Activation of mitogen-activated protein kinases after permanent cerebral artery occlusion in mouse brain

Inhibition of cyclin-dependent kinases improves CA1 neuronal survival and behavioral performance after global ischemia in the rat

Increasing evidence suggests that cyclin-dependent kinases participate in neuronal death induced by multiple stresses in vitro. However, their role in cell death paradigms in vivo is not well characterized. Accordingly, the authors examined whether cyclin-dependent kinase inhibition resulted in functionally relevant and sustained neuroprotection in a model of global ischemia. Intracerebroventricular administration of the cyclin-dependent kinase inhibitor flavopiridol, immediately or at 4 hours postreperfusion after a global insult, reduced injury in the CA1 of the hippocampus when examined 7 days after reperfusion. No significant protection was observed when flavopiridol was administered 8 hours after reperfusion. The tumor-suppressor retinoblastoma protein, a substrate of cyclin-dependent kinase, was phosphorylated on a cyclin-dependent kinase consensus site after the global insult; this phosphorylation was inhibited by flavopiridol administration. Importantly, flavopiridol had no effect on core body temperature, suggesting that the mechanism of neuroprotection was through cyclin-dependent kinase inhibition but not through hypothermia. Furthermore, inhibition of cyclin-dependent kinases improved spatial learning behavior as assessed by the Morris water maze 7 to 9 days after reperfusion. However, the histologic protection observed at day 7 was absent 28 days after reperfusion. These results indicate that cyclin-dependent kinase inhibition provides an extended period of morphologic and functional neuroprotection that may allow time for other neuroprotective modalities to be introduced.

Cyclin-dependent kinases as potential targets to improve stroke outcome

Increasing evidence suggests that cyclin-dependent kinases (CDKs), enzymes that normally regulate cell cycle progression, may also participate in the death of neurons. This has led to the proposal that CDKs may serve as a therapeutic target for neuropathological conditions such as stroke. This brief review will serve to examine the evidence supporting the role of CDKs in neuronal death, and will evaluate the potential of CDK inhibitors as a neuroprotective strategy for ischemic injury.

Differential expression of active, phosphorylation-dependent MAP kinases, MAPK/ERK, SAPK/JNK and p38, and specific transcription factor substrates following quinolinic acid excitotoxicity in the rat

Excitotoxicity is considered a major cell death inductor in neurodegeneration. Yet mechanisms involved in cell death and cell survival following excitotoxic insults are poorly understood. Expression of active, phosphorylation-dependent mitogen-activated extracellular signal-regulated kinases (MAPK/ERKs), stress activated c-Jun N-terminal kinases (SAPK/JNKs) and p38 kinases, as well as their putative active specific transcriptional factor substrates CREB, Elk-1, ATF-2, c-Myc and c-Jun, have been examined following intracortical injection of the glutamate analogue quinolinic acid (QA). Increased JNK(P) and p38(P) immunoreactivity has been found in the core at 1 h following QA injection, whereas increased MAPK(P) immunoreactivity occurs in neurons and glial cells localised around the lesion and in neurons in remote cortical regions. This is accompanied by strong phosphorylated Ser63 c-Jun (c-Jun(P)) immunoreactivity in the core at 3 h, and by strong phosphorylated CREB, Elk-1 and ATF-2 (CREB(P), Elk-1(P) and ATF-2(P)) immunoreactivity mainly in neurons around the core at 24 h following QA injection. Examination with the method of in situ end-labelling of nuclear DNA fragmentation has revealed large numbers of positive cells with no apoptotic morphology in the core at 24 h, thus indicating that JNK(P), p38(P) and c-Jun(P) over-expression precedes cell death. In contrast, MAPK(P), CREB(P), Elk-1(P) and ATF-2(P), but not phosphorylated c-Myc (c-Myc(P)), over-expression correlates with cell survival. Examination of cleaved, active caspase-3 has shown specific immunoreactivity restricted to a few hematogenous cells in the area of injection. Since cleaved caspase-3 is not expressed by dying cells in the present paradigm, JNK(P), p38(P) and c-Jun(P) expression is not associated with caspase-3 activation. The present results demonstrate selective activation of specific MAPK signals which are involved either in cell death or cell survival triggered by excitotoxic insult.

Cyclin-dependent kinases and stroke

Cyclin-dependent kinases (CDKs) are a group of enzymes predominately known for their role in cell cycle regulation in proliferating cell types. Increasing evidence, however, suggests that CDKs also promote death in neurones. These observations have lead to the notion that CDKs may serve as a therapeutic target for neuropathological conditions such as stroke. Accordingly, in this review, we will examine the evidence which indicates a role for CDKs in neuronal death and evaluate the potential of CDK inhibitors as a therapeutic target for stroke.