Retinal pigment epithelial (RPE) cell death is thought to be the primary mechanism for the development of geographic atrophy (GA) in age-related macular degeneration (AMD). Along with choroidal neovascularization (CNV), GA is responsible for most of the vision loss in AMD. However, unlike CNV, GA typically develops late in the course of AMD suggesting that there are mechanisms which RPE utilize to avoid cell death. Since there are known treatments are available for GA, the study of these mechanisms is important to generate novel therapies for GA. In initial reports from this laboratory, evidence was been collected and published on the programmed cell death pathway in RPE cells. It was demonstrated that unlike the conventional programmed cell death pathways which utilize cytochrome c, caspase 3, 9 and PARP to initiate cell death, in RPE cells these pathways are not activated. Instead, the novel programmed cell death molecule, apoptosis induced factor (AIF) appears to be involved in RPE cell death. In an extension of this work, RPE cells were exposed to sublethal injury and microarray analysis and cellular responses to this injury were assessed. To verify the nonlethal condition of the oxidative stimulus, absence of AIF translocation, maintenance of thymidine incorporation and trypan blue penetrance and absence of DNA laddering were demonstrated. As previously observed, membrane blebbing as well as actin cytoskeleton rearrangement are prominent features of the nonlethal injury response. Kinetic microarray analysis of several time points over a 48 hrs period revealed significant upregulation of genes involved in ameliorating the oxidative stress, chaperone proteins, anti-apoptotic factors and DNA repair factors and downregulation of pro-apoptotic genes. In particular, IAP (Inhibitory apoptosis protein) was especially unregulated. Recovery of RPE cells after the oxidative injury was confirmed by the normalization of gene expression dysregulation back to baseline levels within 48 hours. These results indicate the RPE cells utilize an active series of programs to avoid cell death and that IAP may play a prominent role. Recently, dysregulation of extracellular matrix proteins have also been demonstrated to be an integral part of the RPE injury response cascade. These processes may have important implications for the alterations in Bruch's membrane, a critical component of the RPE matrix changes observed in AMD. On-going work is also establishing proteomic techniques in RPE cells to elucidate the corresponding protein changes occurring both with injury and cell death. Effective methodologies have now been established and results indicated high concordance with above-outlined RNA response profile of the RPE to injury. These techniques are now being used to study the injury response from human RPE cells cultured from donor eyes diagnosed, by electron microscopic criteria, as either age-matched control or AMD eyes. Genotyping of the cells is delineating the presence of various polymorphisms principally within the complement factor H gene. Unique injury response profiles may be dependent on the Y402H mutation in CFH especially in the presence or absence of various modifying genes.
