Activated human microglia stimulate neuroblastoma cells to upregulate production of beta amyloid protein and tau: implications for Alzheimer's disease pathogenesis

Unveiling the Involvement of Herpes Simplex Virus-1 in Alzheimer's Disease: Possible Mechanisms and Therapeutic Implications

Viruses pose a significant challenge and threat to human health, as demonstrated by the current COVID-19 pandemic. Neurodegeneration, particularly in the case of Alzheimer's disease (AD), is significantly influenced by viral infections. AD is a neurodegenerative disease that affects people of all ages and poses a significant threat to millions of individuals worldwide. The precise mechanism behind its development is not yet fully understood; however, the emergence and advancement of AD can be hastened by various environmental factors, such as bacterial and viral infections. There has been a longstanding suspicion that the herpes simplex virus-1 (HSV-1) may have a role to play in the development or advancement of AD. Reactivation of HSV-1 could potentially lead to damage to neurons, either by direct means or indirectly by triggering inflammation. This article provides an overview of the connection between HSV-1 infections and immune cells (astrocytes, microglia, and oligodendrocytes) in the progression of AD. It summarizes recent scientific research on how HSV-1 affects neurons, which could potentially shed light on the clinical features and treatment options for AD. In addition, the paper has explored the impact of HSV-1 on neurons and its role in various aspects of AD, such as Aβ secretion, tau hyperphosphorylation, metabolic dysregulation, oxidative damage, apoptosis, and autophagy. It is believed that the immune response triggered by HSV-1 reactivation plays a role in the development of neurodegeneration in AD. Despite the lack of a cure for AD, researchers have made significant efforts to study the clinical and pathological aspects of the disease, identify biomarkers, and gain insight into its underlying causes. The goal is to achieve early diagnosis and develop treatments that can modify the progression of the disease. The current article discusses the most promising therapy for combating the viral impacts, which provides additional evidence for the frequent reactivations of latent HSV-1 in the AD brain. However, further research is still required to establish the molecular and cellular mechanisms underlying the development of AD through the reactivation of HSV-1. This could potentially lead to new insights in drug development aimed at preventing HSV-1 reactivation and the subsequent development and progression of AD.

Rotating magnetic field improved cognitive and memory impairments in a sporadic ad model of mice by regulating microglial polarization

Neuroinflammation, triggered by aberrantly activated microglia, is widely recognized as a key contributor to the initiation and progression of Alzheimer's disease (AD). Microglial activation in the central nervous system (CNS) can be classified into two distinct phenotypes: the pro-inflammatory M1 phenotype and the anti-inflammatory M2 phenotype. In this study, we investigated the effects of a non-invasive rotating magnetic field (RMF) (0.2T, 4Hz) on cognitive and memory impairments in a sporadic AD model of female Kunming mice induced by AlCl3 and D-gal. Our findings revealed significant improvements in cognitive and memory impairments following RMF treatment. Furthermore, RMF treatment led to reduced amyloid-beta (Aβ) deposition, mitigated damage to hippocampal morphology, prevented synaptic and neuronal loss, and alleviated cell apoptosis in the hippocampus and cortex of AD mice. Notably, RMF treatment ameliorated neuroinflammation, facilitated the transition of microglial polarization from M1 to M2, and inhibited the NF-кB/MAPK pathway. Additionally, RMF treatment resulted in reduced aluminum deposition in the brains of AD mice. In cellular experiments, RMF promoted the M1-M2 polarization transition and enhanced amyloid phagocytosis in cultured BV2 cells while inhibiting the TLR4/NF-кB/MAPK pathway. Collectively, these results demonstrate that RMF improves memory and cognitive impairments in a sporadic AD model, potentially by promoting the M1 to M2 transition of microglial polarization through inhibition of the NF-кB/MAPK signaling pathway. These findings suggest the promising therapeutic applications of RMF in the clinical treatment of AD.

Microglial Drivers of Alzheimer's Disease Pathology: An Evolution of Diverse Participating States

Microglia, the resident immune-competent cells of the brain, become dysfunctional in Alzheimer's disease (AD), and their aberrant immune responses contribute to the accumulation of pathological proteins and neuronal injury. Genetic studies implicate microglia in the development of AD, prompting interest in developing immunomodulatory therapies to prevent or ameliorate disease. However, microglia take on diverse functional states in disease, playing both protective and detrimental roles in AD, which largely overlap and may shift over the disease course, complicating the identification of effective therapeutic targets. Extensive evidence gathered using transgenic mouse models supports an active role of microglia in pathology progression, though results vary and can be contradictory between different types of models and the degree of pathology at the time of study. Here, we review microglial immune signaling and responses that contribute to the accumulation and spread of pathological proteins or directly affect neuronal health. We additionally explore the use of induced pluripotent stem cell (iPSC)-derived models to study living human microglia and how they have contributed to our knowledge of AD and may begin to fill in the gaps left by mouse models. Ultimately, mouse and iPSC-derived models have their own limitations, and a comprehensive understanding of microglial dysfunction in AD will only be established by an integrated view across models and an appreciation for their complementary viewpoints and limitations.

Microglia measured by TSPO PET are associated with Alzheimer's disease pathology and mediate key steps in a disease progression model

INTRODUCTION

Evidence suggests microglial activation precedes regional tau and neurodegeneration in Alzheimer's disease (AD). We characterized microglia with translocator protein (TSPO) positron emission tomography (PET) within an AD progression model where global amyloid beta (Aβ) precedes local tau and neurodegeneration, resulting in cognitive impairment.

METHODS

Florbetaben, PBR28, and MK-6240 PET, T1 magnetic resonance imaging, and cognitive measures were performed in 19 cognitively unimpaired older adults and 22 patients with mild cognitive impairment or mild AD to examine associations among microglia activation, Aβ, tau, and cognition, adjusting for neurodegeneration. Mediation analyses evaluated the possible role of microglial activation along the AD progression model.

RESULTS

Higher PBR28 uptake was associated with higher Aβ, higher tau, and lower MMSE score, independent of neurodegeneration. PBR28 mediated associations between tau in early and middle Braak stages, between tau and neurodegeneration, and between neurodegeneration and cognition.

DISCUSSION

Microglia are associated with AD pathology and cognition and may mediate relationships between subsequent steps in AD progression.

Echinacea purpurea extract intervention for counteracting neurochemical and behavioral changes induced by bifenthrin

This study was conducted to elucidate the possible protective efficiency of Echinacea purpurea hydroethanolic extract (EchEE) against bifenthrin (BIF)-induced neuro-chemical and behavioral changes in rats. Total phenolics content, reducing power and radical scavenging activity of EchEE were estimated. Four groups of adult male albino rats were used (10 rats each) as follows: 1) Control healthy rats ingested with placebo, 2) Healthy rats orally received EchEE (465 mg/kg/day), 3) Rats intoxicated with BIF (7mg/kg/day) dissolved in olive oil, and 4) Rats co-treated with EchEE (465 mg/kg/day) besides to BIF (7mg/kg/day) intoxication. After 30 days, some neuro-chemical and behavioral tests were assessed. The behavioral tests revealed that rats received BIF exhibited exploratory behavior and spatial learning impairments, memory and locomotion dysfunction, and enhanced anxiety level. Biochemical findings revealed that BIF induced-oxidative stress in the cortex and hippocampus; this was appeared from the significant rise in malondialdehyde (MDA) and nitric oxide (NO) levels, coupled with decreased catalase (CAT), superoxide dismutase (SOD), paraoxonase-1 (PON-1) activities, and reduced glutathione (GSH) level in both brain areas. Also, BIF induced a significant increase caspas-3, tumor necrosis factor alpha (TNF), and interleukin-1beta (IL-1ß) in both areas; dopamine and serotonin levels, and ACh-ase activity were markedly decreased in both areas. Interestingly, treatment of rats with EchEE in combination with BIF resulted in a significant decrease in oxidative stress damage, and modulation of the apoptotic and pro-inflammatory markers. Also, EchEE markedly improved behavioral activities and neurotransmitters level that were impaired by BIF. In conclusion, the present study clearly indicated that EchEE can attenuate brain dysfunction induced by pesticides exposure through preventing the oxidative stress. This may be attributed to its high antioxidant component.

TREM2: Potential therapeutic targeting of microglia for Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, resulting in the loss of cognitive ability and memory. However, there is no specific treatment to mechanistically inhibit the progression of Alzheimer's disease, and most drugs only provide symptom relief and do not fundamentally reverse AD. Current studies show that triggering receptor expressed on myeloid cells 2 (TREM2) is predominantly expressed in microglia of the central nervous system (CNS) and is involved in microglia proliferation, survival, migration and phagocytosis. The current academic view suggests that TREM2 and its ligands have CNS protective effects in AD. Specifically, TREM2 acts by regulating the function of microglia and promoting the clearance of neuronal toxic substances and abnormal proteins by microglia. In addition, TREM2 is also involved in regulating inflammatory response and cell signaling pathways, affecting the immune response and regulatory role of microglia. Although the relationship between TREM2 and Alzheimer's disease has been extensively studied, its specific mechanism of action is not fully understood. The purpose of this review is to provide a comprehensive analysis of the research of TREM2, including its regulation of the inflammatory response, lipid metabolism and phagocytosis in microglia of CNS in AD, and to explore the potential application prospects as well as limitations of targeting TREM2 for the treatment of AD.

Autophagy Balances Neuroinflammation in Alzheimer's Disease

Autophagy is a highly evolutionary conserved process that degrades cytosolic macromolecules or damaged organelles (e.g., mitochondria), as well as intracellular pathogens for energy and survival. Dysfunction of autophagy has been associated with the pathologies of Alzheimer's disease (AD), including Aβ plaques and neurofibrillary tangles. Recently, the presence of sustained immune response in the brain has been considered a new core pathology in AD. Accumulating evidence suggests that autophagy activation may suppress inflammation response through degrading inflammasomes or pro-inflammatory cytokines and improving immune system function in both clinical trials and preclinical studies. This review provides an overview of updated information on autophagy and inflammation and their potential mediators in AD. In summary, we believe that understanding the relationship between autophagy and inflammation will provide insightful knowledge for future therapeutic implications in AD.

TREM2 Inhibits Tau Hyperphosphorylation and Neuronal Apoptosis via the PI3K/Akt/GSK-3β Signaling Pathway In vivo and In vitro

Triggering receptor expressed on myeloid cells-2 (TREM2), a cell surface receptor mainly expressed on microglia, has been shown to play a critical role in Alzheimer's disease (AD) pathogenesis and progression. Our recent results showed that overexpression of TREM2 inhibited inflammatory response in APP/PS1 mice and BV2 cells. Several studies indicated that TREM2 ameliorated tau hyperphosphorylation might be ascribed to the inhibition of neuroinflammation. However, the precise signaling pathways underlying the effect of TREM2 on tau pathology and neuronal apoptosis have not been fully elucidated. In the present study, upregulation of TREM2 significantly inhibited tau hyperphosphorylation at Ser199, Ser396, and Thr205, respectively, as well as prevented neuronal loss and apoptosis. We also found that upregulation of TREM2 alleviated behavioral deficits and improved the spatial cognitive ability of APP/PS1 mice. Further study revealed that TREM2 could activate phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway, resulting in an inhibitory effect on glycogen synthase kinase-3β (GSK-3β), which is a major kinase responsible for tau hyperphosphorylation in AD. In line with in vivo findings, TREM2-overexpressing BV2 microglia following β-amyloid (Aβ) stimulation led to a significant increase in the phosphorylation of PI3K, Akt, and GSK-3β, accompanied by a decrease in tau hyperphosphorylation and apoptosis in co-cultured SH-SY5Y cells. Furthermore, LY294002, a specific PI3K inhibitor, was observed to abolish the beneficial effects of TREM2 on tau hyperphosphorylation, neuronal apoptosis, and spatial cognitive impairments in vivo and in vitro. Thus, our findings indicated that TREM2 inhibits tau hyperphosphorylation and neuronal apoptosis, at least in part, by the activation of the PI3K/Akt/GSK-3β signaling pathway. Taken together, the above results allow us to better understand how TREM2 protects against tau pathology and suggest that upregulation of TREM2 may provide new ideas and therapeutic targets for AD.

Exercise suppresses neuroinflammation for alleviating Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease, with the characteristics of neurofibrillary tangle (NFT) and senile plaque (SP) formation. Although great progresses have been made in clinical trials based on relevant hypotheses, these studies are also accompanied by the emergence of toxic and side effects, and it is an urgent task to explore the underlying mechanisms for the benefits to prevent and treat AD. Herein, based on animal experiments and a few clinical trials, neuroinflammation in AD is characterized by long-term activation of pro-inflammatory microglia and the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasomes. Damaged signals from the periphery and within the brain continuously activate microglia, thus resulting in a constant source of inflammatory responses. The long-term chronic inflammatory response also exacerbates endoplasmic reticulum oxidative stress in microglia, which triggers microglia-dependent immune responses, ultimately leading to the occurrence and deterioration of AD. In this review, we systematically summarized and sorted out that exercise ameliorates AD by directly and indirectly regulating immune response of the central nervous system and promoting hippocampal neurogenesis to provide a new direction for exploring the neuroinflammation activity in AD.

Therapeutic effects of carvacrol on beta-amyloid-induced impairments in in vitro and in vivo models of Alzheimer's disease

Due to the complex nature of Alzheimer's disease (AD), it is important to investigate agents with multiple effects in the treatment of AD. Carvacrol possesses anti-acetylcholinesterase, anti-oxidant, and neuroprotective properties. We therefore investigated therapeutic effects of carvacrol on cell viability, oxidative stress, and cognitive impairment in Aβ1-42-induced in vitro and in vivo models of AD. SH-SY5Y cells differentiated into neurons by retinoic acid were pretreated with carvacrol or galantamine before Aβ1-42 administration. For in vivo experiments, a rat model of AD was established by bilateral intrahippocampal injection of Aβ1-42. The groups received 1% DMSO, carvacrol, or galantamine intraperitoneally twice a day (morning and afternoon) for 6 days. Cell viability was determined using MTT and LDH tests. Learning and memory functions were assessed using a passive-avoidance test. Oxidant-antioxidant parameters (MDA, H₂ O₂ , SOD, and CAT) and Tau, Aβ1-40, and Aβ1-42 peptide levels in in vitro supernatant or in vivo serum and hippocampal samples were measured using ELISA. Carvacrol increased cell viability and exhibited a protective effect against oxidative stress by preventing Aβ1-42-induced cytotoxicity, LDH release, and increments in MDA and H₂ O₂ levels in vitro. Additionally, it improved memory impairment by reversing Aβ1-42-induced changes on passive-avoidance test. Carvacrol ameliorated Aβ1-42-induced increments in MDA and H₂ O₂ levels in in vitro supernatant and in vivo hippocampal samples. However, none of the treatments changed in vitro SOD and Tau-peptide levels, or in vivo serum levels of MDA, H₂ O₂ , SOD, CAT, Tau peptide, Aβ1-40, or Aβ1-42. Our results suggest that multi-target pharmacological agent carvacrol may be promising in treatment of AD by preventing beta-amyloid-induced neurotoxicity, oxidative stress, and memory deficits.

Analysis of Risk Factors for Cerebral Microbleeds and the Relationship between Cerebral Microbleeds and Cognitive Impairment

(1) Background: Cerebral microbleeds (CMBs) are attracting increasing attention. Nevertheless, the risk factors for CMBs remain poorly identified, and the relationship between CMBs and cognitive impairment is still up for debate; (2) Objective: The present study analyzed the risk factors for CMBs and probed into the potential correlations between the presence, number, and location of CMBs and cognition; (3) Methods: This study enrolled 406 subjects who underwent both brain 3.0-T magnetic resonance imaging scans and cognitive testing. Spearman correlation was used to assess the relationship between the number of CMBs and cognition. Multiple linear regression was utilized to analyze the relationship between the regions of CMBs and each cognitive domain; (4) Results: Multivariate logistic regression analysis results showed that age (odds ratio (OR) = 1.045, 95% confidence interval (95%CI; 1.009, 1.082)), smoking (OR = 3.604, 95%CI (1.995, 6.509)), hypertension (OR = 3.607, 95%CI (2.204, 5.901)), total cholesterol (OR = 0.611, 95%CI (0.467, 0.799)), and Amyloid-β1-42 (Aβ1-42) (OR = 1.028, 95%CI (1.018, 1.037)) were the influencing factors of CMBs. Education years (OR = 0.959, 95%CI (0.930, 0.988)), white matter lesions (OR = 2.687, 95%CI (1.782, 4.051)), and CMBs (OR = 21.246, 95%CI (5.728, 21.576)) were the risk factors for cognitive impairment. Hypertension increased the probability of deep CMBs (OR = 12.54, 95%CI (2.21, 71.28)), while Aβ1-42 elevated the probability of lobar CMBs (OR = 1.02, 95%CI (1.00, 1.03)). There was a linear correlation between the number of CMBs and Montreal Cognitive Assessment scores (r = −0.756, p < 0.001). However, CMBs in each region were not related to specific cognitive domains (p > 0.05), except CMBs in the mixed group that were negatively correlated with attention (OR = −0.669, 95%CI (−0.034, −5.270)); (5) Conclusions: Taken together, serum Aβ1-42 levels are related to the presence of CMBs. Cognitive impairment is correlated with the number of CMBs rather than their region. These findings suggest that CMBs play a role in cognitive impairment and that CMBs mark the presence of diffuse vascular injury and neurodegenerative brain damage.

Targeting the cannabinoid system to counteract the deleterious effects of stress in Alzheimer’s disease

Alzheimer’s disease is a progressive neurodegenerative disorder characterized histologically in postmortem human brains by the presence of dense protein accumulations known as amyloid plaques and tau tangles. Plaques and tangles develop over decades of aberrant protein processing, post-translational modification, and misfolding throughout an individual’s lifetime. We present a foundation of evidence from the literature that suggests chronic stress is associated with increased disease severity in Alzheimer’s patient populations. Taken together with preclinical evidence that chronic stress signaling can precipitate cellular distress, we argue that chronic psychological stress renders select circuits more vulnerable to amyloid- and tau- related abnormalities. We discuss the ongoing investigation of systemic and cellular processes that maintain the integrity of protein homeostasis in health and in degenerative conditions such as Alzheimer’s disease that have revealed multiple potential therapeutic avenues. For example, the endogenous cannabinoid system traverses the central and peripheral neural systems while simultaneously exerting anti-inflammatory influence over the immune response in the brain and throughout the body. Moreover, the cannabinoid system converges on several stress-integrative neuronal circuits and critical regions of the hypothalamic-pituitary-adrenal axis, with the capacity to dampen responses to psychological and cellular stress. Targeting the cannabinoid system by influencing endogenous processes or exogenously stimulating cannabinoid receptors with natural or synthetic cannabis compounds has been identified as a promising route for Alzheimer’s Disease intervention. We build on our foundational framework focusing on the significance of chronic psychological and cellular stress on the development of Alzheimer’s neuropathology by integrating literature on cannabinoid function and dysfunction within Alzheimer’s Disease and conclude with remarks on optimal strategies for treatment potential.

Unraveling the Mechanobiology Underlying Traumatic Brain Injury with Advanced Technologies and Biomaterials

Traumatic brain injury (TBI) is a worldwide health and socioeconomic problem, associated with prolonged and complex neurological aftermaths, including a variety of functional deficits and neurodegenerative disorders. Research on the long-term effects has highlighted that TBI shall be regarded as a chronic health condition. The initiation and exacerbation of TBI involve a series of mechanical stimulations and perturbations, accompanied by mechanotransduction events within the brain tissues. Mechanobiology thus offers a unique perspective and likely promising approach to unravel the underlying molecular and biochemical mechanisms leading to neural cells dysfunction after TBI, which may contribute to the discovery of novel targets for future clinical treatment. This article investigates TBI and the subsequent brain dysfunction from a lens of neuromechanobiology. Following an introduction, the mechanobiological insights are examined into the molecular pathology of TBI, and then an overview is given of the latest research technologies to explore neuromechanobiology, with particular focus on microfluidics and biomaterials. Challenges and prospects in the current field are also discussed. Through this article, it is hoped that extensive technical innovation in biomedical devices and materials can be encouraged to advance the field of neuromechanobiology, paving potential ways for the research and rehabilitation of neurotrauma and neurological diseases.

Microglia: Friend and foe in tauopathy

Aggregation of misfolded microtubule associated protein tau into abnormal intracellular inclusions defines a class of neurodegenerative diseases known as tauopathies. The consistent spatiotemporal progression of tau pathology in Alzheimer's disease (AD) led to the hypothesis that tau aggregates spread in the brain via bioactive tau "seeds" underlying advancing disease course. Recent studies implicate microglia, the resident immune cells of the central nervous system, in both negative and positive regulation of tau pathology. Polymorphisms in genes that alter microglial function are associated with the development of AD and other tauopathies. Experimental manipulation of microglia function can alter tau pathology and microglia-mediated neuroinflammatory cascades can exacerbate tau pathology. Microglia also exert protective functions by mitigating tau spread: microglia internalize tau seeds and have the capacity to degrade them. However, when microglia fail to degrade these tau seeds there are deleterious consequences, including secretion of exosomes containing tau that can spread to neurons. This review explores the intersection of microglia and tau from the perspective of neuropathology, neuroimaging, genetics, transcriptomics, and molecular biology. As tau-targeted therapies such as anti-tau antibodies advance through clinical trials, it is critical to understand the interaction between tau and microglia.

The interaction and pathogenesis between cognitive impairment and common cardiovascular diseases in the elderly

Both cognitive impairment and cardiovascular diseases have a high incidence in the elderly population, increasing the burden of care and reducing the quality of life. Studies have suggested that cognitive impairment interacts with cardiovascular diseases such as coronary heart disease, abnormal blood pressure, heart failure, and arrhythmia. On one hand, cognitive impairment in the elderly influences the progression and self-management of cardiovascular diseases and increases the risk of cardiovascular-related adverse events. On the other hand, coronary heart disease, heart failure, higher blood pressure variability, orthostatic hypotension, and atrial fibrillation may aggravate cognitive impairment. The role of blood pressure levels on cognition remains controversial. Several shared biological pathways have been proposed as the underlying mechanism for the association. Cardiovascular diseases may lead to cognitive decline even dementia through cerebral perfusion damage, brain structural changes, inflammation, β-amyloid deposition, and neuroendocrine disorders. It is of great significance to study the interaction and put forward effective interventions in an overall perspective to reduce care burden and improve the quality of life of the elderly patients.

Disrupting Neurons and Glial Cells Oneness in the Brain-The Possible Causal Role of Herpes Simplex Virus Type 1 (HSV-1) in Alzheimer's Disease

Current data strongly suggest herpes simplex virus type 1 (HSV-1) infection in the brain as a contributing factor to Alzheimer's disease (AD). The consequences of HSV-1 brain infection are multilateral, not only are neurons and glial cells damaged, but modifications also occur in their environment, preventing the transmission of signals and fulfillment of homeostatic and immune functions, which can greatly contribute to the development of disease. In this review, we discuss the pathological alterations in the central nervous system (CNS) cells that occur, following HSV-1 infection. We describe the changes in neurons, astrocytes, microglia, and oligodendrocytes related to the production of inflammatory factors, transition of glial cells into a reactive state, oxidative damage, Aβ secretion, tau hyperphosphorylation, apoptosis, and autophagy. Further, HSV-1 infection can affect processes observed during brain aging, and advanced age favors HSV-1 reactivation as well as the entry of the virus into the brain. The host activates pattern recognition receptors (PRRs) for an effective antiviral response during HSV-1 brain infection, which primarily engages type I interferons (IFNs). Future studies regarding the influence of innate immune deficits on AD development, as well as supporting the neuroprotective properties of glial cells, would reveal valuable information on how to harness cytotoxic inflammatory milieu to counter AD initiation and progression.

Amelioration effects of Cirsium japonicum var. maackii extract/fractions on amyloid beta25-35-induced neurotoxicity in SH-SY5Y cells and identification of the main bioactive compound

Amyloid beta (Aβ) is a neurotoxic peptide, and the accumulation of Aβ in the brain is the major characteristic of Alzheimer's disease (AD). Recently, the beneficial effects of Cirsium japonicum var. maackii (CJM) on brain health has attracted much attention. In the present study, we investigated the ability and protective mechanisms of CJM to attenuate neuronal toxicity caused by Aβ using SH-SY5Y cells. Aβ25-35 treatment decreased cell viability, whereas CJM extract/fractions increased cell viability in Aβ25-35-treated cells. We found that CJM treatment prevented the accumulation of reactive oxygen species observed in Aβ25-35-treated control cells. Furthermore, Aβ25-35-mediated production of inflammatory cytokines such as interleukin-1β was significantly suppressed by CJM. In addition, apoptotic factors were modulated in CJM-treated cells by downregulating B-cell lymphoma-2-associated X protein and upregulating B-cell lymphoma-2 protein expression. The assays showed that the ethyl acetate (EtOAc) fraction of CJM has greater neuroprotective bioactivities compared with the other extract/fractions. The main neuroprotective active compound from the EtOAc fraction of CJM was identified as pectolinarin using ultraperformance liquid chromatography-quadrupole time-of-flight-mass spectrometry. Collectively, this study not only describes the neuroprotective effect of CJM against Aβ25-35via the regulation of oxidative, inflammatory, and apoptotic signaling pathways, but also provides useful information for future studies on the mechanism of novel medicinal sources based on pectolinarin isolated from CJM.

The anesthetic sevoflurane induces tau trafficking from neurons to microglia

Accumulation and spread of tau in Alzheimer's disease and other tauopathies occur in a prion-like manner. However, the mechanisms and downstream consequences of tau trafficking remain largely unknown. We hypothesized that tau traffics from neurons to microglia via extracellular vesicles (EVs), leading to IL-6 generation and cognitive impairment. We assessed mice and neurons treated with anesthetics sevoflurane and desflurane, and applied nanobeam-sensor technology, an ultrasensitive method, to measure tau/p-tau amounts. Sevoflurane, but not desflurane, increased tau or p-tau amounts in blood, neuron culture medium, or EVs. Sevoflurane increased p-tau amounts in brain interstitial fluid. Microglia from tau knockout mice took up tau and p-tau when treated with sevoflurane-conditioned neuron culture medium, leading to IL-6 generation. Tau phosphorylation inhibitor lithium and EVs generation inhibitor GW4869 attenuated tau trafficking. GW4869 mitigated sevoflurane-induced cognitive impairment in mice. Thus, tau trafficking could occur from neurons to microglia to generate IL-6, leading to cognitive impairment.

Microglia in Aging and Alzheimer's Disease: A Comparative Species Review

Microglia are the primary immune cells of the central nervous system that help nourish and support neurons, clear debris, and respond to foreign stimuli. Greatly impacted by their environment, microglia go through rapid changes in cell shape, gene expression, and functional behavior during states of infection, trauma, and neurodegeneration. Aging also has a profound effect on microglia, leading to chronic inflammation and an increase in the brain's susceptibility to neurodegenerative processes that occur in Alzheimer's disease. Despite the scientific community's growing knowledge in the field of neuroinflammation, the overall success rate of drug treatment for age-related and neurodegenerative diseases remains incredibly low. Potential reasons for the lack of translation from animal models to the clinic include the use of a single species model, an assumption of similarity in humans, and ignoring contradictory data or information from other species. To aid in the selection of validated and predictive animal models and to bridge the translational gap, this review evaluates similarities and differences among species in microglial activation and density, morphology and phenotype, cytokine expression, phagocytosis, and production of oxidative species in aging and Alzheimer's disease.

SH-SY5Y-derived neurons: a human neuronal model system for investigating TAU sorting and neuronal subtype-specific TAU vulnerability

The microtubule-associated protein (MAP) TAU is mainly sorted into the axon of healthy brain neurons. Somatodendritic missorting of TAU is a pathological hallmark of many neurodegenerative diseases, including Alzheimer's disease (AD). Cause, consequence and (patho)physiological mechanisms of TAU sorting and missorting are understudied, in part also because of the lack of readily available human neuronal model systems. The human neuroblastoma cell line SH-SY5Y is widely used for studying TAU physiology and TAU-related pathology in AD and related tauopathies. SH-SY5Y cells can be differentiated into neuron-like cells (SH-SY5Y-derived neurons) using various substances. This review evaluates whether SH-SY5Y-derived neurons are a suitable model for (i) investigating intracellular TAU sorting in general, and (ii) with respect to neuron subtype-specific TAU vulnerability. (I) SH-SY5Y-derived neurons show pronounced axodendritic polarity, high levels of axonally localized TAU protein, expression of all six human brain isoforms and TAU phosphorylation similar to the human brain. As SH-SY5Y cells are highly proliferative and readily accessible for genetic engineering, stable transgene integration and leading-edge genome editing are feasible. (II) SH-SY5Y-derived neurons display features of subcortical neurons early affected in many tauopathies. This allows analyzing brain region-specific differences in TAU physiology, also in the context of differential vulnerability to TAU pathology. However, several limitations should be considered when using SH-SY5Y-derived neurons, e.g., the lack of clearly defined neuronal subtypes, or the difficulty of mimicking age-related tauopathy risk factors in vitro. In brief, this review discusses the suitability of SH-SY5Y-derived neurons for investigating TAU (mis)sorting mechanisms and neuron-specific TAU vulnerability in disease paradigms.

Platelets transport β-amyloid from the peripheral blood into the brain by destroying the blood-brain barrier to accelerate the process of Alzheimer's disease in mouse models

Extracellular aggregation of the β-amyloid (Aβ) peptide into toxic multimers in the brain is a prominent event occurring in the pathogenesis of Alzheimer's disease (AD), and a large amount of Aβ in the blood is derived from platelets. Thus, we speculated that platelets may play an important role in the process of AD. We first investigated the changes in platelet Aβ secretion with age. Then, we injected platelets from aged amyloid precursor protein APP/PS1 mice into young C57 mice and assessed their memory capacity along with their brain and peripheral blood Aβ expression levels. The Aβ content in mouse platelets increased with age. Exogenously aged APP/PS1 platelets changed the permeability of the blood-brain barrier in vitro, accelerating Aβ deposition in the brain and increasing the Aβ content in peripheral blood, leading to learning and memory deficits in the recipient mice. Subsequently, aspirin was administered to mice as an inhibitor of platelet activation, which effectively alleviated these toxic processes. Finally, we chose an in vitro blood-brain barrier model to explore the possible cytotoxicity of these platelets.

Chlorogenic acid enhances autophagy by upregulating lysosomal function to protect against SH-SY5Y cell injury induced by H2O2

Autophagy serves an important role in amyloid-β (Aβ) metabolism and τ processing and clearance in Alzheimer's disease. The progression of Aβ plaque accumulation and hyperphosphorylation of τ proteins are enhanced by oxidative stress. A hydrogen peroxide (H₂O₂) injury cell model was established using SH-SY5Y cells. Cells were randomly divided into normal, H₂O₂ and chlorogenic acid (5-caffeoylquinic acid; CGA) groups. The influence of CGA on cell viability was evaluated using a Cell Counting Kit-8 assay and cell death was assessed using Hoechst 33342 nuclear staining. Autophagy induction and fusion of autophagic vacuoles assays were performed using monodansylcadaverine staining. Additionally, SH-SY5Y cells expressing Ad-mCherry-green fluorescent protein-LC3B were established to detect autophagic flow. LysoTracker Red staining was used to evaluate lysosome function and LysoSensor™ Green staining assays were used to assess lysosomal acidification. The results demonstrated that CGA decreased the apoptosis rate, increased cell viability and improved cell morphology in H₂O₂-treated SH-SY5Y cells. Furthermore, CGA alleviated the accumulation of autophagic vacuoles, reduced the LC3BII/I ratio and decreased P62 levels, resulting in increased autophagic flux. Additionally, CGA upregulated lysosome acidity and increased the expression levels of cathepsin D. Importantly, these effects of CGA on H₂O₂-treated SH-SY5Y cells were mediated via the mTOR-transcription factor EB signaling pathway. These results indicated that CGA protected cells against H₂O₂-induced oxidative damage via the upregulation of autophagosomes, which promoted autophagocytic degradation and increased autophagic flux.

Axonal TAU Sorting Requires the C-terminus of TAU but is Independent of ANKG and TRIM46 Enrichment at the AIS

Somatodendritic missorting of the axonal protein TAU is a hallmark of Alzheimer's disease and related tauopathies. Rodent primary neurons and iPSC-derived neurons are used for studying mechanisms of neuronal polarity, including TAU trafficking. However, these models are expensive, time-consuming, and/or require the killing of animals. In this study, we tested four differentiation procedures to generate mature neuron cultures from human SH-SY5Y neuroblastoma cells and assessed the TAU sorting capacity. We show that SH-SY5Y-derived neurons, differentiated with sequential RA/BDNF treatment, are suitable for investigating axonal TAU sorting. These human neurons show pronounced neuronal polarity, axodendritic outgrowth, expression of the neuronal maturation markers TAU and MAP2, and, importantly, efficient axonal sorting of endogenous and transfected human wild-type TAU, similar to mouse primary neurons. We demonstrate that the N-terminal half of TAU is not sufficient for axonal targeting, as a C-terminus-lacking construct (N-term-TAU^HA) is not axonally enriched in both neuronal cell models. Importantly, SH-SY5Y-derived neurons do not show the formation of a classical axon initial segment (AIS), indicated by the lack of ankyrin G (ANKG) and tripartite motif-containing protein 46 (TRIM46) at the proximal axon, which suggests that successful axonal TAU sorting is independent of classical AIS formation. Taken together, our results provide evidence that (i) SH-SY5Y-derived neurons are a valuable human neuronal cell model for studying TAU sorting readily accessible at low cost and without animal need, and that (ii) efficient axonal TAU targeting is independent of ANKG or TRIM46 enrichment at the proximal axon in these neurons.

Resolution of Inflammation in Neurodegenerative Diseases: The Role of Resolvins

Acute inflammation has been described as a reactive dynamic process, promoted by the secretion of proinflammatory mediators, including lipid molecules like leukotrienes and prostaglandins, and counterbalanced by proresolving mediators including omega-3 polyunsaturated fatty-acid- (PUFA-) derived molecules. The switch from the initiation to the resolution phase of acute inflammatory response is crucial for tissue homeostasis, whereas the failure to resolve early inflammation by specialized proresolving mediators leads to chronic inflammation and tissue damage. Among PUFA-derived proresolving mediators, different eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derivatives have been described, namely, resolvins (resolution phase interaction products), which exert their anti-inflammatory and immune-regulatory activities through specific G-protein-coupled receptors. In recent years, compelling evidence has shown that impairment of resolution of inflammation is a crucial pathogenic hallmark in different neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. This review summarizes current knowledge on the role of resolvins in resolution of inflammation and highlights available evidence showing the neuroprotective potential of EPA- and DHA-derived resolvins (E-series and D-series resolvins, respectively) in neurodegenerative diseases.

Associations between brain inflammatory profiles and human neuropathology are altered based on apolipoprotein E ε4 genotype

Alzheimer disease (AD) is a chronic neurodegenerative disease with a multitude of contributing genetic factors, many of which are related to inflammation. The apolipoprotein E (APOE) ε4 allele is the most common genetic risk factor for AD and is related to a pro-inflammatory state. To test the hypothesis that microglia and AD-implicated cytokines were differentially associated with AD pathology based on the presence of APOE ε4, we examined the dorsolateral frontal cortex from deceased participants within a community-based aging cohort (n = 154). Cellular density of Iba1, a marker of microglia, was positively associated with tau pathology only in APOE ε4 positive participants (p = 0.001). The cytokines IL-10, IL-13, IL-4, and IL-1α were negatively associated with tau pathology, independent of Aβ_1–42 levels, only in APOE ε4 negative participants. Overall, the association of mostly anti-inflammatory cytokines with less tau pathology suggests a protective effect in APOE ε4 negative participants. These associations are largely absent in the presence of APOE ε4 where tau pathology was significantly associated with increased microglial cell density. Taken together, these results suggest that APOE ε4 mediates an altered inflammatory response and increased tau pathology independent of Aβ_1–42 pathology.

Anti-neuroinflammation ameliorates systemic inflammation-induced mitochondrial DNA impairment in the nucleus of the solitary tract and cardiovascular reflex dysfunction

BACKGROUND

Decreased heart rate variability (HRV) leads to cardiovascular diseases and increased mortality in clinical studies. However, the underlying mechanisms are still inconclusive. Systemic inflammation-induced neuroinflammation is known to impair the autonomic center of cardiovascular regulation. The dynamic stability of blood pressure and heart rate (HR) is regulated by modulation of the reciprocal responses of sympathetic and parasympathetic tone by the baroreflex, which is controlled by the nucleus of the solitary tract (NTS).

METHODS

Systemic inflammation was induced by E. coli lipopolysaccharide (LPS, 1.2 mg/kg/day, 7 days) peritoneal infusion via an osmotic minipump in normotensive Sprague-Dawley rats. Systolic blood pressure (SBP) and HR were measured by femoral artery cannulation and recorded on a polygraph under anesthesia. The low-frequency (LF; 0.25-0.8 Hz) and high-frequency (HF; 0.8-2.4 Hz) components of SBP were adopted as the indices for sympathetic vasomotor tone and parasympathetic vasomotor tone, while the baroreflex effectiveness index (BEI) was adopted from the analysis of SBP and pulse interval (PI). The plasma levels of proinflammatory cytokines and mitochondrial DNA (mtDNA) oxidative damage were analyzed by ELISA. Protein expression was evaluated by Western blot. The distribution of oxidative mtDNA was probed by immunofluorescence. Pharmacological agents were delivered via infusion into the cisterna magna with an osmotic minipump.

RESULTS

The suppression of baroreflex sensitivity was concurrent with increased SBP and decreased HR. Neuroinflammatory factors, including TNF-α, CD11b, and Iba-1, were detected in the NTS of the LPS group. Moreover, indices of mtDNA damage, including 8-OHdG and γ-H2AX, were significantly increased in neuronal mitochondria. Pentoxifylline or minocycline intracisternal (IC) infusion effectively prevented mtDNA damage, suggesting that cytokine and microglial activation contributed to mtDNA damage. Synchronically, baroreflex sensitivity was effectively protected, and the elevated blood pressure was significantly relieved. In addition, the mtDNA repair mechanism was significantly enhanced by pentoxifylline or minocycline.

CONCLUSION

These results suggest that neuronal mtDNA damage in the NTS induced by neuroinflammation could be the core factor in deteriorating baroreflex desensitization and subsequent cardiovascular dysfunction. Therefore, the enhancement of base excision repair (BER) signaling in mitochondria could be a potential therapeutic strategy for cardiovascular reflex dysregulation.

Active Fraction Combination from Liuwei Dihuang Decoction (LW-AFC) Alleviated the LPS-Induced Long-Term Potentiation Impairment and Glial Cells Activation in Hippocampus of Mice by Modulating Immune Responses

Neuroinflammation is known as a typical feature associated with many neurodegenerative diseases including Alzheimer's disease (AD) and impairs the synaptic plasticity of the hippocampus. LW-AFC is an active fraction combination being extracted from Liuwei Dihuang decoction, a classic traditional Chinese medicine prescription. This study aimed to investigate the effects of LW-AFC on synaptic plasticity in mice with lipopolysaccharide (LPS) treatment. The results showed that the administration of LPS caused fever and long-term potentiation (LTP) impairment in mice. The pretreatment with LW-AFC had an antipyretic effect on fever and improved the impaired LTP induced by LPS, alleviated the microglia and astrocytes activation in the hippocampus, regulated the abnormal T-lymphocyte subpopulation in the spleen and blood caused by LPS, and reduced the aberrant secretion of cytokines in the brain and plasma. The compounds paeoniflorin, morroniside, and loganic acid in LW-AFC regulated the TNF-α secretion in non-LPS- and LPS-stimulated BV-2 cells. These data suggest that LW-AFC improves the LPS-induced impairment of LTP and alleviates the activation of glial cells in the hippocampus, which might be associated with modulating immune responses.

Role of Microglial Cells in Alzheimer's Disease Tau Propagation

Uncontrolled immune response in the brain contributes to the progression of all neurodegenerative disease, including Alzheimer's disease (AD). Recent investigations have documented the prion-like features of tau protein and the involvement of microglial changes with tau pathology. While it is still unclear what sequence of events is causal, it is likely that tau seeding potential and microglial contribution to tau propagation act together, and are essential for the development and progression of degenerative changes. Based on available evidence, targeting tau seeds and controlling some signaling pathways in a complex inflammation process could represent a possible new therapeutic approach for treating neurodegenerative diseases. Recent findings propose novel diagnostic assays and markers that may be used together with standard methods to complete and improve the diagnosis and classification of these diseases. In conclusion, a novel perspective on microglia-tau relations reveals new issues to investigate and imposes different approaches for developing therapeutic strategies for AD.

Microglial priming of antigen presentation and adaptive stimulation in Alzheimer's disease

The prominent pathological consequences of Alzheimer's disease (AD) are the misfolding and mis-sorting of two cellular proteins, amyloid-β and microtubule-associated protein Tau. The accumulation of toxic phosphorylated Tau inside the neurons induces the increased processing of amyloid-β-associated signaling cascade and vice versa. Neuroinflammation-driven synaptic depletion and cognitive decline are substantiated by the cross talk of activated microglia and astroglia, leading to neuron degeneration. Microglia are the brain-resident immune effectors that prove their diverse functions in maintaining CNS homeostasis via collaboration with astrocytes and T lymphocytes. Age-related senescence and chronic inflammation activate microglia with increased pro-inflammatory markers, oxidative damage and phagocytosis. But the improper processing of misfolded protein via lysosomal pathway destines the spreading of 'seed' constituents to the nearby healthy neurons. Primed microglia process and present self-antigen such as amyloid-β and modified Tau to the infiltrated T lymphocytes through MHC I/II molecules. After an effective conversation with CD4+ T cells, microglial phenotype can be altered from pro-active M1 to neuro-protective M2 type, which corresponds to the tissue remodeling and homeostasis. In this review, we are focusing on the change in functionality of microglia from innate to adaptive immune response in the context of neuroprotection, which may help in the search of novel immune therapy in AD.

Microglial activation correlates in vivo with both tau and amyloid in Alzheimer's disease

Alzheimer's disease is characterized by the histopathological presence of amyloid-β plaques and tau-containing neurofibrillary tangles. Microglial activation is also a recognized pathological component. The relationship between microglial activation and protein aggregation is still debated. We investigated the relationship between amyloid plaques, tau tangles and activated microglia using PET imaging. Fifty-one subjects (19 healthy controls, 16 mild cognitive impairment and 16 Alzheimer's disease subjects) participated in the study. All subjects had neuropsychometric testing, MRI, amyloid (18F-flutemetamol), and microglial (11C-PBR28) PET. All subjects with mild cognitive impairment and Alzheimer's disease and eight of the controls had tau (18F-AV1451) PET. 11C-PBR28 PET was analysed using Logan graphical analysis with an arterial plasma input function, while 18F-flutemetamol and 18F-AV1451 PET were analysed as target:cerebellar ratios to create parametric standardized uptake value ratio maps. Biological parametric mapping in the Statistical Parametric Mapping platform was used to examine correlations between uptake of tracers at a voxel-level. There were significant widespread clusters of positive correlation between levels of microglial activation and tau aggregation in both the mild cognitive impairment (amyloid-positive and amyloid-negative) and Alzheimer's disease subjects. The correlations were stronger in Alzheimer's disease than in mild cognitive impairment, suggesting that these pathologies increase together as disease progresses. Levels of microglial activation and amyloid deposition were also correlated, although in a different spatial distribution; correlations were stronger in mild cognitive impairment than Alzheimer's subjects, in line with a plateauing of amyloid load with disease progression. Clusters of positive correlations between microglial activation and protein aggregation often targeted similar areas of association cortex, indicating that all three processes are present in specific vulnerable brain areas. For the first time using PET imaging, we show that microglial activation can correlate with both tau aggregation and amyloid deposition. This confirms the complex relationship between these processes. These results suggest that preventative treatment for Alzheimer's disease should target all three processes.

NF-κB-mediated inflammatory damage is differentially affected in SH-SY5Y and C6 cells treated with 27-hydroxycholesterol

Previous studies have demonstrated that 27-hydroxycholesterol (27-OHC), a cholesterol metabolite, was involved in the inflammatory process of Alzheimer's disease (AD). The present study aimed to investigate the 27-OHC-induced inflammatory damage to neurons and astrocytes and the underlying mechanism(s) accounting for this damage. Human neuroblastoma cells (SH-SY5Y cells) and rat glioma cells (C6 cells) were treated with vehicle or 27-OHC (5, 10, or 20 μM) for 24 hr. The levels of secreted interleukin-1β (IL-1β), interleukin-10 (IL-10), tumor necrosis factor alpha (TNF-α), and inducible nitric oxide synthase (iNOS) were determined by using an enzyme-linked immunosorbent assay (ELISA). Immunofluorescence staining was used to determine the cellular expression of toll-like receptor 4 (TLR4) and transforming growth factor-β (TGF-β). The mRNA and protein expression levels of nuclear factor-κB p65 (NF-κB p65), nuclear factor-κB p50 (NF-κB p50) and cyclooxygenase-2 (COX-2) in both SH-SY5Y and C6 cells were also detected by real-time PCR and Western blot, respectively. The results of this study showed that 27-OHC treatment increased secretion of TNF-α and iNOS and decreased secretion of IL-10, upregulated expression of TGF-β, NF-κB p65 and p50, and downregulated expression of COX-2 in SH-SY5Y cells. In C6 cells, treatment with 27-OHC resulted in decreased secretion of IL-1β, IL-10, TNF-α, and iNOS, and increased expression of TLR4 and TGF-β. These results suggest that 27-OHC may cause inflammatory damage to neurons by activating the TGF-β/NF-κB signaling pathway and to astrocytes by activating the TLR4/TGF-β signaling, which results in the subsequent release of inflammatory cytokines.

The Link Between Tau and Insulin Signaling: Implications for Alzheimer's Disease and Other Tauopathies

The microtubule-associated protein tau (MAPT) is mainly identified as a tubulin binding protein essential for microtubule dynamics and assembly and for neurite outgrowth. However, several other possible functions for Tau remains to be investigated. Insulin signaling is important for synaptic plasticity and memory formation and therefore is essential for proper brain function. Tau has recently been characterized as an important regulator of insulin signaling, with evidence linking Tau to brain and peripheral insulin resistance and beta cell dysfunction. In line with this notion, the hypothesis of Tau pathology as a key trigger of impaired insulin sensitivity and secretion has emerged. Conversely, insulin resistance can also favor Tau dysfunction, resulting in a vicious cycle of these events. In this review article, we discuss recent evidence linking Tau pathology, insulin resistance and insulin deficiency. We further highlight the deleterious consequences of Tau pathology-induced insulin resistance to the brain and/or peripheral tissues, suggesting that these are key events mediating cognitive decline in Alzheimer’s disease (AD) and other tauopathies.

Effects of Microglial Cytokines on Alzheimer's Disease-Related Phenomena

Recent association studies indicate several genes highly expressed by microglia influence Alzheimer's disease (AD) risk, which suggests microglial function contributes to this disease. Here, we evaluated how one component of microglial function, cytokine release, affects AD-related phenomena. First, we used a 3-hour lipopolysaccharide (LPS) treatment to activate mouse BV2 microglial cells. Next, we removed the LPS-containing medium, added LPS-free medium, and after 6 hours collected the medium conditioned by the activated BV2 microglial cells. We then exposed human neuronal SH-SY5Y cells to the conditioned medium for 24 hours. At the end of the 24-hour exposure, we assessed amyloid-β protein precursor (AβPP), tau, apolipoprotein E (ApoE), and lipid status. The amount of AβPP was unaffected, although a slight decrease in soluble AβPPα suggested a subtle reduction in AβPP non-amyloidogenic processing occurred. Tau mRNA increased, but total and phosphorylated tau levels were unchanged. ApoE mRNA increased, while ApoE protein levels were lower. Per cell lipid droplet number decreased and lipid oxidation increased. These results show cytokine release by activated microglial cells can influence specific AD-relevant physiologies and pathologies.

Microglia changes associated to Alzheimer's disease pathology in aged chimpanzees

In Alzheimer's disease (AD), the brain's primary immune cells, microglia, become activated and are found in close apposition to amyloid beta (Aβ) protein plaques and neurofibrillary tangles (NFT). The present study evaluated microglia density and morphology in a large group of aged chimpanzees (n = 20, ages 37-62 years) with varying degrees of AD-like pathology. Using immunohistochemical and stereological techniques, we quantified the density of activated microglia and morphological variants (ramified, intermediate, and amoeboid) in postmortem chimpanzee brain samples from prefrontal cortex, middle temporal gyrus, and hippocampus, areas that show a high degree of AD pathology in humans. Microglia measurements were compared to pathological markers of AD in these cases. Activated microglia were consistently present across brain areas. In the hippocampus, CA3 displayed a higher density than CA1. Aβ42 plaque volume was positively correlated with higher microglial activation and with an intermediate morphology in the hippocampus. Aβ42-positive vessel volume was associated with increased hippocampal microglial activation. Activated microglia density and morphology were not associated with age, sex, pretangle density, NFT density, or tau neuritic cluster density. Aged chimpanzees displayed comparable patterns of activated microglia phenotypes as well as an association of increased microglial activation and morphological changes with Aβ deposition similar to AD patients. In contrast to human AD brains, activated microglia density was not significantly correlated with tau lesions. This evidence suggests that the chimpanzee brain may be relatively preserved during normal aging processes but not entirely protected from neurodegeneration as previously assumed.

MAPT (Tau) expression is a biomarker for an increased rate of survival in pediatric neuroblastoma

Although the impact of MAPT (Tau) expression has been well documented for neuronal cells in the context of tauopathies and neurodegenerative diseases, the impact and role of Tau expression in cancer, and specifically cancers of neuronal origin, is in its infancy. To determine the correlation between MAPT expression and survival in pediatric neuroblastoma, MAPT gene expression for samples from the TARGET pediatric neuroblastoma dataset was assessed. Initial analyses indicated that increased MAPT expression correlated with increased overall survival in neuroblastoma but not in ovarian cancer. Expression of apoptosis- and proliferation-effector genes in the neuroblastoma samples was consistent with the MAPT related survival result. Furthermore, we determined that higher neuroblastoma expression of APP also associated with neurodegeneration, correlated with better neuroblastoma survival rates. In sum, Gene expression associated with neuronal degenerative diseases was associated with a better neuroblastoma outcome. Abbreviations: ALS: Amyotrophic Lateral Sclerosis; APP: Amyloid Precursor Protein gene; CASP3: Caspase 3 gene; CASP9: Caspase 9 gene; H2AFX: H2A histone family, member X gene; HIST1H2AL: Histone H2A type 1 gene; HIST1H2BK: Histone H2B type 1-K gene; HIST1H3J: Histone H3J gene; HIST1H4B: Histone H4B gene; HIST2H2BE: Histone H2B type 2-E gene; HUGO: human genome organization; KM: Kaplan-Meier survival curve; MAPT: Tau gene; OV: Ovarian cancer; SNCA: alpha-syneculin gene; TARDBP: Transactive response DNA binding protein 43 kDa; TCGA: the cancer genome atlas.

Partial reduction of microglia does not affect tau pathology in aged mice

Background

Activation of inflammation pathways in the brain occurs in Alzheimer’s disease and may contribute to the accumulation and spread of pathological proteins including tau. The goal of this study was to identify how changes in microglia, a key inflammatory cell type, may contribute to tau protein accumulation and pathology-associated changes in immune and non-immune cell processes such as neuronal degeneration, astrocyte physiology, cytokine expression, and blood vessel morphology.

Methods

We used PLX3397 (290 mg/kg), a colony-stimulating factor receptor 1 (CSF1R) inhibitor, to reduce the number of microglia in the brains of a tau-overexpressing mouse model. Mice were fed PLX3397 in chow or a control diet for 3 months beginning at 12 months of age and then were subsequently analyzed for changes in blood vessel morphology by in vivo two-photon microscopy and tissues were collected for biochemistry and histology.

Results

PLX3397 reduced microglial numbers by 30% regardless of genotype compared to control diet-treated mice. No change in tau burden, cortical atrophy, blood vessels, or astrocyte activation was detected. All Tg4510 mice were observed to have an increased in “disease-associated” microglial gene expression, but PLX3397 treatment did not reduce expression of these genes. Surprisingly, PLX3397 treatment resulted in upregulation of CD68 and Tgf1β.

Conclusions

Manipulating microglial activity may not be an effective strategy to combat tau pathological lesions. Higher doses of PLX3397 may be required or earlier intervention in the disease course. Overall, this indicates a need for a better understanding of specific microglial changes and their relation to the disease process.

TREM2 Ameliorates Neuronal Tau Pathology Through Suppression of Microglial Inflammatory Response

As a recently identified susceptibility gene for Alzheimer's disease (AD), triggering receptor expressed on myeloid cells 2 (TREM2) encodes an immune receptor that is uniquely expressed on microglia, functioning as a modulator of microglial functions including phagocytosis and inflammatory response. Several lines of evidence suggest that TREM2 is upregulated and positively correlates with tau pathology in the brains of AD patients. Meanwhile, our recent study showed that knockdown of TREM2 markedly exacerbated neuronal tau hyperphosphorylation in the brains of P301S-tau transgenic mice, implying that TREM2 might exert a protective role against tau pathology under AD context. However, the precise mechanisms underlying this observation remain largely unclear. In this study, by employing a microglial-neuronal co-culture model, we showed that microglial inflammatory response induced by lipopolysaccharide led to tau hyperphosphorylation in neurons via activation of a major tau kinase glycogen synthase kinase 3β, confirming the pathogenic effects of activated microglia on the progression of tau pathology. More importantly, by manipulating TREM2 levels in microglia with a lentiviral-mediated strategy, we demonstrated that TREM2 ameliorated the pathological effects of activated microglia on neuronal tau hyperphosphorylation via suppression of microglial inflammatory response. Taken together, these findings uncover the underlying mechanisms by which TREM2 protects against tau pathology and highlight TREM2 as a potential therapeutic target for AD.

Eriodictyol Attenuates LPS-Induced Neuroinflammation, Amyloidogenesis, and Cognitive Impairments via the Inhibition of NF-κB in Male C57BL/6J Mice and BV2 Microglial Cells

Eriodictyol, a natural flavonoid mainly distributed in citrus fruits and peanut, has been well-documented with possession of excellent anti-inflammatory, antioxidant, and anticancer bioactivities. This work focus on the protective effects of eriodictyol on LPS-induced neuroinflammation, amyloidogenesis, cognitive impairment, and the potential mechanisms involved. Behavioral tests and histological examinations showed that eriodictyol significantly prevented the memory and neuronal damage triggered by LPS. Consistently, eriodictyol (100 mg/kg) reduced the formation of Aβ_1-42 by 28.37 ± 16.71 pg/mL compared to the LPS group. In addition, high dose eriodictyol (100 mg/kg) also equilibrated the cholinergic system via suppressing AChE activity (0.1996 ± 0.0831 U/mgprot) and elevating ChAT activity (41.81 ± 24.72 U/g) as well as ACh level (5.093 ± 3.531 μg/mgprot) compared to the LPS group. Western blot results indicated that compared to the LPS group, eriodictyol suppressed LPS-induced glial overactivation (84.29% ± 27.21%) and regulated inflammatory mediators and cytokines by inhibiting the NF-κB and MAPK pathways. These results indicated that eriodictyol alleviated amyloidogenesis and memory impairment triggered by LPS via inhibiting TLR4, MAPKs, and PI3K/Akt, and activating Sirt1 pathways and thus blocking downstream translocation of NF-κB, which offers a potential nutritional preventive strategy for neuroinflammation diseases such as Alzheimer's disease (AD).

The role of microglia in processing and spreading of bioactive tau seeds in Alzheimer's disease

Background

Misfolding of microtubule-associated protein tau (MAPT) within neurons into neurofibrillary tangles is an important pathological feature of Alzheimer’s disease (AD). Tau pathology correlates with cognitive decline in AD and follows a stereotypical anatomical course; several recent studies indicate that tau pathology spreads inter-neuronally via misfolded tau “seeds.” Previous research has focused on neurons as the source of these tau seeds. However, recent studies as well as the data contained herein suggest that microglia, the resident immune cells of the central nervous system, play a direct role in the spread of tau pathology.

Methods

Primary adult microglia were isolated from human AD cases and the rTg4510 tauopathy mouse model and used for analysis of gene expression, tau protein by Simoa technology, and quantification of tau seeding using a highly sensitive fluorescence resonance energy transfer (FRET) biosensing cell line for tau seeding and aggregation.

Results

Here, we show that microglia isolated from both human tauopathy and AD cases and the rTg4510 tauopathy mouse model stably contain tau seeds, despite not synthesizing any tau. Microglia releases these tau seeds in vitro into their conditioned media (CM). This suggests that microglia have taken up tau but are incapable of entirely neutralizing its seeding activity. Indeed, when in vitro microglia are given media containing tau seeds, they reduce (but do not eliminate) tau seeding. When microglia are treated with inflammagens such as lipopolysaccharide (LPS), interleukin-1β (IL1β), tumor necrosis factor α (TNFα), or amyloid-β, their ability to reduce tau seeding is unchanged and these factors do not induce seeding activity on their own.

Conclusions

Overall, these data suggest that microglia have a complex role: they are capable of taking up and breaking down seed competent tau, but do so inefficiently and could therefore potentially play a role in the spread of tau pathology.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1309-z) contains supplementary material, which is available to authorized users.

Walnut Protein Hydrolysates Play a Protective Role on Neurotoxicity Induced by d-Galactose and Aluminum Chloride in Mice

In recent years, with an increase in the aging population, neurodegenerative diseases have attracted more and more attention. This study aimed to investigate the potential neuroprotective effect of defatted walnut meal protein hydrolysates (DWMPH) on neurotoxicity induced by d-galactose (d-gal) and aluminum chloride (AlCl₃) in mice. The animal models were established by combining treatments with d-gal (200 mg/kg/day, subcutaneously) and AlCl₃ (100 mg/kg in drinking water) for 90 days. During the 90 days, 1 g/kg of DWMPH was administrated orally every day. The results indicated that DWMPH treatment alleviated oxidative stress, reversed cholinergic dysfunction, and suppressed the release of proinflammatory cytokines in the brains of d-gal + AlCl₃-treated mice, and thus improving the learning and memory functions of these mice, which was closely correlated with the strong antioxidant activity of DWMPH. This finding suggests that DWMPH might be a promising dietary supplement in improving neuronal dysfunctions of the brain.

DHA, EPA and their combination at various ratios differently modulated Aβ25-35-induced neurotoxicity in SH-SY5Y cells

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), have been reported to prevent neurodegenerative diseases such as Alzheimer's disease (AD) in both experimental and clinical/epidemiological studies. However, whether DHA and EPA from natural products exert similar or different neuroprotective effects and how these n-3 PUFAs target cellular and molecular mechanisms associated with neurodegenerative disease pathogenesis are unknown. In the present study, we used amyloid-β (Aβ)_25-35-treated differentiated SH-SY5Y cells as a model of AD to compare the neuroprotective effect of DHA, EPA and their combination at various ratios. Administration of 20μM Aβ_25-35 significantly decreased SH-SY5Y cell viability, the expression of nerve growth factor (NGF), its TrkA receptor, and the level of glutathione (GSH) and increased reactive oxygen species (ROS), nitric oxide, tumor necrosis factor (TNF)-α, brain derived neurotrophic factor (BDNF) and its TrkB receptor. Aβ_25-35 also increased the Bax/Bcl-2 ratio and the expression of Caspase-3 in these cells. Compared with the Aβ group, pretreatment with DHA/EPA significantly reduced cell death, especially at ratio of 1:1 and 2:1 DHA/EPA or pure DHA. However, the most efficient ratio for reducing changes in ROS and GSH and for decreasing TNF-α appeared at ratio of 1:2 and 1:1, respectively. The ratio of 1:1, 2:1 and pure DHA resulted in significant increase in the level of NGF. Furthermore, pure DHA was the most efficient for reducing Bax/Bcl ratio and Caspase-3 expression. In conclusion, DHA, EPA and their combination differently modulated Aβ_25-35-induced neurotoxicity in SH-SY5Y cells by exerting anti-oxidative, anti-inflammatory and neurotrophic effects.

Genetic reduction of Nrf2 exacerbates cognitive deficits in a mouse model of Alzheimer's disease

Aging is the major risk factor for several neurodegenerative diseases, including Alzheimer's disease (AD). However, the mechanisms by which aging contributes to neurodegeneration remain elusive. The nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a transcription factor that regulates expression of a vast number of genes by binding to the antioxidant response element. Nrf2 levels decrease as a function of age, and reduced Nrf2 levels have been reported in postmortem human brains and animal models of AD. Nevertheless, it is still unknown whether Nrf2 plays a role in the cognitive deficits associated with AD. To address this question, we used a genetic approach to remove the Nrf2 gene from APP/PS1 mice, a widely used animal model of AD. We found that the lack of Nrf2 significantly exacerbates cognitive deficits in APP/PS1, without altering gross motor function. Specifically, we found an exacerbation of deficits in spatial learning and memory, as well as in working and associative memory. Different brain regions control these behavioral tests, indicating that the lack of Nrf2 has a global effect on brain function. The changes in cognition were linked to an increase in Aβ and interferon-gamma (IFNγ) levels, and microgliosis. The changes in IFNγ levels are noteworthy as previously published evidence indicates that IFNγ can increase microglia activation and induce Aβ production. Our data suggest a clear link between Nrf2 and AD-mediated cognitive decline and further strengthen the connection between Nrf2 and AD.

Engineered commensal bacteria prevent systemic inflammation-induced memory impairment and amyloidogenesis via producing GLP-1

The anti-obesity drug GLP-1 has been proven to have an impact on central nervous system, while its extremely short half-life greatly limited its use. In this study, our group constructed two engineering strains MG1363-pMG36e-GLP-1 and VNP20009-pLIVE-GLP-1 to continuously express GLP-1, and supplementation of these strains, especially MG1363-pMG36e-GLP-1, had significantly restored the spatial learning and memory impairment of mice caused by LPS (p < 0.05), suppressed glia activation and Aβ accumulation, and downregulated inflammatory expressions of COX-2, TLR-4, TNF-a, and IL-1β. In addition, MG1363-pMG36e-GLP-1 had significantly blocked the translocation of NF-κB signal and inhibited the phosphorylation of redox-sensitive cytoplasmic signalings of MAPKs and PI3K/AKT. These data suggest that MG1363-pMG36e-GLP-1 could be used as a safe and effective nonabsorbed oral treatment for neuroinflammation-related diseases such as Alzheimer's disease (AD).

Chronically raised C-reactive protein is inversely associated with cortical β-amyloid in older adults with subjective memory complaints

BACKGROUND

Inflammation promotes amyloidogenesis in animals and markers of inflammation are associated with β-amyloid (Aβ) in humans. Hence, we sought to examine the cross-sectional associations between chronically elevated plasma C reactive protein (CRP) and cortical Aβ in 259 non-demented elderly individuals reporting subjective memory complaints from the Multidomain Alzheimer Preventive Trial (MAPT).

METHODS

Cortical-to-cerebellar standard uptake value ratios were obtained using [¹⁸F] florbetapir positron emission tomography (PET). CRP was measured in plasma using immunoturbidity. Chronically raised CRP was defined as having 2 consecutively high CRP readings (>3 mg/l ≤ 10 mg/l) between study baseline and the 1 year visit (visits were performed at baseline, 6 months, 1 year and then annually). Associations were explored using adjusted multiple linear regression.

RESULTS

Chronically raised CRP was found to be inversely associated with cortical Aβ (B-coefficient: -0.054, SE: 0.026, p = 0.040) and this association seemed to be specific to apolipoprotein E (Apo E) ε4 carriers (B-coefficient: -0.130, SE: 0.058, p = 0.027). CRP as an isolated reading measured closest to PET scan was also inversely associated with cortical Aβ when CRP was treated as a dichotomized variable (high CRP > 3 mg/l ≤ 10 mg/l, B-coefficient: -0.048, SE: 0.023, p = 0.043).

CONCLUSIONS

Our preliminary findings suggest that inflammation might be beneficial in the early stages of Alzheimer's disease as the immune systems attempts to combat Aβ pathology particularly in ApoE ε4 carriers. Investigating the temporal relationships between cerebral Aβ and a panel of inflammatory markers would provide further evidence as to whether chronic inflammation might modulate amyloidogenesis in vivo.

Principles for central nervous system inflammation research: A call for a consortium approach

INTRODUCTION

Neuroinflammation is now considered to be of pathophysiologic significance in Alzheimer's disease and other neurodegenerative conditions. Nonetheless, there is no consensus as to what inflammatory mechanisms need to be combated (or facilitated), how therapies for them should be applied, or when they might be efficacious.

METHODS

This article seeks to put forward cornerstone facts about neuroinflammation, with suggestions for future directions.

RESULTS

Multiple scientific points about neuroinflammation still remain unaddressed. The main issue, however, is political. An expert body is needed that can sort through the myriad findings and provide consensus advice to agencies that fund basic and clinical research.

DISCUSSION

Consortium approaches have shown immense value in other Alzheimer's disease research areas and are badly needed in neuroinflammation research. Lacking a consensus, neuroinflammation is just a very large number of isolated articles clamoring for attention.

Imaging Translocator Protein as a Biomarker of Neuroinflammation in Dementia

Neuroinflammation has long been considered a potential contributor to neurodegenerative disorders that result in dementia. Accumulation of abnormal protein aggregates in Alzheimer's disease, frontotemporal dementia, and dementia with Lewy bodies is associated with the activation of microglia and astrocytes into proinflammatory states, and chronic low-level activation of glial cells likely contributes to the pathological changes observed in these and other neurodegenerative diseases. The 18kDa translocator protein (TSPO) is a key biomarker for measuring inflammation in the brain via positron emission tomography (PET). Increased TSPO density has been observed in brain tissue from patients with neurodegenerative diseases and colocalizes to activated microglia and reactive astrocytes. Several radioligands have been developed to measure TSPO density in vivo with PET, and these have been used in clinical studies of different dementia syndromes. However, TSPO radioligands have limitations, including low specific-to-nonspecific signal and differential affinity to a polymorphism on the TSPO gene, which must be taken into consideration in designing and interpreting human PET studies. Nonetheless, most PET studies have shown that increased TSPO binding is associated with various dementias, suggesting that TSPO has potential as a biomarker to further explore the role of neuroinflammation in dementia pathogenesis and may prove useful in monitoring disease progression.

Chronic traumatic encephalopathy-integration of canonical traumatic brain injury secondary injury mechanisms with tau pathology

In recent years, a new neurodegenerative tauopathy labeled Chronic Traumatic Encephalopathy (CTE), has been identified that is believed to be primarily a sequela of repeated mild traumatic brain injury (TBI), often referred to as concussion, that occurs in athletes participating in contact sports (e.g. boxing, American football, Australian football, rugby, soccer, ice hockey) or in military combatants, especially after blast-induced injuries. Since the identification of CTE, and its neuropathological finding of deposits of hyperphosphorylated tau protein, mechanistic attention has been on lumping the disorder together with various other non-traumatic neurodegenerative tauopathies. Indeed, brains from suspected CTE cases that have come to autopsy have been confirmed to have deposits of hyperphosphorylated tau in locations that make its anatomical distribution distinct for other tauopathies. The fact that these individuals experienced repetitive TBI episodes during their athletic or military careers suggests that the secondary injury mechanisms that have been extensively characterized in acute TBI preclinical models, and in TBI patients, including glutamate excitotoxicity, intracellular calcium overload, mitochondrial dysfunction, free radical-induced oxidative damage and neuroinflammation, may contribute to the brain damage associated with CTE. Thus, the current review begins with an in depth analysis of what is known about the tau protein and its functions and dysfunctions followed by a discussion of the major TBI secondary injury mechanisms, and how the latter have been shown to contribute to tau pathology. The value of this review is that it might lead to improved neuroprotective strategies for either prophylactically attenuating the development of CTE or slowing its progression.