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1.  Atypical PKC-ζ regulates SDF-1–mediated migration and development of human CD34+ progenitor cells 
Journal of Clinical Investigation  2005;115(1):168-176.
The chemokine stromal cell–derived factor–1 (SDF-1) and its receptor, CXCR4, play a major role in migration, retention, and development of hematopoietic progenitors in the bone marrow. We report the direct involvement of atypical PKC-ζ in SDF-1 signaling in immature human CD34+-enriched cells and in leukemic pre-B acute lymphocytic leukemia (ALL) G2 cells. Chemotaxis, cell polarization, and adhesion of CD34+ cells to bone marrow stromal cells were found to be PKC-ζ dependent. Overexpression of PKC-ζ in G2 and U937 cells led to increased directional motility to SDF-1. Interestingly, impaired SDF-1–induced migration of the pre-B ALL cell line B1 correlated with reduced PKC-ζ expression. SDF-1 triggered PKC-ζ phosphorylation, translocation to the plasma membrane, and kinase activity. Furthermore we identified PI3K as an activator of PKC-ζ, and Pyk-2 and ERK1/2 as downstream targets of PKC-ζ. SDF-1–induced proliferation and MMP-9 secretion also required PKC-ζ activation. Finally, we showed that in vivo engraftment, but not homing, of human CD34+-enriched cells to the bone marrow of NOD/SCID mice was PKC-ζ dependent and that injection of mice with inhibitory PKC-ζ pseudosubstrate peptides resulted in mobilization of murine progenitors. Our results demonstrate a central role for PKC-ζ in SDF-1–dependent regulation of hematopoietic stem and progenitor cell motility and development.
PMCID: PMC539190  PMID: 15630457
2.  HGF, SDF-1, and MMP-9 are involved in stress-induced human CD34+ stem cell recruitment to the liver 
Journal of Clinical Investigation  2003;112(2):160-169.
Hematopoietic stem cells rarely contribute to hepatic regeneration, however, the mechanisms governing their homing to the liver, which is a crucial first step, are poorly understood. The chemokine stromal cell–derived factor-1 (SDF-1), which attracts human and murine progenitors, is expressed by liver bile duct epithelium. Neutralization of the SDF-1 receptor CXCR4 abolished homing and engraftment of the murine liver by human CD34+ hematopoietic progenitors, while local injection of human SDF-1 increased their homing. Engrafted human cells were localized in clusters surrounding the bile ducts, in close proximity to SDF-1–expressing epithelial cells, and differentiated into albumin-producing cells. Irradiation or inflammation increased SDF-1 levels and hepatic injury induced MMP-9 activity, leading to both increased CXCR4 expression and SDF-1–mediated recruitment of hematopoietic progenitors to the liver. Unexpectedly, HGF, which is increased following liver injury, promoted protrusion formation, CXCR4 upregulation, and SDF-1–mediated directional migration by human CD34+ progenitors, and synergized with stem cell factor. Thus, stress-induced signals, such as increased expression of SDF-1, MMP-9, and HGF, recruit human CD34+ progenitors with hematopoietic and/or hepatic-like potential to the liver of NOD/SCID mice. Our results suggest the potential of hematopoietic CD34+/CXCR4+cells to respond to stress signals from nonhematopoietic injured organs as an important mechanism for tissue targeting and repair.
PMCID: PMC164291  PMID: 12865405
3.  Stromal derived factor-1 regulates bone morphogenetic protein 2-induced osteogenic differentiation of primary mesenchymal stem cells 
Stromal derived factor-1 (SDF-1) is a chemokine signaling molecule that binds to its transmembrane receptor CXC chemokine receptor-4 (CXCR4). While we previously detected that SDF-1 was co-required with bone morphogenetic protein 2 (BMP2) for differentiating mesenchymal C2C12 cells into osteoblastic cells, it is unknown whether SDF-1 is similarly involved in the osteogenic differentiation of mesenchymal stem cells (MSCs). Therefore, here we examined the role of SDF-1 signaling during BMP2-induced osteogenic differentiation of primary MSCs that were derived from human and mouse bone marrow. Our data showed that blocking of the SDF-1/CXCR4 signal axis or adding SDF-1 protein to MSCs significantly affected BMP2-induced alkaline phosphatase (ALP) activity and osteocalcin (OCN) synthesis, markers of preosteoblasts and mature osteoblasts, respectively. Moreover, disrupting the SDF-1 signaling impaired bone nodule mineralization during terminal differentiation of MSCs. Furthermore, we detected that blocking of the SDF-1 signaling inhibited the BMP2-induced early expression of Runt-related factor-2 (Runx2) and osterix (Osx), two “master” regulators of osteogenesis, and the SDF-1 effect was mediated via intracellular Smad and Erk activation. In conclusion, our results demonstrated a regulatory role of SDF-1 in BMP2-induced osteogenic differentiation of MSCs, as perturbing the SDF-1 signaling affected the differentiation of MSCs towards osteoblastic cells in response to BMP2 stimulation. These data provide novel insights into molecular mechanisms underlying MSC osteogenesis, and will contribute to the development of MSC therapies for enhancing bone formation and regeneration in broad orthopaedic situations.
PMCID: PMC2992806  PMID: 20362069
Bone morphogenetic protein 2; CXC chemokine receptor-4; Mesenchymal stem cell; Osteogenic differentiation; Stromal derived factor-1
4.  Stromal cell derived factor-1: its influence on invasiveness and migration of breast cancer cells in vitro, and its association with prognosis and survival in human breast cancer 
Breast Cancer Research  2005;7(4):R402-R410.
Stromal cell-derived factor (SDF)-1 (CXC chemokine ligand-12) is a member of the CXC subfamily of chemokines, which, through its cognate receptor (CXC chemokine receptor [CXCR]4), plays an important role in chemotaxis of cancer cells and in tumour metastasis. We conducted the present study to evaluate the effect of SDF-1 on the invasiveness and migration of breast cancer cells, and we analyzed the expression of SDF-1 and its relation to clinicopathological features and clinical outcomes in human breast cancer.
Expression of SDF-1 mRNA in breast cancer, endothelial (HECV) and fibroblast (MRC5) cell lines and in human breast tissues were studied using RT-PCR. MDA-MB-231 cells were transfected with a SDF-1 expression vector, and their invasiveness and migration was tested in vitro. In addition, the expression of SDF-1 was investigated using immunohistochemistry and quantitative RT-PCR in samples of normal human mammary tissue (n = 32) and mammary tumour (n = 120).
SDF-1 expression was identified in MRC5, MDA-MB-435s and MDA-MB-436 cell lines, but CXCR4 expression was detected in all cell lines and breast tissues. An autocrine loop was created following transfection of MDA-MB-231 (which was CXCR4 positive and SDF-1 negative) with a mammalian expression cassette encoding SDF-1 (MDA-MB-231SDF1+/+) or with control plasmid pcDNA4/GFP (MDA-MB-231+/-). MDA-MB-231SDF1+/+ cells exhibited significantly greater invasion and migration potential (in transfected cells versus in wild type and empty MDA-MB-231+/-; P < 0.01). In mammary tissues SDF-1 staining was primarily seen in stromal cells and weakly in mammary epithelial cells. Significantly higher levels of SDF-1 were seen in node-positive than in node-negative tumours (P = 0.05), in tumours that metastasized (P = 0.05), and tumours from patients who died (P = 0.03) than in tumours from patients who were disease free. It was most notable that levels of SDF-1 correlated significantly with overall survival (P = 0.001) and incidence-free survival (P = 0.035).
SDF-1 can increase the invasiveness and migration of breast cancer cells. Its levels correlated with node involvement and long-term survival in patients with breast cancer. SDF-1 may therefore have potential value in assessing clinical outcomes of patients with breast cancer.
PMCID: PMC1175055  PMID: 15987445
5.  A Transduced Living Hyaline Cartilage Graft Releasing Transgenic Stromal Cell-Derived Factor-1 Inducing Endogenous Stem Cell Homing In Vivo 
Tissue Engineering. Part A  2013;19(9-10):1091-1099.
Stromal cell-derived factor-1 (SDF-1), also known as a homing factor, is a potent chemokine that activates and directs mobilization, migration, and retention of certain cell species via systemic circulation. The responding homing cells largely consist of activated stem cells, so that, in case of tissue lesions, such SDF-1-induced cell migration may execute recruitment of endogenous stem cells to perform autoreparation and compensatory regeneration in situ. In this study, a recombinant adenoviral vector carrying SDF-1 transgene was constructed and applied to transduce a novel scaffold-free living hyaline cartilage graft (SDF-t-LhCG). As an engineered transgenic living tissue, SDF-t-LhCG is capable of continuously producing and releasing SDF-1 in vitro and in vivo. The in vitro trials were examined with ELISA, while the in vivo trials were subsequently performed via a subcutaneous implantation of SDF-t-LhCG in a nude mouse model, followed by series of biochemical and biological analyses. The results indicate that transgenic SDF-1 enhanced the presence of this chemokine in mouse's circulation system; in consequence, SDF-1-induced activation and recruitment of endogenous stem cells were also augmented in both peripheral blood and SDF-t-LhCG implant per se. These results were obtained via flow cytometry analyses on mouse blood samples and implanted SDF-t-LhCG samples, indicating an upregulation of the CXCR4+(SDF-1 receptor) cell population, accompanied by upregulation of the CD34+, CD44+, and Sca-1+ cell populations as well as a downregulation of the CD11b+ cell population. With the supply of SDF-1-recruited endogenous stem cells, enhanced chondrogenesis was observed in SDF-t-LhCG implants in situ.
PMCID: PMC3609611  PMID: 23167782
6.  SDF-1α/CXCR4 Axis Mediates The Migration of Mesenchymal Stem Cells to The Hypoxic-Ischemic Brain Lesion in A Rat Model 
Cell Journal (Yakhteh)  2015;16(4):440-447.
Transplantation of mesenchymal stem cells (MSCs) can promote functional recovery of the brain after hypoxic-ischemic brain damage (HIBD). However, the mechanism regulating MSC migration to a hypoxic-ischemic lesion is poorly understood. Interaction between stromal cell-derived factor-1α (SDF-1α) and its cognate receptor CXC chemokine receptor 4 (CXCR4) is crucial for homing and migration of multiple stem cell types. In this study, we investigate the potential role of SDF-1α/CXCR4 axis in mediating MSC migration in an HIBD model.
Materials and Methods
In this experimental study, we first established the animal model of HIBD using the neonatal rat. Bone marrow MSCs were cultured and labeled with 5-bromo-21-deoxyuridine (BrdU) after which 6×106 cells were intravenously injected into the rat. BrdU positive MSCs in the hippocampus were detected by immunohistochemical analyses. The expression of hypoxia-inducible factor-1α (HIF-1α) and SDF-1α in the hippocampus of hypoxic-ischemic rats was detected by Western blotting. To investigate the role of hypoxia and SDF-1α on migration of MSCs in vitro, MSCs isolated from normal rats were cultured in a hypoxic environment (PO2=1%). Migration of MSCs was detected by the transwell assay. The expression of CXCR4 was tested using Western blotting and flow cytometry.
BrdU-labeled MSCs were found in the rat brain, which suggested that transplanted MSCs migrated to the site of the hypoxic-ischemic brain tissue. HIF-1α and SDF-1α significantly increased in the hippocampal formations of HIBD rats in a time-dependent manner. They peaked on day 7 and were stably expressed until day 21. Migration of MSCs in vitro was promoted by SDF-1α under hypoxia and inhibited by the CXCR4 inhibitor AMD3100. The expression of CXCR4 on MSCs was elevated by hypoxia stimulation as well as microdosage treatment of SDF-1α.
This observation illustrates that SDF-1α/CXCR4 axis mediate the migration of MSCs to a hypoxic-ischemic brain lesion in a rat model.
PMCID: PMC4297482
Mesenchymal Stem Cells; Migration; SDF-1α; CXCR 4
7.  Essential but differential role for CXCR4 and CXCR7 in the therapeutic homingof human renal progenitor cells 
Recently, we have identified a population of renal progenitor cells in human kidneys showing regenerative potential for injured renal tissue of SCID mice. We demonstrate here that among all known chemokine receptors, human renal progenitor cells exhibit high expression of both stromal-derived factor-1 (SDF-1) receptors, CXCR4 and CXCR7. In SCID mice with acute renal failure (ARF), SDF-1 was strongly up-regulated in resident cells surrounding necrotic areas. In the same mice, intravenously injected renal stem/progenitor cells engrafted into injured renal tissue decreased the severity of ARF and prevented renal fibrosis. These beneficial effects were abolished by blocking either CXCR4 or CXCR7, which dramatically reduced the number of engrafting renal progenitor cells. However, although SDF-1–induced migration of renal progenitor cells was only abolished by an anti-CXCR4 antibody, transendothelial migration required the activity of both CXCR4 and CXCR7, with CXCR7 being essential for renal progenitor cell adhesion to endothelial cells. Moreover, CXCR7 but not CXCR4 was responsible for the SDF-1–induced renal progenitor cell survival. Collectively, these findings suggest that CXCR4 and CXCR7 play an essential, but differential, role in the therapeutic homing of human renal progenitor cells in ARF, with important implications for the development of stem cell–based therapies.
PMCID: PMC2271008  PMID: 18268039
8.  Bone-derived SDF-1 stimulates IL-6 release via CXCR4, ERK and NF-κB pathways and promotes osteoclastogenesis in human oral cancer cells 
Carcinogenesis  2008;29(8):1483-1492.
Oral squamous cell carcinoma (SCC) has a striking tendency to invade to bone. The chemokine stromal cell-derived factor-1 (SDF-1) is constitutively secreted by osteoblasts and plays a key role in homing of hematopoietic cells to the bone marrow. Interleukin (IL)-6 plays an important role in osteoclastogenesis. Herein, we found that SDF-1α increased the secretion of IL-6 in cultured human SCC cells, as shown by reverse transcriptase–polymerase chain reaction and enzyme-linked immunosorbent assay. SDF-1α also increased the surface expression of chemokine receptor 4 (CXCR4) in SCC cells. CXCR4-neutralizing antibody, CXCR4-specific inhibitor (AMD3100) or small interfering RNA against CXCR4 inhibited SDF-1α-induced increase IL-6 production. The transcriptional regulation of IL-6 by SDF-1α was mediated by phosphorylation of extracellular signal-regulated kinases (ERKs) and activation of the nuclear factor-kappa B (NF-κB) components p65 and p50. The binding of p65 and p50 to the NF-κB element on the IL-6 promoter was enhanced by SDF-1α. In addition, IL-6 antibody antagonized the SCC-conditioned medium-increased osteoclastogenesis. These results suggested that SDF-1α from osteoblasts could induce release of IL-6 in human SCC cells via activation of CXCR4, ERK and NF-κB pathway and thereby promote osteoclastogenesis.
PMCID: PMC2516485  PMID: 18310089
9.  Proteolytic processing of SDF-1α by matrix metalloproteinase-2 impairs CXCR4 signaling and reduces neural progenitor cell migration 
Protein & cell  2012;3(11):875-882.
Neural stem cells and neural progenitor cells (NPCs) exist throughout life and are mobilized to replace neurons, astrocytes and oligodendrocytes after injury. Stromal cell-derived factor 1 (SDF-1, now named CXCL12) and its receptor CXCR4, an α-chemokine receptor, are critical for NPC migration into damaged areas of the brain. Our previous studies demonstrated that immune activated and/or HIV-1-infected human monocyte-derived- macrophages (MDMs) induced a substantial increase of SDF-1 production by human astrocytes. However, matrix metalloproteinase (MMP)-2, a protein up-regulated in HIV-1-infected macrophages, is able to cleave four amino acids from the N-terminus of SDF-1, resulting in a truncated SDF-1(5–67). In this study, we investigate the diverse signaling and function induced by SDF-1α and SDF-1(5–67) in human cortical NPCs. SDF-1(5–67) was generated by incubating human recombinant SDF-1α with MMP-2 followed by protein determination via mass spectrometry, Western blotting and ELISA. SDF-1α induced time-dependent phosphorylation of extracellular signal-regulated kinases (ERK) 1/2, Akt-1, and diminished cyclic adenosine monophosphate (cAMP). In contrast, SDF-1(5–67) failed to induce these signaling. SDF-1α activation of CXCR4 induced migration of NPCs, an effect that is dependent on ERK1/2 and Akt-1 pathways; whereas SDF-1(5–67) failed to induce NPC migration. This observation provides evidence that MMP-2 may affect NPC migration through post-translational processing of SDF-1α.
PMCID: PMC3973535  PMID: 23143873
proteolysis; chemokine; neurogenesis; migration
10.  Cationic Liposome-Mediated CXCR4 Gene Delivery into Hematopoietic Stem/Progenitor Cells: Implications for Clinical Transplantation and Gene Therapy 
Stem Cells and Development  2011;21(10):1587-1596.
The chemokine stromal cell-derived factor (SDF)-1α/CXCL12 and its receptor CXC chemokine receptor 4 (CXCR4) play a crucial role in the homing/engraftment and retention of hematopoietic stem/progenitor cells (HSPCs) in the bone marrow. It has been shown using the viral gene transfer technique that CXCR4 overexpression on human CD34+ HSPC significantly improves their engraftment in murine models. However, clinical trials with gene therapy have revealed safety concerns related to the immunogenicity of the viral carriers, due to the random integration of viral genes into the host genome. Therefore, a method for CXCR4 gene delivery into HSPC that is safe, nonviral, and highly efficient is needed to improve clinical transplantation and gene therapies. In this work, we investigated the nonviral CXCR4 gene delivery into HSPC using the cationic liposome agent IBAfect. We used CD34+ cells from cord blood and the models of immature hematopoietic cells expressing CD34 antigen, namely, leukemic cell lines KG-1a and KG-1. Transfection efficiency was determined by flow cytometric analysis 12, 24, 48, and 72 h after transfection, and the viability of cells analyzed by trypan blue exclusion and MTS assays. The functional response of CXCR4-transfected HSPC toward an SDF-1α gradient was determined by chemotaxis assay. We found that ∼25% transfection is achieved for KG-1a and KG-1 cells and 20% for HSPC, and that the viability of CXCR4-transfected HSPC is not significantly altered. More importantly, overexpression of CXCR4 using IBAfect significantly increased the chemotaxis of KG-1 cells and HSPC toward SDF-1α. However, we tested 2 other commercially available cationic liposomes (Lipofectamine 2000 and 1,2-dioleoyl-3-trimethylammonium-propane [DOTAP]) in parallel, and we found that they failed to deliver the CXCR4 gene into cells under the same conditions. These results suggest that IBAfect-mediated in vitro gene delivery to overexpress CXCR4 on HSPC is a safe and efficient technique with great potential for improving the efficacy of HSPC transplantation and gene therapy protocols.
PMCID: PMC3376461  PMID: 22047530
11.  Stromal-Derived Factor-1 and Its Receptor, CXCR4, Are Constitutively Expressed by Mouse Liver Sinusoidal Endothelial Cells: Implications for the Regulation of Hematopoietic Cell Migration to the Liver During Extramedullary Hematopoiesis 
Stem Cells and Development  2011;21(12):2142-2151.
Stromal-derived factor (SDF)-1 is the main regulating factor for trafficking/homing of hematopoietic stem cells (HSC) to the bone marrow (BM). It is possible that this chemokine may also play a fundamental role in regulating the migration of HSC to several organs during extramedullary hematopoiesis. Because liver sinusoidal endothelial cells (LSEC) constitute an extramedullary niche for HSC, it is possible that these cells represent one of the main cellular sources of SDF-1 at the liver. Here, we show that LSEC express SDF-1 at the mRNA and protein level. Biological assays showed that conditioned medium from LSEC (LSEC-CM) stimulated the migration of BM progenitor lineage-negative (BM/Lin−) cells. This effect was significantly reduced by AMD3100, indicating that the SDF-1/CXCR4 axis is involved in the stimulatory migrating effect induced by LSEC-CM. Early localization of HSC in SDF-1–expressing LSEC microenvironment together with increased levels of this chemokine in hepatic homogenates was found in an experimental model of liver extramedullary hematopoiesis. Flow cytometry studies showed that LSEC express the CXCR4 receptor. Functional assays showed that activation of this receptor by SDF-1 stimulated the migration of LSEC and increased the expression of PECAM-1. Our findings suggest that LSEC through the production of SDF-1 may constitute a fundamental niche for regulation of HSC migration to the liver. To our knowledge, this is the first report showing that LSEC not only express and secrete SDF-1, but also its receptor CXCR4.
PMCID: PMC3411357  PMID: 22121892
12.  Stem cell attraction via SDF-1α expressing fat tissue grafts 
Mesenchymal stromal cell (MSCs) are key cellular components for site-specific tissue regeneration. The chemokine stromal derived factor 1 alpha (SDF-1α) is known to attract stem cells via the C-X-C chemokine receptor-4 (CXCR4) receptor. The aim of the study was to develop a model for stem cell attraction using SDF-1α overexpressing fat tissue grafts. Murine MSCs were lentiviral transduced to express the genes for enhanced green fluorescent protein, firefly luciferace, and human CXCR4 (hCXCR4). Murine fat tissue was adenoviral transduced to express SDF-1α and red fluorescent protein transgenes. MSCs were cultured on transwells with SDF-1α containing supernatants from transduced fat tissue. The numbers of migrated MSCs in four groups (with hCXCR4 positive (+) or hCXCR4 negative (−) MSCs with or without SDF-1α containing supernatant) were investigated. After 36 h of culture, 9025 ± 925 cells migrated through the membrane of the transwells in group 1 (CXCR4+/SDF-1α+), 4817 ± 940 cells in group 2 (CXCR4-/SDF-1α+), 2050 ± 766 cells in group 3 (CXCR4+/SDF-1α−), and 2108 ± 426 cells in group 4 (CXCR4-/SDF-1α-). Both, the presence of SDF-1α and the expression of hCXCR4 significantly increased the migration rates (p < 0.0001). MSCs overexpressing the CXCR4 receptor by lentiviral transduction are highly attracted by medium from SDF-1α expressing fat tissue in vitro. Thus, SDF-1α activated tissue grafts may be a strategy to enhance site-specific musculoskeletal tissue regeneration.
PMCID: PMC4056675  PMID: 23281045
MSC migration; SDF-1; CXCR4; adenovirus; lentivirus
13.  Identification of E-Selectin as a Novel Target for the Regulation of Post-Natal Neovascularization: Implications for Diabetic Wound Healing 
Annals of Surgery  2010;252(4):625-634.
We previously reported that stromal cell-derived factor-1α (SDF-1α, a homing signal for recruiting endothelial progenitor cells (EPC) to areas of neovascularization), is down-regulated in diabetic wounds 1. We now investigate signals whereby mature endothelial cells (EC) and circulating EPC achieve SDF-1α-mediated EPC homing.
SDF-1α in diabetic wounds were therapeutically increased by injection of SDF-1α–engineered bone marrow-derived fibroblasts versus control cells (N= 48 (20, NOD), (28, STZ-C57)). PCR-array gene expression differences were validated by Western blotting and immunohistochemistry. The role of adhesion molecule(s) in mediating SDF-1α-induced EPC homing and wound healing was furthered studied using antagonists in vitro and in vivo.
Increasing wound SDF-1α via cell-base therapy promotes healing in diabetic mice (~20% increase in healing rates by day 3, p=0.006). SDF-1α increased EC-EPC adhesion and specifically upregulated E-selectin expression in human microvascular EC (2.3-fold increase, p<0.01). This effect was also significant in blood vessels of the experimental mice and resulted in increased wound neovascularization. The regulatory effects of SDF-1α on EC-EPC adhesion and EPC homing were specifically mediated by E-selectin, as the application of E-selectin antagonists significantly inhibited SDF-1α-induced EC-EPC adhesion, EPC homing, wound neovascularization, and wound healing.
SDF-1α–engineered cell-based therapy promotes diabetic wound healing in mice by specifically upregulating E-selectin expression in mature EC leading to increase EC-EPC adhesion, EPC homing and increased wound neovascularization. These findings provide novel insight into the signals underlying the biological effect of SDF-1α on EPC homing and point to E-selectin as a new potential target for therapeutic manipulation of EPC trafficking in diabetic wound healing.
PMCID: PMC3391745  PMID: 20881769
14.  Stromal Cell-Derived Factor-1β Potentiates Bone Morphogenetic Protein-2-Stimulated Osteoinduction of Genetically Engineered Bone Marrow-Derived Mesenchymal Stem Cells In Vitro 
Tissue Engineering. Part A  2012;19(1-2):1-13.
Skeletal injuries are among the most prevalent clinical problems and bone marrow-derived mesenchymal stem/stromal cells (BMSCs) have successfully been used for the treatment thereof. Stromal cell-derived factor-1 (SDF-1; CXCL12) is a member of the CXC chemokine family with multiple splice variants. The two most abundant variants, SDF-1α and SDF-1β, share identical amino acid sequences, except for four additional amino acids at the C-terminus of SDF-1β, which may mediate surface stabilization via glycosaminoglycans and protect SDF-1β from proteolytic cleavage, rendering it twice as potent as SDF-1α. Increasing evidence suggests that SDF-1 is involved in bone formation through regulation of recruitment, engraftment, proliferation, and differentiation of stem/progenitor cells. The underlying molecular mechanisms, however, have not yet been fully elucidated. In this study, we tested the hypothesis that SDF-1β can potentiate bone morphogenetic protein-2 (BMP-2)-stimulated osteogenic differentiation and chemotaxis of BMSCs in vitro. Utilizing retrovirus-mediated gene transfer to generate novel Tet-Off-SDF-1β BMSCs, we found that conditional SDF-1β expression is tightly regulated by doxycycline in a dose-dependent and temporal fashion, leading to significantly increased SDF-1β mRNA and protein levels. In addition, SDF-1β was found to enhance BMP-2-stimulated mineralization, mRNA and protein expression of key osteogenic markers, and regulate BMP-2 signal transduction via extracellular signal-regulated kinases 1/2 (Erk1/2) phosphorylation in genetically engineered BMSCs in vitro. We also showed that SDF-1β promotes the migratory response of CXC chemokine receptor 4 (CXCR4)-expressing BMSCs in vitro. Taken together, these data support that SDF-1β can play an important role in BMP-2-stimulated osteogenic differentiation of BMSCs and may exert its biological activity in both an autocrine and paracrine fashion.
PMCID: PMC3530941  PMID: 22779446
15.  Stromal Cell-Derived Factor-1 Receptor CXCR4-Overexpressing Bone Marrow Mesenchymal Stem Cells Accelerate Wound Healing by Migrating into Skin Injury Areas 
Cellular Reprogramming  2013;15(3):206-215.
Stromal cell-derived factor-1 (SDF-1) and its membrane receptor C-X-C chemokine receptor type 4 (CXCR4) are involved in the homing and migration of multiple stem cell types, neovascularization, and cell proliferation. This study investigated the hypothesis that bone marrow–derived mesenchymal stem cells (BMSCs) accelerate skin wound healing in the mouse model by overexpression of CXCR4 in BMSCs. We compared SDF-1 expression and skin wound healing times of BALB/c mice, severe combined immunodeficiency (SCID) mice, and immune system–deficient nude mice after 60Co radiation–induced injury of their bone marrow. The occurrence of transplanted adenovirus-transfected CXCR4-overexpressing male BMSCs in the wound area was compared with the occurrence of untransfected male BALB/c BMSCs in 60Co-irradiated female mice skin wound healing areas by Y chromosome marker analyses. The wound healing time of BALB/c mice was 14.00±1.41 days, whereas for the nude and SCID mice it was 17.16±1.17 days and 19.83±0.76 days, respectively. Male BMSCs could be detected in the surrounding areas of 60Co-irradiated female BALB/c mice wounds, and CXCR4-overexpressing BMSCs accelerated the wound healing time. CXCR4-overexpressing BMSCs migrate in an enhanced manner to skin wounds in a SDF-1–expression-dependent manner, thereby reducing the skin wound healing time.
PMCID: PMC3666362  PMID: 23713431
16.  miR-27b Represses Migration of Mouse MSCs to Burned Margins and Prolongs Wound Repair through Silencing SDF-1a 
PLoS ONE  2013;8(7):e68972.
Interactions between stromal cell-derived factor-1α (SDF-1α) and its cognate receptor CXCR4 are crucial for the recruitment of mesenchymal stem cells (MSCs) from bone marrow (BM) reservoirs to damaged tissues for repair during alarm situations. MicroRNAs are differentially expressed in stem cell niches, suggesting a specialized role in stem cell regulation. Here, we gain insight into the molecular mechanisms involved in regulating SDF-1α.
MSCs from green fluorescent protein transgenic male mice were transfused to irradiated recipient female C57BL/6 mice, and skin burn model of bone marrow-chimeric mice were constructed. Six miRNAs with differential expression in burned murine skin tissue compared to normal skin tissue were identified using microarrays and bioinformatics. The expression of miR-27b and SDF-1α was examined in burned murine skin tissue using quantitative real-time PCR (qPCR) and immunohistochemistry (IHC), enzyme-linked immunosorbent assay (ELISA). The Correlation of miR-27b and SDF-1α expression was analyzed by Pearson analysis Correlation. miRNAs suppressed SDF-1α protein expression by binding directly to its 3′UTR using western blot and luciferase reporter assay. The importance of miRNAs in MSCs chemotaxis was further estimated by decreasing SDF-1α in vivo and in vitro.
miR-23a, miR-27a and miR-27b expression was significantly lower in the burned skin than in the normal skin (p<0.05). We also found that several miRNAs suppressed SDF-1α protein expression, while just miR-27a and miR-27b directly bound to the SDF-1α 3′UTR. Moreover, the forced over-expression of miR-27a and miR-27b significantly reduced the directional migration of mMSCs in vitro. However, only miR-27b in burn wound margins significantly inhibited the mobilization of MSCs to the epidermis.
miR-27b may be a unique signature of the stem cell niche in burned mouse skin and can suppress the directional migration of mMSCs by targeting SDF-1α by binding directly to its 3′UTR.
PMCID: PMC3718818  PMID: 23894385
17.  The Expanding Family of Bone Marrow Homing Factors for Hematopoietic Stem Cells: Stromal Derived Factor 1 Is Not the Only Player in the Game 
The Scientific World Journal  2012;2012:758512.
The α-chemokine stromal derived factor 1 (SDF-1), which binds to the CXCR4 and CXCR7 receptors, directs migration and homing of CXCR4+ hematopoietic stem/progenitor cells (HSPCs) to bone marrow (BM) and plays a crucial role in retention of these cells in stem cell niches. However, this unique role of SDF-1 has been recently challenged by several observations supporting SDF-1-CXCR4-independent BM homing. Specifically, it has been demonstrated that HSPCs respond robustly to some bioactive lipids, such as sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P), and migrate in response to gradients of certain extracellular nucleotides, including uridine triphosphate (UTP) and adenosine triphosphate (ATP). Moreover, the responsiveness of HSPCs to an SDF-1 gradient is enhanced by some elements of innate immunity (e.g., C3 complement cascade cleavage fragments and antimicrobial cationic peptides, such as cathelicidin/LL-37 or β2-defensin) as well as prostaglandin E2 (PGE2). Since all these factors are upregulated in BM after myeloblative conditioning for transplantation, a more complex picture of homing emerges that involves several factors supporting, and in some situations even replacing, the SDF-1-CXCR4 axis.
PMCID: PMC3373139  PMID: 22701372
18.  A novel CXCR4 antagonist derived from human SDF-1β enhances angiogenesis in ischaemic mice 
Cardiovascular Research  2009;82(3):513-521.
The effects on angiogenesis of a novel CXC chemokine receptor 4 (CXCR4) antagonist, SDF-1βP2G, derived from human stromal cell-derived factor-1β (SDF-1β), were examined in a model of hind limb ischaemia in mice.
Methods and results
The antagonistic activities of SDF-1βP2G against CXCR4 were evaluated in vitro and in vivo and compared with phosphate-buffered saline and AMD3100 (a small bicyclam antagonist of SDF-1). Angiogenesis, muscle regeneration and the expression of pro-angiogenic factors were evaluated in ischaemic gastrocnemius muscles. Distant toxic effects of SDF-1βP2G were evaluated by inflammatory and apoptotic markers. SDF-1βP2G induced CXCR4 internalization and competitively inhibited the chemotaxis of SDF-1β but did not mediate migration, calcium influx, or the phosphorylation of Akt and extracellular signal-regulated kinase in cultured T-lymphoblastic leukaemia cells or H9C2 cells. SDF-1βP2G enhanced blood flow, angiogenesis, and muscle regeneration in ischaemic hind limbs, and the enhancement was significantly better than that of AMD3100. Markers of angiogenesis and progenitor cell migration, including phosphorylated Akt, vascular endothelial growth factor (VEGF), SDF-1 and CXCR4, were up-regulated by SDF-1βP2G and co-localized with CD31-positive cells. Neutralization of VEGF with its specific antibody abolished SDF-1βP2G-induced blood reperfusion and angiogenesis. No apparent inflammatory and apoptotic effects were found in heart, liver, kidneys, and testes after SDF-1βP2G administration.
Our findings indicate that the novel CXCR4 antagonist, SDF-1βP2G, can efficiently enhance ischaemic angiogenesis, blood flow restoration, and muscle regeneration without apparent adverse effects, most likely through a VEGF-dependent pathway.
PMCID: PMC2682612  PMID: 19196827
CXCR4 antagonist; SDF-1; AMD3100; Limb ischaemic injury; Angiogenesis
19.  Stromal cell-derived factor-1 overexpression induces gastric dysplasia through expansion of stromal myofibroblasts and epithelial progenitors 
Gut  2012;62(2):192-200.
Stromal cell-derived factor-1 (SDF-1/CXCL12), the main ligand for CXCR4, is overexpressed in human cancer. This study addressed the precise contribution of SDF-1 to gastric carcinogenesis.
SDF-1 transgenic mice were created and a Helicobacter-induced gastric cancer model was used in combination with H/K-ATPase-IL-1β mice. Gastric tissue was analysed by histopathology and cells isolated from the stomach were analysed by molecular biological methods.
Analysis of the H/K-ATPase/SDF-1 transgenic (SDF-Tg) mice showed that SDF-1 overexpression results in significant gastric epithelial hyperproliferation, mucous neck cell hyperplasia and spontaneous gastric dysplasia (wild-type mice 0/15 (0%) vs SDF-Tg mice 4/14 (28.6%), p=0.042, Fisher exact test) but has minimal effects on inflammation. SDF-Tg mice also showed a dramatic expansion of α-smooth muscle actin-positive myofibroblasts and CXCR4-expressing gastric epithelial cells in the progenitor zone, both of which preceded the development of significant gastritis or dysplasia. Gremlin 1-expressing mesenchymal stem cells, the putative precursors of myofibroblasts, were also increased within the dysplastic stomachs of SDF-Tg mice and showed chemotaxis in response to SDF-1 stimulation. SDF-1 overexpression alone resulted in minimal recruitment of haematopoietic cells to the gastric mucosa, although macrophages were increased late in the disease. When SDF-Tg mice were crossed with H/K-ATPase-IL-1β mice or infected with Helicobacter felis, however, there were dramatic synergistic effects on recruitment of bone marrow-derived cells and progression to preneoplasia.
Activation of the SDF-1/CXCR4 axis can contribute to early stages of carcinogenesis primarily through recruitment of stromal cells and modulation of the progenitor niche.
PMCID: PMC4136650  PMID: 22362916
20.  Quantitation of CXCR4 Expression in Myocardial Infarction using 99mTc-Labeled SDF-1α 
The chemokine stromal cell-derived factor 1α (SDF-1α, CXCL12) and its receptor CXCR4 are implicated as key mediators of hematopoietic stem cell retention, cancer metastasis, and HIV infection. Their role in myocardial infarction is not as well defined. The non-invasive in vivo quantitation of CXCR4 expression is central to understanding its importance in these diverse processes as well in the cardiac response to injury.
Using high specific activity [99mTc-MAS3]-NHS prepared by solid-phase pre-loading, recombinant SDF-1α was radiolabeled under aprotic conditions and purified by gel-filtration chromatography (GFC). Radiotracer stability and transmetallation under harsh conditions were quantified by GFC. Affinity, specificity, and Bmax were quantified, with adenoviral-expressed CXCR4 on non-expressing cells and endogenous receptor on rat neonatal cardiomyocytes, using a high-throughput live-cell binding assay. Blood half-life, biodistribution, and clearance of intravenously injected [99mTc-MAS3]-SDF-1α were quantified in Sprague-Dawley rats before and after experimentally induced myocardial infarction.
[99mTc-MAS3]-SDF-1α could be prepared in 2 hr total with a specific activity of 8.0 × 107 MBq/mmol (2,166 Ci/mmol) and a radiochemical purity >98%. Degradation of the radiotracer after boiling for 5 min, with and without 1 mM dithiothreitol (DTT), and transmetallation in 100% serum at 37°C for 4 hr, were negligible. [99mTc-MAS3]-SDF-1α exhibits high specificity for CXCR4 on the surface of living rat neonatal cardiomyocytes, with an affinity of 2.7 ± 0.9 nM and a Bmax of 4.8 × 104 binding sites per cell. After intravenous injection, 99mTc-labeled SDF-1α displays a blood half-life of 25.8 ± 4.6 min, rapid renal clearance with only 26.2 ± 6.1% ID remaining in the carcass at 2 hr, consistently low uptake in most organs (<0.1% ID/g), and no evidence of blood-brain barrier penetration. In the setting of myocardial infarction, CXCR4 expression levels in the myocardium increased over 5-fold, as quantified using [99mTc-MAS3]-SDF-1α and confirmed using confocal immunofluorescence.
We describe a 99mTc-labeled SDF-1α radiotracer that can be used as a sensitive and specific probe for CXCR4 expression in vivo, and demonstrate that this radiotracer is able to quantify changes in CXCR4 expression under different physiologic and pathologic states. Taken together, CXCR4 levels should now be quantifiable in vivo in a variety of animal model systems of human diseases.
PMCID: PMC2712574  PMID: 18483105
SDF-1α; CXCR4; Chemokines; SPECT Radiotracers; Myocardial Infarction
21.  CXCR4 Expression and Treatment with SDF-1α or Plerixafor Modulate Proliferation and Chemosensitivity of Colon Cancer Cells1 
Translational Oncology  2013;6(2):124-132.
BACKGROUND: Signaling through stromal cell-derived factor-1α (SDF-1α), strongly secreted by bone marrow stromal cells and the CXC chemokine receptor 4 (CXCR4) exposed on tumor cells has pivotal roles in proliferation, metastasis, and tumor cell “dormancy.” Dormancy is associated with cytostatic drug resistance and is probably a property of tumor stem cells and minimal residual disease. Thus, hampering the SDF-1α/CXCR4 cross talk by a CXCR4 antagonist like Plerixafor (AMD3100) should overcome tumor cell dormancy bymobilization of tumor cells from “sanctuary” niches. Our aim was to elucidate the direct effects exerted by SDF-1α and Plerixafor on proliferation, chemosensitivity, and apoptosis of CXCR4-expressing tumor cells. METHODS: The ability of SDF-1α and Plerixafor to regulate intracellular signaling, proliferation, and invasion was investigated using two colon cancer cell lines (HT-29 and SW480) with either high endogenous or lentiviral expression of CXCR4 compared to their respective low CXCR4-expressing counterparts as a model system. Efficacy of Plerixafor on sensitivity of these cell lines against 5-fluorouracil, irinotecan, or oxaliplatin was determined in a cell viability assay as well as stroma-dependent cytotoxicity and apoptosis assays. RESULTS: SDF-1α increased proliferation, invasion, and ERK signaling of endogenously and lentivirally CXCR4-expressing cells. Exposure to Plerixafor reduced proliferation, invasion, and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling. Combination of chemotherapy with Plerixafor showed an additive effect on chemosensitivity and apoptosis in CXCR4-overexpressing cells. An SDF-1-secreting feeder layer provideda“protective niche” for CXCR4-overexpressing cells resulting in decreased chemosensitivity. CONCLUSION: CXCR4-antagonistic therapy mobilizes and additionally sensitizes tumor cells toward cytoreductive chemotherapy.
PMCID: PMC3610551  PMID: 23544165
22.  The Chemokine Stromal Cell-Derived Factor-1 Regulates GABAergic Inputs to Neural Progenitors in the Postnatal Dentate Gyrus 
Stromal cell-derived factor-1 (SDF-1) and its receptor CXC chemokine receptor 4 (CXCR4) are important regulators of the development of the dentate gyrus (DG). Both SDF-1 and CXCR4 are also highly expressed in the adult DG. We observed that CXCR4 receptors were expressed by dividing neural progenitor cells located in the subgranular zone (SGZ) as well as their derivatives including doublecortin-expressing neuroblasts and immature granule cells. SDF-1 was located in DG neurons and in endothelial cells associated with DG blood vessels. SDF-1-expressing neurons included parvalbumin-containing GABAergic interneurons known as basket cells. Using transgenic mice expressing an SDF-1-mRFP1 (monomeric red fluorescence protein 1) fusion protein we observed that SDF-1 was localized in synaptic vesicles in the terminals of basket cells together with GABA-containing vesicles. These terminals were often observed to be in close proximity to dividing nestin-expressing neural progenitors in the SGZ. Electrophysiological recordings from slices of the DG demonstrated that neural progenitors received both tonic and phasic GABAergic inputs and that SDF-1 enhanced GABAergic transmission, probably by a postsynaptic mechanism. We also demonstrated that, like GABA, SDF-1 was tonically released in the DG and that GABAergic transmission was partially dependent on coreleased SDF-1. These data demonstrate that SDF-1 plays a novel role as a neurotransmitter in the DG and regulates the strength of GABAergic inputs to the pool of dividing neural progenitors. Hence, SDF-1/CXCR4 signaling is likely to be an important regulator of adult neurogenesis in the DG.
PMCID: PMC2720755  PMID: 18579746
cytokine; dentate gyrus; GABA; hippocampus; neurogenesis; transgenic; SDF-1/CXCL12; CXCR4
23.  Overexpression of SDF-1α Enhanced Migration and Engraftment of Cardiac Stem Cells and Reduced Infarcted Size via CXCR4/PI3K Pathway 
PLoS ONE  2012;7(9):e43922.
Cardiac stem cells (CSCs) can home to the infarcted area and regenerate myocardium. Stromal cell-derived factor-1α/C-X-C chemokine receptor type 4 (SDF-1α/CXCR4) axis is pivotal in inducing CSCs migration. However, the mechanisms remain unclear. This study set out to detect if SDF-1α promotes migration and engraftment of CSCs through the CXCR4/PI3K (phosphatidylinositol 3-kinase) pathway. In the in vitro experiment, c-kit+ cells were isolated from neonatal mouse heart fragment culture by magnetic cell sorting. Fluorescence-activated cell sorting results demonstrated that a few c-kit+ cells expressed CD45 (4.54%) and Sca-1 (2.58%), the hematopoietic stem cell marker. Conditioned culture could induce c-kit+ cells multipotent differentiation, which was confirmed by cardiac troponin I (cTn-I), α-smooth muscle actin (α-SMA), and von Willebrand factor (vWF) staining. In vitro chemotaxis assays were performed using Transwell cell chambers to detect CSCs migration. The results showed that the cardiomyocytes infected with rAAV1-SDF-1α-eGFP significantly increased SDF-1α concentration, 5-fold more in supernatant than that in the control group, and subsequently attracted more CSCs migration. This effect was diminished by administration of AMD3100 (10 µg/ml, CXCR4 antagonist) or LY294002 (20 µmol/L, PI3K inhibitor). In myocardial infarction mice, overexpression of SDF-1α in the infarcted area by rAAV1-SDF-1α-eGFP infection resulted in more CSCs retention to the infarcted myocardium, a higher percentage of proliferation, and reduced infarcted area which was attenuated by AMD3100 or ly294002 pretreatment. These results indicated that overexpression of SDF-1α enhanced CSCs migration in vitro and engraftment of transplanted CSCs and reduced infarcted size via CXCR4/PI3K pathway.
PMCID: PMC3439464  PMID: 22984452
24.  Extracellular calcium increases CXCR4 expression on bone marrow-derived cells and enhances pro-angiogenesis therapy 
Cell surface receptors play major roles in the mobilization and homing of progenitor cells from the bone marrow to peripheral tissues. CXCR4 is an important receptor that regulates homing of leucocytes and endothelial progenitors in response to the chemokine stromal cell-derived factor-1 (SDF-1). Ionic calcium is also known to regulate chemotaxis of selective bone marrow cells (BMCs) through the calcium-sensing receptor, CaR. Here we show that calcium regulates CXCR4 expression and BMC responses to SDF-1. CaCl2 treatment of BMC induced a time- and dose-dependent increase in both the transcription and cell surface expression of CXCR4. BMC subpopulations expressing VEGFR2+, CD34+ and cKit+/Sca-1+ were especially sensitive to calcium. The effects were blocked by calcium influx inhibitors, anti-CaR antibody and the protein synthesis inhibitor cycloheximide, but not by the CXCR4 antagonist AMD3100. Calcium treatment also enhanced SDF-1-mediated CXCR4 internalization. These changes were reflected in significantly improved chemotaxis by SDF-1, which was abolished by AMD3100 and by antibody against CXCR4. Calcium pre-treatment improved homing of CD34+ BMCs to ischemic muscle in vivo, and enhanced revascularization in ischemic mouse hindlimbs. Our results identify calcium as a positive regulator of CXCR4 expression that promotes stem cell mobilization, homing and therapy.
PMCID: PMC3124762  PMID: 19220581
CXCR4; SDF-1; calcium; progenitor cells; bone marrow
25.  Paracrine Modulation of CXCR4 by IGF-1 and VEGF: Implications for Choroidal Neovascularization 
Adult vascular maintenance and repair are mediated in part by endothelial progenitor cells, recruited by chemokines such as stromal-derived factor (SDF)-1. The authors examined the interaction between growth factors such as IGF and VEGF and the SDF-1 receptor CXCR4, and showed that localized inhibition of CXCR4 may prove beneficial in treating aberrant neovascular disease.
Modulators of angiogenesis typically work in an orchestrated manner. The authors examined the interaction between insulinlike growth factor (IGF)-1, vascular endothelial growth factor (VEGF), and stromal derived factor (SDF)-1 in vivo and in vitro using angiogenesis models.
The angiogenic effect of SDF-1, alone or in combination with IGF-1 and VEGF, was assessed in human lung microvascular endothelial cells using capillary tube formation and thymidine incorporation. Immunohistochemical analysis for CD31, SDF-1, and CXCR4 was performed on mouse eyes 2 weeks after the initiation of laser rupture of Bruch's membrane, a choroidal neovascularization (CNV) model. CXCR4 antagonist and CXCR4 blocking antibody were tested on inhibition of CNV lesion size in this model. Real-time PCR was used to determine mRNA levels for SDF-1, VEGF, IGF-1, and their cognate receptors in the retinal pigment epithelium/choroid complex of mice that underwent this CNV model.
IGF-1 and VEGF demonstrated an additive effect on SDF-1–induced in vitro angiogenesis. CXCR4 immunoreactivity was present in both normal and laser-injured mice at the laser burn site and at the ganglion cell layer, the anterior portion of the inner nuclear layer, photoreceptors, and choroidal stroma. SDF-1 was observed in identical locations but was not seen in photoreceptors. mRNA levels for SDF-1, VEGF, and IGF-1 and their receptors were increased after laser injury. CXCR4-neutralizing antibody reduced neovascularization when injected subretinally but not intraperitoneally or intravitreally.
The potent proangiogenic factors IGF-1 and VEGF both stimulate SDF-1–induced angiogenesis. Local inhibition of CXCR4 is required for an antiangiogenic effect in CNV lesions.
PMCID: PMC2868476  PMID: 20007826

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