Interactions between apoptotic signal transduction and capacitation in human spermatozoa.
BACKGROUND
Capacitation of sperm is a prerequisite for successful fertilization, determined by hyperactivated motility, increased tyrosine phosphorylation (TyrP) and membrane changes. However, the exact molecular mechanism is not fully clarified. The calpain-calmodulin-system is essential for membrane fusion during capacitation. Recently, interactions with caspase (CP) activation, a main feature of apoptotic cells, were postulated. The objective of our study was to examine interactions between apoptosis signalling and the calpain-calmodulin-system during capacitation.


METHODS
Semen samples from 20 healthy donors were incubated in human tubal fluid at 37 degrees C, 5% CO(2) for 3 h without additives (control), with 3% BSA (capacitation), 10 microM calpain-inhibitor III, 20 microM CP-1 inhibitor or 20 microM calmodulin-antagonist. Capacitation was monitored by computer assisted sperm motion analyzer, chlortetracycline (CTC)-assay and western blot (TyrP). Activation of caspases and integrity of transmembrane mitochondrial potential (TMP) were evaluated by flow cytometry.


RESULTS
Capacitation, as measured by CTC assay, increased TyrP levels and hyperactivation, resulted in inactivation of CP-9, CP-3 and improved integrity of the TMP. Inhibition of calpain and CP-1 during capacitation reduced the capacitation-related parameters, but did not lead to apoptosis. Inhibition of calmodulin resulted in blocking of capacitation and stimulation of apoptosis.


CONCLUSIONS
Interaction of the capacitation and apoptosis signalling systems seems to enable the capacitation process by prevention of apoptosis.
Grunewald
S
S
Department of Dermatology, Training Center of the European Academy of Andrology, University of Leipzig, Ph.-Rosenthal-Str. 23, 04103 Leipzig, Germany. sonja.grunewald@medizin.uni-leipzig.de
Kriegel
C
C
Baumann
T
T
Glander
H-J
HJ
Paasch
U
U
D017209:Apoptosis / Q000502:physiology*; D002147:Calmodulin / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002751:Chlortetracycline / Q000378:metabolism; D004151:Dipeptides / Q000494:pharmacology; D006801:Humans; D008297:Male; D010766:Phosphorylation; D015398:Signal Transduction; D013075:Sperm Capacitation / Q000502:physiology*; D013081:Sperm Motility / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology*
D002147:Calmodulin; D004151:Dipeptides; D002154:Calpain; D053148:Caspase 3; D053453:Caspase 9; C058076:calpain inhibitor III; D002751:Chlortetracycline