Biology subjects

Sen, N.-E.

Publications and source records attributed to Sen, N.-E..

6 recordsLinked to original sources

bioRxiv2025

ATXN2 polyglutamine expansion impairs QKI-dependent alternative splicing and oligodendrocyte maintenance

BackgroundPolyglutamine (polyQ) tract expansion mutations in Ataxin-2 gene (ATXN2) are associated with neurodegenerative diseases spinocerebellar ataxia type 2 (SCA2) and amyotrophic lateral sclerosis (ALS), while the therapeutic reduction of ATXN2 confers strong health-/lifespan extension in models of both disorders. Although the involvement of ATXN2 in peripheral lipid metabolism has been elaborated in Atxn2 knock-out mice, its impact on nervous system lipid maintenance and a potential influence on oligodendrocytes remains unexplored. MethodsWe examine the nervous tissue of an authentic ATXN2 polyQ expansion mouse model in terms of (i) gross morphology of the brain and differential glial affection via immunohistochemical analyses, (ii) spinocerebellar proteome profile via label-free mass spectroscopy and (iii) alternative splicing patterns of oligodendroglial transcripts via quantitative RT-PCR. Finally, electrophysiological recording of sensory response in cerebellar Purkinje cells was performed as a phenotypic measure of demyelination. ResultsWe demonstrate a massive impairment in myelin maintenance due to ATXN2 polyQ expansion, affecting key oligodendroglial proteins accompanied by their splicing anomalies much earlier than disease manifestation. Oligodendroglial ATXN2 aggregates were documented for the first time in cerebellum, which sequestrated the RNA splicing factor Quaking (QKI). As an outcome of demyelination, our SCA2 model showed a significant delay in response to sensory stimuli. ConclusionsOverall, we provide pioneer evidence of oligodendroglial proteotoxicity leading to myelin maintenance defects in an authentic mouse model of SCA2. Our findings suggest that not only neuronal metabolism, but also that of oligodendroglia depends on ATXN2 and is affected during the disease course. This novel aspect of ATXN2 pathomechanism sheds light on potential outcomes of its therapeutic manipulation, and makes it relevant also for demyelination syndromes next to SCA2 and other polyQ disorders.

neuroscience↗

bioRxiv2025

Multiomics approach identifies SERPINB1 as candidate progression biomarker for Spinocerebellar Ataxia type 2

BackgroundSpinocerebellar ataxia type 2 (SCA2) is a polyglutamine disorder, and variants in its disease protein Ataxin-2 act as modifiers in the progression of Amyotrophic Lateral Sclerosis. There are no reliable molecular progression biomarkers for SCA2. ObjectivesThe aim of this study was to define novel molecular progression biomarker candidates for SCA2. MethodsUsing cerebellar and cervicothoracic spinal cord RNA from Atxn2-CAG100-KnockIn and wildtype mice, a multi-omics study was conducted, followed by validation in mice and humans. Global transcriptome studies were conducted using the Clariom D microarray. Extracted proteins were analyzed by LC-MS/MS for global proteomics, and Immobilized Metal Affinity Chromatography for phosphoproteomics. Validation assessed expression by RT-qPCR, and protein abundance by quantitative immunoblots and ELISA. Patients with SCA2 were diagnosed following standard procedures, and the age at onset, SARA score, INAS count, and disease duration were used as clinical severity markers. ResultsVenn diagram comparisons across all OMICS datasets indicated that only Serpinb1a-transcript, SERPINB1A-protein and -phosphopeptides were consistently downregulated at terminal stage in 14-month-old KnockIn mice. Expression studies in cerebellum and spinal cord from 10 weeks (pre-manifest), 6-month-old (early ataxic), and 14-month-old (late ataxic stage) mice confirmed this progressive decrease at mRNA and protein level. SERPINB1 plasma levels were significantly lower in SCA2 patients, and displayed a significant association with the CAG repeat length at expanded ATXN2 alleles and the age at onset, also showing a trend towards significance with the SARA score. ConclusionsSERPINB1 was identified as novel promising biomarker with specificity for SCA2 pathomechanisms.

molecular biology↗

bioRxiv2024

Spinal cord phosphoproteome of a SCA2/ALS13 mouse model reveals alteration of ATXN2-N-term SH3-actin interactome and of autophagy via WNK1-MYO6-OPTN-SQSTM1

Toxic polyglutamine (polyQ) expansions in ATXN2 trigger neurodegenerative processes, causing Spinocerebellar Ataxia type 2 (SCA2), and enhancing TDP-43-dependent pathology in Amyotrophic Lateral Sclerosis (ALS) / Fronto-Temporal Dementia (FTD). Primary disease events can be compensated transiently, delaying disease manifestation. To define potential therapy targets, we documented how cells modify their phospho-signals and how the ATXN2 interactome changes, using preferentially affected nervous tissues from end-stage Atxn2-CAG100-KnockIn mice. The spinal cord phosphorylome revealed massive hyperphosphorylations flanking the polyQ expansion in ATXN2 and for SQSTM1, and moderate hyperphosphorylations also for ALS proteins OPTN, UBQLN2, TNIP1 and TBK1-targeted TAX1BP1, versus strong hypophosphorylations of WNK1, SPARCL1 and PSMD9. Significant enrichments of SH3-containing proteins, autophagy / endocytosis factors, and actin modulators could be explained by N-terminal, polyQ-adjacent, proline-rich motifs in ATXN2. Coimmunoprecipitation profiling in cerebellum documented known associations with RNA-binding proteins like PABPC1 and TDP-43 with its modifier PPIA to decrease upon expansion, contrasting with increased binding of SH3-proteins, like MYO6, RPL21 and DLG4. Validation of protein and mRNA levels in mouse spinal cord, and embryonic fibroblasts or patient fibroblasts after bafilomycin or arsenite treatment, observed polyQ-dependent OPTN deficiency and SQSTM1 induction impairment. Overall, this combined phosphoproteome / interactome study efficiently revealed key pathways and molecular events.

molecular biology↗

bioRxiv2021

Poly(A)-binding protein is an ataxin-2 chaperone that emulsifies biomolecular condensates.

Biomolecular condensation underlies the biogenesis of an expanding array of membraneless assemblies, including stress granules (SGs) which form under a variety of cellular stresses. Advances have been made in understanding the molecular grammar that dictates the behavior of a few key scaffold proteins that make up these phases but how the partitioning of hundreds of other SG proteins is regulated remains largely unresolved. While investigating the rules that govern the condensation of ataxin-2, a SG protein implicated in neurodegenerative disease, we unexpectedly identified a short 14aa sequence that acts as an ataxin-2 condensation switch and is conserved across the eukaryote lineage. We identify poly(A)-binding proteins as unconventional RNA-dependent chaperones that control this regulatory switch. Our results uncover a hierarchy of cis and trans interactions that fine-tune ataxin-2 condensation and reveal a new molecular function for ancient poly(A)-binding proteins as emulsifiers of biomolecular condensate proteins. These findings may inspire novel approaches to therapeutically target aberrant phases in disease.

cell biology↗

bioRxiv2019

Atxn2-CAG100-KnockIn mouse spinal cord shows progressive TDP43 pathology associated with cholesterol biosynthesis suppression

Large polyglutamine expansions in Ataxin-2 (ATXN2) cause multi-system nervous atrophy in Spinocerebellar Ataxia type 2 (SCA2). Intermediate size expansions carry a risk for selective motor neuron degeneration, known as Amyotrophic Lateral Sclerosis (ALS). Conversely, the depletion of ATXN2 prevents disease progression in ALS. Although ATXN2 interacts directly with RNA, and in ALS pathogenesis there is a crucial role of RNA toxicity, the affected functional pathways remain ill defined. Here, we examined an authentic SCA2 mouse model with Atxn2-CAG100-KnockIn for a first definition of molecular mechanisms in spinal cord pathology. Neurophysiology of lower limbs detected sensory neuropathy rather than motor denervation. Triple immunofluorescence demonstrated cytosolic ATXN2 aggregates sequestrating TDP43 and TIA1 from the nucleus. In immunoblots, this was accompanied by elevated CASP3, RIPK1 and PQBP1 abundance. RT-qPCR showed increase of Grn, Tlr7 and Rnaset2 mRNA versus Eif5a2, Dcp2, Uhmk1 and Kif5a decrease. These SCA2 findings overlap well with known ALS features. Similar to other ataxias and dystonias, decreased mRNA levels for Unc80, Tacr1, Gnal, Ano3, Kcna2, Elovl5 and Cdr1 contrasted with Gpnmb increase. Preterminal stage tissue showed strongly activated microglia containing ATXN2 aggregates, with parallel astrogliosis. Global transcriptome profiles from stages of incipient motor deficit versus preterminal age identified molecules with progressive downregulation, where a cluster of cholesterol biosynthesis enzymes including Dhcr24, Msmo1, Idi1 and Hmgcs1 was prominent. Gas chromatography demonstrated a massive loss of crucial cholesterol precursor metabolites. Overall, the ATXN2 protein aggregation process affects diverse subcellular compartments, in particular stress granules, endoplasmic reticulum and receptor tyrosine kinase signaling. These findings identify new targets and potential biomarkers for neuroprotective therapies.

neuroscience↗

bioRxiv2018

Atxn2-CAG100-knock-in affects mouse lifespan and vestibulo-cerebellar function via neural disconnection

Unstable expansions in the Q22-polyglutamine domain of human ATXN2 mediate risks for motor neuron diseases such as ALS/FTLD or cause the autosomal dominant Spinocerebellar Ataxia type 2 (SCA2), but the pathogenesis is not understood and models are unavailable.\n\nWe generated a novel knock-in mouse line with CAG100 expansion in Atxn2, transmitted unstably. The mutant protein accumulated in neuronal cytosolic aggregates, with a characteristic pattern of multi-system-atrophy. Loss-of-function phenotypes included less mutant offspring, initial weight gain and motor hyperactivity. Progressive toxic aggregation effects started around 20 weeks in homozygous animals showing weight loss, reduced muscle strength and gait ataxia. Lifespan was decreased. In the cerebellum, neuronal soma and dendrites were remarkably spared. However, myelin proteins MBP, CNP, PLP1 and transcripts Mal, Mobp, Rtn4 decreased markedly, especially adhesion factors MAG and MOG. In neurons, strong reductions were found for mRNAs of perineuronal elements Haplnl, Hapln2, Hapln4, of axonal myelin interactors Prnp and Klk6. At protein level, the adhesion factor neuroplastin and neurofilaments were strongly reduced, while presynaptic alpha-synuclein increased two-fold.\n\nOverall, this authentic SCA2 mouse model elucidates how altered function and aggregation toxicity of ATXN2 conspire to trigger axon-myelin disconnection. This model will promote the development of neuroprotective therapies and disease biomarkers.

neuroscience↗