Dexamethasone modifies mitomycin C-triggered interleukin-8 secretion in isolated human Tenon's capsule fibroblasts

Abstract

Intraoperative mitomycin C (MMC) is widely used to prevent pterygium recurrence and glaucoma filtering bleb failure, but it has been shown to induce corneal inflammation and cell death. Postoperative dexamethasone (DEX) is advocated to reduce MMC-related inflammation and cell death in corneal fibroblasts. Nevertheless, its long-term regulation mechanism in Tenon's capsule remains to be explored. The purpose of this study was to investigate how DEX modifies MMC's effects in human Tenon's capsule fibroblasts (HTFs). HTFs isolated from the pterygium surgical patients (n = 6) were treated with MMC at 0, 0.1, 0.2, and 0.4 mg/ml for 5 min and incubated in DEX at 10 μM for 0, 1, 2, and 3 days. Recombinant interleukin-8 (IL-8) was used to verify the effect of MMC-related IL-8 secretion. Cell proliferation of all the treated cells was analyzed by WST-1 assay. The amount of IL-8 secretion in HTFs was determined by enzyme-linked immunosorbent assay. Immunoblotting assay was used to analyze the expression of peroxisome-proliferator-activated receptor gamma (PPARγ) and B-cell lymphoma-extra large (Bcl-xL). Our results revealed that MMC significantly reduced the HTF cell proliferation rate. Additionally, MMC significantly upregulated IL-8 secretion in HTFs concentration-dependently. At 3 days post treatment (dpt), 5-min exposures to 0.1, 0.2, and 0.4 mg/ml MMC resulted in 1.4-fold (p = 0.012), 1.6-fold (p = 0.012), and 2.5-fold (p = 0.001) increases of IL-8 secretion. In contrast, DEX reversed the MMC-retarded cell proliferation rate (p = 0.036) and repressed MMC-related IL-8 secretion by 33.5% at 3 dpt (p = 0.003). Addition of recombinant IL-8 noticeably suppressed HTF cell proliferation in a concentration-dependent manner. DEX stimulated upregulation of both PPARγ and Bcl-xL at 1 dpt in normal HTFs and at 2 dpt in MMC-treated HTFs. PPARγ silencing reduced expression of PPARγ and Bcl-xL, but enhanced IL-8 secretion (p < 0.001). On the other hand, Bcl-xL silencing enhanced IL-8 secretion (p < 0.001), but did not affect PPARγ expression. These revealed that IL-8 secretion in HTFs is modulated by PPARγ-dependent Bcl-xL signaling. We conclude that DEX reversed the MMC-inhibited HTF cell proliferation via diminishing the MMC-induced IL-8 secretion, which resulted from a late-phase upregulation of the PPARγ and Bcl-xL. These long-term effects suggest a beneficial postoperative DEX treatment following intraoperative MMC application.

Keywords: Bcl-xL; IL-8; PPARγ; dexamethasone; human Tenon's capsule fibroblasts; mitomycin C.