Transcriptional response of murine microglia in Alzheimer’s disease and inflammation

Sugar utilization by microglia in Alzheimer's disease

Diabetes is a major risk factor for Alzheimer's disease (AD), yet the effect of specific carbohydrate sources in the diet on AD pathology remains unclear. The primary neuroimmune cell, microglia, undergo a metabolic shift during neuroinflammation associated with AD pathology. We utilized existing gene expression data and identified changes in sugar transporters (increased Slc2a1 (glucose) and decreased Slc2a5 (fructose) expression). To examine gene expression with respect to primary sugar source, N9 cells, a mouse microglia cell line, were cultured in glucose or fructose supplemented media and stimulated with lipopolysaccharide (LPS). RNA-sequencing analyses indicated significant changes between control and sugar supplemented media and several differentially expressed genes between glucose and fructose media. Concurrently, 5XFAD mice received equicaloric diets with specific carbohydrate sources: dextrose or fructose. Regardless of diet, sex, or genotype, all mice developed high blood sugar levels; confocal microscopy analyses indicated similar amyloid plaque burden and microglial response relative to the control diet, but there was a change in the microglial response between dextrose and fructose fed mice. Overall, these data indicate microglia preferentially express sugar transporters and sugar source may influence microglial reactivity in response to plaque pathology.

Microglial TLR4-Lyn kinase is a critical regulator of neuroinflammation, Aβ phagocytosis, neuronal damage, and cell survival in Alzheimer's disease

Disease-Associated Microglia (DAM) are a focus in Alzheimer's disease (AD) research due to their central involvement in the response to amyloid-beta plaques. Microglial Toll-like receptor 4 (TLR4) is instrumental in the binding of fibrillary amyloid proteins, while Lyn kinase (Lyn) is a member of the Src family of non-receptor tyrosine kinases involved in immune signaling. Lyn is a novel, non-canonical, intracellular adaptor with diverse roles in cell-specific signaling which directly binds to TLR4 to modify its function. Lyn can be activated in response to TLR4 stimulation, leading to phosphorylation of various substrates and modulation of inflammatory and phagocytosis signaling pathways. Here, we investigated the TLR4-Lyn interaction in neuroinflammation using WT, 5XFAD, and 5XFAD x Lyn-/- mouse models by western blotting (WB), co-immunoprecipitation (co-IP), immunohistochemistry (IHC) and flow cytometric (FC) analysis. A spatial transcriptomic analysis of microglia in WT, 5XFAD, and 5XFAD x Lyn-/- mice revealed essential genes involved in neuroinflammation, Aβ phagocytosis, and neuronal damage. Finally, we explored the effects of a synthetic, TLR4-Lyn modulator protein (TLIM) through an in vitro AD model using primary murine microglia. Our WB, co-IP, IHC, and FC data show an increased, novel, direct protein-protein interaction between TLR4 and Lyn kinase in the brains of 5XFAD mice compared to WT. Furthermore, in the absence of Lyn (5XFAD x Lyn-/- mice); increased expression of protective Syk kinase was observed, enhanced microglial Aβ phagocytosis, increased astrocyte activity, decreased neuronal dystrophy, and a further increase in the cell survival signaling and protective DAM population was noted. The DAM population in 5XFAD mice which produce more inflammatory cytokines and phagocytose more Aβ were observed to express greater levels of TLR4 and Lyn. Pathway analysis comparison between WT, 5XFAD, and 5XFAD x Lyn-/- mice supported these findings via our microglial spatial transcriptomic analysis. Finally, we created an in vitro co-culture system with primary murine microglial and primary murine hippocampal cells exposed to Aβ as a model of AD. When these co-cultures were treated with our TLR4-Lyn Interaction Modulators (TLIMs), an increase in Aβ phagocytosis and a decrease in neuronal dystrophy was seen. Lyn kinase has a central role in modulating TLR4-induced inflammation and Syk-induced protection in a 5XFAD mouse model. Our TLIMs ameliorate AD sequalae in an in vitro model of AD and could be a promising therapeutic strategy to treat AD.

Targeting CB2 receptor with a novel antagonist reverses cognitive decline, neurodegeneration and pyroptosis in a TAU-dependent frontotemporal dementia mouse model

Frontotemporal dementia (FTD) comprises a group of disorders characterized by a progressive decline in behavior or language linked to the degeneration of the frontal and anterior temporal lobes followed by hippocampal atrophy. There are no effective treatments for FTD and for this reason, novel pharmacological targets, such as the endocannabinoid system (ECS), are being explored. Previous results from our laboratory showed a TAUP301L-dependent increase in CB2 receptor expression in hippocampal neurons of a FTD mouse model, alongside the neuroprotective impact of CB2 ablation. In this study, we evaluated the therapeutic potential of a new CB2 antagonist (PGN36) in our TAU-dependent FTD mouse model. Six-month-old mice received stereotaxic injections of an adeno-associated virus expressing human TAUP301L protein (AAV-TAUP301L) into the right hippocampus and were treated daily with PGN36 (5 mg/kg, i.p.) or vehicle for three weeks. By integrating behavioral tests, RNA-seq, qPCR expression analysis, and immunofluorescence in the AAV expressing TAU mouse model, we found that PGN36 treatment reverses key features of the neurodegenerative process triggered by TAUP301L overexpression. PGN36 treatment effectively countered TAUP301L-induced cognitive decline by reducing TAU protein expression levels and restoring markers of synaptic plasticity. Notably, we observed neuroprotection in the dentate gyrus granular layer, which we attribute to the modulation of pyroptosis. This programmed cell death pathway, is triggered by TAUP301L overexpression. PGN36 appears to modulate the pyroptotic cascade, thereby preventing the pyroptosis-induced neuronal loss. These findings collectively underscore the neuroprotective potential of this novel CB2 antagonist treatment against TAU-associated FTD.

Enhanced BBB penetration and microglia-targeting nanomodulator for the two-pronged modulation of chronically activated microglia-mediated neuroinflammation in Alzheimer's disease

Intervention in chronically activated microglia-mediated neuroinflammation is a novel approach to treat Alzheimer's disease (AD). The low permeability of the blood‒brain barrier (BBB) and non-selective distribution in the brain severely restrict AD drugs' disease-modifying efficacy. Here, an immunosuppressant TREM2-lowing antisense oligonucleotides (ASOs) and resveratrol co-loaded cationic liposome is developed as an immune reprogramming nanomodulator modified by acid-cleavable BBB-targeting peptide and microglia-targeting peptide (Res@TcMNP/ASO) for AD management. Res@TcMNP/ASO can enter brain endothelial cells via D-T7 peptides. Then D-T7 undergoes an acid-responsive cleavage, facilitating the escape of Res@MNP/ASO from endo/lysosomes to cross the BBB. The detached Res@MNP/ASO specifically targets M1-phenotype microglia via exposed MG1 peptides to prompt the simultaneous delivery of two drugs into activated microglia. This nanomodulator can not only restore the immune function of microglia through TREM2-lowing ASO but also mitigate the immune stimulation to microglia caused by reactive oxygen species (ROS) through resveratrol, thereby synergistically inhibiting the chronic activation of microglia to alleviate neuroinflammation in AD. Our results indicate that this combination treatment can achieve significant behavioral and cognitive improvements in late APP/PS1 mice.

Characterization of gut microbiota dynamics in an Alzheimer's disease mouse model through clade-specific marker-based analysis of shotgun metagenomic data

Alzheimer's disease (AD) is a complex neurodegenerative disorder significantly impairing cognitive faculties, memory, and physical abilities. To characterize the modulation of the gut microbiota in an in vivo AD model, we performed shotgun metagenomics sequencing on 3xTgAD mice at key time points (i.e., 2, 6, and 12 months) of AD progression. Fecal samples from both 3xTgAD and wild-type mice were collected, DNA extracted, and sequenced. Quantitative taxon abundance assessment using MetaPhlAn 4 ensured precise microbial community representation. The analysis focused on species-level genome bins (SGBs) including both known and unknown SGBs (kSGBs and uSGBs, respectively) and also comprised higher taxonomic categories such as family-level genome bins (FGBs), class-level genome bins (CGBs), and order-level genome bins (OGBs). Our bioinformatic results pinpointed the presence of extensive gut microbial diversity in AD mice and showed that the largest proportion of AD- and aging-associated microbiome changes in 3xTgAD mice concern SGBs that belong to the Bacteroidota and Firmicutes phyla, along with a large set of uncharacterized SGBs. Our findings emphasize the need for further advanced bioinformatic studies for accurate classification and functional analysis of these elusive microbial species in relation to their potential bridging role in the gut-brain axis and AD pathogenesis.

Knockdown of microglial iron import gene, Slc11a2, worsens cognitive function and alters microglial transcriptional landscape in a sex-specific manner in the APP/PS1 model of Alzheimer's disease

BACKGROUND

Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer's disease (AD). In vitro, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of microglial-specific knockdown of Slc11a2 on AD-related cognitive decline and microglial transcriptional phenotype.

METHODS

In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1Cre-ERT2;Slc11a2flfl;APP/PS1+or - mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b+ microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted.

RESULTS

DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2KD APP/PS1 females displayed significant increases in Enpp2, Ttr, and the iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2KD cells from APP/PS1 females also exhibited decreased expression of markers associated with subsets of disease-associated microglia (DAMs), such as Apoe, Ctsb, Ly9, Csf1, and Hif1α.

CONCLUSIONS

This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in microglia and cognitive deficits in Slc11a2KD APP/PS1 female mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

Knockdown of microglial iron import gene, DMT1, worsens cognitive function and alters microglial transcriptional landscape in a sex-specific manner in the APP/PS1 model of Alzheimer's disease

Background

Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer's disease (AD). In vitro, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of microglial-specific knockdown of Slc11a2 on AD-related cognitive decline and microglial transcriptional phenotype.

Methods

In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1 Cre - ERT2 ;Slc11a2 flfl;APP/PS1 + or - mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b + microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted.

Results

DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2 KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2 KD APP/PS1 females displayed significant increases in Enpp2, Ttr, and the iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2 KD cells from APP/PS1 females also exhibited decreased expression of markers associated with disease-associated microglia (DAMs), such as Apoe, Ctsb, Csf1, and Hif1α.

Conclusions

This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in microglia and cognitive deficits in Slc11a2 KD APP/PS1 female mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

Mitigation of CXCL10 secretion by metabolic disorder drugs in microglial-mediated neuroinflammation

Metabolic disorders are associated with several neurodegenerative diseases. We previously identified C-X-C motif chemokine ligand 10 (CXCL10), also known as interferon gamma-induced protein 10 (IP-10), as a major contributor to the type I interferon response in microglial-mediated neuroinflammation. Therefore, we hypothesized FDA-approved metabolic disorder drugs that attenuate CXCL10 secretion may be repurposed as a treatment for neurodegenerative diseases. Screening, dose curves, and cytotoxicity assays in LPS-stimulated microglia yielded treprostinil (hypertension), pitavastatin (hyperlipidemia), and eplerenone (hypertension) as candidates that significantly reduced CXCL10 secretion (in addition to other pro-inflammatory mediators) without impacting cell viability. Altogether, these data suggest metabolic disorder drugs that attenuate CXCL10 as potential treatments for neurodegenerative disease through mitigating microglial-mediated neuroinflammation.

Zinc utilization by microglia in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia defined by two key pathological characteristics in the brain, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Microglia, the primary innate immune cells of the central nervous system (CNS), provide neuroprotection through Aβ and tau clearance but may also be neurotoxic by promoting neuroinflammation to exacerbate Aβ and tau pathogenesis in AD. Recent studies have demonstrated the importance of microglial utilization of nutrients and trace metals in controlling their activation and effector functions. Trace metals, such as zinc, have essential roles in brain health and immunity, and zinc dyshomeostasis has been implicated in AD pathogenesis. As a result of these advances, the mechanisms by which zinc homeostasis influences microglial-mediated neuroinflammation in AD is a topic of continuing interest since new strategies to treat AD are needed. Here, we review the roles of zinc in AD, including zinc activation of microglia, the associated neuroinflammatory response, and the application of these findings in new therapeutic strategies.

Endothelial senescence alleviates cognitive impairment in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is among the most prevalent age-related neurodegenerative diseases. Endothelial cell (EC) senescence was discovered in the AD brain, but its function in AD pathogenesis was unidentified. Here we created an AD mouse model with EC senescence (APP/PS1;TERF2DN mice) by intercrossing APP/PS1 mice with Tie2 promoter-driven dominant negative telomeric repeat-binding factor 2 transgenic mice (TERF2DN-Tg mice). We evaluated cognitive functions and AD brain pathology in APP/PS1;TERF2DN mice. Surprisingly, compared with the control APP/PS1 mice, APP/PS1;TERF2DN mice demonstrated the attenuation of cognitive impairment and amyloid-β (Aβ) pathology, accompanied by the compaction of Aβ plaques with increased microglial coverage and reduced neurite dystrophy. Moreover, we evaluated whether EC senescence could affect microglial morphology and phagocytosis of Aβ. Compared with wild-type mice, microglia in TERF2DN-Tg mice display increased numbers of endpoints (a morphometric parameter to quantify the number of processes) and Aβ phagocytosis and related gene expression. Single-cell RNA-sequencing analysis showed that compared with APP/PS1 mouse microglia, APP/PS1;TERF2DN mouse microglia displayed a modest decline in disease-associated microglia, accompanied by an altered direction of biological process branching from antigen synthesis and arrangement to ribonucleoprotein complex biogenesis. Our outcomes indicate that EC senescence alters microglia toward a protective phenotype with a rise in phagocytic and barrier roles, and may offer a clue to create a novel preventive/therapeutic method to treat AD.

Gene Association Study of the Urokinase Plasminogen Activator and Its Receptor Gene in Alzheimer's Disease

Background

The role of the innate immune system has long been associated with Alzheimer's disease (AD). There is now accumulating evidence that the soluble Urokinase Plasminogen Activator Receptor pathway, and its genes, PLAU and PLAUR may be important in AD, and yet there have been few genetic association studies to explore this.

Objective

This study utilizes the DNA bank of the Brains for Dementia Research cohort to investigate the genetic association of common polymorphisms across the PLAU and PLAUR genes with AD.

Methods

TaqMan genotyping assays were used with standard procedures followed by association analysis in PLINK.

Results

No association was observed between the PLAU gene and AD; however, two SNPs located in the PLAUR gene were indicative of a trend towards association but did not surpass multiple testing significance thresholds.

Conclusions

Further genotyping studies and exploration of the consequences of these SNPs on gene expression and alternative splicing are warranted to fully uncover the role this system may have in AD.

Lipid metabolism transcriptomics of murine microglia in Alzheimer's disease and neuroinflammation

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-β (Aβ) plaques followed by intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. An unrestrained immune response by microglia, the resident cells of the central nervous system (CNS), leads to neuroinflammation which can amplify AD pathology. AD pathology is also driven by metabolic dysfunction with strong correlations between dementia and metabolic disorders such as diabetes, hypercholesterolemia, and hypertriglyceridemia. Since elevated cholesterol and triglyceride levels appear to be a major risk factor for developing AD, we investigated the lipid metabolism transcriptome in an AD versus non-AD state using RNA-sequencing (RNA-seq) and microarray datasets from N9 cells and murine microglia. We identified 52 differentially expressed genes (DEG) linked to lipid metabolism in LPS-stimulated N9 microglia versus unstimulated control cells using RNA-seq, 86 lipid metabolism DEG in 5XFAD versus wild-type mice by microarray, with 16 DEG common between both datasets. Functional enrichment and network analyses identified several biological processes and molecular functions, such as cholesterol homeostasis, insulin signaling, and triglyceride metabolism. Furthermore, therapeutic drugs targeting lipid metabolism DEG found in our study were identified. Focusing on drugs that target genes associated with lipid metabolism and neuroinflammation could provide new targets for AD drug development.

Cell-Type-Specific Gene Regulatory Networks of Pro-Inflammatory and Pro-Resolving Lipid Mediator Biosynthesis in the Immune System

Lipid mediators are important regulators in inflammatory responses, and their biosynthetic pathways are targeted by commonly used anti-inflammatory drugs. Switching from pro-inflammatory lipid mediators (PIMs) to specialized pro-resolving (SPMs) is a critical step toward acute inflammation resolution and preventing chronic inflammation. Although the biosynthetic pathways and enzymes for PIMs and SPMs have now been largely identified, the actual transcriptional profiles underlying the immune cell type-specific transcriptional profiles of these mediators are still unknown. Using the Atlas of Inflammation Resolution, we created a large network of gene regulatory interactions linked to the biosynthesis of SPMs and PIMs. By mapping single-cell sequencing data, we identified cell type-specific gene regulatory networks of the lipid mediator biosynthesis. Using machine learning approaches combined with network features, we identified cell clusters of similar transcriptional regulation and demonstrated how specific immune cell activation affects PIM and SPM profiles. We found substantial differences in regulatory networks in related cells, accounting for network-based preprocessing in functional single-cell analyses. Our results not only provide further insight into the gene regulation of lipid mediators in the immune response but also shed light on the contribution of selected cell types in their biosynthesis.

Genome-wide identification of murine interferon genes in microglial-mediated neuroinflammation in Alzheimer's disease

Interferons play a major role in microglial-mediated neuroinflammation in Alzheimer's disease (AD). We investigated the interferon transcriptome (AD versus non-AD) using N9 and murine microglia. We identified 64 interferon-related differentially expressed genes (DEG) in LPS-stimulated N9 microglia versus control cells, 26 DEG in microglia from 5XFAD versus wild-type mice, with 13 DEG common to both datasets. Network analyses identified potential key mediators (Cxcl10, Ifit3) of the interferon response in AD. Gene-drug interaction analysis identified therapeutics targeting interferon-related genes. These data characterize the microglial interferon response in AD, providing new targets and therapeutics directed towards interferon-related neuroinflammation in AD.

Astrocytic Yin Yang 1 is critical for murine brain development and protection against apoptosis, oxidative stress, and inflammation

The transcription factor Yin Yang 1 (YY1) is ubiquitously expressed in mammalian cells, regulating the expression of a variety of genes involved in proliferation, differentiation, and apoptosis in a context-dependent manner. While it is well-established that global YY1 knockout (KO) leads to embryonic death in mice and that YY1 deletion in neurons or oligodendrocytes induces impaired brain function, the role of astrocytic YY1 in the brain remains unknown. We investigated the role of astrocytic YY1 in the brain using a glial fibrillary acidic protein (GFAP)-specific YY1 conditional KO (YY1 cKO) mouse model to delete astrocytic YY1. Astrocytic YY1 cKO mice were tested for behavioral phenotypes, such as locomotor activity, coordination, and cognition, followed by an assessment of relevant biological pathways using RNA-sequencing analysis, immunoblotting, and immunohistochemistry in the cortex, midbrain, and cerebellum. YY1 cKO mice showed abnormal phenotypes, movement deficits, and cognitive dysfunction. At the molecular level, astrocytic YY1 deletion altered the expression of genes associated with proliferation and differentiation, p53/caspase apoptotic pathways, oxidative stress response, and inflammatory signaling including NF-κB, STAT, and IRF in all regions. Astrocytic YY1 deletion significantly increased the expression of GFAP as astrocytic activation and Iba1 as microglial activation, indicating astrocytic YY1 deletion activated microglia as well. Accordingly, multiple inflammatory cytokines and chemokines including TNF-α and CXCL10 were elevated. Combined, these novel findings suggest that astrocytic YY1 is a critical transcription factor for normal brain development and locomotor activity, motor coordination, and cognition. Astrocytic YY1 is also essential in preventing pathological oxidative stress, apoptosis, and inflammation.

Neuroimmune mechanisms underlying Alzheimer's disease: Insights into central and peripheral immune cell crosstalk

Alzheimer's disease (AD) is a highly life-threatening neurodegenerative disease. Dysregulation of the immune system plays a critical role in promoting AD, which has attracted extensive attention recently. Central and peripheral immune responses are involved in the pathogenesis of AD. Immune changes precede Aβ-associated senile plaque formation and tau-related neurofibrillary tangles, which are the recognised pathological features of AD. Therefore, elucidating immune-related mechanisms underlying the development of AD can help to prevent and treat AD at the source by blocking its progression before the development of pathological changes. To understand the specific pathogenesis of AD, it is important to examine the role of central and peripheral immunity in AD. This review summarises immune-related mechanisms underlying the pathogenesis of AD, focusing on the effect of various central and peripheral immune cells, and describes the possible crosstalk between central and peripheral immunity during the development of AD. This review provides novel insights into the treatment of AD and offers a new direction for immune-related research on AD in the future.

Common Genetic Factors and Pathways in Alzheimer's Disease and Ischemic Stroke: Evidences from GWAS

Alzheimer's disease (AD) and ischemic stroke (IS) are common neurological disorders, and the comorbidity of these two brain diseases is often seen. Although AD and IS were regarded as two distinct disease entities, in terms of different etiologies and clinical presentation, recent genome-wide association studies (GWASs) revealed that there were common risk genes between AD and IS, indicating common molecular pathways and their common pathophysiology. In this review, we summarize AD and IS risk single nucleotide polymorphisms (SNPs) and their representative genes from the GWAS Catalog database, and find thirteen common risk genes, but no common risk SNPs. Furthermore, the common molecular pathways associated with these risk gene products are summarized from the GeneCards database and clustered into inflammation and immunity, G protein-coupled receptor, and signal transduction. At least seven of these thirteen genes can be regulated by 23 microRNAs identified from the TargetScan database. Taken together, the imbalance of these molecular pathways may give rise to these two common brain disorders. This review sheds light on the pathogenesis of comorbidity of AD and IS, and provides molecular targets for disease prevention, manipulation, and brain health maintenance.

Dual role of Apolipoprotein D as long-term instructive factor and acute signal conditioning microglial secretory and phagocytic responses

Microglial cells are recognized as very dynamic brain cells, screening the environment and sensitive to signals from all other cell types in health and disease. Apolipoprotein D (ApoD), a lipid-binding protein of the Lipocalin family, is required for nervous system optimal function and proper development and maintenance of key neural structures. ApoD has a cell and state-dependent expression in the healthy nervous system, and increases its expression upon aging, damage or neurodegeneration. An extensive overlap exists between processes where ApoD is involved and those where microglia have an active role. However, no study has analyzed the role of ApoD in microglial responses. In this work, we test the hypothesis that ApoD, as an extracellular signal, participates in the intercellular crosstalk sensed by microglia and impacts their responses upon physiological aging or damaging conditions. We find that a significant proportion of ApoD-dependent aging transcriptome are microglia-specific genes, and show that lack of ApoD in vivo dysregulates microglial density in mouse hippocampus in an age-dependent manner. Murine BV2 and primary microglia do not express ApoD, but it can be internalized and targeted to lysosomes, where unlike other cell types it is transiently present. Cytokine secretion profiles and myelin phagocytosis reveal that ApoD has both long-term pre-conditioning effects on microglia as well as acute effects on these microglial immune functions, without significant modification of cell survival. ApoD-triggered cytokine signatures are stimuli (paraquat vs. Aβ oligomers) and sex-dependent. Acute exposure to ApoD induces microglia to switch from their resting state to a secretory and less phagocytic phenotype, while long-term absence of ApoD leads to attenuated cytokine induction and increased myelin uptake, supporting a role for ApoD as priming or immune training factor. This knowledge should help to advance our understanding of the complex responses of microglia during aging and neurodegeneration, where signals received along our lifespan are combined with damage-triggered acute signals, conditioning both beneficial roles and limitations of microglial functions.

The Inflammatory Gene PYCARD of the Entorhinal Cortex as an Early Diagnostic Target for Alzheimer's Disease

The incidence of Alzheimer's disease (AD) is increasing year by year, which brings great challenges to human health. However, the pathogenesis of AD is still unclear, and it lacks early diagnostic targets. The entorhinal cortex (EC) is a key brain region for the occurrence of AD neurodegeneration, and neuroinflammation plays a significant role in EC degeneration in AD. This study aimed to reveal the close relationship between inflammation-related genes in the EC and AD by detecting key differentially expressed genes (DEGs) via gene function enrichment pathway analysis. GSE4757 and GSE21779 gene expression profiles of AD were downloaded from the Gene Expression Omnibus (GEO) database. R language was used for the standardization and differential analysis of DEGs. Then, significantly enriched Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were analyzed to predict the potential biological functions of the DEGs. Finally, the significant expressions of identified DEGs were verified, and the therapeutic values were detected by a receiver operating characteristic (ROC) curve. The results showed that eight up-regulated genes (SLC22A2, ITGB2-AS1, NIT1, FGF14-AS2, SEMA3E, PYCARD, PRORY, ADIRF) and two down-regulated genes (AKAIN1, TRMT2B) may have a potential diagnostic value for AD, and participate in inflammatory pathways. The area under curve (AUC) results of the ten genes showed that they had potential diagnostic value for AD. The AUC of PYCARD was 0.95, which had the most significant diagnostic value, and it is involved in inflammatory processes such as the inflammasome complex adaptor protein. The DEGs screened, and subsequent pathway analysis revealed a close relationship between inflammation-related PYCARD and AD, thus providing a new basis for an early diagnostic target for AD.

Exploring the zinc-related transcriptional landscape in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurological disorder, and increasing evidence suggests AD pathology is driven by metabolic dysfunction in the brain. Zinc is the second most abundant trace element found in the human body and is required by all living organisms. Zinc is used extensively in many biological processes, and alterations in zinc levels are implicated in the pathogenesis of numerous diseases, including AD. Since small fluctuations in brain zinc levels appear to effect AD progression, we investigated the zinc-related transcriptional responses in an AD versus non-AD state using microarray and RNA-sequencing (RNA-seq) datasets from cultured cells, mice, and humans. We identified 582 zinc-related differentially expressed genes (DEG) in human dorsolateral prefrontal cortex samples of late-onset AD (LOAD) versus non-AD controls, 146 zinc-related DEG in 5XFAD versus wild-type mice, and 95 zinc-related DEG in lipopolysaccharide (LPS)-stimulated N9 microglia versus unstimulated control cells, with 19 zinc-related DEG common to all three datasets. Of the 19 common DEG, functional enrichment and network analyses identified several biological processes and molecular functions, such as mRNA destabilization and nucleic acid binding, which may be important in neuroinflammation and AD development. Furthermore, therapeutic drugs targeting zinc-related DEG in the human dataset were identified. Taken together, these data provide insights into zinc utilization for gene transcription during AD progression which may further our understanding of AD pathogenesis and could identify new targets for therapeutic strategies targeted towards AD.