Cross-talk between TGF-β1 and IL-6 in human trabecular meshwork cells

[摘要] Purpose: To investigate the relationshipbetween transforming growth factor beta-1 (TGF-β1) and interleukin-6(IL-6) in human trabecular meshwork (HTM) cells as well as to identifythe signaling pathway/s involved in the increased IL-6 expression thatoccurs in response to mechanical stress and TGF-β1. Methods: All experiments were performedin confluent monolayers of HTM cells at passage 3. Secreted IL–6 wasquantified by ELISA. Levels of IL-6 mRNA were evaluated bypolymerase chain reaction (PCR) analysis. Activation of the IL-6and TGF-β1 promoters was monitored by measuring secretedalkaline phosphatase protein (SEAP) released into the culture medium byHTM cells infected with an adenovirus expressing the SEAPreporter gene that was controlled by either the IL-6 promoter(AdIL6–SEAP) or the TGF-β1 promoter (AdTGFβ1-SEAP). Cyclicmechanical stress (5% elongation, one cycle per second) was appliedusing the Flexcell System. Reagents used in this study included humanTGF–β1, human IL-6, and the inhibitors for the p38 mitogen-activatedprotein kinase (MAPK; SB202190), c-jun NH2-terminal kinase(JNK; SP600125), extracellular-regulating kinase (ERK; PD98059), andTGF type I activin receptor (SB431542). Results: Incubation of HTM cells withTGF–β1 (5 ng/ml) resulted in a significant increase in the protein andmRNA levels of IL-6, which was significantly diminished in thepresence of the inhibitors for p38 MAPK or JNK. No transcriptionalactivation of the exogenous IL-6 promoter was observedfollowing TGF-β1 treatment. In addition, the presence of inhibitors forthe p38 MAPK, ERK, and TGF-β1 pathways significantly decreased theincreased expression of IL-6 by cyclic mechanical stress. Furthermore,exposure of HTM cells to IL-6 (100 ng/ml) demonstrated thetranscriptional activation of TGF-β1 promoter, which wasseverely impaired by blocking the p38 MAPK pathway. Conclusions: Our results indicate thatTGF-β1 participates in the regulation of basal expression and thestretch-induced expression of IL-6 and suggest the possible existencein cultured HTM cells of an autocrine loop between IL-6 and TGF-β1. Wealso found that p38 MAPK might play a contributing role in themaintenance of such a loop.

[学科分类] 生物化学/生物物理