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Functional analysis of a gene-edited mouse model to gain insights into the disease mechanisms of a titin missense variant

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He Jiang, Charlotte Hooper, Matthew Kelly, Violetta Steeples, Jillian N. Simon, Julia Beglov, Amar J. Azad, Lisa Leinhos, Pauline Bennett, Elisabeth Ehler, Jacinta I. Kalisch-Smith, Duncan B. Sparrow, Roman Fischer, Raphael Heilig, Henrik Isackson, Mehroz Ehsan, Giannino Patone, Norbert Huebner, Benjamin Davies, Hugh Watkins & 1 more Katja Gehmlich

Original languageEnglish
Article number14
JournalBasic Research in Cardiology
Volume116
Issue number1
DOIs
PublishedDec 2021

Bibliographical note

Funding Information: This work was supported by the British Heart Foundation (BHF) [FS/12/40/29712 and PG/15/113/31944 to KG, FS/17/55/33100 to DBS and JIK-S]; the Oxford BHF Centre of Research Excellence [RE/13/1/30181 to KG, DBS and JIK-S]; the Wellcome Trust [201543/B/16/Z to KG, HJ, CH, VS and HW, Core Award 090532/Z09/Z to BD]; and the John Fell Oxford University Press Research Fund [0006108 to DBS and JIK-S]. ME received a Clarendon Fund doctoral scholarship. HI was supported by a scholarship from the Swedish Society of Medical Research (SSMF) and by the Åke Wiberg Foundation. Work in EE’s laboratory is funded by the BHF and the Medical Research Council. The Institute of Cardiovascular Sciences, University of Birmingham, has received an Accelerator Award by the British Heart Foundation [AA/18/2/34218]. Publisher Copyright: © 2021, The Author(s). Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

King's Authors

Abstract

Titin truncating variants are a well-established cause of cardiomyopathy; however, the role of titin missense variants is less well understood. 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. Heterozygous and homozygous mice carrying the titin A178D missense variant were characterised in vivo by echocardiography. Heterozygous mice had no detectable phenotype at any time point investigated (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 foetal gene programme and hypertrophic signalling pathways in homozygous mice, and these were confirmed at the protein level. Unsupervised proteomics identified downregulation of telethonin and four-and-a-half LIM domain 2, as well as the upregulation of heat shock proteins and myeloid leukaemia factor 1. Loss of telethonin from the cardiac Z-disc was accompanied by proteasomal degradation; however, unfolded telethonin accumulated in the cytoplasm, leading to a proteo-toxic response in the mice.We show 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.

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