Non-invasive detection of neurochemical changes prior to overt pathology in a mouse model of spinocerebellar ataxia type 1

Regional sex differences in neurochemical profiles of healthy mice measured by magnetic resonance spectroscopy at 9.4 tesla

Objective

To determine sex differences in the neurochemical concentrations measured by in vivo proton magnetic resonance spectroscopy (1H MRS) of healthy mice on a genetic background commonly used for neurodegenerative disease models.

Methods

1H MRS data collected from wild type mice with C57BL/6 or related genetic backgrounds in seven prior studies were used in this retrospective analysis. To be included, data had to be collected at 9.4 tesla magnetic field using advanced 1H MRS protocols, with isoflurane anesthesia and similar animal handling protocols, and a similar number of datasets from male and female mice had to be available for the brain regions analyzed. Overall, 155 spectra from female mice and 166 spectra from male mice (321 in total), collected from six brain regions (brainstem, cerebellum, cortex, hippocampus, hypothalamus, and striatum) at various ages were included.

Results

Concentrations of taurine, total creatine (creatine + phosphocreatine), ascorbate, glucose and glutamate were consistently higher in male vs. female mice in most brain regions. Striatum was an exception with similar total creatine in male and female mice. The sex difference pattern in the hypothalamus was notably different from other regions. Interaction between sex and age was significant for total creatine and taurine in the cerebellum and hippocampus.

Conclusion

Sex differences in regional neurochemical levels are small but significant and age-dependent, with consistent male-female differences across most brain regions. The neuroendocrine region hypothalamus displays a different pattern of sex differences in neurochemical levels. Differences in energy metabolism and cellular density may underlie the differences, with higher metabolic rates in females and higher osmoregulatory and antioxidant capacity in males.

Reactive Bergmann glia play a central role in spinocerebellar ataxia inflammation via the JNK pathway

The spinocerebellar ataxias (SCAs) are devastating neurological diseases characterized by progressive cerebellar incoordination. While neurons bear the brunt of the pathology, a growing body of evidence suggests that glial cells are also affected. It has, however, been difficult to understand the role of glia, given the diversity of subtypes, each with their individual contributions to neuronal health. Using human SCA autopsy samples we have discovered that Bergmann glia-the radial glia of the cerebellum, which form intimate functional connections with cerebellar Purkinje neurons-display inflammatory JNK-dependent c-Jun phosphorylation. This phosphorylation defines a signaling pathway not observed in other activated glial populations, providing an opportunity to isolate the role of Bergmann glia in SCA inflammation. Turning to an SCA1 mouse model as a paradigmatic SCA, we demonstrate that inhibiting the JNK pathway reduces Bergmann glia inflammation accompanied by improvements in the SCA1 phenotype both behaviorally and pathologically. These findings demonstrate the causal role for Bergmann glia inflammation in SCA1 and point to a novel therapeutic strategy that could span several ataxic syndromes where Bergmann glia inflammation is a major feature.

Clinically Meaningful Magnetic Resonance Endpoints Sensitive to Preataxic Spinocerebellar Ataxia Types 1 and 3

OBJECTIVE

This study was undertaken to identify magnetic resonance (MR) metrics that are most sensitive to early changes in the brain in spinocerebellar ataxia type 1 (SCA1) and type 3 (SCA3) using an advanced multimodal MR imaging (MRI) protocol in the multisite trial setting.

METHODS

SCA1 or SCA3 mutation carriers and controls (n = 107) underwent MR scanning in the US-European READISCA study to obtain structural, diffusion MRI, and MR spectroscopy data using an advanced protocol at 3T. Morphometric, microstructural, and neurochemical metrics were analyzed blinded to diagnosis and compared between preataxic SCA (n = 11 SCA1, n = 28 SCA3), ataxic SCA (n = 14 SCA1, n = 37 SCA3), and control (n = 17) groups using nonparametric testing accounting for multiple comparisons. MR metrics that were most sensitive to preataxic abnormalities were identified using receiver operating characteristic (ROC) analyses.

RESULTS

Atrophy and microstructural damage in the brainstem and cerebellar peduncles and neurochemical abnormalities in the pons were prominent in both preataxic groups, when patients did not differ from controls clinically. MR metrics were strongly associated with ataxia symptoms, activities of daily living, and estimated ataxia duration. A neurochemical measure was the most sensitive metric to preataxic changes in SCA1 (ROC area under the curve [AUC] = 0.95), and a microstructural metric was the most sensitive metric to preataxic changes in SCA3 (AUC = 0.92).

INTERPRETATION

Changes in cerebellar afferent and efferent pathways underlie the earliest symptoms of both SCAs. MR metrics collected with a harmonized advanced protocol in the multisite trial setting allow detection of disease effects in individuals before ataxia onset with potential clinical trial utility for subject stratification. ANN NEUROL 2023;93:686-701.

Antisense Oligonucleotide Therapy Targeted Against ATXN3 Improves Potassium Channel-Mediated Purkinje Neuron Dysfunction in Spinocerebellar Ataxia Type 3

Spinocerebellar ataxia type 3 (SCA3) is the second-most common CAG repeat disease, caused by a glutamine-encoding expansion in the ATXN3 protein. SCA3 is characterized by spinocerebellar degeneration leading to progressive motor incoordination and early death. Previous studies suggest that potassium channel dysfunction underlies early abnormalities in cerebellar cortical Purkinje neuron firing in SCA3. However, cerebellar cortical degeneration is often modest both in the human disease and mouse models of SCA3, raising uncertainty about the role of cerebellar dysfunction in SCA3. Here, we address this question by investigating Purkinje neuron excitability in SCA3. In early-stage SCA3 mice, we confirm a previously identified increase in excitability of cerebellar Purkinje neurons and associate this excitability with reduced transcripts of two voltage-gated potassium (K_V) channels, Kcna6 and Kcnc3, as well as motor impairment. Intracerebroventricular delivery of antisense oligonucleotides (ASO) to reduce mutant ATXN3 restores normal excitability to SCA3 Purkinje neurons and rescues transcript levels of Kcna6 and Kcnc3. Interestingly, while an even broader range of K_V channel transcripts shows reduced levels in late-stage SCA3 mice, cerebellar Purkinje neuron physiology was not further altered despite continued worsening of motor impairment. These results suggest the progressive motor phenotype observed in SCA3 may not reflect ongoing changes in the cerebellar cortex but instead dysfunction of other neuronal structures within and beyond the cerebellum. Nevertheless, the early rescue of both K_V channel expression and neuronal excitability by ASO treatment suggests that cerebellar cortical dysfunction contributes meaningfully to motor dysfunction in SCA3.

Mood alterations in mouse models of Spinocerebellar Ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by abnormal expansion of glutamine-encoding CAG repeats in the Ataxin-1 (ATXN1) gene. SCA1 is characterized by progressive motor deficits, cognitive decline, and mood changes including anxiety and depression, with longer number of repeats correlating with worse disease outcomes. While mouse models have been very useful in understanding etiology of ataxia and cognitive decline, our understanding of mood symptoms in SCA1 has lagged. It remains unclear whether anxiety or depression stem from an underlying brain pathology or as a consequence of living with an untreatable and lethal disease. To increase our understanding of the etiology of SCA1 mood alterations, we used the elevated-plus maze, sucrose preference and forced swim tests to assess mood in four different mouse lines. We found that SCA1 knock-in mice exhibit increased anxiety that correlated with the length of CAG repeats, supporting the idea that underlying brain pathology contributes to SCA1-like anxiety. Additionally, our results support the concept that increased anxiety is caused by non-cerebellar pathology, as Purkinje cell specific SCA1 transgenic mice exhibit decreased anxiety-like behavior. Regarding the molecular mechanism, partial loss of ATXN1 may play a role in anxiety, based on our results for Atxn1 haploinsufficient and null mice.

Neurochemical Differences in Spinocerebellar Ataxia Type 14 and 1

Autosomal-dominant spinocerebellar ataxias (SCA) are neurodegenerative diseases characterized by progressive ataxia. Here, we report on neurometabolic alterations in spinocerebellar ataxia type 1 (SCA1; SCA-ATXN1) and 14 (SCA14; SCA-PRKCG) assessed by non-invasive ¹H magnetic resonance spectroscopy. Three Tesla ¹H magnetic resonance spectroscopy was performed in 17 SCA14, 14 SCA1 patients, and in 31 healthy volunteers. We assessed metabolites in the cerebellar vermis, right cerebellar hemisphere, pons, prefrontal, and motor cortex. Additionally, clinical characteristics were obtained for each patient to correlate them with metabolites. In SCA14, metabolic changes were restricted to the cerebellar vermis compared with widespread neurochemical alterations in SCA1. In SCA14, total N-acetylaspartate (tNAA) was reduced in the vermis by 34%. In SCA1, tNAA was reduced in the vermis (24%), cerebellar hemisphere (26%), and pons (25%). SCA14 patients showed 24% lower glutamate+glutamine (Glx) and 46% lower γ-aminobutyric acid (GABA) in the vermis, while SCA1 patients showed no alterations in Glx and GABA. SCA1 revealed a decrease of aspartate (Asp) in the vermis (62%) and an elevation in the prefrontal cortex (130%) as well as an elevation of myo-inositol (Ins) in the cerebellar hemisphere (51%) and pons (46%). No changes of Asp and Ins were detected in SCA14. Beyond, glucose (Glc) was increased in the vermis of both SCA14 (155%) and SCA1 (247%). ¹H magnetic resonance spectroscopy revealed differing neurochemical profiles in SCA1 and SCA14 and confirmed metabolic changes that may be indicative for neuronal loss and dysfunctional energy metabolism. Therefore, ¹H magnetic resonance spectroscopy represents a helpful tool for in-vivo tracking of disease-specific pathophysiology.

In Vivo Molecular Signatures of Cerebellar Pathology in Spinocerebellar Ataxia Type 3

BACKGROUND

No treatment exists for the most common dominantly inherited ataxia Machado-Joseph disease, or spinocerebellar ataxia type 3 (SCA3). Successful evaluation of candidate therapeutics will be facilitated by validated noninvasive biomarkers of disease pathology recapitulated by animal models.

OBJECTIVE

We sought to identify shared in vivo neurochemical signatures in two mouse models of SCA3 that reflect the human disease pathology.

METHODS

Cerebellar neurochemical concentrations in homozygous YACMJD84.2 (Q84/Q84) and hemizygous CMVMJD135 (Q135) mice were measured by in vivo magnetic resonance spectroscopy at 9.4 tesla. To validate the neurochemical biomarkers, levels of neurofilament medium (NFL; indicator of neuroaxonal integrity) and myelin basic protein (MBP; indicator of myelination) were measured in cerebellar lysates from a subset of mice and patients with SCA3. Finally, NFL and MBP levels were measured in the cerebellar extracts of Q84/Q84 mice upon silencing of the mutant ATXN3 gene.

RESULTS

Both Q84/Q84 and Q135 mice displayed lower N-acetylaspartate than wild-type littermates, indicating neuroaxonal loss/dysfunction, and lower myo-inositol and total choline, indicating disturbances in phospholipid membrane metabolism and demyelination. Cerebellar NFL and MBP levels were accordingly lower in both models as well as in the cerebellar cortex of patients with SCA3 than controls. Importantly, N-acetylaspartate and total choline correlated with NFL and MPB, respectively, in Q135 mice. Long-term sustained RNA interference (RNAi)-mediated reduction of ATXN3 levels increased NFL and MBP in Q84/Q84 cerebella.

CONCLUSIONS

N-acetylaspartate, myo-inositol, and total choline levels in the cerebellum are candidate biomarkers of neuroaxonal and oligodendrocyte pathology in SCA3, aspects of pathology that are reversible by RNAi therapy. © 2020 International Parkinson and Movement Disorder Society.

Spinocerebellar ataxias: prospects and challenges for therapy development

The spinocerebellar ataxias (SCAs) comprise more than 40 autosomal dominant neurodegenerative disorders that present principally with progressive ataxia. Within the past few years, studies of pathogenic mechanisms in the SCAs have led to the development of promising therapeutic strategies, especially for SCAs caused by polyglutamine-coding CAG repeats. Nucleotide-based gene-silencing approaches that target the first steps in the pathogenic cascade are one promising approach not only for polyglutamine SCAs but also for the many other SCAs caused by toxic mutant proteins or RNA. For these and other emerging therapeutic strategies, well-coordinated preparation is needed for fruitful clinical trials. To accomplish this goal, investigators from the United States and Europe are now collaborating to share data from their respective SCA cohorts. Increased knowledge of the natural history of SCAs, including of the premanifest and early symptomatic stages of disease, will improve the prospects for success in clinical trials of disease-modifying drugs. In addition, investigators are seeking validated clinical outcome measures that demonstrate responsiveness to changes in SCA populations. Findings suggest that MRI and magnetic resonance spectroscopy biomarkers will provide objective biological readouts of disease activity and progression, but more work is needed to establish disease-specific biomarkers that track target engagement in therapeutic trials. Together, these efforts suggest that the development of successful therapies for one or more SCAs is not far away.

Antisense oligonucleotide-mediated ataxin-1 reduction prolongs survival in SCA1 mice and reveals disease-associated transcriptome profiles

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited ataxia caused by expansion of a translated CAG repeat encoding a glutamine tract in the ataxin-1 (ATXN1) protein. Despite advances in understanding the pathogenesis of SCA1, there are still no therapies to alter its progressive fatal course. RNA-targeting approaches have improved disease symptoms in preclinical rodent models of several neurological diseases. Here, we investigated the therapeutic capability of an antisense oligonucleotide (ASO) targeting mouse Atxn1 in Atxn1154Q/2Q-knockin mice that manifest motor deficits and premature lethality. Following a single ASO treatment at 5 weeks of age, mice demonstrated rescue of these disease-associated phenotypes. RNA-sequencing analysis of genes with expression restored to WT levels in ASO-treated Atxn1154Q/2Q mice was used to demonstrate molecular differences between SCA1 pathogenesis in the cerebellum and disease in the medulla. Finally, select neurochemical abnormalities detected by magnetic resonance spectroscopy in vehicle-treated Atxn1154Q/2Q mice were reversed in the cerebellum and brainstem (a region containing the pons and the medulla) of ASO-treated Atxn1154Q/2Q mice. Together, these findings support the efficacy and therapeutic importance of directly targeting ATXN1 RNA expression as a strategy for treating both motor deficits and lethality in SCA1.

Oxidation Resistance 1 Modulates Glycolytic Pathways in the Cerebellum via an Interaction with Glucose-6-Phosphate Isomerase

Glucose metabolism is essential for the brain: it not only provides the required energy for cellular function and communication but also participates in balancing the levels of oxidative stress in neurons. Defects in glucose metabolism have been described in neurodegenerative disease; however, it remains unclear how this fundamental process contributes to neuronal cell death in these disorders. Here, we investigated the molecular mechanisms driving the selective neurodegeneration in an ataxic mouse model lacking oxidation resistance 1 (Oxr1) and discovered an unexpected function for this protein as a regulator of the glycolytic enzyme, glucose-6-phosphate isomerase (GPI/Gpi1). Initially, we present a dysregulation of metabolites of glucose metabolism at the pre-symptomatic stage in the Oxr1 knockout cerebellum. We then demonstrate that Oxr1 and Gpi1 physically and functionally interact and that the level of Gpi1 oligomerisation is disrupted when Oxr1 is deleted in vivo. Furthermore, we show that Oxr1 modulates the additional and less well-understood roles of Gpi1 as a cytokine and neuroprotective factor. Overall, our data identify a new molecular function for Oxr1, establishing this protein as important player in neuronal survival, regulating both oxidative stress and glucose metabolism in the brain.

Neurochemical abnormalities in premanifest and early spinocerebellar ataxias

OBJECTIVE

To investigate whether early neurochemical abnormalities are detectable by high-field magnetic resonance spectroscopy (MRS) in individuals with spinocerebellar ataxias (SCAs) 1, 2, 3, and 6, including patients without manifestation of ataxia.

METHODS

A cohort of 100 subjects (N = 18-21 in each SCA group, including premanifest mutation carriers; mean score on the Scale for the Assessment and Rating of Ataxia [SARA] <10 for all genotypes, and 22 matched controls) was scanned at 7 Tesla to obtain neurochemical profiles of the cerebellum and brainstem. A novel multivariate approach (distance-weighted discrimination) was used to combine regional profiles into an "MRS score."

RESULTS

MRS scores robustly distinguished individuals with SCA from controls, with misclassification rates of 0% (SCA2), 2% (SCA3), 5% (SCA1), and 17% (SCA6). Premanifest mutation carriers with estimated disease onset within 10 years had MRS scores in the range of early-manifest SCA subjects. Levels of neuronal and glial markers significantly correlated with SARA and an Activities of Daily Living score in subjects with SCA. Regional neurochemical alterations were different between SCAs at comparable disease severity, with SCA2 displaying the most extensive neurochemical abnormalities, followed by SCA1, SCA3, and SCA6.

INTERPRETATION

Neurochemical abnormalities are detectable in individuals before manifest disease, which may allow premanifest enrollment in future SCA trials. Correlations with ataxia and quality-of-life scores show that neurochemical levels can serve as clinically meaningful endpoints in trials. Ranking of SCA types by degree of neurochemical abnormalities indicates that the neurochemistry may reflect synaptic function or density. Ann Neurol 2018;83:816-829.

Mitochondrial impairments contribute to Spinocerebellar ataxia type 1 progression and can be ameliorated by the mitochondria-targeted antioxidant MitoQ

Spinocerebellar ataxia type 1 (SCA1), due to an unstable polyglutamine expansion within the ubiquitously expressed Ataxin-1 protein, leads to the premature degeneration of Purkinje cells (PCs), decreasing motor coordination and causing death within 10-15 years of diagnosis. Currently, there are no therapies available to slow down disease progression. As secondary cellular impairments contributing to SCA1 progression are poorly understood, here, we focused on identifying those processes by performing a PC specific proteome profiling of Sca1(154Q/2Q) mice at a symptomatic stage. Mass spectrometry analysis revealed prominent alterations in mitochondrial proteins. Immunohistochemical and serial block-face scanning electron microscopy analyses confirmed that PCs underwent age-dependent alterations in mitochondrial morphology. Moreover, colorimetric assays demonstrated impairment of the electron transport chain complexes (ETC) and decrease in ATPase activity. Subsequently, we examined whether the mitochondria-targeted antioxidant MitoQ could restore mitochondrial dysfunction and prevent SCA1-associated pathology in Sca1(154Q/2Q) mice. MitoQ treatment both presymptomatically and when symptoms were evident ameliorated mitochondrial morphology and restored the activities of the ETC complexes. Notably, MitoQ slowed down the appearance of SCA1-linked neuropathology such as lack of motor coordination as well as prevented oxidative stress-induced DNA damage and PC loss. Our work identifies a central role for mitochondria in PC degeneration in SCA1 and provides evidence for the supportive use of mitochondria-targeted therapeutics in slowing down disease progression.

Ataxin-1 regulates the cerebellar bioenergetics proteome through the GSK3β-mTOR pathway which is altered in Spinocerebellar ataxia type 1 (SCA1)

A polyglutamine expansion within the ataxin-1 protein (ATXN1) underlies spinocerebellar ataxia type-1 (SCA1), a neurological disorder mainly characterized by ataxia and cerebellar deficits. In SCA1, both loss and gain of ATXN1 biological functions contribute to cerebellar pathogenesis. However, the critical ATXN1 functions and pathways involved remain unclear. To further investigate the early signalling pathways regulated by ATXN1, we performed an unbiased proteomic study of the Atxn1-KO 5-week-old mice cerebellum. Here, we show that lack of ATXN1 expression induces early alterations in proteins involved in glycolysis [pyruvate kinase, muscle, isoform 1 protein (PKM-i1), citrate synthase (CS), glycerol-3-phosphate dehydrogenase 2 (GPD2), glucose-6-phosphate isomerase (GPI), alpha -: enolase (ENO1)], ATP synthesis [CS, Succinate dehydrogenase complex,subunit A (SDHA), ATP synthase subunit d, mitochondrial (ATP5H)] and oxidative stress [peroxiredoxin-6 (PRDX6), aldehyde dehydrogenase family 1, subfamily A1, 10-formyltetrahydrofolate dehydrogenase]. In the SCA1 mice, several of these proteins (PKM-i1, ATP5H, PRDX6, proteome subunit A6) were down-regulated and ATP levels decreased. The underlying mechanism does not involve modulation of mitochondrial biogenesis, but dysregulation of the activity of the metabolic regulators glycogen synthase kinase 3B (GSK3β), decreased in Atxn1-KO and increased in SCA1 mice, and mechanistic target of rapamycin (serine/threonine kinase) (mTOR), unchanged in the Atxn1-KO and decreased in SCA1 mice cerebellum before the onset of ataxic symptoms. Pharmacological inhibition of GSK3β and activation of mTOR in a SCA1 cell model ameliorated identified ATXN1-regulated metabolic proteome and ATP alterations. Taken together, these results point to an early role of ATXN1 in the regulation of bioenergetics homeostasis in the mouse cerebellum. Moreover, data suggest GSK3β and mTOR pathways modulate this ATXN1 function in SCA1 pathogenesis that could be targeted therapeutically prior to the onset of disease symptoms in SCA1 and other pathologies involving dysregulation of ATXN1 functions.

Proceedings of the workshop on Cerebellum, Basal Ganglia and Cortical Connections Unmasked in Health and Disorder held in Brno, Czech Republic, October 17th, 2013

The proceedings of the workshop synthesize the experimental, preclinical, and clinical data suggesting that the cerebellum, basal ganglia (BG), and their connections play an important role in pathophysiology of various movement disorders (like Parkinson's disease and atypical parkinsonian syndromes) or neurodevelopmental disorders (like autism). The contributions from individual distinguished speakers cover the neuroanatomical research of complex networks, neuroimaging data showing that the cerebellum and BG are connected to a wide range of other central nervous system structures involved in movement control. Especially, the cerebellum plays a more complex role in how the brain functions than previously thought.

Assessing recovery from neurodegeneration in spinocerebellar ataxia 1: Comparison of in vivo magnetic resonance spectroscopy with motor testing, gene expression and histology

Suppression of transgene expression in a conditional transgenic mouse model of spinocerebellar ataxia 1 (SCA1) reverses the Purkinje cell pathology and motor dysfunction that are hallmarks of SCA1. We previously showed that cerebellar neurochemical levels measured by magnetic resonance spectroscopy (MRS) correlate with progression of pathology and clinical status of patients and that abnormal neurochemical levels normalize upon suppression of transgene expression, indicating their potential as robust surrogate markers of treatment effects. Here we investigated the relative sensitivities of MRS, histology, transgene expression and motor behavioral testing to disease reversal in conditional SCA1 mice. Transgene expression was suppressed by doxycycline administration and treated and untreated mice were assessed by MRS at 9.4tesla before and after treatment and with an accelerating Rotarod, histology and quantitative polymerase chain reaction (qPCR) for ataxin-1 transgene expression following doxycycline treatment. The MRS-measured N-acetylaspartate-to-myo-inositol ratio (NAA/Ins) correlated significantly with the molecular layer (ML) thickness and transgene expression. NAA/Ins, ML thickness and transgene expression were highly significantly different between the treated vs. untreated groups (p<0.0001), while the Rotarod assessment showed a trend for treatment effect. MRS, qPCR and histology had high sensitivity/specificity to distinguish treated from untreated mice, all with areas under the curve (AUC)=0.97-0.98 in receiver operating characteristic (ROC) analyses, while Rotarod had significantly lower sensitivity and specificity (AUC=0.72). Therefore, MRS accurately reflects the extent of recovery from neurodegeneration with sensitivity similar to invasive measures, further validating its potential as a surrogate marker in pre-clinical and clinical treatment trials.

From pathways to targets: understanding the mechanisms behind polyglutamine disease

The history of polyglutamine diseases dates back approximately 20 years to the discovery of a polyglutamine repeat in the androgen receptor of SBMA followed by the identification of similar expansion mutations in Huntington's disease, SCA1, DRPLA, and the other spinocerebellar ataxias. This common molecular feature of polyglutamine diseases suggests shared mechanisms in disease pathology and neurodegeneration of disease specific brain regions. In this review, we discuss the main pathogenic pathways including proteolytic processing, nuclear shuttling and aggregation, mitochondrial dysfunction, and clearance of misfolded polyglutamine proteins and point out possible targets for treatment.