Mechanism of mammalian sperm protection by extender components and development of novel extenders free of products of animal origin

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Agriculture Canada reported that Canada exported more than 100 million dollars worth of bull semen to over 100 countries in 2013. This represents more than 20% of world export of bull semen. The most commonly used protective agents to conserve mammalian sperm contain 20% egg yolk or milk and 6-7% glycerol in buffers. This basic constituent of sperm preservation media (commonly called diluters or extenders) has remained the same since the practice of artificial insemination was introduced some 75 years ago. Egg yolk and milk being products of animal origin represent a potential risk of transmission of diseases. Therefore, there is an urgent need for developing novel extenders, which are free of products of animal origin. However, in view of the lack of knowledge on “how Egg yolk and milk protect sperm during conservation in liquid and/or frozen state”, the development of novel extenders has been hindered. Consequently, we focused our effort in the past 15 years to understand the molecular mechanism of sperm protection by extenders during conservation. We discovered that most hoofed animals (bull, stallion, ram, goat, bison, etc) semen contains detrimental proteins called Binder of Sperm (BSP) proteins. These BSPs, secreted by seminal vesicles and added to sperm at ejaculation, bind to sperm membrane and extract lipids (cholesterol and phospholipids), which make sperm sensitive to storage during cooling and cryopreservation. Interestingly, BSPs interact with low-density lipoproteins, the main constituents of egg yolk extenders. While these BSPs bind to sperm membrane, they exert a detrimental effect on sperm but when they associate with low-density proteins, the detrimental effect on sperm is subdued and sperm are protected. Based on the above, we concluded that the sequestration of BSPs by extender components is the general mechanism of sperm protection. In recent years, we also discovered that dextrans coupled with diethyl aminoethyl groups, bind BSPs, and this interaction preserves sperm functions just like egg yolk. Thus, the short-term objectives of the present program are to test bull sperm conservation in synthetic extenders, in order to develop novel extenders free of animal products for artificial insemination application. The long-term goal of this program is to develop novel extenders for mammalian sperm conservation (other farm animals, domestic animals, zoo animals, and endangered species). Canadian breeders would benefit from having access to safe semen extenders and might state this claim internationally, thus promoting their own herd. This program would also generate highly qualified personnel (HQPs), who would have the job opportunity in highly specialized areas such as Artificial Insemination Industries and/or Fertility Clinics.