The Fas/FasL apoptotic pathway is involved in kappa-opioid-induced apoptosis of human endometrial stromal cells

Human endometrium expresses specific kappa -opioid binding sites and their endogenous ligands, the dynorphins. In neural crest-derived tissues, kappa -opioids affect apoptosis, a phenomenon of major significance in endometria l stroma physiology. Our hypothesis was that endometrial kappa -opioids may play a role in endometrial stromal cell apoptosis. Thus, we examined the e ffect of the synthetic ic-opioid agonist, U69593, on the apoptotic rate of human endometrial stromal cells in primary culture. Apoptosis of endometria l stromal cells was elevated after 3 h exposure to 100 nmol/l U69593, and r emained elevated for up to 3 days. This effect was dose-dependent and was r eversed by the general opioid antagonist, naloxone, suggesting that it is m ediated via opioid receptors. In parallel, semi-quantitative Western blot a nd flow cytometry analysis showed that U69593 caused a rapid but transient up-regulation of Fas protein, suggesting that its effect on apoptosis is me diated by activation of the Fas/FasL apoptotic pathway. Additionally, U6959 3 increased the content of the anti-apoptotic members of the Bcl-2 family o f proteins, the Bcl-2 and Bcl-X-L, whereas it had no significant effect on the apoptosis-promoting homologues Bax, Bcl-x(S) and Bak. This implies that a transient survival mechanism is activated in stromal cells as a parallel rescue response to the apoptosis-inducing factor. In conclusion, our data suggest that endometrial opioid dynorphins may participate in the apoptotic processes related to endometrial tissue remodelling during early pregnancy or menstruation.