Cortical bone maturation in mice requires SOCS3 suppression of gp130/STAT3 signalling in osteocytes

Abstract

Bone strength is determined by its dense cortical shell, generated by unknown mechanisms. Here we use the <i>Dmp1^Cre:Socs3^f/f</i> mouse, with delayed cortical bone consolidation, to characterise cortical maturation and identify control signals. We show that cortical maturation requires a reduction in cortical porosity, and a transition from low to high density bone, which continues even after cortical shape is established. Both processes were delayed in <i>Dmp1^Cre:Socs3^f/f</i> mice. SOCS3 (suppressor of cytokine signalling 3) inhibits signalling by leptin, G-CSF, and IL-6 family cytokines (gp130). In <i>Dmp1^Cre:Socs3^f/f</i> bone, STAT3 phosphorylation was prolonged in response to gp130-signalling cytokines, but not G-CSF or leptin. Deletion of gp130 in <i>Dmp1^Cre:Socs3^f/f</i> mice suppressed STAT3 phosphorylation in osteocytes and osteoclastic resorption within cortical bone, leading to rescue of the corticalisation defect, and restoration of compromised bone strength. We conclude that cortical bone development includes both pore closure and accumulation of high density bone, and that these processes require suppression of gp130-STAT3 signalling in osteocytes.