Comparative proteomic analysis of spermatozoa isolated by swim-up or density gradient centrifugation

Reports about the morphologic and functional characteristics of spermatozoa prepared by density gradient centrifugation (DC) or swim-up (SU) have produced discordant results. We have performed a proteomic comparison of cells prepared by DC and SU providing a molecular insight into the differences between these two methods of sperm cell isolation.

Protein maps were obtained by 2-dimensional (2-D) separations consisting of isoelectrofocusing (IEF) from pI 3 to 11 followed by SDS-polyacrylamide gel electrophoresis. 2-D gels were stained with Sypro Ruby. Map images of DC and SU spermatozoa were compared using dedicated software. Intensities of a given spot were considered different between DC and SU when their group mean differed by >1.5-fold (p<0.05, Anova).

No differences were observed for 853 spots, indicating a 98.7% similarity between DC and SU. Five spots were DC>SU and 1 was SU>DC. Proteins present in 3 of the differential spots could be identified. One DC>SU spot contained lactate dehydrogenase C and gamma-glutamylhydrolase, a second DC>SU spot contained fumarate hydratase and glyceraldehyde-3-phosphate dehydrogenase-2, and a SU>DC spot contained pyruvate kinase M1/M2.

The differences in protein levels found on comparison of DC with SU spermatozoa indicate possible dissimilarities in their glycolytic metabolism and DNA methylation and suggest that DC cells may have a better capacitation potential.