Quality Assessments of Sperm from Gnrh-II Receptor Knockdown (KD) Boars

Abstract Pigs are the only livestock species encoding functional proteins for both the second form of gonadotropin-releasing hormone (GnRH-II) and its receptor (GnRHR-II). Previously, we determined that GnRHR-II localizes to the connecting piece of ejaculated sperm, whereas GnRH-II is present within seminal plasma, suggesting an autocrine/paracrine interaction influencing porcine sperm function. To examine the GnRH-II/GnRHR-II system further, we produced a swine line with reduced endogenous expression of GnRHR-II (GnRHR-II KD). Therefore, our objective was to assess sperm quality of ejaculates collected from GnRHR-II KD (n = 3) and littermate control (n = 3) boars. Semen was extended (37.5 x 106 sperm/mL) in Androstar Plus and subjected to flow cytometry (Kuster Research and Consulting, Inc.; Atkinson, IL). Assays measured DNA compaction, membrane fluidity and viability, acrosome integrity, mitochondrial depolarization, and morphology. Data were analyzed using the MIXED procedure of SAS; the model included ejaculate as the experimental unit and line as a fixed effect. DNA compaction, membrane fluidity, acrosome integrity, mitochondrial depolarization, and morphology were not statistically different between lines (P > 0.05). However, the percentage of sperm with a viable (intact) plasma membrane was reduced in GnRHR-II KD boars (87.4 ± 0.8%) compared with controls (89.6 ± 0.8%; P < 0.05). Although differences did not reach significance, DNA compaction (a measure of sperm chromatin integrity when undergoing acid stress) was doubled and mitochondrial depolarization (reflective of mitochondrial function) was 11% greater in sperm from transgenic males relative to littermate controls, indicating that GnRHR-II KD sperm are more susceptible to environmental stressors and have altered energy production. Thus, these initial data suggest disruptions in the function and fertilizing capacity of GnRHR-II KD sperm, implying that GnRHR-II may represent a potential biomarker for boar fertility. Supported by USDA/NIFA AFRI (2017-67015-26508) and Hatch Multistate (NEB-26-244) funds. USDA is an equal opportunity provider and employer.