TXNL6 is a novel oxidative stress-induced reducing system for methionine sulfoxide reductase a repair of α-crystallin and cytochrome C in the eye lens

Optimal Control with RdCVFL for Degenerating Photoreceptors

Both the rod and cone photoreceptors, along with the retinal pigment epithelium have been experimentally and mathematically shown to work interdependently to maintain vision. Further, the theoredoxin-like rod-derived cone viability factor (RdCVF) and its long form (RdCVFL) have proven to increase photoreceptor survival in experimental results. Aerobic glycolysis is the primary source of energy production for photoreceptors and RdCVF accelerates the intake of glucose into the cones. RdCVFL helps mitigate the negative effects of reactive oxidative species and has shown promise in slowing the death of cones in mouse studies. However, this potential treatment and its effects have never been studied in mathematical models. In this work, we examine an optimal control with the treatment of RdCVFL. We mathematically illustrate the potential this treatment might have for treating degenerative retinal diseases such as retinitis pigmentosa, as well as compare this to the results of an updated control model with RdCVF.

Epigallocatechin gallate delays age-related cataract development via the RASSF2/AKT pathway

Age-related cataract (ARC) is a common eye disease, the main cause of which is oxidative stress-mediated apoptosis of lens epithelial cells (LECs). Epigallocatechin gallate (EGCG) is the most potent antioxidant in green tea. Our results demonstrated that EGCG could effectively reduce apoptosis of LECs and retard lens clouding in aged mice. By comparing transcriptome sequencing results of three groups of mice (young control, untreated aged, and EGCG-treated) and screening using GO and KEGG analyses, we selected RASSF2 as the effector gene of EGCG for mechanistic exploration. We verified that the differential expression of RASSF2 was associated with the occurrence of ARC in clinical samples and mouse tissues by immunohistochemistry and western blotting, respectively. We showed that high RASSF2 expression plays a crucial role in the oxidative induction of apoptosis in LECs, as revealed by overexpression and interference experiments. Further studies showed that RASSF2 mediates the inhibitory effect of EGCG on apoptosis and ARCogenesis in LECs by regulating AKT (Ser473) phosphorylation. In this study, we found for the first time the retarding effect of EGCG on lens clouding in mice and revealed the mechanism of action of RASSF2/AKT in it, which provides a theoretical basis for the targeted treatment of EGCG.

Modulating antioxidant systems as a therapeutic approach to retinal degeneration

The human retina is facing a big challenge of reactive oxygen species (ROS) from endogenous and exogenous sources. Excessive ROS can cause damage to DNA, lipids, and proteins, triggering abnormal redox signaling, and ultimately lead to cell death. Thus, oxidative stress has been observed in inherited retinal diseases as a common hallmark. To counteract the detrimental effect of ROS, cells are equipped with various antioxidant defenses. In this review, we will focus on the antioxidant systems in the retina and how they can protect retina from oxidative stress. Both small antioxidants and antioxidant enzymes play a role in ROS removal. Particularly, the thioredoxin and glutaredoxin systems, as the major antioxidant systems in mammalian cells, exert functions in redox signaling regulation via modifying cysteines in proteins. In addition, the thioredoxin-like rod-derived cone viability factor (RdCVFL) and thioredoxin interacting protein (TXNIP) can modulate metabolism in photoreceptors and promote their survival. In conclusion, elevating the antioxidant capacity in retina is a promising therapy to curb the progress of inherited retinal degeneration.

Role of short-wavelength blue light in the formation of cataracts and the expression of caspase-1, caspase-11, Gasdermin D in rat lens epithelial cells: insights into a novel pathogenic mmechanism of cataracts

Background

With the popularity of blue-rich light-emitting diode (LED)-backlit display devices, our eyes are now exposed to more short-wavelength blue light than they were in the past. The goal of this study was to investigate the pathogenesis of cataracts after short-wavelength light exposure.

Methods

Sprague-Dawley (SD) rats were selected and randomly divided into a control group (10 rats each for the 4-, 8-, and 12-week groups) and an experimental group (10 rats each for the 4-, 8-, and 12-week groups). The rats in the experimental group were exposed to a short-wavelength blue LED lamp for 12 h per day. After exposure to the blue LED lamp, the rats were maintained in total darkness for 12 h, after which a 12-h light/dark cycle was resumed. The intensity of the lamp was 3000 lx. At the end of the short-wavelength blue LED lamp exposure (for 4, 8, and 12 weeks), the expression levels of caspase-1, caspase-11 and gasdermin D (GSDMD) were examined in rat lens epithelial cells (LECs) using qRT-PCR and Western blot analyses. An illuminance of 2500 lx was used to study the potential effect of blue LED light on HLE-B3 hLECs in vitro. AC-YVAD-CMK, a caspase-1 inhibitor, was used to confirm the pyroptosis of LECs by flow cytometry.

Results

After 6 weeks, cataracts developed in the experimental rats (4/20 eyes). The clarity of the lens gradually worsened with the duration of exposure. Twelve weeks later, all of the rat eyes had developed cataracts. The expression levels of caspase-1, caspase-11 and GSDMD at 4, 8, and 12 weeks were significantly higher in the samples from rats exposed to a short-wavelength blue LED lamp than in the samples from control rats (p<0.05). The proportions of double-positive hLECs were significantly increased in the 5-h and 10-h short-wavelength blue light exposure subgroups compared with the 5-h and 10-h caspase-1 inhibitor subgroups (p < 0.05).

Conclusion

The data indicate that pyroptosis plays a key role in cataract induction after short-wavelength blue light exposure. This study might provide new insights into a novel pathogenic mechanism of cataracts.

Metabolic and Redox Signaling of the Nucleoredoxin-Like-1 Gene for the Treatment of Genetic Retinal Diseases

The loss of cone photoreceptor function in retinitis pigmentosa (RP) severely impacts the central and daily vision and quality of life of patients affected by this disease. The loss of cones follows the degeneration of rods, in a manner independent of the causing mutations in numerous genes associated with RP. We have explored this phenomenon and proposed that the loss of rods triggers a reduction in the expression of rod-derived cone viability factor (RdCVF) encoded by the nucleoredoxin-like 1 (NXNL1) gene which interrupts the metabolic and redox signaling between rods and cones. After providing scientific evidence supporting this mechanism, we propose a way to restore this lost signaling and prevent the cone vision loss in animal models of RP. We also explain how we could restore this signaling to prevent cone vision loss in animal models of the disease and how we plan to apply this therapeutic strategy by the administration of both products of NXNL1 encoding the trophic factor RdCVF and the thioredoxin enzyme RdCVFL using an adeno-associated viral vector. We describe in detail all the steps of this translational program, from the design of the drug, its production, biological validation, and analytical and preclinical qualification required for a future clinical trial that would, if successful, provide a treatment for this incurable disease.

Endocrine Imbalance Associated With Proteome Changes in Diabetes

The dynamics of cellular metabolism involves rapid interactions between proteins and nucleic acids, proteins and proteins, and signaling. These involve the interactions with respect to the sulfur bond, noncovalent electrostatic interactions, protein structure stabilization and protein-ligand binding, weak electrostatic interactions in proteins, oxygen radicals that initiate a change in conformation and a chain of events. We review a development in molecular medicine that is a very promising work in progress. We also review the current and future research methods involving mitochondria. Long-term effects of diabetes include glycation of proteins, for example, glycohemoglobin (HbA1c), increased risk of cardiovascular diseases, atherosclerosis, retinopathy, nephropathy, and neurological dysfunctions. Tissues are exposed to significant quantities of highly reactive chemical species including nitric oxide ^• NO and reactive oxygen species ROS over months to years, to an extent generated by mitochondrial activities. The reactions of ^• NO can be broadly discussed with reference to three main processes which control their fate in biological systems: (1) diffusion and intra-cellular consumption; (2) autooxidation to form nitrous anhydride N₂ O₃ ; and (3) reaction with superoxide O2^• - to form peroxynitrite ONOO-. Reactive nitrogen species produced by macrophages and neutrophils in the interstitial space, with emphasis on ^• NO, N₂ O₃ , ONOO-, and nitrogen dioxide radicals ^• NO₂ generate protein and DNA damage. Serum thiol (-SH) groups act as an important extracellular scavenger of peroxides and are therefore helpful in protecting the surrounding tissues. The events described here are a homeostatic endocrine imbalance that is associated with proteostasis. The advances we have seen in untangling this web of interactions are sure to continue at a breathtaking pace. J. Cell. Biochem. 118: 3569-3576, 2017. © 2017 Wiley Periodicals, Inc.

Parkin elimination of mitochondria is important for maintenance of lens epithelial cell ROS levels and survival upon oxidative stress exposure

Age-related cataract is associated with oxidative stress and death of lens epithelial cells (LECs) whose survival is dependent on functional mitochondrial populations. Oxidative stress-induced depolarization/damage of LEC mitochondria results in increased reactive oxygen species (ROS) levels and cell death suggesting the need for a LEC mechanism to remove mitochondria depolarized/damaged upon oxidative stress exposure to prevent ROS release and LEC death. To date, a mechanism(s) for removal of depolarized/damaged LEC mitochondria has yet to be identified and the importance of eliminating oxidative stress-damaged mitochondria to prevent LEC ROS release and death has not been established. Here, we demonstrate that Parkin levels increase in LECs exposed to H₂O₂-oxidative stress. We establish that Parkin translocates to LEC mitochondria depolarized upon oxidative stress exposure and that Parkin recruits p62/SQSTM1 to depolarized LEC mitochondria. We demonstrate that translocation of Parkin results in the elimination of depolarized/damaged mitochondria and that Parkin clearance of LEC mitochondria is dependent on its ubiquitin ligase activity. Importantly, we demonstrate that Parkin elimination of damaged LEC mitochondria results in reduced ROS levels and increased survival upon oxidative stress exposure. These results establish that Parkin functions to eliminate LEC mitochondria depolarized/damaged upon oxidative stress exposure and that elimination of damaged mitochondria by Parkin is important for LEC homeostasis and survival. The data also suggest that mitochondrial quality control by Parkin could play a role in lens transparency.

Metabolic and redox signaling in the retina

Visual perception by photoreceptors relies on the interaction of incident photons from light with a derivative of vitamin A that is covalently linked to an opsin molecule located in a special subcellular structure, the photoreceptor outer segment. The photochemical reaction produced by the photon is optimal when the opsin molecule, a seven-transmembrane protein, is embedded in a lipid bilayer of optimal fluidity. This is achieved in vertebrate photoreceptors by a high proportion of lipids made with polyunsaturated fatty acids, which have the detrimental property of being oxidized and damaged by light. Photoreceptors cannot divide, but regenerate their outer segments. This is an enormous energetic challenge that explains why photoreceptors metabolize glucose through aerobic glycolysis, as cancer cells do. Uptaken glucose produces metabolites to renew that outer segment as well as reducing power through the pentose phosphate pathway to protect photoreceptors against oxidative damage.

The Thioredoxin Encoded by the Rod-Derived Cone Viability Factor Gene Protects Cone Photoreceptors Against Oxidative Stress

AIMS

Rod-derived cone viability factor long (RdCVFL) is an enzymatically active thioredoxin encoded by the nucleoredoxin-like-1 (Nxnl1) gene. The second product of the gene, RdCVF, made by alternative splicing is a novel trophic factor secreted by rods that protects cones in rodent models of retinitis pigmentosa, the most prevalent inherited retinal disease. It acts on cones by stimulating aerobic glycolysis through its interaction with a complex containing basigin-1 and the glucose transporter GLUT1. We studied the role of Nxnl1 in cones after its homologous recombination using a transgenic line expressing Cre recombinase under the control of a cone opsin promoter.

RESULTS

We show that the cones of these mice are dysfunctional and degenerate by 8 months of age. The age-related deficit in cones is exacerbated in young animals by exposure to high level of oxygen. In agreement with this phenotype, we found that the cones express only one of the two Nxnl1 gene products, the thioredoxin RdCVFL. Administration of RdCVFL to the mouse carrying a deletion of the Nxnl1 gene in cones reduces the damage produced by oxidative stress. Silencing the expression of RdCVFL in cone-enriched culture reduces cell viability, showing that RdCVFL is a cell-autonomous mechanism of protection.

INNOVATION

This novel mode of action is certainly relevant for the therapy of retinitis pigmentosa since the delivery into cones of the rd10 mouse, a recessive model of the disease, rescues cones.

CONCLUSION

Our work highlights the duality of the Nxnl1 gene, which protects the cones by two distinct mechanisms. Antioxid. Redox Signal. 24, 909-923.

Self-oxidation of cytochrome c at methionine80 with molecular oxygen induced by cleavage of the Met-heme iron bond

Met80 of cytochrome c (cyt c) has been shown to dissociate from its heme iron when cyt c interacts with cardiolipin (CL), which triggers the release of cyt c into the cytosol initiating apoptosis. We found that the mass of human cyt c increases by 16 Da in the Met80-Lys86 region by reaction with molecular oxygen in the presence of CL-containing liposomes and dithiothreitol (DTT). To investigate the effect of Met80 dissociation on the reaction of cyt c with molecular oxygen without affecting its secondary structures, a human cyt c mutant (Δ8384 cyt c) was constructed by removing two amino acids (Val83 and Gly84) from the loop containing Met80. According to MALDI-TOF-MS and tandem mass measurements, Met80 of Δ8384 cyt c was modified site-specifically to methionine sulfoxide when purified in the presence of molecular oxygen, whereas Met80 was not modified in the absence of molecular oxygen. A red-shift of the Soret band from 406 to 412 nm and absorption increase at ∼536 and ∼568 nm were observed for Δ8384 cyt c when it reacted with DTT and molecular oxygen, followed by a further red-shift of the Soret band to 416 nm and absorption increase at ∼620 and ∼650 nm. These results indicate that Met80 of cyt c is oxidized site-specifically by formation of the oxy and subsequent compound I-like species when Met80 dissociates from the heme iron, where the Met80 modification may affect its peroxidase activity related to apoptosis.

Thioredoxin rod-derived cone viability factor protects against photooxidative retinal damage

Rod-derived cone viability factor (RdCVF) is a trophic factor of the thioredoxins family that promotes the survival of cone photoreceptors. It is encoded by the nucleoredoxin-like gene 1 Nxnl1 which also encodes by alternative splicing a long form of RdCVF (RdCVFL), a thioredoxin enzyme that interacts with TAU. The known role of thioredoxins in the defense mechanism against oxidative damage led us to examine the retinal phenotype of the Nxnl1(-/-) mice exposed to photooxidative stress. Here we found that, in contrast to wild-type mice, the rod photoreceptors of Nxnl1(-/-) mice are more sensitive to light after exposure to 1700 or 2500 lx. The delivery of RdCVF by AAV to mice deficient of Nxnl1(-/-) protects rod photoreceptors from light damage. Interestingly, the RdCVF2L protein, encoded by the paralog gene Nxnl2, is able to reduce TAU phosphorylation, as does RdCVFL, but does not protect the rod from light damage. Our result shows that the Nxnl1 gene, through the thioredoxin RdCVFL, is part of an endogenous defense mechanism against photooxidative stress that is likely of great importance for human vision.

Viral-mediated RdCVF and RdCVFL expression protects cone and rod photoreceptors in retinal degeneration

Alternative splicing of nucleoredoxin-like 1 (Nxnl1) results in 2 isoforms of the rod-derived cone viability factor. The truncated form (RdCVF) is a thioredoxin-like protein secreted by rods that promotes cone survival, while the full-length isoform (RdCVFL), which contains a thioredoxin fold, is involved in oxidative signaling and protection against hyperoxia. Here, we evaluated the effects of these different isoforms in 2 murine models of rod-cone dystrophy. We used adeno-associated virus (AAV) to express these isoforms in mice and found that both systemic and intravitreal injection of engineered AAV vectors resulted in RdCVF and RdCVFL expression in the eye. Systemic delivery of AAV92YF vectors in neonates resulted in earlier onset of RdCVF and RdCVFL expression compared with that observed with intraocular injection using the same vectors at P14. We also evaluated the efficacy of intravitreal injection using a recently developed photoreceptor-transducing AAV variant (7m8) at P14. Systemic administration of AAV92YF-RdCVF improved cone function and delayed cone loss, while AAV92YF-RdCVFL increased rhodopsin mRNA and reduced oxidative stress by-products. Intravitreal 7m8-RdCVF slowed the rate of cone cell death and increased the amplitude of the photopic electroretinogram. Together, these results indicate different functions for Nxnl1 isoforms in the retina and suggest that RdCVF gene therapy has potential for treating retinal degenerative disease.

Differentiation state-specific mitochondrial dynamic regulatory networks are revealed by global transcriptional analysis of the developing chicken lens

The mature eye lens contains a surface layer of epithelial cells called the lens epithelium that requires a functional mitochondrial population to maintain the homeostasis and transparency of the entire lens. The lens epithelium overlies a core of terminally differentiated fiber cells that must degrade their mitochondria to achieve lens transparency. These distinct mitochondrial populations make the lens a useful model system to identify those genes that regulate the balance between mitochondrial homeostasis and elimination. Here we used an RNA sequencing and bioinformatics approach to identify the transcript levels of all genes expressed by distinct regions of the lens epithelium and maturing fiber cells of the embryonic Gallus gallus (chicken) lens. Our analysis detected more than 15,000 unique transcripts expressed by the embryonic chicken lens. Of these, more than 3000 transcripts exhibited significant differences in expression between lens epithelial cells and fiber cells. Multiple transcripts coding for separate mitochondrial homeostatic and degradation mechanisms were identified to exhibit preferred patterns of expression in lens epithelial cells that require mitochondria relative to lens fiber cells that require mitochondrial elimination. These included differences in the expression levels of metabolic (DUT, PDK1, SNPH), autophagy (ATG3, ATG4B, BECN1, FYCO1, WIPI1), and mitophagy (BNIP3L/NIX, BNIP3, PARK2, p62/SQSTM1) transcripts between lens epithelial cells and lens fiber cells. These data provide a comprehensive window into all genes transcribed by the lens and those mitochondrial regulatory and degradation pathways that function to maintain mitochondrial populations in the lens epithelium and to eliminate mitochondria in maturing lens fiber cells.

Effect of methionine sulfoxide reductase B1 (SelR) gene silencing on peroxynitrite-induced F-actin disruption in human lens epithelial cells

F-actin plays a crucial role in fundamental cellular processes, and is extremely susceptible to peroxynitrite attack due to the high abundance of tyrosine in the peptide. Methionine sulfoxide reductase (Msr) B1 is a selenium-dependent enzyme (selenoprotein R) that may act as a reactive oxygen species (ROS) scavenger. However, its function in coping with reactive nitrogen species (RNS)-mediated stress and the physiological significance remain unclear. Thus, the present study was conducted to elucidate the role and mechanism of MsrB1 in protecting human lens epithelial (hLE) cells against peroxynitrite-induced F-actin disruption. While exposure to high concentrations of peroxynitrite and gene silencing of MsrB1 by siRNA alone caused disassembly of F-actin via inactivation of extracellular signal-regulated kinase (ERK) in hLE cells, the latter substantially aggravated the disassembly of F-actin triggered by the former. This aggravation concurred with elevated nitration of F-actin and inactivation of ERK compared with that induced by the peroxynitrite treatment alone. In conclusion, MsrB1 protected hLE cells against the peroxynitrite-induced F-actin disruption, and the protection was mediated by inhibiting the resultant nitration of F-actin and inactivation of ERKs.

Redox metabolism in Trypanosoma cruzi: functional characterization of tryparedoxins revisited

Tryparedoxins (TXNs) are multipurpose oxidoreductases from trypanosomatids that transfer reducing equivalents from trypanothione to various thiol proteins. In Trypanosoma cruzi, two genes coding for TXN-like proteins have been identified: TXNI, previously characterized as a cytoplasmic protein, and TXNII, a putative tail-anchored membrane protein. In this work, we performed a comparative functional characterization of T. cruzi TXNs. Particularly, we cloned the gene region coding for the soluble version of TXNII for its heterologous expression. The truncated recombinant protein (without its 22 C-terminal transmembrane amino acids) showed TXN activity. It was also able to transfer reducing equivalents from trypanothione, glutathione, or dihydrolipoamide to various acceptors, including methionine sulfoxide reductases and peroxiredoxins. The results support the occurrence and functionality of a second tryparedoxin, which appears as a new component in the redox scenario for T. cruzi.

The eye as a model of ageing in translational research--molecular, epigenetic and clinical aspects

The eye and visual system are valuable in many areas of translational research such as stem cell therapy, transplantation research and gene therapy. Changes in many ocular tissues can be measured directly, easily and objectively in vivo (e.g. lens transparency; retinal blood vessel calibre; corneal endothelial cell counts) and so the eye may also be a uniquely useful site as a model of ageing. This review details cellular, molecular and epigenetic mechanisms related to ageing within the eye, and describes ocular parameters that can be directly measured clinically and which might be of value in ageing research as the translational "window to the rest of the body". The eye is likely to provide a valuable model for validating biomarkers of ageing at molecular, epigenetic, cellular and clinical levels. A research agenda to definitively establish the relationship between biomarkers of ageing and ocular parameters is proposed.

Involvement of MsrB1 in the regulation of redox balance and inhibition of peroxynitrite-induced apoptosis in human lens epithelial cells

Methionine sulfoxide reductases (Msrs) in lens cells are important for the maintenance of lens cell viability and resistance to oxidative stress damage. Peroxynitrite (ONOO(-)), as a strong oxidizing and nitrating agent, occurred in diabetic retinopathy patients and diabetic model animal. In an attempt to shed light on the roles of MsrB1, known as selenoprotein R, in protecting human lens epithelial (HLE) cells against peroxynitrite damage, and contribution of loss of its normal activity to cataract, the influences of MsrB1 gene silencing on peroxynitrite-induced apoptosis in HLE cells were studied. The results showed that both exogenous peroxynitrite and MsrB1 gene silencing by short interfering RNA (siRNA) independently resulted in oxidative stress, endoplasmic reticulum (ER) stress, activation of caspase-3 as well as an increase of apoptosis in HLE cells; moreover, when MsrB1-gene-silenced cells were exposed to 300 μM peroxynitrite, these indexes were further aggravated at the same conditions and DNA strand breaks occurred. The results demonstrate that in HLE cells MsrB1 may play important roles in regulating redox balance and mitigating ER stress as induced by oxidative stress under physiological conditions; MsrB1 may also protect HLE cells against peroxynitrite-induced apoptosis by inhibiting the activation of caspase-3 and oxidative damage of DNA under pathological conditions. Our results imply that loss of its normal activity is likely to contribute to cataract.

Role of the ubiquitin-proteasome in protein quality control and signaling: implication in the pathogenesis of eye diseases

The ubiquitin-proteasome pathway (UPP) plays important roles in many cellular functions, such as protein quality control, cell cycle control, and signal transduction. The selective degradation of aberrant proteins by the UPP is essential for the timely removal of potential cytotoxic damaged or otherwise abnormal proteins. Conversely, accumulation of the cytotoxic abnormal proteins in eye tissues is etiologically associated with many age-related eye diseases such as retina degeneration, cataract, and certain types of glaucoma. Age- or stress-induced impairment or overburdening of the UPP appears to contribute to the accumulation of abnormal proteins in eye tissues. Cell cycle and signal transduction are regulated by the conditional UPP-dependent degradation of the regulators of these processes. Impairment or overburdening of the UPP could also result in dysregulation of cell cycle control and signal transduction. The consequences of the improper cell cycle and signal transduction include defects in ocular development, wound healing, angiogenesis, or inflammatory responses. Methods that enhance or preserve UPP function or reduce its burden may be useful strategies for preventing age-related eye diseases.