Mammalian sperm preservation: mechanism sperm protection by milk and development of novel extenders

点击翻译按钮获取中文摘要

The cryopreservation of bull semen represents one of the most important achievements in dairy farming after the introduction of artificial insemination. These two approaches have enabled the worldwide distribution and use of desired genetic lines at a reasonable cost. Canada represents <3% of the global economy but provides >20% of world bovine semen exports (~70 million dollars/annum). Egg yolk (EY) and skimmed milk are the most used protective agents to freeze mammalian sperm. EY and milk, being products of animal origin, represent a potential risk of contamination of semen and moreover, their composition is not uniform. Thus, there is an urgent need of developing novel media free of products from animal origin to conserve semen. However, it is difficult to find replacement component for EY or milk because the mechanisms involved in sperm protection by EY and milk against cooling, freezing and storage damages remains unclear. Over the past six years we provided evidences, which indicate that the sperm protection by EY involves an association of EY low-density lipoproteins (LDL) with seminal plasma proteins that are detrimental to sperm storage. These detrimental proteins originally discovered in bovine seminal plasma (hence BSP proteins) have the potential to extract lipids from the sperm membrane thereby adversely affecting the ability of sperm to be preserved. However, when these BSP proteins are associated with LDL, they lose their ability to extract lipid from the sperm membrane, which is the origin for sperm protection (novel concept). Interestingly, skimmed milk, which does not contain lipoproteins, also protects sperm during storage. Thus we hypothesize that the casein micelles and whey proteins, which are the major components of milk bind to BSP proteins and this interaction is the key for sperm protection. The current program is aimed at understanding of the mechanisms involved in sperm protection by egg yolk and milk, which would help us to develop novel extenders for commercial application that do not contain animal products.