Insulin activates the PI3K-Akt survival pathway in vulnerable neurons following global brain ischemia.
Insulin is neuroprotective following transient global brain ischemia; however, the mechanisms by which insulin exerts its salutary effects remain unclear.


OBJECTIVE
We assessed insulin's effect on the PI3K-Akt survival system and consequent modulation of the pro-apoptotic proteins Bim, Bad and FoxO3a.


METHODS
We utilized rats subjected to 10 minutes of global brain ischemia, with or without insulin administered at the onset of reperfusion.


RESULTS
In sham-operated animals, minimal pAkt immunofluorescence was detected in the CA1. Moreover, at 30 minute reperfusion, there was no change in pAkt in CA1 neurons. Single bolus high-dose insulin treatment resulted in an early increase in pAkt after 30 minutes, preservation of CA1 neurons to 14 days of reperfusion and preservation of spatial learning ability. Insulin treatment increased cytoplasmic and nuclear staining for pAkt in both CA1 and cortex. Insulin-induced Akt phosphorylation was suppressed by the PI3K inhibitor wortmannin. Neither reperfusion nor insulin induced any change in the phosphorylation or subcellular localization of FoxO3a, Bim or Bad. A single bolus of high-dose insulin reduced CA1 neuronal cell death and thus represents a potential therapeutic intervention for global brain ischemia.


CONCLUSIONS
These results reveal that proximal elements of a known cell-survival pathway are triggered by high-dose insulin during early reperfusion. Insulin induces robust PI3K-dependent phosphorylation of Akt by 30 minute reperfusion and results in improvement of hippocampal structure and function. However, the Akt substrates FoxO3a, Bim and Bad do not undergo corresponding changes in phosphorylation or subcellular localization in this model of global brain ischemia. The downstream components of insulin-induced Akt survival signaling after transient global brain ischemia remain to be identified.
Sanderson
Thomas H
TH
Department of Emergency Medicine, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Kumar
Rita
R
Murariu-Dobrin
Alina C
AC
Page
Andrea B
AB
Krause
Gary S
GS
Sullivan
Jonathon M
JM
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000187:drug effects / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D002545:Brain Ischemia / Q000188:drug therapy* / Q000201:enzymology / Q000503:physiopathology; D056547:CA1 Region, Hippocampal / Q000187:drug effects / Q000201:enzymology / Q000503:physiopathology; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000187:drug effects / Q000378:metabolism; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D008569:Memory Disorders / Q000188:drug therapy / Q000201:enzymology / Q000503:physiopathology; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology; D018696:Neuroprotective Agents / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D020318:Rats, Long-Evans; D015427:Reperfusion Injury / Q000188:drug therapy / Q000201:enzymology / Q000503:physiopathology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051025:bcl-Associated Death Protein / Q000187:drug effects / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D007328:Insulin; D008565:Membrane Proteins; D018696:Neuroprotective Agents; D019869:Phosphatidylinositol 3-Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051025:bcl-Associated Death Protein; C494821:Bad protein, rat; C000606778:Bcl2l11 protein, rat; C499515:FOXO3 protein, rat