The relationship between oxidative stress and cardiac stiffness is thought to involve modifications to the giant muscle protein titin, which in turn can determine the progression of heart disease. In vitro studies have shown that S-glutathionylation and disulfide bonding of titin fragments could alter the elastic properties of titin; however, whether and where titin becomes oxidized in vivo is less certain. Here we demonstrate, using multiple models of oxidative stress in conjunction with mechanical loading, that immunoglobulin domains preferentially from the distal titin spring region become oxidized in vivo through the mechanism of unfolded domain oxidation (UnDOx). Via oxidation type-specific modification of titin, UnDOx modulates human cardiomyocyte passive force bidirectionally. UnDOx also enhances titin phosphorylation and, importantly, promotes nonconstitutive folding and aggregation of unfolded domains. We propose a mechanism whereby UnDOx enables the controlled homotypic interactions within the distal titin spring to stabilize this segment and regulate myocardial passive stiffness.

氧化应激和心脏僵硬度之间的关系被认为涉及巨肌蛋白肌联蛋白的修饰，而肌联蛋白又可以决定心脏病的进展。体外研究表明肌联蛋白片段的S-谷胱甘肽化和二硫键可以改变肌联蛋白的弹性特性；然而，肌动蛋白在体内是否以及在何处被氧化还不太确定。在这里，我们使用多种氧化应激模型与机械负荷结合证明，来自远端肌动蛋白弹簧区域的免疫球蛋白结构域优先通过未折叠结构域氧化（UnDOx）机制在体内被氧化。通过对肌联蛋白的氧化类型特异性修饰，UnDOx 双向调节人心肌细胞被动力。 UnDOx 还增强肌联蛋白磷酸化，重要的是，促进未折叠结构域的非组成型折叠和聚集。我们提出了一种机制，UnDOx 能够在远端肌腱弹簧内实现受控的同型相互作用，从而稳定该节段并调节心肌被动僵硬度。