Elsevier

Cytokine

Volume 56, Issue 3, December 2011, Pages 732-738
Cytokine

Interleukin-2 enhances angiogenesis and preserves cardiac function following myocardial infarction

https://doi.org/10.1016/j.cyto.2011.09.023Get rights and content

Abstract

We previously demonstrated that injection of IL-2-activated natural killer (NK) cells contribute to vascular remodeling via a4b7 integrin and killer cell lectin-like receptor (KLRG) 1 and promote cardiac repair following myocardial infarction (MI). The aim of the present study is to test the hypothesis that injection of recombinant human interleukin (rhIL)-2 improves angiogenesis and preserves heart function after MI. A single IV injection of rhIL-2 two days following MI improved by 27.7% the left ventricular (LV) fractional shortening of immune competent (C57Bl6) mice, but had no effect on cardiac function of immune-deficient (NOD-SCID IL2Rγnull) mice. Immunohistochemical analysis of C57Bl6 cross sections of heart revealed that collagen deposition was reduced by 23.1% and that capillary density was enhanced in the scar area and the border zone of the infarct respectively by 22.4% and 33.6% following rhIL-2 injection. In addition, rhIL-2 enhanced 1.6-fold the in vivo endothelial cell proliferation index and 1.8-fold the number of NK cell infiltrating the infarcted heart, but had no effect on the number of cardiac CD4 and CD8 cells. In vitro, rhIL-2 activated NK cells enhanced cardiac endothelial cell proliferation by 17.2%. Here we show that a single IV injection of rhIL-2 positively impacted cardiac function by improving angiogenesis through a process involving NK cells.

Highlights

IV injection of rhIL-2 preserves LV fractional shortening and remodeling after MI. ► rhIL-2 enhances cardiac angiogenesis. ► rhIL-2 helps preserve the integrity and function of myocardium after MI. ► Proangiogenic effect of rhIL-2 correlated with the infiltration of NK cells.

Introduction

Coronary artery occlusion leads to rapid death of cardiomyocytes in the affected area of the myocardium [1], [2]. The resulting inflammatory reaction has been shown to be essential in initiating cardiac healing through structural changes that lead to necrotic tissue replacement and scar formation [3], [4]. Leukocytes invade the myocardial wound within the first day after myocardial infarction (MI), and regulate extracellular matrix metabolism through the synthesis of metalloproteinases (MMPs), cytokines and growth factors [5], [6], [7]. In particular, neutrophils migrate to the site of ischemia 24–48 h after MI to participate in removal of necrotic cardiomyocytes [1]. We have previously characterized the dynamics of inflammatory cell infiltration within immune-competent and immune-deficient mouse infarcted hearts. Our data indicate that neutrophils were the first cells to invade the infarcted myocardium, followed in chronological order by monocytes, macrophages and NK cells [8]. Lymphocytes infiltrate the heart 4–6 days following MI and have been shown to be required to preserve cardiac function [9]. In a recent study it was shown that c-kit-mediated mobilization of NK cells contributes to improved cardiac function and rescues mice after MI [10]. It is also well established that cytokines and chemokines released during the inflammatory process play a central role in regulating the cardiac outcome [11], [12]. Regeneration of myocardium in mammals is however virtually absent, and damaged myocardium is replaced by scar tissue consisting of a myofibroblast-derived collagen network leading to cardiac remodeling and progressive decline in left ventricular (LV) performance. The ideal therapy would therefore be directed toward limiting the early and massive loss of cardiac tissue. Early reperfusion has been shown to reduce infarct size and preserve LV function by limiting the loss of viable myocardium [13]. One potential approach would thus consist in improving angiogenesis during the early stage of the MI in order to prevent cardiomyocyte death [14]. Recently, we showed that IL-2-activated natural killer (NK) cells interact with TNF-α-stimulated endothelial cells to induce their proliferation and promote angiogenesis through a mechanism involving a4b7 integrin and killer cell lectin-like receptor (KLRG) 1 (companion manuscript). The aim of our study is to verify whether recombinant human interleukin (rhIL)-2 would improve cardiac function following infarction. We have thus tested the hypothesis that early stimulation of lymphoid cells using a single intravenous (IV) injection of rhIL-2 modulates angiogenesis, reduces cardiac tissue loss and preserves heart function following MI. Our data suggest that NK cells are involved in rhIL-2 induced angiogenesis although they might not be the only element responsible of cardiac angiogenesis improvement.

Section snippets

Reagents

Anti-NK-1.1 (clone PK136) antibody was obtained from R&D systems (Minneapolis, Minnesota, USA). Ki67 (clone SP6) antibody was from Abcam (Cambridge, Massachusetts, USA). Anti-CD144 (clone 11D4.1) antibody was from BD Biosciences (Mississauga, Ontario, Canada). ELISA for cardiac troponin I (cTNI) was obtained from Life Diagnostics (Westchester, Pennsylvania, USA). RPMI and DMEM were purchased from Hyclone (Logan, Utah, USA).

Animal models

All experiments were carried out in agreement with local guidelines for

rhIL-2 preserves LV fractional shortening in C57Bl/6 mice but has no effect on NOD-SCID IL2Rγnull mice after MI

To test the hypothesis that rhIL-2 affects outcome of MI, we evaluated LV fractional shortening and LV mass following anterior coronary ligation-induced MI and rhIL-2 injection in immune-competent (C57Bl/6) and immune-deficient (NOD-SCID IL2Rγnull) mice. The results in Fig. 1 show that rhIL-2 enhanced LV fractional shortening by 27.7% (n = 8, p = 0.01) in C57Bl/6 mice but had no effect on NOD-SCID IL2Rγnull mice (n = 6). Also, rhIL-2 treatment induced a trend, albeit without achieving significance (n =

Discussion

The cardiac healing process following MI has been divided into four phases [1]. Phase 1 is characterized by cardiomyocyte death. It occurs as early as 6 h after the occlusion of a coronary artery and lasts until 4 days after MI [29]. An acute inflammatory reaction takes place 12–16 h after the onset of ischemia and is characterized by early infiltration of neutrophils followed by macrophages and lymphocytes (phase 2) [30]. Two to three days after MI, formation of granulation tissue starts in the

Acknowledgement

This work was supported by Grants 72553 (to JG) and 82790 (to ELS) from the Canadian Institutes for Health Research (CIHR), a Canada Research Chair (CRC, to ELS) from the CRC/CIHR program of the Government of Canada, Canadian Stem Cell Network (CSCN) and Fonds de Recherche en Santé du Quebec (FRSQ).

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