Interleukin-1 receptor type I signaling critically regulates infarct healing and cardiac remodeling

Abstract

The proinflammatory cytokine interleukin (IL)-1 signals exclusively through the type I IL-1 receptor (IL-1RI). IL-1 expression is markedly induced in the infarcted heart; however, its role in cardiac injury and repair remains controversial. We examined the effects of disrupted IL-1 signaling on infarct healing and cardiac remodeling using IL-1RI(-/-) mice. After reperfused infarction IL-1RI-null mice exhibited decreased infiltration of the infarcted myocardium with neutrophils and macrophages and reduced chemokine and cytokine expression. In the absence of IL-1 signaling, suppressed inflammation was followed by an attenuated fibrotic response. Infarcted IL-1RI(-/-) mice had decreased myofibroblast infiltration and reduced collagen deposition in the infarcted and remodeling myocardium. IL-1RI deficiency protected against the development of adverse remodeling; however, infarct size was comparable between groups suggesting that the beneficial effects of IL-1RI gene disruption were not attributable to decreased cardiomyocyte injury. Reduced chamber dilation in IL-1RI-null animals was associated with decreased collagen deposition and attenuated matrix metalloproteinase (MMP)-2 and MMP-3 expression in the peri-infarct area, suggesting decreased fibrotic remodeling of the noninfarcted heart. IL-1beta stimulated MMP mRNA synthesis in wild-type, but not in IL-1RI-null cardiac fibroblasts. In conclusion, IL-1 signaling is essential for activation of inflammatory and fibrogenic pathways in the healing infarct, playing an important role in the pathogenesis of remodeling after infarction. Thus, interventional therapeutics targeting the IL-1 system may have great benefits in myocardial infarction.

Figure 1

IL-1RI-null mice exhibited markedly reduced infiltration of the infarcted myocardium with neutrophils. Immunohistochemical staining demonstrated intense infiltration of WT infarcts with neutrophils after 24 hours (A) and 72 hours (B) of reperfusion. IL-1RI^−/− animals had markedly decreased neutrophil infiltration after 24 hours (D) and 72 hours (E) of reperfusion. Both WT (C) and IL-1RI KO mice (F) showed complete resolution of the neutrophil infiltrate after 7 days of reperfusion. G: Quantitative analysis of neutrophil density in the healing infarct (**P < 0.01 versus corresponding WT mice).

Figure 2

IL-1RI-null animals had significantly decreased macrophage infiltration after 24 hours of reperfusion. Immunohistochemical staining with Mac2 identified macrophages infiltrating infarcted WT hearts after 24 hours (A), 72 hours (B), and 7 days (C) of reperfusion. D: IL-1RI-null mice had decreased macrophage infiltration after 24 hours of reperfusion. However, macrophage density in IL-1RI^−/− infarcts after 72 hours (E) and 7 days (F) of reperfusion was comparable with WT animals. G: Quantitative analysis of macrophage density in the infarcted heart (*P < 0.05 versus corresponding WT mice).

Figure 3

IL-1RI^−/− mice exhibited markedly reduced chemokine up-regulation in the infarcted heart. WT mice showed marked early mRNA induction of the chemokines MIP-1β (A), MIP-1α (B), MIP2 (C), and MCP-1 (E) in the infarcted myocardium. D: IP-10 induction showed a biphasic response. IL-1RI gene disruption prevented the early chemokine response in the infarcted heart suggesting a key role for IL-1 signaling in mediating chemokine synthesis after ischemia and reperfusion (***P < 0.001, **P < 0.01, *P < 0.05 versus corresponding WT mice).

Figure 4

IL-1RI^−/− mice had decreased cytokine up-regulation in the infarcted heart. mRNA expression of the proinflammatory cytokines TNF-α (A), IL-6 (B), IL-1β (C), and M-CSF (E) peaked after 6 hours of reperfusion in WT mouse infarcts. IL-1RI KO mice exhibited decreased peak IL-6 (B), IL-1β (C), and M-CSF (E) mRNA expression. A: In contrast, TNF-α expression levels were comparable between groups. D: Furthermore, IL-1RI-deficient mice had significantly attenuated induction of the inhibitory cytokine IL-10 after 24 hours of reperfusion (*P < 0.05, **P < 0.01 versus corresponding WT mice).

Figure 5

IL-1RI deficiency is associated with reduced myofibroblast infiltration and decreased TGF-β isoform expression in the infarcted heart. Myofibroblasts were identified as spindle-shaped, α-SMA-expressing cells, predominantly located in the border zone of WT (A) and IL-1RI-null (B) infarcts (arrows). C: Quantitative analysis demonstrated that peak myofibroblast density in the infarcted myocardium was significantly lower in IL-1RI-null animals. D–F: TGF-β is a key mediator involved in myofibroblast differentiation and fibrous tissue deposition. TGF-β1 (D), TGF-β2 (E), and TGF-β3 (F) mRNA levels were significantly lower in infarcted IL-1RI KO hearts after 24 hours of reperfusion (*P < 0.05 versus corresponding WT mice).

Figure 6

IL-1RI-null mice exhibited attenuated fibrotic remodeling of the infarcted ventricle. Picrosirius red staining was used to label the collagen network in WT (A) and IL-1RI-null (B) infarcts. Collagen content was quantitatively assessed in the infarct (arrowheads), the peri-infarct area (Peri-I, arrows), and the remote myocardium. C: IL-1RI KO mice had significantly lower collagen percent content in the infarct and the peri-infarct area (**P < 0.01, *P < 0.05 versus corresponding WT).

Figure 7

IL-1RI^−/− animals had attenuated adverse remodeling after myocardial infarction. Remodeling after infarction was assessed using morphometric (A: WT; D: IL-1RI^−/−) and echocardiographic techniques (B: WT; E: IL-1RI^−/−). Although WT and KO animals had comparable infarct size after 7 days of reperfusion (C), IL-1RI deficiency protected from the development of ventricular dilation. Both echocardiographically derived LVEDD (F) and morphometrically assessed LVEDV (G) were lower in infarcted IL-1RI-null mice 7 days after reperfusion in comparison with WT animals (^##P < 0.01 versus pre or sham, *P < 0.05 versus corresponding WT).