The fate of systemically administrated allogeneic mesenchymal stem cells in mouse femoral fracture healing.
BACKGROUND
The fate and whereabouts of the allogenic mesenchymal stem cells (MSCs) following their transplantation are not well understood. The present study investigated the fate of systemically administrated allogeneic MSCs in mouse fracture healing by using in vivo imaging and immunohistochemistry methods.


METHODS
Open femoral fracture with internal fixation was established in 30 FVB mice, which were assigned to three groups receiving phosphate-buffered saline (PBS) injection, MSC systemic injection, or MSC local injection. Luc-MSCs (5 × 10(5)) isolated from the luciferase transgenic mice with FVB background were injected at 4 days after fracture. All animals were terminated at 5 weeks after fracture; examinations included bioluminescence-based in vivo imaging, micro-computer tomography, mechanical testing, histology, immunohistochemistry, and double immunofluorescence staining.


RESULTS
The bioluminescence signals of the Luc-MSCs at the fracture site could be detected for 12-14 days following their injection in the Luc-MSC local injection group, whereas in the Luc-MSC systemic injection group, Luc-MSCs were initially trapped in lungs for about 8-9 days and then gradually redistributed to the fracture site. Bone mineral density, bone volume/tissue volume, ultimate load, and E-modulus in the MSC injection groups were significantly higher than those in the PBS group. Double immunostaining demonstrated that the MSC local injection group had more Luc-positive cells, and there was a higher apoptotic rate at the fracture site than the MSC systemic injection group. Both Luciferase-positive MSCs and osteoblasts were present in the callus in the MSC injection groups at 5 weeks after fracture, suggesting that some of allogenic Luc-MSCs contributed to the new bone formation. Only less than 3 % of injected Luc-MSCs remained at the fracture site in the MSC injection groups at 5 weeks following the fracture, and the rest of the injected Luc-MSCs disappeared.


CONCLUSIONS
Our data showed that both systemic and local injection of allogeneic MSCs promoted fracture healing through enhancing biomechanical properties, bone content, and enlarged callus sizes. Immunohistochemistry confirmed that the injected MSCs are still present in the fracture site and can differentiate into osteoblasts to participate in fracture healing even at 5 weeks following the fracture. These findings provide useful information for the use of allogenic MSCs for cell therapy applications.
Department of Orthopaedics & Traumatology, Faculty of Medicine, Room 904, 9/F, Li Ka Shing Institute of Health Institute, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, SAR, PR China. huangshuo82@gmail.com.|Stem Cells and Regenerative Medicine Laboratory, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, PR China. huangshuo82@gmail.com.
Shuo
S
Huang
Department of Orthopaedics & Traumatology, Faculty of Medicine, Room 904, 9/F, Li Ka Shing Institute of Health Institute, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, SAR, PR China. xuliang@ort.cuhk.edu.hk.|Stem Cells and Regenerative Medicine Laboratory, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, PR China. xuliang@ort.cuhk.edu.hk.
Liangliang
L
Xu
Department of Orthopaedics & Traumatology, Faculty of Medicine, Room 904, 9/F, Li Ka Shing Institute of Health Institute, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, SAR, PR China. gangli1967@gmail.com.|Stem Cells and Regenerative Medicine Laboratory, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, PR China. gangli1967@gmail.com.
Yuxin
Y
Sun
Department of Orthopaedics & Traumatology, Faculty of Medicine, Room 904, 9/F, Li Ka Shing Institute of Health Institute, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, SAR, PR China. syx011235@163.com.
Yifeng
Y
Zhang
Department of Orthopaedics & Traumatology, Faculty of Medicine, Room 904, 9/F, Li Ka Shing Institute of Health Institute, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, SAR, PR China. gangli@cuhk.edu.hk.|Stem Cells and Regenerative Medicine Laboratory, Li Ka Shing Institute of Health Sciences, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, PR China. gangli@cuhk.edu.hk.|Key Laboratory for Regenerative Medicine, Ministry of Education, School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Shatin NT, Hong Kong, SAR, China. gangli@cuhk.edu.hk.|The CUHK-ACC Space Medicine Centre on Health Maintenance of Musculoskeletal System, The Chinese University of Hong Kong Shenzhen Research Institute, No. 10, 2nd Yuexing Road, South District, Hi-tech Park, Nanshan, 518057, Shenzhen, PR China. gangli@cuhk.edu.hk.|Lui Che Woo Institute of Innovative Medicine, Faculty of Medicine, The Chinese University of Hong Kong, 30-32 Ngan Shing Street, Shatin, NT, Hong Kong, SAR, China. gangli@cuhk.edu.hk.
Gang
G
Li
D000818:Animals; D017209:Apoptosis; D058948:Cell Tracking; D002478:Cells, Cultured; D005260:Female; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000628:therapy*; D017102:Fracture Healing; D008297:Male; D045164:Mesenchymal Stem Cell Transplantation; D059630:Mesenchymal Stem Cells / Q000502:physiology*; D008822:Mice, Transgenic; D011859:Radiography; D014184:Transplantation, Homologous