Progesterone induction of chondroitin sulfate proteoglycan aggrecan expression in human endometrial epithelial cells

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan species in the human endometrium, but the expression profile of CS proteoglycans (PGs) in this mucosal tissue remains fully undetermined. In this study, we aimed to clarify the expression of CSPGs including aggrecan, neurocan, melanoma-associated CSPG, neuroglycan C, and brevican in the human cycling endometrium. By reverse transcription-polymerase chain reaction, the gene transcripts for aggrecan core protein were detected in all samples examined, while other CSPGs were not. Western blotting showed the immunoreactivity for aggrecan core protein at approximately 370 kDa size after enzymatic digestion of CS-A and CS-C side chains. The expression level of aggrecan core protein was significantly higher in the secretory phase than in the proliferative phase. The immunostaining for aggrecan was detected in the endometrial microvascular endothelium throughout the menstrual cycle. The immunostaining in the glandular epithelium was faint during the proliferative and early secretory phase, but distinct during the mid-to-late-secretory phase. Progesterone, but not 17β-estradiol, induced aggrecan core protein expression in cultured endometrial epithelial cells. The endometrial expression pattern of aggrecan was distinct from that of other known CSPGs, suggesting the unique role of this proteoglycan at the implantation site.