The sperm acrosome: functional and clinical aspects

The acrosome of mammalian spermatozoa contains high amounts of acrosin, which is believed to be essential for gamete fusion, particularly for binding to, and penetration of, the zona pellucida. In addition, its activation from proacrosin seems to be associated with the capacitation process. Furthermore, it might facilitate cervical mucus penetration and intrauterine sperm migration by releasing kinins from kininogen, as well as participating in the acrosome reaction and in chromatin decondensation in the oocyte. Considering these functions of the acrosome during the process of fertilization, the morphology and functional integrity of the acrosome in ejaculated human spermatozoa are of fundamental importance in attachment, species-specific binding and zona penetration preceding gamete fusion. It is therefore mandatory to focus on acrosomal membrane functions and consider particularly the occurrence of acrosomal disturbances in spermatozoa from men of barren marriages. For this purpose, biochemical and immunocytochemical methods have been used to investigate acrosin activity and possible alterations of the acrosomal membrane system in different groups of sub- and infertile patients. Of particular interest is the ability of spermatozoa to undergo the acrosome reaction, which can be studied using the triple-stain technique. Of all the spermatological groups investigated (normo-, astheno-, oligo-, terato- and polyzoospermia), polyzoospermic semen samples showed severe acrosomal disturbances indicating functionally defective acrosomes which might hinder fertilization. The data indicate the need for the introduction of acrosomal markers in clinical andrology for proper diagnosis of acrosomal sperm defects.