Aquaporins in the human testis and spermatozoa - identification, involvement in sperm volume regulation and clinical relevance.

Despite the high water-permeability of human spermatozoa, little is known about the identity and the role of aquaporins (AQP) in them or germ cells. Using ejaculates from donors, sperm AQPs were identified by western blotting followed by the analysis of mRNA with RT-PCR. Protein expression in the testis and spermatozoa was localized by immunocytochemistry. Inhibitors were used to investigate the involvement of aquaporins in water transport when ejaculated spermatozoa were swollen in medium mimicking uterine hypo-osmolality by quinine that blocks volume regulation. Sperm AQP7 and AQP8 in 39 infertile patients and 11 healthy donors were quantified by flow cytometry. AQP1 was absent from spermatozoa. Sperm and testicular AQP7-9 had nucleotide sequences identical to those of somatic cells but AQP8 mRNA also showed shorter variants. AQP7 was expressed abundantly by round and elongated spermatids and ejaculated spermatozoa, AQP8 by all germ cells and spermatozoa, and AQP9 rarely by spermatocytes or Sertoli cells. Protein bands showed specificity by western blotting for AQP7 and AQP8 but not AQP9. The absence of sperm AQP9 was further suggested by the ineffectiveness of its inhibitor phloretin in blocking quinine-induced swelling, but HgCl(2,) which inhibits AQP8, was effective. Sperm AQP7 expression was correlated with progressive motility and was lower in patients than in donors. Sperm AQP8 expression was inversely correlated with the extent of sperm coiling, which is a swelling phenomenon, but showed no difference between patients and donors. In conclusion, AQP7 and AQP8 were identified in human spermatozoa and could play a role in glycerol metabolism and water transport respectively.