Dataset Information

Insights into the role of a cardiomyopathy-causing genetic var-iant in ACTN2

ABSTRACT: Pathogenic variants in ACTN2, coding for alpha-actinin 2, are known to be rare causes of Hyper-trophic Cardiomyopathy. However, little is known about the underlying disease mechanisms. Adult heterozygous mice carrying the Actn2 M228T variant were phenotyped by echocardiog-raphy. For homozygous mice, viable E15.5 embryonic hearts were analysed by High Resolution Episcopic Microscopy and wholemount staining, complemented by unbiased proteomics, qPCR and Western blotting. Heterozygous Actn2 M228T mice have no overt phenotype. Only mature males show molecular parameters indicative of cardiomyopathy. By contrast, the variant is em-bryonically lethal in the homozygous setting and E15.5 hearts show multiple morphological ab-normalities. Molecular analyses, including unbiased proteomics, identified quantitative abnormal-ities in sarcomeric parameters, cell cycle defects and mitochondrial dysfunction. The mutant al-pha-actinin protein is found to be destabilised, associated with increased activity of the ubiqui-tin-proteosomal system. This missense variant in alpha-actinin renders the protein less stable. In response, the ubiquitin-proteosomal system is activated; a mechanism which has been implicated in cardiomyopathies previously. In parallel, lack of functional alpha-actinin is thought to cause energetic defects through mitochondrial dysfunction. This seems, together with cell cycle defects, the likely cause of death of the embryos. The defects also have wide-ranging morphological con-sequences.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Heart, Embryo

SUBMITTER: Sophie Broadway-Stringer

LAB HEAD: Katja Gehmlich

PROVIDER: PXD039226 | Pride | 2023-05-10

REPOSITORIES: Pride

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Publications

Insights into the Role of a Cardiomyopathy-Causing Genetic Variant in ACTN2.

Broadway-Stringer Sophie S Jiang He H Wadmore Kirsty K Hooper Charlotte C Douglas Gillian G Steeples Violetta V Azad Amar J AJ Singer Evie E Reyat Jasmeet S JS Galatik Frantisek F Ehler Elisabeth E Bennett Pauline P Kalisch-Smith Jacinta I JI Sparrow Duncan B DB Davies Benjamin B Djinovic-Carugo Kristina K Gautel Mathias M Watkins Hugh H Gehmlich Katja K

Cells 20230224 5

Pathogenic variants in ACTN2, coding for alpha-actinin 2, are known to be rare causes of Hypertrophic Cardiomyopathy. However, little is known about the underlying disease mechanisms. Adult heterozygous mice carrying the Actn2 p.Met228Thr variant were phenotyped by echocardiography. For homozygous mice, viable E15.5 embryonic hearts were analysed by High Resolution Episcopic Microscopy and wholemount staining, complemented by unbiased proteomics, qPCR and Western blotting. Heterozy ...[more]

PMID: 36899856

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Project description:Aims: Pathogenic truncating variants in the largest human protein TITIN are a leading cause of dilated cardiomyopathy. Because of the size of the gene encoding TITIN, many missense variations are identified. These are difficult to evaluate in genetic testing, as even individually rare variants are common in aggregate in normal populations. While the majority will be benign, a small subset is pathogenic, but distinction is challenging. Here, we describe the generation of a mouse model to investigate the underlying disease mechanism of a previously reported TITIN A178D missense variant identified in a family with non-compaction and dilated cardiomyopathy. Methods and Results: Heterozygous and homozygous mice carrying the TITIN A178D missense variant were characterised in vivo. Heterozygous mice had no detectable phenotype at any time point observed (up to 1 year). By contrast, homozygous mice developed dilated cardiomyopathy from 3 months. Chronic adrenergic stimulation aggravated the phenotype. Targeted transcript profiling revealed induction of the fetal gene programme and hypertrophic signalling pathways in homozygous mice, and these were confirmed at the protein level. Unsupervised proteomics identified down-regulation of TELETHONIN and FOUR-AND-A-HALF LIM DOMAIN 2, as well as the up-regulation of heat shock proteins and MYELOID LEUKEMIA FACTOR 1. Loss of TELETHONIN from the cardiac Z-disc was accompanied by proteasomal degradation; however, TELETHONIN also accumulated in the cytoplasm. In parallel, a proteo-toxic response was observed in the mice. Conclusions: We have shown that the TITIN A178D missense variant is pathogenic in homozygous mice, resulting in cardiomyopathy. We also provide evidence of the disease mechanism. Because the TITIN A178D variant abolishes binding of TELETHONIN, this leads to its abnormal cytoplasmic accumulation. Subsequent degradation of TELETHONIN by the proteasome results in proteasomal overload, and activation of a proteo-toxic response. The latter appears to be a driving factor for the cardiomyopathy observed in the mouse model.

Dataset Information

Insights into the role of a cardiomyopathy-causing genetic var-iant in ACTN2

Publications

Insights into the Role of a Cardiomyopathy-Causing Genetic Variant in <i>ACTN2</i>.

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