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Gonadotropin-Releasing Hormone II and its Receptor are Critical Regulators of Steroidogenesis Within Porcine Leydig Cells

Amy T Desaulniers, University of Nebraska - Lincoln

Abstract

Paradoxically, the interaction of GnRH-II with its receptor (GnRHR-II) does not stimulate gonadotropin secretion. Instead, both are abundantly produced within swine testes and have been implicated in autocrine/paracrine regulation of steroidogenesis. To further study the role of GnRH-II and its receptor in this system, a knockdown (KD) swine line was generated with 70% lower testicular GnRHR-II mRNA levels compared with littermate controls. During pubertal development, testosterone concentrations tended to be reduced in transgenic versus littermate control boars, yet luteinizing hormone (LH) concentrations were unaffected. In adults, basal testosterone secretion was constitutively impaired in GnRHR-II KD males but LH production was normal. Mass spectrometry revealed that gonadal steroids were impacted by GnRHR-II KD; serum concentrations of progestogens (17α-hydroxyprogesterone and progesterone), androgens (dehydroepiandrosterone, dihydrotestosterone and androsterone) and estrogens (estrone and 17α-estradiol) were significantly decreased and 3 hormones (testosterone, dehydroepiandrosterone sulfate and androstenedione) tended to be reduced in transgenic boars; however, corticosteroids were largely unaffected. Next, the sensitivity of GnRHR-II KD and littermate control boars to GnRH and LH analogues was assessed. Transgenic males were less responsive to treatment with a GnRHR antagonist (SB-75), known to bind GnRHR-II. Compared with littermate control boars, GnRHR-II KD males also produced less testosterone in response to analogue 135-18, GnRH-II, and human chorionic gonadotropin. In order to determine if reduced gonadal steroidogenesis affected semen quality, ejaculates were subjected to computer-assisted semen analysis. Both sperm production and motility parameters were reduced in GnRHR-II KD boars, demonstrating impaired semen quality. At euthanasia, testicular tissue from GnRHR-II KD boars produced less testosterone after 3 h of culture. Histological analyses revealed that GnRHR-II KD boars had fewer, hypertrophic Leydig cells but interstitial area was not different between lines. Likewise, free and total cholesterol levels in testicular homogenates from GnRHR-II KD and littermate control boars were similar. However, CYP17A1 and CYP11A1 protein levels were elevated in transgenic testes. These data indicate that GnRHR-II KD boars exhibit compensatory mechanisms at both the cellular and protein level in an attempt to enhance testicular testosterone secretion. Ultimately, this data reveals that GnRH-II and its receptor are critical modulators of steroidogenesis within porcine Leydig cells.^

Subject Area

Biology

Recommended Citation

Desaulniers, Amy T, "Gonadotropin-Releasing Hormone II and its Receptor are Critical Regulators of Steroidogenesis Within Porcine Leydig Cells" (2018). ETD collection for University of Nebraska - Lincoln. AAI10793663.
http://digitalcommons.unl.edu/dissertations/AAI10793663

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