Effects of human follicular fluid and high-density lipoproteins on early spermatozoa hyperactivation and cholesterol efflux

Abstract

The preovulatory human follicular fluid contains only HDLs as a lipoprotein class with a typically high proportion of preβ HDL. We first examined the role of follicular fluid and HDL subfractions on human spermatozoa capacitation, a process characterized by a hyperactivation of the flagellar movement and a depletion of plasma membrane cholesterol. Whole follicular fluid and isolated HDL, used at constant free cholesterol concentration, were both able to promote an early flagellar hyperactivation. Moreover, incubation of [3H]cholesterol-labeled spermatozoa with follicular fluid induced a rapid cholesterol efflux from spermatozoa that was confirmed by mass measurements of cholesterol transfer. Using isolated HDL, the cholesterol efflux had a similar time course and represented 70% of that mediated by whole follicular fluid. We then analyzed the time course of radioactive labeling of HDL subfractions. In the first minute of incubation, we found that the preβ HDL fraction incorporated the main part of the radioactivity (60%), with the rest being found in α-HDL, but strikingly, the labeling of α-HDL increased with time at the expense of preβ HDL.Thus, our results indicate that HDLs are involved in both spermatozoa hyperactivation and cholesterol effl ux and suggest the role of preβ-HDL particles as fi rst cellular cholesterol acceptors.

Keywords

• oocyte
• capacitation
• cholesterol depletion
• cholesterol acceptor
• preβ-HDL
• α-HDL