Nitric oxide-induced accumulation of lipofuscin-like materials is caused by inhibition of cathepsin S

SIG-1451, a Novel, Non-Steroidal Anti-Inflammatory Compound, Attenuates Light-Induced Photoreceptor Degeneration by Affecting the Inflammatory Process

Age-related macular degeneration is a progressive retinal disease that is associated with factors such as oxidative stress and inflammation. In this study, we evaluated the protective effects of SIG-1451, a non-steroidal anti-inflammatory compound developed for treating atopic dermatitis and known to inhibit Toll-like receptor 4, in light-induced photoreceptor degeneration. SIG-1451 was intraperitoneally injected into rats once per day before exposure to 1000 lx light for 24 h; one day later, optical coherence tomography showed a decrease in retinal thickness, and electroretinogram (ERG) amplitude was also found to have decreased 3 d after light exposure. Moreover, SIG-1451 partially protected against this decrease in retinal thickness and increase in ERG amplitude. One day after light exposure, upregulation of inflammatory response-related genes was observed, and SIG-1451 was found to inhibit this upregulation. Iba-1, a microglial marker, was suppressed in SIG-1451-injected rats. To investigate the molecular mechanism underlying these effects, we used lipopolysaccharide (LPS)-stimulated rat immortalised Müller cells. The upregulation of C-C motif chemokine 2 by LPS stimulation was significantly inhibited by SIG-1451 treatment, and Western blot analysis revealed a decrease in phosphorylated I-κB levels. These results indicate that SIG-1451 indirectly protects photoreceptor cells by attenuating light damage progression, by affecting the inflammatory responses.

Mitochondrial contribution to lipofuscin formation

Mitochondria have been in the focus of oxidative stress and aging research for decades due to their permanent production of ROS during the oxidative phosphorylation. The hypothesis exists that mitochondria are involved in the formation of lipofuscin, an autofluorescent protein aggregate that accumulates progressively over time in lysosomes of post-mitotic and senescent cells. To investigate the influence and involvement of mitochondria in lipofuscinogenesis, we analyzed lipofuscin amounts as well as the mitochondrial function in young and senescent cells. In addition we used an aging model and Lon protease deficient HeLa cells to investigate the influence of mitochondrial degradation processes on lipofuscin formation.

We were able to show that mitophagy is impaired in senescent cells resulting in an increased mitochondrial mass and superoxide formation. In addition, the inhibition of mitochondrial fission leads to increased lipofuscin formation.

Moreover, we observed that Lon protease downregulation is linked to a higher lipofuscinogenesis whereas the application of the mitochondrial-targeted antioxidant mitoTEMPO is able to prevent the accumulation of this protein aggregate.

Local and systemic responses following intravitreous injection of AAV2-encoded modified Volvox channelrhodopsin-1 in a genetically blind rat model

We previously designed a modified channelrhodopsin-1 (mVChR1) protein chimera with a broader action than that of Chlamydomonas channelrhodopsin-2 and reported that its transduction into retinal ganglion cells can restore visual function in genetically blind, dystrophic Royal College of Surgeons (RCS) rats, with photostimuli ranging from 486 to 640 nm. In the current study, we sought to investigate the safety and influence of mVChR1 transgene expression. Adeno-associated virus type 2 encoding mVChR1 was administered by intravitreous injection into dystrophic RCS rats. Reverse-transcription PCR was used to monitor virus and transgene dissemination and the results demonstrated that their expression was restricted specifically within the eye tissues, and not in non-target organs. Moreover, examination of the blood, plasma and serum revealed that no excess immunoreactivity was present, as determined using standard clinical hematological parameters. Serum antibodies targeting the recombinant adeno-associated virus (rAAV) capsid increased after the injection; however, no increase in mVChR1 antibody was detected during the observation period. In addition, retinal histological examination showed no signs of inflammation in rAAV-injected rats. In conclusion, our results demonstrate that mVChR1 can be exogenously expressed without harmful immunological reactions in vivo. These findings will aid in studies of AAV gene transfer to restore vision in late-stage retinitis pigmentosa.

Large-scale purification of porcine or bovine photoreceptor outer segments for phagocytosis assays on retinal pigment epithelial cells

Analysis of one of the vital functions of retinal pigment epithelial (RPE) cells, the phagocytosis of spent aged distal fragments of photoreceptor outer segments (POS) can be performed in vitro. Photoreceptor outer segments with stacks of membranous discs containing the phototransduction machinery are continuously renewed in the retina. Spent POS are eliminated daily by RPE cells. Rodent, porcine/bovine and human RPE cells recognize POS from various species in a similar manner. To facilitate performing large series of experiments with little variability, a large stock of POS can be isolated from porcine eyes and stored frozen in aliquots. This protocol takes advantage of the characteristic of photopigments that display an orange color when kept in the dark. Under dim red light, retinae are collected in a buffer from opened eyecups cut in halves. The retinal cell suspension is homogenized, filtered and loaded onto a continuous sucrose gradient. After centrifugation, POS are located in a discrete band in the upper part of the gradient that has a characteristic orange color. POS are then collected, spun, resuspended sequentially in wash buffers, counted and aliquoted. POS obtained this way can be used for phagocytosis assays and analysis of protein activation, localization or interaction at various times after POS challenge. Alternatively, POS can be labeled with fluorophores, e.g., FITC, before aliquoting for subsequent fluorescence quantification of POS binding or engulfment. Other possible applications include the use of modified POS or POS challenge combined with stress conditions to study the effect of oxidative stress or aging on RPE cells.

Essential role of thioredoxin 2 in mitigating oxidative stress in retinal epithelial cells

The retina is constantly subjected to oxidative stress, which is countered by potent antioxidative systems present in retinal pigment epithelial (RPE) cells. Disruption of these systems leads to the development of age-related macular degeneration. Thioredoxin 2 (Trx2) is a potent antioxidant, which acts directly on mitochondria. In the present study, oxidative stress was induced in the human RPE cell line (ARPE-19) using 4-hydroxynonenal (4-HNE) or C2-ceramide. The protective effect of Trx2 against oxidative stress was investigated by assessing cell viability, the kinetics of cell death, mitochondrial metabolic activity, and expression of heat shock proteins (Hsps) in Trx2-overexpressing cell lines generated by transfecting ARPE cells with an adeno-associated virus vector encoding Trx2. We show that overexpression of Trx2 reduced cell death induced by both agents when they were present in low concentrations. Moreover, early after the induction of oxidative stress Trx2 played a key role in the maintenance of the cell viability through upregulation of mitochondrial metabolic activity and inhibition of Hsp70 expression.

Formation of lipofuscin-like material in the RPE Cell by different components of rod outer segments

The mechanisms that control the natural rate of lipofuscin accumulation in the retinal pigment epithelial (RPE) cell and its stability over time are not well understood. Similarly, the contributions of retinoids, phospholipids and oxidation to the rate of accumulation of lipofuscin are uncertain. The experiments in this study were conducted to explore the individual contribution of rod outer segments (ROS) components to lipofuscin formation and its accumulation and stability over time. During the period of 14 days incubation of ROS, lipofuscin-like autofluorescence (LLAF) determined at two wavelengths (530 and 585 nm) by fluorescence-activated cell sorting (FACS) was measured from RPE cells. The autofluorescence increased in an exponential manner with a strong linear component between days 1 and 7. The magnitude of the increase was larger in cells incubated with 4-hydroxynonenal (HNE-ROS) compared with cells incubated with either bleached or unbleached ROS, but with a different spectral profile. A small (10-15%) decrease in LLAF was observed after stopping the ROS feeding for 14 days. The phagocytosis rate of HNE-ROS was higher than that of either bleached or unbleached ROS during the first 24 h of supplementation. Among the different ROS components, the increase of LLAF was highest in cells incubated with all-trans-retinal. Surprisingly, incubation with 11-cis-retinal and 9-cis-retinal also resulted in strong LLAF increase, comparable to the increase induced by all-trans-retinal. Supplementation with liposomes containing phosphatidylethanolamine (22: 6-PE) and phosphatidylcholine (18:1-PC) also increased LLAF, while incubation with opsin had little effect. Cells incubated with retinoids demonstrated strong dose-dependence in LLAF increase, and the magnitude of the increase was 2-3 times higher at 585 nm compared to 530 nm, while cells incubated with liposomes showed little dose-dependence and similar increase at both wavelengths. Very little difference in LLAF was noted between cells incubated with either unbleached or bleached ROS under any conditions. In summary, results from this study suggest that supplementation with various ROS components can lead to an increase in LLAF, although the autofluorescence generated by the different classes of components has distinct spectral profiles, where the autofluorescence induced by retinoids results in a spectral profile closest to the one observed from human lipofuscin. Future fluorescence characterization of LLAF in vitro would benefit from an analysis of multiple wavelengths to better match the spectral characteristics of lipofuscin in vivo.

Establishment of monocular-limited photoreceptor degeneration models in rabbits

Background

Numerous rodent models of photoreceptor degeneration have been developed for the study of visual function. However, no viable model has been established in a species that is more closely related to Homo sapiens. Here, we present a rabbit model of monocular photoreceptor degeneration.

Methods

We tested 2 chemicals, verteporfin and sodium nitroprusside (SNP), for developing a 1-eye limited photoreceptor degeneration model in pigmented rabbits. After the intravenous injection of verteporfin, the retina was exposed to light from a halogen lamp for 0, 10, 30, or 60 min. Alternately, 100 μL of various concentrations of sodium nitroprusside (0.1 mM, 0.5 mM, and 1 mM) were intravitreously injected into the rabbit eye. Retinal degeneration was evaluated by fundus photography, electroretinogram (ERG), and histological examinations.

Results

Fundus photographs of animals in the verteporfin- or SNP-treated groups showed evidence of retinal degeneration. The severity of this degradation depended on the duration of light exposure and the concentration of SNP administered. The degeneration was clearly limited to the light-exposed areas in the verteporfin-treated groups. Extensive retinal atrophy was observed in the SNP-treated groups. The a- and b-wave amplitudes were dramatically decreased on the ERGs from SNP-treated groups. Histological examination revealed that either verteporfin or SNP induced severe photoreceptor degeneration. High-dose SNP treatment (1 mM) was also associated with inner retinal layer degeneration.

Conclusions

Both SNP and verteporfin clearly caused photoreceptor degeneration without any effect on the contralateral eye. These compounds therefore represent valuable tools for the empirical investigation of visual function recovery. The findings will inform guidelines for clinical applications such as retinal prostheses, cell-based therapy, and gene therapy.

Different anti-oxidant effects of thioredoxin 1 and thioredoxin 2 in retinal epithelial cells

Age-related macular degeneration (AMD) affects the retina and is the most common cause of blindness in elderly persons in developed countries. The retina is constantly subjected to oxidative stress; to avoid the effects of oxidative stress, retinal pigment epithelial (RPE) cells possess potent anti-oxidant systems. Disruption of these systems leads to dysfunction of RPE cells, which then accelerates the development of AMD. Here, we investigated the role of thioredoxins (TRXs), scavengers of intracellular reactive oxygen species, by assessing the effect of TRX overexpression on cell viability, morphology, NF-κB expression, and mitochondrial membrane potential, in RPE cells. TRX-overexpressing cell lines were generated by infection of an established human RPE cell line (ARPE) with adeno-associated virus vectors encoding either TRX1 or TRX2. We showed that overexpression of TRXs reduced cell death caused by 4-hydroxynonenal (4-HNE)-induced oxidative stress; TRX2 was more effective than TRX1 in promoting cell survival. 4-HNE caused perinuclear NF-κB accumulation, which was absent in TRX-overexpressing cells. Moreover, overexpression of TRXs prevented depolarization of mitochondrial membranes; again, TRX2 was more effective than TRX1 in maintaining the membrane potential. The difference in the protective effects of these TRXs against oxidative stress may be due to their expression profile. TRX2 was expressed in the mitochondria, while TRX1 was expressed in the cytoplasm. Thus, TRX2 may directly protect mitochondria by preventing depolarization. These results demonstrate that TRXs are potent antioxidant proteins in RPE cells and their direct effect on mitochondria may be a key to prevent oxidative stress.

Adipokine levels in subretinal fluid from patients with rhegmatogenous retinal detachment

Adipokines have recently emerged as a novel group of mediators with important roles in inflammatory and immune responses and in the process of wound healing. This study investigated the involvement of several adipokines in the future development of proliferative vitreoretinopathy (PVR) following reattachment surgery for rhegmatogenous retinal detachment (RRD). A multiplex immunoassay was used to measure 6 different adipokines in 75 subretinal fluid samples collected during reattachment surgery for primary RRD. Twenty-one patients who developed a redetachment due to postoperative PVR after scleral buckling surgery (PVR group) were compared with age-, sex-, and storage-time-matched RRD samples from 54 patients with an uncomplicated postoperative course (RRD group). Levels of adiponectin (P = 0.006), cathepsin S (P = 0.001), and leptin (P = 0.041) were significantly elevated in the PVR group as compared to the RRD group. Levels of tissue inhibitor of metalloproteinase (TIMP)-1 were significantly lower in the PVR group than in the RRD group (P = 0.044). After correction for diabetes, body mass index (BMI), macular involvement, and preoperative PVR, the association between postoperative PVR development and adiponectin, cathepsin S, and TIMP-1 remained statistically significant (P < 0.05), whereas the significant correlation between PVR and elevated leptin levels was lost (P = 0.068). There were no significant differences in levels of chemerin (P = 0.351) and adipsin (P = 0.915). Of all adipokines investigated, multivariate logistic regression analysis showed that adiponectin was the exclusive predictor of the development of postoperative PVR after scleral buckling surgery (P = 0.003). Our findings indicate that, at the time of surgery for primary RRD, an altered expression of certain adipokines is associated with the future development of postoperative PVR.

Age-related macular degeneration: activation of innate immunity system via pattern recognition receptors

Age-related macular degeneration (AMD) is the most common cause of irreversible loss of central vision. Histopathological studies have demonstrated that inflammation is the key player in the pathogenesis of AMD. Genetic studies have revealed that complement factor H is a strong risk factor for the development of AMD. However, innate immunity defence involves several other pattern recognition receptors (PRRs) which can trigger inflammatory responses. Retinal pigment epithelial (RPE) cells have the main role in the immune defence in macula. In this study, we examine in detail the endogenous danger signals which can activate different PRRs in RPE cells, such as Toll-like, NOD-like and scavenger receptors along with complement system. We also characterise the signalling pathways triggered by PRRs in evoking inflammatory responses. In addition, we will discuss whether AMD pathology could represent the outcome of chronic activation of the innate immunity defence in human macula.