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David G Standaert

Publications and source records attributed to David G Standaert.

At least 19 recordsLinked to original sources
PubMed2007

Molecular markers of early Parkinson's disease based on gene expression in blood.

Parkinson's disease (PD) progresses relentlessly and affects five million people worldwide. Laboratory tests for PD are critically needed for developing treatments designed to slow or prevent progression of the disease. We performed a transcriptome-wide scan in 105 individuals to interrogate the molecular processes perturbed in cellular blood of patients with early-stage PD. The molecular multigene marker here identified is associated with risk of PD in 66 samples of the training set comprising healthy and disease controls [third tertile cross-validated odds ratio of 5.7 (P for trend 0.005)]. It is further validated in 39 independent test samples [third tertile odds ratio of 5.1 (P for trend 0.04)]. Insights into disease-linked processes detectable in peripheral blood are offered by 22 unique genes differentially expressed in patients with PD versus healthy individuals. These include the co-chaperone ST13, which stabilizes heat-shock protein 70, a modifier of alpha-synuclein misfolding and toxicity. ST13 messenger RNA copies are lower in patients with PD (mean +/- SE 0.59 +/- 0.05) than in controls (0.96 +/- 0.09) (P = 0.002) in two independent populations. Thus, gene expression signals measured in blood can facilitate the development of biomarkers for PD.

Biomarkers↗
PubMed2006

No alteration in tau exon 10 alternative splicing in tangle-bearing neurons of the Alzheimer's disease brain.

Defective splicing of tau mRNA, promoting a shift between tau isoforms with (4R tau) and without (3R tau) exon 10, is believed to be a pathological consequence of certain tau mutations causing frontotemporal dementia. By assessing protein and mRNA levels of 4R tau and 3R tau in 27 AD and 20 control temporal cortex, we investigated whether altered tau splicing is a feature also in Alzheimer's disease (AD). However, apart from an expected increase of sarcosyl-insoluble tau in AD, there were no significant differences between the groups. Next, by laser-capture microscopy and quantitative PCR, we separately analyzed CA1 hippocampal neurons with and without neurofibrillary pathology from six of the AD and seven of the control brains. No statistically significant differences in 4R tau/3R tau mRNA were found between the different subgroups. Moreover, we confirmed the absence of significant ratio differences in a second data set with laser-captured entorhinal cortex neurons from four AD and four control brains. Finally, the 4R tau/3R tau ratio in CA1 neurons was roughly half of the ratio in temporal cortex, indicating region-specific differences in tau mRNA splicing. In conclusion, this study indicated region-specific and possibly cell-type-specific tau splicing but did not lend any support to overt changes in alternative splicing of tau exon 10 being an underlying factor in AD pathogenesis.

Aged↗
PubMed2006

Dopamine D1 activation potentiates striatal NMDA receptors by tyrosine phosphorylation-dependent subunit trafficking.

Interactions between dopaminergic and glutamatergic afferents in the striatum are essential for motor learning and the regulation of movement. An important mechanism for these interactions is the ability of dopamine, through D1 receptors, to potentiate NMDA glutamate receptor function. Here we show that, in striatal neurons, D1 receptor activation leads to rapid trafficking of NMDA receptor subunits, with increased NR1 and NR2B subunits in dendrites, enhanced coclustering of these subunits with the postsynaptic density scaffolding molecule postsynaptic density-95, and increased surface expression. The dopamine D1 receptor-mediated NMDA receptor trafficking is blocked by an inhibitor of tyrosine kinases. Blockers of tyrosine phosphatases also induce NMDA subunit trafficking, but this effect is nonselective and alters both NR2A- and NR2B-containing receptors. Furthermore, tyrosine phosphatase inhibition leads to the clustering of tyrosine-phosphorylated NR2B subunit along dendritic shafts. Our findings reveal that D1 receptor activation can potentiate striatal NMDA subunit function by directly promoting the surface insertion of the receptor complexes. This effect is regulated by the reciprocal actions of protein tyrosine phosphatases and tyrosine kinases. Modification of these pathways may be a useful therapeutic target for Parkinson's disease and other basal ganglia disorders in which abnormal function of striatal NMDA receptors contributes to the symptoms of the diseases.

Animals↗
PubMed2005

Impaired motor learning in mice expressing torsinA with the DYT1 dystonia mutation.

Primary early-onset generalized dystonia is an autosomal dominant disorder caused by a deletion (DeltaGAG) in the DYT1 gene encoding torsinA. The gene defect has incomplete penetrance, with approximately 30% of carriers developing clinically evident dystonia. We describe lines of transgenic mice that express either human mutant torsinA (hMT) or human wild-type (hWT) torsinA. All mice demonstrated moderately increased levels of torsinA in the brain by Western blot analysis and normal subcellular distribution of torsinA in neurons by confocal microscopy. No animals had dystonic features. However, mice overexpressing hMT, but not hWT, torsinA displayed a reduced ability to learn motor skills in an accelerating rotarod paradigm. This pattern resembles the impaired motor sequence learning demonstrated in human nonmanifesting carriers of the DeltaGAG mutation. Open-field testing showed no differences in spontaneous activity between transgenic mice and their nontransgenic littermates, indicating that mice overexpressing hMT torsinA did not develop overtly abnormal motor behavior. Together, these data suggest that these transgenic mice provide a useful model of the DeltaGAG carrier state that can be used to probe genetic and environmental factors that can trigger the dystonic state.

Animals↗
PubMed2005

Alpha-synuclein and chaperones in dementia with Lewy bodies.

The protein alpha-synuclein (ASYN) is thought to be involved in the development of dementia with Lewy bodies (DLB). Overexpression of ASYN has been linked to cellular toxicity and human disease, and in experimental models, chaperones such as heat shock proteins (HSPs) are protective against ASYN toxicity. We have assessed the abundance of mRNA for ASYN and chaperones and the abundance and solubility of the encoded proteins in temporal cortex from sporadic human DLB. We found a reduction of ASYN mRNA in DLB (44.9% of control). The abundance of the Triton-soluble fraction (bioavailable protein) was not altered, but there was an increase of the Triton-insoluble component (likely representing aggregates). We evaluated 3 chaperones: HSP70, HSP90, and HDJ1. HSP70 mRNA was increased in DLB, whereas the mRNAs for HSP90 and HDJ1 were unchanged. HSP70 accumulated in the Triton-soluble fraction, whereas HSP90 and HDJ1 proteins accumulated in the Triton-insoluble fraction. These observations suggest that sporadic DLB is not associated with overexpression of ASYN. Rather, the persistence of normal soluble ASYN protein levels, despite the reduction of its mRNA, suggests a primary defect in clearance of the protein. However, this reduced clearance cannot be attributed to a failure of chaperone expression, because their mRNA is unchanged or increased in the DLB brain.

Case-Control Studies↗
PubMed2004

Somatic mitochondrial DNA mutations in single neurons and glia.

Somatic mitochondrial DNA (mtDNA) point mutations reach high levels in the brain. However, the cell types that accumulate mutations and the patterns of mutations within individual cells are not known. We have quantified somatic mtDNA mutations in 28 single neurons and in 18 single glia from post-mortem human substantia nigra of six control subjects. Both neurons and glia contain mtDNA with somatic mutations. Single neurons harbor a geometric mean (95% CI) of 200.3 (152.9-262.4) somatic mtDNA point mutations per million base pairs, compared to 133.8 (97.5-184.9) for single glia (p=0.0251). If mutations detected multiple times in the same cell are counted only once, the mean mutation level per million base pairs remains elevated in single neurons (146.9; 124.0-174.2) compared to single glia (100.5; 81.5-126.5; p=0.009). Multiple distinct somatic point mutations are present in different cells from the same subject. Most of these mutations are individually present at low levels (less than 10-20% of mtDNA molecules), but with high aggregate mutation levels, particularly in neurons. These mutations may contribute to changes in brain function during normal aging and neurodegenerative disorders.

Adult↗
PubMed2004

Transcriptional dysregulation in striatal projection- and interneurons in a mouse model of Huntington's disease: neuronal selectivity and potential neuroprotective role of HAP1.

Transcriptional dysregulation has been described as a central mechanism in the pathogenesis of Huntington's disease (HD), in which medium spiny projection neurons (MSN) selectively degenerate whereas neuronal nitric-oxide-synthase-positive interneurons (nNOS-IN) survive. In order to begin to understand this differential vulnerability we compared mRNA levels of selected genes involved in N-methyl-D-aspartate (NMDA) glutamate receptor and calcium (Ca2+) signaling pathways in MSN and nNOS-IN from 12-week-old R6/2 mice, a transgenic mouse model of HD and wild-type littermates. We undertook a laser capture microdissection (LCM) study to examine the contribution of transcriptional dysregulation in candidate genes involved in these two signaling pathways in discrete populations of striatal neurons. The use of LCM in combination with quantitative real-time polymerase chain reaction (Q-PCR) allowed us to quantify the neuronal abundance of candidate mRNAs. We found different transcriptional alterations in R6/2 neurons for both MSN and nNOS-IN, indicating that global transcriptional dysregulation alone does not account for selective vulnerability. Further, we observed a striking enrichment of several mRNAs in the nNOS-IN population, including that for the NMDA receptor subunit NR2D, the postsynaptic density protein 95 (PSD-95) and the huntingtin-associated protein 1 (HAP1) as well as nitric-oxide-synthase (nNOS) mRNA itself. The higher expression levels of these molecules in nNOS-IN when compared with MSN together with an association of nNOS, NR2D and HAP1 in a protein complex with PSD-95 suggest that these proteins may be involved in protective pathways that contribute to the resistance of this interneuron population to neurodegeneration in HD.

Animals↗
PubMed2004

L-type Ca2+ channels mediate adaptation of extracellular signal-regulated kinase 1/2 phosphorylation in the ventral tegmental area after chronic amphetamine treatment.

L-type Ca2+ channels (LTCCs) play an important role in chronic psychostimulant-induced behaviors. However, the Ca2+ second messenger pathways activated by LTCCs after acute and recurrent psychostimulant administration that contribute to drug-induced molecular adaptations are poorly understood. Using a chronic amphetamine treatment paradigm in rats, we have examined the role of LTCCs in activating the mitogen-activated protein (MAP) kinase pathway in the ventral tegmental area (VTA), a primary target for the reinforcing properties of psychostimulants. Using immunoblot and immunohistochemical analyses, we find that in chronic saline-treated rats a challenge injection of amphetamine increases phosphorylation of MAP [extracellular signal-regulated kinase 1/2 (ERK1/2)] kinase in the VTA that is independent of LTCCs. However, in chronic amphetamine-treated rats there is no increase in amphetamine-mediated ERK1/2 phosphorylation unless LTCCs are blocked, in which case there is robust phosphorylation in VTA dopamine neurons. Examination of the expression of phosphatases reveals an increase in calcineurin [protein phosphatase 2B (PP2B)] and MAP kinase phosphatase-1 (MKP-1) in the VTA. Using in situ hybridization histochemistry and immunoblot analyses, we further examined the mRNA and protein expression of the LTCC subtypes Ca(v)1.2 and Ca(v)1.3 in VTA dopamine neurons in drug-naive animals and in rats after chronic amphetamine treatment. We found an increase in Ca(v)1.2 mRNA and protein levels, with no change in Ca(v)1.3. Together, our results suggest that one aspect of LTCC-induced changes in second messenger pathways after chronic amphetamine exposure involves activation of the MAP kinase phosphatase pathway by upregulation of Ca(v)1.2 in VTA dopaminergic neurons.

Amphetamine↗
PubMed2004

NMDA-R1 antisense oligodeoxynucleotides modify formalin-induced nociception and spinal c-Fos expression in rat spinal cord.

Noxious peripheral stimuli (thermal, mechanical, or chemical) produce long-term adaptations in the sensitivity of central nociceptive neurons to subsequent noxious stimuli. The mechanisms responsible for this central sensitization are multifactorial, but the activation of spinal N-methyl-D-aspartate (NMDA) receptors plays a pivotal role. Using antisense oligodeoxynucleotides, we tested the role of the NR1 subunit of the NMDA receptor in the nociception and expression of the immediate early gene c-fos following formalin-induced pain. Rats received NMDA-R1 antisense, sense, or missense oligodeoxynucleotides intrathecally three times over a 48-h interval. The day after the last injection of the oligodeoxynucleotide, the formalin test was performed. Pain-related behavior was quantified by counting the incidence of flinching of the injected paw for 60 min, and the animals were perfused and the spinal cord removed for c-Fos immunohistochemistry 60 min later. Immunopositive cells were counted in the laminae I/II(0) and V of the lumbar enlargement. Treatment with NR1 antisense oligodeoxynucleotide resulted in a marked decrease in flinching. Similarly, the antisense oligodeoxynucleotide virtually abolished formalin-induced expression of c-Fos-like immunoreactivity (Fos-IR) in the spinal cord dorsal horn ipsilateral to injection. In contrast, the corresponding sense or missense oligodeoxynucleotides had no effect on either formalin-evoked behavior or c-Fos immunoreactivity. We conclude that an NR1 antisense oligodeoxynucleotide inhibits both nociceptive behavior and c-fos expression following formalin injection in rats, demonstrating that NR1 plays an important role in the development of noxious stimulation induced c-fos expression in this model.

Animals↗
PubMed2004

Rationale for and use of NMDA receptor antagonists in Parkinson's disease.

N-Methyl-d-aspartate (NMDA) glutamate receptors are a class of excitatory amino acid receptors, which have several important functions in the motor circuits of the basal ganglia, and are viewed as important targets for the development of new drugs to prevent or treat Parkinson's disease (PD). NMDA receptors are ligand-gated ion channels composed of multiple subunits, each of which has distinct cellular and regional patterns of expression. They have complex regulatory properties, with both agonist and co-agonist binding sites and regulation by phosphorylation and protein-protein interactions. They are found in all of the structures of the basal ganglia, although the subunit composition in the various structures is different. NMDA receptors present in the striatum are crucial for dopamine-glutamate interactions. The abundance, structure, and function of striatal receptors are altered by the dopamine depletion and further modified by the pharmacological treatments used in PD. In animal models, NMDA receptor antagonists are effective antiparkinsonian agents and can reduce the complications of chronic dopaminergic therapy (wearing off and dyskinesias). Use of these agents in humans has been limited because of the adverse effects associated with nonselective blockade of NMDA receptor function, but the development of more potent and selective pharmaceuticals holds the promise of an important new therapeutic approach for PD.

Animals↗
PubMed2004

Changes in the expression of the NR2B subunit during aging in macaque monkeys.

Humans, non-human primates and rodents show declines in spatial memory abilities with increased age. Some of these declines in mice are related to changes in the expression of the epsilon2 (epsilon2) (NR2B) subunit of the N-methyl-D-aspartate receptor. The purpose of this study was to determine whether primates show changes during aging in the mRNA expression of the NR2B subunit. In situ hybridization was performed on tissue sections from three different ages of Rhesus monkeys (Macaca mulatta; 6-8, 10-12, and 24-26 years). There was a significant decrease in the mRNA expression of the NR2B subunit overall in the prefrontal cortex and in the caudate nucleus between young and old monkeys. There were no significant changes in NR2B mRNA expression in the hippocampus or the parahippocampal gyrus. The results in the prefrontal cortex, caudate and hippocampus were similar to those seen previously in C57BL/6 mice during aging, which suggests that mice may be useful as a model for primates to further examine the age-related changes in the expression of the NR2B subunit of the NMDA receptor in several important regions of the brain.

Aging↗
PubMed2004

Dopamine D1-dependent trafficking of striatal N-methyl-D-aspartate glutamate receptors requires Fyn protein tyrosine kinase but not DARPP-32.

Interactions between dopaminergic and glutamatergic systems in the striatum are thought to underlie both the symptoms and adverse effects of treatment of Parkinson's disease. We have previously reported that activation of the dopamine D1 receptor triggers a rapid redistribution of striatal N-methyl-d-aspartate (NMDA) receptors between intracellular and postsynaptic sub-cellular compartments. To unravel the signaling pathways underlying this trafficking, we studied mice with targeted disruptions of either the gene that encodes the dopamine- and cAMP-regulated phosphoprotein (DARPP-32), a potent and selective inhibitor of protein phosphatase-1, or the protein tyrosine kinase Fyn. In striatal tissue from DARPP-32-depleted mice, basal tyrosine and serine phosphorylation of striatal NMDA receptor subunits NR1, NR2A, and NR2B was normal, and activation of dopamine D1 receptors with the agonist SKF-82958 [(+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetra-hydro-1H-benzazepine] produced redistribution of NMDA receptors from vesicular compartments (P3 and LP2) to synaptosomal membranes (LP1). In the Fyn knockout mice, basal tyrosine phosphorylation of NR2A and NR2B was drastically reduced, whereas serine phosphorylation of these NMDA subunits was unchanged. In the Fyn knockout mice, the dopamine D1 receptor agonist failed to induce subcellular redistribution of NMDA receptors. In addition, Fyn-depleted mice lesioned with 6-hydroxydopamine also failed to exhibit l-DOPA-induced behavioral sensitization, but this may be caused, at least in part, by resistance of these mice to the neurotoxic lesion. These findings suggest a novel mechanism for the trafficking of striatal NMDA receptors by signaling pathways that are independent of DARPP-32 but require Fyn protein tyrosine kinase. Strategies that prevent NMDA receptor subcellular redistribution through inhibition of Fyn kinase may prove useful in the treatment of Parkinson's disease.

Animals↗
PubMed2003

Distribution and ultrastructural localization of torsinA immunoreactivity in the human brain.

We have examined the distribution and ultrastructural localization of torsinA, the protein product of the TOR1A gene, in the normal adult human and Macaque brain. TorsinA immunoreactivity was visualized using a monoclonal antibody raised against a fusion protein encoding exon 4 of human torsinA. Western blot analysis of brain homogenates revealed a major species of about 39 kDa, consistent with the predicted size of glycosylated torsinA protein. By light microscopy, torsinA like-immunoreactivity was enriched in gray matter in all brain regions examined. Immunoreactivity was concentrated in the neuropil and immunopositive cell bodies were not observed. Structures particularly enriched in torsinA like-immunoreactivity included the cerebral cortex, the caudate-putamen, globus pallidus, the hippocampal formation, the thalamus, the substantia nigra and molecular cell layer of the cerebellar cortex. Cell bodies of pigmented dopamine neurons in the substantia nigra pars compacta were immunonegative. Biochemical fractionation of the human striata revealed a concentration of torsinA immunoreactivity in particulate fractions. Ultrastructural studies of the human and Macaque striata further revealed an association of torsinA immunostaining with small vesicles within axons and presynaptic terminals forming symmetric synapses. These ultrastructural studies are consistent with a pre-synaptic localization of torsinA protein in the adult striatum and are consistent with a role of torsinA in modulating striatal signaling, although the widespread localization of the protein suggests it probably also participates in signaling in other regions.

Animals↗
PubMed2003

Lighting up the senses: FM1-43 loading of sensory cells through nonselective ion channels.

We describe a novel mechanism for vital fluorescent dye entry into sensory cells and neurons: permeation through ion channels. In addition to the slow conventional uptake of styryl dyes by endocytosis, small styryl dyes such as FM1-43 rapidly and specifically label hair cells in the inner ear by entering through open mechanotransduction channels. This labeling can be blocked by pharmacological or mechanical closing of the channels. This phenomenon is not limited to hair cell transduction channels, because human embryonic kidney 293T cells expressing the vanilloid receptor (TRPV1) or a purinergic receptor (P2X2) rapidly take up FM1-43 when those receptor channels are opened and not when they are pharmacologically blocked. This channel permeation mechanism can also be used to label many sensory cell types in vivo. A single subcutaneous injection of FM1-43 (3 mg/kg body weight) in mice brightly labels hair cells, Merkel cells, muscle spindles, taste buds, enteric neurons, and primary sensory neurons within the cranial and dorsal root ganglia, persisting for several weeks. The pattern of labeling is specific; nonsensory cells and neurons remain unlabeled. The labeling of the sensory neurons requires dye entry through the sensory terminal, consistent with permeation through the sensory channels. This suggests that organic cationic dyes are able to pass through a number of different sensory channels. The bright and specific labeling with styryl dyes provides a novel way to study sensory cells and neurons in vivo and in vitro, and it offers new opportunities for visually assaying sensory channel function.

Animals↗
PubMed2003

Complex alteration of NMDA receptors in transgenic Huntington's disease mouse brain: analysis of mRNA and protein expression, plasma membrane association, interacting proteins, and phosphorylation.

We analyzed NMDA receptor subunit mRNAs, proteins, and anchoring proteins in mice transgenic for exon 1 of the HD gene. R6/2 mice had decreased levels of mRNAs encoding epsilon1 and epsilon2 NMDA receptor subunits (mouse orthologs of rat NR2A and NR2B subunits), but not the zeta1 subunit (mouse ortholog of NR1), as assessed by gene expression profiling and Northern blotting. In situ hybridization resolved mRNA decreases spatially to the CA1 field of hippocampus. Western blotting revealed decreases in plasma membrane-associated epsilon1 and epsilon2 subunits in hippocampus, and decreases in plasma membrane-associated zeta1 subunit in cortex and hippocampus. In addition, PSD-95 and alpha-actinin-2, proteins essential for anchoring NMDA receptors, were decreased. Finally, we found a decreased level of tyrosine-phosphorylated epsilon1 subunit, another determinant of NMDA receptor trafficking, in R6/2 hippocampus. Taken together, these data demonstrate multiple levels of NMDA receptor dysregulation, including abnormalities in mRNA expression levels, receptor stoichiometry, protein phosphorylation, and receptor trafficking.

Actinin↗