Mobilizing of haematopoietic stem cells to ischemic myocardium by plasmid mediated stromal-cell-derived factor-1alpha (SDF-1alpha) treatment

A concentration gradient of stromal-cell-derived factor-1alpha (SDF-1alpha) is the major mechanism for homing of haematopoietic stem cells (HSCs) in bone marrow. We tested the hypothesis that a gene therapy using SDF-1alpha can enhance HSCs recruiting to the heart upon myocardial infarction (MI). Adult mice with surgically induced myocardial ischemia were injected intramyocardially with either saline (n=12) or SDF-1alpha plasmid (n=12) in 50 microl volume in the ischemic border zone of the infarcted heart 2 weeks after myocardial infarction. Donor Lin-c-kit+ HSCs from isogenic BalB/c mice were harvested, sorted through magnetic cell sorting (MACS) and labeled with PKH26 Red. Three days after plasmid or saline injection, 1x10(5) labeled cells were injected intravenously (i.v.) into saline mice (n=4) and SDF-1alpha plasmid mice (n=4). The hearts and other tissue were removed for Western blot assay 2 weeks after plasmid or saline treatment. The labeled Lin-c-kit+ cells were identified with immunofluoresent staining and endogenous c-kit+ cells were identified by immunohistochemical staining. In mice killed at 1 month postinfarct, Western blot showed higher levels of SDF-1alpha expression in SDF-1alpha-treated mouse ischemic hearts compared to saline-treated hearts and other tissues. In the SDF-1alpha plasmid-treated hearts, SDF-1alpha is overexpressed in the periinfarct zone. The labeled stem cells engrafted to the SDF-1alpha positive site in the myocardium. There was also evidence for endogenous stem cell recruiting. The density of c-kit+ cells in border zone, an index of endogenous stem cell mobilization, was significantly higher in the SDF-1alpha-treated group than in the saline group (14.63+/-1.068 cells/hpf vs. 11.31+/-0.65 cells/hpf, P=0.013) at 2 weeks after SDF-1alpha or saline treatment. Following myocardial infarction, treatment with SDF-1alpha recruits stem cells to damaged heart where they may have a role in repairing and regeneration. The gene therapy with an SDF-1alpha vector offers a promising therapeutic strategy for mobilizing stem cells to the ischemic myocardium.     

SDF-1 and CXCR4 in normal and malignant hematopoiesis

Over recent years it has become apparent that the chemokine SDF-1 and its receptor CXCR4 play pivotal roles in normal hematopoiesis. They are essential for the normal ontogeny of hematopoiesis during embryogenesis and continue to play a key role in retaining hematopoietic progenitors within the bone marrow microenvironment in the adult. As a result of this role disruption of SDF-1/CXCR4 interactions results in mobilization of hematopoietic progenitors and standard mobilization protocols disrupt this axis. Similarly SDF-1/CXCR4 interactions are required for homing and engraftment of hematopoietic stem cells during transplantation. SDF-1 regulates the localisation of leukemic cells and like their normal counterparts most leukemic cells respond to SDF-1 with increased adhesion, survival and proliferation. However in some instances leukemic cell responses to SDF-1 can be disregulated, the impact of which on the progression of disease in not known. In this review we discuss the pleiotropic roles of SDF-1/CXCR4 interactions in human hematopoietic stem cell ontogeny, bone marrow homing and engraftment, mobilization and how these interactions impact on malignant hematopoiesis.     

SDF-1/CXCR4轴在缺氧缺血性脑损伤中的研究进展

干细胞在许多组织器官显示巨大的细胞分化潜能,其治疗缺血缺氧性疾病成为当前研究的热点。已知局部缺血可诱导干细胞的动员,并能感受组织损伤而定向迁移到损伤区并进行分化。具有趋化因子受体4（CXC chemokine receptor 4,CXCR4）的干细胞迁移到高表达间质细胞来源的因子-1（stromal cell-derived factor-1,SDF-1）的组织区域,这种细胞的迁移运动能被CXCR4拈抗剂所阻断或通过CXCR4的过表达增强迁移的运动。SDF-1-CXCR4轴是体内各种类型的干细胞迁移及细胞在骨髓的滞留和归巢中的重要调节物质。本文就缺氧缺血性脑损伤的骨髓间质干细胞（bone marrow stromal cell,BMSC）治疗,SDF- 1-CXCR4轴在MSCs动员和损伤、修复中的作用作一综述。     

L-selectin and SDF-1 enhance the migration of mouse and human cardiac mesoangioblasts

Efficient delivery of stem cells to heart regions is still a major problem for cell therapy. Here, we report experiments aimed to improve migration of mouse and human cardiac mesoangioblasts to the damaged heart. Cardiac mesoangioblasts were induced to transmigrate through the endothelium by factors released by cardiomyocytes or cytokines, among which stromal-derived factor 1 (SDF-1) was the most potent. Cardiac mesoangioblasts were also delivered into the left ventricular (LV) chamber of mice after coronary artery ligation (CAL), and their in vivo homing to the damaged heart was found to be quite modest. Pretreatment of cardiac mesoangioblasts with SDF-1 or transient expression of L-selectin induced a two- to three-fold increase in their transmigration and homing to the damaged heart. Therefore, combined pretreatment with SDF-1 and L-selectin generated modified cardiac mesoangioblasts, 50% of which, after injection into the LV chamber of mice early after CAL, home directly to the damaged free wall of the heart. Finally, modified mouse cardiac mesoangioblasts, injected into the LV chamber regenerate a larger surface of the ventricle in long-term experiments in comparison with their control counterparts. This study defines the requirements for efficient homing of cardiac mesoangioblasts to the damaged heart and offers a new potent tool to optimize efficiency of future cell therapy protocols for cardiovascular diseases.     

SDF-1/CXCR4 轴在间充质干细胞归巢机制中的研究进展

间充质干细胞(Mesenchymal Stem Cells,MSCs)是一种具有多向分化潜能的成体干细胞,其具有分泌营养物质和调节炎症反应的能力,虽然间充质干细胞在组织修复、重塑和免疫调节方面已得到临床运用,但MSCs趋化和归巢的机制仍不清楚。基质细胞衍生因子-1(stromal cell-derived factor 1,SDF-1)和其趋化因子受体4(C-X-C chemokine receptor 4,CXCR4)在介导MSCs的分化、迁移和归巢中起着至关重要的作用,若能深入探讨、明确其在归巢中的作用,期望给间充质干细胞在临床的应用开辟新的应用前景。     

Resveratrol Upregulates Cardiac SDF-1 in Mice with Acute Myocardial Infarction through the Deacetylation of Cardiac p53

Aims

We previously demonstrated that resveratrol (RSV) administration causes cardiac stromal cell-derived factor (SDF)-1 upregulation and can enhance the mobilization of stem cells in mice with acute myocardial infarction (AMI). However, the upstream signal transduction involved in SDF-1 regulation in the setting of AMI and RSV administration remains unclear. Because RSV is a sirtuin 1 (SIRT1) activator and SIRT proteins act as deacetylases, we investigated the role of SIRT1 in SDF-1 upregulation and its subsequent effects.

Methods and Results

In vitro experiments with H9C2 cardiomyocytes under hypoxia and serum-deprivation conditions showed that p53 acted upstream of SDF-1. RSV could not regulate SDF-1 effectively after SIRT1 silencing, indicating that it is dependent on SIRT1. Subsequently, male C57BL/6 mice were divided into four groups: 1) sham, 2) MI, 3) MI+RSV, and 4) MI+RSV plus nicotinamide, an inhibitor of the deacetylase activity of SIRT (MI+RSV+NAM). Compared with the sham mice, AMI caused a slight increase in the cardiac p53 level and resulted in significant SIRT1 downregulation and p53 acetylation or activation. Compared with the MI mice, MI+RSV administration improved the cardiac SDF-1 level and reversed the reduction of SIRT1 and the activation of p53. Furthermore, we observed less cardiac dysfunction in MI+RSV mice and determined that NAM abolished the effects of RSV.

Conclusions

RSV enhances cardiac SDF-1 excretion after AMI partially through a SIRT1 normalization/p53 inactivation pathway.     

SDF-1 induces TNF-mediated apoptosis in cardiac myocytes

Chemokines are small secreted proteins with chemoattractant properties that play a key role in inflammation. One such chemokine, Stromal cell-derived factor-1 (SDF-1) also known as CXCL12, and its receptor, CXCR4, are expressed and functional in cardiac myocytes. SDF-1 both stimulates and enhances the cellular signal which attracts potentially beneficial stem cells for tissue repair within the ischemic heart. Paradoxically however, this chemokine is known to act in concert with the inflammatory cytokines of the innate immune response which contributes to cellular injury through the recruitment of inflammatory cells during ischemia. In the present study, we have demonstrated that SDF-1 has dose dependent effects on freshly isolated cardiomyocytes. Using Tunnel and caspase 3-activation assays, we have demonstrated that the treatment of isolated adult rat cardiac myocyte with SDF-1 at higher concentrations (pathological concentrations) induced apoptosis. Furthermore, ELISA data demonstrated that the treatment of isolated adult rat cardiac myocyte with SDF-1 at higher concentrations upregulated TNF-α protein expression which directly correlated with subsequent apoptosis. There was a significant reduction in SDF-1 mediated apoptosis when TNF-α expression was neutralized which suggests that SDF-1 mediated apoptosis is TNF-α-dependent. The fact that certain stimuli are capable of driving cardiomyocytes into apoptosis indicates that these cells are susceptible to clinically relevant apoptotic triggers. Our findings suggest that the elevated SDF-1 levels seen in a variety of clinical conditions, including ischemic myocardial infarction, may either directly or indirectly contribute to cardiac cell death via a TNF-α mediated pathway. This highlights the importance of this receptor/ligand in regulating the cardiomyocyte response to stress conditions.     

Stromal-derived factor-1 (SDF-1) expression during early chick development

Cell migration plays a fundamental role in a wide variety of biological processes including development, tissue repair and disease. These processes depend on directed cell migration along and through cell layers. Chemokines are small secretory proteins that exert their effects by activating a family of G-protein coupled receptors and have been shown to play numerous fundamental roles in the control of physiological and pathological processes during development and in adult tissues, respectively. Stromal-derived factor-1 (SDF-1/CXCL12), a ligand of the chemokine receptor, CXCR4, is involved in providing cells with directional cues as well as in controlling their proliferation and differentiation. Here we studied the expression pattern of SDF-1 in the developing chick embryo. We could detect a specific expression of SDF-1 in the ectoderm, the sclerotome, the intersomitic spaces and the developing limbs. The expression domains of SDF-1 reflect its role in somitic precursor migration and vessel formation in the limbs.     

Cell surface peptidase CD26/dipeptidylpeptidase IV regulates CXCL12/stromal cell-derived factor-1 alpha-mediated chemotaxis of human cord blood CD34+ progenitor cells

CD26/dipeptidylpeptidase IV (DPPIV) is a membrane-bound extracellular peptidase that cleaves dipeptides from the N terminus of polypeptide chains. The N terminus of chemokines is known to interact with the extracellular portion of chemokine receptors, and removal of these amino acids in many instances results in significant changes in functional activity. CD26/DPPIV has the ability to cleave the chemokine CXCL12/stromal cell-derived factor 1alpha (SDF-1alpha) at its position two proline. CXCL12/SDF-1alpha induces migration of hemopoietic stem and progenitor cells, and it is thought that CXCL12 plays a crucial role in homing/mobilization of these cells to/from the bone marrow. We found that CD26/DPPIV is expressed by a subpopulation of CD34(+) hemopoietic cells isolated from cord blood and that these cells have DPPIV activity. The involvement of CD26/DPPIV in CD34(+) hemopoietic stem and progenitor cell migration has not been previously examined. Functional studies show that the N-terminal-truncated CXCL12/SDF-1alpha lacks the ability to induce the migration of CD34(+) cord blood cells and acts to inhibit normal CXCL12/SDF-1alpha-induced migration. Finally, inhibiting the endogenous CD26/DPPIV activity on CD34(+) cells enhances the migratory response of these cells to CXCL12/SDF-1alpha. This process of CXCL12/SDF-1alpha cleavage by CD26/DPPIV on a subpopulation of CD34(+) cells may represent a novel regulatory mechanism in hemopoietic stem and progenitor cells for the migration, homing, and mobilization of these cells. Inhibition of the CD26/DPPIV peptidase activity may therefore represent an innovative approach to increasing homing and engraftment during cord blood transplantation.     

Migration of human umbilical cord blood mesenchymal stem cells mediated by stromal cell-derived factor-1/CXCR4 axis via Akt, ERK, and p38 signal transduction pathways

Human mesenchymal stem cells (hMSCs) have been used for cell-based therapies in degenerative disease and as vehicles for delivering therapeutic genes to sites of injury and tumors. Recently, umbilical cord blood (UCB) was identified as a source for MSCs, and human UCB-derived MSCs (hUCB-MSCs) can serve as an alternative source of bone marrow-derived mesenchymal stem cells (BM-MSCs). However, migration signaling pathways required for homing and recruitment of hUCB-MSCs are not fully understood. Stromal cell-derived factor-1 (SDF-1), a ligand for the CXCR4 chemokine receptor, plays a pivotal role in mobilization and homing of stem cells and modulates different biological responses in various stem cells. In this study, expression of CXCR4 in hUCB-MSCs was studied by western blot analysis and the functional role of SDF-1 was assessed. SDF-1 induced the migration of hUCB-MSCs in a dose-dependent manner. The induced migration was inhibited by the CXCR4-specific peptide antagonist (AMD3100) and by inhibitors of phosphoinositide 3-kinase (LY294002), mitogen-activated protein kinase/extracellular signal related kinase (PD98059) and p38MAPK inhibitor (SB203580). hUCB-MSCs treated with SDF-1 displayed increased phosphorylation of Akt, ERK and p38, which were inhibited by AMD3100. Small-interfering RNA-mediated knock-down of Akt, ERK and p38 blocked SDF-1 induced hUCB-MSC migration. In addition, SDF-1-induced actin polymerization was also blocked by these inhibitors. Taken together, these results demonstrate that Akt, ERK and p38 signal transduction pathways may be involved in SDF-1-mediated migration of hUCB-MSCs.     

miR-27b Represses Migration of Mouse MSCs to Burned Margins and Prolongs Wound Repair through Silencing SDF-1a

Background

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.

Methods

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.

Results

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.

Conclusion

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.     

SDF-1 Enhances Wound Healing of Critical-Sized Calvarial Defects beyond Self-Repair Capacity

Host blood circulating stem cells are an important cell source that participates in the repair of damaged tissues. The clinical challenge is how to improve the recruitment of circulating stem cells into the local wound area and enhance tissue regeneration. Stromal-derived factor-1 (SDF-1) has been shown to be a potent chemoattractant of blood circulating stem cells into the local wound microenvironment. In order to investigate effects of SDF-1 on bone development and the repair of a large bone defect beyond host self-repair capacity, the BMP-induced subcutaneous ectopic bone formation and calvarial critical-sized defect murine models were used in this preclinical study. A dose escalation of SDF-1 were loaded into collagen scaffolds containing BMP, VEGF, or PDGF, and implanted into subcutaneous sites at mouse dorsa or calvarial critical-sized bone defects for 2 and 4 weeks. The harvested biopsies were examined by microCT and histology. The results demonstrated that while SDF-1 had no effect in the ectopic bone model in promoting de novo osteogenesis, however, in the orthotopic bone model of the critical-sized defects, SDF-1 enhanced calvarial critical-sized bone defect healing similar to VEGF, and PDGF. These results suggest that SDF-1 plays a role in the repair of large critical-sized defect where more cells are needed while not impacting de novo bone formation, which may be associated with the functions of SDF-1 on circulating stem cell recruitment and angiogenesis.     

高同型半胱氨酸血症对心肌梗死后心肌组织中SCF表达的影响

目的通过观察高同型半胱氨酸血症(HHCY)对心肌梗死后大鼠心肌组织中干细胞因子(SCF)表达的影响,探讨HHCY在心肌梗死(MI)后干细胞归巢并修复梗死心肌过程中的作用。方法饮食诱导大鼠HHCY的动物模型;随后建立大鼠MI模型;利用免疫组织化学染色及RT-PCR技术分别检测HHCY对MI后大鼠MI区域及MI灶周围心肌组织内SCF表达的影响。结果MI后大鼠MI灶周围心肌组织中SCF的表达增强(与假结扎组相比);高蛋氨酸饮食组大鼠MI灶周围心肌组织内SCF的表达显著减少(与对照组相比);补充叶酸降低了大鼠血清中同型半胱氨酸浓度,增强了MI灶周围心肌组织内SCF的表达。结论MI上调了MI灶周围心肌组织中SCF的表达,有利于干细胞的归巢并修复梗死的心肌;HHCY抑制了MI灶周围心肌组织内SCF的表达,从而减少由SCF所诱导的干细胞归巢到MI区域,进而抑制了梗死后心肌的修复。     

Mobilization of bone marrow-derived progenitor cells in acute coronary syndromes

Two hypotheses explain the role of adult progenitor cells in myocardial regeneration. Stem cell plasticity which involves mobilization of stem cells from the bone marrow and other niches, homing to the area of tissue injury and transdifferentiation into functional cardiomyocytes. Alternative hypothesis is based on the observations that bone marrow harbors a heterogenous population of cells positive for CXCR4 - receptor for chemokine SDF-1. This population of non-hematopoietic cells expresses genes specific for early muscle, myocardial and endothelial progenitor cells (EPC). These tissue-committed stem cells circulate in the peripheral blood at low numbers and can be mobilized by hematopoietic cytokines in the setting of myocardial ischemia. Endothelial precursors capable of transforming into mature, functional endothelial cells are present in the pool of peripheral mononuclear cells in circulation. Their number significantly increases in acute myocardial infarction (AMI) with subsequent decrease after 1 month, as well as in patients with unstable angina in comparison to stable coronary heart disease (CHD). There are numerous physiological and pathological stimuli which influence the number of circulating EPC such as regular physical activity, medications (statins, PPAR-gamma agonists, estrogens), as well as numerous inflammatory and hematopoietic cytokines. Mobilization of stem cells in AMI involves not only the endothelial progenitors but also hematopoietic, non-hematopoietic stem cells and most probably the mesenchymal cells. In healthy subjects and patients with stable CHD, small number of circulating CD34+, CXCR4+, CD117+, c-met+ and CD34/CD117+ stem cells can be detected. In patients with AMI, a significant increase in CD34+/CXCR4+, CD117+, c-met+ and CD34/CD117+ stem cell number the in peripheral blood was demonstrated with parallel increase in mRNA expression for early cardiac, muscle and endothelial markers in peripheral blood mononuclear cells. The maximum number of stem cells was found early in ST-segment elevation myocardial infarction (<12 hours) with subsequent decrease through the 7-day follow-up and with concomitant changes in the levels of cytokines involved in the inflammatory response and stem cell recruitment. Moreover, peak expression of cardiac muscle and endothelial markers occurred at the same time as the most significant increase in CD34/CXCR4+ stem cell number. The SDF-1/CXCR-4 axis seems particularly important in stem/muscle progenitor cell homing, chemotaxis, engraftment and retention in ischaemic myocardium. The significance of autologous stem cells mobilization in terms of cardiac salvage and regeneration needs to be proved in humans but it seems to be a reparative mechanism triggered early in the course of acute coronary syndromes.     

SDF-1/CXCR4 mediates acute protection of cardiac function through myocardial STAT3 signaling following global ischemia/reperfusion injury

Stromal cell-derived factor-1α (SDF-1) has been reported to mediate cardioprotection through the mobilization of stem cells into injured tissue and an increase in local angiogenesis after myocardial infarction. However, little is known regarding whether SDF-1 induces acute protection following global myocardial ischemia/reperfusion (I/R) injury and if so, by what molecular mechanism. SDF-1 binding to its cognate receptor CXCR4 has been shown to activate STAT3 in a variety of cells. STAT3 is a cardioprotective factor and may mediate SDF-1/CXCR4-induced acute protection. We hypothesized that SDF-1 would improve myocardial function through CXCR4-increased STAT3 activation following acute I/R. Isolated mouse hearts were subjected to 25-min global ischemia/40-min reperfusion and divided into groups of 1) vehicle; 2) SDF-1; 3) AMD3100, a CXCR4 inhibitor; 4) SDF-1 + AMD3100; 5) Stattic, a STAT3 inhibitor; 6) SDF-1 + Stattic; 7) cardiomyocyte-restricted ablation of STAT3 (STAT3KO); 8) STAT3KO + SDF-1; 9) Ly294002, an inhibitor of the Akt pathway; and 10) SDF-1 + Ly294002. Reagents were infused into hearts within 5 min before ischemia. SDF-1 administration significantly improved postischemic myocardial functional recovery in a dose-dependent manner. Additionally, pretreatment with SDF-1 reduced cardiac apoptotic signaling and increased myocardial STAT3 activation following acute I/R. Inhibition of the SDF-1 receptor CXCR4 neutralized these protective effects by SDF-1 in hearts subjected to I/R. Notably, inhibition of the STAT3 pathway or use of STAT3KO hearts abolished SDF-1-induced acute protection following myocardial I/R. Our results represent the first evidence that the SDF-1/CXCR4 axis upregualtes myocardial STAT3 activation and, thereby, mediates acute cardioprotection in response to global I/R.     

microRNA-27b suppresses mouse MSC migration to the liver by targeting SDF-1αin vitro

The SDF-1/CXCR4 axis is critical for inducing stem cell mobilization into the circulation, for homing stem cells to the site of injury, and for stem cell participation in the regeneration of liver tissue. In this study, we have gained insight into the molecular mechanisms involved in regulating the expression of SDF-1α by miRNAs. Using microarray and bioinformatics approaches, we identified six miRNAs with differential expression in damaged liver tissue (21 days after liver injury) compared to normal C57BL/6 murine liver tissue and further confirmed these observations by qPCR; miR-23a, which was identified by other researchers, was also included for comparative purposes. We found that miR-23a, miR-27a and miR-27b expression was significantly lower in the damaged liver than in the normal liver (p<0.05). We further confirmed that miR-27b could directly interact with the 3'UTR of SDF-1α to suppress SDF-1α protein expression using a luciferase reporter assay and Western blot analysis. In addition, we found that the over-expression of miR-27b significantly reduced the directional migration of primary cultured CRCX4-positive murine mesenchymal stem cells (mMSCs) in vitro using a transwell assay. These results suggest that miR-27b may be a unique signature of the stem cell niche in the damaged mouse liver and that mir-27b can suppress the directional migration of mMSCs by down-regulating SDF-1α expression by binding directly to the SDF-1α 3'UTR.     

Sca-1+ cardiac stem cells mediate acute cardioprotection via paracrine factor SDF-1 following myocardial ischemia/reperfusion

Background

Cardiac stem cells (CSCs) promote myocardial recovery following ischemia through their regenerative properties. However, little is known regarding the implication of paracrine action by CSCs in the setting of myocardial ischemia/reperfusion (I/R) injury although it is well documented that non-cardiac stem cells mediate cardioprotection via the production of paracrine protective factors. Here, we studied whether CSCs could initiate acute protection following global myocardial I/R via paracrine effect and what component from CSCs is critical to this protection.

Methodology/Principal Findings

A murine model of global myocardial I/R was utilized to investigate paracrine effect of Sca-1+ CSCs on cardiac function. Intracoronary delivery of CSCs or CSC conditioned medium (CSC CM) prior to ischemia significantly improved myocardial function following I/R. siRNA targeting of VEGF in CSCs did not affect CSC-preserved myocardial function in response to I/R injury. However, differentiation of CSCs to cardiomyocytes (DCSCs) abolished this protection. Through direct comparison of the protein expression profiles of CSCs and DCSCs, SDF-1 was identified as one of the dominant paracrine factors secreted by CSCs. Blockade of the SDF-1 receptor by AMD3100 or downregulated SDF-1 expression in CSCs by specific SDF-1 siRNA dramatically impaired CSC-induced improvement in cardiac function and increased myocardial damage following I/R. Of note, CSC treatment increased myocardial STAT3 activation after I/R, whereas downregulation of SDF-1 action by blockade of the SDF-1 receptor or SDF-1 siRNA transfection abolished CSC-induced STAT3 activation. In addition, inhibition of STAT3 activation attenuated CSC-mediated cardioprotection following I/R. Finally, post-ischemic infusion of CSC CM was shown to significantly protect I/R-caused myocardial dysfunction.

Conclusions/Significance

This study suggests that CSCs acutely improve post-ischemic myocardial function through paracrine factor SDF-1 and up-regulated myocardial STAT3 activation.     

SDF-1/CXCR4 axis modulates bone marrow mesenchymal stem cell apoptosis,migration and cytokine secretion

Bone marrow mesenchymal stem cells (MSCs) are considered as a promising cell source to treat the acute myocardial infarction. However, over 90% of the stem cells usually die in the first three days of transplantation. Survival potential, migration ability and paracrine capacity have been considered as the most important three factors for cell transplantation in the ischemic cardiac treatment. We hypothesized that stromal-derived factor-1 (SDF-1)/CXCR4 axis plays a critical role in the regulation of these processes. In this study, apoptosis was induced by exposure of MSCs to H₂O₂ for 2 h. After re-oxygenation, the SDF-1 pretreated MSCs demonstrated a significant increase in survival and proliferation. SDF-1 pretreatment also enhanced the migration and increased the secretion of pro-survival and angiogenic cytokines including basic fibroblast growth factor and vascular endothelial growth factor. Western blot and RT-PCR demonstrated that SDF-1 pretreatment significantly activated the pro-survival Akt and Erk signaling pathways and up-regulated Bcl-2/Bax ratio. These protective effects were partially inhibited by AMD3100, an antagonist of CXCR4. We conclude that the SDF-1/CXCR4 axis is critical for MSC survival, migration and cytokine secretion.     

Apelin-13 increases myocardial progenitor cells and improves repair postmyocardial infarction

Apelin is an endogenous ligand for the angiotensin-like 1 receptor (APJ) and has beneficial effects against myocardial ischemia-reperfusion injury. Little is known about the role of apelin in the homing of vascular progenitor cells (PCs) and cardiac functional recovery postmyocardial infarction (post-MI). The present study investigated whether apelin affects PC homing to the infarcted myocardium, thereby mediating repair and functional recovery post-MI. Mice were infarcted by coronary artery ligation, and apelin-13 (1 mg·kg(-1)·day(-1)) was injected for 3 days before MI and for 14 days post-MI. Homing of vascular PCs [CD133(+)/c-Kit(+)/Sca1(+), CD133(+)/stromal cell-derived factor (SDF)-1α(+), and CD133(+)/CXC chemokine receptor (CXCR)-4(+)] into the ischemic area was examined. Myocardial Akt, endothelial nitric oxide synthase (eNOS), VEGF, jagged1, notch3, SDF-1α, and CXCR-4 expression were assessed at 24 h and 14 days post-MI. Functional analyses were performed on day 14 post-MI. Mice that received apelin-13 treatment demonstrated upregulation of SDF-1α/CXCR-4 expression and dramatically increased the number of CD133(+)/c-Kit(+)/Sca1(+), CD133(+)/SDF-1α(+), and c-Kit(+)/CXCR-4(+) cells in infarcted hearts. Apelin-13 also significantly increased Akt and eNOS phosphorylation and upregulated VEGF, jagged1, and notch3 expression in ischemic hearts. This was accompanied by a significant reduction of myocardial apoptosis. Furthermore, treatment with apelin-13 promoted myocardial angiogenesis and attenuated cardiac fibrosis and hypertrophy together with a significant improvement of cardiac function at 14 days post-MI. Apelin-13 increases angiogenesis and improves cardiac repair post-MI by a mechanism involving the upregulation of SDF-1α/CXCR-4 and homing of vascular PCs.