ESCRT (Endosomal Sorting Complex Required for Transport) machinery is essential for acrosomal exocytosis in human sperm

POCOGNONI CA; BERBERIAN MV; MAYORGA LS

BIOLOGY OF REPRODUCTION

SOC STUDY REPRODUCTION

Lugar: Madison; Año: 2015

0006-3363

The sperm acrosome reaction is a unique regulated exocytosis characterized by the secretion of the acrosomal content and the release of hybrid vesicles formed by patches of the outer acrosomal and plasma membranes. In previous reports, we have shown that inward invaginations of the acrosomal membrane delineate ring-shaped membrane microdomains that contact the plasma membrane. We have postulated that the opening and expansion of fusion pores along these rings trigger acrosomal exocytosis. The invaginations of the acrosomal membrane topologically resemble the deformations of the endosomal membrane leading to the assembly of luminal vesicles in multivesicular bodies. In fact, intraacrosomal vesicles are also formed during acrosomal exocytosis. Endosomal Sorting Complex Required for Transport (ESCRT) participates in the organization of membrane microdomains that are invaginated and released as intraluminal vesicles in endosomes. We report here that members of ESCRT I (TSG101), ESCRT III (CHMP4), and the AAA ATPase VPS4 are present in the acrosomal region of the human sperm. Perturbing the function of these factors with antibodies or recombinant proteins inhibited acrosomal exocytosis in permeabilized cells. A similar effect was observed with a dominant negative mutant of VPS4A cross-linked to a cell penetrating peptide in not-permeabilized sperm stimulated with a calcium ionophore. When the function of ESCRT complexes was inhibited, acrosomes showed abnormal deformation of the acrosomal membrane and SNARE proteins that participate in acrosomal exocytosis failed to be stabilized in neurotoxin-resistant complexes. However, the growing of membrane invaginations was not blocked and numerous intraacrosomal vesicles were observed. These observations indicate that ESCRT-mediated processes are essential for acrosomal secretion, implicating these multifunctional complexes in an exocytic event crucial for sperm-egg fusion.