Evaluation of boar and bull sperm capacitation and the acrosome reaction by flow cytometry

Authors: Purdy, Phil; GRAHAM, JAMES - Colorado State University; AZEVEDO, HYMERSON - Brazilian Agricultural Research Corporation (EMBRAPA)

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2021
Publication Date: 9/11/2021
Citation: Purdy, P.H., Graham, J.K., Azevedo, H.C. 2021. Evaluation of boar and bull sperm capacitation and the acrosome reaction by flow cytometry. Animal Reproduction Science. 246. Article e106846. https://doi.org/10.1016/j.anireprosci.2021.106846.
DOI: https://doi.org/10.1016/j.anireprosci.2021.106846

Interpretive Summary: Higher quality methods to evaluate sperm function are needed to better estimate sample quality. In exploratory experiments, boar and bull sperm were frozen, thawed, and incubated in conditions that will prepare sperm to fertilize an egg. The effects of freezing and the incubation process were evaluated using flow cytometry, a technique that enables evaluation of tens of thousands of cells that are stained with fluorescent probes in less than a minute, to determine their impact on sperm function and viability. The type of media that is used to freeze boar sperm has a strong influence on whether the cells will survive the freezing process and their potential to fertilize an egg. Similarly, the type of media that is used to incubate bull sperm after freezing and thawing will influence the fertilizing potential of a sample as well. The media used for freezing and artificially inducing the initial stages of the fertilization process are important components that determine the quality of a sperm sample and hopefully, further development of these flow cytometric analyses will provide more subtle information about sperm quality and function.

Technical Abstract: Flow cytometry can evaluate many sperm attributes and Dr. Duane Garner was influential in developing assays to understand sperm physiology and function. We review some of Dr. Garner’s work and describe two experiments that evaluate sperm capacitation in different conditions, using Dr. Garner’s philosophy. In exploratory experiments, boar sperm cryopreserved in 2 freezing diluents (LEY and BF5), were incubated in one capacitating medium. In another experiment, frozen-thawed bull sperm were incubated in two capacitating media (TALP-Ca or CFDM1). In both experiments, sperm viability and capacitation status were evaluated using multiple probes. Boar sperm frozen in LEY exhibited higher initial survival rates (38%) than sperm frozen in BF5 (22%; P<0.05) but did not capacitate as effectively as sperm in BF5 (P<0.05). In experiment 2, bull sperm survived better when incubated in TALP-Ca than in CFDM1 (P<0.05), and sperm in TALP-Ca exhibited higher capacitation levels for most parameters (P<0.05). Of particular interest, 77% of sperm incubated in TALP-Ca exhibited activated second messenger systems involved in capacitation, while <5% of sperm incubated in CFDM1 showed similar activation, after 3h. These experiments show that different freezing and capacitating media elicit different responses to sperm capacitation, but also differences in various sperm attributes. If only sperm viability and acrosomal integrity were evaluated, these experimental results would be interpreted very differently. Dr. Garner’s philosophy of evaluating multiple sperm parameters allowed us to determine unique treatment differences which help us understand sperm capacitation and design further experiments to determine how media cause differences in sperm physiology.