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

Abstract

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.

Cytokines, Interleukins, Receptors, Signal transduction, Statins