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

Thioredoxin-2 suppresses hydrogen peroxide-activated nuclear factor kappa B signaling via alleviating oxidative stress in bovine adipocytes

During the periparturient period, both oxidative stress, and inflammation of adipose tissue are considered high risk factors for metabolic disorder of dairy cows. Oxidative stress can activate transcription factor nuclear factor kappa B (NF-κB), which lead to the upregulation of genes involved in inflammatory pathways. Thioredoxin-2 (TXN2) is a mitochondrial protein that regulates cellular redox by suppressing mitochondrial reactive oxygen species (ROS) generation in nonruminant, whereas the function of TXN2 in bovine adipocytes was unclear. Thus, the objective of this study was to evaluate how or by which mechanisms TXN2 regulates oxidative stress and NF-κB signaling pathway in bovine adipocytes. Bovine pre-adipocytes isolated from 5 healthy Holstein cows were differentiated and used for (1) treatment with different concentrations of hydrogen peroxide (H2O2; 0, 25, 50, 100, 200, or 400 μM) for 2 h; (2) transfection with or without TXN2 small interfering RNA (si-TXN2) for 48 h and then treated with or without 200 μM H2O2 for 2 h; (3) transfection with scrambled negative control siRNA (si-control) or si-TXN2 for 48 h, and then treatment with or without 10 mM N-acetylcysteine (NAC) for 2 h; (4) transfection with or without TXN2-overexpressing plasmid for 48 h and then treatment with or without 200 μM H2O2 for 2 h. High concentrations of H2O2 (200 and 400 μM) decreased protein and mRNA abundance of TXN2, reduced total antioxidant capacity (T-AOC) and ATP content in adipocytes. Moreover, 200 and 400 μM H2O2 reduced protein abundance of inhibitor of kappa B α (IκBα), increased phosphorylation of NF-κB and upregulated mRNA abundance of tumor necrosis factor-α (TNFA) and interleukin-1B (IL-1B), suggesting that H2O2-induced oxidative stress and activated NF-κB signaling pathway. Silencing of TXN2 increased intracellular ROS content, phosphorylation of NF-κB and mRNA abundance of TNFA and IL-1B, decreased ATP content and protein abundance of IκBα in bovine adipocytes. Knockdown of TXN2 aggravated H2O2-induced oxidative stress and inflammation. In addition, treatment with antioxidant NAC ameliorated oxidative stress and inhibited NF-κB signaling pathway in adipocytes transfected with si-TXN2. In bovine adipocytes treated with H2O2, overexpression of TXN2 reduced the content of ROS and elevated the content of ATP and T-AOC. Overexpression of TXN2 alleviated H2O2-induced inflammatory response in adipocytes, as demonstrated by decreased expression of phosphorylated NF-κB, TNFA, IL-1B, as well as increased expression of IκBα. Furthermore, the protein and mRNA abundance of TXN2 was lower in adipose tissue of dairy cows with clinical ketosis. Overall, our studies contribute to the understanding of the role of TXN2 in adipocyte oxidative stress and inflammatory response.

Members of the Capsicum annuum CaTrxh Family Respond to High Temperature and Exhibit Dynamic Hetero/Homo Interactions

Climate change adversely affects the water and temperature conditions required for plant growth, leading to a decrease in yield. In high temperatures, oxidative stress causes cellular damage in plant cells, which is a negative factor for crop production. Thioredoxin (Trx) is a small redox protein containing a conserved WC(G/P)PC motif that catalyzes the exchange of disulfide bonds. It is known to play an important role in maintaining cellular redox homeostasis. Trx proteins are widely distributed across various subcellular locations, and they play a crucial role in responding to cellular stresses. In this study, seven CaTrxh-type genes present in pepper were identified and the CaTrxh-type family was classified into three subgroups. CaTrxh genes responded to heat stress. Moreover, subcellular locations of the CaTrxh family exhibited dynamic patterns in normal conditions, and we observed relocalizations in heat stress conditions. Each CaTrxh family protein member formed homo-/heteromeric protein complexes in BiFC assay. Unexpectedly, subgroup III CaTrxh9 and CaTrxh10 can recruit subgroup I and II CaTrxh proteins into the plasma membrane. Thus, the function of the CaTrxh-type family is expected to play a protective role in the cell in response to high-temperature stress via protein complex formations. CaTrxh may have potential applications in the development of crops with enhanced tolerance to oxidative stress.

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.

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.

Updates on sphingolipids: Spotlight on retinopathy

The sphingolipids ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (Sph), and sphingosine-1-phosphate (S1P)) are key signaling molecules that regulate many patho-biological processes. During the last decade, they have gained increasing attention since they may participate in important and numerous retinal processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Cer for instance has emerged as a key mediator of inflammation and death of neuronal and retinal pigment epithelium cells in experimental models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. S1P may have opposite biological actions, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1- phosphate may also contribute to uveitis. Furthermore, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), have been shown to preserve neuronal viability and retinal function. Collectively, the expanding role for these sphingolipids in the modulation of vital processes in retina cell types and in their dysregulation in retinal degenerations makes them attractive therapeutic targets.

Mitochondrial TXN2 attenuates amyloidogenesis via selective inhibition of BACE1 expression

Thioredoxin-2 (TXN2) is a mitochondrial protein and represents one of the intrinsic antioxidant enzymes. It has long been recognized that mitochondrial dysfunction and oxidative stress contribute to the pathogenesis of Alzheimer's disease (AD). We hypothesized that mitochondrial TXN2 might play a role in AD-like pathology. In this study, we found that in SH-SY5Y and HEK cells stably express full-length human amyloid-β precursor protein (HEK-APP), TXN2 silencing or over-expression selectively increased or decreased the transcription of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), respectively, without altering the protein levels of others enzymes involved in the catalytic processing of APP. As a result, β-amyloid protein (Aβ) levels were significantly decreased by TXN2. In addition, in cells treated with 3-nitropropionic acid (3-NP) that is known to increase reactive oxygen species (ROS) and promote mitochondrial dysfunction, TXN2 silencing resulted in further enhancement of BACE1 protein levels, suggesting a role of TXN2 in ROS removal. The downstream signaling might involve NFκB, as TXN2 reduced the phosphorylation of p65 and IκBα; and p65 knockdown significantly attenuated TXN2-mediated regulation of BACE1. Concomitantly, the levels of cellular ROS, apoptosis-related proteins and cell viability were altered by TXN2 silencing or over-expression. In APPswe/PS1E9 mice, an animal model of AD, the cortical and hippocampal TXN2 protein levels were decreased at 12 months but not at 6 months, suggesting an age-dependent decline. Collectively, TXN2 regulated BACE1 expression and amyloidogenesis via cellular ROS and NFκB signaling. TXN2 might serve as a potential target especially for early intervention of AD.

Thioredoxin 1 Plays a Protective Role in Retinas Exposed to Perinatal Hypoxia-Ischemia

Thioredoxin family proteins are key modulators of cellular redox regulation and have been linked to several physiological functions, including the cellular response to hypoxia-ischemia. During perinatal hypoxia-ischemia (PHI), the central nervous system is subjected to a fast decrease in O₂ and nutrients with a subsequent reoxygenation that ultimately leads to the production of reactive species impairing physiological redox signaling. Particularly, the retina is one of the most affected tissues, due to its high oxygen consumption and exposure to light. One of the main consequences of PHI is retinopathy of prematurity, comprising changes in retinal neural and vascular development, with further compensatory mechanisms that can ultimately lead to retinal detachment and blindness. In this study, we have analyzed long-term changes that occur in the retina using two well established in vivo rat PHI models (perinatal asphyxia and carotid ligation model), as well as the ARPE-19 cell line that was exposed to hypoxia and reoxygenation. We observed significant changes in the protein levels of the cytosolic oxidoreductase thioredoxin 1 (Trx1) in both animal models and a cell model. Knock-down of Trx1 in ARPE-19 cells affected cell morphology, proliferation and the levels of specific differentiation markers. Administration of recombinant Trx1 decreased astrogliosis and improved delayed neurodevelopment in animals exposed to PHI. Taken together, our results suggest therapeutical implications for Trx1 in retinal damage induced by hypoxia-ischemia during birth.

4-HNE induces proinflammatory cytokines of human retinal pigment epithelial cells by promoting extracellular efflux of HSP70

Oxidative stress and subsequent chronic inflammation result in dysfunction of the retinal pigment epithelium (RPE) and represent therapeutic targets in the context of age-related macular degeneration (AMD). However, molecular mechanisms that linked oxidative stress and inflammation still unclear. As an important byproduct of oxidative stress, 4-hydroxynonenal (4-HNE) induces apoptosis and lysosome dysregulation of RPE cells. In the present study, we evaluated cytokines production of RPE cells induced by 4-HNE by using cytokine array and confirmed that 4-HNE induced IL-6, IL-1β and TNF-α production in a concentration dependent manner. Specifically, 4-HNE also induced IL-10 and TGF-β production in low concentration. Molecular analysis revealed that intracellular HSP70 inhibited 4-HNE-induced production of pro-inflammatory cytokines, and 4-HNE exerted proinflammatory effects in RPE cells by enhancing extracellular release of HSP70, as efflux inhibitor Methyl-β-cyclodextrin (MBC) treatment significantly blocked the release of HSP70 and decreased IL-6 production of RPE cells induced by 4-HNE. Meanwhile, HSP70 inducer arimoclomol increased intracellular HSP70 production, but showed no influence on its extracellular level, also performed anti-inflammatory effects in 4-HNE-stimulated RPE cells. Whereas the anti-inflammatory effects of paeoniflorin, an HSP70 inducer simultaneously promoted its extracellular efflux, was lower than arimoclomol. In addition, we further confirmed that MBC exhibited synergetic effect with both paeoniflorin and arimoclomol to inhibit the production of proinflammatory cytokines induced by 4-HNE. Taken together, these results indicate that HSP70 plays a vital role in regulating inflammation of RPE cells induced by oxidative stress and might be a potential novel target for clinical treatment of AMD.

Neuroprotective effect of a dietary supplement against glutamate-induced excitotoxicity in retina

AIM

To evaluate the neuroprotective effect of a dietary supplement (ClearVision EX^®; CV) against glutamate-induced excitotoxicity in retina.

METHODS

We evaluated the protective effects CV on glutamate-induced cell toxicity of an immortalized mouse hippocampal cell line (HT-22) in vitro and N-methyl-D-aspartate (NMDA) induced retinal injury in vivo. Once-daily oral administration of CV or vehicle (5% Arabic gum) was started the day before the NMDA injection and continued until the end of the study. Electroretinograms (ERGs) were recorded to evaluate the retinal function at 2d after NMDA injection. Furthermore, a histological evaluation, Western blot analysis, and immunohistochemistry were performed for assessing the signal transduction pathway.

RESULTS

HT-22 cell death was induced by the addition of glutamate and co-incubation with CV protected against it. Oral administration of CV inhibited the decrease in scotopic threshold response amplitudes induced by the intravitreal injection of NMDA and those of the thickness of the inner retinal layer in the histological evaluation. The increased phosphorylated levels of extracellular signal-regulated kinase (ERK) but not cAMP response element binding protein (CREB) or Akt were observed 1h after NMDA injection in both the vehicle- and CV-treated rats; however, pERK activation was no more upregulated at 3h after NMDA injection. pERK upregulation was observed in Müller cells.

CONCLUSION

CV shows a protective effect against both glutamate-induced HT-22 cell death and NMDA-induced retinal damage. pERK upregulation in the Müller cells plays a key role in the protective effect of CV against glutamate-induced retinal toxicity.

Antioxidants and HNE in redox homeostasis

Under physiological conditions, cells are in a stable state known as redox homeostasis, which is maintained by the balance between continuous ROS/RNS generation and several mechanisms involved in antioxidant activity. ROS overproduction results in alterations in the redox homeostasis that promote oxidative damage to major components of the cell, including the biomembrane phospholipids. Lipid peroxidation subsequently generates a diverse set of products, including α,β-unsaturated aldehydes. Of these products, 4-hydroxy-2-nonenal (HNE) is the most studied aldehyde on the basis of its involvement in cellular physiology and pathology. This review summarizes the current knowledge in the field of HNE generation, metabolism, and detoxification, as well as its interactions with various cellular macromolecules (protein, phospholipid, and nucleic acid). The formation of HNE-protein adducts enables HNE to participate in multi-step regulation of cellular metabolic pathways that include signaling and transcription of antioxidant enzymes, pro-inflammatory factors, and anti-apoptotic proteins. The most widely described roles for HNE in the signaling pathways are associated with its activation of kinases, as well as transcription factors that are responsible for redox homeostasis (Ref-1, Nrf2, p53, NFκB, and Hsf1). Depending on its level, HNE exerts harmful or protective effects associated with the induction of antioxidant defense mechanisms. These effects make HNE a key player in maintaining redox homeostasis, as well as producing imbalances in this system that participate in aging and the development of pathological conditions.

4-hydroxynonenal regulates mitochondrial function in human small airway epithelial cells

Prolonged exposure to oxidative stress causes Acute Lung Injury (ALI) and significantly impairs pulmonary function. Previously we have demonstrated that mitochondrial dysfunction is a key pathological factor in hyperoxic ALI. While it is known that hyperoxia induces the production of stable, but toxic 4-hydroxynonenal (4-HNE) molecule, it is unknown how the reactive aldehyde disrupts mitochondrial function. Our previous in vivo study indicated that exposure to hyperoxia significantly increases 4-HNE-Protein adducts, as well as levels of MDA in total lung homogenates. Based on the in vivo studies, we explored the effects of 4-HNE in human small airway epithelial cells (SAECs). Human SAECs treated with 25 μM of 4-HNE showed a significant decrease in cellular viability and increased caspase-3 activity. Moreover, 4-HNE treated SAECs showed impaired mitochondrial function and energy production indicated by reduced ATP levels, mitochondrial membrane potential, and aconitase activity. This was followed by a significant decrease in mitochondrial oxygen consumption and depletion of the reserve capacity. The direct effect of 4-HNE on the mitochondrial respiratory chain was confirmed using Rotenone. Furthermore, SAECs treated with 25 μM 4-HNE showed a time-dependent depletion of total Thioredoxin (Trx) proteins and Trx activity. Taken together, our results indicate that 4-HNE induces cellular and mitochondrial dysfunction in human SAECs, leading to an impaired endogenous antioxidant response.

miR-17-3p Exacerbates Oxidative Damage in Human Retinal Pigment Epithelial Cells

Oxidative stress has been shown to contribute to the development of age-related macular degeneration (AMD). MicroRNAs (miRNA) are small non-coding RNA molecules that function in RNA silencing and post-transcriptional regulation of gene expression. We showed miR-17-3p to be elevated in macular RPE cells from AMD patients and in ARPE-19 cells under oxidative stress. Transfection of miR-17-3p mimic in ARPE-19 induced cell death and exacerbated oxidative lethality that was alleviated by miR-17-3p inhibitor. The expression of antioxidant enzymes manganese superoxide dismutase (MnSOD) and thioredoxin reductase-2 (TrxR2) were suppressed by miR-17-3p mimic and reversed by miR-17-3p inhibitor. These results suggest miR-17-3p aggravates oxidative damage-induced cell death in human RPE cells, while miR-17-3p inhibitor acts as a potential protector against oxidative stress by regulating the expression of antioxidant enzymes.

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.