Mitochondrial dysfunction and oxidative stress are thought to be relevant to the pathogenesis of age-related macular degeneration (AMD). Glutathione (GSH) homeostasis fulfills a number of important roles in mitochondria, such as maintenance of mitochondrial DNA and respiratory competency of cells. Although the transport of mitochondrial GSH (mGSH) is not fully understood, increasing evidence from non-ocular tissues suggests that OGC (2-oxoglutarate carrier, SLC25A11) and DIC (dicarboxylate carrier, SLC25A10) are involved in mGSH transport. However, whether OGC and DIC mediate the transfer of GSH into the mitochondria of retinal pigment epithelial cells (RPE) remains unknown. Thus, we investigated the expression, localization, and function of OGC and DIC in human RPE (hRPE) in relation to oxidative stress and GSH. Both OGC and DIC are expressed in hRPE and are localized in mitochondria. We also found a dose and time-dependent decrease of OGC and DIC expression under oxidative stress and increased expression in polarized RPE. Our data show that the downregulation of OGC and DIC resulted in increased apoptosis and mGSH depletion which can be overcome by co-treatment with GSH-MEE. These findings suggest that overexpression of OGC and DIC may be an effective strategy to decrease susceptibility to mitochondrial toxicants by elevation of mGSH.

Retinal pigment epithelium (RPE) replacement therapy is evolving as a feasible approach to treat age-related macular degeneration (AMD). In majority of the preclinical studies, RPE cells are transplanted as cell suspension into immunosuppressed animal eyes and transplant effects were monitored only short-term. We investigated long-term effects of human iPSC derived RPE transplants in immunodeficient Royal College of Surgeons (RCS) rat model, in which RPE dysfunction lead to photoreceptor degeneration. iPSC-RPE cultured as polarized monolayer on nanoengineered ultrathin parylene C scaffold was transplanted into the subretinal space of 28-day old immunodeficient RCS rat pups and evaluated after 1, 4 and 11 months. Assessment at early time points showed good iPSC-RPE survival. The transplants remained as a monolayer, expressed RPE specific markers, performed phagocytic function and contributed to vision preservation. At 11-month post-implantation, RPE survival was observed only in 50% of the eyes that were concomitant with vision preservation. Loss of RPE monolayer characteristics at the 11month time point was associated with peri-membrane fibrosis, immune reaction through activation of macrophages (CD 68 expression) and transition of cell fate (expression of mesenchymal markers). The overall study outcome supports the therapeutic potential of RPE grafts despite the loss of some transplant benefits during long-term observations.