Stallion spermatozoa preferentially utilize oxidative phosphorylation (OXPHOS) over glycolysis to generate ATP and support motility. Whilst efficient with regard to ATP production, OXPHOS generates high levels of damaging reactive oxygen species (ROS) and thus impedes storage of stallion sperm at ambient temperature (i.e. without chilling or cryopreservation). At the same time, sperm storage media often contain relatively high concentrations of glucose, despite the limited ability of stallion sperm to utilize it for ATP generation.
In this study we look to anti-diabetic pharmaceuticals that directly target the enhancement of glycolytic metabolism, and propose that encouraging more effective utilization of glucose, whilst decreasing the reliance on OXPHOS, would improve our capacity to store stallion sperm in vitro.
Specifically, rosiglitazone is an anti-diabetic compound that enhances metabolic flexibility and glucose utilization in various cell types, but its effects on sperm metabolism are unknown. We investigated the effects of rosiglitazone on stallion sperm function in vitro, and the potential role of AMP-activated kinase (AMPK) in mediating these effects. Spermatozoa were incubated with or without rosiglitazone, and Compound C (an AMPK inhibitor). Samples incubated with rosiglitazone displayed significantly higher motility, improved mitochondrial membrane potential, and higher ATP content and glucose uptake capacity, while sperm viability was unaffected. Mitochondrial ROS levels were also significantly lower in rosiglitazone-treated samples. AMPK localized to the sperm midpiece, and its phosphorylation was increased in rosiglitazone-treated spermatozoa. Compound C decreased sperm AMPK phosphorylation and inhibited the effects of rosiglitazone. Inclusion of rosiglitazone in a room temperature sperm storage medium maintained sperm motility above 60% for six days, attaining significantly higher total and progressive motilities than sperm stored in control media. Thus we show that rosiglitazone can substantially alleviate deterioration of stallion spermatozoa by diverting metabolism away from OXPHOS and towards glycolysis, with significant implications for applied preservation of sperm function.