Interleukin-6-dependent phenotypic modulation of cardiac fibroblasts after acute myocardial infarction

Interleukin-6 (IL-6) is a multifunctional cytokine that orchestrates the immune response to a wide variety of pathophysiologic challenges but also contributes to tissue homeostasis. Furthermore, IL-6 is elevated in patients with acute myocardial infarction. Hyaluronan (HA) is an extracellular carbohydrate that has been implicated in wound healing and accumulates after acute myocardial infarction (AMI). Aim of this study was to investigate the involvement of IL-6 in the regulation of the HA-matrix in the early phase of infarct healing. In the present study, we show by the use of a blocking anti-IL-6 antibody, that endogenous IL-6 rapidly but transiently increased HA-synthase (HAS) 1 and 2 expression resulting in the formation of a HA-rich matrix acutely after AMI in mice. In vitro, IL-6 induced HAS1 and 2 via STAT3 phosphorylation in cardiac fibroblasts (CF) and supported a myofibroblastic phenotype in a HA-dependent manner. Furthermore, CCL5 and MCP1 expression were dependent on IL-6, HA-synthesis and the HA-receptor CD44 as shown in cultured CF derived from CD44 knockout mice. In vivo after AMI, blocking IL-6 decreased HA-matrix formation in the peri-infarct region and alpha-smooth muscle actin-positive myofibroblasts. Blocking IL-6 also reduced neutrophil infiltration in infarcted left ventricles. Moreover, treatment with the blocking IL-6 antibody reduced cardiac ejection fraction and increased infarct size 3 weeks after AMI. These findings support a functionally important role for IL-6 in CF by transiently inducing a HA-rich matrix that in turn promotes a myofibroblastic phenotype and inflammatory responses, and ultimately establishes a cardioprotective program after AMI.