Joint Reconstituted Signaling of the IL-6 Receptor via Extracellular Vesicles

Abstract

Interleukin-6 (IL-6) signaling is a crucial regulatory event important for many biological functions, such as inflammation and tissue regeneration. Accordingly, several pathological conditions are associated with dysregulated IL-6 activity, making it an attractive therapeutic target. For instance, blockade of IL-6 or its α-receptor (IL-6R) by monoclonal antibodies has been successfully used to treat rheumatoid arthritis. However, based on different signaling modes, IL-6 function varies between pro- and anti-inflammatory activity, which is critical for therapeutic intervention. So far, three modes of IL-6 signaling have been described, the classic anti-inflammatory signaling, as well as pro-inflammatory trans-signaling, and trans-presentation. The IL-6/IL-6R complex requires an additional β-receptor (gp130), which is expressed on almost all cells of the human body, to induce STAT3 (signal transducer and activator of signal transcription 3) phosphorylation and subsequent transcriptional regulation. In contrast, the IL-6R is expressed on a limited number of cells, including hepatocytes and immune cells. However, the proteolytic release of the IL-6R enables trans-signaling on cells expressing gp130 only. Here, we demonstrate a fourth possibility of IL-6 signaling that we termed joint reconstituted signaling (JRS). We show that IL-6R on extracellular vesicles (EVs) can also be transported to and fused with other cells that lack the IL-6R on their surface. Importantly, JRS via EVs induces delayed STAT3 phosphorylation compared to the well-established trans-signaling mode. EVs isolated from human serum were already shown to carry the IL-6R, and thus this new signaling mode should be considered with regard to signal intervention.

Proteolysis of CD44 at the cell surface controls a downstream protease network

“…Another effect that is often seen in condition where a sheddase is missing, is the release of proteolytic substrates on extracellular vesicles. This was shown for the ADAM10 substrate prion protein (Linsenmeier et al, 2018), the ADAM10/ADAM17 and meprin β substrate IL-6R (Arnold et al, 2020) and the meprin β substrate CD109 (Luckstadt et al, 2021). Whether this effect holds true for CD44 and has any biological effect on cells, has to be elucidated in future research projects.…”

Cell Surface Processing of CD109 by Meprin β Leads to the Release of Soluble Fragments and Reduced Expression on Extracellular Vesicles

“…It was previously demonstrated that CD109 can be sorted onto EVs ( Sakakura et al, 2016 ; Yamamoto et al, 2019 ), and here we can show that proteolytic activity at the cell surface reduces this CD109 secretion mechanism. It was shown previously for the IL-6 receptor ( Arnold et al, 2020 ) and the Prion protein ( Linsenmeier et al, 2018 ) that proteolytic activity controls the amount of membrane proteins sorted onto EVs. The vesicular morphology was, however, unchanged when comparing CD109 containing or non-containing vesicles, unlike for the release of PRDX4, where larger vesicles were detected ( Lipinski et al, 2019 ).…”

“…For extracellular measurements in negative staining transmission electron microscopy (TEM) or for dynamic light scattering analysis (DLS), samples must be free from any matrix as it would be found in the abovementioned isolation kit. Therefore, EVs were isolated using ultracentrifugation as described previously ( Arnold et al, 2020 ).…”

A Molecular Analysis of Cytokine Content across Extracellular Vesicles, Secretions, and Intracellular Space from Different Site-Specific Adipose-Derived Stem Cells

“…In classical signalling, IL-6 has regenerative and anti-inflammatory functions, which are enacted through STAT3 activation of the signalling pathway via the surface IL-6 receptor [ 36 ]. However, for an anti-inflammatory function, a trans-signalling processes is achieved via a soluble receptor gp130 [ 37 ] or through active IL-6 uptake linked to EV packaging and translocation in cells that lack an IL-6 receptor [ 38 ]. In this study, the IL-6 thigh ADSC EV content ratio was substantially higher than that in abdomen ADSCs and chin ADSCs.…”