Abstract 221: IKKe Deficiency Aggravates Cardiac Inflammation with Dysregulation of p52 and p38 in Myocardial Infarction

Abstract

Inhibitor of NF-κB kinase (IKK), an upstream of nuclear factor-kappa B (NF-κB), is a critical modulator for pathophysiological inflammation. IKKε is a non-classical IKK and has been studied in infectious diseases and cancers. However, the role of IKKε in a myocardial infarction (MI) has not been addressed. In this study, we used IKKε knockout mice to induce MI by coronary artery ligation. Cardiac function was analyzed by echocardiograph after 2 weeks, and fractional shortening (FS) was 16.36±4.46% in the wild type group and 13.47±1.21% in the knockout group. Cardiac fibrosis and macrophage infiltration deteriorated in the knockout group. Next, we investigated the inflammatory responses and found that the expression of inducible nitric oxide synthase (iNOS), an inflammatory marker, was much higher in both infarcted heart tissues and bone marrow-derived macrophages (BMDM) isolated from knockout mice than from wild type mice. Besides, cardiac macrophages displayed more inflammatory phenotype in the IKKε knockout group than in the wild type group. To explore the responsible mediator, we performed phosphorylated protein array and found phosphorylated p38 was significantly downregulated in the IKKε knockout BMDM. Conversely, both knockdown of p38 by siRNA and inhibition of p38 by SB203580 treatment in RAW264.7 cells upregulated iNOS induction. In the infarcted heart tissue, non-canonical NF-κB2 (p52) protein was dramatically upregulated in the IKKε knockout group than in the wild type group, while mRNA level was not different in the both groups. Immunohistochemical analysis showed nuclear accumulation of p52 in cardiomyocytes and fibroblasts in the peri-infarct lesion. Our data showed excessive inflammation in IKKε knockout mice was associated with inactivation of p38 in macrophages and upregulated p52 in the infarcted myocardium. Collectively, IKKε is involved in the control of inflammation resolution through modulating p38 activity and p52 post-translational modification in the infarcted myocardium.