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W Robberecht

Publications and source records attributed to W Robberecht.

At least 19 recordsLinked to original sources
PubMed2002

[A man with plasma cell dyscrasia and polyneuropathy due to POEMS syndrome].

In a 52-year-old man with general malaise, muscle stiffness and weakness, POEMS-syndrome was diagnosed based on polyneuropathy, splenomegaly, lymphadenopathy, subclinical hypothyroidism and the presence of a monoclonal paraprotein with osteosclerotic lesions and an indurated skin (POEMS is an acronym for Polyneuropathy, Organomegaly, Endocrinopathy, Monoclonal protein, Skin changes). This is a rare systemic disease from the clinical spectrum of plasma cell dyscrasias with polyneuropathy. The clinical picture is broader and more pleomorphic than the acronym suggests. The possibility of a POEMS syndrome should be considered in the differential diagnosis of polyneuropathy in association with monoclonal gammopathy. Quite often it is associated with osteosclerotic myeloma or mixed osteoscleroticlytic lesions. The patient described was treated with high dose corticosteroids which were gradually decreased over the next three months, upon which a marked improvement could be seen. The general malaise subsided, as did the splenomegaly, and the skin became supple again.

Adrenal Cortex Hormones↗
PubMed2002

Protective effect of parvalbumin on excitotoxic motor neuron death.

The mechanism responsible for the selective vulnerability of motor neurons in amyotrophic lateral sclerosis (ALS) is poorly understood. Several lines of evidence indicate that susceptibility of motor neurons to Ca(2+) overload induced by excitotoxic stimuli is involved. In this study, we investigated whether the high density of Ca(2+)-permeable AMPA receptors on motor neurons gives rise to higher Ca(2+) transients in motor neurons compared to dorsal horn neurons. Dorsal horn neurons were chosen as controls as these cells do not degenerate in ALS. In cultured spinal motor neurons, the rise of the cytosolic Ca(2+) concentration induced by kainic acid (KA) and mediated by the AMPA receptor was almost twice as high as in spinal neurons from the dorsal horn. Furthermore, we investigated whether increasing the motor neuron's cytosolic Ca(2+)-buffering capacity protects them from excitotoxic death. To obtain motor neurons with increased Ca(2+) buffering capacity, we generated transgenic mice overexpressing parvalbumin (PV). These mice have no apparent phenotype. PV overexpression was present in the central nervous system, kidney, thymus, and spleen. Motor neurons from these transgenic mice expressed PV in culture and were partially protected from KA-induced death as compared to those isolated from nontransgenic littermates. PV overexpression also attenuated KA-induced Ca(2+) transients, but not those induced by depolarization. We conclude that the high density of Ca(2+)-permeable AMPA receptors on the motor neuron's surface results in high Ca(2+) transients upon stimulation and that the low cytosolic Ca(2+)-buffering capacity of motor neurons may contribute to the selective vulnerability of these cells in ALS. Overexpression of a high-affinity Ca(2+) buffer such as PV protects the motor neuron from excitotoxicity and this protective effect depends upon the mode of Ca(2+) entry into the cell.

Amyotrophic Lateral Sclerosis↗
PubMed2002

An alpha-mercaptoacrylic acid derivative (PD150606) inhibits selective motor neuron death via inhibition of kainate-induced Ca2+ influx and not via calpain inhibition.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by selective motor neuron death. The exact mechanism responsible for this selectivity is not clear, although it is known that motor neurons are very sensitive to excitotoxicity. This high sensitivity is due to a high density of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors on their surface and to a limited Ca(2+) buffering capacity. Ca(2+) can enter the cell upon stimulation through voltage-operated Ca(2+) channels and through the Ca(2+)-permeable portion of AMPA receptors. How this Ca(2+) kills motor neurons is incompletely understood. In the present study, we report that kainate (KA)-induced motor neuron death is purely mediated through Ca(2+) entering motor neurons through Ca(2+)-permeable AMPA receptors and that voltage-operated Ca(2+) channels play no significant role. In contrast to what has been observed in other neuronal models or after N-methyl-D-aspartate stimulation, NO synthase inhibition and a number of antioxidants did not protect motor neurons from KA-induced death. Only PD150606, derived from alpha-mercaptoacrylic acid and considered as a selective calpain antagonist, inhibited dose-dependently the KA-induced motor neuron death. However, other calmodulin and calpain inhibitors were not effective. At least part of the inhibitory effect of PD150606 is due to an irreversible inhibition of the Ca(2+) influx through the Ca(2+)-permeable AMPA receptor. These results demonstrate the interesting property of PD150606 to interfere with excitotoxicity-dependent motor neuron death and show that PD150606 is not an exclusive calpain/calmodulin antagonist.

Acrylates↗
PubMed2002

Na(+) entry through AMPA receptors results in voltage-gated k(+) channel blockade in cultured rat spinal cord motoneurons.

alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor currents, evoked with the agonist kainate, were studied with the gramicidin perforated-patch-clamp technique in cultured rat spinal cord motoneurons. Kainate-induced currents could be blocked by the AMPA receptor antagonist LY 300164 and displayed an apparent strong inward rectification. This inward rectification was not a genuine property of AMPA receptor currents but was a result of a concomitant decrease in outward current at potentials positive to -40.5 +/- 1.3 mV. The AMPA receptor current itself was nearly linear (rectification index 0.91). The kainate-inhibited outward current had a reversal potential close to the estimated K(+) equilibrium potential and was blocked by 30 mM tetraethylammonium. When voltage steps were applied, it was found that kainate inhibited both the delayed rectifier K(+) current K(V) and the transient outward K(+) current, K(A). The kainate-induced inhibition of K(+) currents was dependent on ion flux through the AMPA receptor, because no change in the membrane conductance was noticed in the presence of LY 300164. Removing extracellular Ca(2+) had no effect, whereas replacing extracellular Na(+) or clamping the membrane close to the estimated Na(+) equilibrium potential during kainate application attenuated the inhibition of the K(+) current. Sustained Na(+) influx induced by application of the Na(+) ionophore monensin could mimic the effect of kainate on K(+) conductance. These findings demonstrate that Na(+) influx through AMPA receptors results in blockade of voltage-gated K(+) channels.

Animals↗
PubMed2002

GluR2-dependent properties of AMPA receptors determine the selective vulnerability of motor neurons to excitotoxicity.

AMPA receptor-mediated excitotoxicity has been implicated in the selective motor neuron loss in amyotrophic lateral sclerosis. In some culture models, motor neurons have been shown to be selectively vulnerable to AMPA receptor agonists due to Ca(2+) influx through Ca(2+)-permeable AMPA receptors. Because the absence of GluR2 in AMPA receptors renders them highly permeable to Ca(2+) ions, it has been hypothesized that the selective vulnerability of motor neurons is due to their relative deficiency in GluR2. However, conflicting evidence exists about the in vitro and in vivo expression of GluR2 in motor neurons, both at the mRNA and at the protein level. In this study, we quantified electrophysiological properties of AMPA receptors, known to be dependent on the relative abundance of GluR2: sensitivity to external polyamines, rectification index, and relative Ca(2+) permeability. Cultured rat spinal cord motor neurons were compared with dorsal horn neurons (which are resistant to excitotoxicity) and with motor neurons that survived an excitotoxic insult. Motor neurons had a higher sensitivity to external polyamines, a lower rectification index, and a higher relative Ca(2+) permeability ratio than dorsal horn neurons. These findings confirm that motor neurons are relatively deficient in GluR2. The AMPA receptor properties correlated well with each other and with the selective vulnerability of motor neurons because motor neurons surviving an excitotoxic event had similar characteristics as dorsal horn neurons. These data indicate that the relative abundance of GluR2 in functional AMPA receptors may be a major determinant of the selective vulnerability of motor neurons to excitotoxicity in vitro.

Animals↗
PubMed2001

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration.

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Amyotrophic Lateral Sclerosis↗
PubMed2001

Subcellular localization of calcium-permeable AMPA receptors in spinal motoneurons.

Activation of Ca(2+)-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors has been linked to potent effects on survival and dendritic outgrowth of spinal motoneurons. Ca(2+) permeability of AMPA receptors is controlled by the GluR2 subunit. Whole-cell electrophysiological studies have suggested that GluR2-containing and GluR2-lacking AMPA receptors may coexist in individual motoneurons. However, there has not been a direct demonstration of heterogeneity in AMPA receptor subunit composition in single motoneurons, nor of distinct subcellular distributions of GluR2-containing and GluR2-lacking receptors. In the present study, we have used confocal microscopy, immunocytochemistry and Ca(2+) imaging to characterize the subcellular localization of AMPA receptors in cultured rat spinal motoneurons. Immunoreactivity for GluR2 and GluR4 was concentrated in clusters, the vast majority of which were found in dendrites at synapses. Double-labelling for GluR2 and GluR4 revealed variability in relative expression of GluR2 and GluR4 between clusters within individual motoneurons; most AMPA receptor clusters were immunoreactive for both GluR2 and GluR4, but a significant minority of clusters were immunoreactive for GluR2 only or for GluR4 only. The majority of GluR2-immunonegative AMPA receptor clusters was present in dendrites, but the relative proportion of GluR2-immunonegative and GluR2-immunopositive clusters was similar in dendrites and soma. Imaging of [Ca(2+)](i) rises triggered by AMPA receptor activation confirmed Ca(2+) influx in motoneuron dendrites. These findings strongly support a model in which GluR2-containing and GluR2-lacking AMPA receptors coexist in motoneurons, clustered at synapses, and mixed in a relative proportion that varies considerably between cell membrane microdomains.

Animals↗
PubMed2001

Amyotrophic lateral sclerosis: pathogenesis.

Amyotrophic lateral sclerosis (ALS) is a devastating paralytic disorder caused by motor neuron degeneration. A subgroup of familial cases arises from mutations in the gene encoding cytosolic superoxide dismutase (SOD1). This review considers insight now being gained into ALS pathogenesis from the study of mutant SOD1 protein and its possible mechanisms of adverse effect on nerve cells. Also discussed are the status of other genetic forms of ALS and the elusive question of why this disorder so specifically targets motor neurons. Ultimately, it is hoped that insights from these types of studies will improve the prospects for developing meaningful therapies of ALS.

Amyotrophic Lateral Sclerosis↗
PubMed2000

Ca(2+)-permeable AMPA receptors and selective vulnerability of motor neurons.

To evaluate the role of excitotoxicity in the pathogenesis of amyotrophic lateral sclerosis (ALS), we compared the sensitivity of motor neurons and that of dorsal horn neurons to kainic acid (KA). Short exposure to KA resulted in the death of motor neurons, while dorsal horn neurons were unaffected. This selective motor neuron death was completely dependent on extracellular Ca(2+) and insensitive to inhibitors of voltage-operated Ca(2+) or Na(+) channels. It was also completely inhibited by the specific AMPA antagonist LY300164 and by Joro spider toxin (JSTx), a selective blocker of AMPA receptors that lack the edited GluR2 subunit. KA selectively killed those motor neurons that stained positive for the Co(2+) histochemical staining, a measure for the presence of Ca(2+)-permeable AMPA receptors. These results suggest that Ca(2+) entry via Ca(2+)-permeable AMPA receptors is responsible for the selective motor neuron death. As the Ca(2+) permeability of the AMPA receptor is regulated by its GluR2 subunit, we stained motor neurons for GluR2. Immunoreactivity was present in all motor neurons, albeit to a variable degree. However, double-staining experiments demonstrated that motor neurons clearly expressing GluR2, also expressed Ca(2+)-permeable AMPA receptors. This indicates that despite the abundant expression of GluR2, this subunit is excluded from a subset of AMPA receptors and that the activation of these receptors is responsible for the selective motor neuron death.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2000

Preface

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Journal Article↗
PubMed2000

Different receptors mediate motor neuron death induced by short and long exposures to excitotoxicity.

We compared the effect of short and long exposures of cultured motor neurons to glutamate and kainate (KA) and studied the receptors involved in these two types of excitotoxicity. There was no difference in the receptor type used between short and long glutamate exposures as activation of the N-methyl-D-asparate (NMDA) receptor was in both cases responsible for the motor neuron death. Cell death through activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors only became apparent when desensitization of these receptors was prevented. In such conditions, motor neurons became much more sensitive to excitotoxicity, and activation of different types of AMPA receptors mediated motor neuron death after short, compared to long, exposures to the non-desensitizing AMPA receptor agonist, KA. Short KA exposures selectively affected motor neurons containing Ca(2+)-permeable AMPA receptors, as the KA effect was completely inhibited by Joro spider toxin and only motor neurons that were positive for the histochemical Co(2+) staining were killed. A long exposure to KA affected motor neurons through both Ca(2+)-permeable and Ca(2+)-impermeable AMPA receptors. The selective death of motor neurons vs. dorsal horn neurons was observed after short KA exposures indicating that the selective vulnerability of motor neurons to excitotoxicity is related to the presence of Ca(2+)-permeable AMPA receptors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2000

AMPA receptor current density, not desensitization, predicts selective motoneuron vulnerability.

Spinal motoneurons are more susceptible to AMPA receptor-mediated injury than are other spinal neurons, a property that has been implicated in their selective degeneration in amyotrophic lateral sclerosis (ALS). The aim of this study was to determine whether this difference in vulnerability between motoneurons and other spinal neurons can be attributed to a difference in AMPA receptor desensitization and/or to a difference in density of functional AMPA receptors. Spinal motoneurons and dorsal horn neurons were isolated from embryonic rats and cultured on spinal astrocytes. Single-cell RT-PCR quantification of the relative abundance of the flip and flop isoforms of the AMPA receptor subunits, which are known to affect receptor desensitization, did not reveal any difference between the two cell populations. Examination of AMPA receptor desensitization by patch-clamp electrophysiological measurements on nucleated and outside-out patches and in the whole-cell mode also yielded similar results for the two cell groups. However, AMPA receptor current density was two- to threefold higher in motoneurons than in dorsal horn neurons, suggesting a higher density of functional AMPA receptors in motoneuron membranes. Pharmacological reduction of AMPA receptor current density in motoneurons to the level found in dorsal horn neurons eliminated selective motoneuron vulnerability to AMPA receptor activation. These results suggest that the greater AMPA receptor current density of spinal motoneurons may be sufficient to account for their selective vulnerability to AMPA receptor agonists in vitro.

Animals↗
PubMed2000

AMPA receptor calcium permeability, GluR2 expression, and selective motoneuron vulnerability.

AMPA receptor-mediated excitotoxicity is proposed to play a major pathogenic role in the selective motoneuron death of amyotrophic lateral sclerosis. Motoneurons have been shown in various models to be more susceptible to AMPA receptor-mediated injury than other spinal neurons. It has been hypothesized that this selective vulnerability of motoneurons is caused by the expression of highly Ca(2+)-permeable AMPA receptors and a complete or relative lack of the AMPA receptor subunit Glu receptor 2 (GluR2). The aim of this study was to quantify the relative Ca(2+) permeability of AMPA receptors and the fractional expression of GluR2 in motoneurons by combining whole-cell patch-clamp electrophysiology and single-cell RT-PCR and to compare these properties with those of dorsal horn neurons. Spinal motoneurons and dorsal horn neurons were isolated from embryonic rats and cultured on spinal astrocytes. As in previous studies, motoneurons were significantly more vulnerable to AMPA and kainate than dorsal horn neurons. However, all motoneurons expressed GluR2 mRNA ( approximately 40% of total AMPA receptor subunit mRNA), and their AMPA receptors had intermediate whole-cell relative Ca(2+) permeability (P(Ca(2+))/P(Cs(+)) approximately 0. 4). AMPA receptor P(Ca(2+))/P(Cs(+)) and the relative abundance of GluR2 varied more widely in dorsal horn neurons than in motoneurons, but the mean values did not differ significantly between the two cell populations. GluR2 was virtually completely edited at the Q/R site both in motoneurons and dorsal horn neurons. These results indicate that the selective vulnerability of motoneurons to AMPA receptor agonists is not determined solely by whole-cell relative Ca(2+) permeability of AMPA receptors.

Amyotrophic Lateral Sclerosis↗
PubMed2000

Oxidative stress in amyotrophic lateral sclerosis.

The pathogenesis of amyotrophic lateral sclerosis is poorly understood. In one or two percentage of patients, mutations in the SOD1 gene are known to underly the disease. Even in these cases, the mechanism of cell death remains unclear. Most researchers agree that damage by reactive oxygen species is involved in this process, but whether the latter plays a primary role or is an epiphenomenon is uncertain. As evidence for oxidative stress is not only found in mutant SOD1-related familial amyotrophic lateral sclerosis, but also in sporadic amyotrophic lateral sclerosis, it is tempting to speculate that a similar mechanism is at work in both forms of the disease.

Amyotrophic Lateral Sclerosis↗
PubMed2000

Abnormal intracellular ca(2+)homeostasis and disease.

A whole range of cell functions are regulated by the free cytosolic Ca(2+)concentration. Activator Ca(2+)from the extracellular space enters the cell through various types of Ca(2+)channels and sometimes the Na(+)/Ca(2+)-exchanger, and is actively extruded from the cell by Ca(2+)pumps and Na(+)/Ca(2+)-exchangers. Activator Ca(2+)can also be released from internal Ca(2+)stores through inositol trisphosphate or ryanodine receptors and is taken up into these organelles by means of Ca(2+)pumps. The resulting Ca(2+)signal is highly organized in space, frequency and amplitude because the localization and the integrated free cytosolic Ca(2+)concentration over time contain specific information. Mutations or functional abnormalities in the various Ca(2+)transporters, which in vitro seem to induce trivial functional alterations, therefore, often lead to a plethora of diseases. Skeletal-muscle pathology can be caused by mutations in ryanodine receptors (malignant hyperthermia, porcine stress syndrome, central-core disease), dihydropyridine receptors (familial hypokalemic periodic paralysis, malignant hyperthermia, muscular dysgenesis) or Ca(2+)pumps (Brody disease). Ca(2+)-pump mutations in cutaneous epidermal keratinocytes and cochlear hair cells lead to, skin diseases (Darier and Hailey-Hailey) and hearing/vestibular problems respectively. Mutated Ca(2+)channels in the photoreceptor plasma membrane cause vision problems. Hemiplegic migraine, spinocerebellar ataxia type-6, one form of episodic ataxia and some forms of epilepsy can be due to mutations in plasma-membrane Ca(2+)channels, while antibodies against these channels play a pathogenic role in all patients with the Lambert-Eaton myasthenic syndrome and may be of significance in sporadic amyotrophic lateral sclerosis. Brain inositol trisphosphate receptors have been hypothesized to contribute to the pathology in opisthotonos mice, manic-depressive illness and perhaps Alzheimer's disease. Various abnormalities in Ca(2+)-handling proteins have been described in heart during aging, hypertrophy, heart failure and during treatment with immunosuppressive drugs and in diabetes mellitus. In some instances, disease-causing mutations or abnormalities provide us with new insights into the cell biology of the various Ca(2+)transporters.

Animals↗
PubMed2000

Demographic characteristics and prognosis in a Flemish amyotrophic lateral sclerosis population.

We describe the genetic and demographic characteristics of patients with amyotrophic lateral sclerosis (ALS) in Flanders, Belgium. Prognostic factors related to survival are examined. ALS was familial in 8.6% of all MND patients. In 6 of 8 apparently unrelated families, an SOD1 mutation was found. In sporadic ALS, mean age at onset was 57.1 years. There was a male preponderance (1.2:1) and the disease had a bulbar onset in 19%. Median survival was 32 months (95% CI 26-46). The presence of an APOE-epsilon 4 allele was not associated with a bulbar onset of ALS, an earlier age at onset or a shorter median survival. Variables examined in a multivariate analysis included age, sex, site of onset, delay from onset to diagnosis, and % forced vital capacity. Shorter survival was independently associated with higher age, bulbar onset, a short diagnostic delay, and a lower percent-predicted vital capacity at study entry. Simple clinical baseline characteristics can assist the clinician in estimating prognosis in ALS. The demographic characteristics of the Flemish ALS population do not seem to differ from those described in other parts of the world.

Adult↗
PubMed2000

Genetics of amyotrophic lateral sclerosis.

The genetic cause of amyotrophic lateral sclerosis (ALS) is known in a minority of cases. Mutations in SOD1, the gene encoding a superoxide dismutase on chromosome 21, are indeed found in 20% of familial ALS patients, who constitute only 5 or 10% of all ALS patients. In rare cases, a mutation in NFH, the gene encoding the heavy subunit of neurofilament, is present. Familial ALS has been linked to other loci but the genes involved remain to be identified. A genetic component is also thought to at least contribute to the pathogenesis of sporadic ALS. Their identification is now possible thanks to progress in molecular genetics.

Amyotrophic Lateral Sclerosis↗