An antibody that targets cell‐surface glucose‐regulated protein‐78 inhibits expression of inflammatory cytokines and plasminogen activator inhibitors by macrophages

Abstract

AbstractGlucose‐regulated protein‐78 (Grp78) is an endoplasmic reticulum chaperone, which is secreted by cells and associates with cell surfaces, where it functions as a receptor for activated α2‐macroglobulin (α2M) and tissue‐type plasminogen activator (tPA). In macrophages, α2M and tPA also bind to the transmembrane receptor, LDL receptor‐related protein‐1 (LRP1), activating a cell‐signaling receptor assembly that includes the NMDA receptor (NMDA‐R) to suppress innate immunity. Herein, we demonstrate that an antibody targeting Grp78 (N88) inhibits NFκB activation and expression of proinflammatory cytokines in bone marrow‐derived macrophages (BMDMs) treated with the toll‐like receptor‐4 (TLR4) ligand, lipopolysaccharide, or with agonists that activate TLR2, TLR7, or TLR9. Pharmacologic inhibition of the NMDA‐R or deletion of the gene encoding LRP1 (Lrp1) in BMDMs neutralizes the activity of N88. The fibrinolysis protease inhibitor, plasminogen activator inhibitor‐1 (PAI1), has been implicated in diverse diseases including metabolic syndrome, cardiovascular disease, and type 2 diabetes. Deletion of Lrp1 independently increased expression of PAI1 and PAI2 in BMDMs, as did treatment of wild‐type BMDMs with TLR agonists. tPA, α2M, and N88 inhibited expression of PAI1 and PAI2 in BMDMs treated with TLR‐activating agents. Inhibiting Src family kinases blocked the ability of both N88 and tPA to function as anti‐inflammatory agents, suggesting that the cell‐signaling pathway activated by tPA and N88, downstream of LRP1 and the NMDA‐R, may be equivalent. We conclude that targeting cell‐surface Grp78 may be effective in suppressing innate immunity by a mechanism that requires LRP1 and the NMDA‐R.