Multiparameter Characterization Confirms Apoptosis as the Primary Cause of Reduced Self-renewal Capacity in Cultured Human Fetal Neural Stem Cells

Background: Human fetal striatum-derived neural stem cells (hfsNSCs) are important in regenerative medicine; however, their ability to self-renew diminishes quickly following passages in culture. Typically when hfsNSC-derived neurospheres are dissociated by accutase, more than 90% of the cells survive, but only 6-8% of the cells are able to form secondary neurospheres. Our hypothesis is that the hfsNSCs that are unable to form new neurospheres become apoptotic. Methods/Results: Because the NSC apoptosis process has never been characterized in detail, we characterized hfsNSC apoptosis using multiparameter analysis and determined that the majority of hfsNSCs undergo apoptosis after passaging, which leads to a reduction in self-renewal. The replacement of trituration with vortexing decreases apoptosis, increases self-renewal, and does not affect NSC differentiation. When we used live cell staining with Annexin V, Hoechst 33342, and PI together, the apoptotic index was in agreement with what could be obtained using fixed-cell staining methods, including TUNEL and activated caspase-3 immunocytochemistry. NSC apoptosis could be divided into 9 stage types based on our live cell assay. Several types during early and late stages had similar staining profiles that could be further discriminated based on cell size. Conclusion: Apoptosis largely contributes to the low self-renewal of neurospheres, and replacing trituration with vortexing aided in alleviating NSC apoptosis. Multiparameter analysis is required for the identification of NSC apoptosis, particularly when live cell staining is used.