Transcriptional Profile Analysis of RPGRORF15 frameshift mutation

Purpose: To identify genes and molecular mechanisms associated with disease progression during (7 weeks of age) and after (16 weeks) the peak of photoreceptor death in dogs affected with XLPRA2, a canine model of early-onset XLRP caused by a microdeletion in RPGR exon ORF15. Methods: Expression profiles of diseased and normal dog retinas at both ages were compared using a canine retinal custom cDNA microarray. Data normalization and filtering were performed with GeneSpring, statistical analysis with Significance Analysis of Microarrays. Real-time PCR using Taqman probes, western blot and immunohistochemistry (IHC) were applied on selected genes to confirm and expand the microarray results. Results: At 7 and 16 weeks, respectively, 56 and 18 transcripts were down-regulated in mutant retinas compared to normals. None of the transcripts was differentially expressed (DE) at both ages, suggesting the involvement of temporally distinct molecular pathways. Down-regulated genes included PAX6, CHML, and RDH11 at 7 weeks and CRX and SAG at 16 weeks, which are necessary for visual system development and function. Genes directly or indirectly active in apoptotic processes were altered at 7 weeks (CAMK2G, NTRK2, PRKCB, RALA, RBBP6, RNF41, SEPT5, SMYD3, SPP1, and TUBB2C) and 16 weeks (SLC25A5 and NKAP). Furthermore, DE genes at 7 weeks (ELOVL6, GLOD4, NDUFS4, and REEP1) and 16 weeks (SLC25A5 and TARS2) are related to mitochondrial functions. Real-time PCR of 11 genes confirmed the microarray results and showed differential expression for additional genes not on the array, such as GFAP, RHO, OPN1SW, CNGB3 and the mutated RPGR. Western blotting and IHC analysis also confirmed the high reliability of the presented transcriptomic data. Conclusions: A list of mutated genes in RPGRORF15 diseased retinas, which are likely candidates to further study their role in age-related photoreceptor degeneration diseases, is reported at different crucial ages. The results indicate that at 7 weeks a combination of non-classical anti- and pro-apoptotic genes appears to be involved in photoreceptor degeneration, whereas at both 7 and 16 weeks expression of mitochondria related genes indicates they may play a relevant role in the disease process. 3 biological replicates each for normal and XLPRA2 affected retinas were analyzed at 7 and 16 weeks of age. Each individual sample was hybridized in a reference design using a custom-made retinal cDNA microarray against brain pool to enable cross comparison between groups. Retina was labeled with Cy5 in all samples but 5615 (GSM474350).