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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 #330960
Title: Testicular gonadotropin-releasing hormone II receptor (GnRHR-II) knockdown constitutively impairs diurnal testosterone secretion in the boar

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

Submitted to: Reproduction, Fertility and Development
Publication Type: Abstract Only
Publication Acceptance Date: 8/12/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The second mammalian GnRH isoform (GnRH-II) and its specific receptor (GnRHR-II) are highly expressed in the testis, suggesting an important role in testis biology. Gene coding errors prevent the production of GnRH-II and GnRHR-II in many species, but both genes are functional in swine. We have demonstrated that GnRHR-II localizes to porcine Leydig cells and exogenous GnRH-II stimulates testosterone secretion from testicular explants. Likewise, GnRH-II robustly stimulates testosterone production in vivo despite minimal luteinizing hormone (LH) secretion. These data suggest that GnRH-II has a direct effect on steroidogenesis in the boar testis. A GnRHR-II knockdown (KD) swine line was produced to explore this hypothesis. During pubertal development, serum testosterone concentrations were significantly reduced in GnRHR-II KD compared to littermate control males, despite similar concentrations of LH. These data indicate that GnRHR-II KD impairs steroidogenesis directly at the testis instead of via the classical androgen stimulator, LH. The objective of this study was to compare secretory patterns of testosterone in mature transgenic and littermate control males via intensive blood sampling. GnRHR-II KD (n = 5) and littermate control (n = 5) boars were fitted with indwelling cannulae and blood was collected every 15 min for 8 h. Serum was assayed for testosterone concentration via radioimmunoassay. Next, GnRHR-II KD (n = 5) and littermate control (n = 4) boars were euthanized; testis, kidney and body weight were recorded and testicular tissue was collected for RNA isolation. Digital droplet PCR was performed to quantify GnRHR-II mRNA abundance (normalized to ß-actin expression). Hormone data were analyzed using the MIXED procedure of the Statistical Analysis System with line (transgenic or control), time and their interaction as fixed effects. Litter was a random effect and time was a repeated measure. GnRHR-II mRNA levels as well as organ and body weights were also analyzed using PROC MIXED; line was the fixed effect and litter was a random effect. Body, kidney and testis weights were similar between lines (P > 0.05). We did not detect (P > 0.05) an effect of time or a line by time interaction on testosterone concentrations but we did observe an effect of line (P < 0.05). Dramatically, testosterone concentrations were significantly reduced (82%) in GnRHR-II KD (0.75 ± 0.05 ng/ml) compared to littermate controls (4.09 ± 0.29 ng/ml) despite similar testis weights (P > 0.05). Testicular GnRHR-II mRNA levels were reduced by 69% in transgenics (P < 0.001). These data demonstrate that GnRH-II and its receptor play a critical role in modulating testosterone secretion from swine testes, revealing novel regulators of testicular function in the boar and challenging the central dogma of testosterone regulation. Given that testosterone secretion classically dictates male reproductive success, GnRH-II and its receptor will likely become novel molecular targets to improve fertility in swine. Partially supported by NIFA Hatch (NEB-26-199; BRW) and AFRI (2011-67015; CAL) funds.