Modulation of Stromal Cell-Derived Factor-1/CXC Chemokine Receptor 4 Axis Enhances rhBMP-2-Induced Ectopic Bone Formation

Abstract

Enhancement of in vivo mobilization and homing of endogenous mesenchymal stem cells (MSCs) to an injury site is an innovative strategy for improvement of bone tissue engineering and repair. The present study was designed to determine whether mobilization by AMD3100 and/or local homing by delivery of stromal cellderived factor-1 (SDF-1) enhances recombinant human bone morphogenetic protein-2 (rhBMP-2) induced ectopic bone formation in an established rat model. Rats received an injection of either saline or AMD3100 treatment 1 h before harvesting of bone marrow for in vitro colony-forming unit-fibroblasts (CFU-F) culture or the in vivo subcutaneous implantation of absorbable collagen sponges (ACSs) loaded with saline, recombinant human bone morphogenetic protein-2 (rhBMP-2), SDF-1, or the combination of SDF-1 and rhBMP-2. AMD3100 treatment resulted in a significant decrease in CFU-F number, compared with saline, which confirmed that a single systemic AMD3100 treatment rapidly mobilized MSCs from the bone marrow. At 28 and 56 days, bone formation in the explanted ACS was assessed by microcomputed tomography (mCT) and histology. At 28 days, AMD3100 and/or SDF-1 had no statistically significant effect on bone volume (BV) or bone mineral content (BMC), but histology revealed more active bone formation with treatment of AMD3100, loading of SDF-1, or the combination of both AMD3100 and SDF-1, compared with saline-treated rhBMP-2 loaded ACS. At 56 days, the addition of AMD3100 treatment, loading of SDF-1, or the combination of both resulted in a statistically significant stimulatory effect on BV and BMC, compared with the saline-treated rhBMP-2 loaded ACS. Histology of the 56-day ACS were consistent with the mCT analysis, exhibiting more mature and mineralized bone formation with AMD3100 treatment, SDF-1 loading, or the combination of both, compared with the saline-treated rhBMP-2 loaded ACS. The present study is the first that provides evidence of the efficacy of AMD3100 and SDF-1 treatment to stimulate trafficking of MSCs to an ectopic implant site, in order to ultimately enhance rhBMP-2 induced long-term bone formation.

Adult Stem Cell Mobilization Enhances Intramembranous Bone Regeneration: A Pilot Study

“…The existing data from our study and other studies [57,59] document the use of the CXCR4 antagonist, AMD3100, has an effect on bone formation in at least three microenvironments: ectopic, cranial, and appendicular in this model. The concept should therefore be further explored to improve bone regeneration after trauma-or surgical-induced damage to bone.…”

“…While the finding at 21 days appears to be a modest increase, Wang et al [57] showed treatment with AMD3100 for 15 continuous days starting 3 days after a critical-size cranial defect was created improved bone healing at 56 and 112 days but not at 28 days. In a recent report from our laboratory, we noted a single injection of AMD3100 enhanced bone volume in a rat model of ectopic bone formation [59]. The effect was observed at 56 days but not at 28 days, although at the earlier time point there was qualitative evidence of active bone formation in the treated animals whereas the control animals already had a relatively well-established marrow compartment.…”

“…It is plausible this strategy simply mimics and amplifies normal repair mechanisms as progenitor cells are mobilized to the PB after stroke [41], vascular trauma [20], musculoskeletal trauma [31,32], fracture [3,34], distraction osteogenesis [34], and myocardial infarction [60]. An important pathway for stem cell mobilization is the SDF-1/CXCR4 axis and there are recent data supporting the concept that transient disruption of this receptor-ligand complex through the CXCR4 antagonist, AMD3100, enhances bone formation in vivo [57,59]. In this study, we assessed the utility of the mouse marrow ablation model of intramembranous bone regeneration for examining this new therapeutic strategy by posing the following questions: Does AMD3100 mobilize adult stem cells in C57BL/6 mice?…”

“…The stromal cell-derived factor 1/C-X-C chemokine receptor type 4 (SDF-1/ CXCR4) axis is a particularly interesting target because of its known role in HSC mobilization [13] and its likely role in bone repair [28]. Transient antagonism of CXCR4 by the small molecule known as AMD3100 induces mobilization [48] and improves bone formation in an ectopic model [59] and in a cranial defect model [57] but has not yet been investigated in a marrow ablation model. The ablation model was chosen as a model with relevance to situations where intramembranous bone regeneration is important, such as implant fixation, distraction osteogenesis, and fracture repair using fixators.…”

Low-Dose Bone Morphogenetic Protein-2/Stromal Cell-Derived Factor-1β Cotherapy Induces Bone Regeneration in Critical-Size Rat Calvarial Defects

“…24 These in vitro findings were later extended using primary mouse and human bone-marrow-derived mesenchymal stem cells (BMSCs), 25 setting the stage for investigating the BMP-2/SDF-1 interaction employing orthotopic and ectopic bone formation models. [26][27][28][29] Previous studies have suggested that the CXCR4/SDF-1 axis functions in postnatal bone formation by regulating osteoblast development in cooperation with BMP signaling, and that CXCR4 acts as an endogenous signaling component necessary for bone formation. 29 We 30 and others 31 have shown that bone marrow endothelial and stromal cells, and osteoblasts express both major SDF-1 splice variants, and that unexpectedly the beta isoform may be present at a high level in bone tissues.…”