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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #339135
Title: Knockdown of the GnRH-II receptor in the porcine testis impairs the biosynthesis of 10 gonadal steroids

Author
item DESAULNIERS, AMY - University Of Nebraska
item CEDERBERG, REBECCA - University Of Nebraska
item Lents, Clay
item WHITE, BRETT - University Of Nebraska

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/12/2017
Publication Date: 7/10/2017
Citation: Desaulniers, A.T., Cederberg, R.A., Lents, C.A., White, B.R. 2017. Knockdown of the GnRH-II receptor in the porcine testis impairs the biosynthesis of 10 gonadal steroids [abstract]. In: Proceedings of Society for the Study of Reproduction Annual Meeting, 13-16 July 2018, Washington, DC. S22.4, p. 275. Available: https://www.ssr.org/17Program.

Interpretive Summary:

Technical Abstract: The second mammalian GnRH isoform (GnRH-II) and its cognate receptor (GnRHR-II) are poor modulators of gonadotropin secretion in swine. However, both are abundantly produced within the porcine testis suggesting an autocrine/paracrine role. Within the boar testis, GnRHR-II immunolocalizes to the plasma membrane of Leydig cells, indicative of a role in steroidogenesis. Indeed, treatment with GnRH-II robustly stimulates testosterone biosynthesis in vivo and ex vivo independent of the classical androgen stimulator, luteinizing hormone (LH). To further study the role of GnRH-II and its receptor in pigs, our laboratory generated a GnRHR-II knockdown (KD) swine line with 70% lower testicular GNRHR2 mRNA levels compared to littermate control boars. During pubertal development, testosterone concentrations tended to be lower in transgenic versus littermate control boars, yet LH concentrations were unaffected. Testosterone secretion was significantly reduced (82%) in adult GnRHR-II KD boars during 8 h of serial blood collections. Based on these data together, we hypothesize that GnRHR-II activation on porcine Leydig cells stimulates LH-independent testosterone secretion. The objective of this study was to compare steroid profiles between GnRHR-II KD (n = 5) and littermate control (n = 5) males to help identify how suppression of testosterone biosynthesis occurs in transgenics. Serum samples collected via indwelling jugular cannulae were subjected to high performance liquid chromatography tandem mass spectrometry at Biocrates Life Sciences AG (Innsbruck, Austria) using the AbsoluteIDQ Stero17 Panel. Data were analyzed using the MIXED procedure of SAS with line (transgenic or control) as the fixed effect and litter as a random effect. Serum concentrations of glucocorticoids (11-deoxycorticosterone, corticosterone, cortisol and cortisone) and mineralocorticoids (aldosterone) were unaffected by GnRHR-II KD with the exception of 11-deoxycortisol which was lower (P < 0.05) in transgenic boars. However, steroids of gonadal origin were dramatically impacted by GnRHR-II KD. Serum concentrations of progestogens (17a-hydroxyprogesterone and progesterone), androgens (dehydroepiandrosterone, dihydrotestosterone and androsterone) and estrogens (estrone and 17ß-estradiol) were reduced (P < 0.05) in transgenic compared to littermate control boars. In addition, concentrations of testosterone, dehydroepiandrosterone sulfate and androstenedione tended (P < 0.10) to be lower in GnRHR-II KD boars. Therefore, sex steroid production was preferentially impaired in GnRHR-II KD animals whereas corticosteroid secretion was largely unaffected. In addition, these results reveal that both the '4 and '5 steroidogenic pathways are impacted by GnRHR-II KD indicating that the inhibition of testosterone secretion may occur prior to the production of pregnenolone. Ultimately, these data support our hypothesis and demonstrate that GnRH-II and its receptor are critical modulators of steroidogenesis within porcine Leydig cells. This animal model will be utilized in subsequent studies to identify the molecular link between GnRHR-II activation and steroidogenic output in the boar. Given that testosterone and its metabolites govern male fertility (e.g., sex differentiation, reproductive tract maintenance, libido, spermatogenesis, accessory sex gland function), GnRH-II and its receptor are emerging molecular targets to enhance reproductive efficiency in the boar. Partially supported by USDA NIFA AFRI ELI predoctoral fellowship (2017-67011-26036; ATD), Hatch (NEB-26-199; BRW) and AFRI (2011-67015; CAL) funds.