Pluripotent Stem Cells for Cardiac Regeneration - Current Status, Challenges, and Future Perspectives

Are There Hopeful Therapeutic Strategies to Regenerate the Infarcted Hearts?

Ischemic heart disease remains the primary cause of morbidity and mortality worldwide. Despite significant advancements in pharmacological and revascularization techniques in the late 20th century, heart failure prevalence after myocardial infarction has gradually increased over the last 2 decades. After ischemic injury, pathological remodeling results in cardiomyocytes (CMs) loss and fibrosis, which leads to impaired heart function. Unfortunately, there are no clinical therapies to regenerate CMs to date, and the adult heart's limited turnover rate of CMs hinders its ability to self-regenerate. In this review, we present novel therapeutic strategies to regenerate injured myocardium, including (1) reconstruction of cardiac niche microenvironment, (2) recruitment of functional CMs by promoting their proliferation or differentiation, and (3) organizing 3-dimensional tissue construct beyond the CMs. Additionally, we highlight recent mechanistic insights that govern these strategies and identify current challenges in translating these approaches to human patients.

Intracoronary transplantation of pluripotent stem cell-derived cardiomyocytes: Inefficient procedure for cardiac regeneration

Advances in stem cell biology have facilitated cardiac regeneration, and many animal studies and several initial clinical trials have been conducted using human pluripotent stem cell-derived cardiomyocytes (PSC-CMs). Most preclinical and clinical studies have typically transplanted PSC-CMs via the following two distinct approaches: direct intramyocardial injection or epicardial delivery of engineered heart tissue. Both approaches present common disadvantages, including a mandatory thoracotomy and poor engraftment. Furthermore, a standard transplantation approach has yet to be established. In this study, we tested the feasibility of performing intracoronary administration of PSC-CMs based on a commonly used method of transplanting somatic stem cells. Six male cynomolgus monkeys underwent intracoronary administration of dispersed human PSC-CMs or PSC-CM aggregates, which are called cardiac spheroids, with multiple cell dosages. The recipient animals were sacrificed at 4 weeks post-transplantation for histological analysis. Intracoronary administration of dispersed human PSC-CMs in the cynomolgus monkeys did not lead to coronary embolism or graft survival. Although the transplanted cardiac spheroids became partially engrafted, they also induced scar formation due to cardiac ischemic injury. Cardiac engraftment and scar formation were reasonably consistent with the spheroid size or cell dosage. These findings indicate that intracoronary transplantation of PSC-CMs is an inefficient therapeutic approach.

Approaches to the use of stem cells in regenerative medicine

PURPOSE

The goal of regenerative medicine is to replace or restore missing, dysfunctional, or damaged cells, tissues and organs of a person to reproduce their normal function. The main approaches are cell therapy, tissue engineering, and gene therapy. Postnatal neural crest-derived multipotent stem cells (NC-MSC) are a promising cell type for use in regenerative medicine. This is due to the specific features of their embryonic origin and the role of the neural crest in phylogeny and ontogeny of vertebrates.

METHODS

The study used research in vitro culture (monolayer cell culture, 3D culture based on hydrogels, organotypic culture of hippocampal slices, spherogenesis, directed differentiation); flow cytometry; cytochemical, immune-cytochemical and histomorphometric analysis; molecular genetic (RNA (ribonucleic acid) isolation, PCR (polymerase chain reaction) with reverse transcription, real-time PCR, nucleic acid electrophoresis); microscopy (transmitted light, phase contrast, fluorescent, confocal laser scanning); microsurgical; statistical analysis.

RESULTS

In this systematic review, the results showed that recently the neural crest-derived cells have been isolated from a wide range of tissues and organs of mammals at the postnatal stage of development. These cells, at least in vitro, demonstrate the ability to self-repair and multilinear differentiation into neurons, Schwann cells, melanocytes, adipocytes, osteoblasts, chondrocytes, and other types of cells, that is, according to their functional characteristics, they are multipotent stem cells.

CONCLUSION

According to the obtained results, tissue sources of postnatal neural crest-derived multipotent stem cells differ considerably in the degree of invasiveness of biopsy sampling, as well as the possibility of obtaining a homogeneous population of NC-MSCs, which is important for further clinical use.

Recent Advances in Gene Therapy for Cardiac Tissue Regeneration

Cardiovascular diseases (CVDs) are responsible for enormous socio-economic impact and the highest mortality globally. The standard of care for CVDs, which includes medications and surgical interventions, in most cases, can delay but not prevent the progression of disease. Gene therapy has been considered as a potential therapy to improve the outcomes of CVDs as it targets the molecular mechanisms implicated in heart failure. Cardiac reprogramming, therapeutic angiogenesis using growth factors, antioxidant, and anti-apoptotic therapies are the modalities of cardiac gene therapy that have led to promising results in preclinical studies. Despite the benefits observed in animal studies, the attempts to translate them to humans have been inconsistent so far. Low concentration of the gene product at the target site, incomplete understanding of the molecular pathways of the disease, selected gene delivery method, difference between animal models and humans among others are probable causes of the inconsistent results in clinics. In this review, we discuss the most recent applications of the aforementioned gene therapy strategies to improve cardiac tissue regeneration in preclinical and clinical studies as well as the challenges associated with them. In addition, we consider ongoing gene therapy clinical trials focused on cardiac regeneration in CVDs.