Poly(ADP-ribose) polymerase: a guardian angel protecting the genome and suppressing tumorigenesis

Poly(ADP-ribosyl)ation is an immediate cellular response to DNA damage generated either exogenously or endogenously. This post-translational modification is catalyzed by poly(ADP-ribose) polymerase (PARP, PARP-1, EC 2.4.2.30). It is proposed that this protein plays a multifunctional role in many cellular processes, including DNA repair, recombination, cell proliferation and death, as well as genomic stability. Chemical inhibitors of the enzyme, dominant negative or null mutations of PARP-1 cause a high degree of genomic instability in cells. Inhibition of PARP activity by chemical inhibitors renders mice or rats susceptible to carcinogenic agents in various tumor models, indicating a role for PARP-1 in suppressing tumorigenesis. Despite the above observations, PARP-1 knockout mice are generally not prone to the development of tumors. An enhanced tumor development was observed, however, when the PARP-1 null mutation was introduced into severely compromised immune-deficient mice (a mutation in DNA-dependent protein kinase) or mice lacking other DNA repair or chromosomal guardian molecules, such as p53 or Ku80. These studies indicate that PARP-1 functions as a cofactor to suppress tumorigenesis via its role in stabilization of the genome, and/or by interacting with other DNA strand break-sensing molecules. Studies using PARP-1 mutants and chemical inhibitors have started to shed light on the role of this protein and of the specific protein post-translational modification in the control of genomic stability and hence its involvement in cancer.     

Poly(ADP-ribosyl)ation of p53 Contributes to TPEN-Induced Neuronal Apoptosis

Depletion of intracellular zinc by N,N,N′,N′-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) induces p53-mediated protein synthesis-dependent apoptosis of mouse cortical neurons. Here, we examined the requirement for poly(ADP-ribose) polymerase (PARP)-1 as an upstream regulator of p53 in zinc depletion-induced neuronal apoptosis. First, we found that chemical inhibition or genetic deletion of PARP-1 markedly attenuated TPEN-induced apoptosis of cultured mouse cortical neurons. Poly(ADP-ribosyl)ation of p53 occurred starting 1 h after TPEN treatment. Suggesting the critical role of PARP-1, the TPEN-induced increase of stability and activity of p53 as well as poly(ADP-ribosyl)ation of p53 was almost completely blocked by PARP inhibition. Consistent with this, the induction of downstream proapoptotic proteins PUMA and NOXA was noticeably reduced by chemical inhibitors or genetic deletion of PARP-1. TPEN-induced cytochrome C release into the cytosol and caspase-3 activation were also blocked by inhibition of PARP-1. Taken together, these findings indicate that PARP-1 is essential for TPEN-induced neuronal apoptosis.     

p53-dependent neuronal cell death in a DJ-1-deficient zebrafish model of Parkinson's disease

Mutations in DJ-1 lead to early onset Parkinson's disease (PD). The aim of this study was to elucidate further the underlying mechanisms leading to neuronal cell death in DJ-1 deficiency in vivo and determine whether the observed cell loss could be prevented pharmacologically. Inactivation of DJ-1 in zebrafish, Danio rerio, resulted in loss of dopaminergic neurons after exposure to hydrogen peroxide and the proteasome inhibitor MG132. DJ-1 knockdown by itself already resulted in increased p53 and Bax expression levels prior to toxin exposure without marked neuronal cell death, suggesting subthreshold activation of cell death pathways in DJ-1 deficiency. Proteasome inhibition led to a further increase of p53 and Bax expression with widespread neuronal cell death. Pharmacological p53 inhibition either before or during MG132 exposure in vivo prevented dopaminergic neuronal cell death in both cases. Simultaneous knockdown of DJ-1 and the negative p53 regulator mdm2 led to dopaminergic neuronal cell death even without toxin exposure, further implicating involvement of p53 in DJ-1 deficiency-mediated neuronal cell loss. Our study demonstrates the utility of zebrafish as a new animal model to study PD gene defects and suggests that modulation of downstream mechanisms, such as p53 inhibition, may be of therapeutic benefit.     

MPTP/MPP+ 诱导神经元凋亡的机制研究

1982年人们发现1-甲基-4-苯基-1,2,3,6-四氢吡啶(MPTP)能诱发PD,它的有效成分是1-甲基-4-苯基吡啶离子(MPP+)。目前,MPTP/MPP+广泛的被用作诱导PD实验模型的有效药物,可诱导神经元细胞发生凋亡性死亡。MPTP/MPP+诱导细胞凋亡的机制牵涉Bcl-2、p53、caspase家族、JNK通路、ERK通路和PARP等多种机制,它们共同参与了MPTP/MPP+诱导的细胞凋亡的调控和执行阶段。本文主要综述MPTP/MPP+诱导的神经元细胞凋亡机制。     

Transduced Tat-DJ-1 protein protects against oxidative stress-induced SH-SY5Y cell death and Parkinson disease in a mouse model

Parkinson's disease (PD) is a well known neurodegenerative disorder characterized by selective loss of dopaminergic neurons in the substantia nigra pars compact (SN). Although the exact mechanism remains unclear, oxidative stress plays a critical role in the pathogenesis of PD. DJ-1 is a multifunctional protein, a potent antioxidant and chaperone, the loss of function of which is linked to the autosomal recessive early onset of PD. Therefore, we investigated the protective effects of DJ-1 protein against SH-SY5Y cells and in a PD mouse model using a cell permeable Tat-DJ-1 protein. Tat-DJ-1 protein rapidly transduced into the cells and showed a protective effect on 6-hydroxydopamine (6-OHDA)-induced neuronal cell death by reducing the reactive oxygen species (ROS). In addition, we found that Tat-DJ-1 protein protects against dopaminergic neuronal cell death in 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP)-induced PD mouse models. These results suggest that Tat-DJ-1 protein provides a potential therapeutic strategy for against ROS related human diseases including PD.     

AMP-activated protein kinase is activated in Parkinson’s disease models mediated by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The selective loss of dopaminergic neurons in the substantia nigra pars compacta is a feature of Parkinson’s disease (PD). 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity is the most common experimental model used to investigate the pathogenesis of PD. Administration of MPTP in mice produces neuropathological defects as observed in PD and 1-methyl-4-pyridinium (MPP⁺) induces cell death when neuronal cell cultures are used. AMP-activated protein kinase (AMPK) is a key regulator of energy homeostasis. In the present study, we demonstrated that AMPK is activated by MPTP in mice and MPP⁺ in SH-SY5Y cells. The inhibition of AMPK by compound C resulted in an increase in MPP⁺-induced cell death. We further showed that overexpression of AMPK increased cell viability after exposure to MPP⁺ in SH-SY5Y cells. Based on these results, we suggest that activation of AMPK might prevent neuronal cell death and play a role as a survival factor in PD.     

Poly(ADP-ribosyl)ation affects stabilization of Che-1 protein in response to DNA damage

Poly(ADP-ribose) polymerase 1 (PARP-1) catalyzes a post-translational modification that plays a crucial role in coordinating the signalling cascade in response to stress stimuli. During the DNA damage response, phosphorylation by ataxia telangiectasia mutated (ATM) kinase and checkpoint kinase Chk2 induces the stabilization of Che-1 protein, which is critical for the maintenance of G2/M arrest. In this study we showed that poly(ADP-ribosyl)ation, beyond phosphorylation, is involved in the regulation of Che-1 stabilization following DNA damage. We demonstrated that Che-1 accumulation upon doxorubicin treatment is reduced after the inhibition of PARP activity in HCT116 cells and in PARP-1 knock-out or silenced cells. In accordance, impairment in Che-1 accumulation by PARP inhibition reduced Che-1 occupancy at p21 promoter and affected the expression of the corresponding gene. Epistasis experiments showed that the effect of poly(ADP-ribosyl)ation on Che-1 stabilization is independent from ATM kinase activity. Indeed we demonstrated that Che-1 protein co-immunoprecipitates with ADP-ribose polymers and that PARP-1 directly interacts with Che-1, promoting its modification in vitro and in vivo.     

MPTP/MPP＋诱导神经元凋亡的机制研究

1982年人们发现1-甲基-4-苯基-1,2,3,6-四氢吡啶（MPTP）能诱发PD,它的有效成分是1-甲基-4-苯基吡啶离子（MPP＋）。目前,MPTP/MPP＋广泛的被用作诱导PD实验模型的有效药物,可诱导神经元细胞发生凋亡性死亡。MPTP/MPP＋诱导细胞凋亡的机制牵涉Bcl-2、p53、caspase家族、JNK通路、ERK通路和PARP等多种机制,它们共同参与了MPTP/MPP＋诱导的细胞凋亡的调控和执行阶段。本文主要综述MPTP/MPP＋诱导的神经元细胞凋亡机制。     

Embryonic stem cell-derived neuron models of Parkinson's disease exhibit delayed neuronal death

Establishment of a Parkinson's disease (PD) neuron model was attempted with mouse embryonic stem (ES) cells. ES cell lines over-expressing mouse nuclear receptor-related 1 (Nurr1), together with human wild-type and alanine 30 --> proline (A30P) and alanine 53 --> threonine (A53T) mutant alpha-synuclein were established and subjected to differentiation into dopaminergic neurons. The ES cell-derived dopaminergic neurons expressing wild-type or mutant alpha-synuclein exhibited the fundamental characteristics consistent with dopaminergic neurons in the substantia nigra. The ES cell-derived PD model neurons exhibited increased susceptibility to oxidative stress, proteasome inhibition, and mitochondrial inhibition. Cell viability of PD model neurons and the control neurons was similar until 28 days after differentiation. Nonetheless, after that time, PD model neurons gradually began to undergo neuronal death over the course of 1 month, showing cytoplasmic aggregate formation and an increase of insoluble alpha-synuclein protein. Such delayed neuronal death was observed in a mutant alpha-synuclein protein level-dependent manner, which was slightly inhibited by a c-jun N-terminal kinase inhibitor and a caspase inhibitor. Such cell death was not observed when the same ES cell lines were differentiated into oligodendrocytes. The ES cell-derived PD model neurons are considered as prospective candidates for a new prototype modelling PD that would allow better investigation of the underlying neurodegenerative pathophysiology.     

Attenuation of MPTP-induced neurotoxicity and locomotor dysfunction in Nucling-deficient mice via suppression of the apoptosome pathway

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity is one of the experimental models most commonly used to study the pathogenesis of Parkinson's disease (PD). Although the biochemical mechanisms underlying the cell death induced by MPTP remain to be clarified, it has been found that the mitochondrial apoptotic signaling pathway plays an important role in the neurotoxicity of MPTP. Nucling is a novel type of apoptosis-associated molecule, essential for cytochrome c, apoptosis protease activating factor 1 (Apaf-1), pro-caspase-9 apoptosome induction and caspase-9 activation following pro-apoptotic stress. Here we found that Nucling-deficient mice treated with MPTP did not exhibit locomotor dysfunction in an open-field test. The substantia nigra dopaminergic neurons of Nucling-deficient mice were resistant to the damaging effects of the neurotoxin MPTP. Up-regulated expression of apoptosome was attenuated in Nucling-deficient mice treated with MPTP. These results indicate an important role for Nucling in MPTP-induced neuronal degeneration and suggest that the suppression of Nucling would be of therapeutic benefit for the treatment of neurodegeneration in PD.     

p53 regulates a non-apoptotic death induced by ROS

DNA damage induced by reactive oxygen species and several chemotherapeutic agents promotes both p53 and poly (ADP-ribose) polymerase (PARP) activation. p53 activation is well known to regulate apoptotic cell death, whereas robust activation of PARP-1 has been shown to promote a necrotic cell death associated with energetic collapse. Here we identify a novel role for p53 in modulating PARP enzymatic activity to regulate necrotic cell death. In mouse embryonic fibroblasts, human colorectal and human breast cancer cell lines, loss of p53 function promotes resistance to necrotic, PARP-mediated cell death. We therefore demonstrate that p53 can regulate both necrotic and apoptotic cell death, mutations or deletions in this tumor-suppressor protein may be selected by cancer cells to provide not only their resistance to apoptosis but also to necrosis, and explain resistance to chemotherapy and radiation even when it kills via non-apoptotic mechanisms.     

Apoptosis in Parkinson's disease: is p53 the missing link between genetic and sporadic Parkinsonism?

Parkinson's disease (PD) is a major age-related neurodegenerative disorder characterized by a massive and specific loss of dopaminergic neurons of the substantia nigra pars compacta. The cellular alterations are clinically translated into an invalidating movement disability associated to three canonical symptoms that are bradykinesia, resting tremor and rigidity. The exact causes of this neuronal loss are unknown, but a network of evidences indicates a major contribution of orchestrated cell death processes, also known as apoptosis. Apoptotic cell death is a normal process, the alteration of which triggers several pathologies including cancer and neurodegenerative disorders. Exhaustive work has been done to delineate the cellular mechanisms responsible for the exacerbated cell death of dopaminergic neurons observed in PD. Overall, the oncogene p53 has been identified as a key effector protein.This review will focus on the clues linking p53 to the etiology of PD and the evidences that this protein may be at the center of multiple signaling cascades not only altered by mutations of various proteins responsible for familial cases of PD but also on more general sporadic cases of this devastating disease.     

PEP-1-heat shock protein 27 protects from neuronal damage in cells and in a Parkinson's disease mouse model

Heat shock proteins (HSPs) are a highly conserved family of proteins that are induced in response to various environmental stressors including reactive oxygen species. HSP27 is a chaperone protein with the ability to increase cell survival in response to oxidative stress. Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons. Although the mechanism of PD remains unclear, oxidative stress is known to be important in its pathogenesis. This study investigated the protective effects of PEP-1-HSP27 on neuronal damage induced by 1-methyl-4-phenyl pyridinium (MPP(+) ) in SH-SY5Y cells and in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model. PEP-1-HSP27 rapidly entered the cells and protected them against MPP(+) -induced toxicity by inhibiting the reactive oxygen species levels and DNA fragmentation. Furthermore, transduced PEP-1-HSP27 prevented dopaminergic neuronal cell death in the substantia nigra of MPTP-induced PD mouse models. These results demonstrate that PEP-1-HSP27 provides a potential strategy for therapeutic delivery against various diseases and is a potential tool for the treatment of PD.     

Protective effects of PEP-1-Catalase on stress-induced cellular toxicity and MPTP-induced Parkinson’s disease

Parkinson’s disease (PD) is a neurodegenerative disability caused by a decrease of dopaminergic neurons in the substantia nigra (SN). Although the etiology of PD is not clear, oxidative stress is believed to lead to PD. Catalase is antioxidant enzyme which plays an active role in cells as a reactive oxygen species (ROS) scavenger. Thus, we investigated whether PEP-1-Catalase protects against 1-methyl-4-phenylpyridinium (MPP⁺) induced SH-SY5Y neuronal cell death and in a 1-methyl-4-phenyl-1,2,3,6-trtrahydropyridine (MPTP) induced PD animal model. PEP-1-Catalase transduced into SH-SY5Y cells significantly protecting them against MPP⁺-induced death by decreasing ROS and regulating cellular survival signals including Akt, Bax, Bcl-2, and p38. Immunohistochemical analysis showed that transduced PEP-1-Catalase markedly protected against neuronal cell death in the SN in the PD animal model. Our results indicate that PEP-1-Catalase may have potential as a therapeutic agent for PD and other oxidative stress related diseases. [BMB Reports 2015; 48(7): 395-400]     

The Peptidyl-prolyl Isomerase Pin1 Up-regulation and Proapoptotic Function in Dopaminergic Neurons: RELEVANCE TO THE PATHOGENESIS OF PARKINSON DISEASE*

Parkinson disease (PD) is a chronic neurodegenerative disease characterized by a slow and progressive degeneration of dopaminergic neurons in substantia nigra. The pathophysiological mechanisms underlying PD remain unclear. Pin1, a major peptidyl-prolyl isomerase, has recently been associated with certain diseases. Notably, Ryo et al. (Ryo, A., Togo, T., Nakai, T., Hirai, A., Nishi, M., Yamaguchi, A., Suzuki, K., Hirayasu, Y., Kobayashi, H., Perrem, K., Liou, Y. C., and Aoki, I. (2006) J. Biol. Chem. 281, 4117–4125) implicated Pin1 in PD pathology. Therefore, we sought to systematically characterize the role of Pin1 in PD using cell culture and animal models. To our surprise we observed a dramatic up-regulation of Pin1 mRNA and protein levels in dopaminergic MN9D neuronal cells treated with the parkinsonian toxicant 1-methyl-4-phenylpyridinium (MPP⁺) as well as in the substantia nigra of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model. Notably, a marked expression of Pin1 was also observed in the substantia nigra of human PD brains along with a high co-localization of Pin1 within dopaminergic neurons. In functional studies, siRNA-mediated knockdown of Pin1 almost completely prevented MPP⁺-induced caspase-3 activation and DNA fragmentation, indicating that Pin1 plays a proapoptotic role. Interestingly, multiple pharmacological Pin1 inhibitors, including juglone, attenuated MPP⁺-induced Pin1 up-regulation, α-synuclein aggregation, caspase-3 activation, and cell death. Furthermore, juglone treatment in the MPTP mouse model of PD suppressed Pin1 levels and improved locomotor deficits, dopamine depletion, and nigral dopaminergic neuronal loss. Collectively, our findings demonstrate for the first time that Pin1 is up-regulated in PD and has a pathophysiological role in the nigrostriatal dopaminergic system and suggest that modulation of Pin1 levels may be a useful translational therapeutic strategy in PD.     

Pramipexole protects against MPTP toxicity in non-human primates

The neurotoxin MPTP induces nigral dopaminergic cell death in primates and produces a partial model of Parkinson's disease (PD). Pramipexole is a D2/D3 dopamine receptor agonist used in the symptomatic treatment of PD, and which also protects neuronal cells against dopaminergic toxins in vitro. We now demonstrate that pramipexole partially prevents MPTP toxicity in vivo in a primate species. Common marmosets were repeatedly treated with pramipexole either before, coincidentally with, or after low-dose MPTP treatment designed to induce a partial lesion of the substantia nigra. Animals pretreated with pramipexole had a significantly greater number of surviving tyrosine hydroxylase (TH) positive neurones in the pars compacta of the substantia nigra. Pramipexole pretreatment also prevented degeneration of striatal dopamine terminals. Treatment with pramipexole concurrently with MPTP or following MPTP did not prevent TH-positive cell loss. Pramipexole pretreatment appears to induce adaptive changes that protect against dopaminergic cell loss in primates.     

Oxidative post-translational modifications of alpha-synuclein in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease

Structural and functional alterations of alpha-synuclein is a presumed culprit in the demise of dopaminergic neurons in Parkinson's disease (PD). Alpha-synuclein mutations are found in familial but not in sporadic PD, raising the hypothesis that effects similar to those of familial PD-linked alpha-synuclein mutations may be achieved by oxidative post-translational modifications. Here, we show that wild-type alpha-synuclein is a selective target for nitration following peroxynitrite exposure of stably transfected HEK293 cells. Nitration of alpha-synuclein also occurs in the mouse striatum and ventral midbrain following administration of the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Conversely, beta-synuclein and synaptophysin were not nitrated in MPTP-intoxicated mice. Our data demonstrate that alpha-synuclein is a target for tyrosine nitration, which, by disrupting its biophysical properties, may be relevant to the putative role of alpha-synuclein in the neurodegeneration associated with MPTP toxicity and with PD.