Keap1 is localized in neuronal and glial cytoplasmic inclusions in various neurodegenerative diseases

Behavioral and histological assessment of a novel treatment of neuroHIV in humanized mice

Neurocognitive deficits are prevalent among people living with HIV, likely due to chronic inflammation and oxidative stress in the brain. To date, no pharmaceutical treatments beyond antiretroviral therapy (ARV) has been shown to reduce risk for, or severity of, HIV-associated neurocognitive disorder. Here we investigate a novel compound, CDDO-Me, with documented neuroprotective effects via activation of the nrf2 and inhibition of the NFkB pathways.

Methods

We conducted three studies to assess the efficacy of CDDO-Me alone or in combination with antiretroviral therapy in humanized mice infected with HIV; behavioral, histopathological, and immunohistochemical.

Results

CDDO-Me in combination with ARV rescued social interaction deficits; however, only ARV was associated with preserved functioning in other behaviors, and CDDO-Me may have attenuated those benefits. A modest neuroprotective effect was found for CDDO-Me when administered with ARV, via preservation of PSD-95 expression; however, ARV alone had a more consistent protective effect. No significant changes in antioxidant enzyme expression levels were observed in CDDO-Me-treated animals. Only ARV use seemed to affect some antioxidant levels, indicating that it is ARV rather than CDDO-Me that is the major factor providing neuroprotection in this animal model. Finally, immunohistochemical analysis found that several cellular markers in various brain regions varied due to ARV rather than CDDO-Me.

Conclusion

Limited benefit of CDDO-Me on behavior and neuroprotection were observed. Instead, ARV was shown to be the more beneficial treatment. These experiments support the future use of this chimeric mouse for behavioral experiments in neuroHIV research.

Extracellular Alpha-Synuclein: Mechanisms for Glial Cell Internalization and Activation

Alpha-synuclein (α-syn) is a small protein composed of 140 amino acids and belongs to the group of intrinsically disordered proteins. It is a soluble protein that is highly expressed in neurons and expressed at low levels in glial cells. The monomeric protein aggregation process induces the formation of oligomeric intermediates and proceeds towards fibrillar species. These α-syn conformational species have been detected in the extracellular space and mediate consequences on surrounding neurons and glial cells. In particular, higher-ordered α-syn aggregates are involved in microglial and oligodendrocyte activation, as well as in the induction of astrogliosis. These phenomena lead to mitochondrial dysfunction, reactive oxygen and nitrogen species formation, and the induction of an inflammatory response, associated with neuronal cell death. Several receptors participate in cell activation and/or in the uptake of α-syn, which can vary depending on the α-syn aggregated state and cell types. The receptors involved in this process are of outstanding relevance because they may constitute potential therapeutic targets for the treatment of PD and related synucleinopathies. This review article focuses on the mechanism associated with extracellular α-syn uptake in glial cells and the consequent glial cell activation that contributes to the neuronal death associated with synucleinopathies.

Oncogenic Pathways in Neurodegenerative Diseases

Cancer and neurodegenerative diseases are two of the leading causes of premature death in modern societies. Their incidence continues to increase, and in the near future, it is believed that cancer will kill more than 20 million people per year, and neurodegenerative diseases, due to the aging of the world population, will double their prevalence. The onset and the progression of both diseases are defined by dysregulation of the same molecular signaling pathways. However, whereas in cancer, these alterations lead to cell survival and proliferation, neurodegenerative diseases trigger cell death and apoptosis. The study of the mechanisms underlying these opposite final responses to the same molecular trigger is key to providing a better understanding of the diseases and finding more accurate treatments. Here, we review the ten most common signaling pathways altered in cancer and analyze them in the context of different neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD), and Huntington's (HD) diseases.

The principal molecular mechanisms behind the activation of Keap1/Nrf2/ARE pathway leading to neuroprotective action in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder. PD is associated with the loss of dopaminergic neurons in the substantia nigra pars compacta region of the midbrain. Present therapies for PD provide only symptomatic relief by restoring the dopamine (DA) level. However, they are not disease modifying agents and so they do not delay the disease progression. Alpha-synuclein aggregation, oxidative stress, mitochondrial dysfunction and chronic inflammation are considered to be the major pathological mechanisms mediating neurodegeneration in PD. To resist oxidative stress, the human body has an antioxidant defence mechanism consisting of many antioxidants and cytoprotective genes. The expression of those genes are largely controlled by the Kelch-like ECH-associated protein 1/Nuclear factor - erythroid - 2 - related factor 2/Antioxidant response element (Keap1/Nrf2/ARE) signalling pathway. The transcription factor Nrf2 is activated in response to oxidative or electrophilic stress and protects the cells from oxidative stress and inflammation. Nrf2 has been widely considered as a therapeutic target for neurodegeneration and several drugs are now being tested in clinical trials. Regulation of the Keap1/Nrf2/ARE pathway by small molecules which can act as Nrf2 activators could be effective for treating oxidative stress and neuroinflammation in PD. In this review, we had discussed the principal molecular mechanisms behind the neuroprotective effects of Keap1/Nrf2/ARE pathway in PD. Additionally, we also discussed the small molecules and phytochemicals that could activate the Nrf2 mediated anti-oxidant pathway for neuroprotection in PD.

Oxyphylla A ameliorates cognitive deficits and alleviates neuropathology via the Akt-GSK3β and Nrf2-Keap1-HO-1 pathways in vitro and in vivo murine models of Alzheimer's disease

Introduction

Alzheimer’s disease (AD) is a progressive brain disorder, and one of the most common causes of dementia and amnesia. Due to the complex pathogenesis of AD, the underlying mechanisms remain unclear. Although scientists have made increasing efforts to develop drugs for AD, no effective therapeutic agents have been found.

Objectives

Natural products and their constituents have shown promise for treating neurodegenerative diseases, including AD. Thus, in-depth study of medical plants, and the main active ingredients thereof against AD, is necessary to devise therapeutic agents.

Methods

In this study, N2a/APP cells and SAMP8 mice were employed as in vitro and in vivo models of AD. Multiple molecular biological methods were used to investigate the potential therapeutic actions of oxyphylla A, and the underlying mechanisms.

Results

Results showed that oxyphylla A, a novel compound extracted from Alpinia oxyphylla, could reduce the expression levels of amyloid precursor protein (APP) and amyloid beta (Aβ) proteins, and attenuate cognitive decline in SAMP8 mice. Further investigation of the underlying mechanisms showed that oxyphylla A exerted an antioxidative effect through the Akt-GSK3β and Nrf2-Keap1-HO-1 pathways.

Conclusions.

Taken together, our results suggest a new horizon for the discovery of therapeutic agents for AD.

The NRF2-Dependent Transcriptional Regulation of Antioxidant Defense Pathways: Relevance for Cell Type-Specific Vulnerability to Neurodegeneration and Therapeutic Intervention

Oxidative stress has been implicated in the etiology and pathobiology of various neurodegenerative diseases. At baseline, the cells of the nervous system have the capability to regulate the genes for antioxidant defenses by engaging nuclear factor erythroid 2 (NFE2/NRF)-dependent transcriptional mechanisms, and a number of strategies have been proposed to activate these pathways to promote neuroprotection. Here, we briefly review the biology of the transcription factors of the NFE2/NRF family in the brain and provide evidence for the differential cellular localization of NFE2/NRF family members in the cells of the nervous system. We then discuss these findings in the context of the oxidative stress observed in two neurodegenerative diseases, Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), and present current strategies for activating NFE2/NRF-dependent transcription. Based on the expression of the NFE2/NRF family members in restricted populations of neurons and glia, we propose that, when designing strategies to engage these pathways for neuroprotection, the relative contributions of neuronal and non-neuronal cell types to the overall oxidative state of tissue should be considered, as well as the cell types which have the greatest intrinsic capacity for producing antioxidant enzymes.

Impaired antioxidant KEAP1-NRF2 system in amyotrophic lateral sclerosis: NRF2 activation as a potential therapeutic strategy

BACKGROUND

Oxidative stress (OS) is an imbalance between oxidant and antioxidant species and, together with other numerous pathological mechanisms, leads to the degeneration and death of motor neurons (MNs) in amyotrophic lateral sclerosis (ALS).

MAIN BODY

Two of the main players in the molecular and cellular response to OS are NRF2, the transcription nuclear factor erythroid 2-related factor 2, and its principal negative regulator, KEAP1, Kelch-like ECH (erythroid cell-derived protein with CNC homology)-associated protein 1. Here we first provide an overview of the structural organization, regulation, and critical role of the KEAP1-NRF2 system in counteracting OS, with a focus on its alteration in ALS. We then examine several compounds capable of promoting NRF2 activity thereby inducing cytoprotective effects, and which are currently in different stages of clinical development for many pathologies, including neurodegenerative diseases.

CONCLUSIONS

Although challenges associated with some of these compounds remain, important advances have been made in the development of safer and more effective drugs that could actually represent a breakthrough for fatal degenerative diseases such as ALS.

EK100 and Antrodin C Improve Brain Amyloid Pathology in APP/PS1 Transgenic Mice by Promoting Microglial and Perivascular Clearance Pathways

Alzheimer’s disease (AD) is characterized by the deposition of β-amyloid peptide (Aβ). There are currently no drugs that can successfully treat this disease. This study first explored the anti-inflammatory activity of seven components isolated from Antrodia cinnamonmea in BV2 cells and selected EK100 and antrodin C for in vivo research. APPswe/PS1dE9 mice were treated with EK100 and antrodin C for one month to evaluate the effect of these reagents on AD-like pathology by nesting behavior, immunohistochemistry, and immunoblotting. Ergosterol and ibuprofen were used as control. EK100 and antrodin C improved the nesting behavior of mice, reduced the number and burden of amyloid plaques, reduced the activation of glial cells, and promoted the perivascular deposition of Aβ in the brain of mice. EK100 and antrodin C are significantly different in activating astrocytes, regulating microglia morphology, and promoting plaque-associated microglia to express oxidative enzymes. In contrast, the effects of ibuprofen and ergosterol are relatively small. In addition, EK100 significantly improved hippocampal neurogenesis in APPswe/PS1dE9 mice. Our data indicate that EK100 and antrodin C reduce the pathology of AD by reducing amyloid deposits and promoting nesting behavior in APPswe/PS1dE9 mice through microglia and perivascular clearance, indicating that EK100 and antrodin C have the potential to be used in AD treatment.

Random forest-integrated analysis in AD and LATE brain transcriptome-wide data to identify disease-specific gene expression

Alzheimer's disease (AD) is a complex neurodegenerative disorder that affects thinking, memory, and behavior. Limbic-predominant age-related TDP-43 encephalopathy (LATE) is a recently identified common neurodegenerative disease that mimics the clinical symptoms of AD. The development of drugs to prevent or treat these neurodegenerative diseases has been slow, partly because the genes associated with these diseases are incompletely understood. A notable hindrance from data analysis perspective is that, usually, the clinical samples for patients and controls are highly imbalanced, thus rendering it challenging to apply most existing machine learning algorithms to directly analyze such datasets. Meeting this data analysis challenge is critical, as more specific disease-associated gene identification may enable new insights into underlying disease-driving mechanisms and help find biomarkers and, in turn, improve prospects for effective treatment strategies. In order to detect disease-associated genes based on imbalanced transcriptome-wide data, we proposed an integrated multiple random forests (IMRF) algorithm. IMRF is effective in differentiating putative genes associated with subjects having LATE and/or AD from controls based on transcriptome-wide data, thereby enabling effective discrimination between these samples. Various forms of validations, such as cross-domain verification of our method over other datasets, improved and competitive classification performance by using identified genes, effectiveness of testing data with a classifier that is completely independent from decision trees and random forests, and relationships with prior AD and LATE studies on the genes linked to neurodegeneration, all testify to the effectiveness of IMRF in identifying genes with altered expression in LATE and/or AD. We conclude that IMRF, as an effective feature selection algorithm for imbalanced data, is promising to facilitate the development of new gene biomarkers as well as targets for effective strategies of disease prevention and treatment.

The Prion-Like Spreading of Alpha-Synuclein in Parkinson's Disease: Update on Models and Hypotheses

The pathological aggregation of the presynaptic protein α-synuclein (α-syn) and propagation through synaptically coupled neuroanatomical tracts is increasingly thought to underlie the pathophysiological progression of Parkinson's disease (PD) and related synucleinopathies. Although the precise molecular mechanisms responsible for the spreading of pathological α-syn accumulation in the CNS are not fully understood, growing evidence suggests that de novo α-syn misfolding and/or neuronal internalization of aggregated α-syn facilitates conformational templating of endogenous α-syn monomers in a mechanism reminiscent of prions. A refined understanding of the biochemical and cellular factors mediating the pathological neuron-to-neuron propagation of misfolded α-syn will potentially elucidate the etiology of PD and unravel novel targets for therapeutic intervention. Here, we discuss recent developments on the hypothesis regarding trans-synaptic propagation of α-syn pathology in the context of neuronal vulnerability and highlight the potential utility of novel experimental models of synucleinopathies.

Contribution of the Nrf2 Pathway on Oxidative Damage and Mitochondrial Failure in Parkinson and Alzheimer's Disease

The increase in human life expectancy has become a challenge to reduce the deleterious consequences of aging. Nowadays, an increasing number of the population suffer from age-associated neurodegenerative diseases including Parkinson's disease (PD) and Alzheimer's disease (AD). These disorders present different signs of neurodegeneration such as mitochondrial dysfunction, inflammation, and oxidative stress. Accumulative evidence suggests that the transcriptional factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) plays a vital defensive role orchestrating the antioxidant response in the brain. Nrf2 activation promotes the expression of several antioxidant enzymes that exert cytoprotective effects against oxidative damage and mitochondrial impairment. In this context, several studies have proposed a role of Nrf2 in the pathogenesis of PD and AD. Thus, we consider it important to summarize the ongoing literature related to the effects of the Nrf2 pathway in the context of these diseases. Therefore, in this review, we discuss the mechanisms involved in Nrf2 activity and its connection with mitochondria, energy supply, and antioxidant response in the brain. Furthermore, we will lead our discussion to identify the participation of the Nrf2 pathway in mitochondrial impairment and neurodegeneration present in PD and AD. Finally, we will discuss the therapeutic effects that the Nrf2 pathway activation could have on the cognitive impairment, neurodegeneration, and mitochondrial failure present in PD and AD.

α-Synuclein pathology in Parkinson disease activates homeostatic NRF2 anti-oxidant response

Circumstantial evidence points to a pathological role of alpha-synuclein (aSyn; gene symbol SNCA), conferred by aSyn misfolding and aggregation, in Parkinson disease (PD) and related synucleinopathies. Several findings in experimental models implicate perturbations in the tissue homeostatic mechanisms triggered by pathological aSyn accumulation, including impaired redox homeostasis, as significant contributors in the pathogenesis of PD. The nuclear factor erythroid 2-related factor (NRF2/Nrf2) is recognized as ‘the master regulator of cellular anti-oxidant response’, both under physiological as well as in pathological conditions. Using immunohistochemical analyses, we show a robust nuclear NRF2 accumulation in post-mortem PD midbrain, detected by NRF2 phosphorylation on the serine residue 40 (nuclear active p-NRF2, S40). Curated gene expression analyses of four independent publicly available microarray datasets revealed considerable alterations in NRF2-responsive genes in the disease affected regions in PD, including substantia nigra, dorsal motor nucleus of vagus, locus coeruleus and globus pallidus. To further examine the putative role of pathological aSyn accumulation on nuclear NRF2 response, we employed a transgenic mouse model of synucleionopathy (M83 line, expressing the mutant human A53T aSyn), which manifests widespread aSyn pathology (phosphorylated aSyn; S129) in the nervous system following intramuscular inoculation of exogenous fibrillar aSyn. We observed strong immunodetection of nuclear NRF2 in neuronal populations harboring p-aSyn (S129), and found an aberrant anti-oxidant and inflammatory gene response in the affected neuraxis. Taken together, our data support the notion that pathological aSyn accumulation impairs the redox homeostasis in nervous system, and boosting neuronal anti-oxidant response is potentially a promising approach to mitigate neurodegeneration in PD and related diseases.

Emerging Evidence Highlighting the Importance of Redox Dysregulation in the Pathogenesis of Amyotrophic Lateral Sclerosis (ALS)

The cellular redox state, or balance between cellular oxidation and reduction reactions, serves as a vital antioxidant defence system that is linked to all important cellular activities. Redox regulation is therefore a fundamental cellular process for aerobic organisms. Whilst oxidative stress is well described in neurodegenerative disorders including amyotrophic lateral sclerosis (ALS), other aspects of redox dysfunction and their contributions to pathophysiology are only just emerging. ALS is a fatal neurodegenerative disease affecting motor neurons, with few useful treatments. Hence there is an urgent need to develop more effective therapeutics in the future. Here, we discuss the increasing evidence for redox dysregulation as an important and primary contributor to ALS pathogenesis, which is associated with multiple disease mechanisms. Understanding the connection between redox homeostasis, proteins that mediate redox regulation, and disease pathophysiology in ALS, may facilitate a better understanding of disease mechanisms, and lead to the design of better therapeutic strategies.

Efficacy of Sulforaphane in Neurodegenerative Diseases

Sulforaphane (SFN) is a phytocompound belonging to the isothiocyanate family. Although it was also found in seeds and mature plants, SFN is mainly present in sprouts of many cruciferous vegetables, including cabbage, broccoli, cauliflower, and Brussels sprouts. SFN is produced by the conversion of glucoraphanin through the enzyme myrosinase, which leads to the formation of this isothiocyanate. SFN is especially characterized by antioxidant, anti-inflammatory, and anti-apoptotic properties, and for this reason, it aroused the interest of researchers. The aim of this review is to summarize the experimental studies present on Pubmed that report the efficacy of SFN in the treatment of neurodegenerative disease, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and multiple sclerosis (MS). Therefore, thanks to its beneficial effects, SFN could be useful as a supplement to counteracting neurodegenerative diseases.

Antioxidant and Anti-inflammatory Effect of Nrf2 Inducer Dimethyl Fumarate in Neurodegenerative Diseases

Neurodegenerative diseases (NDs) represents debilitating conditions characterized by degeneration of neuronal cells in specific brain areas, causing disability and death in patients. In the pathophysiology of NDs, oxidative stress, apoptosis and neuroinflammation have a key role, as demonstrated by in vivo and in vitro models. Therefore, the use of molecules with antioxidant and anti-inflammatory activities represents a possible strategy for the treatment of NDs. Many studies demonstrated the beneficial effects of fumaric acid esters (FAEs) to counteract neuroinflammation and oxidative stress. Among these molecules, dimethyl fumarate (DMF) showed a valid therapeutic approach to slow down neurodegeneration and relieve symptoms in patients with NDs. DMF is a methyl ester of fumaric acid and acts as modulator of the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway as well as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) translocation. Therefore, this review aims to examine the potential beneficial effects of DMF to counteract oxidative stress and inflammation in patients with NDs.

Centella Asiatica Improves Memory and Promotes Antioxidative Signaling in 5XFAD Mice

Centella asiatica (CA) herb is a traditional medicine, long reputed to provide cognitive benefits. We have reported that CA water extract (CAW) treatment improves cognitive function of aged Alzheimer’s disease (AD) model Tg2576 and wild-type (WT) mice, and induces an NRF2-regulated antioxidant response in aged WT mice. Here, CAW was administered to AD model 5XFAD female and male mice and WT littermates (age: 7.6 +/− 0.6 months), and object recall and contextual fear memory were tested after three weeks treatment. CAW’s impact on amyloid-β plaque burden, and markers of neuronal oxidative stress and synaptic density, was assessed after five weeks treatment. CAW antioxidant activity was evaluated via nuclear transcription factor (erythroid-derived 2)-like 2 (NRF2) and NRF2-regulated antioxidant response element gene expression. Memory improvement in both genders and genotypes was associated with dose-dependent CAW treatment without affecting plaque burden, and marginally increased synaptic density markers in the hippocampus and prefrontal cortex. CAW treatment increased Nrf2 in hippocampus and other NRF2 targets (heme oxygenase-1, NAD(P)H quinone dehydrogenase 1, glutamate-cysteine ligase catalytic subunit). Reduced plaque-associated SOD1, an indicator of oxidative stress, was observed in the hippocampi and cortices of CAW-treated 5XFAD mice. We postulate that CAW treatment leads to reduced oxidative stress, contributing to improved neuronal health and cognition.

Shaping the Nrf2-ARE-related pathways in Alzheimer's and Parkinson's diseases

A failure in redox homeostasis is a common hallmark of Alzheimer's Disease (AD) and Parkinson's Disease (PD), two age-dependent neurodegenerative disorders (NDD), causing increased oxidative stress, oxidized/damaged biomolecules, altered neuronal function and consequent cell death. Activation of nuclear factor erythroid 2-related factor 2 (Nrf2), a redox-regulated transcription factor, results in upregulation of cytoprotective and antioxidant enzymes/proteins, protecting against oxidative stress. Nrf2 regulation is achieved by various proteins and pathways, at both cytoplasmatic and nuclear level; however, the elaborate network of mechanisms involved in Nrf2 regulation may restrain Nrf2 pathway normal activity. Indeed, altered Nrf2 activity is involved in aging and NDD, such as AD and PD. Therefore, understanding the diversity of Nrf2 control mechanisms and regulatory proteins is of high interest, since more effective NDD therapeutics can be identified. In this review, we first introduce Keap1-Nrf2-ARE structure, function and regulation, with a special focus on the several pathways involved in Nrf2 positive and negative modulation, namely p62, PKC, PI3K/Akt/GSK-3β, NF-kB and p38 MAPK. We then briefly describe the evidences for oxidative stress and Nrf2 pathway deregulation in different stages of NDDs. Finally, we discuss the potential of Nrf2-related pathways as potential therapeutic targets to possibly prevent or slowdown NDD progression.

Anti-Diabetic Countermeasures Against Tobacco Smoke-Dependent Cerebrovascular Toxicity: Use and Effect of Rosiglitazone

Tobacco smoking (TS) is one of the most addictive habit sand a main public health hazards, impacting the vascular endothelium through oxidative stress (OS) stimuli, exposure to nicotine, and smoking-induced inflammation in a dose-dependent manner. Increasing evidence also suggested that TS increases glucose intolerance and the risk factor of developing type-2 diabetes mellitus (2DM), which, along with TS, is connected to blood–brain barrier (BBB) injuries, and heightens the risk of cerebrovascular disorders. Although the exact mechanism of rosiglitazone (RSG) is unknown, our previous in vitro work showed how RSG, an oral anti-diabetic drug belonging to the family of thiazolidinedione class, can protect BBB integrity through enhancement of nuclear factor erythroid 2-related factor (Nrf2) activity. Herein, we have validated the protective role of rosiglitazone against TS-induced BBB impairment in vivo. Our results revealed that RSG as a peroxisome proliferator-activated receptor gamma (PPARγ), activates counteractive mechanisms primarily associated with the upregulation of Nrf2 and PPARγ pathways which reduce TS-dependent toxicity at the cerebrovascular level. In line with these findings, our results show that RSG reduces inflammation and protects BBB integrity. In conclusion, RSG offers a novel and promising therapeutic application to reduce TS-induced cerebrovascular dysfunction through activation of the PPARγ-dependent and/or PPARγ-independent Nrf2 pathway.

Cerebrovascular and Neurological Disorders: Protective Role of NRF2

Cellular defense mechanisms, intracellular signaling, and physiological functions are regulated by electrophiles and reactive oxygen species (ROS). Recent works strongly considered imbalanced ROS and electrophile overabundance as the leading cause of cellular and tissue damage, whereas oxidative stress (OS) plays a crucial role for the onset and progression of major cerebrovascular and neurodegenerative pathologies. These include Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), Huntington’s disease (HD), stroke, and aging. Nuclear factor erythroid 2-related factor (NRF2) is the major modulator of the xenobiotic-activated receptor (XAR) and is accountable for activating the antioxidative response elements (ARE)-pathway modulating the detoxification and antioxidative responses of the cells. NRF2 activity, however, is also implicated in carcinogenesis protection, stem cells regulation, anti-inflammation, anti-aging, and so forth. Herein, we briefly describe the NRF2–ARE pathway and provide a review analysis of its functioning and system integration as well as its role in major CNS disorders. We also discuss NRF2-based therapeutic approaches for the treatment of neurodegenerative and cerebrovascular disorders.

Basic Concepts on the Role of Nuclear Factor Erythroid-Derived 2-Like 2 (Nrf2) in Age-Related Diseases

The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) is one of the most important oxidative stress regulator in the human body. Once Nrf2 regulates the expression of a large number of cytoprotective genes, it plays a crucial role in the prevention of several diseases, including age-related disorders. However, the involvement of Nrf2 on these conditions is complex and needs to be clarified. Here, a brief compilation of the Nrf2 enrollment in the pathophysiology of the most common age-related diseases and bring insights for future research on the Nrf2 pathway is described. This review shows a controversial response of this transcriptional factor on the presented diseases. This reinforces the necessity of more studies to investigate modulation strategies for Nrf2, making it a possible therapeutic target in the treatment of age-related disorders.

Trehalose intake and exercise upregulate a glucose transporter, GLUT8, in the brain

Physical exercise influences cognitive function through a cascade of cellular processes that promote angiogenesis and neurogenesis. Autophagy is a cellular degradation system that is capable of producing energy in response to various conditions such as starvation, physical exercise and several treatments. Our previous report demonstrated that a disaccharide, trehalose, induced autophagy in the brain and reduced the levels of potentially toxic proteins. To achieve more efficient induction of autophagy in the brain, in this study, we examined the effect of disaccharide intake combined with exercise on autophagy in vivo. Consistent with the results of previous studies, our biochemical analyses demonstrated that trehalose increased the level of lipidated LC3 (LC3II) in the brain and liver of adult mice. However, contrary to our expectation, treadmill exercise reduced the level of LC3II in the brain and liver. Interestingly, glycogen storage was preserved in the liver of trehalose-intake mice even after exercise. Moreover, the trehalose transporter GLUT8 was increased in the liver by trehalose or in the brain by trehalose together with exercise. In contrast, the level of GLUT4 remained stable in the liver and brain even after exercise. These findings suggest that trehalose and GLUT8 coordinately contribute to energy supply in the brain.

Assessing the protective effect of rosiglitazone against electronic cigarette/tobacco smoke-induced blood-brain barrier impairment

BACKGROUND

Smoking (TS) and recently e-cigarettes (EC) vaping, have been associated with vascular endothelial dysfunction primarily relevant to oxidative stress, exposure to nicotine, and smoking-induced inflammation. It is accepted that both EC and TS enhance glucose intolerance and the risk of developing type-2 diabetes mellitus which is also one of the causes of blood-brain barrier (BBB) damage and the higher risk of cerebrovascular diseases. Recent studies have shown how Metformin, the first common antidiabetic drug, can protect the BBB integrity through enhancement of nuclear factor erythroid 2-related factor (Nrf2) activity. Herein, we investigated the role of rosiglitazone (RSG; family of thiazolidinedione class used oral anti-diabetic drug) in TS/EC-induced BBB impairment.

RESULTS

Although the exact mechanism of RSG is not fully understood, previous studies have revealed that RSG can promote counteractive protective mechanisms primarily associated with the enhancement of Nrf2 activity through activation of the peroxisome proliferator-activated receptor gamma. In line with these findings, our results show an increased expression of PPARy by RSG, enhancement of Nrf2 activity and BBB protection against TS/EC exposure including reduced inflammation, oxidative stress, tight junction downregulation and loss of BBB integrity.

CONCLUSIONS

RSG could be considered as a promising therapeutic potential to prevent TS/EC induced cerebrovascular dysfunction and possibly other xenobiotic substances which may impact the BBB via oxidative stress-mediated effects. However, additional in vivo studies and clinical setting will be needed to validate our results and assess the full extent of RSG protective effects.

Nrf2/ARE Pathway Modulation by Dietary Energy Regulation in Neurological Disorders

Nuclear factor erythroid 2-related factor 2 (Nrf2) regulates the expression of an array of enzymes with important detoxifying and antioxidant functions. Current findings support the role of high levels of oxidative stress in the pathogenesis of neurological disorders. Given the central role played by Nrf2 in counteracting oxidative damage, a number of studies have targeted the modulation of this transcription factor in order to confer neuroprotection. Nrf2 activity is tightly regulated by oxidative stress and energy-based stimuli. Thus, many dietary interventions based on energy intake regulation, such as dietary energy restriction (DER) or high-fat diet (HFD), modulate Nrf2 with consequences for a variety of cellular processes that affect brain health. DER, by either restricting calorie intake or meal frequency, activates Nrf2 thereby triggering its protective effects, whilst HFD inhibit this pathway, thereby exacerbating oxidative stress. Consequently, DER protocols can be valuable strategies in the management of central nervous system (CNS) disorders. Herein, we review current knowledge of the role of Nrf2 signaling in neurological diseases, namely Alzheimer’s disease, Parkinson’s disease, multiple sclerosis and cerebral ischemia, as well as the potential of energy intake regulation in the management of Nrf2 signaling.

NRF2 and NF-қB interplay in cerebrovascular and neurodegenerative disorders: Molecular mechanisms and possible therapeutic approaches

Electrophiles and reactive oxygen species (ROS) play a major role in modulating cellular defense mechanisms as well as physiological functions, and intracellular signaling. However, excessive ROS generation (endogenous and exogenous) can create a state of redox imbalance leading to cellular and tissue damage (Ma and He, 2012) [1]. A growing body of research data strongly suggests that imbalanced ROS and electrophile overproduction are among the major prodromal factors in the onset and progression of several cerebrovascular and neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), stroke, Alzheimer's disease (AD), Parkinson's disease (PD), and aging (Ma and He, 2012; Ramsey et al., 2017; Salminen et al., 2012; Sandberg et al., 2014; Sarlette et al., 2008; Tanji et al., 2013) [1-6]. Cells offset oxidative stress by the action of housekeeping antioxidative enzymes (such as superoxide dismutase, catalase, glutathione peroxidase) as well direct and indirect antioxidants (Dinkova-Kostova and Talalay, 2010) [7]. The DNA sequence responsible for modulating the antioxidative and cytoprotective responses of the cells has been identified as the antioxidant response element (ARE), while the nuclear factor erythroid 2-related factor (NRF2) is the major regulator of the xenobiotic-activated receptor (XAR) responsible for activating the ARE-pathway, thus defined as the NRF2-ARE system (Ma and He, 2012) [1]. In addition, the interplay between the NRF2-ARE system and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-ĸB, a protein complex that controls cytokine production and cell survival), has been further investigated in relation to neurodegenerative and neuroinflammatory disorders. On these premises, we provide a review analysis of current understanding of the NRF2-NF-ĸB interplay, their specific role in major CNS disorders, and consequent therapeutic implication for the treatment of neurodegenerative and cerebrovascular diseases.

Preventive and Protective Roles of Dietary Nrf2 Activators Against Central Nervous System Diseases

Central nervous system diseases are major health issues and are often associated with disability or death. Most central nervous system disorders are characterized by high levels of oxidative stress. Nuclear factor erythroid 2 related factor (Nrf2) is known for its ability to regulate the expression of a series of enzymes with antioxidative, prosurvival, and detoxification effects. Under basal conditions, Nrf2 forms a complex with Kelch-like ECH associated protein 1, leading to Nrf2 inactivation via ubiquitination and degradation. However, following exposure of Keap1 to oxidative stress, Nrf2 is released from Keap1, activated, and translocated into the nucleus. Upon nuclear entry, Nrf2 binds to antioxidant response elements (ARE), thereby inducing the expression of genes such as glutathione s-transferase, heme oxygenase 1, and NADPH quinine oxidoreductase 1. Many dietary phytochemicals have been reported to activate the protective Nrf2/ARE pathway. Here, we review the preventive and protective effects of dietary Nrf2 activators against CNS diseases, including stroke, traumatic brain injury, Alzheimer's disease, and Parkinson's disease.

Oxidative Stress, Synaptic Dysfunction, and Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder without a cure. Most AD cases are sporadic where age represents the greatest risk factor. Lack of understanding of the disease mechanism hinders the development of efficacious therapeutic approaches. The loss of synapses in the affected brain regions correlates best with cognitive impairment in AD patients and has been considered as the early mechanism that precedes neuronal loss. Oxidative stress has been recognized as a contributing factor in aging and in the progression of multiple neurodegenerative diseases including AD. Increased production of reactive oxygen species (ROS) associated with age- and disease-dependent loss of mitochondrial function, altered metal homeostasis, and reduced antioxidant defense directly affect synaptic activity and neurotransmission in neurons leading to cognitive dysfunction. In addition, molecular targets affected by ROS include nuclear and mitochondrial DNA, lipids, proteins, calcium homeostasis, mitochondrial dynamics and function, cellular architecture, receptor trafficking and endocytosis, and energy homeostasis. Abnormal cellular metabolism in turn could affect the production and accumulation of amyloid-β (Aβ) and hyperphosphorylated Tau protein, which independently could exacerbate mitochondrial dysfunction and ROS production, thereby contributing to a vicious cycle. While mounting evidence implicates ROS in the AD etiology, clinical trials with antioxidant therapies have not produced consistent results. In this review, we will discuss the role of oxidative stress in synaptic dysfunction in AD, innovative therapeutic strategies evolved based on a better understanding of the complexity of molecular mechanisms of AD, and the dual role ROS play in health and disease.

Unhealthy smokers: scopes for prophylactic intervention and clinical treatment

BACKGROUND

Globally, tobacco use causes approximately 6 million deaths per year, and predictions report that with current trends; more than 8 million deaths are expected annually by 2030. Cigarette smokings is currently accountable for more than 480,000 deaths each year in United States (US) and is the leading cause of preventable death in the US. On average, smokers die 10 years earlier than nonsmokers and if smoking continues at its current proportion among adolescents, one in every 13 Americans aged 17 years or younger is expected to die prematurely from a smoking-related illness. Even though there has been a marginal smoking decline of around 5% in recent years (2005 vs 2015), smokers still account for 15% of the US adult population. What is also concerning is that 41,000 out of 480,000 deaths results from secondhand smoke (SHS) exposure. Herein, we provide a detailed review of health complications and major pathological mechanisms including mutation, inflammation, oxidative stress, and hemodynamic and plasma protein changes associated with chronic smoking. Further, we discuss prophylactic interventions and associated benefits and provide a rationale for the scope of clinical treatment.

CONCLUSIONS

Considering these premises, it is evident that much detailed translational and clinical studies are needed. Factors such as the length of smoking cessation for ex-smokers, the level of smoke exposure in case of SHS, pre-established health conditions, genetics (and epigenetics modification caused by chronic smoking) are few of the criteria that need to be evaluated to begin assessing the prophylactic and/or therapeutic impact of treatments aimed at chronic and former smokers (especially early stage ex-smokers) including those frequently subjected to second hand tobacco smoke exposure. Herein, we provide a detailed review of health complications and major pathological mechanisms including mutation, inflammation, oxidative stress, and hemodynamic and plasma protein changes associated with chronic smoking. Further, we discuss about prophylactic interventions and associated benefits and provide a rationale and scope for clinical treatment.

Are Astrocytes the Predominant Cell Type for Activation of Nrf2 in Aging and Neurodegeneration?

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates hundreds of antioxidant genes, and is activated in response to oxidative stress. Given that many neurodegenerative diseases including Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, Huntington’s disease and multiple sclerosis are characterised by oxidative stress, Nrf2 is commonly activated in these diseases. Evidence demonstrates that Nrf2 activity is repressed in neurons in vitro, and only cultured astrocytes respond strongly to Nrf2 inducers, leading to the interpretation that Nrf2 signalling is largely restricted to astrocytes. However, Nrf2 activity can be observed in neurons in post-mortem brain tissue and animal models of disease. Thus this interpretation may be false, and a detailed analysis of the cell type expression of Nrf2 in neurodegenerative diseases is required. This review describes the evidence for Nrf2 activation in each cell type in prominent neurodegenerative diseases and normal aging in human brain and animal models of neurodegeneration, the response to pharmacological and genetic modulation of Nrf2, and clinical trials involving Nrf2-modifying drugs.

Redox-based therapeutics in neurodegenerative disease

This review describes recent developments in the search for effective therapeutic agents that target redox homeostasis in neurodegenerative disease. The disruption to thiol redox homeostasis in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and multiple sclerosis is discussed, together with the experimental strategies that are aimed at preventing, or at least minimizing, oxidative damage in these diseases. Particular attention is given to the potential of increasing antioxidant capacity by targeting the Nrf2 pathway, the development of inhibitors of NADPH oxidases that are likely candidates for clinical use, together with strategies to reduce nitrosative stress and mitochondrial dysfunction. We describe the shortcomings of compounds that hinder their progression to the clinic and evaluate likely avenues for future research.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

Non-canonical activation of NRF2: New insights and its relevance to disease

PURPOSE OF REVIEW

The goal of this review is to summarize the current knowledge in the field regarding the non-canonical activation of the NRF2 pathway. Specifically, we address what role p62 plays in mediating this pathway, which pathologies have been linked to the p62-dependent activation of NRF2, as well as what therapeutic strategies could be used to treat diseases associated with the non-canonical pathway.

RECENT FINDINGS

It has recently been shown that autophagic dysfunction leads to the aggregation or autophagosomal accumulation of p62, which sequesters KEAP1, resulting in prolonged activation of NRF2. The ability of p62 to outcompete NRF2 for KEAP1 binding depends on its abundance, or post-translational modifications to its key domains. Furthermore, the relevance of the p62-dependent activation of NRF2 in disease has been demonstrated in human hepatocellular carcinomas, as well as neurodegenerative diseases.

SUMMARY

These findings indicate that targeting p62, or the enzymes that modify it, could prove to be an advantageous strategy for treating diseases associated with autophagy dysregulation and prolonged activation of NRF2. Other therapeutic possibilities include restoring proper autophagic function, or directly inhibiting NRF2 or its targets, to restore redox and metabolic homeostasis. Future studies will help further clarify the mechanisms, regulation, and relevance of the non-canonical pathway in driving disease pathogenesis.

Activation of the Keap1/Nrf2 stress response pathway in autophagic vacuolar myopathies

Nrf2 (nuclear factor [erythroid-derived 2]-like 2; the transcriptional master regulator of the antioxidant stress response) is regulated through interaction with its cytoplasmic inhibitor Keap1 (Kelch-like ECH-associated protein 1), which under basal conditions targets Nrf2 for proteasomal degradation. Sequestosome 1 (SQSTM1)/p62–a multifunctional adapter protein that accumulates following autophagy inhibition and can serve as a diagnostic marker for human autophagic vacuolar myopathies (AVMs)–was recently shown to compete with Nrf2 for Keap1 binding, resulting in activation of the Nrf2 pathway. In this study, we used 55 human muscle biopsies divided into five groups [normal control, hydroxychloroquine- or colchicine-treated non-AVM control, hydroxychloroquine- or colchicine-induced toxic AVM, polymyositis, and inclusion body myositis (IBM)] to evaluate whether Keap1-SQSTM1 interaction led to increased Nrf2 signaling in human AVMs. In toxic AVMs and IBM, but not in control muscle groups or polymyositis, Keap1 antibody labeled sarcoplasmic protein aggregates that can be used as an alternate diagnostic marker for both AVM types; these Keap1-positive aggregates were co-labeled with the antibody against SQSTM1 but not with the antibody against autophagosome marker LC3 (microtubule-associated protein 1 light chain 3). In human AVM muscle, sequestration of Keap1 into the SQSTM1-positive protein aggregates was accompanied by an increase in mRNA and protein levels of Nrf2 target genes; similarly, treatment of differentiated C2C12 myotubes with autophagy inhibitor chloroquine led to an increase in the nuclear Nrf2 protein level and an increase in expression of the Nrf2-regulated genes. Taken together, our findings demonstrate that Nrf2 signaling is upregulated in autophagic muscle disorders and raise the possibility that autophagy disruption in skeletal muscle leads to dysregulation of cellular redox homeostasis.

Role of Nrf2/HO-1 system in development, oxidative stress response and diseases: an evolutionarily conserved mechanism

The multifunctional regulator nuclear factor erythroid 2-related factor (Nrf2) is considered not only as a cytoprotective factor regulating the expression of genes coding for anti-oxidant, anti-inflammatory and detoxifying proteins, but it is also a powerful modulator of species longevity. The vertebrate Nrf2 belongs to Cap 'n' Collar (Cnc) bZIP family of transcription factors and shares a high homology with SKN-1 from Caenorhabditis elegans or CncC found in Drosophila melanogaster. The major characteristics of Nrf2 are to some extent mimicked by Nrf2-dependent genes and their proteins including heme oxygenase-1 (HO-1), which besides removing toxic heme, produces biliverdin, iron ions and carbon monoxide. HO-1 and their products exert beneficial effects through the protection against oxidative injury, regulation of apoptosis, modulation of inflammation as well as contribution to angiogenesis. On the other hand, the disturbances in the proper HO-1 level are associated with the pathogenesis of some age-dependent disorders, including neurodegeneration, cancer or macular degeneration. This review summarizes our knowledge about Nrf2 and HO-1 across different phyla suggesting their conservative role as stress-protective and anti-aging factors.

ALS-FTLD associated mutations of SQSTM1 impact on Keap1-Nrf2 signalling

The transcription factor Nrf2 and its repressor protein Keap1 play key roles in the regulation of antioxidant stress responses and both Keap1-Nrf2 signalling and oxidative stress have been implicated in the pathogenesis of the ALS-FTLD spectrum of neurodegenerative disorders. The Keap1-binding partner and autophagy receptor SQSTM1/p62 has also recently been linked genetically to ALS-FTLD, with some missense mutations identified in patients mapping within or close to its Keap1-interacting region (KIR, residues 347–352). Here we report the effects on protein function of four different disease associated mutations of SQSTM1/p62 which affect the KIR region. Only mutations mapping precisely to the KIR (P348L and G351A) were associated with a loss of Keap1 binding in co-immunoprecipitations comparable to wild-type SQSTM1/p62. These selective effects on Keap1 recognition were entirely rational based on protein structural models. Consistent with impaired Keap1 binding, the P348L and G351A KIR mutants showed reduced ability to activate Nrf2 signalling compared to wild-type SQSTM1/p62 in antioxidant response element (ARE)-luciferase reporter assays. The results suggest that SQSTM1 mutations within the KIR of SQSTM1/p62 contribute to aetiology of some cases of ALS-FTLD through a mechanism involving aberrant expression or regulation of oxidative response genes.

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ALS-FTLD associated KIR mutations of SQSTM1/p62 disrupt Keap1 binding.

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KIR mutants of SQSTM1/p62 are unable to activate Nrf2 signalling in reporter assays.

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Some SQSTM1 mutations may contribute to ALS-FTLD through an aberrant antioxidant stress response.

Nrf2--a therapeutic target for the treatment of neurodegenerative diseases

The brain is very sensitive to changes in redox status; thus maintaining redox homeostasis in the brain is critical for the prevention of accumulating oxidative damage. Aging is the primary risk factor for developing neurodegenerative diseases. In addition to age, genetic and environmental risk factors have also been associated with disease development. The primary reactive insults associated with the aging process are a result of oxidative stress (OS) and nitrosative stress (NS). Markers of increased oxidative stress, protein and DNA modification, inflammation, and dysfunctional proteostasis have all been implicated in contributing to the progression of neurodegeneration. The ability of the cell to combat OS/NS and maintain a clearance mechanism for misfolded aggregating proteins determines whether or not it will survive. A critical pathway in this regard is the Nrf2 (nuclear factor erythroid 2-related factor 2)- antioxidant response element (ARE) pathway. Nrf2 activation has been shown to mitigate a number of pathologic mechanisms associated with Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis. This review will focus on the role of Nrf2 in these diseases and the potential for Nrf2 activation to attenuate disease progression.

[Multiple system atrophy and autophagy]

Macroautophagy is a dynamic process whereby cytoplasmic molecules are sequestered within autophagosomes. There exist two groups of mammalian autophagy-related gene (Atg) 8 homologues (LC3 and GABARAPs), which play essential role in autophagosomal formation. We determined whether Atg8 homologues are affected in Lewy body disease (LBD) and multiple system atrophy (MSA). The level of LC3 was increased in an insoluble fraction from the brain of patients with LBD, whereas the level of GABARAPs was decreased in LBD. The level of matured GABARAPs was significantly decreased in the cerebellum of MSA, and that the higher levels of matured and lipidated LC3 were detected in detergent-insoluble fraction of MSA. Furthermore, immunohistochemical staining revealed that both LC3 and GABARAPs were localized in Lewy bodies and glial cytoplasmic inclusions in MSA were positive for LC3. These findings suggest that autophagic function is impaired through alteration of Atg8 homologues in LBD and MSA. Autophagy-enhancing strategies can therefore have therapeutic efficacy for various neurodegenerative diseases including LBD and MSA.

RBM45 Modulates the Antioxidant Response in Amyotrophic Lateral Sclerosis through Interactions with KEAP1

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the selective loss of motor neurons. Various factors contribute to the disease, including RNA binding protein dysregulation and oxidative stress, but their exact role in pathogenic mechanisms remains unclear. We have recently linked another RNA binding protein, RBM45, to ALS via increased levels of protein in the cerebrospinal fluid of ALS patients and its localization to cytoplasmic inclusions in ALS motor neurons. Here we show RBM45 nuclear exit in ALS spinal cord motor neurons compared to controls, a phenotype recapitulated in vitro in motor neurons treated with oxidative stressors. We find that RBM45 binds and stabilizes KEAP1, the inhibitor of the antioxidant response transcription factor NRF2. ALS lumbar spinal cord lysates similarly show increased cytoplasmic binding of KEAP1 and RBM45. Binding of RBM45 to KEAP1 impedes the protective antioxidant response, thus contributing to oxidative stress-induced cellular toxicity. Our findings thus describe a novel link between a mislocalized RNA binding protein implicated in ALS (RBM45) and dysregulation of the neuroprotective antioxidant response seen in the disease.

Role of the Keap1/Nrf2 pathway in neurodegenerative diseases

As the elderly population increases, a growing number of individuals suffer from age-associated neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD). Oxidative stress is considered to play a crucial role in the pathogenesis of age-related diseases. The transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) is activated by oxidative stress and regulates the expression of a variety of antioxidant enzymes and proteins that exert cytoprotective effects against oxidative stress. Numerous studies have addressed the role of Nrf2 in age-related diseases, including neurodegenerative diseases, using animal or in vitro cell culture models. Here, we introduce the role of oxidative stress in the pathogenesis of neurodegenerative diseases and critically examine the recent findings concerning the role for Nrf2 in the amelioration of AD and PD. Nrf2 not only regulates antioxidant proteins but also regulates the genes associated with autophagy and nerve growth factor signaling. Current research unequivocally demonstrates that the activation of the Nrf2 pathway is a promising novel strategy for the prevention and modification of neurodegenerative diseases.

Clearance of misfolded and aggregated proteins by aggrephagy and implications for aggregation diseases

Processing of misfolded proteins is important in order for the cell to maintain its normal functioning and homeostasis. Three systems control the quality of proteins: chaperone-mediated refolding, proteasomal degradation of ubiquitinated proteins, and finally, when the two others fail, aggrephagy, as selective form of autophagy, degrades ubiquitin-labelled aggregated cargos. In this route misfolded proteins gradually form larger aggregates, aggresomes and they eventually become double membrane-wrapped organelles called autophagosomes, which become degraded when they fuse to lysosomes, for reuse by the cell. The stages, the main molecules participating in the process, and the regulation of aggrephagy are discussed here, as is the role of protein aggregation in protein accumulation diseases. In particular, we emphasize that both Alzheimer's disease and age-related macular degeneration, two of the most common pathologies in the aged, are characterized by altered protein clearance and deposits. Based on the hypothesis that manipulations of autophagy may be potentially useful in these and other aggregation-related diseases, we will discuss some promising therapeutic strategies to counteract protein aggregates-induced cellular toxicity.

The role of the immune system in neurodegenerative disorders: Adaptive or maladaptive?

Neurodegenerative diseases share common features, including catastrophic neuronal loss that leads to cognitive or motor dysfunction. Neuronal injury occurs in an inflammatory milieu that is populated by resident and sometimes, infiltrating, immune cells - all of which participate in a complex interplay between secreted inflammatory modulators and activated immune cell surface receptors. The importance of these immunomodulators is highlighted by the number of immune factors that have been associated with increased risk of neurodegeneration in recent genome-wide association studies. One of the more difficult tasks for designing therapeutic strategies for immune modulation against neurodegenerative diseases is teasing apart beneficial from harmful signals. In this regard, learning more about the immune components of these diseases has yielded common themes. These unifying concepts should eventually enable immune-based therapeutics for treatment of Alzheimer׳s and Parkinson׳s diseases and amyotrophic lateral sclerosis. Targeted immune modulation should be possible to temper maladaptive factors, enabling beneficial immune responses in the context of neurodegenerative diseases. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Increased Alzheimer's disease-like pathology in the APP/ PS1ΔE9 mouse model lacking Nrf2 through modulation of autophagy

The presence of senile plaques is one of the major pathologic hallmarks of the brain with Alzheimer's disease (AD). The plaques predominantly contain insoluble amyloid β-peptide, a cleavage product of the larger amyloid precursor protein (APP). Two enzymes, named β and γ secretase, generate the neurotoxic amyloid-β peptide from APP. Mature APP is also turned over endogenously by autophagy, more specifically by the endosomal-lysosomal pathway. A defective lysosomal system is known to be pathogenic in AD. Modulation of NF-E2 related factor 2 (Nrf2) has been shown in several neurodegenerative disorders, and Nrf2 has become a potential therapeutic target for various neurodegenerative disorders, including AD, Parkinson's disease, and amyotrophic lateral sclerosis. In the current study, we explored the effect of genetic ablation of Nrf2 on APP/Aβ processing and/or aggregation as well as changes in autophagic dysfunction in APP/PS1 mice. There was a significant increase in inflammatory response in APP/PS1 mice lacking Nrf2. This was accompanied by increased intracellular levels of APP, Aβ (1-42), and Aβ (1-40), without a change total full-length APP. There was a shift of APP and Aβ into the insoluble fraction, as well as increased poly-ubiquitin conjugated proteins in mice lacking Nrf2. APP/PS1-mediated autophagic dysfunction is also enhanced in Nrf2-deficient mice. Finally, neurons in the APP/PS1/Nrf2-/- mice had increased accumulation of multivesicular bodies, endosomes, and lysosomes. These outcomes provide a better understanding of the role of Nrf2 in modulating autophagy in an AD mouse model and may help design better Nrf2 targeted therapeutics that could be efficacious in the treatment of AD.

Causes of metabolic syndrome and obesity-related co-morbidities Part 1: A composite unifying theory review of human-specific co-adaptations to brain energy consumption

One line summary

Metabolic syndrome and obesity-related co-morbidities are largely explained by co-adaptations to the energy use of the large human brain in the cortico-limbic-striatal and NRF2 systems.

The medical, research and general community is unable to effect significantly decreased rates of central obesity and related type II diabetes mellitus (TIIDM), cardiovascular disease (CVD) and cancer. All conditions seem to be linked by the concept of the metabolic syndrome (MetS), but the underlying causes are not known. MetS markers may have been mistaken for causes, thus many treatments are destined to be suboptimal.

The current paper aims to critique current paradigms, give explanations for their persistence, and to return to first principles in an attempt to determine and clarify likely causes of MetS and obesity related comorbidities. A wide literature has been mined, study concepts analysed and the basics of human evolution and new biochemistry reviewed. A plausible, multifaceted composite unifying theory is formulated.

The basis of the theory is that the proportionately large, energy-demanding human brain may have driven co-adaptive mechanisms to provide, or conserve, energy for the brain. A ‘dual system’ is proposed. 1) The enlarged, complex cortico-limbic-striatal system increases dietary energy by developing strong neural self-reward/motivation pathways for the acquisition of energy dense food, and (2) the nuclear factor-erythroid 2-related factor 2 (NRF2) cellular protection system amplifies antioxidant, antitoxicant and repair activity by employing plant chemicals, becoming highly energy efficient in humans.

The still-evolving, complex human cortico-limbic-striatal system generates strong behavioural drives for energy dense food procurement, including motivating agricultural technologies and social system development. Addiction to such foods, leading to neglect of nutritious but less appetizing ‘common or garden’ food, appears to have occurred. Insufficient consumption of food micronutrients prevents optimal human NRF2 function. Inefficient oxidation of excess energy forces central and non-adipose cells to store excess toxic lipid. Oxidative stress and metabolic inflammation, or metaflammation, allow susceptibility to infectious, degenerative atherosclerotic cardiovascular, autoimmune, neurodegenerative and dysplastic diseases.

Other relevant human-specific co-adaptations are examined, and encompass the unusual ability to store fat, certain vitamin pathways, the generalised but flexible intestine and microbiota, and slow development and longevity.

This theory has significant past and future corollaries, which are explored in a separate article by McGill, A-T, in Archives of Public Health, 72: 31.

Phosphorylation of serine 349 of p62 in Alzheimer's disease brain

Background

Extensive research on p62 has established its role in oxidative stress, protein degradation and in several diseases such as Paget’s disease of the bone, frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Importantly, previous studies showed that p62 binds directly to Keap1, which is a ubiquitin E3 ligase responsible for degrading Nrf2. Indeed, colocalisation of p62 and Keap1 occurs in tumorigenesis and neurodegeneration. A serine (S) residue in the Keap1-interacting region of p62 is phosphorylated in hepatocellular carcinoma, and this phosphorylation contributes to tumour growth through the higher affinity of p62 to Keap1. However, it remains largely unknown whether p62 is phosphorylated in the Keap1-interacting region under neurodegenerative conditions.

Results

To answer this question, we generated an antibody against phosphorylated S349 (P-S349) of p62 and showed that S349 is phosphorylated following disruption of protein degradation. In particular, the ratio of P-S349 to total p62 levels was significantly increased in the brains with Alzheimer’s disease (AD) compared with controls. We also compared the reactivity of the P-S349 antibody with P-S403 of p62 and showed that these two phosphorylated sites on p62 cause different responses with proteasome inhibition and show distinct localisation patterns in AD brains. In addition to disruption of protein degradation systems, activation of oxidative stress can induce P-S349.

Conclusion

These results support the hypothesis that disruption of protein degradation systems and sustained activation of the Keap1-Nrf2 system occur in the brains with AD.

Electronic supplementary material

The online version of this article (doi:10.1186/2051-5960-2-50) contains supplementary material, which is available to authorized users.

Genetic, transcriptomic, and epigenetic studies of HIV-associated neurocognitive disorder

The Human Genome Project, coupled with rapidly evolving high-throughput technologies, has opened the possibility of identifying heretofore unknown biological processes underlying human disease. Because of the opaque nature of HIV-associated neurocognitive disorder (HAND) neuropathogenesis, the utility of such methods has gained notice among NeuroAIDS researchers. Furthermore, the merging of genetics with other research areas has also allowed for application of relatively nascent fields, such as neuroimaging genomics, and pharmacogenetics, to the context of HAND. In this review, we detail the development of genetic, transcriptomic, and epigenetic studies of HAND, beginning with early candidate gene association studies and culminating in current "omics" approaches that incorporate methods from systems biology to interpret data from multiple levels of biological functioning. Challenges with this line of investigation are discussed, including the difficulty of defining a valid phenotype for HAND. We propose that leveraging known associations between biology and pathology across multiple levels will lead to a more reliable and valid phenotype. We also discuss the difficulties of interpreting the massive and multitiered mountains of data produced by current high-throughput omics assays and explore the utility of systems biology approaches in this regard.

Reprint of: Nrf2/ARE-mediated antioxidant actions of pro-electrophilic drugs

Living cells maintain a balance between oxidation and reduction, and perturbations of this redox balance are thought to contribute to various diseases. Recent attempts to regulate redox state have focused on electrophiles (EPs), which activate potent cellular defense systems against oxidative stress. One example of this approach is exemplified by carnosic acid (CA) and carnosol (CS), compounds that are found in the herb rosemary (Rosmarinus officinalis). Importantly, CA and CS themselves are not electrophilic, but in response to oxidation, become electrophilic, and then activate the Keap1/Nrf2/ARE (antioxidant-response element) transcription pathway to synthesize endogenous antioxidant "phase 2"enzymes. As a result of our efforts to develop these compounds as therapeutics for brain health, we have formulated two innovative criteria for drug development: the first concept is the use of pro-electrophilic drugs (PEDs) that are innocuous in and of themselves; and the second concept involves the use of compounds that are pathologically activated therapeutics (PATs); i.e., these small molecules are chemically converted to their active form by the very oxidative stress that they are designed to then combat. The chemical basis for PED and PAT drugs is embodied in the ortho- and para-hydroquinone electrophilic cores of the molecules, which are oxidized by the Cu(2+)/Cu(+) cycling system (or potentially by other transition metals). Importantly, this cycling pathway is under stringent regulation by the cell redox state. We propose that redox-dependent quinone formation is the predominant mechanism for formation of PED and PAT drugs from their precursor compounds. In fact, redox-dependent generation of the active form of drug from the "pro-form" distinguishes this therapeutic approach from traditional EPs such as curcumin, and results in a decrease in clinical side effects at therapeutic concentrations, e.g., lack of reaction with other thiols such as glutathione (GSH), which can result in lowering GSH and inducing oxidative stress in normal cells. We consider this pro-drug quality of PED/PAT compounds to be a key factor for generating drugs to be used to combat neurodegenerative diseases that will be clinically tolerated. Given the contribution of oxidative stress to the pathology of multiple neurodegenerative diseases, the Keap1/Nrf2/ARE pathway represents a promising drug target for these PED/PAT agents.

Nrf2/ARE-mediated antioxidant actions of pro-electrophilic drugs

Living cells maintain a balance between oxidation and reduction, and perturbations of this redox balance are thought to contribute to various diseases. Recent attempts to regulate redox state have focused on electrophiles (EPs), which activate potent cellular defense systems against oxidative stress. One example of this approach is exemplified by carnosic acid (CA) and carnosol (CS), compounds that are found in the herb rosemary (Rosmarinus officinalis). Importantly, CA and CS themselves are not electrophilic, but in response to oxidation, become electrophilic, and then activate the Keap1/Nrf2/ARE (antioxidant-response element) transcription pathway to synthesize endogenous antioxidant "phase 2" enzymes. As a result of our efforts to develop these compounds as therapeutics for brain health, we have formulated two innovative criteria for drug development: the first concept is the use of pro-electrophilic drugs (PEDs) that are innocuous in and of themselves; and the second concept involves the use of compounds that are pathologically activated therapeutics (PATs);i.e., these small molecules are chemically converted to their active form by the very oxidative stress that they are designed to then combat. The chemical basis for PED and PAT drugs is embodied in the ortho- and para-hydroquinone electrophilic cores of the molecules, which are oxidized by the Cu(2+)/Cu(+) cycling system (or potentially by other transition metals). Importantly, this cycling pathway is under stringent regulation by the cell redox state. We propose that redox-dependent quinone formation is the predominant mechanism for formation of PED and PAT drugs from their precursor compounds. In fact, redox-dependent generation of the active form of drug from the "pro-form" distinguishes this therapeutic approach from traditional EPs such as curcumin, and results in a decrease in clinical side effects at therapeutic concentrations, e.g., lack of reaction with other thiols such as glutathione (GSH), which can result in lowering GSH and inducing oxidative stress in normal cells. We consider this pro-drug quality of PED/PAT compoundsto be a key factor for generating drugs to be used to combat neurodegenerative diseases that will be clinically tolerated. Given the contribution of oxidative stress to the pathology of multiple neurodegenerative diseases, the Keap1/Nrf2/ARE pathway represents a promising drug target for these PED/PAT agents.