Endonuclease G does not play an obligatory role in poly(ADP-ribose) polymerase-dependent cell death after transient focal cerebral ischemia

Abstract

Activation of poly(ADP-ribose) polymerase (PARP) and subsequent translocation of apoptosis-inducing factor contribute to caspase-independent neuronal injury from N-methyl-d-aspartate, oxygen-glucose deprivation, and ischemic stroke. Some studies have implicated endonuclease G in the DNA fragmentation associated with caspase-independent cell death. Here, we compared wild-type and endonuclease G null mice to investigate whether endonuclease G plays a role in the PARP-dependent injury that results from transient focal cerebral ischemia. Latex casts did not reveal differences in the cerebral arterial distribution territory or posterior communicating arterial diameter, and the decrease in laser-Doppler flux during middle cerebral artery occlusion was similar in wild-type and endonuclease G null mice. After 90 min of occlusion and 1 day of reperfusion, similar degrees of nuclear translocation of apoptosis-inducing factor and DNA degradation were evident in male wild-type and null mice. At 3 days of reperfusion, infarct volume and neurological deficit scores were not different between male wild-type and endonuclease G null mice or between female wild-type and endonuclease G null mice. These data demonstrate that endonuclease G is not required for the pathogenesis of transient focal ischemia in either male or female mice. Treatment with a PARP inhibitor decreased infarct volume and deficit scores equivalently in male wild-type and endonuclease G null mice, indicating that the injury in endonuclease G null mice remains dependent on PARP. Thus endonuclease G is not obligatory for executing PARP-dependent injury during ischemic stroke.

Cell Biology of Ischemia/Reperfusion Injury

“…Endonuclease G, which induces nuclear DNA fragmentation during apoptosis, is also released from mitochondria following cerebral ischemia (Nielsen et al, 2008). However, endoG-deficient mice were still sensitive to prolonged I/R (Xu et al, 2010). …”

Ischemia/Reperfusion

“…Indeed, pharmacologic or genetic inhibition of Omi/HtrA2 attenuates postischemic death by apoptotic mechanisms (419, 590), but such approaches have not yet been used to more clearly define a causal role for Smac/DIABLO in I/R injury. Although cerebral ischemia induces release of mitochondrial endonuclease G (588), mice genetically deficient in this inducer of nuclear DNA fragmentation during apoptosis retained their sensitivity to prolonged I/R (864). …”

“…This uncoupling can also occur by dissociation of NOS from associated proteins (e.g., HSP90) that are necessary for coupled function, oxidation of BH 4 secondary to overproduction of O 2 − or ONOO − , oxidation of the zinc-thiolate complex that stabilizes the NOS homodimer, or via S-glutathionylation (663). NOS uncoupling appears to be an important contributor to I/R injury, and can be reversed by administration of L-arg, BH 4 , or the BH 4 precurser sepiaterin in animal models (212, 663, 708, 864). …”

A nuclease that mediates cell death induced by DNA damage and poly(ADP-ribose) polymerase-1

“…S1C); thus, EndoG is unlikely to be the main contributor to PARP-1–dependent large DNA fragmentation and MNNG-induced cell death (fig. S1) (13, 15). …”

“…AIF itself has no obvious nuclease activity (2). Although it has been suggested that CED-3 protease suppressor (CPS)–6, an endonuclease G (EndoG) homolog in Caenorhabditis elegans , cooperates with the worm AIF homolog (WAH-1) to promote DNA degradation (12), mammalian EndoG does not seem to have an essential role in PARP-dependent chromatinolysis and cell death (13, 14) and after transient focal cerebral ischemia in mammals (15). Thus, the nuclease responsible for the chromatinolysis during parthanatos is not known.…”