Microglial receptor for advanced glycation end product-dependent signal pathway drives beta-amyloid-induced synaptic depression and long-term depression impairment in entorhinal cortex

Neurotoxic β-amyloid oligomers cause mitochondrial dysfunction-the trigger for PANoptosis in neurons

As the global population ages, the incidence of elderly patients with dementia, represented by Alzheimer's disease (AD), will continue to increase. Previous studies have suggested that β-amyloid protein (Aβ) deposition is a key factor leading to AD. However, the clinical efficacy of treating AD with anti-Aβ protein antibodies is not satisfactory, suggesting that Aβ amyloidosis may be a pathological change rather than a key factor leading to AD. Identification of the causes of AD and development of corresponding prevention and treatment strategies is an important goal of current research. Following the discovery of soluble oligomeric forms of Aβ (AβO) in 1998, scientists began to focus on the neurotoxicity of AβOs. As an endogenous neurotoxin, the active growth of AβOs can lead to neuronal death, which is believed to occur before plaque formation, suggesting that AβOs are the key factors leading to AD. PANoptosis, a newly proposed concept of cell death that includes known modes of pyroptosis, apoptosis, and necroptosis, is a form of cell death regulated by the PANoptosome complex. Neuronal survival depends on proper mitochondrial function. Under conditions of AβO interference, mitochondrial dysfunction occurs, releasing lethal contents as potential upstream effectors of the PANoptosome. Considering the critical role of neurons in cognitive function and the development of AD as well as the regulatory role of mitochondrial function in neuronal survival, investigation of the potential mechanisms leading to neuronal PANoptosis is crucial. This review describes the disruption of neuronal mitochondrial function by AβOs and elucidates how AβOs may activate neuronal PANoptosis by causing mitochondrial dysfunction during the development of AD, providing guidance for the development of targeted neuronal treatment strategies.

Zexieyin formula alleviates atherosclerosis with cognitive impairment: A novel role in the treatment of comorbidities and its underlying mechanisms

ETHNOPHARMACOLOGICAL RELEVANCY

Zexieyin formula (ZXYF) has been identified to have therapeutic actions of atherosclerosis (AS). It's unknown that whether ZXYF has therapeutic potential of atherosclerosis (AS) with cognitive impairment (CI) and its underlying mechanisms.

AIM OF THE STUDY

To elucidate therapeutic effect of ZXYF for AS with CI as well as its underlying mechanisms in AS with CI mice model.

METHODS AND MATERIALS

To establish AS with CI model, we fed ApoE-/- mice with high-fat diet (HFD) for 8 weeks. Oil red O staining (ORO) and Hematoxylin-eosin staining (HE) were used to detect aortic plaque area. Morris water maze (MWM) and Y-maze were used to measure cognitive function and cognitive improvement after administration of ZXYF and atorvastatin (ATO). Network pharmacology was used to screen for potential mechanisms for improving cognitive function. Western blot was used to detect expressions of MAPK, Aβ and synaptic proteins in hippocampus.

RESULTS

HFD caused and accelerated the AS in ApoE-/- mice, while it was easier able to produce CI than normal mice. Administration of ZXYF or ATO for 8 weeks significantly reduced aortic plaque area in ORO and HE tests, and improved cognitive abilities in MWM and Y-maze tests. Network pharmacology results showed that MAPK or synaptic proteins were highly associated with CI. HFD contributed to abnormal expressions of MAPK (pERK, pP38, pJNK), NF-kB, synaptic proteins (PSD95, synapsin1) and β-amyloid (Aβ) in hippocampus, which were all reversed by ZXYF. However, ERK and PSD95 expressions were not reversed by ATO in hippocampus.

CONCLUSIONS

ZXYF mitigated AS, further alleviating CI by modulating MAPK signaling, relating to synaptic proteins enhancing and Aβ protein decreasing in the hippocampus. This study firstly lit up the new clinical application of ZXYF, which might promote the use of ZXYF in AS and CI patients.

Maladaptive plasticity induced by morphine is mediated by hippocampal astrocytic Connexin-43

AIMS

Drug addiction is an aberrant learning process that involves the recruitment of memory systems. We have previously demonstrated that morphine exposure causes maladaptive synaptic plasticity which involved hippocampal glial cells, especially astrocytes. Morphine addiction has been associated with astrocytic connexin 43 (Cx43), which plays a role in synaptic homeostasis. This study aimed to examine the role of hippocampal astrocytic Cx43 in morphine-induced maladaptive plasticity as a mechanism of addiction.

MAIN METHODS

Male rats were injected with morphine (10 mg/kg) subcutaneously every 12 h for nine days to induce dependence. Cx43 was inhibited by TAT-Gap19 (1 μl/1 nmol) microinjection in the CA1 region of the hippocampus 30 min before each morning morphine injection. Field potential recordings were used to assess synaptic plasticity. fEPSP was recorded from the CA1 area following CA3 stimulation.

KEY FINDINGS

Electrophysiological results showed that morphine treatment altered baseline synaptic responses. It also appears that morphine treatment augmented long-term potentiation (LTP) compared with the control group. Hippocampal astrocytic Cx43 inhibition, with the TAT-Gap19, undermines these effects of morphine on baseline synaptic responses and LTP. Despite this, long-term depression (LTD) did not differ significantly between the groups. Additionally, in the morphine-receiving group, inhibition of Cx43 significantly reduced the paired-pulse index at an 80-millisecond inter-pulse interval when assessing short-term plasticity.

SIGNIFICANCE

The results of this study demonstrated that inhibiting Cx43 reduced synaptic plasticity induced by morphine. It can be concluded that hippocampal astrocytes through Cx43 are involved in morphine-induced metaplasticity.

Folate Deficiency Increased Microglial Amyloid-β Phagocytosis via the RAGE Receptor in Chronic Unpredictable Mild-Stress Rat and BV2 Cells

Depression is often considered one of the prevalent neuropsychiatric symptoms of Alzheimer's disease (AD). β-amyloid (Aβ) metabolism disorders and impaired microglia phagocytosis are potential pathological mechanisms between depression and AD. Folate deficiency (FD) is a risk factor for depression and AD. In this study, we used a chronic unpredictable mild stress (CUMS) rat model and a model of Aβ phagocytosis by BV2 cells to explore the potential mechanisms by which FD affects depression and AD. The results revealed that FD exacerbated depressive behavior and activated microglia in CUMS rats, leading to an increase in intracellular Aβ and phagocytosis-related receptors for advanced glycation end products (RAGE). Then, in vitro results showed that the expression of the RAGE receptor and M2 phenotype marker (CD206) were upregulated by FD treatment in BV2 cells, leading to an increase in Aβ phagocytosis. However, there was no significant difference in the expression of toll-like receptor 4 (TLR4) and clathrin heavy chain (CHC). Furthermore, when using the RAGE-specific inhibitor FPS-ZM1, there was no significant difference in Aβ uptake between folate-normal (FN) and FD BV2 cell groups. In conclusion, these findings suggest FD may promote microglia phagocytosis Aβ via regulating the expression of RAGE or microglia phenotype under Aβ treatment.

Neuroprotective compounds from marine invertebrates

Background

Neuroinflammation is a key pathological feature of a wide variety of neurological disorders, including Parkinson’s, multiple sclerosis, Alzheimer’s, and Huntington’s disease. While current treatments for these disorders are primarily symptomatic, there is a growing interest in developing new therapeutics that target the underlying neuroinflammatory processes.

Main body

Marine invertebrates, such as coral, sea urchins, starfish, sponges, and sea cucumbers, have been found to contain a wide variety of biologically active compounds that have demonstrated potential therapeutic properties. These compounds are known to target various key proteins and pathways in neuroinflammation, including 6-hydroxydopamine (OHDH), caspase-3 and caspase-9, p-Akt, p-ERK, p-P38, acetylcholinesterase (AChE), amyloid-β (Aβ), HSF-1, α-synuclein, cellular prion protein, advanced glycation end products (AGEs), paraquat (PQ), and mitochondria DJ-1.

Short conclusion

This review focuses on the current state of research on the neuroprotective effects of compounds found in marine invertebrates and the potential therapeutic implications of these findings for treating neuroinflammatory disorders. We also discussed the challenges and limitations of using marine-based compounds as therapeutics, such as sourcing and sustainability concerns, and the need for more preclinical and clinical studies to establish their efficacy and safety.

Graphical abstract

Microglia in Alzheimer's disease: pathogenesis, mechanisms, and therapeutic potentials

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by protein aggregation in the brain. Recent studies have revealed the critical role of microglia in AD pathogenesis. This review provides a comprehensive summary of the current understanding of microglial involvement in AD, focusing on genetic determinants, phenotypic state, phagocytic capacity, neuroinflammatory response, and impact on synaptic plasticity and neuronal regulation. Furthermore, recent developments in drug discovery targeting microglia in AD are reviewed, highlighting potential avenues for therapeutic intervention. This review emphasizes the essential role of microglia in AD and provides insights into potential treatments.

Microglial extracellular vesicles induce Alzheimer's disease-related cortico-hippocampal network dysfunction

β-Amyloid is one of the main pathological hallmarks of Alzheimer's disease and plays a major role in synaptic dysfunction. It has been demonstrated that β-amyloid can elicit aberrant excitatory activity in cortical-hippocampal networks, which is associated with behavioural abnormalities. However, the mechanism of the spreading of β-amyloid action within a specific circuitry has not been elucidated yet. We have previously demonstrated that the motion of microglia-derived large extracellular vesicles carrying β-amyloid, at the neuronal surface, is crucial for the initiation and propagation of synaptic dysfunction along the entorhinal-hippocampal circuit. Here, using chronic EEG recordings, we show that a single injection of extracellular vesicles carrying β-amyloid into the mouse entorhinal cortex could trigger alterations in the cortical and hippocampal activity that are reminiscent of those found in Alzheimer's disease mouse models and human patients. The development of EEG abnormalities was associated with progressive memory impairment as assessed by an associative (object-place context recognition) and non-associative (object recognition) task. Importantly, when the motility of extracellular vesicles, carrying β-amyloid, was inhibited, the effect on network stability and memory function was significantly reduced. Our model proposes a new biological mechanism based on the extracellular vesicles-mediated progression of β-amyloid pathology and offers the opportunity to test pharmacological treatments targeting the early stages of Alzheimer's disease.

The neuroprotective N-terminal amyloid-β core hexapeptide reverses reactive gliosis and gliotoxicity in Alzheimer's disease pathology models

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by accumulation of extracellular amyloid beta (Aβ) and intracellular neurofibrillary tangles, leading to chronic activation of astrocytes and microglia and persistent neuroinflammation. Aβ-linked activation of microglia and astrocytes leads to increased intracellular calcium and production of proinflammatory cytokines, impacting the progression of neurodegeneration. An N-terminal Aβ fragment (Aβ_1-15) and a shorter hexapeptide core sequence within the N-Aβ fragment (N-Aβcore: Aβ_10-15) have previously been shown to protect against Aβ-induced mitochondrial dysfunction, oxidative stress and apoptosis in neurons and rescue synaptic and spatial memory deficits in an APP/PSEN1 mouse model. Here, we hypothesized that the N-Aβ fragment and N-Aβcore are protective against Aβ-induced gliotoxicity, promoting a neuroprotective environment and potentially alleviating the characteristically persistent neuroinflammation present in AD.

METHODS

We treated ex vivo organotypic brain slice cultures from an aged familial AD mouse model, 5xFAD, with the N-Aβcore and used immunocytochemistry to assess the impact on astrogliosis and microgliosis and alterations in synaptophysin-positive puncta engulfed by microglia. Isolated neuron/glia cultures, mixed glial cultures or a microglial cell line were treated with oligomeric human Aβ at concentrations mimicking the pathogenic concentrations (μM) observed in AD in the absence or presence of the non-toxic N-terminal Aβ fragments. Resultant changes in synaptic density, gliosis, oxidative stress, mitochondrial dysfunction, apoptosis, and the expression and release of proinflammatory markers were then determined.

RESULTS

We demonstrate that the N-terminal Aβ fragments mitigated the phenotypic switch leading to astrogliosis and microgliosis induced by pathological concentrations of Aβ in mixed glial cultures and organotypic brain slice cultures from the transgenic 5xFAD mouse model, while protecting against Aβ-induced oxidative stress, mitochondrial dysfunction and apoptosis in isolated astrocytes and microglia. Moreover, the addition of the N-Aβcore attenuated the expression and release of proinflammatory mediators in microglial cells activated by Aβ and rescued microglia-mediated loss of synaptic elements induced by pathological levels of Aβ.

CONCLUSIONS

Together, these findings indicate the protective functions of the N-terminal Aβ fragments extend to reactive gliosis and gliotoxicity induced by Aβ, by preventing or reversing glial reactive states indicative of neuroinflammation and synaptic loss central to AD pathogenesis.

Is Drp1 a link between mitochondrial dysfunction and inflammation in Alzheimer's disease?

Recent advances highlight that inflammation is critical to Alzheimer Disease (AD) pathogenesis. Indeed, several diseases characterized by inflammation are considered risk factors for AD, such as type 2 diabetes, obesity, hypertension, and traumatic brain injury. Moreover, allelic variations in genes involved in the inflammatory cascade are risk factors for AD. AD is also characterized by mitochondrial dysfunction, which affects the energy homeostasis of the brain. The role of mitochondrial dysfunction has been characterized mostly in neuronal cells. However, recent data are demonstrating that mitochondrial dysfunction occurs also in inflammatory cells, promoting inflammation and the secretion of pro-inflammatory cytokines, which in turn induce neurodegeneration. In this review, we summarize the recent finding supporting the hypothesis of the inflammatory-amyloid cascade in AD. Moreover, we describe the recent data that demonstrate the link between altered mitochondrial dysfunction and the inflammatory cascade. We focus in summarizing the role of Drp1, which is involved in mitochondrial fission, showing that altered Drp1 activation affects the mitochondrial homeostasis and leads to the activation of the NLRP3 inflammasome, promoting the inflammatory cascade, which in turn aggravates Amyloid beta (Ab) deposition and tau-induced neurodegeneration, showing the relevance of this pro-inflammatory pathway as an early event in AD.

Emerging Roles of Extracellular Vesicles in Alzheimer's Disease: Focus on Synaptic Dysfunction and Vesicle-Neuron Interaction

Alzheimer's disease (AD) is considered by many to be a synaptic failure. Synaptic function is in fact deeply affected in the very early disease phases and recognized as the main cause of AD-related cognitive impairment. While the reciprocal involvement of amyloid beta (Aβ) and tau peptides in these processes is under intense investigation, the crucial role of extracellular vesicles (EVs) released by different brain cells as vehicles for these molecules and as mediators of early synaptic alterations is gaining more and more ground in the field. In this review, we will summarize the current literature on the contribution of EVs derived from distinct brain cells to neuronal alterations and build a working model for EV-mediated propagation of synaptic dysfunction in early AD. A deeper understanding of EV-neuron interaction will provide useful targets for the development of novel therapeutic approaches aimed at hampering AD progression.

Role of Aβ in Alzheimer’s-related synaptic dysfunction

Synaptic dysfunction is closely related to Alzheimer’s disease (AD) which is also recognized as synaptic disorder. β-amyloid (Aβ) is one of the main pathogenic factors in AD, which disrupts synaptic plasticity and mediates the synaptic toxicity through different mechanisms. Aβ disrupts glutamate receptors, such as NMDA and AMPA receptors, which mediates calcium dyshomeostasis and damages synapse plasticity characterized by long-term potentiation (LTP) suppression and long-term depression (LTD) enhancement. As Aβ stimulates and Ca2+ influx, microglial cells and astrocyte can be activated and release cytokines, which reduces glutamate uptake and further impair synapse function. Besides, extracellular glutamate accumulation induced by Aβ mediates synapse toxicity resulting from reduced glutamate receptors and glutamate spillovers. Aβ also mediates synaptic dysfunction by acting on various signaling pathways and molecular targets, disrupting mitochondria and energy metabolism. In addition, Aβ overdeposition aggravates the toxic damage of hyperphosphorylated tau to synapses. Synaptic dysfunction plays a critical role in cognitive impairment of AD. The review addresses the possible mechanisms by which Aβ mediates AD-related synaptic impairment from distant perspectives.

Luteolin-7-O-Glucuronide Improves Depression-like and Stress Coping Behaviors in Sleep Deprivation Stress Model by Activation of the BDNF Signaling

Stress exposure is a major risk factor for mental disorders such as depression. Because of the limitations of classical antidepressants such as side effects, low efficacy, and difficulty in long-term use, new natural medicines and bioactive molecules from plants with greater safety and efficacy have recently attracted attention. Luteolin-7-O-glucuronide (L7Gn), a bioactive molecule present in Perilla frutescens, is known to alleviate severe inflammatory responses and oxidative stress in macrophages. However, its antistress and antidepressant effects have not been elucidated. The present study aims to explore the antidepressant the effect of L7Gn on stress-induced behaviors and the underlying mechanism in a mouse sleep deprivation (SD) model. L7Gn treatment improved depression-like and stress coping behaviors induced by SD stress, as confirmed by the tail suspension test and forced swimming test. Furthermore, L7Gn treatment reduced the blood corticosterone and hippocampal proinflammatory cytokine levels which were increased by SD stress, and L7Gn also increased the mRNA and protein levels of hippocampal brain-derived neurotrophic factor (BDNF) which were reduced by SD stress. Additionally, treatment with L7Gn resulted in increases in the phosphorylation of tropomyosin-related kinase B (TrkB), extracellular signal-regulated kinase (ERK), and cAMP response element-binding protein (CREB), which are downstream molecules of BDNF signaling. These findings suggest that L7Gn have therapeutic potential for SD-induced stress, via activating the BDNF signaling.

Pathophysiology of RAGE in inflammatory diseases

The receptor for advanced glycation end products (RAGE) is a non-specific multi-ligand pattern recognition receptor capable of binding to a range of structurally diverse ligands, expressed on a variety of cell types, and performing different functions. The ligand-RAGE axis can trigger a range of signaling events that are associated with diabetes and its complications, neurological disorders, cancer, inflammation and other diseases. Since RAGE is involved in the pathophysiological processes of many diseases, targeting RAGE may be an effective strategy to block RAGE signaling.

The Combination of Salidroside and Hedysari Radix Polysaccharide Inhibits Mitochondrial Damage and Apoptosis via the PKC/ERK Pathway

Background. Beta-amyloid (Aβ) peptide is a widely recognized pathological marker of Alzheimer’s disease (AD). Salidroside and Hedysari Radix polysaccharide (HRP) were extracted from Chinese herb medicine Rhodiola rosea L and Hedysarum polybotrys Hand-Mazz, respectively. The neuroprotective effects and mechanisms of the combination of salidroside and Hedysari Radix polysaccharide (CSH) against Aβ25–35 induced neurotoxicity remain unclear. Objective. This study aims to investigate the neuroprotective effects and pharmacological mechanisms of CSH on Aβ25–35-induced HT22 cells. Materials and Methods. HT22 cells were pretreated with various concentrations of salidroside or HRP for 24 h, followed by exposed to 20 μm Aβ25–35 in the presence of salidroside or RHP for another 24 h. In a CSH protective assay, HT22 cells were pretreated with 40 μm salidroside and 20 μg/mL HRP for 24 h. The cell viability assay, cell morphology observation, determination of mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and cell apoptosis rate were performed. The mRNA expression of protein kinase C-beta (PKCβ), Bax, and Bcl-2 were measured by qRT-PCR. The protein expression levels of cleaved caspase-3, Cyt-C, PKCβ, phospho-ERK1/2, Bax, and Bcl-2 were measured by Western blot. Results. CSH treatment increased cell viability, MMP, and decreased ROS generation in Aβ25–35-induced HT22 cells. PKCβ and Bcl-2 mRNA expression were elevated by CSH while Bax was decreased. CSH increased the protein expression levels of PKCβ, Bcl-2, and phospho-ERK1/2, and decreased those of Bax, Cyt-C, and cleaved caspase-3. Conclusions. CSH treatment have protective effects against Aβ25–35-induced cytotoxicity through decreasing ROS levels, increasing MMP, inhibiting early apoptosis, and regulating PKC/ERK pathway in HT22 cells. CSH may be a potential therapeutic agent for treating or preventing neurodegenerative diseases.

Microglia in Alzheimer’s Disease: A Favorable Cellular Target to Ameliorate Alzheimer’s Pathogenesis

Microglial cells serve as molecular sensors of the brain that play a role in physiological and pathological conditions. Under normal physiology, microglia are primarily responsible for regulating central nervous system homeostasis through the phagocytic clearance of redundant protein aggregates, apoptotic cells, damaged neurons, and synapses. Furthermore, microglial cells can promote and mitigate amyloid β phagocytosis and tau phosphorylation. Dysregulation of the microglial programming alters cellular morphology, molecular signaling, and secretory inflammatory molecules that contribute to various neurodegenerative disorders especially Alzheimer’s disease (AD). Furthermore, microglia are considered primary sources of inflammatory molecules and can induce or regulate a broad spectrum of cellular responses. Interestingly, in AD, microglia play a double-edged role in disease progression; for instance, the detrimental microglial effects increase in AD while microglial beneficiary mechanisms are jeopardized. Depending on the disease stages, microglial cells are expressed differently, which may open new avenues for AD therapy. However, the disease-related role of microglial cells and their receptors in the AD brain remain unclear. Therefore, this review represents the role of microglial cells and their involvement in AD pathogenesis.

HMGB1 signaling pathway in diabetes-related dementia: Blood-brain barrier breakdown, brain insulin resistance, and Aβ accumulation

Diabetes contributes to the onset of various diseases, including cancer and cardiovascular and neurodegenerative diseases. Recent studies have highlighted the similarities and relationship between diabetes and dementia as an important issue for treating diabetes-related cognitive deficits. Diabetes-related dementia exhibits several features, including blood-brain barrier disruption, brain insulin resistance, and Aβ over-accumulation. High-mobility group box1 (HMGB1) is a protein known to regulate gene transcription and cellular mechanisms by binding to DNA or chromatin via receptor for advanced glycation end-products (RAGE) and toll-like receptor 4 (TLR4). Recent studies have demonstrated that the interplay between HMGB1, RAGE, and TLR4 can impact both neuropathology and diabetic alterations. Herein, we review the recent research regarding the roles of HMGB1-RAGE-TLR4 axis in diabetes-related dementia from several perspectives and emphasize the importance of the influence of HMGB1 in diabetes-related dementia.

1-(7-Chloroquinolin-4-yl)-N-(4-Methoxybenzyl)-5-Methyl-1H-1,2, 3-Triazole-4- carboxamide Reduces Aβ Formation and Tau Phosphorylation in Cellular Models of Alzheimer's Disease

1-(7-Chloroquinolin-4-yl)-N-(4-methoxybenzyl)-5-methyl-1H-1,2,3-triazole-4- carboxamide (QTC-4-MeOBnE) is a new multi-target directed ligand (MTDL) rationally designed to have affinity with β-secretase (BACE), Glycogen Synthase Kinase 3β (GSK3β) and acetylcholinesterase, which are considered promising targets on the development of disease-modifying therapies against Alzheimer's Disease (AD). Previously, QTC-4-MeOBnE treatment showed beneficial effects in preclinical AD-like models by influencing in vivo neurogenesis, oxidative and inflammatory pathways. However, the biological effect and mechanism of action exerted by QTC-4-MeOBnE in AD cellular models have not been elucidated yet. Hereby we investigate the acute effect of QTC-4-MeOBnE on neuronal cells overexpressing Amyloid Protein Precursor (APP) or human tau protein, the two main features of the AD pathophysiology. When compared to the control group, QTC-4-MeOBnE treatment prevented amyloid beta (Aβ) formation through the downregulation of APP and BACE levels in APPswe-expressing cells. Furthermore, in N2a cells overexpressing human tau, QTC-4-MeOBnE reduced the levels of phosphorylated forms of tau via the modulation of the GSK3β pathway. Taken together, our findings provide new insights into the mechanism of action exerted by QTC-4-MeOBnE in AD cellular models, and further support its potential as an interesting therapeutic strategy against AD.

OUP accepted manuscript

Synaptic dysfunction is an early mechanism in Alzheimer’s disease that involves progressively larger areas of the brain over time. However, how it starts and propagates is unknown.

Here we show that amyloid-β released by microglia in association with large extracellular vesicles (Aβ-EVs) alters dendritic spine morphology in vitro, at the site of neuron interaction, and impairs synaptic plasticity both in vitro and in vivo in the entorhinal cortex–dentate gyrus circuitry. One hour after Aβ-EV injection into the mouse entorhinal cortex, long-term potentiation was impaired in the entorhinal cortex but not in the dentate gyrus, its main target region, while 24 h later it was also impaired in the dentate gyrus, revealing a spreading of long-term potentiation deficit between the two regions. Similar results were obtained upon injection of extracellular vesicles carrying Aβ naturally secreted by CHO7PA2 cells, while neither Aβ₄₂ alone nor inflammatory extracellular vesicles devoid of Aβ were able to propagate long-term potentiation impairment. Using optical tweezers combined to time-lapse imaging to study Aβ-EV–neuron interaction, we show that Aβ-EVs move anterogradely at the axon surface and that their motion can be blocked through annexin-V coating. Importantly, when Aβ-EV motility was inhibited, no propagation of long-term potentiation deficit occurred along the entorhinal–hippocampal circuit, implicating large extracellular vesicle motion at the neuron surface in the spreading of long-term potentiation impairment.

Our data indicate the involvement of large microglial extracellular vesicles in the rise and propagation of early synaptic dysfunction in Alzheimer’s disease and suggest a new mechanism controlling the diffusion of large extracellular vesicles and their pathogenic signals in the brain parenchyma, paving the way for novel therapeutic strategies to delay the disease.

Shared genetic architecture between the two neurodegenerative diseases: Alzheimer's disease and glaucoma

BACKGROUND

Considered as the representatives of neurodegenerative diseases, Alzheimer's disease (AD) and glaucoma are complex progressive neuropathies affected by both genetic and environmental risk factors and cause irreversible damages. Current research indicates that there are common features between AD and glaucoma in terms of epidemiology and pathophysiology. However, the understandings and explanations of their comorbidity and potential genetic overlaps are still limited and insufficient.

METHOD

Genetic pleiotropy analysis was performed using large genome-wide association studies summary statistics of AD and glaucoma, with an independent cohort of glaucoma for replication. Conditional and conjunctional false discovery rate methods were applied to identify the shared loci. Biological function and network analysis, as well as the expression level analysis were performed to investigate the significance of the shared genes.

RESULTS

A significant positive genetic correlation between AD and glaucoma was identified, indicating that there were significant polygenetic overlaps. Forty-nine shared loci were identified and mapped to 11 shared protein-coding genes. Functional genomic analyses of the shared genes indicate their modulation of critical physiological processes in human cells, including those occurring in the mitochondria, nucleus, and cellular membranes. Most of the shared genes indicated a potential modulation of metabolic processes in human cells and tissues. Furthermore, human protein-protein interaction network analyses revealed that some of the shared genes, especially MTCH2, NDUFS3, and PTPMT1, as well as SPI1 and MYBPC3, may function concordantly. The modulation of their expressions may be related to metabolic dysfunction and pathogenic processes.

CONCLUSION

Our study identified a shared genetic architecture between AD and glaucoma, which may explain their shared features in epidemiology and pathophysiology. The potential involvement of these shared genes in molecular and cellular processes reflects the "inter-organ crosstalk" between AD and glaucoma. These results may serve as a genetic basis for the development of innovative and effective therapeutics for AD, glaucoma, and other neurodegenerative diseases.

Downregulating expression of OPTN elevates neuroinflammation via AIM2 inflammasome- and RIPK1-activating mechanisms in APP/PS1 transgenic mice

BACKGROUND

Neuroinflammation is thought to be a cause of Alzheimer's disease (AD), which is partly caused by inadequate mitophagy. As a receptor of mitophagy, we aimed to reveal the regulatory roles of optineurin (OPTN) on neuroinflammation in the pathogenesis of AD.

METHODS

BV2 cells and APP/PS1 transgenic (Tg) mice were used as in vitro and in vivo experimental models to determine the regulatory roles of OPTN in neuroinflammation of AD. Sophisticated molecular technologies including quantitative (q) RT-PCR, western blot, enzyme linked immunosorbent assay (ELISA), co-immunoprecipitation (Co-IP) and immunofluorescence (IF) were employed to reveal the inherent mechanisms.

RESULTS

As a consequence, key roles of OPTN in regulating neuroinflammation were identified by depressing the activity of absent in melanoma 2 (AIM2) inflammasomes and receptor interacting serine/threonine kinase 1 (RIPK1)-mediated NF-κB inflammatory mechanisms. In detail, we found that expression of OPTN was downregulated, which resulted in activation of AIM2 inflammasomes due to a deficiency in mitophagy in APP/PS1 Tg mice. By ectopic expression, OPTN blocks the effects of Aβ oligomer (Aβo) on activating AIM2 inflammasomes by inhibiting mRNA expression of AIM2 and apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), leading to a reduction in the active form of caspase-1 and interleukin (IL)-1β in microglial cells. Moreover, RIPK1 was also found to be negatively regulated by OPTN via ubiquitin protease hydrolysis, resulting in the synthesis of IL-1β by activating the transcriptional activity of NF-κB in BV2 cells. As an E3 ligase, the UBAN domain of OPTN binds to the death domain (DD) of RIPK1 to facilitate its ubiquitination. Based on these observations, ectopically expressed OPTN in APP/PS1 Tg mice deactivated microglial cells and astrocytes via the AIM2 inflammasome and RIPK-dependent NF-κB pathways, leading to reduce neuroinflammation.

CONCLUSIONS

These results suggest that OPTN can alleviate neuroinflammation through AIM2 and RIPK1 pathways, suggesting that OPTN deficiency may be a potential factor leading to the occurrence of AD.

Alzheimer's Disease: A Molecular View of β-Amyloid Induced Morbific Events

Amyloid-β (Aβ) is a dynamic peptide of Alzheimer’s disease (AD) which accelerates the disease progression. At the cell membrane and cell compartments, the amyloid precursor protein (APP) undergoes amyloidogenic cleavage by β- and γ-secretases and engenders the Aβ. In addition, externally produced Aβ gets inside the cells by receptors mediated internalization. An elevated amount of Aβ yields spontaneous aggregation which causes organelles impairment. Aβ stimulates the hyperphosphorylation of tau protein via acceleration by several kinases. Aβ travels to the mitochondria and interacts with its functional complexes, which impairs the mitochondrial function leading to the activation of apoptotic signaling cascade. Aβ disrupts the Ca²⁺ and protein homeostasis of the endoplasmic reticulum (ER) and Golgi complex (GC) that promotes the organelle stress and inhibits its stress recovery machinery such as unfolded protein response (UPR) and ER-associated degradation (ERAD). At lysosome, Aβ precedes autophagy dysfunction upon interacting with autophagy molecules. Interestingly, Aβ act as a transcription regulator as well as inhibits telomerase activity. Both Aβ and p-tau interaction with neuronal and glial receptors elevate the inflammatory molecules and persuade inflammation. Here, we have expounded the Aβ mediated events in the cells and its cosmopolitan role on neurodegeneration, and the current clinical status of anti-amyloid therapy.

Amyloid-β (1-42) peptide induces rapid NMDA receptor-dependent alterations at glutamatergic synapses in the entorhinal cortex

The hippocampus and entorhinal cortex (EC) accumulate amyloid beta peptides (Aβ) that promote neuropathology in Alzheimer's disease, but the early effects of Aβ on excitatory synaptic transmission in the EC have not been well characterized. To assess the acute effects of Aβ1-42 on glutamatergic synapses, acute brain slices from wildtype rats were exposed to Aβ1-42 or control solution for 3 hours, and tissue was analyzed using protein immunoblotting and quantitative PCR. Presynaptically, Aβ1-42 induced marked reductions in synaptophysin, synapsin-2a mRNA, and mGluR3 mRNA, and increased both VGluT2 protein and Ca2+-activated channel KCa2.2 mRNA levels. Postsynaptically, Aβ1-42 reduced PSD95 and GluN2B protein, and also downregulated GluN2B and GluN2A mRNA, without affecting scaffolding elements SAP97 and PICK1. mGluR5 mRNA was strongly increased, while mGluR1 mRNA was unaffected. Blocking either GluN2A- or GluN2B-containing NMDA receptors did not significantly prevent synaptic changes induced by Aβ1-42, but combined blockade did prevent synaptic alterations. These findings demonstrate that Aβ1-42 rapidly disrupts glutamatergic transmission in the EC through mechanisms involving concurrent activation of GluN2A- and GluN2B-containing NMDA receptors.

Role of Oxidative Damage in Alzheimer's Disease and Neurodegeneration: From Pathogenic Mechanisms to Biomarker Discovery

Alzheimer’s disease (AD) is a neurodegenerative disorder accounting for over 50% of all dementia patients and representing a leading cause of death worldwide for the global ageing population. The lack of effective treatments for overt AD urges the discovery of biomarkers for early diagnosis, i.e., in subjects with mild cognitive impairment (MCI) or prodromal AD. The brain is exposed to oxidative stress as levels of reactive oxygen species (ROS) are increased, whereas cellular antioxidant defenses are decreased. Increased ROS levels can damage cellular structures or molecules, leading to protein, lipid, DNA, or RNA oxidation. Oxidative damage is involved in the molecular mechanisms which link the accumulation of amyloid-β and neurofibrillary tangles, containing hyperphosphorylated tau, to microglia response. In this scenario, microglia are thought to play a crucial role not only in the early events of AD pathogenesis but also in the progression of the disease. This review will focus on oxidative damage products as possible peripheral biomarkers in AD and in the preclinical phases of the disease. Particular attention will be paid to biological fluids such as blood, CSF, urine, and saliva, and potential future use of molecules contained in such body fluids for early differential diagnosis and monitoring the disease course. We will also review the role of oxidative damage and microglia in the pathogenesis of AD and, more broadly, in neurodegeneration.

Microglia in Alzheimer's Disease

Alzheimer's Disease (AD) is the most frequent neurodegenerative disorder. Although proteinaceous aggregates of extracellular Amyloid-β (Aβ) and intracellular hyperphosphorylated microtubule- associated tau have long been identified as characteristic neuropathological hallmarks of AD, a disease- modifying therapy against these targets has not been successful. An emerging concept is that microglia, the innate immune cells of the brain, are major players in AD pathogenesis. Microglia are longlived tissue-resident professional phagocytes that survey and rapidly respond to changes in their microenvironment. Subpopulations of microglia cluster around Aβ plaques and adopt a transcriptomic signature specifically linked to neurodegeneration. A plethora of molecules and pathways associated with microglia function and dysfunction has been identified as important players in mediating neurodegeneration. However, whether microglia exert either beneficial or detrimental effects in AD pathology may depend on the disease stage. In this review, we summarize the current knowledge about the stage-dependent role of microglia in AD, including recent insights from genetic and gene expression profiling studies as well as novel imaging techniques focusing on microglia in human AD pathology and AD mouse models.

New insights in drug development for Alzheimer's disease based on microglia function

One of the biggest challenges in drug development for Alzheimer's disease (AD) is how to effectively remove deposits of amyloid-beta (Aβ). Recently, the relationship between microglia and Aβ has become a research hotspot. Emerging evidence suggests that Aβ-induced microglia-mediated neuroinflammation further aggravates the decline of cognitive function, while microglia are also involved in the process of Aβ clearance. Hence, microglia have become a potential therapeutic target for the treatment or prevention of AD. An in-depth understanding of the role played by microglia in the development of AD will help us to broaden therapeutic strategies for AD. In this review, we provide an overview of the dual roles of microglia in AD progression: the positive effect of phagocytosis of Aβ and its negative effect on neuroinflammation after over-activation. With the advantages of novel structure, high efficiency, and low toxicity, small-molecule compounds as modulators of microglial function have attracted considerable attention in the therapeutic areas of AD. In this review, we also summarize the therapeutic potential of small molecule compounds (SMCs) and their structure-activity relationship for AD treatment through modulating microglial phagocytosis and inhibiting neuroinflammation. For example, the position and number of phenolic hydroxyl groups on the B ring are the key to the activity of flavonoids, and the substitution of hydroxyl groups on the benzene ring enhances the anti-inflammatory activity of phenolic acids. This review is expected to be useful for developing effective modulators of microglial function from SMCs for the amelioration and treatment of AD.

Alzheimer's Disease Pathogenesis: Role of Autophagy and Mitophagy Focusing in Microglia

Alzheimer's disease (AD) is a debilitating neurological disorder, and currently, there is no cure for it. Several pathologic alterations have been described in the brain of AD patients, but the ultimate causative mechanisms of AD are still elusive. The classic hallmarks of AD, including amyloid plaques (Aβ) and tau tangles (tau), are the most studied features of AD. Unfortunately, all the efforts targeting these pathologies have failed to show the desired efficacy in AD patients so far. Neuroinflammation and impaired autophagy are two other main known pathologies in AD. It has been reported that these pathologies exist in AD brain long before the emergence of any clinical manifestation of AD. Microglia are the main inflammatory cells in the brain and are considered by many researchers as the next hope for finding a viable therapeutic target in AD. Interestingly, it appears that the autophagy and mitophagy are also changed in these cells in AD. Inside the cells, autophagy and inflammation interact in a bidirectional manner. In the current review, we briefly discussed an overview on autophagy and mitophagy in AD and then provided a comprehensive discussion on the role of these pathways in microglia and their involvement in AD pathogenesis.

Advanced glycation end products (AGEs) and other adducts in aging-related diseases and alcohol-mediated tissue injury

Advanced glycation end products (AGEs) are potentially harmful and heterogeneous molecules derived from nonenzymatic glycation. The pathological implications of AGEs are ascribed to their ability to promote oxidative stress, inflammation, and apoptosis. Recent studies in basic and translational research have revealed the contributing roles of AGEs in the development and progression of various aging-related pathological conditions, such as diabetes, cardiovascular complications, gut microbiome-associated illnesses, liver or neurodegenerative diseases, and cancer. Excessive chronic and/or acute binge consumption of alcohol (ethanol), a widely consumed addictive substance, is known to cause more than 200 diseases, including alcohol use disorder (addiction), alcoholic liver disease, and brain damage. However, despite the considerable amount of research in this area, the underlying molecular mechanisms by which alcohol abuse causes cellular toxicity and organ damage remain to be further characterized. In this review, we first briefly describe the properties of AGEs: their formation, accumulation, and receptor interactions. We then focus on the causative functions of AGEs that impact various aging-related diseases. We also highlight the biological connection of AGE-alcohol-adduct formations to alcohol-mediated tissue injury. Finally, we describe the potential translational research opportunities for treatment of various AGE- and/or alcohol-related adduct-associated disorders according to the mechanistic insights presented.

T1AM-TAAR1 signalling protects against OGD-induced synaptic dysfunction in the entorhinal cortex

Abnormalities in thyroid hormones (TH) availability and/or metabolism have been hypothesized to contribute to Alzheimer's disease (AD) and to be a risk factor for stroke. Recently, 3-iodothyronamine (T₁AM), an endogenous amine putatively derived from TH metabolism, gained interest for its ability to promote learning and memory in the mouse. Moreover, T₁AM has been demonstrated to rescue the β-Amyloid dependent LTP impairment in the entorhinal cortex (EC), a brain area crucially involved in learning and memory and early affected during AD. In the present work, we have investigated the effect of T₁AM on ischemia-induced EC synaptic dysfunction. In EC brain slices exposed to oxygen-glucose deprivation (OGD), we demonstrated that the acute perfusion of T₁AM (5 μM) was capable of preventing ischemia-induced synaptic depression and that this protective effect was mediated by the trace amine-associated receptor 1 (TAAR1). Moreover, we demonstrated that activation of the BDNF-TrkB signalling is required for T₁AM action during ischemia. The protective effect of T₁AM was more evident when using EC slices from transgenic mutant human APP (mhAPP mice) that are more vulnerable to the effect of OGD. Our results confirm that the TH derivative T₁AM can rescue synaptic function after transient ischemia, an effect that was also observed in a Aβ-enriched environment.

Apoptotic neurons and amyloid-beta clearance by phagocytosis in Alzheimer's disease: Pathological mechanisms and therapeutic outlooks

Neuronal survival and axonal renewal following central nervous system damage and in neurodegenerative illnesses, such as Alzheimer's disease (AD), can be enhanced by fast clearance of neuronal apoptotic debris, as well as the removal of amyloid beta (Aβ) by phagocytic cells through the process of efferocytosis. This process quickly inhibits the release of proinflammatory and antigenic autoimmune constituents, enhancing the formation of a microenvironment vital for neuronal survival and axonal regeneration. Therefore, the detrimental features associated with microglial phagocytosis uncoupling, such as the accumulation of apoptotic cells, inflammation and phagoptosis, could exacerbate the pathology in brain disease. Some mechanisms of efferocytosis could be targeted by several promising agents, such as curcumin, URMC-099 and Y-P30, which have emerged as potential treatments for AD. This review aims to investigate and update the current research regarding the signaling molecules and pathways involved in efferocytosis and how these could be targeted as a potential therapy in AD.

Cerebral sterile inflammation in neurodegenerative diseases

Therapeutic strategies for regulating neuroinflammation are expected in the development of novel therapeutic agents to prevent the progression of central nervous system (CNS) pathologies. An understanding of the detailed molecular and cellular mechanisms of neuroinflammation in each CNS disease is necessary for the development of therapeutics. Since the brain is a sterile organ, neuroinflammation in Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS) is triggered by cerebral cellular damage or the abnormal accumulation of inflammatogenic molecules in CNS tissue through the activation of innate and acquired immunity. Inflammation and CNS pathologies worsen each other through various cellular and molecular mechanisms, such as oxidative stress or the accumulation of inflammatogenic molecules induced in the damaged CNS tissue. In this review, we summarize the recent evidence regarding sterile immune responses in neurodegenerative diseases.

Involvement of p38 MAPK in Synaptic Function and Dysfunction

Many studies have revealed a central role of p38 MAPK in neuronal plasticity and the regulation of long-term changes in synaptic efficacy, such as long-term potentiation (LTP) and long-term depression (LTD). However, p38 MAPK is classically known as a responsive element to stress stimuli, including neuroinflammation. Specific to the pathophysiology of Alzheimer’s disease (AD), several studies have shown that the p38 MAPK cascade is activated either in response to the Aβ peptide or in the presence of tauopathies. Here, we describe the role of p38 MAPK in the regulation of synaptic plasticity and its implication in an animal model of neurodegeneration. In particular, recent evidence suggests the p38 MAPK α isoform as a potential neurotherapeutic target, and specific inhibitors have been developed and have proven to be effective in ameliorating synaptic and memory deficits in AD mouse models.

Impact of JNK and Its Substrates on Dendritic Spine Morphology

The protein kinase JNK1 exhibits high activity in the developing brain, where it regulates dendrite morphology through the phosphorylation of cytoskeletal regulatory proteins. JNK1 also phosphorylates dendritic spine proteins, and Jnk1-/- mice display a long-term depression deficit. Whether JNK1 or other JNKs regulate spine morphology is thus of interest. Here, we characterize dendritic spine morphology in hippocampus of mice lacking Jnk1-/- using Lucifer yellow labelling. We find that mushroom spines decrease and thin spines increase in apical dendrites of CA3 pyramidal neurons with no spine changes in basal dendrites or in CA1. Consistent with this spine deficit, Jnk1-/- mice display impaired acquisition learning in the Morris water maze. In hippocampal cultures, we show that cytosolic but not nuclear JNK, regulates spine morphology and expression of phosphomimicry variants of JNK substrates doublecortin (DCX) or myristoylated alanine-rich C kinase substrate-like protein-1 (MARCKSL1), rescue mushroom, thin, and stubby spines differentially. These data suggest that physiologically active JNK controls the equilibrium between mushroom, thin, and stubby spines via phosphorylation of distinct substrates.

Exogenous 3-Iodothyronamine Rescues the Entorhinal Cortex from β-Amyloid Toxicity

Background: A novel form of thyroid hormone (TH) signaling is represented by 3-iodothyronamine (T₁AM), an endogenous TH derivative that interacts with specific molecular targets, including trace amine-associated receptor 1 (TAAR₁), and induces pro-learning and anti-amnestic effects in mice. Dysregulation of TH signaling has long been hypothesized to play a role in Alzheimer's disease (AD). In the present investigation, we explored the neuroprotective role of T₁AM in beta amyloid (Aβ)-induced synaptic and behavioral impairment, focusing on the entorhinal cortex (EC), an area that is affected early by AD pathology. Methods: Field potentials were evoked in EC layer II, and long-term potentiation (LTP) was elicited by high frequency stimulation (HFS). T₁AM (5 μM) and/or Aβ(1-42) (200 nM), were administered for 10 minutes, starting 5 minutes before HFS. Selective TAAR₁ agonist RO5166017 (250 nM) and TAAR₁ antagonist EPPTB (5 nM) were also used. The electrophysiological experiments were repeated in EC-slices taken from a mouse model of AD (mutant human amyloid precursor protein [mhAPP], J20 line). We also assessed the in vivo effects of T₁AM on EC-dependent associative memory deficits, which were detected in mhAPP mice by behavioral evaluations based on the novel-object recognition paradigm. TAAR₁ expression was determined by Western blot, whereas T₁AM and its metabolite 3-iodothyroacetic acid (TA₁) were assayed by high-performance liquid chromatography coupled to mass spectrometry. Results: We demonstrate the presence of endogenous T₁AM and TAAR₁ in the EC of wild-type and mhAPP mice. Exposure to Aβ(1-42) inhibited LTP, and T₁AM perfusion (at a concentration of 5 μM, leading to an actual concentration in the perfusion buffer ranging from 44 to 298 nM) restored it, whereas equimolar amounts of 3,5,3'-triiodo-L-thyronine (T₃) and TA₁ were ineffective. The response to T₁AM was abolished by the TAAR₁ antagonist EPPTB, whereas it was mimicked by the TAAR₁ agonist RO5166017. In the EC of APPJ20 mice, LTP could not be elicited, but it was rescued by T₁AM. The intra-cerebro-ventricular administration of T₁AM (0.89 μg/kg) also restored recognition memory that was impaired in mhAPP mice. Conclusions: Our results suggest that T₁AM and TAAR₁ are part of an endogenous system that can be modulated to prevent synaptic and behavioral deficits associated with Aβ-related toxicity.

Development of a Multicomponent Intervention to Prevent Alzheimer's Disease

Recent advances in vascular risk management have successfully reduced the prevalence of Alzheimer's Disease (AD) in several epidemiologic investigations. It is now widely accepted that cerebrovascular disease is both directly and indirectly involved in AD pathogenesis. Herein, we review the non-pharmacological and pharmacological therapeutic approaches for AD treatment. MIND [Mediterranean and DASH (Dietary Approaches to Stop Hypertension) Intervention for Neurodegenerative Delay] diet is an important dietary treatment for prevention of AD. Multi domain intervention including diet, exercise, cognitive training, and intensive risk managements also prevented cognitive decline in the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) study. To confirm these favorable effects of life-style intervention, replica studies are being planned worldwide. Promotion of β-amyloid (Aβ) clearance has emerged as a promising pharmacological approach because insufficient removal of Aβ is more important than excessive Aβ production in the pathogenesis of the majority of AD patients. Most AD brains exhibit accompanying cerebral amyloid angiopathy, and Aβ distribution in cerebral amyloid angiopathy closely corresponds with the intramural periarterial drainage (IPAD) route, emphasizing the importance of Aβ clearance. In view of these facts, promotion of the major vascular-mediated Aβ elimination systems, including capillary transcytosis, the glymphatic system, and IPAD, have emerged as new treatment strategies in AD. In particular, the beneficial effects of cilostazol were shown in several clinical observation studies, and cilostazol facilitated IPAD in a rodent AD model. The COMCID (Cilostazol for prevention of Conversion from MCI to Dementia) trial, evaluating the efficacy of cilostazol for patients with mild cognitive impairment is currently ongoing in Japan. Such therapeutic approaches involving maintenance of cerebrovascular integrity and promotion of vascular-mediated Aβ clearance have the potential to be mainstream treatments for sporadic AD.

Anxiety and task performance changes in an aging mouse model

Due to the increasing focus on aging as an important risk factor for many serious diseases and an emphasis on animal models that have translational value, an increasing number of animal models are being aged. Animal behavior tests can be used to assess effects of aging in mouse models. Female mice begin exhibiting anxiety-like behaviors at 12 months of age which become more serious at 24 months, while males exhibit no age-induced anxiety-like behaviors. Males and females equally demonstrate a failure of daily task performance at 24 months. Despite these cognitive changes, the mice do not show changes in gross motor function. These results suggest cognitive impairment in non-genetically modified aging mice.

Inflammatory mechanisms in neurodegeneration

This review discusses the profound connection between microglia, neuroinflammation, and Alzheimer's disease (AD). Theories have been postulated, tested, and modified over several decades. The findings have further bolstered the belief that microglia-mediated inflammation is both a product and contributor to AD pathology and progression. Distinct microglia phenotypes and their function, microglial recognition and response to protein aggregates in AD, and the overall role of microglia in AD are areas that have received considerable research attention and yielded significant results. The following article provides a historical perspective of microglia, a detailed discussion of multiple microglia phenotypes including dark microglia, and a review of a number of areas where microglia intersect with AD and other pathological neurological processes. The overall breadth of important discoveries achieved in these areas significantly strengthens the hypothesis that neuroinflammation plays a key role in AD. Future determination of the exact mechanisms by which microglia respond to, and attempt to mitigate, protein aggregation in AD may lead to new therapeutic strategies.

HMG-CoA Reductase Inhibitors Attenuate Neuronal Damage by Suppressing Oxygen Glucose Deprivation-Induced Activated Microglial Cells

Ischemic stroke is usually followed by inflammatory responses mediated by microglia. However, the effect of statins on directly preventing posthypoxia microglia inflammatory factors to prevent injury to surrounding healthy neurons is unclear. Atorvastatin and rosuvastatin, which have different physical properties regarding their lipid and water solubility, are the most common HMG-CoA reductase inhibitors (statins) and might directly block posthypoxia microglia inflammatory factors to prevent injury to surrounding neurons. Neuronal damage and microglial activation of the peri-infarct areas were investigated by Western blotting and immunofluorescence after 24 hours in a middle cerebral artery occlusion (MCAO) rat model. The decrease in neurons was in accordance with the increase in microglia, which could be reversed by both atorvastatin and rosuvastatin. The effects of statins on blocking secretions from posthypoxia microglia and reducing the secondary damage to surrounding normal neurons were studied in a coculture system in vitro. BV2 microglia were cultured under oxygen glucose deprivation (OGD) for 3 hours and then cocultured following reperfusion for 24 hours in the upper wells of transwell plates with primary neurons being cultured in the bottom wells. Inflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and cyclooxygenase-2 (COX2), which are activated by the nuclear factor-kappa B (NF-κB) signaling pathway in OGD-induced BV2 microglia, promoted decreased release of the anti-inflammatory cytokine IL-10 and apoptosis of neurons in the coculture systems according to ELISA and Western blotting. However, pretreatment with atorvastatin or rosuvastatin significantly reduced neuronal death, synaptic injury, and amyloid-beta (Aβ) accumulation, which might lead to increased low-density lipoprotein receptors (LDLRs) in BV2 microglia. We concluded that the proinflammatory mediators released from postischemia damage could cause damage to surrounding normal neurons, while HMG-CoA reductase inhibitors prevented neuronal apoptosis and synaptic injury by inactivating microglia through blocking the NF-κB signaling pathway.

Anti-Depressive Effectiveness of Baicalin In Vitro and In Vivo

Baicalin (BA), a major polyphenol compound isolated from the extracts of Scutellaria radix, has been previously reported to ameliorate depressive-like behaviors in mice with chronic unpredictable mild stress (CUMS). However, its underlying antidepressant mechanisms remain unclear. This study was designed to confirm the antidepressant-like effects of BA on CUMS induced behavioral abnormalities in mice, and sought to explore the pharmacological mechanisms in vivo and in vitro. The CUMS procedure was carried out to induce depression in mice. Afterwards, the tail suspension test (TST), forced swim test (FST), and open field test (OFT) were performed within 24 h, then sucrose preference test (SPT) was conducted. Additionally, PC12 cells were pretreated with BA for 2 h, then further stimulated with corticosterone for 24 h. The levels of Interleukin-1β (IL-1β), IL-6 and Tumor Necrosis Factor-α (TNF-α) in serum, hippocampus homogenate and cell culture medium were determined using the enzyme-linked immunosorbent assay (ELISA) method. The protein expressions of inhibition of high mobility group box 1 protein (HMGB1)/Toll-like receptor 4 (TLR4)/nuclear factor kappa B (NF-κB) pathways in hippocampus and PC12 cells were detected. Our results showed that CUMS-treated mice presented notable depressive-like symptoms, such as decreased sucrose consumption, increased FST and TST immobility time. While BA (25, 50 mg/kg) significantly attenuated these changes. Besides, BA treatment considerably inhibited inflammatory cytokinesl (IL-1β, IL-6, TNF-α) levels in serum, hippocampus homogenate and cell culture medium. Western blot analysis indicated that BA inhibited the expressions of HMGB1, TLR4, and p-NF-κBp65 both in vivo and in vitro. In conclusion, the present study confirmed that BA possessed efficient antidepressant effects on depression, which was possibly related to the inhibition of HMGB1/TLR4/NF-κB pathways.

Microglia in neurodegeneration

The neuroimmune system is involved in development, normal functioning, aging, and injury of the central nervous system. Microglia, first described a century ago, are the main neuroimmune cells and have three essential functions: a sentinel function involved in constant sensing of changes in their environment, a housekeeping function that promotes neuronal well-being and normal operation, and a defense function necessary for responding to such changes and providing neuroprotection. Microglia use a defined armamentarium of genes to perform these tasks. In response to specific stimuli, or with neuroinflammation, microglia also have the capacity to damage and kill neurons. Injury to neurons in Alzheimer's, Parkinson's, Huntington's, and prion diseases, as well as in amyotrophic lateral sclerosis, frontotemporal dementia, and chronic traumatic encephalopathy, results from disruption of the sentinel or housekeeping functions and dysregulation of the defense function and neuroinflammation. Pathways associated with such injury include several sensing and housekeeping pathways, such as the Trem2, Cx3cr1 and progranulin pathways, which act as immune checkpoints to keep the microglial inflammatory response under control, and the scavenger receptor pathways, which promote clearance of injurious stimuli. Peripheral interference from systemic inflammation or the gut microbiome can also alter progression of such injury. Initiation or exacerbation of neurodegeneration results from an imbalance between these microglial functions; correcting such imbalance may be a potential mode for therapy.

High mobility group box-1 (HMGB1) is increased in injured mouse spinal cord and can elicit neurotoxic inflammation

Inflammation is a ubiquitous but poorly understood consequence of spinal cord injury (SCI). The mechanisms controlling this response are unclear but culminate in the sequential activation of resident and recruited immune cells. Collectively, these cells can exert divergent effects on cell survival and tissue repair. HMGB1 is a ubiquitously expressed DNA binding protein and also a potent inflammatory stimulus. Necrotic cells release HGMB1, but HMGB1 also is actively secreted by inflammatory macrophages. A goal of this study was to quantify spatio-temporal patterns of cellular HMGB1 expression in a controlled mouse model of experimental SCI then determine the effects of HMGB1 on post-SCI neuroinflammation and recovery of function. We documented SCI-induced changes in nuclear and cytoplasmic distribution of HMGB1 in various cell types after SCI. The data reveal a time-dependent increase in HMGB1 mRNA and protein with protein reaching maximal levels 24-72 h post-injury then declining toward baseline 14-28 days post-SCI. Although most cells expressed nuclear HMGB1, reduced nuclear labeling with increased cytoplasmic expression was found in a subset of CNS macrophages suggesting that those cells begin to secrete HMGB1 at the injury site. In vitro data indicate that extracelluar HMGB1 helps promote the development of macrophages with a neurotoxic phenotype. The ability of HMGB1 to elicit neurotoxic macrophage functions was confirmed in vivo; 72 h after injecting 500 ng of recombinant HMGB1 into intact spinal cord ventral horn, inflammatory CNS macrophages co-localized with focal areas of neuronal killing. However, attempts to confer neuroprotection after SCI by blocking HMGB1 with a neutralizing antibody were unsuccessful. Collectively, these data implicate HMGB1 as a novel regulator of post-SCI inflammation and suggest that inhibition of HMGB1 could be a novel therapeutic target after SCI. Future studies will need to identify better methods to deliver optimal concentrations of HMGB1 antagonists to the injured spinal cord.

Mitochondrial Dysfunction Triggers Synaptic Deficits via Activation of p38 MAP Kinase Signaling in Differentiated Alzheimer's Disease Trans-Mitochondrial Cybrid Cells

Loss of synapse and synaptic dysfunction contribute importantly to cognitive impairment in Alzheimer's disease (AD). Mitochondrial dysfunction and oxidative stress are early pathological features in AD-affected brain. However, the effect of AD mitochondria on synaptogenesis remains to be determined. Using human trans-mitochondrial "cybrid" (cytoplasmic hybrid) neuronal cells whose mitochondria were transferred from platelets of patients with sporadic AD or age-matched non-AD subjects with relatively normal cognition, we provide the first evidence of mitochondrial dysfunction compromises synaptic development and formation of synapse in AD cybrid cells in response to chemical-induced neuronal differentiation. Compared to non-AD control cybrids, AD cybrid cells showed synaptic loss which was evidenced by a significant reduction in expression of two synaptic marker proteins: synaptophysin (presynaptic marker) and postsynaptic density protein-95, and neuronal proteins (MAP-2 and NeuN) upon neuronal differentiation. In parallel, AD-mediated synaptic deficits correlate to mitochondrial dysfunction and oxidative stress as well as activation of p38 MAP kinase. Notably, inhibition of p38 MAP kinase by pharmacological specific p38 inhibitor significantly increased synaptic density, improved mitochondrial function, and reduced oxidative stress. These results suggest that activation of p38 MAP kinase signaling pathway contributes to AD-mediated impairment in neurogenesis, possibly by inhibiting the neuronal differentiation. Our results provide new insight into the crosstalk of dysfunctional AD mitochondria to synaptic formation and maturation via activation of p38 MAP kinase. Therefore, blockade of p38 MAP kinase signal transduction could be a potential therapeutic strategy for AD by alleviating loss of synapses.

The retina as a window to early dysfunctions of Alzheimer's disease following studies with a 5xFAD mouse model

Alzheimer's disease (AD) is a progressive neurodegenerative disease leading to neuronal dysfunctions with cognitive impairment. AD can affect visual pathways and visual cortex and result in various visual changes and problems. However, how early the visual dysfunctions occur in AD is still a matter of discussion. Here, we used electrophysiological techniques to show the presence of early anomalies in AD visual system. To this aim, we used a familial AD (FAD) model, the 5xFAD transgenic mouse, characterized by severe progressive amyloid pathology and cognitive deficits. We investigated the retina and primary visual cortex responsivity together with behavioral assessment of the visual acuity. Visual tests and recordings were conducted at different ages in 5xFAD mice, corresponding to different phases of neurodegeneration and beta amyloid accumulation. We showed that the visual system is impaired in 5xFAD mice. In particular, we found that the inner retina impairment precedes neuronal disorders in other brain areas and cognitive deficits. Thus, noninvasive retinal electrophysiology can provide a support for assessing early visual dysfunctions in AD.

Amyloid-Beta and Phosphorylated Tau Accumulations Cause Abnormalities at Synapses of Alzheimer's disease Neurons

Amyloid-beta (Aβ) and hyperphosphorylated tau are hallmark lesions of Alzheimer's disease (AD). However, the loss of synapses and dysfunctions of neurotransmission are more directly tied to disease severity. The role of these lesions in the pathoetiological progression of the disease remains contested. Biochemical, cellular, molecular, and pathological studies provided several lines of evidence and improved our understanding of how Aβ and hyperphosphorylated tau accumulation may directly harm synapses and alter neurotransmission. In vitro evidence suggests that Aβ and hyperphosphorylated tau have both direct and indirect cytotoxic effects that affect neurotransmission, axonal transport, signaling cascades, organelle function, and immune response in ways that lead to synaptic loss and dysfunctions in neurotransmitter release. Observations in preclinical models and autopsy studies support these findings, suggesting that while the pathoetiology of positive lesions remains elusive, their removal may reduce disease severity and progression. The purpose of this article is to highlight the need for further investigation of the role of tau in disease progression and its interactions with Aβ and neurotransmitters alike.

Shared pathological pathways of Alzheimer's disease with specific comorbidities: current perspectives and interventions

Alzheimer's disease (AD) belongs to one of the most multifactorial, complex and heterogeneous morbidity-leading disorders. Despite the extensive research in the field, AD pathogenesis is still at some extend obscure. Mechanisms linking AD with certain comorbidities, namely diabetes mellitus, obesity and dyslipidemia, are increasingly gaining importance, mainly because of their potential role in promoting AD development and exacerbation. Their exact cognitive impairment trajectories, however, remain to be fully elucidated. The current review aims to offer a clear and comprehensive description of the state-of-the-art approaches focused on generating in-depth knowledge regarding the overlapping pathology of AD and its concomitant ailments. Thorough understanding of associated alterations on a number of molecular, metabolic and hormonal pathways, will contribute to the further development of novel and integrated theranostics, as well as targeted interventions that may be beneficial for individuals with age-related cognitive decline.

Amyloid β causes excitation/inhibition imbalance through dopamine receptor 1-dependent disruption of fast-spiking GABAergic input in anterior cingulate cortex

Alzheimer’s disease (AD) is the most common cause of dementia in the elderly. At the early stages of AD development, the soluble β-amyloid (Aβ) induces synaptic dysfunction, perturbs the excitation/inhibition balance of neural circuitries, and in turn alters the normal neural network activity leading to cognitive decline, but the underlying mechanisms are not well established. Here by using whole-cell recordings in acute mouse brain slices, we found that 50 nM Aβ induces hyperexcitability of excitatory pyramidal cells in the cingulate cortex, one of the most vulnerable areas in AD, via depressing inhibitory synaptic transmission. Furthermore, by simultaneously recording multiple cells, we discovered that the inhibitory innervation of pyramidal cells from fast-spiking (FS) interneurons instead of non-FS interneurons is dramatically disrupted by Aβ, and perturbation of the presynaptic inhibitory neurotransmitter gamma-aminobutyric acid (GABA) release underlies this inhibitory input disruption. Finally, we identified the increased dopamine action on dopamine D1 receptor of FS interneurons as a key pathological factor that contributes to GABAergic input perturbation and excitation/inhibition imbalance caused by Aβ. Thus, we conclude that the dopamine receptor 1-dependent disruption of FS GABAergic inhibitory input plays a critical role in Aβ-induced excitation/inhibition imbalance in anterior cingulate cortex.

Knowledge-driven binning approach for rare variant association analysis: application to neuroimaging biomarkers in Alzheimer's disease

Background

Rapid advancement of next generation sequencing technologies such as whole genome sequencing (WGS) has facilitated the search for genetic factors that influence disease risk in the field of human genetics. To identify rare variants associated with human diseases or traits, an efficient genome-wide binning approach is needed. In this study we developed a novel biological knowledge-based binning approach for rare-variant association analysis and then applied the approach to structural neuroimaging endophenotypes related to late-onset Alzheimer’s disease (LOAD).

Methods

For rare-variant analysis, we used the knowledge-driven binning approach implemented in Bin-KAT, an automated tool, that provides 1) binning/collapsing methods for multi-level variant aggregation with a flexible, biologically informed binning strategy and 2) an option of performing unified collapsing and statistical rare variant analyses in one tool. A total of 750 non-Hispanic Caucasian participants from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohort who had both WGS data and magnetic resonance imaging (MRI) scans were used in this study. Mean bilateral cortical thickness of the entorhinal cortex extracted from MRI scans was used as an AD-related neuroimaging endophenotype. SKAT was used for a genome-wide gene- and region-based association analysis of rare variants (MAF (minor allele frequency) < 0.05) and potential confounding factors (age, gender, years of education, intracranial volume (ICV) and MRI field strength) for entorhinal cortex thickness were used as covariates. Significant associations were determined using FDR adjustment for multiple comparisons.

Results

Our knowledge-driven binning approach identified 16 functional exonic rare variants in FANCC significantly associated with entorhinal cortex thickness (FDR-corrected p-value < 0.05). In addition, the approach identified 7 evolutionary conserved regions, which were mapped to FAF1, RFX7, LYPLAL1 and GOLGA3, significantly associated with entorhinal cortex thickness (FDR-corrected p-value < 0.05). In further analysis, the functional exonic rare variants in FANCC were also significantly associated with hippocampal volume and cerebrospinal fluid (CSF) Aβ_1–42 (p-value < 0.05).

Conclusions

Our novel binning approach identified rare variants in FANCC as well as 7 evolutionary conserved regions significantly associated with a LOAD-related neuroimaging endophenotype. FANCC (fanconi anemia complementation group C) has been shown to modulate TLR and p38 MAPK-dependent expression of IL-1β in macrophages. Our results warrant further investigation in a larger independent cohort and demonstrate that the biological knowledge-driven binning approach is a powerful strategy to identify rare variants associated with AD and other complex disease.

Synaptic Dysfunction in Alzheimer's Disease and Glaucoma: From Common Degenerative Mechanisms Toward Neuroprotection

Alzheimer’s disease (AD) and glaucoma are two distinct multifactorial neurodegenerative diseases, primarily affecting the elderly. Common pathophysiological mechanisms have been elucidated in the past decades. First of all both diseases are progressive, with AD leading to dementia and glaucoma inducing blindness. Pathologically, they all feature synaptic dysfunction with changes of neuronal circuitry, progressive accumulation of protein aggregates such as the beta amyloid (Aβ) and intracellular microtubule inclusions containing hyperphosphorylated tau, which belongs to microtubule associated protein family. During an early phase of degeneration, both diseases are characterized by synaptic dysfunction and changes of mitogen-activated protein kinases (MAPK). Common degenerative mechanisms underlying both diseases are discussed here, along with recent results on the potential use of the visual system as a biomarker for diagnosis and progression of AD. Common neuropathological changes and mechanisms in AD and glaucoma have facilitated the transfer of therapeutic strategies between diseases. In particular, we discuss past and present evidence for neuroprotective effects of brain-derived neurotrophic factor (BDNF).

Advanced glycation end-products produced systemically and by macrophages: A common contributor to inflammation and degenerative diseases

Advanced glycation end products (AGEs) and their receptor have been implicated in the progressions of many intractable diseases, such as diabetes and atherosclerosis, and are also critical for pathologic changes in chronic degenerative diseases, such as Alzheimer's disease, Parkinson's disease, and alcoholic brain damage. Recently activated macrophages were found to be a source of AGEs, and the most abundant form of AGEs, AGE-albumin excreted by macrophages has been implicated in these diseases and to act through common pathways. AGEs inhibition has been shown to prevent the pathogenesis of AGEs-related diseases in human, and therapeutic advances have resulted in several agents that prevent their adverse effects. Recently, anti-inflammatory molecules that inhibit AGEs have been shown to be good candidates for ameliorating diabetic complications as well as degenerative diseases. This review was undertaken to present, discuss, and clarify current understanding regarding AGEs formation in association with macrophages, different diseases, therapeutic and diagnostic strategy and links with RAGE inhibition.