Interleukin-6–mediated trans-signaling inhibits transforming growth factor-β signaling in trabecular meshwork cells

Abstract

Glaucoma is one of the major causes of blindness, and transforming growth factor-β2 (TGF-β2) has been found to be elevated in the aqueous humor of eyes with primary open-angle glaucoma (POAG). TGF-β2 in aqueous humor causes the glaucoma-related fibrosis of human trabecular meshwork (HTM), suggesting an important role of TGF-β in POAG pathogenesis. Here, we sought to elucidate the effects of IL-6 trans-signaling on TGF-β signaling in HTM cells. Using a multiplex immunoassay, POAG patients decreased IL-6 levels and increased soluble IL-6 receptor (sIL-6R) levels compared with the controls. In experiments, we observed that the IL-6 level was increased in the conditioned medium of HTM cells after TGF-β2 stimulation. To elucidate the relationship between TGF-β2 and IL-6 in HTM cells, we conducted Western blotting and immunohistochemical analyses, and we noted that the combination of IL-6 and sIL-6R (IL6/sIL-6R) suppressed TGF-β-induced up-regulation of α-smooth muscle actin in HTM cells, whereas IL-6 alone did not. This suggests that trans-signaling, not classic signaling, of IL-6 suppresses TGF-β-induced fibrosis of HTM. IL6/sIL-6R also suppressed TGF-β-mediated activation of myosin light chain 2 (MLC2), Smad2, and p38. Of note, these inhibitory effects of IL6/sIL-6R on TGF-β were partly reduced by siRNA-mediated knockdown of STAT3. Moreover, IL-6/sIL-6R partly inhibited TGF-β-induced activation of the Smad-sensitive promoter detected with luciferase reporter gene assays and up-regulation of TGFRI and TGFRII, evaluated by quantitative real-time RT-PCR. Strikingly, overexpression of TGFRI and TGFRII diminished these inhibitory effects of IL-6/sIL-6R. We conclude that of IL-6-mediated trans-signaling potently represses TGF-β signaling in HTM cells.

The role of IL-6-174 G/C polymorphism and intraocular IL-6 levels in the pathogenesis of ocular diseases: a systematic review and meta-analysis

“…This is possibly due to secondary glaucoma being caused by underlying diseases that are associated with a high IL-6 level, including PEX syndrome, intraocular inflammation, DR, ROP and RD 248 . And in regard to the lack of IL-6 increase in primary glaucoma, it is interesting to note previous reports showing that soluble IL-6 receptor (sIL-6R) but not IL-6 is elevated in the aqueous humour of POAG 49 . This interaction between IL-6 and sIL6R is known to exhibit the inhibitory action of TGF-β-induced up-regulation of fibrotic changes in vitro 49 , suggesting that trans-signalling of IL-6 could be a potential target of POAG treatment.…”

“…And in regard to the lack of IL-6 increase in primary glaucoma, it is interesting to note previous reports showing that soluble IL-6 receptor (sIL-6R) but not IL-6 is elevated in the aqueous humour of POAG 49 . This interaction between IL-6 and sIL6R is known to exhibit the inhibitory action of TGF-β-induced up-regulation of fibrotic changes in vitro 49 , suggesting that trans-signalling of IL-6 could be a potential target of POAG treatment. Despite the fact that IL-6 may not directly contribute to OAG pathogenesis, studies confirmed an elevated level of TNFα and IL-8 in the OAG eye 249 , 250 , which emphasizes that the inflammatory process is involved in the OAG progression.…”

Association of IL-6 -174G>C (rs1800795) polymorphism with cervical cancer susceptibility

“…Interleukin-6 (IL-6) is a phosphorylated glycoprotein containing 185 amino acids. IL-6 is one of the most widely recognized cytokines associated with inflammation [ 11 , 12 ]. It regulates several important cellular pathways including: cell proliferation, differentiation, immune responses, invasion, metastasis as well as carcinogenesis [ 13–16 ].…”

Can Polyphenols in Eye Drops Be Useful for Trabecular Protection from Oxidative Damage?

“…Therefore, we can speculate that, in our experimental conditions, TGF-β exerts a role as a key regulator of the cell-matrix interactions [62]. In our platform, chronic activation of IL6, due to oxidative stress, did not repress the TGF-signaling [53] but, on the contrary, its effect resulted in an increase in outflow resistance with a 3D-HTMC-contractility alteration [61].…”

“…In our 3D-Model, the exposure of TM cells to only oxidative stress led to an increase in pro-inflammatory and pro-fibrotic cytokines and MMP gene expression [51][52][53][54] (Figure 4A-C).…”