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Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are autosomal dominant neuromuscular diseases caused by microsatellite expansions and belong to the family of RNA dominant disorders. Availability of cellular models in which the DM mutation is expressed within its natural context is essential to facilitate efforts to identify new therapeutic compounds. Here we generated immortalized DM1 and DM2 human muscle cell lines that display nuclear RNA-aggregates of expanded repeats, a hallmark of myotonic dystrophy. Selected clones of DM1 and DM2 immortalized myoblasts behave as parental primary myoblasts with a reduced fusion capacity of immortalized DM1 myoblasts when compared to control and DM2 cells. Alternative splicing defects were observed in differentiated DM1 but not in DM2 muscle cell lines. Splicing alterations did not result from differentiation delay because similar changes were found in immortalized DM1 transdifferentiated fibroblasts in which the myogenic differentiation has been forced by MyoD overexpression. As a proof-of-concept, we showed that antisense approaches alleviate disease-associated defects and a RNA-seq analysis confirmed that the vast majority of misspliced events in immortalized DM1 muscle cells were affected by antisense treatment, with half of them significantly rescued in treated DM1 cells. In summary, immortalized DM1 muscle cell lines display characteristic disease-associated molecular features such as nuclear RNA-aggregates and splicing defects that can be used as robust readouts for the screening of therapeutic compounds. Therefore, immortalized DM1 and DM2 muscle cell lines represent new models and tools to investigate molecular pathophysiologic mechanisms and evaluate in vitro effects of compounds on RNA toxicity associated with myotonic dystrophy mutations.

Cardiac complications such as electrical abnormalities including conduction delays and arrhythmias are the main cause of death in individuals with Myotonic Dystrophy type 1 (DM1). We developed a disease model using iPSC-derived cardiomyocytes (iPSC-CMs) from a healthy individual and two DM1 patients with different CTG repeats lengths and clinical history (DM1-1300 and DM1-300). We confirmed the presence of toxic RNA foci and mis-spliced MBNL1/2 transcripts in DM1 iPSC-CMs. In DM1-1300, we identified a switch in the cardiac sodium channel SCN5A from the adult to the neonatal isoform. The down-regulation of adult SCN5A isoforms is consistent with a shift in the sodium current activation to depolarized potentials observed in DM1-1300. L-type calcium current density was higher in iPSC-CMs from DM1-1300, which is correlated with the overexpression of the Ca V 1.2 transcript and proteins. Importantly, I Na and I CaL dysfunctions resulted in prolonged action potentials duration, slower velocities, and decreased overshoots. Optical mapping analysis revealed a slower conduction velocity in DM1-1300 iPSC-CM monolayers. In conclusion, our data revealed two distinct ions channels perturbations in DM1 iPSC-CM from the patient with cardiac dysfunction, one affecting Na + channels and one affecting Ca 2+ channels. Both have an impact on cardiac APs and ultimately on heart conduction.

Secreted protein, acidic and rich in cysteine (SPARC) is differentially associated with cell proliferation and extracellular matrix (ECM) assembly. We show here the effect of exogenous SPARC inhibition/induction on ECM and mitochondrial proteins expression and on the differentiation of C2C12 cells. The cells were cultured in growth medium (GM) supplemented with different experimental conditions. The differentiation of myoblasts was studied for 5 days, the expressions of ECM and mitochondrial proteins were measured and the formation of the myotubes was quantified after exogenous induction/inhibition of SPARC. The results indicate that the addition of recombinant SPARC protein (rSPARC) in cell culture medium increased the differentiation of C2C12 myoblasts and myogenin expression during the myotube formation. However, the treatment with antibody specific for SPARC (anti-SPARC) prevented the differentiation and decreased myogenin expression. The induction of SPARC in the proliferating and differentiating C2C12 cells increased collagen 1a1 protein expression, whereas the inhibition decreased it. The effects on fibronectin protein expression were opposite. Furthermore, the addition of rSPARC in C2C12 myoblast increased the expression of mitochondrial proteins, ubiquinol-cytochrome c reductase core protein II (UQCRC2) and succinate dehydrogenase iron-sulfur subunit (SDHB), whereas the anti-SPARC decreased them. During the differentiation, only the anti-SPARC had the effects on mitochondrial proteins, NADH dehydrogenase ubiquinone 1 beta subcomplex subunit 8 (NADHB8), SDHB and cytochrome c oxidase 1 (MTCO1). Thus, SPARC plays a crucial role in the proliferation and differentiation of C2C12 and may be involved in the link between the ECM remodeling and mitochondrial function.

Myotonic dystrophy type 1 and type 2 (DM1, DM2) are caused by expansions of CTG and CCTG repeats, respectively. RNAs containing expanded CUG or CCUG repeats interfere with the metabolism of other RNAs through titration of the Muscleblind-like (MBNL) RNA binding proteins. DM2 follows a more favorable clinical course than DM1, suggesting that specific modifiers may modulate DM severity. Here, we report that the rbFOX1 RNA binding protein binds to expanded CCUG RNA repeats, but not to expanded CUG RNA repeats. Interestingly, rbFOX1 competes with MBNL1 for binding to CCUG expanded repeats and overexpression of rbFOX1 partly releases MBNL1 from sequestration within CCUG RNA foci in DM2 muscle cells. Furthermore, expression of rbFOX1 corrects alternative splicing alterations and rescues muscle atrophy, climbing and flying defects caused by expression of expanded CCUG repeats in a Drosophila model of DM2. Myotonic dystrophy (DM) type 2 is a neuromuscular pathology caused by large expansions of CCTG repeats. Here the authors find that rbFOX1 RNA binding protein binds to CCUG RNA repeats and competes with MBNL1 for the binding to CCUG repeats, releasing MBNL1 from sequestration in DM2 muscle cells.

Myotonic dystrophy type 1 (DM1) is the most frequent muscular dystrophy in adult. The aim of this study was to investigate the natural history of skeletal muscle weakness in adults, in a cross-sectional, retrospective study. In a cohort of 204 adult DM1 patients, we quantified muscle impairment, handgrip force and physical disability. Muscle strength was similarly affected in the legs and in the arms, the right and left side, and distally more than proximally in patients. The earliest and the most affected skeletal muscles were the digit flexors, foot dorsiflexors and neck flexors; whereas the elbow and knee extensors and flexors were the least affected muscle groups. The rate of decline of the muscle strength was −0.111 units/year. The handgrip values were lower in DM1 patients than the normative values and the rate of decline in handgrip force per year was −0.24 kg. Limitation in mobility or walking is observed in 84 % of DM1 patients but requirement of wheelchair is infrequent (3 %). The decrease in muscle strength, handgrip force and the increase in physical disability were highly correlated with duration of the disease and the number of CTG repeats in the blood. Significant association was found between decline in muscle strength and the age at onset, physical disability and the age of patients at evaluation, handgrip force and gender. Decline in muscle weakness is very slow and although limitation when walking is a common manifestation of DM1 in patients, the requirement of wheelchair is infrequent.

Background: The migraine-specific monoclonal antibody Erenumab targeting the calcitonin gene related peptide receptor is an effective and well tolerated preventive treatment of episodic and chronic migraine. However, its price limits its use as a first line therapy against migraine. Therefore, identifying patients who will adequately respond to such treatment is paramount. Methods: In this retrospective, real-life cohort study, 172 adult patients with refractory episodic or chronic migraine treated with Erenumab were included. To identify the predictors of response to Erenumab, bivariate subgroup analysis of several potential factors was performed, and multivariate logistic regression modeling was done to obtain Odds Ratio (OR). Results: Of the 172 patients, 57.0% achieved a successful treatment response (reduction of monthly migraine days by ≥50%). Statistically significant predictors of a treatment response were the presence of chronic migraine, tension-type headache, and a positive response to triptan with an odd ratio of 0.473 (95% CI, 0.235–0.952), 0.485 (95% CI, 0.245–0.962) and 3.985 (95% CI, 1.811–8.770), respectively (P < 0.05). Conclusions: Successful Erenumab treatment response rate was 57.0% in this retrospective cohort. As chronic migraine and tension-type headache were negative predictors of Erenumab response while triptan response was a positive predictor, this data suggests the potential for Erenumab monotherapy without the need for traditional preventive treatment in refractory migraine sufferers improving side effect profile and treatment adherence for a cohort of patients difficult to treat.

Myotonic dystrophy type 1 (DM1) is caused by an unstable CTG repeat expansion in the 3'UTR of the DM protein kinase (DMPK) gene. DMPK transcripts carrying CUG expansions form nuclear foci and affect splicing regulation of various RNA transcripts. Furthermore, bidirectional transcription over the DMPK gene and non-conventional RNA translation of repeated transcripts have been described in DM1. It is clear now that this disease may involve multiple pathogenic pathways including changes in gene expression, RNA stability and splicing regulation, protein translation, and micro-RNA metabolism. We previously generated transgenic mice with 45-kb of the DM1 locus and >300 CTG repeats (DM300 mice). After successive breeding and a high level of CTG repeat instability, we obtained transgenic mice carrying >1,000 CTG (DMSXL mice). Here we described for the first time the expression pattern of the DMPK sense transcripts in DMSXL and human tissues. Interestingly, we also demonstrate that DMPK antisense transcripts are expressed in various DMSXL and human tissues, and that both sense and antisense transcripts accumulate in independent nuclear foci that do not co-localize together. Molecular features of DM1-associated RNA toxicity in DMSXL mice (such as foci accumulation and mild missplicing), were associated with high mortality, growth retardation, and muscle defects (abnormal histopathology, reduced muscle strength, and lower motor performances). We have found that lower levels of IGFBP-3 may contribute to DMSXL growth retardation, while increased proteasome activity may affect muscle function. These data demonstrate that the human DM1 locus carrying very large expansions induced a variety of molecular and physiological defects in transgenic mice, reflecting DM1 to a certain extent. As a result, DMSXL mice provide an animal tool to decipher various aspects of the disease mechanisms. In addition, these mice can be used to test the preclinical impact of systemic therapeutic strategies on molecular and physiological phenotypes.

With the goal of identifying splicing alterations in myotonic dystrophy 1 (DM1) tissues that may yield insights into targets or mechanisms, we have surveyed mis-splicing events in three systems using a RT-PCR screening and validation platform. First, a transgenic mouse model expressing CUG-repeats identified splicing alterations shared with other mouse models of DM1. Second, using cell cultures from human embryonic muscle, we noted that DM1-associated splicing alterations were significantly enriched in cytoskeleton (e.g. SORBS1, TACC2, TTN, ACTN1 and DMD) and channel (e.g. KCND3 and TRPM4) genes. Third, of the splicing alterations occurring in adult DM1 tissues, one produced a dominant negative variant of the splicing regulator RBFOX1. Notably, half of the splicing events controlled by MBNL1 were co-regulated by RBFOX1, and several events in this category were mis-spliced in DM1 tissues. Our results suggest that reduced RBFOX1 activity in DM1 tissues may amplify several of the splicing alterations caused by the deficiency in MBNL1.

Myotonic dystrophy type 1 (DM1), a dominant hereditary muscular dystrophy, is caused by an abnormal expansion of a (CTG)n trinucleotide repeat in the 3′ UTR of the human dystrophia myotonica protein kinase (DMPK) gene. As a consequence, mutant transcripts containing expanded CUG repeats are retained in nuclear foci and alter the function of splicing regulatory factors members of the MBNL and CELF families, resulting in alternative splicing misregulation of specific transcripts in affected DM1 tissues. In the present study, we treated DMSXL mice systemically with a 2′-4′-constrained, ethyl-modified (ISIS 486178) antisense oligonucleotide (ASO) targeted to the 3′ UTR of the DMPK gene, which led to a 70% reduction in CUGexp RNA abundance and foci in different skeletal muscles and a 30% reduction in the heart. Furthermore, treatment with ISIS 486178 ASO improved body weight, muscle strength, and muscle histology, whereas no overt toxicity was detected. This is evidence that the reduction of CUGexp RNA improves muscle strength in DM1, suggesting that muscle weakness in DM1 patients may be improved following elimination of toxic RNAs.

Myotonic dystrophy type 1 (DM1) is a rare genetic disorder, characterised by muscular dystrophy, myotonia, and other symptoms. DM1 is caused by the expansion of a CTG repeat in the 3'-untranslated region of DMPK. Longer CTG expansions are associated with greater symptom severity and earlier age at onset. The primary mechanism of pathogenesis is thought to be mediated by a gain of function of the CUG-containing RNA, that leads to trans-dysregulation of RNA metabolism of many other genes. Specifically, the alternative splicing (AS) and alternative polyadenylation (APA) of many genes is known to be disrupted. In the context of clinical trials of emerging DM1 treatments, it is important to be able to objectively quantify treatment efficacy at the level of molecular biomarkers. We show how previously described candidate mRNA biomarkers can be used to model an effective reduction in CTG length, using modern high-dimensional statistics (machine learning), and a blood and muscle mRNA microarray dataset. We show how this model could be used to detect treatment effects in the context of a clinical trial.