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Sharmila Masli, Laura Soriano-Romani, Bruce Turpie; Low concentration of thrombospondin-derived CD47 agonist inhibits IL-17 mediated leukocyte adhesion to vascular endothelial cells.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5729.
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In chronic inflammatory diseases putative pathogenic Th17 cells can promote tissue infiltration of leukocytes by upregulating VCAM-1 expression on vascular endothelium. Previously thrombospondin-derived CD47 agonist peptide was reported to reduce severity of chronic ocular surface inflammation associated with Sjögren’s syndrome in a mouse model. However, it was not clear whether this is achieved by direct influence on vascular endothelium. We hypothesize that CD47 agonist peptide inhibits IL-17 mediated VCAM-1 expression and associated leukocyte adhesion.
Expression of VCAM-1 on primary cultures of mouse (C57BL/6) lung vascular endothelial cells (ECs) untreated or treated with IL-17 (10 ng/ml) and TSP-derived CD47 agonist peptide (10 nM) for 24 hr was determined by immunostaining and real-time PCR. Adhesion of leukocytes was assessed by overlaying treated endothelial cells with fluorescence-labeled leukocytes for 1 hr followed by the removal of non-adherent cells and measurement of fluorescence of adherent cells. In vivo leukocyte adhesion was visualized in retina flatmounts after infusion of fluorescence-conjugated Con.A in C57BL/6 mice induced to develop chronic uveitic inflammation via IRBP/CFA immunization and treated topically with CD47 agonist or control peptide 10 mg/mouse for 1 week post-immunization.
While VCAM-1 expression in IL-17-treated ECs was significantly increased, treatment with 10 nM CD47 agonist peptide significantly reduced this expression as compared to the control peptide (AUF 3.2+0.7 vs. 1.4+0.5 resp., p<0.05). These changes were consistent with changes in VCAM-1 message detected by real-time PCR. Similarly in vitro leukocyte adhesion was significantly reduced in CD47 agonist treated ECs compared to control peptide treated cells (13,122+1861 vs. 18,831+493, p<0.05). Furthermore, leukocyte adhesion in uveitic retinal vessels was significantly reduced in mice treated with CD47 agonist peptide as compared to those treated with control peptide (69.95+12.34 vs. 11.98+1.18, p<0.05).
Our results support the hypothesis that TSP-derived CD47 agonist peptide inhibits IL-17 induced leukocyte adhesion to vascular endothelium. Therefore this peptide may offer a viable alternative to VLA-4 blockade approach that is although beneficial in the treatment of chronic inflammation is associated with a severe adverse event.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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