Cardiospheres and tissue engineering for myocardial regeneration: potential for clinical application

Tissue engineering is an increasingly expanding area of research in the cardiovascular field that involves engineering, chemistry, biology and medicine. Cardiac tissue engineering (CTE) aims to regenerate myocardial damage by combining cells, matrix, biological active molecules and physiological stimuli. The rationale behind CTE applications is that in order to regenerate the ventricular wall after a myocardial infarction it is necessary to combine procedures that regenerate both cardiomyocytes and the extracellular matrix. The application of (stem) cells together with a matrix could represent an environment protected from the inflammatory and pro-apoptotic signals, a stemness/survival reservoir slowly releasing cells and factors promoting tissue regeneration and angiogenesis. This review will focus on the applications and advantages that CTE application could offer compared to conventional cell therapy.     

Adaptive inflammatory microenvironment for cell-based regeneration in ischemic cardiovascular disease

Cell-based therapy has emerged to be a promising strategy for alleviating the heavy burden of ischemic cardiovascular disease for nearly two decades, despite a variety of pending questions about its availability and efficacy. One question is whether and how the cells behave for regeneration in vivo, which could be limited or potentiated by the inflammatory microenvironment following myocardial infarction or critical limb ischemia. To this end, we hypothesize that the “adaptive inflammatory microenvironment” is pertinent to the cell-based regeneration, and make a brief comment on it based upon recent evidence.     

Injectable cardiac tissue engineering for the treatment of myocardial infarction

Heart disease is a leading cause of morbidity and mortality worldwide. Myocardial infarction leads to permanent loss of cardiac tissue and ultimately heart failure. However, current therapies could only stall the progression of the disease. Thus, new therapies are needed to regenerate damaged hearts to overcome poor prognosis of patients with heart failure. The shortage of heart donors is also a factor for innovating new therapies. Although the cardiac performance by cell-based therapy has improved, unsatisfactory cell retention and transplant survival still plague this technique. Because biomaterials can improve the cell retention, survival and differentiation, cardiac tissue engineering is now being explored as an approach to support cell-based therapies and enhance their efficacy for cardiac disease. In the last decade, cardiac tissue engineering has made considerable progress. Among different kinds of approaches in the cardiac tissue engineering, the approach of injectable cardiac tissue engineering is more minimally invasive than that of in vitro engineered tissue or epicardial patch implantation. It is therefore clinically appealing. In this review, we strive to describe the major progress in the flied of injectable cardiac tissue engineering, including seeding cell sources, biomaterials and novel findings in preclinical studies and clinical applications. The remaining problems will also be discussed.     

Stem cell-biomaterial interactions for regenerative medicine

The synergism of stem cell biology and biomaterial technology promises to have a profound impact on stem-cell-based clinical applications for tissue regeneration. Biomaterials development is rapidly advancing to display properties that, in a precise and physiological fashion, could drive stem-cell fate both in vitro and in vivo. Thus, the design of novel materials is trying to recapitulate the molecular events involved in the production, clearance and interaction of molecules within tissue in pathologic conditions and regeneration of tissue/organs. In this review we will report on the challenges behind translating stem cell biology and biomaterial innovations into novel clinical therapeutic applications for tissue and organ replacements (graphical abstract).     

Bone repair with a form of BMP-2 engineered for incorporation into fibrin cell ingrowth matrices

Most growth factors naturally involved in development and regeneration demonstrate strong binding to the extracellular matrix and are retained there until being locally mobilized by cells. In spite of this feedback between cell activity and growth factor mobilization in the extracellular matrix, this approach has not been extensively explored in therapeutic situations. We present an engineered bone morphogenetic protein-2 (BMP-2) fusion protein that mimics such function in a surgically relevant matrix, fibrin, incorporated into the matrix until it is locally liberated by cell surface-associated proteases. A tripartite fusion protein, denoted TG-pl-BMP-2, was designed and produced recombinantly. An N-terminal transglutaminase substrate (TG) domain provides covalent attachment to fibrin during coagulation under the influence of the blood transglutaminase factor XIIIa. A central plasmin substrate (pl) domain provides a cleavage site for local release of the attached growth factor from the fibrin matrix under the influence of cell-activated plasmin. A C-terminal human BMP-2 domain provides osteogenic activity. TG-pl-BMP-2 in fibrin was evaluated in vivo in critical-size craniotomy defects in rats, where it induced 76% more defect healing with bone at 3 weeks with a dose of 1 mug/defect than wildtype BMP-2 in fibrin. After a dosing study in rabbits, the engineered growth factor in fibrin was evaluated in a prospective clinical study for pancarpal fusion in dogs, where it induced statistically faster and more extensive bone bridging than equivalent treatment with cancellous bone autograft. The strong healing response shown by fibrin including a bound BMP-2 variant suggests that with the combination of bound growth factor and ingrowth matrix, it may be possible to improve upon the natural growth factor and even upon tissue autograft.     

Local activation of cardiac stem cells for post‐myocardial infarction cardiac repair

The prognosis of patients with myocardial infarction (MI) and resultant chronic heart failure remains extremely poor despite continuous advancements in optimal medical therapy and interventional procedures. Animal experiments and clinical trials using adult stem cell therapy following MI have shown a global improvement of myocardial function. The emergence of stem cell transplantation approaches has recently represented promising alternatives to stimulate myocardial regeneration. Regarding their tissue‐specific properties, cardiac stem cells (CSCs) residing within the heart have advantages over other stem cell types to be the best cell source for cell transplantation. However, time‐consuming and costly procedures to expanse cells prior to cell transplantation and the reliability of cell culture and expansion may both be major obstacles in the clinical application of CSC‐based transplantation therapy after MI. The recognition that the adult heart possesses endogenous CSCs that can regenerate cardiomyocytes and vascular cells has raised the unique therapeutic strategy to reconstitute dead myocardium via activating these cells post‐MI. Several strategies, such as growth factors, mircoRNAs and drugs, may be implemented to potentiate endogenous CSCs to repair infarcted heart without cell transplantation. Most molecular and cellular mechanism involved in the process of CSC‐based endogenous regeneration after MI is far from understanding. This article reviews current knowledge opening up the possibilities of cardiac repair through CSCs activation in situ in the setting of MI.     

Injectable biodegradable hydrogels for embryonic stem cell transplantation: improved cardiac remodelling and function of myocardial infarction

In this study, an injectable, biodegradable hydrogel composite of oligo[poly(ethylene glycol) fumarate] (OPF) was investigated as a carrier of mouse embryonic stem cells (mESCs) for the treatment of myocardial infarction (MI). The OPF hydrogels were used to encapsulate mESCs. The cell differentiation in vitro over 14 days was determined via immunohistochemical examination. Then, mESCs encapsulated in OPF hydrogels were injected into the LV wall of a rat MI model. Detailed histological analysis and echocardiography were used to determine the structural and functional consequences after 4 weeks of transplantation. With ascorbic acid induction, mESCs could differentiate into cardiomyocytes and other cell types in all three lineages in the OPF hydrogel. After transplantation, both the 24-hr cell retention and 4-week graft size were significantly greater in the OPF + ESC group than that of the PBS + ESC group (P < 0.01). Four weeks after transplantation, OPF hydrogel alone significantly reduced the infarct size and collagen deposition and improved the cardiac function. The heart function and revascularization improved significantly, while the infarct size and fibrotic area decreased significantly in the OPF + ESC group compared with that of the PBS + ESC, OPF and PBS groups (P < 0.01). All treatments had significantly reduced MMP2 and MMP9 protein levels compared to the PBS control group, and the OPF + ESC group decreased most by Western blotting. Transplanted mESCs expressed cardiovascular markers. This study suggests the potential of a method for heart regeneration involving OPF hydrogels for stem cell encapsulation and transplantation.     

Recent advances in heart regeneration

Although cardiac stem cells (CSCs) and tissue engineering are very promising for cardiac regenerative medicine, studies with model organisms for heart regeneration will provide alternative therapeutic targets and opportunities. Here, we present a review on heart regeneration, with a particular focus on the most recent work in mouse and zebrafish. We attempt to summarize the recent progresses and bottlenecks of CSCs and tissue engineering for heart regeneration; and emphasize what we have learned from mouse and zebrafish regenerative models on discovering crucial genetic and epigenetic factors for stimulating heart regeneration; and speculate the potential application of these regenerative factors for heart failure. A brief perspective highlights several important and promising research directions in this exciting field. Birth Defects Research (Part C) 99:160–169, 2013. © 2013 Wiley Periodicals, Inc.     

From gristle to chondrocyte transplantation: treatment of cartilage injuries

This review addresses the progress in cartilage repair technology over the decades with an emphasis on cartilage regeneration with cell therapy. The most abundant cartilage is the hyaline cartilage that covers the surface of our joints and, due to avascularity, this tissue is unable to repair itself. The cartilage degeneration seen in osteoarthritis causes patient suffering and is a huge burden to society. The surgical approach to cartilage repair was non-existing until the 1950s when new surgical techniques emerged. The use of cultured cells for cell therapy started as experimental studies in the 1970s that developed over the years to a clinical application in 1994 with the introduction of the autologous chondrocyte transplantation technique (ACT). The technology is now spread worldwide and has been further refined by combining arthroscopic techniques with cells cultured on matrix (MACI technology). The non-regenerating hypothesis of cartilage has been revisited and we are now able to demonstrate cell divisions and presence of stem-cell niches in the joint. Furthermore, cartilage derived from human embryonic stem cells and induced pluripotent stem cells could be the base for new broader cell treatments for cartilage injuries and the future technology base for prevention and cure of osteoarthritis.     

Stem cell-based composite tissue constructs for regenerative medicine

A major task of contemporary medicine and dentistry is restoration of human tissues and organs lost to diseases and trauma. A decade-long intense effort in tissue engineering has provided the proof of concept for cell-based replacement of a number of individual tissues such as the skin, cartilage, and bone. Recent work in stem cell-based in vivo restoration of multiple tissue phenotypes by composite tissue constructs such as osteochondral and fibro-osseous grafts has demonstrated probable clues for bioengineered replacement of complex anatomical structures consisting of multiple cell lineages such as the synovial joint condyle, tendon-bone complex, bone-ligament junction, and the periodontium. Of greater significance is a tangible contribution by current attempts to restore the structure and function of multitissue structures using cell-based composite tissue constructs to the understanding of ultimate biological restoration of complex organs such as the kidney or liver. The present review focuses on recent advances in stem cell-based composite tissue constructs and attempts to outline challenges for the manipulation of stem cells in tailored biomaterials in alignment with approaches potentially utilizable in regenerative medicine of human tissues and organs.     

Immune regulatory targets of mesenchymal stromal cell exosomes/small extracellular vesicles in tissue regeneration

Mesenchymal stromal cell (MSC) therapies have demonstrated therapeutic efficacy in a wide-ranging array of tissue injury and disease indications. An important aspect of MSC-mediated therapeutic activities is immune modulation. Consistent with the concentration of MSC therapeutic potency in its secretion, a significant proportion of MSC immune potency resides in the small extracellular vesicles (sEVs) secreted by MSCs. These sEVs, which also include exosomes, carry a large cargo enriched in proteins with potent immunomodulatory activities. They have been reported to exert potent effects on humoral and cellular components of the immune system in vitro and in vivo, and may have the potential to support the diametrically opposite pro- and anti-inflammatory functions necessary for tissue repair and regeneration following injury. Following injury, pro-inflammatory activities are necessary to neutralize injury and remove dead or injured tissue, while anti-inflammatory activities to facilitate migration and proliferation of reparative cell types and to increase vascularization and nutrient supply are necessary to repair and regenerate new tissue. Therefore, a critical immunomodulatory requisite of MSC sEVs in tissue regeneration is the capacity to support the appropriate immune activities at the appropriate time. Here, we review how some of the immune regulatory targets of MSC sEVs could support the dynamic immunomodulatory activities during tissue repair and regeneration.     

Dentin regeneration based on tooth tissue engineering: A review

Missing or damaged teeth due to caries, genetic disorders, oral cancer, or infection may contribute to physical and mental impairment that reduces the quality of life. Despite major progress in dental tissue repair and those replacing missing teeth with prostheses, clinical treatments are not yet entirely satisfactory, as they do not regenerate tissues with natural teeth features. Therefore, much of the focus has centered on tissue engineering (TE) based on dental stem/progenitor cells to create bioengineered dental tissues. Many in vitro and in vivo studies have shown the use of cells in regenerating sections of a tooth or a whole tooth. Tooth tissue engineering (TTE), as a promising method for dental tissue regeneration, can form durable biological substitutes for soft and mineralized dental tissues. The cell-based TE approach, which directly seeds cells and bioactive components onto the biodegradable scaffolds, is currently the most potential method. Three essential components of this strategy are cells, scaffolds, and growth factors (GFs). This study investigates dentin regeneration after an injury such as caries using TE and stem/progenitor cell-based strategies. We begin by discussing about the biological structure of a dentin and dentinogenesis. The engineering of teeth requires knowledge of the processes that underlie the growth of an organ or tissue. Then, the three fundamental requirements for dentin regeneration, namely cell sources, GFs, and scaffolds are covered in the current study, which may ultimately lead to new insights in this field.     

Prospects for translational regenerative medicine

Translational medicine is an evolutional concept that encompasses the rapid translation of basic research for use in clinical disease diagnosis, prevention and treatment. It follows the idea "from bench to bedside and back", and hence relies on cooperation between laboratory research and clinical care. In the past decade, translational medicine has received unprecedented attention from scientists and clinicians and its fundamental principles have penetrated throughout biomedicine, offering a sign post that guides modern medical research toward a patient-centered focus. Translational regenerative medicine is still in its infancy, and significant basic research investment has not yet achieved satisfactory clinical outcomes for patients. In particular, there are many challenges associated with the use of cell- and tissue-based products for clinical therapies. This review summarizes the transformation and global progress in translational medicine over the past decade. The current obstacles and opportunities in translational regenerative medicine are outlined in the context of stem cell therapy and tissue engineering for the safe and effective regeneration of functional tissue. This review highlights the requirement for multi-disciplinary and inter-disciplinary cooperation to ensure the development of the best possible regenerative therapies within the shortest timeframe possible for the greatest patient benefit.     

心脏干/祖细胞与心肌损伤修复

细胞移植是一种有希望的组织再生的治疗手段.多种类型的细胞已经用于动物心 肌损伤的修复中,包括胚胎干细胞、胚胎和新生动物的心肌细胞、骨骼肌成肌细胞、 骨髓干细胞、脂肪来源的干细胞、可诱导的多能干细胞等.但是,这些用于移植的细胞 存在成活率低、在心脏局部存留少、与宿主心肌细胞不能整合和免疫排斥等问题,这 些问题限制了它们的应用.心脏自身存在的干细胞因为没有其他来源细胞存在的种种 问题,因而成为备受关注的治疗心肌梗死的种子细胞.但是,心脏干/祖细胞也有自身 弊端,包括干细胞群的细胞生物学或遗传学标志没有统一,在心肌中数量极少,体外 扩增能力有限等,因而限制了心脏干/祖细胞的有效应用.如何能有效动员和促进心脏 干/祖细胞增殖,依赖于人们对心脏干/祖细胞增殖、分化、归巢的调控机制,包括心 脏干/祖细胞修复损伤心肌的分子机制的深入了解.本文将就近年来在心脏再生领域中 ,心脏干/祖细胞的研究新进展进行综述.     

Application of mesenchymal stem cells in regenerative medicine: A new approach in modern medical science

Mesenchymal Stem Cells (MSCs) are non-hematopoietic and multipotent stem cells, which have been considered in regenerative medicine. These cells are easily separated from different sources, such as bone marrow (BM), umbilical cord (UC), adipose tissue (AT), and etc. MSCs have the differentiation capability into chondrocytes, osteocytes, and adipocytes; This differentiation potential along with the paracrine properties have made them a key choice for tissue repair. MSCs also have various advantages over other stem cells, which is why they have been extensively studied in recent years. The effectiveness of MSCs-based therapies depend on several factors, including differentiation status at the time of use, concentration per injection, delivery method, the used vehicle, and the nature and extent of the damage. Although, MSCs have emerged promising sources for regenerative medicine, there are potential risks regarding their safety in their clinical use, including tumorigenesis, lack of availability, aging, and sensitivity to toxic environments. In this study, we aimed to discuss how MSCs may be useful in treating defects and diseases. To this aim, we will review recent advances of MSCs action mechanisms in regenerative medicine, as well as the most recent clinical trials. We will also have a brief overview of MSCs resources, differences between their sources, culture conditions, extraction methods, and clinical application of MSCs in various fields of regenerative medicine.     

Irisin promotes cardiac progenitor cell-induced myocardial repair and functional improvement in infarcted heart

Irisin, a newly identified hormone and cardiokine, is critical for modulating body metabolism. New evidence indicates that irisin protects the heart against myocardial ischemic injury. However, whether irisin enhances cardiac progenitor cell (CPC)-induced cardiac repair remains unknown. This study examines the effect of irisin on CPC-induced cardiac repair when these cells are introduced into the infarcted myocardium. Nkx2.5⁺ CPC stable cells were isolated from mouse embryonic stem cells. Nkx2.5 ⁺ CPCs (0.5 × 10 ⁶) were reintroduced into the infarcted myocardium using PEGlylated fibrin delivery. The mouse myocardial infarction model was created by permanent ligation of the left anterior descending (LAD) artery. Nkx2.5 ⁺ CPCs were pretreated with irisin at a concentration of 5 ng/ml in vitro for 24 hr before transplantation. Myocardial functions were evaluated by echocardiographic measurement. Eight weeks after engraftment, Nkx2.5 ⁺ CPCs improved ventricular function as evident by an increase in ejection fraction and fractional shortening. These findings are concomitant with the suppression of cardiac hypertrophy and attenuation of myocardial interstitial fibrosis. Transplantation of Nkx2.5 ⁺ CPCs promoted cardiac regeneration and neovascularization, which were increased with the pretreatment of Nkx2.5 ⁺ CPCs with irisin. Furthermore, irisin treatment promoted myocyte proliferation as indicated by proliferative markers Ki67 and phosphorylated histone 3 and decreased apoptosis. Additionally, irisin resulted in a marked reduction of histone deacetylase 4 and increased p38 acetylation in cultured CPCs. These results indicate that irisin promoted Nkx2.5 ⁺ CPC-induced cardiac regeneration and functional improvement and that irisin serves as a novel therapeutic approach for stem cells in cardiac repair.