Sodium-dependent Vitamin C transporter 2 deficiency impairs myelination and remyelination after injury: Roles of collagen and demethylation.

Peripheral nerve myelination involves rapid production of tightly bound lipid layers requiring cholesterol biosynthesis and myelin protein expression, but also a collagen-containing extracellular matrix providing mechanical stability. In previous studies, we showed a function of ascorbic acid in peripheral nerve myelination and extracellular matrix formation in adult mice. Here, we sought the mechanism of action of ascorbic acid in peripheral nerve myelination using different paradigms of myelination in vivo and in vitro. We found impaired myelination and reduced collagen expression in Sodium-dependent Vitamin C Transporter 2 heterozygous mice (SVCT2+/- ) during peripheral nerve development and after peripheral nerve injury. In dorsal root ganglion (DRG) explant cultures, hypo-myelination could be rescued by precoating with different collagen types. The activity of the ascorbic acid-dependent demethylating Ten-eleven-translocation (Tet) enzymes was reduced in ascorbic acid deprived and SVCT2+/- DRG cultures. Further, in ascorbic acid-deprived DRG cultures, methylation of a CpG island in the collagen alpha1 (IV) and alpha2 (IV) bidirectional promoter region was increased compared to wild-type and ascorbic acid treated controls. Taken together, these results provide further evidence for the function of ascorbic acid in myelination and extracellular matrix formation in peripheral nerves and suggest a putative molecular mechanism of ascorbic acid function in Tet-dependent demethylation of collagen promoters.

The Gdap1 knockout mouse mechanistically links redox control to Charcot-Marie-Tooth disease.

The ganglioside-induced differentiation-associated protein 1 (GDAP1) is a mitochondrial fission factor and mutations in GDAP1 cause Charcot-Marie-Tooth disease. We found that Gdap1 knockout mice (Gdap1(-/-)), mimicking genetic alterations of patients suffering from severe forms of Charcot-Marie-Tooth disease, develop an age-related, hypomyelinating peripheral neuropathy. Ablation of Gdap1 expression in Schwann cells recapitulates this phenotype. Additionally, intra-axonal mitochondria of peripheral neurons are larger in Gdap1(-/-) mice and mitochondrial transport is impaired in cultured sensory neurons of Gdap1(-/-) mice compared with controls. These changes in mitochondrial morphology and dynamics also influence mitochondrial biogenesis. We demonstrate that mitochondrial DNA biogenesis and content is increased in the peripheral nervous system but not in the central nervous system of Gdap1(-/-) mice compared with control littermates. In search for a molecular mechanism we turned to the paralogue of GDAP1, GDAP1L1, which is mainly expressed in the unaffected central nervous system. GDAP1L1 responds to elevated levels of oxidized glutathione by translocating from the cytosol to mitochondria, where it inserts into the mitochondrial outer membrane. This translocation is necessary to substitute for loss of GDAP1 expression. Accordingly, more GDAP1L1 was associated with mitochondria in the spinal cord of aged Gdap1(-/-) mice compared with controls. Our findings demonstrate that Charcot-Marie-Tooth disease caused by mutations in GDAP1 leads to mild, persistent oxidative stress in the peripheral nervous system, which can be compensated by GDAP1L1 in the unaffected central nervous system. We conclude that members of the GDAP1 family are responsive and protective against stress associated with increased levels of oxidized glutathione.

Mutations in SEPT9 cause hereditary neuralgic amyotrophy.

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant recurrent neuropathy affecting the brachial plexus. HNA is triggered by environmental factors such as infection or parturition. We report three mutations in the gene septin 9 (SEPT9) in six families with HNA linked to chromosome 17q25. HNA is the first monogenetic disease caused by mutations in a gene of the septin family. Septins are implicated in formation of the cytoskeleton, cell division and tumorigenesis.

Autosomal-dominant striatal degeneration is caused by a mutation in the phosphodiesterase 8B gene.

Autosomal-dominant striatal degeneration (ADSD) is an autosomal-dominant movement disorder affecting the striatal part of the basal ganglia. ADSD is characterized by bradykinesia, dysarthria, and muscle rigidity. These symptoms resemble idiopathic Parkinson disease, but tremor is not present. Using genetic linkage analysis, we have mapped the causative genetic defect to a 3.25 megabase candidate region on chromosome 5q13.3-q14.1. A maximum LOD score of 4.1 (Theta = 0) was obtained at marker D5S1962. Here we show that ADSD is caused by a complex frameshift mutation (c.94G>C+c.95delT) in the phosphodiesterase 8B (PDE8B) gene, which results in a loss of enzymatic phosphodiesterase activity. We found that PDE8B is highly expressed in the brain, especially in the putamen, which is affected by ADSD. PDE8B degrades cyclic AMP, a second messenger implied in dopamine signaling. Dopamine is one of the main neurotransmitters involved in movement control and is deficient in Parkinson disease. We believe that the functional analysis of PDE8B will help to further elucidate the pathomechanism of ADSD as well as contribute to a better understanding of movement disorders.

Sodium-dependent vitamin C transporter 2 deficiency causes hypomyelination and extracellular matrix defects in the peripheral nervous system.

Ascorbic acid (vitamin C) is necessary for myelination of Schwann cell/neuron cocultures and has shown beneficial effects in the treatment of a Charcot-Marie-Tooth neuropathy 1A (CMT1A) mouse model. Although clinical studies revealed that ascorbic acid treatment had no impact on CMT1A, it is assumed to have an important function in peripheral nerve myelination and possibly in remyelination. However, the transport pathway of ascorbic acid into peripheral nerves and the mechanism of ascorbic acid function in peripheral nerves in vivo remained unclear. In this study, we used sodium-dependent vitamin C transporter 2-heterozygous (SVCT2(+/-)) mice to elucidate the functions of SVCT2 and ascorbic acid in the murine peripheral nervous system. SVCT2 and ascorbic acid levels were reduced in SVCT2(+/-) peripheral nerves. Morphometry of sciatic nerve fibers revealed a decrease in myelin thickness and an increase in G-ratios in SVCT2(+/-) mice. Nerve conduction velocities and sensorimotor performance in functional tests were reduced in SVCT2(+/-) mice. To investigate the mechanism of ascorbic acid function, we studied the expression of collagens in the extracellular matrix of peripheral nerves. Here, we show that expression of various collagen types was reduced in sciatic nerves of SVCT2(+/-) mice. We found that collagen gene transcription was reduced in SVCT2(+/-) mice but hydroxyproline levels were not, indicating that collagen formation was regulated on the transcriptional and not the posttranslational level. These results help to clarify the transport pathway and mechanism of action of ascorbic acid in the peripheral nervous system and may lead to novel therapeutic approaches to peripheral neuropathies by manipulation of SVCT2 function.

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.

Bex1 is involved in the regeneration of axons after injury.

Successful axonal regeneration is a complex process determined by both axonal environment and endogenous neural capability of the regenerating axons in the central and the peripheral nervous systems. Numerous external inhibitory factors inhibit axonal regeneration after injury. In response, neurons express various regeneration-associated genes to overcome this inhibition and increase the intrinsic growth capacity. In the present study, we show that the brain-expressed X-linked (Bex1) protein was over-expressed as a result of peripheral axonal damage. Bex1 antagonized the axon outgrowth inhibitory effect of myelin-associated glycoprotein. The involvement of Bex1 in axon regeneration was further confirmed in vivo. We have demonstrated that Bex1 knock-out mice showed lower capability for regeneration after peripheral nerve injury than wild-type animals. Wild-type mice could recover from sciatic nerve injury much faster than Bex1 knock-out mice. Our findings suggest that Bex1 could be considered as regeneration-associated gene.

Varying survival of motoneurons and activation of distinct molecular mechanism in response to altered peripheral myelin protein 22 gene dosage.

Alteration in the expression level of peripheral myelin protein 22 (PMP22) is the most frequent cause for demyelinating neuropathies of Charcot-Marie-Tooth type. Here, we demonstrate a loss of motoneurons (MNs) in the spinal cords from transgenic mice over-expressing Pmp22 (Pmp22(tg)) while mice lacking Pmp22 [Pmp22(ko); knockout (ko)] exhibited normal MN numbers at the symptomatic age of 60 days. In order to describe the molecular changes in affected MNs, these cells were isolated from lumbar spinal cords by laser-capture microdissection. Remarkably, the MNs of the Pmp22(ko) and Pmp22(tg) mice showed different expression profiles because of the altered Pmp22 expression. The changes in the expression profile of MNs from Pmp22(ko) mice resemble those described in MNs from mice after nerve injury and included genes that had been described in neuronal growth and regeneration like Gap43 and Sprr11a. The changes detected in the expression pattern of MNs from Pmp22(tg) mice exhibited fewer similarities to other expression patterns. The specific expression pattern in the MNs of the Pmp22(ko) mice might contribute to the better survival of the MNs. Our study also revealed induction of genes like brain-expressed X-linked 1 (Bex1) and desmoplakin (Dsp) that had recently been found up-regulated in MNs of human amyotrophic lateral sclerosis patients.

Inhibition of N-cadherin and beta-catenin function reduces axon-induced Schwann cell proliferation.

N-cadherin and beta-catenin are involved in cell adhesion and cell cycle in tumor cells and neural crest. Both are expressed at key stages of Schwann cell (SC) development, but little is known about their function in the SC lineage. We studied the role of these molecules in adult rat derived SC-embryonic dorsal root ganglion cocultures by using low-Ca(2+) conditions and specific blocking antibodies to interfere with N-cadherin function and by using small interfering RNA (siRNA) to decrease beta-catenin expression in both SC-neuron cocultures and adult rat-derived SC monocultures. N-cadherin blocking conditions decreased SC-axon association and reduced axon-induced SC proliferation. In SC monocultures, beta-catenin reduction diminished the proliferative response of SCs to the mitogen beta1-heregulin, and, in SC-DRG cocultures, beta-catenin reduction inhibited axon-contact-dependent SC proliferation. Stimulation of SC cultures with beta1-heregulin increased total beta-catenin protein amount, phosphorylation of GSK-3beta and beta-catenin presence in nuclear extracts. In conclusion, our findings suggest a previously unrecognized contribution of beta-catenin and N-cadherin to axon-induced SC proliferation.

Oncostatin M induces growth arrest by inhibition of Skp2, Cks1, and cyclin A expression and induced p21 expression.

Oncostatin M has been characterized as a potent growth inhibitor for various tumor cells. Oncostatin M-treated glioblastoma cells cease proliferation and instigate astrocytal differentiation. The oncostatin M-induced cell cycle arrest in G(1) phase is characterized by increased level of the cyclin-dependent kinase (CDK) inhibitory proteins p21(Cip1/Waf1/Sdi1) and p27(Kip1). Induction of p21 protein corresponds to increased mRNA level, whereas p27 accumulates due to increased stability of the protein. Interestingly, stabilization of p27(Kip1) occurs even in S phase, showing that p27 stabilization is a direct consequence of oncostatin M signaling and not a result of the cell cycle arrest. Degradation of p27 in late G(1) and S phase is initiated by the ubiquitin ligase complex SCF-Skp2/Cks1. Oncostatin M inhibits expression of two components of this E3 ligase complex (Skp2 and Cks1). Although combined overexpression of Skp2 and Cks1 rescues p27 degradation in S phase, it can not override p27 accumulation in G(1) phase and cell cycle arrest by oncostatin M. In addition to increasing Cdk inhibitor level, oncostatin M also impairs cyclin A expression. Cyclin A mRNA and protein level decline shortly after oncostatin M addition. The accumulation of two CDK inhibitor proteins and the repression of cyclin A expression may explain the broad and potent antiproliferative effect of the cytokine.

Idiopathic Hypersomnia Patients Revealed Longer Circadian Period Length in Peripheral Skin Fibroblasts.

The vast majority of living organisms have evolved a circadian rhythm of roughly 24 h in adaptation to ever-changing environmental conditions, such as the cycle of light and darkness. In some sleep disorders like idiopathic hypersomnia (IH) this adaptation is defective. As the etiology of this disease is largely unknown, we examined the in vitro circadian period length of patients suffering from IH. The patients were diagnosed according to the ICSD3-criteria by clinical history, polysomnography (PSG), and multiple sleep latency testing (MSLT). In order to gain insight into the molecular mechanism of this sleep disorder we collected fibroblasts from skin biopsies of IH patients and healthy subjects. We determined the circadian period length of the primary fibroblast cells by lentiviral infection with a construct expressing a luciferase gene under the control of a BMAL1 promoter. The group of IH patients revealed on average a prolonged circadian period length. In comparison to the group of healthy controls (HC) the mean period length was estimated to be 0.82 h (95%-CI 0.44-1.20 h) longer in the patient group. This finding further stresses a disturbed regulation of the circadian rhythm in IH patients as part of the pathophysiology of this complex and poorly understood primary sleep disorder.

Delineating an oncostatin M-activated STAT3 signaling pathway that coordinates the expression of genes involved in cell cycle regulation and extracellular matrix deposition of MCF-7 cells.

A number of studies have demonstrated that the STAT pathway is an important signaling cascade utilized by the IL-6 cytokine family to regulate a variety of cell functions. However, the downstream target genes of STAT activation that mediate the cytokine-induced cellular responses are largely uncharacterized. The aims of the current study are to determine whether the STAT signaling pathway is critically involved in the oncostatin M (OM)-induced growth inhibition and morphological changes of MCF-7 cells and to identify STAT3-target genes that are utilized by OM to regulate cell growth and morphology. We show that expression of a dominant negative (DN) mutant of STAT3 in MCF-7 cells completely eliminated the antiproliferative activity of OM, whereas expression of DN STAT1 had no effect. The growth inhibition of breast cancer cells was achieved through a concerted action of OM on cell cycle components. We have identified four cell cycle regulators including c-myc, cyclin D1, c/EBPdelta, and p53 as downstream effectors of the OM-activated STAT3 signaling cascade. The expression of these genes is differentially regulated by OM in MCF-7 cells, but is unaffected by OM in MCF-7-dnStat3 stable clones. We also demonstrate that the OM-induced morphological changes are correlated with increased cell motility in a STAT3-dependent manner. Expression analysis of extracellular matrix (ECM) proteins leads to the identification of fibronectin as a novel OM-regulated ECM component. Our studies further reveal that STAT3 plays a key role in the robust induction of fibronectin expression by OM in MCF-7 and T47D cells. These new findings provide a molecular basis for the mechanistic understanding of the effects of OM on cell growth and migration.

High-throughput analysis of genome-wide receptor tyrosine kinase expression in human cancers identifies potential novel drug targets.

Novel high-throughput analyses in molecular biology allow sensitive and rapid identification of disease-related genes and drug targets. We have used quantitative real-time reverse transcription-PCR reactions (n = 23000) to analyze expression of all human receptor tyrosine kinases (n = 56) in malignant tumors (n = 313) of different origins and normal control samples (n = 58). The different tumor types expressed very different numbers of receptor tyrosine kinases: whereas brain tumors and testicular cancer expressed 50 receptor tyrosine kinases, acute myeloid leukemia (AML) samples expressed only 20 different ones. Specimens of similar tumor origin exhibited characteristic receptor tyrosine kinase expression patterns and were grouped together in hierarchical cluster analyses. When we focused on specific tumor entities, receptor tyrosine kinases were identified that were disease and/or stage specific. Leukemic blasts from AML bone marrow samples differed significantly in receptor tyrosine kinase expression compared with normal bone marrow and purified CD34+ cells. Among the differentially expressed receptor tyrosine kinases, we found FLT3, c-kit, CSF1 receptor, EPHB6, leukocyte tyrosine kinase, and ptk7 to be highly overexpressed in AML samples. Whereas expression changes of some of these were associated with altered differentiation patterns (e.g., CSF1 receptor), others, such as FLT3, were genuinely overexpressed in leukemic blasts. These data and the associated database (http://medweb.uni-muenster.de/institute/meda/research/) provide a comprehensive view of receptor tyrosine kinase expression in human cancer. This information can assist in the definition of novel drug targets.

Altered dynamics in the circadian oscillation of clock genes in dermal fibroblasts of patients suffering from idiopathic hypersomnia.

From single cell organisms to the most complex life forms, the 24-hour circadian rhythm is important for numerous aspects of physiology and behavior such as daily periodic fluctuations in body temperature and sleep-wake cycles. Influenced by environmental cues - mainly by light input -, the central pacemaker in the thalamic suprachiasmatic nuclei (SCN) controls and regulates the internal clock mechanisms which are present in peripheral tissues. In order to correlate modifications in the molecular mechanisms of circadian rhythm with the pathophysiology of idiopathic hypersomnia, this study aimed to investigate the dynamics of the expression of circadian clock genes in dermal fibroblasts of idiopathic hypersomniacs (IH) in comparison to those of healthy controls (HC). Ten clinically and polysomnographically proven IH patients were recruited from the department of sleep medicine of the University Hospital of Muenster. Clinical diagnosis was done by two consecutive polysomnographies (PSG) and Multiple Sleep Latency Test (MSLT). Fourteen clinical healthy volunteers served as control group. Dermal fibroblasts were obtained via punch biopsy and grown in cell culture. The expression of circadian clock genes was investigated by semiquantitative Reverse Transcriptase-PCR qRT-PCR analysis, confirming periodical oscillation of expression of the core circadian clock genes BMAL1, PER1/2 and CRY1/2. The amplitude of the rhythmically expressed BMAL1, PER1 and PER2 was significantly dampened in dermal fibroblasts of IH compared to HC over two circadian periods whereas the overall expression of only the key transcriptional factor BMAL1 was significantly reduced in IH. Our study suggests for the first time an aberrant dynamics in the circadian clock in IH. These findings may serve to better understand some clinical features of the pathophysiology in sleep - wake rhythms in IH.

HSJ1-related hereditary neuropathies: novel mutations and extended clinical spectrum.

OBJECTIVES: To determine the nature and frequency of HSJ1 mutations in patients with hereditary motor and hereditary motor and sensory neuropathies. METHODS: Patients were screened for mutations by genome-wide or targeted linkage and homozygosity studies, whole-exome sequencing, and Sanger sequencing. RNA and protein studies of skin fibroblasts were used for functional characterization. RESULTS: We describe 2 additional mutations in the HSJ1 gene in a cohort of 90 patients with autosomal recessive distal hereditary motor neuropathy (dHMN) and Charcot-Marie-Tooth disease type 2 (CMT2). One family with a dHMN phenotype showed the homozygous splice-site mutation c.229+1G>A, which leads to retention of intron 4 in the HSJ1 messenger RNA with a premature stop codon and loss of protein expression. Another family, presenting with a CMT2 phenotype, carried the homozygous missense mutation c.14A>G (p.Tyr5Cys). This mutation was classified as likely disease-related by several automatic algorithms for prediction of possible impact of an amino acid substitution on the structure and function of proteins. Both mutations cosegregated with autosomal recessive inheritance of the disease and were absent from the general population. CONCLUSIONS: Taken together, in our cohort of 90 probands, we confirm that HSJ1 mutations are a rare but detectable cause of autosomal recessive dHMN and CMT2. We provide clinical and functional information on an HSJ1 splice-site mutation and report the detailed phenotype of 2 patients with CMT2, broadening the phenotypic spectrum of HSJ1-related neuropathies.

Alterations of lymphoid enhancer factor-1 isoform expression in solid tumors and acute leukemias.

Two major transcripts of lymphoid enhancer factor-1 (LEF-1) have been described. The long isoform with b-catenin binding domain functions as a transcriptional enhancer factor. The short isoform derives from an intronic promoter and exhibits dominant negative activity. Recently, alterations of LEF-1 isoforms distribution have been described in colon cancer. In the current study we employed a quantitative real-time reverse transcription PCR method (TaqMan) to analyze expression of LEF-1 isoforms in a large cohort of human tumor (n = 304) and tumor-free control samples (n = 56). The highest expression level of LEF-1 was found in carcinoma samples whereas brain cancer samples expressed little. Expression of LEF-1 was different in distinct cancer types. For example, the mRNA level of LEF-1 was lower in testicular tumor samples compared with tumor-free control samples. Besides epithelial cancers, significant LEF-1 expression was also found in hematopoietic cells. In hematological malignancies, overall LEF-1 level was higher in lymphocytic leukemias compared with myeloid leukemias and normal hematopoiesis. However, acute myeloid leukemia and acute lymphocytic leukemia showed a significantly increased fraction of the oncogenic LEF-1 compared with chronic lymphocytic leukemia and chronic myeloid leukemia. Taken together, these data suggest that LEF-1 is abundantly expressed in human tumors and the ratio of the oncogenic and the dominant negative short isoform altered not only in carcinomas but also in leukemia.

Inhibition of EGF-mediated receptor activity and cell proliferation by HK1-ceramide, a stable analog of the ganglioside GM3-lactone.

Gangliosides have been described as modulators of growth factor receptor activity and subsequent cellular function. Due to the lower-pH environment found in tumor cells, ganglosides are thought to be formed (at least to some extent) into their lactone forms. The aim of the study was to analyze the mode of action of the lactone of the ganglioside GM3 on epidermal growth factor (EGF) signaling in human ovarial epidermoid carcinoma A431 cells and cell growth in human oral epidermoid carcinoma KB cells by applying the GM3 lactone analog HK1-ceramide 2, which is stable under hydrolytic conditions. Specific inhibition of EGF-dependent receptor tyrosine phosphorylation was observed by HK1-ceramide 2 at 25 microM, whereas GM3 showed a comparable inhibition at eightfold higher concentrations. In cells exposed to low pH, where GM3 is thought to form its lactone to a higher extent, addition of GM3 showed no further inhibitory effect on EGF-dependent receptor phosphorylation. Similarly to GM3, HK1-ceramide 2 does not affect binding of (125)I-EGF to the cell surface receptor. EGF-dependent growth of KB cells was also found to be inhibited by HK1-ceramide 2 at much lower concentrations compared to GM3. In conclusion, our results indicate that the GM3 lactone analog HK1-ceramide 2 is a specific inhibitor of EGF receptor function and is more potent in reducing EGF-dependent tyrosine phosphorylation of the receptor in A431 cells and in inhibiting EGF-dependent growth of KB cells compared to GM3.

E-cadherin controls adherens junctions in the epidermis and the renewal of hair follicles.

E-cadherin is thought to mediate intercellular adhesion in the mammalian epidermis and in hair follicles as the adhesive component of adherens junctions. We have tested this role of E-cadherin directly by conditional gene ablation in the mouse. We show that postnatal loss of E-cadherin in keratinocytes leads to a loss of adherens junctions and altered epidermal differentiation without accompanying signs of inflammation. Overall tissue integrity and desmosomal structures were maintained, but skin hair follicles were progressively lost. Tumors were not observed and beta-catenin levels were not strongly altered in the mutant skin. We conclude that E-cadherin is required for maintaining the adhesive properties of adherens junctions in keratinocytes and proper skin differentiation. Furthermore, continuous hair follicle cycling is dependent on E-cadherin.