Mitochondrial membrane potential disruption pattern in human sperm

Loss of mitochondrial membrane potential (delta Psi(m)) in spermatozoa is correlated with high levels of reactive oxygen species in semen, abnormal spermiogram parameters, and low success rates of IVF. In somatic cells, the loss of delta Psi(m) is primarily associated with several mechanisms of cell death, mainly the activation of caspases. The impact of mitochondrial dysfunction on sperm function is still not fully elucidated, although disruption of delta Psi(m) and activation of caspases are processes thoroughly studied in human ejaculates. Disruption of delta Psi(m) in sperm can be externally triggered by the antineoplastic agent betulinic acid (BA). In this study, we determined whether caspase activation is necessary for the BA-induced disruption of delta Psi(m) in human sperm. Viable and highly motile sperm cells were selected through a swim-up process and incubated with 90 mu g/ml BA. To elucidate the caspase dependency of BA-triggered disruption of delta Psi(m), we used the pan-caspase inhibitor zVAD-fmk and the caspase-3/7 inhibitor DEVD-cho. Exposing highly motile sperm to BA caused a specific disruption of delta Psi(m) (P < 0.001 versus control) and a corresponding increase in caspase-3/7 activity (P < 0.001 versus control). Pre-incubation of the sperm with zVAD-fmk or DEVD-cho only partially inhibited BA-induced loss of delta Psi(m) (P < 0.05 versus control). We found that caspases directly participate in the loss of delta Psi(m) caused by BA in human sperm cells. However, caspase-independent pathways may also be present.