Spinocerebellar Ataxia type 2 (SCA2) and Amyotrophic Lateral Sclerosis type 13 (ALS13) are triggered by polyglutamine expansion in Ataxin-2 (ATXN2). To understand these neurodegenerative disorders at the molecular level, the brains of 10-month-old Atxn2-CAG100-knockin mice were analyzed as microglial, astroglial and neuronal fractions via global RNA sequencing. Data were validated by comparison with the spinal cord oligonucleotide microarray profile or filtered by RNA-seq consistency. Here, we show that the mutation causes a massive inflammatory response in microglia and a reciprocal loss of neuronal transcripts in glial fractions, suggesting severe synapse loss. Beyond these general neurodegenerative signs, we identify pathognomonic changes in the machinery for protein translation and RNA splicing. Glial fractions showed upregulation of Gpnmb (to 2082%), Cst7, Clec7a, Axl, Csf1, Lgals3, Lgals3bp, Slc11a1, and Usp18 as an unspecific neuroinflammatory signature, versus downregulation of axonal Nefh (to <19%), and synaptic Scn4b, Camk2b, Rab15, and Grin1 mRNAs correlating with circuit disconnection. In all fractions, reductions in Kif5a, Rph3a, and Cplx1 were noted versus disease-specific inductions of ribosomal subunits, presumably mirroring the partial loss-of-function of ATXN2 as RNA translation modulator. Selective accumulations of embryonic factors Rnu1b2 and Eef1a1 versus downregulation of adult Eef1a2 specify the mutation impact on splicing and translation elongation. As a potential underpinning of toxic gain-of-function, the proteostasis transcript Rnf213 appeared increased in astroglial and microglial fractions. These transcriptome data suggest altered ribosomal and spliceosome machinery, with massive microgliosis versus mild astrogliosis, at the core of SCA2 and ALS13.

Polyglutamine expansion in Ataxin-2 (ATXN2) is responsible for rare, dominantly inherited Spinocerebellar Ataxia type 2 (SCA2). Together with its paralog Ataxin-2-like (ATXN2L), both proteins have received much interest, since the deletion of their yeast and fly orthologs alleviates TDP-43-triggered neurotoxicity in Amyotrophic Lateral Sclerosis models. Their typical structure across evolution combines LSm with LSm-Associated Domains and a PAM2 motif. To understand the physiological regulation and functions of Ataxin-2 homologs, the phylogenesis of sequences was analyzed. Human ATXN2 harbors multiple alternative start codons, e.g., from an intrinsically disordered sequence (IDR) present since armadillo, or from the polyQ sequence that arose since amphibians, or from the LSm domain since primitive eukaryotes. Multiple smaller isoforms also exist across the C-terminus. Therapeutic knockdown of polyQ expansions in human ATXN2 should selectively target exon 1B. PolyQ repeats developed repeatedly, usually framed and often interrupted by (poly)Pro, originally near PAM2. The LSmAD sequence appeared in algae as the characteristic Ataxin-2 feature with strong conservation. Frequently, Ataxin-2 has added domains, likely due to transcriptional readthrough of neighbor genes during cell stress. These chimerisms show enrichment of rRNA processing; nutrient store mobilization; membrane strengthening via lipid, protein, and glycosylated components; and cell protrusions. Thus, any mutation of Ataxin-2 has complex effects, also affecting membrane resilience.

Toxic polyglutamine (polyQ) expansions in ataxin-2 (ATXN2) trigger neurodegenerative processes, causing spinocerebellar ataxia type 2, and enhancing TAR DNA-binding protein 43-dependent pathology in amyotrophic lateral sclerosis/frontotemporal dementia. Primary disease events can be compensated transiently, delaying disease manifestation. To define potential therapy targets, here we studied how cells modify phosphoprotein signals, using preferentially affected nervous tissue from end-stage Atxn2-CAG100-Knockin mice. The spinal cord phosphoproteome revealed massive hyperphosphorylations flanking the polyQ expansion in ATXN2 and for SQSTM1 and moderate hyperphosphorylations also for amyotrophic lateral sclerosis proteins, OPTN (optineurin), UBQLN2 (ubiquilin-2), TNIP1 (TNFAIP3 interacting protein 1), and TBK1-targeted TAX1BP1. Conversely, strong hypophosphorylations of WNK1 (protein kinase with no lysine 1), SPARCL1 (secreted protein acidic and cysteine rich-like 1), and PSMD9 (proteasome 19S regulator non-ATPase assembly chaperone P27) were found. Significant enrichments of SRC-homology domain type 3-containing proteins, autophagy/endocytosis factors, and actin modulators could be explained by N-terminal, polyQ-adjacent, proline-rich motifs in ATXN2, suggesting that spinocerebellar ataxia type 2 pathogenesis is highly similar to Huntington's disease, where neurotoxicity is mediated by abnormal polyQ-proline-rich motif-SRC-homology domain type 3 interactions. Validation of protein and mRNA levels was done in mouse spinal cord and embryonic fibroblasts or patient fibroblasts after bafilomycin or arsenite treatment, observing polyQ-dependent OPTN deficiency and SQSTM1 induction impairment. Overall, this phosphoproteome profile identified and quantified the main cellular efforts in adapting autophagy pathways to the aggregation propensity of the ATXN2-N-term.

Background Polyglutamine (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. Methods We 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. Results We 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. Conclusions Overall, 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. ### Competing Interest Statement GA has received research funding from Roche Pharmaceuticals and has served as a consultant for Takeda Pharmaceuticals. The authors declare no competing interests. * A2BP1 : Ataxin-2-binding protein 1, RBFOX1 ACTB : Actin beta ALS : Amyotrophic lateral sclerosis ASD-1 : Alternative splicing defective 1, A2BP1/RBFOX1 ortholog in C. elegans ASPA : Aspartoacylase Atx2 : Ataxin-2 ortholog in C. elegans Atxn1 : Ataxin-1 ATXN2 : Ataxin-2 BMI : Body mass index BrdU : 5-bromo-2-deoxyuridine CAG : Cytosine-Adenosine-Guanine CALB1 : Calbindin 1 CC1 : Anti-adenomatous polyposis coli (APC) clone CC1 CGH-1 : Conserved germline helicase 1, DDX6 ortholog in C. elegans CNP : 2’,3’-Cyclic nucleotide 3’ phosphodiesterase DAPI : 4′,6-diamidino-2-phenylindole dbcAMP : Dibutyryl cyclic adenosine monophosphate DDX6 : DEAD-box helicase 6 Dm-20 : Shorter splice variant of Plp1 pre-mRNA that lacks exon IIIb ERGIC : Endoplasmic reticulum-Golgi intermediate compartment FDR : False discovery rate FUS : Fused in sarcoma FYN : FYN proto-oncogene, Src family tyrosine kinase GABA : Gamma-aminobutyric acid GFAP : Glial fibrillary acidic protein GLD-1 : Defective in germ line development 1, QKI ortholog in C. elegans GluA1 : Glutamate ionotropic receptor AMPA type subunit 1 GM : Gray matter GRB2 : Growth factor receptor bound protein 2 Hapln1-4 : Hyaluronan and proteoglycan link protein 1-4 IBA1 : Allograft inflammatory factor 1, AIF1 Ina : Internexin neuronal intermediate filament alpha KH : K-homology domain Ki67 : Marker of proliferation Ki-67 KIN : Knock-in KO : Knock-out LC : Liquid chromatography LSm : Like-SM RNA binding domain LSmAD : LSm-associated domain MAG : Myelin associated glycoprotein Mal : Myelin and lymphocyte protein MAP-Tau : Microtubule associated protein Tau MBP : Myelin Basic Protein Mobp : Myelin-associated oligodendrocyte basic protein MOG : Myelin oligodendrocyte glycoprotein MS : Mass spectroscopy MSA : Multiple system atrophy mTOR : Mechanistic target of rapamycin NAA : N-acetylaspartate NaAsO2 : Sodium arsenite NAT8L : N-acetyltransferase 8 like NEFH-M-L : Neurofilament heavy-medium-light chain NG2 : Chondroitin sulfate proteoglycan 4, CSPG4 NgR1 : Nogo (Reticulon 4) receptor 1 Nogo-A : Reticulon 4, RTN4 NOTCH1 : Notch receptor 1 NPTN : Neuroplastin OL : Oligodendroglial lineage OLIG2 : Oligodendrocyte transcription factor 2 OPC : Oligodendrocyte precursor cell Pab1 : Poly(A) binding protein, PABP ortholog in S. cerevisiae PABP : Poly(A)-binding protein PAM2 : PABP-interacting motif 2 Pbp1 : Pab1-binding protein, ATXN2 ortholog in S. cerevisiae Pcp2 : Purkinje cell protein 2 PDGFR⍺ : Platelet derived growth factor receptor alpha PLP1 : Proteolipid protein 1 polyQ : Poly-glutamine Q : Glutamine QKI : Quaking RBFOX1 : RNA binding Fox-1 homolog 1, A2BP1 RBP : RNA-binding protein RT : Room temperature RT-PCR : Reverse transcription PCR Rtn4 : Reticulon-4 / Nogo SAM68 : KH RNA binding domain containing, signal transduction associated 1 SCA2 : Spinocerebellar ataxia type 2 SG : Stress granule SH3 : SRC homology 3 domain SNCA : Synuclein alpha SRC : Protooncogene SRC, Rous sarcoma STAR : Signal transduction and activation of RNA family of proteins TBP : TATA-Box binding protein TDP-43 : TAR DNA binding protein TEM : Transmission electron microscopy Tg : Transgenic TUBA4A : Tubulin alpha 4a UTR : Untranslated region WM : White matter WT : Wild type Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64 Max Planck Society, https://ror.org/01hhn8329 Health Holland, https://ror.org/056cwr036

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 perinuclear, 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.

Spinocerebellar 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 biomarkers for SCA2. The aim of this study was to define novel molecular biomarker candidates for SCA2. Using cerebellar and cervicothoracic spinal cord RNA/protein from Atxn2-CAG100-KnockIn (KIN) and wildtype mice, a multi-omics study was conducted based on the integration of global transcriptomic, proteomic, and phosphoproteomic data, followed by validation in mice and humans. Venn 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 KIN 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 early-stage SCA2 patients, and displayed a significant association with the CAG repeat length at expanded ATXN2 alleles, the age at onset and INAS count. However, these human data from this SCA2 founder population were not robust, so reappraisal in large international studies and at later disease stages of SCA2 is needed. SERPINB1 was identified as novel candidate progression biomarker for SCA2 pathomechanisms.

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 / endo-cytosis factors, and actin modulators could be explained by N-terminal, polyQ-adjacent, pro-line-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. ### Competing Interest Statement The authors have declared no competing interest.

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited neurodegenerative disease, which belongs to the trinucleotide repeat disease group with a CAG repeat expansion in exon 1 of the ATXN2 gene resulting in an ataxin-2 protein with an expanded polyglutamine (polyQ)-stretch. The disease is late manifesting leading to early death. Today, therapeutic interventions to cure the disease or even to decelerate disease progression are not available yet. Furthermore, primary readout parameter for disease progression and therapeutic intervention studies are limited. Thus, there is an urgent need for quantifiable molecular biomarkers such as ataxin-2 becoming even more important due to numerous potential protein-lowering therapeutic intervention strategies. The aim of this study was to establish a sensitive technique to measure the amount of soluble polyQ-expanded ataxin-2 in human biofluids to evaluate ataxin-2 protein levels as prognostic and/or therapeutic biomarker in SCA2. Time-resolved fluorescence energy transfer (TR-FRET) was used to establish a polyQ-expanded ataxin-2-specific immunoassay. Two different ataxin-2 antibodies and two different polyQ-binding antibodies were validated in three different concentrations and tested in cellular and animal tissue as well as in human cell lines, comparing different buffer conditions to evaluate the best assay conditions. We established a TR-FRET-based immunoassay for soluble polyQ-expanded ataxin-2 and validated measurements in human cell lines including iPSC-derived cortical neurons. Additionally, our immunoassay was sensitive enough to monitor small ataxin-2 expression changes by siRNA or starvation treatment. We successfully established the first sensitive ataxin-2 immunoassay to measure specifically soluble polyQ-expanded ataxin-2 in human biomaterials.

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 of a few scaffold proteins that make up these phases, but how the partitioning of hundreds of SG proteins is regulated remains largely unresolved. While investigating the rules that govern the condensation of ataxin-2, an SG protein implicated in neurodegenerative disease, we unexpectedly identified a short 14 aa sequence that acts as a 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 an unexpected molecular function for ancient poly(A)-binding proteins as regulators of biomolecular condensate proteins. These findings may inspire approaches to therapeutically target aberrant phases in disease.

Abstract Background Spinocerebellar Ataxia Type 2 (SCA2) belongs to a group of neurodegenerative diseases, inherited as an autosomal dominant trait. SCA2 is a trinucleotide repeat disease with a CAG repeat expansion in exon 1 of the ATXN2gene resulting in an ataxin-2 protein with an expanded polyglutamine (polyQ)-stretch. The disease is late manifesting leading to premature death. Today, therapeutic interventions to cure the disease or even to decelerate disease progression are not available yet. Furthermore, primary readout parameter for disease progression and therapeutic intervention studies are limited. Thus, there is an urgent need for quantifiable molecular biomarkers such as ataxin-2 becoming even more important due to numerous potential protein reducing therapeutic intervention strategies. Objective Aim of this study was to establish a sensitive technique to measure the amount of polyQ-expanded ataxin-2 in human biofluids to evaluate ataxin-2 protein levels as prognostic and/ -or therapeutic biomarker in SCA2. Methods Time-Resolved Fluorescence Energy Transfer (TR-FRET) was used to establish a polyQ-expanded ataxin-2-specific immunoassay. Two different ataxin-2 antibodies and two different polyQ-binding antibodies were validated in three different concentrations and tested in cellular and animal tissue as well as in human cell lines, comparing different buffer conditions as well as total protein concentrations to evaluate the best assay conditions. Results We established a TR-FRET-based immunoassay for polyQ-expanded ataxin-2 and validated measurements in human cell lines including primary skin fibroblasts, induced pluripotent stem cells (iPSCs) and iPSC-derived cortical neurons. Additionally, our immunoassay was sensitive enough to monitor small ataxin-2 expression changes by siRNA or starvation treatment. Conclusion We successfully established the first sensitive ataxin-2 immunoassay to measure specifically polyQ-expanded ataxin-2 in human biomaterials.

The genetic and epidemiological features of hereditary ataxias have been reported in several populations; however, Turkey is still unexplored. Due to high consanguinity, recessive ataxias are more common in Turkey than in Western European populations.

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.

Spinocerebellar ataxia type 2 (SCA2) is caused by polyglutamine expansion in Ataxin-2 (ATXN2). This factor binds RNA/proteins to modify metabolism after stress, and to control calcium (Ca2+) homeostasis after stimuli. Cerebellar ataxias and corticospinal motor neuron degeneration are determined by gain/loss in ATXN2 function, so we aimed to identify key molecules in this atrophic process, as potential disease progression markers. Our Atxn2-CAG100-Knock-In mouse faithfully models features observed in patients at pre-onset, early and terminal stages. Here, its cerebellar global RNA profiling revealed downregulation of signaling cascades to precede motor deficits. Validation work at mRNA/protein level defined alterations that were independent of constant physiological ATXN2 functions, but specific for RNA/aggregation toxicity, and progressive across the short lifespan. The earliest changes were detected at three months among Ca2+ channels/transporters (Itpr1, Ryr3, Atp2a2, Atp2a3, Trpc3), IP3 metabolism (Plcg1, Inpp5a, Itpka), and Ca2+-Calmodulin dependent kinases (Camk2a, Camk4). CaMKIV–Sam68 control over alternative splicing of Nrxn1, an adhesion component of glutamatergic synapses between granule and Purkinje neurons, was found to be affected. Systematic screening of pre/post-synapse components, with dendrite morphology assessment, suggested early impairment of CamKIIα abundance together with the weakening of parallel fiber connectivity. These data reveal molecular changes due to ATXN2 pathology, primarily impacting excitability and communication.

The last decade has proven that amyotrophic lateral sclerosis (ALS) is clinically and genetically heterogeneous, and that the genetic component in sporadic cases might be stronger than expected. This study investigates 1,200 patients to revisit ALS in the ethnically heterogeneous yet inbred Turkish population. Familial ALS (fALS) accounts for 20% of our cases. The rates of consanguinity are 30% in fALS and 23% in sporadic ALS (sALS). Major ALS genes explained the disease cause in only 35% of fALS, as compared with ~70% in Europe and North America. Whole exome sequencing resulted in a discovery rate of 42% (53/127). Whole genome analyses in 623 sALS cases and 142 population controls, sequenced within Project MinE, revealed well-established fALS gene variants, solidifying the concept of incomplete penetrance in ALS. Genome-wide association studies (GWAS) with whole genome sequencing data did not indicate a new risk locus. Coupling GWAS with a coexpression network of disease-associated candidates, points to a significant enrichment for cell cycle- and division-related genes. Within this network, literature text-mining highlights DECR1, ATL1, HDAC2, GEMIN4, and HNRNPA3 as important genes. Finally, information on ALS-related gene variants in the Turkish cohort sequenced within Project MinE was compiled in the GeNDAL variant browser (www.gendal.org).

Depletion of yeast/fly Ataxin-2 rescues TDP-43 overexpression toxicity. In mouse models of Amyotrophic Lateral Sclerosis via TDP-43 overexpression, depletion of its ortholog ATXN2 mitigated motor neuron degeneration and extended lifespan from 25 days to >300 days. There is another ortholog in mammals, named ATXN2L (Ataxin-2-like), which is almost uncharacterized but also functions in RNA surveillance at stress granules. We generated mice with Crispr/Cas9-mediated deletion of Atxn2l exons 5-8, studying homozygotes prenatally and heterozygotes during aging. Our novel findings indicate that ATXN2L absence triggers mid-gestational embryonic lethality, affecting female animals more strongly. Weight and development stages of homozygous mutants were reduced. Placenta phenotypes were not apparent, but brain histology showed lamination defects and apoptosis. Aged heterozygotes showed no locomotor deficits or weight loss over 12 months. Null mutants in vivo displayed compensatory efforts to maximize Atxn2l expression, which were prevented upon nutrient abundance in vitro. Mouse embryonal fibroblast cells revealed more multinucleated giant cells upon ATXN2L deficiency. In addition, in human neural cells, transcript levels of ATXN2L were induced upon starvation and glucose and amino acids exposure, but this induction was partially prevented by serum or low cholesterol administration. Neither ATXN2L depletion triggered dysregulation of ATXN2, nor a converse effect was observed. Overall, this essential role of ATXN2L for embryogenesis raises questions about its role in neurodegenerative diseases and neuroprotective therapies.

Iron deprivation activates mitophagy and extends lifespan in nematodes. In patients suffering from Parkinson's disease (PD), PINK1-PRKN mutations via deficient mitophagy trigger iron accumulation and reduce lifespan. To evaluate molecular effects of iron chelator drugs as a potential PD therapy, we assessed fibroblasts by global proteome profiles and targeted transcript analyses. In mouse cells, iron shortage decreased protein abundance for iron-binding nucleotide metabolism enzymes (prominently XDH and ferritin homolog RRM2). It also decreased the expression of factors with a role for nucleotide surveillance, which associate with iron-sulfur-clusters (ISC), and are important for growth and survival. This widespread effect included prominently Nthl1-Ppat-Bdh2, but also mitochondrial Glrx5-Nfu1-Bola1, cytosolic Aco1-Abce1-Tyw5, and nuclear Dna2-Elp3-Pold1-Prim2. Incidentally, upregulated Pink1-Prkn levels explained mitophagy induction, the downregulated expression of Slc25a28 suggested it to function in iron export. The impact of PINK1 mutations in mouse and patient cells was pronounced only after iron overload, causing hyperreactive expression of ribosomal surveillance factor Abce1 and of ferritin, despite ferritin translation being repressed by IRP1. This misregulation might be explained by the deficiency of the ISC-biogenesis factor GLRX5. Our systematic survey suggests mitochondrial ISC-biogenesis and post-transcriptional iron regulation to be important in the decision, whether organisms undergo PD pathogenesis or healthy aging.

Hereditary Parkinson’s disease (PD) can be triggered by an autosomal dominant overdose of alpha-Synuclein (SNCA) as stressor or the autosomal recessive deficiency of PINK1 Serine/Threonine-phosphorylation activity as stress-response. We demonstrated the combination of PINK1-knockout with overexpression of SNCAA53T in double mutant (DM) mice to exacerbate locomotor deficits and to reduce lifespan. To survey posttranslational modifications of proteins underlying the pathology, brain hemispheres of old DM mice underwent quantitative label-free global proteomic mass spectrometry, focused on Ser/Thr-phosphorylations. As an exceptionally strong effect, we detected >300-fold reductions of phosphoThr1928 in MAP1B, a microtubule-associated protein, and a similar reduction of phosphoSer3781 in ANK2, an interactor of microtubules. MAP1B depletion is known to trigger perturbations of microtubular mitochondria trafficking, neurite extension, and synaptic function, so it was noteworthy that relevantly decreased phosphorylation was also detected for other microtubule and microfilament factors, namely MAP2S1801, MARK1S394, MAP1AT1794, KIF1AS1537, 4.1NS541, 4.1GS86, and ADD2S528. While the MAP1B heavy chain supports regeneration and growth cones, its light chain assists DAPK1-mediated autophagy. Interestingly, relevant phosphorylation decreases of DAPK2S299, VPS13DS2429, and VPS13CS2480 in the DM brain affected regulators of autophagy, which are implicated in PD. Overall, significant downregulations were enriched for PFAM C2 domains, other kinases, and synaptic transmission factors upon automated bioinformatics, while upregulations were not enriched for selective motifs or pathways. Validation experiments confirmed the change of LC3 processing as reflection of excessive autophagy in DM brain, and dependence of ANK2/MAP1B expression on PINK1 levels. Our new data provide independent confirmation in a mouse model with combined PARK1/PARK4/PARK6 pathology that MAP1B/ANK2 phosphorylation events are implicated in Parkinsonian neurodegeneration. These findings expand on previous observations in Drosophila melanogaster that the MAP1B ortholog futsch in the presynapse is a primary target of the PARK8 protein LRRK2, and on a report that MAP1B is a component of the pathological Lewy body aggregates in PD patient brains. Similarly, ANK2 gene locus variants are associated with the risk of PD, ANK2 interacts with PINK1/Parkin-target proteins such as MIRO1 or ATP1A2, and ANK2-derived peptides are potent inhibitors of autophagy.

Ataxin-2 (human gene symbol ATXN2) acts during stress responses, modulating mRNA translation and nutrient metabolism. Ataxin-2 knockout mice exhibit progressive obesity, dyslipidemia, and insulin resistance. Conversely, the progressive ATXN2 gain of function due to the fact of polyglutamine (polyQ) expansions leads to a dominantly inherited neurodegenerative process named spinocerebellar ataxia type 2 (SCA2) with early adipose tissue loss and late muscle atrophy. We tried to understand lipid dysregulation in a SCA2 patient brain and in an authentic mouse model. Thin layer chromatography of a patient cerebellum was compared to the lipid metabolome of Atxn2-CAG100-Knockin (KIN) mouse spinocerebellar tissue. The human pathology caused deficits of sulfatide, galactosylceramide, cholesterol, C22/24-sphingomyelin, and gangliosides GM1a/GD1b despite quite normal levels of C18-sphingomyelin. Cerebellum and spinal cord from the KIN mouse showed a consistent decrease of various ceramides with a significant elevation of sphingosine in the more severely affected spinal cord. Deficiency of C24/26-sphingomyelins contrasted with excess C18/20-sphingomyelin. Spinocerebellar expression profiling revealed consistent reductions of CERS protein isoforms, Sptlc2 and Smpd3, but upregulation of Cers2 mRNA, as prominent anomalies in the ceramide–sphingosine metabolism. Reduction of Asah2 mRNA correlated to deficient S1P levels. In addition, downregulations for the elongase Elovl1, Elovl4, Elovl5 mRNAs and ELOVL4 protein explain the deficit of very long-chain sphingomyelin. Reduced ASMase protein levels correlated to the accumulation of long-chain sphingomyelin. Overall, a deficit of myelin lipids was prominent in SCA2 nervous tissue at prefinal stage and not compensated by transcriptional adaptation of several metabolic enzymes. Myelination is controlled by mTORC1 signals; thus, our human and murine observations are in agreement with the known role of ATXN2 yeast, nematode, and mouse orthologs as mTORC1 inhibitors and autophagy promoters.

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disorder caused by CAG-expansion mutations in the ATXN2 gene, mainly affecting motor neurons in the spinal cord and Purkinje neurons in the cerebellum. While the large expansions were shown to cause SCA2, the intermediate length expansions lead to increased risk for several atrophic processes including amyotrophic lateral sclerosis and Parkinson variants, e.g. progressive supranuclear palsy. Intense efforts to pioneer a neuroprotective therapy for SCA2 require longitudinal monitoring of patients and identification of crucial molecular pathways. The ataxin-2 (ATXN2) protein is mainly involved in RNA translation control and regulation of nutrient metabolism during stress periods. The preferential mRNA targets of ATXN2 are yet to be determined. In order to understand the molecular disease mechanism throughout different prognostic stages, we generated an Atxn2-CAG100-knock-in (KIN) mouse model of SCA2 with intact murine ATXN2 expression regulation. Its characterization revealed somatic mosaicism of the expansion, with shortened lifespan, a progressive spatio-temporal pattern of pathology with subsequent phenotypes, and anomalies of brain metabolites such as N-acetylaspartate (NAA), all of which mirror faithfully the findings in SCA2 patients. Novel molecular analyses from stages before the onset of motor deficits revealed a strong selective effect of ATXN2 on Nat8l mRNA which encodes the enzyme responsible for NAA synthesis. This metabolite is a prominent energy store of the brain and a well-established marker for neuronal health. Overall, we present a novel authentic rodent model of SCA2, where in vivo magnetic resonance imaging was feasible to monitor progression and where the definition of earliest transcriptional abnormalities was possible. We believe that this model will not only reveal crucial insights regarding the pathomechanism of SCA2 and other ATXN2-associated disorders, but will also aid in developing gene-targeted therapies and disease prevention.