Stromal cell-derived factor 1 regulates primitive hematopoiesis by suppressing apoptosis and by promoting G(0)/G(1) transition in CD34(+) cells: evidence for an autocrine/paracrine mechanism

GPRASP protein deficiency triggers lymphoproliferative disease by affecting B-cell differentiation

Gprasp1 and Gprasp2 encode proteins that control the stability and cellular trafficking of CXCR4, a master regulator of hematopoiesis whose dynamic regulation is required for appropriate trafficking of B-cells in the germinal center (GC). Here, we report that Gprasp1 and Gprasp2-deficient B-cells accumulate in the GC and show transcriptional abnormalities, affecting the mechanisms controlling Aicda expression and exposing them to excessive somatic hypermutation. Consequently, about 30% of mice transplanted with Gprasp-deficient hematopoietic stem and progenitor cells developed a biologically aggressive and fatal B-cell hyperproliferative disease by 20-50 weeks posttransplant. Histological and molecular profiling reveal that Gprasp1- and Gprasp2-deficient neoplasms morphologically resemble human high-grade B-cell lymphomas of germinal center origin with shared morphologic features of both Burkitt Lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL), and molecular features consistent with DLBCL, as well as elevated mutational burden and heterogenous transcriptional and mutational signature. Thus, reduced Gprasp1 and Gprasp2 gene expression perturbs B-cell maturation and increases the risk of B-cell neoplasms of germinal center origin. As this model recapitulates the essential features of the heterogenous group of human hematopoietic malignancies, it could be a powerful tool to interrogate the mechanisms of lymphomagenesis for these cancers.

CXCR3-independent role of CXCL10 in alveolar epithelial repair

The alveolar type II epithelial cells (AEC2s) act as stem cells in the lung for alveolar epithelial maintenance and repair. Chemokine C-X-C motif chemokine 10 (CXCL10) is expressed in injured tissues, modulating multiple cellular functions. AEC2s, previously reported to release chemokines to recruit leukocytes, were found in our study to secrete CXCL10 after bleomycin injury. We found that Sftpc-Cxcl10 transgenic mice were protected from bleomycin injury. The transgenic mice showed an increase in the AEC2 population in the lung by flow cytometry analysis. Both endogenous and exogenous CXCL10 promoted the colony formation efficiency of AEC2s in a three-dimensional (3-D) organoid growth assay. We identified that the regenerative effect of CXCL10 was CXCR3 independent using Cxcr3-deficient mice, but it was related to the TrkA pathway. Binding experiments showed that CXCL10 interacted with TrkA directly and reversibly. This study demonstrates a previously unidentified AEC2 autocrine signaling of CXCL10 to promote their regeneration and proliferation, probably involving a CXCR3-independent TrkA pathway.NEW & NOTEWORTHY CXCL10 may aid in lung injury recovery by promoting the proliferation of alveolar stem cells and using a distinct regulatory pathway from the classical one.

Efficacy of Rectal Systemic Administration of Mesenchymal Stem Cells to Injury Sites via the CXCL12/CXCR4 Axis to Promote Regeneration in a Rabbit Skeletal Muscle Injury Model

Mesenchymal stem cells (MSCs) have been transplanted directly into lesions or injected intravenously. The administration of MSCs using these delivery methods requires specialized knowledge, techniques, and facilities. Here, we describe intrarectal systemic administration of MSCs, a simple, non-invasive route for homing to the injury sites to promote the regeneration of skeletal muscle injuries. Using a cardiotoxin (CTX)-induced rabbit skeletal muscle injury model, homing to the site of muscle injury was confirmed by intrarectal administration of MSCs; the time required for homing after intrarectal administration was approximately 5 days. In addition, the C-X-C chemokine ligand 12 (CXCL12)/C-X-C chemokine receptor-4 (CXCR4) axis was found to be involved in the homing process. Histopathological examinations showed that skeletal muscle regeneration was promoted in the MSCs-administered group compared to the CTX-only group. Myosin heavy polypeptide 3 (Myh3) expression, an indicator of early muscle regeneration, was detected earlier in the intrarectal MSCs group compared to the CTX-only group. These findings indicate that intrarectal administration of MSCs is effective in homing to the injured area, where they promote injury repair. Since intrarectal administration is a simple and non-invasive delivery route, these findings may be valuable in future research on stem cell therapy.

Hematopoietic stem progenitor cells with malignancy-related gene mutations in patients with acquired aplastic anemia are characterized by the increased expression of CXCR4

The phenotypic changes in hematopoietic stem progenitor cells (HSPCs) with somatic mutations of malignancy-related genes in patients with acquired aplastic anemia (AA) are poorly understood. As our initial study showed increased CXCR4 expression on HLA allele-lacking (HLA[-]) HSPCs that solely support hematopoiesis in comparison to redundant HLA(+) HSPCs in AA patients, we screened the HSPCs of patients with various types of bone marrow (BM) failure to investigate their CXCR4 expression. In comparison to healthy individuals (n = 15, 12.3%-49.9%, median 43.2%), the median CXCR4+ cell percentages in the HSPCs of patients without somatic mutations were low: 29.3% (14.3%-37.3%) in the eight patients without HLA(-) granulocytes, 8.8% (4.1%-9.8%) in the five patients with HLA(-) cells accounting for >90% of granulocytes, and 7.8 (2.1%-8.7%) in the six patients with paroxysmal nocturnal hemoglobinuria. In contrast, the median percentage was much higher (78% [61.4%-88.7%]) in the five AA patients without HLA(-) granulocytes possessing somatic mutations (c-kit, t[8;21], monosomy 7 [one for each], ASXL1 [n = 2]), findings that were comparable to those (66.5%, 63.1%-88.9%) in the four patients with advanced myelodysplastic syndromes. The increased expression of CXCR4 may therefore reflect intrinsic abnormalities of HSPCs caused by somatic mutations that allow them to evade restriction by BM stromal cells.

Combined Effect of Co-administration of Stromal Cell-Derived Factor-1 and Granulocyte-Colony Stimulating Factor on Rat Model of Alzheimer's Disease

Introduction

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by amyloid plaque deposits, neuronal cell loss, and memory impairment. Granulocyte-colony stimulating factor (G-CSF) is a growth factor associated with AD improvement. Stromal cell-derived factor-1 (SDF-1) mediates therapeutic effects of G-CSF. This study investigated the effect of combination treatment of G-CSF and SDF-1 on amyloid plaque deposits, apoptosis, and behavior of AD rats.

Methods

Intracerebroventricular amyloid-beta [Aβ(1-42)] peptide was used to induce AD in Aβ rats. There were six groups including naive control, sham-operated, Aβ, Aβ + G-CSF, Aβ + SDF-1, and Aβ + G-CSF + SDF-1. SDF-1 intra-cerebroventricular (ICV), G-CSF Subcutaneous (SC), or a combination of them were administered to Aβ rats weekly for 2 months. The cognition and memory were assessed using the novel object recognition, passive avoidance, and Morris water maze tests. Next, rat brains were removed and the amyloid plaque and apoptosis were detected in the brain and hippocampus using immunohistochemistry and TUNEL assay, respectively.

Results

The amyloid-beta and apoptotic cell levels dropped in groups receiving SDF-1 and G-CSF combination compared to the Aβ group. Also, number of microglial cells increased significantly in the combination group compared to other treatment groups. Moreover, learning and memory were significantly improved in the combination group compared to the Aβ groups (P < 0.05).

Conclusion

SDF-1 and G-CSF combination therapy can offer a promising strategy for AD.

Engineering strategies to achieve efficient in vitro expansion of haematopoietic stem cells: development and improvement

Haematopoietic stem cells are the basis for building and maintaining lifelong haematopoietic mechanisms and important resources for the treatment of blood disorders. Haematopoietic niches are microenvironment in the body where...

GPRASP proteins are critical negative regulators of hematopoietic stem cell transplantation

Hematopoietic stem cell (HSC) transplantation (HSCT) is often exploited to treat hematologic disease. Donor HSCs must survive, proliferate, and differentiate in the damaged environment of the reconstituting niche. Illuminating molecular mechanisms regulating the activity of transplanted HSCs will inform efforts to improve HSCT. Here, we report that G-protein-coupled receptor-associated sorting proteins (GPRASPs) function as negative regulators of HSCT. Silencing of Gprasp1 or Gprasp2 increased the survival, quiescence, migration, niche retention, and hematopoietic repopulating activity of hematopoietic stem and progenitor cells (HSPCs) posttransplant. We further show that GPRASP1 and GPRASP2 promote the degradation of CXCR4, a master regulator of HSC function during transplantation. CXCR4 accumulates in Gprasp-deficient HSPCs, boosting their function posttransplant. Thus, GPRASPs negatively regulate CXCR4 stability in HSCs. Our work reveals GPRASP proteins as negative regulators of HSCT and CXCR4 activity. Disruption of GPRASP/CXCR4 interactions could be exploited in the future to enhance the efficiency of HSCT.

Predicting Angiogenesis by Endothelial Progenitor Cells Relying on In-Vitro Function Assays and VEGFR-2 Expression Levels

Clinical trials have demonstrated the safety and efficacy of autologous endothelial progenitor cell (EPC) therapy in various diseases. Since EPCs' functions are influenced by genetic, systemic and environmental factors, the therapeutic potential of each individual EPCs is unknown and may affect treatment outcome. Therefore, our aim was to compare EPCs function among healthy donors in order to predict blood vessel formation (angiogenesis) before autologous EPC transplantation. Human EPCs were isolated from the blood of ten volunteers. EPCs proliferation rate, chemoattractant ability, and CXCR4 mRNA levels were different among donors (p < 0.0001, p < 0.01, p < 0.001, respectively). A positive correlation was found between SDF-1, CXCR4, and EPCs proliferation (R = 0.736, p < 0.05 and R = 0.8, p < 0.01, respectively). In-vivo, blood vessels were counted ten days after EPCs transplantation in a subcutaneous mouse model. Mean vessel density was different among donors (p = 0.0001); nevertheless, donors with the lowest vessel densities were higher compared to control (p < 0.05). Finally, using a linear regression model, a mathematical equation was generated to predict blood vessel density relying on: (i) EPCs chemoattractivity, and (ii) VEGFR-2 mRNA levels. Results reveal differences in EPCs functions among healthy individuals, emphasizing the need for a potency assay to pave the way for standardized research and clinical use of human EPCs.

Skin commensal bacteria Staphylococcus epidermidis promote survival of melanocytes bearing UVB-induced DNA damage, while bacteria Propionibacterium acnes inhibit survival of melanocytes by increasing apoptosis

BACKGROUND/PURPOSE

Skin commensal bacteria have been described to help orchestrate skin homeostasis, signaling through innate immunity pathways. This study for the first time aimed at studying the relationship between skin commensals and melanocytes after UVB exposure.

METHODS

An in vitro UVB radiation model with normal human epidermal melanocytes (NHMs) and skin commensal bacteria supernatant from Staphylococcus epidermidis and Propionibacterium acnes was established. Melanocytes DNA damage, cyclobutane pyrimidine dimers (CPD), and cellular proliferation marker Ki-67 were measured by ELISA and immunofluorescence staining. Cell apoptosis was assessed by flow cytometry and PCR array and RT-qPCR.

RESULTS

Normal human epidermal melanocytes are able to survive and proliferate while bearing DNA damage after UVB radiation. Skin commensal bacteria S. epidermidis and its by-product LTA promote melanocytes survival by inducing upregulation of TRAF1, CASP14, CASP5, and TP73. On the other hand, P. acnes can inhibit UVB-irradiated melanocytes survival by increasing apoptosis.

CONCLUSION

Our studies show different aspects of commensal activity on melanocytes during irradiation. The possible balance achieved by the different skin commensal can influence NHM potential to become cancer cells.

A single amino acid substitution in CXCL12 confers functional selectivity at the beta-arrestin level

CXCL12/CXCR4 axis relies on both heterotrimeric G_i protein and β-arrestin coupling to trigger downstream responses. G protein activation allows for calcium flux, chemotaxis and early extracellular-signal regulated kinases 1/2 (ERK1/2) phosphorylation, whereas β-arrestin recruitment leads to late signaling, receptor desensitization and internalization. Together they may regulate the balance between transactivation and transinhibition of epithelial growth factor receptor 1 (HER1). Since we have previously noted significant differences between CXCL12 and its structural variant [N33A]CXCL12 in CXCR4 signaling, we sought to better characterize them by performing cAMP inhibition and β-arrestin recruitment assays, as well as functional tests that separately investigate G protein and β-arrestin-induced responses. [N33A]CXCL12 showed reduced potency both in Gα_i coupling and β-arrestin recruitment as compared to the wild type chemokine, acting as an unbiased ligand. While these findings translated into reduced potency within Gα_i-dependent functions, β-arrestin-dependent modules were affected in a more peculiar way. Unlike CXCL12, the mutant analogue did not restore HB-EGF-stimulated HER1 from CXCR4-induced transinhibition, and did not trigger the late wave of ERK1/2 phosphorylation. Instead, CXCR4 internalization was not impaired upon [N33A]CXCL12 stimulation. These differences highlight the novel opportunity to dissect CXCL12 signaling within the β-arrestin layer, in which the mutant chemokine clearly favors the internalization module over the other pathways. Such functional selectivity has an impact on HER1 activation status and may play a relevant part in the crosstalk between tyrosine kinase and seven transmembrane receptors.

Targeted release of stromal cell-derived factor-1α by reactive oxygen species-sensitive nanoparticles results in bone marrow stromal cell chemotaxis and homing, and repair of vascular injury caused by electrical burns

Rapid repair of vascular injury is an important prognostic factor for electrical burns. This repair is achieved mainly via stromal cell-derived factor (SDF)-1α promoting the mobilization, chemotaxis, homing, and targeted differentiation of bone marrow mesenchymal stem cells (BMSCs) into endothelial cells. Forming a concentration gradient from the site of local damage in the circulation is essential to the role of SDF-1α. In a previous study, we developed reactive oxygen species (ROS)-sensitive PPADT nanoparticles containing SDF-1α that could degrade in response to high concentration of ROS in tissue lesions, achieving the goal of targeted SDF-1α release. In the current study, a rat vascular injury model of electrical burns was used to evaluate the effects of targeted release of SDF-1α using PPADT nanoparticles on the chemotaxis of BMSCs and the repair of vascular injury. Continuous exposure to 220 V for 6 s could damage rat vascular endothelial cells, strip off the inner layer, significantly elevate the local level of ROS, and decrease the level of SDF-1α. After injection of Cy5-labeled SDF-1α-PPADT nanoparticles, the distribution of Cy5 fluorescence suggested that SDF-1α was distributed primarily at the injury site, and the local SDF-1α levels increased significantly. Seven days after injury with nanoparticles injection, aggregation of exogenous green fluorescent protein-labeled BMSCs at the injury site was observed. Ten days after injury, the endothelial cell arrangement was better organized and continuous, with relatively intact vascular morphology and more blood vessels. These results showed that SDF-1α-PPADT nanoparticles targeted the SDF-1α release at the site of injury, directing BMSC chemotaxis and homing, thereby promoting vascular repair in response to electrical burns.

Bioreducible Polymer Micelles Based on Acid-Degradable Poly(ethylene glycol)-poly(amino ketal) Enhance the Stromal Cell-Derived Factor-1α Gene Transfection Efficacy and Therapeutic Angiogenesis of Human Adipose-Derived Stem Cells

Adipose-derived stem cells (ADSCs) have the potential to treat ischemic diseases. In general, ADSCs facilitate angiogenesis by secreting various pro-angiogenic growth factors. However, transplanted ADSCs have a low therapeutic efficacy in ischemic tissues due to their poor engraftment and low viability. Stromal cell-derived factor-1α (SDF-1α) improves the survival rate of stem cells transplanted into ischemic regions. In this study, we developed acid-degradable poly(ethylene glycol)-poly(amino ketal) (PEG-PAK)-based micelles for efficient intracellular delivery of SDF-1α plasmid DNA. The SDF-1α gene was successfully delivered into human ADSCs (hADSCs) using PEG-PAK micelles. Transfection of SDF-1α increased SDF-1α, vascular endothelial growth factor, and basic fibroblast growth factor gene expression and decreased apoptotic activity in hADSCs cultured under hypoxic conditions in comparison with conventional gene transfection using polyethylenimine. SDF-1α-transfected hADSCs also showed significantly increased SDF-1α and VEGF expression together with reduced apoptotic activity at 4 weeks after transplantation into mouse ischemic hindlimbs. Consequently, these cells improved angiogenesis in ischemic hindlimb regions. These PEG-PAK micelles may lead to the development of a novel therapeutic modality for ischemic diseases based on an acid-degradable polymer specialized for gene delivery.

Fibroblast-derived CXCL12/SDF-1α promotes CXCL6 secretion and co-operatively enhances metastatic potential through the PI3K/Akt/mTOR pathway in colon cancer

AIM

To investigate the underlying mechanism by which CXCL12 and CXCL6 influences the metastatic potential of colon cancer and internal relation of colon cancer and stromal cells.

METHODS

Western blotting was used to detect the expression of CXCL12 and CXCL6 in colon cancer cells and stromal cells. The co-operative effects of CXCL12 and CXCL6 on proliferation and invasion of colon cancer cells and human umbilical vein endothelial cells (HUVECs) were determined by enzyme-linked immunosorbent assay, and proliferation and invasion assays. The angiogenesis of HUVECs through interaction with cancer cells and stromal cells was examined by angiogenesis assay. We eventually investigated activation of PI3K/Akt/mTOR signaling by CXCL12 involved in the metastatic process of colon cancer.

RESULTS

CXCL12 was expressed in DLD-1 cancer cells and fibroblasts. The secretion level of CXCL6 by colon cancer cells and HUVECs were significantly promoted by fibroblasts derived from CXCL12. CXCL6 and CXCL2 could significantly enhance HUVEC proliferation and migration (P < 0.01). CXCL6 and CXCL2 enhanced angiogenesis by HUVECs when cultured with fibroblast cells and colon cancer cells (P < 0.01). CXCL12 also enhanced the invasion of colon cancer cells. Stromal cell-derived CXCL12 promoted the secretion level of CXCL6 and co-operatively promoted metastasis of colon carcinoma through activation of the PI3K/Akt/mTOR pathway.

CONCLUSION

Fibroblast-derived CXCL12 enhanced the CXCL6 secretion of colon cancer cells, and both CXCL12 and CXCL6 co-operatively regulated the metastasis via the PI3K/Akt/mTOR signaling pathway. Blocking this pathway may be a potential anti-metastatic therapeutic target for patients with colon cancer.

The JAK2V617F-bearing vascular niche promotes clonal expansion in myeloproliferative neoplasms

The acquired kinase mutation JAK2V617F plays a central role in myeloproliferative neoplasms (MPNs). However, the mechanisms responsible for the malignant hematopoietic stem/progenitor cell (HSPC) expansion seen in patients with MPNs are not fully understood, limiting the effectiveness of current treatment. Endothelial cells (ECs) are an essential component of the hematopoietic niche, and they have been shown to express the JAK2V617F mutation in patients with MPNs. We show that the JAK2V617F-bearing vascular niche promotes the expansion of the JAK2V617F HSPCs in preference to JAK2WT HSPCs, potentially contributing to poor donor cell engraftment and disease relapse following stem cell transplantation. The expression of Chemokine (C-X-C motif) ligand 12 (CXCL12) and stem cell factor (SCF) were upregulated in JAK2V617F-bearing ECs compared to wild-type ECs, potentially accounting for this observation. We further identify that the thrombopoietin (TPO)/MPL signaling pathway is critical for the altered vascular niche function. A better understanding of how the vascular niche contributes to HSPC expansion and MPN development is essential for the design of more effective therapeutic strategies for patients with MPNs.

Endothelial progenitor cells dysfunction and impaired tissue reparation: The missed link in diabetes mellitus development

Diabetes mellitus (DM) is considered a leading cause of premature cardiovascular (CV) mortality and morbidity in general population and in individuals with known CV disease. Recent animal and clinical studies have shown that reduced number and weak function of endothelial progenitor cells (EPCs) may not only indicate to higher CV risk, but contribute to the impaired heart and vessels reparation in patients with DM. Moreover, EPCs having a protective impact on the vasculature may mediate the functioning of other organs and systems. Therefore, EPCs dysfunction is probably promising target for DM treatment strategy, while the role of restoring of EPCs number and functionality in CV risk diminish and reduce of DM-related complications is not fully clear. The aim of the review is summary of knowledge regarding EPCs dysfunction in DM patients.

Extracellular molecules in hematopoietic stem cell mobilisation

Hematopoietic stem cells are a remarkable resource currently used for the life saving treatment, hematopoietic stem cell transplantation. Today, hematopoietic stem cells are primarily obtained from mobilized peripheral blood following treatment of the donor with the cytokine G-CSF, and in some settings, chemotherapy and/or the CXCR4 antagonist plerixafor. The collection of hematopoietic stem cells is contingent on adequate and timely mobilization of these cells into the peripheral blood. The use of healthy donors, particularly when unrelated to the patient, requires mobilization strategies be safe for the donor. While current mobilization strategies are largely successful, adequate mobilization fails to occur in a significant portion of donors. Understanding the mechanisms involved in the egress of stem cells from the bone marrow provides opportunities to further improve the process of collecting hematopoietic stem cells. Here, the role extracellular components of the blood and bone marrow in the mobilization process are discussed.

Cilostazol Improves Proangiogenesis Functions in Human Early Endothelial Progenitor Cells through the Stromal Cell-Derived Factor System and Hybrid Therapy Provides a Synergistic Effect In Vivo

This study investigated the effect of cilostazol on proangiogenesis functions in human early endothelial progenitor cells (EPCs) in vitro and the therapeutic implication of hybrid therapy with cilostazol and human early EPCs in vivo. Cilostazol significantly increased colony-forming units and enhanced differentiation of EPCs toward endothelial lineage. Treatments resulted in antiapoptotic effects and stimulated proliferation and migration and in vitro vascular tube formation through activation of stromal cell-derived factor-1 (SDF-1)/C-X-C chemokine receptor type 4 (CXCR4)/phosphatidylinositol-3 kinase (PI3K)/Akt signaling pathway. Blood flow recovery and capillary density in murine ischemic hindlimbs were significantly improved in cilostazol-treated, human early EPCs-treated, and cotreatment groups. The effects were attenuated with SDF-1α inhibition. Plasma SDF-1α levels were significantly higher in 3 active treatment groups after surgery, with greatest effects observed in hybrid therapy. The angiogenic effects of transplanted EPCs pretreated with cilostazol ex vivo were superior to untreated EPCs using in vivo Matrigel assay. Implanted EPCs were incorporated into the capillary, with pretreatment or cotreatment with cilostazol resulting in enhanced effects. Taken together, cilostazol promotes a large number of proangiogenic functions in human early EPCs through activation of SDF-1/CXCR4/PI3K/Akt signaling, and hybrid therapy provides a synergistic effect in vivo. Cotreatment may be beneficial in ischemic disease.

Multiple genetically engineered humanized microenvironments in a single mouse

Background

Immunodeficient mouse models that accept human cell and tissue grafts can contribute greater knowledge to human stem cell research. In this technical report, we used biomaterial implants seeded with genetically engineered stromal cells to create several unique microenvironments in a single mouse. The scope of study was focused on human CD34 hematopoietic stem/progenitor cell (HSPC) engraftment and differentiation within the engineered microenvironment.

Results

A mouse model system was created using subdermal implant sites that overexpressed a specific human cytokines (Vascular Endothelial Growth Factor A (hVEGFa), Stromal Derived Factor 1 Alpha (hSDF1a), or Tumor Necrosis Factor Alpha (hTNFa)) by stromal cells in a three-dimensional biomaterial matrix. The systemic exposure of locally overexpressed cytokines was minimized by controlling the growth of stromal cells, which led to autonomous local, concentrated sites in a single mouse for study. This biomaterial implant approach allowed for the local analysis of each cytokine on hematopoietic stem cell recruitment, engraftment and differentiation in four different tissue microenvironments in the same host. The engineered factors were validated to have bioactive effects on human CD34+ hematopoietic progenitor cell differentiation.

Conclusions

This model system can serve as a new platform for the study of multiple human proteins and their local effects on hematopoietic cell biology for in vivo validation studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s40824-016-0066-2) contains supplementary material, which is available to authorized users.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.

Junctional Adhesion Molecule-A Is Highly Expressed on Human Hematopoietic Repopulating Cells and Associates with the Key Hematopoietic Chemokine Receptor CXCR4

Hematopoietic stem/progenitor cells (HSPCs) reside in specialized bone marrow microenvironmental niches, with vascular elements (endothelial/mesenchymal stromal cells) and CXCR4-CXCL12 interactions playing particularly important roles for HSPC entry, retention, and maintenance. The functional effects of CXCL12 are dependent on its local concentration and rely on complex HSPC-niche interactions. Two Junctional Adhesion Molecule family proteins, Junctional Adhesion Molecule-B (JAM)-B and JAM-C, are reported to mediate HSPC-stromal cell interactions, which in turn regulate CXCL12 production by mesenchymal stromal cells (MSCs). Here, we demonstrate that another JAM family member, JAM-A, is most highly expressed on human hematopoietic stem cells with in vivo repopulating activity (p < .01 for JAM-A(high) compared to JAM-A(Int or Low) cord blood CD34(+) cells). JAM-A blockade, silencing, and overexpression show that JAM-A contributes significantly (p < .05) to the adhesion of human HSPCs to IL-1β activated human bone marrow sinusoidal endothelium. Further studies highlight a novel association of JAM-A with CXCR4, with these molecules moving to the leading edge of the cell upon presentation with CXCL12 (p < .05 compared to no CXCL12). Therefore, we hypothesize that JAM family members differentially regulate CXCR4 function and CXCL12 secretion in the bone marrow niche. Stem Cells 2016;34:1664-1678.

A promiscuous recognition mechanism between GPR17 and SDF-1: Molecular insights

Recent data and publications suggest a promiscuous behaviour for GPR17, a class-A GPCR operated by different classes of ligands, such as uracil nucleotides, cysteinyl-leukotrienes and oxysterols. This observation, together with the ability of several class-A GPCRs to form homo- and hetero-dimers, is likely to unveil new pathophysiological roles and novel emerging pharmacological properties for some of these GPCRs, including GPR17. This receptor shares structural, phylogenetic and functional properties with some chemokine receptors, CXCRs. Both GPR17 and CXCR2 are operated by oxysterols, and both GPR17 and CXCR ligands have been demonstrated to have a role in orchestrating inflammatory responses and oligodendrocyte precursor cell differentiation to myelinating cells in acute and chronic diseases of the central nervous system. Here, by combining in silico modelling data with in vitro validation in (i) a classical reference pharmacological assay for GPCR activity and (ii) a model of maturation of primary oligodendrocyte precursor cells, we demonstrate that GPR17 can be activated by SDF-1, a ligand of chemokine receptors CXCR4 and CXCR7, and investigate the underlying molecular recognition mechanism. We also demonstrate that cangrelor, a GPR17 orthosteric antagonist, can block the SDF-1-mediated activation of GPR17 in a concentration-dependent manner. The ability of GPR17 to respond to different classes of GPCR ligands suggests that this receptor modifies its function depending on the extracellular mileu changes occurring under specific pathophysiological conditions and advocates it as a strategic target for neurodegenerative diseases with an inflammatory/immune component.

Biomaterial strategies for controlling stem cell fate via morphogen sequestration

This review explores the role of protein sequestration in the stem cell niche and how it has inspired the design of biomaterials that exploit natural protein sequestration to influence stem cell fate.

Stromal-Derived Factor-1α and Interleukin-7 Treatment Improves Homeostatic Proliferation of Naïve CD4(+) T Cells after Allogeneic Stem Cell Transplantation

Graft-versus-host disease (GVHD) impairs immune reconstitution after allogeneic stem cell transplantation (allo-SCT) and effective therapies aimed at restoring T cell counts in GVHD patients have yet to be developed. During GVHD, CD4(+) T cell reconstitution is particularly affected and current models hold that GVHD insult to the peripheral lymphoid niche is responsible for this effect. Here, we show that naïve CD4(+) T cell homeostatic proliferation (HP) is lost during GVHD because of low systemic IL-7 and impaired dendritic cell (DC) regeneration. We assessed factors involved in DC differentiation and found that although fms-like tyrosine kinase 3 ligand (Flt3-L) levels were normal, stromal-derived factor-1α (SDF-1α) was diminished in the blood of GVHD mice. Unlike Flt3-L treatment, the administration of SDF-1α specifically increased CD8α(+) DC numbers and did not worsen GVHD. Importantly, CD4(+) T cell HP was enhanced only when IL-7 and SDF-1α or Flt3L were coadministered, confirming the crucial role of DCs and IL-7 in restoring CD4(+) T cell regeneration during GVHD. Altogether, our results indicate that CD8α(+) DCs are part of the peripheral niche that controls CD4(+) T cell HP and that their depletion, combined with low systemic IL-7, explains how GVHD constrains naïve CD4(+) T cell reconstitution after allo-SCT.

Downregulation of CXCR4 in Metastasized Breast Cancer Cells and Implication in Their Dormancy

Our understanding of the mechanism of cancer dormancy is emerging, but the underlying mechanisms are not fully understood. Here we analyzed mouse xenograft tumors derived from human breast cancer tissue and the human breast cancer cell line MDA-MB-231 to identify the molecules associated with cancer dormancy. In immunohistological examination using the proliferation marker Ki-67, the tumors included both proliferating and dormant cancer cells, but the number of dormant cells was remarkably increased when they metastasized to the lung. In the gene expression analysis of the orthotopic cancer cells by a single-cell multiplex real-time quantitative reverse transcription PCR followed by flow cytometric analysis, restrained cellular proliferation was associated with downregulation of the chemokine receptor CXCR4. In the immunohistological and flow cytometric analyses, the expression level of CXCR4 in the metastasized cancer cells was decreased compared with that in the cancer cells in orthotopic tumors, although the expression level of the CXCR4 ligand CXCL12 was not reduced in the lung. In addition, the proliferation of the metastasized cancer cells was further decreased by the CXCR4 antagonist administration. In the ex vivo culture of the metastasized cancer cells, the expression level of CXCR4 was increased, and in the xenotransplantation of ex vivo cultured cancer cells, the expression level of CXCR4 was again decreased in the metastasized cancer cells in the lung. These findings indicate that CXCR4 is downregulated in metastasized breast cancer cells and implicated in their dormancy.

CXCL12+ stromal cells as bone marrow niche for CD34+ hematopoietic cells and their association with disease progression in myelodysplastic syndromes

The bone marrow microenvironment, known as 'hematopoietic stem cell niche,' is essential for the survival and maintenance of hematopoietic stem cells. Myelodysplastic syndromes (MDS) are a group of clonal hematopoietic stem cell diseases, which eventually result in leukemic transformation (acute myelogenous leukemia with myelodysplasia-related changes, AML-MRC). However, the precise components and functions of the MDS niche remain unclear. Recently, CXCL12-abundant reticular cells were shown to act as a hematopoietic stem cell niche in the murine bone marrow. Using immunohistochemistry, we show here that CXCL12(+) cells were located in the cellular marrow or perivascular area, and were in contact with CD34(+) hematopoietic cells in control and MDS/AML-MRC bone marrow. MDS bone marrow exhibited higher CXCL12(+) cell density than control or AML, not otherwise specified (AML-NOS) bone marrow. Moreover, AML-MRC bone marrow also exhibited higher CXCL12(+) cell density than control bone marrow. CXCL12(+) cell density correlated positively with bone marrow blast ratio in MDS cases. CXCL12 mRNA level was also higher in MDS bone marrow than in control or AML-NOS bone marrow. In vitro coculture analysis revealed that overexpression of CXCL12 in stromal cells upregulated BCL-2 expression of leukemia cell lines. Triple immunostaining revealed that the CD34(+) hematopoietic cells of MDS bone marrow in contact with CXCL12(+) cells were BCL-2-positive and TUNEL-negative. In the bone marrow of MDS cases, CXCL12-high group showed significantly higher Bcl-2(+)/CD34(+) cell ratio and lower apoptotic cell ratio than CXCL12-low group. Moreover, CXCL12-high refractory cytopenia with multilineage dysplasia (RCMD) cases had a greater tendency to progress to refractory anemia with excess blasts (RAEBs) or AML-MRC than CXCL12-low RCMD cases. These results suggest that CXCL12(+) cells constitute the niche for CD34(+) hematopoietic cells, and may be associated with the survival/antiapoptosis of CD34(+) hematopoietic cells and disease progression in MDS. Thus, CXCL12(+) cells may represent a novel MDS therapeutic target.

SDF-1 chemokine signalling modulates the apoptotic responses to iron deprivation of clathrin-depleted DT40 cells

We have previously deleted both endogenous copies of the clathrin heavy-chain gene in the chicken pre B-cell-line DT40 and replaced them with clathrin under the control of a tetracycline-regulatable promoter (Tet-Off). The originally derived cell-line DKO-S underwent apoptosis when clathrin expression was repressed. We have also described a cell-line DKO-R derived from DKO-S cells that was less sensitive to clathrin-depletion. Here we show that the restriction of transferrin uptake, resulting in iron deprivation, is responsible for the lethal consequence of clathrin-depletion. We further show that the DKO-R cells have up-regulated an anti-apoptotic survival pathway based on the chemokine SDF-1 and its receptor CXCR4. Our work clarifies several puzzling features of clathrin-depleted DT40 cells and reveals an example of how SDF-1/CXCR4 signalling can abrogate pro-apoptotic pathways and increase cell survival. We propose that the phenomenon described here has implications for the therapeutic approach to a variety of cancers.

[CXCR4: a new therapeutic target of the leukaemic cell? Role of the SDF-1/CXCR4 axis in acute myeloid leukaemia]

CXCR4, receptor of the chemokine SDF-1 (stromal cell-derived factor 1) plays a major role in the normal hematopoiesis but also in the biology of the leukaemic cell. This receptor is expressed on the surface of blasts and is a key molecule in "the anchoring" of the leukaemic stem cell (LSC) within the bone marrow niche. The interactions of the LSC with the bone marrow microenvironment promote survival signals and drug resistance. Recent flow cytometry analyses reported that CXCR4 expression levels have a major prognostic impact in acute myeloid leukaemia (AML). CXCR4 expression is associated with poor prognosis and can be useful to stratify patients, according to their phenotype, in order to establish risk-adapted strategies. Newly diagnosed AML are now routinely stratified according to molecular markers which guide prognosis and treatment. Many leukaemia are composed of multiples subclones with differential susceptibility to treatment and specific targeted therapies are missing. Despite therapeutic improvements for the treatment of AML, long term survival remains poor. Targeting CXCR4 is a novel promising approach of therapy. CXCR4 antagonists are used in combination with chemotherapy in preclinical and clinical studies. This review summarises our current knowledge regarding the key role of CXCR4 in AML and discusses how targeting this pathway could provide an interesting approach to eradicate the LSC.

Downregulated CXCL12 expression in mesenchymal stem cells associated with severe aplastic anemia in children

The mechanisms of idiopathic severe aplastic anemia (SAA) in children are not completely understood. Insufficiency of the bone marrow microenvironment, in which mesenchymal stem cells (MSCs) are an important element, can be a potential factor associated with hematopoietic impairment. In the current study, we studied whether aberrant gene expression could be found in MSCs from children with SAA. Using microarray analysis, two different patterns of global gene expression were detected in the SAA MSCs. Fourteen genes (POLE2, HGF, KIF20A, TK1, IL18R1, KITLG, FGF18, RRM2, TTK, CXCL12, DLG7, TOP2A, NUF2, and TYMS), which are related to DNA synthesis, cytokines, or growth factors, were significantly downregulated. Further, knockdown of gene expression was performed using the small hairpin RNA (shRNA)-containing lentivirus method. We found that knockdown of CXCL12, HGF, IL-18R1, FGF18, or RRM2 expression compelled MSCs from the controls to behave like those from the SAA children, with decreased survival and differentiation potential. Among them, inhibition of CXCL12 gene expression had the most profound effects on the behavior of MSCs. Further experiments regarding re-introduction of the CXCL12 gene could largely recover the survival and differentiation potential in MSCs with inhibition of CXCL12 expression. Our findings suggest that MSCs from children with SAA exhibit aberrant gene expression profiles and downregulation of CXCL12 gene may be associated with alterations in the bone marrow microenvironment.

IGF-1-mediated osteoblastic niche expansion enhances long-term hematopoietic stem cell engraftment after murine bone marrow transplantation

The efficiency of hematopoietic stem cell (HSC) engraftment after bone marrow (BM) transplantation depends largely on the capacity of the marrow microenvironment to accept the transplanted cells. While radioablation of BM damages osteoblastic stem cell niches, little is known about their restoration and mechanisms governing their receptivity to engraft transplanted HSCs. We previously reported rapid restoration and profound expansion of the marrow endosteal microenvironment in response to marrow radioablation. Here, we show that this reorganization represents proliferation of mature endosteal osteoblasts which seem to arise from a small subset of high-proliferative, relatively radio-resistant endosteal cells. Multiple layers of osteoblasts form along the endosteal surface within 48 hours after total body irradiation, concomitant with a peak in marrow cytokine expression. This niche reorganization fosters homing of the transplanted hematopoietic cells to the host marrow space and engraftment of long-term-HSC. Inhibition of insulin-like growth factor (IGF)-1-receptor tyrosine kinase signaling abrogates endosteal osteoblast proliferation and donor HSC engraftment, suggesting that the cytokine IGF-1 is a crucial mediator of endosteal niche reorganization and consequently donor HSC engraftment. Further understanding of this novel mechanism of IGF-1-dependent osteoblastic niche expansion and HSC engraftment may yield clinical applications for improving engraftment efficiency after clinical HSC transplantation.

The CXCR4/SDF1 axis improves muscle regeneration through MMP-10 activity

The CXCR4/SDF1 axis participates in various cellular processes, including cell migration, which is essential for skeletal muscle repair. Although increasing evidence has confirmed the role of CXCR4/SDF1 in embryonic muscle development, the function of this pathway during adult myogenesis remains to be fully elucidated. In addition, a role for CXCR4 signaling in muscle maintenance and repair has only recently emerged. Here, we have demonstrated that CXCR4 and stromal cell-derived factor-1 (SDF1) are up-regulated in injured muscle, suggesting their involvement in the repair process. In addition, we found that notexin-damaged muscles showed delayed muscle regeneration on treatment with CXCR4 agonist (AMD3100). Accordingly, small-interfering RNA-mediated silencing of SDF1 or CXCR4 in injured muscles impaired muscle regeneration, whereas the addition of SDF1 ligand accelerated repair. Furthermore, we identified that CXCR4/SDF1-regulated muscle repair was dependent on matrix metalloproteinase-10 (MMP-10) activity. Thus, our findings support a model in which MMP-10 activity modulates CXCR4/SDF1 signaling, which is essential for efficient skeletal muscle regeneration.

Ex vivo expansion of functional human UCB-HSCs/HPCs by coculture with AFT024-hkirre cells

Kiaa1867 (human Kirre, hKirre) has a critical role in brain development and/or maintenance of the glomerular slit diaphragm in kidneys. Murine homolog of this gene, mKirre expressed in OP9 and AFT024 cells could support hematopoietic stem cells/hematopoietic progenitor cells (HSC/HPC) expansion in vitro. HKirre is also expressed in human FBMOB-hTERT cell line and fetal liver fibroblast-like cells but its function has remained unclear. In this paper, we cloned a hKirre gene from human fetal liver fibroblast-like cells and established a stably overexpressing hKirre-AFT024 cell line. Resultant cells could promote self-renewal and ex vivo expansion of HSCs/HPCs significantly higher than AFT024-control cells transformed with mock plasmid. The Expanded human umbilical cord blood (hUCB) CD34⁺ cells retained the capacity of multipotent differentiation as long as 8 weeks and successfully repopulated the bone marrow of sublethally irradiated NOD/SCID mice, which demonstrated the expansion of long-term primitive transplantable HSCs/HPCs. Importantly, hkirre could upregulate the expressions of Wnt-5A, BMP4, and SDF-1 and downregulate TGF-β with other hematopoietic growth factors. By SDS-PAGE and Western Blot analysis, a ~89 kDa protein in total lysate of AFT024-hKirre was identified. Supernatants from AFT024-hkirre could also support CD34⁺CD38⁻ cells expansion. These results demonstrated that the AFT024-hKirre cells have the ability to efficiently expand HSCs/HPCs.

Combination of imatinib with CXCR4 antagonist BKT140 overcomes the protective effect of stroma and targets CML in vitro and in vivo

Functional role of CXCR4 in chronic myelogenous leukemia (CML) progression was evaluated. Elevated CXCR4 significantly increased the in vitro survival and proliferation in response to CXCL12. CXCR4 stimulation resulted in activation of extracellular signal-regulated kinase (Erk)-1/2, Akt, S6K, STAT3, and STAT5 prosurvival signaling pathways. In accordance, we found that in vitro treatment with CXCR4 antagonist BKT140 directly inhibited the cell growth and induced cell death of CML cells. Combination of BKT140 with suboptimal concentrations of imatinib significantly increased the anti-CML effect. BKT140 induced apoptotic cell death, decreasing the levels of HSP70 and HSP90 chaperones and antiapoptotic proteins BCL-2 and BCL-XL, subsequently promoting the release of mitochondrial factors cytochrome c and SMAC/Diablo. Bone marrow (BM) stromal cells (BMSC) markedly increased the proliferation of CML cells and protected them from imatinib-induced apoptosis. Furthermore, BMSCs elevated proto-oncogene BCL6 expression in the CML cells in response to imatinib treatment, suggesting the possible role of BCL6 in stroma-mediated TKI resistance. BKT140 reversed the protective effect of the stroma, effectively promoted apoptosis, and decreased BCL6 levels in CML cells cocultured with BMSCs. BKT140 administration in vivo effectively reduced the growth of subcutaneous K562-produced xenografts. Moreover, the combination of BKT140 with low-dose imatinib markedly inhibited tumor growth, achieving 95% suppression. Taken together, our data indicate the importance of CXCR4/CXCL12 axis in CML growth and CML-BM stroma interaction. CXCR4 inhibition with BKT140 antagonist efficiently cooperated with imatinib in vitro and in vivo. These results provide the rational basis for CXCR4-targeted therapy in combination with TKI to override drug resistance and suppress residual disease.

Mesenchymal stem cells in immune-mediated bone marrow failure syndromes

Immune-mediated bone marrow failure syndromes (BMFS) are characterized by ineffective marrow haemopoiesis and subsequent peripheral cytopenias. Ineffective haemopoiesis is the result of a complex marrow deregulation including genetic, epigenetic, and immune-mediated alterations in haemopoietic stem/progenitor cells, as well as abnormal haemopoietic-to-stromal cell interactions, with abnormal release of haemopoietic growth factors, chemokines, and inhibitors. Mesenchymal stem/stromal cells (MSCs) and their progeny (i.e., osteoblasts, adipocytes, and reticular cells) are considered as key cellular components of the bone marrow haemopoietic niche. MSCs may interfere with haemopoietic as well as immune regulation. Evidence suggests that bone marrow MSCs may be involved in immune-mediated BMFS underlying pathophysiology, harboring either native abnormalities and/or secondary defects, caused by exposure to activated marrow components. This review summarizes previous as well as more recent information related to the biologic/functional characteristics of bone marrow MSCs in myelodysplastic syndromes, acquired aplastic anemia, and chronic idiopathic neutropenia.

CXCR7 participates in CXCL12-induced CD34+ cell cycling through β-arrestin-dependent Akt activation

In addition to its well-known effect on migration and homing of hematopoietic stem/progenitor cells (HSPCs), CXCL12 chemokine also exhibits a cell cycle and survival-promoting factor for human CD34(+) HSPCs. CXCR4 was suggested to be responsible for CXCL12-induced biological effects until the recent discovery of its second receptor, CXCR7. Until now, the participation of CXCR7 in CXCL12-induced HSPC cycling and survival is unknown. We show here that CXCL12 was capable of binding CXCR7 despite its scarce expression at CD34(+) cell surface. Blocking CXCR7 inhibited CXCL12-induced Akt activation as well as the percentage of CD34(+) cells in cycle, colony formation, and survival, demonstrating its participation in CXCL12-induced functional effects in HSPCs. At steady state, CXCR7 and β-arrestin2 co-localized near the plasma membrane of CD34(+) cells. After CXCL12 treatment, β-arrestin2 translocated to the nucleus, and this required both CXCR7 and CXCR4. Silencing β-arrestin expression decreased CXCL12-induced Akt activation in CD34(+) cells. Our results demonstrate for the first time the role of CXCR7, complementary to that played by CXCR4, in the control of HSPC cycling, survival, and colony formation induced by CXCL12. We also provide evidence for the involvement of β-arrestins as signaling hubs downstream of both CXCL12 receptors in primary human HSPCs.

SP/drug efflux functionality of hematopoietic progenitors is controlled by mesenchymal niche through VLA-4/CD44 axis

Hematopoiesis is orchestrated by interactions between hematopoietic stem/progenitor cells (HSPCs) and stromal cells within bone marrow (BM) niches. Side population (SP) functionality is a major characteristic of HSPCs related to quiescence and resistance to drugs and environmental stresses. At steady state, SP cells are mainly present in the BM and are mostly absent from the circulation except in stress conditions, raising the hypothesis of the versatility of the SP functionality. However, the mechanism of SP phenotype regulation is unclear. Here we show for the first time that the SP functionality can be induced in lin(-) cells from unmobilized peripheral blood after nesting on mesenchymal stromal cells (MSCs). This MSC-induced SP fraction contains HSPCs as demonstrated by their (i) CD34(+) cell percentage, (ii) quiescent status, (iii) in vitro proliferative and clonogenic potential, (iv) engraftment in NSG (NOD SCID gamma chain) mice and (v) stemness gene expression profile. We demonstrate that SP phenotype acquisition/reactivation by circulating lin(-) cells is dependent on interactions with MSCs through VLA-4/α4β1-integrin and CD44. A similar integrin-dependent mechanism of SP phenotype acquisition in acute myeloid leukemia circulating blasts suggests an extrinsic regulation of ATP-binding cassette-transporter activity that could be of importance for a better understanding of adhesion-mediated chemoresistance mechanisms.

Megakaryocytes promote murine osteoblastic HSC niche expansion and stem cell engraftment after radioablative conditioning

Successful hematopoietic stem cell (HSC) transplantation requires donor HSC engraftment within specialized bone marrow microenvironments known as HSC niches. We have previously reported a profound remodeling of the endosteal osteoblastic HSC niche after total body irradiation (TBI), defined as relocalization of surviving megakaryocytes to the niche site and marked expansion of endosteal osteoblasts. We now demonstrate that host megakaryocytes function critically in expansion of the endosteal niche after preparative radioablation and in the engraftment of donor HSC. We show that TBI-induced migration of megakaryocytes to the endosteal niche depends on thrombopoietin signaling through the c-MPL receptor on megakaryocytes, as well as CD41 integrin-mediated adhesion. Moreover, niche osteoblast proliferation post-TBI required megakaryocyte-secreted platelet-derived growth factor-BB. Furthermore, blockade of c-MPL-dependent megakaryocyte migration and function after TBI resulted in a significant decrease in donor HSC engraftment in primary and competitive secondary transplantation assays. Finally, we administered thrombopoietin to mice beginning 5 days before marrow radioablation and ending 24 hours before transplant to enhance megakaryocyte function post-TBI, and found that this strategy significantly enhanced donor HSC engraftment, providing a rationale for improving hematopoietic recovery and perhaps overall outcome after clinical HSC transplantation.

Stromal cell-derived factor-1β mediates cell survival through enhancing autophagy in bone marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem/stromal cells (BMSCs) hold great potential for cell-based therapy, yet the therapeutic efficacy remains uncertain. Transplanted BMSCs often fail to engraft within the bone marrow (BM), in part due to the poor survival of donor cells in response to inflammatory reactions, hypoxia, oxidative stress, or nutrient starvation. Two basic cell processes, apoptosis and autophagy, could potentially be responsible for the impaired survival of transplanted BMSCs. However, the functional relationship between apoptosis and autophagy in BMSC homeostasis is complex and not well understood. The stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) signaling axis appears to be critical in maintaining proliferation and survival of BM stem cell populations through improving cell proliferation and survival in response to stress; however, the exact mechanisms remain unclear. We recently described novel genetically engineered Tet-Off-SDF-1β BMSCs, which over-express SDF-1β under tight doxycycline-control, thus providing an ideal model system to investigate the isolated effects of SDF-1β. In this study we tested the hypothesis that SDF-1β can mediate cell survival of BMSCs in vitro through increasing autophagy. We found that SDF-1β had no effect on BMSC proliferation; however, SDF-1β significantly protected genetically engineered BMSCs from H2O2-induced cell death through increasing autophagy and decreasing caspase-3-dependent apoptosis. Taken together, we provide novel evidence that the SDF-1/CXCR4 axis, specifically activated by the SDF-1β isoform, plays a critical role in regulating BMSC survival under oxidative stress through increasing autophagy.

Role of stromal-derived factor-1<alpha>/CXCR4 in neo-intimal repair

Abstract

Neo-intimal hyperplasia is one of the major causes of restenosis in which stromal cell-derived factor-1<alpha> (SDF-1α) and its receptor CXCR4 play an important role. In a rat common carotid artery balloon injury model, the number of CD34⁺CXCR4⁺ cells was significantly increased immediately after injury (p < 0.01), followed by a gradual decrease to baseline seven days after the injury. Furthermore, the plasma (SDF-1α) level was markedly elevated, and peaked 24 hours after injury (p < 0.01), followed by a rapid decrease to baseline level seven days after the injury. In the injured common carotid artery, the mRNA expression of (SDF-1α) was elevated immediately after injury, followed by a gradual decline, but that of CXCR4 was increased four days after injury.

Immuno-histochemistry displayed CXCR4-positive staining one day after injury, which then gradually increased and continued for at least one month. In addition, administration of AMD3100 (200 ng/kg, i.p.), a CXCR4 antagonist, did not affect the number of CD34⁺CXCR4⁺ cells, the elevated level of plasma (SDF-1α) and expression of (SDF-1α) mRNA. The expression of CXCR4 mRNA and protein however was markedly decreased, and detectable CXCR4-positive cells occurred four days after injury, followed by a decreased intensity of staining. We also found that, three months after balloon injury, stenosis of the carotid artery intima in the group that received AMD3100 was significantly less than in the untreated group (p < 0.05). Therefore, (SDF-1α)/CXCR4 played a crucial role in the intimal hyperplasia, and restenosis may have be attenuated after inhibition of CD34⁺CXCR4⁺ cells in the intima.

Innate immunity derived factors as external modulators of the CXCL12-CXCR4 axis and their role in stem cell homing and mobilization

The α-chemokine CXCL12 (stromal derived factor-1; SDF-1) and its corresponding G_αI protein-coupled CXCR4 receptor axis play an important role in retention of hematopoietic stem progenitor cells (HSPCs) in bone marrow (BM) stem cell niches. CXCL12 has also been identified as a strong chemoattractant for HSPCs and implicated both in homing of HSPCs to BM after transplantation and in egress of these cells from BM into peripheral blood (PB). However, since CXCL12, as a peptide, is highly susceptible to degradation by proteolytic enzymes, its real biological availability in biological fluids may be somewhat limited. In this review, we will present data demonstrating that the CXCL12-CXCR4 axis is positively modulated by innate immunity-derived several external factors, ensuring that even low (near threshold) doses of CXCL12 still exert a robust chemotactic influence on HSPCs.

Umbilical cord blood-derived stromal cells regulate megakaryocytic proliferation and migration through SDF-1/PECAM-1 pathway

We have previously reported that human umbilical cord blood-derived stromal cells (hUCBDSCs) are able to enhance the expansion of CFU-Meg in vitro, particularly promote the megakaryocytic lineage recovery, and effectively protect the survival of irradiated mice. In this study, we demonstrated that hUCBDSCs secreted SDF-1 to stimulate PECAM-1 expression in HEL cells (MK cell line), and consequently promoted the proliferation and migration of HEL cells. On the other hand, SDF-1 knock down in hUCBDSCs or PECAM-1 knock down in HEL cells diminished or abrogated the above effect. In addition, SDF-1/PECAM-1 probably activated PI3K/Akt and MAPK/ERK1/2 pathways. This report for the first time defines a SDF-1/PECAM-1 signaling pathway in the proliferation and migration of MKs, which provides supportive evidence for the clinical applications of hUCBDSCs in the treatment of megakaryocytic injury.

Dipeptidylpeptidase 4 negatively regulates colony-stimulating factor activity and stress hematopoiesis

Enhancement of hematopoietic recovery after radiation, chemotherapy, or hematopoietic stem cell (HSC) transplantation is clinically relevant. Dipeptidylpeptidase (DPP4) cleaves a wide variety of substrates, including the chemokine stromal cell-derived factor-1 (SDF-1). In the course of experiments showing that inhibition of DPP4 enhances SDF-1-mediated progenitor cell survival, ex vivo cytokine expansion and replating frequency, we unexpectedly found that DPP4 has a more general role in regulating colony-stimulating factor (CSF) activity. DPP4 cleaved within the N-termini of the CSFs granulocyte-macrophage (GM)-CSF, G-CSF, interleukin-3 (IL-3) and erythropoietin and decreased their activity. Dpp4 knockout or DPP4 inhibition enhanced CSF activities both in vitro and in vivo. The reduced activity of DPP4-truncated versus full-length human GM-CSF was mechanistically linked to effects on receptor-binding affinity, induction of GM-CSF receptor oligomerization and signaling capacity. Hematopoiesis in mice after radiation or chemotherapy was enhanced in Dpp4(-/-) mice or mice receiving an orally active DPP4 inhibitor. DPP4 inhibition enhanced engraftment in mice without compromising HSC function, suggesting the potential clinical utility of this approach.