Neuroimmune contributions to Alzheimer's disease: a focus on human data

Astrocytic-derived vascular remodeling factors are independently associated with blood brain barrier permeability in Alzheimer's disease

Astrocytes in Alzheimer's disease (AD) exert a pivotal role in the maintenance of blood-brain barrier (BBB) integrity essentially through structural support and release of soluble factors. This study provides new insights into the vascular remodeling processes occurring in AD, and reveals, in vivo, a pathological profile of astrocytic secretion involving Vascular Endothelial Growth Factor (VEGF), Matrix Metalloproteinases (MMP)-9, MMP-2 and Endothelin-1 (ET-1). Cerebrospinal fluid (CSF) levels of VEGF, MMP-2/-9 were lower in patients belonging to the AD continuum, compared to aged-matched controls. CSF levels of VEGF and ET-1 positively correlated with MMP-9 but negatively with MMP-2, suggesting a complex vascular remodeling process occurring in AD. Only MMP-2 levels were significantly associated with CSF AD biomarkers. Conversely, higher MMP-2 (β = 0.411, p < 0.001), ET-1 levels (β = 0.344, p < 0.001) and VEGF (β = 0.221, p = 0.022), were associated with higher BBB permeability. Astrocytic-derived vascular remodeling factors are altered in AD, disclosing the failure of important protective mechanisms which proceed independently alongside AD pathology.

Associations of infections and vaccines with Alzheimer's disease point to a role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been associated with Alzheimer's disease (AD) and related traits in various studies. This suggests that compromised immunity, rather than specific microbes, may play a role in AD by increasing an individual's vulnerability to various infections, which could contribute to neurodegeneration. If true, then vaccines that have heterologous effects on immunity, extending beyond protection against the targeted disease, may hold a potential for AD prevention.

METHODS

We evaluated the associations of common adult infections (herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses), and vaccinations against shingles and pneumonia, with the risks of AD and other dementias in a pseudorandomized sample of the Health and Retirement Study (HRS).

RESULTS

Shingles, pneumonia and mycoses, diagnosed between ages 65 and 75, were all associated with significantly increased risk of AD later in life, by 16 %-42 %. Pneumococcal and shingles vaccines administered between ages 65-75 were both associated with a significantly lower risk of AD, by 15 %-21 %. These effects became less pronounced when AD was combined with other dementias.

DISCUSSION

Our findings suggest that both the pneumococcal polysaccharide vaccine and the live attenuated zoster vaccine can offer significant protection against AD. It remains to be determined if non-live shingles vaccine has a similar beneficial effect on AD. This study also found significant associations of various infections with the risk of AD, but not with the risks of other dementias. This indicates that vulnerability to infections may play a more significant role in AD than in other types of dementia, which warrants further investigation.

Monocytes release cystatin F dimer to associate with Aβ and aggravate amyloid pathology and cognitive deficits in Alzheimer's disease

BACKGROUND

Understanding the molecular mechanisms of Alzheimer's disease (AD) has important clinical implications for guiding therapy. Impaired amyloid beta (Aβ) clearance is critical in the pathogenesis of sporadic AD, and blood monocytes play an important role in Aβ clearance in the periphery. However, the mechanism underlying the defective phagocytosis of Aβ by monocytes in AD remains unclear.

METHODS

Initially, we collected whole blood samples from sporadic AD patients and isolated the monocytes for RNA sequencing analysis. By establishing APP/PS1 transgenic model mice with monocyte-specific cystatin F overexpression, we assessed the influence of monocyte-derived cystatin F on AD development. We further used a nondenaturing gel to identify the structure of the secreted cystatin F in plasma. Flow cytometry, enzyme-linked immunosorbent assays and laser scanning confocal microscopy were used to analyse the internalization of Aβ by monocytes. Pull down assays, bimolecular fluorescence complementation assays and total internal reflection fluorescence microscopy were used to determine the interactions and potential interactional amino acids between the cystatin F protein and Aβ. Finally, the cystatin F protein was purified and injected via the tail vein into 5XFAD mice to assess AD pathology.

RESULTS

Our results demonstrated that the expression of the cystatin F protein was specifically increased in the monocytes of AD patients. Monocyte-derived cystatin F increased Aβ deposition and exacerbated cognitive deficits in APP/PS1 mice. Furthermore, secreted cystatin F in the plasma of AD patients has a dimeric structure that is closely related to clinical signs of AD. Moreover, we noted that the cystatin F dimer blocks the phagocytosis of Aβ by monocytes. Mechanistically, the cystatin F dimer physically interacts with Aβ to inhibit its recognition and internalization by monocytes through certain amino acid interactions between the cystatin F dimer and Aβ. We found that high levels of the cystatin F dimer protein in blood contributed to amyloid pathology and cognitive deficits as a risk factor in 5XFAD mice.

CONCLUSIONS

Our findings highlight that the cystatin F dimer plays a crucial role in regulating Aβ metabolism via its peripheral clearance pathway, providing us with a potential biomarker for diagnosis and potential target for therapeutic intervention.

Identification of immunogenic cell death-related genes involved in Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia worldwide, with recent studies highlighting the potential role of immunogenic cell death (ICD) in the pathogenesis of this neurodegenerative disorder. A total of 52 healthy controls and 64 patients with AD were included. Compared to the controls, the patients with AD exhibited 2392 differentially expressed genes (DEGs), of which 1015 and 1377 were upregulated and downregulated genes, respectively. Among them, nine common genes were identified by intersecting the AD-related module genes with the DEGs and ICD-associated genes. Gene ontology (GO)analysis further revealed "positive regulation of cytokine production" as the most significant term. Moreover, the enriched molecular functions were primarily related to the inflammatory body complex, while the overlapping genes were significantly enriched in lipopolysaccharide binding. Kyoto encyclopedia of genes and genomes (KEGG) analysis also indicated that these overlapping genes were mainly enriched in immunity, inflammation, and lipid metabolism pathways. Furthermore, the following four hub genes were detected using machine learning algorithms: P2RX7, HSP90AA1, NT5E, and NLRP3. These genes demonstrated significant differences in expression between the AD and healthy control groups (P < 0.05). Additionally, the area under the curve values of these four genes were all > 0.7, indicating their potential diagnostic value for AD. We further validated the protein levels of these four genes in the hippocampus of 3xTg-AD and C57BL/6J mice, showing P2RX7 and HSP90AA1 expression levels consistent with the previously analyzed trends. Finally, the single-sample gene set enrichment analysis (ssGSEA) algorithm provided additional evidence by demonstrating the crucial role of immune cell infiltration and its link with the hub genes in AD progression. Our study results suggest that ICD-mediated elevation of HSP90AA1 and P2RX7 levels and the resulting induction of tau hyperphosphorylation and neuroinflammation are vital in the AD pathogenic mechanism.

Cell States and Interactions of CD8 T Cells and Disease-Enriched Microglia in Human Brains with Alzheimer's Disease

Alzheimer's disease (AD) is a multi-stage neurodegenerative disorder characterized by beta-amyloid accumulation, hyperphosphorylated Tau deposits, neurodegeneration, neuroinflammation, and cognitive impairment. Recent studies implicate CD8 T cells as neuroimmune responders to the accumulation of AD pathology in the brain and potential contributors to toxic neuroinflammation. However, more evidence is needed to understand lymphocytes in disease, including their functional states, molecular mediators, and interacting cell types in diseased brain tissue. The scarcity of lymphocytes in brain tissue samples has limited the unbiased profiling of disease-associated cell types, cell states, drug targets, and relationships to common AD genetic risk variants based on transcriptomic analyses. However, using recent large-scale, high-quality single-nuclear sequencing datasets from over 84 Alzheimer's disease and control cases, we leverage single-nuclear RNAseq data from 800 lymphocytes collected from 70 individuals to complete unbiased molecular profiling. We demonstrate that effector memory CD8 T cells are the major lymphocyte subclass enriched in the brain tissues of individuals with AD dementia. We define disease-enriched interactions involving CD8 T cells and multiple brain cell subclasses including two distinct microglial disease states that correlate, respectively, to beta-amyloid and tau pathology. We find that beta-amyloid-associated microglia are a major hub of multicellular cross-talk gained in disease, including interactions involving both vulnerable neuronal subtypes and CD8 T cells. We reproduce prior reports that amyloid-response microglia are depleted in APOE4 carriers. Overall, these human-based studies provide additional support for the potential relevance of effector memory CD8 T cells as a lymphocyte population of interest in AD dementia and provide new candidate interacting partners and drug targets for further functional study.

A Stable Micellar Formulation of RAD001 for Intracerebroventricular Delivery and the Treatment of Alzheimer's Disease and Other Neurological Disorders

A large body of evidence, replicated in many mouse models of Alzheimer's disease (AD), supports the therapeutic efficacy of the oral mammalian target of rapamycin inhibitors (mTOR-Is). Our preliminary data show that intracerebroventricular (ICV) administration of everolimus (RAD001) soon after clinical onset greatly diminished cognitive impairment and the intracellular beta amyloid and neurofibrillary tangle load. However, RAD001 shows >90% degradation after 7 days in solution at body temperature, thus hampering the development of proper therapeutic regimens for patients. To overcome such a drawback, we developed a stable, liquid formulation of mTOR-Is by loading RAD001 into distearoylphosphatidylethanolamine-polyethylene glycol 2000 (DSPE-PEG2000) micelles using the thin layer evaporation method. The formulation showed efficient encapsulation of RAD001 and a homogeneous colloidal size and stabilised RAD001, with over 95% of activity preserved after 14 days at 37 °C with a total decay only occurring after 98 days. RAD001-loaded DSPE-PEG2000 micelles were unchanged when stored at 4 and 25 °C over the time period investigated. The obtained formulation may represent a suitable platform for expedited clinical translation and effective therapeutic regimens in AD and other neurological diseases.

Sepsis exacerbates Alzheimer's disease pathophysiology, modulates the gut microbiome, increases neuroinflammation and amyloid burden

While our understanding of the molecular biology of Alzheimer's disease (AD) has grown, the etiology of the disease, especially the involvement of peripheral infection, remains a challenge. In this study, we hypothesize that peripheral infection represents a risk factor for AD pathology. To test our hypothesis, APP/PS1 mice underwent cecal ligation and puncture (CLP) surgery to develop a polymicrobial infection or non-CLP surgery. Mice were euthanized at 3, 30, and 120 days after surgery to evaluate the inflammatory mediators, glial cell markers, amyloid burden, gut microbiome, gut morphology, and short-chain fatty acids (SCFAs) levels. The novel object recognition (NOR) task was performed 30 and 120 days after the surgery, and sepsis accelerated the cognitive decline in APP/PS1 mice at both time points. At 120 days, the insoluble Aβ increased in the sepsis group, and sepsis modulated the cytokines/chemokines, decreasing the cytokines associated with brain homeostasis IL-10 and IL-13 and increasing the eotaxin known to influence cognitive function. At 120 days, we found an increased density of IBA-1-positive microglia in the vicinity of Aβ dense-core plaques, compared with the control group confirming the predictable clustering of reactive glia around dense-core plaques within 15 μm near Aβ deposits in the brain. In the gut, sepsis negatively modulated the α- and β-diversity indices evaluated by 16S rRNA sequencing, decreased the levels of SCFAs, and significantly affected ileum and colon morphology in CLP mice. Our data suggest that sepsis-induced peripheral infection accelerates cognitive decline and AD pathology in the AD mouse model.

Single-cell RNA-seq reveals alterations in peripheral CX3CR1 and nonclassical monocytes in familial tauopathy

BACKGROUND

Emerging evidence from mouse models is beginning to elucidate the brain's immune response to tau pathology, but little is known about the nature of this response in humans. In addition, it remains unclear to what extent tau pathology and the local inflammatory response within the brain influence the broader immune system.

METHODS

To address these questions, we performed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) from carriers of pathogenic variants in MAPT, the gene encoding tau (n = 8), and healthy non-carrier controls (n = 8). Primary findings from our scRNA-seq analyses were confirmed and extended via flow cytometry, droplet digital (dd)PCR, and secondary analyses of publicly available transcriptomics datasets.

RESULTS

Analysis of ~ 181,000 individual PBMC transcriptomes demonstrated striking differential expression in monocytes and natural killer (NK) cells in MAPT pathogenic variant carriers. In particular, we observed a marked reduction in the expression of CX3CR1-the gene encoding the fractalkine receptor that is known to modulate tau pathology in mouse models-in monocytes and NK cells. We also observed a significant reduction in the abundance of nonclassical monocytes and dysregulated expression of nonclassical monocyte marker genes, including FCGR3A. Finally, we identified reductions in TMEM176A and TMEM176B, genes thought to be involved in the inflammatory response in human microglia but with unclear function in peripheral monocytes. We confirmed the reduction in nonclassical monocytes by flow cytometry and the differential expression of select biologically relevant genes dysregulated in our scRNA-seq data using ddPCR.

CONCLUSIONS

Our results suggest that human peripheral immune cell expression and abundance are modulated by tau-associated pathophysiologic changes. CX3CR1 and nonclassical monocytes in particular will be a focus of future work exploring the role of these peripheral signals in additional tau-associated neurodegenerative diseases.

Implication of tau propagation on neurodegeneration in Alzheimer's disease

Propagation of tau fibrils correlate closely with neurodegeneration and memory deficits seen during the progression of Alzheimer's disease (AD). Although it is not well-established what drives or attenuates tau spreading, new studies on human brain using positron emission tomography (PET) have shed light on how tau phosphorylation, genetic factors, and the initial epicenter of tau accumulation influence tau accumulation and propagation throughout the brain. Here, we review the latest PET studies performed across the entire AD continuum looking at the impact of amyloid load on tau pathology. We also explore the effects of structural, functional, and proximity connectivity on tau spreading in a stereotypical manner in the brain of AD patients. Since tau propagation can be quite heterogenous between individuals, we then consider how the speed and pattern of propagation are influenced by the starting localization of tau accumulation in connected brain regions. We provide an overview of some genetic variants that were shown to accelerate or slow down tau spreading. Finally, we discuss how phosphorylation of certain tau epitopes affect the spreading of tau fibrils. Since tau pathology is an early event in AD pathogenesis and is one of the best predictors of neurodegeneration and memory impairments, understanding the process by which tau spread from one brain region to another could pave the way to novel therapeutic avenues that are efficient during the early stages of the disease, before neurodegeneration induces permanent brain damage and severe memory loss.

The toxic metal hypothesis for neurological disorders

Multiple sclerosis and the major sporadic neurogenerative disorders, amyotrophic lateral sclerosis, Parkinson disease, and Alzheimer disease are considered to have both genetic and environmental components. Advances have been made in finding genetic predispositions to these disorders, but it has been difficult to pin down environmental agents that trigger them. Environmental toxic metals have been implicated in neurological disorders, since human exposure to toxic metals is common from anthropogenic and natural sources, and toxic metals have damaging properties that are suspected to underlie many of these disorders. Questions remain, however, as to how toxic metals enter the nervous system, if one or combinations of metals are sufficient to precipitate disease, and how toxic metal exposure results in different patterns of neuronal and white matter loss. The hypothesis presented here is that damage to selective locus ceruleus neurons from toxic metals causes dysfunction of the blood-brain barrier. This allows circulating toxicants to enter astrocytes, from where they are transferred to, and damage, oligodendrocytes, and neurons. The type of neurological disorder that arises depends on (i) which locus ceruleus neurons are damaged, (ii) genetic variants that give rise to susceptibility to toxic metal uptake, cytotoxicity, or clearance, (iii) the age, frequency, and duration of toxicant exposure, and (iv) the uptake of various mixtures of toxic metals. Evidence supporting this hypothesis is presented, concentrating on studies that have examined the distribution of toxic metals in the human nervous system. Clinicopathological features shared between neurological disorders are listed that can be linked to toxic metals. Details are provided on how the hypothesis applies to multiple sclerosis and the major neurodegenerative disorders. Further avenues to explore the toxic metal hypothesis for neurological disorders are suggested. In conclusion, environmental toxic metals may play a part in several common neurological disorders. While further evidence to support this hypothesis is needed, to protect the nervous system it would be prudent to take steps to reduce environmental toxic metal pollution from industrial, mining, and manufacturing sources, and from the burning of fossil fuels.

Impact of asthma on the brain: evidence from diffusion MRI, CSF biomarkers and cognitive decline

Chronic systemic inflammation increases the risk of neurodegeneration, but the mechanisms remain unclear. Part of the challenge in reaching a nuanced understanding is the presence of multiple risk factors that interact to potentiate adverse consequences. To address modifiable risk factors and mitigate downstream effects, it is necessary, although difficult, to tease apart the contribution of an individual risk factor by accounting for concurrent factors such as advanced age, cardiovascular risk, and genetic predisposition. Using a case-control design, we investigated the influence of asthma, a highly prevalent chronic inflammatory disease of the airways, on brain health in participants recruited to the Wisconsin Alzheimer's Disease Research Center (31 asthma patients, 186 non-asthma controls, aged 45-90 years, 62.2% female, 92.2% cognitively unimpaired), a sample enriched for parental history of Alzheimer's disease. Asthma status was determined using detailed prescription information. We employed multi-shell diffusion weighted imaging scans and the three-compartment neurite orientation dispersion and density imaging model to assess white and gray matter microstructure. We used cerebrospinal fluid biomarkers to examine evidence of Alzheimer's disease pathology, glial activation, neuroinflammation and neurodegeneration. We evaluated cognitive changes over time using a preclinical Alzheimer cognitive composite. Using permutation analysis of linear models, we examined the moderating influence of asthma on relationships between diffusion imaging metrics, CSF biomarkers, and cognitive decline, controlling for age, sex, and cognitive status. We ran additional models controlling for cardiovascular risk and genetic risk of Alzheimer's disease, defined as a carrier of at least one apolipoprotein E (APOE) ε4 allele. Relative to controls, greater Alzheimer's disease pathology (lower amyloid-β42/amyloid-β40, higher phosphorylated-tau-181) and synaptic degeneration (neurogranin) biomarker concentrations were associated with more adverse white matter metrics (e.g. lower neurite density, higher mean diffusivity) in patients with asthma. Higher concentrations of the pleiotropic cytokine IL-6 and the glial marker S100B were associated with more salubrious white matter metrics in asthma, but not in controls. The adverse effects of age on white matter integrity were accelerated in asthma. Finally, we found evidence that in asthma, relative to controls, deterioration in white and gray matter microstructure was associated with accelerated cognitive decline. Taken together, our findings suggest that asthma accelerates white and gray matter microstructural changes associated with aging and increasing neuropathology, that in turn, are associated with more rapid cognitive decline. Effective asthma control, on the other hand, may be protective and slow progression of cognitive symptoms.

Proteogenomic analysis of human cerebrospinal fluid identifies neurologically relevant regulation and informs causal proteins for Alzheimer's disease

The integration of quantitative trait loci (QTL) with disease genome-wide association studies (GWAS) has proven successful at prioritizing candidate genes at disease-associated loci. QTL mapping has mainly been focused on multi-tissue expression QTL or plasma protein QTL (pQTL). Here we generated the largest-to-date cerebrospinal fluid (CSF) pQTL atlas by analyzing 7,028 proteins in 3,107 samples. We identified 3,373 independent study-wide associations for 1,961 proteins, including 2,448 novel pQTLs of which 1,585 are unique to CSF, demonstrating unique genetic regulation of the CSF proteome. In addition to the established chr6p22.2-21.32 HLA region, we identified pleiotropic regions on chr3q28 near OSTN and chr19q13.32 near APOE that were enriched for neuron-specificity and neurological development. We also integrated this pQTL atlas with the latest Alzheimer's disease (AD) GWAS through PWAS, colocalization and Mendelian Randomization and identified 42 putative causal proteins for AD, 15 of which have drugs available. Finally, we developed a proteomics-based risk score for AD that outperforms genetics-based polygenic risk scores. These findings will be instrumental to further understand the biology and identify causal and druggable proteins for brain and neurological traits.

Genetic insights into the association between inflammatory bowel disease and Alzheimer's disease

Background

Myeloid cells, including monocytes, macrophages, microglia, dendritic cells and neutrophils are a part of innate immunity, playing a major role in orchestrating innate and adaptive immune responses. Microglia are the resident myeloid cells of the central nervous system, and many Alzheimer's disease (AD) risk loci are found in or near genes that are highly or sometimes uniquely expressed in myeloid cells. Similarly, inflammatory bowel disease (IBD) loci are also enriched for genes expressed by myeloid cells. However, the extent to which there is overlap between the effects of AD and IBD susceptibility loci in myeloid cells remains poorly described, and the substantial IBD genetic maps may help to accelerate AD research.

Methods

Here, we leveraged summary statistics from large-scale genome-wide association studies (GWAS) to investigate the causal effect of IBD (including ulcerative colitis and Crohn's disease) variants on AD and AD endophenotypes. Microglia and monocyte expression Quantitative Trait Locus (eQTLs) were used to examine the functional consequences of IBD and AD risk variants enrichment in two different myeloid cell subtypes.

Results

Our results showed that, while PTK2B is implicated in both diseases and both sets of risk loci are enriched for myeloid genes, AD and IBD susceptibility loci largely implicate distinct sets of genes and pathways. AD loci are significantly more enriched for microglial eQTLs than IBD. We also found that genetically determined IBD is associated with a lower risk of AD, which may driven by a negative effect on the accumulation of neurofibrillary tangles (beta=-1.04, p=0.013). In addition, IBD displayed a significant positive genetic correlation with psychiatric disorders and multiple sclerosis, while AD showed a significant positive genetic correlation with amyotrophic lateral sclerosis.

Conclusion

To our knowledge, this is the first study to systematically contrast the genetic association between IBD and AD, our findings highlight a possible genetically protective effect of IBD on AD even if the majority of effects on myeloid cell gene expression by the two sets of disease variants are distinct. Thus, IBD myeloid studies may not help to accelerate AD functional studies, but our observation reinforces the role of myeloid cells in the accumulation of tau proteinopathy and provides a new avenue for discovering a protective factor.

The emerging mechanism behind viral infections and extracellular vesicles hypotheses leading to neuroinflammation and Alzheimer's disease pathology

Despite decades of repeated and intense research, the etiology of sudden Alzheimer's disease (AD) symptoms is still unclear. AD progressive pathology mainly involves neuron damage, depositions of amyloid-beta (Aβ), and hyperphosphorylated tau protein. All these defects are manifested by exaggerated cytokine storm and neuroinflammation leading to irreversible brain damage in the long term. Despite the numerous risks and drawbacks associated with AD, it is believed that there is a hidden unknown causative and predisposing factors for AD. Extracellular vesicles (EVs) are small vesicles released by cells as a type of intercellular communication. Several pieces of evidence support the inclusion of viral components within EVs facilitating their penetration into the blood-brain barrier leading to neuroinflammation. In light of the SARS-CoV-19 pandemic and its related neurological complications, it is mandatory to highlight the possibility and viability of viral infections such as varicella-zoster virus (VZV) and herpes simplex virus (HSV) on the onset of AD. Herein, the author is investigating the potential role of VZV and HSV along with highlighting the suggested route of pathogenesis entry resulting in AD manifestations. Additionally, this review aims to summarize the role of EVs in mediating the central nervous system viral infections leading to AD.

The Vascular-Immune Hypothesis of Alzheimer's Disease

Alzheimer's disease (AD) is a devastating and irreversible neurodegenerative disorder with unknown etiology. While its cause is unclear, a number of theories have been proposed to explain the pathogenesis of AD. In large part, these have centered around potential causes for intracerebral accumulation of beta-amyloid (βA) and tau aggregates. Yet, persons with AD dementia often exhibit autopsy evidence of mixed brain pathologies including a myriad of vascular changes, vascular brain injuries, complex brain inflammation, and mixed protein inclusions in addition to hallmark neuropathologic lesions of AD, namely insoluble βA plaques and neurofibrillary tangles (NFTs). Epidemiological data demonstrate that overlapping lesions diminish the βA plaque and NFT threshold necessary to precipitate clinical dementia. Moreover, a subset of persons who exhibit AD pathology remain resilient to disease while other persons with clinically-defined AD dementia do not exhibit AD-defining neuropathologic lesions. It is increasingly recognized that AD is a pathologically heterogeneous and biologically multifactorial disease with uncharacterized biologic phenomena involved in its genesis and progression. Here, we review the literature with regard to neuropathologic criteria and incipient AD changes, and discuss converging concepts regarding vascular and immune factors in AD.

Clonal hematopoiesis, somatic mosaicism, and age-associated disease

Somatic mosaicism, the occurrence of multiple genetically distinct cell clones within the same tissue, is an evitable consequence of human aging. The hematopoietic system is no exception to this, where studies have revealed the presence of expanded blood cell clones carrying mutations in preleukemic driver genes and/or genetic alterations in chromosomes. This phenomenon is referred to as clonal hematopoiesis and is remarkably prevalent in elderly individuals. While clonal hematopoiesis represents an early step toward a hematological malignancy, most individuals will never develop blood cancer. Somewhat unexpectedly, epidemiological studies have found that clonal hematopoiesis is associated with an increase in the risk of all-cause mortality and age-related disease, particularly in the cardiovascular system. Studies using murine models of clonal hematopoiesis have begun to shed light on this relationship, suggesting that driver mutations in mature blood cells can causally contribute to aging and disease by augmenting inflammatory processes. Here we provide an up-to-date review of clonal hematopoiesis within the context of somatic mosaicism and aging and describe recent epidemiological studies that have reported associations with age-related disease. We will also discuss the experimental studies that have provided important mechanistic insight into how driver mutations promote age-related disease and how this knowledge could be leveraged to treat individuals with clonal hematopoiesis.

Chemotherapy promotes astrocytic response to Aβ deposition, but not Aβ levels, in a mouse model of amyloid and APOE

Many cancer survivors experience cancer-related cognitive impairment (CRCI), which is characterized by problems of attention, working memory, and executive function following chemotherapy and/or hormonal treatment. APOE4, the strongest genetic risk factor for Alzheimer's Disease (AD), is also a risk factor for CRCI, especially among survivors exposed to chemotherapy. We explored whether the effects of APOE genotype to chemotherapy were associated with an increase in AD pathological processes, using a mouse model of amyloid (5XFAD) along with the E3 or E4 alleles of human APOE (E3FAD and E4FAD). Six-month-old female E3FAD mice (control n = 5, treated n = 5) and E4FAD (control n = 6, treated n = 6) were treated with two doses of doxorubicin (total 10 mg/kg) or DMSO vehicle. After six weeks, mice were euthanized and brains were analyzed by immunohistochemistry and biochemical assays. Doxorubicin-treated mice had the same level of Aβ in the brain as control mice, as measured by 6E10 immunohistochemistry, Aβ40 and Aβ42 ELISAs, and plaque morphologies. Doxorubicin significantly increased the level of the astrocytic response to Aβ deposits, which was independent of APOE genotype; no effects of doxorubicin were observed on the microglial responses. These data are consistent with a model in which the effects of doxorubicin on risk of CRCI are unrelated amyloid accumulation, but possibly related to glial responses to damage.

Patient-specific monocyte-derived microglia as a screening tool for neurodegenerative diseases

Microglia, the main driver of neuroinflammation, play a central role in the initiation and exacerbation of various neurodegenerative diseases and are now considered a promising therapeutic target. Previous studies on in vitro human microglia and in vivo rodent models lacked scalability, consistency, or physiological relevance, which deterred successful therapeutic outcomes for the past decade. Here we review human blood monocyte-derived microglia-like cells as a robust and consistent approach to generate a patient-specific microglia-like model that can be used in extensive cohort studies for drug testing. We will highlight the strength and applicability of human blood monocyte-derived microglia-like cells to increase translational outcomes by reviewing the advantages of human blood monocyte-derived microglia-like cells in addressing patient heterogeneity and stratification, the basis of personalized medicine.

Glycyrrhizin and boswellic acids, the golden nutraceuticals: multitargeting for treatment of mild-moderate COVID-19 and prevention of post-COVID cognitive impairment

Breakthrough infections have been reported in fully vaccinated persons. Furthermore, rebound symptoms have been reported following the new FDA granted emergency use to combat SARS-CoV-2. Glycyrrhizin (GR) and boswellic acids (BAs) combination has been shown to have highly successful actions against COVID-19 in our recent clinical trial. However, the study is limited by the small sample size, and therefore, the aim of this article is to comprehensively evaluate recent evidence on the efficacy of GR and BAs in preventing the development of COVID-19 in patients with mild and moderate infections and in preventing post-COVID-19 cognitive impairment, which is the most important symptom after recovery from Covid-19 disease. We have reviewed and discussed information published since the outbreak of the COVID-19 pandemic until July 2022 on preclinical (in vivo, in vivo and bioinformatics) and clinical studies related to the antiviral, anti-inflammatory and immunomodulatory activity of Gr and BAs. Sixteen studies were performed to determine the efficacy of GR against SARS-CoV-2. Ten studies were used primarily for in vitro and in vivo assays and six used molecular docking studies. However, the antiviral activity of BAs against SARS-CoV-2 was determined in only five studies using molecular modeling and bioinformatics. All these studies confirmed that GR n and BAs have strong antiviral activity and can be used as a therapeutic agent for COVID-19 and as a protective agent against SARS-CoV-2. They may act by inhibiting the main protease SARS-CoV-2 (Mpro) responsible for replication and blocking spike protein-mediated cell entry. Only seven rigorously designed clinical trials regarding the usefulness of GR, BAs or their combinations in the treatment of COVID-19 have been published as of July 2022. Although there is no clinical study regarding the treatment of cognitive impairment after COVID-19 that has been published so far, several preclinical and clinical studies have demonstrated the potential effect of GR and BAs in the prevention and treatment of cognitive impairment by inhibiting the activity of several molecules that activate inflammatory signaling pathway. In conclusion, the findings of our study documented the beneficial use of GR and BAs to treat SARS-CoV-2 and its variants and prevent post-COVID cognitive impairment. However, it warrants further studies with a larger randomized sample size to ensure that the studies have sufficient evidence of benefits against COVID-19 and post-COVID-19 symptoms.

Neuro-immune interactions at single-cell resolution in neurodevelopmental, infectious, and neurodegenerative diseases

Recent technological advance in single-cell and single-nucleus transcriptomics has made it possible to generate an unprecedentedly detailed landscape of neuro-immune interactions in healthy and diseased brains. In this review, we overview the recent literature that catalogs single-cell-level gene expression in brains with signs of inflammation, focusing on maternal immune activation, viral infection, and auto-immune diseases. The literature also includes a series of papers that provide strong evidence for immunological contributions to neurodegenerative diseases, which, in a strict sense, are not considered neuroinflammatory. To help with the discussion, we present a diagram of experimental and analytical flows in the single-cell analysis of the brain. We also discuss the recurring themes of neuro-immune interactions and suggest future research directions.