Poly(ADP-ribose) polymerase gene disruption renders mice resistant to cerebral ischemia

Nitric oxide modulates hypoxia-inducible factor-1 and poly(ADP-ribose) polymerase-1 cross talk in response to hypobaric hypoxia

The physiological response to hypobaric hypoxia represents a complex network of biochemical pathways in which the nitrergic system plays an important role. Previous studies have provided evidence for an interplay between the hypoxia-inducible factor-1 (HIF-1) and poly(ADP-ribose) polymerase-1 (PARP-1) under hypoxia. Here, we evaluate the potential involvement of nitric oxide (NO) in the cross talk between these two proteins. With this aim, we studied comparatively the effect of pharmacological inhibitors of NO production or PARP activity in the response of the mouse cerebral cortex to 4 h of exposure to a simulated altitude of 31,000 ft. Particularly, we analyzed the NO and reactive oxygen species production, the expression of NO synthase (NOS) isoforms, PARP-1 activity, HIF-1α expression and HIF-1 transcriptional activity, the protein level of the factor inhibiting HIF, and, finally, beclin-1 and fractin expression, as markers of cellular damage. Our results demonstrate that the reduction of NO level did not affect reactive oxygen species production but significantly 1) dampened the posthypoxic increase in neuronal NOS and inducible NOS expression without altering endothelial NOS protein level; 2) prevented PARP activation; 3) decreased HIF-1α response to hypoxia; 4) achieved a higher long-term HIF-1 transcriptional activity by reducing factor inhibiting HIF expression; and 5) reduced hypoxic damage. The pharmacological inhibition of PARP reproduced the NOS expression pattern and the HIF-1α response observed in NOS-inhibited mice, supporting its involvement in the NO-dependent regulation of hypoxia. As a whole, these results provide new data about the molecular mechanism underlying the beneficial effects of controlling NO production under hypobaric hypoxic conditions.

Minocycline protects cardiac myocytes against simulated ischemia–reperfusion injury by inhibiting poly(ADP-ribose) polymerase-1

There is an increase in reactive oxygen and nitrogen species in cardiomyocytes during myocardial ischemia/reperfusion injury. This leads to oxidative DNA damage and activation of nuclear repair enzymes such as poly(ADP-ribose) polymerase-1 (PARP-1). PARP-1 activation promotes DNA repair under normal conditions. However, excessive activation of PARP-1 leads to cell death. We report that PARP-1 enzymatic activity is directly inhibited by minocycline, and we propose that one mechanism of minocycline cardioprotection is the result of PARP-1 inhibition. Using cultured adult rat cardiac myocytes, we evaluated the mechanism of minocycline protection in which PARP-1 activation was induced by simulated ischemia/reperfusion injury using oxygen–glucose deprivation.We found an increase in reactive oxygen species production, PARP-1 activation, and PARP-1-mediated cell death after simulated ischemia/reperfusion. Cell death was significantly reduced by the PARP inhibitors 3, 4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone (10 μM) and PJ-34 (500 nM) or by minocycline (500 nM). Cellular NAD(+) depletion and poly(ADP-ribose) formation, which are biochemical markers of PARP-1 activation, were also blocked by minocycline. Finally, simulated ischemia/reperfusion led to induction of the mitochondrial permeability transition, which was prevented by minocycline. Therefore, we propose that the protective effect of minocycline on cardiac myocyte survival is the result of inhibition of PARP-1 activity.

Metabolic stress-induced activation of FoxO1 triggers diabetic cardiomyopathy in mice

The leading cause of death in diabetic patients is cardiovascular disease; diabetic cardiomyopathy is typified by alterations in cardiac morphology and function, independent of hypertension or coronary disease. However, the molecular mechanism that links diabetes to cardiomyopathy is incompletely understood. Insulin resistance is a hallmark feature of diabetes, and the FoxO family of transcription factors, which regulate cell size, viability, and metabolism, are established targets of insulin and growth factor signaling. Here, we set out to evaluate a possible role of FoxO proteins in diabetic cardiomyopathy. We found that FoxO proteins were persistently activated in cardiac tissue in mice with diabetes induced either genetically or by high-fat diet (HFD). FoxO activity was critically linked with development of cardiomyopathy: cardiomyocyte-specific deletion of FoxO1 rescued HFD-induced declines in cardiac function and preserved cardiomyocyte insulin responsiveness. FoxO1-depleted cells displayed a shift in their metabolic substrate usage, from free fatty acids to glucose, associated with decreased accumulation of lipids in the heart. Furthermore, we found that FoxO1-dependent downregulation of IRS1 resulted in blunted Akt signaling and insulin resistance. Together, these data suggest that activation of FoxO1 is an important mediator of diabetic cardiomyopathy and is a promising therapeutic target for the disease.

The hypoxic preconditioning agent deferoxamine induces poly(ADP-ribose) polymerase-1-dependent inhibition of the mitochondrial respiratory chain

We previously reported that treatment with a single dose of deferoxamine (DFO), which acts as a hypoxic-mimetic agent, only induces reactive oxygen species (ROS) production in the presence of poly(ADP-ribose) polymerase (PARP-1). Given that mitochondria are one of the main sources of ROS, the present study was designed to assess the effect of DFO treatment on the activity of mitochondrial respiratory chain complexes, and more importantly, to determine whether this effect is modulated by PARP-1. We found that DFO treatment induced a progressive decline in complex II and IV activity, but that this activity was preserved in PARP-1 knock-out cells, demonstrating that this decrease is mediated by PARP-1. We also confirmed that complex II inhibition after DFO treatment occurs in parallel with poly-ADP ribosylation. Consequently, we recommend that PARP-1 activation be taken into account when using DFO as a hypoxia-mimetic agent, because it mediates alteration of the mitochondrial respiratory chain.

Pre-B-cell colony-enhancing factor exerts a neuronal protection through its enzymatic activity and the reduction of mitochondrial dysfunction in in vitro ischemic models

Pre-B-cell colony-enhancing factor (PBEF) is known as a rate-limiting enzyme that converts nicotinamide (NAM) to NMN in the salvage pathway of mammalian NAD⁺ biosynthesis. Previously we found PBEF is exclusively expressed in neurons in the mouse brain; heterozygous PBEF knockout (Pbef⁺/⁻) mice have larger ischemic lesion than wild type mice in photothrombosis-induced ischemia. For the mechanistic study of neuronal protective role of PBEF, we used in vitro oxygen-glucose deprivation (OGD) and glutamate excitotoxicity models of primary cultured neurons in current study. Our results showed that the treatments of neurons with NAM and NAD⁺, the substrate and downstream product of PBEF, respectively, significantly reduced neuronal death after OGD and glutamate excitotoxicity, while treatment of neurons treated with FK866, a PBEF inhibitor, increased neuronal death after OGD. Furthermore, over-expression of human PBEF reduced glutamate excitotoxicity, while over-expression of human PBEF mutants (i.e. H247A and H247E) without enzymatic activity had no effect on neuronal death. We further tested the effect of PBEF on mitochondrial function and biogenesis. Our results show that addition of NAD⁺ and NAM increased mitochondrial biogenesis in neurons after OGD. Over-expression of PBEF in neurons reduced mitochondrial membrane potential depolarization following glutamate stimulation, while over-expression of H247A and H247E did not affect mitochondrial membrane potential depolarization. We conclude that PBEF has a neuroprotective effect in ischemia through its enzymatic activity for NAD⁺ production that can ameliorate mitochondrial dysfunction.

NAD+ depletion or PAR polymer formation: which plays the role of executioner in ischaemic cell death?

Multiple cell death pathways are activated in cerebral ischaemia. Much of the initial injury, especially in the core of the infarct where cerebral blood flow is severely reduced, is necrotic and secondary to severe energy failure. However, there is considerable evidence that delayed cell death continues for several days, primarily in the penumbral region. As reperfusion therapies grow in number and effectiveness, restoration of blood flow early after injury may lead to a shift towards apoptosis. It is important to elucidate what are the key mediators of apoptotic cell death after stroke, as inhibition of apoptosis may have therapeutic implications. There are two well described pathways that lead to apoptotic cell death; the caspase pathway and the more recently described caspase-independent pathway triggered by poly-ADP-ribose polymers (PARP) activation. Caspase-induced cell death is initiated by release of mitochondrial cytochrome c, formation of the cytosolic apoptosome, and activation of endonucleases leading to a multitude of small randomly cleaved DNA fragments. In contrast caspase-independent cell death is secondary to activation of apoptosis inducing factor (AIF). Mitochondrial AIF translocates to the nucleus, where it induces peripheral chromatin condensation, as well as characteristic high-molecular-weight (50 kbp) DNA fragmentation. Although caspase-independent cell death has been recognized for some time and is known to contribute to ischaemic injury, the upstream triggering events leading to activation of this pathway remain unclear. The two major theories are that ischaemia leads to nicotinamide adenine dinucleotide (NAD+) depletion and subsequent energy failure, or alternatively that cell death is directly triggered by a pro-apoptotic factor produced by activation of the DNA repair enzyme PARP. PARP activation is robust in the ischaemic brain producing variable lengths of poly-ADP-ribose (PAR) polymers as byproducts of PARP activation. PAR polymers may be directly toxic by triggering mitochondrial AIF release independently of NAD+ depletion. Recently, sex differences have been discovered that illustrate the importance of understanding these molecular pathways, especially as new therapeutics targeting apoptotic cell death are developed. Cell death in females proceeds primarily via caspase activation whereas caspase-independent mechanisms triggered by the activation of PARP predominate in the male brain. This review summarizes the current literature in an attempt to clarify the roles of NAD+ and PAR polymers in caspase-independent cell death, and discuss sex specific cell death to provide an example of the possible importance of these downstream mediators.

Modulation of ischemia-induced NMDAR1 activation by environmental enrichment decreases oxidative damage

In this study, we examined whether enriched environment (EE) housing has direct neuroprotective effects on oxidative damage following transient global cerebral ischemia. Fifty-two adult male Wistar rats were included in the study and received either ischemia or sham surgery. Once fully awake, rats in each group were randomly assigned to either: EE housing or socially paired housing (CON). Animals remained in their assigned environment for 7 days, and then were killed. Our data showed that glutamate receptor expression was significantly higher in the hippocampus of the ischemia CON group than in the ischemia EE group. Furthermore, the oxidative DNA damage, protein oxidation, and neurodegeneration in the hippocampus of the ischemia CON group were significantly increased compared to the ischemia EE group. These results suggest that EE housing possibly modulated the ischemia-induced glutamate excitotoxicity, which then attenuated the oxidative damage and neurodegeneration in the ischemia EE rats.

Molecular Mechanisms Underlying Cell Death in Spinal Networks in Relation to Locomotor Activity After Acute Injury in vitro

Understanding the pathophysiological changes triggered by an acute spinal cord injury is a primary goal to prevent and treat chronic disability with a mechanism-based approach. After the primary phase of rapid cell death at the injury site, secondary damage occurs via autodestruction of unscathed tissue through complex cell-death mechanisms that comprise caspase-dependent and caspase-independent pathways. To devise novel neuroprotective strategies to restore locomotion, it is, therefore, necessary to focus on the death mechanisms of neurons and glia within spinal locomotor networks. To this end, the availability of in vitro preparations of the rodent spinal cord capable of expressing locomotor-like oscillatory patterns recorded electrophysiologically from motoneuron pools offers the novel opportunity to correlate locomotor network function with molecular and histological changes long after an acute experimental lesion. Distinct forms of damage to the in vitro spinal cord, namely excitotoxic stimulation or severe metabolic perturbation (with oxidative stress, hypoxia/aglycemia), can be applied with differential outcome in terms of cell types and functional loss. In either case, cell death is a delayed phenomenon developing over several hours. Neurons are more vulnerable to excitotoxicity and more resistant to metabolic perturbation, while the opposite holds true for glia. Neurons mainly die because of hyperactivation of poly(ADP-ribose) polymerase-1 (PARP-1) with subsequent DNA damage and mitochondrial energy collapse. Conversely, glial cells die predominantly by apoptosis. It is likely that early neuroprotection against acute spinal injury may require tailor-made drugs targeted to specific cell-death processes of certain cell types within the locomotor circuitry. Furthermore, comparison of network size and function before and after graded injury provides an estimate of the minimal network membership to express the locomotor program.

Programmed necrosis, not apoptosis, in the heart

It is well known that apoptosis is an actively mediated cell suicide process. In contrast, necrosis, a morphologically distinct form of cell death, has traditionally been regarded as passive and unregulated. Over the past decade, however, experiments in Caenorhabditis elegans and mammalian cells have revealed that a significant proportion of necrotic death is, in fact, actively mediated by the doomed cell. Although a comprehensive understanding of necrosis is still lacking, some key molecular events have come into focus. Cardiac myocyte apoptosis and necrosis are prominent features of the major cardiac syndromes. Accordingly, the recognition of necrosis as a regulated process mandates a reexamination of cell death in the heart. This review discusses pathways that mediate programmed necrosis, how they intersect with apoptotic pathways, roles of necrosis in heart disease, and new therapeutic opportunities that the regulated nature of necrosis presents.

Thrombin mutant W215A/E217A treatment improves neurological outcome and reduces cerebral infarct size in a mouse model of ischemic stroke

BACKGROUND AND PURPOSE

Treatment of ischemic stroke by activation of endogenous plasminogen using tissue plasminogen activator is limited by bleeding side effects. In mice, treatment of experimental ischemic stroke with activated protein C improves outcomes; however, activated protein C also has bleeding side effects. In contrast, activation of endogenous protein C using thrombin mutant W215A/E217A (WE) is antithrombotic without hemostasis impairment in primates. Therefore, we investigated the outcome of WE-treated experimental ischemic stroke in mice.

METHODS

The middle cerebral artery was occluded with a filament for 60 minutes to induce ischemic stroke. Vehicle, recombinant WE, or tissue plasminogen activator was administered during middle cerebral artery occlusion or 2 hours after middle cerebral artery occlusion. Neurological performance was scored daily. Intracranial bleeding and cerebral infarct size, defined by 2,3,5-triphenyltetrazolium chloride exclusion, were determined on autopsy. Hemostasis was evaluated using tail bleeding tests.

RESULTS

WE improved neurological performance scores, increased laser Doppler flowmetry-monitored post-middle cerebral artery occlusion reperfusion of the parietal cortex, and reduced 2,3,5-triphenyltetrazolium chloride-defined cerebral infarct size versus vehicle controls. However, unlike tissue plasminogen activator, WE did not increase tail bleeding or intracranial hemorrhage.

CONCLUSIONS

WE treatment is neuroprotective without hemostasis impairment in experimental acute ischemic stroke in mice and thus may provide an alternative to tissue plasminogen activator for stroke treatment.

Studies of locomotor network neuroprotection by the selective poly(ADP-ribose) polymerase-1 inhibitor PJ-34 against excitotoxic injury to the rat spinal cord in vitro

Delayed neuronal destruction after acute spinal injury is attributed to excitotoxicity mediated by hyperactivation of poly(ADP-ribose) polymerase-1 (PARP-1) that induces 'parthanatos', namely a non-apoptotic cell death mechanism. With an in vitro model of excitotoxicity, we have previously observed parthanatos of rat spinal cord locomotor networks to be decreased by a broad spectrum PARP-1 inhibitor. The present study investigated whether the selective PARP-1 inhibitor N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-(N,N-dimethylamino)acetamide.HCl (PJ-34) not only protected networks from kainate-evoked excitotoxicity, but also prevented loss of locomotor patterns recorded as fictive locomotion from lumbar (L) ventral roots (VRs) 24 h later. PJ-34 (60 μm) blocked PARP-1 activation and preserved dorsal, central and ventral gray matter with maintained reflex activity even after a large dose of kainate. Fictive locomotion could not, however, be restored by either electrical stimulation or bath-applied neurochemicals (N-methyl-D-aspartate plus 5-hydroxytryptamine). A low kainate concentration induced less histological damage that was widely prevented by PJ-34. Nonetheless, fictive locomotion was observed in just over 50% of preparations whose histological profile did not differ (except for the dorsal horn) from those lacking such a rhythm. Our data show that inhibition of PARP-1 could amply preserve spinal network histology after excitotoxicity, with return of locomotor patterns only when the excitotoxic stimulus was moderate. These results demonstrated divergence between histological and functional outcome, implying a narrow borderline between loss of fictive locomotion and neuronal preservation. Our data suggest that either damage of a few unidentified neurons or functional network inhibition was critical for ensuring locomotor cycles.

Zinc: new clues to diverse roles in brain ischemia

Cerebral ischemia is a leading cause of morbidity and mortality, reflecting the extraordinary sensitivity of the brain to a brief loss of blood flow. A significant goal has been to identify pathways of neuronal injury that are selectively activated after stroke and may be amenable to drug therapy. An important advance was made nearly 25 years ago when Ca(2+) overload was implicated as a critical link between glutamate excitotoxicity and ischemic neurodegeneration. However, early hope for effective therapies faded as glutamate-targeted trials repeatedly failed to demonstrate efficacy in humans. In a review in 2000 in this journal, we described new evidence linking a related cation, zinc (Zn(2+)), to neuronal injury, emphasizing sources and mechanisms of Zn(2+) toxicity. The current review highlights progress over the last decade, emphasizing mechanisms through which Zn(2+) ions (from multiple sources) participate together with Ca(2+) in different stages of cascades of ischemic injury.

Effects of 6(5H)-phenanthridinone, an inhibitor of poly(ADP-ribose)polymerase-1 activity (PARP-1), on locomotor networks of the rat isolated spinal cord

Excitotoxicity is considered to be a major pathophysiological mechanism responsible for extensive neuronal death after acute spinal injury. The chief effector of such a neuronal death is thought to be the hyperactivation of intracellular PARP-1 that leads to cell energy depletion and DNA damage with the manifestation of non-apoptotic cell death termed parthanatos. An in vitro lesion model using the neonatal rat spinal cord has recently shown PARP-1 overactivity to be closely related to neuronal losses after an excitotoxic challenge by kainate: in this system the PARP-1 inhibitor 6(5H)-phenanthridinone (PHE) appeared to be a moderate histological neuroprotector. This article investigated whether PHE could actually preserve the function of locomotor networks in vitro from excitotoxicity. Bath-applied PHE (after a 60 min kainate application) failed to recover locomotor network function 24 h later. When the PHE administration was advanced by 30 min (during the administration of kainate), locomotor function could still not be recovered, while basic network rhythmicity persisted. Histochemical analysis showed that, even if the number of surviving neurons was improved with this protocol, it had failed to reach the threshold of minimal network membership necessary for expressing locomotor patterns. These results suggest that PARP-1 hyperactivity was a rapid onset mechanism of neuronal loss after an excitotoxic challenge and that more selective and faster-acting PARP-1 inhibitors are warranted to explore their potential neuroprotective role.

Novel targeted therapeutics: inhibitors of MDM2, ALK and PARP

We reviewed preclinical data and clinical development of MDM2 (murine double minute 2), ALK (anaplastic lymphoma kinase) and PARP (poly [ADP-ribose] polymerase) inhibitors. MDM2 binds to p53, and promotes degradation of p53 through ubiquitin-proteasome degradation. JNJ-26854165 and RO5045337 are 2 small-molecule inhibitors of MDM2 in clinical development. ALK is a transmembrane protein and a member of the insulin receptor tyrosine kinases. EML4-ALK fusion gene is identified in approximately 3-13% of non-small cell lung cancer (NSCLC). Early-phase clinical studies with Crizotinib, an ALK inhibitor, in NSCLC harboring EML4-ALK have demonstrated promising activity with high response rate and prolonged progression-free survival. PARPs are a family of nuclear enzymes that regulates the repair of DNA single-strand breaks through the base excision repair pathway. Randomized phase II study has shown adding PARP-1 inhibitor BSI-201 to cytotoxic chemotherapy improves clinical outcome in patients with triple-negative breast cancer. Olaparib, another oral small-molecule PARP inhibitor, demonstrated encouraging single-agent activity in patients with advanced breast or ovarian cancer. There are 5 other PARP inhibitors currently under active clinical investigation.

Poly(ADP-ribose) (PAR) binding to apoptosis-inducing factor is critical for PAR polymerase-1-dependent cell death (parthanatos)

The mitochondrial protein apoptosis-inducing factor (AIF) plays a pivotal role in poly(ADP-ribose) polymerase-1 (PARP-1)-mediated cell death (parthanatos), during which it is released from the mitochondria and translocates to the nucleus. We show that AIF is a high-affinity poly(ADP-ribose) (PAR)-binding protein and that PAR binding to AIF is required for parthanatos both in vitro and in vivo. AIF bound PAR at a site distinct from AIF's DNA binding site, and this interaction triggered AIF release from the cytosolic side of the mitochondrial outer membrane. Mutation of the PAR binding site in AIF did not affect its NADH (reduced form of nicotinamide adenine dinucleotide) oxidase activity, its ability to bind FAD (flavin adenine dinucleotide) or DNA, or its ability to induce nuclear condensation. However, this AIF mutant was not released from mitochondria and did not translocate to the nucleus or mediate cell death after PARP-1 activation. These results suggest a mechanism for PARP-1 to initiate AIF-mediated cell death and indicate that AIF's bioenergetic cell survival-promoting functions are separate from its effects as a mitochondrially derived death effector. Interference with the PAR-AIF interaction or PAR signaling may provide notable opportunities for preventing cell death after activation of PARP-1.

Sex differences in the response to poly(ADP-ribose) polymerase-1 deletion and caspase inhibition after stroke

BACKGROUND AND PURPOSE

Emerging data suggest that the molecular cell death pathways triggered by ischemic insults differ in the male and female brain. Cell death in males is initiated by poly(ADP-ribose) polymerase-1 (PARP-1) activation; however, manipulation of this pathway paradoxically increases ischemic damage in females. In contrast, females are exquisitely sensitive to caspase-mediated cell death. The effect of caspase inhibition in PARP-1 knockout mice was evaluated to determine if the detrimental effects of PARP deletion in females were secondary to increased caspase activation.

METHODS

Focal stroke was induced by transient or permanent middle cerebral artery occlusion (MCAO) in wild-type (WT) and PARP-1(-/-) mice of both sexes. The pan-caspase inhibitor, quinoline-Val-Asp(Ome)-CH2-O-phenoxy (Q-VD-OPh), was administered 90 minutes after middle cerebral artery occlusion. Infarct size and neurological sores were assessed. Separate cohorts were used for protein analysis for PAR, Apoptosis inducing factor (AIF), caspase-9, and caspase-3.

RESULTS

WT mice of both sexes had increased nuclear AIF after stroke compared to PARP-1(-/-) mice. PARP-1(-/-) females had higher mitochondrial cytochrome C and activated caspase-9 and -3 levels than WT female mice. PARP-1(-/-) females also had an increase in stroke-induced cytosolic cytochrome C release compared with WT females, which was not seen in males. Q-VD-OPh decreased caspase-9 in both males and females but only led to reduction of infarct in females. PARP-1(-/-) males had smaller infarcts, whereas PARP-1(-/-) females had larger strokes compared with WT. Q-VD-OPh significantly decreased infarct in both WT and PARP-1(-/-) females in both transient and permanent MCAO models, but had no effect in males.

CONCLUSIONS

Deletion of PARP-1 reduces infarct in males but exacerbates injury in females. PARP-1(-/-) females have enhanced caspase activation. The detrimental effects of PARP loss in females can be reversed with caspase inhibition.

Metformin induces both caspase-dependent and poly(ADP-ribose) polymerase-dependent cell death in breast cancer cells

There is substantial evidence that metformin, a drug used to treat type 2 diabetics, is potentially useful as a therapeutic agent for cancer. However, a better understanding of the molecular mechanisms through which metformin promotes cell-cycle arrest and cell death of cancer cells is necessary. It will also be important to understand how the response of tumor cells differs from normal cells and why some tumor cells are resistant to the effects of metformin. We have found that exposure to metformin induces cell death in all but one line, MDA-MB-231, in a panel of breast cancer cell lines. MCF10A nontransformed breast epithelial cells were resistant to the cytotoxic effects of metformin, even after extended exposure to the drug. In sensitive lines, cell death was mediated by both apoptosis and a caspase-independent mechanism. The caspase-independent pathway involves activation of poly(ADP-ribose) polymerase (PARP) and correlates with enhanced synthesis of PARP and nuclear translocation of apoptosis-inducing factor (AIF), which plays an important role in mediating cell death. Metformin-induced, PARP-dependent cell death is associated with a striking enlargement of mitochondria. Mitochondrial enlargement was observed in all sensitive breast cancer cell lines but not in nontransformed cells or resistant MDA-MB-231. Mitochondrial enlargement was prevented by inhibiting PARP activity or expression. A caspase inhibitor blocked metformin-induced apoptosis but did not affect PARP-dependent cell death or mitochondrial enlargement. Thus, metformin has cytotoxic effects on breast cancer cells through 2 independent pathways. These findings will be pertinent to efforts directed at using metformin or related compounds for cancer therapy.

Anti-inflammatory mechanism of taurine against ischemic stroke is related to down-regulation of PARP and NF-κB

Taurine is reported to reduce tissue damage induced by inflammation and to protect the brain against experimental stroke. The objective of this study was to investigate whether taurine reduced ischemic brain damage through suppressing inflammation related to poly (ADP-ribose) polymerase (PARP) and nuclear factor-kappaB (NF-κB) in a rat model of stroke. Rats received 2 h ischemia by intraluminal filament and were then reperfused. Taurine (50 mg/kg) was administered intravenously 1 h after ischemia. Treatment with taurine markedly reduced neurological deficits, lessened brain swelling, attenuated cell death, and decreased the infarct volume 72 h after ischemia. Our data showed the up-regulation of PARP and NF-κB p65 in cytosolic fractions in the core and nuclear fractions in the penumbra and core, and the increases in the nuclear poly (ADP-ribose) levels and the decreases in the intracellular NAD+ levels in the penumbra and core at 22 h of reperfusion; these changes were reversed by taurine. Moreover, taurine significantly reduced the levels of tumor necrosis factor-α, interleukin-1β, inducible nitric oxide synthase, and intracellular adhesion molecule-1, lessened the activities of myeloperoxidase and attenuated the infiltration of neutrophils in the penumbra and core at 22 h of reperfusion. These data demonstrate that suppressing the inflammatory reaction related to PARP and NF-κB-driven expression of inflammatory mediators may be one mechanism of taurine against ischemic stroke.

Neuronal Sirt3 protects against excitotoxic injury in mouse cortical neuron culture

Background

Sirtuins (Sirt), a family of nicotinamide adenine nucleotide (NAD) dependent deacetylases, are implicated in energy metabolism and life span. Among the known Sirt isoforms (Sirt1-7), Sirt3 was identified as a stress responsive deacetylase recently shown to play a role in protecting cells under stress conditions. Here, we demonstrated the presence of Sirt3 in neurons, and characterized the role of Sirt3 in neuron survival under NMDA-induced excitotoxicity.

Methodology/Principal Findings

To induce excitotoxic injury, we exposed primary cultured mouse cortical neurons to NMDA (30 µM). NMDA induced a rapid decrease of cytoplasmic NAD (but not mitochondrial NAD) in neurons through poly (ADP-ribose) polymerase-1 (PARP-1) activation. Mitochondrial Sirt3 was increased following PARP-1 mediated NAD depletion, which was reversed by either inhibition of PARP-1 or exogenous NAD. We found that massive reactive oxygen species (ROS) produced under this NAD depleted condition mediated the increase in mitochondrial Sirt3. By transfecting primary neurons with a Sirt3 overexpressing plasmid or Sirt3 siRNA, we showed that Sirt3 is required for neuroprotection against excitotoxicity.

Conclusions

This study demonstrated for the first time that mitochondrial Sirt3 acts as a prosurvival factor playing an essential role to protect neurons under excitotoxic injury.

Small interfering RNA mediated Poly (ADP-ribose) Polymerase-1 inhibition upregulates the heat shock response in a murine fibroblast cell line

Poly (ADP-ribose) polymerase-1 (PARP-1) is a highly conserved multifunctional enzyme, and its catalytic activity is stimulated by DNA breaks. The activation of PARP-1 and subsequent depletion of nicotinamide adenine dinucleotide (NAD⁺) and adenosine triphosphate (ATP) contributes to significant cytotoxicity in inflammation of various etiologies. On the contrary, induction of heat shock response and production of heat shock protein 70 (HSP-70) is a cytoprotective defense mechanism in inflammation. Recent data suggests that PARP-1 modulates the expression of a number of cellular proteins at the transcriptional level. In this study, small interfering RNA (siRNA) mediated PARP-1 knockdown in murine wild-type fibroblasts augmented heat shock response as compared to untreated cells (as evaluated by quantitative analysis of HSP-70 mRNA and HSP-70 protein expression). These events were associated with increased DNA binding of the heat shock factor-1 (HSF-1), the major transcription factor of the heat shock response. Co-immunoprecipitation experiments in nuclear extracts of the wild type cells demonstrated that PARP-1directly interacted with HSF-1. These data demonstrate that, in wild type fibroblasts, PARP-1 plays a pivotal role in modulating the heat shock response both through direct interaction with HSF-1 and poly (ADP-ribosylation).

Robust protective effects of a novel multimodal neuroprotectant oxopropanoyloxy benzoic acid (a salicylic acid/pyruvate ester) in the postischemic brain

Cerebral ischemia leads to brain injury via a complex series of pathophysiological events. Therefore, multidrug treatments or multitargeting drug treatments are attractive options in efficiently limiting brain damage. Here, we report a novel multifunctional compound oxopropanoyloxy benzoic acid (OBA-09), a simple ester of pyruvate and salicylic acid. This protective effect was manifested by recoveries from neurological and behavioral deficits. OBA-09 exhibited antioxidative effects in the postischemic brain, which was evidenced by remarkable reduction of lipid peroxidation and 4-hydroxy-2-nonenal staining in OBA-09-administered animals. Reactive oxygen species generation was markedly suppressed in primary cortical cultures under oxygen-glucose deprivation. More interestingly, OBA-09 was capable of scavenging hydroxyl radical in cell-free assays. High-performance liquid chromatography results demonstrated that OBA-09 was hydrolyzed to salicylic acid and pyruvate with t(1/2) = 43 min in serum and 4.2 h in brain parenchyma, indicating that antioxidative function of OBA-09 is executed by itself and also by salicylic acid after the hydrolysis. In addition to antioxidative function, OBA-09 exerts anti-excitotoxic and anti-Zn(2+)-toxic functions, which might be attributed to attenuation of ATP and nicotinamide adenine dinucleotide depletion and to the suppression of nuclear factor-κB activity induction. Together these results indicate that OBA-09 has a potent therapeutic potential as a multimodal neuroprotectant in the postischemic brain and these effects were conferred by OBA-09 itself and subsequently its hydrolyzed products.

Regulation of MKP-1 expression and MAPK activation by PARP-1 in oxidative stress: a new mechanism for the cytoplasmic effect of PARP-1 activation

Previously, it was suggested that the release of nuclearly formed ADP-ribose polymers or ADP-ribosylated proteins could be responsible for the cytosolic and mitochondrial effects of poly(ADP-ribose) polymerase (PARP)-1 activation in oxidative stress. In this report, we provide a novel alternative mechanism. We found that reactive oxygen species-activated PARP-1 regulated the activation of JNK and p38 mitogen-activated protein kinases (MAPKs) because inhibition of PARP-1 by pharmacons, small interfering RNA silencing of PARP-1 expression, or the transdominant expression of enzymatically inactive PARP-1 resulted in the inactivation of these MAPKs. This regulation was achieved by increased expression and enlarged cytoplasmic localization of MAPK phosphatase-1 (MKP-1) upon PARP-1 inhibition in oxidative stress because changes in MKP-1 expression were reflected in the phosphorylation states of JNK and p38. Furthermore, we found that in MKP-1-silenced cells, PARP inhibition was unable to exert its protective effect, indicating the pivotal roles of JNK and p38 in mediating the oxidative-stress-induced cell death as well as that of increased MKP-1 expression in mediating the protective effect of PARP inhibition. We suggest that regulation of a protein that can directly influence cytoplasmic signaling cascades at the expression level represents a novel mechanism for the cytoplasmic action of PARP-1 inhibition.

Cellular stress responses, the hormesis paradigm, and vitagenes: novel targets for therapeutic intervention in neurodegenerative disorders

Despite the capacity of chaperones and other homeostatic components to restore folding equilibrium, cells appear poorly adapted for chronic oxidative stress that increases in cancer and in metabolic and neurodegenerative diseases. Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This article introduces the concept of hormesis and its applications to the field of neuroprotection. It is argued that the hormetic dose response provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose-response relationships, their mechanistic foundations, and their relationship to the concept of biological plasticity, as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This article describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways, including sirtuin and Nrf2 and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. Particular attention is given to the emerging role of nitric oxide, carbon monoxide, and hydrogen sulfide gases in hormetic-based neuroprotection and their relationship to membrane radical dynamics and mitochondrial redox signaling.

Neuronal protective role of PBEF in a mouse model of cerebral ischemia

Pre-B-cell colony-enhancing factor (PBEF) (also known as nicotinamide phosphoribosyltransferase) is a rate-limiting enzyme in the salvage pathway for mammalian biosynthesis of nicotinamide adenine dinucleotide (NAD(+)). By synthesizing NAD(+), PBEF functions to maintain an energy supply that has critical roles in cell survival. Cerebral ischemia is a major neural disorder with a high percentage of mortality and disability. Ischemia leads to energy depletion and eventually neuronal death and brain damage. This study investigated the role of PBEF in cerebral ischemia using a photothrombosis mouse model. Using immunostaining, we initially determined that PBEF is highly expressed in neurons, but not in glial cells in the mouse brain. To study the role of PBEF in ischemia in vivo, we used PBEF knockout heterozygous (Pbef+/-) mice. We showed that these mice have lower PBEF expression and NAD(+) level than do wild-type (WT) mice. When subjected to photothrombosis, Pbef+/- mice have significantly larger infarct volume than do age-matched WT mice at 24 hours after ischemia. Higher density of degenerating neurons was detected in the penumbra of Pbef+/- mice than in WT mice using Fluoro-Jade B staining. Our study shows that PBEF has a neuronal protective role in cerebral ischemia presumably through enhanced energy metabolism.

PARP1 gene knock-out increases resistance to retinal degeneration without affecting retinal function

Retinitis pigmentosa (RP) is a group of inherited neurodegenerative diseases affecting photoreceptors and causing blindness in humans. Previously, excessive activation of enzymes belonging to the poly-ADP-ribose polymerase (PARP) group was shown to be involved in photoreceptor degeneration in the human homologous rd1 mouse model for RP. Since there are at least 16 different PARP isoforms, we investigated the exact relevance of the predominant isoform - PARP1 - for photoreceptor cell death using PARP1 knock-out (KO) mice. In vivo and ex vivo morphological analysis using optic coherence tomography (OCT) and conventional histology revealed no major alterations of retinal phenotype when compared to wild-type (wt). Likewise, retinal function as assessed by electroretinography (ERG) was normal in PARP1 KO animals. We then used retinal explant cultures derived from wt, rd1, and PARP1 KO animals to test their susceptibility to chemically induced photoreceptor degeneration. Since photoreceptor degeneration in the rd1 retina is triggered by a loss-of-function in phosphodiesterase-6 (PDE6), we used selective PDE6 inhibition to emulate the rd1 situation on non-rd1 genotypes. While wt retina subjected to PDE6 inhibition showed massive photoreceptor degeneration comparable to rd1 retina, in the PARP1 KO situation, cell death was robustly reduced. Together, these findings demonstrate that PARP1 activity is in principle dispensable for normal retinal function, but is of major importance for photoreceptor degeneration under pathological conditions. Moreover, our results suggest that PARP dependent cell death or PARthanatos may play a major role in retinal degeneration and highlight the possibility to use specific PARP inhibitors for the treatment of RP.

Oxidative stress initiates DNA damager MNNG-induced poly(ADP-ribose)polymerase-1-dependent parthanatos cell death

The alkylating agent N-methyl-N'-nitro-N'-nitrosoguanidine (MNNG) can cause excess DNA strand breaks that lead to poly(ADP-ribose)polymerase-1 (PARP-1) overactivation and cell death (parthanatos). However, the detail mechanism of MNNG-induced parthanatos was not well-investigated. In this study, we used MNNG-treated mouse embryonic fibroblasts (MEFs) to elucidate the signaling pathways of MNNG-induced parthanatos. We found that MNNG-induced cell death accompanied by rapid PARP-1 activation, c-Jun N-terminal kinase (JNK) activation, biphasic reactive oxygen species (ROS) production and intracellular calcium increase. The early ROS production occurring at 1 min and peaking at 5-15 min after MNNG treatment partially resulted from NADPH oxidase. In contrast, the late phase of ROS production occurring at 30 min and time-dependently increasing up to 6h after MNNG treatment was generated by mitochondria. The antioxidant, NAC can abrogate all phenomena caused by MNNG. Results indicate that the calcium rise was downstream of early ROS production, and was involved in PARP-1 and JNK activation. Moreover, the PARP inhibitor was able to reduce MNNG-induced late-phase ROS production, calcium elevation, and cell death. Results further indicated the involvement of RIP1 in sustained ROS production and calcium increase. We characterized the interactive roles of ROS, calcium, JNK, and RIP1 in MNNG-induced cell death. We found that in addition to the alkylating property previously demonstrated, ROS production triggered by MNNG results in enhanced DNA damage and PARP-1 activation. Moreover, intracellular calcium elevation and ROS production have mutual amplification effects and thus contribute to PARP-1-mediated parthanatos.

Posttranslational modification of mammalian AP endonuclease (APE1)

A key issue in studying mammalian DNA base excision repair is how its component proteins respond to a plethora of cell-signaling mediators invoked by DNA damage and stress-inducing agents such as reactive oxygen species, and how the actions of individual BER proteins are attributed to cell survival or apoptotic/necrotic death. This article reviews the past and recent progress on posttranslational modification (PTM) of mammalian apurinic/apyrimidinic (AP) endonuclease 1 (APE1).

Sex shapes experimental ischemic brain injury

Biologic sex and sex steroids are important factors in clinical and experimental stroke. This review evaluates key evidence that biological sex strongly alters mechanisms and outcomes from cerebral ischemia. The role of androgens in male stroke is understudied and important to pursue given that male sex is a well known risk factor for human stroke. To date, male sex steroids remain largely evaluated at the bench rather than the bedside. We review recent advances in our understanding of androgens in the context of ischemic cell death and neuroprotection. We also highlight some possible molecular mechanisms by which androgens impact ischemic outcomes.

Modulation of PARP-1 and PARP-2 expression by L-carnosine and trehalose after LPS and INFγ-induced oxidative stress

Poly(ADP-ribose) polymerases (PARPs) play a crucial role in DNA damage surveillance through their nick sensor functions. Since PARPs' over activation leads to an excessive consumption of NAD(+) and ATP depletion, these enzymes also are involved in the early events of programmed cell death as well as in necrosis. In order to verify the protective action of L: -carnosine and trehalose against NO induced cell death, in the present study we examined their effects on the expression of PARP-1, PARP-2 and iNOS in primary rat astrocyte and oligodendrocyte cells, treated with lipopolysaccharide (LPS) and interferon gamma (INFγ), through semi-quantitative PCR and western analysis. To further characterize the molecular mechanisms underlying L-carnosine and trehalose action, we measured cell viability, nitrite production and LDH release. The data obtained clearly demonstrate that in the stress model employed L-carnosine and trehalose down regulate PARP-1 and PARP-2 expression in both cell phenotypes, thus suggesting their possible application in clinical trials.

Oxidative stress and NAD+ in ischemic brain injury: current advances and future perspectives

Numerous studies have indicated oxidative stress as a key pathological factor in ischemic brain injury. One of the key links between oxidative stress and cell death is excessive activation of poly(ADP-ribose) polymerase-1 (PARP-1), which plays an important role in the ischemic brain damage in male animals. Multiple studies have also suggested that NAD+ depletion mediates PARP-1 cytotoxicity, and NAD+ administration can decrease ischemic brain injury. A number of recent studies have provided novel information regarding the mechanisms underlying the roles of oxidative stress and NAD+-dependent enzymes in ischemic brain injury. Of particular interest, there have been exciting progresses regarding the mechanisms underlying the roles of NADPH oxidase and PARP-1 in cerebral ischemia. For examples, it has been suggested that androgen signaling and binding of PARP-1 onto estrogen receptors could account for the intriguing findings that PARP-1 plays remarkably differential roles in the ischemic brain damage of male and female animals; and some studies have suggested casein kinase 2, copper-zinc superoxide dismutase, and estrogen signaling can modulate the expression and activity of NADPH oxidase. This review summarizes these important current advances, and proposes future perspectives for the studies on the roles of oxidative stress and NAD+ in cerebral ischemia. It is increasingly likely that future studies on NAD- and NADP-dependent enzymes, such as NADPH oxidase, PARP-1, and sirtuins, would expose novel mechanisms underlying the roles of oxidative stress in cerebral ischemia, and suggest new therapeutic strategies for treating the debilitating disease.

Tumor necrosis factor-like weak inducer of apoptosis and fibroblast growth factor-inducible 14 mediate cerebral ischemia-induced poly(ADP-ribose) polymerase-1 activation and neuronal death

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fibroblast growth factor-inducible 14 (Fn14) are expressed in neurons. Here we demonstrate that TWEAK induces a dose-dependent increase in neuronal death and that this effect is independent of tumor necrosis factor alpha (TNF-α) and mediated by nuclear factor-kappa B (NF-κB) pathway activation. Incubation with TWEAK induces apoptotic cell death in wild-type (Wt) but not in Fn14 deficient (Fn14(-/-)) neurons. Intracerebral injection of TWEAK induces accumulation of poly(ADP-ribose) polymers (PAR) in Wt but not in Fn14(-/-) mice. Exposure to oxygen-glucose deprivation (OGD) conditions increases TWEAK and Fn14 mRNA expression in Wt neurons, and decreases cell survival in Wt but not in Fn14(-/-) or TWEAK deficient (TWEAK(-/-)) neurons. Experimental middle cerebral artery occlusion (MCAO) increases the expression of TWEAK and Fn14 mRNA and active caspase-3, and the cleavage of poly(ADP-ribose) polymerase-1 (PARP-1) with accumulation of PAR in the ischemic area in Wt but not Fn14(-/-) mice. Together, these results suggest a model where in response to hypoxia/ischemia the interaction between TWEAK and Fn14 in neurons induces PARP-1 activation with accumulation of PAR polymers and cell death via NF-κB pathway activation. This is a novel pathway for hypoxia/ischemia-induced TWEAK-mediated cell death and a potential therapeutic target for ischemic stroke.

Kainate-mediated excitotoxicity induces neuronal death in the rat spinal cord in vitro via a PARP-1 dependent cell death pathway (Parthanatos)

Kainate is an effective excitotoxic agent to lesion spinal cord networks, thus providing an interesting model for investigating basic mechanisms of spinal cord injury. The present study aimed at revealing the type and timecourse of cell death in rat neonatal spinal cord preparations in vitro exposed to 1 h excitotoxic insult with kainate. Substantial numbers of neurons rather than glia showed pyknosis (albeit without necrosis and with minimal apoptosis occurrence) already apparent on kainate washout and peaking 12 h later with dissimilar spinal topography. Neurons appeared to suffer chiefly through a process involving anucleolytic pyknosis mediated by strong activation of poly(ADP-ribose)polymerase-1 (PARP-1) that generated poly ADP-ribose and led to nuclear translocation of the apoptotic inducing factor (AIF) with DNA damage. This process had the hallmarks of parthanatos-type neuronal death. The PARP-1 inhibitor 6-5(H)-phenathridione applied immediately after kainate washout significantly prevented pyknosis in a dose-dependent fashion and inhibited PARP-1-dependent nuclear AIF translocation. Conversely, the caspase-3 inhibitor II was ineffective against neuronal damage. Our results suggest that excitotoxicity of spinal networks was mainly directed to neurons and mediated by PARP-1 death pathways, indicating this mechanism as a potential target for neuroprotection to limit the acute damage to the local circuitry.

Microglial activation in stroke: therapeutic targets

Microglial activation is an early response to brain ischemia and many other stressors. Microglia continuously monitor and respond to changes in brain homeostasis and to specific signaling molecules expressed or released by neighboring cells. These signaling molecules, including ATP, glutamate, cytokines, prostaglandins, zinc, reactive oxygen species, and HSP60, may induce microglial proliferation and migration to the sites of injury. They also induce a nonspecific innate immune response that may exacerbate acute ischemic injury. This innate immune response includes release of reactive oxygen species, cytokines, and proteases. Microglial activation requires hours to days to fully develop, and thus presents a target for therapeutic intervention with a much longer window of opportunity than acute neuroprotection. Effective agents are now available for blocking both microglial receptor activation and the microglia effector responses that drive the inflammatory response after stroke. Effective agents are also available for targeting the signal transduction mechanisms linking these events. However, the innate immune response can have beneficial as well deleterious effects on outcome after stoke, and a challenge will be to find ways to selectively suppress the deleterious effects of microglial activation after stroke without compromising neurovascular repair and remodeling.

Perinatal asphyxia: current status and approaches towards neuroprotective strategies, with focus on sentinel proteins

Delivery is a stressful and risky event menacing the newborn. The mother-dependent respiration has to be replaced by autonomous pulmonary breathing immediately after delivery. If delayed, it may lead to deficient oxygen supply compromising survival and development of the central nervous system. Lack of oxygen availability gives rise to depletion of NAD⁺ tissue stores, decrease of ATP formation, weakening of the electron transport pump and anaerobic metabolism and acidosis, leading necessarily to death if oxygenation is not promptly re-established. Re-oxygenation triggers a cascade of compensatory biochemical events to restore function, which may be accompanied by improper homeostasis and oxidative stress. Consequences may be incomplete recovery, or excess reactions that worsen the biological outcome by disturbed metabolism and/or imbalance produced by over-expression of alternative metabolic pathways. Perinatal asphyxia has been associated with severe neurological and psychiatric sequelae with delayed clinical onset. No specific treatments have yet been established. In the clinical setting, after resuscitation of an infant with birth asphyxia, the emphasis is on supportive therapy. Several interventions have been proposed to attenuate secondary neuronal injuries elicited by asphyxia, including hypothermia. Although promising, the clinical efficacy of hypothermia has not been fully demonstrated. It is evident that new approaches are warranted. The purpose of this review is to discuss the concept of sentinel proteins as targets for neuroprotection. Several sentinel proteins have been described to protect the integrity of the genome (e.g. PARP-1; XRCC1; DNA ligase IIIα; DNA polymerase β, ERCC2, DNA-dependent protein kinases). They act by eliciting metabolic cascades leading to (i) activation of cell survival and neurotrophic pathways; (ii) early and delayed programmed cell death, and (iii) promotion of cell proliferation, differentiation, neuritogenesis and synaptogenesis. It is proposed that sentinel proteins can be used as markers for characterising long-term effects of perinatal asphyxia, and as targets for novel therapeutic development and innovative strategies for neonatal care.

Serine racemase deletion protects against cerebral ischemia and excitotoxicity

D-Serine, formed from L-serine by serine racemase (SR), is a physiologic coagonist at NMDA receptors. Using mice with targeted deletion of SR, we demonstrate a role for D-serine in NMDA receptor-mediated neurotoxicity and stroke. Brain cultures of SR-deleted mice display markedly diminished nitric oxide (NO) formation and neurotoxicity. In intact SR knock-out mice, NO formation and nitrosylation of NO targets are substantially reduced. Infarct volume following middle cerebral artery occlusion is dramatically diminished in several regions of the brains of SR mutant mice despite evidence of increased NMDA receptor number and sensitivity.

Poly(ADP-ribose)polymerase inhibitor can attenuate the neuronal death after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity in mice

An excessive expression of poly(ADP-ribose)polymerase (PARP) has been demonstrated to play a key role in the pathogenesis of Parkinson's disease (PD). Here we investigated the therapeutic effect of the PARP inhibitor benzamide against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice. In our HPLC and Western blot analysis, pretreatment with benzamide showed a neuroprotective effect against MPTP neurotoxicity in mice. Posttreatment with benzamide also attenuated MPTP neurotoxicity in mice. Furthermore, our immunohistochemical study showed that posttreatment with benzamide significantly prevented neuronal damage by suppressing overexpression of neuronal, microglial, and astroglial PARP after MPTP treatment. These findings have important implications for the therapeutic time window and choice of PARP inhibitors in PD patients. Our present findings provide further evidence that PARP inhibitor may offer a novel therapeutic strategy for PD.

Increased nuclear apoptosis-inducing factor after transient focal ischemia: a 12/15-lipoxygenase-dependent organelle damage pathway

12/15-lipoxygenase (12/15-LOX) contributes to acute neuronal injury and edema formation in mouse models of middle cerebral artery occlusion (MCAO). The apoptosis-inducing factor (AIF) is implicated in caspase-independent forms of apoptosis, and has been linked to ischemic neuronal cell death. We show here that increased AIF in the peri-ischemic cortex of mouse colocalizes with 12/15-LOX after 2 h of MCAO. The 12/15-LOX inhibitor baicalein prevents the increase and nuclear localization of AIF, suggesting this pathway may be partially responsible for the neuroprotective qualities of baicalein. Using an established cell line model of neuronal oxidative stress, we show that 12/15-LOX activated after glutathione depletion leads to AIF translocation to the nucleus, which is abrogated by the 12/15-LOX inhibitor baicalein (control: 19.3%+/-6.8% versus Glutamate: 64.0%+/-8.2% versus glutamate plus baicalein: 11.4%+/-2.2%). Concomitantly, resident proteins of the ER are dispersed throughout the cell (control: 31.0%+/-8.4% versus glutamate: 70.0%+/-5.5% versus glutamate plus baicalein: 8.0%+/-2.7%), suggesting cell death through organelle damage. Taken together, these findings show that 12/15-LOX and AIF are sequential actors in a common cell death pathway that may contribute to stroke-induced brain damage.

Diabetic Cardiomyopathy: Mechanisms and Therapeutic Targets

The incidence and prevalence of diabetes mellitus are each increasing rapidly in our society. The majority of patients with diabetes succumb ultimately to heart disease, much of which stems from atherosclerotic disease and hypertension. However, cardiomyopathy can develop independent of elevated blood pressure or coronary artery disease, a process termed diabetic cardiomyopathy. This disorder is a complex diabetes-associated process characterized by significant changes in the physiology, structure, and mechanical function of the heart. Here, we review recently derived insights into mechanisms and molecular events involved in the pathogenesis of diabetic cardiomyopathy.

The role of PARP activation in glutamate-induced necroptosis in HT-22 cells

Oxidative cell death contributes to neuronal cell death in many neurological diseases such as stroke, brain trauma, and Alzheimer's disease. In this study, we explored the involvement of poly(ADP-ribose)-polymerase (PARP) in oxidative stress-induced necroptosis. We showed that PJ34, a potent and specific inhibitor of PARP, can completely inhibit glutamate-induced necroptosis in HT-22 cells. This protective effect was still observed 8h after glutamate exposure followed by PJ34 treatment. These results suggest that PARP activation plays a critical role in glutamate-induced necroptosis. We also examined the interaction between PARP and a necroptosis inhibitor called necrostatin-1 (Nec-1). Previously, we showed that Nec-1 protects against glutamate-induced oxytosis by inhibiting the translocation of cellular apoptosis-inducing factor (AIF), a downstream target of PARP-1 activation. In this study, Nec-1 reduced PARP activity but had no effect on the expression of PARP-1 in cells treated with glutamate. Nec-1 also did not protect against cell death mediated by the PARP activator N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), although PJ34 did protect against MNNG-mediated cell death. These findings suggest that Nec-1 is not a direct PARP inhibitor and that its signaling target is located upstream of PARP.

NAD+ depletion is necessary and sufficient for poly(ADP-ribose) polymerase-1-mediated neuronal death

Poly(ADP-ribose)-1 (PARP-1) is a key mediator of cell death in excitotoxicity, ischemia, and oxidative stress. PARP-1 activation leads to cytosolic NAD(+) depletion and mitochondrial release of apoptosis-inducing factor (AIF), but the causal relationships between these two events have been difficult to resolve. Here, we examined this issue by using extracellular NAD(+) to restore neuronal NAD(+) levels after PARP-1 activation. Exogenous NAD(+) was found to enter neurons through P2X(7)-gated channels. Restoration of cytosolic NAD(+) by this means prevented the glycolytic inhibition, mitochondrial failure, AIF translocation, and neuron death that otherwise results from extensive PARP-1 activation. Bypassing the glycolytic inhibition with the metabolic substrates pyruvate, acetoacetate, or hydroxybutyrate also prevented mitochondrial failure and neuron death. Conversely, depletion of cytosolic NAD(+) with NAD(+) glycohydrolase produced a block in glycolysis inhibition, mitochondrial depolarization, AIF translocation, and neuron death, independent of PARP-1 activation. These results establish NAD(+) depletion as a causal event in PARP-1-mediated cell death and place NAD(+) depletion and glycolytic failure upstream of mitochondrial AIF release.

Tumor necrosis factor-mediated cell death: to break or to burst, that's the question

In this review, we discuss the signal-transduction pathways of three major cellular responses induced by tumor necrosis factor (TNF): cell survival through NF-kappaB activation, apoptosis, and necrosis. Recruitment and activation of caspases plays a crucial role in the initiation and execution of TNF-induced apoptosis. However, experimental inhibition of caspases reveals an alternative cell death pathway, namely necrosis, also called necroptosis, suggesting that caspases actively suppress the latter outcome. TNF-induced necrotic cell death crucially depends on the kinase activity of receptor interacting protein serine-threonine kinase 1 (RIP1) and RIP3. It was recently demonstrated that ubiquitination of RIP1 determines whether it will function as a pro-survival or pro-cell death molecule. Deeper insight into the mechanisms that control the molecular switches between cell survival and cell death will help us to understand why TNF can exert so many different biological functions in the etiology and pathogenesis of human diseases.

Contributions of poly(ADP-ribose) polymerase-1 and -2 to nuclear translocation of apoptosis-inducing factor and injury from focal cerebral ischemia

Excessive oxidative damage to DNA leads to activation of poly(ADP-ribose) polymerase-1 (PARP-1), accumulation of PAR polymers, translocation of apoptosis-inducing factor (AIF) from mitochondria to the nucleus, and cell death. In this study, we compared the effect of gene deletion of PARP-1 and PARP-2, enzymes activated by DNA oxidative damage, in male mice subjected to 2 h of focal cerebral ischemia. Infarct volume at 3 days of reperfusion was markedly decreased to a similar extent in PARP-1- and PARP-2-null mice. The ischemia-induced increase in nuclear AIF accumulation was largely suppressed in both knockout genotypes. The transient increase in PAR during early reperfusion was nearly blocked in PARP-1-null mice, but only moderately decreased at 1-h reperfusion in PARP-2-null mice. Differences in the tissue volume at risk, as assessed by arterial casts and autoradiographic analysis of regional blood flow, did not fully account for the large reductions in AIF translocation and infarct volume in both PARP null mice. Cell death was attenuated in PARP-2-null neurons exposed to a submaximal concentration of 100 microM NMDA for 5 min, but not in those exposed to a near-maximal toxic concentration of 500 microM NMDA. We conclude that PARP-2 contributes substantially to nuclear translocation of AIF and infarct size after transient focal cerebral ischemia in male mice, but that protection is disproportionate to the attenuation of overall PARP activity.

Optical Microangiography: A Label Free 3D Imaging Technology to Visualize and Quantify Blood Circulations within Tissue Beds in vivo

Optical microangiography (OMAG) is a recently developed volumetric imaging technique that is capable of producing 3D images of dynamic blood perfusion within microcirculatory tissue beds in vivo. The imaging contrast of OMAG image is based on the intrinsic optical scattering signals backscattered by the moving blood cells in patent blood vessels, thus it is a label free imaging technique. In this paper, I will first discuss its recent developments that use a constant modulation frequency introduced in the spectral interferograms to achieve the blood perfusion imaging. I will then introduce its latest development that utilizes the inherent blood flow to modulate the spectral interferograms to realize the blood perfusion imaging. Finally, examples of using OMAG to delineate the dynamic blood perfusion, down to capillary level resolution, within living tissues are given, including cortical blood perfusion in the brain of small animals and blood flow within human retina and choroids.