Adiponectin protects against toll-like receptor 4-mediated cardiac inflammation and injury

Abstract

Aims Adiponectin (APN) is an immunomodulatory and cardioprotective adipocytokine. Toll-like receptor (TLR) 4 mediates autoimmune reactions that cause myocarditis resulting in inflammation-induced cardiac injury. Here, we investigated whether APN inhibits inflammation and injury in autoimmune myocarditis by interfering with TLR4 signalling. Methods and results APNoverexpression inmurine experimental autoimmunemyocarditis (EAM) down-regulated cardiac expression of TLR4 and its downstream targets tumour necrosis factor (TNF)α, interleukin (IL)-6, IL-12, CC chemokine ligand (CCL)2, and intercellular adhesion molecule (ICAM)-1 resulting in reduced infiltration with cluster of differentiation (CD)3+, CD14+, andCD45+immune cells aswell as diminishedmyocardial apoptosis. Expression ofTLR4 signalling pathway components was unchanged in hearts and spleens of APN-knockout (APN-KO) mice. In vitro APN had no effect on TLR4 expression in cardiac and immune cells but induced dissociation of APN receptors from the activated TLR4/CD14 signalling complex. APNinhibited the expression of a TLR4-mediated inflammatory phenotype induced by exogenous and endogenous TLR4 ligands as assessed by attenuated nuclear factor (NF)-κB activation and reduced expression of TNFα, IL-6, CCL2, and ICAM-1. Accordingly, followingTLR4 ligation, splenocytes fromAPN-KOmice showed enhanced expression of TNFα, IL-6, IL-12, CCL2, and ICAM-1, whereas dendritic cells (DCs) from APN-KOmice demonstrated increased activation and T-cell priming capacity. Moreover, APN diminished TLR4-mediated splenocyte migration towards cardiac cells as well as cardiomyocyte apoptosis after co-cultivation with splenocytes. Mechanistically, APN inhibited TLR4 signalling through cyclooxygenase (COX)-2, protein kinase A (PKA), and meiosis-specific serine/threonine kinase (MEK)1. Conclusion Our observations indicate that APN protects against inflammation and injury in autoimmune myocarditis by diminishing TLR4 signalling thereby attenuating inflammatory activation and interaction of cardiac and immune cells.