G-CSF Inhibits Growths of Osteoblasts and Osteocytes by Upregulating Nitric Oxide Production in Neutrophils.

Abstract

OBJECTIVE\nGranulocyte colony-stimulating factor (G-CSF) is the critical regulator of the proliferation, differentiation, and survival of granulocytes. Recently, it has been shown that G-CSF can adversely affect bone health in both animal models and patients. Here, the authors aimed to investigate whether G-CSF could inhibit the growth of osteoblasts and osteocytes by regulating nitric oxide.\n\n\nMETHODS\nThe C57BL/6 mice were divided into the control group, G-CSF treatment group and recovery group (G-CSF+L-NAME). The morphology of femurs was assessed by histology and immunohistochemistry. The expression of apoptosis-related molecules in femurs was detected by immunohistochemistry and quantitative RT-PCR, respectively. To examine if neutrophil-secreted factors can induce apoptosis in osteoblasts, Gr1-positive (Gr1+) neutrophils from the bone marrow of wild-type mice were sorted and co-cultured with MC3T3 pre-osteoblasts for 2 days.\n\n\nRESULTS\nThe number of osteoblasts and newly embedding osteocytes significantly decreased and markers related to osteoblasts and osteocytes were downregulated in the G-CSF treatment compared to the control group. Moreover, G-CSF treatment did not change proliferation markers but induced apoptosis in osteoblast-lineage cells. The combined treatment of mice with G-CSF and a nitric oxide inhibitor partially restored the number of osteoblasts and osteocyte parameters.\n\n\nCONCLUSIONS\nThe G-CSF can inhibit osteoblasts and osteocytes by upregulating nitric oxide.