By Dr. Stuart Meyers
Photography: UC Davis

The sperm mitochondrion is one of the most damaged organelles during cryopreservation and is likely responsible for the majority of loss in motility and fertility after a freeze-thaw cycle. Our laboratory at UC Davis has focused on developing an increased understanding of mitochondrial bioenergetics in sperm that could provide strong rationale for marked improvement in preservation and assisted reproduction techniques.

Most stallions produce sperm that is fully functional, able to fertilize with artificial insemination (AI) or assisted reproductive techniques including intracytoplasmic sperm injection (ICSI), but when a problem arises for a stallion, the costs in management and fertility loss can be surprisingly high, and often hidden. The economics in the breeding industry are frequently staggering from age-related or idiopathic declines in stallion fertility. Stallions are unique among livestock in that they are often asked to breed long into their senior years. Since sperm motility is powered by its mitochondrial energy, the mitochondria have been long-neglected as a study subject critical to maintenance of motility during the aging process. A number of research laboratories around the world have taken up this subject and with recently developed tools to understand sperm in the laboratory, there has been a quiet upsurge in understanding about sperm motility.

Mitochondria

Mitochondrial function in ejaculated sperm is ultimately reflected by ATP (adenosine triphosphate) production, mitochondrial oxidative efficiency, and production of reactive oxygen species. The balance of these factors may become compromised in aging stallions and may be confounded during the process of cryopreservation. The sperm flagellum is powered by adenosine triphosphate (ATP) produced by a complex of mitochondrial enzyme systems including the electron transport chain (ETC). As such, the powerhouse of the cell, the mitochondrion, is likely the foundation of sperm pathophysiology and structure.
Species differences in energy requirements for mitochondria for optimal sperm function are becoming evident and individually tailored sperm handling and storage techniques are likely to become clinical reality as the biochemistry and cellular physiology of sperm are uncovered. Media modifications for sperm processing and storage may become necessary in order to provide appropriate energy substrates to minimize sperm damage and improve sperm longevity after cryo-preservation. In fact, damage to the sperm’s mitochondria is one of the most marked organ-elle changes during cryo-preservation and is likely responsible for the majority of loss in motility and fertility after cryo-preservation.
An understanding of sperm mitochondrial bio-energetics provides strong rationale to make considerable improvement in preservation and assisted reproduction techniques... To read the complete article you need to be a subscriber

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