Genetic deficiency of C–C chemokine receptor 4 protects against angiotensin II-induced abdominal aortic aneurysm formation in mice
Background: The dysregulated immune system, which drives chronic vascular inflammation and remodeling, plays a critical role in the pathogenesis of abdominal aortic aneurysm (AAA). C–C chemokine receptor 4 (CCR4), which is predominantly expressed on T cells and mediates their responses, has been shown to protect against inflammatory diseases including atherosclerosis. However, its role in AAA remains unknown. Methods: By analyzing hypercholesterolemic CCR4-deficient (Ccr4-/-) mice on an apolipoprotein E-deficient (Apoe-/-) background, we investigated the role of CCR4 in the development of angiotensin II-induced AAA, with a particular focus on T cell-mediated immune responses, by performing histological analysis, flow cytometry, biochemical assays, and single-cell RNA sequencing analysis. Results: Genetic deletion of CCR4 on an Apoe-/- background dramatically reduced the incidence and severity of angiotensin II-induced AAA without affecting mortality due to rupture, along with attenuated inflammatory cell recruitment and preserved elastic lamellae. This protective effect was associated with a shift in the T helper cell balance toward T helper type 1 cell predominance, characterized by promoted IFN-? production and suppressed B cell-mediated immunity including lower plasma IgE levels. Single-cell RNA sequencing analysis of abdominal aortic tissues revealed lower proportions of myofibroblasts and modulated smooth muscle cells highly expressing genes associated with extracellular matrix remodeling in angiotensin II-infused Ccr4-/-/Apoe-/- mice, potentially driven by downregulated TGF-ß signaling due to T helper type 1 cell-derived IFN-? predominance. Conclusions: Our data suggest that CCR4 blockade may serve as a promising immunotherapeutic approach for AAA. Overall design: Abdominal aortas were isolated from angiotensin II-infused Apoe-/- or Ccr4-/-Apoe-/- mice and frozen in liquid nitrogen within 6 hours after sample collection. For single cell RNA-seq, the libraries were prepared as according to the 10x Genomics Chromium Fixed RNA Profiling for Multiplexed Samples v1 guidelines (CG000527).