Excessive activation of the nuclear enzyme, poly(ADP-ribose) polymerase-1 (PARP-1) plays a prominent role in various of models of cellular injury. Here, we identify poly(ADP-ribose) (PAR) polymer, a product of PARP-1 activity, as a previously uncharacterized cell death signal. PAR polymer is directly toxic to neurons, and degradation of PAR polymer by poly(ADP-ribose) glycohydrolase (PARG) or phosphodiesterase 1 prevents PAR polymer-induced cell death. PARP-1-dependent, NMDA excitotoxicity of cortical neurons is reduced by neutralizing antibodies to PAR and by overexpression of PARG. Neuronal cultures with reduced levels of PARG are more sensitive to NMDA excitotoxicity than WT cultures. Transgenic mice overexpressing PARG have significantly reduced infarct volumes after focal ischemia. Conversely, mice with reduced levels of PARG have significantly increased infarct volumes after focal ischemia compared with WT littermate controls. These results reveal PAR polymer as a signaling molecule that induces cell death and suggests that interference with PAR polymer signaling may offer innovative therapeutic approaches for the treatment of cellular injury.excitotoxicity ͉ poly(ADP-ribose) glycohydrolase ͉ poly(ADP-ribose) polymerase ͉ stroke P oly(ADP-ribose) polymerase-1 (PARP-1) is an abundant nuclear protein that is involved in the DNA base excision repair system, where it is potently activated by DNA strand nicks and breaks (1, 2). Using NAD ϩ as a substrate, PARP-1 builds up homopolymers of ADP ribose units on various nuclear proteins including histones, DNA polymerases, topoisomerases, DNA ligase-2, transcription factors (3, 4), and PARP-1 itself (5, 6). Although the exact physiologic function of PARP-1 is not completely understood, in some tissues it plays an important role in DNA repair and genomic stability (5,7,8). Poly(ADP-ribose) (PAR) catabolism and metabolism is a dynamic process, with PAR glycohydrolase (PARG) playing the major role in the degradation of the polymer (9).Recent studies using pharmacologic inhibition of PARP or genetic KO of PARP-1 indicate that PARP-1 plays a dramatic and significant role in cellular injury after stroke, trauma, ischemiareperfusion of the heart, spleen, skeletal muscle, and retina, arthritis, ␤-islet cytotoxicity͞diabetes mellitus, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease, experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis, endotoxic shock, multiple-system organ failure, and liver damage (for review, see refs. 1 and 10). PARP-1 activation also plays a prominent role in NMDA excitotoxicity, because PARP-1 KO mice are remarkably resistant both in vitro and in vivo to the excitotoxic effects of glutamate and NMDA (11,12). A cell-suicide hypothesis has been proposed (1,2,13,14) to explain the actions of PARP-1 in mediating cell death. However, studies in mice lacking PARG suggest that PAR polymer formed during the activation of PARP-1 might play a role in PARP-1-dependent cell death. PARG KO mice die at embryoni...

Intracerebral hemorrhage (ICH) causes high mortality and morbidity, but our knowledge of post-ICH neuronal death and related mechanisms is limited. In this study, we first demonstrated that ferroptosis, a newly identified form of cell death, occurs in the collagenase-induced ICH model in mice. We found that administration of ferrostatin-1, a specific inhibitor of ferroptosis, prevented neuronal death and reduced iron deposition induced by hemoglobin in organotypic hippocampal slice cultures (OHSCs). Mice treated with ferrostatin-1 after ICH exhibited marked brain protection and improved neurologic function. Additionally, we found that ferrostatin-1 reduced lipid reactive oxygen species production and attenuated the increased expression level of and its gene product cyclooxygenase-2 ex vivo and in vivo. Moreover, ferrostatin-1 in combination with other inhibitors that target different forms of cell death prevented hemoglobin-induced cell death in OHSCs and human induced pluripotent stem cell-derived neurons better than any inhibitor alone. These results indicate that ferroptosis contributes to neuronal death after ICH, that administration of ferrostatin-1 protects hemorrhagic brain, and that cyclooxygenase-2 could be a biomarker of ferroptosis. The insights gained from this study will advance our knowledge of the post-ICH cell death cascade and be essential for future preclinical studies.

Background and Purpose-Assessment of autoregulation in the time domain is a promising monitoring method for actively optimizating cerebral perfusion pressure (CPP) in critically ill patients. The ability to detect loss of autoregulatory vasoreactivity to spontaneous fluctuations in CPP was tested with a new time-domain method that used near-infrared spectroscopic measurements of tissue oxyhemoglobin saturation in an infant animal model. Methods-Piglets were made progressively hypotensive over 4 to 5 hours by inflation of a balloon catheter in the inferior vena cava, and the breakpoint of autoregulation was determined using laser-Doppler flowmetry. The cerebral oximetry index (COx) was determined as a moving linear correlation coefficient between CPP and INVOS cerebral oximeter waveforms during 300-second periods. A laser-Doppler derived time-domain analysis of spontaneous autoregulation with the same parameters (LDx) was also determined. Results-An increase in the correlation coefficient between cerebral oximetry values and dynamic CPP fluctuations, indicative of a pressure-passive relationship, occurred when CPP was below the steady state autoregulatory breakpoint. This COx had 92% sensitivity (73% to 99%) and 63% specificity (48% to 76%) for detecting loss of autoregulation attributable to hypotension when COx was above a threshold of 0.36. The area under the receiver-operator characteristics curve for the COx was 0.89. COx correlated with LDx when values were sorted and averaged according to the CPP at which they were obtained (rϭ0.67). Conclusions-The COx is sensitive for loss of autoregulation attributable to hypotension and is a promising monitoring tool for determining optimal CPP for patients with acute brain injury.

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