Caspase activation in human spermatozoa in response to physiological and pathological stimuli.

OBJECTIVE To investigate caspase activation in response to a variety of pathological and physiological stimuli in light of the fact that current research offers no clear consensus about caspase activation pathways in spermatozoa. DESIGN A prospective, controlled study. SETTING Male infertility clinic, Glickman Urological Institute, Cleveland Clinic Foundation, Cleveland, Ohio. PATIENT(S) Fifteen healthy volunteers. INTERVENTION(S) Spermatozoa were exposed to [1] Fibroblast-associated (Fas) death receptor activation, [2] mitochondrial apoptosis induction using betulinic acid, [3] oxidative stress, and [4] prolonged incubation up to 3 hours without any external stimuli. MAIN OUTCOME MEASURE(S) Active caspases-1, -3, -8, and -9 were examined in human spermatozoa by flow cytometry using carboxyfluorescein derivatives. RESULT(S) Inducing Fas antibody did not result in any caspase activation. Conversely, betulinic acid significantly triggered caspase-9 and -3 activation. The application of oxidative stress and prolonged incubation (3 hours) failed to result in caspase activation. CONCLUSION(S) These results suggest that Fas has no functional relevance in mediating caspase activation in human ejaculated spermatozoa. Although spermatozoal mitochondria are highly susceptible to specific agonists of apoptosis such as betulinic acid via caspase activation, oxidative stress-induced apoptosis appears to be caspase independent.