Defects in autophagosome-lysosome fusion underlie Vici syndrome, a neurodevelopmental disorder with multisystem involvement

Ikumi Hori,Tomohiro Morio,Daigo Kajikawa,Tamotsu Yoshimori,Jun Tohyama,Yutaka Nonoda,Yoshiya Yukitake,Takanobu Otomo,Tatsuhiko Tsunoda,Nobuhiko Okamoto,Naomichi Matsumoto,Yonehiro Kanemura,Ichizo Nishino,Kenjiro Kosaki,Hiroaki Shiraishi ,Fuyuki Miya,Hirotomo Saitsu,Konomi Shimoda,Nobutoshi Ando ,Yutaka Negishi,Takeshi Kumagai,Shinichi Magara,Motoo Nakagawa,Ayako Hattori,Mitsuhiro Kato,Mami Yamasaki,Mitsuko Nakashima,Shinji Saitoh

doi:10.1038/s41598-017-02840-8

Abstract

Vici syndrome (VICIS) is a rare, autosomal recessive neurodevelopmental disorder with multisystem involvement characterized by agenesis of the corpus callosum, cataracts, cardiomyopathy, combined immunodeficiency, developmental delay, and hypopigmentation. Mutations in EPG5, a gene that encodes a key autophagy regulator, have been shown to cause VICIS, however, the precise pathomechanism underlying VICIS is yet to be clarified. Here, we describe detailed clinical (including brain MRI and muscle biopsy) and genetic features of nine Japanese patients with VICIS. Genetic dissection of these nine patients from seven families identified 14 causative mutations in EPG5. These included five nonsense, two frameshift, three splicing, one missense, and one multi-exon deletion mutations, and two initiation codon variants. Furthermore, cultured skin fibroblasts (SFs) from two affected patients demonstrated partial autophagic dysfunction. To investigate the function of EPG5, siRNA based EPG5 knock-down, and CRISPR/Cas9 mediated EPG5 knock-out HeLa cells were generated. EPG5-depleted cells exhibited a complete block of autophagic flux caused by defective autophagosome-lysosome fusion. Unexpectedly, endocytic degradation was normal in both VICIS SFs and EPG5 depleted cells, suggesting that EPG5 function is limited to the regulation of autophagosome-lysosome fusion.

Highlights

Vici syndrome (VICIS) is a rare, autosomal recessive neurodevelopmental disorder with multisystem involvement characterized by agenesis of the corpus callosum, cataracts, cardiomyopathy, combined immunodeficiency, developmental delay, and hypopigmentation
Since EPG5 has been reported to function in autophagic and endocytic pathways[12, 20, 24, 25], we analyzed these functions in patient Skin fibroblasts (SFs)
Cultured SFs isolated from two patients were treated with nutrient-rich or starvation medium for 6 hours with/without the lysosomal inhibitor Bafilomycin A1 (BafA1), LC3 expression determined by western blot

Summary

Introduction

Vici syndrome (VICIS) is a rare, autosomal recessive neurodevelopmental disorder with multisystem involvement characterized by agenesis of the corpus callosum, cataracts, cardiomyopathy, combined immunodeficiency, developmental delay, and hypopigmentation. We describe detailed clinical (including brain MRI and muscle biopsy) and genetic features of nine Japanese patients with VICIS Genetic dissection of these nine patients from seven families identified 14 causative mutations in EPG5. Endocytic degradation was normal in both VICIS SFs and EPG5 depleted cells, suggesting that EPG5 function is limited to the regulation of autophagosomelysosome fusion. We studied nine patients with VICIS from seven families and identified 14 causative mutations in EPG5. Skin fibroblasts (SFs) from VICIS patients and EPG5 knock-down (KD) and KO HeLa cells demonstrated normal endocytic function, but impaired autophagic function due to defects in autophagosome-lysosome fusion

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