Demonstration by fluorescence resonance energy transfer of a close association between activated MAP kinase and neurofibrillary tangles: implications for MAP kinase activation in Alzheimer disease

Novel Synthetic Coumarin-Chalcone Derivative (E)-3-(3-(4-(Dimethylamino)Phenyl)Acryloyl)-4-Hydroxy-2H-Chromen-2-One Activates CREB-Mediated Neuroprotection in Aβ and Tau Cell Models of Alzheimer's Disease

Abnormal accumulations of misfolded Aβ and tau proteins are major components of the hallmark plaques and neurofibrillary tangles in the brains of Alzheimer's disease (AD) patients. These abnormal protein deposits cause neurodegeneration through a number of proposed mechanisms, including downregulation of the cAMP-response-element (CRE) binding protein 1 (CREB) signaling pathway. Using CRE-GFP reporter cells, we investigated the effects of three coumarin-chalcone derivatives synthesized in our lab on CREB-mediated gene expression. Aβ-GFP- and ΔK280 tau_RD-DsRed-expressing SH-SY5Y cells were used to evaluate these agents for possible antiaggregative, antioxidative, and neuroprotective effects. Blood-brain barrier (BBB) penetration was assessed by pharmacokinetic studies in mice. Of the three tested compounds, (E)-3-(3-(4-(dimethylamino)phenyl)acryloyl)-4-hydroxy-2H-chromen-2-one (LM-021) was observed to increase CREB-mediated gene expression through protein kinase A (PKA), Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), and extracellular signal-regulated kinase (ERK) in CRE-GFP reporter cells. LM-021 exhibited antiaggregative, antioxidative, and neuroprotective effects mediated by the upregulation of CREB phosphorylation and its downstream brain-derived neurotrophic factor and BCL2 apoptosis regulator genes in Aβ-GFP- and ΔK280 tau_RD-DsRed-expressing SH-SY5Y cells. Blockage of the PKA, CaMKII, or ERK pathway counteracted the beneficial effects of LM-021. LM-021 also exhibited good BBB penetration ability, with brain to plasma ratio of 5.3%, in in vivo pharmacokinetic assessment. Our results indicate that LM-021 works as a CREB enhancer to reduce Aβ and tau aggregation and provide neuroprotection. These findings suggest the therapeutic potential of LM-021 in treating AD.

Pathological Links between Traumatic Brain Injury and Dementia: Australian Pre-Clinical Research

Traumatic brain injury (TBI) can cause persistent cognitive changes and ongoing neurodegeneration in the brain. Accumulating epidemiological and pathological evidence implicates TBI in the development of Alzheimer's disease, the most common cause of dementia. Further, the TBI-induced form of dementia, called chronic traumatic encephalopathy, shares many pathological hallmarks present in multiple different diseases which cause dementia. The inflammatory and neuritic responses to TBI and dementia overlap, indicating that they may share common pathological mechanisms and that TBI may ultimately cause a pathological cascade culminating in the development of dementia. This review explores Australian pre-clinical research investigating the pathological links between TBI and dementia.

Type 1 cannabinoid receptor ligands display functional selectivity in a cell culture model of striatal medium spiny projection neurons

Modulation of type 1 cannabinoid receptor (CB1) activity has been touted as a potential means of treating addiction, anxiety, depression, and neurodegeneration. Different agonists of CB1 are known to evoke varied responses in vivo. Functional selectivity is the ligand-specific activation of certain signal transduction pathways at a receptor that can signal through multiple pathways. To understand cannabinoid-specific functional selectivity, different groups have examined the effect of individual cannabinoids on various signaling pathways in heterologous expression systems. In the current study, we compared the functional selectivity of six cannabinoids, including two endocannabinoids (2-arachidonyl glycerol (2-AG) and anandamide (AEA)), two synthetic cannabinoids (WIN55,212-2 and CP55,940), and two phytocannabinoids (cannabidiol (CBD) and Δ(9)-tetrahydrocannabinol (THC)) on arrestin2-, Gα(i/o)-, Gβγ-, Gα(s)-, and Gα(q)-mediated intracellular signaling in the mouse STHdh(Q7/Q7) cell culture model of striatal medium spiny projection neurons that endogenously express CB1. In this system, 2-AG, THC, and CP55,940 were more potent mediators of arrestin2 recruitment than other cannabinoids tested. 2-AG, AEA, and WIN55,212-2, enhanced Gα(i/o) and Gβγ signaling, with 2-AG and AEA treatment leading to increased total CB1 levels. 2-AG, AEA, THC, and WIN55,212-2 also activated Gα(q)-dependent pathways. CP55,940 and CBD both signaled through Gα(s). CP55,940, but not CBD, activated downstream Gα(s) pathways via CB1 targets. THC and CP55,940 promoted CB1 internalization and decreased CB1 protein levels over an 18-h period. These data demonstrate that individual cannabinoids display functional selectivity at CB1 leading to activation of distinct signaling pathways. To effectively match cannabinoids with therapeutic goals, these compounds must be screened for their signaling bias.

FRET and FRAP imaging: approaches to characterise tau and stathmin interactions with microtubules in cells

Microtubules (MTs) are involved in many crucial processes such as cell morphogenesis, mitosis and motility. These dynamic structures resulting from the complex assembly of tubulin are tightly regulated by stabilising MT-associated proteins (MAPs) such as tau and destabilising proteins, notably stathmin. Because of their key role, these MAPs and their interactions have been extensively studied using biochemical and biophysical approaches, particularly in vitro. Nevertheless, numerous questions remain unanswered and the mechanisms of interaction between MT and these proteins are still unclear in cells. Techniques coupling cell imaging and fluorescence methods, such as Förster resonance energy transfer and fluorescence recovery after photobleaching, are excellent tools to study these interactions in situ. After describing these methods, we will present emblematic data from the literature and unpublished experimental results from our laboratory concerning the interactions between MTs, tau and stathmin in cells.

Identification of oligomers at early stages of tau aggregation in Alzheimer's disease

Neurofibrillary tangles (NFTs) are a pathological hallmark of Alzheimer's disease (AD); however, the relationship between NFTs and disease progression remains controversial. Analyses of tau animal models suggest that phenotypes coincide with accumulation of soluble aggregated tau species but not the accumulation of NFTs. The pathological role of prefilamentous tau aggregates, e.g., tau oligomeric intermediates, is poorly understood, in part because of methodological challenges. Here, we engineered a novel tau oligomer-specific antibody, T22, and used it to elucidate the temporal course and biochemical features of oligomers during NFT development in AD brain. We found that tau oligomers in human AD brain samples were 4-fold higher than those in the controls. We also revealed the role of oligomeric tau conformers in pretangles, neuritic plaques, and neuropil threads in the frontal cortex tissue from AD brains; this analysis uncovers a consistent code that governs tau oligomerization with regard to degree of neuronal cytopathology. These data are the first to characterize the role of tau oligomers in the natural history of NFTs, and they highlight the suitability of tau oligomers as therapeutic targets in AD and related tauopathies.

Activation of glycogen synthase kinase-3 beta mediates β-amyloid induced neuritic damage in Alzheimer's disease

β-Amyloid (Aβ) plaques in Alzheimer (AD) brains are surrounded by severe dendritic and axonal changes, including local spine loss, axonal swellings and distorted neurite trajectories. Whether and how plaques induce these neuropil abnormalities remains unknown. We tested the hypothesis that oligomeric assemblies of Aβ, seen in the periphery of plaques, mediate the neurodegenerative phenotype of AD by triggering activation of the enzyme GSK-3β, which in turn appears to inhibit a transcriptional program mediated by CREB. We detect increased activity of GSK-3β after exposure to oligomeric Aβ in neurons in culture, in the brain of double transgenic APP/tau mice and in AD brains. Activation of GSK-3β, even in the absence of Aβ, is sufficient to produce a phenocopy of Aβ-induced dendritic spine loss in neurons in culture, while pharmacological inhibition of GSK-3β prevents spine loss and increases expression of CREB-target genes like BDNF. Of note, in transgenic mice GSK-3β inhibition ameliorated plaque-related neuritic changes and increased CREB-mediated gene expression. Moreover, GSK-3β inhibition robustly decreased the oligomeric Aβ load in the mouse brain. All these findings support the idea that GSK3β is aberrantly activated by the presence of Aβ, and contributes, at least in part, to the neuronal anatomical derangement associated with Aβ plaques in AD brains and to Aβ pathology itself.

Simvastatin overcomes the resistance to serum withdrawal-induced apoptosis of lymphocytes from Alzheimer's disease patients

Statins may exert beneficial effects on Alzheimer's disease (AD) patients. Based on the antineoplastic and apoptotic effects of statins in a number of cell types, we hypothesized that statins may be able to protect neurons by controlling the regulation of cell cycle and/or apoptosis. A growing body of evidence indicates that neurodegeneration involves the cell-cycle activation in postmitotic neurons. Failure of cell-cycle control is not restricted to neurons in AD patients, but occurs in peripheral cells as well. For these reasons, we studied the role of simvastatin (SIM) on cell survival/death in lymphoblasts from AD patients. We report here that SIM induces apoptosis in AD lymphoblasts deprived of serum. SIM interacts with PI3K/Akt and ERK1/2 signaling pathways thereby decreasing the serum withdrawal-enhanced levels of the CDK inhibitor p21(Cip1) (p21) and restoring the vulnerability of AD cells to trophic factor deprivation.

Chronic CXCL10 alters the level of activated ERK1/2 and transcriptional factors CREB and NF-kappaB in hippocampal neuronal cell culture

Signal transduction pathways may be important targets of chemokines during neuroinflammation. In the current study, Western blot analyses show that in rat hippocampal neuronal/glial cell cultures chronic CXCL10 increases the level of protein for ERK1/2 as well as for the transcriptional factors CREB and NF-kappaB. Bcl-2, an anti-apoptotic protein whose expression can be regulated by a pathway involving ERK1/2, CREB and NF-kappaB, was also increased in the CXCL10 treated cultures. These results implicate a role for ERK1/2, CREB and NF-kappaB in effects of CXCL10 on hippocampal cells and suggest that chronic CXCL10 may have a protective role during certain neuroinflammatory conditions.

Abnormal processing of tau in the brain of aged TgCRND8 mice

Amyloid plaques and neurofibrillary tangles are the main histopathological hallmarks of Alzheimer's disease (AD). In the neocortex and hippocampus of aged TgCRND8 mice, tau is hyperphosphorylated at different sites recognized by PHF-1, AT100, AT8 and CP13 antibodies. Phospho-SAPK/JNK levels were increased in the tg mouse brain, where activated SAPK/JNK co-localizes with PHF-1-positive cells. Phosphorylated tau-positive cells showed Bielschowsky- and Thioflavine S-positive intraneuronal deposits. PHF-1 and nitrotyrosine immunoreactivity merged within neurons surrounding amyloid deposits in cortical and hippocampal areas and immunoprecipitation studies confirmed that tau is nitrosylated. Our findings, demonstrating the presence of hyperphosphorylated and nitrosylated tau protein as well as of insoluble aggregates after the onset of amyloid deposition in the TgCRND8 mouse brain, indicate that the abnormal processing of tau may occur subsequently to cerebral amyloidosis and that activation of SAPK/JNK and induction of nitrosative stress are the more likely connecting factors between amyloidosis and tauopathy in AD.

Microtubule-associated protein tau as a therapeutic target in neurodegenerative disease

Interest in the biology of the microtubule-associated protein tau, not only as a pathologic marker, but as a therapeutic target has surged considerably over the last few years. This is due, in part, to the discovery of mutations in tau causing a group of aggressively degenerative neurologic disorders characterized by abnormalities of tau very similar to what is seen in Alzheimer's disease where mutations in tau are absent. As these same mutations also precipitate authentic forms of neurofibrillary degeneration in tau transgenic mice, the gateways to testing therapeutic ideas preclinically have opened. Other Alzheimer's disease animal models have been notoriously bare of this feature, limiting their predictive power for clinical success. In this review, the authors discuss some of the main therapeutic ideas presently advanced in the field and their molecular rationales.

Atypical protein kinase C in neurodegenerative disease II: PKCiota/lambda in tauopathies and alpha-synucleinopathies

To study the role of atypical protein kinase C (aPKC) in neurodegenerative disease, we investigated the distribution of PKCiota/lambda, an aPKC isoform, in a variety of tauopathies and alpha-synucleinopathies. Immunohistochemical study revealed PKCiota/lambda within tau-positive neurofibrillary inclusions in Alzheimer disease (AD), progressive supranuclear palsy, corticobasal degeneration (CBD), and Pick disease (PiD), within alpha-synuclein-positive Lewy bodies in idiopathic Parkinson disease and dementia with Lewy bodies, as well as within glial inclusions in multisystem atrophy. We also observed PKCiota/lambda label of actin-rich Hirano bodies in AD, PiD, and elderly individuals. Double immunolabeling and fluorescence resonance energy transfer demonstrated close physical association between PKCiota/lambda and phospho-tau or alpha-synuclein in some neurofibrillary tangles and Lewy bodies. Furthermore, PKCiota/lambda colocalized with p62, a chaperone protein that binds to both aPKC and ubiquitin, in most of these inclusions. PKCiota/lambda also closely associated with the inactivated form of glycogen synthase kinase-3beta, GSK-3beta[ser9]. Together, these findings suggest that PKCiota/lambda may play a role in common mechanisms involving the pathogenesis of neurodegenerative disease.

Intracellular domains of amyloid precursor-like protein 2 interact with CP2 transcription factor in the nucleus and induce glycogen synthase kinase-3β expression

Amyloid precursor protein (APP) is a member of a gene family that includes two APP-like proteins, APLP1 and 2. Recently, it has been reported that APLP1 and 2 undergo presenilin-dependent gamma-secretase cleavage, as does APP, resulting in the release of an approximately 6 kDa intracellular C-terminal domain (ICD), which can translocate into the nucleus. In this study, we demonstrate that the APLP2-ICDs interact with CP2/LSF/LBP1 (CP2) transcription factor in the nucleus and induce the expression of glycogen synthase kinase 3beta (GSK-3beta), which has broad-ranged substrates such as tau- and beta-catenin. The significance of this finding is substantiated by the in vivo evidence of the increase in the immunoreactivities for the nuclear C-terminal fragments of APLP2, and for GSK-3beta in the AD patients' brain. Taken together, these results suggest that APLP2-ICDs contribute to the AD pathogenesis, by inducing GSK-3beta expression through the interaction with CP2 transcription factor in the nucleus.

The 73-kDa heat shock cognate protein is a CXCR4 binding protein that regulates the receptor endocytosis and the receptor-mediated chemotaxis

The CXCR4 chemokine receptor is a G protein-coupled receptor that plays an important role in leukocyte homing, cancer metastasis, and human immunodeficiency virus infection. In response to ligand stimulation, chemokine receptors undergo endocytosis through clathrin-coated vesicle (CCV). Uncoating of CCV, a process involving heat shock cognate protein and several other proteins, is critical for fusion of CCV to endosomal compartments. The present study demonstrated that CXCR4 was associated with the 73-kDa heat shock cognate protein (Hsc73) in human embryonic kidney 293 cells in response to ligand stimulation. Truncation of the carboxyl terminal domain of CXCR4 reduced the association with Hsc73 and a glutathione S-transferase-CXCR4 carboxyl terminal fusion protein associated with Hsc73 in vitro, suggesting involvement of the carboxyl terminal domain of the receptor in the interaction. In response to ligand stimulation, CXCR4 underwent internalization and colocalization with Hsc73, but the receptor endocytosis was blocked by knockdown of Hsc73 with RNA interference. Moreover, Hsc73 knockdown significantly reduced the CXCR4-mediated chemotaxis of U87 glioma cell lines. These findings suggest that Hsc73 plays a role in chemokine receptor trafficking and the receptor-mediated chemotaxis.

Interaction of Tau with Fe65 links tau to APP

The beta-amyloid precursor protein APP and the microtubule-associated protein Tau play a crucial role in the pathogenesis of Alzheimer's disease (AD). However, the possible molecular events linking these two proteins are still unknown. Here, we show that Fe65, one of the ligands of the APP cytodomain, is associated with Tau in vivo and in vitro, as demonstrated by co-immunoprecipitation, co-localization, and FRET experiments. Deletion studies indicated that the N-terminal domain of Tau and the PTB1 domain of Fe65 are required for this association. This interaction is regulated by the phosphorylation of Tau at selected sites, by glycogen synthase kinase-3beta (GSK3beta) and cyclin-dependent kinase 5 (Cdk5), and requires an intact microtubule network. Furthermore, laser scanner microscopy and co-immunoprecipitation experiments provide preliminary evidence of possible complex(es) involving Tau, Fe65, APP. These findings open new perspectives for the study of the possible crosstalk between these proteins in the pathogenesis of AD.

Does beta-amyloid plaque formation cause structural injury to neuronal processes?

The precise role of beta-amyloid plaque formation in the cascade of brain cell changes that lead to neurodegeneration and dementia in Alzheimer's disease has been unclear. Studies have indicated that neuronal processes surrounding and within plaques undergo a series of biochemical and morphological alterations. Morphological alterations include reactive, degenerative and sprouting-related 'dystrophic' neuritic structures, derived principally from axons, which involve specific changes in cytoskeletal proteins such as tau and NF triplet proteins. More compact and fibrous plaques are associated with more extensive neuritic pathology than non-fibrillar, diffuse beta-amyloid deposits. Cortical apical dendritic processes are either 'clipped' by plaque formation or are bent around more compact plaques. Examination of cases of 'pathological' brain ageing, which may represent a preclinical form of Alzheimer's disease, demonstrated that the earliest neuritic pathology associated with plaques was similar to the reactive changes that follow structural injury to axons. In vivo and in vitro experimental models of structural injury to axons produce identical reactive changes that subsequently lead to an attempt at regenerative sprouting by damaged axons. Thus, beta-amyloid plaque formation may cause structural injury to axons that is subsequently followed by an aberrant sprouting response that presages neurodegeneration and dementia. Identification of the key neuronal alterations underlying the pathology of Alzheimer's disease may provide new avenues for therapeutic intervention.

Mitogen-activated protein kinases and the evolution of Alzheimer's: a revolutionary neurogenetic axis for therapeutic intervention?

Alzheimer's disease (AD) is a neurogenetic condition that affects the processes via which the brain functions. Major observable hallmarks of AD are accumulated clusters of proteins in the brain. These clusters, termed neurofibrillary tangles (NFT), resemble pairs of threads wound around each other in a helix fashion accumulating within neurons. These tangles consist of a protein called Tau, which binds to tubulin, thus forming microtubules. Unlike NFTs, deposits of amyloid precursor protein (beta-APP) gather in the spaces between nerve cells. The nearby neurons often look swollen and deformed, and the clusters of protein are usually accompanied by reactive inflammatory cells, microglia, which are part of the brain's immune system responsible for degrading and removing damaged neurons or plaques. Since phosphorylation/dephosphorylation mechanisms are crucial in the regulation of Tau and beta-APP, a superfamily of mitogen-activated protein kinases (MAPKs) has recently emerged as key regulators of the formation of plagues, eventually leading to dementia and AD. The complex molecular interactions between MAPKs and proteins (plagues) associated with the evolution of AD form a cornerstone in the knowledge of a still burgeoning field of neurodegenerative diseases and ageing. This review overviews current understanding of the molecular pathways related to MAPKs and their role in the development of AD and, possibly, dementia. MAPKs, therefore, may constitute a neurogenetic, therapeutic target for the diagnosis and evolution of a preventative medical strategy for early detection, and likely treatment, of Alzheimer's.

Expression of stress-activated kinases c-Jun N-terminal kinase (SAPK/JNK-P) and p38 kinase (p38-P), and tau hyperphosphorylation in neurites surrounding βA plaques in APP Tg2576 mice

Hyperphosphorylated tau in neurites surrounding beta-amyloid (betaA) deposits, as revealed with phospho-specific anti-tau antibodies, are found in amyloid precursor protein (APP) Tg2576 mice. Because betaA is a source of oxidative stress and may be toxic for cultured cells, the present study examines the expression of phosphorylated (active) stress-activated kinase c-Jun N-terminal kinase (SAPK/JNK-P) and p38 kinase (p38-P), which have the capacity to phosphorylate tau at specific sites, and their specific substrates c-Jun and ATF-2, which are involved in cell death and survival in several paradigms, in Tg2576 mice. The study was planned to shed light about the involvement of these kinases in tau phosphorylation in cell processes surrounding amyloid plaques, as well as in the possible phosphorylation (activation) of c-Jun and activating transcription factor-2 (ATF-2) in relation to betaA deposition. Moderate increase in the expression of phosphorylated mitogen-activated protein kinase and extracelullar signal-regulated kinase (MAPK/ERK-P) occurs in a few amyloid plaques. However, strong expression of SAPK/JNK-P and p38-P is found in the majority of, if not all, amyloid plaques, as seen in serial consecutive sections stained for betaA and stress kinases. Moreover, confocal microscopy reveals colocalization of phospho-tau and SAPK/JNK-P, and phospho-tau and p38-P in many dystrophic neurites surrounding amyloid plaques. Increased expression levels of nonbound tau, SAPK/JNK-P and p38-P are corroborated by Western blots of total cortical homogenate supernatants in Tg2576 mice when compared with age-matched controls. No increase in phosphorylated c-JunSer63 (c-Jun-P) and ATF-2Thr71 (ATF-2-P) is found in association with betaA deposits. In addition, no expression of active (cleaved) caspase-3 (17 kDa) has been found in transgenic mice. Taken together, these observations provide a link between betaA-induced oxidative stress, activation of stress kinases SAPK/JNK and p38, and tau hyperphosphorylation in neurites surrounding amyloid plaques, but activation of these kinases is not associated with accumulation of c-Jun-P and ATF-2-P, nor with activation of active caspase-3 in the vicinity of betaA deposits.

Neuronal protein NP25 interacts with F-actin

Neuronal protein NP25 is a neuron-specific protein present in highly differentiated neural cells, but its functional properties have not been well characterized. NP25 shows high amino acid sequence homology with the smooth muscle cell cytoskeleton-associated proteins, SM22, mp20, and calponin. To gain an insight into the biological functions of NP25, we first examined its subcellular localization in the human neuroblastoma cell line, SK-N-SH. NP25 diffusely distributed in the cytoplasm and fiber-like staining was also observed. It showed that NP25 co-localized with F-actin on stress fibers. A co-sedimentation assay demonstrated that NP25 bound to filamentous actin. Further investigations using fluorescence resonance energy transfer (FRET) technique revealed intracellular binding of NP25 and actin. The significance of the interaction between NP25 and F-actin is discussed.

Impairment of phosphatase 2A contributes to the prolonged MAP kinase phosphorylation in Alzheimer's disease fibroblasts

The serine/threonine phosphatase 2A (PP2A) has been implicated in the pathogenesis of Alzheimer's disease (AD) due to its important role in regulating dephosphorylation of the microtubule-associated protein tau and mitogen-activated protein (MAP) kinase. In the present study, we show that PP2A was responsible for dephosphorylation of the extracellular signal-regulated kinase 1/2 (Erk1/2) following its activation by BK stimulation. Abnormal gene and protein expressions of PP2A, as well as its activity, were found to contribute to the abnormally prolonged Erk1/2 phosphorylation in the AD fibroblasts. Inhibition of PP2A with okadiac acid produced enhanced and more lasting Erk1/2 phosphorylation after BK stimulation, whereas FK506, an inhibitor of PP2B and FK-binding protein, inhibited the BK-stimulated Erk1/2 phosphorylation. Furthermore, while the phosphorylated Erk1/2 was concentrated in the nucleus of AC cells, it was mainly distributed in the extranuclear compartments of AD cells. These results suggest that the delayed dephosphorylation of Erk1/2 in AD cells following its BK-stimulated activation may be due to deficits of PP2A activity and impaired nuclear translocation of phosphorylated Erk1/2.

Rb binding protein Che-1 interacts with Tau in cerebellar granule neurons. Modulation during neuronal apoptosis

Che-1 is a recently identified human Rb binding protein that inhibits the Rb growth-suppressing function and regulates cell proliferation. Che-1 contacts the Rb and competes with HDAC1 for Rb-binding site, removing HDAC1 from the Rb/E2F cell cycle-regulated promoters. We have investigated the expression of Che-1 in neuronal cells and we showed that Che-1 directly interacts with Tau. Tau is a microtubule-associated protein involved in the assembly and stabilization of neuronal microtubules network that plays a crucial role modulating neuronal morphogenesis, axonal shape, and transport. In rat cerebellar granule neurons (CGNs) Che-1 partially colocalizes with Tau in the cytoplasm. Che-1 binds the amino-terminal region of Tau protein, which is not involved in microtubule interactions. Tau and Che-1 endogenous proteins coimmunoprecipitate from CGNs cellular lysates. In addition, Che-1/Tau interaction was demonstrated both in overexpressing COS-7 cells and CGNs by FRET analysis. Finally, we observed that Tau/Che-1 interaction is modulated during neuronal apoptosis.

A1 adenosine receptors accumulate in neurodegenerative structures in Alzheimer disease and mediate both amyloid precursor protein processing and tau phosphorylation and translocation

Immunostaining of adenosine receptors in the hippocampus and cerebral cortex from necropsies of Alzheimer disease (AD) patients shows that there is a change in the pattern of expression and a redistribution of receptors in these brain areas when compared with samples from controls. Adenosine A1 receptor (A1R) immunoreactivity was found in degenerating neurons with neurofibrillary tangles and in dystrophic neurites of senile plaques. A high degree of colocalization for A1R and betaA4 amyloid in senile plaques and for A1R and tau in neurons with tau deposition, but without tangles, was seen. Additionally, adenosine A2A receptors, located mainly in striatal neurons in controls, appeared in glial cells in the hippocampus and cerebral cortex of patients. On comparing similar samples from controls and patients, no significant change was evident for metabotropic glutamate receptors. In the human neuroblastoma SH-SY5Y cell line, agonists for A1R led to a dose-dependent increase in the production of soluble forms of amyloid precursor protein in a process mediated by PKC. A1R agonist induced p21 Ras activation and ERK1/2 phosphorylation. Furthermore, activation of A1R led to and ERK-dependent increase of tau phosphorylation and translocation towards the cytoskeleton. These results indicate that adenosine receptors are potential targets for AD.

Gene-environment interplay in neurogenesis and neurodegeneration

Factors associated with predisposition and vulnerability to neurodegenerative disorders may be described usefully within the context of gene-environment interplay. There are many identified genetic determinants for so-called genetic disorders, and it is possible to duplicate many elements of recognized human neurodegenerative disorders in either knock-in or knock-out mice. However, there are similarly, many identifiable environmental influences on outcomes of the genetic defects; and the course of a progressive neurodegenerative disorder can be greatly modified by environmental elements. Constituent cellular defense mechanisms responsive to the challenge of increased reactive oxygen species represent only one crossroad whereby environment can influence genetic predisposition. In this paper we highlight some of the major neurodegenerative disorders and discuss possible links of gene-environment interplay. The process of adult neurogenesis in brain is also presented as an additional element that influences gene-environment interplay. And the so-called priming processes (i.e., production of receptor supersensitization by repeated drug dosing), is introduced as yet another process that influences how genes and environment ultimately and co-dependently govern behavioral ontogeny and outcome. In studies attributing the influence of genetic alteration on behavioral phenotypy, it is essential to carefully control environmental influences.

Stress kinases involved in tau phosphorylation in Alzheimer's disease, tauopathies and APP transgenic mice

Hyperphosphorylation and accumulation of tau in neurons (and glial cells) is one of the main pathologic hallmarks in Alzheimer's disease (AD) and other tauopathies, including Pick's disease (PiD), progressive supranuclear palsy, corticobasal degeneration, argyrophilic grain disease and familial frontotemporal dementia and parkinsonism linked to chromosome 17 due to mutations in the tau gene (FTDP-17-tau). Recent studies have shown increased expression of select active kinases, including stress-activated kinase, c-Jun N-terminal kinase (SAPK/JNK) and kinase p38 in brain homogenates in all the tauopathies. Strong active SAPK/JNK and p38 immunoreactivity has been observed restricted to neurons and glial cells containing hyperphosphorylated tau, as well as in dystrophic neurites of senile plaques in AD. Moreover, SAPK/JNK- and p38-immunoprecipitated sub-cellular fractions enriched in abnormal hyperphosphorylated tau have the capacity to phosphorylate recombinat tau and c-Jun and ATF-2 which are specific substrates of SAPK/JNK and p38 in AD and PiD. Interestingly, increased expression of phosphorylated SAPK/JNK and p38 in association with hyperphosphorylated tau containing neurites have been observed around betaA4 amyloid deposits in the brain of transgenic mice (Tg2576)carrying the double APP Swedish mutation. These findings suggest that betaA4 amyloid has the capacity to trigger the activation of stress kinases which, in turn, phosphorylate tau in neurites surrounding amyloid deposits. Reduction in the amyloid burden and decreased numbers of amyloid plaques but not of neurofibrillary degeneration has been observed in the brain of two AD patients who participated in an amyloid-beta immunization trial. Activation of stress kinases SAPK/JNK and p38 were reduced together with decreased tau hyperphosphorylation of aberrant neurites in association with decreased amyloid plaques. These findings support the amyloid cascade hypothesis of tau phosphorylation mediated by stress kinases in dystrophic neurites of senile plaques but not that of neurofibrillary tangles and neuropil threads in AD.

Okadaic-acid-induced inhibition of protein phosphatase 2A produces activation of mitogen-activated protein kinases ERK1/2, MEK1/2, and p70 S6, similar to that in Alzheimer's disease

In Alzheimer's disease (AD) brain the activity of protein phosphatase (PP)-2A is compromised and that of the extracellular signal-regulated protein kinase (ERK1/2) of the mitogen-activated protein kinase (MAPK) family, which can phosphorylate tau, is up-regulated. We investigated whether a decrease in PP-2A activity could underlie the activation of these kinases and the abnormal hyperphosphorylation of tau. Rat brain slices, 400-microm-thick, kept under metabolically active conditions in oxygenated (95% O(2), 5% CO(2)) artificial CSF were treated with 1.0 micromol/L okadaic acid (OA) for 1 hour at 33 degrees C. Under this condition, PP-2A activity was decreased to approximately 35% of the vehicle-treated control slices, and activities of PP-1 and PP-2B were not affected. In the OA-treated slices, we observed a dramatic increase in the phosphorylation/activation of ERK1/2, MEK1/2, and p70 S6 kinase both immunohistochemically and by Western blots using phosphorylation-dependent antibodies against these kinases. Treatment of 6-microm sections of the OA-treated slices with purified PP-2A reversed the phosphorylation/activation of these kinases. Hyperphosphorylation of tau at several abnormal hyperphosphorylation sites was also observed, as seen in AD brain. These results suggest 1) that PP-2A down-regulates ERK1/2, MEK1/2, and p70 S6 kinase activities through dephosphorylation at the serine/threonine residues of these kinases, and 2) that in AD brain the decrease in PP-2A activity could have caused the activation of ERK1/2, MEK1/2, and p70 S6 kinase, and the abnormal hyperphosphorylation of tau both via an increase in its phosphorylation and a decrease in its dephosphorylation.

Demonstration by FRET of BACE interaction with the amyloid precursor protein at the cell surface and in early endosomes

Amyloid-beta peptide, which accumulates in senile plaques in Alzheimer's disease, is derived from the amyloid precursor protein (APP) by proteolytic processing. beta-secretase (Asp2), which cleaves APP at the N-terminus of amyloid-beta, has recently been identified to be the protease BACE. In the present study, we examined the subcellular localization of interactions between APP and BACE by using both double immunofluorescence and a fluorescence resonance energy transfer (FRET) approach. Cell surface APP and BACE, studied by using antibodies directed against their ectodomains in living H4 neuroglioma cells co-transfected with APP and BACE, showed exquisite co-localization and demonstrated a very close interaction by FRET analysis. The majority of cell surface APP and BACE were internalized after 15 minutes, but they remained strongly co-localized together in the early endosomal compartment, where FRET analysis demonstrated a continued close interaction. By contrast, at later timepoints, almost no co-localization or FRET was observed in lysosomal compartments. To determine whether the APP-BACE interaction on cell surface and endosomes contributed to amyloid-beta synthesis, we labeled cell surface APP and demonstrated detectable levels of labeled amyloid-beta within 30 minutes. APP-Swedish mutant protein enhanced amyloid-beta synthesis from cell surface APP, consistent with the observation that it is a better BACE substrate than wild-type APP. Taken together, these data confirm a close APP-BACE interaction in early endosomes, and highlight the cell surface as an additional potential site of APP-BACE interaction.

Fluorescence resonance energy transfer determinations using multiphoton fluorescence lifetime imaging microscopy to characterize amyloid-beta plaques

We describe the implementation of a commercial fluorescence lifetime imaging microscopy (FLIM) instrument used in conjunction with a commercial laser scanning multiphoton microscope. The femtosecond-pulsed near-infrared laser is an ideal excitation source for time-domain fluorescence lifetime measurements. With synchronization from the x-y scanners, fluorescence lifetimes can be acquired on a pixel-by-pixel basis, with high spatial resolution. Multiexponential curve fits for each pixel result in two-dimensional fluorescence resonance energy transfer (FRET) measurements that allow the determination of both proximity of fluorescent FRET pairs, as well as the fraction of FRET pairs close enough for FRET to occur. Experiments are described that characterize this system, as well as commonly used reagents valuable for FRET determinations in biological systems. Constructs of CFP and YFP were generated to demonstrate FRET between this pair of green fluorescent protein (GFP) color variants. The lifetime characteristics of the FRET pair fluorescein and rhodamine, commonly used for immunohistochemistry, were also examined. Finally, these fluorophores were used to demonstrate spatially resolved FRET with senile plaques obtained from transgenic mouse brain. Together these results demonstrate that FLIM allows sensitive measurements of protein-protein interactions on a spatial scale less than 10 nm using commercially available components.

Tau phosphorylation and kinase activation in familial tauopathy linked to deln296 mutation

Tau phosphorylation has been examined by immunohistochemistry in the brain of a patient affected with familial tauopathy with progressive supranuclear palsy-like phenotype linked to the delN296 mutation in the tau gene. Phospho-specific tau antibodies Thr181, Ser202, Ser214, Ser396 and Ser422, and antibodies to glycogen synthase kinase-3alpha/beta (GSK-3alpha/beta) and to phosphorylated (P) mitogen-activated protein kinase/extracellular signal-regulated kinases (MAPK/ERK), stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), p38 kinase (p38) and GSK-3betaSer9 have been used to gain understanding of the identification of phosphorylation sites, as well as of the specific kinases that regulate tau phosphorylation at those specific sites, in a familial tauopathy. The neuropathological examination disclosed atrophy of the right precentral gyrus and the brainstem. Neurone loss and gliosis were observed in the substantia nigra, several nuclei of the brainstem and diencephalon. Hyper-phosphorylated tau accumulated in neurones with neurofibrillary tangles and in neurones with pretangles in the substantia nigra, locus ceruleus, peri-aqueductal grey matter, reticular formation, motor nuclei of the brainstem, and thalamus, amygdala and hippocampus. tau-immunoreactive astrocytes and, particularly, oligodendrocytes with coiled bodies were widespread in the brainstem, diencephalons, cerebral white matter and cerebral cortex. Increased expression of MAPK/ERK-P, SAPK/JNK-P, p-38-P and GSK-3beta-P was observed in select subpopulations of neurones with neurofibrillary tangles and in neurones with pretangles. MAPK/ERK-P, SAPK/JNK-P, p38-P and GSK-3beta-P were also expressed in tau-containing astrocytes and in oligodendrocytes with coiled bodies. These findings show, for the first time, activation of precise kinases that regulate tau phosphorylation at specific sites in familial tauopathy.

Phosphorylated protein kinases associated with neuronal and glial tau deposits in argyrophilic grain disease

Tau phosphorylation was examined in argyrophilic grain disease (AGD) by using the phosphospecific tau antibodies Thr181, Ser202, Ser214, Ser 396 and Ser422, and antibodies to non-phosphorylated and phosphorylated mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinases (ERK), stress-activated kinase (SAPK), c-Jun N-terminal kinase (JNK), p38 kinase (p-38), alpha-calcium/calmodulin-dependent kinase II (alphaCaM kinase II), and glycogen synthase kinase-3 (GSK-3), all of which regulate phosphorylation at specific sites of tau. This is the first study in which the role of protein kinases in tau phosphorylation has been examined in AGD. Hyperphosphorylated tau accumulated in grains and pre-tangles in the hippocampus, dentate gyrus, entorhinal and trans-entorhinal cortices, and amygdala in all cases. Ballooned neurons in the amygdala, entorhinal, insular and cingulate cortex, and claustrum contained alphaB-crystallyn and phosphorylated neurofilament epitopes. Some astrocytes and scattered oligodendrocytes containing coiled bodies were recognized with anti-tau antibodies. A few tangles were observed in the entorhinal cortex and hippocampus corresponding to Alzheimer's disease (AD) stages I-III of Braak and Braak. None of the present cases was associated with progressive supranuclear palsy or with alpha-synuclein pathology. Two bands of phospho-tau of 64 and 68 kDa were observed in Western blots of sarkosyl-insoluble fractions enriched with abnormal filaments in AGD, a pattern that contrasts with the 4-band pattern obtained in AD. No modifications in the expression of non-phosphorylated MEK-1, ERK2 and GSK-3alpha/beta, as revealed by immunohistochemistry, were seen in AGD, but sarkosyl-insoluble fractions were particularly enriched in JNK-1 and alphaCaM kinase II. Increased expression of the phosphorylated (P) forms of MAPK/ERK, SAPK/JNK, p38 and GSK-3beta was found in grains and tau-containing cells in AGD. MAPK/ERK-P immunoreactivity was observed in pre-tangles and, diffusely, in the cytoplasm of ballooned neurons, but not in grains. Strong SAPK/JNK-P and P38-P, and moderate GSK-3b-P immunoreactivities selectively occured in grains, in neurons with pre-tangles and in the peripheral region of the cytoplasm of ballooned neurons. MAPK/ERK-P, SAPK/JNK-P, p38-P and GSK-3beta-P were expressed in tau-containing astrocytes and in oligodendrocytes with coiled bodies. Western blots revealed kinase expression in sarkosyl-insoluble fractions but none of the phospho-kinase antibodies recognized hyper-phosphorylated tau protein. These findings indicate complex, specific profiles of tau phosphorylation and concomitant activation of precise kinases that have the capacity to phosphorylate tau at specific sites in AGD. These kinases co-localize abnormal tau in selected structures and cells, including neurons with pre-tangles, ballooned neurons, astrocytes and oligodendrocytes. Most of these kinases are involved in cell death and cell survival in certain experimental paradigms. However, double-labeling studies with the method of in situ end-labeling of nuclear DNA fragmentation and cleaved (active) caspase-3 immunohistochemistry show no expression of apoptosis and death markers in cells bearing phosphorylated kinases.

Up-regulation of mitogen-activated protein kinases ERK1/2 and MEK1/2 is associated with the progression of neurofibrillary degeneration in Alzheimer's disease

The abnormal hyperphosphorylation of tau in Alzheimer's disease (AD) has been proposed to involve the extracellular-signal-regulated protein kinase (ERK) of the mitogen-activated protein (MAP) kinase family. ERK is phosphorylated and thereby activated by MAP kinase kinase (MEK). In the present study, we determined the intracellular and regional distribution of the active forms of both MEK1/2 and ERK1/2, i.e. p-MEK1/2 and p-ERK1/2 in the entorhinal, hippocampal, and temporal cortices of 49 brains staged for neurofibrillary changes according to Braak and Braak's protocol. We found that p-MEK1/2 and p-ERK1/2 were present in the initial stages of neurofibrillary degeneration in the projecting neurons in the transentorhinal region, and extended into other brain regions co-incident with the progressive sequence of neurofibrillary changes up to and including Braak stage VI. It appeared that the accumulation of p-MEK1/2 and p-ERK1/2 was initiated in the cytoplasm of pretangle neurons in varying size granules, which grew into large aggregates co-existing with the progressive development of neurofibrillary tangles. Accumulation of p-MEK1/2 and p-ERK1/2 was found in cases with stages I-III neurofibrillary degeneration, which were devoid of amyloid deposition. These data provide direct in situ evidence consistent with the possible involvement of MAP kinase pathway in the hyperphosphorylation of tau and the presence of this lesion before deposition of beta-amyloid in AD.

MAP kinase signaling cascade dysfunction specific to Alzheimer's disease in fibroblasts

Mitogen-activated protein kinases (such as Erk1/2) regulate phosphorylation of the microtubule-associated protein tau and processing of the amyloid protein beta, both events critical to the pathophysiology of Alzheimer's disease (AD). Here we report that enhanced and prolonged Erk1/2 phosphorylation in response to bradykinin (BK) was detected in fibroblasts of both familial and sporadic AD, but not age-matched controls (AC). The AD-associated abnormality in Erk1/2 phosphorylation was not seen in fibroblasts from Huntington's disease patients with dementia. The elevation of Erk1/2 phosphorylation occurred immediately after BK stimulation and required an IP3-sensitive Ca(2+) release as well as activation of PKC and c-src as upstream events. Treatment of cells with the PI-3 kinase blocker LY924002 partially inhibited the BK-stimulated Erk1/2 phosphorylation in AC, but had no effect in AD cells, suggesting that the BK-induced Erk1/2 phosphorylation in AD cells is independent of PI-3 kinase. Activation of the cAMP-responsive element binding protein (CREB) monitored as an increase in phosphorylation at Ser-133 was also observed after BK stimulation. Unlike the AD-specific differences for Erk1/2, however, the BK-stimulated CREB phosphorylation was not different between AC and AD cells. Abnormal Erk1/2 activities may alter downstream cellular processes such as gene transcription, amyloid precursor protein processing, and tau protein phosphorylation, which contribute to the pathogenesis of AD. Moreover, detection of AD-specific differences in MAP kinase in peripheral tissues may provide an efficient means for early diagnosis of AD as well as help us to identify therapeutic targets for drug discovery.

Intracellular A-beta amyloid, a sign for worse things to come?

In this review the authors discuss the possible neuropathological role of intracellular amyloid-beta accumulation in Alzheimer's disease (AD) pathology. There is abundant evidence that at early stages of the disease, prior to A-beta amyloid plaque formation, A-beta peptides accumulate intraneuronally in the cerebral cortex and the hippocampus. The experimental evidence would indicate that intracellular amyloid-beta could originate both by intracellular biosynthesis and also from the uptake of amyloidogenic peptides from the extracellular milieu. Herein the aspects of the possible impact of intracellular amyloid-beta in human AD pathology are discussed, as well as recent observations from a rat transgenic model with a phenotype of intracellular accumulation of A-beta fragments in neurons of the hippocampus and cortex, without plaque formation. In this model, the intracellular amyloid-beta phenotype is accompanied by increased MAPK/ERK activity and tau hyperphosphorylation. Finally, the authors discuss the hypothesis that, prior to plaque formation, intracellular A-beta accumulation induces biochemical and pathological changes in the brain at the cellular level priming neurons to further cytotoxic attack of extracellular amyloidogenic peptides.

Direct visualization of the gamma secretase-generated carboxyl-terminal domain of the amyloid precursor protein: association with Fe65 and translocation to the nucleus

Amyloid-beta, the peptide that deposits as senile plaques in Alzheimer's disease, is derived from the amyloid precursor protein (APP) by a gamma secretase-mediated intramembranous cleavage. In addition to amyloid-beta, this cleavage produces a carboxyl-terminal intracellular fragment which has an unknown function. The carboxyl-terminal domain of APP interacts in the cytoplasm with an adapter protein, Fe65. We demonstrate by laser scanning confocal microscopy that a gamma secretase generated APP carboxyl-terminal domain, tagged with green fluorescent protein (GFP), translocates to the nucleus in a manner dependent upon stabilization by the adapter protein Fe65; APP which has been mutated to block interactions with Fe65 cannot be detected in the nucleus. The APP-CT domain continues to interact with Fe65 in the nucleus, as determined by both colocalization and fluorescence resonance energy transfer (FRET). Visualization of the APP-CT-Fe65 complex in the nucleus may serve as a readout for processes that modify gamma secretase release of APP-CT.

Colocalization and fluorescence resonance energy transfer between cdk5 and AT8 suggests a close association in pre-neurofibrillary tangles and neurofibrillary tangles

Cyclin-dependent kinase 5 (cdk5) is a serine/threonine kinase that, when activated, induces neurite outgrowth. Recent in vitro studies have shown that cdk5 phosphorylates tau at serine 199, serine 202, and threonine 205 and that p25, an activator of cdk5, is increased in Alzheimer disease (AD). Since tau is hyperphosphorylated at these sites in neurofibrillary tangles, we examined brain tissue from patients with AD and normal elderly control cases to determine whether cdk5 and these phosphoepitopes colocalize in neurofibrillary tangles. Adjacent temporal lobe sections were double immunostained with a polyclonal anti-cdk5 and monoclonal AT8 (which recognizes phosphorylated serine 199, serine 202, and threonine 205 in tau) antibodies. A subset of AT8 phosphotau-positive neurons was immunoreactive for cdk5 in entorhinal (area 28) and perirhinal (area 35) cortices and CA1 of the hippocampus. We assessed the ratio of cdk5-positive cells to AT8-positive cells and found that there is a higher degree of colocalization in pre-neurofibrillary tangles as opposed to intraneuronal and extraneuronal neurofibrillary tangles. We further examined colocalization using fluorescence resonance energy transfer. This suggests a close, stable intermolecular association between cdk5 and phosphorylated tau, consistent with phosphorylation of tau by cdk5 in AD brain.

Disordered proteins in dementia

Aggregates of dysfunctional proteins and peptides in or between brain neurons are key neuropathological features of dementia and are believed to directly cause or substantially contribute to the development of these diseases. Fundamental parts of the mechanisms underlying the dysregulation of proteins in Alzheimer's disease, frontotemporal dementia, prion diseases and other dementing disorders are now well characterized, mainly due to the discovery of genes causing dominantly inherited disease forms (Table 1). As of today, no efficient pharmacotherapies are available, but new insights into the underlying molecular mechanisms are providing strategies to prevent or even cure these devastating disorders.

Demonstration by fluorescence resonance energy transfer of two sites of interaction between the low-density lipoprotein receptor-related protein and the amyloid precursor protein: role of the intracellular adapter protein Fe65

Amyloid-beta, the major constituent of senile plaques in Alzheimer's disease, is derived from the amyloid precursor protein (APP) by proteolysis. Kunitz protease inhibitor (KPI) containing forms of APP (APP751/770) interact with a multifunctional endocytic receptor, the low-density lipoprotein receptor-related protein (LRP), which modulates its proteolytic processing affecting production of amyloid-beta. We used fluorescence resonance energy transfer (FRET) using labeled LRP and APP in H4 cell line to examine the subcellular localization and the molecular domains involved in the APP-LRP interaction. KPI-containing forms of APP (APP770) demonstrated FRET with LRP that was sensitive to the LRP inhibitor receptor-associated protein (RAP), suggesting an interaction between the extracellular domains of APP770 and LRP. APP695 also interacts with LRP to lesser degree (as measured by extracellular domain probes), and this ectodomain interaction is not altered by RAP. By using C-terminally tagged LRP and APP, we demonstrate a second site of interaction between the C termini of both APP695 and APP770 and the C terminus of LRP, and that the interactions at these regions are not sensitive to RAP. We next examined the possibility that the C-termini APP-LRP interaction was mediated by Fe65, an adaptor protein that interacts with the cytoplasmic tails of LRP and APP. FRET studies confirmed a close proximity between the amino Fe65 phosphotyrosine binding (PTB) domain and LRP cytoplasmic domain and between the carboxyl Fe65 PTB domain and the APP cytoplasmic domain. These findings demonstrate that LRP interaction with APP occurs via both extracellular and intracellular protein interaction domains.

A close association of torsinA and alpha-synuclein in Lewy bodies: a fluorescence resonance energy transfer study

TorsinA, a novel protein in which a mutation causes dominant, early onset torsion dystonia, may serve as a chaperone for misfolded proteins that require refolding or degradation. It has been hypothesized that misfolded alpha-synuclein, a protein in which two mutations cause autosomal dominantly inherited Parkinson's disease, serves as a nidus for the development of a Lewy body. We hypothesized that torsinA plays a role in the cellular processing of alpha-synuclein. We demonstrate that anti-torsin antibodies stain Lewy bodies and Lewy neurites in the substantia nigra and cortex. Using sensitive fluorescent resonance energy transfer (FRET) techniques, we find evidence of a close association between torsinA and alpha-synuclein in Lewy bodies.

Interaction of alpha-synuclein and synphilin-1: effect of Parkinson's disease-associated mutations

alpha-Synuclein is a major component of Lewy bodies, a neuropathological feature of Parkinson's disease. Two alpha-synuclein mutations, Ala53Thr and Ala30Pro, are associated with early onset, familial forms of the disease. Recently, synphilin-1, a protein found to interact with alpha-synuclein by yeast two hybrid techniques, was detected in Lewy bodies. In this study we report the interaction of alpha-synuclein and synphilin-1 in human neuroglioma cells using a sensitive fluorescence resonance energy transfer technique. We demonstrate that the C-terminus of alpha-synuclein is closely associated with the C-terminus of synphilin-1. A weak interaction occurs between the N-terminus of alpha-synuclein and synphilin-1. The familial Parkinson's disease associated mutations of alpha-synuclein (Ala53Thr and Ala30Pro) also demonstrate a strong interaction between their C-terminal regions and synphilin-1. However, compared with wild-type alpha-synuclein, significantly less energy transfer occurs between the C-terminus of Ala53Thr alpha-synuclein and synphilin-1, suggesting that the Ala53Thr mutation alters the conformation of alpha-synuclein in relation to synphilin-1.

Hyperphosphorylation of tau is mediated by ERK activation during anticancer drug-induced apoptosis in neuroblastoma cells

Phosphorylated tau protein is the major component of paired helical filaments in Alzheimer disease (AD). We have previously shown that abnormal tau phosphorylation was induced in neuroblastoma SK-N-SH cells by the anticancer drug, paclitaxel, during apoptosis [Guise et al., 1999: Apoptosis 4:47-58]. In the present study, we first demonstrated a shift from fetal tau to hyperphosphorylated tau after incubation with paclitaxel, that showed some similarities with the hyperphosphorylated tau in AD, by using several tau antibodies, N-Term, Tau-1 and AT-8. Tau phosphorylation occurred independently of caspase-3 activation. We next showed that a sustained activation of ERK (extracellular signal-regulated kinase) induced both tau phosphorylation and apoptosis during paclitaxel treatment (1 microM). The inhibition of ERK activation by using the pharmacological MEK1/2 inhibitor, PD98059 (50 microM), or an antisense strategy, reduced tau phosphorylation and neuronal apoptosis (P < 0.001), indicating a link between ERK activation, tau phosphorylation and apoptosis. Doxorubicin (0.2 microM), an anticancer drug whose mechanism of action is independent of microtubules, also induced ERK activation, tau phosphorylation and apoptosis. Moreover, doxorubicin induced some morphological features of neurodegeneration such as loss of neurites and disorganization of the cytoskeleton in apoptotic neuroblastoma cells. Altogether, our results suggest that tau phosphorylation plays a significant role in apoptosis enhancing disruption of microtubules that in turn leads to formation of apoptotic bodies, suggesting that neurodegeneration and apoptosis are related.

Interleukin-1 promotion of MAPK-p38 overexpression in experimental animals and in Alzheimer's disease: potential significance for tau protein phosphorylation

Activated (phosphorylated) mitogen-activated protein kinase p38 (MAPK-p38) and interleukin-1 (IL-1) have both been implicated in the hyperphosphorylation of tau, a major component of the neurofibrillary tangles in Alzheimer's disease. This, together with findings showing that IL-1 activates MAPK-p38 in vitro and is markedly overexpressed in Alzheimer brain, suggest a role for IL-1-induced MAPK-p38 activation in the genesis of neurofibrillary pathology in Alzheimer's disease. We found frequent colocalization of hyperphosphorylated tau protein (AT8 antibody) and activated MAPK-p38 in neurons and in dystrophic neurites in Alzheimer brain, and frequent association of these structures with activated microglia overexpressing IL-1. Tissue levels of IL-1 mRNA as well as of both phosphorylated and non-phosphorylated isoforms of tau were elevated in these brains. Significant correlations were found between the numbers of AT8- and MAPK-p38-immunoreactive neurons, and between the numbers of activated microglia overexpressing IL-1 and the numbers of both AT8- and MAPK-p38-immunoreactive neurons. Furthermore, rats bearing IL-1-impregnated pellets showed a six- to seven-fold increase in the levels of MAPK-p38 mRNA, compared with rats with vehicle-only pellets (P<0.0001). These results suggest that microglial activation and IL-1 overexpression are part of a feedback cascade in which MAPK-p38 overexpression and activation leads to tau hyperphosphorylation and neurofibrillary pathology in Alzheimer's disease.

Phosphorylation of human tau protein by microtubule-associated kinases: GSK3beta and cdk5 are key participants

Microtubules (MTs), primarily composed of alpha and beta tubulin polymers, must often work in concert with microtubule-associated proteins (MAPs) in order to modulate their functional demands. In a mature brain neuron, one of the key MAPs that resides primarily in the axonal compartment is the tau protein. Tau, in the adult human brain, is a set of six protein isoforms, whose binding affinity to MTs can be modulated by phosphorylation. In addition to the role that phosphorylation of tau plays in the "normal" physiology of neurons, hyperphosphorylated tau is the primary component of the fibrillary pathology in Alzheimer's disease (AD). Although many protein kinases are known to phosphorylate tau in vitro, the in vivo players contributing to the hyperphosphorylation of tau remain elusive. The experiments in this study attempt to define which protein kinases and protein phosphatases reside in the associated network of microtubules, thereby being strategically positioned to influence the phosphorylation of tau. Microtubule fractions are utilized to determine which of the microtubule-associated kinases most readily impacts the phosphorylation of tau at "AD-like" sites. Results from this study indicate that PKA, CK1, GSK3beta, and cdk5 associate with microtubules. Among the MT-associated kinases, GSK3beta and cdk5 most readily contribute to the ATP-induced "AD-like" phosphorylation of tau.

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.

Expression of the chemokine receptor CXCR3 on neurons and the elevated expression of its ligand IP-10 in reactive astrocytes: in vitro ERK1/2 activation and role in Alzheimer's disease

Inflammatory mediators have been implicated in the pathophysiology of neurodegenerative diseases. Here we report the presence of the chemokine receptor CXCR3 and its ligand, IP-10, in normal and Alzheimer's disease (AD) brains. CXCR3 was detected constitutively on neurons and neuronal processes in various cortical and subcortical regions; IP-10 was observed in a subpopulation of astrocytes in normal brain, and was markedly elevated in astrocytes in AD brains. Many IP-10(+) astrocytes were associated with senile plaques and had an apparently coordinated upregulation of MIP-1beta. Moreover, we showed that CXCR3 ligands, IP-10 and Mig, were able to activate ERK1/2 pathway in mouse cortical neurons, suggesting a novel mechanism of neuronal-glial interaction.

Association of active extracellular signal-regulated protein kinase with paired helical filaments of inclusion-body myositis muscle suggests its role in inclusion-body myositis tau phosphorylation

The possible role of extracellular signal-regulated kinase (ERK) in the pathogenesis of inclusion-body myositis (IBM) was investigated by immunostaining the active phosphorylated form of ERK in muscle biopsies of six IBM and 14 control patients. Between 80% and 90% of IBM vacuolated muscle fibers contained well-defined ERK-immunoreactive inclusions, which were co-localized by light microscopy, with phosphorylated tau in 70 to 80% of those fibers. Immunoelectronmicroscopy colocalized ERK to small amorphous tufts adjacent to the muscle fiber paired-helical filaments. Strong ERK immunoreactivity was also present at the postsynaptic domain of all human neuromuscular junctions. Our study suggests 1) that ERK, a signal transducer, might play a role in IBM pathogenesis, including participation in the pathological phosphorylation of IBM tau; and 2) that signal transduction abnormalities may be a component of the IBM pathogenic cascade. Our novel immunolocalization of ERK at the postsynaptic domain of human neuromuscular junctions supports a role in transcription of junctional-protein genes. The ERK localized in nonjunctional regions of IBM fibers may underlie the known pathological up-regulation of junctional proteins there.

Membrane association and protein conformation of alpha-synuclein in intact neurons. Effect of Parkinson's disease-linked mutations

Two missense mutations (Ala-30 --> Pro and Ala-53 --> Thr) in the gene encoding alpha-synuclein are associated with rare autosomal dominant forms of familial Parkinson's disease. In addition, alpha-synuclein is an abundant component of Lewy bodies in sporadic Parkinson's disease and diffuse Lewy body disease. However, the normal conformation of alpha-synuclein, its cellular localization in neurons, and the effects of the mutations remain to be determined. In the present study, we examine these questions using sensitive fluorescence resonance energy transfer techniques. Transient transfection of alpha-synuclein expression constructs into primary cortical neurons and counterstaining with the lipophilic fluorescent marker, DiI, demonstrates a close association between alpha-synuclein and cellular membranes. Both the N- and C-terminal regions of alpha-synuclein are tightly associated with membranes. A weak interaction also occurs between the N and C termini themselves. The Parkinson's disease-associated mutations have no effect on membrane interaction; however, the Ala-30 --> Pro mutation alters the three-dimensional conformation of alpha-synuclein, as measured by significantly increased fluorescence resonance energy transfer between the N and C termini.