Increased Retinal Expression of the Pro-Angiogenic Receptor GPR91 via BMP6 in a Mouse Model of Juvenile Hemochromatosis

• Type of Material: Article
• Authors: Pachiappan Arjunan, Georgia Regents University; Jaya P. Gnanaprakasam, Georgia Regents University; Sudha Ananth, Georgia Regents University; Michelle Romej, Emory University; Veeranan-Karmegam Rajalakshmi, Georgia Regents University; Puttur D. Prasad, Georgia Regents University; Pamela M. Martin, Georgia Regents University; Mariappan Gurusamy, Georgia Regents University; Muthusamy Thangaraju, Georgia Regents University; Yangzom D. Bhutia, Georgia Regents University; Vadivel Ganapathy, Georgia Regents University
• Language: English
• Date: 2016-04-01
• Publisher: Association for Research in Vision and Ophthalmology (ARVO)
• Publication Version: Final Published Version
• Copyright Statement: © 2016 Association for Research in Vision and Ophthalmology Inc. All rights reserved.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1167/iovs.15-17437
• Title of Journal or Parent Work: Investigative Ophthalmology & Visual Science
• ISSN: 0146-0404
• Volume: 57
• Issue: 4
• Start Page: 1612
• End Page: 1619
• Grant/Funding Information: Supported by grant from the National Eye Institute (EY019672).
• Keywords: HEMOJUVELIN; NON-HFE HEMOCHROMATOSIS; retinal pigment epithelium; MESSENGER-RNA; Ophthalmology; ACID; IRON-REGULATORY PROTEIN; HEREDITARY HEMOCHROMATOSIS; LOCALIZATION; BMP6 signaling; Life Sciences & Biomedicine; juvenile hemochromatosis; Science & Technology; PIGMENT EPITHELIUM; HAEMOJUVELIN; HOMEOSTASIS; succinate receptor-GPR91; age-related macular degeneration
• Research Categories: Biology, Cell; Chemistry, Biochemistry

Abstract

PURPOSE. Hemochromatosis, an iron-overload disease, occurs as adult and juvenile types. Mutations in hemojuvelin (HJV), an iron-regulatory protein and a bone orphogenetic protein (BMP) coreceptor, underlie most of the juvenile type. Hjv-/-mice accumulate excess iron in retina and exhibit aberrant vascularization and angiomas. A succinate receptor, GPR91, is pro-angiogenic in retina. We hypothesized that Hjv-/-retinas have increased BMP signaling and increased GPR91 expression as the basis of angiomas. METHODS. Expression of GPR91 was examined by qPCR, immunofluorescence, and Western blot in wild-type and Hjv-/-mouse retinas and pRPE cells. Influence of excess iron and BMP6 on GPR91 expression was investigated in ARPE-19 cells, and wild-type and Hjv-/-pRPE cells. Succinate was used to activate GPR91 and determine the effects of GPR91 signaling on VEGF expression. Signaling of BMP6 was studied by the expression of Smad1/5/8 and pSmad4, and the BMP-target gene Id1. The interaction of pSmad4 with GPR91 promoter was studied by ChIP. RESULTS. Expression of GPR91 was higher in Hjv-/-retinas and RPE than in wild-type counterparts. Unexpectedly, BMP signaling was increased, not decreased, in Hjv-/-retinas and RPE. Bone morphogenetic protein 6 induced GPR91 in RPE, suggesting that increased BMP signaling in Hjv-/-retinas was likely responsible for GPR91 upregulation. Exposure of RPE to excess iron and succinate as well as BMP6 and succinate increased VEGF expression. Bone morphogenetic protein 6 promoted the interaction of pSmad4 with GPR91 promoter in RPE. CONCLUSIONS. G-protein-coupled receptor 91 is a BMP6 target and Hjv deletion enhances BMP signaling in retina, thus underscoring a role for excess iron and hemochromatosis in abnormal retinal vascularization.