Abstract 17949: Recruitment of Pro-Inflammatory Ly6ChighCCR2+ Monocytes to the Myocardium is Critical to the Development of Hypertension Related Myocardial Fibrosis
Background: Monocytes/macrophages (Mφ) are key regulators of myocardial inflammation and fibrosis. It is known that Ly6ChighCCR2+ monocytes are the primary infiltrating cell in hypertension-dependent myocardial fibrosis, with recent evidence identifying the spleen as an additional source. Changes in monocyte/Mφ subsets between spleen, circulation, and heart in hypertension-dependent myocardial fibrosis remains poorly understood. Here, we characterized this interrelationship in a well-described model of hypertension.
Method: C57BL/6 mice were infused with saline or Angiotensin-II (Ang-II; 2.8 mg/kg/d) via osmotic mini-pumps for 3d, after which tissues and blood were harvested and purified over a Ficoll gradient for mononuclear cell isolation, then counted and stained (CD11b, Ly6C, CCR2, CX3CR1) for flow cytometry.
Results: We identified a CX3CR1+CCR2+ Mφ population that are Ly6Clow in control hearts, suggestive of resident cardiac Mφ (210.6 ± 30.2 cells/mg). Ang-II exposure led to an influx of CX3CR1+CCR2+ Mφ (1035 ± 197.3 cells/mg, p ≤ 0.01) with a phenotypic shift to pro-inflammatory CD11bhighLy6Chigh (1676 ± 343.0 vs. 617 ± 61.9 Ly6C MFI, p ≤ 0.05). In the Ang-II spleen, a 2.7-fold reduction was observed in isolated cells compared to control (7.9x107 ± 1.6x107 vs. 2.9x107 ± 6.1x106 cells/tissue p ≤ 0.05). We observed two subpopulations of splenic CD11b+ monocytes – (1) CD11bhigh, primarily Ly6ChighCCR2+, and (2) CD11blow, primarily Ly6ClowCCR2low. The ratio of CD11blowLy6ClowCCR2low to CD11bhighLy6ChighCCR2+ cells was reduced in the Ang-II spleen compared to controls (3.7 ± 1.4 vs 8.9 ± 1.1, p ≤ 0.05), suggesting a pro-inflammatory phenotypic shift. No significant differences in circulating CD11b+ subpopulations were seen at 3d, suggesting prior splenic deployment and recovery from bone marrow/spleen.
Conclusion: We provide evidence that a significant influx of cardiac Mφ in the context of hypertension arise from splenic reservoir. Furthermore, we demonstrate significant changes in myocardial Mφ composition towards pro-inflammatory Ly6ChighCCR2+ Mφ at the expense of immunomodulatory Ly6Clow Mφ. This offers novel insight into therapies that would prevent the recruitment of splenic monocytes to control myocardial inflammation.
Author Disclosures: C. Wong: Other Research Support; Modest; Heart and Stroke Foundation. A. Falkenham: None. T. Myers: None. J. Legare: None.
- © 2016 by American Heart Association, Inc.