The role of innate immune genes in Alzheimer's disease

Neuronal γ-secretase regulates lipid metabolism, linking cholesterol to synaptic dysfunction in Alzheimer's disease

Presenilin mutations that alter γ-secretase activity cause familial Alzheimer's disease (AD), whereas ApoE4, an apolipoprotein for cholesterol transport, predisposes to sporadic AD. Both sporadic and familial AD feature synaptic dysfunction. Whether γ-secretase is involved in cholesterol metabolism and whether such involvement impacts synaptic function remains unknown. Here, we show that in human neurons, chronic pharmacological or genetic suppression of γ-secretase increases synapse numbers but decreases synaptic transmission by lowering the presynaptic release probability without altering dendritic or axonal arborizations. In search of a mechanism underlying these synaptic impairments, we discovered that chronic γ-secretase suppression robustly decreases cholesterol levels in neurons but not in glia, which in turn stimulates neuron-specific cholesterol-synthesis gene expression. Suppression of cholesterol levels by HMG-CoA reductase inhibitors (statins) impaired synaptic function similar to γ-secretase inhibition. Thus, γ-secretase enables synaptic function by maintaining cholesterol levels, whereas the chronic suppression of γ-secretase impairs synapses by lowering cholesterol levels.

Ferroptosis, Pyroptosis, and Cuproptosis in Alzheimer's Disease

Alzheimer's disease (AD), the most common type of dementia, is a neurodegenerative disorder characterized by progressive cognitive dysfunction. Epidemiological investigation has demonstrated that, after cardiovascular and cerebrovascular diseases, tumors, and other causes, AD has become a major health issue affecting elderly individuals, with its mortality rate acutely increasing each year. Regulatory cell death is the active and orderly death of genetically determined cells, which is ubiquitous in the development of living organisms and is crucial to the regulation of life homeostasis. With extensive research on regulatory cell death in AD, increasing evidence has revealed that ferroptosis, pyroptosis, and cuproptosis are closely related to the occurrence, development, and prognosis of AD. This paper will review the molecular mechanisms of ferroptosis, pyroptosis, and cuproptosis and their regulatory roles in AD to explore potential therapeutic targets for the treatment of AD.

The effects of tea polyphenols on emotional homeostasis: Understanding dementia risk through stress, mood, attention & sleep

Decades of research provide evidence that certain phytochemicals in tea (Camellia sinensis) and other herbal beverages are protective against the development of sporadic types of dementia in later life. Since tea drinking is an economical and widely adopted social-cultural practice across all age groups, it is an ideal product to target in designing low-cost dietary interventions for Alzheimer's Disease (AD), the most prevalent form of dementia. In this review, we focus on the protective roles of tea-derived polyphenols and other phytochemicals on mood, the stress response, attention, and sleep, in keeping with the perspective that many early neuropathological events in AD may stem, in part, from allostatic overload. This approach aligns with the perspective that many forms of dementia, including AD, begin to take root in the brain decades prior to symptom onset, underscoring the need for early uptake of accessible and viable lifestyle interventions. The findings reviewed here suggest that consuming green and oolong tea can improve mood and reduce overall stress. However, given the caffeine content in tea and its association with stress reactivity, the effects of daily whole tea consumption on the emotional state are likely dose-dependent with an inverted-U relationship to wellbeing. Plant-based beverages that are to be consumed in high daily quantities for health purposes and which are naturally free of caffeine, such as Rooibos, may be more appropriate as a dietary supplement for managing emotional regulation over the lifetime.

Nasal administration of anti-CD3 monoclonal antibody ameliorates disease in a mouse model of Alzheimer's disease

Emerging evidence suggests that dysregulation of neuroinflammation, particularly that orchestrated by microglia, plays a significant role in the pathogenesis of Alzheimer's disease (AD). Danger signals including dead neurons, dystrophic axons, phosphorylated tau, and amyloid plaques alter the functional phenotype of microglia from a homeostatic (M0) to a neurodegenerative or disease-associated phenotype, which in turn drives neuroinflammation and promotes disease. Thus, therapies that target microglia activation constitute a unique approach for treating AD. Here, we report that nasally administered anti-CD3 monoclonal antibody in the 3xTg AD mouse model reduced microglial activation and improved cognition independent of amyloid beta deposition. In addition, gene expression analysis demonstrated decreased oxidative stress, increased axogenesis and synaptic organization, and metabolic changes in the hippocampus and cortex of nasal anti-CD3 treated animals. The beneficial effect of nasal anti-CD3 was associated with the accumulation of T cells in the brain where they were in close contact with microglial cells. Taken together, our findings identify nasal anti-CD3 as a unique form of immunotherapy to treat Alzheimer's disease independent of amyloid beta targeting.

The biology of TREM receptors

Triggering receptors expressed on myeloid cells (TREMs) encompass a family of cell-surface receptors chiefly expressed by granulocytes, monocytes and tissue macrophages. These receptors have been implicated in inflammation, neurodegenerative diseases, bone remodelling, metabolic syndrome, atherosclerosis and cancer. Here, I review the structure, ligands, signalling modes and functions of TREMs in humans and mice and discuss the challenges that remain in understanding TREM biology.

NEK7 inhibition attenuates Aβ42-induced cognitive impairment by regulating TLR4/NF-κB and the NLRP3 inflammasome in mice

NEK7 is a serine/threonine kinase that regulates cell mitosis and the activation of the nucleotide-binding oligomerization domain-like (NOD-like) receptor thermal protein domain associated protein 3 (NLRP3) inflammasome, and is related to neuroinflammation and neuronal damage. The purpose of this study was to explore the role and mechanism of NEK7 in cognitive impairment in Alzheimer's disease (AD). BV2 cells, a microglia cell line, was treated with Aβ42. NEK7 expression was measured with reverse transcription-quantitative polymerase chain reaction and Western blotting. An apoptosis kit was used to determine the apoptotic rate. APPswe/PS1dE9 (APP/PS1) transgenic mice were used as an in vivo AD model. The experimental mice were infected with sh-NEK7 lentivirus to downregulate NEK7. The Morris water maze was conducted to explore the effect of NEK7 downregulation on cognitive ability. The results showed that Aβ42 significantly upregulated NEK7 in BV2 cells. Silencing NEK7 suppressed the decrease in BV2 viability and the increase in inflammation, oxidative stress and apoptosis induced by Aβ42. NEK7 mediated it effects through the TLR4/NF-κB signalling pathway and the NLRP3 inflammasome. Finally, inhibition of NEK7 alleviated the cognitive impairment in APP/PS1 mice. In conclusion, Silencing NEK7 suppresses Aβ42-induced cell apoptosis, inflammation and oxidative stress, and improves cognitive performance in AD mice. NEK7 may be a potential target for AD treatment.

Microglial cGAS deletion protects against amyloid-β induced Alzheimer's disease pathogenesis

Innate immune activation plays a vital role in the development of Alzheimer's disease (AD) and related dementias (ADRD). Among which, the DNA sensing cyclic GMP-AMP synthase (cGAS)- STING pathway has been implicated in diverse aspects of AD progression. In the current study, we showed that the cGAS-STING signaling was up-regulated in AD and this elevation was mainly contributed by the microglial population other than non-microglial cell types in the brain. By establishing an inducible, microglia-specific cGAS knockout mouse model in 5xFAD background, we found that deleting microglial cGAS at the onset of amyloid-β (Aβ) pathology significantly limited plaque formation, and protected mice from Aβ-induced cognitive impairment. Mechanistically, we found cGAS was necessary for plaque-associated microglial enrichment potentially driven by IRF8, and was indispensable for the development of disease-associated microglia (DAM) phenotype. Meanwhile, the loss of microglial cGAS reduced the levels of dystrophic neurites which led to preserved synaptic integrity and neuronal function. Our study provides new insights in understanding the effects of innate immune in AD via a cell-type specific manner, and lays the foundation for potential targeted intervention of the microglial cGAS-STING pathway toward the improvement of AD.

A dynamical systems approach for multiscale synthesis of Alzheimer's pathogenesis

Alzheimer's disease (AD) is a spatially dynamic pathology that implicates a growing volume of multiscale data spanning genetic, cellular, tissue, and organ levels of the organization. These data and bioinformatics analyses provide clear evidence for the interactions within and between these levels. The resulting heterarchy precludes a linear neuron-centric approach and necessitates that the numerous interactions are measured in a way that predicts their impact on the emergent dynamics of the disease. This level of complexity confounds intuition, and we propose a new methodology that uses non-linear dynamical systems modeling to augment intuition and that links with a community-wide participatory platform to co-create and test system-level hypotheses and interventions. In addition to enabling the integration of multiscale knowledge, key benefits include a more rapid innovation cycle and a rational process for prioritization of data campaigns. We argue that such an approach is essential to support the discovery of multilevel-coordinated polypharmaceutical interventions.

Role of neuroinflammation in neurodegeneration development

Studies in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease and Amyotrophic lateral sclerosis, Huntington's disease, and so on, have suggested that inflammation is not only a result of neurodegeneration but also a crucial player in this process. Protein aggregates which are very common pathological phenomenon in neurodegeneration can induce neuroinflammation which further aggravates protein aggregation and neurodegeneration. Actually, inflammation even happens earlier than protein aggregation. Neuroinflammation induced by genetic variations in CNS cells or by peripheral immune cells may induce protein deposition in some susceptible population. Numerous signaling pathways and a range of CNS cells have been suggested to be involved in the pathogenesis of neurodegeneration, although they are still far from being completely understood. Due to the limited success of traditional treatment methods, blocking or enhancing inflammatory signaling pathways involved in neurodegeneration are considered to be promising strategies for the therapy of neurodegenerative diseases, and many of them have got exciting results in animal models or clinical trials. Some of them, although very few, have been approved by FDA for clinical usage. Here we comprehensively review the factors affecting neuroinflammation and the major inflammatory signaling pathways involved in the pathogenicity of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Amyotrophic lateral sclerosis. We also summarize the current strategies, both in animal models and in the clinic, for the treatment of neurodegenerative diseases.

Akkermansia muciniphila in neuropsychiatric disorders: friend or foe?

An accumulating body of evidence suggests that the bacterium Akkermansia muciniphila exhibits positive systemic effects on host health, mainly by improving immunological and metabolic functions, and it is therefore regarded as a promising potential probiotic. Recent clinical and preclinical studies have shown that A. muciniphila plays a vital role in a variety of neuropsychiatric disorders by influencing the host brain through the microbiota-gut-brain axis (MGBA). Numerous studies observed that A. muciniphila and its metabolic substances can effectively improve the symptoms of neuropsychiatric disorders by restoring the gut microbiota, reestablishing the integrity of the gut mucosal barrier, regulating host immunity, and modulating gut and neuroinflammation. However, A. muciniphila was also reported to participate in the development of neuropsychiatric disorders by aggravating inflammation and influencing mucus production. Therefore, the exact mechanism of action of A. muciniphila remains much controversial. This review summarizes the proposed roles and mechanisms of A. muciniphila in various neurological and psychiatric disorders such as depression, anxiety, Parkinson's disease, Alzheimer's disease, multiple sclerosis, strokes, and autism spectrum disorders, and provides insights into the potential therapeutic application of A. muciniphila for the treatment of these conditions.

Analyzing the glial proteome in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline, memory loss, and changes in behavior. Accumulating evidence indicates that dysfunction of glial cells, including astrocytes, microglia, and oligodendrocytes, may contribute to the development and progression of AD. Large-scale analysis of glial proteins sheds light on their roles in cellular processes and diseases. In AD, glial proteomics has been utilized to understand glia-based pathophysiology and identify potential biomarkers and therapeutic targets.

AREA COVERED

In this review, we provide an updated overview of proteomic analysis of glia in the context of AD. Additionally, we discuss current challenges in the field, involving glial complexity and heterogeneity, and describe some cutting-edge proteomic technologies to address them.

EXPERT OPINION

Unbiased comprehensive analysis of glial proteomes aids our understanding of the molecular and cellular mechanisms of AD pathogenesis. These investigations highlight the crucial role of glial cells and provide novel insights into the mechanisms of AD pathology. A deeper understanding of the AD-related glial proteome could offer a repertoire of potential biomarkers and therapeutics. Further technical advancement of glial proteomics will enable us to identify proteins within individual cells and specific cell types, thus significantly enhancing our comprehension of AD pathogenesis.

Comparative physiological anthropogeny: exploring molecular underpinnings of distinctly human phenotypes

Anthropogeny is a classic term encompassing transdisciplinary investigations of the origins of the human species. Comparative anthropogeny is a systematic comparison of humans and other living nonhuman hominids (so-called "great apes"), aiming to identify distinctly human features in health and disease, with the overall goal of explaining human origins. We begin with a historical perspective, briefly describing how the field progressed from the earliest evolutionary insights to the current emphasis on in-depth molecular and genomic investigations of "human-specific" biology and an increased appreciation for cultural impacts on human biology. While many such genetic differences between humans and other hominids have been revealed over the last two decades, this information remains insufficient to explain the most distinctive phenotypic traits distinguishing humans from other living hominids. Here we undertake a complementary approach of "comparative physiological anthropogeny," along the lines of the preclinical medical curriculum, i.e., beginning with anatomy and considering each physiological system and in each case considering genetic and molecular components that are relevant. What is ultimately needed is a systematic comparative approach at all levels from molecular to physiological to sociocultural, building networks of related information, drawing inferences, and generating testable hypotheses. The concluding section will touch on distinctive considerations in the study of human evolution, including the importance of gene-culture interactions.

Uncovering neuroinflammation-related modules and potential repurposing drugs for Alzheimer's disease through multi-omics data integrative analysis

Background

Neuroinflammation is one of the key factors leading to neuron death and synapse dysfunction in Alzheimer's disease (AD). Amyloid-β (Aβ) is thought to have an association with microglia activation and trigger neuroinflammation in AD. However, inflammation response in brain disorders is heterogenous, and thus, it is necessary to unveil the specific gene module of neuroinflammation caused by Aβ in AD, which might provide novel biomarkers for AD diagnosis and help understand the mechanism of the disease.

Methods

Transcriptomic datasets of brain region tissues from AD patients and the corresponding normal tissues were first used to identify gene modules through the weighted gene co-expression network analysis (WGCNA) method. Then, key modules highly associated with Aβ accumulation and neuroinflammatory response were pinpointed by combining module expression score and functional information. Meanwhile, the relationship of the Aβ-associated module to the neuron and microglia was explored based on snRNA-seq data. Afterward, transcription factor (TF) enrichment and the SCENIC analysis were performed on the Aβ-associated module to discover the related upstream regulators, and then a PPI network proximity method was employed to repurpose the potential approved drugs for AD.

Results

A total of 16 co-expression modules were primarily obtained by the WGCNA method. Among them, the green module was significantly correlated with Aβ accumulation, and its function was mainly involved in neuroinflammation response and neuron death. Thus, the module was termed the amyloid-β induced neuroinflammation module (AIM). Moreover, the module was negatively correlated with neuron percentage and showed a close association with inflammatory microglia. Finally, based on the module, several important TFs were recognized as potential diagnostic biomarkers for AD, and then 20 possible drugs including ibrutinib and ponatinib were picked out for the disease.

Conclusion

In this study, a specific gene module, termed AIM, was identified as a key sub-network of Aβ accumulation and neuroinflammation in AD. Moreover, the module was verified as having an association with neuron degeneration and inflammatory microglia transformation. Moreover, some promising TFs and potential repurposing drugs were presented for AD based on the module. The findings of the study shed new light on the mechanistic investigation of AD and might make benefits the treatment of the disease.

The contribution of the peripheral immune system to neurodegeneration

Microglial cells are the major immune cells of the central nervous system (CNS), and directly react to neurodegeneration, but other immune cell types are also able to react to pathology and can modify the course of neurodegenerative processes. These mainly include monocytes/macrophages and lymphocytes. While these peripheral immune cells were initially considered to act only after infiltrating the CNS, recent evidence suggests that some of them can also act directly from the periphery. We will review the existing and emerging evidence for a role of peripheral immune cells in neurodegenerative diseases, both with and without CNS infiltration. Our focus will be on amyotrophic lateral sclerosis, but we will also compare to Alzheimer's disease and Parkinson's disease to highlight similarities or differences. Peripheral immune cells are easily accessible, and therefore may be an attractive therapeutic target for neurodegenerative diseases. Thus, understanding how these peripheral immune cells communicate with the CNS deserves deeper investigation.

Dimethyl Fumarate as Potential Treatment for Alzheimer's Disease: Rationale and Clinical Trial Design

Alzheimer's Disease (AD) is a debilitating disease that leads to severe cognitive impairment and functional decline. The role of tau hyperphosphorylation and amyloid plaque deposition in the pathophysiology of AD has been well described; however, neuroinflammation and oxidative stress related to sustained microglial activation is thought to play a significant role in the disease process as well. NRF-2 has been identified in modulating the effects of inflammation and oxidative stress in AD. Activation of NRF-2 leads to an increased production of antioxidant enzymes, including heme oxygenase, which has been shown to have protective effects in neurodegenerative disorders such as AD. Dimethyl fumarate and diroximel fumarate (DMF) have been approved for the use in relapsing-remitting multiple sclerosis. Research indicates that they can modulate the effects of neuroinflammation and oxidative stress through the NRF-2 pathway, and as such, could serve as a potential therapeutic option in AD. We propose a clinical trial design that could be used to assess DMF as a treatment option for AD.

A review on the reciprocal interactions between neuroinflammatory processes and substance use and misuse, with a focus on alcohol misuse

Background: The last decade has witnessed a surge of findings implicating neuroinflammatory processes as pivotal players in substance use disorders. The directionality of effects began with the expectation that the neuroinflammation associated with prolonged substance misuse contributes to long-term neuropathological consequences. As the literature grew, however, it became evident that the interactions between neuroinflammatory processes and alcohol and drug intake were reciprocal and part of a pernicious cycle in which disease-relevant signaling pathways contributed to an escalation of drug intake, provoking further inflammation-signaling and thereby exacerbating the neuropathological effects of drug misuse.Objectives: The goal of this review and its associated special issue is to provide an overview of the emergent findings relevant to understanding these reciprocal interactions. The review highlights the importance of preclinical and clinical studies in testing and validation of immunotherapeutics as viable targets for curtailing substance use and misuse, with a focus on alcohol misuse.Methods: A narrative review of the literature on drug and neuroinflammation was conducted, as well as articles published in this Special Issue on Alcohol- and Drug-induced Neuroinflammation: Insights from Pre-clinical Models and Clinical Research.Results: We argue that (a) demographic variables and genetic background contribute unique sensitivity to drug-related neuroinflammation; (b) co-morbidities between substance use disorders and affect dysfunction may share common inflammation-related signatures that predict the efficacy of immunotherapeutic drugs; and (c) examination of polydrug interactions with neuroinflammation is a critical area where greater research emphasis is needed.Conclusions: This review provides an accessible and example-driven review of the relationship between drug misuse, neuroinflammatory processes, and their resultant neuropathological outcomes.

Large multi-ethnic genetic analyses of amyloid imaging identify new genes for Alzheimer disease

Amyloid PET imaging has been crucial for detecting the accumulation of amyloid beta (Aβ) deposits in the brain and to study Alzheimer's disease (AD). We performed a genome-wide association study on the largest collection of amyloid imaging data (N = 13,409) to date, across multiple ethnicities from multicenter cohorts to identify variants associated with brain amyloidosis and AD risk. We found a strong APOE signal on chr19q.13.32 (top SNP: APOE ɛ4; rs429358; β = 0.35, SE = 0.01, P = 6.2 × 10-311, MAF = 0.19), driven by APOE ɛ4, and five additional novel associations (APOE ε2/rs7412; rs73052335/rs5117, rs1081105, rs438811, and rs4420638) independent of APOE ɛ4. APOE ɛ4 and ε2 showed race specific effect with stronger association in Non-Hispanic Whites, with the lowest association in Asians. Besides the APOE, we also identified three other genome-wide loci: ABCA7 (rs12151021/chr19p.13.3; β = 0.07, SE = 0.01, P = 9.2 × 10-09, MAF = 0.32), CR1 (rs6656401/chr1q.32.2; β = 0.1, SE = 0.02, P = 2.4 × 10-10, MAF = 0.18) and FERMT2 locus (rs117834516/chr14q.22.1; β = 0.16, SE = 0.03, P = 1.1 × 10-09, MAF = 0.06) that all colocalized with AD risk. Sex-stratified analyses identified two novel female-specific signals on chr5p.14.1 (rs529007143, β = 0.79, SE = 0.14, P = 1.4 × 10-08, MAF = 0.006, sex-interaction P = 9.8 × 10-07) and chr11p.15.2 (rs192346166, β = 0.94, SE = 0.17, P = 3.7 × 10-08, MAF = 0.004, sex-interaction P = 1.3 × 10-03). We also demonstrated that the overall genetic architecture of brain amyloidosis overlaps with that of AD, Frontotemporal Dementia, stroke, and brain structure-related complex human traits. Overall, our results have important implications when estimating the individual risk to a population level, as race and sex will needed to be taken into account. This may affect participant selection for future clinical trials and therapies.

Identification of novel biomarkers linking depressive disorder and Alzheimer's disease based on an integrative bioinformatics analysis

BACKGROUND

Previous reports revealed that a history of major depressive disorder (MDD) increased the risk of Alzheimer's disease (AD). The immune disorder is associated with MDD and AD pathophysiology. We aimed to identify differentially expressed immune-related genes (DEIRGs) that are involved in the pathogenesis of MDD and AD.

METHODS

We downloaded mRNA expression profiles (GSE76826 and GSE5281) from the Gene Expression Omnibus (GEO) database. The R software was used to identify DEIRGs for the two diseases separately. Functional enrichment analysis and PPI network of DEIRGs were performed. Finally, the relationship between shared DEIRGs and immune infiltrates of AD and MDD were analyzed, respectively.

RESULTS

A total of 121 DEIRGs linking AD and MDD were identified. These genes were significantly enriched in immune-related pathways, such as the JAK-STAT signaling pathway, regulation of chemotaxis, chemotaxis, cytokine-cytokine receptor interaction, and primary immunodeficiency. Furthermore, three shared DEIRGs (IL1R1, CHGB, and NRG1) were identified. Correlation analysis between DEIRGs and immune cells revealed that IL1R1 and NRG1 had a negative or positive correlation with some immune cells both in AD and MDD.

CONCLUSION

Both DEIRGs and immune cell infiltrations play a vital role in the pathogenesis of AD and MDD. Our findings indicated that there are common genes and biological processes between MDD and AD, which provides a theoretical basis for the study of the comorbidity of MDD and AD.

CD33 isoforms in microglia and Alzheimer's disease: Friend and foe

Alzheimer's disease (AD) is the most common form of neurodegenerative disease and is considered the main cause of dementia worldwide. Genome-wide association studies combined with integrated analysis of functional datasets support a critical role for microglia in AD pathogenesis, identifying them as important potential therapeutic targets. The ability of immunomodulatory receptors on microglia to control the response to pathogenic amyloid-β aggregates has gained significant interest. Siglec-3, also known as CD33, is one of these immunomodulatory receptors expressed on microglia that has been identified as an AD susceptibility factor. Here, we review recent advances made in understanding the multifaceted roles that CD33 plays in microglia with emphasis on two human-specific CD33 isoforms that differentially correlate with AD susceptibility. We also describe several different therapeutic approaches for targeting CD33 that have been advanced for the purpose of skewing microglial cell responses.

Myelin in Alzheimer's disease: culprit or bystander?

Alzheimer's disease (AD) is a neurodegenerative disorder with neuronal and synaptic losses due to the accumulation of toxic amyloid β (Αβ) peptide oligomers, plaques, and tangles containing tau (tubulin-associated unit) protein. While familial AD is caused by specific mutations, the sporadic disease is more common and appears to result from a complex chronic brain neuroinflammation with mitochondriopathies, inducing free radicals' accumulation. In aged brain, mutations in DNA and several unfolded proteins participate in a chronic amyloidosis response with a toxic effect on myelin sheath and axons, leading to cognitive deficits and dementia. Αβ peptides are the most frequent form of toxic amyloid oligomers. Accumulations of misfolded proteins during several years alters different metabolic mechanisms, induce chronic inflammatory and immune responses with toxic consequences on neuronal cells. Myelin composition and architecture may appear to be an early target for the toxic activity of Aβ peptides and others hydrophobic misfolded proteins. In this work, we describe the possible role of early myelin alterations in the genesis of neuronal alterations and the onset of symptomatology. We propose that some pathophysiological and clinical forms of the disease may arise from structural and metabolic disorders in the processes of myelination/demyelination of brain regions where the accumulation of non-functional toxic proteins is important. In these forms, the primacy of the deleterious role of amyloid peptides would be a matter of questioning and the initiating role of neuropathology would be primarily the fact of dysmyelination.

Integrin β3-Mediated Cell Senescence Associates with Gut Inflammation and Intestinal Degeneration in Models of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and personality changes that ultimately lead to dementia. Currently, 50 million people worldwide suffer from dementia related to AD, and the pathogenesis underlying AD pathology and cognitive decline is unknown. While AD is primarily a neurological disease of the brain, individuals with AD often experience intestinal disorders, and gut abnormalities have been implicated as a major risk factor in the development of AD and relevant dementia. However, the mechanisms that mediate gut injury and contribute to the vicious cycle between gut abnormalities and brain injury in AD remain unknown. In the present study, a bioinformatics analysis was performed on the proteomics data of variously aged AD mouse colon tissues. We found that levels of integrin β3 and β-galactosidase (β-gal), two markers of cellular senescence, increased with age in the colonic tissue of mice with AD. The advanced artificial intelligence (AI)-based prediction of AD risk also demonstrated the association between integrin β3 and β-gal and AD phenotypes. Moreover, we showed that elevated integrin β3 levels were accompanied by senescence phenotypes and immune cell accumulation in AD mouse colonic tissue. Further, integrin β3 genetic downregulation abolished upregulated senescence markers and inflammatory responses in colonic epithelial cells in conditions associated with AD. We provide a new understanding of the molecular actions underpinning inflammatory responses during AD and suggest integrin β3 may function as novel target mediating gut abnormalities in this disease.

The β-adrenergic hypothesis of synaptic and microglial impairment in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease originating partly from amyloid β protein-induced synaptic failure. As damaging of noradrenergic neurons in the locus coeruleus (LC) occurs at the prodromal stage of AD, activation of adrenergic receptors could serve as the first line of defense against the onset of the disease. Activation of β₂ -ARs strengthens long-term potentiation (LTP) and synaptic activity, thus improving learning and memory. Physical stimulation of animals exposed to an enriched environment (EE) leads to the activation of β₂ -ARs and prevents synaptic dysfunction. EE also suppresses neuroinflammation, suggesting that β₂ -AR agonists may play a neuroprotective role. The β₂ -AR agonists used for respiratory diseases have been shown to have an anti-inflammatory effect. Epidemiological studies further support the beneficial effects of β₂ -AR agonists on several neurodegenerative diseases. Thus, I propose that β₂ -AR agonists may provide therapeutic value in combination with novel treatments for AD.

Clinical and biological significance of RNA N6-methyladenosine regulators in Alzheimer disease

RNA N6-methyladenosine (m6A) regulators are essential for a variety of biological functions, such as early development, viral infections, and cancer. However, their roles in Alzheimer disease (AD) are still not very clear. Here, 16 significant m6A regulators were identified using difference analysis between AD patients and non-demented controls based on the GSE132903 dataset from the Gene Expression Omnibus database. Using these 16 m6A regulators, a nomogram model was established to predict the prevalence of AD. We found that patients could obtain a good clinical benefit based on this model. In addition, we revealed 2 distinct m6A patterns and 2 distinct m6A gene patterns in AD and demonstrated their prognostic and risk assessment significance. This present work comprehensively evaluated the functions of m6A regulators in the diagnosis and subtype classification of AD. These results suggested they have potential prognostic and risk assessment significance in AD.

Functionalized graphene-based electrochemical array sensors for the identification of distinct conformational states of Amyloid Beta in Alzheimer's disease

Aβ oligomers have been widely accepted as significant biomarkers for Alzheimer's disease (AD) detection, monitoring, and therapy since they are highly correlated with AD development. In this work, an electrochemical array-based sensing platform was successfully built using a group of functionalized graphene with different physicochemical features. Since the electro-insulated Aβ peptide species severely interfered with the electron transport on the electrode surface, the presence of Aβ led to a significant change in the electrochemical impedance signal. The resulting variety of the impedance was then classified and processed by linear discriminant analysis. The constructed sensing platform can discriminate different Aβ forms, the mixture of various Aβ forms, and different ratios of Aβ42 to Aβ40 with 100% accuracy by only the combination of dual probes. Furthermore, it also exhibited excellent performance for screening Aβ inhibitors and metal chelators. The strategy utilizes the infinitesimal general discrepancy instead of specific biomarker recognition, exhibiting the advantage of no requirement to know the exact information about the specific ligand and receptor in advance, which is promising to be widened for the other biosensing detection fields.

Inflammatory Diseases, Inflammatory Biomarkers, and Alzheimer Disease: An Observational Analysis and Mendelian Randomization

BACKGROUND AND OBJECTIVES

Whether chronic autoimmune inflammatory diseases causally affect the risk of Alzheimer disease (AD) is controversial. We characterized the relationship between inflammatory diseases and risk of AD and explored the role of circulating inflammatory biomarkers in the relationships between inflammatory diseases and AD.

METHODS

We performed observational analyses for chronic autoimmune inflammatory diseases and risk of AD using data from 2,047,513 participants identified in the UK Clinical Practice Research Datalink (CPRD). Using data of a total of more than 1,100,000 individuals from 15 large-scale genome-wide association study data sets, we performed 2-sample Mendelian randomizations (MRs) to investigate the relationships between chronic autoimmune inflammatory diseases, circulating inflammatory biomarker levels, and risk of AD.

RESULTS

Cox regression models using CPRD data showed that the overall incidence of AD was higher among patients with inflammatory bowel disease (hazard ratio [HR] 1.17; 95% CI 1.15-1.19; p = 2.1 × 10-4), other inflammatory polyarthropathies and systematic connective tissue disorders (HR 1.13; 95% CI 1.12-1.14; p = 8.6 × 10-5), psoriasis (HR 1.13; 95% CI 1.10-1.16; p = 2.6 × 10-4), rheumatoid arthritis (HR 1.08; 95% CI 1.06-1.11; p = 4.0 × 10-4), and multiple sclerosis (HR 1.06; 95% CI 1.04-1.07; p = 2.8 × 10-4) compared with the age (±5 years) and sex-matched comparison groups free from all inflammatory diseases under investigation. Bidirectional MR analysis identified relationships between chronic autoimmune inflammatory diseases and circulating inflammatory biomarkers. Particularly, circulating monokine induced by gamma interferon (MIG) level was suggestively associated with a higher risk of AD (odds ratio from inverse variance weighted [ORIVW] 1.23; 95% CI 1.06-1.42; p IVW = 0.007) and lower risk of Crohn disease (ORIVW 0.73; 95% CI -0.62 to 0.86; p IVW = 1.3 × 10-4). Colocalization supported a common causal single nucleotide polymorphism for MIG and Crohn disease (posterior probability = 0.74), but not AD (posterior probability = 0.03). Using a 2-sample MR approach, genetically predicted risks of inflammatory diseases were not associated with higher AD risk.

DISCUSSION

Our data suggest that the association between inflammatory diseases and risk of AD is unlikely to be causal and may be a result of confounding. In support, although inflammatory biomarkers showed evidence for causal associations with inflammatory diseases, evidence was weak that they affected both inflammatory disease and AD.

The neuroimmune axis of Alzheimer's disease

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder with multifaceted neuropathological features, including β-amyloid plaques, neurofibrillary tangles, and neuroinflammation. Over the past decade, emerging evidence has implicated both beneficial and pathological roles for innate immune genes and immune cells, including peripheral immune cells such as T cells, which can infiltrate the brain and either ameliorate or exacerbate AD neuropathogenesis. These findings support a neuroimmune axis of AD, in which the interplay of adaptive and innate immune systems inside and outside the brain critically impacts the etiology and pathogenesis of AD. In this review, we discuss the complexities of AD neuropathology at the levels of genetics and cellular physiology, highlighting immune signaling pathways and genes associated with AD risk and interactions among both innate and adaptive immune cells in the AD brain. We emphasize the role of peripheral immune cells in AD and the mechanisms by which immune cells, such as T cells and monocytes, influence AD neuropathology, including microglial clearance of amyloid-β peptide, the key component of β-amyloid plaque cores, pro-inflammatory and cytotoxic activity of microglia, astrogliosis, and their interactions with the brain vasculature. Finally, we review the challenges and outlook for establishing immune-based therapies for treating and preventing AD.

Advances in the Study of APOE and Innate Immunity in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive degenerative disease of the nervous system (CNS) with an insidious onset. Clinically, it is characterized by a full range of dementia manifestations including memory impairment, aphasia, loss of speech, loss of use, loss of recognition, impairment of visuospatial skills, and impairment of executive function, as well as changes in personality and behavior. The exact cause of AD has not yet been identified. Nevertheless, modern research indicates that genetic factors contribute to 70% of human's risk of AD. Apolipoprotein (APOE) accounts for up to 90% of the genetic predisposition. APOE is a crucial gene that cannot be overstated. In addition, innate immunity plays a significant role in the etiology and treatment of AD. Understanding the different subtypes of APOE and their interconnections is of paramount importance. APOE and innate immunity, along with their relationship to AD, are primary research motivators for in-depth research and clinical trials. The exploration of novel technologies has led to an increasing trend in the study of AD at the cellular and molecular levels and continues to make more breakthroughs and progress. As of today, there is no effective treatment available for AD around the world. This paper aims to summarize and analyze the role of APOE and innate immunity, as well as development trends in recent years. It is anticipated that APOE and innate immunity will provide a breakthrough for humans to hinder AD progression in the near future.

Inflammation context in Alzheimer's disease, a relationship intricate to define

Alzheimer's disease (AD), the most common form of dementia, is characterized by the accumulation of amyloid β (Aβ) and hyperphosphorylated tau protein aggregates. Importantly, Aβ and tau species are able to activate astrocytes and microglia, which release several proinflammatory cytokines, such as tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), together with reactive oxygen (ROS) and nitrogen species (RNS), triggering neuroinflammation. However, this inflammatory response has a dual function: it can play a protective role by increasing Aβ degradation and clearance, but it can also contribute to Aβ and tau overproduction and induce neurodegeneration and synaptic loss. Due to the significant role of inflammation in the pathogenesis of AD, several inflammatory mediators have been proposed as AD markers, such as TNF-α, IL-1β, Iba-1, GFAP, NF-κB, TLR2, and MHCII. Importantly, the use of anti-inflammatory drugs such as NSAIDs has emerged as a potential treatment against AD. Moreover, diseases related to systemic or local inflammation, including infections, cerebrovascular accidents, and obesity, have been proposed as risk factors for the development of AD. In the following review, we focus on key inflammatory processes associated with AD pathogenesis.

The impact of increasing levels of blood C-reactive protein on the inflammatory loci SPI1 and CD33 in Alzheimer's disease

Apolipoprotein ε4 (APOE ε4) is the most significant genetic risk factor for late-onset Alzheimer's disease (AD). Elevated blood C-reactive protein (CRP) further increases the risk of AD for people carrying the APOE ε4 allele. We hypothesized that CRP, as a key inflammatory element, could modulate the impact of other genetic variants on AD risk. We selected ten single nucleotide polymorphisms (SNPs) in reported AD risk loci encoding proteins related to inflammation. We then tested the interaction effects between these SNPs and blood CRP levels on AD incidence using the Cox proportional hazards model in UK Biobank (n = 279,176 white participants with 803 incident AD cases). The five top SNPs were tested for their interaction with different CRP cutoffs for AD incidence in the Framingham Heart Study (FHS) Generation 2 cohort (n = 3009, incident AD = 156). We found that for higher concentrations of serum CRP, the AD risk increased for SNP genotypes in 3 AD-associated genes (SPI1, CD33, and CLU). Using the Cox model in stratified genotype analysis, the hazard ratios (HRs) for the association between a higher CRP level (≥10 vs. <10 mg/L) and the risk of incident AD were 1.94 (95% CI: 1.33-2.84, p < 0.001) for the SPI1 rs1057233-AA genotype, 1.75 (95% CI: 1.20-2.55, p = 0.004) for the CD33 rs3865444-CC genotype, and 1.76 (95% CI: 1.25-2.48, p = 0.001) for the CLU rs9331896-C genotype. In contrast, these associations were not observed in the other genotypes of these genes. Finally, two SNPs were validated in 321 Alzheimer's Disease Neuroimaging (ADNI) Mild Cognitive Impairment (MCI) patients. We observed that the SPI1 and CD33 genotype effects were enhanced by elevated CRP levels for the risk of MCI to AD conversion. Furthermore, the SPI1 genotype was associated with CSF AD biomarkers, including t-Tau and p-Tau, in the ADNI cohort when the blood CRP level was increased (p < 0.01). Our findings suggest that elevated blood CRP, as a peripheral inflammatory biomarker, is an important moderator of the genetic effects of SPI1 and CD33 in addition to APOE ε4 on AD risk. Monitoring peripheral CRP levels may be helpful for precise intervention and prevention of AD for these genotype carriers.

Emerging roles of innate and adaptive immunity in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease, with characteristic extracellular amyloid-β (Aβ) deposition and intracellular accumulation of hyperphosphorylated, aggregated tau. Several key regulators of innate immune pathways are genetic risk factors for AD. While these genetic risk factors as well as in vivo data point to key roles for microglia, emerging evidence also points to a role of the adaptive immune response in disease pathogenesis. We review the roles of innate and adaptive immunity, their niches, their communication, and their contributions to AD development and progression. We also summarize the cellular compositions and physiological functions of immune cells in the parenchyma, together with those in the brain border structures that form a dynamic disease-related immune niche. We propose that both innate and adaptive immune responses in brain parenchyma and border structures could serve as important therapeutic targets for treating both the pre-symptomatic and the symptomatic stages of AD.

Gut Microbiota and Immunotherapy for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that eventually leads to dementia and death of the patient. Currently, no effective treatment is available that can slow or halt the progression of the disease. The gut microbiota can modulate the host immune system in the peripheral and central nervous system through the microbiota-gut-brain axis. Growing evidence indicates that gut microbiota dysbiosis plays an important role in the pathogenesis of AD, and modulation of the gut microbiota may represent a new avenue for treating AD. Immunotherapy targeting Aβ and tau has emerged as the most promising disease-modifying therapy for the treatment of AD. However, the underlying mechanism of AD immunotherapy is not known. Importantly, preclinical and clinical studies have highlighted that the gut microbiota exerts a major influence on the efficacy of cancer immunotherapy. However, the role of the gut microbiota in AD immunotherapy has not been explored. We found that immunotherapy targeting tau can modulate the gut microbiota in an AD mouse model. In this article, we focused on the crosstalk between the gut microbiota, immunity, and AD immunotherapy. We speculate that modulation of the gut microbiota induced by AD immunotherapy may partially underlie the efficacy of the treatment.

Selective Vulnerability of the Locus Coeruleus Noradrenergic System and its Role in Modulation of Neuroinflammation, Cognition, and Neurodegeneration

Locus coeruleus (LC) noradrenergic (NE) neurons supply the main adrenergic input to the forebrain. NE is a dual modulator of cognition and neuroinflammation. NE neurons of the LC are particularly vulnerable to degeneration both with normal aging and in neurodegenerative disorders. Consequences of this vulnerability can be observed in both cognitive impairment and dysregulation of neuroinflammation. LC NE neurons are pacemaker neurons that are active during waking and arousal and are responsive to stressors in the environment. Chronic overactivation is thought to be a major contributor to the vulnerability of these neurons. Here we review what is known about the mechanisms underlying this neuronal vulnerability and combinations of environmental and genetic factors that contribute to confer risk to these important brainstem neuromodulatory and immunomodulatory neurons. Finally, we discuss proposed and potential interventions that may reduce the overall risk for LC NE neuronal degeneration.

Suicide-Related Single Nucleotide Polymorphisms, rs4918918 and rs10903034: Association with Dementia in Older Adults

Dementia has enormous implications for patients and the health care system. Genetic markers are promising for detecting the risk of cognitive impairment. We hypothesized that genetic variants associated with suicide risk might significantly increase the risk of cognitive decline because suicide in older adults is often a consequence of cognitive impairment. We investigated several single-nucleotide polymorphisms that were initially associated with suicide risk in dementia older adults and identified the APOE gene alleles. The study was performed with subjects over the age of 65: 112 patients with dementia and 146 healthy volunteers. The MMSE score was used to assess cognitive functions. Study participants were genotyped using real-time PCR (APOE: rs429358, rs7412; genes associated with suicide: rs9475195, rs7982251, rs2834789, rs358592, rs4918918, rs3781878, rs10903034, rs165774, rs16841143, rs11833579 rs10898553, rs7296262, rs3806263, and rs2462021). Genotype analysis revealed the significance of APOEε4, APOEε2, and rs4918918 (SORBS1) when comparing dementia and healthy control groups. The association of APOEε4, APOEε2, and rs10903034 (IFNLR1) with the overall MMSE score was indicated. The study found an association with dementia of rs4918918 (SORBS1) and rs10903034 (IFNLR1) previously associated with suicide and confirmed the association of APOEε4 and APOEε2 with dementia.

TREM2 improves neurological dysfunction and attenuates neuroinflammation, TLR signaling and neuronal apoptosis in the acute phase of intracerebral hemorrhage

Neuroinflammation contributes to secondary brain injury following intracerebral hemorrhage (ICH). Triggering receptor expressed on myeloid cells 2 (TREM2) confers strong neuroprotective effect by suppressing neuroinflammatory response in experimental ischemic stroke. This study aimed to clarify the neuroprotective role of TREM2 and potential underlying mechanism in a mouse model of ICH and in vitro. Adeno-associated virus (AAV) and green fluorescent protein-lentivirus (GFP-LV) strategies were employed to enhance TREM2 expression in the C57/BL6 mice and BV2 cells, respectively. The adult male C57/BL6 mice were subjected to ICH by administration of collagenase-IV in 1 month after the AAV particles injection. An in vitro ICH model was performed with oxygen hemoglobin in BV2 cells. Toll-like receptor 4 (TLR4) antagonist TAK242 was applied at 6 h following ICH. Neurological function, TREM2, pro-inflammatory cytokines, brain water content and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were evaluated at 24 h following ICH. TLR4, NF-κB and mitogen-activated protein kinases (MAPK) signaling pathways were also determined by Western blot analysis at the same time point. The levels of TREM2 were increased at 12 h, peaked at 24 h and recovered on 7d following ICH. TREM2 overexpression ameliorated ICH induced neurological dysfunction, inhibited neuroinflammation, and attenuated apoptosis and brain edema. Further mechanistic study revealed that TREM2 overexpression inhibited TLR4 activation and NF-κB and MAPK signaling pathways. ICH increased the percentage of TUNEL-positive cells, which was markedly decreased by TREM2 overexpression. A similar improvement was also observed by the administration of TAK242 following ICH. TREM2 improves neurological dysfunction and attenuates neuroinflammation and neuronal apoptosis in the acute phase of ICH, which is, at least in part, mediated by negatively regulating TLR4 signaling pathway. These findings highlight TREM2 as a potential target for early brain injury following ICH.

Recent Studies on Protective Effects of Walnuts against Neuroinflammation

Neuroinflammation plays a significant role in the aging process and the pathophysiology of neurodegenerative diseases, such as Alzheimer’s disease. Accordingly, possible therapeutic strategies aimed at anti-inflammatory effects may be beneficial to brain health. Walnut kernels contain large quantities of unsaturated fatty acids, peptides, and phenolic compounds that have anti-inflammatory effects. The long-term intake of walnuts has been found to improve cognitive function and memory in rats and humans. However, the modulatory effect of walnuts on neuroinflammation has received much less attention. This review focuses on the potential influence and main regulating mechanisms of walnuts and their active ingredients on neuroinflammation, including the regulation of microglia activation induced by amyloid β or lipopolysaccharides, inhibition of peripheral inflammation mediated by macrophages, reduction in oxidative stress by decreasing free radical levels and boosting antioxidant defenses, and control of gut microbes to maintain homeostasis. However, the majority of evidence of the beneficial effects of walnuts or their components on neuroinflammation and neurodegeneration comes from experimental work, whereas evidence from clinical studies on the beneficial effects is scarcer and less conclusive. This review aims to provide new insights into the neuroinflammation-regulating mechanisms and natural active ingredients of walnuts and the development of walnut-based functional foods for the alleviation of neurodegenerative diseases.

Somatic Mutations and Alzheimer’s Disease

Alzheimer’s disease (AD) represents a global health challenge, with an estimated 55 million people suffering from the non-curable disease across the world. While amyloid-β plaques and tau neurofibrillary tangles in the brain define AD proteinopathy, it has become evident that diverse coding and non-coding regions of the genome may significantly contribute to AD neurodegeneration. The diversity of factors associated with AD pathogenesis, coupled with age-associated damage, suggests that a series of triggering events may be required to initiate AD. Since somatic mutations accumulate with aging, and aging is a major risk factor for AD, there is a great potential for somatic mutational events to drive disease. Indeed, recent data from the Gozes team/laboratories as well as other leading laboratories correlated the accumulation of somatic brain mutations with the progression of tauopathy. In this review, we lay the current perspectives on the principal genetic factors associated with AD and the potential causes, highlighting the contribution of somatic mutations to the pathogenesis of late onset Alzheimer’s disease. The roles that artificial intelligence and big data can play in accelerating the progress of causal somatic mutation markers/biomarkers identification, and the associated drug discovery/repurposing, have been highlighted for future AD and other neurodegenerative studies, with the aim to bring hope for the vulnerable aging population.

Glial Cell-Mediated Neuroinflammation in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder; it is the most common cause of dementia and has no treatment. It is characterized by two pathological hallmarks, the extracellular deposits of amyloid beta (Aβ) and the intraneuronal deposits of Neurofibrillary tangles (NFTs). Yet, those two hallmarks do not explain the full pathology seen with AD, suggesting the involvement of other mechanisms. Neuroinflammation could offer another explanation for the progression of the disease. This review provides an overview of recent advances on the role of the immune cells' microglia and astrocytes in neuroinflammation. In AD, microglia and astrocytes become reactive by several mechanisms leading to the release of proinflammatory cytokines that cause further neuronal damage. We then provide updates on neuroinflammation diagnostic markers and investigational therapeutics currently in clinical trials to target neuroinflammation.

Identification of genetic molecular markers and immune infiltration characteristics of Alzheimer's disease through weighted gene co-expression network analysis

Background

Alzheimer's disease (AD) is a progressive neurodegenerative disease that leads to cognitive impairment and memory loss. Currently, the pathogenesis and underlying causative genes of AD remain unclear, and there exists no effective treatment for this disease. This study explored AD-related diagnostic and therapeutic biomarkers from the perspective of immune infiltration by analyzing public data from the NCBI Gene Expression Omnibus database.

Method

In this study, weighted gene co-expression network analysis (WGCNA) was conducted to identify modules and hub genes contributing to AD development. A protein–protein interaction network was constructed when the genes in the modules were enriched and examined by Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Furthermore, a gene network was established using topological WGCNA, from which five hub genes were selected. Logistic regression analysis and receiver operating characteristic curve analysis were performed to explore the clinical value of genes in AD diagnosis. The genes in the core module intersected with the hub genes, and four intersection genes (ATP2A2, ATP6V1D, CAP2, and SYNJ1) were selected. These four genes were enriched by gene set enrichment analysis (GSEA). Finally, an immune infiltration analysis was performed.

Results

The GO/KEGG analysis suggested that genes in the core module played a role in the differentiation and growth of neural cells and in the transmission of neurotransmitters. The GSEA of core genes showed that these four genes were mainly enriched in immune/infection pathways (e.g., cholera infection and Helicobacter pylori infection pathways) and other metabolic pathways. An investigation of immune infiltration characteristics revealed that activated mast cells, regulatory T cells, plasma cells, neutrophils, T follicular helper cells, CD8 T cells, resting memory CD4 T cells, and M1 macrophages were the core immune cells contributing to AD progression. qRT-PCR analysis showed that the ATP6V1D is upregulated in AD.

Conclusion

The results of enrichment and immuno-osmotic analyses indicated that immune pathways and immune cells played an important role in the occurrence and development of AD. The selected key genes were used as biomarkers related to the pathogenesis of AD to further explore the pathways and cells, which provided new perspectives on therapeutic targets in AD.

Symptomatic and Disease-Modifying Therapy Pipeline for Alzheimer's Disease: Towards a Personalized Polypharmacology Patient-Centered Approach

Since 1906, when Dr. Alois Alzheimer first described in a patient "a peculiar severe disease process of the cerebral cortex", people suffering from this pathology have been waiting for a breakthrough therapy. Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative brain disorder and the most common form of dementia in the elderly with a long presymptomatic phase. Worldwide, approximately 50 million people are living with dementia, with AD comprising 60-70% of cases. Pathologically, AD is characterized by the deposition of amyloid β-peptide (Aβ) in the neuropil (neuritic plaques) and blood vessels (amyloid angiopathy), and by the accumulation of hyperphosphorylated tau in neurons (neurofibrillary tangles) in the brain, with associated loss of synapses and neurons, together with glial activation, and neuroinflammation, resulting in cognitive deficits and eventually dementia. The current competitive landscape in AD consists of symptomatic treatments, of which there are currently six approved medications: three AChEIs (donepezil, rivastigmine, and galantamine), one NMDA-R antagonist (memantine), one combination therapy (memantine/donepezil), and GV-971 (sodium oligomannate, a mixture of oligosaccharides derived from algae) only approved in China. Improvements to the approved therapies, such as easier routes of administration and reduced dosing frequencies, along with the developments of new strategies and combined treatments are expected to occur within the next decade and will positively impact the way the disease is managed. Recently, Aducanumab, the first disease-modifying therapy (DMT) has been approved for AD, and several DMTs are in advanced stages of clinical development or regulatory review. Small molecules, mAbs, or multimodal strategies showing promise in animal studies have not confirmed that promise in the clinic (where small to moderate changes in clinical efficacy have been observed), and therefore, there is a significant unmet need for a better understanding of the AD pathogenesis and the exploration of alternative etiologies and therapeutic effective disease-modifying therapies strategies for AD. Therefore, a critical review of the disease-modifying therapy pipeline for Alzheimer's disease is needed.

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.

Understanding neuroinflammation through central nervous system infections

Neuroinflammation is now recognized to compound many central nervous system (CNS) pathologies, from stroke to dementia. As immune responses evolved to handle infections, studying CNS infections can offer unique insights into the CNS immune response and address questions such as: What defenses and strategies do CNS parenchymal cells deploy in response to a dangerous pathogen? How do CNS cells interact with each other and infiltrating immune cells to control microbes? What pathways are beneficial for the host or for the pathogen? Here, we review recent studies that use CNS-tropic infections in combination with cutting-edge techniques to delve into the complex relationships between microbes, immune cells, and cells of the CNS.

Microglial mTOR Activation Upregulates Trem2 and Enhances β-Amyloid Plaque Clearance in the 5XFAD Alzheimer's Disease Model

The mechanistic target of rapamycin (mTOR) signaling pathway plays a major role in key cellular processes including metabolism and differentiation; however, the role of mTOR in microglia and its importance in Alzheimer's disease (AD) have remained largely uncharacterized. We report that selective loss of Tsc1, a negative regulator of mTOR, in microglia in mice of both sexes, caused mTOR activation and upregulation of Trem2 with enhanced β-Amyloid (Aβ) clearance, reduced spine loss, and improved cognitive function in the 5XFAD AD mouse model. Combined loss of Tsc1 and Trem2 in microglia led to reduced Aβ clearance and increased Aβ plaque burden revealing that Trem2 functions downstream of mTOR. Tsc1 mutant microglia showed increased phagocytosis with upregulation of CD68 and Lamp1 lysosomal proteins. In vitro studies using Tsc1-deficient microglia revealed enhanced endocytosis of the lysosomal tracker indicator Green DND-26 suggesting increased lysosomal activity. Incubation of Tsc1-deficient microglia with fluorescent-labeled Aβ revealed enhanced Aβ uptake and clearance, which was blunted by rapamycin, an mTOR inhibitor. In vivo treatment of mice of relevant genotypes in the 5XFAD background with rapamycin, affected microglial activity, decreased Trem2 expression and reduced Aβ clearance causing an increase in Aβ plaque burden. Prolonged treatment with rapamycin caused even further reduction of mTOR activity, reduction in Trem2 expression, and increase in Aβ levels. Together, our findings reveal that mTOR signaling in microglia is critically linked to Trem2 regulation and lysosomal biogenesis, and that the upregulation of Trem2 in microglia through mTOR activation could be exploited toward better therapeutic avenues to Aβ-related AD pathologies.SIGNIFICANCE STATEMENT Mechanistic target of rapamycin (mTOR) signaling pathway is a key regulator for major cellular metabolic processes. However, the link between mTOR signaling and Alzheimer's disease (AD) is not well understood. In this study, we provide compelling in vivo evidence that mTOR activation in microglia would benefit β-Amyloid (Aβ)-related AD pathologies, as it upregulates Trem2, a key receptor for Aβ plaque uptake. Inhibition of mTOR pathway with rapamycin, a well-established immunosuppressant, downregulated Trem2 in microglia and reduced Aβ plaque clearance indicating that mTOR inactivation may be detrimental in Aβ-associated AD patients. This finding will have a significant public health impact and benefit, regarding the usage of rapamycin in AD patients, which we believe will aggravate the Aβ-related AD pathologies.

Primary microglia dysfunction or microgliopathy: A cause of dementias and other neurological or psychiatric disorders

Microglia are unique cells in the central nervous system (CNS), being considered a sub-type of CNS macrophage. These cells monitor nearby micro-regions, having roles that far exceed immunological and scavengering functions, being fundamental for developing, protecting and maintaining the integrity of grey and white matter. Microglia might become dysfunctional, causing abnormal CNS functioning early or late in the life of patients, leading to neurologic or psychiatric disorders and premature death in some patients. Observations that the impairment of normal microglia function per se could lead to neurological or psychiatric diseases have been mainly obtained from genetic and molecular studies of Nasu-Hakola disease, caused by TYROBP or TREM2 mutations, and from studies of adult-onset leukoencephalopathy with axonal spheroids (ALSP), caused by CSF1R mutations. These classical microgliopathies are being named here Microgliopathy Type I. Recently, mutations in TREM2 have also been associated with Alzheimer Disease. However, in Alzheimer Disease TREM2 allele variants lead to an impaired, but functional TREM2 protein, so that patients do not develop Nasu-Hakola disease but are at increased risk to develop other neurodegenerative diseases. Alzheimer Disease is the prototype of the neurodegenerative disorders associated with these TREM2 variants, named here the Microgliopathies Type II. Here, we review clinical, pathological and some molecular aspects of human diseases associated with primary microglia dysfunctions and briefly comment some possible therapeutic approaches to theses microgliopathies. We hope that our review might update the interesting discussion about the impact of intrinsic microglia dysfunctions in the genesis of some pathologic processes of the CNS.

Will Sirtuin 2 Be a Promising Target for Neuroinflammatory Disorders?

Neuroinflammatory disorder is a general term that is associated with the progressive loss of neuronal structure or function. At present, the widely studied diseases with neuroinflammatory components are mainly divided into neurodegenerative and neuropsychiatric diseases, namely, Alzheimer’s disease, Parkinson’s disease, depression, stroke, and so on. An appropriate neuroinflammatory response can promote brain homeostasis, while excessive neuroinflammation can inhibit neuronal regeneration and damage the central nervous system. Apart from the symptomatic treatment with cholinesterase inhibitors, antidepressants/anxiolytics, and neuroprotective drugs, the treatment of neuroinflammation is a promising therapeutic method. Sirtuins are a host of class III histone deacetylases, that require nicotinamide adenine dinucleotide for their lysine residue deacetylase activity. The role of sirtuin 2 (SIRT2), one of the sirtuins, in modulating senescence, myelin formation, autophagy, and inflammation has been widely studied. SIRT2 is associated with many neuroinflammatory disorders considering it has deacetylation properties, that regulate the entire immune homeostasis. The aim of this review was to summarize the latest progress in regulating the effects of SIRT2 on immune homeostasis in neuroinflammatory disorders. The overall structure and catalytic properties of SIRT2, the selective inhibitors of SIRT2, the relationship between immune homeostasis and SIRT2, and the multitasking role of SIRT2 in several diseases with neuroinflammatory components were discussed.

Innate Immune Cell Death in Neuroinflammation and Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder molecularly characterized by the formation of amyloid β (Aβ) plaques and type 2 microtubule-associated protein (Tau) abnormalities. Multiple studies have shown that many of the brain's immunological cells, specifically microglia and astrocytes, are involved in AD pathogenesis. Cells of the innate immune system play an essential role in eliminating pathogens but also regulate brain homeostasis and AD. When activated, innate immune cells can cause programmed cell death through multiple pathways, including pyroptosis, apoptosis, necroptosis, and PANoptosis. The cell death often results in the release of proinflammatory cytokines that propagate the innate immune response and can eliminate Aβ plaques and aggregated Tau proteins. However, chronic neuroinflammation, which can result from cell death, has been linked to neurodegenerative diseases and can worsen AD. Therefore, the innate immune response must be tightly balanced to appropriately clear these AD-related structural abnormalities without inducing chronic neuroinflammation. In this review, we discuss neuroinflammation, innate immune responses, inflammatory cell death pathways, and cytokine secretion as they relate to AD. Therapeutic strategies targeting these innate immune cell death mechanisms will be critical to consider for future preventive or palliative treatments for AD.

Human brain sialoglycan ligand for CD33, a microglial inhibitory Siglec implicated in Alzheimer's disease

Alzheimer's disease (AD) is characterized by accumulation of misfolded proteins. Genetic studies implicate microglia, brain-resident phagocytic immune cells, in AD pathogenesis. As positive effectors, microglia clear toxic proteins, whereas as negative effectors, they release proinflammatory mediators. An imbalance of these functions contributes to AD progression. Polymorphisms of human CD33, an inhibitory microglial receptor, are linked to AD susceptibility; higher CD33 expression correlates with increased AD risk. CD33, also called Siglec-3, is a member of the sialic acid-binding immunoglobulin-type lectin (Siglec) family of immune regulatory receptors. Siglec-mediated inhibition is initiated by binding to complementary sialoglycan ligands in the tissue environment. Here, we identify a single sialoglycoprotein in human cerebral cortex that binds CD33 as well as Siglec-8, the most abundant Siglec on human microglia. The ligand, which we term receptor protein tyrosine phosphatase zeta (RPTPζ)S3L, is composed of sialylated keratan sulfate chains carried on a minor isoform/glycoform of RPTPζ (phosphacan) and is found in the extracellular milieu of the human brain parenchyma. Brains from human AD donors had twofold higher levels of RPTPζS3L than age-matched control donors, raising the possibility that RPTPζS3L overexpression limits misfolded protein clearance contributing to AD pathology. Mice express the same structure, a sialylated keratan sulfate RPTPζ isoform, that binds mouse Siglec-F and crossreacts with human CD33 and Siglec-8. Brains from mice engineered to lack RPTPζ, the sialyltransferase St3gal4, or the keratan sulfate sulfotransferase Chst1 lacked Siglec binding, establishing the ligand structure. The unique CD33 and Siglec-8 ligand, RPTPζS3L, may contribute to AD progression.