Removal of sialic acid from bull sperm decreases motility and mucus penetration ability but increases zona pellucida binding and polyspermic penetration in vitro

Abstract

This study tested the hypothesis that sperm sialic acid (Sia) is required to reach the site of fertilization, and that successful fertilization requires recognition of Sia from both the sperm and oocyte to occur. In addition, it has recently been reported that Siglecs (Sia-binding-immunoglobulin-like lectins) are present on the sperm surface. Thus, the possibility that the recognition of oocyte Sia was sperm-Siglec-mediated was also addressed. Sperm exposed to neuraminidase (NMase) exhibited lower overall and progressive motility, which translated to a decreased ability to swim through cervical mucus from cows in oestrus. In addition, when either sperm or cumulus-oocyte complexes (COCs) were treated with NMase, a decrease in cleavage and blastocyst rate was observed. However, incubation of sperm with increasing concentrations of anti-Siglec-2, -5, -6 and -10 antibodies prior to fertilization had no effect on their fertilizing ability. Interestingly, treatment with NMase increased the number of sperm bound to the ZP but also the rate of polyspermic fertilization. Flow cytometry analysis revealed no differences in the percentage of capacitated or acrosome-reacted sperm. These results suggest that Sia are required to reach the site of fertilization but need to be removed for sperm-oocyte interaction. However, fine regulation is needed to avoid abnormal fertilization which can lead to impaired embryo development.

A Higher Abundance of O-Linked Glycans Confers a Selective Advantage to High Fertile Buffalo Spermatozoa for Immune-Evasion From Neutrophils

“…Similarly, a differential PNA binding has been associated with the fertility status of the HF and LF bulls, indicating the differential abundance of asialylated galactosyl (ß-1, 3) N-acetylgalactosamine in their spermatozoa ( 79 , 93 , 94 ). Likewise, a decrease in the sialic acid content from the cattle bulls was found to decrease the motility and the CMP ability, nevertheless, raised the incidence of polyspermic penetration of the eggs ( 19 , 77 ). A differential or probably anomalous spatial arrangement of O-linked and N-linked glycans, for example, those associated with the LF-SpAGT, is expected to render a distinct conformation on the spermatozoa of HF bulls.…”

“…The glycoconjugates (GCs) of the glycocalyx are crucial components of several molecular mechanisms which underlie the regulation of interactions between the spermatozoa and the various cells and impediments encountered by the spermatozoa during its transit in the immunologic milieu, across the FRT ( 5 , 19 , 77 , 78 ). A spatial variation in the abundance of a variety of glycan moieties of the GCs was observed on the buffalo sperm surface in this study.…”

“…Likewise, the removal of sialic acid from the sperm-surface by sialidase has been reported to increase the phagocytosis by neutrophils ( 5 ) and by macrophages ( 59 ). This removal was also found to affect the sperm motility and its cervical mucus and egg penetration abilities, eventually affecting the fertilization capability of the sperm ( 19 ). The oligo-mannosidic chains, nonetheless, have been proposed to act as a recognition signal for eliminating the incompetent sperm during their transit in the FRT ( 26 , 113 ).…”

“…The glycosylated proteins acquired by the spermatozoa during their transit in the epididymis and pre-ejaculatory ducts are known to play crucial roles in successful fertilization ( 14 – 18 ). These radical changes in the sperm-surface are thus crucial not merely for surmounting the various physio-chemical and immunological barriers in the FRT but also for the molecular mechanisms responsible for sperm-egg interactions ( 14 , 19 ). The epididymis, therefore, acts as a site of high extracellular glycosyl metabolism involving somatic modifications of the glycocalyx (transglycosylation).…”

Cervical mucus sialic acid content determines the ability of frozen-thawed ram sperm to migrate through the cervix

“…Yu et al (2018) proposed that phagocytosis in the female reproductive tract is mediated through L-selectin on leukocytes which binds sialic acid on the sperm surface, thus providing further evidence that the sperm sialome is correlated with spermatozoa survival within the female genital tract (Ma et al 2016). Recently our group demonstrated that while the removal of sialic acid from bull spermatozoa decreased motility and mucus penetration ability, its removal increased zona pellucida binding and polyspermic penetration in vitro (Fernandez-Fuertes et al 2018), thus providing further evidence of a key role in sperm transport prior to capacitation.…”