1.
Calpastatin modulates APP processing in the brains of β-amyloid depositing but not wild-type mice.
Source
Nathan Kline Institute for Psychiatric Research, Orangeburg, NY, USA; New York University School of Medicine, New York, NY, USA.
Abstract
We report that neuronal overexpression of the endogenous inhibitor of calpains, calpastatin (CAST), in a mouse model of human Alzheimer's disease (AD) β-amyloidosis, the APP23 mouse, reduces β-amyloid (Aβ) pathology and Aβ levels when comparing aged, double transgenic (tg) APP23/CAST with APP23 mice. Concurrent with Aβ plaque deposition, aged APP23/CAST mice show a decrease in the steady-state brain levels of the amyloid precursor protein (APP) and APP C-terminal fragments (CTFs) when compared with APP23 mice. This CAST-dependent decrease in APP metabolite levels was not observed in single tg CAST mice expressing endogenous APP or in younger, Aβ plaque predepositing APP23/CAST mice. We also determined that the CAST-mediated inhibition of calpain activity in the brain is greater in the CAST mice with Aβ pathology than in non-APP tg mice, as demonstrated by a decrease in calpain-mediated cytoskeleton protein cleavage. Moreover, aged APP23/CAST mice have reduced extracellular signal-regulated kinase 1/2 (ERK1/2) activity and tau phosphorylation when compared with APP23 mice. In summary, in vivo calpain inhibition mediated by CAST transgene expression reduces Aβ pathology in APP23 mice, with our findings further suggesting that APP metabolism is modified by CAST overexpression as the mice develop Aβ pathology. Our results indicate that the calpain system in neurons is more responsive to CAST inhibition under conditions of Aβ pathology, suggesting that in the disease state neurons may be more sensitive to the therapeutic use of calpain inhibitors.
Copyright © 2011 Elsevier Inc. All rights reserved.
Brain Insulin Signaling and Alzheimer's Disease: Current Evidence and Future Directions.
Source
Department of Neuroscience, Uppsala University, Box 593, Husargatan 3, Uppsala, Sweden.
Abstract
Insulin receptors in the brain are found in high densities in the hippocampus, a region that is fundamentally involved in the acquisition, consolidation, and recollection of new information. Using the intranasal method, which effectively bypasses the blood-brain barrier to deliver and target insulin directly from the nose to the brain, a series of experiments involving healthy humans has shown that increased central nervous system (CNS) insulin action enhances learning and memory processes associated with the hippocampus. Since Alzheimer's disease (AD) is linked to CNS insulin resistance, decreased expression of insulin and insulin receptor genes and attenuated permeation of blood-borne insulin across the blood-brain barrier, impaired brain insulin signaling could partially account for the cognitive deficits associated with this disease. Considering that insulin mitigates hippocampal synapse vulnerability to amyloid beta and inhibits thephosphorylation of tau, pharmacological strategies bolstering brain insulin signaling, such as intranasal insulin, could have significant therapeutic potential to deter AD pathogenesis.
Combined Chemotherapy or Biotherapy with Jasmonates: Targeting Energy Metabolism for Cancer Treatment.
Source
Department of Clinical Microbiology and Immunology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 69978, Israel. flascher@post.tau.ac.il.
Abstract
Mitochondria are known to play a key role in various cellular processes essential to both the life and death of cells, including calcium homeostasis, programmed cell death, and energy metabolism. Over 80 years ago, Otto Warburg discovered that in contrast to normal cells which produce most of their ATP via mitochondrial oxidative phosphorylation, cancer cells preferentially utilize glycolysis for production of ATP, a phenomenon known today as the "Warburg effect", and one which has been of great importance in the emergence of novel drugs and chemotherapeutic agents specifically targeting cancer cells. Several groups have reported in recent years that members of the plant stress hormones family of jasmonates, and some of their synthetic derivatives, exhibit anti-cancer activity in vitro and in vivo. Jasmonates have been shown to act directly on mitochondria of cancer cells, leading to mitochondrial swelling, membrane depolarization and cytochrome c release. Throughout the last few years, different groups have demonstrated that combination of jasmonates and various cytotoxic and chemotherapeutic agents yielded a synergistic cytotoxic effect. These results have been demonstrated in a variety of different cancer cell lines and may provide a strong basis for future clinical treatments which involve combination of MJ and different anti-cancerous agents. The potential synergistic effect may allow reduction of the administered dose, decrease of unwanted side effects, and reduction of the likelihood that the tumor will display resistance to the combined therapy.
- PMID:
- 22201595
- [PubMed - as supplied by publisher]
Isoflurane-induced spatial memory impairment by a mechanism independent of amyloid-beta levels and tau protein phosphorylation changes in aged rats.
Source
Chaoyang Hospital, Capital Medical University, Beijing, China.
Abstract
OBJECTIVES:
The molecular mechanism of postoperative cognitive dysfunction is largely unknown. Isoflurane has been shown to promote Alzheimer's disease neuropathogenesis. We set out to determine whether the effect of isoflurane on spatial memory is associated with amyloid-beta (A-beta) levels and tau phosphorylation in aged rats.
METHODS:
Eighteen-month-old male Sprague-Dawley rats were randomly assigned as anesthesia group (n = 31, received 1·4% isoflurane for 2 hours and had behavioral testing), training group (n = 20, received no anesthesia but had behavioral testing), and control group (n = 10, received no anesthesia and had no behavioral testing). Spatial memory was measured before and 2 days after the anesthesia by the Morris water maze. We divided the anesthesia group into an isoflurane-induced severe memory impairment group (SIG, n = 6) and a no severe memory impairment group (NSIG, n = 25), according to whether the escape latency was more than 1·96 stand deviation of that from the training group. Levels of A-beta and tau in the hippocampus were determined by enzyme-linked immunosorbent assay and quantitative western blot at the end of behavioral testing.
RESULTS:
We found that isoflurane increased the escape latency in the SIG as compared to that in the training group and NSIG without affecting swimming speed. However, there were no differences in the levels of A-beta and tau among SIG, NSIG, training, and control groups.
CONCLUSIONS:
Isoflurane may induce spatial memory impairment through non-A-beta or tau neuropathogenesis mechanisms in aged rats.
- PMID:
- 22196855
- [PubMed - in process]
WW domain-containing oxidoreductase promotes neuronal differentiation via negative regulation of glycogen synthase kinase 3β
Source
Institute of Clinical Medicine, National Cheng Kung University Medical College, Tainan, Taiwan.
Abstract
WW domain-containing oxidoreductase (WWOX), a putative tumour suppressor, is suggested to be involved in the hyperphosphorylation of Alzheimer's Tau. Tau is a microtubule-associated protein that has an important role in microtubule assembly and stability. Glycogen synthase kinase 3β (GSK3β) has a vital role in Tau hyperphosphorylation at its microtubule-binding domains. Hyperphosphorylated Tau has a low affinity for microtubules, thus disrupting microtubule stability. Bioinformatics analysis indicated that WWOX contains two potential GSK3β-binding FXXXLI/VXRLE motifs. Immunofluorescence, immunoprecipitation and molecular modelling showed that WWOX interacts physically with GSK3β. We demonstrated biochemically that WWOX can bind directly to GSK3β through its short-chain alcohol dehydrogenase/reductase domain. Moreover, the overexpression of WWOX inhibited GSK3β-stimulated S396 and S404 phosphorylation within the microtubule domains of Tau, indicating that WWOX is involved in regulating GSK3β activity in cells. WWOX repressed GSK3β activity, restored the microtubule assembly activity of Tau and promoted neurite outgrowth in SH-SY5Y cells. Conversely, RNAi-mediated knockdown of WWOX in retinoic acid (RA)-differentiated SH-SY5Y cells inhibited neurite outgrowth. These results suggest that WWOX is likely to be involved in regulating GSK3β activity, reducing the level of phosphorylated Tau, and subsequently promoting neurite outgrowth during neuron differentiation. In summary, our data reveal a novel mechanism by which WWOX promotes neuronal differentiation in response to RA.Cell Death and Differentiation advance online publication, 23 December 2011; doi:10.1038/cdd.2011.188.
[Suppressing poly(ADP-ribose)polymerase-1 inhibits tau phosphorylation in HEK293/tau441 cells].
Source
College of Life Science, Huazhong Normal University, Wuhan 430079, China. E-mail: wsh2002505@163.com.
Abstract
The study aimed to investigate the effect of inhibition of poly(ADP-ribose) polymerase-1 (PARP-1) activity on tauphosphorylation in HEK293/tau441 cells and its mechanism. HEK293/tau441 cells were treated with 3-aminobenzamide (3-AB), a PARP-1 inhibitor, at different doses (0.5, 1, 2, 4 mmol/L). After 24 h, the cell morphology was observed under phase contrast microscope, tau phosphorylation level in different sites (tau-1, tau-5, Thr231) and the activity of glycogen synthase kinase 3 (GSK-3) were detected by Western blotting. The results showed: (1) 3-AB at different doses failed to change the morphology of cells; (2) The 3-AB-induced decrease in activity of PARP-1 resulted in increase of unphosphorylation level in tau-1(Ser195/198/199/202) sites; (3) The phosphorylation of tau was decreased in Thr231 site, while the total tau was slightly changed after 3-AB treatment; (4) With the increased phosphorylation of GSK-3 at Ser9 site, the activity of GSK-3 was decreased after 3-AB treatment. The results suggest that the inhibition of PARP-1 by 3-AB could decrease tau phosphorylation in HEK293/tau441 cells probably through decreasing GSK-3 activity.
Endoplasmic reticulum stress: a new playER in tauopathies.
Source
Center for Neuroscience and Cell Biology, University of Coimbra, Portugal.
Abstract
The accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum (ER) activates the unfolded protein response (UPR), which involves a set of protein signalling pathways and transcription factors that re-establish homeostasis and normal ER function, adapting cells to ER stress. If this adaptive response is insufficient, the UPR triggers an apoptotic program to eliminate irreversibly damaged cells. Recent observations suggest that ER stress plays an important role in the pathogenesis of various neurodegenerative disorders such as Alzheimer's disease, which is characterized by the deposition of amyloid-beta (Abeta) and hyperphosphorylated tau in susceptible brain regions. Moreover, several studies demonstrate that Abeta induces UPR activation, which in turn promotes tau phosphorylation. In the study by Nijholt and colleagues, reported in the current issue of The Journal of Pathology, the association between UPR activation and tau pathology was investigated in the brain of patients diagnosed with sporadic or familial tauopathies in which Abeta deposits are absent. The authors described that increased levels of UPR activation markers are predominantly observed in neurons within the hippocampus, being correlated with early tau phosphorylation. These findings suggest that UPR activation, which occurs in an Abeta-independent manner, is an early event during taupathology and point to a functional crosstalk between these molecular mechanisms in tauopathies. A better understanding of UPR activation in tauopathies can thus contribute to the design of new therapeutic strategies with the purpose of promoting neuronal cell survival in these disorders. Copyright © 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Copyright © 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Propyl isomerase Pin1 promotes APP protein turnover by inhibiting GSK3β kinase activity: A novel mechanism for Pin1 to protect against Alzheimer's disease.
Source
Beth Israel Deaconese Medical Center, United States;
Abstract
Alzheimer's disease (AD) is characterized by the presence of senile plaques of amyloid-beta peptides (Aβ) derived from amyloid precursor protein (APP) and neurofibrillary tangles composed of hyperphosphorylated tau. Increasing APP gene dosage or expression has been shown to cause familial early-onset AD. However, whether protein stability of APP is regulated is unclear. The prolyl isomerase Pin1 and glycogen synthase 3β (GSK3β) have been shown to have the opposite effects on APP processing and tau hyperphosphorylation, relevant to the pathogenesis of AD. However, nothing is known about their relationship. In this study, we found that Pin1 binds to the pT330-P motif in GSK3β to inhibit its kinase activity. Furthermore, Pin1 promotes protein turnover of APP by inhibiting GSK3β activity. A point mutation either at T330, the Pin1-binding site in GSK3β, or T668, the GSK3β phosphorylation site in APP, abolished the regulation of GSK3β activity, T668 phosphorylation and APP stability by Pin1, resulting in reduced non-amyloidogenic APP processing and increased APP levels. These results uncover a novel role of Pin1 in inhibiting GSK3β kinase activity to reduce APP protein levels, providing a previously unrecognized mechanism by which Pin1 protects against Alzheimer's disease.
Effect of chronic administration of estradiol, progesterone, and tibolone on the expression and phosphorylation of glycogen synthase kinase-3β and the microtubule-associated protein tau in the hippocampus and cerebellum of female rat.
Source
Unidad de Investigación Médica en Farmacología, Hospital de Especialidades, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, México D.F., México.
Abstract
Gonadal hormones regulate expression and activation of protein tau. Tibolone is a drug used as first- choice comprehensive treatment for the relief of menopausal symptoms, because it and its various metabolites have estrogenic properties and progestogenic/androgenic effects; however, the effect on the activation of tau protein and its signaling cascade in the brain is unknown. We studied the effect of chronic administration of estradiol (E2), progesterone (P4), and tibolone (TIB) on the expression and phosphorylation of microtubule-associated protein tau and glycogen synthase kinase-3β (GSK3β) in the hippocampus and cerebellum of ovariectomized rats. Ovariectomized adult female rats were implanted with pellets of vehicle, E2, or P4 or were treated with TIB by oral administration for 60 days. The animals were sacrificed, and tissue proteins were analyzed by Western blot. We observed that, in the hippocampus, administration of E2, P4, or TIB significantly decreased the protein content of hyperphosphorylated tau and increased the taudephosphorylated form, whereas only treatment with TIB increased the content of the phosphorylated form of GSK3β. In the cerebellum, E2 and TIB treatments resulted in a significant decrease in the expression of hyperphosphorylated tau, whereas E2 and TIB increased phosphorylated GSK3β; P4 had no effect. These results indicate that chronic administration of gonadal hormones and tibolone modulates tau and GSK3β phosphorylation in hippocampus and cerebellum of the rat and may exert a neuroprotective effect in these tissues. © 2011 Wiley Periodicals, Inc.
Copyright © 2011 Wiley Periodicals, Inc.
Targeting hyperphosphorylated tau with sodium selenate suppresses seizures in rodent models.
Source
Department of Medicine, The Royal Melbourne Hospital, The University of Melbourne, Parkville, VIC, Australia.
Abstract
Tau hyperphosphorylation has been implicated in the pathogenesis of a variety of forms of human epilepsy. Here we investigated whether treatment with sodium selenate, a drug which reduces pathological hyperphosphorylated tau by enhancement of PP2A activity, would inhibit seizures in rodent models. In vitro, sodium selenate reduced tauphosphorylation in human neuroblastoma cells and reversed the increase in tau phosphorylation induced by the PP2A inhibitor, okadaic acid. Sodium selenate treatment was then tested against three different rodent seizure models. Firstly the propensity of 6-Hz electrical corneal stimulation to induce seizures in adult mice was assessed following acute treatment with different doses of sodium selenate. Secondly, the number of seizures induced by pentylenetetrazole (PTZ) was quantified in rats following chronic sodium selenate treatment via drinking water. Finally, amygdala kindled rats were chronically treated with sodium selenate in drinking water and the length and the severity of the seizures evoked by stimulation of the amygdala recorded. The results demonstrated a dose-dependent protection of sodium selenate against 6-Hz stimulation induced seizures, and significant reduction in the total number of seizures following PTZ injection. Amygdala kindled rats chronically treated with sodium selenate had significantly shorter seizure duration compared controls, with more pronounced effects observed as the duration of treatment increased. The results of this study indicate that targeting hyperphosphorylated tau by treatment with sodium selenate has anti-seizure effects in a broad range of rodent models, and may represent a novel approach to treatment of patients with epilepsy.
Copyright © 2011. Published by Elsevier Inc.
Tau-Targeted Immunization Impedes Progression of Neurofibrillary Histopathology in Aged P301L Tau Transgenic Mice.
Source
Laboratory for Translational Neurodegeneration, Brain and Mind Research Institute, The University of Sydney, Camperdown, New South Wales, Australia.
Abstract
In Alzheimer's disease (AD) brains, the microtubule-associated protein tau and amyloid-β (Aβ) deposit as intracellular neurofibrillary tangles (NFTs) and extracellular plaques, respectively. Tau deposits are furthermore found in a significant number of frontotemporal dementia cases. These diseases are characterized by progressive neurodegeneration, the loss of intellectual capabilities and behavioral changes. Unfortunately, the currently available therapies are limited to symptomatic relief. While active immunization against Aβ has shown efficacy in both various AD mouse models and patients with AD, immunization against pathogenic tau has only recently been shown to prevent pathology in young tautransgenic mice. However, if translated to humans, diagnosis and treatment would be routinely done when symptoms are overt, meaning that the histopathological changes have already progressed. Therefore, we used active immunization to target pathogenic tau in 4, 8, and 18 months-old P301L tau transgenic pR5 mice that have an onset of NFT pathology at 6 months of age. In all age groups, NFT pathology was significantly reduced in treated compared to control pR5 mice. Similarly, phosphorylation of tau at pathological sites was reduced. In addition, increased astrocytosis was found in the oldest treated group. Taken together, our data suggests that tau-targeted immunization slows the progression of NFT pathology in mice, with practical implications for human patients.
Mechanistic involvement of the calpain-calpastatin system in Alzheimer neuropathology.
Source
*Laboratory for Proteolytic Neuroscience, Rikagaku Kenkyūjo (RIKEN) Brain Science Institute, Wako, Saitama, Japan;
Abstract
The mechanism by which amyloid-β peptide (Aβ) accumulation causes neurodegeneration in Alzheimer's disease (AD) remains unresolved. Given that Aβ perturbs calcium homeostasis in neurons, we investigated the possible involvement of calpain, a calcium-activated neutral protease. We first demonstrated close postsynaptic association of calpain activation with Aβ plaque formation in brains from both patients with AD and transgenic (Tg) mice overexpressing amyloid precursor protein (APP). Using a viral vector-based tracer, we then showed that axonal termini were dynamically misdirected to calpain activation-positive Aβ plaques. Consistently, cerebrospinal fluid from patients with AD contained a higher level of calpain-cleaved spectrin than that of controls. Genetic deficiency of calpastatin (CS), a calpain-specific inhibitor protein, augmented Aβ amyloidosis, tau phosphorylation, microgliosis, and somatodendritic dystrophy, and increased mortality in APP-Tg mice. In contrast, brain-specific CS overexpression had the opposite effect. These findings implicate that calpain activation plays a pivotal role in the Aβ-triggered pathological cascade, highlighting a target for pharmacological intervention in the treatment of AD.-Higuchi, M., Iwata, N., Matsuba, Y., Takano, J., Suemoto, T., Maeda, J., Ji, B., Ono, M., Staufenbiel, M., Suhara, T., Saido, T. C. Mechanistic involvement of the calpain-calpastatin system in Alzheimer neuropathology.
Autophagic degradation of tau in primary neurons and its enhancement by trehalose.
Source
Max-Planck-Unit for Structural Molecular Biology, Hamburg, Germany; DZNE, German Center for Neurodegenerative Diseases, and CAESAR, Bonn, Germany.
Abstract
Modulating the tau level may represent a therapeutic target for Alzheimer's disease (AD), as accumulating evidence shows that Abeta-induced neurodegeneration is mediated by tau. It is therefore important to understand the expression and degradation of tau in neurons. Recently we showed that overexpressed mutant tau and tau aggregates are degraded via the autophagic pathway in an N2a cell model. Here we investigated whether autophagy is involved in the degradation of endogenous tau in cultured primary neurons. We activated this pathway in primary neurons with trehalose, an enhancer of autophagy. This resulted in the reduction of endogenous tau protein. Tau phosphorylation at several sites elevated in AD pathology had little influence on its degradation by autophagy. Furthermore, by using a neuronal cell model of tauopathy, we showed that activation of autophagy suppresses tau aggregation and eliminates cytotoxicity. Notably, apart from activating autophagy, trehalose also inhibits tau aggregation directly. Thus, trehalose may be a good candidate for developing therapeutic strategies for AD and other tauopathies.
Copyright © 2011 Elsevier Inc. All rights reserved.
Early Improved and Late Defective Cognition Is Reflected by Dendritic Spines in Tau.P301L Mice.
Source
Laboratory of Experimental Genetics and Transgenesis/Experimental Genetics Group, Department of Human Genetics, Katholieke Universiteit Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium.
Abstract
Cognitive demise correlates with progressive brain tauopathy in dementing patients. Improved cognition of youngTau.P301L mice contrasts with dysfunction later in life and remains unexplained (Boekhoorn et al., 2006). To unravel early mechanisms, we composed a correlative time line of clinical symptoms, cognitive defects, and biochemical and pathological traits, including comprehensive analysis of dendritic spines in specified regions of the cortex and hippocampus of young and adult Tau.P301L mice. Remarkably, young Tau.P301L mice have not more, but more mature spines than wild-type mice, revealing the anatomical substrate for their improved cognition and LTP. Spine maturation remained high in the hippocampus of adult Tau.P301L mice. However, spines regressed in length paralleling impaired cognition and increased Tau phosphorylation (Terwel et al., 2005). Conversely, spine maturation was unaffected in adultTau.4R mice, while spine density was increased and length reduced similar to Tau.P301L mice. To explain how proteinTau promoted spinogenesis, we analyzed hippocampal synaptosomes and dendritic spines for mouse and human Tau. While synaptosomes were positive for both mouse and human Tau, weak variable reaction in spines was observed only after fixation according to Bouin. Mouse Tau was absent from spines in wild-type mice, dissociating the pathological actions of Tau in transgenic mice by relocalization into dendrites and spines from the physiological actions of proteinTau in axons only. We conclude that mutant protein Tau modulates cognition and morphology of spines similarly and in both directions, with pathology later in life coinciding with increased phosphorylation and relocalization of Tau from axons to soma and processes.
Enriched odor exposure decrease tau phosphorylation in the rat hippocampus and cortex.
Source
Department of Pathophysiology, Key Laboratory of Neurological Diseases of Education Committee of China, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, PR China.
Abstract
Abnormally hyperphosphorylated microtubule-associated protein tau is the main component of the neurofibrillary tangles (NFT), a hallmark pathological feature of Alzheimer's disease (AD). A lot of studies suggested that there is highly neurobiological correlation between olfactory dysfunction and AD-like pathology, but the effect of the odor stimulation ontau phosphorylation remains unknown. Here, we examined the effect of short-term and long-term enriched odor exposure on the alterations of tau phosphorylation at multiple sites in the rat brains. We found that short-term odor enrichment did not affect the phosphorylation of tau, while long-term odor enrichment dramatically reduce the phosphorylation level oftau at Ser198/199/202, Thr231, Ser396, and Ser404 sites both in the hippocampus and cortex. These data suggest that long-term odor exposure prevent tau phosphorylation and may be a new therapeutic strategy of AD.
Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.
Presynaptic dopamine D3 receptor mediates cocaine-induced structural plasticity in mesencephalic dopaminergic neurons via ERK and Akt pathways.
Source
Department of Biomedical Sciences and Biotechnologies, National Institute of Neuroscience-Italy Woman Health Center-Camillo Golgi Foundation, University of Brescia, Brescia, Italy IRCCS San Camillo Hospital, Venice, Italy Neuronal Targets DPU, Respiratory TAU, GlaxoSmithKline, King of Prussia, PA, USA Division of Psychopharmacology, Institut de Recherches Servier, Croissy-Sur-Seine (Paris), France.
Abstract
Exposure to psychostimulants results in neuroadaptive changes of the mesencephalic dopaminergic system including morphological reorganization of dopaminergic neurons. Increased dendrite arborization and soma area were previously observed in primary cultures of mesencephalic dopaminergic neurons after 3-day exposure to dopamine agonists via activation of D3 autoreceptors (D3R). In this work we showed that cocaine significantly increased dendritic arborization and soma area of dopaminergic neurons from E12.5 mouse embryos by activating phosphorylation of extracellular signal-regulated kinase (ERK) and thymoma viral proto-oncogene (Akt). These effects were dependent on functional D3R expression since cocaine did not produce morphological changes or ERK/Akt phosphorylation neither in primary cultures of D3R mutant mice (D3KO) nor following pharmacologic blockade with D3R antagonists SB-277011-A and S-33084. Cocaine effects on morphology and ERK/Akt phosphorylation were inhibited by pre-incubation with the phosphatidylinositol 3-kinase inhibitor LY294002. These observations were corroborated in vivo by morphometrical assessment of mesencephalic dopaminergic neurons of P1 newborns exposed to cocaine from E12.5 to E16.5. Cocaine increased the soma area of wild-type but not of D3KO mice, supporting the translational value of primary culture. These findings indicate a direct involvement of D3R and ERK/Akt pathways as critical mediators of cocaine-induced structural plasticity, suggesting their involvement in psychostimulant addiction.
Journal of Neurochemistry © 2011 International Society for Neurochemistry.
Insights into Mitochondrial Dysfunction: Aging, Amyloid-β and Tau - a deleterious trio.
Source
Universitäre Psychiatrische Kliniken Basel, Neurobiology Lab for Brain Aging & Mental Health, Basel, Switzerland; karen.schmitt@upkbs.ch.
Abstract
Significance. Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder mainly affecting elderly individuals. The pathology of AD is characterized by amyloid plaques (aggregates of amyloid-β (Aβ)) and neurofibrillary tangles (aggregates of tau), but the mechanisms underlying this dysfunction are still partially unclear. Recent Advances. A growing body of evidence supports mitochondrial dysfunction as a prominent and early, chronic oxidative stress-associated event that contributes to synaptic abnormalities and, ultimately, selective neuronal degeneration in AD. Critical issues. In this review, we discuss on the one hand whether mitochondrial decline observed in brain aging is a determinant event in the onset of AD and on the other hand the close inter-relationship of this organelle with Aβ and tauin the pathogenic process underlying AD. Moreover, we summarize evidence from aging and Alzheimer models showing that the harmful trio "aging, Aβ and tau protein" triggers mitochondrial dysfunction through a number of pathways, such as impairment of oxidative phosphorylation, elevation of reactive oxygen species production and interaction with mitochondrial proteins, contributing to the development and progression of the disease. Future Directions. The aging process may weaken the mitochondrial OXPHOS system in a more general way over many years providing a basis for the specific and destructive effects of Aβ and tau. Establishing strategies involving efforts to protect cells at the mitochondrial level by stabilizing or restoring mitochondrial function and energy homeostasis appears to be challenging, but very promising route on the horizon.
Dyrk1A Positively Stimulates ASK1-JNK Signaling Pathway during Apoptotic Cell Death.
Source
Department of Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea.
Abstract
Dual-specificity tyrosine (Y)-phosphorylation-regulated protein kinase 1A (Dyrk1A) is the mammalian homologue of Drosophila melanogaster minibrain and its human gene is mapped to the Down syndrome critical region of chromosome 21. Dyrk1A phosphorylates several transcription factors, including NFAT and CREB and a number of cytosolic proteins such as APP, tau, and α-synuclein. Although Dyrk1A is involved in the control of cell growth and postembryonic neurogenesis, its potential role during cell death and signaling pathway is not clearly understood. In the present study, we show that Dyrk1A is activated under the condition of apoptotic cell death. In addition, Dyrk1A is coupled to JNK1 activation, and directly interacts with apoptosis signal-regulating kinase 1 (ASK1). Moreover, Dyrk1A positively regulates ASK1-mediated JNK1-signaling, and appears to directly phosphorylate ASK1. These data indicate that Dyrk1A regulates cell death through facilitating ASK1-mediated signaling events.
MED1 coactivation of androgen receptor-dependent transcription is mediated through a newly discovered noncanonical binding motif.
Source
Robert Wood Johnson Medical School, UMDNJ, United States;
Abstract
Nuclear receptor (NR) activation by cognate ligand generally involves allosteric realignment of carboxy-terminal α-helices thus generating a binding surface for coactivators containing canonical LxxLL α-helical motifs. The androgen receptor (AR) is uncommon among NRs in that ligand triggers an intramolecular interaction between its amino- and carboxy-terminal domains (termed the N/C interaction) and that coactivators can alternatively bind to surfaces in the AR amino-terminal or hinge regions. The evolutionary conserved Mediator complex plays a key coregulatory role in steroid hormone-dependent transcription and is chiefly targeted to NRs via the LxxLL-containing MED1 subunit. Whereas MED1 has been demonstrated to serve as a key transcriptional coactivator for AR, the mechanisms by which AR recruits MED1 have remained unclear. Here we show that MED1 binds to a distinct AR amino-terminal region termed transactivation unit-1 (Tau-1) via two newly discovered noncanonical α-helical motifs located between MED1 residues 505 and 537. Neither of the two MED1 LxxLL motifs are required for AR binding whereas loss of the intramolecular AR N/C interaction decreases MED1 binding. We further demonstrate that mitogen-activated protein kinase phosphorylationof MED1 enhances the AR-MED1 interaction in prostate cancer cells. In sum, our findings reveal a novel AR-coactivator binding mechanism that may have clinical implications for AR activity in prostate cancer.
Endoplasmic Reticulum Stress Induces Tau Pathology and Forms a Vicious Cycle: Implication in Alzheimer's Disease Pathogenesis.
Source
Laboratory of Neurodegenerative Diseases, Department of Anatomy, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
Abstract
Accumulation of unfolded proteins can disturb the functions of the endoplasmic reticulum (ER), leading to ER-stress or unfolded protein response (UPR). Recent data have shown that activation of UPR can be found in postmortem brains of Alzheimer's disease (AD) patients; and biological markers for activation of UPR are abundant in neurons with diffuse phosphorylated tau. Although these observations suggest a linkage between ER-stress and tau pathology, little is known of their relationship. In this study, we found that high levels of phosphorylated PKR-like ER-resident kinase (p-PERK) and phosphorylated eukaryotic initiation factor 2 alpha (p-eIF2α) as markers for activation of UPR in the hippocampus of aged P301L mutant tau transgenic mice. The immunoreactivity of p-PERK was found to co-localize with that of phosphorylated tau. We then hypothesized that phosphorylation of tau could induce ER-stress and vice versa in promoting AD-like pathogenesis. By using the protein phosphatase 2A inhibitor okadaic acid (OA) as an inducer forphosphorylation of tau, we found that primary cultures of rat cortical neurons treated with OA triggered UPR as indicated by increased levels of p-PERK and p-eIF2α, splicing of mRNA for xbp-1 and elevated levels of mRNA for GADD153. On the other hand, thapsigargin as an ER-stress inducer stimulated phosphorylation of tau at Thr231, Ser262 and Ser396. Thapsigargin also induced activation of caspase-3 and cleavage of tau. These findings suggested that ER-stress and hyperphosphorylation of tau could be induced by each other to form a vicious cycle to propagate AD-like neurodegeneration.
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