Cardiac stromal cells as hub for regeneration and healing in the infarcted heart.

• Applicants: Dr. Julia Hesse; Professor Dr. Jürgen Schrader
• Subject Area: Cardiology, Angiology ; Anatomy and Physiology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458365199

Epicardial stromal cells (EpiSC) are generated in the activated epicardium after myocardial infarction (MI) and are considered as endogenous progenitor cells involved in cardiac tissue repair. Taking advantage of a recently developed technique for the simultaneous isolation of EpiSC and myocardial activated cardiac stromal cells (aCSC) from the infarcted mouse heart, we have successfully explored cellular heterogeneity of EpiSC in comparison to aCSC at the single-cell level using scRNAseq, combined with RNA in situ hybridization and lineage tracing via the epicardial activation marker Wilms tumor protein 1 (WT1) at day 5 post MI. We found 11 molecularly distinct EpiSC populations with a clear epicardial location, differential expression of established progenitor markers and a unique transcriptional profile. EpiSC populations also differed from aCSC in expression of paracrine factors, cardiogenic and hypoxia/HIF-1α-responsive genes. In a second recently finished study we found by lineage tracing of aCSC with periostin-dependent expression of tdTomato, that cell therapy of infarcted hearts with unrestricted somatic stem cells (USSC) profoundly stimulated the formation of tdTomato+ cardiomyocytes, which was paralleled by significant functional improvement. Based on these findings (two manuscripts submitted), we now plan to explore: (1) Temporal changes of Wt1+ and Wt1- EpiSC populations after MI as influenced by thymosin β4, a known inducer of cardiomyogenesis, using scRNAseq and cell-specific transcriptomics (SLAM-ITseq). (2) The influence of HIF-1α, specifically overexpressed in Wt1+ EpiSC and periostin+ aCSC, on cellular heterogeneity, gene expression and heart function by scRNAseq and functional measurements by MRI. (3) Temporal changes and molecular mechanisms which trigger the conversion of Postn+ aCSC into cardiomyocytes after USSC transplantation with scRNAseq and SLAM-ITseq. Together these studies will for the first time delineate the cellular and molecular mechanisms of tissue repair and cardiomyogenesis in EpiSC and aCSC. Potentially this will open new strategies for treatment of the infarcted heart.

• DFG Programme: Research Grants