Effect of granulocyte colony-stimulating factor on enhancing osteogenesis in osteoporotic bone

Abstract

Osteoporosis is an increasing health burden globally. In osteoporotic bone, the bone regeneration ability is compromised, which brings great challenge to fracture healing or bone reconstruction in orthopedics. Granulocyte-colony stimulating factor (G-CSF) is a clinical available growth factor, which is capable of mobilizing hematopoietic stem cells (HSCs), endothelial progenitor cells (EPCs) and mesenchymal stem cell (MSCs) into peripheral blood. These stem cells are closely involved in bone repair. Although some preliminary studies showed promising results, the effect of G-CSF on bone healing are not fully understood. To evaluate the effect of G-CSF on osteoporotic bone, the present study aims to: 1) investigate the alterations of bone density and microarchitecture in multiple skeletal sites using an ovariectomized (OVX) rat model; 2) evaluate the effect of locally administrated G-CSF on bone healing in skull and long bones in an osteoporosis model; 3) study the influence of different dosages of G-CSF on human endothelial cells (HUVECs) and human osteoblasts (hOBs) in vitro.

In the first study, adult female Spraque-Dawley (SD) rats received OVX or sham operation and were sacrificed at week 2, 4, 12, 24 and 36 post-surgery. Micro-computed tomography (micro-CT) analysis revealed a similar trend of bone loss in long bone, spine and ilium post-OVX, with tibia and femur suffered the most bone loss and spine the least. Upon OVX, jaw bones and cranial bones only exhibited a minor reduction in bone mineral density at week 36. Significant deterioration of trabecular structure was detected in long bones, spine and ilium post-OVX, while jaw bones remained relatively stable.

The effect of locally applied G-CSF on osteoporotic bone was evaluated using this animal model. Three month after OVX, 2 mm-defect in femur and 5 mm-defect in cranial bone were created. The defects were left untreated, filled with gelfoam alone or gelfoam loaded with G-CSF. The animals were sacrificed at week 1, 4, 8 and 12 post-surgery. Micro-CT and histomorphometric analysis demonstrated more advanced bone repair in femur in the control group without fillings at the early stage; while by week 12, all groups achieved cortical closure. In cranial bone, more advanced bone repair was exhibited in G-CSF treated group at both early and late stage. These results suggested that the local administration of G-CSF contributed to bone healing where spontaneous bone repair was insufficient.

To further understand the influence of G-CSF on cellular level, different dosages of G-CSF were tested on HUVECs and hOBs at 1000 ng/ml, 100 ng/ml and 10 ng/ml. When applied to HUVECs at 100 ng/ml, G-CSF significantly stimulated cell migration, and promoted tube formation, which were crucial processes during angiogenesis. However, no influence of G-CSF was observed on hOBs.

In conclusion, G-CSF promoted bone healing in defects where the spontaneous bone repair was insufficient, in osteoporotic bone. G-CSF at 100 ng/ml promoted angiogenic effects in HUVECs, while its interaction with hOBs was not observed.