Hippocampal T cell infiltration promotes neuroinflammation and cognitive decline in a mouse model of tauopathy

Microglia prevent peripheral immune cell invasion and promote an anti-inflammatory environment in the brain of APP-PS1 transgenic mice

Background

Undoubtedly, neuroinflammation is a major contributor to Alzheimer’s disease (AD) progression. Neuroinflammation is characterized by the activity of brain resident glial cells, in particular microglia, but also by peripheral immune cells, which infiltrate the brain at certain stages of disease progression. The specific role of microglia in shaping AD pathology is still controversially discussed. Moreover, a possible role of microglia in the interaction and recruitment of peripheral immune cells has so far been completely ignored.

Methods

We ablated microglia cells in 12-month-old WT and APP-PS1 transgenic mice for 4 weeks using the CSF1R inhibitor PLX5622 and analyzed its consequences to AD pathology and in particular to peripheral immune cell infiltration.

Results

PLX5622 treatment successfully reduced microglia numbers. Interestingly, it uncovered a treatment-resistant macrophage population (Iba1⁺/TMEM119⁻). These cells strongly expressed the phagocytosis marker CD68 and the lymphocyte activation, homing, and adhesion molecule CD44, specifically at sites of amyloid-beta plaques in the brains of APP-PS1 mice. In consequence, ablation of microglia significantly raised the number of CD3⁺/CD8⁺ T-cells and reduced the expression of anti-inflammatory genes in the brains of APP-PS1 mice.

Conclusion

We conclude that in neurodegenerative conditions, chronically activated microglia might limit CD3⁺/CD8⁺ T-cell recruitment to the brain and that local macrophages connect innate with adaptive immune responses. Investigating the role of peripheral immune cells, their interaction with microglia, and understanding the link between innate and adaptive immune responses in the brain might be a future directive in treating AD pathology.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1304-4) contains supplementary material, which is available to authorized users.

Therapeutic implications of how TNF links apolipoprotein E, phosphorylated tau, α-synuclein, amyloid-β and insulin resistance in neurodegenerative diseases

While cytokines such as TNF have long been recognized as essential to normal cerebral physiology, the implications of their chronic excessive production within the brain are now also increasingly appreciated. Syndromes as diverse as malaria and lead poisoning, as well as non‐infectious neurodegenerative diseases, illustrate this. These cytokines also orchestrate changes in tau, α‐synuclein, amyloid‐β levels and degree of insulin resistance in most neurodegenerative states. New data on the effects of salbutamol, an indirect anti‐TNF agent, on α‐synuclein and Parkinson's disease, APOE4 and tau add considerably to the rationale of the anti‐TNF approach to understanding, and treating, these diseases. Therapeutic advances being tested, and arguably useful for a number of the neurodegenerative diseases, include a reduction of excess cerebral TNF, whether directly, with a specific anti‐TNF biological agent such as etanercept via Batson's plexus, or indirectly via surgically implanting stem cells. Inhaled salbutamol also warrants investigating further across the neurodegenerative disease spectrum. It is now timely to integrate this range of new information across the neurodegenerative disease spectrum, rather than keep seeing it through the lens of individual disease states.

A Closer Look into the Role of Protein Tau in the Identification of Promising Therapeutic Targets for Alzheimer's Disease

One of the most commonly known chronic neurodegenerative disorders, Alzheimer's disease (AD), manifests the common type of dementia in 60⁻80% of cases. From a clinical standpoint, a patent cognitive decline and a severe change in personality, as caused by a loss of neurons, is usually evident in AD with about 50 million people affected in 2016. The disease progression in patients is distinguished by a gradual plummet in cognitive functions, eliciting symptoms such as memory loss, and eventually requiring full-time medical care. From a histopathological standpoint, the defining characteristics are intracellular aggregations of hyper-phosphorylated tau protein, known as neurofibrillary tangles (NFT), and depositions of amyloid β-peptides (Aβ) in the brain. The abnormal phosphorylation of tau protein is attributed to a wide gamut of neurological disorders known as tauopathies. In addition to the hyperphosphorylated tau lesions, neuroinflammatory processes could occur in a sustained manner through astro-glial activation, resulting in the disease progression. Recent findings have suggested a strong interplay between the mechanism of Tau phosphorylation, disruption of microtubules, and synaptic loss and pathology of AD. The mechanisms underlying these interactions along with their respective consequences in Tau pathology are still ill-defined. Thus, in this review: (1) we highlight the interplays existing between Tau pathology and AD; and (2) take a closer look into its role while identifying some promising therapeutic advances including state of the art imaging techniques.

Emerging Roles of Astrocytes in Neuro-Vascular Unit and the Tripartite Synapse With Emphasis on Reactive Gliosis in the Context of Alzheimer's Disease

Astrocytes, which are five-fold more numerous than neurons in the central nervous system (CNS), are traditionally viewed to provide simple structural and nutritional supports for neurons and to participate in the composition of the blood brain barrier (BBB). In recent years, the active roles of astrocytes in regulating cerebral blood flow (CBF) and in maintaining the homeostasis of the tripartite synapse have attracted increasing attention. More importantly, astrocytes have been associated with the pathogenesis of Alzheimer's disease (AD), a major cause of dementia in the elderly. Although microglia-induced inflammation is considered important in the development and progression of AD, inflammation attributable to astrogliosis may also play crucial roles. A1 reactive astrocytes induced by inflammatory stimuli might be harmful by up-regulating several classical complement cascade genes thereby leading to chronic inflammation, while A2 induced by ischemia might be protective by up-regulating several neurotrophic factors. Here we provide a concise review of the emerging roles of astrocytes in the homeostasis maintenance of the neuro-vascular unit (NVU) and the tripartite synapse with emphasis on reactive astrogliosis in the context of AD, so as to pave the way for further research in this area, and to search for potential therapeutic targets of AD.

Overexpression of 5-Lipoxygenase Worsens the Phenotype of a Mouse Model of Tauopathy

Brain accumulation of increasing amount of phosphorylated microtubule associated tau protein is one the major hallmark lesions of Alzheimer's disease (AD) and related tauopathies. Consistent evidence from clinical and animal studies has shown that neuroinflammation characterizes these diseases. The 5-lipoxygenase (5LO) is an enzyme protein whose metabolic products are lipids with potent inflammatory actions. Previously, we showed that blockade of 5LO activation ameliorates the phenotype of the htau transgenic mice. Here, by employing a vector system to overexpress 5LO in the brain of the same mouse model, we investigated its role and contribution to their behavioral deficits and development of tau neuropathology. Compared with controls, 5LO gene targeted mice manifested significant impairments in their memory and learning ability. On the other hand, brain tissues of the same mice had higher 5LO protein level and activity which resulted in intense neuroinflammation and synaptic pathology. Further, the same mice had a significant elevation of tau phosphorylation, which associated with the activation of the cdk5 kinase and an accumulation of insoluble tau. The functional involvement of this kinase in the 5LO-dependent tau phosphorylation was confirmed in neuronal cells. Taken together, our findings demonstrate that neuronal 5LO is directly involved in tau phosphorylation and tau neuropathology, and for this reason, it should be considered a good therapeutic target for tauopathies.

Granulocyte-macrophage colony-stimulating factor neuroprotective activities in Alzheimer's disease mice

We investigated the effects of granulocyte-macrophage colony stimulating factor (GM-CSF) on behavioral and pathological outcomes in Alzheimer's disease (AD) and non-transgenic mice. GM-CSF treatment in AD mice reduced brain amyloidosis, increased plasma Aβ, and rescued cognitive impairment with increased hippocampal expression of calbindin and synaptophysin and increased levels of doublecortin-positive cells in the dentate gyrus. These data extend GM-CSF pleiotropic neuroprotection mechanisms in AD and include regulatory T cell-mediated immunomodulation of microglial function, Aβ clearance, maintenance of synaptic integrity, and induction of neurogenesis. Together these data support further development of GM-CSF as a neuroprotective agent for AD.

PQQ ameliorates D-galactose induced cognitive impairments by reducing glutamate neurotoxicity via the GSK-3β/Akt signaling pathway in mouse

Oxidative stress is known to be associated with various age-related diseases. D-galactose (D-gal) has been considered a senescent model which induces oxidative stress response resulting in memory dysfunction. Pyrroloquinoline quinone (PQQ) is a redox cofactor which is found in various foods. In our previous study, we found that PQQ may be converted into a derivative by binding with amino acid, which is beneficial to several pathological processes. In this study, we found a beneficial glutamate mixture which may diminish neurotoxicity by oxidative stress in D-gal induced mouse. Our results showed that PQQ may influence the generation of proinflammatory mediators, including cytokines and prostaglandins during aging process. D-gal-induced mouse showed increased MDA and ROS levels, and decreased T-AOC activities in the hippocampus, these changes were reversed by PQQ supplementation. Furthermore, PQQ statistically enhanced Superoxide Dismutase SOD2 mRNA expression. PQQ could ameliorate the memory deficits and neurotoxicity induced by D-gal via binding with excess glutamate, which provide a link between glutamate-mediated neurotoxicity, inflammation and oxidative stress. In addition, PQQ reduced the up-regulated expression of p-Akt by D-gal and maintained the activity of GSK-3β, resulting in a down-regulation of p-Tau level in hippocampus. PQQ modulated memory ability partly via Akt/GSK-3β pathway.

Inflammation in CNS neurodegenerative diseases

Neurodegenerative diseases, the leading cause of morbidity and disability, are gaining increased attention as they impose a considerable socioeconomic impact, due in part to the ageing community. Neuronal damage is a pathological hallmark of Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, Huntington's disease, spinocerebellar ataxia and multiple sclerosis, although such damage is also observed following neurotropic viral infections, stroke, genetic white matter diseases and paraneoplastic disorders. Despite the different aetiologies, for example, infections, genetic mutations, trauma and protein aggregations, neuronal damage is frequently associated with chronic activation of an innate immune response in the CNS. The growing awareness that the immune system is inextricably involved in shaping the brain during development as well as mediating damage, but also regeneration and repair, has stimulated therapeutic approaches to modulate the immune system in neurodegenerative diseases. Here, we review the current understanding of how astrocytes and microglia, as well as neurons and oligodendrocytes, shape the neuroimmune response during development, and how aberrant responses that arise due to genetic or environmental triggers may predispose the CNS to neurodegenerative diseases. We discuss the known interactions between the peripheral immune system and the brain, and review the current concepts on how immune cells enter and leave the CNS. A better understanding of neuroimmune interactions during development and disease will be key to further manipulating these responses and the development of effective therapies to improve quality of life, and reduce the impact of neuroinflammatory and degenerative diseases.

Antileukotriene therapy by reducing tau phosphorylation improves synaptic integrity and cognition of P301S transgenic mice

The 5‐lipoxygenase (5LO) is a source of inflammatory leukotrienes and is upregulated in Alzheimer's disease and related tauopathies. However, whether it directly modulates tau phosphorylation and the development of its typical neuropathology in the absence of Aβ or is a secondary event during the course of the disease pathogenesis remains to be fully elucidated. The goal of this study was to evaluate the effect that pharmacologic blockade of this inflammatory pathway has on the phenotype of a transgenic mouse model of tauopathy, the P301S mice. Starting at 3 months of age, P301S mice were randomized to receive zileuton, a specific 5LO blocker, for 7 months; then, its effect on their behavioral deficits and neuropathology was assessed. Inhibition of leukotrienes formation was associated with a reduction in tau phosphorylation and an amelioration of memory and learning as well as synaptic integrity, which were secondary to a downregulation of the cdk5 kinase pathway. Our results demonstrate that the 5LO enzyme is a key player in modulating tau phosphorylation and pathology and that blockade of its enzymatic activity represents a desirable disease‐modifying therapeutic approach for tauopathy.

Update on tauopathies

PURPOSE OF REVIEW

The purpose of this review is to provide an update on the role of tau beyond the stabilization of microtubules and on the clinical, pathological, diagnostic and therapeutic aspects of tauopathies.

RECENT FINDINGS

Beyond its function as a microtubule-associated tau protein, tau is also involved in gene regulation, signal transduction and metabolism. Experimental models allow for the development of new diagnostic and therapeutic tools. Tauopathies encompass different disorders that may manifest with various clinical syndromes. Differential diagnosis with other proteinopathies is still challenging. Cerebrospinal fluid biomarkers and radiotracers were extensively studied in the last year. Although diagnostic accuracy remains deceiving in non-Alzheimer's disease tauopathies, positron emission tomography tau tracers could be used to monitor disease progression.

SUMMARY

Despite the advent of novel therapeutic approaches and the increasing number of clinical trials in tauopathies, accurate clinical diagnosis is still an unmet need and better tau biomarkers are still desperately needed. Although primary taupathies are rare and heterogeneous disorders, their combined prevalence and the importance of tau disorder in Alzheimer's disease and secondary tauopathies makes research on tauopathy a priority - because it could benefit many patients.

A Novel Association of Polymorphism in the ITGA4 Gene Encoding the VLA-4 α4 Subunit with Increased Risk of Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent cause of dementia in elderly people worldwide. Many studies support the hypothesis that the inflammation of the CNS contributes to the neurodegeneration and disease progression. The integrin molecule α4β1, also known as very late antigen 4 (VLA-4), belongs to adhesion molecules that activate the inflammatory process through the migration of immune cells into the CNS. Therefore, the objective of our study was to analyze the association between two polymorphisms located in the ITGA4 gene encoding the α4 subunit of VLA-4 and the risk of AD. 104 late-onset AD patients and 206 control subjects from Slovakia were genotyped for ITGA4 gene SNP polymorphism rs113276800 (-269C/A) and rs1143676 (+3061A/G). The same study cohorts were also genotyped for the APOE-ε4, which is a known genetic factor associated with increased risk of AD developing. ITGA4 polymorphism analysis revealed significantly higher frequency of the +3061AG carriers in AD group compared to the controls (P ≤ 0.05). Following the APOE-ε4 stratification of study groups, the association remained significant only in APOE-ε4 noncarriers. Our study suggests a novel association of ITGA4 +3061A/G polymorphism with AD and its possible contribution to the disease pathology.

Complex role of chemokine mediators in animal models of Alzheimer's Disease

Chemokines are a family of cytokines, first described to play a role in the immune system. However, neurons and glial cells also express chemokines and their receptors. In the central nervous system, chemokines are involved in several neural functions, in particular in the control of cell communications and neuronal activity. In pathological conditions, chemokines participate in neuroinflammatory and neurodegenerative processes. In Alzheimer's disease (AD), chemokines play a role in the development of the two main lesions, amyloid β plaques and neurofibrillary tangles. In addition, they contribute to the inflammatory response by recruiting T cells and controlling microglia/macrophages activation. Actually, targeting inflammatory pathways seems a promising therapeutic approach for the treatment of AD patients. This review summarizes our current knowledge on the roles of chemokines in AD animal models and the underlying mechanisms in which they take part. Better knowledge of the role of chemokines and their cellular receptors in AD could open new therapeutic perspectives.

Tau and neuroinflammation: What impact for Alzheimer's Disease and Tauopathies?

Alzheimer's Disease (AD) is a chronic neurodegenerative disorder and the most common type of dementia (60–80% of cases). In 2016, nearly 44 million people were affected by AD or related dementia. AD is characterized by progressive neuronal damages leading to subtle and latter obvious decline in cognitive functions including symptoms such as memory loss or confusion, which ultimately require full-time medical care. Its neuropathology is defined by the extracellular accumulation of amyloid-β (Aβ) peptide into amyloid plaques, and intraneuronal neurofibrillary tangles (NFT) consisting of aggregated hyper- and abnormal phosphorylation of tau protein. The latter, identified also as Tau pathology, is observed in a broad spectrum of neurological diseases commonly referred to as “Tauopathies”. Besides these lesions, sustained neuroinflammatory processes occur, involving notably micro- and astro-glial activation, which contribute to disease progression. Recent findings from genome wide association studies further support an instrumental role of neuroinflammation. While the interconnections existing between this innate immune response and the amyloid pathogenesis are widely characterized and described as complex, elaborated and evolving, only few studies focused on Tau pathology. An adaptive immune response takes place conjointly during the disease course, as indicated by the presence of vascular and parenchymal T-cell in AD patients' brain. The underlying mechanisms of this infiltration and its consequences with regards to Tau pathology remain understudied so far. In the present review, we highlight the interplays existing between Tau pathology and the innate/adaptive immune responses.

Long-Term Neuroinflammation Induced by Influenza A Virus Infection and the Impact on Hippocampal Neuron Morphology and Function

Acute influenza infection has been reported to be associated with neurological symptoms. However, the long-term consequences of an infection with neurotropic and non-neurotropic influenza A virus (IAV) variants for the CNS remain elusive. We can show that spine loss in the hippocampus after infection with neurotropic H7N7 (rSC35M) and non-neurotropic H3N2 (maHK68) in female C57BL/6 mice persists well beyond the acute phase of the disease. Although spine number was significantly reduced at 30 d postinfection (dpi) with H7N7 or H3N2, full recovery could only be observed much later at 120 dpi. Infection with H1N1 virus, which was shown previously to affect spine number and hippocampus-dependent learning acutely, had no significant long-term effects. Spine loss was associated with an increase in the number of activated microglia, reduced long-term potentiation in the hippocampus, and impairment in spatial memory formation, indicating that IAV-associated inflammation induced functional and structural alterations in hippocampal networks. Transcriptome analyses revealed regulation of many inflammatory and neuron- and glia-specific genes in H3N2- and H7N7-infected mice at day 18 and in H7N7-infected mice at day 30 pi that related to the structural and functional alterations. Our data provide evidence that neuroinflammation induced by neurotropic H7N7 and infection of the lung with a non-neurotropic H3N2 IAV result in long-term impairments in the CNS. IAV infection in humans may therefore not only lead to short-term responses in infected organs, but may also trigger neuroinflammation and associated chronic alterations in the CNS.SIGNIFICANCE STATEMENT In the acute phase of influenza infection, neuroinflammation can lead to alterations in hippocampal neuronal morphology and cognitive deficits. The results of this study now also provide evidence that neuroinflammation induced by influenza A virus (IAV) infection can induce longer-lasting, virus-specific alterations in neuronal connectivity that are still detectable 1 month after infection and are associated with impairments in spatial memory formation. IAV infection in humans may therefore not only lead to short-term responses in infected organs, but may also trigger neuroinflammation and associated chronic alterations in the CNS.

Brain 5-lipoxygenase over-expression worsens memory, synaptic integrity, and tau pathology in the P301S mice

Progressive accumulation of highly phosphorylated tau protein isoforms is the main feature of a group of neurodegenerative diseases collectively called tauopathies. Data from human and animal models of these diseases have shown that neuroinflammation often accompanies their pathogenesis. The 5-lipoxygenase (5LO) is an enzyme widely expressed in the brain and a source of potent pro-inflammatory mediators, while its pharmacological inhibition modulates the phenotype of a tau transgenic mouse model, the htau mice. By employing an adeno-associated viral vector system to over-express 5LO in the brain, we examined its contribution to the behavioral deficits and neuropathology in a different transgenic mouse model of tauopathy, the P301S mouse line. Compared with controls, 5LO-targeted gene brain over-expression in these mice resulted in a worsening of behavioral and motor deficits. Over-expression of 5LO resulted in microglia and astrocyte activation and significant synaptic pathology, which was associated with a significant elevation of tau phosphorylation at specific epitopes, tau insoluble fraction, and activation of the cdk5 kinase. In vitro studies confirmed that 5LO directly modulates tau phosphorylation at the same epitopes via the cdk5 kinase pathway. These data demonstrate that 5LO plays a direct role in tau phosphorylation and is an active player in the development of the entire tau phenotype. They provide further support to the hypothesis that 5LO is a viable therapeutic target for the treatment and/or prevention of human tauopathy.

Functional and structural damage of neurons by innate immune mechanisms during neurodegeneration

Over the past decades, our view on neurodegenerative diseases has been mainly centered around neurons and their networks. Only recently it became evident that immunological processes arise alongside degenerating neurons, raising the question whether these represent just meaningless bystander reactions or in turn, contribute to pathogenesis and disease symptoms. When considering any effect of inflammatory events on the CNS one has to consider the site, duration and nature of immune activation. Likewise, one has to distinguish between mechanisms which directly impact the neuronal compartment and indirect mechanisms, which affect cells that are important for neuronal functioning and survival. As discussed in this review, both types of mechanisms may be present at the same time and additively or synergistically lead to neuronal demise. Inflammatory mediators released by the principle innate immune cells of the brain, microglia and astrocytes, can compromise the function and structure of neurons, thereby playing important roles in the pathogenesis of neurodegenerative diseases.

Molecular and functional signatures in a novel Alzheimer's disease mouse model assessed by quantitative proteomics

Background

Alzheimer’s disease (AD), the most common neurodegenerative disorder, is characterized by the deposition of extracellular amyloid plaques and intracellular neurofibrillary tangles. To understand the pathological mechanisms underlying AD, developing animal models that completely encompass the main features of AD pathologies is indispensable. Although mouse models that display pathological hallmarks of AD (amyloid plaques, neurofibrillary tangles, or both) have been developed and investigated, a systematic approach for understanding the molecular characteristics of AD mouse models is lacking.

Methods

To elucidate the mechanisms underlying the contribution of amyloid beta (Aβ) and tau in AD pathogenesis, we herein generated a novel animal model of AD, namely the AD-like pathology with amyloid and neurofibrillary tangles (ADLP^APT) mice. The ADLP^APT mice carry three human transgenes, including amyloid precursor protein, presenilin-1, and tau, with six mutations. To characterize the molecular and functional signatures of AD in ADLP^APT mice, we analyzed the hippocampal proteome and performed comparisons with individual-pathology transgenic mice (i.e., amyloid or neurofibrillary tangles) and wild-type mice using quantitative proteomics with 10-plex tandem mass tag.

Results

The ADLP^APT mice exhibited accelerated neurofibrillary tangle formation in addition to amyloid plaques, neuronal loss in the CA1 area, and memory deficit at an early age. In addition, our proteomic analysis identified nearly 10,000 protein groups, which enabled the identification of hundreds of differentially expressed proteins (DEPs) in ADLP^APT mice. Bioinformatics analysis of DEPs revealed that ADLP^APT mice experienced age-dependent active immune responses and synaptic dysfunctions.

Conclusions

Our study is the first to compare and describe the proteomic characteristics in amyloid and neurofibrillary tangle pathologies using isobaric label-based quantitative proteomics. Furthermore, we analyzed the hippocampal proteome of the newly developed ADLP^APT model mice to investigate how both Aβ and tau pathologies regulate the hippocampal proteome. Because the ADLP^APT mouse model recapitulates the main features of AD pathogenesis, the proteomic data derived from its hippocampus has significant utility as a novel resource for the research on the Aβ-tau axis and pathophysiological changes in vivo.

Electronic supplementary material

The online version of this article (10.1186/s13024-017-0234-4) contains supplementary material, which is available to authorized users.

Mutual Relationship between Tau and Central Insulin Signalling: Consequences for AD and Tauopathies?

Alzheimer disease (AD) is a progressive neurodegenerative disorder mainly characterized by cognitive deficits and neuropathological changes such as Tau lesions and amyloid plaques, but also associated with non-cognitive symptomatology. Metabolic and neuroendocrine abnormalities, such as alterations in body weight, brain insulin impairments, and lower brain glucose metabolism, which often precede clinical diagnosis, have been extensively reported in AD patients. However, the origin of these symptoms and their relation to pathology and cognitive impairments remain misunderstood. Insulin is a hormone involved in the control of energy homeostasis both peripherally and centrally, and insulin-resistant state has been linked to increased risk of dementia. It is now well established that insulin resistance can exacerbate Tau lesions, mainly by disrupting the balance between Tau kinases and phosphatases. On the other hand, the emerging literature indicates that Tau protein can also modulate insulin signalling in the brain, thus creating a detrimental vicious circle. The following review will highlight our current understanding of the role of insulin in the brain and its relation to Tau protein in the context of AD and tauopathies. Considering that insulin signalling is prone to be pharmacologically targeted at multiple levels, it constitutes an appealing approach to improve both insulin brain sensitivity and mitigate brain pathology with expected positive outcome in terms of cognition.

Involvement of Astrocytes in Alzheimer's Disease from a Neuroinflammatory and Oxidative Stress Perspective

Alzheimer disease (AD) is a frequent and devastating neurodegenerative disease in humans, but still no curative treatment has been developed. Although many explicative theories have been proposed, precise pathophysiological mechanisms are unknown. Due to the importance of astrocytes in brain homeostasis they have become interesting targets for the study of AD. Changes in astrocyte function have been observed in brains from individuals with AD, as well as in AD in vitro and in vivo animal models. The presence of amyloid beta (Aβ) has been shown to disrupt gliotransmission, neurotransmitter uptake, and alter calcium signaling in astrocytes. Furthermore, astrocytes express apolipoprotein E and are involved in the production, degradation and removal of Aβ. As well, changes in astrocytes that precede other pathological characteristics observed in AD, point to an early contribution of astroglia in this disease. Astrocytes participate in the inflammatory/immune responses of the central nervous system. The presence of Aβ activates different cell receptors and intracellular signaling pathways, mainly the advanced glycation end products receptor/nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, responsible for the transcription of pro-inflammatory cytokines and chemokines in astrocytes. The release of these pro-inflammatory agents may induce cellular damage or even stimulate the production of Aβ in astrocytes. Additionally, Aβ induces the appearance of oxidative stress (OS) and production of reactive oxygen species and reactive nitrogen species in astrocytes, affecting among others, intracellular calcium levels, NADPH oxidase (NOX), NF-κB signaling, glutamate uptake (increasing the risk of excitotoxicity) and mitochondrial function. Excessive neuroinflammation and OS are observed in AD, and astrocytes seem to be involved in both. The Aβ/NF-κB interaction in astrocytes may play a central role in these inflammatory and OS changes present in AD. In this paper, we also discuss therapeutic measures highlighting the importance of astrocytes in AD pathology. Several new therapeutic approaches involving phenols (curcumin), phytoestrogens (genistein), neuroesteroids and other natural phytochemicals have been explored in astrocytes, obtaining some promising results regarding cognitive improvements and attenuation of neuroinflammation. Novel strategies comprising astrocytes and aimed to reduce OS in AD have also been proposed. These include estrogen receptor agonists (pelargonidin), Bambusae concretio Salicea, Monascin, and various antioxidatives such as resveratrol, tocotrienol, anthocyanins, and epicatechin, showing beneficial effects in AD models.

The direct role of 5-lipoxygenase on tau pathology, synaptic integrity and cognition in a mouse model of tauopathy

Neurodegenerative tauopathies are characterized by pathological accumulation of highly phosphorylated isoforms of tau protein, which leads to progressive neuronal loss. Neuroinflammation often accompanies tau-driven diseases; however, the direct role of neuroinflammation in tauopathies remains unknown. The 5-lipoxygenase (5LO) is a pro-inflammatory enzyme, which produces several bioactive metabolites and is widely expressed in the central nervous system. Previously, our group showed that 5LO influences the Alzheimer's disease (AD) phenotype of APP transgenic mice as well as a mouse model with plaques and tangles. However, whether this protein directly modulates tau phosphorylation and subsequent neuropathology remains to be fully investigated. In the current study, we provide evidence for an age-dependent and region-specific upregulation of the 5LO pathway (protein, message and activity) in a transgenic mouse model of tauopathy, the P301S line. In addition, we demonstrate that genetic deletion of 5LO in this mouse model results in significant memory improvement, reduces tau phosphorylation at specific epitopes as well as neuroinflammation and rescues synaptic pathology. In vitro studies confirmed that 5LO directly modulates tau phosphorylation at the same epitopes as for the brain tissues. Taken together, our data reveal an active involvement of the 5LO pathway in the development of the tauopathy phenotype and provide strong support to the hypothesis that this enzymatic protein should be considered a novel and viable therapeutic target for the treatment of human tauopathy.

Autoimmunity as a Driving Force of Cognitive Evolution

In the last decades, increasingly robust experimental approaches have formally demonstrated that autoimmunity is a physiological process involved in a large range of functions including cognition. On this basis, the recently enunciated “brain superautoantigens” theory proposes that autoimmunity has been a driving force of cognitive evolution. It is notably suggested that the immune and nervous systems have somehow co-evolved and exerted a mutual selection pressure benefiting to both systems. In this two-way process, the evolutionary-determined emergence of neurons expressing specific immunogenic antigens (brain superautoantigens) has exerted a selection pressure on immune genes shaping the T-cell repertoire. Such a selection pressure on immune genes has translated into the emergence of a finely tuned autoimmune T-cell repertoire that promotes cognition. In another hand, the evolutionary-determined emergence of brain-autoreactive T-cells has exerted a selection pressure on neural genes coding for brain superautoantigens. Such a selection pressure has translated into the emergence of a neural repertoire (defined here as the whole of neurons, synapses and non-neuronal cells involved in cognitive functions) expressing brain superautoantigens. Overall, the brain superautoantigens theory suggests that cognitive evolution might have been primarily driven by internal cues rather than external environmental conditions. Importantly, while providing a unique molecular connection between neural and T-cell repertoires under physiological conditions, brain superautoantigens may also constitute an Achilles heel responsible for the particular susceptibility of Homo sapiens to “neuroimmune co-pathologies” i.e., disorders affecting both neural and T-cell repertoires. These may notably include paraneoplastic syndromes, multiple sclerosis as well as autism, schizophrenia and neurodegenerative diseases. In the context of this theoretical frame, a specific emphasis is given here to the potential evolutionary role exerted by two families of genes, namely the MHC class II genes, involved in antigen presentation to T-cells, and the Foxp genes, which play crucial roles in language (Foxp2) and the regulation of autoimmunity (Foxp3).

Antibiotic-induced perturbations in microbial diversity during post-natal development alters amyloid pathology in an aged APPSWE/PS1ΔE9 murine model of Alzheimer's disease

Recent evidence suggests the commensal microbiome regulates host immunity and influences brain function; findings that have ramifications for neurodegenerative diseases. In the context of Alzheimer’s disease (AD), we previously reported that perturbations in microbial diversity induced by life-long combinatorial antibiotic (ABX) selection pressure in the APP_SWE/PS1_ΔE9 mouse model of amyloidosis is commensurate with reductions in amyloid-β (Aβ) plaque pathology and plaque-localised gliosis. Considering microbiota-host interactions, specifically during early post-natal development, are critical for immune- and neuro-development we now examine the impact of microbial community perturbations induced by acute ABX exposure exclusively during this period in APP_SWE/PS1_ΔE9 mice. We show that early post-natal (P) ABX treatment (P14-P21) results in long-term alterations of gut microbial genera (predominantly Lachnospiraceae and S24-7) and reduction in brain Aβ deposition in aged APP_SWE/PS1_ΔE9 mice. These mice exhibit elevated levels of blood- and brain-resident Foxp3⁺ T-regulatory cells and display an alteration in the inflammatory milieu of the serum and cerebrospinal fluid. Finally, we confirm that plaque-localised microglia and astrocytes are reduced in ABX-exposed mice. These findings suggest that ABX-induced microbial diversity perturbations during post-natal stages of development coincide with altered host immunity mechanisms and amyloidosis in a murine model of AD.

Acute Hypoxia Induced an Imbalanced M1/M2 Activation of Microglia through NF-κB Signaling in Alzheimer's Disease Mice and Wild-Type Littermates

Alzheimer’s disease (AD) is the most common neurodegenerative disease mainly caused by abnormal tau phosphorylation, amyloid β (Aβ) deposition and neuroinflammation. As an important environmental factor, hypoxia has been reported to aggravate AD via exacerbating Aβ and tau pathologies. However, the link between hypoxia and neuroinflammation, especially the changes of pro-inflammatory M1 or anti-inflammation M2 microglia phenotypes in AD, is still far from being clearly investigated. Here, we evaluated the activation of microglia in the brains of APP^swe/PS1^dE9 transgenic (Tg) mice and their wild type (Wt) littermates, after a single episode of acute hypoxia (24 h) exposure. We found that acute hypoxia activated M1 microglia in both Tg and Wt mice as evidenced by the elevated M1 markers including cluster of differentiation 86 (CD86), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), C-C motif chemokine ligand 2 (CCL2) and CCL3. In addition, the markers of M2 microglia phenotype (arginase-1 (Arg-1), CD206, IL-4 and IL-10) were decreased after acute hypoxia exposure, suggesting an attenuated M2 phenotype of microglia. Moreover, the activation of microglia and the release of cytokines and chemokines were associated with Nuclear factor-κB (NF-κB) induction through toll-like receptor 4 (TLR4). In summary, our findings revealed that acute hypoxia modulated microglia M1/M2 subgroup profile, indicating the pathological role of hypoxia in the neuroinflammation of AD.

Coconut (Cocos nucifera) Ethanolic Leaf Extract Reduces Amyloid-β (1-42) Aggregation and Paralysis Prevalence in Transgenic Caenorhabditis elegans Independently of Free Radical Scavenging and Acetylcholinesterase Inhibition

Virgin coconut oil (VCO) has been the subject of several studies which have aimed to alleviate Alzheimer’s disease (AD) pathology, focusing on in vitro antioxidant and acetylcholinesterase (AChE) inhibitory activities. Here, we studied an underutilized and lesser-valued part of the coconut tree, specifically the leaves, using in vitro and in vivo approaches. Coconut leaf extract (CLE) was screened for antioxidant and AChE inhibitory properties in vitro and therapeutic effects in two strains of transgenic Caenorhabditis elegans expressing amyloid-β_1–42 (Aβ_1-42) in muscle cells. CLE demonstrated free radical scavenging activity with an EC₅₀ that is 79-fold less compared to ascorbic acid, and an AChE inhibitory activity that is 131-fold less compared to Rivastigmine. Surprisingly, in spite of its low antioxidant activity and AChE inhibition, CLE reduced Aβ deposits by 30.31% in CL2006 in a dose-independent manner, and reduced the percentage of paralyzed nematodes at the lowest concentration of CLE (159.38 μg/mL), compared to dH₂O/vehicle (control). Phytochemical analysis detected glycosides, anthocyanins, and hydrolyzable tannins in CLE, some of which are known to be anti-amyloidogenic. Taken together, these findings suggest that CLE metabolites alternatively decrease AB_1–42 aggregation and paralysis prevalence independently of free radical scavenging and AChE inhibition, and this warrants further investigation on the bioactive compounds of CLE.