The KEAP1-NRF2 System and Neurodegenerative Diseases

E3 ligases and DUBs target ferroptosis: A potential therapeutic strategy for neurodegenerative diseases

Ferroptosis is a form of cell death mediated by iron and lipid peroxidation (LPO). Recent studies have provided compelling evidence to support the involvement of ferroptosis in the pathogenesis of various neurodegenerative diseases (NDDs), such as Alzheimer's disease (AD), Parkinson's disease (PD). Therefore, understanding the mechanisms that regulate ferroptosis in NDDs may improve disease management. Ferroptosis is regulated by multiple mechanisms, and different degradation pathways, including autophagy and the ubiquitinproteasome system (UPS), orchestrate the complex ferroptosis response by directly or indirectly regulating iron accumulation or lipid peroxidation. Ubiquitination plays a crucial role as a protein posttranslational modification in driving ferroptosis. Notably, E3 ubiquitin ligases (E3s) and deubiquitinating enzymes (DUBs) are key enzymes in the ubiquitin system, and their dysregulation is closely linked to the progression of NDDs. A growing body of evidence highlights the role of ubiquitin system enzymes in regulating ferroptosis sensitivity. However, reports on the interaction between ferroptosis and ubiquitin signaling in NDDs are scarce. In this review, we first provide a brief overview of the biological processes and roles of the UPS, summarize the core molecular mechanisms and potential biological functions of ferroptosis, and explore the pathophysiological relevance and therapeutic implications of ferroptosis in NDDs. In addition, reviewing the roles of E3s and DUBs in regulating ferroptosis in NDDs aims to provide new insights and strategies for the treatment of NDDs. These include E3- and DUB-targeted drugs and ferroptosis inhibitors, which can be used to prevent and ameliorate the progression of NDDs.

The role of Nrf2 signaling pathways in nerve damage repair

The protein, Nuclear factor-E2-related factor 2 (Nrf2), is a transitory protein that acts as a transcription factor and is involved in the regulation of many cytoprotective genes linked to xenobiotic metabolism and antioxidant responses. Based on the existing clinical and experimental data, it can be inferred that neurodegenerative diseases are characterized by an excessive presence of markers of oxidative stress (OS) and a reduced presence of antioxidant defense systems in both the brain and peripheral tissues. The presence of imbalances in the homeostasis between oxidants and antioxidants has been recognized as a substantial factor in the pathogenesis of neurodegenerative disorders. The dysregulations include several cellular processes such as mitochondrial failure, protein misfolding, and neuroinflammation. These dysregulations all contribute to the disruption of proteostasis in neuronal cells, leading to their eventual mortality. A noteworthy component of Nrf2, as shown by recent research undertaken over the last decade, is to its role in the development of resistance to OS. Nrf2 plays a pivotal role in regulating systems that defend against OS. Extant research offers substantiation for the protective and defensive roles of Nrf2 in the context of neurodegenerative diseases. The purpose of this study is to provide a comprehensive analysis of the influence of Nrf2 on OS and its function in regulating antioxidant defense systems within the realm of neurodegenerative diseases. Furthermore, we evaluate the most recent academic inquiries and empirical evidence about the beneficial and potential role of certain Nrf2 activator compounds within the realm of therapeutic interventions.

NRF2: New Mechanistic Insights and Therapeutic Perspectives

Targeted modulation of a dynamic interplay between transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) and its negative regulator, Kelch-like ECH-associated protein 1 (KEAP1), is of paramount importance in maintaining redox, metabolic, and protein homeostasis and regulating inflammation responses. Indeed, inducible NRF2 activation promotes cytoprotective mechanisms against many immune, neurodegenerative, and metabolic disorders with oxidative stress and inflammation as underlying pathological features. In this ARS Forum, five state-of-the-art reviews and two original research communications report on canonical and newly discovered molecular mechanisms by which the NRF2-KEAP1 axis controls fundamental cell life or death decisions and exerts biological functions under environmental and endogenous stress conditions. Although the use of NRF2 activators represents a promising pharmacological strategy to regain and maintain homeostasis, challenges regarding their double-edged character, target specificity, pharmacodynamic properties, efficacy, and safety must be critically considered. More translational studies are warranted before NRF2 agonists (inducers or enhancers) become an integral part of our therapeutic armamentarium. Antioxid. Redox Signal. 40, 632-635.

Quercetin: A promising therapy for diabetic encephalopathy through inhibition of hippocampal ferroptosis

BACKGROUND

The pathophysiology of diabetic encephalopathy (DE), a significant diabetes-related pathological complication of the central nervous system, is poorly understood. Ferroptosis is an iron-dependent regulated necrotic cell death process that mediates the development of neurodegenerative and diabetes-related lesions. Quercetin (QE) exerts anti-ferroptotic effects in various diseases. However, the roles of ferroptosis in DE and the potential anti-ferroptotic mechanisms of QE are unclear.

PURPOSE

This study aimed to investigate if quercetin can ameliorate DE by inhibiting ferroptosis and to elucidate the potential anti-ferroptotic mechanisms of QE, thus providing a new perspective on the pathogenesis and prevention of DE.

METHODS

The spontaneously type 2 diabetic Goto-Kakizak rats and high glucose (HG)-induced PC12 cells were used as animal and in vitro models, respectively. The Morris water maze test was performed to evaluate the cognition of rats. Pathological damage was examined using hematoxylin and eosin staining. Mitochondrial damage was assessed using transmission electron microscopy. Lipid peroxidation was evaluated by examining the levels of malondialdehyde, superoxide dismutase, and glutathione. Additionally, the contents of iron ions were quantified. Immunofluorescence and western blotting were carried out to poke the protein levels. Network pharmacology analysis was conducted to construct a protein-protein interaction network for the therapeutic targets of QE in DE. Additionally, molecular docking and cellular thermal shift assay was performed to examine the target of QE.

RESULTS

QE alleviated cognitive impairment, decreased lipid peroxidation and iron deposition in the hippocampus, and upregulated the Nrf2/HO-1 signaling pathway. HG-induced ferroptosis in PC12 cells resulted in decreased cell viability accompanied by lipid peroxidation and iron deposition. QE mitigated HG-induced ferroptosis by upregulating the Nrf2/HO-1 pathway, which was partially suppressed upon Nrf2 inhibition. Network pharmacology analysis further indicated that the Nrf2/HO-1 signaling pathway is a key target of QE. Molecular docking experiments revealed that QE binds to KEAP1 through four hydrogen bonds. Moreover, QE altered the thermostability of KEAP1.

CONCLUSION

These results indicated that QE inhibits ferroptosis in the hippocampal neurons by binding to KEAP1 and subsequently upregulating the Nrf2/HO-1 signaling pathway.

Uncovering Cell Cycle Dysregulations and Associated Mechanisms in Cancer and Neurodegenerative Disorders: A Glimpse of Hope for Repurposed Drugs

The cell cycle is the sequence of events orchestrated by a complex network of cell cycle proteins. Unlike normal cells, mature neurons subsist in a quiescent state of the cell cycle, and aberrant cell cycle activation triggers neuronal death accompanied by neurodegeneration. The periodicity of cell cycle events is choreographed by various mechanisms, including DNA damage repair, oxidative stress, neurotrophin activity, and ubiquitin-mediated degradation. Given the relevance of cell cycle processes in cancer and neurodegeneration, this review delineates the overlapping cell cycle events, signaling pathways, and mechanisms associated with cell cycle aberrations in cancer and the major neurodegenerative disorders. We suggest that dysregulation of some common fundamental signaling processes triggers anomalous cell cycle activation in cancer cells and neurons. We discussed the possible use of cell cycle inhibitors for neurodegenerative disorders and described the associated challenges. We propose that a greater understanding of the common mechanisms driving cell cycle aberrations in cancer and neurodegenerative disorders will open a new avenue for the development of repurposed drugs.

Redox imbalance and metabolic defects in the context of Alzheimer disease

Redox reactions play a critical role for intracellular processes, including pathways involved in metabolism and signaling. Reactive oxygen species (ROS) act either as second messengers or generators of protein modifications, fundamental mechanisms for signal transduction. Disturbance of redox homeostasis is associated with many disorders. Among these, Alzheimer's disease is a neurodegenerative pathology that presents hallmarks of oxidative damage such as increased ROS production, decreased activity of antioxidant enzymes, oxidative modifications of macromolecules, and changes in mitochondrial homeostasis. Interestingly, alteration of redox homeostasis is closely associated with defects of energy metabolism, involving both carbohydrates and lipids, the major energy fuels for the cell. As the brain relies exclusively on glucose metabolism, defects of glucose utilization represent a harmful event for the brain. During aging, a progressive perturbation of energy metabolism occurs resulting in brain hypometabolism. This condition contributes to increase neuronal cell vulnerability ultimately resulting in cognitive impairment. The current review discusses the crosstalk between alteration of redox homeostasis and brain energy defects that seems to act in concert in promoting Alzheimer's neurodegeneration.

MicroRNA-204-5p Ameliorates Renal Injury via Regulating Keap1/Nrf2 Pathway in Diabetic Kidney Disease

Background

Diabetic kidney disease (DKD) is characterized by renal fibrosis, and the pathogenesis of renal fibrosis is still not definitely confirmed. MiR-204-5p plays an important role in the regulation of fibrosis, autophagy and oxidative stress. In this study, we aimed to investigate the role of miR-204-5p on renal damage in diabetic kidneys and the underlying mechanisms involved.

Methods

In vivo, AAV-Ksp-miR-204-5p mimics were injected into mice via tail vein. In vitro, high glucose-induced HK-2 cells were treated with miR-204-5p inhibitor, miR-204-5p mimics, ATG5 siRNA, tertiary butyl hydroquinone (TBHQ), ML385, or 3-Methyladenine (3-MA). FISH and qRT-PCR were used to detect miR-204-5p expression. The expressions of protein and mRNA were detected by Western blotting, immunofluorescence, immunohistochemistry and qRT-PCR. The concentration of fibronectin in HK-2 cells culture medium was detected by ELISA.

Results

The expression of miR-204-5p in diabetic kidneys was significantly inhibited than that in control group. Delivering miR-204-5p mimics increased miR-204-5p expression, improved renal function, inhibited renal fibrosis and oxidative stress, and restored autophagy in db/db mice. In vitro, the expression of miR-204-5p was inhibited by HG treatment in HK-2 cells. MiR-204-5p mimics effectively increased miR-204-5p expression and reduced fibronectin and collagen I expression, restored autophagy dysfunction, and increased Nrf2 expression, whereas these alterations were abrogated by Nrf2 inhibitor ML385, autophagy inhibitor 3-methyladenine (3-MA, 5 mM) treatment or ATG5 siRNA transfection in HG-induced HK-2 cells. In addition, miR-204-5p inhibitor significantly inhibited miR-204-5p expression and aggravated HG-induced fibronectin and collagen I expression, autophagy dysfunction, and decreased Nrf2 expression, while these alterations were abolished by Nrf2 activator TBHQ. Furthermore, the binding of miR-204-5p with Keap1 was confirmed by luciferase reporter assay and miR-204-5p negatively regulated Keap1 expression, resulting in the activation of Nrf2 pathway.

Conclusion

MicroRNA-204-5p protects against the progression of diabetic renal fibrosis by restoring autophagy via regulating Keap1/Nrf2 pathway.

Understanding mechanisms of antioxidant action in health and disease

Several different reactive oxygen species (ROS) are generated in vivo. They have roles in the development of certain human diseases whilst also performing physiological functions. ROS are counterbalanced by an antioxidant defence network, which functions to modulate ROS levels to allow their physiological roles whilst minimizing the oxidative damage they cause that can contribute to disease development. This Review describes the mechanisms of action of antioxidants synthesized in vivo, antioxidants derived from the human diet and synthetic antioxidants developed as therapeutic agents, with a focus on the gaps in our current knowledge and the approaches needed to close them. The Review also explores the reasons behind the successes and failures of antioxidants in treating or preventing human disease. Antioxidants may have special roles in the gastrointestinal tract, and many lifestyle features known to promote health (especially diet, exercise and the control of blood glucose and cholesterol levels) may be acting, at least in part, by antioxidant mechanisms. Certain reactive sulfur species may be important antioxidants but more accurate determinations of their concentrations in vivo are needed to help assess their contributions.

Effect of Inducers and Inhibitors of the Keap1/Nrf2/ARE System on the Viability and Functional Activity of Model Neuronal-Like and Glial Cells

On mouse neuroblastoma (Neuro-2a) and human glioblastoma (U-87 MG) cell lines, we studied the effect of inducers and inhibitors of redox-sensitive signaling system of the antioxidant-responsive element Keap1/Nrf2/ARE on the main processes that determine nerve cell viability and vital activity (proliferative activity, apoptosis, autophagy, and activation of the Keap1/Nrf2/ARE system). Inhibitors of the Keap1/Nrf2/ARE system stimulate apoptosis more pronouncedly than inducers, have a weaker effect on autophagy, and do not change the nuclear to cytoplasmic Nrf2 ratio. In general, the revealed effects testify in favor of the potential effectiveness of stimulating the Keap1/Nrf2/ARE system for the prevention and adjuvant therapy of neurodegenerative diseases.

Bivalent inhibitors of the BTB E3 ligase KEAP1 enable instant NRF2 activation to suppress acute inflammatory response

Most BTB-containing E3 ligases homodimerize to recognize a single substrate by engaging multiple degrons, represented by E3 ligase KEAP1 dimer and its substrate NRF2. Inactivating KEAP1 to hinder ubiquitination-dependent NRF2 degradation activates NRF2. While various KEAP1 inhibitors have been reported, all reported inhibitors bind to KEAP1 in a monovalent fashion and activate NRF2 in a lagging manner. Herein, we report a unique bivalent KEAP1 inhibitor, biKEAP1 (3), that engages cellular KEAP1 dimer to directly release sequestered NRF2 protein, leading to an instant NRF2 activation. 3 promotes the nuclear translocation of NRF2, directly suppressing proinflammatory cytokine transcription. Data from in vivo experiments showed that 3, with unprecedented potency, reduced acute inflammatory burden in several acute inflammation models in a timely manner. Our findings demonstrate that the bivalent KEAP1 inhibitor can directly enable sequestered substrate NRF2 to suppress inflammatory transcription response and dampen various acute inflammation injuries.

Nrf2 enhances the therapeutic efficiency of adipose-derived stem cells in the treatment of neurogenic erectile dysfunction in a rat model

BACKGROUND

Erectile dysfunction (ED) caused by intraoperative nerve injury is a major complication of pelvic surgery. Adipose-derived stem cells (ADSCs) have presented therapeutic potential in a rat model of bilateral cavernous nerve injury (BCNI), while inadequate in vivo viability has largely limited their application. Nuclear factor-E2-related Factor (Nrf2) is a key transcription factor that regulates cellular anti-oxidative stress. In this work, we investigated the effect of Nrf2 expression regulation on the viability of ADSCs, and explore its repair potential in a BCNI rat model.

RESULTS

The survival time of tert-Butylhydroquinone (tBHQ)-ADSCs in BCNI model increased obviously. In addition, the tBHQ-ADSCs group presented better restoration of major pelvic ganglion (MPG) nerve contents and fibers, better improvement of erectile function, and less penile fibrosis than the other groups. Moreover, the expression of Nrf2 and superoxide dismutase 1 (SOD1) were higher than those of other groups.

CONCLUSION

Nrf2 could enhance the anti-oxidative stress ability of ADSCs, so as to improve the therapeutic effect of ADSCs on BCNI rat model.

NOX-induced oxidative stress is a primary trigger of major neurodegenerative disorders

Neurodegenerative diseases (NDDs) causing cognitive impairment and dementia are difficult to treat due to the lack of understanding of primary initiating factors. Meanwhile, major sporadic NDDs share many risk factors and exhibit similar pathologies in their early stages, indicating the existence of common initiation pathways. Glucose hypometabolism associated with oxidative stress is one such primary, early and shared pathology, and a likely major cause of detrimental disease-associated cascades; targeting this common pathology may therefore be an effective preventative strategy for most sporadic NDDs. However, its exact cause and trigger remain unclear. Recent research suggests that early oxidative stress caused by NADPH oxidase (NOX) activation is a shared initiating mechanism among major sporadic NDDs and could prove to be the long-sought ubiquitous NDD trigger. We focus on two major NDDs - Alzheimer's disease (AD) and Parkinson's disease (PD), as well as on acquired epilepsy which is an increasingly recognized comorbidity in NDDs. We also discuss available data suggesting the relevance of the proposed mechanisms to other NDDs. We delve into the commonalities among these NDDs in neuroinflammation and NOX involvement to identify potential therapeutic targets and gain a deeper understanding of the underlying causes of NDDs.

Identification of ferroptosis-related genes in acute phase of temporal lobe epilepsy based on bioinformatic analysis

BACKGROUND

Epilepsy is a prevalent neurological disorder, and while its precise mechanism remains elusive, a connection to ferroptosis has been established. This study investigates the potential clinical diagnostic significance of ferroptosis-related genes (FRGs) during the acute phase of temporal lobe epilepsy.

METHODS

To identify differentially expressed genes (DEGs), we accessed data from the GEO database and performed an intersection analysis with the FerrDB database to pinpoint FRGs. A protein-protein interaction (PPI) network was constructed. To assess the diagnostic utility of the discovered feature genes for the disease, ROC curve analysis was conducted. Subsequently, qRT-PCR was employed to validate the expression levels of these feature genes.

RESULTS

This study identified a total of 25 FRGs. PPI network analysis revealed six feature genes: IL6, PTGS2, HMOX1, NFE2L2, TLR4, and JUN. ROC curve analysis demonstrated that the combination of these six feature genes exhibited the highest diagnostic potential. qRT-PCR validation confirmed the expression of these feature genes.

CONCLUSION

We have identified six feature genes (IL6, PTGS2, HMOX1, NFE2L2, TLR4, and JUN) strongly associated with ferroptosis in epilepsy, suggesting their potential as biomarkers for the diagnosis of temporal lobe epilepsy.

AMPK-Mediated Phosphorylation of Nrf2 at S374/S408/S433 Favors Its βTrCP2-Mediated Degradation in KEAP1-Deficient Cells

Nrf2 is a transcription factor facilitating cells' resilience against redox and various other forms of stress. In the absence of stressors, KEAP1 and/or βTrCP mediate the ubiquitination of Nrf2 and prevent Nrf2-dependent gene expression and detoxification. AMPK regulates cellular energy homeostasis and redox balance. Previous studies indicated a potential Nrf2-AMPK cooperativity. In line with this, our lab had previously identified three AMPK-dependent phosphorylation sites (S374/408/433) in Nrf2. Given their localization in or near the Neh6 domain, known to regulate βTrCP-mediated degradation, we examined whether they may influence the βTrCP-driven degradation of Nrf2. By employing expression plasmids for WT and triple mutant (TM)-Nrf2 (Nrf2S374/408/433→A), (co)immunoprecipitation, proximity ligation, protein half-life, knockdown, ubiquitination experiments, and qPCR in Keap1-null mouse embryonic fibroblasts, we show that TM-Nrf2S→A374/408/433 had enhanced stability due to impeded interaction with βTrCP2 and reduced ubiquitination in comparison to WT-Nrf2. In addition, TM-Nrf2 elicited higher expression of the Nrf2 target gene Gclc, potentiated in the presence of a pharmacological AMPK activator. Overall, we propose that AMPK-dependent phospho-sites of Nrf2 can favor its βTrCP2-mediated degradation and dampen the extent of Nrf2 target gene expression. Therefore, targeting AMPK might be able to diminish Nrf2-mediated responses in cells with overactive Nrf2 due to KEAP1 deficiency.

MicroRNA-27b Impairs Nrf2-Mediated Angiogenesis in the Progression of Diabetic Foot Ulcer

Nuclear factor erythroid-2-related factor 2 (Nrf2) is a stress-activated transcription factor regulating antioxidant genes, and a deficiency thereof, slowing lymphangiogenesis, has been reported in diabetic foot ulcer (DFU). The mode of Nrf2 regulation in DFU has been less explored. Emerging studies on miRNA-mediated target regulation show miRNA to be the leading player in the pathogenesis of the disease. In the present study, we demonstrated the role of miR-27b in regulating Nrf2-mediated angiogenesis in DFU. A lower expression of mRNA targets, such as Nrf2, HO-1, SDF-1α, and VEGF, was observed in tissue biopsied from chronic DFU subjects, which was in line with miR-27b, signifying a positive correlation with Nrf2. Similarly, we found significantly reduced expression of miR-27b and target mRNAs Nrf2, HO-1, SDF-1α, and VEGF in endothelial cells under a hyperglycemic microenvironment (HGM). To confirm the association of miR-27b on regulating Nrf2-mediated angiogenesis, we inhibited its expression through RNA interference-mediated knockdown and observed disturbances in angiogenic signaling with reduced endothelial cell migration. In addition, to explore the role of miR-27b and angiogenesis in the activation of Nrf2, we pretreated the endothelial cells with two well-known pharmacological compounds-pterostilbene and resveratrol. We observed that activation of Nrf2 through these compounds ameliorates impaired angiogenesis on HGM-induced endothelial cells. This study suggests a positive role of miR-27b in regulating Nrf2, which seems to be decreased in DFU and improves on treatment with pterostilbene and resveratrol.

Opioids Alleviate Oxidative Stress via the Nrf2/HO-1 Pathway in LPS-Stimulated Microglia

Opioids are known to have antioxidant effects and to modulate microglial function under certain conditions. It has been previously shown that opioid ligands can effectively inhibit the release of proinflammatory cytokines when stimulated with lipopolysaccharide (LPS) and convert microglia to an anti-inflammatory polarization state. Here, we used C8-B4 cells, the mouse microglial cell line activated by LPS as a model to investigate the anti-inflammatory/antioxidant potential of selected opioid receptor agonists (DAMGO, DADLE, and U-50488). We found that all of these ligands could exert cytoprotective effects through the mechanism affecting LPS-induced ROS production, NADPH synthesis, and glucose uptake. Interestingly, opioids elevated the level of reduced glutathione, increased ATP content, and enhanced mitochondrial respiration in microglial cells exposed to LPS. These beneficial effects were associated with the upregulation of the Nrf2/HO-1 pathway. The present results indicate that activation of opioid signaling supports the preservation of mitochondrial function with concomitant elimination of ROS in microglia and suggest that an Nrf2/HO-1 signaling pathway-dependent mechanism is involved in the antioxidant efficacy of opioids. Opioid receptor agonists may therefore be considered as agents to suppress oxidative stress and inflammatory responses of microglia.

Mechanisms of and Potential Medications for Oxidative Stress in Ovarian Granulosa Cells: A Review

Granulosa cells are essential for follicle initiation and development, and their abnormal function or apoptosis is a crucial factor leading to follicular atresia. A state of oxidative stress occurs when the balance between the production of reactive oxygen species and the regulation of the antioxidant system is disturbed. Oxidative stress is one of the most important causes of the abnormal function and apoptosis of granulosa cells. Oxidative stress in granulosa cells causes female reproductive system diseases, such as polycystic ovary syndrome and premature ovarian failure. In recent years, studies have confirmed that the mechanism of oxidative stress in granulosa cells is closely linked to the PI3K-AKT signaling pathway, MAPK signaling pathway, FOXO axis, Nrf2 pathway, NF-κB signaling pathway, and mitophagy. It has been found that drugs such as sulforaphane, Periplaneta americana peptide, and resveratrol can mitigate the functional damage caused by oxidative stress on granulosa cells. This paper reviews some of the mechanisms involved in oxidative stress in granulosa cells and describes the mechanisms underlying the pharmacological treatment of oxidative stress in granulosa cells.