Peripheral and central immune system crosstalk in Alzheimer disease - a research prospectus

Neuronal guidance signaling in neurodegenerative diseases: Key regulators that function at neuron-glia and neuroimmune interfaces

The nervous system processes a vast amount of information, performing computations that underlie perception, cognition, and behavior. During development, neuronal guidance genes, which encode extracellular cues, their receptors, and downstream signal transducers, organize neural wiring to generate the complex architecture of the nervous system. It is now evident that many of these neuroguidance cues and their receptors are active during development and are also expressed in the adult nervous system. This suggests that neuronal guidance pathways are critical not only for neural wiring but also for ongoing function and maintenance of the mature nervous system. Supporting this view, these pathways continue to regulate synaptic connectivity, plasticity, and remodeling, and overall brain homeostasis throughout adulthood. Genetic and transcriptomic analyses have further revealed many neuronal guidance genes to be associated with a wide range of neurodegenerative and neuropsychiatric disorders. Although the precise mechanisms by which aberrant neuronal guidance signaling drives the pathogenesis of these diseases remain to be clarified, emerging evidence points to several common themes, including dysfunction in neurons, microglia, astrocytes, and endothelial cells, along with dysregulation of neuron-microglia-astrocyte, neuroimmune, and neurovascular interactions. In this review, we explore recent advances in understanding the molecular and cellular mechanisms by which aberrant neuronal guidance signaling contributes to disease pathogenesis through altered cell-cell interactions. For instance, recent studies have unveiled two distinct semaphorin-plexin signaling pathways that affect microglial activation and neuroinflammation. We discuss the challenges ahead, along with the therapeutic potentials of targeting neuronal guidance pathways for treating neurodegenerative diseases. Particular focus is placed on how neuronal guidance mechanisms control neuron-glia and neuroimmune interactions and modulate microglial function under physiological and pathological conditions. Specifically, we examine the crosstalk between neuronal guidance signaling and TREM2, a master regulator of microglial function, in the context of pathogenic protein aggregates. It is well-established that age is a major risk factor for neurodegeneration. Future research should address how aging and neuronal guidance signaling interact to influence an individual's susceptibility to various late-onset neurological diseases and how the progression of these diseases could be therapeutically blocked by targeting neuronal guidance pathways.

Icariin Supplementation Alleviates Cognitive Impairment Induced by d-Galactose via Modulation of the Gut-Brain Axis

Aging-related cognitive impairment seriously diminishes individuals' life quality. Icariin (ICA), a natural flavonoid separated from the herb Epimedium, is applied in the food industry to bolster immunity and cognitive function in Chinese culture, demonstrating considerable potential in alleviating aging-related cognitive impairment. However, the mechanisms by which ICA mitigates aging-related cognitive impairment have yet to be elucidated. In the study, an 8 week ICA administration strongly improved spatial learning and memory ability, reduced neural damage, and restored hippocampal mitochondrial ultrastructure in mice subjected to d-galactose (d-gal) induction. Mechanically, ICA alleviated colonic pathology and upregulated the expression of tight junction proteins. Moreover, ICA reshaped microbial composition, enriched short-chain fatty acid (SCFA)-producing genera, and upregulated microbiota-derived SCFA contents. Additionally, ICA enhanced cognitively related anti-inflammatory properties and antioxidant capacity. Intriguingly, SCFAs regulated by ICA mitigated mitochondrial dysfunction in vitro, namely, reversing inflammatory cytokine levels and antioxidant capacity, elevating ATP contents, and mitochondrial membrane potential. Furthermore, SCFAs regulated by ICA alleviated mitochondrial dysfunction by enhancing the oxidative phosphorylation pathway and upregulating mRNA expression of genes related to mitochondrial respiratory chain, thus improving cognitive function. The findings suggest that ICA alleviates d-gal-induced cognitive impairment via modulation of the gut-brain axis and mitochondrial function. The investigation underscores the potential therapeutic benefits of incorporating an ICA-enriched diet for cognitive enhancement.

Mitochondrial Alterations in Alzheimer's Disease: Insight from the 5xFAD Mouse Model

Mitochondrial dysfunction is increasingly recognized as a key factor in Alzheimer's disease (AD) pathogenesis, but the precise relationship between mitochondrial dynamics and proteinopathies in AD remains unclear. This study investigates the role of mitochondrial dynamics and function in the hippocampal tissue and peripheral blood mononuclear cells (PBMCs) of 5xFAD transgenic mice, as a model of AD. The levels of mitochondrial fusion proteins OPA1 and MFN2 and fission proteins DRP1 and phospho-DRP1 (S616) at 3, 6, and 9 months of age were assessed. Western blot analysis revealed significantly lower levels of OPA1 and MFN2 in the hippocampus of 6- and 9-month-old transgenic (TG) 5xFAD mice compared to controls (CTR), while DRP1 and pDRP1 levels were increased in 9-month-old TG mice. Additionally, MFN2 were decreased in the PBMCs of 9-month-old TG mice, indicating systemic mitochondrial alterations. Ultrastructural analysis of hippocampal tissues showed substantial alterations in mitochondrial morphology, including abnormalities in size and shape, a preponderance of teardrop-shaped mitochondria, and alterations in the somatic mitochondria-ER complex. Notably, mitochondria-associated ER contact sites were more distant in TG mice, suggesting functional impairments. Flow cytometric measurements demonstrated decreased mitochondrial membrane potential and mass, along with increased superoxide production, in the PBMCs of TG mice, particularly at 9 months, highlighting compromised mitochondrial function. Levels of key mitochondrial proteins including VDAC, TOM2O, and mitophagy-related protein PINK1 levels altered in both central and peripheral tissue of TG mice. These findings suggest that mitochondrial dysfunction and altered dynamics are early events in AD development in 5xFAD mice, manifesting in both central and peripheral tissues, and support the notion that mitochondrial abnormalities are an integral component of AD pathology. These insights might lead to the development of targeted therapies that modulate mitochondrial dynamics and function to mitigate AD progression.

Proteomic signatures of corona and herpes viral antibodies identify IGDCC4 as a mediator of neurodegeneration

Mechanisms underlying the dynamic relationships of viral infections and neurodegeneration warrant examination. Using a community-based cohort of older adults, the current study characterized the neurocognitive (cognitive functioning, brain volumes, Alzheimer's disease positron emission tomography, and plasma biomarkers) and plasma proteomic (7268 proteins) profiles of four common coronavirus and six herpesvirus antibody titers. Genetic inference techniques demonstrated the associations between viral antibody titers and neurocognitive outcomes may be attributed to altered expression in a subset of mechanistically relevant proteins in plasma. One of these proteins, IGDCC4 (immunoglobulin superfamily deleted in colorectal cancer subclass member 4), was related to 20-year dementia risk, cognitive functioning, and amyloid-β positivity using data from two independent cohorts, while its plasma and intrathecal abundance were causally implicated in dementia risk and clinically relevant brain atrophy. Our findings illuminate the biological basis by which host immune responses to viruses may affect neurocognitive outcomes in older adults and identify IGDCC4 as an important molecular mediator of neurodegeneration.

Identification of Hub Genes and Pathways Associated with Ageing in Diabetic Encephalopathy Based on Transcriptome Analysis

This study aimed to identify key genes and pathways associated with ageing in diabetic encephalopathy (DE) through transcriptome analysis and to explore their roles and mechanisms in accelerating brain ageing in diabetes. We used db/db mice to establish a model of type 2 diabetes mellitus DE. Moreover, ribonucleic acid sequencing was performed on hippocampal tissue, and differentially expressed genes (DEGs) were analysed. Ageing-related DEGs (Ag-DEGs) were identified based on the GenAge and CellAge databases. A protein-protein interaction (PPI) network of Ag-DEGs was constructed using the Search Tool for the Retrieval of Interacting Genes/Proteins database, and hub genes were identified using the Molecular Complex Detection and CytoHubba plugins of Cytoscape. Finally, immune infiltration analysis was conducted based on transcriptome data to investigate the role of immune cells in diabetic brain ageing. A total of 98 Ag-DEGs were identified, primarily involved in hypoxia, tumour necrosis factor-alpha signalling via nuclear factor kappa B, apoptosis and P53 pathways. The PPI network analysis identified 14 hub genes: HDAC1, IGF2, EGR1, BCL2, FOS, ATM, EGF, PARP1, MAPK3, APOE, SOX2, CAV1, HSPA5 and NFKBIA. These genes play significant roles in apoptosis pathways in cancer, lipid metabolism, atherosclerosis and human immunodeficiency virus-1 infection. Immune infiltration analysis revealed significant differences in the distribution of natural killer cells, resting mast cells and plasma cells within the diabetic brain. This study identified Ag-DEGs and hub genes in a DE model, revealing potential mechanisms of diabetes-accelerated brain ageing. These findings provide new insights into the pathological mechanisms of diabetic brain ageing and may offer new targets for therapeutic interventions.

Engineering blood-brain barrier microphysiological systems to model Alzheimer's disease monocyte penetration and infiltration

Alzheimer's disease (AD) is a progressive and neurodegenerative disease, predominantly causing dementia. Despite increasing clinical evidence suggesting the involvement of peripheral immune cells such as monocytes in AD pathology, the dynamic penetration and infiltration of monocytes crossing blood-brain barrier (BBB) and inducing neuroinflammation is largely understudied in an AD brain. Herein, we engineer BBB-like microphysiological system (BBB-MPS) models for recapitulating the dynamic penetration and infiltration of monocytes in an AD patient's brain. Each BBB-MPS model can be engineered by integrating a functional BBB-like structure on a human cortical organoid using a 3D-printed device within a well of a plate. By coculturing these BBB-MPS models with monocytes from AD patients and age-matched healthy donors, we found that AD monocytes exhibit significantly greater BBB penetration and brain infiltration compared to age-matched control monocytes. Moreover, we also tested the interventions including Minocycline and Bindarit, and found they can effectively inhibit AD monocyte infiltration, subsequently reducing neuroinflammation and neuronal apoptosis. We believe these scalable and user-friendly BBB-MPS models may hold promising potential in modeling and advancing therapeutics for neurodegenerative and neuroinflammatory diseases.

The same but different: impact of animal facility sanitary status on a transgenic mouse model of Alzheimer's disease

The gut-brain axis has emerged as a key player in the regulation of brain function and cognitive health. Gut microbiota dysbiosis has been observed in preclinical models of Alzheimer's disease and patients. Manipulating the composition of the gut microbiota enhances or delays neuropathology and cognitive deficits in mouse models. Accordingly, the health status of the animal facility may strongly influence these outcomes. In the present study, we longitudinally analyzed the fecal microbiota composition and amyloid pathology of 5XFAD mice housed in a specific opportunistic pathogen-free (SOPF) and a conventional facility. The composition of the microbiota of 5XFAD mice after aging in conventional facility showed marked differences compared to WT littermates that were not observed when the mice were bred in SOPF facility. The development of amyloid pathology was also enhanced by conventional housing. We then transplanted fecal microbiota (FMT) from both sources into wild-type (WT) mice and measured memory performance, assessed in the novel object recognition test, in transplanted animals. Mice transplanted with microbiota from conventionally bred 5XFAD mice showed impaired memory performance, whereas FMT from mice housed in SOPF facility did not induce memory deficits in transplanted mice. Finally, 18 weeks of housing SOPF-born animals in a conventional facility resulted in the reappearance of specific microbiota compositions in 5XFAD vs WT mice. In conclusion, these results show a strong impact of housing conditions on microbiota-associated phenotypes and question the relevance of breeding preclinical models in specific pathogen-free (SPF) facilities.

IMPORTANCE

Housing conditions affect the composition of the gut microbiota. Gut microbiota of 6-month-old conventionally bred Alzheimer's mice is dysbiotic. Gut dysbiosis is absent in Alzheimer's mice housed in highly sanitized facilities. Transfer of fecal microbiota from conventionally bred mice affects cognition. Microbiota of mice housed in highly sanitized facilities has no effect on cognition.

Distinct systemic impacts of Aβ42 and Tau revealed by whole-organism snRNA-seq

Both neuronal and peripheral tissues become disrupted in Alzheimer's disease (AD). However, a comprehensive understanding of how AD impacts different tissues across the whole organism is lacking. Using Drosophila, we generated an AD Fly Cell Atlas (AD-FCA) based on whole-organism single-nucleus transcriptomes of 219 cell types from flies expressing AD-associated proteins, either human amyloid-β 42 peptide (Aβ42) or Tau, in neurons. We found that Aβ42 primarily affects the nervous system, including sensory neurons, while Tau induces accelerated aging in peripheral tissues. We identified a neuronal cluster enriched in Aβ42 flies, which has high lactate dehydrogenase (LDH) expression. This LDH-high cluster is conserved in 5XFAD mouse and human AD datasets. We found a conserved defect in fat metabolism from both fly and mouse tauopathy models. The AD-FCA offers new insights into how Aβ42 or Tau systemically and differentially affects a whole organism and provides a valuable resource for understanding brain-body communication in neurodegeneration.

Bacterial Extracellular Vesicles: Bridging Pathogen Biology and Therapeutic Innovation

The main role of bacterial extracellular vesicles (BEVs) has been associated with various processes such as intercellular communication and host-pathogen interactions. This comprehensive review explores the multifaceted functions of BEVs across different biological domains, emphasizing their dual nature as contributors to disease and potential vehicles for therapeutic intervention. We examine the intricate interactions of BEVs within bacterial communities and between bacteria and hosts, their involvement in disease development through cargo delivery mechanisms, and their beneficial impact on microbial ecology. The review also highlights BEVs' applications in biomedical field, where they are revolutionizing vaccine development, targeted drug delivery, and cancer therapy. By utilizing the inherent properties of BEVs for controlled drug release, targeted antigen delivery, and immune modulation, they offer a promising frontier in precision medicine. In addition, the diagnostic potential of BEVs is explored through their utility as biomarkers, providing valuable insights into disease states and treatment efficacy. Looking forward, this review underscores the challenges and opportunities in translating BEV research to clinical practice, promoting the need of standardized methods in BEV characterization and scaling up production. The diverse abilities of BEVs, ranging from contributing to pathogen virulence to driving therapeutic innovation, highlight their potential as a cornerstone in the future of biomedical advancements. STATEMENT OF SIGNIFICANCE: Bacterial extracellular vesicles (BEVs) are emerging as pivotal players in both pathogenesis and therapeutic innovation. This review explores their dual nature as agents of disease and as promising biomaterials for biomedical applications, and provides a comprehensive survey on their involvement in disease mechanisms and microbial ecology, and their potential in biomedical applications such as vaccine development, targeted drug delivery, cancer therapy, and diagnosis. It highlights the complex interactions of BEVs within bacterial communities and between bacteria and hosts. This review also addresses current advancements, challenges, and opportunities in translating BEV research into clinical practice. The insights presented here position BEVs as a cornerstone in the future of biomedical advancements, advocating for standardized methods in BEV characterization and scalable production techniques.

Peripheral innate immunophenotype in neurodegenerative disease: blood-based profiles and links to survival

The innate immune system plays an integral role in the progression of many neurodegenerative diseases. In addition to central innate immune cells (e.g., microglia), peripheral innate immune cells (e.g., blood monocytes, natural killer cells, and dendritic cells) may also differ in these conditions. However, the characterization of peripheral innate immune cell types across different neurodegenerative diseases remains incomplete. This study aimed to characterize peripheral innate immune profiles using flow cytometry for immunophenotyping of peripheral blood mononuclear cells in n = 148 people with Alzheimer's disease (AD), frontotemporal dementia (FTD), corticobasal syndrome (CBS), progressive supranuclear palsy (PSP), Lewy body dementia (LBD) as compared to n = 37 healthy controls. To compare groups, we used multivariate dissimilarity analysis and principal component analysis across 19 innate immune cell types. We identified pro-inflammatory profiles that significantly differ between patients with all-cause dementia and healthy controls, with some significant differences between patient groups. Regression analysis confirmed that time to death following the blood test correlated with the individuals' immune profile weighting, positively to TREM2+ and non-classical monocytes and negatively to classical monocytes. Taken together, these results describe transdiagnostic peripheral immune profiles and highlight the link between prognosis and the monocyte cellular subdivision and function (as measured by surface protein expression). The results suggest that blood-derived innate immune profiles can inform sub-populations of cells relevant for specific neurodegenerative diseases that are significantly linked to accelerated disease progression and worse survival outcomes across diagnoses. Blood-based innate immune profiles may contribute to enhanced precision medicine approaches in dementia, helping to identify and monitor therapeutic targets and stratify patients for candidate immunotherapies.

Alzheimer's Disease and Frontotemporal Dementia: A Review of Pathophysiology and Therapeutic Approaches

Alzheimer's disease (AD) is a devastating form of dementia, with the number of affected individuals rising sharply. The main hallmarks of the disease include amyloid-beta plaque deposits and neurofibrillary tangles consisting of hyperphosphorylated tau protein, besides other pathological features that contribute to the disease's complexity. The causes of sporadic AD are multifactorial and mostly age-related and involve risk factors such as diabetes and cardiovascular or cerebrovascular disorders. Frontotemporal dementia (FTD) is another type of dementia characterized by a spectrum of behaviors, memory, and motor abnormalities and associated with abnormal depositions of protein aggregation, including tau protein. Currently approved medications are symptomatic, and no disease-modifying therapy is available to halt the disease progression. Therefore, the development of multi-targeted therapeutic approaches could hold promise for the treatment of AD and other neurodegenerative disorders, including tauopathies. In this article, we will discuss the pathophysiology of AD and FTD, the proposed hypotheses, and current therapeutic approaches, highlighting the development of novel drug candidates and the progress of clinical trials in this field of research.

Microglia-targeting nanosystems that cooperatively deliver Chinese herbal ingredients alleviate behavioral and cognitive deficits in Alzheimer's disease model mice

The effective treatment of Alzheimer's disease (AD) is challenging because of its complex and controversial pathological mechanisms. Moreover, multiple barriers, such as the blood-brain barrier (BBB), reduce drug delivery efficiency. Microglia-related neuroinflammation has recently attracted increasing attention as a possible cause of AD and has become a novel therapeutic target. Therefore, overcoming the BBB and targeted delivery of anti-inflammatory agents to microglia seem to be effective practical strategies for treating AD. A large proportion of natural active extracts possess exceptional immunomodulating capabilities. In this study, the cooperative delivery of berberine (Ber) and palmatine (Pal) by transferrin-decorated extracellular vesicles (Tf-hEVs-Ber/Pal), which can cross the BBB and precisely target microglia, was performed. This nanosystem effectively cleared amyloid β-protein (Aβ) aggregates, significantly regulated the neuroinflammatory environment both in vitro and in vivo and markedly altered the behavior and improved the cognitive and learning abilities of AD model mice. The efficacy of a microglia-targeting combined therapeutic approach for AD was demonstrated, which broadens the potential application of Chinese herbal ingredients.

Analysis and interpretation of inflammatory fluid markers in Alzheimer's disease: a roadmap for standardization

Growing interest in the role of the immune response in Alzheimer's Disease and related dementias (ADRD) has led to widespread use of fluid inflammatory markers in research studies. To standardize the use and interpretation of inflammatory markers in AD research, we build upon prior guidelines to develop consensus statements and recommendations to advance application and interpretation of these markers. In this roadmap paper, we propose a glossary of terms related to the immune response in the context of biomarker discovery/validation, discuss current conceptualizations of inflammatory markers in research, and recommend best practices to address key knowledge gaps. We also provide consensus principles to summarize primary conceptual, methodological, and interpretative issues facing the field: (1) a single inflammatory marker is likely insufficient to describe an entire biological cascade, and multiple markers with similar or distinct functions should be simultaneously measured in a panel; (2) association studies in humans are insufficient to infer causal relationships or mechanisms; (3) neuroinflammation displays time-dependent and disease context-dependent patterns; (4) neuroinflammatory mechanisms should not be inferred based solely on blood inflammatory marker changes; and (5) standardized reporting of CSF inflammatory marker assay validation and performance will improve incorporation of inflammatory markers into the biological AD criteria.

Blood-brain barrier biomarkers modulate the associations of peripheral immunity with Alzheimer's disease

The association between peripheral immunity and Alzheimer's disease (AD) has been increasingly recognized, but the underlying mechanisms are still unclear. We used multiple linear regression models to explore the association between peripheral immune biomarkers / blood-brain barrier (BBB)-related biomarkers and AD biomarkers. And we used causal mediation analysis with 10,000 bootstrapped iterations to investigate the functions of BBB-related biomarkers in mediating the associations between peripheral immune biomarkers and AD pathology, cerebral atrophy degree, as well as cognitive function. A total of 543 participants (38.7% female, mean age of 74.8 years) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were involved. Neutrophils percent (NEU%), lymphocytes percent (LYM%), neutrophils / lymphocytes (NLR), and chemotactic factor-3 (CCL26) were significantly associated with cerebrospinal fluid (CSF) β-amyloid-42 (Aβ-42), phosphorylated-tau (P-tau), total tau (T-tau)/Aβ-42 and P-tau/Aβ-42, the associations of NEU% with AD pathology were mediated by CCL26 (proportion: 18-24%; p < 0.05). NEU%, LYM%, NLR, CCL26, CD40 and matrix metalloproteinase-10 (MMP10) were significantly associated with whole brain, hippocampal volume, middle temporal lobe (MTL) volume, and entorhinal cortex (EC) thickness, the associations of peripheral immune biomarkers with cerebral atrophy degree were mediated by BBB-related biomarkers (proportion: 7-17%; p < 0.05). NEU%, LYM%, NLR, CCL26, CD40 and MMP10 were significantly associated with global cognition, executive function, memory function, immediate recall, and delayed recall, the associations of peripheral immune biomarkers with cognitive function were mediated by BBB-related biomarkers (proportion: 9-24%; p < 0.05). This study suggests that peripheral immunity may influence AD through influencing BBB function, providing a more robust and comprehensive evidence chain for the potential role of inflammation in AD.

ASO-mediated knock-down of GPNMB in mutant-GRN and in Grn-deficient peripheral myeloid cells disrupts lysosomal function and immune responses

BACKGROUND

GPNMB has been discussed as a potential therapeutic target in GRN-mediated neurodegeneration, based on the observed reproducible upregulation in FTD-GRN cerebrospinal fluid (CSF) and post-mortem brain. However, the functional impacts of up-regulated GPNMB are currently unknown, and it is currently unclear if targeting GPNMB will be protective or deleterious. Increases in GPNMB seen in FTD-GRN are reproduced in brains of aged Grn-deficient mice. Importantly, although brains of young Grn-deficient mice do not exhibit upregulated Gpnmb expression, peripheral immune cells of these mice exhibit increased Gpnmb expression as young as 5-to-6 months, suggesting the effects of Grn-deficiency in the periphery proceed those in the brain. Grn-deficiency is known to alter peripheral immune cell function, including impaired autophagy and altered cytokine secretion. GPNMB has potential effects on these processes, but has never been studied in peripheral immune cells of patients or preclinical models. Informing the functional significance of GPNMB upregulation in Grn-deficient states in myeloid cells has potential to inform GPNMB as a therapeutic candidate.

METHODS

The effects of GPNMB knock-down via antisense oligonucleotide (ASO) were assessed in peripheral blood mononuclear cells (PBMCs) from 25 neurologically healthy controls (NHCs) and age- and sex-matched FTD-GRN patients, as well as peritoneal macrophages (pMacs) from progranulin-deficient (Grn -/-) and B6 mice. Lysosomal function, antigen presentation and MHC-II processing and recycling were assessed, as well as cytokine release and transcription.

RESULTS

ASO-mediated knock-down of GPNMB increased lysosomal burden and IL1β cytokine secretion in FTD-GRN carriers and NHCs monocytes. ASO-mediated knock-down of Gpnmb in Grn-deficient macrophages decreased lysosomal pan-cathepsin activity and protein degradation. In addition, ASO-mediated knock-down of Gpnmb increased MHC-II surface expression, which was driven by decreased MHC-II uptake and recycling, in macrophages from Grn-deficient females. Finally, ASO-mediated knock-down of Gpnmb dysregulated IFN γ -stimulated IL6 cytokine transcription and secretion by mouse macrophages due to the absence of regulatory actions of the Gpnmb extracellular fragment (ECF).

CONCLUSIONS

Our data herein reveal that GPNMB has a regulatory effect on multiple immune effector functions, including capping inflammation and immune responses in myeloid cells, potentially via secretion of its ECF. Therefore, in progranulin-deficient states, the marked upregulation in GPNMB transcript and protein may represent a compensatory mechanism to preserve lysosomal function in myeloid cells. These novel findings indicate that targeted depletion of GPNMB in FTD-GRN would not be a rational therapeutic strategy because it is likely to dysregulate important immune cell effector functions mediated by GPNMB. Specifically, our data indicate that therapeutic strategies inhibiting GPNMB levels and/or activity may worsen the effects of GRN deficiency.

Dietary salt, vascular dysfunction, and cognitive impairment

Excessive salt consumption is a major health problem worldwide leading to serious cardiovascular events including hypertension, heart disease, and stroke. Additionally, high-salt diet has been increasingly associated with cognitive impairment in animal models and late-life dementia in humans. High-salt consumption is harmful for the cerebral vasculature, disrupts blood supply to the brain, and could contribute to Alzheimer's disease pathology. Although animal models have advanced our understanding of the cellular and molecular mechanisms, additional studies are needed to further elucidate the effects of salt on brain function. Furthermore, the association between excessive salt intake and cognitive impairment will have to be more thoroughly investigated in humans. Since the harmful effects of salt on the brain are independent by its effect on blood pressure, in this review, I will specifically discuss the evidence, available in experimental models and humans, on the effects of salt on vascular and cognitive function in the absence of changes in blood pressure. Given the strong effects of salt on the function of immune cells, I will also discuss the evidence linking salt consumption to gut immunity dysregulation with particular attention to the ability of salt to disrupt T helper 17 (Th17) cell homeostasis. Lastly, I will briefly discuss the data implicating IL-17A, the major cytokine produced by Th17 cells, in vascular dysfunction and cognitive impairment.

Spatial transcriptomics of the aging mouse brain reveals origins of inflammation in the white matter

To systematically understand age-induced molecular changes, we performed spatial transcriptomics of young, middle-aged, and old mouse brains and identified seven transcriptionally distinct regions. All regions exhibited age-associated upregulation of inflammatory mRNAs and downregulation of mRNAs related to synaptic function. Notably, aging white matter fiber tracts showed the most prominent changes with pronounced effects in females. The inflammatory signatures indicated major ongoing events: microglia activation, astrogliosis, complement activation, and myeloid cell infiltration. Immunofluorescence and quantitative MRI analyses confirmed physical interaction of activated microglia with fiber tracts and concomitant reduction of myelin in old mice. In silico analyses identified potential transcription factors influencing these changes. Our study provides a resourceful dataset of spatially resolved transcriptomic features in the naturally aging murine brain encompassing three age groups and both sexes. The results link previous disjointed findings and provide a comprehensive overview of brain aging identifying fiber tracts as a focal point of inflammation.

Amyloid precursor protein and presenilin-1 knock-in immunodeficient mice exhibit intraneuronal Aβ pathology, microgliosis, and extensive neuronal loss

INTRODUCTION

Transgenic mice overexpressing familial Alzheimer's disease (AD) mutations (FAD) show non-physiological traits, and their immunocompetent backgrounds limit their use in AD immunotherapy research. Preclinical models that reflect human immune responses in AD are needed.

METHODS

Using CRISPR-Cas9, we developed single (NA) and double (NAPS) knock-in (KI) amyloid precursor protein (APP)KM670,671NL (Swedish) and presenilin 1 (PS 1)M146VFAD mutations on an immunodeficient NOG (NOD.Cg-PrkdcscidIl2rgtm1Sug/JicTac) background. The models were confirmed by Sanger sequencing and evaluated for AD-like pathology.

RESULTS

Both NA and NAPS mice developed pathology without overexpression artifacts. Mutation-induced upregulation of APP-CTF-β led to intraneuronal human amyloid beta (Aβ) (6E10) deposits and amyloid-associated microgliosis as early as 3 months, which increased with age. The addition of the PS 1M146V mutation doubled the amyloid load. The models displayed broad neuronal loss, resulting in brain atrophy in older mice.

DISCUSSION

These models replicate intraneuronal amyloid pathology and, with human immune reconstitution potential, enable novel studies of human immune responses in AD.

HIGHLIGHTS

A novel Alzheimer's disease (AD) knock-in (KI) mouse was developed and characterized on an immunodeficient NOG background. The model provides a platform for human immune studies and the evaluation of immunotherapies for AD. The KI mice demonstrate intraneuronal Aβ deposits and amyloid-associated microglial reactions. KI mice demonstrate extensive neuronal loss. Human immune reconstitution enables studies of infectious AD co-morbidities, such as the human immunodeficiency and herpes simplex viruses.

Associations between plasma complement C1q and cerebrospinal fluid biomarkers of Alzheimer's disease pathology in cognitively intact adults: The CABLE study

BackgroundC1q is a promoter of the classical pathway of complement and its massive expression may be associated with the development of Alzheimer's disease (AD). However, the relationships between C1q and the major pathological challenges, including amyloid-β (Aβ) and tau deposition, remain undetermined in the preclinical AD phase.ObjectiveThis study aims to investigate the connections between plasma C1q and CSF AD biomarkers.MethodsThe cognitively intact participants (N = 1264) from the Chinese Alzheimer's Biomarker and LifestylE (CABLE) study were categorized into four groups, including Stage 0 [normal Amyloid-β1-42 (Aβ1-42), Phosphorylated-tau (P-tau) and Total-tau (T-tau)], Stage 1 (abnormal Aβ1-42, but normal P-tau or T-tau), Stage 2 (abnormal Aβ1-42 and abnormal P-tau or T-tau), and suspected non-Alzheimer disease pathology (SNAP) (abnormal P-tau or T-tau, but normal amyloid levels). The changes in plasma C1q levels among these groups and the correlation between C1q levels and cerebrospinal fluid (CSF) AD biomarkers were performed.ResultsThe results demonstrated plasma C1q levels are lower in Stage 0 (p = 0.010) and SNAP (p < 0.001) compared with Stage 1. A significant association between C1q levels and CSF AD pathology, including Aβ1-42 (β = -0.143, p < 0.001), Aβ1-42/Aβ1-40 (β = -0.173, p < 0.001), P-tau/Aβ1-42 (β = 0.156, p < 0.001), and T-tau/Aβ1-42 (β = 0.130, p < 0.001) has been identified.ConclusionsThe current research elucidates a positive correlation between elevated plasma C1q levels and CSF Aβ pathology, with C1q amplifying concomitantly with the pathological and clinical progression of AD.

Immune modulation to treat Alzheimer's disease

Immune mechanisms play a fundamental role in Alzheimer's disease (AD) pathogenesis, suggesting that approaches which target immune cells and immunologically relevant molecules can offer therapeutic opportunities beyond the recently approved amyloid beta monoclonal therapies. In this review, we provide an overview of immunomodulatory therapeutics in development, including their preclinical evidence and clinical trial results. Along with detailing immune processes involved in AD pathogenesis and highlighting how these mechanisms can be therapeutically targeted to modify disease progression, we summarize knowledge gained from previous trials of immune-based interventions, and provide a series of recommendations for the development of future immunomodulatory therapeutics to treat AD.

Elucidating the role of peripheral monocyte nicotinic acetylcholine receptors and inflammation in cognitive outcomes in older adults

Nicotinic acetylcholine receptors (nAChRs) are important regulators of brain and immune function that play critical roles in the neuropathology and progression of Alzheimer's disease and related dementias (ADRD). However, quantifying nAChRs in the brain remains elusive, and little is known about peripheral measures of nAChR in older adults or their relationship to cognition. Here, we examined associations between nAChR expression and immunoregulatory function in peripheral blood monocytes and cognitive performance among 167 older adults (age 72.3 ± 7.6 years; 71% female). Penalized linear and logistic regression were used to identify nAChR-related features in classical, intermediate, and nonclassical monocytes, as well as immunophenotypes, clinical and sociodemographic factors, associated with cognitive status (Montreal Cognitive Assessment; MoCA). Intermediate monocytes had the highest expression of alpha-7 nAChRs and greater ex vivo inflammatory responses (83.7% TNF-ɑ+ cells) relative to classical (68.4%, d = 1.98, P < 0.001) or nonclassical monocytes (58.9%, d = 3.20, P < 0.001). Participants with mild cognitive impairment (MCI: N = 76) had higher soluble CD14 levels (1777 ± 377 pg/uL) and greater anticholinergic medication burden (ACB; mean = 1.76) than normocognitive participants (NC: N = 91; 1638 ± 352 pg/uL sCD14, t155 = 2.78, P = 0.006; mean ACB: 1.05, t143 = 3.13, P = 0.002). Multivariate regression models indicated that stronger nAChR-mediated immunoregulation in intermediate monocytes was associated with higher MoCA scores (beta = 0.13) and 14% lower odds of MCI, as well as lower ACB (beta = - 2.10; 95% CI - 4.14, - 0.61). This study demonstrates that peripheral monocytes exhibit subset-specific differences in nAChR phenotypes in older adults and provides preliminary evidence for their association with cognitive function and a potential mediating role between ACB and cognitive impairment.

Multi-omics analysis of druggable genes to facilitate Alzheimer's disease therapy: A multi-cohort machine learning study

BACKGROUND

The swift rise in the prevalence of Alzheimer's disease (AD) alongside its significant societal and economic impact has created a pressing demand for effective interventions and treatments. However, there are no available treatments that can modify the progression of the disease.

METHODS

Eight AD brain tissues datasets and three blood datasets were obtained. Consensus clustering was utilized as a method to discern the various subtypes of AD. Then, module genes were screened using weighted correlation network analysis (WGCNA). Furthermore, screening hub genes was conducted through machine-learning analyses. Finally, A comprehensive analysis using a systematic approach to druggable genome-wide Mendelian randomization (MR) was conducted.

RESULTS

Two AD subclasses were identified, namely cluster.A and cluster.B. The levels of gamma secretase activity, beta secretase activity, and amyloid-beta 42 were found to be significantly elevated in patients classified within cluster A when compared to those in cluster B. Furthermore, by utilizing the differentially expressed genes shared among these clusters, along with identifying druggable genes and applying WGCNA to these subtypes, we were able to develop a scoring system referred to as DG.score. This scoring system has demonstrated remarkable predictive capability for AD when evaluated against multiple datasets. Besides, A total of 30 distinct genes that may serve as potential drug targets for AD were identified across at least one of the datasets investigated, whether derived from brain samples or blood analyses. Among the identified genes, three specific candidates that are considered druggable (LIMK2, MAPK8, and NDUFV2) demonstrated significant expression levels in both blood and brain tissues. Furthermore, our research also revealed a potential association between the levels of LIMK2 and concentrations of CSF Aβ (OR 1.526 (1.155-2.018)), CSF p-tau (OR 1.106 (1.024-01.196)), and hippocampal size (OR 0.831 (0.702-0.948)).

CONCLUSIONS

This study provides a notable advancement to the existing literature by offering genetic evidence that underscores the potential therapeutic advantages of focusing on the druggable gene LIMK2 in the treatment of AD. This insight not only contributes to our understanding of AD but also guides future drug discovery efforts.

Associations of Frailty, Concerns About Falling, and Fall Risk in Community-Dwelling Older Adults in Orlando, Florida: A Preliminary Analysis

Objectives

This study examines relationships between frailty, concerns about falling (CaF), and fall risk in community-dwelling older adults (≥60 years old).

Methods

Frailty, CaF, and fall risk were cross-sectionally assessed using the FRAIL, short FES-I, and STEADI questionnaires in 178 participants. Spearman correlations, logistical regression, and ordinal regression analysis were performed.

Results

38.2% of participants were robust, 48.9% pre-frail, and 12.9% frail. Logistic regressions revealed that frail individuals were 91.4% more likely to have CaF compared to non-frail individuals, and individuals with lower fall risk were 5.7 times less likely to have CaF than those with no fall risk. Pre-frail individuals were more likely to have fall risk than non-frail individuals. Individuals with low CaF were 6 times less likely to have fall risk than those with high CaF. Ordinal logistic regressions revealed that for individuals with no CaF and no fall risk, the odds of being frail were 69.5% and 86.7% lower, respectively, than those with high CaF and high fall risk.

Conclusions

Frailty relationships with fall risk and CaF indicate the importance of addressing frailty to aid in fall prevention in older adults. Further, addressing the CaF mentality is important in fall prevention in older adults. ClinicalTrials.gov ID: NCT05778604.

Longitudinal and concurrent C-reactive protein and diet associations with cognitive function in the population-based Tromsø study

BackgroundImmune dysregulation has been implicated in Alzheimer's disease; however, precise mechanisms and timing have not been established.ObjectiveTo investigate the concurrent and longitudinal associations of serum C-reactive protein (CRP) and dietary inflammatory index (DII) with cognitive decline as observed in Alzheimer's disease.MethodsThe study was based on 7613 individuals who participated in Tromsø6 (2007-2008) and Tromsø7 (2015-2016). We analyzed the relationship between CRP levels, DII, and cognitive function cross-sectionally using linear regression. We used mediation analysis to examine if CRP mediates the effects of DII on cognitive function. Further, we related baseline serum CRP to cognitive function and to change in cognitive function after 7 years of follow up. We used linear mixed models to relate changes in CRP levels to changes in cognitive function measured at two time points with 7 years apart.ResultsBoth CRP level and DII were cross-sectionally inversely associated with cognitive function (psychomotor speed, executive function). There was no prospective relationship between CRP level at baseline and cognitive function after 7 years of follow up. Increase in CRP levels was associated with decrease in cognitive function (psychomotor speed, executive function, and verbal memory) observed between two measurements 7 years apart. The mediation model did not show convincing evidence of a mediating effect of CRP in the association between diet and cognitive function.ConclusionsAfter comprehensive analysis of associations between CRP, DII and cognitive function, we conclude that CRP is likely to reflect the changes in inflammatory environment occurring in parallel with cognitive decline.

Toxicological mechanisms of carbon polymers in accelerating cognitive decline in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is the primary cause of dementia and is emerging as a global threat to human health. Increased availability of processed food is identified as a crucial environmental risk factor underlying the prevalence of Alzheimer's disease. Carbon polymers (CPs), as neo-formed substances and ubiquitous in thermally processed foods, the relationship between them and AD onset is remains unclear.

OBJECTIVES

The effect of CPs on AD onset was examined and the toxicological mechanisms of prolonged exposure to CPs derived from thermal processed foods on AD progression were comprehensively investigated using a scopolamine-induced neuroinflammatory cell models and the transgenic APPswe/PSEN1dE9 (APP/PS1) AD mouse.

METHODS

The CPs were extracted from thermally processed foods and the effects of CPs exposure on oxidative stress in neuroinflammatory cells were evaluated using scopolamine-induced PC12 cells as a neuroinflammation model. Furthermore, APP/PS1 AD mice were used to validate the potential adverse impacts of prolonged exposure to CPs on AD progression through the Morris water maze and open field test. In addition, histopathological examination, including immunofluorescence, immunohistochemistry, Nissl staining, and H&E, of the brain tissue in AD mice after chronic CPs treatment was performed to elucidate the underlying risk of dietary exposure to CPs on AD progression.

RESULTS

Exposure to CPs enhanced oxidative damage in neuroinflammatory cells, as demonstrated by impaired mitochondrial function and activated NF-κB/MAPK signaling pathways. Further results from electron spin resonance substantiated the catalytic properties of CPs, which accelerated oxidative damage through promoting free radical generation. Using transgenic AD mice model, our findings also demonstrated that prolonged CPs exposure aggravated AD-associated pathology, as evidenced by increased amyloid-beta deposition and glial cell activation, ultimately accelerating cognitive decline.

CONCLUSION

These findings provide compelling evidence of the potential health risks associated with long-term dietary exposure to CPs and provide insight into the relationship between foodborne risk factors and neurodegenerative diseases.

Associations between neutrophil-lymphocyte ratio and risk of cognitive impairment among Chinese older adults

BACKGROUND

Associations between the neutrophil-lymphocyte ratio (NLR) and cognitive performance in older population are rarely reported. We investigated the associations between NLR and risk of cognitive impairment in Chinese community-dwelling older adults.

METHODS

Individuals aged ≥ 65 years from the 2011 and 2014 waves of the Chinese Longitudinal Healthy Longevity Survey were enrolled. We used the Chinese version of the Mini-Mental State Examination to evaluate cognitive function, with a score <18 indicating cognitive impairment. NLR was expressed as derived NLR (white blood cell count - lymphocyte count]/lymphocyte count). Logistic regression was used to evaluate the association between NLR levels and risk of cognitive impairment.

RESULTS

The study enrolled 2375 cognitively healthy participants and 838 with cognitive impairment. Significantly higher NLR values were noted in the latter than in the former group. In the cross-sectional analysis, NLR values in the highest than in the lowest quartile indicated significantly increased risk of cognitive impairment, after controlling for all confounding factors. During follow-up, 134 of the 1173 healthy participants at baseline developed cognitive impairment. NLR values in the highest two quartiles indicated higher risk of cognitive impairment than those in the lowest quartile. When NLR was classified into dichotomous groups, the risk of cognitive impairment was significantly higher in the high-inflammation than in the noninflammatory status group, regardless of the analysis used (cross-sectional or prospective).

CONCLUSIONS

Elevated NLR status is associated with increased risk of cognitive impairment in Chinese community-dwelling older adults.

Identification of biomarkers in Alzheimer's disease and COVID-19 by bioinformatics combining single-cell data analysis and machine learning algorithms

BACKGROUND

Since its emergence in 2019, COVID-19 has become a global epidemic. Several studies have suggested a link between Alzheimer's disease (AD) and COVID-19. However, there is little research into the mechanisms underlying these phenomena. Therefore, we conducted this study to identify key genes in COVID-19 associated with AD, and evaluate their correlation with immune cells characteristics and metabolic pathways.

METHODS

Transcriptome analyses were used to identify common biomolecular markers of AD and COVID-19. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed on gene chip datasets (GSE213313, GSE5281, and GSE63060) from AD and COVID-19 patients to identify genes associated with both conditions. Gene ontology (GO) enrichment analysis identified common molecular mechanisms. The core genes were identified using machine learning. Subsequently, we evaluated the relationship between these core genes and immune cells and metabolic pathways. Finally, our findings were validated through single-cell analysis.

RESULTS

The study identified 484 common differentially expressed genes (DEGs) by taking the intersection of genes between AD and COVID-19. The black module, containing 132 genes, showed the highest association between the two diseases according to WGCNA. GO enrichment analysis revealed that these genes mainly affect inflammation, cytokines, immune-related functions, and signaling pathways related to metal ions. Additionally, a machine learning approach identified eight core genes. We identified links between these genes and immune cells and also found a association between EIF3H and oxidative phosphorylation.

CONCLUSION

This study identifies shared genes, pathways, immune alterations, and metabolic changes potentially contributing to the pathogenesis of both COVID-19 and AD.

Immune Modulation in Alzheimer's Disease: From Pathogenesis to Immunotherapy

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the leading cause of dementia, affecting a significant proportion of the elderly population. AD is characterized by cognitive decline and functional impairments due to pathological hallmarks like amyloid β-peptide (Aβ) plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Microglial activation, chronic neuroinflammation, and disruptions in neuronal communication further exacerbate the disease. Emerging research suggests that immune modulation could play a key role in AD treatment given the significant involvement of neuroinflammatory processes. This review focuses on recent advancements in immunotherapy strategies aimed at modulating immune responses in AD, with a specific emphasis on microglial behavior, amyloid clearance, and tau pathology. By exploring these immunotherapeutic approaches, we aim to provide insights into their potential to alter disease progression and improve patient outcomes, contributing to the evolving landscape of AD treatment.

Rebalancing Immune Interactions within the Brain-Spleen Axis Mitigates Neuroinflammation in an Aging Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia worldwide, characterized by accumulation of amyloid-β protein and hyperphosphorylated tau protein in the brain. Neuroinflammation, resulting from chronic activation of brain-resident innate immune cells as well as enhanced peripheral leukocyte access across the blood-brain barrier, crucially affects AD progression. In this context, TNFSF10, a cytokine substantially expressed in the AD brain, has been shown to modulate both the innate and the adaptive branches of the immune response in AD-related neuroinflammation. In this study, we explored whether a TNFSF10-neutralizing treatment could represent a tool to re-balance the overall overshooting inflammatory response in a mouse model of AD. Specifically, 3xTg-AD mice were treated sub-chronically with an anti-TNFSF10 monoclonal antibody for three months, and were then sacrificed at 15 months. TNFSF10 neutralization reduced the expression of the inflammatory marker CD86, inversely related to levels of the anti-inflammatory marker CD206 in the brain of 3xTg-AD mice, suggesting a switch of microglia towards a neuroprotective phenotype. Similar results were observed in the splenic macrophage population. Moreover, flow cytometry revealed a significant decrease of CD4+CD25+FOXP3+ T regulatory cells as well as reduced number of CD11b+LY6Chigh proinflammatory monocytes in both the brain and the spleen of 3xTg-AD mice treated with anti-TNFSF10 monoclonal antibody. Finally, the treatment resulted in lower count of splenic CD4+ and CD8+ T cells expressing PD1. The data suggest that TNFSF10 system-targeted treatment effectively restrain overshooting central and peripheral inflammation by rebalancing the overall immune response, mitigating the progression of AD pathology.

Blood inflammation relates to neuroinflammation and survival in frontotemporal lobar degeneration

Neuroinflammation is an important pathogenic mechanism in many neurodegenerative diseases, including those caused by frontotemporal lobar degeneration. Post-mortem and in vivo imaging studies have shown brain inflammation early in these conditions, proportional to symptom severity and rate of progression. However, evidence for corresponding blood markers of inflammation and their relationships to central inflammation and clinical outcome are limited. There is a pressing need for such scalable, accessible and mechanistically relevant blood markers because these will reduce the time, risk and costs of experimental medicine trials. We therefore assessed inflammatory patterns of serum cytokines from 214 patients with clinical syndromes associated with frontotemporal lobar degeneration in comparison to healthy controls, including their correlation with brain regional microglial activation and disease progression. Serum assays used the MesoScale Discovery V-Plex-Human Cytokine 36 plex panel plus five additional cytokine assays. A subgroup of patients underwent 11C-PK11195 mitochondrial translocator protein PET imaging, as an index of microglial activation. A principal component analysis was used to reduce the dimensionality of cytokine data, excluding cytokines that were undetectable in >50% of participants. Frequentist and Bayesian analyses were performed on the principal components to compare each patient cohort with controls and test for associations with central inflammation, neurodegeneration-related plasma markers and survival. The first component identified by the principal component analysis (explaining 21.5% variance) was strongly loaded by pro-inflammatory cytokines, including TNF-α, TNF-R1, M-CSF, IL-17A, IL-12, IP-10 and IL-6. Individual scores of the component showed significant differences between each patient cohort and controls. The degree to which a patient expressed this peripheral inflammatory profile at baseline was correlated negatively with survival (higher inflammation, shorter survival), even when correcting for baseline clinical severity. Higher pro-inflammatory profile scores were associated with higher microglial activation in frontal and brainstem regions, as quantified with 11C-PK11195 mitochondrial translocator protein PET. A permutation-based canonical correlation analysis confirmed the association between the same cytokine-derived pattern and central inflammation across brain regions in a fully data-based manner. This data-driven approach identified a pro-inflammatory profile across the frontotemporal lobar degeneration clinical spectrum, which is associated with central neuroinflammation and worse clinical outcome. Blood-based markers of inflammation could increase the scalability and access to neuroinflammatory assessment of people with dementia, to facilitate clinical trials and experimental medicine studies.

Transcriptome analysis of early- and late-onset Alzheimer's disease in Korean cohorts

INTRODUCTION

The molecular mechanisms underlying early-onset Alzheimer's disease (EOAD) and late-onset Alzheimer's disease (LOAD) remain incompletely understood, particularly in Asian populations.

METHODS

RNA-sequencing was carried out on blood samples from 248 participants in the Seoul National University Bundang Hospital cohort to perform differential gene expression (DGE) and weighted gene co-expression network analysis. Findings were replicated in an independent Korean cohort (N = 275).

RESULTS

DGE analysis identified 18 and 88 dysregulated genes in EOAD and LOAD, respectively. Network analysis identified a LOAD-associated module showing a significant enrichment in pathways related to mitophagy, 5' adenosine monophosphate-activated protein kinase signaling, and ubiquitin-mediated proteolysis. In the replication cohort, downregulation of SMOX and PLVAP in LOAD was replicated, and the LOAD-associated module was highly preserved. In addition, SMOX and PLVAP were associated with brain amyloid beta deposition.

DISCUSSION

Our findings suggest distinct molecular signatures for EOAD and LOAD in a Korean population, providing deeper understanding of their diagnostic potential and molecular mechanisms.

HIGHLIGHTS

Analysis identified 18 and 88 dysregulated genes in early-onset Alzheimer's disease (EOAD) and late-onset Alzheimer's disease (LOAD), respectively. Expression levels of SMOX and PLVAP were downregulated in LOAD. Expression levels of SMOX and PLVAP were associated with brain amyloid beta deposition. Pathways including mitophagy and 5' adenosine monophosphate-activated protein kinase signaling were enriched in a LOAD module. A LOAD module was highly preserved across two independent cohorts.

Mechanisms of comorbidity between Alzheimer's disease and pain

Clinical studies have revealed a significant correlation between pain and neurodegenerative diseases, particularly Alzheimer's disease (AD). However, due to cognitive and speech impairments, AD patients, especially those in moderate to severe stages, are often overlooked in pain management. The challenges in obtaining pain-related information from this population exacerbate the issue. Although recent clinical research has increasingly recognized the comorbidity of AD and pain, the pathological alterations and interactive mechanisms underlying this relationship remain inadequately explored. This review provides a comprehensive analysis of the clinical features and pathological mechanisms of AD with and without pain comorbidity. It examines underlying processes, including neuroinflammation, peripheral-central immune interactions, and neurotransmitter dynamics. Furthermore, it highlights current pain assessment and management strategies in AD patients. By offering a theoretical framework, this review aims to support the development of effective pain management approaches and serve as a reference for clinical interventions targeting AD-associated pain. HIGHLIGHTS: The comorbidity between AD and CP encompasses multiple interrelated biological pathways, such as neurodegeneration and inflammatory responses. The damage to neurons and synapses in AD patients influences the brain regions responsible for processing pain, thereby reducing the pain response. Neuroinflammation plays a vital role in the development of both AD and CP. Enhanced inflammatory responses have an impact on the CNS and promote sensitization. Common neurotransmitter alterations exist in the comorbidity of AD and CP, influencing cognition, emotion, and pain perception.

Association of a multiplex immune marker panel with incident cognitive impairment and dementia: The Northern Manhattan Study

Objective

To determine whether a panel of immune markers adds significant information to known correlates of risk of dementia and cognitive impairment.

Background

The impact of immune mechanisms on dementia risk is incompletely characterized.

Design/methods

A subsample of the Northern Manhattan Study, a prospective cohort study in the racially/ethnically diverse population of New York City, underwent comprehensive neuropsychological testing up to three times, at approximately 5-year intervals. Cognitive outcomes were adjudicated as no cognitive impairment, mild cognitive impairment (MCI), or dementia. Immune markers were assessed using a multiplex immunoassay on plasma samples collected at the time of the first neuropsychological test. Least absolute shrinkage and selection operator (LASSO) techniques were employed to yield a panel of immune markers linearly related to the outcome of dementia/MCI vs. no cognitive impairment. Nested logistic regression models were run to determine the independent association of the immune marker panel with dementia/MCI after adjusting for other predictors of risk.

Results

Among 1179 participants (mean age 70.0 ± 8.9 years, 60% women, 68% Hispanic), immune markers improved model fit above demographic and vascular risk factors (p-value for likelihood ratio test <0.0001) as correlates of MCI/dementia. Individual immune markers found to be associated with dementia/MCI were C-X-C Motif Chemokine Ligand 9 (CXCL9) and C-C Motif Chemokine Ligand 2 (CCL2). The effect of the immune markers was comparable to traditional risk factors, with CCL2 (per SD) having almost the same effect as 1 year of aging and CXCL9 (per SD) showing approximately twice this magnitude.

Conclusion

Immune markers are associated with cognitive decline and dementia outcomes in a multi-ethnic cohort. More work is needed to further characterize these associations and determine therapeutic strategies. (Funded by the National Institute of Health/National Institute of Neurological Disorders and Stroke; grant number R01 29993 (Sacco/Elkind)).

Plasma proteomics for cognitive decline and dementia-A Southeast Asian cohort study

INTRODUCTION

The prognostic utility of plasma proteomics for cognitive decline and dementia in a Southeast Asian population characterized by high cerebrovascular disease (CeVD) burden is underexplored.

METHODS

We examined this in a Singaporean memory clinic cohort of 528 subjects (n = 300, CeVD; n = 167, incident cognitive decline) followed-up for 4 years.

RESULTS

Of 1441 plasma proteins surveyed, a 12-protein signature significantly predicted cognitive decline (q-value < .05). Sixteen diverse biological processes were implicated in cognitive decline. Ten proteins independently predicted incident dementia (q-value < .05). A unified prediction model combining plasma proteins with clinical risk factors increased the area under the curve for outcome prediction from 0.62 to 0.85. External validation in the cerebrospinal fluid proteome of an independent Caucasian cohort replicated four of the significantly predictive plasma markers for cognitive decline namely: GFAP, NEFL, AREG, and PPY.

DISCUSSION

The prognostic proteins prioritized in our study provide robust signals in two different biological matrices, representing potential mechanistic targets for dementia and cognitive decline.

HIGHLIGHTS

A total of 1441 plasma proteins were profiled in a Singaporean memory clinic cohort. We report prognostic plasma protein signatures for cognitive decline and dementia. External validation was performed in the cerebrospinal fluid proteome of a Caucasian cohort. A concordant proteomic signature was identified across both biofluids and cohorts. Further studies are needed to explore the therapeutic implications of these proteins for dementia.

Immune mechanisms and shared immune targets in neurodegenerative diseases

The immune system plays a major part in neurodegenerative diseases. In some, such as multiple sclerosis, it is the primary driver of the disease. In others, such as Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, it has an amplifying role. Immunotherapeutic approaches that target the adaptive and innate immune systems are being explored for the treatment of almost all neurological diseases, and the targets and approaches are often common across diseases. Microglia are the primary immune cells in the brain that contribute to disease pathogenesis, and are consequently a common immune target for therapy. Other therapeutic approaches target components of the peripheral immune system, such as regulatory T cells and monocytes, which in turn act within the CNS. This Review considers in detail how microglia, monocytes and T cells contribute to the pathogenesis of multiple sclerosis, Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, and their potential as shared therapeutic targets across these diseases. The microbiome is also highlighted as an emerging therapeutic target that indirectly modulates the immune system. Therapeutic approaches being developed to target immune function in neurodegenerative diseases are discussed, highlighting how immune-based approaches developed to treat one disease could be applicable to multiple other neurological diseases.

Blood levels of cytokines highlight the role of inflammation in Alzheimer's disease

Inflammation and angiogenesis have been defined as potential mechanisms associated with clinical progression from a cognitively normal state to Alzheimer's disease (AD). In this observational case-control study, we aimed to determine plasma levels of cytokines as indicators of inflammation involved in cognitive decline. We measured 30 plasma proteins in 49 controls (CTL), 36 individuals with mild cognitive impairment (MCI) and 52 patients diagnosed with probable AD. After applying strict filters for quantification limits, only 13 analytes were included in the analysis. Kruskal-Wallis tests showed significant differences between diagnostic groups for nine cytokines (IL-16, IL-7, VEGF, IL-8, eotaxin, MCP-1, MCP-4, MDC and TARC). Non-parametric MANCOVA showed that sex and diagnosis affected cytokine levels in the blood. To determine the sensitivity and specificity of the markers, we performed receiver operating characteristic (ROC) curve analysis. Only those analytes that showed an area under the curve (AUC) ≥ 0.70 were included in the multivariate logistic regression models to better understand the contribution of cytokines to clinical status. Three models: 1) CTL vs. AD; 2) CTL vs. MCI, and 3) MCI vs. AD were developed, with sex and age as covariates. In each model, two cytokines remained significantly different (model 1: IL-16 and MDC; model 2: eotaxin and MDC and model 3: IL-7 and VEGF). Taken together, this report identifies a set of plasma markers of inflammation and strengthens the role of glial biology in different clinical stages of AD.

Novel insights into the ROCK-JAK-STAT signaling pathway in upper respiratory tract infections and neurodegenerative diseases

Acute upper respiratory tract infections are a major public health issue, with uncontrolled inflammation triggered by upper respiratory viruses being a significant cause of patient deterioration or death. This study focuses on the Janus kinase-signal transducer and activator of transcription Rho-associated coiled-coil containing protein kinase (JAK-STAT-ROCK) signaling pathway, providing an in-depth analysis of the interplay between uncontrolled inflammation after upper respiratory tract infections and the development of neurodegenerative diseases. It offers a conceptual framework for understanding the lung-brain-related immune responses and potential interactions. The relationship between the ROCK-JAK-STAT signaling pathway and inflammatory immunity is a complex and multi-layered research area and exploring potential common targets could open new avenues for the prevention and treatment of related inflammation.

Brain inflammation co-localizes highly with tau in mild cognitive impairment due to early-onset Alzheimer's disease

Brain inflammation, with an increased density of microglia and macrophages, is an important component of Alzheimer's disease and a potential therapeutic target. However, it is incompletely characterized, particularly in patients whose disease begins before the age of 65 years and, thus, have few co-pathologies. Inflammation has been usefully imaged with translocator protein (TSPO) PET, but most inflammation PET tracers cannot image subjects with a low-binder TSPO rs6971 genotype. In an important development, participants with any TSPO genotype can be imaged with a novel tracer, 11C-ER176, that has a high binding potential and a more favourable metabolite profile than other TSPO tracers currently available. We applied 11C-ER176 to detect brain inflammation in mild cognitive impairment (MCI) caused by early-onset Alzheimer's disease. Furthermore, we sought to correlate the brain localization of inflammation, volume loss, elevated amyloid-β (Aβ)and tau. We studied brain inflammation in 25 patients with early-onset amnestic MCI (average age 59 ± 4.5 years, 10 female) and 23 healthy controls (average age 65 ± 6.0 years, 12 female), both groups with a similar proportion of all three TSPO-binding affinities. 11C-ER176 total distribution volume (VT), obtained with an arterial input function, was compared across patients and controls using voxel-wise and region-wise analyses. In addition to inflammation PET, most MCI patients had Aβ (n = 23) and tau PET (n = 21). For Aβ and tau tracers, standard uptake value ratios were calculated using cerebellar grey matter as region of reference. Regional correlations among the three tracers were determined. Data were corrected for partial volume effect. Cognitive performance was studied with standard neuropsychological tools. In MCI caused by early-onset Alzheimer's disease, there was inflammation in the default network, reaching statistical significance in precuneus and lateral temporal and parietal association cortex bilaterally, and in the right amygdala. Topographically, inflammation co-localized most strongly with tau (r = 0.63 ± 0.24). This correlation was higher than the co-localization of Aβ with tau (r = 0.55 ± 0.25) and of inflammation with Aβ (0.43 ± 0.22). Inflammation co-localized least with atrophy (-0.29 ± 0.26). These regional correlations could be detected in participants with any of the three rs6971 TSPO polymorphisms. Inflammation in Alzheimer's disease-related regions correlated with impaired cognitive scores. Our data highlight the importance of inflammation, a potential therapeutic target, in the Alzheimer's disease process. Furthermore, they support the notion that, as shown in experimental tissue and animal models, the propagation of tau in humans is associated with brain inflammation.

Transcriptomic predictors of rapid progression from mild cognitive impairment to Alzheimer's disease

BACKGROUND

Effective treatment for Alzheimer's disease (AD) remains an unmet need. Thus, identifying patients with mild cognitive impairment (MCI) who are at high-risk of progressing to AD is crucial for early intervention.

METHODS

Blood-based transcriptomics analyses were performed using a longitudinal study cohort to compare progressive MCI (P-MCI, n = 28), stable MCI (S-MCI, n = 39), and AD patients (n = 49). Statistical DESeq2 analysis and machine learning methods were employed to identify differentially expressed genes (DEGs) and develop prediction models.

RESULTS

We discovered a remarkable gender-specific difference in DEGs that distinguish P-MCI from S-MCI. Machine learning models achieved high accuracy in distinguishing P-MCI from S-MCI (AUC 0.93), AD from S-MCI (AUC 0.94), and AD from P-MCI (AUC 0.92). An 8-gene signature was identified for distinguishing P-MCI from S-MCI.

CONCLUSIONS

Blood-based transcriptomic biomarker signatures show great utility in identifying high-risk MCI patients, with mitochondrial processes emerging as a crucial contributor to AD progression.

Plasma proteomics identify biomarkers and undulating changes of brain aging

Proteomics enables the characterization of brain aging biomarkers and discernment of changes during brain aging. We leveraged multimodal brain imaging data from 10,949 healthy adults to estimate brain age gap (BAG), an indicator of brain aging. Proteome-wide association analysis across 4,696 participants of 2,922 proteins identified 13 significantly associated with BAG, implicating stress, regeneration and inflammation. Brevican (BCAN) (β = -0.838, P = 2.63 × 10-10) and growth differentiation factor 15 (β = 0.825, P = 3.48 × 10-11) showed the most significant, and multiple, associations with dementia, stroke and movement functions. Dysregulation of BCAN affected multiple cortical and subcortical structures. Mendelian randomization supported the causal association between BCAN and BAG. We revealed undulating changes in the plasma proteome across brain aging, and profiled brain age-related change peaks at 57, 70 and 78 years, implicating distinct biological pathways during brain aging. Our findings revealed the plasma proteomic landscape of brain aging and pinpointed biomarkers for brain disorders.

Peripheral Immune Cells Contribute to the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder with progressive memory and cognitive loss. Neuroinflammation is a central mechanism involved in the progression of AD. With the disruption of the blood-brain barrier (BBB), peripheral immune cells and inflammatory molecules enter into AD brain. However, the exact relationship between peripheral immune cells and AD remains unknown due to various challenges. This study aimed to investigate the potential causal association between peripheral immune cells and AD by using a two-sample Mendelian randomization (TSMR) analysis. We conducted a TSMR to decipher the causal relationship between AD and 731 types of peripheral immune cell parameters from the TBNK, regulatory T cell (Treg), myeloid cell, monocyte, maturation stages of T cell, dendritic cell (DC), and B cell panels.  Various analytical methods were employed, including inverse variance weighting (IVW), MR Egger, and weighted median methods. The Cochran's Q statistic, MR-Egger intercept, and MR-PRESSO tests were used to verify the heterogeneity and horizontal pleiotropy of the results. To further verify our results, we also conducted a replication analysis. The analysis identified CD33 on CD14 + monocyte (OR = 1.03; 95% CI, 1.01-1.04; p = 1.14E-04; adjust-p = 0.042) had an increased risk association for AD, which was verified by the replication study. CD33 on CD33dim HLA DR + CD11b- cell (OR = 1.02; 95% CI, 1.01-1.04; p = 2.87E-04; adjust-p = 0.035) had an increased risk association for AD, while secreting CD4 regulatory T cell %CD4 regulatory T cell (OR = 0.97; 95% CI, 0.96-0.99; p = 1.90E-04; adjust-p = 0.046) and CD25 on switched memory B cell (OR = 0.95; 95% CI, 0.92-0.98; p = 2.87E-04; adjust-p = 0.042) were discovered to be related to a lower risk of AD. However, the causal effect of these three immune cells on AD was insufficiently validated in the replication analysis. The MR analysis suggests a potential causal relationship between peripheral immune cells and the risk of AD. Further extensive research is needed on the specific role of peripheral immune cells in AD.

The Interplay Between Accumulation of Amyloid-Beta and Tau Proteins, PANoptosis, and Inflammation in Alzheimer's Disease

Alzheimer's disease (AD) is a common progressive neurodegenerative disorder, and the vast majority of cases occur in elderly patients. Recently, the accumulation of Aβ and tau proteins has drawn considerable attention in AD research. This review explores the multifaceted interactions between these proteins and their contribution to the pathological landscape of AD, encompassing synaptic dysfunction, neuroinflammation, and PANoptosis. PANoptosis is a collective term for programmed cell death (PCD) modalities that encompass elements of apoptosis, pyroptosis, and necroptosis. The accumulation of Aβ peptides and tau proteins, along with the immune response in brain cells, may trigger PANoptosis, thus advancing the progression of the disease. Recent advancements in molecular imaging and genetics have provided deeper insights into the interactions between Aβ peptides, tau proteins, and the immune response. The review also discusses the role of mitochondrial dysregulation in AD. The exploration of the interplay between neurodegeneration, immune responses, and cell death offers promising avenues for the development of innovative treatments.

Association of critically short telomeres with brain and blood markers of ageing and Alzheimer's disease in older adults

BACKGROUND

Accumulation of critically short telomeres (CST) is implicated in decreased tissular regenerative capacity and increased susceptibility to degenerative diseases such as Alzheimer's disease (AD). Telomere shortening has also been associated with age-related brain changes. However, it remains unclear whether CST accumulation is directly associated with AD markers or instead amplifies age-related effects, potentially increasing susceptibility of developing AD in cognitively healthy older adults.

METHODS

This cross-sectional study used baseline data of 129 community-dwelling cognitively healthy older adults from the Age-Well trial (NCT02977819), aged 65 years and older enrolled between 2016 and 2018, in France. Using linear regressions, we analyzed the relationship between an innovative marker of telomere shortening, the percentage of CST (%CST), structural, functional and molecular neuroimaging outcomes, and multiple blood-based biomarkers related to AD pathophysiology. The effect of apolipoprotein E ε4 genotype (APOE4) was assessed on these relationships using interaction analysis.

RESULTS

A higher %CST was associated with lower global kurtosis fractional anisotropy (β = -.230; P = .010), particularly in frontal and temporal regions. A higher %CST was also related to higher plasma levels of Neurofilament light chain (β = .195; P = .020) and a lower subiculum volume (β = -.206; P = .020), although these associations did not meet the threshold for multiple comparisons. %CST was not associated with AD-related neuroimaging markers, including the AD-sensitive gray matter pattern (β = -.060; P = .441), glucose metabolism pattern (β = -.099; P = .372), brain perfusion pattern (β = -.106; P = .694) or hippocampus volume (β = -.106; P = .194). In APOE4 carriers, higher %CST was associated with lower subiculum (β = -.423; P = 0.003), DG (β = -.410; P = 0.018) and CA1 volumes (β = -.373; P = 0.024), even though associations with DG and CA1 volumes did not survive multiple comparison.

CONCLUSIONS

Although an increase in %CST does not appear to be directly linked to the pathophysiology of AD in cognitively healthy older adults, it could heighten the susceptibility of APOE4 carriers to develop AD plausibly due to greater vulnerability to age-related effects. However, longitudinal studies would be necessary to determine whether %CST influences the development and progression of AD later in life.

Unraveling the Role of the Blood-Brain Barrier in the Pathophysiology of Depression: Recent Advances and Future Perspectives

Depression is a highly prevalent psychological disorder characterized by persistent dysphoria, psychomotor retardation, insomnia, anhedonia, suicidal ideation, and a remarkable decrease in overall well-being. Despite the prevalence of accessible antidepressant therapies, many individuals do not achieve substantial improvement. Understanding the multifactorial pathophysiology and the heterogeneous nature of the disorder could lead the way toward better outcomes. Recent findings have elucidated the substantial impact of compromised blood-brain barrier (BBB) integrity on the manifestation of depression. BBB functions as an indispensable defense mechanism, tightly overseeing the transport of molecules from the periphery to preserve the integrity of the brain parenchyma. The dysfunction of the BBB has been implicated in a multitude of neurological disorders, and its disruption and consequent brain alterations could potentially serve as important factors in the pathogenesis and progression of depression. In this review, we extensively examine the pathophysiological relevance of the BBB and delve into the specific modifications of its components that underlie the complexities of depression. A particular focus has been placed on examining the effects of peripheral inflammation on the BBB in depression and elucidating the intricate interactions between the gut, BBB, and brain. Furthermore, this review encompasses significant updates on the assessment of BBB integrity and permeability, providing a comprehensive overview of the topic. Finally, we outline the therapeutic relevance and strategies based on BBB in depression, including COVID-19-associated BBB disruption and neuropsychiatric implications. Understanding the comprehensive pathogenic cascade of depression is crucial for shaping the trajectory of future research endeavors.

Glymphatic system: a gateway for neuroinflammation

The glymphatic system is a relatively recently identified fluid exchange and transport system in the brain. Accumulating evidence indicates that glymphatic function is impaired not only in central nervous system disorders but also in systemic diseases. Systemic diseases can trigger the inflammatory responses in the central nervous system, occasionally leading to sustained inflammation and functional disturbance of the central nervous system. This review summarizes the current knowledge on the association between glymphatic dysfunction and central nervous system inflammation. In addition, we discuss the hypothesis that disease conditions initially associated with peripheral inflammation overwhelm the performance of the glymphatic system, thereby triggering central nervous system dysfunction, chronic neuroinflammation, and neurodegeneration. Future research investigating the role of the glymphatic system in neuroinflammation may offer innovative therapeutic approaches for central nervous system disorders.

Brain-immune interactions: implication for cognitive impairments in Alzheimer's disease and autoimmune disorders

Progressive memory loss and cognitive dysfunction, encompassing deficits in learning, memory, problem solving, spatial reasoning, and verbal expression, are characteristics of Alzheimer's disease and related dementia. A wealth of studies has described multiple roles of the immune system in the development or exacerbation of dementia. Individuals with autoimmune disorders can also develop cognitive dysfunction, a phenomenon termed "autoimmune dementia." Together, these findings underscore the pivotal role of the neuroimmune axis in both Alzheimer's disease and related dementia and autoimmune dementia. The dynamic interplay between adaptive and innate immunity, both in and outside the brain, significantly affects the etiology and progression of these conditions. Multidisciplinary research shows that cognitive dysfunction arises from a bidirectional relationship between the nervous and immune systems, though the specific mechanisms that drive cognitive impairments are not fully understood. Intriguingly, this reciprocal regulation occurs at multiple levels, where neuronal signals can modulate immune responses, and immune system-related processes can influence neuronal viability and function. In this review, we consider the implications of autoimmune responses in various autoimmune disorders and Alzheimer's disease and explore their effects on brain function. We also discuss the diverse cellular and molecular crosstalk between the brain and the immune system, as they may shed light on potential triggers of peripheral inflammation, their effect on the integrity of the blood-brain barrier, and brain function. Additionally, we assess challenges and possibilities associated with developing immune-based therapies for the treatment of cognitive decline.

The Neural Palette of Heme: Altered Heme Homeostasis Underlies Defective Neurotransmission, Increased Oxidative Stress, and Disease Pathogenesis

Heme, a complex iron-containing molecule, is traditionally recognized for its pivotal role in oxygen transport and cellular respiration. However, emerging research has illuminated its multifaceted functions in the nervous system, extending beyond its canonical roles. This review delves into the diverse roles of heme in the nervous system, highlighting its involvement in neural development, neurotransmission, and neuroprotection. We discuss the molecular mechanisms by which heme modulates neuronal activity and synaptic plasticity, emphasizing its influence on ion channels and neurotransmitter receptors. Additionally, the review explores the potential neuroprotective properties of heme, examining its role in mitigating oxidative stress, including mitochondrial oxidative stress, and its implications in neurodegenerative diseases. Furthermore, we address the pathological consequences of heme dysregulation, linking it to conditions such as Alzheimer's disease, Parkinson's disease, and traumatic brain injuries. By providing a comprehensive overview of heme's multifunctional roles in the nervous system, this review underscores its significance as a potential therapeutic target and diagnostic biomarker for various neurological disorders.

A Transcriptomics-Based Machine Learning Model Discriminating Mild Cognitive Impairment and the Prediction of Conversion to Alzheimer's Disease

The clinical spectrum of Alzheimer's disease (AD) ranges dynamically from asymptomatic and mild cognitive impairment (MCI) to mild, moderate, or severe AD. Although a few disease-modifying treatments, such as lecanemab and donanemab, have been developed, current therapies can only delay disease progression rather than halt it entirely. Therefore, the early detection of MCI and the identification of MCI patients at high risk of progression to AD remain urgent unmet needs in the super-aged era. This study utilized transcriptomics data from cognitively unimpaired (CU) individuals, MCI, and AD patients in the Alzheimer's Disease Neuroimaging Initiative (ADNI) cohort and leveraged machine learning models to identify biomarkers that differentiate MCI from CU and also distinguish AD from MCI individuals. Furthermore, Cox proportional hazards analysis was conducted to identify biomarkers predictive of the progression from MCI to AD. Our machine learning models identified a unique set of gene expression profiles capable of achieving an area under the curve (AUC) of 0.98 in distinguishing those with MCI from CU individuals. A subset of these biomarkers was also found to be significantly associated with the risk of progression from MCI to AD. A linear mixed model demonstrated that plasma tau phosphorylated at threonine 181 (pTau181) and neurofilament light chain (NFL) exhibit the prognostic value in predicting cognitive decline longitudinally. These findings underscore the potential of integrating machine learning (ML) with transcriptomic profiling in the early detection and prognostication of AD. This integrated approach could facilitate the development of novel diagnostic tools and therapeutic strategies aimed at delaying or preventing the onset of AD in at-risk individuals. Future studies should focus on validating these biomarkers in larger, independent cohorts and further investigating their roles in AD pathogenesis.

Identification of altered immune cell types and molecular mechanisms in Alzheimer's disease progression by single-cell RNA sequencing

Introduction

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by gradual loss of cognitive function. Understanding the molecular mechanisms is crucial for developing effective therapies.

Methods

Data from single-cell RNA sequencing (scRNA-seq) in the GSE181279 dataset and gene chips in the GSE63060 and GSE63061 datasets were collected and analyzed to identify immune cell types and differentially expressed genes. Cell communication, pseudotime trajectory, enrichment analysis, co- expression network, and short time-series expression miner were analyzed to identify disease-specific molecular and cellular mechanisms.

Results

We identified eight cell types (B cells, monocytes, natural killer cells, gamma-delta T cells, CD8+ T cells, Tem/Temra cytotoxic T cells, Tem/Trm cytotoxic T cells, and mucosal-associated invariant T cells) using scRNA-seq. AD samples were enriched in monocytes, CD8+ T cells, Tem/Temra cytotoxic T cells, and Tem/Trm cytotoxic T cells, whereas samples from healthy controls were enriched in natural killer and mucosal-associated invariant T cells. Five co-expression modules that were identified through weighted gene correlation network analysis were enriched in immune- inflammatory pathways. Candidate genes with higher area under the receiver operating characteristic curve values were screened, and the expression trend of Ubiquitin-Fold Modifier Conjugating Enzyme 1 (UFC1) gradually decreased from healthy controls to mild cognitive impairment and then to AD.

Conclusion

Our study suggests that peripheral immune cells may be a potential therapeutic target for AD. Candidate genes, particularly UFC1, may serve as potential biomarkers for progression of AD.

Changes in Gene Expression Profile with Age in SAMP8: Identifying Transcripts Involved in Cognitive Decline and Sporadic Alzheimer's Disease

Background: The senescence-accelerated mouse 8 (SAMP8) represents a model for Alzheimer's disease (AD) research because it exhibits age-related learning and memory impairments consistent with early onset and rapid progression of senescence. To identify transcriptional changes during AD progression, in this study, we analyzed and compared the gene expression profiles involved in molecular pathways of neurodegeneration and cognitive impairment in senescence-accelerated resistant 1 (SAMR1) and SAMP8 mice. Methods: In total, 48 female SAMR1 and SAMP8 mice were randomly divided into six groups (SAMR1 and SAMP8 at 3, 7, and 9 months of age). Microarray analysis of 22,000 genes was performed, followed by functional analysis using Gene Ontology (NCBI) and examination of altered molecular pathways using the KEGG (Kyoto Encyclopedia of Genes and Genomes). Results: SAMP8 mice had 2516 dysregulated transcripts at 3 months, 2549 transcripts at 7 months, and 2453 genes at 9 months compared to SAMR1 mice of the same age. These accounted for 11.3% of the total number. This showed that with age, the gene expression of downregulated transcripts increases, and that of over-expressed transcripts decreases. Most of these genes were involved in neurodegenerative metabolic pathways associated with Alzheimer's disease: apoptosis, inflammatory response, oxidative stress, and mitochondria. The qPCR results indicated that Ndufs4, TST/Rhodanese, Wnt3, and Sema6a expression was differentially expressed during aging. Conclusions: These results further revealed significant differences in gene expression profiles at different ages between SAMR1 and SAMP8 and showed alteration in genes involved in age-related cognitive decline and mitochondrial processes, demonstrating the relevance of the SAMP8 model as a model for sporadic AD.