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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 2

The COL6A1 pseudoexon is translated and exerts a dominant-negative effect on collagen VI matrix assembly in cultured dermal fibroblasts.

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The COL6A1 pseudoexon is translated and exerts a dominant-negative effec...
(A) Schematic representing the exon composition of the triple helical domains’ N-terminal ends for each of the 3 α chains of collagen VI, including the predicted pseudoexon peptide sequence (shown in red) inserted between exons 11 and 12 of the α1 chain. The positions of the cysteine residues critical for dimer and tetramer stabilization are indicated for each chain. (B) A polyclonal antibody [Pex11-α1(VI)] was raised against the pseudoexon peptide, and used to probe a denaturing and reducing immunoblot of cell lysate (cellular, C) and media (secreted, S) protein extracts from cultured dermal fibroblasts of 2 patients and 1 unaffected individual. Probing with the preimmune sera is shown (right). (C) An immunoblot prepared as described in B was probed with the Pex11-α1(VI) antibody (left), then stripped and probed with an antibody detecting α1(VI) collagen [α1(VI)-C] (right). (D) Dermal fibroblasts were cultured in the presence of L-ascorbic acid, and medium was collected to measure collagen VI microfibrillar length using rotary shadowing electron microscopy (EM). Representative negative-staining EM images showing isolated collagen VI microfibrils (13 to 44 microfibrils were imaged per sample). Scale bars: 200 nm. The collagen VI microfibrillar length (number of tetramers per microfibril) is reported as a dot plot (below), where lines represent mean ± standard deviation. *P < 0.001 by Mann-Whitney U test, Bonferroni corrected for 2 comparisons. (E) Dermal fibroblasts from 1 unaffected individual, 1 patient carrying the glycine substitution COL6A1 G290R, and 2 +189C>T patients were cultured for 3 days in the presence of L-ascorbic acid, and then cells were fixed and immunostained for matrix-deposited collagen VI (green) and with the nuclear stain DAPI (blue). Scale bars: 25 μm.

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