• Cytotoxicity
• Infection
• Osteoblasts
• Teriparatide
• Vancomycin

• Humans
• Vancomycin/toxicity
• Teriparatide/pharmacology
• Teriparatide/therapeutic use
• Alkaline Phosphatase
• Cell Differentiation
• Osteogenesis
• Osteoblasts

• Bone lengthening
• Distraction osteogenesis
• Parathyroid hormone
• Teriparatide

• Animals
• Humans
• Parathyroid Hormone/pharmacology
• Parathyroid Hormone/therapeutic use
• Bone Regeneration
• Bony Callus
• Osteogenesis
• Osteogenesis, Distraction

• Distinguished Research Professor grant National Research Council of Thailand
• CMU excellent center award Chiang Mai University
• NSTDA Research chair grant National Science and Technology Development Agency Thailand

As clusters of peptides or steroids capable of high-efficiency information transmission, hormones have been substantiated to coordinate metabolism, growth, development, and other physiological processes, especially in bone physiology and repair metabolism. In recent years, the application of hormones for implant osseointegration has become a research hotspot. Herein, we provide a comprehensive overview of the relevant reports on endogenous hormones and their corresponding supplementary preparations to explore the association between hormones and the prognosis of implants. We also discuss the effects and mechanisms of insulin, parathyroid hormone, melatonin, vitamin D, and growth hormone on osseointegration at the molecular and body levels to provide a foothold and guide future research on the systemic conditions that affect the implantation process and expand the relative contraindications of the implant, and the pre-and post-operative precautions. This review shows that systemic hormones can regulate the osseointegration of oral implants through endogenous or exogenous drug-delivery methods.

Periodontitis is a series of inflammatory processes caused by bacterial infection. Parathyroid hormone (PTH) plays a critical role in bone remodeling. The present study aimed to investigate the influences of PTH on human bone marrow mesenchymal stem cells (HBMSCs) pretreated with lipopolysaccharide (LPS). The proliferative ability was measured using cell counting kit-8 (CCK-8) and flow cytometry. The optimal concentrations of PTH and LPS were determined using alkaline phosphatase (ALP) activity assay, ALP staining, and Alizarin Red staining. Osteogenic differentiation was further assessed by quantitative reverse-transcription polymerase chain reaction (RT-qPCR), Western blot analysis, and immunofluorescence staining. PTH had no effects on the proliferation of HBMSCs. Also, 100 ng/ml LPS significantly inhibited HBMSC osteogenesis, while 10⁻⁹ mol/l PTH was considered as the optimal concentration to reverse the adverse effects. Mechanistically, c-Jun N-terminal kinase (JNK) phosphorylation was activated by PTH in LPS-induced HBMSCs. SP600125, a selective inhibitor targeting JNK mitogen-activated protein kinase (MAPK) signaling, weakened the effects of PTH. Taken together, the findings revealed the role and mechanism of PTH and JNK pathway in promoting the osteogenic differentiation of LPS-induced HBMSCs, which offered an alternative for treating periodontal diseases.

• Human bone marrow mesenchymal stem cells
• Lipopolysaccharides
• Mitogen-activated protein kinase signaling pathway
• Osteogenic differentiation
• Parathyroid hormone

• Bone healing. Parathyroid Hormone (PTH). Bone defects. Allograft. Graft revitalization

• Artificial selection
• Bone formation
• Genome editing
• Intermuscular bones
• Intramembranous ossification
• Molecular mechanisms

• osteoporosis
• pain
• teriparatide

• Dietary supplement
• Inflammation
• Intestinal permeability
• Microbiome
• Probiotic
• Trauma

The ability of intermittent parathyroid hormone (1-34) [PTH(1-34)] treatment to enhance bone-implant osseo-integration was recently demonstrated in vivo. However, the mechanisms through which PTH (1-34) regulates bone marrow-derived stromal cells (BMSCs) remain unclear. The present study thus aimed to investigate the effects of PTH(1-34) on the migration and adhesion of, and rictor/mammalian target of rapamycin complex 2 (mTORC2) signaling in BMSCs. In the present study, BMSCs were isolated from Sprague-Dawley rats treated with various concentrations of PTH(1-34) for different periods of time. PTH(1-34) treatment was performed with or without an mTORC1 inhibitor (20 nM rapamycin) and mTORC1/2 inhibitor (10 µM PP242). Cell migration was assessed by Transwell cell migration assays and wound healing assays. Cell adhesion and related mRNA expression were investigated through adhesion assays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), respectively. The protein expression of chemokine receptors (CXCR4 and CCR2) and adhesion factors [intercellular adhesion molecule 1 (ICAM-1), fibronectin and integrin β1] was examined by western blot analysis. The results revealed that various concentrations (1, 10, 20, 50 and 100 nM) of PTH(1-34) significantly increased the migration and adhesion of BMSCs, as well as the expression of CXCR4, CCR2, ICAM-1, fibronectin and integrin β1. In addition, the p-Akt and p-S6 levels were also upregulated by PTH(1-34). BMSCs subjected to mTORC1/2 signaling pathway inhibition or rictor silencing exhibited a markedly reduced PTH-induced migration and adhesion, while no such effect was observed for the BMSCs subjected to mTORC1 pathway inhibition or raptor silencing. These results indicate that PTH(1-34) promotes BMSC migration and adhesion through rictor/mTORC2 signaling in vitro. Taken together, the results of the present study reveal an important mechanism for the therapeutic effects of PTH(1-34) on bone-implant osseointegration and suggest a potential treatment strategy based on the effect of PTH(1-34) on BMSCs.

• Ligamentum flavum
• Mesenchymal stem cells
• Ossification of the posterior longitudinal ligament
• Parathyroid hormone 1 receptor
• Teriparatide

• Teriparatide
• bisphosphonate
• immobility-induced osteoporosis
• skeletal pain

• Chondroclasts
• Fracture callus
• Gene arrays
• Osteoclasts
• Regulatory network
• Transcriptomics

• Runx1
• callus remodeling
• chondro-osseous junction
• fracture
• osteoclasts

• parathyroid hormone
• periodontitis
• regeneration
• self-assembling peptide

Osteoporosis is a common osteopathy, resulting in fractures, especially in elder people. Sesamin has many pharmacological effects, including supplying calcium. However, how sesamin might prevent osteoporosis is still under study.

Bone marrow stromal cells (BMSCs) extracted from rat femur were induced for osteoblastic differentiation. Cell proliferation, alkaline phosphatase (ALP), osterix (OSX), SRY-box 9 (SOX9), runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), β-catenin, low density lipoprotein receptor-related protein 5 (LRP5), and glycogen synthase kinase-3β (GSK-3β) levels in BMSCs were detected in the presence or absence of sesamin (1 μM or 10 μM). In addition, FH535 (1 μM) was used to silence Wnt/β-catenin in vitro. Ovariectomized (OVX) rats were established and intragastrically administrated sesamin (80 mg/kg), and then the rat bones were analyzed by micro-computed tomography. Osteocalcin and collagen type I were measured in the rat femurs.

Sesamin had no influence on BMSC proliferation. Higher sesamin concentration promoted Wnt/β-catenin activity and enhanced more expressions of ALP, OSX, SOX9, RUNX2, and OCN, gradually and significantly (P<0.05). Silencing Wnt/β-catenin weakened the enhancement on RUNX2 and OCN expression. Sesamin (80 mg/kg) promoted bone structure in ovariectomized rats, and significantly enhanced osteocalcin and collage type I expression (P<0.05).

Sesamin promoted osteoblastic differentiation of rat BMSCs by regulating the Wnt/β-catenin pathway, and improved rat bone structure. Sesamin could have therapeutic and preventive effects on osteoporosis.

The age-related osteoporosis is an increasing risk severely threatening the live quality of aged people. Human parathyroid hormone (hPTH) is applied to the therapy of osteoporosis successfully, however, the mechanism, especially the signaling pathway activated in the healing fracture by PTH is still unknown.

The once daily injections of hPTH(1–34) and GR (1–34) (the PLC deficient analog) into the orchiectomized male mice with bone fracture, were started at the second day after fracture and lasted for 4 weeks. To explore the role of phospholipase C signaling in the androgen-deficient fracture healing, the fracture healing were evaluated via radiography, micro-CT, biomechanics testing, serum biochemistry, bone marrow cell culture and gene expression quantification.

After two weeks of fracture, both peptides significantly increased bone mineral density (BMD), bone mass content (BMC) and bone volume (BV/TV) in the healing area. However, compared to hPTH(1–34), GR(1–34) induced more woven bones, the higher BMC and BMD, as well as the less serum TRAP and osteoclasts. After four weeks of treatment, the effects of hPTH(1–34) on fracture healing showed no difference to those of GR(1–34). Consistently, GR(1–34) induced the similar osteogenesis but less osteoclastogenesis under the ex vivo condition immediately after administration compared to hPTH(1–34), which was verified by the weaker activation of RANKL, NFATC1, TRAP and Cathepsin K in GR(1–34) treatment.

These results indicated that the PLC signaling activated by the intermittent injection of hPTH(1–34) leads to the bone resorption by rapidly activating the osteoclastogenesis in the fracture healing zone.

The online version of this article (10.1186/s12891-018-2231-3) contains supplementary material, which is available to authorized users.

• Fracture healing
• Osteoclastogenesis
• Osteoporosis
• Parathyroid hormone
• Phopholipase C

• bone regeneration
• bone scaffold
• bone tissue engineering
• growth factor
• stem cell

• fracture repair
• gene therapy
• non-union

• Apoptosis
• Fracture healing
• MicroRNA-185
• PTH gene
• Proliferation
• Wnt/β -catenin axis

Grafting β-tricalcium phosphate (TCP) is a well-established method for restoring bone defects; however, there is concern that the mechanical stability of the grafted β-TCP is not maintained during bone translation. Teriparatide has an anabolic effect, stimulating bone formation and increasing bone mineral density for the treatment of osteoporosis. The aim of the present study was to evaluate the effect of intermittent teriparatide treatment on changes in bone grafted with β-TCP using a rabbit bone defect model. Bone defects (5×15 mm) were created in the distal femoral condyle of Japanese white rabbits, and β-TCP granules of two different total porosities were manually grafted. Teriparatide (40 µg/kg) or 0.2% rabbit serum albumin solution as a vehicle control was subcutaneously injected three times per week following the surgery. At 4 or 8 weeks post-surgery, serum samples were obtained and the levels of γ-carboxylated osteocalcin (Gla-OC) were quantified using ELISA. Histomorphometry was also performed using sections of graft sites following staining for tartrate resistant acid phosphatase. Activity and mechanical strength (maximum shear strength, maximum shear stiffness and total energy absorption) were evaluated using an axial push-out load to failure test. Teriparatide treatment significantly increased (P<0.05) the serum levels of Gla-OC, a specific marker for bone formation, suggesting that teriparatide enhances bone formation in β-TCP-grafted rabbits. Furthermore teriparatide increased the degradation of β-TCP by bone remodeling (P<0.05) and promoted the formation of new bone following application of the graft compared with the control group (P<0.01). Furthermore, teriparatide suppressed the reduction in mechanical strength (P<0.05) during bone translation in bone defects grafted with β-TCP. The results of the present study demonstrate that teriparatide is effective in maintaining the mechanical stability of grafted β-TCP, possibly by promoting new bone formation.

• bone graft
• bone metabolism
• mechanical strength
• teriparatide
• β-tricalcium phosphate

In this study, we engineered mesenchymal stem cells (MSCs) to over‐express basic fibroblast growth factor (bFGF) and evaluated its effects on fracture healing. Adipose‐derived mouse MSCs were transduced to express bFGF and green fluorescence protein (ADSC^bFGF‐GFP). Closed‐femoral fractures were performed with osterix‐mCherry reporter mice of both sexes. The mice received 3 × 10⁵ ADSCs transfected with control vector or bFGF via intramuscular injection within or around the fracture sites. Mice were euthanized at days 7, 14, and 35 to monitor MSC engraftment, osteogenic differentiation, callus formation, and bone strength. Compared to ADSC culture alone, ADSC^bFGF increased bFGF expression and higher levels of bFGF and vascular endothelial growth factor (VEGF) in the culture supernatant for up to 14 days. ADSC^bFGF treatment increased GFP‐labeled MSCs at the fracture gaps and these cells were incorporated into the newly formed callus. quantitative reverse transcription polymerase chain reaction (qRT‐PCR) from the callus revealed a 2‐ to 12‐fold increase in the expression of genes associated with nervous system regeneration, angiogenesis, and matrix formation. Compared to the control, ADSC^bFGF treatment increased VEGF expression at the periosteal region of the callus, remodeling of collagen into mineralized callus and bone strength. In summary, MSC^bFGF accelerated fracture healing by increasing the production of growth factors that stimulated angiogenesis and differentiation of MSCs to osteoblasts that formed new bone and accelerated fracture repair. This novel treatment may reduce the time required for fracture healing. Stem Cells Translational Medicine2017;6:1880–1893

• Basic fibroblast growth factor
• Bone strength
• Callus
• Mesenchymal stromal cells
• Osteoblasts

• Alkaline Phosphatase/genetics
• Alkaline Phosphatase/metabolism
• Animals
• Cell Line
• Cell Proliferation/drug effects
• Cell Proliferation/physiology
• Chloride Channels/genetics
• Chloride Channels/metabolism
• Core Binding Factor Alpha 1 Subunit/genetics
• Core Binding Factor Alpha 1 Subunit/metabolism
• Mice
• Osteoblasts/drug effects
• Osteoblasts/metabolism
• Osteocalcin/genetics
• Osteocalcin/metabolism
• Osteogenesis/drug effects
• Osteogenesis/physiology
• Osteopontin/genetics
• Osteopontin/metabolism
• Parathyroid Hormone/pharmacology
• RNA, Small Interfering
• Signal Transduction/drug effects
• Sp7 Transcription Factor
• Transcription Factors/genetics
• Transcription Factors/metabolism

• National Natural Science Foundation of China (CN)

A devastating condition that leads to trauma-related morbidity, multiple rib fractures, remain a serious unmet clinical need. Systemic administration of mesenchymal stem cells (MSCs) has been shown to regenerate various tissues. We hypothesized that parathyroid hormone (PTH) therapy would enhance MSC homing and differentiation, ultimately leading to bone formation that would bridge rib fractures.

The combination of human MSCs (hMSCs) and a clinically relevant PTH dose was studied using immunosuppressed rats. Segmental defects were created in animals’ fifth and sixth ribs. The rats were divided into four groups: a negative control group, in which animals received vehicle alone; the PTH-only group, in which animals received daily subcutaneous injections of 4 μg/kg teriparatide, a pharmaceutical derivative of PTH; the hMSC-only group, in which each animal received five injections of 2 × 10⁶ hMSCs; and the hMSC + PTH group, in which animals received both treatments. Longitudinal in vivo monitoring of bone formation was performed biweekly using micro-computed tomography (μCT), followed by histological analysis.

Fluorescently-dyed hMSCs were counted using confocal microscopy imaging of histological samples harvested 8 weeks after surgery. PTH significantly augmented the number of hMSCs that homed to the fracture site. Immunofluorescence of osteogenic markers, osteocalcin and bone sialoprotein, showed that PTH induced cell differentiation in both exogenously administered cells and resident cells. μCT scans revealed a significant increase in bone volume only in the hMSC + PTH group, beginning by the 4^th week after surgery. Eight weeks after surgery, 35% of ribs in the hMSC + PTH group had complete bone bridging, whereas there was complete bridging in only 6.25% of ribs (one rib) in the PTH-only group and in none of the ribs in the other groups. Based on the μCT scans, biomechanical analysis using the micro-finite element method demonstrated that the healed ribs were stiffer than intact ribs in torsion, compression, and bending simulations, as expected when examining bone callus composed of woven bone.

Administration of both hMSCs and PTH worked synergistically in rib fracture healing, suggesting this approach may pave the way to treat multiple rib fractures as well as additional fractures in various anatomical sites.

The online version of this article (doi:10.1186/s13287-017-0502-9) contains supplementary material, which is available to authorized users.

• Parathyroid hormone
• Rib fracture
• Systemic stem cell administration

The aim of this experiment was to assemble parathyroid hormone (PTH) coatings on titanium surfaces and evaluate the effect on implant osseointegration.

• OI
• brittle bone
• clinical research
• dog
• mouse
• zebrafish

• PTH(1-34)
• collagen texture
• fracture healing
• osteoblasts
• osteocytes
• rat model

• Adipose-derived stromal cells
• Angiogenesis Osteogenesis
• Bone-targeted
• Fracture healing

• bone mesenchymal stromal cells
• cyclic adenosine monophosphate/protein kinase A pathway
• osteogenic differentiation
• parathyroid hormone (1-34)

Although most fractures heal, critical defects in bone fail due to aberrant differentiation of mesenchymal stem cells towards fibrosis rather than osteogenesis. While conventional bioengineering solutions to this problem have focused on enhancing angiogenesis, which is required for bone formation, recent studies have shown that fibrotic non-unions are associated with arteriogenesis in the center of the defect and accumulation of mast cells around large blood vessels. Recently, recombinant parathyroid hormone (rPTH; teriparatide; Forteo) therapy have shown to have anti-fibrotic effects on non-unions and critical bone defects due to inhibition of arteriogenesis and mast cell numbers within the healing bone. As this new direction holds great promise towards a solution for significant clinical hurdles in craniofacial reconstruction and limb salvage procedures, this work reviews the current state of the field, and provides insights as to how teriparatide therapy could be used as an adjuvant for healing critical defects in bone. Finally, as teriparatide therapy is contraindicated in the setting of cancer, which constitutes a large subset of these patients, we describe early findings of adjuvant therapies that may present future promise by directly inhibiting arteriogenesis and mast cell accumulation at the defect site.

• arteriogenesis
• critical bone defect
• fibrosis
• mast cells
• osteogenesis
• recombinant parathyroid hormone (rPTH; teriparatide; Forteo)

• P30 AR069655 NIAMS NIH HHS
• P50 AR054041 NIAMS NIH HHS
• R01 DE019902 NIDCR NIH HHS
• P30 AR061307 NIAMS NIH HHS
• R01 AR067859 NIAMS NIH HHS
• R01 AR066517 NIAMS NIH HHS
• S10 RR027340 NCRR NIH HHS

Mice in which Cbl is unable to bind PI3K (YF mice) display increased bone volume due to enhanced bone formation and repressed bone resorption during normal bone homeostasis. We investigated the effects of disrupted Cbl-PI3K interaction on fracture healing to determine whether this interaction has an effect on bone repair. Mid-diaphyseal femoral fractures induced in wild type (WT) and YF mice were temporally evaluated via micro-computed tomography scans, biomechanical testing, histological and histomorphometric analyses. Imaging analyses revealed no change in soft callus formation, increased bony callus formation, and delayed callus remodeling in YF mice compared to WT mice. Histomorphometric analyses showed significantly increased osteoblast surface per bone surface and osteoclast numbers in the calluses of YF fractured mice, as well as increased incorporation of dynamic bone labels. Furthermore, using laser capture micro-dissection of the fracture callus we found that cells lacking Cbl-PI3K interaction have higher expression of Osterix, TRAP, and Cathepsin K. We also found increased expression of genes involved in propagating PI3K signaling in cells isolated from the YF fracture callus, suggesting that the lack of Cbl-PI3K interaction perhaps results in enhanced PI3K signaling, leading to increased bone formation, but delayed remodeling in the healing femora.

• Animals
• Bone Remodeling
• Mice
• Mice, Inbred C57BL
• Models, Animal
• Phosphatidylinositol 3-Kinases/metabolism
• Proto-Oncogene Proteins c-cbl/metabolism

• R01 AR055601 NIAMS NIH HHS
• T90 DE021989 NIDCR NIH HHS
• AR055601 NIAMS NIH HHS
• AR060867 NIAMS NIH HHS

• orthopedic surgery
• biologic
• adjuvant
• bone
• graft extender
• growth factor

• CATHEPSIN K
• HEMATOPOIESIS
• OSTEOCLAST PRECURSORS
• OSTEOPETROSIS

• PTH 1-34
• adhesions
• biomechanics
• forteo
• tendon healing

• Animals
• Biomechanical Phenomena/drug effects
• Biomechanical Phenomena/physiology
• Collagen/metabolism
• Extracellular Matrix/drug effects
• Extracellular Matrix/metabolism
• Fibronectins/metabolism
• Male
• Metatarsophalangeal Joint/physiology
• Mice
• Mice, Inbred C57BL
• Models, Animal
• Parathyroid Hormone/pharmacology
• Parathyroid Hormone/therapeutic use
• Range of Motion, Articular/drug effects
• Range of Motion, Articular/physiology
• Tendon Injuries/drug therapy
• Tendon Injuries/metabolism
• Tendon Injuries/surgery
• Tendons/drug effects
• Tendons/metabolism
• Tendons/surgery
• Tensile Strength/drug effects
• Tensile Strength/physiology
• Wound Healing/drug effects
• Wound Healing/physiology

• T32 GM07356 NIGMS NIH HHS
• R01AR056696 NIAMS NIH HHS
• T32 AR053459 NIAMS NIH HHS
• R01 AR056696 NIAMS NIH HHS
• P50 AR054041 NIAMS NIH HHS
• P50AR954041 NIAMS NIH HHS

• antiresorptive drugs
• bone formation
• osteoblasts
• osteogenesis
• rankl inhibitors

• Antibodies, Monoclonal, Humanized/therapeutic use
• Bone Density Conservation Agents/therapeutic use
• Bone Diseases/drug therapy
• Denosumab
• Diphosphonates/therapeutic use
• Female
• Humans
• Male
• Osteogenesis/drug effects
• Selective Estrogen Receptor Modulators/therapeutic use
• Teriparatide/therapeutic use
• Thiophenes/therapeutic use

• Fracture healing
• Mesenchymal stem cell
• Parathyroid hormone
• Periosteum
• Wnt-β-catenin signaling

• Aging/drug effects
• Anabolic Agents/pharmacology
• Anabolic Agents/therapeutic use
• Animals
• Biomechanical Phenomena/drug effects
• Bone Regeneration/drug effects
• Bony Callus/drug effects
• Bony Callus/pathology
• Cartilage/drug effects
• Cartilage/pathology
• Cell Proliferation/drug effects
• Cellular Senescence/drug effects
• Female
• Fracture Healing/drug effects
• Humans
• Mice, Inbred C57BL
• Osteogenesis/drug effects
• Parathyroid Hormone/pharmacology
• Parathyroid Hormone/therapeutic use
• Periosteum/cytology
• Stem Cells/cytology
• Stem Cells/drug effects
• Stem Cells/metabolism
• Tibial Fractures/drug therapy
• Tibial Fractures/pathology
• Tibial Fractures/physiopathology
• Wnt Signaling Pathway/drug effects

• P50AR054041 NIAMS NIH HHS
• P50 AR054041 NIAMS NIH HHS
• P50AR954041 NIAMS NIH HHS
• R01 AR48681 NIAMS NIH HHS
• R01 AR048681 NIAMS NIH HHS

• Fracture healing
• Primary healing
• Secondary healing

• Arthritis/diagnostic imaging
• Arthritis/drug therapy
• Arthritis/surgery
• Bone Density/drug effects
• Bone and Bones/drug effects
• Female
• Fracture Fixation, Internal
• Fracture Healing
• Glucocorticoids/adverse effects
• Humans
• Male
• Osteoporosis/drug therapy
• Osteoporotic Fractures/prevention & control
• Parathyroid Hormone/metabolism
• Peptide Fragments/metabolism
• Postmenopause
• Radiography
• Risk
• Teriparatide/therapeutic use

• Animals
• Body Weight/drug effects
• Bone Remodeling/drug effects
• Bony Callus
• Calcification, Physiologic/drug effects
• Cartilage/drug effects
• Cartilage/pathology
• Cathepsin K/antagonists & inhibitors
• Cathepsin K/metabolism
• Cell Count
• Fracture Healing/drug effects
• Fractures, Bone/diagnostic imaging
• Fractures, Bone/drug therapy
• Fractures, Bone/enzymology
• Fractures, Bone/physiopathology
• Mice
• Mice, Inbred C57BL
• Osteoclasts/drug effects
• Osteoclasts/pathology
• Osteogenesis/drug effects
• Protease Inhibitors/administration & dosage
• Protease Inhibitors/metabolism
• Protease Inhibitors/pharmacology
• Protease Inhibitors/therapeutic use
• Radiography

• bone graft
• bone graft substitute
• fractures
• nonunion
• orthobiologics

Muscle satellite cells make up a stem cell population that is capable of differentiating into myocytes and contributing to muscle regeneration upon injury. In this work we investigate the mechanism by which these muscle progenitor cells adopt an alternative cell fate, the cartilage fate. We show that chick muscle satellite cells that normally would undergo myogenesis can be converted to express cartilage matrix proteins in vitro when cultured in chondrogenic medium containing TGFß3 or BMP2. In the meantime, the myogenic program is repressed, suggesting that muscle satellite cells have undergone chondrogenic differentiation. Furthermore, ectopic expression of the myogenic factor Pax3 prevents chondrogenesis in these cells, while chondrogenic factors Nkx3.2 and Sox9 act downstream of TGFß or BMP2 to promote this cell fate transition. We found that Nkx3.2 and Sox9 repress the activity of the Pax3 promoter and that Nkx3.2 acts as a transcriptional repressor in this process. Importantly, a reverse function mutant of Nkx3.2 blocks the ability of Sox9 to both inhibit myogenesis and induce chondrogenesis, suggesting that Nkx3.2 is required for Sox9 to promote chondrogenic differentiation in satellite cells. Finally, we found that in an in vivo mouse model of fracture healing where muscle progenitor cells were lineage-traced, Nkx3.2 and Sox9 are significantly upregulated while Pax3 is significantly downregulated in the muscle progenitor cells that give rise to chondrocytes during fracture repair. Thus our in vitro and in vivo analyses suggest that the balance of Pax3, Nkx3.2 and Sox9 may act as a molecular switch during the chondrogenic differentiation of muscle progenitor cells, which may be important for fracture healing.

• Animals
• Bone Morphogenetic Protein 2/genetics
• Bone Morphogenetic Protein 2/metabolism
• Cell Differentiation
• Cells, Cultured
• Chick Embryo
• Chickens
• Chondrogenesis
• Fracture Healing
• Fractures, Bone/genetics
• Fractures, Bone/metabolism
• Homeodomain Proteins/genetics
• Homeodomain Proteins/metabolism
• Mice
• Muscle Development/genetics
• Muscle Proteins/genetics
• Muscle Proteins/metabolism
• PAX3 Transcription Factor
• Paired Box Transcription Factors/genetics
• Paired Box Transcription Factors/metabolism
• SOX9 Transcription Factor/genetics
• SOX9 Transcription Factor/metabolism
• Satellite Cells, Skeletal Muscle/metabolism
• Transcription Factors/genetics
• Transcription Factors/metabolism
• Transforming Growth Factor beta/genetics
• Transforming Growth Factor beta/metabolism

• R01 AR059106 NIAMS NIH HHS
• R03 AR054611 NIAMS NIH HHS
• 5R25HL007786 NHLBI NIH HHS
• R01AR059106 NIAMS NIH HHS
• R25 HL007786 NHLBI NIH HHS
• 457245 Medical Research Council

• aml1
• chondrocytes
• cartilage development
• fracture repair