Targeting Microglia-Synapse Interactions in Alzheimer's Disease

Switch to phagocytic microglia by CSFR1 inhibition drives amyloid-beta clearance from glutamatergic terminals rescuing LTP in acute hippocampal slices

Microglia, traditionally regarded as innate immune cells in the brain, drive neuroinflammation and synaptic dysfunctions in the early phases of Alzheimer disease (AD), acting upstream to Aβ accumulation. Colony stimulating factor 1-receptor (CSF-1R) is predominantly expressed on microglia and its levels are significantly increased in neurodegenerative diseases, possibly contributing to the chronic inflammatory microglial response. On the other hand, CSF-1R inhibitors confer neuroprotection in preclinical models of neurodegenerative diseases. Here, we determined the effects of the CSF-1R inhibitor PLX3397 on the Aβ-mediated synaptic alterations in ex vivo hippocampal slices. Electrophysiological findings show that PLX3397 rescues LTP impairment and neurotransmission changes induced by Aβ. In addition, using confocal imaging experiments, we demonstrate that PLX3397 stimulates a microglial transition toward a phagocytic phenotype, which in turn promotes the clearance of Aβ from glutamatergic terminals. We believe that the selective pruning of Aβ-loaded synaptic terminals might contribute to the restoration of LTP and excitatory transmission alterations observed upon acute PLX3397 treatment. This result is in accordance with the mechanism proposed for CSF1R inhibitors, that is to eliminate responsive microglia and replace it with newly generated, homeostatic microglia, capable of promoting brain repair. Overall, our findings identify a connection between the rapid microglia adjustments and the early synaptic alterations observed in AD, possibly highlighting a novel disease-modifying target.

Mitochondrial Treatment Improves Cognitive Impairment Induced by Lipopolysaccharide in Mice

Neuroinflammation has been proven to drive cognitive impairment associated with neurodegenerative diseases. It has been demonstrated that mitochondrial dysfunction is associated with cognitive impairment caused by neuroinflammation. We hypothesized that the transfer of exogenous mitochondria may be beneficial to the therapy of cognitive impairment induced by neuroinflammation. In the study, the effect of exogenous mitochondria on cognitive impairment induced by neuroinflammation was investigated. The results showed that mitochondrial treatment ameliorated the cognitive performance of lipopolysaccharide (LPS)-treated mice. Additionally, mitochondrial therapy attenuated neuronal injury and down-regulated the expression of proinflammatory cytokines, including TNF-α and pro- and cleaved IL-1β, and the expression of Iba-1 and GFAP in the hippocampus and cortex of LPS-treated mice. Additionally, mitochondrial treatment increased mitochondrial ΔΨm, ATP level, and SOD activity and attenuated MDA level and ROS production in the brains of LPS-treated mice. The study reports the beneficial effect of mitochondrial treatment against cognitive impairment of LPS-treated mice, thereby providing a potential strategy for the treatment of cognitive impairment caused by neuroinflammation.

Proteomic analysis identifies HSP90AA1, PTK2B, and ANXA2 in the human entorhinal cortex in Alzheimer's disease: Potential role in synaptic homeostasis and Aβ pathology through microglial and astroglial cells

Alzheimer's disease (AD), the most prevalent neurodegenerative disorder worldwide, is clinically characterized by cognitive deficits. Neuropathologically, AD brains accumulate deposits of amyloid-β (Aβ) and tau proteins. Furthermore, these misfolded proteins can propagate from cell to cell in a prion-like manner and induce native proteins to become pathological. The entorhinal cortex (EC) is among the earliest areas affected by tau accumulation along with volume reduction and neurodegeneration. Neuron-glia interactions have recently come into focus; however, the role of microglia and astroglia in the pathogenesis of AD remains unclear. Proteomic approaches allow the determination of changes in the proteome to better understand the pathology underlying AD. Bioinformatic analysis of proteomic data was performed to compare ECs from AD and non-AD human brain tissue. To validate the proteomic results, western blot, immunofluorescence, and confocal studies were carried out. The findings revealed that the most disturbed signaling pathway was synaptogenesis. Because of their involvement in synapse function, relationship with Aβ and tau proteins and interactions in the pathway analysis, three proteins were selected for in-depth study: HSP90AA1, PTK2B, and ANXA2. All these proteins showed colocalization with neurons and/or astroglia and microglia and with pathological Aβ and tau proteins. In particular, ANXA2, which is overexpressed in AD, colocalized with amoeboid microglial cells and Aβ plaques surrounded by astrocytes. Taken together, the evidence suggests that unbalanced expression of HSP90AA1, PTK2B, and ANXA2 may play a significant role in synaptic homeostasis and Aβ pathology through microglial and astroglial cells in the human EC in AD.

Circulating small extracellular vesicles in Alzheimer's disease: a case-control study of neuro-inflammation and synaptic dysfunction

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease characterized by Aβ plaques and neurofibrillary tangles. Chronic inflammation and synaptic dysfunction lead to disease progression and cognitive decline. Small extracellular vesicles (sEVs) are implicated in AD progression by facilitating the spread of pathological proteins and inflammatory cytokines. This study investigates synaptic dysfunction and neuroinflammation protein markers in plasma-derived sEVs (PsEVs), their association with Amyloid-β and tau pathologies, and their correlation with AD progression.

METHODS

A total of 90 [AD = 35, mild cognitive impairment (MCI) = 25, and healthy age-matched controls (AMC) = 30] participants were recruited. PsEVs were isolated using a chemical precipitation method, and their morphology was characterized by transmission electron microscopy. Using nanoparticle tracking analysis, the size and concentration of PsEVs were determined. Antibody-based validation of PsEVs was done using CD63, CD81, TSG101, and L1CAM antibodies. Synaptic dysfunction and neuroinflammation were evaluated with synaptophysin, TNF-α, IL-1β, and GFAP antibodies. AD-specific markers, amyloid-β (1-42), and p-Tau were examined within PsEVs using Western blot and ELISA.

RESULTS

Our findings reveal higher concentrations of PsEVs in AD and MCI compared to AMC (p < 0.0001). Amyloid-β (1-42) expression within PsEVs is significantly elevated in MCI and AD compared to AMC. We could also differentiate between the amyloid-β (1-42) expression in AD and MCI. Similarly, PsEVs-derived p-Tau exhibited elevated expression in MCI compared with AMC, which is further increased in AD. Synaptophysin exhibited downregulated expression in PsEVs from MCI to AD (p = 0.047) compared to AMC, whereas IL-1β, TNF-α, and GFAP showed increased expression in MCI and AD compared to AMC. The correlation between the neuropsychological tests and PsEVs-derived proteins (which included markers for synaptic integrity, neuroinflammation, and disease pathology) was also performed in our study. The increased number of PsEVs correlates with disease pathological markers, synaptic dysfunction, and neuroinflammation.

CONCLUSIONS

Elevated PsEVs, upregulated amyloid-β (1-42), and p-Tau expression show high diagnostic accuracy in AD. The downregulated synaptophysin expression and upregulated neuroinflammatory markers in AD and MCI patients suggest potential synaptic degeneration and neuroinflammation. These findings support the potential of PsEV-associated biomarkers for AD diagnosis and highlight synaptic dysfunction and neuroinflammation in disease progression.

Role of microglia after subarachnoid hemorrhage

Subarachnoid hemorrhage is a devastating sequela of aneurysm rupture. Because it disproportionately affects younger patients, the population impact of hemorrhagic stroke from subarachnoid hemorrhage is substantial. Secondary brain injury is a significant contributor to morbidity after subarachnoid hemorrhage. Initial hemorrhage causes intracranial pressure elevations, disrupted cerebral perfusion pressure, global ischemia, and systemic dysfunction. These initial events are followed by two characterized timespans of secondary brain injury: the early brain injury period and the delayed cerebral ischemia period. The identification of varying microglial phenotypes across phases of secondary brain injury paired with the functions of microglia during each phase provides a basis for microglia serving a critical role in both promoting and attenuating subarachnoid hemorrhage-induced morbidity. The duality of microglial effects on outcomes following SAH is highlighted by the pleiotropic features of these cells. Here, we provide an overview of the key role of microglia in subarachnoid hemorrhage-induced secondary brain injury as both cytotoxic and restorative effectors. We first describe the ontogeny of microglial populations that respond to subarachnoid hemorrhage. We then correlate the phenotypic development of secondary brain injury after subarachnoid hemorrhage to microglial functions, synthesizing experimental data in this area.

Correlation of Presynaptic and Postsynaptic Proteins with Pathology in Alzheimer's Disease

Synaptic transmission is essential for nervous system function and the loss of synapses is a known major contributor to dementia. Alzheimer's disease dementia (ADD) is characterized by synaptic loss in the mesial temporal lobe and cerebral neocortex, both of which are brain areas associated with memory and cognition. The association of synaptic loss and ADD was established in the late 1980s, and it has been estimated that 30-50% of neocortical synaptic protein is lost in ADD, but there has not yet been a quantitative profiling of different synaptic proteins in different brain regions in ADD from the same individuals. Very recently, positron emission tomography (PET) imaging of synapses is being developed, accelerating the focus on the role of synaptic loss in ADD and other conditions. In this study, we quantified the densities of two synaptic proteins, the presynaptic protein Synaptosome Associated Protein 25 (SNAP25) and the postsynaptic protein postsynaptic density protein 95 (PSD95) in the human brain, using enzyme-linked immunosorbent assays (ELISA). Protein was extracted from the cingulate gyrus, hippocampus, frontal, primary visual, and entorhinal cortex from cognitively unimpaired controls, subjects with mild cognitive impairment (MCI), and subjects with dementia that have different levels of Alzheimer's pathology. SNAP25 is significantly reduced in ADD when compared to controls in the frontal cortex, visual cortex, and cingulate, while the hippocampus showed a smaller, non-significant reduction, and entorhinal cortex concentrations were not different. In contrast, all brain areas showed lower PSD95 concentrations in ADD when compared to controls without dementia, although in the hippocampus, this failed to reach significance. Interestingly, cognitively unimpaired cases with high levels of AD pathology had higher levels of both synaptic proteins in all brain regions. SNAP25 and PSD95 concentrations significantly correlated with densities of neurofibrillary tangles, amyloid plaques, and Mini Mental State Examination (MMSE) scores. Our results suggest that synaptic transmission is affected by ADD in multiple brain regions. The differences were less marked in the entorhinal cortex and the hippocampus, most likely due to a ceiling effect imposed by the very early development of neurofibrillary tangles in older people in these brain regions.

Identifying potential genetic epistasis implicated in Alzheimer's disease via detection of SNP-SNP interaction on quantitative trait CSF Aβ42

Although genome-wide association studies have identified multiple Alzheimer's disease (AD)-associated loci by selecting the main effects of individual single-nucleotide polymorphisms (SNPs), the interpretation of genetic variance in AD is limited. Based on the linear regression method, we performed genome-wide SNP-SNP interaction on cerebrospinal fluid Aβ42 to identify potential genetic epistasis implicated in AD, with age, gender, and diagnosis as covariates. A GPU-based method was used to address the computational challenges posed by the analysis of epistasis. We found 368 SNP pairs to be statistically significant, and highly significant SNP-SNP interactions were identified between the marginal main effects of SNP pairs, which explained a relatively high variance at the Aβ42 level. Our results replicated 100 previously reported AD-related genes and 5 gene-gene interaction pairs of the protein-protein interaction network. Our bioinformatics analyses provided preliminary evidence that the 5-overlapping gene-gene interaction pairs play critical roles in inducing synaptic loss and dysfunction, thereby leading to memory decline and cognitive impairment in AD-affected brains.

CircDYM attenuates microglial apoptosis via CEBPB/ZC3H4 axis in LPS-induced mouse model of depression

Major depressive disorder (MDD) is a highly prevalent condition and one of the most common psychiatric disorders worldwide. Circular RNA (circRNA) has been increasingly implicated in MDD. However, a comprehensive understanding of circRNA and microglial apoptosis in depression is incomplete. Here, we show that circDYM inhibits microglial apoptosis induced by LPS via CEBPB/ZC3H4 axis. CircDYM prevents the translocation of CEBPB from cytoplasm to the nucleus by binding with CEBPB. Moreover, LPS-induced CEBPB nuclear entry downregulates the expression of ZC3H4, in which promotes autophagy and apoptosis in microglia. Taken together, our findings provide new insights into the relationship between circDYM and microglial apoptosis and shed new light on the function of this novel mechanism in depression-associated complex changes in the brain.

Neurovascular glial unit: A target of phytotherapy for cognitive impairments

BACKGROUND

Neurovascular glial unit (NVGU) dysfunction has been reported to be an early and critical event in the pathophysiology of Alzheimer's disease (AD) and vascular dementia (VD). Although herbal medicines, with their favorable safety profiles and low adverse effects, have been suggested to be useful for the treatment of cognitive impairment, the potential role of the NVGU as the target of the effects of herbal medicines is still unclear.

PURPOSE

This review aimed to retrieve evidence from experimental studies of phytopharmaceuticals targeting the NVGU for the treatment of cognitive impairment in AD and VD, and discussed the potential of phytopharmaceuticals to improve cognitive impairment from the perspective of the NVGU.

STUDY DESIGN AND METHODS

We systematically searched PubMed, Google Scholar, Web of Science, and CNKI. The keywords used for searching information on the NVGU in the treatment of cognitive impairments included "Alzheimer's disease," "Vascular dementia," "Herbal medicines," "Natural products," "Neurovascular," "Adverse reaction," and "Toxicity, etc." We selected studies on the basis of predefined eligibility criteria.

RESULTS

NVGU mainly consists of endothelial cells, pericytes, astrocytes, microglia, oligodendrocytes, and neurons, and damage to these cells can induce cognitive impairment by impairing the blood-brain barrier (BBB) and cerebral blood flow (CBF) as well as neuronal function. The active components of herbal medicines, including Ginkgo biloba L., Ginseng Radix et Rhizoma, Epimedium Folium, Chuanxiong Rhizoma, Carthami flos, and Acorus tatarinowii Schott, as well as traditional Chinese medicine prescriptions have shown the potential to improve BBB function and increase CBF to prevent cognitive impairment by inhibiting astrocyte and microglia activation, protecting oligodendrocyte myelin function, reducing neuronal apoptosis, and promoting angiogenesis.

CONCLUSIONS

Herbal medicines demonstrate great potential to prevent cognitive impairment. Multiple components from herbal medicines may function through different signaling pathways to target the NVGU. Future studies using novel drug-carrier or delivery systems targeting the NVGU will certainly facilitate the development of phytopharmaceuticals for AD and VD.

TREM2, microglial and ischemic stroke

Ischemic stroke (IS) is a leading cause of morbidity and mortality worldwide. Immunity and inflammation are key factors in the pathophysiology of IS. The inflammatory response is involved in all stages of stroke, and microglia are the predominant cells involved in the post-stroke inflammatory response. Resident microglia are the main immune cells of the brain and the first line of defense of the nervous system. After IS, activated microglia can be both advantageous and detrimental to surrounding tissue; they can be divided into the harmful M1 types or the neuro-protective M2 type. Currently, with the latest progress of transcriptomics analysis, different and more complex phenotypes of microglia activation have been described, such as disease-related microglia (DAM) associated with Alzheimer's disease (AD), white matter associated microglia (WAMs) in aging, and stroke-related microglia (SAM) etc. The triggering receptor expressed on myeloid cell 2 (TREM2) is an immune-related receptor on the surface of microglia. Its expression increases after IS, which is related to microglial inflammation and phagocytosis, however, its relationship with the microglia phenotype is not clear. This paper reviews the following: 1) the phenotypic changes of microglia in various pathological stages after IS and its relationship with inflammatory factors; 2) the relationship between the expression of the TREM2 receptor and inflammatory factors; 3) the relationship between phenotypic changes of microglia and its surface receptor TREM2; 4) the TREM2-related signalling pathway of microglia after IS and treatment for TREM2 receptor; and finally 5) To clarify the relationship among TREM2, inflammation, and microglia phenotype after IS, as well as the mechanism among them and the some possible treatment of IS targeting TREM2. Moreover, the relationship between the new phenotype of microglia such as SAM and TREM2 has also been systematically summarized, but there are no relevant research reports on the relationship between TREM2 and SAM after IS.

Engineered macrophage-biomimetic versatile nanoantidotes for inflammation-targeted therapy against Alzheimer's disease by neurotoxin neutralization and immune recognition suppression

Immune recognition of excessive neurotoxins by microglia is a trigger for the onset of neuroinflammation in the brain, leading to neurodegeneration in Alzheimer's disease (AD). Blocking active recognition of microglia while removing neurotoxins holds promise for fundamentally alleviating neurotoxin-induced immune responses, but is very challenging. Herein, an engineered macrophage-biomimetic versatile nanoantidote (OT-Lipo@M) is developed for inflammation-targeted therapy against AD by neurotoxin neutralization and immune recognition suppression. Coating macrophage membranes can not only endow OT-Lipo@M with anti-phagocytic and inflammation-tropism capabilities to target inflammatory lesions in AD brain, but also efficiently reduce neurotoxin levels to prevent them from activating microglia. The loaded oxytocin (OT) can be slowly released to downregulate the expression of immune recognition site Toll-like receptor 4 (TLR4) on microglia, inhibiting TLR4-mediated pro-inflammatory signalling cascade. Benefiting from this two-pronged immunosuppressive strategy, OT-Lipo@M exhibits outstanding therapeutic effects on ameliorating cognitive deficits, inhibiting neuronal apoptosis, and enhancing synaptic plasticity in AD mice, accompanied by the delayed hippocampal atrophy and brain microstructural disruption by in vivo 9.4T MR imaging. This work provides new insights into potential AD therapeutics targeting microglia-mediated neuroinflammation at the source.

Exploratory Assessment of Proteomic Network Changes in Cerebrospinal Fluid of Mild Cognitive Impairment Patients: A Pilot Study

(1) Background: Despite the existence of well-established, CSF-based biomarkers such as amyloid-β and phosphorylated-tau, the pathways involved in the pathophysiology of Alzheimer's disease (AD) remain an active area of research. (2) Methods: We measured 3072 proteins in CSF samples of AD-biomarker positive mild cognitive impairment (MCI) participants (n = 38) and controls (n = 48), using the Explore panel of the Olink proximity extension assay (PEA). We performed group comparisons, association studies with diagnosis, age, and APOE ε4 status, overrepresentation analysis (ORA), and gene set enrichment analysis (GSEA) to determine differentially expressed proteins and dysregulated pathways. (3) Results: GSEA results demonstrated an enrichment of granulocyte-related and chemotactic pathways (core enrichment proteins: ITGB2, ITGAM, ICAM1, SELL, SELP, C5, IL1A). Moreover, some of the well-replicated, differentially expressed proteins in CSF included: ITGAM, ITGB2, C1QA, TREM2, GFAP, NEFL, MMP-10, and a novel tau-related marker, SCRN1. (4) Conclusion: Our results highlight the upregulation of neuroinflammatory pathways, especially chemotactic and granulocyte recruitment in CSF of early AD patients.

Guizhi Fuling capsule relieves memory deficits by inhibition of microglial neuroinflammation through blocking JAK2/STAT3 pathway in presenilin1/2 conditional double knockout mice

Chronic neuroinflammation has been regarded as an important part of the pathological initiation of Alzheimer's disease (AD), which is associated with the regulation of microglial activation. Preventing microglial activation to inhibit neuroinflammation may become a potential target for the treatment of neurodegenerative diseases. Guizhi Fuling capsule (GZFL) has a strong repression on inflammatory responses. Here, the presenilin1/2 conditional double knockout (PS cDKO) mice, a well-established mouse model of AD, were divided into: WT mice (WT), WT mice+GZFL (WT+GZFL), PS cDKO mice (cDKO), and PS cDKO mice+GZFL (cDKO+GZFL). Mice in the WT+GZFL and cDKO+GZFL group were fed standard chow containing 2000 ppm GZFL for 90 days. After 60 days of GZFL treatment, mice were given to behavioral tests for 30 days in order to explore the effects of GZFL on cognitive and motor function. Then, mice were sacrificed for examining the effects of GZFL on inflammation. Furthermore, primary microglia were obtained from neonatal Sprague-Dawley rats and pretreated with or without GZFL (50 μg/ml) for 1 h in the absence or presence of lipopolysaccharide (LPS) (100 ng/ml) stimulation to speculate whether the underlying mechanism of GZFL's anti-inflammatory potential was closely associated with Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathway. Our findings indicated that GZFL has the ability to alleviate memory deficits in PS cDKO mice, which attributes to the improvement of neuroinflammation by inhibiting microglial activation and the levels of pro-inflammatory mediators. In addition, GZFL could inverse the tau hyperphosphorylation and the lessened expression of synaptic proteins in hippocampus of PS cDKO mice. Furthermore, GZFL prevented LPS-induced neuroinflammatory responses in primary microglia by decreasing the levels of pro-inflammatory mediators. It is noteworthy that therapeutic effects of GZFL on memory impairment are depended on the inhibition of neuroinflammatory responses by the blockage of JAK2/STAT3 signaling pathway. Taken together, GZFL may be an effective compound Chinese medicine for the improvement and postponement of neurodegenerative progression in AD.

N,N-dimethylacetamide targets neuroinflammation in Alzheimer's disease in in-vitro and ex-vivo models

Alzheimer's disease (AD) is a chronic degenerative brain disorder with no clear pathogenesis or effective cure, accounting for 60-80% of cases of dementia. In recent years, the importance of neuroinflammation in the pathogenesis of AD and other neurodegenerative disorders has come into focus. Previously, we made the serendipitous discovery that the widely used drug excipient N,N-dimethylacetamide (DMA) attenuates endotoxin-induced inflammatory responses in vivo. In the current work, we investigate the effect of DMA on neuroinflammation and its mechanism of action in in-vitro and ex-vivo models of AD. We show that DMA significantly suppresses the production of inflammatory mediators, such as reactive oxygen species (ROS), nitric oxide (NO) and various cytokines and chemokines, as well as amyloid-β (Aβ), in cultured microglia and organotypic hippocampal slices induced by lipopolysaccharide (LPS). We also demonstrate that DMA inhibits Aβ-induced inflammation. Finally, we show that the mechanism of DMA's effect on neuroinflammation is inhibition of the nuclear factor kappa-B (NF-κB) signaling pathway and we show how DMA dismantles the positive feedback loop between NF-κB and Aβ synthesis. Taken together, our findings suggest that DMA, a generally regarded as safe compound that crosses the blood brain barrier, should be further investigated as a potential therapy for Alzheimer's disease and neuroinflammatory disorders.

Synapse pathology in Alzheimer's disease

Synapse loss and damage are central features of Alzheimer's disease (AD) and contribute to the onset and progression of its behavioural and physiological features. Here we review the literature describing synapse pathology in AD, from what we have learned from microscopy in terms of its impacts on synapse architecture, to the mechanistic role of Aβ, tau and glial cells, mitochondrial dysfunction, and the link with AD risk genes. We consider the emerging view that synapse pathology may operate at a further level, that of synapse diversity, and discuss the prospects for leveraging new synaptome mapping methods to comprehensively understand the molecular properties of vulnerable and resilient synapses. Uncovering AD impacts on brain synapse diversity should inform therapeutic approaches targeted at preserving or replenishing lost and damaged synapses and aid the interpretation of clinical imaging approaches that aim to measure synapse damage.

Alzheimer’s disease as a synaptopathy: Evidence for dysfunction of synapses during disease progression

The synapse has consistently been considered a vulnerable and critical target within Alzheimer’s disease, and synapse loss is, to date, one of the main biological correlates of cognitive decline within Alzheimer’s disease. This occurs prior to neuronal loss with ample evidence that synaptic dysfunction precedes this, in support of the idea that synaptic failure is a crucial stage within disease pathogenesis. The two main pathological hallmarks of Alzheimer’s disease, abnormal aggregates of amyloid or tau proteins, have had demonstrable effects on synaptic physiology in animal and cellular models of Alzheimer’s disease. There is also growing evidence that these two proteins may have a synergistic effect on neurophysiological dysfunction. Here, we review some of the main findings of synaptic alterations in Alzheimer’s disease, and what we know from Alzheimer’s disease animal and cellular models. First, we briefly summarize some of the human evidence to suggest that synapses are altered, including how this relates to network activity. Subsequently, animal and cellular models of Alzheimer’s disease are considered, highlighting mouse models of amyloid and tau pathology and the role these proteins may play in synaptic dysfunction, either in isolation or examining how the two pathologies may interact in dysfunction. This specifically focuses on neurophysiological function and dysfunction observed within these animal models, typically measured using electrophysiology or calcium imaging. Following synaptic dysfunction and loss, it would be impossible to imagine that this would not alter oscillatory activity within the brain. Therefore, this review also discusses how this may underpin some of the aberrant oscillatory patterns seen in animal models of Alzheimer’s disease and human patients. Finally, an overview of some key directions and considerations in the field of synaptic dysfunction in Alzheimer’s disease is covered. This includes current therapeutics that are targeted specifically at synaptic dysfunction, but also methods that modulate activity to rescue aberrant oscillatory patterns. Other important future avenues of note in this field include the role of non-neuronal cell types such as astrocytes and microglia, and mechanisms of dysfunction independent of amyloid and tau in Alzheimer’s disease. The synapse will certainly continue to be an important target within Alzheimer’s disease for the foreseeable future.

Alzheimer's disease as an innate autoimmune disease (AD2): A new molecular paradigm

A new model of Alzheimer's disease (AD) is presented: Alzheimer's disease as an autoimmune disease (AD2).  In response to pathogen-/damage-associated molecular pattern-stimulating events (e.g., infection, trauma, ischemia, pollution), amyloid beta (Aβ) is released as an early responder cytokine triggering an innate immunity cascade in which Aβ exhibits immunomodulatory/antimicrobial duality.  However, Aβ's antimicrobial properties result in a misdirected attack upon "self" neurons, arising from the electrophysiological similarities between neurons and bacteria in terms of transmembrane potential gradients and anionic charges on outer membrane macromolecules. The subsequent breakdown products of necrotic neurons elicit further release of Aβ leading to a chronic, self-perpetuating cycle. In AD2, amino acid (trp, arg) metabolism is a central control player in modulating AD autoimmunity.  AD2 includes Aβ as an important molecular player, but rejects the "amyloid hypothesis," recognizing Aβ as a physiologically oligomerizing cytokine and part of a larger immunopathic conceptualization of AD.

Synaptic loss and gliosis in the nucleus tractus solitarii with streptozotocin-induced Alzheimer's disease

Obstructive sleep apnea is highly prevalent in Alzheimer's disease (AD). However, brainstem centers controlling respiration have received little attention in AD research, and mechanisms behind respiratory dysfunction in AD are not understood. The nucleus tractus solitarii (nTS) is an important brainstem center for respiratory control and chemoreflex function. Alterations of nTS integrity, like those shown in AD patients, likely affect neuronal processing and adequate control of breathing. We used the streptozotocin-induced rat model of AD (STZ-AD) to analyze cellular changes in the nTS that corroborate previously documented respiratory dysfunction. We used 2 common dosages of STZ (2 and 3 mg/kg STZ) for model induction and evaluated the early impact on cell populations in the nTS. The hippocampus served as control region to identify site-specific effects of STZ. There was significant atrophy in the caudal nTS of the 3 mg/kg STZ-AD group only, an area known to integrate chemoafferent information. Also, the hippocampus had significant atrophy with the highest STZ dosage tested. Both STZ-AD groups showed respiratory dysfunction along with multiple indices for astroglial and microglial activation. These changes were primarily located in the caudal and intermediate nTS. While there was no change of astrocytes in the hippocampus, microglial activation was accompanied by a reduction in synaptic density. Together, our data demonstrate that STZ-AD induces site-specific effects on all major cell types, primarily in the caudal/intermediate nTS. Both STZ dosages used in this study produced a similar outcome and can be used for future studies examining the initial symptoms of STZ-AD.

Perspectives of ozone induced neuropathology and memory decline in Alzheimer's disease: A systematic review of preclinical evidences

This systematic review aims to discover the plausible mechanism of Ozone in A.D., to boost translational research. The main focus of our review lies in understanding the effects of ozone pollution on the human brain and causing degenerative disease. Owing to the number of works carried out as preclinical evidence in association with oxidative stress and Alzheimer's disease and the lack of systematic review or meta-analysis prompted us to initiate a study on Alzheimer's risk due to ground-level ozone. We found relevant studies from PubMed, ScienceDirect, Proquest, DOAJ, and Scopus, narrowing to animal studies and the English language without any time limit. The searches will be re-run before the final analysis. This work was registered in Prospero with Reg ID CRD42022319360, followed the PRISMA-P framework, and followed the PICO approach involving Population, Intervention/Exposure, Comparison, and Outcomes data. Bibliographic details of 16 included studies were studied for Exposure dose of ozone, duration, exposure, and frequency with control and exposure groups. Primary and secondary outcomes were assessed based on pathology significance, and results were significant in inducing Alzheimer-like pathology by ozone. In conclusion, ozone altered oxidative stress, metabolic pathway, and amyloid plaque accumulation besides endothelial stress response involving mitochondria as the critical factor in ATP degeneration, caspase pathway, and neuronal damage. Thus, ozone is a criteria pollutant to be focused on in mitigating Alzheimer's Disease pathology.

The relationships between neuroglial alterations and neuronal changes in Alzheimer's disease, and the related controversies I: Gliopathogenesis and glioprotection

Since Alois Alzheimer described the pathology of Alzheimer's disease in 1907, an increasing number of studies have attempted to discover its causes and possible ways to treat it. For decades, research has focused on neuronal degeneration and the disruption to the neural circuits that occurs during disease progression, undervaluing in some extent the alterations to glial cells even though these alterations were described in the very first studies of this disease. In recent years, it has been recognized that different families of neuroglia are not merely support cells for neurons but rather key and active elements in the physiology and pathology of the nervous system. Alterations to different types of neuroglia (especially astroglia and microglia but also mature oligodendroglia and oligodendroglial progenitors) have been identified in the initial neuropathological changes that lead to dementia, suggesting that they may represent therapeutic targets to prevent neurodegeneration. In this review, based on our own studies and on the relevant scientific literature, we argue that a careful and in-depth study of glial cells will be fundamental to understanding the origin and progression of Alzheimer's disease. In addition, we analyze the main issues regarding the neuroprotective and neurotoxic role of neuroglial changes, reactions and/or involutions in both humans with Alzheimer's disease and in experimental models of this condition.

The Innate and Adaptive Immune Cells in Alzheimer’s and Parkinson’s Diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common neurodegenerative disorders of the central nervous system (CNS). Increasing evidence supports the view that dysfunction of innate immune cells initiated by accumulated and misfolded proteins plays essential roles in the pathogenesis and progression of these diseases. The TLR family was found to be involved in the regulation of microglial function in the pathogenesis and progression of AD or PD, making it as double-edged sword in these diseases. Altered function of peripheral innate immune cells was found in AD and PD and thus contributed to the development and progression of AD and PD. Alteration of different subsets of T cells was found in the peripheral blood and CNS in AD and PD. The CNS-infiltrating T cells can exert both neuroprotective and neurotoxic effects in the pathogenesis and progression. Here, we review recent evidences for the roles of innate and adaptive immune cells in the pathogenesis and progression of AD and PD.

Pharmacological targeting of microglia dynamics in Alzheimer's disease: Preclinical and clinical evidence

Numerous clinical trials of anti-amyloid agents for Alzheimer's disease (AD) were so far unsuccessful thereby challenging the validity of the amyloid hypothesis. This lack of progress has encouraged researchers to investigate alternative mechanisms in non-neuronal cells, among which microglia represent nowadays an attractive target. Microglia play a key role in the developing brain and contribute to synaptic remodeling in the mature brain. On the other hand, the intimate relationship between microglia and synapses led to the so-called synaptic stripping hypothesis, a process in which microglia selectively remove synapses from injured neurons. Synaptic stripping, along with the induction of a microglia-mediated chronic neuroinflammatory environment, promote the progressive synaptic degeneration in AD. Therefore, targeting microglia may pave the way for a new disease modifying approach. This review provides an overview of the pathophysiological roles of the microglia cells in AD and describes putative targets for pharmacological intervention. It also provides evidence for microglia-targeted strategies in preclinical AD studies and in early clinical trials.

The Role of Exosomes as Mediators of Neuroinflammation in the Pathogenesis and Treatment of Alzheimer’s Disease

Alzheimer’s disease (AD) is a common neurodegenerative disease characterized by progressive dementia. Accumulation of β–amyloid peptide 1–42 and phosphorylation of tau protein in the brain are the two main pathological features of AD. However, comprehensive studies have shown that neuroinflammation also plays a crucial role in the pathogenesis of AD. Neuroinflammation is associated with neuronal death and abnormal protein aggregation and promotes the pathological process of β-amyloid peptide 1–42 and tau protein. The inflammatory components associated with AD include glial cells, complement system, cytokines and chemokines. In recent years, some researchers have focused on exosomes, a type of membrane nano vesicles. Exosomes can transport proteins, lipids, microRNAs and other signaling molecules to participate in a variety of signaling pathways for signal transmission or immune response, affecting the activity of target cells and participating in important pathophysiological processes. Therefore, exosomes play an essential role in intercellular communication and may mediate neuroinflammation to promote the development of AD. This paper reviews the occurrence and development of neuroinflammation and exosomes in AD, providing a deeper understanding of the pathogenesis of AD. Furthermore, the role of exosomes in the pathogenesis and treatment of AD is further described, demonstrating their potential as therapeutic targets for neuroinflammation and AD in the future.

The Specific Mechanism of TREM2 Regulation of Synaptic Clearance in Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease. Synaptic dysfunction is an integral feature of AD pathophysiology and a significant factor in early cognitive impairment in AD. Microglia, which are intrinsic immune cells in the central nervous system, play important regulatory roles in the process of synapse formation. Microglia can refine synaptic connections through synaptic clearance to ensure accurate synaptic transmission. Synaptic clearance is not only existed during central nervous system development but also aberrantly activated during AD pathology. However, the mechanisms of synaptic clearance in AD remain to be investigated. TREM2 is involved in the synaptic clearance of microglia, acting alone or with other molecules, such as apolipoprotein E (APOE). In addition, C1q is essential for microglia-mediated synaptic clearance. In this review, we systematically summarized the potential mechanisms of microglia involved in synaptic clearance, comprehensively reviewed the role of TREM2 in microglia regulating synaptic clearance and proposed our hypothesis that TREM2 interacts with APOE and C1q to promote synaptic clearance. This review provides new insights into the role of TREM2 regulation in microglia synaptic clearance and provides potential prospects for the treatment of AD.

Novel Somatostatin Receptor-4 Agonist SM-I-26 Mitigates Lipopolysaccharide-Induced Inflammatory Gene Expression in Microglia

Somatostatin receptor subtype 4 (SSTR4) is expressed in BV2 microglia, suggesting that SSTR4 agonists may impact microglia function. This study assessed the high-affinity SSTR4 agonist SM-I-26 (SMI) (0 nM, 10 nM, 1000 nM) against lipopolysaccharide (LPS)-induced inflammation (0, 10 or 100 ng/ml) over 6 or 24 h in BV2 microglia. Cell viability, nitrite output and mRNA expression changes of genes associated with our target (Sstr4), inflammation (Tnf-α, Il-6, Il-1β, inos), anti-inflammatory and anti-oxidant actions (Il-10, Catalase), and mediators of Aβ binding/phagocytosis (Msr1, Cd33, Trem1, Trem2) were measured. At 6 h SMI showed no effect across all conditions. At 24 h SMI (10 and 1000 nM) upregulated Sstr4 expression under inflammatory and non-inflammatory conditions. At 24 h SMI downregulated expression of the inflammatory cytokines Tnf-α (1000 nM within all LPS concentrations) and Il-6 (10 nM within 0 and 10 ng/ml LPS). At 24 h 10 nM SMI upregulated Il-10, while 1000 nM upregulated Catalase under inflammatory and non-inflammatory conditions. At 24 h Msr1 and Cd33 were upregulated by 1000 nM SMI under non-inflammatory conditions, while Trem1 was downregulated by 10 and 1000 nM SMI under mildly inflammatory and non-inflammatory conditions. These results show that SMI had concentration and time-dependent effects on mRNA expression of genes associated with different states of microglial activation. The SMI reduced Tnf-α and Il-6 inflammatory gene expression, and increased Il-10 anti-inflammatory gene expression, identifies anti-inflammatory actions of SSTR4 agonists extend to microglia.

Current status of sevoflurane anesthesia in association with microglia inflammation and neurodegenerative diseases

Sevoflurane is one of the most commonly used volatile anesthetics in clinical practice and is often used in pediatric anesthesia and intraoperative maintenance. Microglia exist in the central nervous system and are innate immune cells in the central nervous system. Under external stimulation, microglia are divided into two phenotypes: proinflammatory (M1 type) and anti-inflammatory (M2 type), maintaining the stability of the central nervous system through induction, housekeeping, and defense functions. Sevoflurane can activate microglia, increase the expression of inflammatory factors through various inflammatory signaling pathways, release inflammatory mediators to cause oxidative stress, damage nerve tissues, and eventually develop into neurodegenerative diseases. In this article, the relationship between sevoflurane anesthesia and microglia inflammation expression and the occurrence of neurodegenerative diseases is reviewed as follows.

Synapses, Microglia, and Lipids in Alzheimer's Disease

Alzheimer's disease (AD) is characterised by synaptic dysfunction accompanied by the microscopically visible accumulation of pathological protein deposits and cellular dystrophy involving both neurons and glia. Late-stage AD shows pronounced loss of synapses and neurons across several differentially affected brain regions. Recent studies of advanced AD using post-mortem brain samples have demonstrated the direct involvement of microglia in synaptic changes. Variants of the Apolipoprotein E and Triggering Receptors Expressed on Myeloid Cells gene represent important determinants of microglial activity but also of lipid metabolism in cells of the central nervous system. Here we review evidence that may help to explain how abnormal lipid metabolism, microglial activation, and synaptic pathophysiology are inter-related in AD.

Tissue-Engineered Constructions in Biophysics, Neurology and Other Fields and Branches of Medicine

This paper describes the gangliopexy method, a method for creating a new center of local neurohumoral regulation, based on the formation of new connections discovered between the nervous system and the vascular system. The prospects for the development of this method are studied. At the same time, novel concepts about the cycles of nitric oxide and the superoxide anion radical are introduced. A possible role of these cycles is examined in the protection of cells and the body as a whole against oxidative and nitrosative stress, which develops when (in 5-30% of cases) destructive changes in the displaced ganglion lead to vascular complications and an increased risk of mortality. Mechanisms that can protect nerve cells, prevent the development of destructive changes in these cells and reduce the risk of mortality are also investigated.

Neuroinflammation in neurological disorders: pharmacotherapeutic targets from bench to bedside

Neuroinflammation is one of the host defensive mechanisms through which the nervous system protects itself from pathogenic and or infectious insults. Moreover, neuroinflammation occurs as one of the most common pathological outcomes in various neurological disorders, makes it the promising target. The present review focuses on elaborating the recent advancement in understanding molecular mechanisms of neuroinflammation and its role in the etiopathogenesis of various neurological disorders, especially Alzheimer's disease (AD), Parkinson's disease (PD), and Epilepsy. Furthermore, the current status of anti-inflammatory agents in neurological diseases has been summarized in light of different preclinical and clinical studies. Finally, possible limitations and future directions for the effective use of anti-inflammatory agents in neurological disorders have been discussed.

Masitinib for the treatment of Alzheimer's disease

The actual standard treatment for mild-to-moderately severe Alzheimer's disease only attacks its symptoms. Masitinib is a potent and selective phenylaminothiazole-type tyrosine kinase inhibitor which is currently in Phase III studies for the treatment of Alzheimer's disease (AD) with the aim of modifying its evolution and with multiple pharmacological targets such as inhibition of mast cells activity, inhibition of microglia activation, modulation of Aβ and Tau protein signaling pathway and prevention of synaptic damage. Here, we review the preclinical and clinical studies that investigated the administration of masitinib treatment in monotherapy in AD. All research studies revealed positive effects concerning the cognitive functions in AD and generally with good safety and tolerability.