Distribution of hyaluronan in human endometrium across the menstrual cycle. Implications for implantation and menstruation.

Hyaluronan is a molecule with many known roles in cellular physiology and is often associated with tissue remodeling. The human endometrium undergoes dramatic remodeling during the course of the normal menstrual cycle but its regulation is not well understood. This study examined the levels of deposition of hyaluronan in human cycling endometrium by histochemical localization, using a highly specific hyaluronan-binding peptide. This was facilitated by avoiding conventional formalin fixation, which results in serious loss of the water-soluble hyaluronan. Peaks of hyaluronan deposition were observed in the stromal compartment during the mid-proliferative (days 5-10) and the mid-secretory phase (days 19-23) of the cycle. In physiological terms, the first phase corresponds to the time of rapid cellular proliferation of undifferentiated cells, whereas the second phase coincides with the time when the implantation of the conceptus would be initiated in a fertile cycle. By the time menstruation starts, very little hyaluronan remains in the stroma. In contrast with the stromal staining, hyaluronan deposition around blood vessels was constant throughout the cycle. The dramatic changes in hyaluronan deposition and their correlation with the cyclic growth and remodeling in the human endometrium suggest a major role for hyaluronan in the physiology of this tissue.