Immunohistochemical localization of carboxypeptidases E and D in the humanplacenta and umbilical cord

Carboxypeptidase E (CPE) is highly concentrated in neuroendocrine tissues a nd is the only carboxypeptidase detected in mature secretory vesicles. Carb oxypeptidase D (CPD), a carboxypeptidase with CPE-like activity, is widely distributed in tissues and is present in the trans-Golgi network. Previous work had shown that both CPE and CPD are expressed in the human placenta an d that CPD is expressed at much higher levels than CPE. The present work pr ovides evidence for the co-localization of CPE and CPD to basal plate extra villous trophoblasts and maternal uteroplacental vascular endothelial cells , chorionic villous endothelial cells, amnionic epithelial cells, and umbil ical venous and arterial smooth muscle cells. Whereas the intensity of CPD immunostaining is similar in the placenta and umbilical cord, CPE staining in the placenta is much weaker than in the umbilical cord, suggesting that CPD plays a more important role in the processing of placental peptides. Im munoelectron microscopy of umbilical venous smooth muscle cells shows subce llular localization of both enzymes to the rough endoplasmic reticulum. In addition, CPE is present just subjacent to the cell membrane. The differenc e in cellular and subcellular localization between the two enzymes indicate s that they perform distinct functions in the processing of placental pepti des and proteins.