Ischemic Brain Injury is Mediated by the Activation of Poly(ADP-Ribose)Polymerase

Abstract

Poly(ADP-ribose)polymerase (PARP, EC 2.4.2.30), an abundant nuclear protein activated by DNA nicks, mediates cell death in vitro by nicotinamide adenine dinucleotide (NAD) depletion after exposure to nitric oxide. The authors examined whether genetic deletion of PARP (PARP null mice) or its pharmacologic inhibition by 3-aminobenzamide (3-AB) attenuates tissue injury after transient cerebral ischemia. Twenty-two hours after reperfusion following 2 hours of filamentous middle cerebral artery occlusion, ischemic injury was decreased in PARP-/- and PARP+/- mice compared with PARP+/+ litter mates, and also was attenuated in 129/SV wild-type mice after 3-AB treatment compared with controls. Infarct sparing was accompanied by functional recovery in PARP-/- and 3-AB-treated mice. Increased poly(ADP-ribose) immunostaining observed in ischemic cell nuclei 5 minutes after reperfusion was reduced by 3-AB treatment. Levels of NAD--the substrate of PARP--were reduced 2 hours after reperfusion and were 35% of contralateral levels at 24 hours. The decreases were attenuated in PARP-/- mice and in 3-AB-treated animals. Poly(ADP-ribose)polymerase cleavage by caspase-3 (CPP-32) has been proposed 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-labelled (TUNEL +) cells, however, did not differ in ischemic brain tissue of PARP-/- mice or in 3-AB-treated animals versus controls, although there were differences in the number of TUNEL-stained cells reflecting the 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 apoptotic cell death at earlier or later stages in ischemic cell death. Inhibitors of PARP activation could provide a potential therapy in acute stroke.

Ischemic Nitric Oxide and Poly (ADP-Ribose) Polymerase-1 in Cerebral Ischemia: Male Toxicity, Female Protection

“…Key evidence in establishing NO toxicity/PARP-1 activation as a major cytotoxic mechanism has accumulated from exclusively male animals with targeted deletions of nNOS (nNOSÀ/À) or PARP (PARPÀ/À). In each case, these knockouts are resistant to brain injury from focal and global cerebral ischemic insults, as are primary neuronal cell cultures derived from fetal brain obtained from mixed sexes (Huang et al, 1994;Eliasson et al, 1997;Endres et al, 1997;Samdani et al, 1997;Goto et al, 2002). Similar findings of neuroprotection using pharmacological inhibitors of nNOS and PARP-1 in male animals and mixed sex neuronal cell cultures have been widely reported (for reviews, see Beckman and Koppenol, 1996;Virag and Szabo, 2002;Virag et al, 2003;Ha and Snyder, 2000;Yu et al, 2003).…”

Cerebral Endothelial Cell Apoptosis after Ischemia—Reperfusion: Role of PARP Activation and AIF Translocation

“…Similarly, the earlier successes of PARP-1 inhibition or deletion strategies in reducing ischemic brain injury in vivo (Ding et al, 2001;Eliasson et al, 1997;Endres et al, 1997;Takahashi et al, 1999) may have their mechanistic basis in the secondary reduction in nuclear AIF translocation (Cao et al, 2003;Plesnila et al, 2004).…”

Bcl-2 prevents topoisomerase II inhibitor GL331-induced apoptosis is mediated by down-regulation of poly(ADP-ribose)polymerase activity

“…Another possibility is that di erent apoptosis inducers may through distinct apoptotic mechanisms, i.e., PARP-dependent or -independent. Supportive of this concept, two studies (Endres et al, 1997;Eliasson et al, 1997) have demonstrated that PARP-knockout mice are resistant to peroxynitriteinduced ischemic injury via inhibiting apoptotic cell death.…”