Localization and Expression of Messenger RNAs for the Peroxisome Proliferator-Activated Receptors in Ovarian Tissue from Naturally Cycling and Pseudopregnant Rats1

Abstract

Structural and functional development of the corpus luteum (CL) involves tissue remodeling, angiogenesis, lipid metabolism, and steroid production. The peroxisome proliferator-activated receptors (PPARs) have been shown to play a role in these as well as in a multitude of other cellular processes. To examine the expression of mRNA corresponding to the PPAR family members (alpha, delta, and gamma) in luteal tissue, ovaries were collected from gonadotropin-treated, immature rats on Days 1, 4, 8, and 14 of pseudopregnancy and from adult, cycling animals on each day of the estrous cycle. Ovaries were processed for in situ hybridization or RNA isolation for analysis by RNase protection assay. The expression of PPARgamma mRNA was abundant in granulosa cells of developing follicles during both pseudopregnancy and the estrous cycle and was low to undetectable in CL from pseudopregnant rats. However, luteal tissue in cycling animals, especially CL remaining from previous cycles, had high levels of PPARgamma mRNA. The PPARalpha mRNA was localized mainly in the theca and stroma, and PPARdelta mRNA was expressed throughout the ovary. Levels of mRNA for PPARgamma decreased between Days 1 and 4 of pseudopregnancy, and PPARalpha mRNA levels were lower on the day of estrus compared to pro- and metestrus (P < 0.05). The PPARdelta mRNA levels remained steady throughout the estrous cycle and pseudopregnancy. These data illustrate a difference in the luteal expression of mRNA for PPARgamma between the adult, cycling rat and the immature, gonadotropin-treated rat. This differential pattern of expression may be related to the difference in timing of the preovulatory prolactin surge, because the gonadotropin-primed animals would not experience a prolactin surge coincident with the LH surge, as occurs in adult, cycling animals. Additionally, the expression pattern of PPARdelta mRNA indicates that it may be involved in cellular functions involved with maintaining basal ovarian function, whereas PPARalpha may play a role in lipid metabolism in the theca and stroma.

Potential role for peroxisome proliferator-activated receptor γ in regulating luteal lifespan in the rat

“…PPARg was also identified in luteal tissue of the naturally cycling rat (Komar & Curry 2002). Interestingly, the expression of mRNA for PPARg was higher in luteal tissue from previous ovulations compared with luteal tissue forming from the most recent ovulation (Komar & Curry 2002).…”

Peroxisome proliferator-activated receptors in the regulation of female reproductive functions

“…Many studies have shown that PPARs gene and/or protein expression varies depending on ovarian cell type, physiological status and the species [14,[22][23][24][25][26]. It has also been frequently reported that PPARs are engaged in the regulation of various ovarian functions.…”

Effect of hyperandrogenism on ovarian function

“…PPARs have three subtypes, a, b/d, and g (Issemann & Green 1990, Komar 2005, which are detected in the ovary of several species, including the rat (Komar 2005). PPARg is expressed primarily in the granulosa cells of developing follicles (Komar & Curry 2002), where it regulates the synthesis of steroid hormones (Huang 2008). At the end of follicular development, the luteinizing hormone surge downregulates the expression of ovarian PPARg (Komar et al 2001, Froment et al 2003.…”

“…At the end of follicular development, the luteinizing hormone surge downregulates the expression of ovarian PPARg (Komar et al 2001, Froment et al 2003. In the rat, PPARg expression is low in newly forming luteal tissue and higher in luteal tissue present from previous ovulations (Komar & Curry 2002).…”