236 research outputs found
Endogenous Aβ causes cell death via early tau hyperphosphorylation
No full textAlzheimer's disease (AD) is characterized by A beta overproduction and tau hyperphosphorylation. We report that an early, transient and site-specific AD-like tau hyperphosphorylation at Ser262 and Thr231 epitopes is temporally and causally related with an activation of the endogenous amyloidogenic pathway that we previously reported in hippocampal neurons undergoing cell death upon NGF withdrawal [Matrone, C., Ciotti, M. T., Mercanti, D., Marolda, R., Calissano, P., 2008b. NGF and BDNF signaling control amyloidogenic route and Ab production in hippocampal neurons. Proc. Natl. Acad. Sci. 105, 13138-13143]. Such tau hyperphosphorylation, as well as apoptotic death, is (i) blocked by 4G8 and 6E10 A beta antibodies or by specific beta and/or gamma-secretases inhibitors; (ii) temporally precedes tau cleavage mediated by a delayed (6-12 h after NGF withdrawal) activation of caspase-3 and calpain-I; (iii) under control of Akt-GSK3 beta-mediated signaling. Finally, we show that such site-specific tau hyperphosphorylation causes tau detachment from microtubules and an impairment of mitochondrial traffickin
Endogenous A beta causes cell death via early tau hyperphosphorylation
No full textAlzheimer's disease (AD) is characterized by A beta overproduction and tau hyperphosphorylation. We report that an early, transient and site-specific AD-like tau hyperphosphorylation at Ser262 and Thr231 epitopes is temporally and causally related with an activation of the endogenous amyloidogenic pathway that we previously reported in hippocampal neurons undergoing cell death upon NGF withdrawal [Matrone, C., Ciotti, M. T., Mercanti, D., Marolda, R., Calissano, P., 2008b. NGF and BDNF signaling control amyloidogenic route and Ab production in hippocampal neurons. Proc. Natl. Acad. Sci. 105, 13138-13143]. Such tau hyperphosphorylation, as well as apoptotic death, is (i) blocked by 4G8 and 6E10 A beta antibodies or by specific beta and/or gamma-secretases inhibitors; (ii) temporally precedes tau cleavage mediated by a delayed (6-12 h after NGF withdrawal) activation of caspase-3 and calpain-I; (iii) under control of Akt-GSK3 beta-mediated signaling. Finally, we show that such site-specific tau hyperphosphorylation causes tau detachment from microtubules and an impairment of mitochondrial trafficking.These results depict, for the first time, a rapid interplay between endogenous A beta and tau post-translational modifications which act co-ordinately to compromise neuronal functions in the same neuronal system, under physiological conditions as seen in AD brain. (C) 2009 Elsevier Inc. All rights reserved
In vitro cultured neurons for molecular studies correlating apoptosis with events related to Alzheimer disease
No full textThis short review analyses the possible molecular events linking a general program of death such as apoptosis to highly specific intracellular pathways involving the function and degradation of two proteins - tau and amyloid precursor protein - which in their aggregated state constitute the hallmark of Alzheimer disease. By surveying the recent studies carried out in 'in vitro' neuronal cultures - with special emphasis to cerebellar granule neurons - the apparent correlation between onset of apoptosis, tau cleavage with formation of potential toxic fragments, and activation of an amyloidogenic route are discussed. Within this framework, proteasomes seem to play a crucial role upstream of the proteolytic cascade involving caipain(s) and caspase(s) by contributing to tau and amyloid precursor protein-altered breakdown and consequent tendency to aggregation of their degradation fragments. Thus, apoptotic death due to altered supply of anti apoptotic agents, neurotrophic factors, deafferentiation or other causes, may constitute a major trigger of the onset of Alzheimer disease
Nerve growth factor inhibits the synthesis of a single-stranded DNA binding protein in pheochromocytoma cells (clone PC12)
No full textArrest of mitosis and neurite outgrowth induced by nerve growth factor (NGF) in rat pheochromocytoma cells (clone PC12) is accompanied by a progressive inhibition of the synthesis of a protein that binds to single-stranded but not to double-stranded DNA. Time course experiments show that this inhibition is already apparent after a 2-day incubation with NGF and is maximum (85-95%) upon achievement of complete PC12 cell differentiation. Inhibition of the synthesis of this single-stranded DNA binding protein after 48 hr of incubation with NGF is potentiated by concomitant treatment of PC12 cells with antimitotic drugs acting at different levels of DNA replication. Purification on a preparative scale of this protein and analysis of its major physicochemical properties show that: (i) it constitutes 0.5% of total soluble proteins of naive PC12 cells; (ii) its molecular weight measured by NaDodSO4/PAGE is Mr 34,000 (sucrose gradient centrifugation under nondenaturing conditions yields a sedimentation coefficient s20,w of 8.1 S, indicating that the native protein is an oligomer); (iii) amino acid analysis demonstrates a preponderance of acidic over basic residues, while electrofocusing experiments show that it has an isoelectric point around 8.0; (iv) approximately 15% of the protein is phosphorylated in vivo. It is postulated that control of the synthesis of this protein is connected with activation of a differentiative program triggered by NGF in the PC12 neoplastic cell line at some step(s) of DNA activity
A macromolecular structure favouring microtubule assembly in NGF-differentiated pheochromocytoma cells (PC12)
No full textCellular extracts derived from pheochromocytoma cells (PC12-) inhibit the assembly of calf brain tubulin, while those derived from nerve growth factor-differentiated cells (PC12+) do not display this effect. Incubation with RNase abolishes the inhibition by PC12- extracts and reveals the presence of an activating effect exerted by PC12+ extracts. Activation of microtubule assembly is enhanced when extracts are prepared from PC12+ cells exposed for 1 day to 1.0 microM taxol and is abolished when PC12+ extracts are: (a) prepared from cells incubated for 1 day with 1 microM colchicine, (b) treated with the non-ionic detergent Nonidet P-40 or (c) centrifuged at 100 000 g instead of 80 000 g. 2D gel electrophoresis of the proteins of the 100 000 g pellet responsible for the activating effect (referred to as 100 K g pellet) reveals the presence of 100 K, 88 K and 32 K proteins which are markedly enriched in PC12+ extracts. The 88 K protein is further enriched in taxol-treated cells and markedly reduced in the same cells incubated with colchicine. A correlation between the differential protein composition of the 100 K g pellets and their effect on microtubule formation is postulated
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