Paracrine mechanisms in adult stem cell signaling and therapy

Transplantation of nonhematopoietic adult bone marrow stem/progenitor cells isolated by p75 nerve growth factor receptor into the penis rescues erectile function in a rat model of cavernous nerve injury

PURPOSE

Radical prostatectomy for prostate cancer frequently results in erectile dysfunction and decreased quality of life. We investigated the effects of transplanting nonhematopoietic adult bone marrow stem/progenitor cells (multipotent stromal cells) into the corpus cavernosum in a rat model of bilateral cavernous nerve crush injury.

MATERIALS AND METHODS

Multipotent stromal cells were isolated from the bone marrow of transgenic green fluorescent protein rats by plastic adherence (rat multipotent stromal cells) or magnetic activated cell sorting using antibodies against p75 low affinity nerve growth factor receptor (p75 derived multipotent stromal cells). Bilateral cavernous nerve crush injury was induced in adult male Sprague-Dawley rats. Immediately after injury 8 rats each were injected intracavernously with phosphate buffered saline (vehicle control), fibroblasts (cell control), rat multipotent stromal cells (cell treatment) or p75 derived multipotent stromal cells (cell treatment). Another 8 rats underwent sham operation (phosphate buffered saline injection). Four weeks after the procedures we assessed erectile function by measuring the intracavernous-to-mean arterial pressure ratio and total intracavernous pressure during cavernous nerve stimulation.

RESULTS

Intracavernous injection of p75 derived multipotent stromal cells after bilateral cavernous nerve crush injury resulted in a significantly higher mean intracavernous-to-mean arterial pressure ratio and total intracavernous pressure compared with all other groups except the sham operated group (p <0.05). Rats injected with typical multipotent stromal cells had partial erectile function rescue compared with animals that received p75 derived multipotent stromal cells. Fibroblast (cell control) and phosphate buffered saline (vehicle control) injection did not improve erectile function. Enzyme-linked immunosorbent assay suggested that basic fibroblast growth factor secreted by p75 derived multipotent stromal cells protected the cavernous nerve after bilateral cavernous nerve crush injury.

CONCLUSIONS

Transplantation of adult stem/progenitor cells may provide an effective treatment for erectile dysfunction after radical prostatectomy.

Paracrine mechanisms of stem cell reparative and regenerative actions in the heart

Stem cells play an important role in restoring cardiac function in the damaged heart. In order to mediate repair, stem cells need to replace injured tissue by differentiating into specialized cardiac cell lineages and/or manipulating the cell and molecular mechanisms governing repair. Despite early reports describing engraftment and successful regeneration of cardiac tissue in animal models of heart failure, these events appear to be infrequent and yield too few new cardiomyocytes to account for the degree of improved cardiac function observed. Instead, mounting evidence suggests that stem cell mediated repair takes place via the release of paracrine factors into the surrounding tissue that subsequently direct a number of restorative processes including myocardial protection, neovascularization, cardiac remodeling, and differentiation. The potential for diverse stem cell populations to moderate many of the same processes as well as key paracrine factors and molecular pathways involved in stem cell-mediated cardiac repair will be discussed in this review. This article is part of a special issue entitled, "Cardiovascular Stem Cells Revisited".

Mechanisms of cardiac fibrosis in inflammatory heart disease

Heart injury from many causes can end up in a common final pathway of pathologic remodeling and fibrosis, promoting heart failure development. Dilated cardiomyopathy is an important cause of heart failure and often results from virus-triggered myocarditis. Monocytes and monocyte-like cells represent a major subset of heart-infiltrating cells at the injury site. These bone marrow-derived cells promote not only tissue injury in the short term but also angiogenesis and collagen deposition in the long term. Thus, they are critically involved in the typical tissue fibrosis, which evolves in the dilating ventricle during the process of pathologic remodeling. Recent findings suggest that heart-infiltrating monocyte-like cells indeed contain a pool of progenitors, which represent the cellular source both for accumulation of differentiated monocytes during the acute inflammatory phase and for transforming growth factor-beta-mediated myocardial fibrosis during the later chronic stages of disease. Obviously, a delicate balance of proinflammatory and profibrotic cytokines dictates the fate of bone marrow-derived heart-infiltrating progenitors and directly influences the morphologic phenotype of the affected heart. In this minireview, we provide an update on these mechanisms and discuss their significance in pathologic remodeling and heart failure progression after myocarditis.

Exosomes/microvesicles as a mechanism of cell-to-cell communication

Microvesicles (MVs) are circular fragments of membrane released from the endosomal compartment as exosomes or shed from the surface membranes of most cell types. An increasing body of evidence indicates that they play a pivotal role in cell-to-cell communication. Indeed, they may directly stimulate target cells by receptor-mediated interactions or may transfer from the cell of origin to various bioactive molecules including membrane receptors, proteins, mRNAs, microRNAs, and organelles. In this review we discuss the pleiotropic biologic effects of MVs that are relevant for communication among cells in physiological and pathological conditions. In particular, we discuss their potential involvement in inflammation, renal disease, and tumor progression, and the evidence supporting a bidirectional exchange of genetic information between stem and injured cells. The transfer of gene products from injured cells may explain stem cell functional and phenotypic changes without the need of transdifferentiation into tissue cells. On the other hand, transfer of gene products from stem cells may reprogram injured cells to repair damaged tissues.

The advantages and disadvantages of sfrp1 and sfrp2 expression in pathological events

Secreted Frizzled Related Proteins (Sfrps) are a family of secreted proteins that can bind both to Wnt ligands and Frizzled receptors, thereby modulating the Wnt signalling cascades. Recent studies have shown that Sfrps can also interact with Wnt unrelated molecules such as RANKL, a member of the tumor necrosis factor family, Tolloid metalloproteinases or integrin-fibronectin complexes. Alterations in the levels of Sfrp expression have been recently associated with different pathological conditions, including tumor formation and bone and myocardial disorders. Here, we summarise the evidence that relates Sfrps with these diseases and discuss how the proposed multiple Sfrp interactions with Wnt related and unrelated pathways may explain their implication in such diverse pathologies.

Neuregulin/ErbB signaling regulates cardiac subtype specification in differentiating human embryonic stem cells

RATIONALE

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) exhibit either a "working" chamber or a nodal-like phenotype. To generate optimal hESC-CM preparations for eventual clinical application in cell-based therapies, we will need to control their differentiation into these specialized cardiac subtypes.

OBJECTIVE

To demonstrate intact neuregulin (NRG)-1β/ErbB signaling in hESC-CMs and test the hypothesis that this signaling pathway regulates cardiac subtype abundance in hESC-CM cultures.

METHODS AND RESULTS

All experiments used hESC-CM cultures generated using our recently reported directed differentiation protocol. To support subsequent action potential phenotyping approaches and provide a higher-throughput method of determining cardiac subtype, we first developed and validated a novel genetic label that identifies nodal-type hESC-CMs. Next, control hESC-CM preparations were compared to those differentiated in the presence of exogenous NRG-1β, an anti-NRG-1β neutralizing antibody, or the ErbB antagonist AG1478. We used 3 independent approaches to determine the ratio of cardiac subtypes in the resultant populations: direct action potential phenotyping under current-clamp, activation of the aforementioned genetic label, and subtype-specific marker expression by RT-PCR. Using all 3 end points, we found that inhibition of NRG-1β/ErbB signaling greatly enhanced the proportion of cells showing the nodal phenotype.

CONCLUSIONS

NRG-1β/ErbB signaling regulates the ratio of nodal- to working-type cells in differentiating hESC-CM cultures and presumably functions similarly during early human heart development. We speculate that, by manipulating NRG-1β/ErbB signaling, it will be possible to generate preparations of enriched working-type myocytes for infarct repair, or, conversely, nodal cells for potential use in a biological pacemaker.

Telocytes in human epicardium

The existence of the epicardial telocytes was previously documented by immunohistochemistry (IHC) or immunofluorescence. We have also demonstrated recently that telocytes are present in mice epicardium, within the cardiac stem-cell niches, and, possibly, they are acting as nurse cells for the cardiomyocyte progenitors. The rationale of this study was to show that telocytes do exist in human (sub)epicardium, too. Human autopsy hearts from 10 adults and 15 foetuses were used for conventional IHC for c-kit/CD117, CD34, vimentin, S-100, τ, Neurokinin 1, as well as using laser confocal microscopy. Tissue samples obtained by surgical biopsies from 10 adults were studied by digital transmission electron microscopy (TEM). Double immunolabelling for c-kit/CD34 and, for c-kit/vimentin suggests that in human beings, epicardial telocytes share similar immunophenotype features with myocardial telocytes. The presence of the telocytes in human epicardium is shown by TEM. Epicardial telocytes, like any of the telocytes are defined by telopodes, their cell prolongations, which are very long (several tens of μm), very thin (0.1-0.2 μm, below the resolving power of light microscopy) and with moniliform configuration. The interconnected epicardial telocytes create a 3D cellular network, connected with the 3D network of myocardial telocytes. TEM documented that telocytes release shed microvesicles or exocytotic multivesicular bodies in the intercellular space. The human epicardial telocytes have similar phenotype (TEM and IHC) with telocytes located among human working cardiomyocyte. It remains to be established the role(s) of telocytes in cardiac renewing/repair/regeneration processes, and also the pathological aspects induced by their 'functional inhibition', or by their variation in number. We consider telocytes as a real candidate for future developments of autologous cell-based therapy in heart diseases.

Transplantation of expanded bone marrow-derived very small embryonic-like stem cells (VSEL-SCs) improves left ventricular function and remodelling after myocardial infarction

Adult bone marrow-derived very small embryonic-like stem cells (VSEL-SCs) exhibit a Sca-1⁺/Lin^–/CD45^– phenotype and can differentiate into various cell types, including cardiomyocytes and endothelial cells. We have previously reported that transplantation of a small number (1 × 10⁶) of freshly isolated, non-expanded VSEL-SCs into infarcted mouse hearts resulted in improved left ventricular (LV) function and anatomy. Clinical translation, however, will require large numbers of cells. Because the frequency of VSEL-SCs in the marrow is very low, we examined whether VSEL-SCs can be expanded in culture without loss of therapeutic efficacy. Mice underwent a 30 min. coronary occlusion followed by reperfusion and, 48 hrs later, received an intramyocardial injection of vehicle (group I, n= 11), 1 × 10⁵ enhanced green fluorescent protein (EGFP)-labelled expanded untreated VSEL-SCs (group II, n= 7), or 1 × 10⁵ EGFP-labelled expanded VSEL-SCs pre-incubated in a cardiogenic medium (group III, n= 8). At 35 days after myocardial infarction (MI), mice treated with pre-incubated VSEL-SCs exhibited better global and regional LV systolic function and less LV hypertrophy compared with vehicle-treated controls. In contrast, transplantation of expanded but untreated VSEL-SCs did not produce appreciable reparative benefits. Scattered EGFP⁺ cells expressing α-sarcomeric actin, platelet endothelial cell adhesion molecule (PECAM)-1, or von Willebrand factor were present in VSEL-SC-treated mice, but their numbers were very small. No tumour formation was observed. We conclude that VSEL-SCs expanded in culture retain the ability to alleviate LV dysfunction and remodelling after a reperfused MI provided that they are exposed to a combination of cardiomyogenic growth factors and cytokines prior to transplantation. Counter intuitively, the mechanism whereby such pre-incubation confers therapeutic efficacy does not involve differentiation into new cardiac cells. These results support the potential therapeutic utility of VSEL-SCs for cardiac repair.

Dynamics of progenitor cells and ventricular assist device intervention

Experimental and clinical evidence suggests that a heterogeneous group of bone-marrow-derived circulating progenitor cells, with variations in phenotype and function, provide an endogenous repair mechanism, contributing to vascular healing and remodeling under physiological and pathological conditions, such as cancer, atherosclerosis, myocardial infarction, and end-stage heart failure. Implantation of ventricular assist devices (VADs) for circulatory support is indicated in selected patients with end-stage heart failure as a bridge to heart transplantation, however seldom; improvement of ventricular contractility has been well documented with prolonged cardiac unloading. The current review summarizes recent findings from in vitro and in vivo studies, focusing on the biological features and the possible role of progenitor cells in the transient myocardial recovery, occasionally seen after VAD implantation, and speculates on their clinical utilities for the treatment of the failing human heart.

Mesenchymal stem cells provide better results than hematopoietic precursors for the treatment of myocardial infarction

OBJECTIVES

The purpose of this study was to compare the ability of human CD34(+) hematopoietic stem cells and bone marrow mesenchymal stem cells (MSC) to treat myocardial infarction (MI) in a model of permanent left descendent coronary artery (LDA) ligation in nude rats.

BACKGROUND

Transplantation of human CD34(+) cells and MSC has been proved to be effective in treating MI, but no comparative studies have been performed to elucidate which treatment prevents left ventricular (LV) remodelling more efficiently.

METHODS

Human bone marrow MSC or freshly isolated CD34(+) cells from umbilical cord blood were injected intramyocardially in infarcted nude rats. Cardiac function was analyzed by echocardiography. Ventricular remodelling was evaluated by tissue histology and electron microscopy, and neo-formed vessels were quantified by immunohistochemistry. Chronic local inflammatory infiltrates were evaluated in LV wall by hematoxylin-eosin staining. Apoptosis of infarcted tissue was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

RESULTS

Both cell types induced an improvement in LV cardiac function and increased tissue cell proliferation in myocardial tissue and neoangiogenesis. However, MSC were more effective for the reduction of infarct size and prevention of ventricular remodelling. Scar tissue was 17.48 +/- 1.29% in the CD34 group and 10.36 +/- 1.07% in the MSC group (p < 0.001 in MSC vs. CD34). Moreover, unlike MSC, CD34(+)-treated animals showed local inflammatory infiltrates in LV wall that persisted 4 weeks after transplantation.

CONCLUSIONS

Mesenchymal stem cells might be more effective than CD34(+) cells for the healing of the infarct. This study contributes to elucidate the mechanisms by which these cell types operate in the course of MI treatment.

Mesenchymal stem cells reduce inflammation while enhancing bacterial clearance and improving survival in sepsis

RATIONALE

Sepsis refers to the clinical syndrome of severe systemic inflammation precipitated by infection. Despite appropriate antimicrobial therapy, sepsis-related morbidity and mortality remain intractable problems in critically ill patients. Moreover, there is no specific treatment strategy for the syndrome of sepsis-induced multiple organ dysfunction.

OBJECTIVES

We hypothesized that mesenchymal stem cells (MSCs), which have been shown to have immunomodulatory properties, would reduce sepsis-induced inflammation and improve survival in a polymicrobial model of sepsis.

METHODS

Sepsis was induced in C57Bl/6J mice by cecal ligation and puncture (CLP), followed 6 hours later by an intravenous injection of MSCs or saline. Twenty-eight hours after CLP, plasma, bronchoalveolar lavage fluid and tissues were collected for analyses. Longer-term studies were performed with antibiotic coadministration to assess the effect of MSCs on survival.

MEASUREMENTS AND MAIN RESULTS

MSC treatment significantly reduced mortality in septic mice receiving appropriate antimicrobial therapy. MSCs alone reduced systemic and pulmonary cytokine levels in mice with CLP-induced sepsis, preventing acute lung injury and organ dysfunction, despite the low levels of cell persistence. Microarray data highlighted an overall down-regulation of inflammation and inflammation-related genes (such as IL-10, IL-6) and a shift toward up-regulation of genes involved in promoting phagocytosis and bacterial killing. Finally, bacterial clearance was significantly greater in MSC-treated mice, in part due to enhanced phagocytotic activity of the host immune cells.

CONCLUSIONS

These data demonstrate that MSCs have beneficial effects on experimental sepsis, possibly by paracrine mechanisms, and suggest that immunomodulatory cell therapy may be an effective adjunctive treatment to reduce sepsis-related morbidity and mortality.

Diabetic cardiomyopathy: signaling defects and therapeutic approaches

Diabetes mellitus is the world's fastest growing disease with high morbidity and mortality rates, predominantly as a result of heart failure. A significant number of diabetic patients exhibit diabetic cardiomyopathy; that is, left ventricular dysfunction independent of coronary artery disease or hypertension. The pathogenesis of diabetic cardiomyopathy is complex, and is characterized by dysregulated lipid metabolism, insulin resistance, mitochondrial dysfunction and disturbances in adipokine secretion and signaling. These abnormalities lead to impaired calcium homeostasis, ultimately resulting in lusitropic and inotropic defects. This article discusses the impact of these hallmark factors in diabetic cardiomyopathy, and concludes with a survey of available and emerging therapeutic modalities.

3-dimensional structures to enhance cell therapy and engineer contractile tissue

Experimental studies in animals and recent human clinical trials have revealed the current limitations of cellular transplantation, which include poor cell survival, lack of cell engraftment, and poor differentiation. Evidence in animals suggests that use of a 3-dimensional scaffold may enhance cell therapy and engineer myocardial tissue by improving initial cell retention, survival, differentiation, and integration. Several scaffolds of synthetic or natural origin are under development. Until now, contractility has been demonstrated in vitro only in biological scaffolds prepared from decellularized organs or tissue, or in collagenic porous scaffold obtained by crosslinking collagen fibers. While contractility of a cellularized collagen construct is poor, it can be greatly enhanced by tumor basement membrane extract. Recent advances in biochemistry have shown improved cell-matrix interactions by coupling adhesion molecules to achieve an efficient and safe bioartificial myocardium with no tumoral component. Fixation of adhesion molecules may also be a way to enhance cell homing and/or differentiation to increase local angiogenesis. Whatever the clinically successful combination ultimately proves to be, it is likely that cell therapy will require providing a supportive biochemical, physical, and spatial environment that will allow the cells to optimally differentiate and integrate within the target myocardial tissue.

Aesthetic cardiology: adipose-derived stem cells for myocardial repair

Stem cell biology has increasingly gained scientific and public interest in recent years. In particular, the use of stem cells for treatment of heart disease has been strongly pursued within the scientific and medical communities. Significant effort has gone into the use of adult tissue-derived stem cells for cardiac repair including bone marrow, blood, and cardiac-derived cell populations. Significant interest in this area has been balanced by the difficulties of understanding stem cells, cardiac injury, and the amalgamation of these areas of investigation in translational medicine. Recent studies have emerged on adipose-derived stem cells which show the potential for cardiac lineage development in vitro and may have application in cell-mediated in vivo therapy for the diseased heart. This review provides a summary of current findings within the field of adipose-derived stem cell biology regarding their cardiac differentiation potential.

Bone marrow derived stem cells in regenerative medicine as advanced therapy medicinal products

Bone marrow derived stem cells administered after minimal manipulation represent an important cell source for cell-based therapies. Clinical trial results, have revealed both safety and efficacy of the cell reinfusion procedure in many cardiovascular diseases. Many of these early clinical trials were performed in a period before the entry into force of the US and European regulation on cell-based therapies. As a result, conflicting data have been generated on the effectiveness of those therapies in certain conditions as acute myocardial infarction. As more academic medical centers and private companies move toward exploiting the full potential of cell-based medicinal products, needs arise for the development of the infrastructure necessary to support these investigations. This review describes the regulatory environment surrounding the production of cell based medicinal products and give practical aspects for cell isolation, characterization, production following Good Manufacturing Practice, focusing on the activities associated with the investigational new drug development.

Mesenchymal stem cells: paracrine signaling and differentiation during cutaneous wound repair

Cutaneous wounds persist as a health care crisis in spite of increased understanding of the cellular and molecular responses to injury. Contributing significantly to this crisis is the lack of reliable therapies for treatment of wounds that are slow to heal including chronic wounds and deep dermal wounds that develop hypertrophic scars. This article will review the growing evidence demonstrating the promise of multipotent mesenchymal stem/stromal (MSCs) for the treatment of impaired wound healing. MSCs are often referred to as mesenchymal stem cells despite concerns that these cells are not truly stem cells given the lack of evidence demonstrating self-renewal in vivo. Regardless, abundant evidence demonstrates the therapeutic potential of MSCs for repair and regeneration of damaged tissue due to injury or disease. To date, MSC treatment of acute and chronic wounds results in accelerated wound closure with increased epithelialization, granulation tissue formation and angiogenesis. Although there is evidence for MSC differentiation in the wound, most of the therapeutic effects are likely due to MSCs releasing soluble factors that regulate local cellular responses to cutaneous injury. Important challenges need to be overcome before MSCs can be used effectively to treat wounds that are slow to heal.

Cardiomyocyte progenitor cell-derived exosomes stimulate migration of endothelial cells

Patients suffering from heart failure as a result of myocardial infarction are in need of heart transplantation. Unfortunately the number of donor hearts is very low and therefore new therapies are subject of investigation. Cell transplantation therapy upon myocardial infarction is a very promising strategy to replace the dead myocardium with viable cardiomyocytes, smooth muscle cells and endothelial cells, thereby reducing scarring and improving cardiac performance. Despite promising results, resulting in reduced infarct size and improved cardiac function on short term, only a few cells survive the ischemic milieu and are retained in the heart, thereby minimizing long-term effects. Although new capillaries and cardiomyocytes are formed around the infarcted area, only a small percentage of the transplanted cells can be detected months after myocardial infarction. This suggests the stimulation of an endogenous regenerative capacity of the heart upon cell transplantation, resulting from release of growth factor, cytokine and other paracrine molecules by the progenitor cells--the so-called paracrine hypothesis. Here, we focus on a relative new component of paracrine signalling, i.e. exosomes. We are interested in the release and function of exosomes derived from cardiac progenitor cells and studied their effects on the migratory capacity of endothelial cells.

Oxidized low-density lipoprotein induces apoptosis in endothelial progenitor cells by inactivating the phosphoinositide 3-kinase/Akt pathway

We tested the hypothesis that oxidized low-density lipoprotein (oxLDL)-induced inactivation of Akt within endothelial progenitor cells (EPCs) is mediated at the level of phosphoinositide 3-kinase (PI3K), specifically by nitrosylation of the p85 subunit of PI3K, and that this action is critical in provoking oxLDL-induced EPC apoptosis. Hypercholesterolemic ApoE null mice had a significant reduction of the phosphorylated Akt (p-Akt)/Akt ratio in EPCs, as well as a greater percentage of apoptosis in these cells than EPCs isolated from wild-type (WT) C57Bl/6 mice. EPCs were isolated from WT spleen and exposed to oxLDL in vitro. oxLDL increased O₂⁻ and H₂O₂ in these cells and induced a dose- and time-dependent reduction in the p-Akt/Akt ratio and increase in EPC apoptosis. These effects were significantly reduced by the antioxidants superoxide dismutase, L-NAME, epicatechin and FeTPPs. oxLDL also induced nitrosylation of the p85 subunit of PI3K and subsequent dissociation of the p85 and p110 subunits, an effect significantly reduced by all the antioxidant agents tested. EPC transfection with a constitutively active Akt isoform (Ad-myrAkt) significantly reduced oxLDL-induced apoptosis of WT EPCs. The present findings indicate that oxLDL disrupts the PI3K/Akt signaling pathway at the level of p85 in EPCs. This dysfunction can be reversed by ex vivo antioxidant therapy.

Mesenchymal stem cells: From bench to bedside

Human mesenchymal stem cells (hMSCs) have tremendous promise for use in a variety of clinical applications. The ability of these cells to self-renew and differentiate into multiple tissues makes them an attractive cell source for a new generation of cell-based regenerative therapies. Encouraging results from clinical trials have also generated growing enthusiasm regarding MSC therapy and related treatment, but gaps remain in understanding MSC tissue repair mechanisms and in clinical strategies for efficient cell delivery and consistent therapeutic outcomes. For these reasons, discoveries from basic research and their implementation in clinical trials are essential to advance MSC therapy from the laboratory bench to the patient's bedside.

New insights into paracrine mechanisms of human cardiac progenitor cells

AIMS

Cardiac progenitor cells (CPCs) have been shown to promote cardiac regeneration in vivo. Understanding the function of CPCs is essential for further implementation of these cells in the treatment of cardiac diseases. The present study tested the hypothesis that adult CPC exert paracrine effects that lead to an improvement in the functional characteristics of cardiomyocytes. This study also investigated whether aging (we included patients aged between 4 months and 81 years) has any effect on the paracrine mechanisms of CPC.

METHODS AND RESULTS

The supernatant of CPC generated both from human and rat hearts-so called 'conditioned cardiosphere medium' improved the contractile behaviour of isolated adult cardiomyocytes in a concentration-dependent manner after incubation for 24 h and increased the SERCA/NCX ratio. The observed positive effects on contractile behaviour were independent of the CPC donors' age. Conditioned cardiosphere media also normalized angiotensin II-induced contractile dysfunction. Cytokines released by CPC into the media were detected by cytokine arrays.

CONCLUSION

The observed diversity of cytokines released by CPC needs to be further elucidated in detail. Nevertheless, CPC are a promising therapeutic approach in the field of cardiac disease. The methods described allow investigation of the underlying paracrine mechanisms in a standardized in vitro situation.

Mesenchymal stem cells rescue cardiomyoblasts from cell death in an in vitro ischemia model via direct cell-to-cell connections

Background

Bone marrow derived mesenchymal stem cells (MSCs) are promising candidates for cell based therapies in myocardial infarction. However, the exact underlying cellular mechanisms are still not fully understood. Our aim was to explore the possible role of direct cell-to-cell interaction between ischemic H9c2 cardiomyoblasts and normal MSCs. Using an in vitro ischemia model of 150 minutes of oxygen glucose deprivation we investigated cell viability and cell interactions with confocal microscopy and flow cytometry.

Results

Our model revealed that adding normal MSCs to the ischemic cell population significantly decreased the ratio of dead H9c2 cells (H9c2 only: 0.85 ± 0.086 vs. H9c2+MSCs: 0.16 ± 0.035). This effect was dependent on direct cell-to-cell contact since co-cultivation with MSCs cultured in cell inserts did not exert the same beneficial effect (ratio of dead H9c2 cells: 0.90 ± 0.055). Confocal microscopy revealed that cardiomyoblasts and MSCs frequently formed 200-500 nm wide intercellular connections and cell fusion rarely occurred between these cells.

Conclusion

Based on these results we hypothesize that mesenchymal stem cells may reduce the number of dead cardiomyoblasts after ischemic damage via direct cell-to-cell interactions and intercellular tubular connections may play an important role in these processes.

Characterizing functional stem cell-cardiomyocyte interactions

Despite the progress in traditional pharmacological and organ transplantation therapies, heart failure still afflicts 5.3 million Americans. Since June 2000, stem cell-based approaches for the prevention and treatment of heart failure have been pursued in clinics with great excitement; however, the exact mechanisms of how transplanted cells improve heart function remain elusive. One of the main difficulties in answering these questions is the limited ability to directly access and study interactions between implanted cells and host cardiomyocytes in situ. With the growing number of candidate cell types for potential clinical use, it is becoming increasingly more important to establish standardized, well-controlled in vitro and in situ assays to compare the efficacy and safety of different stem cells in cardiac repair. This article describes recent innovative methodologies to characterize direct functional interactions between stem cells and cardiomyocytes, aimed to facilitate the rational design of future cell-based therapies for heart disease.

ES and iPS cell research for cardiovascular regeneration

Embryonic stem (ES) cells and induced pluripotent stem (iPS) cells, which are ES-like stem cells induced from adult tissues, are twin stem cells with currently (with the exception of fertilized eggs) the broadest differentiation potentials. These two stem cells show various similarities in appearance, maintenance methods, growth and differentiation potentials, i.e. theoretically, those cells can give rise to all kinds of cells including germ-line cells. Generation of human ES and iPS cells is further facilitating the researches towards the realization of regenerative medicine. The following three issues are important purposes of ES and iPS cell researches for regenerative medicine: (1) dissection of differentiation mechanisms, (2) application to cell transplantation, and (3) drug discovery. In this review, the current status of cardiovascular regenerative trials using ES and iPS cells is briefly discussed.

Magnetic targeting enhances engraftment and functional benefit of iron-labeled cardiosphere-derived cells in myocardial infarction

RATIONALE

The success of cardiac stem cell therapies is limited by low cell retention, due at least in part to washout via coronary veins.

OBJECTIVE

We sought to counter the efflux of transplanted cells by rendering them magnetically responsive and imposing an external magnetic field on the heart during and immediately after injection.

METHODS AND RESULTS

Cardiosphere-derived cells (CDCs) were labeled with superparamagnetic microspheres (SPMs). In vitro studies revealed that cell viability and function were minimally affected by SPM labeling. SPM-labeled rat CDCs were injected intramyocardially, with and without a superimposed magnet. With magnetic targeting, cells were visibly attracted toward the magnet and accumulated around the ischemic zone. In contrast, the majority of nontargeted cells washed out immediately after injection. Fluorescence imaging revealed more retention of transplanted cells in the heart, and less migration into other organs, in the magnetically targeted group. Quantitative PCR confirmed that magnetic targeting enhanced cell retention (at 24 hours) and engraftment (at 3 weeks) in the recipient hearts by approximately 3-fold compared to nontargeted cells. Morphometric analysis revealed maximal attenuation of left ventricular remodeling, and echocardiography showed the greatest functional improvement, in the magnetic targeting group. Histologically, more engrafted cells were evident with magnetic targeting, but there was no incremental inflammation.

CONCLUSIONS

Magnetic targeting enhances cell retention, engraftment and functional benefit. This novel method to improve cell therapy outcomes offers the potential for rapid translation into clinical applications.

Genetic modification of mesenchymal stem cells overexpressing CCR1 increases cell viability, migration, engraftment, and capillary density in the injured myocardium

RATIONALE

Although mesenchymal stem cell (MSC) transplantation has been shown to promote cardiac repair in acute myocardial injury in vivo, its overall restorative capacity appears to be restricted mainly because of poor cell viability and low engraftment in the ischemic myocardium. Specific chemokines are upregulated in the infarcted myocardium. However the expression levels of the corresponding chemokine receptors (eg, CCR1, CXCR2) in MSCs are very low. We hypothesized that this discordance may account for the poor MSC engraftment and survival.

OBJECTIVE

To determine whether overexpression of CCR1 or CXCR2 chemokine receptors in MSCs augments their cell survival, migration and engraftment after injection in the infarcted myocardium.

METHODS AND RESULTS

Overexpression of CCR1, but not CXCR2, dramatically increased chemokine-induced murine MSC migration and protected MSC from apoptosis in vitro. Moreover, when MSCs were injected intramyocardially one hour after coronary artery ligation, CCR1-MSCs accumulated in the infarcted myocardium at significantly higher levels than control-MSCs or CXCR2-MSCs 3 days postmyocardial infarction (MI). CCR1-MSC-injected hearts exhibited a significant reduction in infarct size, reduced cardiomyocytes apoptosis and increased capillary density in injured myocardium 3 days after MI. Furthermore, intramyocardial injection of CCR1-MSCs prevented cardiac remodeling and restored cardiac function 4 weeks after MI.

CONCLUSIONS

Our results demonstrate the in vitro and in vivo salutary effects of genetic modification of stem cells. Specifically, overexpression of chemokine receptor enhances the migration, survival and engraftment of MSCs, and may provide a new therapeutic strategy for the injured myocardium.

More insight into mesenchymal stem cells and their effects inside the body

IMPORTANCE OF THE FIELD

The pan-tissue existence and multipotency of differentiation make mesenchymal stem cells (MSCs) an attractive source of cells as tissue repair cells, seeds of engineered tissue, vehicles for gene therapy or in combination to promote tissue regeneration in wound healing and disease recovery.

AREAS COVERED IN THIS REVIEW

This review focuses on recent understanding on MSC's basic biological characteristics and the mechanisms underlying the therapeutic effects of MSCs in vivo.

WHAT THE READER WILL GAIN

The gene expression profiles for mRNA, protein, microRNA and cell surface marker of MSCs are summarized. Special attention is given to miRNA expression and its relationship with the characteristics of MSCs. The mechanisms of therapeutic effects of MSCs are attributed to their ability to migrate along chemokine gradients, differentiate into tissue-specific cells, enhance angiogenesis of wound tissue and regulate immune response. As examples, a detailed description is given on the regeneration of functional sweat glands on burned skin as well as neural cells in middle cerebral artery occlusion (MCAO) animals upon MSC transplantation.

TAKE HOME MESSAGE

Based on current data, although limited, the mesenchymal-epithelial transition is proposed to be one of the important ways for MSCs to participate tissue repair.

Human adult vena saphena contains perivascular progenitor cells endowed with clonogenic and proangiogenic potential

BACKGROUND

Clinical trials in ischemic patients showed the safety and benefit of autologous bone marrow progenitor cell transplantation. Non-bone marrow progenitor cells with proangiogenic capacities have been described, yet they remain clinically unexploited owing to their scarcity, difficulty of access, and low ex vivo expansibility. We investigated the presence, antigenic profile, expansion capacity, and proangiogenic potential of progenitor cells from the saphenous vein of patients undergoing coronary artery bypass surgery.

METHODS AND RESULTS

CD34-positive cells, negative for the endothelial marker von Willebrand factor, were localized around adventitial vasa vasorum. After dissection of the vein from surrounding tissues and enzymatic digestion, CD34-positive/CD31-negative cells were isolated by selective culture, immunomagnetic beads, or fluorescence-assisted cell sorting. In the presence of serum, CD34-positive/CD31-negative cells gave rise to a highly proliferative population that expressed pericyte/mesenchymal antigens together with the stem cell marker Sox2 and showed clonogenic and multilineage differentiation capacities. We called this population "saphenous vein-derived progenitor cells" (SVPs). In culture, SVPs integrated into networks formed by endothelial cells and supported angiogenesis through paracrine mechanisms. Reciprocally, endothelial cell-released factors facilitated SVP migration. These interactive responses were inhibited by Tie-2 or platelet-derived growth factor-BB blockade. Intramuscular injection of SVPs in ischemic limbs of immunodeficient mice improved neovascularization and blood flow recovery. At 14 days after transplantation, proliferating SVPs were still detectable in the recipient muscles, where they established N-cadherin-mediated physical contact with the capillary endothelium.

CONCLUSIONS

SVPs generated from human vein CD34-positive/CD31-negative progenitor cells might represent a new therapeutic tool for angiogenic therapy in ischemic patients.

Hsp20-engineered mesenchymal stem cells are resistant to oxidative stress via enhanced activation of Akt and increased secretion of growth factors

Although heat-shock preconditioning has been shown to promote cell survival under oxidative stress, the nature of heat-shock response from different cells is variable and complex. Therefore, it remains unclear whether mesenchymal stem cells (MSCs) modified with a single heat-shock protein (Hsp) gene are effective in the repair of a damaged heart. In this study, we genetically engineered rat MSCs with Hsp20 gene (Hsp20-MSCs) and examined cell survival, revascularization, and functional improvement in rat left anterior descending ligation (LAD) model via intracardial injection. We observed that overexpression of Hsp20 protected MSCs against cell death triggered by oxidative stress in vitro. The survival of Hsp20-MSCs was increased by approximately twofold by day 4 after transplantation into the infarcted heart, compared with that of vector-MSCs. Furthermore, Hsp20-MSCs improved cardiac function of infarcted myocardium as compared with vector-MSCs, accompanied by reduction of fibrosis and increase in the vascular density. The mechanisms contributing to the beneficial effects of Hsp20 were associated with enhanced Akt activation and increased secretion of growth factors (VEGF, FGF-2, and IGF-1). The paracrine action of Hsp20-MSCs was further validated in vitro by cocultured adult rat cardiomyocytes with a stress-conditioned medium from Hsp20-MSCs. Taken together, these data support the premise that genetic modification of MSCs before transplantation could be salutary for treating myocardial infarction.

Secreted proteome of the murine multipotent hematopoietic progenitor cell line DKmix

Administration of the multipotent hematopoietic progenitor cell (HPC) line DKmix improved cardiac function after myocardial infarction and accelerated dermal wound healing due to paracrine mechanisms. The aim of this study was to analyse the secreted proteins of DKmix cells in order to identify the responsible paracrine factors and assess their relevance to the wide spectrum of therapeutic effects. A mass spectrometry (MS)-based approach was used to identify secreted proteins of DKmix cells. Serum free culture supernatants of DKmix-conditioned medium were collected and the proteins present were separated, digested by trypsin and the resulting peptides were then analyzed by matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) MS. Overall 95 different proteins were identified. Among them, secretory proteins galectin-3 and gelsolin were identified. These proteins are known to stimulate cell migration and influence wound healing and cardiac remodelling. The remaining proteins originate from intracellular compartments like cytoplasm (69%), nucleus (12%), mitochondria (4%), and cytoplasmic membrane (3%) indicating permeable or leaky DKmix cells in the conditioned medium. Additionally, a sandwich immunoassay was used to detect and quantify cytokines and chemokines. Interleukin-6 (IL-6), interleukin-13 (IL-13), monocyte-chemoattractant protein-1 (MCP-1), monocyte-chemoattractant protein-3 (MCP-3), monocyte-chemoattractant protein-1alpha (MIP-1alpha) and monocyte-chemoattractant protein-1beta (MIP-1beta) were detected in low concentrations. This study identified a subset of proteins present in the DKmix-conditioned medium that act as paracrine modulators of tissue repair. Moreover, it suggests that DKmix-derived conditioned medium might have therapeutic potency by promoting tissue regeneration.

Culture-modified bone marrow cells attenuate cardiac and renal injury in a chronic kidney disease rat model via a novel antifibrotic mechanism

BACKGROUND

Most forms of chronic kidney disease are characterized by progressive renal and cardiac fibrosis leading to dysfunction. Preliminary evidence suggests that various bone marrow-derived cell populations have antifibrotic effects. In exploring the therapeutic potential of bone marrow derived cells in chronic cardio-renal disease, we examined the anti-fibrotic effects of bone marrow-derived culture modified cells (CMCs) and stromal cells (SCs).

METHODOLOGY/PRINCIPAL FINDINGS

In vitro, CMC-conditioned medium, but not SC-conditioned medium, inhibited fibroblast collagen production and cell signalling in response to transforming growth factor-beta. The antifibrotic effects of CMCs and SCs were then evaluated in the 5/6 nephrectomy model of chronic cardio-renal disease. While intravascular infusion of 10(6) SCs had no effect, 10(6) CMCs reduced renal fibrosis compared to saline in the glomeruli (glomerulosclerosis index: 0.8+/-0.1 v 1.9+/-0.2 arbitrary units) and the tubulointersitium (% area type IV collagen: 1.2+/-0.3 v 8.4+/-2.0, p<0.05 for both). Similarly, 10(6) CMCs reduced cardiac fibrosis compared to saline (% area stained with picrosirius red: 3.2+/-0.3 v 5.1+/-0.4, p<0.05), whereas 10(6) SCs had no effect. Structural changes induced by CMC therapy were accompanied by improved function, as reflected by reductions in plasma creatinine (58+/-3 v 81+/-11 micromol/L), urinary protein excretion (9x/divided by 1 v 64x/divided by 1 mg/day), and diastolic cardiac stiffness (left ventricular end-diastolic pressure-volume relationship: 0.030+/-0.003 v 0.058+/-0.011 mm Hg/microL, p<0.05 for all). Despite substantial improvements in structure and function, only rare CMCs were present in the kidney and heart, whereas abundant CMCs were detected in the liver and spleen.

CONCLUSIONS/SIGNIFICANCE

Together, these findings provide the first evidence suggesting that CMCs, but not SCs, exert a protective action in cardio-renal disease and that these effects may be mediated by the secretion of diffusible anti-fibrotic factor(s).

In vitro functional comparison of therapeutically relevant human vasculogenic progenitor cells used for cardiac cell therapy

OBJECTIVE

In cardiac cell therapy almost every cell type tested experimentally has yielded some benefit. However, there is a lack of studies directly comparing the function of various stem/progenitor cell populations. This study describes the expansion of peripheral blood CD133(+) cells and compares their functional properties with those of other commonly used human progenitor cell populations.

METHODS

CD133(+) cells were generated from the CD133(-) fraction of peripheral blood, either serially (pooled-derived) or after 14 days of culture (derived). Their phenotypic, migratory, and vasculogenic properties were compared with those of 4 commonly used progenitor cell populations in vitro.

RESULTS

Serial expansion resulted in an 11-fold increase in the number of CD133(+) cells. The proportion of derived CD133(+) cells collected between 0 and 8 days also expressing CD34 and vascular endothelial growth factor receptor 2 was similar (approximately 60%, P = .41). Adherent, 4-day cultured endothelial progenitor cells demonstrated enhanced migration compared with each of the other 5 cell populations (all P < or = .002). The migration of derived CD133(+) progenitors was enhanced by coculture with CD133(-) cells or their supernatant (P < .05). In vitro vasculogenesis assays revealed that derived and pooled-derived CD133(+) cells had superior vasculogenic potential compared with other progenitor populations (P < or = .03).

CONCLUSIONS

A novel source of expandable CD133(+) cells can be generated from the CD133(-) fraction of peripheral blood. The CD133 phenotypic marker translates into the cell being vasculogenically more potent in vitro, which could be beneficial to inducing vasculogenesis in the ischemic heart. Furthermore, intercellular interactions appear important for improving the therapeutic efficacy of cell transplantation.

Adriamycin nephropathy: a failure of endothelial progenitor cell-induced repair

Adriamycin-associated nephropathy (AAN) remains poorly understood. We hypothesized that adriamycin affects endothelial progenitor cells (EPCs), leading to impaired regeneration. We analyzed renal hematopoietic stem cells (HSCs) and EPCs in mice with AAN and examined the potential contribution of adoptive transfer of intact EPCs to the repair processes. FACS analyses revealed that populations of HSCs and EPCs were scarcely represented in control kidneys and did not change numerically in kidneys obtained from mice with AAN. The observed defect in engraftment was attributable to the decreased viability and increased senescence of EPCs. Adoptive transfer of intact EPCs improved proteinuria and renal function, with a threefold decrease in mortality. Infusion of EPCs to adriamycin-treated mice reduced plasma levels of interleukin-1alpha and -beta and granulocyte-colony stimulating factor as well as increased the level of vascular endothelial growth factor with concomitant improvement of vascular density and reduction of apoptosis. An additional mechanism of tissue repair is proposed based on tunneling nanotube formation between EPCs and endothelial cells exposed to adriamycin, leading to the multiple rounds of exchange between EPCs and mature cells. In conclusion, AAN is associated with development of EPC incompetence; adoptive transfer of intact EPCs blunts morphological and functional manifestations of AAN; and the proposed mechanisms of repair by EPCs include direct incorporation into blood vessels, paracrine signaling, and tunneling nanotube renewal of mitochondrial pool in endothelial cells.

Regenerative medicine in the treatment of peripheral arterial disease

The last decade has witnessed a dramatic increase in the mechanistic understanding of angiogenesis and arteriogenesis, the two processes by which the body responds to obstruction of large conduit arteries. This knowledge has been translated into novel therapeutic approaches to the treatment of peripheral arterial disease, a condition characterized by progressive narrowing of lower extremity arteries and heretofore solely amenable to surgical revascularization. Clinical trials of molecular, genetic, and cell-based treatments for peripheral artery obstruction have generally provided encouraging results.

Double-blind and placebo-controlled study of the effectiveness and safety of extracorporeal cardiac shock wave therapy for severe angina pectoris

BACKGROUND

Low-energy shock wave (SW) therapy has improved myocardial ischemia in both a porcine model and in patients with severe angina pectoris.

METHODS AND RESULTS

To further confirm the effectiveness and safety of SW therapy, 8 patients with severe angina pectoris were treated with SW therapy in a double-blind, placebo-controlled and cross-over manner. SW therapy, but not placebo, significantly improved chest pain symptoms and cardiac function without any complications or adverse effects.

CONCLUSIONS

Extracorporeal cardiac SW therapy is an effective, safe and non-invasive therapeutic option for severe angina pectoris.

Relative roles of direct regeneration versus paracrine effects of human cardiosphere-derived cells transplanted into infarcted mice

RATIONALE

Multiple biological mechanisms contribute to the efficacy of cardiac cell therapy. Most prominent among these are direct heart muscle and blood vessel regeneration from transplanted cells, as opposed to paracrine enhancement of tissue preservation and/or recruitment of endogenous repair.

OBJECTIVE

Human cardiac progenitor cells, cultured as cardiospheres (CSps) or as CSp-derived cells (CDCs), have been shown to be capable of direct cardiac regeneration in vivo. Here we characterized paracrine effects in CDC transplantation and investigated their relative importance versus direct differentiation of surviving transplanted cells.

METHODS AND RESULTS

In vitro, many growth factors were found in media conditioned by human adult CSps and CDCs; CDC-conditioned media exerted antiapoptotic effects on neonatal rat ventricular myocytes, and proangiogenic effects on human umbilical vein endothelial cells. In vivo, human CDCs secreted vascular endothelial growth factor, hepatocyte growth factor, and insulin-like growth factor 1 when transplanted into the same SCID mouse model of acute myocardial infarction where they were previously shown to improve function and to produce tissue regeneration. Injection of CDCs in the peri-infarct zone increased the expression of Akt, decreased apoptotic rate and caspase 3 level, and increased capillary density, indicating overall higher tissue resilience. Based on the number of human-specific cells relative to overall increases in capillary density and myocardial viability, direct differentiation quantitatively accounted for 20% to 50% of the observed effects.

CONCLUSIONS

Together with their spontaneous commitment to cardiac and angiogenic differentiation, transplanted CDCs serve as "role models," recruiting endogenous regeneration and improving tissue resistance to ischemic stress. The contribution of the role model effect rivals or exceeds that of direct regeneration.

Improving regenerating potential of the heart after myocardial infarction: factor-based approach

The emerging evidence that the heart has the potential to regenerate, albeit not ideally, has stimulated considerable interest in the field of cardiac regenerative medicine. Several lines of research demonstrated that factor-based therapy is feasible and effective, whether it is used independently or as an adjunct to cell therapy. The ultimate goal of the factor-based approach is to improve the regenerating potential of the heart as a means to treat patients with cardiovascular disease. This article reviews recent approaches involving factor-based therapy for cardiac repair and regeneration including some of the advantages of this type of therapy as well as some of the hurdles that must be overcome before this therapeutic approach becomes a standard part of clinical medicine.

Cardiac progenitor cell cycling stimulated by pim-1 kinase

RATIONALE

Cardioprotective effects of Pim-1 kinase have been previously reported but the underlying mechanistic basis may involve a combination of cellular and molecular mechanisms that remain unresolved. The elucidation of the mechanistic basis for Pim-1 mediated cardioprotection provides important insights for designing therapeutic interventional strategies to treat heart disease.

OBJECTIVE

Effects of cardiac-specific Pim-1 kinase expression on the cardiac progenitor cell (CPC) population were examined to determine whether Pim-1 mediates beneficial effects through augmenting CPC activity.

METHODS AND RESULTS

Transgenic mice created with cardiac-specific Pim-1 overexpression (Pim-wt) exhibit enhanced Pim-1 expression in both cardiomyocytes and CPCs, both of which show increased proliferative activity assessed using 5-bromodeoxyuridine (BrdU), Ki-67, and c-Myc relative to nontransgenic controls. However, the total number of CPCs was not increased in the Pim-wt hearts during normal postnatal growth or after infarction challenge. These results suggest that Pim-1 overexpression leads to asymmetric division resulting in maintenance of the CPC population. Localization and quantitation of cell fate determinants Numb and alpha-adaptin by confocal microscopy were used to assess frequency of asymmetric division in the CPC population. Polarization of Numb in mitotic phospho-histone positive cells demonstrates asymmetric division in 65% of the CPC population in hearts of Pim-wt mice versus 26% in nontransgenic hearts after infarction challenge. Similarly, Pim-wt hearts had fewer cells with uniform alpha-adaptin staining indicative of symmetrically dividing CPCs, with 36% of the CPCs versus 73% in nontransgenic sections.

CONCLUSIONS

These findings define a mechanistic basis for enhanced myocardial regeneration in transgenic mice overexpressing Pim-1 kinase.