Biology subjects

Auburger, G.

Publications and source records attributed to Auburger, G..

14 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↗

bioRxiv2025

ATXN2L primarily interacts with NUFIP2, the absence of ATXN2L results in NUFIP2 depletion, and the ATXN2-polyQ expansion triggers NUFIP2 accumulation

The cytoplasmic Ataxin-2 (ATXN2) protein associates with TDP-43 in stress granules (SG) where RNA quality control occurs. Mutations in this pathway underlie Spinocerebellar Ataxia type 2 (SCA2) and Amyotrophic Lateral Sclerosis. In contrast, Ataxin-2-like (ATXN2L) is predominantly nuclear, more abundant, and essential for embryonic life. Its sequestration into ATXN2 aggregates may contribute to disease. In this study, we utilized two approaches to clarify the roles of ATXN2L. First, we identified interactors through co-immunoprecipitation in both wild-type and ATXN2L-null murine embryonic fibroblasts. Second, we assessed the proteome profile effects using mass spectrometry in these cells. Additionally, we examined the accumulation of ATXN2L interactors in the SCA2 mouse model, Atxn2-CAG100-KnockIn (KIN). We observed that RNA-binding proteins, including PABPN1, NUFIP2, MCRIP2, RBMS1, LARP1, PTBP1, FMR1, RPS20, FUBP3, MBNL2, ZMAT3, SFPQ, CSDE1, HNRNPK, and HNRNPDL, exhibit a stronger association with ATXN2L compared to established interactors like ATXN2, PABPC1, LSM12, and G3BP2. Additionally, ATXN2L interacted with components of the actin complex, such as SYNE2, LMOD1, ACTA2, FYB, and GOLGA3. We noted that oxidative stress increased HNRNPK but decreased SYNE2 association, which likely reflects the relocalization of SG. Proteome profiling revealed that NUFIP2 and SYNE2 are depleted in ATXN2L-null fibroblasts. Furthermore, NUFIP2 homodimers and SYNE1 accumulate during the ATXN2 aggregation process in KIN 14-month-old spinal cord tissues. The functions of ATXN2L and its interactors are therefore critical in RNA granule trafficking and surveillance, particularly for the maintenance of differentiated neurons.

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↗

bioRxiv2024

The ataxia-telangiectasia disease protein ATM controls vesicular protein secretion via CHGA and microtubule dynamics via CRMP5

The autosomal recessive disease ataxia-telangiectasia (A-T) presents with cerebellar degeneration, immunodeficiency, radiosensitivity, capillary dilatations, and pulmonary infections. Most symptoms outside the nervous system can be explained by failures of the disease protein ATM as Ser/Thr-kinase to coordinate DNA damage repair. However, ATM in adult neurons has cytoplasmic localization and vesicle association, where its roles remain unclear. Here, we defined novel ATM protein targets in human neuroblastoma cells and filtered initial pathogenesis events in ATM-null mouse cerebellum. Profiles of global proteome and phosphorylome - both direct ATM/ATR-phosphopeptides and overall phosphorylation changes - confirmed previous findings on NBN, MRE11, MDC1, CHEK1, EIF4EBP1, AP3B2, PPP2R5C, SYN1 and SLC2A1. Even stronger downregulation of ATM/ATR-phosphopeptides after ATM-depletion was documented for CHGA, EXPH5, NBEAL2 and CHMP6 as key factors of protein secretion and endosome dynamics, as well as for CRMP5, DISP2, PHACTR1, PLXNC1, INA and TPX2 as neurite extension factors. Prominent affection of semaphorin-CRMP5-microtubule signals and ATM association with CRMP5 were validated. As a functional consequence, microtubules were stabilized, and neurite retraction ensued. The ATM impact on secretory granules confirms previous ATM-null cerebellar transcriptome findings. Our study provides the first link of A-T neural atrophy to growth cone collapse and aberrant microtubule dynamics.

cell biology↗

bioRxiv2023

Translation fidelity and respiration deficits in CLPP-deficient tissues: Mechanistic insights from mitochondrial complexome

Mitochondrial matrix peptidase CLPP is crucial during cell stress. Its loss causes Perrault syndrome type 3 (PRLTS3) with infertility, neurodegeneration and growth deficit. Its target proteins are disaggregated by CLPX, which also regulates heme biosynthesis via unfolding ALAS enzyme, providing access of pyridoxal-5-phosphate (PLP). Despite efforts in diverse organisms with multiple techniques, CLPXP substrates remain controversial. Here, avoiding recombinant overexpression, we employed complexomics in mitochondria from three mouse tissues to identify endogenous targets. CLPP absence caused accumulation and dispersion of CLPX-VWA8 as AAA+ unfoldases, and of PLPBP. Similar changes and CLPX-VWA8 comigration were evident for mitoribosomal central protuberance clusters, translation factors like GFM1-HARS2, RNA granule components LRPPRC-SLIRP, and enzymes OAT-ALDH18A1. Mitochondrially translated proteins in testis showed reductions to <30% for MTCO1-3, misassembly of complex-IV supercomplex, and accumulated metal-binding assembly factors COX15-SFXN4. Indeed, heavy metal levels were increased for iron, molybdenum, cobalt and manganese. RT-qPCR showed compensatory downregulation only for Clpx mRNA, most accumulated proteins appeared transcriptionally upregulated. Immunoblots validated VWA8, MRPL38, MRPL18, GFM1 and OAT accumulation. Coimmunoprecipitation confirmed CLPX binding to MRPL38, GFM1 and OAT, so excess CLPX and PLP may affect their activity. Our data elucidate mechanistically the mitochondrial translation fidelity deficits, which underlie progressive hearing impairment in PRLTS3.

molecular biology↗

bioRxiv2022

Structured and disordered regions of Ataxin-2 contribute differently to the specificity and efficiency of mRNP granule formation.

Ataxin-2 (ATXN2) is a gene implicated in spinocerebellar ataxia type II (SCA2), amyotrophic lateral sclerosis (ALS) and Parkinsonism. The encoded protein is a therapeutic target for ALS and related conditions. ATXN2 (or Atx2 in insects) can function in translational activation, translational repression, mRNA stability and in the assembly of mRNP-granules, a process mediated by intrinsically disordered regions (IDRs). Previous work has shown that the LSm (Like-Sm) domain of Atx2, which can help stimulate mRNA translation, antagonizes mRNP-granule assembly. Here we advance these findings through a series of experiments on Drosophila and human Ataxin-2 proteins. Results of Targets of RNA-Binding Proteins Identified by Editing (TRIBE), co-localization and immunoprecipitation experiments indicate that a polyA-binding protein (PABP) interacting, PAM2 motif of Ataxin-2 may be a major determinant of the mRNA and protein content of Ataxin-2 mRNP granules. Transgenic experiments in Drosophila indicate that while the Atx2-LSm domain may protect against neurodegeneration, structured PAM2- and unstructured IDR- interactions both support Atx2-induced cytotoxicity. Taken together, the data lead to a proposal for how Ataxin-2 interactions are remodelled during translational control and how structured and non-structured interactions contribute differently to the specificity and efficiency of RNP granule condensation as well as to neurodegeneration.

neuroscience↗

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↗

bioRxiv2020

Huntingtin lowering reduces somatic instability at CAG-expanded loci

Expanded trinucleotide repeats cause many human diseases, including Huntingtons disease (HD). Recent studies indicate that somatic instability of these repeats contributes to pathogenesis in several expansion disorders. We find that lowering huntingtin protein (HTT) levels reduces somatic instability of both the Htt and Atxn2 CAG tracts in knockin mouse models, and the HTT CAG tract in human iPSC-derived neurons, revealing an unexpected role for HTT in regulating somatic instability.

neuroscience↗

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↗

bioRxiv2019

MISTERMINATE Mechanistically Links Mitochondrial Dysfunction with Proteostasis Failure

Mitochondrial dysfunction and proteostasis failure frequently coexist as hallmarks of neurodegenerative disease. How these pathologies are related is not well understood. Here we describe a phenomenon termed MISTERMINATE (mitochondrial stress-induced translational termination impairment and protein carboxyl terminal extension), which mechanistically links mitochondrial dysfunction with proteostasis failure. We show that mitochondrial dysfunction impairs translational termination of nuclear-encoded mitochondrial mRNAs including complex-I 30kD subunit (C-I30) mRNA, occurring on mitochondrial surface in Drosophila and mammalian cells. Ribosomes stalled at the normal stop codon continue to add to the C-terminus of C-I30 certain amino acids non-coded by mRNA template. C-terminally-extended C-I30 is toxic when assembled into C-I and forms aggregates in the cytosol. Enhancing co-translational quality control prevents C-I30 C-terminal extension and rescues mitochondrial and neuromuscular degeneration in a Parkinsons disease model. These findings emphasize the importance of efficient translation termination and reveal unexpected link between mitochondrial health and proteome homeostasis mediated by MISTERMINATE.

cell biology↗

bioRxiv2018

Bipolar multiplex families have an increased burden of common risk variants for psychiatric disorders

Multiplex families with a high prevalence of a psychiatric disorder are often examined to identify rare genetic variants with large effect sizes. In the present study, we analysed whether the risk for bipolar disorder (BD) in BD multiplex families is influenced by common genetic variants. Furthermore, we investigated whether this risk is conferred mainly by BD-specific risk variants or by variants also associated with the susceptibility to schizophrenia or major depression. In total, 395 individuals from 33 Andalusian BD multiplex families as well as 438 subjects from an independent, sporadic BD case-control cohort were analysed. Polygenic risk scores (PRS) for BD, schizophrenia, and major depression were calculated and compared between the cohorts. Both the familial BD cases and unaffected family members had significantly higher PRS for all three psychiatric disorders than the independent controls, suggesting a high baseline risk for several psychiatric disorders in the families. Moreover, familial BD cases showed significantly higher BD PRS than unaffected family members and sporadic BD cases. A plausible hypothesis is that, in multiplex families with a general increase in risk for psychiatric disease, BD development is attributable to a high burden of common variants that confer a specific risk for BD. The present analyses, therefore, demonstrated that common genetic risk variants for psychiatric disorders are likely to contribute to the high incidence of affective psychiatric disorders in the multiplex families. The PRS explained only part of the observed phenotypic variance and rare variants might have also contributed to disease development.

genetics↗

bioRxiv2018

Ataxia Telangiectasia triggers deficits in Reelin pathway

Autosomal recessive Ataxia Telangiectasia (A-T) is characterized by radiosensitivity, immunodeficiency and cerebellar neurodegeneration. A-T is caused by inactivating mutations in the Ataxia-Telangiectasia-Mutated (ATM) gene, a serine-threonine protein kinase involved in DNA-damage response and excitatory neurotransmission. The selective vulnerability of cerebellar Purkinje neurons (PN) to A-T is not well understood.\n\nEmploying global proteomic profiling of cerebrospinal fluid from patients at ages around 15 years we detected reduced Calbindin, Reelin, Cerebellin-1, Cerebellin-3, Protocadherin Fat 2, Sempahorin 7A and increased Apolipoprotein -B, -H, -J peptides. Bioinformatic enrichment was observed for pathways of chemical response, locomotion, calcium binding and complement immunity. This seemed important, since secretion of Reelin from glutamatergic afferent axons is crucial for PN radial migration and spine homeostasis. Reelin expression is downregulated by irradiation and its deficiency is a known cause of ataxia. Validation efforts in 2-month-old Atm-/- mice before onset of motor deficits confirmed transcript reductions for Reelin receptors Apoer2/Vldlr with increases for their ligands Apoe/Apoh and cholesterol 24-hydroxylase Cyp46a1. Concomitant dysregulations were found for Vglut2/Sema7a as climbing fiber markers, glutamate receptors like Grin2b and calcium homeostasis factors (Atp2b2, Calb1, Itpr1), while factors involved in DNA damage, oxidative stress, neuroinflammation and cell adhesion were normal at this stage.\n\nThese findings show that deficient levels of Reelin signaling factors reflect the neurodegeneration in A-T in a sensitive and specific way. As an extracellular factor, Reelin may be accessible for neuroprotective interventions.

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↗