Prominent tauopathy and intracellular ß-amyloid accumulation triggered by genetic deletion of cathepsin D: implications for Alzheimer disease pathogenesis.

BACKGROUND: Cathepsin D (CatD) is a lysosomal protease that degrades both the amyloid-ß protein (Aß) and the microtubule-associated protein, tau, which accumulate pathognomonically in Alzheimer disease (AD), but few studies have examined the role of CatD in the development of Aß pathology and tauopathy in vivo. METHODS: CatD knockout (KO) mice were crossed to human amyloid precursor protein (hAPP) transgenic mice, and amyloid burden was quantified by ELISA and immunohistochemistry (IHC). Tauopathy in CatD-KO mice, as initially suggested by Gallyas silver staining, was further characterized by extensive IHC and biochemical analyses. Controls included human tau transgenic mice (JNPL3) and another mouse model of a disease (Krabbe A) characterized by pronounced lysosomal dysfunction. Additional experiments examined the effects of CatD inhibition on tau catabolism in vitro and in cultured neuroblastoma cells with inducible expression of human tau. RESULTS: Deletion of CatD in hAPP transgenic mice triggers large increases in cerebral Aß, manifesting as intense, exclusively intracellular aggregates; extracellular Aß deposition, by contrast, is neither triggered by CatD deletion, nor affected in older, haploinsufficient mice. Unexpectedly, CatD-KO mice were found to develop prominent tauopathy by just ∼ 3 weeks of age, accumulating sarkosyl-insoluble, hyperphosphorylated tau exceeding the pathology present in aged JNPL3 mice. CatD-KO mice exhibit pronounced perinuclear Gallyas silver staining reminiscent of mature neurofibrillary tangles in human AD, together with widespread phospho-tau immunoreactivity. Striking increases in sarkosyl-insoluble phospho-tau (∼ 1250%) are present in CatD-KO mice but notably absent from Krabbe A mice collected at an identical antemortem interval. In vitro and in cultured cells, we show that tau catabolism is slowed by blockade of CatD proteolytic activity, including via competitive inhibition by Aß42. CONCLUSIONS: Our findings support a major role for CatD in the proteostasis of both Aß and tau in vivo. To our knowledge, the CatD-KO mouse line is the only model to develop detectable Aß accumulation and profound tauopathy in the absence of overexpression of hAPP or human tau with disease-associated mutations. Given that tauopathy emerges from disruption of CatD, which can itself be potently inhibited by Aß42, our findings suggest that impaired CatD activity may represent a key mechanism linking amyloid accumulation and tauopathy in AD.

[Age-dependent expression of HSP90 in the hippocampus of APP/PS1 mice].

The present study aims to observe the change in expression of heat shock protein 90 (HSP90) along with amyloid-ß (Aß) and phosphorylated Tau (p-Tau) protein levels in the hippocampus tissue of Alzheimer's disease (AD) transgenic animal model with age. APP/PS1 transgenic mice at age of 6-, 9- and 12-month and C57BL/6J mice of the same age were used. The cognitive abilities of these animals were evaluated using a Morris water maze. Western blot or immunohistochemistry was used to detect the expressions of HSP90 and Aß1-42, as well as the phosphorylation levels of Tau protein in the hippocampus. The hsp90 mRNA levels and the morphology and number of cells in the hippocampus were detected with real-time quantitative polymerase chain reaction (qRT-PCR) and Nissl staining, respectively. The results showed that compared with C57BL/6J mice of the same age, HSP90 and hsp90 mRNA expression were decreased (P < 0.05 or P < 0.01), while Aß1-42 and p-Tau protein levels were increased (P < 0.05 or P < 0.01) in the hippocampal tissue of APP/PS1 transgenic mice. Meanwhile, the decrease in HSP90 and hsp90 mRNA expression (P < 0.05 or P < 0.01), the increase in Aß1-42 and p-Tau levels (P < 0.01 or P < 0.05) in hippocampal tissue and the reduction in behavioral ability showed a progressive development with the advancing of age in the APP/PS1 transgenic mice. In conclusion, in the hippocampal tissue of APP/PS1 mice, the decrease in HSP90 expression and the increase in Aß1-42 and p-Tau levels together with the decline of their cognitive ability are age-dependent.

Spatial-Temporal Mapping Reveals the Golgi as the Major Processing Site for the Pathogenic Swedish APP Mutation: Familial APP Mutant Shifts the Major APP Processing Site.

Alzheimer's disease is associated with increased levels of amyloid beta (Aß) generated by sequential intracellular cleavage of amyloid precursor protein (APP) by membrane-bound secretases. However, the spatial and temporal APP cleavage events along the trafficking pathways are poorly defined. Here, we use the Retention Using Selective Hooks (RUSH) to compare in real time the anterograde trafficking and temporal cleavage events of wild-type APP (APPwt) with the pathogenic Swedish APP (APPswe) and the disease-protective Icelandic APP (APPice). The analyses revealed differences in the trafficking profiles and processing between APPwt and the APP familial mutations. While APPwt was predominantly processed by the ß-secretase, BACE1, following Golgi transport to the early endosomes, the transit of APPswe through the Golgi was prolonged and associated with enhanced amyloidogenic APP processing and Aß secretion. A 20°C block in cargo exit from the Golgi confirmed ß- and γ-secretase processing of APPswe in the Golgi. Inhibition of the ß-secretase, BACE1, restored APPswe anterograde trafficking profile to that of APPwt. APPice was transported rapidly through the Golgi to the early endosomes with low levels of Aß production. This study has revealed different intracellular locations for the preferential cleavage of APPwt and APPswe and Aß production, and the Golgi as the major processing site for APPswe, findings relevant to understand the molecular basis of Alzheimer's disease.

Probable Novel APP Met671Leu Mutation in a Chinese Han Family with Early-Onset Alzheimer's Disease.

Familial Alzheimer's disease (AD) is a rare disease caused by autosomal-dominant mutations. APP (encoding amyloid precursor protein), PSEN1 (encoding presenilin 1), and PSEN2 (encoding presenilin 2) are the most common genes cause dominant inherited AD. This study aimed to demonstrate a Chinese early-onset AD pedigree presenting as progressive memory impairment, apraxia, visual-spatial disorders, psychobehavioral disorders, and personality changes with a novel APP gene mutation. The family contains four patients, three carries and three normal family members. The proband underwent brain magnetic resonance imaging (MRI), 18F-fludeoxyglucose positron emission tomography (18F-FDG-PET), cerebrospinal fluid amyloid detection, 18F-florbetapir (AV-45) Positron Emission Computed Tomography (PET) imaging, whole-exome sequencing and Sanger sequencing. Brain MRI images showed brain atrophy, especially in the entorhinal cortex, temporal hippocampus, and lateral ventricle dilation. The FDG-PET showed hypometabolism in the frontotemporal, parietal, and hippocampal regions. 18F-florbetapir (AV-45) PET imaging showed cerebral cortex Aß protein deposition. The cerebrospinal fluid amyloid protein test showed Aß42/Aß40 ratio decreases, pathological phosphor-tau level increases. Whole-exome sequencing detected a new missense mutation of codon 671 (M671L), which was a heterozygous A to T point mutation at position 2011 (c.2011A > T) in exon 16 of the amyloid precursor protein, resulting in the replacement of methionine to Leucine. The co-separation analysis was validated in this family. The mutation was found in 3 patients, 3 clinical normal members in the family, but not in the other 3 unaffected family members, 100 unrelated normal subjects, or 100 sporadic patients with AD. This mutation was probably pathogenic and novel in a Chinese Han family with early-onset AD.

A novel mouse model for N-terminal truncated Aß2-x generation through meprin ß overexpression in astrocytes.

Neurotoxic amyloid-ß (Aß) peptides cause neurodegeneration in Alzheimer's disease (AD) patients' brains. They are released upon proteolytic processing of the amyloid precursor protein (APP) extracellularly at the ß-secretase site and intramembranously at the γ-secretase site. Several AD mouse models were developed to conduct respective research in vivo. Most of these classical models overexpress human APP with mutations driving AD-associated pathogenic APP processing. However, the resulting pattern of Aß species in the mouse brains differs from those observed in AD patients' brains. Particularly mutations proximal to the ß-secretase cleavage site (e.g., the so-called Swedish APP (APPswe) fostering Aß1-x formation) lead to artificial Aß production, as N-terminally truncated Aß peptides are hardly present in these mouse brains. Meprin ß is an alternative ß-secretase upregulated in brains of AD patients and capable of generating N-terminally truncated Aß2-x peptides. Therefore, we aimed to generate a mouse model for the production of so far underestimated Aß2-x peptides by conditionally overexpressing meprin ß in astrocytes. We chose astrocytes as meprin ß was detected in this cell type in close proximity to Aß plaques in AD patients' brains. The meprin ß-overexpressing mice showed elevated amyloidogenic APP processing detected with a newly generated neo-epitope-specific antibody. Furthermore, we observed elevated Aß production from endogenous APP as well as AD-related behavior changes (hyperlocomotion and deficits in spatial memory). The novel mouse model as well as the established tools and methods will be helpful to further characterize APP cleavage and the impact of different Aß species in future studies.

Live and Heat-Inactivated Streptococcus thermophilus MN-ZLW-002 Mediate the Gut-Brain Axis, Alleviating Cognitive Dysfunction in APP/PS1 Mice.

Research on regulating brain functions with probiotics and postbiotics through the gut-brain axis is attracting attention, offering the possibility of adjuvant therapy for Alzheimer's disease (AD). Three-month-old male APP/PS1 mice were gavaged with live and heat-inactivated S. thermophilus MN-002 for three months. This study demonstrated that live and heat-inactivated S. thermophilus MN-002 improved cognitive dysfunctions in APP/PS1 mice, especially in spatial memory. However, the main effects of live S. thermophilus MN-002 directly altered the intestinal microbiota composition and increased serum IL-1ß and IL-6. Heat-inactivated S. thermophilus MN-002 increased colonic propionic acid levels and enhanced the hippocampus's antioxidant capacity. Furthermore, the changes were more obvious in the high-dose group, such as astrogliosis in the hippocampus. These results indicate that different forms and doses of the same strain, S. thermophilus MN-002, can partly improve cognitive functions in AD model mice via the gut-brain axis.

Efficacy of Sailuotong on neurovascular unit in amyloid precursor protein/presenilin-1 transgenic mice with Alzheimer's disease.

OBJECTIVE: To discuss the influence of Sailuotong (, SLT) on the Neurovascular Unit (NVUs) of amyloid precursor protein (APP)/presenilin-1(PS1) mice and evaluate the role of gas supplementation in activating blood circulation during the progression of Alzheimer's disease (AD). METHODS: The mice were allocated into the following nine groups: (a) the C57 Black (C57BL) sham-operated group (control group), (b) ischaemic treatment in C57BL mice (the C57 ischaemic group), (c) the APP/PS1 sham surgery group (APP/PS1 model group), (d) ischaemic treatment in APP/PS1 mice (APP/PS1 ischaemic group), (e) C57BL mice treated with aspirin following ischaemic treatment (C57BL ischaemic + aspirin group), (f) C57BL mice treated with SLT following ischaemic treatment (C57BL ischaemic + SLT group), (g) APP/PS1 mice treated with SLT (APP/PS1 + SLT group), (h) APP/PS1 mice treated with donepezil hydrochloride following ischaemic treatment (APP/PS1 ischaemic + donepezil hydrochloride group) and (i) APP/PS1 mice treated with SLT following ischaemic treatment (APP/PS1 ischaemic + SLT group). The ischaemic model was established by operating on the bilateral common carotid arteries and creating a microembolism. The Morris water maze and step-down tests were used to detect the spatial behaviour and memory ability of mice. The hippocampus of each mouse was observed by haematoxylin and eosin (HE) and Congo red staining. The ultrastructure of NVUs in each group was observed by electron microscopy, and various biochemical indicators were detected by enzyme-linked immunosorbent assay (ELISA). The protein expression level was detected by Western blot. The mRNA expression was detected by quantitative real-time polymerase chain reaction (qRT-PCR). RESULTS: The results of the Morris water maze and step-down tests showed that ischemia reduced learning and memory in the mice, which were restored by SLT. The results of HE staining showed that SLT restored the pathological changes of the NVUs. The Congo red staining results revealed that SLT also improved the scattered orange-red sediments in the upper cortex and hippocampus of the APP/PS1 and APP/PS1 ischaemic mice. Furthermore, SLT significantly reduced the content of Aß, improved the vascular endothelium and repaired the mitochondrial structures. The ELISA detection, western blot detection and qRT-PCR showed that SLT significantly increased the vascular endothelial growth factor (VEGF), angiopoietin and basic fibroblast growth factor, as well as the levels of gene and protein expression of low-density lipoprotein receptor-related protein-1 (LRP-1) and VEGF in brain tissue. CONCLUSIONS: By increasing the expression of VEGF, SLT can promote vascular proliferation, up-regulate the expression of LRP-1, promote the clearance of Aß and improve the cognitive impairment of APP/PS1 mice. These results confirm that SLT can improve AD by promoting vascular proliferation and Aß clearance to protect the function of NVUs.

Role of GABAB receptors in cognition and EEG activity in aged APP and PS1 transgenic mice.

Alzheimer's disease (AD) is the most common cause of dementia in the elderly. Recent evidence suggests that gamma-aminobutyric acid B (GABAB) receptor-mediated inhibition is a major contributor to AD pathobiology, and GABAB receptors have been hypothesized to be a potential target for AD treatment. The aim of this study is to determine how GABAB regulation alters cognitive function and brain activity in an AD mouse model. Early, middle and late stage (8-23 months) amyloid precursor protein (APP) and presenilin 1 (PS1) transgenic mice were used for the study. The GABAB agonist baclofen (1 and 2.5 mg/kg, i. p.) and the antagonist phaclofen (0.5 mg/kg, i. p.) were used. Primarily, we found that GABAB activation was able to improve spatial and/or working memory performance in early and late stage AD animals. In addition, GABAB activation and inhibition could regulate global and local EEG oscillations in AD animals, with activation mainly regulating low-frequency activity (delta-theta bands) and inhibition mainly regulating mid- and high-frequency activity (alpha-gamma bands), although the regulated magnitude at some frequencies was reduced in AD. The cognitive improvements in AD animals may be explained by the reduced EEG activity in the theta frequency band (2-4 Hz). This study provides evidence for a potential therapeutic effect of baclofen in the elderly AD brain and for GABAB receptor-mediated inhibition as a potential therapeutic target for AD.

Updates on mouse models of Alzheimer's disease.

Alzheimer's disease (AD) is the most common neurodegenerative disease in the United States (US). Animal models, specifically mouse models have been developed to better elucidate disease mechanisms and test therapeutic strategies for AD. A large portion of effort in the field was focused on developing transgenic (Tg) mouse models through over-expression of genetic mutations associated with familial AD (FAD) patients. Newer generations of mouse models through knock-in (KI)/knock-out (KO) or CRISPR gene editing technologies, have been developed for both familial and sporadic AD risk genes with the hope to more accurately model proteinopathies without over-expression of human AD genes in mouse brains. In this review, we summarized the phenotypes of a few commonly used as well as newly developed mouse models in translational research laboratories including the presence or absence of key pathological features of AD such as amyloid and tau pathology, synaptic and neuronal degeneration as well as cognitive and behavior deficits. In addition, advantages and limitations of these AD mouse models have been elaborated along with discussions of any sex-specific features. More importantly, the omics data from available AD mouse models have been analyzed to categorize molecular signatures of each model reminiscent of human AD brain changes, with the hope to guide future selection of most suitable models for specific research questions to be addressed in the AD field.

Early amyloid-induced changes in microglia gene expression in male APP/PS1 mice.

Alzheimer's disease (AD) is a progressive neurodegenerative disease and the most common cause of dementia, characterized by deposition of extracellular amyloid-beta (Aß) aggregates and intraneuronal hyperphosphorylated Tau. Many AD risk genes, identified in genome-wide association studies (GWAS), are expressed in microglia, the innate immune cells of the central nervous system. Specific subtypes of microglia emerged in relation to AD pathology, such as disease-associated microglia (DAMs), which increased in number with age in amyloid mouse models and in human AD cases. However, the initial transcriptional changes in these microglia in response to amyloid are still unknown. Here, to determine early changes in microglia gene expression, hippocampal microglia from male APPswe/PS1dE9 (APP/PS1) mice and wild-type littermates were isolated and analyzed by RNA sequencing (RNA-seq). By bulk RNA-seq, transcriptomic changes were detected in hippocampal microglia from 6-months-old APP/PS1 mice. By performing single-cell RNA-seq of CD11c-positive and negative microglia from 6-months-old APP/PS1 mice and analysis of the transcriptional trajectory from homeostatic to CD11c-positive microglia, we identified a set of genes that potentially reflect the initial response of microglia to Aß.

A M1 muscarinic acetylcholine receptor-specific positive allosteric modulator VU0486846 reduces neurogliosis in female Alzheimer's mice.

Alzheimer's disease (AD) is the most prevalent type of dementia, disproportionately affecting females, who make up nearly 60% of diagnosed cases. In AD patients, the accumulation of beta-amyloid (Aß) in the brain triggers a neuroinflammatory response driven by neuroglia, worsening the condition. We have previously demonstrated that VU0486846, an orally available positive allosteric modulator (PAM) targeting M1 muscarinic acetylcholine receptors, enhances cognitive function and reduces Aß pathology in female APPswe/PSEN1ΔE9 (APP/PS1) mice. However, it remained unclear whether these improvements were linked to a decrease in neuroglial activation. To investigate, we treated nine-month-old APP/PS1 and wildtype mice with VU0486846 for 8 weeks and analyzed brain slices for markers of microglial activation (ionized calcium binding adaptor molecule 1, Iba1) and astrocyte activation (Glial fibrillary acidic protein, GFAP). We find that VU0486846 reduces the presence of Iba1-positive microglia and GFAP-positive astrocytes in the hippocampus of female APP/PS1 mice and limits the recruitment of these cells to remaining Aß plaques. This study sheds light on an additional mechanism through which novel M1 mAChR PAMs exhibit disease-modifying effects by reducing neuroglial activation and underscore the potential of these ligands for the treatment of AD, especially in females.

Chronic evoked seizures in young pre-symptomatic APP/PS1 mice induce serotonin changes and accelerate onset of Alzheimer's disease-related neuropathology.

OBJECTIVE: Hyperexcitability is intimately linked to Alzheimer's disease (AD) pathology, but the precise timing and contributions of neuronal hyperexcitability to disease progression is unclear. Seizure induction in rodent AD models can uncover new therapeutic targets. Further, investigator-evoked seizures can directly establish how hyperexcitability and AD-associated risk factors influence neuropathological hallmarks and disease course at presymptomatic stages. METHODS: Corneal kindling is a well-characterized preclinical epilepsy model that allows for precise control of seizure history to pair to subsequent behavioral assessments. 2-3-month-old APP/PS1, PSEN2-N141I, and transgenic control male and female mice were thus sham or corneal kindled for 2 weeks. Seizure-induced changes in glia, serotonin pathway proteins, and amyloid ß levels in hippocampus and prefrontal cortex were quantified. RESULTS: APP/PS1 females were more susceptible to corneal kindling. However, regardless of sex, APP/PS1 mice experienced extensive seizure-induced mortality versus kindled Tg- controls. PSEN2-N141I mice were not negatively affected by corneal kindling. Mortality correlated with a marked downregulation of hippocampal tryptophan hydroxylase 2 and monoamine oxidase A protein expression versus controls; these changes were not detected in PSEN2-N141I mice. Kindled APP/PS1 mice also exhibited soluble amyloid ß upregulation and glial reactivity without plaque deposition. SIGNIFICANCE: Evoked convulsive seizures and neuronal hyperexcitability in pre-symptomatic APP/PS1 mice promoted premature mortality without pathological Aß plaque deposition, whereas PSEN2-N141I mice were unaffected. Disruptions in serotonin pathway metabolism in APP/PS1 mice was associated with increased glial reactivity without Aß plaque deposition, demonstrating that neuronal hyperexcitability in early AD causes pathological Aß overexpression and worsens long-term outcomes through a serotonin-related mechanism.

Aged AßPPswe/PS1ΔE9 mice as a useful animal model for studying the link between immunological senescence and diseases.

The APPswe/PS1ΔE9 mouse is a double transgenic murine model that harbors two transgenes for Alzheimer's Disease (AD)-related mutant proteins. We previously discovered that this double transgenic animal had a premature immunosenescence phenotype. However, it is unclear how this phenotype progresses to a later stage. This study aimed to elucidate the changes in systemic characteristics aside from those associated with AD between elderly APPswe/PS1ΔE9 mice and littermate control wild-type mice. Tumors in all organs were considerably more frequent in AD mice aged 24 months than in the control wild-type mice. In addition, the survival rate of aged AD mice was considerably lower than that of wild-type control mice. Further, we discovered that the phenotypic difference was mainly caused by severe immunological aging, as evidenced by a high proportion of exhausted T lymphocytes in AD mice compared to wild-type mice of the same age. Based on our findings, the harm produced by normal aging is not as severe as immunological senescence. Addressing immunological aging, as opposed to anti-aging alone, may be a more crucial target for a long life free of cancer.

Alpha-, Beta-, and Gamma-Secretase, Amyloid Precursor Protein, and Tau Protein Genes in the Hippocampal CA3 Subfield in an Ischemic Model of Alzheimer's Disease with Survival up to 2 Years.

Background: Understanding the phenomena underlying the non-selective susceptibility to ischemia of pyramidal neurons in the CA3 is important from the point of view of elucidating the mechanisms of memory loss and the development of dementia. Objective: The aim of the study was to investigate changes in genes expression of amyloid precursor protein, its cleaving enzymes and tau protein in CA3 post-ischemia with survival of 12-24 months. Methods: We used an ischemic model of Alzheimer's disease to study the above genes using an RT-PCR protocol. Results: The expression of the amyloid precursor protein gene was above the control values at all times post-ischemia. The expression of the α-secretase gene also exceeded the control values post-ischemia. The expression of the ß-secretase gene increased 12 and 24 months post-ischemia, and 18 months was below control values. Presenilin 1 and 2 genes expression was significantly elevated at all times post-ischemia. Also, tau protein gene expression was significantly elevated throughout the observation period, and peak gene expression was present 12 months post-ischemia. Conclusions: The study suggests that the genes studied are involved in the non-amyloidogenic processing of amyloid precursor protein. Additionally data indicate that brain ischemia with long-term survival causes damage and death of pyramidal neurons in the CA3 area of the hippocampus in a modified tau protein-dependent manner. Thus defining a new and important mechanism of pyramidal neuronal death in the CA3 area post-ischemia. In addition expression of tau protein gene modification after brain ischemia is useful in identifying ischemic mechanisms occurring in Alzheimer's disease.

Potential Therapeutic Effects of Bifidobacterium breve MCC1274 on Alzheimer's Disease Pathologies in AppNL-G-F Mice.

We previously demonstrated that orally supplemented Bifidobacterium breve MCC1274 (B. breve MCC1274) mitigated Alzheimer's disease (AD) pathologies in both 7-month-old AppNL-G-F mice and wild-type mice; thus, B. breve MCC1274 supplementation might potentially prevent the progression of AD. However, the possibility of using this probiotic as a treatment for AD remains unclear. Thus, we investigated the potential therapeutic effects of this probiotic on AD using 17-month-old AppNL-G-F mice with memory deficits and amyloid beta saturation in the brain. B. breve MCC1274 supplementation ameliorated memory impairment via an amyloid-cascade-independent pathway. It reduced hippocampal and cortical levels of phosphorylated extracellular signal-regulated kinase and c-Jun N-terminal kinase as well as heat shock protein 90, which might have suppressed tau hyperphosphorylation and chronic stress. Moreover, B. breve MCC1274 supplementation increased hippocampal synaptic protein levels and upregulated neuronal activity. Thus, B. breve MCC1274 supplementation may alleviate cognitive dysfunction by reducing chronic stress and tau hyperphosphorylation, thereby enhancing both synaptic density and neuronal activity in 17-month-old AppNL-G-F mice. Overall, this study suggests that B. breve MCC1274 has anti-AD effects and can be used as a potential treatment for AD.

A systematic review and meta-analysis of tau phosphorylation in mouse models of familial Alzheimer's disease.

Transgenic models of familial Alzheimer's disease (AD) serve as valuable tools for probing the molecular mechanisms associated with amyloid-beta (Aß)-induced pathology. In this meta-analysis, we sought to evaluate levels of phosphorylated tau (p-tau) and explore potential age-related variations in tau hyperphosphorylation, within mouse models of AD. The PubMed and Scopus databases were searched for studies measuring soluble p-tau in 5xFAD, APPswe/PSEN1de9, J20 and APP23 mice. Data were extracted and analyzed using standardized procedures. For the 5xFAD model, the search yielded 36 studies eligible for meta-analysis. Levels of p-tau were higher in 5xFAD mice relative to control, a difference that was evident in both the carboxy-terminal (CT) and proline-rich (PR) domains of tau. Age negatively moderated the relationship between genotype and CT phosphorylated tau in studies using hybrid mice, female mice, and preparations from the neocortex. For the APPswe/PSEN1de9 model, the search yielded 27 studies. Analysis showed tau hyperphosphorylation in transgenic vs. control animals, evident in both the CT and PR regions of tau. Age positively moderated the relationship between genotype and PR domain phosphorylated tau in the neocortex of APPswe/PSEN1de9 mice. A meta-analysis was not performed for the J20 and APP23 models, due to the limited number of studies measuring p-tau levels in these mice (<10 studies). Although tau is hyperphosphorylated in both 5xFAD and APPswe/PSEN1de9 mice, the effects of ageing on p-tau are contingent upon the model being examined. These observations emphasize the importance of tailoring model selection to the appropriate disease stage when considering the relationship between Aß and tau, and suggest that there are optimal intervention points for the administration of both anti-amyloid and anti-tau therapies.

Targeting blood brain barrier-Remote ischemic conditioning alleviates cognitive impairment in female APP/PS1 rats.

AIMS: Alzheimer's disease (AD) is a significant global health concern, and it is crucial that we find effective methods to prevent or slow down AD progression. Recent studies have highlighted the essential role of blood vessels in clearing Aß, a protein that contributes to AD. Scientists are exploring blood biomarkers as a potential tool for future AD diagnosis. One promising method that may help prevent AD is remote ischemic conditioning (RIC). RIC involves using sub-lethal ischemic-reperfusion cycles on limbs. However, a comprehensive understanding of how RIC can prevent AD and its long-term effectiveness is still lacking. Further research is essential to fully comprehend the potential benefits of RIC in preventing AD. METHODS: Female wild-type (WT) and APP/PS1 transgenic rats, aged 12 months, underwent ovariectomy and were subsequently assigned to WT, APP/PS1, and APP/PS1 + RIC groups. RIC was conducted five times a week for 4 weeks. The rats' depressive and cognitive behaviors were evaluated using force swimming, open-field tests, novel objective recognition, elevated plus maze, and Barnes maze tests. Evaluation of the neurovascular unit (NVU), synapses, vasculature, astrocytes, and microglia was conducted using immunofluorescence staining (IF), Western blot (WB), and transmission electron microscopy (TEM). Additionally, the cerebro-vasculature was examined using micro-CT, and cerebral blood flow (CBF) was measured using Speckle Doppler. Blood-brain barrier (BBB) permeability was determined by measuring the Evans blue leakage. Finally, Aß levels in the rat frontal cortex were measured using WB, ELISA, or IF staining. RESULTS: RIC enhanced memory-related protein expression and rescued depressive-like behavior and cognitive decline in APP/PS1 transgenic rats. Additionally, the intervention protected NVU in the rat frontal cortex, as evidenced by (1) increased expression of TJ (tight junction) proteins, pericyte marker PDGFRß, and glucose transporter 1 (GLUT1), as well as decreased VCAM1; (2) mitigation of ultrastructure impairment in neuron, cerebral vascular, and astrocyte; (3) upregulation of A2 astrocyte phenotype markers and downregulation of A1 phenotype markers, indicating a shift toward a healthier phenotype. Correspondingly, RIC intervention alleviated neuroinflammation, as evidenced by the decreased Iba1 level, a microglia marker. Meanwhile, RIC intervention elevated CBF in frontal cortex of the rats. Notably, RIC intervention effectively suppressed Aß toxicity, as demonstrated by the enhancement of α-secretase and attenuation of ß-secretase (BACE1) and γ- secretase and Aß1-42 and Aß1-40 levels as well. CONCLUSION: Chronic RIC intervention exerts vascular and neuroprotective roles, suggesting that RIC could be a promising therapeutic strategy targeting the BBB and NVU during AD development.

Inflammasome signaling is dispensable for ß-amyloid-induced neuropathology in preclinical models of Alzheimer's disease.

Background: Alzheimer's disease (AD) is the most common neurodegenerative disorder affecting memory and cognition. The disease is accompanied by an abnormal deposition of ß-amyloid plaques in the brain that contributes to neurodegeneration and is known to induce glial inflammation. Studies in the APP/PS1 mouse model of ß-amyloid-induced neuropathology have suggested a role for inflammasome activation in ß-amyloid-induced neuroinflammation and neuropathology. Methods: Here, we evaluated the in vivo role of microglia-selective and full body inflammasome signalling in several mouse models of ß-amyloid-induced AD neuropathology. Results: Microglia-specific deletion of the inflammasome regulator A20 and inflammasome effector protease caspase-1 in the AppNL-G-F and APP/PS1 models failed to identify a prominent role for microglial inflammasome signalling in ß-amyloid-induced neuropathology. Moreover, global inflammasome inactivation through respectively full body deletion of caspases 1 and 11 in AppNL-G-F mice and Nlrp3 deletion in APP/PS1 mice also failed to modulate amyloid pathology and disease progression. In agreement, single-cell RNA sequencing did not reveal an important role for Nlrp3 signalling in driving microglial activation and the transition into disease-associated states, both during homeostasis and upon amyloid pathology. Conclusion: Collectively, these results question a generalizable role for inflammasome activation in preclinical amyloid-only models of neuroinflammation.

Abnormal amyloid precursor protein processing in periodontal tissue in a murine model of periodontitis induced by Porphyromonas gingivalis.

OBJECTIVE: The study aimed to investigate the change of amyloid precursor protein (APP) processing and amyloid ß (Aß) metabolites in linking periodontitis to Alzheimer's disease (AD). BACKGROUND: Aß is one of the main pathological features of AD, and few studies have discussed changes in its expression in peripheral tissues or analyzed the relationship between the peripheral imbalance of Aß production and clearance. METHODS: A murine model of periodontitis was established by oral infection with Porphyromonas gingivalis (P. gingivalis). Micro-computed tomography (Micro-CT) was used to observe the destruction of the alveolar bone. Nested quantitative polymerase chain reaction (qPCR) was used to measure small quantities of P.gingivalis DNA in different tissues. Behavioral experiments were performed to measure cognitive function in the mice. The mRNA levels of TNF-α, IL-6, IL-8, RANKL, OPG, APP695, APP751, APP770, and BACE1 in the gingival tissues or cortex were detected by RT-PCR. The levels of Aß1-40 and Aß1-42 in gingival crevicular fluid (GCF) and plasma were tested by ELISA. RESULTS: P. gingivalis oral infection was found to cause alveolar bone resorption and impaired learning and memory. P.gingivalis DNA was detected in the gingiva, blood and cortex of the P.gingivalis group by nested qPCR (p < .05). The mRNA expression of TNF-α, IL-6, IL-8, RANKL/OPG, and BACE1 in the gingival tissue was significantly higher than that in the control group (p < .05). Similarly, upregulated mRNA levels of APP695 and APP770 were observed in the gingival tissuses and cortex of the P. gingivalis group (p < .05). The levels of Aß1-40 and Aß1-42 in the GCF and plasma of the P. gingivalis group were significantly higher than those in the control group (p < .05). CONCLUSION: P. gingivalis can directly invade the brain via hematogenous infection. The invasion of P. gingivalis could trigger an immune response and lead to an imbalance between Aß production and clearance in peripheral tissues, which may trigger an abnormal Aß metabolite in the brain, resulting in the occurrence and development of AD.

New precision medicine avenues to the prevention of Alzheimer's disease from insights into the structure and function of γ-secretases.

Two phase-III clinical trials with anti-amyloid peptide antibodies have met their primary goal, i.e. slowing of Alzheimer's disease (AD) progression. However, antibody therapy may not be the optimal therapeutic modality for AD prevention, as we will discuss in the context of the earlier small molecules described as "γ-secretase modulators" (GSM). We review here the structure, function, and pathobiology of γ-secretases, with a focus on how mutations in presenilin genes result in early-onset AD. Significant progress has been made in generating compounds that act in a manner opposite to pathogenic presenilin mutations: they stabilize the proteinase-substrate complex, thereby increasing the processivity of substrate cleavage and altering the size spectrum of Aß peptides produced. We propose the term "γ-secretase allosteric stabilizers" (GSAS) to distinguish these compounds from the rather heterogenous class of GSM. The GSAS represent, in theory, a precision medicine approach to the prevention of amyloid deposition, as they specifically target a discrete aspect in a complex cell biological signalling mechanism that initiates the pathological processes leading to Alzheimer's disease.