Mutant frizzled-4 disrupts retinal angiogenesis in familial exudative vitreoretinopathy

Dysfunction of Calcyphosine-Like gene impairs retinal angiogenesis through the MYC axis and is associated with familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a severe genetic disorder characterized by incomplete vascularization of the peripheral retina and associated symptoms that can lead to vision loss. However, the underlying genetic causes of approximately 50% of FEVR cases remain unknown. Here, we report two heterozygous variants in calcyphosine-like gene (CAPSL) that is associated with FEVR. Both variants exhibited compromised CAPSL protein expression. Vascular endothelial cell (EC)-specific inactivation of Capsl resulted in delayed radial/vertical vascular progression, compromised endothelial proliferation/migration, recapitulating the human FEVR phenotypes. CAPSL-depleted human retinal microvascular endothelial cells (HRECs) exhibited impaired tube formation, decreased cell proliferation, disrupted cell polarity establishment, and filopodia/lamellipodia formation, as well as disrupted collective cell migration. Transcriptomic and proteomic profiling revealed that CAPSL abolition inhibited the MYC signaling axis, in which the expression of core MYC targeted genes were profoundly decreased. Furthermore, a combined analysis of CAPSL-depleted HRECs and c-MYC-depleted human umbilical vein endothelial cells uncovered similar transcription patterns. Collectively, this study reports a novel FEVR-associated candidate gene, CAPSL, which provides valuable information for genetic counseling of FEVR. This study also reveals that compromised CAPSL function may cause FEVR through MYC axis, shedding light on the potential involvement of MYC signaling in the pathogenesis of FEVR.

Familial Exudative Vitreoretinopathy With and Without Pathogenic Variants of Norrin/β-Catenin Signaling Genes

Purpose

To determine the clinical characteristics of familial exudative vitreoretinopathy (FEVR) associated with or without pathogenic variants of the Norrin/β-catenin genes.

Design

This was a multicenter, cross-sectional, observational, and genetic study.

Subjects

Two-hundred eighty-one probands with FEVR were studied.

Methods

Whole-exome sequence and/or Sanger sequence was performed for the Norrin/β-catenin genes, the FZD4, LRP5, TSPAN12, and NDP genes on blood collected from the probands. The clinical symptoms of the probands with or without the pathogenic variants were assessed as well as differences in the inter Norrin/β-catenin genes.

Main Outcome Measures

The phenotype associated with or without pathogenic variants of the Norrin/β-catenin genes.

Results

One-hundred eight probands (38.4%) had 88 different pathogenic or likely pathogenic variants in the genes: 24 with the FZD4, 42 with the LRP5, 10 with the TSPAN12, and 12 with the NDP gene. Compared with the 173 probands without pathogenic variants, the 108 variant-positive probands had characteristics of familial predisposition (63.9% vs. 37.6%, P < 0.0001), progression during infancy (75.0% vs. 53.8%, P = 0.0004), asymmetrical severity between the 2 eyes (50.0% vs. 37.6%, P = 0.0472), and nonsyndromic characteristics (10.2% vs. 17.3%, P = 0.1185). The most frequent stage at which the more severe eye conditions was present was at stage 4 in both groups (40.7% vs. 34.7%). However, the advanced stages of 3 to 5 in the more severe eye were found more frequently in probands with variants than in those without variants (83.3% vs. 58.4%, P < 0.0001). Patients with rhegmatogenous retinal detachments progressed from stage 1 or 2 were found less frequently in the variant-positive probands (8.3% vs. 17.3%, P = 0.0346). Nine probands with NDP variants had features different from probands with typical Norrin/β-catenin gene variants including the sporadic, symmetrical, and systemic characteristics consistent with Norrie disease.

Conclusions

The results showed that the clinical characteristics of FEVR of patients with variants in the Norrin/β-catenin genes are different from those with other etiologies. We recommend that clinicians who diagnose a child with FEVR perform genetic testing so that the parents can be informed on the prognosis of the vision and general health in the child.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Frizzled receptors (FZDs) in Wnt signaling: potential therapeutic targets for human cancers

Frizzled receptors (FZDs) are key contributors intrinsic to the Wnt signaling pathway, activation of FZDs triggering the Wnt signaling cascade is frequently observed in human tumors and intimately associated with an aggressive carcinoma phenotype. It has been shown that the abnormal expression of FZD receptors contributes to the manifestation of malignant characteristics in human tumors such as enhanced cell proliferation, metastasis, chemotherapy resistance as well as the acquisition of cancer stemness. Given the essential roles of FZD receptors in the Wnt signaling in human tumors, this review aims to consolidate the prevailing knowledge on the specific status of FZD receptors (FZD1-10) and elucidate their respective functions in tumor progression. Furthermore, we delineate the structural basis for binding of FZD and its co-receptors to Wnt, and provide a better theoretical foundation for subsequent studies on related mechanisms. Finally, we describe the existing biological classes of small molecule-based FZD inhibitors in detail in the hope that they can provide useful assistance for design and development of novel drug candidates targeted FZDs.

Multimodal imaging of white preretinal lesions in atypical familial exudative vitreoretinopathy: Case report and literature review

Purpose

To report a rare clinical finding of preretinal granules associated with atypical familial exudative vitreoretinopathy (FEVR) and perform a review of the literature.

Observations

An asymptomatic 18-year-old male was referred for unilateral peripheral avascular retina evaluation in association with presumed FEVR. He was first noted to have white preretinal granules on fundus examination at five years of age. The lesions remained unchanged over the subsequent years. Genetic testing did not reveal a pathogenic or likely pathogenic variant in a known FEVR gene. A review of the literature revealed five other cases of FEVR with similar findings.

Conclusions and Importance

Literature review suggests preretinal granules may present rarely in FEVR. Negative genetic screening of known FEVR genes in our patient with atypical FEVR suggests either a molecularly distinct etiology supporting the rarity of this association with FEVR or, alternatively, the presence of granules in developmental retinal vascular anomalies that are not specific to FEVR. Future study and genetic testing is necessary to better understand the cause of these preretinal granules and the clinical manifestations of FEVR.

Genotypic and phenotypic diversity in X-linked retinoschisis: Findings from a South Indian patient cohort

PURPOSE

Retinoschisis is a distinctive condition characterized by intraretinal layer clefts, primarily associated with X-linked recessive inheritance due to RS1 gene mutations. This study aims to uncover the RS1 mutation spectrum in a cohort of 22 X-linked retinoschisis cases from South India and emphasizes the genotypic and phenotypic associations within patients harboring only RS1 mutations.

METHODS

A total of 22 probands were suspected of having X-linked retinoschisis. All study subjects underwent ophthalmic investigations, including assessments of visual acuity, fundus examination, optical coherence tomography (OCT), and electroretinogram (ERG). RS1 gene screening was conducted using Sanger sequencing, and the pathogenicity of the variants was assessed through Sorting Intolerant from Tolerant (SIFT) and PolyPhen-2 in silico tools.

RESULTS

The study found that the probands had an average visual acuity of 0.79 ± 0.39 log of minimum angle of resolution (logMAR), ranging from 0.17 to 1.77. During fundus examination, the probands exhibited a characteristic spoke wheel-like pattern in the macular region. Furthermore, OCT analysis revealed distinct alterations in the inner retinal microstructure, and ERG results consistently showed a reduction in b-wave amplitude. Eventually, Sanger sequencing results showed hemizygous mutations in the RS1 gene in only 12 probands, including a novel missense mutation in the RS1 gene's signal sequence.

CONCLUSION

This study provides valuable insights into the spectrum of RS1 mutations in X-linked retinoschisis probands from South India. It reveals distinct genotypic-phenotypic associations and highlights the clinical manifestations associated with the disease pathogenesis.

Clinical and genetic characteristics and natural history of Finnish families with familial exudative vitreoretinopathy due to pathogenic FZD4 variants

PURPOSE

To report clinical and genetic characteristics of familial exudative vitreoretinopathy (FEVR) in the Finnish population.

METHODS

Detailed clinical and genetic data of 35 individuals with heterozygous pathogenic variants in FZD4 were gathered and analysed.

RESULTS

Thirty-two individuals with FZD4 c.313A>G variant and three individuals with FZD4 c.40_49del were included in the study. The clinical phenotype was variable even among family members with the same FZD4 variant. Only 34% (N = 12/35) of variant-positive individuals had been clinically diagnosed with FEVR. The median age of the onset of symptoms was 2.3 years, ranging between 0 to 25 years. Median visual acuity was 0.1 logMAR (0.8 Snellen decimal), ranging between light perception and -0.1 logMAR (1.25 Snellen decimal). Most (N = 33/35, 94%) were classified as not visually impaired. Despite unilateral visual loss present in some, they did not meet the criteria of visual impairment according to the WHO classification. Two study patients (N = 2/35, 6%) had severe visual impairment. The most common FEVR stage in study patient's eyes (N = 28/70 eyes, 40%) was FEVR stage 1, that is, avascular periphery or abnormal vascularisation. Most of FZD4-variant-positive study patient's eyes (N = 31/50 eyes, 62%) were myopic. Two individuals presented with persistent hyperplastic primary vitreous expanding the phenotypic spectrum of FEVR. Shared haplotypes extending approximately 0.9 Mb around the recurrent FZD4 c.313A>G variant were identified.

CONCLUSION

Most study patients were unaffected or had mild clinical manifestations by FEVR. Myopia seemed to be overly common in FZD4-variant-positive individuals.

Retinopathy With Variant of Unknown Significance and Atypical Chorioretinal Coloboma in the Setting of Prematurity

A 37-week-old girl underwent ophthalmic examination. Born at 32 weeks, the infant weighed 680 grams and received high-flow nasal cannula for respiratory distress of the newborn. Dilated fundus examination of the right eye revealed an atypical chorioretinal coloboma; the left eye revealed hyperpigmentary changes in the macula. Fluorescein angiography of both eyes showed retinal vascularization to zone II. Genetic testing revealed a heterozygous variant of uncertain significance in the catenin Alpha 1 (CTNNA1) gene. CTNNA1 gene abnormalities have been implicated as causes of familial exudative vitreoretinopathy (FEVR). It is important to recognize possible simultaneous retinopathy of prematurity and FEVR. [Ophthalmic Surg Lasers Imaging Retina 2024;55:285-288.].

Identification of Novel FZD4 Mutations in Familial Exudative Vitreoretinopathy and Investigating the Pathogenic Mechanisms of FZD4 Mutations

Purpose

The purpose of this study is to report five novel FZD4 mutations identified in familial exudative vitreoretinopathy (FEVR) and to analyze and summarize the pathogenic mechanisms of 34 of 96 reported missense mutations in FZD4.

Methods

Five probands diagnosed with FEVR and their family members were enrolled in the study. Ocular examinations and targeted gene panel sequencing were conducted on all participants. Plasmids, each carrying 29 previously reported FZD4 missense mutations and five novel mutations, were constructed based on the selection of mutations from each domain of FZD4. These plasmids were used to investigate the effects of mutations on protein expression levels, Norrin/β-catenin activation capacity, membrane localization, norrin binding ability, and DVL2 recruitment ability in HEK293T, HEK293STF, and HeLa cells.

Results

All five novel mutations (S91F, V103E, C145S, E160K, C377F) responsible for FEVR were found to compromise Norrin/β-catenin activation of FZD4 protein. After reviewing a total of 34 reported missense mutations, we categorized all mutations based on their functional changes: signal peptide mutations, cysteine mutations affecting disulfide bonds, extracellular domain mutations influencing norrin binding, transmembrane domain (TM) 1 and TM7 mutations impacting membrane localization, and intracellular domain mutations affecting DVL2 recruitment.

Conclusions

We expanded the spectrum of FZD4 mutations relevant to FEVR and experimentally demonstrated that missense mutations in FZD4 can be classified into five categories based on different functional changes.

Characterization of a novel heterozygous frameshift variant in NDP gene that causes familial exudative vitreoretinopathy in female patients

Familial exudative vitreoretinopathy (FEVR) is a severe inherited disease characterized by defective retinal vascular development. With genetic and clinical heterogeneity, FEVR can be inherited in different patterns and characterized by phenotypes ranging from moderate visual defects to complete vision loss. This study was conducted to unravel the genetic and functional etiology of a 4-month-old female FEVR patient. Targeted gene panel and Sanger sequencing were utilized for genetic evaluation. Luciferase assays, western blot, quantitive real-time PCR, and immunocytochemistry were performed to verify the functional defects in the identified candidate variant. Here, we report a 4-month-old girl with bilateral retinal folds and peripheral avascularization, and identified a novel frameshift heterozygous variant c.37dup (p.Leu13ProfsTer13) in NDP. In vitro experiments revealed that the Leu13ProfsTer13 variant led to a prominent decrease in protein levels instead of mRNA levels, resulting in compromised Norrin/β-catenin signaling activity. Human androgen receptor assay further revealed that a slight skewing of X chromosome inactivation could partially cause FEVR. Thus, the pathogenic mechanism by which heterozygous frameshift or nonsense variants in female carriers cause FEVR might largely result from a loss-of-function variant in one X chromosome allele and a slightly skewed X-inactivation. Further recruitment of more FEVR-affected females carrying NDP variants and genotype-phenotype correlation analysis can ultimately offer valuable information for the prognosis prediction of FEVR.

Mutations in TSPAN12 gene causing familial exudative vitreoretinopathy

BACKGROUND

To report newly found TSPAN12 mutations with a unique form of familial exudative vitreoretinopathy (FEVR) and find out the possible mechanism of a repeated novel intronic variant in TSPAN12 led to FEVR.

RESULTS

Nine TSPAN12 mutations with a unique form of FEVR were detected by panel-based NGS. MINI-Gene assay showed two splicing modes of mRNA that process two different bands A and B, and mutant-type shows replacement with the splicing mode of Exon11 hopping. Construction of wild-type and mutant TSPAN12 vector showed the appearance of premature termination codons (PTC). In vitro expression detection showed significant down-regulated expression level of TSPAN12 mRNAs and proteins in cells transfected with mutant vectors compared with in wild-type group. On the contrary, translation inhibitor CHX and small interfering RNA of UPF1 (si-UPF1) significantly increased mRNA or protein expression of TSPAN12 in cells transfected with the mutant vectors.

CONCLUSIONS

Nine mutations in TSPAN12 gene are reported in 9 FEVR patients with a unique series of ocular abnormalities. The three novel TSPAN12 mutations trigger NMD would cause the decrease of TSPAN12 proteins that participate in biosynthesis and assembly of microfibers, which might lead to FEVR, and suggest that intronic sequence analysis might be a vital tool for genetic counseling and prenatal diagnoses.

Loss-of-function of kinesin-5 KIF11 causes microcephaly, chorioretinopathy, and developmental disorders through chromosome instability and cell cycle arrest

Kinesin motors play a fundamental role in development by controlling intracellular transport, spindle assembly, and microtubule organization. In humans, patients carrying mutations in KIF11 suffer from an autosomal dominant inheritable disease called microcephaly with or without chorioretinopathy, lymphoedema, or mental retardation (MCLMR). While mitotic functions of KIF11 proteins have been well documented in centrosome separation and spindle assembly, cellular mechanisms underlying KIF11 dysfunction and MCLMR remain unclear. In this study, we generate KIF11-inhibition chick and zebrafish models and find that KIF11 inhibition results in microcephaly, chorioretinopathy, and severe developmental defects in vivo. Notably, loss-of-function of KIF11 causes the formation of monopolar spindle and chromosome misalignment, which finally contribute to cell cycle arrest, chromosome instability, and cell death. Our results demonstrate that KIF11 is crucial for spindle assembly, chromosome alignment, and cell cycle progression of progenitor stem cells, indicating a potential link between polyploidy and MCLMR. Our data have revealed that KIF11 inhibition cause microcephaly, chorioretinopathy, and development disorders through the formation of monopolar spindle, polyploid, and cell cycle arrest.

Deciphering a crucial dimeric interface governing Norrin dimerization and the pathogenesis of familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is a hereditary eye disease that could cause blindness. It has been established that Norrin forms dimers to activate β-catenin signaling, yet the core interface for Norrin dimerization and the precise mechanism by which Norrin dimerization contributes to the pathogenesis of FEVR remain elusive. Here, we report an NDP variant, c.265T>C (p.Phe89Leu), that interrupted β-catenin signaling by disrupting Norrin dimerization. Structural and functional analysis revealed that the Phe-89 of one Norrin monomer interacts with Pro-98, Ser-101, Arg-121, and Ile-123 of another, forming two core symmetrical dimerization interfaces that are pivotal for the formation of a "hand-by-arm" dimer. Intriguingly, we proved that one of the two core symmetrical interfaces is sufficient for dimerization and activation of β-catenin signaling, with a substantial contribution from the Phe-89/Pro-98 interaction. Further functional analysis revealed that the disruption of both dimeric interfaces eliminates potential binding sites for LRP5, which could be partially restored by over-expression of TSPAN12. In conclusion, our findings unveil a core dimerization interface that regulates Norrin/LRP5 interaction, highlighting the essential role of Norrin dimerization on β-catenin signaling and providing potential therapeutic avenues for the treatment of FEVR.

The co-receptor Tspan12 directly captures Norrin to promote ligand-specific β-catenin signaling

Wnt/β-catenin signaling directs animal development and tissue renewal in a tightly controlled, cell- and tissue-specific manner. In the central nervous system, the atypical ligand Norrin controls angiogenesis and maintenance of the blood-brain barrier and blood-retina barrier through the Wnt/β-catenin pathway. Like Wnt, Norrin activates signaling by binding and heterodimerizing the receptors Frizzled (Fzd) and Low-density lipoprotein receptor-related protein 5 or 6 (LRP5/6), leading to membrane recruitment of the intracellular transducer Dishevelled (Dvl); this ultimately results in the stabilization of the transcriptional coactivator β-catenin. Unlike Wnt, the cysteine-knot ligand Norrin only signals through Fzd4 and additionally requires the co-receptor Tspan12; however, the mechanism underlying Tspan12-mediated signal enhancement is unclear. It has been proposed that Tspan12 integrates into the Norrin-Fzd4 complex to enhance Norrin-Fzd4 affinity or otherwise allosterically modulate Fzd4 signaling. Here, we measure direct, high-affinity binding between purified Norrin and Tspan12 in a lipid environment and use AlphaFold models to interrogate this interaction interface. We find that Tspan12 and Fzd4 can simultaneously bind Norrin and that a pre-formed Tspan12/Fzd4 heterodimer, as well as cells co-expressing Tspan12 and Fzd4, more efficiently capture low concentrations of Norrin than Fzd4 alone. We also show that Tspan12 competes with both heparan sulfate proteoglycans and LRP6 for Norrin binding and that Tspan12 does not impact Fzd4-Dvl affinity in the presence or absence of Norrin. Our findings suggest that Tspan12 does not allosterically enhance Fzd4 binding to Norrin or Dvl, but instead functions to directly capture Norrin upstream of signaling.

RETINAL MANIFESTATIONS OF WALKER-WARBURG SYNDROME IN TWO SIBLINGS WITH RXYLT1 MUTATIONS

PURPOSE

We report two siblings with genetically confirmed Walker-Warburg syndrome (WWS), studied with multimodal imaging, who presented with different retinal manifestations.

METHODS

This is a retrospective report of two WWS cases with ultra-widefield fundus photography, fluorescein angiography, and ultrasound. Molecular diagnosis was achieved using panel testing and targeted variant testing.

RESULTS

Two siblings, one male and one female, born 17 months apart with a diagnosis of WWS underwent retinal examination with imaging. The 3-month-old female infant exhibited microphthalmia, persistent hyaloidal arteries, and retrolental membranes with total tractional retinal detachments on ultrasound in both eyes. The 22-day-old male newborn exhibited persistent hyaloidal arteries and extensive peripheral avascular retina on angiography in both eyes. Both were found to be positive for the same two pathogenic variants in the RXYLT1/TMEM5 gene, which accounts for approximately 9% of cases of genetically confirmed WWS.

CONCLUSION

Siblings with genetically confirmed WWS can have variable presentations despite identical genotype. This highlights the phenotypic disease spectrum of WWS, which may be similar to that seen in familial exudative vitreoretinopathy.

A Literary Pediatric Retina Fellowship With Michael T. Trese, MD

Michael T. Trese, MD (1946-2022), a vitreoretinal surgeon, made significant contributions to the field of retina. Although most known for his work in pediatric retina surgery, he was a pioneer in areas such as medical retina, translational research, and telemedicine. This article reviews his major contributions to spread his knowledge more widely to vitreoretinal trainees and specialists. We discuss six areas where Trese made a lasting impact: lens-sparing vitrectomy, familial exudative vitreoretinopathy, congenital X-linked retinoschisis, autologous plasmin enzyme, regenerative medicine, and telemedicine. [Ophthalmic Surg Lasers Imaging Retina 2023;54:701-712.].

Assessment of Inner Blood-Retinal Barrier: Animal Models and Methods

Proper functioning of the neural retina relies on the unique retinal environment regulated by the blood-retinal barrier (BRB), which restricts the passage of solutes, fluids, and toxic substances. BRB impairment occurs in many retinal vascular diseases and the breakdown of BRB significantly contributes to disease pathology. Understanding the different molecular constituents and signaling pathways involved in BRB development and maintenance is therefore crucial in developing treatment modalities. This review summarizes the major molecular signaling pathways involved in inner BRB (iBRB) formation and maintenance, and representative animal models of eye diseases with retinal vascular leakage. Studies on Wnt/β-catenin signaling are highlighted, which is critical for retinal and brain vascular angiogenesis and barriergenesis. Moreover, multiple in vivo and in vitro methods for the detection and analysis of vascular leakage are described, along with their advantages and limitations. These pre-clinical animal models and methods for assessing iBRB provide valuable experimental tools in delineating the molecular mechanisms of retinal vascular diseases and evaluating therapeutic drugs.

Identifying novel candidate compounds for therapeutic strategies in retinopathy of prematurity via computational drug-gene association analysis

Purpose

Retinopathy of prematurity (ROP) is the leading cause of preventable childhood blindness worldwide. Although interventions such as anti-VEGF and laser have high success rates in treating severe ROP, current treatment and preventative strategies still have their limitations. Thus, we aim to identify drugs and chemicals for ROP with comprehensive safety profiles and tolerability using a computational bioinformatics approach.

Methods

We generated a list of genes associated with ROP to date by querying PubMed Gene which draws from animal models, human studies, and genomic studies in the NCBI database. Gene enrichment analysis was performed on the ROP gene list with the ToppGene program which draws from multiple drug-gene interaction databases to predict compounds with significant associations to the ROP gene list. Compounds with significant toxicities or without known clinical indications were filtered out from the final drug list.

Results

The NCBI query identified 47 ROP genes with pharmacologic annotations present in ToppGene. Enrichment analysis revealed multiple drugs and chemical compounds related to the ROP gene list. The top ten most significant compounds associated with ROP include ascorbic acid, simvastatin, acetylcysteine, niacin, castor oil, penicillamine, curcumin, losartan, capsaicin, and metformin. Antioxidants, NSAIDs, antihypertensives, and anti-diabetics are the most common top drug classes derived from this analysis, and many of these compounds have potential to be readily repurposed for ROP as new prevention and treatment strategies.

Conclusion

This bioinformatics analysis creates an unbiased approach for drug discovery by identifying compounds associated to the known genes and pathways of ROP. While predictions from bioinformatic studies require preclinical/clinical studies to validate their results, this technique could certainly guide future investigations for pathologies like ROP.

A comprehensive functional analysis on the pathogenesis of novel TSPAN12 and NDP variants in familial exudative vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is an inherited blinding disorder; however, the known FEVR-associated variants account for approximately only 50% cases. Currently, the pathogenesis of most reported variants is not well studied, we aim to identify novel variants from FEVR-associated genes and perform a comprehensive functional analysis to uncover the pathogenesis of variants that cause FEVR. Using targeted gene panel and Sanger sequencing, we identified six novel and three known variants in TSPAN12 and NDP. These variants were demonstrated to cause significant inhibition of Norrin/β-catenin pathway by dual-luciferase reporter assay and western blot analysis. Structural analysis and co-immunoprecipitation revealed compromised interactions between missense variants and binding partners in the Norrin/β-catenin pathway. Immunofluorescence and subcellular protein extraction were performed to reveal the abnormal subcellular trafficking. Additionally, over-expression of TSPAN12 successfully enhanced the Norrin/β-catenin signaling activity by strengthening the binding affinity of mutant Norrin with FZD4 or LRP5. Together, these observations expanded the spectrum of FEVR-associated variants for the genetic counseling and prenatal diagnosis of FEVR, as well providing a potential therapeutic strategy for the treatment of FEVR.

Familial Exudative Vitreoretinopathy and Systemic Abnormalities in Patients With CTNNB1 Mutations

Purpose

Familial exudative vitreoretinopathy (FEVR) is an inherited vitreoretinopathy. This study aimed to analyze the ocular phenotypes and systemic features of patients with CTNNB1 mutations.

Methods

Whole exome sequencing was performed in the probands, and Sanger sequencing was used to verify the mutations and perform segregation analysis in the available family members. A luciferase assay was used to assess the effect of the mutant β-catenin on transcription. Comprehensive ocular examinations were performed on the probands and family members. Systemic features were evaluated and followed up.

Results

A total of 763 FEVR families were enrolled. Seven different CTNNB1 mutations, including 5 novels and 2 known mutations, were detected in 8 families, accounting for 1.05% of all FEVR families. Compared to wild-type CTNNB1, the CTNNB1 mutants failed to induce luciferase reporter activity in SuperTopFlash (STF) cells. Among the 16 eyes of the 8 probands, 2 (12.5%) eyes were classified as stage 2 FEVR, 8 (50.0%) as stage 4, and 6 (37.5%) as stage 5. All the patients had varying degrees of systemic abnormalities and presented with motor, speech, and developmental delays over time. Among the eight families with CTNNB1 mutations, seven were de novo mutations, and one proband inherited the mutation from his asymptomatic mother.

Conclusions

This study provides detailed descriptions of the ocular phenotypes of patients with CTNNB1 mutations that presented as severe FEVR, and accompanied with other systemic abnormalities. Five novel mutations identified in this study, expanded the mutation spectrum of CTNNB1-associated FEVR.

Novel truncating variants in CTNNB1 cause familial exudative vitreoretinopathy

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is an inheritable blinding disorder with clinical and genetic heterogeneity. Heterozygous variants in the CTNNB1 gene have been reported to cause FEVR. However, the pathogenic basis of CTNNB1-associated FEVR has not been fully explored.

METHODS

Whole-exome sequencing was performed on the genomic DNA of probands. Dual-luciferase reporter assay, western blotting and co-immunoprecipitation were used to characterise the impacts of variants. Quantitative real-time PCR, EdU (5-ethynyl-2'-deoxyuridine) incorporation assay and immunocytochemistry were performed on the primary human retinal microvascular endothelial cells (HRECs) to investigate the effect of CTNNB1 depletion on the downstream genes involved in Norrin/β-catenin signalling, cell proliferation and junctional integrity, respectively. Transendothelial electrical resistance assay was applied to measure endothelial permeability. Heterozygous endothelial-specific Ctnnb1-knockout mouse mice were generated to verify FEVR-like phenotypes in the retina.

RESULTS

We identified two novel heterozygous variants (p.Leu103Ter and p.Val199LeufsTer11) and one previously reported heterozygous variant (p.His369ThrfsTer2) in the CTNNB1 gene. These variants caused truncation and degradation of β-catenin that reduced Norrin/β-catenin signalling activity. Additionally, knockdown (KD) of CTNNB1 in HRECs led to diminished mRNA levels of Norrin/β-catenin targeted genes, reduced cell proliferation and compromised junctional integrity. The Cre-mediated heterozygous deletion of Ctnnb1 in mouse endothelial cells (ECs) resulted in FEVR-like phenotypes. Moreover, LiCl treatment partially rescued the defects in CTNNB1-KD HRECs and EC-specific Ctnnb1 heterozygous knockout mice.

CONCLUSION

Our findings reinforced the current pathogenesis of Norrin/β-catenin for FEVR and expanded the causative variant spectrum of CTNNB1 for the prenatal diagnosis and genetic counselling of FEVR.

Kinesin-5 Eg5 is essential for spindle assembly, chromosome stability and organogenesis in development

Chromosome stability relies on bipolar spindle assembly and faithful chromosome segregation during cell division. Kinesin-5 Eg5 is a plus-end-directed kinesin motor protein, which is essential for spindle pole separation and chromosome alignment in mitosis. Heterozygous Eg5 mutations cause autosomal-dominant microcephaly, primary lymphedema, and chorioretinal dysplasia syndrome in humans. However, the developmental roles and cellular mechanisms of Eg5 in organogenesis remain largely unknown. In this study, we have shown that Eg5 inhibition leads to the formation of the monopolar spindle, chromosome misalignment, polyploidy, and subsequent apoptosis. Strikingly, long-term inhibition of Eg5 stimulates the immune responses and the accumulation of lymphocytes in the mouse spleen through the innate and specific immunity pathways. Eg5 inhibition results in metaphase arrest and cell growth inhibition, and suppresses the formation of somite and retinal development in zebrafish embryos. Our data have revealed the essential roles of kinesin-5 Eg5 involved in cell proliferation, chromosome stability, and organogenesis during development. Our findings shed a light on the cellular basis and pathogenesis in microcephaly, primary lymphedema, and chorioretinal dysplasia syndrome of Eg5-mutation-positive patients.

Decrease of FZD4 exon 1 methylation in probands from FZD4-associated FEVR family of phenotypic heterogeneity

Familial exudative vitreoretinopathy (FEVR) is an important cause of childhood blindness and is clinically characterized by phenotypic heterogeneity. FEVR patients harboring the same genetic mutation vary widely in disease severity. The purpose of this study was to explore non-genetic factors that regulate FEVR phenotypic heterogeneity. We detected methylation levels of 21 CpG sites located at the FZD4 exon 1 region of 11 probands, 12 asymptomatic/paucisymptomatic carriers and 11 non-carriers from 10 unrelated FZD4-associated FEVR families using bisulfite amplicon sequencing (BSAS). Our results showed reduced methylation level of FZD4 exon 1 in probands, suggesting that FZD4 exon 1 methylation level may be negatively linked with FEVR disease severity. It provided a new research direction for follow-up research, helping us better understand the complexity of the FEVR-causing mechanism.

Severe Familial Exudative Vitreoretinopathy, Congenital Hearing Loss, and Developmental Delay in a Child With Biallelic Variants in FZD4

Question

Are FZD4 variants associated with familial exudative vitreoretinopathy (FEVR) with extraocular features?

Findings

This case series included a patient with biallelic FZD4 variants with severe FEVR in infancy, congenital hearing loss, and developmental delay. Each parent was carrying 1 of the alleles and manifested mild FEVR; cell-based FZD4 receptor-activation assays determined that FZD4 function was dramatically decreased in the presence of these compound heterozygous variants.

Meaning

Biallelic variants in FZD4 can result in a severe ocular phenotype with systemic features, which may represent a novel syndrome.

Importance

Familial exudative vitreoretinopathy (FEVR) is a nonsyndromic autosomal dominant retinal disorder commonly caused by variants in the FZD4 gene. This study investigates the potential role beyond ocular abnormalities for FZD4 gene variants in patients with FEVR.

Objective

To evaluate the role of FZD4 in symptoms beyond those associated with FEVR through a patient with biallelic variants in FZD4.

Design, Setting, and Participants

This case series included the DNA testing and phenotyping of 1 patient proband and her parents, combined with signaling assays, to determine the association of patient-derived compound heterozygous variants on FZD4 signaling and biologic function.

Main Outcomes and Measures

FZD4 genes were tested using next-generation sequencing and Sanger sequencing. Cell-based assays measured the effect of the variants on FZD4 signaling.

Results

The proband presented with absent red reflexes from complete tractional retinal detachments diagnosed at 3 days of age and failed the newborn screening hearing test. Auditory brainstem response at 6 months of age showed bilateral mild to moderate high-frequency sensorineural hearing loss. The patient manifested developmental delays in speech and walking. Intravenous fluorescein angiography (IVFA) of the patient’s parents detected stage 1 FEVR. Genetic testing revealed 2 FZD4 variants in the patient, each variant found in 1 parent. Signaling assays confirmed that the presence of both variants was associated with significantly worse signaling activity compared with the heterozygous state.

Conclusions and Relevance

Results of this case series suggest that extraocular syndromic FEVR was associated with FZD4 variants. The decrease in FZD4 signaling owing to the biallelic nature of the disease resulted in hearing deficits, developmental delays, and a more severe retinal phenotype.

SZN-413, a FZD4 Agonist, as a Potential Novel Therapeutic for the Treatment of Diabetic Retinopathy

Purpose

There remains a high unmet need for therapies with new mechanisms of action to achieve reperfusion of ischemic retina in diabetic retinopathy. We examined whether a novel frizzled class receptor 4 (FZD4) agonist could promote regeneration of functional blood vessels in animal models of retinopathy.

Methods

We developed a novel Norrin mimetic (SZN-413-p) targeting FZD4 and low-density lipoprotein receptor-related protein 5 (LRP5) and examined its effect on retinal and brain endothelial cells in vitro. SZN-413-p was subsequently humanized, resulting in the therapeutic candidate SZN-413, and was examined in animal models of retinopathy. In an oxygen-induced retinopathy mouse model, avascular and neovascularization areas were measured. Furthermore, in a vascular endothelial growth factor (VEGF)-induced retinal vascular leakage rabbit model, the impact on vascular leakage by SZN-413 was examined by measuring fluorescein leakage.

Results

SZN-413-p induced Wnt/β-catenin signaling and upregulated blood-brain barrier/blood-retina barrier gene expressions in endothelial cells. In the oxygen-induced retinopathy mouse model, SZN-413-p and SZN-413 significantly reduced the neovascularization area size (P < 0.001) to a level comparable to, or better than the positive control aflibercept. Both agonists also showed a reduction in avascular area size compared to vehicle (P < 0.001) and aflibercept groups (P < 0.05 and P < 0.01 for SZN-413-p and SZN-413, respectively). In the VEGF-induced retinal vascular leakage rabbit model, SZN-413 reduced retinal vascular leakage by ∼80%, compared to the vehicle-treated group (P < 0.01).

Conclusions

Reduction of neovascular tufts and avascular areas and of VEGF-driven retinal vascular leakage suggests that SZN-413 can simultaneously address retinal non-perfusion and vascular leakage.

Translational Relevance

FZD4 signaling modulation by SZN-413 is a novel mechanism of action that can offer a new therapeutic strategy for diabetic retinopathy.

Mutation spectrum in a cohort with familial exudative vitreoretinopathy

Purpose

To expand the mutation spectrum of patients with familial exudative vitreoretinopathy (FEVR) disease.

Participants

74 probands (53 families and 21 sporadic probands) with familial exudative vitreoretinopathy (FEVR) disease and their available family members (n = 188) were recruited for sequencing.

Methods

Panel‐based targeted screening was performed on all subjects. Before sanger sequencing, variants of LRP5, NDP, FZD4, TSPAN12, ZNF408, KIF11, RCBTB1, JAG1, and CTNNA1 genes were verified by a series of bioinformatics tools and genotype–phenotype co‐segregation analysis.

Results

40.54% (30/74) of the probands were sighted to possess at least one etiological mutation of the nine FEVR‐causative genes. The etiological mutation detection rate was 37.74% (20/53) in family‐attainable probands while 47.62% (10/21) in sporadic cases. The diagnosis rate of patients in the early‐onset subgroup (≤5 years old, 45.4%) is higher than that of the children or adolescence‐onset subgroup (6–16 years old, 42.1%) and the late‐onset subgroup (≥17 years old, 39.4%). A total of 36 etiological mutations were identified in this study, comprising 26 novel mutations and 10 reported mutations. LRP5 was the most prevalent mutant gene among the 36 mutation types with a percentage of 41.67% (15/36). Followed by FZD4 (10/36, 27.78%), TSPAN12 (5/36, 13.89%), NDP (4/36, 11.11%), KIF11 (1/36, 2.78%), and RCBTB1 (1/36, 2.78%). Among these mutations, 63.89% (23/36) were missense mutations, 25.00% (9/36) were frameshift mutations, 5.56% (2/36) were splicing mutations, 5.56% (2/36) were nonsense mutations. Moreover, the clinical pathogenicity of these variants was defined according to American College of Medical Genetics (ACMG) and genomics guidelines: 41.67% (15/36) were likely pathogenic variants, 27.78% (10/36) pathogenic variants, 30.55% (11/36) variants of uncertain significance. No etiological mutations discovered in the ZNF408, JAG1, and CTNNA1 genes in this FEVR cohort.

Conclusions

We systematically screened nine FEVR disease‐associated genes in a cohort of 74 Chinese probands with FEVR disease. With a detection rate of 40.54%, 36 etiological mutations of six genes were authenticated in 30 probands, including 26 novel mutations and 10 reported mutations. The most prevalent mutated gene is LRP5, followed by FZD4, TSPAN12, NDP, KIF11, and RCBTB1. In total, a de novo mutation was confirmed. Our study significantly clarified the mutation spectrum of variants bounded up to FEVR disease.

Developmental regulation of barrier- and non-barrier blood vessels in the CNS

The blood-brain barrier (BBB) is essential for creating and maintaining tissue homeostasis in the central nervous system (CNS), which is key for proper neuronal function. In most vertebrates, the BBB is localized to microvascular endothelial cells that acquire barrier properties during angiogenesis of the neuroectoderm. Complex and continuous tight junctions, and the lack of fenestrae combined with low pinocytotic activity render the BBB endothelium a tight barrier for water-soluble molecules that may only enter the CNS via specific transporters. The differentiation of these unique endothelial properties during embryonic development is initiated by endothelial-specific flavours of the Wnt/β-catenin pathway in a precise spatiotemporal manner. In this review, we summarize the currently known cellular (neural precursor and endothelial cells) and molecular (VEGF and Wnt/β-catenin) mechanisms mediating brain angiogenesis and barrier formation. Moreover, we introduce more recently discovered crosstalk with cellular and acellular elements within the developing CNS such as the extracellular matrix. We discuss recent insights into the downstream molecular mechanisms of Wnt/β-catenin in particular, the recently identified target genes like Foxf2, Foxl2, Foxq1, Lef1, Ppard, Zfp551, Zic3, Sox17, Apcdd1 and Fgfbp1 that are involved in refining and maintaining barrier characteristics in the mature BBB endothelium. Additionally, we elute to recent insight into barrier heterogeneity and differential endothelial barrier properties within the CNS, focussing on the circumventricular organs as well as on the neurogenic niches in the subventricular zone and the hippocampus. Finally, open questions and future BBB research directions are highlighted in the context of taking benefit from understanding BBB development for strategies to modulate BBB function under pathological conditions.

CTNND1 variants cause familial exudative vitreoretinopathy through Wnt/Cadherin axis

Familial exudative vitreoretinopathy (FEVR) is a hereditary disorder that can cause vision loss. The CTNND1 gene encodes a cellular adhesion protein p120-catenin (p120), which is essential for vascularization, yet the function of p120 in postnatal physiological angiogenesis remains unclear. Here, we applied whole-exome sequencing (WES) on 140 probands of FEVR families and identified three candidate variants in the human CTNND1 gene. We performed inducible deletion of Ctnnd1 in the postnatal mouse endothelial cells (ECs) and observed typical phenotypes of FEVR. Immunofluorescence of retina flat mounts also revealed immune responses, including reactive astrogliosis and microgliosis accompanied by abnormal Vegfa expression. Using an unbiased proteomics analysis in combination with in vivo or in vitro approaches, we propose that p120 is critical for the integrity of cadherin/catenin complex, and that p120 activates Wnt signaling activity by protecting β-catenin from Gsk3β-ubiquitin-guided degradation. Treatment of CTNND1-depleted HRECs with Gsk3β inhibitors LiCl or CHIR-99021 successfully enhanced cell proliferation by preventing β-catenin from degradation. Moreover, LiCl treatment increased vessel density in Ctnnd1-deficient mouse retinas. Functional analysis also revealed that variants in CTNND1 cause FEVR by compromising the expression of adherens junctions (AJs) and Wnt signaling activity. Additionally, genetic interactions between p120 and β-catenin or α-catenin revealed by double heterozygous deletion in mice further confirmed that p120 regulates vascular development through the Wnt/Cadherin axis. Together, we propose that CTNND1 is a novel candidate gene associated with FEVR, and that variants in CTNND1 can cause FEVR through the Wnt/Cadherin axis.

Heterozygote loss-of-function variants in the LRP5 gene cause familial exudative vitreoretinopathy

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is an inherited ocular disease with clinical manifestations of aberrant retinal vasculature. We aimed to identify novel causative variants responsible for FEVR and provided evidence for the genetic counselling of FEVR.

METHODS

We applied whole-exome sequencing (WES) on the genomic DNA samples from the probands and performed Sanger sequencing for variant validation. Western blot analysis and luciferase assays were performed to test the expression levels and the activity of mutant proteins.

RESULTS

We identified one novel heterozygous nonsense variant, and three novel heterozygous frameshift variants including c.1801G>T (p.G601*), c.1965delC (p.H656Tfs*41), c.4445delC (p.S1482Cfs*17), and c.4482delC (p.P1495Rfs*4), which disabled the function of LRP5 on the Norrin/β-catenin signalling. Overexpression of variant-carrying LRP5 proteins resulted in down regulation of the protein levels of β-catenin and the Norrin/β-catenin signalling target genes c-Myc and Glut1.

CONCLUSION

Our study showed that four inherited LRP5 variants can cause autosomal dominant FEVR via down regulation of Norrin/β-catenin signalling and expanded the spectrum of FEVR-associated LRP5 variants.

FZD4 in a Large Chinese Population With Familial Exudative Vitreoretinopathy: Molecular Characteristics and Clinical Manifestations

Purpose

The purpose of this study was to establish a genotype-phenotype correlation of familial exudative vitreoretinopathy (FEVR) caused by FZD4 gene mutations.

Methods

Six hundred fifty-one probands and their family members were recruited based on a clinical diagnosis of FEVR between 2015 and 2021 at Zhongshan Ophthalmic Center. Ocular examinations were performed in all participants. Targeted gene panel sequencing and whole-exome sequencing were performed in the probands, and Sanger sequencing was used to verify the mutations and segregation analysis was performed in the family members.

Results

Fifty-one FZD4 mutations (24 novels and 27 known) were detected in 84 families. Of these 168 eyes with FEVR, the eyes at stages 1, 2, 3, 4, and 5 were 29 (17.3%), 15 (8.9%), 19 (11.3%), 55 (32.7%), and 12 (7.1%), respectively. Exact stage of 38 (22.6%) eyes could not be determined. The FEVR phenotypes were more severe in the probands than the phenotypes in the family members (P < 0.001). The families were divided into two groups, probands that inherited the variant from the mother, and probands that inherited the variant from the father. In addition, the FEVR stage differences between these two groups were different (P < 0.05). Despite the mutations being located in different domains of FZD4, no significant differences were identified among the domains in terms of FEVR staging, retinal folds, retinal detachment, temporal midperipheral vitreoretinal interface abnormality, and foveal hypoplasia.

Conclusions

The FZD4 probands had severer phenotype than the family members, and the FEVR stage difference was greater between the probands and mothers than that between the probands and fathers.

Reaching a FEVR Pitch: A Case Series of Familial Exudative Vitreoretinopathy in Northern Ireland

PURPOSE

To evaluate the heterogeneity of both the clinical features and genetics of familial exudative vitreoretinopathy (FEVR) in a Northern Irish population.

METHODS

A retrospective trawl of a secure pediatric database was completed, as well as communication with all Northern Ireland ophthalmologists to identify adult cases. Cases were cross-referenced with a regional genetics database. Data on patient demographics, clinical findings, genetic testing, and patient treatment were collected.

RESULTS

Sixteen patients were identified. Average age at presentation was 11.8 years (range: 4 months to 38 years). Earlier age at presentation was associated with more advanced disease and those presenting later had more subtle signs such as retinal tear or vitreous hemorrhage. Four types of gene mutations were identified in 7 patients (NDP, TSPAN12, FZD4, and KIF11). Thirteen patients had complications associated with FEVR and associated systemic conditions were found in 5 patients. Twelve eyes received active treatment to control disease.

CONCLUSIONS

FEVR is a sight-threatening disease affecting prenatal retinal angiogenesis with a spectrum of disease and diverse genetic basis. Clinicians should look for signs of systemic and other ophthalmic sequelae in patients with FEVR because this could point to a genetic cause. Vigilance should also be exercised in older patients with unexplained vitreous hemorrhage or retinal tear with consideration of widefield angiography if FEVR is suspected. [J Pediatr Ophthalmol Strabismus. 2022;59(2):102-109.].

LMBR1L regulates proliferation and migration of endothelial cells through Norrin/β-catenin signaling

Precise Norrin/β-catenin signaling is critical for proper angiogenesis. Dysregulation of the signaling leads various diseases, of which retinal exudative vitreoretinopathy is the most prevalent. Here, we used global knockout mouse model to show that endothelial cells-derived limb region 1 like (LMBR1L), a transmembrane protein of unknown function in angiogenesis, is essential for retinal vascular development. In vitro experiments revealed that LMBR1L depletion resulted in aberrant activation of Norrin/β-catenin signaling pathway via decreased ubiquitination of FZD4, increased Norrin co-receptor LRP5 and p-GSK3β-Ser9 expression level, which caused accumulation of β-catenin. Moreover, inhibition of LMBR1L in human retinal microvascular endothelial cells (HRECs) caused increased proliferation ability and defective cell migration, which might due to upregulated expression levels of the AJ components. Treatment of p-GSK3β-Ser9 inhibitor AR-A014418 restored the phenotypes in LMBR1L-null HRECs, which further demonstrated the important regulatory role of LMBR1L in Norrin/β-catenin signaling pathway. Taken together, our data unravels an essential role of LMBR1L in angiogenesis.

The timing of auditory sensory deficits in Norrie disease has implications for therapeutic intervention

Norrie disease is caused by mutation of the NDP gene, presenting as congenital blindness followed by later onset of hearing loss. Protecting patients from hearing loss is critical for maintaining their quality of life. This study aimed to understand the onset of pathology in cochlear structure and function. By investigating patients and juvenile Ndp-mutant mice, we elucidated the sequence of onset of physiological changes (in auditory brainstem responses, distortion product otoacoustic emissions, endocochlear potential, blood-labyrinth barrier integrity) and determined the cellular, histological, and ultrastructural events leading to hearing loss. We found that cochlear vascular pathology occurs earlier than previously reported and precedes sensorineural hearing loss. The work defines a disease mechanism whereby early malformation of the cochlear microvasculature precedes loss of vessel integrity and decline of endocochlear potential, leading to hearing loss and hair cell death while sparing spiral ganglion cells. This provides essential information on events defining the optimal therapeutic window and indicates that early intervention is needed. In an era of advancing gene therapy and small-molecule technologies, this study establishes Ndp-mutant mice as a platform to test such interventions and has important implications for understanding the progression of hearing loss in Norrie disease.

Unlocking the Wnt pathway: Therapeutic potential of selective targeting FZD7 in cancer

The Wnt signaling is of paramount pathophysiological importance. Despite showing promising anticancer activities in pre-clinical studies, current Wnt pathway inhibitors face complications in clinical trials resulting from on-target toxicity. Hence, the targeting of pathway component(s) that are essential for cancer but dispensable for normal physiology is key to the development of a safe Wnt signaling inhibitor. Frizzled₇ (FZD₇) is a Wnt pathway receptor that is redundant in healthy tissues but crucial in various cancers. FZD₇ modulates diverse aspects of carcinogenesis, including cancer growth, metastasis, maintenance of cancer stem cells, and chemoresistance. In this review, we describe state-of-the-art knowledge of the functions of FZD₇ in carcinogenesis and adult tissue homeostasis. Next, we overview the development of small molecules and biomolecules that target FZD₇. Finally, we discuss challenges and possibilities in developing FZD₇-selective antagonists.

Wnt Signaling in Inner Blood-Retinal Barrier Maintenance

The retina is a light-sensing ocular tissue that sends information to the brain to enable vision. The blood-retinal barrier (BRB) contributes to maintaining homeostasis in the retinal microenvironment by selectively regulating flux of molecules between systemic circulation and the retina. Maintaining such physiological balance is fundamental to visual function by facilitating the delivery of nutrients and oxygen and for protection from blood-borne toxins. The inner BRB (iBRB), composed mostly of inner retinal vasculature, controls substance exchange mainly via transportation processes between (paracellular) and through (transcellular) the retinal microvascular endothelium. Disruption of iBRB, characterized by retinal edema, is observed in many eye diseases and disturbs the physiological quiescence in the retina's extracellular space, resulting in vision loss. Consequently, understanding the mechanisms of iBRB formation, maintenance, and breakdown is pivotal to discovering potential targets to restore function to compromised physiological barriers. These unraveled targets can also inform potential drug delivery strategies across the BRB and the blood-brain barrier into retinas and brain tissues, respectively. This review summarizes mechanistic insights into the development and maintenance of iBRB in health and disease, with a specific focus on the Wnt signaling pathway and its regulatory role in both paracellular and transcellular transport across the retinal vascular endothelium.

Catenin α 1 mutations cause familial exudative vitreoretinopathy by overactivating Norrin/β-catenin signaling

Familial exudative vitreoretinopathy (FEVR) is a severe retinal vascular disease that causes blindness. FEVR has been linked to mutations in several genes associated with inactivation of the Norrin/β-catenin signaling pathway, but these account for only approximately 50% of cases. We report that mutations in α-catenin (CTNNA1) cause FEVR by overactivating the β-catenin pathway and disrupting cell adherens junctions. We identified 3 heterozygous mutations in CTNNA1 (p.F72S, p.R376Cfs*27, and p.P893L) by exome sequencing and further demonstrated that FEVR-associated mutations led to overactivation of Norrin/β-catenin signaling as a result of impaired protein interactions within the cadherin-catenin complex. The clinical features of FEVR were reproduced in mice lacking Ctnna1 in vascular endothelial cells (ECs) or with overactivated β-catenin signaling by an EC-specific gain-of-function allele of Ctnnb1. In isolated mouse lung ECs, both CTNNA1-P893L and F72S mutants failed to rescue either the disrupted F-actin arrangement or the VE-cadherin and CTNNB1 distribution. Moreover, we discovered that compound heterozygous Ctnna1 F72S and a deletion allele could cause a similar phenotype. Furthermore, in a FEVR family, we identified a mutation of LRP5, which activates Norrin/β-catenin signaling, and the corresponding knockin mice exhibited a partial FEVR-like phenotype. Our study demonstrates that the precise regulation of β-catenin activation is critical for retinal vascular development and provides new insights into the pathogenesis of FEVR.

Novel mutation in TSPAN12 associated with familial exudative vitreoretinopathy in a Chinese pedigree

BACKGROUND

Familial exudative vitreoretinopathy (FEVR) is a rare retinal disorder characterised by incomplete retinal vascular development. Symptoms vary widely from none to blindness even within the same family. Multiple genes related to the Wnt pathway have been found to be associated with FEVR. Recent studies identified tetraspanin 12 (TSPAN12) as a cause of the autosomal dominant inheritance form of FEVR. Here, we describe a novel TSPAN12 mutation in a Chinese family with FEVR.

METHODS

Targeted next-generation sequencing was performed on the proband to define the TSPAN12 mutation. Sanger sequencing was used to confirm the mutation in five family members (I-1, II-2, II-3, II-4, and III-3) in a three-generation FEVR pedigree. Ophthalmologic examinations and diagnostic imaging related to FEVR were performed.

RESULTS

The proband (II-3) was a 32-year-old man with early-stage peripheral retinal vascular anomalies, but no visual acuity problems. DNA sequencing identified a heterozygous missense mutation (c.241 G > A: p.Gly81Arg) in TSPAN12 in the proband. The mutation was in a highly conserved region and was predicted to affect the normal protein structure. The patient's father and daughter were also diagnosed with FEVR and carried the same mutation, with varying degrees of manifestations. Other family members had good vision and normal eye examinations with negative genetic testing.

CONCLUSIONS

We identified a novel missense mutation in TSPAN12 associated with autosomal dominant FEVR. These results will facilitate the diagnosis, prognosis, and genetic counselling for this disease. Further studies are needed to identify the mechanisms underlying clinical variations among individuals in the family.

Whole exome sequencing in patients with Williams-Beuren syndrome followed by disease modeling in mice points to four novel pathways that may modify stenosis risk

Supravalvular aortic stenosis (SVAS) is a narrowing of the aorta caused by elastin (ELN) haploinsufficiency. SVAS severity varies among patients with Williams-Beuren syndrome (WBS), a rare disorder that removes one copy of ELN and 25-27 other genes. Twenty percent of children with WBS require one or more invasive and often risky procedures to correct the defect while 30% have no appreciable stenosis, despite sharing the same basic genetic lesion. There is no known medical therapy. Consequently, identifying genes that modify SVAS offers the potential for novel modifier-based therapeutics. To improve statistical power in our rare-disease cohort (N = 104 exomes), we utilized extreme-phenotype cohorting, functional variant filtration and pathway-based analysis. Gene set enrichment analysis of exome-wide association data identified increased adaptive immune system variant burden among genes associated with SVAS severity. Additional enrichment, using only potentially pathogenic variants known to differ in frequency between the extreme phenotype subsets, identified significant association of SVAS severity with not only immune pathway genes, but also genes involved with the extracellular matrix, G protein-coupled receptor signaling and lipid metabolism using both SKAT-O and RQTest. Complementary studies in Eln+/-; Rag1-/- mice, which lack a functional adaptive immune system, showed improvement in cardiovascular features of ELN insufficiency. Similarly, studies in mixed background Eln+/- mice confirmed that variations in genes that increase elastic fiber deposition also had positive impact on aortic caliber. By using tools to improve statistical power in combination with orthogonal analyses in mice, we detected four main pathways that contribute to SVAS risk.

Circular RNAs in metabolism and metabolic disorders

Metabolic syndrome (MetS) is a serious health condition triggered by hyperglycemia, dyslipidemia, and abnormal adipose deposition. Recently, circular RNAs (circRNAs) have been proposed as key molecular players in metabolic homeostasis due to their regulatory effects on genes linked to the modulation of multiple aspects of metabolism, including glucose and lipid homeostasis. Dysregulation of circRNAs can lead to metabolic disorders, indicating that circRNAs represent plausible potential targets to alleviate metabolic abnormalities. More recently, a series of circulating circRNAs have been identified to act as both essential regulatory molecules and biomarkers for the progression of metabolism-related disorders, including type 2 diabetes mellitus (T2DM or T2D) and cardiovascular disease (CVD). The findings of this study highlight the function of circRNAs in signaling pathways implicated in metabolic diseases and their potential as future therapeutics and disease biomarkers.

Whole-Gene Deletions of FZD4 Cause Familial Exudative Vitreoretinopathy

Familial exudative vitreoretinopathy (FEVR) is an inherited disorder characterized by abnormalities in the retinal vasculature. The FZD4 gene is associated with FEVR, but the prevalence and impact of FZD4 copy number variation (CNV) on FEVR patients are unknown. The aim of this study was to better understand the genetic features and clinical manifestations of patients with FZD4 CNVs. A total of 651 FEVR families were recruited. Families negative for mutations in FEVR-associated genes were selected for CNV analysis using SeqCNV. Semiquantitative multiplex polymerase chain reaction and multiplex ligation-dependent probe amplification were conducted to verify the CNVs. Four probands were found to carry whole-gene deletions of FZD4, accounting for 5% (4/80) of probands with FZD4 mutations and 0.6% (4/651) of all FEVR probands. The four probands exhibited similar phenotypes of unilateral retinal folds. FEVR in probands with CNVs was not more severe than in probands with FZD4 missense mutations (p = 1.000). Although this is the first report of FZD4 CNVs and the associated phenotypes, the interpretation of FZD4 CNVs should be emphasized when analyzing the next-generation sequencing data of FEVR patients because of their high prevalence.

Whole-Exome Sequencing Reveals Novel TSPAN12 Variants in Autosomal Dominant Familial Exudative Vitreoretinopathy

Background: Familial exudative vitreoretinopathy (FEVR), a group of rare inherited retinal vascular disorders, is the major cause of vision loss in juveniles. At present, the diagnosis of FEVR remains difficult due to its clinical and genetic heterogeneities. Aims: To identify the causative genetic variants in two unrelated FEVR-affected families: one Indian family and one Chinese Han family. Materials and Methods: Five affected patients from two families were recruited for this study. Whole-exome sequencing was applied to the probands, and Sanger sequencing was performed for validation. Stringent whole-exome sequence data analyses were performed to evaluate all of the identified pathogenic variants. Results: Two novel variants in the TSPAN12 gene, were identified: a missense variant c.437 T > G (p.Leu146Arg); and a nonsense variant c.477 C > A (p.Cys159*). Both variants cosegregated with the disease in the investigated FEVR-affected families. Additionally, both variants inactivated the ability of TSPAN12 protein to enhance Norrin/β-catenin signaling. Conclusion: This study expands the mutational spectrum of TSPAN12 for FEVR.

Circular RNAs: Novel target of diabetic retinopathy

In diabetic patients, diabetic retinopathy (DR) is the leading cause of blindness and seriously affects the quality of life. However, current treatment methods of DR are not satisfactory. Advances have been made in understanding abnormal protein interactions and signaling pathways in DR pathology, but little is known about epigenetic regulation. Non-coding RNAs, such as circular RNAs (circRNAs), have been shown to be associated with DR. In this review, we summarized the function of circRNAs and indicated their roles in the pathogenesis of DR, which may provide new therapeutic targets for clinical treatment.

Retinal Features of Family Members With Familial Exudative Vitreoretinopathy Caused By Mutations in KIF11 Gene

Purpose

To determine the clinical characteristics of patients and family members with familial exudative vitreoretinopathy (FEVR) caused by mutations in the KIF11 gene.

Methods

Twenty-one patients from 10 FEVR families with mutations in the KIF11 gene were studied. The retinal and systemic features were examined. The genetic analyses performed included Sanger sequencing of the KIF11 gene, whole exome sequencing, as well as array comparative genomic hybridization (CGH) analysis and multiple ligation probe assay (MLPA).

Results

Sequence analysis revealed seven different KIF11 mutations. Array CGH with MLPA revealed two different exon deletions. All probands had advanced FEVR with retinal detachments (RDs) and microcephaly with or without developmental disabilities. Patients with bilateral RDs were more frequently associated with developmental disabilities (P = 0.023). Multimodal imaging of the family members revealed that six of nine patients without RDs (66%) had varying degrees of chorioretinopathy. The retinal folds in FEVR patients were associated with severe retinal avascularization. However, funduscopic changes in the peripheral retina were unremarkable in family members without RDs. A score representing the peripheral vascular anomalies determined from the fluorescein angiograms was lower than that of control eyes of patients with mutations of the Wnt signaling genes (P = 0.0029).

Conclusions

The probands with KIF11 mutations were associated with severe ocular and systemic pathologies, whereas affected family members showed highly variable clinical manifestations. Peripheral vascular anomalies can often be unremarkable in eyes without RDs.

Translational Relevance

These findings highlight more diverse mechanisms that underlie the pathological changes in patients with FEVR.

Planar cell polarity (PCP) proteins support spermatogenesis through cytoskeletal organization in the testis

Few reports are found in the literature regarding the role of planar cell polarity (PCP) in supporting spermatogenesis in the testis. Yet morphological studies reported decades earlier have illustrated the directional alignment of polarized developing spermatids, most notably step 17-19 spermatids in stage V-early VIII tubules in the testis, across the plane of the epithelium in seminiferous tubules of adult rats. Such morphological features have unequivocally demonstrated the presence of PCP in developing spermatids, analogous to the PCP noted in hair cells of the cochlea in mammals. Emerging evidence in recent years has shown that Sertoli and germ cells express numerous PCP proteins, mostly notably, the core PCP proteins, PCP effectors and PCP signaling proteins. In this review, we discuss recent findings in the field regarding the two core PCP protein complexes, namely the Van Gogh-like 2 (Vangl2)/Prickle (Pk) complex and the Frizzled (Fzd)/Dishevelled (Dvl) complex. These findings have illustrated that these PCP proteins exert their regulatory role to support spermatogenesis through changes in the organization of actin and microtubule (MT) cytoskeletons in Sertoli cells. For instance, these PCP proteins confer PCP to developing spermatids. As such, developing haploid spermatids can be aligned and orderly packed within the limited space of the seminiferous tubules in the testes for the production of sperm via spermatogenesis. Thus, each adult male in the mouse, rat or human can produce an upward of 30, 50 or 300 million spermatozoa on a daily basis, respectively, throughout the adulthood. We also highlight critical areas of research that deserve attention in future studies. We also provide a hypothetical model by which PCP proteins support spermatogenesis based on recent studies in the testis. It is conceivable that the hypothetical model shown here will be updated as more data become available in future years, but this information can serve as the framework by investigators to unravel the role of PCP in spermatogenesis.

Evaluation of the Foveal Avascular Zone in Familial Exudative Vitreoretinopathy Using Optical Coherence Tomography Angiography

Purpose

To evaluate the foveal avascular zone (FAZ) and retinal structure in familial exudative vitreoretinopathy (FEVR).

Patients and Methods

Eighteen eyes with stage 1 or 2 FEVR and 20 control eyes were evaluated. The central retinal thickness (CRT), foveal inner retinal thickness (IRT), surface retinal vessel density (SRVD), and deep retinal vessel density (DRVD) were measured using optical coherence tomography. The FAZ area was calculated using ImageJ software. The equivalent spherical value (SE) and axial length (AL) were measured.

Results

The CRT (232.5±3.086 vs 211±12.6325 μm; p=0.003) and foveal IRT (15.83±13.95 vs 0.9±4.02 μm; p=0.002) were thicker in the FEVR group than in the control group. The surface FAZ area (0.265±0.08 vs 0.364±0.09 mm²; p=0.004) and the deep FAZ area (0.364±0.1 vs 0.484±0.11 mm²; p=0.03) were smaller in the FEVR group than in the control group. The SRVD values did not differ among the sectors, but the DRVD was higher in the FEVR group except for the inferior sector (superior, p=0.027; inferior, p=0.88; temporal, p=0.035; nasal, p=0.027). The SE and AL did not differ between the two groups. There were no correlations between the surface and deep layer FAZ area and age, CRT, SE, and AL. The surface, deep FAZ area, and foveal IRT were correlated negatively (surface, r = -0.47, p=0.033; deep layer FAZ area, r = -0.46, p=0.037).

Conclusion

Eyes with FEVR have a smaller FAZ because the vascular structure in the inner retina remained in the fovea.

Whole-Exome Sequencing Identified DLG1 as a Candidate Gene for Familial Exudative Vitreoretinopathy

Purpose: Familial exudative vitreoretinopathy (FEVR) is a blinding retinal vascular disease. Clinically, FEVR is characterized by incomplete vascularization of the peripheral retina and pathological neovascularization. Only about 50% of FEVR cases can be explained by known FEVR disease gene variations. This study aimed to identify novel genes associated with the FEVR phenotype and explore their pathogenic mechanisms. Materials and Methods: Exome sequencing analyses were conducted on one Chinese family with FEVR whose affected members did not exhibit pathogenic variants in the known FEVR genes (verified using Sanger sequencing analysis). Functions of the affected proteins were evaluated using reporter assays. Western blot analysis was used to detect mutant protein expression and the genes' pathogenic mechanisms. Results: A rare novel heterozygous variant in DLG1 (c.1792A>G; p.S598G) was identified. The amino acid residues surrounding the identified variant are highly conserved among vertebrates. A luciferase reporter assay revealed that the mutant DLG1 protein DLG1-S598G lost its ability to activate Wnt signaling. Moreover, a knockdown (KD) of DLG1 in human primary retinal endothelial cells impaired tube formation. Mechanistically, DLG1 KD led to a reduction in phosphorylated VEGFR2, an essential receptor for the angiogenic potency that signals the vascular endothelial growth factor molecule. Conclusions: The data reported here demonstrate that DLG1 is a novel candidate gene for FEVR.

β-catenin in adrenal zonation and disease

The Wnt signaling pathway is a critical mediator of the development and maintenance of several tissues. The adrenal cortex is highly dependent upon Wnt/β-catenin signaling for proper zonation and endocrine function. Adrenocortical cells emerge in the peripheral capsule and subcapsular cortex of the gland as progenitor cells that centripetally differentiate into steroid hormone-producing cells of three functionally distinct concentric zones that respond robustly to various endocrine stimuli. Wnt/β-catenin signaling mediates adrenocortical progenitor cell fate and tissue renewal to maintain the gland throughout life. Aberrant Wnt/β-catenin signaling contributes to various adrenal disorders of steroid production and growth that range from hypofunction and hypoplasia to hyperfunction, hyperplasia, benign adrenocortical adenomas, and malignant adrenocortical carcinomas. Great strides have been made in defining the molecular underpinnings of adrenocortical homeostasis and disease, including the interplay between the capsule and cortex, critical components involved in maintaining the adrenocortical Wnt/β-catenin signaling gradient, and new targets in adrenal cancer. This review seeks to examine these and other recent advancements in understanding adrenocortical Wnt/β-catenin signaling and how this knowledge can inform therapeutic options for adrenal disease.

Novel Norrie disease gene mutations in Chinese patients with familial exudative vitreoretinopathy

Purpose

This study aims to analyze the Norrie disease gene (NDP) variants in patients with familial exudative vitreoretinopathy (FEVR) and their clinical features.

Methods

Thirty-three Chinese patients (22 familial and 11 simplex) who were diagnosed as FEVR underwent detailed ocular examinations in Beijing Tongren Hospital. Peripheral venous blood was drawn from the patients and their family members for the extraction of genomic DNA. All exons of NDP gene were analyzed by direct sequencing of PCR-amplified DNA fragments.

Results

Four novel mutations in NDP gene were identified in four X-linked FEVR families: a C → T transversion, c. 625C → T, in exon 3, resulting in a serine-to-proline change in codon 73 (S73P); a C → G transition, c. 751C → G, in exon 3, resulting in an arginine-to-glycine change in codon 115 (R115G); a T → C transversion of nucleotide 331 at 5’UTR in exon 2 (c.331 T → C); and a C → T transversion of the nucleotide 5 in intron 1 (IVS1 + 5C → T). The mutations were not present in the control group (n = 100).

Conclusions

Our results extend the spectrum of NDP gene mutations. The mutations in the non-coding region of NDP may play a crucial role in the pathogenesis of FEVR.