Activation of PKN mediates survival of cardiac myocytes in the heart during ischemia/reperfusion.
BACKGROUND
The function of PKN, a stress-activated protein kinase, in the heart is poorly understood.


OBJECTIVE
We investigated the functional role of PKN during myocardial ischemia/reperfusion (I/R).


RESULTS
PKN is phosphorylated at Thr774 in hearts subjected to ischemia and reperfusion. Myocardial infarction/area at risk (MI/AAR) produced by 45 minutes of ischemia and 24 hours of reperfusion was significantly smaller in transgenic mice with cardiac-specific overexpression of constitutively active (CA) PKN (Tg-CAPKN) than in nontransgenic (NTg) mice (15+/-5 versus 38+/-5%, P<0.01). The number of TUNEL-positive nuclei was significantly lower in Tg-CAPKN (0.3+/-0.2 versus 1.0+/-0.2%, P<0.05). Both MI/AAR (63+/-9 versus 45+/-8%, P<0.05) and the number of TUNEL-positive cells (7.9+/-1.0 versus 1.3+/-0.9%, P<0.05) were greater in transgenic mice with cardiac-specific overexpression of dominant negative PKN (Tg-DNPKN) than in NTg mice. Thr774 phosphorylation of PKN was also observed in response to H(2)O(2) in cultured cardiac myocytes. Stimulation of PKN prevented, whereas inhibition of PKN aggravated, cell death induced by H(2)O(2), suggesting that the cell-protective effect of PKN is cell-autonomous in cardiac myocytes. PKN induced phosphorylation of alpha B crystallin and increased cardiac proteasome activity. The infarct reducing effect in Tg-CAPKN mice was partially inhibited by epoxomicin, a proteasome inhibitor.


CONCLUSIONS
PKN is activated by I/R and inhibits apoptosis of cardiac myocytes, thereby protecting the heart from I/R injury. PKN mediates phosphorylation of alpha B crystallin and stimulation of proteasome activity, which, in part, mediates the protective effect of PKN in the heart.
Takagi
Hiromitsu
H
Cardiovascular Research Institute, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, 185 S Orange Avenue, Newark, NJ 07103, USA.
Hsu
Chiao-Po
CP
Kajimoto
Katsuya
K
Shao
Dan
D
Yang
Yanfei
Y
Maejima
Yasuhiro
Y
Zhai
Peiyong
P
Yehia
Ghassan
G
Yamada
Chikaomi
C
Zablocki
Daniela
D
Sadoshima
Junichi
J
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D002470:Cell Survival; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004789:Enzyme Activation; D006861:Hydrogen Peroxide / Q000494:pharmacology; D019157:Ischemic Preconditioning, Myocardial; D051379:Mice; D008822:Mice, Transgenic; D009203:Myocardial Infarction / Q000201:enzymology / Q000235:genetics / Q000473:pathology / Q000517:prevention & control*; D015425:Myocardial Reperfusion / Q000009:adverse effects*; D015428:Myocardial Reperfusion Injury / Q000201:enzymology / Q000235:genetics / Q000473:pathology / Q000517:prevention & control*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D009842:Oligopeptides / Q000494:pharmacology; D010766:Phosphorylation; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013912:Threonine; D013997:Time Factors; D038203:alpha-Crystallin B Chain / Q000378:metabolism
C525420:Cryab protein, mouse; D009842:Oligopeptides; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D038203:alpha-Crystallin B Chain; D013912:Threonine; D006861:Hydrogen Peroxide; C061570:protein kinase N; D011493:Protein Kinase C; D046988:Proteasome Endopeptidase Complex; C078846:epoxomicin