Apoptosis of cardiac myocytes during cardiac allograft rejection. Relation to induction of nitric oxide synthase.
BACKGROUND
Apoptosis is a distinct form of programmed cell death characterized by activation of endonucleases that cleave nuclear DNA, condensation and fragmentation of nuclear chromatin, blebbing of intact membranes, and cell shrinkage and fragmentation. The mechanisms responsible are unclear, but nitric oxide (NO) generated by inducible NO synthase (iNOS) has been demonstrated to induce apoptosis in macrophages in vitro. This study investigated whether apoptosis occurs during cardiac allograft rejection and examined the relationship of apoptosis to iNOS expression.


RESULTS
Heterotopic abdominal transplantation from Lewis to Wistar-Furth rats was used as a model of cardiac allograft rejection; Lewis-to-Lewis grafts served as controls. Apoptosis was identified by DNA ladders after electrophoresis on agarose gels and by in situ labeling of DNA fragments; cell types were determined by immunohistochemistry. The number of apoptotic cardiac myocytes increased sharply from day 3 (0.31/mm2 ventricular tissue) to day 5 (1.27/mm2) after transplantation. At day 5, allografts showed a significant increase (P < .01) in apoptotic cardiac myocytes, macrophages, and endothelial cells compared with syngeneic grafts. The expression of iNOS mRNA, protein, and enzyme activity paralleled in time and extent the apoptosis of cardiac myocytes. iNOS immunostaining of infiltrating macrophages and cardiac muscle fibers increased significantly in the allografts at days 3 to 5 and was accompanied by immunostaining of both cell types for nitrotyrosine, which is indicative of peroxynitrite formation.


CONCLUSIONS
Apoptosis of myocardial cells occurs during cardiac allograft rejection. Apoptosis during rejection parallels the expression of iNOS, which suggests that apoptosis may be triggered by NO and peroxynitrite.
Szabolcs
M
M
Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
Michler
R E
RE
Yang
X
X
Aji
W
W
Roy
D
D
Athan
E
E
Sciacca
R R
RR
Minanov
O P
OP
Cannon
P J
PJ
D000818:Animals; D017209:Apoptosis; D004790:Enzyme Induction; D006084:Graft Rejection / Q000201:enzymology / Q000473:pathology*; D016027:Heart Transplantation; D008264:Macrophages / Q000473:pathology; D008297:Male; D009206:Myocardium / Q000201:enzymology / Q000473:pathology*; D009566:Nitrates / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D011920:Rats, Inbred WF; D014443:Tyrosine / Q000378:metabolism
D009566:Nitrates; D012333:RNA, Messenger; D014443:Tyrosine; D019001:Nitric Oxide Synthase