Chemical-induced cardiac reprogramming in vivo

In situ reprogramming of cardiac fibroblasts into cardiomyocytes in mouse heart with chemicals

Cardiomyocytes are terminal differentiated cells and have limited ability to proliferate or regenerate. Condition like myocardial infarction causes massive death of cardiomyocytes and is the leading cause of death. Previous studies have demonstrated that cardiac fibroblasts can be induced to transdifferentiate into cardiomyocytes in vitro and in vivo by forced expression of cardiac transcription factors and microRNAs. Our previous study have demonstrated that full chemical cocktails could also induce fibroblast to cardiomyocyte transdifferentiation both in vitro and in vivo. With the development of tissue clearing techniques, it is possible to visualize the reprogramming at the whole-organ level. In this study, we investigated the effect of the chemical cocktail CRFVPTM in inducing in situ fibroblast to cardiomyocyte transdifferentiation with two strains of genetic tracing mice, and the reprogramming was observed at whole-heart level with CUBIC tissue clearing technique and 3D imaging. In addition, single-cell RNA sequencing (scRNA-seq) confirmed the generation of cardiomyocytes from cardiac fibroblasts which carries the tracing marker. Our study confirms the use of small molecule cocktails in inducing in situ fibroblast to cardiomyocyte reprogramming at the whole-heart level and proof-of-conceptly providing a new source of naturally incorporated cardiomyocytes to help heart regeneration.

The mechanisms of exercise improving cardiovascular function by stimulating Piezo1 and TRP ion channels: a systemic review

Mechanosensitive ion channels are widely distributed in the heart, lung, bladder and other tissues, and plays an important role in exercise-induced cardiovascular function promotion. By reviewing the PubMed databases, the results were summarized using the terms "Exercise/Sport", "Piezo1", "Transient receptor potential (TRP)" and "Cardiovascular" as the keywords, 124-related papers screened were sorted and reviewed. The results showed that: (1) Piezo1 and TRP channels play an important role in regulating blood pressure and the development of cardiovascular diseases such as atherosclerosis, myocardial infarction, and cardiac fibrosis; (2) Exercise promotes cardiac health, inhibits the development of pathological heart to heart failure, regulating the changes in the characterization of Piezo1 and TRP channels; (3) Piezo1 activates downstream signaling pathways with very broad pathways, such as AKT/eNOS, NF-κB, p38MAPK and HIPPO-YAP signaling pathways. Piezo1 and Irisin regulate nuclear localization of YAP and are hypothesized to act synergistically to regulate tissue mechanical properties of the cardiovascular system and (4) The cardioprotective effects of exercise through the TRP family are mostly accomplished through Ca2+ and involve many signaling pathways. TRP channels exert their important cardioprotective effects by reducing the TRPC3-Nox2 complex and mediating Irisin-induced Ca2+ influx through TRPV4. It is proposed that exercise stimulates the mechanosensitive cation channel Piezo1 and TRP channels, which exerts cardioprotective effects. The activation of Piezo1 and TRP channels and their downstream targets to exert cardioprotective function by exercise may provide a theoretical basis for the prevention of cardiovascular diseases and the rehabilitation of clinical patients.

Bioactive materials for in vivo sweat gland regeneration

Loss of sweat glands (SwGs) commonly associated with extensive skin defects is a leading cause of hyperthermia and heat stroke. In vivo tissue engineering possesses the potential to take use of the body natural ability to regenerate SwGs, making it more conducive to clinical translation. Despite recent advances in regenerative medicine, reconstructing SwG tissue with the same structure and function as native tissue remains challenging. Elucidating the SwG generation mechanism and developing biomaterials for in vivo tissue engineering is essential for understanding and developing in vivo SwG regenerative strategies. Here, we outline the cell biology associated with functional wound healing and the characteristics of bioactive materials. We critically summarize the recent progress in bioactive material-based cell modulation approaches for in vivo SwG regeneration, including the recruitment of endogenous cells to the skin lesion for SwG regeneration and in vivo cellular reprogramming for SwG regeneration. We discussed the re-establishment of microenvironment via bioactive material-mediated regulators. Besides, we offer promising perspectives for directing in situ SwG regeneration via bioactive material-based cell-free strategy, which is a simple and effective approach to regenerate SwG tissue with both fidelity of structure and function. Finally, we discuss the opportunities and challenges of in vivo SwG regeneration in detail. The molecular mechanisms and cell fate modulation of in vivo SwG regeneration will provide further insights into the regeneration of patient-specific SwGs and the development of potential intervention strategies for gland-derived diseases.

Stem cell heterogeneity, plasticity, and regulation

As a population of homogeneous cells with both self-renewal and differentiation potential, stem cell pools are highly compartmentalized and contain distinct subsets that exhibit stable but limited heterogeneity during homeostasis. However, their striking plasticity is showcased under natural or artificial stress, such as injury, transplantation, cancer, and aging, leading to changes in their phenotype, constitution, metabolism, and function. The complex and diverse network of cell-extrinsic niches and signaling pathways, together with cell-intrinsic genetic and epigenetic regulators, tightly regulate both the heterogeneity during homeostasis and the plasticity under perturbation. Manipulating these factors offers better control of stem cell behavior and a potential revolution in the current state of regenerative medicine. However, disruptions of normal regulation by genetic mutation or excessive plasticity acquisition may contribute to the formation of tumors. By harnessing innovative techniques that enhance our understanding of stem cell heterogeneity and employing novel approaches to maximize the utilization of stem cell plasticity, stem cell therapy holds immense promise for revolutionizing the future of medicine.

Transplantation of Chemical Compound-Induced Cells from Human Fibroblasts Improves Locomotor Recovery in a Spinal Cord Injury Rat Model

The development of regenerative medicine using cell therapy is eagerly awaited for diseases such as spinal cord injury (SCI), for which there has been no radical cure. We previously reported the direct conversion of human fibroblasts into neuronal-like cells using only chemical compounds; however, it is unclear whether chemical compound-induced neuronal-like (CiN) cells are clinically functional. In this study, we partially modified the method of inducing CiN cells (termed immature CiN cells) and examined their therapeutic efficacy, in a rat model of SCI, to investigate whether immature CiN cells are promising for clinical applications. Motor function recovery, after SCI, was assessed using the Basso, Beattie, and Bresnahan (BBB) test, as well as the CatWalk analysis. We found that locomotor recovery, after SCI in the immature CiN cell-transplanted group, was partially improved compared to that in the control group. Consistent with these results, magnetic resonance imaging (MRI) and histopathological analyses revealed that nerve recovery or preservation improved in the immature CiN cell-transplanted group. Furthermore, transcriptome analysis revealed that immature CiN cells highly express hepatocyte growth factor (HGF), which has recently been shown to be a promising therapeutic agent against SCI. Our findings suggest that immature CiN cells may provide an alternative strategy for the regenerative therapy of SCI.

Chemical reprogramming for cell fate manipulation: Methods, applications, and perspectives

Chemical reprogramming offers an unprecedented opportunity to control somatic cell fate and generate desired cell types including pluripotent stem cells for applications in biomedicine in a precise, flexible, and controllable manner. Recent success in the chemical reprogramming of human somatic cells by activating a regeneration-like program provides an alternative way of producing stem cells for clinical translation. Likewise, chemical manipulation enables the capture of multiple (stem) cell states, ranging from totipotency to the stabilization of somatic fates in vitro. Here, we review progress in using chemical approaches for cell fate manipulation in addition to future opportunities in this promising field.

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.

Transcriptome-based chemical screens identify CDK8 as a common barrier in multiple cell reprogramming systems

Fibroblasts can be chemically induced to pluripotent stem cells (CiPSCs) through an extraembryonic endoderm (XEN)-like state or directly converted into other differentiated cell lineages. However, the mechanisms underlying chemically induced cell-fate reprogramming remain unclear. Here, a transcriptome-based screen of biologically active compounds uncovered that CDK8 inhibition was essential to enable chemically induced reprogramming from fibroblasts into XEN-like cells, then CiPSCs. RNA-sequencing analysis showed that CDK8 inhibition downregulated proinflammatory pathways that suppress chemical reprogramming and facilitated the induction of a multi-lineage priming state, indicating the establishment of plasticity in fibroblasts. CDK8 inhibition also resulted in a chromatin accessibility profile like that under initial chemical reprogramming. Moreover, CDK8 inhibition greatly promoted reprogramming of mouse fibroblasts into hepatocyte-like cells and induction of human fibroblasts into adipocytes. These collective findings thus highlight CDK8 as a general molecular barrier in multiple cell reprogramming processes, and as a common target for inducing plasticity and cell fate conversion.

Direct cardiac reprogramming: A new technology for cardiac repair

Cardiovascular disease is one of the leading causes of morbidity and mortality worldwide, with myocardial infarctions being amongst the deadliest manifestations. Reduced blood flow to the heart can result in the death of cardiac tissue, leaving affected patients susceptible to further complications and recurrent disease. Further, contemporary management typically involves a pharmacopeia to manage the metabolic conditions contributing to atherosclerotic and hypertensive heart disease, rather than regeneration of the damaged myocardium. With modern healthcare extending lifespan, a larger demographic will be at risk for heart disease, driving the need for novel therapeutics that surpass those currently available in efficacy. Transdifferentiation and cellular reprogramming have been looked to as potential methods for the treatment of diseases throughout the body. Specifically targeting the fibrotic cells in cardiac scar tissue as a source to be reprogrammed into induced cardiomyocytes remains an appealing option. This review aims to highlight the history of and advances in cardiac reprogramming and describe its translational potential as a treatment for cardiovascular disease.

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.

Development of direct cardiac reprogramming for clinical applications

The incidence of cardiovascular diseases is increasing worldwide, and cardiac regenerative therapy has great potential as a new treatment strategy, especially for ischemic heart disease. Direct cardiac reprogramming is a promising new cardiac regenerative therapy that uses defined factors to induce transdifferentiation of endogenous cardiac fibroblasts (CFs) into induced cardiomyocyte-like cells (iCMs). In vivo reprogramming is expected to restore lost cardiac function without necessitating cardiac transplantation by converting endogenous CFs that exist abundantly in cardiac tissues directly into iCMs. Indeed, we and other groups have demonstrated that in vivo cardiac reprogramming improves cardiac contractile function and reduces scar area after acute myocardial infarction (MI). Recently, we demonstrated that in vivo cardiac reprogramming is an innovative cardiac regenerative therapy that not only regenerates the myocardium, but also reverses fibrosis by inducing the quiescence of pro-fibrotic fibroblasts, thereby improving heart failure in chronic MI. In this review, we summarize the recent progresses in in vivo cardiac reprogramming, and discuss its prospects for future clinical applications and the challenges of direct human reprogramming, which has been a longstanding issue.

Three-dimensional heart extracellular matrix enhances chemically induced direct cardiac reprogramming

Direct cardiac reprogramming has emerged as a promising therapeutic approach for cardiac regeneration. Full chemical reprogramming with small molecules to generate cardiomyocytes may be more amenable than genetic reprogramming for clinical applications as it avoids safety concerns associated with genetic manipulations. However, challenges remain regarding low conversion efficiency and incomplete cardiomyocyte maturation. Furthermore, the therapeutic potential of chemically induced cardiomyocytes (CiCMs) has not been investigated. Here, we report that a three-dimensional microenvironment reconstituted with decellularized heart extracellular matrix can enhance chemical reprogramming and cardiac maturation of fibroblasts to cardiomyocytes. The resultant CiCMs exhibit elevated cardiac marker expression, sarcomeric organization, and improved electrophysiological features and drug responses. We investigated the therapeutic potential of CiCMs reprogrammed in three-dimensional heart extracellular matrix in a rat model of myocardial infarction. Our platform can facilitate the use of CiCMs for regenerative medicine, disease modeling, and drug screening.

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.

The heart of cardiac reprogramming: The cardiac fibroblasts

Cardiovascular disease is the leading cause of death worldwide, outpacing pulmonary disease, infectious disease, and all forms of cancer. Myocardial infarction (MI) dominates cardiovascular disease, contributing to four out of five cardiovascular related deaths. Following MI, patients suffer adverse and irreversible myocardial remodeling associated with cardiomyocyte loss and infiltration of fibrotic scar tissue. Current therapies following MI only mitigate the cardiac physiological decline rather than restore damaged myocardium function. Direct cardiac reprogramming is one strategy that has promise in repairing injured cardiac tissue by generating new, functional cardiomyocytes from cardiac fibroblasts (CFs). With the ectopic expression of transcription factors, microRNAs, and small molecules, CFs can be reprogrammed into cardiomyocyte-like cells (iCMs) that display molecular signatures, structures, and contraction abilities similar to endogenous cardiomyocytes. The in vivo induction of iCMs following MI leads to significant reduction in fibrotic cardiac remodeling and improved heart function, indicating reprogramming is a viable option for repairing damaged heart tissue. Recent work has illustrated different methods to understand the mechanisms driving reprogramming, in an effort to improve the efficiency of iCM generation and create an approach translational into clinic. This review will provide an overview of CFs and describe different in vivo reprogramming methods.

Small compound-based direct cell conversion with combinatorial optimization of pathway regulations

MOTIVATION

Direct cell conversion, direct reprogramming (DR), is an innovative technology that directly converts source cells to target cells without bypassing induced pluripotent stem cells. The use of small compounds (e.g. drugs) for DR can help avoid carcinogenic risk induced by gene transfection; however, experimentally identifying small compounds remains challenging because of combinatorial explosion.

RESULTS

In this article, we present a new computational method, COMPRENDRE (combinatorial optimization of pathway regulations for direct reprograming), to elucidate the mechanism of small compound-based DR and predict new combinations of small compounds for DR. We estimated the potential target proteins of DR-inducing small compounds and identified a set of target pathways involving DR. We identified multiple DR-related pathways that have not previously been reported to induce neurons or cardiomyocytes from fibroblasts. To overcome the problem of combinatorial explosion, we developed a variant of a simulated annealing algorithm to identify the best set of compounds that can regulate DR-related pathways. Consequently, the proposed method enabled to predict new DR-inducing candidate combinations with fewer compounds and to successfully reproduce experimentally verified compounds inducing the direct conversion from fibroblasts to neurons or cardiomyocytes. The proposed method is expected to be useful for practical applications in regenerative medicine.

AVAILABILITY AND IMPLEMENTATION

The code supporting the current study is available at the http://labo.bio.kyutech.ac.jp/~yamani/comprendre.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Graphene Nanosheets Mediate Efficient Direct Reprogramming into Induced Cardiomyocytes

In vivo cardiac reprogramming is a potential therapeutic strategy to replace cardiomyocytes in patients with myocardial infarction. However, low conversion efficiency is a limitation of In vivo cardiac reprogramming for heart failure. In this study, we showed that graphene nanosheets mediated efficient direct reprogramming into induced cardiomyocytes In vivo. We observed that the administration of graphene nanosheets led to the accumulation of H3K4me3, which resulted in direct cardiac reprogramming. Importantly, the administration of graphene nanosheets combined with cardiac reprogramming factors in a mouse model of myocardial infarction enhanced the effectiveness of directly reprogrammed cell-based cardiac repair. Collectively, our findings suggest that graphene nanosheets can be used as an excellent biomaterial to promote cardiac cell fate conversion and provide a robust reprogramming platform for cardiac regeneration in ischemic heart disease.

Direct chemical induction of hepatocyte-like cells with capacity for liver repopulation

BACKGROUND AND AIMS

Cell fate can be directly reprogrammed from accessible cell types (e.g., fibroblasts) into functional cell types by exposure to small molecule stimuli. However, no chemical reprogramming method has been reported to date that successfully generates functional hepatocyte-like cells that can repopulate liver tissue, casting doubt over the feasibility of chemical reprogramming approaches to obtain desirable cell types for therapeutic applications.

APPROACH AND RESULTS

Here, through chemical induction of phenotypic plasticity, we provide a proof-of-concept demonstration of the direct chemical reprogramming of mouse fibroblasts into functional hepatocyte-like cells using exposure to small molecule cocktails in culture medium to successively stimulate endogenous expression of master transcription factors associated with hepatocyte development, such as hepatocyte nuclear factor 4a, nuclear receptor subfamily 1, group I, member 2, and nuclear receptor subfamily 1, group H, member 4. RNA sequencing analysis, metabolic assays, and in vivo physiological experiments show that chemically induced hepatocytes (CiHeps) exhibit comparable activity and function to primary hepatocytes, especially in liver repopulation to rescue liver failure in fumarylacetoacetate hydrolase^-/- recombination activating gene 2^-/- interleukin 2 receptor, gamma chain^-/- mice in vivo. Single-cell RNA-seq further revealed that gastrointestinal-like and keratinocyte-like cells were induced along with CiHeps, resembling the activation of an intestinal program within hepatic reprogramming as described in transgenic approaches.

CONCLUSIONS

Our findings show that direct chemical reprogramming can generate hepatocyte-like cells with high-quality physiological properties, providing a paradigm for establishing hepatocyte identity in fibroblasts and demonstrating the potential for chemical reprogramming in organ/tissue repair and regeneration therapies.

Signaling cascades in the failing heart and emerging therapeutic strategies

Chronic heart failure is the end stage of cardiac diseases. With a high prevalence and a high mortality rate worldwide, chronic heart failure is one of the heaviest health-related burdens. In addition to the standard neurohormonal blockade therapy, several medications have been developed for chronic heart failure treatment, but the population-wide improvement in chronic heart failure prognosis over time has been modest, and novel therapies are still needed. Mechanistic discovery and technical innovation are powerful driving forces for therapeutic development. On the one hand, the past decades have witnessed great progress in understanding the mechanism of chronic heart failure. It is now known that chronic heart failure is not only a matter involving cardiomyocytes. Instead, chronic heart failure involves numerous signaling pathways in noncardiomyocytes, including fibroblasts, immune cells, vascular cells, and lymphatic endothelial cells, and crosstalk among these cells. The complex regulatory network includes protein-protein, protein-RNA, and RNA-RNA interactions. These achievements in mechanistic studies provide novel insights for future therapeutic targets. On the other hand, with the development of modern biological techniques, targeting a protein pharmacologically is no longer the sole option for treating chronic heart failure. Gene therapy can directly manipulate the expression level of genes; gene editing techniques provide hope for curing hereditary cardiomyopathy; cell therapy aims to replace dysfunctional cardiomyocytes; and xenotransplantation may solve the problem of donor heart shortages. In this paper, we reviewed these two aspects in the field of failing heart signaling cascades and emerging therapeutic strategies based on modern biological techniques.

Translational perspectives on cardiac reprogramming

Loss of cardiac muscle after cardiac injury is replaced by cardiac fibrosis, due to very limited regenerative capacity of the heart. Although initially beneficial, persistent cardiac fibrosis leads to pump failure and conduction abnormalities, common modes of death following cardiac injury. Thus, directly reprogramming cardiac fibroblasts into induced cardiomyocyte-like cells (iCMs) by forced expression of cardiogenic factors (referred to as cardiac reprogramming) is particularly attractive in that it targets cardiac fibroblasts, a major source of cardiac fibrosis, to induce new cardiac muscle. Over the last decade, remarkable progresses have been made on cardiac reprogramming, particularly focusing on how to enhance conversion of fibroblasts to iCMs in vitro. However, it still remains elusive whether this new regenerative approach can be translated into clinical practice. This review discusses progresses and challenges of cardiac reprogramming in the translational context.

Direct reprogramming as a route to cardiac repair

Ischemic heart disease is the leading cause of morbidity, mortality, and healthcare expenditure worldwide due to an inability of the heart to regenerate following injury. Thus, novel heart failure therapies aimed at promoting cardiomyocyte regeneration are desperately needed. In recent years, direct reprogramming of resident cardiac fibroblasts to induced cardiac-like myocytes (iCMs) has emerged as a promising therapeutic strategy to repurpose the fibrotic response of the injured heart toward a functional myocardium. Direct cardiac reprogramming was initially achieved through the overexpression of the transcription factors (TFs) Gata4, Mef2c, and Tbx5 (GMT). However, this combination of TFs and other subsequent cocktails demonstrated limited success in reprogramming adult human and mouse fibroblasts, constraining the clinical translation of this therapy. Over the past decade, significant effort has been dedicated to optimizing reprogramming cocktails comprised of cardiac TFs, epigenetic factors, microRNAs, or small molecules to yield efficient cardiac cell fate conversion. Yet, efficient reprogramming of adult human fibroblasts remains a significant challenge. Underlying mechanisms identified to accelerate this process have been centered on epigenetic remodeling at cardiac gene regulatory regions. Further studies to achieve a refined understanding and directed means of overcoming epigenetic barriers are merited to more rapidly translate these promising therapies to the clinic.

Application of Human Induced Pluripotent Stem Cell Technology for Cardiovascular Regenerative Pharmacology

Cardiovascular diseases are one of the leading causes of mortality in the western world. Myocardial infarction is among the most prevalent and results in significant cell loss within the myocardium. Similarly, numerous drugs have been identified as having cardiotoxic side effects. The adult human heart is however unable to instigate an effective repair mechanism and regenerate the myocardium in response to such damage. This is in large part due to the withdrawal of cardiomyocytes (CMs) from the cell cycle. Thus, identifying, screening, and developing agents that could enhance the proliferative capacity of CMs holds great potential in cardiac regeneration. Human induced pluripotent stem cells (hiPSCs) and their cardiovascular derivatives are excellent tools in the search for such agents. This chapter outlines state-of-the art techniques for the two-dimensional differentiation and attainment of hiPSC-derived CMs and endothelial cells (ECs). Bioreactor systems and three-dimensional spheroids derived from hiPSC-cardiovascular derivatives are explored as platforms for drug discovery before focusing on relevant assays that can be employed to assess cell proliferation and viability.

Resuscitating the Field of Cardiac Regeneration: Seeking Answers from Basic Biology

Heart failure (HF) is one of the leading causes for hospital admissions worldwide. HF patients are classified based on the chronic changes in left ventricular ejection fraction (LVEF) as preserved (LVEF ≥ 50%), reduced (LVEF ≤ 40%), or mid-ranged (40% < LVEF < 50%) HFs. Treatments nowadays can prevent HFrEF progress, whereas only a few of the treatments have been proven to be effective in improving the survival of HFpEF. In this review, numerous mediators involved in the pathogenesis of HF are summarized. The regional upstream signaling and their diagnostic and therapeutic potential are also discussed. Additionally, the recent challenges and development in cardiac regenerative therapy that hold opportunities for future research and clinical translation are discussed.

Small molecules for cell reprogramming: a systems biology analysis

If somatic stem cells would be able to maintain their regenerative capacity over time, this might, to a great extent, resolve rejuvenation issues. Unfortunately, the pool of somatic stem cells is limited, and they undergo cell aging with a consequent loss of functionality. During the last decade, low molecular weight compounds that are able to induce or enhance cell reprogramming have been reported. They were named “Small Molecules” (SMs) and might present definite advantages compared to the exogenous introduction of stemness-related transcription factors (e.g. Yamanaka’s factors). Here, we undertook a systemic analysis of SMs and their potential gene targets. Data mining and curation lead to the identification of 92 SMs. The SM targets fall into three major functional categories: epigenetics, cell signaling, and metabolic “switchers”. All these categories appear to be required in each SM cocktail to induce cell reprogramming. Remarkably, many enriched pathways of SM targets are related to aging, longevity, and age-related diseases, thus connecting them with cell reprogramming. The network analysis indicates that SM targets are highly interconnected and form protein-protein networks of a scale-free topology. The extremely high contribution of hubs to network connectivity suggests that (i) cell reprogramming may require SM targets to act cooperatively, and (ii) their network organization might ensure robustness by resistance to random failures. All in all, further investigation of SMs and their relationship with longevity regulators will be helpful for developing optimal SM cocktails for cell reprogramming with a perspective for rejuvenation and life span extension.

Bioengineering Methods in MicroRNA-Mediated Direct Reprogramming of Fibroblasts Into Cardiomyocytes

Ischemic heart disease is the major cause of mortality worldwide. Despite the most recent pharmacological progresses, cardiac regeneration is yet not possible, and heart transplantation is the only therapeutic option for end-stage heart failure. Traditional cardiac regenerative medicine approaches, such as cell therapies and tissue engineering, have failed in the obtainment of human functional cardiac tissue, mainly due to unavailability of high quantities of autologous functional cardiomyocytes (CMs), low grafting efficiency, and/or arrhythmic events. Direct reprogramming (DR) of fibroblasts into induced CMs (iCMs) has emerged as a new promising approach for myocardial regeneration by in situ transdifferentiation or providing additional CM source for cell therapy. Among available DR methods, non-viral transfection with microRNAs (miRcombo: miR-1, miR-133, miR-208, and miR-499) appears promising for future clinical translation. MiRcombo transfection of fibroblasts could be significantly improved by the development of safe nanocarriers, efficiently delivering their cargo to target cells at the required stoichiometric ratio and overall dose in due times. Newly designed in vitro 3D culture microenvironments, providing biomimetic biophysical and biochemical stimuli to miRcombo-transfected cells, significantly increase the yield of fibroblast transdifferentiation into iCMs, enhancing CM gene expression. Epigenetic regulation of gene expression programs, critical to cell lineage commitment, can also be promoted by the administration of specific anti-inflammatory and anti-fibrotic soluble factors, helping in suppressing fibroblast signature. The aim of this mini-review is to introduce the readers to a relatively unknown field of cardiac research integrating bioengineering tools as relevant for the progress of miRNA-mediated cardiac DR.

Advanced Technologies to Target Cardiac Cell Fate Plasticity for Heart Regeneration

The adult human heart can only adapt to heart diseases by starting a myocardial remodeling process to compensate for the loss of functional cardiomyocytes, which ultimately develop into heart failure. In recent decades, the evolution of new strategies to regenerate the injured myocardium based on cellular reprogramming represents a revolutionary new paradigm for cardiac repair by targeting some key signaling molecules governing cardiac cell fate plasticity. While the indirect reprogramming routes require an in vitro engineered 3D tissue to be transplanted in vivo, the direct cardiac reprogramming would allow the administration of reprogramming factors directly in situ, thus holding great potential as in vivo treatment for clinical applications. In this framework, cellular reprogramming in partnership with nanotechnologies and bioengineering will offer new perspectives in the field of cardiovascular research for disease modeling, drug screening, and tissue engineering applications. In this review, we will summarize the recent progress in developing innovative therapeutic strategies based on manipulating cardiac cell fate plasticity in combination with bioengineering and nanotechnology-based approaches for targeting the failing heart.

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.

Myocardial infarction cardiomyocytes-derived exosomal miR-328-3p promote apoptosis via Caspase signaling

Exosomal miRNAs are used as novel non-invasive biomarkers for detection strategies of human disease. Here, we aimed to investigate the potential clinical value of exosomal miRNAs for myocardial infarction (MI) diagnosis and treatment. Differentially expressed miRNAs were obtained from normal cardiomyocytes, MI cardiomyocytes and adjacent normal cardiomyocytes using miRNA microarray analysis. Exosomes were isolated by centrifugation and identified by transmission electron microscopy (TEM) and western blot. The expression of miR-328-3p in exosomes was then verified by qRT-PCR. Cell apoptosis was measured using flow cytometry and TUNEL analysis. The MI severity was confirmed by masson's trichrome staining and echocardiography. MiR-328-3p was significantly increased in the MI cardiomyocytes and adjacent normal cardiomyocytes. We further confirmed miR-328-3p increasing in the exosomes from MI cardiomyocytes, which can be taken into normal cardiomyocytes. Furthermore, exogenous exosomal miR-328-3p increased apoptosis of cardiomyocytes and promoted MI. Genes regulated by miR-328-3p are mainly enriched in Caspase signaling, which is an important apoptosis regulating signaling pathway. Additionally, Caspase-3 inhibitor, Z-DEVD-FMK, reversed apoptosis and MI promoting function of miR-328-3p. Exosomal miR-328-3p is a potential novel diagnostic biomarker and therapeutic target for MI, and Z-DEVD-FMK could reverse the apoptosis progression induced by miR-328-3p.

In vivo chemical reprogramming of astrocytes into neurons

In mammals, many organs lack robust regenerative abilities. Lost cells in impaired tissue could potentially be compensated by converting nearby cells in situ through in vivo reprogramming. Small molecule-induced cell reprogramming offers a temporally flexible and non-integrative strategy for altering cell fate, which is, in principle, favorable for in vivo reprogramming in organs with notoriously poor regenerative abilities, such as the brain. Here, we demonstrate that in the adult mouse brain, small molecules can reprogram astrocytes into neurons. The in situ chemically induced neurons resemble endogenous neurons in terms of neuron-specific marker expression, electrophysiological properties, and synaptic connectivity. Our study demonstrates the feasibility of in vivo chemical reprogramming in the adult mouse brain and provides a potential approach for developing neuronal replacement therapies.

Cardiac Regeneration: New Insights Into the Frontier of Ischemic Heart Failure Therapy

Ischemic heart disease is the leading cause of morbidity and mortality in the world. While pharmacological and surgical interventions developed in the late twentieth century drastically improved patient outcomes, mortality rates over the last two decades have begun to plateau. Following ischemic injury, pathological remodeling leads to cardiomyocyte loss and fibrosis leading to impaired heart function. Cardiomyocyte turnover rate in the adult heart is limited, and no clinical therapies currently exist to regenerate cardiomyocytes lost following ischemic injury. In this review, we summarize the progress of therapeutic strategies including revascularization and cell-based interventions to regenerate the heart: transiently inducing cardiomyocyte proliferation and direct reprogramming of fibroblasts into cardiomyocytes. Moreover, we highlight recent mechanistic insights governing these strategies to promote heart regeneration and identify current challenges in translating these approaches to human patients.

Cardiomyocyte Induction and Regeneration for Myocardial Infarction Treatment: Cell Sources and Administration Strategies

Occlusion of coronary artery and subsequent damage or death of myocardium can lead to myocardial infarction (MI) and even heart failure-one of the leading causes of deaths world wide. Notably, myocardium has extremely limited regeneration potential due to the loss or death of cardiomyocytes (i.e., the cells of which the myocardium is comprised) upon MI. A variety of stem cells and stem cell-derived cardiovascular cells, in situ cardiac fibroblasts and endogenous proliferative epicardium, have been exploited to provide renewable cellular sources to treat injured myocardium. Also, different strategies, including direct injection of cell suspensions, bioactive molecules, or cell-incorporated biomaterials, and implantation of artificial cardiac scaffolds (e.g., cell sheets and cardiac patches), have been developed to deliver renewable cells and/or bioactive molecules to the MI site for the myocardium regeneration. This article briefly surveys cell sources and delivery strategies, along with biomaterials and their processing techniques, developed for MI treatment. Key issues and challenges, as well as recommendations for future research, are also discussed.

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.

Small Molecule Epigenetic Modulators in Pure Chemical Cell Fate Conversion

Although innovative technologies for somatic cell reprogramming and transdifferentiation provide new strategies for the research of translational medicine, including disease modeling, drug screening, artificial organ development, and cell therapy, recipient safety remains a concern due to the use of exogenous transcription factors during induction. To resolve this problem, new induction approaches containing clinically applicable small molecules have been explored. Small molecule epigenetic modulators such as DNA methylation writer inhibitors, histone methylation writer inhibitors, histone acylation reader inhibitors, and histone acetylation eraser inhibitors could overcome epigenetic barriers during cell fate conversion. In the past few years, significant progress has been made in reprogramming and transdifferentiation of somatic cells with small molecule approaches. In the present review, we systematically discuss recent achievements of pure chemical reprogramming and transdifferentiation.

Mapping regulators of cell fate determination: Approaches and challenges

Given the limited regenerative capacities of most organs, strategies are needed to efficiently generate large numbers of parenchymal cells capable of integration into the diseased organ. Although it was initially thought that terminally differentiated cells lacked the ability to transdifferentiate, it has since been shown that cellular reprogramming of stromal cells to parenchymal cells through direct lineage conversion holds great potential for the replacement of post-mitotic parenchymal cells lost to disease. To this end, an assortment of genetic, chemical, and mechanical cues have been identified to reprogram cells to different lineages both in vitro and in vivo. However, some key challenges persist that limit broader applications of reprogramming technologies. These include: (1) low reprogramming efficiencies; (2) incomplete functional maturation of derived cells; and (3) difficulty in determining the typically multi-factor combinatorial recipes required for successful transdifferentiation. To improve efficiency by comprehensively identifying factors that regulate cell fate, large scale genetic and chemical screening methods have thus been utilized. Here, we provide an overview of the underlying concept of cell reprogramming as well as the rationale, considerations, and limitations of high throughput screening methods. We next follow with a summary of unique hits that have been identified by high throughput screens to induce reprogramming to various parenchymal lineages. Finally, we discuss future directions of applying this technology toward human disease biology via disease modeling, drug screening, and regenerative medicine.

Conversion of Fibroblast into Functional Leydig-like Cell Using Defined Small Molecules

Recent studies have demonstrated that fibroblasts can be directly converted into functional Leydig cells by transcription factors. However, the transgenic approach used in these studies raises safety concerns for its future application. Here, we report that fibroblasts can be directly reprogrammed into Leydig-like cells by exposure to a combination of forskolin, 20α-hydroxycholesterol, luteinizing hormone, and SB431542. These chemical compound-induced Leydig-like cells (CiLCs) express steroidogenic genes and have a global gene expression profile similar to that of progenitor Leydig cells, although not identical. In addition, these cells can survive in testis and produce testosterone in a circadian rhythm. This induction strategy is applicable to reprogramming human periodontal ligament fibroblasts toward Leydig-like cells. These findings demonstrated fibroblasts can be directly converted into Leydig-like cells by pure chemical compounds. This strategy overcomes the limitations of conventional transgenic-based reprogramming and provides a simple, effective approach for Leydig cell-based therapy while simultaneously preserving the hypothalamic-pituitary-gonadal axis.

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Direct induction of fibroblasts into Leydig-like cells (CiLCs) by chemicals

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CiLCs were modulated by HPG axis and produced testosterone in a diurnal rhythm

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Conversion process toward CiLCs did not pass through an intermediate state

Heart Regeneration by Endogenous Stem Cells and Cardiomyocyte Proliferation: Controversy, Fallacy, and Progress

Ischemic heart disease is the leading cause of death worldwide. Myocardial infarction results in an irreversible loss of cardiomyocytes with subsequent adverse remodeling and heart failure. Identifying new sources for cardiomyocytes and promoting their formation represents a goal of cardiac biology and regenerative medicine. Within the past decade, many types of putative cardiac stem cells (CSCs) have been reported to regenerate the injured myocardium by differentiating into new cardiomyocytes. Some of these CSCs have been translated from bench to bed with reported therapeutic effectiveness. However, recent basic research studies on stem cell tracing have begun to question their fundamental biology and mechanisms of action, raising serious concerns over the myogenic potential of CSCs. We review the history of different types of CSCs within the past decade and provide an update of recent cell tracing studies that have challenged the origin and existence of CSCs. In addition to the potential role of CSCs in heart regeneration, proliferation of preexisting cardiomyocytes has recently gained more attention. This review will also evaluate the methodologic and technical aspects of past and current studies on CSCs and cardiomyocyte proliferation, with emphasis on technical strengths, advantages, and potential limitations of research approaches. While our understanding of cardiomyocyte generation and regeneration continues to evolve, it is important to address the shortcomings and inaccuracies in this field. This is best achieved by embracing technological advancements and improved methods to label single cardiomyocytes/progenitors and accurately investigate their developmental potential and fate/lineage commitment.

Sweat gland regeneration: Current strategies and future opportunities

For patients with extensive skin defects, loss of sweat glands (SwGs) greatly decreases their quality of life. Indeed, difficulties in thermoregulation, ion reabsorption, and maintaining fluid balance might render them susceptible to hyperthermia, heatstroke, or even death. Despite extensive studies on the stem cell biology of the skin in recent years, in-situ regeneration of SwGs with both structural and functional fidelity is still challenging because of the limited regenerative capacity and cell fate control of resident progenitors. To overcome these challenges, one must consider both the intrinsic factors relevant to genetic and epigenetic regulation and cues from the cellular microenvironment. Here, we describe recent progress in molecular biology, developmental pathways, and cellular evolution associated with SwGdevelopment and maturation. This is followed by a summary of the current strategies used for cell-fate modulation, transmembrane drug delivery, and scaffold design associated with SwGregeneration. Finally, we offer perspectives for creating more sophisticated systems to accelerate patients' innate healing capacity and developing engineered skin constructs to treat or replace damaged tissues structurally and functionally.

Bmi1 inhibitor PTC-209 promotes Chemically-induced Direct Cardiac Reprogramming of cardiac fibroblasts into cardiomyocytes

The development of therapeutic approaches based on direct cardiac reprogramming of fibroblasts into induced-cardiomyocytes (iCM) has emerged as an attractive strategy to repair the injured myocardium. The identification of the mechanisms driving lineage conversion represents a crucial step toward the development of new and more efficient regenerative strategies. To this aim, here we show that pre-treatment with the Bmi1 inhibitor PTC-209 is sufficient to increase the efficiency of Chemical-induced Direct Cardiac Reprogramming both in mouse embryonic fibroblasts and adult cardiac fibroblasts. PTC-209 induces an overall increase of spontaneously beating iCM at end-stage of reprogramming, expressing high levels of late cardiac markers Troponin T and myosin muscle light chain-2v. The inhibition of Bmi1 expression occurring upon PTC-209 pre-treatment was maintained throughout the reprogramming protocol, contributing to a significant gene expression de-regulation. RNA profiling revealed that, upon Bmi1 inhibition a significant down-regulation of genes associated with immune and inflammatory signalling pathways occurred, with repression of different genes involved in interleukin, cytokine and chemokine pathways. Accordingly, we observed the down-regulation of both JAK/STAT3 and MAPK/ERK1-2 pathway activation, highlighting the crucial role of these pathways as a barrier for cardiac reprogramming. These findings have significant implications for the development of new cardiac regenerative therapies.

Arrhythmogenic risks of stem cell replacement therapy for cardiovascular diseases

Ischemic heart disease and congestive heart failure are major contributors to high morbidity and mortality. Approximately 1.5 million cases of myocardial infarction occur annually in the United States; the yearly incidence rate is approximately 600 cases per 100,000 people. Although significant progress to improve the survival rate has been made by medications and implantable medical devices, damaged cardiomyocytes are unable to be recovered by current treatment strategies. After almost two decades of research, stem cell therapy has become a very promising approach to generate new cardiomyocytes and enhance the function of the heart. Along with clinical trials with stem cells conducted in cardiac regeneration, concerns regarding safety and potential risks have emerged. One of the contentious issues is the electrical dysfunctions of cardiomyocytes and cardiac arrhythmia after stem cell therapy. In this review, we focus on the cell sources currently used for stem cell therapy and discuss related arrhythmogenic risk.

Isoform Specific Effects of Mef2C during Direct Cardiac Reprogramming

Direct conversion of cardiac fibroblasts into induced cardiomyocytes (iCMs) by forced expression of defined factors holds great potential for regenerative medicine by offering an alternative strategy for treatment of heart disease. Successful iCM conversion can be achieved by minimally using three transcription factors, Mef2c (M), Gata4(G), and Tbx5 (T). Despite increasing interest in iCM mechanistic studies using MGT(polycistronic construct with optimal expression of M,G and T), the reprogramming efficiency varies among different laboratories. Two main Mef2c isoforms (isoform2, Mi2 and isoform4, Mi4) are present in heart and are used separately by different labs, for iCM reprogramming. It is currently unknown if differently spliced isoform of Mef2c contributes to varied reprogramming efficiency. Here, we used Mi2 and Mi4 together with Gata4 and Tbx5 in separate vectors or polycistronic vector, to convert fibroblasts to iCMs. We found that Mi2 can induce higher reprogramming efficiency than Mi4 in MEFs. Addition of Hand2 to MGT retroviral cocktail or polycistronic Mi2-GT retroviruses further enhanced the iCM conversion. Overall, this study demonstrated the isoform specific effects of Mef2c, during iCM reprogramming, clarified some discrepancy about varied efficiency among labs and might lead to future research into the role of alternative splicing and the consequent variants in cell fate determination.

Impelling force and current challenges by chemicals in somatic cell reprogramming and expansion beyond hepatocytes

In the field of regenerative medicine, generating numerous transplantable functional cells in the laboratory setting on a large scale is a major challenge. However, the in vitro maintenance and expansion of terminally differentiated cells are challenging because of the lack of specific environmental and intercellular signal stimulations, markedly hindering their therapeutic application. Remarkably, the generation of stem/progenitor cells or functional cells with effective proliferative potential is markedly in demand for disease modeling, cell-based transplantation, and drug discovery. Despite the potent genetic manipulation of transcription factors, integration-free chemically defined approaches for the conversion of somatic cell fate have garnered considerable attention in recent years. This review aims to summarize the progress thus far and discuss the advantages, limitations, and challenges of the impact of full chemicals on the stepwise reprogramming of pluripotency, direct lineage conversion, and direct lineage expansion on somatic cells. Owing to the current chemical-mediated induction, reprogrammed pluripotent stem cells with reproducibility difficulties, and direct lineage converted cells with marked functional deficiency, it is imperative to generate the desired cell types directly by chemically inducing their potent proliferation ability through a lineage-committed progenitor state, while upholding the maturation and engraftment capacity posttransplantation in vivo. Together with the comprehensive understanding of the mechanism of chemical drives, as well as the elucidation of specificity and commonalities, the precise manipulation of the expansion for diverse functional cell types could broaden the available cell sources and enhance the cellular function for clinical application in future.

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.

Chemically induced cell fate reprogramming and the acquisition of plasticity in somatic cells

The nature of somatic cell fate has always been considered relatively unchangeable. Only in rare cases, in response to highly specific environmental cues, do differentiated mammalian somatic cells transform into other cell types. However, the fact that cell fate reprogramming can be accomplished by utilizing chemical cocktails, in the absence of any genetic alterations, suggests that the fate determination of somatic cells is much more malleable than previously believed. The use of chemical cocktails to directly alter cell fate sheds light on an important, yet less explored approach to regenerative medicine: the use of chemicals to restore functions to injured, aging or diseased tissues. Here, we review and discuss the recent developments, inspirations, and challenges encountered when modulating cell fate reprogramming with chemicals, and investigate how chemical biology impacts the future of cell fate reprogramming and regenerative medicine.

Cellular Reprogramming as a Therapeutic Target in Cancer

Cancer heterogeneity has long been recognized as an important clinical determinant of patient outcomes and, thus, many new cancer treatments have been designed to target these different cells. Despite the short-term achievements of current therapies, including chemotherapy, antiangiogenesis therapy, radiotherapy, and immunotherapy, the long-term success of cancer regression remains poor. Therefore, researchers have investigated a new property, cellular reprogramming, in cancer that not only contributes to the classic hallmarks of cancer, but also suggests that cancer is a dynamic event rather than a static cellular entity. Here, we discuss the mechanisms by which the cellular reprogramming of cancer cells can explain some of the phenotypic and functional heterogeneity observed among cancer cells.

Impact of Biomaterials on Differentiation and Reprogramming Approaches for the Generation of Functional Cardiomyocytes

The irreversible loss of functional cardiomyocytes (CMs) after myocardial infarction (MI) represents one major barrier to heart regeneration and functional recovery. The combination of different cell sources and different biomaterials have been investigated to generate CMs by differentiation or reprogramming approaches although at low efficiency. This critical review article discusses the role of biomaterial platforms integrating biochemical instructive cues as a tool for the effective generation of functional CMs. The report firstly introduces MI and the main cardiac regenerative medicine strategies under investigation. Then, it describes the main stem cell populations and indirect and direct reprogramming approaches for cardiac regenerative medicine. A third section discusses the main techniques for the characterization of stem cell differentiation and fibroblast reprogramming into CMs. Another section describes the main biomaterials investigated for stem cell differentiation and fibroblast reprogramming into CMs. Finally, a critical analysis of the scientific literature is presented for an efficient generation of functional CMs. The authors underline the need for biomimetic, reproducible and scalable biomaterial platforms and their integration with external physical stimuli in controlled culture microenvironments for the generation of functional CMs.

Regenerating the Cardiovascular System Through Cell Reprogramming; Current Approaches and a Look Into the Future

Cardiovascular disease (CVD), despite the advances of the medical field, remains one of the leading causes of mortality worldwide. Discovering novel treatments based on cell therapy or drugs is critical, and induced pluripotent stem cells (iPS Cells) technology has made it possible to design extensive disease-specific in vitro models. Elucidating the differentiation process challenged our previous knowledge of cell plasticity and capabilities and allows the concept of cell reprogramming technology to be established, which has inspired the creation of both in vitro and in vivo techniques. Patient-specific cell lines provide the opportunity of studying their pathophysiology in vitro, which can lead to novel drug development. At the same time, in vivo models have been designed where in situ transdifferentiation of cell populations into cardiomyocytes or endothelial cells (ECs) give hope toward effective cell therapies. Unfortunately, the efficiency as well as the concerns about the safety of all these methods make it exceedingly difficult to pass to the clinical trial phase. It is our opinion that creating an ex vivo model out of patient-specific cells will be one of the most important goals in the future to help surpass all these hindrances. Thus, in this review we aim to present the current state of research in reprogramming toward the cardiovascular system's regeneration, and showcase how the development and study of a multicellular 3D ex vivo model will improve our fighting chances.