Ceramide regulates acrosomal exocytosis in human sperm

VAQUER, CINTIA CELINA; SUHAIMAN, LAILA; PELLETAN, LEONARDO E; MAYORGA, LUIS S; BELMONTE, SILVIA A

Mendoza

Congreso; XLVIII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular. SAIB.; 2012

SAIB

Sphingolipid metabolism involves multiple metabolic steps that constitute a complex network. Ceramide is a metabolic hub because is generated either via de novo pathway or the sphingomyelin and it occupies a central position in sphingolipid biosynthesis andcatabolism. Ceramide positively regulates membrane fusion in some biological systems even though has the opposite effect in other cell types. Regulated secretion is a central issue; for instance, mammalian sperm acrosomal exocytosis (AE) is essential for egg fertilization. Since we demonstrated that sphingosine-1-phosphate, an almost immediate product of ceramide breakdown, induces AE we wondered if ceramide has any effect on exocitosis and if it is sowhether it is produced by itself or through the synthesis of bioactive lipids. By usingWestern blot of sperm extracts, we found a ~84 kDa band corresponding to neutral ceramidase, a hydrolase that removes the fatty acyl groups from ceramides at neutral pH. It binds to spermmembranes in a calcium independent manner. The alkaline ceramidase (aprox 31 kDa), was also present in human sperm. Neutral sphingomyelinase, which generates ceramide, is present in sperm extracts (aprox 48 kDa). Functional assays demonstrated ceramide regulation of AE. Here, we present the first piece of evidence indicating the presence of sphingolipids metabolism enzymes in human sperm and the importance of ceramides in AE.