SummaryExosomes are membranous nanovesicles of endocytic origin that carry and transfer regulatory bioactive molecules and mediate intercellular communication between cells and tissues. Although seminal exosomes have been identified in human seminal plasma, their exact composition and possible physiologic function remain unknown. The objective of this study was to perform a comprehensive proteomics analysis of exosomes derived from human seminal plasma. Seminal exosomes were isolated and purified from 12 healthy donors using a 30% sucrose cushion‐based exosome‐isolation protocol, followed by characterization by western blot, transmission electron microscopy, and nanoparticle tracking analysis before performing extensive liquid chromatography tandem mass spectrometry proteomics analysis. The identified proteins were analyzed by bioinformatics analysis, and seminal exosomes‐associated proteins were selectively validated by western blot. A total of 1474 proteins were identified in all seminal exosomes samples, with Gene Ontology analysis demonstrating that these identified seminal exosomes‐associated proteins were mostly linked to ‘exosomes,’ ‘cytoplasm,’ and ‘cytosol.’ Bioinformatics analysis indicated that these proteins were mainly involved in biologic processes, including metabolism, energy pathways, protein metabolism, cell growth and maintenance, and transport. Of these identified proteins, PHGDH, LGALS3BP, SEMG1, ACTB, GAPDH, and the exosomal‐marker protein ALIX were validated by western blot. This study provided a more comprehensive description of the seminal exosomes proteome and could also be a resource for further screening of biomarkers and comparative proteomics studies, including those associated with male infertility and prostate cancer.

Background Semenogelin 1 (SEMG1) is an important secretory protein in spermatozoa involved in the formation of a gel matrix encasing ejaculated spermatozoa. Previous studies show that the SEMG1 gene is highly expressed in spermatozoa from patients with asthenozoospermia (AZS); however, the underlying molecular mechanisms are not yet clear. Objectives To study the molecular mechanism of high expression of SEMG1 gene and its potential roles in AZS. Materials and Methods Western blot and real‐time PCR were used to detect the expression levels of SEMG1 protein and mRNA in the ejaculated spermatozoa from normozoospermic males and AZS patients. Bioinformatics analysis was used to predict miRNAs targeting for SEMG1 3′‐untranslated region detection of the expression levels of all the candidate miRNAs in ejaculatory spermatozoa in AZS patients or normozoospermic volunteers. Luciferase reporter assays were performed to confirm it can directly bind to SEMG1. Correlation of miR‐525‐3p and SEMG1 mRNA expression with clinical sperm parameters were also analyzed. Finally, we conducted a follow‐up study of reproductive history about all the subjects. Results SEMG1 mRNA and protein level were significantly higher in AZS patients compared to that in normozoospermic volunteers (p < 0.001). Subsequently, microRNA‐525‐3p (miR‐525‐3p) which was predicted as a candidate regulator of SEMG1 was found lower expressed in ejaculatory spermatozoa in AZS patients (p = 0.0074). Luciferase experiment revealed that microRNA‐525‐3p could directly target SEMG1 3′‐untranslated region and suppress its expression. Importantly, our retrospective follow‐up study showed that both low miR‐525‐3p expression and high SEMG1 expression level was significantly associated with low progressive sperm motility, abnormal sperm morphology, and infertility. Discussion and Conclusion The elevated expression of SEMG1 and reduced expression of miR‐525‐3p are associated with AZS and male infertility. Our study provides a potential therapeutic target for the treatment of male infertility or for male contraception.