The Role of Reduced Oxygen Supply and Transcription Factors cJUN and CREB in Progesterone Production during the Corpus Luteum Rescue in Gilts

Simple Summary Appropriate function of the corpus luteum and progesterone secretion are fundamental for the establishment and maintenance of pregnancy. Still, there are gaps in the knowledge of mechanisms regulating the maintenance of steroidogenic machinery of porcine corpus luteum during early pregnancy. In the present study, we analyzed the in vitro effects of decreasing oxygen concentration on progesterone production, expression of hypoxia inducible factor-1 subunit alpha (HIF-1A) and expression of genes encoding key stimulators of steroidogenesis, STAR and VEGFA, in the luteal tissue collected from cyclic and early pregnant gilts. In vitro experiments indicate that: (1) progesterone production and genes expression are modulated by decreasing oxygen concentrations and (2) luteal tissue of cyclic and pregnant gilts is similarly sensitive to reduction of oxygen. We also determined the mRNA and protein expression of HIF-1 alpha, STAR, and VEGFA as well as transcription factors-cJUN and CREB, which are known regulators of STAR expression, in the luteal tissue of cyclic and pregnant gilts ex vivo. The relatively high level of STAR, phosphorylated forms of cJUN and CREB and progesterone concentration in the luteal tissue of early pregnant gilts suggests the role of these transcription factors in extension of luteal function. This regulation may be important in supporting luteal rescue during early pregnancy to maintain the production of progesterone. A reduced concentration of oxygen could be involved in the process of corpora lutea regression in gilts. The corpus luteum plays a fundamental role in regulating reproduction via progesterone production. Still, there is little data on factors regulating the maintenance of luteal function during early pregnancy in gilts. Previous studies emphasize the role of hypoxia and HIF-1 in the regulation of steroidogenic and angiogenic genes expression and progesterone production by ovarian cells. Using the corpus luteum of cyclic and early pregnant gilts we analyzed: (1) the in vitro effects of reduced oxygen tension on progesterone production and mRNA expression of HIF1A and luteal function regulators, STAR and VEGFA; (2) the ex vivo profiles of mRNA and protein expression of HIF-1 alpha, STAR, VEGFA and transcription factors-cJUN and CREB, regulating STAR expression, in the corpus luteum of cyclic and pregnant gilts. The synthesis of progesterone was gradually inhibited in cyclic or pregnant gilt luteal tissue (on day 13 of cycle or pregnancy) incubated in a decreasing concentration-20%, 10%, and 3% of oxygen (O-2). Luteal tissues of pregnant gilts produced trace amounts of progesterone in 10% O-2, which was similar to cyclic gilts in 3% O-2. HIF1A expression increased after 24 h of incubation in tissues of cyclic gilts in 3% vs. 20% O-2 (p < 0.01), whereas levels of STAR and VEGFA increased significantly in cyclic and pregnant gilt tissues incubated in 10% and 3% vs. 20% O-2. The ex vivo mRNA expression of HIF1A and VEGFA was elevated (p < 0.001) on day 14 vs. day 12 of pregnancy. The protein expression of HIF-1 and VEGFA increased (p < 0.001), whereas the level of STAR (mRNA and protein) and progesterone dropped (p < 0.001) on day 14 of the estrous cycle vs. a parallel day of pregnancy and/or day 12 of the estrous cycle. The content of phosphorylated cJUN and CREB was elevated (p < 0.01) in the luteal tissue on day 12 or 14 of pregnancy vs. parallel days of the estrous cycle. These increases of phosphorylated cJUN and CREB may be involved in STAR expression in the luteal tissue during early pregnancy in gilts.

Automated summary

The study analyzed the effects of decreased oxygen concentration on the function and progesterone production of the corpus luteum in pigs, revealing that the luteal tissues of cyclic and pregnant gilts have similar sensitivity to reduced oxygen. Furthermore, transcription factors cJUN and CREB may play a role in regulating STAR expression during early pregnancy in gilts.