Calcium/calmodulin dependent protein kinase II mRNA in the gerbil brain after cerebral ischemia

Hypothermia enhances the colocalization of calmodulin kinase IIα with neuronal nitric oxide synthase in the hippocampus following cerebral ischemia

Hypothermia has been shown to have neuroprotective effects against neurotrauma and cerebrovascular disease. Cerebral ischemia induces the activation of calcium/calmodulin kinase II (CaM-KII), which modulates many enzymes. We have previously demonstrated that CaM-KIIα downregulates neuronal nitric oxide synthase (nNOS) activity. However, precise details regarding the neuroprotective mechanism of hypothermia largely remain to be elucidated. Therefore, in this study, we investigated the neuroprotective mechanism of hypothermia, focusing on the association between CaM-KIIα and nNOS in CA1 hippocampus after focal cerebral ischemia in mice. The temperature was maintained at normothermia (36.5-37.5°C) or mild hypothermia (31.5-32.5°C) during these procedures. Focal cerebral ischemia induced significant dissociation of CaM-KIIα from nNOS in the CA1 hippocampus but not in the cerebral cortex under normothermia. Hypothermia did not change the expression of nNOS, but it significantly induced the colocalization of CaM-KIIα with nNOS in CA1 hippocampus immediately after cerebral ischemia. These results presumably result in the attenuation of nNOS activity and could contribute to the tolerance to post-ischemic damage. This effect could be one of the neuroprotective mechanisms of hypothermia.

DNA microarray analysis of cortical gene expression during early recirculation after focal brain ischemia in rat

Focal brain ischemia is followed by changes in gene expression as reflected by altered mRNA levels. DNA microarray analysis can be used to survey thousands of genes for differential expression triggered by ischemic metabolic stress. In this study, Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion (MCAO) using an intravascular poly-L-lysine-coated filament, and brains were removed after 3 h of recirculation for mRNA isolation. A differential measurement of mRNAs from post-ischemic and sham control animals was performed using the Mouse UniGene 1 microarray. Established values for differential expression were used (> or =1.7 or < or =-1.7 fold), and hits (n=2-3 arrays) divided into known 'ischemia-hypoxia response' genes and 'newly connected' annotated genes. n=28 ischemia-hypoxia response genes were up-regulated and n=6 were down-regulated. Regulated genes comprised immediate early genes, heat shock proteins, anti-oxidative enzymes, trophic factors, and genes involved in RNA metabolism, inflammation and cell signaling. Based on the ability of the microarray to replicate known changes in gene expression, n=35 newly connected genes were found up-regulated and n=41 down-regulated. DNA microarray analysis allows one to develop novel working hypotheses for responses to brain ischemia based on the regulation of annotated genes.

Characteristics of protective effects of NMDA antagonist and calcium channel antagonist on ischemic calcium accumulation in rat hippocampal CA1 region

Effects of excitatory amino acid receptor antagonists and voltage-dependent Ca(2+) channel antagonists on ischemia-induced intracellular free Ca(2+) accumulation in rat hippocampal slices were examined. Ischemia caused a large Ca(2+) accumulation in CA1 region but a small Ca(2+) accumulation in CA3 and dentate gyrus regions. When applied during ischemia, the NMDA receptor antagonist MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine maleate) inhibited the ischemic Ca(2+) accumulation only in the CA1, but the non-NMDA receptor antagonist CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) inhibited it in all the three regions. The L-type Ca(2+) channel antagonists nifedipine and verapamil inhibited the ischemic Ca(2+) accumulation only in the CA1 region, but omega-conotoxin, a N- and L-type Ca(2+) channel antagonist inhibited the Ca(2+) accumulation in all the three regions of the hippocampus. When applied after 5-min ischemia, nifedipine but not MK-801, inhibited sustained postiscehmic Ca(2+) elevation in the CA1 region but not in the CA3 and dentate gyrus regions. These findings suggest that the enhanced ischemia-induced Ca(2+) accumulation in the CA1 region is mediated via activation of both NMDA receptors and L-type-like Ca(2+) channels. It appears that sustained postischemic Ca(2+) elevation in the CA1 region is mediated via activation of L-type-like Ca(2+) channels, but not of NMDA receptors.

Subcellular distribution and autophosphorylation of calcium/calmodulin-dependent protein kinase II-alpha in rat hippocampus in a model of ischemic tolerance

A brief period of sublethal ischemia induces resistance to a subsequent, otherwise lethal, ischemic insult, a process named ischemic tolerance or preconditioning. A persistently disturbed cell signaling during reperfusion after cerebral ischemia has been proposed to contribute to ischemic cell death. Here, we report on the effect of ischemic preconditioning on the levels of the regulatory alpha-subunit of calcium/calmodulin protein kinase II and its phosphorylation in the hippocampal CA1 region. We found that during and following lethal cerebral ischemia, calcium/calmodulin protein kinase II-alpha is persistently translocated to cell membranes, where it becomes phosphorylated at threonine 286. In contrast, in the preconditioned brains the translocation and phosphorylation are transient and return to preischemic values after one day of reperfusion. At this time of reperfusion, the total level of calcium/calmodulin protein kinase II-alpha is significantly lower in preconditioned animals compared to the sham and non-conditioned animals. After one day of reperfusion, the level of calcium/calmodulin protein kinase II-alpha messenger RNA decreases in the non-conditioned brains, whereas it is unchanged in preconditioned brains. We conclude that, during and after ischemia, calcium/calmodulin protein kinase II-alpha is translocated to cell membranes and becomes phosphorylated at threonine 286. This could detrimentally influence cell survival by changing receptor function and ion channel conductance. Ischemic preconditioning prevents the persistent presence of calcium/calmodulin protein kinase II-alpha at cell membranes, presumably by enhancing its degradation, which could be part of a neuroprotective mechanism of ischemic tolerance.

Traumatic injury induces differential expression of cell death genes in organotypic brain slice cultures determined by complementary DNA array hybridization

The expression of a large panel of selected genes hypothesized to play a central role in post-traumatic cell death was shown to be differentially altered in response to a precisely controlled, mechanical injury applied to an organotypic slice culture of the rat brain. Within 48 h of injury, the expression of nerve growth factor messenger RNA was significantly increased whereas the levels of bcl-2, alpha-subunit of calcium/calmodulin-dependent protein kinase II, cAMP response element binding protein, 65,000 mol. wt isoform of glutamate decarboxylase, 1beta isoform of protein kinase C, and ubiquitin messenger RNA were significantly decreased. Because the expression levels of a number of other messenger RNAs such as the neuron-specific amyloid precursor protein, beta(2) microglobulin, bax, bcl(xl), brain-derived neurotrophic factor, cyclooxygenase-2, interleukin-1beta, interleukin-6, tumor necrosis factor-alpha, receptor tyrosine kinase A, and receptor tyrosine kinase B were unaffected, these selective changes may represent components of an active and directed response of the brain initiated by mechanical trauma. Interpretation of these co-ordinated alterations suggests that mechanical injury to the central nervous system may lead to disruption of calcium homeostasis resulting in altered gene expression, an impairment of intracellular cascades responsible for trophic factor signaling, and initiation of apoptosis via multiple pathways. An understanding of these transcriptional changes may contribute to the development of novel therapeutic strategies to enhance beneficial and blunt detrimental, endogenous, post-injury response mechanisms.

Transient cerebral ischemia decreases calcium/calmodulin-dependent protein kinase II immunoreactivity, but not mRNA levels in the gerbil hippocampus

During transient cerebral ischemia, intracellular calcium increases initiating a cascade of events which leads to the delayed death of neurons located in the hippocampus. Coupled to this calcium disturbance is the rapid decrease of calcium/calmodulin kinase II (CaM kinase) activity, a protein kinase critical to neuronal functioning. The present study correlated the increased locomotor activity following ischemic insult with alterations in CaM kinase mRNA levels and immunocytochemical labeling of alpha and beta CaM kinase subunits in the hippocampus. The protective effect of hypothermia was also compared with CaM kinase mRNA levels and immunoreactivity. Levels of CaM kinase message for either alpha or beta subunits was not altered in ischemic gerbils compared to sham or hypothermic ischemic conditions. Immunoreactivity for both the alpha and beta subunits was markedly reduced in the vulnerable CA1 region of ischemic animals compared to sham controls. Gerbils that underwent the ischemic insult while hypothermic showed no decrement in staining. CaM kinase-like immunoreactivity in the ischemia-resistant CA3 sector was not altered following ischemia. These data suggest that the loss of hippocampal CaM kinase immunoreactivity observed at 24 h following ischemia is not associated with a reduction in CaM kinase mRNA levels and support the notion that the rapid decline in CaM kinase activity following ischemic insult is a result of a posttranslational modification and/or translocation of the enzyme.

Alterations of Ca2+/calmodulin-dependent protein kinase II and its messenger RNA in the rat hippocampus following normo- and hypothermic ischemia

The change in the subcellular distribution of Ca2+/calmodulin-dependent protein kinase II was studied in the rat hippocampus following normothermic and hypothermic transient cerebral ischemia of 15 min duration. A decrease in immunostaining of Ca2+/calmodulin-dependent protein kinase II was observed at 1 h of reperfusion which persisted until cell death in the CA1 region. In the CA3 and dentate gyrus areas immunostaining recovered at one to three days of reperfusion. The CA2+/calmodulin-dependent protein kinase II was translocated to synaptic junctions during ischemia and reperfusion which could be due to a persistent change in the intracellular calcium ion homeostasis. The expression of the messenger RNA of the alpha-subunit of Ca2+/calmodulin-dependent protein kinase II decreased in the entire hippocampus during reperfusion, and was most marked in the dentate gyrus at 12 h of reperfusion. This decrease could be a feedback downregulation of the mRNA due to increased Ca2+/calmodulin-dependent protein kinase II activation. Intraischemic hypothermia protected against ischemic neuronal damage and attenuated the ischemia-induced decrease of Ca2+/calmodulin-dependent protein kinase II immunostaining in all hippocampal regions. Hypothermia also reduced the translocation of Ca2+/calmodulin-dependent protein kinase II and restored Ca2+/calmodulin-dependent protein kinase II alpha messenger RNA after ischemia. The data suggest that ischemia leads to an aberrant Ca2+/calmodulin-dependent protein kinase II mediated signal transduction in the CA1 region, which is important for the development of delayed neuronal damage. Hypothermia enhances the restoration of the Ca2+/calmodulin-dependent protein kinase II mediated cell signalling.

Calcium/calmodulin-dependent protein kinase II immunostaining is preserved in Alzheimer's disease hippocampal neurons

Alterations in protein phosphorylation may be important in the pathogenesis of Alzheimer's disease and recent observations suggest that a subset of protein kinase pathways may be selectively altered. Calcium/calmodulin-dependent protein kinase II CaM kinase II) is the most abundant protein kinase in the brain and is believed to play an important role in the regulation of synaptic transmission, long-term potentiation and other forms of neuronal plasticity. We have now evaluated brains of individuals with Alzheimer's disease for changes in the distribution and density of immunoreactivity for the alpha subunit of CaM kinase II. CaM kinase II immunoreactivity was found in cytoarchitectural areas and neurons vulnerable to the formation of neurofibrillary angles and senile plaques. Over 80% of neurons bearing neurofibrillary tangles expressed CaM kinase II. Loss of CaM kinase II immunoreactivity was found in CA1, commensurate with neuronal loss in this area. Remaining CA1 neurons, however, had preserved CaM kinase II immunoreactivity. Preservation in the distribution and density of CaM kinase II immunoreactivity was observed in other hippocampal regions and in a multimodal association area, area 20. These results suggest CaM kinase II expression in the Alzheimer's disease brain is unaltered despite marked neuropathological changes.