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Truncation of mutant huntingtin in knock-in mice via CRISPR-Cas9 uncovers exon1 huntingtin as a key pathogenic form

ABSTRACT: It remains unknown how polyglutamine expansion in widely expressed proteins can cause selective neurodegeneration. In Huntington’s disease (HD), proteolytic processing generates toxic N-terminal huntingtin (HTT) fragments that preferentially kill striatal neurons. Considerable efforts have been devoted to investigating how HTT is cleaved and whether blocking its cleavage is therapeutically beneficial. However, using CRISPR-Cas9 to truncate full-length mutant Htt in HD140Q knock-in (KI) mice, we found that exon1 Htt is stably present in the brain, regardless of truncation sites in full-length Htt. This N-terminal Htt led to similar HD phenotypes and age-dependent Htt accumulation in striatum in different KI mice. Exon1 Htt is constantly generated but its selective accumulation in the striatum is caused by the age-dependent expression of striatum-enriched HspBP1, a chaperone inhibitory protein. Our findings suggest that tissue-specific chaperone function accounts for the selective neuropathology in HD and highlight therapeutic importance in regulating this function.

ORGANISM(S): Mus musculus

PROVIDER: GSE145879 | GEO | 2020/04/21

REPOSITORIES: GEO

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Identification of full length wild-type and mutant huntingtin interacting proteins by crosslinking immunoprecipitation in mice brain cortex

Project description:Huntington’s Disease is a neurodegenerative disorder caused by a CAG expansion in exon1 of the huntingtin (Htt) gene. The resulting polyglutamine expansion in the ubiquitously expressed mutant Htt (mHtt) protein leads to selective neurodegeneration. In this study we set out to identify interacting proteins of full length wild-type and mHtt protein in the mice cortex brain region in order to get a better understanding of the processes involved in HD pathology.

2021-06-21 | PXD024254 | Pride

Proteolysis resistant huntingtin isoform induced by antisense oligonucleotide maintains normal huntingtin function in mouse

Project description:Huntington’s disease (HD) is a late onset neurological disorder for which no neuroprotective therapies efficiently delay onset or progression. A key pathological mechanism in disease involves the proteolysis of polyglutamine (polyQ)-expanded mutant huntingtin (mHTT) generating polyQ-containing N-terminal fragments that are crucial contributors to HD pathogenesis since inhibition of the cleavage at the putative caspase-6 site reduces pathology in a HD mouse model. Interestingly, a naturally occurring alternative spliced form of HTT lacking exon12 (HTTΔ12) leads to a protein with an internal deletion of the caspase-6 N-terminal cleavage site. Here, we have taken a multidisciplinary approach to characterize the therapeutic potential of targeting exon12 of HTT. We show that HTTΔ12 is fully resistant to caspase-6 cleavage in both cell-free and tissue lysate assays, while maintaining overall biochemical and structural properties similar to wild-type (wt)-HTT. We generated mouse deleted for exon12 and found that exon12 is dispensable for HTT main physiological functions including embryonic development and intracellular trafficking such as BDNF transport. Finally, we pharmacologically induced HTTΔ12 using an antisense oligonucleotide (ASO). QRX-704 ASO efficiently distributes in the whole brain, is stable several months, and reduces pathogenic proteolysis. Thus, ASO-induced exon12 deletion of HT We performed gene expression profiling analysis using data obtained from RNA-seq of brain tissue (cortex and striatum) samples originating from mouse littermates from HttΔ12 (Δ12;KI) and HttKO (KO) lines at 3 month of age.

2022-07-29 | GSE209893 | GEO

Uninterrupted Mutant Huntingtin CAG-repeat but Not Polyglutamine Length Predicts Striatal Nuclear Pathogenesis and Transcriptionopathy in HD Mice

Project description:Huntington’s disease (HD) is caused by CAG repeat expansion at the N-terminal region of huntingtin (HTT) gene and characterize by neuronal cell loss and neuroinflammation transcriptional profile change in striatum, cortex and other brain regions. Here we reported generation and characterization of BAC-CAG, a novel full length human HD mouse model host over 120 uninterrupted CAG repeats. we performed RNA-seq analysis of the striatum and cortex of BAC-CAG mice at 2m, 6m and 12m of age (N=6 per genotype, sex balanced). We observed an age-dependent transcriptionopathy in the striatum of BAC-CAG mice, with only 7 and 36 significant DE genes in 2m and 6m striatum respectively (FDR<0.1), but 820 DE genes (538 downregulated and 282 upregulated genes) at 12m of age (FDR<0.1). The transcriptomic deficits in this model are highly striatum-selective, as we only detected 4, 3 and 14 DE genes (FDR<0.1) at 2m, 6m and 12m respectively in BAC-CAG cortices compared to WT controls. Remarkably, we found a highly significant positive transcriptome-wide correlation (r=0.62) of DE Z statistics between BAC-CAG vs WT at 12m and Q140 vs WT at 6m (p<1e-200). This result demonstrates a high concordance of both upregulated and downregulated genes in the BAC-CAG striatum compared to that of allelic series KI mice; but RNA-seq studies of BACHD mice at 12m and found only 50 genes significantly differentially expressed (DE) genes (FDR<0.1) in the striatum at 12m of age compared to WT littermates, 31 downregulated and 19 upregulated genes. In the cortex at 12m of age, BACHD only showed 6 significantly downregulated genes and 7 upregulated genes comapred to WT controls (FDR<0.1).

2022-02-02 | GSE153827 | GEO

HTT-OMNI: A Web-based Platform for Huntingtin Interaction Exploration and Multi-omics Data Integration

Project description:We have developed a web-based platform for HTT PPI visualization, exploration, and multi-omic integration called HTT-OMNI. We demonstrate the utility of this platform not only for exploring and filtering existing huntingtin (HTT) PPIs, but also for investigating user-generated omics datasets. For example, we demonstrate the comparison of a published HTT IP-MS experiment, performed in the striatum brain region of a mouse HD model, to unpublished HTT IP-MS experiments in the cortex brain region. Overall, HTT-OMNI summarizes and integrates known HTT PPIs with polyQ-dependent transcriptome and proteome measurements, providing an all-in-one exploratory platform that facilitates the prioritization of target genes that may contribute to HD pathogenesis.

2022-08-15 | PXD034158 | Pride

PolyQ-expansion does not alter the huntingtin-HAP40 complex

Project description:The amplification of a CAG repeat in the gene coding for huntingtin (HTT) leads to Huntington’s disease (HD). At the protein level, this translates into the expansion of a poly-glutamine (polyQ) stretch in the HTT N-terminus, which renders HTT aggregation-prone by unknown mechanisms. Here we investigate the effects of polyQ expansion on the HTT-HAP40 complex, where HTT structure is substantially stabilized. Surprisingly, our biophysical, cryo-EM and crosslinking mass spectrometry experiments reveal no major changes between 17QHTT-HAP40 (wild type), 46QHTT-HAP40 (typical polyQ length in HD patients) and 128QHTT-HAP40 (extreme polyQ length). Thus, the proposed destabilizing effect of HTT polyQ expansion may not suffice to alter the HTT-HAP40 complex, suggesting that polyQ expansion does not have a major global effect on HTT structure.

2021-03-19 | PXD018451 | Pride

PTMs of HTT protein - Post-translational modifications (PTMs), identified on endogenous huntingtin, cluster within proteolytic domains between HEAT repeats

Project description:Post-translational modifications (PTMs) of proteins regulate various cellular processes. PTMs of polyglutamine-expanded huntingtin (Htt) protein, causative of Huntington’s disease (HD), are likely modulators of HD pathogenesis. Previous studies have identified and characterized several PTMs on exogenously expressed Htt fragments, however none of these studies were designed to systematically characterize PTMs on the endogenous full-length Htt protein.We found that full-length endogenous Htt, immunoprecipitated from HD knock-in mouse and human post mortem brain, is suitable for detection of PTMs by mass spectrometry. Using label-free mass spectrometry, we identified around 40 PTMs, of which half are novel. These findings will be instrumental in the further assembling the Htt PTM framework, and validate PTMs of Htt as promising therapeutic targets for HD.

2017-06-29 | PXD005753 | Pride

Small molecule activation of a pseudoexon triggers huntingtin-lowering (AmpliSeq)

Project description:Huntington’s disease (HD) is a hereditary neurodegenerative disorder caused by abnormal expansion of cytosine-adenine-guanine (CAG) trinucleotide repeats in the huntingtin gene (HTT). The resultant mutant protein is ubiquitously expressed and drives pathogenesis of HD through a toxic gain-of-function mechanism. Animal models of HD have demonstrated that reducing huntingtin protein (HTT) levels alleviates HD-associated motor and neuropathological abnormalities, confirming the importance of huntingtin-lowering as a therapeutic approach. Several therapies in development repress HTT transcription or translation, including antisense oligonucleotides, virally-delivered microRNAs, and zinc finger protein transcription factors. However, they all require invasive procedures to reach the central nervous system (CNS) and do not distribute evenly to target areas in the brain. Systemically distributed therapeutics are needed to address the CNS and peripheral dysfunctions associated with HD. Here we report the discovery of small molecule splicing modifiers that lower HTT expression by selective modulation of pre-mRNA splicing. These compounds promote the inclusion of a pseudoexon containing a premature termination codon triggering HTT mRNA degradation and a reduction of HTT protein levels in vitro and in vivo. These orally bioavailable small molecules represent a non-invasive treatment option for HD and our findings support their continued development for the treatment of HD.

2021-07-01 | GSE162812 | GEO

Small molecule activation of a pseudoexon triggers huntingtin-lowering (RNA-Seq)

2021-07-01 | GSE162813 | GEO

In vivo cell-autonomous transcriptional abnormalities revealed in mice expressing mutant huntingtin in striatal but not cortical neurons

Project description:Huntington’s disease (HD), caused by a CAG repeat expansion in the huntingtin (HTT) gene, is characterized by abnormal protein aggregates and motor and cognitive dysfunction. Htt protein is ubiquitously expressed, but the striatal medium spiny neuron (MSN) is most susceptible to neuronal dysfunction and death. Abnormal gene expression represents a core pathogenic feature of HD, but the relative roles of cell-autonomous and non-cell-autonomous effects on transcription remain unclear. To determine the extent of cell-autonomous dysregulation in the striatum in vivo, we examined genome-wide RNA expression in symptomatic D9-N171-98Q (a.k.a. DE5) transgenic mice in which the forebrain expression of the first 171 amino acids of human Htt with a 98Q repeat expansion is limited to MSNs. Microarray data generated from these mice were compared to those generated on the identical array platform from a pan-neuronal HD mouse model, R6/2, carrying two different CAG repeat lengths, and a relatively high degree of overlap of changes in gene expression was revealed. We further focused on known canonical pathways associated with excitotoxicity, oxidative stress, mitochondrial dysfunction, dopamine signaling and trophic support, among others. While genes related to excitotoxicity, dopamine signaling and trophic support, were altered in both DE5 and R6/2 transgenic mice, which may be either cell-autonomous or non-cell-autonomous,, genes related to mitochondrial dysfunction, oxidative stress and the peroxisome proliferator-activated receptor are primarily affected in DE5 transgenic mice, indicating cell autonomous mechanisms Overall, our results demonstrate that HD-induced dysregulation of the striatal transcriptome can be largely attributed to intrinsic effects of mutant Htt,,such that mutant Htt-induced effects in cortical neurons is not necessary for striatal dysfunction/degeneration. Striatum from DE5 transgenic mice vs. wt littermate controls

2011-01-01 | E-GEOD-25232 | biostudies-arrayexpress

Huntingtin polyglutamine expansion modulates protein interaction dynamics in the striatum

Project description:Huntington’s disease is a monogenic disorder, with only one known causative gene, huntingtin (HTT). Expansion of a trinucleotide (CAG) repeat within the HTT gene results in a mutant protein containing polyglutamine (polyQ) stretches. While mutant HTT is the primary driver of cellular degeneration in the brain, the molecular and cellular mechanisms are incompletely understood. To further understand the role of polyQ in disease pathogenesis, we studied the dynamics of HTT protein-protein interactions (PPIs) in the striatum of mice with wild-type (Q20) and mutant (Q140) HTT at pre-symptomatic and manifest HD ages using label-free and isotope-labeled IP-MS approaches. Combining these approaches, we demonstrated that HTT PPI dynamics are distinct in early and later disease phases. Computational analysis pointed to early protein interaction changes involving synaptic transmission and vesicle fusion functions, while later interactions underlie changes in synapse morphogenesis and impact the actin cytoskeletal network.

2022-02-20 | PXD025510 | Pride

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