Mutations and mechanisms in congenital and age-related cataracts

Association of IGF1R polymorphisms (rs1546713) with susceptibility to age-related cataract in a Han Chinese population

AIM

To explore the susceptible association between the insulin-like growth factor-1 receptor (IGF1R) single nucleotide polymorphism (SNP) and age-related cataract (ARC), and investigate the underlying mechanisms in human lens epithelium (HLE) cells.

METHODS

Totally 1190 unrelated participants, comprising 690 ARC patients and 500 healthy individuals in Han Chinese population were recruited and genotyped for target SNP. The χ ²-test was used to detect genotypic distribution between the patient and control groups and the logistic regression was performed to adjust the age and gender. Meanwhile, different biological experimental methods, such as cell counting kit 8 (CCK-8) assay, flow cytometry, quantitative real time polymerase chain reaction (Q-PCR) and Western blot, were used to detect cell viability, cell cycle progression and apoptosis in HLE cells or IGF1R knockdown HLE cells.

RESULTS

The rs1546713 in IGF1R gene was identified (P=0.046, OR: 1.606, 95%CI: 1.245-2.071), which shown a significant relevance with ARC risk under the dominant model. The results demonstrated that IGF1R knockdown inhibited cell proliferation by inducing cell cycle arrested at S phase and promoting apoptosis. Mechanistically, the cell cycle blocked at S phase was linked with the alterations of cyclin A, cyclin B, cyclin E and P21. The pro-apoptosis function of IGF1R may related with stimulating the activation of Caspase-3 and altering the expression levels of apoptotic proteins, including Bcl-2, Bax and Caspase-3.

CONCLUSION

This study first report that IGF1R polymorphisms may affect susceptibility to ARCs in Han Chinese population and provide new clues to understand the pathogenic mechanism of ARCs. Notably, IGF1R is likely a potential target for ARC prevention and treatment.

A novel missense mutation of CRYBB1 causes congenital cataract in a Chinese family

OBJECTIVE OF THE STUDY

To identify the pathogenic gene and mutation site of a Chinese family with congenital cataract.

METHODS

Eight family members and 100 controls were employed, and targeted exome sequencing was used to identify the genetically pathogenic factor of the proband.

RESULTS

Targeted next-generation sequencing identified a novel missense mutation c.209A>C (p.Q70P) of CRYBB1 gene in the family. Sanger sequencing results showed that this heterozygous mutation was a causative mutation, which was not found in unaffected family members and healthy controls. Bioinformatics predicts that the effect of this mutation on protein function is probably harmful.

CONCLUSION

We demonstrate that c.209A>C of CRYBB1 gene is a pathogenic mutation in the family of congenital nuclear cataract in this study. This is the first report that this mutation leads to congenital nuclear cataract, which broadens the mutation spectrum of CRYBB1 gene in congenital nuclear cataract.

Glucose Oxidase- and UVA-Induced Changes in the Expression Patterns of Seven De-sumoylation Enzymes (SENPs) Are Associated with Cataract Development

OBJECTIVE

It has been well established that sumoylation acts as an important regulatory mechanism that controls many different cellular processes. We and others have shown that sumoylation plays an indispensable role during mouse eye development. Whether sumoylation is implicated in ocular pathogenesis remains to be further studied. In the present study, we have examined the expression patterns of the de-sumoylation enzymes (SENPs) in the in vitro cataract models induced by glucose oxidase and UVA irradiation.

METHODS

Four-week-old C57BL/6J mice were used in our experiments. Lenses were carefully dissected out from mouse eyes and cultured in M199 medium for 12 hours. Transparent lenses (without surgical damage) were selected for experimentation. The lenses were exposed to UVA for 60 min or treated with 20 mU/mL glucose oxidase (GO) to induce cataract formation. The mRNA levels were analyzed with qRT-PCR. The protein levels were determined with western blot analysis and quantitated with Image J.

RESULTS

GO treatment and UVA irradiation can induce cataract formation in lens cultured in vitro. GO treatment significantly down-regulated the mRNA levels for SENPs from 50% to 85%; on the other hand, expression of seven SENP proteins under GO treatment appeared in 3 situations: upregulation for SENP1, 2 and 6; downregulation for SENP 5 and 8; and unchanged for SENP3 and 7. UVA irradiation upregulates the mRNAs for all seven SENPs; In contrast to the mRNA levels for 7 SENPs, the expression levels for 6 SENPs (SENP1-3, 5-6 and 8) appeared down-regulated from 10% to 50%, and only SENP7 was slightly upregulated.

CONCLUSION

Our results for the first time established the differentiation expression patterns of 7 de-sumoylation enzymes (SENPs) under treatment by GO or UVA, which provide preliminary data to link sumoylation to stress-induced cataractogenesis.

Inherited cataracts: molecular genetics, clinical features, disease mechanisms and novel therapeutic approaches

Cataract is the most common cause of blindness in the world; during infancy and early childhood, it frequently results in visual impairment. Congenital cataracts are phenotypically and genotypically heterogeneous and can occur in isolation or in association with other systemic disorders. Significant progress has been made in identifying the molecular genetic basis of cataract; 115 genes to date have been found to be associated with syndromic and non-syndromic cataract and 38 disease-causing genes have been identified to date to be associated with isolated cataract. In this review, we briefly discuss lens development and cataractogenesis, detail the variable cataract phenotypes and molecular mechanisms, including genotype-phenotype correlations, and explore future novel therapeutic avenues including cellular therapies and pharmacological treatments.

In silico analysis and high-risk pathogenic phenotype predictions of non-synonymous single nucleotide polymorphisms in human Crystallin beta A4 gene associated with congenital cataract

In order to provide a cost-effective method to narrow down the number of pathogenic Crystallin beta A4 (CRYBA4) non-synonymous single nucleotide polymorphisms (nsSNPs), we collected nsSNP information of the CRYBA4 gene from SNP databases and literature, predicting the pathogenicity and possible changes of protein properties and structures using multiple bioinformatics tools. The nsSNP data of the CRYBA4 gene were collected from 4 databases and published literature. According to 12 criteria, six bioinformatics tools were chosen to predict the pathogenicity. I-Mutant 2.0, Mupro and INPS online tools were used to analyze the effects of amino acid substitution on protein stability by calculating the value of ΔΔG. ConSurf, SOPMA, GETAREA and HOPE online tools were used to predict the evolutionary conservation of amino acids, solvent accessible surface areas, and the physical and chemical properties and changes of protein structure. All 157 CRYBA4 nsSNPs were analyzed. Forty-four CRYBA4 high-risk pathogenic nsSNPs (predicted to be pathogenic by all six software tools) were detected out of the 157 CRYBA4 nsSNPs, four of which (c.283C>T, p.R95W; c.449T>A, p.V150D; c.475G>A, p.G159R; c.575G>C, p.R192P) should be focused on because of their high potential pathogenicity and possibility of changing protein properties. Thirty high-risk nsSNPs were predicted to cause a decrease of protein stability. Twenty-nine high-risk nsSNPs occurred in evolutionary conserved positions. Twenty-two high-risk nsSNPs occurred in the core of the protein. It is predicted that these high-risk pathogenic nsSNPs can cause changes in the physical and chemical properties of amino acids, resulting in structural changes of proteins and changes in the interactions between domains and other molecules, thus affecting the function of proteins. This study provides important reference value when narrowing down the number of pathogenic CRYBA4 nsSNPs and studying the pathogenesis of congenital cataracts. By using this method, we can easily find 44 high-risk pathogenic nsSNPs out of 157 CRYBA4 nsSNPs.

A contiguous microdeletion syndrome at Xp23.13 with non-obstructive azoospermia and congenital cataracts

Non-obstructive azoospermia accounts for 10-15% of male infertility, resulting in 60% of all cases of azoospermia and affecting about 1% of the male population. About 30% of these cases are due to Y chromosome microdeletions, chromosome abnormalities, or hormonal disorders. Pathogenic variants in genes on the sex chromosomes have key roles in spermatogenic failure. The co-occurrence of azoospermia and congenital cataracts ranges between 1 in 165,000 and 1 in 500,000. Our 28-year-old patient with normal intelligence and abnormally shaped teeth presented with both disorders. A microarray revealed a microdeletion at Xp23.13 with a whole NHS gene deletion as well as a contiguous deletion of two other genes [SCML1 and RAI2]. This observation represents the first report of non-obstructive azoospermia with congenital cataracts and a contiguous deletion of the SCML1 gene, a transcript of which is exclusively expressed in the testis. SCML1 is the putative culprit gene, which requires functional study or animal experiments. Our analysis of 60 known spermatogenesis failure-related genes by whole-exome sequencing revealed no other candidate. The Nance-Horan syndrome due to pathogenic variants in the NHS gene at Xp23.13 including whole gene deletion does not have azoospermia as a feature. Our report adds to the completeness of genetic counseling for an individual with azoospermia and congenital cataracts.

Congenital cataract: a guide to genetic and clinical management

Worldwide 20,000-40,000 children with congenital or childhood cataract are born every year with varying degrees and patterns of lens opacification with a broad aetiology. In most cases of bilateral cataract, a causative genetic mutation can be identified, with autosomal dominant inheritance being most common in 44% of cases. Variants in genes involve lens-specific proteins or those that regulate eye development, thus giving rise to other associated ocular abnormalities. Approximately 15% of cases have systemic features, hence paediatric input is essential to minimise comorbidities and support overall development of children at high risk of visual impairment. In some metabolic conditions, congenital cataract may be the presenting sign, and therefore prompt diagnosis is important where there is an available treatment. Multidisciplinary management of children is essential, including ophthalmic surgeons, orthoptists, paediatricians, geneticists and genetic counsellors, and should extend beyond the medical team to include school and local paediatric visual support services. Early surgery and close follow up in ophthalmology is important to optimise visual potential and prevent amblyopia. Routine genetic testing is essential for the complete clinical management of patients, with next-generation sequencing of 115 genes shown to expedite molecular diagnosis, streamline care pathways and inform genetic counselling and reproductive options for the future.

Lay abstract

Childhood cataract: how to manage patients Cataract is a clouding of the lens in the eye. Cataract occurring in children has many different causes, which may include infections passed from mother to child during pregnancy, trauma, medications and exposure to radiation. In most cases of cataract occurring in both eyes, a genetic cause can be found which may be inherited from parents or occur sporadically in the developing baby itself while in the womb. Cataracts may occur on their own, with other eye conditions or be present with other disorders in the body as part of a syndrome. Genetic testing is important for all children with cataract as it can provide valuable information about cause, inheritance and risk to further children and signpost any other features of the disease in the rest of the body, permitting the assembly of the correct multidisciplinary care team. Genetic testing currently involves screening for mutations in 115 genes already known to cause cataract and has been shown to expedite diagnosis and help better manage children. Genetic counselling services can support families in understanding their diagnosis and inform future family planning. In order to optimise vision, early surgery for cataract in children is important. This is because the brain is still developing and an unobstructed pathway for light to reach the back of the eye is required for normal visual development. Any obstruction (such as cataract) if left untreated may lead to permanent sight impairment or blindness, even if it is removed later. A multidisciplinary team involved in the care of a child with cataract should include ophthalmic surgeons, orthoptists, paediatricians, geneticists and genetic counsellors, and should extend beyond the medical team to include school and local child visual support services. They will help to diagnose and manage systemic conditions, optimise vision potential and help patients and their families access best supportive care.

Age-related changes in eye lens biomechanics, morphology, refractive index and transparency

Life-long eye lens function requires an appropriate gradient refractive index, biomechanical integrity and transparency. We conducted an extensive study of wild-type mouse lenses 1-30 months of age to define common age-related changes. Biomechanical testing and morphometrics revealed an increase in lens volume and stiffness with age. Lens capsule thickness and peripheral fiber cell widths increased between 2 to 4 months of age but not further, and thus, cannot account for significant age-dependent increases in lens stiffness after 4 months. In lenses from mice older than 12 months, we routinely observed cataracts due to changes in cell structure, with anterior cataracts due to incomplete suture closure and a cortical ring cataract corresponding to a zone of compaction in cortical lens fiber cells. Refractive index measurements showed a rapid growth in peak refractive index between 1 to 6 months of age, and the area of highest refractive index is correlated with increases in lens nucleus size with age. These data provide a comprehensive overview of age-related changes in murine lenses, including lens size, stiffness, nuclear fraction, refractive index, transparency, capsule thickness and cell structure. Our results suggest similarities between murine and primate lenses and provide a baseline for future lens aging studies.

Molecular genetics of congenital cataracts

Congenital cataracts, the most common cause of visual impairment and blindness in children worldwide, have diverse etiologies. According to statistics analysis, about one quarter of congenital cataracts caused by genetic defects. Various mutations of more than one hundred genes have been identified in hereditary cataracts so far. In this review, we briefly summarize recent developments about the genetics, molecular mechanisms, and treatments of congenital cataracts. The studies of these pathogenic mutations and molecular genetics is making it possible for us to comprehend the underlying mechanisms of cataractogenesis and providing new insights into the preventive, diagnostic and therapeutic approaches of cataracts.

Structural analysis of missense mutations occurring in the DNA-binding domain of HSF4 associated with congenital cataracts

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High-resolution structures of wild-type and K23N mutant DBD in HSF4 were determined.

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Cataract-related mutations in HSF4 were structurally analyzed through MD simulation.

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Mutations Q61R, K64E, R73H, R116H and R119C likely perturb DNA-binding activity.

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Mutations K23N, P60H and L114P probably affect trimer formation or folding dynamics.

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Mutations A19D, H35Y and I86V may be false positives leading to trivial impacts.

Congenital cataract (CC) is the major cause of childish blindness, and nearly 50% of CCs are hereditary disorders. HSF4, a member of the heat shock transcription factor family, acts as a key regulator of cell growth and differentiation during the development of sensory organs. Missense mutations in the HSF4-encoding gene have been reported to cause CC formation; in particular, those occurring within the DNA-binding domain (DBD) are usually autosomal dominant mutations. To address how the identified mutations lead to HSF4 malfunction by placing adverse impacts on protein structure and DNA-binding specificity and affinity, we determined two high-resolution structures of the wild-type DBD and the K23N mutant of human HSF4, built DNA-binding models, conducted in silico mutations and molecular dynamics simulations. Our analysis suggests four possible structural mechanisms underlining the missense mutations in HSF4-DBD and cataractogenesis: (i), disruption of HSE recognition; (ii), perturbation of protein-DNA interactions; (iii), alteration of protein folding; (iv), other impacts, e.g. inhibition of protein oligomerization.

A Novel Mutation p.S93R in CRYBB1 Associated with Dominant Congenital Cataract and Microphthalmia

Purpose: To identify the pathogenetic mutations in a four-generation Chinese family with dominant congenital cataracts and microphthalmia.Methods: A four-generation Chinese family with dominant congenital cataracts were recruited. Genomic DNAs were collected from their peripheral blood leukocytes and subjected to whole exome sequencing. The genetic mutations were identified by bioinformatic analyses and verified by Sanger sequencing.Results: Whole exome sequencing revealed a c.279C>G point mutation in the CRYBB1 gene which was further verified by Sanger sequencing. The nucleotide replacement results in a novel mutation p.S93R in a conserved residue of βB1 crystallin which is predicted to disrupt normal βB1 structure and function.Conclusions: We identified a novel missense mutation p.S93R in CRYBB1 in a Chinese family with autosomal dominant congenital cataracts and microphthalmia. This serine residue is extremely conserved evolutionarily in more than 50 βγ-crystallins of many species. These data will be very helpful to further understand the structural and functional features of crystallins.

Novel mutations associated with autosomal-dominant congenital cataract identified in Chinese families

As the leading cause of impaired vision, congenital cataracts, particularly autosomal dominant congenital cataract (ADCC), have been considered as a hereditary disease. The present study aimed to identify genetic defects in Chinese pedigrees with ADCC. A total of 6 Chinese families with ADCC were included, comprising 103 members and 27 patients assessed in total. Genomic DNA samples were extracted from the peripheral blood of probands; mutations were determined using a specific eye disease enrichment panel with next-generation sequencing. Following pathogenicity prediction, sites with notable pathogenicity were screened for further validation. Sanger sequencing was performed in the remaining individuals of the families and 100 normal controls. The pathogenic effects of the mutations, including amino acid substitutions, as well as structural and functional alterations of proteins linked to ADCC, were investigated via bioinformatics analysis. A total of seven mutations in six candidate genes associated with ADCC were identified in the 6 families: Myosin heavy chain 9 (MYH9) c.4150G>C, β-crystallin A4 (CRYBA4) c.169T>C, RPGR-interacting protein 1 (RPGRRIP1) c.2669G>A, wolframin (WFS1) c.1235T>C, CRYBA4 c.26C>T, Ephrin receptor subfamily 2 (EPHA2) c.2663+1G>A and paired box 6 (PAX6) c.11-2A>G. The seven mutations were only detected in affected individuals. Among them, there were three novel mutations (MYH9: c.4150G>C; CRYBA4: c.169T>C; RPGRRIP1: c.2669G>A) and four previously reported ones. Mutations in RPGRIP1 (c.2669G>A) and CRYBA4 (c.26C>T) were predicted to be benign according to bioinformatics analysis. Conversely, other mutations in EPHA2, PAX6, MYH9, CRYBA4 (c.169T>C) and WFS1 were determined to be pathogenic. The present study reported two novel heterozygous mutations (MYH9 c.4150G>C and CRYBA4 c.169T>C) identified by analyzing 6 Chinese families with ADCC, supporting their important roles in the development of the disease.

Biology of Inherited Cataracts and Opportunities for Treatment

Cataract, the clinical correlate of opacity or light scattering in the eye lens, is usually caused by the presence of high-molecular-weight (HMW) protein aggregates or disruption of the lens microarchitecture. In general, genes involved in inherited cataracts reflect important processes and pathways in the lens including lens crystallins, connexins, growth factors, membrane proteins, intermediate filament proteins, and chaperones. Usually, mutations causing severe damage to proteins cause congenital cataracts, while milder variants increasing susceptibility to environmental insults are associated with age-related cataracts. These may have different pathogenic mechanisms: Congenital cataracts induce the unfolded protein response and apoptosis. By contrast, denatured crystallins in age-related cataracts are bound by α-crystallin and form light-scattering HMW aggregates. New therapeutic approaches to age-related cataracts use chemical chaperones to solubilize HMW aggregates, while attempts are being made to regenerate lenses using endogenous stem cells to treat congenital cataracts.

Molecular Mechanism of Aggregation of the Cataract-Related γD-Crystallin W42R Variant from Multiscale Atomistic Simulations

The mechanisms leading to aggregation of the crystallin proteins of the eye lens remain largely unknown. We use atomistic multiscale molecular simulations to model the solution-state conformational dynamics of γD-crystallin and its cataract-related W42R variant at both infinite dilution and physiologically relevant concentrations. We find that the W42R variant assumes a distinct conformation in solution that leaves the Greek key domains of the native fold largely unaltered but lacks the hydrophobic interdomain interface that is key to the stability of wild-type γD-crystallin. At physiologically relevant concentrations, exposed hydrophobic regions in this alternative conformation become primary sites for enhanced interprotein interactions leading to large-scale aggregation.

The impact of GJA3 SNPs on susceptibility to age-related cataract

AIM

To determine the association of gap junction protein alpha 3 (GJA3) gene tag single-nucleotide polymorphisms (SNPs) with susceptibility to age-related cataract (ARC).

METHODS

In total, 486 ARC patients were matched with 500 healthy controls. All the participants underwent complete ophthalmic examinations. Haplotype-tagging SNPs of GJA3 gene were selected from the HapMap Beijing Han Chinese population. Genomic DNA was extracted from the peripheral blood leukocytes of all the subjects. Under three different genetic models: dominant, recessive, and additive, the association between SNPs and ARC was examined. After adjusting for age and sex, the genetic effects of the GJA3 SNPs were evaluated with logistic regression analysis.

RESULTS

Four tag GJA3 SNPs (rs6490519, rs9506430, rs9509053, and rs9552089) were included in the present study. None of the SNPs showed a significant relationship with an altered risk of total ARC under the dominant, recessive, or additive models. In the subgroup analysis, rs9506430 had a significant effect on the formation of a posterior subcapsular cataract (P=0.002, OR: 0.227, 95%CI: 0.088-0.590) under the recessive model.

CONCLUSION

Our study indicates that GJA3 variants may influence the development of posterior subcapsular cataracts. Further studies need to be designed to confirm this possibility.

C-Terminal End of Aquaporin 0 Regulates Lens Gap Junction Channel Function

Purpose

We reported previously that aquaporin 0 (AQP0) modulates lens fiber cell gap junction (GJ) channel function. The present study was conducted to find out whether the C-terminal end of AQP0 is involved in this regulation.

Methods

A mouse model, AQP0ΔC/ΔC, was genetically engineered to express AQP0 with 1-246 amino acids, without the normal intact AQP0 (1-263 amino acids) in the lens. Transparency and focusing of the lens were assessed. Intracellular impedance was measured to determine GJ coupling resistance. Intracellular hydrostatic pressure (HP) was also determined. Western blotting was performed to determine connexin (Cx46 and Cx50) expression levels.

Results

At postnatal day 10, AQP0ΔC/ΔC mouse lenses relative to age-matched wild-type lenses showed loss of transparency and abnormal optical distortion; GJ coupling resistance increased in the differentiating (1.6-fold) and mature (8-fold) fiber cells; lens HP increased approximately 1.5-fold at the junction between the differentiating and mature fiber cells and approximately 2.0-fold in the center; there was no significant change (P > 0.05) in expression levels of Cx46 or Cx50.

Conclusions

The increase in GJ coupling resistance was not associated with reduced connexin expression, suggesting either a reduction in the open probability or some physical change in plaque location. The increase in resistance was significantly greater than the increase in HP, suggesting less pressure-driven water flow through each open GJ channel. These changes may lead to a loss of transparency and abnormal optical distortion. Overall, our data demonstrate the C-terminal end of AQP0 is involved in modulating GJ coupling to maintain lens transparency and homeostasis.

Genetic modifiers of rodent animal models: the role in cataractogenesis

Visual impairment leads to a decrease in quality of life. Cataract is the most commonly observed ocular disease in humans that causes vision disorders. The risk factors associated with cataract development include aging, infections, eye injuries, environmental causes, such as radiation and exposure to ultraviolet rays in sunlight, and genetic mutations. Additionally, several cataract patients display phenotypic heterogeneity, suggesting the role of genetic modifiers in the modulation of severity and onset time of cataractogenesis. However, the genetic modifiers associated with cataract have not been identified in humans yet. In contrast, the identification and mapping of genetic modifiers have been successfully carried out in mice and rats. In this review, we focus on the genetic modifiers of cataract in the rodent models.

Dissimilarity in the Contributions of the N-Terminal Domain Hydrophobic Core to the Structural Stability of Lens β/γ-Crystallins

Vertebrate lens β/γ-crystallins share a conserved tertiary structure consisting of four Greek-key motifs divided into two globular domains. Numerous inherited mutations in β/γ-crystallins have been linked to cataractogenesis. In this research, the folding mechanism underlying cataracts caused by the I21N mutation in βB2 was investigated by comparing the effect of mutagenesis on the structural features and stability of four β/γ-crystallins, βB1, βB2, γC, and γD. Our results showed that the four β/γ-crystallins differ greatly in solubility and stability against various stresses. The I21N mutation greatly impaired βB2 solubility and native structure as well as its stability against denaturation induced by guanidine hydrochloride, heat treatment, and ultraviolet irradiation. However, the deleterious effects were much weaker for mutations at the corresponding sites in βB1, γC, and γD. Molecular dynamics simulations indicated that the introduction of a nonnative hydrogen bond contributed to twisting Greek-key motif I outward, which might direct the misfolding of the I21N mutant of βB2. Meanwhile, partial hydration of the hydrophobic interior of the domain induced by the mutation destabilized βB1, γC, and γD. Our findings highlight the importance of nonnative hydrogen bond formation and hydrophobic core hydration in crystallin misfolding caused by inherited mutations.

Profiling of chromatin accessibility and identification of general cis-regulatory mechanisms that control two ocular lens differentiation pathways

BACKGROUND

Promoters and enhancers are cis-regulatory DNA sequences that control specificity and quantity of transcription. Both are rich on clusters of cis-acting sites that interact with sequence-specific DNA-binding transcription factors (TFs). At the level of chromatin, these regions display increased nuclease sensitivity, reduced nucleosome density, including nucleosome-free regions, and specific combinations of posttranslational modifications of core histone proteins. Together, "open" and "closed" chromatins represent transcriptionally active and repressed states of individual genes, respectively. Cellular differentiation is marked by changes in local chromatin structure. Lens morphogenesis, regulated by TF Pax6, includes differentiation of epithelial precursor cells into lens fibers in parallel with differentiation of epithelial precursors into the mature lens epithelium.

RESULTS

Using ATAC-seq, we investigated dynamics of chromatin changes during mouse lens fibers and epithelium differentiation. Tissue-specific features of these processes are demonstrated via comparative studies of embryonic stem cells, forebrain, and liver chromatins. Unbiased analysis reveals cis-regulatory logic of lens differentiation through known (e.g., AP-1, Ets, Hsf4, Maf, and Pax6 sites) and novel (e.g., CTCF, Tead, and NF1) motifs. Twenty-six DNA-binding TFs, recognizing these cis-motifs, are markedly up-regulated in differentiating lens fibers. As specific examples, our ATAC-seq data uncovered both the regulatory regions and TF binding motifs in Foxe3, Prox1, and Mip loci that are consistent with previous, though incomplete, experimental data. A cross-examination of Pax6 binding with ATAC-seq data demonstrated that Pax6 bound to both open (H3K27ac and P300-enriched) and closed chromatin domains in lens and forebrain.

CONCLUSIONS

Our study has generated the first lens chromatin accessibility maps that support a general model of stage-specific chromatin changes associated with transcriptional activities of batteries of genes required for lens fiber cell formation. Analysis of active (or open) promoters and enhancers reveals important cis-DNA motifs that establish the molecular foundation for temporally and spatially regulated gene expression in lens. Together, our data and models open new avenues for the field to conduct mechanistic studies of transcriptional control regions, reconstruction of gene regulatory networks that govern lens morphogenesis, and identification of cataract-causing mutations in noncoding sequences.

A High-Throughput Assay for Congenital and Age-Related Eye Diseases in Zebrafish

Debilitating visual impairment caused by cataracts or microphthalmia is estimated to affect roughly 20 million people in the United States alone. According to the National Eye Institute, by 2050 that number is expected to more than double to roughly 50 million. The identification of candidate disease-causing alleles for cataracts and microphthalmia has been accelerated with advanced sequencing technologies creating a need for verification of the pathophysiology of these genes. Zebrafish pose many advantages as a high-throughput model for human eye disease. By 5 days post-fertilization, zebrafish have quantifiable behavioral responses to visual stimuli. Their small size, many progeny, and external fertilization allows for rapid screening for vision defects. We have adapted the OptoMotor Response to assay visual impairment in zebrafish models of cataracts and microphthalmia. This research demonstrates an inexpensive, high-throughput method for analyzing candidate genes involved in visual impairment.

Characterization of a p.R76H mutation in Cx50 identified in a Chinese family with congenital nuclear cataract

BACKGROUND/PURPOSE

A three-generation Chinese family with autosomal dominant congenital nuclear cataract was recruited. This study aimed to identify the disease-causing gene for nuclear cataract with functional dissections of the identified mutant.

METHODS

Detailed clinical data and family history were recorded. Candidate gene sequencing was performed to identify the disease-causing mutation. Recombinant connexin50 (Cx50) wild type and mutant constructs were synthesized. Triton X-100 solubility and subcellular localization of the recombinant Cx50 proteins were analyzed in HeLa cells. Apoptosis was assayed as the percentage of fragmented nuclei in transfected cells.

RESULTS

All affected individuals in the family displayed clear phenotypes of dense nuclear cataracts. A c.227 G > A variation was found in the coding region of Cx50, which arginine residue at position 76 was substituted by histidine (p.R76H). This mutation was co-segregated with the disease in the family, and was not observed in 110 unrelated Chinese controls. No statistically significant differences were found in the Triton X-100 solubility and apoptosis rate between wild type and mutant Cx50 in HeLa cells. However, Cx50 mutant was unable to form gap junctional plaques between adjacent cells as the wild type proteins did.

CONCLUSION

This study identified a novel cataract phenotype caused by the p.R76H mutation in Cx50, providing evidence of further phenotypic heterogeneity associated with this mutation. Functional analysis showed that the mutation affected the formation of gap junction channels and led to opacity in the lens.

Proteome-transcriptome analysis and proteome remodeling in mouse lens epithelium and fibers

Epithelial cells and differentiated fiber cells represent distinct compartments in the ocular lens. While previous studies have revealed proteins that are preferentially expressed in epithelial vs. fiber cells, a comprehensive proteomics library comparing the molecular compositions of epithelial vs. fiber cells is essential for understanding lens formation, function, disease and regenerative potential, and for efficient differentiation of pluripotent stem cells for modeling of lens development and pathology in vitro. To compare protein compositions between the lens epithelium and fibers, we employed tandem mass spectrometry (2D-LC/MS) analysis of microdissected mouse P0.5 lenses. Functional classifications of the top 525 identified proteins into gene ontology categories by molecular processes and subcellular localizations, were adapted for the lens. Expression levels of both epithelial and fiber proteomes were compared with whole lens proteome and mRNA levels using E14.5, E16.5, E18.5, and P0.5 RNA-Seq data sets. During this developmental time window, multiple complex biosynthetic and catabolic processes generate the molecular and structural foundation for lens transparency. As expected, crystallins showed a high correlation between their mRNA and protein levels. Comprehensive data analysis confirmed and/or predicted roles for transcription factors (TFs), RNA-binding proteins (e.g. Carhsp1), translational apparatus including ribosomal heterogeneity and initiation factors, microtubules, cytoskeletal [e.g. non-muscle myosin IIA heavy chain (Myh9) and βB2-spectrin (Sptbn2)] and membrane proteins in lens formation and maturation. Our data highlighted many proteins with unknown functions in the lens that were preferentially enriched in epithelium or fibers, setting the stage for future studies to further dissect the roles of these proteins in fiber cell differentiation vs. epithelial cell maintenance. In conclusion, the present proteomic datasets represent the first mouse lens epithelium and fiber cell proteomes, establish comparative analyses of protein and RNA-Seq data, and characterize the major proteome remodeling required to form the mature lens fiber cells.

A splice-site variant in the lncRNA gene RP1-140A9.1 cosegregates in the large Volkmann cataract family

Purpose

To identify the mutation for Volkmann cataract (CTRCT8) at 1p36.33.

Methods

The genes in the candidate region 1p36.33 were Sanger and parallel deep sequenced, and informative single nucleotide polymorphisms (SNPs) were identified for linkage analysis. Expression analysis with reverse transcription polymerase chain reaction (RT-PCR) of the candidate gene was performed using RNA from different human tissues. Quantitative transcription polymerase chain reaction (qRT-PCR) analysis of the GNB1 gene was performed in affected and healthy individuals. Bioinformatic analysis of the linkage regions including the candidate gene was performed.

Results

Linkage analysis of the 1p36.33 CCV locus applying new marker systems obtained with Sanger and deep sequencing reduced the candidate locus from 2.1 Mb to 0.389 Mb flanked by the markers STS-22AC and rs549772338 and resulted in an logarithm of the odds (LOD) score of Z = 21.67. The identified mutation, rs763295804, affects the donor splice site in the long non-coding RNA gene RP1-140A9.1 (ENSG00000231050). The gene including splice-site junctions is conserved in primates but not in other mammalian genomes, and two alternative transcripts were shown with RT-PCR. One of these transcripts represented a lens cell-specific transcript. Meta-analysis of the Cross-Linking-Immuno-Precipitation sequencing (CLIP-Seq) data suggested the RNA binding protein (RBP) eIF4AIII is an active counterpart for RP1-140A9.1, and several miRNA and transcription factors binding sites were predicted in the proximity of the mutation. ENCODE DNase I hypersensitivity and histone methylation and acetylation data suggest the genomic region may have regulatory functions.

Conclusions

The mutation in RP1-140A9.1 suggests the long non-coding RNA as the candidate cataract gene associated with the autosomal dominant inherited congenital cataract from CCV. The mutation has the potential to destroy exon/intron splicing of both transcripts of RP1-140A9.1. Sanger and massive deep resequencing of the linkage region failed to identify alternative candidates suggesting the mutation in RP1-140A9.1 is causative for the CCV phenotype.

Altered Expression Patterns of the Sumoylation Enzymes E1, E2 and E3 Are Associated with Glucose Oxidase- and UVA-Induced Cataractogenesis

PURPOSE

Protein sumoylation is a well established regulatory mechanism that regulates chromatin structure and dynamics, cell proliferation and differentiation, stress response and cell apoptosis. In the vertebrate eye, we and others have shown that sumoylation plays an indispensable role in regulating eye development. During stress induction and aging process, the ocular tissues gradually loss their normality and develop major ocular diseases such as cataract and aging-related macular degeneration. We have recently demonstrated that sumoylation actively regulates differentiation of lens cells, whether this process is implicated in lens pathogenesis remains to be investigated. In this study, we have demonstrated that transparent mouse lenses treated with glucose oxidase and UVA irradiation undergo in vitro cataract formation, and associated with this process, the expression patterns of the 3 sumoylation enzymes have been found significantly altered.

METHODS

Four-week-old C57BL/6J mice were used in our experiment. Lenses were carefully excised from eyes and cultured in M199 medium (Sigma 3769) for at least 12 hours. Transparent lenses (without surgical damage) were selected for experimentation. The lenses were exposed to UVA for 60 min or treated with 30 mU/mL glucose oxidase (GO, MP Biomedicals, 1673) to induce cataract formation. The mRNA levels were analysed with qRT-PCR. The protein levels were determined with western blot analysis and quantitated with Image J.

RESULTS

we have obtained the following results: 1) Both GO treatment and UVA irradiation can induce cataract formation in the in vitro cultured mouse lenses; 2) With GO treatment, the mRNAs and proteins for the 5 sumoylation enzymes were all significantly downregulated; 3) With UVA irradiation, the changes in the expression patterns of the mRNAs and proteins for the SAE1, UBA2 , UBC9 and PIAS1 were opposite, while the mRNAs were upregulated either significantly (for SAE1, UBA2 and UBC9) or slightly (PIAS1), the proteins for all 4 sumoylation enzymes were downregulated; For RanBP2, the UVA induced changes in both mRNA and protein are consist with the GO treatment.

CONCLUSION

Under GO and UVA irradiation conditions, the expression levels of both mRNA and protein for the three major sumoylation enzymes were significantly changed. Our results suggest that altered expression patterns of the sumoylation enzymes are associated with oxidative stressinduced cataractogenesis.

Structure of native lens connexin 46/50 intercellular channels by cryo-EM

Gap junctions establish direct pathways for cell-to-cell communication through the assembly of twelve connexin subunits that form intercellular channels connecting neighbouring cells. Co-assembly of different connexin isoforms produces channels with unique properties and enables communication across cell types. Here we used single-particle cryo-electron microscopy to investigate the structural basis of connexin co-assembly in native lens gap junction channels composed of connexin 46 and connexin 50 (Cx46/50). We provide the first comparative analysis to connexin 26 (Cx26), which-together with computational studies-elucidates key energetic features governing gap junction permselectivity. Cx46/50 adopts an open-state conformation that is distinct from the Cx26 crystal structure, yet it appears to be stabilized by a conserved set of hydrophobic anchoring residues. 'Hot spots' of genetic mutations linked to hereditary cataract formation map to the core structural-functional elements identified in Cx46/50, suggesting explanations for many of the disease-causing effects.

Lanosterol and 25-hydroxycholesterol dissociate crystallin aggregates isolated from cataractous human lens via different mechanisms

Cataract, a crystallin aggregation disease, is the leading cause of human blindness worldwide. Surgery is the only established treatment of cataracts and no anti-cataract drugs are available thus far. Recently lanosterol and 25-hydroxycholesterol have been reported to redissolve crystallin aggregates and partially restore lens transparency in animals. However, the efficacies of these two compounds have not been quantitatively studied ex vivo using patient tissues. In this research, we developed a quantitative assay applicable to efficacy validations and mechanistic studies by a protocol to isolate protein aggregates from the surgically removed cataractous human lens. Our results showed that both compounds were effective for human cataractous samples with EC50 values at ten micromolar level. The efficacies of both compounds strongly depended on cataract severity. Lanosterol and 25-hydroxycholesterol were two mechanistically different lead compounds of anti-cataract drug design.

Dotting the eyes: mouse strain dependency of the lens epithelium to low dose radiation-induced DNA damage

PURPOSE

Epidemiological evidence regarding the radiosensitivity of the lens of the eye and radiation cataract development has led to changes in the EU Basic Safety Standards for protection of the lens against ionizing radiation. However, mechanistic details of lens radiation response pathways and their significance for cataractogenesis remain unclear. Radiation-induced DNA damage and the potential impairment of repair pathways within the lens epithelium, a cell monolayer that covers the anterior hemisphere of the lens, are likely to be involved.

MATERIALS AND METHODS

In this work, the lens epithelium has been analyzed for its DNA double-strand break (DSB) repair response to ionizing radiation. The responses of epithelial cells located at the anterior pole (central region) have been compared to at the very periphery of the monolayer (germinative and transitional zones). Described here are the different responses in the two regions and across four strains (C57BL/6, 129S2, BALB/c and CBA/Ca) over a low dose (0-25 mGy) in-vivo whole body X-irradiation range up to 24 hours post exposure.

RESULTS

DNA damage and repair as visualized through 53BP1 staining was present across the lens epithelium, although repair kinetics appeared non-uniform. Epithelial cells in the central region have significantly more 53BP1 foci. The sensitivities of different mouse strains have also been compared.

CONCLUSIONS

129S2 and BALB/c showed higher levels of DNA damage, with BALB/c showing significantly less inter-individual variability and appearing to be a more robust model for future DNA damage and repair studies. As a result of this study, BALB/c was identified as a suitable radiosensitive lens strain to detect and quantify early low dose ionizing radiation DNA damage effects in the mouse eye lens specifically, as an indicator of cataract formation.

The impact of GJA8 SNPs on susceptibility to age-related cataract

The gap junction protein alpha 8 (GJA8) gene has been widely studied in human congenital cataracts. However, little is known about its relationship with age-related cataract (ARC). In this study, three GJA8-tagged single nucleotide polymorphisms related to an increased ARC risk were identified: rs2132397 for general ARC under both dominant and additive models; rs7541950 for general ARC under both recessive and additive models; and rs6657114 for cortical cataract under the recessive model. To uncover the underlying mechanisms, this study also sought to explore whether GJA8 is involved in the autophagy process in human lens epithelial cells. The results showed that GJA8 may participate in autophagy to maintain the intracellular environment, which may be a novel mechanism for cataract formation induced by GJA8. In conclusion, this study identified the genetic susceptibility of GJA8 polymorphisms on ARC and provides new clues for fully understanding the pathological mechanism of GJA8 variants in affecting lens opacity.

Genetic landscape of isolated pediatric cataracts: extreme heterogeneity and variable inheritance patterns within genes

Pediatric cataract represents an important cause of pediatric visual impairment. While both genetic and environmental causes for pediatric cataract are known, a large proportion remains idiopathic. The purpose of this review is to discuss genes involved in isolated pediatric cataract, with a focus on variable inheritance patterns within genes. Mutations in over 52 genes are known to cause isolated pediatric cataract, with a major contribution from genes encoding for crystallins, transcription factors, membrane proteins, and cytoskeletal proteins. Interestingly, both dominant and recessive inheritance patterns have been reported for mutations in 13 different cataract genes. For some genes, dominant and recessive alleles represent distinct types of mutations, but for many, especially missense variants, there are no clear patterns to distinguish between dominant and recessive alleles. Further research into the functional effects of these mutations, as well as additional data on the frequency of the identified variants, is needed to clarify variant pathogenicity. Exome sequencing continues to be successful in identifying novel genes associated with congenital cataract but is hindered by the extreme genetic heterogeneity of this condition. The large number of idiopathic cases suggests that more genes and potentially novel mechanisms of gene disruption remain to be identified.

Mutation update of transcription factor genes FOXE3, HSF4, MAF, and PITX3 causing cataracts and other developmental ocular defects

Mutations in the transcription factor genes FOXE3, HSF4, MAF, and PITX3 cause congenital lens defects including cataracts that may be accompanied by defects in other components of the eye or in nonocular tissues. We comprehensively describe here all the variants in FOXE3, HSF4, MAF, and PITX3 genes linked to human developmental defects. A total of 52 variants for FOXE3, 18 variants for HSF4, 20 variants for MAF, and 19 variants for PITX3 identified so far in isolated cases or within families are documented. This effort reveals FOXE3, HSF4, MAF, and PITX3 to have 33, 16, 18, and 7 unique causal mutations, respectively. Loss-of-function mutant animals for these genes have served to model the pathobiology of the associated human defects, and we discuss the currently known molecular function of these genes, particularly with emphasis on their role in ocular development. Finally, we make the detailed FOXE3, HSF4, MAF, and PITX3 variant information available in the Leiden Online Variation Database (LOVD) platform at https://www.LOVD.nl/FOXE3, https://www.LOVD.nl/HSF4, https://www.LOVD.nl/MAF, and https://www.LOVD.nl/PITX3. Thus, this article informs on key variants in transcription factor genes linked to cataract, aphakia, corneal opacity, glaucoma, microcornea, microphthalmia, anterior segment mesenchymal dysgenesis, and Ayme-Gripp syndrome, and facilitates their access through Web-based databases.

New GJA8 variants and phenotypes highlight its critical role in a broad spectrum of eye anomalies

GJA8 encodes connexin 50 (Cx50), a transmembrane protein involved in the formation of lens gap junctions. GJA8 mutations have been linked to early onset cataracts in humans and animal models. In mice, missense mutations and homozygous Gja8 deletions lead to smaller lenses and microphthalmia in addition to cataract, suggesting that Gja8 may play a role in both lens development and ocular growth. Following screening of GJA8 in a cohort of 426 individuals with severe congenital eye anomalies, primarily anophthalmia, microphthalmia and coloboma, we identified four known [p.(Thr39Arg), p.(Trp45Leu), p.(Asp51Asn), and p.(Gly94Arg)] and two novel [p.(Phe70Leu) and p.(Val97Gly)] likely pathogenic variants in seven families. Five of these co-segregated with cataracts and microphthalmia, whereas the variant p.(Gly94Arg) was identified in an individual with congenital aphakia, sclerocornea, microphthalmia and coloboma. Four missense variants of unknown or unlikely clinical significance were also identified. Furthermore, the screening of GJA8 structural variants in a subgroup of 188 individuals identified heterozygous 1q21 microdeletions in five families with coloboma and other ocular and/or extraocular findings. However, the exact genotype-phenotype correlation of these structural variants remains to be established. Our data expand the spectrum of GJA8 variants and associated phenotypes, confirming the importance of this gene in early eye development.

Identification of PITX3 mutations in individuals with various ocular developmental defects

BACKGROUND

Congenital cataract displays large phenotypic (syndromic and isolated cataracts) and genetic heterogeneity. Mutations in several transcription factors involved in eye development, like PITX3, have been associated with congenital cataracts and anterior segment mesenchymal disorders.

MATERIALS AND METHODS

Targeted sequencing of 187 genes involved in ocular development was performed in 96 patients with mainly anophthalmia and microphthalmia. Additionally, Sanger sequencing analysis of PITX3 was performed on a second cohort of 32 index cases with congenital cataract and Peters anomaly and/or sclereocornea.

RESULTS

We described five families with four different PITX3 mutations, two of which were novel. In Family 1, the heterozygous recurrent c.640_656dup (p.Gly220Profs*95) mutation cosegregated with eye anomalies ranging from congenital cataract to Peters anomaly. In Family 2, the novel c.669del [p.(Leu225Trpfs*84)] mutation cosegregated with dominantly inherited eye anomalies ranging from posterior embryotoxon to congenital cataract in heterozygous carriers and congenital sclereocornea and cataract in a patient homozygous for this mutation. In Family 3, we identified the recurrent heterozygous c.640_656dup (p.Gly220Profs*95) mutation segregating with congenital cataract. In Family 4, the de novo c.582del [p.(Ile194Metfs*115)] mutation was identified in a patient with congenital cataract, microphthalmia, developmental delay and autism. In Family 5, the c.38G>A (p.Ser13Asn) mutation segregated dominantly in a family with Peters anomaly, which is a novel phenotype associated with the c.38G>A variant compared with the previously reported isolated congenital cataract.

CONCLUSIONS

Our study unveils different phenotypes associated with known and novel mutations in PITX3, which will improve the genetic counselling of patients and their families.

INPP5K variant causes autosomal recessive congenital cataract in a Pakistani family

Congenital cataract (CC) is clinically and genetically highly heterogeneous. Here, we enrolled a consanguineous kindred (LUCC15) from Pakistan, with 3 affected individuals suffering with CC. Exome sequencing revealed a transition mutation [c.149 T > C; p.(Ile50Thr)] in INPP5K. Inositol polyphosphate-5-phosphatase K, encoded by INPP5K, is involved in dephosphorylation of phosphatidylinositol (PtdIns) 4,5-bisphosphate, and PtdIns 3,4,5-trisphosphate. Recently, pathogenic variants in INPP5K have been reported in families with congenital muscular dystrophies, intellectual disability, and cataract. In our family LUCC15, mild to moderate intellectual disability along with speech impairment was observed in 2 affected individuals. Magnetic resonance imaging of brain and muscles tissues did not reveal any cerebellar or muscular atrophy. However, electromyography of both upper and lower limbs revealed irritable myopathy. Comparison of clinical phenotype of all the known affected individuals, including LUCC15 family, homozygous for INPP5K alleles revealed reduced penetrance of muscular dystrophy and intellectual disability. Similarly, skeletal muscle abnormalities were highly variable among inpp5ka zebrafish mutants analyzed in this study. These phenotypic variabilities may be due to epigenetic factors and/or genetic modifiers.

Light-focusing human micro-lenses generated from pluripotent stem cells model lens development and drug-induced cataract in vitro

Cataracts cause vision loss and blindness by impairing the ability of the ocular lens to focus light onto the retina. Various cataract risk factors have been identified, including drug treatments, age, smoking and diabetes. However, the molecular events responsible for these different forms of cataract are ill-defined, and the advent of modern cataract surgery in the 1960s virtually eliminated access to human lenses for research. Here, we demonstrate large-scale production of light-focusing human micro-lenses from spheroidal masses of human lens epithelial cells purified from differentiating pluripotent stem cells. The purified lens cells and micro-lenses display similar morphology, cellular arrangement, mRNA expression and protein expression to human lens cells and lenses. Exposing the micro-lenses to the emergent cystic fibrosis drug Vx-770 reduces micro-lens transparency and focusing ability. These human micro-lenses provide a powerful and large-scale platform for defining molecular disease mechanisms caused by cataract risk factors, for anti-cataract drug screening and for clinically relevant toxicity assays.

Germ-line and somatic EPHA2 coding variants in lens aging and cataract

Rare germ-line mutations in the coding regions of the human EPHA2 gene (EPHA2) have been associated with inherited forms of pediatric cataract, whereas, frequent, non-coding, single nucleotide variants (SNVs) have been associated with age-related cataract. Here we sought to determine if germ-line EPHA2 coding SNVs were associated with age-related cataract in a case-control DNA panel (> 50 years) and if somatic EPHA2 coding SNVs were associated with lens aging and/or cataract in a post-mortem lens DNA panel (> 48 years). Micro-fluidic PCR amplification followed by targeted amplicon (exon) next-generation (deep) sequencing of EPHA2 (17-exons) afforded high read-depth coverage (1000x) for > 82% of reads in the cataract case-control panel (161 cases, 64 controls) and > 70% of reads in the post-mortem lens panel (35 clear lens pairs, 22 cataract lens pairs). Novel and reference (known) missense SNVs in EPHA2 that were predicted in silico to be functionally damaging were found in both cases and controls from the age-related cataract panel at variant allele frequencies (VAFs) consistent with germ-line transmission (VAF > 20%). Similarly, both novel and reference missense SNVs in EPHA2 were found in the post-mortem lens panel at VAFs consistent with a somatic origin (VAF > 3%). The majority of SNVs found in the cataract case-control panel and post-mortem lens panel were transitions and many occurred at di-pyrimidine sites that are susceptible to ultraviolet (UV) radiation induced mutation. These data suggest that novel germ-line (blood) and somatic (lens) coding SNVs in EPHA2 that are predicted to be functionally deleterious occur in adults over 50 years of age. However, both types of EPHA2 coding variants were present at comparable levels in individuals with or without age-related cataract making simple genotype-phenotype correlations inconclusive.

Two novel mutations identified in ADCC families impair crystallin protein distribution and induce apoptosis in human lens epithelial cells

Congenital cataract (CC) is a clinical and genetically heterogeneous eye disease that primarily causes lens disorder and even amblyopic blindness in children. As the mechanism underlying CC is genetically inherited, identification of CC-associated gene mutations and their role in protein distribution are topics of both pharmacological and biological research. Through physical and ophthalmic examinations, two Chinese pedigrees with autosomal dominant congenital cataract (ADCC) were recruited for this study. Mutation analyses of CC candidate genes by next-generation sequencing (NGS) and Sanger sequencing revealed a novel missense mutation in CRYBB2 (p.V146L) and a deletion mutation in CRYAA (p.116_118del). Both mutations fully co-segregated were not observed in unaffected family members or in 100 unrelated healthy controls. The CRYBB2 missense mutation disrupts the distribution of CRYBB2 in human lens epithelial cells (HLEpiCs), and the CRYAA deletion mutation causes hyperdispersion of CRYAA. Furthermore, these two crystallin mutations result in aberrant expression of unfolded protein response (UPR) marker genes as well as apoptosis in HLEpiCs. Collectively, these findings broaden the genetic spectrum of ADCC.

Aquaporin 0 Modulates Lens Gap Junctions in the Presence of Lens-Specific Beaded Filament Proteins

Purpose

The objective of this study was to understand the molecular and physiologic mechanisms behind the lens cataract differences in Aquaporin 0-knockout-Heterozygous (AQP0-Htz) mice developed in C57 and FVB (lacks beaded filaments [BFs]) strains.

Methods

Lens transparency was studied using dark field light microscopy. Water permeability (P_f) was measured in fiber cell membrane vesicles. Western blotting/immunostaining was performed to verify expression of BF proteins and connexins. Microelectrode-based intact lens intracellular impedance was measured to determine gap junction (GJ) coupling resistance. Lens intracellular hydrostatic pressure (HP) was determined using a microelectrode/manometer system.

Results

Lens opacity and spherical aberration were more distinct in AQP0-Htz lenses from FVB than C57 strains. In either background, compared to wild type (WT), AQP0-Htz lenses showed decreased P_f (approximately 50%), which was restored by transgenic expression of AQP1 (TgAQP1/AQP0-Htz), but the opacities and differences between FVB and C57 persisted. Western blotting revealed no change in connexin expression levels. However, in C57 AQP0-Htz and TgAQP1/AQP0-Htz lenses, GJ coupling resistance decreased approximately 2.8-fold and the HP gradient decreased approximately 1.9-fold. Increased P_f in TgAQP1/AQP0-Htz did not alter GJ coupling resistance or HP.

Conclusions

In C57 AQP0-Htz lenses, GJ coupling resistance decreased. HP reduction was smaller than the coupling resistance reduction, a reflection of an increase in fluid circulation, which is one reason for the less severe cataract in C57 than FVB. Overall, our results suggest that AQP0 modulates GJs in the presence of BF proteins to maintain lens transparency and homeostasis.

HSF4 regulates lens fiber cell differentiation by activating p53 and its downstream regulators

Cataract refers to opacities of the lens that impede the passage of light. Mutations in heat shock transcription factor 4 (HSF4) have been associated with cataract; however, the mechanisms regarding how mutations in HSF4 cause cataract are still obscure. In this study, we generated an hsf4 knockout zebrafish model using TALEN technology. The mutant zebrafish developed an early-onset cataract with multiple developmental defects in lens. The epithelial cells of the lens were overproliferated, resulting in the overabundance of lens fiber cells in hsf4^null zebrafish lens. Consequently, the arrangement of the lens fiber cells became more disordered and irregular with age. More importantly, the terminal differentiation of the lens fiber cell was interrupted as the organelles cannot be cleaved in due time. In the cultured human lens epithelial cells, HSF4 could stabilize and retain p53 in the nucleus to activate its target genes such as fas cell surface death receptor (Fas) and Bcl-2-associated X apoptosis regulator (Bax). In the hsf4^null fish, both p53 and activated-caspase3 were significantly decreased. Combined with the finding that the denucleation defect could be partially rescued through microinjection of p53, fas and bax mRNA into the mutant embryos, we directly proved that HSF4 promotes lens fiber cell differentiation by activating p53 and its downstream regulators. The data we presented suggest that apoptosis-related genes are involved in the lens fiber cell differentiation. Our finding that HSF4 functions in the upstream to activate these genes highlighted the new regulatory modes of HSF4 in the terminal differentiation of lens fiber cell.

Signaling and Gene Regulatory Networks in Mammalian Lens Development

Ocular lens development represents an advantageous system in which to study regulatory mechanisms governing cell fate decisions, extracellular signaling, cell and tissue organization, and the underlying gene regulatory networks. Spatiotemporally regulated domains of BMP, FGF, and other signaling molecules in late gastrula-early neurula stage embryos generate the border region between the neural plate and non-neural ectoderm from which multiple cell types, including lens progenitor cells, emerge and undergo initial tissue formation. Extracellular signaling and DNA-binding transcription factors govern lens and optic cup morphogenesis. Pax6, c-Maf, Hsf4, Prox1, Sox1, and a few additional factors regulate the expression of the lens structural proteins, the crystallins. Extensive crosstalk between a diverse array of signaling pathways controls the complexity and order of lens morphogenetic processes and lens transparency.

Human diseases associated with connexin mutations

Gap junctions and hemichannels comprised of connexins impact many cellular processes. Significant advances in our understanding of the functional role of these channels have been made by the identification of a host of genetic diseases caused by connexin mutations. Prominent features of connexin disorders are the inability of other connexins expressed in the same cell type to compensate for the mutated one, and the ability of connexin mutants to dominantly influence the activity of other wild-type connexins. Functional studies have begun to identify some of the underlying mechanisms whereby connexin channel mutation contributes to the disease state. Detailed mechanistic understanding of these functional differences will help to facilitate new pathophysiology driven therapies for the diverse array of connexin genetic disorders. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Novel Mutations in the Crystallin Gene in Age-Related Cataract Patients from a North Indian Population

Cataract is the most prevalent leading cause of visual impairment and blindness worldwide. In comparison to congenital cataract, which affects relatively few individuals, age-related cataract is responsible for slightly half of all cases of blindness worldwide. Although significant work has been done, the genetic aspect of age-related cataract is still in its infancy. The current study was performed to analyze the mutations and polymorphisms in the CRYAA, CRYAB, CRYBB1, and GJA8 genes in 40 unrelated age-related cataract patients. Mutational analysis of the above-mentioned genes in 40 cataract cases revealed 14 different substitutions of which 8 variants were novel and 6 were reported SNPs. Two disease-causing mutations, g.44590631G>A (p.R65Q) and g.44592224G>A (p.R119H), were also observed in the CRYAA gene. The disease-causing variants mildly affect the stability, functionality, and localization of crystallin, and, with progressing age, a small change in the microenvironment of the crystallin lens occurs. This change in combination with a mutation may significantly alter the functionality of the crystallin protein, leading to age-related cataract.