Fertilization and early embryology: Fertilization potential in vitro is correlated with head-specific mannose — ligand receptor expression, acrosome status and membrane cholesterol content*

Abstract

Normozoospermic men who do not fertilize human eggs in vitro constitute a clearly identifiable class of occult male factor infertility. We have studied the relationships between in-vitro fertilization (IVF) outcomes and the appearance of sperm surface mannose lectin/zona pellucida ligand activity measured by the binding of fluorescein isothiocyanate (FITC)-labelled mannosylated albumin. Of 338 semen specimens with normal profiles, 10 (2.96%) failed to fertilize in vitro (IVF-). Motile spermatozoa from six of these were analysed retrospectively for zona ligand binding activity on the sperm head in relation to acrosome status and the free cholesterol content of their plasma membrane. IVF+ males and fertile donors served as controls. The six IVF- occult male factor cases were distinguished from controls by their failure to show time-dependent increases in the percentage of spermatozoa exhibiting head-directed mannose ligand activity, by the slow loss or apparent increase in membrane cholesterol and by the absence of spontaneous and/or mannose-induced acrosome exocytosis.

Unesterified Cholesterol Content of Human Sperm Regulates the Response of the Acrosome to the Agonist, Progesterone1

“…In support of Davis' model, some researchers reported that sperm cholesterol decreased when sperm were incubated in albumin-containing medium in vitro [10,14,[17][18][19], although in only one case [10] was the loss of cholesterol shown to be correlated with the sperm's becoming capacitated. Arguing against the loss of sperm cholesterol during incubation in vitro were reports that sperm cholesterol did not decrease or that the decrease was not statistically significant [20][21][22].…”

Major Proteins of Bovine Seminal Plasma Modulate Sperm Capacitation by High-Density Lipoprotein1

“…This is a widely accepted theoretical model that warrants continued investigation. Many studies have shown that albumin [7][8][9][10][11][12] and high-density lipoprotein (HDL) [13,14] present in the female genital tract facilitate the efflux of cholesterol that occurs during the early step of capacitation. HDL, probably derived from plasma, is the only class of lipoprotein present in bovine follicular and oviductal fluids [13,15,16].…”

Sperm Biology from Production to Ejaculation

“…This process helps to dispel the contents of the acrosome, including surface antigens and enzymes, for successful fertilization. D-mannose binding lectins on the sperm surface, for example, have been shown to help bind spermatozoa to the zona pellucida [39,40]. The acrosomal enzymes digest the outer acrosomal membrane and the plasma membrane to which it is attached.…”