From cardiac repair to cardiac regeneration – ready to translate?

Cardiovascular disease is a major public health challenge in the western world. Mortality of acute events has improved, but more patients develop HF – a condition affecting up to 22 million people worldwide. Cell transplantation is the first therapy to attempt replacement of lost cardiomyocytes and vasculature to restore lost contractile function. Since the first reported functional repair after injection of autologous skeletal myoblasts into the injured heart in 1998, a variety of cell types have been proposed for transplantation in different stages of cardiovascular disease. Fifteen years of preclinical research and the rapid move into clinical studies have left us with promising results and a better understanding of cells as a potential clinical tool. Cell-based cardiac repair has been the first step, but cardiac regeneration remains the more ambitious goal. Promising new cell types and the rapidly evolving concept of adult stem and progenitor cell fate may enable us to move towards regenerating viable and functional myocardium. Meeting a multidisciplinary consensus will be required to translate these findings into safe and applicable clinical tools.     

Cell and gene therapy for severe heart failure patients: The time and place for Pim-1 kinase

Regenerative therapy in severe heart failure patients presents a challenging set of circumstances including a damaged myocardial environment that accelerates senescence in myocytes and cardiac progenitor cells. Failing myocardium suffers from deterioration of contractile function coupled with impaired regenerative potential that drives the heart toward decompensation. Efficacious regenerative cell therapy for severe heart failure requires disruption of this vicious circle that can be accomplished by alteration of the compromised myocyte phenotype and rejuvenation of progenitor cells. This review focuses upon potential for Pim-1 kinase to mitigate chronic heart failure by improving myocyte quality through preservation of mitochondrial integrity, prevention of hypertrophy and inhibition of apoptosis. In addition, cardiac progenitors engineered with Pim-1 possess enhanced regenerative potential, making Pim-1 an important player in future treatment of severe heart failure.     

Cell‐based therapies for cardiac disease: a cellular therapist's perspective

Cell‐based therapy is an exciting, promising, and a developing new treatment for cardiac diseases. Stem cell–based therapies have the potential to fundamentally transform the treatment of ischemic cardiac injury and heart failure by achieving what would have been unthinkable only a few years ago—the Holy Grail of myocardial regeneration. Recent therapeutic approaches involve bone marrow (BM)‐derived mononuclear cells and their subsets such as mesenchymal stem/stromal cells (MSCs), endothelial progenitor cells as well as adipose tissue–derived MSCs, cardiac tissue–derived stem cells, and cell combinations. Clinical trials employing these cells have demonstrated that cellular therapy is feasible and safe. Regarding delivery methods, the safety of catheter‐based, transendocardial and ‐epicardial stem cell injection has been established. However, the results, while variable, suggest rather modest clinical efficacy overall in both heart failure and ischemic heart disease, such as in acute myocardial infarction. Future studies will focus on determining the most efficacious cell type(s) and/or cell combinations and the most reasonable indications and optimal timing of transplantation, as well as the mechanisms underlying their therapeutic effects. We will review and summarize the clinical trial results to date. In addition, we discuss challenges and operational issues in cell processing for cardiac applications.     

Secondary Sphere Formation Enhances the Functionality of Cardiac Progenitor Cells

Loss of cardiomyocytes impairs cardiac function after myocardial infarction (MI). Recent studies suggest that cardiac stem/progenitor cells could repair the damaged heart. However, cardiac progenitor cells are difficult to maintain in terms of purity and multipotency when propagated in two-dimensional culture systems. Here, we investigated a new strategy that enhances potency and enriches progenitor cells. We applied the repeated sphere formation strategy (cardiac explant → primary cardiosphere (CS) formation → sphere-derived cells (SDCs) in adherent culture condition → secondary CS formation by three-dimensional culture). Cells in secondary CS showed higher differentiation potentials than SDCs. When transplanted into the infarcted myocardium, secondary CSs engrafted robustly, improved left ventricular (LV) dysfunction, and reduced infarct sizes more than SDCs did. In addition to the cardiovascular differentiation of transplanted secondary CSs, robust vascular endothelial growth factor (VEGF) synthesis and secretion enhanced neovascularization in the infarcted myocardium. Microarray pathway analysis and blocking experiments using E-selectin knock-out hearts, specific chemicals, and small interfering RNAs (siRNAs) for each pathway revealed that E-selectin was indispensable to sphere initiation and ERK/Sp1/VEGF autoparacrine loop was responsible for sphere maturation. These results provide a simple strategy for enhancing cellular potency for cardiac repair. Furthermore, this strategy may be implemented to other types of stem/progenitor cell-based therapy.     

Mesenchymal stem cells overexpressing Akt dramatically repair infarcted myocardium and improve cardiac function despite infrequent cellular fusion or differentiation.

We previously reported that intramyocardial injection of bone marrow-derived mesenchymal stem cells overexpressing Akt (MSC-Akt) efficiently repaired infarcted rat myocardium and improved cardiac function. Controversy still exists over the mechanisms by which MSC contribute to tissue repair. Herein, we tested if cellular fusion of MSC plays a determinant role in cardiac repair. We injected MSC expressing Cre recombinase, with or without Akt, into Cre reporter mice. In these mice, LacZ is expressed only after Cre-mediated excision of a loxP-flanked stop signal and is indicative of fusion. MSC engraftment within infarcted myocardium was transient but significantly enhanced by Akt. MSC fusion with cardiomyocytes was observed as early as 3 days, but was infrequent, and we found a low rate of differentiation of MSC into cardiomyocytes. MSC-Akt decreased infarct size at 3 days and restored early cardiac function. In conclusion, MSC-Akt improved early repair despite transient engraftment, low levels of cellular fusion, and differentiation. These new observations further confirm our recently reported data that early paracrine mechanisms mediated by MSC are responsible for enhancing the survival of existing myocytes and that Akt could alter the secretion of various cytokines and growth factors.     

Cellular cardiomyoplasty: a new therapeutic approach for regenerating the myocardium

One of the most promising new therapeutic techniques for the augmentation and regeneration of the myocardium is cellular cardiomyoplasty. Reports from animal and clinical investigations indicate that the transplant of different cell types, such as autologous skeletal myoblasts and adult stem cells, into injured myocardium results in the generation of new cardiac myocytes and improvement in myocardial performance. Although there is no consensus with regard to the best cell type to transplant or the extent of myocardial renewal and regeneration, the technique of cardiac cellular myoplasty may become one of the most important advancements in the treatment of cardiovascular diseases such as myocardial infarction and heart failure.     

From cardiac repair to cardiac regeneration--ready to translate?

Cardiovascular disease is a major public health challenge in the western world. Mortality of acute events has improved, but more patients develop HF--a condition affecting up to 22 million people worldwide. Cell transplantation is the first therapy to attempt replacement of lost cardiomyocytes and vasculature to restore lost contractile function. Since the first reported functional repair after injection of autologous skeletal myoblasts into the injured heart in 1998, a variety of cell types have been proposed for transplantation in different stages of cardiovascular disease. Fifteen years of preclinical research and the rapid move into clinical studies have left us with promising results and a better understanding of cells as a potential clinical tool. Cell-based cardiac repair has been the first step, but cardiac regeneration remains the more ambitious goal. Promising new cell types and the rapidly evolving concept of adult stem and progenitor cell fate may enable us to move towards regenerating viable and functional myocardium. Meeting a multidisciplinary consensus will be required to translate these findings into safe and applicable clinical tools.     

Pretreatment with adult progenitor cells improves recovery and decreases native myocardial proinflammatory signaling after ischemia

Cardiogenic shock from myocardial ischemia is the leading cause of death of both men and women. Although adult progenitor cells have emerged as a potential therapy for heart disease, reports indicate that transplanted adult progenitor cells may not differentiate into heart muscle. We hypothesized that pretreatment with adult progenitor cells may protect myocardium from acute ischemic damage. Treatment immediately before an ischemic event removes the possibility that differentiation to heart muscle may account for the observed effects. In the present study, we determined that adult progenitor cells from three different sources (human bone marrow, rat bone marrow, and human adipose tissue) immediately protect native myocardium against ischemia and decrease myocardial proinflammatory and proapoptotic signaling. Postischemic recovery of adult progenitor cell-pretreated hearts was significantly better than that of control hearts. This was correlated with a 50% decrease in proinflammatory cytokine production. The use of a differentiated cell control had no such effect. Therefore, adult progenitor cell pretreatment improved postischemic myocardial function, decreased myocardial production of inflammatory mediators, and limited proapoptotic signaling. These results represent the first demonstration that pretreatment with progenitor cells is myocardial protective. These findings may not only have mechanistic implications regarding the benefit of progenitor cells but may also have clinical therapeutic implications before planned ischemic events.     

Cardiospheres and cardiosphere-derived cells as therapeutic agents following myocardial infarction

Heart disease is a major cause of morbidity and mortality. Cellular therapies hold significant promise for patients with heart disease. Heart-derived progenitor cells are capable of repairing a diseased heart through modulation of growth factor milieu and temporary engraftment leading to endogenous repair. The proof-of-concept CADUCEUS clinical trial using cardiosphere-derived cells has shown evidence of therapeutic cardiac tissue regeneration. Future clinical trials are now being planned to generate additional safety and efficacy data in the hopes of building toward an approved cellular therapy for heart disease.     

内皮祖细胞移植对犬心肌梗死后血管新生、心肌修复及心功能的影响

目的:本实验采用犬外周血血管内皮祖细胞(EPCs)体外扩增后,经皮穿刺行心肌梗死犬心外膜下移植,观察其对急性心肌梗死后心肌再生及心功能改变的影响。方法:犬自体EPCs体外扩增后,在超声引导下,经皮穿刺行心肌梗死犬心外膜下局部注射移植入心肌梗死区域,1、2、4、8周后取心肌标本,应用超声心动图检测心功能,应用TTC染色法检测梗死心肌面积及免疫组织化学方法检测梗死区血管密度。结果:自体血管内皮祖细胞移植1、2、4、8周后梗死区血管密度高于对照组(P<0.01),且随移植观察时间的延长,血管密度逐渐增加。移植1、2、4、8周后梗死心肌面积明显小于对照组(P<0.01),且随移植观察时间的延长,梗死心肌面积逐渐减少。内皮祖细胞移植组梗死心肌瘢痕边缘毛细血管密度明显高于对照组。内皮祖细胞移植组的左室射血分数较对照组明显提高(P<0.01),且随移植观察时间的延长,左室射血分数逐渐升高。结论:自体血管内皮祖细胞移植到心肌梗死犬缺血心肌后能分化为毛细血管内皮细胞,促进梗死后心肌血管新生及心肌修复,改善心功能。     

Progenitor/stem cell transplantation for repair of myocardial infarction: Hype or hope?

Despite significant therapeutic advances, heart failure remains the predominant cause of mortality worldwide. Currently, progenitor/stem cell biology holds great promise for a new era of cell-based therapy for salvaging the failing heart. However, the translational arm of progenitor/stem cell science is in a relatively primitive state. For the time being, the clinical trials have been both encouraging and disappointing. How to improve the engraftment, long-term survival and appropriate differentiation of transplanted progenitor/stem cell within the cardiovascular tissues may be the key issues to facilitate the transition of cardiogenic stem cell research from bench to bedside. In this review article we discuss the state-of-the-art in adult stem cell therapies for cardiovascular diseases and approaches to release cardiac regeneration potentials of progenitor/stem cells.     

Cardiac regeneration using human‐induced pluripotent stem cell‐derived biomaterial‐free 3D‐bioprinted cardiac patch in vivo

One of the leading causes of death worldwide is heart failure. Despite advances in the treatment and prevention of heart failure, the number of affected patients continues to increase. We have recently developed 3D‐bioprinted biomaterial‐free cardiac tissue that has the potential to improve cardiac function. This study aims to evaluate the in vivo regenerative potential of these 3D‐bioprinted cardiac patches. The cardiac patches were generated using 3D‐bioprinting technology in conjunction with cellular spheroids created from a coculture of human‐induced pluripotent stem cell‐derived cardiomyocytes, fibroblasts, and endothelial cells. Once printed and cultured, the cardiac patches were implanted into a rat myocardial infarction model (n = 6). A control group (n = 6) without the implantation of cardiac tissue patches was used for comparison. The potential for regeneration was measured 4 weeks after the surgery with histology and echocardiography. 4 weeks after surgery, the survival rates were 100% and 83% in the experimental and the control group, respectively. In the cardiac patch group, the average vessel counts within the infarcted area were higher than those within the control group. The scar area in the cardiac patch group was significantly smaller than that in the control group. (Figure S1 ) Echocardiography showed a trend of improvement of cardiac function for the experimental group, and this trend correlated with increased patch production of extracellular vesicles. 3D‐bioprinted cardiac patches have the potential to improve the regeneration of cardiac tissue and promote angiogenesis in the infarcted tissues and reduce the scar tissue formation.     

The Human Heart: A Self‐Renewing Organ

The dogma that the heart is a static organ which contains an irreplaceable population of cardiomyocytes prevailed in the cardiovascular field for the last several decades. However, the recent identification of progenitor cells that give rise to differentiated myocytes has prompted a re‐interpretation of cardiac biology. The heart cannot be viewed any longer as a postmitotic organ characterized by a predetermined number of myocytes that is defined at birth and is preserved throughout life. The myocardium constitutes a dynamic entity in which new young parenchymal cells are formed to substitute old damaged dying myocytes. The regenerative ability of the heart was initially documented with a classic morphometric approach and more recently with the demonstration that DNA synthesis, mitosis, and cytokinesis take place in the newly formed myocytes of the normal and pathologic heart. Importantly, replicating myocytes correspond to the differentiated progeny of cardiac stem cells. These findings point to the possibility of novel therapeutic strategies for the diseased heart.     

Cellular cardiac regenerative therapy in which patients?

Cell-based myocardial regenerative therapy is undergoing experimental and clinical trials in order to limit the consequences of decreased contractile function and compliance of damaged ventricles owing to ischemic and nonischemic myocardial diseases. A variety of myogenic and angiogenic cell types have been proposed, such as skeletal myoblasts, mononuclear and mesenchymal bone marrow cells, circulating blood-derived progenitors, adipose-derived stromal cells, induced pluripotent stem cells, umbilical cord cells, endometrial mesenchymal stem cells, adult testis pluripotent stem cells and embryonic cells. Current indications for stem cell therapy concern patients who have had a left- or right-ventricular infarction or idiopathic dilated cardiomyopathies. Other indications and potential applications include patients with diabetic cardiomyopathy, Chagas heart disease (American trypanosomiasis), ischemic mitral regurgitation, left ventricular noncompacted myocardium and pediatric cardiomyopathy. Suitable sources of cells for cardiac implant will depend on the types of diseases to be treated. For acute myocardial infarction, a cell that reduces myocardial necrosis and augments vascular blood flow will be desirable. For heart failure, cells that replace or promote myogenesis, reverse apoptopic mechanisms and reactivate dormant cell processes will be useful. It is important to note that stem cells are not an alternative to heart transplantation; selected patients should be in an early stage of heart failure as the goal of this regenerative approach is to avoid or delay organ transplantation. Since the cell niche provides crucial support needed for stem cell maintenance, the most interesting and realistic perspectives include the association of intramyocardial cell transplantation with tissue-engineered scaffolds and multisite cardiac pacing in order to transform a passive regenerative approach into a ‘dynamic cellular support’, a promising method for the creation of ‘bioartificial myocardium’.     

SIRS大鼠心肌葡萄糖6磷酸酶活性的测定和线粒体形态变化

目的：对大鼠全身炎症反应综合征（SIRS）阶段心肌细胞浆内参与葡萄代谢的酶活性进行研究,并观察心肌细胞线粒体形态结构,从酶学及亚细胞结构的角度深入了解SIRS时心肌能量代谢的改变。方法：（1）腹注射内毒素（LPS）20mg/kg,以直肠温度、心率、呼吸、血白细胞（WBC）、中性粒细胞数量及血肿瘤坏死因子－α（TNF－α,免疫组化法）含量变化作为SIRS的指标,制造大鼠SIRS的动物模型。（2）酶组织化学方法检测SIRS大鼠心肌细胞葡萄糖6－磷酸酶,图像分析进行半定时测定其活性的变化。（3）SIRS大鼠球后静脉丛取血测血糖。（4）SIRS大鼠心肌细胞的透射电镜观察。结果：（1）注射LPS后1小时大鼠心肌细胞葡萄糖6－磷酸酶活性较对照组明显增强,3小时后则明显减弱,差异性均显著（P均＜0．05）。（2）注射LPS1小时后血糖明显升高,3小时后降低。（3）透射电镜观察可见SIRS大鼠心肌细胞线粒增多,排列紊乱,出现空泡变性,肌纤维水肿。结论：SIRS时存在葡萄糖代谢紊乱及能量代谢障碍,可能为SIRS时MODS的发生的重要原因。     

自体骨骼肌卫星细胞移植治疗急性心肌梗死的研究

目的　研究自体骨骼肌卫星细胞 (SC)移植对心肌梗死的治疗作用。方法　雄性苏中幼猪 10头 ,随机分为实验组与对照组。实验组采用改良Dorfman法培养SC ,开胸结扎冠状动脉对角支制作急性心肌梗死模型。实验组心肌内注射种植体外扩增的自体SC ,对照组注射等量细胞培养液。通过心血池显像了解心功能变化 ,评估SC移植对心肌梗死的治疗作用。 4周后处死动物 ,取出心脏标本 ,通过病理形态学观察SC存活和分化情况。结果　SC呈梭形 ,贴壁生长 ,延迟分瓶或降低培养液中胎牛血清浓度 ,SC生长停滞 ,相互融合形成肌管 ;实验组梗死区内见新生的带横纹的肌纤维 ,排列方向大体一致 ,多核 ,核位于周边 ,细胞间未见闰盘样结构 ;实验组术后左室射血分数 (EF)、 1/3射血分数 (1/3EF)优于对照组。结论　SC易于获取和体外扩增培养 ,移植于自体心脏可存活并改善心功能。自体SC移植为缺血性心脏病的治疗提供了一条新的途径     

Toll4 (TLR4) expression in cardiac myocytes in normal and failing myocardium

Expression of innate immune response proteins, including IL-1beta, TNF, and the cytokine-inducible isoform of nitric oxide synthase (iNOS), have been documented in the hearts of humans and experimental animals with heart failure regardless of etiology, although the proximal events leading to their expression are unknown. Noting that expression of a human homologue of Drosophila Toll, a proximal innate immunity transmembrane signaling protein in the fly, now termed human Toll-like receptor 4 (hTLR4), appeared to be relatively high in the heart, we examined TLR4 mRNA and protein abundance in isolated cellular constituents of cardiac muscle and in normal and abnormal murine, rat, and human myocardium. TLR4 expression levels in cardiac myocytes and in coronary microvascular endothelial cells could be enhanced by either LPS or IL-1beta, an effect inhibited by the oxygen radical scavenger PDTC. Transfection of a constitutively active TLR4 construct, CD4/hTLR4, resulted in activation of a nuclear factor-kappaB reporter construct, but not of an AP-1 or an iNOS reporter construct, in cardiac myocytes. In normal murine, rat, and human myocardium, TLR4 expression was diffuse, and presumably cytoplasmic, in cardiac myocytes. However, in remodeling murine myocardium remote from sites of ischemic injury and in heart tissue from patients with idiopathic dilated cardiomyopathy, focal areas of intense TLR4 staining were observed in juxtaposed regions of 2 or more adjacent myocytes; this staining was not observed in control myocardium. Increased expression and signaling by TLR4, and perhaps other Toll homologues, may contribute to the activation of innate immunity in injured myocardium.     

Progress and prospects: cell based regenerative therapy for cardiovascular disease

Experimental and clinical studies are progressing simultaneously to investigate the mechanisms and efficacy of progenitor cell treatment after an acute myocardial infarction and in chronic congestive heart failure. Multipotent progenitor cells appear to be capable of improving cardiac perfusion and/or function; however, the mechanisms still are unclear, and the issue of whether or not trans-differentiation occurs remains unsettled. Both experimentally and clinically, cells originating from different tissues have been shown capable of restoring cardiac function, but more recently multiple groups have identified resident cardiac progenitor cells that seem to participate in regenerating the heart after injury. Clinically, cells originating from blood or bone marrow have been proven to be safe whereas injection of skeletal myoblasts has been associated with the occurrence of ventricular arrhythmias. Myoblasts can transform into rapidly beating myotubes; however, thus far convincing evidence for electro-mechanical coupling between myoblasts and cardiomyocytes is lacking. Moving forward, mechanistic studies will benefit from the use of genetic markers and Cre/lox reporter systems that are less prone to misinterpretation than fluorescent antibodies, and a more convincing answer regarding therapeutic efficacy will come from adequately powered randomized placebo controlled trials.