NMDA receptors mediate heat shock protein induction in the mouse brain following administration of the ibotenic acid analogue AMAA

HSP70 induction and oxidative stress protection mediated by a subtoxic dose of NMDA in the retinoic acid-differentiated C6 glioma cell line

NMDA class of glutamate receptors plays an important role in regulating toxic and plastic responses in CNS. Astrocytes are the predominant cell type in the adult CNS and recent studies have suggested their role in many aspects of CNS function and dysfunction. We report here the protective effect of a subtoxic dose of NMDA in retinoic acid differentiated C6 glioma cell cultures. C6 glioma cell cultures differentiated with retinoic acid (10 microM) were exposed to NMDA (100 microM) or to antagonist MK-801 (200 nM) alone as well as with NMDA and cells were harvested after 24h of treatment to study the expression of HSP70 and for biochemical assay of free radical scavenger system. The protection imparted by a subtoxic dose of NMDA was checked by challenging the differentiated controls as well as NMDA treated and MK-801 treated cultures with a toxic dose of glutamate and subsequently estimating the free radical scavenger system profile. Biochemical analysis revealed a significant increase in the activities of glutathione peroxidase (GPx), copper zinc-superoxide dismutase (CuZnSOD) and reduced glutathione (GSH) content upon exposure to NMDA. No significant change was observed in the level of lipid peroxidation (LPx). A significant increase was observed in HSP70 expression as seen by Western blotting and immunocytofluorescent studies in NMDA treated cultures. Treatment of cultures with MK-801 alone, a non-competitive NMDA receptor antagonist, or pretreatment with MK-801 prior to NMDA exposure prevented the NMDA mediated changes indicating the involvement of NMDA receptors mediated mechanism. The results illustrate the protective effect of a subtoxic dose of NMDA in RA differentiated C6 glioma cell line.

Neuroprotection mediated by subtoxic dose of NMDA in SH-SY5Y neuroblastoma cultures: activity-dependent regulation of PSA-NCAM expression

The NMDA class of glutamate receptors plays a critical role in CNS, such as synaptic plasticity, axonal sprouting, growth, and migration. NMDA receptor stimulation has been shown to regulate polysialylated neural cell adhesion molecule (PSA-NCAM) expression in glial cell cultures and in hippocampal slice cultures. There is also growing evidence that molecular chaperons and ROS are related to the synaptic plasticity phenomena. We have examined the neuroprotective effect of subtoxic dose of NMDA in retinoic acid differentiated SH-SY5Y neuroblastoma cells. SH-SY5Y cell line differentiated with retinoic acid (10 muM) was exposed to NMDA (100 microM) or to antagonist MK-801 (200 nM) + NMDA and cells harvested after 24 h of treatment for PSA-NCAM, NCAM, and HSP70 expression study and for biochemical analysis. A significant increase was observed in PSA-NCAM, NCAM-180, NCAM-140, and HSP70 expression as seen by Western blotting and immunocytofluorescent studies in NMDA-treated cultures. Biochemical analysis revealed a significant increase in the activities of glutathione peroxidase (GPx) and copper zinc-superoxide dismutase (CuZnSOD) upon exposure to NMDA. No significant change was observed in the level of lipid peroxidation. All the changes observed reverted back to the control values upon pretreatment of cultures with MK-801, a non-competitive NMDA receptor antagonist, prior to NMDA exposure indicating the involvement of NMDA receptor in these changes. These results illustrate the neuroprotective role of subtoxic dose of NMDA in SH-SY5Y neuroblastoma cells.

Characterization of spinal HSP72 induction and development of ischemic tolerance after spinal ischemia in rats

Induction of heat shock protein (HSP72) has been implicated in the development of ischemic tolerance in several tissue organs including brain and spinal cord. In the present study, using an aortic balloon occlusion model in rats, we characterized the effect of transient noninjurious (3 or 6 min) or injurious intervals (10 min) of spinal ischemia followed by 4-72 h of reflow on spinal expression of HSP72 and GFAP protein. In a separate group of animals, the effect of ischemic preconditioning (3 or 6 min) on the recovery of function after injurious interval of spinal ischemia (10 min) was studied. After 3 min of ischemia, there was a modest increase in HSP72 protein immunoreactivity in the dorsal horn neurons at 12 h after reperfusion. After 6 min of ischemia, a more robust and wide spread HSP72 protein expression in both dorsal and ventral horn neurons was detected. The peak of the expression was seen at 24 h after ischemia. At the same time point, a significant increase in spinal tissue GFAP expression was measured with Western blots and corresponded morphologically with the presence of activated astrocytes in spinal segments that had been treated similarly. After 10 min of ischemia and 24 h of reflow, a significant increase in spinal neuronal HSP72 expression in perinecrotic regions was seen. Behaviorally, 3 min preconditioning ischemia led to the development of a biphasic ischemic tolerance (the first at 30 min and the second at 24 h after preconditioning) and was expressed as a significantly better recovery of motor function after exposure to a second 10-min interval of spinal ischemia. After 6 min ischemic preconditioning, a more robust ischemic tolerance at 24 h after preconditioning then seen after 3-min preconditioning was detected. These data indicate that 3 min of spinal ischemia represents a threshold for spinal neuronal HSP72 induction, however, a longer sublethal interval (6 min) of preconditioning ischemia is required for a potent neuronal HSP72 induction. More robust neurological protection, seen after 6 min of preconditioning ischemia, also indicates that HSP72 expression in spinal interneurons seen at 24 h after preconditioning may represent an important variable in modulating ischemic tolerance observed during this time frame.

Glutamate receptor antagonists modulate heat shock protein response in focal brain ischemia

Neurons and glia reacting to ischemic injury exhibit delayed expression of heat shock proteins (HSPs). We tested the hypothesis that glutamate receptor antagonists alter neuronal and glial activation during focal cerebral ischemia, as shown by spatio-temporal changes in HSP immunoreactivity. Rats underwent focal ischemia by permanent occlusion of the middle cerebral artery. All animals were pre-treated with NBQX (30 mg kg-1), a competitive antagonist of the AMPA/kainate receptor, or CGS-19755 (10 mg kg-1), a competitive NMDA receptor antagonist, and euthanatized after 6 or 24 h of ischemia to demonstrate regional immunoreactivity of HSP-72 or 32 in brain. Neurons immunolabeled for HSP-72 appeared in the penumbral region adjacent to the infarct at 24 h and increased in number and distribution after pretreatment with NBQX or CGS-19755. Immunolabeling for HSP-32 revealed that pre-treatment with CGS-19755 caused ramified glia to infiltrate the ischemic cortex at 6 h, a pattern that was not seen in ischemic controls until 24 h. Blockade of the NMDA or AMPA/kainate receptor modulates cellular stress responses in both neurons and glia within the developing infarct. We conclude that early, rather than delayed, expression of HSP-32 is a sensitive indicator of glial activation induced specifically by CGS-19755.

Psychophysiological stress induces heat shock cognate protein 70 messenger RNA in the hippocampus of rats

Psychophysiological stress has been shown to increase 70,000 mol. wt heat shock protein messenger RNAs with northern blotting in rats. However, its localization is unknown. With in situ hybridization, we tested our hypothesis that restraint water-immersion stress may induce heat shock cognate protein 70 messenger RNA expression simultaneously with some morphological changes selectively in the hippocampus of rats. Stress for 6 h significantly increased heat shock cognate protein 70 messenger RNAs in the hippocampus, with maximal intensity in the CA3 subfield of the Ammon's horn and to a lesser extent in CA2. Stress for 12 h significantly increased heat shock cognate protein 70 messenger RNAs in the whole hemisphere including the cerebral cortex, the thalamus, the hypothalamus, and the hippocampus with the highest density in CA3. Heat shock cognate protein 70 messenger RNA in rats with stress for 6 h followed by recovery for 6 h significantly increased at CA3 and CA2 compared with the controls or rats stressed for 6 h without recovery. No overt histological changes were detected in neuronal or glial cells in the slides of hematoxylin-eosin or Cresyl Violet staining. These results show that psychophysiological stress induces heat shock cognate protein 70 messenger RNA in the most stress-vulnerable brain structure, hippocampal CA3, probably for cytoprotection.

Differential cellular distribution and dynamics of HSP70, cyclooxygenase-2, and c-Fos in the rat brain after transient focal ischemia or kainic acid

Cerebral ischemia and also excitotoxicity induce the expression of 72,000 mol. wt heat shock protein (Hsp70), c-Fos, and cyclooxygenase-2. In the present work we have examined whether Hsp70, c-Fos and cyclooxygenase-2 are expressed by the same cells in the rat brain at 6, 12 and 24 h following transient focal ischemia or kainic acid administration, by means of single and double immunohistochemistry. At 6 h after kainic acid, some co-localization of Hsp70 with c-Fos and cyclooxygenase-2 was seen in pyramidal hippocampal neurons and superficial cortical layers, however by 24 h such colocalization became rare within the cortex but was partially maintained in the hippocampus. Cyclooxygenase-2 was seen in many neurons that were also immunoreactive for c-Fos in superficial cortical layers, dentate gyrus and pyramidal cell layer of the hippocampus from 6 h after kainic acid. Co-localization of cyclooxygenase-2 and c-Fos was also observed in superficial cortical layers within the ipsilateral hemisphere at 6 h following focal ischemia. Also, some co-localization of Hsp70 with c-Fos and cyclooxygenase-2 was seen at this time. However, by 24 h cyclooxygenase-2 and c-Fos-immunoreactive cells were restricted to perifocal regions, and only a very limited co-localization with Hsp70 was seen in perifocal neurons located in the border of the penumbra-like area that surrounds the ischemic core and is strongly immunoreactive for Hsp70. This study shows a selective and dynamic cellular expression of inducible proteins following either ischemia or kainic acid, with a remarkable neuronal co-localization of c-Fos and cyclooxygenase-2. The results suggest that, first, stimuli underlying neuronal c-Fos expression can also lead to the induction of cyclooxygenase-2; second, transient co-localization of Hsp70 and c-Fos can take place in non-vulnerable neurons; and finally, expression of c-Fos, cyclooxygenase-2, and/or Hsp70 at a given time-point is part of the response to altered environmental conditions and can be related to the particular cellular sensitivity rather than the pathological outcome.

The heat shock stress response after brain lesions: induction of 72 kDa heat shock protein (cell types involved, axonal transport, transcriptional regulation) and protein synthesis inhibition

The cerebral stress response is examined following a variety of pathological conditions such as focal and global ischemia, administration of excitotoxins, and hyperthermia. Expression of 72 kDa heat shock protein (Hsp70) and hsp70 mRNA, the mechanism underlying induction of hsp70 mRNA involving activation of heat shock factor 1, and inhibition of cerebral protein synthesis are different aspects of the stress response considered here. The results are compared with those in the literature on induction, transcriptional regulation, expression, and cellular location of Hsp70, with a view to getting more insight into the function of the stress response in the injured brain. The present results illustrate that Hsp70 can be expressed in cells affected at various degrees following an insult that will either survive or dic as the brain lesion develops, depending on the severity of cell injury. This indicates that, under certain circumstances, synthesized Hsp70 might be necessary but not sufficient to ensure cell survival. Other situations involve uncoupling between synthesis of hsp70 mRNA and protein, probably due to very strict protein synthesis blockade, and often result in cell loss. Cells eventually will die if protein synthesis rates do not go back to normal after a period of protein synthesis inhibition. The stress response is a dynamic event that is switched on in neural cells sensitive to a brain insult. The stress response is, however, tricky, as affected cells seem to need it, have to deal transiently with it, but eventually be able to get rid of it, in order to survive. Putative therapeutic treatments can act either selectively, potentiating the synthesis of Hsp70 protein and recovery of protein synthesis, or preventing the stress response by deadening the insult severity.