Epac activation induces an extracellular Ca 2+ ‐independent Ca 2+ wave that triggers acrosome reaction in human spermatozoa

MATA MARTÍNEZ, ESPERANZA; SÁNCHEZ TUSIE, ANA ALICIA; DARSZON, ALBERTO; MAYORGA, LUIS S.; TREVIÑO, CLAUDIA L.; DE BLAS, GERARDO A.

Andrology

wiley online library

Año: 2021

2047-2919

Background: The signaling pathways of the intracellular second messengers cAMPand Ca2+ play a crucial role in numerous physiological processes in human spermatozoa.One such process is the acrosome reaction (AR), which is necessary for spermatozoato traverse the egg envelope and to expose a fusogenic membrane allowingthe egg?spermfusion. Progesterone and zona pellucida elicit an intracellular Ca2+increase that is needed for the AR in the mammalian spermatozoa. This increase ismediated by an initial Ca2+ influx but also by a release from intracellular Ca2+ stores.It is known that intracellular Ca2+ stores play a central role in the regulation of [Ca2+]iand in the generation of complex Ca2+ signals such as oscillations and waves. In thehuman spermatozoa, it has been proposed that the cAMP analog and specific agonistof Epac 8-(p-chlorophenylthio)-2´-O-methyladenosine-3?,5´-cyclicmonophosphate(2´-O-Me-cAMP)elicits an intracellular Ca2+ release involved in the AR.Objective: To identify the molecular entities involved in the Ca2+ mobilization triggeredby 2´-O-Me-cAMPin human spermatozoa.Materials and Methods: In capacitated human spermatozoa, we monitored Ca2+ dynamicsand the occurrence of the AR in real time using Fluo 3-AMand FM4-64in aCa2+-freemedium.Results: Epac activation by 2´-O-Me-cAMPinduced a Ca2+ wave that started in themidpiece and propagated to the acrosome region. This Ca2+ response was sensitiveto rotenone, CGP, xestospongin, NED-19,and thapsigargin, suggesting the participationof different ion transporters (mitochondrial complex I and Na+/Ca2+ exchanger,inositol 3-phosphatereceptors, two-porechannels and internal store Ca2+-ATPases).Discussion: Our results suggest that Epac activation promotes a dynamic crosstalkbetween three different intracellular Ca2+ stores: the mitochondria, the redundantnuclear envelope, and the acrosome.Conclusion: The Ca2+ wave triggered by Epac activation is necessary to induce the ARand to enhance the flagellar beat.