Biallelic GLTP mutations cause nonsyndromic epidermal differentiation disorder via disrupted epidermal glucosylceramide transport
Zeqiao Zhang, Shimiao Huang, Adam Jackson, Elizabeth A Jones, Siddharth Banka, Chao Yang, Sisi Zhao, Kunlun Lv, Sha Peng, Zhimiao Lin, Huijun Wang
Zeqiao Zhang, Shimiao Huang, Adam Jackson, Elizabeth A Jones, Siddharth Banka, Chao Yang, Sisi Zhao, Kunlun Lv, Sha Peng, Zhimiao Lin, Huijun Wang
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Research Article Dermatology Genetics Metabolism

Biallelic GLTP mutations cause nonsyndromic epidermal differentiation disorder via disrupted epidermal glucosylceramide transport

Abstract

Ceramides are essential skin lipids for maintaining the mammalian skin permeability barrier, which protects against external stimuli. The precursor of epidermal ceramides, glucosylceramides (GlcCer), is synthesized within granular keratinocytes while its precise cellular transport mechanisms remain poorly characterized. Here, we identified 3 pathogenic variants in the GLTP gene, which encodes glycolipid transfer protein, in 5 unrelated families with nonsyndromic epidermal differentiation disorder presenting with generalized skin scaling. The biallelic GLTP variants resulted in loss of competent GLTP expression. CRISPR/Cas9-generated Gltp-knockout mice exhibited lethal barrier defects, partially recapitulating the clinical features of our patients. We demonstrated that GLTP facilitated GlcCer transport in differentiated keratinocytes, with its deficiency causing impaired GlcCer trafficking and consequent aberrant retention in lysosomes, thereby disrupting lysosome function. The lysosomal dysfunction impaired autophagy flux, resulting in delayed keratinocyte terminal differentiation, which is expected to compromise the skin barrier integrity and ultimately lead to abnormal scaling. Pharmacological inhibition of GlcCer synthesis effectively rescued both autophagy and keratinocyte differentiation defects. Our findings establish GLTP as a novel underlying gene for nonsyndromic epidermal differentiation disorders and unravel its essential role in maintaining skin homeostasis during terminal differentiation by mediating epidermal GlcCer transport.

Authors

Zeqiao Zhang, Shimiao Huang, Adam Jackson, Elizabeth A Jones, Siddharth Banka, Chao Yang, Sisi Zhao, Kunlun Lv, Sha Peng, Zhimiao Lin, Huijun Wang

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Figure 5

Aberrant glucosylceramide transport in GLTP-deficient differentiated keratinocytes.

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Aberrant glucosylceramide transport in GLTP-deficient differentiated ker...
(A) Nile Red staining shows dot-like aggregates in the corneocytes of patient 3 (P3) compared with the continuous linear lipid structures observed in the healthy controls (HC). Scale bars: 20 μm. (B) Immunofluorescence of glucosylceramide (GlcCer) in the frozen skin section reveals increased GlcCer accumulation within the SG of the patient, in contrast to the presence in SC layer of the HC section. Scale bars: 50 μm. (C) Double immunofluorescent staining of GLTP and ceramide in primary human keratinocytes. Under undifferentiated condition, both GLTP and GlcCer/ceramide show cytoplasmic localization. GlcCer/ceramide immunocytochemistry demonstrated congested patterns of ceramide in undifferentiated si-GLTP keratinocytes. Change in localization of GLTP from cytoplasmic appearance to a both membranous and cytoplasmic appearance in response to Ca2+-induced differentiation. In contrast with downregulation and cell membranous distribution of ceramide in the si-NC differentiated keratinocytes, GlcCer/ceramide demonstrated accumulation and congested patterns of ceramide in differentiated si-GLTP keratinocytes. Scale bars: 10 μm.