IL‐21 promotes myocardial ischaemia/reperfusion injury through the modulation of neutrophil infiltration

Background and Purpose The immune system plays an important role in driving the acute inflammatory response following myocardial ischaemia/reperfusion injury (MIRI). IL‐21 is a pleiotropic cytokine with multiple immunomodulatory effects, but its role in MIRI is not known. Experimental Approach Myocardial injury, neutrophil infiltration and the expression of neutrophil chemokines KC (CXCL1) and MIP‐2 (CXCL2) were studied in a mouse model of MIRI. Effects of IL‐21 on the expression of KC and MIP‐2 in neonatal mouse cardiomyocytes (CMs) and cardiac fibroblasts (CFs) were determined by real‐time PCR and ELISA. The signalling mechanisms underlying these effects were explored by western blot analysis. Key Results IL‐21 was elevated within the acute phase of murine MIRI. Neutralization of IL‐21 attenuated myocardial injury, as illustrated by reduced infarct size, decreased cardiac troponin T levels and improved cardiac function, whereas exogenous IL‐21 administration exerted opposite effects. IL‐21 increased the infiltration of neutrophils and increased the expression of KC and MIP‐2 in myocardial tissue following MIRI. Moreover, neutrophil depletion attenuated the IL‐21‐induced myocardial injury. Mechanistically, IL‐21 increased the production of KC and MIP‐2 in neonatal CMs and CFs, and enhanced neutrophil migration, as revealed by the migration assay. Furthermore, we demonstrated that this IL‐21‐mediated increase in chemokine expression involved the activation of Akt/NF‐κB signalling in CMs and p38 MAPK/NF‐κB signalling in CFs. Conclusions and Implications Our data provide novel evidence that IL‐21 plays a pathogenic role in MIRI, most likely by promoting cardiac neutrophil infiltration. Therefore, targeting IL‐21 may have therapeutic potential as a treatment for MIRI. Linked Articles This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc