Identification of the genetic defect in the original Wagner syndrome family

PURPOSE: The aim of the present study was to determine the genetic defect in Wagner syndrome, a rare disorder belonging to the group of hereditary vitreoretinal degenerations. This disease has been genetically mapped to chromosome 5q14.3. METHODS: Molecular analysis was performed in the progeny of the original pedigree described by Wagner in 1938. We searched for pathogenic mutations and their effects in two candidate genes, CSPG2 and EDIL3, which locate to the critical chromosomal interval. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis was used to investigate potential splice defects of CSPG2 transcripts. RESULTS: While no alterations were detected in the exons of EDIL3, several changes were identified in the CSPG2 gene. Only one of the novel changes, a heterozygous G to A substitution of the first nucleotide in intron 8, cosegregates with the disease phenotype. This change disrupts the highly conserved splice donor sequence. In blood cells of an index patient, we found CSPG2 transcripts with normally spliced exon 8/9 junction but also two additional CSPG2 transcripts, which were not detected in the control. One lacks the entire exon 8, while the other is missing only the last 21 bp of exon 8. CONCLUSIONS: CSPG2 encodes versican, a large proteoglycan, which is an extracellular matrix component of the human vitreous and participates in the formation of the vitreous gel. The splice site mutation described here may lead to a complete lack of exon 8 in CSPG2 transcripts, which shortens the predicted protein by 1754 amino acids and leads to severe reduction of glycosaminoglycan attachment sites

A potential mouse model for the erosive vitreoretinopathy of Wagner disease

Patients with the very rare eye pathology Wagner disease (OMIM #143200) present with an abnormal (empty) vitreous, retinal detachment and altered electroretinogram (ERG). The disease is progressive and can eventually lead to blindness. No therapy can be offered to date. The genetic basis is the presence of mutations in the VCAN gene, encoding the large extracellular matrix molecule versican, which is a component of the vitreous. All identified mutations map to the canonical splice sites flanking exon 8, resulting in low number of aberrant splice products and a severe increase in two (V2, V3) of the four naturally occurring splice variants. The pathomechanism of Wagner's disease is poorly understood and a mouse model may afford further insight. The hdf -/- mice, named for their initial phenotype of heart defects, carry a null allele for Vcan that leads to embryonic lethality when homozygous, but heterozygote animals are viable. Here we investigated a possible eye phenotype in the heterozygous animals. While the overall morphology of retina and ciliary body appears to be normal, older (17 months) mutant animals show a decrease in ERG signaling profiles affecting the a-, b- and c-waves. This aspect of altered ERG profile demonstrates similarities to the human disease manifestation and underlines the suitability of heterozygous hdf+/- mice as a model for Wagner disease

Dysfunctional LAT2 amino acid transporter is associated with cataract in mouse and humans

Cataract, the loss of ocular lens transparency, accounts for ∼50% of worldwide blindness and has been associated with water and solute transport dysfunction across lens cellular barriers. We show that neutral amino acid antiporter LAT2 (Slc7a8) and uniporter TAT1 (Slc16a10) are expressed on mouse ciliary epithelium and LAT2 also in lens epithelium. Correspondingly, deletion of LAT2 induced a dramatic decrease in lens essential amino acid levels that was modulated by TAT1 defect. Interestingly, the absence of LAT2 led to increased incidence of cataract in mice, in particular in older females, and a synergistic effect was observed with simultaneous lack of TAT1. Screening SLC7A8 in patients diagnosed with congenital or age-related cataract yielded one homozygous single nucleotide deletion segregating in a family with congenital cataract. Expressed in HeLa cells, this LAT2 mutation did not support amino acid uptake. Heterozygous LAT2 variants were also found in patients with cataract some of which showed a reduced transport function when expressed in HeLa cells. Whether heterozygous LAT2 variants may contribute to the pathology of cataract needs to be further investigated. Overall, our results suggest that defects of amino acid transporter LAT2 are implicated in cataract formation, a situation that may be aggravated by TAT1 defects

EPHA2 Is Associated with Age-Related Cortical Cataract in Mice and Humans

Age-related cataract is a major cause of blindness worldwide, and cortical cataract is the second most prevalent type of age-related cataract. Although a significant fraction of age-related cataract is heritable, the genetic basis remains to be elucidated. We report that homozygous deletion of Epha2 in two independent strains of mice developed progressive cortical cataract. Retroillumination revealed development of cortical vacuoles at one month of age; visible cataract appeared around three months, which progressed to mature cataract by six months. EPHA2 protein expression in the lens is spatially and temporally regulated. It is low in anterior epithelial cells, upregulated as the cells enter differentiation at the equator, strongly expressed in the cortical fiber cells, but absent in the nuclei. Deletion of Epha2 caused a significant increase in the expression of HSP25 (murine homologue of human HSP27) before the onset of cataract. The overexpressed HSP25 was in an underphosphorylated form, indicating excessive cellular stress and protein misfolding. The orthologous human EPHA2 gene on chromosome 1p36 was tested in three independent worldwide Caucasian populations for allelic association with cortical cataract. Common variants in EPHA2 were found that showed significant association with cortical cataract, and rs6678616 was the most significant in meta-analyses. In addition, we sequenced exons of EPHA2 in linked families and identified a new missense mutation, Arg721Gln, in the protein kinase domain that significantly alters EPHA2 functions in cellular and biochemical assays. Thus, converging evidence from humans and mice suggests that EPHA2 is important in maintaining lens clarity with age

ICF, An Immunodeficiency Syndrome: DNA Methyltransferase 3B Involvement, Chromosome Anomalies, and Gene Dysregulation

The immunodeficiency, centromeric region instability, and facial anomalies syndrome (ICF) is the only disease known to result from a mutated DNA methyltransferase gene, namely, DNMT3B. Characteristic of this recessive disease are decreases in serum immunoglobulins despite the presence of B cells and, in the juxtacentromeric heterochromatin of chromosomes 1 and 16, chromatin decondensation, distinctive rearrangements, and satellite DNA hypomethylation. Although DNMT3B is involved in specific associations with histone deacetylases, HP1, other DNMTs, chromatin remodelling proteins, condensin, and other nuclear proteins, it is probably the partial loss of catalytic activity that is responsible for the disease. In microarray experiments and real-time RT-PCR assays, we observed significant differences in RNA levels from ICF vs. control lymphoblasts for pro- and anti-apoptotic genes (BCL2L10, CASP1, and PTPN13); nitrous oxide, carbon monoxide, NF-κB, and TNFa signalling pathway genes (PRKCH, GUCY1A3, GUCY1B3, MAPK13; HMOX1, and MAP4K4); and transcription control genes (NR2F2 and SMARCA2). This gene dysregulation could contribute to the immunodeficiency and other symptoms of ICF and might result from the limited losses of DNA methylation although ICF-related promoter hypomethylation was not observed for six of the above examined genes. We propose that hypomethylation of satellite 2at1qh and 16qh might provoke this dysregulation gene expression by trans effects from altered sequestration of transcription factors, changes in nuclear architecture, or expression of noncoding RNAs

Regulatory regions of the paraoxonase 1 (PON1) gene are associated with neovascular age-related macular degeneration (AMD)

Physiological stress response and oxidative damage are factors for aging processes and, as such, are thought to contribute to neovascular age-related macular degeneration (AMD). Paraoxonase 1 (PON1) is an enzyme that plays an important role in oxidative stress and aging. We investigated association of DNA sequence variants (SNP) within the upstream regulatory region of the PON1 gene with neovascular AMD in 305 patients and 288 controls. Four of the seven tested SNPs (rs705379, rs705381, rs854573, and rs757158) were more frequently found in AMD patients compared to controls (P = 0.0099, 0.0295, 0.0121, and 0.0256, respectively), and all but one (SNP rs757158) are in linkage disequilibrium. Furthermore, haplotype TGGCCTC conferred protection (odds ratio (OR) = 0.76, (CI) = 0.60-0.97) as it was more frequently found in control individuals, while haplotype CGATGCT increased the risk (OR = 1.55, CI = 1.09-2.21) for AMD. These results were also reflected when haplotypes for the untranscribed and the 5'untranslated regions (5'UTR) were analyzed separately. To assess haplotype correlation with levels of gene expression, the three SNPs within the 5'UTR were tested in a luciferase reporter assay. In retinal pigment epithelium-derived ARPE19 cells, we were able to measure significant differences in reporter levels, while this was not observed in kidney-derived HEK293 cells. The presence of the risk allele A (SNP rs705381) caused an increase in luciferase activity of approximately twofold. Our data support the view that inflammatory reactions mediated through anti-oxidative activity may be relevant to neovascular age-related macular degeneration

Lack of paraoxonase 1 alters phospholipid composition, but not morphology and function of the mouse retina

PURPOSE: Biochemical and genetic analyses established a contribution of lipid metabolism to AMD pathology. Paraoxonase 1 (PON1) is an antioxidative protein involved in high density lipoprotein (HDL) function and was found to be associated with AMD. Here, we used Pon1(-/-) mice to study the influence of PON1 on retinal physiology and to reveal the potential impact of PON1 on AMD etiology. METHODS: Laser capture microdissection served to isolate single retinal layers. Retinal function was assessed by ERG. Retinal and RPE morphology were monitored by fundus imaging, fluorescein angiography, light and transmission electron microscopy, and immunofluorescence microscopy. Levels of mRNA and composition of phospholipid species were determined by real-time PCR and LC-MS, respectively. RESULTS: Adult (8 weeks old) Pon1(-/-) mice displayed normal retinal function and morphology, but their retinas contained reduced amounts of lysophosphatidylcholines (LPCs) compared to controls. Aged (12 months old) Pon1(-/-) animals did not show any morphologic or molecular signs of photoreceptor or RPE degeneration, or of accelerated aging. Photoreceptors of Pon1(-/-) and control mice were similarly susceptible to light damage. CONCLUSIONS: Results indicated that PON1 is not essential for normal development, function, ageing, and the defense against light damage of the mouse retina. Reduced levels of LPCs in eyes of Pon1(-/-) mice may reflect a decreased activity of phospholipase A2 or altered antioxidative activity in aged eyes

Degenerative aortic valve stenosis, but not coronary disease, is associated with shorter telomere length in the elderly

OBJECTIVE: The mechanisms responsible for the age-related increase in the incidence of calcific aortic valve stenosis (CAS) are unclear but may include telomere-driven cellular senescence. Because telomere length varies widely among individuals of the same age, we hypothesized that patients with shorter telomeres would be prone to develop CAS late in life. METHODS AND RESULTS: Mean telomere length was measured in leukocytes from a cohort of 193 patients > or =70 years of age with and without CAS. Pilot experiments performed in 30 patients with CAS and controls pair-matched for age, sex, and presence or absence of coronary disease demonstrated significantly shorter telomeres in the CAS group both by Southern blot hybridization (5.75+/-0.55 kbp versus 6.27+/-0.7 kbp, P=0.0023) and by a quantitative polymerase chain reaction-based technique (relative telomere length 0.88+/-0.19 versus 1.0+/-0.19, P=0.01). This finding was then confirmed in the whole cohort (CAS n=64, controls n=129, relative telomere length=0.86+/-0.16 versus 0.94+/-0.12, P=0.0003). Both groups were comparable for potential confounding characteristics. Subgroup analysis according to the presence or absence of coronary disease demonstrated no association of this disorder with telomere length. CONCLUSIONS: In the elderly, calcific aortic stenosis, but not coronary disease, is associated with shorter leukocyte telomere length

Novel VCAN mutations and evidence for unbalanced alternative splicing in the pathogenesis of Wagner syndrome

Wagner syndrome (WS) is an autosomal dominant vitreoretinopathy affecting various ocular features and is caused by mutations in the canonical splice sites of the VCAN gene, which encodes the large chondroitin sulfate proteoglycan, versican. We report the identification of novel splice acceptor and donor-site mutations (c.4004-1G>C and c.9265+2T>A) in two large WS families from France and the United Kingdom. To characterize their pathogenic mechanisms we performed qRT-PCR experiments on RNA from patient-derived tissues (venous blood and skin fibroblasts). We also analyzed RNA from the original Swiss family reported by Wagner (who has the previously reported c.9265+1G>A mutation). All three mutations resulted in a quantitative increase of transcript variants lacking exons 7 and/or 8. However, the magnitude of the increase varied between tissues and mutations. We discuss altered balance of VCAN splice variants in combination with reduction in glycosaminoglycan protein modifications as possible pathogenic mechanisms