BACKGROUND - The pro-inflammatory cytokines, tumor necrosis factor (TNF)-α, and interleukin (IL)-17, have been implicated in the pathogenesis of liver fibrosis. In this study, we investigated the role of TNFα and IL-17 toward induction of profibrotic factor, periostin.
METHODS - HepG2 cells were cultured and treated with inflammatory cytokines, TNFα and IL-17. Computational promoter sequence analysis of the periostin promoter was performed to define the putative binding sites for transcription factors. Transcription factors were analyzed by Western blot and Chromatin Immunoprecipitation. Periostin and transcription factor expression analysis was performed by RT-PCR, Western blot, and fluorescence microscopy. Type I collagen expression from fibroblast cultures was analyzed by Western blot and Sircol soluble collagen assay.
RESULTS - Activation of HepG2 Cells with TNFα and IL-17 enhanced the expression of periostin (3.5 and 4.4 fold, respectively p<0.05) compared to untreated cells. However, combined treatment with both TNFα and IL-17 at similar concentration demonstrated a 13.3 fold increase in periostin (p<0.01), thus suggesting a synergistic role of these cytokines. Periostin promoter analysis and specific siRNA knock-down revealed that TNFα induces periostin through cJun, while IL-17 induced periostin via STAT-3 signaling mechanisms. Treatment of the supernatant from the cytokine activated HepG2 cells on fibroblast cultures induced enhanced expression of type I collagen (>9.1 fold, p<0.01), indicative of a direct fibrogenic effect of TNFα and IL-17.
CONCLUSION - TNFα and IL-17 induced fibrogenesis through cJun and STAT-3 mediated expression of profibrotic biomarker, periostin. Therefore, periostin might serve as a novel biomarker in early diagnosis of liver fibrosis.
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