Identification of sterol acceptors that stimulate cholesterol efflux from human spermatozoa during in vitro capacitation

Abstract

The nature of cholesterol-binding proteins acting upon human spermatozoa during in vitro capacitation was determined by measuring the efflux of [3H]cholesterol and of [3H]cholesteryl sulfate from labeled spermatozoa. Efflux of [3H]sterols was stimulated when the labeled gametes were incubated in Ham's F-10 medium supplemented with female serum or follicular fluid. Upon centrifugation of capacitated spermatozoa and application of the supernatant to density-gradient ultracentrifugation for lipoprotein analysis, both [3H]cholesterol and [3H]cholesteryl sulfate were found to be carried by very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL), high-density lipoproteins (HDL), as well as the albumin fraction (d greater than 1.21) in serum. When the capacitation medium was supplemented with follicular fluid, the [3H]sterols were bound to HDL's and to the albumin fraction; when the latter fraction was analysed by molecular sieve chromatography, 60-70% of the radioactivity eluted in fractions with a mean molecular weight corresponding to that of human serum albumin. Sperm cholesterol efflux was also stimulated when serum or follicular fluid was added to a simplified medium (50 mM Tris-HCl, 0.56% NaCl, pH 7.8); efflux of [3H]cholesterol from labeled gametes progressed in a time-dependent manner, but was low in the absence of serum components. The [3H]cholesterol/cholesterol ratios were higher in the albumin and HDL fractions, indicating some degree of specificity of these sterol acceptors. It was observed that follicular fluid albumin has a [3H]sterol binding capacity that is 2-3-fold higher than that of serum albumin. Commercial human serum albumin also promoted sperm cholesterol efflux. These results provide new information concerning those components of follicular fluid which may play a role in human sperm capacitation and provide further support for the concept that loss of cholesterol from the sperm plasma membrane is an important component of the capacitation process.

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

“…The fact that FF is in vitro the best capaciting agent ( 8 ) can be explained, at least in part, by the presence of cholesterol acceptors, such as HDL and albumin, that we and others found out ( 10,13,33 ). Moreover, we evidenced that HDL is the single class of lipoprotein during the preovulatory period ( 13 ) and that pre ␤ HDLs represent about 18% of total HDL of the FF ( 14 ).…”

“…We fi rst evaluated the effects of varying FF concentrations (5,10,20,30,40, and 50%, v/v in modifi ed B2 medium) on spermatozoa hyperactivation process after 5 min of incubation at 37°C ( Fig. 1A ).…”

Distribution and Transport of Cholesterol inCaenorhabditis elegans

“…In mammals newly ejaculated sperm is inactive and needs to be capacitated by several factors (Chang, 1951;Austin, 1952). It is well established that cholesterol efflux plays an important role in the capacitation of mammalian sperm (Langlais et al, 1988). This efflux triggers a signaling cascade that includes phosphorylation of several sperm proteins and elevation of Ca 2ϩ concentration (Visconti et al, 1999).…”

More Than a Simple Lock and Key Mechanism: Unraveling the Intricacies of Sperm-Zona Pellucida Binding

“…Following the release of these decapacitation factors, spermatozoa experience a dramatic efflux of cholesterol from the plasma membrane (Davis, 1981). This efflux appears to be driven by active sequestration upon exposure of the spermatozoa to an environment rich in appropriate cholesterol sinks (Davis, et al, 1979, Langlais, et al, 1988, Visconti, et al, 1999, and accounts for a striking increase in membrane fluidity. Bovine serum albumin is commonly used within in vitro capacitating media as a cholesterol acceptor, although analogous acceptor(s) are believed to be present within the female reproductive tract.…”

“…Bovine serum albumin is commonly used within in vitro capacitating media as a cholesterol acceptor, although analogous acceptor(s) are believed to be present within the female reproductive tract. Indeed, studies of human follicular fluid have identified the presence high concentrations of albumin and other cholesterol sinks (Langlais, et al, 1988). Cholesterol efflux from the plasma membrane has also been correlated with an influx of bicarbonate ions (HCO3 -) into the cell (Boatman and Robbins, 1991, Chen, et al, 2000, Garty and Salomon, 1987, Okamura, et al, 1985.…”