Anti-diabetic drug metformin has been shown to enhance osteoblasts differentiation and inhibit osteoclast differentiation in vitro and prevent bone loss in ovariectomized (OVX) rats. But the mechanisms through which metformin regulates osteoclastogensis are not known. Osteoprotegerin (OPG) and receptor activator of nuclear factor κB ligand (RANKL) are cytokines predominantly secreted by osteoblasts and play critical roles in the differentiation and function of osteoclasts. In this study, we demonstrated that metformin dose-dependently stimulated OPG and reduced RANKL mRNA and protein expression in mouse calvarial osteoblasts and osteoblastic cell line MC3T3-E1. Inhibition of AMP-activated protein kinase (AMPK) and CaM kinase kinase (CaMKK), two targets of metformin, suppressed endogenous and metformin-induced OPG secretion in osteoblasts. Moreover, supernatant of osteoblasts treated with metformin reduced formation of tartrate resistant acid phosphatase (TRAP)-positive multi-nucleated cells in Raw264.7 cells. Most importantly, metformin significantly increased total body bone mineral density, prevented bone loss and decreased TRAP-positive cells in OVX rats proximal tibiae, accompanied with an increase of OPG and decrease of RANKL expression. These in vivo and in vitro studies suggest that metformin reduces RANKL and stimulates OPG expression in osteoblasts, further inhibits osteoclast differentiation and prevents bone loss in OVX rats.

Precise coordination of cell growth, proliferation and differentiation is essential for the development of multicellular organisms. Here, we report that although the mechanistic target of rapamycin complex 1 (mTORC1) activity is required for chondrocyte growth and proliferation, its inactivation is essential for chondrocyte differentiation. Hyperactivation of mTORC1 via TSC1 gene deletion in chondrocytes causes uncoupling of the normal proliferation and differentiation programme within the growth plate, resulting in uncontrolled cell proliferation, and blockage of differentiation and chondrodysplasia in mice. Rapamycin promotes chondrocyte differentiation and restores these defects in mutant mice. Mechanistically, mTORC1 downstream kinase S6K1 interacts with and phosphorylates Gli2, and releases Gli2 from SuFu binding, resulting in nuclear translocation of Gli2 and transcription of parathyroid hormone-related peptide (PTHrP), a key regulator of bone development. Our findings demonstrate that dynamically controlled mTORC1 activity is crucial to coordinate chondrocyte proliferation and differentiation partially through regulating Gli2/PTHrP during endochondral bone development.

Communication between osteoblasts and endothelial cells (ECs) is essential for bone turnover, but the molecular mechanisms of such communication are not well defined. Here we identify Cxcl9 as an angiostatic factor secreted by osteoblasts in the bone marrow microenvironment. We show that Cxcl9 produced by osteoblasts interacts with vascular endothelial growth factor and prevents its binding to ECs and osteoblasts, thus abrogating angiogenesis and osteogenesis both in mouse bone and in vitro. The mechanistic target of rapamycin complex 1 activates Cxcl9 expression by transcriptional upregulation of STAT1 and increases binding of STAT1 to the Cxcl9 promoter in osteoblasts. These findings reveal the essential role of osteoblast-produced Cxcl9 in angiogenesis and osteogenesis in bone, and Cxcl9 can be targeted to elevate bone angiogenesis and prevent bone loss-related diseases.

There are few articles in the literature concerning anterior instrumentation in the surgical management of spinal tuberculosis in the exudative stage. So we report here 23 cases of active thoracolumbar spinal tuberculosis treated by one-stage anterior interbody autografting and instrumentation to verify the importance of early reconstruction of spinal stability and to evaluate the results of one-stage interbody autografting and anterior instrumentation in the surgical management of the exudative stage of throracolumbar spinal tuberculosis. Twenty-three patients, including two children (9 and 15 years old, respectively) and 21 adults with thoracolumbar spinal tuberculosis were treated surgically. T9 to L4 spinal segments were affected, and MRI/CT showed evident collapse of the vertebrae because of tuberculous destruction and paravertebral abscess. Neurological deficits were found in 15 patients. Before surgery, patients received standard anti-tuberculosis chemotherapy for 2 to 3 weeks. Under general endotracheal anaesthesia, the patients were placed in right recumbent positions, and a transthoracic, lateral extracavitary or extrapleural approach was chosen according to the tuberculosis lesion segment. After exposure, the tuberculous lesion region, including the collapsed vertebrae and in-between intervertebral disc, was almost completely resected in order to release the segmental spinal cord. Then, autologous iliac, rib or fibular graft was harvested to complete interbody fusion, and an anterior titanium-alloy plate-screw system was used to reconstruct the stability of the affected segments. Anti-tuberculosis chemotherapy was continued for at least 9 months, and the patients were supported with thoracolumbosacral orthosis for 6 months after surgery. All patients were followed up for an average of 2 years. All 23 cases were healed without chronic sinus formation or any recurrence of tuberculosis during the follow-up period. Spinal fusion occurred at a mean of 3.8 months after surgery. Of all patients with neurological deficits, 14 patients showed obvious improvement; only one patient with Frankel C lesion remained unchanged, but none of the patients got worse. During the follow-up period, a mean of 18 degrees of kyphosis correction was achieved after surgery in the adult group. Moderate progressive kyphosis because of this procedure fusion occurred postoperatively in a 9-year-old child after 2 1/2 years; another 15-year-old child did not demonstrate this phenomenon. Except for the early loosening of one screw in two cases (which did not affect the reconstruction of spinal stability), no other complications associated with this procedure were found during follow-up. Early reconstruction of spinal stability plays an important role in the surgical management of spinal tuberculosis. One-stage anterior interbody autografting and instrumentation in the surgical management of the exudative stage of spinal tuberculosis show more advantages in selected patients, but supplementary posterior fusion should be considered to pre...