Polygenic effects and cigarette smoking account for a portion of the familial aggregation of nuclear sclerosis

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.

A review on ocular findings in mouse lemurs: potential links to age and genetic background

Mouse lemurs, the world's smallest primates, inhabit forests in Madagascar. They are nocturnal, arboreal and dependent on vision for their everyday lives. In the last decades, the grey mouse lemur became increasingly important for biomedical research, in particular aging research. Experiments which require the combination of visual fitness and old age consequently depend on a solid knowledge of ocular pathologies. Although ocular diseases in mouse lemurs have been described as being common, they have not received much attention so far. Yet it is important to know when and why ocular diseases in captive mouse lemurs may occur. This review aims to provide a comprehensive overview of known ocular findings in mouse lemurs. It summarizes the frequency of ocular findings in captive mouse lemur colonies and points to their likely causes and treatment options based on the evidence available from other animals and humans. In addition, it shall be discussed whether age or genetic background may affect their development. This review may be used as a reference for future studies which require an assessment of visual performance in mouse lemurs and help to evaluate observed clinical signs and ocular diseases. Furthermore, the high incidence of specific diseases may provide new perspectives and set the groundwork for a new animal model for ocular research.

Photoperiodic regime influences onset of lens opacities in a non-human primate

Background

Opacities of the lens are typical age-related phenomena which have a high influence on photoreception and consequently circadian rhythm. In mouse lemurs, a small bodied non-human primate, a high incidence (more than 50% when >seven years) of cataracts has been previously described during aging. Previous studies showed that photoperiodically induced accelerated annual rhythms alter some of mouse lemurs’ life history traits. Whether a modification of photoperiod also affects the onset of age dependent lens opacities has not been investigated so far. The aim of this study was therefore to characterise the type of opacity and the mouse lemurs’ age at its onset in two colonies with different photoperiodic regimen.

Methods

Two of the largest mouse lemur colonies in Europe were investigated: Colony 1 having a natural annual photoperiodic regime and Colony 2 with an induced accelerated annual cycle. A slit-lamp was used to determine opacities in the lens. Furthermore, a subset of all animals which showed no opacities in the lens nucleus in the first examination but developed first changes in the following examination were further examined to estimate the age at onset of opacities. In total, 387 animals were examined and 57 represented the subset for age at onset estimation.

Results

The first and most commonly observable opacity in the lens was nuclear sclerosis. Mouse lemurs from Colony 1 showed a delayed onset of nuclear sclerosis compared to mouse lemurs from Colony 2 (4.35 ± 1.50 years vs. 2.75 ± 0.99 years). For colony 1, the chronological age was equivalent to the number of seasonal cycles experienced by the mouse lemurs. For colony 2, in which seasonal cycles were accelerated by a factor of 1.5, mouse lemurs had experienced 4.13 ± 1.50 seasonal cycles in 2.75 ± 0.99 chronological years.

Discussion

Our study showed clear differences in age at the onset of nuclear sclerosis formation between lemurs kept under different photoperiodic regimes. Instead of measuring the chronological age, the number of seasonal cycles (N = four) experienced by a mouse lemur can be used to estimate the risk of beginning nuclear sclerosis formation. Ophthalmological examinations should be taken into account when animals older than 5–6 seasonal cycles are used for experiments in which unrestricted visual ability has to be ensured. This study is the first to assess and demonstrate the influence of annual photoperiod regime on the incidence of lens opacities in a non-human primate.

Increased VEGF-A promotes multiple distinct aging diseases of the eye through shared pathomechanisms

While increased VEGF‐A has been associated with neovascular age‐related macular degeneration (AMD), it is not known whether VEGF‐A may also promote other age‐related eye diseases. Here, we show that an increase in VEGF‐A is sufficient to cause multiple distinct common aging diseases of the eye, including cataracts and both neovascular and non‐exudative AMD‐like pathologies. In the lens, increased VEGF‐A induces age‐related opacifications that are associated with ERK hyperactivation, increased oxidative damage, and higher expression of the NLRP3 inflammasome effector cytokine IL‐1β. Similarly, increased VEGF‐A induces oxidative stress and IL‐1β expression also in the retinal pigment epithelium (RPE). Targeting NLRP3 inflammasome components or Il1r1 strongly inhibited not only VEGF‐A‐induced cataract formation, but also both neovascular and non‐exudative AMD‐like pathologies. Moreover, increased VEGF‐A expression specifically in the RPE was sufficient to cause choroidal neovascularization (CNV) as in neovascular AMD, which could be inhibited by RPE‐specific inactivation of Flk1, while Tlr2 inactivation strongly reduced CNV. These findings suggest a shared pathogenic role of VEGF‐A‐induced and NLRP3 inflammasome‐mediated IL‐1β activation for multiple distinct ocular aging diseases.

Mitochondrial oxygen metabolism in primary human lens epithelial cells: Association with age, diabetes and glaucoma

PURPOSE

The hypoxic environment around the lens is important for maintaining lens transparency. Lens epithelial cells (LECs) play a key role in lens metabolism. We measured oxygen consumption to assess the role of human LECs in maintaining hypoxia around the lens, as well as the impact of systemic and ocular diagnosis on these cells.

METHODS

Baseline cellular respiration was measured in rabbit LECs (NN1003A), canine kidney epithelial cells (MDCK), trabecular meshwork cells (TM-5), and bovine corneal endothelial cells (CCEE) using a XF96 Extracellular Flux Analyzer (Seahorse Bioscience, North Billerica, MA), which measures oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in vitro. Following informed written consent, lens capsule epithelial cells were obtained from patients during cataract surgery and were divided into small explants in 96-well plates. Capsules were removed when LECs became confluent. OCR was normalized to the number of cells per well using rabbit LECs as a standard. The effect of patient age, sex, race, and presence of diabetes or glaucoma on oxygen consumption was assessed by using the Mann-Whitney U test and multivariate regression analysis.

RESULTS

Primary LECs were obtained from 69 patients. The OCR from donors aged 70 and over was lower than that of those under 70 years (2.21±1.037 vs. 2.86±1.383 fmol/min/cell; p<0.05). Diabetic patients had lower OCR than non-diabetic patients (2.02±0.911 vs. 2.79±1.332fmol/min/cell; p<0.05), and glaucoma patients had lower OCR than non-glaucoma patients (2.27±1.19 vs. 2.83±1.286 fmol/min/cell; p<0.05). Multivariate regression analysis confirmed that donors aged 70 and over (p<0.05), diabetic patients (p<0.01), and glaucoma patients (p<0.05) had significantly lower OCR, independent of other variables. Gender and race had no significant effect on OCR.

CONCLUSIONS

The lower oxygen consumption rate of human LECs in older donors and patients with diabetes or glaucoma could contribute to cataract development. Diabetes and glaucoma are particularly important factors associated with decreased OCR, independent of age. Ongoing studies are examining pO2 at the anterior surface of the lens in vivo and oxygen consumption in the patient's LECs.

Density of common complex ocular traits in the aging eye: analysis of secondary traits in genome-wide association studies

Genetic association studies are identifying genetic risks for common complex ocular traits such as age-related macular degeneration (AMD). The subjects used for discovery of these loci have been largely from clinic-based, case-control studies. Typically, only the primary phenotype (e.g., AMD) being studied is systematically documented and other complex traits (e.g., affecting the eye) are largely ignored. The purpose of this study was to characterize these other or secondary complex ocular traits present in the cases and controls of clinic-based studies being used for genetic study of AMD. The records of 100 consecutive new patients (of any diagnosis) age 60 or older for which all traits affecting the eye had been recorded systematically were reviewed. The average patient had 3.5 distinct diagnoses. A subset of 10 complex traits was selected for further study because they were common and could be reliably diagnosed. The density of these 10 complex ocular traits increased by 0.017 log-traits/year (P = 0.03), ranging from a predicted 2.74 at age 60 to 4.45 at age 90. Trait-trait association was observed only between AMD and primary vitreomacular traction (P = 0.0009). Only 1% of subjects age 60 or older had no common complex traits affecting the eye. Extrapolations suggested that a study of 2000 similar subjects would have sufficient power to detect genetic association with an odds ratio of 2.0 or less for 4 of these 10 traits. In conclusion, the high prevalence of complex traits affecting the aging eye and the inherent biases in referral patterns leads to the potential for confounding by undocumented secondary traits within case-control studies. In addition to the primary trait, other common ocular phenotypes should be systematically documented in genetic association studies so that adjustments for potential trait-trait associations and other bias can be made and genetic risk variants identified in secondary analyses.

Epidemiology of cataract: accomplishments over 25 years and future directions

The purpose of this review is to highlight the advances made by epidemiologic research into cataract. Considerable progress has been made in characterizing phenotypes, determining the prevalence and incidence in various population groups, and understanding risk factors for cataract. Cataract surgery research has documented functional improvements following surgery and has identified aspects of surgery delivery that could be made. Cataract is an independent marker of early mortality, providing a possible system for studying the aging process. Promising future work in cataract epidemiology is highlighted. Despite the availability of cataract surgery, cataract is still the leading cause of blindness worldwide. From a public health standpoint, research that can identify ways to delay onset or progression, or achieve the holy grail of prevention of cataract, should remain a leading priority.

Maintaining transparency: a review of the developmental physiology and pathophysiology of two avascular tissues

The lens and cornea are transparent and usually avascular. Controlling nutrient supply while maintaining transparency is a physiological challenge for both tissues. During sleep and with contact lens wear the endothelial layer of the cornea may become hypoxic, compromising its ability to maintain corneal transparency. The mechanism responsible for establishing the avascular nature of the corneal stroma is unknown. In several pathological conditions, the stroma can be invaded by abnormal, leaky vessels, leading to opacification. Several molecules that are likely to help maintain the avascular nature of the corneal stroma have been identified, although their relative contributions remain to be demonstrated. The mammalian lens is surrounded by capillaries early in life. After the fetal vasculature regresses, the lens resides in a hypoxic environment. Hypoxia is likely to be required to maintain lens transparency. The vitreous body may help to maintain the low oxygen level around the lens. The hypothesis is presented that many aspects of the aging of the lens, including increased hardening, loss of accommodation (presbyopia), and opacification of the lens nucleus, are caused by exposure to oxygen. Testing this hypothesis may lead to prevention for nuclear cataract and insight into the mechanisms of lens aging. Although they are both transparent, corneal pathology is associated with an insufficient supply of oxygen, while lens pathology may involve excessive exposure to oxygen.

Optometrists as key providers in the prevention and early detection of malignancies

Optometrists have become active in many aspects of primary health care. Opportunities exist for optometrists to join other health care providers in the fight against cancer. The purpose of this article is to review information about cancer epidemiology, describe cancer screening guidelines, and to provide examples of ways for optometrists to become involved in promoting goals for reducing cancer risk and increasing the early detection of cancer. In addition to diagnosing ocular cancers and metastases to the eye and orbital region, optometrists may provide cancer information as part of their case history, provide positive health messages to reduce cancer risk factors, and directly observe signs of skin cancer.

2005 Gregg Lecture: Congenital cataract--from rubella to genetics

On the 65th anniversary of Gregg's observation "Congenital cataract following German measles in the mother", rubella has retired as the leading cause of congenital cataract, from 87% of Gregg's cohort to less than 3% over the last 25 years and almost zero now in Australia and other developed countries. However, people must keep vigilance in maintaining immunization rates and encourage immunization in developing countries. At least one-fifth of congenital cataract is familial. Understanding the genetics of familial cataract will lead to better treatment of congenital as well as age-related cataract.