Familial exudative vitreoretinopathy (FEVR) is a human disease characterized by defective retinal angiogenesis and associated complications that can result in vision loss. Defective Wnt/β-catenin signaling is an established cause of FEVR, whereas other molecular alterations contributing to the disease remain insufficiently understood. Here, we show that integrin-linked kinase (ILK), a mediator of cell-matrix interactions, is indispensable for retinal angiogenesis. Inactivation of the murine Ilk gene in postnatal endothelial cells results in sprouting defects, reduced endothelial proliferation and disruption of the blood-retina barrier, resembling phenotypes seen in established mouse models of FEVR. Retinal vascularization defects are phenocopied by inducible inactivation of the gene for α-parvin (Parva), an interactor of ILK. Screening genomic DNA samples from exudative vitreoretinopathy patients identifies three distinct mutations in human ILK, which compromise the function of the gene product in vitro. Together, our data suggest that defective cell-matrix interactions are linked to Wnt signaling and FEVR.

Retinitis pigmentosa (RP) is a disease that primarily affects the peripheral retina and ultimately causes visual impairment. X-chromosomal forms of RP are frequently caused by mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. We show that the novel splice donor site (SDS) mutation c.1245+3A>T in intron 10 of RPGR cosegregates with RP in a five-generation Caucasian family. The mutation causes in-frame skipping of exon 10 from RPGR transcripts in patient-derived primary fibroblasts. To correct the splice defect, we developed a gene therapeutic approach using mutation-adapted U1 small nuclear RNA (U1). U1 is required for SDS recognition of pre-mRNAs and initiates the splice process. The mutation described herein interferes with the recognition of the SDS by U1. To overcome the deleterious effects of the mutation, we generated four U1 isoforms with increasing complementarity to the SDS. Lentiviral particles were used to transduce patient-derived fibroblasts with these U1 variants. Full complementarity of U1 corrects the splice defect partially and increases recognition of the mutant SDS. The therapeutic effect is U1-concentration dependent as we show for endogenously expressed RPGR transcripts in patient-derived cells. U1-based gene therapeutic approaches constitute promising technologies to treat SDS mutations in inherited diseases including X-linked RP.

Inherited monogenic diseases of the retina and vitreous affect approximately 1 in 2000 individuals. They are characterized by tremendous genetic heterogeneity and clinical variability involving mutations in approximately 250 genes and more than 20 different clinical phenotypes. Clinical manifestations of retinal dystrophies (RDs) range from mild retinal dysfunctions to severe congenital forms of blindness. A detailed clinical diagnosis and the identification of causative mutations are crucial for genetic counseling of affected patients and their families, for understanding genotype-phenotype correlations and developing therapeutic approaches. Using whole exome sequencing (WES) we have established a reliable and efficient high-throughput analysis pipeline to identify disease-causing mutations. Our data indicate that this approach enables us to genetically diagnose approximately 64% of the patients (n = 58) with variant(s) in known disease-associated genes. We report 20 novel and 26 recurrent variants in genes associated with RDs. We also identified a novel phenotype for mutations in C2orf71 and provide functional evidence for exon skipping due to a splice-site variant identified in FLVCR1. In conclusion, WES can rapidly identify variants in various families affected with different forms of RDs. Our study also expands the clinical and allelic spectrum of genes associated with RDs in the Swiss population.

Mutations in Norrin, the ligand of a receptor complex consisting of FZD4, LRP5 and TSPAN12, cause severe developmental blood vessel defects in the retina and progressive loss of the vascular system in the inner ear, which lead to congenital blindness and progressive hearing loss, respectively. We now examined molecular pathways involved in developmental retinal angiogenesis in a mouse model for Norrie disease. Comparison of morphometric parameters of the superficial retinal vascular plexus (SRVP), including the number of filopodia, vascular density and number of branch points together with inhibition of Notch signaling by using DAPT, suggest no direct link between Norrin and Notch signaling during formation of the SRVP. We noticed extensive vessel crossing within the SRVP, which might be a loss of Wnt- and MAP kinase-characteristic feature. In addition, endomucin was identified as a marker for central filopodia, which were aligned in a thorn-like fashion at P9 in Norrin knockout (Ndp^y/−) mice. We also observed elevated mural cell coverage in the SRVP of Ndp^y/− mice and explain it by an altered expression of PDGFβ and its receptor (PDGFRβ). In vivo cell proliferation assays revealed a reduced proliferation rate of isolectin B4-positive cells in the SRVP from Ndp^y/− mice at postnatal day 6 and a decreased mitogenic activity of mutant compared with the wild-type Norrin. Our results suggest that the delayed outgrowth of the SRVP and decreased angiogenic sprouting in Ndp^y/− mice are direct effects of the reduced proliferation of endothelial cells from the SRVP.

Purpose. Mutations in the NDP gene impair angiogenesis in the eyes of patients diagnosed with a type of blindness belonging to the group of exudative vitreoretinopathies. This study was conducted to investigate the differential gene expression caused by the absence of Norrin (the NDP protein) in the developing mouse retina and to elucidate early pathogenic events. methods. A comparative gene expression analysis was performed on postnatal day (p)7 retinas from a knockout mouse model for Norrie disease using gene microarrays. Subsequently, results were verified by quantitative real-time PCR analyses. Immunohistochemistry was performed for the vascular permeability marker plasmalemma vesicle associated protein (Plvap). results. Our study identified expression differences in Ndph ^y/– versus wild-type mice retinas at p7. Gene transcription of the neutral amino acid transporter Slc38a5, apolipoprotein D (ApoD), and angiotensin II receptor-like 1 (Agtrl1) was decreased in the knockout mouse, whereas transcript levels of adrenomedullin (Adm) and of the plasmalemma vesicle associated protein (Plvap) were increased in comparison to the wild-type. In addition, ectopic expression of Plvap was found in the developing retinal vasculature of Norrin-knockout mice on the protein level. conclusions. These data provide molecular evidence for a role of Norrin in the development of the retinal vasculature. Expression of two genes, Plvap and Slc38a5, is considerably altered in retinal development of Norrin-knockout mice and may reflect or contribute to the pathogenesis of the disease. In particular, ectopic expression of Plvap is consistent with hallmark disease symptoms in mice and humans.