Antisense oligonucleotides (ASOs) targeting pathologic RNAs have shown promising therapeutic corrections for many genetic diseases including myotonic dystrophy (DM1). Thus, ASO strategies for DM1 can ...abolish the toxic RNA gain-of-function mechanism caused by nucleus-retained mutant DMPK (DM1 protein kinase) transcripts containing CUG expansions (CUGexps). However, systemic use of ASOs for this muscular disease remains challenging due to poor drug distribution to skeletal muscle. To overcome this limitation, we test an arginine-rich Pip6a cell-penetrating peptide and show that Pip6a-conjugated morpholino phosphorodiamidate oligomer (PMO) dramatically enhanced ASO delivery into striated muscles of DM1 mice following systemic administration in comparison with unconjugated PMO and other ASO strategies. Thus, low-dose treatment with Pip6a-PMO-CAG targeting pathologic expansions is sufficient to reverse both splicing defects and myotonia in DM1 mice and normalizes the overall disease transcriptome. Moreover, treated DM1 patient-derived muscle cells showed that Pip6a-PMO-CAG specifically targets mutant CUGexp-DMPK transcripts to abrogate the detrimental sequestration of MBNL1 splicing factor by nuclear RNA foci and consequently MBNL1 functional loss, responsible for splicing defects and muscle dysfunction. Our results demonstrate that Pip6a-PMO-CAG induces long-lasting correction with high efficacy of DM1-associated phenotypes at both molecular and functional levels, and strongly support the use of advanced peptide conjugates for systemic corrective therapy in DM1.
Myotonic dystrophy, or dystrophia myotonica type 1 (DM1), is a multi-systemic disorder and is the most common adult form of muscular dystrophy. It affects not only muscles but also many organs, ...including the brain. Cerebral impairments include cognitive deficits, daytime sleepiness, and loss of visuospatial and memory functions. The expression of mutated transcripts with CUG repeats results in a gain of toxic mRNA function. The antisense oligonucleotide (ASO) strategy to treat DM1 brain deficits is limited by the fact that ASOs do not cross the blood-brain barrier after systemic administration, indicating that other methods of delivery should be considered. ASO technology has emerged as a powerful tool for developing potential new therapies for a wide variety of human diseases, and its potential has been proven in a recent clinical trial. Targeting DMPK mRNA in neural cells derived from human induced pluripotent stem cells obtained from a DM1 patient with the IONIS 486178 ASO abolished CUG-expanded foci, enabled nuclear redistribution of MBNL1/2, and corrected aberrant splicing. Intracerebroventricular injection of the IONIS 486178 ASO in DMSXL mice decreased the levels of mutant DMPK mRNAs by up to 70% throughout different brain regions. It also reversed behavioral abnormalities following neonatal administration. The present study indicated that the IONIS 486178 ASO targets mutant DMPK mRNAs in the brain and strongly supports the feasibility of a therapy for DM1 patients based on the intrathecal injection of an ASO.
Myotonic dystrophy type 1 (DM1) is a progressive neuromuscular disease caused by expanded CUG repeats, which misregulate RNA metabolism through several RNA-binding proteins, including CUG-binding ...protein/CUGBP1 elav-like factor 1 (CUGBP1/CELF1) and muscleblind 1 protein. Mutant CUG repeats elevate CUGBP1 and alter CUGBP1 activity via a glycogen synthase kinase 3β (GSK3β)-cyclin D3-cyclin D-dependent kinase 4 (CDK4) signaling pathway. Inhibition of GSK3β corrects abnormal activity of CUGBP1 in DM1 mice human skeletal actin mRNA, containing long repeats ( HSA
) model. Here, we show that the inhibition of GSK3β in young HSA
mice prevents development of DM1 muscle pathology. Skeletal muscle in 1-yr-old HSA
mice, treated at 1.5 mo for 6 wk with the inhibitors of GSK3, exhibits high fiber density, corrected atrophy, normal fiber size, with reduced central nuclei and normalized grip strength. Because CUG-GSK3β-cyclin D3-CDK4 converts the active form of CUGBP1 into a form of translational repressor, we examined the contribution of CUGBP1 in myogenesis using Celf1 knockout mice. We found that a loss of CUGBP1 disrupts myogenesis, affecting genes that regulate differentiation and the extracellular matrix. Proteins of those pathways are also misregulated in young HSA
mice and in muscle biopsies of patients with congenital DM1. These findings suggest that the correction of GSK3β-CUGBP1 pathway in young HSA
mice might have a positive effect on the myogenesis over time.-Wei, C., Stock, L., Valanejad, L., Zalewski, Z. A., Karns, R., Puymirat, J., Nelson, D., Witte, D., Woodgett, J., Timchenko, N. A., Timchenko, L. Correction of GSK3β at young age prevents muscle pathology in mice with myotonic dystrophy type 1.
Objective
To investigate Tau pathology using multimodal biomarkers of neurodegeneration and neurocognition in participants with myotonic dystrophy type 1 (DM1).
Methods
We recruited twelve ...participants with DM1 and, for comparison, two participants with Alzheimer’s Disease (AD). Participants underwent cognitive screening and social cognition testing using the Dépistage Cognitif de Québec (DCQ), among other tests. Biomarkers included Tau PET with 18F-AV-1451, CSF (Aβ, Tau, phospho-Tau), and plasma (Aβ, Tau, Nf-L, GFAP) studies.
Results
Of the twelve DM1 participants, seven completed the full protocol (Neurocognition 11/12; PET 7/12, CSF 9/12, plasma 12/12). Three DM1 participants were cognitively impaired (CI). On average, CI DM1 participants had lower scores on the DCQ compared to cognitively unimpaired (CU) DM1 participants (75.5/100 vs. 91.4/100) and were older (54 vs. 44 years old) but did not differ in years of education (11.3 vs. 11.1). The majority (6/7) of DM1 participants had no appreciable PET signal. Only one of the CI participants presented with elevated Tau PET SUVR in bilateral medial temporal lobes. This participant was the eldest and most cognitively impaired, and had the lowest CSF Aβ 1-42 and the highest CSF Tau levels, all suggestive of co-existing AD. CSF Tau and phospho-Tau levels were higher in the 3 CI compared to CU DM1 participants, but with a mean value lower than that typically observed in AD. Nf-L and GFAP were elevated in most DM1 participants (9/11 and 8/11, respectively). Finally, CSF phospho-Tau was significantly correlated with plasma Nf-L concentrations.
Conclusions and relevance
We observed heterogenous cognitive and biomarker profiles in individuals with DM1. While some participants presented with abnormal PET and/or CSF Tau, these patterns were highly variable and only present in a small subset. Although DM1 may indeed represent a non-AD Tauopathy, the Tau-PET tracer used in this study was unable to detect an in vivo Tau DM1 signature in this small cohort. Interestingly, most DM1 participants presented with elevated plasma Nf-L and GFAP levels, suggestive of other, possibly related, central brain alterations which motivate further research. This pioneering study provides novel insights towards the potential relationship between biomarkers and neurocognitive deficits commonly seen in DM1.
There are numerous examples in the literature of gene therapy applications for recessive disorders. There are precious few instances, however, of studies conducted to treat dominantly inherited ...pathologies. The reasons are simple: there are fewer cases of dominantly inherited diseases on one hand, but mostly it is far easier to correct recessive mutations than dominant ones. Typically recessive mutations cause a loss of (or reduced) gene function which can be compensated for by introduction of a replacement allele into the cell. In contrast, dominant negative mutations not only display impaired function, but also exhibit a novel one that is pathologic to the cell. Treating these conditions by gene therapy implies silencing the dominant allele without altering the expression of the wild-type gene. We describe here different strategies aimed at silencing dominant mutations through mRNA destruction and provide examples of their application to known autosomal dominant diseases. An overview of the most common molecular tools (antisense DNA and RNA, ribozymes and RNA interference) suitable to utilize these strategies is also presented and we discuss the relevant aspects involved in the choice of a particular approach in a gene therapy experiment.
Key points
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Na+ channels are pores present at the surface of every muscle cell; the initiation of muscle contraction requires the opening of a large number of Na+ channels.
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Nav1.4 channels are ...encoded by the SCN4A gene and represent over 90% of Na+ channels in adult skeletal muscle cells; the M1476I mutation of Nav1.4 causes potassium‐aggravated myotonia in a French Canadian population of the Saguenay‐Lac‐Saint‐Jean region of Quebec.
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Individuals carrying this mutation exhibit typical features ranging from asymptomatic myotonic discharges on electromyography to severe diffuse myotonia, as well as unusual cold‐induced, painful myotonia.
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Our study provides a detailed characterization of the underlying biophysical defect of the M1476I mutation, including an increased persistent Na+ current, a disruption of fast inactivation and an accelerated recovery from inactivation; cooling further enhances the abnormalities of fast inactivation of the mutant channels.
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Our data suggest that mexiletine could be used as a therapeutic for patients carrying this mutation.
M1476I, a French Canadian founder mutation of Na+ channel Nav1.4, causes potassium‐aggravated myotonia, with cold‐induced myotonia as the most distinctive clinical feature. Mexiletine, a class 1B local anaesthetic, relieves the myotonic symptoms of patients carrying the M1476I mutation. We used the patch‐clamp method to investigate the functional characteristics of this mutation by heterologous expression in tsA201 cells. The M1476I mutation caused an increased persistent Na+ current, a 2‐ to 3‐fold slower fast inactivation, a 6.4 mV depolarizing shift in the midpoint of steady‐state inactivation, and an accelerated recovery from fast inactivation compared to the wild‐type (WT) channel. Cooling slowed the kinetics of both channel types and increased the amplitude of the persistent current in M1476I channels. Mexiletine suppressed the persistent Na+ current generated by the M1476I mutation and blocked both WT and M1476I channels in a use‐dependent manner. The inactivation‐deficient M1476I channels were less susceptible to mexiletine during repetitive pulses. The decreased use‐dependent block of M1476I channels might have resulted from the slower onset of mexiletine block, and/or the faster recovery from mexiletine block, given that the affinity of mexiletine for the inactivated state of the WT and mutant channels was similar. Increased extracellular concentrations of potassium had no effect on either M1476I or WT currents. These results indicated that cooling can augment the disruption of the voltage dependence of fast inactivation by M1476I channels. The therapeutic efficacy of mexiletine in M1476I carriers may be partly due to the open‐channel block targeting the persistent Na+ currents generated by M1476I channels.
Antisense oligonucleotides (ASOs) targeting pathologic RNAs have shown promising therapeutic corrections for many genetic diseases including myotonic dystrophy (DM1). Thus, ASO strategies for DM1 can ...abolish the toxic RNA gain-offunction mechanism caused by nucleus-retained mutant DMPK (DM1 protein kinase) transcripts containing CUG expansions (CUGexps). However, systemic use of ASOs for this muscular disease remains challenging due to poor drug distribution to skeletal muscle. To overcome this limitation, we test an arginine-rich Pip6a cell-penetrating peptide and show that Pip6aconjugated morpholino phosphorodiamidate oligomer (PMO) dramatically enhanced ASO delivery into striated muscles of DM1 mice following systemic administration in comparison with unconjugated PMO and other ASO strategies. Thus, low-dose treatment with Pip6a-PMO-CAG targeting pathologic expansions is sufficient to reverse both splicing defects and myotonia in DM1 mice and normalizes the overall disease transcriptome. Moreover, treated DM1 patient-derived muscle cells showed that Pip6a-PMO-CAG specifically targets mutant CUGexp-DMPK transcripts to abrogate the detrimental sequestration of MBNL1 splicing factor by nuclear RNA foci and consequently MBNL1 functional loss, responsible for splicing defects and muscle dysfunction. Our results demonstrate that Pip6a-PMO-CAG induces long-lasting correction with high efficacy of DM1associated phenotypes at both molecular and functional levels, and strongly support the use of advanced peptide conjugates for systemic corrective therapy in DM1.
Myotonic dystrophy type 1 (DM1) is a progressive neuromuscular disease caused by expanded CUG repeats, which misregulate RNA metabolism through several RNA‐binding proteins, including CUG‐binding ...protein/CUGBP1 elav‐like factor 1 (CUGBP1/CELF1) and muscleblind 1 protein. Mutant CUG repeats elevate CUGBP1 and alter CUGBP1 activity via a glycogen synthase kinase 3β (GSK3β)‐cyclin D3‐cyclin D‐dependent kinase 4 (CDK4) signaling pathway. Inhibition of GSK3β corrects abnormal activity of CUGBP1 in DM1 mice human skeletal actin mRNA, containing long repeats (HSALR) model. Here, we show that the inhibition of GSK3β in young HSALR mice prevents development of DM1 muscle pathology. Skeletal muscle in 1‐yr‐old hsalr mice, treated at 1.5 mo for 6 wk with the inhibitors of GSK3, exhibits high fiber density, corrected atrophy, normal fiber size, with reduced central nuclei and normalized grip strength. Because CUG‐GSK3β‐cyclin D3‐CDK4 converts the active form of CUGBP1 into a form of translational repressor, we examined the contribution of CUGBP1 in myogenesis using Celf1 knockout mice. We found that a loss of CUGBP1 disrupts myogenesis, affecting genes that regulate differentiation and the extracellular matrix. Proteins of those pathways are also misregulated in young hsalr mice and in muscle biopsies of patients with congenital DM1. These findings suggest that the correction of GSK3β‐CUGBP1 pathway in young hsalr mice might have a positive effect on the myogenesis over time.— Wei, C., Stock, L., Valanejad, L., Zalewski, Z. A., Karns, R., Puymirat, J., Nelson, D., Witte, D., Woodgett, J., Timchenko, N. A., Timchenko, L. Correction of GSK3ß at young age prevents muscle pathology in mice with myotonic dystrophy type 1. FASEB J. 32, 2073–2085 (2018). www.fasebj.org
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