Hypertrophic cardiomyopathy (HCM) is the most common heritable heart disease. Although the genetic cause of HCM has been linked to mutations in genes encoding sarcomeric proteins, the ability to predict clinical outcomes based on specific mutations in HCM patients is limited. Moreover, how mutations in different sarcomeric proteins can result in highly similar clinical phenotypes remains unknown. Posttranslational modifications (PTMs) and alternative splicing regulate the function of sarcomeric proteins; hence, it is critical to study HCM at the level of proteoforms to gain insights into the mechanisms underlying HCM. Herein, we employed high-resolution mass spectrometry–based top-down proteomics to comprehensively characterize sarcomeric proteoforms in septal myectomy tissues from HCM patients exhibiting severe outflow track obstruction (n = 16) compared to nonfailing donor hearts (n = 16). We observed a complex landscape of sarcomeric proteoforms arising from combinatorial PTMs, alternative splicing, and genetic variation in HCM. A coordinated decrease of phosphorylation in important myofilament and Z-disk proteins with a linear correlation suggests PTM cross-talk in the sarcomere and dysregulation of protein kinase A pathways in HCM. Strikingly, we discovered that the sarcomeric proteoform alterations in the myocardium of HCM patients undergoing septal myectomy were remarkably consistent, regardless of the underlying HCM-causing mutations. This study suggests that the manifestation of severe HCM coalesces at the proteoform level despite distinct genotype, which underscores the importance of molecular characterization of HCM phenotype and presents an opportunity to identify broad-spectrum treatments to mitigate the most severe manifestations of this genetically heterogenous disease.

肥厚型心肌病（HCM）是最常见的遗传性心脏病。尽管HCM的遗传原因与编码肌节蛋白的基因突变有关，但基于HCM患者特定突变预测临床结果的能力仍然有限。此外，尚不清楚在不同的肌节蛋白中的突变如何导致高度相似的临床表型。翻译后修饰（PTM）和选择性剪接调节了肌节蛋白的功能；因此，至关重要的是在蛋白形式水平上研究HCM，以深入了解HCM的潜在机制。在本文中，我们采用了基于高分辨率质谱的自上而下的蛋白质组学技术，对患有严重流出道梗阻的HCM患者的隔肌切除组织中的肌节蛋白形态进行了全面表征（n = 16）与未失败的捐献者心脏（n= 16）。我们观察到由组合PTM，替代剪接和HCM遗传变异引起的复杂的肌节蛋白形式。重要的肌丝和Z盘蛋白中磷酸化水平的降低与线性相关性提示，STM中的PTM串扰和HCM中蛋白激酶A通路的失调。令人惊讶的是，我们发现进行间隔肌切除术的HCM患者心肌中的肌节蛋白形式变化非常一致，无论潜在的HCM突变为何。这项研究表明，尽管存在不同的基因型，重度HCM的表现仍在蛋白状水平上融合，