PROGESTERONE AND INTERFERON TAU REGULATE HYPOXIA-INDUCIBLE FACTOR (HIF) ALPHA SUBUNIT IN THE OVINE ENDOMETRIUM DURING THE PERI-IMPLANTATION PERIOD OF PREGNANCY

Abstract

Hypoxia-inducible factors (HIFs) are members of the basic helix-loophelix- PAS protein superfamily and act as mediators of oxygen homeostasis by regulating transcription of genes. The HIF alpha (HIF1A or HIF2A) subunits can heterodimerize with the HIF beta (HIF1B, HIF2B, HIF3B) subunits without specificity for their dimerization partners and transactivate their target genes. In the mouse uterus, Hif1a is primarily regulated by progesterone, but estrogen transiently regulates Hif2a expression. Further, both Hif1a and Hif2a regulate spongiotrophoblast differentiation during mouse placental development. These studies determined effects of the estrous cycle, pregnancy, progesterone (P4) and interferon tau (IFNT) on HIFs expressed in the ovine uterus. In Study One, ewes (n=5 per day) were hysterectomized on Days 10 to 16 of the estrous cycle or on Days 10 to 20 of early pregnancy. In cyclic ewes, endometrial HIF1A and HIF2A mRNA levels were low on Day 10, increased about 1.3-fold and 1.7-fold from Days 10 to 14, and declined to Day 16. HIF1A mRNA levels were not different in pregnant ewes. In contrast, endometrial HIF2A mRNA levels increased 4.8-fold between Days 10 and 20 of pregnancy (P<0.01, day x status). In situ hybridization analyses found that HIF1A and HIF2A were expressed specifically in the endometrial luminal (LE) and superficial glandular (sGE) epithelia of the uterus and also in the conceptus. Overall, HIF1B, HIF2B, and HIF3B were low in endometria of cyclic and pregnant ewes, and in situ hybridization analyses revealed expression in endometrial LE and GE as well as in the conceptus. Study Two determined effects of P4 and ovine IFNT on HIFs in the uterus. Ewes (n=5/treatment) were ovariectomized and fitted with intrauterine (i.u.) catheters on Day 5 and treated daily as follows: (1) 50 mg P4 from Days 5 to 16 and i.u. control proteins from Days 11 to 16 (P4+CX); (2) P4 and 75 mg ZK136.317 (a progesterone receptor antagonist) from Days 11 to 15 and i.u. control proteins (P4+ZK+CX); (3) P4 and i.u. IFNT (1x108 antiviral units) from Days 11 to 15 (P4+IFN); and (4) P4 and ZK and IFNT (P4+ZK+IFN). All ewes were hysterectomized on Day 17. Treatment with P4 induced a 4.4-fold and 10-fold increase in endometrial HIF1A and HIF2A mRNA (P<0.01, P4+CX vs P4+ZK+CX). IFNT stimulated a 1.6-fold increase (P<0.01) in HIF2A mRNA, respectively, in P4-treated, but not in P4+ZK-treated ewes. The effects of P4 and/or IFNT on HIF1A and HIF2A were specific to endometrial LE/sGE. HIF1B, HIF2B, and HIF3B expression was not regulated by P4 or IFNT, but their mRNAs were present in the endometrial LE and GE. These studies identified novel P4-induced (HIF1A and HIF2A) and IFNTstimulated (HIF2A) genes in the uterine LE. Collectively, these results support the hypothesis that that HIF pathway in the endometrium is regulated by the conceptus via IFNT and is likely involved in growth, remodeling and function of the endometrium and conceptus during early pregnancy. Supported by NIH 5 R01 HD32534. (poster)