缺氧缺血新生大鼠脑组织caspase-1和白细胞介素18mRNA表达及其关系探讨

Expression of and relationship between caspase-1 and interleukin-18 mRNA in brain tissue of hypoxic-ischemic neonatal rats

目的研究caspase1及其底物之一白细胞介素(IL)18mRNA的表达在缺氧缺血性脑损伤(HIBD)中的作用及其意义。方法112只7日龄新生Wistar大鼠按照完全随机化方法分为对照组、HIBD3、8、24h、3、6和14d组,每组16只。其中8只采用RTPCR方法检测caspase1和IL18mRNA在HIBD后脑皮层中的表达及其相关性,另外8只光镜下观察脑组织病理学改变。结果对照组有caspase1mRNA少量表达(0.2918±0.0809),HIBD24h组其水平开始增加(0.5222±0.0941,与对照组比较P<0.01),6d达高峰(0.7886±0.0480,与其余各组相比P<0.01),此后下降,但HIBD14d(0.5314±0.1272)仍可检测出。对照组IL18mRNA水平为0.3218±0.0466,HIBD24h至6d其表达逐渐增加(24h:0.5823±0.0740;3d:0.6976±0.1073;6d:0.9110±0.0647,与对照组比较均为P<0.01),并达高峰(HIBD6d组与其余各组相比P<0.01)。HIBD后IL18mRNA的表达在时间上与caspase1具有紧密相关性(r=0.871,P<0.01)。组织学检查发现神经元变性、坏死在HIBD1～6天逐渐加重。结论HIBD后caspase1和IL18mRNA的表达逐渐增加,其变化规律与光镜观察到的脑损伤进展的时间框架吻合,提示它们均参与了新生鼠HIBD的病理形成过程。

Objective Caspase-1 is a member of cysteinyl aspartate specific protease family and it plays important roles in the pathophysiology of many diseases for its proinflammatory and proapoptotic peculiarity. Interleukin （IL）-18, one of its substrates, is a pleiotropic cytokine and processed by caspase-1 to become fully bioactive. The aim of this study was to investigate the relationship and effect of caspase-1 and IL-18 mRNA expressions after hypoxic-ischemic brain damage （HIBD） in neonatal rats. Methods Totally 112 seven-day-old Wistar rats were assigned to control group, HIBD 3 h, 8 h, 24 h, 3 d, 6 d and 14 d groups via complete randomization （n = 16 per group）, and the model of HIBD was induced by unilateral carotid ligation followed by timed exposure to 8% oxygen. In each group, 8 rats were used for measuring the mRNA for caspase-1 and IL-18 in the cerebral cortex by semi-quantitative RT-PCR, and the brains of another 8 rats were observed for light microscopic changes by HE staining. Results The expression of caspase-1 mRNA was low in control group （0. 2918 ± 0. 0809）. After HIBD, the level of caspase-1 mRNA in ischemic cortex began to increase at 24 h （0.5222 ± 0.0941, P〈0.01 vs. control）, peaked at 6 d（0.7886 ± 0.0480, P〈0.01 vs. the other groups） and decreased at 14 d （0.5314 ± 0. 1272）. The level of IL-18 mRNA was 0. 3218 ± 0. 0466 in control group. After HIBD, the expression of mRNA for IL-l8 increased progressively at 24 h to 6 d （24 h： 0. 5823 ± 0. 0740; 3 d： 0. 6976 ± 0. 1073 ; 6 d： 0. 9110±0.0647, P〈0.01 vs. control）, reached its greatest level at 6 d （P 〈0.01 vs. other groups）. The expression of IL-18 mRNA after HIBD showed a close correlation to caspase-1 in time （ r = 0. 871, P 〈0. 01 ）. Histological study showed that the degenerated and necrotic neurons increased progressively at 1 d to 6 d after HIBD, at the same time the proliferation of glial cells appeared. Conclusion The increasede xpression of caspase-1 and IL-18 mRNA after HIBD, regularity of which was consistent with the time frame for development of brain injury, implied that they may play important roles in the pathogenesis of HIBD in neonatal rats.