Abstract

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 NETs induction in vitro by sperm or embryos and the effects of DNase I on NETs. NETs stimulated by mouse sperm and embryos were visualized and analyzed using confocal microscopy. The formation and quantification of NETs were studied using inhibitors and PicoGreen. Sperm motility was assessed using computer-aided sperm analysis. Our findings indicated that mouse sperm can activate PMNs by 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, and p38 MAPK signaling pathways. Furthermore, NETs reduced sperm motility and significantly decreased the success rates of in vitro fertilization (IVF). 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 embryonic implantation process. This study presents the first demonstration in a mouse model of the molecular mechanisms underlying sperm-induced NET formation through multiple signaling pathways, as well as the physical entanglement of spermatozoa and embryos within these extracellular structures. These findings may offer novel strategies for managing infertility- related conditions.