Induction of prostacyclin/PGI₂ synthase expression after cerebral ischemia-reperfusion

Prostacyclin (PGI₂), a potent vasodilator and inhibitor of platelet aggregation and leukocyte activation, is crucial in vascular diseases such as stroke. Prostacyclin synthase (PGIS) is the key enzyme for PGI ₂ synthesis. Although expression of PGIS was noted in the brain, its role in ischemic insult remains unclear. Here we reported the temporal and spatial expression of PGIS mRNA and protein after 60-min transient ischemia. Northern blot and in situ hybridization revealed a delayed increase of PGIS mRNA in the ischemic cortex at 24- to 72-h after ischemia; PGIS was detected mainly in the ipsilateral penumbra area, pyriform cortex, hippocampus, and leptomeninges. Western blot and immunohistochemical analysis revealed that PGIS proteins were expressed temporally and spatially similar to PGIS mRNA. PGIS was heavily colocalized with PECAM-1 to endothelial cells at the leptomeninges, large and small vessels, and localized to neuronal cells, largely at the penumbra area. A substantial amount of PGIS was also detected in the macrophage and glial cells. To evaluate its role against ischemic infarct, we overexpressed PGIS by adenoviral gene transfer. When infused 72 h before ischemia (-72 h), Adv-PGIS reduced infarct volume by ∼50%. However, it had no effect on infarct volume when infused immediately after ischemia (0 h). Eicosanoid analysis revealed selective elevation of PGI₂ at -72 h while PGI ₂ and TXB₂ were both elevated at 0 h, altering the PGI₂/thromboxane A₂ (TXA₂) ratio from 10 to 4. These findings indicate that PGIS protects the brain by enhancing PGI ₂ synthesis and creating a favorable PGI₂/TXA₂ ratio.