Morphological changes in mesothelial cells induced by shed menstrual endometrium in vitro are not primarily due to apoptosis or necrosis

In a previous study on the pathogenesis of endometriosis, me observed that constituents of menstrual effluent induce morphological alterations in huma n mesothelial cells. In this study, we investigated whether these alteratio ns were associated with apoptosis or necrosis or were the result of cellula r remodelling. After overnight incubation of confluent monolayers of human omental mesothelial cells (HOMEC) with conditioned media prepared from mens trual effluent shed anterogradely, severe alterations in morphology were ob served. Typical polygonal mesothelial cell cultures at confluency acquired elongated spindle morphology, resulting in gaps between the cells. In contr ast, mesothelial cells from the control groups receiving culture medium onl y, retained a normal morphology, Immunofluorescence staining revealed that cytokeratin, vimentin and actin filaments were still present, homogeneously distributed in the cell cytoplasm following changes in morphology. To eval uate whether the morphological alterations were associated with apoptosis a nd/or necrosis, the cells were stained with the M30 CytoDeath antibody or a nnexin V with propidium iodide and analysed using flow cytometry, The resul ts showed that only a small percentage (1-7%) of the affected HOMEC were un dergoing apoptosis or necrosis, We conclude that the profoundly altered mor phology of HOMEC is a result of cellular remodelling and that the role of a poptosis and necrosis is negligible. Soluble paracrine factors released by cells isolated from menstrual effluent shed anterogradely may induce a reor ganization of the cytoskeleton, As a result, the underlying basement membra ne will be exposed and the mesothelium may no longer prevent implantation o f endometrium shed retrogradely into the peritoneum, thus facilitating the development of endometriosis.