Cardiomyocyte Dedifferentiation and Proliferation Revealed by Massive Parallel Single-Nucleus Transciprotmic Analysis in Adult Mouse Hearts

We have demonstrated previously that adult cardiomyocytes can dedifferentiate and proliferate when cultured in vitro. To determine if cardiomyocyte dedifferentiation and cell cycling/proliferation happens in vivo, we applied here a novel multi-reporter transgenic mouse model (aMH-CMerCreMer;mT/MG;aMHC-H2BBFP) carrying reporter genes for permanent cardiomyocyte lineage mapping and maturity (dedifferentiation) reporting. With this new model, we deciphered the cellular sources and processes of cardiomyocyte dedifferentiation and proliferation in adult hearts. In this study, we used single-nucleus RNA-sequencing to tackle the challenges in analyzing the highly heterogeneous heart cell populations, and obtained datasets for a large number of cardiac single nuclei (both myocytes and non-myocytes) for control and post-infarct hearts. We identified specific cell populations in the heart using distinct transcriptomic clusters, transgenic reporters for ACM lineage and dedifferentiation, as well as cell cycle markers. The results demonstrated that the dedifferentiation and cell cycle progression of pre-existing CMs was augmented in post-infarct hearts, with a number of signaling pathways and gene sets affected. This is the first study dissecting the transcriptomic profiles and signaling pathways associated with cardiomyocyte dedifferentiation and cycling/proliferation in vivo using unbiased high-throughput single-nucleus RNA-Seq analysis, in junction with novel cell lineage (e.g. cardiomyocyte) and phenotyping (e.g. dedifferentiation) transgenic model systems. Overall design: Massive parallel single-nucleus RNA profiles of whole-ventricular nuclei containing all heart cell populations from novel transgenic mouse model aMH-CMerCreMer;mT/MG;aMHC-H2BBFP; Included a control and two 5-day post-infarct hearts; data generated by deep sequencing with 10x Genomics platform and Illumina sequencer.