CXCR4 expression determines functional activity of bone marrow-derived mononuclear cells for therapeutic neovascularization in acute ischemia

Nef-M1, a CXCR4 Peptide Antagonist, Enhances Apoptosis and Inhibits Primary Tumor Growth and Metastasis in Breast Cancer

Results from studies with animal models suggest that, in many cancers, CXCR4 is an important therapeutic target and that CXCR4 antagonists may be promising treatments for primary cancers and for metastases. The Nef protein effectively competes with CXCR4’s natural ligand, SDF-1α, and induces apoptosis. As described in this report, the Nef-M1 peptide (Nef protein amino acids 50 – 60) inhibits primary tumor growth and metastasis of breast cancer (BC). Four BC cell lines (MDA-MB-231, MDA-MB-468, MCF 7, and DU4475) and primary human mammary epithelium (HME) cells were evaluated for their response to the Nef protein and to the Nef-M1 peptide. The presence of CXCR4 receptors in these cells was determined by RT-PCR, Western blot (WB), and immunohistochemical analyses. The apoptotic effect of Nef-M1 was assessed by terminal transferase dUTP nick-end labeling (TUNEL). WBs was used to assess caspase 3 activation. BC xenografts grown in SCID mice were evaluated for the presence of CXCR4 and for their metastatic potential. CXCR4 was presented in MDA-MB-231, MCF 7, and DU 4475 BC cells but not in MDA-MB-468 BC or HME cells. Cells expressing CXCR4 and treated with Nef-M1 peptide or the Nef protein had higher rates of apoptosis than untreated cells. Caspase-3 activation increased in MDA-MB 231 cells treated with the Nef protein, the Nef 41 – 60 peptide, or Nef-M1. Nef-M1, administered to mice starting at the time of xenograft implantation, inhibited growth of primary tumors and metastatic spread. Untreated mice developed diffuse intraperitoneal metastases. We conclude that, in BCs, Nef-M1, through interaction with CXCR4, inhibits primary tumor growth and metastasis by causing apoptosis.

Angiogenesis following cell injection is induced by an excess inflammatory response coordinated by bone marrow cells

The aim of this study was to identify novel angiogenic mechanisms underlying the regenerative process. To that end, interactions between adipose tissue-derived stromal cells (ASCs) and bone marrow cells (BMCs) were initially investigated using real-time fluorescence optical imaging. To monitor cell behavior in mice, we injected green fluorescent protein-positive (GFP(+)) BMCs into the tail vein and injected PKH26-labeled ASCs behind the ears. Angiogenesis and inflammation were observed at these sites via an optical imaging probe. Injected GFP(+) BMCs migrated from the blood vessels into the tissues surrounding the ASC injection sites. Many of the migrating GFP(+) BMCs discovered at the ASC injection sites were inflammatory cells, including Gr-1(+), CD11b(+), and F4/80(+) cells. ASCs cocultured with inflammatory cells secreted increased levels of chemokines such as macrophage inflammatory protein (MIP)-1α, MIP-1β, keratinocyte-derived chemokines, and monocyte chemotactic protein 1. Similarly, these ASCs secreted increased levels of angiogenic growth factors such as hepatocyte growth factor and vascular endothelial growth factor. However, when anti-CXC chemokine receptor type 4 antibody was injected at regular intervals, the migration of GFP(+) BMCs (especially Gr-1(+) and CD11b(+) cells) to ASC injection sites was inhibited, as was angiogenesis. The collective influence of the injected ASCs and BMC-derived inflammatory cells promoted acute inflammation and angiogenesis. Together, the results suggest that the outcome of cell-based angiogenic therapy is influenced not only by the injected cells but also by the effect of intrinsic inflammatory cells.

Heparin disrupts the CXCR4/SDF-1 axis and impairs the functional capacity of bone marrow-derived mononuclear cells used for cardiovascular repair

RATIONALE

Cell therapy is a promising option for the treatment of acute or chronic myocardial ischemia. The intracoronary infusion of cells imposes the potential risk of cell clotting, which may be prevented by the addition of anticoagulants. However, a comprehensive analysis of the effects of anticoagulants on the function of the cells is missing.

OBJECTIVE

Here, we investigated the effects of heparin and the thrombin inhibitor bivalirudin on bone marrow-derived mononuclear cell (BMC) functional activity and homing capacity.

METHODS AND RESULTS

Heparin, but not bivalirudin profoundly and dose-dependently inhibited basal and stromal cell-derived factor 1 (SDF-1)-induced BMC migration. Incubation of BMCs with 20 U/mL heparin for 30 minutes abrogated SDF-1-induced BMC invasion (16±8% of control; P<0.01), whereas no effects on apoptosis or colony formation were observed (80±33% and 100±44% of control, respectively). Pretreatment of BMCs with heparin significantly reduced the homing of the injected cells in a mouse ear-wound model (69±10% of control; P<0.05). In contrast, bivalirudin did not inhibit in vivo homing of BMCs. Mechanistically, heparin binds to both, the chemoattractant SDF-1 and its receptor, chemokine receptor 4 (CXCR4), blocking CXCR4 internalization as well as SDF-1/CXCR4 signaling after SDF-1 stimulation.

CONCLUSIONS

Heparin blocks SDF-1/CXCR4 signaling by binding to the ligand as well as the receptor, thereby interfering with migration and homing of BMCs. In contrast, the thrombin inhibitor bivalirudin did not interfere with BMC homing or SDF-1/CXCR4 signaling. These findings suggest that bivalirudin but not heparin might be recommended as an anticoagulant for intracoronary infusion of BMCs for cell therapy after cardiac ischemia.

Critical reevaluation of endothelial progenitor cell phenotypes for therapeutic and diagnostic use

Diverse subsets of endothelial progenitor cells (EPCs) are used for the treatment of ischemic diseases in clinical trials, and circulating EPCs levels are considered as biomarkers for coronary and peripheral artery disease. However, despite significant steps forward in defining their potential for both therapeutic and diagnostic purposes, further progress has been mired by unresolved questions around the definition and the mechanism of action of EPCs. Diverse culturing methods and detection of various combinations of different surface antigens were used to enrich and identify EPCs. These attempts were particularly challenged by the close relationship and overlapping markers of the endothelial and hematopoietic lineages. This article will critically review the most commonly used protocols to define EPCs by culture assays or by fluorescence-activated cell sorter in the context of their therapeutic or diagnostic use. We also delineate new research avenues to move forward our knowledge on EPC biology.

Regulation of cardiac microRNAs by bone marrow mononuclear cell therapy in myocardial infarction

BACKGROUND

Cell therapy with bone marrow-derived mononuclear cells (BMCs) can improve recovery of cardiac function after ischemia; however, the molecular mechanisms are not yet fully understood. MicroRNAs (miRNAs) are key regulators of gene expression and modulate the pathophysiology of cardiovascular diseases.

METHODS AND RESULTS

We demonstrated that intramyocardial delivery of BMCs in infarcted mice regulates the expression of cardiac miRNAs and significantly downregulates the proapoptotic miR-34a. In vitro studies confirmed that the supernatant of BMC inhibited the expression of H(2)O(2)-induced miR-34a and cardiomyocytes apoptosis. These effects were blocked by neutralizing antibodies directed against insulin-like growth factor-1 (IGF-1). Indeed, IGF-1 significantly inhibited H(2)O(2)-induced miR-34a expression, and miR-34a overexpression abolished the antiapoptotic effect of IGF-1. Likewise, inhibition of IGF-1 signaling in vivo abolished the BMC-mediated inhibition of miR-34 expression and the protective effect on cardiac function and increased apoptosis and cardiac fibrosis. IGF-1 specifically blocked the expression of the precursor and the mature miR-34a, but did not interfere with the transcription of the primary miR-34a demonstrating that IGF-1 blocks the processing of miR-34a.

CONCLUSIONS

Together, our data demonstrate that the paracrine regulation of cardiac miRNAs by transplanted BMCs contributes to the protective effects of cell therapy. BMCs release IGF-1, which inhibits the processing of miR-34a, thereby blocking cardiomyocyte apoptosis.

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.

Homing of progenitor cells to ischemic tissues

Progenitor cells mobilized from the bone marrow are recruited to ischemic tissues and increase neovascularization. Cell therapy is a promising new therapeutic option for treating patients with ischemic disorders. The efficiency of cell therapy to augment recovery after ischemia depends on the sufficient recruitment and engraftment of the cells to the target tissue. Homing to sites of active neovascularization is a complex process depending on a timely and spatially orchestrated interplay between chemokines, chemokine receptors, adhesion molecules (selectins and integrins), and intracellular signaling cascades, including also oxidative signaling. This review will focus on the homing mechanisms of progenitor and stem cells to ischemic tissues. Specifically, we discuss the role of chemokines and adhesion molecules such as selectins and integrins and the crosstalk between chemokines and integrins in progenitor cell homing.

Impaired CXCR4 expression and cell engraftment of bone marrow-derived cells from aged atherogenic mice

OBJECTIVES

Reduced numbers and activity of circulating progenitor cells are associated with aging and have been linked with coronary artery disease. To determine the impact of aging and atherosclerotic disease on the chemotaxic activity of bone marrow derived cells (BMCs), we examined CXCR4 surface expression on BMCs from aged and atherosclerotic mice.

METHODS

CXCR4 expression and cellular mobility were compared between BMCs of young (6-week old) ApoE null mice (ApoE(-/-)) and aged ApoE(-/-) mice that had been fed with a high-fat, high-cholesterol diet for 6-months.

RESULTS

Age and atherosclerosis correlated with significantly lower surface expression of CXCR4 that was less inducible by calcium. The impaired calcium response was associated with defective calcium influx and was partially recovered by treatment with the calcium ionophore ionomycin. ApoE(-/-) mice fed high fat diet for 6-months had defective CXCR4 expression and SDF-1 regulation that is equivalent to that of 24-month old wild type mice. BMCs from aged, atherogenic ApoE(-/-) mice also displayed defective homing to SDF-1, and the animals had lower serum and bone marrow levels of SDF-1.

CONCLUSION

Evolution of atherosclerosis in ApoE(-/-) mice is paralleled by progressive loss of mobility of BMCs with reductions of CXCR4 expression, and reduced levels of SDF-1 in both serum and bone marrow. These changes mute the homing capability of BMCs and may contribute to the progression of atherosclerosis in this model.

Ex vivo acidic preconditioning enhances bone marrow ckit+ cell therapeutic potential via increased CXCR4 expression

Aims

The chemokine receptor CXCR4 modulates endothelial progenitor cell migration, homing, and differentiation, and plays a key role in cardiovascular regeneration. Here we examined the effect of ex vivo acidic preconditioning (AP) on CXCR4 expression and on the regenerative potential of mouse bone marrow (BM) ckit⁺ cells.

Methods and results

Acidic preconditioning was achieved by exposing BM ckit⁺ cells to hypercarbic acidosis (pH 7.0) for 24 h; control cells were kept at pH 7.4. Acidic preconditioning enhanced CXCR4 and stromal cell-derived factor 1 (SDF-1) mRNA levels, as well as CXCR4 phosphorylation. Acidic preconditioning ability to modulate CXCR4 expression depended on cytosolic calcium [Ca²⁺]_i mobilization and on nitric oxide (NO), as determined by [Ca²⁺]_i buffering with BAPTA, and by treatment with the NO donor (DETA/NO) and the NO synthase inhibitor (L-NAME). Further, AP increased SDF-1-driven chemotaxis, transendothelial migration, and differentiation toward the endothelial lineage in vitro. In a mouse model of hindlimb ischaemia, control and AP ckit⁺ cells were transplanted into the ischaemic muscle; AP cells accelerated blood flow recovery, increased capillary, and arteriole number as well as the number of regenerating muscle fibres vs. control. These effects were abolished by treating AP cells with L-NAME.

Conclusion

Acidic preconditioning represents a novel strategy to enhance BM ckit⁺ cell therapeutic potential via NO-dependent increase in CXCR4 expression.

Foxc2 overexpression enhances benefit of endothelial progenitor cells for inhibiting neointimal formation by promoting CXCR4-dependent homing

OBJECTIVE

Endothelial progenitor cells (EPCs) are capable of enhancing re-endothelialization and attenuating neointimal formation. However, inefficient homing limits the therapeutic efficacy of EPCs transplantation. CXCR4 plays a critical role in regulating EPCs homing. Here, we studied the effect of Foxc2 overexpression on CXCR4 expression and the homing capacity of EPCs as well as the EPCs-mediated therapeutic benefit after artery injury.

METHODS

Bone marrow-derived EPCs were transfected with Foxc2 expression vector (Foxc2-EPCs) or empty control vector (Ctrl-EPCs) and examined 48 hours later. CXCR4 expression of EPCs was detected by flow cytometry and quantitative reverse transcriptase-polymerase chain reaction. The migration of EPCs toward SDF-1α was evaluated in a transwell migration assay, and the adhesion to fibronectin was determined using a static adhesion assay. For in vivo studies, EPCs were injected intravenously into the mice subjected to carotid injury. At 3 days after green fluorescent protein (GFP)/EPCs delivery, the recruited cells to the injury sites were detected by fluorescent microscopy. Re-endothelialization and neointimal formation were, respectively, assessed by Evans blue dye at 7 days and by the morphometric analysis for neointima and media area ratio (N/M) at 28 days after EPCs transfusion.

RESULTS

Foxc2 overexpression significantly increased the surface expression of CXCR4 on EPCs (about 1.9-fold of Ctrl-EPCs, P < .05). Foxc2-EPCs showed an increased migration toward SDF-1α (P < .05); Foxc2 overexpression increased also the adhesion capacity of EPCs (P < .05). In vivo, the number of recruited GFP cells was significantly higher in the mice transfused with Foxc2-GFP/EPCs compared with Ctrl-GFP/EPCs (about 2-fold of Ctrl-GFP/EPCs). The degree of re-endothelialization was higher in mice transfused with Foxc2-EPCs compared with Ctrl-EPCs (90.3% ± 1.6% vs 57.2% ± 1.3%; P < .05). Foxc2-EPCs delivery resulted in a greater inhibition of neointimal hyperplasia than Ctrl-EPCs administration (N/M: 0.38 ± 0.03 vs 0.67 ± 0.05, P < .05). Preincubation with CXCR4-Ab, AMD3100, or LY294002 significantly attenuated the enhanced in vitro and in vivo effects of Foxc2-EPCs.

CONCLUSIONS

Our findings indicate that Foxc2 overexpression increases CXCR4 expression of EPCs and efficiently enhances the homing potential of EPCs, thereby improving EPCs-mediated therapeutic benefit after endothelial injury. Foxc2 may be a novel molecular target for improving the therapeutic efficacy of EPCs transplantation.

Age-Dependent Availability and Functionality of Bone Marrow Stem Cells in an Experimental Model of Acute and Chronic Myocardial Infarction

The aim of this study was to investigate the effect of aging and timing of left ventricular ischemic injury on the availability and functionality of stem cells. We studied young and aged male inbred Lewis rats that were used as donors of bone marrow mononuclear cells (BM-MNCs), divided in four experimental groups: controls, sham operated, 48 h post-myocardial infarction (MI), and 28 days post-MI. In vitro studies included flow cytometry analysis, hematopoietic colony-forming capacity, and invasion assays of migration capacity. BM-MNCs from these groups were transplanted in female rats after MI induction. Late engraftment was evaluated by real-time PCR of the SRY chromosome. Percentage of CD34+/CD45+low cells was similar among different experimental groups in young rats, but was significantly higher in aged animals ( p < 0.001), particularly 28 days post-MI. KDR+/CD34+ cells were increased 48 h after MI and decreased 28 days post-MI in young animals, while they were profoundly reduced in the aged group ( p < 0.001). Triple staining for CD44+/CD29+/CD71+ cells was similar in different groups of aged rats, but we observed an intense increase 48 h post-MI in young animals. Colony-forming units and cytokine-induced migration were significantly attenuated 28 days after the MI. Late engraftment in infarcted transplanted female hearts was present, but considerably heterogeneous. Finally, recovery of left ventricular systolic function in transplanted female recipients was significantly influenced by donors' BM-MNCs groups ( p < 0.01). We have demonstrated that aging and timing of myocardial injury are factors that may act synergistically in determining stem cell availability and function. Such interaction should be considered when planning new cell therapy strategies for acute and chronic ischemic heart disease in the clinical arena.

A collagen–chitosan hydrogel for endothelial differentiation and angiogenesis

Cell therapy for the treatment of cardiovascular disease has been hindered by low cell engraftment, poor survival, and inadequate phenotype and function. In this study, we added chitosan to a previously developed injectable collagen matrix, with the aim of improving its properties for cell therapy and neovascularization. Different ratios of collagen and chitosan were mixed and chemically crosslinked to produce hydrogels. Swell and degradation assays showed that chitosan improved the stability of the collagen hydrogel. In culture, endothelial cells formed significantly more vascular-like structures on collagen–chitosan than collagen-only matrix. While the differentiation of circulating progenitor cells to CD31+ cells was equal on all matrices, vascular endothelial-cadherin expression was increased on the collagen–chitosan matrix, suggesting greater maturation of the endothelial cells. In addition, the collagen–chitosan matrix supported a significantly greater number of CD133+ progenitor cells than the collagen-only matrix. In vivo, subcutaneously implanted collagen–chitosan matrices stimulated greater vascular growth and recruited more von Willebrand factor (vWF+) and CXCR4+ endothelial/angiogenic cells than the collagen-only matrix. These results indicate that the addition of chitosan can improve the physical properties of collagen matrices, and enhance their ability to support endothelial cells and angiogenesis for use in cardiovascular tissue engineering applications.

Parathyroid hormone is a DPP-IV inhibitor and increases SDF-1-driven homing of CXCR4(+) stem cells into the ischaemic heart

AIMS

Parathyroid hormone (PTH) has been shown to promote stem cell mobilization into peripheral blood. Moreover, PTH treatment after myocardial infarction (MI) improved survival and myocardial function associated with enhanced homing of bone marrow-derived stem cells (BMCs). To unravel the molecular mechanisms of PTH-mediated stem cell trafficking, we analysed wild-type (wt) and green fluorescent protein (GFP)-transgenic mice after MI with respect to the pivotal stromal cell-derived factor-1 (SDF-1)/chemokine receptor type 4 (CXCR4) axis.

METHODS AND RESULTS

WT and GFP-transgenic mice (C57BL/6J) were infarcted by coronary artery ligation and PTH (80 μg/kg/day) was injected for 6 days afterwards. Number of BMCs was analysed by flow cytometry. SDF-1 protein levels and activity of dipeptidyl peptidase-IV (DPP-IV) were investigated by ELISA and activity assay. Functional analyses were performed at day 30 after MI. PTH-treated animals revealed an enhanced homing of CXCR4(+) BMCs associated with an increased protein level of the corresponding homing factor SDF-1 in the ischaemic heart. In vitro and in vivo, PTH inhibited the activity of DPP-IV, which cleaves and inactivates SDF-1. Functionally, PTH significantly improved myocardial function after MI. Both stem cell homing as well as functional recovery were reversed by the CXCR4 antagonist AMD3100.

CONCLUSION

In summary, PTH is a DPP-IV inhibitor leading to an increased cardiac SDF-1 level, which enhances recruitment of CXCR4(+) BMCs into the ischaemic heart associated with attenuated ischaemic cardiomyopathy. Since PTH is already clinically used our findings may have direct impact on the initiation of studies in patients with ischaemic disorders.

Intraarterial administration of bone marrow mononuclear cells in patients with critical limb ischemia: a randomized-start, placebo-controlled pilot trial (PROVASA)

BACKGROUND

Critical limb ischemia due to peripheral arterial occlusive disease is associated with a severely increased morbidity and mortality. There is no effective pharmacological therapy available. Injection of autologous bone marrow-derived mononuclear cells (BM-MNC) is a promising therapeutic option in patients with critical limb ischemia, but double-blind, randomized trials are lacking.

METHODS AND RESULTS

Forty patients with critical limb ischemia were included in a multicenter, phase II, double-blind, randomized-start trial to receive either intraarterial administration of BM-MNC or placebo followed by active treatment with BM-MNC (open label) after 3 months. Intraarterial administration of BM-MNC did not significantly increase ankle-brachial index and, thus, the trial missed its primary end point. However, cell therapy was associated with significantly improved ulcer healing (ulcer area, 3.2±4.7 cm(2) to 1.89±3.5 cm(2) [P=0.014] versus placebo, 2.92±3.5 cm(2) to 2.89±4.1 cm(2) [P=0.5]) and reduced rest pain (5.2±1.8 to 2.2±1.3 [P=0.009] versus placebo, 4.5±2.4 to 3.9±2.6 [P=0.3]) within 3 months. Limb salvage and amputation-free survival rates did not differ between the groups. Repeated BM-MNC administration and higher BM-MNC numbers and functionality were the only independent predictors of improved ulcer healing. Ulcer healing induced by repeated BM-MNC administration significantly correlated with limb salvage (r=0.8; P<0.001).

CONCLUSIONS

Intraarterial administration of BM-MNC is safe and feasible and accelerates wound healing in patients without extensive gangrene and impending amputation. These exploratory findings of this pilot trial need to be confirmed in a larger randomized trial in patients with critical limb ischemia and stable ulcers.

CXCR4+ progenitors derived from bone mesenchymal stem cells differentiate into endothelial cells capable of vascular repair after arterial injury

Recent findings indicate that bone marrow mesenchymal stem cells (BMSCs) participate in the process of neovascularization in response to repair to injury and are involved in postinfarction myocardial repair. It is unclear what special characteristics the vascular progenitors of bone marrow origin has. CXCR4(+) stem/progenitor cells mobilized to the infarct area and improved the myocardial repair. In present study, we aimed to determine whether CXCR4(+)BMSCs contribute to the angiogenic capacity in vitro and in vivo. CXCR4(+)BMSCs were separated by using paramagnetic microbeads and cultured. RT-PCR and FACS analysis confirmed the gene expression phenotype. The uptake of acetylated low density lipoprotein (acLDL) and the tube formation evaluated the function of CXCR4(+)BMSCs. The effect of CXCR4(+)BMSCs transplantation on neovascularization was investigated in a murine model hindlimb ischemia. After induced by VEGF, CXCR4(+)BMSCs expressed the endothelial cells (ECs) phenotype. The expression of EC markers, PECAM-1, and von Willebrand factor (vWF) increased significantly at both the mRNA and protein levels. In addition, CXCR4(+)BMSCs enhanced the uptakes of Dil-acLDL and form capillary-like tubes in vitro. In vivo the local transfer of CXCR4(+)BMSCs increased neovascularization in ischemic hindlimb. These results demonstrate that CXCR4(+)BMSCs differentiate into ECs and contribute to neovascularization in the vascular lesion,, which indicate the important therapeutic implications for cardiovascular diseases and a new cell source for cell-based vascular engineering and repair in the future.

Endothelial and cardiac progenitors: boosting, conditioning and (re)programming for cardiovascular repair

Preclinical studies performed in cell culture and animal systems have shown the outstanding ability of stem cells to repair ischemic heart and lower limbs by promoting the formation of new blood vessels and new myocytes. In contrast, clinical studies of stem cell administration in patients with myocardial ischemia have revealed only modest, although promising, results. Basic investigations have shown the feasibility of adult cells reprogramming into pluripotent cells by defined factors, thus opening the way to the devise of protocols to ex vivo derive virtually unexhausted cellular pools. In contrast, cellular and molecular studies have indicated that risk factors limit adult-derived stem cell survival, proliferation and engraftment in ischemic tissues. The use of fully reprogrammed cells raises safety concerns; therefore, adult cells remain a primary option for clinicians interested in therapeutic cardiovascular repair. Pharmacologic approaches have been devised to restore the cardiovascular repair ability of failing progenitors from patients at risk. In the present contribution, the most advanced pharmacologic approaches to (re)program, boost, and condition endothelial and cardiac progenitor cells to enhance cardiovascular regeneration are discussed.

SDF-1-enhanced cardiogenesis requires CXCR4 induction in pluripotent stem cells

Transformation of pluripotent stem cells into cardiac tissue is the hallmark of cardiogenesis, yet pro-cardiogenic signals remain partially understood. Preceding cardiogenic induction, a surge in CXCR4 chemokine receptor expression in the early stages of stem cell lineage specification coincides with the acquisition of pre-cardiac profiles. Accordingly, CXCR4 selection, in conjunction with mesoderm-specific VEGF type II receptor FLK-1 co-expression, segregates cardiogenic populations. To assess the functionality of the CXCR4 biomarker, targeted activation and disruption were here exploited in the context of embryonic stem cell-derived cardiogenesis. Implicated as a cardiogenic hub through unbiased bioinformatics analysis, induction of the CXCR4/SDF-1 receptor-ligand axis triggered enhanced beating activity in stem cell progeny. Gene expression knockdown of CXCR4 disrupted spontaneous embryoid body differentiation and blunted the expression of cardiogenic markers MEF2C, Nkx2.5, MLC2a, MLC2v, and cardiac-MHC. Exogenous SDF-1 treatment failed to rescue cardiogenic-deficient phenotype, demonstrating a requirement for CXCR4 expression in mediating SDF-1 effects. Thus, a pro-cardiogenic signaling role for the CXCR4/SDF1 axis is herein revealed within pluripotent stem cell progenitors, exposing a functional target to promote lineage-specific differentiation.

Expression of a retinoic acid signature in circulating CD34 cells from coronary artery disease patients

Background

Circulating CD34+ progenitor cells have the potential to differentiate into a variety of cells, including endothelial cells. Knowledge is still scarce about the transcriptional programs used by CD34+ cells from peripheral blood, and how these are affected in coronary artery disease (CAD) patients.

Results

We performed a whole genome transcriptome analysis of CD34+ cells, CD4+ T cells, CD14+ monocytes, and macrophages from 12 patients with CAD and 11 matched controls. CD34+ cells, compared to other mononuclear cells from the same individuals, showed high levels of KRAB box transcription factors, known to be involved in gene silencing. This correlated with high expression levels in CD34+ cells for the progenitor markers HOXA5 and HOXA9, which are known to control expression of KRAB factor genes. The comparison of expression profiles of CD34+ cells from CAD patients and controls revealed a less naïve phenotype in patients' CD34+ cells, with increased expression of genes from the Mitogen Activated Kinase network and a lowered expression of a panel of histone genes, reaching levels comparable to that in more differentiated circulating cells. Furthermore, we observed a reduced expression of several genes involved in CXCR4-signaling and migration to SDF1/CXCL12.

Conclusions

The altered gene expression profile of CD34+ cells in CAD patients was related to activation/differentiation by a retinoic acid-induced differentiation program. These results suggest that circulating CD34+ cells in CAD patients are programmed by retinoic acid, leading to a reduced capacity to migrate to ischemic tissues.

Distinct kinin-induced functions are altered in circulating cells of young type 1 diabetic patients

AIMS/HYPOTHESIS

We aimed to understand early alterations in kinin-mediated migration of circulating angio-supportive cells and dysfunction of kinin-sensitive cells in type-1 diabetic (T1D) patients before the onset of cardiovascular disease.

METHODS

Total mononuclear cells (MNC) were isolated from peripheral blood of 28 T1D patients free from cardiovascular complications except mild background retinopathy (age: 34.8+/-1.6 years, HbA(1C): 7.9+/-0.2%) and 28 age- and sex-matched non-diabetic controls (H). We tested expression of kinin receptors by flow cytometry and migratory capacity of circulating monocytes and progenitor cells towards bradykinin (BK) in transwell migration assays. MNC migrating towards BK (BK(mig)) were assessed for capacity to support endothelial cell function in a matrigel assay, as well as generation of nitric oxide (NO) and superoxide (O(2) (-)*) by using the fluorescent probes diaminofluorescein and dihydroethidium.

RESULTS

CD14(hi)CD16(neg), CD14(hi)CD16(pos) and CD14(lo)CD16(pos) monocytes and circulating CD34(pos) progenitor cells did not differ between T1D and H subjects in their kinin receptor expression and migration towards BK. T1D BK(mig) failed to generate NO upon BK stimulation and supported endothelial cell network formation less efficiently than H BK(mig). In contrast, O(2) (-)* production was similar between groups. High glucose disturbed BK-induced NO generation by MNC-derived cultured angiogenic cells.

CONCLUSIONS/INTERPRETATION

Our data point out alterations in kinin-mediated functions of circulating MNC from T1D patients, occurring before manifest macrovascular damage or progressed microvascular disease. Functional defects of MNC recruited to the vessel wall might compromise endothelial maintenance, initially without actively promoting endothelial damage, but rather by lacking supportive contribution to endothelial regeneration and healing.

Bone marrow transplantation in mice as a tool for studying the role of hematopoietic cells in metabolic and cardiovascular diseases

Hematopoietic cells have been established as major players in cardiovascular disease, with an important role in the etiology of atherosclerotic plaque. In addition, hematopoietic cells, and in particular the cells of monocyte and macrophage lineages, have recently been unmasked as one of the main causes of metabolic abnormalities leading to insulin resistance and type 2 diabetes. With the availability of transgenic mouse models that reproduce many aspects of these diseases, research in these areas has been able to make exceptional progress. Much of the work exploring the role of hematopoietic cells has been carried out on chimeric mice made by the recipient disease model mice being given donor bone marrow cells from transgenic mice harboring a genetic alteration in a relevant pathway. Here, we will describe the potential of the bone marrow transplantation approach and discuss recent developments, including the use of virally transduced cells. We will explain some of the caveats, their effect on the experimental outcomes, and some possible solutions. Taken as a whole, this technology offers great advantages in efficiency and cost-effectiveness, and it is expected to continue to be a crucial technique in cardiovascular research work.

Circulating endothelial progenitor cells are not affected by acute systemic inflammation

Vascular injury causes acute systemic inflammation and mobilizes endothelial progenitor cells (EPCs) and endothelial cell (EC) colony-forming units (EC-CFUs). Whether such mobilization occurs as part of a nonspecific acute phase response or is a phenomenon specific to vascular injury remains unclear. We aimed to determine the effect of acute systemic inflammation on EPCs and EC-CFU mobilization in the absence of vascular injury. Salmonella typhus vaccination was used as a model of acute systemic inflammation. In a double-blind randomized crossover study, 12 healthy volunteers received S. typhus vaccination or placebo. Phenotypic EPC populations enumerated by flow cytometry [CD34(+)VEGF receptor (VEGF)R-2(+)CD133(+), CD14(+)VEGFR-2(+)Tie2(+), CD45(-)CD34(+), as a surrogate for late outgrowth EPCs, and CD34(+)CXCR-4(+)], EC-CFUs, and serum cytokine concentrations (high sensitivity C-reactive protein, IL-6, and stromal-derived factor-1) were quantified during the first 7 days. Vaccination increased circulating leukocyte (9.8 + or - 0.6 vs. 5.1 + or - 0.2 x 10(9) cells/l, P < 0.0001), serum IL-6 [0.95 (0-1.7) vs. 0 (0-0) ng/l, P = 0.016], and VEGF-A [60 (45-94) vs. 43 (21-64) pg/l, P = 0.006] concentrations at 6 h and serum high sensitivity C-reactive protein at 24 h [2.7 (1.4-3.6) vs. 0.4 (0.2-0.8) mg/l, P = 0.037]. Vaccination caused a 56.7 + or - 7.6% increase in CD14(+) cells at 6 h (P < 0.001) and a 22.4 + or - 6.9% increase in CD34(+) cells at 7 days (P = 0.04). EC-CFUs, putative vascular progenitors, and the serum stromal-derived factor-1 concentration were unaffected throughout the study period (P > 0.05 for all). In conclusion, acute systemic inflammation causes nonspecific mobilization of hematopoietic progenitor cells, although it does not selectively mobilize putative vascular progenitors. We suggest that systemic inflammation is not the primary stimulus for EPC mobilization after acute vascular injury.