Heart-resident CCR2+ macrophages promote neutrophil extravasation through TLR9/MyD88/CXCL5 signaling
Wenjun Li, … , Kory J. Lavine, Daniel Kreisel
Wenjun Li, … , Kory J. Lavine, Daniel Kreisel
Published August 4, 2016
Citation Information: JCI Insight. 2016;1(12):e87315. https://doi.org/10.1172/jci.insight.87315.
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Research Article Inflammation Transplantation

Heart-resident CCR2+ macrophages promote neutrophil extravasation through TLR9/MyD88/CXCL5 signaling

Abstract

It is well established that maladaptive innate immune responses to sterile tissue injury represent a fundamental mechanism of disease pathogenesis. In the context of cardiac ischemia reperfusion injury, neutrophils enter inflamed heart tissue, where they play an important role in potentiating tissue damage and contributing to contractile dysfunction. The precise mechanisms that govern how neutrophils are recruited to and enter the injured heart are incompletely understood. Using a model of cardiac transplant–mediated ischemia reperfusion injury and intravital 2-photon imaging of beating mouse hearts, we determined that tissue-resident CCR2+ monocyte–derived macrophages are essential mediators of neutrophil recruitment into ischemic myocardial tissue. Our studies revealed that neutrophil extravasation is mediated by a TLR9/MyD88/CXCL5 pathway. Intravital 2-photon imaging demonstrated that CXCL2 and CXCL5 play critical and nonredundant roles in guiding neutrophil adhesion and crawling, respectively. Together, these findings uncover a specific role for a tissue-resident monocyte-derived macrophage subset in sterile tissue inflammation and support the evolving concept that macrophage ontogeny is an important determinant of function. Furthermore, our results provide the framework for targeting of cell-specific signaling pathways in myocardial ischemia reperfusion injury.

Authors

Wenjun Li, Hsi-Min Hsiao, Ryuji Higashikubo, Brian T. Saunders, Ankit Bharat, Daniel R. Goldstein, Alexander S. Krupnick, Andrew E. Gelman, Kory J. Lavine, Daniel Kreisel

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Figure 3

Intravital 2-photon imaging reveals impaired neutrophil extravasation into heart grafts that lack MyD88 expression.

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Intravital 2-photon imaging reveals impaired neutrophil extravasation in...
Neutrophil trafficking in (A) WT (see Supplemental Video 5; n = 4 mice) and (B) MyD88-deficient hearts (see Supplemental Video 6; n = 4 mice). Scale bars: 50 μm. (C) Percentage of neutrophils that entered myocardial tissue during imaging period was significantly lower when heart grafts were deficient in MyD88 compared with WT cardiac grafts. (D) Neutrophil rolling velocities were significantly higher in coronary veins of cardiac grafts that lacked expression of MyD88 when compared with WT hearts. (E) Intraluminal crawling velocities of neutrophils were significantly lower when hearts lacked expression of MyD88 when compared with WT cardiac grafts. Neutrophil trafficking in (F) cardiac grafts derived from control MyD88-floxed mice (see Supplemental Video 8; n = 4 mice) and (G) mice that lack MyD88 selectively in Lysozyme M+ cells (see Supplemental Video 9; n = 4 mice). Relative time is displayed in hrs:min:sec. Scale bars: 50 μm. (H) Percentage of neutrophils that entered myocardial tissue during imaging period was significantly lower when heart grafts were deficient in MyD88 in Lysozyme M–expressing cells compared with control MyD88-floxed hearts. (I) Neutrophil rolling velocities were significantly higher in coronary veins of cardiac grafts that lacked expression of MyD88 in Lysozyme M–expressing cells compared with control MyD88-floxed hearts. (J) Intraluminal crawling velocities of neutrophils were significantly lower when hearts lacked expression of MyD88 in Lysozyme M–expressing cells compared with control MyD88-floxed hearts. *P < 0.05; **P < 0.01; ***P < 0.001 (t test). Data in C–E and H–J are derived from 4 mice for each experimental group. C–E and H–J represent averages obtained from individual mice with over 30 neutrophils examined per mouse, horizontal bars denote means, and error bars denote ±SEM.