ERK and p38 MAPK, but not NF-κB, Are Critically Involved in Reactive Oxygen Species–Mediated Induction of IL-6 by Angiotensin II in Cardiac Fibroblasts

Abstract

Abstract-We recently reported that angiotensin II (Ang II) induced IL-6 mRNA expression in cardiac fibroblasts, which played an important role in Ang II-induced cardiac hypertrophy in paracrine fashion. The present study investigated the regulatory mechanism of Ang II-induced IL-6 gene expression, focusing especially on reactive oxygen species (ROS)-mediated signaling in cardiac fibroblasts. Ang II increased intracellular ROS in cardiac fibroblasts, and the increase was completely inhibited by the AT-1 blocker candesartan and the NADH/NADPH oxidase inhibitor diphenyleneiodonium (DPI). We first confirmed that antioxidant N-acetylcysteine, superoxide scavenger Tiron, and DPI suppressed Ang II-induced IL-6 expression. Because we observed that exogenous H 2 O 2 also increased IL-6 mRNA, the signaling pathways downstream of Ang II and exogenous H 2 O 2 were compared. Ang II, as well as exogenous H 2 O 2 , activated ERK, p38 MAPK, and JNK, which were significantly inhibited by N-acetylcysteine and DPI. In contrast with exogenous H 2 O 2 , however, Ang II did not influence phosphorylation and degradation of IB-␣/␤ or nuclear translocation of p65, nor did it increase NF-B promoter activity. PD98059 and SB203580 inhibited Ang II-induced IL-6 expression. Truncation and mutational analysis of the IL-6 gene promoter showed that CRE was an important cis-element in Ang II-induced IL-6 gene expression. NF-B-binding site was important for the basal expression of IL-6, but was not activated by Ang II. Ang II phosphorylated CREB through the ERK and p38 MAPK pathway in a ROS-sensitive manner. Collectively, these data indicated that Ang II stimulated ROS production via the AT1 receptor and NADH/NADPH oxidase, and that these ROS mediated activation of MAPKs, which culminated in IL-6 gene expression through a CRE-dependent, but not NF-B-dependent, pathway in cardiac fibroblasts. Key Words: angiotensin II Ⅲ interleukin-6 Ⅲ reactive oxygen species Ⅲ mitogen-activated protein kinase Ⅲ cardiac fibroblast C linical, experimental, and genetic data have demonstrated that the renin angiotensin system is linked to the pathogenesis of a variety of cardiac diseases. Expression of angiotensin II (Ang II), the key effector molecule of the renin angiotensin system, is increased under various pathophysiological conditions and stimulates cardiomyocyte hypertrophy and interstitial fibrosis coinciding with accumulation of extracellular matrix. Recent reports had shown that Ang II stimulates membrane-bound NAD(P)H oxidase, which generates reactive oxygen species (ROS) in a variety of nonphagocytic cells. 1 ROS may act as a second messenger that regulates various intracellular signal transduction cascades and the activity of various transcription factors. NF-B and AP-1 are the best characterized transcription factors to be influenced by the cellular oxidation-reduction (redox) state. 2,3 The primary target of activation of NF-B by ROS appears to be the phosphorylation and subsequent degradation of IB. 4 Another well-characterized redox sensitive signali...

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