Nrf2 promotes reparative angiogenesis through regulation of NADPH oxidase-2 in oxygen-induced retinopathy

MDSCs promote pathological angiogenesis in ocular neovascular disease

BACKGROUND

Ocular neovascular diseases, which contribute significantly to vision loss, lack effective preventive treatments. Recent studies have highlighted the significant involvement of immune cells in neovascular retinopathy. Myeloid-derived suppressor cells (MDSCs) promote the development of neovascularization, but it is unknown whether they participate in pathological neovascularization and whether they are expected to be a therapeutic target.

METHOD

We investigated the role of MDSCs in promoting pathological angiogenesis using an oxygen-induced retinopathy (OIR) model, employing flow cytometry, immunofluorescence, and smart-seq analysis. Then, we evaluated the proportion of MDSCs in patient blood samples using flow cytometry. Additionally, we assessed the effect of MDSC depletion using an anti-Gr-1 monoclonal antibody on retinal vasculopathy and alterations in retinal microglia.

RESULTS

In the OIR model, an elevated ratio of MDSCs was observed in both blood and retinal tissue during phase II (Neovascularization). The depletion of MDSCs resulted in reduced retinal neovascularization and vaso-obliteration, along with a decrease in microglia within the neovascularization area. Furthermore, analysis of gene transcripts associated with MDSCs indicated activation of vascular endothelial growth factor (VEGF) regulation and inflammation. Importantly, infants with ROP exhibited a higher proportion of MDSCs in their blood samples.

CONCLUSION

Our results suggested that excessive MDSCs represent an unrecognized feature of ocular neovascular diseases and be responsible for the retinal vascular inflammation and angiogenesis, providing opportunities for new therapeutic approaches to ocular neovascular disease.

Notoginseng leaf triterpenes promotes angiogenesis by activating the Nrf2 pathway and AMPK/SIRT1-mediated PGC-1/ERα axis in ischemic stroke

Notoginseng leaf triterpenes (PNGL), derived from the dried stems and leaves of P. notoginseng, is a phytoestrogen that exerts many neuroprotective effects in vivo and in vitro of ischemic stroke. However, its impact on neurological restoration specifically in relation to angiogenesis following ischemic stroke remains unexplored. The aim of this study was to assess the effects of PNGL on angiogenesis subsequent to ischemic stroke. Male Sprague-Dawley rats were utilized in this study and were subjected to middle cerebral artery occlusion/reperfusion (MCAO/R). Post-ischemia, PNGL were administered through intraperitoneal (i.p.) injection. The high-performance liquid chromatography (HPLC) fingerprinting, triphenyltetrazolium chloride (TTC) staining, immunofluorescent staining, network pharmacology and western blot analyses were assessed to determine the therapeutical effect and molecular mechanisms of PNGL on cerebral ischemia/reperfusion injury. Our findings demonstrate that PNGL effectively reduced infarct volume, enhanced cerebral blood flow, and induced angiogenesis in rats subjected to MCAO/R. Notably, PNGL also facilitated neuronal proliferation and migration in HUMECs in vitro. The proangiogenic effects of PNGL were found to be linked to the activation of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway and the AMPK/SIRT1-mediated PGC-1/ERα axis, as well as the activation of neurological function. Our study provides evidence that PNGL hold promise as an active ingredient of inducing proangiogenic effects, potentially through the activation of the Nrf2 pathway and the AMPK/SIRT1-mediated PGC-1/ERα axis. These findings contribute to the understanding of novel mechanisms involved in the restoration of neurological function following PNGL treatment for ischemic stroke.

Formyl Peptide Receptor 1 Inhibits Reparative Angiogenesis and Aggravates Neuroretinal Dysfunction in Ischemic Retinopathy

PURPOSE

Ischemic retinopathy is the major cause of vision-threatening conditions. Inflammation plays an important role in the pathogenesis of ischemic retinopathy. Formyl peptide receptor 1 (FPR1) has been reported to be implicated in the regulation of inflammatory disorders. However, the role of FPR1 in the progression of ischemic retinal injury has not been fully explained.

METHODS

The activation of FPR1 was measured by real-time PCR and western blotting in the retina of OIR. The effect of FPR1 on the expression of inflammatory cytokines and relevant pro-angiogenic factors was assessed between wild-type and FPR1-deficiency OIR mice. The impact of FPR1 on retinal angiogenesis was evaluated through quantifying retinal vaso-obliteration and neovascularization between FPR1+/+ and FPR1-/- OIR mice. At last, the neuronal effect of FPR1 on the ischemic retina was investigated by ERG between wild-type and FPR1-deficient OIR mice.

RESULTS

The expression of FPR1 significantly increased in the retina of OIR. Furthermore, FPR1 deficiency downregulated pro-inflammatory and pro-angiogenic factors. Ablation of FPR1 suppressed the retinal pathological neovascularization and promoted reparative revascularization, ultimately improving retinal neural function after ischemic injury.

CONCLUSION

In ischemic retinopathy, FPR1 aggravates inflammation and inhibits reparative angiogenesis to exacerbate neuronal dysfunction.

Rebalancing NOX2/Nrf2 to limit inflammation and oxidative stress across gut-brain axis in migraine

Migraine is one of the most common neurological illnesses, and it is characterized by complicated neurobiology. It was confirmed the influence of inflammation and oxidative stress in migraines and also in distal organs such as the intestine. Indeed, the constant bidirectional communication between the Central Nervous System (CNS) and the gastrointestinal (GI) tract, known as the gut-brain axis, has become an attractive target involved in different human disorders. Herein, we explored the role of NADPH oxidase 2 (NOX2) in nitroglycerin (NTG)-induced migraine in mice models to discover the mechanism by which, during migraine attack, oxidative stress is sustained within trigeminal neurons and GI. Considering the inverse relationship between NOX2 and Nrf2, Nrf2 upregulation seems to be a promising approach to decrease NOX2 expression and consequently limit oxidative stress and inflammation spread in neurological and non-neurological diseases. With this aim, we exploited tempol's Nrf2-inducer ability to better understand the involvement of Nrf2/NOX2 axis in migraine and associated GI comorbidities. Behavioral tests confirmed that tempol, in a dose-dependent manner, moderated clinical signs of migraine and abdominal pain. Moreover, we demonstrated that the decrease in migraine-related symptomatology was strongly linked to the modulation of Nrf2/NOX2 signaling pathway in the brain and colon. In the brain, the rebalancing of Nrf2/NOX2 prevented neuronal loss, decreased glia reactivity while inhibiting NF-κB and NLRP3 inflammasome activation. In the colon, Nrf2 upregulation and consequent NOX2 decrease reduced the histological damage, mast cells infiltration as well as tumor necrosis factor (TNF)-α and interleukin (IL)-1β release. Furthermore, the attenuation of inflammation and oxidative stress led to the restoration of the intestinal barrier through TJs replacement. Taken as a whole, data suggested that the regulation of Nrf2/NOX2 balance is a successful way to reduce neurological and related intestinal impairments during migraine and could be of relevance for migraine-like attacks in humans.

Recent advances in the treatment and delivery system of diabetic retinopathy

Diabetic retinopathy (DR) is a highly tissue-specific neurovascular complication of type 1 and type 2 diabetes mellitus and is among the leading causes of blindness worldwide. Pathophysiological changes in DR encompass neurodegeneration, inflammation, and oxidative stress. Current treatments for DR, including anti-vascular endothelial growth factor, steroids, laser photocoagulation, and vitrectomy have limitations and adverse reactions, necessitating the exploration of novel treatment strategies. This review aims to summarize the current pathophysiology, therapeutic approaches, and available drug-delivery methods for treating DR, and discuss their respective development potentials. Recent research indicates the efficacy of novel receptor inhibitors and agonists, such as aldose reductase inhibitors, angiotensin-converting enzyme inhibitors, peroxisome proliferator-activated receptor alpha agonists, and novel drugs in delaying DR. Furthermore, with continuous advancements in nanotechnology, a new form of drug delivery has been developed that can address certain limitations of clinical drug therapy, such as low solubility and poor penetration. This review serves as a theoretical foundation for future research on DR treatment. While highlighting promising therapeutic targets, it underscores the need for continuous exploration to enhance our understanding of DR pathogenesis. The limitations of current treatments and the potential for future advancements emphasize the importance of ongoing research in this field.

Protective effect of ethyl ferulate against hypoxic injury in retinal cells and retinal neovascularization in an oxygen-induced retinopathy model

BACKGROUND

Pathological neovascularization is a major cause of visual impairment in hypoxia-induced retinopathy. Ethyl ferulate (EF), the natural ester derivative of ferulic acid commonly found in Ferula and Angelica Sinensis, has been shown to exert antioxidant, neuroprotective, and anti-inflammatory properties. However, whether EF exerts a protective effect on retinal neovascularization and the underlying mechanisms are not well known.

PURPOSE

The aim of the study was to investigate the effect of EF on retinal neovascularization and explore its underlying molecular mechanisms.

STUDY-DESIGN/METHODS

We constructed hypoxia models induced by cobalt chloride (CoCl2) in ARPE-19 cells and Rhesus choroid-retinal vascular endothelial (RF/6A) cells in vitro, as well as a retinal neovascularization model in oxygen-induced retinopathy (OIR) mice in vivo.

RESULTS

In this work, we demonstrated that EF treatment inhibited hypoxia-induced vascular endothelial growth factor A (VEGFA) expression in ARPE-19 cells and abrogated hypoxia-induced tube formation in RF/6A cells. As expected, intravitreal injection of EF significantly suppressed retinal neovascularization in a dose-dependent manner in OIR retinas. We also found that hypoxia increased VEGFA expression by blocking autophagic flux, whereas EF treatment enhanced autophagic flux, thereby reducing VEGFA expression. Furthermore, EF activated the sequestosome 1 (p62) / nuclear factor E2-related factor 2 (Nrf-2) pathway via upregulating oxidative stress-induced growth inhibitor 1 (OSGIN1) expression, thus alleviating oxidative stress and reducing VEGFA expression.

CONCLUSION

As a result of our findings, EF has an inhibitory effect on retinal neovascularization, implying a potential therapeutic strategy for hypoxia-induced retinopathy.

Quantitative proteomic analyses uncover regulatory roles of Nrf2 in human endothelial cells

Nuclear factor erythroid 2-related factor 2 (Nrf2), a transcriptional regulator, is the predominant factor in modulating oxidative stress and other cellular signaling responses. Studies from our lab and others highlighted that activation of the Nrf2 pathway by small molecules improves endothelial function by suppressing oxidative and endoplasmic reticulum (ER) stress. However, the exact mechanisms by which Nrf2 elicits these effects are unknown. In the present study, we developed CRISPR/Cas9-mediated Nrf2 knocked-out human endothelial cells, and proteomic signature was studied using LC-MS/MS. We identified 723 unique proteins, of which 361 proteins were found to be differentially regulated and further screened in the Nrf2ome online database, where we identified a highly interconnected signaling network in which 70 proteins directly interact with Nrf2. These proteins were found to regulate some key cellular and metabolic processes in the regulation actin cytoskeleton, ER stress, angiogenesis, inflammation, Hippo signaling pathway, and epidermal growth factor/fibroblast growth factor (EGF/FGF) signaling pathway. Our findings suggest the role of Nrf2 in maintaining endothelium integrity and its relationship with the crucial cellular processes which help develop novel therapeutics against endothelial dysfunction and its associated complications.

The tissue-specific transcriptional landscape underlines the involvement of endothelial cells in health and disease

Endothelial cells (ECs) that line vascular and lymphatic vessels are being increasingly recognized as important to organ function in health and disease. ECs participate not only in the trafficking of gases, metabolites, and cells between the bloodstream and tissues but also in the angiocrine-based induction of heterogeneous parenchymal cells, which are unique to their specific tissue functions. The molecular mechanisms regulating EC heterogeneity between and within different tissues are modeled during embryogenesis and become fully established in adults. Any changes in adult tissue homeostasis induced by aging, stress conditions, and various noxae may reshape EC heterogeneity and induce specific transcriptional features that condition a functional phenotype. Heterogeneity is sustained via specific genetic programs organized through the combinatory effects of a discrete number of transcription factors (TFs) that, at the single tissue-level, constitute dynamic networks that are post-transcriptionally and epigenetically regulated. This review is focused on outlining the TF-based networks involved in EC specialization and physiological and pathological stressors thought to modify their architecture.

Role of Hydroxytyrosol and Oleuropein in the Prevention of Aging and Related Disorders: Focus on Neurodegeneration, Skeletal Muscle Dysfunction and Gut Microbiota

Aging is a multi-faceted process caused by the accumulation of cellular damage over time, associated with a gradual reduction of physiological activities in cells and organs. This degeneration results in a reduced ability to adapt to homeostasis perturbations and an increased incidence of illnesses such as cognitive decline, neurodegenerative and cardiovascular diseases, cancer, diabetes, and skeletal muscle pathologies. Key features of aging include a chronic low-grade inflammation state and a decrease of the autophagic process. The Mediterranean diet has been associated with longevity and ability to counteract the onset of age-related disorders. Extra virgin olive oil, a fundamental component of this diet, contains bioactive polyphenolic compounds as hydroxytyrosol (HTyr) and oleuropein (OLE), known for their antioxidant, anti-inflammatory, and neuroprotective properties. This review is focused on brain, skeletal muscle, and gut microbiota, as these systems are known to interact at several levels. After the description of the chemistry and pharmacokinetics of HTyr and OLE, we summarize studies reporting their effects in in vivo and in vitro models of neurodegenerative diseases of the central/peripheral nervous system, adult neurogenesis and depression, senescence and lifespan, and age-related skeletal muscle disorders, as well as their impact on the composition of the gut microbiota.

Protective Effect of NO2-OA on Oxidative Stress, Gliosis, and Pro-Angiogenic Response in Müller Glial Cells

Inflammation and oxidative and nitrosative stress are involved in the pathogenesis of proliferative retinopathies (PR). In PR, a loss of balance between pro-angiogenic and anti-angiogenic factors favors the secretion of vascular endothelial growth factor (VEGF). This vascular change results in alterations in the blood-retinal barrier, with extravasation of plasma proteins such as α₂-macroglobulin (α₂M) and gliosis in Müller glial cells (MGCs, such as MIO-M1). It is well known that MGCs play important roles in healthy and sick retinas, including in PR. Nitro-fatty acids are electrophilic lipid mediators with anti-inflammatory and cytoprotective properties. Our aim was to investigate whether nitro-oleic acid (NO₂-OA) is beneficial against oxidative stress, gliosis, and the pro-angiogenic response in MGCs. Pure synthetic NO₂-OA increased HO-1 expression in a time- and concentration-dependent manner, which was abrogated by the Nrf2 inhibitor trigonelline. In response to phorbol 12-myristate 13-acetate (PMA) and lipopolysaccharide (LPS), NO₂-OA prevented the ROS increase and reduced the gliosis induced by α₂M. Finally, when hypoxic MGCs were incubated with NO₂-OA, the increase in VEGF mRNA expression was not affected, but under hypoxia and inflammation (IL-1β), NO₂-OA significantly reduced VEGF mRNA levels. Furthermore, NO₂-OA inhibited endothelial cell (BAEC) tubulogenesis. Our results highlight NO₂-OA's protective effect on oxidative damage, gliosis; and the exacerbated pro-angiogenic response in MGCs.

The loss of pancreatic islet NADPH oxidase (NOX)2 improves islet transplantation

Islet transplantation is a promising treatment strategy for type 1 diabetes mellitus (T1DM) patients. However, oxidative stress-induced graft failure due to an insufficient revascularization is a major problem of this therapeutic approach. NADPH oxidase (NOX)2 is an important producer of reactive oxygen species (ROS) and several studies have already reported that this enzyme plays a crucial role in the endocrine function and viability of β-cells. Therefore, we hypothesized that targeting islet NOX2 improves the outcome of islet transplantation. To test this, we analyzed the cellular composition and viability of isolated wild-type (WT) and Nox2-/- islets by immunohistochemistry as well as different viability assays. Ex vivo, the effect of Nox2 deficiency on superoxide production, endocrine function and anti-oxidant protein expression was studied under hypoxic conditions. In vivo, we transplanted WT and Nox2-/- islets into mouse dorsal skinfold chambers and under the kidney capsule of diabetic mice to assess their revascularization and endocrine function, respectively. We found that the loss of NOX2 does not affect the cellular composition and viability of isolated islets. However, decreased superoxide production, higher glucose-stimulated insulin secretion as well as expression of nuclear factor erythroid 2-related factor (Nrf)2, heme oxygenase (HO)-1 and superoxide dismutase 1 (SOD1) was detected in hypoxic Nox2-/- islets when compared to WT islets. Moreover, we detected an early revascularization, a higher take rate and restoration of normoglycemia in diabetic mice transplanted with Nox2-/- islets. These findings indicate that the suppression of NOX2 activity represents a promising therapeutic strategy to improve engraftment and function of isolated islets.

tBHQ attenuates podocyte injury in diabetic nephropathy by inhibiting NADPH oxidase-derived ROS generation via the Nrf2/HO-1 signalling pathway

Aims

Oxidative stress plays a crucial role in podocyte injury in diabetic nephropathy (DN). tert-Butylhydroquinone (tBHQ) is an activator of Nrf2 that exerts protective effects in diabetic mice, but the underlying mechanism of tBHQ in the podocytes of DN is not fully understood.

Materials and methods

A high glucose (HG)-induced HK2 cell model and streptozotocin-induced rat model of DN were established and treated with tBHQ or apocynin. The expression levels of Nrf2, HO-1, NOX2 and NOX4 were determined by Western blot or immunohistochemical staining. The level of oxidative stress in podocytes or kidney tissues was assessed using DCFH-DA or dihydroethidium (DHE) staining. Cell injury was assessed by F-actin staining and flow cytometry analysis.

Key findings

We showed that HG treatment increased the expressions of NOX2 and NOX4 and enhanced ROS production in podocytes. Inhibition of NADPH oxidase activity by apocynin dramatically attenuated HG-induced ROS production and further alleviated cell injury and apoptosis in podocytes. Moreover, we found that HG inhibited the Nrf2/HO-1 signalling pathway in podocytes; however, tBHQ treatment significantly activated the Nrf2 signalling pathway, inhibited NADPH oxidase activity, and attenuated ROS production and cell injury in HG-treated podocytes. Furthermore, we observed that tBHQ treatment partially attenuated renal injury, activated the Nrf2 signalling pathway, inhibited NADPH oxidase activity and reduced ROS generation in the kidneys of STZ-induced diabetic rats.

Significance

These results suggest that tBHQ exerts a protective role in hyperglycaemia-induced podocyte injury, and that the potential protective mechanism of tBHQ involves inhibiting NADPH oxidase-derived ROS generation by activating the Nrf2/HO-1 signalling pathway.

The Effects of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) Oxidase and Erythropoietin, and Their Interactions in Angiogenesis: Implications in Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a leading cause of vision impairment and blindness in premature infants. Oxidative stress is implicated in its pathophysiology. NADPH oxidase (NOX), a major enzyme responsible for reactive oxygen species (ROS) generation in endothelial cells, has been studied for its involvement in physiologic and pathologic angiogenesis. Erythropoietin (EPO) has gained interest recently due to its tissue protective and angiogenic effects, and it has been shown to act as an antioxidant. In this review, we summarize studies performed over the last five years regarding the role of various NOXs in physiologic and pathologic angiogenesis. We also discuss the effect of EPO in tissue and vasoprotection, and the intersection of EPO and NOX-mediated oxidative stress in angiogenesis and the pathophysiology of ROP.

Edaravone dexborneol protects cerebral ischemia reperfusion injury through activating Nrf2/HO-1 signaling pathway in mice

Stroke is the leading cause of disability and death. When blood flow is restored after prolonged ischemia and hypoxia, it leads to excessive production of reactive oxygen species (ROS), increased local inflammation, and apoptosis, which are the cause of most cerebral ischemia reperfusion injury (CIRI), leading to secondary brain tissue damage. Edaravone dexborneol is a novel neuroprotective agent consisting of edaravone and borneol. Studies have shown that it has synergistic antioxidant and anti‐inflammatory effects. However, whether Edaravone dexborneol stimulates the Nrf2/HO‐1 pathway to regulate NADPH oxidase 2 (NOX2) remains unclear. In this study, wild‐type (WT) mice and Nrf2 knockout (KO) mice were used to investigate the antioxidant, anti‐inflammatory, and anti‐apoptotic effects of Edaravone dexborneol on CIRI and its mechanism. The cognitive function of mice was evaluated with the Morris water maze (MWM), test and the cell structures of hippocampus were observed by hematoxylin and eosin (H&E) staining. Nrf2, HO‐1, and NOX2 proteins and apoptosis‐related proteins Bcl‐2, Bax, and Caspase 3 were detected by western blotting. Nrf2, HO‐1, NOX2, and inflammatory factors TNF‐α, IL‐1β, IL‐4, and IL‐10 were detected by real‐time polymerase chain reaction. The results showed that Edaravone dexborneol treatment improved learning and memory performance, neuronal damage, and enhanced antioxidant, inflammation, and apoptosis in CIRI mice. In addition, Edaravone dexborneol induced the activation Nrf2/HO‐1 signaling pathway activation while inhibiting NOX2 expression. Overall, these results indicate that Edaravone dexborneol ameliorates CIRI‐induced memory impairments by activating Nrf2/HO‐1 signaling pathway and inhibiting NOX2.

Renoprotective effect of vinpocetine against ischemia/reperfusion injury: Modulation of NADPH oxidase/Nrf2, IKKβ/NF-κB p65, and cleaved caspase-3 expressions

Ischemia/reperfusion injury (IRI) during kidney transplantation is a serious clinical problem with a high mortality rate and a lack of therapy. Therefore, there is a need to improve the ability of the kidney to tolerate IRI during transplantation. This study aimed to investigate the possible protective effect of vinpocetine; a derivative of vincamine alkaloid; against renal IRI in rats with the elucidation of the involved mechanisms. Vinpocetine (25 mg/kg; i.p.) was administered for 10 successive days before the induction of ischemia by bilateral clamping of both renal pedicles for 45 min followed by 24 h of reperfusion. Blood and renal tissue samples were then collected for biochemical, molecular, and histopathological investigations. Vinpocetine significantly reduced serum creatinine and blood urea nitrogen levels in rats subjected to IRI. It also reduced mRNA expression of NADPH oxidase and renal content of malondialdehyde, while enhanced Nrf2 protein expression and renal content of reduced glutathione. The suppression of the provoked inflammatory response was evident by the downregulation of IKKβ and NF-κB p65 protein expressions, as well as their downstream inflammatory markers; tumor necrosis factor-α, interleukin-6, and myeloperoxidase. In addition, vinpocetine reduced protein expression of the apoptotic executioner cleaved caspase-3. These nephroprotective effects were confirmed by the improvement in histopathological features. Collectively, the protective effect of vinpocetine against IRI could be attributed to modulation of NADPH oxidase/Nrf2, IKKβ/NF-κB p65, and cleaved caspase-3 expressions. Thus, vinpocetine could improve oxidant/antioxidant balance, suppress triggered inflammatory response, and promote renal cell survival after IRI.

Annexin A1 promotes reparative angiogenesis and ameliorates neuronal injury in ischemic retinopathy

PURPOSE

Retinal ischemia is the main reason for vision threatening. Inflammation and aberrant angiogenesis play an important role in the pathogenesis of ischemia. Annexin A1 is an endogenous protein modulating anti-inflammatory processes, and its therapeutic potential has been reported in a range of inflammatory diseases. However, the effect of annexin A1 on ischemic retinal injury has not been examined.

METHODS

Expression of annexin A1 was assessed by real time PCR and western blotting, and location of annexin A1 was evaluated by immunofluorescence staining in retina of OIR. The activation of annexin A1 were assayed in HRECs after hypoxia stimuli. The effect of annexin A1 on vascularization of OIR mouse through quantification vaso-obliteration and neovascularization, as well as expression of relevant angiogenic factors and inflammatory cytokines was compared between wild type and annexin A1 deficiency mice. We also investigated the effect of annexin A1 on retinal neuronal degeneration as measured by ERG and OCT.

RESULTS

In retinas of OIR, the expression of annexin A1 significantly increased and located in inner retinal layers. Annexin A1 was induced in HRECs after hypoxic stimuli. Furthermore, annexin A1 deficiency increased pro-angiogenic and pro-inflammatory cytokines. Ablation of annexin A1 suppressed aortic outgrowth and retinal reparative revascularization and promoted pathological neovascularization to exacerbate retinal dysfunction after ischemia injury.

CONCLUSION

Annexin A1 inhibits angiogenic and inhibits pro-inflammatory cytokines and promotes reparative angiogenesis, thus exhibits neuronal protective function in ischemic retinopathy.

Myeloid cell modulation by a GLP-1 receptor agonist regulates retinal angiogenesis in ischemic retinopathy

Ischemic retinopathies including diabetic retinopathy are major causes of blindness. Although neurons and Müller glia are recognized as important regulators of reparative and pathologic angiogenesis, the role of mononuclear phagocytes (MPs) — particularly microglia, the resident retinal immune cells — is unclear. Here, we found MP activation in human diabetic retinopathy, especially in neovessels from human neovascular membranes in proliferative retinopathy, including TNF-α expression. There was similar activation in the mouse oxygen-induced retinopathy (OIR) model of ischemia-induced neovascularization. Glucagon-like peptide-1 receptor (GLP-1R) agonists are in clinical use for glycemic control in diabetes and are also known to modulate microglia. Herein, we investigated the effect of a long-acting GLP-1R agonist, NLY01. Following intravitreal administration, NLY01 selectively localized to MPs in retina with OIR. NLY01 modulated MPs but not retinal endothelial cell viability, apoptosis, and tube formation in vitro. In OIR, NLY01 treatment inhibited MP infiltration and activation, including MP expression of cytokines in vivo. NLY01 significantly suppressed global induction of retinal inflammatory cytokines, promoted reparative angiogenesis, and suppressed pathologic retinal neovascularization. Collectively, these findings indicate the important role of mononuclear phagocytes in regulation of retinal vascularization in ischemia and suggest modulation of MPs as a potentially new treatment strategy for ischemic retinopathies.

Nutrigenetic reprogramming of oxidative stress

Retinal disorders such as retinitis pigmentosa, age-related retinal degeneration, oxygen-induced retinopathy, and ischemia-reperfusion injury cause debilitating and irreversible vision loss. While the exact mechanisms underlying these conditions remain unclear, there has been a growing body of evidence demonstrating the pathological contributions of oxidative stress across different cell types within the eye. Nuclear factor erythroid-2-related factor (Nrf2), a transcriptional activator of antioxidative genes, and its regulator Kelch-like ECH-associated protein 1 (Keap1) have emerged as promising therapeutic targets. The purpose of this review is to understand the protective role of the Nrf2-Keap1 pathway in different retinal tissues and shed light on the complex mechanisms underlying these processes. In the photoreceptors, we highlight that Nrf2 preserves their survival and function by maintaining oxidation homeostasis. In the retinal pigment epithelium, Nrf2 similarly plays a critical role in oxidative stabilization but also maintains mitochondrial motility and autophagy-related lipid metabolic processes. In endothelial cells, Nrf2 seems to promote proper vascularization and revascularization through concurrent activation of antioxidative and angiogenic factors as well as inhibition of inflammatory cytokines. Finally, Nrf2 protects retinal ganglion cells against apoptotic cell death. Importantly, we show that Nrf2-mediated protection of the various retinal tissues corresponds to a preservation of functional vision. Altogether, this review underscores the potential of the Nrf2-Keap1 pathway as a powerful tool against retinal degeneration. Key insights into this elegant oxidative defense mechanism may ultimately pave the path toward a universal therapy for various inherited and environmental retinal disorders.

Long-term inhibition of UCHL1 decreases hypertension and retinopathy in spontaneously hypertensive rats

OBJECTIVE

To investigate the role of the deubiquitinase ubiquitin C-terminal hydrolase L1 (UCHL1) in hypertension and retinopathy in the spontaneously hypertensive rat (SHR).

METHODS

Wistar-Kyoto (WKY) rats and SHRs were administered the UCHL1 inhibitor LDN57444 (20 μg/kg/day) for 4 months. Pathological changes were detected with hematoxylin and eosin, immunofluorescence, and dihydroethidium staining. The mRNA and protein expression of UCHL1 were examined by real-time PCR and immunoblotting analysis.

RESULTS

At 6 months of age, SHRs showed significantly increased mRNA and protein levels of UCHL1 in the retina compared with WKY rats. Moreover, SHRs exhibited significantly increased central retinal thickness, inflammation, and reactive oxygen species production compared with WKY rats, and these effects were markedly attenuated by systemic administration of the UCHL1 inhibitor LDN57444. The beneficial effects of LDN57444 were possibly associated with reduced blood pressure and the inactivation of several signaling pathways.

CONCLUSION

UCHL1 is involved in hypertension and retinopathy in SHRs, suggesting that UCHL1 may be used as a potential therapeutic target for treating hypertensive retinopathy.

Stress Signal Regulation by Na/K-ATPase As a New Approach to Promote Physiological Revascularization in a Mouse Model of Ischemic Retinopathy

Purpose

The identification of target pathways to block excessive angiogenesis while simultaneously restoring physiological vasculature is an unmet goal in the therapeutic management of ischemic retinopathies. pNaKtide, a cell-permeable peptide that we have designed by mapping the site of α1 Na/K-ATPase (NKA)/Src binding, blocks the formation of α1 NKA/Src/reactive oxygen species (ROS) amplification loops and restores physiological ROS signaling in a number of oxidative disease models. The aim of this study was to evaluate the importance of the NKA/Src/ROS amplification loop and the effect of pNaKtide in experimental ischemic retinopathy.

Methods

Human retinal microvascular endothelial cells (HRMECs) and retinal pigment epithelium (ARPE-19) cells were used to evaluate the effect of pNaKtide on viability, proliferation, and angiogenesis. Retinal toxicity and distribution were assessed in those cells and in the mouse. Subsequently, the role and molecular mechanism of NKA/Src in ROS stress signaling were evaluated biochemically in the retinas of mice exposed to the well-established protocol of oxygen-induced retinopathy (OIR). Finally, pNaKtide efficacy was assessed in this model.

Results

The results suggest a key role of α1 NKA in the regulation of ROS stress and the Nrf2 pathway in mouse OIR retinas. Inhibition of α1 NKA/Src by pNaKtide reduced pathologic ROS signaling and restored normal expression of hypoxia-inducible factor 1-α/vascular endothelial growth factor (VEGF). Unlike anti-VEGF agents, pNaKtide did promote retinal revascularization while inhibiting neovascularization and inflammation.

Conclusions

Targeting α1 NKA represents a novel strategy to develop therapeutics that not only inhibit neovascularization but also promote physiological revascularization in ischemic eye diseases.

TAK1 signaling is a potential therapeutic target for pathological angiogenesis

Angiogenesis plays a critical role in both physiological responses and disease pathogenesis. Excessive angiogenesis can promote neoplastic diseases and retinopathies, while inadequate angiogenesis can lead to aberrant perfusion and impaired wound healing. Transforming growth factor β activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase family, is a key modulator involved in a range of cellular functions including the immune responses, cell survival and death. TAK1 is activated in response to various stimuli such as proinflammatory cytokines, hypoxia, and oxidative stress. Emerging evidence has recently suggested that TAK1 is intimately involved in angiogenesis and mediates pathogenic processes related to angiogenesis. Several detailed mechanisms by which TAK1 regulates pathological angiogenesis have been clarified, and potential therapeutics targeting TAK1 have emerged. In this review, we summarize recent studies of TAK1 in angiogenesis and discuss the crosstalk between TAK1 and signaling pathways involved in pathological angiogenesis. We also discuss the approaches for selectively targeting TAK1 and highlight the rationales of therapeutic strategies based on TAK1 inhibition for the treatment of pathological angiogenesis.

Nattokinase Attenuates Retinal Neovascularization Via Modulation of Nrf2/HO-1 and Glial Activation

PURPOSE

Nattokinase (NK), an active ingredient extracted from traditional food Natto, has been studied for prevention and treatment of cardiovascular diseases due to various vasoprotective effects, including fibrinolytic, antihypertensive, anti-atherosclerotic, antiplatelet, and anti-inflammatory activities. Here, we reported an antineovascular effect of NK against experimental retinal neovascularization.

METHODS

The inhibitory effect of NK against retinal neovascularization was evaluated using an oxygen-induced retinopathy murine model. Expressions of Nrf2/HO-1 signaling and glial activation in the NK-treated retinae were measured. We also investigated cell proliferation and migration of human umbilical vein endothelial cells (HUVECs) after NK administration.

RESULTS

NK treatment significantly attenuated retinal neovascularization in the OIR retinae. Consistently, NK suppressed VEGF-induced cell proliferation and migration in a concentration-dependent manner in cultured vascular endothelial cells. NK ameliorated ischemic retinopathy partially via activating Nrf2/HO-1. In addition, NK orchestrated reactive gliosis and promoted microglial activation toward a reparative phenotype in ischemic retina. Treatment of NK exhibited no cell toxicity or anti-angiogenic effects in the normal retina.

CONCLUSIONS

Our results revealed the anti-angiogenic effect of NK against retinal neovascularization via modulating Nrf2/HO-1, glial activation and neuroinflammation, suggesting a promising alternative treatment strategy for retinal neovascularization.

Evaluation of antioxidant capacity and immunomodulatory effects of yeast hydrolysates for hepatocytes of blunt snout bream (Megalobrama amblycephala)

An in-vitro study was carried out to examine the effects of yeast hydrolysate (YH) on antioxidant capacity and innate immunity of blunt snout bream (Megalobrama amblycephala) hepatocytes. Fish primary hepatocytes were seeded at a density of 3 × 10⁵ cells mL^-1 in 6-well tissue culture plates and treated with two different media including: 1) DMEM/F12 medium (control), and 2) YH medium [DMEM/F12 + 0.1 g L^-1 YH]. After incubation for 24 h, the culture medium and primary hepatocytes were collected for subsequent analyses. The results showed no significant (P > 0.05) effect of YH on aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) activities and urea nitrogen (UN) concentration in the conditioned medium. However, significantly (P < 0.05) higher ALT and AST activities were found in YH treated hepatocytes compared to control. Moreover, YH supplementation led to significant enhancement of superoxide dismutase (SOD), catalase (CAT), alternative complement pathway (ACH50) and glutathione peroxidase (GPX) activities and reduction of malondialdehyde (MDA) concentration in the conditioned medium. Furthermore, YH application upregulated the expression of SOD, CAT and NOX2 genes and downregulated mRNA levels of Keap1, Nrf2 and Bach1 in hepatocytes. Also, markedly higher lysozyme activity and albumin concentration were found in the conditioned medium of YH group compared to the control. Additionally, expression of immune-related genes such as antimicrobial peptides 1 (Leap 1) and Leap 2 were significantly upregulated by YH application. Down-regulated expression of NADPH oxidase-2 (NOX2), Kelch-like-ECH-associated protein 1 (Keap1), NF-E2-related factor 2 (Nrf2) and BTB and CNC homolog 1 (Bach1) were observed in YH treated hepatocytes. To conclude, YH supplementation improved antioxidant capacity and innate immunity of blunt snout bream hepatocytes.

The role of reactive oxygen species in the pathogenesis and treatment of retinal diseases

Reactive oxygen species (ROS) normally play an important physiological role in health regulating cellular processes and signal transduction. The amount of ROS is usually kept in fine balance with the generation of ROS largely being offset by the body's antioxidants. A tipping of this balance has increasingly been recognised as a contributor to human disease. The retina, as a result of its cellular anatomy and physical location, is a potent generator of ROS that has been linked to several major retinal diseases. This review will provide a summary of the role of oxidative stress in the pathogenesis of diabetic retinopathy, age-related macular degeneration, myopia, retinal vein occlusion, retinitis pigmentosa and retinopathy of prematurity. Therapies aimed at controlling oxidative stress in these diseases are also examined.

Oxidative Stress and Vascular Dysfunction in the Retina: Therapeutic Strategies

Many retinal diseases, such as diabetic retinopathy, glaucoma, and age-related macular (AMD) degeneration, are associated with elevated reactive oxygen species (ROS) levels. ROS are important intracellular signaling molecules that regulate numerous physiological actions, including vascular reactivity and neuron function. However, excessive ROS formation has been linked to vascular endothelial dysfunction, neuron degeneration, and inflammation in the retina. ROS can directly modify cellular molecules and impair their function. Moreover, ROS can stimulate the production of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) causing inflammation and cell death. However, there are various compounds with direct or indirect antioxidant activity that have been used to reduce ROS accumulation in animal models and humans. In this review, we report on the physiological and pathophysiological role of ROS in the retina with a special focus on the vascular system. Moreover, we present therapeutic approaches for individual retinal diseases targeting retinal signaling pathways involving ROS.

CircPDE4B inhibits retinal pathological angiogenesis via promoting degradation of HIF-1α though targeting miR-181c

Retinopathy of prematurity is a major cause of childhood blindness worldwide. Hence, exploring the proper treatment methods is a must in tacking this disease. qRT-PCR and western blot were used to detect the expression of genes and proteins, respectively. The proliferation of human retinal vascular endothelial cells (HRECs) was ensured by MTT assay. The luciferase activity was measured through luciferase assay. The inverted phase-contrast light microscope was used to observe the formation of a vascular tube. In the present study, our data demonstrated that circPDE4B was downregulated, while hypoxia-inducible factor-1α (HIF-1α) and VEGFA were upregulated in the retinopathy of prematurity model in vitro and in vivo. CircPDE4B increasing remarkably inhibited the expression of HIF-1α and VEGFA in hypoxia-induced HRECs and subsequent repressed cell proliferation and pathological angiogenesis. We further found that miR-181c suppressed the expression of von Hippel-Lindau (VHL), while circPDE4B could promote VHL expression via binding to miR-181c. Finally, our results revealed that circPDE4B inhibited the expression of VEGFA and pathological angiogenesis via facilitating VHL-mediated ubiquitin degradation of HIF-1α. In conclusion, circPDE4B suppressed the expression of VEGFA and pathological angiogenesis via promoting VHL-mediated ubiquitin degradation of HIF-1α through binding to miR-181c. Our study indicated that circPDE4B might be an effective therapeutic target of retinopathy of prematurity.

Novel Anti-Interleukin-1β Therapy Preserves Retinal Integrity: A Longitudinal Investigation Using OCT Imaging and Automated Retinal Segmentation in Small Rodents

Retinopathy of prematurity (ROP) is the leading cause of blindness in neonates. Inflammation, in particular interleukin-1β (IL-1β), is increased in early stages of the disorder, and contributes to inner and outer retinal vasoobliteration in the oxygen-induced retinopathy (OIR) model of ROP. A small peptide antagonist of IL-1 receptor, composed of the amino acid sequence, rytvela, has been shown to exert beneficial anti-inflammatory effects without compromising immunovigilance-related NF-κB in reproductive tissues. We conducted a longitudinal study to determine the efficacy of “rytvela” in preserving the integrity of the retina in OIR model, using optical coherence tomography (OCT) which provides high-resolution cross-sectional imaging of ocular structures in vivo. Sprague–Dawley rats subjected to OIR and treated or not with “rytvela” were compared to IL-1 receptor antagonist (Kineret). OCT imaging and custom automated segmentation algorithm used to measure retinal thickness (RT) were obtained at P14 and P30; gold-standard immunohistochemistry (IHC) was used to confirm retinal anatomical changes. OCT revealed significant retinal thinning in untreated animals by P30, confirmed by IHC; these changes were coherently associated with increased apoptosis. Both rytvela and Kineret subsided apoptosis and preserved RT. As anticipated, Kineret diminished both SAPK/JNK and NF-κB axes, whereas rytvela selectively abated the former which resulted in preserved monocyte phagocytic function. Altogether, OCT imaging with automated segmentation is a reliable non-invasive approach to study longitudinally retinal pathology in small animal models of retinopathy.

Evaluation of antioxidant capacity and immunomodulatory effects of cottonseed meal protein hydrolysate and its derivative peptides for hepatocytes of blunt snout bream (Megalobrama amblycephala)

Two in vitro trials were conducted to identify a peptide with antioxidant activity and immunoenhancement from cottonseed meal protein hydrolysate (CPH) for fish. Primary hepatocytes of Megalobrama amblycephala were treated with CPH. In experiment 1, CPH significantly increased aspartate aminotransferase (GOT), alanine aminotransferase (GPT), total superoxide dismutase (t-SOD), catalase (CAT), and lysozyme activities, as well as up-regulated SOD, CAT, antimicrobial peptides 1 (Leap 1) and Leap 2 mRNA levels (p < 0.05). However, CPH significantly down-regulated the expression of NADPH oxidase-2 (NOX2), Kelch-like-ECH-associated protein 1 (Keap1), NF-E2-related factor 2 (Nrf2) and BTB and CNC homolog 1 (Bach1) mRNA (p < 0.05) in fish hepatocytes. Experiment 2 showed that the molecular mass of CPH was distributed mainly in the 700-1024 Da range. Peptide 1 (P1) and P2 significantly decreased GOT and GPT activities in conditioned medium (p < 0.05); however, P4 and P6 did not affect GOT and GPT activities (p > 0.05). Furthermore, P4 significantly increased hepatocyte GOT, GPT, t-SOD, CAT levels and lysozyme activities (p < 0.05), up-regulated SOD, CAT, Leap1 and Leap2 mRNA expression levels, and down-regulated the expression of Nrf2 and NOX2 mRNA (p < 0.05) in fish hepatocytes. The above results indicated that CPH and P4 enhanced hepatocyte metabolism, as well as improved antioxidant capacities and innate immunity of blunt snout bream hepatocytes.

Control of tumor angiogenesis and metastasis through modulation of cell redox state

Redox reactions pervade all biology. The control of cellular redox state is essential for bioenergetics and for the proper functioning of many biological functions. This review traces a timeline of findings regarding the connections between redox and cancer. There is ample evidence of the involvement of cellular redox state on the different hallmarks of cancer. Evidence of the control of tumor angiogenesis and metastasis through modulation of cell redox state is reviewed and highlighted.

Inhibition of the Keap1-Nrf2 protein-protein interaction protects retinal cells and ameliorates retinal ischemia-reperfusion injury

The Nrf2-Keap1 pathway regulates transcription of a wide array of antioxidant and cytoprotective genes and offers critical protection against oxidative stress. This pathway has demonstrated benefit for a variety of retinal conditions. Retinal ischemia plays a pivotal role in many vision threatening diseases. Retinal vascular endothelial cells are an important participant in ischemic injury. In this setting, Nrf2 provides a protective pathway via amelioration of oxidative stress and inflammation. In this study, we investigated a potent small molecule inhibitor of the Nrf2-Keap1 protein-protein interaction (PPI), CPUY192018, for its therapeutic potential in retinal cells and retinal ischemia-reperfusion injury. In human retinal endothelial cells (HREC), treatment with CPUY192018 increased Nrf2 protein levels and nuclear translocation, stimulated Nrf2-ARE-induced transcriptional capacity, and induced Nrf2 target gene expression. Furthermore, CPUY192018 protected HREC against oxidative stress and inflammatory activation. CPUY192018 also activated Nrf2 and suppressed inflammatory response in macrophages. In the retinal ischemia-reperfusion (I/R) model, administration of CPUY192018 induced Nrf2 target gene activation in the retina. Both systemic and topical treatment with CPUY192018 rescued visual function after ischemia-reperfusion injury. Taken together, these findings indicate that small molecule Keap1-Nrf2 PPI inhibitors can activate the Nrf2 pathway in the retina and provide protection against retinal ischemic and inflammatory injury, suggesting Keap1-Nrf2 PPI inhibition in the treatment of retinal conditions.

Oxidative Stress and Microvascular Alterations in Diabetic Retinopathy: Future Therapies

Diabetes is a disease that can be treated with oral antidiabetic agents and/or insulin. However, patients' metabolic control is inadequate in a high percentage of them and a major cause of chronic diseases like diabetic retinopathy. Approximately 15% of patients have some degree of diabetic retinopathy when diabetes is first diagnosed, and most will have developed this microvascular complication after 20 years. Early diagnosis of the disease is the best tool to prevent or delay vision loss and reduce the involved costs. However, diabetic retinopathy is an asymptomatic disease and its development to advanced stages reduces the effectiveness of treatments. Today, the recommended treatment for severe nonproliferative and proliferative diabetic retinopathy is photocoagulation with an argon laser and intravitreal injections of anti-VEGF associated with, or not, focal laser for diabetic macular oedema. The use of these therapeutic approaches is severely limited, such as uncomfortable administration for patients, long-term side effects, the costs they incur, and the therapeutic effectiveness of the employed management protocols. Hence, diabetic retinopathy is the widespread diabetic eye disease and a leading cause of blindness in adults in developed countries. The growing interest in using polyphenols, e.g., resveratrol, in treatments related to oxidative stress diseases has spread to diabetic retinopathy. This review focuses on analysing the sources and effects of oxidative stress and inflammation on vascular alterations and diabetic retinopathy development. Furthermore, current and antioxidant therapies, together with new molecular targets, are postulated for diabetic retinopathy treatment.

Nrf2 Sequesters Keap1 Preventing Podosome Disassembly: A Quintessential Duet Moonlights in Endothelium

AIMS

Nrf2 (nuclear factor erythroid 2-like 2) is a transcription factor known to modulate blood vessel formation. Various experimental settings, however, attribute to Nrf2 either stimulatory or repressive influence on angiogenesis. Our findings unveil the mechanism of Nrf2-dependent vessel formation, which reaches beyond transactivation of gene expression and reconciles previous discrepancies.

RESULTS

We provide evidence that growth differentiation factor 15 (GDF-15)- and stromal cell-derived factor 1 (SDF-1)-induced angiogenesis strongly depends on the presence of Nrf2 protein but does not rely on its transcriptional activity. Instead, Nrf2 serves as a protein restraining Keap1 (Kelch-like ECH-associated protein 1), its known transcriptional repressor. Angiogenic response is abrogated in Nrf2-deficient endothelial cells but not in cells expressing dominant negative form or Keap1-binding fragment of Nrf2. Deficiency of Nrf2 protein available for Keap1 leads to the overabundance of RhoGAP1 (Rho GTPase-activating protein 1), the protein regulating cell division cycle 42 (Cdc42) activity. This impairs podosome assembly and disrupts actin rearrangements, thereby preventing angiogenesis. Effects of Nrf2 deficiency can be rescued by concomitant knockdown of RhoGAP1 or Keap1. Importantly, in the established murine model of Nrf2 deficiency, the N-terminal fragment of Nrf2 containing Keap1 binding domain is preserved. Thus, this model can be used to characterize Nrf2 as a transcription factor, but not as a Keap1-sequestering protein. Innovation and Conclusion: To date, the significance of Nrf2 in cell function has been ascribed solely to the regulation of transcription. We demonstrate that Nrf2 serves as a protein tethering Keap1 to allow podosome assembly and angiogenesis. Moreover, we emphasize that the new Nrf2 function of a Keap1 scavenger implies revisiting the interpretation of some of the previous data on the Nrf2-Keap1 system.

Exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCPP) induces vascular toxicity through Nrf2-VEGF pathway in zebrafish and human umbilical vein endothelial cells

The growing production and extensive use of organophosphate flame retardants (OPFRs) have led to an increase in their environmental distribution and human exposure. Developmental toxicity is a major concern of OPFRs' adverse health effects. However, the impact of OPFRs exposure on vascular development and the toxicity pathway for developmental defects are poorly understood. In this study, we investigated the effects of exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCPP), a frequently detected OPFR, on early vascular development, and the possible role of nuclear factor erythroid 2-related factor (Nrf2)-dependent angiogenic pathway in TDCPP's vascular toxicity. TDCPP exposure at 300 and 500 μg/L impeded the growth of intersegmental vessels (ISV), a type of microvessels, as early as 30 hpf. Consistently, a similar pattern of decreased extension and remodeling of common cardinal vein (CCV), a typical macrovessel, was observed in zebrafish at 48 hpf and 72 hpf. Developing vasculature in zebrafish was more sensitive than general developmental parameters to TDCPP exposure. The expression of genes related to VEGF signaling pathway dose-dependently decreased in TDCPP-treated larvae. In in vitro experiments using human umbilical vein endothelial cells (HUVECs), the increased cell proliferation induced by VEGF was suppressed by TDCPP exposure in a dose-dependent fashion. In addition, we found a repression of Nrf2 expression and activity in TDCPP-treated larvae and HUVECs. Strikingly, the application of CDDO-Im, a potent Nrf2 activator, enhanced VEGF and protected against defective vascular development in zebrafish. Our results reveal that vascular impairment is a sensitive index for early exposure to TDCPP, which could be considered in the environmental risk assessment of OPFRs. The identification of Nrf2-mediating VEGF pathway provides new insight into the adverse outcome pathway (AOP) of OPFRs.

Salutary effect of fenofibrate on type 1 diabetic retinopathy via inhibiting oxidative stress-mediated Wnt/β-catenin pathway activation

Fenofibrate has been shown to have therapeutic effects on diabetic retinopathy (DR). Our previous studies demonstrated that the oxidative stress-activated Wnt/β-catenin pathway plays a pathogenic role in diabetic complications. In the present study, we evaluate the effect and mechanism of fenofibrate on regulating the oxidative stress-activated Wnt/β-catenin pathway by using the genetic type 1 diabetes model of C57BL/6J-Ins2^Akita mice and high glucose (HG)-treated ARPE-19. Our results demonstrated that retinal phosphorylation of LRP6 and nuclear β-catenin were increased in C57BL/6J-Ins2^Akita mice suggesting activation of Wnt/β-catenin signaling. Meanwhile, C57BL/6J-Ins2^Akita showed upregulation of oxidant enzyme Nox4 and Nox2 and downregulation of antioxidant enzyme SOD1 and SOD2. All these alterations were reversed in C57BL/6J-Ins2^Akita mice with fenofibrate treatment. Moreover, fenofibrate significantly ameliorated diabetes-induced retinal vascular leakage in C57BL/6J-Ins2^Akita mice. In cultured ARPE-19, fenofibrate decreased HG-induced Nox2 and Nox4 upregulation, attenuated SOD1 and SOD2 downregulation and inhibited LRP6 phosphorylation. Moreover, activation of Wnt/β-catenin by Wnt3a conditional medium (WCM) reduced SOD1 and SOD2 and did not affect Nox2 and Nox4. Fenofibrate suppressed WCM-induced LRP6 phosphorylation and reversed SOD downregulation. Importantly, Nox4 overexpression directly phosphorylated LPR6 in ARPE19; conversely, Nox4 knockdown suppressed HG-induced LPR6 phosphorylation. Taken together, Nox-mediated oxidative stress contributes to Wnt/β-catenin activation in DR. Fenofibrate ameliorated DR through coordinate attenuation of oxidative stress and blockade of Wnt/β-catenin signaling.

Therapeutic targets for altering mitochondrial dysfunction associated with diabetic retinopathy

INTRODUCTION

Retinopathy remains as one of the most feared blinding complications of diabetes, and with the prevalence of this life-long disease escalating at an alarming rate, the incidence of retinopathy is also climbing. Although the cutting edge research has identified many molecular mechanisms associated with its development, the exact mechanism how diabetes damages the retina remains obscure, limiting therapeutic options for this devastating disease. Areas covered: This review focuses on the central role of mitochondrial dysfunction/damage in the pathogenesis of diabetic retinopathy, and how damaged mitochondria initiates a self-perpetuating vicious cycles of free radicals. We have also reviewed how mitochondria could serve as a therapeutic target, and the challenges associated with the complex double mitochondrial membranes and a well-defined blood-retinal barrier for optimal pharmacologic/molecular approach to improve mitochondrial function. Expert opinion: Mitochondrial dysfunction provides many therapeutic targets for ameliorating the development of diabetic retinopathy including their biogenesis, DNA damage and epigenetic modifications. New technology to enhance pharmaceuticals uptake inside the mitochondria, nanotechnology to deliver drugs to the retina, and maintenance of mitochondrial homeostasis via lifestyle changes and novel therapeutics to prevent epigenetic modifications, could serve as some of the welcoming avenues for a diabetic patient to target this sight-threatening disease.

Effects of various feeding patterns of Bacillus coagulans on growth performance, antioxidant response and Nrf2-Keap1 signaling pathway in juvenile gibel carp (Carassius auratus gibelio)

The present study was conducted to evaluate the effects of various Bacillus coagulans feeding patterns on growth, antioxidant parameter and Nrf2 pathway in juvenile gibel carp. The similar size of gibel carp (initial weight: 14.33 ± 0.15 g) were subjected to three levels of B. coagulans supplementation (0, 500, and 1000 mg/kg) and two feeding modes (supplementing B. coagulans continuously or for two days of B. coagulans after 5 days of a basal diet) according to a 3 × 2 factorial design. The fish that were continuously fed 500 mg/kg B. coagulans (P2) and those fed the first basal diet for 5 days followed by 500 mg/kg or 1000 mg/kg B.coagulans for 2 days (P4 or P5) showed higher weight gain rate and specific growth rate than the other groups. Blood respiratory burst (RB), myeloperoxidase (MPO), and anti-superoxide anion free radical (AFASER) activities in the P4 group were higher than those of the control. White blood cell count (WBC), RB activity, MPO activity, and glutathione (GSH) content in the P5 group were also higher than those of the control. A similar higher trend was observed in the gene expressions of NADPH oxidase 2 (NOX2), NFE2-related factor (Nrf2), Kelch-like-ECH-associated protein(Keap1) in the P4 and NOX2, NRF2, CNC homolog 1 (Bach1), peroxiredoxin 2 (Prx2) in the P5 group compared with the control. Additionally, we observed a significantly lower level of plasma aspartate aminotransferase (AST), lower activity of alanine aminotransferase (ALT), a higher level of MPO, higher GPX activity, and increased NRF2 and Prx2 expression were all observed in the P2 treatment group compared with the control. Furthermore, the malondialdehyde (MDA) content in the P2, P3, and P4 groups was lower than that of the control. These results indicate that a diet supplemented with appropriate levels of B.coagulans could improve the growth, immune response, and antioxidant capability of gibel carp. We concluded that the pattern of two days of 500 or 1000 mg/kg B. coagulans after 5 days of a basal diet was recommended for gibel carp.

Direct Activation of NADPH Oxidase 2 by 2-Deoxyribose-1-Phosphate Triggers Nuclear Factor Kappa B-Dependent Angiogenesis

AIMS

Deoxyribose-1-phosphate (dRP) is a proangiogenic paracrine stimulus released by cancer cells, platelets, and macrophages and acting on endothelial cells. The objective of this study was to clarify how dRP stimulates angiogenic responses in human endothelial cells.

RESULTS

Live cell imaging, electron paramagnetic resonance, pull-down of dRP-interacting proteins, followed by immunoblotting, gene silencing of different NADPH oxidases (NOXs), and their regulatory cosubunits by small interfering RNA (siRNA) transfection, and experiments with inhibitors of the sugar transporter glucose transporter 1 (GLUT1) were utilized to demonstrate that dRP acts intracellularly by directly activating the endothelial NOX2 complex, but not NOX4. Increased reactive oxygen species generation in response to NOX2 activity leads to redox-dependent activation of the transcription factor nuclear factor kappa B (NF-κB), which, in turn, induces vascular endothelial growth factor receptor 2 (VEGFR2) upregulation. Using endothelial tube formation assays, gene silencing by siRNA, and antibody-based receptor inhibition, we demonstrate that the activation of NF-κB and VEGFR2 is necessary for the angiogenic responses elicited by dRP. The upregulation of VEGFR2 and NOX2-dependent stimulation of angiogenesis by dRP were confirmed in excisional wound and Matrigel plug vascularization assays in vivo using NOX2^-/- mice.

INNOVATION

For the first time, we demonstrate that dRP acts intracellularly and stimulates superoxide anion generation by direct binding and activation of the NOX2 enzymatic complex.

CONCLUSIONS

This study describes a novel molecular mechanism underlying the proangiogenic activity of dRP, which involves the sequential activation of NOX2 and NF-κB and upregulation of VEGFR2. Antioxid. Redox Signal. 28, 110-130.

Fenofibrate ameliorates diabetic retinopathy by modulating Nrf2 signaling and NLRP3 inflammasome activation

Oxidative stress and neuroinflammation contribute significantly to the development and progression of diabetic retinopathy. Fenofibrate has received great attention as it benefits diabetic patients by reducing retinal laser requirement. Nuclear factor erythroid-2-related factor 2 (Nrf2) is a master regulator of anti-oxidative defense. Activation of nucleotide binding domain, leucine-rich repeat-containing receptor (NLR), pyrin domain-containing 3 (NLRP3) inflammasome plays a pivotal role in neuroinflammation. The purpose of this study is to determine whether fenofibrate protects retinas from oxidative damage and neuroinflammation via modulating the Nrf2 pathway and blocking NLRP3 inflammasome activation during diabetes. Diabetes is induced by intraperitoneal injection of streptozotocin in mice. Fenofibrate was given to mice in rodent chow. Upregulation of Nrf2 and NLRP3 inflammasome, enhanced ROS formation, and increased leukostasis and vascular leakage were observed in diabetic mouse retinas. Notably, Nrf2 and Caspase-1 were mainly colocalized with glutamine synthetase, one of the Mȕller cell markers. Fenofibrate further increased the expression of Nrf2 and its target gene NQO-1 and HO-1 and reduced ROS formation in diabetic retinas. In addition, retinal expression of NLRP3, Caspase-1 p20, IL-1β p17, and ICAM-1 were dramatically increased in vehicle-treated diabetic mice, which were abolished by fenofibrate intervention. Moreover, fenofibrate treatment also attenuated diabetes-induced retinal leukostasis and vascular leakage in mice. Taken together, fenofibrate attenuates oxidative stress and neuroinflammation in diabetic retinas, which is at least partially through modulating Nrf2 expression and NLRP3 inflammasome activation.

Myeloid differentiation protein 2 induced retinal ischemia reperfusion injury via upregulation of ROS through a TLR4-NOX4 pathway

Retinal ischemia reperfusion (I/R) injury is common in many ophthalmic diseases. Recent studies have shown that toll-like receptor 4 (TLR4) is involved in ischemic retinal injury. Activation of TLRs requires specific accessory proteins such as myeloid differentiation protein 2 (MD2), which facilitate in ligand responsiveness. Therefore, inhibiting MD2 may be a novel approach to modulate TLR4 signaling and deleterious downstream effects in ischemic retinal injury. We used human Müller MIO-M1 cells treated with tert-butyl hydroperoxide (TBHP) to establish an in vitro I/R model of oxidative injury and tested the therapeutic effect of inhibiting MD2. Furthermore, we inhibited MD2 in a mouse model of retinal I/R injury and confirmed the results using MD2 knockout mice. Our studies show that pharmacological inhibition of MD2 prevented TBHP-induced reactive oxygen species (ROS) generation, inflammation and subsequent apoptosis in Müller cells. We also show that retinal I/R injury in mice induced functional deficits, increased ROS levels, inflammation and apoptosis. These pathological changes were not observed in MD2 knockout mice and attenuated when MD2 was inhibited in wildtype mice. In addition, we discovered that the mechanism of these therapeutic effects involved regulation of NADPH oxidase 4 (NOX4)-MD2-TLR4 complex formation. This study provides evidence that MD2 plays a key role in the pathogenesis of retinal I/R damage by participating in TLR4-NOX4 complex formation and elaboration of oxidative and inflammatory damage. Hence, inhibition of MD2 may reduce TLR-dependent damage during retinal I/R injury.

Antioxidant and pro-angiogenic effects of corilagin in rat cerebral ischemia via Nrf2 activation

The nuclear factor erythroid-2-related factor 2 (Nrf2) pathway has been considered as a potential target for neuroprotection in stroke. The aim of present study was to determine whether corilagin, a novel Nrf2 activator, can protect against ischemia-reperfusion injury and explore the underlying mechanism involved. In vivo, rats exposed to middle cerebral artery occlusion were applied to establish an ischemic stroke model. Posttreatment of corilagin significantly reduced infarct volumes and apoptotic cells as well as improved neurologic score after reperfusion, together with increased vascular density in the ischemic penumbra. Meanwhile, posttreatment with corilagin in MCAO rats significantly decreased malondialdehyde levels, restored the superoxide dismutase and glutathione activity, elevating the Nrf2, heme oxygenase-1, the vascular endothelial growth factor (VEGF) and VEGF receptor 2 (VEGFR2) expression. However, consecutive intrathecal injection of short interference RNAs targeting Nrf2 at 24-h intervals 72 h before ischemia reduced the beneficial effects of corilagin. In primary cultured neurons, corilagin dose-dependently protected against oxygen and glucose deprivation-induced insult, but the protective effect of corilagin was attenuated by knockdown of Nrf2. In conclusion, these findings indicate that corilagin exerts protective effects against cerebral ischemic injury by attenuating oxidative stress and enhancing angiogenesis via activation of Nrf2 signaling pathway.

Roles of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) Oxidase in Angiogenesis: Isoform-Specific Effects

Angiogenesis is the formation of new blood vessels from preexisting ones and is implicated in physiologic vascular development, pathologic blood vessel growth, and vascular restoration. This is in contrast to vasculogenesis, which is de novo growth of vessels from vascular precursors, or from vascular repair that occurs when circulating endothelial progenitor cells home into an area and develop into blood vessels. The objective of this review is to discuss the isoform-specific role of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) in physiologic and pathologic angiogenesis and vascular repair, but will not specifically address vasculogenesis. As the major source of reactive oxygen species (ROS) in vascular endothelial cells (ECs), NOX has gained increasing attention in angiogenesis. Activation of NOX leads to events necessary for physiologic and pathologic angiogenesis, including EC migration, proliferation and tube formation. However, activation of different NOX isoforms has different effects in angiogenesis. Activation of NOX2 promotes pathologic angiogenesis and vascular inflammation, but may be beneficial in revascularization in the hindlimb ischemic model. In contrast, activation of NOX4 appears to promote physiologic angiogenesis mainly by protecting the vasculature during ischemia, hypoxia and inflammation and by restoring vascularization, except in models of oxygen-induced retinopathy and diabetes where NOX4 activation leads to pathologic angiogenesis.

The effects of emodin on cell viability, respiratory burst and gene expression of Nrf2-Keap1 signaling molecules in the peripheral blood leukocytes of blunt snout bream (Megalobrama amblycephala)

We determined the effects of emodin on the cell viability, respiratory burst activity, mRNA levels of antioxidative enzymes (Cu-Zn SOD, CAT and NOX2), and gene expressions of the Nrf2-Keap1 signaling molecules in the peripheral blood leukocytes of blunt snout bream. Triplicate groups of cultured cells were treated with different concentrations of emodin (0.04-25 μg/ml) for 24 h. Results showed that the emodin caused a dramatic loss in cell viability, and occurred in a dose-dependent manner. Emodin exposure (1-25 μg/ml) were significantly induced the ROS generation compared to the control. The respiratory burst and NADPH oxidase activities were significantly induced at a concentration of 0.20 μg/ml, and inhibited at 25 μg/ml. Besides, mRNA levels of antioxidant enzyme genes were dramatically regulated by emodin exposure for 24 h. During low concentrations of exposure, mRNA levels of Cu-Zn SOD in the cells treated with 0.04, 0.20 μg/ml, CAT, NOX2 and Nrf2 in the cells treated with 1 μg/ml were sharply increased, respectively. Whereas, high concentrations were dramatically down-regulated the gene expressions of CAT in the cells treated with 5, 25 μg/ml and NOX2 in the cells treated with 25 μg/ml. Furthermore, sharp increase in Keap1and Bach1 expression levels were observed a dose-dependent manner. In conclusion, this study demonstrated that emodin could induce antioxidant defenses which were involved in cytotoxic activities, respiratory burst and the transcriptional regulation levels of antioxidant enzymes and Nrf2-Keap1 signaling molecules.

Epigenetic regulation of redox signaling in diabetic retinopathy: Role of Nrf2

Diabetic retinopathy is a major vision threatening disease among working age adults, and increased oxidative stress is one of the prime causative factors in its pathogenesis. Increased reactive oxygen species (ROS) in the cytosol damage mitochondria, and due to compromised antioxidant signaling system and dysfunctional mitochondria with damaged mitochondrial DNA, ROS continue to pile up, accelerating capillary cell loss. In addition to other cellular and enzymatic defense systems, the retina is also equipped with the nuclear erythroid-2-p45-related factor-2 (Nrf2) antioxidant response element signaling pathway, which controls the expression of genes important in detoxification and elimination of ROS. However, in diabetes, its transcriptional activity is impaired, further exacerbating and exposing the retina to elevated stress. Diabetic milieu also alters epigenetic factors responsible for chromatin modifications and gene regulation, and kelch-like ECH-associated protein 1 (Keap1), important in regulating Nrf2-antioxidant signaling axis, is epigenetically modified, impeding nuclear translocation of Nrf2, and this inhibits the transcription of genes with Antioxidant Response Element. This review discusses antioxidant signaling, especially the role of Nrf2, in diabetic retinopathy, and possible involvement of epigenetic modifications in antioxidant signaling and Nrf2 transcriptional activity. Therapies targeting Nrf2 activation, including epigenetic modifications, have potentional to prevent mitochondrial damage and inhibit the development, and progression of this sight-threatening disease which most of the patients get after 20-25 years of diabetes.