| Background and Purpose:In clinical emergencies, many accidents lead to transient global cerebral ischemia, such ascardiac arrest, acute heart failure, and severe hypotension during shock. Sublethal hypoxicpostconditioning, an intervention that conducted immediately after reperfusion, can reduce brainischemia and reperfusion injury. Moderate hypoxia does not cause neuronal death and is performedafter the onset of ischemia. Therefore it may be safer and more effectively to be applied in clinicalpractice. We recently demonstrated that postconditioning with60-120min hypoxia significantlyreduced cell death in hippocampal CA1subregion after10min of tGCI and postconditioning waseffective only when applied1-2days after tGCI. The maximum protection was observed with60min of hypoxia and1day interval between ischemia and hypoxia. The protection afforded byhypoxic postconditioning against cell death induced by transient ischemia is dramatic. However, theprecise mechanisms by which hypoxic postconditioning protects the brain against cell deathsecondary to ischemia/reperfusion remain poorly understood. In the present study, we investigatethe changes of Hsp27and MK2to explore whether Hsp27and MK2participates inneuroprotection induced by HPC.Material and Methods:Experiments were performed on male adult Wistar rats weighing250-300g. Transient globalcerebral ischemia with the four-vessel occlusion was performed. Hypoxia postconditioning wasperformed by expositing rats to a2h period of systemic hypoxia （8%O2+92%N2）24h aftera tGCI. Animals were randomized into Sham-operated group, tGCI group and hypoxic postconditioning group. Neuronal damage in the dorsal hippocampus was assessed7days later byNissl staining and Fluoro–Jade B staining. The expressions of Hsp27, phospho-Hsp27andphospho-MK2were studied after10min of global ischemia with or without hypoxicpostconditioning in the hippocampal CA1subregion with immunohistochemistry and Western blot,respectively. Double-fluorescent immunohistochemistry was conducted to demonstrate the celltypes and the exact position that expressed Hsp27and phospho-Hsp27.Results:（1）The hippocampal CA1subregion of rats subjected to10min of ischemia showed severe neuronalloss and the number of Fluoro–Jade B positive neurons increased significantly, whereas those fromhypoxic postconditioning rats demonstrated significant neuroprotection as manifested by increasednumber of surviving cells and decreased number of Fluoro–Jade B positive neurons in CA1subregion of adult rats.（2） In the hippocampal CA1region not receiving hypoxic postconditioning（tGCI group）, Hsp27increased immediately after ischemia, and the maximum Hsp27-positive cellsnumber was observed4h of reperfusion. Phospho-Hsp27increased significantly from4h to26h ofreperfusion and then returned to basal level50h after reperfusion. Immunohistochemistry studyshowed phospho-MK2positive cells increased immediately after ischemia, and the maximumphospho-MK2-positive cells number was observed4h of reperfusion. Furthermore, hypoxicpostconditioning dramatically increased the number of Hsp27, phospho-Hsp27, and phospho-MK2positive cells in the hippocampal CA1subregion26h and50h after tGCI.（3） Immunofluorescentdouble staining showed that Hsp27was co-labeled with MAP-2, and phospho-Hsp27was co-labeledmainly with Neu-N and slightly with MAP-2in ischemic brains with hypoxic postconditioning.Conclusions:These results suggest that delayed hypoxic postconditioning exerts neuroprotection againsttGCI-induced injury in adult rats. The preservation of protein levels of Hsp27and activation ofMK2/Hsp27pathways by postconditioning contributed to the neuroprotection against tGCI. |
