title: Cathepsin D in human reproductive tissues: cellular localization in testis and epididymis and surface distribution in different sperm conditions.
abstract: Mammalian sperm surface antigens are acquired either during spermatogenesis  or sperm maturation in the epididymis. These antigens, many of which are  hydrolytic enzymes, are actively synthesized and secreted by the resident  epithelial cells and adsorbed to the sperm membrane as part of posttesticular  sperm modification. In this study, we aimed to investigate the expression of  cathepsin-D (CAT-D) in human reproductive tissues and its distribution on the  sperm surface in different sperm conditions. Immunohistochemical results  revealed the expression of CAT-D in the somatic Sertoli and Leydig cells  without showing any immunoreactivity in any germ cells, despite their  engagement of the acrosomal system. A strong immunoreactivity of  anti-CAT-D was also detected in the epididymal epithelium, chiefly in  the principal cells, which are known to actively synthesize and secrete  proteins into the epididymal lumen. The absence of CAT-D in the clear cells  was unexpected because these cells are known to engage the endosomal  machinery. We further showed that CAT-D was anchored on the sperm surface  confined to the postacrosomal region without any lateral redistribution within  the membrane during sperm capacitation. However, the enzyme underwent changes  to be an active form of a 29/30-kd doublet during sperm capacitation. Using  CAT-D as a marker, we were able to demonstrate here localization of the enzyme  in human reproductive tissues, as well as reveal membrane modification in  human sperm during maturation and capacitation processes.
authors.affiliation: Department of Anatomy, Faculty of Medicine, Siriraj Hospital, Mahidol University, Prannok Rd, Bangkok Noi, Bangkok, 10700 Thailand.
authors.forename: Arpornrad
authors.initials: A
authors.lastname: Saewu
authors.forename: Somluk
authors.initials: S
authors.lastname: Asuvapongpatana
authors.forename: Charoonroj
authors.initials: C
authors.lastname: Chotwiwatthanakun
authors.forename: Anuphana
authors.initials: A
authors.lastname: Tantiwongse
authors.forename: Wattana
authors.initials: W
authors.lastname: Weerachatyanukul
authors.forename: Siriporn
authors.initials: S
authors.lastname: Thitilertdecha
mesh_terms: D000954:Antigens, Surface / Q000032:analysis; D002402:Cathepsin D / Q000378:metabolism*; D004822:Epididymis / Q000201:enzymology*; D004847:Epithelial Cells / Q000201:enzymology; D006801:Humans; D008297:Male; D013075:Sperm Capacitation / Q000502:physiology; D013079:Sperm Maturation / Q000502:physiology; D013094:Spermatozoa; D013737:Testis / Q000201:enzymology*
chemical_list: D000954:Antigens, Surface; D002402:Cathepsin D