In Vivo and In Vitro Activities of the gp130-Stimulating Designer Cytokine Hyper-IL-6

Abstract

IL-6 is a multifactorial cytokine mediating acute inflammatory responses in the liver. When IL-6 binds to a specific receptor (IL-6R), the IL-6/IL-6R complex associates with the signal transducer gp130, initiating intracellular signaling. A soluble form of the IL-6R (sIL-6R) renders target cells sensitive to IL-6 that do not express the IL-6R on their surfaces. A designer cytokine, termed Hyper-IL-6, consisting of IL-6 covalently linked to the sIL-6R was fully active on gp130-expressing cells at 100- to 1000-fold lower concentrations than unlinked IL-6 and IL-6R. Mice were injected i.p. with Hyper-IL-6 or IL-6. Upon injection of Hyper-IL-6 into mice, the acute phase response, as measured by haptoglobin mRNA expression in the liver, was markedly increased and lasted significantly longer compared with that in mice injected with a 10-fold higher dose of IL-6 alone. On human hepatoma cells, Hyper-IL-6 caused similar effects, indicating that the longer lasting response to the fusion protein could not only be explained by the longer plasma half-life of the fusion protein. Experiments using iodinated IL-6 and Hyper-IL-6 revealed that Hyper-IL-6 bound with high affinity to gp130 and was less efficiently internalized. This effect might explain the longer lasting activity of this protein on cells. The highly active IL-6/sIL-6R designer protein might be of significant clinical importance for the stimulation of cells that are more responsive to the IL-6/sIL-6R complex than to IL-6 alone. Such cells include hemopoietic progenitor cells and hepatocytes.

Targeting IL-6 trans-signalling: past, present and future prospects

“…In contrast, stimulation with the complex of IL-6 and sIL-6R activated all gp130 receptors on the cell surface. Moreover, stimulation with IL-6 alone led to the rapid internalization of the IL-6–mIL-6R–gp130 signalling complex, whereas stimulation with the IL-6–sIL-6R complex led to reduced gp130 internalization and therefore longer signalling duration; however, no qualitative differences between intracellular IL-6 classic signalling and trans-signalling pathways (for example, in terms of JAK–STAT and MAPK activation) were detected 57 , 58 . We concluded that cells stimulated via IL-6 trans-signalling showed a more sustained IL-6 response with a higher amplitude than cells expressing mIL-6R when stimulated with IL-6 in the absence of sIL-6R 54 .…”

Efficiently Restored Thrombopoietin Production by Ashwell‐Morell Receptor and IL‐6R Induced Janus Kinase 2/Signal Transducer and Activator of Transcription Signaling Early After Partial Hepatectomy

“…To analyze whether recombinant IL-6 is able to stimulate thrombopoiesis after PHx, we treated mice with recombinant hyper-IL6 (hIL-6) because hIL-6 has a 10 times higher bioactivity than IL-6 alone and a longer bioavailability in vivo. (29) Although no differences in platelet counts could be observed after hIL6 treatment, enhanced platelet size was measured in hIL-6-treated mice compared to controls (Supporting Fig. S8A,B).…”

The Crosstalk between Mesenchymal Stromal/Stem Cells and Hepatocytes in Homeostasis and under Stress

“…Since hepatocytes express more gp130 than IL-6R, the presence of IL-6 and sIL-6R results in greater gp130 activation and, therefore, higher IL-6 signal amplitude. Moreover, the IL-6/sIL-6R complex was shown to be internalized less efficiently than IL-6/IL-6R, resulting in longer IL-6 signal duration when mediated by trans-signaling [107]. Accordingly, hepatocytes permanently proliferated in IL-6/sIL-6R double transgenic mice in the absence of any liver insults but did not show any mitogenic response in IL-6 single transgenic mice.…”