Ultrastructural localization of angiotensin-converting enzyme in ejaculated human spermatozoa

Abstract

Angiotensin-converting enzyme (ACE) is known to be released from human spermatozoa during capacitation. However, it has not yet been localized ultrastructurally in ejaculated sperm cells. Therefore, the purpose of the present study was to demonstrate the location of ACE by means of immunoelectron microscopy and direct immunofluorescence. In addition, ACE activity of spermatozoa was correlated with standard semen parameters. The activity of angiotensin-converting enzyme was measured in spermatozoa from 115 donors and patients attending the andrological outpatient department. Progressive motility was negatively correlated with sperm ACE activity (Spearman rank correlation r=-0.364, P < 0.0001), whereas no statistically significant correlations with sperm concentration, total motility and morphology were observed. Immunoelectron microscopy demonstrated that ACE is mainly located at the plasma membrane of the acrosomal region, equatorial segment, postacrosomal region and midpiece. In contrast, only weak ACE-like immunoreactivity was found at the flagellum. In cases of cells with missing plasma membranes ACE seems also to be located at the surface of the outer acrosomal membrane. By means of immunohistochemical methods, different patterns of ACE-like immunofluorescence were observed: (i) fluorescence of the acrosome or the entire sperm head, midpiece and flagellum; (ii) fluorescence of the postacrosomal region, midpiece and flagellum; (iii) bright fluorescence of the equatorial segment with less intensive labelling of the postacrosomal region and flagellum. Induction of the acrosome reaction by calcium ionophore A23187 resulted in an increase of spermatozoa with weak acrosomal fluorescence, indicating loss of the plasma membrane.

Identification of differentially expressed proteins in fresh and frozen–thawed boar spermatozoa by iTRAQ-coupled 2D LC–MS/MS

“…The levels of ACE on the surface of spermatozoa have been shown to be inversely proportional to their fertilization capacity (Kohn et al 1998, Shibahara et al 2001. Therefore, the increase in ACE levels in frozen-thawed spermatozoa may reasonably explain the problem of low fertility rate.…”

Quantitative study of testicular angiotensin-converting enzyme on the surface of human spermatozoa

“…Previous studies revealed no relationships between the concentration/morphological characteristics of spermatozoa and ACE activity [7]. A positive correlation was revealed between ACE activity and motility of human and bovine spermatozoa [6].…”

“…ACE gene knockout mice do not differ from intact animals by the number, motility, and morphological characteristics of spermatozoa. However, these cells are unable to pass through female genital tract and fertilize the oocyte [8,9].Previous studies revealed no relationships between the concentration/morphological characteristics of spermatozoa and ACE activity [7]. A positive correlation was revealed between ACE activity and motility of human and bovine spermatozoa [6].…”

“…A positive correlation was revealed between ACE activity and motility of human and bovine spermatozoa [6]. However, recent studies found a negative correlation between enzyme activity and motility of pig and human spermatozoa [7,11,12]. Moreover, ACE activity in normospermic patients is lower than in patients with oligospermia [11].…”

The contribution of proteomics to understanding epididymal maturation of mammalian spermatozoa

“…Accession number (a) Spermatozoa surface references 14-3-3 protein zeta chain YWHAZ 253706 Aconitase ACO1 5821963 Acrosin ACR 164703 [Mori et al 1995;Suter and Habenicht 1998] Aldose reductase ALDR2 8569627 [Kobayashi et al 2002;Frenette et al 2003] Alpha enolase ENO1 2661039 [Gitlits et al 2000] Alpha-mannosidase MAN2C1 1017779 [Okamura et al 1995;Pereira et al 1998;Kuno et al 2000] Angiotensin-converting enzyme ACE 145279215 [Kohn et al 1998;Gatti, et al 1999;Nikolaeva et al 2006 Zona pellucida-binding protein 1 ZPBP 47523020 [Yu et al 2006;Mori, et al 1995] a) Accession code for the identification in NCBI database…”