C. Oliver Hanemann

Pathological Adhesion of Primary Human Schwannoma Cells is Dependent on Altered Expression of Integrins

Mutations in the tumor suppressor gene coding for merlin cause Neurofibromatosis type 2 (NF2), all spontaneous schwannomas, and a majority of meningiomas. Merlin links transmembrane proteins to the cytoskeleton. Accordingly, primary human schwannoma cells lacking merlin show an increased number of lamellipodia and filopodia as well as increased cell spreading. We show enhanced adhesion in primary human schwannoma cells and present evidence that this is dependent on the integrin chains α6β1 and α6β4. We further demonstrate that the integrin chains β1 and β4 are upregulated in schwannomas using different complementary methods, and report higher expression of these integrins per schwannoma cell by fluorescence assisted cell sorting (FACS). Finally we report clustering of the integrin chains α6, β1, and β4 on schwannoma cells. Our findings fit well into recent data on the role of merlin in signaling cascades connected to integrins and help explain pathological ensheathment of extracellular matrix or pseudomesaxon formation which is a hallmark of schwannoma histopathology.

Reduced Apoptosis Rates in Human Schwannomas

Schwannomas, tumors originating from Schwann cells, represent a frequent neurological tumor and can occur both in a genetic disorder called neurofibromatosis type 2 (NF2) and sporadically. In both cases the genetic background is identical as all schwannomas are caused by biallelic mutations in the tumor suppressor gene NF2 coding for merlin. Mutations in this gene have also been found to be responsible for 50% to 60% of spontaneous and 100% of the NF2 associated meningiomas. The NF2 gene product, merlin, links transmembrane proteins to the cytoskeleton and is involved in intracellular signaling processes. It has previously been shown that reexpression of wild‐type merlin in primary human schwannoma cells leads to an increase in the number of apoptotic cells. Here, we report in vivo and in vitro evidence that the basal apoptosis rate of primary human schwannoma cells is reduced in comparison to that of normal Schwann cells, supporting the idea that in this benign tumor type, apoptosis has a role in tumorigenesis.

MR-pathologic comparison of the upper spinal cord in different motor neuron diseases.

This MRI study was performed to evaluate in vivo alterations of the spinal cord in defined subgroups of motor neuron diseases. Standard MRI examinations of the cervical and thoracic spinal cord in sporadic amyotrophic lateral sclerosis (ALS; n = 39), sporadic lower motor neuron disease (LMND; n = 19), Kennedy’s disease (KD; n = 19) and a control group (n = 96) were analyzed with respect to spinal cord signal changes and the thickness of the spinal cord. No significant changes in thickness or signal alterations were observed when comparing ALS, LMND and control groups with one another. However, in KD patients significant upper spinal cord atrophy was detected at the cervical level as compared with all other groups. At the thoracic level, KD patients had significant upper cord atrophy as compared with controls and LMND. Marked atrophy of the upper spinal cord seems to be a feature of the KD-associated central-peripheral distal axonopathy.

Rearrangements of the intermediate filament GFAP in primary human schwannoma cells.

Loss of the tumor suppressor protein merlin causes a variety of benign tumors such as schwannomas, meningiomas, and gliomas in man. We previously reported primary human schwannoma cells to show enhanced integrin-dependent adhesion and a hyperactivation of the small RhoGTPase Rac1. Here we show that the main intermediate filament protein of Schwann cells, the glial fibrillary acidic protein, is collapsed to the perinuclear region instead of being well-spread from the nucleus to the cell periphery. This cytoskeletal reorganization is accompanied by changes in cell shape and increased cell motility. Moreover, we report tyrosine phosphorylation to be enhanced in schwannoma cells, already described earlier in intermediate filament breakdown. Thus, we believe that Rac activation via tyrosine kinase stimulation leads to GFAP collapse in human schwannoma cells, and suggest that this process plays an important role in vivo where schwannoma cells become motile, unspecifically ensheathing extracellular matrix and forming pseudomesaxons.

Secondary axon atrophy and neurological dysfunction in demyelinating neuropathies.

Purpose of the reviewSecondary axonal atrophy is common in most if not all demyelinating neuropathies and is likely responsible for the majority of clinical symptoms. We review clinical, electrophysiological and morphological evidence for secondary axonal atrophy in demyelinating neuropathies and summarize recent hypotheses on possible pathomechanisms. Recent findingsElucidation of genetic defects responsible for hereditary demyelinating neuropathies and insights into axon-Schwann cell interactions have allowed longitudinal studies of genetically defined demyelinating neuropathies and research into the pathomechanism of secondary axonal atrophy. SummaryThere is ample clinical electrophysiological and electropathological evidence that secondary axonal atrophy is found in hereditary and demyelinating neuropathies. Recognizing secondary axonal atrophy as a main cause for clinical disability in demyelinating neuropathies is important for the clinician and may reveal a therapeutic target common to all different forms of demyelinating neuropathies.

Complicated hereditary spastic paraplegia with thin corpus callosum: variation of phenotypic expression over time.

Sirs: The hereditary spastic paraplegias (HSP) encompass a group of heterogeneous neurodegenerative disorders. Clinical variability led to a classification into pure and complicated forms; in the latter, symptoms additional to spastic paraplegia are found, e. g. muscular atrophy or mental retardation [6, 10, 12]. Disease-causing genes have been described for both forms; however, identical genotypes can give rise to pure as well as complicated HSP and conversely similar phenotypes have been described in families with linkage to distinct gene loci. Thus it seems important to examine whether the HSP phenotype changes during the course of disease and which symptoms result from developmental changes and which from progressive neurodegeneration [5, 9]. In this regard, complicated autosomal recessive HSP (AR-HSP) with hypoplasia of the corpus callosum (CC) is of special interest [1]. It can originate from different genetic backgrounds, leading to definition of distinct entities [2, 3, 6, 11]. We describe a longitudinal investigation in two sisters from nonconsanguine parents suffering from a novel, as yet genetically unidentified form of AR-HSP with thin CC, negative for known mutations in the genes coding for maspardin, spartin and the K+/Cl–-cotransporter [12–14]. Diseases which have been described to mimic HSP were excluded [10]. Studies were performed at age 17 and 20 and again 3 and 7 years later, respectively. The clinical picture consisted of progressive spastic paraparesis, a delay in developmental milestones, early mental impairment, behavioral changes, short stature, progressive distal symmetric motor neuropathy, and mild pseudobulbar dysarthria (Table 1). Neuropsychological investigaLETTER TO THE EDITORS

Sensitive Detection of Deletions of One or More Exons in the Neurofibromatosis Type 2 (NF2) Gene by Multiplexed Gene Dosage Polymerase Chain Reaction

Mutation detection in the neurofibromatosis type 2 (NF2) gene is challenging because when combining mutation detection methods such as single-strand conformational polymorphism and heteroduplex analysis, denaturing gradient gel electrophoresis, and direct sequencing of aberrant polymerase chain reaction (PCR) fragments only 30 to 60% of the constitutional mutations are detected. Because large deletions and complete chromosome rearrangements are also described methods such as microarray-comparative genomic hybridization and fluorescence in situ hybridization are also used. The one type of mutation often missed corresponds to deletions encompassing one or few exons. To detect this type we have developed a swift and reliable method. We perform a gene dosage analysis with two fluorescent multiplex PCR assays that amplify 15 of the 17 NF2 exons. The labeled PCR products are quantified and gene dose is calculated with respect to controls. We tested the reliability of this method with DNA from eight NF2 patients with known heterozygous NF2 deletions, eight controls and four unknown NF2 patients. In all of the patients with known heterozygous deletions we found in several exons a reduction of gene dosage to 50 to 69%. In one NF2 patient with previously unknown mutation and a severe phenotype we found the gene dosage of two exons reduced by 50% indicating a deletion of these two exons on one allele. This finding was validated by reverse transcriptase-PCR on fibroblast and schwannoma cell cultures of this patient and cDNA sequencing. Our gene dosage assay will detect deletions of one or more exons as well as gross deletions of the whole coding region of the gene. It can complement the existing screening methods because it is faster and easier.

Motor protein diseases of the nervous system

Motor proteins link concepts of impaired axonal transport with concepts of impaired energy metabolism in motor neuron disease. Thus it is not surprising that in recent years several reports on the relevance of motor protein function in mice models for motor neuron disease as well as motor neuron patients have appeared. This article summarizes the broad spectrum of neurological phenotypes, which are caused by alterations of motor protein function. This is likely to add to the understanding of motor neuron disease and may be relevant in terms of future therapeutic approaches.