Alterations in the Interleukin-1/Interleukin-1 Receptor Antagonist Balance Modulate Cardiac Remodeling following Myocardial Infarction in the Mouse

Background Healing after acute myocardial infarction (AMI) is characterized by an intense inflammatory response and increased Interleukin-1 (IL-1) tissue activity. Genetically engineered mice lacking the IL-1 receptor (IL-1R1-/-, not responsive to IL-1) or the IL-1 receptor antagonist (IL-1Ra, enhanced response to IL-1) have an altered IL-1/IL-1Ra balance that we hypothesize modulates infarct healing and cardiac remodeling after AMI. Methods IL-1R1-/- and IL-1Ra-/- male mice and their correspondent wild-types (WT) were subjected to permanent coronary artery ligation or sham surgery. Infarct size (trichrome scar size), apoptotic cell death (TUNEL) and left ventricular (LV) dimensions and function (echocardiography) were measured prior to and 7 days after surgery. Results When compared with the corresponding WT, IL-1R1-/- mice had significantly smaller infarcts (−25%), less cardiomyocyte apoptosis (−50%), and reduced LV enlargement (LV end-diastolic diameter increase [LVEDD], −20%) and dysfunction (LV ejection fraction [LVEF] decrease, −50%), whereas IL-1Ra-/- mice had significantly larger infarcts (+75%), more apoptosis (5-fold increase), and more severe LV enlargement (LVEDD increase,+30%) and dysfunction (LVEF decrease, +70%)(all P values \u3c0.05). Conclusions An imbalance in IL-1/IL-1Ra signaling at the IL-1R1 level modulates the severity of cardiac remodeling after AMI in the mouse, with reduced IL-1R1 signaling providing protection and unopposed IL-1R1 signaling providing harm

Intracellular Function of Interleukin-1 Receptor Antagonist in Ischemic Cardiomyocytes

Background: Loss of cardiac myocytes due to apoptosis is a relevant feature of ischemic heart disease. It has been described in infarct and peri-infarct regions of the myocardium in coronary syndromes and in ischemia-linked heart remodeling. Previous studies have provided protection against ischemia-induced cardiomyocyte apoptosis by the anti-inflammatory cytokine interleukin-1 receptor-antagonist (IL-1Ra). Mitochondria triggering of caspases plays a central role in ischemia-induced apoptosis. We examined the production of IL-1Ra in the ischemic heart and, based on dual intra/extracellular function of some other interleukins, we hypothesized that IL-1Ra may also directly inhibit mitochondria-activated caspases and cardiomyocyte apoptosis. Methodology/Principal Findings: Synthesis of IL-1Ra was evidenced in the hearts explanted from patients with ischemic heart disease. In the mouse ischemic heart and in a mouse cardiomyocyte cell line exposed to long-lasting hypoxia, IL-1Ra bound and inhibited mitochondria-activated caspases, whereas inhibition of caspase activation was not observed in the heart of mice lacking IL-1Ra (Il-1ra−/−) or in siRNA to IL-1Ra-interfered cells. An impressive 6-fold increase of hypoxia-induced apoptosis was observed in cells lacking IL-1Ra. IL-1Ra down-regulated cells were not protected against caspase activation and apoptosis by knocking down of the IL-1 receptor, confirming the intracellular, receptor-independent, anti-apoptotic function of IL-1Ra. Notably, the inhibitory effect of IL-1Ra was not influenced by enduring ischemic conditions in which previously described physiologic inhibitors of apoptosis are neutralized. Conclusions/Significance: These observations point to intracellular IL-1Ra as a critical mechanism of the cell self-protection against ischemia-induced apoptosis and suggest that this cytokine plays an important role in the remodeling of heart by promoting survival of cardiomyocytes in the ischemic regions

Body weight and left ventricular mass in IL-1R1-/- and IL-1Ra-/- mice.

<p>Genetically modified mice (both IL-1R1-/- and IL-1Ra-/- ) have significantly smaller body weights compared with the respective wild-type animals (WT). Left ventricular (LV) mass calculated at echocardiography was not statistically different comparing IL-1R1-/- and IL-1Ra-/- and respectively WT, but the IL-1R1-/- had significantly greater LV mass/weight ratio. N = 8–10 per group.</p

Indirect comparison between the IL-1R1-/- and the IL-1Ra-/-.

<p>Considering that IL-1R1-/- and the IL-1Ra-/- mice were generated in different backgrounds, a direct comparison between the 2 strains cannot be made. The Figure shows an indirect comparison between the 2 strains in which the value of each strain is normalized to the corresponding wild-type mouse. In the comparison, the IL-1R1-/- mouse shows to have smaller infarcts, less apoptosis and more favorable remodeling, wheras the IL-1Ra-/- mouse shows large infarcts, more apoptosis, and more unfavorable remodeling.</p

Infarct size, apoptosis and left ventricular remodeling in wild-type and IL-1Ra-/- mice.

<p>When compared with the corresponding wild-type mice, infarct scar size (Masson's trichrome stain) and cardiomyocyte apoptotic rate (in-situ end labelling of DNA fragmentation–TUNEL) were significantly greater in IL-1Ra-/- mice. Moreover, IL-1Ra-/- mice had less left ventricular enlargement and systolic dysfunction 1 week after AMI. N = 6–8 per group.</p

Coimmunoprecipitation of IL-1Ra with mitochondria-activated caspases.

<p>(a) Coimmunoprecipitation of IL-1Ra with caspase-9 and (b) with caspase-3, -6, and -7 in cultured HL-1 cardiomyocytes after 6 hr hypoxia. Detection by western blot with monoclonal Abs to caspases or to IL-1Ra, or to control proteins IL-1beta, IL-1 type I receptor (IL-1R1) and IL-1R Ancillary Protein (IL-1R AcP). Proteins immunoprecipitated (IP) by Abs to caspases or to IL-1Ra, or to IL-1beta (control) are compared to unbound (free) supernatant proteins. The data are compiled from different gels in three separate experiments; [ ] not detected.</p