The purpose of this study was to assess the therapeutic efficacy of rAAV8-hGRK1-Tlcd3b in a Tlcd3b-/- mouse model of retinal generation and validate TLCD3B's role as a ceramide synthase in vivo.
...Using Tlcd3b-/- mice as an inherited retinal disease animal model, we performed subretinal injection of rAAV8-hGRK1-Tlcd3b and evaluated the efficacy of gene replacement therapy. Tlcd3b-/- mice were treated at two time points: postnatal day 21 (P21) and postnatal day 120 (P120) with various dosages.
Tlcd3b overexpression rescued retinal degeneration in the mutant mice, as indicated by significantly improved photoreceptor function and preservation of photoreceptor cells over the course of 1 year. Although Tlcd3b is expressed in all cell types in the retina, photoreceptor cell-specific expression of Tlcd3b is sufficient to rescue the phenotype, indicating the primary function of TLCD3B is in photoreceptors. Consistent with the idea that TLCD3B is a ceramide synthase, mass spectrometry analyses of the mutant retina indicate the reduction of C16-, C18-, and C20-ceramides in the retina, which are restored with Tlcd3b overexpression.
Our findings demonstrated the therapeutic efficacy of gene therapy in treating Tlcd3b mutant retina, laying the foundation for developing future therapy for TLCD3B retinopathy.
Inherited retinal dystrophies caused by dominant mutations in photoreceptor (PR) cell expressed genes are a major cause of irreversible vision loss. Oligonucleotide therapy has been of interest in ...diseases that conventional medicine cannot target. In the early days, small interfering RNAs (siRNAs) were explored in clinical trials for retinal disorders with limited success due to a lack of stability and efficient cellular delivery. Thus, an unmet need exists to identify siRNA chemistry that targets PR cell expressed genes. Here, we evaluated 12 different fully chemically modified siRNA configurations, where the valency and conjugate structure were systematically altered. The impact on retinal distribution following intravitreal delivery was examined. We found that the increase in valency (tetravalent siRNA) supports the best PR accumulation. A single intravitreal administration induces multimonths efficacy in rodent and porcine retinas while demonstrating a good safety profile. The data suggest that this configuration can treat retinal diseases caused by PR cell expressed genes with 1–2 intravitreal injections per year.
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Punzo and colleagues have identified in a screen a chemically modified tetrameric siRNA that exhibits efficient long-term gene silencing in photoreceptor cells of mouse and swine eyes. This tetrameric siRNA chemistry may be used for the treatment of retinal diseases caused by mutations in photoreceptor cell expressed genes.
Collectively, retinal neurodegenerative diseases are comprised of numerous subtypes of disorders which result in loss of a varying cell types in the retina. These diseases can range from glaucoma, ...which results in retinal ganglion cell death, to age-related macular degeneration and retinitis pigmentosa, which result in cell death of the retinal pigment epithelium, photoreceptors, or both. Regardless of the disease, it's been recently found that increased release of proinflammatory cytokines and proliferation of active microglia result in a remarkably proinflammatory microenvironment that assists in the pathogenesis of the disease; however, many of the details of these inflammatory events have yet to be elucidated. In an ongoing study, we have used systems genetics to identify possible models of spontaneous polygenic age-related macular degeneration by mining the BXD family of mice using single nucleotide polymorphism analyses of known genes associated with the human retinal disease. One BXD strain (BXD32) was removed from the study as the rate of degeneration observed in these animals was markedly increased with a resultant loss of most all photoreceptors by 6 months of age. Using functional and anatomical exams including optokinetic nystamography, funduscopy, fluorescein angiography, and optical coherence tomography, along with immunohistochemical analyses, we show that the BXD32 mouse strain exhibits a severe neurodegenerative phenotype accompanied by adverse effects on the retinal vasculature. We also expose the concurrent establishment of a chronic proinflammatory microenvironment including the TNFα secretion and activation of the NF-κB and JAK/STAT pathways with an associated increase in activated macrophages and phagoptosis. We conclude that the induced neuronal death and proinflammatory pathways work synergistically in the disease pathogenesis to enhance the rate of degeneration in this spontaneous polygenic model of inherited retinal dystrophy.
Increasing evidence has supported the role of ceramide as a mediator of photoreceptor dysfunction or cell death in ceramide accumulation and deficiency contexts. TLCD3B, a non-canonical ceramide ...synthase, was previously identified in addition to the six canonical ceramide synthases (CerSs), and the Tlcd3b-/- mouse model exhibited both retinal dysfunction and degeneration. As previous canonical CerS-deficient mouse models failed to display retinal degeneration, the mechanisms of how TLCD3B interacts with CerSs have not been investigated. Additionally, as the ceramide profile of each CerS is distinct, it is unclear whether the overall level or the homeostasis of different ceramide species plays a critical role in photoreceptor degeneration. Interactions between TLCD3B with canonical CerSs expressed in the retina were examined by subretinally injecting recombinant adeno-associated virus 8 vectors containing the Cers2 (rAAV8-CerS2), Cers4 (rAAV8-CerS4) and Cers5 (rAAV8-CerS5) genes. Injection of all three rAAV8-CerS vectors restored retinal functions as indicated by improved electroretinogram responses, but only rAAV8-CerS5 successfully retained retinal morphology in Tlcd3b-/- mice. CerSs and TLCD3B played partially redundant roles. Additionally, rather than acting as an integral entity, different ceramide species had different impacts on retinal cells, suggesting that the maintenance of the overall ceramide profile is critical for retinal function.
To report on the presence of autosomal dominant and compound dominant-null RP1-related retinitis pigmentosa in the same non-consanguineous family.
The father was minimally symptomatic and referred by ...his optometrist aged 38. He was diagnosed with rod-cone dystrophy, confirmed to be caused by the previously reported RP1 c.2613dupA mutation. He was reassured that his 11-year-old daughter had a 50% chance of inheriting the same mutation and that the condition, if she had it, would most likely be similar. Clinical phenotyping of his daughter however revealed an early onset cone-rod dystrophy. The mother was entirely asymptomatic and clinically normal. Sanger sequencing of the RP1 gene in the daughter confirmed the presence of biallelic mutations – the dominant c.2613dupA variant from her father and a c.3843dupT truncating variant inherited from her mother, both located in exon 4 of the RP1 gene. The maternal c.3843dupT has previously been reported.
Pathogenic variants in exon 4 of RP1 are known to cause differential dominant and recessive disease. The presence of both phenotypes in a single family has not yet been reported. The father, being minimally symptomatic, is affected by a known dominant variant which truncates the RP1 protein more proximally. However, inheritance of both variants in a compound heterozygous state in the daughter resulted in a much more severe, early onset cone-rod phenotype in a pattern akin to recessive disease. This raises challenges for genetic counselling and development of gene-based therapies for RP1 mutations.
Inherited retinal dystrophies are a significant cause of vision loss and are characterized by the loss of photoreceptors and the retinal pigment epithelium (RPE). Mutations in approximately 250 genes ...cause inherited retinal degenerations with a high degree of genetic heterogeneity. New techniques in next-generation sequencing are allowing the comprehensive analysis of all retinal disease genes thus changing the approach to the molecular diagnosis of inherited retinal dystrophies. This review serves to analyze clinical progress in genetic diagnostic testing and implications for retinal gene therapy.
A literature search of PubMed and OMIM was conducted to relevant articles in inherited retinal dystrophies.
Next-generation genetic sequencing allows the simultaneous analysis of all the approximately 250 genes that cause inherited retinal dystrophies. Reported diagnostic rates range are high and range from 51% to 57%. These new sequencing tools are highly accurate with sensitivities of 97.9% and specificities of 100%. Retinal gene therapy clinical trials are underway for multiple genes including RPE65, ABCA4, CHM, RS1, MYO7A, CNGA3, CNGB3, ND4, and MERTK for which a molecular diagnosis may be beneficial for patients.
Comprehensive next-generation genetic sequencing of all retinal dystrophy genes is changing the paradigm for how retinal specialists perform genetic testing for inherited retinal degenerations. Not only are high diagnostic yields obtained, but mutations in genes with novel clinical phenotypes are also identified. In the era of retinal gene therapy clinical trials, identifying specific genetic defects will increasingly be of use to identify patients who may enroll in clinical studies and benefit from novel therapies.
Inherited retinal dystrophies are often associated with mutations in the genes involved in the phototransduction cascade in photoreceptors, a paradigmatic signaling pathway mediated by G ...protein-coupled receptors. Photoreceptor viability is strictly dependent on the levels of the second messengers cGMP and Ca
2+
. Here we explored the possibility of modulating the phototransduction cascade in mouse rods using direct or liposome-mediated administration of a recombinant protein crucial for regulating the interplay of the second messengers in photoreceptor outer segments. The effects of administration of the free and liposome-encapsulated human guanylate cyclase-activating protein 1 (GCAP1) were compared in biological systems of increasing complexity (in cyto, ex vivo, and in vivo). The analysis of protein biodistribution and the direct measurement of functional alteration in rod photoresponses show that the exogenous GCAP1 protein is fully incorporated into the mouse retina and photoreceptor outer segments. Furthermore, only in the presence of a point mutation associated with cone-rod dystrophy in humans p.(E111V), protein delivery induces a disease-like electrophysiological phenotype, consistent with constitutive activation of the retinal guanylate cyclase. Our study demonstrates that both direct and liposome-mediated protein delivery are powerful complementary tools for targeting signaling cascades in neuronal cells, which could be particularly important for the treatment of autosomal dominant genetic diseases.
Genetic forms of focal and segmental glomerulosclerosis (FSGS) often have extra-renal manifestations. This study examined FSGS-associated genes from the Genomics England Renal proteinuria ...panel for reported and likely ocular features. Thirty-two of the 55 genes (58%) were associated with ocular abnormalities in human disease, and a further 12 (22%) were expressed in the retina or had an eye phenotype in mouse models. The commonest genes affected in congenital nephrotic syndrome (
NPHS1
,
NPHS2
,
WT1
,
LAMB2
,
PAX2
but not
PLCE1
) may have ocular manifestations . Many genes affected in childhood–adolescent onset FSGS (
NPHS1
,
NPHS2
,
WT1
,
LAMB2
,
SMARCAL1
,
NUP107
but not
TRPC6
or
PLCE1
) have ocular features. The commonest genes affected in adult-onset FSGS (
COL4A3–COL4A5,
GLA
) have ocular abnormalities but not the other frequently affected genes (
ACTN4
,
CD2AP
,
INF2
,
TRPC6
). Common ocular associations of genetic FSGS include cataract, myopia, strabismus, ptosis and retinal atrophy. Mitochondrial forms of FSGS (MELAS, MIDD, Kearn’s Sayre disease) are associated with retinal atrophy and inherited retinal degeneration. Some genetic kidney diseases (CAKUT, ciliopathies, tubulopathies) that result in secondary forms of FSGS also have ocular features. Ocular manifestations suggest a genetic basis for FSGS, often help identify the affected gene, and prompt genetic testing. In general, ocular abnormalities require early evaluation by an ophthalmologist, and sometimes, monitoring or treatment to improve vision or prevent visual loss from complications. In addition, the patient should be examined for other syndromic features and first degree family members assessed.
Purpose
To assess the longitudinal vision‐related quality of life among patients with CRB1‐associated inherited retinal dystrophies.
Methods
In this longitudinal questionnaire study, the National Eye ...Institute Visual Function Questionnaire (39 items, NEI VFQ‐39) was applied at baseline, two‐year follow‐up, and 4‐year follow‐up in patients with pathogenic CRB1 variants. Correction added on 20 November 2023, after first online publication: The preceding sentence has been updated in this version. Classical test theory was performed to obtain subdomain scores and in particular ‘near activities’ and ‘total composite’ scores. The Rasch analysis based on previous calibrations of the NEI VFQ‐25 was applied to create visual functioning and socio‐emotional subscales.
Results
In total, 22 patients with a CRB1‐associated retinal dystrophy were included, … with a median age of 25.0 years (interquartile range: 13–31 years) at baseline and mean follow‐up of 4.0 ± 0.3 years. Correction added on 20 November 2023, after first online publication: The preceding sentence has been updated in this version. A significant decline at 4 years was observed for ‘near activities’ (51.0 ± 23.8 vs 35.4 ± 14.7, p = 0.004) and ‘total composite’ (63.0 ± 13.1 vs 52.0 ± 12.1, p = 0.001) subdomain scores. For the Rasch‐scaled scores, the ‘visual functioning’ scale significantly decreased after 2 years (−0.89 logits; p = 0.012), but not at 4‐year follow‐up (+0.01 logits; p = 0.975). Correction added on 20 November 2023, after first online publication: In the preceding sentence, “…after 4 years…” has been corrected to “…after 2 years…” in this version. The ‘socio‐emotional’ scale also showed a significant decline after 2 years (−0.78 logits, p = 0.033) and 4 years (−0.83 logits, p = 0.021).
Conclusion
In the absence of an intervention, a decline in vision‐related quality of life is present in patients with pathogenic CRB1 variants at 4‐year follow‐up. Patient‐reported outcome measures should be included in future clinical trials, as they can be a potential indicator of disease progression and treatment efficacy.
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