Abstract
Capacitation drives sperm biophysical and biochemical changes for sperm-oocyte interactions. It is a well-known fact that the molecular complex arylsulfatase A (ARSA), hyaluronidase sperm adhesion molecule 1 (SPAM1), and heat shock protein 2 (HSPA2) plays a significant role in sperm–zona pellucida (ZP) binding. However, the time-dependent capacitation effects on the sperm surface ARSA presence and specific topographic distributions remain to be elucidated. Here, we quantified the ARSA density and specific membrane domain locations before (US) and after in vitro capacitation (one and four hours; CS1–CS4) in human sperm using high-resolution field emission scanning electron microscopy (FE-SEM) and immunogold labeling. Our results showed a significant and progressive capacitation-mediated increase of labeled spermatozoa from the US (37%) to CS4 (100%) physiological conditions. In addition, surface mapping revealed a close relationship between the ARSA residues and their acrosomal repositioning. Compared with the ARSA surface heterogeneous distribution found in US, the CS1–4 conditions exhibited clustering on the peri-acrosomal region, showing that time-dependent capacitation also induced a ARSA residue dramatic translocation on sperm surfaces. Our findings provide novel insights into the molecular remodeling events preceding sperm-oocyte interactions.
Highlights
Prior to fertilization success, capacitation provides the spermatozoa with the ability to interact and fuse with the oocyte plasma membrane [1], which involves the reorganization of molecular receptors needed for a sperm-oocyte interaction [2,3]The protein complex constituted by arylsulfatase A (ARSA), heat shock protein A2 (HSPA2), and hyaluronidase sperm adhesion molecule 1 (SPAM1) is a molecular receptor complex involved in sperm-oocyte recognition and is crucial for male fertility [2]
Tyrosine phosphorylation was analyzed before and after different incubation times to support the success of sperm capacitation
Our results showed a higher percentage of spermatozoa with flagellar phosphorylated tyrosine in the CS4 subpopulation (32.4%) compared to those before and after one-hour capacitation (7.7% and 14.3%, respectively; p < 0.01)
Summary
The protein complex constituted by arylsulfatase A (ARSA), heat shock protein A2 (HSPA2), and hyaluronidase sperm adhesion molecule 1 (SPAM1) is a molecular receptor complex involved in sperm-oocyte recognition and is crucial for male fertility [2]. In this context, using immunofluorescence techniques, the ARSA presence in human capacitated spermatozoa and its colocalization with the proteins of the complex (HSPA2/SPAM1) in the peri-acrosomal region is proposed as the mediator of sperm–zona pellucida (ZP) binding [3]. The aim of this study was to analyze the density and topographic distribution of ARSA by FE-SEM during time-dependent (one- and four-hour) in vitro capacitation in human spermatozoa
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