Purpose: Emerging evidence indicates that the phosphatidylinositol 3-kinase (PI3K)-AKT pathway is involved in the pathogenesis of Graves' orbitopathy (GO). In this study, the therapeutic effects of idelalisib, a selective PI3Kδ inhibitor, on adipogenesis were evaluated in GO orbital fibroblasts in vitro.
Methods: Orbital fibroblasts were cultured from orbital connective tissues obtained from individuals with GO and healthy control subjects. Cells were pretreated with idelalisib for 1 hour before stimulation with IL-1β. Inflammatory cytokine expression was measured by Western blotting and ELISAs. The adipogenesis-related downstream mediators of the PI3K/AKT cascade, that is, forkhead box protein O1 (FOXO1) and mammalian target of rapamycin (mTOR), also were measured by Western blotting. After adipogenic differentiation and idelalisib treatment, cells were stained with Oil Red O and the levels of peroxisome proliferator activator γ (PPARγ) and CCAAT-enhancer-binding proteins (C/EBP) α/β were determined by Western blot analyses.
Results: AKT phosphorylation decreased in a dose-dependent manner upon treatment with idelalisib in GO and non-GO orbital fibroblasts. Treatment with idelalisib inhibited the IL-1β-induced expression of IL-6 and IL-8. Idelalisib attenuated the phosphorylation of mTOR and FOXO1, downstream regulators of the PI3K pathway. Oil Red-O staining results revealed a decrease in lipid droplets and suppressed expression of PPARγ and c/EBPα/β upon treatment with idelalisib during adipose differentiation.
Conclusions: Idelalisib inhibited proinflammatory cytokine production and adipogenesis in GO orbital fibroblasts in vitro. These results support the potential use of PI3K inhibitors in GO management.