Sperm viability is influenced in vitro by the bovine seminal protein aSFP: effects on motility, mitochondrial activity and lipid peroxidation.

The 13 kDa acidic seminal fluid protein (aSFP) is a major component of bovine semen exerting growth factor-like activity. The influence of the pure protein on sperm viability was observed by evaluating sperm motility using computer-assisted semen analysis. Furthermore, mitochondrial dehydrogenase activity as a parameter of sperm metabolism and the integrity of sperm membranes using a metal catalyzed lipid peroxidation assay were measured. Over a wide physiological range (0.003 to 4 g/l) aSFP did not influence motility and average-path velocity of sperm, but at the highest concentration (6 g/l) a significant reduction in motility could be observed. Mitochondrial activity was significantly stimulated at medium concentrations (0.125 to 2 g/l), whereas a 40% suppression was observed at maximum levels (4 g/l). A dose-dependent inhibition of lipid peroxidation could be demonstrated for medium and high concentrations of aSFP (0.125 to 4 g/l). Compared with other reducing agents, aSFP showed the highest potency in preventing oxidative stress. Such effects might be explained by the remarkable redox behavior of the protein. We suggest that in the bull aSFP may play a role in the regulation of sperm metabolism and the protection of sperm membranes from oxidative damage.

Immunolocalization and quantitation of acidic seminal fluid protein (aSFP) in ejaculated, swim-up, and capacitated bull spermatozoa.

Acidic seminal fluid protein (aSFP, 12.9 kDa), a major protein of bull seminal plasma, belongs to the spermadhesin protein family. Boar spermadhesins become bound to the sperm head's surface at ejaculation and are thought to play a role as capacitation factors and/or in gamete recognition and binding. Here, we have investigated the topographical distribution and fate of bovine spermadhesin aSFP during sperm capacitation in order to assess whether aSFP could be involved in similar aspects of the fertilization process as its boar homologous proteins. 5.7 +/- 2.1 x 10(6) molecules/spermatozoa were quantitated on the surface of fresh ejaculated and washed sperm. The binding site of aSFP was restricted to a thin coat at the apical part of the acrosomal cap. The amount of aSFP in swim-up sperm was 1.8 +/- 1.0 x 10(6) molecules/spermatozoa, but decreased dramatically to 22 +/- 10 x 10(3) and to undetectable levels after incubation of sperm for 1.5 h and 18 h, respectively, in capacitation medium. This indicates that the bull spermatozoa surface may be completely depleted of spermadhesin aSFP before spermatozoa reach the surroundings of the investing egg. Therefore, our results suggest that aSFP may act as a decapacitation factor on bull spermatozoa rather than as a zona pellucida binding molecule.