In situ reprogramming to transdifferentiate fibroblasts into cardiomyocytes using adenoviral vectors: Implications for clinical myocardial regeneration

Abstract

Objective The reprogramming of cardiac fibroblasts into induced cardiomyocyte-like cells improves ventricular function in myocardial infarction models. Only integrating persistent expression vectors have thus far been used to induce reprogramming, potentially limiting its clinical applicability. We therefore tested the reprogramming potential of nonintegrating, acute expression adenoviral (Ad) vectors. Methods Ad or lentivirus vectors encoding Gata4 (G), Mef2c (M), and Tbx5 (T) were validated in vitro. Sprague-Dawley rats then underwent coronary ligation and Ad-mediated administration of vascular endothelial growth factor to generate infarct prevascularization. Three weeks later, animals received Ad or lentivirus encoding G, M, or T (AdGMT or LentiGMT) or an equivalent dose of a null vector (n = 11, 10, and 10, respectively). Outcomes were analyzed by echocardiography, magnetic resonance imaging, and histology. Results Ad and lentivirus vectors provided equivalent G, M, and T expression in vitro. AdGMT and LentiGMT both likewise induced expression of the cardiomyocyte marker cardiac troponin T in approximately 6% of cardiac fibroblasts versus <1% cardiac troponin T expression in AdNull (adenoviral vector that does not encode a transgene)-treated cells. Infarcted myocardium that had been treated with AdGMT likewise demonstrated greater density of cells expressing the cardiomyocyte marker beta myosin heavy chain 7 compared with AdNull-treated animals. Echocardiography demonstrated that AdGMT and LentiGMT both increased ejection fraction compared with AdNull (AdGMT: 21% ± 3%, LentiGMT: 14% ± 5%, AdNull: −0.4% ± 2%; P < .05). Conclusions Ad vectors are at least as effective as lentiviral vectors in inducing cardiac fibroblast transdifferentiation into induced cardiomyocyte-like cells and improving cardiac function in postinfarct rat hearts. Short-term expression Ad vectors may represent an important means to induce cardiac cellular reprogramming in humans.

Cardiac reprogramming factor Gata4 reduces postinfarct cardiac fibrosis through direct repression of the profibrotic mediator snail

“…Although we were able to demonstrate differences between groups despite this variability, we do not have a good explanation for this variability between groups. In this context, we would note that we assayed RNA expression at 14 days after reprogramming factor infection based upon original research in this field suggesting that cellular reprogramming occurs over several weeks, 31,32 but additional studies demonstrated similar expression patterns as early as 5 days post-infection (data not shown).…”

Cardiac cellular reprogramming with transient expression vectors: Less is more

“…The purported benefits of adenoviral delivery are that the viral elements do not integrate into the host genome, leading only to transient expression of the transgenes. Mathison and colleagues 5 found that adenovirally mediated GMT delivery successfully transformed some cardiac fibroblasts into iCMs and was associated with improved ejection fraction at 4 weeks. These results are notable for several reasons.…”

“…There are 2 main limitations of study of Mathison and colleagues. 5 First, only a small proportion of iCMs were produced by these methods, and the long-term functional performance of these cells after 4 weeks is not known. Second, the efficacy of this therapy in human beings remains to be proved, and in the human system immune-mediated destruction and clearance of adenovirally infected cells may be of greater significance than in the murine system.…”

“…Second, the efficacy of this therapy in human beings remains to be proved, and in the human system immune-mediated destruction and clearance of adenovirally infected cells may be of greater significance than in the murine system. 6 Despite these unanswered questions, the study by Mathison and colleagues 5 represents an important step forward. It demonstrates that brief expression of reprogramming factors without genomic integration is a feasible, and arguably superior, approach to myocardial regeneration.…”

Tissue-specific promoter-based reporter system for monitoring cell differentiation from iPSCs to cardiomyocytes

“…This appealing technique does not require the full reprogramming of cells into iPSCs, but may involve partial reprogramming via cardiac progenitor cells. Unfortunately, so far published protocols have not been very effective 14,15 and based on induction with transcription factors 16 or viral transduction 17 , which makes the process expensive and not clinically applicable. Additionally, one may change the selection of small molecule combinations to replace the currently used genomic origin factors 18 .…”