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Abstract
Capacitated spermatozoa initiate fertilization by binding to the zona pellucida (ZP). Defective spermatozoa-ZP binding causes infertility. The sialyl-Lewis(x) (SLeX) sequence is the most abundant terminal sequence on the glycans of human ZP glycoproteins involving in spermatozoa-ZP binding. This study aimed to identify and characterize the SLeX-binding proteins on human spermatozoa. By using affinity chromatography followed by mass spectrometric analysis, chromosome 1 open reading frame 56 (C1orf56) was identified to be a SLeX-binding protein of capacitated spermatozoa. The acrosomal region of spermatozoa possessed C1orf56 immunoreactive signals with intensities that increased after capacitation indicating translocation of C1orf56 to the cell surface during capacitation. Treatment with antibody against C1orf56 inhibited spermatozoa-ZP binding and ZP-induced acrosome reaction. Purified C1orf56 from capacitated spermatozoa bound to human ZP. A pilot clinical study was conducted and found no association between the percentage of capacitated spermatozoa with C1orf56 expression and in vitro fertilization (IVF) rate in assisted reproduction treatment. However, the percentage of C1orf56 positive spermatozoa in the acrosome-reacted population was significantly (P < 0.05) lower in cycles with a fertilization rate < 60% when compared to those with a higher fertilization rate, suggesting that C1orf56 may have functions after ZP-binding and acrosome reaction. A larger clinical trial is needed to determine the possible use of sperm C1orf56 content for the prediction of fertilization potential of sperm samples.
Highlights
Human oocytes are surrounded by a ∼7–20 μm thick porous cellular extracellular matrix termed zona pellucida (ZP), which is the main player in spermatozoa-oocyte interactions and species-specific fertilization
Mass spectrometry analysis of the SLeX-bovine serum albumin (BSA) affinity purified sperm membrane fraction identified a total of 59 proteins with Mascot protein score higher than 653
Proteins were selected for studies when they were absent in the LeX-BSA (Dextra) affinity purified fraction and when they had been reported to be present only in human sperm head region
Summary
Human oocytes are surrounded by a ∼7–20 μm thick porous cellular extracellular matrix termed zona pellucida (ZP), which is the main player in spermatozoa-oocyte interactions and species-specific fertilization. Spermatozoa-ZP binding is the first event in fertilization. Defective spermatozoa-ZP binding leads to infertility and is an important cause of reduced fertilization rates. Sperm Sialyl-Lewis(x)-Interacting Protein in assisted reproduction (Liu and Baker, 2000). A metaanalysis has shown high predictive power of spermatozoa-ZP binding on fertilization outcome (Oehninger et al, 2000). Defective spermatozoa-ZP binding is more frequent for men with abnormal semen parameters, especially those with severe teratozoospermia and oligozoospermia (Liu and Baker, 2004). Despite the importance of spermatozoa-ZP interaction, the mechanisms regulating the process are unclear partly due to failure in the identification of ZP receptor(s) on human spermatozoa
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