Requirement for nitric oxide activation of p21(ras)/extracellular regulated kinase in neuronal ischemic preconditioning

The mechanisms underlying neuronal ischemic preconditioning, a phenomenon i n which brief episodes of ischemia protect against the lethal effects of su bsequent periods of prolonged ischemia, are poorly understood. Ischemia can be modeled in vitro by oxygen-glucose deprivation (OGD), We report here th at OGD preconditioning induces p21(ras) (Ras) activation in an N-methyl-D-a spartate receptor- and NO-dependent, but cGMP-independent, manner. We demon strate that Pas activity is necessary and sufficient far OGD tolerance in n eurons, Pharmacological inhibition of Pas, as well as a dominant negative m utant Pas, block OGD preconditioning whereas a constitutively active form o f Pas promotes neuroprotection against lethal OGD insults, In contrast, the activity of phosphatidyl inositol 3-kinase is not required for OGD precond itioning because inhibition of phosphatidyl inositol 3-kinase with a chemic al inhibitor or with a dominant negative mutant does not have any effect on the development of OGD tolerance. Furthermore, using recombinant adenoviru ses and pharmacological inhibitors, we show that downstream of Pas the extr acellular regulated kinase cascade is required for OGD preconditioning. Our observations indicate that activation of the Ras/extracellular regulated k inase cascade by NO is a critical mechanism for the development of OGD tole rance in cortical neurons, which may also play an important role in ischemi c preconditioning in vivo.