Cholesterol content regulates acrosomal exocytosis by enhancing Rab3A plasma membrane association

BELMONTE, S.A.; LÓPEZ, C.I.; ROGGERO, C.M.; DE BLAS, G.A; TOMES, C.N.; MAYORGA, L.S.

DEVELOPMENTAL BIOLOGY

ACADEMIC PRESS INC ELSEVIER SCIENCE

Año: 2005 vol. 285 p. 393 - 408

0012-1606

The acrosome is an exocytic granule that overlies the spermatozoan nucleus. In response to different stimuli, it undergoes calciumregulatedexocytosis. Freshly ejaculated mammalian sperm are not immediately capable of undergoing acrosome reaction. The acquisition ofthis ability is called capacitation and involves a series of still not well-characterized changes in the sperm physiology. Plasma membranecholesterol removal is one of the sperm modifications that are associated with capacitation. However, how sterols affect acrosomal exocytosisis unknown. Here, we show that short incubations with cyclodextrin, a cholesterol removal agent, just before stimulation promote acrosomalexocytosis. Moreover, the effect was also observed in permeabilized cells stimulated with calcium, indicating that cholesterol plays a directrole in the calcium-dependent exocytosis associated with acrosome reaction. Using a photo-inhibitable calcium chelator, we show thatcholesterol affects an early event of the exocytic cascade rather than the lipid bilayers mixing. Functional data indicate that one target for thecholesterol effect is Rab3A. The sterol content does not affect the Rab3A activation?deactivation cycle but regulates its membraneanchoring. Western blot analysis and immunoelectron microscopy confirmed that cholesterol efflux facilitates Rab3A association to spermplasma membrane. Our data indicate that the cholesterol efflux occurring during capacitation optimizes the conditions for the productiveassembly of the fusion machinery required for acrosome reaction.