Oestrous sheep serum modifies caspase activity in ram spermatozoa during in vitro capacitation

Abstract

In the ram, oestrous sheep serum (OSS) is considered to be necessary for in vitro capacitation and fertilization. OSS increases membrane fluidity and tyrosine phosphorylation, and produce changes in the motility pattern. We hypothesized that in addition to the already known actions of OSS, its actions could be related to apoptotic processes. Thus, thawed sperm samples from nine rams were incubated at 38.5°C and 5% CO2 in Synthetic Oviductal Fluid (SOF-HEPES), under capacitating (10% of OSS) and non-capacitating conditions. Caspase activity was evaluated using the Vybrant© FAMTM Poly caspases assay kit. Sperm samples were evaluated previously (Control) and after 30 min of incubation (capacitating and non-capacitating conditions). Initially, the percentage of viable spermatozoa with no caspase activity (%NCAS) was 22.3% +/- 3.0. After 30 min of incubation, this percentage significantly decreased in non-capacitating conditions (12.3% +/- 3.0; p = 0.03), but when sperm samples were incubated with 10% OSS, the %NCAS remained similar (23.7% +/- 3.0; p = 0.01 vs. non-capacitating). Thus, after 30 min of incubation, fewer spermatozoa showed caspase activation if serum was present, providing evidence of a possible delaying of the apoptotic process during in vitro capacitation. OSS might benefit in vitro fertilisation by different ways. Supported by Education and Science Council (JCCM; PAI09-0006-3806) and by INIA (RZ2010-00006-CO2-01).