In Vitro fertilization failure of normozoospermic men: search for a lack of testicular isozyme of angiotensin-converting enzyme

BACKGROUND Angiotensin converting enzyme (ACE) is a metalloprotease with two isoforms. The somatic isoform is a key component of the renin-angiotensin system; its main function is to hydrolyse angiotensin I into angiotensin II. The germinal or testicular isoform (tACE) located at the plasma membrane of the spermatozoa, plays a crucial role in the spermatozoa-oocyte interaction during in vivo fertilization, in rodents. Disruption of the tACE in mice has revealed that homozygous male tACE-/- sire few pups despite mating normally. Few spermatozoa from these tACE-/- mice are bound to the zona pellucida (ZP) despite normal semen parameters. Based on these findings in mice models, we hypothesized that some infertile men that have the same phenotype as the tACE-/- mice, ie normal semen parameters and a lack of sperm bind to the ZP in vitro, may have a tACE defect. METHODS Twenty four men participated to this study. The case subjects (n = 10) had normal semen parameters according to the WHO guidelines (WHO 1999) but a total in vitro fertilization failure with absence of sperm fixation to the ZP. The control subjects (n = 14) also had normal semen parameters and a normal fertilization rate ≥65%. We investigated the tACE expression in spermatozoa by Western-Blot and performed a DNA sequencing of the tACE gene. RESULTS Three case-subjects and one control-subject had no tACE expression. There were no statistic differences between the two groups. No mutation was detected in the tACE DNA sequence. CONCLUSIONS Our results didn't show any involvement of tACE in human fertilization especially in ZP binding.