Fig. 1. Induction of apoptosis in hMSCs using lentivirus vector expressing a constitutive (CC8) or an inducible caspase-8 (FKC8). (A) Human MSCs at passage four were transduced with lentivirus vector containing FKC8. Graphs show the cultures before or after treatment with the FKC8 activator AP20187. Bar, 20 µm. (B) Quantification of apoptotic cells after caspase-8 activation. Human MSCs were transduced with CC8 or FKC8. FKC8 was activated with 100 nM AP20187 (+AP) and caspase activity was inhibited with 50 nM Z-VAD.fmk (+Z). Treatments were carried out for 6 hours. Nuclei were stained with DAPI. Histograms show the fraction of cells with condensed DNA as calculated from a population of 250 nuclei. (C) Detection of FKC8-activation pathway using immunostaining. Human MSCs at passage six were transduced with FKC8 followed by AP20187 treatment for 6 hours (+FKC8). Control cells were left non-transduced. Subsequently, cells were fixed and immunostained with anti-caspase-8 (green) or anti-cleaved caspase-3 (red) antibodies. DAPI staining was used to monitor changes in DNA morphology. Nuclear morphology is indicated on the left side. Bars, 10 µm.