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DOI: 10.1055/s-0036-1571717
Underlying Mechanism of Soluble CD74/Macrophage Migration Inhibitory Factor Complex Formation in Myocardial Protection
Objectives: The cardioprotective effects of macrophage migration inhibitory factor (MIF) in myocardial ischemia and reperfusion (I/R) seem to be further increased by application of the soluble form of MIF receptor CD74 ectodomain (sCD74). Therefore, we aimed to assess the underlying mechanisms of enhanced myocardial protective effects of MIF/sCD74 complex formation by stimulating cardiac cells with MIF alone or in complex with sCD74.
Methods: Cardiac cells were isolated from neonatal WT, MIF−/− and CD74−/− mice. Cells were incubated with MIF, sCD74 or MIF/sCD74 complex for 30min followed by H2O2 treatment for 90min. Cell survival was confirmed by a Trypan blue cell count. To investigate the influence of sCD74 on kinases activated by MIF, the relative phosphorylation levels of ERK and JNK were assessed by Western blotting. All experimental procedures were approved by the Animal Care and Use Committee of the local authorities (AZ 50.203.2 AC, LANUV, NRW, Germany).
Results: The addition of sCD74 further enhances MIF's cardioprotective properties in oxidative stressed cardiac cells isolated from WT. The same experimental setup was performed in cardiac cells derived from MIF−/− and CD74−/−. As expected, MIF treatment resulted in higher survival rates of H2O2-treated cells from MIF−/− as well as CD74−/−. This MIF-mediated cardioprotection could be increased by sCD74 in MIF−/−. Interestingly, the presence of sCD74/MIF complexes diminishes cardioprotective effects completely in CD74−/− cells. First Western blotting results indicate that sCD74 functions as scavenger and inhibits MIF-mediated ERK phosphorylation and activates MIF-induced JNK inhibition. In oxidative-stressed cardiac cells, sCD74/MIF complex formation leads to increased activation of both kinases.
Conclusion: These results suggest that cardioprotective effects of MIF can be increased by complex formation with sCD74 in oxidative-stressed cardiac cells. The MIF-mediated protective effects seem to be CD74-independent whereas the enhancing effect of MIF/sCD74 complex appears to be CD74-dependent. The CD74 ectodomain may function as scavenger and thereby inhibiting MIF-induced signaling. These results indicate that antioxidant activity of MIF might be the most pivotal feature to rescue cells rather than signaling through its receptor CD74 which is in accordance with our preliminary data. Therefore, sCD74 might be an attractive target to limit myocardial I/R injury.