The benefits of ‘good’ cholesterol in reproduction: how high-density lipoproteins help to prepare sperm for fertilisation in breeding rams

The use of assisted reproductive technologies—such as artificial insemination (AI) or in vitro fertilisation (IVF)—has revolutionised breeding in livestock industries. Assisted reproductive technologies can improve both the quality and reproductive potential of the herd, leading to an increase in overall production efficiency. Improvements in the application of these technologies to the sheep industry is reliant on a greater understanding of the physiology of fertilisation in this species. In particular, there is a need to better understand the process of sperm capacitation—a maturation event that prepares sperm for fertilisation—in the ram.

In a recent study, researchers at the University of Sydney and Utrecht University examined the effectiveness of different media components to support capacitation-related processes in ram sperm. They focussed on a particular aspect of sperm capacitation known as cholesterol efflux, where cholesterol is removed from the sperm plasma membrane. High-density lipoproteins (HDLs) were investigated for their potential to remove cholesterol from the ram sperm membrane during capacitation. HDLs, known as the ‘good’ cholesterol, are known to promote cholesterol efflux in other cells, including sperm in different species, and have been identified in fluids derived from the female reproductive tract.

The researchers found that cholesterol efflux was indeed stimulated in ram sperm exposed to HDLs during capacitation and at a rate that was similar to bovine serum albumin (BSA), which is traditionally used to support this process. Remarkably, HDLs, unlike BSA, also stimulated an increase in sperm tail movement, otherwise known as hyperactivation. This change in tail movement propels sperm to the site of fertilisation and is required to penetrate and fertilise the oocyte (egg). Therefore, HDLs supported multiple sperm functions that are important for successful fertilisation.

This exciting research suggests HDL supplementation to media used for sperm capacitation could improve the capacity for fertilisation in ram sperm, and as a result, could potentially be used in IVF systems for breeding herds.

Written by Naomi Bernecic