Regulatory role of IKKα in myocardial ischemia/reperfusion injury by the determination of M1 versus M2 polarization of macrophages

The I kappa B 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-kappa B family. Particularly, IKK alpha, 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 IKK alpha knockout (mIKK alpha(-/-)) mice and their IKK alpha(flox/flox) 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 mIKK alpha(-/-) mice exhibited significantly increased inflammation and macrophage aggregation as compared to their IKK alpha(flox/flox) littermates. Moreover, in the mIKK alpha(-/-) 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 IKK alpha. We discovered that a deficiency of IKK alpha 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 IKK alpha overexpression. Mechanistically, IKK alpha directly combined with RelB to regulate macrophage polarization. Furthermore, IKK alpha regulated MEK1/2-ERK1/2 and downstream p65 signaling cascades after LPS stimulation. Overall, our data reveals that IKK alpha is a novel mediator protecting against the development of myocardial I/R injury via negative regulation of macrophage polarization to M1 phenotype. Thus, IKK alpha may serve as a valuable therapeutic target for the treatment of myocardial I/R injury.