Abstract
Purpose: :
To discover therapeutic targets for age-related macular degeneration (AMD) using a multi-pronged gene profiling strategy incorporating gene expression related to AMD, retinal pigment epithelium (RPE) phagocytosis, and smoking.
Methods: :
Gene expression profiling, including both a custom profiling of genes expressed in RPE called CHANGE and an exon-based whole-genome strategy, was performed with RNA from AMD patients’ retina and eyecup (EC, containing RPE/choroid), RPE undergoing rod outer segment (ROS) phagocytosis, and retina and EC of mice exposed to tobacco smoke, with controls. Genes showing similar differential expression in all 3 criteria were identified and further analyzed by individual expression studies, employing northern hybridization and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) amplification.
Results: :
Among the AMD-phagocytosis (AMDP) genes fulfilling the 3 criteria was ADAM15 (metargidin), a gene with dual functions of a metalloproteinase and a disintegrin. ADAM15 showed an increase in expression at 5 and 32 hr in ROS-fed RPE, indicating a relationship to RPE phagocytosis. In AMD samples, the expression of this gene was increased in retina and EC, in approximate correlation with the severity of the disease (grade 1-4). In a 14-day laser photocoagulation protocol to induce chorioneovascularization (CNV) in mice, ADAM15 showed a delayed increase (at 6-14 days) in the EC, and a down-and-up pattern of expression in the retina. In mice chronically exposed to tobacco smoke, a firmly established environmental factor for AMD, an increase in this gene was observed after 3-5 weeks of exposure in the retina and EC. In the normal rodent retina and EC, ADAM15 showed a diurnal pattern of expression with peaks at 6 PM and 12 AM, respectively. Significantly, exposure to tobacco smoke phase-shifted both of these peaks by 9 hours.
Conclusions: :
Increases in expression of ADAM15 were observed in human AMD eyes, and in mouse models of laser-induced CNV, and of cigarette smoking, with smoke exposure also causing a phase-shift in the expression peaks of ADAM15. Given its known functions, and its involvement in circadian RPE phagocytosis, we hypothesize that this gene plays a causative role in AMD, making it a strong therapeutic candidate for this condition.
Keywords: age-related macular degeneration • gene microarray • candidate gene analysis