Abstract WP165: Prevention of JNK Phosphorylation and Activation of Dual Specificity Phosphatase as a Mechanism for Rosiglitazone in Neuroprotection after Transient Cerebral Ischemia.

Rosiglitazone, a synthetic peroxisome proliferator-activated receptor-γ (PPAR γ) agonist, prevents cell death after cerebral ischemia in animal models, but the underlying mechanism has not been clarified. We examined how rosiglitazone protects neurons against ischemia. Mice treated with rosiglitazone were subjected to 60 minutes of focal ischemia followed by reperfusion. Rosiglitazone reduced infarct volume after ischemia and reperfusion. We found that this neuroprotective effect was reversed with a PPAR γ antagonist. Western blot analysis showed a significant increase in expression of phosphorylated stress-activated protein kinases (c-Jun N-terminal kinase [JNK] and p38) in ischemic brain tissue, especially in the cortex area after early reperfusion (3 hr). Rosiglitazone blocked this increase of phosphorylation which caused cell death signaling activation. Furthermore, we observed that rosiglitazone increased expression of the dual-specificity phosphatase 8 (DUSP8) protein and mRNA in ischemic brain tissue. DUSP8 is a mitogen-activated protein kinase phosphatase that can dephosphorylate JNK and p38. Another key finding of the present study was that knockdown of DUSP8 in primary cultured cortical neurons that were subjected to oxygen-glucose deprivation diminished rosiglitazone’s effect on downregulation of JNK phosphorylation. Thus, rosiglitazone’s neuroprotective effect after ischemia is mediated by blocking JNK phosphorylation induced by ischemia via DUSP8 upregulation.