Myofibril damage during low-flow ischemia

描述（由申请人提供）：低血流缺血发作后的可逆性收缩功能障碍被认为是对冠状动脉血流减少和/或短暂性心肌损伤的适应性反应。从概念上讲，当血流和功能在某种程度上匹配时，心脏被认为已经适应了保持心肌活力。如果尽管恢复了正常的冠状动脉血流，但收缩功能仍然受到抑制，则血流和功能变得不匹配，并且心肌被称为顿抑。在长期仪器犬心脏的研究表明，有活力的心肌细胞显示，当流量和功能仍然不匹配的中断肌原纤维的地区。低流量缺血后出现的肌原纤维异常包括肌节内的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磷酸化状态的变化可能有助于引发粗丝紊乱、中断和收缩功能障碍。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，中间丝的破坏和微管的解聚。小的热休克蛋白HSP 27和aB-晶状体蛋白分别与肌动蛋白和结蛋白相互作用，HSC 70与微管蛋白形成高分子量聚集体。在这个提议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的去磷酸化是否引发粗丝紊乱和破坏;（3）小热休克蛋白和HSC 7 O的再分布是否保护肌原纤维和细胞骨架蛋白？识别低流量缺血后改变肌原纤维结构的机制可能会控制流量-功能匹配，保持心肌细胞活力，并最大限度地减少反复缺血发作引起的心肌损伤。

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.