Elsevier

Neuroscience

Volume 93, Issue 1, June 1999, Pages 81-88
Neuroscience

Activation of the extracellular signal-regulated protein kinase cascade in the hippocampal CA1 region in a rat model of global cerebral ischemic preconditioning

https://doi.org/10.1016/S0306-4522(99)00137-2Get rights and content

Abstract

A short period of sublethal preconditioning ischemia (3 min) followed by two days of reperfusion provides almost complete protection against ischemic cell death induced by a second (9 min) lethal ischemic episode. Here, we have investigated the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase, two kinases known to activate gene transcription and to be of importance for cell survival, after sublethal preconditioning ischemia in the rat hippocampal CA1 region. The activation levels of these two kinases were also studied after a second ischemic episode both in preconditioned and nonconditioned brains. An increased phosphorylation of the extracellular signal-regulated protein kinase kinase was found in neuronal cell bodies, particularly in the nucleus, 30 min, 4 h and two days of reperfusion after preconditioning ischemia. Two days after preconditioning ischemia both extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase were markedly phosphorylated. During the early reperfusion period (30 min) after the second ischemic insult the phosphorylation levels of these two kinases were increased in both nonconditioned and preconditioned brains. In the late reperfusion time (one day), the phosphorylation levels of the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase were decreased in preconditioned brains, but remained elevated in nonconditioned brains.

We conclude that phosphorylation of the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase after sublethal ischemia correlates with the neuroprotection induced by preconditioning, possibly by transcriptional activation of neuroprotective genes. Also, preconditioning enhances normalization of the disturbed cell signaling through the extracellular signal-regulated protein kinase cascade induced by lethal ischemia.

Section snippets

Experimental groups

The experimental designs for histopathological, western blot, and immunohistochemical analyses are shown in Fig. 1A, B and C, respectively. The different experimental groups and the number of animals in each group are indicted in Table 1. Animals in the nonconditioned and preconditioned groups were subjected to sham surgery and 3 min of ischemia, respectively, followed by two days of recovery, and then subjected to 9 min of ischemia. Both non-conditioned and preconditioned groups were allowed a

Histopathological outcome after preconditioning ischemia

There was no significant difference in blood PO2, PCO2, mean arterial blood pressure, blood pH or blood glucose values between preconditioned and non-conditioned groups, when recorded prior to, during, and after ischemic insults or sham surgery (data not shown).

Seven days after 3 min of preconditioning ischemia there were only a few degenerated neurons in the CA1 region. After two months of reperfusion there was no statistical difference between the number of neurons in the 3-min ischemia group

Discussion

The main findings of this study are that (i) the MEK1/2 becomes phosphorylated during reperfusion after 3 min of preconditioning ischemia. At day two of reperfusion both MEK1/2 and ERK1/2 remain phosphorylated; (ii) that the MEK1/2 and ERK1/2 are persistently phosphorylated in nonconditioned brains after the second ischemic insult, whereas transiently phosphorylated in preconditioned brains. Below we will discuss the effects of preconditioning on the ERK signaling cascade in the rat CA1 region

Conclusions

Our results demonstrate that ischemic preconditioning leads to a prolonged and persistent activation of the ERK cascade after preconditioning ischemia and to a normalization of cell signaling after the second ischemic insult. We speculate that preconditioning ischemia protects CA1 neurons against a subsequent ischemic insult, by activating mechanisms which induce regulatory and protective proteins, and down-regulate detrimental cell signaling.

Acknowledgements

The authors wish to thank Ulrika Sparrhult for excellent technical assistance. This work was supported by the Swedish Medical Research Council (grant no. 8644), The European Union (BIOMED II grant BMH4-CT95-0527), the Swedish Society for Medical Research, the Stroke Foundation, the Bergendahls Foundation, the Fysiografiska Sallskapet in Lund, the Swedish Society of Medicine and the Wiberg Foundation. We thank Professor Anders Holtsberg at Lund University, for valuable help concerning the

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