TGF-β dampens IL-6 signaling in articular chondrocytes by decreasing IL-6 receptor expression

Abstract

Objective: Transforming growth factor-b (TGF-b) is an important homeostatic regulator of cartilage. In contrast, interleukin-6 (IL-6) is a pro-inflammatory cytokine implicated in cartilage degeneration. Crosstalk between TGF-b and IL-6 is reported in tissues other than articular cartilage. Here, we investigated regulation of IL-6 signaling by TGF-b in articular chondrocytes. Design: Human primary chondrocytes and the human G6 chondrocyte cell line were stimulated with TGF-b1 or interleukin-1b (IL-1b). Expression of IL-6 and IL-6 receptor (IL-6R) was determined on mRNA and protein level. TGF-b regulation of IL-6 signaling via phosho-STAT3 (p-STAT3) was determined using Western blot, in presence of inhibitors for IL-6R, and Janus kinase(JAK)-and activin receptor-like kinase ALK)5 kinase activity. Furthermore, induction of STAT3-responsive genes was used as a read-out for IL-6 induced gene expression. Results: TGF-b1 increased IL-6 mRNA and protein expression in both G6 and primary chondrocytes. Moreover, TGF-b1 stimulation clearly induced p-STAT3), which was abolished by inhibition of either IL-6R, JAK-or ALK5 kinase activity. However, TGF-b1 did not increase expression of the STAT3-responsive gene SOCS3 and pre-treatment with TGF-b1 even inhibited induction of p-STAT3 and SOCS3 by rhIL-6. Interestingly, TGF-b1 potently decreased IL-6R expression. In contrast, IL-1b did increase IL-6 levels, but did not affect IL-6R expression. Finally, addition of recombinant IL-6R abolished the inhibitory effect of TGF-b1 on IL-6-induced p-STAT3 and downstream SOCS3, BCL3, SAA1 and MMP1 expression. Conclusions: In this study we show that TGF-b decreases IL-6R expression, thereby dampening IL-6 signaling in chondrocytes. This reveals a novel effect of TGF-b, possibly important to restrict proinflammatory IL-6 effects to preserve cartilage homeostasis.

Gene Expression Signatures of Synovial Fluid Multipotent Stromal Cells in Advanced Knee Osteoarthritis and Following Knee Joint Distraction

“…In contrast to an animal model studies where a significant effect of KJD on joint inflammation was found ( Chen et al, 2015 ; Wiegant et al, 2015 ), early results on the effects of KJD on SF pro-inflammatory mediators in OA patients remain puzzling. For example, pro-inflammatory IL-6 and MCP1 SF levels were found increased following KJD in Watt et al (2020) study, although IL-6 was negatively correlated with pro-chondrogenic TGFb1, as would be expected ( Wiegertjes et al, 2019 ). Larger studies investigating more SF analytes and SF MSC transcripts using the same cohort of patients (validation cohort), ideally at more time-points, during the course of distraction and comparing responders and non-responders, would be needed to shed more light on the effects of joint off-loading on SF cellular and molecular responses.…”

Resveratrol inhibit interleukin-1β induced inflammatory response in human osteoarthritis chondrocytes through NF-κB signaling pathway

“…As reported, IL-1β could remarkably enhance the expressions exhibited by pro-inflammatory cytokines and MMPs in the chondrocyte; therefore, it enjoys a wide application in the stimulation of inflammatory response in the chondrocyte to simulate OA in vitro [11] . When we used IL-1β stimulate the chondrocytes, we found an obviously up-regulated MMP-1, MMP-3 and MMP-13 [12] . MMPs serve as the major enzymes regulating the remodeling of tissue as well as the degradation of extracellular matrix like collagens and aggrecan.…”

“…We used CCK-8 kit to measure chondrocytes viability following the instruction of manufacturers. In brief, we seeded human OA chondrocytes in 96-well plates (5×10 5 cells/ml) and treated them with or without resveratrol (6,12,24, 48 μM) for 24h. After that, we added 10 uL CCK-8 into the plates.…”

Kartogenin mediates cartilage regeneration via stimulating the IL-6/Stat3-dependent proliferation of cartilage stem/progenitor cells

“…In cartilage, IL-6 is mainly thought to be harmful and associated with the catabolic metabolism of chondrocytes and consequently with the OA pathology. [36][37][38] On the other hand, a number of studies have demonstrated that IL-6 can also be produced by stem cells, in particular MSC, [39,40,27] as a paracrine factor, where their physiological role remains to be clarified. Recent studies indicate that IL-6 is implicated in MSC growth through JAK/STAT3 signaling and that IL-6 contributes to the maintenance of MSC in their undifferentiated state.…”