Poly(ADP-ribose) Accumulation and Enhancement of Postischemic Brain Damage in 110-kDa Poly(ADP-ribose) Glycohydrolase Null Mice

Abstract

Poly(ADP-ribose) (PAR) is a polymer synthesized by poly(ADP-ribose) polymerases (PARPs) and metabolized into free adenosine diphosphate (ADP)-ribose units by poly(ADP-ribose) glycohydrolase (PARG). Perturbations in PAR synthesis have been shown to play a key role in brain disorders including postischemic brain damage. A single parg gene but two PARG isoforms (110 and 60 kDa) have been detected in mouse cells. Complete suppression of parg gene causes early embryonic lethality, whereas mice selectively lacking the 110 kDa PARG isoform (PARG 110 À/À ) develop normally. We used PARG 110 À/À mice to evaluate the importance of PAR catabolism to postischemic brain damage. Poly(ADP-ribose) contents were higher in the brain tissue of PARG 110 À/À than PARG 110 + / + mice, both under basal conditions and after PARP activation. Distal middle cerebral artery occlusion caused higher increase of brain PAR levels and larger infarct volumes in PARG 110 À/À mice than in wildtype counterparts. Of note, the brain of PARG 110 À/À mice showed reduced heat-shock protein (HSP)-70 and increased cyclooxygenase-2 expression under both control and ischemic conditions. No differences were detected in brain expression/activation of procaspase-3, PARP-1, Akt, HSP-25 and interleukin-1b. Our findings show that PAR accumulation worsens ischemic brain injury, and highlight the therapeutic potential of strategies capable of maintaining PAR homeostasis.

Two small enzyme isoforms mediate mammalian mitochondrial poly(ADP-ribose) glycohydrolase (PARG) activity

“…Interestingly, the splice variants reported here encode PARG proteins that are devoid of the putative regulatory A-domain. Functions of this domain are not yet well understood, but its absence in the PARG Δ2-3/Δ2-3 mouse is responsible for a complex phenotype of hypersensitivity against genotoxic stress [18] and the loss of the three large PARG proteins results in cytotoxic cerebral [20] and splanchnic [21] accumulation of cellular PAR after ischemiareperfusion injury, illustrating its importance in regulating PARG activity, and thus PAR turnover. Recently, it has been reported that PARG physically interacts with PARP-1, regulating its activity and that both form a complex with XRCC1 after MNNG induced DNA damage [57].…”

“…In this model, AIF released from the mitochondria rapidly translocates to the nucleus and activates an endonuclease facilitating chromatinolysis and cell death in a caspase-independent manner [61][62][63]. While it is possible that NAD+ depletion as a result of PAR formation may affect the mitochondrial membrane potential ( [64,65] ), there also is accumulating evidence that PAR itself may be acting as a cell death signaling molecule triggering the formation of a mitochondrial pore transition (MPT) in a yet unknown way [66]. Moreover, it has been shown that monomeric ADP-ribose (ADPR) produced by activation of PARP/PARG enzymes contributes to oxidative stress induced cell death by specifically activating the cell membrane Ca 2+ channel TRPM2 by binding to its nudix motif [67,68] and, hypothetically, the novel PARG isoforms could contribute to the release of ADPR from the mitochondria.…”

“…Cellular accumulation of PAR beyond a short period of time has been shown to be deleterious [14,15] and is involved in caspase-independent cell death regulation [16], reviewed in [17]. Alterations of PAR metabolism are causally involved in the pathogenesis of inflammatory [18] and autoimmune disease [19] , ischemia reperfusion injury in brain [20] , heart and intestine [21][22][23] , neuronal degeneration and neurotoxicity [24] , genetic and genomic instability (reviewed in [25]) and cancer (reviewed in [26,27] ). Targeting of the poly(ADP-ribose) metabolic pathway has therefore become an important focus in research on cancer therapy (recent reviews in [28][29][30]), cardiovascular disease intervention [31][32][33][34] and a number of other pathophysiological conditions [35,36] .…”

Poly(ADP-Ribose) Glycohydrolase Activity Mediates Post-Traumatic Inflammatory Reaction after Experimental Spinal Cord Trauma

“…It is interesting to note that KO mutant mice are hypersensitive to lipopolysaccharide-induced septic shock (Cortes et al, 2004) as well as to postischemic brain damage (Cozzi et al, 2005). Because PARP-1 can still be activated in KO mutant mice but with a low degree of automodification, DNA damage-induced cell death pathway may become prominent in this model.…”

Brain Ischemic Preconditioning Does Not Require PARP-1

“…9 Infarcts were measured 3 days after MCAO to rule out transient neuroprotection. The anti-PAR antibody and the Caspase-3 activity determination kit were from Alexis, the anti-PARP-1, and anti-caspase-3 antibodies were from Cell Signaling.…”