The flow cytometry study of AnnexinV binding by human spermatozoa – is it a marker of apoptosis?

Abstract
Apoptosis is a physiological process whereby cell activates an intrinsic death or suicide and kills itself in a controlled way. A sequence of morphological and biochemical changes occurs in cell during this process, one of these is the loss of plasma membrane asymmetry. In early phase of apoptosis the particles of phosphatydylserin are presented on the outer leaflet of plasma membrane, what can be detected by Annexin V binding. However, AnnexinV identifies both apoptotic and necrotic cells. To distinguish these two groups the DNA binding propidium iodide that stains permeable cells should be used. In this study to broaden the knowledge of the spermatozoa programmed cell death we analyzed Annexin V binding by these cells as early marker of apoptosis. We tested semen samples from 31 patients diagnosed because of married infertility. Annexin V binding was assessed with flow cytometry technique. We observed that human ejaculated spermatozoa do bind either AnnexinV or AnnexinV along with PI, however only very low number are double negative. Thus, it can be concluded that changes in spermatozoa membrane structure are not caused by the beginning of apoptosis, as in somatic cells. These changes may be a consequence of some other physiological processes like capacitation or spermatogenesis, what requires to be elucidated precisely yet.