MAPKs are differentially modulated in arctic ground squirrels during hibernation

Hibernating animals are very tolerant of trauma to the central nervous system such that dramatic fluctuations in cerebral blood flow occur during hibernation and arousal without apparent damage. Indeed, it was demonstrated that Arctic ground squirrels (AGS) experience acute and severe systemic hypoxia along with the dramatic fluctuation in cerebral blood flow when the animals are aroused from hibernation. While initial hypotheses concerned protective mechanisms in the hibernating state, recent evidence of sustained elevation of HIF1alpha in euthermic AGS from our laboratory suggests that a preparatory program of protective gene expression is chronically expressed in euthermic AGS. In this study we evaluated potential neuroprotective adaptations by examining the alteration of intracellular MAPK pathways that may be modulated by hypoperfusion/reperfusion in AGS during hibernation and arousal. We found that ERK and JNK are activated in both euthermic and aroused AGS compared to the hibernating group which positively correlated with HIF1alpha levels. The activation of ERK and JNK associated with HIF1alpha may play an important role in mediating neuroprotective adaptations that is essential for successful hibernation. Interestingly, p38 is activated in euthermic AGS but not in aroused AGS, which shows strong correlation with iNOS induction. Therefore, the attenuation of p38 activation and iNOS induction in hibernating and aroused animals may contribute to the attenuation of inflammation that plays important neuroprotective roles during hibernation. Taken together, the differential modulation of the MAPK pathways may be critical for neuroprotection of AGS necessary for fluctuations in oxygen and nutrient delivery during hibernation.