Blood levels of MCP-1 modulate the genetic risks of Alzheimer's disease mediated by HLA-DRB1 and APOE for Alzheimer's disease

Microglial activation as a hallmark of neuroinflammation in Alzheimer's disease

Microglial activation has emerged as a hallmark of neuroinflammation in Alzheimer's disease (AD). Central to this process is the formation and accumulation of amyloid beta (Aβ) peptide and neurofibrillary tangles, both of which contribute to synaptic dysfunction and neuronal cell death. Aβ oligomers trigger microglial activation, leading to the release of pro-inflammatory cytokines, which further exacerbates neuroinflammation and neuronal damage. Importantly, the presence of activated microglia surrounding amyloid plaques is correlated with heightened production of cytokines such as interleukin (IL)-1β and tumor necrosis factor-alpha (TNF-α), creating a vicious cycle of inflammation. While microglia play a protective role by clearing Aβ plaques during the early stages of AD, their chronic activation can lead to detrimental outcomes, including enhanced tau pathology and neuronal apoptosis. Recent studies have highlighted the dualistic nature of microglial activation, showcasing both inflammatory (M1) and anti-inflammatory (M2) phenotypes that fluctuate based on the surrounding microenvironment. Disruption in microglial function and regulation can lead to neurovascular dysfunction, further contributing to the cognitive decline seen in AD. Moreover, emerging biomarkers and imaging techniques are unveiling the complexity of microglial responses in AD, providing avenues for targeted therapeutics aimed at modulating these cells. Understanding the intricate interplay between microglia, Aβ, and tau pathology is vital for developing potential interventions to mitigate neuroinflammation and its impact on cognitive decline in AD. This review synthesizes current findings regarding microglial activation and its implications for AD pathogenesis, offering insights into future therapeutic strategies.

The effect of C-reactive protein and interleukin-3 on mild cognitive impairment with APOE ɛ4

BackgroundThe apolipoprotein E ε4 allele (APOE ε4) and inflammation are associated with Alzheimer's disease (AD) pathology. Mild cognitive impairment (MCI) is considered the preclinical and early stage of AD. However, the comprehensive effects of APOE ε4 and inflammatory mediators on MCI patients with specific APOE ε4 genotypes remain poorly understood.ObjectiveOur study aimed to explore how different numbers of the APOE ε4 alleles affect plasma C-reactive protein (CRP) and interleukin-3 (IL-3) levels and their associations with brain structure.MethodsA total of 339 MCI patients from the Alzheimer's Disease Neuroimaging Initiative study were enrolled. We compared their plasma concentrations of CRP and IL-3, cognitive performance, and cerebrospinal fluid (CSF) AD biomarkers levels across different APOE ε4 genotypes. Structural magnetic resonance imaging was utilized to measure gray matter volume outcomes. Pearson correlation analysis was used to explore the associations between the above indicators.ResultsPlasma CRP levels increased in the APOE ε4 carriers, but IL-3 expression notably decreased, and the homozygous state is the most significant. A negative correlation between CRP and several cognitive abilities was observed only in APOE ε4 homozygotes. Additionally, a positive correlation between IL-3, cognitive scores, and CSF biomarker levels was confirmed only in APOE ε4 homozygotes. Imaging data demonstrated that the gray matter volume of the right middle frontal gyrus was associated with CRP only in APOE ε4 non-carriers.ConclusionsOur study demonstrated that peripheral inflammatory mediators' effect on cognitive function and brain structure in MCI patients differs based on their APOE ε4 allele carrier status.

The influences of ApoE isoforms on endothelial adherens junctions and actin cytoskeleton responding to mCRP

Apolipoprotein E4 (ApoE4) plays an important role responding to monomeric C-reactive protein (mCRP) via binding to CD31 leading to cerebrovascular damage and Alzheimer's disease (AD). Using phosphor-proteomic profiling, we found altered cytoskeleton proteins in the microvasculature of AD brains, including increased levels of hyperphosphorylated tau (pTau) and the actin-related protein, LIMA1. To address the hypothesis that cytoskeletal changes serve as early pathological signatures linked with CD31 in brain endothelia in ApoE4 carriers, ApoE4 knock-in mice intraperitoneal injected with mCRP revealed that mCRP increased the expressions of phosphorylated CD31 (pCD31) and LIMA1, and facilitate the binding of pCD31 to LIMA1. mCRP combined with recombinant APOE4 protein decreased interaction of CD31 and VE-Cadherin at adherens junctions (AJs), along with altered the expression of various actin cytoskeleton proteins, causing microvasculature damage. Notably, the APOE2 protein attenuated these changes. Overall, our study demonstrates that ApoE4 responds to mCRP to disrupt the endothelial AJs which link with the actin cytoskeleton and this pathway could play a key role in the barrier dysfunction leading to AD risk.

Identification of neutrophil extracellular trap-related genes in Alzheimer's disease based on comprehensive bioinformatics analysis

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease. There are currently no effective interventions to slow down or prevent the occurrence and progression of AD. Neutrophil extracellular traps (NETs) have been proven to be tightly linked to AD. This project attempted to identify hub genes for AD based on NETs. Gene expression profiles of the training set and validation set were downloaded from the Gene Expression Omnibus (GEO) database, including non-demented (ND) controls and AD samples. NET-related genes (NETRGs) were collected from the literature. Differential analysis identified 21 AD differentially expressed NETRGs (AD-DE-NETRGs) majorly linked to functions such as defense response to bacterium as well as pathways including IL-17 signaling pathway, as evidenced by enrichment analyses of Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Protein-protein interaction (PPI) network, Minutia Cylinder-Code (MCC) algorithm, and molecular complex detection (MCODE) algorithm in the CytoHubba plug-in were employed to identify five hub genes (NFKBIA, SOCS3, CCL2, TIMP1, ACTB). Their diagnostic ability was validated in the validation set using receiver operating characteristic (ROC) curves and gene differential expression analysis. A total of 16 miRNAs and 132 lncRNAs were predicted through the mirDIP and ENCORI databases, and a lncRNA-miRNA-mRNA regulatory network was constructed using Cytoscape software. Small molecular compounds such as Benzo(a)pyrene and Copper Sulfate were predicted to target hub genes using the CTD database. This project successfully identified five hub genes, which may serve as potential biomarkers for AD, proffering clues for new therapeutic targets.

Human Leukocyte Antigen and microRNAs as Key Orchestrators of Mild Cognitive Impairment and Alzheimer's Disease: A Systematic Review

The expression of inflamma-miRs and human leukocyte antigen (HLA) haplotypes could indicate mild cognitive impairment (MCI) and Alzheimer's disease (AD). We used international databases to conduct a systematic review of studies on HLA variants and a meta-analysis of research on microRNAs (miRNAs). We aimed to analyze the discriminative value of HLA variants and miRNAs in MCI, AD and controls to evaluate the protective or causative effect of HLA in cognitive decline, establish the role of miRNAs as biomarkers for the early detection of AD, and find a possible link between miRNAs and HLA. Statistical analysis was conducted using Comprehensive Meta-analysis software, version 2.2.050 (Biostat Inc., Englewood, NJ, USA). The effect sizes were estimated by the logarithm base 2 of the fold change. The systematic review revealed that some HLA variants, such as HLA-B*4402, HLA-A*33:01, HLA-A*33:01, HLA-DPB1, HLA-DR15, HLA-DQB1*03:03, HLA-DQB1*06:01, HLA-DQB1*03:01, SNPs on HLA-DRB1/DQB1, and HLA-DQA1, predisposed to cognitive decline before the occurrence of AD, while HLA-A1*01, HLA-DRB1∗13:02, HLA-DRB1*04:04, and HLA-DRB1*04:01 demonstrated a protective role. The meta-analysis identified let-7 and miR-15/16 as biomarkers for the early detection of AD. The association between these two miRNA families and the HLA variants that predispose to AD could be used for the early screening and prevention of MCI.

Amplified fluorogenic immunoassay for early diagnosis and monitoring of Alzheimer's disease from tear fluid

Accurate diagnosis of Alzheimer's disease (AD) in its earliest stage can prevent the disease and delay the symptoms. Therefore, more sensitive, non-invasive, and simple screening tools are required for the early diagnosis and monitoring of AD. Here, we design a self-assembled nanoparticle-mediated amplified fluorogenic immunoassay (SNAFIA) consisting of magnetic and fluorophore-loaded polymeric nanoparticles. Using a discovery cohort of 21 subjects, proteomic analysis identifies adenylyl cyclase-associated protein 1 (CAP1) as a potential tear biomarker. The SNAFIA demonstrates a low detection limit (236 aM), good reliability (R2 = 0.991), and a wide analytical range (0.320-1000 fM) for CAP1 in tear fluid. Crucially, in the verification phase with 39 subjects, SNAFIA discriminates AD patients from healthy controls with 90% sensitivity and 100% specificity in under an hour. Utilizing tear fluid as a liquid biopsy, SNAFIA could potentially aid in long-term care planning, improve clinical trial efficiency, and accelerate therapeutic development for AD.