Insights into the Role of a Cardiomyopathy-Causing Genetic Variant in <i>ACTN2</i>
Sophie Broadway-Stringer,
He Jiang,
Kirsty Wadmore,
Charlotte Hooper,
Gillian Douglas,
Violetta Steeples,
Amar J. Azad,
Evie Singer,
Jasmeet S. Reyat,
Frantisek Galatik,
Elisabeth Ehler,
Pauline Bennett,
Jacinta I. Kalisch-Smith,
Duncan B. Sparrow,
Benjamin Davies,
Kristina Djinovic-Carugo,
Mathias Gautel,
Hugh Watkins,
Katja Gehmlich
Affiliations
Sophie Broadway-Stringer
Institute of Cardiovascular Sciences, University of Birmingham, Birmingham B15 2TT, UK
He Jiang
Division of Cardiovascular Medicine, Radcliffe Department of Medicine and British Heart Foundation Centre of Research Excellence Oxford, University of Oxford, Oxford OX3 9DU, UK
Kirsty Wadmore
Institute of Cardiovascular Sciences, University of Birmingham, Birmingham B15 2TT, UK
Charlotte Hooper
Division of Cardiovascular Medicine, Radcliffe Department of Medicine and British Heart Foundation Centre of Research Excellence Oxford, University of Oxford, Oxford OX3 9DU, UK
Gillian Douglas
Division of Cardiovascular Medicine, Radcliffe Department of Medicine and British Heart Foundation Centre of Research Excellence Oxford, University of Oxford, Oxford OX3 9DU, UK
Violetta Steeples
Division of Cardiovascular Medicine, Radcliffe Department of Medicine and British Heart Foundation Centre of Research Excellence Oxford, University of Oxford, Oxford OX3 9DU, UK
Amar J. Azad
Institute of Cardiovascular Sciences, University of Birmingham, Birmingham B15 2TT, UK
Evie Singer
Institute of Cardiovascular Sciences, University of Birmingham, Birmingham B15 2TT, UK
Jasmeet S. Reyat
Institute of Cardiovascular Sciences, University of Birmingham, Birmingham B15 2TT, UK
Frantisek Galatik
Department of Physiology, Faculty of Science, Charles University, 12800 Prague, Czech Republic
Elisabeth Ehler
Randall Centre for Cell and Molecular Biophysics, King’s College London, London SE1 9RT, UK
Pauline Bennett
Randall Centre for Cell and Molecular Biophysics, King’s College London, London SE1 9RT, UK
Jacinta I. Kalisch-Smith
Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
Duncan B. Sparrow
Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
Benjamin Davies
Transgenic Core, Wellcome Centre for Human Genetics, University of Oxford, Oxford OX3 7BN, UK
Kristina Djinovic-Carugo
European Molecular Biology Laboratory, 38000 Grenoble, France
Mathias Gautel
School of Basic and Medical Biosciences, British Heart Foundation Centre of Research Excellence, King’s College London, London SE1 9RT, UK
Hugh Watkins
Division of Cardiovascular Medicine, Radcliffe Department of Medicine and British Heart Foundation Centre of Research Excellence Oxford, University of Oxford, Oxford OX3 9DU, UK
Katja Gehmlich
Institute of Cardiovascular Sciences, University of Birmingham, Birmingham B15 2TT, UK
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. Heterozygous Actn2 p.Met228Thr mice have no overt phenotype. Only mature males show molecular parameters indicative of cardiomyopathy. By contrast, the variant is embryonically lethal in the homozygous setting and E15.5 hearts show multiple morphological abnormalities. Molecular analyses, including unbiased proteomics, identified quantitative abnormalities in sarcomeric parameters, cell-cycle defects and mitochondrial dysfunction. The mutant alpha-actinin protein is found to be destabilised, associated with increased activity of the ubiquitin-proteasomal system. This missense variant in alpha-actinin renders the protein less stable. In response, the ubiquitin-proteasomal system is activated; a mechanism that has been implicated in cardiomyopathies previously. In parallel, a 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 the death of the embryos. The defects also have wide-ranging morphological consequences.
