Transplantation of Mesenchymal Stem Cells Improves Atrioventricular Conduction in a Rat Model of Complete Atrioventricular Block

TBX3 transfection and nodal signal pathway inhibition promote differentiation of adipose mesenchymal stem cell to cardiac pacemaker-like cells

BACKGROUND

Mesenchymal stem cells (MSCs) are known as one of the best candidate cells to produce cardiac pacemaker-like cells (CPLCs). Upregulation of TBX3 transcription factor and inhibition of the nodal signal pathway have a significant role in the formation of cardiac pacemaker cells such as sinoatrial and atrioventricular nodes, which initiate the heartbeat and control the rhythm of heart contractions. This study aimed to confirm the effects of transfection of TBX3 transcription factor and inhibition of the nodal signal pathway on differentiating adipose-derived MSCs (AD-MSCs) to CPLCs. AD-MSCs were characterized using flow cytometry and three-lineage differentiation staining.

METHODS

The transfection of TBX3 plasmid was carried out using lipofectamine, and inhibition of the nodal signal pathway was done using the small-molecule SB431542. The morphology of the cells was observed using a light microscope. Pacemaker-specific markers, including TBX3, Cx30, HCN4, HCN1, HCN3, and KCNN4, were evaluated using the qRT-PCR method. For protein level, TBX3 and Cx30 were evaluated using ELISA and immunofluorescence staining. The electrophysiology of cells was evaluated using a patch clamp.

RESULTS

The TBX3 expression in the TBX3, SM, and TBX + SM groups significantly higher (p < 0.05) compared to the control group and cardiomyocytes. The expression of Cx40 and Cx43 genes were lower in TBX3, SM, TBX + SM groups. In contrast, Cx30 gene showed higher expression in TBX3 group. The expression HCN1, HCN3, and HCN4 genes are higher in TBX3 group.

CONCLUSION

The transfection of TBX3 and inhibition of the nodal signal pathway by small-molecule SB431542 enhanced differentiation of AD-MSCs to CPLCs.

Influence of Diameter and Cyclic Mechanical Stimulation on the Beating Frequency of Myocardial Cell-Laden Fibers

Atrioventricular block (AVB) is a severe disease for pediatric patients. The repetitive operations needed in the case of the pacemaker implantation to maintain the electrical signal at the atrioventricular node (AVN) affect the patient's life quality. In this study, we present a method of biofabrication of multi-cell-laden cylindrical fibrin-based fibers that can restore the electrical signal at the AVN. We used human umbilical vein smooth muscle cells (HUVSMCs), human umbilical vein endothelial cells (HUVECs) and induced pluripotent stem cell cardiomyocytes (iPSC-CMs) cultivated either statically or dynamically to mimic the native AVN. We investigated the influence of cell composition, construct diameter and cyclic stretch on the function of the fibrin hydrogels in vitro. Immunohistochemistry analyses showed the maturity of the iPSC-CMs in the constructs through the expression of sarcomeric alpha actinin (SAA) and electrical coupling through Connexin 43 (Cx43) signal. Simultaneously, the beating frequency of the fibrin hydrogels was higher and easy to maintain whereas the concentration of iPSC-CMs was higher compared with the other types of cylindrical constructs. In total, our study highlights that the combination of fibrin with the cell mixture and geometry is offering a feasible biofabrication method for tissue engineering approaches for the treatment of AVB.

General anesthesia and electrocardiographic parameters in in vivo experiments involving rats

In in vivo cardiovascular or toxicological studies involving rat models, changes in selected electrocardiographic (ECG) parameters are monitored after various interventions to assess the origin and development of heart rhythm disorders. Each ECG parameter has diagnostic significance; as such, commonly evaluated ECG parameters, including heart rate, PR interval, P wave duration, P wave amplitude, QRS complex, QT and QTc interval duration, R wave and T wave amplitude, of rats under various types of general anesthesia were the focus of this study. Studies that performed in vivo cardiovascular or toxicological experiments in rats were retrieved from a search of the Web of Science database for articles published mainly between 2000 and 2021. In total, the search retrieved 123 articles. ECG parameters that were reported as baseline or control values were summarized and averages with ranges were calculated. It is important to be cautious when interpreting results and, in discussions addressing the mechanisms underlying a given type of arrhythmia, acknowledge that initial ECG parameters may already be affected to some extent by the general anesthesia as well as by sex and the time of day the experiments were performed.

A rat model of complete atrioventricular block recapitulates clinical indices of bradycardia and provides a platform to test disease-modifying therapies

Complete atrioventricular block (CAVB) is a life-threatening arrhythmia. A small animal model of chronic CAVB that properly reflects clinical indices of bradycardia would accelerate the understanding of disease progression and pathophysiology, and the development of therapeutic strategies. We sought to develop a surgical model of CAVB in adult rats, which could recapitulate structural remodeling and arrhythmogenicity expected in chronic CAVB. Upon right thoracotomy, we delivered electrosurgical energy subepicardially via a thin needle into the atrioventricular node (AVN) region of adult rats to create complete AV block. The chronic CAVB animals developed dilated and hypertrophied ventricles with preserved systolic functions due to compensatory hemodynamic remodeling. Ventricular tachyarrhythmias, which are difficult to induce in the healthy rodent heart, could be induced upon programmed electrical stimulation in chronic CAVB rats and worsened when combined with β-adrenergic stimulation. Focal somatic gene transfer of TBX18 to the left ventricular apex in the CAVB rats resulted in ectopic ventricular beats within days, achieving a de novo ventricular rate faster than the slow atrioventricular (AV) junctional escape rhythm observed in control CAVB animals. The model offers new opportunities to test therapeutic approaches to treat chronic and severe CAVB which have previously only been testable in large animal models.

Implantation of engineered conduction tissue in the rat heart

Engineered conduction tissues (ECTs) are cardiac conduction tissues fabricated in vitro to allow for more precisely targeted in vivo transplantation therapy. The transplantation of ECTs may be ideal for the treatment of atrioventricular conduction block and could have a significant impact on the future application of biological pacemakers. However, there is little published information regarding the conduction function of ECTs in vivo. In the present study, ECTs were constructed by seeding cardiac progenitor cells (CPCs) into a collagen sponge and were then transplanted into animal hearts to determine whether they could act as an atrioventricular conduction pathway. The results demonstrated that the transplanted ECTs were adequately vascularized at the early stage of transplantation and could survive in the atrioventricular junction area of rats. A large number of myocardial tissue (≥29% of the new muscle fiber tissue formation area in the implanted ECTs) were observed by Masson's trichrome staining at 60 days post-transplantation. Positive staining for connexin-40, connexin-43, HCN2 and cTnT was exhibited during the period of 20 to 90 days post-transplantation. This result suggested that the transplanted ECTs formed gap junctions with the allogeneic myocardium and developed into cardiac conduction tissues with certain myocardial components. Electrocardiography (ECG) confirmed that there was a clear pre-excitation syndrome in the rats transplanted with ECTs during the period of 20 to 90 days post-transplantation. The recovery rate in the rats implanted with ECTs was 61.54% within 1 h following atrioventricular block, and the heart rhythm following recovery was close to normal. By contrast, the recovery rate was only 4.17% in the rats implanted with blank collagen sponges (BCSs), and none of the sham rats exhibited atrioventricular block recovery. In conclusion, ECTs can survive and mechanically integrate with the allogeneic myocardium following transplantation into rat hearts. An atrioventricular accessory pathway similar to Kent bundles could be established between the atria and ventricles of rats following implantation. It is suggested that ECTs may be a potential substitution therapy for atrioventricular conduction block.

Biological therapies targeting arrhythmias: are cells and genes the answer?

INTRODUCTION

Arrhythmias can cause symptoms ranging from simple dizziness to life-threatening circulatory collapse. Current management includes medical therapy and procedures such as catheter ablation or device implantation. However, these strategies still pose a risk of serious side effects, and some patients remain symptomatic. Advancement in our understanding of how arrhythmias develop on the cellular level has made more targeted approaches possible. In addition, contemporary studies have found that several genes are involved in the pathogenesis of arrhythmias.

AREAS COVERED

In the present review, the authors explore the cellular and genetic mechanisms leading to arrhythmias as well as the progress that has been made in using both gene and cell therapy to treat tachy- and bradyarrhythmias. They also consider why gene and cell therapy has resulted into a few clinical trials with promising results, however still not applicable in routine clinical practice.

EXPERT OPINION

The question currently is whether such biological therapies could replace current established approaches. The contemporary evidence suggests that despite recent advances in this field, it will need more work in experimental models before this is applied into clinical practice. Gene and cell studies targeting conduction and repolarization are promising, but still not ready for use in the clinical setting.

Restoring heart function and electrical integrity: closing the circuit

Cardiovascular diseases are the main cause of death in the world and are often associated with the occurrence of arrhythmias due to disruption of myocardial electrical integrity. Pathologies involving dysfunction of the specialized cardiac excitatory/conductive tissue are also common and constitute an added source of morbidity and mortality since current standard therapies withstand a great number of limitations. As electrical integrity is essential for a well-functioning heart, innovative strategies have been bioengineered to improve heart conduction and/or promote myocardial repair, based on: (1) gene and/or cell delivery; or (2) conductive biomaterials as tools for cardiac tissue engineering. Herein we aim to review the state-of-art in the area, while briefly describing the biological principles underlying the heart electrical/conduction system and how this system can be disrupted in heart disease. Suggestions regarding targets for future studies are also presented.

Therapeutic potential of mesenchymal stem cells for pulmonary complications associated with preterm birth

Preterm infants frequently suffer from pulmonary complications resulting in significant morbidity and mortality. Physiological and structural lung immaturity impairs perinatal lung transition to air breathing resulting in respiratory distress. Mechanical ventilation and oxygen supplementation ensure sufficient oxygen supply but enhance inflammatory processes which might lead to the establishment of a chronic lung disease called bronchopulmonary dysplasia (BPD). Current therapeutic options to prevent or treat BPD are limited and have salient side effects, highlighting the need for new therapeutic approaches. Mesenchymal stem cells (MSCs) have demonstrated therapeutic potential in animal models of BPD. This review focuses on MSC-based therapeutic approaches to treat pulmonary complications and critically compares results obtained in BPD models. Thereby bottlenecks in the translational systems are identified that are preventing progress in combating BPD. Notably, current animal models closely resemble the so-called "old" BPD with profound inflammation and injury, whereas clinical improvements shifted disease pathology towards a "new" BPD in which arrest of lung maturation predominates. Future studies need to evaluate the utility of MSC-based therapies in animal models resembling the "new" BPD though promising in vitro evidence suggests that MSCs do possess the potential to stimulate lung maturation. Furthermore, we address the mode-of-action of MSC-based therapies with regard to lung development and inflammation/fibrosis. Their therapeutic efficacy is mainly attributed to an enhancement of regeneration and immunomodulation due to paracrine effects. In addition, we discuss current improvement strategies by genetic modifications or precondition of MSCs to enhance their therapeutic efficacy which could also prove beneficial for BPD therapies.

Intractable diseases treated with intra-bone marrow-bone marrow transplantation

Bone marrow transplantation (BMT) is used to treat hematological disorders, autoimmune diseases (ADs) and lymphoid cancers. Intra bone marrow-BMT (IBM-BMT) has been proven to be a powerful strategy for allogeneic BMT due to the rapid hematopoietic recovery and the complete restoration of T cell functions. IBM-BMT not only replaces hematopoietic stem cells (HSCs) but also mesenchymal stromal cells (MSCs). MSCs are multi-potent stem cells that can be isolated from bone marrow (BM), umbilical cord blood (UCB), and adipose tissue. MSCs play an important role in the support of hematopoiesis, and modify and influence the innate and adaptive immune systems. MSCs also differentiate into mesodermal, endodermal and ectodermal lineage cells to repair tissues. This review aims to summarize the functions of BM-derived-MSCs, and the treatment of intractable diseases such as rheumatoid arthritis (RA) and malignant tumors with IBM-BMT.

Gene Therapy for Restoring Heart Rhythm

Efforts to use gene therapy to create a biological pacemaker as an adjunct or replacement of electronic pacemakers have been ongoing for about 15 years. For the past decade, most of these efforts have focused on the hyperpolarization-activated cyclic nucleotide gated-(HCN) gene family of channels alone or in combination with other genes. The HCN gene family is the molecular correlate of the cardiac pacemaker current, If. It is a suitable basis for a biological pacemaker because it generates a depolarizing inward current primarily during diastole and is directly regulated by cyclic adenosine monophosphate (cAMP), thereby incorporating autonomic responsiveness. However, biological pacemakers based either on native HCN channels or on mutated HCN channels designed to optimize biophysical characteristics have failed to attain the desired basal and maximal physiological heart rates in large animals. More recent work has explored dual gene therapy approaches, combining an HCN variant with another gene to reduce outward current, increase an additional inward current, or enhance cAMP synthesis. Several of these dual gene therapy approaches have demonstrated appropriate basal and maximal heart rates with little or no reliance on a backup electronic pacemaker during the period of study. Future research, besides examining the efficacy of other gene combinations, will need to consider the additional issues of safety and persistence of the viral vectors often used to deliver these genes to a specific cardiac region.

Optimization of the cardiovascular therapeutic properties of mesenchymal stromal/stem cells-taking the next step

Despite current treatment options, cardiac failure is associated with significant morbidity and mortality highlighting a compelling clinical need for novel therapeutic approaches. Based on promising pre-clinical data, stem cell therapy has been suggested as a possible therapeutic strategy. Of the candidate cell types evaluated, mesenchymal stromal/stem cells (MSCs) have been widely evaluated due to their ease of isolation and ex vivo expansion, potential allogeneic utility and capacity to promote neo-angiogenesis and endogenous cardiac repair. However, the clinical application of MSCs for mainstream cardiovascular use is currently hindered by several important limitations, including suboptimal retention and engraftment and restricted capacity for bona fide cardiomyocyte regeneration. Consequently, this has prompted intense efforts to advance the therapeutic properties of MSCs for cardiovascular disease. In this review, we consider the scope of benefit from traditional plastic adherence-isolated MSCs and the lessons learned from their conventional use in preclinical and clinical studies. Focus is then given to the evolving strategies aimed at optimizing MSC therapy, including discussion of cell-targeted techniques that encompass the preparation, pre-conditioning and manipulation of these cells ex vivo, methods to improve their delivery to the heart and innovative substrate-directed strategies to support their interaction with the host myocardium.

Platelet-mediated mesenchymal stem cells homing to the lung reduces monocrotaline-induced rat pulmonary hypertension

Bone marrow mesenchymal stem cell (BM-MSC) transplantation has been suggested to be a promising method for the treatment of pulmonary arterial hypertension (PAH), a fatal disease currently without effective preventive/therapeutic strategies. However, the detailed mechanisms underlying BM-MSC therapy are largely unknown. We designed the present study to test the hypothesis that circulating platelets facilitate BM-MSC homing to the lung vasculature in a rat model of PAH induced by monocrotalin (MCT). A single subcutaneous administration of MCT induced a marked rise in right ventricular systolic pressure (RVSP) and the weight ratio of right to left ventricle plus septum (RV/LV+S) 3 weeks after injection. The injection of MSCs via tail vein 3 days after MCT significantly reduced the increase of RVSP and RV/LV+S. The fluorescence-labeled MSCs injected into the PAH rat circulation were found mostly distributed in the lungs, particularly on the pulmonary vascular wall, whereas cell homing was abolished by an anti-P-selectin antibody and the GPIIb/IIIa inhibitor tirofiban. Furthermore, using an in vitro flow chamber, we demonstrated that MSC adhesion to the major extracellular matrix collagen was facilitated by platelets and their P-selectin and GPIIb/IIIa. Therefore, the current study suggested that platelet-mediated MSC homing prevented the aggravation of MCT-induced rat PAH, via P-selectin and GPIIb/IIIa-mediated mechanisms.

Mesenchymal stem cells improve cardiac conduction by upregulation of connexin 43 through paracrine signaling

Mesenchymal stem cells (MSCs) were shown to improve cell survival and alleviate cardiac arrhythmias when transplanted into cardiac tissue; however, little is known about the mechanism by which MSCs modify the electrophysiological properties of cardiac tissue. We aimed to distinguish the influence of cell-cell coupling between myocytes and MSCs from that of MSC-derived paracrine factors on the spontaneous activity and conduction velocity (θ) of multicellular cardiomyocyte preparations. HL-1 cells were plated on microelectrode arrays and their spontaneous activity and θ was determined from field potential recordings. In heterocellular cultures of MSCs and HL-1 cells the beating frequency was attenuated (t(0h): 2.26 ± 0.18 Hz; t(4h): 1.98 ± 0.26 Hz; P < 0.01) concomitant to the intercellular coupling between MSCs and cardiomyocytes. In HL-1 monolayers supplemented with MSC conditioned media (ConM) or tyrode (ConT) θ significantly increased in a time-dependent manner (ConT: t(0h): 2.4 cm/s ± 0.2; t(4h): 3.1 ± 0.4 cm/s), whereas the beating frequency remained constant. Connexin (Cx)43 mRNA and protein expression levels also increased after ConM or ConT treatment over the same time period. Enhanced low-density lipoprotein receptor-related protein 6 (LRP6) phosphorylation after ConT treatment implicates the Wnt signaling pathway. Suppression of Wnt secretion from MSCs (IWP-2; 5 μmol/l) reduced the efficacy of ConT to induce phospho-LRP6 and to increase θ. Inhibition of β-catenin (cardamonin; 10 μmol/l) or GSK3-α/β (LiCl; 5 mmol/l) also suppressed changes in θ, further supporting the hypothesis that MSC-mediated Cx43 upregulation occurs in part through secreted Wnt ligands and activation of the canonical Wnt signaling pathway.

Cell and gene therapy for arrhythmias: Repair of cardiac conduction damage

Action potentials generated in the sinoatrial node (SAN) dominate the rhythm and rate of a healthy human heart. Subsequently, these action potentials propagate to the whole heart via its conduction system. Abnormalities of impulse generation and/or propagation in a heart can cause arrhythmias. For example, SAN dysfunction or conduction block of the atrioventricular node can lead to serious bradycardia which is currently treated with an implanted electronic pacemaker. On the other hand, conduction damage may cause reentrant tachyarrhythmias which are primarily treated pharmacologically or by medical device-based therapies, including defibrillation and tissue ablation. However, drug therapies sometimes may not be effective or are associated with serious side effects. Device-based therapies for cardiac arrhythmias, even with well developed technology, still face inadequacies, limitations, hardware complications, and other challenges. Therefore, scientists are actively seeking other alternatives for antiarrhythmic therapy. In particular, cells and genes used for repairing cardiac conduction damage/defect have been investigated in various studies both in vitro and in vivo. Despite the complexities of the excitation and conduction systems of the heart, cell and gene-based strategies provide novel alternatives for treatment or cure of cardiac arrhythmias. This review summarizes some highlights of recent research progress in this field.

Systemic administration of a novel human umbilical cord mesenchymal stem cells population accelerates the resolution of acute liver injury

BACKGROUND

Hepatocytes and stem cells transplantation may be an alternative to liver transplantation in acute or chronic liver disease. We aimed to evaluate the therapeutic potential of mesenchymal stem cells from human umbilical cord (UCMSCs), a readily available source of mesenchymal stem cells, in the CCl4-induced acute liver injury model.

METHODS

Mesenchymal stem cells profile was analyzed by flow cytometry. In order to evaluate the capability of our UCMSCs to differentiate in hepatocytes, cells were seeded on three different supports, untreated plastic support, MatrigelTM and human liver acellular matrix. Cells were analyzed by immunocitochemistry for alpha-fetoprotein and albumin expression, qPCR for hepatocyte markers gene expression, Periodic Acid-Schiff staining for glycogen storage, ELISA for albumin detection and colorimetric assay for urea secretion.To assess the effects of undifferentiated UCMSCs in hepatic regeneration after an acute liver injury, we transplanted them via tail vein in mice injected intraperitoneally with a single dose of CCl4. Livers were analyzed by histological evaluation for damage quantification, immunostaining for Kupffer and stellate cells/liver myofibroblasts activation and for UCMSCs homing. Pro- and anti-inflammatory cytokines gene expression was evaluated by qPCR analysis and antioxidant enzyme activity was measured by catalase quantification.Data were analyzed by Mann-Whitney U-test, Kruskal-Wallis test and Cuzick's test followed by Bonferroni correction for multiple comparisons.

RESULTS

We have standardized the isolation procedure to obtain a cell population with hepatogenic properties prior to in vivo transplantation. When subjected to hepatogenic differentiation on untreated plastic support, UCMSCs differentiated in hepatocyte-like cells as demonstrated by their morphology, progressive up-regulation of mature hepatocyte markers, glycogen storage, albumin and urea secretion. However, cells seeded on 3D-supports showed a minor or negligible differentiation capacity.UCMSCs-transplanted mice showed a more rapid damage resolution, as shown by histological analysis, with a lower inflammation level and an increased catalase activity compared to CCl4-treated mice.

CONCLUSIONS

Our findings show that UCMSCs can be reliably isolated, have hepatogenic properties and following systemic administration are able to accelerate the resolution of an acute liver injury without any differentiation and manipulation. These features make UCMSCs strong candidates for future application in regenerative medicine for human acute liver disease.

Stem cell therapy for arterial restenosis: potential parameters contributing to the success of bone marrow-derived mesenchymal stromal cells

PURPOSE

Restenosis is a complex and heterogeneous pathophysiological phenomenon occurring in patients submitted to revascularization procedures. Previous studies proved the antirestenotic properties of injected allogenic mesenchymal stromal cells (MSCs) in an experimental model of rat carotid (re)stenosis induced through arteriotomy. In this study we describe some of the effects subsequent to MSC treatment of rats submitted to carotid arteriotomy and possibly responsible for their antirestenotic effect.

METHODS

Rat MSCs were isolated from bone marrow, expanded in vitro and characterized. Subsequently, we evaluated the effects of MSC administration via tail vein at 3 and 7 days after carotid arteriotomy both in rat serum and in injured carotids, focusing on DNA oxidative damage (8-oxo-dG detection), cell proliferation index (BrdU incorporation assay), apoptotic index (TUNEL assay), the expression of inflammation- and proliferation-related genes (RT-PCR), the release of growth factors and of inflammation-related cytokines (antibody arrays and ELISA).

RESULTS

MSC administration induced a greater cell proliferation in carotids after arteriotomy, together with an increased level of VEGF in the serum and with the higher expression of VEGF mRNA in injured carotids. Serum analysis also revealed a decreased level of the pro-inflammatory cytokines CXCL1, CXCL5, L-Selectin, ICAM-1 and LIX, and of TIMP1 and SDF-1alpha in MSC-treated rats. The MSC immunomodulatory activity was confirmed by the decreased expression of TLR2 and TLR4 in injured carotids.

CONCLUSIONS

MSCs play an immunomodulatory paracrine role when injected in rats submitted to carotid arteriotomy, accompanied by the release of VEGF, possibly contributing to the accelerated repair of the injured vascular wall.

Soluble factors from multipotent mesenchymal stromal cells have antinecrotic effect on cardiomyocytes in vitro and improve cardiac function in infarcted rat hearts

The mechanisms underlying the functional improvement after injection of multipotent mesenchymal stromal cells (MSCs) in infarcted hearts remain incompletely understood. The aim of this study was to investigate if soluble factors secreted by MSCs promote cardioprotection. For this purpose, conditioned medium (CM) was obtained after three passages from MSC cultures submitted to 72 h of conditioning in serum-free DMEM under normoxia (NCM) or hypoxia (HCM) conditions. CM was concentrated 25-fold before use (NCM-25X, concentrated normoxia conditioned medium; HCM-25X, concentrated hypoxia conditioned medium). The in vitro cardioprotection was evaluated in neonatal ventricular cardiomyocytes by quantifying apoptosis after 24 h of serum deprivation associated with hypoxia (1% O(2)) in the absence or presence of NCM and HCM (nonconcentrated and 25-fold concentrated). The in vivo cardioprotection of HCM was tested in a model of myocardial infarction (MI) induced in Wistar male rats by permanent left coronary occlusion. Intramyocardial injection of HCM-25X (n = 14) or nonconditioned DMEM (n = 16) was performed 3 h after coronary occlusion and cardiac function was evaluated 19-21 days after medium injection. Cardiac function was evaluated by electro- and echocardiogram, left ventricular catheterization, and treadmill test. The in vitro results showed that HCM was able to decrease cardiomyocyte necrosis. The in vivo results showed that HCM-25X administered 3 h after AMI was able to promote a significant reduction (35%) in left ventricular end-diastolic pressure and improvement of cardiac contractility (15%) and relaxation (12%). These results suggest that soluble factors released in vitro by MSCs are able to promote cardioprotection in vitro and improve cardiac function in vivo.

Mesenchymal stem cells or cardiac progenitors for cardiac repair? A comparative study

In the past, clinical trials transplanting bone marrow-derived mononuclear cells reported a limited improvement in cardiac function. Therefore, the search for stem cells leading to more successful stem cell therapies continues. Good candidates are the so-called cardiac stem cells (CSCs). To date, there is no clear evidence to show if these cells are intrinsic stem cells from the heart or mobilized cells from bone marrow. In this study we performed a comparative study between human mesenchymal stem cells (hMSCs), purified c-kit(+) CSCs, and cardiosphere-derived cells (CDCs). Our results showed that hMSCs can be discriminated from CSCs by their differentiation capacity towards adipocytes and osteocytes and the expression of CD140b. On the other hand, cardiac progenitors display a greater cardiomyogenic differentiation capacity. Despite a different isolation protocol, no distinction could be made between c-kit(+) CSCs and CDCs, indicating that they probably derive from the same precursor or even are the same cells.

Regenerative therapies in electrophysiology and pacing: introducing the next steps

The morbidity and mortality of cardiac arrhythmias are major international health concerns. Drug and device therapies have made inroads but alternative approaches are still being sought. For example, gene and cell therapies have been explored for treatment of brady- and tachyarrhythmias, and proof of concept has been obtained for both biological pacing in the setting of heart block and gene therapy for ventricular tachycardias. This paper reviews the state of the art developments with regard to gene and cell therapies for cardiac arrhythmias and discusses next steps.

Stem cell research in cell transplantation: sources, geopolitical influence, and transplantation

If the rapidly progressing field of stem cell research reaches its full potential, successful treatments and enhanced understanding of many diseases are the likely results. However, the full potential of stem cell science will only be reached if all possible avenues can be explored and on a worldwide scale. Until 2009, the US had a highly restrictive policy on obtaining cells from human embryos and fetal tissue, a policy that pushed research toward the use of adult-derived cells. Currently, US policy is still in flux, and retrospective analysis does show the US lagging behind the rest of the world in the proportional increase in embryonic/fetal stem cell research. The majority of US studies being on either a limited number of cell lines, or on cells derived elsewhere (or funded by other sources than Federal) rather than on freshly isolated embryonic or fetal material. Neural, mesenchymal, and the mixed stem cell mononuclear fraction are the most commonly investigated types, which can generally be classified as adult-derived stem cells, although roughly half of the neural stem cells are fetal derived. Other types, such as embryonic and fat-derived stem cells, are increasing in their prominence, suggesting that new types of stem cells are still being pursued. Sixty percent of the reported stem cell studies involved transplantation, of which over three quarters were allogeneic transplants. A high proportion of the cardiovascular systems articles were on allogeneic transplants in a number of different species, including several autologous studies. A number of pharmaceutical grade stem cell products have also recently been tested and reported on. Stem cell research shows considerable promise for the treatment of a number of disorders, some of which have entered clinical trials; over the next few years it will be interesting to see how these treatments progress in the clinic.

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: Mechanisms of immunomodulation and homing

Mesenchymal stem cell (MSC) transplantation has been explored as a new clinical approach to repair injured tissue. A growing corpus of studies have highlighted two important aspects of MSC therapy: 1) MSCs can modulate T-cell-mediated immunological responses, and (2) systemically administered MSCs home to sites of ischemia or injury. In this review, we describe the known mechanisms of immunomodulation and homing of MSCs. First, we examine the low immunogenicity of MSCs and their antigen presentation capabilities. Next, we discuss the paracrine interactions between MSCs and innate [dendritic cells (DC)] and adaptive immune cells (T lymphocytes) with a focus on prostaglandin E(2) (PGE(2)), indoleamine 2,3-dioxygenase (IDO), and toll-like receptor (TLR) signaling pathways. We transition to outline the steps of activation, rolling/adhesion, and transmigration of MSCs into target tissues during inflammatory or ischemic conditions. These aspects of MSC grafts--immunomodulation and homing--are contextualized to understand a reported side effect of MSC therapy, cancer development.