Endogenous prostaglandin D2 and its metabolites protect the heart against ischemia-reperfusion injury by activating Nrf2.

We recently demonstrated that glucocorticoids markedly upregulate the expression of cyclooxygenase-2 in cardiomyocytes and protect hearts from ischemia-reperfusion (I/R) injury by activating lipocalin-type prostaglandin D (PGD) synthase (L-PGDS)-derived PGD(2) biosynthesis. We examined a downstream mechanism of cardioprotection elicited by PGD(2) biosynthesis. Acute PGD(2) treatment did not protect hearts against I/R injury. We then speculated that PGD(2) and its metabolite 15-deoxy-Δ12,14-PGJ(2) activate gene expression networks to mediate the glucocorticoid-mediated cardioprotection. Using an unbiased approach, we identified that glucocorticoids induce a number of well-known erythroid-derived 2-like 2 (Nrf2) target genes in the heart in an L-PGDS-dependent manner and that the cardioprotective effect of glucocorticoids against I/R injury was not seen in Nrf2-knockout hearts. We showed relatively low expression of PGD(2) receptors (ie, DP1 and DP2) in the heart but abundant expression of PGF(2α) receptor (FP), which binds PGF(2α) and PGD(2) with equal affinity. Glucocorticoids also failed to induce the expression of L-PGDS-dependent Nrf2 target genes in FP-knockout hearts. PGD(2) acted through its metabolite 15-deoxy-Δ12,14-PGJ(2) in the heart as evidenced by the glucocorticoid-mediated activation of peroxisome proliferator-activated receptor-γ. In turn, glucocorticoids failed to induce the expression of L-PGDS-dependent Nrf2 target genes in hearts pretreated with peroxisome proliferator-activated receptor-γ antagonist GW9662, and glucocorticoid-mediated cardioprotection against I/R injury was compromised in FP-knockout mice and GW9662-treated mice. In conclusion, PGD(2) protects heart against I/R injury by activating Nrf2 predominantly via FP receptor. In addition, we propose activation of peroxisome proliferator-activated receptor-γ by the dehydrated metabolite of PGD(2) (15-deoxy-Δ12,14-PGJ(2)) as another mechanism by which glucocorticoids induce cardioprotection.