Small Heat Shock Protein 22 Improves Cognition and Learning in the Tauopathic Brain.

The microtubule-associated protein tau pathologically accumulates and aggregates in Alzheimer's disease (AD) and other tauopathies, leading to cognitive dysfunction and neuronal loss. Molecular chaperones, like small heat-shock proteins (sHsps), can help deter the accumulation of misfolded proteins, such as tau. Here, we tested the hypothesis that the overexpression of wild-type Hsp22 (wtHsp22) and its phosphomimetic (S24,57D) Hsp22 mutant (mtHsp22) could slow tau accumulation and preserve memory in a murine model of tauopathy, rTg4510. Our results show that Hsp22 protected against deficits in synaptic plasticity and cognition in the tauopathic brain. However, we did not detect a significant change in tau phosphorylation or levels in these mice. This led us to hypothesize that the functional benefit was realized through the restoration of dysfunctional pathways in hippocampi of tau transgenic mice since no significant benefit was measured in non-transgenic mice expressing wtHsp22 or mtHsp22. To identify these pathways, we performed mass spectrometry of tissue lysates from the injection site. Overall, our data reveal that Hsp22 overexpression in neurons promotes synaptic plasticity by regulating canonical pathways and upstream regulators that have been characterized as potential AD markers and synaptogenesis regulators, like EIF4E and NFKBIA.

Hsp22 with an N-Terminal Domain Truncation Mediates a Reduction in Tau Protein Levels.

Misfolding, aggregation and accumulation of proteins are toxic elements in the progression of a broad range of neurodegenerative diseases. Molecular chaperones enable a cellular defense by reducing or compartmentalizing these insults. Small heat shock proteins (sHsps) engage proteins early in the process of misfolding and can facilitate their proper folding or refolding, sequestration, or clearance. Here, we evaluate the effects of the sHsp Hsp22, as well as a pseudophosphorylated mutant and an N-terminal domain deletion (NTDΔ) variant on tau aggregation in vitro and tau accumulation and aggregation in cultured cells. Hsp22 wild-type (WT) protein had a significant inhibitory effect on heparin-induced aggregation in vitro and the pseudophosphorylated mutant Hsp22 demonstrated a similar effect. When co-expressed in a cell culture model with tau, these Hsp22 constructs significantly reduced soluble tau protein levels when transfected at a high ratio relative to tau. However, the Hsp22 NTDΔ protein drastically reduced the soluble protein expression levels of both tau WT and tau P301L/S320F even at lower transfection ratios, which resulted in a correlative reduction of the triton-insoluble tau P301L/S320F aggregates.

Plasma cytokine IL-6 levels and subjective cognitive decline: preliminary findings.

OBJECTIVE: Detection of Alzheimer's disease (AD) prior to clinical inception will be paramount for introducing disease modifying treatments. We have begun collecting baseline characteristics of a community cohort for longitudinal assessment and testing of antecedent blood-based biomarkers. We describe the baseline visit from the first 131 subjects in relationship to a commonly described cytokine, interleukin 6 (IL-6). METHODS: Subjects from the community presented for a free memory screening with varying degrees of memory concern. We quantified the baseline plasma levels of the cytokine IL-6 and assessed cognition (Montreal Cognitive Assessment, MoCA) and mood (Geriatric Depression Scale, GDS) in relationship to their memory concern. RESULTS: Baseline MoCA scores were inversely related to age, and this association was influenced by an AD risk factor, Apolipoprotein E (APOE4) carrier status. The degree of subjective cognitive decline correlated with GDS and was inversely related to MoCA scores. Interleukin 6 levels were related to age, body mass index, and years of education. CONCLUSIONS: It will be important to assess how these baseline IL-6 levels and forthcoming novel biomarkers relate to future cognitive decline. Copyright © 2017 John Wiley & Sons, Ltd.

The spleen tyrosine kinase (Syk) regulates Alzheimer amyloid-ß production and Tau hyperphosphorylation.

We have previously shown that the L-type calcium channel (LCC) antagonist nilvadipine reduces brain amyloid-ß (Aß) accumulation by affecting both Aß production and Aß clearance across the blood-brain barrier (BBB). Nilvadipine consists of a mixture of two enantiomers, (+)-nilvadipine and (-)-nilvadipine, in equal proportion. (+)-Nilvadipine is the active enantiomer responsible for the inhibition of LCC, whereas (-)-nilvadipine is considered inactive. Both nilvadipine enantiomers inhibit Aß production and improve the clearance of Aß across the BBB showing that these effects are not related to LCC inhibition. In addition, treatment of P301S mutant human Tau transgenic mice (transgenic Tau P301S) with (-)-nilvadipine reduces Tau hyperphosphorylation at several Alzheimer disease (AD) pertinent epitopes. A search for the mechanism of action of (-)-nilvadipine revealed that this compound inhibits the spleen tyrosine kinase (Syk). We further validated Syk as a target-regulating Aß by showing that pharmacological inhibition of Syk or down-regulation of Syk expression reduces Aß production and increases the clearance of Aß across the BBB mimicking (-)-nilvadipine effects. Moreover, treatment of transgenic mice overexpressing Aß and transgenic Tau P301S mice with a selective Syk inhibitor respectively decreased brain Aß accumulation and Tau hyperphosphorylation at multiple AD relevant epitopes. We show that Syk inhibition induces an increased phosphorylation of the inhibitory Ser-9 residue of glycogen synthase kinase-3ß, a primary Tau kinase involved in Tau phosphorylation, by activating protein kinase A, providing a mechanism explaining the reduction of Tau phosphorylation at GSK3ß-dependent epitopes following Syk inhibition. Altogether our data highlight Syk as a promising target for preventing both Aß accumulation and Tau hyperphosphorylation in AD.

Role of the cannabinoid system in the transit of beta-amyloid across the blood-brain barrier.

Emerging evidence suggests beta-amyloid (Aß) deposition in the Alzheimer's disease (AD) brain is the result of impaired clearance, due in part to diminished Aß transport across the blood-brain barrier (BBB). Recently, modulation of the cannabinoid system was shown to reduce Aß brain levels and improve cognitive behavior in AD animal models. The purpose of the current studies was to investigate the role of the cannabinoid system in the clearance of Aß across the BBB. Using in vitro and in vivo models of BBB clearance, Aß transit across the BBB was examined in the presence of cannabinoid receptor agonists and inhibitors. In addition, expression levels of the Aß transport protein, lipoprotein receptor-related protein1 (LRP1), were determined in the brain and plasma of mice following cannabinoid treatment. Cannabinoid receptor agonism or inhibition of endocannabinoid-degrading enzymes significantly enhanced Aß clearance across the BBB (2-fold). Moreover, cannabinoid receptor inhibition negated the stimulatory influence of cannabinoid treatment on Aß BBB clearance. Additionally, LRP1 levels in the brain and plasma were elevated following cannabinoid treatment (1.5-fold), providing rationale for the observed increase in Aß transit from the brain to the periphery. The current studies demonstrate, for the first time, a role for the cannabinoid system in the transit of Aß across the BBB. These findings provide insight into the mechanism by which cannabinoid treatment reduces Aß burden in the AD brain and offer additional evidence on the utility of this pathway as a treatment for AD.

A multifaceted role for apoE in the clearance of beta-amyloid across the blood-brain barrier.

BACKGROUND: While apolipoprotein E4 (apoE4) is highly correlated with the development of Alzheimer's disease (AD), its role in AD pathology and, in particular, beta-amyloid (Aß) removal from the brain, is not clearly defined. OBJECTIVE: To elucidate the influence of apoE on the clearance of Aß across the blood-brain barrier (BBB). METHODS: Aß(1-42) was intracerebrally administered to transgenic mice expressing human apoE isoforms and examined in the periphery. RESULTS: apoE3 and apoE4 mice had 5 times and 2 times, respectively, more Aß(1-42) appearing in the plasma than wild-type or apoE knockout mice, indicating an enhanced clearance of Aß from the brain to the periphery. In vitro, unbound basolateral apoE3 (i.e., not bound to Aß), and to a lesser extent unbound apoE4, at concentrations ≤10 nM facilitated basolateral-to-apical fluorescein-Aß(1-42) transcytosis across a BBB model, while apoE isoforms bound to Aß significantly disrupted Aß transcytosis. Additionally, following apical exposure to the BBB model, we found that apoE4 bound to Aß is able to penetrate the BBB more readily than apoE3 bound to Aß and does so via the RAGE (receptor for advanced glycation end products) transporter. CONCLUSION: These studies indicate a multifaceted, isoform-dependent role for apoE in the exchange of Aß across the BBB and may partially explain the association of apoE4 and Aß brain accumulation in AD.

Benzothiazole Substitution Analogs of Rhodacyanine Hsp70 Inhibitors Modulate Tau Accumulation.

The accumulation and aggregation of the microtubule-associated protein tau (tau) into intracellular neuronal tangles are a hallmark of a range of progressive neurodegenerative tauopathies, including Alzheimer's disease (AD), frontotemporal dementia, Pick's disease, and progressive supranuclear palsy. The aberrant phosphorylation of tau is associated with tau aggregates in AD. Members of the heat shock protein 70 kDa (Hsp70) family of chaperones bind directly to tau and modulate tau clearance and aggregation. Small molecules that inhibit the Hsp70 family of chaperones have been shown to reduce the accumulation of tau, including phosphorylated tau. Here, eight analogs of the rhodacyanine inhibitor, JG-98, were synthesized and evaluated. Like JG-98, many of the compounds inhibited ATPase activity of the cytosolic heat shock cognate 70 protein (Hsc70) and reduced total, aggregated, and phosphorylated tau accumulation in cultured cells. Three compounds, representing divergent clogP values, were evaluated for in vivo blood-brain barrier penetration and tau reduction in an ex vivo brain slice model. AL69, the compound with the lowest clogP and the lowest membrane retention in a parallel artificial membrane permeability assay (PAMPA), reduced phosphorylated tau accumulation. Our results suggest that benzothiazole substitutions of JG-98 that increase hydrophilicity may increase the efficacy of these Hsp70 inhibitors to reduce phosphorylated tau.

BIN1 is a key regulator of proinflammatory and neurodegeneration-related activation in microglia.

BACKGROUND: The BIN1 locus contains the second-most significant genetic risk factor for late-onset Alzheimer's disease. BIN1 undergoes alternate splicing to generate tissue- and cell-type-specific BIN1 isoforms, which regulate membrane dynamics in a range of crucial cellular processes. Whilst the expression of BIN1 in the brain has been characterized in neurons and oligodendrocytes in detail, information regarding microglial BIN1 expression is mainly limited to large-scale transcriptomic and proteomic data. Notably, BIN1 protein expression and its functional roles in microglia, a cell type most relevant to Alzheimer's disease, have not been examined in depth. METHODS: Microglial BIN1 expression was analyzed by immunostaining mouse and human brain, as well as by immunoblot and RT-PCR assays of isolated microglia or human iPSC-derived microglial cells. Bin1 expression was ablated by siRNA knockdown in primary microglial cultures in vitro and Cre-lox mediated conditional deletion in adult mouse brain microglia in vivo. Regulation of neuroinflammatory microglial signatures by BIN1 in vitro and in vivo was characterized using NanoString gene panels and flow cytometry methods. The transcriptome data was explored by in silico pathway analysis and validated by complementary molecular approaches. RESULTS: Here, we characterized microglial BIN1 expression in vitro and in vivo and ascertained microglia expressed BIN1 isoforms. By silencing Bin1 expression in primary microglial cultures, we demonstrate that BIN1 regulates the activation of proinflammatory and disease-associated responses in microglia as measured by gene expression and cytokine production. Our transcriptomic profiling revealed key homeostatic and lipopolysaccharide (LPS)-induced inflammatory response pathways, as well as transcription factors PU.1 and IRF1 that are regulated by BIN1. Microglia-specific Bin1 conditional knockout in vivo revealed novel roles of BIN1 in regulating the expression of disease-associated genes while counteracting CX3CR1 signaling. The consensus from in vitro and in vivo findings showed that loss of Bin1 impaired the ability of microglia to mount type 1 interferon responses to proinflammatory challenge, particularly the upregulation of a critical type 1 immune response gene, Ifitm3. CONCLUSIONS: Our convergent findings provide novel insights into microglial BIN1 function and demonstrate an essential role of microglial BIN1 in regulating brain inflammatory response and microglial phenotypic changes. Moreover, for the first time, our study shows a regulatory relationship between Bin1 and Ifitm3, two Alzheimer's disease-related genes in microglia. The requirement for BIN1 to regulate Ifitm3 upregulation during inflammation has important implications for inflammatory responses during the pathogenesis and progression of many neurodegenerative diseases.

Evidence against a contribution of the CCAAT-enhancer binding protein homologous protein (CHOP) in mediating neurotoxicity in rTg4510 mice.

Tau accumulation and progressive loss of neurons are associated with Alzheimer's disease (AD). Aggregation of tau has been associated with endoplasmic reticulum (ER) stress and the activation of the unfolded protein response (UPR). While ER stress and the UPR have been linked to AD, the contribution of these pathways to tau-mediated neuronal death is still unknown. We tested the hypothesis that reducing C/EBP Homologous Protein (CHOP), a UPR induced transcription factor associated with cell death, would mitigate tau-mediated neurotoxicity through the ER stress pathway. To evaluate this, 8.5-month-old male rTg4510 tau transgenic mice were injected with a CHOP-targeting or scramble shRNA AAV9 that also expressed EGFP. Following behavioral assessment, brain tissue was collected at 12 months, when ER stress and neuronal loss is ongoing. No behavioral differences in locomotion, anxiety-like behavior, or learning and memory were found in shCHOP mice. Unexpectedly, mice expressing shCHOP had higher levels of CHOP, which did not affect neuronal count, UPR effector (ATF4), or tau tangles. Overall, this suggests that CHOP is a not a main contributor to neuronal death in rTg4510 mice. Taken together with previous studies, we conclude that ER stress, including CHOP upregulation, does not worsen outcomes in the tauopathic brain.

Impaired orthotopic glioma growth and vascularization in transgenic mouse models of Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia among the aging population and is characterized pathologically by the progressive intracerebral accumulation of beta-amyloid (Abeta) peptides and neurofibrillary tangles. The level of proangiogenic growth factors and inflammatory mediators with proangiogenic activity is known to be elevated in AD brains which has led to the supposition that the cerebrovasculature of AD patients is in a proangiogenic state. However, angiogenesis depends on the balance between proangiogenic and antiangiogenic factors and the brains of AD patients also show an accumulation of endostatin and Abeta peptides which have been shown to be antiangiogenic. To determine whether angiogenesis is compromised in the brains of two transgenic mouse models of AD overproducing Abeta peptides (Tg APPsw and Tg PS1/APPsw mice), we assessed the growth and vascularization of orthotopically implanted murine gliomas since they require a high degree of angiogenesis to sustain their growth. Our data reveal that intracranial tumor growth and angiogenesis is significantly reduced in Tg APPsw and Tg PS1/APPsw mice compared with their wild-type littermates. In addition, we show that Abeta inhibits the angiogenesis stimulated by glioma cells when cocultured with human brain microvascular cells on a Matrigel layer. Altogether our data suggest that the brain of transgenic mouse models of AD does not constitute a favorable environment to support neoangiogenesis and may explain why vascular insults synergistically precipitate the cognitive presentation of AD.

Selective antihypertensive dihydropyridines lower Aß accumulation by targeting both the production and the clearance of Aß across the blood-brain barrier.

Several large population-based or clinical trial studies have suggested that certain dihydropyridine (DHP) L-type calcium channel blockers (CCBs) used for the treatment of hypertension may confer protection against the development of Alzheimer disease (AD). However, other studies with drugs of the same class have shown no beneficial clinical effects. To determine whether certain DHPs are able to impact underlying disease processes in AD (specifically the accumulation of the Alzheimer Aß peptide), we investigated the effect of several antihypertensive DHPs and non-DHP CCBs on Aß production. Among the antihypertensive DHPs tested, a few, including nilvadipine, nitrendipine and amlodipine inhibited Aß production in vitro, whereas others had no effect or raised Aß levels. In vivo, nilvadipine and nitrendipine acutely reduced brain Aß levels in a transgenic mouse model of AD (Tg PS1/APPsw) and improved Aß clearance across the blood-brain barrier (BBB), whereas amlodipine and nifedipine were ineffective showing that the Aß-lowering activity of the DHPs is independent of their antihypertensive activity. Chronic oral treatment with nilvadipine decreased Aß burden in the brains of Tg APPsw (Tg2576) and Tg PS1/APPsw mice, and also improved learning abilities and spatial memory. Our data suggest that the clinical benefit conferred by certain antihypertensive DHPs against AD is unrelated to their antihypertensive activity, but rely on their ability to lower brain Aß accumulation by affecting both Aß production and Aß clearance across the BBB.

Epitope-dependent effects of Beta-amyloid antibodies on Beta-amyloid clearance in an in vitro model of the blood-brain barrier.

OBJECTIVE: To investigate the role of RAGE in the epitope-dependent effects of Aß antibodies used as a peripheral sink therapy in AD. METHODS: An in vitro model of the BBB was used to examine the effect of various Aß antibodies or Aß peptide fragments on Aß exchange across the BBB. RESULTS: An N-terminal Aß antibody significantly enhanced the basolateral-to-apical transcytosis of fluorescein-Aß(1-42) across the BBB model (41%), while no effect was apparent with a C-terminal Aß antibody. Interestingly, modulation of RAGE in the presence of a C-terminal Aß antibody resulted in a 65% increase in Aß clearance across the BBB model, suggesting the C-terminal antibody-Aß complex is susceptible to RAGE transport. Additionally, N-terminal peptide fragments of Aß attenuated the brain penetration of full length Aß in the BBB model, indicating the N-terminal region of Aß is required for brain uptake. CONCLUSIONS: Antibodies masking the N-terminal region of Aß increase Aß clearance across the BBB by preventing Aß from interacting with the RAGE transporter, whereas antibodies bound to the C-terminus of Aß are taken up by RAGE and, hence, do not influence the BBB clearance of Aß.

Induction of drug efflux protein expression by venlafaxine but not desvenlafaxine.

Venlafaxine and its metabolite desvenlafaxine are serotonin-norepinephrine reuptake inhibitors currently prescribed for the treatment of depression. Previously, it was reported that venlafaxine is an inducer of MDR1, the gene responsible for P-glycoprotein (P-gp). The present study expanded upon these findings by examining the effect of venlafaxine and desvenlafaxine on the expression of both P-gp and the breast cancer resistance protein (BCRP) in human brain endothelial cells (HBMEC), an in vitro model of the blood-brain barrier (BBB). The HBMEC were treated for 1 h with various concentrations (500 nM to 50 µM) of venlafaxine and desvenlafaxine. Western blot analysis revealed treatment with venlafaxine significantly induced the expression of P-gp (2-fold) and BCRP (1.75-fold) in a dose-dependent manner, while treatment with desvenlafaxine had no effect on drug efflux transporter expression. To determine the functional significance of this effect, the permeability of a known drug efflux probe, rhodamine 123, across the BBB model and Caco-2 cells, a model of intestinal absorption, were examined. Treatment with venlafaxine (1-50 µM) for 1 h significantly reduced the apical-to-basolateral permeability of R123 across the BBB model (30%) and Caco-2 cell monolayers (25%), indicative of increased drug efflux transporter expression at the apical membrane. Conversely, desvenlafaxine had no effect on R123 permeability in either cellular model. These studies indicate that venlafaxine, but not desvenlafaxine is an inducer of drug efflux transporter expression, which consequently increases the potential for clinical drug-drug interactions. Therefore, based on these preliminary results, caution should be taken when prescribing venlafaxine with other P-gp substrates.

Hsp90 co-chaperones, FKBP52 and Aha1, promote tau pathogenesis in aged wild-type mice.

The microtubule associated protein tau is an intrinsically disordered phosphoprotein that accumulates under pathological conditions leading to formation of neurofibrillary tangles, a hallmark of Alzheimer's disease (AD). The mechanisms that initiate the accumulation of phospho-tau aggregates and filamentous deposits are largely unknown. In the past, our work and others' have shown that molecular chaperones play a crucial role in maintaining protein homeostasis and that imbalance in their levels or activity can drive tau pathogenesis. We have found two co-chaperones of the 90 kDa heat shock protein (Hsp90), FK506-binding protein 52 (FKBP52) and the activator of Hsp90 ATPase homolog 1 (Aha1), promote tau aggregation in vitro and in the brains of tau transgenic mice. Based on this, we hypothesized that increased levels of these chaperones could promote tau misfolding and accumulation in the brains of aged wild-type mice. We tested this hypothesis by overexpressing Aha1, FKBP52, or mCherry (control) proteins in the hippocampus of 9-month-old wild-type mice. After 7 months of expression, mice were evaluated for cognitive and pathological changes. Our results show that FKBP52 overexpression impaired spatial reversal learning, while Aha1 overexpression impaired associative learning in aged wild-type mice. FKBP52 and Aha1 overexpression promoted phosphorylation of distinct AD-relevant tau species. Furthermore, FKBP52 activated gliosis and promoted neuronal loss leading to a reduction in hippocampal volume. Glial activation and phospho-tau accumulation were also detected in areas adjacent to the hippocampus, including the entorhinal cortex, suggesting that after initiation these pathologies can propagate through other brain regions. Overall, our findings suggest a role for chaperone imbalance in the initiation of tau accumulation in the aging brain.

FKBP52 overexpression accelerates hippocampal-dependent memory impairments in a tau transgenic mouse model.

Abnormal accumulation of hyperphosphorylated tau induces pathogenesis in neurodegenerative diseases, like Alzheimer's disease. Molecular chaperones with peptidyl-prolyl cis/trans isomerase (PPIase) activity are known to regulate these processes. Previously, in vitro studies have shown that the 52 kDa FK506-binding protein (FKBP52) interacts with tau inducing its oligomerization and fibril formation to promote toxicity. Thus, we hypothesized that increased expression of FKBP52 in the brains of tau transgenic mice would alter tau phosphorylation and neurofibrillary tangle formation ultimately leading to memory impairments. To test this, tau transgenic (rTg4510) and wild-type mice received bilateral hippocampal injections of virus overexpressing FKBP52 or GFP control. We examined hippocampal-dependent memory, synaptic plasticity, tau phosphorylation status, and neuronal health. This work revealed that rTg4510 mice overexpressing FKBP52 had impaired spatial learning, accompanied by long-term potentiation deficits and hippocampal neuronal loss, which was associated with a modest increase in total caspase 12. Together with previous studies, our findings suggest that FKBP52 may sensitize neurons to tau-mediated dysfunction via activation of a caspase-dependent pathway, contributing to memory and learning impairments.

Alzheimer's beta-amyloid peptide blocks vascular endothelial growth factor mediated signaling via direct interaction with VEGFR-2.

Beta-amyloid peptides (Abeta) are the major constituents of senile plaques and cerebrovascular deposits in the brains of Alzheimer's disease patients. We have shown previously that soluble forms of Abeta are anti-angiogenic both in vitro and in vivo. However, the mechanism of the anti-angiogenic activity of Abeta peptides is unclear. In this study, we examined the effects of Abeta1-42 on vascular endothelial growth factor receptor 2 (VEGFR-2) signaling, which plays a key role in angiogenesis. Abeta inhibited VEGF-induced migration of endothelial cells, as well as VEGF-induced permeability of an in vitro model of the blood brain barrier. Consistently, exogenous VEGF dose-dependently antagonized the anti-angiogenic activity of Abeta in a capillary network assay. Abeta1-42 also blocked VEGF-induced tyrosine phosphorylation of VEGFR-2 in two types of primary endothelial cells, suggesting an antagonistic action of Abeta toward VEGFR-2 signaling in cells. Moreover, Abeta was able to directly interact with the extracellular domain of VEGFR-2 and to compete with the binding of VEGF to its receptor in a cell-free assay. Co-immunoprecipitation experiments confirmed that Abeta can bind VEGFR-2 both in vitro and in vivo. Altogether, our data suggest that Abeta acts as an antagonist of VEGFR-2 and provide a mechanism explaining the anti-angiogenic activity of Abeta peptides.

Reduction of beta-amyloid pathology by celastrol in a transgenic mouse model of Alzheimer's disease.

BACKGROUND: Abeta deposits represent a neuropathological hallmark of Alzheimer's disease (AD). Both soluble and insoluble Abeta species are considered to be responsible for initiating the pathological cascade that eventually leads to AD. Therefore, the identification of therapeutic approaches that can lower Abeta production or accumulation remains a priority. NFkappaB has been shown to regulate BACE-1 expression level, the rate limiting enzyme responsible for the production of Abeta. We therefore explored whether the known NFkappaB inhibitor celastrol could represent a suitable compound for decreasing Abeta production and accumulation in vivo. METHODS: The effect of celastrol on amyloid precursor protein (APP) processing, Abeta production and NFkappaB activation was investigated by western blotting and ELISAs using a cell line overexpressing APP. The impact of celastrol on brain Abeta accumulation was tested in a transgenic mouse model of AD overexpressing the human APP695sw mutation and the presenilin-1 mutation M146L (Tg PS1/APPsw) by immunostaining and ELISAs. An acute treatment with celastrol was investigated by administering celastrol intraperitoneally at a dosage of 1 mg/Kg in 35 week-old Tg PS1/APPsw for 4 consecutive days. In addition, a chronic treatment (32 days) with celastrol was tested using a matrix-driven delivery pellet system implanted subcutaneously in 5 month-old Tg PS1/APPsw to ensure a continuous daily release of 2.5 mg/Kg of celastrol. RESULTS: In vitro, celastrol dose dependently prevented NFkappaB activation and inhibited BACE-1 expression. Celastrol potently inhibited Abeta1-40 and Abeta1-42 production by reducing the beta-cleavage of APP, leading to decreased levels of APP-CTFbeta and APPsbeta. In vivo, celastrol appeared to reduce the levels of both soluble and insoluble Abeta1-38, Abeta1-40 and Abeta1-42. In addition, a reduction in Abeta plaque burden and microglial activation was observed in the brains of Tg PS1/APPsw following a chronic administration of celastrol. CONCLUSIONS: Overall our data suggest that celastrol is a potent Abeta lowering compound that acts as an indirect BACE-1 inhibitor possibly by regulating BACE-1 expression level via an NFkappaB dependent mechanism. Additional work is required to determine whether chronic administration of celastrol can be safely achieved with cognitive benefits in a transgenic mouse model of AD.

Alzheimer's disease pathological lesions activate the spleen tyrosine kinase.

The pathology of Alzheimer's disease (AD) is characterized by dystrophic neurites (DNs) surrounding extracellular Aß-plaques, microgliosis, astrogliosis, intraneuronal tau hyperphosphorylation and aggregation. We have previously shown that inhibition of the spleen tyrosine kinase (Syk) lowers Aß production and tau hyperphosphorylation in vitro and in vivo. Here, we demonstrate that Aß-overexpressing Tg PS1/APPsw, Tg APPsw mice, and tau overexpressing Tg Tau P301S mice exhibit a pathological activation of Syk compared to wild-type littermates. Syk activation is occurring in a subset of microglia and is age-dependently increased in Aß-plaque-associated dystrophic neurites of Tg PS1/APPsw and Tg APPsw mice. In Tg Tau P301S mice, a pure model of tauopathy, activated Syk occurs in neurons that show an accumulation of misfolded and hyperphosphorylated tau in the cortex and hippocampus. Interestingly, the tau pathology is exacerbated in neurons that display high levels of Syk activation supporting a role of Syk in the formation of tau pathological species in vivo. Importantly, human AD brain sections show both pathological Syk activation in DNs around Aß deposits and in neurons immunopositive for pathological tau species recapitulating the data obtained in transgenic mouse models of AD. Additionally, we show that Syk overexpression leads to increased tau accumulation and promotes tau hyperphosphorylation at multiple epitopes in human neuron-like SH-SY5Y cells, further supporting a role of Syk in the formation of tau pathogenic species. Collectively, our data show that Syk activation occurs following Aß deposition and the formation of tau pathological species. Given that we have previously shown that Syk activation also promotes Aß formation and tau hyperphosphorylation, our data suggest that AD pathological lesions may be self-propagating via a Syk dependent mechanism highlighting Syk as an attractive therapeutic target for the treatment of AD.

Correction: Chronic Anatabine Treatment Reduces Alzheimer's Disease (AD)-Like Pathology and Improves Socio-Behavioral Deficits in a Transgenic Mouse Model of AD.

[This corrects the article DOI: 10.1371/journal.pone.0128224.].