Cell- and region-specific localization of lysosomal and secretory proteinsand endocytic receptors in epithelial cells of the cauda epididymidis and vas deferens of the adult rat

The epithelial cells lining the cauda epididymidis and vas deferens are act ive in endocytosis and have an abundance of lysosomes and a well-characteri zed secretory apparatus. However, little is known about the nature of lysos omal proteins contained within lysosomes, the types of receptors on the cel l surface, and the types of proteins secreted by these cells. In the presen t study, cathepsins A, D, B, and sulfated glycoprotein (SGP)-1, well-charac terized lysosomal proteins, as well as SGP-2, a secretory protein and low-d ensity lipoprotein receptor-related protein-2 (LRP-2), an endocytic recepto r, were immunolocalized at the light-microscopic level within epithelial ce lls of the cauda epididymidis and vas deferens. Principal cells showed nume rous intensely reactive lysosomes for cathepsins A, D, and SGP-1 in all reg ions of the cauda and vas deferens and for cathepsin B only in the cauda ep ididymidis. Basal cells were intensely reactive for cathepsin A, unreactive for cathepsins D and B, and weakly reactive for SGP-1 in the cauda region. In the vas deferens, these cells were intensely reactive for cathepsin A a nd SGP-1 and unreactive for cathepsin B; in the case of cathepsin D, basal cells were weakly reactive in the proximal vas deferens but intensely react ive in the middle and distal vas deferens. Clear cells, present in the caud a region and proximal vas deferens, were intensely reactive for cathepsin A , weakly reactive for SGP-1, and unreactive for cathepsins D and B, while n arrow cells found mainly in the proximal vas deferens were intensely reacti ve for cathepsins A, D, and SGP-1 and unreactive for cathepsin B. Thus, the expression of different lysosomal enzymes in the cauda epididymidis and va s deferens is not only cell- but also region-specific, suggesting differenc es in the type of substrates internalized by these cells. SGP-2, a secretor y protein, showed a checkerboardlike staining pattern in the cytoplasm of p rincipal cells of the cauda epididymidis, while the cytoplasm of all princi pal cells were intensely reactive in the vas deferens. This type of reactio n, as well as staining of sperm, suggests that SGP-2 is secreted into the l umen, where it functions in relation to sperm. The endocytic receptor LRP-2 was noted only on the apical surface of principal cells of the cauda and v as deferens and in spherical structures indicative of endosomes suggestive of their role in the uptake of various ligands, including SGP-2, for which it has a high binding affinity. Thus SGP-2 in the cauda and vas deferens is not only secreted but endocytosed by principal cells, suggestive of an act ive turnover in the lumen. In summary, the epithelial cells of the cauda an d vas deferens show marked differences in expression of lysosomal proteins, SGP-2, and LRP-2 suggestive of differences in their functional activity wh ile sperm are stored and protected in these regions.