Abstract
Upon insemination, sperm cells are exposed to components of the female reproductive tract (FRT) fluids, such as urea and epidermal growth factor (EGF). It has been shown that both urea and EGF use EGF receptor signaling and produce reactive oxygen species (ROS) that are required at certain levels for sperm capacitation and acrosome reaction. We therefore hypothesized that during bovine sperm capacitation, a high level of urea and EGF could interfere with sperm function through overproduction of ROS. High-level urea (40 mg/dl urea is equal to 18.8 mg/dl of blood urea nitrogen) significantly increased ROS production and TUNEL-positive sperm (sperm DNA fragmentation, sDF) percentage, but decreased HOS test score, progressive motility, acrosome reaction and capacitation. The EGF reversed the negative effects of urea on all sperm parameters, with the exception of ROS production and DNA fragmentation, which were higher in urea-EGF-incubated sperm than in control-sperm. The developmental competence of oocytes inseminated with urea-EGF-incubated sperm was significantly reduced compared to the control. A close association of ROS production or sDF with 0-pronuclear and sperm non-capacitation rates was found in the network analysis. In conclusion, EGF enhanced urea-reduced sperm motility; however, it failed to reduce urea-increased sperm ROS or sDF levels and to enhance subsequent oocyte competence. The data suggests that any study to improve sperm quality should be followed by a follow-up assessment of the fertilization outcome.
Highlights
Upon insemination, sperm cells are exposed to components of the female reproductive tract (FRT) fluids, such as urea and epidermal growth factor (EGF)
Frozen-thawed sperm cells were incubated for 30 min with different doses of EGF (0, 1, 10, 100, and 1000 ng/ml) and progressive sperm motility was measured to assess the effective dose of EGF (Fig. 1a)
In order to determine the effective dose of urea, sperm cells were incubated for 30 min with different levels of urea (0, 20, and 40 mg/dl), and progressive motility (Fig. 1b) and sperm DNA fragmentation (sDF) were evaluated
Summary
Sperm cells are exposed to components of the female reproductive tract (FRT) fluids, such as urea and epidermal growth factor (EGF). Frozen-thawed sperm may have a condition in the female reproductive tract (FRT), i.e., elevated levels of urea and epidermal growth factor (EGF), which may decrease sperm fertility to a higher degree. In order to be able to fertilize an oocyte, sperm cells need to reside in the FRT for a few hours and undergo biochemical changes, such as capacitation and acrosome r eaction[4] Various factors, such as EGF, are normally present in FRT fluids that contribute to sperm acrosome reaction. High-protein diets, 17–19% crude p rotein[12], are fed to sustain the milk production potential of high-producing dairy cows This can, in turn, lead to elevated blood urea nitrogen (BUN) levels and increased urea levels in FRT fluids, such as oviductal fluids[13]. The predictive power and cut-off point of ROS production/sDF were tested for high-quality sperm using the area under the receiver operating characteristic (ROC) curve (AUC)
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