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Revised

The identification of high-performing antibodies for TDP-43 for use in Western Blot, immunoprecipitation and immunofluorescence

[version 2; peer review: 2 approved]
PUBLISHED 20 Jun 2023
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This article is included in the Cell & Molecular Biology gateway.

This article is included in the YCharOS (Antibody Characterization through Open Science) gateway.

Abstract

TAR DNA-binding protein 43 (TDP-43) is a DNA/RNA binding protein playing a critical role in the regulation of transcription, splicing and RNA stability. Mutations in TARDBP leading to aggregation, are suspected to be a characteristic feature of various neurogenerative diseases. The lack of well-characterized anti- TDP-43 antibodies acts as a barrier to establish reproducible TDP-43 research. In this study, we characterized eighteen TDP-43 commercial antibodies for Western blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. We identified many well-performing antibodies and encourage readers to use this report as a guide to select the most appropriate antibody for their specific needs.

Keywords

Uniprot ID Q13148, TARDBP, TDP-43, antibody characterization, antibody validation, Western Blot, immunoprecipitation, immunofluorescence

Revised Amendments from Version 1

In this new version of the article, we have added the DOI to references 9,12 and 13. This is to make it easier for readers to access the citations. Thank you.

See the authors' detailed response to the review by Makoto Urushitani

Introduction

TDP-43, encoded by the TARDBP gene, is a DNA/RNA-binding protein implicated in RNA metabolism and processing.1 Belonging to the heterogeneous nuclear ribonucleoprotein (hnRNP) family of proteins that bind to RNA via highly conserved RNA recognition motifs, TDP-43 binds to UG-repeats with high specificity.1,2

Mutations in TARDBP that result in TDP-43 aggregation and neuropathology have been observed in distinct neurodegenerative diseases, known as TDP-43 proteinopathies.3,4 Various studies have identified a subset of amyotrophic lateral sclerosis (ALS) patients that possess TARDBP mutations, suggesting that TDP-43 gain of toxic function or loss of function is a causative factor in sporadic and/or familial ALS.46 Mechanistic studies would be greatly facilitated by the availability of high-quality antibodies.

Here, we compared the performance of a range of commercially available antibodies for TDP-43 and characterized high-quality antibodies for Western blot, immunoprecipitation and immunofluorescence, enabling biochemical and cellular assessment of TDP-43 properties and function.

Results and discussion

Our standard protocol involved comparing readouts from wild-type (WT) and TARDBP knockout (KO) cells.7,8 The first step was to identify a cell line(s) that expresses sufficient levels of TDP-43 to generate a measurable signal. To this end, we examined the DepMap transcriptomics database to identify all cell lines that express the target at levels greater than 2.5 log2 (transcripts per million “TPM” +1), which we have found to be a suitable cut-off (Cancer Dependency Map Portal, RRID: SCR_017655). Commercially available HAP1 cells expressed the TARDBP transcript at RNA levels above the average range of cancer cells analyzed. Parental and TARDBP knockout HAP1 cells were obtained from Horizon Discovery (Table 1).

Table 1. Summary of the cell lines used.

InstitutionCatalog numberRRID (Cellosaurus)Cell lineGenotype
Horizon DiscoveryC631CVCL_Y019HAP1WT
Horizon DiscoveryHZGHC003730c001CVCL_TR64HAP1TADRBP KO

For Western Blot experiments, we resolved proteins from WT and TARDBP KO cell extracts and probed them side-by-side with all antibodies in parallel (Figure 1).

abba8528-654e-4454-af88-aee11cd26c2c_figure1.gif

Figure 1. TDP-43 antibody screening by Western blot.

Lysates of HAP1 (WT and TARDBP KO) were prepared and 50 μg of protein were processed for Western blot with the indicated TDP-43 antibodies. The Ponceau stained transfers of each blot are shown. Antibody dilutions were chosen according to the recommendations of the antibody supplier. Exceptions were given for antibody 80001-1-RR**, which was titrated to 1/1000 as the signal was too weak when following the supplier’s recommendations. When the concentration was not indicated by the supplier, which was the case for antibody 80002-1-RR**, we tested the antibody at 1/1000. Antibody dilution used: 10782-2-AP at 1/5000, 12892-1-AP at 1/1000, 800001-1-RR** at 1/1000, 80002-1-RR** at 1/1000, MAB7778* at 1/500, NBP1-92695* at 1/1000, 711051** at 1/1000, MA5-27828* at 1/1000, MA5-32627** at 1/1000, A19123** at 1/1000, 89789** at 1/1000, 89718** at 1/1000, GTX630196* at 1/500, GTX630197* at 1/500, ab109535** at 1/2000, ab133547** at 1/1000, ab190963** at 1/1000, ab254166** at 1/1000. Predicted band size: 45 kDa. *Monoclonal antibody, **Recombinant antibody.

For immunoprecipitation experiments, we used the antibodies to immunopurify TDP-43 from HAP1 cell extracts. The performance of each antibody was evaluated by detecting the TDP-43 protein in extracts, in the immunodepleted extracts and in the immunoprecipitates (Figure 2).

abba8528-654e-4454-af88-aee11cd26c2c_figure2.gif

Figure 2. TDP-43 antibody screening by immunoprecipitation.

HAP1 lysates were prepared, and IP was performed using 2.0 μg of the indicated TDP-43 antibodies pre-coupled to Dynabeads protein G or protein A. Samples were washed and processed for Western blot with the indicated TDP-43 antibody. For Western blot, 80002-1-RR** was used at 1/1000. The Ponceau stained transfers of each blot are shown for similar reasons as in Figure 1. SM=4% starting material; UB=4% unbound fraction; IP=immunoprecipitate. *Monoclonal antibody, **Recombinant antibody.

For immunofluorescence, as described previously, antibodies were screened using a mosaic strategy.9 In brief, we plated WT and KO cells together in the same well and imaged both cell types in the same field of view to reduce staining, imaging and image analysis bias (Figure 3).

abba8528-654e-4454-af88-aee11cd26c2c_figure3.gif

Figure 3. TDP-43 antibody screening by immunofluorescence.

HAP1 WT and TARDBP KO cells were labelled with a green or a far-red fluorescent dye, respectively. WT and KO cells were mixed and plated to a 1:1 ratio in a 96-well plate with a glass bottom. Cells were stained with the indicated TDP-43 antibodies and with the corresponding Alexa-fluor 555 coupled secondary antibody including DAPI. Acquisition of the blue (nucleus-DAPI), green (identification of WT cells), red (antibody staining) and far-red (identification of KO cells) channels was performed. Representative images of the merged blue and red (grayscale) channels are shown. WT and KO cells are outlined on both channels with green and magenta dashed lines, respectively. Antibody dilutions were chosen according to the recommendations of the antibody supplier. Exceptions were given for antibodies 12892-1-AP, MA5-32627**, A19123**, 89789**, 89718** and ab133547** which were titrated to 1/400, 1/1000, 1/900, 1/30, 1/10 and 1/700, respectively, as the signals were too weak when following the supplier’s recommendations When the concentration was not indicated by the supplier, which was the case for antibodies 80001-1-RR**, GTX630196* and ab254166**, we tested antibodies at 1/700, 1/1000 and 1/500, respectively. At these concentrations, the signal from each antibody was in the range of detection of the microscope used. Antibody dilution used: 10782-2-AP at 1/400, 12892-1-AP at 1/250, 800001-1-RR** at 1/700, 80002-1-RR** at 1/250, MAB7778* at 1/500, NBP1-92695* at 1/1000, 711051** at 1/500, MA5-27828* at 1/1000, MA5-32627** at 1/1000, A19123** at 1/900, 89789** at 1/30, 89718** at 1/10, GTX630196* at 1/1000, GTX630197* at 1/1000, ab109535** at 1/30, ab133547** at 1/700, ab190963** at 1/800, ab254166** at 1/500. Bars = 10 μm. *Monoclonal antibody, **Recombinant antibody.

In conclusion, we have screened TDP-43 commercial antibodies by Western Blot, immunoprecipitation and immunofluorescence and identified several high-performing antibodies under our standardized experimental conditions.

Methods

Antibodies

All TDP-43 antibodies are listed in Table 2, together with their corresponding Research Resource Identifiers (RRID), to ensure the antibodies are cited properly.10 Peroxidase-conjugated goat anti-mouse and anti-rabbit antibodies are from Thermo Fisher Scientific (cat. number 62-6520 and 65-6120). Alexa-555-conjugated goat anti-mouse and anti-rabbit secondary antibodies are from Thermo Fisher Scientific (cat. number A21424 and A21429).

Table 2. Summary of the TDP-43 antibodies tested.

CompanyCatalog numberLot numberRRID (Antibody Registry)ClonalityClone IDHostConcentration (μg/μl)Vendors recommended applications
Proteintech10782-2-AP97534AB_615042polyclonal-rabbit0.60Wb, IF
Proteintech12892-1-AP94163AB_2200505polyclonal-rabbit0.65Wb, IP, IF
Proteintech80001-1-RR**23000002AB_2882933recombinant-mono11N20rabbit0.25Wb
Proteintech80002-1-RR**23000003AB_2882934recombinant-mono16A22rabbit0.25IF
Bio-TechneMAB7778*CHGW0121061AB_29205731monoclonal671834mouse0.50Wb
Bio-TechneNBP1-92695*122117AB_11005586monoclonal3H8mouse1.00Wb, IF
Thermo Fisher Scientific711051**2352341AB_2633110recombinant-poly1HCLCrabbit0.50Wb, IP, IF
Thermo Fisher ScientificMA5-27828*XB3501489AB_2735390monoclonalGT733mouse1.00Wb, IF
Thermo Fisher ScientificMA5-32627**XB3501035AB_2809904recombinant-monoJM51-10rabbit1.00Wb, IP, IF
ABclonalA19123**4000000492AB_2862616recombinant-monoARC0492rabbit0.93Wb, IF
Cell Signaling Technology89789**1AB_2800143recombinant-monoD9R3Lrabbit0.003Wb, IF
Cell Signaling Technology89718**1AB_29205721recombinant-monoE2G6Grabbit0.014Wb
GeneTexGTX630196*41505AB_2888198monoclonalGT225mouse1.00Wb, IF
GeneTexGTX630197*41505AB_2888199monoclonalGT733mouse1.00Wb, IF
Abcamab109535**GR3324454-4AB_10859634recombinant-monoEPR5810rabbit0.03Wb, IF-Methanol
Abcamab133547**GR3345629-4AB_29206211recombinant-monoEPR5811rabbit0.67Wb, IF
Abcamab190963**GR233962-6AB_29206221recombinant-monoEPR18554rabbit0.79Wb, IP, IF
Abcamab254166**GR3316998-3AB_29206201recombinant-monoDB9mouse0.47Wb

* Monoclonal antibody.

** Recombinant antibody.

1 Refer to RRID recently added to the Antibody Registry (on January 2023), they will be available on the Registry website in coming weeks.

Cell culture

Both HAP1 WT and TARDBP KO cell lines used are listed in Table 1, together with their corresponding RRID, to ensure the cell lines are cited properly.11 Cells were cultured in DMEM high glucose (GE Healthcare cat. number SH30081.01) containing 10% fetal bovine serum (Wisent, cat. number 080450), 2 mM L-glutamate (Wisent, cat. number 609065), 100 IU penicillin and 100 μg/ml streptomycin (Wisent cat. number 450201).

Antibody screening by Western blot

Western blots were performed as described in our standard operating procedure.12 HAP1 WT and TARDBP KO were collected in RIPA buffer (25mM Tris-HCl pH 7.6, 150mM NaCl, 1% NP-40, 1% sodium deoxycholate, 0.1% SDS) from Thermo Fisher Scientific (cat. number 0089901), supplemented with protease inhibitor from MilliporeSigma (cat. number P8340). Lysates were sonicated briefly and incubated for 30 min on ice. Lysates were spun at ~110,000 x g for 15 min at 4°C and equal protein aliquots of the supernatants were analyzed by SDS-PAGE and Western blot. BLUelf prestained protein ladder from GeneDireX (cat. number PM008-0500) was used.

Western blots were performed with precast midi 4-20% Tris-Glycine polyacrylamide gels from Thermo Fisher Scientific (cat. number WXP42012BOX) and transferred on nitrocellulose membranes. Proteins on the blots were visualized with Ponceau staining which is scanned to show together with individual Western blots. Blots were blocked with 5% milk for 1 hr, and antibodies were incubated overnight at 4°C with 5% bovine serum albumin (BSA) (Wisent, cat number 800-095) in TBS with 0,1% Tween 20 (TBST) (Cell Signaling Technology, cat. number 9997). Following three washes with TBST, the peroxidase conjugated secondary antibody was incubated at a dilution of ~0.2 μg/ml in TBST with 5% milk for 1 hr at room temperature followed by three washes with TBST. Membranes were incubated with ECL (Thermo Fisher Scientific, cat. number 32106) prior to detection with the iBright™ CL1500 Imaging System (Thermo Fisher Scientific, cat. number A44240).

Antibody screening by immunoprecipitation

Immunoprecipitation was performed as described in our standard operating procedure.13 Antibody-bead conjugates were prepared by adding 2 μg to 500 μl of Pierce IP Lysis Buffer from Thermo Fisher Scientific (cat. number 87788) in a 1.5 ml microcentrifuge tube, together with 30 μl of Dynabeads protein A- (for rabbit antibodies) or protein G- (for mouse antibodies) from Thermo Fisher Scientific (cat. number 10002D and 10004D, respectively). Tubes were rocked for ~2 hrs at 4°C followed by two washes to remove unbound antibodies.

HAP1 WT were collected in Pierce IP buffer (25 mM Tris-HCl pH 7.4, 150 mM NaCl, 1 mM EDTA, 1% NP-40 and 5% glycerol) (Thermo Fisher Scientific, cat. number 87788), supplemented with protease inhibitor (Millipore Sigma, cat. number P8340). Lysates were rocked for 30 min at 4°C and spun at 110,000× g for 15 min at 4°C. 0.5 ml aliquots at 2.0 mg/ml of lysate were incubated with an antibody-bead conjugate for ~2 hrs at 4°C. The unbound fractions were collected, and beads were subsequently washed three times with 1.0 ml of IP lysis buffer and processed for SDS-PAGE and Western blot on precast midi 4-20% Tris-Glycine polyacrylamide gels. Prot-A: HRP (MilliporeSigma, cat. number P8651) was used as a secondary detection system at a dilution of 0.4 μg/ml for an experiment where a rabbit antibody was used for both immunoprecipitation and its corresponding Western blot.

Antibody screening by immunofluorescence

Immunofluorescence was performed as described in our standard operating procedure.9 HAP1 WT and TARDBP KO were labelled with CellTrackerTM green (Thermo Fisher Scientific, cat. number C2925) or CellTrackerTM deep red (Thermo Fisher Scientific, cat. number C34565) fluorescence dye, respectively. The nuclei were labelled with DAPI (Thermo Fisher Scientific, cat. number D3571) fluorescent stain. WT and KO cells were plated on glass coverslips as a mosaic and incubated for 24 hrs in a cell culture incubator at 37°C, 5% CO2. Cells were fixed in 4% paraformaldehyde (PFA) (Beantown chemical, cat. number 140770-10 ml) in phosphate buffered saline (PBS) (Wisent, cat. number 311-010-CL) for 15 min at room temperature and then washed 3 times with PBS. Cells were permeabilized in PBS with 0,1% Triton X-100 (Thermo Fisher Scientific, cat. number BP151-500) for 10 min at room temperature and blocked with PBS with 5% BSA, 5% goat serum (Gibco, cat. no 16210-064) and 0.01% Triton X-100 for 30 min at room temperature. Cells were incubated with IF buffer (PBS, 5% BSA, 0,01% Triton X-100) containing the primary TDP-43 antibodies overnight at 4°C. Cells were then washed 3 × 10 min with IF buffer and incubated with corresponding Alexa Fluor 555-conjugated secondary antibodies in IF buffer at a dilution of 1.0 μg/ml for 1 hr at room temperature with DAPI. Cells were washed 3 × 10 min with IF buffer and once with PBS.

Images were acquired on an ImageXpress micro widefield high-content microscopy system (Molecular Devices), using a 20×/0.45 NA air objective lens and scientific CMOS camera (16-bit, 1.97 mm field of view), equipped with 395, 475, 555 and 635 nm solid state LED lights (Lumencor Aura III light engine) and bandpass emission filters (432/36 nm, 520/35 nm, 600/37 nm and 692/40 nm) to excite and capture fluorescence emission for DAPI, CellTrackerTM Green, Alexa fluor 555 and CellTrackerTM Red, respectively. Images had pixel sizes of 0.68 × 0.68 microns. Exposure time was set with maximal (relevant) pixel intensity ~80% of dynamic range and verified on multiple wells before acquisition. Since the IF staining varied depending on the primary antibody used, the exposure time was set using the most intensely stained well as reference. Frequently, the focal plane varied slightly within a single field of view. To remedy this issue, a stack of three images per channel was acquired at a z-interval of 4 microns per field and best focus projections were generated during the acquisition (MetaExpress v6.7.1, Molecular Devices). Segmentation was carried out on the projections of CellTrackerTM channels using CellPose v1.0 on green (WT) and far-red (KO) channels, using as parameters the ‘cyto’ model to detect whole cells, and using an estimated diameter tested for each cell type, between 15 and 20 microns.14 Masks were used to generate cell outlines for intensity quantification. Figures were assembled with Adobe Illustrator.

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Worrall D, Ayoubi R, Fotouhi M et al. The identification of high-performing antibodies for TDP-43 for use in Western Blot, immunoprecipitation and immunofluorescence [version 2; peer review: 2 approved] F1000Research 2023, 12:277 (https://doi.org/10.12688/f1000research.131852.2)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
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Reviewer Report 14 Jun 2023
Seiji Watanabe, Department of Neuroscience and Pathobiology, Research Institute of Environmental Medicine, Nagoya University, Nagoya, Aichi Prefecture, Japan 
Approved
VIEWS 19
Various antibodies against TDP-43 are now commercially available from several companies, but their validation is still insufficient. This study comprehensively validated the performance of various antibodies, which will provide important information for researchers when they select TDP-43 antibodies for their ... Continue reading
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Watanabe S. Reviewer Report For: The identification of high-performing antibodies for TDP-43 for use in Western Blot, immunoprecipitation and immunofluorescence [version 2; peer review: 2 approved]. F1000Research 2023, 12:277 (https://doi.org/10.5256/f1000research.144735.r178389)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
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Reviewer Report 20 Mar 2023
Makoto Urushitani, Department of Neurology, Shiga University of Medical Science, Otsu, Japan 
Approved
VIEWS 40
Due to the continuing significance of morphological assay to clarify TDP-43 proteinopathy, the characteristics of the antibody are crucial to drawing convincing and replicable results. Numerous antibodies against TDP-43 are commercially available to meet the needs. As is often the ... Continue reading
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HOW TO CITE THIS REPORT
Urushitani M. Reviewer Report For: The identification of high-performing antibodies for TDP-43 for use in Western Blot, immunoprecipitation and immunofluorescence [version 2; peer review: 2 approved]. F1000Research 2023, 12:277 (https://doi.org/10.5256/f1000research.144735.r166439)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 22 Mar 2023
    Kathleen Southern, Department of Neurology and Neurosurgery, Structural Genomics Consortium, The Montreal Neurological Institute, McGill University, Montreal, H3A 2B4, Canada
    22 Mar 2023
    Author Response
    Thank you to Makoto Urushitani for your review of our publication. Although there is an abundance of commercial antibodies available for TDP-43, there lacks guidance to help researchers find the ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 22 Mar 2023
    Kathleen Southern, Department of Neurology and Neurosurgery, Structural Genomics Consortium, The Montreal Neurological Institute, McGill University, Montreal, H3A 2B4, Canada
    22 Mar 2023
    Author Response
    Thank you to Makoto Urushitani for your review of our publication. Although there is an abundance of commercial antibodies available for TDP-43, there lacks guidance to help researchers find the ... Continue reading

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Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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