Optimizing cardiac repair and regeneration through activation of the endogenous cardiac stem cell compartment

Targeting the redox system for cardiovascular regeneration in aging

Cardiovascular aging presents a formidable challenge, as the aging process can lead to reduced cardiac function and heightened susceptibility to cardiovascular diseases. Consequently, there is an escalating, unmet medical need for innovative and effective cardiovascular regeneration strategies aimed at restoring and rejuvenating aging cardiovascular tissues. Altered redox homeostasis and the accumulation of oxidative damage play a pivotal role in detrimental changes to stem cell function and cellular senescence, hampering regenerative capacity in aged cardiovascular system. A mounting body of evidence underscores the significance of targeting redox machinery to restore stem cell self-renewal and enhance their differentiation potential into youthful cardiovascular lineages. Hence, the redox machinery holds promise as a target for optimizing cardiovascular regenerative therapies. In this context, we delve into the current understanding of redox homeostasis in regulating stem cell function and reprogramming processes that impact the regenerative potential of the cardiovascular system. Furthermore, we offer insights into the recent translational and clinical implications of redox-targeting compounds aimed at enhancing current regenerative therapies for aging cardiovascular tissues.

Transplantation of Skeletal Muscle-Derived Sca-1+/PW1+/Pax7- Interstitial Cells (PICs) Improves Cardiac Function and Attenuates Remodeling in Mice Subjected to Myocardial Infarction

We have previously shown that skeletal muscle-derived Sca-1+/PW1+/Pax7- interstitial cells (PICs) are multi-potent and enhance endogenous repair and regeneration. Here, we investigated the regenerative potential of PICs following intramyocardial transplantation in mice subjected to an acute myocardial infarction (MI). MI was induced through the ligation of the left anterior descending coronary artery in 8-week old male C57BL/6 mice. 5 × 105 eGFP-labelled PICs (MI + PICs; n = 7) or PBS (MI-PBS; n = 7) were injected intramyocardially into the border zone. Sham mice (n = 8) were not subjected to MI, or the transplantation of PICs or PBS. BrdU was administered via osmotic mini-pump for 14 days. Echocardiography was performed prior to surgery (baseline), and 1-, 3- and 6-weeks post-MI and PICs transplantation. Mice were sacrificed at 6 weeks post-MI + PICs transplantation, and heart sections were analysed for fibrosis, hypertrophy, engraftment, proliferation, and differentiation of PICs. A significant (p < 0.05) improvement in ejection fraction (EF) and fractional shortening was observed in the MI-PICs group, compared to MI + PBS group at 6-weeks post MI + PICs transplantation. Infarct size/fibrosis of the left ventricle significantly (p < 0.05) decreased in the MI-PICs group (14.0 ± 2.5%), compared to the MI-PBS group (32.8 ± 2.2%). Cardiomyocyte hypertrophy in the border zone significantly (p < 0.05) decreased in the MI-PICs group compared to the MI-PBS group (330.0 ± 28.5 µM2 vs. 543.5 ± 26.6 µm2), as did cardiomyocyte apoptosis (0.6 ± 0.9% MI-PICs vs. 2.8 ± 0.8% MI-PBS). The number of BrdU+ cardiomyocytes was significantly (p < 0.05) increased in the infarct/border zone of the MI-PICs group (7.0 ± 3.3%), compared to the MI-PBS group (1.7 ± 0.5%). The proliferation index (total BrdU+ cells) was significantly increased in the MI-PICs group compared to the MI-PBS group (27.0 ± 3.4% vs. 7.6 ± 1.0%). PICs expressed and secreted pro-survival and reparative growth factors, supporting a paracrine effect of PICs during recovery/remodeling. Skeletal muscle-derived PICs show significant reparative potential, attenuating cardiac remodelling following transplantation into the infarcted myocardium. PICs can be easily sourced from skeletal muscle and therefore show promise as a potential cell candidate for supporting the reparative and regenerative effects of cell therapies.

Myocardial regeneration protocols towards the routine clinical scenario: An unseemly path from bench to bedside

Heart failure secondary to cardiomyocyte loss and/or dysfunction is the number one killer worldwide. The field of myocardial regeneration with its far-reaching primary goal of cardiac remuscularization and its hard-to-accomplish translation from bench to bedside, has been filled with ups and downs, steps forward and steps backward, controversies galore and, unfortunately, scientific scandals. Despite the present morass in which cardiac remuscularization is stuck in, the search for clinically effective regenerative approaches remains keenly active. Starting with a concise overview of the still highly debated regenerative capacity of the adult mammalian heart, we focus on the main interventions, that have reached or are close to clinical use, critically discussing key findings, successes, and failures. Finally, some promising and innovative approaches for myocardial repair/regeneration still at the pre-clinical stage are discussed to offer a holistic view on the future of myocardial repair/regeneration for the prevention/management of heart failure in the clinical scenario.

FUNDING

This research was funded by Grants from the Ministry of University and Research PRIN2015 2015ZTT5KB_004; PRIN2017NKB2N4_005; PON-AIM - 1829805-2.

The Role of MSC Therapy in Attenuating the Damaging Effects of the Cytokine Storm Induced by COVID-19 on the Heart and Cardiovascular System

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) has led to 47 m infected cases and 1. 2 m (2.6%) deaths. A hallmark of more severe cases of SARS-CoV-2 in patients with acute respiratory distress syndrome (ARDS) appears to be a virally-induced over-activation or unregulated response of the immune system, termed a "cytokine storm," featuring elevated levels of pro-inflammatory cytokines such as IL-2, IL-6, IL-7, IL-22, CXCL10, and TNFα. Whilst the lungs are the primary site of infection for SARS-CoV-2, in more severe cases its effects can be detected in multiple organ systems. Indeed, many COVID-19 positive patients develop cardiovascular complications, such as myocardial injury, myocarditis, cardiac arrhythmia, and thromboembolism, which are associated with higher mortality. Drug and cell therapies targeting immunosuppression have been suggested to help combat the cytokine storm. In particular, mesenchymal stromal cells (MSCs), owing to their powerful immunomodulatory ability, have shown promise in early clinical studies to avoid, prevent or attenuate the cytokine storm. In this review, we will discuss the mechanistic underpinnings of the cytokine storm on the cardiovascular system, and how MSCs potentially attenuate the damage caused by the cytokine storm induced by COVID-19. We will also address how MSC transplantation could alleviate the long-term complications seen in some COVID-19 patients, such as improving tissue repair and regeneration.

Cardiac Stem Cell-Loaded Delivery Systems: A New Challenge for Myocardial Tissue Regeneration

Cardiovascular disease (CVD) remains the leading cause of death in Western countries. Post-myocardial infarction heart failure can be considered a degenerative disease where myocyte loss outweighs any regenerative potential. In this scenario, regenerative biology and tissue engineering can provide effective solutions to repair the infarcted failing heart. The main strategies involve the use of stem and progenitor cells to regenerate/repair lost and dysfunctional tissue, administrated as a suspension or encapsulated in specific delivery systems. Several studies demonstrated that effectiveness of direct injection of cardiac stem cells (CSCs) is limited in humans by the hostile cardiac microenvironment and poor cell engraftment; therefore, the use of injectable hydrogel or pre-formed patches have been strongly advocated to obtain a better integration between delivered stem cells and host myocardial tissue. Several approaches were used to refine these types of constructs, trying to obtain an optimized functional scaffold. Despite the promising features of these stem cells’ delivery systems, few have reached the clinical practice. In this review, we summarize the advantages, and the novelty but also the current limitations of engineered patches and injectable hydrogels for tissue regenerative purposes, offering a perspective of how we believe tissue engineering should evolve to obtain the optimal delivery system applicable to the everyday clinical scenario.

Unravelling the Biology of Adult Cardiac Stem Cell-Derived Exosomes to Foster Endogenous Cardiac Regeneration and Repair

Cardiac remuscularization has been the stated goal of the field of regenerative cardiology since its inception. Along with the refreshment of lost and dysfunctional cardiac muscle cells, the field of cell therapy has expanded in scope encompassing also the potential of the injected cells as cardioprotective and cardio-reparative agents for cardiovascular diseases. The latter has been the result of the findings that cell therapies so far tested in clinical trials exert their beneficial effects through paracrine mechanisms acting on the endogenous myocardial reparative/regenerative potential. The endogenous regenerative potential of the adult heart is still highly debated. While it has been widely accepted that adult cardiomyocytes (CMs) are renewed throughout life either in response to wear and tear and after injury, the rate and origin of this phenomenon are yet to be clarified. The adult heart harbors resident cardiac/stem progenitor cells (CSCs/CPCs), whose discovery and characterization were initially sufficient to explain CM renewal in response to physiological and pathological stresses, when also considering that adult CMs are terminally differentiated cells. The role of CSCs in CM formation in the adult heart has been however questioned by some recent genetic fate map studies, which have been proved to have serious limitations. Nevertheless, uncontested evidence shows that clonal CSCs are effective transplantable regenerative agents either for their direct myogenic differentiation and for their paracrine effects in the allogeneic setting. In particular, the paracrine potential of CSCs has been the focus of the recent investigation, whereby CSC-derived exosomes appear to harbor relevant regenerative and reparative signals underlying the beneficial effects of CSC transplantation. This review focuses on recent advances in our knowledge about the biological role of exosomes in heart tissue homeostasis and repair with the idea to use them as tools for new therapeutic biotechnologies for "cell-less" effective cardiac regeneration approaches.

Isolation, Characterization and Differentiation of Mouse Cardiac Progenitor Cells

Despite several strategies developed for replenishing the dead myocardium after myocardial infarction (MI), stem cell therapy remains the leading method to regenerate new myocardium. Although induced pluripotent stem cells (iPS) and transdifferentiation of the differentiated cells have been used as novel approaches for myocardial regeneration, these approaches did not yield very successful results for myocardial regeneration in in vivo studies. Asynchronous contractility of newly formed cardiomyocytes with the existing cardiomyocytes is the most important issue with iPS approach, while very low yield of transdifferentiated cardiomyocytes and their less chances to beat in the same rhythm as existing cardiomyocytes in the MI heart are important caveats with transdifferentiation approach. CSCs are present in the heart and they have the potential to differentiate into myocardial cells. However, the number of resident CSCs is very low. Therefore, it is important to get maximum yield of CSCs during isolation process from the heart. Increasing the number of CSCs and initiating their differentiation ex vivo are crucial for CSC-based stem cell therapy. Here, we present a better method for isolation, characterization and differentiation of CSCs from the mouse heart. We also demonstrated morphological changes in the CSCs after 2 days, 3 days, and 7 days in maintenance medium and a separate group of CSCs cultured for 12 days in differentiation medium using Phase-Contrast microscopy. We have used different markers for identification of CSCs isolated from the mouse heart such as marker for mouse CSC, Sca-1, cardiac-specific markers NKX2-5, MEF2C, GATA4, and stemness markers OCT4 and SOX2. To characterize the differentiated CSCs, we used CSCs maintained in differentiation medium for 12 days. To evaluate differentiation of CSCs, we determined the expression of cardiomyocyte-specific markers actinin and troponin I. Overall; we described an elegant method for isolation, identification, differentiation and characterization of CSCs from the mouse heart.

Combining cell and gene therapy to advance cardiac regeneration

INTRODUCTION

The characterization of multipotent endogenous cardiac stem cells (eCSCs) and the breakthroughs of somatic cell reprogramming to boost cardiomyocyte replacement have fostered the prospect of achieving functional heart repair/regeneration.

AREAS COVERED

Allogeneic CSC therapy through its paracrine stimulation of the endogenous resident reparative/regenerative process produces functional meaningful myocardial regeneration in pre-clinical porcine myocardial infarction models and is currently tested in the first-in-man human trial. The in vivo test of somatic reprogramming and cardioregenerative non-coding RNAs revived the interest in gene therapy for myocardial regeneration. The latter, together with the advent of genome editing, has prompted most recent efforts to produce genetically-modified allogeneic CSCs that secrete cardioregenerative factors to optimize effective myocardial repair.

EXPERT OPINION

The current war against heart failure epidemics in western countries seeks to find effective treatments to set back the failing hearts prolonging human lifespan. Off-the-shelf allogeneic-genetically-modified CSCs producing regenerative agents are a novel and evolving therapy set to be affordable, safe, effective and available at all times for myocardial regeneration to either prevent or treat heart failure.

Transplantation of Allogeneic PW1pos/Pax7neg Interstitial Cells Enhance Endogenous Repair of Injured Porcine Skeletal Muscle

•

Allogeneic PICs express and secrete an array of pro-regenerative paracrine factors that stimulate a regenerative response in a preclinical muscle injury model applicable to humans.

•

Paracrine factors secreted by allogeneic PICs stimulate endogenous progenitor cell activation and differentiation, leading to accelerated and improved myofiber regeneration and microvessel formation.

•

Allogeneic PICs survive long enough to exert their action before being cleared by the host immune system. Therefore, the cells transplanted are allogeneic but the regeneration is completely autologous.

•

Administration of HGF and IGF-1 improves skeletal muscle regeneration, but not to the same extent as PIC transplantation.

Skeletal muscle-derived PW1^pos/Pax7^neg interstitial cells (PICs) express and secrete a multitude of proregenerative growth factors and cytokines. Utilizing a porcine preclinical skeletal muscle injury model, delivery of allogeneic porcine PICs (pPICs) significantly improved and accelerated myofiber regeneration and neocapillarization, compared with saline vehicle control-treated muscles. Allogeneic pPICs did not contribute to new myofibers or capillaries and were eliminated by the host immune system. In conclusion, allogeneic pPIC transplantation stimulated the endogenous stem cell pool to bring about enhanced autologous skeletal muscle repair and regeneration. This allogeneic cell approach is considered a cost-effective, easy to apply, and readily available regenerative therapeutic strategy.

Exosomal miRNAs in Heart Disease

Micro-RNAs (miRNAs) are small noncoding RNAs involved in the posttranscriptional regulation of gene expression. Exosomes have recently emerged as novel elements of intercellular communication in the cardiovascular system. Exosomal miRNAs could be key players in intercellular cross-talk, particularly during different diseases such as myocardial infarction (MI) and heart failure (HF). This review addresses the functional role played by exosomal miRNAs in heart disease and their potential use as new biomarkers.

Calcific Aortic Valve Disease: Part 2-Morphomechanical Abnormalities, Gene Reexpression, and Gender Effects on Ventricular Hypertrophy and Its Reversibility

In part 1, we considered cytomolecular mechanisms underlying calcific aortic valve disease (CAVD), hemodynamics, and adaptive feedbacks controlling pathological left ventricular hypertrophy provoked by ensuing aortic valvular stenosis (AVS). In part 2, we survey diverse signal transduction pathways that precede cellular/molecular mechanisms controlling hypertrophic gene expression by activation of specific transcription factors that induce sarcomere replication in-parallel. Such signaling pathways represent potential targets for therapeutic intervention and prevention of decompensation/failure. Hypertrophy provoking signals, in the form of dynamic stresses and ligand/effector molecules that bind to specific receptors to initiate the hypertrophy, are transcribed across the sarcolemma by several second messengers. They comprise intricate feedback mechanisms involving gene network cascades, specific signaling molecules encompassing G protein-coupled receptors and mechanotransducers, and myocardial stresses. Future multidisciplinary studies will characterize the adaptive/maladaptive nature of the AVS-induced hypertrophy, its gender- and individual patient-dependent peculiarities, and its response to surgical/medical interventions. They will herald more effective, precision medicine treatments.

Accelerating skin wound healing by M-CSF through generating SSEA-1 and -3 stem cells in the injured sites

Wound healing is a complicated process requiring the collaborative efforts of different cell lineages. Our recent studies have found that one subset of hematopoietic cells can be induced to dedifferentiate into multipotent stem cells by means of a proliferating fibroblast releasable factor, M-CSF. Understanding the importance of stem cells on skin wound healing, here we evaluate the biological significance of M-CSF on skin wound healing. In an in vivo mouse skin excisional wound model, we found that SSEA-positive stem cells were present in wounded but not normal skin. After isolating skin cells from either normal or wounded skin by collagenase digestion, and analyzing the SSEA-1 positive cells by flow cytometry, we found a significant increase in the number of SSEA-1 positive cells in wounded skin. Topical application of M-CSF in skin wounds accelerated healing remarkably, while application of M-CSF-neutralizing antibody slowed wound healing. Furthermore, injection of EGFP-labeled hematopoietic cell-derived stem cells generated from M-CSF treated splenocytes resulted in EGFP-labeled cells being enriched in the skin wound site and further differentiated into functional organ-specific cells. Together, these data demonstrated that M-CSF makes a significant contribution to the healing process by inducing hematopoietic cell dedifferentiation into stem cells.

Controlled Release of Collagen-Binding SDF-1α Improves Cardiac Function after Myocardial Infarction by Recruiting Endogenous Stem Cells

Stromal cell-derived factor-1α (SDF-1α) is a well-characterized chemokine that mobilizes stem cells homing to the ischemic heart, which is beneficial for cardiac regeneration. However, clinically administered native SDF-1α diffuses quickly, thus decreasing its local concentration, and results in side effects. Thus, a controlled release system for SDF-1α is required to produce an effective local concentration in the ischemic heart. In this study, we developed a recombinant chemokine, consisting of SDF-1α and a collagen-binding domain, which retains both the SDF-1α and collagen-binding activity (CBD-SDF-1α). In an in vitro assay, CBD-SDF-1α could specifically bind to a collagen gel and achieve sustained release. An intramyocardial injection of CBD-SDF-1α after acute myocardial infarction demonstrated that the protein was largely tethered in the ischemic area and that controlled release had been achieved. Furthermore, CBD-SDF-1α enhanced the recruitment of c-kit positive (c-kit⁺) stem cells, increased capillary density and improved cardiac function, whereas NAT-SDF-1α had no such beneficial effects. Our findings demonstrate that CBD-SDF-1α can specifically bind to collagen and achieve controlled release both in vitro and in vivo. Local delivery of this protein could mobilize endogenous stem cells homing to the ischemic heart and improve cardiac function after myocardial infarction.

Systems-based technologies in profiling the stem cell molecular framework for cardioregenerative medicine

Over the last decade, advancements in stem cell biology have yielded a variety of sources for stem cell-based cardiovascular investigation. Stem cell behavior, whether to maintain its stable state of pluripotency or to prime toward the cardiovascular lineage is governed by a set of coordinated interactions between epigenetic, transcriptional, and translational mechanisms. The science of incorporating genes (genomics), RNA (transcriptomics), proteins (proteomics), and metabolites (metabolomics) data in a specific biological sample is known as systems biology. Integrating systems biology in progression with stem cell biologics can contribute to our knowledge of mechanisms that underlie pluripotency maintenance and guarantee fidelity of cardiac lineage specification. This review provides a brief summarization of OMICS-based strategies including transcriptomics, proteomics, and metabolomics used to understand stem cell fate and to outline molecular processes involved in heart development. Additionally, current efforts in cardioregeneration based on the "one-size-fits-all" principle limit the potential of individualized therapy in regenerative medicine. Here, we summarize recent studies that introduced systems biology into cardiovascular clinical outcomes analysis, allowing for predictive assessment for disease recurrence and patient-specific therapeutic response.

Cellular and molecular characterization of human cardiac stem cells reveals key features essential for their function and safety

Cell therapy of heart diseases is emerging as one of the most promising known treatments in recent years. Transplantation of cardiac stem cells (CSCs) may be one of the best strategies to cure adult or pediatric heart diseases. As these patient-derived stem cells need to be isolated from small heart biopsies, it is important to select the best isolation method and CSC subpopulation with the best cardiogenic functionality. We employed three different protocols including c-KIT(+) cell sorting, clonogenic expansion, and explants culture to isolate c-KIT(+) cells, clonogenic expansion-derived cells (CEDCs), and cardiosphere-derived cells (CDCs), respectively. Evaluation of isolated CSC characteristics in vitro and after rat myocardial infarction (MI) model transplantation revealed that although c-KIT(+) and CDCs had higher MI regenerative potential, CEDCs had more commitment into cardiomyocytes and needed lower passages that were essential to reach a definite cell count. Furthermore, genome-wide expression analysis showed that subsequent passages caused changes in characteristics of cells, downregulation of cell cycle-related genes, and upregulation of differentiation and carcinogenic genes, which might lead to senescence, commitment, and possible tumorigenicity of the cells. Because of different properties of CSC subpopulations, we suggest that appropriate CSCs subpopulation should be chosen based on their experimental or clinical use.

Delayed administration of allogeneic cardiac stem cell therapy for acute myocardial infarction could ameliorate adverse remodeling: experimental study in swine

Background

The optimal timing of cardiac stem cells administration is still unclear. We assessed the safety of same-day and delayed (one week) delivery and the possible influence of the timing on the therapeutic outcomes of allogeneic porcine cardiac stem cells administration after acute myocardial infarction in a closed-chest ischemia-reperfusion model.

Methods

Female swine surviving 90 min occlusion of the mid left anterior descending coronary artery received an intracoronary injection of 25x10⁶ porcine cardiac stem cells either two hours (n = 5, D0) or 7 days (n = 6, D7) after reperfusion. Controls received intracoronary injection of vehicle on day 7 (n = 6, CON). Safety was defined in terms of absence of major cardiac events, changes to the ECG during injection, post-administration coronary flow assessed using the TIMI scale and cardiac troponin I determination after the intervention. Cardiac Magnetic Resonance was performed for morphological and functional assessment prior to infarction, before injection (D7 and CON groups only), at one and 10 weeks. Samples were taken from the infarct and transition areas for pathological examination.

Results

No major adverse cardiac events were seen during injection in any group. Animals receiving the therapy on the same day of infarction (D0 group) showed mild transient ST changes during injection (n = 4) and, in one case, slightly compromised coronary flow (TIMI 2). Cardiac function parameters and infarct sizes were not significantly different between groups, with a trend towards higher ejection fraction in the treated groups. Ventricular volumes indexed to body surface area increased over time in control animals, and decreased by the end of the study in animals receiving the therapy, significantly so when comparing End Diastolic Volume between CON and D7 groups (CON: 121.70 ml/m² ± 26.09 ml/m², D7: 98.71 ml/m² ± 8.30 ml/m², p = 0.037). The treated groups showed less organization of the collagenous scar, and a significantly (p = 0.019) higher amount of larger, more mature vessels at the infarct border.

Conclusions

The intracoronary injection of 25x10⁶ allogeneic cardiac stem cells is generally safe, both early and 7 days after experimental infarction, and alleviates myocardial dysfunction, with a greater limitation of left ventricular remodeling when performed at one week.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0512-2) contains supplementary material, which is available to authorized users.

Iron oxide nanoparticle-mediated development of cellular gap junction crosstalk to improve mesenchymal stem cells' therapeutic efficacy for myocardial infarction

Electrophysiological phenotype development and paracrine action of mesenchymal stem cells (MSCs) are the critical factors that determine the therapeutic efficacy of MSCs for myocardial infarction (MI). In such respect, coculture of MSCs with cardiac cells has windowed a platform for cardiac priming of MSCs. Particularly, active gap junctional crosstalk of MSCs with cardiac cells in coculture has been known to play a major role in the MSC modification through coculture. Here, we report that iron oxide nanoparticles (IONPs) significantly augment the expression of connexin 43 (Cx43), a gap junction protein, of cardiomyoblasts (H9C2), which would be critical for gap junctional communication with MSCs in coculture for the generation of therapeutic potential-improved MSCs. MSCs cocultured with IONP-harboring H9C2 (cocultured MSCs: cMSCs) showed active cellular crosstalk with H9C2 and displayed significantly higher levels of electrophysiological cardiac biomarkers and a cardiac repair-favorable paracrine profile, both of which are responsible for MI repair. Accordingly, significantly improved animal survival and heart function were observed upon cMSC injection into rat MI models compared with the injection of unmodified MSCs. The present study highlights an application of IONPs in developing gap junctional crosstalk among the cells and generating cMSCs that exceeds the reparative potentials of conventional MSCs. On the basis of our finding, the potential application of IONPs can be extended in cell biology and stem cell-based therapies.

The non-coding road towards cardiac regeneration

Our understanding of cardiovascular disease has evolved rapidly, leading to a number of treatments that have improved patient quality of life and mortality rates. However, there is still no cure for heart failure. This has led to the pursuit of cardiac regeneration to prevent, and ultimately cure, this debilitating condition. To this end, several approaches have been proposed, including activation of cardiomyocyte proliferation, activation of endogenous or exogenous stem/progenitor cells, delivery of de novo cardiomyocytes, and in situ direct reprogramming of cardiac fibroblasts. While these different methodologies are currently being intensely investigated, there are still a number of caveats limiting their application in the clinic. Given the emerging regulatory potential of non-coding RNAs for controlling diverse cellular processes, these molecules may offer potential solutions in this pursuit of cardiac regeneration. In this concise review, we discuss the potential role of non-coding RNAs in a variety of different cardiac regenerative approaches.

Adult stem cells and cardiac regeneration

There is worldwide demand for therapies to promote the robust repair and regeneration with maximum regain of function of particular tissues and organs damaged by disease or injury. The potential role of adult stem cells has been highlighted by an increasing number of in vitro and in vivo studies. Nowhere is this more evident than in adult stem cell-based therapies being explored to promote cardiac regeneration. In spite of encouraging advances, significant challenges remain.

Porcine skeletal muscle-derived multipotent PW1pos/Pax7neg interstitial cells: isolation, characterization, and long-term culture

Developing effective strategies for the regeneration of solid tissue requires an understanding of the biology underlying the tissue's endogenous repair mechanisms. PW1/Peg3(pos)/Pax7(neg) skeletal muscle-derived interstitial progenitor cells (PICs) were first identified recently in the interstitium of murine skeletal muscle and shown to contribute to muscle fiber regeneration in vivo. PICs, therefore, represent a novel candidate resident progenitor cell for muscle regeneration. To explore the potential of these cells for clinical translation, we must ascertain the presence of PICs in larger mammalian species and identify criteria to successfully isolate and expand this population. In this study, we report the isolation, characterization, and maintenance of multipotent PICs from juvenile porcine skeletal muscle. We show that porcine PICs can be reproducibly isolated from skeletal muscle, express stem/progenitor cell markers, and have a stable phenotype and karyotype through multiple passages. Furthermore, porcine PICs are clonogenic and multipotent, giving rise to skeletal myoblast/myotubes, smooth muscle, and endothelial cells. In addition, PICs can be induced to differentiate into cardiomyocyte-like cells. These results demonstrate, in an animal model with size and physiology extrapolatable to the human, that porcine skeletal muscle-derived PW1(pos)/Pax7(neg) PICs are a source of stem/progenitor cells. These findings open new avenues for a variety of solid tissue engineering and regeneration using a single multipotent stem cell type isolated from an easily accessible source, such as skeletal muscle.

Concise review: heart regeneration and the role of cardiac stem cells

Acute myocardial infarction leads to irreversible loss of cardiac myocytes, thereby diminishing the pump function of the heart. As a result, the strenuous workload imposed on the remaining cardiac myocytes often gives rise to subsequent cell loss until the vicious circle ends in chronic heart failure (CHF). Thus, we are in need of a therapy that could ameliorate or even reverse the disease progression of CHF. Endogenous regeneration of the mammalian heart has been shown in the neonatal heart, and the discovery that it may still persist in adulthood sparked hope for novel cardioregenerative therapies. As the basis for cardiomyocyte renewal, multipotent cardiac stem/progenitor cells (CSCs) that reside in the heart have been shown to differentiate into cardiac myocytes, smooth muscle cells, and vascular endothelial cells. These CSCs do have the potential to actively regenerate the heart but clearly fail to do so after abundant and segmental loss of cells, such as what occurs with myocardial infarction. Therefore, it is vital to continue research for the most optimal therapy based on the use or in situ stimulation of these CSCs. In this review, we discuss the current status of the cardioregenerative field. In particular, we summarize the current knowledge of CSCs as the regenerative substrate in the adult heart and their use in preclinical and clinical studies to repair the injured myocardium.

Current stem cell delivery methods for myocardial repair

Heart failure commonly results from an irreparable damage due to cardiovascular diseases (CVDs), the leading cause of morbidity and mortality in the United States. In recent years, the rapid advancements in stem cell research have garnered much praise for paving the way to novel therapies in reversing myocardial injuries. Cell types currently investigated for cellular delivery include embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and adult stem cell lineages such as skeletal myoblasts, bone-marrow-derived stem cells (BMSCs), mesenchymal stem cells (MSCs), and cardiac stem cells (CSCs). To engraft these cells into patients' damaged myocardium, a variety of approaches (intramyocardial, transendocardial, transcoronary, venous, intravenous, intracoronary artery and retrograde venous administrations and bioengineered tissue transplantation) have been developed and explored. In this paper, we will discuss the pros and cons of these delivery modalities, the current state of their therapeutic potentials, and a multifaceted evaluation of their reported clinical feasibility, safety, and efficacy. While the issues of optimal delivery approach, the best progenitor stem cell type, the most effective dose, and timing of administration remain to be addressed, we are highly optimistic that stem cell therapy will provide a clinically viable option for myocardial regeneration.