Figure 1.

Schematic showing ovarian hormonal changes during proliferative, secretory, and menses phases affecting cellular and tissue processes in human endometrium

Endometrial MSCs (eMSCs) are located around the vessels (v). A schematic enlargement of blood vessels shows the different vascular cell types according to their identified surface markers (pericytes, perivascular eMSCs, and endothelial cells). During the secretory phase, increased progesterone levels and other paracrine molecules induce the differentiation of endometrial stromal/stem cells into secretory decidualized cells that contribute to amplify the decidualization process within the endometrium stroma. In the absence of conception, hormone withdrawal is sensed by stromal cells that upregulate intracellular inflammatory signaling, recruit leukocytes, and secrete growth factors, cytokines, and proteolytic enzymes, provoking and propagating the tissue shedding of menstruation. This signaling also participates in tissue repair after menstruation. Menstrual blood contains a variety of cells whose identity has not been deeply analyzed, but when they are subjected to adherent culture conditions, a cell type called menstrual-blood derived stromal cell (MenSC) can be identified by its ISCT surface MSC-markers and multipotent phenotype, although its specific identity markers need further study.