Interactions between apoptotic signal transduction and capacitation in human spermatozoa
S Grunewald1, C Kriegel, T Baumann
1Department 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
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.
Conclusion:
Interaction of the capacitation and apoptosis signalling systems seems to enable the capacitation process by prevention of apoptosis.
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