Attenuated acute cardiac rejection in NOS2 -/- recipients correlates with reduced apoptosis.
BACKGROUND
The mechanisms through which NOS2-mediated pathways regulate graft failure in acute cardiac rejection are ill defined. To determine whether apoptosis promoted by NOS2 may contribute, we used a heterotopic transplant model to study mouse cardiac allografts placed in recipients with targeted gene deletion of NOS2.


RESULTS
Using 5 different indexes of apoptosis, we showed that mouse cardiac allografts placed in NOS2 -/- recipients (n=7) had reduced apoptotic activity compared with those in NOS2 +/+ controls (n=8). There were significantly fewer TUNEL-positive nuclei per high-powered field (P<0.01), less DNA fragmentation (antinucleosome ELISA; P<0.05), lower corrected transcript levels for caspase-1 and -3 (32P reverse transcriptase-polymerase chain reaction; P<0.01), and reduced caspase-3 activity (cleavage of DEVD-pNA [P<0.001] and poly [ADP-ribose] polymerase) in grafts from NOS2 -/- recipients. This concordant reduction in apoptotic indexes paralleled the improved histological outcome of grafts transplanted into NOS2 -/- recipients (assessed as rejection scores; P=0.012). To identify pathways controlled by NOS2, we compared intragraft transcript levels of potential triggers and regulators. Whereas Fas ligand/Fas and tumor necrosis factor (TNF)-alpha/TNF receptor-1 levels were not altered by NOS2 deficiency, transcript levels for p53 were significantly lower in grafts from NOS2 -/- recipients, coinciding with a significant increase in the antiapoptotic Bcl-2/Bax balance and decrease in Bcl-Xl levels.


CONCLUSIONS
Using NOS2 knockout mice, we demonstrated that NOS2-mediated pathways can promote acute rejection, at least in part, by inducing apoptotic cell death. When NOS2 is present, p53 might control NOS2-mediated apoptosis by stimulating Bax and repressing Bcl-2 and Bcl-Xl expression, which may activate the cell death program in the rejecting heart.
Koglin
J
J
Cardiovascular Biology Laboratory, Harvard School of Public Health, Boston, Mass. 02115, USA.
Granville
D J
DJ
Glysing-Jensen
T
T
Mudgett
J S
JS
Carthy
C M
CM
McManus
B M
BM
Russell
M E
ME
D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003374:Coumarins / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D017931:DNA Primers; D004789:Enzyme Activation / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic; D006084:Graft Rejection / Q000201:enzymology*; D016027:Heart Transplantation; D020287:In Situ Nick-End Labeling; D051379:Mice; D008808:Mice, Inbred CBA; D018345:Mice, Knockout; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000201:enzymology / Q000637:transplantation*; D009206:Myocardium / Q000737:chemistry / Q000166:cytology / Q000201:enzymology; D009566:Nitrates / Q000032:analysis; D019001:Nitric Oxide Synthase / Q000235:genetics* / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009842:Oligopeptides / Q000494:pharmacology; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D011506:Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D014181:Transplantation Immunology; D014184:Transplantation, Homologous; D016159:Tumor Suppressor Protein p53 / Q000235:genetics; D014443:Tyrosine / Q000032:analysis