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

Abstract

Background: CaMKII (Ca 2+ /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-δ is the predominant isoform and further alternatively spliced into 11 variants. In humans, CaMKII-δ9 and CaMKII-δ3, 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-δ9 prevents cardiac I/R injury and, if so, what is the underlying mechanism. Here, we aim to investigate the cardioprotective effect of specific CaMKII-δ9 inhibition against myocardial I/R damage and determine the underlying mechanisms. Methods: The role and mechanism of CaMKII-δ9 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-δ9 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-δ9 inhibition, and compared with the previously well-studied CaMKII-δ2, CaMKII-δ9 overexpression caused more profound cardiac inflammation. Mechanistically, in addition to IKKβ (inhibitor of NF-κB [nuclear factor-κB] kinase subunit β), CaMKII-δ9, but not δ2, directly interacted with IκBα (NF-κB inhibitor α) with its feature exon 13-16-17 combination and increased IκBα phosphorylation and consequently elicited more pronounced activation of NF-κB signaling and inflammatory response. Furthermore, the essential role of CaMKII-δ9 in myocardial inflammation and damage was confirmed in human cardiomyocytes. Conclusions: We not only identified CaMKII-δ9-IKK/IκB-NF-κB signaling as a new regulator of human cardiomyocyte inflammation but also demonstrated that specifically targeting CaMKII-δ9, the most abundant CaMKII-δ splice variant in human heart, markedly suppresses I/R-induced cardiac NF-κB activation, inflammation, and injury and subsequently ameliorates myocardial remodeling and heart failure, providing a novel therapeutic strategy for various ischemic heart diseases.

Splicing and Dicing: A Deeper Dive Into CaMKIIδ and Cardiac Inflammation

“…The actions of δ9, a cytosolic enzyme, are ostensibly similar to those previously reported for δC. In vivo expression of either δC or δ9 in the mouse heart leads to severe cardiomyopathy and heart failure, 2,13 but direct comparison in the current article suggests a stronger phenotype with δ9. CaMKIIδ9 was shown to elicit cardiomyocyte cell death due to phosphorylation and downregulation of a DNA repair enzyme called UBET.…”

“…In particular, CaMKIIδ9 affects not only activation of the upstream IKK, implicated previously in the response to CaMKIIδC, 6 but also binds to and regulates the inhibitory IkB subunit. 13 The more robust development of HF seen with cardiac expression of CaMKIIδ9 versus CaMKIIδC could reflect either greater cell death or more robust NF-κB activation and inflammation elicited through δ9 signaling.…”

“…The article in this issue of Circulation Research also presents studies in which δ9 is selectively deleted by knockout of exon 16 of the CaMKIIδ gene. 13 Deleting δ9 protects the mouse heart against I/R-induced infarct development (assessed at 24 hours after I/R) and cardiomyopathy (assessed at 4 weeks after I/R). This finding serves as evidence for the importance of the δ9 splice variant, even in the mouse heart where the equivalently expressed δC splice variant is not deleted.…”

Novel Biosensor Identifies Ruxolitinib as a Potent and Cardioprotective CaMKII Inhibitor

“…Due to on-target JAK1/2 inhibition, prolonged treatment can result in thrombocytopenia and anemia. Thus, we predict that repurposing will be most efficacious for indications that require rapid CaMKII inhibition, such as arrhythmias (86,87), 'electrical storm' (88,89), and acute ischemia/reperfusion injury (6,14,19,(90)(91)(92).…”

Citrus flavanone glucoside hesperidin acts as a novel CaMKII-δ inhibitor to ameliorate cardiac ischemia/reperfusion Injury

“…As the most abundant CaMKII-δ splice variant, CaMKII-δ9 is mainly located in the human heart acting as a crucial mediator of DNA damage and death of cardiomyocyte (Zhang et al, 2019). Mechanistically, CaMKII-δ9 directly interacted with IκBα (NF-κB inhibitor α) to prompt IκBα phosphorylation and activation of I/R-induced cardiac NF-κB signaling pathway (Yao et al, 2022).…”