Hyperhomocysteinemia-induced death of retinal ganglion cells: The role of Müller glial cells and NRF2
Soumya Navneet,
Jing Zhao,
Jing Wang,
Barbara Mysona,
Shannon Barwick,
Navneet Ammal Kaidery,
Alan Saul,
Ismail Kaddour-Djebbar,
Wendy B. Bollag,
Bobby Thomas,
Kathryn E. Bollinger,
Sylvia B. Smith
Affiliations
Soumya Navneet
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA
Jing Zhao
James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA; Department of Ophthalmology, Medical College of Georgia, Augusta University, Augusta, GA, USA
Jing Wang
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA
Barbara Mysona
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA; Department of Ophthalmology, Medical College of Georgia, Augusta University, Augusta, GA, USA
Shannon Barwick
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA
Navneet Ammal Kaidery
Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta University, Augusta, GA, USA; Department of Pediatrics, Medical University of South Carolina, Charleston, SC, USA
Alan Saul
James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA; Department of Ophthalmology, Medical College of Georgia, Augusta University, Augusta, GA, USA
Ismail Kaddour-Djebbar
Department of Physiology, Medical College of Georgia, Augusta University, Augusta, GA, USA; Charlie Norwood VA Medical Center, One Freedom Way, Augusta, GA, 30904, USA
Wendy B. Bollag
Department of Physiology, Medical College of Georgia, Augusta University, Augusta, GA, USA; Charlie Norwood VA Medical Center, One Freedom Way, Augusta, GA, 30904, USA
Bobby Thomas
Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta University, Augusta, GA, USA; Department of Pediatrics, Medical University of South Carolina, Charleston, SC, USA; Department of Neuroscience, Medical University of South Carolina, Charleston, SC, USA; Department of Drug Discovery, Medical University of South Carolina, Charleston, SC, USA
Kathryn E. Bollinger
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA; Department of Ophthalmology, Medical College of Georgia, Augusta University, Augusta, GA, USA
Sylvia B. Smith
Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, Augusta, GA, USA; James and Jean Culver Vision Discovery Institute, Augusta University, Augusta, GA, USA; Department of Ophthalmology, Medical College of Georgia, Augusta University, Augusta, GA, USA; Corresponding author. Department of Cellular Biology and Anatomy, Medical College of Georgia, Augusta University, 1120 15th Street, CB 1114, Augusta, GA, 30912-2000, USA.
Hyperhomocysteinemia (Hhcy), or increased levels of the excitatory amino acid homocysteine (Hcy), is implicated in glaucoma, a disease characterized by increased oxidative stress and loss of retinal ganglion cells (RGCs). Whether Hhcy is causative or merely a biomarker for RGC loss in glaucoma is unknown. Here we analyzed the role of NRF2, a master regulator of the antioxidant response, in Hhcy-induced RGC death in vivo and in vitro. By crossing Nrf2−/− mice and two mouse models of chronic Hhcy (Cbs+/- and Mthfr+/- mice), we generated Cbs+/-Nrf2−/− and Mthfr+/-Nrf2−/− mice and performed systematic analysis of retinal architecture and visual acuity followed by assessment of retinal morphometry and gliosis. We observed significant reduction of inner retinal layer thickness and reduced visual acuity in Hhcy mice lacking NRF2. These functional deficits were accompanied by fewer RGCs and increased gliosis. Given the key role of Müller glial cells in maintaining RGCs, we established an ex-vivo indirect co-culture system using primary RGCs and Müller cells. Hhcy-exposure decreased RGC viability, which was abrogated when cells were indirectly cultured with wildtype (WT) Müller cells, but not with Nrf2−/− Müller cells. Exposure of WT Müller cells to Hhcy yielded a robust mitochondrial and glycolytic response, which was not observed in Nrf2−/− Müller cells. Taken together, the in vivo and in vitro data suggest that deleterious effects of Hhcy on RGCs are likely dependent upon the health of retinal glial cells and the availability of an intact retinal antioxidant response mechanism. Keywords: Retina, Ganglion cells, Hyperhomocysteinemia, Cystathionine β-synthase, Methylene tetrahydrofolate reductase, Mouse, Glaucoma, Homocysteine, NRF2
