Reprogramming barriers and enhancers: strategies to enhance the efficiency and kinetics of induced pluripotency

Abstract

Induced pluripotent stem cells are powerful tools for disease modeling, drug screening, and cell transplantation therapies. These cells can be generated directly from somatic cells by ectopic expression of defined factors through a reprogramming process. However, pluripotent reprogramming is an inefficient process because of various defined and unidentified barriers. Recent studies dissecting the molecular mechanisms of reprogramming have methodically improved the quality, ease, and efficiency of reprogramming. Different strategies have been applied for enhancing reprogramming efficiency, including depletion/inhibition of barriers (p53, p21, p57, p16Ink4a/p19Arf, Mbd3, etc.), overexpression of enhancing genes (e.g., FOXH1, C/EBP alpha, UTF1, and GLIS1), and administration of certain cytokines and small molecules. The current review provides an in-depth overview of the cutting-edge findings regarding distinct barriers of reprogramming to pluripotency and strategies to enhance reprogramming efficiency. By incorporating the mechanistic insights from these recent findings, a combined method of inhibition of roadblocks and application of enhancing factors may yield the most reliable and effective approach in pluripotent reprogramming.

Human Induced Pluripotent Stem Cells as a Platform for Personalized and Precision Cardiovascular Medicine

“…Rais et al (225) and Lujan et al (168) also demonstrated in both human and mouse cells that almost 100% of cells in a differentiated population are capable of reprogramming following depletion of Mbd3, a core member of the Mbd3/NuRD (nucleosome remodeling and deacetylation) repressor complex. Even though some controversy exists around this topic, likely due to due technical differences (64), these studies potentially demonstrate that while iPSC reprogramming is typically a stochastic process, it can become deterministic upon epigenetic manipulation.…”

Direct Cardiac Cellular Reprogramming for Cardiac Regeneration

“…In particular, the recently discovered resistance of human cells to reprogramming is an important barrier to the clinical application of this heart failure treatment strategy [23, 38, 40–42]. The resistance of adult human cardiac fibroblasts to reprogramming compared to rodent cells may be related to the relatively more complex gene regulatory network of the former, which may include rigorous epigenetic barriers to reprogramming that likely normally serve, for example, to impede promiscuous gene activation and tumorigenesis [44]. Systemic gene surveys have for example revealed that over 956 genes encompassing multiple functions such as chromatin regulation, transcription regulation, intracellular signaling, and cell adhesion are opposed to reprogramming in human cells [45].…”

Translational Prospects and Challenges in Human Induced Pluripotent Stem Cell Research in Drug Discovery

“…iPS cells have ushered in a new era of translational medicine because they can be used to generate patient-derived pluripotent stem cell lines that can recapitulate not only disease phenotypes but also the process of disease development [11]. Importantly, even though Retro- and Lenti-viral vectors have been the first methods of choice to reprogram somatic cells to pluripotency while still offering one of the highest reprogramming efficiencies, utilizing non-integrating, zero-footprint methods—such as those based on mRNA—miRNA, episomal vectors, and Sendai virus have brought iPS cell (iPSC)-derived cells closer to the clinical application stage [12,13,14]. These improved methods for iPSC reprogramming prevent the risk of vectors randomly integrating into the host’s genome, with no noticeable differences in the frequency and the type of karyotypic change observed [15].…”