IDENTIFICATION OF GENES REGULATED BY ACCELERATED DEBRIS ACCUMULATION IN THE RETINAL PIGMENT EPITHELIAL CELLS OF THE MCD1 TRANSGENIC MOUSE

Abstract

Abstract: : Purpose: To generate a profile of genes modified by debris accumulation in RPE and sub–RPE space in a transgenic mouse model of non–neovascular Age Related Macular Degeneration (AMD). Methods: The MCD1 transgenic mouse is characterised by inactive lysosomal enzyme Cathepsin D, which leads to defective digestion of phagocytosed photoreceptor outer segments (POS). Impaired POS digestion results in an amplified accumulation of metabolic deposits within the RPE cells and in the Bruch’s membrane. We examined the effect of impaired debris accumulation in RPE cells on transcriptome of retinas and subretinal structures from 13 eyes of 70–76 weeks old MCD1 and 15 age matched C57B1/6J control mice. Gene expression was determined with the Affymetrix MOE430A oligonucleotide array covering 34,000 mouse genes. The data were analysed using the RMA (Robust Multi–Chip Analysis) algorithm. Results: Twenty four genes and ESTs were differentially expressed in MCD1 samples versus controls. Genes that were upregulated in MCD1 tissue samples included: crystallins, lecithin retinol acyltransferas and heat shock protein 70. The downregulated genes included: WNT pathway modulator secreted frizzled related protein 2, immunoglobulin kappa chain 8 and extracellular proteinase inhibitor. Several cytoskeletal protein transcripts were slightly downregulated. The expression profiles of selected genes were confirmed by quantitative real time PCR. Conclusions:Loading of RPE cells with excessive amounts of metabolic debris induces production of molecules with UV–protection, anti–apoptotic and chaperoning activities. Lrat upregulation suggests presence of high amounts of vitamin A and/or its derivatives in or around the RPE layer, due to increased death of photoreceptors. We speculate that anti–inflammatory and antiproliferative properties of vitamin A may be partly responsible for lack of neovascularization and lack of RPE movement across the patches of geographic atrophy.

Keywords: age–related macular degeneration • gene/expression • gene microarray