Thin filament disinhibition by restrictive cardiomyopathy mutant R193H troponin I induces Ca2+-independent mechanical tone and acute myocyte remodeling
Thin filament disinhibition by restrictive cardiomyopathy mutant R193H troponin I induces Ca2+-independent mechanical tone and acute myocyte remodeling
复制标题
DOI：
10.1161/01.res.0000268412.34364.50
复制
发表时间：
2007-05-25
影响因子：
20.1
通讯作者：
Metzger, Joseph M.
中科院分区：
文献类型：
--
作者：
Davis, Jennifer;Wen, Haitao;Metzger, Joseph M.
遗传性限制性心肌病（RCM）是一种衰弱性疾病，其特征是心脏僵硬，心室舒张受损。心脏肌钙蛋白I （cTnI）突变被确定为RCM的原因。成人心肌细胞的急性基因工程被用来鉴定突变cTnI的主要结构/功能影响。由于R193H cTnI等位基因预后较差，研究主要集中在R193H cTnI上。与野生型cTnI相比，R193H突变型cTnI更有效地融入肌节，在肌节中对基础和动态收缩功能发挥剂量依赖性作用。在负荷条件下，通透性心肌细胞Ca2+对张力的敏感性增加，而被动张力-伸展关系不受R193H cTnI的影响。正常的杆状心肌细胞形态急剧转变为“短蹲”表型，在没有舒张期Ca2+改变的情况下，与R193H的进行性化学计量结合一致。特异性肌球蛋白抑制剂blebbistatin完全阻断了这种转变。R193H肌丝增加Ca2+缓冲，而不是肌浆网Ca2+处理的改变，减缓了Ca2+瞬态的衰减速率。R193H赋予的不完全机械松弛在起搏频率增加时加剧，与舒张期Ca2+升高无关。R193H ctni依赖的机械张力导致急性重塑到准收缩状态，而不是由其他Ca2+敏化蛋白引起的，并且与体内RCM的僵硬心脏特征直接相关。这些结果指向Ca2+处理的下游目标，特别是细丝调节和肌动蛋白-肌球蛋白相互作用，在设计治疗策略以纠正RCM的原代细胞形态和机械基础时。
Inherited restrictive cardiomyopathy (RCM) is a debilitating disease characterized by a stiff heart with impaired ventricular relaxation. Mutations in cardiac troponin I (cTnI) were identified as causal for RCM. Acute genetic engineering of adult cardiac myocytes was used to identify primary structure/function effects of mutant cTnI. Studies focused on R193H cTnI owing to the poor prognosis of this allele. Compared with wild-type cTnI, R193H mutant cTnI more effectively incorporated into the sarcomere, where it exerted dose-dependent effects on basal and dynamic contractile function. Under loaded conditions, permeabilized myocyte Ca2+ sensitivity of tension was increased, whereas the passive tension-extension relationship was not altered by R193H cTnI. Normal rod-shaped myocyte morphology acutely transitioned to a " short- squat" phenotype in concert with progressive stoichiometric incorporation of R193H in the absence of altered diastolic Ca2+ . The specific myosin inhibitor blebbistatin fully blocked this transition. Heightened Ca2+ buffering by the R193H myofilaments, and not alterations in Ca2+ handling by the sarcoplasmic reticulum, slowed the decay rate of the Ca2+ transient. Incomplete mechanical relaxation conferred by R193H was exacerbated at increasing pacing frequencies independent of elevated diastolic Ca2+. R193H cTnI-dependent mechanical tone caused acute remodeling to a quasicontracted state not elicited by other Ca2+-sensitizing proteins and is a direct correlate of the stiff heart characteristic of RCM in vivo. These results point toward targets downstream of Ca2+ handling, notably thin filament regulation and actin-myosin interaction, in designing therapeutic strategies to redress the primary cell morphological and mechanical underpinnings of RCM.