Dysregulation of autophagy in melanocytes contributes to hypopigmented macules in tuberous sclerosis complex

• Published in: Journal of dermatological science Vol. 89; no. 2; pp. 155 - 164
• Main Authors: Yang, Fei, Yang, Lingli, Wataya-Kaneda, Mari, Hasegawa, Junya, Yoshimori, Tamotsu, Tanemura, Atsushi, Tsuruta, Daisuke, Katayama, Ichiro
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.02.2018
• Subjects: Allyl Compounds - pharmacology; Autophagy; Autophagy - drug effects; Autophagy - physiology; Epidermis - cytology; Epidermis - metabolism; Epidermis - ultrastructure; Gene Knockdown Techniques; Humans; Hypopigmentation - drug therapy; Hypopigmentation - genetics; Hypopigmentation - physiopathology; Immunosuppressive Agents - pharmacology; Immunosuppressive Agents - therapeutic use; Macrolides - pharmacology; Melanins - metabolism; Melanocytes - drug effects; Melanocytes - physiology; Melanocytes - ultrastructure; Microscopy, Electron; Microtubule-Associated Proteins - metabolism; mTOR; Pigmentation; Primary Cell Culture; Quinazolines - pharmacology; Rapamycin; RNA, Small Interfering - metabolism; Signal Transduction - drug effects; Signal Transduction - genetics; Sirolimus - pharmacology; Sirolimus - therapeutic use; TOR Serine-Threonine Kinases - antagonists & inhibitors; TOR Serine-Threonine Kinases - metabolism; TSC; Tuberous Sclerosis - drug therapy; Tuberous Sclerosis - genetics; Tuberous Sclerosis - physiopathology; Tumor Suppressor Proteins - genetics; Tumor Suppressor Proteins - metabolism; mTOR; Rapamycin; TSC; Autophagy; Pigmentation
• ISSN: 0923-1811; 1873-569X
• DOI: 10.1016/j.jdermsci.2017.11.002

•Autophagic activity is altered in melanocytes of TSC-related hypopigmented macules.•Dysregulation of autophagy tends to correlate with depigmentation.•Induction of autophagy completely reverses depigmentation in TSC2-KD melanocytes.•Present findings provide new insight into mechanisms responsible for the hypopigmented macules that are hallmarks of TSC. 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. Recently emerging evidence supports a role for autophagy in skin pigmentation. Herein, we investigated the impact of autophagic dysregulation on TSC-associated hypopigmentation. 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. 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. 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.