UV-mediated cataractogenesis: a radical perspective

BLM can regulate cataract progression by influencing cell vitality and apoptosis

Age-related cataract (ARC) is the most common cause of severe visual impairment and blindness. The precise mechanisms of ARC are not completely understood, but it is well accepted that oxidative damage plays an important role in the disease pathogenesis. BLM, the key enzyme of the double-strand break repair (DSBR) pathway, is part of a family of DNA unwinding enzymes and has a crucial role in multiple steps of the DNA recombination, replication and repair processes. We have recently shown that BLM-rs1063147 is initially associated with nuclear ARC in a cross-section study. Therefore, we wanted to study the effects of BLM on ARC progression. In ARC patients, BLM transcription in lens capsules was decreased, so did the BLM protein, and after UVB irradiation, BLM mRNA and protein levels were increased in SRA01/04 cells. Upon silencing BLM in SRA01/04 cells and rat lens, cell vitality and apoptosis were altered, and the rat lens opacification was considerable. In conclusion, BLM can regulate cataract progression by influencing cell vitality and apoptosis.

PARP-1/PAR Activity in Cultured Human Lens Epithelial Cells Exposed to Two Levels of UVB Light

This study investigated poly(ADP-ribose) polymerase-1 (PARP-1) activation in cultured human lens epithelial cells exposed to two levels of UVB light (312 nm peak wavelength), 0.014 and 0.14 J cm^-2 ("low" and "high" dose, respectively). At the low dose, PARP-1 and poly(ADP-ribose) (PAR) polymers acted to repair DNA strand breaks rapidly with no subsequent major effects on either cell morphology or viability. However, following the high UVB dose, there was a dramatic second phase of PARP-1 activation, 90 min later, which included a sudden reappearance of DNA strand breaks, bursts of reactive oxygen species (ROS) formation within both the mitochondria and nucleus, a translocation of PAR from the nucleus to the mitochondria and an ultimate 70% loss of cell viability occurring after 24 h. The results provide evidence for an important role for PARP-1 in protecting the human lens epithelium against low levels of UVB light, and possibly participating in the triggering of cell death following exposure to toxic levels of radiation.

Expression of DNA repair genes in lens cortex of age-related cortical cataract

The formation and development of age-related cataract (ARC) has been demonstrated to have the involvement of defective DNA repair in lens epithelial cells (LECs). This study aimed to investigate DNA repair genes expression in human lens cortex collected from age-related cortical cataract (ARCC) and controls during surgery. The expression levels of the genes were evaluated by xx genes microarray analysis. The results were further confirmed by Quantitative Real-Time PCR (qRT-PCR). The mRNA levels of 7 genes decreased and 4 genes out of 92 genes increased in lens cortex of ARCCs compared with controls with the fold change >1.5. Using Comet assay, we found the DNA breaks in the LECs of ARCCs were obviously severer than that of controls. The present data provide a global perspective on expression of DNA repair genes that may contribute to cataract pathogenesis. The DNA damage and repair pathway might be an effective target to delay the onset of ARC.

Ultraviolet-B induces ERCC6 repression in lens epithelium cells of age-related nuclear cataract through coordinated DNA hypermethylation and histone deacetylation

Background

Ultraviolet-B (UVB) exposure attributes to the formation of age-related nuclear cataract (ARNC), which is mediated with DNA damage. DNA damage, an important factor for pathogenesis of ARNC, is induced by UVB, and is generally resolved by the nucleotide excision repair (NER) repair mechanism. Cockayne syndrome complementation group B (CSB) protein coded by ERCC6 is a vital component for NER. However, we found no association between selected ERCC6 polymorphisms and ARNC. In this study, we investigated whether UVB exposure could alter ERCC6 expression and the process could involve epigenetic changes of DNA methylation and/or histone acetylation of ERCC6 in the lens epithelial cells (LECs). We also assessed the involvement of those coordinated changes in lens tissue from ARNC patients.

Results

mRNA and protein expression of ERCC6 in lens tissue (LECs) were lower in ARNCs than those in the controls. This reduction corresponded to methylation of a CpG site at the ERCC6 promoter and histone modifications (methylation and acetylation) nearby this site. UVB-treated human lens epithelium B3 (HLE-B3) and 239T cell presented (1) increased apoptosis, suggesting reduced UV-damage repair, (2) hypermethylation of the CpG site located at position -441 (relative to transcription start site) within the binding region for transcriptional factor Sp1 in the ERCC6 promoter, (3) the enhancement of histone H3K9 deacetylation, (4) induction in DNA methyltransferases 3b (DNMT3b) and histone deacetylase1 (HDAC1) associated to the CpG site of ERCC6 by CHIP assay.

Conclusions

These findings suggest an orchestrated mechanism triggered by UVB radiation where the concurrent association of specific hypermethylation CpG site, H3K9 deacetylation of ERCC6, and repression of ERCC6 gene expression. Taken together, with the similar changes in the lens tissue from ARNC patients, our data unveiled a possible mechanism of epigenetic modification of DNA repair gene in the pathogenesis of ARNC.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0229-y) contains supplementary material, which is available to authorized users.

Oxidative stress to the cornea, changes in corneal optical properties, and advances in treatment of corneal oxidative injuries

Oxidative stress is involved in many ocular diseases and injuries. The imbalance between oxidants and antioxidants in favour of oxidants (oxidative stress) leads to the damage and may be highly involved in ocular aging processes. The anterior eye segment and mainly the cornea are directly exposed to noxae of external environment, such as air pollution, radiation, cigarette smoke, vapors or gases from household cleaning products, chemical burns from splashes of industrial chemicals, and danger from potential oxidative damage evoked by them. Oxidative stress may initiate or develop ocular injury resulting in decreased visual acuity or even vision loss. The role of oxidative stress in the pathogenesis of ocular diseases with particular attention to oxidative stress in the cornea and changes in corneal optical properties are discussed. Advances in the treatment of corneal oxidative injuries or diseases are shown.

Ocular aldehyde dehydrogenases: protection against ultraviolet damage and maintenance of transparency for vision

Aldehyde dehydrogenase (ALDH) enzymes catalyze the NAD(P)(+)-dependent oxidation of a wide variety of endogenous and exogenous aldehydes to their corresponding acids. Some members of the ALDH superfamily of enzymes are abundantly expressed in the mammalian cornea and lens in a taxon-specific manner. Considered to be corneal and lens crystallins, they confer protective and transparent properties upon these ocular tissues. ALDH3A1 is highly expressed in the cornea of most mammals, with the exception of rabbit that expresses exclusively ALDH1A1 in the cornea. ALDH1A1 is present in both the cornea and lens of several animal species. As a result of their catalytic and non-catalytic functions, ALDH3A1 and ALDH1A1 proteins protect inner ocular tissues from ultraviolet radiation and reactive oxygen-induced damage. In addition, these corneal crystallins contribute to cellular transparency in corneal stromal keratocytes, supporting a structural role of these ALDH proteins. A putative regulatory function of ALDH3A1 on corneal cell proliferation has also been proposed. Finally, the three retinaldehyde dehydrogenases cooperatively mediate retinoic acid signaling during the eye development.

Effect of two different UVA doses on the rabbit cornea and lens

The aim of the present paper was to examine the irradiation effect of two doses of UVA rays (365 nm) on the rabbit cornea and lens. Corneas of anesthetized adult albino rabbits were irradiated with UVA rays for 5 days (daily dose 1.01 J cm(-2) in one group of rabbits and daily dose 2.02 J cm(-2) in the second group of animals). The third day after the last irradiation, the rabbits were killed, and their eyes were employed for spectrophotometrical, biochemical and immunohistochemical investigations. Normal eyes served as controls. Absorption spectra of the whole corneal centers were recorded over the UV-VIS (visible) spectral range. Levels of antioxidant and prooxidant enzymes, nitric oxide synthases and nitric oxide (indirectly measured as nitrate concentration) were investigated in the cornea. Malondialdehyde, a byproduct of lipid peroxidation, was examined in the cornea and lens. The results show that the staining for endothelial nitric oxide synthase was more pronounced in corneas irradiated with the higher UVA dose. Otherwise, UVA rays at either dose did not significantly change corneal light absorption properties and did not cause statistically significant metabolic changes in the cornea or lens. In conclusion, UVA rays at the employed doses did not evoke harmful effects in the cornea or lens.

Can lenticular factors improve the posttrauma fate of neurons?

The intraocular lens has recently been recognized as a potential source for neuroprotective and neurite-promoting activities. The lens is ontogenetically and functionally a peculiar intraocular tissue with the unique feature of performing incomplete cellular apoptosis throughout the lifetime. The ectodermally derived epithelial cells permanently divide to produce the nuclei- and organelle-free lens fibre cells that allow for the optical transparency. The underlying extremely specific physical, biochemical, metabolic and structural mechanism lead to efficient protection from photo-oxidative stress caused by exposure to short-wavelength light. The fact that fibre cells undergo incomplete apoptosis is also of crucial importance to other cellular systems. In particular, injured nerve cells such as axotomized retinal ganglion cells may profit from the apoptosis-blocking mechanisms operating within the lens fibres. In this review we first discuss some factors involved in the lens differentiation and partial apoptosis as a basic principle of long-term survival. We then present recent experimental evidence that lenticular factors also operate outside the lens, and in particular within the retina to contribute to axonal regeneration, e.g. after a trauma. In turn, factors such as GAP-43 that were thought to be exclusively expressed within nervous tissue have now also been discovered within the lenticular tissue. Experiments of the direct confrontation of lenticular epithelial and fibre cells with regenerating ganglion cell axons in vitro are presented. It is concluded that survival factors supplied by the lens might be used to facilitate survival within neuronal tissue.

Long-term lens organ culture system to determine age-related effects of UV irradiation on the eye lens

Aging of the eye lens represents the life-long accumulation of damage. Factors responsible for age-related cataract are unknown because medical evaluations of aged populations demonstrate a wide range of systemic diseases and medical disorders. There are some main suspected factors, which may contribute to accumulated age-related damage in the eye lens. (1) Diseases, such as diabetes, substantially increase the probability of cataract formation in the age group from 40 to 49, and double or triple this probability for ages 50 to 69. (2) Drugs, including systemic medications such as steroids. (3) Environmental factors, such as UV radiation, heat and electromagnetic radiation. Our study represents an effort to determine the effects of suspected cataractogenic factors on the eye lens. The experiments are performed using a unique long-term lens organ culture system of bovine lenses. In our system it is possible to give controlled amounts of insult and monitor changes in lens optical quality throughout the culture period of 8-15 days. The optical properties, monitored in association with biochemical analysis of lens epithelium, cortex and nuclear samples, help in determining the mechanisms of cataract formation. The present study investigates mechanisms by which UV-A radiation at 365 nm causes damage to the lens. It is believed that solar radiation is one of the major environmental factors involved in lens cataractogenesis. Bovine lenses were placed in our special culture cells for pre-incubation of 24 hr followed by irradiation of 29 or 33 J cm(-2). The lenses were maintained in the cells during irradiation. After irradiation, lens optical quality was monitored throughout the culture period and lens epithelium was taken for enzyme analysis. Using the culture system we learned that: (a) young lenses (less than one-year-old) are less sensitive to UV radiation than 3-year-old lenses; (b) the lenses have the ability to recover in organ culture conditions; (c) applying the insult in one step results in less damage than dividing the same insult in 4 steps with 24 hr interval between each one; and (d) the damage from UV is greater if the intervals between each irradiation stage are insufficient to permit full recovery.

Oxidative deoxyribonucleic acid damage in the eyes of glaucoma patients

BACKGROUND

Little is known about the molecular mechanisms responsible for the development of glaucoma, the leading cause of irreversible blindness worldwide. Some investigators have hypothesized that oxidative damage may be involved. We evaluated oxidative deoxyribonucleic acid (DNA) damage, in terms of 8-hydroxy-2'-deoxyguanosine (8-OH-dG), in the eyes of glaucoma patients.

METHODS

Levels of 8-OH-dG were measured in the trabecular meshwork region from 42 patients with glaucoma and 45 controls of similar age and sex. Genotypes of glutathione S-transferase isoenzymes (GSTM1 and GSTT1) were assessed by polymerase chain reaction in the same DNA samples.

RESULTS

Levels of 8-OH-dG were significantly higher in glaucoma patients than in controls. Oxidative DNA damage in patients with glaucoma correlated significantly with intraocular pressure; in patients with primary open-angle glaucoma, it also correlated with visual field defects. GSTT1 was similar in the two groups, and had no effect on 8-OH-dG levels. Conversely, 8-OH-dG levels were significantly higher in GSTM1-null than in GSTM1-positive subjects. The GSTM1-null genotype was significantly more common in patients with primary open-angle glaucoma than in controls.

CONCLUSION

Oxidative DNA damage is significantly increased in the trabecular meshwork of glaucoma patients. GSTM1 gene deletion, which has been associated with an increased risk of cancer at various sites and molecular lesions in atherosclerosis, predisposes to more severe oxidative DNA damage in glaucoma patients. These findings may contribute to understanding the pathogenesis of glaucoma and may be useful in the prevention and treatment of this disease.

Health effects from stratospheric ozone depletion and interactions with climate change

The potential health effects of elevated levels of ambient UV-B radiation are diverse, and it is difficult to quantify the risks, especially as they are likely to be considerably modified by human behaviour. Nevertheless epidemiological and experimental studies have confirmed that UV radiation is a definite risk factor for certain types of cataract, with peak efficacy in the UV-B waveband. The causal link between squamous cell carcinoma and cumulative solar UV exposure has been well established. New findings regarding the genetic basis of skin cancer, including studies on genetically modified mice, have confirmed the epidemiological evidence that UV radiation contributes to the formation of basal cell carcinomas and cutaneous melanomas, For the latter, animal models have demonstrated that UV exposure at a very young age is more detrimental than exposure in adulthood. Although suppression of certain immune responses has been recognised following UV exposure, the impact of this suppression on the control of infectious and autoimmune diseases is largely unknown. However, studies on several microbial infections have indicated significant consequences in terms of symptoms or reactivation of disease. The possibility that the immune response to vaccination could be depressed by UV-B exposure is of considerable concern. Newly emerging possibilities regarding interactions between ozone depletion and global climate change further complicate the risk assessments for human health but might result in an increased incidence of cataracts and skin cancer, plus alterations in the patterns of certain categories of infectious and other diseases.