Sphingosine kinase 1 es involved in the acrosomal exocytosis of human spermatozoa

SUHAIMAN LAILA, MAYORGA LUIS S., BELMONTE SILVIA A.

Mar del Plata, Buenos Aires, Argentina

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular. SAIB.; 2007

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular, SAIB

The acrosome is an exocytic granule overlying the sperm nucleus. In response to progesterone or zona pellucida, it undergoes calcium-regulated exocytosis. We demonstrated that sphingosine 1-phosphate (S1P), produced by sphingosine phosphorylation catalyzed by sphingosine kinase (SK), triggers acrosome reaction (AR) in human sperm. The fusion process triggered by S1P was inhibited by BAPTA suggesting a dependency of extracellular calcium. We hypothesized that S1P activates exocytosis via a receptor-mediated mechanism that opens SOC channels. Ni2+, an inhibitor of SOCCs, blocked S1P triggered exocytosis. Furthermore, voltage-dependent calcium channel inhibitors, such as verapamil and nifedipine, blocked S1P-induced AR. No effect of S1P was observed in permeabilized sperm suggesting that S1P exerts its effect through S1P receptors (S1PR). We blocked S1P-induced AR by using Pertussis Toxin, confirming the presence of a Gi-coupled S1PR. S1P stimulus could proceed from the oocyte or from sperm cells during fertilization. To unveil this riddle, we used DMS, a SK1 inhibitor, in functional assays. DMS blocked S1P induced-AR, and this effect was overcome by exogenously added S1P. We detected SK1 by western blot and indirect immunofluorescence assays. We conclude that SK1 is present in human sperm, its distribution pattern changes after a stimulus and actively participates in sperm AR.