Mitochondrial membrane potential disruption pattern in human sperm.
BACKGROUND
Loss of mitochondrial membrane potential (DeltaPsi(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 DeltaPsi(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 DeltaPsi(m) and activation of caspases are processes thoroughly studied in human ejaculates. Disruption of DeltaPsi(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 DeltaPsi(m) in human sperm.


METHODS
Viable and highly motile sperm cells were selected through a swim-up process and incubated with 90 microg/ml BA. To elucidate the caspase dependency of BA-triggered disruption of DeltaPsi(m), we used the pan-caspase inhibitor zVAD-fmk and the caspase-3/7 inhibitor DEVD-cho.


RESULTS
Exposing highly motile sperm to BA caused a specific disruption of DeltaPsi(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 DeltaPsi(m) (P < 0.05 versus control).


CONCLUSIONS
We found that caspases directly participate in the loss of DeltaPsi(m) caused by BA in human sperm cells. However, caspase-independent pathways may also be present.
Espinoza
Jaime A
JA
Centro de Biotecnología en Reproducción, Universidad de La Frontera, Temuco, Chile.
Paasch
Uwe
U
Villegas
Juana V
JV
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism*; D053179:Caspase 7 / Q000378:metabolism; D006801:Humans; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects*; D008928:Mitochondria / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology; D053978:Pentacyclic Triterpenes; D013094:Spermatozoa / Q000502:physiology*; D014315:Triterpenes / Q000494:pharmacology; D000094062:Betulinic Acid
D000590:Amino Acid Chloromethyl Ketones; D009842:Oligopeptides; D053978:Pentacyclic Triterpenes; D014315:Triterpenes; C108637:aspartyl-glutamyl-valyl-aspartal; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D000094062:Betulinic Acid