Background: Topographic differences in RPE and choroid between macular and peripheral areas of the eye may predispose to morphologic and cell survival changes with aging. An understanding of the molecular events that distinguish RPE and choroid by their spatial location could give hints for the identification of survival factors and the development of new therapeutic approaches. To determine the mRNA expression of functionally important genes in RPE and choroid of morphologically normal human eyes, tissue patches were dissected from the macula and peripheral locations.
Methods: The mRNA levels of 29 genes with known functions or expression in the RPE/choroid were quantified in these sections by real time RT-PCR. Variations in the mRNA expression were determined due to differences in the mean normalized expression (MNE) between different peripheral locations, left and right eye of the same donor, and eyes of different donors.
Results: In the macula, the lysosomal enzyme cathepsin D (1.27E+00+/-1.54E-01) and the MERTK ligand Gas6 (1.08E+00+/-1.60E-01) had the highest MNE, whereas the apoptosis inducer Fas-Ligand (1.41E-04+/-6.46E-05) and the ROS internalization receptor CD36 (2.15E-04+/-1.11E-05) demonstrated the lowest expression. Interestingly, the PEDF expression (1.80E-01+/-4.56E-02) was 10 times higher than the VEGF expression (1.84E-02+/-2.46E-03) in the macular area. For most of the analyzed genes (52%, e.g. MERTK, integrin alphaV and beta5, RPE65, tyrosinase, VEGF) there was equal gene expression in the macula and in the periphery. For 31% of the genes (e.g. CD36, MAP1B) there was higher expression in the macula and for 17% of the genes (e.g. 11-cis RDH, VEGF-R2, PEDF) there was higher expression in the periphery.
Conclusions: Whereas most of the analyzed genes expressed in RPE and choroid had equal mRNA expression levels in the macula and the periphery with donor dependent variations, there are important exceptions in genes that are involved in the maintenance of a specific vascular status in the macula (PEDF, VEGF and VEGR-R2) and in the recycling of rod outer segments (11-cis RDH). Applying this technique to the gene expression analysis of patients with AMD could identify those genes that are involved in molding of the disease.