Stromal cell-derived factor-1alpha is cardioprotective after myocardial infarction

Functional regeneration of ischemic myocardium by transplanted cells overexpressing stromal cell-derived factor-1 (SDF-1): intramyocardial injection versus scaffold-based application

OBJECTIVE

Stromal cell-derived factor-1 (SDF-1) is a potent chemotaxin. Increased SDF-1 levels can be found in ischemic myocardium and might protect against ischemia-reperfusion injury. We hypothesized that transplantation of stem cells overexpressing SDF-1 might improve cardiac function after myocardial infarction (MI). We compared intramyocardial injection with a scaffold-based application of SDF-1-transfected cells.

METHODS

Skeletal myoblasts (SkMs) were isolated and expanded from newborn Lewis rats. Cells were transfected with pcDNA3-huSDF-1 and seeded on polyurethane (PU) scaffolds or diluted in medium for cell injection. Two weeks after myocardial infarction, seeded scaffolds were implanted epicardially into rats (group: PU-SDF-1-SkM) or the injection solution was applied intramyocardially (Inj-SDF-1-SkM). Additional groups were treated with non-transfected myoblasts either by injection (Inj-SkM) or by scaffold-based application (PU-SkM) or received a sham operation (Sham). Before this intervention and 6 weeks later, hemodynamic parameters were measured. Infarction size and neovascularization were assessed by histology at study end.

RESULTS

In sham animals, we detected a clear decrease in systolic function from intervention to study end. In group Inj-SkM and PU-SkM, all hemodynamic parameters that were assessed remained unchanged during observation time. Systolic function as measured by dP/dt(max) and SB-Emax was significantly improved in groups Inj-SDF-1-SkM and PU-SDF-1-SkM at study end without a difference between the two SDF-1 groups. Diastolic function measured by post-interventional dP/dt(min) was also increased in group Inj-SDF-1-SkM but not in PU-SDF-1-SkM. Histological analysis revealed a reduced infarction size in all treatment groups at study end but enhanced neovascularization was not observable.

CONCLUSIONS

Transplantation of myoblasts overexpressing SDF-1 improves cardiac function after MI. The restoration of hemodynamic parameters is accompanied by a reduction in infarction size. This reverse remodeling capacity is independent of a scaffold-based application of the SDF-1-transfected cells.

Managing diabetes in Asia: overcoming obstacles and the role of DPP-IV inhibitors

Asia bears the world's greatest burden of type 2 diabetes (T2DM) and prevalence is increasing rapidly. Compared to other races, Asians develop T2DM younger, at a lower degree of obesity, suffer longer from its complications and die earlier. Curbing this epidemic requires an integrated, risk-based, and multidisciplinary approach. Inadequately managed T2DM has macrovascular and microvascular sequelae, Asians with T2DM being particularly susceptible to diabetic nephropathy. Earlier and more intensive monitoring and management of risk factors are required, especially for patients with, or at risk of, renal impairment. Particular challenges of T2DM management in Asia include: lack of access to specialist healthcare, insufficient clinical evaluation and delayed diagnosis. As in Caucasians, conventional treatment modalities are limited by deteriorating glycaemic control with disease progression and there is an unmet need for efficacious, safe, cost-effective and convenient pharmacotherapies for treating different stages of T2DM and preventing its complications, particularly in high-risk patients. There is a trend towards increasing use of DPP-IV inhibitors, which are no less efficacious and safe in Asians than Caucasians and may have some advantages over existing oral antidiabetic agents, particularly for certain high-risk groups. Such agents may play a significant future role in the management of T2DM.

Myocardial tissue elastic properties determined by atomic force microscopy after stromal cell-derived factor 1α angiogenic therapy for acute myocardial infarction in a murine model

OBJECTIVES

Ventricular remodeling after myocardial infarction begins with massive extracellular matrix deposition and resultant fibrosis. This loss of functional tissue and stiffening of myocardial elastic and contractile elements starts the vicious cycle of mechanical inefficiency, adverse remodeling, and eventual heart failure. We hypothesized that stromal cell-derived factor 1α (SDF-1α) therapy to microrevascularize ischemic myocardium would rescue salvageable peri-infarct tissue and subsequently improve myocardial elasticity.

METHODS

Immediately after left anterior descending coronary artery ligation, mice were randomly assigned to receive peri-infarct injection of either saline solution or SDF-1α. After 6 weeks, animals were killed and samples were taken from the peri-infarct border zone and the infarct scar, as well as from the left ventricle of noninfarcted control mice. Determination of tissues' elastic moduli was carried out by mechanical testing in an atomic force microscope.

RESULTS

SDF-1α-treated peri-infarct tissue most closely approximated the elasticity of normal ventricle and was significantly more elastic than saline-treated peri-infarct myocardium (109 ± 22.9 kPa vs 295 ± 42.3 kPa; P < .0001). Myocardial scar, the strength of which depends on matrix deposition from vasculature at the peri-infarct edge, was stiffer in SDF-1α-treated animals than in controls (804 ± 102.2 kPa vs 144 ± 27.5 kPa; P < .0001).

CONCLUSIONS

Direct quantification of myocardial elastic properties demonstrates the ability of SDF-1α to re-engineer evolving myocardial infarct and peri-infarct tissues. By increasing elasticity of the ischemic and dysfunctional peri-infarct border zone and bolstering the weak, aneurysm-prone scar, SDF-1α therapy may confer a mechanical advantage to resist adverse remodeling after infarction.

Repair after myocardial infarction, between fantasy and reality: the role of chemokines

Despite considerable progress over the last decades, acute myocardial infarction continues to remain the major cause of morbidity and mortality worldwide. The present therapies include only cause-dependent interventions, which are not able to reduce myocardial necrosis and optimize cardiac repair following infarction. This review highlights the cellular and molecular processes after myocardial injury and focuses on chemokines, the main modulators of the inflammatory and reparatory events, as the most valuable drug targets.

Stem cells for cardiac repair in acute myocardial infarction

Despite recent advances in medical therapy, reperfusion strategies, implantable cardioverter-defibrillators and cardiac assist devices, ischemic heart disease is a frequent cause of morbidity and mortality worldwide. Cell therapy has been introduced as a new treatment modality to regenerate lost cardiomyocytes. At present, several cell types seem to improve left ventricular function in animal models as well as in humans, but evidence for true generation of new myocardium is confined to the experimental models. In the clinical perspective, myocardial regeneration has been replaced by myocardial repair, as other mechanisms seem to be involved. Clinical studies on adult stem cells suggest, at best, moderate beneficial effects on surrogate end points, but some applications may qualify for evaluation in larger trials. Complete regeneration of the myocardium by cell therapy after a large myocardial infarction is still visionary, but pluripotent stem cells and tissue engineering are important tools to solve the puzzle.

The bispecific SDF1-GPVI fusion protein preserves myocardial function after transient ischemia in mice

BACKGROUND

CXCR4-positive bone marrow cells (BMCs) are critically involved in cardiac repair mechanisms contributing to preserved cardiac function. Stromal cell-derived factor-1 (SDF-1) is the most prominent BMC homing factor known to augment BMC engraftment, which is a limiting step of stem cell-based therapy. After myocardial infarction, SDF-1 expression is rapidly upregulated and promotes myocardial repair.

METHODS AND RESULTS

We have established a bifunctional protein consisting of an SDF-1 domain and a glycoprotein VI (GPVI) domain with high binding affinity to the SDF-1 receptor CXCR4 and extracellular matrix proteins that become exposed after tissue injury. SDF1-GPVI triggers chemotaxis of CXCR4-positive cells, preserves cell survival, enhances endothelial differentiation of BMCs in vitro, and reveals proangiogenic effects in ovo. In a mouse model of myocardial infarction, administration of the bifunctional protein leads to enhanced recruitment of BMCs, increases capillary density, reduces infarct size, and preserves cardiac function.

CONCLUSIONS

These results indicate that administration of SDF1-GPVI may be a promising strategy to treat myocardial infarction to promote myocardial repair and to preserve cardiac function.

Progenitor cell mobilization and recruitment: SDF-1, CXCR4, α4-integrin, and c-kit

Progenitor cell retention and release are largely governed by the binding of stromal-cell-derived factor 1 (SDF-1) to CXC chemokine receptor 4 (CXCR4) and by α4-integrin signaling. Both of these pathways are dependent on c-kit activity: the mobilization of progenitor cells in response to either CXCR4 antagonism or α4-integrin blockade is impaired by the loss of c-kit kinase activity; and c-kit-kinase inactivation blocks the retention of CXCR4-positive progenitor cells in the bone marrow. SDF-1/CXCR4 and α4-integrin signaling are also crucial for the retention of progenitor cells in the ischemic region, which may explain, at least in part, why clinical trials of progenitor cell therapy have failed to display the efficacy observed in preclinical investigations. The lack of effectiveness is often attributed to poor retention of the transplanted cells and, to date, most of the trial protocols have mobilized cells with injections of granulocyte colony-stimulating factor (G-CSF), which activates extracellular proteases that irreversibly cleave cell-surface adhesion molecules, including α4-integrin and CXCR4. Thus, the retention of G-CSF-mobilized cells in the ischemic region may be impaired, and the mobilization of agents that reversibly disrupt SDF-1/CXCR4 binding, such as AMD3100, may improve patient response. Efforts to supplement SDF-1 levels in the ischemic region may also improve progenitor cell recruitment and the effectiveness of stem cell therapy.

Activation of growth hormone releasing hormone (GHRH) receptor stimulates cardiac reverse remodeling after myocardial infarction (MI)

Both cardiac myocytes and cardiac stem cells (CSCs) express the receptor of growth hormone releasing hormone (GHRH), activation of which improves injury responses after myocardial infarction (MI). Here we show that a GHRH-agonist (GHRH-A; JI-38) reverses ventricular remodeling and enhances functional recovery in the setting of chronic MI. This response is mediated entirely by activation of GHRH receptor (GHRHR), as demonstrated by the use of a highly selective GHRH antagonist (MIA-602). One month after MI, animals were randomly assigned to receive: placebo, GHRH-A (JI-38), rat recombinant GH, MIA-602, or a combination of GHRH-A and MIA-602, for a 4-wk period. We assessed cardiac performance and hemodynamics by using echocardiography and micromanometry derived pressure-volume loops. Morphometric measurements were carried out to determine MI size and capillary density, and the expression of GHRHR was assessed by immunofluorescence and quantitative RT-PCR. GHRH-A markedly improved cardiac function as shown by echocardiographic and hemodynamic parameters. MI size was substantially reduced, whereas myocyte and nonmyocyte mitosis was markedly increased by GHRH-A. These effects occurred without increases in circulating levels of growth hormone and insulin-like growth factor I and were, at least partially, nullified by GHRH antagonism, confirming a receptor-mediated mechanism. GHRH-A stimulated CSCs proliferation ex vivo, in a manner offset by MIA-602. Collectively, our findings reveal the importance of the GHRH signaling pathway within the heart. Therapy with GHRH-A although initiated 1 mo after MI substantially improved cardiac performance and reduced infarct size, suggesting a regenerative process. Therefore, activation of GHRHR provides a unique therapeutic approach to reverse remodeling after MI.

SDF-1α and CXCR4 as therapeutic targets in cardiovascular disease

SDF-1α/CXCR4 signaling is important for endogenous processes, including organogenesis and hematopoeisis, as well as in response to tissue injury. The secretion of SDF-1α acts as a chemoattractant to facilitate the homing of circulating CXCR4 positive cells as well as other stem cells to the site of injury for the initiation organ regeneration and repair. In the case of cardiovascular disease, and particularly myocardial infarction, this signaling axis is implicated in many of these processes, and has an additional role in providing trophic support for cells and utilizing paracrine mechanisms to enhance cell survival, promote angiogenesis, and stimulate differentiation. Current research is focused on elucidating these complex events, and so far have produced promising results that have led to the development of cell therapies that can more effectively repair cardiac tissue following ischemic injury than currently used treatments. Despite these advancements, much remains to be discovered so that in the future, new treatments will be better able to regenerate tissue and recover function.

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.

The combined administration of multiple soluble factors in the repair of chronically infarcted rat myocardium

The purpose of this study was to investigate a potential benefit of simultaneous administration of multiple soluble factors (SFs) in the repair of chronically infarcted rat myocardium. Rats subjected to a permanent coronary artery occlusion (myocardial infarction) received a cocktail of SF or a phosphate buffer. Four SFs, fibroblast growth factor-2 (2 μg), insulin-like growth factor-1 (1 μg), hepatocyte growth factor (2 μg), and stromal cell-derived factor-1α (0.6 μg) were injected directly into the ischemic myocardium at the onset of occlusion and subsequently at 3, 7, 14, and 21 days of surgery (intraperitoneally). Cardiac contractile function, infarct size and remodeling, and blood vessel density were studied at 4 weeks postsurgery. Infarct size, left ventricular circumference and cavity volume, thinning ratio, and expansion index were not statistically different between groups. Treatment of SF did not alter ejection fraction, compared with control. No statistical difference in total blood vessel density in the infarct zone was observed in SF versus control. In conclusion, our results that there were no enhancements in cardiac function, reductions in infarct size, improvements in remodeling, or increases in vasculature density in SF versus control do not support the study hypothesis that the combined use of multiple SF benefits the hearts with myocardial infarct.

Stromal cell derived factor-1 (SDF-1) targeting reperfusion reduces myocardial infarction in isolated rat hearts

Recent studies have shown that stromal cell derived factor-1 (SDF-1), first known as a cytokine involved in recruiting stem cells into injured organs, confers myocardial protection in myocardial infarction, which is not dependent on stem cell recruitment but related with modulation of ischemia-reperfusion (I/R) injury. However, the effect of SDF has been studied only in a preischemic exposure model, which is not clinically relevant if SDF is to be used as a therapeutic agent. Our study was aimed at evaluating whether or not SDF-1 confers cardioprotection during the reperfusion period. Hearts from SD rats were isolated and perfused with the Langendorff system. Proximal left coronary artery ligation, reperfusion, and SDF perfusion in KH buffer was done according to study protocol. Area of necrosis (AN) relative to area at risk (AR) was the primary endpoint of the study. Significant reduction of AN/AR by SDF in an almost dose-dependent manner was noted during both the preischemic exposure and reperfusion periods. In particular, infusion of a high concentration of SDF (25 nM/L) resulted in a dramatic reduction of infarct size, which was greater than that achieved with ischemic pre- or postconditioning. SDF perfusion during reperfusion was associated with a similar significant reduction of infarct size as preischemic SDF exposure. Further studies are warranted to assess the potential of SDF as a therapeutic agent for reducing I/R injury in clinical practice.

Myocardial production and release of MCP-1 and SDF-1 following myocardial infarction: differences between mice and man

Background

Stem cell homing to the heart is mediated by the release of chemo-attractant cytokines. Stromal derived factor -1 alpha (SDF-1a) and monocyte chemotactic factor 1(MCP-1) are detectable in peripheral blood after myocardial infarction (MI). It remains unknown if they are produced by, and released from, the heart in order to attract stem cells to repair the damaged myocardium.

Methods

Murine hearts were studied for expression of MCP-1 and SDF-1a at day 3 and day 28 following myocardial infarction to determine whether production is increased following MI. In addition, we studied the coronary artery and coronary sinus (venous) blood from patients with normal coronary arteries, stable coronary artery disease (CAD), unstable angina and MI to determine whether these cytokines are released from the heart into the systemic circulation following MI.

Results

Both MCP-1 and SDF-1a are constitutively produced and released by the heart. MCP-1 mRNA is upregulated following murine experimental MI, but SDF-1a is suppressed. There is less release of SDF-1a into the systemic circulation in patients with all stages of CAD including MI, mimicking the animal model. However MCP-1 release from the human heart following MI is also suppressed, which is the exact opposite of the animal model.

Conclusions

SDF-1a and MCP-1 release from the human heart are suppressed following MI. In the case of SDF-1a, the animal model appropriately reflects the human situation. However, for MCP-1 the animal model is the exact opposite of the human condition. Human observational studies like this one are paramount in guiding translation from experimental studies to clinical trials.

Heterogeneity in SDF-1 expression defines the vasculogenic potential of adult cardiac progenitor cells

Rationale

The adult myocardium has been reported to harbor several classes of multipotent progenitor cells (CPCs) with tri-lineage differentiation potential. It is not clear whether c-kit+CPCs represent a uniform precursor population or a more complex mixture of cell types.

Objective

To characterize and understand vasculogenic heterogeneity within c-kit+presumptive cardiac progenitor cell populations.

Methods and Results

c-kit+, sca-1+ CPCs obtained from adult mouse left ventricle expressed stem cell-associated genes, including Oct-4 and Myc, and were self-renewing, pluripotent and clonogenic. Detailed single cell clonal analysis of 17 clones revealed that most (14/17) exhibited trilineage differentiation potential. However, striking morphological differences were observed among clones that were heritable and stable in long-term culture. 3 major groups were identified: round (7/17), flat or spindle-shaped (5/17) and stellate (5/17). Stellate morphology was predictive of vasculogenic differentiation in Matrigel. Genome-wide expression studies and bioinformatic analysis revealed clonally stable, heritable differences in stromal cell-derived factor-1 (SDF-1) expression that correlated strongly with stellate morphology and vasculogenic capacity. Endogenous SDF-1 production contributed directly to vasculogenic differentiation: both shRNA-mediated knockdown of SDF-1 and AMD3100, an antagonist of the SDF-1 receptor CXC chemokine Receptor-4 (CXCR4), reduced tube-forming capacity, while exogenous SDF-1 induced tube formation by 2 non-vasculogenic clones. CPCs producing SDF-1 were able to vascularize Matrigel dermal implants in vivo, while CPCs with low SDF-1 production were not.

Conclusions

Clonogenic c-kit+, sca-1+ CPCs are heterogeneous in morphology, gene expression patterns and differentiation potential. Clone-specific levels of SDF-1 expression both predict and promote development of a vasculogenic phenotype via a previously unreported autocrine mechanism.

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.

Bone marrow-derived cell therapy stimulates endogenous cardiomyocyte progenitors and promotes cardiac repair

Cell therapy can improve cardiac function in animals and humans after injury, but the mechanism is unclear. We performed cell therapy experiments in genetically engineered mice that permanently express green fluorescent protein (GFP) only in cardiomyocytes after a pulse of 4-OH-tamoxifen. Myocardial infarction diluted the GFP(+) cardiomyocyte pool, indicating refreshment by non-GFP(+) progenitors. Cell therapy with bone marrow-derived c-kit(+) cells, but not mesenchymal stem cells, further diluted the GFP(+) pool, consistent with c-kit(+) cell-mediated augmentation of cardiomyocyte progenitor activity. This effect could not be explained by transdifferentiation to cardiomyocytes by exogenously delivered c-kit(+) cells or by cell fusion. Therapy with c-kit(+) cells but not mesenchymal stem cells improved cardiac function. These findings suggest that stimulation of endogenous cardiogenic progenitor activity is a critical mechanism of cardiac cell therapy.

Stromal Cell-Derived Factor-1 Retention and Cardioprotection for Ischemic Myocardium

Background—

Stromal cell-derived factor-1 (SDF-1) is a chemoattractant of stem/progenitor cells, and several studies have shown that SDF-1 may improve ventricular function after infarction. SDF-1 is cleaved by proteases including matrix metalloproteinase-2 (MMP-2) and CD26/dipeptidylpeptidase-4 (DPP-4), which are activated in injured tissues.

Methods and Results—

We investigated the biodistribution and functional roles of SDF-1 in experimental ischemia/reperfusion injury in rats. Radiolabeled SDF-1 given by intracoronary injection was selectively concentrated in ischemic myocardium. The enhanced uptake of SDF-1 in ischemic myocardium was not mediated by its receptor, CXCR4. Mass spectrometry and Western analyses showed that SDF-1 was cleaved by DPP-4 in plasma and myocardium, whereas a bioengineered MMP-2/DPP-4–resistant form of SDF-1, SSDF-1(S4V), was highly stable. A single dose of SSDF-1(S4V) exhibited greater potency for cardioprotection than wild-type SDF-1. SSDF-1(S4V) improved cardiac function in rats even after a 3-hour ischemic period.

Conclusions—

These results show that a single dose of protease-resistant SSDF-1(S4V) after myocardial infarction leads to dramatic improvement in angiogenesis and ventricular function even 3 hours after the onset of ischemia, revealing a simple, clinically feasible approach to prevention of heart failure.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

Estrogen-induced SDF-1 production is mediated by estrogen receptor-α in female hearts after acute ischemia and reperfusion

BACKGROUND

Gender differences exist in myocardial response to acute ischemia/reperfusion (I/R) injury and estrogen mediates cardioprotection in the female heart after I/R. Accumulating evidence has indicated that stromal cell-derived factor-1 (SDF-1) is increased in the ischemic heart and initiates cardioprotective effects. However, it is unknown whether SDF-1 plays a role in gender-specific response to myocardial I/R and in estrogen-induced acute protection. Therefore, we hypothesize that (1) increased SDF-1 production will be observed in female hearts compared with male hearts in response to I/R, which is attributable to the effect of estrogen; and that (2) estrogen receptor (ER)α, not ERβ mediates estrogen-contributed SDF-1 expression in female hearts after I/R.

METHODS

Heart tissue subjected to I/R injury was assessed for myocardial expression of SDF-1 (by enzyme-linked immunosorbent assay) and SDF-1 receptor-CXCR4 (Western blot). Groups were as follows: Rat hearts from adult male, female, ovariectomized female (OVX F), and male and OVX F supplemented with chronic 17β-estradiol (E2), and mouse hearts from adult male and female wild-type, ERα knockout (ERαKO) and ERβKO.

RESULTS

I/R significantly increased myocardial SDF-1 expression in both genders. Higher levels of SDF-1 existed in female hearts after I/R compared with males. Depletion of endogenous estrogen by ovariectomy reduced cardiac SDF-1 production in females after I/R. E2 supplementation significantly restored SDF-1 expression in OVX F and males compared with their counterparts. Notably, ablation of ERα, not ERβ, markedly decreased SDF-1 production in females after I/R. Unlike SDF-1, cardiac CXCR4 expression was not affected by gender, sex hormone, or ERs in the ischemic heart.

CONCLUSION

Our study represents the first evidence that female hearts exhibit higher levels of SDF-1 expression compared with males after acute I/R. This increased myocardial SDF-1 production in females is partly owing to effect of estrogen through ERα, but not ERβ.

The use of stem cells for the repair of cardiac tissue in ischemic heart disease

Ischemic heart diseases are the leading cause of death in the Western world. With increasing numbers of patients surviving their acute myocardial infarction owing to effective heart catheter techniques and intensive care treatment, congestive heart failure has become an increasing health concern. With therapeutic options for the prevention and treatment of ischemic heart disease being limited at present, huge efforts have been made in the field of stem cell research to try to establish new approaches for myocardial tissue regeneration. Owing to their pronounced differentiation potential, pluripotent stem cells seem to represent the most promising cell source for future engineering of myocardial replacement tissue. However, several crucial hurdles regarding cell yield and purity of the cultured cardiovascular progenitor cells have still not been overcome to facilitate a clinical application today. By contrast, plenty of adult stem and progenitor cells have already been well characterized and investigated in human disease. However, all of these heterogeneous cell lines primarily seem to work in a paracrine manner on ischemic myocardial tissue, rather than transdifferentiating into contractile cardiomyocytes. This article will focus on the production, application and present limitations of stem cells potentially applicable for myocardial repair.

Pharmacologic and genetic strategies to enhance cell therapy for cardiac regeneration

Cell-based therapy is emerging as an exciting potential therapeutic approach for cardiac regeneration following myocardial infarction (MI). As heart failure (HF) prevalence increases over time, development of new interventions designed to aid cardiac recovery from injury are crucial and should be considered more broadly. In this regard, substantial efforts to enhance the efficacy and safety of cell therapy are continuously growing along several fronts, including modifications to improve the reprogramming efficiency of inducible pluripotent stem cells (iPS), genetic engineering of adult stem cells, and administration of growth factors or small molecules to activate regenerative pathways in the injured heart. These interventions are emerging as potential therapeutic alternatives and/or adjuncts based on their potential to promote stem cell homing, proliferation, differentiation, and/or survival. Given the promise of therapeutic interventions to enhance the regenerative capacity of multipotent stem cells as well as specifically guide endogenous or exogenous stem cells into a cardiac lineage, their application in cardiac regenerative medicine should be the focus of future clinical research. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Dual stem cell therapy after myocardial infarction acts specifically by enhanced homing via the SDF-1/CXCR4 axis

BACKGROUND

G-CSF based stem cell mobilization and stabilization of cardiac SDF-1 by DPP-IV-inhibition (dual stem cell therapy) improve heart function and survival after myocardial infarction. However, it is barely understood whether this new approach acts specifically through the SDF-1/CXCR4 axis, stimulation of resident cardiac stem cells and improved myocardial perfusion. Therefore, we aimed to clarify the role of the SDF1/CXCR4 axis with respect to the benefits of a dual stem cell based therapy.

METHODOLOGY/PRINCIPAL FINDINGS

After surgically induced ligation of the LAD, SDF-1/CXCR4 interactions were specifically blocked by the CXCR4 receptor antagonist AMD3100 in G-CSF and Diprotin A treated C57BL/6 mice. G-CSF+DipA treated and non-treated animals served as controls. Because AMD3100 is known to mobilize bone marrow derived stem cells (BMCs) in high concentrations, the optimal dosage (1.25mg per kg body weight) sufficient to block CXCR4 without stimulating mobilization was established. AMD3100 treatment of G-CSF and Diprotin A stimulated mice significantly decreased myocardial homing of circulating stem cells (FACS analysis) and inverted the beneficial effects of (i) cardiac remodeling (histological analyses), (ii) heart function (Millar tip catheterization) and (iii) survival (Kaplan-Meier curves). G-CSF treatment in combination with DPP-IV inhibition enhanced neovascularization at the infarct border zone which was related to an improved myocardial blood flow as measured by SPECT. Moreover, dual stem cell treatment effectively stimulated the pool of resident cardiac stem cells (FACS) which was reversed by AMD3100 treatment.

CONCLUSIONS/SIGNIFICANCE

Our data give final proof that homing through the SDF-1/CXCR-4 axis is essential for the success of dual stem cell therapy.

Dual stem cell therapy after myocardial infarction acts specifically by enhanced homing via the SDF-1/CXCR4 axis

BACKGROUND

G-CSF based stem cell mobilization and stabilization of cardiac SDF-1 by DPP-IV-inhibition (dual stem cell therapy) improve heart function and survival after myocardial infarction. However, it is barely understood whether this new approach acts specifically through the SDF-1/CXCR4 axis, stimulation of resident cardiac stem cells and improved myocardial perfusion. Therefore, we aimed to clarify the role of the SDF1/CXCR4 axis with respect to the benefits of a dual stem cell based therapy.

METHODOLOGY/PRINCIPAL FINDINGS

After surgically induced ligation of the LAD, SDF-1/CXCR4 interactions were specifically blocked by the CXCR4 receptor antagonist AMD3100 in G-CSF and Diprotin A treated C57BL/6 mice. G-CSF+DipA treated and non-treated animals served as controls. Because AMD3100 is known to mobilize bone marrow derived stem cells (BMCs) in high concentrations, the optimal dosage (1.25mg per kg body weight) sufficient to block CXCR4 without stimulating mobilization was established. AMD3100 treatment of G-CSF and Diprotin A stimulated mice significantly decreased myocardial homing of circulating stem cells (FACS analysis) and inverted the beneficial effects of (i) cardiac remodeling (histological analyses), (ii) heart function (Millar tip catheterization) and (iii) survival (Kaplan-Meier curves). G-CSF treatment in combination with DPP-IV inhibition enhanced neovascularization at the infarct border zone which was related to an improved myocardial blood flow as measured by SPECT. Moreover, dual stem cell treatment effectively stimulated the pool of resident cardiac stem cells (FACS) which was reversed by AMD3100 treatment.

CONCLUSIONS/SIGNIFICANCE

Our data give final proof that homing through the SDF-1/CXCR-4 axis is essential for the success of dual stem cell therapy.

Syndecan-4 prevents cardiac rupture and dysfunction after myocardial infarction

RATIONALE

Syndecan-4 (Syn4), a cell-surface heparan sulfate proteoglycan, has been detected in the infarct region after myocardial infarction (MI), but its functional significance has not been elucidated.

OBJECTIVE

We examined whether and how Syn4 regulates the cardiac healing process after MI.

METHODS AND RESULTS

Although the heart in Syn4-deficient (Syn4(-/-)) mice was morphologically and functionally normal, Syn4(-/-) mice exhibited impaired heart function and increased mortality rate as a result of cardiac ruptures after MI. Cardiac ruptures in Syn4(-/-) mice were associated with reduced inflammatory reaction and impaired granulation tissue formation during the early phase of MI, as evidenced by reduced numbers of leukocytes, fibroblasts, myofibroblasts, macrophages, and capillary vessels, along with reduced extracellular matrix protein deposition in the infarct region after MI. Transforming growth factor-β1-dependent cell signaling was preserved, whereas cell migration, fibronectin-induced cell signaling, and differentiation into myofibroblasts were defective in Syn4(-/-) cardiac fibroblasts. We also found that Syn4 was involved in basic fibroblast growth factor-dependent endothelial cell signaling, cell proliferation, and tube formation. Finally, overexpression of the shed form of Syn4 before MI creation led to an increase in mortality due to cardiac rupture via its action as a dominant-negative inhibitor of endogenous Syn4 signaling, which suggested a protective role of Syn4 signaling in MI.

CONCLUSIONS

These results suggest that Syn4 plays an important role in the inflammatory response and granulation tissue formation, thereby preventing cardiac rupture and dysfunction after MI.

β2-Adrenergic receptor signaling in the cardiac myocyte is modulated by interactions with CXCR4

Chemokines are small secreted proteins with chemoattractant properties that play a key role in inflammation, metastasis, and embryonic development. We previously demonstrated a nonchemotactic role for one such chemokine pair, stromal cell-derived factor-1α and its G-protein coupled receptor, CXCR4. Stromal cell-derived factor-1/CXCR4 are expressed on cardiac myocytes and have direct consequences on cardiac myocyte physiology by inhibiting contractility in response to the nonselective β-adrenergic receptor (βAR) agonist, isoproterenol. As a result of the importance of β-adrenergic signaling in heart failure pathophysiology, we investigated the underlying mechanism involved in CXCR4 modulation of βAR signaling. Our studies demonstrate activation of CXCR4 by stromal cell-derived factor-1 leads to a decrease in βAR-induced PKA activity as assessed by cAMP accumulation and PKA-dependent phosphorylation of phospholamban, an inhibitor of SERCA2a. We determined CXCR4 regulation of βAR downstream targets is β2AR-dependent. We demonstrated a physical interaction between CXCR4 and β2AR as determined by coimmunoprecipitation, confocal microscopy, and BRET techniques. The CXCR4-β2AR interaction leads to G-protein signal modulation and suggests the interaction is a novel mechanism for regulating cardiac myocyte contractility. Chemokines are physiologically and developmentally relevant to myocardial biology and represent a novel receptor class of cardiac modulators. The CXCR4-β2AR complex could represent a hitherto unknown target for therapeutic intervention.

Downregulation of the CXC chemokine receptor 4/stromal cell-derived factor 1 pathway enhances myocardial neovascularization, cardiomyocyte survival, and functional recovery after myocardial infarction

OBJECTIVES

Although adequate numbers of hematopoietic progenitor cells reside in the human bone marrow, the extent of endogenous neovascularization after myocardial infarction remains insufficient. The aim of this study was to identify the role of the CXC chemokine receptor 4/stromal cell-derived factor 1 axis in the mobilization and homing of hematopoietic progenitor cells in the ischemic heart.

METHODS

Human bone marrow-derived hematopoietic progenitor cells or saline were injected systemically into athymic nude rats 48 hours after myocardial infarction. Myocardial and bone marrow expression of stromal cell-derived factor 1 and chemotaxis of hematopoietic progenitor cells were measured in vitro in the presence or absence of stromal cell-derived factor 1. The role of the CXC chemokine receptor 4/stromal cell-derived factor 1 axis was investigated by means of antibody blockade or systemic administration of granulocyte colony-stimulating factor. Morphologic analysis included measurement of the infarct area, capillary density, and apoptosis, whereas left ventricular function was measured by means of echocardiographic analysis.

RESULTS

Expression of postinfarct stromal cell-derived factor 1 was increased by 67% in the bone marrow and decreased by 43% in myocardium. Disruption of bone marrow stromal cell-derived factor 1/CXC chemokine receptor 4 interactions by antibody blockade resulted in a redirection of human hematopoietic progenitor cells from the bone marrow to the ischemic heart and augmented neovascularization and cardiomyocyte survival. Similarly, systemic administration of granulocyte colony-stimulating factor to block CXC chemokine receptor 4/stromal cell-derived factor 1 interaction resulted in increased mobilization and homing of hematopoietic progenitor cells to the ischemic heart, which translated to augmented myocardial neovascularization, prevention of apoptosis, and improved cardiac function.

CONCLUSIONS

Bone marrow stromal cell-derived factor 1 upregulation after myocardial ischemia prevents mobilization of endogenous hematopoietic progenitor cells. We provide evidence that disruption of stromal cell-derived factor 1/CXC chemokine receptor 4 interactions allows redirection of hematopoietic progenitor cells to ischemic myocardium and enhances recovery of left ventricular function.

Control of autocrine and paracrine myocardial signals: an emerging therapeutic strategy in heart failure

A growing body of evidence supports the hypothesis that autocrine and paracrine mechanisms, mediated by factors released by the resident cardiac cells, could play an essential role in the reparative process of the failing heart. Such signals may influence the function of cardiac stem cells via several mechanisms, among which the most extensively studied are cardiomyocyte survival and angiogenesis. Moreover, besides promoting cytoprotection and angiogenesis, paracrine factors released by resident cardiac cells may alter cardiac metabolism and extracellular matrix turnover, resulting in more favorable post-injury remodeling. It is reasonable to believe that critical intracellular signals are activated and modulated in a temporal and spatial manner exerting different effects, overall depending on the microenvironment changes present in the failing myocardium. The recent demonstration that chemically, mechanically or genetically activated cardiac cells may release peptides to protect tissue against ischemic injury provides a potential route to achieve the delivery of specific proteins produced by these cells for innovative pharmacological regenerative therapy of the heart. It is important to keep in mind that therapies currently used to treat heart failure (HF) and leading to improvement of cardiac function fail to induce tissue repair/regeneration. As a matter of facts, if specific autocrine/paracrine cell-derived factors that improve cardiac function will be identified, pharmacological-based therapy might be more easily translated into clinical benefits than cell-based therapy. This review will focus on the recent development of potential pharmacologic targets to promote and drive at molecular level the cardiac repair/regeneration in HF.

Regulation of the stromal cell-derived factor-1alpha-CXCR4 axis in human dental pulp cells

INTRODUCTION

Although the presence of the stromal cell-derived factor (SDF)-1alpha-CXCR4 axis has been reported in dental pulp tissue, little has been known about the underlying regulation of this axis in dental pulp stem cells (DPSCs). The purpose of this study was to investigate whether inflammation or hypoxia can regulate this axis in cultured human dental pulp cells (DPCs).

METHODS

Primary cultures of DPCs were stimulated by various concentrations of lipopolysaccharide (LPS) for 48 hours, and the production of SDF-1alpha or CXCR4 was assessed through the enzyme-linked immunosorbent assay and Western blotting, respectively. Additionally, DPCs were incubated in a hypoxic condition (1% O(2)) for 24 hours, and the cell proliferation ability was detected by methylthiazol tetrazolum assay. Quantitative reverse-transcription polymerase chain reaction (RT-PCR) was used to observe messenger RNA level changes of hypoxia inducible factor-1alpha(HIF-alpha), SDF-1alpha, and CXCR4. The effects of hypoxia on cell migration ability were further confirmed by transmigration assay.

RESULTS

All concentrations of LPS inhibited SDF-1alpha production except that 1 microg/mL LPS increased the expression of CXCR4. Hypoxia promoted the proliferation of DPCs in a 24-hour culture period. Quantitative RT-PCR showed that messenger RNA levels of HIF-alpha and CXCR4 increased, whereas SDF-1alpha decreased in hypoxic DPCs. Transmigration assay indicated that hypoxia increased the migration ability of DPCs.

CONCLUSIONS

These results suggested that inflammation and hypoxia might play an important role in regulating the SDF-1alpha-CXCR4 axis, which further recruits DPSCs to participate in reparative dentinogenesis.

Chronic AMD3100 antagonism of SDF-1alpha-CXCR4 exacerbates cardiac dysfunction and remodeling after myocardial infarction

The role of the SDF-1alpha-CXCR4 axis in response to myocardial infarction is unknown. We addressed it using the CXCR4 antagonist, AMD3100, to block SDF-1alpha interaction with CXCR4 after chronic coronary artery ligation. Chronic AMD3100 treatment decreased ejection fraction and fractional shortening in mice 20days after myocardial infarction compared with vehicle-treated mice (echocardiography). Morphometric analysis showed hearts of AMD3100-treated infarcted mice to have expanded scar, to be hypertrophic (confirmed by myocyte cross-section area) and dilated, with increased LV end systolic and end diastolic dimensions, and to have decreased scar collagen content; p-AKT levels were attenuated and this was accompanied by increased apoptosis. Despite increased injury, c-kit(pos) cardiac progenitor cells (CPCs) were increased in the risk region of AMD3100-treated infarcted mice; CPCs were CD34(neg)/CD45(neg) with the majority undergoing symmetric cell division. c-kit(pos)/MHC(pos) CPCs also increased in the risk region of the AMD3100-treated infarcted group. In this group, GSK-3beta signaling was attenuated compared to vehicle-treated, possibly accounting for increased proliferation and increased cardiac committed MHC(pos) CPCs. Increased proliferation following AMD3100 treatment was supported by increased levels of cyclin D1, a consequence of increased prolyl isomerase, Pin1, and decreased cyclin D1 phosphorylation. In summary, pharmacologic antagonism of CXCR4 demonstrates that SDF-1alpha-CXCR4 signaling plays an important role during and after myocardial infarction and that it exerts pleiotropic salubrious effects, protecting the myocardium from apoptotic cell death, facilitating scar formation, restricting CPC proliferation, and directing CPCs toward a cardiac fate.

Protein therapeutics for cardiac regeneration after myocardial infarction

Although most medicines have historically been small molecules, many newly approved drugs are derived from proteins. Protein therapies have been developed for treatment of diseases in almost every organ system, including the heart. Great excitement has now arisen in the field of regenerative medicine, particularly for cardiac regeneration after myocardial infarction. Every year, millions of people suffer from acute myocardial infarction, but the adult mammalian myocardium has limited regeneration potential. Regeneration of the heart after myocardium infarction is therefore an exciting target for protein therapeutics. In this review, we discuss different classes of proteins that have therapeutic potential to regenerate the heart after myocardial infarction. Protein candidates have been described that induce angiogenesis, including fibroblast growth factors and vascular endothelial growth factors, although thus far clinical development has been disappointing. Chemotactic factors that attract stem cells, e.g., hepatocyte growth factor and stromal cell-derived factor-1, may also be useful. Finally, neuregulins and periostin are proteins that induce cell-cycle reentry of cardiomyocytes, and growth factors like IGF-1 can induce growth and differentiation of stem cells. As our knowledge of the biology of regenerative processes and the role of specific proteins in these processes increases, the use of proteins as regenerative drugs could develop as a cardiac therapy.

SDF-1 provides morphological and functional protection against renal ischaemia/reperfusion injury

BACKGROUND

The chemokine stromal cell-derived factor-1 (SDF-1) is thought to be involved in mediating tissue repair by promoting migration of bone marrow stem or progenitor cells to the site of injury. Increased levels of renal SDF-1 are found after kidney injury. However, recently, we showed that SDF-1 does not play an important role in the migration of haematopoietic stem cells to the post-ischaemic kidney. The function of increased post-ischaemic renal SDF-1 expression in modulating renal ischaemia/reperfusion injury remains, therefore, unknown.

METHODS

We studied the role of SDF-1 in renal ischaemia/reperfusion injury by locally decreasing SDF-1 expression and subsequent SDF-1 signalling in the corticomedullary region of the kidney using antisense oligonucleotide treatment in mice.

RESULTS

Renal SDF-1 protein increased significantly in the early phase of ischaemia/reperfusion injury. Antisense treatment resulted in a reduction of corticomedullary SDF-1 expression which was accompanied by severely increased tubular injury and decreased renal function. We did not observe any difference in mobilization or retention of CXCR4-positive haematopoietic stem or progenitor cells after induction of renal ischaemia. Rather, antisense-treated animals showed markedly increased apoptosis of the tubular epithelium accompanied by an increased renal inflammatory response. Conclusions. These data indicate a new role for SDF-1 in renal pathogenesis by mediating tubular epithelial protection against ischaemic injury and suggest that SDF-1 by itself is not crucial for the influx of haematopoietic stem or progenitor cells towards the ischaemic injured kidney.

Role of the SDF-1-CXCR4 axis in stem cell-based therapies for ischemic cardiomyopathy

IMPORTANCE OF THE FIELD

Ischemic disorders are the leading cause of mortality worldwide, current therapies only delay progression of the disease. Data suggest a role of the SDF-1-CXCR4 axis in attenuation of ischemic disorders.

AREAS COVERED IN THIS REVIEW

We discuss the importance of SDF-1-CXCR4 interactions during development and postnatal mobilization and migration of stem cells. We focus on the role of the SDF-1-CXCR4 axis in stem-cell-based applications for attenuation of ischemic cardiomyopathy.

WHAT THE READER WILL GAIN

During development the SDF-1-CXCR4 axis plays a critical role in gradient-guided cell movements. In adults, the SDF-1-CXCR4 axis is involved in retention and mobilization of stem cells. Since SDF-1 is upregulated during hypoxic tissue damage, strategies to augment or stabilize SDF-1 have been utilized to target blood-derived stem cells to ischemic tissue. We exploited this concept by preventing SDF-1 degradation with dipeptidylpeptidaseIV (DPPIV) inhibition and mobilization of stem cells by G-CSF after acute myocardial infarction. This targeted CD34(+)CXCR4(+) cells to ischemic heart and attenuated ischemic cardiomyopathy.

TAKE HOME MESSAGE

The SDF-1-CXCR4 axis plays a role in stem cell homing during embryogenesis and adulthood especially after ischemia. Preserving functional SDF-1 by DPPIV inhibition after ischemia may enhance stem cell therapies.

Single administration of the CXC chemokine-binding protein Evasin-3 during ischemia prevents myocardial reperfusion injury in mice

OBJECTIVE

Evasins (chemokine-binding proteins) have been shown to selectively neutralize chemokine bioactivity. We investigated the potential benefits of Evasin-3 on mouse myocardial ischemia/reperfusion injury.

METHODS AND RESULTS

In vivo and ex vivo (Langendorff model) left coronary artery ligature was performed in C57Bl/6 mice. Coronary occlusion was maintained for 30 minutes, followed by different times (up to 24 hours) of reperfusion. Five minutes after coronary occlusion, mice received 1 intraperitoneal injection of Evasin-3 or vehicle. Infarct size was assessed histologically and by serum cardiac troponin I ELISA. In vitro neutrophil chemotaxis, immunohistology, oxidative stress quantification, real-time RT-PCR analysis of leukocyte chemoattractants, and Western blots for cardioprotective intracellular pathway activation were performed. Evasin-3 reduced infarct size and cardiac troponin I levels compared with vehicle. This effect was associated with the reduction of neutrophil infiltration and reactive oxygen species production within the infarcted myocardium. Evasin-3 did not reduce infarct size in the absence of circulating neutrophils (Langendorff model). Evasin-3 did not influence the activation of intracellular cardioprotective pathways or the expression of leukocyte chemoattractants during early phases of reperfusion.

CONCLUSIONS

Single administration of Evasin-3 during myocardial ischemia significantly reduced infarct size by preventing CXC chemokine-induced neutrophil recruitment and reactive oxygen species production in myocardial ischemia/reperfusion.

G-CSF enhanced SDF-1 gradient between bone marrow and liver associated with mobilization of peripheral blood CD34+ cells in rats with acute liver failure

The role of stromal cell-derived factor-1 (SDF-1) in modulating massive liver damage is not well known. In this study, expression of SDF-1 in bone marrow and liver was investigated in rats with acute liver failure (ALF) when mobilized using granulocyte colony-stimulating factor (G-CSF). ALF was induced in rats by D-galactosamine (D-GalN). Starting after 2 hours following D-GalN induction, the animals were injected with G-CSF 50 microg/kg daily or saline as placebo for 5 days. The percentages of CD34+ cells in peripheral blood and the expression of SDF-1 in bone marrow and liver were then determined. The percentages of peripheral CD34+ cells demonstrated a transient increase in placebo rats following D-GalN induction and a significant increase in rats after G-CSF administration. SDF-1 expression showed a transient decrease in bone marrow and a transient increase in liver tissue from placebo rats. However, a significant decrease of SDF-1 expression in bone marrow and a remarkable increase in liver tissue were observed in animals from the G-CSF group. It was concluded that G-CSF can enhance the reduced expression of SDF-1 in bone marrow and increased expression in liver in ALF rats, forming a greater SDF-1 gradient, and chemoattracting CD34+ cells' migration from bone marrow to an injured liver.

Role of the SDF-1/CXCR4 system in myocardial infarction

Myocardial infarction (MI) is accompanied by an inflammatory response, leading to the recruitment of leukocytes and subsequent myocardial injury and healing. Chemokines are potent chemoattractant cytokines that regulate leukocyte trafficking in inflammatory processes. Recent evidence indicates that chemokines play a role not only in leukocyte trafficking but also in angiogenesis and cardioprotection. In particular, stromal cell-derived factor-1alpha (SDF-1alpha) has generated considerable interest for its role in the pathophysiology of MI. This review will focus on the role of SDF-1 and its receptor CXC chemokine receptor 4 (CXCR4; ie, the SDF-1/CXCR4 system) in the pathophysiology of MI and discuss their potential as therapeutic targets for MI.

Mesenchymal stem cells modified with stromal cell-derived factor 1 alpha improve cardiac remodeling via paracrine activation of hepatocyte growth factor in a rat model of myocardial infarction

Mesenchymal stem cells (MSCs) are a promising source for cell-based treatment of myocardial infarction (MI), but existing strategies are restricted by low cell survival and engraftment. We examined whether SDF-1 transfection improve MSC viability and paracrine action in infarcted hearts. We found SDF-1-modified MSCs effectively expressed SDF-1 for at least 21 days after exposure to hypoxia. The apoptosis of Ad-SDF-1-MSCs was 42% of that seen in Ad-EGFP-MSCs and 53% of untreated MSCs. In the infarcted hearts, the number of DAPI-labeling cells in the Ad-SDF-1-MSC group was 5-fold that in the Ad-EGFP-MSC group. Importantly, expression of antifibrotic factor, HGF, was detected in cultured MSCs, and HGF expression levels were higher in Ad-SDF-MSC-treated hearts, compared with Ad-EGFP-MSC or control hearts. Compared with the control group, Ad-SDF-MSC transplantation significantly decreased the expression of collagens I and III and matrix metalloproteinase 2 and 9, but heart function was improved in d-SDF-MSC-treated animals. In conclusion, SDF-1-modified MSCs enhanced the tolerance of engrafted MSCs to hypoxic injury in vitro and improved their viability in infarcted hearts, thus helping preserve the contractile function and attenuate left ventricle (LV) remodeling, and this may be at least partly mediated by enhanced paracrine signaling from MSCs via antifibrotic factors such as HGF.

Monomeric structure of the cardioprotective chemokine SDF-1/CXCL12

The chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) directs leukocyte migration, stem cell homing, and cancer metastasis through activation of CXCR4, which is also a coreceptor for T-tropic HIV-1. Recently, SDF-1 was shown to play a protective role after myocardial infarction, and the protein is a candidate for development of new anti-ischemic compounds. SDF-1 is monomeric at nanomolar concentrations but binding partners promote self-association at higher concentrations to form a typical CXC chemokine homodimer. Two NMR structures have been reported for the SDF-1 monomer, but only one matches the conformation observed in a series of dimeric crystal structures. In the other model, the C-terminal helix is tilted at an angle incompatible with SDF-1 dimerization. Using a rat heart explant model for ischemia/reperfusion injury, we found that dimeric SDF-1 exerts no cardioprotective effect, suggesting that the active species is monomeric. To resolve the discrepancy between existing models, we solved the NMR structure of the SDF-1 monomer in different solution conditions. Irrespective of pH and buffer composition, the C-terminal helix remains tilted at an angle with no evidence for the perpendicular arrangement. Furthermore, we find that phospholipid bicelles promote dimerization that necessarily shifts the helix to the perpendicular orientation, yielding dipolar couplings that are incompatible with the NOE distance constraints. We conclude that interactions with the alignment medium biased the previous structure, masking flexibility in the helix position that may be essential for the distinct functional properties of the SDF-1 monomer.

Synergy between CD26/DPP-IV inhibition and G-CSF improves cardiac function after acute myocardial infarction

Ischemic cardiomyopathy is one of the main causes of death, which may be prevented by stem cell-based therapies. SDF-1alpha is the major chemokine attracting stem cells to the heart. Since SDF-1alpha is cleaved and inactivated by CD26/dipeptidylpeptidase IV (DPP-IV), we established a therapeutic concept--applicable to ischemic disorders in general--by combining genetic and pharmacologic inhibition of DPP-IV with G-CSF-mediated stem cell mobilization after myocardial infarction in mice. This approach leads to (1) decreased myocardial DPP-IV activity, (2) increased myocardial homing of circulating CXCR-4+ stem cells, (3) reduced cardiac remodeling, and (4) improved heart function and survival. Indeed, CD26 depletion promoted posttranslational stabilization of active SDF-1alpha in heart lysates and preserved the cardiac SDF-1-CXCR4 homing axis. Therefore, we propose pharmacological DPP-IV inhibition and G-CSF-based stem cell mobilization as a therapeutic concept for future stem cell trials after myocardial infarction.

Targeting VEGF-encapsulated immunoliposomes to MI heart improves vascularity and cardiac function

Recent attempts at rebuilding the myocardium using stem cells have yielded disappointing results. The lack of a supporting vasculature may, in part, explain these disappointing findings. However, concerns over possible side effects have hampered attempts at revascularizing the infarcted myocardium using systemic delivery of proangiogenic compounds. In this study, we develop the technology to enhance the morphology and function of postinfarct neovasculature. Previously, we have shown that the up-regulated expression of endothelial cell adhesion molecules in the myocardial infarction (MI) region provides a potential avenue for selectively targeting drugs to infarcted tissue. After treatment with anti-P-selectin-conjugated liposomes containing vascular endothelial growth factor (VEGF), changes in cardiac function and vasculature post-MI were quantified in a rat MI model. Targeted delivery of VEGF to post-MI tissue resulted in significant increase in fractional shortening and improved systolic function. These functional improvements were accompanied by a 21% increase in the number of anatomical vessels and a 74% increase in the number of perfused vessels in the MI region of treated animals. No significant improvements in cardiac function were observed in untreated, systemic VEGF-treated, nontargeted liposome-treated, or blank immunoliposome-treated animals. Targeted delivery of low doses of proangiogenic compounds to post-MI tissue results in significant improvements in cardiac function and vascular structure.

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.

Hypoxic preconditioning protects rat hearts against ischaemia-reperfusion injury: role of erythropoietin on progenitor cell mobilization

Preconditioning, such as by brief hypoxic exposure, has been shown to protect hearts against severe ischaemia. Here we hypothesized that hypoxic preconditioning (HPC) protects injured hearts by mobilizing the circulating progenitor cells. Ischaemia-reperfusion (IR) injury was induced by left coronary ligation and release in rats kept in room air or preconditioned with 10% oxygen for 6 weeks. To study the role of erythropoietin (EPO), another HPC + IR group was given an EPO receptor (EPOR) antibody via a subcutaneous mini-osmotic pump 3 weeks before IR induction. HPC alone gradually increased haematocrit, cardiac and plasma EPO, and cardiac vascular endothelial growth factor (VEGF) only in the first two weeks. HPC improved heart contractility, reduced ischaemic injury, and maintained EPO and EPOR levels in the infarct tissues of IR hearts, but had no significant effect on VEGF. Interestingly, the number of CD34(+)CXCR4(+) cells in the peripheral blood and their expression in HPC-treated hearts was higher than in control. Preconditioning up-regulated cardiac expression of stromal derived factor-1 (SDF-1) and prevented its IR-induced reduction. The EPOR antibody abolished HPC-mediated functional recovery, and reduced SDF-1, CXCR4 and CD34 expression in IR hearts, as well as the number of CD34(+)CXCR4(+) cells in blood. The specificity of neutralizing antibody was confirmed in an H9c2 culture system. In conclusion, exposure of rats to moderate hypoxia leads to an increase in progenitor cells in the heart and circulation. This effect is dependent on EPO, which induces cell homing by increased SDF-1/CXCR4 and reduces the heart susceptibly to IR injury.