Aberrant Expression of a Non-muscle RBFOX2 Isoform Triggers Cardiac Conduction Defects in Myotonic Dystrophy

Myotonic Dystrophy type 1 (DM1), the most prevalent form of adult-onset muscular dystrophy, is caused by CTG trinucleotide repeat expansion in the 3’-UTR of the DMPK gene. Heart dysfunctions occur in nearly 80% of DM1 patients, and cardiac arrhythmias or conduction abnormalities are a prominent cause of mortality in affected individuals. Yet, the underlying mechanisms causing such abnormalities are not well understood. We recently demonstrated that aberrant expression of a non-muscle splice isoform of RNA-binding protein RBFOX2 triggers cardiac conduction delay, atrioventricular heart blocks, and spontaneous arrhythmogenesis in DM1 hearts. Here we studied the mechanism(s) by which non-muscle RBFOX2 induces mis-splicing of cardiac conduction genes and tested new therapeutic strategies for treating the lethal cardiac symptoms of this disease. By performing eCLIP and high-resolution RNA-sequencing studies on cardiomyocytes isolated from wild type (expressing the normal muscle-specific RBFOX2 43 isoform), Rbfox2 Δ43/Δ43 (expressing the non-muscle RBFOX2 40 isoform), and RBFOX2 40 overexpressing (OE) mice, we deconstructed the splicing regulatory networks of RBFOX2 43 and RBFOX2 40 isoforms, characterized their respective RNA binding landscapes, and determined the RBFOX2 40 -driven transcriptome alterations in DM1 heart tissue. We acquired induced pluripotent stem cells (iPSC) from healthy, moderate (238 CTG repeats) and severely (1001 CTG repeats) affected DM1 individuals and differentiated them into cardiomyocytes (iPSC-CMs) to generate a human cardiac cell culture model of DM1. Utilizing anti-sense oligonucleotides and RNAi-based approaches, we restored the muscle-specific Rbfox2 splicing pattern and depleted the non-muscle RBFOX2 isoform in the DM1 IPS-CMs. We are currently analyzing the spontaneous electrical phenotypes of normal and DM1 iPSC-CMs. Collectively, our studies provide an in-depth understanding of the molecular basis for DM1-related electrophysiological abnormalities and offer an avenue to test the potential therapeutic utility of targeting the non-muscle RBFOX2 40 isoform in treating cardiac features of DM1.

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Faculty Opinions recommendation of Reversible model of RNA toxicity and cardiac conduction defects in myotonic dystrophy.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1040694.489717 ◽

2006 ◽

Author(s):

David Brook

Keyword(s):

Myotonic Dystrophy ◽

Cardiac Conduction ◽

Rna Toxicity

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807-4 CUG expansions in a myotonic dystrophy mouse model cause cardiac conduction abnormalities and pathologic electrophysiology findings

Journal of the American College of Cardiology ◽

10.1016/s0735-1097(04)90511-6 ◽

2004 ◽

Vol 43 (5) ◽

pp. A122 ◽

Cited By ~ 1

Author(s):

Cordula M Wolf ◽

Megan C Sherwood ◽

Dorothy Branco ◽

Sita Reddy ◽

Charles I Berul

Keyword(s):

Mouse Model ◽

Myotonic Dystrophy ◽

Cardiac Conduction ◽

Conduction Abnormalities

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Author response: Straightjacket/α2δ3 deregulation is associated with cardiac conduction defects in myotonic dystrophy type 1

10.7554/elife.51114.sa2 ◽

2019 ◽

Author(s):

Emilie Auxerre-Plantié ◽

Masayuki Nakamori ◽

Yoan Renaud ◽

Aline Huguet ◽

Caroline Choquet ◽

...

Keyword(s):

Myotonic Dystrophy ◽

Cardiac Conduction ◽

Author Response ◽

Myotonic Dystrophy Type 1 ◽

Myotonic Dystrophy Type

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Abstract P104: Reactivation of Embryonic Gene Program due to CUG Repeat RNA Expression in Myotonic Dystrophy

Circulation Research ◽

10.1161/res.109.suppl_1.ap104 ◽

2011 ◽

Vol 109 (suppl_1) ◽

Author(s):

Auinash Kalsotra ◽

Ravi Singh ◽

Chad Creighton ◽

Thomas Cooper

Keyword(s):

Gene Expression ◽

Myotonic Dystrophy ◽

Rna Binding ◽

Rna Binding Proteins ◽

Expression Patterns ◽

Causative Mutation ◽

Inherited Disease ◽

Aberrant Expression ◽

Organ Systems ◽

General Response

Myotonic dystrophy type 1 (DM1) is a dominantly inherited disease that affects multiple organ systems. Cardiac involvement, which is characterized by conduction defects and arrhythmias, is the second leading cause of death in DM1 patients. The causative mutation is a CTG expansion in the 3' untranslated region of DMPK gene resulting in aberrant expression of CUG repeat RNA that accumulates into nuclear foci and causes misregulation in alternative splicing. Here we show that heart-specific and inducible expression of CUG repeat RNA in a DM1 mouse model results in global reactivation of embryonic gene expression program in adult heart that is distinct from a general hypertrophic stress response. Using q-PCR TaqMan arrays, we identified 54 miRNAs that were differentially expressed in DM1 mouse hearts one week following induction of CUG repeat RNA. Interestingly, 83% (45/54) of them exhibited a developmental shift in expression towards the embryonic pattern. Because over 90% (41/45) of them were down regulated within 72 hr after induction of repeat RNA and only 2/22 examined decreased in two unrelated mouse models of heart disease, we conclude their reduced expression is specific to DM1 and not simply a general response to cardiac injury. Microarray studies revealed a developmental switch not only in the miRNA expression patterns but also a pervasive shift in mRNA steady state levels of a number of genes to embryonic stage. Intriguingly, we found that loss of MBNL1 or gain of CELF1 activity, two major RNA binding proteins disrupted in DM1, are not driving the miRNA misregulation since their expression is indistinguishable between wild type, MBNL1 knock out and CELF1 over expressing mice. Moreover, comparable decrease in ten out of ten primary miRNA transcripts examined suggests loss of expression is not due to a processing defect. Instead, we discovered that adult-to-embryonic shift in expression of select micro- and messenger RNAs in DM1 heart occurs due to specific inactivation of a Mef2 transcriptional program. We are currently determining causal contributions of this Mef2-miRNA circuitry in the developmental reprogramming of gene expression in DM1 as well as its direct role in cardiac manifestations of this disease.

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Abstract 191: Deletion or Knockdown of Myotonic Dystrophy Protein Kinase Does Not Affect Cardiac Conduction or Ejection Fraction in Mice

Circulation Research ◽

10.1161/res.117.suppl_1.191 ◽

2015 ◽

Vol 117 (suppl_1) ◽

Author(s):

Samuel Carrell ◽

David Auerbach ◽

Sanjay Pandey ◽

Frank Bennett ◽

Robert Dirksen ◽

...

Keyword(s):

Ejection Fraction ◽

Myotonic Dystrophy ◽

Cardiac Conduction ◽

Nuclear Retention ◽

Rna Toxicity ◽

Lv Dysfunction ◽

Av Conduction ◽

Myotonic Dystrophy Protein Kinase ◽

Toxic Rna

Myotonic dystrophy type 1 (DM1), the most common form of muscular dystrophy in adults, causes dominantly-inherited muscle weakness, defects of cardiac conduction, variable LV dysfunction, and risk of sudden death. The genetic basis is an expanded CTG repeat in the 3’ untranslated region of DMPK. DM1 patients are functionally hemizygous for DMPK protein, due to nuclear retention of mRNA having expanded repeats. The cardiac aspects are attributed to DMPK loss, toxicity of RNA with expanded repeats, or both. Dmpk heterozygous (+/-) and homozygous knockout (-/-) mice were reported to show AV conduction abnormalities resembling DM1 (Berul et al, JCI, 1999). In an effort to reduce RNA toxicity, antisense oligonucleotides (ASOs) targeting DMPK mRNA have recently entered clinical trials. DM1 phenotypes in skeletal muscle were corrected by ASO knockdown of toxic RNA in mice (Wheeler et al, Nature, 2012). While ASOs may have similar potential to mitigate RNA toxicity in the heart, there is risk of aggravated DMPK deficiency. To reexamine the role of DMPK in the conduction system we studied mice with Dmpk gene deletion or ASO knockdown. We obtained ECGs and echocardiograms on Dmpk -/- and +/- mice, compared to WT littermates. The +/- mice were treated with Dmpk-targeting ASOs or saline. Subcutaneous injection of 50 mg/kg/wk ASO was started at age 2 months, then shifted to biweekly injections after 6 weeks. Dmpk expression in hearts of +/- mice was ~50% of WT, and was further reduced by ASOs (84 ± 3% decrease of mRNA, 93 ± 2% decrease of protein, relative to WT). Surface ECGs and echocardiography at 6 and 10 months showed no differences of heart rate, cardiac conduction, or ejection fraction in WT, saline-treated +/-, ASO-treated +/-, or -/- mice. Conscious, unrestrained ECGs obtained at 11-12 months by radiotelemetry showed no differences among WT, saline-treated +/-, ASO-treated +/-, or -/- mice. We conclude that ASOs can induce posttranscriptional silencing of Dmpk in murine hearts. Constitutive absence of DMPK did not impact cardiac conduction or contractility, and the same was true for ASO knockdown to levels <15% of WT. Our data support the idea that cardiac dysfunction in DM1 results mainly from RNA toxicity, which potentially could be prevented or alleviated by ASOs.

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Mexiletine in myotonic dystrophy type-1

Neurology ◽

10.1212/wnl.0000000000011002 ◽

2020 ◽

pp. 10.1212/WNL.0000000000011002

Author(s):

Chad Heatwole ◽

Elizabeth Luebbe ◽

Spencer Rosero ◽

Katy Eichinger ◽

William Martens ◽

...

Keyword(s):

Myotonic Dystrophy ◽

Cardiac Conduction ◽

Myotonic Dystrophy Type 1 ◽

Myotonic Dystrophy Type ◽

Walk Distance ◽

Hand Grip ◽

Minute Walk Distance ◽

Minute Walk

ObjectiveTo assess mexiletine's long-term safety and effect on 6 minute walk distance in a well-defined cohort of myotonic dystrophy type-1 (DM1) patients.MethodsWe performed a randomized, double-blind, placebo-controlled trial of mexiletine (150 mg 3 times daily) to evaluate its efficacy and safety in a homogenous cohort of adult ambulatory DM1 patients. The primary outcome was change in 6-minute walk distance at 6 months. Secondary outcomes included changes in hand grip myotonia, strength, swallowing, forced vital capacity, lean muscle mass, Myotonic Dystrophy Health Index scores, and 24-hour Holter and EKG results at 3 and 6 months.ResultsForty-two participants were randomized and 40 completed the 6-month follow-up (n = 20 in both groups). No significant effects of mexiletine were observed on 6-minute walk distance, but hand grip myotonia was improved with mexiletine treatment. There were no differences between the mexiletine and placebo groups with respect to the frequency or type of adverse events. Changes in PR, QRS, and QTc intervals were similar in mexiletine and placebo-treated participants.ConclusionsThere was no benefit of mexiletine on six-minute walk distance at 6 months. Although mexiletine had a sustained positive effect on objectively measured hand grip myotonia, this was not seen in measures reflecting participants' perceptions of their myotonia. No effects of mexiletine on cardiac conduction parameters were seen over the 6-month follow-up period.Classification of evidenceThis study provides Class I evidence that for ambulatory patients with DM1 mexiletine does not significantly change six-minute walk distance at 6 months.

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Myotonic Dystrophy

10.1093/med/9780190685157.003.0034 ◽

2018 ◽

Author(s):

Andrea Johnson

Keyword(s):

Skeletal Muscle ◽

Cognitive Impairment ◽

Sleep Apnea ◽

Myotonic Dystrophy ◽

Pediatric Patients ◽

Autosomal Dominant ◽

Anesthetic Management ◽

Cardiac Conduction ◽

Autosomal Dominant Disorder ◽

Skeletal Muscle Weakness

Myotonic dystrophy (DM) is a multisystemic autosomal dominant disorder. Individuals may present with symptoms at any age, but pediatric patients typically will present before 10 years of age. The clinical features of DM differ depending on the type of dystrophy and include skeletal muscle weakness, myotonia, sleep apnea, decreased gastrointestinal motility, insulin hypersecretion, cardiac conduction abnormalities, and occasionally cognitive impairment. Anesthetic management of the patient with DM should begin in the preoperative arena and should take into account the postoperative considerations and concerns for the patient with DM. This chapter will help the clinician develop an appropriate anesthetic plan and implement a safe and effective perioperative experience.

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Cardiac Conduction Disorders as Markers of Cardiac Events in Myotonic Dystrophy Type 1

Journal of the American Heart Association ◽

10.1161/jaha.119.015709 ◽

2020 ◽

Vol 9 (17) ◽

Cited By ~ 1

Author(s):

Hideki Itoh ◽

Takashi Hisamatsu ◽

Takuhisa Tamura ◽

Kazuhiko Segawa ◽

Toshiaki Takahashi ◽

...

Keyword(s):

Sudden Death ◽

Myotonic Dystrophy ◽

Cardiac Conduction ◽

Myotonic Dystrophy Type 1 ◽

Myotonic Dystrophy Type ◽

Cardiac Events ◽

Conduction Disorders ◽

Qrs Duration

Background Myotonic dystrophy type 1 involves cardiac conduction disorders. Cardiac conduction disease can cause fatal arrhythmias or sudden death in patients with myotonic dystrophy type 1. Methods and Results This study enrolled 506 patients with myotonic dystrophy type 1 (aged ≥15 years; >50 cytosine‐thymine‐guanine repeats) and was treated in 9 Japanese hospitals for neuromuscular diseases from January 2006 to August 2016. We investigated genetic and clinical backgrounds including health care, activities of daily living, dietary intake, cardiac involvement, and respiratory involvement during follow‐up. The cause of death or the occurrence of composite cardiac events (ie, ventricular arrhythmias, advanced atrioventricular blocks, and device implantations) were evaluated as significant outcomes. During a median follow‐up period of 87 months (Q1–Q3, 37–138 months), 71 patients expired. In the univariate analysis, pacemaker implantations (hazard ratio [HR], 4.35; 95% CI, 1.22–15.50) were associated with sudden death. In contrast, PQ interval ≥240 ms, QRS duration ≥120 ms, nutrition, or respiratory failure were not associated with the incidence of sudden death. The multivariable analysis revealed that a PQ interval ≥240 ms (HR, 2.79; 95% CI, 1.9–7.19, P <0.05) or QRS duration ≥120 ms (HR, 9.41; 95% CI, 2.62–33.77, P < 0.01) were independent factors associated with a higher occurrence of cardiac events than those observed with a PQ interval <240 ms or QRS duration <120 ms; these cardiac conduction parameters were not related to sudden death. Conclusions Cardiac conduction disorders are independent markers associated with cardiac events. Further investigation on the prediction of occurrence of sudden death is warranted.

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Ventricular tachycardia in patients with type 1 myotonic dystrophy: a case series

European Heart Journal - Case Reports ◽

10.1093/ehjcr/ytz095 ◽

2019 ◽

Vol 3 (2) ◽

Cited By ~ 3

Author(s):

Anish Nikhanj ◽

Soori Sivakumaran ◽

Bailey Miskew-Nichols ◽

Zaeem A Siddiqi ◽

Gavin Y Oudit

Keyword(s):

Ventricular Tachycardia ◽

Myotonic Dystrophy ◽

Ventricular Arrhythmias ◽

Case Series ◽

Cardiac Conduction ◽

Cardiac Resynchronization ◽

Angiotensin Converting Enzyme Inhibition ◽

Mineralocorticoid Receptor Antagonist ◽

Medical Therapies

Abstract Background Type 1 myotonic dystrophy (DM1) is associated with a variety of cardiac conduction abnormalities and the frequent need for permanent pacing. However, the role of ventricular tachycardia (VT) and the implied risk of sudden cardiac death (SCD) is poorly understood. Case summary This study examined a 56-patient DM1 cohort of men and women, and identified five patients (two females and three males) with ventricular arrhythmias (8.9%). Patients were reviewed on a case-by-case basis, with their clinical presentation and management of VT and the associated cardiomyopathy indicated. Patient cardiac function was determined by 12-lead electrocardiogram, 48-h Holter monitor, and transthoracic echocardiography. These patients were therefore suitable candidates for implantable cardioverter-defibrillator implantation and received these devices; four of the five patients also received cardiac resynchronization therapy. Medical therapies included angiotensin converting enzyme inhibition, mineralocorticoid receptor antagonist, and following device implantation, beta-blocker therapy was initiated. Discussion Our case series demonstrates the prevalence of VT in patients with DM1 highlighting the associated risks of SCD in this patient population. The burden of ventricular arrhythmias, advanced conduction disease, and cardiomyopathy are best treated with a combination of device and medical therapies.

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