Myofibril damage during low-flow ischemia

描述（由申请人提供）：低流量缺血发作后的可逆性收缩功能障碍被认为是冠状动脉血流减少和/或一过性心肌损伤的适应性反应。从概念上讲，当流量和功能在一定程度上匹配时，心脏被认为已经适应了保持心肌活力。如果在冠状动脉血流恢复正常的情况下，收缩功能仍然下降，那么血流和功能就会不匹配，心肌就会被称为休克。在长期使用仪器的犬心脏中进行的研究表明，当血流和功能仍然不匹配时，活的心肌细胞显示出被破坏的肌原纤维区域。低流量缺血后出现的肌原纤维异常包括肌节内粗丝紊乱和肌原纤维粗丝断裂。这些结构改变伴随着肌球蛋白结合蛋白c （MyBP-C）磷酸化的变化。由于MyBP-C被认为调节粗丝结构和功能，MyBP-C磷酸化状态的改变可能有助于引发粗丝紊乱、破坏和收缩功能障碍。其他细胞骨架元素也发生改变，包括肌动蛋白聚集体的形成，中间细丝的破坏和微管的解聚。热休克小蛋白HSP27和aB-crystallin分别与actin和desmin相互作用，hsc70与微管蛋白形成高分子量聚集体。本提案中概述的实验旨在回答以下问题：(1)MyBP-C的去磷酸化是否诱导收缩功能障碍；(2) MyBP-C的去磷酸化是否会引发粗丝紊乱和断裂；(3)小热休克蛋白和hsc70的重新分配是否能保护肌原纤维蛋白和细胞骨架蛋白？确定低流量缺血后改变肌原纤维结构的机制可能使控制血流功能匹配、保持心肌活力和减少反复缺血发作造成的心肌损伤成为可能。

DESCRIPTION (provided by applicant): The reversible contractile dysfunction that follows episodes of low-flow ischemia is believed to represent an adaptive response to reduced coronary flow and/or transient myocardial injury. Conceptually, when flow and function are matched at some reduced level, the heart is thought to have adapted to preserve myocardial viability. If contractile function remains depressed despite the restoration of normal coronary flow, then flow and function become mismatched and the myocardium is said to be stunned. Studies in the chronically instrumented canine heart demonstrate that viable cardiac myocytes disclose areas of disrupted myofibrils when flow and function remain mismatched. Myofibril anomalies that appear following low-flow ischemia include the development of thick filament disorder within the sarcomere and myofibrillar thick filament disruption. These structural alterations are accompanied by changes in the phosphorylation of myosin binding protein-C (MyBP-C). Since MyBP-C is believed to regulate thick filament structure and function, changes in the phosphorylated state of MyBP-C may be instrumental in initiating thick filament disorder, disruption and contractile dysfunction. Other cytoskeletal elements are altered as well, including the formation of actin aggregates, disruption of intermediate filaments and depolymerization of microtubules. Small heat shock proteins, HSP27 and aB-crystallin, interact with actin and desmin, respectively, and HSC7O forms high molecular weight aggregates with tubulin. Experiments outlined in this proposal are designed to answer the following questions: (1) does dephosphorylation of MyBP-C induce contractile dysfunction; (2) does dephosphorylation of MyBP-C initiate thick filament disorder and disruption; and (3) does redistribution of small heat shock proteins and HSC7O protect myofibrillar and cytoskeletal proteins? Identifying the mechanism(s) that alter myofibril structure following low-flow ischemia may make it possible to control flow-function matching, preserve cardiocyte viability and minimize myocardial injury from repeated ischemic episodes.