The IκB kinase (IKK) complex plays a well-documented role in cancer and immune system. This function has been widely attributed to its role as the master regulator of the NF-κB family. Particularly, IKKɑ, a member of IKK complex, is reported to have various regulating effects in inflammatory and malignant diseases. However, its role as well as its mechanism of function in macrophages following myocardial ischemia and reperfusion (I/R) injury remains unexplored. In vivo, sham or I/R operations were performed on macrophage-specific IKKɑ knockout (mIKKɑ) mice and their IKKɑ littermates. We ligated the left anterior descending (LAD) coronary artery of I/R groups simulating ischemia for 30 min, followed by a reperfusion period of 3 days and 7 days, respectively. The hearts of mIKKɑ mice exhibited significantly increased inflammation and macrophage aggregation as compared to their IKKɑ littermates. Moreover, in the mIKKɑ group subjected to I/R macrophages had a tendency to polarize to M1 phenotype. In vitro, we stimulated RAW264.7 cells with Lipopolysaccharides (LPS) after infection by the lentivirus, either knocking-down or overexpressing IKKɑ. We discovered that a deficiency of IKKɑ in RAW264.7 caused increased expression of pro-inflammatory markers compared to normal RAW264.7 after LPS stimulation. Inversely, pro-inflammatory factors were inhibited with IKKɑ overexpression. Mechanistically, IKKɑ directly combined with RelB to regulate macrophage polarization. Furthermore, IKKɑ regulated MEK1/2-ERK1/2 and downstream p65 signaling cascades after LPS stimulation. Overall, our data reveals that IKKɑ is a novel mediator protecting against the development of myocardial I/R injury via negative regulation of macrophage polarization to M1 phenotype. Thus, IKKɑ may serve as a valuable therapeutic target for the treatment of myocardial I/R injury.

BACKGROUND:The IκB kinase (IKK) complex has been found to have critical functions in cancer and the immune system. In particular, IKKα, which is a member of the IKK complex, has been shown to influence the inflammatory response and malignant diseases. However, the role of IKKα in macrophages after myocardial infarction (MI) remains largely unknown. METHODS:Sham or MI operations were performed on macrophage-specific IKKɑ knockout (mIKKɑ) mice and IKKɑ littermates. We ligated the left anterior descending coronary artery of the MI group and observed the results at 3, 7, and 30 days after MI. RESULTS:We discovered more severe cardiac dysfunction with reduced angiogenesis, fibrosis, and collagen deposition in mIKKɑ than in IKKɑ. In addition, we also observed that macrophages in mIKKɑ were easier to polarize to the M1 phenotype and expressed more proinflammatory factors than IKKɑ. Mechanistically, IKKα deficiency in macrophages inhibited the alternative nuclear factor-κB/RelB pathway and enhanced the MEK1/2/ERK1/2 pathway. CONCLUSIONS:Overall, our data identified IKKɑ in the heart as a novel mediator that protected the heart from a severe inflammatory response and attenuated ventricular remodelling after MI by negatively regulating macrophage polarization to the M1 phenotype. Therefore, IKKα may serve as a potential therapeutic target for treatment after MI.