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Tatyana Appelbaum, William A Beltran, Evelyn Santana, Gustavo D Aguirre; Early disease phenotype in canine RPGRORF15 model is characterized by strong up-regulation of pro-inflammatory genes and down-regulation of neuroretinal maintenance genes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4648.
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© ARVO (1962-2015); The Authors (2016-present)
Canine X-linked progressive retinal atrophy 1 (XLPRA1) is caused by a 5 nucleotide deletion that introduces a premature stop codon in RPGR exon ORF15, which is also a mutation hotspot in human X-linked retinitis pigmentosa 3 (RP3). The disease shows extensive phenotypic variability in a colony of dogs that all inherited the same RPGR mutation from a single ancestor. In this study, genes associated with photoreceptor protein trafficking and maintenance, were investigated as candidate disease modifiers. Additionally, we examined genes involved in retinal inflammation, apoptosis and innate immune response to determine possible involvement in early stages of the disease.
Samples from a pedigree derived from XLPRA1 affected male dog outcrossed to unrelated normal mix bred or purebred females were used. Single nucleotide polymorphisms (SNPs) spanning the entire RPGR interacting and protein trafficking genes (RAB8B, RAB8A, RPGRIP1L, WHRN, CEP290, CC2D2A, RAB3IP, MAP9, OPTN, SSX2IP, RAB11B and RP2) were genotyped on the pedigree. RNA from 16 week old normal and XLPRA1 retinas was isolated using a standard TRIzol-based protocol. Retinal gene expression was determined by quantitative RT-PCR for a total of 45 genes, including above 12 genes.
Among 45 genes analyzed, 6 genes (GFAP, TNF, IL6, IL1B, FGF2 and TLR4) were highly up-regulated while 4 genes (CNTFR, PDGFRA, PDGFRB and INSR) were down-regulated in 16 week old XLPRA1 retinas. Three SNPs in intron 1 of RAB8A were the only mutations associated with severe XLPRA1 phenotype (P<0.05). No mutations in other 11 candidate modifier genes were associated with the disease.
We have shown that early stage of canine XLPRA1 is characterized by strong increase in expression of pro-inflammatory cytokines and innate immune response genes as well as by down regulation of some genes responsible for maintenance of retinal cells. This may be the underlying cause of retinal inflammation and photoreceptor apoptosis in advanced form of the disease. In addition, intronic RAB8A mutations can be taken into consideration as putative genetic modifier of the disease phenotype observed in the XLPRA1 pedigree, while RAB8B, RPGRIP1L, WHRN, CEP290, CC2D2A, RAB3IP, MAP9, OPTN, SSX2IP, RAB11B and RP2 genes can be eliminated as candidates.
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