Cathepsin D sorting in mammalian epididymal cells

MORALES CR; AGUILERA CA; CARVELLI L; ÁLVAREZ P; SOSA MA

Virtual

Congreso; IV Reunión Conjunta de Sociedades de Biología de la República Argentina; 2020

Sociedad de Biología de Cuyo

In mammals, sperm maturation occurs in the environment provided by the lumen of epididymal duct. The epididymal epithelium secretes high amounts of acid hydrolases, but the function of the enzymes and the mechanism of that secretion are still unclear. In the most cell types, the lysosomal enzyme cathepsin D (CatD) is transported from TGN to endo-lysosomal compartments through the mannose 6 phosphate receptors (CI- and CD-MPR), but alternative routes, mediated by Sortilin (Sor) or other receptors are known. Sor can transport CatD to lysosomes when the protease is complexed with the lysosomal protein, prosaposin. Previous results in the epididymal cell line RCE-1 confirmed that CatD forms complexes with prosaposin, suggesting that Sor participates in the CatD sorting. In our laboratory, a sortilin-knockdown epididymal cell line (RCE-1K) has been established, where CD-MPR expression is increased as a counterpart, suggesting that an interregulation between both receptors exists. Here, we correlated the distribution of CatD with that of CD-MPR in normal and RCE-1K cells by indirect immunofluorescence and quantitative co-localization analysis. Normal RCE-1 cells showed a perinuclear network-like Sor distribution. We also observed a high co-localization of CatD with Sor, but not with CD-MPR. In turn, CatD also co-localizes with endo-lysosomal markers. When RCE-1 cells are depleted of Sor (RCE1-KD), CatD still reaches lysosomes and its colocalization with CD-MPR through to the entire cytoplasm is increased. These results indicate that, Sor and CD-MPR could work cooperatively for CatD sorting in epididymal cells and provide new and important insights for the study of sperm maturation process.