Anti-apoptotic mechanism of ischemic preconditioning against hypoxic-ischemic injury in the neonatal rat brain

• Main Authors: Wan-Ying Lin, 林宛瑩
• Other Authors: Chao-Ching Huang
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/7j466r

碩士 === 國立成功大學 === 分子醫學研究所 === 93 === Neonatal hypoxic-ischemic (HI) brain injury is a major cause of neonatal mortality and long-term disability. Currently, there are still no effective therapies against neonatal HI brain injury. A sublethal stress, such as a brief episode of ischemia, before a lethal injury may reduce neuronal death against subsequent lethal injury; a phenomenon called “preconditioning”. Elucidating the underlying mechanisms of preconditioning may provide potential neuroprotective therapy for neonatal HI brain injury. Permanent ligation of unilateral carotid artery followed by systemic hypoxia (8% O2 for 2 h) could induce ipsilateral cerebral HI injury in 7-day-old rat pups. To test whether the ischemia preconditioning (IP) could be established in neonatal brain in a time-dependent manner, rat pups were subjected to HI at 22 h (IP-22h group), 6 h (IP-6h group) or 2 h (IP-2h group) after reversible unilateral carotid artery ligation for 2 h. The outcome was measured by behavior assessment (P35) and pathology (P40) (percentage of brain weight reduction) and behavior (Morris water maze) on P35-P40. Compared to the No-IP group, all the three IP groups had significantly neuroprotective effect at morphological and behavioral levels. Among the three IP groups, the IP-6h group had the worst behavioral performance and also showed more TUNEL positive cells in the cortex and hippocampus. Twenty-four hours after HI, the reactive oxygen species (ROS) production and the expression levels of the cleavaged form of pro-apoptotic markers, such as caspase-3, caspase-8, caspase-9, poly (ADP-ribose) polymerase, and apoptosis inducing factor, were significantly lower in the IP-22h group compared to the no-IP group. In addition, the release of cytochrome c and Smac from mitochondria to cytosol after HI was also significantly reduced in the IP-22h group. In contrast, the expression of anti-apoptotic markers, such as cellular inhibitor of apoptosis-1(cIAP-1) and BCL2, but not X-linked inhibitor of apoptosis, were significantly higher in the IP-22h group. Increased expression of cIAP-1 but not activated caspase-3 was also found in the IP-22h group during preconditioning phase. Our study suggests that but both rapid and delayed phase of IP can be established in the immature brain, suggesting the unique plasticity in the development brain. In addition, IP-mediated neuroprotective mechanisms in the immature brain involve not only the inhibition of apoptosis (caspase-dependent and caspase-independent pathways, and intrinsic and extrinsic pathways) but also increase expression of anti-apoptotic markers, such as cIAP-1. Further work will be extended to determine the role of cIAP-1 in IP and elucidate its upstream signaling during IP in the immature rat brain.