Study of mechanism of ischemic neuronal death.a molecular biological approach

我们发现脑缺血后的神经元死亡有四种类型，分别是丘脑网状核的超早型缺血性神经元损伤、能量衰竭引起的经典急性缺血性神经元死亡、被认为与细胞凋亡有关的延迟性神经元死亡、局灶性脑梗死引起的边远区缓慢进行性神经元死亡。以下是脑缺血后神经元死亡的机制。我们尝试用MRI检测大鼠MCA闭塞后的远程变化。然后，我们发现，在远离原发性缺血性病变的区域，MR成像有两种类型的继发性变性。在大鼠局灶性缺血后，研究了原癌基因c-myc、s-myc和抑癌基因p53以及原癌基因bcl-2 mrna的可能诱导作用，这些基因已知可诱导细胞凋亡，而原癌基因bcl-2可抑制细胞凋亡。c-myc基因表达呈时间依赖性快速显著诱导。结果提示c-myc基因的高水平表达可能参与了包括细胞凋亡在内的缺血细胞事件。近年来有研究认为鞘磷脂降解产生的神经酰胺在细胞凋亡中起第二信使的作用。测定了局灶性缺血大鼠大脑皮层内腺苷、鞘磷脂、脑苷和神经节苷的含量。神经酰胺在缺血6小时开始升高。增加的神经酰胺中氨基脂肪酸完全由非羟基脂肪酸组成，以硬脂酸最为突出。鞘磷脂的氨基脂肪酸主要为硬脂酸，呈时间依赖性下降。结果表明，神经酰胺在缺血早期通过鞘磷脂的破坏在大脑皮层产生。

We found that there are four types of neuronal death following cerebral ischemia, such as ultra-early-type ischemic neuronal injury in the thalamic reticular nucleus, classical acute ischemic neuronal death due to energy failure, delayd neuronal death which is considered to be related to apoptosis, slowly progressive neuronal death in remote areas from focal cerebral infarction. Mechanisms of teses types of nuronal death after cerebral ischemia were studied as follows.We tried to detect the remote changes using MRI after MCA occlusion in the rat. Then, we found that, in areas remote from a primary ischemic lesion, there are two types of secondary degeneration with MR imaging.Possible induction of mRNAs for proto-oncogene c-myc and s-myc and oncosupressor gene p53, which are known to induce apoptosis, and protooncogene bcl-2, which inhibits apoptosis, was examined following focal ischemia in the rat. The c-myc gene expression was rapidly and markedly induced in a timedependent manner. The results indicate a possibility that high level expression of the c-myc gene may be involved in the ischemic cellular events including apoptosis.It is recently suggested that ceramide, generated by sphingomyelin degradation, plays a role as a second messenger in apoptosis. Level of ceremide, sphingomyelin, cerebroside and gangliosides were determined in rat cerebral cortex during focal ischemia. Ceramide began to increase at 6 hours of ischemia. Aminolinked fatty acids in increased ceramide were composed solely of non-hydroxy fatty acids, and stearic acid was the most prominent. Sphingomyelin, whose aminolinked fatty acids were mostly stearic acid, decreased in a time-dependent manner. The results suggested that ceramide was produced in the cerebral cortex by the breakdown of sphingomyelin during early ischemia.