Glycogen synthase kinase 3 alteration in Alzheimer disease is related to neurofibrillary tangle formation

Traditional Chinese Medicine studies for Alzheimer's disease via network pharmacology based on entropy and random walk

Alzheimer's disease (AD) is a common neurodegenerative disease having complex pathogenesis, approved drugs can only alleviate symptoms of AD for a period of time. Traditional Chinese medicine (TCM) contains multiple active ingredients that can act on multiple targets simultaneously. In this paper, a novel algorithm based on entropy and random walk with the restart of heterogeneous network (RWRHE) is proposed for predicting active ingredients for AD and screening out the effective TCMs for AD. First, Six TCM compounds containing 20 herbs from the AD drug reviews in the CNKI (China National Knowledge Internet) are collected, their active ingredients and targets are retrieved from different databases. Then, comprehensive similarity networks of active ingredients and targets are constructed based on different aspects and entropy weight, respectively. A comprehensive heterogeneous network is constructed by integrating the known active ingredient-target association information and two comprehensive similarity networks. Subsequently, bi-random walks are applied on the heterogeneous network to predict active ingredient-target associations. AD related targets are selected as the seed nodes, a random walk is carried out on the target similarity network to predict the AD-target associations, and the associations of AD-active ingredients are inferred and scored. The effective herbs and compounds for AD are screened out based on their active ingredients' scores. The results measured by machine learning and bioinformatics show that the RWRHE algorithm achieves better prediction accuracy, the top 15 active ingredients may act as multi-target agents in the prevention and treatment of AD, Danshen, Gouteng and Chaihu are recommended as effective TCMs for AD, Yiqitongyutang is recommended as effective compound for AD.

Molecular insights into the pathogenic impact of vitamin D deficiency in neurological disorders

Neurological disorders are the major cause of disability, leading to a decrease in quality of life by impairing cognitive, sensorimotor, and motor functioning. Several factors have been proposed in the pathogenesis of neurobehavioral changes, including nutritional, environmental, and genetic predisposition. Vitamin D (VD) is an environmental and nutritional factor that is widely distributed in the central nervous system's subcortical grey matter, neurons of the substantia nigra, hippocampus, thalamus, and hypothalamus. It is implicated in the regulation of several brain functions by preserving neuronal structures. It is a hormone rather than a nutritional vitamin that exerts a regulatory role in the pathophysiology of several neurological disorders, including Alzheimer's disease, Parkinson's disease, epilepsy, and multiple sclerosis. A growing body of epidemiological evidence suggests that VD is critical in neuronal development and shows neuroprotective effects by influencing the production and release of neurotrophins, antioxidants, immunomodulatory, regulation of intracellular calcium balance, and direct effect on the growth and differentiation of nerve cells. This review provides up-to-date and comprehensive information on vitamin D deficiency, risk factors, and clinical and preclinical evidence on its relationship with neurological disorders. Furthermore, this review provides mechanistic insight into the implications of vitamin D and its deficiency on the pathogenesis of neurological disorders. Thus, an understanding of the crucial role of vitamin D in the neurobiology of neurodegenerative disorders can assist in the better management of vitamin D-deficient individuals.

In Vitro and In Vivo Evaluation of GSK-3 Radioligands in Alzheimer's Disease: Preliminary Evidence of Sex Differences

Glycogen synthase kinase-3 (GSK-3) is a positron emission tomography (PET) imaging target with implications in the pathogenesis of Alzheimer's disease (AD). This preliminary study evaluates human AD and transgenic P301L mouse brain tissues using the GSK-3-targeting radiotracers [³H]PF-367 and [³H]OCM-44 in radioligand binding assays. A saturation analysis showed decreased GSK-3 density in female human AD compared to a normal healthy brain. Equivalence in density (B _max), affinity (K _d), and apparent affinity (K _i) of both radiotracers was demonstrated to enable their interchangeability for in vitro evaluations of GSK-3 expression. An evaluation of P301L mouse brain by [³H]/[¹¹C]OCM-44 delineated differences in the B _max of GSK-3 between the control and transgenic mice within male subjects. PET imaging showed similar trends to those observed in vitro. Sex differences are revealed as a potential parameter to consider in the development of GSK-3-targeted diagnostics and therapeutics and could guide recruitment for clinical studies.

Sphingolipids and Inositol Phosphates Regulate the Tau Protein Phosphorylation Status in Humanized Yeast

Hyperphosphorylation of protein tau is a hallmark of Alzheimer's disease (AD). Changes in energy and lipid metabolism have been correlated with the late onset of this neurological disorder. However, it is uncertain if metabolic dysregulation is a consequence of AD or one of the initiating factors of AD pathophysiology. Also, it is unclear whether variations in lipid metabolism regulate the phosphorylation state of tau. Here, we show that in humanized yeast, tau hyperphosphorylation is stimulated by glucose starvation in coincidence with the downregulation of Pho85, the yeast ortholog of CDK5. Changes in inositol phosphate (IP) signaling, which has a central role in energy metabolism, altered tau phosphorylation. Lack of inositol hexakisphosphate kinases Kcs1 and Vip1 (IP6 and IP7 kinases in mammals) increased tau hyperphosphorylation. Similar effects were found by mutation of IPK2 (inositol polyphosphate multikinase), or PLC1, the yeast phospholipase C gene. These effects may be explained by IP-mediated regulation of Pho85. Indeed, this appeared to be the case for plc1, ipk2, and kcs1. However, the effects of Vip1 on tau phosphorylation were independent of the presence of Pho85, suggesting additional mechanisms. Interestingly, kcs1 and vip1 strains, like pho85, displayed dysregulated sphingolipid (SL) metabolism. Moreover, genetic and pharmacological inhibition of SL biosynthesis stimulated the appearance of hyperphosphorylated forms of tau, while increased flux through the pathway reduced its abundance. Finally, we demonstrated that Sit4, the yeast ortholog of human PP2A protein phosphatase, is a downstream effector of SL signaling in mediating the tau phosphorylation state. Altogether, our results add new knowledge on the molecular effectors involved in tauopathies and identify new targets for pharmacological intervention.

Cellular Signaling and Anti-Apoptotic Effects of Prolactin-Releasing Peptide and Its Analog on SH-SY5Y Cells

Prolactin-releasing peptide (PrRP), a natural ligand for the GPR10 receptor, is a neuropeptide with anorexigenic and antidiabetic properties. Due to its role in the regulation of food intake, PrRP is a potential drug for obesity treatment and associated type 2 diabetes mellitus (T2DM). Recently, the neuroprotective effects of lipidized PrRP analogs have been proven. In this study, we focused on the molecular mechanisms of action of natural PrRP31 and its lipidized analog palm¹¹-PrRP31 in the human neuroblastoma cell line SH-SY5Y to describe their cellular signaling and possible anti-apoptotic properties. PrRP31 significantly upregulated the phosphoinositide-3 kinase-protein kinase B/Akt (PI3K-PKB/Akt) and extracellular signal-regulated kinase/cAMP response element-binding protein (ERK-CREB) signaling pathways that promote metabolic cell survival and growth. In addition, we proved via protein kinase inhibitors that activation of signaling pathways is mediated specifically by PrRP31 and its palmitoylated analog. Furthermore, the potential neuroprotective properties were studied through activation of anti-apoptotic pathways of PrRP31 and palm¹¹-PrRP31 using the SH-SY5Y cell line and rat primary neuronal culture stressed with toxic methylglyoxal (MG). The results indicate increased viability of the cells treated with PrRP and palm¹¹-PrRP31 and a reduced degree of apoptosis induced by MG, suggesting their potential use in the treatment of neurological disorders.

Loss of biliverdin reductase-A favors Tau hyper-phosphorylation in Alzheimer's disease

Hyper-active GSK-3β favors Tau phosphorylation during the progression of Alzheimer's disease (AD). Akt is one of the main kinases inhibiting GSK-3β and its activation occurs in response to neurotoxic stimuli including, i.e., oxidative stress. Biliverdin reductase-A (BVR-A) is a scaffold protein favoring the Akt-mediated inhibition of GSK-3β. Reduced BVR-A levels along with increased oxidative stress were observed early in the hippocampus of 3xTg-AD mice (at 6 months), thus suggesting that loss of BVR-A could be a limiting factor in the oxidative stress-induced Akt-mediated inhibition of GSK-3β in AD. We evaluated changes of BVR-A, Akt, GSK-3β, oxidative stress and Tau phosphorylation levels: (a) in brain from young (6-months) and old (12-months) 3xTg-AD mice; and (b) in post-mortem inferior parietal lobule (IPL) samples from amnestic mild cognitive impairment (MCI), from AD and from age-matched controls. Furthermore, similar analyses were performed in vitro in cells lacking BVR-A and treated with H₂O₂. Reduced BVR-A levels along with: (a) increased oxidative stress; (b) reduced GSK-3β inhibition; and (c) increased Tau Ser404 phosphorylation (target of GSK-3β activity) without changes of Akt activation in young mice, were observed. Similar findings were obtained in MCI, consistent with the notion that this is a molecular mechanism disrupted in humans. Interestingly, cells lacking BVR-A and treated with H₂O₂ showed reduced GSK-3β inhibition and increased Tau Ser404 phosphorylation, which resulted from a defect of Akt and GSK-3β physical interaction. Reduced levels of Akt/GSK-3β complex were confirmed in both young 3xTg-AD and MCI brain. We demonstrated that loss of BVR-A impairs the neuroprotective Akt-mediated inhibition of GSK-3β in response to oxidative stress, thus contributing to Tau hyper-phosphorylation in early stage AD. Such changes potential provide promising therapeutic targets for this devastating disorder.

Molecular Insights Into Memory-Enhancing Metabolites of Nicotine in Brain: A Systematic Review

Background: The alleged procognitive effects of nicotine and its metabolites in brain are controversial. Objective: Here, we review the pharmacologically active metabolites of nicotine in brain and their effects on neuronal mechanisms involving two main cognitive domains, i.e., learning and memory. Methods: We searched Embase, Medline via PubMed, Scopus, and Web of Science databases for entries no later than May 2018, and restricted the search to articles about nicotine metabolites and cognitive behavior or cognitive mechanisms. Results: The initial search yielded 425 articles, of which 17 were eligible for inclusion after application of exclusion criteria. Of these, 13 were experimental, two were clinical, and two were conference papers. Conclusions: The results revealed three pharmacologically active biotransformations of nicotine in the brain, including cotinine, norcotinine, and nornicotine, among which cotinine and nornicotine both had a procognitive impact without adverse effects. The observed effect was significant only for cotinine.

Molecular differences in Alzheimer's disease between male and female patients determined by integrative network analysis

Alzheimer's disease (AD) is a complex neurodegenerative disease and the most common cause of dementia among the elderly. There has been increasing recognition of sex differences in AD prevalence, clinical manifestation, disease course and prognosis. However, there have been few studies on the molecular mechanism underlying these differences. To address this issue, we carried out global gene expression and integrative network analyses based on expression profiles (GSE84422) across 17 cortical regions of 125 individuals with AD. There were few genes that were differentially expressed across the 17 regions between the two sexes, with only four (encoding glutamate metabotropic receptor 2, oestrogen‐related receptor beta, kinesin family member 26B, and aspartoacylase) that were differentially expressed in three regions. A pan‐cortical brain region co‐expression network analysis identified pathways and genes (eg, glycogen synthase kinase 3β) that were significantly associated with clinical characteristics of AD (such as neurofibrillary score) in males only. Similarity analyses between region‐specific networks indicated that male patients exhibited greater variability, especially in the superior parietal lobule, dorsolateral prefrontal cortex and occipital visual cortex. A network module analysis revealed an association between clinical traits and crosstalk of sex‐specific modules. An examination of temporal and spatial patterns of sex differences in AD showed that molecular networks were more conserved in females than in males in different cortical regions and at different AD stages. These findings provide insight into critical molecular pathways governing sex differences in AD pathology.

Amyloid-Beta and Phosphorylated Tau Accumulations Cause Abnormalities at Synapses of Alzheimer's disease Neurons

Amyloid-beta (Aβ) and hyperphosphorylated tau are hallmark lesions of Alzheimer's disease (AD). However, the loss of synapses and dysfunctions of neurotransmission are more directly tied to disease severity. The role of these lesions in the pathoetiological progression of the disease remains contested. Biochemical, cellular, molecular, and pathological studies provided several lines of evidence and improved our understanding of how Aβ and hyperphosphorylated tau accumulation may directly harm synapses and alter neurotransmission. In vitro evidence suggests that Aβ and hyperphosphorylated tau have both direct and indirect cytotoxic effects that affect neurotransmission, axonal transport, signaling cascades, organelle function, and immune response in ways that lead to synaptic loss and dysfunctions in neurotransmitter release. Observations in preclinical models and autopsy studies support these findings, suggesting that while the pathoetiology of positive lesions remains elusive, their removal may reduce disease severity and progression. The purpose of this article is to highlight the need for further investigation of the role of tau in disease progression and its interactions with Aβ and neurotransmitters alike.

An 18-mer Peptide Derived from Prosaposin Ameliorates the Effects of Aβ1-42 Neurotoxicity on Hippocampal Neurogenesis and Memory Deficit in Mice

The pathological hallmarks of Alzheimer's disease (AD) include amyloid-β (Aβ) accumulation, neurofibrillary tangle formation, synaptic dysfunction, and neuronal loss. The present study was performed to investigate the protective effects and mechanism of action of a prosaposin-derived 18-mer peptide (PS18: LSELIINNATEELLIKGL) on mice hippocampal progenitor cell proliferation, neurogenesis, and memory tasks after intracerebroventricular injection of Aβ1-42 peptide. Seven days after Aβ1-42 injection, significant proliferation of hippocampal progenitor cells and memory impairment were evident. Two weeks after Aβ1-42 peptide injection, elevated numbers of surviving 5-bromo-2-deoxyuridine cells and newly formed neurons were detected. Treatment with PS18 attenuated these effects evoked by Aβ1-42. Our data indicate that treatment with PS18 partially attenuated the increase in hippocampal neurogenesis caused by Aβ1-42-induced neuroinflammation and prevented memory deficits associated with increased numbers of activated glial cells. We observed an increase in ADAM10 and decreases in BACE1, PS1/2, and AβPP protein levels, suggesting that PS18 enhances the nonamyloidogenic AβPP cleavage pathway. Importantly, our results further showed that PS18 activated the PI3K/Akt pathway, phosphorylated GSK-3α/β, and, as a consequence, exerted a neuroprotective effect. In addition, PS18 showed a protective effect against Aβ1-42-induced neurotoxicity via suppression of the caspase pathway; upregulation of Bcl-2; downregulation of BAX, attenuating mitochondrial damage; and inhibition of caspase-3. These findings suggest that PS18 may provide a valuable therapeutic strategy for the treatment of progressive neurodegenerative diseases, such as AD.

Tibolone modulates neuronal plasticity through regulating Tau, GSK3β/Akt/PI3K pathway and CDK5 p35/p25 complexes in the hippocampus of aged male mice

Aging is a key risk factor for cognitive decline and age-related neurodegenerative disorders. Also, an age-related decrease in sex steroid hormones may have a negative impact on the formation of neurofibrillary tangles (NFTs); these hormones can regulate Tau phosphorylation and the principal kinase GSK3β involved in this process. Hormone replacement therapy decreases NFTs, but it increases the risk of some types of cancer. However, other synthetic hormones such as tibolone (TIB) have been used for hormone replacement therapy. The aim of this work was to evaluate the long-term effects of TIB (0.01 mg/kg and 1 mg/kg, intragastrically for 12 weeks) on the content of total and hyperphosphorylated Tau (PHF-1) proteins and the regulation of GSK3β/Akt/PI3K pathway and CDK5/p35/p25 complexes in the hippocampus of aged male mice. We observed that the content of PHF-1 decreased with TIB administration. In contrast, no changes were observed in the active form of GSK3β or PI3K. TIB decreased the expression of the total and phosphorylated form of Akt while increased that of p110 and p85. The content of CDK5 was differentially modified with TIB: it was increased at low doses and decreased at high doses. When we analyzed the content of CDK5 activators, an increase was found on p35; however, the content of p25 decreased with administration of low dose of TIB. Our results suggest a possible mechanism of action of TIB in the hippocampus of aged male mice. Through the regulation of Tau and GSK3β/Akt/PI3K pathway, and CDK5/p35/p25 complexes, TIB may modulate neuronal plasticity and regulate learning and memory processes.

Increased phosphorylation of collapsin response mediator protein-2 at Thr514 correlates with β-amyloid burden and synaptic deficits in Lewy body dementias

Collapsin response mediator protein-2 (CRMP2) regulates axonal growth cone extension, and increased CRMP2 phosphorylation may lead to axonal degeneration. Axonal and synaptic pathology is an important feature of Lewy body dementias (LBD), but the state of CRMP2 phosphorylation (pCRMP2) as well as its correlations with markers of neurodegeneration have not been studied in these dementias. Hence, we measured CRMP2 phosphorylation at Thr509, Thr514 and Ser522, as well as markers of β-amyloid (Aβ), tau-phosphorylation, α-synuclein and synaptic function in the postmortem neocortex of a longitudinally assessed cohort of LBD patients characterized by low (Parkinson’s disease dementia, PDD) and high (dementia with Lewy bodies, DLB) burden of Alzheimer type pathology. We found specific increases of pCRMP2 at Thr514 in DLB, but not PDD. The increased CRMP2 phosphorylation correlated with fibrillogenic Aβ as well as with losses of markers for axon regeneration (β-III-tubulin) and synaptic integrity (synaptophysin) in LBD. In contrast, pCRMP2 alterations did not correlate with tau-phosphorylation or α-synuclein, and also appear unrelated to immunoreactivities of putative upstream kinases glycogen synthase kinase 3β and cyclin-dependent kinase 5, as well as to protein phosphatase 2A. In conclusion, increased pCRMP2 may underlie the axonal pathology of DLB, and may be a novel therapeutic target. However, antecedent signaling events as well as the nature of pCRMP2 association with Aβ and other neuropathologic markers require further study.

Multiplexed Fluorescent Immunodetection Using Low Autofluorescence Immobilon®-FL Membrane

By enabling greater signal linearity and multiplexed detection, fluorescent western immunodetection overcomes many of the inherent technical limitations associated with the traditional chemiluminescent detection method. However, the sensitivity of fluorescence detection can be severely compromised by high background autofluorescence of various blotting membranes. Here, we describe a low autofluorescence PVDF membrane (Immobilon(®)-FL membrane) optimized for fluorescent immunodetection, and we report its use in the quantitative fluorescent western immunodetection of biomarkers associated with Alzheimer's disease (AD). First, membrane autofluorescence of four different commercially available blotting membranes was compared. Immobilon(®)-FL membrane exhibited the lowest autofluorescence with substantially increased detection sensitivity. We also show that the fluorescent immunodetection exhibited greatly increased linear dynamic range (two orders of magnitude, log scale) compared to the traditional chemiluminescent methods (less than one order of magnitude). Immobilon(®)-FL membrane was then used to quantify the expression levels of previously reported biomarkers associated with AD (synaptophysin, GSK3β, and GAP43). Total protein extracts from age-matched brain samples of three AD patients and three normal controls were used. Biomarker expression levels were normalized to that of a housekeeping protein (GAPDH) using multiplexed detection, conserving difficult-to-obtain biological tissue samples and minimizing experimental variation. We found that the expression of GSK3ß and GAP43 biomarkers were significantly reduced in AD brain samples compared to age-matched normal samples. In summary, combining fluorescent immunodetection with a low autofluorescent blotting membrane yields accurate and reliable multiplexed quantitation of AD biomarkers. While this report focuses on the quantitation of AD biomarkers, the described technique is applicable to comparing protein expression in other biological contexts as well.

CDK5 activator protein p25 preferentially binds and activates GSK3β

Glycogen synthase kinase 3β (GSK3β) and cyclin-dependent kinase 5 (CDK5) are tau kinases and have been proposed to contribute to the pathogenesis of Alzheimer's disease. The 3D structures of these kinases are remarkably similar, which led us to hypothesize that both might be capable of binding cyclin proteins--the activating cofactors of all CDKs. CDK5 is normally activated by the cyclin-like proteins p35 and p39. By contrast, we show that GSK3β does not bind to p35 but unexpectedly binds to p25, the calpain cleavage product of p35. Indeed, overexpressed GSK3β outcompetes CDK5 for p25, whereas CDK5 is the preferred p35 partner. FRET analysis reveals nanometer apposition of GSK3β:p25 in cell soma as well as in synaptic regions. Interaction with p25 also alters GSK3β substrate specificity. The GSK3β:p25 interaction leads to enhanced phosphorylation of tau, but decreased phosphorylation of β-catenin. A partial explanation for this situation comes from in silico modeling, which predicts that the docking site for p25 on GSK3β is the AXIN-binding domain; because of this, p25 inhibits the formation of the GSK3β/AXIN/APC destruction complex, thus preventing GSK3β from binding to and phosphorylating β-catenin. Coexpression of GSK3β and p25 in cultured neurons results in a neurodegeneration phenotype that exceeds that observed with CDK5 and p25. When p25 is transfected alone, the resulting neuronal damage is blocked more effectively with a specific siRNA against Gsk3β than with one against Cdk5. We propose that the effects of p25, although normally attributed to activate CDK5, may be mediated in part by elevated GSK3β activity.

Mesenchymal Stem Cells Increase Hippocampal Neurogenesis and Neuronal Differentiation by Enhancing the Wnt Signaling Pathway in an Alzheimer's Disease Model

Neurogenesis in the subgranular zone of the hippocampal dentate gyrus may act as an endogenous repair mechanism in Alzheimer's disease (AD), and the Wnt signaling pathway has been suggested to closely modulate neurogenesis in amyloid-β (Aβ)-related AD models. The present study investigated whether mesenchymal stem cells (MSCs) would modulate hippocampal neurogenesis via modulation of the Wnt signaling pathway in a model of AD. In Aβ-treated neuronal progenitor cells (NPCs), the coculture with MSCs increased significantly the expression of Ki-67, GFAP, SOX2, nestin, and HuD compared to Aβ treatment alone. In addition, MSC treatment in Aβ-treated NPCs enhanced the expression of β-catenin and Ngn1 compared to Aβ treatment alone. MSC treatment in Aβ-treated animals significantly increased the number of BrdU-ir cells in the hippocampus at 2 and 4 weeks compared to Aβ treatment alone. In addition, quantitative analysis showed that the number of BrdU and HuD double-positive cells in the dentate gyrus was significantly higher in the MSC-treated group than in controls or after Aβ treatment alone. These results demonstrate that MSC administration significantly augments hippocampal neurogenesis and enhances the differentiation of NPCs into mature neurons in AD models by augmenting the Wnt signaling pathway. The use of MSCs to modulate endogenous adult neurogenesis may have a significant impact on future strategies for AD treatment.

Hypoxia-triggered m-calpain activation evokes endoplasmic reticulum stress and neuropathogenesis in a transgenic mouse model of Alzheimer's disease

BACKGROUND

Previous studies have demonstrated that endoplasmic reticulum (ER) stress is activated in Alzheimer's disease (AD) brains. ER stress-triggered unfolded protein response (UPR) leads to tau phosphorylation and neuronal death.

AIMS

In this study, we tested the hypothesis that hypoxia-induced m-calpain activation is involved in ER stress-mediated AD pathogenesis.

METHOD

We employed a hypoxic exposure in APP/PS1 transgenic mice and SH-SY5Y cells overexpressing human Swedish mutation APP (APPswe).

RESULTS

We observed that hypoxia impaired spatial learning and memory in the APP/PS1 mouse. In the transgenic mouse brain, hypoxia increased the UPR, upregulated apoptotic signaling, enhanced the activation of calpain and glycogen synthase kinase-3β (GSK3β), and increased tau hyperphosphorylation and β-amyloid deposition. In APPswe cells, m-calpain silencing reduced hypoxia-induced cellular dysfunction and resulted in suppression of GSK3β activation, ER stress and tau hyperphosphorylation reduction as well as caspase pathway suppression.

CONCLUSION

These findings demonstrate that hypoxia-induced abnormal calpain activation may increase ER stress-induced apoptosis in AD pathogenesis. In contrast, a reduction in the expression of the m-calpain isoform reduces ER stress-linked apoptosis that is triggered by hypoxia. These findings suggest that hypoxia-triggered m-calpain activation is involved in ER stress-mediated AD pathogenesis. m-calpain is a potential target for AD therapeutics.

Molecular mechanisms of environmental enrichment: impairments in Akt/GSK3β, neurotrophin-3 and CREB signaling

Experience of mice in a complex environment enhances neurogenesis and synaptic plasticity in the hippocampus of wild type and transgenic mice harboring familial Alzheimer's disease (FAD)-linked APPswe/PS1ΔE9. In FAD mice, this experience also reduces levels of tau hyperphosphorylation and oligomeric β-amyloid. Although environmental enrichment has significant effects on brain plasticity and neuropathology, the molecular mechanisms underlying these effects are unknown. Here we show that environmental enrichment upregulates the Akt pathway, leading to the downregulation of glycogen synthase kinase 3β (GSK3β), in wild type but not FAD mice. Several neurotrophic signaling pathways are activated in the hippocampus of both wild type and FAD mice, including brain derived neurotrophic factor (BDNF) and nerve growth factor (NGF), and this increase is accompanied by the upregulation of the BDNF receptor, tyrosine kinase B (TrkB). Interestingly, neurotrophin-3 (NT-3) is upregulated in the brains of wild type mice but not FAD mice, while insulin growth factor-1 (IGF-1) is upregulated exclusively in the brains of FAD mice. Upregulation of neurotrophins is accompanied by the increase of N-Methyl-D-aspartic acid (NMDA) receptors in the hippocampus following environmental enrichment. Most importantly, we observed a significant increase in levels of cAMP response element- binding (CREB) transcripts in the hippocampus of wild type and FAD mice following environmental enrichment. However, CREB phosphorylation, a critical step for the initiation of learning and memory-required gene transcription, takes place in the hippocampus of wild type but not of FAD mice. These results suggest that experience of wild type mice in a complex environmental upregulates critical signaling that play a major role in learning and memory in the hippocampus. However, in FAD mice, some of these pathways are impaired and cannot be rescued by environmental enrichment.

Synergistic influence of phosphorylation and metal ions on tau oligomer formation and coaggregation with α-synuclein at the single molecule level

Background

Fibrillar amyloid-like deposits and co-deposits of tau and α-synuclein are found in several common neurodegenerative diseases. Recent evidence indicates that small oligomers are the most relevant toxic aggregate species. While tau fibril formation is well-characterized, factors influencing tau oligomerization and molecular interactions of tau and α-synuclein are not well understood.

Results

We used a novel approach applying confocal single-particle fluorescence to investigate the influence of tau phosphorylation and metal ions on tau oligomer formation and its coaggregation with α-synuclein at the level of individual oligomers. We show that Al³⁺ at physiologically relevant concentrations and tau phosphorylation by GSK-3β exert synergistic effects on the formation of a distinct SDS-resistant tau oligomer species even at nanomolar protein concentration. Moreover, tau phosphorylation and Al³⁺ as well as Fe³⁺ enhanced both formation of mixed oligomers and recruitment of α-synuclein in pre-formed tau oligomers.

Conclusions

Our findings provide a new perspective on interactions of tau phosphorylation, metal ions, and the formation of potentially toxic oligomer species, and elucidate molecular crosstalks between different aggregation pathways involved in neurodegeneration.

Insulin receptor expression and activity in the brains of nondiabetic sporadic Alzheimer's disease cases

We investigated the contents of the insulin receptor-beta subunit (IRβ) and [Tyr1162/1163]-phosphorylated IRβ as surrogate indices of total IR content and IR activation in postmortem hippocampal formation brain specimens from nondiabetic sporadic Alzheimer's disease (AD) cases. We found no significant changes in the brain contents of total IRβ or [Tyr1162/1163]-phosphorylated IRβ, suggesting normal IR content and activation in the brains of nondiabetic sporadic AD cases. Moreover, total IRβ and [Tyr1162/1163]-phosphorylated IRβ levels in the hippocampal formation are not correlated with the severity of amyloid or tau-neuropathology. Exploring the regulation of glycogen synthase kinase 3 (GSK3) α/β, key IR-signaling components, we observed significantly lower levels of total GSK3 α/β in brain specimens from nondiabetic AD cases, suggesting that impaired IR signaling mechanisms might contribute to the onset and/or progression of AD dementia. Outcomes from our study support the development of insulin-sensitizing therapeutic strategies to stimulate downstream IR signaling in nondiabetic AD cases.

Synapses and dendritic spines as pathogenic targets in Alzheimer's disease

Synapses are sites of cell-cell contacts that transmit electrical or chemical signals in the brain. Dendritic spines are protrusions on dendritic shaft where excitatory synapses are located. Synapses and dendritic spines are dynamic structures whose plasticity is thought to underlie learning and memory. No wonder neurobiologists are intensively studying mechanisms governing the structural and functional plasticity of synapses and dendritic spines in an effort to understand and eventually treat neurological disorders manifesting learning and memory deficits. One of the best-studied brain disorders that prominently feature synaptic and dendritic spine pathology is Alzheimer's disease (AD). Recent studies have revealed molecular mechanisms underlying the synapse and spine pathology in AD, including a role for mislocalized tau in the postsynaptic compartment. Synaptic and dendritic spine pathology is also observed in other neurodegenerative disease. It is possible that some common pathogenic mechanisms may underlie the synaptic and dendritic spine pathology in neurodegenerative diseases.

Neuroprotection in metabolism-based therapy

Metabolism-based therapy has been used successfully in the treatment of seizures but study of its use in other neurodegenerative disorders is growing. Data demonstrating the use of different forms of metabolism-based therapy in human trials of Alzheimer disease and Parkinson disease are discussed. Animal and in vitro studies have shed light on metabolism-based therapy's mechanisms in these diseases, as well as ALS, aging, ischemia, trauma and mitochondrial cytopathies. Additional insights may be obtained by considering the role of metabolism-based therapy in cell disability and death (specifically apoptosis, excitotoxicity, and autophagy).

A new protocol for predicting novel GSK-3β ATP competitive inhibitors

Glycogen synthase kinase 3β (GSK-3β) is a potential therapeutic target for cancer, type-2 diabetes, and Alzheimer's disease. This paper proposes a new lead identification protocol that predicts new GSK-3β ATP competitive inhibitors with topologically diverse scaffolds. First, three-dimensional quantitative structure-activity relationship (3D QSAR) models were built and validated. These models are based upon known GSK-3β inhibitors, benzofuran-3-yl-(indol-3-yl) maleimides, by means of comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). Second, 28 826 maleimide derivatives were selected from the PubChem database. After filtration via Lipinski's rules, 10 429 maleimide derivatives were left. Third, the FlexX-dock program was employed to virtually screen the 10 429 compounds against GSK-3β. This resulted in 617 virtual hits. Fourth, the 3D QSAR models predicted that from the 617 virtual hits, 93 compounds would have GSK-3β inhibition values of less than 15 nM. Finally, from the 93 predicted active hits, 23 compounds were confirmed as GSK-3β inhibitors from literatures; their GSK-3β inhibition ranged from 1.3 to 480 nM. Therefore, the hits rate of our virtual screening protocol is greater than 25%. The protocol combines ligand- and structure-based approaches and therefore validates both approaches and is capable of identifying new hits with topologically diverse scaffolds.

Huperzine A activates Wnt/β-catenin signaling and enhances the nonamyloidogenic pathway in an Alzheimer transgenic mouse model

Huperzine A (HupA) is a reversible and selective inhibitor of acetylcholinesterase (AChE), and it has multiple targets when used for Alzheimer's disease (AD) therapy. In this study, we searched for new mechanisms by which HupA could activate Wnt signaling and reduce amyloidosis in AD brain. A nasal gel containing HupA was prepared. No obvious toxicity of intranasal administration of HupA was found in mice. HupA was administered intranasally to β-amyloid (Aβ) precursor protein and presenilin-1 double-transgenic mice for 4 months. We observed an increase in ADAM10 and a decrease in BACE1 and APP695 protein levels and, subsequently, a reduction in Aβ levels and Aβ burden were present in HupA-treated mouse brain, suggesting that HupA enhances the nonamyloidogenic APP cleavage pathway. Importantly, our results further showed that HupA inhibited GSK3α/β activity, and enhanced the β-catenin level in the transgenic mouse brain and in SH-SY5Y cells overexpressing Swedish mutation APP, suggesting that the neuroprotective effect of HupA is not related simply to its AChE inhibition and antioxidation, but also involves other mechanisms, including targeting of the Wnt/β-catenin signaling pathway in AD brain.

Amyloid-β triggers the release of neuronal hexokinase 1 from mitochondria

Brain accumulation of the amyloid-β peptide (Aβ) and oxidative stress underlie neuronal dysfunction and memory loss in Alzheimer's disease (AD). Hexokinase (HK), a key glycolytic enzyme, plays important pro-survival roles, reducing mitochondrial reactive oxygen species (ROS) generation and preventing apoptosis in neurons and other cell types. Brain isozyme HKI is mainly associated with mitochondria and HK release from mitochondria causes a significant decrease in enzyme activity and triggers oxidative damage. We here investigated the relationship between Aβ-induced oxidative stress and HK activity. We found that Aβ triggered HKI detachment from mitochondria decreasing HKI activity in cortical neurons. Aβ oligomers further impair energy metabolism by decreasing neuronal ATP levels. Aβ-induced HKI cellular redistribution was accompanied by excessive ROS generation and neuronal death. 2-deoxyglucose blocked Aβ-induced oxidative stress and neuronal death. Results suggest that Aβ-induced cellular redistribution and inactivation of neuronal HKI play important roles in oxidative stress and neurodegeneration in AD.

Novel cell death signaling pathways in neurotoxicity models of dopaminergic degeneration: relevance to oxidative stress and neuroinflammation in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative movement disorder characterized by extensive degeneration of dopaminergic neurons in the nigrostriatal system. Neurochemical and neuropathological analyses clearly indicate that oxidative stress, mitochondrial dysfunction, neuroinflammation and impairment of the ubiquitin-proteasome system (UPS) are major mechanisms of dopaminergic degeneration. Evidence from experimental models and postmortem PD brain tissues demonstrates that apoptotic cell death is the common final pathway responsible for selective and irreversible loss of nigral dopaminergic neurons. Epidemiological studies imply both environmental neurotoxicants and genetic predisposition are risk factors for PD, though the cellular mechanisms underlying selective dopaminergic degeneration remain unclear. Recent progress in signal transduction research is beginning to unravel the complex mechanisms governing dopaminergic degeneration. During the 12th International Neurotoxicology meeting, discussion at one symposium focused on several key signaling pathways of dopaminergic degeneration. This review summarizes two novel signaling pathways of nigral dopaminergic degeneration that have been elucidated using neurotoxicity models of PD. Dr. Anumantha Kanthasamy described a cell death pathway involving the novel protein kinase C delta isoform (PKCdelta) in oxidative stress-induced apoptotic cell death in experimental models of PD. Dr. Ajay Rana presented his recent work on the role of mixed lineage kinase-3 (MLK3) in neuroinflammatory processes in neurotoxic cell death. Collectively, PKCdelta and MLK3 signaling pathways provide new understanding of neurodegenerative processes in PD, and further exploration of these pathways may translate into effective neuroprotective drugs for the treatment of PD.

Why pleiotropic interventions are needed for Alzheimer's disease

Alzheimer's disease (AD) involves a complex pathological cascade thought to be initially triggered by the accumulation of beta-amyloid (Abeta) peptide aggregates or aberrant amyloid precursor protein (APP) processing. Much is known of the factors initiating the disease process decades prior to the onset of cognitive deficits, but an unclear understanding of events immediately preceding and precipitating cognitive decline is a major factor limiting the rapid development of adequate prevention and treatment strategies. Multiple pathways are known to contribute to cognitive deficits by disruption of neuronal signal transduction pathways involved in memory. These pathways are altered by aberrant signaling, inflammation, oxidative damage, tau pathology, neuron loss, and synapse loss. We need to develop stage-specific interventions that not only block causal events in pathogenesis (aberrant tau phosphorylation, Abeta production and accumulation, and oxidative damage), but also address damage from these pathways that will not be reversed by targeting prodromal pathways. This approach would not only focus on blocking early events in pathogenesis, but also adequately correct for loss of synapses, substrates for neuroprotective pathways (e.g., docosahexaenoic acid), defects in energy metabolism, and adverse consequences of inappropriate compensatory responses (aberrant sprouting). Monotherapy targeting early single steps in this complicated cascade may explain disappointments in trials with agents inhibiting production, clearance, or aggregation of the initiating Abeta peptide or its aggregates. Both plaque and tangle pathogenesis have already reached AD levels in the more vulnerable brain regions during the "prodromal" period prior to conversion to "mild cognitive impairment (MCI)." Furthermore, many of the pathological events are no longer proceeding in series, but are going on in parallel. By the MCI stage, we stand a greater chance of success by considering pleiotropic drugs or cocktails that can independently limit the parallel steps of the AD cascade at all stages, but that do not completely inhibit the constitutive normal functions of these pathways. Based on this hypothesis, efforts in our laboratories have focused on the pleiotropic activities of omega-3 fatty acids and the anti-inflammatory, antioxidant, and anti-amyloid activity of curcumin in multiple models that cover many steps of the AD pathogenic cascade (Cole and Frautschy, Alzheimers Dement 2:284-286, 2006).

ADAM19 autolysis is activated by LPS and promotes non-classical secretion of cysteine-rich protein 2

ADAM family proteins are type I transmembrane, zinc-dependent metalloproteases. This family has multiple conserved domains, including a signal peptide, a pro-domain, a metalloprotease domain, a disintegrin (DI) domain, a cysteine-rich (Cys) domain, an EGF-like domain, a transmembrane domain, and a cytoplasmic domain. The Cys and DI domains may play active roles in regulating proteolytic activity or substrate specificity. ADAM19 has an autolytic processing activity within its Cys domain, and the processing is necessary for its proteolytic activity. To identify a new physiological function of ADAM19, we screened for associating proteins by using the extracellular domain of ADAM19 in a yeast two-hybrid system. Cysteine-rich protein 2 (CRIP2) showed an association with ADAM19 through its DI and Cys domains. Sequence analysis revealed that CRIP2 is a secretable protein without a classical signal. CRIP2 secretion was increased by overexpression of ADAM19 and decreased by suppression of ADAM19 expression. Moreover, CRIP2 secretion increased in parallel with the autolytic processing of ADAM19 stimulated by lipopolysaccharide. These findings suggest that ADAM19 autolysis is activated by lipopolysaccharide and that ADAM19 promotes the secretion of CRIP2.

Molecular mechanisms of neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is characterized by cognitive impairment, progressive neurodegeneration and formation of amyloid-beta (Abeta)-containing plaques and neurofibrillary tangles composed of hyperphosphorylated tau. The neurodegenerative process in AD is initially characterized by synaptic damage accompanied by neuronal loss. In addition, recent evidence suggests that alterations in adult neurogenesis in the hippocampus might play a role. Synaptic loss is one of the strongest correlates to the cognitive impairment in patients with AD. Several lines of investigation support the notion that the synaptic pathology and defective neurogenesis in AD are related to progressive accumulation of Abeta oligomers rather than fibrils. Abnormal accumulation of Abeta resulting in the formation of toxic oligomers is the result of an imbalance between the levels of Abeta production, aggregation and clearance. Abeta oligomers might lead to synaptic damage by forming pore-like structures with channel activity; alterations in glutamate receptors; circuitry hyper-excitability; mitochondrial dysfunction; lysosomal failure and alterations in signaling pathways related to synaptic plasticity, neuronal cell and neurogenesis. A number of signaling proteins, including fyn kinase; glycogen synthase kinase-3beta (GSK3beta) and cyclin-dependent kinase-5 (CDK5), are involved in the neurodegenerative progression of AD. Therapies for AD might require the development of anti-aggregation compounds, pro-clearance pathways and blockers of hyperactive signaling pathways.

GSK3 inhibitors show benefits in an Alzheimer's disease (AD) model of neurodegeneration but adverse effects in control animals

The dysregulation of glycogen synthase kinase-3 (GSK3) has been implicated in Alzheimer disease (AD) pathogenesis and in Abeta-induced neurotoxicity, leading us to investigate it as a therapeutic target in an intracerebroventricular Abeta infusion model. Infusion of a specific GSK3 inhibitor SB216763 (SB) reduced a downstream target, phospho-glycogen synthase 39%, and increased glycogen levels 44%, suggesting effective inhibition of enzyme activity. Compared to vehicle, Abeta increased GSK3 activity, and was associated with elevations in levels of ptau, caspase-3, the tau kinase phospho-c-jun N-terminal kinase (pJNK), neuronal DNA fragmentation, and gliosis. Co-infusion of SB corrected all responses to Abeta infusion except the induction of gliosis and behavioral deficits in the Morris water maze. Nevertheless, SB alone was associated with induction of neurodegenerative markers and behavioral deficits. These data support a role for GSK3 hyperactivation in AD pathogenesis, but emphasize the importance of developing inhibitors that do not suppress constitutive activity.

Dissociation of tau toxicity and phosphorylation: role of GSK-3beta, MARK and Cdk5 in a Drosophila model

Hyperphosphorylation of tau at multiple sites has been implicated in the formation of neurofibrillary tangles in Alzheimer’s disease; however, the relationship between toxicity and phosphorylation of tau has not been clearly elucidated. Putative tau kinases that play a role in such phosphorylation events include the proline-directed kinases glycogen synthase kinase-3β (GSK-3β) and cyclin-dependent kinase 5 (Cdk5), as well as nonproline-directed kinases such as microtubule affinity-regulating kinase (MARK)/PAR-1; however, whether the cascade of events linking tau phosphorylation and neurodegeneration involves sequential action of kinases as opposed to parallel pathways is still a matter of controversy. Here, we employed a well-characterized Drosophila model of tauopathy to investigate the interdependence of tau kinases in regulating the phosphorylation and toxicity of tau in vivo. We found that tau mutants resistant to phosphorylation by MARK/PAR-1 were indeed less toxic than wild-type tau; however, this was not due to their resistance to phosphorylation by GSK-3β/Shaggy. On the contrary, a tau mutant resistant to phosphorylation by GSK-3β/Shaggy retained substantial toxicity and was found to have increased affinity for microtubules compared with wild-type tau. The fly homologs of Cdk5/p35 did not have major effects on tau toxicity or phosphorylation in this model. These data suggest that, in addition to tau phosphorylation, microtubule binding plays a crucial role in the regulation of tau toxicity when misexpressed. These data have important implications for the understanding and interpretation of animal models of tauopathy.

Measures of striatal insulin resistance in a 6-hydroxydopamine model of Parkinson's disease

Clinical evidence has shown a correlation between Parkinson's disease (PD) and Type 2 Diabetes (T2D), as abnormal glucose tolerance has been reported in >50% of PD patients. The development of insulin resistance and the degeneration of nigrostriatal dopamine (DA) neurons are both mediated by oxidative mechanisms, and oxidative stress is likely a mechanistic link between these pathologies. Although glucose uptake in neuronal tissues is primarily non-insulin dependent, proteins involved in insulin signaling, such as insulin receptor substrate 2 (IRS2) and glucose transporter 4 (GLUT4), are present in the basal ganglia. The purpose of this study was to determine whether nigrostriatal DA depletion affects measures of insulin resistance in the striatum. Six weeks after 6-hydroxydopamine (6-OHDA) infusion into the medial forebrain bundle, rats were classified as having either partial (20-65%) or severe (90-99%) striatal DA depletion. Increased IRS2 serine phosphorylation, a marker of insulin resistance, was observed in the DA-depleted striatum. Additionally, severe depletion resulted in decreased total IRS2, indicating possible degradation of the protein. Decreased phosphorylation of AKT and expression of the kinase glycogen synthase kinase-3 alpha (GSK3-alpha) was also measured in the striatum of severely DA-depleted animals. Finally, expression of heat shock protein 25 (Hsp25), which is protective against oxidative damage and can decrease stress kinase activity, was decreased in the striatum of lesioned rats. Together, these results support the hypothesis that nigrostriatal DA depletion impairs insulin signaling in the basal ganglia.

Amyloid-beta binds to the extracellular cysteine-rich domain of Frizzled and inhibits Wnt/beta-catenin signaling

The amyloid-beta peptide (Abeta) plays a major role in neuronal dysfunction and neurotoxicity in Alzheimer disease. However, the signal transduction mechanisms involved in Abeta-induced neuronal dysfunction remain to be fully elucidated. A major current unknown is the identity of the protein receptor(s) involved in neuronal Abeta binding. Using phage display of peptide libraries, we have identified a number of peptides that bind Abeta and are homologous to neuronal receptors putatively involved in Abeta interactions. We report here on a cysteine-linked cyclic heptapeptide (denominated cSP5) that binds Abeta with high affinity and is homologous to the extracellular cysteine-rich domain of several members of the Frizzled (Fz) family of Wnt receptors. Based on this homology, we investigated the interaction between Abeta and Fz. The results show that Abeta binds to the Fz cysteine-rich domain at or in close proximity to the Wnt-binding site and inhibits the canonical Wnt signaling pathway. Interestingly, the cSP5 peptide completely blocks Abeta binding to Fz and prevents inhibition of Wnt signaling. These results indicate that the Abeta-binding site in Fz is homologous to cSP5 and that this is a relevant target for Abeta-instigated neurotoxicity. Furthermore, they suggest that blocking the interaction of Abeta with Fz might lead to novel therapeutic approaches to prevent neuronal dysfunction in Alzheimer disease.

Neuroprotective effects of regulators of the glycogen synthase kinase-3beta signaling pathway in a transgenic model of Alzheimer's disease are associated with reduced amyloid precursor protein phosphorylation

The glycogen synthase kinase-3beta (GSK3beta) pathway plays an important role in mediating neuronal fate and synaptic plasticity. In Alzheimer's disease (AD), abnormal activation of this pathway might play an important role in neurodegeneration, and compounds such as lithium that modulate GSK3beta activity have been shown to reduce amyloid production and tau phosphorylation in amyloid precursor protein (APP) transgenic (tg) mice. However, it is unclear whether regulation of GSK3beta is neuroprotective in APP tg mice. In this context, the main objective of the present study was to determine whether pharmacological or genetic manipulations that block the GSK3beta pathway might ameliorate the neurodegenerative alterations in APP tg mice and to better understand the mechanisms involved. For this purpose, two sets of experiments were performed. First, tg mice expressing mutant human APP under the Thy1 promoter (hAPP tg) were treated with either lithium chloride or saline alone. Second, hAPP tg mice were crossed with GSK3beta tg mice, in which overexpression of this signaling molecule results in a dominant-negative (DN) effect with inhibition of activity. hAPP tg mice that were treated with lithium or that were crossed with DN-GSK3beta tg mice displayed improved performance in the water maze, preservation of the dendritic structure in the frontal cortex and hippocampus, and decreased tau phosphorylation. Moreover, reduced activation of GSK3beta was associated with decreased levels of APP phosphorylation that resulted in decreased amyloid-beta production. In conclusion, the present study showed that modulation of the GSK3beta signaling pathway might also have neuroprotective effects in tg mice by regulating APP maturation and processing and further supports the notion that GSK3beta might be a suitable target for the treatment of AD.

Age-related changes in glycogen synthase kinase 3beta (GSK3beta) immunoreactivity in the central nervous system of rats

Although glycogen synthase kinase 3beta (GSK3beta) is emerging as a prominent drug target in the treatment of neurodegenerative diseases such as Alzheimer's disease (AD) and stroke, very little is known about age-related changes in GSK3beta expression and GSK3beta phosphorylation. Therefore, we examined age-related changes in immunoreactivities for GSK3beta and phosphorylated GSK3beta (pGSK3beta) in the central nervous system. In aged rats, there were significant increases in GSK3beta immunoreactivity in the cell bodies and processes of pyramidal cells in most cortical regions. GSK3beta immunoreactivity was also significantly increased in the pyramidal layer of CA1-3 regions, and the granule cell layer of dentate gyrus. Age-related increases were prominent in lateral septal nuclei, compared to the medial septal nuclei. Interestingly, both GSK3beta and pGSK3beta was increased in the prefrontal cortex, while GSK3beta and pGSK3beta was differentially localized in the cerebellar cortex. The first demonstration of age-related alterations in immunoreactivities for GSK3beta and pGSK3beta in the basal forebrain area and cholinergic projection targets may provide useful data for investigating the pathogenesis of age-related neurodegenerative diseases including AD.

Compartmental protein expression of Tau, GSK-3beta and TrkA in cholinergic neurons of aged rats

During aging basal forebrain cholinergic neurons (BFCNs) degenerate, and we hypothesize this to be the result of a degeneration of the cytoskeleton. As a corollary, retrograde transport of the complex of nerve growth factor (NGF) and its activated receptor phospho-TrkA (P-TrkA) is impaired. Using immunocytochemistry, we here compare young and aged rat brains in their subcellular localization of NGF and P-TrkA in relation to the compartmentalization of phosphorylation-dependent tau protein isoforms. Despite lower P-TrkA immunoreactivity in cortex and hippocampus of aged rats, NGF immunoreactivity was not altered in these areas, but was significantly lower in aged basal forebrain. In young animals, expression of tau isoforms and glycogen synthase kinase-3beta (GSK-3beta) was restricted to neuritic structures in cortex, hippocampus, and basal forebrain. In contrast, tau and GSK-3beta labeling was confined to cell bodies in aged rats. Since a somatic localization of phospho-tau is indicative of cytoskeletal breakdown, we suggest this to be the mechanism the breakdown of trophic support in aging BFCNs.

Casein kinase-1 isoforms differentially associate with neurofibrillary and granulovacuolar degeneration lesions

Alzheimer's Disease (AD) is characterized by the appearance of neurofibrillary and granulovacuolar lesions in the brains of affected individuals. The former is composed of hyperphosphorylated aggregates of the microtubule-associated protein tau. The latter is poorly characterized but reacts strongly with anti-phosphoepitope antibodies indicating that it too accumulates phosphoproteins. Both lesions react strongly with antibodies directed against members of the casein kinase-1 family of phosphotransferases, a group of closely related protein kinases that frequently function in tandem with the ubiquitin modification system. To determine whether individual members of the casein kinase-1 family differentially associate with AD lesions, hippocampal sections isolated from late stage cases of AD were subjected to double-label fluorescence immunohistochemistry using a panel of selective anti-casein kinase 1 antibodies and small-molecule fluorochromes thioflavin S and thiazin red. The resultant colocalization patterns revealed that the alpha CK1 isoform strongly correlated with thioflavin S and thiazin red fluorescence, indicating that it preferentially associated with neurofibrillary lesions. In contrast, the delta isoform staining pattern was dominated by colocalization with granulovacuolar degeneration bodies. These findings suggest that granulovacuolar and neurofibrillary lesions occupy separate populations of neurons, and implicate CK1 isoforms in the generation of lesion-associated phosphoepitopes. They also suggest a nexus between the phosphorylation and ubiquitination modifications found in both lesions.

Candidate genes, pathways and mechanisms for bipolar (manic-depressive) and related disorders: an expanded convergent functional genomics approach

Identifying genes for bipolar mood disorders through classic genetics has proven difficult. Here, we present a comprehensive convergent approach that translationally integrates brain gene expression data from a relevant pharmacogenomic mouse model (involving treatments with a stimulant--methamphetamine, and a mood stabilizer--valproate), with human data (linkage loci from human genetic studies, changes in postmortem brains from patients), as a bayesian strategy of crossvalidating findings. Topping the list of candidate genes, we have DARPP-32 (dopamine- and cAMP-regulated phosphoprotein of 32 kDa) located at 17q12, PENK (preproenkephalin) located at 8q12.1, and TAC1 (tachykinin 1, substance P) located at 7q21.3. These data suggest that more primitive molecular mechanisms involved in pleasure and pain may have been recruited by evolution to play a role in higher mental functions such as mood. The analysis also revealed other high-probability candidates genes (neurogenesis, neurotrophic, neurotransmitter, signal transduction, circadian, synaptic, and myelin related), pathways and mechanisms of likely importance in pathophysiology.

Protein levels of glycogen synthase 3 kinase are normal in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a neurodegenerative disorder characterized by pure neurofibrillary tau pathology involving mainly basal ganglia and brain stem nuclei. One of the kinases involved in tau phosphorylation is glycogen synthase 3 kinase (GSK3). In mammals GSK3 is present in two isoforms, alpha and beta regulated by phosphorylation: phosphorylation of Ser9 in GSK3beta or Ser21 in GSK3alpha leads to inactivation while phosphorylation of Tyr216 in GSK3beta or Tyr279 in GSK3alpha leads to activation. We analyzed the protein levels of GSK3alpha/beta and of the phosphorylated forms GSK3beta S(9), GSK3beta Y(216), GSK3alpha Y(279) in brain tissues of subjects with PSP. The analysis failed to show significant differences of all GSK3 isoforms in PSP in comparison to age-matched control cases. This negative result argues against the role of GSK3 in the pathogenesis of PSP.

FRAT1 peptide decreases Abeta production in swAPP(751) cells

Recently, LiCl has been shown to inhibit amyloid beta peptide secretion in association with diminished glycogen synthase kinase beta (GSK3beta) activity. However, it remains unclear if direct inhibition of GSK3beta activity will result in decreased Abeta production. Frequently rearranged in advanced T-cell lymphomas 1 (FRAT1) protein is a negative regulator of GSK3alpha/beta kinase activity. To examine whether direct inhibition of GSK3alpha/beta kinase activity can lower Abeta production, a FRAT1 peptide was expressed in swAPP(751) cells that produce high levels of Abeta. Our data demonstrate that cellular expression of FRAT1 peptide in swAPP(751) cells increases both GSK3alpha and beta phosphorylation on Ser21 and Ser9, respectively, while inhibiting kinase activity of both isoforms. Moreover, as a result of FRAT1 expression, the production of both total Abeta and Abeta(1-42) was significantly decreased. Thus, we provide evidence that direct regulation of GSK3alpha/beta by FRAT1 peptide significantly decreases Abeta production in swAPP(751) cells.

Co-localization of glycogen synthase kinase-3 with neurofibrillary tangles and granulovacuolar degeneration in transgenic mice

Transgenic mice expressing human tau with P301L missense mutation (JNPL3) develop progressive amyotrophy, neurofibrillary degeneration, and neuronal loss. Mating of JNPL3 with transgenic mice expressing mutant amyloid precursor protein (Tg2576) leads to bigenic (TAPP) mice with enhanced neurofibrillary pathology. TAPP and JNPL3 mice were studied with immunocytochemistry and immunoblotting with antibodies to glycogen synthase kinase-3 (GKS3) to determine whether the development of tauopathy is associated with activation or increased expression of GSK3, and when the observed changes occur with respect to neurofibrillary tangle (NFT) formation. Accumulation of GSK3alpha/beta phosphorylated at Y279/216 was observed in neurons containing NFTs and granulovacuolar degeneration (GVD), but not in normal neurons or neurons with pretangles. More GSK3 immunoreactive NFTs were detected in TAPP than JNPL3 mice, especially in the amygdala. These differences were notable only in old animals. There was no significant difference between animals with and without NFTs in the level of total, inactive, or Y216-phosphorylated (pY216)GSK3beta. No apparent GSK3 accumulation was detected in neurons in Tg2576 mice. There was also no significant difference in the distribution of GSK3 in lysates fractionated based on their solubility in various reagents, including the sarkosyl-insoluble fraction. The results suggest that the pY216 GSK3beta accumulates in NFT and GVD due to redistribution rather than increased expression or activation, and that pre-existence of tau abnormalities is required for APP/Abeta to exert their effects on tau pathology in TAPP mice.

An N-terminal fragment of ProSAAS (a granin-like neuroendocrine peptide precursor) is associated with tau inclusions in Pick's disease

The deposition of aggregated tau in cytoplasmic inclusions is one of the common neuropathological features in various dementing neurodegenerative disorders. At present, it remains unclear whether tau inclusions exert neurotoxicity or they are simply the consequence of neurodegeneration. In our approach for the analysis of the composition of tau inclusions, we detected the intense binding of anti-diacylglycerol kinase-zeta (DGK-zeta) antibodies to Pick bodies (PBs), which represent tau inclusions in Pick's disease. The polyclonal antibodies were found to cross-react with a 21-kDa protein, but not with tau or ubiquitin, on Western blots of normal human brain extracts. Analysis of the 21-kDa protein by two-dimensional-gel electrophoresis and mass-spectrometry revealed that the protein is an N-terminal fragment of proSAAS (a human granin-like neuroendocrine peptide precursor). Our results suggest that sequestration of the N-terminal fragment of proSAAS in intracellular PBs may cause a functional disturbance of neurons in Pick's disease.

Alzheimer's presenilin 1 mutations impair kinesin-based axonal transport

Several lines of evidence indicate that alterations in axonal transport play a critical role in Alzheimer's disease (AD) neuropathology, but the molecular mechanisms that control this process are not understood fully. Recent work indicates that presenilin 1 (PS1) interacts with glycogen synthase kinase 3beta (GSK3beta). In vivo, GSK3beta phosphorylates kinesin light chains (KLC) and causes the release of kinesin-I from membrane-bound organelles (MBOs), leading to a reduction in kinesin-I driven motility (Morfini et al., 2002b). To characterize a potential role for PS1 in the regulation of kinesin-based axonal transport, we used PS1-/- and PS1 knock-inM146V (KIM146V) mice and cultured cells. We show that relative levels of GSK3beta activity were increased in cells either in the presence of mutant PS1 or in the absence of PS1 (PS1-/-). Concomitant with increased GSK3beta activity, relative levels of KLC phosphorylation were increased, and the amount of kinesin-I bound to MBOs was reduced. Consistent with a deficit in kinesin-I-mediated fast axonal transport, densities of synaptophysin- and syntaxin-I-containing vesicles and mitochondria were reduced in neuritic processes of KIM146V hippocampal neurons. Similarly, we found reduced levels of PS1, amyloid precursor protein, and synaptophysin in sciatic nerves of KIM146V mice. Thus PS1 appears to modulate GSK3beta activity and the release of kinesin-I from MBOs at sites of vesicle delivery and membrane insertion. These findings suggest that mutations in PS1 may compromise neuronal function by affecting GSK-3 activity and kinesin-I-based motility.

Involvement of aberrant glycosylation in phosphorylation of tau by cdk5 and GSK-3beta

Microtubule-associated protein tau is abnormally hyperphosphorylated, glycosylated, and aggregated in affected neurons in the brains of individuals with Alzheimer's disease (AD). We recently found that the glycosylation might precede hyperphosphorylation of tau in AD. In this study, we investigated the effect of glycosylation on phosphorylation of tau catalyzed by cyclin-dependent kinase 5 (cdk5) and glycogen synthase kinase-3beta (GSK-3beta). The phosphorylation of the longest isoform of recombinant human brain tau, tau(441), at various sites was detected by Western blots and by radioimmuno-dot-blot assay with phosphorylation-dependent and site-specific tau antibodies. We found that cdk5 phosphorylated tau(441) at Thr-181, Ser-199, Ser-202, Thr-205, Thr-212, Ser-214, Thr-217, Thr-231, Ser-235, Ser-396, and Ser-404, but not at Ser-262, Ser-400, Thr-403, Ser-409, Ser-413, or Ser-422. GSK-3beta phosphorylated all the cdk5-catalyzed sites above except Ser-235. Deglycosylation by glycosidases depressed the subsequent phosphorylation of AD-tau (i) with cdk5 at Thr-181, Ser-199, Ser-202, Thr-205, and Ser-404, but not at Thr-212; and (ii) with GSK-3beta at Thr-181, Ser-202, Thr-205, Ser-217, and Ser-404, but not at Ser-199, Thr-212, Thr-231, or Ser-396. These data suggest that aberrant glycosylation of tau in AD might be involved in neurofibrillary degeneration by promoting abnormal hyperphosphorylation by cdk5 and GSK-3beta.