CAG Repeat Expansion Research Articles

A Glimpse of Molecular Biomarkers in Huntington's Disease.

Huntington’s disease (HD) is a devastating neurodegenerative disorder that is caused by an abnormal expansion of CAG repeats in the Huntingtin (HTT) gene. Although the main symptomatology is explained by alterations at the level of the central nervous system, predominantly affecting the basal ganglia, a peripheral component of the disease is being increasingly acknowledged. Therefore, the manifestation of the disease is complex and variable among CAG expansion carriers, introducing uncertainty in the appearance of specific signs, age of onset and severity of disease. The monogenic nature of the disorder allows a precise diagnosis, but the use of biomarkers with prognostic value is still needed to achieve clinical management of the patients in an individual manner. In addition, we need tools to evaluate the patient’s response to potential therapeutic approaches. In this review, we provide a succinct summary of the most interesting molecular biomarkers that have been assessed in patients, mostly obtained from body fluids such as cerebrospinal fluid, peripheral blood and saliva.

Expression profile analysis in cells overexpressing DRPLA cDNA to explore the roles of DRPLAp as a transcriptional coregulator

AbstractBackgroundDentatorubral‐pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder caused by the unstable expansion of CAG repeats encoding polyglutamine stretches in DRPLA gene (ATN1). DRPLAp, the gene product of ATN1, is located in the nucleus and has been shown to function as a transcriptional coregulator. Its target genes, however, remain largely unknown.AimTo elucidate the physiological functions of DRPLAp based on determination of the target genes regulated by wild‐type DRPLAp.MethodsUsing the cultured cells expressing wild‐type full‐length DRPLA cDNA (Q19) encoding DRPLAp under the control of the doxycycline (Dox)‐On system, we searched for genes whose expression levels were regulated by wild‐type DRPLAp (Q19).ResultsOn the basis of detailed RNA‐seq analyses, we identified seven up‐regulated genes and five down‐regulated genes in Q19 cells. In gene ontology analysis, the up‐regulated differentially expressed genes formed clusters featuring skeletal system morphogenesis, transcriptional regulation, and RNA metabolism, which is consistent with the recent report that the mutations in ATN1 lead to recognizable facial form and variable congenital anomalies.ConclusionThese findings support that DRPLAp may play a role as a transcriptional coregulator involved in the regulation of development.

Intermediate alleles of HTT: A new pathway in longevity

Centenarians are the best example of successful aging, reaching extreme longevity escaping age-related diseases. Genome sequencing studies provided evidence for genetic factors linked to heathy long life, including genes related to age-dependent diseases. HTT (Huntingtin) gene is linked to Huntington's Disease, but also associated to longevity in capuchins and mice. HTT Intermediate alleles (IAs) are defined as CAG repeat expansion between 27 and 35. According to recent data IAs might increase Alzheimer's Disease risk, but also might have a neuroprotective effect and can confer an advantage in brain development. Here, we investigated, for the first time, the possible implication of HTT IAs in extreme longevity and their possible association in cognitive decline. We analysed the distribution of IAs in Italian Centenarians (n = 143) and compared with pathological controls with cognitive decline (n = 232, including 80 Alzheimer's Disease, 78 Frontotemporal Dementia and 74 Subjective Cognitive Decline patients) and healthy controls (n = 104). Our data show a statistically significant higher frequency of IAs in Centenarians with respect to pathological controls with cognitive decline (p = .031; OR = 2.3097 95% CI 1.0591 to 5.0371), with a percentage of 11.2 respect to 5.4 respectively. The highest presence of IAs in Centenarians confirms and extends in humans a possible implication of HTT gene in exceptional lifespan and in brain development with a neuroprotective effect.

Accumulation of pathological Ataxin‐7 in the medulla leads to hypoglossal (XII) motor unit pathology

SCA7 is an autosomal dominant neurological disorder caused by a deleterious CAG repeat expansion in the coding region of the ataxin‐7 gene on chromosome 3. Patients with infantile SCA‐7 have the largest repeat expansion characterized by progressive loss of coordination, dysarthria, dysphagia, retinal degeneration and respiratory distress. These infants succumb to death due to severe hypotonia, aspiration pneumonia and respiratory failure. Our objective is to comprehensively analyze the underlying mechanisms that result in upper airway pathology which exacerbates respiratory insufficiency in SCA7. To do this, we will use an infantile SCA7 mouse model: SCA7266Q Knock‐in (KI) mouse. SCA7266Q KI mice exhibit progressive respiratory dysfunction along with irregular breathing and prolonged apneic events with a significant loss of hypoglossal (XII) motoneurons in the medulla. The XII motoneurons innervate the tongue to maintain the shape, stiffness and position of the tongue and regulate the upper airway patency. Therefore, we hypothesize that the expression of pathological ataxin‐7 in the medulla causes XII motor unit pathology leading to upper airway pathology. To confirm if the reduced number of motoneurons resulted in hypoglossal nerve pathology, we analyzed the efferent nerve output of the XII nerve of 9‐week‐old WT control and SCA72666Q KI mice during eupnea and hypercapnia (7% CO2). Later we performed post‐mortem histological analysis of the XII respiratory centers in the medulla and XII nerves. Specifically, we used immunohistochemistry to identify the cells that accumulate ataxin‐7 and we performed TUNEL assay to evaluate the extent of neurodegeneration in the XII motor pool. We analyzed the demyelination of the nerves by light microscopy and electron microscopy. To identify the cellular mechanisms involved in the XII pathology, we performed transcriptome analysis by bulk RNA sequencing of the medulla and confirmed the findings with qPCR.ResultsXII nerve efferent output is blunted at baseline and hypercapnic challenge in SCA7266QKI mice. There is increased TUNEL+ cells in the XII motor pool with intranuclear accumulation of ataxin‐7 in the astrocytes. Further, demyelination is present in the XII nerves in SCA7266QKI mice. RNA sequencing data of the medulla supports these findings and reveals diminished expression of the transcripts regulating the myelination pathway such as Plp1. There is also a significant decrease in activation of astrocytes with attenuated expression of neurotransmitter transporter such as Slc6a9 and Slc710 that are critical for breathing. In conclusion, intranuclear accumulation of ataxin‐7 in SCA7266QKI mice modulates transcription of astrocytes and influences different signaling pathways that result in neurodegeneration, demyelination, and decreased efferent XII nerve output. These findings are clinically relevant and emphasize the importance of neuropathology that results in dysphagia, aspiration pneumonia and respiratory failure in infantile SCA7.

Dilemma of presymptomatic testing in children with history of late onset neurodegenerative spinocerebellar ataxia in Indonesia

Background: Spinocerebellar ataxia (SCA) is a late onset neurodegenerative disorder in which coordination and balance are affected. Although many international guidelines have been established regarding presymptomatic testing, it is still a grey area in Indonesia. We report two large families with advanced stages of SCA who underwent presymptomatic genetic testing in children along counseling process.Case presentation: Thorough examination was performed, including pedigree construction, physical and neurological examination, gene mutation analyses for patients, and presymptomatic testing for family members, including children. SCA3/MJD1 gene mutation analysis was done in both cases, and a full penetrance CAG repeat expansion was found in both affected patients. Two different outcomes were observed in the offspring, who were both children. The risk and consequences of positive results had been explained in a counseling session to family members, who decided to keep the information until the child would have reached legally adult age.Conclusions: In developing countries such as Indonesia, problems arose due to ethical issues, knowledge of genetic diseases, and inaccessible molecular diagnostics. Culture, religion and tribe diversities may create additional challenges. These cases emphasize the need for careful consideration of presymptomatic testing in children, especially in complicated situations where psychological and ethical issues should be addressed.

Paving the Way Toward Meaningful Trials in Ataxias: An Ataxia Global Initiative Perspective.

Paving the Way Toward Meaningful Trials in Ataxias: An Ataxia Global Initiative Perspective.

Evaluation of CAG repeat length in the androgen receptor gene and polycystic ovary syndrome risk in Iranian women: A case-control study.

BackgroundPolycystic ovary syndrome (PCOS) is a heterogeneous disorder, which affects about 15-20% of women of reproductive age. The most important etiopathogenesis factor in its incidence is hyperandrogenism; over 70 candidate genes are known to be associated with this syndrome, such as the androgen receptor (AR) gene which encodes a steroid receptor and is located on the Xq11-12 chromosome. The N-terminus of exon 1 of AR contains a polymorphic trinucleotide repeat (CAG)n region that encodes glutamine tract. There are some studies showing that shorter AR CAG repeats are significantly related to enhanced AR sensitivity.ObjectiveThis study investigated the frequency of the polymorphic expansion of the trinucleotide CAG repeats of AR in PCOS.Materials and Methods160 Iranian women aged 17-40 yr participated in this case-control study: 80 women as PCOS patients and 80 women as healthy controls according to the Rotterdam criteria. Other similar phenotype factors such as hyperandrogenism were not considered as PCOS. The frequency of polymorphic expansion of CAG trinucleotide repeats in PCOS patients was compared with the frequency in non-PCOS controls in using two primer sets for nested polymerase chain reaction. The polymerase chain reaction products were visualized on polyacrylamide gel and then were confirmed by a sequencing process.ResultsThe results did not show a significant correlation between the frequency of CAG repeats in AR and PCOS incidence.ConclusionIn contrast to some previous reports, the present data showed that the CAG length in PCOS cases did not significantly differ from that of controls. So, the AR (CAG)n does not appear to be a major factor for PCOS in Iranian women.

The distribution and density of Huntingtin inclusions across the Huntington disease neocortex: regional correlations with Huntingtin repeat expansion independent of pathologic grade

Huntington disease is characterized by progressive neurodegeneration, especially of the striatum, and the presence of polyglutamine huntingtin (HTT) inclusions. Although HTT inclusions are most abundant in the neocortex, their neocortical distribution and density in relation to the extent of CAG repeat expansion in the HTT gene and striatal pathologic grade have yet to be formally established. We immunohistochemically studied 65 brains with a pathologic diagnosis of Huntington disease to investigate the cortical distributions and densities of HTT inclusions within the calcarine (BA17), precuneus (BA7), motor (BA4) and prefrontal (BA9) cortices; in 39 of these brains, a p62 immunostain was used for comparison. HTT inclusions predominate in the infragranular cortical layers (layers V-VI) and layer III, however, the densities of HTT inclusions across the human cerebral cortex are not uniform but are instead regionally contingent. The density of HTT and p62 inclusions (intranuclear and extranuclear) in layers V-VI increases caudally to rostrally (BA17 < BA7 < BA4 < BA9) with the median burden of HTT inclusions being 38-fold greater in the prefrontal cortex (BA9) than in the calcarine cortex (BA17). Conversely, intranuclear HTT inclusions prevail in the calcarine cortex irrespective of HTT CAG length. Neocortical HTT inclusion density correlates with CAG repeat expansion, but not with the neuropathologic grade of striatal degeneration (Vonsattel grade) or with the duration of clinical disease since motor onset. Extrapolation of these findings suggest that HTT inclusions are at a regionally-contingent, CAG-dependent, density during the advanced stages of HD. The distribution and density of HTT inclusions in HD therefore does not provide a measure of pathologic disease stage but rather infers the degree of pathogenic HTT expansion.

Computational Investigation of Bending Properties of RNA AUUCU, CCUG, CAG, and CUG Repeat Expansions Associated With Neuromuscular Disorders.

Expansions of RNA AUUCU, CCUG, CAG, and CUG repeats cause spinocerebellar ataxia type 10, myotonic dystrophy type 2, Huntington’s disease, and myotonic dystrophy type 1, respectively. By performing extensive molecular dynamic simulations, we investigated the bending propensities and conformational landscapes adopted by 3×3, 2×2, and 1×1 internal loops observed in RNA AUUCU, CCUG, CAG, and CUG repeat expansions using model systems having biologically relevant repeat sizes. We show that the conformational variability experienced by these loops is more complex than previous reports where a variety of unconventional hydrogen bonds are formed. At the global scale, strong bending propensity was observed in r(AUUCU)10, r(CCUG)15, r(CAG)20, and r(CUG)20, and, to a lesser extent, in r(AUUCU)4, r(CCUG)10, r(CAG)10, and r(CUG)10. Furthermore, RNA CAG repeats exhibit a tendency toward bent states with more than 50% of observed conformations having bending angles greater than 50°, while RNA CUG repeats display relatively linear-like conformations with extremely bent conformations accounting for less than 25% of the observed structures. Conformations experienced by RNA AUUCU repeats are a combination of strongly bent and kinked structures. The bent states in RNA CCUG repeats mostly fall into the moderately bent category with a marginal ensemble experiencing extreme bending. The general pattern observed in all the bent structures indicates the collapse of the major groove width as the mechanical trigger for bending, which is caused by alteration of base pair step parameters at multiple locations along the RNA due to local distortions at the loop sites. Overextension is also observed in all the RNA repeats that is attributed to widening of the major groove width as well as undertwisting phenomenon. This information and the rich structural repository could be applied for structure based small molecule design targeting disease-causing RNAs. The bending propensities of these constructs, at the global level, could also have implications on how expanded RNA repeats interact with proteins.

A Review On Huntington Protein: Insight Into Protein Aggregation and Therapeutic Interventions.

Huntington's disease (HD) is a distressing, innate neurodegenerative disease that descends from CAG repeat expansion in the huntingtin gene causing behavioral changes, motor dysfunction, and dementia in children and adults. Mutation in huntingtin (HTT) protein has been suggested to cause neuron loss in the cortex and striatum through various mechanisms, including abnormal regulation of transcription, proteasomal dysfunction, posttranslational modification, and other events regulating toxicity. Pathogenesis of HD involves cleavage of the huntingtin protein followed by the neuronal accumulation of its aggregated form. Several research groups made possible efforts to reduce huntingtin gene expression, protein accumulation, and protein aggregation using inhibitors and molecular chaperones as developing drugs against HD. Herein, we review the mechanism proposed towards the formation of HTT protein aggregation and the impact of therapeutic strategies for the treatment of HD.

Genetic spectrum in a cohort of patients with distal hereditary motor neuropathy.

BackgroundDistal hereditary motor neuropathy (dHMN) is a heterogeneous group of diseases characterized by exclusive degeneration of peripheral motor nerves, while only 20.0–47.8% of dHMN patients are genetically identified. Recently, GGC expansion in the 5’UTR of NOTCH2NLC has been associated with dHMN. Accordingly, short tandem repeat (STR) should be further explored in genetically unsolved patients with dHMN.MethodsA total of 128 patients from 90 unrelated families were clinically diagnosed as dHMN, and underwent a comprehensively genetic screening. Skin biopsies were conducted with routine protocols.ResultsMost patients showed chronic distal weakness of lower limbs (121/128), while 20 patients initially had asymmetrical involvements, 14 had subclinical sensory abnormalities, 11 had pyramidal impairments, five had cerebellar disturbance, and four had hyperCKmia. The rate of genetic detection was achieved in 36.7% (33/90), and the rate increased to 46.7% (42/90) if patients with variants uncertain significance were included. The most common causative genes included chaperone‐related genes (8/33, 24.2%), tRNA synthetase genes (4/33, 12.1%), and cytoskeleton‐related genes (4/33, 12.1%). Additionally, two dominant inherited families were attributed to abnormal expansion of GGC repeats in the 5‘UTR of NOTCH2NLC; and a patient with dHMN and cerebellar symptoms had CAG repeat expansion in the ATXN2 gene. Skin biopsy from patients with GGC expansion in NOTCH2NLC revealed typical intranuclear inclusions on histological and ultrastructural examinations.InterpretationsThis study further extends the genetic heterogeneity of dHMN. Given some dHMN patients may be associated with nucleotides repeat expansion, STR screening is necessary to perform in genetically unsolved patients.

CAG Repeats Within the Non-pathological Range in the HTT Gene Influence Personality Traits in Patients With Subjective Cognitive Decline: A 13-Year Follow-Up Study.

Objective:HTT is a gene containing a key region of CAG repeats. When expanded beyond 39 repeats, Huntington disease (HD) develops. HTT genes with <35 repeats are not associated with HD. The biological function of CAG repeat expansion below the non-pathological threshold is not well understood. In fact higher number of repeats in HTT confer advantageous changes in brain structure and general intelligence, but several studies focused on establishing the association between CAG expansions and susceptibility to psychiatric disturbances and to other neurodegenerative disease than HD. We hypothesized that HTT CAG repeat length below the pathological threshold might influence mood and personality traits in a longitudinal sample of individuals with Subjective Cognitive Decline.MethodsWe included 54 patients with SCD. All patients underwent an extensive neuropsychological battery at baseline, APOE genotyping and analysis of HTT alleles. We used the Big Five Factors Questionnaire (BFFQ) and Hamilton Depression Rating Scale (HDRS), respectively, to assess personality traits of patients and depression at baseline. Patients who did not progress to Mild Cognitive Impairment (MCI) had at least 5-year follow-up time.ResultsIn the whole sample, CAG repeat number in the shorter HTT allele was inversely correlated with conscientiousness (Pearson = −0.364, p = 0.007). There was no correlation between HDRS and CAG repeats. During the follow-up, 14 patients [25.93% (95% C.I. = 14.24–37.61)] progressed to MCI (MCI+) and 40 [74.07% (95% C.I. = 62.39–85.76)] did not (MCI−). When we performed the same analysis in the MCI+ group we found that: CAG repeat length on the shorter allele was inversely correlated with energy (Pearson = 0.639, p = 0.014) and conscientiousness (Pearson = −0.695, p = 0.006). CAG repeat length on the longer allele was inversely correlated with conscientiousness (Pearson = −0.901, p < 0.001) and directly correlated with emotional stability (Pearson = 0.639, p = 0.014). These associations were confirmed also by multivariate analysis. We found no correlations between BFFQ parameters and CAG repeats in the MCI− group.DiscussionPersonality traits and CAG repeat length in the intermediate range have been associated with progression of cognitive decline and neuropathological findings consistent with AD. We showed that CAG repeat lengths in the HTT gene within the non-pathological range influence personality traits.

Single-Tube Screen for Rapid Detection of Repeat Expansions in Seven Common Spinocerebellar Ataxias.

The autosomal dominantly inherited and genetically heterogeneous spinocerebellar ataxias (SCAs) exhibit highly similar clinical presentations. Many are caused by repeat expansions, of which at least 8 involve CAG repeats. Repeat expansion detection is the only method to confirm disease status in symptomatic individuals. We present a novel strategy to simultaneously screen for the presence of CAG repeat expansion in the genes responsible for SCAs 1, 2, 3, 6, 7, 12, and dentatorubral-pallidoluysian atrophy using a simplified single-tube assay. The method employs differentially labeled locus-specific primers and a common triplet-primed primer. Amplified products from each locus are distinguished by a combination of the product size and the fluorophore tag. The upper size limit of the normal allele range was used as the cutoff for distinguishing normal from potentially affected samples, with repeat expansion detected by presence of electrophoretic peaks extending beyond the cutoff. Blinded evaluation of the assay on 60 genotype-known DNA samples correctly detected repeat expansion in the expected SCA repeat locus for all 31 DNA samples. In principle, this strategy can be applied to the simultaneous screening of any group of disease genes sharing the same repetitive units and/or their reverse complement.

Haplotype-specific insertion-deletion variations for allele-specific targeting in Huntington's disease

Huntington's disease (HD) is a dominantly inherited neurodegenerative disease caused by an expanded CAG repeat in huntingtin (HTT). Given an important role for HTT in development and significant neurodegeneration at the time of clinical manifestation in HD, early treatment of allele-specific drugs represents a promising strategy. The feasibility of an allele-specific antisense oligonucleotide (ASO) targeting single-nucleotide polymorphisms (SNPs) has been demonstrated in models of HD. Here, we constructed a map of haplotype-specific insertion-deletion variations (indels) to develop alternative mutant-HTT-specific strategies. We mapped indels annotated in the 1000 Genomes Project data on common HTT haplotypes, revealing candidate indels for mutant-specific HTT targeting. Subsequent sequencing of an HD family confirmed candidate sites and revealed additional allele-specific indels. Interestingly, the most common normal HTT haplotype carries indels of big allele length differences at many sites, further uncovering promising haplotype-specific targets. When patient-derived cells carrying the most common HTT diplotype were treated with ASOs targeting the mutant alleles of candidate indels (rs772629195 or rs72239206), complete mutant specificity was observed. In summary, our map of haplotype-specific indels permits the identification of allele-specific targets in HD subjects, potentially contributing to the development of safe HTT-lowering therapeutics that are suitable for early treatment in HD.

Ultrasonographic evaluation reveals thinning of cervical nerve roots and peripheral nerves in spinal and bulbar muscular atrophy.

Ultrasonography (US) is a noninvasive and patient-friendly tool for the evaluation of peripheral nerves. In motor neuron diseases, amyotrophic lateral sclerosis (ALS) has been reported to show the atrophy of peripheral nerves on US. However, the US findings are still unclear in spinal and bulbar muscular atrophy (SBMA), an adult-onset lower motor neuron disease caused by an abnormal CAG repeat expansion in the androgen receptor gene. We prospectively recruited and evaluated 11 patients with genetically confirmed SBMA and 9 patients with ALS diagnosed according to the revised El Escorial ALS criteria or the Awaji electrodiagnostic criteria. The C5-C7 cervical nerve roots and the median and ulnar nerves were evaluated ultrasonographically. The cross-sectional areas (CSAs) of the C6 and C7 nerve roots, the median nerve in the upper arm and forearm, and the ulnar nerve in the upper arm were smaller in patients with SBMA than those in patients with ALS (p < 0.05), whereas the CSAs of the C5 nerve root and the ulnar nerve in the forearm were not smaller. US showed that the peripheral nerves in patients with SBMA were thinner than those in patients with ALS despite similar degrees of weakness and motor neuron loss. Possible causes include additional sensory nerve involvement and longer disease duration in patients with SBMA than those in patients with ALS.

Detection Methods and Status of CAT Interruption of ATXN1 in Korean Patients With Spinocerebellar Ataxia Type 1.

Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant disease caused by abnormal CAG repeat expansion in the ataxin 1 gene (ATXN1). The presence of CAT interruption(s) is important for diagnosing SCA1 in patients with 39–44 repeat alleles, as only uninterrupted alleles are considered abnormal. Determining the CAT interruption status might also be important for patients with >44 repeats, as the length of the longest uninterrupted CAG repeat stretch has been correlated with age at SCA1 onset. We detected CAT interruption(s) in the archived samples of Korean SCA1 patients using a traditional restriction enzyme method and validated the usefulness of a fluorescence-based tethering PCR procedure. Among the 2,312 alleles analyzed from 1,156 patients, we found 17 expanded alleles with ≥39 repeats, 71% of which harbored 39–44 repeats. Restriction enzyme method of six samples (four with 39–44 repeats and two with >44 repeats) revealed that none of the expanded alleles had CAT interruption(s). Tethering PCR showed the characteristic electropherogram pattern expected without CAT interruption(s). Along with the enzyme restriction method, tethering PCR can be applied to determine the number of allele repeats and provide information on CAT interruption(s) in clinical laboratories.

Advances in Modeling Polyglutamine Diseases Using Genome Editing Tools.

Polyglutamine (polyQ) diseases, including Huntington’s disease, are a group of late-onset progressive neurological disorders caused by CAG repeat expansions. Although recently, many studies have investigated the pathological features and development of polyQ diseases, many questions remain unanswered. The advancement of new gene-editing technologies, especially the CRISPR-Cas9 technique, has undeniable value for the generation of relevant polyQ models, which substantially support the research process. Here, we review how these tools have been used to correct disease-causing mutations or create isogenic cell lines with different numbers of CAG repeats. We characterize various cellular models such as HEK 293 cells, patient-derived fibroblasts, human embryonic stem cells (hESCs), induced pluripotent stem cells (iPSCs) and animal models generated with the use of genome-editing technology.

Quantitative Phosphoproteomics Reveals Extensive Protein Phosphorylation Dysregulation in the Cerebral Cortex of Huntington's Disease Mice Prior to Onset of Symptoms.

Protein phosphorylation plays a role in many important cellular functions such as cellular plasticity, gene expression, and intracellular trafficking. All of these are dysregulated in Huntington's disease (HD), a devastating neurodegenerative disorder caused by an expanded CAG repeat in exon 1 of the huntingtin gene. However, no studies have yet found protein phosphorylation differences in preclinical HD mouse models. Our current study investigated changes occurring in the cortical phosphoproteome of 8-week-old (prior to motor deficits) and 20-week-old (fully symptomatic) R6/1 transgenic HD mice. When comparing 8-week-old HD mice with their wild-type (WT) littermates, we found 660 peptides differentially phosphorylated, which were mapped to 227 phosphoproteins. These proteins were mainly involved in synaptogenesis, cytoskeleton organization, axon development, and nervous system development. Tau protein, found hyperphosphorylated at multiple sites in early symptomatic HD mice, also appeared as a main upstream regulator for the changes observed. Surprisingly, we found fewer changes in the phosphorylation profile of HD mice at the fully symptomatic stage, with 29 peptides differentially phosphorylated compared to WT mice, mapped to 25 phosphoproteins. These proteins were involved in cAMP signaling, dendrite development, and microtubule binding. Furthermore, huntingtin protein appeared as an upstream regulator for the changes observed at the fully symptomatic stage, suggesting impacts on kinases and phosphatases that extend beyond the mutated polyglutamine tract. In summary, our findings show that the most extensive changes in the phosphorylation machinery appear at an early presymptomatic stage in HD pathogenesis and might constitute a new target for the development of treatments.

IKKβ signaling mediates metabolic changes in the hypothalamus of a Huntington disease mouse model

SummaryHuntington disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin (HTT) gene. Metabolic changes are associated with HD progression, but underlying mechanisms are not fully known. As the IKKβ/NF-κB pathway is an essential regulator of metabolism, we investigated the involvement of IKKβ, the upstream activator of NF-κB in hypothalamus-specific HD metabolic changes. We expressed amyloidogenic N-terminal fragments of mutant HTT (mHTT) in the hypothalamus of mice with brain-specific ablation of IKKβ (Nestin/IKKβlox/lox) and control mice (IKKβlox/lox). We assessed effects on body weight, metabolic hormones, and hypothalamic neuropathology. Hypothalamic expression of mHTT led to an obese phenotype only in female mice. CNS-specific inactivation of IKKβ prohibited weight gain in females, which was independent of neuroprotection and microglial activation. Our study suggests that mHTT in the hypothalamus causes metabolic imbalance in a sex-specific fashion, and central inhibition of the IKKβ pathway attenuates the obese phenotype.

SUPT4H1-edited stem cell therapy rescues neuronal dysfunction in a mouse model for Huntington\u2019s disease

Huntington’s disease (HD) is a severe inherited neurological disorder caused by a CAG repeat expansion in the huntingtin gene (HTT), leading to the accumulation of mutant huntingtin with polyglutamine repeats. Despite its severity, there is no cure for this debilitating disease. HTT lowering strategies, including antisense oligonucleotides (ASO) showed promising results very recently. Attempts to develop stem cell-based therapeutics have shown efficacy in preclinical HD models. Using an HD patient’s autologous cells, which have genetic defects, may hamper therapeutic efficacy due to mutant HTT. Pretreating these cells to reduce mutant HTT expression and transcription may improve the transplanted cells’ therapeutic efficacy. To investigate this, we targeted the SUPT4H1 gene that selectively supports the transcription of long trinucleotide repeats. Transplanting SUPT4H1-edited HD-induced pluripotent stem cell-derived neural precursor cells (iPSC-NPCs) into the YAC128 HD transgenic mouse model improved motor function compared to unedited HD iPSC-NPCs. Immunohistochemical analysis revealed reduced mutant HTT expression without compensating wild-type HTT expression. Further, SUPT4H1 editing increased neuronal and decreased reactive astrocyte differentiation in HD iPSC-NPCs compared to the unedited HD iPSC-NPCs. This suggests that ex vivo editing of SUPT4H1 can reduce mutant HTT expression and provide a therapeutic gene editing strategy for autologous stem cell transplantation in HD.