Bmal1 promotes prostaglandin E2 synthesis by upregulating Ptgs2 transcription in response to increasing estradiol levels in day 4 pregnant mice

Prostaglandin G/H synthase 2 (PTGS2) is a rate-limiting enzyme in prostaglandin synthesis. The present study assessed the role of the uterine circadian clock on Ptgs2 transcription in response to steroid hormones during early pregnancy. We demonstrated that the core clock genes (Bmal1, Per2, Nr1d1, and Dbp), Vegf, and Ptgs2, and their encoded proteins, have rhythmic expression in the mouse uterus from days 3.5 to 4.5 (D3.5-4.5) of pregnancy. Progesterone (P-4') treatment of cultured uterus endometrial stromal cells (UESCs) isolated from mPer2(Luciferase) reporter gene knock-in mice on D4 induced a phase shift in PER2::LUCIFERASE oscillations. This P-4-induced phase shift of PER2::LUCIFERASE oscillations was significantly attenuated by the P-4' antagonist RU486. Additionally, the amplitude of PER2::LUCIFERASE oscillations was increased by estradiol (E-2) treatment in the presence of P-4. Consistently, the mRNA levels of clock genes (Bmal1 and Per2), Vegf, and Ptgs2 were markedly increased by E-2 treatment of UESCs in the presence of P-4. Treatment with E-2 also promoted prostaglandin E-2 (PGE(2)) synthesis by UESCs. Depletion of Bmal1 in UESCs by small-interfering RNA (siRNA) decreased the transcript levels of clock genes (Nr1d1 and Dbp), Vegf, and Ptgs2 compared with nonsilencing siRNA treatment. Bmal1 knockdown also inhibited PGE(2) synthesis. Moreover, the mRNA expression levels of clock genes (Nr1d1 and Dbp), Vegf, and Ptgs2, and their respective proteins were significantly decreased in the uterus of Bmal1(-/-) mice. Thus, these data suggest that Bmal1 in mice promotes PGE(2) synthesis by upregulating Ptgs2 in response to increases in E-2 on D4 of pregnancy. NEW & NOTEWORTHY Rhythmic expression of Bmal1 and Ptgs2 was observed in the uterus isolated from D3.5-4.5 of pregnant mice. E2 increased the expression of Bmal1 and Ptg2 in UESCs isolated from mice on D4. The expression of Ptgs2 was significantly decreased in Bmal1-siRNA treated UESCs. Bmal1 knockdown also inhibited PGE(2) synthesis. Thus, these data suggest that Bmal1 in mice promotes PGE(2) synthesis by upregulating Ptgs(2) in response to increases in E-2 on D4 of pregnancy.