Inhibition of microparticle release triggers endothelial cell apoptosis and detachment
Mohammed N. Abid Hussein*, Anita N. Böing*, Augueste Sturk, Chi M. Hau, Rienk Nieuwland
Department of Clinical Chemistry, Academic Medical Center of the University of Amsterdam, Amsterdam, The Netherlands
apoptosis, endothelial cells, microparticles
Endothelial cell cultures contain caspase 3-containing microparticles (EMP), which are reported to form during or after cell detachment. We hypothesize that also adherent endothelial cells release EMP, thus protecting these cells from caspase 3 accumulation, detachment and apoptosis. Human umbilical vein endothelial cells (HUVEC) were incubated with and without inhibitors of microparticle release (Y-27632,calpeptin),both in the absence or presence of additional “external stress”, i.e. the apoptotic agent staurosporin (200 nM) or the activating cytokine interleukin (IL)-1α (5 ng/ml). Control cultures contained mainly viable adherent cells and minor fractions of apoptotic detached cells and microparticles in the absence of inhibitors.In the presence of inhibitors, caspase 3 accumulated in adherent cells and detachment tended to increase. During incubation with either staurosporin or IL-1α in the absence of inhibitors of microparticle release, adherent cells remained viable, and detachment and EMP release increased slightly. In the presence of inhibitors, dramatic changes occurred in staurosporin-treated cultures. Caspase 3 accumulated in adherent cells and >90% of the cells detached within 48 hours. In IL-1α-treated cultures no accumulation of caspase 3 was observed in adherent cells, although detachment increased. Scanning electron microscopy studies confirmed the presence of EMP on both adherent and detached cells. Prolonged culture of detached cells indicated a rapid EMP formation as well as some EMP formation at longer culture periods. Inhibition of EMP release causes accumulation of caspase 3 and promotes cell detachment, although the extent depends on the kind of“external stress”.Thus,the release of caspase 3-containing microparticles may contribute to endothelial cell survival.