Seminal plasma exosomes evoke calcium signal via CatSper channel to regulate human sperm function

Abstract

Seminal plasma exosomes (SPE) have been proposed to regulate intracellular calcium concentration ([Ca2+]i) and sperm function. However, neither the underlying mechanisms by which [Ca2+]i is regulated by SPE nor the physiological and pathological significance of the SPE-evoked calcium signal are fully understood. Here, we successfully isolated and characterized SPE by several methods, including transmission electron microscopy, nanoparticle tracking and nanoflow cytometry analysis. Application of SPE dose-dependently increased human sperm [Ca2+]i via extracellular Ca2+ influx. The Ca2+ influx was mediated by the sperm-specific CatSper channel, because the SPE-elevated [Ca2+]i was suppressed by a CatSper inhibitor, and SPE potentiated the CatSper current in human sperm. The role of CatSper in the SPE-induced elevation of [Ca2+]i was further confirmed by the absence of the SPE-induced [Ca2+]i increase and CatSper current in a CatSper-deficient sample. Furthermore, both protein and no-protein components in SPE were shown to contribute to the elevated [Ca2+]i, as well as the hyperactivated motility of human sperm. Interestingly, when sperm were stimulated with exosomes derived from asthenozoospermic semen, the elevation of [Ca2+]i was significantly lower than that by exosomes isolated from normal seminal plasma. The SPE from normal seminal plasma improved the motility of sperm from asthenozoospermic samples. Taken together, these findings demonstrated that SPE modulates Ca2+ signaling and human sperm function by activating a CatSper channel. The application of SPE to enhance sperm motility may provide a new clinical avenue for asthenozoospermic men.