Change Of COX₂/PGI₂/PPARβ Signaling Pathway In Cortex And Hippocampus Of Global Cerebral Ischemia Reperfusion Rat And Intervention Study

[Objective]To observe the change of COX2/PGI2/PPARβ signaling pathway in cortex and hippocampus of global cerebral ischemia reperfusion (GCIR) rat, and the effect of intervening the signaling pathway on GCIR injury.[Methods]1. The change of COX2/PGI2/PPARβ signaling pathway in cortex and hippocampus of GCIR rat 96 male Sprague-Dawley (SD) rats were randomly divided into eight groups (n=12):sham group, GCIR 30min group, GCIR 2h group, GCIR 6h group, GCIR 24h group, GCIR 48h group, GCIR 7d group and GCIR 15d group. GCIR rat model was established by bilateral common carotid arteries occlusion combining with hypotension. Spatial learning and memory function of rat was detected by using Morris water maze. HE staining was used to observe the change of cortical and hippocampal pathomorphology of rat. Prostacyclin (PGI2) content in cortex and hippocampus was detected by ELISA. RT-PCR was applied to measure mRNA expressions of cyclooxygenase 2 (COX2), prostacyclin synthase (PGIS), prostacyclin receptor (IP) and peroxisome proliferator-activated receptor (3 (PPAR(3) in cortex and hippocampus. The protein expressions of COX2, PGIS, IP and PPARβ were detected by immunohistochemistry.2. Effect of intervening COX2/PGI2/PPARβ signaling pathway on GCIR injury 96 male SD rats were randomly divided into eight groups (n=12):sham group, GCIR+vehicle (CMC-Na) (GCIR+CMC-Na) group, GCIR+ meloxicam 3mg/kg (GCIR+M 3mg) group, GCIR+beraprost sodium 50ug/kg (GCIR+BPS 50μg) group, GCIR+beraprost sodium 100μg/kg (GCIR+BPS 100μg) group, GCIR+vehicle (DMSO) (GCIR+DMSO) group, GCIR+GW0742 100μg group and GCIR+GW0742200μg group. Meloxicam and BPS were administered to experimental rats by intragastric gavage, and GW0742 was administered by intracerebroventricular injection 30min before operation, respectively. The establishment method of GCIR model was as same as that on part one.Morris water maze was used to detect spatial learning and memory function of rat. HE staining was applied to observe the change of cortical and hippocampal pathomorphology of rat. The activity of superoxide dismutase (SOD) and contents of malondialdehyde (MDA), PGI2 and thromboxane A2 (TXA2) in cortex and hippocampus were measured by ELISA. RT-PCR was used to detect mRNA expressions of COX2, PGIS, IP and PPARβ in cortex and hippocampus. The protein expressions of COX2, PGIS, IP, PPARβ and nuclear factor-κB (NF-κB) were detected by immunohistochemistry.[Results]1. Compared with sham group, the escape latency was significantly increased in the GCIR group rat (P<0.01). Cortical and hippocampal neurons showed obviously karyopyknosis, and the cell mortality rate reached the peak on 7d in GCIR group rat (P<0.01). The contents of PGI2 in cortex and hippocampus were both significantly increased from 6h after GCIR (P<0.05), and reached the peak at 48h after GCIR (P<0.01). The mRNA expressions of COX2 in cortex and hippocampus and IP and PPARβ in hippocampus were obviously increased at 30min after GCIR (P<0.05, P<0.01). The mRNA expressions of PPARβ in cortex and PGIS in hippocampus were obviously increased at 2h after GCIR (P<0.01). The mRNA expressions of PGIS and IP in cortex were obviously increased at 6h after GCIR (P<0.05, P<0.01). The mRNA expression of COX2 in cortex reached the peak on 7d after GCIR (P<0.01). The mRNA expression of COX2 in hippocampus reached the peak at 48h after GCIR (P<0.01), that of IP in hippocampus reached the peak at 24h after GCIR (P<0.01), and that of PPARβ in hippocampus reached the peak twice at 6h and 7d after GCIR, respectively (P<0.01). The protein expressions of COX2 and PPARβ in cortex were both significantly increased at 2h after GCIR (P<0.05), and reached the peak on 7d after GCIR (P<0.01). The protein expressions of COX2 and PPARβ in hippocampus were both significantly increased at 30min after GCIR (P<0.05), and reached the peak on 7d and 15d after GCIR, respectively (P<0.01). The protein expressions of PGIS and IP in cortex and hippocampus were both significantly increased at 6h after GCIR (P<0.05), and reached the peak on 7d after GCIR (P<0.01).2. Compared to sham group, the escape latency of rats was significantly increased in the GCIR+ vehicle groups (GCIR+CMC-Na group and GCIR+DMSO group) (P<0.01). Cortical and hippocampal neurons showed obviously karyopyknosis, cell number was decreased, and the cell mortality rate was significantly increased (P<0.01). The activity of SOD was obviously decreased (P<0.01), and the contents of MDA, PGI2 and TXA2 were significantly increased in cortex and hippocampus (P<0.01). The mRNA expressions of COX2, PGIS, IP and PPARβ were obviously increased (P<0.01). The protein expressions of COX2, PGIS, IP, PPARβ and NF-κB were obviously increased (P<0.01).Compared with GCIR+ vehicle groups, the escape latency was significantly shortened in the rats treated with meloxicam, BPS and GW0742, respectively (P<0.01). Meloxicam, BPS and GW0742 administration significantly reduced the histopathological injury and cell mortality rate (P<0.01), increased the activity of SOD (P<0.01), decreased the contents of MDA, PGI2 and TXA2 (P<0.05,P<0.01), reduced the mRNA expression of COX2, PGIS, IP and PPARβ (P<0.05, P<0.01), and decreased the protein expressions of COX2, PGIS, IP, PPARp and NF-κB (P<0.05,P<0.01) in cortex and hippocampus of GCIR rats.[Conclusions]1) GCIR can lead to neuron injury in rat cortex and hippocampus, and lead to decline in spatial learning and memory function of rats.2) PGI2 content and COX2, PGIS, IP and PPARP expressions in cortex and hippocampus of GCIR rat were significantly increased, and the changes were time-dependence. The time course changes of those genes were different between cortex and hippocampus of GCIR rat, and the changes in hippocampus were prior to those of cortex.3) COX2 antagonist (meloxicam), IP agonist (BPS) and PPARβ agonist (GW0742) were all neuroprotective in GCIR injury of rat. Intervening one gene of COX2-PGI2-PPARβ signaling pathway can influence the expressions of the other two genes.4) Increase of COX2 expression was a damage factor in GCIR injury, but increases of IP and PPARβ expressions may be protective to GCIR rat.5) There was COX2-PGI2-PPARβ signaling pathway in cortex and hippocampus of GCIR rat, and re-establishing the balance of the signaling pathway may be a new stragegy for treating GCIR injury.