SDF-1/CXCR4 Axis in Tie2-Lineage Cells Including Endothelial Progenitor Cells Contributes to Bone Fracture Healing

Abstract

CXC chemokine receptor 4 (CXCR4) is a specific receptor for stromal-derived-factor 1 (SDF-1). SDF-1/CXCR4 interaction is reported to play an important role in vascular development. On the other hand, the therapeutic potential of endothelial progenitor cells (EPCs) in fracture healing has been demonstrated with mechanistic insight of vasculogenesis/angiogenesis and osteogenesis enhancement at sites of fracture. The purpose of this study was to investigate the influence of the SDF-1/CXCR4 pathway in Tie2-lineage cells (including EPCs) in bone formation. We created CXCR4 gene conditional knockout mice using the Cre/loxP system and set two groups of mice: Tie2-Cre ER CXCR4 knockout mice (CXCR4 À/À ) and wild-type mice (WT). We report here that in vitro, EPCs derived from of CXCR4 À/À mouse bone marrow demonstrated severe reduction of migration activity and EPC colony-forming activity when compared with those derived from WT mouse bone marrow. In vivo, radiological and morphological examinations showed fracture healing delayed in the CXCR4 À/À group and the relative callus area at weeks 2 and 3 was significantly smaller in CXCR4 À/À group mice. Quantitative analysis of capillary density at perifracture sites also showed a significant decrease in the CXCR4 À/À group. Especially, CXCR4 À/À group mice demonstrated significant early reduction of blood flow recovery at fracture sites compared with the WT group in laser Doppler perfusion imaging analysis. Real-time RT-PCR analysis showed that the gene expressions of angiogenic markers (CD31, VE-cadherin, vascular endothelial growth factor [VEGF]) and osteogenic markers (osteocalcin, collagen 1A1, bone morphogenetic protein 2 [BMP2]) were lower in the CXCR4 À/À group. In the gain-of-function study, the fracture in the SDF-1 intraperitoneally injected WT group healed significantly faster with enough callus formation compared with the SDF-1 injected CXCR4 À/À group. We demonstrated that an EPC SDF-1/CXCR4 axis plays an important role in bone fracture healing using Tie2-Cre ER CXCR4 conditional knockout mice.

Influence of the intensity and loading time of direct current electric field on the directional migration of rat bone marrow mesenchymal stem cells

“…Previous studies have shown that early deletion of the CXCR4 gene in osteoblastogenesis disrupts osteoblast formation and bone development [32]. It has been reported that SDF-1/CXCR4 signaling in the mature osteoblast can feedback to regulate the osteoclast precursor pool size and play a multifunctional role in regulating bone formation and resorption [33]. SDF-1 might induce cell migration to the injury area, which is consistent with the results of the present study.…”

Extracellular signaling molecules to promote fracture healing and bone regeneration

“…Tyrosine Kinase with Immunoglobulin-Like and EGF-like domains (Tie2)-Cre CXCR4 negative endothelial progenitor cells were shown to have reduction of migration and colony forming action in comparison to wild type cells. This effect was confirmed in vivo with delayed fracture healing and smaller callus size in Tie2-cre CXCR4 conditional knockout mice (34). AMD3100 is a CXCR4 inhibitor that induces progenitor cells to migrate to the peripheral blood due to lack of CXCR4/SDF-1 binding that anchors these progenitors in their niches.…”

Matrix elasticity-modified scaffold loaded with SDF-1α improves the in situ regeneration of segmental bone defect in rabbit radius

“…Our data showed that the SDF-1α/Col/HA group had more CD34-positive cells than the Col/HA group, indicating that SDF-1α may magnify the vessel formation ability of the scaffold with optimal matrix elastic modulus. Besides, another important reason is that SDF-1α may involve in attracting of CD34-positive hematopoietic stem cells 23 and endothelial progenitor cells 45 .

Figure 7Immunofluorescent detection of CD34 in scaffolds after subcutaneous implantation. The white arrow indicates typical blood vessel.

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