Immunohistochemical localization of apelin in human normal breast and breast carcinoma

The peptide apelin is a high-affinity ligand for the G-protein coupled receptor APJ. Apelin/APJ signaling plays important roles in blood pressure regulation, body fluid homeostasis, and cardiovascular development. More recently, it has been recognized that apelin/APJ signaling may also be involved in tumor angiogenesis. Studies in experimental animals have shown that apelin is abundantly secreted in the milk, and the mammary gland contains high level of pre-proapelin mRNAs and apelin protein. High level of apelin mRNA is expressed in cultured human breast carcinoma cell line (Hs 578T). However, the status of apelin expression and localization in human breast carcinoma has not been studied. In the present study immunohistochemistry was performed to investigate the expression and localization of apelin in normal human breast tissue and breast carcinoma. Cytoplasmic apelin immunoreactivity was detected in the ductal and lobular epithelial cells and vascular endothelial cells of the normal breast tissue. The myoepithelial cells were negative. The malignant tumor cells of invasive ductal or lobular carcinoma also expressed similar level of immunoreactive apelin. The fuctional significance of apelin expression in normal nonlactating breast and breast carcinoma warrants further investigation.