Tumor Necrosis Factor-α–Induced AT 1 Receptor Upregulation Enhances Angiotensin II–Mediated Cardiac Fibroblast Responses That Favor Fibrosis

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Abstract
Extracellular matrix (ECM) remodeling after myocardial infarction (MI) is an important determinant of cardiac function. Tumor necrosis factor-α (TNF-α) and angiotensin (Ang) II levels increase after MI and both factors affect fibroblast functions. The type 1 (AT 1 ) receptor that mediates most Ang II effects is upregulated after MI in cardiac fibroblasts, and there is evidence that this is caused by TNF-α. We sought to determine if TNF-α–induced AT 1 receptor upregulation alters fibroblast responsiveness to Ang II and if this effect differs from direct TNF-α effects on fibroblast functions. In cultured neonatal rat cardiac fibroblasts, TNF-α reduced cellular [ 3 H]-proline incorporation, increased matrix metalloproteinase-2 (MMP-2) activity and protein, and increased TIMP-1 protein levels. In cardiac fibroblasts with TNF-α–induced AT 1 receptor upregulation, Ang II–stimulated [ 3 H]proline incorporation and TIMP-1 protein production was approximately 2-fold greater than in nonpretreated fibroblasts. Angiotensin II reduced MMP-2 activity and protein level only in TNF-α–pretreated fibroblasts. Angiotensin II effects were inhibited by selective AT 1 (but not AT 2 ) receptor blockers. Thus, TNF-α–induced AT 1 receptor upregulation enhances Ang II–mediated functions that favor fibrosis. These effects are mostly directionally opposite of direct TNF-α effects on cardiac fibroblasts. Recognition of multifaceted TNF-α effects provides new insights into post-MI ECM remodeling.

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