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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 It covers recent published and unpublished in vitro and in vivo research.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.

Oncogenic transformation of postmitotic neurons triggers cell death, but the identity of genes critical for degeneration remain unclear. The antitumor antibiotic mithramycin prolongs survival of mouse models of Huntington's disease in vivo and inhibits oxidative stress-induced death in cortical neurons in vitro. We had correlated protection by mithramycin with its ability to bind to GC-rich DNA and globally displace Sp1 family transcription factors. To understand how antitumor drugs prevent neurodegeneration, here we use structure-activity relationships of mithramycin analogs to discover that selective DNA-binding inhibition of the drug is necessary for its neuroprotective effect. We identify several genes (Myc, c-Src, Hif1α, and p21(waf1/cip1)) involved in neoplastic transformation, whose altered expression correlates with protective doses of mithramycin or its analogs. Most interestingly, inhibition of one these genes, Myc, is neuroprotective, whereas forced expression of Myc induces Rattus norvegicus neuronal cell death. These results support a model in which cancer cell transformation shares key genetic components with neurodegeneration.

Caused by a polyglutamine expansion in the huntingtin protein, Huntington's disease leads to stnatal degeneration via the transcriptional dysregulation of a number of genes, including those involved in mitochondnal biogenesis. Here we show that transglutaminase 2, which is upregulated in HD, exacerbates transcriptional dysregulation by acting as a selective corepressor of nuclear genes; transglutaminase 2 interacts directly with histone H3 in the nucleus. In a cellular model of HD, transglutaminase inhibition de-repressed two established regulators of mitochondrial function, PGC-l alpha and cytochrome c and reversed susceptibility of human HD cells to the mitochondrial toxin, 3-nitroproprionic acid; however, protection mediated by transglutaminase inhibition was not associated with improved mitochondnal bioenergetics. A gene microarray analysis indicated that transglutaminase inhibition normalized expression of not only mitochondrial genes but also 40% of genes that are dysregulated in HD striatal neurons, including chaperone and histone genes. Moreover, transglutaminase inhibition attenuated degeneration in a Drosophila model of HD and protected mouse HD stnatal neurons from excitotoxicity. Altogether these findings demonstrate that selective TG inhibition broadly corrects transcriptional dysregulation in HD and defines a novel HDAC-independent epigenetic strategy for treating neurodegeneration.

Myostatin, a potent negative regulator of myogenesis, is proteolytically processed by furin proteases into active mature myostatin before secretion from myoblasts. Here, we show that mature myostatin auto-regulates its processing during myogenesis. In a cell culture model of myogenesis, Northern blot analysis revealed no appreciable change in myostatin mRNA levels between proliferating myoblasts and differentiated myotubes. However, Western blot analysis confirmed a relative reduction in myostatin processing and secretion by differentiated myotubes as compared to proliferating myoblasts. Furthermore, in vivo results demonstrate a lower level of myostatin processing during fetal muscle development when compared to postnatal adult muscle. Consequently, high levels of circulatory mature myostatin were detected in postnatal serum, while fetal circulatory myostatin levels were undetectable. Since Furin proteases are important for proteolytically processing members of the TGF-[beta] superfamily, we therefore investigated the ability of myostatin to control the transcription of furin and auto-regulate the extent of its processing. Transfection experiments indicate that mature myostatin indeed regulates furin protease promoter activity. Based on these results, we propose a mechanism whereby myostatin negatively regulates its proteolytic processing during fetal development, ultimately facilitating the differentiation of myoblasts by controlling both furin protease gene expression and subsequent active concentrations of mature myostatin peptide. Keywords: Myostatin; Myogenesis; Processing; Secretion; Furin

In this review the current knowledge about the arginine-degrading enzyme arginase and its unexpected roles in survival and regeneration in the central nervous system will be discussed. Recent data suggest the neuroprotective effects of extracellularly applied arginase can be attributed to an activation of the endoplasmic reticulum stress response with a consequent change of the pro-survival gene expression profile. However, the activation of neural regeneration pathways caused by an upregulation of endogenous arginase I is mediated by polyamines, a group of arginase downstream products with widespread biological effects. In light of these new discoveries, there is heightened interest in the regulation of arginase I gene expression within the central nervous system. A number of transcription factors such as Sp1, C/EBP (CCATT/enhancer-binding protein), and CREB seem to be involved in the transcriptional control of arginase I and may contribute to the complex expression pattern of arginase I in distinct brain regions and during development. Beyond molecular mechanisms, this review will also include relevant clinical findings in patients with neurodegenerative diseases. J. Nutr. 134: 2812S-2817S, 2004. KEY WORDS: * arginase * arginine * neurodegeneration

Histone deacetylase (HDAC) inhibitors have been used to promote neuronal survival and ameliorate neurological dysfunction in a host of neurodegenerative disease models. The precise molecular mechanisms whereby HDAC inhibitors prevent neuronal death are currently the focus of intensive research. Here we demonstrate that HDAC inhibition prevents DNA damage-induced neurodegeneration by modifying the acetylation pattern of the tumor suppressor p53, which decreases its DN A-binding and transcriptional activation of target genes. Specifically, we identify that acetylation at K382 and K381 prevents p53 from associating with the pro-apoptotic PUMA gene promoter, activating transcription, and inducing apoptosis in mouse primary cortical neurons. Paradoxically, acetylation of p53 at the same lysines in various cancer cell lines leads to the induction of PUMA expression and death. Together, our data provide a molecular understanding of the specific outcomes of HDAC inhibition and suggest that strategies aimed at enhancing p53 acetylation at K381 and K382 might be therapeutically viable for capturing the beneficial effects in the CNS, without compromising tumor suppression. [ABSTRACT FROM AUTHOR]

It is becoming increasingly clear that epigenetic modifications are critical factors in the regulation of gene expression. With regard to the nervous system, epigenetic alterations play a role in a diverse set of processes and have been implicated in a variety of disorders. Gaining a more complete understanding of the essential components and underlying mechanisms involved in epigenetic regulation could lead to novel treatments for a number of neurological and psychiatric conditions. [ABSTRACT FROM AUTHOR]

Histone deacetylase (HDAC) inhibitors are currently in human clinical trials as antitumor drugs because of their ability to induce cell dysfunction and death in cancer cells. The toxic effects of HDAC inhibitors are also apparent in cortical neurons in vitro, despite the ability of these agents to induce significant protection in the cells they do not kill. Here we demonstrate that pulse exposure of cortical neurons (2 h) in an in vitro model of oxidative stress results in durable neuroprotection without toxicity. Protection was associated with transcriptional upregulation of the cell cycle inhibitor, p21waf1/cip1, both in this model and in an in vivo model of permanent ischemia. Transgenic overexpression of p21waf1/cip1 in neurons can mimic the protective effect of HDAC inhibitors against oxidative stress-induced toxicity, including death induced by glutathione depletion or peroxide addition. The protective effect of p21waf1/cip1 in the context of oxidative stress appears to be unrelated to its ability to act in the nucleus to inhibit cell cycle progression. However, although p21waf1/cip1 is sufficient for neuroprotection, it is not necessary for HDAC inhibitor neuroprotection, because these agents can completely protect neurons cultured from p21waf1/cip1-null mice. Together these findings demonstrate (1) that pulse inhibition of HDACs in cortical neurons can induce neuroprotection without apparent toxicity; (2) that p21waf1/cip1 is sufficient but not necessary to mimic the protective effects of HDAC inhibition; and (3) that oxidative stress in this model induces neuronal cell death via cell cycle-independent pathways that can be inhibited by a cytosolic, noncanonical action of p21waf1/cip1. [ABSTRACT FROM AUTHOR]

Huntington's disease (HD) is a fully penetrant autosomal-dominant inherited neurological disorder caused by expanded CAG repeats in the Huntingtin gene. Transcriptional dysfunction, excitotoxicity, and oxidative stress have all been proposed to play important roles in the pathogenesis of HD. This study was designed to explore the therapeutic potential of mithramycin, a clinically approved guanosine-cytosine-rich DNA binding antitumor antibiotic. Pharmacological treatment of a transgenic mouse model of HD (R6/2) with mithramycin extended survival by 29.1%, greater than any single agent reported to date. Increased survival was accompanied by improved motor performance and markedly delayed neuropathological sequelae. To identify the functional mechanism for the salubrious effects of mithramycin, we examined transcriptional dysfunction in R6/2 mice. Consistent with transcriptional repression playing a role in the pathogenesis of HD, we found increased methylation of lysine 9 in histone H3, a well established mechanism of gene silencing. Mithramycin treatment prevented the increase in H3 methylation observed in R612 mice, suggesting that the enhanced survival and neuroprotection might be attributable to the alleviation of repressed gene expression vital to neuronal function and survival. Because it is Food and Drug Administration-approved, mithramycin is a promising drug for the treatment of HD. [ABSTRACT FROM AUTHOR]

Histone deacetylase (HDAC) inhibitors are currently in human clinical trials as antitumor drugs because of their ability to induce cell dysfunction and death in cancer cells. The toxic effects of HDAC inhibitors are also apparent in cortical neurons in vitro, despite the ability of these agents to induce significant protection in the cells they do not kill. Here we demonstrate that pulse exposure of cortical neurons (2 h) in an in vitro model of oxidative stress results in durable neuroprotection without toxicity. Protection was associated with transcriptional upregulation of the cell cycle inhibitor, p21(waf1/cip1), both in this model and in an in vivo model of permanent ischemia. Transgenic overexpression of p21(waf1/cip1) in neurons can mimic the protective effect of HDAC inhibitors against oxidative stress-induced toxicity, including death induced by glutathione depletion or peroxide addition. The protective effect of p21(waf1/cip1) in the context of oxidative stress appears to be unrelated to its ability to act in the nucleus to inhibit cell cycle progression. However, although p21(waf1/cip1) is sufficient for neuroprotection, it is not necessary for HDAC inhibitor neuroprotection, because these agents can completely protect neurons cultured from p21(waf1/cip1)-null mice. Together these findings demonstrate (1) that pulse inhibition of HDACs in cortical neurons can induce neuroprotection without apparent toxicity; (2) that p21(waf1/cip1) is sufficient but not necessary to mimic the protective effects of HDAC inhibition; and (3) that oxidative stress in this model induces neuronal cell death via cell cycle-independent pathways that can be inhibited by a cytosolic, noncanonical action of p21(waf1/cip1).

Myostatin, a member of the transforming growth factor-beta superfamily, is a secreted growth factor that is proteolytically processed to give COOH-terminal mature myostatin and NH2-terminal latency-associated peptide in myoblasts. Piedmontese cattle are a heavy-muscled breed that express a mutated form of myostatin in which cysteine (313) is substituted with tyrosine. Here we have characterized the biology of this mutated Piedmontese myostatin. Northern and Western analyses indicate that there is increased expression of myostatin mRNA and precursor myostatin protein in the skeletal muscle of Piedmontese cattle. In contrast, a decrease in mature myostatin was observed in Piedmontese skeletal muscle. However, there is no detectable change in the circulatory levels of mature myostatin in Piedmontese cattle. Myoblast proliferation assay performed with normal and Piedmontese myostatin indicated that mature wild-type myostatin protein inhibited the proliferation of C2C12 myoblasts. Piedmontese myostatin, by contrast, failed to inhibit myoblast proliferation. In addition, when added in molar excess, Piedmontese myostatin acted as a potent "competitive inhibitor" molecule. These results indicate that, in Piedmontese myostatin, substitution of cysteine with tyrosine results in the distortion of the "cystine knot" structure and a loss of biological activity of the myostatin. This mutation also appears to affect either processing or stability of mature myostatin without altering the secretion of myostatin.