Department of Medicine, Division of Cardiology, Virginia Commonwealth University, Richmond, VA 23298, United States.
Biochem Biophys Res Commun. 2011 Dec 2;415(4):533-8. doi: 10.1016/j.bbrc.2011.10.037. Epub 2011 Oct 25.
Ubiquitous calpains (calpain I and II) are generally recognized as cytosolic proteins. Recently, mitochondrial localized calpain I (μ-calpain) has been identified. Activation of mito-μ-calpain cleaves apoptosis inducing factor (AIF), a flavoprotein located within the mitochondrial intermembrane space, in liver mitochondria, but not in brain mitochondria. We first tested if activation of mito-μ-calpain cleaves AIF in isolated heart mitochondria. A decrease in AIF content within mitochondria increases cardiac injury during ischemia-reperfusion by augmenting oxidative stress. We hypothesize that the activation of mito-μ-calpain by calcium overload during ischemia-reperfusion results in decreased AIF content within mitochondria by cleaving AIF. The μ-calpain was present within mouse heart mitochondria, mostly in the intermembrane space. Exogenous calcium treatment induced a calpain-dependent decrease of mitochondrial AIF content in isolated mouse heart mitochondria. This process was blocked by a calpain inhibitor (MDL-28170). The Mitochondrial μ-calpain activity was increased by 160 ± 15% during ischemia-reperfusion compared to time control. In contrast, the mitochondrial AIF content was decreased by 52 ± 7% during reperfusion vs. time control in the buffer perfused mouse heart. Inhibition of mito-μ-calpain using MDL-28170 decreased cardiac injury by preserving AIF content within mitochondria during ischemia-reperfusion. Thus, activation of mito-μ-calpain is required to release AIF from cardiac mitochondria. Inhibition of calpains using MDL-28170 decreases cardiac injury by inhibiting both cytosolic calpains and mito-μ-calpain during ischemia-reperfusion.
无处不在的钙蛋白酶（钙蛋白酶 I 和钙蛋白酶 II）通常被认为是细胞质蛋白。最近，已鉴定出线粒体定位的钙蛋白酶 I（μ-钙蛋白酶）。线粒体 μ-钙蛋白酶的激活可切割位于线粒体跨膜间隙中的凋亡诱导因子（AIF），但不会切割脑线粒体中的 AIF。我们首先测试了在分离的心脏线粒体中，线粒体 μ-钙蛋白酶的激活是否会切割 AIF。线粒体中 AIF 含量的减少会通过增加氧化应激来增加缺血再灌注期间的心脏损伤。我们假设，在缺血再灌注期间钙超载导致线粒体 μ-钙蛋白酶的激活，通过切割 AIF 导致线粒体中 AIF 含量减少。μ-钙蛋白酶存在于小鼠心脏线粒体中，主要存在于膜间空间。外源性钙处理可诱导分离的小鼠心脏线粒体中钙蛋白酶依赖性的线粒体 AIF 含量减少。该过程被钙蛋白酶抑制剂（MDL-28170）阻断。与时间对照相比，缺血再灌注期间线粒体 μ-钙蛋白酶活性增加了 160±15%。相比之下，在缓冲液灌注的小鼠心脏中，再灌注期间线粒体 AIF 含量比时间对照减少了 52±7%。使用 MDL-28170 抑制线粒体 μ-钙蛋白酶可通过在缺血再灌注期间保持线粒体中 AIF 的含量来减少心脏损伤。因此，激活线粒体 μ-钙蛋白酶是将 AIF 从心脏线粒体中释放出来所必需的。在缺血再灌注期间，使用 MDL-28170 抑制钙蛋白酶可通过抑制胞质钙蛋白酶和线粒体 μ-钙蛋白酶来减少心脏损伤。
