Cardiac myofibroblast engulfment of dead cells facilitates recovery after myocardial infarction
Michio Nakaya, … , Shigekazu Nagata, Hitoshi Kurose
Michio Nakaya, … , Shigekazu Nagata, Hitoshi Kurose
Published December 5, 2016
Citation Information: J Clin Invest. 2017;127(1):383-401. https://doi.org/10.1172/JCI83822.
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Research Article Cardiology Inflammation

Cardiac myofibroblast engulfment of dead cells facilitates recovery after myocardial infarction

Abstract

Myocardial infarction (MI) results in the generation of dead cells in the infarcted area. These cells are swiftly removed by phagocytes to minimize inflammation and limit expansion of the damaged area. However, the types of cells and molecules responsible for the engulfment of dead cells in the infarcted area remain largely unknown. In this study, we demonstrated that cardiac myofibroblasts, which execute tissue fibrosis by producing extracellular matrix proteins, efficiently engulf dead cells. Furthermore, we identified a population of cardiac myofibroblasts that appears in the heart after MI in humans and mice. We found that these cardiac myofibroblasts secrete milk fat globule-epidermal growth factor 8 (MFG-E8), which promotes apoptotic engulfment, and determined that serum response factor is important for MFG-E8 production in myofibroblasts. Following MFG-E8–mediated engulfment of apoptotic cells, myofibroblasts acquired antiinflammatory properties. MFG-E8 deficiency in mice led to the accumulation of unengulfed dead cells after MI, resulting in exacerbated inflammatory responses and a substantial decrease in survival. Moreover, MFG-E8 administration into infarcted hearts restored cardiac function and morphology. MFG-E8–producing myofibroblasts mainly originated from resident cardiac fibroblasts and cells that underwent endothelial-mesenchymal transition in the heart. Together, our results reveal previously unrecognized roles of myofibroblasts in regulating apoptotic engulfment and a fundamental importance of these cells in recovery from MI.

Authors

Michio Nakaya, Kenji Watari, Mitsuru Tajima, Takeo Nakaya, Shoichi Matsuda, Hiroki Ohara, Hiroaki Nishihara, Hiroshi Yamaguchi, Akiko Hashimoto, Mitsuho Nishida, Akiomi Nagasaka, Yuma Horii, Hiroki Ono, Gentaro Iribe, Ryuji Inoue, Makoto Tsuda, Kazuhide Inoue, Akira Tanaka, Masahiko Kuroda, Shigekazu Nagata, Hitoshi Kurose

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Figure 6

MFG-E8–dependent engulfment by cardiac myofibroblasts influences the conditions of heart after MI.

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MFG-E8–dependent engulfment by cardiac myofibroblasts influences the con...
(A) TUNEL-positive nuclei in the border zone of hearts in WT (n = 4) and MFG-E8 KO (n = 3) mice at day 3 after MI. The percentages indicate the ratio of TUNEL-positive nuclei to DAPI-positive nuclei. Scale bars: 100 μm. (B) Representative LV sections from WT mice that underwent MI were double-stained with anti-TNNI3 (green) and anti-αSMA (red) antibodies (n = 5). The numbers of TNNI3-positive cardiomyocytes per square millimeter of αSMA-positive area in infarcted hearts of WT and MFG-E8 KO mice are shown in the graph. Scale bar: 20 μm. (C) mRNA expression levels of inflammatory genes 3 days after sham operation or MI in the hearts of WT or MFG-E8 KO mice (sham, n = 4; MI, n = 5). (D) Echocardiographic measurements of WT mice (n = 7) or MFG-E8 KO mice (n = 5) at 4 weeks after MI. Ejection fraction (EF) and fractional shortening (FS) are shown. (E) Ratio of heart weight (HW) to body weight (BW) of WT mice (n = 7) or MFG-E8 KO mice (n = 5) at 4 weeks after MI. (F) Representative heart sections of WT mice (n = 6) or MFG-E8 KO mice (n = 5) at 4 weeks after MI stained with Masson’s trichrome. The ratios of the fibrotic area to the LV area were quantitatively estimated and are shown in the graph. Scale bars: 1 mm. Error bars represent the mean ± SEM. (A, B, D–F) *P < 0.05; **P < 0.01; #P < 0.05, unpaired 2-tailed Student’s t test. (C) *P < 0.05; ***P < 0.001; #P < 0.05; ##P < 0.01, 1-way ANOVA followed by Newman-Keuls analysis.