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T M Dawson

Publications and source records attributed to T M Dawson.

At least 37 records · Page 2Linked to original sources
PubMed2001

Neuroimmunophilin ligands exert neuroregeneration and neuroprotection in midbrain dopaminergic neurons.

Immunosuppressant drugs, like FK506, and nonimmunosuppressant compounds like, GPI1046 and L685818, are immunophilin ligands that specifically bind to immunophilins, like FK506 binding protein 12 (FKBP12). Several lines of evidence show that these ligands exert neurotrophic properties in neural injury models and in PC12 cells. However, the mechanism of the neurotrophic function of the immunophilin ligands is poorly known. In the present study, we use MPP+ and 6-OHDA toxicity models to examine both neuroprotective and neuroregenerative effects of immunophilin ligands on primary cultures of midbrain dopaminergic neurons. We find that FK506, GPI1046 and L685818 at concentrations from 0.01 to 1 microM partially, but significantly, protect dopaminergic neurons against both MPP+ and 6-OHDA toxicity. By Western blot analysis, we also find that all three compounds prevent tyrosine hydroxylase (TH) loss induced by MPP+ and 6-OHDA treatments. Morphologic analysis of dopaminergic neurons, by immunocytochemistry, shows that MPP+ and 6-OHDA cause the retraction and loss of neuronal processes, while FK506, GPI1046 and L685818 promote regeneration of these processes as indicated by increases in process number and length. To examine if FKBP12 is required for neurotrophic effects of immunophilin ligands, we cultured dopaminergic neurons from FKBP12 knockout mice and find that FK506 still protects dopaminergic neurons against MPP+ toxicity. These results suggest that FKBP12 is not essential for the neurotrophic properties of immunophilin ligands, and immunophilin ligands are a new class of neuroprotective and neuroregenerative agents that may have therapeutic potential in a variety of neurological disorders.

1-Methyl-4-phenylpyridinium↗
PubMed2001

Epstein-Barr virus, methotrexate, and lymphoma in patients with rheumatoid arthritis and primary Sjögren's syndrome: case series.

OBJECTIVE: Rheumatoid arthritis (RA) and primary Sjögren's syndrome (SS) are associated with an increased risk of lymphoma. Epstein-Barr virus (EBV), a ubiquitous herpes virus, has been linked etiologically to lymphoma in patients with RA and primary SS. Recently, methotrexate (MTX) has also been linked to the development of these lymphomas. We investigated the frequency of EBV in lymphoma tissue of patients with RA and primary SS and the association of MTX with lymphomagenesis. METHODS: Twenty-three patients with RA and 9 with primary SS with a history of lymphoma were identified by writing to all Arthritis Foundation member rheumatologists in Washington State. Formalin fixed, paraffin embedded tissue blocks were then requested from pathology laboratories. Lymph nodes from 5 RA patients without lymphoma were also studied. In situ hybridization using a biotinylated EBER-1 oligonucleotide probe was used to detect EBV in tissue sections. Positive and negative laboratory controls were used to ensure procedural integrity. RESULTS: Specimens from 21 RA patients were obtained, with 2 subsequently excluded due to specimen quality. Specimens from 6 patients with primary SS were obtained. In situ hybridization for EBV was positive in 5/19 (26%) RA patients and 1/6 patients with primary SS. In the nonmalignant lymph nodes no patient showed EBV. One primary SS and 12 RA patients were known to be taking MTX at the time of lymphoma diagnosis. Of the EBV positive RA lymphoma patients, 4/5 were receiving MTX at the time of diagnosis. These results show that EBV is present in lymphoma tissue of some patients with RA and very few with primary SS. CONCLUSION: EBV is over-represented in the lymphomas of patients with RA, but whether MTX plays a role in predisposing patients with RA and primary SS to the development of lymphoma, perhaps by influencing behavior of EBV, remains unclear.

Adult↗
PubMed2001

Critical role for nitric oxide signaling in cardiac and neuronal ischemic preconditioning and tolerance.

Preconditioning to ischemic tolerance is a phenomenon in which brief episodes of a subtoxic insult induce a robust protection against the deleterious effects of subsequent, prolonged, lethal ischemia. The subtoxic stimuli that constitute the preconditioning event are quite diverse, ranging from brief ischemic episodes, spreading depression or potassium depolarization, chemical inhibition of oxidative phosphorylation, exposure to excitotoxins and cytokines. The beneficial effects of preconditioning were first demonstrated in the heart; it is now clear that preconditioning can induce ischemic tolerance in a variety of organ systems including brain, heart, liver, small intestine, skeletal muscle, kidney, and lung. There are two temporally and mechanistically distinct types of protection afforded by preconditioning stimuli, acute and delayed preconditioning. The signaling cascades that initiate the acute and delayed preconditioning responses may have similar biochemical components. However, the protective effects of acute preconditioning are protein synthesis-independent, mediated by post-translational protein modifications, and are short-lived. The effects of delayed preconditioning require new protein synthesis and are sustained for days to weeks. Elucidation of the molecular mechanisms that are involved in preconditioning and ischemic tolerance and identification of drugs that mimic this protective response have the potential to improve the prognosis of patients at risk for ischemic injury. This article focuses on recent findings on the effects of ischemic preconditioning in the cardiac and nervous systems and discusses potential targets for a successful therapeutic approach to limit ischemia-reperfusion injury.

Animals↗
PubMed2001

Identification by mRNA differential display of two up-regulated genes as candidate mediators of AIDS dementia.

BACKGROUND: In the dementia associated with acquired immunodeficiency syndrome (AIDS), indirect pathomechanisms are important mediators of progressive neuronal injury and variable candidate molecules of potential pathogenetic importance have been identified. MATERIALS AND METHODS: In an attempt to characterize additional mediators of human immunodeficiency virus type 1 (HIV-1)-induced neurotoxicity in vivo we have adapted the mRNA differential display technique to monitor the gene expression pattern in postmortem cortical tissue from AIDS patients with (n = 7) and without (n = 8) cognitive impairment as well as from HIV-1 seronegative controls (n = 4). RESULTS: Out of 29 differentially expressed cDNAs, two cDNA clones had confirmed variation of transcriptional regulation as assessed by reverse Northern analysis and gene-specific reverse transcription polymerase chain reaction (RT-PCR) and were up-regulated in the cortex of patients with AIDS dementia. Nucleotide sequence analysis of the two cDNAs identified known genes not previously associated with the pathogenesis of AIDS dementia, including the neurotrophin receptor tyrosine kinase receptor B (TrkB) and the potassium channel human open rectifyer K+ channel (ORK) homologous open reading frame (HOHO1). CONCLUSIONS: The altered expression of these transcripts may contribute to AIDS dementia through the enhancement of microglial activation and immunologic nitric oxide synthase (iNOS) activity by abnormal neurotrophic regulation and interference with membrane excitability through disturbance of local ion homeostasis.

AIDS Dementia Complex↗
PubMed2000

Parkin functions as an E2-dependent ubiquitin- protein ligase and promotes the degradation of the synaptic vesicle-associated protein, CDCrel-1.

Parkinson's disease is a common neurodegenerative disorder in which familial-linked genes have provided novel insights into the pathogenesis of this disorder. Mutations in Parkin, a ring-finger-containing protein of unknown function, are implicated in the pathogenesis of autosomal recessive familial Parkinson's disease. Here, we show that Parkin binds to the E2 ubiquitin-conjugating human enzyme 8 (UbcH8) through its C-terminal ring-finger. Parkin has ubiquitin-protein ligase activity in the presence of UbcH8. Parkin also ubiquitinates itself and promotes its own degradation. We also identify and show that the synaptic vesicle-associated protein, CDCrel-1, interacts with Parkin through its ring-finger domains. Furthermore, Parkin ubiquitinates and promotes the degradation of CDCrel-1. Familial-linked mutations disrupt the ubiquitin-protein ligase function of Parkin and impair Parkin and CDCrel-1 degradation. These results suggest that Parkin functions as an E3 ubiquitin-protein ligase through its ring domains and that it may control protein levels via ubiquitination. The loss of Parkin's ubiquitin-protein ligase function in familial-linked mutations suggests that this may be the cause of familial autosomal recessive Parkinson's disease.

Amino Acid Sequence↗
PubMed2000

NMDA but not non-NMDA excitotoxicity is mediated by Poly(ADP-ribose) polymerase.

Poly(ADP-ribose) polymerase (PARP-1), a nuclear enzyme that facilitates DNA repair, may be instrumental in acute neuronal cell death in a variety of insults including, cerebral ischemia, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism, and CNS trauma. Excitotoxicity is thought to underlie these and other toxic models of neuronal death. Different glutamate agonists may trigger different downstream pathways toward neurotoxicity. We examine the role of PARP-1 in NMDA- and non-NMDA-mediated excitotoxicity. NMDA and non-NMDA agonists were stereotactically delivered into the striatum of mice lacking PARP-1 and control mice in acute (48 hr) and chronic (3 week) toxicity paradigms. Mice lacking PARP-1 are highly resistant to the excitoxicity induced by NMDA but are as equally susceptible to AMPA excitotoxicity as wild-type mice. Restoring PARP-1 protein in mice lacking PARP-1 by viral transfection restored susceptibility to NMDA, supporting the requirement of PARP-1 in NMDA neurotoxicity. Furthermore, Western blot analyses demonstrate that PARP-1 is activated after NMDA delivery but not after AMPA administration. Consistent with the theory that nitric oxide (NO) and peroxynitrite are prominent in NMDA-induced neurotoxicity, PARP-1 was not activated in mice lacking the gene for neuronal NO synthase after NMDA administration. These results suggest a selective role of PARP-1 in glutamate excitoxicity, and strategies of inhibiting PARP-1 in NMDA-mediated neurotoxicity may offer substantial acute and chronic neuroprotection.

Animals↗
PubMed2000

Dynamic regulation of neuronal NO synthase transcription by calcium influx through a CREB family transcription factor-dependent mechanism.

Neuronal nitric oxide (NO) synthase (nNOS) is dynamically regulated in response to a variety of physiologic and pathologic stimuli. Although the dynamic regulation of nNOS is well established, the molecular mechanisms by which such diverse stimuli regulate nNOS expression have not yet been identified. We describe experiments demonstrating that Ca(2+) entry through voltage-sensitive Ca(2+) channels regulates nNOS expression through alternate promoter usage in cortical neurons and that nNOS exon 2 contains the regulatory sequences that respond to Ca(2+). Deletion and mutational analysis of the nNOS exon 2 promoter reveals two critical cAMP/Ca(2+) response elements (CREs) that are immediately upstream of the transcription start site. CREB binds to the CREs within the nNOS gene. Mutation of the nNOS CREs as well as blockade of CREB function results in a dramatic loss of nNOS transcription. These findings suggest that nNOS is a Ca(2+)-regulated gene through the interactions of CREB on the CREs within the nNOS exon 2 promoter and that these interactions are likely to be centrally involved in the regulation of nNOS in response to neuronal injury and activity-dependent plasticity.

Animals↗
PubMed2000

Requirement for nitric oxide activation of p21(ras)/extracellular regulated kinase in neuronal ischemic preconditioning.

The mechanisms underlying neuronal ischemic preconditioning, a phenomenon in which brief episodes of ischemia protect against the lethal effects of subsequent periods of prolonged ischemia, are poorly understood. Ischemia can be modeled in vitro by oxygen-glucose deprivation (OGD). We report here that OGD preconditioning induces p21(ras) (Ras) activation in an N-methyl-D-aspartate receptor- and NO-dependent, but cGMP-independent, manner. We demonstrate that Ras activity is necessary and sufficient for OGD tolerance in neurons. Pharmacological inhibition of Ras, as well as a dominant negative mutant Ras, block OGD preconditioning whereas a constitutively active form of Ras promotes neuroprotection against lethal OGD insults. In contrast, the activity of phosphatidyl inositol 3-kinase is not required for OGD preconditioning because inhibition of phosphatidyl inositol 3-kinase with a chemical inhibitor or with a dominant negative mutant does not have any effect on the development of OGD tolerance. Furthermore, using recombinant adenoviruses and pharmacological inhibitors, we show that downstream of Ras the extracellular regulated kinase cascade is required for OGD preconditioning. Our observations indicate that activation of the Ras/extracellular regulated kinase cascade by NO is a critical mechanism for the development of OGD tolerance in cortical neurons, which may also play an important role in ischemic preconditioning in vivo.

Adenoviridae↗
PubMed2000

Oxidative stress and genetics in the pathogenesis of Parkinson's disease.

Parkinson's Disease (PD) is the second most common chronic neurodegenerative disease characterized by the progressive loss of dopamine neurons, leading to rigidity, slowness of movement, rest tremor, gait disturbances, and imbalance. Although there is effective symptomatic treatment for PD, there is no proven preventative or regenerative therapy. The etiology of this disorder remains unknown. Recent genetic studies have identified mutations in alpha-synuclein as a rare cause of autosomal dominant familial PD and mutations in parkin as a cause of autosomal recessive familial PD. The more common sporadic form of PD is thought to be due to oxidative stress and derangements in mitochondrial complex I activity. Understanding the mechanism by which familial linked mutations and oxidative stress cause PD has tremendous potential for unraveling the mechanisms of dopamine cell death in PD. In this article, we review recent advances in the understanding of the role of genetics and oxidative stress in the pathogenesis of PD.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2000

Stroke outcome in double-mutant antioxidant transgenic mice.

BACKGROUND AND PURPOSE: Both NO and superoxide cytotoxicity are important in experimental stroke; however, it is unclear whether these molecules act within parallel pathological pathways or as coreagents in a common reaction. We examined these alternatives by comparing outcomes after middle cerebral artery occlusion in male and female neuronal NO synthase (nNOS)-deficient (nNOS-/-) or human CuZn superoxide dismutase-overexpressing (hSOD1+/-) mice and a novel strain with both mutations. METHODS: Permanent middle cerebral artery occlusion was performed by use of the intraluminal filament technique (18 hours). Neurological status was scored, and tissue infarction volume was determined by 2,3,5-triphenyltetrazolium staining and image analysis. RESULTS: Hemispheric infarction volume was reduced in each transgenic strain relative to the genetically matched, wild-type, control cohorts (WT mice): nNOS-/- (80+/-6 mm(3)) and double-mutant (49+/-6 mm(3)) mice versus WT mice (114+/-7 mm(3)) and hSOD1+/- mice (52+/-7 mm(3)) versus WT mice (95+/-5 mm(3)). Human CuZn superoxide dismutase had a larger effect on mean infarction volume (30% of contralateral hemisphere) than did nNOS deficiency (46%). Although infarction volume was less in double-mutant mice compared with nNOS-/- mice, injury was not improved relative to hSOD1+/- mice. There was no difference in histological damage by sex within each strain; however, female nNOS-/- mice were not protected from ischemic injury, unlike male mutants. CONCLUSIONS: Superoxide generation contributes to severe ischemic brain injury in vivo to a greater extent than does neuronally derived NO. In vivo, significant superoxide scavenging by CuZn superoxide dismutase occurs within cellular compartments or through biochemical pathways that are not restricted to, and may be distinct from, neuronal NO/superoxide reaction and peroxynitrite synthesis.

Animals↗
PubMed1999

Poly(ADP-ribose) polymerase activation mediates 1-methyl-4-phenyl-1, 2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a neurotoxin that causes parkinsonism in humans and nonhuman animals, and its use has led to greater understanding of the pathogenesis of Parkinson's disease. However, its molecular targets have not been defined. We show that mice lacking the gene for poly(ADP-ribose) polymerase (PARP), which catalyzes the attachment of ADP ribose units from NAD to nuclear proteins after DNA damage, are dramatically spared from MPTP neurotoxicity. MPTP potently activates PARP exclusively in vulnerable dopamine containing neurons of the substantia nigra. MPTP elicits a novel pattern of poly(ADP-ribosyl)ation of nuclear proteins that completely depends on neuronally derived nitric oxide. Thus, NO, DNA damage, and PARP activation play a critical role in MPTP-induced parkinsonism and suggest that inhibitors of PARP may have protective benefit in the treatment of Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1999

Nitric oxide synthase in cardiac sarcoplasmic reticulum.

NO. is a free radical that modulates heart function and metabolism. We report that a neuronal-type NO synthase (NOS) is located on cardiac sarcoplasmic reticulum (SR) membrane vesicles and that endogenous NO. produced by SR-associated NOS inhibits SR Ca2+ uptake. Ca2+-dependent biochemical conversion of L-arginine to L-citrulline was observed from isolated rabbit cardiac SR vesicles in the presence of NOS substrates and cofactors. Endogenous NO. was generated from the vesicles and detected by electron paramagnetic resonance spin-trapping measurements. Immunoelectron microscopy demonstrated labeling of cardiac SR vesicles by using anti-neuronal NOS (nNOS), but not anti-endothelial NOS (eNOS) or anti-inducible NOS (iNOS) antibodies, whereas skeletal muscle SR vesicles had no nNOS immunoreactivity. The nNOS immunoreactivity also displayed a pattern consistent with SR localization in confocal micrographs of sections of human myocardium. Western blotting demonstrated that cardiac SR NOS is larger than brain NOS (160 vs. 155 kDa). No immunodetection was observed in cardiac SR vesicles from nNOS knockout mice or with an anti-nNOS mu antibody, suggesting the possibility of a new nNOS-type isoform. 45Ca uptake by cardiac SR vesicles, catalyzed by Ca2+-ATPase, was inhibited by NO. produced endogenously from cardiac SR NOS, and 7-nitroindazole, a selective nNOS inhibitor, completely prevented this inhibition. These results suggest that a cardiac muscle nNOS isoform is located on SR of cardiac myocytes, where it may respond to intracellular Ca2+ concentration and modulate SR Ca2+ ion active transport in the heart.

Animals↗
PubMed1999

Mechanisms and structural determinants of HIV-1 coat protein, gp41-induced neurotoxicity.

Of the individuals with human immunodeficiency virus type 1 (HIV-1) infection, 20-30% will develop the neurological complication of HIV-associated dementia (HAD). The mechanisms underlying HAD are unknown; however, indirect immunologically mediated mechanisms are theorized to play a role. Recently, the HIV-1 coat protein gp41 has been implicated as a major mediator of HAD through induction of neurocytokines and subsequent neuronal cell death. Using primary mixed cortical cultures from neuronal nitric oxide synthase (NOS) null (nNOS-/-) mice and immunological NOS null (iNOS-/-) mice, we establish iNOS-derived NO as a major mediator of gp41 neurotoxicity. Neurotoxicity elicited by gp41 is markedly attenuated in iNOS-/- cultures compared with wild-type and nNOS-/- cultures. The NOS inhibitor L-nitroarginine methyl ester is neuroprotective in wild-type and nNOS-/- cultures, confirming the role of iNOS-derived NO in gp41 neurotoxicity. Confirming that iNOS-/- cultures lack iNOS, gp41 did not induce iNOS in iNOS-/- cultures, but it markedly induced iNOS in wild-type and nNOS-/- cultures. We elucidate the region of gp41 that is critical for iNOS induction and neuronal cell death by monitoring iNOS induction with overlapping peptides spanning gp41. We show that the N-terminal region of gp41, which we designate as the neurotoxic domain, induces iNOS protein activity and iNOS-dependent neurotoxicity at picomolar concentrations in a manner similar to recombinant gp41 protein. Our experiments suggest that gp41 is eliciting the induction of iNOS through potential cell surface receptors or binding sites because the induction of iNOS is dose dependent and saturable and occurs at physiologically relevant concentrations. These data confirm that the induction of iNOS by gp41 and the production of NO are primary mediators of neuronal damage and identify a neurotoxic domain of gp41 that may play an important role in HAD.

AIDS Dementia Complex↗
PubMed1999

Nuclear targeting of mutant Huntingtin increases toxicity.

Huntington's disease is a neurodegenerative disorder resulting from expansion of the polyglutamine region in huntingtin. Although huntingtin is normally cytoplasmic, in affected brain regions proteolytic fragments of mutant huntingtin containing the polyglutamine repeat form intranuclear inclusions. Here, we examine the contribution of nuclear localization to toxicity by transiently transfecting neuro-2a cells with an N-terminal huntingtin fragment similar in size to that believed to be present in patients. The huntingtin fragment, HD-N63, was targeted either to the cytoplasm with a nuclear export signal (NES) or to the nucleus with a nuclear localization signal (NLS). The NES decreased the number of cells with aggregates in the nucleus while an NLS had the opposite effect. By cotransfecting HD-N63 with GFP as a marker, we observed direct cell loss with constructs containing expanded polyglutamine repeats. Compared to unmodified HD-N63-75Q, adding an NES reduced cell loss by 57% while an NLS increased cell loss by 111%. These results indicate that nuclear localization of mutant huntingtin fragments plays an important role in cell toxicity.

Animals↗
PubMed1999

Glutamate-stimulated calcium activation of Ras/Erk pathway mediated by nitric oxide.

NMDA-type glutamate receptor-mediated increases in intracellular calcium play a critical role in synaptic plasticity involved in learning and memory. Calcium-dependent activation of Ras and extracellular signal-regulated kineses (Erks) may transmit the glutamate signal to the nucleus which is ultimately important for long-lasting neuronal responses. The mechanism by which changes in cytoplasmic calcium mediate NMDA-induced activation of Ras and Erk is not known. In cerebral cortical neurons, this calcium influx through NMDA receptors activates Ras and its downstream effector, Erk, via nitric oxide (NO) generation by calcium-dependent neuronal NO synthase. We propose that NO is a key link between NMDA-mediated increases in cytoplasmic calcium and activity-dependent long-term changes such as differentiation, survival and synaptic plasticity.

Animals↗