Chemical-only reprogramming to pluripotency

Two Sets of Compound Complex Driving for High Efficiency of Nonintegration Reprogramming of Human Fibroblasts

Currently, plentiful chemical-assisted methods have been applied for mouse induced pluripotent stem cells (iPSCs). It has been reported that small-molecule compounds can only reprogram mouse embryonic fibroblasts into mouse chemically induced pluripotent stem cells (mouse CiPSCs). However, human CiPSCs have not been reported. Therefore, it is still necessary to search for safer chemically assisted human pluripotent stem cells, which might realize the potential of human iPSCs. Here, we developed two sets of chemical cocktails to greatly improve the induction efficiency of human nonintegrated iPSCs, including the 4 compound mixture (4M) and the 5 compound mixture (4MI). These two sets of complex driving strategies might greatly improve the reprogramming efficiency to generate integration-free iPSCs.

An Insight into DNA-free Reprogramming Approaches to Generate Integration-free Induced Pluripotent Stem Cells for Prospective Biomedical Applications

More than a decade ago, a pioneering study reported generation of induced Pluripotent Stem Cells (iPSCs) by ectopic expression of a cocktail of reprogramming factors in fibroblasts. This study has revolutionized stem cell research and has garnered immense interest from the scientific community globally. iPSCs hold tremendous potential for understanding human developmental biology, disease modeling, drug screening and discovery, and personalized cell-based therapeutic applications. The seminal study identified Oct4, Sox2, Klf4 and c-Myc as a potent combination of genes to induce reprogramming. Subsequently, various reprogramming factors were identified by numerous groups. Most of these studies have used integrating viral vectors to overexpress reprogramming factors in somatic cells to derive iPSCs. However, these techniques restrict the clinical applicability of these cells as they may alter the genome due to random viral integration resulting in insertional mutagenesis and tumorigenicity. To circumvent this issue, alternative integration-free reprogramming approaches are continuously developed that eliminate the risk of genomic modifications and improve the prospects of iPSCs from lab to clinic. These methods establish that integration of transgenes into the genome is not essential to induce pluripotency in somatic cells. This review provides a comprehensive overview of the most promising DNA-free reprogramming techniques that have the potential to derive integration-free iPSCs without genomic manipulation, such as sendai virus, recombinant proteins, microRNAs, synthetic messenger RNA and small molecules. The understanding of these approaches shall pave a way for the generation of clinical-grade iPSCs. Subsequently, these iPSCs can be differentiated into desired cell type(s) for various biomedical applications.

Cardiac progenitor reprogramming for heart regeneration

Myocardial infarction leads to the loss of a huge number of cardiomyocytes and the reparatory response to this phenomenon is scar tissue formation, which impairs heart function. Direct reprogramming technology offers an alternative strategy for the generation of functional cardiomyocytes not only in vitro, but also in vivo in the site of injury. Results have demonstrated cardiac tissue regeneration and improvement in heart function after myocardial infarction following local injection of vectors encoding reprogramming transcription factors or miRNAs. This shows the great potential of cardiac reprogramming technology for heart regeneration. However, in addition to cardiomyocytes, other cell types, including endothelial cells and smooth muscle cells are also required to be generated in the damaged area in order to achieve complete cardiac tissue regeneration. To this aim induced proliferative/expandable cardiovascular progenitor cells (iCPCs) appear to be an appropriate cell source, which is capable of differentiation into three cardiovascular lineages both in vitro and in vivo. In this regard, this study goes over in vitro and in vivo cardiac reprogramming technology and specifically deals with cardiac progenitor reprogramming and its potential for heart regeneration.

Transcription factors: Time to deliver

Transcription factors (TFs) are at the center of the broad regulatory network orchestrating gene expression programs that elicit different biological responses. For a long time, TFs have been considered as potent drug targets due to their implications in the pathogenesis of a variety of diseases. At the same time, TFs, located at convergence points of cellular regulatory pathways, are powerful tools providing opportunities both for cell type change and for managing the state of cells. This task formulation requires the TF modulation problem to come to the fore. We review several ways to manage TF activity (small molecules, transfection, nanocarriers, protein-based approaches), analyzing their limitations and the possibilities to overcome them. Delivery of TFs could revolutionize the biomedical field. Whether this forecast comes true will depend on the ability to develop convenient technologies for targeted delivery of TFs.

In vivo reprogramming for heart regeneration: A glance at efficiency, environmental impacts, challenges and future directions

Replacing dying or diseased cells of a tissue with new ones that are converted from patient's own cells is an attractive strategy in regenerative medicine. In vivo reprogramming is a novel strategy that can circumvent the hurdles of autologous/allogeneic cell injection therapies. Interestingly, studies have demonstrated that direct injection of cardiac transcription factors or specific miRNAs into the infarct border zone of murine hearts following myocardial infarction converts resident cardiac fibroblasts into functional cardiomyocytes. Moreover, in vivo cardiac reprogramming not only drives cardiac tissue regeneration, but also improves cardiac function and survival rate after myocardial infarction. Thanks to the influence of cardiac microenvironment and the same developmental origin, cardiac fibroblasts seem to be more amenable to reprogramming toward cardiomyocyte fate than other cell sources (e.g. skin fibroblasts). Thus, reprogramming of cardiac fibroblasts to functional induced cardiomyocytes in the cardiac environment holds great promises for induced regeneration and potential clinical purposes. Application of small molecules in future studies may represent a major advancement in this arena and pharmacological reprogramming would convey reprogramming technology to the translational medicine paradigm. This study reviews accomplishments in the field of in vitro and in vivo mouse cardiac reprogramming and then deals with strategies for the enhancement of the efficiency and quality of the process. Furthermore, it discusses challenges ahead and provides suggestions for future research. Human cardiac reprogramming is also addressed as a foundation for possible application of in vivo cardiac reprogramming for human heart regeneration in the future.