Oxidative stress in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is the most common form of muscular dystrophy affecting adults. The genetic basis of DM1 consists of a mutational expansion of a repetitive trinucleotide sequence (CTG). The number of triplets expansion divides patients in four categories related to the molecular changes (E1, E2, E3, E4). The pathogenic mechanisms of multi-systemic involvement of DM1 are still unclear. DM1 has been suspected to be due to premature aging, that is known to be sustained by increased free radicals levels and/or decreased antioxidants activities in neurodegenerative disorders. Recently, the gain-of-function at RNA level hypothesis has gained great attention, but oxidative stress might act in the disease progression. We have investigated 36 DM1 patients belonging to 22 unrelated families, 10 patients with other myotonic disorders (OMD) and 22 age-matched healthy controls from the clinical, biochemical and molecular point of view. Biochemical analysis detected blood levels of superoxide dismutase (SOD), malonilaldehyde (MDA), vitamin E (Vit E), hydroxyl radicals (OH) and total antioxidant system (TAS). Results revealed that DM1 patients showed significantly higher levels of SOD (+40%; MAL (+57%; RAD 2 (+106%; and TAS (+20%; than normal controls. Our data support the hypothesis of a pathogenic role of oxidative stress in DM1 and therefore confirm the detrimental role played by free radicals in this pathology and suggest the opportunity to undertake clinical trials with antioxidants in this disorder.     

Oxidative stress in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is the most common form of muscular dystrophy affecting adults. The genetic basis of DM1 consists of a mutational expansion of a repetitive trinucleotide sequence (CTG). The number of triplets expansion divides patients in four categories related to the molecular changes (E1, E2, E3, E4). The pathogenic mechanisms of multi-systemic involvement of DM1 are still unclear. DM1 has been suspected to be due to premature aging, that is known to be sustained by increased free radicals levels and/or decreased antioxidants activities in neurodegenerative disorders. Recently, the gain-of-function at RNA level hypothesis has gained great attention, but oxidative stress might act in the disease progression. We have investigated 36 DM1 patients belonging to 22 unrelated families, 10 patients with other myotonic disorders (OMD) and 22 age-matched healthy controls from the clinical, biochemical and molecular point of view. Biochemical analysis detected blood levels of superoxide dismutase (SOD), malonilaldehyde (MDA), vitamin E (Vit E), hydroxyl radicals (OH) and total antioxidant system (TAS). Results revealed that DM1 patients showed significantly higher levels of SOD (+40%; MAL (+57%; RAD 2 (+106%; and TAS (+20%; than normal controls. Our data support the hypothesis of a pathogenic role of oxidative stress in DM1 and therefore confirm the detrimental role played by free radicals in this pathology and suggest the opportunity to undertake clinical trials with antioxidants in this disorder.     

Imbalanced oxidant and antioxidant ratio in myotonic dystrophy type 1

Abstract

Myotonic dystrophy type 1 (DM1) is the most common form of muscular dystrophy affecting adults and is due to trinucleotide sequence (CTG) in the 3′ UTR region of DMPK gene located at 19q13.3 chromosome. The pathogenic mechanisms of multisystemic involvement of DM1 are still unclear. The increased levels of reactive oxygen species/free radicals and lipid peroxides and decreased antioxidant levels play an important role in the pathogenesis of DM1. Present study includes 20 DM1 patients and 40 age- and sex-matched controls. Malonilaldehyde (MDA), superoxide dismutase (SOD), glutathione peroxidise (GPX), glutathione-S-transferase (GST), reduced glutathione (GSH), and TAS levels were measured and its association with clinical phenotype were evaluated. Results revealed significantly higher levels of MDA (p = 0.002), SOD (p = 0.006), and TAS p = 0.004) and lower level of GPX (p = 0.003), GST (P < 0.001) and GSH (P = 0.016) in DM1 patients. A significant negative correlation of MDA level with dyspepsia and CK-MB and GST level with serum SCK, CK-MB, and diabetes were observed. However, a significant positive correlation of SOD level with serum CK-MB, CK-MM, and diabetes and negative correlation with facial weakness were noted. Though, GSH level had significant positive correlation with learning and writing disability, speech, and languages disability yet found negative correlation with duration of disease. The GPX and TAS showed no correlation with any clinical findings. Our data further support the pathogenic role of oxidative stress in DM1 of Indian origin and support the opportunity to undertake clinical trials with antioxidants in this disorder.     

The hallmarks of myotonic dystrophy type 1 muscle dysfunction

Myotonic dystrophy type 1 (DM1) is the most prevalent form of muscular dystrophy in adults and yet there are currently no treatment options. Although this disease causes multisystemic symptoms, it is mainly characterised by myopathy or diseased muscles, which includes muscle weakness, atrophy, and myotonia, severely affecting the lives of patients worldwide. On a molecular level, DM1 is caused by an expansion of CTG repeats in the 3′ untranslated region (3′UTR) of the DM1 Protein Kinase (DMPK) gene which become pathogenic when transcribed into RNA forming ribonuclear foci comprised of auto complementary CUG hairpin structures that can bind proteins. This leads to the sequestration of the muscleblind-like (MBNL) family of proteins, depleting them, and the abnormal stabilisation of CUGBP Elav-like family member 1 (CELF1), enhancing it. Traditionally, DM1 research has focused on this RNA toxicity and how it alters MBNL and CELF1 functions as key splicing regulators. However, other proteins are affected by the toxic DMPK RNA and there is strong evidence that supports various signalling cascades playing an important role in DM1 pathogenesis. Specifically, the impairment of protein kinase B (AKT) signalling in DM1 increases autophagy, apoptosis, and ubiquitin–proteasome activity, which may also be affected in DM1 by AMP-activated protein kinase (AMPK) downregulation. AKT also regulates CELF1 directly, by affecting its subcellular localisation, and indirectly as it inhibits glycogen synthase kinase 3 beta (GSK3β), which stabilises the repressive form of CELF1 in DM1. Another kinase that contributes to CELF1 mis-regulation, in this case by hyperphosphorylation, is protein kinase C (PKC). Additionally, it has been demonstrated that fibroblast growth factor-inducible 14 (Fn14) is induced in DM1 and is associated with downstream signalling through the nuclear factor κB (NFκB) pathways, associating inflammation with this disease. Furthermore, MBNL1 and CELF1 play a role in cytoplasmic processes involved in DM1 myopathy, altering proteostasis and sarcomere structure. Finally, there are many other elements that could contribute to the muscular phenotype in DM1 such as alterations to satellite cells, non-coding RNA metabolism, calcium dysregulation, and repeat-associated non-ATG (RAN) translation. This review aims to organise the currently dispersed knowledge on the different pathways affected in DM1 and discusses the unexplored connections that could potentially help in providing new therapeutic targets in DM1 research.     

Altered tracheal smooth muscle activities in an animal model of human myotonic dystrophy.

Although the 20,25 Diazacholesterol-treated rat exhibits several pathological changes involving skeletal muscle and other tissues resembling those seen in human myotonic dystrophy patients, this animal has not hitherto been examined as a model for studying smooth muscle involvement in this human disease. Rats were therefore treated chronically with 20, 25-D and comparisons made with control animals of dose-response curves of tracheal strip preparations to carbamylcholine, before and after partial irreversible blockade of cholinergic receptors by Dibenamine. Tracheas from myotonic animals exhibited diminished contractility and an increased ED₅₀. The dissociation constant for the carbamylcholine-cholinergic receptor interaction was decreased and the percentage receptor occupancy for a given contractile response was increased. These results indicate that tracheal smooth muscle function is altered after 20,25-D administration and suggest that such animals may constitute a model for studying smooth muscle function in human myotonic dystrophy.     

Does quantitative EMG differ myotonic dystrophy type 2 and type 1?

Genetic testing is considered the only reliable diagnostic approach in myotonic dystrophy. However it has recently been reported that a considerable number of patients with genetically proven types of the disease have unusual phenotypic presentation. The aim of our study was to evaluate motor unit reorganization reflected by various electrophysiological abnormalities in myotonic dystrophies and to compare findings between type 1 (DM 1) and type 2 myotonic dystrophy (DM2). Quantitative electromyography (EMG) recordings in 63 patients (33 with DM1 and 30 with DM2) from the biceps brachii (BB), rectus femoris (RF), first dorsal interosseus (FDI), and tibialis anterior (TA) muscles were analyzed. Mean amplitude and size index (SI) of motor unit potentials recorded in TA and RF muscles, mean potential duration in TA, and mean SI and the number of outliers with amplitude above the normal range in BB were significantly increased in DM2 as compared to DM1. Myotonic discharges were recorded more frequently in DM1 than in DM2. EMG findings significantly differ between DM1 and DM2. The presence of high amplitude potentials in lower limb muscles in DM2 patients, atypical for myogenic muscle lesions, could be explained by muscle fiber hypertrophy observed in muscle biopsies.     

IL-1 activates two separate signal transduction pathways in T helper type II cells

We have investigated the signal transduction pathways mediated by IL-1 in the Th 2 cell line D10.A, and we have made the following findings. Interaction of IL-1 with its receptor leads to the translocation of protein kinase C (PKC) from the cytosol to the membrane, phosphorylation of the 80-kDa protein that is substrate for PKC, as well as an increase in the level of cAMP. In addition, IL-1 induced IL-5 mRNA expression in these cells. We have established that the IL-5 gene is activated in D10.A cells in response to either phorbol esters or 8-Br cAMP, and that the two agents act as cofactors. IL-1 is able to synergize with phorbol esters and is additive with 8-Br cAMP for IL-5 mRNA expression. There are two possibilities to explain these results: 1) D10.A cells express two types of functional IL-1R, each linked to an independent signal transduction pathway; or 2) these cells have only one kind of IL-1R which, upon ligand interaction, mediates the activation of both the PKC and the adenylate cyclase pathway.     

Mechanisms regulating Raf-1 activity in signal transduction pathways

Raf-1 is a key protein involved in the transmission of developmental and proliferative signals generated by receptor and nonreceptor tyrosine kinases. Biochemical and genetic studies have demonstrated that Raf-1 functions downstream of activated tyrosine kinases and Ras and upstream of mitogen-activated protein kinase (MAPK) and MAPK kinase (MKK or MEK) in many signaling pathways. A major objective of our laboratory has been to determine how Raf-1 becomes activated in response to signaling events. Using mammalian, baculovirus, and Xenopus systems, we have examined the roles that phosphorylation and protein-protein interactions play in regulating the biological and biochemical activity of Raf-1. Our studies have provided evidence that the activity of Raf-1 can be modulated by both Ras-dependent and Ras-independent pathways. Recently, we reported that Arg89 of Raf-1 is a residue required for the association of Raf-1 and Ras. Mutation of this residue disrupted interaction with Ras and prevented Ras-mediated, but not protein kinase C-or tyrosine kinase-mediated, enzymatic activation of Raf-1 in the baculovirus expression system. Further analysis of this mutant demonstrated that kinase-defective Raf-1 proteins interfere with the propagation of proliferative and developmental signals by binding to Ras and blocking Ras function. Our findings have also shown that phosphorylation events play a role in regulating Raf-1. We have identified sites of in vivo phosphorylation that positively and negatively alter the biological and enzymatic activity of Raf-1. In addition, we have found that some of these phosphorylation sites are involved in mediating the interaction of Raf-1 with potential activators (Fyn and Src) and with other cellular proteins (14-3-3). Results from our work suggest that Raf-1 is regulated at multiple levels by several distinct mechanisms. © 1995 wiley-Liss, Inc.     

Mutant human embryonic stem cells reveal neurite and synapse formation defects in type 1 myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is a multisystem disorder affecting a variety of organs, including the central nervous system. By using neuronal progeny derived from human embryonic stem cells carrying the causal DM1 mutation, we have identified an early developmental defect in genes involved in neurite formation and the establishment of neuromuscular connections. Differential gene expression profiling and quantitative RT-PCR revealed decreased expression of two members of the SLITRK family in DM1 neural cells and in DM1 brain biopsies. In addition, DM1 motoneuron/muscle cell cocultures showed alterations that are consistent with the known role of SLITRK genes in neurite outgrowth, neuritogenesis, and synaptogenesis. Rescue and knockdown experiments suggested that the functional defects can be directly attributed to SLITRK misexpression. These neuropathological mechanisms may be clinically significant for the functional changes in neuromuscular connections associated with DM1.     

Redox imbalance in peripheral blood of type 1 myotonic dystrophy patients

Objectives: The aim of our study was to determine if redox imbalance caused by the activities of antioxidant enzymes existed in erythrocytes of type 1 myotonic dystrophy (DM1) patients.

Methods: The activities of erythrocyte superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase were measured in 30 DM1 patients and 15 healthy controls (HCs). The obtained values were correlated with the Muscular Impairment Rating Scale (MIRS) score and creatine kinase (CK).

Results: Superoxide dismutase and catalase activities were lower in DM1 patients compared to HCs. A positive correlation was found between disease duration and MIRS score as well as with glutathione reductase activity. In DM1 patients, there were positive correlations between catalase, glutathione peroxidase, and glutathione reductase activities. After sub-dividing DM1 patients according to CK levels, superoxide dismutase activity was still statistically different from HCs. However, catalase activity was significantly lower only in DM1 patients with increased CK.

Discussion: Undesirable alterations in antioxidant enzyme activities during DM1 disease progression may result in conditions favoring oxidative stress and changes in metabolism which together could contribute to muscle wasting.     

Deregulated microRNAs in myotonic dystrophy type 2

Myotonic Dystrophy Type-2 (DM2) is an autosomal dominant disease caused by the expansion of a CCTG tetraplet repeat. It is a multisystemic disorder, affecting skeletal muscles, the heart, the eye, the central nervous system and the endocrine system. Since microRNA (miRNA) expression is disrupted in Myotonic Dystrophy Type-1 and many other myopathies, miRNAs deregulation was studied in skeletal muscle biopsies of 13 DM2 patients and 13 controls. Eleven miRNAs were deregulated: 9 displayed higher levels compared to controls (miR-34a-5p, miR-34b-3p, miR-34c-5p, miR-146b-5p, miR-208a, miR-221-3p and miR-381), while 4 were decreased (miR-125b-5p, miR-193a-3p, miR-193b-3p and miR-378a-3p). To explore the relevance of DM2 miRNA deregulation, the predicted interactions between miRNA and mRNA were investigated. Global gene expression was analyzed in DM2 and controls and bioinformatic analysis identified more than 1,000 miRNA/mRNA interactions. Pathway and function analysis highlighted the involvement of the miRNA-deregulated mRNAs in multiple aspects of DM2 pathophysiology. In conclusion, the observed miRNA dysregulations may contribute to DM2 pathogenetic mechanisms.     

Rin1 regulates insulin receptor signal transduction pathways

Rin1 is a multifunctional protein containing several domains, including Ras binding and Rab5 GEF domains. The role of Rin1 in insulin receptor internalization and signaling was examined by expressing Rin1 and deletion mutants in cells utilizing a retrovirus system. Here, we show that insulin-receptor-mediated endocystosis and fluid phase insulin-stimulated endocytosis are enhanced in cells expressing the Rin1:wild type and the Rin1:C deletion mutant, which contain both the Rab5-GEF and GTP-bound Ras binding domains. However, the Rin1:N deletion mutant, which contains both the SH2 and proline-rich domains, blocked insulin-stimulated receptor-mediated and insulin-stimulated fluid phase endocytosis. In addition, the expression of Rin1:delta (429-490), a natural occurring splice variant, also blocked both receptor-mediated and fluid phase endocystosis. Furthermore, association of the Rin1 SH2 domain with the insulin receptor was dependent on tyrosine phosphorylation of the insulin receptor. Morphological analysis indicates that Rin1 co-localizes with insulin receptor both at the cell surface and in endosomes upon insulin stimulation. Interestingly, the expression of Rin1:wild type and both deletion mutants blocks the activation of Erk1/2 and Akt1 kinase activities without affecting either JN or p38 kinase activities. DNA synthesis and Elk-1 activation are also altered by the expression of Rin1:wild type and the Rin1:C deletion mutant. In contrast, the expression of Rin1:delta stimulates both Erk1/2 and Akt1 activation, DNA synthesis and Elk-1 activation. These results demonstrate that Rin1 plays an important role in both insulin receptor membrane trafficking and signaling.     

Two-component signal transduction pathways in Arabidopsis

The two-component system, consisting of a histidine (His) protein kinase that senses a signal input and a response regulator that mediates the output, is an ancient and evolutionarily conserved signaling mechanism in prokaryotes and eukaryotes. The identification of 54 His protein kinases, His-containing phosphotransfer proteins, response regulators, and related proteins in Arabidopsis suggests an important role of two-component phosphorelay in plant signal transduction. Recent studies indicate that two-component elements are involved in plant hormone, stress, and light signaling. In this review, we present a genome analysis of the Arabidopsis two-component elements and summarize the major advances in our understanding of Arabidopsis two-component signaling.     

MicroRNA与肿瘤相关的信号转导通路

信号转导通路在细胞代谢、生长、增殖、应激、发育和凋亡等生命活动中具有极为重要的作用。干扰这些通路将可能影响细胞的正常发育, 甚至导致肿瘤。MicroRNA(miRNA)是近年来在真核生物中发现的、在转录后水平负调节基因表达的一类长度约22个核苷酸的非编码小RNA, 其靶基因数目众多, 生物学功能广泛。在多种肿瘤中发现了miRNA的异常表达, 提示后者与肿瘤发生有关, 可能机制为调控癌基因或肿瘤抑制基因的表达。此外亦发现miRNA的靶基因有许多作用于肿瘤相关的信号转导通路。miRNA在肿瘤发生过程中的重要调控功能预示其将成为人类癌症诊断和治疗方面的新星。     

Wound signal transduction pathways in plants

A significant advancement in our knowledge and understanding of wound-signaling pathways in plants has been made recently. Essential role in the explanation of these processes came from the genetic screens and analysis of mutants which are defective in either jasmonic acid (JA) biosynthesis, JA perception or systemin function. Plants equally react to wound in the tissues directly damaged (local response) as well as in the non-wounded areas (systemic response). Jasmonides and in particular the most studied JA, produced by the octadecanoid pathway, are responsible for the systemic response. Jasmonides functioning as long-distance signal particles transmit the information about wound to distant, non-wounded tissues where defense response is invoked. Peptyd - systemin, identified in some Solanaceous species, acts locally to the wounded area to elicit the production of JA. Jasmonic acid-dependent and -independent wound signal transduction pathways have been identified and partially characterized. JA-dependent wound signaling pathways are responsible for the activation of systemic responses, whereas JA-independent wound signaling pathways, activated close to wound side, have a role in reparation of damaged tissue and in defense against pathogens.