Bibliographic review on the molecular mechanisms involved in epididymal maturation and sperm capacitation: Revisió bibliogràfica sobre els mecanismes moleculars involucrats en la maduració epididimària i la capacitació espermàtica

Abstract

Testicular spermatozoa of all mammalian species are unable to move progressively or fertilize oocytes. To acquire these two abilities, they must undergo two extratesticular maturational processes: epididymal maturation in the male reproductive tract and sperm capacitation in the female reproductive tract. During epididiymal maturation, spermatozoa undergo structural and biochemical modifications which are modulated by the composition of the epididymal fluid. Among these modifications to highlight: changes in membrane phospholipid composition and in cholesterol/phospholipid ratio, increase in net surface negative charge, increases in the number of disulfide bonds, modification, elimination or addition of surface protein, relocalization of surface antigens, and migration of the cytoplasmic droplet. After this process, spermatozoa are stored in the epididymal cauda until ejaculation. Epididymal maturation and ejaculation are key events for further capacitation, since only ejaculated spermatozoa are capable to undergo this process. Capacitation is a complex process of structural and functional changes that takes place during the transit through the female reproductive tract, and it is completed when spermatozoa are able to penetrate zona pellucida by undergoing the acrosome reaction. This process involves modifications in sperm surface protein distribution, alterations in the plasma membrane characteristics, changes in enzymatic activity and modulation of expression of intracellular constituents. All these changes occur as a result of the activation of signaling pathways cascades. Both, epididymal maturation and sperm capacitation are absolutely needed in order to generate fertile spermatozoa. This makes the study of the molecular mechanisms underpinning this two processes very important. This review aims to compile all the information that has been discovered in recent decades about the molecular mechanisms of epididymal maturation and sperm capacitation, and to understand the molecular mechanisms by which spermatozoa acquire fertilizing ability and motility