Blocking Macrophage Migration Inhibitory Factor Protects Against Cisplatin-Induced Acute Kidney Injury in Mice.

Macrophage migration inhibitory factor (MIF) is elevated in patients with acute kidney injury (AKI) and is suggested as a potential predictor for renal replacement therapy in AKI. In this study, we found that MIF also plays a pathogenic role and is a therapeutic target for AKI. In a cisplatin-induced AKI mouse model, elevated plasma MIF correlated with increased serum creatinine and the severity of renal inflammation and tubular necrosis, whereas deletion of MIF protected the kidney from cisplatin-induced AKI by largely improving renal functional and histological injury, and suppressing renal inflammation including upregulation of cytokines such as interleukin (IL)-1ß, tumor necrosis factor-alpha (TNF-α), IL-6, inducible nitric oxide synthase (iNOS), MCP-1, IL-8, and infiltration of macrophages, neutrophils, and T cells. We next developed a novel therapeutic strategy for AKI by blocking the endogenous MIF with an MIF inhibitor, ribosomal protein S19 (RPS19). Similar to the MIF-knockout mice, treatment with RPS19, but not the mutant RPS19, suppressed cisplatin-induced AKI. Mechanistically, we found that both genetic knockout and pharmacological inhibition of MIF protected against AKI by inactivating the CD74-nuclear factor κB (NF-κB) signaling. In conclusion, MIF is pathogenic in cisplatin-induced AKI. Targeting MIF with an MIF inhibitor RPS19 could be a promising therapeutic potential for AKI.

Ribosomal protein S19 is a novel therapeutic agent in inflammatory kidney disease.

RPS19 (ribosomal protein S19), a component of the 40S small ribosomal subunit, has recently been identified to bind the pro-inflammatory cytokine macrophage MIF (migration inhibitory factor). In vitro experiments identify RPS19 as the first endogenous MIF inhibitor by blocking the binding of MIF to its receptor CD74 and MIF functions on monocyte adherence to endothelial cells. In the present study, we sought to establish whether recombinant RPS19 can exert anti-inflammatory effects in a mouse model of anti-GBM (glomerular basement membrane) GN (glomerulonephritis) in which MIF is known to play an important role. Accelerated anti-GBM GN was induced in C57BL/6J mice by immunization with sheep IgG followed 5 days later by administration of sheep anti-mouse GBM serum. Groups of eight mice were treated once daily by intraperitoneal injection with 6 mg of RPS19/kg of body weight or an irrelevant control protein (human secretoglobin 2A1), or received no treatment, from day 0 until being killed on day 10. Mice that received control or no treatment developed severe crescentic anti-GBM disease on day 10 with increased serum creatinine, declined creatinine clearance and increased proteinuria. These changes were associated with up-regulation of MIF and its receptor CD74 activation of ERK (extracellular-signal-regulated kinase) and NF-κB (nuclear factor κB) signalling, prominent macrophage and T-cell infiltration, as well as up-regulation of Th1 [T-bet and IFNγ (interferon γ)] and Th17 [STAT3 (signal transducer and activator of transcription 3) and IL (interleukin)-17A] as well as IL-1ß and TNFα (tumour necrosis factor α). In contrast, RPS19 treatment largely prevented the development of glomerular crescents and glomerular necrosis, and prevented renal dysfunction and proteinuria (all P<0.001). Of note, RPS19 blocked up-regulation of MIF and CD74 and inactivated ERK and NF-κB signalling, thereby inhibiting macrophage and T-cell infiltration, Th1 and Th17 responses and up-regulation of pro-inflammatory cytokines (all P<0.01). These results demonstrate that RPS19 is a potent anti-inflammatory agent, which appears to work primarily by inhibiting MIF signalling.

Ribosomal protein S19 interacts with macrophage migration inhibitory factor and attenuates its pro-inflammatory function.

Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that has been implicated in the pathogenesis of inflammatory disorders such as infection, sepsis, and autoimmune disease. MIF exists preformed in cytoplasmic pools and exhibits an intrinsic tautomerase and oxidoreductase activity. MIF levels are elevated in the serum of animals and patients with infection or different inflammatory disorders. To elucidate how MIF actions are controlled, we searched for endogenous MIF-interacting proteins with the potential to interfere with key MIF functions. Using in vivo biotin-tagging and endogenous co-immunoprecipitation, the ribosomal protein S19 (RPS19) was identified as a novel MIF binding partner. Surface plasmon resonance and pulldown experiments with wild type and mutant MIF revealed a direct physical interaction of the two proteins (K(D) = 1.3 x 10(-6) m). As RPS19 is released in inflammatory lesions by apoptotic cells, we explored whether it affects MIF function and inhibits its binding to receptors CD74 and CXCR2. Low doses of RPS19 were found to strongly inhibit MIF-CD74 interaction. Furthermore, RPS19 significantly compromised CXCR2-dependent MIF-triggered adhesion of monocytes to endothelial cells under flow conditions. We, therefore, propose that RPS19 acts as an extracellular negative regulator of MIF.