Vesicular transfer of membrane components to bovine epididymal spermatozoa

Abstract

Epididymosomes (apocrine secreted epididymal vesicles) are assumed to play a crucial role in sperm maturation. Our aim has been to analyze the fusogenic properties of bovine epididymosomes and their involvement in the transfer of membrane components (lipids, proteins, plasma membrane Ca(2+)-ATPase 4 [PMCA4]) into bovine sperm. The fusogenic properties of epididymosomes with spermatozoa were investigated in vitro by using octadecyl rhodamine-B (R18)-labeled epididymosomes. Spermatozoa isolated from the epididymal caput showed a higher fusion rate than those taken from the cauda. The fusion rate was dependent on pH and time. Furthermore, the lipid and protein content in spermatozoa changed during epididymal transit and after in vitro fusion with epididymosomes. Following the in vitro fusion of caput spermatozoa with epididymosomes, the cholesterol/total phospholipid ratio of the sperm plasma membrane decreased. The effect was comparable with the cholesterol/total phospholipid ratio of native cauda spermatozoa. Co-incubation experiments of spermatozoa with biotinylated epididymosomes additionally revealed that proteins were transferred from epididymosomes to sperm. To examine the potential transfer of epididymis-derived PMCA4 to spermatozoa, immunofluorescence analysis and Ca(2+)-ATPase activity assays were performed. In caput spermatozoa, the PMCA4 fluorescence signal was slightly raised and Ca(2+)-ATPase activity increased after in vitro fusion. Thus, our experiments indicate significant changes in the lipid and protein composition of epididymal sperm following interaction with epididymosomes. Moreover, our results substantiate the presumption that PMCA4 is transferred to spermatozoa via epididymosomes.

Oviductosome-Sperm Membrane Interaction in Cargo Delivery

“…Similar findings were obtained for bovine sperm and epididymosomes (19), and OVS were also shown to deliver PMCA4 in vitro to murine sperm (6). In this study, we show co-immunolocalization of PMCA4 and fluorescently-labeled OVS that were fused to the sperm surface, providing evidence that OVS deliver their cargo via fusion.…”

“…Recently, Schwarz et al (19) proposed a fusogenic mechanism for the transfer of PMCA4 from epididymosomes to bovine sperm, although the molecular basis underlying the process was not investigated (19). While exosomes/microvesicles are known to carry adhesion molecules such as tetraspanin (CD9 and CD81), which build fusion-competent sites (20,21), and integrins which play a potential role in cell-to-cell communication (22), the mechanism of their action in cargo delivery remains unknown (23,24).…”

Prostasomes: extracellular vesicles from the prostate

“…As fructose is a major energy source for spermatozoa, these enzymes may play an important role in sperm cell motility (Frenette et al 2006). In a recent study, in vitro fusion of isolated epididymosomes with sperm was reported (Schwarz et al 2013), presumably explaining how epididymal epithelial cell cytosolic and membrane constituents can be integrated into sperm cells. Sperm capture of epididymosomes is apparently quite efficient, or epididymosomes are subsequently recaptured by epididymal epithelial cells, as the contribution of nonsperm associated free epididymosomes to the total population of EVs in the ejaculate appears to be low.…”

The epididymis and its role on sperm quality and male fertility

“…The fusogenic properties of bovine epididymosomes with spermatozoa were investigated by Schwarz et al who observed that spermatozoa isolated from the epididymal caput showed a higher fusion rate (both pH and time dependent) than those taken from the cauda (Schwarz et al, 2013). Also, the lipid and protein content in spermatozoa changed during epididymal transit and after in vitro fusion with epididymosomes.…”