Long-Term Memory Requires PolyADP-ribosylation

Cellular and subcellular localization of PKMζ

In contrast to protein kinases that participate in long-term potentiation (LTP) induction and memory consolidation, the autonomously active atypical protein kinase C isoform, protein kinase Mzeta (PKMζ), functions in the core molecular mechanism of LTP maintenance and long-term memory storage. Here, using multiple complementary techniques for light and electron microscopic immunolocalization, we present the first detailed characterization of the cellular and subcellular distribution of PKMζ in rat hippocampus and neocortex. We find that PKMζ is widely expressed in forebrain with prominent immunostaining in hippocampal and neocortical grey matter, and weak label in white matter. In hippocampal and cortical pyramidal cells, PKMζ expression is predominantly somatodendritic, and electron microscopy highlights the kinase at postsynaptic densities and in clusters within spines. In addition, nuclear label and striking punctate immunopositive structures in a paranuclear and dendritic distribution are seen by confocal microscopy, occasionally at dendritic bifurcations. PKMζ immunoreactive granules are observed by electron microscopy in cell bodies and dendrites, including endoplasmic reticulum. The widespread distribution of PKMζ in nuclei, nucleoli and endoplasmic reticulum suggests potential roles of this kinase in cell-wide mechanisms involving gene expression, biogenesis of ribosomes and new protein synthesis. The localization of PKMζ within postsynaptic densities and spines suggests sites where the kinase stores information during LTP maintenance and long-term memory.

Neuron-specific chromatin remodeling: a missing link in epigenetic mechanisms underlying synaptic plasticity, memory, and intellectual disability disorders

Long-term memory formation requires the coordinated regulation of gene expression. Until recently nucleosome remodeling, one of the major epigenetic mechanisms for controlling gene expression, had been largely unexplored in the field of neuroscience. Nucleosome remodeling is carried out by chromatin remodeling complexes (CRCs) that interact with DNA and histones to physically alter chromatin structure and ultimately regulate gene expression. Human exome sequencing and gene wide association studies have linked mutations in CRC subunits to intellectual disability disorders, autism spectrum disorder and schizophrenia. However, how mutations in CRC subunits were related to human cognitive disorders was unknown. There appears to be both developmental and adult specific roles for the neuron specific CRC nBAF (neuronal Brg1/hBrm Associated Factor). nBAF regulates gene expression required for dendritic arborization during development, and in the adult, contributes to long-term potentiation, a form of synaptic plasticity, and long-term memory. We propose that the nBAF complex is a novel epigenetic mechanism for regulating transcription required for long-lasting forms of synaptic plasticity and memory processes and that impaired nBAF function may result in human cognitive disorders.

Transient OGG1, APE1, PARP1 and Polβ expression in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a disease of major public health significance, whose pathogenesis is strongly linked to the presence of fibrillar aggregates of amyloid-beta (Aβ) in the aging human brain. We exploited the transgenic (Tg)-ArcSwe mouse model for human AD to explore whether oxidative stress and the capacity to repair oxidative DNA damage via base excision repair (BER) are related to Aβ pathology in AD. Tg-ArcSwe mice express variants of Aβ, accumulating senile plaques at 4-6 months of age, and develop AD-like neuropathology as adult animals. The relative mRNA levels of genes encoding BER enzymes, including 8-oxoguanine glycosylase (OGG1), AP endonuclease 1 (APE1), polymerase β (Polβ) and poly(ADP-ribose) polymerase 1 (PARP1), were quantified in various brain regions of 6 weeks, 4 months and 12 months old mice. The results show that OGG1 transcriptional expression was higher, and APE1 expression lower, in 4 months old Tg-ArcSwe than in wildtype (wt) mice. Furthermore, Polβ transcriptional expression was significantly lower in transgenic 12 months old mice than in wt. Transcriptional profiling also showed that BER repair capacity vary during the lifespan in Tg-ArcSwe and wt mice. The BER expression pattern in Tg-ArcSwe mice thus reflects responses to oxidative stress in vulnerable brain structures.

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.

Vault-poly-ADP-ribose polymerase in the Octopus vulgaris brain: a regulatory factor of actin polymerization dynamic

Our previous behavioural, biochemical and immunohistochemical analyses conducted in selected regions (supra/sub oesophageal masses) of the Octopus vulgaris brain detected a cytoplasmic poly-ADP-ribose polymerase (more than 90% of total enzyme activity). The protein was identified as the vault-free form of vault-poly-ADP-ribose polymerase. The present research extends and integrates the biochemical characterization of poly-ADP-ribosylation system, namely, reaction product, i.e., poly-ADP-ribose, and acceptor proteins, in the O. vulgaris brain. Immunochemical analyses evidenced that the sole poly-ADP-ribose acceptor was the octopus cytoskeleton 50-kDa actin. It was present in both free, endogenously poly-ADP-ribosylated form (70kDa) and in complex with V-poly-ADP-ribose polymerase and poly-ADP-ribose (260kDa). The components of this complex, alkali and high salt sensitive, were purified and characterized. The kind and the length of poly-ADP-ribose corresponded to linear chains of 30-35 ADP-ribose units, in accordance with the features of the polymer synthesized by the known vault-poly-ADP-ribose polymerase. In vitro experiments showed that V-poly-ADP-ribose polymerase activity of brain cytoplasmic fraction containing endogenous actin increased upon the addition of commercial actin and was highly reduced by ATP. Anti-actin immunoblot of the mixture in the presence and absence of ATP showed that the poly-ADP-ribosylation of octopus actin is a dynamic process balanced by the ATP-dependent polymerization of the cytoskeleton protein, a fundamental mechanism for synaptic plasticity.

Whole-exome sequencing and imaging genetics identify functional variants for rate of change in hippocampal volume in mild cognitive impairment

Whole-exome sequencing of individuals with mild cognitive impairment, combined with genotype imputation, was used to identify coding variants other than the apolipoprotein E (APOE) ε4 allele associated with rate of hippocampal volume loss using an extreme trait design. Matched unrelated APOE ε3 homozygous male Caucasian participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were selected at the extremes of the 2-year longitudinal change distribution of hippocampal volume (eight subjects with rapid rates of atrophy and eight with slow/stable rates of atrophy). We identified 57 non-synonymous single nucleotide variants (SNVs) which were found exclusively in at least 4 of 8 subjects in the rapid atrophy group, but not in any of the 8 subjects in the slow atrophy group. Among these SNVs, the variants that accounted for the greatest group difference and were predicted in silico as 'probably damaging' missense variants were rs9610775 (CARD10) and rs1136410 (PARP1). To further investigate and extend the exome findings in a larger sample, we conducted quantitative trait analysis including whole-brain search in the remaining ADNI APOE ε3/ε3 group (N=315). Genetic variation within PARP1 and CARD10 was associated with rate of hippocampal neurodegeneration in APOE ε3/ε3. Meta-analysis across five independent cross sectional cohorts indicated that rs1136410 is also significantly associated with hippocampal volume in APOE ε3/ε3 individuals (N=923). Larger sequencing studies and longitudinal follow-up are needed for confirmation. The combination of next-generation sequencing and quantitative imaging phenotypes holds significant promise for discovery of variants involved in neurodegeneration.

Cellular, molecular, and epigenetic mechanisms in non-associative conditioning: implications for pain and memory

Sensitization is a form of non-associative conditioning in which amplification of behavioral responses can occur following presentation of an aversive or noxious stimulus. Understanding the cellular and molecular underpinnings of sensitization has been an overarching theme spanning the field of learning and memory as well as that of pain research. In this review we examine how sensitization, both in the context of learning as well as pain processing, shares evolutionarily conserved behavioral, cellular/synaptic, and epigenetic mechanisms across phyla. First, we characterize the behavioral phenomenon of sensitization both in invertebrates and vertebrates. Particular emphasis is placed on long-term sensitization (LTS) of withdrawal reflexes in Aplysia following aversive stimulation or injury, although additional invertebrate models are also covered. In the context of vertebrates, sensitization of mammalian hyperarousal in a model of post-traumatic stress disorder (PTSD), as well as mammalian models of inflammatory and neuropathic pain is characterized. Second, we investigate the cellular and synaptic mechanisms underlying these behaviors. We focus our discussion on serotonin-mediated long-term facilitation (LTF) and axotomy-mediated long-term hyperexcitability (LTH) in reduced Aplysia systems, as well as mammalian spinal plasticity mechanisms of central sensitization. Third, we explore recent evidence implicating epigenetic mechanisms in learning- and pain-related sensitization. This review illustrates the fundamental and functional overlay of the learning and memory field with the pain field which argues for homologous persistent plasticity mechanisms in response to sensitizing stimuli or injury across phyla.

Characterization of novel cytoplasmic PARP in the brain of Octopus vulgaris

Recent investigation has focused on the participation of the poly (ADP-ribose) polymerase (PARP) reaction in the invertebrate central nervous system (CNS) during the process of long-term memory (LTM). In this paper, we characterize, localize, and assign a possible role to a cytoplasmic PARP in the brain of Octopus vulgaris. PARP activity was assayed in optic lobes, supraesophageal mass, and optic nerves. The highest levels of enzyme were found in the cytoplasmic fraction. Hyper-activation of the enzyme was detected in Octopus brain after visual discrimination training. Finally, cytoplasmic PARP was found to inhibit Octopus vulgaris actin polymerization. We propose that the cytoplasmic PARP plays a role in vivo to induce the cytoskeletonal reorganization that occurs during learning-induced neuronal plasticity.

Massed training-induced intermediate-term operant memory in aplysia requires protein synthesis and multiple persistent kinase cascades

The Aplysia feeding system with its high degree of plasticity and well characterized neuronal circuitry is well suited for investigations of memory formation. We used an operant paradigm, learning that food is inedible (LFI), to investigate the signaling pathways underlying intermediate-term memory (ITM) in Aplysia. During a single massed training session, the animal associates a specific seaweed with the failure to swallow, generating short-term (30 min) and long-term (24 h) memory. We investigated whether the same training protocol induced the formation of ITM. We found that massed LFI training resulted in temporally distinct protein synthesis-dependent memory evident 4-6 h after training. Through in vivo experiments, we determined that the formation of ITM required protein kinase A, protein kinase C, and MAPK. Moreover, the maintenance of ITM required PKA, PKM Apl III, and MAPK because inhibition of any of these kinases after training or before testing blocked the expression of memory. In contrast, additional experiments determined that the maintenance of long-term memory appeared independent of PKM Apl III. Using Western blotting, we found that sustained MAPK phosphorylation was dependent upon protein synthesis, but not PKA or PKC activity. Thus, massed training-induced intermediate-term operant memory requires protein synthesis as well as persistent or sustained kinase signaling for PKA, PKC, and MAPK. While short-, intermediate-, and long-term memory are induced by the same training protocol, considerable differences exist in both the combination and timing of signaling cascades that induce the formation and maintenance of these temporally distinct memories.

Long term potentiation affects intracellular metalloproteinases activity in the mossy fiber-CA3 pathway

Matrix Metalloproteinases (MMPs) are a family of endopeptidases known to process extracellular proteins. In the last decade, studies carried out mainly on the Schaffer collateral-CA1 hippocampal projection have provided solid evidence that MMPs regulate synaptic plasticity and learning. Recently, our group has shown that MMP blockade disrupts LTP maintenance also in the mossy fiber-CA3 (mf-CA3) projection (Wojtowicz and Mozrzymas, 2010), where LTP mechanisms are profoundly different (NMDAR-independent and presynaptic expression site). However, how plasticity of this pathway correlates with activity and expression of MMPs remains unknown. Interestingly, several potential MMP substrates (especially of gelatinases) are localized intracellularly but little is known about MMP activity in this compartment. In the present study we have asked whether LTP is associated with the expression and activity of gelatinases in apparent intra- and extracellular compartments along mf-CA3 projection. In situ zymography showed that LTP induction was associated with increased gelatinases activity in the cytoplasm of the hilar and CA3 neurons. Using gelatin zymography, immunohistochemistry and immunofluorescent staining we found that this effect was due to de novo synthesis and activation of MMP-9 which, 2-3h after LTP induction was particularly evident in the cytoplasm. In contrast, MMP-2 was localized preferentially in the nuclei and was not affected by LTP induction. In conclusion, we demonstrate that LTP induction in the mf-CA3 pathway correlates with increased expression and activity of MMP-9 and provide the first evidence that this increase is particularly evident in the neuronal cytoplasm and nucleus.

Epigenetic mechanisms in memory and synaptic function

Although the term 'epigenetics' was coined nearly seventy years ago, its critical function in memory processing by the adult CNS has only recently been appreciated. The hypothesis that epigenetic mechanisms regulate memory and behavior was motivated by the need for stable molecular processes that evade turnover of the neuronal proteome. In this article, we discuss evidence that supports a role for neural epigenetic modifications in the formation, consolidation and storage of memory. In addition, we will review the evidence that epigenetic mechanisms regulate synaptic plasticity, a cellular correlate of memory. We will also examine how the concerted action of multiple epigenetic mechanisms with varying spatiotemporal profiles influence selective gene expression in response to behavioral experience. Finally, we will suggest key areas for future research that will help elucidate the complex, vital and still mysterious, role of epigenetic mechanisms in neural function and behavior.

Nitric oxide as a regulator of behavior: new ideas from Aplysia feeding

Nitric oxide (NO) regulates Aplysia feeding by novel mechanisms, suggesting new roles for NO in controlling the behavior of higher animals. In Aplysia, (1) NO helps maintain arousal when produced by neurons responding to attempts to swallow food; (2) NO biases the motor system to reject and reposition food that resists swallowing; (3) if mechanically resistant food is not successfully swallowed, NO mediates the formation and expression of memories of food inedibility; (4) NO production at rest inhibits feeding, countering the effects of food stimuli exciting feeding. At a cellular level, NO-dependent channels contribute to the resting potential of neurons controlling food finding and food consumption. Increases in L-arginine after animals eat act as a post-feeding inhibitory signal, presumably by modulating NO production at rest. NO also signals non-feeding behaviors that are associated with feeding inhibition. Thus, depending on context, NO may enhance or inhibit feeding behavior. The different functions of NO may reflect the evolution of NO signaling from a response to tissue damage that was then elaborated and used for additional functions. These results suggest that in higher animals (1) elicited and background transmitter release may have similar effects; (2) NO may be produced by neurons without firing, influencing adjacent neurons; (3) background NO production may contribute to a neuron's resting potential; (4) circulating factors affecting background NO production may regulate spatially separated neurons; (5) L-arginine can be used to regulate neural activity; (6) L-arginine may be an effective post-ingestion metabolic signal to regulate feeding.

Epigenetic treatments for cognitive impairments

Epigenetic mechanisms integrate signals from diverse intracellular transduction cascades and in turn regulate genetic readout. Accumulating evidence has revealed that these mechanisms are critical components of ongoing physiology and function in the adult nervous system, and are essential for many cognitive processes, including learning and memory. Moreover, a number of psychiatric disorders and syndromes that involve cognitive impairments are associated with altered epigenetic function. In this review, we will examine how epigenetic mechanisms contribute to cognition, consider how changes in these mechanisms may lead to cognitive impairments in a range of disorders and discuss the potential utility of therapeutic treatments that target epigenetic machinery. Finally, we will comment on a number of caveats associated with interpreting epigenetic changes and using epigenetic treatments, and suggest future directions for research in this area that will expand our understanding of the epigenetic changes underlying cognitive disorders.

PKA and PKC are required for long-term but not short-term in vivo operant memory in Aplysia

We investigated the involvement of PKA and PKC signaling in a negatively reinforced operant learning paradigm in Aplysia, learning that food is inedible (LFI). In vivo injection of PKA or PKC inhibitors blocked long-term LFI memory formation. Moreover, a persistent phase of PKA activity, although not PKC activity, was necessary for long-term memory. Surprisingly, neither PKA nor PKC activity was required for associative short-term LFI memory. Additionally, PKA and PKC were not required for the retrieval of short- or long-term memory (STM and LTM, respectively). These studies have identified key differences between the mechanisms underlying nonassociative sensitization, operant reward learning, and LFI memory in Aplysia.

Histone H1 poly[ADP]-ribosylation regulates the chromatin alterations required for learning consolidation

Memory formation requires changes in gene expression, which are regulated by the activation of transcription factors and by changes in epigenetic factors. Poly[ADP]-ribosylation of nuclear proteins has been postulated as a chromatin modification involved in memory consolidation, although the mechanisms involved are not well characterized. Here we demonstrate that poly[ADP]-ribose polymerase 1 (PARP-1) activity and the poly[ADP]-ribosylation of proteins over a specific time course is required for the changes in synaptic plasticity related to memory stabilization in mice. At the molecular level, histone H1 poly[ADP]-ribosylation was evident in the hippocampus after the acquisition period, and it was selectively released in a PARP-1-dependent manner at the promoters of cAMP response element-binding protein and nuclear factor-κB dependent genes associated with learning and memory. These findings suggest that histone H1 poly[ADP]-ribosylation, and its loss at specific loci, is an epigenetic mechanism involved in the reprogramming of neuronal gene expression required for memory consolidation.

Protective effect of nicotinamide against poly(ADP-ribose) polymerase-1-mediated astrocyte death depends on its transporter-mediated uptake

AIM

Poly(ADP-ribose) polymerase-1 (PARP-1) is a DNA repair enzyme, and its excessive activation, following ischemia, trauma, etc., depletes cellular nicotinamide adenine dinucleotide (NAD(+)) as a substrate and eventually leads to brain cell death. Nicotinamide, an NAD(+) precursor and a PARP-1 inhibitor, is known to prevent PARP-1-triggered cell death, but there is no available information on the mechanisms involved in its transport. Here we clarified the transport characteristics of nicotinamide in primary cultured mouse astrocytes.

MAIN METHODS

Uptake characteristics of [(14)C]nicotinamide were assessed by a conventional method with primary cultured mouse astrocytes. Cell viability and PARP-1 activity were determined with intracellular LDH activity and immunocytochemical detection of PAR accumulation, respectively.

KEY FINDINGS

PARP-1 activation was induced by treatment of astrocytes with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), an alkylating agent. MNNG-triggered astrocyte death and PAR accumulation were completely inhibited by treatment with nicotinamide as with DPQ (3,4-dihydro-5-(4-(1-piperidinyl)butoxy)-1(2H)-isoquinolinone), a second generation PARP inhibitor. The uptake of [(14)C]nicotinamide was time-, temperature-, concentration- and pH-dependent, and was inhibited and stimulated by co- and pre-treatment with N-methylnicotinamide, a representative substrate of an organic cation transport system, respectively. Co-treatment of astrocytes with nicotinamide and N-methylnicotinamide resulted in a decrease in PAR accumulation and absolute prevention of cell death.

SIGNIFICANCE

These findings suggest that nicotinamide has a protective effect against PARP-1-induced astrocyte death and that its transporter-mediated uptake, which is extracellular pH-sensitive and common to N-methylnicotinamide, is critical for prevention of PARP-1-triggered cell death.

Nitric oxide and histamine signal attempts to swallow: A component of learning that food is inedible in Aplysia

Memory that food is inedible in Aplysia arises from training requiring three contingent events. Nitric oxide (NO) and histamine are released by a neuron responding to one of these events, attempts to swallow food. Since NO release during training is necessary for subsequent memory and NO substitutes for attempts to swallow, it was suggested that NO functions during training as a signal of attempts to swallow. However, it has been shown that NO may also be released in other contexts affecting feeding, raising the possibility that its role in learning is unrelated to signaling attempts to swallow. We confirmed that NO during learning signals attempts to swallow, by showing that a variety of behavioral effects on feeding of blocking or adding NO do not affect learning and memory that a food is inedible. In addition, histamine had effects similar to NO on learning that food is inedible, as expected if the transmitters are released together when animals attempt to swallow. Blocking histamine during training blocked long-term memory, and exogenous histamine substituted for attempts to swallow. NO also substituted for histamine during training. Histamine at concentrations relevant to learning activates neuron metacerebral cell (MCC). However, MCC activity is not a good monitor of attempts to swallow during training, since the neuron responds equally well to other stimuli. These findings support and extend the hypothesis that NO and histamine signal efforts to swallow during learning, acting on targets other than the MCC that specifically respond to attempts to swallow.

A selective eradication of human nonhereditary breast cancer cells by phenanthridine-derived polyADP-ribose polymerase inhibitors

Introduction

PARP-1 (polyADP-ribose polymerase-1) is known to be activated in response to DNA damage, and activated PARP-1 promotes DNA repair. However, a recently disclosed alternative mechanism of PARP-1 activation by phosphorylated externally regulated kinase (ERK) implicates PARP-1 in a vast number of signal-transduction networks in the cell. Here, PARP-1 activation was examined for its possible effects on cell proliferation in both normal and malignant cells.

Methods

In vitro (cell cultures) and in vivo (xenotransplants) experiments were performed.

Results

Phenanthridine-derived PARP inhibitors interfered with cell proliferation by causing G₂/M arrest in both normal (human epithelial cells MCF10A and mouse embryonic fibroblasts) and human breast cancer cells MCF-7 and MDA231. However, whereas the normal cells were only transiently arrested, G₂/M arrest in the malignant breast cancer cells was permanent and was accompanied by a massive cell death. In accordance, treatment with a phenanthridine-derived PARP inhibitor prevented the development of MCF-7 and MDA231 xenotransplants in female nude mice. Quiescent cells (neurons and cardiomyocytes) are not impaired by these PARP inhibitors.

Conclusions

These results outline a new therapeutic approach for a selective eradication of abundant nonhereditary human breast cancers.

Poly-(ADP-ribose) polymerase-1 is necessary for long-term facilitation in Aplysia

Activity-dependent long-term synaptic plasticity requires gene expression and protein synthesis. Identifying essential genes and studying their transcriptional and translational regulation are key steps to understanding how synaptic changes become long lasting. Recently, the enzyme poly-(ADP-ribose) polymerase 1 (PARP-1) was shown to be necessary for long-term memory (LTM) in Aplysia. Since PARP-1 decondenses chromatin, we hypothesize that this enzyme regulates the expression of specific genes essential for long-term synaptic plasticity that underlies LTM. We cloned Aplysia PARP-1 (ApPARP-1) and determined that its expression in sensory neurons is necessary for serotonin (5-HT)-mediated long-term facilitation (LTF) of sensorimotor neuron synapses. PARP enzymatic activity is also required, since transient application of PARP inhibitors blocked LTF. Differential display and RNA analysis of ganglia dissected from intact animals exposed to 5-HT identified the ribosomal RNA genes as PARP-dependent effector genes. The increase in the expression of rRNAs is long lasting and dynamic. Pulse-labeling RNA studies showed a PARP-dependent increase in rRNAs but not in the total RNA 24 h after 5-HT treatment. Moreover, the expression of both the AprpL27a (Aplysia ribosomal protein L27a) and the ApE2N (Aplysia ubiquitin-conjugating enzyme E2N) mRNAs also increased after 5-HT. Thus, our results suggest that 5-HT, in part by regulating PARP-1 activity, alters the expression of transcripts required for the synthesis of new ribosomes necessary for LTF.

PolyADP-ribosylation is required for long-term memory formation in mammals

PolyADP-ribosylation is a post-translational modification of nuclear proteins, catalyzed by polyADP-ribose polymerases (PARPs). In the nucleus, polyADP-ribosylation catalyzed by PARP-1 alters protein-protein and protein-DNA interactions, and is implicated in chromatin remodeling, DNA transcription, and repair. Previous results linked the activation of PARP-1 with long-term memory formation during learning in the marine mollusk Aplysia ( Science 2004, 304:1820-1822). Furthermore, PARP-1 was highly activated in mammalian cerebral neurons treated with neurotrophins and neurotrophic peptides promoting neurite outgrowth and synaptic plasticity. Here, we examine the possibility that PARP-1 activation is required for memory formation during learning in mammals. Mice were tested in two learning paradigms, object recognition and fear conditioning. PolyADP-ribosylation of PARP-1 and histone H1 were detected in their cerebral cortex and hippocampus immediately after their training session. Moreover, in both behavioral paradigms, suppression of PARP activity in the CNS during learning impaired their long-term memory formation, without damaging their short-term memory. These findings implicate PARP-1 activation in molecular processes underlying long-term memory formation during learning.

Rapamycin inhibits poly(ADP-ribosyl)ation in intact cells

Rapamycin is an immunosuppressive drug, which inhibits the mammalian target of rapamycin (mTOR) kinase activity inducing changes in cell proliferation. Synthesis of poly(ADP-ribose) (PAR) is an immediate cellular response to genotoxic stress catalyzed mostly by poly(ADP-ribose) polymerase 1 (PARP-1), which is also controlled by signaling pathways. Therefore, we investigated whether rapamycin affects PAR production. Strikingly, rapamycin inhibited PAR synthesis in living fibroblasts in a dose-dependent manner as monitored by immunofluorescence. PARP-1 activity was then assayed in vitro, revealing that down-regulation of cellular PAR production by rapamycin was apparently not due to competitive PARP-1 inhibition. Further studies showed that rapamycin did not influence the cellular NAD pool and the activation of PARP-1 in extracts of pretreated fibroblasts. Collectively, our data suggest that inhibition of cellular PAR synthesis by rapamycin is mediated by formation of a detergent-sensitive complex in living cells, and that rapamycin may have a potential as therapeutic PARP inhibitor.

Involvement of histone demethylase LSD1 in Blimp-1-mediated gene repression during plasma cell differentiation

Plasma cell differentiation is orchestrated by the transcriptional repressor B lymphocyte-induced maturation protein-1 (Blimp-1), which silences the gene expression program of mature B cells. The molecular mechanism underlying Blimp-1 suppression of mature B-cell gene expression is not fully understood. Here we report that a proline-rich domain in Blimp-1 directly interacts with LSD1, a histone lysine demethylase. Both LSD1 knockdown and expression of Blimp-1 lacking the proline-rich domain derepressed the activities of Blimp-1-dependent luciferase reporters. Disruption of the Blimp-1 interaction with LSD1 or reduced LSD1 expression attenuated antibody production, demonstrating the biological significance of this interaction. Finally, using chromatin immunoprecipitation, we showed that Blimp-1 binding to its target sites is accompanied by LSD1 binding to those same sites and that LSD1 binding correlates with histone modifications of accessible chromatin. These findings provide further insights into the molecular mechanism of the silencing of mature B-cell genes by Blimp-1 in plasma cell differentiation.

Glutamate regulates the activity of topoisomerase I in mouse cerebellum

Topoisomerase I (topo I) is a nuclear enzyme which participates in most DNA transactions. It was shown to be inhibited in depolarized neurons by poly adenosine diphosphate (ADP)-ribosylation of the enzyme protein. We demonstrated previously an age and sex dependent topo I activity and enzyme protein level in the various regions of mouse brain. A specific distribution pattern of topo I was observed and the inhibitory neurons exhibited the highest enzyme activity and protein level in both the nucleus and the cytoplasm. Here, we show that neurotransmitters (glutamate and gamma-aminobutyric acid (GABA)) regulate the activity of topo I in mouse cerebellum sections. Glutamate exhibited a significant time-dependent inhibition of topo I activity but no effect of the enzyme protein level. GABA in contrary only slightly and transiently inhibited topo I activity. The inhibitory effect of glutamate was mediated by Ca(+2) and by ADP-ribosylation of topo I protein and the glutamate ionotropic receptors were involved. Glutamate also diminished the inhibitory effect of topotecan on topo I. These results point to distinct and highly specific effects of the major neurotransmitters on topo I activity in the cerebellum suggesting that topo I possesses a specific role in the brain which differs from its known biological functions.

Chemical regulation of epigenetic modifications: opportunities for new cancer therapy

Epigenetics is concerned about heritable changes in gene expression without alteration of the coding sequence. Epigenetic modification of chromatin includes methylation of genomic DNA as well as post-translational modification of chromatin-associated proteins, in particular, histones. The spectrum of histone and non-histone modifications ranges from the addition of relatively small groups such as methyl, acetyl and phosphoryl groups to the attachment of larger moieties such as poly(ADP-ribose) and small proteins ubiquitin or small ubiquitin-like modifier (SUMO). The combinatorial nature of DNA methylation and histone modifications constitutes a significant pathway of epigenetic regulation and considerably extends the information potential of the genetic code. Chromatin modification has emerged as a new fundamental mechanism for gene transcriptional activity control associated with many cellular processes like proliferation, growth, and differentiation. Also it is increasingly recognized that epigenetic modifications constitute important regulatory mechanisms for the pathogenesis of malignant transformations. We review here the recent progress in the development of chemical inhibitors/activators that target different chromatin modifying enzymes. Such potent natural or synthetic modulators can be utilized to establish the quantitative contributions of epigenetic modifications in DNA regulated pathways including transcription, replication, recombination and repair, as well as provide leads for developing new cancer therapeutics.

Effects of nerve injury and segmental regeneration on the cellular correlates of neural morphallaxis

Functional recovery of neural networks after injury requires a series of signaling events similar to the embryonic processes that governed initial network construction. Neural morphallaxis, a form of nervous system regeneration, involves reorganization of adult neural connectivity patterns. Neural morphallaxis in the worm, Lumbriculus variegatus, occurs during asexual reproduction and segmental regeneration, as body fragments acquire new positional identities along the anterior-posterior axis. Ectopic head (EH) formation, induced by ventral nerve cord lesion, generated morphallactic plasticity including the reorganization of interneuronal sensory fields and the induction of a molecular marker of neural morphallaxis. Morphallactic changes occurred only in segments posterior to an EH. Neither EH formation, nor neural morphallaxis was observed after dorsal body lesions, indicating a role for nerve cord injury in morphallaxis induction. Furthermore, a hierarchical system of neurobehavioral control was observed, where anterior heads were dominant and an EH controlled body movements only in the absence of the anterior head. Both suppression of segmental regeneration and blockade of asexual fission, after treatment with boric acid, disrupted the maintenance of neural morphallaxis, but did not block its induction. Therefore, segmental regeneration (i.e., epimorphosis) may not be required for the induction of morphallactic remodeling of neural networks. However, on-going epimorphosis appears necessary for the long-term consolidation of cellular and molecular mechanisms underlying the morphallaxis of neural circuitry.

Ethanol-mediated DNA damage and PARP-1 apoptotic responses in cultured fetal cortical neurons

BACKGROUND

Prior studies by many laboratories have illustrated that ethanol can elicit a cascade of caspase-dependent apoptotic events in cultured neurons. Studies in our laboratory have connected this to oxidative stress and effects on fetal cortical neuron glutathione homeostasis.

AIMS

The intent of the following studies is to address mechanisms underlying ethanol-associated DNA damage that may be connected to apoptotic death of neurons.

METHODS

Cultures of fetal rat cerebral cortical neurons were utilized. Estimates of DNA damage was determined by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and nuclear condensation; Poly(ADP-ribose) polymerase-1 (PARP-1) expression was determined by immunostaining and Western blotting; and occurrence of parylation and AIF translocations were assessed by Western blotting.

RESULTS

Ethanol treatment of the neurons generated increases in DNA damage by 4 hours while nuclear condensation was low at the short exposure period but increased markedly by 24 hours. This was temporally related to a marked up-regulation of PARP-1 expression. Activity of PARP-1, as assessed by PolyADP-ribose (PAR) formation, occurred within 15 minutes and peaked by 6 to 8 hours of ethanol treatment. An almost complete translocation of apoptosis inducing factor (AIF) from mitochondria to the nucleus occurred by 24 hours of ethanol treatment (4.0 mg/ml). Ethanol treatment for 4, 12, and 24 hours elicited an increasing caspase-mediated cleavage of PARP-1 to its 24 kDa fragment.

CONCLUSIONS

These data illustrate the rapid occurrence of DNA damage following ethanol exposure and that PARP-1 pathways may play a role in the subsequent apoptotic death of these neurons.

Role of the peroxynitrite-poly(ADP-ribose) polymerase pathway in human disease

Throughout the last 2 decades, experimental evidence from in vitro studies and preclinical models of disease has demonstrated that reactive oxygen and nitrogen species, including the reactive oxidant peroxynitrite, are generated in parenchymal, endothelial, and infiltrating inflammatory cells during stroke, myocardial and other forms of reperfusion injury, myocardial hypertrophy and heart failure, cardiomyopathies, circulatory shock, cardiovascular aging, atherosclerosis and vascular remodeling after injury, diabetic complications, and neurodegenerative disorders. Peroxynitrite and other reactive species induce oxidative DNA damage and consequent activation of the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP-1), the most abundant isoform of the PARP enzyme family. PARP overactivation depletes its substrate NAD(+), slowing the rate of glycolysis, electron transport, and ATP formation, eventually leading to functional impairment or death of cells, as well as up-regulation of various proinflammatory pathways. In related animal models of disease, peroxynitrite neutralization or pharmacological inhibition of PARP provides significant therapeutic benefits. Therefore, novel antioxidants and PARP inhibitors have entered clinical development for the experimental therapy of various cardiovascular and other diseases. This review focuses on the human data available on the pathophysiological relevance of the peroxynitrite-PARP pathway in a wide range of disparate diseases, ranging from myocardial ischemia/reperfusion injury, myocarditis, heart failure, circulatory shock, and diabetic complications to atherosclerosis, arthritis, colitis, and neurodegenerative disorders.

Transcriptional regulation of long-term memory in the marine snail Aplysia

Whereas the induction of short-term memory involves only covalent modifications of constitutively expressed preexisting proteins, the formation of long-term memory requires gene expression, new RNA, and new protein synthesis. On the cellular level, transcriptional regulation is thought to be the starting point for a series of molecular steps necessary for both the initiation and maintenance of long-term synaptic facilitation (LTF). The core molecular features of transcriptional regulation involved in the long-term process are evolutionally conserved in Aplysia, Drosophila, and mouse, and indicate that gene regulation by the cyclic AMP response element binding protein (CREB) acting in conjunction with different combinations of transcriptional factors is critical for the expression of many forms of long-term memory. In the marine snail Aplysia, the molecular mechanisms that underlie the storage of long-term memory have been extensively studied in the monosynaptic connections between identified sensory neuron and motor neurons of the gill-withdrawal reflex. One tail shock or one pulse of serotonin (5-HT), a modulatory transmitter released by tail shocks, produces a transient facilitation mediated by the cAMP-dependent protein kinase leading to covalent modifications in the sensory neurons that results in an enhancement of transmitter release and a strengthening of synaptic connections lasting minutes. By contrast, repeated pulses of 5-hydroxytryptamine (5-HT) induce a transcription- and translation-dependent long-term facilitation (LTF) lasting more than 24 h and trigger the activation of a family of transcription factors in the presynaptic sensory neurons including ApCREB1, ApCREB2 and ApC/EBP. In addition, we have recently identified novel transcription factors that modulate the expression of ApC/EBP and also are critically involved in LTF. In this review, we examine the roles of these transcription factors during consolidation of LTF induced by different stimulation paradigms.

Training with inedible food in Aplysia causes expression of C/EBP in the buccal but not cerebral ganglion

Training with inedible food in Aplysia increased expression of the transcription factor C/EBP in the buccal ganglia, which primarily have a motor function, but not in the cerebral or pleural ganglia. C/EBP mRNA increased immediately after training, as well as 1-2 h later. The increased expression of C/EBP protein lagged the increase in mRNA. Stimulating the lips and inducing feeding responses do not lead to long-term memory and did not cause increased C/EBP expression. Blocking polyADP-ribosylation, a process necessary for long-term memory after training, did not affect the increased C/EBP mRNA expression in the buccal ganglia.

The complex of TFII-I, PARP1, and SFPQ proteins regulates the DYX1C1 gene implicated in neuronal migration and dyslexia

DYX1C1 was first identified as a candidate gene for dyslexia susceptibility, and its role in controlling neuronal migration during embryogenesis and effect on learning in rodents have been verified. In contrast, genetic association studies have been ambiguous in replicating its effects on dyslexia. To better understand the regulation of DYX1C1 and the possible functional role of genetic variation in the promoter of DYX1C1, we selected three single-nucleotide polymorphisms (SNPs) with predicted functional consequences or suggested associations to dyslexia for detailed study. Electrophoretic mobility shift assays suggested the allele-specific binding of the transcription factors TFII-I (to rs3743205) and Sp1 (to rs16787 and rs12899331) that could be verified by competition assays. In addition, we purified a complex of protein factors binding to the previously suggested dyslexia-related SNP, -3G/A (rs3743205). Three proteins, TFII-I, PARP1, and SFPQ, were unambiguously identified by mass spectrometry and protein sequencing. Two SNPs, rs16787 and rs3743205, showed significant allelic differences in luciferase assays. Our results show that TFII-I, PARP1, and SFPQ proteins, each previously implicated in gene regulation, form a complex controlling transcription of DYX1C1. Furthermore, allelic differences in the promoter or 5' untranslated region of DYX1C1 may affect factor binding and thus regulation of the gene.

Transcriptional regulation of mouse mu opioid receptor gene in neuronal cells by poly(ADP-ribose) polymerase-1

The pharmacological actions of morphine and morphine-like drugs such as heroin mediate primarily through the mu opioid receptor (MOR). It represents the target of the most valuable painkiller in contemporary medicine. Here we report that poly(ADP-ribose) polymerase 1 (PARP-1) binds to the double-stranded poly(C) element essential for the MOR promoter and represses promoter activity at the transcriptional level. We identified PARP-1 by affinity column chromatography using the double-stranded poly(C) element, followed by two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry. PARP-1 binding to the poly(C) sequence of the MOR gene was sequence-specific as confirmed by the supershift assay. In cotransfection studies, PARP-1 repressed the MOR promoter only when the poly(C) sequence was intact. When PARP-1 was disrupted in NS20Y cells using siRNA, transcription of the endogenous target MOR gene increased significantly. Chromatin immunoprecipitation assays showed specific binding of PARP-1 to the double-stranded poly(C) element essential for the MOR promoter. Inhibition of PARP-1's catalytic domain with 3-aminobenzamide increased endogenous MOR mRNA levels in cultured NS20Y cells, suggesting that automodification of PARP-1 regulates MOR transcription. Our data suggest that PARP-1 can function as a repressor of MOR transcription dependent on the MOR poly(C) sequence. We demonstrate for the first time a role of PARP-1 as a transcriptional repressor in MOR gene regulation.

Local administration of the poly(ADP-ribose) polymerase inhibitor INO-1001 prevents NAD+ depletion and improves water maze performance after traumatic brain injury in mice

Poly(ADP-ribose) polymerase-1 (PARP-1) is an enzyme best known for its role in DNA repair and as a mediator of NAD+ depletion and energy failure-induced cell death. We tested the effect of the potent and selective ideno-isoquinolone PARP-1 inhibitor INO-1001 after controlled cortical impact (CCI) in mice. Anesthetized adult male mice were subjected to moderate CCI (velocity 6 m/sec, depth 1.2 mm) or sham-injury. Immediately after CCI or sham-injury mice received either INO-1001 (1.6 mg/kg) or vehicle via intracerebral injection (5 microl over 5 min) in a randomized fashion. At 2 h, contused brain tissue was dissected and NAD+ levels were measured. Separate mice underwent neuropathological outcome tests that included spatial memory acquisition (Morris water maze days 14-20), and assessment of contusion volume and hippocampal cell death at day 21. Local treatment with INO-1001 preserved brain NAD+ levels 2 h after CCI (vehicle = 67 +/- 7.6, INO-1001 = 95.8 +/- 4.4 % uninjured hemisphere; n = 6/group, p = 0.03). In the Morris water maze, treatment with INO-1001 reduced the latency to find the hidden platform and increased the time spent in the target quadrant versus vehicle after CCI (n = 11/group, p < or = 0.05). Histological damage did not differ between vehicle and INO-1001-treated mice after CCI. Treatment with INO-1001 prevented NAD+ depletion and improved outcome, although modestly, identifying PARP-mediated energy failure as a contributor to the pathological sequelae of TBI. Further study testing the effects of PARP inhibitors is warranted, specifically in models of brain injury where energy failure is seen.

Identification of poly-ADP-ribosylated mitochondrial proteins after traumatic brain injury

Poly-ADP-ribosylation is a post-translational modification performed by poly(ADP-ribose) polymerases (PARP), involved in many diverse cellular functions including DNA repair, transcription, and long-term potentiation. Paradoxically, PARP over-activation under pathologic conditions including traumatic brain injury (TBI) results in cell death. We previously demonstrated that intra-mitochondrial poly-ADP-ribosylation occurs following excitotoxic and oxidative injury in vitro. Here we sought to identify mitochondrial proteins modified by poly-ADP-ribosylation after TBI in vivo. Poly-ADP-ribosylation within mitochondria from injured brain after experimental TBI in rats was first verified using western blot and immuno-electron microscopy. Poly-ADP-ribosylated mitochondrial proteins identified using a targeted proteomic approach included voltage-dependent anion channel-1, mitofilin, mitochondrial stress proteins, and the electron transport chain components F1F0 ATPase, cytochrome c oxidase, and cytochrome c reductase. To examine the functional consequences of mitochondrial poly-ADP-ribosylation, isolated rat brain mitochondria were exposed to conditions of nitrosative stress known to activate PARP. PARP activation-induced reductions in State 3 respiration were prevented by the PARP-1 inhibitor 5-iodo-6-amino-1,2-benzopyrone or exogenous poly(ADP-ribose) glycohydrolase. As the effects of PARP activation on mitochondrial respiration appear regulated by poly(ADP-ribose) glycohydrolase, a direct effect of poly-ADP-ribosylation on electron transport chain function is suggested. These findings may be of relevance to TBI and other diseases where mitochondrial dysfunction occurs.

DNA-independent PARP-1 activation by phosphorylated ERK2 increases Elk1 activity: a link to histone acetylation

PolyADP-ribose polymerases (PARPs) catalyze a posttranslational modification of nuclear proteins by polyADP-ribosylation. The catalytic activity of the abundant nuclear protein PARP-1 is stimulated by DNA strand breaks, and PARP-1 activation is required for initiation of DNA repair. Here we show that PARP-1 also acts within extracellular signal-regulated kinase (ERK) signaling cascade that mediates growth and differentiation. The findings reveal an alternative mode of PARP-1 activation, which does not involve binding to DNA or DNA damage. In a cell-free system, recombinant PARP-1 was intensively activated and thereby polyADP-ribosylated by a direct interaction with phosphorylated ERK2, and the activated PARP-1 dramatically increased ERK2-catalyzed phosphorylation of the transcription factor Elk1. In cortical neurons treated with nerve growth factors and in stimulated cardiomyocytes, PARP-1 activation enhanced ERK-induced Elk1-phosphorylation, core histone acetylation, and transcription of the Elk1-target gene c-fos. These findings constitute evidence for PARP-1 activity within the ERK signal-transduction pathway.

X-linked mental retardation and epigenetics

The search for the genetic defects in constitutional diseases has so far been restricted to direct methods for the identification of genetic mutations in the patients' genome. Traditional methods such as karyotyping, FISH, mutation screening, positional cloning and CGH, have been complemented with newer methods including array-CGH and PCR-based approaches (MLPA, qPCR). These methods have revealed a high number of genetic or genomic aberrations that result in an altered expression or reduced functional activity of key proteins. For a significant percentage of patients with congenital disease however, the underlying cause has not been resolved strongly suggesting that yet other mechanisms could play important roles in their etiology. Alterations of the 'native' epigenetic imprint might constitute such a novel mechanism. Epigenetics, heritable changes that do not rely on the nucleotide sequence, has already been shown to play a determining role in embryonic development, X-inactivation, and cell differentiation in mammals. Recent progress in the development of techniques to study these processes on full genome scale has stimulated researchers to investigate the role of epigenetic modifications in cancer as well as in constitutional diseases. We will focus on mental impairment because of the growing evidence for the contribution of epigenetics in memory formation and cognition. Disturbance of the epigenetic profile due to direct alterations at genomic regions, or failure of the epigenetic machinery due to genetic mutations in one of its components, has been demonstrated in cognitive derangements in a number of neurological disorders now. It is therefore tempting to speculate that the cognitive deficit in a significant percentage of patients with unexplained mental retardation results from epigenetic modifications.

Poly(ADP-ribose): novel functions for an old molecule

The addition to proteins of the negatively charged polymer of ADP-ribose (PAR), which is synthesized by PAR polymerases (PARPs) from NAD(+), is a unique post-translational modification. It regulates not only cell survival and cell-death programmes, but also an increasing number of other biological functions with which novel members of the PARP family have been associated. These functions include transcriptional regulation, telomere cohesion and mitotic spindle formation during cell division, intracellular trafficking and energy metabolism.

Direct phosphorylation and regulation of poly(ADP-ribose) polymerase-1 by extracellular signal-regulated kinases 1/2

Sustained activation of poly(ADP-ribose) polymerase-1 (PARP-1) and extracellular signal-regulated kinases 1/2 (ERK1/2) both promote neuronal death. Here we identify a direct link between these two cell death pathways. In a rat model of hypoglycemic brain injury, neuronal PARP-1 activation and subsequent neuronal death were blocked by the ERK1/2 inhibitor 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98059). In neuron cultures, PARP-1-mediated neuronal death induced by N-methyl-d-aspartate, peroxynitrite, or DNA alkylation was similarly blocked by ERK1/2 pathway inhibitors. These inhibitors also blocked PARP-1 activation and PARP-1-mediated death in astrocytes. siRNA down-regulation of ERK2 expression in astrocytes also blocked PARP-1 activation and cell death. Direct effects of ERK1/2 on PARP-1 were evaluated by using isolated recombinant enzymes. The activity of recombinant human PARP-1 was reduced by incubation with alkaline phosphatase and restored by incubation with active ERK1 or ERK2. Putative ERK1/2 phosphorylation sites on PARP-1 were identified by mass spectrometry. Using site-directed mutagenesis, these sites were replaced with alanine (S372A and T373A) to block phosphorylation, or with glutamate (S372E and T373E) to mimic constitutive phosphorylation. Transfection of PARP-1 deficient mouse embryonic fibroblasts with the mutant PARP-1 species showed that the S372A and T373A mutations impaired PARP-1 activation, whereas the S372E and T373E mutations increased PARP-1 activity and eliminated the effect of ERK1/2 inhibitors on PARP-1 activation. These results suggest that PARP1 phosphorylation by ERK1/2 is required for maximal PARP-1 activation after DNA damage.

Caspase-like activity is essential for long-term synaptic plasticity in the terrestrial snail Helix

Although caspase activity in the nervous system of mollusks has not been described before, we suggested that these cysteine proteases might be involved in the phenomena of neuroplasticity in mollusks. We directly measured caspase-3 (DEVDase) activity in the Helix lucorum central nervous system (CNS) using a fluorometrical approach and showed that the caspase-3-like immunoreactivity is present in the central neurons of Helix. Western blots revealed the presence of caspase-3-immunoreactive proteins with a molecular mass of 29 kDa. Staurosporin application, routinely used to induce apoptosis in mammalian neurons through the activating cleavage of caspase-3, did not result in the appearance of a smaller subunit corresponding to the active caspase in the snail. However, it did increase the enzyme activity in the snail CNS. This suggests differences in the regulation of caspase-3 activity in mammals and snails. In the snail CNS, the caspase homolog seems to possess an active center without activating cleavage typical for mammals. In electrophysiological experiments with identified snail neurons, selective blockade of the caspase-3 with the irreversible and cell-permeable inhibitor of caspase-3 N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp-(OMe)-fluoro-methylketone prevented development of the long-term stage of synaptic input sensitization, suggesting that caspase is necessary for normal synaptic plasticity in snails. The results of our study give the first direct evidence that the caspase-3-like activity is essential for long-term plasticity in the invertebrate neurons. This activity is presumably involved in removing inhibitory constraints on the storage of long-term memory.

KIF4 Motor Regulates Activity-Dependent Neuronal Survival by Suppressing PARP-1 Enzymatic Activity

In brain development, apoptosis is a physiological process that controls the final numbers of neurons. Here, we report that the activity-dependent prevention of apoptosis in juvenile neurons is regulated by kinesin superfamily protein 4 (KIF4), a microtubule-based molecular motor. The C-terminal domain of KIF4 is a module that suppresses the activity of poly (ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme known to maintain cell homeostasis by repairing DNA and serving as a transcriptional regulator. When neurons are stimulated by membrane depolarization, calcium signaling mediated by CaMKII induces dissociation of KIF4 from PARP-1, resulting in upregulation of PARP-1 activity, which supports neuron survival. After dissociation from PARP-1, KIF4 enters into the cytoplasm from the nucleus and moves to the distal part of neurites in a microtubule-dependent manner. We suggested that KIF4 controls the activity-dependent survival of postmitotic neurons by regulating PARP-1 activity in brain development.

Poly(ADP-ribose) glycohydrolase is a component of the FMRP-associated messenger ribonucleoparticles

PARG [poly(ADP-ribose) glycohydrolase] is the only known enzyme that catalyses the hydrolysis of poly(ADP-ribose), a branched polymer that is synthesized by the poly(ADP-ribose) polymerase family of enzymes. Poly(ADP-ribosyl)ation is a transient post-translational modification that alters the functions of the acceptor proteins. It has mostly been studied in the context of DNA-damage signalling or DNA transaction events, such as replication and transcription reactions. Growing evidence now suggests that poly(ADP-ribosyl)ation could have a much broader impact on cellular functions. To elucidate the roles that could be played by PARG, we performed a proteomic identification of PARG-interacting proteins by mass spectrometric analysis of PARG pulled-down proteins. In the present paper, we report that PARG is resident in FMRP (Fragile-X mental retardation protein)-associated messenger ribonucleoparticles complexes. The localization of PARG in these complexes, which are components of the translation machinery, was confirmed by sedimentation and microscopy analysis. A functional link between poly(ADP-ribosyl)ation modulation and FMRP-associated ribonucleoparticle complexes are discussed in a context of translational regulation.

The expanding role of poly(ADP-ribose) metabolism: current challenges and new perspectives

Recent discoveries have resulted in significant breakthroughs in the understanding of PARPs and PARG functions within a broad range of cellular processes. The novel and sometimes unexpected pathways that are regulated by poly(ADP-ribosylation) bring new questions and hypotheses, some of them being contentious. In this review, we highlight current areas of investigation such as the clinical potential of PARP and PARG inhibitors and the important mitotic regulatory functions of poly(ADP-ribose) in cell-cycle progression, a recent discovery that has broadened our knowledge regarding poly(ADP-ribose) functions. A special emphasis is placed on recent advances in relation to PARG that are stimulating new directions in future research. Noticeably, the existence of various PARG isoforms characterized by distinct cellular localizations and nucleocytoplasmic shuttling properties challenges our current comprehension of pADPr metabolism. Observations and suppositions towards functionally important regulatory elements in the N-terminal portion of PARG are also discussed.

Different roles of two nitric oxide activated pathways in spinal long-term potentiation of C-fiber-evoked field potentials

There is accumulating evidence implicating the involvement of nitric oxide (NO) in spinal central sensitization. The long-term potentiation (LTP) of spinal C-fiber-evoked field potentials is considered as a fundamental mechanism of sensitization of nociceptive neurons in the spinal cord. The present study examined the roles of soluble guanylate cyclase (sGC) or ADP-ribosyltransferase (ADPRT), two potential NO targets, in spinal LTP. The results showed that (1) administration of sGC inhibitors, methyl blue (MB, 4mM, 20 microl) or 1H-[1,2,4]oxadiazolo[4,3-a]-quiloxalin-1-one (ODQ, 10 microM, 20 microl) before tetanic stimulation, significantly inhibited the induction of spinal LTP, and this was reversed by 8-Br-cGMP, a membrane-permeable cGMP analog. However, the maintenance of spinal LTP was not changed when application of ODQ 2h after tetanic stimulation. (2) Although our previous experiments have identified a key role for NO in the induction of spinal LTP, NO synthase (NOS) inhibitor, L-NAME (1mM, 20 microl) or hemoglobin (2mg/ml, 20 microl), a scavenger of NO, had no effect on established spinal LTP when applied 2h after the induction of spinal LTP. (3) The mono-ADPRT inhibitor, nicotinamide (10mM, 20 microl), had no effect on the induction and maintenance of spinal LTP. However, the poly-ADPRT inhibitor, benzamide (100 microM, 20 microl), inhibited its maintenance, but not its induction. The results suggest that NO-stimulated guanylyl cyclase activity plays a critical role in the induction of LTP of C-fiber-evoked field potentials in the spinal cord, whereas NO-related poly-ADPRT activity contributes to the maintenance of spinal LTP.

Detection and quantification of poly-ADP-ribosylated cellular proteins of spleen and liver tissues of mice in vivo by slot and Western blot immunoprobing using polyclonal antibody against mouse ADP-ribose polymer

Poly-ADP-ribosylation (PAR) of cellular proteins has been shown to have decisive roles in diverse cellular functions including carcinogenesis. There are indications that metabolic level of poly-ADP-ribosylated cellular proteins might indicate carcinogenesis and, therefore, could be potentially used in cancer screening program. Keeping in mind the limitations of currently available assays of cellular PAR, a new assay is being reported that measures the metabolic level of poly-ADP-ribosylated cellular proteins. The ELISA based slot and Western blot immunoassay used polyclonal antibody against natural, heterogeneous ADP-ribose polymers. It could be successfully employed to qualitatively and quantitatively assay metabolic levels of poly-ADP-ribosylated proteins of spleen and liver tissues of normal mice or mice exposed to dimethylnitrosamine for up to 8 weeks; potentially PAR of cellular proteins could be assayed in any tissue or biopsy. Implications of the results in cancer screening program have been discussed.