Fei Yang1, Lingli Yang1, Mari Wataya-Kaneda2, Junya Hasegawa3, Tamotsu Yoshimori3, Atsushi Tanemura1, Daisuke Tsuruta4, Ichiro Katayama1. 1. Department of Dermatology, Course of Integrated Medicine, Graduate School of Medicine, Osaka University, Osaka, Japan. 2. Department of Dermatology, Course of Integrated Medicine, Graduate School of Medicine, Osaka University, Osaka, Japan. Electronic address: mkaneda@derma.med.osaka-u.ac.jp. 3. Laboratory of Intracellular Membrane Dynamics, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan. 4. Department of Dermatology, Graduate School of Medicine, Osaka City University, Osaka, Japan.
Abstract
BACKGROUND: Tuberous sclerosis complex (TSC) gene mutations lead to constitutive activation of the mammalian target of rapamycin (mTOR) pathway, resulting in a broad range of symptoms. Hypopigmented macules are the earliest sign. Although we have already confirmed that topical rapamycin treatment (an mTOR inhibitor) protects patients with TSC against macular hypopigmentation, the pathogenesis of such lesions remains poorly understood. OBJECTIVE: Recently emerging evidence supports a role for autophagy in skin pigmentation. Herein, we investigated the impact of autophagic dysregulation on TSC-associated hypopigmentation. METHODS: Skin samples from 10 patients with TSC, each bearing characteristic hypopigmented macules, and 6 healthy donors were subjected to immunohistochemical and electron microscopic analyses. In addition, TSC2-knockdown (KD) was investigated in human epidermal melanocytes by melanin content examination, real-time PCR, western blotting analyses, and intracellular immunofluorescence staining. RESULTS: Activation of the mTOR signaling pathway decreased melanocytic pigmentation in hypopigmented macules of patients with TSC and in TSC2-KD melanocytes. In addition, LC3 expression (a marker of autophagy) and autophagosome counts increased, whereas, intracellular accumulation of autophagic degradative substrates (p62 and ubiquitinated proteins) was evident in TSC2-KD melanocytes. Furthermore, depigmentation in TSC2-KD melanocytes was accelerated by inhibiting autophagy (ATG7-KD or bafilomycin A1-pretreatment) and was completely reversed by induction of autophagy via mTOR-dependent (rapamycin) or mTOR-independent (SMER28) exposure. Finally, dysregulation of autophagy, marked by increased LC3 expression and accumulation of ubiquitinated proteins, was also observed in melanocytes of TSC-related hypopigmented macules. CONCLUSION: Our data demonstrate that melanocytes of patients with TSC display autophagic dysregulation, which thereby reduced pigmentation, serving as the basis for the hypomelanotic macules characteristic of TSC.
BACKGROUND:Tuberous sclerosis complex (TSC) gene mutations lead to constitutive activation of the mammalian target of rapamycin (mTOR) pathway, resulting in a broad range of symptoms. Hypopigmented macules are the earliest sign. Although we have already confirmed that topical rapamycin treatment (an mTOR inhibitor) protects patients with TSC against macular hypopigmentation, the pathogenesis of such lesions remains poorly understood. OBJECTIVE: Recently emerging evidence supports a role for autophagy in skin pigmentation. Herein, we investigated the impact of autophagic dysregulation on TSC-associated hypopigmentation. METHODS: Skin samples from 10 patients with TSC, each bearing characteristic hypopigmented macules, and 6 healthy donors were subjected to immunohistochemical and electron microscopic analyses. In addition, TSC2-knockdown (KD) was investigated in human epidermal melanocytes by melanin content examination, real-time PCR, western blotting analyses, and intracellular immunofluorescence staining. RESULTS: Activation of the mTOR signaling pathway decreased melanocytic pigmentation in hypopigmented macules of patients with TSC and in TSC2-KD melanocytes. In addition, LC3 expression (a marker of autophagy) and autophagosome counts increased, whereas, intracellular accumulation of autophagic degradative substrates (p62 and ubiquitinated proteins) was evident in TSC2-KD melanocytes. Furthermore, depigmentation in TSC2-KD melanocytes was accelerated by inhibiting autophagy (ATG7-KD or bafilomycin A1-pretreatment) and was completely reversed by induction of autophagy via mTOR-dependent (rapamycin) or mTOR-independent (SMER28) exposure. Finally, dysregulation of autophagy, marked by increased LC3 expression and accumulation of ubiquitinated proteins, was also observed in melanocytes of TSC-related hypopigmented macules. CONCLUSION: Our data demonstrate that melanocytes of patients with TSC display autophagic dysregulation, which thereby reduced pigmentation, serving as the basis for the hypomelanotic macules characteristic of TSC.
Authors: Virginie Carmignac; Cyril Mignot; Emmanuelle Blanchard; Paul Kuentz; Marie-Hélène Aubriot-Lorton; Victoria E R Parker; Arthur Sorlin; Sylvie Fraitag; Jean-Benoît Courcet; Yannis Duffourd; Diana Rodriguez; Rachel G Knox; Satyamaanasa Polubothu; Anne Boland; Robert Olaso; Marc Delepine; Véronique Darmency; Melissa Riachi; Chloé Quelin; Paul Rollier; Louise Goujon; Sarah Grotto; Yline Capri; Marie-Line Jacquemont; Sylvie Odent; Daniel Amram; Martin Chevarin; Catherine Vincent-Delorme; Benoît Catteau; Laurent Guibaud; Alexis Arzimanoglou; Malika Keddar; Catherine Sarret; Patrick Callier; Didier Bessis; David Geneviève; Jean-François Deleuze; Christel Thauvin; Robert K Semple; Christophe Philippe; Jean-Baptiste Rivière; Veronica A Kinsler; Laurence Faivre; Pierre Vabres Journal: Genet Med Date: 2021-04-08 Impact factor: 8.822