Blood cell-produced amyloid-β induces cerebral Alzheimer-type pathologies and behavioral deficits

Extracellular vesicles from hiPSC-derived NSCs protect human neurons against Aβ-42 oligomers induced neurodegeneration, mitochondrial dysfunction and tau phosphorylation

BACKGROUND

Alzheimer's disease (AD) is characterized by the accumulation of amyloid beta-42 (Aβ-42) in the brain, causing various adverse effects. Thus, therapies that reduce Aβ-42 toxicity in AD are of great interest. One promising approach is to use extracellular vesicles from human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSC-EVs) because they carry multiple therapeutic miRNAs and proteins capable of protecting neurons against Aβ-42-induced toxicity. Therefore, this in vitro study investigated the proficiency of hiPSC-NSC-EVs to protect human neurons from Aβ-42 oligomers (Aβ-42o) induced neurodegeneration.

METHODS

We isolated hiPSC-NSC-EVs using chromatographic methods and characterized their size, ultrastructure, expression of EV-specific markers and proficiency in getting incorporated into mature human neurons. Next, mature human neurons differentiated from two different hiPSC lines were exposed to 1 µM Aβ-42o alone or with varying concentrations of hiPSC-NSC-EVs. The protective effects of hiPSC-NSC-EVs against Aβ-42o-induced neurodegeneration, oxidative stress, mitochondrial dysfunction, impaired autophagy, and tau phosphorylation were ascertained using multiple measures and one-way ANOVA with Newman-Keuls multiple comparisons post hoc tests.

RESULTS

A significant neurodegeneration was observed when human neurons were exposed to Aβ-42o alone. Neurodegeneration was associated with (1) elevated levels of reactive oxygen species (ROS), mitochondrial superoxide, malondialdehyde (MDA) and protein carbonyls (PCs), (2) increased expression of proapoptotic Bax and Bad genes and proteins, and genes encoding mitochondrial complex proteins, (3) diminished mitochondrial membrane potential and mitochondria, (4) reduced expression of the antiapoptotic gene and protein Bcl-2, and autophagy-related proteins, and (5) increased phosphorylation of tau. However, the addition of an optimal dose of hiPSC-NSC-EVs (6 × 109 EVs) to human neuronal cultures exposed to Aβ-42o significantly reduced the extent of neurodegeneration, along with diminished levels of ROS, superoxide, MDA and PCs, normalized expressions of Bax, Bad, and Bcl-2, and autophagy-related proteins, higher mitochondrial membrane potential and mitochondria, enhanced expression of genes linked to mitochondrial complex proteins, and reduced tau phosphorylation.

CONCLUSIONS

An optimal dose of hiPSC-NSC-EVs could significantly decrease the degeneration of human neurons induced by Aβ-42o. The results support further research into the effectiveness of hiPSC-NSC-EVs in AD, particularly their proficiency in preserving neurons and slowing disease progression.

Mechanisms mediating effects of cardiotonic steroids in mammalian blood cells

Cardiotonic steroids (CTSs) were known as steroidal plant compounds that exert cellular effects by the binding to Na,K-ATPase. Earlier, plant (exogenous) CTSs were used to treat chronic heart failure. By now, endogenous CTS have been identified in mammals, and their concentrations in the blood, normally in a subnanomolar range, are altered in numerous pathologies. This indicates their role as endogenous regulators of physiological processes. CTS transport occurs primarily in the blood, yet the CTS effects on blood cells remain poorly understood. This review summarizes the CTS effects on blood cells of animals and humans under normal and pathological conditions, and analyzes their action based on known mechanisms of action in mammalian cells. At high concentrations (greater than 10-9 M), CTS binding to Na,K-ATPase inhibits the enzyme, whereas lower concentrations of CTSs induce signaling cascades or activate the enzyme. All these mechanisms are shown to be present in blood cells. The particular CTS effect is determined by the CTS type, its concentration, the isoform composition of the catalytic α-subunit of Na,K-ATPase in the cell, and other cell features. It has been demonstrated that all blood cell types (erythrocytes, leukocytes, and platelets) expressed both ubiquitously distributed α1-isoform and tissue-specific α3-subunit, which exhibits a different ion and CTS affinity compared to α1. This results in a wide spectrum of blood cell responses to fluctuations in CTS levels in the blood. In particular, an increase in the level of endogenous CTSs by a more twofold is sufficient to induce a decline in the activity of erythrocyte Na,K-ATPase. The administration of exogenous CTSs is able to modulate the proinflammatory activity of leukocytes, which is attributed to the activation of signaling cascades, and to exert an influence on platelet activation. Hence, alterations of CTS levels in bloodstream significantly affect the functionality of blood cells, contributing to the organism's adaptive response. On top of this, a comparison of the effects of CTSs on human leukocytes and rodent leukocytes carrying the CTS-resistant α1-isoform often reveals opposite effects, thus indicating that rodents are an unsuitable model for studying CTS effects on these cells.

Could Blood Transfusion Increase the Risk of Alzheimer's Disease? A Narrative Review

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease, and its pathogenesis is complex. In addition to amyloid-β and phosphorylated tau, inflammation and microbial infections also play a role in the development of AD. Currently, there is no effective clinical intervention to cure AD or completely halt its progression. Blood transfusion, a critical life-saving medical procedure widely employed in modern healthcare, faces growing demand due to global population aging. However, whether blood transfusion could increase the risk of AD is still not clear. Aβ and tau play major roles in the pathogenesis of AD and may possess the potential for transmission through blood transfusion. Iron overload and chronic inflammation, which can independently influence AD pathogenesis, may result from repeated transfusions. Additionally, herpesvirus, known to accelerate AD progression, can also be potentially transmitted by blood transfusion. In this study, recent advances in the associations between blood transfusion and the occurrence and development of AD were reviewed, and whether blood transfusion could increase the risk of AD was discussed. Furthermore, the related proposals for blood management and future research were advanced to provide references for the prevention and control of AD.

Peripheral proteinopathy in neurodegenerative diseases

Proteinopathies in neurology typically refer to pathological changes in proteins associated with neurological diseases, such as the aggregation of amyloid β and Tau in Alzheimer's disease, α-synuclein in Parkinson's disease and multiple system atrophy, and TAR DNA-binding protein 43 in amyotrophic lateral sclerosis and frontotemporal dementia. Interestingly, these proteins are also commonly found in peripheral tissues, raising important questions about their roles in neurological disorders. Multiple studies have shown that peripherally derived pathological proteins not only travel to the brain through various routes, aggravating brain pathology, but also contribute significantly to peripheral dysfunction, highlighting their crucial impact on neurological diseases. Investigating how these peripherally derived proteins influence the progression of neurological disorders could open new horizons for achieving early diagnosis and treatment. This review summarizes the distribution, transportation pathways, and pathogenic mechanisms of several neurodegenerative disease-related pathological proteins in the periphery, proposing that targeting these peripheral pathological proteins could be a promising strategy for preventing and managing neurological diseases.

Trajectory of brain-derived amyloid beta in Alzheimer's disease: where is it coming from and where is it going?

Alzheimer's disease (AD) is a progressive neurological disorder that primarily impacts cognitive function. Currently there are no disease-modifying treatments to stop or slow its progression. Recent studies have found that several peripheral and systemic abnormalities are associated with AD, and our understanding of how these alterations contribute to AD is becoming more apparent. In this review, we focuse on amyloid‑beta (Aβ), a major hallmark of AD, summarizing recent findings on the source of brain-derived Aβ and discussing where and how the brain-derived Aβ is cleared in vivo. Based on these findings, we propose future strategies for AD prevention and treatment, from a novel perspective on Aβ metabolism.

Crosstalk between bone and brain in Alzheimer's disease: Mechanisms, applications, and perspectives

Alzheimer's disease (AD) is a neurodegenerative disease that involves multiple systems in the body. Numerous recent studies have revealed bidirectional crosstalk between the brain and bone, but the interaction between bone and brain in AD remains unclear. In this review, we summarize human studies of the association between bone and brain and provide an overview of their interactions and the underlying mechanisms in AD. We review the effects of AD on bone from the aspects of AD pathogenic proteins, AD risk genes, neurohormones, neuropeptides, neurotransmitters, brain-derived extracellular vesicles (EVs), and the autonomic nervous system. Correspondingly, we elucidate the underlying mechanisms of the involvement of bone in the pathogenesis of AD, including bone-derived hormones, bone marrow-derived cells, bone-derived EVs, and inflammation. On the basis of the crosstalk between bone and the brain, we propose potential strategies for the management of AD with the hope of offering novel perspectives on its prevention and treatment. HIGHLIGHTS: The pathogenesis of AD, along with its consequent changes in the brain, may involve disturbing bone homeostasis. Degenerative bone disorders may influence the progression of AD through a series of pathophysiological mechanisms. Therefore, relevant bone intervention strategies may be beneficial for the comprehensive management of AD.

Aβ-Aggregation-Generated Blue Autofluorescence Illuminates Senile Plaques as well as Complex Blood and Vascular Pathologies in Alzheimer's Disease

Senile plaque blue autofluorescence was discovered around 40 years ago, however, its impact on Alzheimer's disease (AD) pathology has not been fully examined. We analyzed senile plaques with immunohistochemistry and fluorescence imaging on AD brain sections and also Aβ aggregation in vitro. In DAPI or Hoechst staining, the nuclear blue fluorescence could only be correctly assigned after subtracting the blue plaque autofluorescence. The flower-like structures wrapping dense-core blue fluorescence formed by cathepsin D staining could not be considered central-nucleated neurons with defective lysosomes since there was no nuclear staining in the plaque core when the blue autofluorescence was subtracted. Both Aβ self-oligomers and Aβ/hemoglobin heterocomplexes generated blue autofluorescence. The Aβ amyloid blue autofluorescence not only labels senile plaques but also illustrates red cell aggregation, hemolysis, cerebral amyloid angiopathy, vascular plaques, vascular adhesions, and microaneurysms. In summary, we conclude that Aβ-aggregation-generated blue autofluorescence is an excellent multi-amyloidosis marker in Alzheimer's disease.

Research progress on humoral biomarkers of Alzheimer's disease: A review

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss. The main pathological features are neuronal fibrillary tangles caused by amyloid beta deposition and hyperphosphorylation of tau protein, accompanied by neuronal death and loss of synaptic structure. Early diagnosis is the key to the treatment of AD. It is known that some small molecular components are related to the pathogenesis of AD. This article will summarize the common AD biomarkers in cerebrospinal fluid and blood and analyze the current status of AD biomarkers and future research directions. This review summarizes the promising biomarkers for the diagnosis of AD in the last decade and describes their changes in AD body fluids. The diagnostic biomarkers related to AD were mainly distributed in cerebrospinal fluid and blood. Significant changes in these molecules can be detected in cerebrospinal fluid and blood, and they are correlated with AD severity. These humoral molecules have necessary relationship with AD and can be used as AD biomarkers to assist early diagnosis of AD.

Low-Density Lipoprotein Receptor-Related Protein 1 as a Potential Therapeutic Target in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease impacting the lives of millions of people worldwide. The formation of amyloid β (Aβ) plagues in the brain is the main pathological hallmark of AD. The Aβ deposits are formed due to the imbalance between the production and Aβ clearance in the brain and across the blood-brain barrier (BBB). In this respect, low-density lipoprotein receptor-related protein 1 (LRP1) plays a significant role by mediating both brain Aβ production and clearance. Due to its important role in AD pathogenesis, LRP1 is considered an attractive drug target for AD therapies. In the present review, we summarize the current knowledge about the role of LRP1 in AD pathogenesis as well as recent findings on changes in LRP1 expression and function in AD. Finally, we discuss the advances in utilizing LRP1 as a drug target for AD treatments as well as future perspectives on LRP1 research.

Extracellular Vesicles from hiPSC-derived NSCs Protect Human Neurons against Aβ-42 Oligomers Induced Neurodegeneration, Mitochondrial Dysfunction and Tau Phosphorylation

Background

One of the hallmarks of Alzheimer's disease (AD) is the buildup of amyloid beta-42 (Aβ-42) in the brain, which leads to various adverse effects. Therefore, therapeutic interventions proficient in reducing Aβ-42-induced toxicity in AD are of great interest. One promising approach is to use extracellular vesicles from human induced pluripotent stem cell-derived neural stem cells (hiPSC-NSC-EVs) because they carry multiple therapeutic miRNAs and proteins capable of protecting neurons against Aβ-42-induced pathological changes. Therefore, this in vitro study investigated the proficiency of hiPSC-NSC-EVs to protect human neurons derived from two distinct hiPSC lines from Aβ-42o-induced neurodegeneration.

Methods

We isolated hiPSC-NSC-EVs using chromatographic methods and characterized their size, ultrastructure, expression of EV-specific markers and proficiency in getting incorporated into mature human neurons. Next, mature human neurons differentiated from two different hiPSC lines were exposed to 1 µM Aβ-42 oligomers (Aβ-42o) alone or with varying concentrations of hiPSC-NSC-EVs. The protective effects of hiPSC-NSC-EVs against Aβ-42o-induced neurodegeneration, increased oxidative stress, mitochondrial dysfunction, impaired autophagy, and tau phosphorylation were ascertained using multiple measures and one-way ANOVA with Newman-Keuls multiple comparisons post hoc tests.

Results

Significant neurodegeneration was observed when human neurons were exposed to Aβ-42o alone. Notably, neurodegeneration was associated with elevated levels of oxidative stress markers malondialdehyde (MDA) and protein carbonyls (PCs), increased expression of proapoptotic Bax and Bad genes and proteins, reduced expression of the antiapoptotic gene and protein Bcl-2, increased expression of genes encoding mitochondrial complex proteins, decreased expression of autophagy-related proteins Beclin-1 and microtubule-associated protein 1 light chain 3B, and increased phosphorylation of tau. However, the addition of an optimal dose of hiPSC-NSC-EVs (6 x 10 9 EVs) to human neuronal cultures exposed to Aβ-42o significantly reduced the extent of neurodegeneration, along with diminished levels of MDA and PCs, normalized expressions of Bax, Bad, and Bcl-2, and genes linked to mitochondrial complex proteins, and reduced tau phosphorylation.

Conclusions

The findings demonstrate that an optimal dose of hiPSC-NSC-EVs could significantly decrease the degeneration of human neurons induced by Aβ-42o. The results also support further research into the effectiveness of hiPSC-NSC-EVs in AD, particularly their proficiency in preserving neurons and slowing disease progression.

Assessment of brain-derived extracellular vesicle enrichment for blood biomarker analysis in age-related neurodegenerative diseases: An international overview

INTRODUCTION

Brain-derived extracellular vesicles (BEVs) in blood allows for minimally-invasive investigations of central nervous system (CNS) -specific markers of age-related neurodegenerative diseases (NDDs). Polymer-based EV- and immunoprecipitation (IP)-based BEV-enrichment protocols from blood have gained popularity. We systematically investigated protocol consistency across studies, and determined CNS-specificity of proteins associated with these protocols.

METHODS

NDD articles investigating BEVs in blood using polymer-based and/or IP-based BEV enrichment protocols were systematically identified, and protocols compared. Proteins used for BEV-enrichment and/or post-enrichment were assessed for CNS- and brain-cell-type-specificity, extracellular domains (ECD+), and presence in EV-databases.

RESULTS

A total of 82.1% of studies used polymer-based (ExoQuick) EV-enrichment, and 92.3% used L1CAM for IP-based BEV-enrichment. Centrifugation times differed across studies. A total of 26.8% of 82 proteins systematically identified were CNS-specific: 50% ECD+, 77.3% were listed in EV-databases.

CONCLUSIONS

We identified protocol steps requiring standardization, and recommend additional CNS-specific proteins that can be used for BEV-enrichment or as BEV-biomarkers.

HIGHLIGHTS

Across NDDs, we identified protocols commonly used for EV/BEV enrichment from blood. We identified protocol steps showing variability that require harmonization. We assessed CNS-specificity of proteins used for BEV-enrichment or found in BEV cargo. CNS-specific EV proteins with ECD+ or without were identified. We recommend evaluation of blood-BEV enrichment using these additional ECD+ proteins.

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.

Peripheral extracellular vesicles in neurodegeneration: pathogenic influencers and therapeutic vehicles

Neurodegenerative diseases (NDDs) such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis epitomize a class of insidious and relentless neurological conditions that are difficult to cure. Conventional therapeutic regimens often fail due to the late onset of symptoms, which occurs well after irreversible neurodegeneration has begun. The integrity of the blood-brain barrier (BBB) further impedes efficacious drug delivery to the central nervous system, presenting a formidable challenge in the pharmacological treatment of NDDs. Recent scientific inquiries have shifted focus toward the peripheral biological systems, investigating their influence on central neuropathology through the lens of extracellular vesicles (EVs). These vesicles, distinguished by their ability to breach the BBB, are emerging as dual operatives in the context of NDDs, both as conveyors of pathogenic entities and as prospective vectors for therapeutic agents. This review critically summarizes the burgeoning evidence on the role of extracerebral EVs, particularly those originating from bone, adipose tissue, and gut microbiota, in modulating brain pathophysiology. It underscores the duplicity potential of peripheral EVs as modulators of disease progression and suggests their potential as novel vehicles for targeted therapeutic delivery, positing a transformative impact on the future landscape of NDD treatment strategies. Search strategy A comprehensive literature search was conducted using PubMed, Web of Science, and Scopus from January 2000 to December 2023. The search combined the following terms using Boolean operators: "neurodegenerative disease" OR "Alzheimer's disease" OR "Parkinson's disease" OR "Amyotrophic lateral sclerosis" AND "extracellular vesicles" OR "exosomes" OR "outer membrane vesicles" AND "drug delivery systems" AND "blood-brain barrier". MeSH terms were employed when searching PubMed to refine the results. Studies were included if they were published in English, involved human subjects, and focused on the peripheral origins of EVs, specifically from bone, adipose tissue, and gut microbiota, and their association with related diseases such as osteoporosis, metabolic syndrome, and gut dysbiosis. Articles were excluded if they did not address the role of EVs in the context of NDDs or did not discuss therapeutic applications. The titles and abstracts of retrieved articles were screened using a dual-review process to ensure relevance and accuracy. The reference lists of selected articles were also examined to identify additional relevant studies.

Post-translational modifications of beta-amyloid alter its transport in the blood-brain barrier in vitro model

One of the hallmarks of Alzheimer's disease (AD) is the accumulation of beta-amyloid peptide (Aβ) leading to formation of soluble neurotoxic Aβ oligomers and insoluble amyloid plaques in various parts of the brain. Aβ undergoes post-translational modifications that alter its pathogenic properties. Aβ is produced not only in brain, but also in the peripheral tissues. Such Aβ, including its post-translationally modified forms, can enter the brain from circulation by binding to RAGE and contribute to the pathology of AD. However, the transport of modified forms of Aβ across the blood-brain barrier (BBB) has not been investigated. Here, we used a transwell BBB model as a controlled environment for permeability studies. We found that Aβ42 containing isomerized Asp7 residue (iso-Aβ42) and Aβ42 containing phosphorylated Ser8 residue (pS8-Aβ42) crossed the BBB better than unmodified Aβ42, which correlated with different contribution of endocytosis mechanisms to the transport of these isoforms. Using microscale thermophoresis, we observed that RAGE binds to iso-Aβ42 an order of magnitude weaker than to Aβ42. Thus, post-translational modifications of Aβ increase the rate of its transport across the BBB and modify the mechanisms of the transport, which may be important for AD pathology and treatment.

Amyloid-β mediates intestinal dysfunction and enteric neurons loss in Alzheimer's disease transgenic mouse

Alzheimer's disease (AD) is traditionally considered as a brain disorder featured by amyloid-β (Aβ) deposition. The current study on whether pathological changes of AD extend to the enteric nervous system (ENS) is still in its infancy. In this study, we found enteric Aβ deposition, intestinal dysfunction, and colonic inflammation in the young APP/PS1 mice. Moreover, these mice exhibited cholinergic and nitrergic signaling pathways damages and enteric neuronal loss. Our data show that Aβ42 treatment remarkably affected the gene expression of cultured myenteric neurons and the spontaneous contraction of intestinal smooth muscles. The intra-colon administration of Aβ42 induced ENS dysfunction, brain gliosis, and β-amyloidosis-like changes in the wild-type mice. Our results suggest that ENS mirrors the neuropathology observed in AD brains, and intestinal pathological changes may represent the prodromal events, which contribute to brain pathology in AD. In summary, our findings provide new opportunities for AD early diagnosis and prevention.

Assessment of brain-derived extracellular vesicle enrichment for blood biomarker analysis in age-related neurodegenerative diseases: An international overview

INTRODUCTION

Brain-derived extracellular vesicles (BEVs) in blood allows for minimally- invasive investigations of CNS-specific markers of age-related neurodegenerative diseases (NDDs). Polymer-based EV- and immunoprecipitation (IP)-based BEV-enrichment protocols from blood have gained popularity. We systematically investigated protocol consistency across studies, and determined CNS-specificity of proteins associated with these protocols.

METHODS

NDD articles investigating BEVs in blood using polymer-based and/or IP-based BEV enrichment protocols were systematically identified, and protocols compared. Proteins used for BEV-enrichment and/or post-enrichment were assessed for CNS- and brain-cell-type- specificity; extracellular domains (ECD+); and presence in EV-databases.

RESULTS

82.1% of studies used polymer-based (ExoQuick) EV-enrichment, and 92.3% used L1CAM for IP-based BEV-enrichment. Centrifugation times differed across studies. 26.8% of 82 proteins systematically identified were CNS-specific: 50% ECD+, 77.3% were listed in EV- databases.

DISCUSSION

We identified protocol steps requiring standardization, and recommend additional CNS-specific proteins that can be used for BEV-enrichment or as BEV-biomarkers.

Crosstalk between peripheral immunity and central nervous system in Alzheimer's disease

The significance of peripheral immunity in the pathogenesis and progression of Alzheimer's diseases (AD) has been recognized. Brain-infiltrated peripheral immune components transporting across the blood-brain barrier (BBB) may reshape the central immune environment. However, mechanisms of how these components open the BBB for AD occurrence and development and correlations between peripheral and central immunity have not been fully explored. Herein, we formulate a hypothesis whereby peripheral immunity as a critical factor allows AD to progress. Peripheral central immune cell crosstalk is associated with early AD pathology and related risk factors. The damaged BBB permits peripheral immune cells to enter the central immune system to deprive its immune privilege promoting the progression toward developing AD. This review summarizes the influences of risk factors on peripheral immunity, alongside their functions, highlighting the concept of peripheral and central immunity as an integrated system in AD pathogenesis, which has received scant attention before.

Associations of Blood and Cerebrospinal Fluid Aβ and tau Levels with Renal Function

Amyloid β (Aβ) and tau play pivotal roles in the pathogenesis of Alzheimer's disease (AD). Previous studies have shown that brain-derived Aβ and tau can be cleared through transport into the periphery, and the kidneys may be vital organs involved in the clearance of Aβ and tau. However, the effects of deficiency in the clearance of Aβ and tau by the kidneys on brain AD-type pathologies in humans remain largely unknown. In this study, we first recruited 41 patients with chronic kidney disease (CKD) and 40 age- and sex-matched controls with normal renal function to analyze the associations of the estimated glomerular filtration rate (eGFR) with plasma Aβ and tau levels. To analyze the associations of eGFR with cerebrospinal fluid (CSF) AD biomarkers, we recruited 42 cognitively normal CKD patients and 150 cognitively normal controls with CSF samples. Compared with controls with normal renal function, CKD patients had higher plasma levels of Aβ40, Aβ42 and total tau (T-tau), lower CSF levels of Aβ40 and Aβ42 and higher levels of CSF T-tau/Aβ42 and phosphorylated tau (P-tau)/Aβ42. Plasma Aβ40, Aβ42, and T-tau levels were negatively correlated with eGFR. In addition, eGFR was negatively correlated with CSF levels of T-tau, T-tau/Aβ42, and P-tau/Aβ42 but positively correlated with Mini-Mental State Examination (MMSE) scores. Thus, this study showed that the decline in renal function was correlated with abnormal AD biomarkers and cognitive decline, which provides human evidence that renal function may be involved in the pathogenesis of AD.

Translating blood biomarkers into clinical practice for Alzheimer's disease: Challenges and perspectives

Early and accurate diagnosis of Alzheimer's disease (AD) in clinical practice is urgent with advances in AD treatment. Blood biomarker assays are preferential diagnostic tools for widespread clinical use with the advantages of being less invasive, cost effective, and easily accessible, and they have shown good performance in research cohorts. However, in community-based populations with maximum heterogeneity, great challenges are still faced in diagnosing AD based on blood biomarkers in terms of accuracy and robustness. Here, we analyze these challenges, including the confounding impact of systemic and biological factors, small changes in blood biomarkers, and difficulty in detecting early changes. Furthermore, we provide perspectives on several potential strategies to overcome these challenges for blood biomarkers to bridge the gap from research to clinical practice.

The effects of high plasma levels of Aβ1-42 on mononuclear macrophage in mouse models of Alzheimer's disease

More and more evidences are proving that microglia play a crucial role in the pathogenesis of Alzheimer's disease (AD) and the plasma Aβ_1-42 levels significantly increased 15 years before the onset of dominantly inherited AD. However, the effects of high plasma levels of Aβ_1-42 on mononuclear macrophage, the peripheral counterparts of microglia, remain unclear. In the present study, we used APP/PS1 transgenic (Tg) mice and a parabiotic model of wild type (Wt) mice and Tg mice (Parabiotic Wt-Tg, Pa (Wt-Tg)) to investigate the effects of high plasma levels of Aβ_1-42 on peripheral mononuclear macrophage. Our results showed that in the early stage of Tg mice (7 months) and Pa (Wt-Tg) mice (4 months), the proportions of pro-inflammatory macrophages in peritoneal cavity, myeloid derived suppressor cells (MDSCs) in spleen, granulocyte-monocyte progenitors (GMPs) in bone marrow, and the plasma levels of interleukin-6 (IL-6) were significantly decreased. While the proportions of pro-inflammatory macrophages, MDSCs, GMPs, and the plasma levels of IL-6 and tumor necrosis factor (TNF)-α, as well as the numbers of bone marrow-derived macrophages (BMDMs) in mice brain were increased in the late stage of Tg mice (11 months) and Pa (Wt-Tg) mice (8 months). In addition, the proportions of monocytes in spleen and the proliferation of bone marrow cells (BMCs) were enhanced consistently, and the phagocytic function of macrophages kept stably after high plasma levels of Aβ_1-42 sustaining stimulation. These results demonstrated that high plasma levels of Aβ_1-42 play a biphasic regulating role at different stages of the disease, namely inhibiting effects on peripheral pro-inflammatory macrophages in the early stage of AD model, while promoting effects in the late stage of AD model. The mechanism behind this may be associated with their effects on MDSCs in spleen and myeloid progenitor cells in bone marrow. Therefore, intervening the effects of plasma Aβ_1-42 on pro-inflammatory macrophages might offer a new therapeutic approach to AD.

The platelet transcriptome and proteome in Alzheimer's disease and aging: an exploratory cross-sectional study

Introduction: Alzheimer's disease (AD) and aging are associated with platelet hyperactivity. However, the mechanisms underlying abnormal platelet function in AD and aging are yet poorly understood. Methods: To explore the molecular profile of AD and aged platelets, we investigated platelet activation (i.e., CD62P expression), proteome and transcriptome in AD patients, non-demented elderly, and young individuals as controls. Results: AD, aged and young individuals showed similar levels of platelet activation based on CD62P expression. However, AD and aged individuals had a proteomic signature suggestive of increased platelet activation compared with young controls. Transcriptomic profiling suggested the dysregulation of proteolytic machinery involved in regulating platelet function, particularly the ubiquitin-proteasome system in AD and autophagy in aging. The functional implication of these transcriptomic alterations remains unclear and requires further investigation. Discussion: Our data strengthen the evidence of enhanced platelet activation in aging and provide a first glimpse of the platelet transcriptomic changes occurring in AD.

Immune-mediated platelet depletion augments Alzheimer's disease neuropathological hallmarks in APP-PS1 mice

In Alzheimer's disease (AD), platelets become dysfunctional and might contribute to amyloid beta deposition. Here, we depleted platelets in one-year-old APP Swedish PS1 dE9 (APP-PS1) transgenic mice for five days, using intraperitoneal injections of an anti-CD42b antibody, and assessed changes in cerebral amyloidosis, plaque-associated neuritic dystrophy and gliosis. In APP-PS1 female mice, platelet depletion shifted amyloid plaque size distribution towards bigger plaques and increased neuritic dystrophy in the hippocampus. In platelet-depleted females, plaque-associated Iba1+ microglia had lower amounts of fibrillar amyloid beta cargo and GFAP+ astrocytic processes showed a higher overlap with thioflavin S+ amyloid plaques. In contrast to the popular hypothesis that platelets foster plaque pathology, our data suggest that platelets might limit plaque growth and attenuate plaque-related neuritic dystrophy at advanced stages of amyloid plaque pathology in APP-PS1 female mice. Whether the changes in amyloid plaque pathology are due to a direct effect on amyloid beta deposition or are a consequence of altered glial function needs to be further elucidated.

Aβ1-42-containing platelet-derived extracellular vesicle is associated with cognitive decline in Parkinson's disease

Background

Cortical amyloid deposition is a common observation in Parkinson's disease dementia (PDD) patients. Aβ1-42 is linked to a more rapid progression of dementia. Platelets, which degranulate upon activation, are a primary source of Aβ. It has been repeatedly reported that peripheral extracellular vesicles (EVs) can partially reach the central nervous system. Thus, we speculate that activated platelet-derived Aβ1-42-containing EVs (PEV-Aβ1-42) play a crucial role in the cognitive decline of PD patients.

Methods

The study included 189 participants: 66 with non-dementia PD, 73 with PDD, and 50 healthy controls. All participants underwent blood collection and clinical assessments. Twenty PD patients underwent re-examination and repeated blood collection 14 months later. A nano-scale flow cytometry assay was used to detect PEVs and PEV-Aβ1-42 using fluorescence-labeled CD62P and Aβ1-42 antibodies.

Results

Parkinson's disease dementia patients had higher PEV-Aβ1-42 concentrations than healthy controls (p = 0.028). The ratio of PEV-Aβ1-42 to PEV was significantly higher in PDD patients compared to those in non-dementia PD and healthy controls (p _PD-ND < 0.001, p _HC = 0.041). The PEV-Aβ1-42/PEV ratio appears to influence the odds of developing dementia (OR = 1.76, p < 0.001). The change in the PEV-Aβ1-42/PEV ratio was also correlated with cognitive decline over 14 months (r = -0.447, p < 0.05).

Conclusion

The plasma PEV-Aβ1-42/PEV ratio may serve as a diagnostic and prognostic biomarker for PDD patients.

Distinct Effects of Beta-Amyloid, Its Isomerized and Phosphorylated Forms on the Redox Status and Mitochondrial Functioning of the Blood-Brain Barrier Endothelium

The Alzheimer's disease (AD)-associated breakdown of the blood-brain barrier (BBB) promotes the accumulation of beta-amyloid peptide (Aβ) in the brain as the BBB cells provide Aβ transport from the brain parenchyma to the blood, and vice versa. The breakdown of the BBB during AD may be caused by the emergence of blood-borne Aβ pathogenic forms, such as structurally and chemically modified Aβ species; their effect on the BBB cells has not yet been studied. Here, we report that the effects of Aβ₄₂, Aβ₄₂, containing isomerized Asp7 residue (iso-Aβ₄₂) or phosphorylated Ser8 residue (p-Aβ₄₂) on the mitochondrial potential and respiration are closely related to the redox status changes in the mouse brain endothelial cells bEnd.3. Aβ₄₂ and iso-Aβ₄₂ cause a significant increase in nitric oxide, reactive oxygen species, glutathione, cytosolic calcium and the mitochondrial potential after 4 h of incubation. P-Aβ₄₂ either does not affect or its effect develops after 24 h of incubation. Aβ₄₂ and iso-Aβ₄₂ activate mitochondrial respiration compared to p-Aβ₄₂. The isomerized form promotes a greater cytotoxicity and mitochondrial dysfunction, causing maximum oxidative stress. Thus, Aβ₄₂, p-Aβ₄₂ and iso-Aβ₄₂ isoforms differently affect the BBBs' cell redox parameters, significantly modulating the functioning of the mitochondria. The changes in the level of modified Aβ forms can contribute to the BBBs' breakdown during AD.

Senile plaques in Alzheimer's disease arise from Aβ- and Cathepsin D-enriched mixtures leaking out during intravascular haemolysis and microaneurysm rupture

Senile plaques are a pathological hallmark of Alzheimer's disease (AD), yet the mechanism underlying their generation remains unknown. Beta-amyloid peptide (Aβ) is a major component of senile plaques. We analysed AD brain tissues with histochemistry, immunohistochemistry and fluorescence imaging to examine the neural, vascular or blood Aβ contribution to senile plaque development. We found little neural marker co-expression with plaque Aβ, while co-expression of blood markers, such as Haemin and ApoE, was abundant. The plaque cores were structured with vascular and glial proteins outside and blood metabolites inside, co-localizing with a characteristic of Hoechst staining-independent blue autofluorescence. Erythrocyte-interacting Aβ is linked to coagulation, elevated calcium and blue autofluorescence, and it is associated with intravascular haemolysis, atherosclerosis, cerebral amyloid angiopathy, microaneurysm, and often with Cathepsin D co-expression. We identified microaneurysms as major sites of amyloid formation. Our data suggest that senile plaques arise from Aβ- and Cathepsin D-enriched mixtures leaking out during intravascular haemolysis and microaneurysm rupture.

Erythropoietin signaling in peripheral macrophages is required for systemic β-amyloid clearance

Impaired clearance of beta-amyloid (Aβ) is a primary cause of sporadic Alzheimer's disease (AD). Aβ clearance in the periphery contributes to reducing brain Aβ levels and preventing Alzheimer's disease pathogenesis. We show here that erythropoietin (EPO) increases phagocytic activity, levels of Aβ-degrading enzymes, and Aβ clearance in peripheral macrophages via PPARγ. Erythropoietin is also shown to suppress Aβ-induced inflammatory responses. Deletion of EPO receptor in peripheral macrophages leads to increased peripheral and brain Aβ levels and exacerbates Alzheimer's-associated brain pathologies and behavioral deficits in AD-model mice. Moreover, erythropoietin signaling is impaired in peripheral macrophages of old AD-model mice. Exogenous erythropoietin normalizes impaired EPO signaling and dysregulated functions of peripheral macrophages in old AD-model mice, promotes systemic Aβ clearance, and alleviates disease progression. Erythropoietin treatment may represent a potential therapeutic approach for Alzheimer's disease.

Impact prediction of translocation of the mitochondrial outer membrane 70 as biomarker in Alzheimer's disease

Mitochondrial dysfunction plays a key role in the pathogenesis of Alzheimer's disease (AD). The translocase of the outer membrane (TOM) complex controls the input of mitochondrial precursor proteins to maintain mitochondrial function under pathophysiological conditions. However, its role in AD development remains unclear. TOM70 is an important translocase present in the TOM complex. In the current study, we found that TOM70 levels were reduced in the peripheral blood and hippocampus of the APP/PS1 mice. In addition, we examined the whole-blood mRNA levels of TOM70 in patients with AD, dementia with Lewy bodies (DLB), and post-stroke dementia (PSD). Our study revealed that the mRNA level of TOM70 was decreased in the blood samples of patients with AD, which was also correlated with the progression of clinical stages. Therefore, we proposed that the expression of TOM70 could be a promising biomarker for AD diagnosis and monitoring of disease progression.

The Role of Circulating Aβ Seeds in the Progression of Cerebral Amyloidosis

While understudied, it is suspected that peripheral Aβ peptides affect Alzheimer's disease (AD)-associated pathological changes in the brain. The peripheral sink hypothesis postulates that the central and peripheral pools of Aβ co-exist in equilibrium. As such, cerebral amyloid levels may be modulated by intervening circulating Aβ. In this commentary, we discuss relevant literature supporting the potential role of peripheral Aβ in exacerbating brain amyloidosis in both humans and mouse models of AD. Moreover, we highlight the need to further understand the mechanisms by which circulating Aβ peptides may reach the brain and contribute to neuropathology. Finally, we discuss the implications of targeting peripheral Aβ as a therapeutic approach in treating AD.

The Role of Amyloid-β, Tau, and α-Synuclein Proteins as Putative Blood Biomarkers in Patients with Cerebral Amyloid Angiopathy

BACKGROUND

Cerebral amyloid angiopathy (CAA) is a cerebrovascular disorder characterized by the deposition of amyloid-β protein (Aβ) within brain blood vessels that develops in elderly people and Alzheimer's disease (AD) patients. Therefore, the investigation of biomarkers able to differentiate CAA patients from AD patients and healthy controls (HC) is of great interest, in particular in peripheral fluids.

OBJECTIVE

The current study aimed to detect the neurodegenerative disease (ND)-related protein (i.e., Aβ 1 - 40, Aβ 1 - 42, tau, and α-synuclein) levels in both red blood cells (RBCs) and plasma of CAA patients and HC, evaluating their role as putative peripheral biomarkers for CAA.

METHODS

For this purpose, the proteins' concentration was quantified in RBCs and plasma by homemade immunoenzymatic assays in an exploratory cohort of 20 CAA patients and 20 HC.

RESULTS

The results highlighted a significant increase of Aβ 1 - 40 and α-synuclein concentrations in both RBCs and plasma of CAA patients, while higher Aβ 1 - 42 and t-tau levels were detected only in RBCs of CAA individuals compared to HC. Moreover, Aβ 1 - 42/Aβ 1 - 40 ratio increased in RBCs and decreased in plasma of CAA patients. The role of these proteins as candidate peripheral biomarkers easily measurable with a blood sample in CAA needs to be confirmed in larger studies.

CONCLUSION

In conclusion, we provide evidence concerning the possible use of blood biomarkers for contributing to CAA diagnosis and differentiation from other NDs.

Effects of Chemotherapy on Neuroinflammation, Neuronal Damage, Neurogenesis, and Behavioral Performance in Bone Marrow Transplantation Recipient Mice

As bone marrow transplant (BMT) is gradually applied to the study of central nervous system (CNS) disease, it is needed to investigate the proper dose of chemotherapy to eradicate bone marrow cells while bringing little damage to brain. In the present study, we established a BMT model with varied busulfan and cyclophosphamide (Bu-Cy) dosages. The recipient mice's chimera rate, neuronal death, neuroinflammation, and behavioral functions were all investigated. Chimerism of peripheral blood cells was shown to rise with Bu-Cy treatment doses, with 60.7% in the Bu(20 mg/kg)/Cy(100 mg/kg) group and 93.0% in the Bu(35 mg/kg)/Cy(100 mg/kg) group. Recipients with Bu(35 mg/kg)/Cy(100 mg/kg) therapy had brain injury, increased neuroinflammation, diminished neurogenesis and cognitive abnormalities, whereas animals given a lesser dosage had no such brain damages. Conclusively, considering the chimerism and the possibility to damage brain, we recommend Bu(20 mg/kg)/Cy(100 mg/kg) is the ideal dose in BMT for studying CNS diseases in the C57/BL6 mouse strain.

Toll-like Receptor 4, Osteoblasts and Leukemogenesis; the Lesson from Acute Myeloid Leukemia

Toll-like receptor 4 (TLR4) is a pattern-recognizing receptor that can bind exogenous and endogenous ligands. It is expressed by acute myeloid leukemia (AML) cells, several bone marrow stromal cells, and nonleukemic cells involved in inflammation. TLR4 can bind a wide range of endogenous ligands that are present in the bone marrow microenvironment. Furthermore, the TLR4-expressing nonleukemic bone marrow cells include various mesenchymal cells, endothelial cells, differentiated myeloid cells, and inflammatory/immunocompetent cells. Osteoblasts are important stem cell supporting cells localized to the stem cell niches, and they support the proliferation and survival of primary AML cells. These supporting effects are mediated by the bidirectional crosstalk between AML cells and supportive osteoblasts through the local cytokine network. Finally, TLR4 is also important for the defense against complicating infections in neutropenic patients, and it seems to be involved in the regulation of inflammatory and immunological reactions in patients treated with allogeneic stem cell transplantation. Thus, TLR4 has direct effects on primary AML cells, and it has indirect effects on the leukemic cells through modulation of their supporting neighboring bone marrow stromal cells (i.e., modulation of stem cell niches, regulation of angiogenesis). Furthermore, in allotransplant recipients TLR4 can modulate inflammatory and potentially antileukemic immune reactivity. The use of TLR4 targeting as an antileukemic treatment will therefore depend both on the biology of the AML cells, the biological context of the AML cells, aging effects reflected both in the AML and the stromal cells and the additional antileukemic treatment combined with HSP90 inhibition.

Can blood amyloid levels be used as a biomarker for Alzheimer’s disease?

Alzheimer’s disease (AD) increasingly affects society due to aging populations. Even at pre‐clinical stages, earlier and accurate diagnoses are essential for optimal AD management and improved clinical outcomes. Biomarkers such as beta‐amyloid (Aβ) or tau protein in cerebrospinal fluid (CSF) have been used as reliable markers to distinguish AD from non‐AD, and predicting clinical outcomes, to attain these goals. However, given CSF access methods’ invasiveness, these biomarkers are not used extensively in clinical settings. Blood Aβ has been proposed as an alternative biomarker since it is less invasive than CSF; however, sampling heterogeneity has limited its clinical applicability. In this review, we investigated blood Aβ as a biomarker in AD and explored how Aβ can be facilitated as a viable biomarker for successful AD management.

The Analysis of Oxidative Stress Markers May Increase the Accuracy of the Differential Diagnosis of Alzheimer's Disease with and without Depression

Introduction

The aim of work is to assess the usefulness of oxidative stress parameters in the differential diagnosis of dementia of the Alzheimer’s type and dementia of the Alzheimer’s type with coexisting depression.

Methods

The study involved three groups of people: patients with Alzheimer’s disease (AD) (AD; N=27), patients with Alzheimer’s disease and depression (D) (AD+D; N=30), and a control group that consisted of people without dementia and without depression (C; N=24). The assessment of cognitive functioning was carried out using among alia, Auditory Verbal Learning Test and Verbal Fluency Test. Furthermore, we determined the activity of superoxide dismutase (SOD-1) and superoxide anion radical.

Results

Multiple models with different combinations of independent variables showed that SOD together with Rey delayed recall were the best significant predictors of AD with the area under curve (AUC) of 0.893 (p = 0.001) and superoxide anion radical (O2^•−) together with verbal fluency – sharp objects were the best significant predictors of AD +D diagnosis with the AUC of 0.689 (p = 0.034).

Conclusion

This study confirmed the value of neuropsychological diagnosis and analysis of oxidative stress markers in the diagnosis of AD and major depressive disorder (MDD) in the course of AD. The combination of the use of biochemical markers and neuropsychological tests seems particularly important for differential diagnosis.

Exploiting Common Aspects of Obesity and Alzheimer's Disease

Alzheimer’s disease (AD) is an example of age-related dementia, and there are still no known preventive or curative measures for this disease. Obesity and associated metabolic changes are widely accepted as risk factors of age-related cognitive decline. Insulin is the prime mediator of metabolic homeostasis, which is impaired in obesity, and this impairment potentiates amyloid-β (Aβ) accumulation and the formation of neurofibrillary tangles (NFTs). Obesity is also linked with functional and morphological alterations in brain mitochondria leading to brain insulin resistance (IR) and memory deficits associated with AD. Also, increased peripheral inflammation and oxidative stress due to obesity are the main drivers that increase an individual’s susceptibility to cognitive deficits, thus doubling the risk of AD. This enhanced risk of AD is alarming in the context of a rapidly increasing global incidence of obesity and overweight in the general population. In this review, we summarize the risk factors that link obesity with AD and emphasize the point that the treatment and management of obesity may also provide a way to prevent AD.