AMPK可能经减轻心肌细胞内质网应激而发挥抗凋亡作用

The AMP-activated protein kinase (AMPK) inhibits apoptosis of cardiomyocytes, and plays an importantly protective role in cardiac ischemia-reperfusion injury. However, the mechanisms underlying the inhibition to apoptosis are still unclear. We have found that the expression of AMPK reduced in hearts of simulated weightlessness rats, and that AMPK could regulate apoptosis of cardiomyocytes through affecting the endoplasmic reticulum stress. Therefore, The aims of this study are (1) to prove that activated AMPK could reduce apoptosis rate in ischemia marginal zone and decreased the infarct size of heart in 4-week simulated weightlessness rats; and (2) to illuminate the mechanisms inhibited apoptosis by AMPK would involve that AMPK reduces the endoplasmic reticulum stress through the inhibition of protein synthesis which alleviates higher endoplasmic reticulum stress. The downstream pathway (CHOP-Ero1-IP3R pathway) induced by the endoplasmic reticulum over-stress would not be activated, and the calcium transport from endoplasmic reticulum to mitochondrion may be reduced. Without the calcium overload in mitochondrion, the endogenous mitochondrial apoptosis pathway may not be activated, and the apoptosis rate would be reduced during ischemia-reperfusion. This study will provide the theoretical basis for preventing astronauts' heart injury induced by orthostatic intolerance after long-term spaceflight, and for exploring new treatment of cardiac ischemia-reperfusion injury in clinical.

腺苷酸活化蛋白激酶(AMPK)可抑制细胞凋亡，在心脏缺血-再灌注损伤中发挥重要的保护作用，但其抑制凋亡的机制尚未探明。我们发现模拟失重4周大鼠心肌AMPK表达降低，可影响内质网应激而调节心肌细胞凋亡。本研究拟采用模拟失重4周大鼠，在心脏缺血-再灌注条件下，证明激活AMPK明显降低心肌缺血边界区心肌细胞凋亡率，从而缩小心肌梗死面积，发挥心保护作用。同时阐明AMPK可能通过以下新机制而抑制凋亡：AMPK经抑制蛋白质合成而减轻内质网应激程度；从而阻断因内质网过度应激导致的下游信号转导通路(CHOP-Ero1-IP3R通路)激活，防止内质网钙离子向线粒体的转运；防止因线粒体钙离子超载导致内源性线粒体凋亡通路的激活，从而降低心肌细胞凋亡率。该结果在航天员返回地面时防止立位耐力不良引起心肌损伤中，具有一定的理论参考价值；亦可为临床上防治心肌缺血-再灌注损伤提供新思路。

尾部悬吊4周的模拟失重大鼠心肌内AMPK表达降低。AMPK在心肌发生缺血再灌注时可以增加糖酵解和脂肪代谢，减少蛋白质合成，以维持细胞内能量供给，保护心肌细胞。AMPK表达降低使得模拟失重大鼠离体心脏发生缺血-再灌注后，心肌收缩功能受损更加显著，梗死面积明显增大。使用AMPK变构激动剂A-69662，可明显改善大鼠缺血-再灌注期心肌收缩功能，缩小心肌梗死面积。AMPK对蛋白质合成的抑制作用不仅减少了ATP消耗，也减轻了内质网内由于缺氧导致大量错误折叠蛋白堆积而形成的“内质网应激”。内质网应激过大或持续存在时，PERK经ATF4激活CHOP信号转导通路，使Ero1激活，开放内质网上的Ca2+通道IP3R，使内质网中Ca2+向线粒体转运，导致线粒体Ca2+过载，进而降低线粒体膜电位，释放细胞色素c，启动内源性凋亡通路。提高AMPK的活性可以通过削弱内质网应激，阻碍内质网与线粒体之间的Ca2+转运，减少心肌细胞凋亡。本研究阐明了AMPK可以通过抑制内源性线粒体凋亡途径而发挥心肌保护作用。这一结果为寻找心肌缺血再灌注损伤的保护机制提供了一条新的思路。