Amyloid Precursor Protein Transgenic Mice Research Articles

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

BackgroundCathepsin D (CatD) is a lysosomal protease that degrades both the amyloid-β protein (Aβ) 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 Aβ pathology and tauopathy in vivo.MethodsCatD 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.ResultsDeletion of CatD in hAPP transgenic mice triggers large increases in cerebral Aβ, manifesting as intense, exclusively intracellular aggregates; extracellular Aβ 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 Aβ42.ConclusionsOur findings support a major role for CatD in the proteostasis of both Aβ and tau in vivo. To our knowledge, the CatD-KO mouse line is the only model to develop detectable Aβ 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 Aβ42, our findings suggest that impaired CatD activity may represent a key mechanism linking amyloid accumulation and tauopathy in AD.

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.

Aged APP AD Mice Demonstrate Spontaneous Ca2+ Oscillations of Pancreatic Acinar Cells: First Evidence of Amyloid pores in AD Model

Alzheimer’s disease (AD), the primary cause of dementia, involves the accumulation of beta-amyloid peptides (Aβ) in brain plaques. Aβ’s precise toxic mechanisms remain unclear. The Aβ channel hypothesis suggests Aβ forms Ca<sup>2+</sup>-permeable channels in cell membranes, possibly leading to Ca<sup>2+</sup> signal disruption and neurodegeneration. Detecting Aβ-formed Ca<sup>2+</sup>channels in native cells of AD model animals is a key question. In our study, we identified Aβ-formed Ca<sup>2+</sup> channels in aged amyloid precursor protein (APP) transgenic AD mice. Measuring intracellular Ca<sup>2+</sup> signals in mouse pancreatic acinar cells, we observed spontaneous Ca<sup>2+</sup> oscillations following whole-cell configuration formation. Ca<sup>2+</sup> influx triggered these oscillations, as external Ca<sup>2+</sup> removal halted them. Notably, we couldn’t replicate these oscillations in pancreatic acinar cells from age-matched wildtype (WT) mice or younger APP mice. Given the absence of voltage-gated Ca<sup>2+</sup> channels in pancreatic acinar cells, external Ca<sup>2+</sup>influx-triggered oscillations may involve Aβ-formed Ca<sup>2+</sup>-permeable channels. Supporting this, we found Aβ plaques in pancreatic sections from aged APP mice, and in adult WT mice’s pancreatic acinar cells, Aβ application produced Ca<sup>2+</sup> oscillations dependent on external Ca<sup>2+</sup>. Furthermore, adding oligomer Aβ1-42 into patch pipette solution enabled Aβ-perforated channel measurement, and fluorescent-tagged Aβ1-42 in primary hippocampal cultures revealed Aβ spots within cells. This study provides experimental evidence that Aβ can form Ca<sup>2+</sup> permeable channels in pancreatic acinar cells in aged APP AD model mice, shedding light on novel mechanisms for understanding altered Ca<sup>2+</sup> homeostasis and neurotoxicity in AD pathogenesis.

Transgenic amyloid precursor protein mouse models of amyloidosis. Incomplete models for Alzheimer's disease but effective predictors of anti-amyloid therapies.

Amyloid precursor protein (APP) transgenic mice are models of Alzheimer's disease (AD) amyloidosis, not all of AD. Diffuse, compacted, and vascular deposits in APP mice mimic those found in AD cases. Most interventional studies in APP mice start treatment early in the process of amyloid deposition, consistent with a prevention treatment regimen. Most clinical trials treat patients with established amyloid deposits in a therapeutic treatment regimen. The first treatment to reduce amyloid and cognitive impairment in mice was immunotherapy. The APP mouse models not only predicted efficacy, but presaged the vascular leakage called ARIA. The recent immunotherapy clinical trials that removed amyloid and slowed cognitive decline confirms the utility of these early APP models when used in therapeutic designs. New mouse models of AD pathologies will add to the research armamentarium, but the early models have accurately predicted responses to amyloid therapies in humans.

Mitochondria in Memory Retrieval in Wild‐Type Mice and in the Impairment of Memory Retrieval in Amyloid Precursor Protein Transgenic Mice

AbstractBackgroundTreatment of Alzheimer’s disease (AD) would benefit from earlier diagnosis and a better understanding of the biochemical and cellular events underlying memory loss. This study, which follows our previous work identifying early deficits in long‐term memory retrieval and memory‐associated glucose uptake in amyloid precursor protein transgenic (APPtg) mice, aims to a) test our hypothesis of stimulus‐dependent synaptic mitochondrial activity as a mechanism underlying memory retrieval, and b) investigate any mitochondrial abnormalities possibly associated with the impairment of memory retrieval in APPtg mice (and possibly in presymptomatic AD).MethodThe J20 APPtg mouse line has been used. Two genotypes (APPtg and wild‐type) and two behavioral groups have been analysed, a) a group subject to criterion‐based watermaze training, sacrificed 20 sec following a probe trial seven days after learning the task (the memory retrieval group), and b) a group with no behavioral training (the basal levels group). Synaptosome forebrain samples (enriched in synapses) from 16 mice (four mice from each of the genotype/behavioral combinations) have been subjected to proteomics, Western blot and electron microscopy analyses. Oxygen consumption and enzymatic activity assay analyses are ongoing.ResultOur previous behavioral result of significantly impaired 7‐day memory retrieval has been reproduced. Our proteomics analysis has suggested higher synaptic levels of mitochondrial proteins during memory retrieval, compared to basal levels in wild‐type mice, a phenotype also present but less evident in APPtg mice. Western analysis has indicated lower synaptic levels of proteins involved in mitochondrial fusion and fission during memory retrieval, compared to basal levels. No difference was identified by electron microscopy in a) numbers of synaptic mitochondria or b) synaptic mitochondrial area. Our oxygen consumption and enzymatic activity assay results are planned to be collected on time for this presentation.ConclusionOur data provide evidence supporting our hypothesis of mitochondrial involvement a) in memory retrieval and b) in the impairment of memory retrieval in APPtg mice and possibly in early AD. They also provide some clues on the exact mitochondrial mechanisms, which is the focus of our current research.

Seed‐competent, high‐molecular‐weight Aβ species is abundantly extracted in the cerebrovasculature and meninges in Alzheimer’s disease

AbstractBackgroundSoluble high‐molecular‐weight (HMW) amyloid β (Aβ) species extracted from autopsied brains of patients with Alzheimer’s disease (AD) have been demonstrated to exhibit a seeding potency to induce cerebral β‐amyloidosis. However, it remains unknown where Aβ seed species resides and how it propagates throughout human AD brains. Our objective is to detect Aβ seed in human AD brain cerebrovasculature and meninges that are enriched with cerebral amyloid angiopathy (CAA).MethodWe examined eight autopsied human AD brains with abundant CAA and eight AD brains without immunohistochemically detectable CAA. Tris‐buffered saline (TBS)‐soluble fractions from the brain parenchyma or meningeal tissues were separated by size‐exclusion chromatography (SEC) with Superdex 75 column, and the concentrations of Aβ in each SEC‐separated fraction were measured by enzyme‐linked immunosorbent assay (ELISA). The TBS‐soluble, high‐molecular‐weight Aβ‐positive fractions were stereotaxically injected into the unilateral hippocampus or cisterna magna of 3‐month‐old amyloid precursor protein (APP) transgenic (tg) mice, and Aβ deposition in the hippocampus was assessed after four months.ResultHMW Aβ species were detected in TBS‐soluble fractions of the meninges and cerebrovasculature isolated from human AD brains. The concentration of HMW Aβ species extracted from meninges and cerebrovasculature was significantly higher than that from brain parenchyma in the same cases. Meningeal HMW Aβ species induced a robust Aβ deposition in the hippocampus, the area of which was significantly higher than that from the same weight of brain parenchyma. Moreover, the concentration of HMW Aβ species in CAA‐rich AD brains with meninges removed was significantly higher than those of CAA‐minimal AD brains. Intracisternal injection of HMW Aβ species derived from human AD brains induced not only CAA but also Aβ plaque.ConclusionSeed competent Aβ species are more abundant in cerebrovasculature and meninges than in brain parenchyma, and may accumulate in CAA in human AD brains. The possibility that HMW Aβ species in CAA contributes to Aβ plaque formation warrants further investigation in future studies.

Hippocampal Reduction of α-Synuclein via RNA Interference Improves Neuropathology in Alzheimer's Disease Mice.

Alzheimer's disease (AD) cases are often characterized by the pathological accumulation of α-synuclein (α-syn) in addition to amyloid-β (Aβ) and tau hallmarks. The role of α-syn has been extensively studied in synucleinopathy disorders, but less so in AD. Recent studies have shown that α-syn may also play a role in AD and its downregulation may be protective against the toxic effects of Aβ accumulation. We hypothesized that selectively knocking down α-syn via RNA interference improves the neuropathological and biochemical findings in AD mice. Here we used amyloid precursor protein transgenic (APP-Tg) mice to model AD and explore pathologic and behavioral phenotypes with knockdown of α-syn using RNA interference. We selectively reduced α-syn levels by stereotaxic bilateral injection of either LV-shRNA α-syn or LV-shRNA-luc (control) into the hippocampus of AD mice. We found that downregulation of α-syn results in significant reduction in the number of Aβ plaques. In addition, mice treated with LV-shRNA α-syn had amelioration of abnormal microglial activation (Iba1) and astrocytosis (GFAP) phenotypes in AD mice. Our data suggests a novel link between Aβ and α-syn pathology as well as a new therapeutic angle for targeting AD.

Suppression of epileptiform activity by treatment with antiepileptic drugs or by genetic ablation of tau in aged human amyloid precursor protein transgenic mice

AbstractBackgroundNeural network dysfunction, including subclinical epileptiform activity, occurs in a substantial proportion of Alzheimer’s disease (AD) patients and related mouse models. Treatment with the anti‐epileptic drug levetiracetam (LEV) or genetically ablating the protein tau effectively reduces epileptiform activity and behavioral abnormalities in human amyloid precursor protein (hAPP) transgenic mice. These findings support the hypothesis that network dysfunction may promote cognitive deficits in AD. While LEV treatment and tau reduction have beneficial effects in young adult hAPP mice, it is not known whether there are similarly beneficial effects in aged mice, whose pathological condition may be more similar to that of AD. To address this gap, we tested the efficacy of LEV treatment and tau reduction in preventing or reversing network, immune and cognitive dysfunctions in aged hAPP mice.MethodWe treated 22–26‐month‐old, male hAPP mice and age‐ and sex‐matched wildtype (WT) controls with placebo or LEV for four months using chow formulations. To genetically ablate tau, we generated a cohort of male and female Mapt +/+ and Mapt –/– mice that did or did not express hAPP. Mice were assessed by electroencephalography (EEG) and behavior. Brain tissues were subjected to transcriptome analysis and immunohistochemistry.ResultsIntracranial EEG recordings revealed that placebo‐treated hAPP mice had aberrantly increased epileptiform activity as compared with placebo‐treated WT controls and that this neural network dysfunction was effectively suppressed by chronic LEV treatment or by tau ablation. Both manipulations reduced behavioral deficits detected in aged hAPP mice. Hippocampal levels of inflammation‐related transcripts were analyzed using a NanoString Neuroinflammation panel. Compared to WT mice, more inflammation‐related transcripts were increased than decreased in hAPP mice. LEV treatment reversed and tau ablation prevented the altered expression of many inflammation‐related genes in the hippocampus of hAPP mice. Immunolabeling tissues with an antibody against human Aβ revealed extensive amyloid deposition in aged hAPP mice but LEV treatment nor tau ablation changed the number or size of amyloid plaques.ConclusionLEV treatment and tau ablation reduce network, immune and cognitive dysfunctions, but not amyloid load, in aged hAPP mice. These findings demonstrate that LEV treatment and tau reduction counteract AD‐related pathophysiological abnormalities independent of age.

Fasting-mimicking diet cycles reduce neuroinflammation to attenuate cognitive decline in Alzheimer's models.

The effects of fasting-mimicking diet (FMD) cycles in reducing many aging and disease risk factors indicate it could affect Alzheimer's disease (AD). Here, we show that FMD cycles reduce cognitive decline and AD pathology in E4FAD and 3xTg AD mouse models, with effects superior to those caused by protein restriction cycles. In 3xTg mice, long-term FMD cycles reduce hippocampal Aβ load and hyperphosphorylated tau, enhance genesis of neural stem cells, decrease microglia number, and reduce expression of neuroinflammatory genes, including superoxide-generating NADPH oxidase (Nox2). 3xTg mice lacking Nox2 or mice treated with the NADPH oxidase inhibitor apocynin also display improved cognition and reduced microglia activation compared with controls. Clinical data indicate that FMD cycles are feasible and generally safe in a small group of AD patients. These results indicate that FMD cycles delay cognitive decline in AD models in part by reducing neuroinflammation and/or superoxide production in the brain.

Seeding, maturation and propagation of amyloid β-peptide aggregates in Alzheimer's disease.

Alzheimer's disease is neuropathologically characterized by the deposition of the amyloid β-peptide (Aβ) as amyloid plaques. Aβ plaque pathology starts in the neocortex before it propagates into further brain regions. Moreover, Aβ aggregates undergo maturation indicated by the occurrence of post-translational modifications. Here, we show that propagation of Aβ plaques is led by presumably non-modified Aβ followed by Aβ aggregate maturation. This sequence was seen neuropathologically in human brains and in amyloid precursor protein transgenic mice receiving intracerebral injections of human brain homogenates from cases varying in Aβ phase, Aβ load and Aβ maturation stage. The speed of propagation after seeding in mice was best related to the Aβ phase of the donor, the progression speed of maturation to the stage of Aβ aggregate maturation. Thus, different forms of Aβ can trigger propagation/maturation of Aβ aggregates, which may explain the lack of success when therapeutically targeting only specific forms of Aβ.

Lactobacillus Spp.-Enhanced Memory is Strain-Dependent and Associated, in Part, with Amyloidogenic and anti-Oxidant/Oxidative Stress Interplay in Amyloid Beta Precursor Protein Transgenic Mice

This study explored mechanisms underpinning enhanced memory in amyloid precursor protein (APP) transgenic mice (male; 10-12 months; n = 6/group) supplemented with Lactobacillus plantarum LAB12 (LAB12)/Lactobacillus casei Shirota (LcS). Morris Water Maze test was performed before brains were harvested for gene expression and biochemical studies. LAB-supplemented mice exhibited reduced escape latency and distance but significant increased time spent in platform zone. This was associated with downregulated beta-site APP cleaving enzyme-1 (BACE1) mRNA and significant reduced nitric oxide in brains. LAB12 also significantly increased glutathione. The LAB-enhanced memory is strain-dependent and could be mediated, in part, through amyloidogenic pathway and anti-oxidant/oxidative stress interplay.

Isotope-labeled amyloid-β does not transmit to the brain in a prion-like manner after peripheral administration.

Findings of early cerebral amyloid‐β deposition in mice after peripheral injection of amyloid‐β‐containing brain extracts, and in humans following cadaveric human growth hormone treatment raised concerns that amyloid‐β aggregates and possibly Alzheimer’s disease may be transmissible between individuals. Yet, proof that Aβ actually reaches the brain from the peripheral injection site is lacking. Here, we use a proteomic approach combining stable isotope labeling of mammals and targeted mass spectrometry. Specifically, we generate 13C‐isotope‐labeled brain extracts from mice expressing human amyloid‐β and track 13C‐lysine‐labeled amyloid‐β after intraperitoneal administration into young amyloid precursor protein‐transgenic mice. We detect injected amyloid‐β in the liver and lymphoid tissues for up to 100 days. In contrast, injected 13C‐lysine‐labeled amyloid‐β is not detectable in the brain whereas the mice incorporate 13C‐lysine from the donor brain extracts into endogenous amyloid‐β. Using a highly sensitive and specific proteomic approach, we demonstrate that amyloid‐β does not reach the brain from the periphery. Our study argues against potential transmissibility of Alzheimer’s disease while opening new avenues to uncover mechanisms of pathophysiological protein deposition.

GRK5 Deficiency Causes Mild Cognitive Impairment due to Alzheimer's Disease.

Prevention of Alzheimer's disease (AD) is a high priority mission while searching for a disease modifying therapy for AD, a devastating major public health crisis. Clinical observations have identified a prodromal stage of AD for which the patients have mild cognitive impairment (MCI) though do not yet meet AD diagnostic criteria. As an identifiable transitional stage before the onset of AD, MCI should become the high priority target for AD prevention, assuming successful prevention of MCI and/or its conversion to AD also prevents the subsequent AD. By pulling this string, one demonstrated cause of amnestic MCI appears to be the deficiency of G protein-coupled receptor-5 (GRK5). The most compelling evidence is that GRK5 knockout (GRK5KO) mice naturally develop into aMCI during aging. Moreover, GRK5 deficiency was reported to occur during prodromal stage of AD in CRND8 transgenic mice. When a GRK5KO mouse was crossbred with Tg2576 Swedish amyloid precursor protein transgenic mouse, the resulted double transgenic GAP mice displayed exaggerated behavioral and pathological changes across the spectrum of AD pathogenesis. Therefore, the GRK5 deficiency possesses unique features and advantage to serve as a prophylactic therapeutic target for MCI due to AD.

Soluble brain homogenates from diverse human and mouse sources preferentially seed diffuse Aβ plaque pathology when injected into newborn mouse hosts.

Seeding of pathology related to Alzheimer's disease (AD) and Lewy body disease (LBD) by tissue homogenates or purified protein aggregates in various model systems has revealed prion-like properties of these disorders. Typically, these homogenates are injected into adult mice stereotaxically. Injection of brain lysates into newborn mice represents an alternative approach of delivering seeds that could direct the evolution of amyloid-β (Aβ) pathology co-mixed with either tau or α-synuclein (αSyn) pathology in susceptible mouse models. Homogenates of human pre-frontal cortex were injected into the lateral ventricles of newborn (P0) mice expressing a mutant humanized amyloid precursor protein (APP), human P301L tau, human wild type αSyn, or combinations thereof. The homogenates were prepared from AD and AD/LBD cases displaying variable degrees of Aβ pathology and co-existing tau and αSyn deposits. Behavioral assessments of APP transgenic mice injected with AD brain lysates were conducted. For comparison, homogenates of aged APP transgenic mice that preferentially exhibit diffuse or cored deposits were similarly injected into the brains of newborn APP mice. We observed that lysates from the brains with AD (Aβ+, tau+), AD/LBD (Aβ+, tau+, αSyn+), or Pathological Aging (Aβ+, tau-, αSyn-) efficiently seeded diffuse Aβ deposits. Moderate seeding of cerebral amyloid angiopathy (CAA) was also observed. No animal of any genotype developed discernable tau or αSyn pathology. Performance in fear-conditioning cognitive tasks was not significantly altered in APP transgenic animals injected with AD brain lysates compared to nontransgenic controls. Homogenates prepared from aged APP transgenic mice with diffuse Aβ deposits induced similar deposits in APP host mice; whereas homogenates from APP mice with cored deposits induced similar cored deposits, albeit at a lower level. These findings are consistent with the idea that diffuse Aβ pathology, which is a common feature of human AD, AD/LBD, and PA brains, may arise from a distinct strain of misfolded Aβ that is highly transmissible to newborn transgenic APP mice. Seeding of tau or αSyn comorbidities was inefficient in the models we used, indicating that additional methodological refinement will be needed to efficiently seed AD or AD/LBD mixed pathologies by injecting newborn mice.

Fingolimod mitigates synaptic deficits and psychosis-like behavior in APP/PSEN1 mice.

IntroductionCurrent treatments for psychosis in Alzheimer's disease (AD), a syndrome characterized by more rapid deterioration and reduced synaptic protein abundance relative to non‐psychotic AD, are inadequate. Fingolimod, a currently US Food and Drug Administration (FDA)–approved pharmacotherapy for multiple sclerosis, alters synaptic protein expression and warrants preclinical appraisal as a candidate pharmacotherapy for psychosis in AD.MethodsPresenilin and amyloid precursor protein transgenic mice (APPswe/PSEN1dE9) and wild‐type mice were randomized to fingolimod or saline for 7 days. Psychosis‐associated behaviors were quantified by open field testing, pre‐pulse inhibition of the acoustic startle response testing, and habituation of the acoustic startle response testing. Synaptic proteins were quantified by liquid chromatography/mass spectrometry in homogenate and postsynaptic density fractions.ResultsFingolimod treatment increased the synaptic protein abundance in cortical homogenates and normalized psychosis‐associated behaviors in APPswe/PSEN1dE9 mice relative to saline. Mitochondrial‐related proteins were preferentially altered by fingolimod treatment and correlated with improvements in psychosis‐associated behaviors.DiscussionPreclinical studies employing complementary psychosis‐associated behavioral assessments and proteomic evaluations across multiple AD‐related models are warranted to replicate the current study and further investigate fingolimod as a candidate treatment for psychosis in AD.

Endocannabinoid metabolism and Alzheimer's disease.

Endocannabinoid metabolism and Alzheimer's disease.

Interdependence of neural network dysfunction and microglial alterations in Alzheimer’s disease-related models

SummaryNonconvulsive epileptiform activity and microglial alterations have been detected in people with Alzheimer’s disease (AD) and related mouse models. However, the relationship between these abnormalities remains to be elucidated. We suppressed epileptiform activity by treatment with the antiepileptic drug levetiracetam or by genetic ablation of tau and found that these interventions reversed or prevented aberrant microglial gene expression in brain tissues of aged human amyloid precursor protein transgenic mice, which simulate several key aspects of AD. The most robustly modulated genes included multiple factors previously implicated in AD pathogenesis, including TREM2, the hypofunction of which increases disease risk. Genetic reduction of TREM2 exacerbated epileptiform activity after mice were injected with kainate. We conclude that AD-related epileptiform activity markedly changes the molecular profile of microglia, inducing both maladaptive and adaptive alterations in their activities. Increased expression of TREM2 seems to support microglial activities that counteract this type of network dysfunction.

Altered stress hormone levels affect in vivo vascular function in the hAPP23+/- overexpressing mouse model of Alzheimer's disease.

Alzheimer's disease (AD) has long been considered a brain-specific dementia syndrome. However, in recent decades, the occurrence of cardiovascular (CV) disease in the progression of AD has been confirmed by increasing epidemiological evidence. In this study, we conducted an in-depth cardiovascular characterization of a humanized amyloid precursor protein (APP) overexpressing mouse model (hAPP23+/-), which overexpresses the Swedish mutation (KM670/671NL). At the age of 6 mo, hAPP23+/- mice had a lower survival, lower body weight, and increased corticosterone and VMA levels compared with C57BL/6 littermates. Systolic blood pressure was increased in hAPP23+/- animals compared with C57BL/6 littermates, but diastolic blood pressure was not statistically different. Pulse pressure remained unchanged but abdominal and carotid pulse-wave velocity (aPWV and cPWV) were increased in hAPP23+/- compared with C57BL/6 mice. Echocardiography showed no differences in systolic or diastolic cardiac function. Ex vivo evaluation of vascular function showed decreased adreno receptor dependent vasoconstriction of hAPP23+/- aortic segments, although the isobaric biomechanics of the aortic wall were similar to C57BL/6 aortic segments. In conclusion, hAPP23+/- mice exhibited high serum corticosterone levels, elevated systolic blood pressure, and increased arterial stiffness in vivo. However, ex vivo aortic stiffness of hAPP23+/- aortic segments was not changed and vascular reactivity to α1-adrenoceptor stimulation was attenuated. These findings highlight the need for more frequent assessment of circulating stress hormone levels and PWV measurements in daily clinical practice for people at risk of AD.NEW & NOTEWORTHY We showed that male amyloid precursor protein (APP) transgenic mice have higher circulating stress hormone levels. As a result, higher systolic blood pressure and pulse-wave velocity were measured in vivo in addition to a smaller α-adrenergic receptor-dependent contraction upon ex vivo stimulation with phenylephrine. Our findings highlight the need for more frequent assessment of circulating stress hormone levels and PWV measurements in daily clinical practice for people at risk of Alzheimer's disease.

Differential interaction with TREM2 modulates microglial uptake of modified Aβ species.

Rare coding variants of the microglial triggering receptor expressed on myeloid cells 2 (TREM2) confer an increased risk for Alzheimer's disease (AD) characterized by the progressive accumulation of aggregated forms of amyloid β peptides (Aβ). Aβ peptides are generated by proteolytic processing of the amyloid precursor protein (APP). Heterogeneity in proteolytic cleavages and additional post-translational modifications result in the production of several distinct Aβ variants that could differ in their aggregation behavior and toxic properties. Here, we sought to assess whether post-translational modifications of Aβ affect the interaction with TREM2. Biophysical and biochemical methods revealed that TREM2 preferentially interacts with oligomeric Aβ, and that phosphorylation of Aβ increases this interaction. Phosphorylation of Aβ also affected the TREM2 dependent interaction and phagocytosis by primary microglia and in APP transgenic mouse models. Thus, TREM2 function is important for sensing phosphorylated Aβ variants in distinct aggregation states and reduces the accumulation and deposition of these toxic Aβ species in preclinical models of Alzheimer's disease.

Curcumin Alleviates Aβ42-Induced Neuronal Metabolic Dysfunction via the Thrb/SIRT3 Axis and Improves Cognition in APPTG Mice.

Curcumin has been reported to have a therapeutic effect on Alzheimer's disease (AD), but the specific mechanism remains to be elucidated. In the present research, we aimed to investigate the effect and molecular mechanism of curcumin on AD. Mouse primary hippocampal neuron cells were treated with various concentrations of beta-amyloid 42 (Aβ42) and the results found that Aβ42 inhibited cell viability in a dose-dependent manner. Compared with 50ng/mL Aβ42, 500ng/mL Aβ42 could further promote cell apoptosis, reduce the ratio of Nicotinamide adenine dinucleotide (NAD(+))/Nicotinamide adenine diphosphate hydride (NADH) and Adenosine 5'-triphosphate (ATP) level, and inhibit Sirtuins 3 (SIRT3) deacetylation activity and protein expression of Thyroid hormone receptor beta (Thrb) and SIRT3. Hence, 500ng/mL Aβ42 was used to establish a cell model of AD. Curcumin significantly reversed the inhibitory effects of Aβ42 on cell viability, SIRT3 deacetylation activity, the ratio of NAD+/NADH, ATP level and the protein expression of Thrb and SIRT3, and the promotive effect on apoptosis. ChIPBase was used to predict the binding region of Thrb and SIRT3. Dual luciferase reporter gene and Chromatin immune precipitation (ChIP) assays were employed to verify the relationship between Thrb and promoter of SIRT3 mRNA. Overexpression of Thrb recovered Aβ42 induced metabolic dysfunction, while Thrb silence aggravated Aβ42 induced metabolic dysfunction. Moreover, Thrb silence or 3-TYP (a selective inhibitor of SIRT3) treatment abolished the amelioration of curcumin on Aβ42 induced metabolic dysfunction. Additionally, curcumin attenuated memory deficits in Amyloid precursor protein transgenic (APPTG) mice. Collectively, curcumin alleviated Aβ42-induced neuronal metabolic dysfunction through increasing Thrb expression and SIRT3 activity and improved cognition in APPTG mice.