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Disruption of endocytic trafficking in frontotemporal dementia with CHMP2B mutations.

Urwin H, Authier A, Nielsen JE, Metcalf D, Powell C, Froud K, Malcolm DS, Holm I, Johannsen P, Brown J, Fisher EM, van der Zee J, Bruyland M, FReJA ConsortiumVan Broeckhoven C, Collinge J, Brandner S, Futter C, Isaacs AM - Hum. Mol. Genet. (2010)

Bottom Line: Mutations in CHMP2B cause frontotemporal dementia (FTD) in a large Danish pedigree, which is termed FTD linked to chromosome 3 (FTD-3), and also in an unrelated familial FTD patient.CHMP2B is a component of the ESCRT-III complex, which is required for function of the multivesicular body (MVB), an endosomal structure that fuses with the lysosome to degrade endocytosed proteins.We report a novel endosomal pathology in CHMP2B mutation-positive patient brains and also identify and characterize abnormal endosomes in patient fibroblasts.

View Article: PubMed Central - PubMed

Affiliation: MRC Prion Unit, UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK.

ABSTRACT
Mutations in CHMP2B cause frontotemporal dementia (FTD) in a large Danish pedigree, which is termed FTD linked to chromosome 3 (FTD-3), and also in an unrelated familial FTD patient. CHMP2B is a component of the ESCRT-III complex, which is required for function of the multivesicular body (MVB), an endosomal structure that fuses with the lysosome to degrade endocytosed proteins. We report a novel endosomal pathology in CHMP2B mutation-positive patient brains and also identify and characterize abnormal endosomes in patient fibroblasts. Functional studies demonstrate a specific disruption of endosome-lysosome fusion but not protein sorting by the MVB. We provide evidence for a mechanism for impaired endosome-lysosome fusion whereby mutant CHMP2B constitutively binds to MVBs and prevents recruitment of proteins necessary for fusion to occur, such as Rab7. The fusion of endosomes with lysosomes is required for neuronal function and the data presented therefore suggest a pathogenic mechanism for FTD caused by CHMP2B mutations.

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Ultrastructural analysis of patient fibroblasts. (A) Aberrantly formed multivesicular bodies (MVBs) were found in fibroblast cell lines from two FTD-3 patients (b and c) and the Q165X patient (d). In contrast to normal MVBs (a), these were typically enlarged and showed unusual peripheral membrane deformations or sparsity of ILVs. Scale bar = 100 nm. (B) These aberrant structures were positive for CD63, which also decorated normal MVBs and heavily decorated lysosomes in patient and control cell lines. (e) Normal MVB from a control cell line; (f) normal lysosome from a control cell line; (g) abnormal compartments from an FTD-3 cell line. Anti-CD63, 10 nm gold; scale bars = 100 nm.
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DDQ100F4: Ultrastructural analysis of patient fibroblasts. (A) Aberrantly formed multivesicular bodies (MVBs) were found in fibroblast cell lines from two FTD-3 patients (b and c) and the Q165X patient (d). In contrast to normal MVBs (a), these were typically enlarged and showed unusual peripheral membrane deformations or sparsity of ILVs. Scale bar = 100 nm. (B) These aberrant structures were positive for CD63, which also decorated normal MVBs and heavily decorated lysosomes in patient and control cell lines. (e) Normal MVB from a control cell line; (f) normal lysosome from a control cell line; (g) abnormal compartments from an FTD-3 cell line. Anti-CD63, 10 nm gold; scale bars = 100 nm.

Mentions: Examination of the ultrastructure of these enlarged endosomes by electron microscopy suggested that they were dysmorphic MVBs. Unusual vesicular structures present in three patient cell lines, including the CHMP2BQ165X patient, were not seen in age-matched controls (Fig. 4A). These structures were typically enlarged vacuoles with aberrant membrane deformation at the periphery, or ILVs which did not fill the lumen. In contrast, normal MVBs, which were seen in both patient and control cells, were smaller and packed with ILVs. Immunolabelling showed that these characteristic structures were likely to be late endosomes as they were positive for CD63, which also labelled normal degradative compartments and MVBs in patient and control cells (Fig. 4B).


Disruption of endocytic trafficking in frontotemporal dementia with CHMP2B mutations.

Urwin H, Authier A, Nielsen JE, Metcalf D, Powell C, Froud K, Malcolm DS, Holm I, Johannsen P, Brown J, Fisher EM, van der Zee J, Bruyland M, FReJA ConsortiumVan Broeckhoven C, Collinge J, Brandner S, Futter C, Isaacs AM - Hum. Mol. Genet. (2010)

Ultrastructural analysis of patient fibroblasts. (A) Aberrantly formed multivesicular bodies (MVBs) were found in fibroblast cell lines from two FTD-3 patients (b and c) and the Q165X patient (d). In contrast to normal MVBs (a), these were typically enlarged and showed unusual peripheral membrane deformations or sparsity of ILVs. Scale bar = 100 nm. (B) These aberrant structures were positive for CD63, which also decorated normal MVBs and heavily decorated lysosomes in patient and control cell lines. (e) Normal MVB from a control cell line; (f) normal lysosome from a control cell line; (g) abnormal compartments from an FTD-3 cell line. Anti-CD63, 10 nm gold; scale bars = 100 nm.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2865375&req=5

DDQ100F4: Ultrastructural analysis of patient fibroblasts. (A) Aberrantly formed multivesicular bodies (MVBs) were found in fibroblast cell lines from two FTD-3 patients (b and c) and the Q165X patient (d). In contrast to normal MVBs (a), these were typically enlarged and showed unusual peripheral membrane deformations or sparsity of ILVs. Scale bar = 100 nm. (B) These aberrant structures were positive for CD63, which also decorated normal MVBs and heavily decorated lysosomes in patient and control cell lines. (e) Normal MVB from a control cell line; (f) normal lysosome from a control cell line; (g) abnormal compartments from an FTD-3 cell line. Anti-CD63, 10 nm gold; scale bars = 100 nm.
Mentions: Examination of the ultrastructure of these enlarged endosomes by electron microscopy suggested that they were dysmorphic MVBs. Unusual vesicular structures present in three patient cell lines, including the CHMP2BQ165X patient, were not seen in age-matched controls (Fig. 4A). These structures were typically enlarged vacuoles with aberrant membrane deformation at the periphery, or ILVs which did not fill the lumen. In contrast, normal MVBs, which were seen in both patient and control cells, were smaller and packed with ILVs. Immunolabelling showed that these characteristic structures were likely to be late endosomes as they were positive for CD63, which also labelled normal degradative compartments and MVBs in patient and control cells (Fig. 4B).

Bottom Line: Mutations in CHMP2B cause frontotemporal dementia (FTD) in a large Danish pedigree, which is termed FTD linked to chromosome 3 (FTD-3), and also in an unrelated familial FTD patient.CHMP2B is a component of the ESCRT-III complex, which is required for function of the multivesicular body (MVB), an endosomal structure that fuses with the lysosome to degrade endocytosed proteins.We report a novel endosomal pathology in CHMP2B mutation-positive patient brains and also identify and characterize abnormal endosomes in patient fibroblasts.

View Article: PubMed Central - PubMed

Affiliation: MRC Prion Unit, UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK.

ABSTRACT
Mutations in CHMP2B cause frontotemporal dementia (FTD) in a large Danish pedigree, which is termed FTD linked to chromosome 3 (FTD-3), and also in an unrelated familial FTD patient. CHMP2B is a component of the ESCRT-III complex, which is required for function of the multivesicular body (MVB), an endosomal structure that fuses with the lysosome to degrade endocytosed proteins. We report a novel endosomal pathology in CHMP2B mutation-positive patient brains and also identify and characterize abnormal endosomes in patient fibroblasts. Functional studies demonstrate a specific disruption of endosome-lysosome fusion but not protein sorting by the MVB. We provide evidence for a mechanism for impaired endosome-lysosome fusion whereby mutant CHMP2B constitutively binds to MVBs and prevents recruitment of proteins necessary for fusion to occur, such as Rab7. The fusion of endosomes with lysosomes is required for neuronal function and the data presented therefore suggest a pathogenic mechanism for FTD caused by CHMP2B mutations.

Show MeSH
Related in: MedlinePlus