Microglial NFκB-TNFα hyperactivation induces obsessive-compulsive behavior in mouse models of progranulin-deficient frontotemporal dementia.

Frontotemporal dementia (FTD) is the second most common dementia before 65 years of age. Haploinsufficiency in the progranulin (GRN) gene accounts for 10% of all cases of familial FTD. GRN mutation carriers have an increased risk of autoimmune disorders, accompanied by elevated levels of tissue necrosis factor (TNF) α. We examined behavioral alterations related to obsessive-compulsive disorder (OCD) and the role of TNFα and related signaling pathways in FTD patients with GRN mutations and in mice lacking progranulin (PGRN). We found that patients and mice with GRN mutations displayed OCD and self-grooming (an OCD-like behavior in mice), respectively. Furthermore, medium spiny neurons in the nucleus accumbens, an area implicated in development of OCD, display hyperexcitability in PGRN knockout mice. Reducing levels of TNFα in PGRN knockout mice abolished excessive self-grooming and the associated hyperexcitability of medium spiny neurons of the nucleus accumbens. In the brain, PGRN is highly expressed in microglia, which are a major source of TNFα. We therefore deleted PGRN specifically in microglia and found that it was sufficient to induce excessive grooming. Importantly, excessive grooming in these mice was prevented by inactivating nuclear factor κB (NF-κB) in microglia/myeloid cells. Our findings suggest that PGRN deficiency leads to excessive NF-κB activation in microglia and elevated TNFα signaling, which in turn lead to hyperexcitability of medium spiny neurons and OCD-like behavior.

Cyclooxygenase-1 inhibition reduces amyloid pathology and improves memory deficits in a mouse model of Alzheimer's disease.

Several epidemiological and preclinical studies suggest that non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit cyclooxygenase (COX), reduce the risk of Alzheimer's disease (AD) and can lower ß-amyloid (Aß) production and inhibit neuroinflammation. However, follow-up clinical trials, mostly using selective cyclooxygenase (COX)-2 inhibitors, failed to show any beneficial effect in AD patients with mild to severe cognitive deficits. Recent data indicated that COX-1, classically viewed as the homeostatic isoform, is localized in microglia and is actively involved in brain injury induced by pro-inflammatory stimuli including Aß, lipopolysaccharide, and interleukins. We hypothesized that neuroinflammation is critical for disease progression and selective COX-1 inhibition, rather than COX-2 inhibition, can reduce neuroinflammation and AD pathology. Here, we show that treatment of 20-month-old triple transgenic AD (3 × Tg-AD) mice with the COX-1 selective inhibitor SC-560 improved spatial learning and memory, and reduced amyloid deposits and tau hyperphosphorylation. SC-560 also reduced glial activation and brain expression of inflammatory markers in 3 × Tg-AD mice, and switched the activated microglia phenotype promoting their phagocytic ability. The present findings are the first to demonstrate that selective COX-1 inhibition reduces neuroinflammation, neuropathology, and improves cognitive function in 3 × Tg-AD mice. Thus, selective COX-1 inhibition should be further investigated as a potential therapeutic approach for AD.

CCR3 plays a role in murine age-related cognitive changes and T-cell infiltration into the brain.

Targeting immune-mediated, age-related, biology has the potential to be a transformative therapeutic strategy. However, the redundant nature of the multiple cytokines that change with aging requires identification of a master downstream regulator to successfully exert therapeutic efficacy. Here, we discovered CCR3 as a prime candidate, and inhibition of CCR3 has pro-cognitive benefits in mice, but these benefits are not driven by an obvious direct action on central nervous system (CNS)-resident cells. Instead, CCR3-expressing T cells in the periphery that are modulated in aging inhibit infiltration of these T cells across the blood-brain barrier and reduce neuroinflammation. The axis of CCR3-expressing T cells influencing crosstalk from periphery to brain provides a therapeutically tractable link. These findings indicate the broad therapeutic potential of CCR3 inhibition in a spectrum of neuroinflammatory diseases of aging.

Selective targeting of microglia by quantum dots.

BACKGROUND: Microglia, the resident immune cells of the brain, have been implicated in brain injury and various neurological disorders. However, their precise roles in different pathophysiological situations remain enigmatic and may range from detrimental to protective. Targeting the delivery of biologically active compounds to microglia could help elucidate these roles and facilitate the therapeutic modulation of microglial functions in neurological diseases. METHODS: Here we employ primary cell cultures and stereotaxic injections into mouse brain to investigate the cell type specific localization of semiconductor quantum dots (QDs) in vitro and in vivo. Two potential receptors for QDs are identified using pharmacological inhibitors and neutralizing antibodies. RESULTS: In mixed primary cortical cultures, QDs were selectively taken up by microglia; this uptake was decreased by inhibitors of clathrin-dependent endocytosis, implicating the endosomal pathway as the major route of entry for QDs into microglia. Furthermore, inhibiting mannose receptors and macrophage scavenger receptors blocked the uptake of QDs by microglia, indicating that QD uptake occurs through microglia-specific receptor endocytosis. When injected into the brain, QDs were taken up primarily by microglia and with high efficiency. In primary cortical cultures, QDs conjugated to the toxin saporin depleted microglia in mixed primary cortical cultures, protecting neurons in these cultures against amyloid beta-induced neurotoxicity. CONCLUSIONS: These findings demonstrate that QDs can be used to specifically label and modulate microglia in primary cortical cultures and in brain and may allow for the selective delivery of therapeutic agents to these cells.

Molecular and histological correlates of cognitive decline across age in male C57BL/6J mice.

INTRODUCTION: Increasing age is the number one risk factor for developing cognitive decline and neurodegenerative disease. Aged humans and mice exhibit numerous molecular changes that contribute to a decline in cognitive function and increased risk of developing age-associated diseases. Here, we characterize multiple age-associated changes in male C57BL/6J mice to understand the translational utility of mouse aging. METHODS: Male C57BL/6J mice from various ages between 2 and 24 months of age were used to assess behavioral, as well as, histological and molecular changes across three modalities: neuronal, microgliosis/neuroinflammation, and the neurovascular unit (NVU). Additionally, a cohort of 4- and 22-month-old mice was used to assess blood-brain barrier (BBB) breakdown. Mice in this cohort were treated with a high, acute dose of lipopolysaccharide (LPS, 10 mg/kg) or saline control 6 h prior to sacrifice followed by tail vein injection of 0.4 kDa sodium fluorescein (100 mg/kg) 2 h later. RESULTS: Aged mice showed a decline in cognitive and motor abilities alongside decreased neurogenesis, proliferation, and synapse density. Further, neuroinflammation and circulating proinflammatory cytokines were increased in aged mice. Additionally, we found changes at the BBB, including increased T cell infiltration in multiple brain regions and an exacerbation in BBB leakiness following chemical insult with age. There were also a number of readouts that were unchanged with age and have limited utility as markers of aging in male C57BL/6J mice. CONCLUSIONS: Here we propose that these changes may be used as molecular and histological readouts that correspond to aging-related behavioral decline. These comprehensive findings, in the context of the published literature, are an important resource toward deepening our understanding of normal aging and provide an important tool for studying aging in mice.

Fyn kinase regulates the association between amyloid precursor protein and Dab1 by promoting their localization to detergent-resistant membranes.

The adaptor protein Disabled1 (Dab1) interacts with amyloid precursor protein (APP) and decreases its pathological processing, an effect mediated by Fyn tyrosine kinase. Fyn is highly enriched in lipid rafts, a major site of pathological APP processing. To investigate the role of Fyn in the localization and phosphorylation of APP and Dab1 in lipid rafts, we isolated detergent-resistant membrane (DRM) fractions from wild-type and Fyn knock-out mice. In wild-type mice, all of the Fyn kinase, 17% of total APP, and 33% of total Dab1 were found in DRMs. Nearly all of the tyrosine phosphorylated forms of APP and Dab1 were in DRMs. APP and Dab1 co-precipitated both in and out of DRM fractions, indicating an association that is independent of subcellular localization. Fyn knock-out mice had decreased APP, Dab1, and tyrosine-phosphorylated Dab1 in DRMs but increased co-immunoprecipitation of DRM APP and Dab1. Expression of phosphorylation deficient APP or Dab1 constructs revealed that phosphorylation of APP increases, whereas phosphorylation of Dab1 decreases, the interaction between APP and Dab1. Consistent with these observations, Reelin treatment led to increased Dab1 phosphorylation and decreased association between APP and Dab1. Reelin also caused increased localization of APP and Dab1 to DRMs, an effect that was not seen in Fyn knock-out neurons. These findings suggest that Reelin treatment promotes the localization of APP and Dab1 to DRMs, and affects their phosphorylation by Fyn, thus regulating their interaction.

The cytoplasmic adaptor protein X11alpha and extracellular matrix protein Reelin regulate ApoE receptor 2 trafficking and cell movement.

The goal of this study was to determine the effect of X11alpha on ApoE receptor 2 (ApoEr2) trafficking and the functional significance of this interaction on cell movement in MCF 10A epithelial cells. We found that X11alpha increased surface levels of ApoEr2 by 64% compared to vector control, as determined by surface protein biotinylation. To examine the functional significance of this effect, we tested whether ApoEr2 played a novel role in cell movement in a wound-healing assay. We found that overexpression of ApoEr2 in MCF 10A cells increased cell migration velocity by 87% (P<0.01, n=4) compared to GFP control. Cotransfection of X11alpha had an additive effect on average velocity compared to ApoEr2 alone (13%; P<0.05, n=4). In addition, we tested whether ApoEr2 ligands altered the effect of ApoEr2 on cell movement. We found that treatment with concentrated medium containing the extracellular matrix protein Reelin, but not control medium, further increased the velocity of ApoEr2- but not APP-transfected cells (20%; P<0.001, n=4). Similarly, Reelin treatment increased cell velocity in the presence of ApoEr2 and X11alpha (10%; P<0.05, n=4). In the present study, we are the first to demonstrate that ApoEr2 regulates cell movement, and both X11alpha and Reelin enhance this effect.

Therapeutic versus neuroinflammatory effects of passive immunization is dependent on Aß/amyloid burden in a transgenic mouse model of Alzheimer's disease.

BACKGROUND: Passive immunization with antibodies directed to Aß decreases brain Aß/amyloid burden and preserves memory in transgenic mouse models of Alzheimer's disease (AD). This therapeutic strategy is under intense scrutiny in clinical studies, but its application is limited by neuroinflammatory side effects (autoimmune encephalitis and vasogenic edema). METHODS: We intravenously administered the monoclonal Aß protofibril antibody PFA1 to aged (22 month) male and female 3 × tg AD mice with intermediate or advanced AD-like neuropathologies, respectively, and measured brain and serum Aß and CNS cytokine levels. We also examined 17 month old 3 × tg AD female mice with intermediate pathology to determine the effect of amyloid burden on responses to passive immunization. RESULTS: The 22 month old male mice immunized with PFA1 had decreased brain Aß, increased serum Aß, and no change in CNS cytokine levels. In contrast, 22 month old immunized female mice revealed no change in brain Aß, decreased serum Aß, and increased CNS cytokine levels. Identical experiments in younger (17 month old) female 3 × tg AD mice with intermediate AD-like neuropathologies revealed a trend towards decreased brain Aß and increased serum Aß accompanied by a decrease in CNS MCP-1. CONCLUSIONS: These data suggest that passive immunization with PFA1 in 3 × tg AD mice with intermediate disease burden, regardless of sex, is effective in mediating potentially therapeutic effects such as lowering brain Aß. In contrast, passive immunization of mice with a more advanced amyloid burden may result in potentially adverse effects (encephalitis and vasogenic edema) mediated by certain proinflammatory cytokines.

Females exhibit more extensive amyloid, but not tau, pathology in an Alzheimer transgenic model.

Epidemiological studies indicate that women have a higher risk of Alzheimer's disease (AD) even after adjustment for age. Though transgenic mouse models of AD develop AD-related amyloid beta (Abeta) and/or tau pathology, gender differences have not been well documented in these models. In this study, we found that female 3xTg-AD transgenic mice expressing mutant APP, presenilin-1 and tau have significantly more aggressive Abeta pathology. We also found an increase in beta-secretase activity and a reduction of neprilysin in female mice compared to males; this suggests that a combination of increased Abeta production and decreased Abeta degradation may contribute to higher risk of AD in females. In contrast to significantly more aggressive Abeta pathology in females, gender did not affect the levels of phosphorylated tau in 3xTg-AD mice. These results point to the involvement of Abeta pathways in the higher risk of AD in women. In addition to comparison of pathology between genders at 9, 16 and 23 months of age, we examined the progression of Abeta pathology at additional age points; i.e., brain Abeta load, intraneuronal oligomeric Abeta distribution and plaque load, in male 3xTg-AD mice at 3, 6, 9, 12, 16, 20 and 23 months of age. These findings confirm progressive Abeta pathology in 3xTg-AD transgenic mice, and provide guidance for their use in therapeutic research.

Intranasal NAP administration reduces accumulation of amyloid peptide and tau hyperphosphorylation in a transgenic mouse model of Alzheimer's disease at early pathological stage.

Accumulation of beta-amyloid (Abeta) peptide and hyperphosphorylation of tau in the brain are pathological hallmarks of Alzheimer's disease (AD). Agents altering these pathological events might modify clinical disease progression. NAP (Asn-Ala-Pro-Val-Ser-Ile-Pro-Gln) is an octapeptide that has shown neuroprotective effects in various in vitro and in vivo neurodegenerative models. Previous studies showed that NAP protected against Abeta-induced neurotoxicity, inhibited Abeta aggregation, and, by binding to tubulin, prevented disruption of microtubules. In this study, we investigated the effect of NAP on Abeta and tau pathology using a transgenic mouse model that recapitulates both aspects of AD. We administered NAP intranasally (0.5 microg/mouse per day, daily from Monday through Friday) for 3 mo, starting from 9 mo of age, which is a prepathological stage in these mice. NAP treatment significantly lowered levels of Abeta 1-40 and 1-42 in brain. In addition, NAP significantly reduced levels of hyperphosphorylated tau. Of particular interest, hyperphosphorylation at the threonine 231 site was reduced; phosphorylation at this site influences microtubule binding. Our results indicate that NAP treatment of transgenic mice initiated at an early stage reduced both Abeta and tau pathology, suggesting that NAP might be a potential therapeutic agent for AD.

Chemotopic representations of aromatic odorants in the rat olfactory bulb.

Our laboratory has characterized spatial patterns of evoked neural activity across the entire glomerular layer of the rat olfactory bulb using primarily aliphatic odorants that differ systematically in functional groups and hydrocarbon structures. To represent more fully the true range of odorant chemistry, we investigated aromatic compounds, which have a more rigid molecular structure than most aliphatic compounds and are particularly salient olfactory stimuli for humans. We first investigated glomerular patterns of 2-deoxyglucose uptake in response to aromatic compounds that differ in the nature and position of their functional groups (e.g., xylenes, trimethylbenzenes, tolualdehydes, benzaldehydes, methyl toluates, and anisaldehydes). We also studied the effects of systematic increases in the number and length of alkyl substituents. We found that most aromatic compounds activated glomeruli in the dorsal part of the bulb. Within this general area, aromatic odorants with oxygen-containing substituents favored activation of more rostral regions, and aromatic hydrocarbons activated more posterior regions. The nature of substituents greatly affected the pattern of glomerular activation, whereas isomers differing in substitution position evoked very similar overall patterns. These relationships between the structure of aromatic compounds and their spatial representation in the bulb are contrasted with our previous findings with aliphatic odorants.

Acetylated Tau Obstructs KIBRA-Mediated Signaling in Synaptic Plasticity and Promotes Tauopathy-Related Memory Loss.

Tau toxicity has been implicated in the emergence of synaptic dysfunction in Alzheimer's disease (AD), but the mechanism by which tau alters synapse physiology and leads to cognitive decline is unclear. Here we report abnormal acetylation of K274 and K281 on tau, identified in AD brains, promotes memory loss and disrupts synaptic plasticity by reducing postsynaptic KIdney/BRAin (KIBRA) protein, a memory-associated protein. Transgenic mice expressing human tau with lysine-to-glutamine mutations to mimic K274 and K281 acetylation (tauKQ) exhibit AD-related memory deficits and impaired hippocampal long-term potentiation (LTP). TauKQ reduces synaptic KIBRA levels and disrupts activity-induced postsynaptic actin remodeling and AMPA receptor insertion. The LTP deficit was rescued by promoting actin polymerization or by KIBRA expression. In AD patients with dementia, we found enhanced tau acetylation is linked to loss of KIBRA. These findings suggest a novel mechanism by which pathogenic tau causes synaptic dysfunction and cognitive decline in AD pathogenesis.

Reducing inflammation and rescuing FTD-related behavioral deficits in progranulin-deficient mice with α7 nicotinic acetylcholine receptor agonists.

Mutations in the progranulin gene cause frontotemporal dementia (FTD), a debilitating neurodegenerative disease that involves atrophy of the frontal and temporal lobes and affects personality, behavior, and language. Progranulin-deficient mouse models of FTD exhibit deficits in compulsive and social behaviors reminiscent of patients with FTD, and develop excessive microgliosis and increased release of inflammatory cytokines. Activation of nicotinic acetylcholine receptors (nAChRs) by nicotine or specific α7 nAChR agonists reduces neuroinflammation. Here, we investigated whether activation of nAChRs by nicotine or α7 agonists improved the excessive inflammatory and behavioral phenotypes of a progranulin-deficient FTD mouse model. We found that treatment with selective α7 agonists, PHA-568487 or ABT-107, strongly suppressed the activation of NF-κB in progranulin-deficient cells. Treatment with ABT-107 also reduced microgliosis, decreased TNFα levels, and reduced compulsive behavior in progranulin-deficient mice. Collectively, these data suggest that targeting activation of the α7 nAChR pathway may be beneficial in decreasing neuroinflammation and reversing some of the behavioral deficits observed in progranulin-deficient FTD.

Critical role of acetylation in tau-mediated neurodegeneration and cognitive deficits.

Tauopathies, including frontotemporal dementia (FTD) and Alzheimer's disease (AD), are neurodegenerative diseases in which tau fibrils accumulate. Recent evidence supports soluble tau species as the major toxic species. How soluble tau accumulates and causes neurodegeneration remains unclear. Here we identify tau acetylation at Lys174 (K174) as an early change in AD brains and a critical determinant in tau homeostasis and toxicity in mice. The acetyl-mimicking mutant K174Q slows tau turnover and induces cognitive deficits in vivo. Acetyltransferase p300-induced tau acetylation is inhibited by salsalate and salicylate, which enhance tau turnover and reduce tau levels. In the PS19 transgenic mouse model of FTD, administration of salsalate after disease onset inhibited p300 activity, lowered levels of total tau and tau acetylated at K174, rescued tau-induced memory deficits and prevented hippocampal atrophy. The tau-lowering and protective effects of salsalate were diminished in neurons expressing K174Q tau. Targeting tau acetylation could be a new therapeutic strategy against human tauopathies.

Progranulin protects against amyloid ß deposition and toxicity in Alzheimer's disease mouse models.

Haploinsufficiency of the progranulin (PGRN) gene (GRN) causes familial frontotemporal lobar degeneration (FTLD) and modulates an innate immune response in humans and in mouse models. GRN polymorphism may be linked to late-onset Alzheimer's disease (AD). However, the role of PGRN in AD pathogenesis is unknown. Here we show that PGRN inhibits amyloid ß (Aß) deposition. Selectively reducing microglial expression of PGRN in AD mouse models impaired phagocytosis, increased plaque load threefold and exacerbated cognitive deficits. Lentivirus-mediated PGRN overexpression lowered plaque load in AD mice with aggressive amyloid plaque pathology. Aß plaque load correlated negatively with levels of hippocampal PGRN, showing the dose-dependent inhibitory effects of PGRN on plaque deposition. PGRN also protected against Aß toxicity. Lentivirus-mediated PGRN overexpression prevented spatial memory deficits and hippocampal neuronal loss in AD mice. The protective effects of PGRN against Aß deposition and toxicity have important therapeutic implications. We propose enhancing PGRN as a potential treatment for PGRN-deficient FTLD and AD.

Fyn knock-down increases Aß, decreases phospho-tau, and worsens spatial learning in 3×Tg-AD mice.

Fyn kinase phosphorylates tau and exacerbates amyloid beta (Aß)-mediated synaptic dysfunction. However, Fyn also increases the nonpathological cleavage of amyloid precursor protein (APP), suggesting opposing roles for Fyn in the pathogenesis of Alzheimer's disease (AD). To determine the effect of Fyn on both Aß and tau pathologies, we crossed homozygous Alzheimer's disease triple transgenic (3×Tg) mice harboring mutations in amyloid precursor protein, presenilin-1, and tau with wild-type or Fyn knockout mice to generate Fyn(+/+)3×Tg(+/-) or Fyn(+/-)3×Tg(+/-) mice. We found that Fyn(+/-)3×Tg(+/-) mice had increased soluble and intracellular Aß, and these changes were accompanied by impaired performance on the Morris water maze at 18 months. Fyn(+/-)3×Tg(+/-) mice had decreased phosphorylated tau at 15-18 months (as did Fyn knockout mice), but Fyn(+/-)3×Tg(+/-) mice had increased phosphorylated tau by 24 months. In addition, we observed that Fyn(+/-)3×Tg(+/-) males were delayed in developing Aß pathology compared with females, and displayed better spatial learning performance at 18 months. Overall, these findings suggest that loss of Fyn at early stages of disease increases soluble Aß accumulation and worsens spatial learning in the absence of changes in tau phosphorylation.

Decreased dendritic spine density and abnormal spine morphology in Fyn knockout mice.

Fyn is a Src-family tyrosine kinase that affects long term potentiation (LTP), synapse formation, and learning and memory. Fyn is also implicated in dendritic spine formation both in vitro and in vivo. However, whether Fyn's regulation of dendritic spine formation is brain-region specific and age-dependent is unknown. In the present study, we systematically examined whether Fyn altered dendritic spine density and morphology in the cortex and hippocampus and if these effects were age-dependent. We found that Fyn knockout mice trended toward a decrease in dendritic spine density in cortical layers II/III, but not in the hippocampus, at 1 month of age. Additionally, Fyn knockout mice had significantly decreased dendritic spine density in both the cortex and hippocampus at 3 months and 1 year, and Fyn's effect on dendritic spine density was age-dependent in the hippocampus. Moreover, Fyn knockout mice had wider spines at the three time points (1 month, 3 months, 1 year) in the cortex. These findings suggest that Fyn regulates dendritic spine number and morphology over time and provide further support for Fyn's role in maintaining proper synaptic function in vivo.

ApoE mimetic peptide decreases Abeta production in vitro and in vivo.

BACKGROUND: Apolipoprotein E (apoE) is postulated to affect brain Abeta levels through multiple mechanisms--by altering amyloid precursor protein (APP) processing, Abeta degradation, and Abeta clearance. We previously showed that an apoE-derived peptide containing a double repeat of the receptor-binding region was similarly effective in increasing APP processing in vivo. Here, we further examined whether peptides containing tandem repeats of the apoE receptor-binding region (amino acids 141-149) affected APP trafficking, APP processing, and Abeta production. RESULTS: We found that peptides containing a double or triple tandem repeat of the apoE receptor-binding region, LRKLRKRLL, increased cell surface APP and decreased Abeta levels in PS1-overexpressing PS70 cells and in primary neurons. This effect was potentiated by a sequential increase in the number of apoE receptor-binding domain repeats (trimer > dimer > monomer). We previously showed that the apoE dimer increased APP CTF in vivo; to determine whether the dimer also affected secreted APP or Abeta levels, we performed a single hippocampal injection of the apoE dimer in wild-type mice and analyzed its effect on APP processing. We found increased sAPPalpha and decreased Abeta levels at 24 hrs after treatment, suggesting that the apoE dimer may increase alpha-secretase cleavage. CONCLUSIONS: These data suggest that small peptides consisting of tandem repeats of the apoE receptor-binding region are sufficient to alter APP trafficking and processing. The potency of these peptides increased with increasing repeats of the receptor binding domain of apoE. In addition, in vivo administration of the apoE peptide (dimer) increased sAPPalpha and decreased Abeta levels in wild-type mice. Overall, these findings contribute to our understanding of the effects of apoE on APP processing and Abeta production both in vitro and in vivo.

Fyn modulation of Dab1 effects on amyloid precursor protein and ApoE receptor 2 processing.

Dab1 is an intracellular adaptor protein that interacts with amyloid precursor protein (APP) and apoE receptor 2 (apoEr2), increases their levels on the cell surface, and increases their cleavage by alpha-secretases. To investigate the mechanism underlying these alterations in processing and trafficking of APP and apoEr2, we examined the effect of Fyn, an Src family-tyrosine kinase known to interact with and phosphorylate Dab1. Co-immunoprecipitation, co-immunostaining, and fluorescence lifetime imaging demonstrated an association between Fyn and APP. Fyn induced phosphorylation of APP at Tyr-757 of the (757)YENPTY(762) motif and increased cell surface expression of APP. Overexpression of Fyn alone did not alter levels of sAPPalpha or cytoplasmic C-terminal fragments, although it significantly decreased production of Abeta. However, in the presence of Dab1, Fyn significantly increased sAPPalpha and C-terminal fragments. Fyn-induced APP phosphorylation and cell surface levels of APP were potentiated in the presence of Dab1. Fyn also induced phosphorylation of apoEr2 and increased its cell surface levels and, in the presence of Dab1, affected processing of its C-terminal fragment. In vivo studies showed that sAPPalpha was decreased in the Fyn knock-out, supporting a role for Fyn in APP processing. These data demonstrate that Fyn, due in part to its effects on Dab1, regulates the phosphorylation, trafficking, and processing of APP and apoEr2.

BACE1 inhibition reduces endogenous Abeta and alters APP processing in wild-type mice.

Accumulation of amyloid beta peptide (Abeta) in brain is a hallmark of Alzheimer's disease (AD). Inhibition of beta-site amyloid precursor protein (APP)-cleaving enzyme-1 (BACE1), the enzyme that initiates Abeta production, and other Abeta-lowering strategies are commonly tested in transgenic mice overexpressing mutant APP. However, sporadic AD cases, which represent the majority of AD patients, are free from the mutation and do not necessarily have overproduction of APP. In addition, the commonly used Swedish mutant APP alters APP cleavage. Therefore, testing Abeta-lowering strategies in transgenic mice may not be optimal. In this study, we investigated the impact of BACE1 inhibition in non-transgenic mice with physiologically relevant APP expression. Existing Abeta ELISAs are either relatively insensitive to mouse Abeta or not specific to full-length Abeta. A newly developed ELISA detected a significant reduction of full-length soluble Abeta 1-40 in mice with the BACE1 homozygous gene deletion or BACE1 inhibitor treatment, while the level of x-40 Abeta was moderately reduced due to detection of non-full-length Abeta and compensatory activation of alpha-secretase. These results confirmed the feasibility of Abeta reduction through BACE1 inhibition under physiological conditions. Studies using our new ELISA in non-transgenic mice provide more accurate evaluation of Abeta-reducing strategies than was previously feasible.