DeGracia D J, Adamczyk S, Folbe A J, Konkoly L L, Pittman J E, Neumar R W, Sullivan J M, Scheuner D, Kaufman R J, White B C, Krause G S
Department of Emergency Medicine, Wayne State University School of Medicine, Detroit, Michigan, 48201, USA.
Exp Neurol. 1999 Feb;155(2):221-7. doi: 10.1006/exnr.1998.6986.
When ischemic brain is reperfused, there is in vulnerable neurons immediate inhibition of protein synthesis associated with a large increase in phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 [eIF2alpha, phosphorylated form eIF2alpha(P)]. We examined eIF2alpha kinase and eIF2alpha(P) phosphatase activity in brain homogenate postmitochondrial supernatants obtained from rats after 3 to 30 min of global brain ischemia (cardiac arrest), after 5 min of ischemia and 5 min of reperfusion (5R), and after 10 min of ischemia and 90 min reperfusion (90R). Because it has been suggested that PKR might be specifically responsible for producing eIF2alpha(P) during reperfusion, we also examined in brain homogenates from wild-type and PKR0/0 C57BL/6J x 129/SV mice the effect of 5 min of ischemia and 5 min of reperfusion on eIF2alpha(P). Cytosolic brain eIF2alpha(P) in the 5R and 90R rats was 18- and 23-fold that of nonischemic controls without any change in the rate of eIF2alpha(P) dephosphorylation. There was no change in eIF2alpha kinase activity between 3 and 30 min of ischemia but an 85% decrease in the 5R group; the 90R group was similar to controls. In wild-type and PKR0/0 mice total eIF2alpha was identical, and there was an identical 16-fold increase in eIF2alpha(P) at 5 min of reperfusion. Our observations contradict hypotheses that PKR activation, loss of eIF2alpha(P) phosphatase activity, or any general increase in eIF2alpha kinase activity are responsible for reperfusion-induced phosphorylation of eIF2alpha, and we suggest that the mechanism may involve regulation of the availability of eIF2alpha to a kinase.
当缺血性脑再灌注时，易损神经元中蛋白质合成会立即受到抑制，同时真核起始因子2的α亚基（eIF2α，磷酸化形式为eIF2α(P)）的磷酸化大幅增加。我们检测了从经历3至30分钟全脑缺血（心脏骤停）、5分钟缺血加5分钟再灌注（5R）以及10分钟缺血加90分钟再灌注（90R）的大鼠获得的脑匀浆线粒体后上清液中的eIF2α激酶和eIF2α(P)磷酸酶活性。由于有人提出PKR可能在再灌注期间特异性地负责产生eIF2α(P)，我们还检测了野生型和PKR0/0 C57BL/6J×129/SV小鼠脑匀浆中5分钟缺血和5分钟再灌注对eIF2α(P)的影响。5R和90R大鼠脑胞质中的eIF2α(P)分别是非缺血对照组的18倍和23倍，而eIF2α(P)的去磷酸化速率没有任何变化。缺血3至30分钟期间eIF2α激酶活性没有变化，但5R组下降了85%；90R组与对照组相似。在野生型和PKR0/0小鼠中，总eIF2α相同，再灌注5分钟时eIF2α(P)均增加了16倍。我们的观察结果与以下假设相矛盾：PKR激活、eIF2α(P)磷酸酶活性丧失或eIF2α激酶活性的任何普遍增加是再灌注诱导的eIF2α磷酸化的原因，我们认为其机制可能涉及对eIF2α向激酶的可利用性的调节。
