Ascorbic acid inhibits PMP22 expression by reducing cAMP levels

Current Treatment Methods for Charcot-Marie-Tooth Diseases

Charcot-Marie-Tooth (CMT) disease, the most common inherited neuromuscular disorder, exhibits a wide phenotypic range, genetic heterogeneity, and a variable disease course. The diverse molecular genetic mechanisms of CMT were discovered over the past three decades with the development of molecular biology and gene sequencing technologies. These methods have brought new options for CMT reclassification and led to an exciting era of treatment target discovery for this incurable disease. Currently, there are no approved disease management methods that can fully cure patients with CMT, and rehabilitation, orthotics, and surgery are the only available treatments to ameliorate symptoms. Considerable research attention has been given to disease-modifying therapies, including gene silencing, gene addition, and gene editing, but most treatments that reach clinical trials are drug treatments, while currently, only gene therapies for CMT2S have reached the clinical trial stage. In this review, we highlight the pathogenic mechanisms and therapeutic investigations of different subtypes of CMT, and promising therapeutic approaches are also discussed.

Mechanisms and Treatments in Demyelinating CMT

Demyelinating forms of Charcot-Marie-Tooth disease (CMT) are genetically and phenotypically heterogeneous and result from highly diverse biological mechanisms including gain of function (including dominant negative effects) and loss of function. While no definitive treatment is currently available, rapid advances in defining the pathomechanisms of demyelinating CMT have led to promising pre-clinical studies, as well as emerging clinical trials. Especially promising are the recently completed pre-clinical genetic therapy studies in PMP-22, GJB1, and SH3TC2-associated neuropathies, particularly given the success of similar approaches in humans with spinal muscular atrophy and transthyretin familial polyneuropathy. This article focuses on neuropathies related to mutations in PMP-22, MPZ, and GJB1, which together comprise the most common forms of demyelinating CMT, as well as on select rarer forms for which promising treatment targets have been identified. Clinical characteristics and pathomechanisms are reviewed in detail, with emphasis on therapeutically targetable biological pathways. Also discussed are the challenges facing the CMT research community in its efforts to advance the rapidly evolving biological insights to effective clinical trials. These considerations include the limitations of currently available animal models, the need for personalized medicine approaches/allele-specific interventions for select forms of demyelinating CMT, and the increasing demand for optimal clinical outcome assessments and objective biomarkers.

Therapeutic Development in Charcot Marie Tooth Type 1 Disease

Charcot–Marie–Tooth disease (CMT) is the most frequent hereditary peripheral neuropathies. It is subdivided in two main groups, demyelinating (CMT1) and axonal (CMT2). CMT1 forms are the most frequent. The goal of this review is to present published data on 1—cellular and animal models having opened new potential therapeutic approaches. 2—exploration of these tracks, including clinical trials. The first conclusion is the great increase of publications on CMT1 subtypes since 2000. We discussed two points that should be considered in the therapeutic development toward a regulatory-approved therapy to be proposed to patients. The first point concerns long term safety if treatments will be a long-term process. The second point relates to the evaluation of treatment efficiency. Degradation of CMT clinical phenotype is not linear and progressive.

Squalenoyl siRNA PMP22 nanoparticles are effective in treating mouse models of Charcot-Marie-Tooth disease type 1 A

Charcot-Marie-Tooth disease type 1 A (CMT1A) lacks an effective treatment. We provide a therapy for CMT1A, based on siRNA conjugated to squalene nanoparticles (siRNA PMP22-SQ NPs). Their administration resulted in normalization of Pmp22 protein levels, restored locomotor activity and electrophysiological parameters in two transgenic CMT1A mouse models with different severity of the disease. Pathological studies demonstrated the regeneration of myelinated axons and myelin compaction, one major step in restoring function of myelin sheaths. The normalization of sciatic nerve Krox20, Sox10 and neurofilament levels reflected the regeneration of both myelin and axons. Importantly, the positive effects of siRNA PMP22-SQ NPs lasted for three weeks, and their renewed administration resulted in full functional recovery. Beyond CMT1A, our findings can be considered as a potent therapeutic strategy for inherited peripheral neuropathies. They provide the proof of concept for a new precision medicine based on the normalization of disease gene expression by siRNA.

Gait parameters as tools for analyzing phenotypic alterations of a mouse model of Charcot-Marie-Tooth disease

Charcot-Marie-Tooth disease (CMT), a genetically heterogeneous group of diseases in the peripheral nervous system, is characterized by progressive and symmetrical distal weakness resulting in gait abnormality. The necessity of the diagnostic and prognostic biomarkers has been raised for both basic research and clinical practice in CMT. Since biomarkers for animal study of CMT are limited, we evaluated the feasibility of gait parameters as tool for measuring disease phenotype of CMT mouse model. Using a Trembler-J (Tr-J) mouse, a CMT type 1 (CMT1) mouse model, we analyzed kinematic parameters such as angles of hip, knee and ankle (sagittal plane), and spatial parameters including step width and stride length (transverse plane). Regarding of kinematic parameters, Tr-J mice exhibited less plantarflexed ankle during the swing phase and more dorsiflexed ankle at the terminal stance compared to control mice. The range of motion in ankle angle of Tr-J mice was significantly greater than that of control mice. In spatial parameter, Tr-J mice exhibited wider step width compared to control mice. These results are similar to previously reported gait patterns of CMT1 patients. In comparison with other markers such as nerve conduction study and rotarod test, gait parameters dynamically reflected the disease progression of CMT1 mice. Therefore, these data imply that gait parameters can be used as useful tools to analyzed the disease phenotype and progression during preclinical study of peripheral neuropathy such as CMT.

Treating PMP22 gene duplication-related Charcot-Marie-Tooth disease: the past, the present and the future

Charcot-Marie-Tooth (CMT) disease is the most frequent inherited neuropathy, affecting 1/1500 to 1/10000. CMT1A represents 60%-70% of all CMT and is caused by a duplication on chromosome 17p11.2 leading to an overexpression of the Peripheral Myelin Protein 22 (PMP22). PMP22 gene is under tight regulation and small changes in its expression influences myelination and affect motor and sensory functions. To date, CMT1A treatment is symptomatic and classic pharmacological options have been disappointing. Here, we review the past, present, and future treatment options for CMT1A, with a special emphasis on the highly promising potential of PMP22-targeted small interfering RNA and antisense oligonucleotides.

Regulating PMP22 expression as a dosage sensitive neuropathy gene

Structural variation in the human genome has emerged as a major cause of disease as genomic data have accumulated. One of the most common structural variants associated with human disease causes the heritable neuropathy known as Charcot-Marie-Tooth (CMT) disease type 1A. This 1.4 Mb duplication causes nearly half of the CMT cases that are genetically diagnosed. The PMP22 gene is highly induced in Schwann cells during development, although its precise role in myelin formation and homeostasis is still under active investigation. The PMP22 gene can be considered as a nucleoprotein complex with enzymatic activity to produce the PMP22 transcript, and the complex is allosterically regulated by transcription factors that respond to intracellular signals and epigenomic modifications. The control of PMP22 transcript levels has been one of the major therapeutic targets of therapy development, and this review summarizes those approaches as well as efforts to characterize the regulation of the PMP22 gene.

miR-381 Attenuates Peripheral Neuropathic Phenotype Caused by Overexpression of PMP22

Charcot-Marie Tooth disease type 1A (CMT1A), the major type of CMT, is caused by duplication of peripheral myelin protein 22 (PMP22) gene whose overexpression causes structural and functional abnormalities in myelination. We investigated whether miRNA-mediated regulation of PMP22 expression could reduce the expression level of PMP22, thereby alleviating the demyelinating neuropathic phenotype of CMT1A. We found that several miRNAs were down-regulated in C22 mouse, a CMT1A mouse model. Among them, miR-381 could target 3′ untranslated region (3′UTR) of PMP22 in vitro based on Western botting and quantitative Real Time-PCR (qRT-PCR) results. In vivo efficacy of miR-381 was assessed by administration of LV-miR-381, an miR-381 expressing lentiviral vector, into the sciatic nerve of C22 mice by a single injection at postnatal day 6 (p6). Administration of LV-miR-381 reduced expression level of PMP22 along with elevated level of miR-381 in the sciatic nerve. Rotarod performance analysis revealed that locomotor coordination of LV-miR-381 administered C22 mice was significantly enhanced from 8 weeks post administration. Electrophysiologically, increased motor nerve conduction velocity was observed in treated mice. Histologically, toluidine blue staining and electron microscopy revealed that structural abnormalities of myelination were improved in sciatic nerves of LV-miR-381 treated mice. Therefore, delivery of miR-381 ameliorated the phenotype of peripheral neuropathy in CMT1A mouse model by down-regulating PMP22 expression. These data suggest that miRNA can be used as a potent therapeutic strategy to control diseases with copy number variations such as CMT1A.

Vitamin C in Cancer: A Metabolomics Perspective

There is an ongoing interest in cellular antioxidants and oxidants as well as cellular mechanisms underlying their effects. Several reports suggest that vitamin C (L-ascorbic acid) functions as a pro-oxidant with selective toxicity against specific types of tumor cells. In addition, reduced glutathione plays an emerging role in reducing oxidative stress due to xenobiotic toxins such as metals and oxidants associated with diseases such as cancer, cardiovascular disease, and stroke. High-dose intravenous vitamin C and intravenous glutathione have been used as complementary, alternative, and adjuvant medicines. Here, we review the molecular mechanisms underlying the regulation of oxidation/reduction systems, focusing on the altered metabolomics profile in cancer cells following treatment with pharmacological vitamin C. This review focuses on the role of vitamin C in energy metabolism in terms of adenosine triphosphate, cysteine, and reduced glutathione levels, affecting cancer cell death.

Pharmacology and drug development in rare diseases: the attractiveness and expertise of the French medical pharmacology

Developing drugs for rare disease can be challenging due to specific rare disease characteristics. The French Medical Pharmacology is structured and positioned to play a major role in orphan drug research and development due to the required expertise concentrated into pharmacology departments, exclusively implemented within the French university hospitals, public hospitals that are linked to a medical school (and often a pharmacy school) with numerous INSERM or CNRS labelled research units. In addition, these structures allow a close collaboration between researchers, academic institutions and biotech start-up (most of them being spin-off of the academic structures). Also, within university hospitals are located the clinical investigation centres, linking to the F-CRIN network and also to Inserm and hospitals, that enable care staff and researchers to be associated and clinical research protocols to be carried out on site, in full respect with ethic and regulatory aspects. As a consequence, this intra and multidisciplinary expertise offers all resource to elaborate a tailored approach for orphan drug development, in new entities as well as in repositioning. For preclinical development: drug screening, candidate selection (taking into account PK, metabolism, variability and potential toxicity) and preclinical models (iPS, animal models) that could allow a better translation to human research. For clinical development, we will mention here dose determination, safety evaluation and Orphan Drug Designation and Protocol Assistance preparation and submission. For post marketing evaluation and surveys, the pharmacovigilance, addictovigilance and pharmacoepidemiology expertise, combined with access to large databases allow a better approach to orphan drug use and safety. As outlined through two success stories (Charcot Marie Tooth, vascular Ehlers-Danlos syndrome), the added value of French Medical Pharmacology structures and expertise has been evidenced in the know-how, multidimensional and multidisciplinary approaches, allowing the development of numerous drugs that have been granted with Orphan Drug Designation and later Market Approval. Even if specific and possibly even more, the field of orphan drugs requires the respect of highest standards of safety and quality. French Medical Pharmacology intends to continue on this way and constantly improve his involvement in this field, committed to a single objective: answer the unmet medical need of patients with rare diseases.

Caveats in the Established Understanding of CMT1A

Charcot‐Marie‐Tooth disease type‐1A (CMT1A) is one of the most common types of inherited peripheral nerve diseases. It is caused by the trisomy of chromosome 17p12 (c17p12), a large DNA segment of 1.4 Mb containing PMP22 plus eight other genes. The size of c17p12 is formidable for any cloning technique to manipulate, and thus precludes production of models in vitro and in vivo that can precisely recapitulate the genetic alterations in humans with CMT1A. This limitation and other factors have led to several assumptions, which have yet been carefully scrutinized, serving as key principles in our understanding of the disease. For instance, one extra copy of c17p12 in patients with CMT1A results in a higher gene dosage of PMP22, thereby expected to produce a higher level of PMP22 mRNA/proteins that cause the disease. However, there has been increasing evidence that PMP22 levels are highly variable among patients with CMT1A and may fall into the normal range at a given time point. This raises an alternative mechanism causing the disease by dysregulation of PMP22 expression or excessive fluctuation of PMP22 levels, not the absolute increase of PMP22. This has become a pressing issue since recent clinical trials using ascorbic acid failed to alter the clinical outcome of CMT1A patients, leaving no effective therapy for the disease. In this article, we will discuss how this fundamental issue might be investigated. In addition, several other key issues in CMT1A will be discussed, including potential mechanisms responsible for the uniform slowing of conduction velocities. A clear understanding of these issues could radically change how therapies should be developed against CMT1A.

Genome-wide expression profiling establishes novel modulatory roles of vitamin C in THP-1 human monocytic cell line

Background

Vitamin C (vit C) is an essential dietary nutrient, which is a potent antioxidant, a free radical scavenger and functions as a cofactor in many enzymatic reactions. Vit C is also considered to enhance the immune effector function of macrophages, which are regarded to be the first line of defence in response to any pathogen. The THP-1 cell line is widely used for studying macrophage functions and for analyzing host cell-pathogen interactions.

Results

We performed a genome-wide temporal gene expression and functional enrichment analysis of THP-1 cells treated with 100 μM of vit C, a physiologically relevant concentration of the vitamin. Modulatory effects of vitamin C on THP-1 cells were revealed by differential expression of genes starting from 8 h onwards. The number of differentially expressed genes peaked at the earliest time-point i.e. 8 h followed by temporal decline till 96 h. Further, functional enrichment analysis based on statistically stringent criteria revealed a gamut of functional responses, namely, ‘Regulation of gene expression’, ‘Signal transduction’, ‘Cell cycle’, ‘Immune system process’, ‘cAMP metabolic process’, ‘Cholesterol transport’ and ‘Ion homeostasis’. A comparative analysis of vit C-mediated modulation of gene expression data in THP-1cells and human skin fibroblasts disclosed an overlap in certain functional processes such as ‘Regulation of transcription’, ‘Cell cycle’ and ‘Extracellular matrix organization’, and THP-1 specific responses, namely, ‘Regulation of gene expression’ and ‘Ion homeostasis’. It was noteworthy that vit C modulated the ‘Immune system’ process throughout the time-course.

Conclusions

This study reveals the genome-wide effects of physiological levels of vit C on THP-1 gene expression. The multitude of effects impacted by vit C in macrophages highlights its role in maintaining homeostasis of several cellular functions. This study provides a rational basis for the use of the Vitamin C- THP-1 cell model, to study biochemical and cellular responses to stresses, including infection with M. tuberculosis and other intracellular pathogens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3635-4) contains supplementary material, which is available to authorized users.

Intracellular ascorbate tightens the endothelial permeability barrier through Epac1 and the tubulin cytoskeleton

Vitamin C, or ascorbic acid, both tightens the endothelial permeability barrier in basal cells and also prevents barrier leak induced by inflammatory agents. Barrier tightening by ascorbate in basal endothelial cells requires nitric oxide derived from activation of nitric oxide synthase. Although ascorbate did not affect cyclic AMP levels in our previous study, there remains a question of whether it might activate downstream cyclic AMP-dependent pathways. In this work, we found in both primary and immortalized cultured endothelial cells that ascorbate tightened the endothelial permeability barrier by ∼30%. In human umbilical vein endothelial cells, this occurred at what are likely physiologic intracellular ascorbate concentrations. In so doing, ascorbate decreased measures of oxidative stress and also flattened the cells to increase cell-to-cell contact. Inhibition of downstream cyclic AMP-dependent proteins via protein kinase A did not prevent ascorbate from tightening the endothelial permeability barrier, whereas inhibition of Epac1 did block the ascorbate effect. Although Epac1 was required, its mediator Rap1 was not activated. Furthermore, ascorbate acutely stabilized microtubules during depolymerization induced by colchicine and nocodazole. Over several days in culture, ascorbate also increased the amount of stable acetylated α-tubulin. Microtubule stabilization was further suggested by the finding that ascorbate increased the amount of Epac1 bound to α-tubulin. These results suggest that physiologic ascorbate concentrations tighten the endothelial permeability barrier in unstimulated cells by stabilizing microtubules in a manner downstream of cyclic AMP that might be due both to increasing nitric oxide availability and to scavenging of reactive oxygen or nitrogen species.

Update on Charcot-Marie-Tooth disease

PURPOSE OF REVIEW

Charcot-Marie-Tooth disease (CMT) is the common terminology used to describe the hereditary neuropathies. This update reviews advances in the past year in our understanding of these diseases, including some important earlier references.

RECENT FINDINGS

In the past year, advances in next-generation sequencing continued to increase the number of genes associated with CMT. The connection between genotype and phenotype has become more complicated. New insights into the pathogenesis of the diseases are reviewed. Treatment and clinical trial updates coming from these new insights, as well as use of high-throughput screening to match potential treatments with targets, are moving the field forward. There is a discussion of potential next steps, including the use of patient-derived induced pluripotent stem cells, to enhance our understanding of individual genotypes and phenotypes.

SUMMARY

The use of high-throughput screens, and techniques such as RNAi and induced pluripotent stem cell continue to push forward other therapies for specific genetic forms of CMT and are potentially more generalizable to peripheral neuropathies. These developments, along with the development of improved outcome measures and longitudinal natural history data, advance CMT, making the future for finding treatments and/or cures closer than it has ever been.

Promoting peripheral myelin repair

Compared to the central nervous system (CNS), peripheral nerves have a remarkable ability to regenerate and remyelinate. This regenerative capacity to a large extent is dependent on and supported by Schwann cells, the myelin-forming glial cells of the peripheral nervous system (PNS). In a variety of paradigms, Schwann cells are critical in the removal of the degenerated tissue, which is followed by remyelination of newly-regenerated axons. This unique plasticity of Schwann cells has been the target of myelin repair strategies in acute injuries and chronic diseases, such as hereditary demyelinating neuropathies. In one approach, the endogenous regenerative capacity of Schwann cells is enhanced through interventions such as exercise, electrical stimulation or pharmacological means. Alternatively, Schwann cells derived from healthy nerves, or engineered from different tissue sources have been transplanted into the PNS to support remyelination. These transplant approaches can then be further enhanced by exercise and/or electrical stimulation, as well as by the inclusion of biomaterial engineered to support glial cell viability and neurite extension. Advances in our basic understanding of peripheral nerve biology, as well as biomaterial engineering, will further improve the functional repair of myelinated peripheral nerves.

A meta-analysis of randomized double-blind clinical trials in CMT1A to assess the change from baseline in CMTNS and ONLS scales after one year of treatment

CMT1A is the most common inherited peripheral neuropathy. There is currently no approved treatment. We performed a meta-analysis including four randomized, double-blind, Placebo-controlled clinical trials to assess the disease progression after one year under Placebo, Ascorbic Acid (AA) or PXT3003, a combination of three repurposed drugs. We observed a weak deterioration in patients under Placebo, well below the reported natural disease progression. Patients treated with AA were stable after one year but not significantly different from Placebo. Patients undergoing PXT3003 treatment showed an improvement in CMTNS and ONLS, statistically significant versus Placebo and potentially precursory of a meaningful change in the disease course.

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.

A brief review of recent Charcot-Marie-Tooth research and priorities

This brief review of current research progress on Charcot-Marie-Tooth (CMT) disease is a summary of discussions initiated at the Hereditary Neuropathy Foundation (HNF) scientific advisory board meeting on November 7, 2014. It covers recent published and unpublished in vitro and in vivo research. We discuss recent promising preclinical work for CMT1A, the development of new biomarkers, the characterization of different animal models, and the analysis of the frequency of gene mutations in patients with CMT. We also describe how progress in related fields may benefit CMT therapeutic development, including the potential of gene therapy and stem cell research. We also discuss the potential to assess and improve the quality of life of CMT patients. This summary of CMT research identifies some of the gaps which may have an impact on upcoming clinical trials. We provide some priorities for CMT research and areas which HNF can support. The goal of this review is to inform the scientific community about ongoing research and to avoid unnecessary overlap, while also highlighting areas ripe for further investigation. The general collaborative approach we have taken may be useful for other rare neurological diseases.

An exploratory randomised double-blind and placebo-controlled phase 2 study of a combination of baclofen, naltrexone and sorbitol (PXT3003) in patients with Charcot-Marie-Tooth disease type 1A

Background

Charcot-Marie-Tooth type 1A disease (CMT1A) is a rare orphan inherited neuropathy caused by an autosomal dominant duplication of a gene encoding for the structural myelin protein PMP22, which induces abnormal Schwann cell differentiation and dysmyelination, eventually leading to axonal suffering then loss and muscle wasting. We favour the idea that diseases can be more efficiently treated when targeting multiple disease-relevant pathways. In CMT1A patients, we therefore tested the potential of PXT3003, a low-dose combination of three already approved compounds (baclofen, naltrexone and sorbitol). Our study conceptually builds on preclinical experiments highlighting a pleiotropic mechanism of action that includes downregulation of PMP22. The primary objective was to assess safety and tolerability of PXT3003. The secondary objective aimed at an exploratory analysis of efficacy of PXT3003 in CMT1A, to be used for designing next clinical development stages (Phase 2b/3).

Methods

80 adult patients with mild-to-moderate CMT1A received in double-blind for 1 year Placebo or one of the three increasing doses of PXT3003 tested, in four equal groups. Safety and tolerability were assessed with the incidence of related adverse events. Efficacy was assessed using the Charcot-Marie-Tooth Neuropathy Score (CMTNS) and the Overall Neuropathy Limitations Scale (ONLS) as main endpoints, as well as various clinical and electrophysiological outcomes.

Results

This trial confirmed the safety and tolerability of PXT3003. The highest dose (HD) showed consistent evidence of improvement beyond stabilization. CMTNS and ONLS, with a significant improvement of respectively of 8% (0.4% - 16.2%) and 12.1% (2% - 23.2%) in the HD group versus the pool of all other groups, appear to be the most sensitive clinical endpoints to treatment despite their quasi-stability over one year under Placebo. Patients who did not deteriorate over one year were significantly more frequent in the HD group.

Conclusions

These results confirm that PXT3003 deserves further investigation in adults and could greatly benefit CMT1A-diagnosed children, usually less affected than adults.

Trial registration

EudraCT Number: 2010-023097-40. ClinicalTrials.gov Identifier: NCT01401257. The Committee for Orphan Medicinal Products issued in February 2014 a positive opinion on the application for orphan designation for PXT3003 (EMA/OD/193/13).

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-014-0199-0) contains supplementary material, which is available to authorized users.

Collaboration for rare disease drug discovery research

Rare disease research has reached a tipping point, with the confluence of scientific and technologic developments that if appropriately harnessed, could lead to key breakthroughs and treatments for this set of devastating disorders. Industry-wide trends have revealed that the traditional drug discovery research and development (R&D) model is no longer viable, and drug companies are evolving their approach. Rather than only pursue blockbuster therapeutics for heterogeneous, common diseases, drug companies have increasingly begun to shift their focus to rare diseases. In academia, advances in genetics analyses and disease mechanisms have allowed scientific understanding to mature, but the lack of funding and translational capability severely limits the rare disease research that leads to clinical trials. Simultaneously, there is a movement towards increased research collaboration, more data sharing, and heightened engagement and active involvement by patients, advocates, and foundations. The growth in networks and social networking tools presents an opportunity to help reach other patients but also find researchers and build collaborations. The growth of collaborative software that can enable researchers to share their data could also enable rare disease patients and foundations to manage their portfolio of funded projects for developing new therapeutics and suggest drug repurposing opportunities. Still there are many thousands of diseases without treatments and with only fragmented research efforts. We will describe some recent progress in several rare diseases used as examples and propose how collaborations could be facilitated. We propose that the development of a center of excellence that integrates and shares informatics resources for rare diseases sponsored by all of the stakeholders would help foster these initiatives.

The diadenosine homodinucleotide P18 improves in vitro myelination in experimental Charcot-Marie-Tooth type 1A

Charcot-Marie-Tooth 1A (CMT1A) is a demyelinating hereditary neuropathy whose pathogenetic mechanisms are still poorly defined and an etiologic treatment is not yet available. An abnormally high intracellular Ca(2+) concentration ([Ca(2+)]i) occurs in Schwann cells from CMT1A rats (CMT1A SC) and is caused by overexpression of the purinoceptor P2X7. Normalization of the Ca(2+) levels through down-regulation of P2X7 appears to restore the normal phenotype of CMT1A SC in vitro. We recently demonstrated that the diadenosine 5',5'''-P1, P2-diphosphate (Ap2A) isomer P18 behaves as an antagonist of the P2X7 purinergic receptor, effectively blocking channel opening induced by ATP. In addition, P18 behaves as a P2Y11 agonist, inducing cAMP overproduction in P2Y11-overexpressing cells. Here we investigated the in vitro effects of P18 on CMT1A SC. We observed that basal levels of intracellular cAMP ([cAMP]i), a known regulator of SC differentiation and myelination, are significantly lower in CMT1A SC than in wild-type (wt) cells. P18 increased [cAMP]i in both CMT1A and wt SC, and this effects was blunted by NF157, a specific P2Y11 antagonist. Prolonged treatment of organotypic dorsal root ganglia (DRG) cultures with P18 significantly increased expression of myelin protein zero, a marker of myelin production, in both CMT1A and wt cultures. Interestingly, P18 decreased the content of non-phosphorylated neurofilaments, a marker of axonal damage, only in CMT1A DRG cultures. These results suggest that P2X7 antagonists, in combination with [cAMP]i-increasing agents, could represent a therapeutic strategy aimed at correcting the molecular derangements causing the CMT1A phenotype.

Ascorbic acid is a dose-dependent inhibitor of adipocyte differentiation, probably by reducing cAMP pool

Ascorbic acid (AA) is the active component of vitamin C and antioxidant activity was long considered to be the primary molecular mechanism underlying the physiological actions of AA. We recently demonstrated that AA is a competitive inhibitor of adenylate cyclase, acting as a global regulator of intracellular cyclic adenosine monophosphate (cAMP) levels. Our study, therefore, aimed to determine new targets of AA that would account for its potential effect on signal transduction, particularly during cell differentiation. We demonstrated that AA is an inhibitor of pre-adipocyte cell line differentiation, with a dose-dependent effect. Additionally, we describe the impact of AA on the expression of genes involved in adipogenesis and/or the adipocyte phenotype. Moreover, our data suggest that treatment with AA partially reverses lipid accumulation in mature adipocytes. These properties likely reflect the function of AA as a global regulator of the cAMP pool, since an analog of AA without any antioxidant properties elicited the same effect. Additionally, we demonstrated that AA inhibits adipogenesis in OP9 mesenchymal cell line and drives the differentiation of this line toward osteogenesis. Finally, our data suggest that the intracellular transporter SVCT2 is involved in these processes and may act as a receptor for AA.

Charcot-Marie-Tooth disease: an overview of genotypes, phenotypes, and clinical management strategies

Charcot-Marie-Tooth (CMT) disease, which encompasses several hereditary motor and sensory neuropathies, is one of the most common neuromuscular disorders. Our understanding of the molecular genotypes of CMT and the resultant clinical and electrophysiological phenotypes has increased greatly in the past decade. Characterized by electrodiagnostic studies into demyelinating (type 1) and axonal (type 2) forms, subsequent genetic testing often provides an exact diagnosis of a specific subtype of CMT. These advancements have made diagnostic paradigms fairly straightforward. Still, the nature and extent of neuromuscular disability is often complex in persons with CMT, and no curative treatments are yet available. Genotypically homologous animal models of CMT have improved exploration of disease-modifying treatments, of which molecular genetic manipulation and stem cell therapies appear to be the most promising. Research is also needed to develop better rehabilitative strategies that may limit disease burden and improve physical performance and psychosocial integration. Clinical management should be multidisciplinary, including neurologists, physiatrists, neurogeneticists, neuromuscular nurse practitioners, and orthopedists, along with physical and occupational therapists, speech-language pathologists, orthotists, vocational counselors, social workers, and other rehabilitation clinicians. Goals should include maximizing functional independence and quality of life while minimizing disability and secondary morbidity.

Vitamin C Transporters, Recycling and the Bystander Effect in the Nervous System: SVCT2 versus Gluts

Vitamin C is an essential micronutrient in the human diet; its deficiency leads to a number of symptoms and ultimately death. After entry into cells within the central nervous system (CNS) through sodium vitamin C transporters (SVCTs) and facilitative glucose transporters (GLUTs), vitamin C functions as a neuromodulator, enzymatic cofactor, and reactive oxygen species (ROS) scavenger; it also stimulates differentiation. In this review, we will compare the molecular and structural aspects of vitamin C and glucose transporters and their expression in endothelial or choroid plexus cells, which form part of the blood-brain barrier and blood-cerebrospinal fluid (CSF) barrier, respectively. Additionally, we will describe SVCT and GLUT expression in different cells of the brain as well as SVCT2 distribution in tanycytes and astrocytes of the hypothalamic region. Finally, we will describe vitamin C recycling in the brain, which is mediated by a metabolic interaction between astrocytes and neurons, and the role of the "bystander effect" in the recycling mechanism of vitamin C in both normal and pathological conditions.

Ascorbic acid and sodium-dependent vitamin C transporters in the peripheral nervous system: from basic science to clinical trials

SIGNIFICANCE

Ascorbic acid and sodium-dependent vitamin C transporters (SVCT) have been shown to have important functions in the peripheral nervous system (PNS). Ascorbic acid is known to promote myelination in vitro in Schwann cell/dorsal root ganglion co-cultures by the formation of a collagen- and laminin-containing extracellular matrix.

RECENT ADVANCES

Recently, the function of ascorbic acid and SVCT2 in the PNS has been shown in vivo as well. Several studies on ascorbic acid treatment of Charcot-Marie-Tooth neuropathy 1A (CMT1A) have been completed and showed no clinical benefit.

CRITICAL ISSUES

Possible reasons for the failure of ascorbic acid in CMT1A treatment are discussed in this review. More preclinical trials, ideally using different animal models, should be considered before the initiation of clinical trials in humans. More knowledge about ascorbic acid transport kinetics and inter-individual differences in humans is necessary for future studies.

FUTURE DIRECTIONS

Further research into ascorbic acid transport mechanisms in the PNS is warranted. Especially the effects of transgenic or pharmacologic SVCT2 up-regulation on PNS myelination and remyelination will be an interesting area of research in the future. Furthermore, the potential use of ascorbic acid for peripheral neuropathies other than CMT1A would be a possible future research direction.

Multifaceted roles of ultra-rare and rare disease patients/parents in drug discovery

Individual parents and patients are increasingly doing more to fund, discover and develop treatments for rare and ultra-rare diseases that afflict their children, themselves or their friends. They are performing roles in business development that would be classed as entrepreneurial; and their organizational roles in driving the science in some cases are equivalent to those of principal investigators. These roles are in addition to their usual positioning as advocates. Through their efforts and those of the collaborative networks that they have developed, they could be positioned to disrupt the usual course of drug discovery. This can be illustrated using three different ultra-rare disease parent/patient advocate groups and the diseases for which they are developing treatments. This represents an alternative model for pharmaceutical research.

A derivative of ascorbic acid modulates cAMP production

We reported, in previous experiments, that AA is a global regulator of cAMP pools. In this study, we demonstrate that K873, an analog of AA we synthesized and presenting antiproliferative properties, has also an impact on cAMP production. However, K873 has no antioxidant activity, at the contrary of AA. It definitively demonstrates that action of AA on the cAMP production is not linked to antioxidant activity. These data suggest that AA, and derivatives of this molecule, could be promising drug acting on biological processes that are under the control of cAMP dependent pathway.

Ascorbic acid derivatives as a new class of antiproliferative molecules

Ascorbic acid (AA) has long been described as an antiproliferative agent. However, the molecule has to be used at a very high concentrations, which necessitates i.v. injection, and the tight regulation of in-blood and in-cell AA concentrations making it impossible to hold very high concentrations for any substantial length of time. Here we report evidence that AA derivates are antiproliferative and cytotoxic molecules at an IC50 lower than AA itself. Among these new molecules, we selected K873 that has cytotoxic and antiproliferative effects on different human tumor cells at tenth micromolar concentration. In a further step, we demonstrated that K873 selectively to kills only cancer cells without being toxic for normal non-dividing (or poorly dividing) cells. Finally, we tested the effect of treatment with K873 (5-10 mg/kg/d by i.p. route) on tumor progression in xenografted immunodeficient mice (BALB/c Nude). Our data suggest that K873 administration strongly inhibits tumor progression. In a previous study using microarrays, we demonstrated that AA decreases the expression of two genes families involved in cell cycle progression, i.e. initiation factor of translation and tRNA synthetases. Here we show that K873 treatment also decreases the expression of four of these genes in xenografted tumors, in proportions similar to that previously observed with AA. Taken together, our data suggest that AA and K873 share similar action. Our findings suggest that AA derivatives could be a promising new class of anti-cancer drugs, either alone or in combination with other molecules.

Ascorbic acid and a cytostatic inhibitor of glycolysis synergistically induce apoptosis in non-small cell lung cancer cells

Ascorbic acid (AA) exhibits significant anticancer activity at pharmacologic doses achievable by parenteral administration that have minimal effects on normal cells. Thus, AA has potential uses as a chemotherapeutic agent alone or in combination with other therapeutics that specifically target cancer-cell metabolism. We compared the effects of AA and combinations of AA with the glycolysis inhibitor 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3-PO) on the viability of three non-small cell lung cancer (NSCLC) cell lines to the effects on an immortalized lung epithelial cell line. AA concentrations of 0.5 to 5 mM caused a complete loss of viability in all NSCLC lines compared to a <10% loss of viability in the lung epithelial cell line. Combinations of AA and 3-PO synergistically enhanced cell death in all NSCLC cell lines at concentrations well below the IC₅₀ concentrations for each compound alone. A synergistic interaction was not observed in combination treatments of lung epithelial cells and combination treatments that caused a complete loss of viability in NSCLC cells had modest effects on normal lung cell viability and reactive oxygen species (ROS) levels. Combination treatments induced dramatically higher ROS levels compared to treatment with AA and 3-PO alone in NSCLC cells and combination-induced cell death was inhibited by addition of catalase to the medium. Analyses of DNA fragmentation, poly (ADP-ribose) polymerase cleavage, annexin V-binding, and caspase activity demonstrated that AA-induced cell death is caused via the activation of apoptosis and that the combination treatments caused a synergistic induction of apoptosis. These results demonstrate the effectiveness of AA against NSCLC cells and that combinations of AA with 3-PO synergistically induce apoptosis via a ROS-dependent mechanism. These results support further evaluation of pharmacologic concentrations of AA as an adjuvant treatment for NSCLC and that combination of AA with glycolysis inhibitors may be a promising therapy for the treatment of NSCLC.

Dominant Charcot-Marie-Tooth syndrome and cognate disorders

Charcot-Marie-Tooth neuropathy (CMT) is a group of genetically heterogeneous disorders sharing a similar phenotype, characterized by wasting and weakness mainly involving the distal muscles of lower and upper limbs, variably associated with distal sensory loss and skeletal deformities. This chapter deals with dominantly transmitted CMT and related disorders, namely hereditary neuropathy with liability to pressure palsies (HNPP) and hereditary neuralgic amyotrophy (HNA). During the last 20 years, several genes have been uncovered associated with CMT and our understanding of the underlying molecular mechanisms has greatly improved. Consequently, a precise genetic diagnosis is now possible in the majority of cases, thus allowing proper genetic counseling. Although, unfortunately, treatment is still unavailable for all types of CMT, several cellular and animal models have been developed and some compounds have proved effective in these models. The first trials with ascorbic acid in CMT type 1A have been completed and, although negative, are providing relevant information on disease course and on how to prepare for future trials.

Vitamin C and Charcot-Marie-Tooth 1A: Pharmacokinetic considerations

Charcot-Marie-Tooth 1A disease (CMT1A) is a disease for which no drug treatments are available. In 2004, it was reported that ascorbic acid reduced the severity of neuropathy in transgenic mice overexpressing PMP22, an animal model of human CMT1A, compared with untreated mice. Based on those results, clinical trials were undertaken at different centers worldwide and four of them have been completed, but none of them resulted in significant improvements. Based on the pharmacokinetics of ascorbic acid, we propose that the randomized clinical trial carried out thus far confirmed the tight control of ascorbic acid's absorption and proved its tolerability at one and two years. The pharmacokinetic considerations discussed in this article might largely explain the disappointing results of the recent CMT1A trials.

The PMP22 gene and its related diseases

Peripheral myelin protein-22 (PMP22) is primarily expressed in the compact myelin of the peripheral nervous system. Levels of PMP22 have to be tightly regulated since alterations of PMP22 levels by mutations of the PMP22 gene are responsible for >50 % of all patients with inherited peripheral neuropathies, including Charcot-Marie-Tooth type-1A (CMT1A) with trisomy of PMP22, hereditary neuropathy with liability to pressure palsies (HNPP) with heterozygous deletion of PMP22, and CMT1E with point mutations of PMP22. While overexpression and point-mutations of the PMP22 gene may produce gain-of-function phenotypes, deletion of PMP22 results in a loss-of-function phenotype that reveals the normal physiological functions of the PMP22 protein. In this article, we will review the basic genetics, biochemistry and molecular structure of PMP22, followed by discussion of the current understanding of pathogenic mechanisms involving in the inherited neuropathies with mutations in PMP22 gene.

Identification of drug modulators targeting gene-dosage disease CMT1A

The structural integrity of myelin formed by Schwann cells in the peripheral nervous system (PNS) is required for proper nerve conduction and is dependent on adequate expression of myelin genes including peripheral myelin protein 22 (PMP22). Consequently, excess PMP22 resulting from its genetic duplication and overexpression has been directly associated with the peripheral neuropathy called Charcot-Marie-Tooth disease type 1A (CMT1A), the most prevalent type of CMT. Here, in an attempt to identify transcriptional inhibitors with therapeutic value toward CMT1A, we developed a cross-validating pair of orthogonal reporter assays, firefly luciferase (FLuc) and β-lactamase (βLac), capable of recapitulating PMP22 expression, utilizing the intronic regulatory element of the human PMP22 gene. Each compound from a collection of approximately 3,000 approved drugs was tested at multiple titration points to achieve a pharmacological end point in a 1536-well plate quantitative high-throughput screen (qHTS) format. In conjunction with an independent counter-screen for cytotoxicity, the design of our orthogonal screen platform effectively contributed to selection and prioritization of active compounds, among which three drugs (fenretinide, olvanil, and bortezomib) exhibited marked reduction of endogenous Pmp22 mRNA and protein. Overall, the findings of this study provide a strategic approach to assay development for gene-dosage diseases such as CMT1A.

Neural and molecular features on Charcot-Marie-Tooth disease plasticity and therapy

In the peripheral nervous system disorders plasticity is related to changes on the axon and Schwann cell biology, and the synaptic formations and connections, which could be also a focus for therapeutic research. Charcot-Marie-Tooth disease (CMT) represents a large group of inherited peripheral neuropathies that involve mainly both motor and sensory nerves and induce muscular atrophy and weakness. Genetic analysis has identified several pathways and molecular mechanisms involving myelin structure and proper nerve myelination, transcriptional regulation, protein turnover, vesicle trafficking, axonal transport and mitochondrial dynamics. These pathogenic mechanisms affect the continuous signaling and dialogue between the Schwann cell and the axon, having as final result the loss of myelin and nerve maintenance; however, some late onset axonal CMT neuropathies are a consequence of Schwann cell specific changes not affecting myelin. Comprehension of molecular pathways involved in Schwann cell-axonal interactions is likely not only to increase the understanding of nerve biology but also to identify the molecular targets and cell pathways to design novel therapeutic approaches for inherited neuropathies but also for most common peripheral neuropathies. These approaches should improve the plasticity of the synaptic connections at the neuromuscular junction and regenerate cell viability based on improving myelin and axon interaction.

Plasticity of the myelination genomic fabric

This study aimed to quantify the influence of the astrocyte proximity on myelination genomic fabric (MYE) of oligodendrocytes, defined as the most interconnected and stably expressed gene web responsible for myelination. Such quantitation is important to evaluate whether astrocyte signaling may contribute to demyelination when impaired and remyelination when properly restored. For this, we compared changes in the gene expression profiles of immortalized precursor oligodendrocytes (Oli-neu), stimulated to differentiate by the proximity of nontouching astrocytes or treatment with db-cAMP. In a previous paper, we reported that the astrocyte proximity upregulated or turned-on a large number of myelination genes and substantially enriched the Ca(2+)-signaling and cytokine receptor regulatory networks of MYE in Oli-neu cells. Here, we introduce the "transcriptomic distance" to evaluate fabric remodeling and "pair-wise relevance" to identify the most influential gene pairs. Together with the prominence gene analysis used to select and rank the fabric genes, these novel analytical tools provide a comprehensively quantitative view of the physio/pathological transformations of the transcriptomic programs of myelinating cells. Applied to our data, the analyses revealed not only that the astrocyte neighborhood is a substantially more powerful regulator of myelination than the differentiating treatment but also the molecular mechanisms of the two differentiating paradigms are different. By inducing a profound remodeling of MYE and regulatory transcriptomic networks, the astrocyte-oligodendrocyte intercommunication may be considered as a major player in both pathophysiology and therapy of neurodegenerative diseases related to myelination.

Ascorbic Acid and gene expression: another example of regulation of gene expression by small molecules?

Ascorbic acid (vitamin C, AA) has long been considered a food supplement necessary for life and for preventing scurvy. However, it has been reported that other small molecules such as retinoic acid (vitamin A) and different forms of calciferol (vitamin D) are directly involved in regulating the expression of numerous genes. These molecules bind to receptors that are differentially expressed in the embryo and are therefore crucial signalling molecules in vertebrate development. The question is: is ascorbic acid also a signalling molecule that regulates gene expression?

We therefore present and discuss recent publications that demonstrate that AA regulates the expression of a battery of genes. We offer a clue to understanding the biochemical mechanism by which AA regulates gene expression. Finally we will discuss the question of a receptor for AA and its potential involvement in embryonic development and cell differentiation.

Ascorbic acid in Charcot-Marie-Tooth disease type 1A (CMT-TRIAAL and CMT-TRAUK): a double-blind randomised trial

BACKGROUND

Ascorbic acid reduced the severity of neuropathy in transgenic mice overexpressing peripheral myelin protein 22 (PMP22), a model of Charcot-Marie-Tooth disease type 1A (CMT1A) associated with the PMP22 duplication. However, in three 1-year trials, ascorbic acid had no benefit in human beings. We did a multicentre 2-year trial to test the efficacy and tolerability of ascorbic acid in patients with CMT1A.

METHODS

Adult patients (aged 18-70 years) with symptomatic CMT1A were enrolled from nine centres in Italy and the UK, and were randomly assigned (1:1 ratio) to receive 1·5 g/day oral ascorbic acid or matching placebo for 24 months. The randomisation sequence was computer generated by block randomisation, stratified by centre and disease severity, and patients were allocated to treatment by telephone. The primary outcome was change in the CMT neuropathy score (CMTNS) at 24 months. Secondary outcomes were timed 10 m walk test, nine-hole peg test, overall neuropathy limitations scale, distal maximal voluntary isometric contraction, visual analogue scales for pain and fatigue, 36-item short-form questionnaire, and electrophysiological measurements. Patients, treating physicians, and physicians assessing outcome measures were masked to treatment allocation. Analysis of the primary outcome was done on all randomised patients who received at least one dose of study drug. This study is registered, numbers ISRCTN61074476 (CMT-TRAUK) and EudraCT 2006-000032-27 (CMT-TRIAAL).

FINDINGS

We enrolled and randomly assigned 277 patients, of whom six (four assigned to receive ascorbic acid) withdrew consent before receiving treatment; 138 receiving ascorbic acid and 133 receiving placebo were eligible for analysis. Treatment was well tolerated: 241 of 271 patients (89% in each group) completed the study; 20 patients (nine receiving ascorbic acid) dropped out because of adverse events. Mean CMTNS at baseline with missing data imputed was 14·7 (SD 4·8) in the ascorbic acid group and 13·9 (4·2) in the placebo group. Mean worsening of CMTNS was 0·2 (SD 2·8, 95% CI -0·3 to 0·7) in the ascorbic acid group and 0·2 (2·7, -0·2 to 0·7) in the placebo group (mean difference 0·0, 95% CI -0·6 to 0·7; p=0·93). We recorded no differences between the groups for the secondary outcomes at 24 months. 21 serious adverse events occurred in 20 patients, eight in the ascorbic acid group and 13 in the placebo group.

INTERPRETATION

Ascorbic acid supplementation had no significant effect on neuropathy compared with placebo after 2 years, suggesting that no evidence is available to support treatment with ascorbic acid in adults with CMT1A.

FUNDING

Telethon-UILDM and AIFA (Italian Medicines Agency) for CMT-TRIAAL, and Muscular Dystrophy Campaign for CMT-TRAUK.

Regulation of the PMP22 gene through an intronic enhancer

Successful myelination of the peripheral nervous system depends upon induction of major protein components of myelin, such as peripheral myelin protein 22 (PMP22). Myelin stability is also sensitive to levels of PMP22, as a 1.4 Mb duplication on human chromosome 17, resulting in three copies of PMP22, is the most common cause of the peripheral neuropathy Charcot-Marie-Tooth disease. The transcription factor Egr2/Krox20 is required for induction of high level expression of Pmp22 in Schwann cells but its activation elements have not yet been determined. Using chromatin immunoprecipitation analysis of the rat Pmp22 locus, we found a major peak of Egr2 binding within the large intron of the Pmp22 gene. Analysis of a 250 bp region within the largest intron showed that it is strongly activated by Egr2 expression in reporter assays. Moreover, this region contains conserved binding sites not only for Egr2 but also for Sox10, which is also required for Schwann cell development. Our analysis shows that Sox10 is required for optimal activity of the intronic site as well as PMP22 expression. Finally, mouse transgenic analysis revealed tissue-specific expression of this intronic sequence in peripheral nerve. Overall, these data show that Egr2 and Sox10 activity are directly involved in mediating the developmental induction of Pmp22 expression.

TrkB and TrkC agonist antibodies improve function, electrophysiologic and pathologic features in Trembler J mice

Neurotrophic factors have been considered as potential therapeutics for peripheral neuropathies. Previously, we showed that neurotrophin-3 (NT-3) promotes nerve regeneration in Trembler(J) (Tr(J)) mice and in sural nerves from patients with Charcot-Marie-Tooth 1A (CMT1A). The relatively short plasma half-life of NT-3 and other neurotrophins, however, pose a practical difficulty in their clinical application. Therapeutic agonist antibodies (AAb) targeting the neurotrophic receptors may circumvent this obstacle due to their high specificity and long half-life. Using morphological, electrophysiological studies and functional motor testing, we assessed the efficacy of monoclonal TrkC AAb and TrkB AAb in the Tr(J) mice. Treatments of these AAbs individually or in combination over 20 weeks increased compound muscle action potential (CMAP) amplitude, which correlated with improved grip strength, as compared to the PBS control group. Improvements in CMAP amplitude were most prominent with TrkC AAb treatment. In all treatment groups, distal to the crush site of the sciatic nerves exhibited a significantly greater number of myelinated fibers (MFs) indicating improved regenerative response to injury. In the contralateral intact sciatic nerves, the number of MFs as well as the myelin thickness was also increased significantly by the AAb treatments, suggesting that the hypomyelination/amyelination state of the peripheral nerves in Tr(J) improved. Therapeutic response to AAb combination was often, albeit not always, the most prominent, indicating a non-redundant effect of TrkB and TrkC AAbs. An early functional recovery and the correlative morphological changes of enhanced regeneration were seen with TrkC AAb treatment. These results provide evidence for potential therapeutic use of monoclonal agonist antibodies for neurotrophin receptors in CMT1A and other neuropathies.

Signals to promote myelin formation and repair

The myelin sheath wraps large axons in both the CNS and the PNS, and is a key determinant of efficient axonal function and health. Myelin is targeted in a series of diseases, notably multiple sclerosis (MS). In MS, demyelination is associated with progressive axonal damage, which determines the level of patient disability. The few treatments that are available for combating myelin damage in MS and related disorders, which largely comprise anti-inflammatory drugs, only show limited efficacy in subsets of patients. More-effective treatment of myelin disorders will probably be accomplished by early intervention with combinatorial therapies that target inflammation and other processes-for example, signaling pathways that promote remyelination. Indeed, evidence suggests that such pathways might be impaired in pathology and, hence, contribute to the failure of remyelination in such diseases. In this article, we review the molecular basis of signaling pathways that regulate myelination in the CNS and PNS, with a focus on signals that affect differentiation of myelinating glia. We also discuss factors such as extracellular molecules that act as modulators of these pathways. Finally, we consider the few preclinical and clinical trials of agents that augment this signaling.

Sodium-dependent vitamin C transporter 2 (SVCT2) is necessary for the uptake of L-ascorbic acid into Schwann cells

Ascorbic acid has been shown to be an essential component for in vitro myelination and to improve the clinical and pathological phenotype of a mouse model of Charcot-Marie-tooth disease 1A. The mechanism of ascorbic acid uptake into peripheral nerves, however, has not been addressed so far. Hence, we studied the expression and activity of sodium-dependent vitamin C transporters 1 and 2 (SVCT1 and 2) in the peripheral nervous system. Using immunohistochemistry, immunoblotting, and reverse transcription PCR, we could show that SVCT1 and 2 were differentially expressed in myelinated peripheral nerve fibers and Schwann cell (SC) cultures. SVCT1 was expressed at very low levels confined to the axons, whereas SVCT2 was highly expressed both in the axons and in the SCs. SVCT2 was localized particularly in SC compartments of uncompacted myelin. Uptake assays using (14)C-labeled ascorbic acid showed transport of ascorbic acid into SC cultures. Ascorbic acid transport was dependent on the concentration of sodium, magnesium, and calcium in the extracellular medium. Treatment with the flavonoid phloretin, a known inhibitor of SVCT1 and 2, and specific RNA interference with SVCT2 caused significant reductions in ascorbic acid uptake into SCs. Phloretin-inhibited uptake of ascorbic acid was further shown in freshly dissected, cell-culture-naïve rat sciatic nerves. These results provide evidence for the first time that uptake of ascorbic acid in the peripheral nervous system is crucially dependent on the expression and activity of SVCT2.

Lack of evidence for a pathogenic role of T-lymphocytes in an animal model for Charcot-Marie-Tooth disease 1A

We have previously shown that in two distinct models for inherited neuropathies of the Charcot-Marie-Tooth (CMT) type, T-lymphocytes are critically involved in demyelination. In the present study, we tested whether T-lymphocytes have a similar pathogenetic impact in another CMT model, i.e., in mice overexpressing the peripheral myelin protein (PMP)-22, representing the most prevalent form CMT1A. By cross breeding the myelin mutant mice with mutants lacking mature T- and B-lymphocytes (RAG-1-deficient mice), the pathological alterations were not changed in comparison to PMP22 mutants with a normal immune system. Reciprocal enhancement of lymphocyte activation, by inactivation of the lymphocytic co-inhibitor programmed death-1, also did not alter pathological changes, as opposed to models with approved lymphocytic involvement. These findings strongly suggest that lymphocytes are not pathogenetically relevant in this model for CMT1A. We suggest that - in contrast to myelin phagocytosing macrophages - T-lymphocytes are not a promising target for treatment of CMT1A.

Rare structural variants in schizophrenia: one disorder, multiple mutations; one mutation, multiple disorders

Recent studies have established an important role for rare genomic deletions and duplications in the etiology of schizophrenia. This research suggests that the genetic architecture of neuropsychiatric disorders includes a constellation of rare mutations in many different genes. Mutations that confer substantial risk for schizophrenia have been identified at several loci, most of which have also been implicated in other neurodevelopmental disorders, including autism. Genetic heterogeneity is a characteristic of schizophrenia; conversely, phenotypic heterogeneity is a characteristic of all schizophrenia-associated mutations. Both kinds of heterogeneity probably reflect the complexity of neurodevelopment. Research strategies must account for both genetic and clinical heterogeneity to identify the genes and pathways crucial for the development of neuropsychiatric disorders.