Stallion epididymal fluid proteome: Qualitative and quantitative characterization; Secretion and dynamic changes of major proteins

Proteins present in and secreted into the lumen of various regions of the s tallion epididymis were characterized qualitatively and quantitatively by t wo-dimensional electrophoresis. Using this proteomic approach, 201 proteins were found in the lumen and 117 were found that were secreted by the epith elium in various parts of the organ. Eighteen proteins made up 92.6% of the total epididymal secretory activity, lactoferrin (41.2%) and clusterin (24 .8%) being the most abundant. Procathepsin D, HE1/CTP (cholesterol transfer protein), GPX (glutathione peroxidase), beta-N-acetyl-hexosaminidase, and PGDS (prostaglandin D2 synthase) were the other major compounds secreted. T he most abundant proteins found in the luminal fluid were albumin and the s ecreted proteins: lactoferrin, PGDS, GPX, HE1/CTP, and hexosaminidase. Three main secretory epididymal regions were identified from the protein pa ttern, i.e., regions E0-E2, E3-E5, and E6-E9. Region E0-E2 was characterize d by the secretion of clusterin (53%), PGDS (44%), and GPX (6%). Region E3- E5 had the highest number of secreted proteins, the highest protein concent rations (60-80 mg/ml), and the highest spermatocrit value (85%). Lactoferri n (60% in E4), clusterin (29% in E3), hexosaminidase (10% in E3), and proca thepsin D (6.9% in E4) were the mast abundant proteins in this region. Regi on E6-E9, in which few region-specific secreted compounds were found, was c haracterized by a high quantity of lactoferrin in the luminal fluid (2-14 m g/ml). Comparison between the secretion of the major proteins and their con centrations in the lumen throughout the organ showed that the behavior of e ach protein is specific, in particular for the three isoforms of clusterin.