Abstract Body (Do not enter title and authors here): Introduction:
After a myocardial infarction (MI), cardiac fibroblasts are activated to deposit extracellular matrix that while prevents acute cardiac rupture in the short-term, causes long-term diastolic and systolic dysfunction. Despite the clinical burden of cardiac fibrosis, especially after MI, the molecular mechanisms driving cardiac fibroblasts to produce excessive scar tissue are unknown. To study MI scar formation, we sought to characterize the molecular drivers of cardiac fibroblast activation by creating a comprehensive single-cell transcriptomic atlas of cardiac fibroblasts after MI.
Methods:
We generated a comprehensive transcriptomic atlas of cardiac fibroblasts by integrating all single cell RNA sequencing (scRNA-seq) datasets of mouse post-MI samples that are publicly available on the NIH GEO and EBI ArrayExpress databases. We screened 104 total datasets, identifying 26 datasets that met inclusion criteria, which collectively include transcriptomic data from 125 mouse samples (85 MI / 19 sham MI / 1 IR / 1 sham IR / 19 healthy). Transcriptomic data were processed, integrated, and analyzed using Seurat and Harmony. Pseudotime analysis was performed using Monocle3.
Results:
To construct our comprehensive cardiac fibroblast atlas, we integrated scRNA-seq data from nearly 700,000 mouse cells from 125 mouse samples across 26 datasets (Fig. 1A). Using this integrated all-cells atlas, we computationally isolated over 171,000 cardiac fibroblasts. Sub-clustering of the cardiac fibroblasts revealed that there are nine subpopulations. Specifically, we identify that one of these subpopulations, which we term myofibroblasts, expands from ~1% to ~40% of all fibroblasts after MI (Fig. 1B). These myofibroblasts are characterized by increased production of extracellular matrix proteins (e.g., Col1a1, Cthrc1) relative to other fibroblast subpopulations (Fig. 1C). Pseudotime analysis reveals that increased pseudotime is correlated with increased expression of Cthrc1 (Fig. 1D).
Conclusion:
Our comprehensive single-cell atlas of cardiac fibroblasts after MI reveals a myofibroblast subpopulation that emerges after MI to deposit extracellular matrix to cause tissue fibrosis.