|Chronic psychosocial stress triggers cognitive impairment in a novel at-risk model of Alzheimer's disease. |
Tran TT, Srivareerat M, Alkadhi KA
Neurobiology of disease
756-63. Epub 2010 Jan 4.
Although it is generally accepted that Abeta contributes to the pathogenesis of Alzheimer's disease (AD), other factors that impact the severity and time of onset of the disease are not well known. Aside from genetic factors, environmental factors such as stress may also play a critical role in the manifestation of AD. The present study examined the effect of chronic psychosocial stress in an at-risk, subthreshold Abeta (subAbeta) rat model of AD by three approaches: learning and memory tests in the radial arm water maze, electrophysiological recordings of long-term potentiation (LTP) in anesthetized rats, and immunoblot analysis of learning- and memory-related signaling molecules. Chronic psychosocial stress was induced using a rat intruder model. The subAbeta rat model of AD was induced by continuous i.c.v. infusion of 160 pmol/day Abeta(1-42) via a 14-day osmotic pump. Behavioral tests and electrophysiological recordings showed that subAbeta rats were not significantly different from control rats. However, chronically stressed subAbeta rats showed more significant impairment of cognitive functions and early-phase LTP (E-LTP) than that caused by stress alone. Molecular analysis of essential signaling molecules after induction of E-LTP revealed an increase in the levels of p-CaMKII in control as well as subAbeta infused rats, but not in stressed or stressed at-risk rats. In addition, compared to unstimulated control, the levels of both total CaMKII and calcineurin were increased in all stimulated animals groups after HFS. These findings suggest that the stress-induced alterations may accelerate the impairment of cognition and synaptic plasticity in individuals "at-risk" for AD. 2010 Elsevier Inc. All rights reserved.
|Regulation of calcineurin activity in insulin-secreting cells: stimulation by Hsp90 during glucocorticoid-induced apoptosis. |
Felicia Ranta,Martina Düfer,Björn Stork,Sebastian Wesselborg,Gisela Drews,Hans-Ulrich Häring,Florian Lang,Susanne Ullrich
Previously, we described that apoptotic cell death induced by the synthetic glucocorticoid dexamethasone (dex) is inhibited by calcineurin inhibitors, FK506 and deltamethrin, in insulin-secreting cells. The aim of the present study was to examine the mechanism of dex-dependent activation of calcineurin. In INS-1 cells cultured up to 4d with dex (100 nmol/l), the percentage of apoptosis, quantified by condensed nuclei and TUNEL positive cells, increased from 1% to 10.9%. FK506 inhibited dex-mediated cell death. Apoptosis was significantly higher at glucose concentrations that induce [Ca(2+)](i) oscillations than at low, non-stimulatory glucose. Dex had no acute effect on [Ca(2+)](i). Calcineurin activity, measured in control and dex-treated cell homogenates, revealed that maximal activity and the sensitivity to the substrate RII peptide was unaltered. However, dex treatment significantly increased enzyme activity at submaximal, physiological Ca(2+) concentrations. Dex did not stimulate the Ca(2+)-dependent protease calpain, known to activate calcineurin by cleavage, as no cleaved calcineurin was detectable. Furthermore, the calpain inhibitor ALLN did not counteract dex-dependent cell death. Western blotting revealed that in dex-treated cells heat shock protein 90 (Hsp90), a component of the glucocorticoid receptor (GR) known to stimulate calcineurin, was increased while calcineurin protein levels were unchanged. In immunoprecipitates with calcineurin antibodies, Hsp90 was only detected in dex-treated cell homogenates. These data suggest that dex-induced apoptosis involves release of Hsp90 from the stimulated GR complex, subsequent binding to and activation of calcineurin, that may contribute to dex-mediated cell death in the presence of high glucose.
|Differential calcineurin signalling activity and regeneration efficacy in diaphragm and limb muscles of dystrophic mdx mice. |
Nicole Stupka, Belinda J Michell, Bruce E Kemp, Gordon S Lynch
Neuromuscular disorders : NMD
Calcineurin activity is essential for successful skeletal muscle regeneration in young mdx mice and in wild type mice following myotoxic injury and cryodamage. In mature myofibres of adult mdx mice, calcineurin stimulation can ameliorate the dystrophic pathology. The aim of this study was to test the hypothesis that the more severe dystrophic pathology of the diaphragm compared with hindlimb muscles of mdx mice could be attributed to aberrant calcineurin signalling and that due to ongoing regeneration calcineurin activity would be greater in muscles of adult mdx than wild type mice. Differences in markers of regeneration between tibialis anterior and diaphragm muscles were also characterised, to determine whether there was an association between regeneration efficacy and calcineurin activity in dystrophic muscles. In diaphragm muscles of adult mdx mice, the proportion of centrally nucleated fibres and developmental myosin heavy chain protein expression was lower and myogenin protein expression was higher than in tibialis anterior muscles. Calcineurin and activated NFATc1 protein content and calcineurin phosphatase activity were higher in muscles from mdx than wild type mice and calcineurin activation was greater in diaphragm than tibialis anterior muscles of mdx mice. Thus, despite greater calcineurin activity in diaphragm compared to hindlimb muscles, regeneration events downstream of myoblast differentiation and mediated by the injured myofibre were severely compromised.
|The calcineurin signal transduction pathway is essential for successful muscle regeneration in mdx dystrophic mice. |
Nicole Stupka, Paul Gregorevic, David R Plant, Gordon S Lynch
Although mdx mice share the same genetic defect and lack dystrophin expression as in Duchenne muscular dystrophy (DMD), their limb muscles have a high regenerative capacity that ensures a more benign phenotype and essentially normal function. The cellular pathways responsible for this enhanced regenerative capacity are unknown. We tested the hypothesis that the calcineurin signal transduction pathway is essential for the successful regeneration following severe degeneration observed in the limb muscles of young mdx mice (2-4 weeks old) and that inhibition of this pathway using cyclosporine A (CsA) would exacerbate the dystrophic pathology. Eighteen-day-old mdx and C57BL/10 mice were treated with CsA for 16 days. CsA administration severely disrupted muscle regeneration in mdx mice, but had minimal effect in C57BL/10 mice. Muscles from CsA-treated mdx mice had fewer centrally nucleated fibers and extensive collagen, connective tissue, and mononuclear cell infiltration than muscles from vehicle-treated littermates. The deleterious effects of CsA on muscle morphology were accompanied by a 30-35% decrease in maximal force producing capacity. Taken together, these observations indicate that the calcineurin signal transduction pathway is a significant determinant of successful skeletal muscle regeneration in young mdx mice. Up-regulating this pathway may have clinical significance for DMD.