Membrane fluidity and lipid content of human spermatozoa selected by swim‐up method

Abstract

In this work, we examined whether spermatozoa (spz) from normospermic fertile patients and selected by a swim‐up (S‐U) procedure had a particular membrane fluidity related to their maturity and their lipid content as compared with the sperm cells from the whole ejaculate (total sperm). Swim‐up selected sperm had a reduced cytoplasmic space as revealed by a lower creatine kinase (CK) activity compared with total sperm (2 ± 1 vs. 12 ± 5 mUI/107 spz, p < 0.05). The cholesterol (Chol) and total phospholipid (PL) contents were significantly lower in S‐U selected sperm than in total sperm (0.72 ± 0.08 vs. 1.20 ± 0.30 nmol/106 spz for Chol and 1.77 ± 0.17 vs. 2.78 ± 0.50 nmol/106 spz for PL, p < 0.05) and such a decrease was observed for the three major membrane PL: phosphatidylethanolamine (PE), phosphatidylcholine (PC) and sphingomyelin (SM). However, these decreases were not associated with a change in either Chol/PL or PC/(PC + PE) molar ratios. Membrane fluidity estimated by fluorescence polarization remained comparable between the S‐U sperm fraction and total sperm (fluorescence polarization anisotropy, r, which is inversely proportional to the fluidity: 0.235 ± 0.006 vs. 0.230 ± 0.005). The sperm membrane fluidity obtained in normospermic patients was compared with abnormospermic ones (oligoasthenoteratospermia). In abnormospermic patients, the membrane fluidity was decreased in migrated spermatozoa compared with total sperm (anisotropy: 0.210 ± 0.010 vs. 0.250 ± 0.013, p < 0.01). Our data suggest that the S‐U method selected a subpopulation of mature spermatozoa characterised by a low content of Chol and PL, likely related to a reduced membrane area. The fact that Chol/PL and PC/(PC + PE) molar ratios were unchanged shows a maintenance of the membrane quality. This was confirmed by the fluorescence anisotropy measurement showing no difference in plasma membrane fluidity between S‐U selected sperm and total sperm. In abnormal semen the migrated spermatozoa had a lower fluidity compared with total sperm suggesting a defective sperm function. These results bring new elements characterizing the S‐U selected spermatozoa.