Antagonizing CCR2 With Propagermanium Leads to Altered Distribution of Macrophage Subsets and Favorable Tissue Remodeling After Myocardial Infarction in Mice

Abstract

Aims: The aim of the present study was to investigate the inhibition of classically activated macrophages in myocardial infarction (MI) under the influence of the chemokine (C-C motif) receptor 2 (CCR2) antagonist propagermanium (PPG). Methods and Results: Mice (C57BL/6; n = 121) were subjected to occlusion of the left anterior descending artery and were randomized to the following groups: (a) MI with daily oral administration of 0.9% sodium chloride ("MI"), (b) MI with oral administration of 8 mg/kg PPG ("MI + PPG"), and (c) sham-operated mice served as control. Mice were euthanized 2, 5, 10, or 21 days after MI for isolation of total RNA, protein, and immunofluorescence measurements. Flow cytometry was performed to investigate peripheral blood leucocytes. Scar size and cardiac function were determined by MRI on Day 7 after surgery and by trichrome staining on Day 21. PPG administration led to a significantly improved ejection fraction (MI + PPG: 38.5% ± 3.4% vs. MI: 23.8% ± 3.0%; p < 0.05) after MI. MRI also revealed improved wall thickness (34.7% ± 3.2% vs. 21.8% ± 2.9%; p < 0.05) associated with a diminished akinetic area (13.8% ± 4.0% vs. 37.3% ± 5.6%; p < 0.01). Trichrome staining confirmed less collagen scar formation in the PPG-treated group (12.7% ± 1.4% vs. 21.9% ± 3.9%; p < 0.05). Flow cytometry showed fewer peripheral blood monocytes in MI + PPG than in MI 2 days after treatment (4.0% ± 0.7% vs. 12.7% ± 1.2% of total leucocytes; p < 0.05). Immunostaining and western blotting using activation type-specific markers CCR2 and MRC1 demonstrated that the number of alternatively activated macrophages within the infarct zone increased, whereas the overall number was reduced after PPG treatment. PPG led to increased expression of VEGF-α and VEGF-β in THP-1 cells in vitro and increased capillary density in vivo 2 days after MI (MI-PPG: 1071 ± 81/mm² vs. MI: 648 ± 79/mm² (p < 0.05)). Conclusion: Our results suggest that altering the activation type and distribution of invading macrophages in favor of alternative activation improves cardiac remodeling and function following MI.

Keywords: CCR2; macrophages; monocytes; myocardial infarction; propagermanium.