Expandable Cardiovascular Progenitor Cells Reprogrammed from Fibroblasts

Exosomes derived from induced cardiopulmonary progenitor cells alleviate acute lung injury in mice

Cardiopulmonary progenitor cells (CPPs) constitute a minor subpopulation of cells that are commonly associated with heart and lung morphogenesis during embryonic development but completely subside after birth. This fact offers the possibility for the treatment of pulmonary heart disease (PHD), in which the lung and heart are both damaged. A reliable source of CPPs is urgently needed. In this study, we reprogrammed human cardiac fibroblasts (HCFs) into CPP-like cells (or induced CPPs, iCPPs) and evaluated the therapeutic potential of iCPP-derived exosomes for acute lung injury (ALI). iCPPs were created in passage 3 primary HCFs by overexpressing GLI1, WNT2, ISL1 and TBX5 (GWIT). Exosomes were isolated from the culture medium of passage 6-8 GWIT-iCPPs. A mouse ALI model was established by intratracheal instillation of LPS. Four hours after LPS instillation, ALI mice were treated with GWIT-iCPP-derived exosomes (5 × 109, 5 × 1010 particles/mL) via intratracheal instillation. We showed that GWIT-iCPPs could differentiate into cell lineages, such as cardiomyocyte-like cells, endothelial cells, smooth muscle cells and alveolar epithelial cells, in vitro. Transcription analysis revealed that GWIT-iCPPs have potential for heart and lung development. Intratracheal instillation of iCPP-derived exosomes dose-dependently alleviated LPS-induced ALI in mice by attenuating lung inflammation, promoting endothelial function and restoring capillary endothelial cells and the epithelial cells barrier. This study provides a potential new method for the prevention and treatment of cardiopulmonary injury, especially lung injury, and provides a new cell model for drug screening.

Lineage Reprogramming: Genetic, Chemical, and Physical Cues for Cell Fate Conversion with a Focus on Neuronal Direct Reprogramming and Pluripotency Reprogramming

Although lineage reprogramming from one cell type to another is becoming a breakthrough technology for cell-based therapy, several limitations remain to be overcome, including the low conversion efficiency and subtype specificity. To address these, many studies have been conducted using genetics, chemistry, physics, and cell biology to control transcriptional networks, signaling cascades, and epigenetic modifications during reprogramming. Here, we summarize recent advances in cellular reprogramming and discuss future directions.

Strengthening cardiac therapy pipelines using human pluripotent stem cell-derived cardiomyocytes

Advances in hiPSC isolation and reprogramming and hPSC-CM differentiation have prompted their therapeutic application and utilization for evaluating potential cardiovascular safety liabilities. In this perspective, we showcase key efforts toward the large-scale production of hiPSC-CMs, implementation of hiPSC-CMs in industry settings, and recent clinical applications of this technology. The key observations are a need for traceable gender and ethnically diverse hiPSC lines, approaches to reduce cost of scale-up, accessible clinical trial datasets, and transparent guidelines surrounding the safety and efficacy of hiPSC-based therapies.

Fibroblast Reprogramming in Cardiac Repair

Cardiovascular disease is one of the major causes of death worldwide. Limited proliferative capacity of adult mammalian cardiomyocytes has prompted researchers to exploit regenerative therapy after myocardial injury, such as myocardial infarction, to attenuate heart dysfunction caused by such injury. Direct cardiac reprogramming is a recently emerged promising approach to repair damaged myocardium by directly converting resident cardiac fibroblasts into cardiomyocyte-like cells. The achievement of in vivo direct reprogramming of fibroblasts has been shown, by multiple laboratories independently, to improve cardiac function and mitigate fibrosis post-myocardial infarction, which holds great potential for clinical application. There have been numerous pieces of valuable work in both basic and translational research to enhance our understanding and continued refinement of direct cardiac reprogramming in recent years. However, there remain many challenges to overcome before we can truly take advantage of this technique to treat patients with ischemic cardiac diseases. Here, we review recent progress of fibroblast reprogramming in cardiac repair, including the optimization of several reprogramming strategies, mechanistic exploration, and translational efforts, and we make recommendations for future research to further understand and translate direct cardiac reprogramming from bench to bedside. Challenges relating to these efforts will also be discussed.

Cardiomyocyte precursors generated by direct reprogramming and molecular beacon selection attenuate ventricular remodeling after experimental myocardial infarction

BACKGROUND

Direct cardiac reprogramming is currently being investigated for the generation of cells with a true cardiomyocyte (CM) phenotype. Based on the original approach of cardiac transcription factor-induced reprogramming of fibroblasts into CM-like cells, various modifications of that strategy have been developed. However, they uniformly suffer from poor reprogramming efficacy and a lack of translational tools for target cell expansion and purification. Therefore, our group has developed a unique approach to generate proliferative cells with a pre-CM phenotype that can be expanded in vitro to yield substantial cell doses.

METHODS

Cardiac fibroblasts were reprogrammed toward CM fate using lentiviral transduction of cardiac transcriptions factors (GATA4, MEF2C, TBX5, and MYOCD). The resulting cellular phenotype was analyzed by RNA sequencing and immunocytology. Live target cells were purified based on intracellular CM marker expression using molecular beacon technology and fluorescence-activated cell sorting. CM commitment was assessed using 5-azacytidine-based differentiation assays and the therapeutic effect was evaluated in a mouse model of acute myocardial infarction using echocardiography and histology. The cellular secretome was analyzed using mass spectrometry.

RESULTS

We found that proliferative CM precursor-like cells were part of the phenotype spectrum arising during direct reprogramming of fibroblasts toward CMs. These induced CM precursors (iCMPs) expressed CPC- and CM-specific proteins and were selectable via hairpin-shaped oligonucleotide hybridization probes targeting Myh6/7-mRNA-expressing cells. After purification, iCMPs were capable of extensive expansion, with preserved phenotype when under ascorbic acid supplementation, and gave rise to CM-like cells with organized sarcomeres in differentiation assays. When transplanted into infarcted mouse hearts, iCMPs prevented CM loss, attenuated fibrotic scarring, and preserved ventricular function, which can in part be attributed to their substantial secretion of factors with documented beneficial effect on cardiac repair.

CONCLUSIONS

Fibroblast reprogramming combined with molecular beacon-based cell selection yields an iCMP-like cell population with cardioprotective potential. Further studies are needed to elucidate mechanism-of-action and translational potential.

Cellular reprogramming of fibroblasts in heart regeneration

Myocardial infarction causes the loss of cardiomyocytes and the formation of cardiac fibrosis due to the activation of cardiac fibroblasts, leading to cardiac dysfunction and heart failure. Unfortunately, current therapeutic interventions can only slow the disease progression. Furthermore, they cannot fully restore cardiac function, likely because the adult human heart lacks sufficient capacity to regenerate cardiomyocytes. Therefore, intensive efforts have focused on developing therapeutics to regenerate the damaged heart. Several strategies have been intensively investigated, including stimulation of cardiomyocyte proliferation, transplantation of stem cell-derived cardiomyocytes, and conversion of fibroblasts into cardiac cells. Resident cardiac fibroblasts are critical in the maintenance of the structure and contractility of the heart. Fibroblast plasticity makes this type of cells be reprogrammed into many cell types, including but not limited to induced pluripotent stem cells, induced cardiac progenitor cells, and induced cardiomyocytes. Fibroblasts have become a therapeutic target due to their critical roles in cardiac pathogenesis. This review summarizes the reprogramming of fibroblasts into induced pluripotent stem cell-derived cardiomyocytes, induced cardiac progenitor cells, and induced cardiomyocytes to repair a damaged heart, outlines recent findings in utilizing fibroblast-derived cells for heart regeneration, and discusses the limitations and challenges.

Positive effect of miR-2392 on fibroblast to cardiomyocyte-like cell fate transition: an in silico and in vitro study

INTRODUCTION

Somatic cell fate transition is now gained great importance in tissue regeneration. Currently, research is focused on heart tissue regeneration by reprogramming diverse cells into cardiomyocyte-like cells. Here, we examined the possible effect of miRNAs on the transdifferentiation of fibroblasts into cardiomyocyte-like cells.

METHODS

First heart-specific miRNAs were identified by comparing the gene expression profiles of heart tissue to other body tissues using bioinformatic techniques. After identifying heart-specific miRNAs, their cellular and molecular functions were studied using the miRWalk and miRBase databases. Then the candidate miRNA was cloned into a lentiviral vector. Following, human dermal fibroblasts were cultured and treated with compounds forskolin, valproic acid, and CHIR99021. After 24 h, the lentivector harboring miRNA gene was transfected into the cells to initiate the transdifferentiation process. Finally, after a two-week treatment period, the efficiency of transdifferentiation was examined by inspecting the appearance of the cells and measuring the expression levels of cardiac genes and proteins using RT-qPCR and immunocytochemistry techniques.

RESULTS

Nine miRNAs were identified with higher expression in the heart. The miR-2392 was nominated as the candidate miRNA due to its function and specific expression in the heart. This miRNA has a direct connection with genes involved in cell growth and differentiation; e.g., MAPK and Wnt signaling pathways. According to in vitro results cardiac genes and proteins demonstrated an increase in expression in the fibroblasts that simultaneously received the three chemicals and miR-2392.

CONCLUSION

Considering the ability of miR-2392 to induce the expression of cardiac genes and proteins in fibroblast cells, it can induce fibroblasts to differentiate into cardiomyocyte-like cells. Therefore, miR-2392 could be further optimized for cardiomyocyte regeneration, tissue repair, and drug design studies.

Direct Reprogramming of Resident Non-Myocyte Cells and Its Potential for In Vivo Cardiac Regeneration

Cardiac diseases are the foremost cause of morbidity and mortality worldwide. The heart has limited regenerative potential; therefore, lost cardiac tissue cannot be replenished after cardiac injury. Conventional therapies are unable to restore functional cardiac tissue. In recent decades, much attention has been paid to regenerative medicine to overcome this issue. Direct reprogramming is a promising therapeutic approach in regenerative cardiac medicine that has the potential to provide in situ cardiac regeneration. It consists of direct cell fate conversion of one cell type into another, avoiding transition through an intermediary pluripotent state. In injured cardiac tissue, this strategy directs transdifferentiation of resident non-myocyte cells (NMCs) into mature functional cardiac cells that help to restore the native tissue. Over the years, developments in reprogramming methods have suggested that regulation of several intrinsic factors in NMCs can help to achieve in situ direct cardiac reprogramming. Among NMCs, endogenous cardiac fibroblasts have been studied for their potential to be directly reprogrammed into both induced cardiomyocytes and induced cardiac progenitor cells, while pericytes can transdifferentiate towards endothelial cells and smooth muscle cells. This strategy has been indicated to improve heart function and reduce fibrosis after cardiac injury in preclinical models. This review summarizes the recent updates and progress in direct cardiac reprogramming of resident NMCs for in situ cardiac regeneration.

Gene-Edited Human-Induced Pluripotent Stem Cell Lines to Elucidate DAND5 Function throughout Cardiac Differentiation

(1) Background: The contribution of gene-specific variants for congenital heart disease, one of the most common congenital disabilities, is still far from our complete understanding. Here, we applied a disease model using human-induced pluripotent stem cells (hiPSCs) to evaluate the function of DAND5 on human cardiomyocyte (CM) differentiation and proliferation. (2) Methods: Taking advantage of our DAND5 patient-derived iPSC line, we used CRISPR-Cas9 gene-editing to generate a set of isogenic hiPSCs (DAND5-corrected and DAND5 full-mutant). The hiPSCs were differentiated into CMs, and RT-qPCR and immunofluorescence profiled the expression of cardiac markers. Cardiomyocyte proliferation was analysed by flow cytometry. Furthermore, we used a multi-electrode array (MEA) to study the functional electrophysiology of DAND5 hiPSC-CMs. (3) Results: The results indicated that hiPSC-CM proliferation is affected by DAND5 levels. Cardiomyocytes derived from a DAND5 full-mutant hiPSC line are more proliferative when compared with gene-corrected hiPSC-CMs. Moreover, parallel cardiac differentiations showed a differential cardiac gene expression profile, with upregulated cardiac progenitor markers in DAND5-KO hiPSC-CMs. Microelectrode array (MEA) measurements demonstrated that DAND5-KO hiPSC-CMs showed prolonged field potential duration and increased spontaneous beating rates. In addition, conduction velocity is reduced in the monolayers of hiPSC-CMs with full-mutant genotype. (4) Conclusions: The absence of DAND5 sustains the proliferation of hiPSC-CMs, which alters their electrophysiological maturation properties. These results using DAND5 hiPSC-CMs consolidate the findings of the in vitro and in vivo mouse models, now in a translational perspective. Altogether, the data will help elucidate the molecular mechanism underlying this human heart disease and potentiates new therapies for treating adult CHD.

The dynamic cellular landscape of grafts with acute rejection after heart transplantation

BACKGROUND

Acute cellular rejection (ACR) is a major barrier to the long-term survival of cardiac allografts. Although immune cells are well known to play critical roles in ACR, the dynamic cellular landscape of allografts with ACR remains obscure.

METHODS

Single-cell RNA sequencing (scRNA-seq) was carried out for mouse cardiac allografts with ACR. Bioinformatic analysis was performed, and subsequent transplant experiments were conducted to validate the findings.

RESULTS

Despite an overall large depletion of cardiac fibroblasts (CFBs), highly expanded cytotoxic T lymphocytes and a CXCL10+Gbp2+ subcluster of CFBs were enriched within grafts at the late stage. CXCL10+Gbp2+ CFBs featured strong interferon responsiveness and high expression of chemokines and major histocompatibility complex molecules, implying their involvement in the recruitment and activation of immune cells. Cell‒cell communication analysis revealed that CXCL9/CXCL10-CXCR3 might contribute to regulating CXCL10+Gbp2+ CFB-induced chemotaxis and immune cell recruitment. In vivo transplant studies revealed the therapeutic potential of CXCR3 antagonism in transplant rejection.

CONCLUSIONS

The findings of our study unveiled a novel CFB subcluster that might mediate acute cardiac rejection. Targeting CXCR3 could prolong allograft survival.

Updated Perspectives on Direct Vascular Cellular Reprogramming and Their Potential Applications in Tissue Engineered Vascular Grafts

Cardiovascular disease is a globally prevalent disease with far-reaching medical and socio-economic consequences. Although improvements in treatment pathways and revascularisation therapies have slowed disease progression, contemporary management fails to modulate the underlying atherosclerotic process and sustainably replace damaged arterial tissue. Direct cellular reprogramming is a rapidly evolving and innovative tissue regenerative approach that holds promise to restore functional vasculature and restore blood perfusion. The approach utilises cell plasticity to directly convert somatic cells to another cell fate without a pluripotent stage. In this narrative literature review, we comprehensively analyse and compare direct reprogramming protocols to generate endothelial cells, vascular smooth muscle cells and vascular progenitors. Specifically, we carefully examine the reprogramming factors, their molecular mechanisms, conversion efficacies and therapeutic benefits for each induced vascular cell. Attention is given to the application of these novel approaches with tissue engineered vascular grafts as a therapeutic and disease-modelling platform for cardiovascular diseases. We conclude with a discussion on the ethics of direct reprogramming, its current challenges, and future perspectives.

Generation of expandable cardiovascular progenitor cells from mouse and human fibroblasts via direct chemical reprogramming

Here, we present a protocol to reprogram mouse and human fibroblasts into expandable cardiovascular progenitor cells (CPCs) via a defined small-molecule treatment. We describe steps to prepare fibroblasts and generate the chemically induced CPCs (ciCPCs), followed by expansion and differentiation of the ciCPCs. These cells can self-renew in the long term, faithfully retaining the CPC phenotype and cardiovascular differentiation capacity. This protocol provides an autologous and expandable cardiovascular cell source, which may find uses in cardiovascular disease modelling, drug discovery, and cardiac cell therapy. For complete details on the use and execution of this protocol, please refer to Wang et al. (2022).¹.

Advances in Cellular Reprogramming-Based Approaches for Heart Regenerative Repair

Continuous loss of cardiomyocytes (CMs) is one of the fundamental characteristics of many heart diseases, which eventually can lead to heart failure. Due to the limited proliferation ability of human adult CMs, treatment efficacy has been limited in terms of fully repairing damaged hearts. It has been shown that cell lineage conversion can be achieved by using cell reprogramming approaches, including human induced pluripotent stem cells (hiPSCs), providing a promising therapeutic for regenerative heart medicine. Recent studies using advanced cellular reprogramming-based techniques have also contributed some new strategies for regenerative heart repair. In this review, hiPSC-derived cell therapeutic methods are introduced, and the clinical setting challenges (maturation, engraftment, immune response, scalability, and tumorigenicity), with potential solutions, are discussed. Inspired by the iPSC reprogramming, the approaches of direct cell lineage conversion are merging, such as induced cardiomyocyte-like cells (iCMs) and induced cardiac progenitor cells (iCPCs) derived from fibroblasts, without induction of pluripotency. The studies of cellular and molecular pathways also reveal that epigenetic resetting is the essential mechanism of reprogramming and lineage conversion. Therefore, CRISPR techniques that can be repurposed for genomic or epigenetic editing become attractive approaches for cellular reprogramming. In addition, viral and non-viral delivery strategies that are utilized to achieve CM reprogramming will be introduced, and the therapeutic effects of iCMs or iCPCs on myocardial infarction will be compared. After the improvement of reprogramming efficiency by developing new techniques, reprogrammed iCPCs or iCMs will provide an alternative to hiPSC-based approaches for regenerative heart therapies, heart disease modeling, and new drug screening.

Advances in lncRNAs from stem cell-derived exosome for the treatment of cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of mortality globally. Benefiting from the advantages of early diagnosis and precision medicine, stem cell-based therapies have emerged as promising treatment options for CVDs. However, autologous or allogeneic stem cell transplantation imposes a potential risk of immunological rejection, infusion toxicity, and oncogenesis. Fortunately, exosome can override these limitations. Increasing evidence has demonstrated that long non-coding RNAs (lncRNAs) in exosome from stem cell paracrine factors play critical roles in stem cell therapy and participate in numerous regulatory processes, including transcriptional silencing, transcriptional activation, chromosome modification, and intranuclear transport. Accordingly, lncRNAs can treat CVDs by directly acting on specific signaling pathways. This mini review systematically summarizes the key regulatory actions of lncRNAs from different stem cells on myocardial aging and apoptosis, ischemia-reperfusion injury, retinopathy, atherosclerosis, and hypertension. In addition, the current challenges and future prospects of lncRNAs treatment for CVDs are discussed.

Phenotypic screen identifies FOXO inhibitor to counteract maturation and promote expansion of human iPS cell-derived cardiomyocytes

Achieving pharmacological control over cardiomyocyte proliferation represents a prime goal in therapeutic cardiovascular research. Here, we identify a novel chemical tool compound for the expansion of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes. The forkhead box O (FOXO) inhibitor AS1842856 was identified as a significant hit from an unbiased proliferation screen in early, immature hiPSC- cardiomyocytes (eCMs). The mitogenic effects of AS1842856 turned out to be robust, dose-dependent, sustained, and reversible. eCM numbers increased >30-fold as induced by AS1842856 over three passages. Phenotypically as well as by marker gene expression, the compound interestingly appeared to counteract cellular maturation both in immature hiPSC-CMs as well as in more advanced ones. Thus, FOXO inhibitor AS1842856 presents a novel proliferation inducer for the chemically defined, xeno-free expansion of hiPSC-derived CMs, while its de-differentiation effect might as well bear potential in regenerative medicine.

The Art of Reprogramming for Regenerative Medicine

Traditional pharmaceuticals in the forms of small chemical compounds or macromolecules such as proteins or RNAs have provided lifesaving solutions to many acute and chronic conditions to date. However, there are still many unmet medical needs, especially those of degenerative nature. The advent of cell-based therapy holds the promise to meet these challenges. In this review, we highlight a relatively new paradigm for generating or regenerating functional cells for replacement therapy against conditions such as type I diabetes, myocardial infarction, neurodegenerative diseases and liver fibrosis. We focus on the latest progresses in cellular reprogramming for generating diverse functional cell types. We will also discuss the mechanisms involved and conclude with likely general principles underlying reprogramming.

Reprogramming of fibroblasts into expandable cardiovascular progenitor cells via small molecules in xeno-free conditions

A major hurdle in cardiac cell therapy is the lack of a bona fide autologous stem-cell type that can be expanded long-term and has authentic cardiovascular differentiation potential. Here we report that a proliferative cell population with robust cardiovascular differentiation potential can be generated from mouse or human fibroblasts via a combination of six small molecules. These chemically induced cardiovascular progenitor cells (ciCPCs) self-renew long-term in fully chemically defined and xeno-free conditions, with faithful preservation of the CPC phenotype and of cardiovascular differentiation capacity in vitro and in vivo. Transplantation of ciCPCs into infarcted mouse hearts improved animal survival and cardiac function up to 13 weeks post-infarction. Mechanistically, activated fibroblasts revert to a plastic state permissive to cardiogenic signals, enabling their reprogramming into ciCPCs. Expanded autologous cardiovascular cells may find uses in drug discovery, disease modelling and cardiac cell therapy.

MicroRNA Roles in Cell Reprogramming Mechanisms

Cell reprogramming is a groundbreaking technology that, in few decades, generated a new paradigm in biomedical science. To date we can use cell reprogramming to potentially generate every cell type by converting somatic cells and suitably modulating the expression of key transcription factors. This approach can be used to convert skin fibroblasts into pluripotent stem cells as well as into a variety of differentiated and medically relevant cell types, including cardiomyocytes and neural cells. The molecular mechanisms underlying such striking cell phenotypes are still largely unknown, but in the last decade it has been proven that cell reprogramming approaches are significantly influenced by non-coding RNAs. Specifically, this review will focus on the role of microRNAs in the reprogramming processes that lead to the generation of pluripotent stem cells, neurons, and cardiomyocytes. As highlighted here, non-coding RNA-forced expression can be sufficient to support some cell reprogramming processes, and, therefore, we will also discuss how these molecular determinants could be used in the future for biomedical purposes.

CRISPR activation of endogenous genes reprograms fibroblasts into cardiovascular progenitor cells for myocardial infarction therapy

Fibroblasts can be reprogrammed into cardiovascular progenitor cells (CPCs) using transgenic approaches, although the underlying mechanism remains unclear. We determined whether activation of endogenous genes such as Gata4, Nkx2.5, and Tbx5 can rapidly establish autoregulatory loops and initiate CPC generation in adult extracardiac fibroblasts using a CRISPR activation system. The induced fibroblasts (>80%) showed phenotypic changes as indicated by an Nkx2.5 cardiac enhancer reporter. The progenitor characteristics were confirmed by colony formation and expression of cardiovascular genes. Cardiac sphere induction segregated the early and late reprogrammed cells that can generate functional cardiomyocytes and vascular cells in vitro. Therefore, they were termed CRISPR-induced CPCs (ciCPCs). Transcriptomic analysis showed that cell cycle and heart development pathways were important to accelerate CPC formation during the early reprogramming stage. The CRISPR system opened the silenced chromatin locus, thereby allowing transcriptional factors to access their own promoters and eventually forming a positive feedback loop. The regenerative potential of ciCPCs was assessed after implantation in mouse myocardial infarction models. The engrafted ciCPCs differentiated into cardiovascular cells in vivo but also significantly improved contractile function and scar formation. In conclusion, multiplex gene activation was sufficient to drive CPC reprogramming, providing a new cell source for regenerative therapeutics.

Protein and mRNA Quantification in Small Samples of Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes in 96-Well Microplates

We describe a method for protein quantification and for mRNA quantification in small sample quantities of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Demonstrated here is how the capillary-based protein detection system Wes™ by ProteinSimple and the Power SYBR™ Green Cells-to-CT™ Kit by Invitrogen can be applied to individual samples in a 96-well microplate format and thus made compatible with high-throughput (HT) cardiomyocyte assays. As an example of the usage, we illustrate that Cx43 protein and GJA1 mRNA levels in hiPSC-CMs are enhanced when the optogenetic actuator, channelrodopsin-2 (ChR2), is genetically expressed in them. Instructions are presented for cell culture and lysate preparations from hiPSC-CMs, along with optimized parameter settings and experimental protocol steps. Strategies to optimize primary antibody concentrations as well as ways for signal normalization are discussed, i.e., antibody multiplexing and total protein assay. The sensitivity of both the Wes and Cells-to-CT kit enables protein and mRNA quantification in a HT format, which is important when dealing with precious small samples. In addition to being able to handle small cardiomyocyte samples, these streamlined and semi-automated processes enable quick mechanistic analysis.

Pharmaceutical therapeutics for articular regeneration and restoration: state-of-the-art technology for screening small molecular drugs

Articular cartilage damage caused by sports injury or osteoarthritis (OA) has gained increased attention as a worldwide health burden. Pharmaceutical treatments are considered cost-effective means of promoting cartilage regeneration, but are limited by their inability to generate sufficient functional chondrocytes and modify disease progression. Small molecular chemical compounds are an abundant source of new pharmaceutical therapeutics for cartilage regeneration, as they have advantages in design, fabrication, and application, and, when used in combination, act as powerful tools for manipulating cellular fate. In this review, we present current achievements in the development of small molecular drugs for cartilage regeneration, particularly in the fields of chondrocyte generation and reversion of chondrocyte degenerative phenotypes. Several clinically or preclinically available small molecules, which have been shown to facilitate chondrogenesis, chondrocyte dedifferentiation, and cellular reprogramming, and subsequently ameliorate cartilage degeneration by targeting inflammation, matrix degradation, metabolism, and epigenetics, are summarized. Notably, this review introduces essential parameters for high-throughput screening strategies, including models of different chondrogenic cell sources, phenotype readout methodologies, and transferable advanced systems from other fields. Overall, this review provides new insights into future pharmaceutical therapies for cartilage regeneration.

Non-viral approaches for somatic cell reprogramming into cardiomyocytes

Heart disease is the leading cause of human deaths worldwide. Due to lacking cardiomyocytes with replicative capacity and cardiac progenitor cells with differentiation potential in adult hearts, massive loss of cardiomyocytes after ischemic events produces permanent damage, ultimately leading to heart failure. Cellular reprogramming is a promising strategy to regenerate heart by induction of cardiomyocytes from other cell types, such as cardiac fibroblasts. In contrast to conventional virus-based cardiac reprogramming, non-viral approaches greatly reduce the potential risk that includes disruption of genome integrity by integration of foreign DNAs, expression of exogenous genes with oncogenic potential, and appearance of partially reprogrammed cells harmful for the physiological functions of tissues/organs, which impedes their in-vivo applications. Here, we review the recent progress in development of non-viral approaches to directly reprogram somatic cells towards cardiomyocytes and their therapeutic application for heart regeneration.

Surfing the clinical trials of mesenchymal stem cell therapy in ischemic cardiomyopathy

While existing remedies failed to fully address the consequences of heart failure, stem cell therapy has been introduced as a promising approach. The present review is a comprehensive appraisal of the impacts of using mesenchymal stem cells (MSCs) in clinical trials mainly conducted on ischemic cardiomyopathy. The benefits of MSC therapy for dysfunctional myocardium are likely attributed to numerous secreted paracrine factors and immunomodulatory effects. The positive outcomes associated with MSC therapy are scar size reduction, reverse remodeling, and angiogenesis. Also, a decreasing in the level of chronic inflammatory markers of heart failure progression like TNF-α is observed. The intense inflammatory reaction in the injured myocardial micro-environment predicts a poor response of scar tissue to MSC therapy. Subsequently, the interval delay between myocardial injury and MSC therapy is not yet determined. The optimal requested dose of cells ranges between 100 to 150 million cells. Allogenic MSCs have different advantages compared to autogenic cells and intra-myocardial injection is the preferred delivery route. The safety and efficacy of MSCs-based therapy have been confirmed in numerous studies, however several undefined parameters like route of administration, optimal timing, source of stem cells, and necessary dose are limiting the routine use of MSCs therapeutic approach in clinical practice. Lastly, pre-conditioning of MSCs and using of exosomes mediated MSCs or genetically modified MSCs may improve the overall therapeutic effect. Future prospective studies establishing a constant procedure for MSCs transplantation are required in order to apply MSC therapy in our daily clinical practice and subsequently improving the overall prognosis of ischemic heart failure patients.

Small Molecules that Promote Self-Renewal of Stem Cells and Somatic Cell Reprogramming

The ground state of embryonic stem cells (ESCs) is closely related to the development of regenerative medicine. Particularly, long-term culture of ESCs in vitro, maintenance of their undifferentiated state, self-renewal and multi-directional differentiation ability is the premise of ESCs mechanism and application research. Induced pluripotent stem cells (iPSC) reprogrammed from mouse embryonic fibroblasts (MEF) cells into cells with most of the ESC characteristics show promise towards solving ethical problems currently facing stem cell research. However, integration into chromosomal DNA through viral-mediated genes may activate proto oncogenes and lead to risk of cancer of iPSC. At the same time, iPS induction efficiency needs to be further improved to reduce the use of transcription factors. In this review, we discuss small molecules that promote self-renewal and reprogramming, including growth factor receptor inhibitors, GSK-3β and histone deacetylase inhibitors, metabolic regulators, pathway modulators as well as EMT/MET regulation inhibitors to enhance maintenance of ESCs and enable reprogramming. Additionally, we summarize the mechanism of action of small molecules on ESC self-renewal and iPSC reprogramming. Finally, we will report on the progress in identification of novel and potentially effective agents as well as selected strategies that show promise in regenerative medicine. On this basis, development of more small molecule combinations and efficient induction of chemically induced pluripotent stem cell (CiPSC) is vital for stem cell therapy. This will significantly improve research in pathogenesis, individualized drug screening, stem cell transplantation, tissue engineering and many other aspects.

Transient reprogramming of postnatal cardiomyocytes to a dedifferentiated state

In contrast to mammals, lower vertebrates are capable of extraordinary myocardial regeneration thanks to the ability of their cardiomyocytes to undergo transient dedifferentiation and proliferation. Somatic cells can be temporarily reprogrammed to a proliferative, dedifferentiated state through forced expression of Oct3/4, Sox2, Klf4 and c-Myc (OSKM). Here, we aimed to induce transient reprogramming of mammalian cardiomyocytes in vitro utilising an OSKM-encoding non-integrating vector. Reprogramming factor expression in postnatal rat and mouse cardiomyocytes triggered rapid but limited cell dedifferentiation. Concomitantly, a significant increase in cell viability, cell cycle related gene expression and Ki67 positive cells was observed consistent with an enhanced cell cycle activation. The transient nature of this partial reprogramming was confirmed as cardiomyocyte-specific cell morphology, gene expression and contractile activity were spontaneously recovered by day 15 after viral transduction. This study provides the first evidence that adenoviral OSKM delivery can induce partial reprogramming of postnatal cardiomyocytes. Therefore, adenoviral mediated transient reprogramming could be a novel and feasible strategy to recapitulate the regenerative mechanisms of lower vertebrates.

Therapeutic effects of CXCR4+ subpopulation of transgene-free induced cardiosphere-derived cells on experimental myocardial infarction

Objectives

Myocardial infarction (MI) is the most predominant type of cardiovascular diseases with high mortality and morbidity. Stem cell therapy, especially cardiac progenitor cell therapy, has been proposed as a promising approach for cardiac regeneration and MI treatment. Previously, we have successfully generated cardiac progenitor‐like cells, induced cardiosphere (iCS), via somatic reprogramming. However, the genome integration characteristic of virus‐based reprogramming approach hampered their therapeutic applications due to the risk of tumour formation. In the current study, we aim to establish a safer iCS generation strategy with transgene‐free approaches.

Materials and Methods

Four transgene‐free approaches for somatic reprogramming, including episome, minicircle, self‐replicative RNA, and sendai virus, were compared, from the perspective of cardiac progenitor marker expression, iCS formation, and cardiac differentiation. The therapeutic effects were assessed in the mouse model of MI, from the perspective of survival rate, cardiac function, and structural alterations.

Results

The self‐replicative RNA approach produced more iCS, which had cardiomyocyte differentiation ability and therapeutic effects on the mouse model of MI with comparable levels with endogenous cardiospheres and iCS generated with retrovirus. In addition, the CXCR4 (C‐X‐C chemokine receptor 4) positive subpopulation of iCS derived cells (iCSDC) delivered by intravenous injection was found to have similar therapeutic effects with intramyocardial injection on the mouse model of MI, representing a safer delivery approach.

Conclusion

Thus, the optimized strategy for iCS generation is safer and has more therapeutic potentials.

Wnt Activation and Reduced Cell-Cell Contact Synergistically Induce Massive Expansion of Functional Human iPSC-Derived Cardiomyocytes

Modulating signaling pathways including Wnt and Hippo can induce cardiomyocyte proliferation in vivo. Applying these signaling modulators to human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) in vitro can expand CMs modestly (<5-fold). Here, we demonstrate massive expansion of hiPSC-CMs in vitro (i.e., 100- to 250-fold) by glycogen synthase kinase-3β (GSK-3β) inhibition using CHIR99021 and concurrent removal of cell-cell contact. We show that GSK-3β inhibition suppresses CM maturation, while contact removal prevents CMs from cell cycle exit. Remarkably, contact removal enabled 10 to 25 times greater expansion beyond GSK-3β inhibition alone. Mechanistically, persistent CM proliferation required both LEF/TCF activity and AKT phosphorylation but was independent from yes-associated protein (YAP) signaling. Engineered heart tissues from expanded hiPSC-CMs showed comparable contractility to those from unexpanded hiPSC-CMs, demonstrating uncompromised cellular functionality after expansion. In summary, we uncovered a molecular interplay that enables massive hiPSC-CM expansion for large-scale drug screening and tissue engineering applications.

Stem cell-based approaches in cardiac tissue engineering: controlling the microenvironment for autologous cells

Cardiovascular disease is one of the leading causes of mortality worldwide. Cardiac tissue engineering strategies focusing on biomaterial scaffolds incorporating cells and growth factors are emerging as highly promising for cardiac repair and regeneration. The use of stem cells within cardiac microengineered tissue constructs present an inherent ability to differentiate into cell types of the human heart. Stem cells derived from various tissues including bone marrow, dental pulp, adipose tissue and umbilical cord can be used for this purpose. Approaches ranging from stem cell injections, stem cell spheroids, cell encapsulation in a suitable hydrogel, use of prefabricated scaffold and bioprinting technology are at the forefront in the field of cardiac tissue engineering. The stem cell microenvironment plays a key role in the maintenance of stemness and/or differentiation into cardiac specific lineages. This review provides a detailed overview of the recent advances in microengineering of autologous stem cell-based tissue engineering platforms for the repair of damaged cardiac tissue. A particular emphasis is given to the roles played by the extracellular matrix (ECM) in regulating the physiological response of stem cells within cardiac tissue engineering platforms.

Cardiac Cell Therapy for Heart Repair: Should the Cells Be Left Out?

Cardiovascular disease (CVD) is still the leading cause of death worldwide. Coronary artery occlusion, or myocardial infarction (MI) causes massive loss of cardiomyocytes. The ischemia area is eventually replaced by a fibrotic scar. From the mechanical dysfunctions of the scar in electronic transduction, contraction and compliance, pathological cardiac dilation and heart failure develops. Once end-stage heart failure occurs, the only option is to perform heart transplantation. The sequential changes are termed cardiac remodeling, and are due to the lack of endogenous regenerative actions in the adult human heart. Regenerative medicine and biomedical engineering strategies have been pursued to repair the damaged heart and to restore normal cardiac function. Such strategies include both cellular and acellular products, in combination with biomaterials. In addition, substantial progress has been made to elucidate the molecular and cellular mechanisms underlying heart repair and regeneration. In this review, we summarize and discuss current therapeutic approaches for cardiac repair and provide a perspective on novel strategies that holding potential opportunities for future research and clinical translation.

The Future of Direct Cardiac Reprogramming: Any GMT Cocktail Variety?

Direct cardiac reprogramming has emerged as a novel therapeutic approach to treat and regenerate injured hearts through the direct conversion of fibroblasts into cardiac cells. Most studies have focused on the reprogramming of fibroblasts into induced cardiomyocytes (iCMs). The first study in which this technology was described, showed that at least a combination of three transcription factors, GATA4, MEF2C and TBX5 (GMT cocktail), was required for the reprogramming into iCMs in vitro using mouse cells. However, this was later demonstrated to be insufficient for the reprogramming of human cells and additional factors were required. Thereafter, most studies have focused on implementing reprogramming efficiency and obtaining fully reprogrammed and functional iCMs, by the incorporation of other transcription factors, microRNAs or small molecules to the original GMT cocktail. In this respect, great advances have been made in recent years. However, there is still no consensus on which of these GMT-based varieties is best, and robust and highly reproducible protocols are still urgently required, especially in the case of human cells. On the other hand, apart from CMs, other cells such as endothelial and smooth muscle cells to form new blood vessels will be fundamental for the correct reconstruction of damaged cardiac tissue. With this aim, several studies have centered on the direct reprogramming of fibroblasts into induced cardiac progenitor cells (iCPCs) able to give rise to all myocardial cell lineages. Especially interesting are reports in which multipotent and highly expandable mouse iCPCs have been obtained, suggesting that clinically relevant amounts of these cells could be created. However, as of yet, this has not been achieved with human iCPCs, and exactly what stage of maturity is appropriate for a cell therapy product remains an open question. Nonetheless, the major concern in regenerative medicine is the poor retention, survival, and engraftment of transplanted cells in the cardiac tissue. To circumvent this issue, several cell pre-conditioning approaches are currently being explored. As an alternative to cell injection, in vivo reprogramming may face fewer barriers for its translation to the clinic. This approach has achieved better results in terms of efficiency and iCMs maturity in mouse models, indicating that the heart environment can favor this process. In this context, in recent years some studies have focused on the development of safer delivery systems such as Sendai virus, Adenovirus, chemical cocktails or nanoparticles. This article provides an in-depth review of the in vitro and in vivo cardiac reprograming technology used in mouse and human cells to obtain iCMs and iCPCs, and discusses what challenges still lie ahead and what hurdles are to be overcome before results from this field can be transferred to the clinical settings.

Strategies and Challenges to Improve Cellular Programming-Based Approaches for Heart Regeneration Therapy

Limited adult cardiac cell proliferation after cardiovascular disease, such as heart failure, hampers regeneration, resulting in a major loss of cardiomyocytes (CMs) at the site of injury. Recent studies in cellular reprogramming approaches have provided the opportunity to improve upon previous techniques used to regenerate damaged heart. Using these approaches, new CMs can be regenerated from differentiation of iPSCs (similar to embryonic stem cells), the direct reprogramming of fibroblasts [induced cardiomyocytes (iCMs)], or induced cardiac progenitors. Although these CMs have been shown to functionally repair infarcted heart, advancements in technology are still in the early stages of development in research laboratories. In this review, reprogramming-based approaches for generating CMs are briefly introduced and reviewed, and the challenges (including low efficiency, functional maturity, and safety issues) that hinder further translation of these approaches into a clinical setting are discussed. The creative and combined optimal methods to address these challenges are also summarized, with optimism that further investigation into tissue engineering, cardiac development signaling, and epigenetic mechanisms will help to establish methods that improve cell-reprogramming approaches for heart regeneration.

A nitric oxide-releasing hydrogel for enhancing the therapeutic effects of mesenchymal stem cell therapy for hindlimb ischemia

Therapeutic angiogenesis with mesenchymal stem cells (MSCs) is promising for the clinical treatment of peripheral artery disease (PAD). However, the heterogeneous proangiogenic nature of MSCs is a key challenge in developing more effective treatments with MSCs for therapeutic angiogenesis purposes. Here, we propose to enhance the therapeutic function of human placenta-derived MSCs (hP-MSCs) in hindlimb ischemia therapy by using nitric oxide (NO)-releasing chitosan hydrogel (CS-NO). Our data showed that the co-transplantation of CS-NO hydrogel with hP-MSCs remarkably improved the grafting of hP-MSCs and ameliorated the functional recovery of ischemic hindlimbs. Moreover, we found that the neovascularization of damaged hindlimbs was significantly increased after co-transplanting CS-NO hydrogel and hP-MSCs, as confirmed by bioluminescence imaging (BLI). Further analysis revealed an endothelial-like status transformation of hP-MSCs in the presence of NO, which was identified as a potential mechanism contributing to the enhanced endothelium-protective and proangiogenic capacities of hP-MSCs that promote angiogenesis in mouse models of hindlimb ischemia. In conclusion, this study provides a promising approach for using NO hydrogel to improve the proangiogenic potency of MSCs in ischemic diseases, and the strategy used here facilitates the development of controlled-release scaffolds for enhancing the therapeutic efficiency of MSCs in angiogenic therapy. STATEMENT OF SIGNIFICANCE: The heterogeneous proangiogenic nature of mesenchymal stem cells (MSCs) is a key challenge in developing more effective treatments with MSCs for therapeutic angiogenesis purposes. In this study, we investigated whether nitric oxide (NO)-releasing chitosan hydrogel (CS-NO) could improve the proangiogenic potency of MSCs in ischemic diseases. Our results revealed an endothelial-like status transformation of human placenta-derived MSCs (hP-MSCs) in the presence of NO, which was identified as a potential mechanism contributing to the enhanced endothelium-protective and proangiogenic capacities of hP-MSCs that promote angiogenesis in mouse models of hindlimb ischemia. The strategy for enhancing the pro-angiogenic activity of MSCs with biomaterials provides a practical idea for overcoming the challenges associated with the clinical application of MSCs in therapeutic angiogenesis.

Cells, Materials, and Fabrication Processes for Cardiac Tissue Engineering

Cardiovascular disease is the number one killer worldwide, with myocardial infarction (MI) responsible for approximately 1 in 6 deaths. The lack of endogenous regenerative capacity, added to the deleterious remodelling programme set into motion by myocardial necrosis, turns MI into a progressively debilitating disease, which current pharmacological therapy cannot halt. The advent of Regenerative Therapies over 2 decades ago kick-started a whole new scientific field whose aim was to prevent or even reverse the pathological processes of MI. As a highly dynamic organ, the heart displays a tight association between 3D structure and function, with the non-cellular components, mainly the cardiac extracellular matrix (ECM), playing both fundamental active and passive roles. Tissue engineering aims to reproduce this tissue architecture and function in order to fabricate replicas able to mimic or even substitute damaged organs. Recent advances in cell reprogramming and refinement of methods for additive manufacturing have played a critical role in the development of clinically relevant engineered cardiovascular tissues. This review focuses on the generation of human cardiac tissues for therapy, paying special attention to human pluripotent stem cells and their derivatives. We provide a perspective on progress in regenerative medicine from the early stages of cell therapy to the present day, as well as an overview of cellular processes, materials and fabrication strategies currently under investigation. Finally, we summarise current clinical applications and reflect on the most urgent needs and gaps to be filled for efficient translation to the clinical arena.

Modeling Cardiac Disease Mechanisms Using Induced Pluripotent Stem Cell-Derived Cardiomyocytes: Progress, Promises and Challenges

Cardiovascular diseases (CVDs) are a class of disorders affecting the heart or blood vessels. Despite progress in clinical research and therapy, CVDs still represent the leading cause of mortality and morbidity worldwide. The hallmarks of cardiac diseases include heart dysfunction and cardiomyocyte death, inflammation, fibrosis, scar tissue, hyperplasia, hypertrophy, and abnormal ventricular remodeling. The loss of cardiomyocytes is an irreversible process that leads to fibrosis and scar formation, which, in turn, induce heart failure with progressive and dramatic consequences. Both genetic and environmental factors pathologically contribute to the development of CVDs, but the precise causes that trigger cardiac diseases and their progression are still largely unknown. The lack of reliable human model systems for such diseases has hampered the unraveling of the underlying molecular mechanisms and cellular processes involved in heart diseases at their initial stage and during their progression. Over the past decade, significant scientific advances in the field of stem cell biology have literally revolutionized the study of human disease in vitro. Remarkably, the possibility to generate disease-relevant cell types from induced pluripotent stem cells (iPSCs) has developed into an unprecedented and powerful opportunity to achieve the long-standing ambition to investigate human diseases at a cellular level, uncovering their molecular mechanisms, and finally to translate bench discoveries into potential new therapeutic strategies. This review provides an update on previous and current research in the field of iPSC-driven cardiovascular disease modeling, with the aim of underlining the potential of stem-cell biology-based approaches in the elucidation of the pathophysiology of these life-threatening diseases.

Iron overload inhibits self-renewal of human pluripotent stem cells via DNA damage and generation of reactive oxygen species

Iron overload affects the cell cycle of various cell types, but the effect of iron overload on human pluripotent stem cells has not yet been reported. Here, we show that the proliferation capacities of human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) were significantly inhibited by ferric ammonium citrate (FAC) in a concentration‐dependent manner. In addition, deferoxamine protected hESCs/hiPSCs against FAC‐induced cell‐cycle arrest. However, iron overload did not affect pluripotency in hESCs/hiPSCs. Further, treatment of hiPSCs with FAC resulted in excess reactive oxygen species production and DNA damage. Collectively, our findings provide new insights into the role of iron homeostasis in the maintenance of self‐renewal in human pluripotent stem cells.

Stem cell therapy of myocardial infarction: a promising opportunity in bioengineering

Myocardial infarction (MI) is a life-threatening disease resulting from irreversible death of cardiomyocytes (CMs) and weakening of the heart blood-pumping function. Stem cell-based therapies have been studied for MI treatment over the last two decades with promising outcome. In this review, we critically summarize the past work in this field to elucidate the advantages and disadvantages of treating MI using pluripotent stem cells (PSCs) including both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), adult stem cells, and cardiac progenitor cells. The main advantage of the latter is their cytokine production capability to modulate immune responses and control the progression of healing. However, human adult stem cells have very limited (if not 'no') capacity to differentiate into functional CMs in vitro or in vivo. In contrast, PSCs can be differentiated into functional CMs although the protocols for the cardiac differentiation of PSCs are mainly for adherent cells under 2D culture. Derivation of PSC-CMs in 3D, allowing for large-scale production of CMs via modulation of the Wnt/β-catenin signal pathway with defined chemicals and medium, may be desired for clinical translation. Furthermore, the technology of purification and maturation of the PSC-CMs may need further improvements to eliminate teratoma formation after in vivo implantation of the PSC-CMs for treating MI. In addition, in vitro derived PSC-CMs may have mechanical and electrical mismatch with the patient's cardiac tissue, which causes arrhythmia. This supports the use of PSC-derived cells committed to cardiac lineage without beating for implantation to treat MI. In this case, the PSC derived cells may utilize the mechanical, electrical, and chemical cues in the heart to further differentiate into mature/functional CMs in situ. Another major challenge facing stem cell therapy of MI is the low retention/survival of stem cells or their derivatives (e.g., PSC-CMs) in the heart for MI treatment after injection in vivo. This may be resolved by using biomaterials to engineer stem cells for reduced immunogenicity, immobilization of the cells in the heart, and increased integration with the host cardiac tissue. Biomaterials have also been applied in the derivation of CMs in vitro to increase the efficiency and maturation of differentiation. Collectively, a lot has been learned from the past failure of simply injecting intact stem cells or their derivatives in vivo for treating MI, and bioengineering stem cells with biomaterials is expected to be a valuable strategy for advancing stem cell therapy towards its widespread application for treating MI in the clinic.

Engineering Biomaterials with Micro/Nanotechnologies for Cell Reprogramming

Cell reprogramming is a revolutionized biotechnology that offers a powerful tool to engineer cell fate and function for regenerative medicine, disease modeling, drug discovery, and beyond. Leveraging advances in biomaterials and micro/nanotechnologies can enhance the reprogramming performance in vitro and in vivo through the development of delivery strategies and the control of biophysical and biochemical cues. In this review, we present an overview of the state-of-the-art technologies for cell reprogramming and highlight the recent breakthroughs in engineering biomaterials with micro/nanotechnologies to improve reprogramming efficiency and quality. Finally, we discuss future directions and challenges for reprogramming technologies and clinical translation.

High-Resolution Dissection of Chemical Reprogramming from Mouse Embryonic Fibroblasts into Fibrocartilaginous Cells

Articular cartilage injury and degeneration causing pain and loss of quality-of-life has become a serious problem for increasingly aged populations. Given the poor self-renewal of adult human chondrocytes, alternative functional cell sources are needed. Direct reprogramming by small molecules potentially offers an oncogene-free and cost-effective approach to generate chondrocytes, but has yet to be investigated. Here, we directly reprogrammed mouse embryonic fibroblasts into PRG4+ chondrocytes using a 3D system with a chemical cocktail, VCRTc (valproic acid, CHIR98014, Repsox, TTNPB, and celecoxib). Using single-cell transcriptomics, we revealed the inhibition of fibroblast features and activation of chondrogenesis pathways in early reprograming, and the intermediate cellular process resembling cartilage development. The in vivo implantation of chemical-induced chondrocytes at defective articular surfaces promoted defect healing and rescued 63.4% of mechanical function loss. Our approach directly converts fibroblasts into functional cartilaginous cells, and also provides insights into potential pharmacological strategies for future cartilage regeneration.

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A chemical method to derive functional murine articular chondrocytes from fibroblasts

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Chemical-induced chondrocytes promote in vivo regeneration of articular defects

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In single-cell analysis, intermediate reprogramming events resemble cartilage development

Lineage reprogramming of fibroblasts into induced cardiac progenitor cells by CRISPR/Cas9-based transcriptional activators

Overexpression of exogenous lineage-determining factors succeeds in directly reprogramming fibroblasts to various cell types. Several studies have reported reprogramming of fibroblasts into induced cardiac progenitor cells (iCPCs). CRISPR/Cas9-mediated gene activation is a potential approach for cellular reprogramming due to its high precision and multiplexing capacity. Here we show lineage reprogramming to iCPCs through a dead Cas9 (dCas9)-based transcription activation system. Targeted and robust activation of endogenous cardiac factors, including GATA4, HAND2, MEF2C and TBX5 (G, H, M and T; GHMT), can reprogram human fibroblasts toward iCPCs. The iCPCs show potentials to differentiate into cardiomyocytes, smooth muscle cells and endothelial cells in vitro. Addition of MEIS1 to GHMT induces cell cycle arrest in G2/M and facilitates cardiac reprogramming. Lineage reprogramming of human fibroblasts into iCPCs provides a promising cellular resource for disease modeling, drug discovery and individualized cardiac cell therapy.

Cardiac progenitors and paracrine mediators in cardiogenesis and heart regeneration

The mammalian hearts have the least regenerative capabilities among tissues and organs. As such, heart regeneration has been and continues to be the ultimate goal in the treatment against acquired and congenital heart diseases. Uncovering such a long-awaited therapy is still extremely challenging in the current settings. On the other hand, this desperate need for effective heart regeneration has developed various forms of modern biotechnologies in recent years. These involve the transplantation of pluripotent stem cell-derived cardiac progenitors or cardiomyocytes generated in vitro and novel biochemical molecules along with tissue engineering platforms. Such newly generated technologies and approaches have been shown to effectively proliferate cardiomyocytes and promote heart repair in the diseased settings, albeit mainly preclinically. These novel tools and medicines give somehow credence to breaking down the barriers associated with re-building heart muscle. However, in order to maximize efficacy and achieve better clinical outcomes through these cell-based and/or cell-free therapies, it is crucial to understand more deeply the developmental cellular hierarchies/paths and molecular mechanisms in normal or pathological cardiogenesis. Indeed, the morphogenetic process of mammalian cardiac development is highly complex and spatiotemporally regulated by various types of cardiac progenitors and their paracrine mediators. Here we discuss the most recent knowledge and findings in cardiac progenitor cell biology and the major cardiogenic paracrine mediators in the settings of cardiogenesis, congenital heart disease, and heart regeneration.

Direct Reprogramming to Human Induced Neuronal Progenitors from Fibroblasts of Familial and Sporadic Parkinson's Disease Patients

In Parkinson's disease (PD) research, human neuroblastoma and immortalized neural cell lines have been widely used as in vitro models. The advancement in the field of reprogramming technology has provided tools for generating patient-specific induced pluripotent stem cells (hiPSCs) as well as human induced neuronal progenitor cells (hiNPCs). These cells have revolutionized the field of disease modeling, especially in neural diseases. Although the direct reprogramming to hiNPCs has several advantages over differentiation after hiPSC reprogramming, such as the time required and the simple procedure, relatively few studies have utilized hiNPCs. Here, we optimized the protocol for hiNPC reprogramming using pluripotency factors and Sendai virus. In addition, we generated hiNPCs of two healthy donors, a sporadic PD patient, and a familial patient with the LRRK2 G2019S mutation (L2GS). The four hiNPC cell lines are highly proliferative, expressed NPC markers, maintained the normal karyotype, and have the differentiation potential of dopaminergic neurons. Importantly, the patient hiNPCs show different apoptotic marker expression. Thus, these hiNPCs, in addition to hiPSCs, are a favorable option to study PD pathology.

Cardiac Progenitor Cells from Stem Cells: Learning from Genetics and Biomaterials

Cardiac Progenitor Cells (CPCs) show great potential as a cell resource for restoring cardiac function in patients affected by heart disease or heart failure. CPCs are proliferative and committed to cardiac fate, capable of generating cells of all the cardiac lineages. These cells offer a significant shift in paradigm over the use of human induced pluripotent stem cell (iPSC)-derived cardiomyocytes owing to the latter's inability to recapitulate mature features of a native myocardium, limiting their translational applications. The iPSCs and direct reprogramming of somatic cells have been attempted to produce CPCs and, in this process, a variety of chemical and/or genetic factors have been evaluated for their ability to generate, expand, and maintain CPCs in vitro. However, the precise stoichiometry and spatiotemporal activity of these factors and the genetic interplay during embryonic CPC development remain challenging to reproduce in culture, in terms of efficiency, numbers, and translational potential. Recent advances in biomaterials to mimic the native cardiac microenvironment have shown promise to influence CPC regenerative functions, while being capable of integrating with host tissue. This review highlights recent developments and limitations in the generation and use of CPCs from stem cells, and the trends that influence the direction of research to promote better application of CPCs.

miRNAs in Extracellular Vesicles from iPS-Derived Cardiac Progenitor Cells Effectively Reduce Fibrosis and Promote Angiogenesis in Infarcted Heart

Cardiac stem cell therapy offers the potential to ameliorate postinfarction remodeling and development of heart failure but requires optimization of cell-based approaches. Cardiac progenitor cells (CPCs) induction by ISX-9, a small molecule possessing antioxidant, prosurvival, and regenerative properties, represents an attractive potential approach for cell-based cardiac regenerative therapy. Here, we report that extracellular vesicles (EV) secreted by ISX-9-induced CPCs (EV-CPC^ISX-9) faithfully recapitulate the beneficial effects of their parent CPCs with regard to postinfarction remodeling. These EV contain a distinct repertoire of biologically active miRNAs that promoted angiogenesis and proliferation of cardiomyocytes while ameliorating fibrosis in the infarcted heart. Amongst the highly enriched miRNAs, miR-373 was strongly antifibrotic, targeting 2 key fibrogenic genes, GDF-11 and ROCK-2. miR-373 mimic itself was highly efficacious in preventing scar formation in the infarcted myocardium. Together, these novel findings have important implications with regard to prevention of postinfarction remodeling.

Induced cardiac progenitor cells repopulate decellularized mouse heart scaffolds and differentiate to generate cardiac tissue

Native myocardium has limited regenerative potential post injury. Advances in lineage reprogramming have provided promising cellular sources for regenerative medicine in addition to research applications. Recently we have shown that adult mouse fibroblasts can be reprogrammed to expandable, multipotent, induced cardiac progenitor cells (iCPCs) by employing forced expression of five cardiac factors along with activation of canonical Wnt and JAK/STAT signaling. Here we aim to further characterize iCPCs by highlighting their safety, ease of attainability, and functionality within a three-dimensional cardiac extracellular matrix scaffold. Specifically, iCPCs did not form teratomas in contrast to embryonic stem cells when injected into immunodeficient mice. iCPC reprogramming was achieved in wild type mouse fibroblasts without requiring a cardiac-specific reporter, solely utilizing morphological changes to identify, clonally isolate, and expand iCPCs, thus increasing the versatility of this technology. iCPCs also show the ability to repopulate decellularized native heart scaffolds and differentiated into organized structures containing cardiomyocytes, smooth muscle, and endothelial cells. Optical mapping of recellularized scaffolds shows field-stimulated calcium transients that propagate across islands of reconstituted tissue and bipolar local stimulation demonstrates cell-cell coupling within scaffolds. Overall, iCPCs provide a readily attainable, scalable, safe, and functional cell source for a variety of application including drug discovery, disease modeling, and regenerative therapy.

Cardiac Progenitors Induced from Human Induced Pluripotent Stem Cells with Cardiogenic Small Molecule Effectively Regenerate Infarcted Hearts and Attenuate Fibrosis

Cardiac progenitor cells (CPCs) being multipotent offer a promising source for cardiac repair due to their ability to proliferate and multiply into cardiac lineage cells. Here, we explored a novel strategy for human CPCs generation from human induced pluripotent stem cells (hiPSCs) using a cardiogenic small molecule, isoxazole (ISX-9) and their ability to grow in the scar tissue for functional improvement in the infarcted myocardium. CPCs were induced from hiPSCs with ISX-9. CPCs were characterized by immunocytochemistry and RT-PCR. The CPC survival and differentiation in the infarcted hearts were determined by in vivo transplantation in immunodeficient mice following left anterior descending artery ligation and their effects were determined on fibrosis and functional improvement. ISX-9 simultaneously induced expression of cardiac transcription factors, NK2 homeobox 5, islet-1, GATA binding protein 4, myocyte enhancer factor-2 in hiPSCs within 3 days of treatment and successfully differentiated into three cardiac lineages in vitro. Messenger RNA and microRNA-sequencing results showed that ISX-9 targeted multiple cardiac differentiation, proliferation signaling pathways and upregulated myogenesis and cardiac hypertrophy related-microRNA. ISX-9 activated multiple pathways including transforming growth factor β induced epithelial-mesenchymal transition signaling, canonical, and non-canonical Wnt signaling at different stages of cardiac differentiation. CPCs transplantation promoted myoangiogenesis, attenuated fibrosis, and led to functional improvement in treated mice.

Identification of Cardiomyocyte-Fated Progenitors from Human-Induced Pluripotent Stem Cells Marked with CD82

Here, we find that human-induced pluripotent stem cell (hiPSC)-derived cardiomyocyte (CM)-fated progenitors (CFPs) that express a tetraspanin family glycoprotein, CD82, almost exclusively differentiate into CMs both in vitro and in vivo. CD82 is transiently expressed in late-stage mesoderm cells during hiPSC differentiation. Purified CD82⁺ cells gave rise to CMs under nonspecific in vitro culture conditions with serum, as well as in vivo after transplantation to the subrenal space or injured hearts in mice, indicating that CD82 successfully marks CFPs. CD82 overexpression in mesoderm cells as well as in undifferentiated hiPSCs increased the secretion of exosomes containing β-catenin and reduced nuclear β-catenin protein, suggesting that CD82 is involved in fated restriction to CMs through Wnt signaling inhibition. This study may contribute to the understanding of CM differentiation mechanisms and to cardiac regeneration strategies.

Ameliorating the Fibrotic Remodeling of the Heart through Direct Cardiac Reprogramming

Coronary artery disease is the most common form of cardiovascular diseases, resulting in the loss of cardiomyocytes (CM) at the site of ischemic injury. To compensate for the loss of CMs, cardiac fibroblasts quickly respond to injury and initiate cardiac remodeling in an injured heart. In the remodeling process, cardiac fibroblasts proliferate and differentiate into myofibroblasts, which secrete extracellular matrix to support the intact structure of the heart, and eventually differentiate into matrifibrocytes to form chronic scar tissue. Discovery of direct cardiac reprogramming offers a promising therapeutic strategy to prevent/attenuate this pathologic remodeling and replace the cardiac fibrotic scar with myocardium in situ. Since the first discovery in 2010, many progresses have been made to improve the efficiency and efficacy of reprogramming by understanding the mechanisms and signaling pathways that are activated during direct cardiac reprogramming. Here, we overview the development and recent progresses of direct cardiac reprogramming and discuss future directions in order to translate this promising technology into an effective therapeutic paradigm to reverse cardiac pathological remodeling in an injured heart.