Warm-blood cardioplegic arrest induces selective mitochondrial translocation of protein kinase Cepsilon followed by interaction with 6.1 inwardly rectifying potassium channel subunit in viable myocytes overexpressing urocortin.
OBJECTIVE
This study investigates the cardioprotective role and mechanism of action of urocortin in patients undergoing cardiac surgery, with respect to protein kinase Cepsilon expression, activation, and relocation.


BACKGROUND
Cardioplegic arrest and subsequent reperfusion inevitably expose the heart to iatrogenic ischemia/reperfusion injury. We previously reported that iatrogenic ischemia/reperfusion injury caused myocyte induction of urocortin, an endogenous cardioprotective peptide.


METHODS
Two sequential biopsies were obtained from the right atrium of 25 patients undergoing coronary artery bypass grafting at the start of grafting (internal control) and 10 minutes after release of the aortic clamp.


RESULTS
In hearts exposed to iatrogenic ischemia/reperfusion injury, induction of urocortin was documented at both the mRNA (255% of basic levels; P < .05) and the protein (4-fold increase; P < .01) levels. Iatrogenic ischemia/reperfusion injury also induced a selective increase of protein kinase Cepsilon mRNA (225% of internal control; P < .05) and a 2-fold overexpression of total protein kinase Cepsilon (P < .05), which paralleled a 2.9-fold increase in protein kinase Cepsilon phosphorylation (P < .01). Mitochondrial translocation of activated protein kinase Cepsilon was observed only in postcardioplegic samples, using both subcellular fractionation (P < .05) and immunostaining techniques (P < .05). Enhanced protein kinase Cepsilon/mitochondria colocalization was selectively observed in viable myocytes, showing concurrently positive staining for urocortin (P < .05). Finally, co immunoprecipitation experiments documented an iatrogenic ischemia/reperfusion injury-enhanced physical interaction of phosphorylated protein kinase Cepsilon with the 6.1 inwardly rectifying potassium channel subunit of the K(ATP) channels (P < .05).


CONCLUSIONS
After iatrogenic ischemia/reperfusion injury, urocortin expression in viable cells selectively colocalized with enhanced phosphorylation and mitochondrial relocation of protein kinase Cepsilon, suggesting a cardioprotective role for endogenous urocortin. The physical interaction of activated protein kinase Cepsilon with 6.1 inwardly rectifying potassium channel, enhanced by cardioplegic arrest, may represent a conjectural mechanism of urocortin-mediated cardioprotection.
Chen-Scarabelli
Carol
C
VA Ann Arbor Healthcare System, University of Michigan, 2215 Fuller Road (111A), Ann Arbor, MI 48105, USA. cchensc@med.umich.edu
Faggian
Giuseppe
G
Yuan
Zhaokan
Z
Tessari
Maddalena
M
Rungatscher
Alessio
A
Di Rezze
Justin
J
Scarabelli
Gabriele M
GM
Abounit
Kadija
K
McCauley
Roy
R
Saravolatz
Louis
L
Mazzucco
Alessandro
A
Scarabelli
Tiziano M
TM
D000368:Aged; D000704:Analysis of Variance; D017209:Apoptosis; D001706:Biopsy; D015153:Blotting, Western; D001026:Coronary Artery Bypass; D005260:Female; D006324:Heart Arrest, Induced / Q000379:methods*; D006801:Humans; D007049:Iatrogenic Disease; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D008297:Male; D008875:Middle Aged; D008929:Mitochondria, Heart / Q000502:physiology*; D017202:Myocardial Ischemia / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011493:Protein Kinase C / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015427:Reperfusion Injury / Q000378:metabolism*; D013696:Temperature; D054832:Urocortins / Q000096:biosynthesis*
D012333:RNA, Messenger; D054832:Urocortins; D011493:Protein Kinase C