Insulin prevents cardiomyocytes from oxidative stress-induced apoptosis through activation of PI3 kinase/Akt.
BACKGROUND
Loss of cardiomyocytes by apoptosis is proposed to cause heart failure. Reactive oxygen species induce apoptosis in many types of cells including cardiomyocytes. Because insulin has been reported to have protective effects, we examined whether insulin prevents cardiomyocytes from oxidative stress-induced apoptotic death.


RESULTS
Cultured cardiomyocytes of neonatal rats were stimulated by hydrogen peroxide (H(2)O(2)). Apoptosis was evaluated by means of the TUNEL method and DNA laddering. Incubation with 100 micromol/L H(2)O(2) for 24 hours increased the number of TUNEL-positive cardiac myocytes (control, approximately 4% versus H(2)O(2), approximately 23%). Pretreatment with 10(-)(6) mol/L insulin significantly decreased the number of H(2)O(2)-induced TUNEL-positive cardiac myocytes (approximately 12%) and DNA fragmentation induced by H(2)O(2). Pretreatment with a specific phosphatidylinositol 3 kinase (PI3K) inhibitor, wortmannin, and overexpression of dominant negative mutant of PI3K abolished the cytoprotective effect of insulin. Insulin strongly activated both PI3K and the putative downstream effector AKT: Moreover, a proapoptotic protein, BAD:, was significantly phosphorylated and inactivated by insulin through PI3K.


CONCLUSIONS
These results suggest that insulin protects cardiomyocytes from oxidative stress-induced apoptosis through the PI3K pathway.
Aikawa
R
R
Department of Cardiovascular Medicine, University of Tokyo Graduate School of Medicine, Tokyo, Japan.
Nawano
M
M
Gu
Y
Y
Katagiri
H
H
Asano
T
T
Zhu
W
W
Nagai
R
R
Komuro
I
I
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D009206:Myocardium / Q000166:cytology*; D018384:Oxidative Stress / Q000187:drug effects*; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats
D003598:Cytoskeletal Proteins; D006861:Hydrogen Peroxide; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C494920:Akt1 protein, rat