NADPH-oxidase-derived reactive oxygen species mediate the cerebrovascular dysfunction induced by the amyloid beta peptide

Unraveling neurovascular mysteries: the role of endothelial glycocalyx dysfunction in Alzheimer's disease pathogenesis

While cardiovascular disease, cancer, and human immunodeficiency virus (HIV) mortality rates have decreased over the past 20 years, Alzheimer's Disease (AD) deaths have risen by 145% since 2010. Despite significant research efforts, effective AD treatments remain elusive due to a poorly defined etiology and difficulty in targeting events that occur too downstream of disease onset. In hopes of elucidating alternative treatment pathways, now, AD is commonly being more broadly defined not only as a neurological disorder but also as a progression of a variety of cerebrovascular pathologies highlighted by the breakdown of the blood-brain barrier. The endothelial glycocalyx (GCX), which is an essential regulator of vascular physiology, plays a crucial role in the function of the neurovascular system, acting as an essential vascular mechanotransducer to facilitate ultimate blood-brain homeostasis. Shedding of the cerebrovascular GCX could be an early indication of neurovascular dysfunction and may subsequently progress neurodegenerative diseases like AD. Recent advances in in vitro modeling, gene/protein silencing, and imaging techniques offer new avenues of scrutinizing the GCX's effects on AD-related neurovascular pathology. Initial studies indicate GCX degradation in AD and other neurodegenerative diseases and have begun to demonstrate a possible link to GCX loss and cerebrovascular dysfunction. This review will scrutinize the GCX's contribution to known vascular etiologies of AD and propose future work aimed at continuing to uncover the relationship between GCX dysfunction and eventual AD-associated neurological deterioration.

The role of reactive oxygen species in the regulation of the blood-brain barrier

The blood-brain barrier (BBB) regulates the exchange of metabolites and cells between the blood and brain, and maintains central nervous system homeostasis. Various factors affect BBB barrier functions, including reactive oxygen species (ROS). ROS can act as stressors, damaging biological molecules, but they also serve as secondary messengers in intracellular signaling cascades during redox signaling. The impact of ROS on the BBB has been observed in multiple sclerosis, stroke, trauma, and other neurological disorders, making blocking ROS generation a promising therapeutic strategy for BBB dysfunction. However, it is important to consider ROS generation during normal BBB functioning for signaling purposes. This review summarizes data on proteins expressed by BBB cells that can be targets of redox signaling or oxidative stress. It also provides examples of signaling molecules whose impact may cause ROS generation in the BBB, as well as discusses the most common diseases associated with BBB dysfunction and excessive ROS generation, open questions that arise in the study of this problem, and possible ways to overcome them.

Atherosclerotic burden and cerebral small vessel disease: exploring the link through microvascular aging and cerebral microhemorrhages

Cerebral microhemorrhages (CMHs, also known as cerebral microbleeds) are a critical but frequently underestimated aspect of cerebral small vessel disease (CSVD), bearing substantial clinical consequences. Detectable through sensitive neuroimaging techniques, CMHs reveal an extensive pathological landscape. They are prevalent in the aging population, with multiple CMHs often being observed in a given individual. CMHs are closely associated with accelerated cognitive decline and are increasingly recognized as key contributors to the pathogenesis of vascular cognitive impairment and dementia (VCID) and Alzheimer's disease (AD). This review paper delves into the hypothesis that atherosclerosis, a prevalent age-related large vessel disease, extends its pathological influence into the cerebral microcirculation, thereby contributing to the development and progression of CSVD, with a specific focus on CMHs. We explore the concept of vascular aging as a continuum, bridging macrovascular pathologies like atherosclerosis with microvascular abnormalities characteristic of CSVD. We posit that the same risk factors precipitating accelerated aging in large vessels (i.e., atherogenesis), primarily through oxidative stress and inflammatory pathways, similarly instigate accelerated microvascular aging. Accelerated microvascular aging leads to increased microvascular fragility, which in turn predisposes to the formation of CMHs. The presence of hypertension and amyloid pathology further intensifies this process. We comprehensively overview the current body of evidence supporting this interconnected vascular hypothesis. Our review includes an examination of epidemiological data, which provides insights into the prevalence and impact of CMHs in the context of atherosclerosis and CSVD. Furthermore, we explore the shared mechanisms between large vessel aging, atherogenesis, microvascular aging, and CSVD, particularly focusing on how these intertwined processes contribute to the genesis of CMHs. By highlighting the role of vascular aging in the pathophysiology of CMHs, this review seeks to enhance the understanding of CSVD and its links to systemic vascular disorders. Our aim is to provide insights that could inform future therapeutic approaches and research directions in the realm of neurovascular health.

Using Neuroimaging to Study Cerebral Amyloid Angiopathy and Its Relationship to Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) is characterized by amyloid-β aggregation in the media and adventitia of the leptomeningeal and cortical blood vessels. CAA is one of the strongest vascular contributors to Alzheimer's disease (AD). It frequently co-occurs in AD patients, but the relationship between CAA and AD is incompletely understood. CAA may drive AD risk through damage to the neurovascular unit and accelerate parenchymal amyloid and tau deposition. Conversely, early AD may also drive CAA through cerebrovascular remodeling that impairs blood vessels from clearing amyloid-β. Sole reliance on autopsy examination to study CAA limits researchers' ability to investigate CAA's natural disease course and the effect of CAA on cognitive decline. Neuroimaging allows for in vivo assessment of brain function and structure and can be leveraged to investigate CAA staging and explore its associations with AD. In this review, we will discuss neuroimaging modalities that can be used to investigate markers associated with CAA that may impact AD vulnerability including hemorrhages and microbleeds, blood-brain barrier permeability disruption, reduced cerebral blood flow, amyloid and tau accumulation, white matter tract disruption, reduced cerebrovascular reactivity, and lowered brain glucose metabolism. We present possible areas for research inquiry to advance biomarker discovery and improve diagnostics.

Border-associated macrophages promote cerebral amyloid angiopathy and cognitive impairment through vascular oxidative stress

BACKGROUND

Cerebral amyloid angiopathy (CAA) is a devastating condition common in patients with Alzheimer's disease but also observed in the general population. Vascular oxidative stress and neurovascular dysfunction have been implicated in CAA but the cellular source of reactive oxygen species (ROS) and related signaling mechanisms remain unclear. We tested the hypothesis that brain border-associated macrophages (BAM), yolk sac-derived myeloid cells closely apposed to parenchymal and leptomeningeal blood vessels, are the source of radicals through the Aβ-binding innate immunity receptor CD36, leading to neurovascular dysfunction, CAA, and cognitive impairment.

METHODS

Tg2576 mice and WT littermates were transplanted with CD36-/- or CD36+/+ bone marrow at 12-month of age and tested at 15 months. This approach enables the repopulation of perivascular and leptomeningeal compartments with CD36-/- BAM. Neurovascular function was tested in anesthetized mice equipped with a cranial window in which cerebral blood flow was monitored by laser-Doppler flowmetry. Amyloid pathology and cognitive function were also examined.

RESULTS

The increase in blood flow evoked by whisker stimulation (functional hyperemia) or by endothelial and smooth muscle vasoactivity was markedly attenuated in WT → Tg2576 chimeras but was fully restored in CD36-/- → Tg2576 chimeras, in which BAM ROS production was suppressed. CAA-associated Aβ1-40, but not Aβ1-42, was reduced in CD36-/- → Tg2576 chimeras. Similarly, CAA, but not parenchymal plaques, was reduced in CD36-/- → Tg2576 chimeras. These beneficial vascular effects were associated with cognitive improvement. Finally, CD36-/- mice were able to more efficiently clear exogenous Aβ1-40 injected into the neocortex or the striatum.

CONCLUSIONS

CD36 deletion in BAM suppresses ROS production and rescues the neurovascular dysfunction and damage induced by Aβ. CD36 deletion in BAM also reduced brain Aβ1-40 and ameliorated CAA without affecting parenchyma plaques. Lack of CD36 enhanced the vascular clearance of exogenous Aβ. Restoration of neurovascular function and attenuation of CAA resulted in a near complete rescue of cognitive function. Collectively, these data implicate brain BAM in the pathogenesis of CAA and raise the possibility that targeting BAM CD36 is beneficial in CAA and other conditions associated with vascular Aβ deposition and damage.

Cooperation between neurovascular dysfunction and Aβ in Alzheimer's disease

The amyloid-β (Aβ) hypothesis was once believed to represent the pathogenic process of Alzheimer's disease (AD). However, with the failure of clinical drug development and the increasing understanding of the disease, the Aβ hypothesis has been challenged. Numerous recent investigations have demonstrated that the vascular system plays a significant role in the course of AD, with vascular damage occurring prior to the deposition of Aβ and neurofibrillary tangles (NFTs). The question of how Aβ relates to neurovascular function and which is the trigger for AD has recently come into sharp focus. In this review, we outline the various vascular dysfunctions associated with AD, including changes in vascular hemodynamics, vascular cell function, vascular coverage, and blood-brain barrier (BBB) permeability. We reviewed the most recent findings about the complicated Aβ-neurovascular unit (NVU) interaction and highlighted its vital importance to understanding disease pathophysiology. Vascular defects may lead to Aβ deposition, neurotoxicity, glial cell activation, and metabolic dysfunction; In contrast, Aβ and oxidative stress can aggravate vascular damage, forming a vicious cycle loop.

Border-associated macrophages promote cerebral amyloid angiopathy and cognitive impairment through vascular oxidative stress

Background: Cerebral amyloid angiopathy (CAA) is a devastating condition common in patients with Alzheimer's disease but also observed in the general population. Vascular oxidative stress and neurovascular dysfunction have been implicated in CAA but the cellular source of reactive oxygen species (ROS) and related signaling mechanisms remain unclear. We tested the hypothesis that brain border-associated macrophages (BAM), yolk sac-derived myeloid cells closely apposed to parenchymal and leptomeningeal blood vessels, are the source of radicals through the Aβ-binding innate immunity receptor CD36, leading to neurovascular dysfunction, CAA, and cognitive impairment. Methods: Tg2576 mice and WT littermates were transplanted with CD36 -/- or CD36 +/+ bone marrow at 12-month of age and tested at 15 months. This approach enables the repopulation of perivascular and leptomeningeal compartments with CD36 -/- BAM. Neurovascular function was tested in anesthetized mice equipped with a cranial window in which cerebral blood flow was monitored by laser-Doppler flowmetry. Amyloid pathology and cognitive function were also examined. Results: The increase in blood flow evoked by whisker stimulation (functional hyperemia) or by endothelial and smooth muscle vasoactivity was markedly attenuated in WT®Tg2576 chimeras but was fully restored in CD36 -/- ®Tg2576 chimeras, in which BAM ROS production was suppressed. CAA-associated Aβ 1-40 , but not Aβ 1-42 , was reduced in CD36 -/- ®Tg2576 chimeras. Similarly, CAA, but not parenchymal plaques, was reduced in CD36 -/- ®Tg2576 chimeras. These beneficial vascular effects were associated with cognitive improvement. Finally, CD36 -/- mice were able to more efficiently clear exogenous Aβ 1-40 injected into the neocortex or the striatum. Conclusions: CD36 deletion in BAM suppresses ROS production and rescues the neurovascular dysfunction and damage induced by Aβ. CD36 deletion in BAM also reduced brain Aβ 1-40 and ameliorated CAA without affecting parenchyma plaques. Lack of CD36 enhanced the vascular clearance of exogenous Aβ. Restoration of neurovascular function and attenuation of CAA resulted in a near complete rescue of cognitive function. Collectively, these data implicate CNS BAM in the pathogenesis of CAA and raise the possibility that targeting BAM CD36 is beneficial in CAA and other conditions associated with vascular Aβ deposition and damage.

Effect of β-amyloid on blood-brain barrier properties and function

The deposition of beta-amyloid (Aβ) aggregates in the brain, accompanied by impaired cognitive function, is a characteristic feature of Alzheimer's disease (AD). An important role in this process is played by vascular disorders, in particular, a disturbance of the blood-brain barrier (BBB). The BBB controls the entry of Aβ from plasma to the brain via the receptor for advanced glycation end products (RAGE) and the removal of brain-derived Aβ via the low-density lipoprotein receptor-related protein (LRP1). The balance between the input of Aβ to the brain from the periphery and its output is disturbed during AD. Aβ changes the redox-status of BBB cells, which in turn changes the functioning of mitochondria and disrupts the barrier function of endothelial cells by affecting tight junction proteins. Aβ oligomers have the greatest toxic effect on BBB cells, and oligomers are most rapidly transferred by transcytosis from the brain side of the BBB to the blood side. Both the cytotoxic effect of Aβ and the impairment of barrier function are partly due to the interaction of Aβ monomers and oligomers with membrane-bound RAGE. AD therapies based on the disruption of this interaction or the creation of decoys for Aβ are being developed. The question of the transfer of various Aβ isoforms through the BBB is important, since it can influence the development of AD. It is shown that the rate of input of Aβ40 and Aβ42 from the blood into the brain is different. The actual question of the transfer of pathogenic Aβ isoforms with post-translational modifications or mutations through the BBB still remains open.

Vascular oxidative stress causes neutrophil arrest in brain capillaries, leading to decreased cerebral blood flow and contributing to memory impairment in a mouse model of Alzheimer’s disease

INTRODUCTION

In this study, we explore the role of oxidative stress produced by NOX2-containing NADPH oxidase as a molecular mechanism causing capillary stalling and cerebral blood flow deficits in the APP/PS1 mouse model of AD.

METHODS

We inhibited NOX2 in APP/PS1 mice by administering a 10 mg/kg dose of the peptide inhibitor gp91-ds-tat i.p., for two weeks. We used in vivo two-photon imaging to measure capillary stalling, penetrating arteriole flow, and vascular inflammation. We also characterized short-term memory function and gene expression changes in cerebral microvessels.

RESULTS

We found that after NOX2 inhibition capillary stalling, as well as parenchymal and vascular inflammation, were significantly reduced. In addition, we found a significant increase in penetrating arteriole flow, followed by an improvement in short-term memory, and downregulation of inflammatory gene expression pathways.

DISCUSSION

Oxidative stress is a major mechanism leading to microvascular dysfunction in AD, and represents an important therapeutic target.

Microglial inflammatory reactions regulated by oxidative stress

Microglia are immune cells in the brain that can respond to endogenous and exogenous substrates to elicit inflammatory reactions. The transcription factor nuclear factor kappa-light-chain-enhancer of activated B induces proinflammatory gene expression in response to foreign matter via pattern recognition receptors; thus, nuclear factor kappa-light-chain-enhancer of activated B is a master regulator of inflammation. During the inflammatory process, very large amounts of reactive oxygen species are generated and promote the onset and progression of inflammation. Interestingly, nuclear factor kappa-light-chain-enhancer of activated B drives the transcription of superoxide dismutase 2 in many types of cells, including microglia. Superoxide dismutase 2 is an antioxidative enzyme that catalyzes the dismutation of superoxide anions into molecular oxygen and hydrogen peroxide. Of note, nuclear factor kappa-light-chain-enhancer of activated B can initiate inflammation to elicit proinflammatory gene expression, while its transcription product superoxide dismutase 2 can suppress inflammation. In this review, we use recent knowledge to describe the interaction between oxidative stress and nuclear factor kappa-light-chain-enhancer of activated B and discuss the complicated role of microglial superoxide dismutase 2 in inflammation.

Microglia-Mediated Neurovascular Unit Dysfunction in Alzheimer's Disease

The neurovascular unit (NVU) is involved in the pathological changes in Alzheimer's disease (AD). The NVU is a structural and functional complex that maintains microenvironmental homeostasis and metabolic balance in the central nervous system. As one of the most important components of the NVU, microglia not only induce blood-brain barrier breakdown by promoting neuroinflammation, the infiltration of peripheral white blood cells and oxidative stress but also mediate neurovascular uncoupling by inducing mitochondrial dysfunction in neurons, abnormal contraction of cerebral vessels, and pericyte loss in AD. In addition, microglia-mediated dysfunction of cellular components in the NVU, such as astrocytes and pericytes, can destroy the integrity of the NVU and lead to NVU impairment. Therefore, we review the mechanisms of microglia-mediated NVU dysfunction in AD. Furthermore, existing therapeutic advancements aimed at restoring the function of microglia and the NVU in AD are discussed. Finally, we predict the role of pericytes in microglia-mediated NVU dysfunction in AD is the hotspot in the future.

The Hidden Notes of Redox Balance in Neurodegenerative Diseases

Reactive oxygen species (ROS) are versatile molecules that, even if produced in the background of many biological processes and responses, possess pleiotropic roles categorized in two interactive yet opposite domains. In particular, ROS can either function as signaling molecules that shape physiological cell functions, or act as deleterious end products of unbalanced redox reactions. Indeed, cellular redox status needs to be tightly regulated to ensure proper cellular functioning, and either excessive ROS accumulation or the dysfunction of antioxidant systems can perturb the redox homeostasis, leading to supraphysiological concentrations of ROS and potentially harmful outcomes. Therefore, whether ROS would act as signaling molecules or as detrimental factors strictly relies on a dynamic equilibrium between free radical production and scavenging resources. Of notice, the mammalian brain is particularly vulnerable to ROS-mediated toxicity, because it possesses relatively poor antioxidant defenses to cope with the redox burden imposed by the elevated oxygen consumption rate and metabolic activity. Many features of neurodegenerative diseases can in fact be traced back to causes of oxidative stress, which may influence both the onset and progression of brain demise. This review focuses on the description of the dual roles of ROS as double-edge sword in both physiological and pathological settings, with reference to Alzheimer's and Parkinson's diseases.

Nox2 underpins microvascular inflammation and vascular contributions to cognitive decline

Chronic microvascular inflammation and oxidative stress are inter-related mechanisms underpinning white matter disease and vascular cognitive impairment (VCI). A proposed mediator is nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (Nox2), a major source of reactive oxygen species (ROS) in the brain. To assess the role of Nox2 in VCI, we studied a tractable model with white matter pathology and cognitive impairment induced by bilateral carotid artery stenosis (BCAS). Mice with genetic deletion of Nox2 (Nox2 KO) were compared to wild-type (WT) following BCAS. Sustained BCAS over 12 weeks in WT mice induced Nox2 expression, indices of microvascular inflammation and oxidative damage, along with white matter pathology culminating in a marked cognitive impairment, which were all protected by Nox2 genetic deletion. Neurovascular coupling was impaired in WT mice post-BCAS and restored in Nox2 KO mice. Increased vascular expression of chemoattractant mediators, cell-adhesion molecules and endothelial activation factors in WT mice post-BCAS were ameliorated by Nox2 deficiency. The clinical relevance was confirmed by increased vascular Nox2 and indices of microvascular inflammation in human post-mortem subjects with cerebral vascular disease. Our results support Nox2 activity as a critical determinant of VCI, whose targeting may be of therapeutic benefit in cerebral vascular disease.

The Protective Effect of Ubiquinone against the Amyloid Peptide in Endothelial Cells Is Isoprenoid Chain Length-Dependent

Vascular brain pathology constitutes a common feature in neurodegenerative diseases that could underlie their development. Indeed, vascular dysfunction acts synergistically with neurodegenerative changes to exacerbate the cognitive impairment found in Alzheimer’s disease. Different injuries such as hypertension, high glucose, atherosclerosis associated with oxidized low-density lipoprotein or inflammation induce NADPH oxidase activation, overproduction of reactive oxygen species, and apoptosis in endothelial cells. Since it has been shown that pretreatment of cultured endothelial cells with the lipophilic antioxidant coenzyme Q10 (CoQ10) displays a protective effect against the deleterious injuries caused by different agents, this study explores the cytoprotective role of different CoQs homologues against Aβ_25–35-induced damage and demonstrates that only pretreatment with CoQ10 protects endothelial brain cells from Aβ_25–35-induced damage. Herein, we show that CoQ10 constitutes the most effective ubiquinone in preventing NADPH oxidase activity and reducing both reactive oxygen species generation and the increase in free cytosolic Ca²⁺ induced by Aβ_25–35, ultimately preventing apoptosis and necrosis. The specific cytoprotective effect of CoQ with a side chain of 10 isoprenoid units could be explained by the fact that CoQ10 is the only ubiquinone that significantly reduces the entry of Aβ_25–35 into the mitochondria.

Peptide Targeting of PDZ-Dependent Interactions as Pharmacological Intervention in Immune-Related Diseases

PDZ (postsynaptic density (PSD95), discs large (Dlg), and zonula occludens (ZO-1)-dependent interactions are widely distributed within different cell types and regulate a variety of cellular processes. To date, some of these interactions have been identified as targets of small molecules or peptides, mainly related to central nervous system disorders and cancer. Recently, the knowledge of PDZ proteins and their interactions has been extended to various cell types of the immune system, suggesting that their targeting by viral pathogens may constitute an immune evasion mechanism that favors viral replication and dissemination. Thus, the pharmacological modulation of these interactions, either with small molecules or peptides, could help in the control of some immune-related diseases. Deeper structural and functional knowledge of this kind of protein–protein interactions, especially in immune cells, will uncover novel pharmacological targets for a diversity of clinical conditions.

NADPH Oxidases in the Central Nervous System: Regional and Cellular Localization and the Possible Link to Brain Diseases

Significance: The significant role of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) in signal transduction is mediated by the production of reactive oxygen species (ROS), especially in the central nervous system (CNS). The pathogenesis of some neurologic and psychiatric diseases is regulated by ROS, acting as a second messenger or pathogen. Recent Advances: In the CNS, the involvement of Nox-derived ROS has been implicated in the regulation of multiple signals, including cell survival/apoptosis, neuroinflammation, migration, differentiation, proliferation, and synaptic plasticity, as well as the integrity of the blood/brain barrier. In these processes, the intracellular signals mediated by the members of the Nox family vary among different tissues. The present review illuminates the regions and cellular, subcellular localization of Nox isoforms in the brain, the signal transduction, and the role of NOX enzymes in pathophysiology, respectively. Critical Issues: Different signal transduction cascades are coupled to ROS derived from various Nox homologues with varying degrees. Therefore, a critical issue worth noting is the varied role of the homologues of NOX enzymes in different signaling pathways and also they mediate different phenotypes in the diverse pathophysiological condition. This substantiates the effectiveness of selective Nox inhibitors in the CNS. Future Directions: Further investigation to elucidate the role of various homologues of NOX enzymes in acute and chronic brain diseases and signaling mechanisms, and the development of more specific NOX inhibitors for the treatment of CNS disease are urgently needed. Antioxid. Redox Signal. 35, 951-973.

Role of the Extracellular Matrix in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disease with complex pathological characteristics, whose etiology and pathogenesis are still unclear. Over the past few decades, the role of the extracellular matrix (ECM) has gained importance in neurodegenerative disease. In this review, we describe the role of the ECM in AD, focusing on the aspects of synaptic transmission, amyloid-β-plaque generation and degradation, Tau-protein production, oxidative-stress response, and inflammatory response. The function of ECM in the pathological process of AD will inform future research on the etiology and pathogenesis of AD.

Causes and consequences of baseline cerebral blood flow reductions in Alzheimer's disease

Reductions of baseline cerebral blood flow (CBF) of ∼10-20% are a common symptom of Alzheimer's disease (AD) that appear early in disease progression and correlate with the severity of cognitive impairment. These CBF deficits are replicated in mouse models of AD and recent work shows that increasing baseline CBF can rapidly improve the performance of AD mice on short term memory tasks. Despite the potential role these data suggest for CBF reductions in causing cognitive symptoms and contributing to brain pathology in AD, there remains a poor understanding of the molecular and cellular mechanisms causing them. This review compiles data on CBF reductions and on the correlation of AD-related CBF deficits with disease comorbidities (e.g. cardiovascular and genetic risk factors) and outcomes (e.g. cognitive performance and brain pathology) from studies in both patients and mouse models, and discusses several potential mechanisms proposed to contribute to CBF reductions, based primarily on work in AD mouse models. Future research aimed at improving our understanding of the importance of and interplay between different mechanisms for CBF reduction, as well as at determining the role these mechanisms play in AD patients could guide the development of future therapies that target CBF reductions in AD.

Oxidative stress induced by NOX2 contributes to neuropathic pain via plasma membrane translocation of PKCε in rat dorsal root ganglion neurons

Background

Nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2)-induced oxidative stress, including the production of reactive oxygen species (ROS) and hydrogen peroxide, plays a pivotal role in neuropathic pain. Although the activation and plasma membrane translocation of protein kinase C (PKC) isoforms in dorsal root ganglion (DRG) neurons have been implicated in multiple pain models, the interactions between NOX2-induced oxidative stress and PKC remain unknown.

Methods

A spared nerve injury (SNI) model was established in adult male rats. Pharmacologic intervention and AAV-shRNA were applied locally to DRGs. Pain behavior was evaluated by Von Frey tests. Western blotting and immunohistochemistry were performed to examine the underlying mechanisms. The excitability of DRG neurons was recorded by whole-cell patch clamping.

Results

SNI induced persistent NOX2 upregulation in DRGs for up to 2 weeks and increased the excitability of DRG neurons, and these effects were suppressed by local application of gp91-tat (a NOX2-blocking peptide) or NOX2-shRNA to DRGs. Of note, the SNI-induced upregulated expression of PKCε but not PKC was decreased by gp91-tat in DRGs. Mechanical allodynia and DRG excitability were increased by ψεRACK (a PKCε activator) and reduced by εV1-2 (a PKCε-specific inhibitor). Importantly, εV1-2 failed to inhibit SNI-induced NOX2 upregulation. Moreover, the SNI-induced increase in PKCε protein expression in both the plasma membrane and cytosol in DRGs was attenuated by gp91-tat pretreatment, and the enhanced translocation of PKCε was recapitulated by H₂O₂ administration. SNI-induced upregulation of PKCε was blunted by phenyl-N-tert-butylnitrone (PBN, an ROS scavenger) and the hydrogen peroxide catalyst catalase. Furthermore, εV1-2 attenuated the mechanical allodynia induced by H₂O₂

Conclusions

NOX2-induced oxidative stress promotes the sensitization of DRGs and persistent pain by increasing the plasma membrane translocation of PKCε.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02155-6.

A Fundamental Role for Oxidants and Intracellular Calcium Signals in Alzheimer's Pathogenesis-And How a Comprehensive Antioxidant Strategy May Aid Prevention of This Disorder

Oxidative stress and increased cytoplasmic calcium are key mediators of the detrimental effects on neuronal function and survival in Alzheimer's disease (AD). Pathways whereby these perturbations arise, and then prevent dendritic spine formation, promote tau hyperphosphorylation, further amplify amyloid β generation, and induce neuronal apoptosis, are described. A comprehensive program of nutraceutical supplementation, comprised of the NADPH oxidase inhibitor phycocyanobilin, phase two inducers, the mitochondrial antioxidant astaxanthin, and the glutathione precursor N-acetylcysteine, may have important potential for antagonizing the toxic effects of amyloid β on neurons and thereby aiding prevention of AD. Moreover, nutraceutical antioxidant strategies may oppose the adverse impact of amyloid β oligomers on astrocyte clearance of glutamate, and on the ability of brain capillaries to export amyloid β monomers/oligomers from the brain. Antioxidants, docosahexaenoic acid (DHA), and vitamin D, have potential for suppressing microglial production of interleukin-1β, which potentiates the neurotoxicity of amyloid β. Epidemiology suggests that a health-promoting lifestyle, incorporating a prudent diet, regular vigorous exercise, and other feasible measures, can cut the high risk for AD among the elderly by up to 60%. Conceivably, complementing such lifestyle measures with long-term adherence to the sort of nutraceutical regimen outlined here may drive down risk for AD even further.

Implication of Nicotinamide Adenine Dinucleotide Phosphate (NADPH) Oxidase and Its Inhibitors in Alzheimer's Disease Murine Models

Alzheimer’s disease (AD) is one of the main human dementias around the world which is constantly increasing every year due to several factors (age, genetics, environment, etc.) and there are no prevention or treatment options to cure it. AD is characterized by memory loss associated with oxidative stress (OS) in brain cells (neurons, astrocytes, microglia, etc.). OS can be produced by amyloid beta (Aβ) protein aggregation and its interaction with metals, mitochondrial damage and alterations between antioxidants and oxidant enzymes such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. NADPH oxidase produces reactive oxygen species (ROS) and it is overexpressed in AD, producing large amounts of superoxide anions and hydrogen peroxide which damage brain cells and the vasculature. In addition, it has been reported that NADPH oxidase causes an imbalance of pH which could also influence in the amyloid beta (Aβ) production. Therefore, NADPH oxidase had been proposed as a therapeutic target in AD. However, there are no drugs for AD treatment such as an NADPH oxidase inhibitor despite great efforts made to stabilize the ROS production using antioxidant molecules. So, in this work, we will focus our attention on NADPH oxidase (NOX2 and NOX4) in AD as well as in AD models and later discuss the use of NADPH oxidase inhibitor compounds in AD.

Ubiquinol Supplementation Improves Gender-Dependent Cerebral Vasoreactivity and Ameliorates Chronic Inflammation and Endothelial Dysfunction in Patients with Mild Cognitive Impairment

Ubiquinol can protect endothelial cells from multiple mechanisms that cause endothelial damage and vascular dysfunction, thus contributing to dementia. A total of 69 participants diagnosed with mild cognitive impairment (MCI) received either 200 mg/day ubiquinol (Ub) or placebo for 1 year. Cognitive assessment of patients was performed at baseline and after 1 year of follow-up. Patients' cerebral vasoreactivity was examined using transcranial Doppler sonography, and levels of Ub and lipopolysaccharide (LPS) in plasma samples were quantified. Cell viability and necrotic cell death were determined using the microvascular endothelial cell line bEnd3. Coenzyme Q10 (CoQ) levels increased in patients supplemented for 1 year with ubiquinol versus baseline and the placebo group, although higher levels were observed in male patients. The higher cCoQ concentration in male patients improved cerebral vasoreactivity CRV and reduced inflammation, although the effect of Ub supplementation on neurological improvement was negligible in this study. Furthermore, plasma from Ub-supplemented patients improved the viability of endothelial cells, although only in T2DM and hypertensive patients. This suggests that ubiquinol supplementation could be recommended to reach a concentration of 5 μg/mL in plasma in MCI patients as a complement to conventional treatment.

In Vivo/Ex Vivo EPR Investigation of the Brain Redox Status and Blood-Brain Barrier Integrity in the 5xFAD Mouse Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by cognitive decline and total brain atrophy. Despite the substantial scientific effort, the pathological mechanisms underlying neurodegeneration in AD are currently unknown. In most studies, amyloid β peptide has been considered the key pathological change in AD. However, numerous Aβ-targeting treatments have failed in clinical trials. This implies the need to shift the research focus from Aβ to other pathological features of the disease.

OBJECTIVE

The aim of this study was to examine the interplay between mitochondrial dysfunction, oxidative stress and blood-brain barrier (BBB) disruption in AD pathology, using a novel approach that involves the application of electron paramagnetic resonance (EPR) spectroscopy.

METHODS

In vivo and ex vivo EPR spectroscopy using two spin probes (aminoxyl radicals) exhibiting different cell-membrane and BBB permeability were employed to assess BBB integrity and brain tissue redox status in the 5xFAD mouse model of AD. In vivo spin probe reduction decay was analyzed using a two-compartment pharmacokinetic model. Furthermore, 15 K EPR spectroscopy was employed to investigate the brain metal content.

RESULTS

This study has revealed an altered brain redox state, BBB breakdown, as well as ROS-mediated damage to mitochondrial iron-sulfur clusters, and up-regulation of MnSOD in the 5xFAD model.

CONCLUSION

The EPR spin probes were shown to be excellent in vivo reporters of the 5xFAD neuronal tissue redox state, as well as the BBB integrity, indicating the importance of in vivo EPR spectroscopy application in preclinical studies of neurodegenerative diseases.

Retinal biomarkers for Alzheimer's disease and vascular cognitive impairment and dementia (VCID): implication for early diagnosis and prognosis

Cognitive impairment and dementia are major medical, social, and economic public health issues worldwide with significant implications for life quality in older adults. The leading causes are Alzheimer's disease (AD) and vascular cognitive impairment/dementia (VCID). In both conditions, pathological alterations of the cerebral microcirculation play a critical pathogenic role. Currently, the main pathological biomarkers of AD-β-amyloid peptide and hyperphosphorylated tau proteins-are detected either through cerebrospinal fluid (CSF) or PET examination. Nevertheless, given that they are invasive and expensive procedures, their availability is limited. Being part of the central nervous system, the retina offers a unique and easy method to study both neurodegenerative disorders and cerebral small vessel diseases in vivo. Over the past few decades, a number of novel approaches in retinal imaging have been developed that may allow physicians and researchers to gain insights into the genesis and progression of cerebromicrovascular pathologies. Optical coherence tomography (OCT), OCT angiography, fundus photography, and dynamic vessel analyzer (DVA) are new imaging methods providing quantitative assessment of retinal structural and vascular indicators-such as thickness of the inner retinal layers, retinal vessel density, foveal avascular zone area, tortuosity and fractal dimension of retinal vessels, and microvascular dysfunction-for cognitive impairment and dementia. Should further studies need to be conducted, these retinal alterations may prove to be useful biomarkers for screening and monitoring dementia progression in clinical routine. In this review, we seek to highlight recent findings and current knowledge regarding the application of retinal biomarkers in dementia assessment.

Increases in hypertension-induced cerebral microhemorrhages exacerbate gait dysfunction in a mouse model of Alzheimer's disease

Clinical studies show that cerebral amyloid angiopathy (CAA) associated with Alzheimer's disease (AD) and arterial hypertension are independent risk factors for cerebral microhemorrhages (CMHs). To test the hypothesis that amyloid pathology and hypertension interact to promote the development of CMHs, we induced hypertension in the Tg2576 mouse model of AD and respective controls by treatment with angiotensin II (Ang II) and the NO synthesis inhibitor L-NAME. The number, size, localization, and neurological consequences (gait alterations) of CMHs were compared. We found that compared to control mice, in TG2576 mice, the same level of hypertension led to significantly increased CMH burden and exacerbation of CMH-related gait alterations. In hypertensive TG2576 mice, CMHs were predominantly located in the cerebral cortex at the cortical-subcortical boundary, mimicking the clinical picture seen in patients with CAA. Collectively, amyloid pathologies exacerbate the effects of hypertension, promoting the genesis of CMHs, which likely contribute to their deleterious effects on cognitive function. Therapeutic strategies for prevention of CMHs that reduce blood pressure and preserve microvascular integrity are expected to exert neuroprotective effects in high-risk elderly AD patients.

Excitotoxicity as a Target Against Neurodegenerative Processes

The global burden of neurodegenerative diseases is alarmingly increasing in parallel to the aging of population. Although the molecular mechanisms leading to neurodegeneration are not completely understood, excitotoxicity, defined as the injury and death of neurons due to excessive or prolonged exposure to excitatory amino acids, has been shown to play a pivotal role. The increased release and/or decreased uptake of glutamate results in dysregulation of neuronal calcium homeostasis, leading to oxidative stress, mitochondrial dysfunctions, disturbances in protein turn-over and neuroinflammation. Despite the anti-excitotoxic drug memantine has shown modest beneficial effects in some patients with dementia, to date, there is no effective treatment capable of halting or curing neurodegenerative diseases such as Alzheimer's disease, Parkinson disease, Huntington's disease or amyotrophic lateral sclerosis. This has led to a growing body of research focusing on understanding the mechanisms associated with the excitotoxic insult and on uncovering potential therapeutic strategies targeting these mechanisms. In the present review, we examine the molecular mechanisms related to excitotoxic cell death. Moreover, we provide a comprehensive and updated state of the art of preclinical and clinical investigations targeting excitotoxic- related mechanisms in order to provide an effective treatment against neurodegeneration.

p47phox deficiency improves cognitive impairment and attenuates tau hyperphosphorylation in mouse models of AD

Background

Alzheimer’s disease (AD) is characterized by progressive memory loss and cognitive impairment. The aggregation of amyloid β (Aβ) and hyperphosphorylated tau protein are two major pathological features of AD. Nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase, NOX) has been indicated in Aβ pathology; however, whether and how it affects tau pathology are not yet clear.

Methods

The role of NOX2 in cognitive function, amyloid plaque formation, and tau hyperphosphorylation were examined in APP/PS1 transgenic mice mated with p47^phox-deficient mice (with deletion of the gene of neutrophil cytosolic factor 1, Ncf1) and/or in p47^phox-deficient mice receiving intracerebroventricular (ICV) injection of streptozotocin (STZ). The cognitive and non-cognitive functions in these mice were assessed by Morris water maze, Rotarod test, open field, and elevated plus maze. Aβ levels, amyloid plaques, p47^phox expression, and astrocyte activation were evaluated using immunofluorescence staining, ELISA, and/or Western blotting. Cultured primary neuronal cells were treated with okadaic acid or conditioned media (CM) from high glucose-stimulated primary astrocytes. The alteration in tau pathology was determined using Western blotting and immunofluorescence staining.

Results

Deletion of the gene coding for p47^phox, the organizer subunit of NOX2, significantly attenuated cognitive impairment and tau pathology in these mice. p47^phox deficiency decreased the activation of astrocytes but had no effect on Aβ levels and amyloid plaque formation in the brains of aged APP/PS1 mice, which displayed markedly increased expression of p47^phox in neurons and astrocytes. Cell culture studies found that neuronal p47^phox deletion attenuated okadaic acid-induced tau hyperphosphorylation at specific sites in primary cultures of neurons. CM from high glucose-treated WT astrocytes increased tau hyperphosphorylation in primary neurons, whereas this effect was absent from p47^phox-deficient astrocytes.

Conclusions

These results suggest that p47^phox is associated with cognitive function and tau pathology in AD. p47^phox expressed in neurons contributes to tau hyperphosphorylation directly, while p47^phox in astrocytes affect tau hyperphosphorylation by activating astrocytes indirectly. Our results provide new insights into the role of NOX2 in AD and indicate that targeted inhibition of p47^phox may be a new strategy for the treatment of AD.

tPA Deficiency Underlies Neurovascular Coupling Dysfunction by Amyloid-β

The amyloid-β (Aβ) peptide, a key pathogenic factor in Alzheimer's disease, attenuates the increase in cerebral blood flow (CBF) evoked by neural activity (functional hyperemia), a vital homeostatic response in which NMDA receptors (NMDARs) play a role through nitric oxide, and the CBF increase produced by endothelial factors. Tissue plasminogen activator (tPA), which is reduced in Alzheimer's disease and in mouse models of Aβ accumulation, is required for the full expression of the NMDAR-dependent component of functional hyperemia. Therefore, we investigated whether tPA is involved in the neurovascular dysfunction of Aβ. tPA activity was reduced, and the tPA inhibitor plasminogen inhibitor-1 (PAI-1) was increased in male mice expressing the Swedish mutation of the amyloid precursor protein (tg2576). Counteracting the tPA reduction with exogenous tPA or with pharmacological inhibition or genetic deletion of PAI-1 completely reversed the attenuation of the CBF increase evoked by whisker stimulation but did not ameliorate the response to the endothelium-dependent vasodilator acetylcholine. The tPA deficit attenuated functional hyperemia by suppressing NMDAR-dependent nitric oxide production during neural activity. Pharmacological inhibition of PAI-1 increased tPA activity, prevented neurovascular uncoupling, and ameliorated cognition in 11- to 12-month-old tg2576 mice, effects associated with a reduction of cerebral amyloid angiopathy but not amyloid plaques. The data unveil a selective role of the tPA in the suppression of functional hyperemia induced by Aβ and in the mechanisms of cerebral amyloid angiopathy, and support the possibility that modulation of the PAI-1-tPA pathway may be beneficial in diseases associated with amyloid accumulation.SIGNIFICANCE STATEMENT Amyloid-β (Aβ) peptides have profound neurovascular effects that may contribute to cognitive impairment in Alzheimer's disease. We found that Aβ attenuates the increases in blood flow evoked by neural activation through a reduction in tissue plasminogen activator (tPA) caused by upregulation of its endogenous inhibitor plasminogen inhibitor-1 (PAI-1). tPA deficiency prevents NMDA receptors from triggering nitric oxide production, thereby attenuating the flow increase evoked by neural activity. PAI-1 inhibition restores tPA activity, rescues neurovascular coupling, reduces amyloid deposition around blood vessels, and improves cognition in a mouse model of Aβ accumulation. The findings demonstrate a previously unappreciated role of tPA in Aβ-related neurovascular dysfunction and in vascular amyloid deposition. Restoration of tPA activity could be of therapeutic value in diseases associated with amyloid accumulation.

New Insights Into Blood-Brain Barrier Maintenance: The Homeostatic Role of β-Amyloid Precursor Protein in Cerebral Vasculature

Cerebrovascular homeostasis is maintained by the blood-brain barrier (BBB), a highly selective structure that separates the peripheral blood circulation from the brain and protects the central nervous system (CNS). Dysregulation of BBB function is the precursor of several neurodegenerative diseases including Alzheimer’s disease (AD) and cerebral amyloid angiopathy (CAA), both related to β-amyloid (Aβ) accumulation and deposition. The origin of BBB dysfunction before and/or during CAA and AD onset is not known. Several studies raise the possibility that vascular dysfunction could be an early step in these diseases and could even precede significant Aβ deposition. Though accumulation of neuron-derived Aβ peptides is considered the primary influence driving AD and CAA pathogenesis, recent studies highlighted the importance of the physiological role of the β-amyloid precursor protein (APP) in endothelial cell homeostasis, suggesting a potential role of this protein in maintaining vascular stability. In this review, we will discuss the physiological function of APP and its cleavage products in the vascular endothelium. We further suggest how loss of APP homeostatic regulation in the brain vasculature could lead toward pathological outcomes in neurodegenerative disorders.

ROS Generation in Microglia: Understanding Oxidative Stress and Inflammation in Neurodegenerative Disease

Neurodegenerative disorders, such as Alzheimer's disease, are a global public health burden with poorly understood aetiology. Neuroinflammation and oxidative stress (OS) are undoubtedly hallmarks of neurodegeneration, contributing to disease progression. Protein aggregation and neuronal damage result in the activation of disease-associated microglia (DAM) via damage-associated molecular patterns (DAMPs). DAM facilitate persistent inflammation and reactive oxygen species (ROS) generation. However, the molecular mechanisms linking DAM activation and OS have not been well-defined; thus targeting these cells for clinical benefit has not been possible. In microglia, ROS are generated primarily by NADPH oxidase 2 (NOX2) and activation of NOX2 in DAM is associated with DAMP signalling, inflammation and amyloid plaque deposition, especially in the cerebrovasculature. Additionally, ROS originating from both NOX and the mitochondria may act as second messengers to propagate immune activation; thus intracellular ROS signalling may underlie excessive inflammation and OS. Targeting key kinases in the inflammatory response could cease inflammation and promote tissue repair. Expression of antioxidant proteins in microglia, such as NADPH dehydrogenase 1 (NQO1), is promoted by transcription factor Nrf2, which functions to control inflammation and limit OS. Lipid droplet accumulating microglia (LDAM) may also represent a double-edged sword in neurodegenerative disease by sequestering peroxidised lipids in non-pathological ageing but becoming dysregulated and pro-inflammatory in disease. We suggest that future studies should focus on targeted manipulation of NOX in the microglia to understand the molecular mechanisms driving inflammatory-related NOX activation. Finally, we discuss recent evidence that therapeutic target identification should be unbiased and founded on relevant pathophysiological assays to facilitate the discovery of translatable antioxidant and anti-inflammatory therapeutics.

Structural and Functional Remodeling of the Brain Vasculature Following Stroke

Maintenance of cerebral blood vessel integrity and regulation of cerebral blood flow ensure proper brain function. The adult human brain represents only a small portion of the body mass, yet about a quarter of the cardiac output is dedicated to energy consumption by brain cells at rest. Due to a low capacity to store energy, brain health is heavily reliant on a steady supply of oxygen and nutrients from the bloodstream, and is thus particularly vulnerable to stroke. Stroke is a leading cause of disability and mortality worldwide. By transiently or permanently limiting tissue perfusion, stroke alters vascular integrity and function, compromising brain homeostasis and leading to widespread consequences from early-onset motor deficits to long-term cognitive decline. While numerous lines of investigation have been undertaken to develop new pharmacological therapies for stroke, only few advances have been made and most clinical trials have failed. Overall, our understanding of the acute and chronic vascular responses to stroke is insufficient, yet a better comprehension of cerebrovascular remodeling following stroke is an essential prerequisite for developing novel therapeutic options. In this review, we present a comprehensive update on post-stroke cerebrovascular remodeling, an important and growing field in neuroscience, by discussing cellular and molecular mechanisms involved, sex differences, limitations of preclinical research design and future directions.

Brain angiotensin II and angiotensin IV receptors as potential Alzheimer's disease therapeutic targets

Alzheimer's disease (AD) is a neurodegenerative disorder that is multifactorial in nature. Yet, despite being the most common form of dementia in the elderly, AD's primary cause remains unknown. As such, there is currently little to offer AD patients as the vast majority of recently tested therapies have either failed in well-controlled clinical trials or inadequately treat AD. Recently, emerging preclinical and clinical evidence has associated the brain renin angiotensin system (RAS) to AD pathology. Accordingly, various components of the brain RAS were shown to be altered in AD patients and mouse models, including the angiotensin II type 1 (AT1R), angiotensin IV receptor (AT4R), and Mas receptors. Collectively, the changes observed within the RAS have been proposed to contribute to many of the neuropathological hallmarks of AD, including the neuronal, cognitive, and vascular dysfunctions. Accumulating evidence has additionally identified antihypertensive medications targeting the RAS, particularly angiotensin receptor blockers (ARBs) and angiotensin-converting enzyme inhibitors (ACEIs), to delay AD onset and progression. In this review, we will discuss the emergence of the RAS's involvement in AD and highlight putative mechanisms of action underlying ARB's beneficial effects that may explain their ability to modify the risk of developing AD or AD progression. The RAS may provide novel molecular targets for recovering memory pathways, cerebrovascular function, and other pathological landmarks of AD.

Novel MRI Techniques Identifying Vascular Leak and Paravascular Flow Reduction in Early Alzheimer Disease

With beta amyloid and tau antibody treatment trial failures, avenues directed to other facets of the disease pathophysiology are being explored to treat in the preclinical or early clinical state. Clear evidence of blood–brain barrier (BBB) breakdown occurring early in the AD process has recently been established. Likewise, the glymphatic system regulating water and solute inflow and outflow in parallel with the vascular system is affected causing delayed clearance of fluid waste. Its dysfunction as a component of AD along with BBB leak are reasonable candidates to explore for future treatments. Ideally, human medication trials require a minimally invasive method of quantifying both improvements in BBB integrity and glymphatic fluid clearance correlated with clinical outcomes. We will review the known physiology and anatomy of the BBB system, and its relationship to the glymphatic system and the microglial surveillance system. Dysfunction of this tripart system occurring in preclinical Alzheimer disease (AD) will be reviewed along with existing MRI tools for identifying altered flow dynamics useful for monitoring improved functionality with future treatments. High-resolution dynamic contrast enhanced MRI imaging demonstrating BBB leak and the recently reported non-invasive 3D PASL MRI pilot study demonstrating significant delay in glymphatic clearance in AD subjects appear to be the best candidates.

Multifarious roles of mTOR signaling in cognitive aging and cerebrovascular dysfunction of Alzheimer's disease

Age-related cognitive failure is a main devastating incident affecting even healthy people. Alzheimer's disease (AD) is the utmost common form of dementia among the geriatric community. In the pathogenesis of AD, cerebrovascular dysfunction is revealed before the beginning of the cognitive decline. Mounting proof shows a precarious impact of cerebrovascular dysregulation in the development of AD pathology. Recent studies document that the mammalian target of rapamycin (mTOR) acts as a crucial effector of cerebrovascular dysregulation in AD. The mTOR contributes to brain vascular dysfunction and subsequence cerebral blood flow deficits as well as cognitive impairment. Furthermore, mTOR causes the blood-brain barrier (BBB) breakdown in AD models. Inhibition of mTOR hyperactivity protects the BBB integrity in AD. Furthermore, mTOR drives cognitive defect and cerebrovascular dysfunction, which are greatly prevalent in AD, but the central molecular mechanisms underlying these alterations are obscure. This review represents the crucial and current research findings regarding the role of mTOR signaling in cognitive aging and cerebrovascular dysfunction in the pathogenesis of AD.

AT2R's (Angiotensin II Type 2 Receptor's) Role in Cognitive and Cerebrovascular Deficits in a Mouse Model of Alzheimer Disease

Antihypertensive medications targeting the renin-angiotensin system have lowered the incidence and progression of Alzheimer disease. Understanding how these medications function could lead to novel therapeutic strategies. AT4Rs (angiotensin IV receptors) have been associated with angiotensin receptor blockers' cognitive, cerebrovascular, and neuroinflammatory rescue in Alzheimer disease models. Yet, whether AT4Rs act alone or with AT2Rs remains unknown. Here, we investigated whether AT2Rs contribute to losartan's benefits and whether chronic AT2R activation could mimic angiotensin receptor blocker benefits in transgenic mice overexpressing familial Alzheimer disease mutations of the human APP (amyloid precursor protein). Losartan-treated mice (10 mg/kg per day, drinking water, 7 months) received intracerebroventricular (1 month) administration of vehicle or AT2R antagonist PD123319 (1.6 nmol/day). PD123319 countered losartan's benefits on spatial learning and memory, neurovascular coupling, and hampered those on oxidative stress and nitric oxide bioavailability. PD123319 did not oppose losartan's benefits on short-term memory and vasodilatory function and had no benefit on neuroinflammation or Aβ (amyloid β) pathology. Mice receiving either vehicle or selective AT2R agonist compound 21 (intracerebroventricular: 1 nmol/day, 1 month or drinking water: 10 mg/kg per day, 7 months), showed no improvement in memory, vasodilatory function, or nitric oxide bioavailability. Compound 21 treatment normalized neurovascular coupling, reduced astrogliosis independent of persisting microgliosis, and exacerbated oxidative stress in APP mice. Compound 21 reduced dense core Aβ plaques, but not diffuse plaques or Aβ species. Our findings suggest that targeting AT2Rs is not an ideal strategy for restoring Aβ-related cognitive and cerebrovascular deficits.

Neuroprotective Properties of Resveratrol and Its Derivatives-Influence on Potential Mechanisms Leading to the Development of Alzheimer's Disease

The lack of effective Alzheimer's disease treatment is becoming a challenge for researchers and prompts numerous attempts to search for and develop better therapeutic solutions. Compounds that affect several routes of the neurodegeneration cascade leading to the development of disease are of particular interest. An example of such substances is resveratrol and its synthetic and natural derivatives, which have gained popularity in recent years and show promise as a possible new therapeutic option in the approach to Alzheimer's disease treatment. In this article, the state of the art evidence on the role of resveratrol (RSV) in neuroprotection is presented; research results are summarized and the importance of resveratrol and its derivatives in the treatment of Alzheimer's disease are underlined. It also focuses on various modifications of the resveratrol molecule that should be taken into account in the design of future research on drugs against Alzheimer's disease.

Transcriptional profiling and therapeutic targeting of oxidative stress in neuroinflammation

Oxidative stress is a central part of innate-immune induced neurodegeneration. However, the transcriptomic landscape of the central nervous system (CNS) innate immune cells contributing to oxidative stress is unknown, and therapies to target their neurotoxic functions are not widely available. Here, we provide the oxidative stress innate immune cell atlas in neuroinflammatory disease, and report the discovery of new druggable pathways. Transcriptional profiling of oxidative stress-producing CNS innate immune cells (Tox-seq) identified a core oxidative stress gene signature coupled to coagulation and glutathione pathway genes shared between a microglia cluster and infiltrating macrophages. Tox-seq followed by a microglia high-throughput screen (HTS) and oxidative stress gene network analysis, identified the glutathione regulating compound acivicin with potent therapeutic effects decreasing oxidative stress and axonal damage in chronic and relapsing multiple sclerosis (MS) models. Thus, oxidative stress transcriptomics identified neurotoxic CNS innate immune populations and may enable the discovery of selective neuroprotective strategies.

Partial loss of endothelial nitric oxide leads to increased cerebrovascular beta amyloid

Cerebral amyloid angiopathy (CAA) is present in over half of the elderly population and in 80-90% of Alzheimer's disease (AD) patients. CAA is defined by the deposition of beta amyloid (Aβ) in small cerebral arteries and capillaries. Cardiovascular risk factors are associated with an increased incidence of CAA. We utilized 18-month-old endothelial nitric oxide synthase (eNOS) heterozygous knockout (^+/-) mice, a clinically relevant model of endothelial dysfunction, to examine the role of endothelial nitric oxide (NO) in vascular Aβ accumulation. eNOS^+/- mice had significantly higher vascular levels of Aβ40 (P < 0.05). Aβ42 was not detected. There was no difference in Aβ in brain tissue. Amyloid precursor protein and β-site APP cleavage enzyme 1 protein levels were unaltered, while levels of the α-secretase enzyme, a disintegrin and metalloproteinase 10, were significantly lower in eNOS ^+ /- microvascular tissue (P < 0.05). Insulin degrading enzyme and low-density lipoprotein receptor-related protein 1 were significantly increased in eNOS^+/- microvascular tissue, most likely an adaptive response to locally higher Aβ concentrations. Lastly, catalase and CuZn superoxide dismutase were significantly elevated in eNOS^+/- microvascular tissue (P < 0.05). These data demonstrate decreased availability of endothelial NO leads to increased cerebrovascular concentration of Aβ along with compensatory mechanisms to protect the vasculature.

Amyloid-β Causes Mitochondrial Dysfunction via a Ca2+-Driven Upregulation of Oxidative Phosphorylation and Superoxide Production in Cerebrovascular Endothelial Cells

Cerebrovascular pathology is pervasive in Alzheimer's disease (AD), yet it is unknown whether cerebrovascular dysfunction contributes to the progression or etiology of AD. In human subjects and in animal models of AD, cerebral hypoperfusion and hypometabolism are reported to manifest during the early stages of the disease and persist for its duration. Amyloid-β is known to cause cellular injury in both neurons and endothelial cells by inducing the production of reactive oxygen species and disrupting intracellular Ca2+ homeostasis. We present a mechanism for mitochondrial degeneration caused by the production of mitochondrial superoxide, which is driven by increased mitochondrial Ca2+ uptake. We found that persistent superoxide production injures mitochondria and disrupts electron transport in cerebrovascular endothelial cells. These observations provide a mechanism for the mitochondrial deficits that contribute to cerebrovascular dysfunction in patients with AD.

Memory and cerebrovascular deficits recovered following angiotensin IV intervention in a mouse model of Alzheimer's disease

Angiotensin II type 1 receptor antagonists like losartan have been found to lower the incidence and progression to Alzheimer's disease (AD), as well as rescue cognitive and cerebrovascular deficits in AD mouse models. We previously found that co-administration of an angiotensin IV (AngIV) receptor (AT4R) antagonist prevented losartan's benefits, identifying AT4Rs as a possible target to counter AD pathogenesis. Therein, we investigated whether directly targeting AT4Rs could counter AD pathogenesis in a well-characterized mouse model of AD. Wild-type and human amyloid precursor protein (APP) transgenic (J20 line) mice (4.5 months old) received vehicle or AngIV (~1.3 nmol/day, 1 month) intracerebroventricularly via osmotic minipumps. AngIV restored short-term memory, spatial learning and memory in APP mice. AngIV normalized hippocampal AT4R levels, increased hippocampal subgranular zone cellular proliferation and dendritic arborization, and reduced oxidative stress. AngIV rescued whisker-evoked neurovascular coupling, endothelial- and smooth muscle cell-mediated cerebral vasodilatory responses, and cerebrovascular nitric oxide bioavailability. AngIV did not alter blood pressure, neuroinflammation or amyloid-β (Aβ) pathology. These preclinical findings identify AT4R as a promising target to counter Aβ-related cognitive and cerebrovascular deficits in AD.

Hypertension Exacerbates Cerebrovascular Oxidative Stress Induced by Mild Traumatic Brain Injury: Protective Effects of the Mitochondria-Targeted Antioxidative Peptide SS-31

Traumatic brain injury (TBI) induces cerebrovascular oxidative stress, which is associated with neurovascular uncoupling, autoregulatory dysfunction, and persisting cognitive decline in both pre-clinical models and patients. However, single mild TBI (mTBI), the most frequent form of brain trauma, increases cerebral generation of reactive oxygen species (ROS) only transiently. We hypothesized that comorbid conditions might exacerbate long-term ROS generation in cerebral arteries after mTBI. Because hypertension is the most important cerebrovascular risk factor in populations prone to mild brain trauma, we induced mTBI in normotensive and spontaneously hypertensive rats (SHR) and assessed changes in cytoplasmic and mitochondrial superoxide (O₂-) production by confocal microscopy in isolated middle cerebral arteries (MCA) 2 weeks after mTBI using dihydroethidine (DHE) and the mitochondria-targeted redox-sensitive fluorescent indicator dye MitoSox. We found that mTBI induced a significant increase in long-term cytoplasmic and mitochondrial O₂- production in MCAs of SHRs and increased expression of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit Nox4, which were reversed to the normal level by treating the animals with the cell-permeable, mitochondria-targeted antioxidant peptide SS-31 (5.7 mg kg^-1 day^-1, i.p.). Persistent mTBI-induced oxidative stress in MCAs of SHRs was significantly decreased by inhibiting vascular NADPH oxidase (apocyinin). We propose that hypertension- and mTBI-induced cerebrovascular oxidative stress likely lead to persistent dysregulation of cerebral blood flow (CBF) and cognitive dysfunction, which might be reversed by SS-31 treatment.

The role of NOX inhibitors in neurodegenerative diseases

Oxidative stress is a key player in both chronic and acute brain disease due to the higher metabolic demand of the brain. Among the producers of free radicals, NADPH-oxidase (NOX) is a major contributor to oxidative stress in neurological disorders. In the brain, the superoxide produced by NOX is mainly found in leukocytes. However, recent studies have reported that it can be found in several other cell types. NOX has been reported to regulate neuronal signaling, memory processing, and central cardiovascular homeostasis. However, overproduction of NOX can contribute to neurotoxicity, CNS degeneration, and cardiovascular disorders. Regarding the above functions, NOX has been shown to play a crucial role in chronic CNS diseases like Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS), and in acute CNS disorders such as stroke, spinal cord injury, traumatic brain injury (TBI), and related cerebrovascular diseases. NOX is a multi-subunit complex consisting of two membrane-associated and four cytosolic subunits. Thus, in recent years, inhibition of NOX activity has drawn a great deal of attention from researchers in the field of treating chronic and acute CNS disorders and preventing secondary complications. Mounting evidence has shown that NOX inhibition is neuroprotective and that inhibiting NOX in circulating immune cells can improve neurological disease conditions. This review summarizes recent studies on the therapeutic effects and pharmacological strategies regarding NOX inhibitors in chronic and acute brain diseases and focuses on the hurdles that should be overcome before their clinical implementation.

Escitalopram Ameliorates Cognitive Impairment in D-Galactose-Injected Ovariectomized Rats: Modulation of JNK, GSK-3β, and ERK Signalling Pathways

Though selective serotonin reuptake inhibitors (SSRIs) have been found to increase cognitive performance in some studies on patients and animal models of Alzheimer's disease (AD), other studies have reported contradictory results, and the mechanism of action has not been fully described. This study aimed to examine the effect of escitalopram, an SSRI, in an experimental model of AD and to determine the involved intracellular signalling pathways. Ovariectomized rats were administered D-galactose (150 mg/kg/day, i.p) over ten weeks to induce AD. Treatment with escitalopram (10 mg/kg/day, p.o) for four weeks, starting from the 7^th week of D-galactose injection, enhanced memory performance and attenuated associated histopathological changes. Escitalopram reduced hippocampal amyloid β 42, β-secretase, and p-tau, while increasing α-secretase levels. Furthermore, it decreased tumor necrosis factor-α, nuclear factor-kappa B p65, and NADPH oxidase, while enhancing brain-derived neurotrophic factor, phospho-cAMP response element binding protein, and synaptophysin levels. Moreover, escitalopram diminished the protein expression of the phosphorylated forms of c-Jun N-terminal kinase (JNK)/c-Jun, while increasing those of phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β), extracellular signal-regulated kinase (ERK) and its upstream kinases MEK and Raf-1. In conclusion, escitalopram ameliorated D-galactose/ovariectomy-induced AD-like features through modulation of PI3K/Akt/GSK-3β, Raf-1/MEK/ERK, and JNK/c-Jun pathways.

The Role of Mitochondrial Dysfunction in the Progression of Alzheimer's Disease

The current molecular understanding of Alzheimer's disease (AD) has still not resulted in successful interventions. Mitochondrial dysfunction of the AD brain is currently emerging as a hallmark of this disease. One mitochondrial function often affected in AD is oxidative phosphorylation responsible for ATP production, but also for production of reactive oxygen species (ROS) and for the de novo synthesis of pyrimidines. This paper reviews the role of mitochondrial produced ROS and pyrimidines in the aetiology of AD and their proposed role in oxidative degeneration of macromolecules, synthesis of essential phospholipids and maintenance of mitochondrial viability in the AD brain.

NADPH oxidase 2 inhibitors CPP11G and CPP11H attenuate endothelial cell inflammation & vessel dysfunction and restore mouse hind-limb flow

First described as essential to the phagocytic activity of leukocytes, Nox2-derived ROS have emerged as mediators of a range of cellular and tissue responses across species from salubrious to deleterious consequences. Knowledge of their role in inflammation is limited, however. We postulated that TNFα-induced endothelial reactive oxygen species (ROS) generation and pro-inflammatory signaling would be ameliorated by targeting Nox2. Herein, we in silico-modelled two first-in-class Nox2 inhibitors developed in our laboratory, explored their cellular mechanism of action and tested their efficacy in in vitro and mouse in vivo models of inflammation. Our data show that these inhibitors (CPP11G and CPP11H) disrupted canonical Nox2 organizing factor, p47^phox, translocation to Nox2 in the plasma membrane; and abolished ROS production, markedly attenuated stress-responsive MAPK signaling and downstream AP-1 and NFκB nuclear translocation in human cells. Consequently, cell adhesion molecule expression and monocyte adherence were significantly inhibited by both inhibitors. In vivo, TNFα-induced ROS and inflammation were ameliorated by targeted Nox2 inhibition, which, in turn, improved hind-limb blood flow. These studies identify a proximal role for Nox2 in propagated inflammatory signaling and support therapeutic value of Nox2 inhibitors in inflammatory disease.

The Plasma Membrane: A Platform for Intra- and Intercellular Redox Signaling

Membranes are of outmost importance to allow for specific signal transduction due to their ability to localize, amplify, and direct signals. However, due to the double-edged nature of reactive oxygen species (ROS)—toxic at high concentrations but essential signal molecules—subcellular localization of ROS-producing systems to the plasma membrane has been traditionally regarded as a protective strategy to defend cells from unwanted side-effects. Nevertheless, specialized regions, such as lipid rafts and caveolae, house and regulate the activated/inhibited states of important ROS-producing systems and concentrate redox targets, demonstrating that plasma membrane functions may go beyond acting as a securing lipid barrier. This is nicely evinced by nicotinamide adenine dinucleotide phosphate (NADPH)-oxidases (NOX), enzymes whose primary function is to generate ROS and which have been shown to reside in specific lipid compartments. In addition, membrane-inserted bidirectional H₂O₂-transporters modulate their conductance precisely during the passage of the molecules through the lipid bilayer, ensuring time-scaled delivery of the signal. This review aims to summarize current evidence supporting the role of the plasma membrane as an organizing center that serves as a platform for redox signal transmission, particularly NOX-driven, providing specificity at the same time that limits undesirable oxidative damage in case of malfunction. As an example of malfunction, we explore several pathological situations in which an inflammatory component is present, such as inflammatory bowel disease and neurodegenerative disorders, to illustrate how dysregulation of plasma-membrane-localized redox signaling impacts normal cell physiology.

Cerebral Aβ40 and systemic hypertension

Mid-life hypertension and cerebral hypoperfusion may be preclinical abnormalities in people who later develop Alzheimer's disease. Although accumulation of amyloid-beta (Aβ) is characteristic of Alzheimer's disease and is associated with upregulation of the vasoconstrictor peptide endothelin-1 within the brain, it is unclear how this affects systemic arterial pressure. We have investigated whether infusion of Aβ₄₀ into ventricular cerebrospinal fluid modulates blood pressure in the Dahl salt-sensitive rat. The Dahl salt-sensitive rat develops hypertension if given a high-salt diet. Intracerebroventricular infusion of Aβ induced a progressive rise in blood pressure in rats with pre-existing hypertension produced by a high-salt diet ( p < 0.0001), but no change in blood pressure in normotensive rats. The elevation in arterial pressure in high-salt rats was associated with an increase in low frequency spectral density in systolic blood pressure, suggesting autonomic imbalance, and reduced cardiac baroreflex gain. Our results demonstrate the potential for intracerebral Aβ to exacerbate hypertension, through modulation of autonomic activity. Present findings raise the possibility that mid-life hypertension in people who subsequently develop Alzheimer's disease may in some cases be a physiological response to reduced cerebral perfusion complicating the accumulation of Aβ within the brain.

Oxidative Stress: A Major Player in Cerebrovascular Alterations Associated to Neurodegenerative Events

The brain is one of the most exquisite organs in the body with high metabolic demands, and requires a tight regulation of the surrounding environment. This tight control is exerted by the neurovascular unit (NVU) comprising different cell types, where endothelial cells play the commander-in-chief role. Thus, it is assumable that even slight perturbations in NVU might affect, in some cases irreversibly, brain homeostasis and health. In this line, recent findings support the two-hit vascular hypothesis for neurodegenerative conditions, where vascular dysfunction underlies the development of neurodegenerative diseases, such as Alzheimer’s disease (AD). Knowing that endothelial cells are rich in mitochondria and nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, two major reactive oxygen species (ROS) sources, this review aims to gather information on how oxidative stress is in the front line of vascular alterations observed in brain aging and neurodegenerative conditions, particularly AD. Also, a brief discussion about the therapeutic strategies aimed to protect against cerebrovascular diseases is included.

Perspectives on How Human Simultaneous Multi-Modal Imaging Adds Directionality to Spread Models of Alzheimer's Disease

Previous animal research suggests that the spread of pathological agents in Alzheimer’s disease (AD) follows the direction of signaling pathways. Specifically, tau pathology has been suggested to propagate in an infection-like mode along axons, from transentorhinal cortices to medial temporal lobe cortices and consequently to other cortical regions, while amyloid-beta (Aβ) pathology seems to spread in an activity-dependent manner among and from isocortical regions into limbic and then subcortical regions. These directed connectivity-based spread models, however, have not been tested directly in AD patients due to the lack of an in vivo method to identify directed connectivity in humans. Recently, a new method—metabolic connectivity mapping (MCM)—has been developed and validated in healthy participants that uses simultaneous FDG-PET and resting-state fMRI data acquisition to identify directed intrinsic effective connectivity (EC). To this end, postsynaptic energy consumption (FDG-PET) is used to identify regions with afferent input from other functionally connected brain regions (resting-state fMRI). Here, we discuss how this multi-modal imaging approach allows quantitative, whole-brain mapping of signaling direction in AD patients, thereby pointing out some of the advantages it offers compared to other EC methods (i.e., Granger causality, dynamic causal modeling, Bayesian networks). Most importantly, MCM provides the basis on which models of pathology spread, derived from animal studies, can be tested in AD patients. In particular, future work should investigate whether tau and Aβ in humans propagate along the trajectories of directed connectivity in order to advance our understanding of the neuropathological mechanisms causing disease progression.