Barefield David, Kumar Mohit, Gorham Joshua, Seidman Jonathan G, Seidman Christine E, de Tombe Pieter P, Sadayappan Sakthivel
Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, IL, USA.
Department of Genetics, Harvard Medical School, Boston, MA, USA.
J Mol Cell Cardiol. 2015 Feb;79:234-43. doi: 10.1016/j.yjmcc.2014.11.018. Epub 2014 Nov 25.
Mutations in MYBPC3, the gene encoding cardiac myosin binding protein-C (cMyBP-C), account for ~40% of hypertrophic cardiomyopathy (HCM) cases. Most pathological MYBPC3 mutations encode truncated protein products not found in tissue. Reduced protein levels occur in symptomatic heterozygous human HCM carriers, suggesting haploinsufficiency as an underlying mechanism of disease. However, we do not know if reduced cMyBP-C content results from, or initiates the development of HCM. In previous studies, heterozygous (HET) mice with a MYBPC3 C'-terminal truncation mutation and normal cMyBP-C levels show altered contractile function prior to any overt hypertrophy. Therefore, this study aimed to test whether haploinsufficiency occurs, with decreased cMyBP-C content, following cardiac stress and whether the functional impairment in HET MYBPC3 hearts leads to worsened disease progression. To address these questions, transverse aortic constriction (TAC) was performed on three-month-old wild-type (WT) and HET MYBPC3-truncation mutant mice and then characterized at 4 and 12weeks post-surgery. HET-TAC mice showed increased hypertrophy and reduced ejection fraction compared to WT-TAC mice. At 4weeks post-surgery, HET myofilaments showed significantly reduced cMyBP-C content. Functionally, HET-TAC cardiomyocytes showed impaired force generation, higher Ca(2+) sensitivity, and blunted length-dependent increase in force generation. RNA sequencing revealed several differentially regulated genes between HET and WT groups, including regulators of remodeling and hypertrophic response. Collectively, these results demonstrate that haploinsufficiency occurs in HET MYBPC3 mutant carriers following stress, causing, in turn, reduced cMyBP-C content and exacerbating the development of dysfunction at myofilament and whole-heart levels.
编码心肌肌球蛋白结合蛋白-C（cMyBP-C）的基因MYBPC3发生突变，约占肥厚型心肌病（HCM）病例的40%。大多数病理性MYBPC3突变编码在组织中未发现的截短蛋白产物。有症状的杂合子人类HCM携带者中蛋白质水平降低，提示单倍体不足是疾病的潜在机制。然而，我们尚不清楚cMyBP-C含量降低是HCM的病因还是其发病的起始因素。在先前的研究中，具有MYBPC3 C末端截短突变且cMyBP-C水平正常的杂合子（HET）小鼠在出现任何明显的肥大之前就表现出收缩功能改变。因此，本研究旨在测试在心脏应激后，cMyBP-C含量降低时单倍体不足是否会发生，以及HET MYBPC3心脏的功能损害是否会导致疾病进展恶化。为了解决这些问题，对3个月大的野生型（WT）和HET MYBPC3截短突变小鼠进行了横向主动脉缩窄（TAC），然后在术后4周和12周进行特征分析。与WT-TAC小鼠相比，HET-TAC小鼠表现出更明显的肥大和更低的射血分数。术后4周，HET肌丝的cMyBP-C含量显著降低。在功能上，HET-TAC心肌细胞表现出力量产生受损、更高的Ca(2+)敏感性以及力量产生的长度依赖性增加减弱。RNA测序揭示了HET组和WT组之间几个差异调节的基因，包括重塑和肥大反应的调节因子。总的来说，这些结果表明，应激后HET MYBPC3突变携带者会出现单倍体不足，进而导致cMyBP-C含量降低，并加剧肌丝和全心水平的功能障碍发展。
