Identification of CD4 + Sub-population of Resident Cardiac Fibroblasts Linked to Myocardial Fibrosis

Infiltration with inflammatory T-cells and accumulation of cardiac myofibroblasts are hallmarks of cardiac fibrosis and maladaptive remodeling. The origin, identity, and functions of the resident cardiac cells involved in this process are, however, unclear. To determine the identity of cells contained in regions exhibiting fibrosis, mass cytometry profiling was performed using resident human ventricular cardiac fibroblasts and right ventricle autopsy tissues from individuals diagnosed with pulmonary hypertension and SUGEN/hypoxia rats. Results showed that a subpopulation of resident myocardial fibroblasts expresses increased levels of CD4 + , a helper T-cell surface marker, in addition to mesenchymal markers in humans and rats. Characterization of the resident cardiac fibroblast subpopulation, both structurally and functionally, using transcriptome and secretome analysis of the secreted cytokines, chemokines, proteins, and metabolites, evidenced that IL-1β induces a phenotypic switch of human cardiac fibroblasts from mesenchymal to CD4 + lymphoidal lineage in vitro . RNA sequencing (RNA-seq) analysis of FACS-sorted CD4-expressing cardiac fibroblasts further revealed that the transcriptome of such IL-1β-induced CD4 + fibroblast population exhibited classical lymphoidal and stem cell-like signatures. Lastly, reversal of cell clustering, phosphorylation of MAPK p38 and NF-κB p65, and phenotypic switching was achieved with the administration of an IL-1R antagonist. In conclusion, we have identified a subpopulation of cardiac fibroblasts which exhibits structural and functional attributes of both mesenchymal and lymphoid cells which is induced by IL-1β-IL-1R-NFkB pathway for differentiation of cardiac fibroblast cells. These data suggest that cardiac fibroblast transdifferentiation during inflammation may form the basis for maladaptive remodeling during myocardial fibrosis.