Function And Mechanism Study Of EphA4 In Macrophage-mediated Innate Immune Responses

As the biggest Receptor Tyrosine Kinase (RTK) family, Eph receptor family plays important roles in physiological and pathological processes, including neurosciences, development, tumorgenesis and inflammation. Several members of Eph receptor family were found expressed in several innate immune cells. In order to study the function of Eph receptors in macrophage-mediated innate immunity, we tested the expression of Eph receptors in primary macrophages stimulated by various Toll-like receptor agonists. We found that expression of EphA4 in macrophages was substantially upregulated under stimulation of LPS, a ligand of Toll-like receptor 4 (TLR4). Moreover, in addition to TLR4 activated by LPS or E.coli, activation of several other Toll-like receptors including TLR2, TLR3 and TLR9 enhanced the expression of EphA4 to some extent. We also found that the expression of EphA4 was significantly upregulated in LPS-induced Acute Lung Injury and in the peripheral blood white cells of Sepsis patients. Mechanically, TLR4-NFκB pathway is the major signaling pathway that mediated the upregulation of EphA4 mRNA. The p65 subunit of NFκB could bind to the promoter of EphA4 and promote its transcription after activation of NFκB signaling pathway through TLR-NFκB axis. EphA4-conditional knockout mice showed better tolerance than wild-type mice in DSS-induced IBD model and specific depletion of EphA4 in macrophages showed defect cytokine and chemokine release. In conclusion, our findings demonstrated that activation of TLR-NFκB signaling pathway in macrophages significantly increased the expression of EphA4, which may serves as a positive regulator in macrophage-mediated innate immune responses. Besides, these findings shed light on the function of EphA4 as a novel biomarker and potential therapeutic target of sepsis and acute lung injury.