Prostaglandin D₂ protects neonatal mouse brain from hypoxic ischemic injury

Prostaglandin D₂ (PGD) is synthesized by hematopoietic PGD synthase (HPGDS) or lipocalin-type PGDS (L-PGDS), depending on the organ in which it is produced, and binds specifically to either DP₁ or DP ₂ receptors. We investigated the role of PGD₂ in the pathogenesis of hypoxic-ischemic encephalopathy (HIE) in neonatal mice at postnatal day 7. In wild-type mice, hypoxia-ischemia increased PGD₂ production in the brain up to 90-fold compared with the level in sham-operated brains at 10 min after cessation of hypoxia. Whereas the size of the infarct was not changed in L-PGDS or DP₂ knock-out mouse brains compared with that in the wild-type HIE brains, it was significantly increased in HPGDS-L-PGDS double knock-out or DP₁ knock-out mice. The PGD₂ level in L-PGDS, HPGDS, and HPGDS-L-PGDS knock-out mice at 10 min of reoxygenation was 46, 7, and 1%, respectively, of that in the wild-type ones, indicating the infarct size to be in inverse relation to the amount of PGD₂ production. DP₁ receptors were exclusively expressed in endothelial cells after 1 h of reoxygenation, and cerebral blood flow decreased more rapidly after the onset of hypoxia and did not return to the baseline level after reoxygenation in HPGDS-L-PGDS knock-out mice. Endothelial cells were severely damaged in HPGDS-L-PGDS and DP₁ knock-out mice after 1 h of reoxygenation. In the human neonatal HIE brain, HPGDS-positive microglia were increased in number. In conclusion, it is probable that PGD₂ protected the neonatal brain from hypoxic-ischemic injury mainly via DP ₁ receptors by preventing endothelial cell degeneration.