Antisense in vivo knockdown of synaptotagmin I by HVJ–liposome mediated gene transfer attenuates ischemic brain damage in neonatal rats

Synaptic release of the excitatory amino acid glutamate is considered as an important mechanism in the pathogenesis of ischemic brain damage in neonates. Synaptotagmin I is one of exocytosis-related proteins at nerve terminals and considered to accelerate the exocytosis of synaptic vesicles by promoting fusion between the vesicles and plasma membrane. To test the possibility that antisense in vivo knockdown of synaptotagmin I modulates the exocytotic release of glutamate, thus suppressing the excitotoxic intracellular processes leading to neuronal death following ischemia in the neonatal brain, we injected antisense oligodeoxynucleotides (ODNs) targeting synaptotagmin I (0.3 (AS), 0.15 (0.5 AS), or 0.03 μg (0.1 AS), or vehicle) into the lateral ventricles of 7-day-old rats by using a hemagglutinating virus of Japan (HVJ)–liposome mediated gene transfer technique. At 10 days of age, these rats were subjected to an electrical coagulation of the right external and internal carotid arteries, then the insertion of a solid nylon thread into the right common carotid artery toward the ascending aorta up to 10–12 mm from the upper edge of the sternocleidomastoid muscle. Cerebral ischemia was induced by clamping the left external and internal carotid arteries with a clip, and ended by removing the clip 2 h later. Twenty-four hours after the end of ischemia, the extent of ischemic brain damage was neuropathologically and quantitatively evaluated in the neocortex and striatum. While the relative volume of damage in the cerebral cortex and striatum of the vehicle group was extended to 40% and 13.7%, respectively, that in the AS group was significantly reduced to 4.8% and 0.6%. In the 0.5 AS group, the relative volume of ischemic damage in the cerebral cortex and striatum was reduced to 20.5% and 15.4%, respectively, and the difference between the 0.5 AS group and vehicle group was statistically significant in the neocortex, but not in the striatum. These results indicated that antisense in vivo knockdown of synaptotagmin I successfully attenuated ischemic brain damage in neonatal rats and that the effect was dose-dependent. It was also suggested that this treatment was more effective in the neocortex than in the striatum in neonatal rats.