Fig. 5

Illustration of apoptotic cells at the fracture site. A mass of apoptotic cells (brown cells) was observed around the fracture ends within the callus in the Luc-MSC systemic injection group (a), the local injection group (b), and the PBS control group (c) at 5 weeks following the fracture, but none was observed in the negative control (the normal femur) (d). e-h High-resolution images were, respectively, enlarged from the red outlined areas in a–d. Both living Luc-positive cells (light green cells within red circles) and apoptotic Luc-positive cells (dark green cells within white circles) were found in the MSC systemic injection group (e) and the MSC local injection group (f) at 5 weeks following the fracture, but no Luc-positive cells were found in the PBS control group (g) and the negative control (h). Luc-MSC Luciferase labeled mesenchymal stem cell, MSC mesenchymal stem cell, PBS phosphate-buffered saline