The stiffness-controlled release of interleukin-6 by cardiac fibroblasts is dependent on integrin α2β1

Cardiac fibroblasts are able to sense the rigidity of their environment. The present study examines whether the stiffness of the substrate in cardiac fibroblast culture can influence the release of interleukin-6 (IL-6), interleukin-11 (IL-11) and soluble receptor of IL-6 (sIL-6R). It also examines the roles of integrin α2β1 activation and intracellular signalling in these processes. Cardiac fibroblasts were cultured on polyacrylamide gels and grafted to collagen, with an elasticity of E = 2.23 ± 0.8 kPa (soft gel) and E = 8.28 ± 1.06 kPa (stiff gel, measured by Atomic Force Microscope). Flow cytometry and ELISA demonstrated that the fibroblasts cultured on the soft gel demonstrated higher expression of the α2 integrin subunit and increased α2β1 integrin count and released higher levels of IL-6 and sIL-6R than those on the stiff gel. Substrate elasticity did not modify fibroblast IL-11 content. The silencing of the α2 integrin subunit decreased the release of IL-6. Similar effects were induced by TC-I 15 (an α2β1 integrin inhibitor). The IL-6 levels in the serum and heart were markedly lower in α2 integrin-deficient mice B6.Cg-Itga2^{tm1.1Tkun/tm1.1Tkun} than wild type. Inhibition of Src kinase by AZM 475271 modifies the IL-6 level. sIL-6R secretion is not dependent on α2β1 integrin. Conclusion: The elastic properties of the substrate influence the release of IL-6 by cardiac fibroblasts, and this effect is dependent on α2β1 integrin and kinase Src activation.