While most Alzheimer's disease (AD) studies focus on the cognitive aspects of the disease, less focus is given to affective symptoms. In this study, we investigated the long-term consequences of exposure to chronic stress. 5xFAD AD model mice were exposed to unpredictable chronic mild stress, and cognitive and emotional aspects were examined at 3-time points (up to 4 months after exposure to stress). We found that exposure to chronic stress accelerates neuropathology outcomes in the 5xFAD mouse model in adulthood, accompanied by changes in the neurotrophic system. Specifically, we found that chronic stress accelerated the appearance of short-term spatial memory deficits in the 5xFAD mice and decreased tyrosine kinase B full receptor (TrkB.FL) expression levels. In vitro, we showed that corticosterone impairs the ability of microglia to uptake Aβ and reduces microglial activation. To conclude, our study may shed light on the mechanisms through which mild chronic stress might contribute to the onset and progression of Alzheimer's disease symptoms.

Synapse loss and damage are underlying causes of Alzheimer's disease. Duloxetine has been identified as a mimetic of neural adhesion molecule L1CAM, a neuronal synapse component, suggesting duloxetine could be therapeutic for Alzheimer's disease.

Cognitive function in 5xFAD mice was evaluated by open field, novel object recognition, and Morris water maze tests. Hippocampal and cortical Aβ1-40, Aβ1-42 and amyloid plaque deposition were quantified by ELISA and immunohistochemistry. RT-qPCR and western blotting quantified the effects of duloxetine treatment on L1CAM levels and PI3K/Akt/CREB signaling pathway activation. Apoptosis markers Bcl-2 and Bax were also measured by RT-qPCR and western blotting. HT22 cell survival was measured by CCK8 assay.

Duloxetine preserved learning and memory abilities, but had no effect on locomotor performance of 5xFAD mice. Duloxetine decreased Aβ1-42 expression levels, increased Aβ1-40 levels, reduced amyloid plaque formation, and activated the PI3K/Akt/CREB signaling pathway in both cortices and hippocampi of 5xFAD mice. Moreover, duloxetine increased the expression of L1CAM and Bcl-2, and inhibited the expression of Bax, as well as prevented Aβ1-42 cytotoxicity in wild-type, but not L1CAM-knockdown HT22 cells, suggesting a feed-forward mechanism for duloxetine-mediated neuroprotection, whereby duloxetine induces and activates L1CAM to exert neuroprotective effects.

Our findings demonstrate that duloxetine plays a neuroprotective role in 5xFAD mice and HT22 cells through activating L1CAM, likely by regulating the PI3K/Akt/CREB signaling pathway. These results suggest that duloxetine may be a potential reagent for the treatment of Alzheimer's disease.

Pathophysiological changes associated with Alzheimer's disease (AD) begin decades before dementia onset, with age and APOE ε4 genotype as major risk factors [1-4]. Primary risk factors for developing AD include aging and number of copies of the apolipoprotein E (APOE) ε4 allele. Altered sphingolipid metabolism is increasingly implicated in early AD. However, the relationship between early plasma and brain sphingolipid changes-particularly in the context of APOE genotype-remains poorly defined. In this study, we analyzed plasma and brain sphingolipid profiles in transgenic AD mice carrying human APOE3 or APOE4 variants, with or without familial AD mutations (E3FAD and E4FAD). Using liquid chromatography-tandem mass spectrometry (LC-MS/MS), we assessed 110 sphingolipid species across four major classes (ceramides (Cers), hexosylceramides (HexCers), lactosylceramides (LacCers), and sphingomyelins (SMs)) at 2, 4, and 6 months in plasma and at 6 months in brain tissue in the cortex, hippocampus, striatum, and cerebellum. Our results demonstrate that early plasma sphingolipid alterations are largely driven by APOE genotype rather than AD pathology. Specifically, APOE4 carriers showed significant increases in SM species and reductions in Cer species compared to APOE3 carriers, independent of age or AD genotype. Brain lipid profiles showed minimal changes across genotypes after region correction. However, combined p-value analyses revealed APOE- and EFAD-dependent differences in the composition of primarily cortical sphingolipids. ROC analyses demonstrated high discriminative power of plasma sphingolipids for APOE, but not for AD genotype. These findings suggest that early plasma lipid profiles in female 5xFAD mice are more strongly influenced by APOE genotype than by overt AD pathology, potentially reflecting systemic pathways linked to APOE4-associated AD risk, while early disease-associated changes in the brain appear to be subtle and region-specific. These results underscore the importance of accounting for APOE genotype in early-stage AD lipidomic studies and in the interpretation of peripheral lipid biomarkers.

Myelin ensheathment is essential for rapid axonal conduction, metabolic support and neuronal plasticity. In Alzheimer's disease (AD), disruptions in myelin and axonal structures occur, although the underlying mechanisms remain unclear. We implemented proximity labeling subcellular proteomics of the myelin-axon interface in postmortem human brains from AD donors and 15-month-old male and female 5XFAD mice. We uncovered multiple dysregulated signaling pathways and ligand-receptor interactions, including those linked to amyloid-β processing, axonal outgrowth and lipid metabolism. Expansion microscopy confirmed the subcellular localization of top proteomic hits and revealed amyloid-β aggregation within the internodal periaxonal space and paranodal/juxtaparanodal channels. Although overall myelin coverage is preserved, we found reduced paranode density, aberrant myelination and altered paranode positioning around amyloid-plaque-associated dystrophic axons. These findings suggest that the myelin-axon interface is a critical site of protein aggregation and disrupted neuro-glial signaling in AD.

Microglial phagocytosis genes have been linked to increased risk for Alzheimer's disease (AD), but the mechanisms translating genetic association to cellular dysfunction remain unknown. Here, we showed that microglia formed lipid droplets (LDs) upon amyloid-β (Aβ) exposure and that LD loads increased with proximity to amyloid plaques in brains from individuals with AD and the 5xFAD mouse model. LD-laden microglia exhibited defects in Aβ phagocytosis, and unbiased lipidomic analyses identified a parallel decrease in free fatty acids (FFAs) and increase in triacylglycerols (TGs) as the key metabolic transition underlying LD formation. Diacylglycerol O-acyltransferase 2 (DGAT2)-a key enzyme that converts FFAs to TGs-promoted microglial LD formation and was increased in mouse 5xFAD and human AD brains. Pharmacologically targeting DGAT2 improved microglial uptake of Aβ and reduced plaque load and neuronal damage in 5xFAD mice. These findings identify a lipid-mediated mechanism underlying microglial dysfunction that could become a therapeutic target for AD.

Emerging evidence indicates that a baseline level of controlled innate immune signaling is required to support proper brain function. However, little is known about the function of most innate immune pathways in homeostatic neurobiology. Here, we report a role for astrocyte-dependent inflammasome signaling in regulating hippocampal plasticity. Inflammasomes are multiprotein complexes that promote caspase-1-mediated interleukin (IL)-1 and IL-18 production in response to pathogens and tissue damage. We observed that inflammasome complex formation was regularly detected under homeostasis in hippocampal astrocytes and that its assembly is dynamically regulated in response to learning and regional activity. Conditional ablation of caspase-1 in astrocytes limited hyperexcitability in an acute seizure model and impacted hippocampal plasticity via modulation of synaptic protein density, neuronal activity, and perineuronal net coverage. Caspase-1 and IL-18 regulated hippocampal IL-33 production and related plasticity. These findings reveal a homeostatic function for astrocyte inflammasome activity in regulating hippocampal physiology in health and disease.

Alzheimer's disease (AD) is an irreversible disease characterized by a complex pathophysiology. Recent evidence consistently identifies inflammation as one of the contributing factors, along with the pathological aggregation and accumulation of amyloid-β (Aβ) peptides and hyperphosphorylated tau protein. Inflammation is suggested to have specific causative agents, of which lipopolysaccharide (LPS) may be important in AD. Interestingly, elevated LPS levels are found in patients with AD, and these elevated levels cause cognitive dysfunction in AD patients. Moreover, LPS contributes to neuroinflammation and Aβ and tau pathology in AD. However, questions remain about LPS presence/distribution in AD brains and its relationship with AD pathology. This study investigated (1) the changes in LPS presence/distribution in wild-type (WT) and 5XFAD mice, (2) the pathological role of LPS on Aβ and tau aggregation, and (3) the effect of LPS on neuroinflammatory response in vitro and in vivo. LPS accumulations were significantly increased in the 5XFAD brains compared to WT brains. Particularly, LPS distribution is increasing in the 5XFAD brains in an AD progression-dependent manner. Furthermore, LPS significantly increased aggregation of Aβ and tau and deteriorated neuroinflammatory response in vitro and in vivo. Thus, our results suggest that LPS contributes to AD pathology and modulation of LPS levels could be an effective therapeutic strategy for AD.

Genome-wide association studies have identified many gene polymorphisms associated with an increased risk of developing late-onset Alzheimer's disease (LOAD). Many of these LOAD risk-associated alleles alter disease pathogenesis by influencing innate immune responses and lipid metabolism of microglia (MG). Here we show that boosting the expression of angiotensin-converting enzyme (ACE), a genome-wide association study LOAD risk-associated gene product, specifically in MG, reduces amyloid-β (Aβ) plaque load, preserves vulnerable neurons and excitatory synapses, and significantly reduces learning and memory abnormalities in the 5xFAD amyloid mouse model of AD. ACE-expressing MG surround plaques more frequently and they have increased Aβ phagocytosis, endolysosomal trafficking and spleen tyrosine kinase activation downstream of the major Aβ receptors, triggering receptor expressed on myeloid cells 2 (Trem2) and C-type lectin domain family 7 member A (Clec7a). These findings establish a role for ACE in enhancing microglial immune function and they identify a potential use for ACE-expressing MG as a cell-based therapy to augment endogenous microglial responses to Aβ in AD.

N6-methyladenosine (m6A) is an abundant internal RNA modification that can impact gene expression at both post-transcriptional and transcriptional levels. However, the landscapes and functions of m6A in human brains and neurodegenerative diseases, including Alzheimer's disease (AD), are under-explored. Here, we examined RNA m6A methylome using total RNA-seq and meRIP-seq in middle frontal cortex of post-mortem brains from individuals with or without AD, which revealed m6A alteration on both mRNAs and various noncoding RNAs. Notably, many promoter-antisense RNAs (paRNAs) displayed cell-type-specific expression and changes in AD, including one produced adjacent to MAPT that encodes the Tau protein. MAPT-paRNA is highly expressed in neurons, and m6A positively controls its expression. In iPSC-derived human excitatory neurons, MAPT-paRNA does not impact the nearby MAPT mRNA, but instead promotes expression of hundreds of neuronal and synaptic genes, and is protective against excitotoxicity. Analysis of single nuclei RNA-DNA interactome in human brains supports that brain paRNAs interact with both cis- and trans-chromosomal target genes to impact their transcription. These data reveal landscapes and functions of noncoding RNAs and m6A in brain gene regulation and AD pathogenesis.

Defining the progression of blood biomarkers in Alzheimer's disease (AD) is essential for targeting treatments in patients most likely to benefit from early intervention. We delineated the temporal ordering of blood biomarkers a decade prior to the onset of AD, explored associations with AD brain pathology, and examined the relationship between reactive astrocytosis in the brain and plasma in a transgenic mouse model.

We analyzed plasma blood biomarkers using the Quanterix HD-X instrument in case-control and postmortem cohorts from the Baltimore Longitudinal Study on Aging (BLSA). We assessed plasma and cortical reactive astrocytosis, measured by glial fibrillary acidic protein (GFAP), in 5xFAD transgenic and wild-type mice.

In AD-converters (N = 158, 377 samples), higher plasma GFAP levels are observed 10 years prior to the onset of cognitive impairment due to AD compared with individuals who remain cognitively unimpaired (N = 160, 379 samples). Plasma GFAP levels are highest in neuropathologically confirmed AD, intermediate in asymptomatic AD, and lowest in cognitively unimpaired and associated with severity of neuritic plaques and neurofibrillary tangles. GFAP-labeled immunoreactive astrocytes in the cortex of 3- and 7-month-old 5xFAD transgenic mice increased relative to wild-type mice and higher blood GFAP concentration was associated with more GFAP-expressing astrocytes.

Reactive astrocytosis, assessed by elevated GFAP levels, is an early event in the progression of blood biomarker changes in preclinical AD, may be an early marker of AD pathogenesis, and a promising therapeutic target.

Intramural Research Program, NIA.

Alzheimer's Disease (AD) is an incurable and debilitating progressive, neurodegenerative disorder which is the leading cause of dementia worldwide. Neuropathologically, AD is characterized by the accumulation of Aβ amyloid plaques in the microenvironment of brain cells and neurovascular walls, chronic neuroinflammation, resulting in neuronal and synaptic loss, myelin and axonal failure, as well as significant reduction in adult hippocampal neurogenesis. The hippocampal formation is particularly vulnerable to this degenerative process, due to early dysfunction of the cholinergic circuit. Neurotrophic factors consist major regulatory molecules and their decline in AD is considered as an important cause of disease onset and progression. Novel pharmacological approaches are targeting the downstream pathways controlled by neurotrophins, such as nerve growth factor (NGF) receptors, TrkA and p75NTR, which enhance hippocampal neurogenic capacity and neuroprotective mechanisms, and potentially counteract the neurotoxic effects of amyloid deposition. BNN27 is a non-toxic, newly developed 17-spiro-steroid analog, penetrating the blood-brain-barrier (BBB) and mimicking the neuroprotective effects of NGF, acting as selective activator of its receptors, both TrkA and p75NTR, thus promoting survival of various neuronal cell types. Our present research aims at determining whether and which aspects of the AD-related pathology, BNN27 is able to alleviate, exploring the cellular and molecular AD components and link these changes with improvements in the cognitive performance of an animal AD model, the 5xFAD mice. Our results clearly indicate that BNN27 administration significantly reduced amyloid-β load in whole brain of the animals, enhanced adult hippocampal neurogenesis, restored cholinergic function and synaptogenesis, reducing inflammatory activation and leading to significant restoration of cognitive functions. BNN27 may represent a new lead multimodal molecule with neuroprotective, neurogenic and anti-neuroinflammatory actions for developing druggable anti-Alzheimeric agents. Proteomics data are available via ProteomeXchange with the identifier PXD044699.

Alzheimer's disease (AD) is an age-dependent neurodegenerative disorder characterized by neuronal loss leading to dementia and ultimately death. Whilst the loss of neurons is central to this disease, it is becoming clear that glia, specifically astrocytes, contribute to the onset and progression of neurodegeneration. The role of astrocytes in maintaining ion homeostasis in the extracellular milieu is fundamental for multiple brain functions, including synaptic plasticity and neuronal excitability, which are compromised during AD and affect neuronal signalling. In this study, we measured the astrocytic K+ clearance rate in the hippocampus and somatosensory cortex of a mouse model for AD during disease progression. Our results establish that astrocytic [K+]o (extracellular K+ concentration) clearance in the hippocampus is reduced in symptomatic 5xFAD mice, and this decrease is region-specific, as no significant alterations were detected in the superficial layers of the somatosensory cortex. The decrease in the [K+]o clearance rate correlated with a significant reduction in the expression and conductivity of Kir4.1 channels and a decline in the number of primary connected astrocytes. Moreover, astrocytes in the hippocampus of symptomatic 5xFAD mice demonstrated increased reactivity which was accompanied by an increased excitability and altered spiking profile of nearby neurons. These findings indicate that the supportive function astrocytes typically provide to nearby neurons is diminished during disease progression, which affects the neuronal circuit signalling in this area and provides a potential explanation for the increased vulnerability of neurons in AD. KEY POINTS: Astrocytic potassium clearance from the extracellular milleu is fundamental for multiple brain functions. Alterations in the clearance rate can affect the excitability and overall viability of neurons. A symptomatic mouse model for Alzheimer's disease (5xFAD) exhibits a significant decline in astrocytic K+ clearance at the hippocampus, but not the somatosensory cortex. The decrease in the clearance rate correlated with a reduction in the expression and conductivity of astrocytic Kir4.1 channels and a decrease in the number of primary connected astrocytes, specifically at the stratum lacunosum moleculare layer of the CA1 region. Astrocytes in the hippocampus of symptomatic 5xFAD mice displayed increased reactivity. The excitability profile and firing patterns of neurons at the hippocampus were affected by alterations in K+ homeostasis, indicating that the supportive function astrocytes typically provide to nearby neurons is diminished during progression of Alzheimer's disease.

To explore the mechanism by which rop16 Ⅰ/Ⅲ -deficient/gra15 Ⅱ -dominant toxoplasma gondii Chinese 1 genotype Wh3 (TgCtwh3 Δrop16 Ⅰ/Ⅲ ) strain induced neuron apoptosis, APP and BACE1 production in vivo and vitro.

BALB/c mice were infected by intraperitoneal injection with TgCtwh3 wild type (TgCtwh3 WT) and TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites, respectively. One week after infection, the morphology and number of hippocampal neurons were examined by hematoxylin-eosin (H&E) and Nissl staining. Expression levels of apoptosis-related proteins, APP, BACE1 as well as inflammatory factors proteins and genes in the hippocampus were evaluated using western blotting and qRT-PCR. The hippocampal neuron cell line HT22 was infected with TgCtwh3 WT and TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoite, respectively, and the expression of target proteins was analyzed through immunofluorescence staining and western blotting. Furthermore, HT22 apoptosis was assessed using flow cytometry.

BALB/c mice injected with TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites presented abnormal appearance and posture changes as well as declined vitality. The hippocampus assay demonstrated that TgCtwh3 Δrop16 Ⅰ/Ⅲ toxoplasma caused neuron loss, neuron alignment disorder, neuronal nucleus abnormal deep-stained and neuron apoptosis. Furthermore, TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites caused obvious production of APP, BACE1and expression increase of pro-inflammatory factors in hippocampal tissue compared to these in mice infected with TgCtwh3 WT tachyzoites. Contrarily, the expression of transforming growth factor beta 1 (TGF-β1), a pivotal anti-inflammatory cytokine was significantly decreased in TgCtwh3 Δrop16 Ⅰ/Ⅲ infected mice. Further study showed that TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites induced HT22 apoptosis through triggering ERS, meanwhile promoted HT22 to produce APP, BACE1 by activating NF-κB signaling pathway.

Our results indicated that the GRA15Ⅱ effector may play a crucial part in neuron apoptosis, pro-inflammatory factors secretion, and APP, BACE1 production. Inversely, ROP16Ⅰ/Ⅲ effector may play a potentially protective role in this process.

Even though the number of patients suffering from Alzheimer's Disease (AD) is rapidly growing worldwide, only a few symptomatic treatments have been approved for clinical use, pointing out the urgent need for more effective disease-modifying therapies that actually alter the progression of this neurodegenerative disorder which is characterized by co-occurence of both Amyloid beta (Aβ) and tau neuropathologies. Preclinical and clinical evidence suggests that a link between Aβ and tau drives the entire continuum of AD pathobiology. 12A12 is a monoclonal antibody (mAb) which offers neuroprotection into two transgenic lines of AD, including Tg2576 that overexpresses Swedish mutation (KM670/671NL) of Amyloid Precursor Protein (APP, isoform 695) and 3xTg (APP Swedish, MAPT P301L, and PSEN1 M146V), by targeting the 20-22kDa N-terminal tau fragments (NH2htau). In particular, acute (over 14 days with 4 doses), intravenous injection of 12A12mAb leads to significant improvement of cognitive, biochemical and histopathological AD signs in symptomatic 6-month-old Tg2576, a well-established transgenic mouse model that mimics the human amyloidosis with an age-dependent Aβ accumulation/aggregation and plaque deposition. Here, we report that Tg2576 mice, immunized with 12A12mAb at 6 months of age and returned to their home cage for additional 3 months, exhibit preserved spatial memory despite the anticipated interruption of antibody administration (discontinuous treatment). This enduring beneficial effect on memory deficit (up to 90 days after the last injection) is accompanied by normalization in the synaptic imbalance and microgliosis along with decrease of the most toxic A11-positive prefibrillar oligomers and inverse increase in 4kDa monomeric form(s) of Aβ 1-42. These findings reveal that: (i) soluble, pathogenetic tau specie(s) located at the N-terminal domain of protein early synergizes with Aβ in driving the progression of AD neuropathology; (ii) transient immunoneutralization of the NH2htau following short-term treatment with 12A12mAb exerts preventive, long-lasting neuroprotective effects, at least in part by interfering at "pre-plaque" stage with the progressive deposition of insoluble, fibrillar Aβ via a shift of its aggregation pathway into its less harmful, unaggregated monomeric forms. Taken together, these findings represent a strong rationale for the advancement of 12A12mAb to clinical stage aiming at preventing the Aβ-dependent neurodegeneration by lowering the cerebral levels of NH2htau in humans suffering from chronic, slow-progressing AD.

Alzheimer's disease (AD) and traumatic brain injury (TBI) are currently untreatable neurodegenerative disorders afflicting millions of people worldwide. These conditions are pathologically related, and TBI is one of the greatest risk factors for AD. Although blood-brain barrier (BBB) disruption drives progression of both AD and TBI, strategies to preserve BBB integrity have been hindered by lack of actionable targets. Here, we identify 15-hydroxyprostaglandin dehydrogenase (15-PGDH), an enzyme that catabolizes eicosanoids and other anti-inflammatory mediators, as a therapeutic candidate that protects the BBB. We demonstrate that 15-PGDH is enriched in BBB-associated myeloid cells and becomes markedly elevated in human and mouse models of AD and TBI, as well as aging, another major risk factor for AD. Pathological increase in 15-PGDH correlates with pronounced oxidative stress, neuroinflammation, and neurodegeneration, alongside profound BBB structural degeneration characterized by astrocytic endfeet swelling and functional impairment. Pharmacologic inhibition or genetic reduction of 15-PGDH in AD and TBI models strikingly mitigates oxidative damage, suppresses neuroinflammation, and restores BBB integrity. Most notably, inhibiting 15-PGDH not only halts neurodegeneration but also preserves cognitive function at levels indistinguishable from healthy controls. Remarkably, these neuroprotective effects in AD are achieved without affecting amyloid pathology, underscoring a noncanonical mechanism for treating AD. In a murine microglia cell line exposed to amyloid beta oligomer, major protection was demonstrated by multiple anti-inflammatory substrates that 15-PGDH degrades. Thus, our findings position 15-PGDH inhibition as a broad-spectrum strategy to protect the BBB and thereby preserve brain health and cognition in AD and TBI.

In Alzheimer's disease, accumulation of amyloid-β (Aβ) peptide is thought to cause formation of neurofibrillary tangles composed of hyperphosphorylated tau protein, which correlates with neuronal loss and cognitive impairment, but the mechanism linking Aβ and tau pathologies is unknown. Dystrophic neurites, which surround Aβ plaques and accumulate phosphorylated tau and other proteins, may play a role in seeding and spreading of pathologic tau. Here, we investigate the novel hypothesis that improved membrane repair capacity decreases dystrophic neurite formation by protecting axons from Aβ-induced membrane damage. Using a ratiometric calcium sensor and a FRET-based calpain cleavage sensor, we demonstrate that dystrophic neurites in 5XFAD mice have elevated resting calcium levels and calpain activity because of putative membrane damage. Annexin A6, a plasma membrane repair in muscle and neurons, is present at plasma membrane of neurons and dystrophic neurites in murine and human brains. Overexpression of annexin A6 in brains of 5XFAD mice decreased size and quantity of dystrophic neurites and accumulation of phospho-tau181, an early biomarker of amyloid pathology. Phospho-tau231, another early amyloid biomarker, and phosphorylated of tau kinases, c-jun N-terminal kinase (JNK) and Calmodulin Kinase II (CaMKII) accumulate in dystrophic neurites in the brains of amyloid pathology mice and humans with AD, suggesting that dystrophic neurites are sites of active tau phosphorylation. Overexpression of dominant-negative annexin A6 in 5XFAD mice increased dystrophic neurites and phospho-tau181. Intracerebral injection of recombinant annexin A6 in 5XFAD and APP-NLGF knock-in mice resulted in localization of recombinant A6 to membranes of dystrophic neurites, suggesting therapeutic potential of recombinant annexin A6 for AD. In conclusion, dystrophic neurites have Aβ-induced membrane damage characterized by calcium elevation, calpain activation, and accumulation of tau kinases and phosphorylated tau. Overexpression of annexin A6 reduces dystrophic neurites and phospho-tau accumulation, suggesting that annexin A6-mediated membrane repair may represent a novel therapeutic approach for AD.

New drugs to treat Alzheimer´s disease (AD) are urgently needed. Human triggering receptor expressed on myeloid cells 2 (hTREM2) is a validated drug target which is genetically associated with AD. Existing anti-hTREM2 antibodies were raised in animal immune systems, and subsequently humanized, which may incur immunological complications upon repeated preventive or therapeutic applications in vivo in AD patients. In addition, anti-hTREM2 antibodies should be optimized for both, efficacy and safety.

A novel fully human monoclonal brain-targeting anti-hTREM2 antibody M07-TFN was created. Binding affinities, cell viabilities, and agonist potencies were investigated on rhTREM2 and in human microglia. Transcytosis assays modeled blood-brain barrier translocation (BBB). Behavior tests were carried out in 5 × familiar AD (5xFAD) mice of both genders, to test for brain function and cognition as well as hippocampus-dependent spatial memory using the Barnes maze. In addition, amyloid plaque formation was determined on brain sections at the end of the study.

M07-TFN showed higher binding affinities and stronger activation of hTREM2 signaling than all previously described anti-hTREM2 antibodies. p-Syk activation was increased 30-fold in hTREM2-overexpressing HEK293 cells and fourfold in human microglia cells compared to baseline. Human microglia viability significantly improved after stress testing. M07-TFN showed strong BBB translocation in a human BBB model, and exerted cross-reactivity to the mouse TREM2 stalk region, which allowed us to investigate M07-TFN directly in an AD mouse model. In 5xFAD mice, M07-TFN resulted in improved novel object location and better spatial orientation and memory, and significantly reduced plaque load. Additional safety investigations in mice showed no negative effects on blood cells or major organs.

Compared to existing humanized anti-hTREM2 antibodies that have been investigated in clinical trials, M07-TFN showed best-in-class affinities and agonist potencies. Being a fully human anti-hTREM2 antibody, M07-TFN holds the promise of reduced immunogenicity for use in human patients.

: Alzheimer's disease (AD) is a neurodegenerative disorder closely associated with aging, and its pathogenesis involves the interaction of multidimensional pathophysiologic processes. This review outlines the core mechanisms linking aging and AD. The amyloid cascade hypothesis emphasizes that abnormal deposition of amyloid-β (Aβ) triggers neuronal damage and synaptic dysfunction, which is exacerbated by aging-associated declines in protein clearance. Neuroinflammation, a synergistic pathogenetic factor in AD, is mediated by microglia activation, creating a vicious cycle with Aβ and tau pathology. The cholinergic hypothesis states that the degeneration of cholinergic neurons in the basal forebrain can lead to acetylcholine deficiency, which is directly associated with cognitive decline. Endothelial disorders promote neuroinflammation and metabolic waste accumulation through blood-brain barrier dysfunction and cerebral vascular abnormalities. In addition, glutamate-mediated excitotoxicity and mitochondrial dysfunction (e.g., oxidative stress and energy metabolism imbalance) further lead to neuronal death, and aging-associated declines in mitochondrial autophagy exacerbate such damage. This review also explores the application of animal models that mimic AD and aging in studying these mechanisms and summarizes therapeutic strategies targeting these pathways. Future studies need to integrate multi-targeted therapies and focus on the role of the aging microenvironment in regulating AD pathology in order to develop more effective early diagnosis and treatment options.

Brain endothelial cells (BECs) in brain vasculature are critical structural and functional components of the blood brain barrier (BBB). Adeno-associated virus (AAV) capsids have previously been genetically engineered to confer specificity to endothelial cells, but these capsids show limited endothelial cell specificity that varies by delivery conditions. We developed a set of new BEC-enhancer AAV vectors that specifically target BECs based on the cis-regulatory elements identified from single-cell epigenetic datasets. Ex vivo and in vivo characterization of BEC-enhancer AAVs in wild-type, Ai9 reporter, and Alzheimer's disease model mouse brains show their utility for high transduction selectivity of the BECs with little off-target transduction in the liver. Our BEC-enhancer AAVs target the brain vasculature by systemic administration and can be minimally invasive in terms of the route of administration. They are useful new tools for delivering genetic payloads specifically to BECs for normal and diseased brain studies.

Reactive gliosis is a hallmark of neuropathology and offers a potential target for addressing numerous neurological diseases. Here, we show that growth arrest and DNA damage inducible gamma (GADD45G), a stress sensor in astrocytes, is a nodal orchestrator of reactive gliosis and neurodegeneration. GADD45G expression in astrocytes is sufficient to incite astrogliosis, microgliosis, synapse loss, compromised animal behavior, and the aggravation of Alzheimer's disease (AD). Conversely, silencing GADD45G specifically in astrocytes preserves synapses and rescues the histological and behavioral phenotypes of AD. Mechanistically, GADD45G controls the mitogen-activated protein kinase kinase kinase 4 (MAP3K4) and neuroimmune signaling pathways, including nuclear factor κB (NF-κB) and interferon regulatory factor 3 (IRF3), leading to profound molecular changes and the secretion of various factors that regulate both cell-autonomous and cell-nonautonomous reactive gliosis and glia-neuron interactions. These results uncover GADD45G signaling as a promising therapeutic target for AD and potentially for numerous other neurological disorders.

Dysfunction of the glymphatic system, a brain-wide waste clearance network, is strongly linked to Alzheimer's disease (AD) and the accumulation of β-amyloid (Aβ) and tau proteins. Here, we identify an astrocytic signaling pathway that can be targeted to preserve glymphatic function and mitigate neurotoxic protein buildup. Analysis of astrocytes from both human AD brains and two transgenic mouse models (5XFAD and PS19) reveals robust activation of the protein kinase RNA-like endoplasmic reticulum (ER) kinase (PERK)-α subunit of eukaryotic initiation factor 2 (eIF2α) branch of the unfolded protein response. Chronic PERK activation suppresses astrocytic protein synthesis and, through casein kinase 2 (CK2)-dependent mechanisms, disrupts the perivascular localization of aquaporin-4 (AQP4), a water channel essential for glymphatic flow. Importantly, astrocyte-specific PERK deletion or pharmacological inhibition restores AQP4 localization, enhances glymphatic clearance, reduces Aβ and tau pathology, and improves cognitive performance in mice. These findings highlight the critical role of the astrocytic PERK-CK2-AQP4 axis in glymphatic dysfunction and AD pathogenesis, positioning this pathway as a promising therapeutic target.

Peroxisome proliferator-activated receptors (PPARs), ligand-activated transcription factors, have emerged as a key regulator of various biological processes, underscoring their relevance in the pathophysiology and treatment of numerous diseases. PPARs are primarily recognized for their critical role in lipid and glucose metabolism, which underpins their therapeutic applications in managing type 2 diabetes mellitus. Beyond metabolic disorders, they have gained attention for their involvement in immune modulation, making them potential targets for autoimmune-related inflammatory diseases. Furthermore, PPAR's ability to regulate proliferation, differentiation, and apoptosis has positioned them as promising candidates in oncology. Their anti-inflammatory and anti-fibrotic properties further highlight their potential in dermatological and cardiovascular conditions, where dysregulated inflammatory responses contribute to disease progression. Recent advancements have elucidated the molecular mechanisms of different PPAR isoforms, including their regulation of key signalling pathways such as NF-κB and MAPK, which are crucial in inflammation and cellular stress responses. Additionally, their interactions with co-factors and post-translational modifications further diversify their functional roles. The therapeutic potential of various PPAR agonists has been extensively explored, although challenges related to side effects and target specificity remain. This growing body of evidence underscores the significance of PPARs in understanding the molecular basis of diseases and advancing therapeutic interventions, paving way for targeted treatment approach across a wide spectrum of medical conditions. Here, we provide a comprehensive and detailed perspective of PPARs and their potential across different health conditions to advance our understanding, elucidate underlying mechanisms, and facilitate the development of potential treatment strategies.

The fourth session of the 2024 European Society of Toxicologic Pathology (ESTP) Congress brought together lectures focused on the use of in vitro and in vivo models to investigate neurodegenerative diseases. Four presentations highlighted various aspects of neurodegenerative diseases including dementia, immune-mediated conditions, and neuromuscular disorders. The session began with an overview of animal models of dementia underscoring their critical role in understanding disease pathogenesis and supporting the development of effective therapeutic drugs. Subsequent presentations investigated immunological self-tolerance in autoimmune neurodegenerative diseases, such as multiple sclerosis and Guillain-Barré syndrome, and the application of in vitro models to study neuromuscular diseases such as amyotrophic lateral sclerosis. The final presentation examined cannabinoid-based therapeutic options for treating neurodegenerative diseases, highlighting their potential in neuroprotection and neurorepair. This session provided valuable insights into the latest research and advancements in neurodegenerative disease modeling and therapy, offering promising directions for improved modeling and therapeutic strategies.

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

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

Alzheimer's disease, the most common form of dementia, is characterized by age-dependent amyloid beta (Ab) aggregation and accumulation, neuroinflammation, and cognitive deficits. Significantly, there are prominent sex differences in the risk, onset, progression, and severity of AD, as well as response to therapies, with disease burden disproportionately affecting women. Although menopause onset (i.e., perimenopause) may be a critical transition stage for AD susceptibility in women, the role of early ovarian decline in initial disease pathology, particularly key neuroinflammatory processes, is not well understood.

To study this, we developed a unique mouse model of perimenopausal AD by combining an accelerated ovarian failure (AOF) model of menopause induced by 4-vinylcyclohexene diepoxide (VCD) with the 5xFAD transgenic AD mouse model. To target early stages of disease progression, 5xFAD females were studied at a young age (∼4 months) and at the beginning stage of ovarian failure analogous to human perimenopause (termed "peri-AOF"), and compared to age-matched males. Assessment of neuropathology was performed by immunohistochemical labeling of Ab as well as markers of astrocyte and microglia activity in the hippocampus, a brain region involved in learning and memory that is deleteriously impacted during AD.

Our results show that genotype, AOF, and sex contributed to AD-like pathology. Aggregation of Ab was heightened in female 5xFAD mice and further increased at peri-AOF, with hippocampal subregion specificity. Further, select increases in glial activation also paralleled Ab pathology in distinct hippocampal subregions. However, cognitive function was not affected by peri-AOF.

These findings align with the hypothesis that perimenopause constitutes a period of susceptibility for AD pathogenesis in women.

The development of anti-amyloid-beta (Aβ) immunotherapies as the first disease modifying therapy for Alzheimer's Disease (AD) is a breakthrough of basic research and translational science.

Genetically modified mouse models developed to study AD neuropathology and physiology were used for the discovery of Aβ immunotherapies and helped ultimately propel therapies to FDA approval. Nonetheless, the combination of modest efficacy and significant rates of an adverse side effect (amyloid related imaging abnormalities, ARIA), has prompted reverse translational research in these same mouse models to better understand the mechanism of the therapies.

This review considers the use of these mouse models in understanding the mechanisms of Aβ clearance, cerebral amyloid angiopathy (CAA), blood brain barrier breakdown, neuroinflammation, and neuronal dysfunction in response to Aβ immunotherapy.

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

Microglia and border-associated macrophages (BAMs) are critical for brain health, and their dysfunction is associated to disease. Replacing brain macrophages holds substantial therapeutic promise but remains challenging. Here, we demonstrate that monocytes can efficiently replace all brain macrophages. Monocytes readily replaced embryonal BAMs upon their depletion and engrafted as monocyte-derived microglia (Mo-Microglia) upon more sustained niche availability. Mo-Microglia expanded comparably to their embryonic counterparts and showed similar longevity. However, monocytes were unable to replicate the distinct identity of embryonically derived BAMs and microglia. Using xenotransplantation, we found that human monocytes exhibited similar behavior, enabling identification of putative Mo-Microglia in Alzheimer's disease individuals. In mice and humans, monocyte ontogeny shaped their identity as brain macrophages. Importantly, mouse fetal liver monocytes exhibited a distinct epigenetic landscape and could develop a bona fide microglial identity. Our results illuminate brain macrophage development and highlight monocytes as an abundant progenitor source for brain macrophage replacement therapies.

Background: Current treatment modalities for Alzheimer's disease (AD), which is characterized by the accumulation of amyloid β (Aβ), have limitations with regard to their efficacy and safety, posing significant challenges for advances in healthcare. However, recent studies indicated that AD can be treated using monocyte-derived macrophages (MDMs). Reportedly, the protein CD300c regulates monocyte differentiation, indicating that targeting CD300c could offer a treatment for AD. Methods: To confirm this, we developed CB201, a fully human anti-CD300c antibody, and demonstrated its strong and specific binding to CD300c using surface plasmon resonance and binding ELISAs. Results: Treatment of THP-1 and human peripheral blood mononuclear cells with CB201 led to increased levels of pro-inflammatory cytokines and the differentiation of macrophages to MDMs. Moreover, the CB201-differentiated macrophages expressed cytokines and chemokines in a pattern that alleviates AD symptoms. In a 5xFAD mouse model, CB201 treatment improved memory and behavior in both the early and late stages of AD and reduced cerebral Aβ plaque load. Conclusions: These results indicate that CB201 promotes the differentiation of macrophages to MDMs and modulates AD-related inflammatory responses, thereby ameliorating the pathological features of AD. These findings identify CD300c as a potential therapeutic target for AD and indicate that CB201 is a promising candidate for its treatment.

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is a major threat to the aging population. Due to lack of effective therapy, preventive treatments are important strategies to limit AD onset and progression, of which dietary regimes have been implicated as a key factor. Diet with high fiber content is known to have beneficial effects on cognitive decline in AD. However, a global survey on microbiome and brain cell dynamics in response to high fiber intake at single-cell resolution in AD mouse models is still missing.

Here, we show that dietary inulin supplementation synergized with AD progression to specifically increase the abundance of Akkermansia muciniphila in gut microbiome of 5 × Familial AD (FAD) mice. By performing single-nucleus RNA sequencing on different regions of the whole brain with three independent biological replicates, we reveal region-specific changes in the proportion of neuron, astrocyte, and granule cell subpopulations upon inulin supplementation in 5xFAD mice. In addition, we find that astrocytes have more pronounced region-specific diversity than microglia. Intriguingly, such dietary change reduces amyloid-β plaque burden and alleviates microgliosis in the forebrain region, without affecting the spatial learning and memory.