Stromal cell derived factor-1 alpha confers protection against myocardial ischemia/reperfusion injury: role of the cardiac stromal cell derived factor-1 alpha CXCR4 axis

Hypoxic preconditioning enhances the benefit of cardiac progenitor cell therapy for treatment of myocardial infarction by inducing CXCR4 expression

Myocardial infarction rapidly depletes the endogenous cardiac progenitor cell pool, and the inefficient recruitment of exogenously administered progenitor cells limits the effectiveness of cardiac cell therapy. Recent reports indicate that interactions between the CXC chemokine stromal cell-derived factor 1 and its receptor CXC chemokine receptor 4 (CXCR4) critically mediate the ischemia-induced recruitment of bone marrow-derived circulating stem/progenitor cells, but the expression of CXCR4 in cardiac progenitor cells is very low. Here, we studied the influence of hypoxia on CXCR4 expression in cardiac progenitor cells, on the recruitment of intravenously administered cells to ischemic heart tissue, and on the preservation of heart function in a murine myocardial infarction model. We found that hypoxic preconditioning increased CXCR4 expression in CLK (cardiosphere-derived, Lin(-)c-kit(+) progenitor) cells and markedly augmented CLK cell migration (in vitro) and recruitment (in vivo) to the ischemic myocardium. Four weeks after surgically induced myocardial infarction, infarct size and heart function were significantly better in mice administered hypoxia-preconditioned CLK cells than in mice treated with cells cultured under normoxic conditions. Furthermore, these effects were largely abolished by the addition of a CXCR4 inhibitor, indicating that the benefits of hypoxic preconditioning are mediated by the stromal cell-derived factor 1/CXCR4 axis, and that therapies targeting this axis may enhance cardiac-progenitor cell-based regenerative therapy.

Role of stromal cell-derived factor-1alpha, level and value of circulating interleukin-10 and endothelial progenitor cells in patients with acute myocardial infarction undergoing primary coronary angioplasty

BACKGROUND

The relationships among the circulating levels of endothelial progenitor cells (EPC), stromal cell-derived factor (SDF)-1alpha, interleukin (IL)-10 and outcome were examined in patients with ST-segment elevation acute myocardial infarction (ST-se AMI) undergoing primary coronary angioplasty.

METHODS AND RESULTS

Circulating levels of IL-10, SDF-1alpha, and EPCs [defined by staining markers: CD31/CD34 (E(1)) and KDR/CD34 (E(2))] were examined by ELISA and flow cytometry, respectively. The IL-10 level was higher, whereas the circulating level of EPCs (E(1-2)) was lower (all P<0.05) in AMI patients than in normal subjects. Additionally, the SDF-1alpha level was significantly and independently predictive of an increased level of circulating EPCs (E(1-2)) (P<0.0001). Furthermore, patients with a high SDF-1alpha level (>1,500 pg/ml) had lower left ventricular performance, higher Killip score (defined as >or=3), and increased 30-day mortality than those with low SDF-1alpha level (<or=1,500 pg/ml) (all P<0.007). Moreover, high circulating levels of E(2) and IL-10 were the most significant independent predictors of increased 30-day major adverse clinical outcome (MACO) (defined as advanced Killip score >or=3 or 30-day mortality) (P<0.01).

CONCLUSIONS

The serum SDF-1alpha level is independently predictive of an increased level of circulating EPCs (E(1-2)). E(2) and IL-10 are major independent predictors of 30-day MACO in ST-se AMI patients undergoing primary coronary angioplasty.

SDF-1alpha stimulates JNK3 activity via eNOS-dependent nitrosylation of MKP7 to enhance endothelial migration

The chemokine stromal cell-derived factor-1alpha (SDF-1alpha) is a pivotal player in angiogenesis. It is capable of influencing such cellular processes as tubulogenesis and endothelial cell migration, yet very little is known about the actual signaling events that mediate SDF-1alpha-induced endothelial cell function. In this report, we describe the identification of an intricate SDF-1alpha-induced signaling cascade that involves endothelial nitric oxide synthase (eNOS), JNK3, and MAPK phosphatase 7 (MKP7). We demonstrate that the SDF-1alpha-induced activation of JNK3, critical for endothelial cell migration, depends on the prior activation of eNOS. Specifically, activation of eNOS leads to production of NO and subsequent nitrosylation of MKP7, rendering the phosphatase inactive and unable to inhibit the activation of JNK3. These observations reinforce the importance of nitric oxide and S-nitrosylation in angiogenesis and provide a mechanistic pathway for SDF-1alpha-induced endothelial cell migration. In addition, the discovery of this interactive network of pathways provides novel and unexpected therapeutic targets for angiogenesis-dependent diseases.

Extracellular calcium increases CXCR4 expression on bone marrow-derived cells and enhances pro-angiogenesis therapy

Cell surface receptors play major roles in the mobilization and homing of progenitor cells from the bone marrow to peripheral tissues. CXCR4 is an important receptor that regulates homing of leucocytes and endothelial progenitors in response to the chemokine stromal cell-derived factor-1 (SDF-1). Ionic calcium is also known to regulate chemotaxis of selective bone marrow cells (BMCs) through the calcium-sensing receptor, CaR. Here we show that calcium regulates CXCR4 expression and BMC responses to SDF-1. CaCl₂ treatment of BMC induced a time- and dose-dependent increase in both the transcription and cell surface expression of CXCR4. BMC subpopulations expressing VEGFR2⁺, CD34⁺ and cKit⁺/Sca-1⁺ were especially sensitive to calcium. The effects were blocked by calcium influx inhibitors, anti-CaR antibody and the protein synthesis inhibitor cycloheximide, but not by the CXCR4 antagonist AMD3100. Calcium treatment also enhanced SDF-1-mediated CXCR4 internalization. These changes were reflected in significantly improved chemotaxis by SDF-1, which was abolished by AMD3100 and by antibody against CXCR4. Calcium pre-treatment improved homing of CD34⁺ BMCs to ischemic muscle in vivo, and enhanced revascularization in ischemic mouse hindlimbs. Our results identify calcium as a positive regulator of CXCR4 expression that promotes stem cell mobilization, homing and therapy.

Stem cell homing and angiomyogenesis in transplanted hearts are enhanced by combined intramyocardial SDF-1alpha delivery and endogenous cytokine signaling

We used a heterotopic transplanted working heart model to probe the collaborative role of bone marrow-derived progenitor cells (BPCs) and stromal cell-derived factor (SDF)-1alpha in attenuating tissue remodeling in recipient and transplanted hearts. BPCs from male transgenic rats expressing green fluorescent protein (GFP(+) BPCs, 2 x 10(6) cells) were injected intravenously into myeloablated female rats. One month later, heterotopic heart transplantation was performed. The left anterior descending coronary artery (LAD) of the recipient heart was occluded permanently. Mesenchymal stem cells (MSCs; 2 x 10(6) cells) with a null gene (null group) or overexpressing SDF-1alpha (SDF-1alpha group) were injected intramyocardially in the LAD perfusion region of both recipient and transplanted hearts. Recipient and transplanted hearts (n = 10 hearts/group) were harvested 21 days later for analysis. The survival of transplanted hearts was assessed daily by palpation in additional animals (n = 7). Five days after LAD occlusion, subpopulations of GFP(+) BPCs in the circulation were significantly higher in the SDF-1alpha group. Y chromosome, 5-bromo-2'-deoxyuridine, Ki67-positive nuclei, newly formed vessels, and GFP(+) cells significantly increased in transplanted hearts of the SDF-1alpha group at 21 days after the injection of MSCs overexpressing SDF-1alpha, whereas fewer TUNEL-positive nuclei were found. The survival of transplanted hearts was also markedly increased in the SDF-1alpha group (P < 0.05). Supplementation of endogenous cytokines released from the ischemic myocardium with exogenous MSCs overexpressing SDF-1alpha significantly increased BPC homing to acutely ischemic recipient and progressively ischemic transplanted hearts. BPC recruitment resulted in the regeneration of new cardiomyocytes and blood vessels and extended survival of the transplanted hearts.

Cell therapy generates a favourable chemokine gradient for stem cell recruitment into the infarcted heart in rabbits

AIMS

Stem cell recruitment into the heart is determined by a concentration gradient of stromal-derived factor 1 (SDF-1) from bone marrow to peripheral blood and from blood to injured myocardium. However, this gradient is decreased in chronic myocardial infarction (MI). This study evaluated the effect of cell therapy using bone marrow stromal cells (BMSCs) on an SDF-1 gradient in post-infarction rabbits.

METHODS AND RESULTS

Myocardial infarction was induced in male New Zealand white rabbits (2.5-3 kg) by ligation of the left anterior descending coronary artery. Two months later, the rabbits were randomized to either saline or BMSC (2 x 10(6) autologous BMSCs injected into the left ventricular cavity) treatment. Four weeks after therapy, the SDF-1 gradients from bone marrow to blood and from blood to myocardium increased in the BMSC group compared with the saline group. This was accompanied by an increase in cells positive for CD34, CD117, and STRO-1 in the myocardium, resulting in more capillary density, better cardiac function, and a decrease in infarct size.

CONCLUSION

Generation of an SDF-1 gradient towards the heart is a novel effect of BMSC-based cell therapy. This effect facilitates stem cell recruitment into remodelled myocardium and supports improvement in cardiac function.

CXCR4 antagonists: targeting the microenvironment in leukemia and other cancers

Hematopoietic and epithelial cancer cells express CXCR4, a seven-transmembrane G-protein-coupled chemokine receptor. Stromal cells within the bone marrow microenvironment constitutively secrete stromal cell-derived factor-1 (SDF-1/CXCL12), the ligand for CXCR4. Activation of CXCR4 induces leukemia cell trafficking and homing to the marrow microenvironment, where CXCL12 retains leukemia cells in close contact with marrow stromal cells that provide growth and drug resistance signals. CXCR4 antagonists, such as Plerixafor (AMD3100) and T140 analogs, can disrupt adhesive tumor-stroma interactions and mobilize leukemia cells from their protective stromal microenvironment, making them more accessible to conventional drugs. Therefore, targeting the CXCR4-CXCL12 axis is a novel, attractive therapeutic approach that is explored in ongoing clinical trials in leukemia patients. Initially, CXCR4 antagonists were developed for the treatment of HIV, where CXCR4 functions as a co-receptor for virus entry into T cells. Subsequently, CXCR4 antagonists were noticed to induce leukocytosis, and are currently used clinically for mobilization of hematopoietic stem cells. However, because CXCR4 plays a key role in cross-talk between leukemia cells (and a variety of other tumor cells) and their microenvironment, cancer treatment may become the ultimate application of CXCR4 antagonists. Here, we summarize the development of CXCR4 antagonists and their preclinical and clinical activities, focusing on leukemia and other cancers.

Engineered microenvironments for human stem cells

Regulation of cell differentiation and assembly remains a fundamental question in developmental biology. During development, tissues emerge from coordinated sequences of the renewal, differentiation, and assembly of stem cells. Likewise, regeneration of an adult tissue is driven by the migration and differentiation of repair cells. The fields of stem cells and regenerative medicine are starting to realize how important is the entire context of the cell environment, with the presence of other cells, three-dimensional matrices, and sequences of molecular and physical morphogens. The premise is that to unlock the full potential of stem cells, at least some aspects of the dynamic environments normally present in vivo need to be reconstructed in experimental systems used in vitro. We review here some recent work that utilized engineered environments for guiding the embryonic and adult human stem cells, and focus on vasculogenesis as a critical and universally important aspect of tissue development and regeneration. Birth Defects Research (Part C) 84:335-347, 2008. (c) 2008 Wiley-Liss, Inc.

IGF-1-overexpressing mesenchymal stem cells accelerate bone marrow stem cell mobilization via paracrine activation of SDF-1alpha/CXCR4 signaling to promote myocardial repair

We hypothesized that mesenchymal stem cells (MSCs) overexpressing insulin-like growth factor (IGF)-1 showed improved survival and engraftment in the infarcted heart and promoted stem cell recruitment through paracrine release of stromal cell-derived factor (SDF)-1alpha. Rat bone marrow-derived MSCs were used as nontransduced ((Norm)MSCs) or transduced with adenoviral-null vector ((Null)MSCs) or vector encoding for IGF-1 ((IGF-1)MSCs). (IGF-1)MSCs secreted higher IGF-1 until 12 days of observation (P<0.001 versus (Null)MSCs). Molecular studies revealed activation of phosphoinositide 3-kinase, Akt, and Bcl.xL and inhibition of glycogen synthase kinase 3beta besides release of SDF-1alpha in parallel with IGF-1 expression in (IGF-1)MSCs. For in vivo studies, 70 muL of DMEM without cells (group 1) or containing 1.5x10(6) (Null)MSCs (group 2) or (IGF-1)MSCs (group 3) were implanted intramyocardially in a female rat model of permanent coronary artery occlusion. One week later, immunoblot on rat heart tissue (n=4 per group) showed elevated myocardial IGF-1 and phospho-Akt in group 3 and higher survival of (IGF-1)MSCs (P<0.06 versus (Null)MSCs) (n=6 per group). SDF-1alpha was increased in group 3 animal hearts (20-fold versus group 2), with massive mobilization and homing of ckit(+), MDR1(+), CD31(+), and CD34(+) cells into the infarcted heart. Infarction size was significantly reduced in cell transplanted groups compared with the control. Confocal imaging after immunostaining for myosin heavy chain, actinin, connexin-43, and von Willebrand factor VIII showed extensive angiomyogenesis in the infarcted heart. Indices of left ventricular function, including ejection fraction and fractional shortening, were improved in group 3 as compared with group 1 (P<0.05). In conclusion, the strategy of IGF-1 transgene expression induced massive stem cell mobilization via SDF-1alpha signaling and culminated in extensive angiomyogenesis in the infarcted heart.

Myocardial repair: from salvage to tissue reconstruction

Cardiac tissue reconstruction following myocardial infarction represents a major challenge in cardiovascular therapy, as current clinical approaches are limited in their ability to regenerate or replace damaged myocardium. Thus, different novel treatments have been introduced aimed at myocardial salvage and repair. Here, we present a review of recent advancements in cardiac cell, gene-based and tissue engineering therapies. Selected strategies in cell therapy and new tools for myocardial gene transfer are summarized. Finally, we consider novel approaches to myocardial tissue engineering as a platform for the integration of various modalities in an attempt to rejuvenate infarcted tissue in vivo.

Strategies to promote donor cell survival: combining preconditioning approach with stem cell transplantation

Stem cell transplantation has emerged as a potential modality in cardiovascular therapeutics due to their inherent characteristics of self-renewal, unlimited capacity for proliferation and ability to cross lineage restrictions and adopt different phenotypes. Constrained by extensive death in the unfriendly milieu of ischemic myocardium, the results of heart cell therapy in experimental animal models as well as clinical studies have been less than optimal. Several factors which play a role in early cell death after engraftment in the ischemic myocardium include: absence of survival factors in the transplanted heart, disruption of cell-cell interaction coupled with loss of survival signals from matrix attachments, insufficient vascular supply and elaboration of inflammatory cytokines resulting from ischemia and/or cell death. This article reviews various signaling pathways involved in triggering highly complex forms of cell death and provides critical appreciation of different novel anti-death strategies developed from the knowledge gained from using an ischemic preconditioning approach. The use of pharmacological preconditioning for up-regulation of pro-survival proteins and cardiogenic markers in the transplanted stem cells will be discussed.

Cardiomyocyte death and renewal in the normal and diseased heart

During post-natal maturation of the mammalian heart, proliferation of cardiomyocytes essentially ceases as cardiomyocytes withdraw from the cell cycle and develop blocks at the G0/G1 and G2/M transition phases of the cell cycle. As a result, the response of the myocardium to acute stress is limited to various forms of cardiomyocyte injury, which can be modified by preconditioning and reperfusion, whereas the response to chronic stress is dominated by cardiomyocyte hypertrophy and myocardial remodeling. Acute myocardial ischemia leads to injury and death of cardiomyocytes and nonmyocytic stromal cells by oncosis and apoptosis, and possibly by a hybrid form of cell death involving both pathways in the same ischemic cardiomyocytes. There is increasing evidence for a slow, ongoing turnover of cardiomyocytes in the normal heart involving death of cardiomyocytes and generation of new cardiomyocytes. This process appears to be accelerated and quantitatively increased as part of myocardial remodeling. Cardiomyocyte loss involves apoptosis, autophagy, and oncosis, which can occur simultaneously and involve different individual cardiomyocytes in the same heart undergoing remodeling. Mitotic figures in myocytic cells probably represent maturing progeny of stem cells in most cases. Mitosis of mature cardiomyocytes that have reentered the cell cycle appears to be a rare event. Thus, cardiomyocyte renewal likely is mediated primarily by endogenous cardiac stem cells and possibly by blood-born stem cells, but this biological phenomenon is limited in capacity. As a consequence, persistent stress leads to ongoing remodeling in which cardiomyocyte death exceeds cardiomyocyte renewal, resulting in progressive heart failure. Intense investigation currently is focused on cell-based therapies aimed at retarding cardiomyocyte death and promoting myocardial repair and possibly regeneration. Alteration of pathological remodeling holds promise for prevention and treatment of heart failure, which is currently a major cause of morbidity and mortality and a major public health problem. However, a deeper understanding of the fundamental biological processes is needed in order to make lasting advances in clinical therapeutics in the field.

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.