Q. Li: None. C. Wang: None. D.M. Pober: None. I. Wu: None. H.A. Keenan: Employee; Self; Sanofi Genzyme. L.P. Aiello: Advisory Panel; Self; Novo Nordisk A/S. Consultant; Self; Decision Resources Group, KalVista Pharmaceuticals, Inc., Mingsight, Retinal Solutions. Stock/Shareholder; Self; KalVista Pharmaceuticals, Inc. Other Relationship; Self; Optos. J.K. Sun: Research Support; Self; Adaptive Sensory Technology, Boston Micromachines Corporation, Genentech, Inc., KalVista Pharmaceuticals, Inc., Optovue, Incorporated. Other Relationship; Self; Genentech, Inc., Novartis Pharmaceuticals Corporation, Novo Nordisk Inc. G.L. King: Research Support; Self; Sanofi.

Funding
National Eye Institute; National Institute of Diabetes and Digestive and Kidney Diseases; JDRF; Thomas J. Beatson, Jr. Foundation Inc.; Dianne Nunnally Hoppes Scholarship Fund