In neurodegenerative disorders such as Alzheimers, Parkinsons and Huntingtons diseases, neurons may die by a form of programmed cell death called apoptosis. A major effort in the Cellular and Molecular Neurosciences section of the Laboratory of Neurosciences is aimed at establishing what triggers apoptosis in neurodegenerative disorders and how neuronal degeneration might be prevented by targeting specific molecular events in the process of apoptosis. Studies of cultured neurons demonstrated that activation of glutamate receptors can induce a transient damage to DNA which is rapidly repaired as the result of calcium-mediated upregulation of the DNA repair protein APE1. In addition, we have identified a mitochondrial uncoupling protein (UCP4) that can protect neurons in models relevant to stroke and Alzheimers disease by a mechanism involving suppression of oxidative stress and stabilization of cellular calcium homeostasis. We have also established roles for brain-derived neurotrophic factor (BDNF) in preventing the apoptosis of neurons produced from stem cells in the hippocampus, a finding that suggests the possibility of increasing the capacity of the brain to replace lost and damaged neurons. In other studies we have found that newly generated neurons are highly sensitive to DNA damage-induced apoptosis because they have low levels of telomerase and the telomere-associated protein TRF2. Preclinical studies have shown that intravenous immunoglobulin and gamma-secretase inhibotors are effective in stroke models. More recently, we have shown that neurons express several toll-like receptors, and have provided evidence that activation of two of these receptors (TLR2 and TLR4) can trigger apoptosis in cell culture and animal models of Alzheimer's disease and stroke. In other studies we have revealed important roles for plasma membrane redox enzymes in protecting neurons against apoptosis in experimental models of aging and neurodegenerative disorders. We previously showed that calorie restriction ameliorated Huntington's disease (HD) pathogenesis and slowed disease progression in mice that model Huntington's disease (Huntington's disease mice). We now report that overexpression of Sirt1, a mediator of the beneficial metabolic effects of calorie restriction, protects neurons against mutant HTT toxicity, whereas reduction of Sirt1 exacerbates mutant HTT toxicity. Overexpression of Sirt1 improves motor function, reduces brain atrophy and attenuates mutant-HTT-mediated metabolic abnormalities in Huntington's disease mice. Further mechanistic studies suggested that Sirt1 prevents the mutant-HTT-induced decline in BDNF concentrations and the signaling of its receptor, TrkB, and restores dopamine concentrations in the striatum. Sirt1 deacetylase activity is required for Sirt1-mediated neuroprotection in Huntington's disease cell models. Notably, we show that mutant HTT interacts with Sirt1 and inhibits Sirt1 deacetylase activity, which results in hyperacetylation of Sirt1 substrates such as forkhead box O3A (Foxo3a), thereby inhibiting its pro-survival function. Overexpression of Sirt1 counteracts the mutant-HTT-induced deacetylase deficit, enhances the deacetylation of Foxo3a and facilitates cell survival. These findings show a neuroprotective role for Sirt1 in mammalian HD models and open new avenues for the development of neuroprotective strategies in HD. Eukaryotic elongation factor 2 (eEF-2) is an important regulator of the protein translation machinery whereby it controls the movement of the ribosome along the mRNA. The activity of eEF-2 is regulated by changes in cellular energy status and nutrient availability and by posttranslational modifications such as phosphorylation and mono-ADP-ribosylation. However, the mechanisms regulating protein translation under conditions of cellular stress in neurons are unknown. Here we show that when rat hippocampal neurons experience oxidative stress (lipid peroxidation induced by exposure to cumene hydroperoxide;CH), eEF-2 is hyperphosphorylated and ribosylated, resulting in reduced translational activity. The degradation of eEF-2 requires calpain proteolytic activity and is accompanied by accumulation of eEF-2 in the nuclear compartment. The subcellular localization of both native and phosphorylated forms of eEF-2 is influenced by CRM1 and 14.3.3, respectively. In hippocampal neurons p53 interacts with nonphosphorylated (active) eEF-2, but not with its phosphorylated form. The p53-eEF-2 complexes are present in cytoplasm and nucleus, and their abundance increases when neurons experience oxidative stress. The nuclear localization of active eEF-2 depends upon its interaction with p53, as cells lacking p53 contain less active eEF-2 in the nuclear compartment. Overexpression of eEF-2 in hippocampal neurons results in increased nuclear levels of eEF-2 and decreased cell death after exposure to CH. Our results reveal novel molecular mechanisms controlling the differential subcellular localization and activity state of eEF-2 that may influence the survival status of neurons during periods of elevated oxidative stress Nuclear factor E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway is an important cellular stress response pathway involved in neuroprotection. We previously screened several natural phytochemicals and identified plumbagin as a novel activator of the Nrf2/ARE pathway that can protect neurons against ischemic injury. Here we extended our studies to natural and synthetic derivatives of plumbagin. We found that 5,8-dimethoxy-1,4-naphthoquinone (naphthazarin) is a potent activator of the Nrf2/ARE pathway, up-regulates the expression of Nrf2-driven genes in primary neuronal and glial cultures, and protects neurons against glutamate-induced excitotoxicity. Neurons are terminally differentiated cells with a high rate of metabolism and multiple biological properties distinct from their undifferentiated precursors. Previous studies showed that nucleotide excision DNA repair is downregulated in postmitotic muscle cells and neurons. Here, we characterize DNA damage susceptibility and base excision DNA repair (BER) capacity in undifferentiated and differentiated human neural cells. The results show that undifferentiated human SH-SY5Y neuroblastoma cells are less sensitive to oxidative damage than their differentiated counterparts, in part because they have robust BER capacity, which is heavily attenuated in postmitotic neurons. The reduction in BER activity in differentiated cells correlates with diminished protein levels of key long patch BER components, flap endonuclease-1, proliferating cell nuclear antigen, and ligase I. Thus, because of their higher BER capacity, proliferative neural progenitor cells are more efficient at repairing DNA damage compared with their neuronally differentiated progeny. In a related study we found that mice lacking NEIL1 exhibit impaired memory retention in a water maze test, but no abnormalities in tests of motor performance, anxiety, or fear conditioning. NEIL1 deficiency results in increased brain damage and a defective functional outcome in a focal ischemia/reperfusion model of stroke. The incision capacity on a 5-hydroxyuracil-containing bubble substrate was lower in the ipsilateral side of ischemic brains and in the mitochondrial lysates of unstressed old NEIL1-deficient mice. These results indicate that NEIL1 plays an important role in learning and memory and in protection of neurons against ischemic injury.

Agency
National Institute of Health (NIH)
Institute
National Institute on Aging (NIA)
Type
Investigator-Initiated Intramural Research Projects (ZIA)
Project #
1ZIAAG000313-13
Application #
8736518
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
13
Fiscal Year
2013
Total Cost
$508,154
Indirect Cost
Name
National Institute on Aging
Department
Type
DUNS #
City
State
Country
Zip Code
Yang, Jenq-Lin; Lin, Yu-Ting; Chuang, Pei-Chin et al. (2014) BDNF and exercise enhance neuronal DNA repair by stimulating CREB-mediated production of apurinic/apyrimidinic endonuclease 1. Neuromolecular Med 16:161-74
Arguelles, Sandro; Camandola, Simonetta; Cutler, Roy G et al. (2014) Elongation factor 2 diphthamide is critical for translation of two IRES-dependent protein targets, XIAP and FGF2, under oxidative stress conditions. Free Radic Biol Med 67:131-8
Bai, Yun; Lathia, Justin D; Zhang, Peisu et al. (2014) Molecular targeting of TRF2 suppresses the growth and tumorigenesis of glioblastoma stem cells. Glia 62:1687-98
Cheng, Yi-Lin; Park, Jong-Sung; Manzanero, Silvia et al. (2014) Evidence that collaboration between HIF-1* and Notch-1 promotes neuronal cell death in ischemic stroke. Neurobiol Dis 62:286-95
Lee, Jun-Ho; Halperin-Sheinfeld, Meital; Baatar, Dolgar et al. (2014) Tellurium compound AS101 ameliorates experimental autoimmune encephalomyelitis by VLA-4 inhibition and suppression of monocyte and T cell infiltration into the CNS. Neuromolecular Med 16:292-307
Eitan, Erez; Hutchison, Emmette R; Mattson, Mark P (2014) Telomere shortening in neurological disorders: an abundance of unanswered questions. Trends Neurosci 37:256-63
Longo, Valter D; Mattson, Mark P (2014) Fasting: molecular mechanisms and clinical applications. Cell Metab 19:181-92
Hou, Yan; Ghosh, Paritosh; Wan, Ruiqian et al. (2014) Permeability transition pore-mediated mitochondrial superoxide flashes mediate an early inhibitory effect of amyloid beta1-42 on neural progenitor cell proliferation. Neurobiol Aging 35:975-89
Arguelles, Sandro; Camandola, Simonetta; Hutchison, Emmette R et al. (2013) Molecular control of the amount, subcellular location, and activity state of translation elongation factor 2 in neurons experiencing stress. Free Radic Biol Med 61:61-71
Son, Tae Gen; Kawamoto, Elisa M; Yu, Qian-Sheng et al. (2013) Naphthazarin protects against glutamate-induced neuronal death via activation of the Nrf2/ARE pathway. Biochem Biophys Res Commun 433:602-6

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