The neuroprotection of insulin on ischemic brain injury in rat hippocampus through negative regulation of JNK signaling pathway by PI3K/Akt activation

Brain Res. 2005 Aug 2;1052(1):1-9. doi: 10.1016/j.brainres.2005.05.043.

Abstract

Current studies demonstrated that cell survival is determined by a balance among signaling cascades, including those that recruit the Akt and JNK pathways. In our present work, the relationship between Akt1 and JNK1/2 was evaluated after cerebral ischemia-reperfusion in the hippocampus in a four-vessel occlusion model of Sprague-Dawley rats. This paper was based on our present and previous studies. Firstly, Akt1 had one active peak during reperfusion following 15 min ischemia. Secondly, two peaks of JNK1/2 activation occurred during reperfusion, respectively. Thirdly, the phosphorylation of JNK substrates c-Jun and Bcl-2, and the activation of a key protease of caspase-3 were detected. They only had one active peak, respectively, during reperfusion. To clarify the mechanism of Akt1 activation and further define whether JNK1/2 activation could be regulated by Akt1 through PI3K pathway, LY294002 and insulin were, respectively, administrated to the rats prior to ischemia. Our research indicated that LY294002, a PI3K inhibitor, significantly suppressed Akt1 activation. Furthermore, LY294002 significantly strengthened both peaks of JNK1/2 activation, c-Jun activation, Bcl-2 phosphorylation, and the activation of caspase-3 during reperfusion. In contrast, insulin, a PI3K agonist, not only obviously activated Akt1 during early and later reperfusion, but also inhibited phosphorylation of JNK1/2, c-Jun, and Bcl-2 and attenuated the activation of caspase-3. In addition, pretreatment of insulin significantly increased the number of the surviving CA1 pyramidal cells at 5 days of reperfusion. Consequently, our results indicated that the cross-talk between Akt1 and JNK1/2 could be mediated by insulin receptor through PI3K in rat hippocampus during reperfusion. This signaling pathway might play a neuroprotective role against ischemic insults via inhibition of the JNK pathway, involving the death effector of caspase-3.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analysis of Variance
  • Animals
  • Blotting, Western / methods
  • Brain Ischemia / prevention & control*
  • Chromones / pharmacology
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Hippocampus / drug effects*
  • Insulin / therapeutic use*
  • Male
  • Mitogen-Activated Protein Kinases / metabolism*
  • Morpholines / pharmacology
  • Neuroprotective Agents / therapeutic use*
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Protein Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • Proto-Oncogene Proteins c-jun / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Reperfusion / methods
  • Signal Transduction / drug effects
  • Time Factors

Substances

  • Chromones
  • Enzyme Inhibitors
  • Insulin
  • Morpholines
  • Neuroprotective Agents
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-jun
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Akt1 protein, rat
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinases