Expression of membrane progestin receptors (mPRs) in the bovine corpus luteum during the estrous cycle and first trimester of pregnancy

Progesterone (P4) affects luteal cell function through nuclear P4 receptors and via nongenomic mechanisms, presumably involving membrane P4 receptors. There are 2 types of these receptors: progesterone receptor membrane component (PGRMC) and membrane progestin receptor (mPR), including mPR alpha (mPRα), beta (mPRβ), and gamma (mPRγ), which belong to the progestin and adipoQ receptor family (PAQR 7, 8, and 5, respectively). The aim of this study was to evaluate mRNA expression, protein expression, and localization of mPRα, mPRβ, and mPRγ in the bovine corpus luteum (CL) on days 2-5, 6-10, 11-16, and 17-20 of the estrous cycle as well as on weeks 3-5, 6-8, and 9-12 of pregnancy (n = 5/each period). The highest mPRα mRNA expression was found on days 11-16 (P < 0.05) and 17-20 (P < 0.001) of the estrous cycle compared with other stages of the estrous cycle and pregnancy. The mPRβ mRNA level was highest (P < 0.01) on days 11-20 of the estrous cycle and in all stages of pregnancy. mPRγ mRNA expression was highest (P < 0.001) on days 17-20 of the estrous cycle and also during weeks 9-12 of pregnancy compared with the other stages of the estrous cycle and pregnancy. Only the mPRα protein was changed during the estrous cycle; there were no significant differences in protein expression of mPRβ and mPRγ during the estrous cycle and pregnancy. Immunostaining for the mPRα, mPRβ, and mPRγ proteins was detectable in the CL sections at all stages of the estrous cycle and pregnancy. Strong positive staining was observed in small luteal cells; this reaction was less evident in large luteal cells. All proteins were also localized in endothelial cells of blood vessels. The obtained data indicate variable expression of mPRα, mPRβ, and mPRγ in bovine CL during the estrous cycle and first trimester of pregnancy and suggest that P4 may be involved in the regulation of CL function via these membrane receptors during both the estrous cycle and pregnancy.