Externalization of endogenous annexin A5 participates in apoptosis of rat cardiomyocytes.
OBJECTIVE
Annexins are Ca(2+)-dependent phospholipid binding proteins. Externalized annexin A5 has been recently suggested to have a proapoptotic effect. Our aim was to determine whether annexin A5, which is intracellular in cardiomyocytes, could be translocated and/or externalized and play a role during the apoptotic process.


METHODS
Apoptosis was induced in rat cardiomyocytes by continuous incubation with staurosporine or 30 min treatment with H(2)O(2) and was measured by phosphatidylserine (PS) externalization, TUNEL staining and DNA ladder. Immunofluorescence labeling of annexin A5 was performed on permeabilized or nonpermeabilized cardiomyocytes.


RESULTS
Staurosporine or H(2)O(2) treatment of neonatal cardiomyocytes resulted in significant increases of apoptosis at 24 h, but H(2)O(2) treatment led to a faster and higher PS externalization than that observed with ST. In both neonatal and adult cardiomyocytes, annexin A5 was intracellular in control conditions but was found at the external face of sarcolemma during apoptosis. Furthermore, neonatal cardiomyocytes with externalized annexin A5 have apoptotic characteristics and their number increased with time. Interestingly, immediately after H(2)O(2) induction, the number of annexin A5-positive cells was higher than that of PS-positive cells (p</=0.05) and colabeling showed that half annexin A5-positive cells were PS-negative. We further demonstrated by immunoblots that free annexin A5 was absent from the media and could not be released from cardiomyocytes by washes at 1.8 mM Ca(2+). Removing annexin A5 by Ca(2+)-free washes 15 or 30 min after H(2)O(2) treatment or blocking externalized annexin A5 by antibodies lead to a significant decrease of apoptotic cardiomyocytes, cytochrome c release and caspase 3 activity.


CONCLUSIONS
This study indicated for the first time that annexin A5 was externalized at a very early stage of apoptosis and could have a proapoptotic effect in cardiomyocytes.
Monceau
Virginie
V
INSERM U572, IFR Circulation, Hopital Lariboisière, 41 Boulevard de la Chapelle, 75475 Paris Cedex 10, France.
Belikova
Yulia
Y
Kratassiouk
Gueorgui
G
Charue
Dominique
D
Camors
Emmanuel
E
Communal
Catherine
C
Trouvé
Pascal
P
Russo-Marie
Françoise
F
Charlemagne
Danièle
D
D000818:Animals; D017304:Annexin A5 / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020287:In Situ Nick-End Labeling; D018613:Microscopy, Confocal; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology
D017304:Annexin A5; D000911:Antibodies, Monoclonal; D004791:Enzyme Inhibitors; D045304:Cytochromes c; D006861:Hydrogen Peroxide; D011493:Protein Kinase C; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; D019311:Staurosporine