Poly(ADP-ribose) metabolism in brain and its role in ischemia pathology

Modulation of Excitatory Synaptic Transmission During Cannabinoid Receptor Activation

The present research has reported that cannabinoid receptor 1 (CB1) agonist, delta-(9)-tetrahydrocannabinol (THC) modulates synaptogenesis during overexcitation. Microtubule and synaptic distribution, poly(ADP)-ribose (PAR) accumulation were estimated during overexcitation and in the presence of THC. Low concentration of THC (10 nM) increased synaptophysin expression and neurite length, while high concentration of THC (1 µM) induced neurotoxicity. Glutamate caused the loss of neurons, reducing the number and the length of neurites. The high concentration of THC in the presence of glutamate caused the PAR accumulation in the condensed nuclei. Glutamate upregulated genes that are involved in synaptogenesis and excitatory signal cascade. Glutamate downregulated transcription of beta3 tubulin and microtubule-associated protein 2. THC partially regulated gene expression that is implicated in the neurogenesis and excitatory pathways. This suggests that CB1 receptors play a role in neurite growth and the low concentration of THC protects neurons during overexcitation, whereas the high concentration of THC enhances the neurotoxicity.

Poly (ADP-ribose) polymerase: An Overview of Mechanistic Approaches and Therapeutic Opportunities in the Management of Stroke

Stroke is one of the leading causes of morbidity and mortality accompanied by blood supply loss to a particular brain area. Several mechanistic approaches such as inhibition of poly (ADP-ribose) polymerase, therapies against tissue thrombosis, and neutrophils lead to stroke's therapeutic intervention. Evidence obtained with the poly (ADP-ribose) polymerase (PARP) inhibition and animals having a deficiency of PARP enzymes; represented the role of PARP in cerebral stroke, ischemia/reperfusion, and neurotrauma. PARP is a nuclear enzyme superfamily with various isoforms, each with different structural domains and functions, and out of all, PARP-1 is the best-characterized member. It has been shown to perform multiple physiological as well as pathological processes, including its role in inflammation, oxidative stress, apoptosis, and mitochondrial dysfunction. The enzyme interacts with NF-κB, p53, and other transcriptional factors to regulate survival and cell death and modulates multiple downstream signaling pathways. Clinical trials have also been conducted using PARP inhibitors for numerous disorders and have shown positive results. However, additional information is yet to be established for the therapeutic intervention of PARP inhibitors in stroke. These agents' utilization appears to be challenging due to their unknown potential long-term side effects. PARP activity increased during ischemia, but its inhibition provided significant neuroprotection. Despite the increased interest in PARP as a pharmacological modulator for novel therapeutic therapies, the current review focused on stroke and poly ADP-ribosylation.

Perturbed Brain Glucose Metabolism Caused by Absent SIRT3 Activity

Acetylation is a post-translational modification that regulates the activity of enzymes fundamentally involved in cellular and mitochondrial bioenergetic metabolism. NAD⁺ dependent deacetylase sirtuin 3 (SIRT3) is localized to mitochondria where it plays a key role in regulating acetylation of TCA cycle enzymes and the mitochondrial respiratory complexes. Although the SIRT3 target proteins in mitochondria have been identified, the effect of SIRT3 activity on mitochondrial glucose metabolism in the brain remains elusive. The impact of abolished SIRT3 activity on glucose metabolism was determined in SIRT3 knockout (KO) and wild type (WT) mice injected with [1,6-¹³C]glucose using ex vivo ¹³C-NMR spectroscopy. The ¹H-NMR spectra and amino acid analysis showed no differences in the concentration of lactate, glutamate, alanine, succinate, or aspartate between SIRT3 KO and WT mice. However, glutamine, total creatine (Cr), and GABA were lower in SIRT3 KO brain. Incorporation of label from [1,6-¹³C]glucose metabolism into lactate or alanine was not affected in SIRT3 KO brain. However, the incorporation of the label into all isotopomers of glutamate, glutamine, GABA and aspartate was lower in SIRT3 KO brain, reflecting decreased activity of mitochondrial and TCA cycle metabolism in both neurons and astrocytes. This is most likely due to hyperacetylation of mitochondrial enzymes due to suppressed SIRT3 activity in the brain of SIRT3 KO mice. Thus, the absence of Sirt3 results in impaired mitochondrial oxidative energy metabolism and neurotransmitter synthesis in the brain. Since the SIRT3 activity is NAD⁺ dependent, these results might parallel changes in glucose metabolism under pathologic reduction in mitochondrial NAD⁺ pools.

Emerging neuroprotective strategies for the treatment of ischemic stroke: An overview of clinical and preclinical studies

Stroke is the leading cause of disability and thesecond leading cause of death worldwide. With the global population aged 65 and over growing faster than all other age groups, the incidence of stroke is also increasing. In addition, there is a shift in the overall stroke burden towards younger age groups, particularly in low and middle-income countries. Stroke in most cases is caused due to an abrupt blockage of an artery (ischemic stroke), but in some instances stroke may be caused due to bleeding into brain tissue when a blood vessel ruptures (hemorrhagic stroke). Although treatment options for stroke are still limited, with the advancement in recanalization therapy using both pharmacological and mechanical thrombolysis some progress has been made in helping patients recover from ischemic stroke. However, there is still a substantial need for the development of therapeutic agents for neuroprotection in acute ischemic stroke to protect the brain from damage prior to and during recanalization, extend the therapeutic time window for intervention and further improve functional outcome. The current review has assessed the past challenges in developing neuroprotective strategies, evaluated the recent advances in clinical trials, discussed the recent initiative by the National Institute of Neurological Disorders and Stroke in USA for the search of novel neuroprotectants (Stroke Preclinical Assessment Network, SPAN) and identified emerging neuroprotectants being currently evaluated in preclinical studies. The underlying molecular mechanism of each of the neuroprotective strategies have also been summarized, which could assist in the development of future strategies for combinational therapy in stroke treatment.

Modulation of Inflammasome and Pyroptosis by Olaparib, a PARP-1 Inhibitor, in the R6/2 Mouse Model of Huntington's Disease

Pyroptosis is a type of cell death that is caspase-1 (Casp-1) dependent, which leads to a rapid cell lysis, and it is linked to the inflammasome. We recently showed that pyroptotic cell death occurs in Huntington’s disease (HD). Moreover, we previously described the beneficial effects of a PARP-1 inhibitor in HD. In this study, we investigated the neuroprotective effect of Olaparib, an inhibitor of PARP-1, in the mouse model of Huntington’s disease. R6/2 mice were administered Olaparib or vehicle from pre-symptomatic to late stages. Behavioral studies were performed to investigate clinical effects of the compound. Immunohistochemical and Western blotting studies were performed to evaluate neuroprotection and the impact of the compound on the pathway of neuronal death in the HD mice. Our results indicate that Olaparib administration starting from the pre-symptomatic stage of the neurodegenerative disease increased survival, ameliorated the neurological deficits, and improved clinical outcomes in neurobehavioral tests mainly by modulating the inflammasome activation. These results suggest that Olaparib, a commercially available drug already in use as an anti-neoplastic compound, exerts a neuroprotective effect and could be a useful pharmaceutical agent for Huntington’s disease therapy.

The Modified Phenanthridine PJ34 Unveils an Exclusive Cell-Death Mechanism in Human Cancer Cells

This overview summarizes recent data disclosing the efficacy of the PARP inhibitor PJ34 in exclusive eradication of a variety of human cancer cells without impairing healthy proliferating cells. Its cytotoxic activity in cancer cells is attributed to the insertion of specific un-repairable anomalies in the structure of their mitotic spindle, leading to mitotic catastrophe cell death. This mechanism paves the way to a new concept of cancer therapy.

The Novel Role of PPAR Alpha in the Brain: Promising Target in Therapy of Alzheimer's Disease and Other Neurodegenerative Disorders

Peroxisome proliferator activated receptor alpha (PPAR-α) belongs to the family of ligand-regulated nuclear receptors (PPARs). These receptors after heterodimerization with retinoid X receptor (RXR) bind in promotor of target genes to PPAR response elements (PPREs) and act as a potent transcription factors. PPAR-α and other receptors from this family, such as PPAR-β/δ and PPAR-γ are expressed in the brain and other organs and play a significant role in oxidative stress, energy homeostasis, mitochondrial fatty acids metabolism and inflammation. PPAR-α takes part in regulation of genes coding proteins that are involved in glutamate homeostasis and cholinergic/dopaminergic signaling in the brain. Moreover, PPAR-α regulates expression of genes coding enzymes engaged in amyloid precursor protein (APP) metabolism. It activates gene coding of α secretase, which is responsible for non-amyloidogenic pathway of APP degradation. It also down regulates β secretase (BACE-1), the main enzyme responsible for amyloid beta (Aβ) peptide release in Alzheimer Diseases (AD). In AD brain expression of genes of PPAR-α and PPAR-γ coactivator-1 alpha (PGC-1α) is significantly decreased. PPARs are altered not only in AD but in other neurodegenerative/neurodevelopmental and psychiatric disorder. PPAR-α downregulation may decrease anti-oxidative and anti-inflammatory processes and could be responsible for the alteration of fatty acid transport, lipid metabolism and disturbances of mitochondria function in the brain of AD patients. Specific activators of PPAR-α may be important for improvement of brain cells metabolism and cognitive function in neurodegenerative and neurodevelopmental disorders.

Antiapoptotic and Anti-Inflammatory Effects of CPCGI in Rats with Traumatic Brain Injury

BACKGROUND

Compound porcine cerebroside and ganglioside injection (CPCGI) has been used for the treatment of certain brain disorders. Apoptosis and inflammation were reported to be involved in the pathogenesis of traumatic brain injury (TBI). Therefore, this study primarily investigated the effects of CPCGI on mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling in a rat model of controlled cortical impact (CCI).

MATERIALS AND METHODS

CPCGI (0.6 mL/kg) was administered intraperitoneally 30 min after the induction of CCI. Mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling were evaluated 24 h after CCI, and apoptotic cell death, neutrophil infiltration, and astrocyte and microglial activation were determined by TUNEL and immunofluorescent staining 3 days after CCI.

RESULTS

1) CPCGI markedly enhanced cytosolic and mitochondrial Bcl-xL levels, the mitochondrial Bcl-xL/Bax ratio, and mitochondrial cytochrome (cyt) c levels and reduced cytosolic cyt c levels, caspase-3 activity, and nuclear AIF levels in brain tissues after traumatic injury; however, CPCGI had no significant effects on cytosolic or mitochondrial Bax levels, the cytosolic Bcl-xL/Bax ratio, or mitochondrial AIF levels. Moreover, CPCGI markedly reduced the TUNEL staining score in the contusion region. 2) CPCGI markedly reduced cytosolic and nuclear PARP levels and nuclear NF-κB p65 levels in brain tissues after traumatic injury but had no significant effect on cytosolic NF-κB p65 levels. In addition, CPCGI markedly reduced caspase-1 activity and the levels of caspase-1, ICAM-1, TNF-α, and IL-1β in brain tissues after traumatic injury and decreased the immunoreactivities of neutrophils, GFAP and Iba-1 in the region of CCI-induced contusion.

CONCLUSION

These data suggest that CPCGI can reduce brain injury due to trauma by suppressing both mitochondrial apoptotic signaling and PARP/NF-κB inflammatory signaling.

Multi-targeted Effect of Nicotinamide Mononucleotide on Brain Bioenergetic Metabolism

Dysfunctions in NAD⁺ metabolism are associated with neurodegenerative diseases, acute brain injury, diabetes, and aging. Loss of NAD⁺ levels results in impairment of mitochondria function, which leads to failure of essential metabolic processes. Strategies to replenish depleted NAD⁺ pools can offer significant improvements of pathologic states. NAD⁺ levels are maintained by two opposing enzymatic reactions, one is the consumption of NAD⁺ while the other is the re-synthesis of NAD⁺. Inhibition of NAD⁺ degrading enzymes, poly-ADP-ribose polymerase 1 (PARP1) and ectoenzyme CD38, following brain ischemic insult can provide neuroprotection. Preservation of NAD⁺ pools by administration of NAD⁺ precursors, such as nicotinamide (Nam) or nicotinamide mononucleotide (NMN), also offers neuroprotection. However, NMN treatment demonstrates to be a promising candidate as a therapeutic approach due to its multi-targeted effect acting as PARP1 and CD38 inhibitor, sirtuins activator, mitochondrial fission inhibitor, and NAD⁺ supplement. Many neurodegenerative diseases or acute brain injury activate several cellular death pathways requiring a treatment strategy that will target these mechanisms. Since NMN demonstrated the ability to exert its effect on several cellular metabolic pathways involved in brain pathophysiology it seems to be one of the most promising candidates to be used for successful neuroprotection.

HX600, a synthetic agonist for RXR-Nurr1 heterodimer complex, prevents ischemia-induced neuronal damage

Ischemic stroke is amongst the leading causes of death and disabilities. The available treatments are suitable for only a fraction of patients and thus novel therapies are urgently needed. Blockage of one of the cerebral arteries leads to massive and persisting inflammatory reaction contributing to the nearby neuronal damage. Targeting the detrimental pathways of neuroinflammation has been suggested to be beneficial in conditions of ischemic stroke. Nuclear receptor 4A-family (NR4A) member Nurr1 has been shown to be a potent modulator of harmful inflammatory reactions, yet the role of Nurr1 in cerebral stroke remains unknown. Here we show for the first time that an agonist for the dimeric transcription factor Nurr1/retinoid X receptor (RXR), HX600, reduces microglia expressed proinflammatory mediators and prevents inflammation induced neuronal death in in vitro co-culture model of neurons and microglia. Importantly, HX600 was protective in a mouse model of permanent middle cerebral artery occlusion and alleviated the stroke induced motor deficits. Along with the anti-inflammatory capacity of HX600 in vitro, treatment of ischemic mice with HX600 reduced ischemia induced Iba-1, p38 and TREM2 immunoreactivities, protected endogenous microglia from ischemia induced death and prevented leukocyte infiltration. These anti-inflammatory functions were associated with reduced levels of brain lysophosphatidylcholines (lysoPCs) and acylcarnitines, metabolites related to proinflammatory events. These data demonstrate that HX600 driven Nurr1 activation is beneficial in ischemic stroke and propose that targeting Nurr1 is a novel candidate for conditions involving neuroinflammatory component.

Interplay between NAD+ and acetyl‑CoA metabolism in ischemia-induced mitochondrial pathophysiology

Brain injury caused by ischemic insult due to significant reduction or interruption in cerebral blood flow leads to disruption of practically all cellular metabolic pathways. This triggers a complex stress response followed by overstimulation of downstream enzymatic pathways due to massive activation of post-translational modifications (PTM). Mitochondria are one of the most sensitive organelle to ischemic conditions. They become dysfunctional due to extensive fragmentation, inhibition of acetyl‑CoA production, and increased activity of NAD⁺ consuming enzymes. These pathologic conditions ultimately lead to inhibition of oxidative phosphorylation and mitochondrial ATP production. Both acetyl‑CoA and NAD⁺ are essential intermediates in cellular bioenergetics metabolism and also serve as substrates for post-translational modifications such as acetylation and ADP‑ribosylation. In this review we discuss ischemia/reperfusion-induced changes in NAD⁺ and acetyl‑CoA metabolism, how these affect relevant PTMs, and therapeutic approaches that restore the physiological levels of these metabolites leading to promising neuroprotection.

Regulatory T cells increase after treatment with poly (ADP-ribose) polymerase-1 inhibitor in ischemic stroke patients

BACKGROUND

Regulatory T cells (Tregs) are thought to play a modulatory role in immune responses and to improve outcomes after ischemic stroke. Thus, various strategies for increasing Tregs in animal models of ischemic stroke have yielded successful results. The aim of this study was to examine the potential effect of poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor on Treg proportion in stroke patients.

METHODS

Peripheral blood samples were collected from 12 ischemic stroke patients (within 72 h of stroke onset) and 5 healthy control subjects. Flow cytometry analyses and quantitative reverse transcription polymerase chain reactions (qRT-PCR) were performed on peripheral blood mononuclear cells (PBMCs) before and after treating them with PARP-1 inhibitor (3-AB; JPI-289 1 μm, JPI-289 10 μm) for 24 h.

RESULTS

Treg proportions were significantly higher in healthy controls (median 2.8%, IQR 2.6-5.0%) than ischemic stroke patients (median 1.6%, IQR 1.25-2.2%) (p < 0.001). In the latter, Treg proportions were positively correlated with age (r = 0.595, p = 0.041), but not with infarct volume (r = 0.367, p = 0.241). After PARP-1 inhibitor treatment, Treg proportions among PBMCs increased in response to high dose (10 μm) JPI-289 (median 2.3%, IQR 2.0-2.9%) as did Treg-associated transcription factors such as FoxP3 and CTLA-4 mRNA. PARP-1 inhibitor treatment also decreased pro-inflammatory cytokines (IFN-γ, TNF-α, and IL-17) and increased anti-inflammatory cytokines (IL-4, IL-10, and TGF-β1).

CONCLUSION

Treg proportions are reduced in ischemic stroke patients and increased by treatment with high-dose PARP-1 inhibitor JPI-289. The PARP-1 inhibitor also had a possible anti-inflammatory effect on cytokine levels, and may ameliorate the outcome of ischemic stroke by up-regulating Tregs.

Alpha-synuclein alters differently gene expression of Sirts, PARPs and other stress response proteins: implications for neurodegenerative disorders

Alpha-synuclein (ASN) is a presynaptic protein that can easily change its conformation under different types of stress. It's assumed that ASN plays an important role in the pathogenesis of Parkinson's and Alzheimer's disease. However, the molecular mechanism of ASN toxicity has not been elucidated. This study focused on the role of extracellular ASN (eASN) in regulation of transcription of sirtuins (Sirts) and DNA-bound poly(ADP-ribose) polymerases (PARPs) - proteins crucial for cells' survival/death. Our results indicate that eASN enhanced the free radicals level, decreased mitochondria membrane potential, cells viability and activated cells' death. Concomitantly eASN activated expression of antioxidative proteins (Sod2, Gpx4, Gadd45b) and DNA-bound Parp2 and Parp3. Moreover, eASN upregulated expression of Sirt3 and Sirt5, but downregulated of Sirt1, which plays an important role in cell metabolism including Aβ precursor protein (APP) processing. eASN downregulated gene expression of APP alpha secretase (Adam10) and metalloproteinases Mmp2, Mmp10 but upregulated Mmp11. Additionally, expression and activity of pro-survival sphingosine kinase 1 (Sphk1), Akt kinase and anti-apoptotic protein Bcl2 were inhibited. Moreover, higher expression of pro-apoptotic protein Bax and enhancement of apoptotic cells' death were observed. Summarizing, eASN significantly modulates transcription of Sirts and enzymes involved in APP/Aβ metabolism and through these mechanisms eASN toxicity may be enhanced. The inhibition of Sphk1 and Akt by eASN may lead to disturbances of survival pathways. These results suggest that eASN through alteration of transcription and by inhibition of pro-survival kinases may play important pathogenic role in neurodegenerative disorders.

Inferring Molecular Processes Heterogeneity from Transcriptional Data

RNA microarrays and RNA-seq are nowadays standard technologies to study the transcriptional activity of cells. Most studies focus on tracking transcriptional changes caused by specific experimental conditions. Information referring to genes up- and downregulation is evaluated analyzing the behaviour of relatively large population of cells by averaging its properties. However, even assuming perfect sample homogeneity, different subpopulations of cells can exhibit diverse transcriptomic profiles, as they may follow different regulatory/signaling pathways. The purpose of this study is to provide a novel methodological scheme to account for possible internal, functional heterogeneity in homogeneous cell lines, including cancer ones. We propose a novel computational method to infer the proportion between subpopulations of cells that manifest various functional behaviour in a given sample. Our method was validated using two datasets from RNA microarray experiments. Both experiments aimed to examine cell viability in specific experimental conditions. The presented methodology can be easily extended to RNA-seq data as well as other molecular processes. Moreover, it complements standard tools to indicate most important networks from transcriptomic data and in particular could be useful in the analysis of cancer cell lines affected by biologically active compounds or drugs.

Inhibition of poly(ADP-ribose) polymerase-1 alters expression of mitochondria-related genes in PC12 cells: relevance to mitochondrial homeostasis in neurodegenerative disorders

Alzheimer's disease (AD) is characterized by the release of amyloid beta peptides (Aβ) in the form of monomers/oligomers which may lead to oxidative stress, mitochondria dysfunction, synaptic loss, neuroinflammation and, in consequence, to overactivation of poly(ADP-ribose) polymerase-1 (PARP-1). However, Aβ peptides are also released in the brain ischemia, traumatic injury and in inflammatory response. PARP-1 is suggested to be a promising target in therapy of neurodegenerative disorders. We investigated the impact of PARP-1 inhibition on transcription of mitochondria-related genes in PC12 cells. Moreover, the effect of PARP-1 inhibitor (PJ34) on cells subjected to Aβ oligomers (AβO) - evoked stress was analyzed. Our data demonstrated that inhibition of PARP-1 in PC12 cells enhanced the transcription of genes for antioxidative enzymes (Sod1, Gpx1, Gpx4), activated genes regulating mitochondrial fission/fusion (Mfn1, Mfn2, Dnm1l, Opa1, Fis1), subunits of ETC complexes (mt-Nd1, Sdha, mt-Cytb) and modulated expression of several TFs, enhanced Foxo1 and decreased Nrf1, Stat6, Nfkb1. AβO elevated free radicals concentration, decreased mitochondria membrane potential (MMP) and cell viability after 24h. Gene transcription was not affected by AβO after 24h, but was significantly downregulated after 96h. In AβO stress, PJ34 exerted stimulatory effect on expression of several genes (Gpx1, Gpx4, Opa1, Mfn2, Fis1 and Sdha), decreased transcription of numerous TFs (Nrf1, Tfam, Stat3, Stat6, Trp53, Nfkb1) and prevented oxidative stress. Our results indicated that PARP-1 inhibition significantly enhanced transcription of genes involved in antioxidative defense and in regulation of mitochondria function, but was not able to ameliorate cells viability affected by Aβ.

Targeting NAD+ degradation: The therapeutic potential of flavonoids for Alzheimer's disease and cognitive frailty

Flavonoids are efficacious candidates as pharmaceuticals or nutraceuticals in the treatment of Alzheimer's disease (AD), aging and other age-related chronic inflammatory diseases. Natural flavonoids reduce pathological hallmarks, extracellular amyloid deposits and neurofibrillary tangles by mediating amyloid precursor protein (APP) processing, Aβ accumulation and tau pathology. The antioxidant and anti-inflammatory actions as well as modulation of sirtuins and telomeres are also involved in the amelioration of aging, neurodegeneration and other age-related diseases. Recently, some flavonoids were shown to inhibit poly (ADP-ribose) polymerases (PARPs) and cyclic ADP-ribose (cADP) synthases (CD38 and CD157), elevate intracellular nicotinamide adenine dinucleotide⁺ (NAD⁺) levels and activate NAD⁺ dependent sirtuin -mediated signaling pathways. We summarized how flavonoids reduce the degradation of NAD⁺ with an emphasis on the mechanisms through which flavonoids affect the NAD⁺-sirtuin axis to protect against AD. Aging and age-related diseases as well as a decline in the physiological reserve are the risk factors for cognitive frailty. Flavonoids with multiple therapeutic targets may also be potential candidates for the prevention and treatment of cognitive frailty.

Inhibition of Poly(ADP-ribose) Polymerase-1 Enhances Gene Expression of Selected Sirtuins and APP Cleaving Enzymes in Amyloid Beta Cytotoxicity

Poly(ADP-ribose) polymerases (PARPs) and sirtuins (SIRTs) are involved in the regulation of cell metabolism, transcription, and DNA repair. Alterations of these enzymes may play a crucial role in Alzheimer's disease (AD). Our previous results indicated that amyloid beta (Aβ) peptides and inflammation led to activation of PARP1 and cell death. This study focused on a role of PARP1 in the regulation of gene expression for SIRTs and beta-amyloid precursor protein (βAPP) cleaving enzymes under Aβ42 oligomers (AβO) toxicity in pheochromocytoma cells (PC12) in culture. Moreover, the effect of endogenously liberated Aβ peptides in PC12 cells stably transfected with human gene for APP wild-type (APPwt) was analyzed. Our results demonstrated that AβO enhanced transcription of presenilins (Psen1 and Psen2), the crucial subunits of γ-secretase. Aβ peptides in APPwt cells activated expression of β-secretase (Bace1), Psen1, Psen2, and Parp1. The inhibitor of PARP1, PJ-34 in the presence of AβO upregulated transcription of α-secretase (Adam10), Psen1, and Psen2, but also Bace1. Concomitantly, PJ-34 enhanced mRNA level of nuclear Sirt1, Sirt6, mitochondrial Sirt4, and Parp3 in PC12 cells subjected to AβOs toxicity. Our data indicated that Aβ peptides through modulation of APP secretases may lead to a vicious metabolic circle, which could be responsible for maintaining Aβ at high level. PARP1 inhibition, besides activation of nuclear SIRTs and mitochondrial Sirt4 expression, enhanced transcription of enzyme(s) involved in βAPP metabolism, and this effect should be considered in its application against Aβ peptide toxicity.

Effects of Poly(ADP-Ribose) Polymerase-1 Inhibition in a Neonatal Rodent Model of Hypoxic-Ischemic Injury

Background

Hypoxia ischemia (HI) to the developing brain occurs in 1–6 in 1000 live births. Large numbers of survivors have neurological long-term sequelae. However, mechanisms of recovery after HI are not understood and preventive measures or clinical treatments are not effective. Poly(ADP-ribose) polymerase-1 is overactivated in response to ischemia. In neonatal mice HI activates PARP-1 but its role in perinatal brain injury remains uncertain.

Objective

Aim of this study was to explore the effect of TES448 (PARP-1-inhibitor) and hypothermia after an ischemic insult.

Design and Methods

10-day-old Wistar rats underwent HI. TES448 was given 10 min, 3 hrs, and 6 hrs after hypoxia. Hypothermia was started 30 min after HI and brains were dissected at P12. Western blotting and histological staining were used to evaluate for degree of injury.

Results

Protein expression of PARP-1 levels was diminished after TES448 treatment. Cresyl violet and TUNEL staining revealed decreased injury in male rat pups following TES448 and combined treatment. Female rats showed increased numbers of TUNEL-positive cells after combined therapy. TES448 inhibited microglia activation after hypoxic-ischemic injury. A cellular response including NeuN, Olig2, and MBP was not affected by PARP-1-inhibition.

Conclusions

Inhibition of PARP-1 and hypothermia lead to an alteration of injury but this effect is sexually dimorphic.

Opportunities for the repurposing of PARP inhibitors for the therapy of non-oncological diseases

The recent clinical availability of the PARP inhibitor olaparib (Lynparza) opens the door for potential therapeutic repurposing for non-oncological indications. Considering (a) the preclinical efficacy data with PARP inhibitors in non-oncological diseases and (b) the risk-benefit ratio of treating patients with a compound that inhibits an enzyme that has physiological roles in the regulation of DNA repair, we have selected indications, where (a) the severity of the disease is high, (b) the available therapeutic options are limited, and (c) the duration of PARP inhibitor administration could be short, to provide first-line options for therapeutic repurposing. These indications are as follows: acute ischaemic stroke; traumatic brain injury; septic shock; acute pancreatitis; and severe asthma and severe acute lung injury. In addition, chronic, devastating diseases, where alternative therapeutic options cannot halt disease development (e.g. Parkinson's disease, progressive multiple sclerosis or severe fibrotic diseases), should also be considered. We present a preclinical and clinical action plan for the repurposing of PARP inhibitors.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Gastrodin ameliorates subacute phase cerebral ischemia‑reperfusion injury by inhibiting inflammation and apoptosis in rats

Gastrodin (GAS), which is extracted from the Chinese herbal medicine Gastrodia elata Blume, has long been used to improve stroke, epilepsy, dizziness and dementia. However, the effects and underlying mechanisms of GAS on subacute phase cerebral ischemia-reperfusion (I/R) injury remain unknown. The aim of the present study was to investigate the effects and mechanisms of GAS on cerebral I/R injury in rats. The rats were pretreated with GAS by gavage for 7 days followed by I/R surgery, and were then treated with GAS for 7 days after I/R surgery. Neurological deficits were assessed on days 1, 3 and 7 post-cerebral I/R injury. 2,3,5-Triphenyltetrazolium chloride staining was using to measure the infarct volume; morphological alterations were observed by hematoxylin and eosin staining under an optical microscope; apoptosis in the hippocampus and cortex was observed by terminal deoxynucleotidyl transferase dUTP nick end labeling staining; and the level of mRNA and protein expression was tested by reverse transcription-quantitative polymerase chain reation and western blot analysis, respectively. GAS markedly attenuated I/R-induced disability and histological damage, alleviated neuronal apoptosis, and reduced the mRNA and protein expression levels of inflammatory and proapoptotic factors, including interleukin-1β, cyclooxygenase-2, inducible nitric oxide synthase and cleaved caspase-3. These findings suggested that GAS may ameliorate subacute phase cerebral I/R injury by inhibiting inflammation and apoptosis in rats; therefore, GAS may be considered a potential candidate for the treatment of cerebral ischemia.

Sirt1 in cerebral ischemia

Cerebral ischemia is among the leading causes of death worldwide. It is characterized by a lack of blood flow to the brain that results in cell death and damage, ultimately causing motor, sensory, and cognitive impairments. Today, clinical treatment of cerebral ischemia, mostly stroke and cardiac arrest, is limited and new neuroprotective therapies are desperately needed. The Sirtuin family of oxidized nicotinamide adenine dinucleotide (NAD⁺)-dependent deacylases has been shown to govern several processes within the central nervous system as well as to possess neuroprotective properties in a variety of pathological conditions such as Alzheimer's Disease, Parkinson's Disease, and Huntington's Disease, among others. Recently, Sirt1 in particular has been identified as a mediator of cerebral ischemia, with potential as a possible therapeutic target. To gather studies relevant to this topic, we used PubMed and previous reviews to locate, select, and resynthesize the lines of evidence presented here. In this review, we will first describe some functions of Sirt1 in the brain, mainly neurodevelopment, learning and memory, and metabolic regulation. Second, we will discuss the experimental evidence that has implicated Sirt1 as a key protein in the regulation of cerebral ischemia as well as a potential target for the induction of ischemic tolerance.

Identification and mechanism of action analysis of the new PARP-1 inhibitor 2″-hydroxygenkwanol A

BACKGROUND

Poly(ADP-ribose) polymerase 1 (PARP-1) activity has been implicated in the pathogenesis of numerous diseases as cancer, inflammation, diabetes and neurodegenerative disorders, therefore the research for new PARP-1 inhibitors is still an active area.

METHODS

To identify new potential PARP-1 inhibitors, we performed a screening of a small-molecule library consisting of polyphenols isolated from plants used in the traditional medicine, by Surface Plasmon Resonance (SPR). Biochemical and cellular assays were performed to confirm SPR results and select the promising candidate(s). Finally, limited proteolysis and ligand docking analyses allowed defining the protein region involved in the interaction with the putative inhibitor(s).

RESULTS

The dimeric spiro-flavonoid 2″-hydroxygenkwanol A, member of a relatively recently discovered class of flavonoids containing a spirane C-atom, has been identified as possible PARP-1 inhibitor. This compound showed a high affinity for the polymerase (KD: 0.32±0.05μM); moreover PARP-1 activity in the presence of 2″-hydroxygenkwanol A was significantly affected both when using the recombinant protein and when measuring the cellular effects. Finally, our study suggests this compound to efficiently interact with the protein catalytic domain, into the nicotine binding pocket.

CONCLUSION

2″-hydroxygenkwanol A efficiently binds and inhibits PARP-1 at submicromolar concentrations, thus representing a promising lead for the design of a new class of PARP-1 modulators, useful as therapeutic agents and/or biochemical tools.

GENERAL SIGNIFICANCE

Our study has identified an additional class of plant molecules, the spiro-biflavonoids, with known beneficial pharmacological properties but with an unknown mechanism of action, as a possible novel class of PARP-1 activity inhibitors.

Lack of aprataxin impairs mitochondrial functions via downregulation of the APE1/NRF1/NRF2 pathway

Ataxia oculomotor apraxia type 1 (AOA1) is an autosomal recessive disease caused by mutations in APTX, which encodes the DNA strand-break repair protein aprataxin (APTX). CoQ10 deficiency has been identified in fibroblasts and muscle of AOA1 patients carrying the common W279X mutation, and aprataxin has been localized to mitochondria in neuroblastoma cells, where it enhances preservation of mitochondrial function. In this study, we show that aprataxin deficiency impairs mitochondrial function, independent of its role in mitochondrial DNA repair. The bioenergetics defect in AOA1-mutant fibroblasts and APTX-depleted Hela cells is caused by decreased expression of SDHA and genes encoding CoQ biosynthetic enzymes, in association with reductions of APE1, NRF1 and NRF2. The biochemical and molecular abnormalities in APTX-depleted cells are recapitulated by knockdown of APE1 in Hela cells and are rescued by overexpression of NRF1/2. Importantly, pharmacological upregulation of NRF1 alone by 5-aminoimidazone-4-carboxamide ribonucleotide does not rescue the phenotype, which, in contrast, is reversed by the upregulation of NRF2 by rosiglitazone. Accordingly, we propose that the lack of aprataxin causes reduction of the pathway APE1/NRF1/NRF2 and their target genes. Our findings demonstrate a critical role of APTX in transcription regulation of mitochondrial function and the pathogenesis of AOA1 via a novel pathomechanistic pathway, which may be relevant to other neurodegenerative diseases.

Perinatal asphyxia leads to PARP-1 overactivity, p65 translocation, IL-1β and TNF-α overexpression, and apoptotic-like cell death in mesencephalon of neonatal rats: prevention by systemic neonatal nicotinamide administration

Perinatal asphyxia (PA) is a leading cause of neuronal damage in newborns, resulting in long-term neurological and cognitive deficits, in part due to impairment of mesostriatal and mesolimbic neurocircuitries. The insult can be as severe as to menace the integrity of the genome, triggering the overactivation of sentinel proteins, including poly (ADP-ribose) polymerase-1 (PARP-1). PARP-1 overactivation implies increased energy demands, worsening the metabolic failure and depleting further NAD⁺ availability. Using a global PA rat model, we report here evidence that hypoxia increases PARP-1 activity, triggering a signalling cascade leading to nuclear translocation of the NF-κB subunit p65, modulating the expression of IL-1β and TNF-α, pro-inflammatory molecules, increasing apoptotic-like cell death in mesencephalon of neonate rats, monitored with Western blots, qPCR, TUNEL and ELISA. PARP-1 activity increased immediately after PA, reaching a maximum 1–8 h after the insult, while activation of the NF-κB signalling pathway was observed 8 h after the insult, with a >twofold increase of p65 nuclear translocation. IL-1β and TNF-α mRNA levels were increased 24 h after the insult, together with a >twofold increase in apoptotic-like cell death. A single dose of the PARP-1 inhibitor nicotinamide (0.8 mmol/kg, i.p.), 1 h post delivery, prevented the effect of PA on PARP-1 activity, p65 translocation, pro-inflammatory cytokine expression and apoptotic-like cell death. The present study demonstrates that PA leads to PARP-1 overactivation, increasing the expression of pro-inflammatory cytokines and cell death in mesencephalon, effects prevented by systemic neonatal nicotinamide administration, supporting the idea that PARP-1 inhibition represents a therapeutic target against the effects of PA.

N-acetylaspartate decrease in acute stage of ischemic stroke: a perspective from experimental and clinical studies

N-acetylaspartate (NAA) appears in a prominent peak in proton magnetic resonance spectroscopy ((1)H-MRS) of the brain. Exhibition by NAA of time-dependent attenuation that reflects energy metabolism during the acute stage of cerebral ischemia makes this metabolite a unique biomarker for assessing ischemic stroke. Although magnetic resonance (MR) imaging is a powerful technique for inspecting the pathological changes that occur during ischemic stroke, biomarkers that directly reflect the drastic metabolic changes associated with acute-stage ischemia are strongly warranted for appropriate therapeutic decision-making in daily clinical settings. In this review, we provide a brief overview of NAA metabolism and focus on the use of attenuation in NAA as a means for assessing the pathophysiological changes that occur during the acute stage of ischemic stroke.

Parthanatos: mitochondrial-linked mechanisms and therapeutic opportunities

Cells die by a variety of mechanisms. Terminally differentiated cells such as neurones die in a variety of disorders, in part, via parthanatos, a process dependent on the activity of poly (ADP-ribose)-polymerase (PARP). Parthanatos does not require the mediation of caspases for its execution, but is clearly mechanistically dependent on the nuclear translocation of the mitochondrial-associated apoptosis-inducing factor (AIF). The nuclear translocation of this otherwise beneficial mitochondrial protein, occasioned by poly (ADP-ribose) (PAR) produced through PARP overactivation, causes large-scale DNA fragmentation and chromatin condensation, leading to cell death. This review describes the multistep course of parthanatos and its dependence on PAR signalling and nuclear AIF translocation. The review also discusses potential targets in the parthanatos cascade as promising avenues for the development of novel, disease-modifying, therapeutic agents.

Neurological and histological consequences induced by in vivo cerebral oxidative stress: evidence for beneficial effects of SRT1720, a sirtuin 1 activator, and sirtuin 1-mediated neuroprotective effects of poly(ADP-ribose) polymerase inhibition

Poly(ADP-ribose)polymerase and sirtuin 1 are both NAD⁺-dependent enzymes. In vitro oxidative stress activates poly(ADP-ribose)polymerase, decreases NAD⁺ level, sirtuin 1 activity and finally leads to cell death. Poly(ADP-ribose)polymerase hyperactivation contributes to cell death. In addition, poly(ADP-ribose)polymerase inhibition restores NAD⁺ level and sirtuin 1 activity in vitro. In vitro sirtuin 1 induction protects neurons from cell loss induced by oxidative stress. In this context, the role of sirtuin 1 and its involvement in beneficial effects of poly(ADP-ribose)polymerase inhibition were evaluated in vivo in a model of cerebral oxidative stress induced by intrastriatal infusion of malonate in rat. Malonate promoted a NAD⁺ decrease that was not prevented by 3-aminobenzamide, a poly(ADP-ribose)polymerase inhibitor, at 4 and 24 hours. However, 3-aminobenzamide increased nuclear SIRT1 activity/expression ratio after oxidative stress. Malonate induced a neurological deficit associated with a striatal lesion. Both were reduced by 3-aminobenzamide and SRT1720, a sirtuin 1 activator, showing beneficial effects of poly(ADP-ribose)polymerase inhibition and sirtuin 1 activation on oxidative stress consequences. EX527, a sirtuin 1 inhibitor, given alone, modified neither the score nor the lesion, suggesting that endogenous sirtuin 1 was not activated during cerebral oxidative stress. However, its association with 3-aminobenzamide suppressed the neurological improvement and the lesion reduction induced by 3-aminobenzamide. The association of 3-aminobenzamide with SRT1720, the sirtuin 1 activator, did not lead to a better protection than 3-aminobenzamide alone. The present data represent the first demonstration that the sirtuin 1 activator SRT1720 is neuroprotective during in vivo cerebral oxidative stress. Furthermore sirtuin 1 activation is involved in the beneficial effects of poly(ADP-ribose)polymerase inhibition after in vivo cerebral oxidative stress.

Ceramide in the molecular mechanisms of neuronal cell death. The role of sphingosine-1-phosphate

Ceramide and sphingosine-1-phosphate (S1P), two important bioactive sphingolipids, have been suggested as being key players in the pathology of Alzheimer’s disease in inflammation and cancer. However, their role in the molecular mechanisms of neuronal death has not been fully elucidated. Our study indicated that ceramide significantly enhanced the level of free radicals and decreased the viability of the human neuroblastoma cell line (SH-SY5Y) through inhibition of the prosurvival PI3-K/Akt pathway. Ceramide also decreased anti-apoptotic (Bcl-2) and increased pro-apoptotic (Bax, Hrk) mRNA/protein levels. Concomitantly, our study indicated that ceramide induced poly(ADP-ribose) polymerase-1 (PARP-1) activation and accumulation of poly(ADP-ribose) PAR, a signalling molecule involved in mitochondria-nucleus cross-talk and mitochondria integrity. Ceramide treatment significantly decreased the level of apoptosis-inducing factor (AIF) in the mitochondria. The PARP-1 inhibitor (PJ-34) prevented AIF release from the mitochondria. In addition, our data showed that exogenously added S1P increased the viability of SH-SY5Y through the S1P (1,3) receptor-dependent mechanism. It was also revealed that the S1P and PARP-1 inhibitor (PJ-34) decreased oxidative stress, gene expression of the pro-apoptotic Hrk protein and up-regulated the anti-apoptotic Bcl-2 protein. Our data demonstrate that neuronal cell death evoked by ceramide is regulated by PARP/PAR/AIF and by S1P receptor signalling. In summary, our results suggest that PARP-1 inhibitor(s) and modulators of sphingosine-1-phosphate receptor(s) should be considered in potential therapeutic strategies directed at neurodegenerative diseases.

Epigenetics of schizophrenia: an open and shut case

During the last decade and a half, there has been an explosion of data regarding epigenetic changes in schizophrenia. Most initial studies have suggested that schizophrenia is characterized by an overly restrictive chromatin state based on increases in transcription silencing histone modifications and DNA methylation at schizophrenia candidate gene promoters and increases in the expression of enzymes that catalyze their formation. However, recent studies indicate that the pathology is more complex. This complexity may greatly impact pharmacological approaches directed at targeting epigenetic abnormalities in schizophrenia. The current review explores epigenetic studies of schizophrenia and what this can tell us about the underlying pathophysiology. We hypothesize based on recent studies that it is also plausible that drugs that further restrict chromatin may be efficacious.

Predictive biomarkers for cancer therapy with PARP inhibitors

Poly(ADP-ribose) polymerase (PARP) inhibitors have raised high expectations for the treatment of multiple malignancies. PARP inhibitors, which can be used as monotherapies or in combination with DNA-damaging agents, are particularly efficient against tumors with defects in DNA repair mechanisms, in particular the homologous recombination pathway, for instance due to BRCA mutations. Thus, deficient DNA repair provides a framework for the success of PARP inhibitors in medical oncology. Here, we review encouraging results obtained in recent clinical trials investigating the safety and efficacy of PARP inhibitors as anticancer agents. We discuss emerging mechanisms of regulation of homologous recombination and how inhibition of DNA repair might be used in cancer therapy. We surmise that the identification of patients that are likely to benefit from PARP inhibition will improve the clinical use of PARP inhibitors in a defined target population. Thus, we will place special emphasis on biomarker discovery.

Active DNA demethylation in post-mitotic neurons: a reason for optimism

Over the last several years proteins involved in base excision repair (BER) have been implicated in active DNA demethylation. We review the literature supporting BER as a means of active DNA demethylation, and explain how the various components function and cooperate to remove the potentially most enduring means of epigenetic gene regulation. Recent evidence indicates that the same pathways implicated during periods of widespread DNA demethylation, such as the erasure of methyl marks in the paternal pronucleus soon after fertilization, are operational in post-mitotic neurons. Neuronal functional identities, defined here as the result of a combination of neuronal subtype, location, and synaptic connections are largely maintained through DNA methylation. Chronic mental illnesses, such as schizophrenia, may be the result of both altered neurotransmitter levels and neurons that have assumed dysfunctional neuronal identities. A limitation of most current psychopharmacological agents is their focus on the former, while not addressing the more profound latter pathophysiological process. Previously, it was believed that active DNA demethylation in post-mitotic neurons was rare if not impossible. If this were the case, then reversing the factors that maintain neuronal identity, would be highly unlikely. The emergence of an active DNA demethylation pathway in the brain is a reason for great optimism in psychiatry as it provides a means by which previously pathological neurons may be reprogrammed to serve a more favorable role. Agents targeting epigenetic processes have shown much promise in this regard, and may lead to substantial gains over traditional pharmacological approaches.

Prevention of rt-PA induced blood-brain barrier component degradation by the poly(ADP-ribose)polymerase inhibitor PJ34 after ischemic stroke in mice

Recombinant tissue plasminogen activator (rt-PA) is the only pharmacological treatment approved for thrombolysis in patients suffering from ischemic stroke, but its administration aggravates the risk of hemorrhagic transformations. Experimental data demonstrated that rt-PA increases the activity of poly(ADP-ribose)polymerase (PARP). The aim of the present study was to investigate whether PJ34, a potent (PARP) inhibitor, protects the blood-brain barrier components from rt-PA toxicity. In our mouse model of cerebral ischemia, administration of rt-PA (10 mg/kg, i.v.) 6h after ischemia aggravated the post-ischemic degradation of ZO-1, claudin-5 and VE-cadherin, increased the hemorrhagic transformations (assessed by brain hemoglobin content and magnetic resonance imaging). Furthermore, rt-PA also aggravated ischemia-induced functional deficits. Combining PJ34 with rt-PA preserved the expression of ZO-1, claudin-5 and VE-cadherin, reduced the hemorrhagic transformations and improved the sensorimotor performances. In vitro studies also demonstrated that PJ34 crosses the blood-brain barrier and may thus exert its protective effect by acting on endothelial and/or parenchymal cells. Thus, co-treatment with a PARP inhibitor seems to be a promising strategy to reduce rt-PA-induced vascular toxicity after stroke.

Docosahexaenoic acid and tetracyclines as promising neuroprotective compounds with poly(ADP-ribose) polymerase inhibitory activities for oxidative/genotoxic stress treatment

The human genome is exposed to oxidative/genotoxic stress by several endogenous and exogenous compounds. These events evoke DNA damage and activate poly(ADP-ribose) polymerase-1 (PARP-1), the key enzyme involved in DNA repair. The massive stress and over-activation of this DNA-bound enzyme can be responsible for an energy crisis and neuronal death. The last data indicated that product of PARP-1, i.e. poly(ADP-ribose) (PAR), acts as a signalling molecule and plays a significant role in nucleus-mitochondria cross-talk. PAR translocated to the mitochondria can be involved in mitochondrial permeability, the release of an apoptosis-inducing factor (AIF). Its translocation into the nucleus leads to chromatin condensation, fragmentation and cell death. The exact mechanism of this novel death pathway has not yet fully been understood. In this study the relationship between AIF and PARP/PAR in death signalling in the neuronal cell line (HT22) subjected to oxidative/genotoxic stress evoked by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was explored. The neuroprotective influence of docosahexaenoic acid (DHA), major dietary ω-3 long-chain polyunsaturated fatty acids as well as the action of tetracyclines, the novel suppressors of PARP-1, were examined. The effect of these all compounds was compared with specific PARP-1 inhibitors. The oxidative/genotoxic stress evoked by MNNG enhanced the level of PAR in a time-dependent manner with a concomitant significant decrease in the mitochondrial AIF protein level. Moreover, the down-regulation of the anti-apoptotic proteins (Bcl-2 and Bcl-xL) and the up-regulation of the Bax pro-apoptotic protein were presented. In these conditions massive HT22 cell death was observed. Both PARP-1 inhibitors: 3-aminobenzamide (3-AB) and PJ 34, tetracycline: doxocycline and minocycline, as well as DHA protected the cells against PAR formation and AIF translocation. Moreover, all of these compounds enhanced Bcl-xL gene expression and protected the cells against MNNG-induced death. Our data show that both DHA and tetracyclines offer a novel neuroprotective strategy for oxidative/genotoxic stress treatment.

The early activation of PI3K strongly enhances the resistance of cortical neurons to hypoxic injury via the activation of downstream targets of the PI3K pathway and the normalization of the levels of PARP activity, ATP, and NAD⁺

Phosphatidylinositol 3-kinase (PI3K) plays several important roles in neuronal survival. Activation of the pathway is essential for the neuroprotective mechanisms of materials that shield neuronal cells from many stressful conditions. However, there have been no reports to date about the effect of the direct activation of the pathway in hypoxic injury of neuronal cells. We investigated whether the direct activation of the PI3K pathway inhibits neuronal cell death induced by hypoxia. Primary cultured cortical neurons (PCCNs) were exposed to hypoxic conditions (less than 1 mol% O2) and/or treated with PI3K activator. Hypoxia reduced the viability of PCCNs in a time-dependent manner, but treatment with PI3K significantly restored viability in a concentration-dependent manner. Among the signaling proteins involved in the PI3K pathway, those associated with survival, including Akt and glycogen synthase kinase-3β, were decreased shortly after exposure to hypoxia and those associated with cell death, including BAX, apoptosis-induced factor, cytochrome c, caspase-9, caspase-3, and poly(ADP-ribose) polymerase (PARP), were increased. However, treatment with PI3K activator normalized the expression levels of those signaling proteins. PARP activity and levels of ATP and NAD(+) altered by hypoxia were also normalized with direct PI3K activation. All these findings suggest that direct and early activation is important for protecting neuronal cells from hypoxic injury.

Mitochondria, calcium-dependent neuronal death and neurodegenerative disease

Understanding the mechanisms of neuronal dysfunction and death represents a major frontier in contemporary medicine, involving the acute cell death in stroke, and the attrition of the major neurodegenerative diseases, including Parkinson's, Alzheimer's, Huntington's and Motoneuron diseases. A growing body of evidence implicates mitochondrial dysfunction as a key step in the pathogenesis of all these diseases, with the promise that mitochondrial processes represent valuable potential therapeutic targets. Each disease is characterised by the loss of a specific vulnerable population of cells—dopaminergic neurons in Parkinson's disease, spinal motoneurons in Motoneuron disease, for example. We discuss the possible roles of cell type-specific calcium signalling mechanisms in defining the pathological phenotype of each of these major diseases and review central mechanisms of calcium-dependent mitochondrial-mediated cell death.

Neuroprotection: lessons from hibernators

Mammals that hibernate experience extreme metabolic states and body temperatures as they transition between euthermia, a state resembling typical warm blooded mammals, and prolonged torpor, a state of suspended animation where the brain receives as low as 10% of normal cerebral blood flow. Transitions into and out of torpor are more physiologically challenging than the extreme metabolic suppression and cold body temperatures of torpor per se. Mammals that hibernate show unprecedented capacities to tolerate cerebral ischemia, a decrease in blood flow to the brain caused by stroke, cardiac arrest or brain trauma. While cerebral ischemia often leads to death or disability in humans and most other mammals, hibernating mammals suffer no ill effects when blood flow to the brain is dramatically decreased during torpor or experimentally induced during euthermia. These animals, as adults, also display rapid and pronounced synaptic flexibility where synapses retract during torpor and rapidly re-emerge upon arousal. A variety of coordinated adaptations contribute to tolerance of cerebral ischemia in these animals. In this review we discuss adaptations in heterothermic mammals that may suggest novel therapeutic targets and strategies to protect the human brain against cerebral ischemic damage and neurodegenerative disease.

Family-wide chemical profiling and structural analysis of PARP and tankyrase inhibitors

Inhibitors of poly-ADP-ribose polymerase (PARP) family proteins are currently in clinical trials as cancer therapeutics, yet the specificity of many of these compounds is unknown. Here we evaluated a series of 185 small-molecule inhibitors, including research reagents and compounds being tested clinically, for the ability to bind to the catalytic domains of 13 of the 17 human PARP family members including the tankyrases, TNKS1 and TNKS2. Many of the best-known inhibitors, including TIQ-A, 6(5H)-phenanthridinone, olaparib, ABT-888 and rucaparib, bound to several PARP family members, suggesting that these molecules lack specificity and have promiscuous inhibitory activity. We also determined X-ray crystal structures for five TNKS2 ligand complexes and four PARP14 ligand complexes. In addition to showing that the majority of PARP inhibitors bind multiple targets, these results provide insight into the design of new inhibitors.

Visualizing cell death in experimental focal cerebral ischemia: promises, problems, and perspectives

One of the hallmarks of stroke pathophysiology is the widespread death of many different types of brain cells. As our understanding of the complex disease that is stroke has grown, it is now generally accepted that various different mechanisms can result in cell damage and eventual death. A plethora of techniques is available to identify various pathological features of cell death in stroke; each has its own drawbacks and pitfalls, and most are unable to distinguish between different types of cell death, which partially explains the widespread misuse of many terms. The purpose of this review is to summarize the standard histopathological and immunohistochemical techniques used to identify various pathological features of stroke. We then discuss how these methods should be properly interpreted on the basis of what they are showing, as well as advantages and disadvantages that require consideration. As there is much interest in the visualization of stroke using noninvasive imaging strategies, we also specifically discuss how these techniques can be interpreted within the context of cell death.

Lipoxygenases and poly(ADP-ribose) polymerase in amyloid beta cytotoxicity

The 12/15-lipoxygenase(s) (LOX), poly(ADP-ribose) polymerase (PARP-1) activity and mitochondrial apoptosis inducing factor (AIF) protein in the amyloid β (Aβ) toxicity were investigated in PC12 cells that express either wild-type (APPwt) or double Swedish mutation (APPsw) forms of human Aβ precursor protein. Different levels of Aβ secretion and free radicals formation characterize these cells. The results demonstrated a relationship between the Aβ levels and LOX protein expression and activity. High Aβ concentration in APPsw cells correlated with a significant increase in free radicals and LOX activation, which leads to translocation of p65/NF-κB into the nucleus. An increase in AIF expression in mitochondria was observed concurrently with inhibition of PARP-1 activity in the nuclear fraction of APPsw cells. We suggested that AIF accumulation in mitochondria may be involved in adaptive/protective processes. However, inhibition of PARP-1 may be responsible for the disturbances in transcription and DNA repair as well as the degeneration of APP cells. Under conditions of increased nitrosative stress, evoked by the nitric oxide donor, sodium nitroprusside (SNP, 0.5 mM), 70-80% of all cells types died after 24 h, significantly more in APPsw cells. There was no further significant change in mitochondrial AIF level and PARP-1 activity compared to corresponding non-treated cells. Only one exception was observed in PC12 control, where SNP significantly inhibits PARP-1 activity. Moreover, SNP significantly activated gene expression for 12/15-LOX in all types of investigated cells. Inhibitors of all LOX isoforms and specific inhibitor of 12-LOX enhanced the survival of cells that were subjected to SNP. We conclude that the LOX pathways may play a role in Aβ toxicity and in nitrosative-stress-induced cell death and that inhibition of these pathways offers novel protective strategies.

Purification and characterization of poly(ADP-ribosyl)ated DNA replication/repair complexes

PARP-1, the best studied isoform and most abundantly expressed member of the PARP family of 18 proteins, catalyzes the poly(ADP-ribosyl)ation (PARylation) of various nuclear proteins and play key roles in DNA repair, genome maintenance, DNA replication, recombination, apoptosis, gene expression, and regulation of chromatin function. PARylation modulates the functions of target proteins, mainly PARP-1 itself. A multifunctional enzyme, PARP-1 has been localized within DNA replication, repair, recombination, and transcription complexes, and modifies and regulates the functions of specific components of these complexes. PARylation can regulate the activities of replicative enzymes, such as DNA polymerases α, δ, and ε, topo I and II, primase, RPA, and PCNA in isolated enzymes or within DNA replication complexes (DNA synthesome). PARP-1 and PARylation may (1) play dual roles in nuclear processes, depending on the levels of the substrate NAD and the presence of PARP-activating DNA breaks, (2) recruit acceptor proteins to certain sites or complexes through direct association or through binding to PAR and PAR-binding proteins, and (3) alters the nucleosomal structure of DNA by PARylation of nucleosomal proteins, such as histone H1 to destabilize higher order chromatin structures and promote access of DNA repair and replication enzymes as well as transcription factors to these sites. Here, we describe biochemical approaches that have been utilized in our laboratory for the purification and characterization of PARylated DNA replicative complexes. These methods can be modified for the purification of complexes involved in other nuclear processes. This chapter also briefly discusses current methods by which new PARylated complexes are being identified and studied. Identification, evaluation, and characterization of new complexes could aid in the elucidation of the molecular mechanisms by which PARylation and PARP mediates its pleiotropic roles in various nuclear processes.