Mechanism of tumor necrosis factor gene expression in the development of heart failure and cardiac hypertrophy

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Clinical observations indicate that the concentration of tumor necrosis factor (TNF) is elevated in patients with advanced heart failure or hypertrophic cardiomyopathy. However, the mechanisms for TNF production in the setting of these diseases are poorly understood. We recently showed that angiotensin II (ANGII) as well as mechanical stretch stimulate the production of TNF in cardiac fibroblasts. To extend these observations, we have examined the moleculer mechanisms by which ANGII up regulates TNFα gene expression. Using neonatal rat cardiac fibroblasts. Northern blot analysis showed that treatment with ANGII, endothelin-1 (ET1) or lipopolysaccharide (LPS) induced TNFαmRNA expression. These increase in TNFαmRNA level were regulated at transcriptional level as determined by luciferase activity of TNFα promoter gene. Progressive deletion analysis of TNFα promoter gene showed that the ANGII-responsive region lies between -100 to -70bp from the transcription start site. On the other hand, LPS-responsive region lies between -200 to -100bp. Further, mutation analysis indicated that the ANGII-responsive element could interact with Bs and NF-_KB, but the LPS-responsive element could interact with Sp1 . Additional studies were performed to evaluate the intracelluler signaling pathway associated LPS-induced TNFα gene expression. The increase of TNFαmRNA expression was attenuated by KT5823 which is a PKG specific inhibitor, whereas MAP kinase, PKA or PKC inhibitors had no effect on this response. Moreover, 8 bromo-cyclic GMP induced TNFαmRNA expression. We conclude that TNFα gene expression is transcriptionaly activated by ANGII, ET1 and LPS in cardiac fibroblasts. However, this response is mediated through different transcriptional factors by ANGII and LPS. Thus, the mechanisms for TNF production in heart failure or cardiac hypertrophy should differ from those in infectious disease. Further, PKGdependent signaling pathway may be important for this response.