Immunohistology of aquaporin-1 and stem cell factor-receptor in human undescended testes.

Objectives: Both aquaporin (AQP) 1 and the stem-cell factor/C-kit system seem to have a definite role in testis function, but very few studies have been reported in humans, especially in the paediatric age group. With the present study we wanted to investigate the expression of these proteins to better delineate their role in normal and pathologic testes.

Methods: Immunohistology using AQP 1 and C-kit antibodies was performed on paraffin sections of open-testicular biopsies from 32 undescended testes. The testes of cryptorchid patients, with ages ranging from 2 to 15 years, were biopsied during an orchidopexy operation, after obtaining informed consent. Control biopsies, from 8 patients of matched age, were obtained during operations for inguinal hernia or hydrocele, always after obtaining informed consent. Positive results were recorded as diffuse or focal patterns and scored as weak, moderate or strong immunostaining.

Results: AQP 1 antibody strongly depicted microvessel endothelial cells, but was unlabeled in endotubular and interstitial cell lines, in both control and undescended testes. The C-kit immunostaining in normal testes revealed a diffuse, strong staining in the cytoplasm of spermatogonia and primary spermatocytes. However, in the undescended testes a focal C-kit immunolabelling was weakly recognized in both spermatogonial and immature Sertoli cells.

Conclusions: These results indicate a direct involvement of AQP 1 in the regulation of fluid transport across the endothelial cell membranes of testicular microvessels. A role of the C-kit receptor protein is also substantiated by its strong expression in the maturing spermatogonia of the normal testes, but was minimally or not recognizable in undescended prepubertal testes.