Pathogenesis of Charcot-Marie-Tooth 1A (CMT1A) neuropathy

Theophylline Induces Remyelination and Functional Recovery in a Mouse Model of Peripheral Neuropathy

Charcot-Marie-Tooth disease (CMT) is a large group of inherited peripheral neuropathies that are primarily due to demyelination and/or axonal degeneration. CMT type 1A (CMT1A), which is caused by the duplication of the peripheral myelin protein 22 (PMP22) gene, is a demyelinating and the most frequent CMT subtype. Hypermyelination, demyelination, and secondary loss of large-caliber axons are hallmarks of CMT1A, and there is currently no cure and no efficient treatment to alleviate the symptoms of the disease. We previously showed that histone deacetylases 1 and 2 (HDAC1/2) are critical for Schwann cell developmental myelination and remyelination after a sciatic nerve crush lesion. We also demonstrated that a short-term treatment with Theophylline, which is a potent activator of HDAC2, enhances remyelination and functional recovery after a sciatic nerve crush lesion in mice. In the present study, we tested whether Theophylline treatment could also lead to (re)myelination in a PMP22-overexpressing mouse line (C22) modeling CMT1A. Indeed, we show here that a short-term treatment with Theophylline in C22 mice increases the percentage of myelinated large-caliber axons and the expression of the major peripheral myelin protein P0 and induces functional recovery. This pilot study suggests that Theophylline treatment could be beneficial to promote myelination and thereby prevent axonal degeneration and enhance functional recovery in CMT1A patients.

Perspective: DNA Copy Number Variations in Cardiovascular Diseases

Human genome contains many variations, often called mutations, which are difficult to detect and have remained a challenge for years. A substantial part of the genome encompasses repeats and when such repeats are in the coding region they may lead to change in the gene expression profile followed by pathological conditions. Structural variants are alterations which change one or more sequence feature in the chromosome such as change in the copy number, rearrangements, and translocations of a sequence and can be balanced or unbalanced. Copy number variants (CNVs) may increase or decrease the copies of a given region and have a pivotal role in the onset of many diseases including cardiovascular disorders. Cardiovascular disorders have a magnitude of well-established risk factors and etiology, but their correlation with CNVs is still being studied. In this article, we have discussed history of CNVs and a summary on the diseases associated with CNVs. To detect such variations, we shed light on the number of techniques introduced so far and their limitations. The lack of studies on cardiovascular diseases to determine the frequency of such variants needs clinical studies with larger cohorts. This review is a compilation of articles suggesting the importance of CNVs in multitude of cardiovascular anomalies. Finally, future perspectives for better understanding of CNVs and cardiovascular disorders have also been discussed.

Charcot-Marie-Tooth Disease Type 1A: Influence of Body Mass Index on Nerve Conduction Studies and on the Charcot-Marie-Tooth Examination Score

PURPOSE

Charcot-Marie-Tooth Disease type 1A (CMT1A) is caused by a duplication of the peripheral myelin protein gene 22 at chromosome 17p11.2-12. There is limited data regarding whether body mass index (BMI) affects electrophysiological or clinical data in those with CMT1A.

METHODS

Electrophysiological data, the Charcot-Marie-Tooth examination score (CMTES) and BMI from 101 patients with known CMT1A were obtained and analyzed.

RESULTS

When controlling for age, a higher BMI does not affect ulnar motor nerve conduction studies in those with CMT1A, but rather components of the CMTES (loss of pinprick and motor strength in the lower extremities).

CONCLUSIONS

BMI and clinical components of the CMTES are correlated, but it is uncertain which came first-whether the loss of lower extremity pinprick sensation and motor strength results in a higher BMI or if higher BMI results in these signs.

TRKA expression and NTRK1 gene copy number across solid tumours

AIMS

Neurotrophic Tropomyosin Kinase Receptor 1 (NTRK1) gene encodes for the protein Tropomyosin-related kinase A (TRKA). Deregulated activity of TRKA has been shown to have oncogenic potential. We present here the results of an immunohistochemical (IHC) observational cohort study of TRKA expression together with gene copy number (GCN) assessment in various solid tumours.

METHODS

Formalin-fixed, paraffin-embedded consecutive samples of different tumour types were tested for TRKA expression. Samples showing TRKA IHC staining in at least 10% of cells were analysed by fluorescence in situ hybridisation to assess NTRK1 gene rearrangements and/or individual GCN gain. All patients underwent this molecular assessment within the phase I ALKA-001 clinical trial.

RESULTS

1043 samples were tested and annotation for histology was available in 1023. Most of the samples were colorectal adenocarcinoma (CRC) (n=550, 52.7%) and lung adenocarcinoma (n=312, 29.9%). 24 samples (2.3%) were biliary tract carcinoma (BTC). Overall, 17 (1.6%) samples were characterised by TRKA IHC expression (four weak, eight moderate, five strong): 9/17 lung adenocarcinoma, 3/17 CRC, 3/17 BTC, 1/17 thyroid cancer and 1/17 cancer of unknown primary. Of these, 1/17 with strong TRKA IHC staining displayed NTRK1 gene rearrangement and 15/17 NTRK1 GCN gain by FISH. No correlation was found between intensity of TRKA IHC staining and number of copies of NTRK1.

CONCLUSIONS

TRKA expression can be found in 1.6% of solid tumours and can be paralleled by NTRK1 gene rearrangements or mostly GCN gain. The prognostic and translational therapeutic impact of the latter remains to be established.

Short- and long-term effects of chromosome mis-segregation and aneuploidy

Dividing cells that experience chromosome mis-segregation generate aneuploid daughter cells, which contain an incorrect number of chromosomes. Although aneuploidy interferes with the proliferation of untransformed cells, it is also, paradoxically, a hallmark of cancer, a disease defined by increased proliferative potential. These contradictory effects are also observed in mouse models of chromosome instability (CIN). CIN can inhibit and promote tumorigenesis. Recent work has provided insights into the cellular consequences of CIN and aneuploidy. Chromosome mis-segregation per se can alter the genome in many more ways than just causing the gain or loss of chromosomes. The short- and long-term effects of aneuploidy are caused by gene-specific effects and a stereotypic aneuploidy stress response. Importantly, these recent findings provide insights into the role of aneuploidy in tumorigenesis.

Molecular and clinical features of inherited neuropathies due to PMP22 duplication

PMP22 is a transmembrane glycoprotein component of myelin, important for myelin functioning. Mutation of PMP22 gene which encodes for the production of PMP22 glycoprotein is associated with a variety of inherited neuropathies. This literature review sought to review the molecular mechanism and clinical features of inherited neuropathies caused by PMP22 duplication. PMP22 duplication causes CMT1A which accounts for more than half of all CMT cases and about 70% of CMT1 cases. It manifests with muscle weakness, depressed reflexes, impaired distal sensation, hand and foot deformities, slowing of NCV and onion bulbs. With no specific treatment available, it is managed conservatively. Future treatment may be based on the molecular genetics of the disease.

Gene copy-number alterations: a cost-benefit analysis

Changes in DNA copy number, whether confined to specific genes or affecting whole chromosomes, have been identified as causes of diseases and developmental abnormalities and as sources of adaptive potential. Here, we discuss the costs and benefits of DNA copy-number alterations. Changes in DNA copy number are largely detrimental. Amplifications or deletions of specific genes can elicit discrete defects. Large-scale changes in DNA copy number can also cause detrimental phenotypes that are due to the cumulative effects of copy-number alterations of many genes simultaneously. On the other hand, studies in microorganisms show that DNA copy-number alterations can be beneficial, increasing survival under selective pressure. As DNA copy-number alterations underlie many human diseases, we will end with a discussion of gene copy-number changes as therapeutic targets.

Corneal confocal microscopy detects small-fiber neuropathy in Charcot-Marie-Tooth disease type 1A patients

INTRODUCTION

Although unmyelinated nerve fibers are affected in Charcot-Marie-Tooth type 1A (CMT1A) disease, they have not been studied in detail due to the invasive nature of the techniques needed to study them. We established alterations in C-fiber bundles of the cornea in patients with CMT1A using non-invasive corneal confocal microscopy (CCM).

METHODS

Twelve patients with CMT1A and 12 healthy control subjects underwent assessment of neuropathic symptoms and deficits, electrophysiology, quantitative sensory testing, corneal sensitivity, and corneal confocal microscopy.

RESULTS

Corneal sensitivity, corneal nerve fiber density, corneal nerve branch density, corneal nerve fiber length, and corneal nerve fiber tortuosity were significantly reduced in CMT1A patients compared with controls. There was a significant correlation between corneal sensation and CCM parameters with the severity of painful neuropathic symptoms, cold and warm thresholds, and median nerve CMAP amplitude.

CONCLUSIONS

CCM demonstrates significant damage to C-fiber bundles, which relates to some measures of neuropathy in CMT1A patients.

Nerve-dependent changes in skeletal muscle myosin heavy chain after experimental denervation and cross-reinnervation and in a demyelinating mouse model of Charcot-Marie-Tooth disease type 1A

Innervation regulates the contractile properties of vertebrate muscle fibers, in part through the effect of electrical activity on expression of distinct myosins. Herein we analyze the role of innervation in regulating the accumulation of the general, maturational, and adult forms of rodent slow myosin heavy chain (MyHC) that are defined by the presence of distinct antigenic epitopes. Denervation increases the number of fibers that express general slow MyHC, but it decreases the adult slow MyHC epitope. Cross-reinnervation of slow muscle by a fast nerve leads to an increase in the number of fibers that express fast MyHC. In both cases, there is an increase in the number of fibers that express slow and fast IIA MyHCs, but without the adult slow MyHC epitope. The data suggest that innervation is required for maturation and maintenance of diversity of both slow and fast fibers. The sequence of slow MyHC epitope transitions is a useful biomarker, and it may play a significant role during nerve-dependent changes in muscle fiber function. We applied this detailed muscle analysis to a transgenic mouse model of human motor and sensory neuropathy IA, also known as Charcot-Marie-Tooth disease type 1A (CMT1A), in which electrical conduction in some motor nerves is poor due to demyelination. The mice display atrophy of some muscle fibers and changes in slow and fast MyHC epitope expression, suggestive of a progressive increase in innervation of muscle fibers by fast motor neurons, even at early stages. The potential role of these early changes in disease pathogenesis is assessed.

Aneuploidy: cells losing their balance

A change in chromosome number that is not the exact multiple of the haploid karyotype is known as aneuploidy. This condition interferes with growth and development of an organism and is a common characteristic of solid tumors. Here, we review the history of studies on aneuploidy and summarize some of its major characteristics. We will then discuss the molecular basis for the defects caused by aneuploidy and end with speculations as to whether and how aneuploidy, despite its deleterious effects on organismal and cellular fitness, contributes to tumorigenesis.

Neuroactive Steroid Levels in a transgenic rat model of CMT1A Neuropathy

Charcot-Marie-Tooth type 1A (CMT1A) represents 80% of all the demyelinating hereditary motor and sensory neuropathies. As recently suggested, neuroactive steroids may have a role in a therapeutic strategy for peripheral neuropathies, including CMT1A. To this aim, an accurate qualitative and quantitative analysis of neuroactive steroid levels in this disease could be extremely important to define effective pharmacological strategies. We here analyzed by liquid chromatography-tandem mass spectrometry the levels of neuroactive steroids present in the sciatic nerve of male and female peripheral myelin protein 22 transgenic rats (PMP22(tg) rats; i.e., an experimental model of CMT1A) and of the corresponding wild-type littermates. We observed that, both in PMP22(tg) rats and in the wild types, the levels of neuroactive steroids, such as progesterone, tetrahydroprogesterone (THP), isopregnanolone (3beta,5alpha-THP), testosterone, dihydrotestosterone, and 5alpha-androstane-3alpha, 17beta-diol (3alpha-diol) are sexually dimorphic. It is interesting to note that the levels of 3beta,5alpha-THP and of 3alpha-diol, which are exclusively detectable in sciatic nerve of female and male rats, respectively, are strongly decreased in PMP22(tg) rats. 3beta,5alpha-THP and 3alpha-diol are modulators of gamma-amino butyric acid A receptor. Thus, the present findings may be considered an interesting background for experiments aimed to evaluate the possible therapeutic effects of modulators of this neurotransmitter receptor in male and female PMP22(tg) rats.

The Inherited Neuropathies

Neuropathy is one of the most common referrals to neurologic clinics. Patients often undergo extensive testing for acquired etiologies; inherited causes are common. Increasingly, genetic causes are becoming known and commercial testing available. The rate of recent discovery has been rapid and relates to the extent of single gene disorders of nerve, the ease of peripheral nervous system functional examination, and readily accessible pathologic tissue. Foremost in the rate of recent discoveries is the work and tools of the human genome project. the rapidity of the ongoing discovery requires clinicians to be familiar with molecular biologic discoveries and consider wisely which testing should be performed.

Peroneal nerve branching suggests compression palsy in the deformities of Charcot-Marie Tooth disease

Altered expression of the PMP-22 protein may be implicated in Charcot-Marie-Tooth disease and the much rarer disease, hereditary liability to pressure palsy. An element of chronic pressure palsy may explain the unique distribution of motor imbalance in patients with Charcot-Marie-Tooth disease. If this is the case, innervation of the lateral leg motor units should show sufficient anatomic segregation to explain the variable disease patterns. Twelve fresh cadaver specimens were dissected to examine the innervation of the anterior and lateral compartment muscles from the peroneal nerve. Nine specimens had a branch to the peroneus longus at or proximal to nerve passage of the posterior fibular neck. The first branch to the peroneus longus was 2.1 +/- 6.7 mm proximal, and the first branch to the peroneus brevis was 110.9 +/- 19 mm distal. The nerve to the tibialis anterior originated within 5 mm of the reference point and wrapped transversely along the fibular neck for 17.2 +/- 1.4 mm. These discrete pathways to the individual motor units in the anterolateral leg were consistent with the possible implication of chronic pressure palsy in the patterns of atrophy in Charcot-Marie-Tooth disease.

Overexpression of ErbB2 and ErbB3 receptors in Schwann cells of patients with Charcot-Marie-tooth disease type 1A

Axon-derived neuregulins (NRGs) are a family of growth factors whose binding to ErbB tyrosine kinase receptors promotes the maturation, proliferation and survival of Schwann cells (SCs). Correct NRG/ErbB signaling is essential for the homeostasis of axonal-glial complexes and seems to play a role in peripheral nerve repair. The potential involvement of ErbB receptors in human peripheral neuropathies has not been clarified. Therefore, we assessed the immunoreactivity for EGFR (ErbB1), ErbB2, and ErbB3 in nerve biopsies from patients with different forms of Charcot-Marie-Tooth disease, type 1, (CMT1), as compared to others with inflammatory neuropathies and controls. The most notable changes consisted in the overexpression of ErbB2 and ErbB3 by SCs of nerves from CMT1A patients. These findings are consistent with an impairment of SC differentiation and expand the molecular phenotype of CMT1A. The upregulation of these receptors may play a role in the inhibition of myelination or in the promotion of recurrent demyelination and axonal damage.

Experimental Charcot-Marie-Tooth type 1A: a cDNA microarrays analysis

To reveal the spectrum of genes that are modulated in Charcot-Marie-Tooth neuropathy type 1A (CMT1A), which is due to overexpression of the gene coding for the peripheral myelin protein 22 (pmp22), we performed a cDNA microarray experiment with cDNA from sciatic nerves of a rat model of the disease. In homozygous pmp22 overexpressing animals, we found a significant down-regulation of 86 genes, while only 23 known genes were up-regulated, suggesting that the increased dosage of pmp22 induces a general down-regulation of gene expression in peripheral nerve tissue. Classification of the modulated genes into functional categories leads to the identification of some pathways altered by overexpression of pmp22. In particular, a selective down-regulation of the ciliary neurotrophic factor transcript and of genes coding for proteins involved in cell cycle regulation, for cytoskeletal components and for proteins of the extracellular matrix, was observed. Cntf expression was further studied by real-time PCR and ELISA technique in pmp22 transgenic sciatic nerves, human CMT1A sural nerve biopsies, and primary cultures of transgenic Schwann cells. According to the results of cDNA microarray analysis, a down-regulation of cntf, both at the mRNA and protein level, was found in all the conditions tested. These results are relevant to reveal the molecular function of PMP22 and the pathogenic mechanism of CMT1A. In particular, finding a specific reduction of cntf expression in CMT1A Schwann cells suggests that overexpression of pmp22 significantly affects the ability of Schwann cells to offer a trophic support to the axon, which could be a factor, among other, responsible for the development of axonal atrophy in human and experimental CMT1A.

Impairment of PMP22 transgenic Schwann cells differentiation in culture: implications for Charcot-Marie-Tooth type 1A disease

Charcot-Marie-Tooth type 1A (CMT1A) is a hereditary demyelinating neuropathy due to an increased genetic dosage of the peripheral myelin protein 22 (PMP22). The mechanisms leading from PMP22 overexpression to impairment of myelination are still unclear. We evaluated expression and processing of PMP22, viability, proliferation, migration, motility and shaping properties, and ability of forming myelin of PMP22 transgenic (PMP22(tg)) Schwann cells in culture. In basal conditions, PMP22(tg) Schwann cells, although expressing higher PMP22 levels than control ones, show normal motility, migration and shaping properties. Addition of forskolin to the media induces an additional stimulation of PMP22 expression and results in an impairment of cells migration and motility, and a reduction of cell area and perimeter. Similarly, co-culturing transgenic Schwann cells with neurons causes an altered cells differentiation and an impairment of myelin formation. In conclusion, exposure of PMP22(tg) Schwann to the axon or to axonal-mimicking stimuli significantly affects the transition of transgenic Schwann cells to the myelinating phenotype.

Resistance training exercise and creatine in patients with Charcot-Marie-Tooth disease

Resistance exercise and creatine supplementation independently improve strength and function in patients with certain neuromuscular diseases. The purpose of this study was to examine the effects of resistance training with and without creatine supplementation on muscle, strength, and function in patients with Charcot-Marie-Tooth (CMT) disease. Twenty patients with CMT consumed 5 g/day creatine or placebo while participating in resistance training for 12 weeks. Energy metabolites, muscle fiber type and size, strength, and timed activities of daily living were measured before and after training. There were no differences between creatine or placebo groups for any outcome. For the groups combined, exercise training increased type I muscle fiber diameter (48.2 +/- 14.2 microm vs. 55.4 +/- 14.8 microm), strength, and activities of daily living (ADL) times. Thus, patients respond to resistance training with muscle fiber adaptations, and improvements in strength and function. Creatine was not beneficial.

Searching for needles in haystacks-the genetics of multiple sclerosis and other common neurological diseases

Recent years have witnessed considerable advances in our understanding of monogenic neurodegenerative diseases, such as hereditary motor sensory neuropathy and Huntington's Chorea. Progress has been slower in the genetic dissection of other more common neurological diseases with a complex mode of inheritance. The identification of relevant genes in some, such as Alzheimer's disease (AD) or Parkinson's disease (PD), has been facilitated by characteristic pathological findings and autosomal dominant inheritance in a proportion of early onset families. Attempts to identify relevant genes for multiple sclerosis have highlighted the role of the major histocompatibility complex, but so far failed to unequivocally implicate other immunologic or structural candidate genes. Six linkage-based whole genome screens have been completed in multiple sclerosis and several regions of interest have been identified. As technology and progress in the human genome project advance, it has become clear that future studies of common neurological diseases will depend critically on the availability of large sample sizes and will have to address issues of disease heterogeneity.

Alterations in the Arf6-regulated plasma membrane endosomal recycling pathway in cells overexpressing the tetraspan protein Gas3/PMP22

Growth arrest specific 3 (Gas3)/peripheral myelin protein 22 (PMP22) is a component of the compact peripheral nerve myelin, and mutations affecting gas3/PMP22 gene are responsible for a group of peripheral neuropathies in humans. We have performed in vivo imaging in order to investigate in detail the phenotype induced by Gas3/PMP22 overexpression in cultured cells. Here we show that Gas3/PMP22 triggers the accumulation of vacuoles, before the induction of cell death or of changes in cell spreading. Overexpressed Gas3/PMP22 accumulates into two distinct types of intracellular membrane compartments. Gas3/PMP2 accumulates within late endosomes close to the juxtanuclear region, whereas in the proximity of the cell periphery, it induces the formation of actin/phosphatidylinositol (4,5)-bisphosphate (PIP(2))-positive large vacuoles. Gas3/PMP22-induced vacuoles do not contain transferrin receptor, but instead they trap membrane proteins that normally traffic through the ADP-ribosylation factor 6 (Arf6) endosomal compartment. Arf6 and Arf6-Q67L co-localize with Gas3/PMP22 in these vacuoles, and the dominant negative mutant of Arf6, T27N, blocks the appearance of vacuoles in response to Gas3/PMP22, but not its accumulation in the late endosomes. Finally a point mutant of Gas3/PMP22 responsible for the Charcot-Marie-Tooth 1A disease is unable to trigger the accumulation of PIP(2)-positive vacuoles. Altogether these results suggest that increased Gas3/PMP22 levels can alter membrane traffic of the Arf6 plasma-membrane-endosomal recycling pathway and show that, similarly to other tetraspan proteins, Gas3/PMP22 can accumulate in the late endosomes.

Proliferation of Schwann cells and regulation of cyclin D1 expression in an animal model of Charcot-Marie-Tooth disease type 1A

Overexpression of PMP22 is responsible for the most common form of inherited neuropathy, Charcot-Marie-Tooth disease (CMT) type 1A. The PMP22-transgenic rat (CMT rat) is an animal model of CMT1A, and its peripheral nerves show the characteristic features of ongoing demyelination and remyelination that is also seen in CMT1A patients. Since Schwann cell proliferation is a prominent feature of peripheral nerves in inherited peripheral neuropathies, we examined proliferation and the expression of cyclin D1 in CMT rats. D-type cyclins are required for the initial steps in cell division and nuclear import is crucial for the function of cyclin D1 in promoting cell proliferation. Like normal myelinating Schwann cells in wild-type rats, remyelinating Schwann cells in CMT rats show perinuclear cyclin D1 expression. Schwann cells with nuclear cyclin D1 expression, as well as proliferating Schwann cells, were both associated with demyelinated axonal segments. Supernumerary onion bulb Schwann cells, however, do not express cyclin D1 and were not proliferating. Thus, cyclin D1 expression and its subcellular localization correlate directly with distinct physiological states of Schwann cells in this animal model of CMT1A.

PMP22 transgenic dorsal root ganglia cultures show myelin abnormalities similar to those of human CMT1A

Charcot-Marie-Tooth 1A (CMT1A) neuropathy is caused by duplication of the peripheral myelin protein 22 (PMP22) gene, leading to protein overexpression. Although this protein has a role in regulating Schwann cell growth and peripheral myelin compaction, how altered concentrations of PMP22 impair myelination is unknown. We established dorsal root ganglia (DRG) cultures from a transgenic rat overexpressing PMP22 (PMP22tg) to study the behavior of PMP22tg Schwann cells in early stages of development and myelination. We used reverse transcriptase-polymerase chain reaction and light and electron microscopy to study PMP22 expression and myelin formation. Myelin ultrastructure was evaluated in sural nerves from CMT1A patients to compare experimental and human findings. PMP22tg DRG cultures contained a greater number of internodes devoid of myelin, in the absence of remyelination, and increased periodicity of myelin lamellae compared with normal cultures. Widening of myelin lamellae was also observed in CMT1A biopsy specimens. Our results suggest that both functions of PMP22, in regulating Schwann cell differentiation and contributing to peripheral myelin compaction, are affected by its overexpression. The presence of similar myelin abnormalities in PMP22tg cultures and human nerves emphasizes the importance of developing in vitro models of hereditary neuropathies to study their underlying pathomechanisms.

The AN2 protein is a novel marker for the Schwann cell lineage expressed by immature and nonmyelinating Schwann cells

The expression of the 330 kDa AN2 glycoprotein was studied in the rodent peripheral nervous system. AN2 is expressed by immature Schwann cells in vitro and in vivo and downregulated as the cells upregulate myelin genes. A subpopulation of nonmyelinating Schwann cells in the adult sciatic nerve retains expression of AN2. In rat sciatic nerve crushes, where Schwann cell numbers increase after initial axonal loss and markers of immature Schwann cells show an upregulation, no increased expression of AN2 was observed. In contrast, AN2 expression was upregulated in nerves from peripheral myelin protein-22-transgenic rats, where immature Schwann cells expand without axonal loss. Furthermore, coculture with neurons upregulated AN2 expression on Schwann cells in vitro. Polyclonal antibodies against AN2 inhibited the migration of an immortalized Schwann cell clone in an in vitro migration assay, and the purified AN2 protein was shown to be neither inhibitory nor permissive for outgrowing dorsal root ganglion neurites. AN2 is thus a novel marker for the Schwann cell lineage. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of purified AN2 from early postnatal mouse brain demonstrated that AN2 is the murine homolog of the rat NG2 proteoglycan.

Bone marrow transfer from wild-type mice reverts the beneficial effect of genetically mediated immune deficiency in myelin mutants

Inherited demyelinating neuropathies are chronically disabling human disorders caused by various genetic defects, including deletions, single site mutations, and duplications in the respective myelin genes. We have shown in a mouse model of one distinct hereditary demyelinating neuropathy (heterozygous P0-deficiency, P0+-) that an additional null mutation in the recombination activating gene-1 (RAG-1--) leads to a substantially milder disorder, indicating a disease modifying role of T-lymphocytes. In the present study, we addressed the role of lymphocytes in the mouse model by reconstituting bone marrow of P0+-/RAG-1-- mice with bone marrow from immunocompetent wild-type mice. We compared the pathology and nerve conduction in double mutant mice (P0+-/RAG-1-- on a C57BL/6 background) with that in double mutants after receiving a bone marrow transplant. We found that the milder demyelination seen in the lymphocyte-deficient P0+-/RAG-1-- mutants was reverted to the more severe pathology by reestablishing a competent immune system by bone marrow transfer. These data corroborate the concept that the immune system contributes substantially to the pathologic process in this mouse model and may open new avenues to ameliorate human hereditary neuropathies by exploiting immunosuppressive treatments.

Prolonged vecuronium neuromuscular blockade associated with Charcot Marie Tooth neuropathy

Charcot Marie Tooth (CMT) disease comprises a group of disorders characterized by progressive distal muscle weakness and wasting. Review of the anaesthetic literature produced conflicting reports concerning the responses to neuromuscular blocking drugs in these patients. We describe a case in which vecuronium 0.11 mg kg(-1) produced prolonged neuromuscular blockade lasting 115 min in a patient with the condition. Conduction velocity in the facial nerve is usually less affected than the ulnar or peroneal nerve in CMT patients. This nerve may be more useful in monitoring neuromuscular blockade, both in titrating the dose of neuromuscular blocking drug and ensuring adequate reversal at the end of a procedure. Recent advances in molecular biology have enabled identification of the underlying genetic abnormalities and pathophysiology of CMT. These advances are reviewed and implications of CMT for the anaesthetist discussed.

Neurodegeneration is associated to changes in serum insulin-like growth factors

Serum levels of insulin and insulin-like growth factors and their binding proteins (IGFs and IGFBPs, respectively) are changed in human neurodegenerative diseases of very different etiology, such as Alzheimer's disease, amyotrophic lateral sclerosis, or cerebellar ataxia. However, the significance of these endocrine disturbances is not clear. We now report that in two very different inherited neurodegenerative conditions, ataxia-telangiectasia (AT) and Charcot-Marie-Tooth 1A (CMT-1A) disease, serum levels of IGFs are also altered. Both types of patients have increased serum IGF-I and IGFBP-2 levels, and decreased serum IGFBP-1 levels, while only AT patients have high serum insulin levels. Furthermore, serum IGFs are also changed in three different animal models of neurodegeneration: neurotoxin-induced motor discoordination, diabetic neuropathy, and hereditary cerebellar ataxia. In these three models, serum insulin levels are significantly decreased, serum IGF-I and IGFBP-1, -2, and -3 are decreased in diabetic and neurotoxin-injected rats, while serum IGFBP-1 is increased in hereditary ataxic rats. Altogether, these observations indicate that a great variety of neurodegenerative diseases show endocrine perturbations, resulting in changes in serum IGFs levels. These perturbations are disease-specific and are probably due to metabolic and endocrine derangements, nerve cell death, and sickness-related disturbances associated to the neurodegenerative process. Our observations strongly support the need to evaluate serum IGFs in other neurodegenerative conditions.

Exposure at the cell surface is required for gas3/PMP22 To regulate both cell death and cell spreading: implication for the Charcot-Marie-Tooth type 1A and Dejerine-Sottas diseases

Gas3/PMP22 is a tetraspan membrane protein highly expressed in myelinating Schwann cells. Point mutations in the gas3/PMP22 gene account for the dominant inherited peripheral neuropathies Charcot-Marie-Tooth type 1A disease (CMT1A) and Dejerine-Sottas syndrome (DSS). Gas3/PMP22 can regulate apoptosis and cell spreading in cultured cells. Gas3/PMP22 point mutations, which are responsible for these diseases, are defective in this respect. In this report, we demonstrate that Gas3/PMP22-WT is exposed at the cell surface, while its point-mutated derivatives are intracellularly retained, colocalizing mainly with the endoplasmic reticulum (ER). The putative retrieval motif present in the carboxyl terminus of Gas3/PMP22 is not sufficient for the intracellular sequestration of its point-mutated forms. On the contrary, the introduction of a retrieval signal at the carboxyl terminus of Gas3/PMP22-WT leads to its intracellular accumulation, which is accompanied by a failure to trigger cell death as well as by changes in cell spreading. In addition, by substituting the Asn at position 41 required for N-glycosylation, we provide evidence that N-glycosylation is required for the full effect on cell spreading, but it is not necessary for triggering cell death. In conclusion, we suggest that the DSS and the CMT1A neuropathies derived from point mutations of Gas3/PMP22 might arise, at the molecular level, from a reduced exposure of Gas3/PMP22 at the cell surface, which is required to exert its biological functions.

Animal models for inherited peripheral neuropathies: chances to find treatment strategies?

Mutations in four identified genes (peripheral myelin protein 22, P(0), connexin 32, and the early growth response 2 zinc finger protein) are the cause for several forms of inherited peripheral neuropathies that are still incurable disorders. Some forms of these disorders are well mimicked by engineered or spontaneous rodent mutants that might be instrumental for developing treatment strategies. This review focusses on common pathways of pathogenesis of the disorders and emphasizes strategies that might be suitable to ameliorate disease expression.

Uncoupling of myelin assembly and schwann cell differentiation by transgenic overexpression of peripheral myelin protein 22

We have generated previously transgenic rats that overexpress peripheral myelin protein 22 (PMP22) in Schwann cells. In the nerves of these animals, Schwann cells have segregated with axons to the normal 1:1 ratio but remain arrested at the promyelinating stage, apparently unable to elaborate myelin sheaths. We have examined gene expression of these dysmyelinating Schwann cells using semiquantitative reverse transcription-PCR and immunofluorescence analysis. Unexpectedly, Schwann cell differentiation appears to proceed normally at the molecular level when monitored by the expression of mRNAs encoding major structural proteins of myelin. Furthermore, an aberrant coexpression of early and late Schwann cell markers was observed. PMP22 itself acquires complex glycosylation, suggesting that trafficking of the myelin protein through the endoplasmic reticulum is not significantly impaired. We suggest that PMP22, when overexpressed, accumulates in a late Golgi-cell membrane compartment and uncouples myelin assembly from the underlying program of Schwann cell differentiation.

Mutation-dependent alteration in cellular distribution of peripheral myelin protein 22 in nerve biopsies from Charcot-Marie-Tooth type 1A

The hereditary demyelinating neuropathy Charcot-Marie-Tooth type 1A is caused by duplication or by point mutations of the PMP22 gene. Histopathological differences in these genotypes suggest distinct disease mechanisms. In the present investigation we demonstrate a pathologically altered cellular distribution of PMP22 in sural nerve biopsies of patients with PMP22 point mutations. In these patients, in contrast to findings in patients with PMP22 duplication, PMP22 partially accumulates in the Schwann cells instead of being inserted in the myelin sheath. These findings may explain the different histopathology and may suggest different mechanisms of pathogenesis in these genotypes.

The peripheral myelin protein 22 and epithelial membrane protein family

The peripheral myelin protein 22 (PMP22) and the epithelial membrane proteins (EMP-1, -2, and -3) comprise a subfamily of small hydrophobic membrane proteins. The putative four-transmembrane domain structure as well as the genomic structure are highly conserved among family members. PMP22 and EMPs are expressed in many tissues, and functions in cell growth, differentiation, and apoptosis have been reported. EMP-1 is highly up-regulated during squamous differentiation and in certain tumors, and a role in tumorigenesis has been proposed. PMP22 is most highly expressed in peripheral nerves, where it is localized in the compact portion of myelin. It plays a crucial role in normal physiological and pathological processes in the peripheral nervous system. Progress in molecular genetics has revealed that genetic alterations in the PMP22 gene, including duplications, deletions, and point mutations, are responsible for several forms of hereditary peripheral neuropathies, including Charcot-Marie-Tooth disease type 1A (CMT1A), Dejerine-Sottas syndrome (DDS), and hereditary neuropathy with liability to pressure palsies (HNPP). The natural mouse mutants Trembler and Trembler-J contain a missense mutation in different hydrophobic domains of PMP22, resulting in demyelination and Schwann cell proliferation. Transgenic mice carrying many copies of the PMP22 gene and PMP22-null mice display a variety of defects in the initial steps of myelination and/or maintenance of myelination, whereas no pathological alterations are detected in other tissues normally expressing PMP22. Further characterization of the interactions of PMP22 and EMPs with other proteins as well as their regulation will provide additional insight into their normal physiological function and their roles in disease and possibly will result in the development of therapeutic tools.

Neuromuscular disorders of childhood

Neuromuscular disorders are common causes of weakness and hypotonia in the infantile period and in childhood. Accurate diagnosis of specific neuromuscular disorders depends first on identification of which aspect of the peripheral neuromuscular system is affected--the motor neuron in the spinal cord, the nerve root or peripheral nerve, the neuromuscular junction, or the muscle--and then on the determination of the etiology and specific clinical entity. This review provides an overview of the major neuromuscular disorders of childhood with attention to recent advances and emerging areas of research.

Charcot-marie-tooth disease and related neuropathies: molecular basis for distinction and diagnosis

Great advances have been made in understanding the molecular basis of Charcot-Marie-Tooth disease (CMT) and related neuropathies, namely Dejerine-Sottas disease (DSD), hereditary neuropathy with liability to pressure palsies (HNPP) and congenital hypomyelination (CH). The number of newly uncovered mutations and identified genetic loci is rapidly increasing, and, as a consequence, the classification of these disorders is becoming more complicated. Molecular genetics, animal models, and transfected cell studies are shedding light on function and dysfunction of proteins involved in hereditary myelinopathies-peripheral myelin protein 22 (PMP22), myelin protein zero (PO), connexin 32 (Cx32), and early growth response 2 (EGR2). Gene dosage effect, loss of function, gain of toxic function, and dominant negative effect are possible mechanisms whereby different gene mutations may exert their detrimental action on peripheral nerves. A tentative rational approach to clinical and molecular diagnosis based on genotype-phenotype correlation analysis is described.

The monoclonal antibody 23E9 defines a novel developmentally-regulated Schwann cell surface antigen

The present study describes the identification and partial characterization of a novel Schwann cell surface molecule by means of a monoclonal antibody (23E9). The 23E9 antigen was found in association with Schwann cells of the peripheral nerve but not with sensory neurons and satellite cells of the dorsal root ganglion. The expression of the antigen in the sciatic nerve starts after birth, is high around postnatal day 8 and becomes down-regulated towards the adult stage. This suggests that it may be involved in the induction of myelin formation. On Western blots, the antibody identified two major bands of approximately 27 and 42 kDa. Treatment of cultured Schwann cells with forskolin, an agent known to mimic neuronal contact in vitro, stimulated the up-regulation of the antigen. This implies that the expression of 23E9 is induced and maintained by axon-derived signals in vivo. Comparison of the presented data with the literature suggests that we have identified a novel cell surface molecule not previously characterized in the context of Schwann cell biology. To clarify the molecular identity of the antigen and define its physiological relevance, the antibody will be used in future studies for immunoprecipitation and functional in vitro assays.

Molecular basis of inherited neuropathies

Considerable advances in our knowledge of the most frequently encountered group of inherited neuropathies, Charcot-Marie-Tooth neurpathy (CMT) and related disorders, have recently been made by genetic studies demonstrating that these disorders are caused by duplication, deletion or point mutations of specific genes of the peripheral myelin. The present classification of CMT and related disorders is based on a combination of clinical, neurophysiological, and genetic findings, and new genes and distinct mutations responsible for different clinical phenotypes are continuously being added. The genes that encode peripheral myelin protein of 22 kDa, protein zero, connexin-32 and early growth response-2 are the genes known to be involved in the pathogenesis of inherited neuropathies. Overexpression or underexpression of peripheral myelin protein of 22 kDa are causative for the most frequent forms of CMT-CMT1A and hereditary neuropathy with liability to pressure palsies--but the mechanisms that lead to incorrect myelin formation and maintenance are still unknown. Point mutations in the myelin genes can determine a loss of function, but in some cases an aberrant protein can act through a dominant negative or a toxic gain of function mechanism, disrupting the regular and precise relationship between the different myelin genes. Animal and in-vitro models of inherited neuropathies have been developed and will probably give the information that is necessary to clarify the pathogenetic mechanisms of demyelination.

Myelin uncompaction in Charcot-Marie-Tooth neuropathy type 1A with a point mutation of peripheral myelin protein-22

BACKGROUND

The peripheral myelin protein-22 (PMP22) gene has four transmembrane domains, two extracellular loops, and a short cytoplasmic tail. Its roles in the peripheral nervous system remain unclear. The most common cause of Charcot-Marie-Tooth neuropathy type 1A (CMT1A) is a PMP22 gene duplication. Missense point mutations in the transmembrane domains are rare alternative causes that have undetermined pathogenetic mechanisms.

OBJECTIVE

To investigate the phenotype-to-genotype correlations in a pedigree with unusual CMT1A.

METHODS

We identified a pedigree with an autosomal dominant motor-sensory neuropathy and severely reduced nerve conduction velocities who did not have the PMP22 duplication. Specimens from sural nerve biopsies from two patients of different ages were evaluated morphometrically. By automated direct nucleotide sequencing we analyzed PMP22 and the gene of the major structural myelin protein zero (P0).

RESULTS

Nucleotide 159 of PMP22 showed an A-to-T heterozygous mutation, predicted to cause an aspartate-to-valine substitution at codon 37 in the first extracellular loop of the protein. The mutation co-segregated with the disease in the pedigree and was absent in 80 healthy controls. The histopathologic phenotype was a de-remyelinating neuropathy with onion bulb formations, characterized by prominent uncompaction of the myelin sheath in the majority of fibers and by frequent tomacula.

CONCLUSION

We have described a novel mutation in the first extracellular loop of PMP22 associated with an atypical CMT1A that overlaps pathologically with CMT1B caused by point mutations in the extracellular domain of P0.

Embryonic expression of epithelial membrane protein 1 in early neurons

Epithelial membrane protein 1 (EMP1) is a member of the peripheral myelin protein 22 (PMP22) family. This family is best known for the crucial contribution of PMP22 to the development and maintenance of the peripheral nervous system (PNS). PMP22 is widely expressed, with highest levels in myelinating Schwann cells, and mutations affecting the PMP22 gene lead to PNS-restricted neuropathies. We have investigated the spatio-temporal distribution of EMP1 and compared it to that of PMP22. We found that EMP1 and PMP22 mRNA are most conspicuously expressed in the prenatal mouse brain during neurogenesis. In the developing forebrain, we localized EMP1 mRNA and protein to the first set of neurons that are generated and leave the ventricular zone to form the preplate. Later in development, EMP1 was found in derivatives of the preplate, the marginal zone and the subplate. Reduced expression was observed in the newly generated cortical plate neurons. In other parts of the developing CNS and PNS, EMP1 was also detected in early neurons and along the initial fiber tracts. Furthermore, EMP1 was highly expressed by immature neurons in embryonal dorsal root ganglia-explant cultures and in neuroectodermal differentiated P19 cells. While PMP22 functions mainly in Schwann cell growth and differentiation, the spatio-temporal localization of EMP1 suggests a role in neuronal differentiation and neurite outgrowth.

Post-transcriptional regulation of the peripheral myelin protein gene PMP22/gas3

The peripheral myelin protein PMP22 gene has been described as a growth arrest-specific gene gas3 and has been identified as disease gene of various demyelinating neuropathies. The gene consists of two highly conserved alternative noncoding 5'-exons la (CD25) and 1b (SR13), respectively. Differential expression patterns of these transcripts in vivo and in vitro suggest a very complex mode of PMP22 gene regulation, which cannot be explained merely by transcriptional control. In fact, the PMP22 gene is regulated on different post-transcriptional levels. While reverse transcriptase polymerase chain reaction (RT-PCR) analyses revealed no alterations in stability for both PMP22 transcripts in randomly growing Schwann cell cultures of rat sciatic nerve for at least 8 hours, in serum-induced synchronized cultures of resting cells we observed a specific cell cycle-regulated degradation of both transcripts. We further prepared diverse PMP22/CAT fusion genes to study the influence of the alternative 5'UTRs on PMP22 translation. Transient transfection of NIH3T3-fibroblasts and rat Schwann cells demonstrated that the alternative 5'UTRs (CD25 and SR13) and the 3'UTR exert differential regulatory influences on the translation efficiency.