PMC:5590178 / 22601-27208 JSONTXT

{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/5590178","sourcedb":"PMC","sourceid":"5590178","source_url":"https://www.ncbi.nlm.nih.gov/pmc/5590178","text":"Discussion\nHere, we show that a 68-year-old male with ataxia and atrophy of the medulla oblongata, upper cervical cord and the cerebellar hemispheres on brain MRI harbors a p.Asp128Asn GFAP mutation. Furthermore, we demonstrate that the p.Asp128Asn mutation induces more GFAP aggregations in zebrafish embryos than WT GFAP, suggesting that this mutation may cause AxD.\nMost neurodegenerative diseases are protein-misfolding disorders (PMDs), and animal models of PMDs are instrumental in addressing many important questions about their molecular pathogeneses and the development of therapeutic modalities. Hence, several model organisms have been utilized to generate animal models of PMDs. For example, Hart and colleagues expressed polyglutamine tracts in the ASH sensory neurons of Caenorhabditis elegans to model Huntington’s disease and found neurodegeneration and apoptosis of ASH neurons [37]. Zhong and colleagues expressed amyloid-β peptides Aβ42 in the neurons of Drosophila melanogaster and noted amyloid deposits, late-onset progressive neurodegeneration and olfactory learning defects [38]. Ayyagari and colleagues showed that a mutant allele of asparaginase like-1 (ASRGL1) identified in a family with inherited retinal degeneration induced protein aggregation in monkey kidney fibroblast-like COS-7 cells, and retinal photoreceptor degeneration in zebrafish larvae [39]. Hsiao and colleagues generated Tg2576 transgenic mice expressing a Swedish allele of amyloid precursor protein and observed impaired learning and memory and the deposition of amyloid plaques in the brain [19]. Although invertebrate model organisms such as C. elegans and D. melanogaster have been used to model PMDs, they have certain limitations. First, they lack key factors critical to many human PMD pathogeneses, such as myelination, specialized neuronal and glial cell types, and a sophisticated immune system. Second, the anatomical structures of their brains are quite divergent from those of humans [40]. On the other hand, zebrafish are vertebrates such that zebrafish can overcome aforementioned limitations. In addition, zebrafish present other advantages as a model of PMDs, such as small size, transparency, and external embryonic development. Thus, zebrafish can be used not only to investigate the molecular pathogenesis of PMDs, but also to develop therapeutics against PMDs. For example, inhibitors of polyglutamine protein aggregation were identified using zebrafish embryos [41]. As such, the zebrafish GFAP aggregation model we present here will help elucidate the molecular pathogenesis of AxD and serve as a basis for the development of AxD therapeutics.\nIn the present study, plasmids encoding mutant GFAPs were injected into zebrafish embryos at 1 hpf, and GFP aggregates in the embryos were imaged at 30 hpf (Fig. 2d). This signifies that the zebrafish embryo assay system can determine aggregation tendency of mutant GFAPs in less than two days. Therefore, this system would be useful for clinicians to make a swift and accurate diagnosis of AxD.\nWe demonstrated in zebrafish embryos that the p.Asp128Asn induced less GFAP aggregates than p.Arg79Cys, p.Arg79His, p.Arg239Cys and p.Arg239His. The proband’s AxD appears to be classified as adult or type II AxD given the proband’s late AAO, bulbar symptoms, nystagmus and atypical MRI features [3, 10, 11]. Two previously reported cases of p.Asp128Asn also seem to be of the same classification [32, 33]. On the other hand, almost all cases of p.Arg79Cys, p.Arg79His, p.Arg239Cys and p.Arg239His fall under the infantile or type I AxD classification [11]. It is therefore tempting to speculate that the aggregation tendency of GFAP mutants may be related to AAO: high aggregation tendency results in early AAO, thereby infantile or type I AxD, and low aggregation tendency brings about late AAO, leading to adult or type II AxD. This notion is supported by a report by Perng and colleagues that two mutant alleles of GFAP found in infantile AxD, p.Asn386Ile and p.Asp417MetfsX14, induced more GFAP aggregates than did three mutant alleles found in adult AxD, p.Ser393Ile, p.Ser398Phe and p.Ser398Tyr [42]. Of course, this notion warrants further comprehensive investigation.\nMessing and colleagues reported that p.Arg239His GFAP increased Gfap promoter activity in mice compared to WT GFAP [43]. This finding may be extended to other pathogenic GFAP mutations. If this is the case, higher aggregations we observed for pathogenic GFAP mutations might ensue from higher GFAP expression, at least in part. This notion warrants further investigation.","divisions":[{"label":"title","span":{"begin":0,"end":10}},{"label":"p","span":{"begin":11,"end":368}},{"label":"p","span":{"begin":369,"end":2663}},{"label":"p","span":{"begin":2664,"end":3059}},{"label":"p","span":{"begin":3060,"end":4235}}],"tracks":[{"project":"AxD_symptoms","denotations":[{"id":"T51","span":{"begin":54,"end":60},"obj":"Phenotype"},{"id":"T52","span":{"begin":374,"end":400},"obj":"Phenotype"},{"id":"T53","span":{"begin":848,"end":865},"obj":"Phenotype"},{"id":"T54","span":{"begin":1037,"end":1066},"obj":"Phenotype"},{"id":"T55","span":{"begin":1226,"end":1246},"obj":"Phenotype"},{"id":"T56","span":{"begin":3319,"end":3328},"obj":"Phenotype"}],"attributes":[{"id":"A51","pred":"hp_id","subj":"T51","obj":"http://purl.obolibrary.org/obo/HP_0001251"},{"id":"A52","pred":"hp_id","subj":"T52","obj":"http://purl.obolibrary.org/obo/HP_0002180"},{"id":"A53","pred":"hp_id","subj":"T53","obj":"http://purl.obolibrary.org/obo/HP_0002180"},{"id":"A54","pred":"hp_id","subj":"T54","obj":"http://purl.obolibrary.org/obo/HP_0002344"},{"id":"A55","pred":"hp_id","subj":"T55","obj":"http://purl.obolibrary.org/obo/HP_0000546"},{"id":"A56","pred":"hp_id","subj":"T56","obj":"http://purl.obolibrary.org/obo/HP_0000639"},{"subj":"T51","pred":"source","obj":"AxD_symptoms"},{"subj":"T52","pred":"source","obj":"AxD_symptoms"},{"subj":"T53","pred":"source","obj":"AxD_symptoms"},{"subj":"T54","pred":"source","obj":"AxD_symptoms"},{"subj":"T55","pred":"source","obj":"AxD_symptoms"},{"subj":"T56","pred":"source","obj":"AxD_symptoms"}]},{"project":"2_test","denotations":[{"id":"28882119-9874792-12765653","span":{"begin":896,"end":898},"obj":"9874792"},{"id":"28882119-15069204-12765654","span":{"begin":1099,"end":1101},"obj":"15069204"},{"id":"28882119-8810256-12765655","span":{"begin":1591,"end":1593},"obj":"8810256"},{"id":"28882119-22167414-12765656","span":{"begin":1995,"end":1997},"obj":"22167414"},{"id":"28882119-17170113-12765657","span":{"begin":2481,"end":2483},"obj":"17170113"},{"id":"28882119-14572141-12765658","span":{"begin":3356,"end":3357},"obj":"14572141"},{"id":"28882119-14770299-12765659","span":{"begin":3359,"end":3361},"obj":"14770299"},{"id":"28882119-21917775-12765660","span":{"begin":3363,"end":3365},"obj":"21917775"},{"id":"28882119-25997626-12765661","span":{"begin":3457,"end":3459},"obj":"25997626"},{"id":"28882119-18684770-12765662","span":{"begin":3461,"end":3463},"obj":"18684770"},{"id":"28882119-21917775-12765663","span":{"begin":3612,"end":3614},"obj":"21917775"},{"id":"28882119-21756903-12765664","span":{"begin":4162,"end":4164},"obj":"21756903"},{"id":"28882119-23432455-12765665","span":{"begin":4352,"end":4354},"obj":"23432455"}],"attributes":[{"subj":"28882119-9874792-12765653","pred":"source","obj":"2_test"},{"subj":"28882119-15069204-12765654","pred":"source","obj":"2_test"},{"subj":"28882119-8810256-12765655","pred":"source","obj":"2_test"},{"subj":"28882119-22167414-12765656","pred":"source","obj":"2_test"},{"subj":"28882119-17170113-12765657","pred":"source","obj":"2_test"},{"subj":"28882119-14572141-12765658","pred":"source","obj":"2_test"},{"subj":"28882119-14770299-12765659","pred":"source","obj":"2_test"},{"subj":"28882119-21917775-12765660","pred":"source","obj":"2_test"},{"subj":"28882119-25997626-12765661","pred":"source","obj":"2_test"},{"subj":"28882119-18684770-12765662","pred":"source","obj":"2_test"},{"subj":"28882119-21917775-12765663","pred":"source","obj":"2_test"},{"subj":"28882119-21756903-12765664","pred":"source","obj":"2_test"},{"subj":"28882119-23432455-12765665","pred":"source","obj":"2_test"}]}],"config":{"attribute types":[{"pred":"source","value type":"selection","values":[{"id":"AxD_symptoms","color":"#93ecd2","default":true},{"id":"2_test","color":"#ecb893"}]}]}}