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Whole transcriptome analysis of induced cardiomyocytes during direct cardiac reprogramming [expression]

ABSTRACT: Direct lineage conversion offers a new strategy for tissue regeneration and disease modeling. Despite recent success in directly reprogramming fibroblasts into a wide spectrum of cell types, the precise changes that fibroblasts undergo as they progress to target cell fates remain unclear. The inherent heterogeneity and asynchronous nature of the reprogramming process make it difficult to study using bulk genomic techniques. Therefore, a fundamental and detailed understanding of global transcriptome changes at the single cell level is necessary to better optimize reprogramming for therapeutic purposes and to advance the understanding of cell plasticity and cell identity acquisition. Here, we applied single-cell RNA-seq to analyze global transcriptome changes at early stages of induced cardiomyocyte (iCM) reprogramming. Using unsupervised dimensionality reduction and clustering algorithms, we identified molecularly distinct subpopulations of cells along the reprogramming process from fibroblasts to iCMs, including a novel intermediate state that exhibited molecular signatures of both fibroblast and cardiomyocyte. In summary, our single cell transcriptomics approaches enabled us to construct a reprogramming trajectory and uncover the intermediate cell populations, regulatory pathways and genes putatively involved in iCM induction.

ORGANISM(S): Mus musculus

PROVIDER: GSE98570 | GEO | 2017/10/25

SECONDARY ACCESSION(S): PRJNA385604

REPOSITORIES: GEO

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Project description:Direct conversion of fibroblasts to induced cardiomyocytes (iCMs) has great potential for regenerative medicine. Recent publications have reported significant progress, but the evaluation of reprogramming has relied upon non-functional measures such as flow cytometry for cardiomyocyte markers or GFP expression driven by a cardiomyocyte-specific promoter. The issue is one of practicality: the most stringent measures - electrophysiology to detect cell excitation and the presence of spontaneously contracting myocytes - are not readily quantifiable in the large numbers of cells screened in reprogramming experiments. However, excitation and contraction are linked by a third functional characteristic of cardiomyocytes: the rhythmic oscillation of intracellular calcium levels. We set out to optimize direct conversion of fibroblasts to iCMs with a quantifiable calcium reporter to rapidly assess functional transdifferentiation. We constructed a reporter system in which the calcium indicator GCaMP is driven by the cardiomyocyte-specific Troponin T promoter. Using calcium activity as our primary outcome measure, we compared several published combinations of transcription factors along with novel combinations in mouse embryonic fibroblasts. The most effective combination consisted of Hand2, Nkx2.5, Gata4, Mef2c, and Tbx5 (HNGMT). This combination is >50-fold more efficient than GMT alone and produces iCMs with cardiomyocyte marker expression, robust calcium oscillation, and spontaneous beating that persists for weeks following inactivation of reprogramming factors. HNGMT is also significantly more effective than previously published factor combinations for the transdifferentiation of adult mouse cardiac fibroblasts to iCMs. Quantification of calcium function is a convenient and effective means for the identification and evaluation of cardiomyocytes generated by direct reprogramming. Using this stringent outcome measure, we conclude that HNGMT produces iCMs more efficiently than previously published methods. Mouse embryonic fibroblasts were treated with different combinations of transcription factors to drive transdifferentiation to induced cardiomyocytes (iCMs). Putative iCMs were enriched by zeocin selection. Zeocin resistance was conferred to iCMs via the TroponinT-GCaMP5-Zeo lentiviral reporter.

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Whole transcriptome analysis of induced cardiomyocytes during direct cardiac reprogramming [expression]

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