Tristetraprolin in cardiomyocytes has a protective role in pressure-overloaded hearts

Abstract

Abstract Background Elevated circulating levels of TNFα, IL-6 and the soluble TNF receptors predict adverse outcomes in patients with heart failure. However, the targeted anti TNF approaches resulted in worsening heart failure or death. The entire scenario of how the expression levels of inflammatory cytokines are maintained in failing hearts must be elucidated to develop novel and effective treatments for heart failure. Although transcriptional control is a determinant of the kinetics of proinflammatory cytokine gene expression, the stability of the mRNA also has a key function in coordinating immune responses. Tristetraprolin (TTP) has been shown to control mRNA decay by associating with the 3’- untranslated region and critical for the decay of the mRNAs for cytokines. The role of TTP in nonimmune cells such as cardiomyocytes remains to be elucidated. Purpose The purpose of this study is to examine the in vivo role of proinflammatory cytokine degradation by TTP in cardiomyocytes during cardiac remodelling under pressure overload. Methods Cardiomyocyte-specific TTP–deficient mice were generated. The mice were subjected to pressure overload by means of transverse aortic constriction (TAC) to induce heart failure. Cardiac remodelling was assessed by echocardiography as well as histological and molecular analyses 4 weeks after operation. Cytokine mRNA levels were examined by quantitative PCR. Results Cardiomyocyte-specific TTP–deficient mice showed no cardiac phenotypes under baseline conditions. However, the mice exhibited severe systolic dysfunction, indicated by left ventricular fractional shortening, after 4 weeks of pressure overload by means of TAC compared with control littermates (fractional shortening, control littermates 35.8% versus cardiomyocyte-specific TTP-deficient mice 19.9%, p = 0.000). In addition, those hearts showed increases in collagen deposition and the mRNA levels of Col1a2 and Nppb (1.4 times (p = 0.023), 1.5 times (p = 0.033), and 2.0 times (p = 0.020), respectively) compared to corresponding control hearts. Four weeks after TAC, the Il6 mRNA level was upregulated 2.7 times (p = 0.000), but not other cytokine mRNAs, including Tnfα, in cardiomyocyte-specific TTP–deficient hearts compared to controls. Conclusions The degradation of cytokine mRNA by TTP in cardiomyocytes plays a protective role in failing hearts and the TTP–mediated pathway in cardiomyocytes might be a therapeutic target to treat patients with heart failure.