Smith Robert M, Suleman Naushaad, McCarthy Joy, Sack Michael N
Hatter Institute for Cardiology Research, MRC Inter-University Cape Heart Group, University of Cape Town Medical School, Observatory 7925, South Africa.
Cardiovasc Res. 2002 Aug 15;55(3):553-60. doi: 10.1016/s0008-6363(02)00283-3.
Tumor necrosis factor alpha (TNFalpha) is known to mimic ischemic preconditioning (IP). However, it is not known whether TNFalpha-preconditioning is mediated by 'established' preconditioning signaling or via novel signaling cascades. Moreover, whether TNFalpha is required to induce the ischemic preconditioning phenotype has not been determined.
To evaluate the role of TNFalpha, we determined the infarct-sparing effect of IP comparing TNFalpha null (TNFalpha-/-) and wild-type mice. The IP protocol included 4x5 min ischemia/reperfusion (I/R) prior to the index 35 min of global ischemia followed by 45 min of reperfusion in isolated perfused murine hearts. Infarct size was measured as a percentage of cardiac volume. To evoke particular signaling pathways numerous pharmacologic studies were performed.
Following IP, infarct size was significantly reduced by 43% in wild-type mice. In contrast, infarct size was not attenuated by IP in the TNFalpha-/- group versus I/R controls (Infarct size-36+/-3%). Interestingly, pharmacologic preconditioning with adenosine (100 microM) and diazoxide (30 microM) mimicked IP in both the wild-type (infarct size-11+/-4% and 18+/-2%) and in TNFalpha-/- mice (infarct size-15+/-4% and 23+/-3%) versus respective I/R controls. Recombinant TNFalpha (0.5 ng/ml) administered for 7 min followed by a 10-min washout mimicked IP in wild-type mice but not in the TNFalpha deficient mouse hearts. The cardioprotective effects of IP, adenosine and TNFalpha were abolished by the co-administration of the putative mitochondrial K(ATP) blocker 5-hydroxydecanoate.
We demonstrate that cardiac TNFalpha production is required for ischemic preconditioning-induced cardioprotection but not necessary in pharmacologic preconditioning with adenosine or diazoxide in TNFalpha-/- mice. Moreover, TNFalpha administration is sufficient to activate preconditioning in wild-type mice. Finally, as 5-hydroxydecanoate abrogates ischemic, adenosine and TNFalpha induced preconditioning, this suggests that diverse signaling pathways converge at the level of mitochondrial K(ATP) channel activation to mediate this cardioprotection.
已知肿瘤坏死因子α（TNFα）可模拟缺血预处理（IP）。然而，尚不清楚TNFα预处理是由“既定”的预处理信号介导，还是通过新的信号级联反应介导。此外，TNFα是否为诱导缺血预处理表型所必需尚未确定。
为评估TNFα的作用，我们通过比较TNFα基因敲除（TNFα-/-）小鼠和野生型小鼠，确定了IP的梗死灶缩小效应。IP方案包括在35分钟全心缺血前进行4次5分钟的缺血/再灌注（I/R），随后在离体灌注的小鼠心脏中进行45分钟的再灌注。梗死灶大小以心脏体积的百分比来衡量。为激活特定的信号通路，进行了大量药理学研究。
IP后，野生型小鼠的梗死灶大小显著减少43%。相比之下，TNFα-/-组与I/R对照组相比，IP并未使梗死灶大小减小（梗死灶大小为36±3%）。有趣的是，腺苷（100μM）和二氮嗪（30μM）进行药理学预处理在野生型小鼠（梗死灶大小为11±4%和18±2%）和TNFα-/-小鼠（梗死灶大小为15±4%和23±3%）中均模拟了IP，与各自的I/R对照组相比。在野生型小鼠中，给予重组TNFα（0.5 ng/ml）7分钟，随后冲洗10分钟可模拟IP，但在TNFα缺陷的小鼠心脏中则不能。IP、腺苷和TNFα的心脏保护作用通过共同给予假定的线粒体K（ATP）阻滞剂5-羟基癸酸而被消除。
我们证明，缺血预处理诱导的心脏保护需要心脏产生TNFα，但在TNFα-/-小鼠中腺苷或二氮嗪进行药理学预处理时并非必需。此外，给予TNFα足以在野生型小鼠中激活预处理。最后，由于5-羟基癸酸消除了缺血、腺苷和TNFα诱导的预处理作用，这表明不同的信号通路在线粒体K（ATP）通道激活水平汇聚以介导这种心脏保护作用。
