Dissociation of cardiomyocyte apoptosis and dedifferentiation in infarct border zones.
OBJECTIVE
Cardiomyocyte apoptosis is known to occur in infarct border zones, where cardiomyocyte dedifferentiation, as seen in hibernating myocardium, can also be observed. The aim of the study is to determine whether dedifferentiated cardiomyocytes represent a population of cells stably surviving or undergoing apoptosis.


RESULTS
Microinfarctions were induced in sheep (n=8) by intracoronary injection of polymer macrobeads. The sheep were killed when cardiac function was gradually decreased (ejection fraction 37+/-6%, mean+/-SEM), but not earlier than 6 weeks after embolization. Transmural biopsies were taken from embolized and remote areas, based on flow measurements with positron emission tomography. Cells were classified as dedifferentiated when sarcomere content was depleted by >10% and glycogen content increased. Apoptosis was detected using the Tdt-mediated nick-end labelling (TUNEL) method and activated caspase-3 immunolabelling. Dedifferentiated cardiomyocytes were identified by morphology and by immunohistochemical evaluation of dedifferentiation related expression patterns of desmin, titin, cardiotin and alpha-smooth muscle actin. Cardiomyocyte apoptosis was detected in both the infarction border zones and remote areas. Dedifferentiated cardiomyocytes accounted for up to 30% of the cells in embolized areas and were almost exclusively non-apoptotic.


CONCLUSIONS
In embolization induced microinfarcted tissue, dedifferentiated cardiomyocytes are preferentially spared to undergo apoptosis. It is hypothesized that dedifferentiated cardiomyocytes and apoptotic cardiomyocytes represent two different cell populations. The dedifferentiated cells can be considered as stable surviving cells.
Dispersyn
G D
GD
Department of Molecular Cell Biology, Cardiovascular Research Institute Maastricht, Maastricht University, Maastricht, The Netherlands.
Mesotten
L
L
Meuris
B
B
Maes
A
A
Mortelmans
L
L
Flameng
W
W
Ramaekers
F
F
Borgers
M
M
D000199:Actins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D053938:DNA Fragmentation; D004792:Enzyme Precursors; D005260:Female; D019788:Fluorodeoxyglucose F18; D006321:Heart / Q000000981:diagnostic imaging; D020287:In Situ Nick-End Labeling; D009203:Myocardial Infarction / Q000378:metabolism / Q000473:pathology*; D017682:Myocardial Stunning / Q000378:metabolism / Q000473:pathology*; D009206:Myocardium / Q000378:metabolism / Q000473:pathology*; D019275:Radiopharmaceuticals; D012756:Sheep; D014055:Tomography, Emission-Computed
D000199:Actins; D004792:Enzyme Precursors; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D053148:Caspase 3; D020169:Caspases