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

Abstract

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.