BackgroundIL-6 classic signaling is linked to anti-inflammatory functions while the trans-signaling is associated with pro-inflammatory responses. Classic signaling is induced via membrane-bound IL-6 receptor (IL-6R) whereas trans-signaling requires prior binding of IL-6 to the soluble IL-6R. In both cases, association with the signal transducing gp130 receptor is compulsory. However, differences in the downstream signaling mechanisms of IL-6 classic- versus trans-signaling remains largely elusive.MethodsIn this study, we used flow cytometry, quantitative PCR, ELISA and immuno-blotting techniques to investigate IL-6 classic and trans-signaling mechanisms in Human Umbilical Vein Endothelial Cells (HUVECs).ResultsWe show that both IL-6R and gp130 are expressed on the surface of human vascular endothelial cells, and that the expression is affected by pro-inflammatory stimuli. In contrast to IL-6 classic signaling, IL-6 trans-signaling induces the release of the pro-inflammatory chemokine Monocyte Chemoattractant Protein-1 (MCP-1) from human vascular endothelial cells. In addition, we reveal that the classic signaling induces activation of the JAK/STAT3 pathway while trans-signaling also activates the PI3K/AKT and the MEK/ERK pathways. Furthermore, we demonstrate that MCP-1 induction by IL-6 trans-signaling requires simultaneous activation of the JAK/STAT3 and PI3K/AKT pathways.ConclusionsCollectively, our study reports molecular differences in IL-6 classic- and trans-signaling in human vascular endothelial cells; and elucidates the pathways which mediate MCP-1 induction by IL-6 trans-signaling.Electronic supplementary materialThe online version of this article (10.1186/s12964-018-0268-4) contains supplementary material, which is available to authorized users.

Cerebral amyloid angiopathy (CAA) is a vascular dysfunction disorder characterized by deposits of amyloid-β (Aβ) in the walls of cerebral vessels. CAA and Aβ deposition in the brain parenchyma contribute to dementia and Alzheimer's disease (AD). We investigated the contribution of platelets, which accumulate at vascular Aβ deposits, to CAA. We found that synthetic monomeric Aβ40 bound through its RHDS (Arg-His-Asp-Ser) sequence to integrin αIIbβ3, which is the receptor for the extracellular matrix protein fibrinogen, and stimulated the secretion of adenosine diphosphate (ADP) and the chaperone protein clusterin from platelets. Clusterin promoted the formation of fibrillar Aβ aggregates, and ADP acted through its receptors P2Y1 and P2Y12 on platelets to enhance integrin αIIbβ3 activation, further increasing the secretion of clusterin and Aβ40 binding to platelets. Platelets from patients with Glanzmann's thrombasthenia, a bleeding disorder in which platelets have little or dysfunctional αIIbβ3, indicated that the abundance of this integrin dictated Aβ-induced clusterin release and platelet-induced Aβ aggregation. The antiplatelet agent clopidogrel, which irreversibly inhibits P2Y12, inhibited Aβ aggregation in platelet cultures; in transgenic AD model mice, this drug reduced the amount of clusterin in the circulation and the incidence of CAA. Our findings indicate that activated platelets directly contribute to CAA by promoting the formation of Aβ aggregates and that Aβ, in turn, activates platelets, creating a feed-forward loop. Thus, antiplatelet therapy may alleviate fibril formation in cerebral vessels of AD patients.

The sulfated marine polysaccharide fucoidan has been reported to have health benefits ranging from antivirus and anticancer properties to modulation of high blood pressure. Hence, they could enhance the biological function of materials for biomedical applications. However, the incorporation of fucoidan into biomaterials has been difficult, possibly due to its complex structure and lack of suitable functional groups for covalent anchoring to biomaterials. We have developed an approach for a rapid synthesis of fucoidan-mimetic glycopolymer chains through cyanoxyl-mediated free-radical polymerization, a method suitable for chain-end functionalizing and subsequent linkage to biomaterials. The resulting sulfated and nonsulfated methacrylamido α-L-fucoside glycopolymers' fucoidan-mimetic properties were studied in HSV-1 infection and platelet activation assays. The sulfated glycopolymer showed similar properties to natural fucoidan in inducing platelet activation and inhibiting HSV-1 binding and entry to cells, thus indicating successful syntheses of fucoidan-mimetic glycopolymers.

We studied whether the acute-phase protein alpha1-acid glycoprotein (AGP) induces rises in [Ca2+]i in neutrophils and sought to identify the corresponding AGP receptor (or receptors). We found that AGP elicited a minimal rise in [Ca2+]i in Fura-2-loaded neutrophils, and this response was markedly enhanced by pretreatment with anti-L-selectin antibodies. (The EC50 value of the AGP-induced Ca2+ response was 9 microg/ml.) Activation of phospholipase-C, Src tyrosine kinases, and PI3 kinases proved to be essential for the AGP-mediated increase in [Ca2+]i, whereas the p38 MAPK and SYK signaling pathways were not involved. Furthermore, antibodies against sialic acid binding, immunoglobulin-like lectin 5 (Siglec-5) and oligosaccharide 3'-sialyl-lactose both antagonized the AGP-induced response and caused an immediate increase in [Ca2+]i in anti-L-selectin-treated neutrophils, which indicates a signaling capacity of Siglec-5. We used modified forms of AGP (treated with mild periodate or neuraminidase) to establish the importance of sialic acid residues. The modified forms of AGP caused a much smaller rise in [Ca2+]i than did unaltered AGP. Affinity chromatography confirmed that unchanged AGP, but not neuraminidase-treated AGP, bound to Siglec-5. Our report provides the first evidence for a signaling capacity by AGP through a defined receptor. Pre-engagement of L-selectin significantly enhanced this signaling capacity.