Chronic inflammation is a triggering mechanism for many metabolic diseases including atherosclerosis and diabetes. A critical step in the development of chronic inflammation is the accumulation of classically activated pro-inflammatory macrophages in the extracellular matrix (ECM) of peripheral tissues. Recently, we demonstrated that adhesion receptor integrin αDβ2 is upregulated on macrophages in atherosclerotic lesions and inflamed adipose tissue, and promotes the development of atherosclerosis and insulin resistance. This pathophysiological mechanism is mediated by αDβ2-dependent strong adhesion of macrophages to the inflamed ECM, which promotes macrophage retention at the site of inflammation. Typical healthy ECM has a limited ligand capacity for integrin αDβ2. However, we recently found that the end-product of DHA oxidation, 2-(ω-carboxyethyl)pyrrole (CEP) serves as ligand for αDβ2. CEP is preferentially generated during inflammation-mediated oxidation and forms adduct with ECM proteins. CEP-modified proteins are detected in inflamed tissue during atherosclerosis, insulin resistance and pathological angiogenesis. In this project, we propose a new strategy for the treatment of chronic inflammation by targeting macrophage retention in the inflamed tissue by focusing on the development of the inhibitor, which is exclusively specific for αDβ2-CEP interaction. The advantage of CEP as a new therapeutic target resides in its unique formation in inflamed tissue. Using specially designed peptide library, protein-protein interaction measured by Biacore and adhesion assay with integrin-transfected HEK293 cells, we identified a sequence (called P5-peptide), which significantly inhibited αD-CEP binding. In vitro three-dimensional migration assay demonstrated that P5 peptide regulates macrophage migration within ECM but not the transendothelial migration of monocytes. The injection of cyclic P5 peptide in the model of thioglycollate-induced peritoneal inflammation led to 3-fold reduction in the number of macrophages accumulated in the peritoneal cavity after 72 hours. Interestingly, P5 peptide injection had no effect on the accumulation of macrophages in αD-deficient mice, that confirmed the specificity of inhibition. This inhibition only affects the recruitment of macrophages, while it has no effect on the efflux of macrophage from the peritoneal cavity in our in vivo studies. The tracking of adoptively transferred fluorescently-labeled WT and αD-/- monocytes in mice on a high fat diet revealed that αD-deficiency reduced 3 folds the accumulation of macrophages in the adipose tissue. The injection of P5 peptide in this model demonstrated the marked reduction of adoptively transferred WT macrophages in adipose tissue. Taken together, these results demonstrate the importance of αDβ2-CEP interaction for the accumulation of infiltrating macrophages during inflammation and propose P5 peptide as a potential inhibitor of atherogenesis and diabetes. Further studies are required to develop these results.

Neutrophil-macrophage interplay is a fine-tuning mechanism that regulates the innate immune response during infection and inflammation. Cell surface receptors play an essential role in neutrophil and macrophage functions. The same receptor can provide different outcomes within diverse leukocyte subsets in different inflammatory conditions. Understanding the variety of responses mediated by one receptor is critical for the development of anti-inflammatory treatments. In this study, we evaluated the role of a leukocyte adhesive receptor, integrin αDβ2, in the development of acute inflammation. αDβ2 is mostly expressed on macrophages and contributes to the development of chronic inflammation. In contrast, we found that αD-knockout dramatically increases mortality in the cecal ligation and puncture sepsis model and LPS-induced endotoxemia. This pathologic outcome of αD-deficient mice is associated with a reduced number of monocyte-derived macrophages and an increased number of neutrophils in their lungs. However, the tracking of adoptively transferred fluorescently labeled wild-type (WT) and αD−/− monocytes in WT mice during endotoxemia demonstrated only a moderate difference between the recruitment of these two subsets. Moreover, the rescue experiment, using i.v. injection of WT monocytes to αD-deficient mice followed by LPS challenge, showed only slightly reduced mortality. Surprisingly, the injection of WT neutrophils to the bloodstream of αD−/− mice markedly increased migration of monocyte-derived macrophage to lungs and dramatically improves survival. αD-deficient neutrophils demonstrate increased necrosis/pyroptosis. αDβ2-mediated macrophage accumulation in the lungs promotes efferocytosis that reduced mortality. Hence, integrin αDβ2 implements a complex defense mechanism during endotoxemia, which is mediated by macrophages via a neutrophil-dependent pathway.