A Multipotent Fibroblast Population Drives a PDGFR-beta-Dependent Immuno-Fibrotic Response in Heart Failure

About This Grant

Project Summary/Abstract Cardiac fibrosis compromises left ventricular (LV) function and worsens clinical outcomes in heart failure (HF). Currently, there are no clinical therapies that target fibrosis in the failing heart. Platelet-derived growth factor (PDGF), a central mediator of fibrotic responses, acts via two receptors - PDGFRα and PDGFRβ. Our pilot studies using explant cultures, flow sorting, single cell RNA sequencing (scRNAseq), and in vivo mouse models have uncovered a novel stem cell antigen(Sca)-1-expressing PDGFRα+ multipotent cardiac fibroblast population that sources myofibroblasts, interacts with tissue macrophages, and drives fibrotic and inflammatory responses during adverse LV remodeling. During HF, these cells decrease PDGFRα expression and instead upregulate PDGFRβ. The role of PDGFRβ in cardiac fibroblast biology in HF is unknown. We propose the novel hypothesis that a heretofore unrecognized Sca-1+PDGFRβ expressing cardiac fibroblast with mesenchymal stem cell features (termed cFMSCs) are key drivers of a PDGFRβ-dependent immunofibrotic axis in HF. Three Aims will test this hypothesis. In Aim 1, using a murine coronary ligation model, in vitro studies of cell function, scRNAseq, and inducible cardiac fibroblast-specific and Sca1+ cell-specific PDGFRβ-deletion mouse models, we will comprehensively define the importance of PDGFRβ in cFMSC cell function in ischemic HF. We will isolate Sca1+PDGFRα+ cFMSCs and assess PDGFR β-dependent myofibroblast differentiation, multipotency, downstream signaling and immuno-fibrotic secretome, and cFMSC-macrophage interactions. scRNAseq of sorted cells will assess cFMSC subpopulations and changes in transcriptomic profiles. In Aim 2, we will establish the pathogenetic role of cFMSC-localized PDGFRβ in chronic HF, by using inducible cardiac fibroblast-specific PDGFRβ knockout mice, deleting cFMSC PDGFRβ during chronic HF, and assessing late effects on LV remodeling, fibrosis, tissue macrophages, and inflammatory profiles. To establish necessity of cFMSC PDGFRβ signaling, cardiac fibroblast PDGFRβ loss will be induced by tamoxifen in PDGFRβf/f-Tcf21MerCreMer mice 4 w post- MI and LV remodeling, fibrosis, and tissue macrophage and inflammatory profiles will be assessed 6 w Iater. The effects of sustained cardiac fibroblast PDGFRβ activation on LV remodeling will be assessed using PDGFRβ[S]D849V-Tcf21MerCreMer mice. To establish sufficiency of cFMSC PDGFRβ signaling, we will perform intramyocardial adoptive transfer of sorted PDGFRβ-deficient and -competent Sca1+PDGFRα+ cFMSCs from HF mice into naïve mice and assess late LV remodeling and fibrosis. In Aim 3, we will test potentially translatable therapies to antagonize cFMSC PDGFRβ signaling in chronic HF, including CP-67345, a specific small molecule PDGFRβ inhibitor, fibroblast-targeted nanoparticle delivery of PDGFRβ siRNA, and anti-PDGFRβ neutralizing antibody. We will measure the effects of these therapies on LV remodeling, fibrosis, cFMSC abundance, cardiac macrophages, and tissue inflammation. By conclusively defining the role of cFMSCs and fibroblast PDGFRβ in pathological LV remodeling, these studies will provide novel perspectives on the immunofibrotic response in HF.