Aβ-induced Tau Phosphorylation Research Articles

Akt-activated GSK3β inhibitory peptide effectively blocks tau hyperphosphorylation.

Tau hyperphosphorylation and accumulation in neurofibrillary tangles are closely associated with cognitive deficits in Alzheimer's disease (AD). Glycogen synthase kinase 3β (GSK3β) overexpression has been implicated in tau hyperphosphorylation, and many GSK3β inhibitors have been developed as potential therapeutic candidates for AD. However, the potent GSK3β inhibitors produced are prone to side effects because they can interfere with the basic functions of GSK3β. We previously found that when the phosphorylated PPPSPxS motifs in Wnt coreceptor LRP6 can directly inhibit GSK3β, and thus, we produced a novel GSK3β inhibitory peptide (GIP), specifically activated by Akt, by combining the PPPSPxS motif of LRP6 and the Akt targeted sequence (RxRxxS) of GSK3β. GIP effectively blocked GSK3β-induced tau phosphorylation in hippocampal homogenates and, when fused with a cell-permeable sequence, attenuated Aβ-induced tau phosphorylation in human neuroblastoma cells and inhibited cell death. An in vivo study using a 3 × Tg-AD mouse model revealed that intravenous GIP significantly reduced tau phosphorylation in thehippocampus without affecting Aβ plaque levels or neuroinflammation and ameliorated memory defects. The study provides a novel neuroprotective drug development strategy targeting tau hyperphosphorylation in AD.

Astrocyte biomarkers GFAP and YKL-40 mediate early Alzheimer's disease progression.

We studied how biomarkers of reactive astrogliosis mediate the pathogenic cascade in the earliest Alzheimer's disease (AD) stages. We performed path analysis on data from 384 cognitively unimpaired individuals from the ALzheimer and FAmilies (ALFA)+ study using structural equation modeling to quantify the relationships between biomarkers of reactive astrogliosis and the AD pathological cascade. Cerebrospinal fluid (CSF) amyloid beta (Aβ)42/40 was associated with Aβ aggregation on positron emission tomography (PET) and with CSF p-tau181 , which was in turn directly associated with CSF neurofilament light (NfL). Plasma glial fibrillary acidic protein (GFAP) mediated the relationship between CSF Aβ42/40 and Aβ-PET, and CSF YKL-40 partly explained the association between Aβ-PET, p-tau181 , and NfL. Our results suggest that reactive astrogliosis, as indicated by different fluid biomarkers, influences the pathogenic cascade during the preclinical stage of AD. While plasma GFAP mediates the early association between soluble and insoluble Aβ, CSF YKL-40 mediates the latter association between Aβ and downstream Aβ-induced tau pathology and tau-induced neuronal injury. Lower CSF Aβ42/40 was directly linked to higher plasma GFAP concentrations. Plasma GFAP partially explained the relationship between soluble Aβ and insoluble Aβ. CSF YKL-40 mediated Aβ-induced tau phosphorylation and tau-induced neuronal injury.

Acetylcholinesterase inhibitors targeting the cholinergic anti-inflammatory pathway: a new therapeutic perspective in aging-related disorders.

Neuroinflammation and cholinergic dysfunction, leading to cognitive impairment, are hallmarks of aging and neurodegenerative disorders, including Alzheimer's disease (AD). Acetylcholinesterase inhibitors (AChEI), the symptomatic therapy in AD, attenuate and delay the cognitive deficit by enhancing cholinergic synapses. The α7 nicotinic acetylcholine (ACh) receptor has shown a double-edged sword feature, as it binds with high affinity Aβ1-42, promoting intracellular accumulation and Aβ-induced tau phosphorylation, but also exerts neuroprotection by stimulating anti-apoptotic pathways. Moreover, it mediates peripheral and central anti-inflammatoryresponse, being the effector player of the activation of the cholinergic anti-inflammatory pathway (CAIP), that, by decreasing the release of TNF-α, IL-1β, and IL-6, it may have a role in improving cognition. The finding in preclinical models that, in addition to their major function (choline esterase inhibition) AChEIs have neuroprotective properties mediated via α7nAChR and modulate innate immunity, possibly as a result of the increased availability of acetylcholine activating the CAIP, pave the way for new pharmacological intervention in AD and other neurological disorders that are characterized by neuroinflammation. CHRFAM7A is a human-specific gene acting as a dominant negative inhibitor of α7nAChR function, also suggesting a role in affecting human cognition and memory by altering α7nAChR activities in the central nervous system (CNS). This review will summarize the current knowledge on the cholinergic anti-inflammatory pathway in aging-related disorders, and will argue that the presence of the human-restricted CHRFAM7A gene might play a fundamental role in the regulation of CAIP and in the response to AChEI.

Neurotrophin receptor p75 mediates amyloid β-induced tau pathology

Neurofibrillary tangles of hyperphosphorylated tau protein (p-tau) are a key pathological feature of Alzheimer's disease (AD). Tau phosphorylation is suggested to be secondary to amyloid-beta (Aβ) accumulation. However, the mechanism by which Aβ induces tau phosphorylation in neurons remains unclear. Neurotrophin receptor p75 (p75NTR) is a receptor for Aβ and mediates Aβ neurotoxicity, implying that p75NTR may mediate Aβ-induced tau phosphorylation in AD. Here, we showed that Aβ-induced tau hyperphosphorylation and neurodegeneration, including tau phosphorylation, synaptic disorder and neuronal loss, in the brains of both male wild-type (Wt) mice and male P301L transgenic mice (a mouse model of human tauopathy) were alleviated by genetic knockout of p75NTR in the both mouse models. We further confirmed that the activation or inhibition of cyclin-dependent kinase 5 (CDK5) and glycogen synthase kinase-3β (GSK3β) significantly changed Aβ/p75NTR-mediated p-tau levels in neurons. Treatment of male P301L mice with soluble p75NTR extracellular domain (p75ECD-Fc), which antagonizes the binding of Aβ to p75NTR, suppressed tau hyperphosphorylation. Taken together, our findings suggest that p75NTR meditates Aβ-induced tau pathology and is a potential druggable target for AD and other tauopathies.

Amyloid-beta induced retrograde axonal degeneration in a mouse tauopathy model

White matter abnormalities, revealed by Diffusion Tensor Imaging (DTI), are observed in patients with Alzheimer's Disease (AD), representing neural network deficits that underlie gradual cognitive decline in patients. However, how DTI changes related to the development of Amyloid beta (Aβ) and tau pathology, two key hallmarks of AD, remain elusive. We hypothesized that tauopathy induced by Aβ could initiate an axonal degeneration, leading to DTI-detectable white matter abnormalities. We utilized the visual system of the transgenic p301L tau mice as a model system. Aβ was injected in Lateral Geniculate Nucleus (LGN), where the Retinal Ganglion Cell (RGC) axons terminate. Longitudinal DTI was conducted to detect changes in the optic tract (OT) and optic nerve (ON), containing the distal and proximal segments of RGC axons, respectively. Our results showed DTI changes in OT (significant 13.2% reduction in axial diffusion, AxD vs. vehicle controls) followed by significant alterations in ON AxD and fractional anisotropy, FA. Histology data revealed loss of synapses, RGC axons and cell bodies resulting from the Aβ injection. We further tested whether microtubule-stabilizing compound Epothilone D (EpoD) could ameliorate the damage. EpoD co-treatment with Aβ was sufficient to prevent Aβ-induced axon and cell loss. Using an acute injection paradigm, our data suggest that EpoD may mediate its protective effect by blocking localized, acute Aβ-induced tau phosphorylation. This study demonstrates white matter disruption resulting from localized Aβ, the importance of tau pathology induction to changes in white matter connectivity, and the use of EpoD as a potential therapeutic avenue to prevent the axon loss in AD.

A novel DYRK1A (dual specificity tyrosine phosphorylation-regulated kinase 1A) inhibitor for the treatment of Alzheimer's disease: effect on Tau and amyloid pathologies in vitro.

The dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) gene is located within the Down Syndrome (DS) critical region on chromosome 21 and is implicated in the generation of Tau and amyloid pathologies that are associated with the early onset Alzheimer's Disease (AD) observed in DS. DYRK1A is also found associated with neurofibrillary tangles in sporadic AD and phosphorylates key AD players (Tau, amyloid precursor, protein, etc). Thus, DYRK1A may be an important therapeutic target to modify the course of Tau and amyloid beta (Aβ) pathologies. Here, we describe EHT 5372 (methyl 9-(2,4-dichlorophenylamino) thiazolo[5,4-f]quinazoline-2-carbimidate), a novel, highly potent (IC50 = 0.22 nM) DYRK1A inhibitor with a high degree of selectivity over 339 kinases. Models in which inhibition of DYRK1A by siRNA reduced and DYRK1A over-expression induced Tau phosphorylation or Aβ production were used. EHT 5372 inhibits DYRK1A-induced Tau phosphorylation at multiple AD-relevant sites in biochemical and cellular assays. EHT 5372 also normalizes both Aβ-induced Tau phosphorylation and DYRK1A-stimulated Aβ production. DYRK1A is thus as a key element of Aβ-mediated Tau hyperphosphorylation, which links Tau and amyloid pathologies. EHT 5372 and other compounds in its class warrant in vivo investigation as a novel, high-potential therapy for AD and other Tau opathies. Inhibition of the dual specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) is a new high-potential therapeutic approach for Alzheimer disease. Here we describe EHT 5372, a novel potent and selective DYRK1A inhibitor. EHT 5372 inhibits DYRK1A-induced Tau phosphorylation, Aβ production and Aβ effects on phospho-Tau, including Tau aggregation.

New Treatment for Alzheimer’s Disease, Kamikihito, Reverses Amyloid‐β‐Induced Progression of Tau Phosphorylation and Axonal Atrophy

Aims. We previously reported that kamikihito (KKT), a traditional Japanese medicine, improved memory impairment and reversed the degeneration of axons in the 5XFAD mouse model of Alzheimer's disease (AD). However, the mechanism underlying the effects of KKT remained unknown. The aim of the present study was to investigate the mechanism by which KKT reverses the progression of axonal degeneration. Methods. Primary cultured cortical neurons were treated with amyloid beta (Aβ) fragment comprising amino acid residues (25–35) (10 μM) in an in vitro AD model. KKT (10 μg/mL) was administered to the cells before or after Aβ treatment. The effects of KKT on Aβ-induced tau phosphorylation, axonal atrophy, and protein phosphatase 2A (PP2A) activity were investigated. We also performed an in vivo assay in which KKT (500 mg/kg/day) was administered to 5XFAD mice once a day for 15 days. Cerebral cortex homogenates were used to measure PP2A activity. Results. KKT improved Aβ-induced tau phosphorylation and axonal atrophy after they had already progressed. In addition, KKT increased PP2A activity in vitro and in vivo. Conclusions. KKT reversed the progression of Aβ-induced axonal degeneration. KKT reversed axonal degeneration at least in part through its role as an exogenous PP2A stimulator.

Aβ and tau toxicities in Alzheimer’s are linked via oxidative stress-induced p38 activation: Protective role of vitamin E

Oxidative stress is a hallmark of Alzheimer’s disease (AD). We propose that rather than causing damage because of the action of free radicals, oxidative stress deranges signaling pathways leading to tau hyperphosphorylation, a hallmark of the disease. Indeed, incubation of neurons in culture with 5 µM beta-amyloid peptide (Aβ) causes an activation of p38 MAPK (p38) that leads to tau hyperphosphorylation. Inhibition of p38 prevents Aβ-induced tau phosphorylation. Aβ-induced effects are prevented when neurons are co-incubated with trolox (the water-soluble analog of vitamin E).We have confirmed these results in vivo, in APP/PS1 double transgenic mice of AD. We have found that APP/PS1 transgenic mice exhibit a high level of P-p38 in the hippocampus but not in cortex and this is prevented by feeding animals with a diet supplemented with vitamin E.Our results underpin the role of oxidative stress in the altered cell signaling in AD pathology and suggest that antioxidant prevention may be useful in AD therapeutics.

Curcumin attenuates amyloid-β-induced tau hyperphosphorylation in human neuroblastoma SH-SY5Y cells involving PTEN/Akt/GSK-3β signaling pathway

Accumulated amyloid-β peptide (Aβ) and hyperphosphorylated tau proteins are two hallmarks of Alzheimer’s disease (AD). Increasing evidence suggests that Aβ induces tau hyperphosphorylation in AD pathology, but the signaling pathway is not completely understood. Inhibiting Aβ-induced cellular signaling is beneficent to AD treatment. In this study, cellular signaling of tau phosphorylation induced by Aβ and the inhibiting effects of curcumin on this signaling were investigated on human neuroblastoma SH-SY5Y cells. The results indicated that curcumin inhibits Aβ-induced tau phosphorylation at Thr231 and Ser396, over-expression of HDAC6, and decrease in phosphorylation of glycogen synthase kinase-3β (GSK-3β) at Ser9. However, the protective effect of curcumin on dephosphorylation of GSK-3β induced by Aβ is not directly related to cellular oxidative stress. Curcumin depresses Aβ-induced down-regulation of phosphorylations of Akt at Thr308 and Ser473 and 3-phosphoinositide-dependent protein kinase 1 at Ser241, implying that second message PIP3 involves curcumin-protective cell signaling. Furthermore, insulin receptor/phosphatidyl inositol 3-kinase pathway, as a regulatory signaling of second message PIP3, does not participate in Aβ-induced deactivation of Akt (dephosphorylation at Thr308 and Ser473). However, Aβ results in over-expression of Phosphatase and tensin homolog (PTEN), a negative regulator of PIP3. Curcumin depresses Aβ-induced up-regulation of PTEN induced by Aβ. These results imply that curcumin inhibits Aβ-induced tau hyperphosphorylation involving PTEN/Akt/GSK-3β pathway.

Akt-activated GSK3β inhibitory peptide effectively blocks tau phosphorylation

Tau hyperphosphorylation and accumulation in neurofibrillary tangles are closely associated with cognitive deficits in Alzheimer's disease (AD). Abnormal overexpression of GSK3β has been implicated in tau hyperphosphorylation, thus many GSK3β inhibitors have been developed as drug candidates for AD. However, the potent GSK3β inhibitors are prone to show side effects because they can interfere with basal GSK3β function. We have recently reported that the specific motifs in the Wnt coreceptor LRP6 are able to directly inhibit GSK3β when phosphorylated, an thus a novel GSK3β inhibitory peptide (GIP) that can be activated by Akt, was generated by combining the LRP6 motif and an Akt target sequence. In the present study, we tested the effects of a novel GIP on modulating tau phosphorylation and tauopathy. The GSK3β-inhibitory action of GIP was tested ex vivo using hippocampal brain tissue. Human neuroblastoma SH-SY5Y cells were used to determine the protective effects of GIP against Aβ-induced death and tau phosphorylation. We used 3xTg-AD mice to verify the effect of GIP on the tau hyperphosphorylation and Aβ plaques in vivo. GIP effectively blocked GSK3 β -induced tau phosphorylation in hippocampal homogenate. In addition, the GIP fused with a cell permeable sequence attenuated Aβ-induced tau phosphorylation and cell death in human neuroblastoma cells. Interestingly, high Akt activation was observed particularly in the hippocampus assuming that GIP can be activated to inhibit GSK3 β. T he designed GIP significantly reduced tau phosphorylation in the hippocampus of 3 ' Tg-AD mice without affecting levels of Aβ plaques. In conclusion, the current findings provide a novel concept for the drug development targeting tau hyperphosphorylation in AD, and GIP may have potential as a therapeutic drug in tauopathies.

β2 Adrenergic Receptor, Protein Kinase A (PKA) and c-Jun N-terminal Kinase (JNK) Signaling Pathways Mediate Tau Pathology in Alzheimer Disease Models

Alzheimer disease (AD) is characterized by neurodegeneration marked by loss of synapses and spines associated with hyperphosphorylation of tau protein. Accumulating amyloid β peptide (Aβ) in brain is linked to neurofibrillary tangles composed of hyperphosphorylated tau in AD. Here, we identify β2-adrenergic receptor (β2AR) that mediates Aβ-induced tau pathology. In the prefrontal cortex (PFC) of 1-year-old transgenic mice with human familial mutant genes of presenilin 1 and amyloid precursor protein (PS1/APP), the phosphorylation of tau at Ser-214 Ser-262 and Thr-181, and the protein kinases including JNK, GSK3α/β, and Ca(2+)/calmodulin-dependent protein kinase II is increased significantly. Deletion of the β2AR gene in PS1/APP mice greatly decreases the phosphorylation of these proteins. Further analysis reveals that in primary PFC neurons, Aβ signals through a β2AR-PKA-JNK pathway, which is responsible for most of the phosphorylation of tau at Ser-214 and Ser-262 and a significant portion of phosphorylation at Thr-181. Aβ also induces a β2AR-dependent arrestin-ERK1/2 activity that does not participate in phosphorylation of tau. However, inhibition of the activity of MEK, an upstream enzyme of ERK1/2, partially blocks Aβ-induced tau phosphorylation at Thr-181. The density of dendritic spines and synapses is decreased in the deep layer of the PFC of 1-year-old PS1/APP mice, and the mice exhibit impairment of learning and memory in a novel object recognition paradigm. Deletion of the β2AR gene ameliorates pathological effects in these senile PS1/APP mice. The study indicates that β2AR may represent a potential therapeutic target for preventing the development of AD.

Hypoxia Increases Aβ-Induced Tau Phosphorylation by Calpain and Promotes Behavioral Consequences in AD Transgenic Mice

Chronic hypoxia has been reported to contribute to the development of Alzheimer's disease (AD). However, the mechanism of hypoxia in the pathogenesis of AD remains unclear. The purpose of this study was to investigate the effects of chronic hypoxia treatment on β-amyloid, tau pathologies, and the behavioral consequences in the double transgenic (APP/PS1) mice. Double transgenic mice (APP/PS1 mice) were treated with hypoxia, and spatial learning and memory abilities of mice were assessed in the Morris water maze. β-amyloid level and plaque level in APP/PS1 double transgenic mice were detected by immunohistochemistry. Protein tau, p35/p25, cyclin-dependent kinase 5 (CDK5), and calpain were detected by western blotting analysis. Chronic hypoxia treatment decreased memory and cognitive function in AD mice. In addition, chronic hypoxia treatment resulted in increased senile plaques, accompanying with increased tau phosphorylation. The hypoxia-induced increase in the tau phosphorylation was associated with a significant increase in the production of p35 and p25 and upregulation of calpain, suggesting that hypoxia induced aberrant CDK5/p25 activation via upregulation of calpain. Our results showed that chronic hypoxia exposure accelerates not only amyloid pathology but also tau pathology via calpain-mediated tau hyperphosphorylation in an AD mouse model. These pathological changes possibly contribute to the hypoxia-induced behavioral change in AD mice.

Morin attenuates tau hyperphosphorylation by inhibiting GSK3β

Alzheimer's disease (AD) is the major form of age-related dementia and is characterized by progressive cognitive impairment, the accumulation of extracellular amyloid β-peptide (Aβ), and intracellular hyperphosphorylated tau aggregates in affected brain regions. Tau hyperphosphorylation and accumulation in neurofibrillary tangles is strongly correlated with cognitive deficits, and is apparently a critical event in the dementia process because mutations in tau can cause a tangle-only form of dementia called frontotemporal lobe dementia. Among kinases that phosphorylate tau, glycogen synthase kinase 3β (GSK3β) is strongly implicated in AD pathogenesis. In the present study, we established an ELISA to screen for agents that inhibit GSK3β activity and found that the flavonoid morin effectively inhibited GSK3β activity and blocked GSK3β-induced tau phosphorylation in vitro. In addition, morin attenuated Aβ-induced tau phosphorylation and protected human neuroblastoma cells against Aβ cytotoxicity. Furthermore, treatment of 3xTg-AD mice with morin resulted in reductions in tau hyperphosphorylation and paired helical filament-like immunoreactivity in hippocampal neurons. Morin is a novel inhibitor of GSK3β that can reduce tau pathology in vivo and may have potential as a therapeutic agent in tauopathies.

Aroclor1254 interferes with estrogen receptor-mediated neuroprotection against beta-amyloid toxicity in cholinergic SN56 cells

Because estrogen plays important neurotrophic and neuroprotective roles in the brain by activating estrogen receptors (ERs), disruption of normal estrogen signaling can leave neurons vulnerable to a variety of insults, including β-amyloid peptide (Aβ). Aroclor1254 (A1254) belongs to the endocrine-disrupting chemical (EDC) polychlorinated biphenyls and has anti-estrogenic properties. In the present study, we evaluated the effect of A1254 on the protective activity of estrogen against Aβ toxicity in differentiated cholinergic SN56 cells. Aged Aβ25–35 causes apoptotic cell death in differentiated SN56 cells, and the cytotoxic evidences are effectively rescued by estrogen. We found that A1254 abolishes the neuroprotective activity of estrogen against Aβ toxicity, and attenuates the suppressive effect of estrogen on Aβ-induced tau phosphorylation and JNK activation. The effects of A1254 on the neuroprotective effects of estrogen in Aβ toxicity are very similar to the effects of the estrogen receptor antagonist ICI182,780. Thus, exposure to EDCs that have anti-estrogenic activity might interfere with normal estrogen-activated neuroprotective signaling events and leave neurons more vulnerable to dangerous stimuli. Our present results provide new understanding of the mechanisms contributing to the harmful effects of EDCs on the function and viability of neurons, and the possible relevance of EDCs in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease.

Astrocytes are important mediators of Aβ-induced neurotoxicity and tau phosphorylation in primary culture.

Alzheimer's disease (AD) is pathologically characterised by the age-dependent deposition of β-amyloid (Aβ) in senile plaques, intraneuronal accumulation of tau as neurofibrillary tangles, synaptic dysfunction and neuronal death. Neuroinflammation, typified by the accumulation of activated microglia and reactive astrocytes, is believed to modulate the development and/or progression of AD. We have used primary rat neuronal, astrocytic and mixed cortical cultures to investigate the contribution of astrocyte-mediated inflammatory responses during Aβ-induced neuronal loss. We report that the presence of small numbers of astrocytes exacerbate Aβ-induced neuronal death, caspase-3 activation and the production of caspase-3-cleaved tau. Furthermore, we show that astrocytes are essential for the Aβ-induced tau phosphorylation observed in primary neurons. The release of soluble inflammatory factor(s) from astrocytes accompanies these events, and inhibition of astrocyte activation with the anti-inflammatory agent, minocycline, reduces astrocytic inflammatory responses and the associated neuronal loss. Aβ-induced increases in caspase-3 activation and the production of caspase-3-truncated tau species in neurons were reduced when the astrocytic response was attenuated with minocycline. Taken together, these results show that astrocytes are important mediators of the neurotoxic events downstream of elevated Aβ in models of AD, and suggest that mechanisms underlying pro-inflammatory cytokine release might be an important target for therapy.

Minocycline-mediated protection from Aβ is mediated primarily by suppression of astrocytic inflammatory responses

Minocycline is a second generation tetracycline derivative with potent, neuroprotective actions in various models of neurodegenerative disease including Alzheimer's disease that are likely associated with its anti-apoptotic and anti-inflammatory properties. Firstly, to determine if the effectiveness of minocycline in reducing β-amyloid-induced abnormal tau processing and neuronal death is mediated by glia. Secondly to investigate the role of glia in Aβ-mediated degenerative pathways. We have investigated the effect of minocycline treatment on Aβ-induced tau processing and neuronal death in primary neuronal, mixed and glial cultures. Mixed cortical cultures were prepared from E18 rat embryos, and neuronal cultures were derived following the suppression of glial proliferation with cytosine arabinoside. Analysis of mixed cultures by immunocytochemistry determined that these cultures contain 4.3 ± 0.4% astrocytes and negligible numbers of microglia (<0.0001%). Glial cultures, containing astrocytes, microglia and small numbers of oligodendrocytes were prepared from P2 rat pups. Cultures were pre-treated with 20μM minocycline for 24h prior to treatment with 10μM soluble oligomeric Aβ. Neuronal cell death, caspase activation, pathological changes in tau proteins and the secretion of inflammatory mediators were assessed by a variety of methods. We show that the presence of astrocytes accelerates the onset of neuronal death in response to Aβ, and that the neuroprotective influence of minocycline is only observed when astrocytes are present. Furthermore, we observe that astrocytes are required for Aβ-induced tau phosphorylation, and that astrocytes mediate caspase-3-mediated cleavage of tau in response to Aβ. In glial cultures, we find increased secretion of several inflammatory factors upon Aβ treatment, including IL-1α, IL6 and IL10. Pre-treatment of glial cultures with minocycline suppresses the secretion of these pro-inflammatory mediators. The influence of specific inflammatory factors on Aβ-induced neurotoxicity is currently under investigation. These results suggest that glia, and more specifically astrocytes, play a major role in Aβ-induced abnormal tau processing and neuronal death. These findings also confirm that glia are a primary target of minocycline. It is possible that suppression of specific neuroinflammatory responses, either alone or in combination with other treatments, may represent an effective therapeutic strategy for the treatment of Alzheimer's disease.

Alzheimer Aβ Peptide Induces Chromosome Mis-Segregation and Aneuploidy, Including Trisomy 21: Requirement for Tau and APP

Both sporadic and familial Alzheimer's disease (AD) patients exhibit increased chromosome aneuploidy, particularly trisomy 21, in neurons and other cells. Significantly, trisomy 21/Down syndrome patients develop early onset AD pathology. We investigated the mechanism underlying mosaic chromosome aneuploidy in AD and report that FAD mutations in the Alzheimer Amyloid Precursor Protein gene, APP, induce chromosome mis-segregation and aneuploidy in transgenic mice and in transfected cells. Furthermore, adding synthetic Abeta peptide, the pathogenic product of APP, to cultured cells causes rapid and robust chromosome mis-segregation leading to aneuploid, including trisomy 21, daughters, which is prevented by LiCl addition or Ca(2+) chelation and is replicated in tau KO cells, implicating GSK-3beta, calpain, and Tau-dependent microtubule transport in the aneugenic activity of Abeta. Furthermore, APP KO cells are resistant to the aneugenic activity of Abeta, as they have been shown previously to be resistant to Abeta-induced tau phosphorylation and cell toxicity. These results indicate that Abeta-induced microtubule dysfunction leads to aneuploid neurons and may thereby contribute to the pathogenesis of AD.

C-Abl tyrosine kinase modulates tau pathology and Cdk5 phosphorylation in AD transgenic mice

The c-Abl tyrosine kinase is an important link in signal transduction pathways that promote cytoskeletal rearrangement and apoptotic signalling. We have previously shown that amyloid-β-peptide (Aβ) activates c-Abl. Herein we show that c-Abl participates in Aβ-induced tau phosphorylation through Cdk5 activation. We found that intraperitoneal administration of STI571, a specific inhibitor for c-Abl kinase, decreased tau phosphorylation in the APPswe/PSEN1ΔE9 transgenic mouse brain. In addition, when neurons were treated with Aβ we observed: (i) an increase in active c-Abl and tau phosphorylation, (ii) the prevention of tau phosphorylation by STI571 and (iii) the inhibition of c-Abl expression by shRNA, as well as the expression of a c-Abl kinase death mutant, decreased AT8 and PHF1 signals. Furthermore, the increase of c-Abl was associated with Tyr15 phosphorylation of Cdk5 and its association with c-Abl. Brains from APPswe/PSEN1ΔE9 mice showed higher levels of c-Abl and phospho-Cdk5 than wild-type mice. Moreover, STI571 treatment decreased the phospho-Cdk5 levels. Together, the evidence suggests that activation of c-Abl by Aβ promotes tau phosphorylation through Tyr15 phosphorylation-mediated Cdk5 activation.

Neutralization of transthyretin reverses the neuroprotective effects of secreted amyloid precursor protein (APP) in APPSW mice resulting in tau phosphorylation and loss of hippocampal neurons: support for the amyloid hypothesis.

Alzheimer's disease (AD) may be caused by the abnormal processing of the amyloid precursor protein (APP) and the accumulation of beta-amyloid (Abeta). The amyloid precursor protein can be proteolytically cleaved into multiple fragments, many of which have distinct biological actions. Although a high level of Abeta can be toxic, the alpha-secretase cleaved APP (sAPPalpha) is neuroprotective. However, the mechanism of sAPPalpha protection is unknown. Here, we show that sAPPalpha increases the expression levels of several neuroprotective genes and protects organotypic hippocampal cultures from Abeta-induced tau phosphorylation and neuronal death. Antibody interference and small interfering RNA knock-down demonstrate that the sAPPalpha-driven expression of transthyretin and insulin-like growth factor 2 is necessary for protection against Abeta-induced neuronal death. Mice overexpressing mutant APP possess high levels of sAPPalpha and transthyretin and do not develop the tau phosphorylation or neuronal loss characteristic of human AD. Chronic infusion of an antibody against transthyretin into the hippocampus of mice overexpressing APP with the Swedish mutation (APP(Sw)) leads to increased Abeta, tau phosphorylation, and neuronal loss and apoptosis within the CA1 neuronal field. Therefore, the elevated expression of transthyretin is mediated by sAPPalpha and protects APP(Sw) mice from developing many of the neuropathologies observed in AD.