Impaired PI3K/Akt activation-mediated NF-κB inactivation under elevated TNF-α is more vulnerable to apoptosis in vitiliginous Keratinocytes

Levels of the cytokines IL-6, IL-1 alpha, and tumor necrosis factor-alpha(TNF-alpha) are significantly higher in lesional than in non-lesional skin of patients with vitiligo. However, how cytokines affect pigmentation is not fully understood. To examine the mechanism, Western blot analysis with TNF-alpha, Fas ligand ( FasL), and downstream signaling molecules such as I-kappa B, NF-kappa B, TNF-R1- associated factor 2, Akt, and PTEN ( phosphatase and tension homologue) were performed for the suction-blistered depigmented and normally pigmented epidermis from 10 patients. Levels of TNF-alpha and FasL were significantly higher in the depigmented epidermis. Interestingly, phosphorylation levels of I-kappa B, NF-kappa B, and Akt were lower in the depigmented epidermis. Moreover, PTEN, which could inhibit the phosphatidylinositol 3-kinase/proteinkinase B (PI3K/Akt) signaling pathway, was significantly higher in depigmented epidermis, implying that vitiliginous keratinocytes may be more susceptible to TNF-alpha-mediated apoptosis through impaired Akt and NF-kappa B activation. To test this hypothesis, cultured normal human keratinocytes were treated with TNF-alpha in the presence of a PI3K inhibitor to suppress Akt activation. Keratinocytes showing impaired Akt activation demonstrated increased apoptosis with less activation of NF-kappa B. Thus, reduced activation of NF-kappa B via impaired PI3K/Akt activation under increased TNF-alpha levels could result in increased apoptosis of vitiliginous keratinocytes.