Abstract 13073: Adiponectin Protects Against Autoimmune Myocarditis by Inhibiting Toll-Like Receptor 4 Mediated Cardiac Inflammation And Injury
Background: Adiponectin (APN) is an immunomodulatory and cardioprotective adipocytokine that is also expressed in cardiac cells. Toll-like receptor 4 (TLR4) mediates autoimmune reactions that cause myocarditis resulting in tissue injury. Here, we investigated whether APN inhibits cardiac inflammation and injury by interfering with TLR4 signaling.
Methods: APN overexpression in experimental autoimmune myocarditis (EAM) was achieved by adenoviral gene transfer. Gene expression was analyzed by qRT-PCR and ELISA. NFκB activation was measured by ELISA. Splenocyte migration, dendritic cell (DC) activation and T cell proliferation was quantified by flow cytometry. Apoptosis was measured by TUNEL.
Results: APN overexpression in EAM downregulated cardiac expression levels of TLR4 and TLR4 signaling target genes TNFα, IL-6, IL-12, CCL2 and ICAM-1 resulting in reduced infiltration of CD3+, CD14+ and CD45+ immune cells and diminished cardiac apoptosis. In cardiac myocytes and fibroblasts APN inhibited the induction of a TLR4 mediated inflammatory phenotype by exogenous and endogenous TLR4 ligands as assessed by attenuated NFκB activation and reduced expression levels of NFκB controlled genes TNFα, IL-6, CCL2 and ICAM-1. Moreover, APN inhibited the TLR4 mediated increase in TNFα expression in DCs, CD14+ and CD19+ immune cells. Accordingly, splenocytes from APN-KO mice showed enhanced expression levels of TNFα, IL-6, IL-12, CCL2 and ICAM-1 after TLR4 ligation. In addition, TLR4 stimulated DCs from APN-KO mice displayed increased ability to induce T cell proliferation. Finally, APN diminished splenocyte migration towards TLR4 activated cardiac cells and inhibited apoptosis of TLR4 stimulated cardiac myocytes after co-cultivation with splenocytes. Mechanistically, APN interfered with TLR4 signaling through COX-2, PKA and MEK1. In contrast, APN had no influence on expression levels of TLR4, MyD88 and TRIF and APN receptors did not interact with TLR4.
Conclusion: Our observations indicate that APN protects against cardiac inflammation and injury in autoimmune myocarditis through effective interference with TLR4 signaling thereby attenuating the inflammatory activation of cardiac and immune cells and their resulting deleterious interaction.
- © 2012 by American Heart Association, Inc.