Initiation of Progressive Morphological Transition Towards an Echino-Stomato-Spherocytic Phenotype by Phosphatidylserine Externalization and Its Implication in Thrombosis

Morphological changes in erythrocytes during disease, aging, or reactions to external agents are significant as they can influence disease progression. However, the exact mechanisms behind these temporary alterations and their potential to cause dysfunction remain unclear. Using a saponin-induced erythrocyte shape transition (EST) model, we studied the gradual shift of erythrocytes towards echino-stomato-spherocytic forms and its link to hemolysis and thrombosis. We observed that different saponin concentrations elicited varying shape transformations. At low concentrations, erythrocytes transition from discocytic shapes to echinocytic, echino-stomatocytic, and ultimately stomatocytic forms. As the concentration moderately increases, the morphology evolves into stomato-spherocytic forms. At higher saponin concentrations, the erythrocytes completely transform into spherocytic forms. Regardless of the transformation degree, all forms showed increased phosphatidylserine exposure (PS) and microvesicle (MV) production, primarily due to increased scramblase and decreased flippase activity, which were influenced by elevated calcium levels and caspase 3 activity, effectively managing PS distribution and influencing cell membrane expansion and invagination. These alterations increased thrombin production, erythrocyte adhesion, and aggregation, promoting thrombosis in rats. Altogether, our findings indicate that the shift towards echino-stomato-spherocytic forms fosters a hypercoagulable state through PS externalization, heightening thrombotic risk.