G-CSF receptor deletion amplifies cortical bone dysfunction in mice with STAT3 hyperactivation in osteocytes
Journal Title
Journal of Bone and Mineral Research
Publication Type
epub ahead of print
Bone strength is determined by the structure and composition of its thickened outer shell (cortical bone), yet the mechanisms controlling its consolidation are poorly understood. Cortical bone maturation depends on SOCS3-mediated suppression of IL-6 cytokine-induced STAT3 phosphorylation in osteocytes, the cellular network embedded in bone matrix. Since SOCS3 also suppresses G-CSFR signaling, we here tested whether global G-CSFR (Csf3r) ablation influenced bone structure in male and female mice lacking SOCS3 in osteocytes, Dmp1(Cre) :Socs3(f/f) mice. Dmp1Cre:Socs3(f/f) :Csf3r(-/-) mice were generated by crossing Dmp1(Cre) :Socs3(f/f) mice with Csf3r(-/-) mice. Although G-CSFR is not expressed in osteocytes, Csf3r deletion further delayed cortical development in Dmp1(Cre) :Socs3(f/f) mice. Micro-CT images revealed extensive, highly porous low density bone, with little true cortex in the diaphysis, even at 26 weeks of age; there was more low density bone, and less high density bone in Dmp1(Cre) :Socs3(f/f) :Csf3r(-/-) mice than controls. By histology, the area where cortical bone would normally be seen contained immature compressed trabecular bone in Dmp1(Cre) :Socs3(f/f) :Csf3r(-/-) mice with greater than normal intracortical osteoclasts, extensive new woven bone formation, and the presence of more intracortical blood vessels than the already high levels in Dmp1Cre:Socs3(f/f) controls. qRT-PCR of cortical bone from Dmp1(Cre) :Socs3(f/f) :Csf3r(-/-) mice also showed at least a doubling of mRNA levels for osteoclasts, osteoblasts, RANKL and angiogenesis markers. The further delay in cortical bone maturation was associated with significantly more phospho-STAT1 and phospho-STAT3 positive osteocytes, and a 3 fold increase in STAT1 and STAT3 target gene mRNA levels, suggesting G-CSFR deletion further increases STAT signaling beyond that in Dmp1Cre:Socs3(f/f) bone. G-CSFR deficiency therefore promotes STAT1/3 signaling in osteocytes, and when SOCS3 negative feedback is absent, elevated local angiogenesis, bone resorption, and bone formation delays cortical bone consolidation. This points to a critical role of G-CSF in replacing condensed trabecular bone with lamellar bone during cortical bone formation. This article is protected by copyright. All rights reserved.
Jak/stat; cortical bone; osteocyte; vascularization
WEHI Research Division(s)
PubMed ID
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Creation Date: 2022-07-22 09:06:33
Last Modified: 2022-07-22 09:07:14
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