Mutant huntingtin protein induces MLH1 degradation, DNA hyperexcision, and cGAS-STING-dependent apoptosis.

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by an expanded CAG repeat in the huntingtin (HTT) gene. The repeat-expanded HTT encodes a mutated HTT (mHTT), which is known to induce DNA double-strand breaks (DSBs), activation of the cGAS-STING pathway, and apoptosis in HD. However, the mechanism by which mHTT triggers these events is unknown. Here, we show that HTT interacts with both exonuclease 1 (Exo1) and MutLα (MLH1-PMS2), a negative regulator of Exo1. While the HTT-Exo1 interaction suppresses the Exo1-catalyzed DNA end resection during DSB repair, the HTT-MutLα interaction functions to stabilize MLH1. However, mHTT displays a significantly reduced interaction with Exo1 or MutLα, thereby losing the ability to regulate Exo1. Thus, cells expressing mHTT exhibit rapid MLH1 degradation and hyperactive DNA excision, which causes severe DNA damage and cytosolic DNA accumulation. This activates the cGAS-STING pathway to mediate apoptosis. Therefore, we have identified unique functions for both HTT and mHTT in modulating DNA repair and the cGAS-STING pathway-mediated apoptosis by interacting with MLH1. Our work elucidates the mechanism by which mHTT causes HD.

An exploration of the genetics of the mutant Huntingtin (mHtt) gene in a cohort of patients with chorea from different ethnic groups in sub-Saharan Africa.

BACKGROUND: Africans are underrepresented in Huntington's disease (HD) research. A European ancestor was postulated to have introduced the mutant Huntingtin (mHtt) gene to the continent; however, recent work has shown the existence of a unique Htt haplotype in South-Africa specific to indigenous Africans. OBJECTIVE: We aimed to investigate the CAG trinucleotide repeats expansion in the Htt gene in a geographically diverse cohort of patients with chorea and unaffected controls from sub-Saharan Africa. METHODS: We evaluated 99 participants: 43 patients with chorea, 21 asymptomatic first-degree relatives of subjects with chorea, and 35 healthy controls for the presence of the mHtt. Participants were recruited from 5 African countries. Additional data were collected from patients positive for the mHtt gene; these included demographics, the presence of psychiatric and (or) cognitive symptoms, family history, spoken languages, and ethnic origin. Additionally, their pedigrees were examined to estimate the number of people at risk of developing HD and to trace back the earliest account of the disease in each region. RESULTS: HD cases were identified in all countries. Overall, 53.4% of patients with chorea were carriers for the mHTT; median tract size was 45 CAG repeats. Of the asymptomatic relatives, 28.6% (6/21) were carriers for the mHTT; median tract size was 40 CAG. No homozygous carries were identified. Median CAG tract size in controls was 17 CAG repeats. Men and women were equally affected by HD. All patients with HD-bar three who were juvenile onset of <21 years-were defined as adult onset (median age of onset was 40 years). HD transmission followed an autosomal dominant pattern in 84.2% (16/19) of HD families. In familial cases, maternal transmission was higher 52.6% (10/19) than paternal transmission 36.8% (7/19). The number of asymptomatic individuals at risk of developing HD was estimated at ten times more than the symptomatic patients. HD could be traced back to the early 1900s in most African sites. HD cases spread over seven ethnic groups belonging to two distinct linguistic lineages separated from each other approximately 54-16 kya ago: Nilo-Sahara and Niger-Congo. CONCLUSION: This is the first study examining HD in multiple sites in sub-Saharan Africa. We demonstrated that HD is found in multiple ethnic groups residing in five sub-Saharan African countries including the first genetically confirmed HD cases from Guinea and Kenya. The prevalence of HD in the African continent, its associated socio-economic impact, and genetic origins need further exploration and reappraisal.

Preclinical evaluation of the novel [18F]CHDI-650 PET ligand for non-invasive quantification of mutant huntingtin aggregates in Huntington's disease.

PURPOSE: Positron emission tomography (PET) imaging of mutant huntingtin (mHTT) aggregates is a potential tool to monitor disease progression as well as the efficacy of candidate therapeutic interventions for Huntington's disease (HD). To date, the focus has been mainly on the investigation of 11C radioligands; however, favourable 18F radiotracers will facilitate future clinical translation. This work aimed at characterising the novel [18F]CHDI-650 PET radiotracer using a combination of in vivo and in vitro approaches in a mouse model of HD. METHODS: After characterising [18F]CHDI-650 using in vitro autoradiography, we assessed in vivo plasma and brain radiotracer stability as well as kinetics through dynamic PET imaging in the heterozygous (HET) zQ175DN mouse model of HD and wild-type (WT) littermates at 9 months of age. Additionally, we performed a head-to-head comparison study at 3 months with the previously published [11C]CHDI-180R radioligand. RESULTS: Plasma and brain radiometabolite profiles indicated a suitable metabolic profile for in vivo imaging of [18F]CHDI-650. Both in vitro autoradiography and in vivo [18F]CHDI-650 PET imaging at 9 months of age demonstrated a significant genotype effect (p < 0.0001) despite the poor test-retest reliability. [18F]CHDI-650 PET imaging at 3 months of age displayed higher differentiation between genotypes when compared to [11C]CHDI-180R. CONCLUSION: Overall, [18F]CHDI-650 allows for discrimination between HET and WT zQ175DN mice at 9 and 3 months of age. [18F]CHDI-650 represents the first suitable 18F radioligand to image mHTT aggregates in mice and its clinical evaluation is underway.

Passive immunization against phosphorylated tau improves features of Huntington's disease pathology.

Huntington's disease is classically described as a neurodegenerative disorder of monogenic aetiology. The disease is characterized by an abnormal polyglutamine expansion in the huntingtin gene, which drives the toxicity of the mutated form of the protein. However, accumulation of the microtubule-associated protein tau, which is involved in a number of neurological disorders, has also been observed in patients with Huntington's disease. In order to unravel the contribution of tau hyperphosphorylation to hallmark features of Huntington's disease, we administered weekly intraperitoneal injections of the anti-tau pS202 CP13 monoclonal antibody to zQ175 mice and characterized the resulting behavioral and biochemical changes. After 12 weeks of treatment, motor impairments, cognitive performance and general health were improved in zQ175 mice along with a significant reduction in hippocampal pS202 tau levels. Despite the lack of effect of CP13 on neuronal markers associated with Huntington's disease pathology, tau-targeting enzymes and gliosis, CP13 was shown to directly impact mutant huntingtin aggregation such that brain levels of amyloid fibrils and huntingtin oligomers were decreased, while larger huntingtin protein aggregates were increased. Investigation of CP13 treatment of Huntington's disease patient-derived induced pluripotent stem cells (iPSCs) revealed a reduction in pS202 levels in differentiated cortical neurons and a rescue of neurite length. Collectively, these findings suggest that attenuating tau pathology could mitigate behavioral and molecular hallmarks associated with Huntington's disease.

Peripheral Biomarkers in Manifest and Premanifest Huntington's Disease.

Huntington's disease (HD) is characterized by clinical motor impairment (e.g., involuntary movements, poor coordination, parkinsonism), cognitive deficits, and psychiatric symptoms. An inhered expansion of the CAG triplet in the huntingtin gene causing a pathogenic gain-of-function of the mutant huntingtin (mHTT) protein has been identified. In this review, we focus on known biomarkers (e.g., mHTT, neurofilament light chains) and on new biofluid biomarkers that can be quantified in plasma or peripheral blood mononuclear cells from mHTT carriers. Circulating biomarkers may fill current unmet needs in HD management: better stratification of patients amenable to etiologic treatment; the initiation of preventive treatment in premanifest HD; and the identification of peripheral pathogenic central nervous system cascades.

A selective inhibitor of the NLRP3 inflammasome as a potential therapeutic approach for neuroprotection in a transgenic mouse model of Huntington's disease.

BACKGROUND: Huntington's disease (HD) is a neurodegenerative disorder caused by the expansion of the CAG repeat in the huntingtin (HTT) gene. When the number of CAG repeats exceeds 36, the translated expanded polyglutamine-containing HTT protein (mutant HTT [mHTT]) interferes with the normal functions of many cellular proteins and subsequently jeopardizes important cellular machineries in major types of brain cells, including neurons, astrocytes, and microglia. The NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome, which comprises NLRP3, ASC, and caspase-1, is involved in the activation of IL-1ß and IL-18 and has been implicated in various biological functions. Although the existence of the NLRP3 inflammasome in the brain has been documented, the roles of the NLRP3 inflammasome in HD remain largely uncharacterized. MCC950 is a highly selective and potent small-molecule inhibitor of NLRP3 that has been used for the treatment of several diseases such as Alzheimer's disease. However, whether MCC950 is also beneficial in HD remains unknown. Therefore, we hypothesized that MCC950 exerts beneficial effects in a transgenic mouse model of HD. METHODS: To evaluate the effects of MCC950 in HD, we used the R6/2 (B6CBA-Tg[HDexon1]62Gpb/1J) transgenic mouse model of HD, which expresses exon 1 of the human HTT gene carrying 120 ± 5 CAG repeats. Male transgenic R6/2 mice were treated daily with MCC950 (10 mg/kg of body weight; oral administration) or water for 5 weeks from the age of 7 weeks. We examined neuronal density, neuroinflammation, and mHTT aggregation in the striatum of R6/2 mice vs. their wild-type littermates. We also evaluated the motor function, body weight, and lifespan of R6/2 mice. RESULTS: Systematic administration of MCC950 to R6/2 mice suppressed the NLRP3 inflammasome, decreased IL-1ß and reactive oxygen species production, and reduced neuronal toxicity, as assessed based on increased neuronal density and upregulation of the NeuN and PSD-95 proteins. Most importantly, oral administration of MCC950 increased neuronal survival, reduced neuroinflammation, extended lifespan, and improved motor dysfunction in R6/2 mice. CONCLUSIONS: Collectively, our findings indicate that MCC950 exerts beneficial effects in a transgenic mouse model of HD and has therapeutic potential for treatment of this devastating neurodegenerative disease.

Longitudinal preclinical evaluation of the novel radioligand [11C]CHDI-626 for PET imaging of mutant huntingtin aggregates in Huntington's disease.

PURPOSE: As several therapies aimed at lowering mutant huntingtin (mHTT) brain levels in Huntington's disease (HD) are currently being investigated, noninvasive positron emission tomography (PET) imaging of mHTT could be utilized to directly evaluate therapeutic efficacy and monitor disease progression. Here we characterized and longitudinally assessed the novel radioligand [11C]CHDI-626 for mHTT PET imaging in the zQ175DN mouse model of HD. METHODS: After evaluating radiometabolites and radioligand kinetics, we conducted longitudinal dynamic PET imaging at 3, 6, 9, and 13 months of age (M) in wild-type (WT, n = 17) and heterozygous (HET, n = 23) zQ175DN mice. Statistical analysis was performed to evaluate temporal and genotypic differences. Cross-sectional cohorts at each longitudinal time point were included for post-mortem [3H]CHDI-626 autoradiography. RESULTS: Despite fast metabolism and kinetics, the radioligand was suitable for PET imaging of mHTT. Longitudinal quantification could discriminate between genotypes already at premanifest stage (3 M), showing an age-associated increase in signal in HET mice in parallel with mHTT aggregate load progression, as supported by the post-mortem [3H]CHDI-626 autoradiography. CONCLUSION: With clinical evaluation underway, [11C]CHDI-626 PET imaging appears to be a suitable preclinical candidate marker to monitor natural HD progression and for the evaluation of mHTT-lowering therapies.

Rhes Tunnels: A Radical New Way of Communication in the Brain's Striatum?

Ras homolog enriched in the striatum (Rhes) is a striatal enriched protein that promotes the formation of thin membranous tubes resembling tunneling nanotubes (TNT)-"Rhes tunnels"-that connect neighboring cell and transport cargoes: vesicles and proteins between the neuronal cells. Here the literature on TNT-like structures is reviewed, and the implications of Rhes-mediated TNT, the mechanisms of its formation, and its potential in novel cell-to-cell communication in regulating striatal biology and disease are emphasized. Thought-provoking ideas regarding how Rhes-mediated TNT, if it exists, in vivo, would radically change the way neurons communicate in the brain are discussed.

Dysregulation of long non-coding RNAs and their mechanisms in Huntington's disease.

Extensive alterations in gene regulatory networks are a typical characteristic of Huntington's disease (HD); these include alterations in protein-coding genes and poorly understood non-coding RNAs (ncRNAs), which are associated with pathology caused by mutant huntingtin. Long non-coding RNAs (lncRNAs) are an important class of ncRNAs involved in a variety of biological functions, including transcriptional regulation and post-transcriptional modification of many targets, and likely contributed to the pathogenesis of HD. While a number of changes in lncRNAs expression have been observed in HD, little is currently known about their functions. Here, we discuss their possible mechanisms and molecular functions, with a particular focus on their roles in transcriptional regulation. These findings give us a better insight into HD pathogenesis and may provide new targets for the treatment of this neurodegenerative disease.

Design, Synthesis, and Structure-Activity Relationship Study of Potent MAPK11 Inhibitors.

Huntington's disease (HD) is a rare single-gene neurodegenerative disease, which can only be treated symptomatically. Currently, there are no approved drugs for HD on the market. Studies have found that MAPK11 can serve as a potential therapeutic target for HD. Regrettably, no MAPK11 small molecule inhibitors have been approved at present. This paper presents three series of compounds that were designed and synthesized based on the structure of skepinone-L, a known MAPK14 inhibitor. Among the synthesized compounds, 13a and 13b, with IC50 values of 6.40 nM and 4.20 nM, respectively, displayed the best inhibitory activities against MAPK11. Furthermore, the structure-activity relationship (SAR) is discussed in detail, which is constructive in optimizing the MAPK11 inhibitors for better activity and effect against HD.