INVESTIGADORES
ROGGERO SAVOINI Carlos Marcelo
congresos y reuniones científicas
Título:
Cholesterol contents regulates acrosomal exocytosis by enhancing Rab3a membrana association.
Autor/es:
BELMONTE, S.A.; LOPEZ, CECILIA; ROGGERO, CARLOS M.; DE BLAS, GERARDO A.; TOMES, CLAUDIA N.; MAYORGA, LUIS S.
Lugar:
Ashburn, Virginia, USA.
Reunión:
Otro; Meeting of Internacional Research Scholars. (HHMI 2006).; 2006
Resumen:
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The acrosome is a
membrane-limited granule that overlies the nucleus of the mature spermatozoon.
In response to stimuli, it undergoes a special type of calcium-dependent
exocytosis termed the acrosome reaction, which is an absolute prerequisite for
fertilization. Freshly ejaculated mammalian sperm are not immediately capable
of undergoing the acrosome reaction. The acquisition of this ability is called
capacitation and involves a series of changes in sperm physiology that are not
yet well characterized.
Plasma membrane cholesterol
removal is one of the sperm modifications associated with
capacitation. However, how
sterols affect acrosomal exocytosis is unknown. By using streptolysin
O-permeabilized human sperm and a photosensitive calcium chelator, we have
shown that cholesterol concentration affects an early event of the exocytic
cascade rather than mixing of the lipid bilayers. Functional data indicate that
one target for
the cholesterol effect is Rab3A.
The sterol content does not affect the Rab3A activation-deactivation 1 cycle
but regulates Rah3A´s membrane anchoring. Western blot analysis and
immunoelectron microscopy confirmed that cholesterol efflux facilitates Rab3A
association with the sperm plasma membrane. To assess whether similar results
could be obtained using nonpermeabilized perm, we added an arginine-rich
peptide to the N-terminus of Rab3A. ´The presence of this polybasic peptide
promotes the diffusion of proteins through the plasma membrane.
Polyarginine-Rab3A entered into nonpermeabilized sperm and triggered exocytosis.
Similar to what we have observed in permeabilized sperm, the action of
polyarginine-Rab3A was modulated by the cholesterol content of membranes. Our
data indicate that the cholesterol efflux occurring during capacitation
optimizes conditions for the productive assembly of the fusion machinery
required for the acrosome reaction.