br Acknowledgments and Disclosures br Introduction In mammal

Acknowledgments and Disclosures
Introduction In mammals, ejaculated sperm requires a finite period of residence in the female reproductive tract to become competent for fertilization (Visconti et al., 1995a, Visconti et al., 1995b). Once oocytes are matured, it is important for these cells to be exposed to sperm that have already been capacitated or are undergoing capacitation (Parrish, 2014). In sperm capacitation several intracellular changes are known to occur, including an increase in membrane fluidity, cholesterol efflux, intracellular Ca2+ and cAMP concentrations and protein tyrosine phosphorylation, together with changes in swimming patterns and chemotactic motility (Breitbart and Naor, 1999). Glycosaminoglycans are mucopolysaccharides that are present in the female genital tract (Lee and Ax, 1984). The exposure of bull sperm to glycosaminoglycans such as heparin or hyaluronic PLX7904 is positively correlated with its in vitro fertilizing ability, in vitro embryo developmental potential and embryonic gene expression (Kim et al., 2013). Heparin, the glycosaminoglycan used routinely to induce sperm capacitation prior to in vitro fertilization (IVF) in bull, binds to bull sperm as a typical receptor-ligand interaction, promoting capacitation (Parrish et al., 1988, Satorre and Córdoba, 2010). Hyaluronic acid is a linear non-sulphated high molecular weight glycosaminoglycan which has been detected in uterine and oviductal fluids in ruminants (Lee and Ax, 1984). The localization of hyaluronic acid cell surface receptor CD44 in the sperm reservoir of bulls could indicate an intracellular signaling pathway generated by the CD44-hyaluronic acid binding, which would have a role in oocyte maturation, sperm storage, sperm capacitation and interactions linked to fertilization (Bergqvist et al., 2005). Human, boar, bull, and ram sperm contain hyaluronic acid receptor CD44 in the plasma membrane (Bain et al., 2002; Tienthai et al., 2003 Bergqvist et al., 2006; Vicente-Carrillo et al., 2015). In several species, such as swine (Suzuki et al., 2002), hyaluronic acid has been used as a capacitation inducer during in vitro conditions. In dogs, this glycosaminoglycan accelerates calcium influx into the sperm cytoplasm and increases lactate dehydrogenase (LDH) activity and cAMP production provoking capacitation (Kawakami et al., 2006). It has previously been demonstrated that hyaluronic acid induces bull sperm capacitation in vitro with an optimal concentration of 1000μg/ml and 60min of incubation (Fernández and Córdoba, 2014a). Hyaluronic acid also was used successfully in IVF, early cleavage and blastocyst production percentages increased with hyaluronic acid and no significant differences were registered between this inductor and heparin (Gutnisky et al., 2007). Male gametes have an active metabolism because these cells possess enzymes involved in metabolic pathways such as glycolysis, Krebs cycle, fatty acid oxidation and respiratory chain (Hafez and Hafez, 2002). Two of the most important enzymes that participate in sperm metabolism are LDH and creatine kinase (CK) (Duan and Goldberg, 2003, Córdoba et al., 2007, Córdoba et al., 2008, Gladden, 2004, Wallimann et al., 2011). The LDH catalyzes the reversible conversion of pyruvate into lactate with NADH re-oxidation. Sperm almost exclusively contain an LDH isoenzyme (LDH-X or LDH-C4), which is not present in other tissues (Blanco et al., 1976, Duan and Goldberg, 2003). This enzyme has been localized in the mitochondrial and soluble fractions, thus demonstrating the presence of cytosolic and mitochondrial isozymes and suggesting the existence of a reduced equivalents shuttle between cytosol and mitochondria in mouse sperm (Burgos et al., 1995). It has also been reported that LDH-X can act in bull sperm in aerobic and anaerobic conditions (Kolb et al., 1970), therefore, it has been considered as a potentially important parameter for sperm motility and semen quality evaluation (Cui et al., 2015).