John W. Crabb, Ph.D.
Professor and Staff
Proteomic biomarker discovery for ocular diseases is a major focus of our laboratory. Our recent progress in assessing susceptibility to age-related macular degeneration (AMD) is outlined below. Other projects in the laboratory using proteomic technology are highlighted in the attached posters and include mechanistic studies of AMD, primary open angle glaucoma, diabetic retinopathy, uveal melanoma and the visual cycle.
Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. Complex genetic and environmental factors contribute to the disease and presently there are no cures. There is growing evidence that AMD is an inflammatory disease involving dysregulation of the complement system. AMD has also been postulated to be a systemic disease, based in part on the presence of retinal drusen in patients with membranoproliferative glomerulonephritis type II and on systemic complement activation in AMD. The molecular cause of the disease remains unknown, however oxidative stress appears to be a catalyst as smoking significantly increases the risk of AMD, antioxidant vitamins can selectively slow AMD progression, and a host of oxidative protein and DNA modifications have been detected at elevated levels in AMD Bruch’s membrane, drusen, retina, RPE and plasma. While AMD susceptibility genes now account for over 50% of AMD cases, many individuals with AMD risk-genotypes may never develop advanced disease. Nevertheless, the prevalence of advanced AMD is increasing and early identification of AMD risk could help slow or prevent disease progression. Some years ago we found elevated levels of carboxyethylpyrrole (CEP), an oxidative protein modification generated from docosahexaenoate (DHA)-containing lipids, in Bruch’s membrane and drusen from AMD patients [2002 Proc Natl Acad Sci USA 99:14682]. Subsequently, we found CEP adducts stimulated neovascularization in vivo, suggesting a role in the induction of choroidal neovascularization or wet AMD [2006 Proc Natl Acad Sci USA 103: 13480]. In a proteomic study of RPE lipofuscin, a fluorescent waste material that accumulates with AMD, we showed lipofuscin granules contain oxidative modifications like CEP but very little protein [2008 Mol & Cell Proteomics 7:1397]. In 2009 we found that the AMD risk predicted for those exhibiting both elevated plasma CEP biomarkers and risk genotypes is 2-3 fold greater than the risk based on genotype alone [2009 Mol & Cell Proteomics 8: 1338]. Our preliminary AMD biomarker study of two plasma protein advanced glycation endproducts (AGEs), namely carboxymethyllysine (CML) and pentosidine, has shown plasma CML and CEP adducts discriminate between AMD and control subjects with equal accuracy (~78%), pentosidine with ~88% accuracy, and CEP plus pentosidine with ~92% accuracy [2009 Mol & Cell Proteomics 8: 1921]. AGEs are a heterogeneous group of mostly oxidative modifications resulting from the Maillard reaction; their association with AMD supports the hypothesis that AMD is a systemic disease. A much larger investigation of plasma protein CML, pentosidine and CEP as AMD biomarkers is currently underway. Most recently, we have identified 99 proteins by quantitative analyses of AMD macular Bruch’s membrane/choroid that are elevated or decreased relative to normal tissues, establishing a foundation for developing proteomic and genomic prognostic signatures of AMD [2010 Mol & Cell Proteomics 9: 1031]. Interestingly, AGEs receptor 3 was the most significantly elevated protein in advanced dry AMD tissues. Our long-term goal is the development of routine prognostic technology for use in clinical medicine to assess AMD risk for severe visual loss and to monitor the efficacy of AMD therapeutics.