Zinc ion flux during mammalian sperm capacitation

Abstract

Sperm capacitation, the ultimate maturation event preparing mammalian spermatozoa for fertilization, was first described in 1951, yet its regulatory mechanisms remain poorly understood. The capacitation process encompasses an influx of bicarbonate and calcium ions, removal of decapacitating factors, changes of pH and sperm proteasomal activities, and the increased protein tyrosine phosphorylation. Here, we document a novel biological phenomenon of a unique zinc (Zn2+) ion redistribution associated with mammalian sperm in vitro capacitation (IVC). Using image-based flow cytometry (IBFC), we identified four distinct types of sperm zinc ion distribution patterns (further zinc signature) and their changes during IVC. The zinc signature was altered after sperm capacitation, reduced by proteasomal inhibitors, removed by zinc chelators, and maintained with addition of external ZnCl2. These findings represent a fundamental shift in the understanding of mammalian fertilization, paving the way for improved semen analysis, in vitro fertilization (IVF), and artificial insemination (AI).

Extracellular vesicles from oviductal isthmus and ampulla stimulate the induced acrosome reaction and signaling events associated with capacitation in bovine spermatozoa

“…The interaction of EV with spermatozoa for 2 hours maintain sperm survival along time as compared to the capacitating medium; this result is of relevance for cryopreserved samples, whose viability dramatically decreases after thawing. Surprisingly, cell viability decreased from 30 minutes in Cap medium, probably due to the presence of bicarbonate in the medium, as suggested by others . In this manner, the interaction of EV with spermatozoa stimulate signaling events associated with capacitation maintaining sperm viability.…”

“…Surprisingly, cell viability decreased from 30 minutes in Cap medium, probably due to the presence of bicarbonate in the medium, as suggested by others. 44 In this manner, the interaction of EV with spermatozoa stimulate signaling events associated with capacitation maintaining sperm viability. Considering that intracellular calcium acts as second messenger for most of the sperm physiological processes, we investigated the effect of EV on calcium levels.…”

Sperm Cohort-Specific Zinc Signature Acquisition and Capacitation-Induced Zinc Flux Regulate Sperm-Oviduct and Sperm-Zona Pellucida Interactions

“…It is widely understood that zinc ions (Zn 2+ ) play an important role in male fertility, in species ranging from with C. elegans [1] through higher order mammals [2][3][4] (for review, see [5][6][7]), but its role in creating subpopulations of fertilization competent spermatozoa was not known until the discovery of the zinc signature in boar, bull, and human spermatozoa [8]. Although pre-requisite for fertility [9,10], sperm capacitation is a terminal maturation event leading to rapid cell death unless fertilization occurs [11].…”

“…Although pre-requisite for fertility [9,10], sperm capacitation is a terminal maturation event leading to rapid cell death unless fertilization occurs [11]. The zinc signature is tied directly to key sperm capacitation states: hyperactivation, acrosomal modification, acrosomal exocytosis, and the ability to detect/penetrate the oocyte zona pellucida (ZP) (beginning, midpoint, late, and final capacitation states, [8]), yet the zinc signature states of the oviductal glycan-bound spermatozoa and the role of zinc ions in the sperm release signaling pathways has not been elucidated.…”

“…Furthermore, spermatozoa from the initial pre-rich fraction are more fit for cryopreservation survival [15] and are overrepresented in the sperm reservoir [16], thus earning its nickname, the "vanguard cohort" [16]. This cohort is much more sensitive to the 26S proteasome inhibition of capacitation than the rich/post-rich fractions [8], indicating a previously unknown, distinct early capacitation event occurring at ejaculation and regulated by sperm-borne proteasomes. What distinguishes these vanguard spermatozoa as biologically different from the rest, remains unknown.…”