Fas antigen (CD95) is expressed on almost all types of human cells and is believed to mediate receptor-specific apoptotic signals. In human endometrial tissues, high Fas and Fas ligand expressions and Fas-mediated apoptosis in endometrial epithelial cells have been discussed in many reports but no study has examined Fas-mediated signals in endometrial stromal cells. In this study we investigated Fas expression and Fas-mediated signals of normal human endometrial stromal cells. Flow cytometric analysis revealed Fas antigen expression on the stromal cells and their Fas expression was enhanced by 8-Br-cAMP, a strong inducer of decidualization. Neither short-term nor long-term cultures with anti-Fas IgM affected proliferation or viability of the stromal cells. Anti-Fas IgM alone affected neither viable cell numbers nor PRL release of unstimulated stromal cells. However, anti-Fas IgM dose-dependently stimulated viable cell numbers of stromal cells co-stimulated with 8-Br-cAMP and anti-Fas IgM, whereas PRL secretion of the co-stimulated cells was not affected. Anti-Fas IgM dose-dependently stimulated viable cell numbers of 8-Br-cAMP-stimulated cells but did not affect PRL secretion of 8-Br-cAMP-induced decidualized cells. These results indicate that Fas antigen on human endometrial stromal cells cannot mediate receptor-specific apoptotic signals, and that Fas-mediated signals stimulate suvival of 8-Br-cAMP-stimulated non-decidualized stromal cells. Thus, stimulation of Fas-antigen on the endometrial stromal cells enhances anti-apoptotic/survival signals in certain stromal cells, autoregulating functional cellular subpopulations of human endometrial stromal cells in a paracrine manner.

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