Abstract
Objective: For more than 3 decades, isotretinoin [13-cis retinoic acid (13-cis RA)] is established as the most potent oral treatment for severe acne. However, the molecular mechanisms of isotretinoin action have not been fully elucidated. Recently, we showed that insulin and insulin-like growth factor 1 (IGF-1) increase differentiation and decrease proliferation of SZ95 sebocytes in vitro via activation of the phosphoinositide 3-kinase (PI3K)/Akt/forkhead box-O1 (FoxO1) pathway. Furthermore, this pathway is activated in patient acne biopsies in vivo. Using SZ95 sebocytes as an in vitro model, the aim of this study was to investigate the effect of isotretinoin on PI3K pathway activation. Methods: SZ95 sebocytes were treated under light protection with 0.1 μM isotretinoin in the presence or absence of 1.0 and 0.1 μM IGF-1 or insulin or 50 μM LY294002 inhibitor in a time- dependent manner. The expression of p-Akt and its downstream target p-FoxO1 was analyzed by Western blot. FoxO transcriptional activity was measured by dual luciferase assay. Nuclear and cytoplasmic mobilization of FoxO1, p-FoxO1, and p-Akt were also determined by immunofluorescence microscopy.Proliferation of sebocytes was measured by [3H]-thymidine incorporation and sebocyte differentiation by oil red O staining. Results: We show that isotretinoin activates the PI3K/Akt pathway and decreases the nuclear content of FoxO1 and its transcriptional activity in sebocytes in vitro and in sebaceous gland biopsies from an isotretinoin-treated acne patient. Isotretinoin reduces the proliferation of IGF-1- or insulin-stimulated sebocytes more effectively than IGF-1 and insulin alone. However, it normalizes the increased lipid accumulation in IGF-1- or insulin-stimulated sebocytes via a PI3K-independent pathway. Conclusion: Our data from the SZ95 sebocyte in vitro model suggest that the potent therapeutic effect of isotretinoin in acne is not mediated via the PI3K/Akt/FoxO1 pathway.
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