Soluble Siglec-5 associates to PSGL-1 and displays anti-inflammatory activity

Abstract

Interactions between endothelial selectins and the leukocyte counter-receptor PSGL1 mediates leukocyte recruitment to inflammation sites. PSGL1 is highly sialylated, making it a potential ligand for Siglec-5, a leukocyte-receptor that recognizes sialic acid structures. Binding assays using soluble Siglec-5 variants (sSiglec-5/C4BP and sSiglec-5/Fc) revealed a dose- and calcium-dependent binding to PSGL1. Pre-treatment of PSGL1 with sialidase reduced Siglec-5 binding by 79 ± 4%. In confocal immune-fluorescence assays, we observed that 50% of Peripheral Blood Mononuclear Cells (PBMCs) simultaneously express PSGL1 and Siglec-5. Duolink-proximity ligation analysis demonstrated that PSGL1 and Siglec-5 are in close proximity (<40 nm) in 31 ± 4% of PBMCs. In vitro perfusion assays revealed that leukocyte-rolling over E- and P-selectin was inhibited by sSiglec-5/Fc or sSiglec-5/C4BP, while adhesion onto VCAM1 was unaffected. When applied to healthy mice (0.8 mg/kg), sSiglec-5/C4BP significantly reduced the number of rolling leukocytes under basal conditions (10.9 ± 3.7 versus 23.5 ± 9.3 leukocytes/field/min for sSiglec-5/C4BP-treated and control mice, respectively; p = 0.0093). Moreover, leukocyte recruitment was inhibited over a 5-h observation period in an in vivo model of TNFalpha-induced inflammation following injection sSiglec-5/C4BP (0.8 mg/kg). Our data identify PSGL1 as a ligand for Siglec-5, and soluble Siglec-5 variants appear efficient in blocking PSGL1-mediated leukocyte rolling and the inflammatory response in general.

Siglec-5 is a novel marker of critical limb ischemia in patients with diabetes

“…Siglec-5 is a member of the CD33-related Siglec subfamily, with four extracellular Ig-like domains and two intra-cellular tyrosine-based signaling motifs 24 , and is found on monocytes and neutrophils as well as on macrophages 25 , 26 . Siglec-5 is involved in the regulation of innate immune responses 14 , 27 – 29 . Although, innate and adaptive immune responses play important roles in the pathogenesis of atherosclerosis 30 , the relationship between Siglec-5 and atherosclerosis remains to be established.…”

“…This is the first study to demonstrate a strong relationship between the plasma levels of siglec-5 and CLI in T2DM patients. Monocytes can adhere to vascular endothelial cells through the interaction of Siglec-5 with P-selectin glycoprotein ligand-1 or von Willebrand factor 27 , 31 , and are recruited to the blood vessel wall by deformation and chemotaxis, resulting in transformation into macrophages. Ox-LDL tends to bind to glycosylated agglutinin-like receptors and Siglec-5 glycosylation may be increased in diabetic environment, thereby facilitating the combination of Siglec-5 with Ox-LDL 32 , 33 .…”

PSGL-1: A New Player in the Immune Checkpoint Landscape

“…Other studies indicate that endogenous mechanisms can also modulate PSGL-1 function. Siglec 5, another sialic acid binding protein expressed by most hematopoietic cells, colocalizes with cell surface PSGL-1 and in soluble form inhibits leukocyte rolling on P- and E- selectin [34]. The association of PSGL-1 with the proteolytic enzyme, ADAM8, causes cleavage of extracellular PSGL-1 and blocks neutrophil rolling [35], whereas association of PSGL-1 with ADAM28 in the decamer repeat domain enhances binding to P-selectin [36].…”

Electrochemiluminescence aptasensor for Siglec-5 detection based on MoS2@Au nanocomposites emitter and exonuclease III-powered DNA walker

“…The other category includes Siglec-1, Siglec-2 (CD22), Siglec-4 and Siglec-15 with low sequence homology (25-50% sequence identity)[ 12 , 13 ]. As one of the most common Siglecs, Siglec-5 has serval-linked conformations (α2-3, α2-6, α2-8) to recognize specific sialic acids and is selectively expressed in human monocytes, neutrophils, basophils and dendritic cells[ 14 ]. Interestingly, this type of Siglec consists of two intracellular “immunoreceptor tyrosine-based inhibitory motifs” (ITIM) that prevent kinase-mediated activation responses and are utilized as inhibitory receptors for leukocytes[ 10 , 15 ].…”