Failure of DNA double-strand break repair by tau mediates Alzheimer’s disease pathology in vitro

DNA double-strand break (DSB) is the most severe form of DNA damage and accumulates with age, in which cytoskeletal proteins are polymerized to repair DSB in dividing cells. Since tau is a microtubule-associated protein, we investigate whether DSB is involved in tau pathologies in Alzheimer’s disease (AD). First, immunohistochemistry reveals the frequent coexistence of DSB and phosphorylated tau in the cortex of AD patients. In vitro studies using primary mouse cortical neurons show that non-p-tau accumulates perinuclearly together with the tubulin after DSB induction with etoposide, followed by the accumulation of phosphorylated tau. Moreover, the knockdown of endogenous tau exacerbates DSB in neurons, suggesting the protective role of tau on DNA repair. Interestingly, synergistic exposure of neurons to microtubule disassembly and the DSB strikingly augments aberrant p-tau aggregation and apoptosis. These data suggest that DSB plays a pivotal role in AD-tau pathology and that the failure of DSB repair leads to tauopathy

Elimination of TDP-43 inclusions linked to amyotrophic lateral sclerosis by a misfolding-specific intrabody with dual proteolytic signals.

Aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) is implicated in the pathogenesis of sporadic and certain familial forms of amyotrophic lateral sclerosis (ALS), suggesting elimination of TDP-43 aggregates as a possible therapeutic strategy. Here we generated and investigated a single-chain variable fragment (scFv) derived from the 3B12A monoclonal antibody (MAb) that recognises D247 of the TDP-43 nuclear export signal, an epitope masked in the physiological state. In transfected HEK293A cells, 3B12A scFv recapitulated the affinity of the full-length MAb to mislocalised TDP-43 with a defective nuclear localising signal and to a TDP-43 inclusion mimic with cysteine-to-serine substitution at RRM1. Moreover, 3B12A scFv accelerated proteasome-mediated degradation of aggregated TDP-43, likely due to an endogenous PEST-like proteolytic signal sequence in the VH domain CDR2 region. Addition of the chaperone-mediated autophagy (CMA)-related signal to 3B12A scFv induced HSP70 transcription, further enhancing TDP-43 aggregate clearance and cell viability. The 3B12A scFv also reduced TDP-43 aggregates in embryonic mouse brain following in utero electroporation while causing no overt postnatal brain pathology or developmental anomalies. These results suggest that a misfolding-specific intrabody prone to synergistic proteolysis by proteasomal and autophagic pathways is a promising strategy for mitigation of TDP-43 proteinopathy in ALS.筋萎縮性側索硬化症の異常凝集体を除去する治療抗体の開発に成功-ALS の根治治療への道を開く -滋賀医科大学プレスリリース. 2018-05-3

CUL2-mediated clearance of misfolded TDP-43 is paradoxically affected by VHL in oligodendrocytes in ALS

The molecular machinery responsible for cytosolic accumulation of misfolded TDP-43 in amyotrophic lateral sclerosis (ALS) remains elusive. Here we identified a cullin-2 (CUL2) RING complex as a novel ubiquitin ligase for fragmented forms of TDP-43. The von Hippel Lindau protein (VHL), a substrate binding component of the complex, preferentially recognized misfolded TDP-43 at Glu246 in RNA-recognition motif 2. Recombinant full-length TDP-43 was structurally fragile and readily cleaved, suggesting that misfolded TDP-43 is cleared by VHL/CUL2 in a step-wise manner via fragmentation. Surprisingly, excess VHL stabilized and led to inclusion formation of TDP-43, as well as mutant SOD1, at the juxtanuclear protein quality control center. Moreover, TDP-43 knockdown elevated VHL expression in cultured cells, implying an aberrant interaction between VHL and mislocalized TDP-43 in ALS. Finally, cytoplasmic inclusions especially in oligodendrocytes in ALS spinal cords were immunoreactive to both phosphorylated TDP-43 and VHL. Thus, our results suggest that an imbalance in VHL and CUL2 may underlie oligodendrocyte dysfunction in ALS, and highlight CUL2 E3 ligase emerges as a novel therapeutic potential for ALS

Conformational change of RNA-helicase DHX30 by ALS/FTD-linked FUS induces mitochondrial dysfunction and cytosolic aggregates.

Genetic mutations in fused in sarcoma (FUS) cause amyotrophic lateral sclerosis (ALS). Although mitochondrial dysfunction and stress granule have been crucially implicated in FUS proteinopathy, the molecular basis remains unclear. Here, we show that DHX30, a component of mitochondrial RNA granules required for mitochondrial ribosome assembly, interacts with FUS, and plays a crucial role in ALS-FUS. WT FUS did not affect mitochondrial localization of DHX30, but the mutant FUS lowered the signal of mitochondrial DHX30 and promoted the colocalization of cytosolic FUS aggregates and stress granule markers. The immunohistochemistry of the spinal cord from an ALS-FUS patient also confirmed the colocalization, and the immunoelectron microscope demonstrated decreased mitochondrial DHX30 signal in the spinal motor neurons. Subcellular fractionation by the detergent-solubility and density-gradient ultracentrifugation revealed that mutant FUS also promoted cytosolic mislocalization of DHX30 and aggregate formation. Interestingly, the mutant FUS disrupted the DHX30 conformation with aberrant disulfide formation, leading to impaired mitochondrial translation. Moreover, blue-native gel electrophoresis revealed an OXPHOS assembly defect caused by the FUS mutant, which was similar to that caused by DHX30 knockdown. Collectively, our study proposes DHX30 as a pivotal molecule in which disulfide-mediated conformational change mediates mitochondrial dysfunction and cytosolic aggregate formation in ALS-FUS

Conserved acidic amino acid residues in a second RNA recognition motif regulate assembly and function of TDP-43.

Accumulating evidence suggests that pathogenic TAR DNA-binding protein (TDP)-43 fragments contain a partial RNA-recognition motif domain 2 (RRM2) in amyotrophic lateral sclerosis (ALS)/frontotemporal lobar degeneration. However, the molecular basis for how this domain links to the conformation and function of TDP-43 is unclear. Previous crystal analyses have documented that the RRM2-DNA complex dimerizes under acidic and high salt conditions, mediated by the intermolecular hydrogen bonds of Glu246-Ile249 and Asp247-Asp247. The aims of this study were to investigate the roles of Glu246 and Asp247 in the molecular assembly of RRM2 under physiological conditions, and to evaluate their potential use as markers for TDP-43 misfolding due to the aberrantly exposed dimer interface. Unexpectedly, gel filtration analyses showed that, regardless of DNA interaction, the RRM2 domain remained as a stable monomer in phosphate-buffered saline. Studies using substitution mutants revealed that Glu246 and, especially, Asp247 played a crucial role in preserving the functional RRM2 monomers. Substitution to glycine at Glu246 or Asp247 induced the formation of fibrillar oligomers of RRM2 accompanied by the loss of DNA-binding affinity, which also affected the conformation and the RNA splicing function of full-length TDP-43. A novel monoclonal antibody against peptides containing Asp247 was found to react with TDP-43 inclusions of ALS patients and mislocalized cytosolic TDP-43 in cultured cells, but not with nuclear wild-type TDP-43. Our findings indicate that Glu246 and Asp247 play pivotal roles in the proper conformation and function of TDP-43. In particular, Asp247 should be studied as a molecular target with an aberrant conformation related to TDP-43 proteinopathy

CUL2-mediated clearance of misfolded TDP-43 is paradoxically affected by VHL in oligodendrocytes in ALS.

神経難病・筋萎縮性側索硬化症の病原蛋白質を分解する新たな仕組みを発見 －ALSの新たな病態の発見と分子標的治療の可能性を開く－. 京都大学プレスリリース. 2016-01-12.The molecular machinery responsible for cytosolic accumulation of misfolded TDP-43 in amyotrophic lateral sclerosis (ALS) remains elusive. Here we identified a cullin-2 (CUL2) RING complex as a novel ubiquitin ligase for fragmented forms of TDP-43. The von Hippel Lindau protein (VHL), a substrate binding component of the complex, preferentially recognized misfolded TDP-43 at Glu246 in RNA-recognition motif 2. Recombinant full-length TDP-43 was structurally fragile and readily cleaved, suggesting that misfolded TDP-43 is cleared by VHL/CUL2 in a step-wise manner via fragmentation. Surprisingly, excess VHL stabilized and led to inclusion formation of TDP-43, as well as mutant SOD1, at the juxtanuclear protein quality control center. Moreover, TDP-43 knockdown elevated VHL expression in cultured cells, implying an aberrant interaction between VHL and mislocalized TDP-43 in ALS. Finally, cytoplasmic inclusions especially in oligodendrocytes in ALS spinal cords were immunoreactive to both phosphorylated TDP-43 and VHL. Thus, our results suggest that an imbalance in VHL and CUL2 may underlie oligodendrocyte dysfunction in ALS, and highlight CUL2 E3 ligase emerges as a novel therapeutic potential for ALS

3B12A recognizes cytosol-redistributed TDP-43.

<p><b>A–D</b>, SHSY-5Y cells were transiently transfected with TDP-43-EGFP of wild type (WT), mutants with defective NLS (mNLS), or deletion mutant of RRM2 deletion (ΔRRM2) (EGFP shown as green). At 48 h after transfection, cells were fixed and stained with 3B12A (red). DAPI was used for counterstaining (blue). <b>A. a–f</b>, Transfected or endogenous WT TDP-43 was rarely stained by 3B12A (unfilled arrowheads). Occasionally, cells with very high fluorescence were labeled (arrowhead). <b>B.</b> Cytosolic redistributed TDP-43 (mNLS) was preferentially stained by 3B12A (arrowheads). 3B12A recognized the mNLS mutant of TDP-43-EGFP even at moderate expression levels, regardless of aggregate formation. <b>c–e</b> are high power fields of <b>a–b</b>. <b>C.</b> Nuclear-excluded WT TDP-43 is recognized by 3B12A. WT TDP-43-EGFP expressing SHSY-5Y cells exposed to 5 µM lactacystin were fixed and stained with 3B12A (arrowheads). <b>D.</b> No reactivity of 3B12A to TDP-43-EGFP devoid of RRM2 (ΔRRM2) (unfilled arrowheads). <b>E.</b> Immunoprecipitation experiment showing that 3B12A preferentially recognized NLS-defective TDP-43 in cell lysates. HEK293A cells were transiently transfected with WT, mNLS, or FALS mutant (A315T and Q331K) forms of TDP-43-FLAG. Total lysates were immunoprecipitated with the 3B12A. Western blot analysis using a rabbit polyclonal anti-FLAG antibody showed that 3B12A predominantly recognized the defective NLS, but more weakly recognized the WT and FALS-linked mutant forms of TDP-43.</p

Pivotal role of Glu246 and Asp247 in the conformation of the RRM2 domain of TDP-43.

<p><b>A. a,</b> Scheme showing the alignment of RRM2 subdomains (residues 232–270 in human TDP-43) in multiple species. Glu246 (E246) and Asp247 (D247) are preserved across all species. <b>b,</b> Chemical properties of amino acid substitution mutants of E246 or D247. E246Q and D247N were used to create substitution mutants with minimal alteration of side chains. E246G and D247G were designed so that the effects of the side chains were eliminated, and the flexibility of the amide bonds was increased. <b>B.</b> Western blot analysis of recombinant RRM2 proteins of wild-type (WT), E246Q/D247N (QN), and E246G/D247G (GG), using an anti-TDP-43 rabbit polyclonal antibody that recognizes the RRM2 domain (Proteintech). The E246G/D247G mutant RRM2 showed marked oligomerization even when incubated at 4°C (vertical line). Note that considerable RRM2 dimers or oligomers were dissociated into monomers in the presence of DTT. Arrowhead and double arrowheads indicate RRM2 monomer and dimers, respectively. Asterisk possibly indicates heat-related high molecular complexes comprising RRM2 domain. <b>C.</b> Thioflavin T (ThT) fluorescence assay showing amyloid fibril formation of RRM2 with mutations in E246 and D247. Each value indicates averaged RFU of ThT with standard error of mean from triplicates. *<i>p</i><0.01 vs. RRM2 WT at RT by one-way ANOVA with Newman-Keuls test. <b>D.</b> Superdex 75 size exclusion chromatography of recombinant RRM2 domain of WT (<b>a</b>), E246Q/D247N (QN, <b>b</b>), and E246G/D247G (GG, <b>c</b>). <b>a</b>, WT RRM2 alone was exclusively monomeric in its native condition (unfilled circle). Heat denaturation at 70°C for 10 min induced higher molecular assembly (filled circle). Arrowhead indicates the RRM2 oligomer. <b>b</b>, E246Q/D247N (QN) mutant RRM2 without stress was predominantly monomeric (unfilled circle). Heat denaturation markedly increased the ratio of oligomers to monomers (filled circle). <b>c,</b> E246G/D247G (GG) mutant existed as a mixture of monomer and oligomers at the baseline condition (unfilled circle). Higher molecular species were prominently induced by heat denaturation (filled circle). Molecular size markers are as follows: bovine serum albumin (66 kDa), ovalbumin (43 kDa), copper zinc superoxide dismutase (32 kDa), myoglobin (17.6 kDa), and aprotinin (6.5 kDa).</p

Substitution mutants of full-length TDP-43 at E246 and D247 are readily misfolded.

<p><b>A.</b> Confocal micrographs of HEK293A cells overexpressing EGFP-fused full-length TDP-43 (<b>a, b,</b> wild-type (WT), <b>c, d,</b> E246G, <b>e, f,</b> D247G, <b>g, h,</b> E246G/D247G). <b>i, j,</b> Percentages of transfected HEK293A cells harboring multiple puncta or inclusions (<b>i</b>, arrowheads) or displaying nucleus-excluded TDP-43 (unfilled arrowhead). (<b>j</b>). Scale bar indicates 30 µm. Data were expressed as the mean ± SEM (N = 7–10). *<i>p</i><0.05 vs. WT, #<i>p</i><0.05 vs. E246G by one-way ANOVA with Newman-Keuls test. NS indicates not significant vs. WT. <b>B. a,</b> Western blotting showing the increased detergent-insolubility of TDP-43 with mutations at E246/D247, with defective nucleus localizing signal (mNLS), or devoid of RRM2 domain (ΔRRM2). Lysates from HEK293A cells transiently transfected with TDP-43-EGFP were separated into 1% TritonX100-soluble or -insoluble fractions. Top panel, anti-GFP; middle panel, anti-actin; bottom panel, anti-GAPDH. The GAPDH blot validates the successful separation between detergent-soluble and -insoluble components. <b>b,</b> Quantified insolubility of TDP-43-EGFP proteins with or without mutation at E246/D247 to glycine. Relative TDP-43-EGFP in the detergent-soluble or -insoluble fraction was obtained from the ratio of the GFP density to actin density from the densitometric value in each fraction (designated as insoluble TDP or soluble TDP, respectively). Insolubility index was obtained from the ratio of insoluble TDP to soluble TDP, and each value was standardized by the average ratio of WT. Data were expressed as the mean ± SEM of four experiments.*<i>p</i><0.05 vs. WT TDP-43-EGFP by one-way ANOVA with Newman-Keuls test. <b>C.</b> Size exclusion chromatography and Western blotting indicating the existence of oligomeric and monomeric states of full-length TDP-43 in cells. WT and E246G/D247G (GG) TDP-43-FLAG genes were expressed in HEK293A cells. Cells were sonicated in PBS, and the supernatants were fractionated by a Superose 12 column (10/300) at a flow rate of 0.5 mL/min in PBS. Fractionated cell extracts were applied to Western blotting by anti-TDP-43 (Proteintech). Mutant TDP-43 (GG) proteins were collected in a larger fraction than 88–440 kDa. The molecular size markers thyroglobulin (669 kDa), ferritin (440 kDa), Mn-SOD (88 kDa), ovalbumin (43 kDa), and RNase (13.7 kDa) were eluted under the same conditions. Abs280 is presented to show the equal amount of proteins between WT and the GG mutant in each fraction.</p

Oligomerization affects the nucleotide interaction and RNA splicing efficiency of TDP-43.

<p><b>A.</b> Exon 9 skipping assay showing that mutations at E246 and D247 affect the RNA splicing activity of full-length TDP-43. <b>a</b>, Agarose gel electrophoresis of PCR products (top). Western blot analysis of the total cell lysates using anti-EGFP (middle) and -actin (bottom) antibodies was also shown. <b>b</b>, Quantification of spliced and unspliced fragments using densitometry. Each value is the ratio of spliced to unspliced PCR products. Data is mean ± standard error of mean from triplicates. *<i>p</i><0.01 vs. Wild-type (WT) TDP-43 by one-way ANOVA with Newman-Keuls test. <b>B.</b> Size exclusion chromatography for recombinant RRM2 proteins of WT (a), or mutants with E246Q/D247N (QN, b) or E246G/D247G (GG, c), and for (TG)12 oligonucleotides. Mixtures of RRM2 mutants and (TG)12 oligonucleotides were centrifuged at 15,000× g for 20 min and subjected to a Superdex75 (10/300) column at a flow rate of 0.5 mL/min in PBS. Only the RRM2 monomer showed a molecular shift with the (TG)12 oligonucleotides to a single peak, indicating their association (arrowheads). Molecular size markers are as follows: bovine serum albumin (66 kDa), ovalbumin (43 kDa), superoxide dismutase 1 (32 kDa), myoglobin (17.6 kDa), and aprotinin (6.5 kDa). *1 indicates free monomeric RRM2, *2 indicates oligomeric RRM2. Note that there is no peak for free (TG)12, indicating all the (TG)₁₂ was bound to RRM2 monomers.</p