Rejuvenating aged microglia by p16ink4a-siRNA-loaded nanoparticles increases amyloid-ß clearance in animal models of Alzheimer's disease.

Age-dependent accumulation of amyloid plaques in patients with sporadic Alzheimer's disease (AD) is associated with reduced amyloid clearance. Older microglia have a reduced ability to phagocytose amyloid, so phagocytosis of amyloid plaques by microglia could be regulated to prevent amyloid accumulation. Furthermore, considering the aging-related disruption of cell cycle machinery in old microglia, we hypothesize that regulating their cell cycle could rejuvenate them and enhance their ability to promote more efficient amyloid clearance. First, we used gene ontology analysis of microglia from young and old mice to identify differential expression of cyclin-dependent kinase inhibitor 2A (p16ink4a), a cell cycle factor related to aging. We found that p16ink4a expression was increased in microglia near amyloid plaques in brain tissue from patients with AD and 5XFAD mice, a model of AD. In BV2 microglia, small interfering RNA (siRNA)-mediated p16ink4a downregulation transformed microglia with enhanced amyloid phagocytic capacity through regulated the cell cycle and increased cell proliferation. To regulate microglial phagocytosis by gene transduction, we used poly (D,L-lactic-co-glycolic acid) (PLGA) nanoparticles, which predominantly target microglia, to deliver the siRNA and to control microglial reactivity. Nanoparticle-based delivery of p16ink4a siRNA reduced amyloid plaque formation and the number of aged microglia surrounding the plaque and reversed learning deterioration and spatial memory deficits. We propose that downregulation of p16ink4a in microglia is a promising strategy for the treatment of Alzheimer's disease.

Chimeric antigen receptor macrophages target and resorb amyloid plaques.

Substantial evidence suggests a role for immunotherapy in treating Alzheimer's disease (AD). While the precise pathophysiology of AD is incompletely understood, clinical trials of antibodies targeting aggregated forms of ß amyloid (Aß) have shown that reducing amyloid plaques can mitigate cognitive decline in patients with early-stage AD. Here, we describe what we believe to be a novel approach to target and degrade amyloid plaques by genetically engineering macrophages to express an Aß-targeting chimeric antigen receptor (CAR-Ms). When injected intrahippocampally, first-generation CAR-Ms have limited persistence and fail to significantly reduce plaque load, which led us to engineer next-generation CAR-Ms that secrete M-CSF and self-maintain without exogenous cytokines. Cytokine secreting "reinforced CAR-Ms" have greater survival in the brain niche and significantly reduce plaque load locally in vivo. These findings support CAR-Ms as a platform to rationally target, resorb, and degrade pathogenic material that accumulates with age, as exemplified by targeting Aß in AD.

Targeting terminal pathway reduces brain complement activation, amyloid load and synapse loss, and improves cognition in a mouse model of dementia.

Complement is dysregulated in the brain in Alzheimer's Disease and in mouse models of Alzheimer's disease. Each of the complement derived effectors, opsonins, anaphylatoxins and membrane attack complex (MAC), have been implicated as drivers of disease but their relative contributions remain unclarified. Here we have focussed on the MAC, a lytic and pro-inflammatory effector, in the AppNL-G-F mouse amyloidopathy model. To test the role of MAC, we back-crossed to generate AppNL-G-F mice deficient in C7, an essential MAC component. C7 deficiency ablated MAC formation, reduced synapse loss and amyloid load and improved cognition compared to complement-sufficient AppNL-G-F mice at 8-10 months age. Adding back C7 caused increased MAC formation in brain and an acute loss of synapses in C7-deficient AppNL-G-F mice. To explore whether C7 was a viable therapeutic target, a C7-blocking monoclonal antibody was administered systemically for one month in AppNL-G-F mice aged 8-9 months. Treatment reduced brain MAC and amyloid deposition, increased synapse density and improved cognitive performance compared to isotype control-treated AppNL-G-F mice. The findings implicate MAC as a driver of pathology and highlight the potential for complement inhibition at the level of MAC as a therapy in Alzheimer's disease.

Aniracetam: An Evidence-Based Model for Preventing the Accumulation of Amyloid-ß Plaques in Alzheimer's Disease.

 Alzheimer's disease is the leading cause of dementia in the world. It affects 6 million people in the United States and 50 million people worldwide. Alzheimer's disease is characterized by the accumulation of amyloid-ß plaques (Aß), an increase in tau protein neurofibrillary tangles, and a loss of synapses. Since the 1990s, removing and reducing Aß has been the focus of Alzheimer's treatment and prevention research. The accumulation of Aß can lead to oxidative stress, inflammation, neurotoxicity, and eventually apoptosis. These insults impair signaling systems in the brain, potentially leading to memory loss and cognitive decline. Aniracetam is a safe, effective, cognitive-enhancing drug that improves memory in both human and animal studies. Aniracetam may prevent the production and accumulation of Aß by increasing α-secretase activity through two distinct pathways: 1) increasing brain derived neurotrophic factor expression and 2) positively modulating metabotropic glutamate receptors. This is the first paper to propose an evidence-based model for aniracetam reducing the accumulation and production of Aß.

Label-Free In Situ Chemical Characterization of Amyloid Plaques in Human Brain Tissues.

The accumulation of amyloid plaques and increased brain redox burdens are neuropathological hallmarks of Alzheimer's disease. Altered metabolism of essential biometals is another feature of Alzheimer's, with amyloid plaques representing sites of disturbed metal homeostasis. Despite these observations, metal-targeting disease treatments have not been therapeutically effective to date. A better understanding of amyloid plaque composition and the role of the metals associated with them is critical. To establish this knowledge, the ability to resolve chemical variations at nanometer length scales relevant to biology is essential. Here, we present a methodology for the label-free, nanoscale chemical characterization of amyloid plaques within human Alzheimer's disease tissue using synchrotron X-ray spectromicroscopy. Our approach exploits a C-H carbon absorption feature, consistent with the presence of lipids, to visualize amyloid plaques selectively against the tissue background, allowing chemical analysis to be performed without the addition of amyloid dyes that alter the native sample chemistry. Using this approach, we show that amyloid plaques contain elevated levels of calcium, carbonates, and iron compared to the surrounding brain tissue. Chemical analysis of iron within plaques revealed the presence of chemically reduced, low-oxidation-state phases, including ferromagnetic metallic iron. The zero-oxidation state of ferromagnetic iron determines its high chemical reactivity and so may contribute to the redox burden in the Alzheimer's brain and thus drive neurodegeneration. Ferromagnetic metallic iron has no established physiological function in the brain and may represent a target for therapies designed to lower redox burdens in Alzheimer's disease. Additionally, ferromagnetic metallic iron has magnetic properties that are distinct from the iron oxide forms predominant in tissue, which might be exploitable for the in vivo detection of amyloid pathologies using magnetically sensitive imaging. We anticipate that this label-free X-ray imaging approach will provide further insights into the chemical composition of amyloid plaques, facilitating better understanding of how plaques influence the course of Alzheimer's disease.

Thiophene-Based Ligands for Specific Assignment of Distinct Aß Pathologies in Alzheimer's Disease.

Aggregated species of amyloid-ß (Aß) are one of the pathological hallmarks in Alzheimer's disease (AD), and ligands that selectively target different Aß deposits are of great interest. In this study, fluorescent thiophene-based ligands have been used to illustrate the features of different types of Aß deposits found in AD brain tissue. A dual-staining protocol based on two ligands, HS-276 and LL-1, with different photophysical and binding properties, was developed and applied on brain tissue sections from patients affected by sporadic AD or familial AD associated with the PSEN1 A431E mutation. When binding to Aß deposits, the ligands could easily be distinguished for their different fluorescence, and distinct staining patterns were revealed for these two types of AD. In sporadic AD, HS-276 consistently labeled all immunopositive Aß plaques, whereas LL-1 mainly stained cored and neuritic Aß deposits. In the PSEN1 A431E cases, each ligand was binding to specific types of Aß plaques. The ligand-labeled Aß deposits were localized in distinct cortical layers, and a laminar staining pattern could be seen. Biochemical characterization of the Aß aggregates in the individual layers also showed that the variation of ligand binding properties was associated with certain Aß peptide signatures. For the PSEN1 A431E cases, it was concluded that LL-1 was binding to cotton wool plaques, whereas HS-276 mainly stained diffuse Aß deposits. Overall, our findings showed that a combination of ligands was essential to identify distinct aggregated Aß species associated with different forms of AD.

Modulation of hippocampal protein expression by a brain penetrant biologic TNF-α inhibitor in the 3xTg Alzheimer's disease mice.

BACKGROUND: Biologic TNF-α inhibitors (bTNFIs) can block cerebral TNF-α in Alzheimer's disease (AD) if these macromolecules can cross the blood-brain barrier (BBB). Thus, a model bTNFI, the extracellular domain of type II TNF-α receptor (TNFR), which can bind to and sequester TNF-α, was fused with a mouse transferrin receptor antibody (TfRMAb) to enable brain delivery via BBB TfR-mediated transcytosis. Previously, we found TfRMAb-TNFR to be protective in a mouse model of amyloidosis (APP/PS1) and tauopathy (PS19), and herein we investigated its effects in mice that combine both amyloidosis and tauopathy (3xTg-AD). METHODS: Eight-month-old female 3xTg-AD mice were injected intraperitoneally with saline (n = 11) or TfRMAb-TNFR (3 mg/kg; n = 11) three days per week for 12 weeks. Age-matched wild-type (WT) mice (n = 9) were treated similarly with saline. Brains were processed for immunostaining and high-resolution multiplex NanoString GeoMx spatial proteomics. RESULTS: We observed regional differences in proteins relevant to Aß, tau, and neuroinflammation in the hippocampus of 3xTg-AD mice compared with WT mice. From 64 target proteins studied using spatial proteomics, a comparison of the Aß-plaque bearing vs. plaque-free regions in the 3xTg-AD mice yielded 39 differentially expressed proteins (DEP) largely related to neuroinflammation (39% of DEP) and Aß and tau pathology combined (31% of DEP). Hippocampal spatial proteomics revealed that the majority of the proteins modulated by TfRMAb-TNFR in the 3xTg-AD mice were relevant to microglial function (⁓ 33%). TfRMAb-TNFR significantly reduced mature Aß plaques and increased Aß-associated microglia around larger Aß deposits in the 3xTg-AD mice. Further, TfRMAb-TNFR increased mature Aß plaque-associated microglial TREM2 in 3xTg-AD mice. CONCLUSION: Overall, despite the low visual Aß load in the 11-month-old female 3xTg-AD mice, our results highlight region-specific AD-relevant DEP in the hippocampus of these mice. Chronic TfRMAb-TNFR dosing modulated several DEP involved in AD pathology and showed a largely microglia-centric mechanism of action in the 3xTg-AD mice.

Composite of KLVFF-Transthyretin-Penetratin and Manganese Dioxide Nanoclusters: A Multifunctional Agent against Alzheimer's ß-Amyloid Fibrillogenesis.

Design of amyloid ß-protein (Aß) inhibitors is considered an effective strategy for the prevention and treatment of Alzheimer's disease (AD). However, the limited blood-brain barrier (BBB) penetration and poor Aß-targeting capability restricts the therapeutic efficiency of candidate drugs. Herein, we have proposed to engineer transthyretin (TTR) by fusion of the Aß-targeting peptide KLVFF and cell-penetrating peptide Penetratin to TTR, and derived a fusion protein, KLVFF-TTR-Penetratin (KTP). Moreover, to introduce the scavenging activity for reactive oxygen species (ROS), a nanocomposite of KTP and manganese dioxide nanoclusters (KTP@MnO2) was fabricated by biomineralization. Results revealed that KTP@MnO2 demonstrated significantly enhanced inhibition on Aß aggregation as compared to TTR. The inhibitory effect was increased from 18%, 33%, and 49% (10, 25, and 50 µg/mL TTR, respectively) to 52%, 81%, and 100% (10, 25, and 50 µg/mL KTP@MnO2). In addition, KTP@MnO2 could penetrate the BBB and target amyloid plaques. Moreover, multiple ROS, including hydroxyl radicals, superoxide radicals, hydrogen peroxide, and Aß-induced-ROS, which cannot be scavenged by TTR, were scavenged by KTP@MnO2, thus resulting in the mitigation of cellular oxidative damages. More importantly, cell culture and in vivo experiments with AD nematodes indicated that KTP@MnO2 at 50 µg/mL increased the viability of Aß-treated cells from 66% to more than 95%, and completely cleared amyloid plaques in AD nematodes and extended their lifespan by 7 d. Overall, despite critical aspects such as the stability, metabolic distribution, long-term biotoxicity, and immunogenicity of the nanocomposites in mammalian models remaining to be investigated, this work has demonstrated the multifunctionality of KTP@MnO2 for targeting Aß in vivo, and provided new insights into the design of multifunctional nanocomposites of protein-metal clusters against AD.

Amyloid PET Imaging: Standard Procedures and Semiquantification.

Amyloid plaques are a neuropathologic hallmark of Alzheimer's disease (AD), which can be imaged through positron emission tomography (PET) technology using radiopharmaceuticals that selectively bind to the fibrillar aggregates of amyloid-ß plaques (Amy-PET). Several radiotracers for amyloid PET have been validated (11C-Pittsburgh compound B and the 18F-labeled compounds such as 18F-florbetaben, 18F-florbetapir, and 18F-flutemetamol). Images can be interpreted by means of visual/qualitative, semiquantitative, and quantitative criteria. Here, we summarize the main differences between the available radiotracers for Amy-PET, the proposed interpretation criteria, and main proposed quantification methods.

Imaging Neuroinflammation: Quantification of Astrocytosis in a Multitracer PET Approach.

The recent progress in the development of in vivo biomarkers is rapidly changing how neurodegenerative diseases are conceptualized and diagnosed and how clinical trials are designed today. Alzheimer's disease (AD) - the most common neurodegenerative disorder - is characterized by a complex neuropathology involving the deposition of extracellular amyloid-ß (Aß) plaques and intracellular neurofibrillary tangles (NFTs) of hyperphosphorylated tau proteins, accompanied by the activation of glial cells, i.e., astrocytes and microglia, and neuroinflammatory response, leading to neurodegeneration and cognitive dysfunction. An increasing diversity of positron emission tomography (PET) imaging radiotracers is available to selectively target the different pathophysiological processes of AD. Along with the success of Aß PET and the more recent tau PET imaging, there is a great interest to develop PET tracers to image glial reactivity and neuroinflammation. While most research to date has focused on imaging microgliosis, there is an upsurge of interest in imaging reactive astrocytes in the AD continuum. There is increasing evidence that reactive astrocytes are morphologically and functionally heterogeneous, with different subtypes that express different markers and display various homeostatic or detrimental roles across disease stages. Therefore, multiple biomarkers are desirable to unravel the complex phenomenon of reactive astrocytosis. In the field of in vivo PET imaging in AD, the research concerning reactive astrocytes has predominantly focused on targeting monoamine oxidase B (MAO-B), most often using either 11C-deuterium-L-deprenyl (11C-DED) or 18F-SMBT-1 PET tracers. Additionally, imidazoline2 binding (I2BS) sites have been imaged using 11C-BU99008 PET. Recent studies in our group using 11C-DED PET imaging suggest that astrocytosis may be present from the early stages of disease development in AD. This chapter provides a detailed description of the practical approach used for the analysis of 11C-DED PET imaging data in a multitracer PET paradigm including 11C-Pittsburgh compound B (11C-PiB) and 18F-fluorodeoxyglucose (18F-FDG). The multitracer PET approach allows investigating the comparative regional and temporal patterns of in vivo brain astrocytosis, fibrillar Aß deposition, glucose metabolism, and brain structural changes. It may also contribute to understanding the potential role of novel plasma biomarkers of reactive astrocytes, in particular the glial fibrillary acidic protein (GFAP), at different stages of disease progression. This chapter attempts to stimulate further research in the field, including the development of novel PET tracers that may allow visualizing different aspects of the complex astrocytic and microglial response in neurodegenerative diseases. Progress in the field will contribute to the incorporation of PET imaging of glial reactivity and neuroinflammation as biomarkers with clinical application and motivate further investigation on glial cells as therapeutic targets in AD and other neurodegenerative diseases.

Insights on the Use of Transgenic Mice Models in Alzheimer's Disease Research.

Alzheimer's disease (AD), the leading cause of dementia, presents a significant global health challenge with no known cure to date. Central to our understanding of AD pathogenesis is the ß-amyloid cascade hypothesis, which underlies drug research and discovery efforts. Despite extensive studies, no animal models of AD have completely validated this hypothesis. Effective AD models are essential for accurately replicating key pathological features of the disease, notably the formation of ß-amyloid plaques and neurofibrillary tangles. These pathological markers are primarily driven by mutations in the amyloid precursor protein (APP) and presenilin 1 (PS1) genes in familial AD (FAD) and by tau protein mutations for the tangle pathology. Transgenic mice models have been instrumental in AD research, heavily relying on the overexpression of mutated APP genes to simulate disease conditions. However, these models do not entirely replicate the human condition of AD. This review aims to provide a comprehensive evaluation of the historical and ongoing research efforts in AD, particularly through the use of transgenic mice models. It is focused on the benefits gathered from these transgenic mice models in understanding ß-amyloid toxicity and the broader biological underpinnings of AD. Additionally, the review critically assesses the application of these models in the preclinical testing of new therapeutic interventions, highlighting the gap between animal models and human clinical realities. This analysis underscores the need for refinement in AD research methodologies to bridge this gap and enhance the translational value of preclinical studies.

Proximity-Induced Pharmacology for Amyloid-Related Diseases.

Proximity-induced pharmacology (PIP) for amyloid-related diseases is a cutting-edge approach to treating conditions such as Alzheimer's disease and other forms of dementia. By bringing small molecules close to amyloid-related proteins, these molecules can induce a plethora of effects that can break down pathogenic proteins and reduce the buildup of plaques. One of the most promising aspects of this drug discovery modality is that it can be used to target specific types of amyloid proteins, such as the beta-amyloid protein that is commonly associated with Alzheimer's disease. This level of specificity could allow for more targeted and effective treatments. With ongoing research and development, it is hoped that these treatments can be refined and optimized to provide even greater benefits to patients. As our understanding of the underlying mechanisms of these diseases continues to grow, proximity-induced pharmacology treatments may become an increasingly important tool in the fight against dementia and other related conditions.

Accumulation of neutral lipids in dystrophic neurites surrounding amyloid plaques in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by the formation ß-amyloid (Aß) deposited neuritic plaques. Recent evidence suggests that abnormal lipid metabolism and accumulation could serve as biomarkers for neurodegenerative diseases, including AD. Tubular endoplasmic reticulum protein, reticulon 3 (RTN3), plays a crucial role in the development of neuritic plaque and lipid metabolism in AD brains. In present study, we sought to investigate a potential association between neutral lipid accumulation and AD pathology. BODIPY 500/510 dye was used to label neutral lipid surrounding Aß plaques in APPNL-G-F mouse and AD postmortem brains samples. Immunofluorescent images were captured using confocal microscope and co-localization between lipid metabolism proteins and neutral lipids were evaluated. Lipid accumulation in Aß plaque surrounding dystrophic neurites (DNs) was observed in the cortical region of AD mouse models and human AD brain samples. The neutral lipid staining was not co-localized with IBA1-labeled microglia or GFAP-labeled astrocytes, but it was co-labeled with VAMP2 and neurofilament. We further showed that neutral lipids were accumulated in RTN3 immunoreactive DNs. Both the neutral lipids accumulation and RIDNs formation showed age-dependent patterns in surrounding amyloid plaques. Mechanistic studies revealed that RTN3 likely contributes to the enrichment of neutral lipids near plaques by interacting with heat shock cognate protein 70 (HSC70) and diminishing its function in chaperone-mediated lipophagy. Our study provides immunohistochemical evidence of neutral lipids being enriched in DNs near amyloid plaques. Our findings shed light on RTN3-mediaed lipid accumulation in AD neuropathology and provide fresh insights into the role of RTN3 in neurodegenerative diseases.

A Combination of Heavy Metals and Intracellular Pathway Modulators Induces Alzheimer Disease-like Pathologies in Organotypic Brain Slices.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is characterized by amyloid-beta (Aß) plaques and tau neurofibrillary tangles (NFT). Modelling aspects of AD is challenging due to its complex multifactorial etiology and pathology. The present study aims to establish a cost-effective and rapid method to model the two primary pathologies in organotypic brain slices. Coronal hippocampal brain slices (150 µm) were generated from postnatal (day 8-10) C57BL6 wild-type mice and cultured for 9 weeks. Collagen hydrogels containing either an empty load or a mixture of human Aß42 and P301S aggregated tau were applied to the slices. The media was further supplemented with various intracellular pathway modulators or heavy metals to augment the appearance of Aß plaques and tau NFTs, as assessed by immunohistochemistry. Immunoreactivity for Aß and tau was significantly increased in the ventral areas in slices with a mixture of human Aß42 and P301S aggregated tau compared to slices with empty hydrogels. Aß plaque- and tau NFT-like pathologies could be induced independently in slices. Heavy metals (aluminum, lead, cadmium) potently augmented Aß plaque-like pathology, which developed intracellularly prior to cell death. Intracellular pathway modulators (scopolamine, wortmannin, MHY1485) significantly boosted tau NFT-like pathologies. A combination of nanomolar concentrations of scopolamine, wortmannin, MHY1485, lead, and cadmium in the media strongly increased Aß plaque- and tau NFT-like immunoreactivity in ventral areas compared to the slices with non-supplemented media. The results highlight that we could harness the potential of the collagen hydrogel-based spreading of human Aß42 and P301S aggregated tau, along with pharmacological manipulation, to produce pathologies relevant to AD. The results offer a novel ex vivo organotypic slice model to investigate AD pathologies with potential applications for screening drugs or therapies in the future.

Spatial Neurolipidomics at the Single Amyloid-ß Plaque Level in Postmortem Human Alzheimer's Disease Brain.

Lipid dysregulations have been critically implicated in Alzheimer's disease (AD) pathology. Chemical analysis of amyloid-ß (Aß) plaque pathology in transgenic AD mouse models has demonstrated alterations in the microenvironment in the direct proximity of Aß plaque pathology. In mouse studies, differences in lipid patterns linked to structural polymorphism among Aß pathology, such as diffuse, immature, and mature fibrillary aggregates, have also been reported. To date, no comprehensive analysis of neuronal lipid microenvironment changes in human AD tissue has been performed. Here, for the first time, we leverage matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) through a high-speed and spatial resolution commercial time-of-light instrument, as well as a high-mass-resolution in-house-developed orbitrap system to characterize the lipid microenvironment in postmortem human brain tissue from AD patients carrying Presenilin 1 mutations (PSEN1) that lead to familial forms of AD (fAD). Interrogation of the spatially resolved MSI data on a single Aß plaque allowed us to verify nearly 40 sphingolipid and phospholipid species from diverse subclasses being enriched and depleted, in relation to the Aß deposits. This included monosialo-gangliosides (GM), ceramide monohexosides (HexCer), ceramide-1-phosphates (CerP), ceramide phosphoethanolamine conjugates (PE-Cer), sulfatides (ST), as well as phosphatidylinositols (PI), phosphatidylethanolamines (PE), and phosphatidic acid (PA) species (including Lyso-forms). Indeed, many of the sphingolipid species overlap with the species previously seen in transgenic AD mouse models. Interestingly, in comparison to the animal studies, we observed an increased level of localization of PE and PI species containing arachidonic acid (AA). These findings are highly relevant, demonstrating for the first time Aß plaque pathology-related alteration in the lipid microenvironment in humans. They provide a basis for the development of potential lipid biomarkers for AD characterization and insight into human-specific molecular pathway alterations.

Numerical and Analytical Simulation of the Growth of Amyloid-ß Plaques.

Numerical and analytical solutions were employed to calculate the radius of an amyloid-ß (Aß) plaque over time. To the author's knowledge, this study presents the first model simulating the growth of Aß plaques. Findings indicate that the plaque can attain a diameter of 50 µm after 20 years of growth, provided the Aß monomer degradation machinery is malfunctioning. A mathematical model incorporates nucleation and autocatalytic growth processes using the Finke-Watzky model. The resulting system of ordinary differential equations was solved numerically, and for the simplified case of infinitely long Aß monomer half-life, an analytical solution was found. Assuming that Aß aggregates stick together and using the distance between the plaques as an input parameter of the model, it was possible to calculate the plaque radius from the concentration of Aß aggregates. This led to the "cube root hypothesis," positing that Aß plaque size increases proportionally to the cube root of time. This hypothesis helps explain why larger plaques grow more slowly. Furthermore, the obtained results suggest that the plaque size is independent of the kinetic constants governing Aß plaque agglomeration, indicating that the kinetics of Aß plaque agglomeration is not a limiting factor for plaque growth. Instead, the plaque growth rate is limited by the rates of Aß monomer production and degradation.

Depth- and curvature-based quantitative susceptibility mapping analyses of cortical iron in Alzheimer's disease.

In addition to amyloid beta plaques and neurofibrillary tangles, Alzheimer's disease (AD) has been associated with elevated iron in deep gray matter nuclei using quantitative susceptibility mapping (QSM). However, only a few studies have examined cortical iron, using more macroscopic approaches that cannot assess layer-specific differences. Here, we conducted column-based QSM analyses to assess whether AD-related increases in cortical iron vary in relation to layer-specific differences in the type and density of neurons. We obtained global and regional measures of positive (iron) and negative (myelin, protein aggregation) susceptibility from 22 adults with AD and 22 demographically matched healthy controls. Depth-wise analyses indicated that global susceptibility increased from the pial surface to the gray/white matter boundary, with a larger slope for positive susceptibility in the left hemisphere for adults with AD than controls. Curvature-based analyses indicated larger global susceptibility for adults with AD versus controls; the right hemisphere versus left; and gyri versus sulci. Region-of-interest analyses identified similar depth- and curvature-specific group differences, especially for temporo-parietal regions. Finding that iron accumulates in a topographically heterogenous manner across the cortical mantle may help explain the profound cognitive deterioration that differentiates AD from the slowing of general motor processes in healthy aging.

A Near-infrared Fluorescence and Positron Emission Tomography Bimodal Probe for In Vivo Imaging of Amyloid-ß Species.

Noninvasive imaging of amyloid-ß (Aß) species in vivo is important for the early diagnosis of Alzheimer's disease (AD). In this paper, we report a near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probe (NIR-[68Ga]) for in vivo imaging of both soluble and insoluble Aß species. NIR-[68Ga] holds a high binding affinity, high selectivity and high sensitivity toward Aß42 monomers, oligomers, and aggregates in vitro. In vivo imaging results show that NIR-[68Ga] can cross the blood-brain-barrier (BBB), and produce significantly higher PET and NIR FL bimodal signals in the brains of APP/PS1 transgenic AD mice relative to that of age-matched wild-type mice, which are also validated by the ex vivo autoradiography and histological staining images. Our results demonstrate that NIR-[68Ga] is an efficient NIR FL and PET bimodal probe for the sensitive imaging of soluble and insoluble Aß species in AD mice.

Unlocking the Molecular Variations of a Micron-Scale Amyloid Plaque in an Early Stage Alzheimer's Disease by a Cellular-Resolution Mass Spectrometry Imaging Platform.

Uncovering the molecular changes at the site where Aß is deposited plays a critical role in advancing the diagnosis and treatment of Alzheimer's disease. However, there is currently a lack of a suitable label-free imaging method with a high spatial resolution for brain tissue analysis. In this study, we propose a modified desorption electrospray ionization (DESI) mass spectrometry imaging (MSI) method, called segmented temperature-controlled DESI (STC-DESI), to achieve high-resolution and high-sensitivity spatial metabolomics observation by precisely controlling desorption and ionization temperatures. By concentrating the spray plume and accelerating solvent evaporation at different temperatures, we achieved an impressive spatial resolution of 20 µm that enables direct observation of the heterogeneity around a single cell or an individual Aß plaque and an exciting sensitivity that allows a variety of low-abundance metabolites and less ionizable neutral lipids to be detected. We applied this STC-DESI method to analyze the brains of transgenic AD mice and identified molecular changes associated with individual Aß aggregates. More importantly, our study provides the first evidence that carnosine is significantly depleted and 5-caffeoylquinic acid (5-CQA) levels rise sharply around Aß deposits. These observations highlight the potential of carnosine as a sensitive molecular probe for clinical magnetic resonance imaging diagnosis and the potential of 5-CQA as an efficient therapeutic strategy for Aß clearance in the early AD stage. Overall, our findings demonstrate the effectiveness of our STC-DESI method and shed light on the potential roles of these molecules in AD pathology, specifically in cellular endocytosis, gray matter network disruption, and paravascular Aß clearance.

Hippocampal TMEM55B overexpression in the 5XFAD mouse model of Alzheimer's disease.

Dysfunction of the endosomal-lysosomal network is a notable feature of Alzheimer's disease (AD) pathology. Dysfunctional endo-lysosomal vacuoles accumulate in dystrophic neurites surrounding amyloid ß (Aß) plaques and may be involved in the pathogenesis and progression of Aß aggregates. Trafficking and thus maturation of these dysfunctional vacuoles is disrupted in the vicinity of Aß plaques. Transmembrane protein 55B (TMEM55B), also known as phosphatidylinositol-4,5-bisphosphate 4-phosphatase 1 (PIP4P1) is an endo-lysosomal membrane protein that is necessary for appropriate trafficking of endo-lysosomes. The present study tested whether overexpression of TMEM55B in the hippocampus could prevent plaque-associated axonal accumulation of dysfunctional endo-lysosomes, reduce Aß plaque load, and prevent hippocampal-dependent learning and memory deficits in the 5XFAD mouse models of Aß plaque pathology. Immunohistochemical analyses revealed a modest but significant reduction in the accumulation of endo-lysosomes in dystrophic neurites surrounding Aß plaques, but there was no change in hippocampal-dependent memory or plaque load. Overall, these data indicate a potential role for TMEM55B in reducing endo-lysosomal dysfunction during AD-like Aß pathology.