Recruitment of primitive peripheral blood cells: synergism of interleukin 12 with interleukin 6 and stromal cell-derived FACTOR-1

Deficiency in Fpr2 results in reduced numbers of Lin-cKit+Sca1+ myeloid progenitor cells

The Lin-c-Kit+ Sca-1+ cell population in the bone marrow (BM) serves as the direct precursor for differentiation of myeloid cells. In this study, we report that deficiency in Fpr2, a G protein-coupled chemoattractant receptor in mice, is associated with reduced BM nucleated cells, including CD31+Ly6C+ (granulocytes and monocytes), CD31-/Ly6Cint (granuloid cells), and CD31-/Ly6Chigh (predominantly monocytes) cells. In particular, the number of Lin-c-Kit+Sca-1+ (LKS) cells was reduced in Fpr2-/- mouse BM. This was supported by observations of the reduced incorporation of intraperitoneally injected bromodeoxyuridine by cells in the c-Kit+ population from Fpr2-/- mouse BM. Purified c-Kit+ cells from Fpr2-/- mice showed reduced expansion when cultured in vitro with stem cell factor (SCF). SCF/c-Kit-mediated phosphorylation of P38, STAT1, Akt (Thr-308), and Akt (Ser-473) was also significantly reduced in c-Kit+ cells from Fpr2-/- mice. Furthermore, Fpr2 agonists enhanced SCF-induced proliferation of c-Kit+ cells. Colony-forming unit assays revealed that CFU-granulocyte-macrophage formation of BM cells from Fpr2-/- mice was significantly reduced. After heat-inactivated bacterial stimulation in the airway, the expansion of c-kit+ Sca-1+ cells in BM and recruitment of Ly6G+ cells to the lungs and CD11b+Ly6C+TNFα+ cells to the spleen of Fpr2-/- mice was significantly reduced. These results demonstrate an important role for Fpr2 in the development of myeloid lineage precursors in mouse BM.

Total body irradiation is permissive for mesenchymal stem cell-mediated new bone formation following local transplantation

Skeletal injury is a major clinical challenge accentuated by the decrease of bone marrow-derived mesenchymal stem/stromal cells (BMSCs) with age or disease. Numerous experimental and clinical studies have revealed that BMSCs hold great promise for regenerative therapies due to their direct osteogenic potential and indirect trophic/paracrine actions. Increasing evidence suggests that stromal cell-derived factor-1 (SDF-1) is involved in modulating the host response to the injury. Common problems with BMSC therapy include poor cell engraftment, which can be addressed by total body irradiation (TBI) prior to transplantation. In this study, we tested the hypothesis that direct tibial transplantation of BMSCs drives endogenous bone formation in a dose-dependent manner, which is enhanced by TBI, and investigated the potential role of SDF-1 in facilitating these events. We found that TBI is permissive for transplanted BMSCs to engraft and contribute to new bone formation. Bone marrow (BM) interstitial fluid analysis revealed no differences of SDF-1 splice variants in irradiated animals compared to controls, despite the increased mRNA and protein levels expressed in whole BM cells. This correlated with increased dipeptidyl peptidase IV activity and the failure to induce chemotaxis of BMSCs in vitro. We found increased mRNA expression levels of the major SDF-1-cleaving proteases in whole BM cells from irradiated animals suggesting distinct spatial differences within the BM in which SDF-1 may play different autocrine and paracrine signaling roles beyond the immediate cell surface microenvironment.

Mesenchymal stem cell expression of stromal cell-derived factor-1β augments bone formation in a model of local regenerative therapy

Bone has the potential for spontaneous healing. However, this process often fails in patients with co-morbidities requiring clinical intervention. Numerous studies have revealed that bone marrow-derived mesenchymal stem/stromal cells (BMSCs) hold great potential for regenerative therapies. Common problems include poor cell engraftment, which can be addressed by irradiation prior to transplantation. Increasing evidence suggests that stromal cell-derived factor-1 (SDF-1) is involved in bone formation. However, osteogenic contributions of the beta splice variant of SDF-1 (SDF-1β), which is highly expressed in bone, remain unclear. Using the tetracycline (Tet)-regulatory system we have shown that SDF-1β enhances BMSC osteogenic differentiation in vitro. Here we test the hypothesis that SDF-1β augments bone formation in vivo in a model of local BMSC transplantation following irradiation. We found that SDF-1β, expressed at high levels in Tet-Off-SDF-1β BMSCs, augments the cell-mediated therapeutic effects resulting in enhanced bone formation, as evidenced by ex vivo μCT and bone histomorphometry. The data demonstrate the specific contribution of SDF-1β to BMSC-mediated bone formation, and validate the feasibility of the Tet-Off technology to regulate SDF-1β expression in vivo. In conclusion, SDF-1β provides potent synergistic effects supporting BMSC-mediated bone formation and appears a suitable candidate for optimization of bone augmentation in translational protocols.

Topical cooling (icing) delays recovery from eccentric exercise-induced muscle damage

It is generally thought that topical cooling can interfere with blood perfusion and may have positive effects on recovery from a traumatic challenge. This study examined the influence of topical cooling on muscle damage markers and hemodynamic changes during recovery from eccentric exercise. Eleven male subjects (age 20.2 ± 0.3 years) performed 6 sets of elbow extension at 85% maximum voluntary load and randomly assigned to topical cooling or sham groups during recovery in a randomized crossover fashion. Cold packs were applied to exercised muscle for 15 minutes at 0, 3, 24, 48, and 72 hours after exercise. The exercise significantly elevated circulating creatine kinase-MB isoform (CK-MB) and myoglobin levels. Unexpectedly, greater elevations in circulating CK-MB and myoglobin above the control level were noted in the cooling trial during 48-72 hours of the post-exercise recovery period. Subjective fatigue feeling was greater at 72 hours after topical cooling compared with controls. Removal of the cold pack also led to a protracted rebound in muscle hemoglobin concentration compared with controls. Measures of interleukin (IL)-8, IL-10, IL-1β, and muscle strength during recovery were not influenced by cooling. A peak shift in IL-12p70 was noted during recovery with topical cooling. These data suggest that topical cooling, a commonly used clinical intervention, seems to not improve but rather delay recovery from eccentric exercise-induced muscle damage.

Correlation between the immature characteristics of umbilical cord blood-derived mesenchymal stem cells and engraftment of hematopoietic stem cells in NOD/SCID mice

Umbilical cord blood (UCB)-derived mesenchymal stem cells (MSC) facilitate the engraftment of human (h) hematopoietic stem cells when transplanted simultaneously in animal and human studies. However, the type of MSCs that preferentially enhance the engraftment of HSCs is unknown. Recent studies have shown that MSCs derived from a single source are heterogeneous in terms of cell size, morphology, proliferation rate, and differentiation potential. This study was designed to investigate the properties of UCB-MSCs, which influence the engraftment of hHSCs in a NOD/SCID mouse model. We categorized MSCs as being the most effective (UCB-352 MSCs) or the least effective (UCB-156 MSCs) at promoting the homing and engraftment of HSCs, and compared the characteristics of these 2 MSC populations. We observed that the 2 populations showed differences in characteristics typical of immature MSCs, and related to proliferation potential. We showed that UCB-352 MSCs, which proliferate quickly, preferentially enhanced the engraftment of HSCs in NOD/SCID mice. In addition, we observed differences in the pattern of both PODXL and Oct4 expression, and in the levels of cytokines such as SDF-1 and SCF using flow cytometry and membrane arrays. The more effective UCB-352 MSCs expressed higher levels of PODXL and Oct4, which were associated with immaturity, than did the UCB-156 MSCs. Furthermore, UCB-352 cells secreted greater levels of SDF-1 and SCF, both of which are required for hematopoiesis. We propose that the proliferation potential of UCB-MSCs, coupled with their immature characteristics, may serve as a novel standard to promote the homing and engraftment of HSCs.

Over-expression of CXCR4 on mesenchymal stem cells augments myoangiogenesis in the infarcted myocardium

Bone marrow mesenchymal stem cells (MSCs) participate in myocardial repair following myocardial infarction. However, their in vivo reparative capability is limited due to lack of their survival in the infarcted myocardium. To overcome this limitation, we genetically engineered male rat MSCs overexpressing CXCR4 in order to maximize the effect of stromal cell-derived factor-1alpha (SDF-1alpha) for cell migration and regeneration. MSCs were isolated from adult male rats and cultured. Adenoviral transduction was carried out to over-express either CXCR4/green fluorescent protein (Ad-CXCR4/GFP) or Ad-null/GFP alone (control). Flow cytometry was used to identify and isolate GFP/CXCR4 over-expressing MSCs for transplantation. Female rats were assigned to one of four groups (n=8 each) to receive GFP-transduced male MSCs (2 x 10(6)) via tail vein injection 3 days after ligation of the left anterior descending (LAD) coronary artery: GFP-transduced MSCs (Ad-null/GFP-MSCs, group 1) or MSCs over-expressing CXCR4/GFP (Ad-CXCR4/GFP-MSCs, group 2), or Ad-CXCR4/GFP-MSCs plus SDF-1alpha (50 ng/microl) (Ad-CXCR4/GFP-MSCs/SDF-1alpha, group 3), or Ad-miRNA targeting CXCR4 plus SDF-1alpha (Ad-miRNA/GFP-MSCs+SDF-1alpha treatment, group 4). Cardiodynamic data were obtained 4 weeks after induction of regional myocardial infarction (MI) using echocardiography after which hearts were harvested for immunohistochemical studies. The migration of GFP and Y-chromosome positive cells increased significantly in the peri- and infarct areas of groups 2 and 3 compared to control group (p<0.05), or miRNA-CXCR4 group (p<0.01). The number of CXCR4 positive cells in groups 2, 3 was intimately associated with angiogenesis and myogenesis. MSCs engraftment was blocked by pretreatment with miRNA (group 4). Cardiac function was significantly improved in rats receiving MSCs over-expressing CXCR4 alone or with SDF-1alpha. The up-regulation of matrix metalloproteinases (MMPs) by CXCR4 overexpressing MSCs perhaps facilitated their engraftment in the collagenous tissue of the infarcted area. CXCR4 over-expression led to enhance in vivo mobilization and engraftment of MSCs into ischemic area where these cells promoted neomyoangiogenesis and alleviated early signs of left ventricular remodeling.

Interferon gamma has dual potential in inhibiting or promoting survival and growth of hematopoietic progenitors: interactions with stromal cell-derived factor 1

We explored the possibility that interferon gamma (IFN-gamma) has bidirectional functions in the survival and growth of hematopoietic progenitors, especially with regard to interactions with stromal cell-derived factor 1 (SDF-1). IFN-gamma partially rescued normal bone marrow CD34+ cells and colony-forming cells from apoptosis induced by serum and hematopoietic growth factor (HGF) deprivation, and SDF-1 further enhanced cell survival. Short-term IFN-gamma treatment of CD34+ cells in the absence of serum and HGFs enhanced the clonal growth of the cells in synergy with SDF-1. In contrast, IFN-gamma inhibited the clonal growth of hematopoietic progenitor cells in a standard methylcellulose clonogenic assay and inhibited the HGF-mediated survival of normal CD34+ cells. The addition of SDF-1 did not alter these outcomes. IFN-gamma did not enhance SDF-1-induced activation of PI3K/Akt or up-regulate the expression of CXCR4 or its function in bone marrow CD34+ cells. IFN-gamma up-regulated Socs1 messenger RNA expression in normal CD34+ cells, which was further enhanced with the addition of HGFs. These results indicate that IFN-gamma, partly in concert with SDF-1, exerts dual effects on the survival and growth of hematopoietic progenitor cells; the effects of IFN-gamma on hematopoietic progenitor cells can differ, depending on the particular in vitro experimental conditions, especially the presence of HGFs.

Overexpression of stromal cell-derived factor-1 enhances endothelium-supported transmigration, maintenance, and proliferation of hematopoietic progenitor cells

To clarify the direct effects of aberrant overexpression of stromal cell-derived factor-1 (SDF-1) by the human endothelium on circulating progenitor cells, we overexpressed the SDF-1 gene in human umbilical vein endothelial cells using an adenoviral vector (HUVEC/AdeSDF-1) and examined the endothelium-supported trafficking and growth of hematopoietic progenitor cells (HPCs) in mobilized peripheral blood (mPB). In culture, the HUVEC/AdeSDF-1 monolayers induced the migration of mPB CD34(+) cells underneath the endothelium within a few hours, whereas HUVEC monolayers that expressed the LacZ gene (HUVEC/AdeLacZ) did not have this effect. In the Transwell system, the HUVEC/AdeSDF-1 cells supported a higher level of spontaneous transmigration of mPB CD34(+) cells than did the HUVEC/AdeLacZ cells. The co-culturing of mPB CD34(+) cells with HUVEC/ AdeSDF-1 cells led to a greater expansion of CD45(+) cells and colony-forming cells and reduced cellular apoptosis. Furthermore, the co-culturing of mPB CD34(+) cells with HUVEC/AdeSDF-1 cells led to the formation of numerous cobblestone-like areas, whereas co-cultures of mPB CD34(+) cells and HUVEC/AdeLacZ supported only a few cobblestone-like areas. These results indicate that SDF- 1 produced by endothelial cells plays an important role not only in the transmigration but also in the growth of HPCs that are in contact with endothelial cells. Our findings suggest that the enhanced expression and production of SDF-1 in the endothelium are essential steps for stem cell or progenitor cell recruitment to specific tissues and for the maintenance of these cells in situ.

Bone marrow stem cell transplantation for cardiac repair

Cardiomyocytes respond to physiological or pathological stress only by hypertrophy and not by an increase in the number of functioning cardiomyocytes. However, recent evidence suggests that adult cardiomyocytes have the ability, albeit limited, to divide to compensate for the cardiomyocyte loss in the event of myocardial injury. Similarly, the presence of stem cells in the myocardium is a good omen. Their activation to participate in the repair process is, however, hindered by some as-yet-undetermined biological impediments. The rationale behind the use of adult stem cell transplantation is to supplement the inadequacies of the intrinsic repair mechanism of the heart and compensate for the cardiomyocyte loss in the event of injury. Various cell types including embryonic, fetal, and adult cardiomyocytes, smooth muscle cells, and stable cell lines have been used to augment the declining cardiomyocyte number and cardiac function. More recently, the focus has been shifted to the use of autologous skeletal myoblasts and bone marrow-derived stem cells. This review is a synopsis of some interesting aspects of the fast-emerging field of bone marrow-derived stem cell therapy for cardiac repair.

Cycling G1 CD34+/CD38+Cells Potentiate the Motility and Engraftment of Quiescent G0 CD34+/CD38−/lowSevere Combined Immunodeficiency Repopulating Cells

The mechanism of human stem cell expansion ex vivo is not fully understood. Furthermore, little is known about the mechanisms of human stem cell homing/repopulation and the role that differentiating progenitor cells may play in these processes. We report that 2- to 3-day in vitro cytokine stimulation of human cord blood CD34(+)-enriched cells induces the production of short-term repopulating, cycling G1 CD34(+)/CD38(+) cells with increased matrix metalloproteinase (MMP)-9 secretion as well as increased migration capacity to the chemokine stromal cell-derived factor-1 (SDF-1) and homing to the bone marrow of irradiated nonobese diabetic severe/combined immunodeficiency (NOD/SCID) mice. These cycling G1 cells enhance SDF-1-mediated in vitro migration and in vivo homing of quiescent G0 CD34(+) cells, which is partially abrogated after inhibition of MMP-2/-9 activity. Moreover, the engraftment potential of quiescent G0 SCID repopulating cells (SRCs) is also increased by the cycling G1 CD34(+)/CD38(+) cells. This effect is significantly abrogated after incubation of cycling G1 cells with a neutralizing anti-CXCR4 antibody. Our data suggest synergistic interactions between accessory cycling G1 CD34(+)/CD38(+) committed progenitor cells and quiescent, primitive G0 CD34(+)/CD38(-/low) SRC/stem cells, the former increasing the motility and engraftment potential of the latter, partly via secretion of MMP-9.

Overexpression of CXCR4 on human CD34+ progenitors increases their proliferation, migration, and NOD/SCID repopulation

A major limitation to clinical stem cell-mediated gene therapy protocols is the low levels of engraftment by transduced progenitors. We report that CXCR4 overexpression on human CD34+ progenitors using a lentiviral gene transfer technique helped navigate these cells to the murine bone marrow and spleen in response to stromal-derived factor 1 (SDF-1) signaling. Cells overexpressing CXCR4 exhibited significant increases in SDF-1-mediated chemotaxis and actin polymerization compared with control cells. A major advantage of CXCR4 overexpression was demonstrated by the ability of transduced CD34+ cells to respond to lower, physiologic levels of SDF-1 when compared to control cells, leading to improved SDF-1-induced migration and proliferation/survival, and finally resulting in significantly higher levels of in vivo repopulation of nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice including primitive CD34+/CD38(-/low) cells. Importantly, no cellular transformation was observed following transduction with the CXCR4 vector. Unexpectedly, we documented lack of receptor internalization in response to high levels of SDF-1, which can also contribute to increased migration and proliferation by the transduced CD34+ cells. Our results suggest CXCR4 overexpression for improved definitive human stem cell motility, retention, and multilineage repopulation, which could be beneficial for in vivo navigation and expansion of hematopoietic progenitors.

Expression of CXCR4 and CXCL12 (SDF-1) in human prostate cancers (PCa) in vivo

Human prostate cancers (PCa) express great variability in their ability to metastasize to bone. The identification of molecules associated with aggressive phenotypes will help to define PCa subsets and will ultimately lead to better treatment strategies. The chemokine stromal-derived factor-1 (SDF-1 or CXCL12) and its receptor CXCR4 are now known to modulate the migration and survival of an increasing array of normal and malignant cell types including breast, pancreatic cancers, glioblastomas, and others. The present investigation extends our previous investigations by determining the expression of CXCR4 and CXCL12 in humans using high-density tissue microarrays constructed from clinical samples obtained from a cohort of over 600 patients. These data demonstrate that CXCR4 protein expression is significantly elevated in localized and metastastic cancers. At the RNA level, human PCa tumors also express CXCR4 and message, but overall, they were not significantly different suggesting post-transcriptional regulation of the receptor plays a major role in regulating protein expression. Similar observations were made for CXCL12 message, but in this case more CXCL12 message was expressed by metastastic lesions as compared to normal tissues. PCa cell lines also express CXCL12 mRNA, and regulate mRNA expression in response to CXCL12 and secrete biologically active protein. Furthermore, neutralizing antibody to CXCL12 decreased the proliferation of bone homing LNCaP C4-2B and PC3 metastastic tumor cells. These investigations provide important new information pertaining to the molecular basis of how tumors may 'home' to bone, and the mechanisms that may account for their growth in selected end organs.

Mechanism of human stem cell migration and repopulation of NOD/SCID and B2mnull NOD/SCID mice. The role of SDF-1/CXCR4 interactions

The mechanism of hematopoietic stem cell migration and repopulation is not fully understood. Murine fetuses that lack the chemokine stromal-derived factor one (SDF-1null) or its receptor CXCR4 (CXCR4null) have multiple defects that are lethal, including impaired bone marrow hematopoiesis. These results suggest a major role for SDF-1/CXCR4 interactions in murine stem cell homing from the fetal liver into the bone marrow and its repopulation during development. SDF-1 is highly conserved between different species. Human and murine SDF-1 are cross-reactive and differ in one amino acid. Recently, we reported that SDF-1 and CXCR4 are essential for homing and repopulation of immune-deficient NOD/SCID and B2mnull NOD/SCID mice by human stem cells. In addition, immature human CD34+ cells and primitive CD34+/CD38-/low cells, which do not migrate toward a gradient of SDF-1 in vitro, and do not home and repopulate in vivo the murine bone marrow, can become functional repopulating cells by short-term 16-48 hr in vitro stimulation with cytokines such as SCF and IL-6 prior to transplantation. These cytokines increase surface CXCR4 expression, migration toward SDF-1, and in vivo homing and repopulation. We discuss the pleiotropic roles of SDF-1/CXCR4 interactions in human stem cell migration, development, and repopulation in transplanted immune-deficient mice.

Induction of the chemokine stromal-derived factor-1 following DNA damage improves human stem cell function

The chemokine stromal-derived factor-1 (SDF-1) controls many aspects of stem cell function. Details of its regulation and sites of production are currently unknown. We report that in the bone marrow, SDF-1 is produced mainly by immature osteoblasts and endothelial cells. Conditioning with DNA-damaging agents (ionizing irradiation, cyclophosphamide, and 5-fluorouracil) caused an increase in SDF-1 expression and in CXCR4-dependent homing and repopulation by human stem cells transplanted into NOD/SCID mice. Our findings suggest that immature osteoblasts and endothelial cells control stem cell homing, retention, and repopulation by secreting SDF-1, which also participates in host defense responses to DNA damage.