Abstract Body (Do not enter title and authors here): Introduction: An impaired cardiac macrophage migration inhibitory factor (MIF) signaling in aging during ischemia and reperfusion (I/R) can be rescued by a MIF agonist, MIF20. Alterations in cardiac metabolic homeostasis cause inflammation under I/R. Thus, MIF agonism with MIF20 could modulate cardiac inflammatory response during I/R.
Hypothesis: MIF20 modulates the polarization of neutrophil subset and rescues the impaired immune response under I/R in aging.
Methods: Young (3-months)/aged (24 months) C57BL/6 wild type (WT) mice and MIF^flox/flox (3 months)/cMIF^-/- (cardiomyocyte MIF deletion, 3 months) were subjected to LAD ligation of for 45 min of ischemia, followed by 24 hr of reperfusion. MIF20 (0.15 µg/kg, i.v.) was injected at 5 minutes before reperfusion. The immune cells were determined with flow cytometry. mRNA and protein were measured by real-time qPCR, immunoblotting/cytokine array.
Results: Administration of MIF20 reduced myocardial infarct by I/R in young/aged WT and MIF^flox/flox but not in cMIF^-/- mice. The flow cytometry showed that I/R stress dramatically triggered neutrophils infiltration, which occurred in both left ventricle and right ventricle. Intriguingly, MIF20 treatment reduced the I/R-induced neutrophil recruitment in hearts. Aged versus young WT myocardium recruited more N1 neutrophils (CD206^-), while MIF20 treatment rescued the impaired N1 neutrophils response in aging. Moreover, MIF20 can increase infiltration of N2 neutrophils (CD206⁺) in both young and aged WT hearts. The recombinant MIF can directly trigger N2 neutrophil polarization and N1 neutrophil reduction in cMIF^-/- hearts, indicating the critical role of MIF/CD74 axis in neutrophil polarization by I/R challenge. The cytokine array showed that MIF20 treatment can trigger cardiac TGF-β levels and upregulate IL-10 levels in serum under I/R, since TGF-β and IL-10 are critical factors involved in the N2 neutrophils’ polarization. Interestingly, MIF20 increased SiglecF marker on neutrophils in the aged versus young hearts, suggesting that MIF20 rescue the long-lived neutrophil population (SiglecF^high) which could enhance phagocytosis to repair damaged myocardium during I/R conditions.
Conclusions: An impairment of metabolic homeostasis and inflammatory response occurred in cardiac aging. MIF agonism with small molecule MIF20 can rescue the capacity of MIF/CD74 signaling to maintain metabolic homeostasis and inflammatory response in aging under I/R pathological conditions.