Cell-based therapy for ischemic heart disease: a clinical update

Investigating the Transient Regenerative Potential of Cardiac Muscle Using a Neonatal Pig Partial Apical Resection Model

Researchers have shown that adult zebrafish have the potential to regenerate 20% of the ventricular muscle within two months of apex resection, and neonatal mice have the capacity to regenerate their heart after apex resection up until day 7 after birth. The goal of this study was to determine if large mammals (porcine heart model) have the capability to fully regenerate a resected portion of the left ventricular apex during the neonatal stage, and if so, how long the regenerative potential persists. A total of 36 piglets were divided into the following groups: 0-day control and surgical groups and seven-day control and surgical groups. For the apex removal groups, each piglet was subjected to a partial wall thickness resection (~30% of the ventricular wall thickness). Heart muscle function was assessed via transthoracic echocardiograms; the seven-day surgery group experienced a decrease in ejection fraction and fractional shortening. Upon gross necropsy, for piglets euthanized four weeks post-surgery, all 0-day-old hearts showed no signs of scarring or any indication of the induced injury. Histological analysis confirmed that piglets in the 0-day surgery group exhibited various degrees of regeneration, with half of the piglets showing full regeneration and the other half showing partial regeneration. However, each piglet in the seven-day surgery group demonstrated epicardial fibrosis along with moderate to severe dissecting interstitial fibrosis, which was accompanied by an abundant collagenous extracellular matrix as the result of a scar formation in the resection site. Histology of one 0-day apex resection piglet (briefly lain on and accidentally killed by the mother sow three days post-surgery) revealed dense, proliferative mesenchymal cells bordering the fibrin and hemorrhage zone and differentiating toward immature cardiomyocytes. We further examined the heart explants at 5-days post-surgery (5D PO) and 1-week post-surgery (1W PO) to assess the repair progression. For the 0-day surgery piglets euthanized at 5D PO and 1W PO, half had abundant proliferating mesenchymal cells, suggesting active regeneration, while the other half showed increased extracellular collagen. The seven-day surgery piglets euthanized at 5D PO, and 1W PO showed evidence of greatly increased extracellular collagen, while some piglets had proliferating mesenchymal cells, suggesting a regenerative effort is ongoing while scar formation seems to predominate. In short, our qualitative findings suggest that the piglets lose the full myocardial regenerative potential by 7 days after birth, but greatly preserve the regenerative potential within 1 day post-partum.

The harsh microenvironment in infarcted heart accelerates transplanted bone marrow mesenchymal stem cells injury: the role of injured cardiomyocytes-derived exosomes

Stem cell therapy can be used to repair and regenerate damaged hearts tissue; nevertheless, the low survival rate of transplanted cells limits their therapeutic efficacy. Recently, it has been proposed that exosomes regulate multiple cellular processes by mediating cell survival and communication among cells. The following study investigates whether injured cardiomyocytes-derived exosomes (cardiac exosomes) affect the survival of transplanted bone marrow mesenchymal stem cells (BMSCs) in infarcted heart. To mimic the harsh microenvironment in infarcted heart that the cardiomyocytes or transplanted BMSCs encounter in vivo, cardiomyocytes conditioned medium and cardiac exosomes collected from H₂O₂-treated cardiomyocytes culture medium were cultured with BMSCs under oxidative stress in vitro. Cardiomyocytes conditioned medium and cardiac exosomes significantly accelerated the injury of BMSCs induced by H₂O₂; increased cleaved caspase-3/caspase-3 and apoptotic percentage, and decreased the ratio of Bcl-2/Bax and cell viability in those cells. Next, we explored the role of cardiac exosomes in the survival of transplanted BMSCs in vivo by constructing a Rab27a knockout (KO) mice model by a transcription activator-like effector nuclease (TALEN) genome-editing technique; Rab27a is a family of GTPases, which has critical role in secretion of exosomes. Male mouse GFP-modified BMSCs were implanted into the viable myocardium bordering the infarction in Rab27a KO and wild-type female mice. The obtained results showed that the transplanted BMSCs survival in infarcted heart was increased in Rab27a KO mice by the higher level of Y-chromosome Sry DNA, GFP mRNA, and the GFP fluorescence signal intensity. To sum up, these findings revealed that the injured cardiomyocytes-derived exosomes accelerate transplanted BMSCs injury in infarcted heart, thus highlighting a new mechanism underlying the survival of transplanted cells after myocardial infarction.

Autophagy mediates the beneficial effect of hypoxic preconditioning on bone marrow mesenchymal stem cells for the therapy of myocardial infarction

Background

Stem cell therapy has emerged as a promising therapeutic strategy for myocardial infarction (MI). However, the poor viability of transplanted stem cells hampers their therapeutic efficacy. Hypoxic preconditioning (HPC) can effectively promote the survival of stem cells. The aim of this study was to investigate whether HPC improved the functional survival of bone marrow mesenchymal stem cells (BM-MSCs) and increased their cardiac protective effect.

Methods

BM-MSCs, isolated from Tg(Fluc-egfp) mice which constitutively express both firefly luciferase (Fluc) and enhanced green fluorescent protein (eGFP), were preconditioned with HPC (1% O₂) for 12 h, 24 h, 36 h, and 48 h, respectively, followed by 24 h of hypoxia and serum deprivation (H/SD) injury.

Results

HPC dose-dependently increased the autophagy in BM-MSCs. However, the protective effects of HPC for 24 h are most pronounced. Moreover, hypoxic preconditioned BM-MSCs (^HPCMSCs) and nonhypoxic preconditioned BM-MSCs (^NPCMSCs) were transplanted into infarcted hearts. Longitudinal in vivo bioluminescence imaging (BLI) and immunofluorescent staining revealed that HPC enhanced the survival of engrafted BM-MSCs. Furthermore, ^HPCMSCs significantly reduced fibrosis, decreased apoptotic cardiomyocytes, and preserved heart function. However, the beneficial effect of HPC was abolished by autophagy inhibition with 3-methyladenine (3-MA) and Atg7siRNA.

Conclusion

This study demonstrates that HPC may improve the functional survival and the therapeutic efficiencies of engrafted BM-MSCs, at least in part through autophagy regulation. Hypoxic preconditioning may serve as a promising strategy for optimizing cell-based cardiac regenerative therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0543-0) contains supplementary material, which is available to authorized users.

Cardiac differentiation of cardiosphere-derived cells in scaffolds mimicking morphology of the cardiac extracellular matrix

Stem cell therapy has the potential to regenerate heart tissue after myocardial infarction (MI). The regeneration is dependent upon cardiac differentiation of the delivered stem cells. We hypothesized that timing of the stem cell delivery determines the extent of cardiac differentiation as cell differentiation is dependent on matrix properties such as biomechanics, structure and morphology, and these properties in cardiac extracellular matrix (ECM) continuously vary with time after MI. In order to elucidate the relationship between ECM properties and cardiac differentiation, we created an in vitro model based on ECM-mimicking fibers and a type of cardiac progenitor cell, cardiosphere-derived cells (CDCs). A simultaneous fiber electrospinning and cell electrospraying technique was utilized to fabricate constructs. By blending a highly soft hydrogel with a relatively stiff polyurethane and modulating fabrication parameters, tissue constructs with similar cell adhesion property but different global modulus, single fiber modulus, fiber density and fiber alignment were achieved. The CDCs remained alive within the constructs during a 1week culture period. CDC cardiac differentiation was dependent on the scaffold modulus, fiber volume fraction and fiber alignment. Two constructs with relatively low scaffold modulus, ∼50-60kPa, most significantly directed the CDC differentiation into mature cardiomyocytes as evidenced by gene expressions of cardiac troponin T (cTnT), calcium channel (CACNA1c) and cardiac myosin heavy chain (MYH6), and protein expressions of cardiac troponin I (cTnI) and connexin 43 (CX43). Of these two low-modulus constructs, the extent of differentiation was greater for lower fiber alignment and higher fiber volume fraction. These results suggest that cardiac ECM properties may have an effect on cardiac differentiation of delivered stem cells.

Survival, integration, and differentiation of unrestricted somatic stem cells in the heart

Unrestricted somatic stem cells (USSCs) derived from human umbilical cord blood represent an attractive cell source to reconstitute the damaged heart. We have analyzed the cardiomyogenic potential and investigated the fate of USSCs after transplantation into rat heart in vivo. USSCs demonstrated cardiomyogenic differentiation properties characterized by the spontaneously beating activity and the robust expression of cardiac α-actinin and troponin T (cTnT) at protein and mRNA level after cocultivation with neonatal rat cardiomyocytes. To study the fate in vivo, eGFP⁺ USSCs were injected transcoronarily into immunosuppressed rats via a catheter-based technique. Nearly 80% USSCs were retained within the myocardium without altering cardiac hemodynamics. After 7 days, 20% of the transplanted cells survived in the host myocardium and showed elongated morphology with weak expression of cardiac-specific markers, while some eGFP⁺ USSCs were found to integrate into the vascular wall. After 21 days, only a small fraction of USSCs were found in the myocardium (0.13%); however, the remaining cells clearly exhibited a sarcomeric structure similar to mature cardiomyocytes. Identical results were also obtained in nude rats. In addition, we found some cells stained positively for activated caspase 3 paralleled by the massive infiltration of CD11b⁺ cells into the myocardium. In summary, USSCs can differentiate into beating cardiomyocytes by cocultivation in vitro. After coronary transplantation in vivo, however, long-term survival of differentiated USSCs was rather low despite a high initial fraction of trapped cells.

Comparison of cardiac stem cells and mesenchymal stem cells transplantation on the cardiac electrophysiology in rats with myocardial infarction

INTRODUCTION

Whether transplanted cardiac stem cells (CSCs) and mesenchymal stem cells (MSCs) improved ventricular fibrillation threshold (VFT) similarly is still unclear. We sought to compare the effects of the CSC and MSC transplantation on the electrophysiological characteristics and VFT in rats with myocardial infarction (MI).

METHODS

MI was induced in 30 male Sprague-Dawley rats. Two weeks later, animals were randomized to receive 5 × 10(6) CSCs labeled with PKH26 in PBS or 5 × 10(6) MSCs labeled with PKH26 in phosphate buffer solution(PBS) or PBS alone injection into the infarcted anterior ventricular free wall. Six weeks after the injection, electrophysiological characteristics and VFT were measured. Labeled CSCs and MSCs were observed in 5 μm cryostat sections from each heart.

RESULTS

Malignant ventricular arrhythmias were significantly (P = 0.0055) less inducible in the CSC group than the MSC group. The VFTs were improved in the CSC group compared with the MSC group. Labeled CSCs and MSCs were identified in the infarct zone and infarct marginal zone. Labeled CSCs expressed Connexin-43, von Willebrand factor, α-smooth muscle actin and α-sarcomeric actin,while the Labeled MSCs expressed von Willebrand factor, α-smooth muscle actin and α-sarcomeric actin in vivo.

CONCLUSIONS

After 6 weeks of cell transplantation, CSCs are superior to MSCs in modulating the electrophysiological abnormality and improving the VFT in rats with MI. CSCs and MSCs express markers that suggest muscle, endothelium and vascular smooth muscle phenotypes in vivo, but MSCs rarely express Connexin-43.

Guidance of stem cells to a target destination in vivo by magnetic nanoparticles in a magnetic field

Stem cells contribute to physiological processes such as postischemic neovascularization and vascular re-endothelialization, which help regenerate myocardial defects or repair vascular injury. However, therapeutic efficacy of stem cell transplantation is often limited by inefficient homing of systemically administered cells, which results in a low number of cells accumulating at sites of pathology. In this study, anti-CD34 antibody-coated magnetic nanoparticles (Fe3O4@PEG-CD34) are shown to have high affinity to stem cells. The results of hemolysis rate and activated partial thromboplastin time (APTT) tests indicate that such nanoparticle may be used safely in the blood system. In vitro studies showed that a nanoparticle concentration of 100 μg/mL gives rise to a significant increase in cell retention using an applicable permanent magnet, exerting minimal negative effect on cell viability and migration. Subsequent in vivo studies indicate that nanopartical can specifically bind stem cells with good magnetic response. Anti-CD34 antibody coated magnetic nanoparticle may be used to help deliver stem cells to a lesion site in the body for better treatment.

Microfluidic artificial "vessels" for dynamic mechanical stimulation of mesenchymal stem cells

Cells in the cardiovascular system are constantly exposed to complex mechanical stimulation due to the pulsatile nature of blood flow and the haemodynamic forces that are key to the regulation of vascular development, remodeling and pathophysiology. Mechanical stretch can also modulate the differentiation of stem cells toward vascular cell lineages (i.e., vascular smooth muscle cells), and represent a critical factor in vascular tissue engineering. Here we report on the development of a microchip platform that can emulate several key aspects of the vascular mechanical environment, such as cyclic stimulation and circumferential strain. This chip consists of an array of microfluidic channels with widths ranging from 20 to 500 micrometers. These channels are covered by suspended deformable membranes, on which cells are cultured and stimulated by cyclic circumferential strain of up to 20% via hydrodynamic actuation of the fluid in the microfluidic channels, thereby mimicking the biomechanical conditions of small blood vessels. We show that human mesenchymal stem cells (MSCs) can be cultured and continuously stimulated by cyclic stretch over a period of 7 days with no evidence of device fatigue or performance degradation. We observed localization and alignment of MSCs when mechanical stretch is larger than 10%, indicating the importance of mechanical stimulation in modulating cellular behavior. We further demonstrated simultaneous detection of proteins in multiple signaling pathways, including SMAD1/SMAD2 and canonical Wnt/β-catenin. This microchip represents a generic and versatile platform for high-throughput and rapid screening of cellular responses, including signal transduction cascades, in response to mechanical cues. The system emulates the physiological conditions of blood vessels and other tissues that are subject to cyclic strain, and may have a wide range of applications in the fields of stem cell mechanobiology, vascular tissue engineering, and other areas of regenerative medicine.

Translational research and therapeutic applications of stem cell transplantation in periodontal regenerative medicine

Stem cells have received a great deal of interest from the research community as potential therapeutic "tools" for a variety of chronic debilitating diseases that lack clinically effective therapies. Stem cells are also of interest for the regeneration of tooth-supporting tissues that have been lost to periodontal disease. Indeed, substantial data have demonstrated that the exogenous administration of stem cells or their derivatives in preclinical animal models of periodontal defects can restore damaged tissues to their original form and function. As we discuss here, however, considerable hurdles must be overcome before these findings can be responsibly translated to novel clinical therapies. Generally, the application of stem cells for periodontal therapy in clinics will not be realized until the best cell(s) to use, the optimal dose, and an effective mode of administration are identified. In particular, we need to better understand the mechanisms of action of stem cells after transplantation in the periodontium and to learn how to preciously control stem cell fates in the pathological environment around a tooth. From a translational perspective, we outline the challenges that may vary across preclinical models for the evaluation of stem cell therapy in situations that require periodontal reconstruction and the safety issues that are related to clinical applications of human stem cells. Although clinical trials that use autologous periodontal ligament stem cells have been approved and have already been initiated, proper consideration of the technical, safety, and regulatory concerns may facilitate, rather than inhibit, the clinical translation of new therapies.

Molecular pathogenesis of myocardial remodeling and new potential therapeutic targets in chronic heart failure

It is well known that the natural history of chronic heart failure (CHF),regardless of age and aetiology,is characterized by progressive cardiac dysfunction refractory to conventional cardiokinetic, diuretic and peripheral vasodilator therapy. Several previous studies, both in animals and humans, showed that the key pathogenetic element of CHF negative clinical evolution is constituted by myocardial remodeling. This is a complex pathologic process of ultrastructural rearrangement of the heart induced by various neuro-humoral factors released by cardiac fibrocells in response to biomechanical stress connected to chronic haemodynamic overload. Typical features of myocardial remodeling are represented by cardiomyocytes hypertrophy and apoptosis, extracellular matrix alterations, mesenchymal fibrotic and phlogistic processes and by cardiac gene expression modifications with fetal genetic program reactivation. In the last years, increasing knowledge of subtle molecular and cellular mechanisms involved in myocardial remodeling has led to the discovery of some new potential therapeutic targets capable of inducing its regression. In this paper our attention is focused on the possible use of antiapoptotic and antifibrotic agents, and on the fascinating perspectives offered by the development of myocardial gene therapy and, in particular, by myocardial regenerative therapy.

Role of molecular imaging in stem cell therapy for myocardial restoration

During the past two decades, stem cells have created enthusiasm as a regenerative therapy for ischemic heart disease. Transplantation of bone marrow stem cells, skeletal myoblasts, and endothelial progenitor cells has shown to improve myocardial function after infarction. Recently, attention has focused on the potential use of embryonic stem cells and induced pluripotent stem cells because they possess the capacity to differentiate into various cell types, including cardiac and endothelial cells. Clinical trials have shown positive effects on the functional recovery of heart after myocardial infarction and have answered questions on timing, dosage, and cell delivery route of stem cells such as those derived from bone marrow. Despite the current advances in stem cell research, one main hurdle remains the lack of reliable information about the fate of cell engraftment, survival, and proliferation after transplantation. This review discusses the different cell types used in cardiac cell therapy as well as molecular imaging modalities relevant to survival issues.

A cellular delivery system fabricated with autologous BMSCs and collagen scaffold enhances angiogenesis and perfusion in ischemic hind limb

Although therapeutic cellular angiogenesis is effective for chronic ischemia, the optimal mode of cellular administration is still under exploration. This study aimed to develop a cellular delivery system to enhance the perfusion and angiogenesis in the ischemic hind limb. Collagen scaffold (CS) was prepared, and for morphology and toxicity analysis, bone marrow-derived mesenchymal stem cells (BMSCs) were isolated, expanded, filtrated, and seeded onto CS to construct BMSCs-CS. The ischemic hind limbs of rabbit models were implanted with autologous BMSCs-CS, CS, and autologous BMSCs; the untreated ischemic or normal animals were considered as the ischemic or normal control groups. Oxygen saturation parameters were regularly measured to determine the perfusion in the extremities. Histological examinations with hematoxylin and eosin immunostaining against von Willebrand factor and smooth muscle (SM) α-actin were performed for capillary and mature vessel evaluation. CS was a multiporous structure without cytotoxicity. At several intervals, the oxygen saturation ratio (OSR) in normal control was the highest. The OSRs in BMSCs-CS and CS were higher than that in BMSCs and ischemic control (p < 0.05); the OSR in BMSCs-CS group was higher than that in CS at 6 and 8 weeks (p < 0.05). The capillaries in BMSCs-CS and CS were higher than that in CS, BMSCs, and the ischemic or normal control (p < 0.05). The mature vessels in BMSCs-CS were higher than that in CS, BMSCs, and the ischemic or normal control (p < 0.05). The autologous cellular delivery system proved to be an effective approach for improving higher ischemic hind limb perfusion and angiogenesis as opposed to cellular therapy alone.

Human Adipose Tissue as a Source of Cells with Angiogenic Potential

Endothelial cells (ECs) are involved in the process of angiogenesis, the outgrowth of new vessels from preexisting blood vessels. If available in sufficiently large numbers, ECs could be used therapeutically to establish blood flow through in vitro engineered tissues and tissues suffering from severe ischemia. Adipose tissue (AT) is an easily available source of large number of autologous ECs. Here we describe the isolation, in vitro expansion, and characterization of human AT derived ECs (AT-ECs). AT-ECs proliferated rapidly through 15–20 population doublings. The cultured cells showed cobblestone morphology and expressed EC markers including CD31, CD144, eNOS, CD309, CD105, von Willebrand factor, CD146, CD54, and CD102. They bound Ulex europaeus agglutinin I lectin and took up DiI-Ac-LDL. The AT-ECs formed capillary-like tubes in Matrigel in vitro and formed functional blood vessels in Matrigel following subcutaneous injection into immunodeficient mice. In conclusion, AT-ECs reach clinically significant cell numbers after few population doublings and are easily accessible from autologous AT, which also contains mesenchymal stem cells/pericytes. Thus, AT yields two cell populations that may be used together in the treatment of tissue ischemia and in clinical applications of tissue engineering.

Stem cell-based cardiac tissue engineering

Cardiovascular diseases are the leading cause of death worldwide, and cell-based therapies represent a potential cure for patients with cardiac diseases such as myocardial infarction, heart failure, and congenital heart diseases. Towards this goal, cardiac tissue engineering is now being investigated as an approach to support cell-based therapies and enhance their efficacy. This review focuses on the latest research in cardiac tissue engineering based on the use of embryonic, induced pluripotent, or adult stem cells. We describe different strategies such as direct injection of cells and/or biomaterials as well as direct replacement therapies with tissue mimics. In this regard, the latest research has shown promising results demonstrating the improvement of cardiac function with different strategies. It is clear from recent studies that the most important consideration to be addressed by new therapeutic strategies is long-term functional improvement. For this goal to be realized, novel and efficient methods of cell delivery are required that enable high cell retention, followed by electrical integration and mechanical coupling of the injected cells or the engineered tissue to the host myocardium.

Imaging long-term fate of intramyocardially implanted mesenchymal stem cells in a porcine myocardial infarction model

The long-term fate of stem cells after intramyocardial delivery is unknown. We used noninvasive, repetitive PET/CT imaging with [(18)F]FEAU to monitor the long-term (up to 5 months) spatial-temporal dynamics of MSCs retrovirally transduced with the sr39HSV1-tk gene (sr39HSV1-tk-MSC) and implanted intramyocardially in pigs with induced acute myocardial infarction. Repetitive [(18)F]FEAU PET/CT revealed a biphasic pattern of sr39HSV1-tk-MSC dynamics; cell proliferation peaked at 33-35 days after injection, in periinfarct regions and the major cardiac lymphatic vessels and lymph nodes. The sr39HSV1-tk-MSC-associated [(18)F]FEAU signals gradually decreased thereafter. Cardiac lymphography studies using PG-Gd-NIRF813 contrast for MRI and near-infrared fluorescence imaging showed rapid clearance of the contrast from the site of intramyocardial injection through the subepicardial lymphatic network into the lymphatic vessels and periaortic lymph nodes. Immunohistochemical analysis of cardiac tissue obtained at 35 and 150 days demonstrated several types of sr39HSV1-tk expressing cells, including fibro-myoblasts, lymphovascular cells, and microvascular and arterial endothelium. In summary, this study demonstrated the feasibility and sensitivity of [(18)F]FEAU PET/CT imaging for long-term, in-vivo monitoring (up to 5 months) of the fate of intramyocardially injected sr39HSV1-tk-MSC cells. Intramyocardially transplanted MSCs appear to integrate into the lymphatic endothelium and may help improve myocardial lymphatic system function after MI.

Improvements of cardiac electrophysiologic stability and ventricular fibrillation threshold in rats with myocardial infarction treated with cardiac stem cells

OBJECTIVES

Arrhythmia is of concern after cardiac stem cell transplantation in repairing infarcted myocardium. However, whether transplantation improved the ventricular fibrillation threshold and whether severe malignant ventricular arrhythmia is induced in the myocardial infarction model are still unclear. We sought to investigate the electrophysiologic characteristics and ventricular fibrillation threshold in rats with myocardial infarction by treatment with allogeneic cardiac stem cells.

DESIGN

Prospective, randomized, controlled study.

SETTING

University-affiliated hospital.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Myocardial infarction was induced in 20 male Sprague-Dawley rats. Two weeks later, animals were randomized to receive 5 × 10(6) cardiac stem cells labeled with PKH26 in phosphate buffer solution or a phosphate buffer solution-alone injection into the infarcted anterior ventricular-free wall.

MEASUREMENTS AND MAIN RESULTS

Six weeks after the cardiac stem cell or phosphate buffer solution injection, electrophysiologic characteristics and ventricular fibrillation threshold were measured at the infarct area, infarct marginal zone, and noninfarct zone. Labeled cardiac stem cells were observed in 5-μm cryostat sections from each harvested heart. The unipolar electrogram activation recovery time dispersions were shorter in the cardiac stem cell group compared with those at the phosphate buffer solution group (15.5 ± 4.4 vs. 38.6 ± 14.9 msecs, p = .000177). Malignant ventricular arrhythmias were significantly (p = .00108) less inducible in the cardiac stem cell group (one of ten) than the phosphate buffer solution group (nine of ten). The ventricular fibrillation thresholds were greatly improved in the cardiac stem cell group compared with the phosphate buffer solution group. Labeled cardiac stem cells were identified in the infarct zone and infarct marginal zone and expressed Connexin-43, von Willebrand factor, α-smooth muscle actin, and α-sarcomeric actin.

CONCLUSIONS

Cardiac stem cells may modulate the electrophysiologic abnormality and improve the ventricular fibrillation threshold in rats with myocardial infarction treated with allogeneic cardiac stem cells and cardiac stem cell express markers that suggest muscle, endothelium, and vascular smooth muscle phenotypes in vivo.

Intracoronary mesenchymal stem cells promote postischemic myocardial functional recovery, decrease inflammation, and reduce apoptosis via a signal transducer and activator of transcription 3 mechanism

BACKGROUND

Signal transducer and activator of transcription 3 (STAT3) regulates myocardial apoptosis, cellular proliferation, and the immune response after ischemia/reperfusion (I/R). STAT3 is also necessary for the production of vascular endothelial growth factor (VEGF) by mesenchymal stem cells (MSCs), which are known to reduce myocardial injury after I/R. However, it remains unknown whether STAT3 is an important mediator of MSC-based cardioprotection. We hypothesized that knockout of stem cell STAT3 would reduce MSC-derived myocardial functional recovery and increase myocardial inflammatory and apoptotic signaling.

STUDY DESIGN

With a Langendorff apparatus, male rat hearts were subjected to 15 minutes of equilibration and 25 minutes of ischemia, followed by 40 minutes of reperfusion. Immediately before ischemia, hearts received intracoronary infusions of vehicle, wild-type MSCs (WT MSCs) or STAT3 knockout MSCs (STAT3KO MSCs). Heart function was measured continuously. Myocardial homogenates were analyzed for production of interleukin (IL)-1, IL-6, and tumor necrosis factor-α (TNF-α). Additionally, MSC production of hepatocyte growth factor (HGF) and insulin-like growth factor-1 (IGF-1) were measured in vitro.

RESULTS

Hearts treated with WT MSCs exhibited the greatest functional recovery, and those treated with STAT3KO MSCs had equivalent recovery to vehicle. The highest proinflammatory cytokine levels were seen in vehicle-treated hearts, and the lowest in the WT MSC group. STAT3KO MSCs produced less IGF-1, but more HGF than WT MSCs. Finally, hearts treated with STAT3KO MSCs or vehicle had significantly higher caspase-3 levels than those treated with WT MSCs.

CONCLUSIONS

Intracoronary infusions of MSCs improve postischemic left ventricular function and reduce proapoptotic and proinflammatory signaling via a STAT3-dependent mechanism.

Functionalized scaffold-mediated interleukin 10 gene delivery significantly improves survival rates of stem cells in vivo

While stem cell transplantation could potentially treat a variety of disorders, clinical studies have not yet demonstrated conclusive benefits. This may be partly because transplanted stem cells have low survival rates, potentially due to host inflammation. The system described herein used two different gene therapy techniques to improve retention of rat mesenchymal stem cells. In the first, stem cells were transfected with interleukin-10 (IL-10) before being loaded into a collagen scaffold. In the second, unmodified stem cells were loaded into a collagen scaffold along with polymer-complexed IL-10 plasmids. The scaffolds were surgically implanted into the dorsum of syngeneic rats. At each endpoint, the scaffolds were explanted and cell retention, IL-10 level and inflammatory response were quantified. All treatment groups had statistically significant increases in cell retention after 7 days, but the group treated with 2 µg of IL-10 polyplexes had a significant improvement even at 21 days. This cell retention was associated with increased IL-10 and decreased levels of proinflammatory cytokines and apoptosis. The primary effect on the inflammatory response appeared to be on macrophage differentiation, encouraging the regulatory phenotype over the cytotoxic lineage. Improving cell survival may be an important step toward realization of the therapeutic potential of stem cells.

Red wine antioxidant resveratrol-modified cardiac stem cells regenerate infarcted myocardium

To study the efficiency of maintaining the reduced tissue environment via pre-treatment with natural antioxidant resveratrol in stem cell therapy, we pre-treated male Sprague-Dawley rats with resveratrol (2.5 mg/kg/day gavaged for 2 weeks). After occlusion of the left anterior descending coronary artery (LAD), adult cardiac stem cells stably expressing EGFP were injected into the border zone of the myocardium. One week after the LAD occlusion, the cardiac reduced environment was confirmed in resveratrol-treated rat hearts by the enhanced expression of nuclear factor-E2-related factor-2 (Nrf2) and redox effector factor-1 (Ref-1). In concert, cardiac functional parameters (left ventricular ejection fraction and fractional shortening) were significantly improved. The improvement of cardiac function was accompanied by the enhanced stem cell survival and proliferation as demonstrated by the expression of cell proliferation marker Ki67 and differentiation of stem cells towards the regeneration of the myocardium as demonstrated by the enhanced expression of EGFP 28 days after LAD occlusion in the resveratrol-treated hearts. Our results demonstrate that resveratrol maintained a reduced tissue environment by overexpressing Nrf2 and Ref-1 in rats resulting in an enhancement of the cardiac regeneration of the adult cardiac stem cells as demonstrated by increased cell survival and differentiation leading to cardiac function.

Ablation of TNF-alpha receptors influences mesenchymal stem cell-mediated cardiac protection against ischemia

Mesenchymal stem cell (MSC) infusion may reduce myocardial ischemic injury. TNF-alpha is a proinflammatory cytokine produced in large quantities during myocardial ischemia that can exert beneficial or detrimental effects on MSC function by binding to a 55-kd receptor (TNFR1) or a 75-kd receptor (TNFR2) on MSCs. We investigated whether genetic modification with ablation of TNFR1 and/or TNFR2 affects MSC-mediated protection against myocardial ischemic injury. The MSCs were harvested from wild-type mice (WT-MSCs) and knockout mice with ablation of TNFR1 and/or TNFR2 (TNFR1KO, TNFR2KO, and TNFR1/R2KO MSCs). After anesthesia was initiated via inhalation of isoflurane, myocardial ischemia was induced in rats via coronary artery ligation. Hearts were then injected with vehicle or MSCs (1 x 10 cells/mL). Myocardial function was assessed 28 days postsurgery with 2-dimensional echocardiograms and isolated heart perfusion. Myocardial tissue was collected for cytokine analysis and infarct measurements. We found that MSC treatment offered significant protection against myocardial ischemia, namely by decreasing infarct size, improving heart function, and decreasing ventricular remodeling compared with vehicle. Compared with WT-MSCs, TNFR1KO MSCs conferred increased cardiac protection, although TNFR2KO and TNFR1/R2KO MSCs conferred less cardiac protection. In addition, treatment with TNFR1KO MSCs was associated with decreased levels of proinflammatory cytokines and an increased level of vascular endothelial growth factor in the myocardium, whereas treatment with TNFR2KO or TNFR1/R2KO MSCs was associated with increased levels of proinflammatory cytokines and a decreased level of vascular endothelial growth factor compared with treatment with WT-MSCs. We conclude that MSC TNFR1 and TNFR2 play important roles in MSC-mediated cardiac protection after myocardial ischemia.

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

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