Macrophage-Derived CCL24 Promotes Cardiac Fibrosis Via Fibroblast CCR3

Inflammation is a significant risk factor and contributor to the development of cardiovascular disease by driving both adaptive and maladaptive responses to cardiac injury. Macrophages are the most abundant immune cells in the heart and play an important role in the remodeling of cardiac tissue. Cardiac resident macrophages are integral components of the myocardium, where they have key roles in the response to inflammation, tissue injury, and remodeling. However, the precise mechanisms by which cardiac resident macrophages regulate remodeling in heart failure remain poorly understood. We have identified a subpopulation of cardiac resident macrophages that expresses high levels of the CCL24 (C-C motif chemokine ligand 24) during pressure overload-induced injury. Following transverse aortic constriction, CCL24 deficiency ameliorated cardiac fibrosis, suggesting a pathological role for CCL24 and revealing that cardiac resident macrophages are a heterogeneous population with dichotomous roles in mediating cardiac remodeling. Mechanistically, CCL24 directly activated cardiac fibroblasts through its sole receptor, CCR3 (C-C chemokine receptor type 3), in an inflammation-independent process. The engagement of the CCR3 receptor promoted fibroblast proliferation and activation via PI3K-induced Akt phosphorylation and the release of the key fibrotic cytokine TGF (transforming growth factor) β. To determine the in vivo role of CCR3 in fibroblast activation during cardiac remodeling, we used CRISPR/Cas9 to generate fibroblast-specific CCR3-deficient mice. Following pressure overload, fibroblast-specific deletion of CCR3 improved cardiac function and reduced fibrosis to a degree comparable to that observed in CCL24-deficient mice. Notably, administration of a CCL24-blocking antibody or a CCR3 antagonist enhanced cardiac function in pressure-overloaded mice, underscoring the CCL24-CCR3 axis as a promising therapeutic target for heart failure. Macrophage-derived CCL24 aggravates fibrosis via the CCR3 receptor, impairing cardiac function in heart failure.