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

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.

Autophagy-mediated occludin degradation contributes to blood–brain barrier disruption during ischemia in bEnd.3 brain endothelial cells and rat ischemic stroke models

“…An increase in the LC3-II protein levels, which indicates an increase in autophagosomes does not always indicate normal autophagy flux. In several pathological conditions, the accumulation of autophagic vacuoles and the corresponding increase in LC3-II were often observed due to a failure of fusion between autophagosomes with lysosomes, and these phenomena were explained as abnormal autophagy rather than autophagic activation [48,49]. We examined the formation of autolysosomes by co-localization of intracellular LAMP1, a lysosomal marker, and LC3 in order to elucidate whether increased LC3-II indicates abnormal autophagy.…”

Morphine-Mediated Brain Region-Specific Astrocytosis Involves the ER Stress-Autophagy Axis

“…Defects in autophagy have been found by genetic association studies to confer susceptibility to several autoimmune and inflammatory disorders, particularly inflammatory bowel disease [70]. A possible explanation for the block in fusion of autophagosome with the lysosomes could be attributed to either the loss of lysosomal acidification and/or loss of lysosomal proteases, thereby leading to accumulation of autophagosomes inside the cells [71–73]. In our study, we found increased accumulation of autophagosomes that was accompanied by defective lysosomal fusion, in astrocytes exposed to morphine.…”

EPG5 c.1007A > G mutation in a sibling pair with rapidly progressing Vici syndrome

“…In addition to these phenotypic features, cardiomyopathy, developmental delay, microcephaly, and failure to thrive were described as typical consequences (Byrne et al., ; Chiyonobu et al., ; del Campo et al., ). Since the first description, more than 40 families have been published with Vici syndrome (VICIS), who were compatible with an autosomal recessive transmission and have extended the variable clinical spectrum with myopathy, epilepsy, elevated aminotransferases, thymus aplasia, thrombocytopenic purpura, sensorineural hearing loss, and renal tubular acidosis (Aggarwal, Tandon, Bhowmik, & Dalal, ; Al‐Owain et al., ; Alzahrani, Alghamdi, & Waggass, ; Balasubramaniam et al., ; Byrne et al., ; Chiyonobu et al., ; Cullup et al., ; del Campo et al., ; Demiral, Sen, Esener, Ceylaner, & Tekedereli, ; El‐Kersh, Jungbluth, Gringras, & Senthilvel, ; Hedberg‐Oldfors, Darin, & Oldfors, ; Hori et al., ; Huenerberg et al., ; Maillard et al., ; McClelland et al., ; Miyata et al., ; Ozkale, Erol, Gümüs, Ozkale, & Alehan, ; Rogers, Aufmuth, & Monesson, ; Said, Soler, & Sewry, ; Shimada et al., ; Waldrop et al., ). The prognosis was found to be poor with a median survival of 42 months (Byrne, Dionisi‐Vici, Smith, Gautel, & Jungbluth, ).…”

“…Mutations of EPG5 (18q12.3) were identified in 2013 by whole exome sequencing (Cullup et al., ). The encoded protein, ectopic P‐granules autophagy protein 5 is a Rab7 effector mediating the fusion specificity between autophagosomes and lysosomes (Cullup et al., ; Hori et al., ; Wang et al., ). Loss of EPG5 results in the accumulation of autophagic cargo in autophagosomes (Byrne et al., ; Ehmke et al., ).…”