Direct cellular reprogramming for cardiac repair and regeneration

Progresses and perspectives on natural polysaccharide based hydrogels for repair of infarcted myocardium

Myocardial infarction (MI) is serious health threat and impairs the quality of life. It is a major causative factor of morbidity and mortality. MI leads to the necrosis of cardio-myocytes, cardiac remodelling and dysfunction, eventually leading to heart failure. The limitations of conventional therapeutic and surgical interventions and lack of heart donors have necessitated the evolution of alternate treatment approaches for MI. Polysaccharide hydrogel based repair of infarcted myocardium have surfaced as viable option for MI treatment. Polysaccharide hydrogels may be injectable hydrogels or cardiac patches. Injectable hydrogels can in situ deliver cells and bio-actives, facilitating in situ cardiac regeneration and repair. Polysaccharide hydrogel cardiac patches reduce cardiac wall stress, and inhibit ventricular expansion and promote angiogenesis. Herein, we discuss about MI pathophysiology and myocardial microenvironment and how polysaccharide hydrogels are designed to mimic and support the microenvironment for cardiac repair. We also put forward the versatility of the different polysaccharide hydrogels in mimicking diverse cardiac properties, and acting as a medium for delivery of cells, and therapeutics for promoting angiogenesis and cardiac repair. The objectives of this review is to summarize the factors leading to MI and to put forward how polysaccharide based hydrogels promote cardiac repair. This review is written to enable researchers understand the factors promoting MI so that they can undertake and design novel hydrogels for cardiac regeneration.

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 cardiac reprogramming: basics and future challenges

BACKGROUND

Heart failure is the leading cause of morbidity and mortality worldwide and is characterized by reduced cardiac function. Currently, cardiac transplantation therapy is applied for end-stage heart failure, but it is limited by the number of available donors.

METHODS AND RESULTS

Following an assessment of available literature, a narrative review was conducted to summarizes the current status and challenges of cardiac reprogramming for clinical application. Scientists have developed different regenerative treatment strategies for curing heart failure, including progenitor cell delivery and pluripotent cell delivery. Recently, a novel strategy has emerged that directly reprograms cardiac fibroblast into a functional cardiomyocyte. In this treatment, transcription factors are first identified to reprogram fibroblast into a cardiomyocyte. After that, microRNA and small molecules show great potential to optimize the reprogramming process. Some challenges regarding cell reprogramming in humans are conversion efficiency, virus utilization, immature and heterogenous induced cardiomyocytes, technical reproducibility issues, and physiological effects of depleted fibroblasts on myocardial tissue.

CONCLUSION

Several strategies have shown positive results in direct cardiac reprogramming. However, direct cardiac reprogramming still needs improvement if it is used as a mainstay therapy in humans, and challenges need to be overcome before cardiac reprogramming can be considered a viable therapeutic strategy. Further advances in cardiac reprogramming studies are needed in cardiac regenerative therapy.

Cardiac Tissue-like 3D Microenvironment Enhances Route towards Human Fibroblast Direct Reprogramming into Induced Cardiomyocytes by microRNAs

The restoration of cardiac functionality after myocardial infarction represents a major clinical challenge. Recently, we found that transient transfection with microRNA combination (miRcombo: miR-1, miR-133, miR-208 and 499) is able to trigger direct reprogramming of adult human cardiac fibroblasts (AHCFs) into induced cardiomyocytes (iCMs) in vitro. However, achieving efficient direct reprogramming still remains a challenge. The aim of this study was to investigate the influence of cardiac tissue-like biochemical and biophysical stimuli on direct reprogramming efficiency. Biomatrix (BM), a cardiac-like extracellular matrix (ECM), was produced by in vitro culture of AHCFs for 21 days, followed by decellularization. In a set of experiments, AHCFs were transfected with miRcombo and then cultured for 2 weeks on the surface of uncoated and BM-coated polystyrene (PS) dishes and fibrin hydrogels (2D hydrogel) or embedded into 3D fibrin hydrogels (3D hydrogel). Cell culturing on BM-coated PS dishes and in 3D hydrogels significantly improved direct reprogramming outcomes. Biochemical and biophysical cues were then combined in 3D fibrin hydrogels containing BM (3D BM hydrogel), resulting in a synergistic effect, triggering increased CM gene and cardiac troponin T expression in miRcombo-transfected AHCFs. Hence, biomimetic 3D culture environments may improve direct reprogramming of miRcombo-transfected AHCFs into iCMs, deserving further study.

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.

Toward Cardiac Regeneration: Combination of Pluripotent Stem Cell-Based Therapies and Bioengineering Strategies

Cardiovascular diseases represent the major cause of morbidity and mortality worldwide. Multiple studies have been conducted so far in order to develop treatments able to prevent the progression of these pathologies. Despite progress made in the last decade, current therapies are still hampered by poor translation into actual clinical applications. The major drawback of such strategies is represented by the limited regenerative capacity of the cardiac tissue. Indeed, after an ischaemic insult, the formation of fibrotic scar takes place, interfering with mechanical and electrical functions of the heart. Hence, the ability of the heart to recover after ischaemic injury depends on several molecular and cellular pathways, and the imbalance between them results into adverse remodeling, culminating in heart failure. In this complex scenario, a new chapter of regenerative medicine has been opened over the past 20 years with the discovery of induced pluripotent stem cells (iPSCs). These cells share the same characteristic of embryonic stem cells (ESCs), but are generated from patient-specific somatic cells, overcoming the ethical limitations related to ESC use and providing an autologous source of human cells. Similarly to ESCs, iPSCs are able to efficiently differentiate into cardiomyocytes (CMs), and thus hold a real regenerative potential for future clinical applications. However, cell-based therapies are subjected to poor grafting and may cause adverse effects in the failing heart. Thus, over the last years, bioengineering technologies focused their attention on the improvement of both survival and functionality of iPSC-derived CMs. The combination of these two fields of study has burst the development of cell-based three-dimensional (3D) structures and organoids which mimic, more realistically, the in vivo cell behavior. Toward the same path, the possibility to directly induce conversion of fibroblasts into CMs has recently emerged as a promising area for in situ cardiac regeneration. In this review we provide an up-to-date overview of the latest advancements in the application of pluripotent stem cells and tissue-engineering for therapeutically relevant cardiac regenerative approaches, aiming to highlight outcomes, limitations and future perspectives for their clinical translation.

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.

Cardiac resident macrophages are involved in hypoxia‑induced postnatal cardiomyocyte proliferation

Induction of cardiomyocyte proliferation, the most promising approach to reverse myocardial attrition, has been gaining importance as a therapy for cardiovascular disease. Hypoxia and macrophages were previously independently reported to promote cardiomyocyte proliferation in mice. However, whether hypoxia promotes cardiomyocyte proliferation in humans, and the association between hypoxia and macrophages in cardiomyocyte proliferation, have not to the best of our knowledge been previously investigated. The present study investigated the cardiomyocyte proliferation in 22 acyanotic and 29 cyanotic patients. Cardiomyocyte proliferation in a hypoxic mouse model (15% O₂) was subsequently performed and the macrophage subsets were analyzed. A C-C chemokine receptor type 2 (CCR2) inhibitor was used to increase the number of resident macrophages in order to investigate the effect of macrophages on cardiomyocyte proliferation. The results demonstrated that cardiomyocyte proliferation in the cyanotic infant group was significantly increased compared with the acyanotic infant group and the hypoxia-treated C57BL/6J neonates confirmed the hypoxia-induced cardiomyocyte proliferation. However, hypoxia did not induce the proliferation of isolated cardiomyocytes. Notably, hypoxia treatment increased the number of cardiac resident macrophages in neonate hearts. Furthermore, increasing the number of resident macrophages significantly enhanced cardiomyocyte proliferation. In conclusion, postnatal hypoxia promoted cardiomyocyte proliferation in humans and animals, and cardiac resident macrophages may be involved in this process. Therefore, this novel mechanism may provide a promising strategy for cardiovascular disease treatment.

Notch Inhibition Enhances Cardiac Reprogramming by Increasing MEF2C Transcriptional Activity

Conversion of fibroblasts into functional cardiomyocytes represents a potential means of restoring cardiac function after myocardial infarction, but so far this process remains inefficient and little is known about its molecular mechanisms. Here we show that DAPT, a classical Notch inhibitor, enhances the conversion of mouse fibroblasts into induced cardiac-like myocytes by the transcription factors GATA4, HAND2, MEF2C, and TBX5. DAPT cooperates with AKT kinase to further augment this process, resulting in up to 70% conversion efficiency. Moreover, DAPT promotes the acquisition of specific cardiomyocyte features, substantially increasing calcium flux, sarcomere structure, and the number of spontaneously beating cells. Transcriptome analysis shows that DAPT induces genetic programs related to muscle development, differentiation, and excitation-contraction coupling. Mechanistically, DAPT increases binding of the transcription factor MEF2C to the promoter regions of cardiac structural genes. These findings provide mechanistic insights into the reprogramming process and may have important implications for cardiac regeneration therapies.

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Notch activation is a barrier for GHMT-induced cardiac cell reprogramming

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Notch blockade by DAPT improves GHMT-induced cardiac reprogramming

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DAPT increases sarcomere organization, calcium flux, and beating in GHMT reprogramming

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DAPT enhances transcriptional activity of MEF2C in GHMT reprogramming

Heart failure 2016: still more questions than answers

Heart failure has reached epidemic proportions given the ageing of populations and is associated with high mortality and re-hospitalization rates. This article reviews and summarizes recent advances in the diagnosis, assessment and treatment of the patients with heart failure. Data are discussed based also on the most recent guidelines indications. Open issues and unmet needs are highlighted.

Direct Cardiac Cellular Reprogramming for Cardiac Regeneration

OPINION STATEMENT

Direct cardiac cellular reprogramming of endogenous cardiac fibroblasts directly into induced cardiomyocytes is a highly feasible, promising therapeutic option for patients with advanced heart failure. The most successful cardiac reprogramming strategy will likely be a multimodal approach involving an optimal combination of cardio-differentiating factors, suppression of fibroblast gene expression, and induction of angiogenic factors.