Mechanism of TNFα-induced IL-1α, IL-1β and IL-6 expression in human cardiac fibroblasts: Effects of statins and thiazolidinediones

Objective: In addition to direct effects on myocardial cell function, tumor necrosis factor α (TNFα) contributes to adverse cardiac remodeling by increasing production of other pro-inflammatory cytokines [e.g. interleukin (IL)-1 and IL-6]. Both statins and thiazolidinediones (TZDs) have beneficial effects on cardiac remodeling, possibly due to their anti-inflammatory properties. The present study examined the mechanisms by which TNFα stimulates expression of pro-inflammatory cytokines in cultured human cardiac fibroblasts and determined the effects of statin or TZD treatment. Methods: Human cardiac fibroblasts were cultured from biopsies of right atrial appendages. Cytokine mRNA expression and secretion was measured using quantitative real-time RT-PCR and ELISA. Activation of signaling pathways was determined by immunoblotting with phospho-specific antibodies. Results: TNFα (0.1-10 ng/ml) stimulated IL-6, IL-1α and IL-1β mRNA expression in cardiac fibroblasts in a concentration-dependent manner. Pharmacological inhibitors and receptor-neutralizing antibodies established that both TNFα-induced IL-6 and IL-1β expression was mediated via the TNFRI receptor and p38 mitogen-activated protein kinase (MAPK), phosphoinositide 3-kinase (PI3K)/Akt and nuclear factor (NF)-κB pathways. In contrast, TNFα-induced IL-1α expression required both TNFRI and TNFRII subtypes and p38 MAPK and PI3K/Akt pathways, but was negatively regulated by the NF-κB pathway. Neither statins (simvastatin, fluvastatin) nor TZDs (ciglitazone, rosiglitazone, troglitazone) had inhibitory effects on TNFα-induced IL-6 secretion or IL-1α/β mRNA expression; indeed, cytokine expression was increased in response to TZDs. Conclusions: Our data provide important insights into the regulation of pro-inflammatory cytokine expression in human cardiac fibroblasts and suggest that the myocardial anti-inflammatory effects of statins and TZDs are not due to inhibition of TNFα-induced IL-1 or IL-6 expression by cardiac fibroblasts.