Rapid Direct Detection of SARS-CoV-2 Aerosols in Exhaled Breath at the Point of Care.

Airborne transmission via virus-laden aerosols is a dominant route for the transmission of respiratory diseases, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Direct, non-invasive screening of respiratory virus aerosols in patients has been a long-standing technical challenge. Here, we introduce a point-of-care testing platform that directly detects SARS-CoV-2 aerosols in as little as two exhaled breaths of patients and provides results in under 60 s. It integrates a hand-held breath aerosol collector and a llama-derived, SARS-CoV-2 spike-protein specific nanobody bound to an ultrasensitive micro-immunoelectrode biosensor, which detects the oxidation of tyrosine amino acids present in SARS-CoV-2 viral particles. Laboratory and clinical trial results were within 20% of those obtained using standard testing methods. Importantly, the electrochemical biosensor directly detects the virus itself, as opposed to a surrogate or signature of the virus, and is sensitive to as little as 10 viral particles in a sample. Our platform holds the potential to be adapted for multiplexed detection of different respiratory viruses. It provides a rapid and non-invasive alternative to conventional viral diagnostics.

Real-time environmental surveillance of SARS-CoV-2 aerosols.

Real-time surveillance of airborne SARS-CoV-2 virus is a technological gap that has eluded the scientific community since the beginning of the COVID-19 pandemic. Offline air sampling techniques for SARS-CoV-2 detection suffer from longer turnaround times and require skilled labor. Here, we present a proof-of-concept pathogen Air Quality (pAQ) monitor for real-time (5 min time resolution) direct detection of SARS-CoV-2 aerosols. The system synergistically integrates a high flow (~1000 lpm) wet cyclone air sampler and a nanobody-based ultrasensitive micro-immunoelectrode biosensor. The wet cyclone showed comparable or better virus sampling performance than commercially available samplers. Laboratory experiments demonstrate a device sensitivity of 77-83% and a limit of detection of 7-35 viral RNA copies/m3 of air. Our pAQ monitor is suited for point-of-need surveillance of SARS-CoV-2 variants in indoor environments and can be adapted for multiplexed detection of other respiratory pathogens of interest. Widespread adoption of such technology could assist public health officials with implementing rapid disease control measures.

Sex-dependent effects of acute stress on amyloid-ß in male and female mice.

The risk of developing Alzheimer's disease is mediated by a combination of genetics and environmental factors, such as stress, sleep abnormalities and traumatic brain injury. Women are at a higher risk of developing Alzheimer's disease than men, even when controlling for differences in lifespan. Women are also more likely to report high levels of stress than men. Sex differences in response to stress may play a role in the increased risk of Alzheimer's disease in women. In this study, we use in vivo microdialysis to measure levels of Aß in response to acute stress in male and female mice. We show that Aß levels are altered differently between female and male mice (APP/PS1 and wild-type) in response to stress, with females showing significantly increased levels of Aß while most males do not show a significant change. This response is mediated through ß-arrestin involvement in Corticotrophin Releasing Factor receptor signalling pathway differences in male and female mice as male mice lacking ß-arrestin show increase in Aß in response to stress similar to females.

An electrochemical approach for rapid, sensitive, and selective detection of dynorphin.

The endogenous opioid peptide systems are critical for analgesia, reward processing, and affect, but research on their release dynamics and function has been challenging. Here, we have developed microimmunoelectrodes (MIEs) for the electrochemical detection of opioid peptides using square-wave voltammetry. Briefly, a voltage is applied to the electrode to cause oxidation of the tyrosine residue on the opioid peptide of interest, which is detected as current. To provide selectivity to these voltammetric measurements, the carbon fiber surface of the MIE is coated with an antiserum selective to the opioid peptide of interest. To test the sensitivity of the MIEs, electrodes are immersed in solutions containing different concentrations of opioid peptides, and peak oxidative current is measured. We show that dynorphin antiserum-coated electrodes are sensitive to increasing concentrations of dynorphin in the attomolar range. To confirm selectivity, we also measured the oxidative current from exposure to tyrosine and other opioid peptides in solution. Our data show that dynorphin antiserum-coated MIEs are sensitive and selective for dynorphin with little to no oxidative current observed in met-enkephalin and tyrosine solutions. Additionally, we demonstrate the utility of these MIEs in an in vitro brain slice preparation using bath application of dynorphin as well as optogenetic activation of dynorphin release. Future work aims to use MIEs in vivo for real-time, rapid detection of endogenous opioid peptide release in awake, behaving animals.

Aqp4 stop codon readthrough facilitates amyloid-ß clearance from the brain.

Alzheimer's disease is initiated by the toxic aggregation of amyloid-ß. Immunotherapeutics aimed at reducing amyloid beta are in clinical trials but with very limited success to date. Identification of orthogonal approaches for clearing amyloid beta may complement these approaches for treating Alzheimer's disease. In the brain, the astrocytic water channel Aquaporin 4 is involved in clearance of amyloid beta, and the fraction of Aquaporin 4 found perivascularly is decreased in Alzheimer's disease. Further, an unusual stop codon readthrough event generates a conserved C-terminally elongated variant of Aquaporin 4 (AQP4X), which is exclusively perivascular. However, it is unclear whether the AQP4X variant specifically mediates amyloid beta clearance. Here, using Aquaporin 4 readthrough-specific knockout mice that still express normal Aquaporin 4, we determine that this isoform indeed mediates amyloid beta clearance. Further, with high-throughput screening and counterscreening, we identify small molecule compounds that enhance readthrough of the Aquaporin 4 sequence and validate a subset on endogenous astrocyte Aquaporin 4. Finally, we demonstrate these compounds enhance brain amyloid-ß clearance in vivo, which depends on AQP4X. This suggests derivatives of these compounds may provide a viable pharmaceutical approach to enhance clearance of amyloid beta and potentially other aggregating proteins in neurodegenerative disease.

Quantifying regional α -synuclein, amyloid ß, and tau accumulation in lewy body dementia.

OBJECTIVE: Parkinson disease (PD) is defined by the accumulation of misfolded α-synuclein (α-syn) in Lewy bodies and Lewy neurites. It affects multiple cortical and subcortical neuronal populations. The majority of people with PD develop dementia, which is associated with Lewy bodies in neocortex and referred to as Lewy body dementia (LBD). Other neuropathologic changes, including amyloid ß (Aß) and tau accumulation, occur in some LBD cases. We sought to quantify α-syn, Aß, and tau accumulation in neocortical, limbic, and basal ganglia regions. METHODS: We isolated insoluble protein from fresh frozen postmortem brain tissue samples for eight brains regions from 15 LBD, seven Alzheimer disease (AD), and six control cases. We measured insoluble α-syn, Aß, and tau with recently developed sandwich ELISAs. RESULTS: We detected a wide range of insoluble α-syn accumulation in LBD cases. The majority had substantial α-syn accumulation in most regions, and dementia severity correlated with neocortical α-syn. However, three cases had low neocortical levels that were indistinguishable from controls. Eight LBD cases had substantial Aß accumulation, although the mean Aß level in LBD was lower than in AD. The presence of Aß was associated with greater α-syn accumulation. Tau accumulation accompanied Aß in only one LBD case. INTERPRETATION: LBD is associated with insoluble α-syn accumulation in neocortical regions, but the relatively low neocortical levels in some cases suggest that other changes contribute to impaired function, such as loss of neocortical innervation from subcortical regions. The correlation between Aß and α-syn accumulation suggests a pathophysiologic relationship between these two processes.

Preclinical and clinical biomarker studies of CT1812: A novel approach to Alzheimer's disease modification.

INTRODUCTION: Amyloid beta (Aß) oligomers are one of the most toxic structural forms of the Aß protein and are hypothesized to cause synaptotoxicity and memory failure as they build up in Alzheimer's disease (AD) patients' brain tissue. We previously demonstrated that antagonists of the sigma-2 receptor complex effectively block Aß oligomer toxicity. CT1812 is an orally bioavailable, brain penetrant small molecule antagonist of the sigma-2 receptor complex that appears safe and well tolerated in healthy elderly volunteers. We tested CT1812's effect on Aß oligomer pathobiology in preclinical AD models and evaluated CT1812's impact on cerebrospinal fluid (CSF) protein biomarkers in mild to moderate AD patients in a clinical trial (ClinicalTrials.gov NCT02907567). METHODS: Experiments were performed to measure the impact of CT1812 versus vehicle on Aß oligomer binding to synapses in vitro, to human AD patient post mortem brain tissue ex vivo, and in living APPSwe /PS1dE9 transgenic mice in vivo. Additional experiments were performed to measure the impact of CT1812 versus vehicle on Aß oligomer-induced deficits in membrane trafficking rate, synapse number, and protein expression in mature hippocampal/cortical neurons in vitro. The impact of CT1812 on cognitive function was measured in transgenic Thy1 huAPPSwe/Lnd+ and wild-type littermates. A multicenter, double-blind, placebo-controlled parallel group trial was performed to evaluate the safety, tolerability, and impact on protein biomarker expression of CT1812 or placebo given once daily for 28 days to AD patients (Mini-Mental State Examination 18-26). CSF protein expression was measured by liquid chromatography with tandem mass spectrometry or enzyme-linked immunosorbent assay in samples drawn prior to dosing (Day 0) and at end of dosing (Day 28) and compared within each patient and between pooled treated versus placebo-treated dosing groups. RESULTS: CT1812 significantly and dose-dependently displaced Aß oligomers bound to synaptic receptors in three independent preclinical models of AD, facilitated oligomer clearance into the CSF, increased synaptic number and protein expression in neurons, and improved cognitive performance in transgenic mice. CT1812 significantly increased CSF concentrations of Aß oligomers in AD patient CSF, reduced concentrations of synaptic proteins and phosphorylated tau fragments, and reversed expression of many AD-related proteins dysregulated in CSF. DISCUSSION: These preclinical studies demonstrate the novel disease-modifying mechanism of action of CT1812 against AD and Aß oligomers. The clinical results are consistent with preclinical data and provide evidence of target engagement and impact on fundamental disease-related signaling pathways in AD patients, supporting further development of CT1812.

Pimavanserin, a 5HT2A receptor inverse agonist, rapidly suppresses Aß production and related pathology in a mouse model of Alzheimer's disease.

Amyloid-ß (Aß) peptide aggregation into soluble oligomers and insoluble plaques is a precipitating event in the pathogenesis of Alzheimer's disease (AD). Given that synaptic activity can regulate Aß generation, we postulated that 5HT2A -Rs may regulate Aß as well. We treated APP/PS1 transgenic mice with the selective 5HT2A inverse agonists M100907 or Pimavanserin systemically and measured brain interstitial fluid (ISF) Aß levels in real-time using in vivo microdialysis. Both compounds reduced ISF Aß levels by almost 50% within hours, but had no effect on Aß levels in 5HT2A -R knock-out mice. The Aß-lowering effects of Pimavanserin were blocked by extracellular-regulated kinase (ERK) and NMDA receptor inhibitors. Chronic administration of Pimavanserin by subcutaneous osmotic pump to aged APP/PS1 mice significantly reduced CSF Aß levels and Aß pathology and improved cognitive function in these mice. Pimavanserin is FDA-approved to treat Parkinson's disease psychosis, and also has been shown to reduce psychosis in a variety of other dementia subtypes including Alzheimer's disease. These data demonstrate that Pimavanserin may have disease-modifying benefits in addition to its efficacy against neuropsychiatric symptoms of Alzheimer's disease. Read the Editorial Highlight for this article on page 560.

Implications of Oligomeric Amyloid-Beta (oAß42) Signaling through α7ß2-Nicotinic Acetylcholine Receptors (nAChRs) on Basal Forebrain Cholinergic Neuronal Intrinsic Excitability and Cognitive Decline.

Neuronal and network-level hyperexcitability is commonly associated with increased levels of amyloid-ß (Aß) and contribute to cognitive deficits associated with Alzheimer's disease (AD). However, the mechanistic complexity underlying the selective loss of basal forebrain cholinergic neurons (BFCNs), a well-recognized characteristic of AD, remains poorly understood. In this study, we tested the hypothesis that the oligomeric form of amyloid-ß (oAß42), interacting with α7-containing nicotinic acetylcholine receptor (nAChR) subtypes, leads to subnucleus-specific alterations in BFCN excitability and impaired cognition. We used single-channel electrophysiology to show that oAß42 activates both homomeric α7- and heteromeric α7ß2-nAChR subtypes while preferentially enhancing α7ß2-nAChR open-dwell times. Organotypic slice cultures were prepared from male and female ChAT-EGFP mice, and current-clamp recordings obtained from BFCNs chronically exposed to pathophysiologically relevant level of oAß42 showed enhanced neuronal intrinsic excitability and action potential firing rates. These resulted from a reduction in action potential afterhyperpolarization and alterations in the maximal rates of voltage change during spike depolarization and repolarization. These effects were observed in BFCNs from the medial septum diagonal band and horizontal diagonal band, but not the nucleus basalis. Last, aged male and female APP/PS1 transgenic mice, genetically null for the ß2 nAChR subunit gene, showed improved spatial reference memory compared with APP/PS1 aged-matched littermates. Combined, these data provide a molecular mechanism supporting a role for α7ß2-nAChR in mediating the effects of oAß42 on excitability of specific populations of cholinergic neurons and provide a framework for understanding the role of α7ß2-nAChR in oAß42-induced cognitive decline.

Effect of escitalopram dose and treatment duration on CSF Aß levels in healthy older adults: A controlled clinical trial.

OBJECTIVE: To determine whether treatment with escitalopram compared with placebo would lower CSF ß-amyloid 42 (Aß42) levels. RATIONALE: Serotonin signaling suppresses Aß42 in animal models of Alzheimer disease (AD) and young healthy humans. In a prospective study in older adults, we examined dose and treatment duration effects of escitalopram. METHODS: Using lumbar punctures to sample CSF levels before and after a course of escitalopram treatment, cognitively normal older adults (n = 114) were assigned to placebo, 20 mg escitalopram × 2 weeks, 20 mg escitalopram × 8 weeks, or 30 mg escitalopram × 8 weeks; CSF sampled pretreatment and posttreatment and within-subject percent change in Aß42 was used as the primary outcome in subsequent analyses. RESULTS: An overall 9.4% greater reduction in CSF Aß42 was found in escitalopram-treated compared with placebo-treated groups (p < 0.001, 95% confidence interval [CI] 4.9%-14.2%, d = 0.81). Positive baseline Aß status (CSF Aß42 levels <250 pg/mL) was associated with smaller Aß42 reduction (p = 0.006, 95% CI -16.7% to 0.5%, d = -0.52) compared with negative baseline amyloid status (CSF Aß42 levels >250 pg/mL). CONCLUSIONS: Short-term longitudinal doses of escitalopram decreased CSF Aß42 in cognitively normal older adults, the target group for AD prevention. CLINICALTRIALSGOV IDENTIFIER: NCT02161458. CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that for cognitively normal older adults, escitalopram decreases CSF Aß42.

Effect of escitalopram on Aß levels and plaque load in an Alzheimer mouse model.

BACKGROUND: Several neurotransmitter receptors activate signaling pathways that alter processing of the amyloid precursor protein (APP) into ß-amyloid (Aß). Serotonin signaling through a subset of serotonin receptors suppresses Aß generation. We proposed that escitalopram, the most specific selective serotonin reuptake inhibitor (SSRI) that inhibits the serotonin transporter SERT, would suppress Aß levels in mice. OBJECTIVES: We hypothesized that acute treatment with escitalopram would reduce Aß generation, which would be reflected chronically with a significant reduction in Aß plaque load. METHODS: We performed in vivo microdialysis and in vivo 2-photon imaging to assess changes in brain interstitial fluid (ISF) Aß and Aß plaque size over time, respectively, in the APP/presenilin 1 mouse model of Alzheimer disease treated with vehicle or escitalopram. We also chronically treated mice with escitalopram to determine the effect on plaques histologically. RESULTS: Escitalopram acutely reduced ISF Aß by 25% by increasing α-secretase cleavage of APP. Chronic administration of escitalopram significantly reduced plaque load by 28% and 34% at 2.5 and 5 mg/d, respectively. Escitalopram at 5 mg/kg did not remove existing plaques, but completely arrested individual plaque growth over time. CONCLUSIONS: Escitalopram significantly reduced Aß in mice, similar to previous findings in humans treated with acute dosing of an SSRI.

Exercise Training Results in Lower Amyloid Plaque Load and Greater Cognitive Function in an Intensity Dependent Manner in the Tg2576 Mouse Model of Alzheimer's Disease.

Three months of exercise training (ET) decreases soluble Aß40 and Aß42 levels in an intensity dependent manner early in life in Tg2576 mice (Moore et al., 2016). Here, we examined the effects of 12 months of low- and high- intensity exercise training on cognitive function and amyloid plaque load in the cortex and hippocampus of 15-month-old Tg2576 mice. Low- (LOW) and high- (HI) intensity ET animals ran at speeds of 15 m/min on a level treadmill and 32 m/min at a 10% grade, respectively, for 60 min/day, five days/week, from 3 to 15 months of age. Sedentary mice (SED) were placed on a level, non-moving, treadmill for the same duration. ET mice demonstrated a significantly lower amyloid plaque load in the cortex and hippocampus that was intensity dependent. Improvement in cognitive function, assessed by Morris Water Maze and Novel Object Recognition tests, was greater in the HI group compared to the LOW and SED groups. LOW mice performed better in the initial latency to the platform location during the probe trial of the Morris Water Maze (MWM) test than SED, but not in any other aspect of MWM or the Novel Object Recognition test. The results of this study indicate that exercise training decreases amyloid plaque load in an intensity dependent manner and that high-intensity exercise training improves cognitive function relative to SED mice, but the intensity of the LOW group was below the threshold to demonstrate robust improvement in cognitive function in Tg2576 mice.

The sleep-wake cycle regulates brain interstitial fluid tau in mice and CSF tau in humans.

The sleep-wake cycle regulates interstitial fluid (ISF) and cerebrospinal fluid (CSF) levels of ß-amyloid (Aß) that accumulates in Alzheimer's disease (AD). Furthermore, chronic sleep deprivation (SD) increases Aß plaques. However, tau, not Aß, accumulation appears to drive AD neurodegeneration. We tested whether ISF/CSF tau and tau seeding and spreading were influenced by the sleep-wake cycle and SD. Mouse ISF tau was increased ~90% during normal wakefulness versus sleep and ~100% during SD. Human CSF tau also increased more than 50% during SD. In a tau seeding-and-spreading model, chronic SD increased tau pathology spreading. Chemogenetically driven wakefulness in mice also significantly increased both ISF Aß and tau. Thus, the sleep-wake cycle regulates ISF tau, and SD increases ISF and CSF tau as well as tau pathology spreading.

Interactions between stress and physical activity on Alzheimer's disease pathology.

Physical activity and stress are both environmental modifiers of Alzheimer's disease (AD) risk. Animal studies of physical activity in AD models have largely reported positive results, however benefits are not always observed in either cognitive or pathological outcomes and inconsistencies among findings remain. Studies using forced exercise may increase stress and mitigate some of the benefit of physical activity in AD models, while voluntary exercise regimens may not achieve optimal intensity to provide robust benefit. We evaluated the findings of studies of voluntary and forced exercise regimens in AD mouse models to determine the influence of stress, or the intensity of exercise needed to outweigh the negative effects of stress on AD measures. In addition, we show that chronic physical activity in a mouse model of AD can prevent the effects of acute restraint stress on Aß levels in the hippocampus. Stress and physical activity have many overlapping and divergent effects on the body and some of the possible mechanisms through which physical activity may protect against stress-induced risk factors for AD are discussed. While the physiological effects of acute stress and acute exercise overlap, chronic effects of physical activity appear to directly oppose the effects of chronic stress on risk factors for AD. Further study is needed to identify optimal parameters for intensity, duration and frequency of physical activity to counterbalance effects of stress on the development and progression of AD.

AMPA-ergic regulation of amyloid-ß levels in an Alzheimer's disease mouse model.

BACKGROUND: Extracellular aggregation of the amyloid-ß (Aß) peptide into toxic multimers is a key event in Alzheimer's disease (AD) pathogenesis. Aß aggregation is concentration-dependent, with higher concentrations of Aß much more likely to form toxic species. The processes that regulate extracellular levels of Aß therefore stand to directly affect AD pathology onset. Studies from our lab and others have demonstrated that synaptic activity is a critical regulator of Aß production through both presynaptic and postsynaptic mechanisms. AMPA receptors (AMPA-Rs), as the most abundant ionotropic glutamate receptors, have the potential to greatly impact Aß levels. METHODS: In order to study the role of AMPA-Rs in Aß regulation, we used in vivo microdialysis in an APP/PS1 mouse model to simultaneously deliver AMPA and other treatments while collecting Aß from the interstitial fluid (ISF). Changes in Aß production and clearance along with inflammation were assessed using biochemical approaches. IL-6 deficient mice were utilized to test the role of IL-6 signaling in AMPA-R-mediated regulation of Aß levels. RESULTS: We found that AMPA-R activation decreases in ISF Aß levels in a dose-dependent manner. Moreover, the effect of AMPA treatment involves three distinct pathways. Steady-state activity of AMPA-Rs normally promotes higher ISF Aß. Evoked AMPA-R activity, however, decreases Aß levels by both stimulating glutamatergic transmission and activating downstream NMDA receptor (NMDA-R) signaling and, with extended AMPA treatment, acting independently of NMDA-Rs. Surprisingly, we found this latter, direct AMPA pathway of Aß regulation increases Aß clearance, while Aß production appears to be largely unaffected. Furthermore, the AMPA-dependent decrease is not observed in IL-6 deficient mice, indicating a role for IL-6 signaling in AMPA-R-mediated Aß clearance. CONCLUSION: Though basal levels of AMPA-R activity promote higher levels of ISF Aß, evoked AMPA-R signaling decreases Aß through both NMDA-R-dependent and -independent pathways. We find that evoked AMPA-R signaling increases clearance of extracellular Aß, at least in part through enhanced IL-6 signaling. These data emphasize that Aß regulation by synaptic activity involves a number of independent pathways that together determine extracellular Aß levels. Understanding how these pathways maintain Aß levels prior to AD pathology may provide insights into disease pathogenesis.

Combination anti-Aß treatment maximizes cognitive recovery and rebalances mTOR signaling in APP mice.

Drug development for Alzheimer's disease has endeavored to lower amyloid ß (Aß) by either blocking production or promoting clearance. The benefit of combining these approaches has been examined in mouse models and shown to improve pathological measures of disease over single treatment; however, the impact on cellular and cognitive functions affected by Aß has not been tested. We used a controllable APP transgenic mouse model to test whether combining genetic suppression of Aß production with passive anti-Aß immunization improved functional outcomes over either treatment alone. Compared with behavior before treatment, arresting further Aß production (but not passive immunization) was sufficient to stop further decline in spatial learning, working memory, and associative memory, whereas combination treatment reversed each of these impairments. Cognitive improvement coincided with resolution of neuritic dystrophy, restoration of synaptic density surrounding deposits, and reduction of hyperactive mammalian target of rapamycin signaling. Computational modeling corroborated by in vivo microdialysis pointed to the reduction of soluble/exchangeable Aß as the primary driver of cognitive recovery.

Astrocytic LRP1 Mediates Brain Aß Clearance and Impacts Amyloid Deposition.

Accumulation and deposition of amyloid-ß (Aß) in the brain represent an early and perhaps necessary step in the pathogenesis of Alzheimer's disease (AD). Aß accumulation leads to the formation of Aß aggregates, which may directly and indirectly lead to eventual neurodegeneration. While Aß production is accelerated in many familial forms of early-onset AD, increasing evidence indicates that impaired clearance of Aß is more evident in late-onset AD. To uncover the mechanisms underlying impaired Aß clearance in AD, we examined the role of low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. Although LRP1 has been shown to play critical roles in brain Aß metabolism in neurons and vascular mural cells, its role in astrocytes, the most abundant cell type in the brain responsible for maintaining neuronal homeostasis, remains unclear. Here, we show that astrocytic LRP1 plays a critical role in brain Aß clearance. LRP1 knockdown in primary astrocytes resulted in decreased cellular Aß uptake and degradation. In addition, silencing of LRP1 in astrocytes led to downregulation of several major Aß-degrading enzymes, including matrix metalloproteases MMP2, MMP9, and insulin-degrading enzyme. More important, conditional knock-out of the Lrp1 gene in astrocytes in the background of APP/PS1 mice impaired brain Aß clearance, exacerbated Aß accumulation, and accelerated amyloid plaque deposition without affecting its production. Together, our results demonstrate that astrocytic LRP1 plays an important role in Aß metabolism and that restoring LRP1 expression and function in the brain could be an effective strategy to facilitate Aß clearance and counter amyloid pathology in AD.SIGNIFICANCE STATEMENT Astrocytes represent a major cell type regulating brain homeostasis; however, their roles in brain clearance of amyloid-ß (Aß) and underlying mechanism are not clear. In this study, we used both cellular models and conditional knock-out mouse models to address the role of a critical Aß receptor, the low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. We found that LRP1 in astrocytes plays a critical role in brain Aß clearance by modulating several Aß-degrading enzymes and cellular degradation pathways. Our results establish a critical role of astrocytic LRP1 in brain Aß clearance and shed light on specific Aß clearance pathways that may help to establish new targets for AD prevention and therapy.

Microglial complement receptor 3 regulates brain Aß levels through secreted proteolytic activity.

Recent genetic evidence supports a link between microglia and the complement system in Alzheimer's disease (AD). In this study, we uncovered a novel role for the microglial complement receptor 3 (CR3) in the regulation of soluble ß-amyloid (Aß) clearance independent of phagocytosis. Unexpectedly, ablation of CR3 in human amyloid precursor protein-transgenic mice results in decreased, rather than increased, Aß accumulation. In line with these findings, cultured microglia lacking CR3 are more efficient than wild-type cells at degrading extracellular Aß by secreting enzymatic factors, including tissue plasminogen activator. Furthermore, a small molecule modulator of CR3 reduces soluble Aß levels and Aß half-life in brain interstitial fluid (ISF), as measured by in vivo microdialysis. These results suggest that CR3 limits Aß clearance from the ISF, illustrating a novel role for CR3 and microglia in brain Aß metabolism and defining a potential new therapeutic target in AD.

Bioactive Compound Screen for Pharmacological Enhancers of Apolipoprotein E in Primary Human Astrocytes.

Pharmacological screening in physiologically relevant brain cells is crucial for identifying neuroactive compounds that better translate into in vivo biology and efficacious therapeutics. Pharmacological enhancement of apolipoprotein E (apoE), a cholesterol-transporting apolipoprotein, has been proposed as a promising therapeutic approach for Alzheimer's disease. Several nuclear receptor agonists were initially shown to increase brain apoE levels together with ATP-binding cassette transporter 1 (ABCA1), but their underlying mechanisms remain unclear. To gain an insight on brain apoE regulation, we performed an unbiased high-throughput screening of known drugs and bioactive compounds in cultured human primary astrocytes, the major apoE-producing cell type in the brain. We have identified several small molecules that increase apoE secretion via previously unknown mechanisms, including those not co-inducing ABCA1. These newly identified compounds are active preferentially in human astrocytes but not in an astrocytoma cell line, furnishing new tools for investigating biological pathways underlying brain apoE production.