MECHANISM OF EXTRACELLULAR ATP-INDUCED AND ADENOSINE-INDUCED APOPTOSIS OF CULTURED PULMONARY-ARTERY ENDOTHELIAL-CELLS

Apoptosis may be important in the exacerbation of endothelial cell inj ury or limitation of endothelial cell proliferation. We have found tha t extracellular ATP (exATP) and adenosine cause endothelial apoptosis and that the development of apoptosis is linked to intracellular metab olism of adenosine [Dawicki, D. D., D. Chatterjee, J. Wyche, and S. Ro unds. Am. J. Physiol. 273 (Lung Cell Mel. Physiol. 17): L485-L494, 199 7]. In the present study, we investigated the mechanism of this effect . We found that exATP, adenosine, and the S-adenosyl-L-homocysteine (S AH) hydrolase inhibitor MDL-28842 caused apoptosis and decreased the r atio of S-adenosyl-L-methionine to SAH compared with untreated control cells. Using release of soluble [H-3]thymidine as a measure of DNA fr agmentation, we found that the effect of adenosine on soluble DNA rele ase was potentiated by coincubation with homocysteine. These results s uggest that the mechanism of exATP- and adenosine-induced endothelial cell apoptosis involves inhibition of SAH hydrolase. exATP-induced apo ptosis was enhanced by an inhibitor of adenosine deaminase, whereas ex ogenous adenosine-induced apoptosis was partially inhibited by an aden osine deaminase inhibitor. These results suggest that adenosine deamin ase may also be involved in the mechanism of adenosine-induced endothe lial cell apoptosis. Adenosine and MDL-28842 caused intracellular acid osis as assessed with the fluorescent probe 2',7'-bis(2-carboxyethyl)- 5(6)-carboxyfluorescein. The cell-permeant base chloroquine prevented adenosine-induced acidosis but not apoptosis. Thus, although intracell ular acidosis is associated with adenosine-induced apoptosis, it is no t necessary for this effect. We speculate that exATP- and adenosine-in duced endothelial cell apoptosis may be due to an inhibition of methyl transferase(s) activity. Purine-induced endothelial cell apoptosis may be important in limiting endothelial cell proliferation after vascula r injury.