Influence of UVA light stress on photoreceptor cell metabolism: decreased rates of rhodopsin regeneration and opsin synthesis

Ultraviolet A-induced oxidation in cornea: Characterization of the early oxidation-related events

Exposure to sunlight ultraviolet-A (UVA), the main component of solar UV reaching the eyes, is suspected to play an important part in the onset of ocular pathologies. UVA primary biological deleterious effects arise from the photo-induction of oxidative stress in cells. However, the molecular bases linking UVA-induced oxidation to UVA toxicity in eyes remain poorly understood, especially with regards to the cornea. To shed some light on this issue, we have investigated the susceptibility and response potential of the different corneal cellular layers (epithelium, stroma and endothelium) to UVA-induced oxidation. We have monitored UVA-induced immediate effects on cellular redox balance, on mitochondrial membrane potential, on 8-Hydroxy-2'-deoxyguanosine (8-OHdG) accumulation in cellular DNA and on S-glutathionylated proteins (PSSG) levels along whole rabbit corneas. Higher redox imbalance was observed in the posterior part of the cornea following irradiation. Conversely, UVA-altered mitochondrial membrane potentials were observed only in anterior portions of the cornea. UVA-induced 8-OHdG were found in nuclear DNA of epithelia, while they were found in both nuclear and mitochondrial DNA in stromal and endothelial cells. Finally, significantly higher levels of cytosolic PSSG were measured in epithelia and endothelia immediately after UVA exposure, but not in stromas. Taken together, our findings indicate that while corneal epithelial cells are subjected to important modifications in response to UVA exposure, they efficiently limit the early manifestations of UVA-induced toxicity. On the other hand, the corneal endothelium is more susceptible to UVA-induced oxidation-related toxicity.

The protective effects of bilberry and lingonberry extracts against UV light-induced retinal photoreceptor cell damage in vitro

Bilberry extract (B-ext) and lingonberry extract (L-ext) are currently used as health supplements. We investigated the protective mechanisms of the B-ext and L-ext against ultraviolet A (UVA)-induced retinal photoreceptor cell damage. Cultured murine photoreceptor (661W) cells were exposed to UVA following treatment with B-ext and L-ext and their main constituents (cyanidin, delphinidin, malvidin, trans-resveratrol, and procyanidin). B-ext, L-ext, and constituents improved cell viability and suppressed ROS generation. Phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK), c-Jun N-terminal kinase (JNK), and protein kinase B (Akt) were analyzed by Western blotting. B-ext and cyanidin inhibited phosphorylation of p38 MAPK, and B-ext also inhibited phosphorylation of JNK by UVA. L-ext, trans-resveratrol, and procyanidin alleviated the reduction of phosphorylated Akt levels by UVA. Finally, a cotreatment with B-ext and L-ext showed an additive effect on cell viability. Our findings suggest that both B-ext and L-ext endow protective effects against UVA-induced retinal damage.

Influence of ultraviolet radiation on selected physiological responses of earthworms

The purpose of this study was to investigate the adverse effects of ultraviolet (UV) radiation on earthworms. Earthworms that crawl out of the soil may die within a few hours after sunrise. This study shows that UV exposure can be lethal. In general, UV-B had a stronger damaging effect than UV-A. Different species of earthworms had different tolerances to UV exposure. In this study, Pontoscolex corethrurus showed the highest tolerance of the three tested species to UV radiation, while Amynthas graciliswas the most sensitive. UV radiation induced both acute and chronic responses. The acute response, which occurred immediately on or after UV exposure, was characterized by the appearance of abnormally strong muscle contractions,including S-shaped movements and jumping behavior, possibly caused by bad coordination between the circular and longitudinal muscles. The chronic response included damage to the skin and muscle cells, which resulted in a high mortality rate. Oxygen consumption by A. gracilis was significantly decreased after exposure to UV-A or UV-B. Since the circulation in earthworms is mediated by muscle contraction and the skin is the main organ of respiration, it is reasonable to expect that abnormal muscle contraction and a damaged epithelium could cause suffocation. Because of their sensitive responses, we propose that some earthworms, such as A. gracilis,could serve as a new model for studying UV-induced photodamage.

Light-induced damage to the retina: role of rhodopsin chromophore revisited

The presence of the regenerable visual pigment rhodopsin has been shown to be primarily responsible for the acute photodamage to the retina. The photoexcitation of rhodopsin leads to isomerization of its chromophore 11-cis-retinal to all-trans-retinal (ATR). ATR is a potent photosensitizer and its role in mediating photodamage has been suspected for over two decades. However, there was lack of experimental evidence that free ATR exists in the retina in sufficient concentrations to impose a risk of photosensitized damage. Identification in the retina of a retinal dimer and a pyridinium bisretinoid, so called A2E, and determination of its biosynthetic pathway indicate that substantial amounts of ATR do accumulate in the retina. Both light damage and A2E accumulation are facilitated under conditions where efficient retinoid cycle operates. Efficient retinoid cycle leads to rapid regeneration of rhodopsin, which may result in ATR release from the opsin "exit site" before its enzymatic reduction to all-trans-retinol. Here we discuss photodamage to the retina where ATR could play a role as the main toxic and/or phototoxic agent. Moreover, we discuss secondary products of (photo)toxic properties accumulating within retinal lipofuscin as a result of ATR accumulation.

Spatio-temporal characterization of retinal opsin gene expression during thyroid hormone-induced and natural development of rainbow trout

The abundance and spatial distribution of retinal cone photoreceptors change during thyroid hormone (TH)-induced and natural development of rainbow trout (Oncorhynchus mykiss). These changes are thought to allow the fish to adapt to different photic environments throughout its life history. To date, the ontogeny of rainbow trout cone photoreceptors has been examined using physiological and morphological approaches. In this study, we extended these observations by measuring opsin gene expression in retinal quadrants during natural and TH-induced development. Gene expression during natural development was investigated in retinae from fish at both parr and smolt stages. The role of TH in modulating opsin gene expression was determined in TH-treated parr and control fish sampled after two, nine, and 22 days of treatment. Total RNA was isolated from each retinal quadrant and steady-state opsin mRNA levels were measured using reverse transcriptase real-time quantitative polymerase chain reaction (QPCR) analysis. Expression of ultraviolet-sensitive opsin (SWS1), rod opsin (RH1), middle wavelength-sensitive opsin (RH2), and long wavelength-sensitive opsin (LWS) transcripts vary spatially in the parr retina. Smolts, compared to parr, had downregulated SWS1 expression in all quadrants, lower LWS expression dorsally, higher RH1 expression nasally, and higher RH2 expression dorsally. In TH-treated parr, SWS1 opsin expression was downregulated in the nasal quadrants by two days. SWS1 displayed the greatest degree of downregulation in all quadrants after nine days of treatment, with an increase in short wavelength-sensitive (SWS2) and RH2 opsin mRNA expression in the temporal quadrants. This study reveals that opsin genes display spatially significant differences within rainbow trout retina in their level of mRNA expression, and that regulation of opsin expression is a dynamic process that is influenced by TH. This is particularly evident for SWS1 gene expression in parr following TH-induced and natural development.