Calcium/calmodulin-dependent protein kinase II (CaMKII), through NMDA receptors and L-Voltage-gated channels, modulates the serine phosphorylation of GluR6 during cerebral ischemia and early reperfusion period in rat hippocampus.

Recent studies have shown that GluR6 is involved in the modulation of neuronal cell death. It has been shown that PKA can phosphorylate recombinant GluR6 homomeric receptors and that this phosphorylation of GluR6 was suggested to underlie an enhancement of whole-cell current responses. Here, we try to find out whether brain ischemia and reperfusion could induce any change in the serine phosphorylation of GluR6. Our results showed that the serine phosphorylation of GluR6 increased in hippocampus during brain ischemia and early reperfusion period. Then, we used several drugs to investigate the mechanism of modulating the serine phosphorylation of GluR6. KT5720, a specific cell-permeable inhibitor of protein kinase A (PKA), had no effect on the increase in serine phosphorylation of GluR6 induced by brain ischemia or reperfusion. On the other hand, KN-62, a selective inhibitor of rat brain Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), diminished the increase in serine phosphorylation of GluR6. Moreover, our results showed that either MK801 (a NMDA receptor antagonist) or Nifedipine (a L-type Ca2+ channel (L-VGCC) blocker) decreased the increase in serine phosphorylation. In conclusion, our results suggest that CaMKII, activated through NMDA receptors and L-VGCCs, mediated the serine phosphorylation of GluR6 during brain ischemia and early reperfusion period.

The neuroprotective action of SP600125, a new inhibitor of JNK, on transient brain ischemia/reperfusion-induced neuronal death in rat hippocampal CA1 via nuclear and non-nuclear pathways.

Increasing evidence suggests that c-Jun N-terminal kinase (JNK) is an important kinase mediating neuronal apoptosis in brain ischemia. To further study the roles of JNK activation in hippocampal CA1 neurons in a rat model of transient global ischemia, we assessed the effect of JNK inhibition by SP600125 on the degree of brain injury. Our results demonstrated that SP600125 significantly increased the number of surviving cells in hippocampal CA1 subfield and decreased the activation of p-JNK1/2 and p-JNK3 at 30 min and 3 days after brain ischemia. Moreover, SP600125 significantly diminished the increased levels of phosphorylated-c-Jun (Ser63/73) and phosphorylated-Bcl-2 (Ser87) at 3 h after brain ischemia. These results indicate that SP600125, a new inhibitor of JNK, protected transient brain ischemia/reperfusion-induced neuronal death in rat hippocampal CA1 region at least via suppressing the activation of nuclear substrate (c-Jun) and inactivating non-nuclear substrate (Bcl-2) induced by ischemic insult. Thus, inhibiting JNK activity by SP600125 may represent a new and effective strategy to treat ischemic stoke.

Postsynaptic density protein 95 antisense oligodeoxynucleotides inhibits the activation of MLK3 and JNK3 via the GluR6.PSD-95.MLK3 signaling module after transient cerebral ischemia in rat hippocampus.

In this study, we investigated the effect of PSD-95 antisense oligodeoxynucleotides on the phosphorylation of MLK3, JNK3 and interactions of MLK3 and PSD-95 with kainate receptor (GluR6) by immunoprecipitation and immunoblotting. Transient (15 min) brain ischemia was induced by the four-vessel occlusion in Sprague-Dawley rats. The antisense oligodeoxynucleotides of PSD-95 were administrated to the SD rats once per day for 3 days before ischemia. Our data show that the antisense oligodeoxynucleotides could inhibit phosphorylation of MLK3 and JNK3 and decrease the interactions of MLK3 and PSD-95 with GluR6. These results indicate that PSD-95 plays an important role in the formation of the GluR6.PSD-95.MLK3 signaling module and MLK3 and JNK3 activation in postischemic rat hippocampus.

Lithium suppressed Tyr-402 phosphorylation of proline-rich tyrosine kinase (Pyk2) and interactions of Pyk2 and PSD-95 with NR2A in rat hippocampus following cerebral ischemia.

It has been indicated that Pyk2/Src signaling pathway is involved in modulation of N-methyl-D-aspartate-type (NMDA) glutamate receptor activity. Lithium protects against glutamate-induced excitotoxicity in cultured neurons and in animal models of diseases. The neuroprotection against excitotoxicity afforded by lithium is time-dependent, requiring treatment for 6-7 days for maximal effect. In this study, we examined the time-course and the effect of lithium on Tyr-402 phosphorylation of Pyk2 and Tyr-416 phosphorylation of Src as well as the association of Pyk2 and NMDA receptor subunit 2A (NR2A) mediated by postsynaptic density protein 95 kDa (PSD-95) in the condition of cerebral ischemia, which was induced by occlusion of the four vessels in Sprague-Dawley rats. At 6 h of reperfusion following 15 min of ischemia (I/R), the effects induced by chronic lithium were observed, including the decrease in enhanced Tyr-402 phosphorylation of Pyk2, the inhibition in increased Tyr-416 phosphorylation of Src and the attenuation in enhanced interactions of Pyk2 and PSD-95 with NR2A. Our results further suggest that the activated Pyk2 potentiates NMDA receptor function during transient brain ischemia followed by reperfusion and the above inhibition induced by lithium is likely to result in the inactivation of NMDA receptor and contributes to the neuroprotection against excitotoxicity.