M. Endres et al., ISCHEMIC BRAIN INJURY IS MEDIATED BY THE ACTIVATION OF POLY(ADP-RIBOSE)POLYMERASE, Journal of cerebral blood flow and metabolism, 17(11), 1997, pp. 1143-1151
Poly(ADP-ribose)polymerase (PARP, EC 2.4.2.30), an abundant nuclear pr
otein activated by DNA nicks, mediates cell death in vitro by nicotina
mide adenine dinucleotide (NAD) depletion after exposure to nitric oxi
de. The authors examined whether genetic deletion of PARP (PARP null m
ice) or its pharmacologic inhibition by 3-aminobenzamide (3-AB) attenu
ates tissue injury after transient cerebral ischemia. Twenty-two hours
after reperfusion following 2 hours of filamentous middle cerebral ar
tery occlusion, ischemic injury was decreased in PARP-/- and PARP+/- m
ice compared with PARP+/+ litter mates, and also was attenuated in 129
/SV wildtype mice after 3-AB treatment compared with controls. Infarct
sparing was accompanied by functional recovery in PARP-/- and S-AB-tr
eated mice. Increased poly(ADP-ribose) immunostaining observed in isch
emic cell nuclei 5 minutes after reperfusion was reduced by 3-AB treat
ment. Levels of NAD-the substrate of PARP-were reduced 2 hours after r
eperfusion and were 35% of contralateral levels at 24 hours. The decre
ases were attenuated in PARP-/- mice and in 3-AB-treated animals. Poly
(ADP-ribose)polymerase cleavage by caspase-3 (CPP-32) has been propose
d as an important step in apoptotic cell death. Markers of apoptosis,
such as oligonucleosomal DNA damage, total DNA fragmentation, and the
density of terminal deoxynucleotidyl transferase dUTP nick-end-labelle
d (TUNEL +) cells, however, did not differ in ischemic brain tissue of
PARP-/- mice or in 3-AB-treated animals versus controls, although the
re were differences in the number of TUNEL-stained cells reflecting th
e decrease in infarct size. Thus, ischemic brain injury activates PARP
and contributes to cell death most likely by NAD depletion and energy
failure, although the authors have not excluded a role for PARP in ap
optotic cell death at earlier or later stages in ischemic cell death.
Inhibitors of PARP activation could provide a potential therapy in acu
te stroke.