Abstract
Purpose: :
AMD (age–related macular degeneration) is the most severe cause of vision loss in the developed world and the number of people affected is expected to increase as the population ages. As one approach to understanding the disease, human cDNA microarrays were used to compare the differences in mRNA expression between human normal and AMD eyes in the retina, retinal pigment epithelium (RPE) and choroid tissues. Functional profiling of these expression patterns may provide useful insights into the physiological changes associated with AMD.
Methods: :
Under a dissecting microscope, the retina and the RPE/choroid were isolated from 10 pairs of normal and 10 pairs of AMD eyes (ages from 71 to 102). Tissues from the left and the right eyes were used sparately. Total RNA was isolated and a control RNA pool combined from 4 normal samples was established. Retina or RPE/choroid RNA of AMD or normal eyes was hybridized with the appropriate control pool on human cDNA microarrays to measure the expression levels of approximately 16,000 genes. Stringent biological and statistical criteria were used to rank genes in terms of the magnitude and significance of differences. Selected microarray expression differences were confirmed by real–time quantitative RT–PCR.
Results: :
By comparing all AMD microarray data with all normal microarray data, there were 200 genes up–regulated (above 1.5 fold) and 18 genes down–regulated (below 0.5 fold) in the AMD retina; while in the AMD RPE/choroid there were 508 genes up–regulated and 62 down–regulated. Only 11 genes were similarly changed in both the retina and the RPE/choroid. Very different pathways were activated in the retina versus the RPE/choroid. Genes involved in Alzheimer’s disease and Parkinson’s disease were, different, interestingly, only in the retina. A very large proportion of complement activation, coagulation cascade and immune function genes were increased in the retina but not in the RPE/choroid. Genes involved in signal transduction particularly calcium dependent, transporter activities, glutamate function, cell adhesion and other distinct metabolic pathways, were only changed in the RPE/choroid. C–Jun was down–regulated in the RPE/choroid while Fos B and several apoptosis inhibitors were down–regulated in the retina.
Conclusions: :
Very distinct sets of genes are changed by AMD in the retina compared to the RPE/choroid. Thus, these tissues are affected very differently in the pathophysiology of macular degeneration. These global patterns of gene expression in the affected tissues may also be useful in identifying the genetic basis and direct effects of age–related macular degeneration.
Keywords: retinal pigment epithelium • retina • choroid