Structural recovery of the retina in a retinoschisin-deficient mouse after gene replacement therapy by solid lipid nanoparticles

X-linked juvenile retinoschisis (XLRS) is a retinal degenerative disorder caused by mutations in the RS1 gene encoding a protein termed retinoschisin. The disease is an excellent candidate for gene replacement therapy as the majority of mutations have been shown to lead to a complete deficiency of the secreted protein in the retinal structures. In this work, we have studied the ability of non-viral vectors based on solid lipid nanoparticles (SLN) to induce the expression of retinoschisin in photoreceptors (PR) after intravitreal administration to Rs1h-deficient mice. We designed two vectors prepared with SLN, protamine, and dextran (DX) or hyaluronic acid (HA), bearing a plasmid containing the human RS1 gene under the control of the murin opsin promoter (mOPS). In vitro, the nanocarriers were able to induce the expression of retinoschisin in a PR cell line. After injection into the murine vitreous, the formulation prepared with HA induced a higher transfection level in PR than the formulation prepared with DX. Moreover, the level of retinoschisin in the inner nuclear layer (INL), where bipolar cells are located, was also higher. Two weeks after vitreal administration into Rs1h-deficient mice, both formulations showed significant improvement of the retinal structure by inducing a decrease of cavities and PR loss, and an increase of retinal and outer nuclear layer (ONL) thickness. HA-SLN resulted in a significant higher increase in the thickness of both retina and ONL, which can be explained by the higher transfection level of PR. In conclusion, we have shown the structural improvement of the retina of Rs1h-deficient mice with PR specific expression of the RS1 gene driven by the specific promoter mOPS, after successful delivery via SLN-based non-viral vectors.

[Inherited retinal or optic nerve disorders – five steps to diagnosis]

An early diagnosis of inherited retinal or optic nerve disorders is often delayed due to unspecific clinical signs, multiple clinical manifestations and striking genetic heterogeneity of the underlying molecular defects. This study represents a retrospective analysis of findings in 4,021 patients with inherited retinal or optic nerve disorders seen between 1986 and 2014 (1,171 with follow-up). In addition to the basic ophthalmological examination, electrophysiological tests (ERG, n = 2,088, since 1986; EOG, n = 381, since 1986; VEP n = 595, since 1986; mfERG, n = 819, since 1998) and non-invasive retinal imaging (fundus autofluorescence (FAF, n = 1,784, since 2002), near-infrared autofluorescence (NIA, n = 1,091, since 2006), spectral domain OCT (SD-OCT, n = 848, since 2008) and three-wavelengths multicolour spectral reflection imaging (MC, n = 366, since 2013) were performed at least once. Molecular DNA testing was done in 383 patients between 2006 and 2014. Based on these data an efficient diagnostic strategy is suggested: 1) inclusion of inherited retinal and optic nerve disorders into the differential diagnosis of visual loss or visual field defects with undefined causes; 2) non-invasive retinal imaging; 3) electrophysiological tests; 4) DNA testing to confirm the initial clinical diagnosis; 5) examination in specialised centres, therapy and follow-up. In recent years, the spectrum of diagnostic techniques has continuously expanded. Importantly, non-invasive retinal imaging has become the primary diagnostic tool and DNA testing based on state-of-the-art high throughput techniques increases the identification of associated gene mutations. In conclusion, a structured process in the diagnostic procedure of inherited retinal and optic nerve disorders greatly reduces a diagnostic delay, enables an earlier counselling and therapy and avoids further unnecessary diagnostic tests.

Differential diagnosis of primary failure of eruption (PFE) with and without evidence of pathogenic mutations in the PTHR1 gene

BACKGROUND

Primary failure of eruption (PFE) may be associated with pathogenic mutations in the PTHR1 gene. It has numerous manifestations and is characterized by severe posterior open bite. However, there are also phenotypically similar types of eruption anomalies not associated with a known pathogenic PTHR1 mutation. The purpose of this study was to evaluate whether a distinction can be made between PTHR1-mutation carriers and noncarriers based on clinical and radiological findings.

PATIENTS AND METHODS

A total of 36 patients with suspected PFE diagnoses were included and analyzed in accordance with specific clinical and radiographic criteria. In addition, all patients underwent Sanger DNA sequencing analysis of all coding sequences (and the immediate flanking intronic sequences) of the PTHR1 gene.

RESULTS

Of these patients, 23 exhibited a heterozygous pathogenic mutation in the PTHR1 gene (PTHR1-mutation carriers), while molecular genetic analysis revealed nosequence alteration in the other 13 patients (non-PTHR1-mutation carriers). Relevant family histories were obtained from 5 patients in the carrier group; hence, this group included a total of 13 familial and 10 simplex cases. The group of noncarriers revealed no relevant family histories. All patients in the carrier group met six of the clinical and radiographic criteria explored in this study: (1) posterior teeth more often affected; (2) eruption disturbance of an anterior tooth in association with additional posterior-teeth involvement; (3) affected teeth resorbing the alveolar bone located coronal to them; (4) involvement of both deciduous and permanent teeth; (5) impaired vertical alveolar-process growth; and (6) severe subsequent finding of posterior open bite. None of the analyzed criteria were, by contrast, met by all patients in the noncarrier group. All patients in the carrier group could be assigned to one of three classifications indicating the extent of eruption disturbance, whereas 4 of the 13 noncarriers presented none of these three patterns. The clinical and radiographic criteria employed in this study would have correctly identified 10 of the 13 PFE patients in the noncarrier group as possessing no detectable PTHR1 mutation.

CONCLUSION

The evaluation of clinical and radiographic characteristics can heighten the specificity of ruling out suspected PTHR1 involvement in PFE patients. A hereditary element of PTHR1-associated PFE is clearly identifiable. More studies with more patients are needed to optimize the sensitivity of this preliminary approach on the differential identification of PTHR1-mutation carriers versus noncarriers by multivariate analysis.

Spontaneous immortalization of neural crest-derived corneal progenitor cells after chromosomal aberration

OBJECTIVES

In a previous study, we have reported the existence of neural crest-derived stem cell-like cells originating from the corneal limbus of juvenile mice (termed murine corneal cells, MCCs). To yield a sufficient number of MCCs, for example, for cell-therapy approaches, here we have investigated MCCs' ability for extensive proliferation, and we have evaluated their stem cell qualities and genetic stability after large-scale culture.

MATERIALS AND METHODS

MCCs were established from corneal limbal tissue of juvenile mice. To determine their cell proliferation and self-renewing potential, MTT tests and an estimation of colony forming unit efficiency were carried out. Multipotency of cell differentiation was examined by applying adipogenic and osteogenic differentiation protocols. Moreover, karyotyping was performed and expression of stem cell markers and cell cycle-associated genes was analysed.

RESULTS

MCCs, as primary cells, could be cultured for more than 60 passages. We observed increased cell proliferation and high number of colony forming units (CFUs) after extensive culture. Interestingly, there were no changes in expression of MCC markers. Furthermore, cell differentiation potentials remained comparable with MCCs at early passages. However, karyotyping revealed numeric chromosomal aberrations at higher passages. Moreover, tumour suppressor genes such as p16 and p21 were found to be down-regulated after large-scale cell culture.

CONCLUSIONS

MCCs immortalize spontaneously after extensive cell culture, but still demonstrate stem cell-like qualities.

Variations in five genes and the severity of age-related macular degeneration: results from the Muenster aging and retina study

AIMS

Little is known about the role of genetic variants in the early stages of age-related macular degeneration (AMD). We aimed to investigate how genetic variations within five well-defined genes relate to AMD severity.

METHODS

We analysed SNPs in the genes for complement factor H (CFH), age-related maculopathy susceptibility (ARMS2), HtrA serine peptidase 1 (HtrA1), complement factor B (CFB), and complement component 2 (C2)in 183 controls and 730 patients with increasing severity of AMD from the Muenster aging and retina study (MARS). Severity scoring was based on the Rotterdam classification of fundus photographs.

RESULTS

Compared with controls, patients with very early AMD showed a significantly increased minor allele frequency (MAF) only for CFH-rs1061170. With increasing severity of AMD, SNPs in CFH-rs1061170,as well as ARMS2-rs10490924, became consistently more common (P<0.001). Likewise, HtrA1-rs11200638 was less clearly associated with AMD severity, whereas C2-rs9332739 and CFB-rs641153 showed no relation. Multifactorial models confirmed CFH and ARMS2 as major determinants of AMD severity, whereas addition of HtrA1, C2 and CFB did not improve model prediction. In the models, age did not contribute to very early but to all more severe AMD stages, whereas smoking history had a significant impact only for late AMD.

CONCLUSION

Our findings indicate that the CFH gene is involved in the onset of AMD, whereas both, the CFH and ARMS2 genes, and more weakly, the HtrA1 gene, appear to account for the advancement of AMD. The results for SNPs in the C2 and CFB genes were inconclusive. Genetic factors dominated in their impact over age and smoking history.

Lipofuscin- and melanin-related fundus autofluorescence visualize different retinal pigment epithelial alterations in patients with retinitis pigmentosa

AIMS

To compare melanin-related near-infrared fundus autofluorescence (FAF; NIA, excitation 787 nm, emission >800 nm) with lipofuscin-related FAF (excitation 488 nm, emission >500 nm) in retinitis pigmentosa (RP).

METHODS

Thirty-three consecutive RP patients with different modes of inheritance were diagnosed clinically, with full-field ERG, and if possible with molecular genetic methods. FAF and NIA imaging were performed with a confocal scanning laser ophthalmoscope (Heidelberg Retina Angiograph 2).

RESULTS

Rings of increased FAF were present within an area of preserved retinal pigment epithelium (RPE) at the posterior pole (31/33). Rings of increased NIA were located in the same region as rings of increased FAF. In contrast to FAF, NIA showed a precipitous decline of NIA peripheral to the ring. In larger areas of preserved NIA (11/31), pericentral and foveal NIA were of similar intensity with an area of lower NIA in between. In smaller areas of preserved NIA (20/31), NIA was homogeneous from the perifovea to the fovea. In one patient without a ring of increased FAF, NIA distribution was normal. In the remaining patient with severely advanced RP, no residual RPE as well as no FAF and NIA were detectable.

CONCLUSION

Characteristic features for FAF and NIA alterations in a heterogeneous group of RP patients indicate a common pathway of RPE degeneration. Patterns of NIA and FAF indicate different pathophysiologic processes involving melanin and lipofuscin. Combined NIA and FAF imaging will provide further insight into the pathogenesis of RP and non-invasive monitoring of future therapeutic interventions.

The role of caspases in photoreceptor cell death of the retinoschisin-deficient mouse

Early schisis cavities in the retinal bipolar cell layer accompanied by progressive loss of cone and rod photoreceptor cells are the hallmark of the retinoschisin-deficient (Rs1h(-/Y)) murine retina. With this study we aimed at elucidating the molecular events underlying the photoreceptor cell death in this established murine model of X-linked juvenile retinoschisis. We show that photoreceptor degeneration in the Rs1h(-/Y) mouse is due to apoptotic events peaking around postnatal day 18. Cell death is accompanied by increased expression of initiator and inflammatory caspases but not by downstream effector caspases. The strong induction of caspase-1 (Casp1) prompted us to explore its involvement in the apoptotic process. We therefore generated double knock-out mice deficient for both retinoschisin and Casp1. No direct influence of the Casp1 genotype on apoptosis could be identified although striking differences in the overall number of resident microglia were observed independent of the Rs1h genotype.

[Y402H polymorphism in complement factor H and age-related macula degeneration (AMD)]

Age-related macular degeneration is a complex genetic disorder. Recent data suggest that the additive genetic risk for late-stage disease is more than two-thirds. Comprehensive genetic studies (candidate gene approaches, linkage and association studies) have been performed in recent years to identity the genetic risk factors at the molecular lavel. Very recently, a significant risk allele, Y402H, has been discovered in the complement factor H (CFH) gene. The relative risk of developing AMD has been estimated between 2.4-4.6 for heterozygotes and 3.3-7.4 for homozygotes. This polymorphism accounts for approximately 20-50% of the overall risk of developing AMD. In this review the results from molecular genetic studies in AMD are summarized, with a special emphasis on the recent data obtained for the CFH gene.

[VMD2 and its role in Best's disease and other retinopathies]

Best's vitelliform macular dystrophy (Best's disease) is an autosomal dominant disease of the central retina and is caused by mutations in the VMD2 gene located on the long arm of chromosome 11. VMD2 encodes bestrophin, a transmembrane protein with putative Ca(2+)-dependent chloride channel activity at the basolateral portion of the retinal pigment epithelium. The N-terminal half of bestrophin reveals high sequence homology to three bestrophin-like proteins in humans but also to protein sequences from evolutionarily distant organisms. Most of the known VMD2 mutations are located within this presumably important functional part of the protein and cause amino acid substitutions and small in-frame deletions of single amino acid residues. The pathogenicity of VMD2 mutations is likely based on a dominant negative effect possibly by oligomerization of normal and mutated bestrophin molecules to form a defective ion channel. Missense mutations in VMD2 were also shown to be associated with vitreoretinochoroidopathy and ocular developmental abnormalities. In this case, the pathogenic sequence changes influence the peptide sequences but simultaneously alter the regulation of mRNA splicing and maturation. Different disease mechanisms may therefore be responsible for the distinct phenotypes associated with VMD2 mutations.

Identifying differentially expressed genes in the mammalian retina and the retinal pigment epithelium by suppression subtractive hybridization

Retina and retinal pigment epithelium (RPE) cells are of neuroectodermal origin with highly specialized functions in light perception. Identification and characterization of genes differentially expressed in these cells will greatly aid our understanding of their functional roles in retinal biology. As a source enriched for gene transcripts from the retina/RPE, we generated a human retina and a bovine RPE cDNA library applying the PCR-based technique of suppression subtractive hybridization (SSH). Sequencing of 1,080 retina and 2,350 RPE SSH clones resulted in the identification of 321 and 343 non-redundant human transcripts, respectively. Of these, only 27 genes were in common between the two cDNA libraries. One transcript expressed exclusively in retina and RPE is the novel gene C4orf11 which is comprised of four exons on chromosome 4q21.2. We report the full-length cloning of two isoforms of C4orf11, 919 bp and 857 bp in length, both of which contain four identical open reading frames (ORFs). While ORFs 1 to 3 show no homologies to known proteins or protein domains, ORF4 reveals 50% sequence identity to RPE-spondin, a hypothetical protein on 8q13.3 with unknown function. We demonstrate that both the retina and the RPE SSH cDNA libraries are excellent resources for identifying known and novel genes exclusively or abundantly expressed in the retina/RPE complex. In combination with other approaches such as microarray analysis or serial analysis of gene expression (SAGE), the availability of highly sensitive and specific SSH cDNA libraries will facilitate the comprehensive description of the retina/RPE transcriptome.

Comparative mapping of human claudin-1 (CLDN1) in great apes

The gene encoding claudin-1 (CLDN1) has been mapped to human chromosome 3 (HSA3; 3q28-->q29) using a radiation hybrid panel. Employing fluorescence in situ hybridization (FISH) we here show that a human P1-derived artificial chromosome (PAC) containing CLDN1 detects the orthologous sites in chromosomes of the great apes, chimpanzee, gorilla, and orangutan. Furthermore, the chromosomal position of CLDN1 was determined in mouse chromosomes by FISH. The position of fluorescent signals is confined to a single chromosomal site in both great apes and mouse and in each case maps to the chromosomal region that has conserved synteny with HSA3 (PTR2q28, GGO2q28, PPY2q38 and MMU16B1). Using a gene-specific probe our results are consistent with reports of the striking similarity of great ape and human genomes as illustrated previously by chromosome painting.

PTEN mutations do not cause nuclear beta-catenin accumulation in endometrial carcinomas

PTEN: and beta-catenin mutations constitute the predominant genetic alterations in endometrioid carcinomas of the endometrium. PTEN encodes a dual-specificity phosphatase with lipid phosphatase and protein tyrosine phosphatase activities that regulate both apoptosis and interactions with the extracellular matrix. Recent studies have associated PTEN mutations with tumorigenesis of prostate carcinoma via the Wnt signaling pathway, leading to nuclear beta-catenin accumulation. To elucidate the potential interaction of PTEN and beta-catenin in endometrial cancer, we performed mutation analyses of the entire PTEN gene and of exon 3 of the beta-catenin gene that is most frequently targeted by mutations. A total of 82 endometrial carcinomas comprising 62 type I endometrioid carcinomas and 20 type II high-grade carcinomas were investigated. In addition in a subset of 22 carcinomas, the intracellular beta-catenin distribution was analyzed by immunohistochemistry. Overall, 20 (24.4%) of 82 tumors revealed mutations in the PTEN gene, and 16 (19.5%) of 82, in the beta-catenin gene. Six tumors (7.3%) showed mutations in both the PTEN and beta-catenin gene. Mutations were mainly detected in endometrioid carcinomas of the endometrium. As expected, a striking nuclear accumulation of beta-catenin could be shown in tumors with beta-catenin mutations. In the vast majority of tumors with PTEN mutations, a regular staining pattern of the cytoplasmic and membranous compartments was found. We therefore conclude that, in contrast to prostate cancer, mutations in the PTEN gene seem not to affect cellular distribution of the beta-catenin protein in endometrial carcinomas.

Cloning and characterization of the murine Vmd2 RFP-TM gene family

Mutations in the human vitelliform macular dystrophy type 2 (VMD2) gene are known to cause autosomal dominant Best macular dystrophy (BMD), a degenerative disorder of the central retina. VMD2, together with VMD2L1, VMD2L2 and VMD2L3, belong to a closely related gene family characterized by several transmembrane (TM) spanning helical domains and an invariant arginine, phenylalanine and proline (RFP) tripeptide motif, thus termed VMD2 RFP-TM. The four genes are thought to encode a novel family of anion channels. We now report the cloning and characterization of the murine orthologs by combining biocomputational analyses and molecular genetic approaches. While the murine Vmd2, Vmd2l1 and Vmd2l3 genes are functional, murine Vmd2l2p was found to be a non-transcribed pseudogene. Expression profiling of the murine Vmd2 RFP-TM family members revealed tissue-restricted expression with predominant transcription of Vmd2 in testis, of Vmd2l1 in colon and of Vmd2l3 in heart. Differential splicing was observed for Vmd2l3 in a number of tissues (e.g. in brain, retina/RPE, kidney) although the functional importance of the splice variants remains to be determined.