Oxidative Stress in Genetic Cataract Formation

BACKGROUND

Cataracts are the leading cause of blindness worldwide, and age-related cataracts are the result of environmental insults that largely lead to oxidative stress imposed on a genetic background that determines susceptibility to these stresses.

METHODS

A comprehensive literature review was performed to identify GWAS, targeted association studies, and TWAS that identified genes associated with age-related cataract. Additional genes associated with age-related cataracts were identified through the CAT-MAP online database. Pathway analysis was performed using Qiagen Ingenuity Pathway Analysis and pathways related to oxidative stress were analyzed using the same program.

RESULTS

A large number of genes have been identified as causes of both Mendelian and complex cataracts. Of these, 10 genes related to oxidative stress were identified, and all were associated with age-related cataracts. These genes fall into seven canonical pathways primarily related to glutathione metabolism and other pathways related to detoxifying reactive oxygen species.

CONCLUSIONS

While a relatively small number of antioxidant related genes were identified as being associated with cataracts, they allow the identification of redox pathways important for lens metabolism and homeostasis. These are largely related to glutathione and its metabolism, other pathways for detoxification of reactive oxygen species, and the transcriptional systems that control their expression.

Through the Cat-Map Gateway: A Brief History of Cataract Genetics

Clouding of the transparent eye lens, or cataract(s), is a leading cause of visual impairment that requires surgical replacement with a synthetic intraocular lens to effectively restore clear vision. Most frequently, cataract is acquired with aging as a multifactorial or complex trait. Cataract may also be inherited as a classic Mendelian trait-often with an early or pediatric onset-with or without other ocular and/or systemic features. Since the early 1990s, over 85 genes and loci have been genetically associated with inherited and/or age-related forms of cataract. While many of these underlying genes-including those for lens crystallins, connexins, and transcription factors-recapitulate signature features of lens development and differentiation, an increasing cohort of unpredicted genes, including those involved in cell-signaling, membrane remodeling, and autophagy, has emerged-providing new insights regarding lens homeostasis and aging. This review provides a brief history of gene discovery for inherited and age-related forms of cataract compiled in the Cat-Map database and highlights potential gene-based therapeutic approaches to delay, reverse, or even prevent cataract formation that may help to reduce the increasing demand for cataract surgery.

Epidemiologic association and shared genetic architecture between cataract and hearing difficulties among middle-aged and older adults

Age-related cataract and hearing difficulties are major sensory disorders that often co-exist in the global-wide elderly and have a tangible influence on the quality of life. However, the epidemiologic association between cataract and hearing difficulties remains unexplored, while little is known about whether the two share their genetic etiology. We first investigated the clinical association between cataract and hearing difficulties using the UK Biobank covering 502,543 individuals. Both unmatched analysis (adjusted for confounders) and a matched analysis (one control matched for each patient with cataract according to confounding factors) were undertaken and confirmed that cataract was associated with hearing difficulties (OR, 2.12; 95% CI, 1.98-2.27; OR, 2.03; 95% CI, 1.86-2.23, respectively). Furthermore, we explored and quantified the shared genetic architecture of these two complex sensory disorders at the common variant level using the bivariate causal mixture model (MiXeR) and conditional/conjunctional false discovery rate method based on the largest available genome-wide association studies of cataract (N = 585,243) and hearing difficulties (N = 323,978). Despite detecting only a negligible genetic correlation, we observe polygenic overlap between cataract and hearing difficulties and identify 6 shared loci with mixed directions of effects. Follow-up analysis of the shared loci implicates candidate genes QKI, STK17A, TYR, NSF, and TCF4 likely contribute to the pathophysiology of cataracts and hearing difficulties. In conclusion, this study demonstrates the presence of epidemiologic association between cataract and hearing difficulties and provides new insights into the shared genetic architecture of these two disorders at the common variant level.

Radiation cataract in Heterogeneous Stock mice after γ-ray or HZE ion exposure

Health effects of space radiation are a serious concern for astronauts on long-duration missions. The lens of the eye is one of the most radiosensitive tissues in the body and, therefore, ocular health risks for astronauts is a significant concern. Studies in humans and animals indicate that ionizing radiation exposure to the eye produces characteristic lens changes, termed "radiation cataract," that can affect visual function. Animal models of radiation cataractogenesis have previously utilized inbred mouse or rat strains. These studies were essential for determining morphological changes and dose-response relationships between radiation exposure and cataract. However, the relevance of these studies to human radiosensitivity is limited by the narrow phenotypic range of genetically homogeneous animal models. To model radiation cataract in genetically diverse populations, longitudinal cataract phenotyping was nested within a lifetime carcinogenesis study in male and female heterogeneous stock (HS/Npt) mice exposed to 0.4 Gy HZE ions (n = 609) or 3.0 Gy γ-rays (n = 602) and in unirradiated controls (n = 603). Cataractous change was quantified in each eye for up to 2 years using Merriam-Focht grading criteria by dilated slit lamp examination. Virtual Optomotry™ measurement of visual acuity and contrast sensitivity was utilized to assess visual function in a subgroup of mice. Prevalence and severity of posterior lens opacifications were 2.6-fold higher in HZE ion and 2.3-fold higher in γ-ray irradiated mice compared to unirradiated controls. Male mice were at greater risk for spontaneous and radiation associated cataracts. Risk for cataractogenesis was associated with family structure, demonstrating that HS/Npt mice are well-suited to evaluate genetic determinants of ocular radiosensitivity. Last, mice were extensively evaluated for cataract and tumor formation, which revealed an overlap between individual susceptibility to both cancer and cataract.

Protective Effects of Different Doses of Ginsenoside-Rb1 Experimental Cataract Model That in Chick Embryos

PURPOSE

There has been increased interest in phytochemical antioxidants to prevent protein damage and aggregate formation in cataract treatment. In this study, the protective effect of different doses of Rb1 (GRb1), one of the ginsenosides of Panax Ginseng, in the experimental cataract model formed in chick embryos was investigated.

METHODS

Five different experimental groups were formed with 100 SPF fertilized eggs: Control (0.9% NaCl to physiological saline), hydrocortisone hemisuccinate sodium (HC), low dose (HC + L-GRb1 (1 mg/kg)), medium dose (HC+). M-GRb1 (2.5 mg/kg)), and high dose (HC + H-GRb1 (5 mg/kg)). All solutions were given to air sack at 15 days of incubation. On the 17th day, the bulbous oculi of the chick embryos were dissected. Cataract formations of the lenses, glutathione (GSH), malondialdehyde (MDA), total antioxidant (TAS), total oxidant (TOS) levels, Caspase-3 H-score, and TUNEL index were determined. In addition, crystalline alpha A (CRYAA) gene expression was evaluated.

RESULTS

Cataracts were observed in the control, HC, HC + L-GRb1, HC + M-GRb1, and HC + H-GRb1 groups with a frequency of 0%, 100%, 75%, 56.25%, and 100%, respectively. There were statistically significant differences between the control and HC groups in terms of TAS, TOS, MDA, GSH, Caspase-3 H-score, and TUNEL index (p < .05). When the therapeutic effect of the GRb1 groups was evaluated, the HC group showed significant differences with the HC + L-GRb1 and HC + M-GRb1 groups in almost all parameters (p < .05), while there was no statistical difference with the HC + H-GRb1 group (p > .05). In addition, gene expression levels differed between the groups, although not statistically significant (p > .05).

CONCLUSION

1 mg/kg and 2.5 mg/kg GRb1 applications show therapeutic properties on the HC-induced cataract model. This effect is more pronounced at 2.5 mg/kg.

Association between single nucleotide polymorphisms in exon 3 of the alpha-A-crystallin gene and susceptibility to age-related cataract

BACKGROUND

The mutations in the αA-crystallin (CRYAA) gene may contribute to the development of age-related cataract (ARC). In this study, we searched for single nucleotide polymorphisms (SNP) in exons of CRYAA and investigated the associations between the identified SNPs and the subtypes of ARC.

MATERIALS AND METHODS

Peripheral venous blood was collected for the extraction of genomic DNA. Three exons of CRYAA were sequenced to detect SNPs. The frequency distributions of alleles and genotypes were compared between the ARC and control groups.

RESULTS

There were 618 patients with various subtypes of ARC (nuclear cataract [NC], cortical cataract [CC], posterior subcapsular cataract [PSC]). The control group comprised 236 patients. The incidence of early-onset cataract was significantly greater in PSC patients (P = .002 for NC; P = .036 for CC). One SNP was detected in exon 3 of CRYAA (rs76740365 G>A). When the distribution of rs76740365 was compared among the ARC subtypes, only the difference between the PSC group and the control group was statistically significant (allele frequency: P = .000057, OR 2.945; genotype distribution frequency: P = .000458). The heterozygote genotype (GA) carried a significantly greater risk than the homozygous wild-type genotype (GG) by 1.742 times for all types of cataracts and 2.369 times for the PSC subtype.

CONCLUSIONS

The SNP rs76740365 G>A in exon 3 of the CRYAA gene is associated with greater susceptibility of ARC, particularly the PSC subtype. Individuals carrying the SNP rs76740365 G>A may be more likely to develop PSC at a younger age than other subtypes.

Polygenic Risk Score Improves Cataract Prediction in East Asian Population

Cataracts, characterized by crystalline lens opacities in human eyes, is the leading cause of blindness globally. Due to its multifactorial complexity, the molecular mechanisms remain poorly understood. Larger cohorts of genome-wide association studies (GWAS) are needed to investigate cataracts’ genetic basis. In this study, a GWAS was performed on the largest Han population to date, analyzing a total of 7079 patients and 13,256 controls from the Taiwan Biobank (TWB) 2.0 cohort. Two cataract-associated SNPs with an adjustment of p < 1 × 10−7 in the older groups and nine SNPs with an adjustment of p < 1 × 10−6 in the younger group were identified. Except for the reported AGMO in animal models, most variations, including rs74774546 in GJA1 and rs237885 in OXTR, were not identified before this study. Furthermore, a polygenic risk score (PRS) was created for the young and old populations to identify high-risk cataract individuals, with areas under the receiver operating curve (AUROCs) of 0.829 and 0.785, respectively, after covariate adjustments. Younger individuals had 17.45 times the risk while older people had 10.97 times the risk when comparing individuals in the highest and lowest PRS quantiles. Validation analysis on an independent TWB1.0 cohort revealed AUROCs of 0.744 and 0.659.

Genotype, Age, Genetic Background, and Sex Influence Epha2-Related Cataract Development in Mice

Purpose

Age-related cataract is the leading cause of blindness worldwide. Variants in the EPHA2 gene increase the disease risk, and its knockout in mice causes cataract. We investigated whether age, sex, and genetic background, risk factors for age-related cataract, and Epha2 genotype influence Epha2-related cataract development in mice.

Methods

Cataract development was monitored in Epha2+/+, Epha2+/-, and Epha2-/- mice (Epha2Gt(KST085)Byg) on C57BL/6J and FVB:C57BL/6J (50:50) backgrounds. Cellular architecture of lenses, endoplasmic reticulum (ER) stress, and redox state were determined using histological, molecular, and analytical techniques.

Results

Epha2-/- and Epha2+/- mice on C57BL/6J background developed severe cortical cataracts by 18 and 38 weeks of age, respectively, compared to development of similar cataract significantly later in Epha2-/- mice and no cataract in Epha2+/- mice in this strain on FVB background, which was previously reported. On FVB:C57BL/6J background, Epha2-/- mice developed severe cortical cataract by 38 weeks and Epha2+/- mice exhibited mild cortical cataract up to 64 weeks of age. Progression of cataract in Epha2-/- and Epha2+/- female mice on C57BL/6J and mixed background, respectively, was slower than in matched male mice. N-cadherin and β-catenin immunolabeling showed disorganized lens fiber cells and disruption of lens architecture in Epha2-/- and Epha2+/- lenses, coinciding with development of severe cataracts. EPHA2 immunolabeling showed intracellular accumulation of the mutant EPHA2-β-galactosidase fusion protein that induced a cytoprotective ER stress response and in Epha2+/- lenses was also accompanied by glutathione redox imbalance.

Conclusions

Both, Epha2-/- and Epha2+/- mice develop age-related cortical cataract; age as a function of Epha2 genotype, sex, and genetic background influence Epha2-related cataractogenesis in mice.

Inherited cataracts: Genetic mechanisms and pathways new and old

Cataract(s) is the clinical equivalent of lens opacity and is caused by light scattering either by high molecular weight protein aggregates in lens cells or disruption of the lens microarchitecture itself. Genetic mutations underlying inherited cataract can provide insight into the biological processes and pathways critical for lens homeostasis and transparency, classically including the lens crystallins, connexins, membrane proteins or components, and intermediate filament proteins. More recently, cataract genes have been expanded to include newly identified biological processes such as chaperone or protein degradation components, transcription or growth factors, channels active in the lens circulation, and collagen and extracellular matrix components. Cataracts can be classified by age, and in general congenital cataracts are caused by severe mutations resulting in major damage to lens proteins, while age related cataracts are associated with variants that merely destabilize proteins thereby increasing susceptibility to environmental insults over time. Thus there might be separate pathways to opacity for congenital and age-related cataracts whereby congenital cataracts induce the unfolded protein response (UPR) and apoptosis to destroy the lens microarchitecture, while in age related cataract high molecular weight (HMW) aggregates formed by denatured crystallins bound by α-crystallin result in light scattering without severe damage to the lens microarchitecture.

Common variants in SOX-2 and congenital cataract genes contribute to age-related nuclear cataract

Nuclear cataract is the most common type of age-related cataract and a leading cause of blindness worldwide. Age-related nuclear cataract is heritable (h² = 0.48), but little is known about specific genetic factors underlying this condition. Here we report findings from the largest to date multi-ethnic meta-analysis of genome-wide association studies (discovery cohort N = 14,151 and replication N = 5299) of the International Cataract Genetics Consortium. We confirmed the known genetic association of CRYAA (rs7278468, P = 2.8 × 10⁻¹⁶) with nuclear cataract and identified five new loci associated with this disease: SOX2-OT (rs9842371, P = 1.7 × 10⁻¹⁹), TMPRSS5 (rs4936279, P = 2.5 × 10⁻¹⁰), LINC01412 (rs16823886, P = 1.3 × 10⁻⁹), GLTSCR1 (rs1005911, P = 9.8 × 10⁻⁹), and COMMD1 (rs62149908, P = 1.2 × 10⁻⁸). The results suggest a strong link of age-related nuclear cataract with congenital cataract and eye development genes, and the importance of common genetic variants in maintaining crystalline lens integrity in the aging eye.

Here, the authors report a multi-ethnic genome wide association meta-analysis of 12 studies from the International Cataract Genetics Consortium. They find six new loci associated with age-related nuclear cataract, in addition to replicating the association at CRYAA, and suggest a strong genetic link between age-related nuclear and congenital cataracts.

Association of Age-Related Cataract With Skin Cancer in an Australian Population

Purpose

Ultraviolet radiation from sunlight contributes to age-related cataract and skin cancer. The EPHA2 gene is implicated in both these diseases. The purpose of this study was to determine whether age-related cataract and skin cancer are associated in a cohort of older Australians.

Methods

A cross-sectional study was performed using the Historical Cohort of the Registry of Senior Australians. Individuals aged ≥65 years or aged ≥50 years and of Aboriginal or Torres Strait Islander descent, who had an aged care eligibility assessment between July 2005 and June 2015, and had a history of cataract surgery and/or skin cancer according to the Australian Government Medicare Benefits Schedule dataset, during the 3-year period prior, were evaluated (N = 599,316). A multivariable logistic regression model was used to determine association and multiple hypothesis correction was employed.

Results

Of the evaluated individuals, 87,097 (14.5%) had a history of cataract and 170,251 (28.4%) a history of skin cancer. Among those with a history of cataract, 20,497 (23.5%), 1127 (1.3%), and 14,730 (16.9%) individuals had a concurrent history of keratinocyte, melanoma, and premalignant/solar keratosis, respectively. Those with a history of cataract were 19% more likely to have a history of skin cancer (odds ratio [OR], 1.19; 95% confidence interval [CI], (1.17–1.21). Co-occurrence of keratinocyte skin cancer was 16% (OR, 1.16; 95% CI, 1.14–1.18), melanoma 21% (OR, 1.21; 95% CI, 1.13–1.29), and premalignant/solar keratosis 19% (OR, 1.19; 95% CI, 1.17–1.22) more in the presence than absence of history of cataract.

Conclusions

Age-related cataract is positively associated with skin cancer and its subtypes, including premalignant lesions in an older Australian population.

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.

Exome Array Analysis of Nuclear Lens Opacity

PURPOSE

Nuclear cataract is the most common subtype of age-related cataract, the leading cause of blindness worldwide. It results from advanced nuclear sclerosis, or opacity in the center of the optic lens, and is affected by both genetic and environmental risk factors, including smoking. We sought to understand the genetic factors associated with nuclear sclerosis through interrogation of rare and low frequency coding variants using exome array data.

METHODS

We analyzed Illumina Human Exome Array data for 1,488 participants of European ancestry in the Beaver Dam Eye Study who were without cataract surgery for association with nuclear sclerosis grade, controlling for age and sex. We performed single-variant regression analysis for 32,138 variants with minor allele frequency (MAF) ≥0.003. In addition, gene-based analysis of 11,844 genes containing at least two variants with MAF < 0.05 was performed using a gene-based unified burden and non-burden sequence kernel association test (SKAT-O). Additionally, both single-variant and gene-based analyses were analyzed stratified by smoking status.

RESULTS

No single-variant test was statistically significant after Bonferroni correction (p < 1.6 × 10^-6; top single nucleotide polymorphism (SNP): rs144458991, p = 2.83 × 10^-5). Gene-based tests were suggestively associated with the gene RNF149 overall (p = 8.29 × 10^-6) and among never smokers (N = 790, p = 2.67 × 10^-6).

CONCLUSIONS

This study did not find a significant genetic association with nuclear sclerosis, the possible association with the RNF149 gene highlights a potential candidate gene for future studies that aim to understand the genetic architecture of nuclear sclerosis.

Peptides for targeting βB2-crystallin fibrils

Crystallins are a major family of proteins located within the lens of the eye. Cataracts are thought to be due to the formation of insoluble fibrillar aggregates, which are largely composed of proteins from the crystallin family. Today the only cataract treatment that exists is surgery and this can be difficult to access for individuals in the developing world. Development of novel pharmacotherapeutic approaches for the treatment of cataract rests on the specific targeting of these structures. βB2-crystallin, a member of β-crystallin family, is a large component of the crystallin proteins within the lens, and as such was used to form model fibrils in vitro. Peptides were identified, using phage display techniques, that bound to these fibrils with high affinity. Fibrillation of recombinantly expressed human βB2-crystallin was performed in 10% (v/v) trifluoroethanol (TFE) solution (pH 2.0) at various temperatures, and its amyloid-like structure was confirmed using Thioflavin-T (ThT) assay, transmission electron microscopy (TEM), and X-ray fiber diffraction (XRFD) analysis. Affinity of identified phage-displayed peptides were analyzed using enzyme-linked immunosorbent assay (ELISA). Specific binding of a cyclic peptide (CKQFKDTTC) showed the highest affinity, which was confirmed using a competitive inhibition assay.

Cataracts

An estimated 95 million people worldwide are affected by cataract. Cataract still remains the leading cause of blindness in middle-income and low-income countries. With the advancement of surgical technology and techniques, cataract surgery has evolved to small-incisional surgery with rapid visual recovery, good visual outcomes, and minimal complications in most patients. With the development of advanced technology in intraocular lenses, the combined treatment of cataract and astigmatism or presbyopia, or both, is possible. Paediatric cataracts have a different pathogenesis, surgical concerns, and postoperative clinical course from those of age-related cataracts, and the visual outcome is multifactorial and dependent on postoperative visual rehabilitation. New developments in cataract surgery will continue to improve the visual, anatomical, and patient-reported outcomes. Future work should focus on promoting the accessibility and quality of cataract surgery in developing countries.

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.

Mutations and mechanisms in congenital and age-related cataracts

The crystalline lens plays an important role in the refractive vision of vertebrates by facilitating variable fine focusing of light onto the retina. Loss of lens transparency, or cataract, is a frequently acquired cause of visual impairment in adults and may also present during childhood. Genetic studies have identified mutations in over 30 causative genes for congenital or other early-onset forms of cataract as well as several gene variants associated with age-related cataract. However, the pathogenic mechanisms resulting from genetic determinants of cataract are only just beginning to be understood. Here, we briefly summarize current concepts pointing to differences in the molecular mechanisms underlying congenital and age-related forms of cataract.

A Genome-Wide Association Study Provides New Evidence That CACNA1C Gene is Associated With Diabetic Cataract

Purpose

Diabetic cataract is one of the major eye complications of diabetes. It was reported that cataract occurs two to five times more frequently in patients with diabetes compared with those with no diabetes. The purpose of this study was to identify genetic contributors of diabetic cataract based on a genome-wide association approach using a well-defined Scottish diabetic cohort.

Methods

We adapted linked e-health records to define diabetic cataract. A diabetic cataract case in this study was defined as a type 2 diabetic patient who has ever been recorded in the linked e-health records to have cataracts in both eyes or who had previous cataract extraction surgeries in at least one eye. A control in this study was defined as a type 2 diabetic individual who has never been diagnosed as cataract in the linked e-health records and had no history of cataract surgeries. A standard genome-wide association approach was applied.

Results

Overall, we have 2341 diabetic cataract cases and 2878 controls in the genetics of diabetes audit and research in Tayside Scotland (GoDARTS) dataset. We found that the P value of rs2283290 in the CACNA1C gene was 8.81 × 10⁻¹⁰, which has reached genome-wide significance. We also identified that the blood calcium level was statistically different between diabetic cataract cases and controls.

Conclusions

We identified supporting evidence that CACNA1C gene is associated with diabetic cataract. The role of calcium in the cataractogenesis needs to be reevaluated in future studies.

Interaction Between Peroxisome Proliferator Activated Receptor δ and Epithelial Membrane Protein 2 Polymorphisms Influences HDL-C Levels in the Chinese Population

Peroxisome proliferator activated receptors (PPARs) are transcription factors involved in the regulation of key metabolic pathways. Numerous in vivo and in vitro studies have established their important roles in lipid metabolism. A few SNPs in PPAR genes have been reported to be associated with lipid levels. In this study, we aimed to investigate the interactive effects between single nucleotide polymorphisms (SNPs) in three PPAR isoforms α/δ/γ and other genetic variants across the genome on plasma high-density lipoprotein-cholesterol (HDL-C) levels. Study subjects (N = 2003) were genotyped using Illumina HumanOmniZhongHua-8 Beadchip. Fifty-three tag SNPs ± 100 kb of PPAR α, δ, and γ (r(2) < 0.2) were selected. The effect of interactions between PPAR SNPs and those across the genome on HDL-C was tested using linear regression models. One statistically significant interaction influencing HDL-C was detected between PPARδ SNP rs2267668 and epithelial membrane protein 2 (EMP2) downstream SNP rs7191411 (N = 1993, β = 0.74, adjusted P = 0.022). This interaction was successfully replicated in the meta-analysis of two additional Chinese cohorts (N = 3948, P = 0.01). The present study showed a novel SNP × SNP interaction between rs2267668 in PPARδ and rs7191411 in EMP2 that has significant impact on circulating HDL-C levels in the Singaporean Chinese population.

A pilot exome-wide association study of age-related cataract in Koreans

Age-related cataract (ARC) is the most common cause of visual impairment and blindness worldwide. A previous study reported that genetic factors could explain approximately 50% of the heritability of cataract. However, a genetic predisposition to ARC and the contributing factors have not yet been elucidated in the Korean population. In this study, we assessed the influence of genetic polymorphisms on the risk of ARC in Koreans, including 156 cataract cases and 138 healthy adults. We conducted an exome-wide association study using Illumina Human Exome-12v1.2 platform to screen 244,770 single nucleotide polymorphisms (SNPs). No SNPs reached exome-wide significance level of association (P < 1×10⁻⁶). B3GNT4 rs7136356 showed the most significant association with ARC (P = 6.54×10⁻⁵). Two loci (MUC16 and P2RY2) among the top 20 ARC-associated SNPs were recognized as probably linked to cataractogenesis. Functions of these genes were potentially related to regulating dehydration or homeostasis of the eyes, and showed a potential association with dry eye disease. This finding suggests that mucin- and dry eye disease-related genes may play a significant role in cataractogenesis. Our study provides insight into the genetic predisposition of ARC in Koreans. Additional studies with larger sample sizes are required to confirm the results of this study.

Genetic and Dietary Factors Influencing the Progression of Nuclear Cataract

Purpose

To determine the heritability of nuclear cataract progression and to explore prospectively the effect of dietary micronutrients on the progression of nuclear cataract.

Design

Prospective cohort study.

Participants

Cross-sectional nuclear cataract and dietary measurements were available for 2054 white female twins from the TwinsUK cohort. Follow-up cataract measurements were available for 324 of the twins (151 monozygotic and 173 dizygotic twins).

Methods

Nuclear cataract was measured using a quantitative measure of nuclear density obtained from digital Scheimpflug images. Dietary data were available from EPIC food frequency questionnaires. Heritability was modeled using maximum likelihood structural equation twin modeling. Association between nuclear cataract change and micronutrients was investigated using linear and multinomial regression analysis. The mean interval between baseline and follow-up examination was 9.4 years.

Main Outcome Measures

Nuclear cataract progression.

Results

The best-fitting model estimated that the heritability of nuclear cataract progression was 35% (95% confidence interval [CI], 13–54), and individual environmental factors explained the remaining 65% (95% CI, 46–87) of variance. Dietary vitamin C was protective against both nuclear cataract at baseline and nuclear cataract progression (β = −0.0002, P = 0.01 and β = −0.001, P = 0.03, respectively), whereas manganese and intake of micronutrient supplements were protective against nuclear cataract at baseline only (β = −0.009, P = 0.03 and β = −0.03, P = 0.01, respectively).

Conclusions

Genetic factors explained 35% of the variation in progression of nuclear cataract over a 10-year period. Environmental factors accounted for the remaining variance, and in particular, dietary vitamin C protected against cataract progression assessed approximately 10 years after baseline.

Polymorphism rs7278468 is associated with Age-related cataract through decreasing transcriptional activity of the CRYAA promoter

CRYAA plays critical functional roles in lens transparency and opacity, and polymorphisms near CRYAA have been associated with age-related cataract (ARC). This study examines polymorphisms in the CRYAA promoter region for association with ARC and elucidates the mechanisms of this association. Three SNPs nominally associated with ARC were identified in the promoter region of CRYAA: rs3761382 (P = 0.06, OR (Odds ratio) = 1.5), rs13053109 (P = 0.04, OR = 1.6), rs7278468 (P = 0.007, OR = 0.6). The C-G-T haplotype increased the risk for ARC overall (P = 0.005, OR = 1.8), and both alleles and haplotypes show a stronger association with cortical cataract (rs3761382, P = 0.002, OR = 2.1; rs13053109, P = 0.002, OR = 2.1; rs7278468, P = 0.0007, OR = 0.5; C-G-T haplotype, P = 0.0003, OR = 2.2). The C-G-T risk haplotype decreased transcriptional activity through rs7278468, which lies in a consensus binding site for the transcription repressor KLF10. KLF10 binding inhibited CRYAA transcription, and both binding and inhibition were greater with the T rs7278468 allele. Knockdown of KLF10 in HLE cells partially rescued the transcriptional activity of CRYAA with rs7278468 T allele, but did not affect activity with the G allele. Thus, our data suggest that the T allele of rs7278468 in the CRYAA promoter is associated with ARC through increasing binding of KLF-10 and thus decreasing CRYAA transcription.

Low-Cell-Number Epigenome Profiling Aids the Study of Lens Aging and Hematopoiesis

Understanding how chromatin modification regulates development and disease can be limited by available material. Despite recent progress, balancing high-quality and reliable mapping using chromatin-immunoprecipitation-based deep sequencing (ChIP-seq) remains a challenge. We report two techniques, recovery via protection (RP)-ChIP-seq and favored amplification RP-ChIP-seq (FARP-ChIP-seq), that provide reproducible mapping in as few as 500 cells. RP-ChIP-seq allows detection of age-associated epigenetic changes in a single mouse lens, whereas FARP-ChIP-seq accurately maps histone H3 lysine 4 trimethylation (H3K4me3) and H3K27me3 in long-term hematopoietic stem cells (LT-HSCs), short-term HSCs (ST-HSCs), and multi-potent progenitors (MPPs) from one mouse. These datasets not only highlight genes that may be involved in lens aging but also indicate a lack of H3K4me3/H3K27me3 bivalency on hematopoietic genes in HSCs.

Molecular Genetics of Cataract

Lens opacities or cataract(s) represent a universally important cause of visual impairment and blindness. Typically, cataract is acquired with aging as a complex disorder involving environmental and genetic risk factors. Cataract may also be inherited with an early onset either in association with other ocular and/or systemic abnormalities or as an isolated lens phenotype. Here we briefly review recent advances in gene discovery for inherited and age-related forms of cataract that are providing new insights into lens development and aging.

Cataract

Cataract is the leading cause of reversible blindness and visual impairment globally. Blindness from cataract is more common in populations with low socioeconomic status and in developing countries than in developed countries. The only treatment for cataract is surgery. Phacoemulsification is the gold standard for cataract surgery in the developed world, whereas manual small incision cataract surgery is used frequently in developing countries. In general, the outcomes of surgery are good and complications, such as endophthalmitis, often can be prevented or have good ouctomes if properly managed. Femtosecond laser-assisted cataract surgery, an advanced technology, can automate several steps; initial data show no superiority of this approach over current techniques, but the results of many large clinical trials are pending. The greatest challenge remains the growing 'backlog' of patients with cataract blindness in the developing world because of lack of access to affordable surgery. Efforts aimed at training additional cataract surgeons in these countries do not keep pace with the increasing demand associated with ageing population demographics. In the absence of strategie that can prevent or delay cataract formation, it is important to focus efforts and resources on developing models for efficient delivery of cataract surgical services in underserved regions. For an illustrated summary of this Primer, visit: http://go.nature.com/eQkKll.

Quantitative proteomics analysis by iTRAQ in human nuclear cataracts of different ages and normal lens nuclei

PURPOSE

The goal of this study was to quantitatively identify the differentially expressed proteins in nuclear cataracts of different ages and normal lens nuclei in humans.

EXPERIMENTAL DESIGN

Forty-eight human lens nucleus samples with hardness grades III, IV were obtained during cataract surgery by extracapsular cataract extraction. Seven normal transparent human lens nuclei were obtained from fresh normal cadaver eyes during corneal transplantation surgery. Lens nuclei were divided into seven groups according to age and optic axis: Group A (average age 80.8 ± 1.2 years), Group B (average age 57.0 ± 4.0 years), Group C average age 80.3 ± 4.5 years), Group D (average age 56.9 ± 4.2 years), Group E (average age 78.1 ± 2.5 years), Group F (average age 57.6 ± 3.3 years) and Group G (seven normal transparent human lenses from normal cadaver eyes, average age 34.7 ± 4.2 years). Water-soluble, water-insoluble, and water-insoluble-urea-soluble protein fractions were extracted from samples. The three-part protein fractions from the individual lenses were combined to form the total proteins of each sample. The proteomic profiles of each group were further analyzed using 8-plex iTRAQ labeling combined with 2D-LC-MS/MS. The data were analyzed with the ProteinPilot software for peptide matching, protein identification, and quantification. Differentially expressed proteins were validated by Western blotting.

RESULTS

We employed biological and technical replicates and selected the intersection of the two results, which included 80 proteins. Nine proteins were differentially expressed among the 80 proteins identified using proteomic techniques. In age-related nuclear cataracts (ARNC), the expression levels of fatty acid-binding protein and pterin-4-alpha-carbinolamine dehydratase were upregulated, whereas the levels of alpha-crystallin B chain (CRYAB), GSH synthetase, phakinin, gamma-crystallin C, phosphoglycerate kinase 1, betaine-homocysteine S-methyltransferase 1 (BHMT1), and spectrin beta chain were downregulated. These proteins may be associated with abnormal protein aggregation and oxidative stress. GSH synthetase and CRYAB expression levels in the nuclear cataract decreased with age. The mass spectrometric analysis results were consistent with the Western blot validation.

CONCLUSION AND CLINICAL RELEVANCE

The results indicate that CRYAB and GSH synthetase may be involved in ARNC pathogenesis. iTRAQ combined with 2D-LC-MS/MS provides new methods for future studies of pathological mechanisms and protective drug development for ARNC.