Expression of membrane fusion proteins in spermatozoa and total fertilisation failure during in vitro fertilisation

Abstract

Background: Couples increasingly experience infertility and seek help from assisted reproductive techniques to become pregnant. However, 5%-15% of the couples that are selected for in vitro fertilisation (IVF) experience a total fertilisation failure (TFF), where no zygotes develop despite oocytes and semen parameters appear to be normal.We hypothesise that TFF during IVF could be related to improper membrane fusion of gametes.Objective: To investigate the membrane integrity and fusion proteins in spermatozoa from men in couples experiencing TFF. Materials and methods: A total of 33 infertile couples, 17 of which experienced TFF during IVF and 16 matched control couples with normal IVF fertilisation rates, were selected and the men re-called to deliver an additional semen sample. Proteins involved in gamete membrane fusion on spermatozoa (IZUMO1, SPESP1 and Syncytin-1) as well as O-glycosylation patterns (Tn and GALNT3), were investigated by immunofluorescence. The DNA fragmentation index, acrosomal integrity and viability of spermatozoa were determined by flow and image cytometry.Results: No significant changes in the expression of GALNT3, Tn and Syncytin-1 were observed between the TFF and control groups. The fraction of spermatozoa expressing SPESP1, the median IZUMO1 staining intensity, and the percentage of viable acrosome-intact spermatozoa were significantly lower in the TFF group compared to controls. Furthermore, following progesterone-induced acrosomal exocytosis, a significant difference in the fraction of spermatozoa expressing SPESP1 and the median IZUMO1 staining intensity were observed between the control and TFF group. Discussion and conclusion: Our results indicate that acrosomal exocytosis, IZUMO1and SPESP1 expression in spermatozoa could play a crucial role in achieving fertilisation during IVF. However, the size of our cohort was quite small, and our results need to be validated with quantitative methods in larger cohorts.

A comprehensive investigation of human endogenous retroviral syncytin proteins and their receptors in men with normozoospermia and impaired semen quality

“…Bjerregaard and colleagues indicated that a strong Syncytin 1 expression was present in the sperm acrosome or the equatorial segment and a weak staining pattern was observed in the midpiece and tail regions [ 53 ]. Recently, a similar expression pattern was also reported by Enoiu and colleagues with visible diffusion to the entire head in all sperm samples [ 54 ]. While the expression of Syncytin 1 in the acrosome, equatorial segment, midpiece, and tail regions of sperm is similar to the previous studies, here, we demonstrated that there is a more complex expression profile of Syncytin 1 suggesting a heterogeneity in human spermatozoa.…”

“…The decreased expression of Syncytin 1 and its receptor may cause failure by negatively affecting fertilization and embryo growth and can be used as important biomarker molecules in the development of new strategies in IVF treatments. A recent study by Enoiu and colleagues investigated the fusion proteins including Syncytin 1 in spermatozoa from men in couples experiencing total fertilization failure during IVF [ 54 ]. However, the study reported that there were not any significant changes in the expression of Syncytin 1 between the total fertilization failure and control groups [ 54 ].…”

“…A recent study by Enoiu and colleagues investigated the fusion proteins including Syncytin 1 in spermatozoa from men in couples experiencing total fertilization failure during IVF [ 54 ]. However, the study reported that there were not any significant changes in the expression of Syncytin 1 between the total fertilization failure and control groups [ 54 ]. However, the number of spermatozoa expressing Syncytin 1 was found to be higher in the control group compared with total fertilization failure even though it was not statistically significant.…”

“…In line with this study, Enoiu and colleagues investigated Syncytin 1 and other membrane fusion proteins in spermatozoa from men experiencing total fertilization failure during IVF by immunofluorescence [ 54 ]. The authors reported a similar localization pattern with previous study by Bjerregaard and colleagues that Syncytin 1 was present predominantly in the acrosomal cap region and also slightly in the midpiece and tail regions of human sperm [ 54 ]. Bergallo and colleagues also showed that there are several retroviral mRNAs including Syncytin 1 in the human sperm, although in low amounts [ 55 ].…”

A novel function for the sperm adhesion protein IZUMO1 in cell–cell fusion

“…IZUMO1 deletion blocks gamete fusion ( Inoue et al, 2005 ), and JUNO was identified as the IZUMO1 receptor in the oocyte ( Bianchi et al, 2014 ). Evidence from infertile patients suggests that these proteins play a role during human fertilization ( Clark and Naz, 2013 ; Yu et al, 2018 ; Enoiu et al, 2022 ). The IZUMO1–JUNO interaction mediates gamete binding ( Matsumura et al, 2021 ) in a species-specific manner ( Bianchi and Wright, 2015 ).…”