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.

肌联蛋白截短变异是心肌病的一个明确病因。然而，肌联蛋白错义变体的作用尚不清楚。在这里，我们描述了小鼠模型的生成，以研究先前报道的在非致密化和扩张型心肌病家族中发现的肌动蛋白 A178D 错义变异的潜在疾病机制。通过超声心动图对携带 titin A178D 错义变体的杂合子和纯合子小鼠进行体内表征。杂合小鼠在任何研究时间点（长达 1 年）都没有可检测到的表型。相比之下，纯合子小鼠从 3 个月起就出现了扩张型心肌病。慢性肾上腺素能刺激加剧了表型。靶向转录谱分析揭示了纯合小鼠中胎儿基因程序和肥大信号通路的诱导，并且这些在蛋白质水平上得到了证实。无监督蛋白质组学发现，telethonin 和四个半 LIM 结构域 2 下调，以及热休克蛋白和骨髓性白血病因子 1 上调。心脏 Z 盘中 telethonin 的损失伴随着蛋白酶体降解。然而，未折叠的telethonin在细胞质中积累，导致小鼠产生蛋白毒性反应。我们发现titin A178D错义变体在纯合子小鼠中具有致病性，导致心肌病。我们还提供了疾病机制的证据：因为titin A178D变异体消除了telethonin的结合，这导致其异常的细胞质积累。随后，蛋白酶体降解电视松宁，导致蛋白酶体超载，并激活蛋白毒性反应。后者似乎是小鼠模型中观察到的心肌病的驱动因素。