Mouse sperms trigger neutrophil extracellular traps which impair sperm motility and entangle with the embryo

Despite recent advancements in diagnostic techniques and infertility treatments, the precise underlying cause of infertility remains elusive in numerous cases. Elevated immune cell levels in the reproductive tract frequently result in decreased sperm motility and a diminished likelihood of successful embryo implantation. This study aimed to investigate the mechanisms of neutrophil extracellular traps (NETs) induction in vitro by sperms or embryos and effects of DNase I on NETs. NETs stimulated by mouse sperms and embryos were visualized and analyzed using confocal microscopy. The formation and quantification of NETs were studied using inhibitors and PicoGreen. Sperm vitality was assessed using computer-aided sperm analysis. Our findings indicated that mouse sperms can activate PMNs through inducing NETs formation, which consisted of DNA with citrullinated histone H3 (citH3) and myeloperoxidase (MPO). The pathways underlying sperm-triggered NETs involve NADPH oxidase, ERK1/2, or p38 MAPK signaling pathways. Furthermore, NETs reduced sperm vitality and significantly decreased the success rates of in vitro fertilization. Treatment with DNase I effectively degraded NETs formation and mitigated these effects mentioned above. Interestingly, it was observed for the first time in vitro that mouse embryos were directly ensnared by NETs, suggesting a potential association with embryonicimplantation process. In conclusion, this is the first report on mouse sperm-induced entanglement between sperms/embryos and NETs structures; these findings may offer novel strategies for managing infertility- related conditions.