Immunohistochemical Localization of Alpha-2 Macroglobulin Receptor/Low-Density Lipoprotein Receptor-Related Protein, Receptor-Associated Protein, and Gp330 in the Human Endometrium

Objective: We investigated the expression of alpha-2 macroglobulin receptor/low-density lipoprotein receptor-related protein (LRP), an analogous receptor Gp330, and the 39-kd receptor-associated protein (RAP) in the human endometrium. Methods: Specific polyclonal and monoclconal antibodies against LRP, Gp330, and RAP were used in standard immunohistochemical analyses of normal secretory and proliferative archival endometrial tissue. Results: There was prominent and uniform stromal staining for LRP in secretary and proliferative endometrium. In both phases, 10-25% of glands stained positive for Gp330, with no appreciable stromal staining for Gp330. Also in both phases, 15-30% of glands stained positive for RAP, with apical staining in proliferative glands and uniform staining in secretory glands. Stromal staining for RAP was patchy and appeared to be more intense in the secretory samples than in the proliferative ones. Conclusions: The human endometrium expresses LRP, RAP, and Gp330. These receptor proteins are known to be involved in endocytosis of multiple ligands. Some of these ligands, such as proteases, plasminogene activators, and cytokines, are produced by the endometrium and play a role in endometrial remodeling and receptivity to implantation. By virtue of their in vitro properties, it is conceivable that endometrial LRP, Gp330, and RAP are involved in endometrial physiology.