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A recurrent COL6A1 pseudoexon insertion causes muscular dystrophy and is effectively targeted by splice-correction therapies
Véronique Bolduc, … , Francesco Muntoni, Carsten G. Bönnemann
Véronique Bolduc, … , Francesco Muntoni, Carsten G. Bönnemann
Published March 21, 2019
Citation Information: JCI Insight. 2019;4(6):e124403. https://doi.org/10.1172/jci.insight.124403.
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Research Article Muscle biology Therapeutics

A recurrent COL6A1 pseudoexon insertion causes muscular dystrophy and is effectively targeted by splice-correction therapies

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Abstract

The clinical application of advanced next-generation sequencing technologies is increasingly uncovering novel classes of mutations that may serve as potential targets for precision medicine therapeutics. Here, we show that a deep intronic splice defect in the COL6A1 gene, originally discovered by applying muscle RNA sequencing in patients with clinical findings of collagen VI–related dystrophy (COL6-RD), inserts an in-frame pseudoexon into COL6A1 mRNA, encodes a mutant collagen α1(VI) protein that exerts a dominant-negative effect on collagen VI matrix assembly, and provides a unique opportunity for splice-correction approaches aimed at restoring normal gene expression. Using splice-modulating antisense oligomers, we efficiently skipped the pseudoexon in patient-derived fibroblast cultures and restored a wild-type matrix. Similarly, we used CRISPR/Cas9 to precisely delete an intronic sequence containing the pseudoexon and efficiently abolish its inclusion while preserving wild-type splicing. Considering that this splice defect is emerging as one of the single most frequent mutations in COL6-RD, the design of specific and effective splice-correction therapies offers a promising path for clinical translation.

Authors

Véronique Bolduc, A. Reghan Foley, Herimela Solomon-Degefa, Apurva Sarathy, Sandra Donkervoort, Ying Hu, Grace S. Chen, Katherine Sizov, Matthew Nalls, Haiyan Zhou, Sara Aguti, Beryl B. Cummings, Monkol Lek, Taru Tukiainen, Jamie L. Marshall, Oded Regev, Dina Marek-Yagel, Anna Sarkozy, Russell J. Butterfield, Cristina Jou, Cecilia Jimenez-Mallebrera, Yan Li, Corine Gartioux, Kamel Mamchaoui, Valérie Allamand, Francesca Gualandi, Alessandra Ferlini, Eric Hanssen, the COL6A1 Intron 11 Study Group, Steve D. Wilton, Shireen R. Lamandé, Daniel G. MacArthur, Raimund Wagener, Francesco Muntoni, Carsten G. Bönnemann

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Figure 3

PMOs efficiently skip the COL6A1 pseudoexon.

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PMOs efficiently skip the COL6A1 pseudoexon.
(A) Location of the phospho...
(A) Location of the phosphorodiamidate morpholino antisense oligomers (PMOs) targeting the splice acceptor (SA), the splice donor (SD), or sequences within the pseudoexon (PEX). Asterisks in PMO-SA, PMO-PEX3, and PMO-PEX4 denote the presence of a mismatch between the oligomer sequence and the target sequence. (B) HEK293T cells expressing the minigene construct Ex-11-13 were transfected with each PMO oligomer at the indicated concentrations, and RNA was isolated 48 hours later. Electrophoretic gels of RT-PCR products amplified as in Figure 1E are shown (top), representative of 3 transfection replicates. PCR fragment densities were quantified from the gel images using ImageJ, to determine the ratio of pseudoexon over normal (pseudoexon/WT) products for each lane. Graph (bottom) reports the pseudoexon/WT ratios from 3 replicate treatments. Lines represent the average of the technical replicates ± standard deviation. PMO-NT = nontargeting PMO. Mock = transfection reagent only. (C) RT-PCR detection of the pseudoexon expression in patient IR1 cultured dermal fibroblasts following a 48-hour treatment with selected PMOs is shown as an example. (D–F) Relative gene expression in patient-derived cultured dermal fibroblasts treated for 48 hours with PMOs at the indicated concentrations, measured by quantitative RT-PCR assays specific for the pseudoexon (D and F) or for total COL6A1 (E). Expression levels were normalized to the housekeeping gene PGK1 and measured as relative to the corresponding mock-treated fibroblasts. Each data point represents the average of 2 to 3 treatments on 1 biological replicate, and lines represent the average of the 3 biological replicates (patients R1, IR1, and CA1). Repeated-measures 2-way ANOVA with Bonferroni’s multiple comparisons test was applied. #P < 0.05 for all concentrations on the graph; *P < 0.05 for the indicated concentration.

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