Levels of tau phosphorylation at different sites in Alzheimer disease brain

The Interplay between GSK3β and Tau Ser262 Phosphorylation during the Progression of Tau Pathology

Tau hyperphosphorylation has been linked directly to the formation of toxic neurofibrillary tangles (NFTs) in tauopathies, however, prior to NFT formation, the sequence of pathological events involving tau phosphorylation remains unclear. Here, the effect of glycogen synthase kinase 3β (GSK3β) on tau pathology was examined independently for each step of transcellular propagation; namely, tau intracellular aggregation, release, cellular uptake and seeding activity. We find that overexpression of GSK3β-induced phosphorylated 0N4R tau led to a higher level of tau oligomerization in SH-SY5Y neuroblastoma cells than wild type 0N4R, as determined by several orthogonal assays. Interestingly, the presence of GSK3β also enhanced tau release. Further, we demonstrated that cells endocytosed more monomeric tau protein when pre-phosphorylated by GSK3β. Using an extracellular vesicle (EVs)-assisted tau neuronal delivery system, we show that exosomal GSK3β-phosphorylated tau, when added to differentiated SH-SY5Y cells, induced more efficient tau transfer, showing much higher total tau levels and increased tau aggregate formation as compared to wild type exosomal tau. The role of a primary tau phosphorylation site targeted by microtubule-affinity regulating kinases (MARKs), Ser262, was tested by pseudo-phosphorylation using site-directed mutagenesis to aspartate (S262D). S262D tau overexpression significantly enhanced tau release and intracellular tau accumulation, which were concurrent with the increase of pathological states of tau, as determined by immunodetection. Importantly, phosphorylation-induced tau accumulation was augmented by co-transfecting S262D tau with GSK3β, suggesting a possible interplay between Ser262 phosphorylation and GSK3β activity in tau pathology. Lastly, we found that pre-treatment of cells with amyloid-β (Aβ) further tau phosphorylation and accumulation when Ser262 pre-phosphorylation was present, suggesting that S262 may be a primary mediator of Aβ-induced tau toxicity. These findings provide a potential therapeutic target for treating tau-related disorders by targeting specific phospho-tau isoforms and further elucidate the GSK3β-mediated pathological seeding mechanisms.

DHCR24 Knock-Down Induced Tau Hyperphosphorylation at Thr181, Ser199, Thr231, Ser262, Ser396 Epitopes and Inhibition of Autophagy by Overactivation of GSK3β/mTOR Signaling

Accumulating evidences supported that knock-down of DHCR24 is linked to the pathological risk factors of AD, suggesting a potential role of DHCR24 in AD pathogenesis. However, the molecular mechanism link between DHCR24 and tauopathy remains unknown. Here, in order to elucidate the relationship between DHCR24 and tauopathy, we will focus on the effect of DHCR24 on the tau hyperphosphorylation at some toxic sites. In present study, we found that DHCR24 knock-down significantly lead to the hyperphosphorylation of tau sites at Thr181, Ser199, Thr231, Ser262, Ser396. Moreover, DHCR24 knock-down also increase the accumulation of p62 protein, simultaneously decreased the ratio of LC3-II/LC3-I and the number of autophagosome compared to the control groups, suggesting the inhibition of autophagy activity. In contrast, DHCR24 knock-in obviously abolished the effect of DHCR24 knock-down on tau hyperphosphrylation and autophagy. In addition, to elucidate the association between DHCR24 and tauopathy, we further showed that the level of plasma membrane cholesterol, lipid raft-anchored protein caveolin-1, and concomitantly total I class PI3-K (p110α), phospho-Akt (Thr308 and Ser473) were significantly decreased, resulting in the disruption of lipid raft/caveola and inhibition of PI3-K/Akt signaling in silencing DHCR24 SH-SY5Y cells compared to control groups. At the same time, DHCR24 knock-down simultaneously decreased the level of phosphorylated GSK3β at Ser9 (inactive form) and increased the level of phosphorylated mTOR at Ser2448 (active form), leading to overactivation of GSK3β and mTOR signaling. On the contrary, DHCR24 knock-in largely increased the level of membrane cholesterol and caveolin-1, suggesting the enhancement of lipid raft/caveola. And synchronously DHCR24 knock-in also abolished the effect of DHCR24 knock-down on the inhibition of PI3-K/Akt signaling as well as the overactivation of GSK3β and mTOR signaling. Collectively, our data strongly supported DHCR24 knock-down lead to tau hyperphosphorylation and the inhibition of autophagy by a lipid raft-dependent PI3-K/Akt-mediated GSK3β and mTOR signaling. Taking together, our results firstly demonstrated that the decrease of plasma membrane cholesterol mediated by DHCR24 deficiency might contribute to the tauopathy in AD and other tauopathies.

Sex Hormone Depletion Augments Glucocorticoid Induction of Tau Hyperphosphorylation in Male Rat Brain

Steroid hormones secreted by the gonads (sex steroids) and adrenal glands (glucocorticoids, GC) are known to influence brain structure and function. While levels of sex steroids wane in late adulthood, corticosteroid levels tend to rise in many individuals due to age-related impairments in their feedback on central mechanisms regulating adrenal function. These fluctuations in sex and adrenal steroid secretion may be relevant to age-related neurodegenerative disorders such as Alzheimer's disease (AD) in which hyperphosphorylation of Tau protein is a key pathological event. We here report that both, long-term GC deprivation (by adrenalectomy) and exogenous GC administration with natural or synthetic glucocorticoid receptor ligands (corticosterone and dexamethasone, respectively) induce Tau hyperphosphorylation in the hippocampus and frontocortical regions at epitopes associated with disruption of cytoskeletal and synaptic function. Interestingly, we observed that the changes in Tau induced by manipulation of the GC milieu of male rats were exacerbated by testosterone depletion (by orchiectomy). While this finding supports previous suggestions of a neuroprotective role of male sex hormones, this is the first study to address interactions between adrenal and sex steroids on Tau hyperphosphorylation and accumulation that are known to endanger neuronal function and plasticity. These results are particularly important for understanding the mechanisms that can precipitate AD because, besides being modulated by age, GC are elevated by stress, a phenomenon now established as a trigger of deficits in neural plasticity and survival, cognitive behaviour and AD-like Tau pathology.

PhIP exposure in rodents produces neuropathology potentially relevant to Alzheimer's disease

Alzheimer's disease (AD) is a public health crisis due to debilitating cognitive symptoms and lack of curative treatments, in the context of increasing prevalence. Thus, it is critical to identify modifiable risk factors. High levels of meat consumption may increase AD risk. Many toxins are formed during meat cooking such as heterocyclic aromatic amines (HAAs). Our prior studies have shown that HAAs produce dopaminergic neurotoxicity. Given the mechanistic and pathological overlap between AD and dopaminergic disorders we investigated whether exposure to 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP), a prevalent dietary HAA formed during high-temperature meat cooking, may produce AD-relevant neurotoxicity. Here, C57BL/6 mice were treated with 100 or 200 mg/kg PhIP for 8 h or 75 mg/kg for 4 weeks and 16 weeks. PhIP exposure for 8 h produced oxidative damage, and AD-relevant alterations in hippocampal synaptic proteins, Amyloid-beta precursor protein (APP), and β-Site amyloid precursor protein cleaving enzyme 1 (BACE1). PhIP exposure for 4 weeks resulted in an increase in BACE1. PhIP exposure for 16 weeks resulted in increased hippocampal oxidative damage, APP, BACE1, Aβ aggregation, and tau phosphorylation. Quantification of intracellular nitrotyrosine revealed oxidative damage in cholinergic neurons after 8 h, 4 weeks and 16 weeks of PhIP exposure. Our study demonstrates that increase in oxidative damage, APP and BACE1 might be a possible mechanism by which PhIP promotes Aβ aggregation. Given many patients with AD or PD exhibit neuropathological overlap, our study suggests that HAA exposure should be further studied for roles in mediating pathogenic overlap.

Behavioral Abnormalities in Knockout and Humanized Tau Mice

Microtubule-associated protein tau assists in stabilizing microtubules and has been particularly implicated in Alzheimer's disease (AD). Given the importance of tau to AD pathogenesis and therapies, it is important to understand non-classic physiological functions for this protein inside and outside the central nervous system (CNS). Our group has previously shown that tau ablation triggers glucose intolerance and pancreatic dysfunction in mice, suggesting that tau plays a role in peripheral metabolic regulation. Little is known about the role of tau in anxiety. Moreover, inconsistent results have been generated regarding the effects of tau deletion in memory. Here, we characterize systemic insulin resistance, anxiety-related behavior and memory in 15 to 20 weeks old Wild-Type (WT), Tau knockout (TauKO) and a distinct hTau mouse model consisting of tau knockout expressing the longest isoform (2N4R) of a non-mutant WT human Tau protein under the prion promoter (hTau). Our findings demonstrate that tau deletion leads to anxiety-related behavior, impaired contextual and cued fear memory. The presence of a human Tau transgene did not ameliorate the phenotypes observed in animals lacking the mouse tau protein and it elicited impairments in learning, memory, and peripheral insulin sensitivity. Our results suggest that tau protein plays a role in memory and anxiety-related behavior. Our findings also indicate that previously unrecognized functions for tau protein may be a complicating factor in using animal models on the TauKO background. Understanding the link between tau pathophysiology and cognitive and metabolic alterations is of great importance to establish the complete contribution of tau protein to AD pathogenesis.

LRRK2, alpha-synuclein, and tau: partners in crime or unfortunate bystanders?

The identification of genetic forms of Parkinson's disease (PD) has tremendously expanded our understanding of the players and mechanisms involved. Mutations in the genes encoding for alpha-synuclein (aSyn), LRRK2, and tau have been associated with familial and sporadic forms of the disease. aSyn is the major component of Lewy bodies and Lewy neurites, which are pathognomonic protein inclusions in PD. Hyperphosphorylated tau protein accumulates in neurofibrillary tangles in the brains of Alzheimer's disease patients but is also seen in the brains of PD patients. LRRK2 is a complex multi-domain protein with kinase and GTPase enzymatic activity. Since aSyn and tau are phosphoproteins, we review the possible interplay between the three proteins. Understanding the interplay between LRRK2, aSyn and tau is extremely important, as this may enable the identification of novel targets and pathways for therapeutic intervention.

Inhibition of glycogen synthase kinase-3 by BTA-EG4 reduces tau abnormalities in an organotypic brain slice culture model of Alzheimer's disease

Organotypic brain slice culture models provide an alternative to early stage in vivo studies as an integrated tissue system that can recapitulate key disease features, thereby providing an excellent platform for drug screening. We recently described a novel organotypic 3xTg-AD mouse brain slice culture model with key Alzheimer’s disease-like changes. We now highlight the potential of this model for testing disease-modifying agents and show that results obtained following in vivo treatment are replicated in brain slice cultures from 3xTg-AD mice. Moreover, we describe novel effects of the amyloid-binding tetra (ethylene glycol) derivative of benzothiazole aniline, BTA-EG₄, on tau. BTA-EG₄ significantly reduced tau phosphorylation in the absence of any changes in the amounts of amyloid precursor protein, amyloid-β or synaptic proteins. The reduction in tau phosphorylation was associated with inactivation of the Alzheimer’s disease-relevant major tau kinase, GSK-3. These findings highlight the utility of 3xTg-AD brain slice cultures as a rapid and reliable in vitro method for drug screening prior to in vivo testing. Furthermore, we demonstrate novel tau-directed effects of BTA-EG₄ that are likely related to the ability of this agent to inactivate GSK-3. Our findings support the further exploration of BTA-EG₄ as a candidate therapeutic for Alzheimer’s disease.

A comprehensive multiomics approach toward understanding the relationship between aging and dementia

Because age is the greatest risk factor for sporadic Alzheimer's disease (AD), phenotypic screens based upon old age-associated brain toxicities were used to develop the potent neurotrophic drug J147. Since certain aspects of aging may be primary cause of AD, we hypothesized that J147 would be effective against AD-associated pathology in rapidly aging SAMP8 mice and could be used to identify some of the molecular contributions of aging to AD. An inclusive and integrative multiomics approach was used to investigate protein and gene expression, metabolite levels, and cognition in old and young SAMP8 mice. J147 reduced cognitive deficits in old SAMP8 mice, while restoring multiple molecular markers associated with human AD, vascular pathology, impaired synaptic function, and inflammation to those approaching the young phenotype. The extensive assays used in this study identified a subset of molecular changes associated with aging that may be necessary for the development of AD.

Diabetes exacerbates amyloid and neurovascular pathology in aging-accelerated mice

Mounting evidence supports a link between diabetes, cognitive dysfunction, and aging. However, the physiological mechanisms by which diabetes impacts brain function and cognition are not fully understood. To determine how diabetes contributes to cognitive dysfunction and age-associated pathology, we used streptozotocin to induce type 1 diabetes (T1D) in senescence-accelerated prone 8 (SAMP8) and senescence-resistant 1 (SAMR1) mice. Contextual fear conditioning demonstrated that T1D resulted in the development of cognitive deficits in SAMR1 mice similar to those seen in age-matched, nondiabetic SAMP8 mice. No further cognitive deficits were observed when the SAMP8 mice were made diabetic. T1D dramatically increased Aβ and glial fibrillary acidic protein immunoreactivity in the hippocampus of SAMP8 mice and to a lesser extent in age-matched SAMR1 mice. Further analysis revealed aggregated Aβ within astrocyte processes surrounding vessels. Western blot analyses from T1D SAMP8 mice showed elevated amyloid precursor protein processing and protein glycation along with increased inflammation. T1D elevated tau phosphorylation in the SAMR1 mice but did not further increase it in the SAMP8 mice where it was already significantly higher. These data suggest that aberrant glucose metabolism potentiates the aging phenotype in old mice and contributes to early stage central nervous system pathology in younger animals.

Functional genomic screen and network analysis reveal novel modifiers of tauopathy dissociated from tau phosphorylation

A functional genetic screen using loss-of-function and gain-of-function alleles was performed to identify modifiers of tau-induced neurotoxicity using the 2N/4R (full-length) isoform of wild-type human tau expressed in the fly retina. We previously reported eye pigment mutations, which create dysfunctional lysosomes, as potent modifiers; here, we report 37 additional genes identified from ∼1900 genes screened, including the kinases shaggy/GSK-3beta, par-1/MARK, CamKI and Mekk1. Tau acts synergistically with Mekk1 and p38 to down-regulate extracellular regulated kinase activity, with a corresponding decrease in AT8 immunoreactivity (pS202/T205), suggesting that tau can participate in signaling pathways to regulate its own kinases. Modifiers showed poor correlation with tau phosphorylation (using the AT8, 12E8 and AT270 epitopes); moreover, tested suppressors of wild-type tau were equally effective in suppressing toxicity of a phosphorylation-resistant S11A tau construct, demonstrating that changes in tau phosphorylation state are not required to suppress or enhance its toxicity. Genes related to autophagy, the cell cycle, RNA-associated proteins and chromatin-binding proteins constitute a large percentage of identified modifiers. Other functional categories identified include mitochondrial proteins, lipid trafficking, Golgi proteins, kinesins and dynein and the Hsp70/Hsp90-organizing protein (Hop). Network analysis uncovered several other genes highly associated with the functional modifiers, including genes related to the PI3K, Notch, BMP/TGF-β and Hedgehog pathways, and nuclear trafficking. Activity of GSK-3β is strongly upregulated due to TDP-43 expression, and reduced GSK-3β dosage is also a common suppressor of Aβ42 and TDP-43 toxicity. These findings suggest therapeutic targets other than mitigation of tau phosphorylation.

Current strategies in the discovery of small-molecule biomarkers for Alzheimer’s disease

With the number of patients suffering from Alzheimer’s disease rapidly increasing, there is a major requirement for an accurate biomarker capable of diagnosing the disease early. Much of the research is focused on protein and genetic approaches; however, small molecules may provide viable marker molecules. Examples that support this approach include known abnormalities in lipid metabolism, glucose utilization and oxidative stress, which have been demonstrated in patients suffering from the disease. Therefore, by-products of this irregular metabolism may provide accurate biomarkers. In this review we present the current approaches previously published in the literature used to investigate potential small-molecule and metabolite markers, and report their findings. A wide range of techniques are discussed, including separation approaches (LC, GC and CE), magnetic resonance technologies (NMR and magnetic resonance spectroscopy), and immunoassays.

Interaction between eye pigment genes and tau-induced neurodegeneration in Drosophila melanogaster

Null mutations in the genes white and brown, but not scarlet, enhance a rough eye phenotype in a Drosophila melanogaster model of tauopathy; however, adding rosy mutations suppresses these effects. Interaction with nucleotide-derived pigments or increased lysosomal dysregulation are potential mechanisms. Finally, tau toxicity correlates with increased GSK-3β activity, but not with tau phosphorylation at Ser202/Thr205.

Endogenous Aβ causes cell death via early tau hyperphosphorylation

Alzheimer's disease (AD) is characterized by Aβ overproduction and tau hyperphosphorylation. We report that an early, transient and site-specific AD-like tau hyperphosphorylation at Ser262 and Thr231 epitopes is temporally and causally related with an activation of the endogenous amyloidogenic pathway that we previously reported in hippocampal neurons undergoing cell death upon NGF withdrawal [Matrone, C., Ciotti, M.T., Mercanti, D., Marolda, R., Calissano, P., 2008b. NGF and BDNF signaling control amyloidogenic route and Ab production in hippocampal neurons. Proc. Natl. Acad. Sci. 105, 13138-13143]. Such tau hyperphosphorylation, as well as apoptotic death, is (i) blocked by 4G8 and 6E10 Aβ antibodies or by specific β and/or γ-secretases inhibitors; (ii) temporally precedes tau cleavage mediated by a delayed (6-12h after NGF withdrawal) activation of caspase-3 and calpain-I; (iii) under control of Akt-GSK3β-mediated signaling. Finally, we show that such site-specific tau hyperphosphorylation causes tau detachment from microtubules and an impairment of mitochondrial trafficking. These results depict, for the first time, a rapid interplay between endogenous Aβ and tau post-translational modifications which act co-ordinately to compromise neuronal functions in the same neuronal system, under physiological conditions as seen in AD brain.

Pyrrolidine dithiocarbamate activates Akt and improves spatial learning in APP/PS1 mice without affecting beta-amyloid burden

Pyrrolidine dithiocarbamate (PDTC) is a clinically tolerated inhibitor of nuclear factor-kappaB (NF-kappaB), antioxidant and antiinflammatory agent, which provides protection in brain ischemia models. In neonatal hypoxia-ischemia model, PDTC activates Akt and reduces activation of glycogen synthase kinase 3beta (GSK-3beta). Because chronic inflammation, oxidative stress, and increased GSK-3beta activity are features of Alzheimer's disease (AD) pathology, we tested whether PDTC reduces brain pathology and improves cognitive function in a transgenic animal model of AD. A 7 month oral treatment with PDTC prevented the decline in cognition in AD mice without altering beta-amyloid burden or gliosis. Moreover, marked oxidative stress and activation of NF-kappaB were not part of the brain pathology. Instead, the phosphorylated form of GSK-3beta was decreased in the AD mouse brain, and PDTC treatment increased the phosphorylation of Akt and GSK-3beta. Also, PDTC treatment increased the copper concentration in the brain. In addition, PDTC rescued cultured hippocampal neurons from the toxicity of oligomeric Abeta and reduced tau phosphorylation in the hippocampus of AD mice. Finally, astrocytic glutamate transporter GLT-1, known to be regulated by Akt pathway, was decreased in the transgenic AD mice but upregulated back to the wild-type levels by PDTC treatment. Thus, PDTC may improve spatial learning in AD by interfering with Akt-GSK pathway both in neurons and astrocytes. Because PDTC is capable of transferring external Cu2+ into a cell, and, in turn, Cu2+ is able to activate Akt, we hypothesize that PDTC provides the beneficial effect in transgenic AD mice through Cu2+-activated Akt pathway.

Alpha-synuclein induces hyperphosphorylation of Tau in the MPTP model of parkinsonism

Many neurodegenerative diseases associated with functional Tau dysregulation, including Alzheimer's disease (AD) and other tauopathies, also show alpha-synuclein (alpha-Syn) pathology, a protein associated with Parkinson's disease (PD) pathology. Here we show that treatment of primary mesencephalic neurons (48 h) or subchronic treatment of wild-type (WT) mice with the Parkinsonism-inducing neurotoxin MPP+/MPTP, results in selective dose-dependent hyperphosphorylation of Tau at Ser396/404 (PHF-1-reactive Tau, p-Tau), with no changes in pSer202 but with nonspecific increases in pSer262 levels. The presence of alpha-Syn was absolutely mandatory to observe MPP+/MPTP-induced increases in p-Tau levels, since no alterations in p-Tau were seen in transfected cells not expressing alpha-Syn or in alpha-Syn-/- mice. MPP+/MPTP also induced a significant accumulation of alpha-Syn in both mesencephalic neurons and in WT mice striatum. MPTP/MPP+ lead to differential alterations in p-Tau and alpha-Syn levels in a cytoskeleton-bound, vs. a soluble, cytoskeleton-free fraction, inducing their coimmunoprecipitation in the cytoskeleton-free fraction and neuronal soma. Subchronic MPTP exposure increased sarkosyl-insoluble p-Tau in striatum of WT but not alpha-Syn-/- mice. These studies describe a novel mechanism for MPTP neurotoxicity, namely a MPTP-inducible, strictly alpha-Syn-dependent, increased formation of PHF-1-reactive Tau, suggesting convergent overlapping pathways in the genesis of clinically divergent diseases such as AD and PD.

Melatonin arrests peroxynitrite-induced tau hyperphosphorylation and the overactivation of protein kinases in rat brain

The purpose of this study was to examine the in vivo effect of melatonin (MEL) on peroxynitrite-induced tau hyperphosphorylation and the involvement of glycogen synthase kinase-3beta (GSK-3beta) and mitogen-activated protein kinase (MAPK) families. Melatonin was injected into the right cerebroventricle of the rats 1 hr before the bilateral hippocampal injection of 3-morpholino-sydnonimine chloride (SIN-1), the recognized donor of peroxynitrite. Thereafter, the phosphorylation level of tau and the activity of the kinases were analyzed. The injection of SIN-1 induced hyperphosphorylation of tau at pS396 epitope with a concomitant activation of GSK-3beta and selective MAPK isoforms including p38alpha, p38beta, and p38delta but not p38gamma. The effect of peroxynitrite was confirmed using uric acid, a recognized scavenger of peroxynitrite. Preinjection of MEL significantly arrested the peroxynitrite-induced hyperphosphorylation of tau and the activation of GSK-3beta and MAPKs. Melatonin also ameliorated peroxynitrite-induced oxidative stress. We conclude that MEL can efficiently arrest peroxynitrite-induced tau hyperphosphorylation, and the underlying mechanism may involve scavenging the reactive species and suppressing the activated GSK-3beta and p38 MAPK family.

GSK-3β Directly Phosphorylates and Activates MARK2/PAR-1

In Alzheimer disease (AD), the microtubule-associated protein tau is found hyperphosphorylated in paired helical filaments. Among many phosphorylated sites in tau, Ser-262 is the major site for abnormal phosphorylation of tau in AD brain. The kinase known to phosphorylate this particular site is MARK2, whose activation mechanism is yet to be studied. Our first finding that treatment of cells with LiCl, a selective inhibitor of another major tau kinase, glycogen synthase kinase-3beta (GSK-3beta), inhibits phosphorylation of Ser-262 of tau led us to investigate the possible involvement of GSK-3beta in MARK2 activation. In vitro kinase reaction revealed that recombinant GSK-3beta indeed phosphorylates MARK2, whereas it failed to phosphorylate Ser-262 of tau. Our further findings led us to conclude that GSK-3beta phosphorylates MARK2 on Ser-212, one of the two reported phosphorylation sites (Thr-208 and Ser-212) found in the activation loop of MARK2. Down-regulation of either GSK-3beta or MARK2 by small interfering RNAs suppressed the level of phosphorylation on Ser-262. These results, respectively, indicated that GSK-3beta is responsible for phosphorylating Ser-262 of tau through phosphorylation and activation of MARK2 and that the phosphorylation of tau at this particular site is predominantly mediated by a GSK-3beta-MARK2 pathway. These findings are of interest in the context of the pathogenesis of AD.

Compartmentalized tau hyperphosphorylation and increased levels of kinases in transgenic mice

The formation of neurofibrillary tangles in Alzheimer's disease is preceded by a pretangle stage of hyperphosphorylated tau. To characterize pretangle tau in vivo, we correlated, in human tau transgenic mice, levels of kinases known to phosphorylate tau in vitro with the phosphorylation of tau at specific epitopes. Levels of cyclin-dependent kinase-5 were increased in axons of CA1 pyramidal neurons, where tau was phosphorylated specifically at the AD2 epitope Ser396/Ser404. The 12E8 epitope serine262/serine356 and the AT180 epitope threonine231/serine235 were phosphorylated in dendrites, and colocalized with increased levels of glycogen synthase kinase-3. CA1 neurons phosphorylated tau at more epitopes than dentate gyrus neurons, suggesting that tau phosphorylation is cell type-specific, a possible explanation for the spatial distribution of neurofibrillary tangles.

S100beta interaction with tau is promoted by zinc and inhibited by hyperphosphorylation in Alzheimer's disease

The zinc-binding protein S100beta has been identified as an interacting partner with the microtubule-associated protein tau. Both proteins are individually affected in Alzheimer's disease (AD). S100beta, is overexpressed in the disease, whereas hyperphosphorylated tau constitutes the primary component of neurofibrillary tangles. In this study, we examine factors that modulate their binding and the potential role the complex may play in AD pathogenesis. Zinc was identified as a critical component in the binding process and a primary modulator of S100beta-associated cellular responses. Abnormally phosphorylated tau extracted from AD tissue displayed a dramatically reduced capacity to bind S100beta, which was restored by pretreatment with alkaline phosphatase. In differentiated SH-SY5Y cells, exogenous S100beta was internalized and colocalized with tau consistent with an intracellular association. This was enhanced by the addition of zinc and eliminated by divalent metal chelators. S100beta uptake was also accompanied by extensive neurite outgrowth that may be mediated by its interaction with tau. S100beta-tau binding may represent a key pathway for neurite development, possibly through S100beta modulation of tau phosphorylation and/or functional stabilization of microtubules and process formation. S100beta-tau interaction may be disrupted by hyperphosphorylation and/or imbalances in zinc metabolism, and this may contribute to the neurite dystrophy associated with AD.

Microtubule-affinity regulating kinase (MARK) is tightly associated with neurofibrillary tangles in Alzheimer brain: a fluorescence resonance energy transfer study

Paired helical filaments, the main structural components of the neurofibrillary tangles in Alzheimer disease, consist of phosphorylated tau protein. Because the levels and degree of phosphorylation are significantly higher in paired helical filament (PHF)-derived tau than in normal adult tau, and because phosphorylation of tau severely disrupts microtubule stability, it is postulated that tau phosphorylation is an important step in PHF formation. The kinases and/or phosphatases that act in vivo to help induce such a pathological state of tau, however, are not yet known. In this study we implicate the non-proline directed kinase MARK in PHF-tau phosphorylation, by virtue of its close intermolecular association with the phosphorylated Ser262 epitope on PHF-tau as assessed by fluorescence resonance energy transfer. Moreover, because this tight enzyme-substrate association is observed in neurofibrillary tangles in Alzheimer tissue, we suggest that PHF-tau phosphorylation may occur to some extent on assembled PHF filaments.

Comparison of A68 levels in Alzheimer diseased and non-Alzheimer's diseased brain by two ALZ50 based methods

A total of 61 human brain specimens were analyzed with both ELISA and Western Blot using the ALZ50 monoclonal antibody. The brain specimens included: Alzheimer's Disease (AD, n=31), AD/Down's (n=2), Normal (n=14), Parkinson's Disease (n=7), Huntington's chorea (n=2), Wernicke-Korsakov's Encephalopathy (n=3), and Motor Neuron Disease (n=2). The non-AD cases (n=28) had no detectable A68 by ELISA, and showed no A68 bands by Western blot. The AD cases (n=33), all were positive for A68 by the ELISA, but only 31 of 33 had visible A68 band by Western blot. Additionally, a method for solubilization of A68 is reported.