A gain-of-function variant in SREBF1 causes generalized skin hyperpigmentation with congenital cataracts.

Abstract

Lipid metabolism plays essential roles in skin barrier formation and the regulation of skin inflammation. Moreover, lipid homeostasis regulates skin melanogenesis, although the underlying mechanism remains largely unknown. Sterol regulatory element binding protein 1 (SREBP-1) is a key transcription factor essential for cellular lipid metabolism. Loss-of-function variants in SREBF1 are responsible for autosomal-dominant ichthyosis follicularis, alopecia, and photophobia syndrome, emphasizing the significance of lipid homeostasis in skin keratinization. To identify the genetic basis of a new entity featuring diffuse skin hyperpigmentation with congenital cataracts, and to unravel the underlying mechanism for the pathogenesis of the SREBF1 variant. Whole-exome sequencing was performed to identify the underlying genetic variants. Quantitative PCR, western blot, and immunofluorescent staining were employed to assess the expression and the subcellular localization of the SREBF1 variant. The transcriptional activity of the mutant SREBP-1 was determined by luciferase reporter assay. A transgenic zebrafish model was constructed. Two patients of different ethnicities presented with generalized skin hyperpigmentation with skin xerosis, congenital cataracts, and extracutaneous symptoms. We identified a de novo nonsense variant c.1289C>A (p.Ser430*) in the SREBF1 gene in both patients. The variant encoded a truncated protein which showed preferential nucleus localization, in contrast to wild-type SREBP-1 which is mainly localized in cytoplasm in sterol-sufficient conditions. Luciferase reporter assay revealed that the Ser430* mutant exhibited an enhanced transcriptional activity. The primary cultured melanocytes from the patient showed increased melanin synthesis compared to those from normal controls. The Ser430* transgenic zebrafish model exhibited more black spots, along with upregulated expression of melanogenic genes at 35 days post-fertilization. We demonstrated that a gain-of-function variant in SREBF1 caused a previously undescribed disorder characterized by generalized skin hyperpigmentation and congenital cataracts. Our study reveals the involvement of SREBP-1 in melanogenesis and lens development and paves the way for developing novel therapeutic targets for skin dyspigmentation or cataracts.