The Precursor Hormone Pregnenolone Increases Sex Steroid Production in the Fathead Minnow (Pimephales promelas) Ovary Without Modulating Enzyme or Receptor Expression
Steroid hormones regulate the development and maturation of oocytes in all vertebrates. Pregnenolone is a hormone synthesized from cholesterol in the steroid biosynthesis pathway and is the major precursor for progestogens, mineralocorticoids, androgens, and estrogens. However, little is known as to the role of this hormone in teleost reproduction. The objectives of this study were to assess the effects of pregnenolone treatment on testosterone (T) and 17β-estradiol (E2) production from the teleost ovary and to determine whether this hormone modulates the expression of transcripts related to steroidogenesis and hormone receptor signaling in this tissue. Ovary explants from individuals were incubated for 12 hours with either control media or one of three concentrations of pregnenolone (10-6 M, 10-8 M, and 10-10 M) which spanned physiological relevance. The highest concentration of pregnenolone (10-6 M) significantly increased T and E2 production from the ovary, but did not affect the expression levels of transcripts involved in the steroid pathway (cyp17, cyp19a, cyp19b, hsd11b2, hsd17b, and steroidogenic acute regulatory protein or star) or steroid hormone receptors (androgen receptor or estrogen receptors esr1, esr2a, esr2b). Interestingly, while T and E2 production was increased at the highest dose of pregnenolone, there was no change in the E2/T ratio in terms of overall production, suggesting that the ovary may act to maintain an overall homeostatic balance, rather than regulating steroids independently. Moreover, as mRNA levels did not significantly change following pregnenolone treatments compared to controls, we propose that the rapid increase in steroid production does not involve de novo transcription of biosynthesis enzymes. Thus, pre-existing proteins are more likely involved in the rapid increase in T and E2. Lastly, Spearman correlation analysis revealed that pregnenolone altered the relationships between transcripts and steroid production. For example, previous studies show that cyp19a is positively and strongly correlated to E2 production in the fathead minnow ovary; however, endogenous pregnenolone treatments negated this relationship.1 This was also true of the negative relationship between androgen receptor expression and testosterone production. This study sheds light on the steroid regulation in the ovary, which can be perturbed by environmental contaminants and endocrine disruptors. As such, continued evaluation of the mechanistic processes underlying steroid production in the ovary is warranted with endogenous hormone treatments.
The authors wish to thank Kelsey Gump of the College of Veterinary Medicine for assistance with sample processing. The authors thank the Florida Veterinary Scholars Program and the College of Veterinary Medicine for financial support of this project.
* Presenting author
1. Cowie AM, Wood RK, Chishti Y, Feswick A, Loughery JR, Martyniuk CJ. 2015. Transcript variability and physiological correlates in the fathead minnow ovary: implications for sample size, and experimental power. Comparative Biochemistry and Physiology. Part B: Biochemistry & Molecular Biology. 22. doi:10.1016/j.cbpb.2015.04.013