Regulation Of Endothelium-Reticulum-Stress-Mediated Apoptotic Cell Death By A Polymethoxylated Flavone, Nobiletin, Through The Inhibition Of Nuclear Translocation Of Glyceraldehyde 3-Phosphate Dehydrogenase In Retinal Muller Cells

In the early stages of diabetic retinopathy (DR), subtle biochemical and functional alterations occur in Muller cells, which are one of the components of the blood-retinal barrier (BRB). Muller cells are the principal glia of the retina and have shown a strong involvement in the maintenance of homeostasis and the development of retinal tissue. Their functional abnormalities and eventual loss have been correlated with a decrease in the tight junctions between endothelial cells and a consequent breakdown of the BRB, leading to the development of DR. We demonstrated that the endothelium reticulum (ER) triggers Muller cell death and that nuclear accumulation of glyceraldehyde 3-phosphate dehydrogenase is closely associated with ER-induced Muller cell death. In addition, induction of ER stress in Muller cells increased vascular endothelial growth factor expression but decreased pigment-epithelium-derived factor (PEDF) expression in Muller cells. We found that nobiletin, a polymethoxylated flavone from citrus explants, exerts protective action against ER-stress-induced Muller cell death. In addition, nobiletin was found to augment PEDF expression in Muller cells, which may lead to the protection of BRB integrity. These results suggest that nobiletin can be an attractive candidate for the protection of the BRB from breakdown in DR.