Abstract 8420: Critical Role of CIKS/Act1 In Lipopolysaccharide (LPS)-Induced Cardiac Dysfunction i n vivo And Cardiomyocyte Contractility in vitro

Abstract

The innate immune system and inflammatory cytokines are critical in the initiation and perpetuation of tissue injury. Toll-like receptor (TLR)4 recognizes bacterial LPS, and is currently known to signal via distinct MyD88-dependent and MyD88-independent (TRAM-dependent) pathways to activate NF-κB and AP-1, and induce proinflammatory cytokines such as interleukin (IL)-18. Since the adapter molecule CIKS (connection to IκB kinase and stress-activated protein kinases; also known as Act1 or traf3ip2) lies upstream of IKK and JNK, and since both TLR4 and CIKS contain TIR (Toll/Interleukin-1 receptor) domains , we hypothesized that CIKS can interact with TLR4, and contribute independently to LPS-induced contractile depression. Treatment with LPS inhibited adult mouse cardiomyocyte contractility by 54% (IonOptix), an effect partially reversed by MyD88 or TRAM knockdown. Significantly, CIKS knockdown also reversed LPS-induced contractile depression. Using GST pull-down and reciprocal immunoprecipitation/immunoblotting, we found that TLR4 can physically associate with CIKS, and this association is enhanced by LPS. LPS upregulates CIKS protein expression, and CIKS knockdown inhibited LPS-induced IKK/NF-κB and JNK/AP-1 activation, IL-18 expression, and contractile depression. LPS-mediated contractile depression was reversed by IL-18 neutralizing Ab and IL-18 binding protein (IL-18BP, a natural inhibitor of IL-18). These results were confirmed in cardiomyocytes isolated from TLR4-mutant, CIKS null, IL-18 null and IL-18BP Tg mice. Notably, systemic LPS administration reduced cardiac ejection fraction by 43% at 6 h in wild type mice, and this effect was markedly attenuated in TLR4-mutant, CIKS and IL-18 null, and IL-18BP Tg mice. These novel observations identify a TLR4/CIKS pathway in NF-κB and AP-1 activation in cardiomyocytes, and appears to be distinct from the well-characterized MyD88 and TRAM-dependent LPS/TLR4 signaling. These data also show that LPS induces contractile dysfunction in part via CIKS-mediated IKK/NF-κB and JNK/AP-1-dependent IL-18 expression. These data identify CIKS as a novel therapeutic target in conditions of innate immune activation and inflammation such as myocardial injury and congestive heart failure.