Recent advances in direct cardiac reprogramming
Introduction
Heart disease remains the leading cause of morbidity and mortality in developed countries [1]. Currently, there are no solutions to replenish cardiomyocytes lost to heart injury. The lost cardiomyocytes in the injured region are replaced by scar tissue formed from activated fibroblasts and the extracellular matrix secreted by those fibroblasts [2]. Mammalian hearts do appear to have a small amount of cardiomyocyte turnover over a lifetime [3, 4]; however, it is insufficient for meaningful regeneration.
Although cell-based efforts for regenerative therapy are aggressively being pursued, an alternative approach to regenerate an injured heart is to directly reprogram resident cardiac fibroblasts (CFs) into induced cardiomyocyte-like cells (iCMs) using a cocktail of developmental regulatory proteins that normally guide cardiac fate during cardiogenesis. While this approach has its own limitations and obstacles, it circumvents some of the obstacles of cell-based therapy, including efficient transplantation and integration within the area of injured myocardium and creation of mature cardiomyocytes for transplantation. Here, we will discuss advances in direct cardiac reprogramming and consider the challenges and potential of this strategy for regenerative medicine.
Section snippets
Reprogramming of mouse fibroblasts into cardiomyocyte-like cells
In 2010, our group reported that mouse cardiac and dermal fibroblasts could be converted into cardiomyocyte-like cells in vitro with ectopic expression of three transcription factors: Gata4, Mef2c, and Tbx5 (GMT) [5••]. This strategy was inspired by the successes in molecular reprogramming from somatic cells into induced pluripotent stem cells (iPSCs) [6, 7, 8] and provided a new potential strategy to regenerate cardiomyocytes. Similar to iPSC reprogramming, a larger population of cells were
In vivo cardiac reprogramming
The initial intention of the in vitro reprogramming effort was to ultimately harness the large pool of endogenous CFs as an alternative resource for cardiac regeneration in situ. Accordingly, in 2012, three groups found that in vivo delivery of the GMT transcription factors directly into the heart using a gene therapy approach converted endogenous mouse non-myocytes into iCMs [9••, 10••, 11]. The mice had decreased infarct size and attenuated cardiac dysfunction after coronary ligation and in
Enhancing efficiency of direct cardiac reprogramming
Since the publication of the initial mouse study of in vitro cardiac reprogramming in 2010, several groups have reported methods to improve the efficiency of this approach. Here we discuss the recent results that reported improvements in mouse cardiac reprogramming by (1) altering the combination of reprogramming factors [9••, 21, 22, 23, 24, 25], (2) manipulating signaling pathways [26, 27], or (3) optimizing the stoichiometry of the reprogramming factors [28]. Some of the strategies for
Direct cardiac reprogramming in human cells
In 2013, three reports demonstrated successful cardiac reprogramming in the human system [30•, 31•, 32•]. All three groups found that neither the combination of GMT nor GHMT was sufficient to reprogram human fibroblasts into iCMs. Each group used additional factors to successfully achieve some degree of human cardiac reprogramming. Nam et al. found that the combination of four human transcription factors (GATA4, HAND2, TBX5 and MYOCD) plus two microRNAs (miR-1 and miR-133) activated cardiac
Challenges and future directions for cardiac reprogramming
Recent advances made in mouse and human systems indicate that cardiac reprogramming efficiency is steadily being advanced by various strategies and might eventually become powerful enough for clinical application and disease modeling studies. One intriguing area worth noting is the qualitative difference observed from iCMs between in vitro and in vivo settings [9••, 10••]. iCMs generated in vivo appeared to be more similar to the endogenous cardiomyocytes than those from in vitro studies,
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Acknowledgements
We thank Bethany Taylor and Gary Howard for their editorial support and all Srivastava lab members for helpful discussion. P.Y. was supported by a CIRM training grant (TG2-01160). D.S. was supported by grants from NHLBI/NIH (U01 HL100405, U01 HL098179, R01 HL057181, P01 HL098707), L.K. Whittier Foundation, William Younger Family Foundation, Eugene Roddenberry Foundation, the California Institute for Regenerative Medicine (CIRM), and by NIH/NCRR grant (C06RR018928) to the Gladstone Institutes.
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2023, Bioactive MaterialsCitation Excerpt :Direct conversion of noncardiomyocytes into CMs seems like a feasible solution for overcoming these challenges. Nevertheless, direct reprogramming of noncardiomyocytes into cardiomyocyte-like cells (iCMs) requires complex reprogramming techniques and with low efficiency [6,7], especially in vivo [8,9]. It is more critical that these reprogrammed cells hold only minor components of the natural CMs, unable to compensate for the loss of CMs completely [10].
Direct reprogramming of adult adipose-derived regenerative cells toward cardiomyocytes using six transcriptional factors
2022, iScienceCitation Excerpt :In the current study, we isolated ADRCs from an αMHC-EGFP reporter mouse expressing GFP, specifically in cardiomyocytes. This system has been extensively used in a series of reprogramming studies as an indicator of transdifferentiation of fibroblast to cardiomyocyte (Ieda et al., 2010; Srivastava and Yu, 2015). We also took advantage of this system and found that six transcriptional factors could induce approximately 2–7% GFP in ADRCs (Figure S2C); however, we could not find mature cardiomyocytes.
Overcoming the Roadblocks to Cardiac Cell Therapy Using Tissue Engineering
2017, Journal of the American College of CardiologyCitation Excerpt :Furthermore, although the fibroproliferative response (i.e., scar formation) is beneficial for short-term stability at the injury site, it interferes with subsequent repair processes, such as vascular growth and potentially remuscularization. Thus, researchers have also begun to investigate methods for controlling or reverting fibrosis by reprogramming fibroblasts into CMs or ECs (68–70), and by identifying the cellular source(s) contributing to scar formation (71,72). The use of tissue-engineered systems may increase in vitro efficacy and improve understanding of the direct cardiac reprogramming processes (73,74), as well as permit well-controlled mechanistic studies of CM/nonmyocyte interactions (75).
The Promise and Challenge of Induced Pluripotent Stem Cells for Cardiovascular Applications
2016, JACC: Basic to Translational ScienceCitation Excerpt :In 2012, in vivo delivery of Gata4, Mef2c, and Tbx5 transcription factors using a gene therapy approach converted mouse nonmyocytes into induced cardiomyocytes with improved cardiac function and reduced scar size after MI (103,104). Compared with the in vitro induced cardiomyocytes, in vivo induced cells appeared more similar to endogenous cardiomyocytes, suggesting the importance of in vivo environmental cues such as electromechanical stimulation, signaling pathways, and extracellular matrix (105). This approach appears promising but carries significant limitations, including low efficiency, incomplete reprogramming, lack of robust experimental reproducibility, and the use of retroviral vectors in vivo (106).
In Vivo Cellular Reprogramming: The Next Generation
2016, CellCitation Excerpt :However, the in vitro efficiency was limited, and most of the iCMs were only partially reprogrammed, suggesting that other factors may enhance reprogramming, at least in vitro. As might be expected for a new technology, other combinations of factors in vitro were later found to convert fibroblasts to iCMs with greater efficiency (reviewed in Srivastava and Yu, 2015). Additional transcription factors such as Hand2 (Song et al., 2012; Srivastava et al., 1997) and miRNAs such as the muscle-specific miRNAs miR-1 and miR-133 (Chen et al., 2006; Heidersbach et al., 2013; Muraoka et al., 2014; Zhao et al., 2007; Zhao et al., 2005) increased the conversion rate in vitro.
Endogenous Mechanisms of Cardiac Regeneration
2016, International Review of Cell and Molecular BiologyCitation Excerpt :This review will not primarily focus on recent advances in exogenous approaches that enhance cardiac regeneration such as biomaterial engineering, regenerative compound synthesis and screening, exogenous stem cell transplantation, in vitro cardiomyocyte differentiation, and cell reprogramming. We refer interested readers to the recent reviews on these topics (Birket and Mummery, 2015; Chong and Murry, 2014; Coulombe et al., 2014; Laflamme and Murry, 2011; Lui et al., 2014; Muraoka and Ieda, 2014; Musunuru et al., 2010; Srivastava and Yu, 2015; Yoshida and Yamanaka, 2011). Rather, we will discuss the cellular and molecular basis for endogenous mechanisms of cardiac regeneration with a particular focus on the remarkable regeneration observed in zebrafish and neonatal mouse heart models.