scholarly journals Control of the structural landscape and neuronal proteotoxicity of mutant Huntingtin by domains flanking the polyQ tract

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Koning Shen ◽  
Barbara Calamini ◽  
Jonathan A Fauerbach ◽  
Boxue Ma ◽  
Sarah H Shahmoradian ◽  
...  
Keyword(s):  
Amyloid Fibrils ◽  
Brain Slices ◽  
Mutant Huntingtin ◽  
Rich Domain ◽  
Mutant Huntingtin Protein ◽  
Exon 1 ◽  
Opposing Effects ◽  
Polyq Tract ◽  
Polyq Expansion

Many neurodegenerative diseases are linked to amyloid aggregation. In Huntington’s disease (HD), neurotoxicity correlates with an increased aggregation propensity of a polyglutamine (polyQ) expansion in exon 1 of mutant huntingtin protein (mHtt). Here we establish how the domains flanking the polyQ tract shape the mHtt conformational landscape in vitro and in neurons. In vitro, the flanking domains have opposing effects on the conformation and stabilities of oligomers and amyloid fibrils. The N-terminal N17 promotes amyloid fibril formation, while the C-terminal Proline Rich Domain destabilizes fibrils and enhances oligomer formation. However, in neurons both domains act synergistically to engage protective chaperone and degradation pathways promoting mHtt proteostasis. Surprisingly, when proteotoxicity was assessed in rat corticostriatal brain slices, either flanking region alone sufficed to generate a neurotoxic conformation, while the polyQ tract alone exhibited minimal toxicity. Linking mHtt structural properties to its neuronal proteostasis should inform new strategies for neuroprotection in polyQ-expansion diseases.

scholarly journals Topological Insights into Mutant Huntingtin Exon 1 and PolyQ Aggregates by Cryo-Electron Tomography

2020 ◽  
Author(s):  
Jesús G. Galaz-Montoya ◽  
Sarah H. Shahmoradian ◽  
Koning Shen ◽  
Judith Frydman ◽  
Wah Chiu
Keyword(s):  
Trinucleotide Repeat ◽  
Electron Tomography ◽  
Mutant Huntingtin ◽  
And Topology ◽  
Cryo Electron Tomography ◽  
Exon 1 ◽  
Subtomogram Averaging ◽  
The Brain ◽  
Polyq Tract

ABSTRACTHuntington disease (HD) is a neurodegenerative trinucleotide repeat disorder caused by an expanded poly-glutamine (polyQ) tract in the mutant huntingtin (mHTT) protein. The formation and topology of filamentous mHTT inclusions in the brain (hallmarks of HD implicated in neurotoxicity) remain elusive. Using cryo-electron tomography and subtomogram averaging, here we show that mHTT exon 1 and polyQ-only aggregates in vitro are structurally heterogenous and filamentous, similar to prior observations with other methods. Yet, we observed some filaments in both types of aggregates under ∼2 nm in width, thinner than previously reported, while other regions form large sheets. In addition, our data show a prevalent subpopulation of filaments exhibiting a lumpy, slab-shaped morphology in both aggregates, supportive of the “polyQ core” model. This provides a basis for future cryoET studies of various aggregated mHTT and polyQ constructs to improve their structure-based modeling and their identification in cells without fusion tags.

scholarly journals Cryo-electron tomography provides topological insights into mutant huntingtin exon 1 and polyQ aggregates

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Jesús G. Galaz-Montoya ◽  
Sarah H. Shahmoradian ◽  
Koning Shen ◽  
Judith Frydman ◽  
Wah Chiu
Keyword(s):  
Trinucleotide Repeat ◽  
Electron Tomography ◽  
Mutant Huntingtin ◽  
And Topology ◽  
Cryo Electron Tomography ◽  
Exon 1 ◽  
Subtomogram Averaging ◽  
The Brain ◽  
Polyq Tract

AbstractHuntington disease (HD) is a neurodegenerative trinucleotide repeat disorder caused by an expanded poly-glutamine (polyQ) tract in the mutant huntingtin (mHTT) protein. The formation and topology of filamentous mHTT inclusions in the brain (hallmarks of HD implicated in neurotoxicity) remain elusive. Using cryo-electron tomography and subtomogram averaging, here we show that mHTT exon 1 and polyQ-only aggregates in vitro are structurally heterogenous and filamentous, similar to prior observations with other methods. Yet, we find filaments in both types of aggregates under ~2 nm in width, thinner than previously reported, and regions forming large sheets. In addition, our data show a prevalent subpopulation of filaments exhibiting a lumpy slab morphology in both aggregates, supportive of the polyQ core model. This provides a basis for future cryoET studies of various aggregated mHTT and polyQ constructs to improve their structure-based modeling as well as their identification in cells without fusion tags.

scholarly journals Topological Insights into Mutant Huntingtin Exon 1 and PolyQ Aggregates by Cryo-Electron Tomography

2020 ◽  
Author(s):  
Jesus Galaz-Montoya ◽  
Sarah Shahmoradian ◽  
Koning Shen ◽  
Judith Frydman ◽  
Wah Chiu
Keyword(s):  
Trinucleotide Repeat ◽  
Electron Tomography ◽  
Mutant Huntingtin ◽  
And Topology ◽  
Cryo Electron Tomography ◽  
Exon 1 ◽  
Subtomogram Averaging ◽  
The Brain ◽  
Polyq Tract

Abstract Huntington disease (HD) is a neurodegenerative trinucleotide repeat disorder caused by an expanded poly-glutamine (polyQ) tract in the mutant huntingtin (mHTT) protein. The formation and topology of filamentous mHTT inclusions in the brain (hallmarks of HD implicated in neurotoxicity) remain elusive. Using cryo-electron tomography and subtomogram averaging, here we show that mHTT exon 1 and polyQ-only aggregates in vitro are structurally heterogenous and filamentous, similar to prior observations with other methods. Yet, we find filaments in both types of aggregates under ~2 nm in width, thinner than previously reported, and regions forming large sheets. In addition, our data show a prevalent subpopulation of filaments exhibiting a lumpy slab morphology in both aggregates, supportive of the polyQ core model. This provides a basis for future cryoET studies of various aggregated mHTT and polyQ constructs to improve their structure-based modeling as well as their identification in cells without fusion tags.

scholarly journals A striatal-enriched intronic GPCR modulates huntingtin levels and toxicity

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Yuwei Yao ◽  
Xiaotian Cui ◽  
Ismael Al-Ramahi ◽  
Xiaoli Sun ◽  
Bo Li ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
G Protein ◽  
Neurodegenerative Disorders ◽  
Treatment Strategies ◽  
Mutant Huntingtin ◽  
Potential Treatment ◽  
Mutant Huntingtin Protein ◽  
G Protein Coupled

Huntington's disease (HD) represents an important model for neurodegenerative disorders and proteinopathies. It is mainly caused by cytotoxicity of the mutant huntingtin protein (Htt) with an expanded polyQ stretch. While Htt is ubiquitously expressed, HD is characterized by selective neurodegeneration of the striatum. Here we report a striatal-enriched orphan G protein-coupled receptor(GPCR) Gpr52 as a stabilizer of Htt in vitro and in vivo. Gpr52 modulates Htt via cAMP-dependent but PKA independent mechanisms. Gpr52 is located within an intron of Rabgap1l, which exhibits epistatic effects on Gpr52-mediated modulation of Htt levels by inhibiting its substrate Rab39B, which co-localizes with Htt and translocates Htt to the endoplasmic reticulum. Finally, reducing Gpr52 suppresses HD phenotypes in both patient iPS-derived neurons and in vivo Drosophila HD models. Thus, our discovery reveals modulation of Htt levels by a striatal-enriched GPCR via its GPCR function, providing insights into the selective neurodegeneration and potential treatment strategies.

scholarly journals α-Synuclein overexpression promotes aggregation of mutant huntingtin

2000 ◽  
Vol 346 (3) ◽  
pp. 577-581 ◽  
Author(s):  
Robert A. FURLONG ◽  
Yolanda NARAIN ◽  
Julia RANKIN ◽  
Andreas WYTTENBACH ◽  
David C. RUBINSZTEIN
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Enhanced Green Fluorescent Protein ◽  
Fluorescent Protein ◽  
Cag Repeats ◽  
Mutant Huntingtin ◽  
Inclusion Formation ◽  
Exon 1 ◽  
Green Fluorescent

Protein aggregates are a neuropathological feature of Huntington's disease and Parkinson's disease. Mutant huntingtin exon 1 with 72 CAG repeats fused to enhanced green fluorescent protein (EGFP) forms hyperfluorescent inclusions in PC12 cells. Inclusion formation is enhanced in cells co-transfected with EGFP-huntingtin-(CAG)72 and α-synuclein, a major component of Parkinson's disease aggregates. However, α-synuclein does not form aggregates by itself, nor does it appear in huntingtin inclusions in vitro.

scholarly journals Therapeutics Advancement for Huntington Disease

2019 ◽  
Author(s):  
Ashok Kumar ◽  
Vijay Kumar ◽  
Kritanjali Singh ◽  
You-Sam Kim ◽  
Yun-Mi Lee ◽  
...  
Keyword(s):  
Huntington Disease ◽  
Review Literature ◽  
Cag Repeats ◽  
Mutant Huntingtin ◽  
Transcriptional Dysregulation ◽  
Psychiatric Disturbances ◽  
Mutant Huntingtin Protein ◽  
Exon 1 ◽  
Disease Modifying ◽  
Novel Therapeutic Strategies

Huntington disease (HD) is an autosomal dominantly inherited fatal neurodegenerative disease. It affects motor, cognitive and psychiatric functions, and ultimately leads to death. The pathology of the disease is due to an expansion of CAG repeats in exon 1 of the huntingtin gene on chromosome 4, which produces a mutant huntingtin protein (mhtt). HD patients manifest a typical phenotype of sporadic, rapid, involuntary control of limb movement, stiffness of limbs, impaired cognition and severe psychiatric disturbances. A variety of symptomatic treatments (which target excitotoxicity, the dopamine pathway, caspases, aggregation, mitochondrial dysfunction, transcriptional dysregulation, mHtt, nucleic acid, neurodegeneration, fetal neural transplants, etc.) are currently available, and new symptomatic and potentially disease-modifying therapies are being actively developed. Recent advances in novel therapeutic strategies, including targeting mutant huntingtin (mhtt) and the htt gene, promise another wave of disease-modifying trials in the near future. A better appreciation of heterogeneous clinical phenomenology and immediate tractable treatment goals coupled with advances in new therapeutics heralds a golden age of HD treatment that will positively impact the quality of life and longevity of HD patients and inform advances in other inherited and neurodegenerative neurological disorders. In the present review literature, our aims to address the latest research on promising therapeutics based on influencing the hypothesized pathological mechanisms associated with HD.

scholarly journals Self-assembly of mutant huntingtin exon-1 fragments into large complex fibrillar structures involves nucleated branching

2017 ◽  
Author(s):  
Anne S. Wagner ◽  
Antonio Z. Politi ◽  
Anne Ast ◽  
Kenny Bravo-Rodriguez ◽  
Katharina Baum ◽  
...  
Keyword(s):  
Self Assembly ◽  
Amyloid Fibrils ◽  
Imaging Techniques ◽  
Critical Role ◽  
Computational Modelling ◽  
Nucleation Process ◽  
Branching Points ◽  
Modelling Studies ◽  
Exon 1

AbstractHuntingtin (HTT) fragments with extended polyglutamine (polyQ) tracts self-assemble into amyloid-like fibrillar aggregates. Elucidating the fibril formation mechanism is critical for understanding Huntington’s disease pathology and for developing novel therapeutic strategies. Here, we performed systematic experimental and theoretical studies to examine the self-assembly of an aggregation-prone N-terminal HTT exon-1 fragment with 49 glutamines (Ex1Q49). Using high resolution imaging techniques such as electron microscopy and atomic force microscopy, we show that Ex1Q49 fragments in cell-free assays spontaneously convert into large, highly complex bundles of amyloid fibrils with multiple ends and fibril branching points. Furthermore, we present experimental evidence that two nucleation mechanisms control spontaneous Ex1Q49 fibrillogenesis: (1) a relatively slow primary fibril-independent nucleation process, which involves the spontaneous formation of aggregation-competent fibrillary structures, and (2) a fast secondary fibril-dependent nucleation process, which involves nucleated branching and promotes the rapid assembly of highly complex fibril bundles with multiple ends. The proposed aggregation mechanism is supported by studies with the small molecule O4, which perturbs early events in the aggregation cascade and delays Ex1Q49 fibril assembly, comprehensive mathematical and computational modelling studies, and seeding experiments with small, preformed fibrillar Ex1Q49 aggregates that promote the assembly of amyloid fibrils. Together, our results suggest that nucleated branchingin vitroplays a critical role in the formation of complex fibrillar HTT exon-1 aggregates with multiple ends.

scholarly journals TRiC’s tricks inhibit huntingtin aggregation

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Sarah H Shahmoradian ◽  
Jesus G Galaz-Montoya ◽  
Michael F Schmid ◽  
Yao Cong ◽  
Boxue Ma ◽  
...  
Keyword(s):  
Electron Tomography ◽  
Structural Description ◽  
Mutant Huntingtin ◽  
Cryo Electron Microscopy ◽  
Amyloid Aggregates ◽  
Cryo Electron Tomography ◽  
Ring Complex ◽  
Exon 1

In Huntington’s disease, a mutated version of the huntingtin protein leads to cell death. Mutant huntingtin is known to aggregate, a process that can be inhibited by the eukaryotic chaperonin TRiC (TCP1-ring complex) in vitro and in vivo. A structural understanding of the genesis of aggregates and their modulation by cellular chaperones could facilitate the development of therapies but has been hindered by the heterogeneity of amyloid aggregates. Using cryo-electron microscopy (cryoEM) and single particle cryo-electron tomography (SPT) we characterize the growth of fibrillar aggregates of mutant huntingtin exon 1 containing an expanded polyglutamine tract with 51 residues (mhttQ51), and resolve 3-D structures of the chaperonin TRiC interacting with mhttQ51. We find that TRiC caps mhttQ51 fibril tips via the apical domains of its subunits, and also encapsulates smaller mhtt oligomers within its chamber. These two complementary mechanisms provide a structural description for TRiC’s inhibition of mhttQ51 aggregation in vitro.

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