CONICET | Buscador de Institutos y Recursos Humanos

The acrosome is a membrane-limited granule that overlies the sperm nucleus. In response to physiological stimuli, sperm undergo a calcium-dependent exocytosis of this granule termed: acrosome reaction (AR). Ceramide´s role in exocytosis is not well defined, since it's been shown that in some cases it positively regulates membrane fusion while in others has the opposite effect. Also, is not well characterized if its effects on secretion are exerted by itself or by related metabolites. We evaluated the role of ceramide and its metabolites in the AR by using biochemical and exocytosis assays. WB and IFI analysis demonstrated the presence of enzymes of the sphingolipid metabolism in human sperm. Both, C6-ceramide (C6-Cer) treatment or endogenous ceramide increase induce AR in capacitated sperm in a percentage similar to progesterone. Human sperm loaded with Fluo3-AM, a calcium sensor, responded to C6-Cer with a transient increase in calcium concentration whose profile was similar to that elicited by progesterone. Furthermore, ceramide increase promotes calcium mobilization from internal stores (ryanodine receptors) however it requires extracellular calcium influx through SOCCs to accomplish acrosome release. The ceramide or progesterone-elicited AR was inhibited by NVP-231, a ceramide kinase blocker, indicating that both inducers require ceramide 1-phosphate (C1P) in the pathway leading to AR. Further, the inhibition was reverted by adding C1P. These findings led us to the conclusion that probably C1P is regulating AR after a ceramide increase. Here, we identified ceramide and C1P as novel molecules integrated in a signaling cascade leading to membrane fusion during acrosomal exocytosis.