Data from: Acute, delayed and chronic remote ischemic conditioning is associated with downregulation of mTOR and enhanced autophagy signaling

Background - Remote ischemic conditioning (RIC), induced by brief periods of limb ischemia has been shown to decrease acute myocardial injury and chronic responses after acute coronary syndromes. While several signaling pathways have been implicated, our understanding of the cardioprotection and its underlying mediators and mechanisms remains incomplete. In this study we examine the effect of RIC on pro- autophagy signaling as a possible mechanism of benefit. Methods and Results - We examined the role of autophagy in the acute/first window (15 minutes after RIC), delayed/second window (24 hours after RIC) and chronic (24 hours after 9 days of repeated RIC) phases of cardioprotection. C57BL/6 mice (N=69) were allocated to each treatment phase and further stratified to receive RIC, induced by four cycles of 5 minutes of limb ischemia followed by 5 minutes of reperfusion, or control treatment consisting solely of handling without transient ischemia. The groups included, group 1 (1W control), group 2 (1W RIC), group 3 (2W control), group 4 (2W RIC), group 5 (3W control) and group 6 (3W RIC). Hearts were isolated for assessment of cardiac function and infarct size after global ischemia using a Langendorff preparation. Infarct size was reduced in all three phases of cardioprotection, in association with improvements in post-ischemic left ventricular end diastolic pressure (LVEDP) and developed pressure (LVDP) (P<0.05). The pattern of autophagy signaling varied; 1W RIC increased AMPK levels and decreased the activation of mammalian target of rapamycin (mTOR), whereas chronic RIC was associated with persistent mTOR suppression and increased levels of autophagosome proteins, LC3II/I and Atg5. Conclusions - Cardioprotection following transient ischemia exists in both the acute and delayed/chronic phases of conditioning. RIC induces pro-autophagy signaling but the pattern of responses varies depending on the phase, with the most complete portfolio of responses observed when RIC is administered chronically.研究背景：由短暂肢体缺血诱导的远程缺血预处理（Remote ischemic conditioning, RIC）已被证实可减轻急性冠脉综合征后的急性心肌损伤与慢性应激反应。尽管已有多项信号通路被发现与此保护作用相关，但目前我们对其心脏保护效应及其潜在介导因子与作用机制的认知仍不全面。本研究旨在探讨远程缺血预处理对促自噬信号通路的影响，以此作为其发挥保护作用的潜在机制之一。 研究方法与结果：本研究考察了自噬在心脏保护作用的三个时相中的作用：急性/第一窗口（远程缺血预处理后15分钟）、延迟/第二窗口（远程缺血预处理后24小时）以及慢性时相（反复9天远程缺血预处理后24小时）。将69只C57BL/6小鼠随机分配至各实验时相组，随后进一步分层接受远程缺血预处理或对照处理：预处理方案为4轮循环的5分钟肢体缺血+5分钟再灌注，对照处理仅进行同等操作但不施加短暂缺血。实验分为6组：第1组（急性窗口对照组）、第2组（急性窗口预处理组）、第3组（延迟窗口对照组）、第4组（延迟窗口预处理组）、第5组（慢性时相对照组）、第6组（慢性时相预处理组）。采用Langendorff离体心脏灌流模型，在全心缺血后分离心脏，评估心功能与梗死面积。结果显示，三个心脏保护时相的梗死面积均显著降低，同时伴随缺血后左心室舒张末期压（left ventricular end diastolic pressure, LVEDP）与左心室发展压（left ventricular developed pressure, LVDP）的改善（P<0.05）。自噬信号通路的活化模式存在差异：急性窗口预处理组可升高腺苷酸活化蛋白激酶（AMP-activated protein kinase, AMPK）水平并降低哺乳动物雷帕霉素靶蛋白（mammalian target of rapamycin, mTOR）的活化，而慢性时相预处理组则表现为mTOR持续受抑制，且自噬体相关蛋白LC3II/I与Atg5的表达水平升高。 研究结论：短暂缺血诱导的心脏保护作用存在于预处理的急性与延迟/慢性时相。远程缺血预处理可激活促自噬信号通路，但不同时相的应答模式存在差异，其中以慢性预处理时的应答谱最为完整。