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ESCRT functions in autophagy and associated disease
Tor Erik Rusten1, Anne Simonsen
1Centre for Cancer Biomedicine, University of Oslo and Department of Biochemistry, The Norwegian Radium Hospital, Montebello, Oslo, Norway.
Abstract:
Mutations in the endosomal sorting complexes required for transport (ESCRT)-III subunit CHMP2B are associated with frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), both human neurodegenerative diseases characterized by accumulation of ubiquitinated proteins aggregates in affected neurons. The ESCRT proteins are known to be involved in diverse cellular processes such as mRNA transport, cytokinesis, transcriptional regulation and sorting of transmembrane proteins into the inner vesicles of the multivesicular body (MVB) during endocytosis. It was until recently not clear how ESCRT function may be involved in neurodegeneration. New findings in mammalian cells and in Drosophila melanogaster show that functional ESCRTs are required for efficient fusion of autophagic vesicles with the endocytic pathway and for degradation of autophagic cargo. Moreover, defective ESCRT function led to the accumulation of cytoplasmic protein aggregates containing ubiquitin, p62/Sequestosome-1 and TAR DNA binding protein 43 (TDP-43). Using cellular and Drosophila models for Huntington's disease it was also shown that reduced ESCRT levels inhibit clearance of expanded polyglutamine aggregates and aggravate their neurotoxic effect. These data indicate that efficient autophagic degradation requires functional MVBs and provides a possible explanation to the observed neurodegenerative phenotype seen in patients with CHMP2B mutations.
Insights
Mutations in CHMP2B disrupt cellular waste removal, leading to toxic protein buildup and neurodegeneration in diseases like FTD and ALS. This highlights the critical role of ESCRT proteins in maintaining neuronal health.
Area of Science:
- Cell Biology
- Neuroscience
- Molecular Biology
Background:
- Mutations in CHMP2B, an endosomal sorting complexes required for transport (ESCRT)-III subunit, are linked to frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS).
- These neurodegenerative diseases are characterized by the accumulation of ubiquitinated protein aggregates in neurons.
- The precise role of ESCRT proteins in neurodegeneration was previously unclear.
Purpose of the Study:
- To investigate the role of functional ESCRT proteins in cellular waste degradation pathways.
- To understand how defective ESCRT function contributes to the accumulation of protein aggregates in neurodegenerative diseases.
- To elucidate the link between ESCRT function, autophagic degradation, and neurotoxicity.
Main Methods:
- Experiments were conducted in mammalian cells and Drosophila melanogaster models.
- Investigated the fusion of autophagic vesicles with the endocytic pathway.
- Analyzed the impact of defective ESCRT function on the accumulation of specific protein aggregates (ubiquitin, p62/Sequestosome-1, TDP-43).
- Utilized cellular and Drosophila models for Huntington's disease to assess the effect of reduced ESCRT levels on polyglutamine aggregate clearance.
Main Results:
- Functional ESCRTs are essential for the efficient fusion of autophagic vesicles with the endocytic pathway and for cargo degradation.
- Defective ESCRT function results in the accumulation of cytoplasmic protein aggregates, including ubiquitin, p62/Sequestosome-1, and TDP-43.
- Reduced ESCRT levels impair the clearance of expanded polyglutamine aggregates and exacerbate neurotoxicity in Huntington's disease models.
Conclusions:
- Efficient autophagic degradation relies on functional multivesicular bodies (MVBs).
- Defective ESCRT function contributes to neurodegeneration by impairing autophagic clearance of protein aggregates.
- These findings provide a mechanistic explanation for the neurodegenerative phenotypes observed in patients with CHMP2B mutations.
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