Age-related macular degeneration (AMD) represents the most common cause of blindness in patients over the age of 60. While both hereditary and environmental factors appear to play a role in the pathogenesis of the disease, the interaction between these factors is unclear. Based on laboratory evidence, one proposed hypothesis for this disease focuses on an altered injury response program of the retinal pigment epithelium. A clinical trial was completed which demonstrated that patterns of gene expression involved in wound repair, cell injury and death are altered in patients with AMD and that these genetic alterations could be detected in peripheral sites other than the eye. Biopsied skin fibroblasts from 7 patients with various forms of age-related macular degeneration and 3 age-matched control patients were obtained, grown in culture and exposed to a sublethal oxidative stress. RNA from these cells was examined and differential expression of a 15,000 genes was analyzed using a gene chip. Results were confirmed by quantitative RT-PCR. The results indicate a marked difference in gene expression profile between these groups of patients. Specifically, patients with more severe forms of AMD had a greater disregulation of affected compared with minimally affected and age-matched control patients. In addition, differences between patients with dry and wet forms of AMD indicated a genetic basis for the differences in these disease phenotypes. These results indicate that an abnormal response to injury may play a role in the pathogenesis of AMD. This study is now being extended to examine retinal pigment epithelial cells from autopsy specimens from aged eyes. Biopsies were being taken of these eyes and electron microscopic confirmation of the presence or absence of age-related macular degeneration changes is being performed. As above, sublethal injury is initiated and both a microarray analysis as well as a proteomic analysis of the differences between age-matched control and affected cells is being initiated. This is the first study of its kind to study so extensive the genetic responses of RPE cells taken when the diagnosis of AMD has been confirmed by the gold standard of accuracy, electron microscopy. In addition, SNP analysis of these cells for mutations within in the complement factor H (CFH) gene has been performed. To date, several interesting observations have been made. First, there appears to be a high discordance between a histologic diagnosis of AMD and the presence and absence of relevant mutations in the CFH gene. When expression profiles are segregated and analyzed based on histologic identification, some differences appear but appear to be smaller than would have been predicated. On-going work is now segregating the microarray data based on the presence or absence of the CFH mutation. A further expansion of these studies is the identification and analysis of peripheral potential vascular progenitor cells in patients with AMD. The hypothesis that serves as the generator for this work is that circulating endothelial progenitor cells may be recruited to the site of choroidal neovascularization. To date, two main types of cells have been identified from the peripheral circulation with both control and AMD patients which appear to express endothelial markers once placed in culture. One cell type, termed late outgrowth endothelial cells (OEC's) appear after 2 - 3 weeks in culture, require more specific culture conditions, have a high proliferative capacity and have a variable appearance and growth profile based on the age and disease state of the patient. The other cell type, termed endothelial progenitor cell (EPC'S), appears earlier in the culture and originates from floating or nonadherent cell population. However, as opposed to OEC's, these cells do not demonstrate a high proliferate capacity but are variable in terms of cytokine and growth factor expression. On-going work is focusing on determining the importance of these two cell types in the development of CNV in patients, the role of the both of these individually or in combination and importance of variable gene expression, as determined both by microarray and functional assay, in the AMD pathogenesis.
| Hathout, Yetrib; Flippin, Jessica; Fan, Chenguang et al. (2005) Metabolic labeling of human primary retinal pigment epithelial cells for accurate comparative proteomics. J Proteome Res 4:620-7 |
| Strunnikova, Nataly; Hilmer, Sara; Flippin, Jessica et al. (2005) Differences in gene expression profiles in dermal fibroblasts from control and patients with age-related macular degeneration elicited by oxidative injury. Free Radic Biol Med 39:781-96 |
| Cousins, Scott W; Espinosa-Heidmann, Diego G; Csaky, Karl G (2004) Monocyte activation in patients with age-related macular degeneration: a biomarker of risk for choroidal neovascularization? Arch Ophthalmol 122:1013-8 |
| Strunnikova, Nataly; Zhang, Connie; Teichberg, Diane et al. (2004) Survival of retinal pigment epithelium after exposure to prolonged oxidative injury: a detailed gene expression and cellular analysis. Invest Ophthalmol Vis Sci 45:3767-77 |
