Role of Epithelial Cells of the Male Excurrent Duct System of the Rat in the Endocytosis or Secretion of Sulfated Glycoprotein-2 (Clusterin)1

Abstract

The localization of sulfated glycoprotein-2 (clusterin; SGP-2) was investigated in the rete testis, efferent ducts, and epididymis of the rat using light (LM) and electron (EM) microscope immunocytochemistry. At the LM level, the epithelial cells of the rete testis and efferent ducts demonstrated an intense immunoperoxidase reaction over their apical and supranuclear regions, and sperm in the lumen of the efferent ducts were unreactive. In the EM, gold particles were found exclusively over the endocytic apparatus of these cells. In the proximal area of the epididymal initial segment, an insignificant immunostaining of epithelial cells and sperm was observed. However, the distal area of the initial segment showed a moderate staining over the epithelial principal cells and sperm, while in the intermediate zone of the epididymis a stronger reaction was observed over these cells. The strongest immunoperoxidase reaction was noted in the caput epididymidis, where it formed a distinct mottled pattern. Thus, while some principal cells were intensely stained, others were moderately or weakly stained; a few were completely unreactive. In the corpus and cauda epididymidis, the staining pattern was similar but not as intense. In the EM, only the secretory apparatus of these cells was found to be immunolabeled with gold particles. Sperm in the lumen of these different regions were also labeled. The epithelial clear cells were unreactive throughout the epididymis. Northern blot analysis substantiated these results and showed the presence of highest levels of SGP-2 mRNA in the caput epididymidis, especially in its proximal area, whereas increasingly lower levels were found in the corpus and cauda epididymidis. In summary, these results suggest that testicular SGP-2 dissociates from the sperm during passage through the rete testis and efferent ducts, where it is endocytosed by the epithelial cells lining these regions. In the epididymis, it is replaced by an epididymal SGP-2 that is secreted by the epithelial principal cells of the epididymis. Furthermore, in the epididymis, the principal cells appear to be in different functional states with respect to the secretion of epididymal SGP-2 within a given region of the duct as well as along the epididymal duct.

Morphological analysis of endocytosis in efferent ductules of estrogen receptor‐α knockout male mouse

“…It dissociates from the spermatozoa when they reach the rete testis and the efferent ductules, and is finally endocytosed by the epithelial cells of these ductules (Hermo et al, 1991b;Igdoura et al, 1994). It is demonstrated that SGP-2 is located within the compartments involved in the endocytotic pathways of the nonciliated cells (Hermo et al, 1991b). Therefore it seems to be an appropriate marker for endocytosis in the efferent ductules.…”

“…Three major pathways have been reported for the epithelium to reabsorb the fluid. First, the nonciliated cells have a well-developed endocytotic apparatus in the apical cytoplasm such as invaginations of the apical membrane, vesicles, endosomes, multivesicular bodies and lysosomes (Hermo and Morales, 1984;Jones and Jurd, 1987;Hermo et al, 1988Hermo et al, , 1991bRobaire and Hermo, 1988). Studies using electron dense tracers confirmed that these organelles are involved in endocytosis (Hermo and Morales, 1984;Veeramachaneni and Amann, 1991;.…”

Presence, localization, and origin of clusterin in normal human spermatozoa

“…Immunohistochemical analysis showed that clusterin was present in spermatogenic cells besides Sertoli cells in the lumen of seminiferous tubules. As mentioned in the introduction, clusterin derived from Sertoli cells bound to the surface of testicular spermatozoa in the rete testis fluid and would be replaced by clusterin from the epididymis or seminal vesicle during sperm migration [3,8,9,32]. Therefore the clusterin observed by us in the inner membrane of normal spermatozoa may have been synthesized by the spermatogenic cells.…”

“…Most previous studies have shown that clusterin is secreted into semen by the epididymis and seminal vesicle, and mainly adheres to the surfaces of abnormal spermatozoa [3,8,9,25,32]. Only a few researchers observed clusterin in normal human spermatozoa [2,26,35].…”

“…Animal experiments have indicated that clusterin in the rete testis fluid is synthesized by Sertoli cells and adheres to the surface of testicular spermatozoa. When spermatozoa move through the rete testis and efferent duct, testis-derived clusterin is replaced by clusterin from the epididymis or seminal vesicle [3,8,9,32]. Clusterin on abnormal spermatozoa is implicated in decreased sperm motility, sperm aggregation and infertility [7,12,13,26].…”