Targeting CaMKII-δ9 Ameliorates Cardiac Ischemia/Reperfusion Injury by Inhibiting Myocardial Inflammation

Background: CaMKII (Ca2+/calmodulin-dependent kinase II) plays a central role in cardiac ischemia/reperfusion (I/R) injury-an important therapeutic target for ischemic heart disease. In the heart, CaMKII-delta is the predominant isoform and further alternatively spliced into 11 variants. In humans, CaMKII-delta 9 and CaMKII-delta 3, the major cardiac splice variants, inversely regulate cardiomyocyte viability with the former pro-death and the latter pro-survival. However, it is unknown whether specific inhibition of the detrimental CaMKII-delta 9 prevents cardiac I/R injury and, if so, what is the underlying mechanism. Here, we aim to investigate the cardioprotective effect of specific CaMKII-delta 9 inhibition against myocardial I/R damage and determine the underlying mechanisms. Methods: The role and mechanism of CaMKII-delta 9 in cardiac I/R injury were investigated in mice in vivo, neonatal rat ventricular myocytes, and human embryonic stem cell-derived cardiomyocytes. Results: We demonstrate that CaMKII-delta 9 inhibition with knockdown or knockout of its feature exon, exon 16, protects the heart against I/R-elicited injury and subsequent heart failure. I/R-induced cardiac inflammation was also ameliorated by CaMKII-delta 9 inhibition, and compared with the previously well-studied CaMKII-delta 2, CaMKII-delta 9 overexpression caused more profound cardiac inflammation. Mechanistically, in addition to IKK beta (inhibitor of NF-kappa B [nuclear factor-kappa B] kinase subunit beta), CaMKII-delta 9, but not delta 2, directly interacted with I kappa B alpha (NF-kappa B inhibitor alpha) with its feature exon 13-16-17 combination and increased I kappa B alpha phosphorylation and consequently elicited more pronounced activation of NF-kappa B signaling and inflammatory response. Furthermore, the essential role of CaMKII-delta 9 in myocardial inflammation and damage was confirmed in human cardiomyocytes. Conclusions: We not only identified CaMKII-delta 9-IKK/I kappa B-NF-kappa B signaling as a new regulator of human cardiomyocyte inflammation but also demonstrated that specifically targeting CaMKII-delta 9, the most abundant CaMKII-delta splice variant in human heart, markedly suppresses I/R-induced cardiac NF-kappa B activation, inflammation, and injury and subsequently ameliorates myocardial remodeling and heart failure, providing a novel therapeutic strategy for various ischemic heart diseases.