Localization and molecular heterogeneity of sulfated glycoprotein-2 (clusterin) among ventral prostate, seminal vesicle, testis, and epididymis of rats.

In the rat reproductive tract, sulfated glycoprotein 2 (SGP-2) is present in the ventral prostate, seminal vesicle, testis, and epididymis. In the ventral prostate, SGP-2 is associated with the process of programmed cell death, while in the testis and epididymis a role for SGP-2 in sperm maturation has been proposed. Available information suggests that there are both inter- and intra-organ variations in SGP-2 localization, molecular forms, and response to androgen ablation. In the present study, localization of SGP-2 within the ventral prostate, seminal vesicle, and epididymis was compared by immunohistochemistry. In the ventral prostate of intact rats, immunoreactive SGP-2 was confined to a discrete population of epithelial cells lining the proximal ducts. Epithelial cells in other regions of the ventral prostate did not stain for SGP-2. A similar staining pattern was observed for the seminal vesicle; a small population of SGP-2-expressing epithelial cells was found in epithelium that did not stain for SGP-2. The epididymis also demonstrated a non-uniform staining pattern. The caput displayed strong immunoperoxidase reaction over the apical membrane and stereocilia of all principal cells. Principal cells also showed variable degrees of cytoplasmic staining ranging from weak to strongly positive. The corpus and cauda showed a similar staining pattern. After castration, all epithelial cells in the ventral prostate and seminal vesicle became intensely positive for SGP-2 staining. In the caput and cauda epididymis there was an increase in the number of principal cells demonstrating strong intracellular staining for SGP-2. These results suggest that as observed previously in the regressing ventral prostate, increased intracellular SGP-2 staining may also be associated with the regressing epididymis and seminal vesicle. Differences in molecular forms of SGP-2 were investigated by two-dimensional Western and lectin blots. Molecular forms of SGP-2 differed between testis and epididymis but were similar between ventral prostate and seminal vesicle. Prostate and seminal vesicle forms of SGP-2 differed from those of both testis and epididymis. Analysis of terminal carbohydrate present on the various SGP-2 molecular forms also confirmed the existence of heterogeneity. These results demonstrate the presence of multiple molecular forms of SGP-2 in various organs of the male reproductive tract in rats and suggest a possible variation in functional activity and/or half-life of SGP-2 in these organs.