Thromboxane A₂ Mediates Iron-Overload Cardiomyopathy in Mice Through Calcineurin-Nuclear Factor of Activated T Cells Signaling Pathway

Abstract

Background: Recent studies demonstrated that iron overload could enhance the production of arachidonic acid and prostanoid, suggesting a causal connection between these signals and iron-overload cardiomyopathy. However, information regarding the downstream signaling is limited. Because thromboxane A₂ (TXA₂) and prostacyclin are the 2 major prostanoids in the cardiovascular system, and TXA₂ plays a major role in vascular atherosclerosis and has pro-inflammatory characteristics, we intended to elucidate the role of TXA₂ in iron-overload cardiomyopathy. Methods and Results: A 4-week iron loading protocol was instituted for both TXAS gene-deleted (TXAS^−/−) mice and wild-type (WT) mice, with less severe cardiac fibrosis and preserved normal left ventricular contraction in the TXAS^−/− mice. Inflammatory profiles, including MCP-1, TNF-α, IL-6, ICAM-1, and myeloperoxidase activity were also lower in the TXAS^−/− as compared with WT littermates. TXAS supplement to the iron-injured TXAS^−/− mice re-aggravated cardiac inflammation. Using a TXA₂ analog, U46619, for NFAT reporter luciferase activity on cardiomyoctes, and intraperitonal injection of U46619 into nuclear factor of activated T cells (NFAT)-luciferase transgenic mice demonstrated that U46619 increase NFAT expression, and this expression, as well as TNF-α expression, can be blocked by TXA₂ receptor antagonist (SQ29548), NFAT-SiRNA, calcineurin inhibitor, or calcium chelator. Finally, intraperitoneal injection of the TNF-α antibody, infliximab, into iron-injured mice decreased TXAS expression and attenuated cardiac fibrosis. Conclusions: TXA₂ mediates iron-overload cardiomyopathy through the TNF-α-associated calcineurin-NFAT signaling pathway.  (Circ J 2013; 77: 2586–2595)