Circulating and luminal testicular factors affect LRP-2 and Apo J expression in the epididymis following efferent duct ligation

Apolipoprotein J (clusterin or sulfated glycoprotein-2) has been shown to b e secreted by the epididymal principal cells, whereupon it binds to sperm i n the lumen. Apolipoprotein J also is endocytosed by principal cells along the epididymis. Recently, it has been demonstrated that low-density lipopro tein receptor-related protein-2 (LRP-2) mediates the endocytosis of Apo J a nd is present in the epididymis. The purpose of the present study was to de termine the factors regulating the synthesis of these 2 proteins in various experimentally treated animals. The epididymides of adult rats were fixed with Bouin's fluid and examined with anti-Ape J and anti-LRP-2 antibodies b y a light microscope immunocytochemical method, In normal adult animals, ex pression of Apo J was evident in principal cells of all epididymal regions except the proximal initial segment. Diffuse cytoplasmic staining indicated Apo J secretion, Reactive apical vesicles, presumably endosomal in nature, suggested endocytosis of Apo J, Lipoprotein receptor-related protein-2 exp ression was solely apical in nature and was seen as an intense apical band in principal cells of all regions except the proximal and distal initial se gment and distal caput regions of the epididymis, Hypophysectomy, up to 28 days after the procedure, did not affect expression of Apo J or LRP-2 in pr incipal cells along the entire epididymis. Orchidectomy, with or without te stosterone replacement at all time intervals examined, also did not affect LRP-2 expression along the entire epididymis. This also was noted for Apo J expression in all regions except the proximal initial segment. Thus, expre ssion of these 2 proteins does not appear to be regulated by testicular or pituitary factors. In contrast, bilateral as well as unilateral (intact and ligated sides) efferent duct ligation resulted in dramatic differences in LRP-2 and Apo J expression in principal cells in the various epididymal reg ions. In the case of LRP-2, a complete absence of reaction was noted in pri ncipal cells along the entire epididymis. As for Apo J, expression in the d istal initial segment, intermediate zone, and caput region remained unchang ed compared with that in normal adult animals, whereas in the corpus and ca uda epididymides, results of cytoplasmic staining were negligible, These re sults suggest that under conditions of efferent duct ligation, a circulatin g factor emanates from the testis to inhibit expression of LRP-2 and Apo J in these epididymal regions. Furthermore, because Apo J was affected in a r egion-specific manner, unlike the case for LRP-2, different factors appear to be involved for each protein, These factors may be produced to inhibit p roteins from being synthesized by the epididymis in the absence of luminal testicular input and may exist in cases of congenital and pathologic epidid ymal tubule blockages as well as after vasectomy. In the case of immunostai ning for Apo J in the proximal initial segment only, normally unreactive pr incipal cells in control adult animals became intensely reactive after orch idectomy as well as bilateral and unilateral (ligated side only) ligation, As this was not the case for hypophysectomized animals and the intact side of unilateral efferent duct-ligated animals, it is suggested that a testicu lar factor entering via the lumen of the efferent ducts serves to inhibit A po J expression in this area, The present data also reveal that after effer ent duct ligation, there are circulating factors that inhibit Apo J express ion in a region-specific manner (corpus and cauda) and that inhibit LRP-2 e xpression along the entire epididymis and that these are derived from the t estis. Furthermore, the data reveal that a testicular luminal factor appears to in hibit Apo J expression in the proximal initial segment of normal adult anim als.