Single cell RNA-seq comparison of cardiac fibroblasts from the left versus right ventricles
Cardiac fibrosis is a key aspect of heart failure, leading to reduced ventricular compliance and impaired electrical conduction in the myocardium. Various pathophysiologic conditions can lead to fibrosis in the left ventricle (LV) and/or right ventricle (RV). Despite growing evidence to support the transcriptomic heterogeneity of cardiac fibroblasts (CFs) in healthy and diseased states, there have been no direct comparisons of CFs in the LV and RV. Given the distinct natures of the ventricles, we hypothesized that LV and RV-derived CFs would display baseline transcriptomic differences that influence their proliferation and differentiation following injury. Bulk RNA sequencing of CFs isolated from healthy left and right cardiac ventricles indicated that left ventricle-derived CFs may be further along the myofibroblast transdifferentiation trajectory than cells isolated from the right ventricle.  Single-cell RNA-sequencing (scRNA-seq) analysis of the two populations confirmed that Postn+ CFs are more enriched in the LV, whereas Igfbp3+ CFs were enriched in the RV at baseline. Notably, following pressure overload injury, the LV developed a larger subpopulation of pro-fibrotic Thbs4+/Cthrc1+ injury-induced CFs, while the RV showed unique expansion of two less-well characterized subpopulations of CFs (Igfbp3+ and Inmt+). These findings demonstrate that LV and RV-derived CFs display baseline subpopulation differences that may dictate their diverging responses to pressure overload injury. Further study of these subpopulations will elucidate their role in the development of fibrosis and inform whether LV and RV fibrosis require distinct treatments. Overall design: Cardiac fibroblasts from the left and right ventricles (LV and RV) of Col1a1-GFP mice were isolated using Fluorescence-activated cell sorting (FACS) according to the presence or absence of GFP signal, and analyzed using scRNA-seq. Samples were prepared from uninjured mice, as well as from mice which underwent surgery to model pressure overload injury in either the LV or RV. LVs were isolated from mice with transverse aortic constriction (TAC) and TAC sham surgeries, while RVs were isolated from mice with pulmonary artery banding (PAB) and PAB sham surgeries. All conditions were studied in both male and female mice. Male and female samples for surgery-operated mice were prepared independently of each other, while sample from the uninjured mice include both male and female tissue.