Maturation of hiPSC-derived cardiomyocytes promotes adult alternative splicing of SCN5A and reveals changes in sodium current associated with cardiac arrhythmia

AIMS

Human-induced pluripotent stem cell-cardiomyocytes (hiPSC-CMs) are widely used to study arrhythmia-associated mutations in ion channels. Among these, the cardiac sodium channel SCN5A undergoes foetal-to-adult isoform switching around birth. Conventional hiPSC-CM cultures, which are phenotypically foetal, have thus far been unable to capture mutations in adult gene isoforms. Here, we investigated whether tri-cellular cross-talk in a three-dimensional (3D) cardiac microtissue (MT) promoted post-natal SCN5A maturation in hiPSC-CMs.

METHODS AND RESULTS

We derived patient hiPSC-CMs carrying compound mutations in the adult SCN5A exon 6B and exon 4. Electrophysiological properties of patient hiPSC-CMs in monolayer were not altered by the exon 6B mutation compared with isogenic controls since it is not expressed; further, CRISPR/Cas9-mediated excision of the foetal exon 6A did not promote adult SCN5A expression. However, when hiPSC-CMs were matured in 3D cardiac MTs, SCN5A underwent isoform switch and the functional consequences of the mutation located in exon 6B were revealed. Up-regulation of the splicing factor muscleblind-like protein 1 (MBNL1) drove SCN5A post-natal maturation in microtissues since its overexpression in hiPSC-CMs was sufficient to promote exon 6B inclusion, whilst knocking-out MBNL1 failed to foster isoform switch.

CONCLUSIONS

Our study shows that (i) the tri-cellular cardiac microtissues promote post-natal SCN5A isoform switch in hiPSC-CMs, (ii) adult splicing of SCN5A is driven by MBNL1 in these tissues, and (iii) this model can be used for examining post-natal cardiac arrhythmias due to mutations in the exon 6B.

TRANSLATIONAL PERSPECTIVE

The cardiac sodium channel is essential for conducting the electrical impulse in the heart. Postnatal alternative splicing regulation causes mutual exclusive inclusion of fetal or adult exons of the corresponding gene, SCN5A. Typically, immature hiPSCCMs fall short in studying the effect of mutations located in the adult exon. We describe here that an innovative tri-cellular three-dimensional cardiac microtissue culture promotes hiPSC-CMs maturation through upregulation of MBNL1, thus revealing the effect of a pathogenic genetic variant located in the SCN5A adult exon. These results help advancing the use of hiPSC-CMs in studying adult heart disease and for developing personalized medicine applications.

[The structure and specific features of the cDNA expression of the human gene MRPL37]

A 147-bp cDNA fragment was isolated from human lymphocytes activated with concanavalin A using the method of direct selection. A complete copy of the selected gene having total homology with the mitochondrial ribosomal gene MRPL37 was obtained by the RACE (rapid amplification of cDNA ends) technique. The MRPL37 gene was localized on human chromosome 1 using a DNA panel composed of somatic cellular human-hamster hybrids. The Northern blotting and RT-PCR (reverse transcription-polymerase chain reaction) demonstrated that the RNA of the human MRPL37 gene is widely represented in the lymphoma populations of Raji B cells and MT4 T cells, as well as in pancreas, liver, and lung embryonic fibroblasts WI-38 and LEH. The highest expression level of the MRPL37 mouse homologue was found in the cells of skeletal muscles, the heart, and organs of reproductive system: the uterus, ovaries, and testicles. A comparative analysis of the MRPL37 amino acid sequence with those of proteins represented in the Fasta33 and GenBank databases showed a homologous region in MRPL37 and PDCD9 (programmed cell death 9, MPRS30) proteins. The chicken homologue of PDCD9 is interesting because its overexpression causes apoptosis of the mouse fibroblasts C3H10T1/2. The existence of a common domain indicates possible similar functional peculiarities of the PDCD9 and MRPL37 genes and may imply the MRPL37 involvement in the process of apoptosis. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2004, vol. 30, no. 5; see also http: // www.maik.ru.