The Dual-Endothelin1/VEGFsp Receptor (DEspR) - Potential Role in Chronic Respiratory Diseases

Abstract

Background The translatability of the dual-endothelin1/VEGFsp receptor (DEspR) in human was first described in 2016 and its functionality is largely unknown since DEspR is not expressed in healthy human tissues except for kidney tissue and certain tumors. Recently, DEspR expression was reported on human neutrophil subsets of acute respiratory distress syndrome (ARDS) and COVID19-ADRS patients. DEspR+ neutrophil levels correlated with disease severity and mortality which may root in their delayed apoptosis and facilitated formation of neutrophil extracellular traps. Neutrophils play a major role in inflammation of chronic respiratory diseases and altered levels of DEspR ligands ET-1 and VEGF are found in COPD and asthma phenotypes. Here, we investigated the DEspR expression on human leukocyte populations of asthmatics, COPD patients and healthy smokers as well as on the human promyelocytic leucaemic cell line HL-60. Methods DEspR expression was measured on undifferentiated, promyelocytic HL-60 cells and after differentiation towards a neutrophilic phenotype using 1.25% DMSO. Expression was also measured after stimulation with 50 μg/mL poly I:C or 100 ng/mL LPS. Whole blood cells of COPD patients (step III, IV), healthy smokers and asthmatics (step III) were stained directly after blood draw or after stimulation with 50 μg/mL poly I:C or 100 ng/mL LPS. HL-60 and whole blood leukocytes were stained with Annexin V, 7AAD, DEspR (rhIgG4, clone 6g8), CD11b, CD14 and CD16a. Results Undifferentiated CD11b-, CD14- CD16a- and differentiated CD11b+, CD14-, CD16a- HL-60 cells did not express DEspR, neither with or without inflammatory stimulation. DespR was not expressed on whole blood leukocytes at baseline level (mean±SD: 0.15±0.26 to 0.91±0.60%) but poly I:C induced DEspR expression on neutrophils (34.10±18.52%), monocytes (29.16±20.00%), lymphocytes (9.67±6.11%) and eosinophils (6.14±4.39%). The distribution of DEspR+ cells upon poly I:C stimulation was not significantly altered among different disease types, however, healthy smokers showed a trend to higher DEspR levels. The median fluorescence intensity was not significantly altered among disease types but among the cell populations. Conclusion First experiments demonstrated that DEspR expression can be induced on leukocytes upon inflammatory stimulation. In contrast to previous results of us, LPS did not induce DEspR expression which might be related to differences in the age and disease severity of investigated patients. Interestingly, poly I:C induced a strong DEspR expression indicating a toll-like receptor 3 related mechanism. The sample size needs to be increased to confirm these first results and to investigate the underlying mechanism in detail.