Capacitation in the presence of methyl-β-cyclodextrin results in enhanced zona pellucida-binding ability of stallion spermatozoa.

This research investigates an effective way to promote and control in vitro capacitation of stallion sperm, which is crucial for the development of horse IVF. It shows that using a bicarbonate-rich medium supplemented with a phosphodiesterase inhibitor, a cyclic AMP analogue, and methyl-β-cyclodextrin can substantially enhance stallion sperm’s competency for zona pellucida binding and acrosomal exocytosis.

Research Context and Purpose

• The research focuses on increasing the efficacy of in vitro fertilisation (IVF) in horses, a technique that hasn’t yielded satisfactory results compared to other domestic species.
• A key challenge lies in the fact that optimal conditions to initiate capacitation, a necessary biological process for sperm fertility, in equine spermatozoa are still undiscovered.
• Added to this is the high susceptibility of stallion spermatozoa to damage during semen handling and transportation.
• The study aims to circumvent these issues by proposing an effective system to manage the in vitro capacitation of horse spermatozoa.

Methods and Findings

• Sperm capacitation was induced in a bicarbonate-rich medium supplemented with a phosphodiesterase inhibitor, a cyclic AMP analogue, and methyl-β-cyclodextrin.
• Methyl-β-cyclodextrinis known for its efficiency in removing cholesterol, an event that is closely associated with the onset of sperm capacitation.
• Post-capacitation, the spermatozoa presented multiple indicators of successful capacitation which included increased levels of tyrosine phosphorylation, reorganisation of the plasma membrane leading to lipid raft coalescence around the acrosomal region of the sperm head, and a significantly enhanced ability for zona pellucida (ZP) binding and inducing acrosomal exocytosis.
• ZP binding refers to the interaction of sperm with the outer protective layer of the egg, which is a necessary step for successful fertilisation.
• On the other hand, the absence of bicarbonate from the medium effectively prevented these transformations, suggesting the crucial role of bicarbonate in this process.

Conclusion and Implications

• These findings underscore the critical role of efficient cholesterol removal in preparing the horse sperm for ZP binding, and thus, successful IVF.
• It provides a promising step towards establishing an effective IVF system for horses.
• While these are encouraging results, further studies may be needed to validate the findings and optimise the conditions for commercial IVF in horses.