Reliable Resolution of Full-Length Huntingtin Alleles by Quantitative Immunoblotting

Background: Therapeutics that lower mutant huntingtin (mHTT) have shown promise in preclinical studies and are in clinical development for the treatment of Huntington’s disease (HD). Multiple assays have been developed that either quantify mHTT or total HTT but may not accurately measure levels of wild type HTT (wtHTT) in biological samples. Objective: To optimize a method that can be used to resolve, quantify and directly compare levels of full length wtHTT and mHTT in HD samples. Methods: We provide a detailed quantitative immunoblotting protocol to reproducibly resolve full length wtHTT and mHTT in multiple HD mouse and patient samples. Results: We show that this assay can be modified, depending on the sample, to resolve wtHTT and mHTT with a wide range of polyglutamine differences (ΔQs 22–179). We also demonstrate that this method can be used to quantify allele-selective lowering of mHTT using an antisense oligonucleotide in HD patient-derived cells. Conclusion: This quantitative immunoblotting method can be used to reliably resolve full length HTT alleles with ΔQs≥22 and allows for direct comparison of wtHTT and mHTT levels in HD samples.

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Identification of Full-Length Wild-Type and Mutant Huntingtin Interacting Proteins by Crosslinking Immunoprecipitation in Mice Brain Cortex

Journal of Huntington s Disease ◽

10.3233/jhd-210476 ◽

2021 ◽

pp. 1-13

Author(s):

Karen A. Sap ◽

Arzu Tugce Guler ◽

Aleksandra Bury ◽

Dick Dekkers ◽

Jeroen A.A. Demmers ◽

...

Keyword(s):

Huntington's Disease ◽

Huntington’S Disease ◽

Brain Cortex ◽

Full Length ◽

Biological Processes ◽

Interacting Proteins ◽

Mutant Huntingtin ◽

Wild Type ◽

Mutant Huntingtin Protein ◽

Mice Brain

Background: Huntington’s disease is a neurodegenerative disorder caused by a CAG expansion in the huntingtin gene, resulting in a polyglutamine expansion in the ubiquitously expressed mutant huntingtin protein. Objective: Here we set out to identify proteins interacting with the full-length wild-type and mutant huntingtin protein in the mice cortex brain region to understand affected biological processes in Huntington’s disease pathology. Methods: Full-length huntingtin with 20 and 140 polyQ repeats were formaldehyde-crosslinked and isolated via their N-terminal Flag-tag from 2-month-old mice brain cortex. Interacting proteins were identified and quantified by label-free liquid chromatography-mass spectrometry (LC-MS/MS). Results: We identified 30 interactors specific for wild-type huntingtin, 14 interactors specific for mutant huntingtin and 14 shared interactors that interacted with both wild-type and mutant huntingtin, including known interactors such as F8a1/Hap40. Syt1, Ykt6, and Snap47, involved in vesicle transport and exocytosis, were among the proteins that interacted specifically with wild-type huntingtin. Various other proteins involved in energy metabolism and mitochondria were also found to associate predominantly with wild-type huntingtin, whereas mutant huntingtin interacted with proteins involved in translation including Mapk3, Eif3h and Eef1a2. Conclusion: Here we identified both shared and specific interactors of wild-type and mutant huntingtin, which are involved in different biological processes including exocytosis, vesicle transport, translation and metabolism. These findings contribute to the understanding of the roles that wild-type and mutant huntingtin play in a variety of cellular processes both in healthy conditions and Huntington’s disease pathology.

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Caspase 3-cleaved N-terminal fragments of wild-type and mutant huntingtin are present in normal and Huntington's disease brains, associate with membranes, and undergo calpain-dependent proteolysis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.221451398 ◽

2001 ◽

Vol 98 (22) ◽

pp. 12784-12789 ◽

Cited By ~ 252

Author(s):

Y. J. Kim ◽

Y. Yi ◽

E. Sapp ◽

Y. Wang ◽

B. Cuiffo ◽

...

Keyword(s):

Huntington's Disease ◽

Huntington’S Disease ◽

Caspase 3 ◽

Mutant Huntingtin ◽

Wild Type

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Huntington's disease: from pathology and genetics to potential therapies

Biochemical Journal ◽

10.1042/bj20071619 ◽

2008 ◽

Vol 412 (2) ◽

pp. 191-209 ◽

Cited By ~ 269

Author(s):

Sara Imarisio ◽

Jenny Carmichael ◽

Viktor Korolchuk ◽

Chien-Wen Chen ◽

Shinji Saiki ◽

...

Keyword(s):

Huntington's Disease ◽

Huntington’S Disease ◽

Trinucleotide Repeat ◽

Mutant Protein ◽

Mutant Huntingtin ◽

Genetic Screens ◽

Wild Type ◽

Biological Studies ◽

Polyglutamine Tract

Huntington's disease (HD) is a devastating autosomal dominant neurodegenerative disease caused by a CAG trinucleotide repeat expansion encoding an abnormally long polyglutamine tract in the huntingtin protein. Much has been learnt since the mutation was identified in 1993. We review the functions of wild-type huntingtin. Mutant huntingtin may cause toxicity via a range of different mechanisms. The primary consequence of the mutation is to confer a toxic gain of function on the mutant protein and this may be modified by certain normal activities that are impaired by the mutation. It is likely that the toxicity of mutant huntingtin is revealed after a series of cleavage events leading to the production of N-terminal huntingtin fragment(s) containing the expanded polyglutamine tract. Although aggregation of the mutant protein is a hallmark of the disease, the role of aggregation is complex and the arguments for protective roles of inclusions are discussed. Mutant huntingtin may mediate some of its toxicity in the nucleus by perturbing specific transcriptional pathways. HD may also inhibit mitochondrial function and proteasome activity. Importantly, not all of the effects of mutant huntingtin may be cell-autonomous, and it is possible that abnormalities in neighbouring neurons and glia may also have an impact on connected cells. It is likely that there is still much to learn about mutant huntingtin toxicity, and important insights have already come and may still come from chemical and genetic screens. Importantly, basic biological studies in HD have led to numerous potential therapeutic strategies.

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A YAC Mouse Model for Huntington’s Disease with Full-Length Mutant Huntingtin, Cytoplasmic Toxicity, and Selective Striatal Neurodegeneration

Neuron ◽

10.1016/s0896-6273(00)80764-3 ◽

1999 ◽

Vol 23 (1) ◽

pp. 181-192 ◽

Cited By ~ 530

Author(s):

J.Graeme Hodgson ◽

Nadia Agopyan ◽

Claire-Anne Gutekunst ◽

Blair R Leavitt ◽

Fred LePiane ◽

...

Keyword(s):

Mouse Model ◽

Huntington's Disease ◽

Huntington’S Disease ◽

Full Length ◽

Mutant Huntingtin

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Lack of mutant huntingtin in cortical efferents improves behavioral inflexibility and corticostriatal dynamics in Huntington’s disease mice

Journal of Neurophysiology ◽

10.1152/jn.00777.2018 ◽

2019 ◽

Vol 122 (6) ◽

pp. 2621-2629

Author(s):

Ana María Estrada-Sánchez ◽

Courtney L. Blake ◽

Scott J. Barton ◽

Andrew G. Howe ◽

George V. Rebec

Keyword(s):

Motor Cortex ◽

Huntington's Disease ◽

Huntington’S Disease ◽

Local Field ◽

Local Field Potential ◽

Primary Motor Cortex ◽

Field Potential ◽

Full Length ◽

Mutant Huntingtin ◽

Local Field Potential Lfp

Abnormal communication between cerebral cortex and striatum plays a major role in the motor symptoms of Huntington’s disease (HD), a neurodegenerative disorder caused by a mutation of the huntingtin gene ( mHTT). Because cortex is the main driver of striatal processing, we recorded local field potential (LFP) activity simultaneously in primary motor cortex (M1) and dorsal striatum (DS) in BACHD mice, a full-length HD gene model, and in a conditional BACHD/Emx-1 Cre (BE) model in which mHTT is suppressed in cortical efferents, while mice freely explored a plus-shaped maze beginning at 20 wk of age. Relative to wild-type (WT) controls, BACHD mice were just as active across >40 wk of testing but became progressively less likely to turn into a perpendicular arm as they approached the choice point of the maze, a sign of HD motor inflexibility. BE mice, in contrast, turned as freely as WT throughout testing. Although BE mice did not exactly match WT in LFP activity, the reduction in alpha (8–13 Hz), beta (13–30 Hz), and low-gamma (30–50 Hz) power that occurred in M1 of turning-impaired BACHD mice was reversed. No reversal occurred in DS. In fact, BE mice showed further reductions in DS theta (4–8 Hz), beta, and low-gamma power relative to the BACHD model. Coherence analysis indicated a dysregulation of corticostriatal information flow in both BACHD and BE mice. Collectively, our results suggest that mHTT in cortical outputs drives the dysregulation of select cortical frequencies that accompany the loss of behavioral flexibility in HD. NEW & NOTEWORTHY BACHD mice, a full-length genetic model of Huntington’s disease (HD), express aberrant local field potential (LFP) activity in primary motor cortex (M1) along with decreased probability of turning into a perpendicular arm of a plus-shaped maze, a motor inflexibility phenotype. Suppression of the mutant huntingtin gene in cortical output neurons prevents decline in turning and improves alpha, beta, and low-gamma activity in M1. Our results implicate cortical networks in the search for therapeutic strategies to alleviate HD motor signs.

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