Interleukin-18 stimulates fibronectin expression in primary human cardiac fibroblasts via PI3K-Akt-dependent NF-κB activation

Fibronectin (FN), a key component of the extracellular matrix, is upregulated in cardiac tissue during myocardial hypertrophy and failure. Here we show that interleukin (IL)-18, a proinflammatory and pro-hypertrophic cytokine, stimulates FN expression in adult human cardiac fibroblasts (HCF), an effect blocked by either the IL-18BP:Fc chimera or IL-18 neutralizing antibodies. IL-18 stimulated FN promoter-reporter activity in HCF, a response attenuated by mutation of an NF-kappa B binding site in the FN promoter. Overexpression of p65 stimulated FN transcription. IL-18 stimulated in vitro (p65, p50) and in vivo NF-kappa B DNA binding activities, and induced kappa B-dependent reporter gene activity. These effects were inhibited by adenoviral transduction of dominant negative (dn) p65 (Ad.dnp65) and dn1KK2 (Ad.dn1KK2). Investigation of signaling intermediates revealed that IL-18 stimulated P13 kinase activity (blocked by wortmannin, LY294002, or Ad.dnP13Kp85), and Akt phosphorylation and kinase activity (blocked by SH-5 or Ad.dnAkt). Furthermore, targeting MyD88, IRAK 1, TRAF6, PI3K, Akt, and NF-kappa B by RNA interference or dn expression vectors blunted IL-18 mediated FN transcription and mRNA expression. Conversely, FIN stimulated IL-18 expression. These data provide the first evidence that IL-18 and FIN stimulate each other's expression in HCF, and suggest a role for IL-18, FN and their crosstalk in myocardial hypertrophy and remodeling, disease states characterized by enhanced FIN expression and fibrosis.