Excessive Tau Phosphorylation Research Articles

GSK3: A potential target and pending issues for treatment of Alzheimer's disease.

Glycogen synthase kinase-3 (GSK3), consisting of GSK3α and GSK3β subtypes, is a complex protein kinase that regulates numerous substrates. Research has observed increased GSK3 expression in the brains of Alzheimer's disease (AD) patients and models. AD is a neurodegenerative disorder with diverse pathogenesis and notable cognitive impairments, characterized by Aβ aggregation and excessive tau phosphorylation. This article provides an overview of GSK3's structure and regulation, extensively analyzing its relationship with AD factors. GSK3 overactivation disrupts neural growth, development, and function. It directly promotes tau phosphorylation, regulates amyloid precursor protein (APP) cleavage, leading to Aβ formation, and directly or indirectly triggers neuroinflammation and oxidative damage. We also summarize preclinical research highlighting the inhibition of GSK3 activity as a primary therapeutic approach for AD. Finally, pending issues like the lack of highly specific and affinity-driven GSK3 inhibitors, are raised and expected to be addressed in future research. In conclusion, GSK3 represents a target in AD treatment, filled with hope, challenges, opportunities, and obstacles.

Role of MARK2 in the nervous system and cancer.

Microtubule-Affinity Regulating Kinase 2 (MARK2), a member of the serine/threonine protein kinase family, phosphorylates microtubule-associated proteins, playing a crucial role in cancer and neurodegenerative diseases. This kinase regulates multiple signaling pathways, including the WNT, PI3K/AKT/mTOR (PAM), and NF-κB pathways, potentially linking it to cancer and the nervous system. As a crucial regulator of the PI3K/AKT/mTOR pathway, the loss of MARK2 inhibits the growth and metastasis of cancer cells. MARK2 is involved in the excessive phosphorylation of tau, thus influencing neurodegeneration. Therefore, MARK2 emerges as a promising drug target for the treatment of cancer and neurodegenerative diseases. Despite its significance, the development of inhibitors for MARK2 remains limited. In this review, we aim to present detailed information on the structural features of MARK2 and its role in various signaling pathways associated with cancer and neurodegenerative diseases. Additionally, we further characterize the therapeutic potential of MARK2 in neurodegenerative diseases and cancer, and hope to facilitate basic research on MARK2 and the development of inhibitors targeting MARK2.

Activation of TRPV4 induces intraneuronal tau hyperphosphorylation via cholesterol accumulation

Transient receptor potential vanilloid 4 (TRPV4) is a non-selective cation channel, whose aberrant function in neurons has been reported to participate in the progression of brain disorders, including Alzheimer's disease (AD). However, the influence of TRPV4 activation on tau hyperphosphorylation in AD has not yet been elucidated. Since disturbed brain cholesterol homeostasis is considered to be related to excessive tau phosphorylation, this study aimed to explore whether dysregulation of TRPV4 affects tau phosphorylation and whether it involves cholesterol unbalance. Our data indicated that TRPV4 activation increased tau phosphorylation in the cortex and hippocampus of P301S tauopathy mouse model and aggravated its cognitive decline. In addition, we detected that TRPV4 activation upregulated cholesterol levels in primary neurons, and the elevation of cholesterol promoted hyperphosphorylation of tau. TRPV4 knockdown improved tau hyperphosphorylation by reducing intracellular cholesterol accumulation. Our results suggest that activation of TRPV4 may take part in the pathological mechanism of AD by promoting intraneuronal tau hyperphosphorylation in a cholesterol-dependent manner.

Development of a system to analyze oral frailty associated with Alzheimer's disease using a mouse model.

The rapid aging of the population makes the detection and prevention of frailty increasingly important. Oral frailty has been proposed as a novel frailty phenotype and is defined as a decrease in oral function coexisting with a decline in cognitive and physical functions. Oral frailty has received particular attention in relation to Alzheimer's disease (AD). However, the pathomechanisms of oral frailty related to AD remain unknown. It is assumed that the mesencephalic trigeminal nucleus (Vmes), which controls mastication, is affected by AD pathology, and as a result, masticatory function may be impaired. To investigate this possibility, we included male 3 × Tg-AD mice and their non-transgenic counterpart (NonTg) of 3–4 months of age in the present study. Immunohistochemistry revealed amyloid-β deposition and excessive tau phosphorylation in the Vmes of 3 × Tg-AD mice. Furthermore, vesicular glutamate transporter 1-immunopositive axon varicosities, which are derived from Vmes neurons, were significantly reduced in the trigeminal motor nucleus of 3 × Tg-AD mice. To investigate whether the AD pathology observed in the Vmes affects masticatory function, we analyzed electromyography of the masseter muscle during feeding. The 3 × Tg-AD mice showed a significant delay in masticatory rhythm compared to NonTg mice. Furthermore, we developed a system to simultaneously record bite force and electromyography of masseter, and devised a new method to estimate bite force during food chewing in mice. Since the muscle activity of the masseter showed a high correlation with bite force, it could be accurately estimated from the muscle activity. The estimated bite force of 3 × Tg-AD mice eating sunflower seeds was predominantly smaller than that of NonTg mice. However, there was no difference in masseter weight or muscle fiber cross-sectional area between the two groups, suggesting that the decreased bite force and delayed mastication rhythm observed in 3 × Tg-AD mice were not due to abnormality of the masseter. In conclusion, the decreased masticatory function observed in 3 × Tg-AD mice was most likely caused by AD pathology in the Vmes. Thus, novel quantitative analyses of masticatory function using the mouse model of AD enabled a comprehensive understanding of oral frailty pathogenesis.

The study of Tau and phospho Tau protein levels in attention deficit and hyperactivity disorder

Background/aim Attention deficit and hyperactivity disorder (ADHD) is a widespread neurodevelopmental disorder that begins in childhood and has negative consequences throughout adult life. The etiology and pathogenesis of ADHD are still unclear. Tau protein is a soluble microtubule-related protein expressed by neurons and localized in the cytoplasm as well as axons. Tau protein provides stability of microtubule in two ways: phosphorylation and isoforms. The excessive phosphorylation of Tau separates the protein from the microtubule, thus making it unstable. In this study, we aimed to investigate whether there is a relationship between serum Tau protein and phospho Tau (p-Tau181) levels and ADHD occurrence.Materials and methods This study included 26 male children aged 7–12 years with newly diagnosed ADHD, who had previously not used any medication for ADHD, and 26 male healthy children. Serum Tau and p-Tau181 concentrations were performed by enzyme-linked immunosorbent assay (ELISA). Results In patients, the Tau levels were not significantly different from those of the controls; the p-Tau181 levels were significantly higher than those of the controls. Conclusion We concluded that high p-Tau181 might be associated with the progression of ADHD and cognitive changes in ADHD.

Alterations in Tau Protein Level and Phosphorylation State in the Brain of the Autistic-Like Rats Induced by Prenatal Exposure to Valproic Acid.

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficient social interaction and communication besides repetitive, stereotyped behaviours. A characteristic feature of ASD is altered dendritic spine density and morphology associated with synaptic plasticity disturbances. Since microtubules (MTs) regulate dendritic spine morphology and play an important role in spine development and plasticity the aim of the present study was to investigate the alterations in the content of neuronal α/β-tubulin and Tau protein level as well as phosphorylation state in the valproic acid (VPA)-induced rat model of autism. Our results indicated that maternal exposure to VPA induces: (1) decrease the level of α/β-tubulin along with Tau accumulation in the hippocampus and cerebral cortex; (2) excessive Tau phosphorylation and activation of Tau-kinases: CDK5, ERK1/2, and p70S6K in the cerebral cortex; (3) up-regulation of mTOR kinase-dependent signalling in the hippocampus and cerebral cortex of adolescent rat offspring. Moreover, immunohistochemical staining showed histopathological changes in neurons (chromatolysis) in both analysed brain structures of rats prenatally exposed to VPA. The observed changes in Tau protein together with an excessive decrease in α/β-tubulin level may suggest destabilization and thus dysfunction of the MT cytoskeleton network, which in consequence may lead to the disturbance in synaptic plasticity and the development of autistic-like behaviours.

Constant Levels of Tau Phosphorylation in the Brain of htau Mice

Excessive tau phosphorylation is the hallmark of tauopathies. Today’s research thus focusses on the development of drugs targeting this pathological feature. To test new drugs in preclinical studies, animal models are needed that properly mimic this pathological hallmark. The htau mouse is a well-known model expressing human but lacking murine tau, allowing to evaluate the efficacy of tau modifying compounds without interference from murine tau. Htau mice are well-characterized for tau pathology at older age, although it is often not specified on which genetic background analyzed animals were bred. Since it was shown that the genetic background can influence the pathology, we evaluated the phosphorylation status of young and adult htau mice on a C57BL/6J background by analyzing ptau Ser202 and ptau Ser396 levels in the cortex and hippocampus of 3 and 12 month old animals by immunofluorescent labelling. Additionally, we evaluated total tau, ptau Thr231 and ptau Thr181 in the soluble and insoluble brain fraction of 3–15 month old htau mice by immunosorbent assay. Our results show that ptau levels of all analyzed residues and age groups are similar without strong increases over age. These data show that tau is already phosphorylated at the age of 3 months suggesting that phosphorylation starts even earlier. The early start of tau phosphorylation in htau mice enables the use of these mice for efficacy studies already at very young age.

Protective effects of chondroitin sulphate nano-selenium on a mouse model of Alzheimer's disease

In this study, the effect of chondroitin sulphate nano-selenium (CS@Se) on Alzheimer's disease (AD) in mice was investigated. CS@Se alleviated anxiety and improved the spatial learning and memory impairment in AD mice. CS@Se significantly reduced cell oedema and pyknosis, protected the mitochondria, and improved abnormal changes in the ultrastructure of hippocampal neuron synapses of AD mice. Moreover, CS@Se significantly increased the levels of superoxide dismutase(SOD), glutathione peroxidase (GSH-Px), Na+/K+-ATPase assay (Na+/K+-ATPase) and acetyltransferase (ChAT), and decreased the levels of malondialdehyde (MDA) and acetylcholinesterase (ChAE) in AD mice. Western blot results showed that CS@Se can attenuate excessive phosphorylation of tau (Ser396/Ser404) by regulating the expression of glycogen synthase kinase-3 beta (GSK-3β). In addition, CS@Se can activate the extracellular signal-regulated kinase 1/2 (ERK 1/2) and p38 mitogen-activated protein kinase (p38 MAPK) signalling pathways to inhibit nuclear transcription factor kappa B (NF-κB) nuclear translocation, thereby regulating the expression of pro-inflammatory cytokines. In summary, CS@Se can reduce oxidative stress damage, inhibit excessive tau phosphorylation, reduce inflammation to delay AD development, and increase the learning and memory capacities of AD mice.

Curcumin Decreases Hyperphosphorylation of Tau by Down-Regulating Caveolin-1/GSK-3β in N2a/APP695swe Cells and APP/PS1 Double Transgenic Alzheimer's Disease Mice.

Caveolin-1, the marker protein of membranal caveolae, is not only involved in cholesterol regulation, but also participates in the cleavage of amyloid [Formula: see text]-protein precursor (APP) and the generation of [Formula: see text]-amyloid peptide. It has been reported to be tightly related with Tau. In our previous studies, curcumin has been confirmed to play a neuroprotective role in Alzheimer's disease (AD), but its effects on Caveolin-1, Tau and their correlation, and the mechanism is still unknown. As such, in the present study, N2a/WT cells, N2a/APP695swe cell and six-month-old APP/PS1 double transgenic mice were enrolled. After curcumin treatment, the expression of Caveolin-1, Tau and their relationship was detected, and the potential mechanisms were explored. The results showed that in the N2a/APP695swe cells, curcumin not only decreased the number of caveolae, but also made their membrane to be thinner; and curcumin could decreased the expression of phosphorylated Tau (P-Tau(ser404)/Tau) and Caveolin-1 ([Formula: see text]), but the expression of phosphorylated GSK-3[Formula: see text] (P-GSK-3[Formula: see text]/GSK-3[Formula: see text] was increased ([Formula: see text]). In APP/PS1 transgenic mice, the same results were observed. Taken together, our data suggest that curcumin may play an important role in AD via reducing Caveolin-1, inactivating GSK-3[Formula: see text] and inhibiting the abnormal excessive phosphorylation of Tau, which will provide a new theory for AD treatment with curcumin.

The Diabetic Brain and Dementia

Alzheimer's Disease (AD) and Diabetes Mellitus (DM) are the two most common and devastating health problems in the elderly. They share a number of common features among which are important impact on quality of life and substantial health care costs. Epidemiological and biological evidence support a pathophysiological link between Type 2 Diabetes Mellitus (DMT2) and cognitive impairment (1-3). A causative association between DM and Alzheimer's disease has been suggested on the basis of clinical, epidemiological, genetic and experimental studies (2,4-9). Persons with DM have a higher incidence of cognitive decline and an increased risk of developing AD and other types of dementia, and comorbidity increases the risk (10,11). Insulin resistance predicts medial temporal hypermetabolism in Mild Cognitive Impairment (MCI) conversion to AD (12) and glucose uptake changes in AD in medial temporal regions predicting worse memory performance (13). DM has been shown to influence the rate of functional decline among patients with mild AD dementia than in those without comorbid DM (14). However, the precise mechanisms involved in the development of AD in diabetics are not yet fully understood, and several pathogenic pathways have been discussed (3,4,15-20). Autopsy studies stated that diabetic patients show significantly less AD pathology (senile plaques, neurofibrillary tangles, cerebral amyloid angiopathy, etc.) but more cerebrovascular lesions including microvascular lesions and white matter changes than subjects without DM (5,21-27). Vasculo-neural dysfunction has been suggested to represent a potential etiological linkage between DMT2 and AD (6,28), while others suggested that the association between DM and dementia is only partially mediated through cerebrovascular disease and that DM is associated independently with overal dementia among elderly, but not with AD or vascular dementia (29). Positive DMT2 status appears to exacerbate AD pathology in the presence of ApoE e4 (30). Although insulin mitigates Aβ deposition and hyperphosphorylation of tau (17,31), DM in combination with ApoE e4 may lead to excessive phosphorylation of tau (32), but only in subjects with late stage AD (21). DM modifies metabolism of Aβ and tau causing Aβ/tau-dependent pathological changes, although there is evidence that suggests an interaction of Aβ/tau-dependent and -independent mechanisms (31). Evidence supports insulin's role in cognition, synaptic remodelling and facilitation of memory (33). On the other hand, insulin has been shown to modulate the level of Aβ, to protect neurons against detrimental effects of Aβ on synapses (33). It further facilitates reduction of amyloid plaques, downregulation of Aβ-derived diffusible ligand-binding sites and also to promote tau hypophosphorylation, which stabilizes microtubules. These data and the observation that the combination of insulin and other antidiabetic medication is associated with lower neuritic plaque density (23,34) are providing a rationale for using insulin to treat AD high-risk patients (35-37).

2015: which new directions for Alzheimer's disease?

2015: which new directions for Alzheimer's disease?

Small molecule p75NTR ligands reduce pathological phosphorylation and misfolding of tau, inflammatory changes, cholinergic degeneration, and cognitive deficits in AβPP(L/S) transgenic mice.

The p75 neurotrophin receptor (p75NTR) is involved in degenerative mechanisms related to Alzheimer's disease (AD). In addition, p75NTR levels are increased in AD and the receptor is expressed by neurons that are particularly vulnerable in the disease. Therefore, modulating p75NTR function may be a significant disease-modifying treatment approach. Prior studies indicated that the non-peptide, small molecule p75NTR ligands LM11A-31, and chemically unrelated LM11A-24, could block amyloid-β-induced deleterious signaling and neurodegeneration in vitro, and LM11A-31 was found to mitigate neuritic degeneration and behavioral deficits in a mouse model of AD. In this study, we determined whether these in vivo findings represent class effects of p75NTR ligands by examining LM11A-24 effects. In addition, the range of compound effects was further examined by evaluating tau pathology and neuroinflammation. Following oral administration, both ligands reached brain concentrations known to provide neuroprotection in vitro. Compound induction of p75NTR cleavage provided evidence for CNS target engagement. LM11A-31 and LM11A-24 reduced excessive phosphorylation of tau, and LM11A-31 also inhibited its aberrant folding. Both ligands decreased activation of microglia, while LM11A-31 attenuated reactive astrocytes. Along with decreased inflammatory responses, both ligands reduced cholinergic neurite degeneration. In addition to the amelioration of neuropathology in AD model mice, LM11A-31, but not LM11A-24, prevented impairments in water maze performance, while both ligands prevented deficits in fear conditioning. These findings support a role for p75NTR ligands in preventing fundamental tau-related pathologic mechanisms in AD, and further validate the development of these small molecules as a new class of therapeutic compounds.

SCM‐198 protects neurons from microglia‐induced neurotoxicity and improves cognitive performances in Alzheimer’s disease models (846.3)

Background: Chronic inflammation in central nervous system is a conspicuous hallmark in Alzheimer’s disease (AD) and microglial activation is now accepted as a key factor in neuroinflammation. SCM‐198 is an alkaloid extracted from Herba leonuri. In the present study, we investigated its direct and indirect neuroprotective effects in neurons and in animal AD models.Methods and Results: (1) Pretreatment of microglia with SCM‐198 could reduce nitric oxide elevation and inhibit iNOS, TNF‐α, IL‐1β mRNA and protein expressions induced by LPS or Aβ1‐40. NF‐κB translocation induced by LPS was effectively mitigated by SCM‐198 in BV‐2 cells. Western blot results showed that IκBα degradation, NF‐κB p65 activation, phosphorylations of JNK1/2 and tau protein were also inhibited in BV‐2 cells. (2) Microglia/neuron co‐culture assay showed that pretreatment of activated microglia with SCM‐198 could significantly increase neuronal survival and alleviate excessive tau phosphorylation and synaptophysin loss in neurons. (3) Pretreatment of primary neurons with SCM‐198 before Aβ1‐40 challenge could reduce lactase dehydrogenase release, inhibit Bax protein elevation, prevent caspase‐3 and ‐9 activations, increase Bcl‐2 protein expressions in neurons. Besides, neuritic morphology was largely preserved under the intervention of SCM‐198. (4) Animal studies demonstrated that SCM‐198 could ameliorate cognitive deficits of both SD rats injected with Aβ1‐40 and APP/PS1 mice in Morris water maze and novel object recognition tests. Suppression of microglial activation could be observed in brain slices of SD rats and less neuronal loss in hippocampus and cortex were found in APP/PS1 mice.Conclusions: Our findings are the first to report that SCM‐198 could directly protect neurons from apoptosis and indirectly protect neurons by inhibiting microglial overactivation through JNK and NF‐κB pathways. Therefore, SCM‐198 might be a new potential drug candidate for AD therapy in the future.Grant Funding Source: This study was supported by the National Science fund for Distinguished Young Scholars of China

The Influence of 5-Lipoxygenase on Alzheimer’s Disease-Related Tau Pathology: In Vivo and In Vitro Evidence

Intracellular deposition of tau protein is a hallmark lesion of Alzheimer's disease. Although it is known this event is secondary to excessive tau phosphorylation, the mechanisms involved remain unknown. We previously reported that the enzyme 5-Lipoxygenase (5LO) acts as a modulator of Aβ peptides formation in vivo, and here we investigate its influence on tau protein. Tg2576 mice overexpressing neuronal 5LO were generated and its contribution to endogenous tau levels and metabolism investigated. Although no differences were noted in the levels of total tau for both groups, compared with controls, Tg2576 mice overexpressing 5LO had a significant increase in the phosphorylation state of tau at S396 and S396/S404, as recognized by the antibodies PHF-13 and PHF-1, respectively. By contrast, no phosphorylation changes were observed in other tau epitopes. This increase was associated with a significant elevation in cyclin dependent kinase-5 but not other kinases that have been involved in tau phosphorylation. Additionally, mice overexpressing 5LO had biochemical evidence of altered synaptic integrity because they manifested a reduction in PSD-95, synaptophysin and MAP2. This study demonstrates a new role for 5LO in regulating endogenous tau metabolism in the central nervous system and supports the hypothesis that its pharmacologic inhibition could be beneficial for Alzheimer's disease-related tau neuropathology.

Glycogen Synthase Kinase‐3

Glycogen synthase kinase-3 (GSK3) is a ubiquitous and promiscuous kinase that has been studied extensively for over four decades. Initial reports beginning in the 1970s described its role in cellular metabolic pathways fundamental to glucose metabolism, but in more recent years the number of reports describing aberrant GSK3 activity in pathological conditions has risen dramatically. Interest in GSK3 in the field of Alzheimer's disease was first sparked in the early 1990s by papers that described the ability of GSK3 to phosphorylate tau. Excessive tau phosphorylation is present in Alzheimer's-disease-affected brain. These early papers provided new insight to the mechanisms that may contribute to tau pathology of Alzheimer's, with GSK3 as a potential central figure. Since then, the research effort invested into GSK3 in Alzheimer's disease has expanded, and mechanistic studies now demonstrate a functional relationship between not only GSK3 and tau, but also GSK3 and amyloid-β. Through weight of numbers, strong evidence now indicates that GSK3 is associated with the two key pathological features of Alzheimer's-disease-affected brain: neurofibrillary tangles and amyloid plaques. The scope of this special issue is to provide an overview of the data that implicate GSK3 in Alzheimer's disease. As an introduction, the special issue begins with a review of the regulation of GSK3 activity (M. Medina and F. Wandosell). This is followed by a report that provides caution by articulating the need to demonstrate the bona fide substrates of GSK3 (C. Sutherland). The role of GSK3 in the brain and neuronal function is then introduced by two reports. The first is on presynaptic function of GSK3 (K. J. Smillie and M. A. Cousin) and the second on GSK3 in brain development and neuronal plasticity (P. Salcedo-Tello et al.). After this the contribution of GSK3 to neurodegenerative diseases is described in four reviews. The first describes GSK3 in neurodegenerative diseases in general (P. Lei et al.) while the following three discuss more specific aspects of Alzheimer's disease, including cell survival mechanisms (M. A. Mines et al.), inflammation (j. Koistinaho et al.), and tau phosphorylation (D. P. Hanger and W. Nobel). Finally, the special issue concludes with two reviews on therapeutic strategies for Alzheimer's disease that focus on GSK3. The potential of targeting GSK3 for therapeutic benefit against oxidative stress is presented (K. Kanninen et al.), followed by an appraisal of GSK3 inhibitors in the next horizon (A. Martinez et al.). Since several GSK3 inhibitors are currently in clinical trials for treatment of neurological and other disorders, we feel this special issue is a timely “snapshot” of our current knowledge of GSK3 function in healthy and diseased brain, and highlights outstanding issues for future research on this important brain kinase. Peter Crouch Adam Cole Michael Cousin Ana Martinez Katja Kanninen

Haloperidol causes cytoskeletal collapse in N1E-115 cells through tau hyperphosphorylation induced by oxidative stress: Implications for neurodevelopment

Haloperidol a typical antipsychotic commonly used in the treatment of schizophrenia causes neuronal damage and extrapiramidal symptoms after several years of treatment. These symptoms have been associated with increased levels of oxidative stress. Reactive oxygen species produce cytoskeletal collapse and an excessive phosphorylation of tau, a microtubule-associated protein that plays a key role in microtubule stabilization, and in growth cone and neurite formation, which are cytoskeletal phenotypes that participate in neurodevelopment. Thus, we hypothesized that haloperidol produces neurocytoskeletal disorganization by increasing free radicals and tau hyperphosphorylation, and consequently, the loss of neurodevelopmental cytoskeletal phenotypes, neurites and growth cones. The purpose of this work was the characterization of neuronal cytoskeletal changes caused by haloperidol in neuroblastoma N1E-115 cells. We also studied the mechanisms by which haloperidol causes cytoskeletal changes. The results showed that haloperidol at 100μM caused a complete cytoskeleton collapse in the majority of the cells. Melatonin, a free radical scavenger, blocks tau hyperphosphorylation, and microtubule disorganization caused by haloperidol in a dose–response mode. Additionally, the indole blocks lipoperoxide formation in haloperidol treated cells. The results indicate that free radicals and tau hyperphosphorylation produced by haloperidol caused a cytoskeletal collapse and the lost of growth cones and neurites. These effects were blocked by melatonin. Data suggest that extrapiramidal symptoms in schizophrenic patients can be produced by cytoskeletal disorganization during adult brain neurodevelopment after prolonged haloperidol treatment that can be prevented by melatonin.

Neuroinflammation, AD, and Dementia

Neuroinflammation, AD, and Dementia

Active c‐jun N‐terminal kinase induces caspase cleavage of tau and additional phosphorylation by GSK‐3β is required for tau aggregation

Neurofibrillary tangles (NFTs), comprising human intracellular microtubule-associated protein tau, are one of the hallmarks of tauopathies, including Alzheimer's disease. Recently, a report that caspase-cleaved tau is present in NFTs has led to the hypothesis that the mechanisms underlying NFT formation may involve the apoptosis cascade. Here, we show that adenoviral infection of tau into COS-7 cells induces activation of c-jun N-terminal kinase (JNK), followed by excessive phosphorylation of tau and its cleavage by caspase. However, JNK activation alone was insufficient to induce sodium dodecyl sulfate (SDS)-insoluble tau aggregation and additional phosphorylation by GSK-3beta was required. In SH-SY5Y neuroblastoma cells, overexpression of active JNK and GSK-3beta increased caspase-3 activation and cytotoxicity more than overexpression of tau alone. Taken together, these results indicate that, although JNK activation may be a primary inducing factor, further phosphorylation of tau is required for neuronal death and NFT formation in neurodegenerative diseases, including those characterized by tauopathy.

Cholesterol homeostasis failure as a unifying cause of synaptic degeneration

We previously showed that fine tuning of neural cholesterol dynamics is essential for basic synapse function, plasticity and behavior. Significant experimental evidence indicates that cholinergic function, ionotropic and metabotropic receptor machinery, excessive tau phosphorylation, the change of amyloid beta (Abeta or Aβ) biochemistry, neural oxidative stress reactions, and other features of neurodegeneration also depend on fine tuning of brain cholesterol homeostasis. This evidence suggest that (i) cholesterol homeostasis break is the unifying primary cause of sporadic and familial Alzheimer's disease (AD), neuromuscular diseases (particularly inclusion-body myositis), Niemann-Pick's type C disease and Down syndrome, and (ii) explains the overlap of neurodegenerative hallmarks across the spectrum of neurodegenerative diseases. Provided is evidence-based explanation of why extremely rare (but scientifically popular) cases of AD associated with mutations in amyloid beta protein precursor (APP) and presenilin (PS) genes, are translated into the disorder via membrane cholesterol sensitivity of APP processing by secretases and Aβ generation. The reciprocal effect of Aβ on cholesterol synthesis, cellular uptake, efflux and esterification is summarized, as well as the potential implication of such biological function for the compensatory Aβ-assisted restoration of the synaptic long-term potentiation (LTP) and resulting inability of tackling amyloid to cure AD.

14-3-3 Binds to and Mediates Phosphorylation of Microtubule-associated Tau Protein by Ser9-phosphorylated Glycogen Synthase Kinase 3β in the Brain

In mammalian brain, tau, glycogen synthase kinase 3beta (GSK3beta), and 14-3-3, a phosphoserine-binding protein, are parts of a multiprotein tau phosphorylation complex. Within the complex, 14-3-3 simultaneously binds to tau and GSK3beta (Agarwal-Mawal, A., Qureshi, H. Y., Cafferty, P. W., Yuan, Z., Han, D., Lin, R., and Paudel, H. K. (2003) J. Biol. Chem. 278, 12722-12728). The molecular mechanism by which 14-3-3 connects GSK3beta to tau within the complex is not clear. In this study, we find that GSK3beta within the tau phosphorylation complex is phosphorylated on Ser(9). From extracts of rat brain and rat primary cultured neurons, Ser(9)-phosphorylated GSK3beta precipitates with glutathione-agarose beads coated with glutathione S-transferase-14-3-3. Similarly, from rat brain extract, Ser(9)-phosphorylated GSK3beta co-immunoprecipitates with tau. In vitro, 14-3-3 binds to GSK3beta only when the kinase is phosphorylated on Ser(9). In transfected HEK-293 cells, 14-3-3 binds to Ser(9)-phosphorylated GSK3beta and does not bind to GSK3beta (S9A). Tau, on the other hand, binds to both GSK3beta (WT) and GSK3beta (S9A). Moreover, 14-3-3 enhances the binding of tau with Ser(9)-phosphorylated GSK3beta by approximately 3-fold but not with GSK3beta (S9A). Similarly, 14-3-3 stimulates phosphorylation of tau by Ser(9)-phosphorylated GSK3beta but not by GSK3beta (S9A). In transfected HEK-293 cells, Ser(9) phosphorylation suppresses GSK3beta-catalyzed tau phosphorylation in the absence of 14-3-3. In the presence of 14-3-3, however, Ser(9)-phosphorylated GSK3beta remains active and phosphorylates tau. Our data indicate that within the tau phosphorylation complex, 14-3-3 connects Ser(9)-phosphorylated GSK3beta to tau and Ser(9)-phosphorylated GSK3beta phosphorylates tau.