TNF stimulates IL-6, CXCL8 and VEGF secretion from human keratinocytes via activation of mTOR, inhibited by tetramethoxyluteolin

Abstract

Psoriasis is an autoimmune skin disease characterized by keratinocyte hyper-proliferation and chronic inflammation. The pathogenesis of psoriasis involves pro-inflammatory cytokines, such as tumor necrosis factor (TNF), but the mechanism of keratinocyte activation is not well understood. Here we show that TNF (10 or 50 ng/mL) stimulates significant (p<0.0001) gene expression and secretion of pro-inflammatory IL-6, CXCL8 and VEGF from both cultured human HaCaT and normal epidermal human keratinocytes (NHEKs). This effect occurs via activation of the mammalian target of rapamycin (mTOR) signaling complex as shown by Western Blot analysis and phospho-ELISAs. Pre-treatment with the novel natural flavonoid tetramethoxyluteolin (10-100 μM) significantly (p<0.0001) inhibits gene expression and secretion (p<0.0001) of all three mediators in a concentration-dependent manner. Moreover, tetramethoxyluteolin (50 μM) appears to be a potent inhibitor of the phosphorylated mTOR substrates (pmTOR^Ser2448, pp70S6K^Thr389 and p4EBP1^Thr37/46) as compared to known mTOR inhibitors in keratinocytes. The present findings indicate that TNF stimulates skin inflammation via mTOR signaling. Inhibition by tetramethoxyluteolin, may be used in the treatment of psoriasis.

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