Epitope: Conformational epitope including amino acids at both 7-9 and 312-342
Immunogen: Alz-50-immunocaptured paired helical filaments from AD brain
Clonality: Monoclonal
Isotype: IgG1
Host: Mouse
Reactivity: Human

Overview

This monoclonal antibody was generated against paired helical filaments isolated from an Alzheimer’s brain. It recognizes a discontinuous epitope formed when tau folds in a way that brings together its N-terminal and third repeat regions. This tau conformation precedes the appearance of neurofibrillary tangles and is considered “pathological” because MC-1 immunoreactivity is not seen in normal brains (however, see exception below).

The neuropathological findings in humans have been extrapolated to rodents, and MC-1 has been used to evaluate tauopathy in mouse models of disease. In addition, passive immunization with MC-1 was shown to prevent or ameliorate tau pathology and functional deficits in transgenic mice that express tau with FTD-linked mutations.

A humanized version of MC-1, zagotenemab, was produced by Eli Lilly and advanced to clinical trials. Further development of zagotenemab as an immunotherapy was halted in 2021, after a Phase II study failed to meet its primary endpoint.

Caution should be exercised in using MC-1 as a detection antibody for western blots, where conditions might artificially create the tau conformation recognized by this antibody. Additionally, MC-1 recognizes a band on western blots of brain lysates from tau knockout mice, showing that a discontinuous epitope in tau, described below, is not an absolute requirement for MC-1 reactivity.

Generation and epitope mapping

MC-1 was generated against paired helical filaments isolated from the brain of an Alzheimer’s patient using monoclonal antibody Alz-50 (Jicha et al., 1997).

The MC-1 epitope was defined by deletion mapping using recombinant tau protein, and it was found that two discontinuous regions are required for antibody binding—amino acids 7-9 near the N terminus and a sequence between amino acids 313 and 322 in the third repeat domain—and that the epitope is formed by intramolecular interactions (Jicha et al., 1997; Jicha et al., 1999). This epitope is found in all six tau isoforms. While not essential for antibody binding, some part of the 300-amino acid intervening sequence is needed for full immunoreactivity, perhaps allowing tau space to fold into the shape that brings the two sections of the epitope together.

The interaction of MC-1 with recombinant tau suggests that post-translational modifications are not required to generate the MC-1 epitope. However, it remains possible that post-translational modifications influence the ability of tau to adopt or maintain the conformation seen by MC-1. Indeed, MC-1 immunoreactivity on western blots was increased by pseudophosphorylation of tau at residues phosphorylated in AD brains (Jeganathan et al., 2008). Removal of the C-terminal region from recombinant tau—either through caspase cleavage after aspartate-421 (Rissman et al., 2004) or expression of a truncated version of the protein lacking amino acids 422-441 (Jeganathan et al., 2008)—also enhanced recognition by MC-1.

Specificity

As mentioned above, MC-1 is considered selective for a tau conformation found in Alzheimer’s disease. Indeed, MC-1 immunoreactivity in Alzheimer’s brains, but not normal brains, has been shown in ELISA (Jicha et al., 1999), dot blot (Koss et al., 2016), and immunohistochemical (Weaver et al., 2000) applications. Yet, the epitope recognized by MC-1 was initially characterized using recombinant tau. This conundrum was addressed by Jicha, Davies, and colleagues (Jicha et al., 1997; Jicha et al., 1999), who suggested that western-blotting conditions like those used in the initial characterization of the antibody could create a tau conformation similar to one that occurs in Alzheimer’s disease. MC-1 immunoreactivity on western blots of lysates of normal brain has been reported (see Jicha et al., 1997, although in this study, AD samples and normal samples were not run on the same blot for comparison). Furthermore, on Western blots, MC-1 detected a protein species in the brains of tau knockout mice (Petry et al., 2014; see below). These findings suggest that caution should be used in interpreting the results when MC-1 is used as a detection antibody for western blots.

MC-1 selectively reacts with a target in Alzheimer’s brains. A) Immunoblot. Left, sample dot blot of lysates of temporal cortices from subjects with neuropathologically confirmed Alzheimer’s disease (Braak stages 4-6) and controls (Braak stages 0-3); right, quantification of dot-blot signals. B) Immunohistochemistry. CA2 region of hippocampus. AD, left; control, right. [A) From Koss et al., 2016, Figure 3.b.i-ii; licensed under Creative Commons BY 4.0. B) Adapted from Weaver et al., 2000, Neurobiology of Aging © 2000 Elsevier Science Inc.]

MC-1 was seen to stain neurons in the brains of transgenic mice that express human tau with the P301L mutation linked to frontotemporal dementia, but staining was absent from non-transgenic animals (Götz et al., 2001; Ramsden et al., 2005). The antibody also stained the brains of transgenic mice that express tau with the ΔK280 mutation that promotes tau aggregation but did not stain neurons in mice carrying “anti-aggregant” tau (tau with three mutations: ΔK280, I277P, I308P) (Eckermann et al., 2007).

MC-1 stains neurons in the brains of transgenic mice expressing human tauP301L. Top, section through the hippocampus of an rTg(tauP301L)4510 mouse. Bottom, section through the hippocampus of an age-matched non-transgenic control. (B) panels shown at 2.5x the magnification of (A). [From Ramsden et al., 2005, Journal of Neuroscience. © 2005 Society for Neuroscience.]

MC-1 stains neurons in the brains of transgenic mice expressing aggregation-prone human tau. A) Section through the hippocampus of a mouse expressing human tau with the ΔK280 mutation that promotes tau aggregation. B) MC-1 immunoreactivity is absent from the brains of transgenic mice expressing human tau with the ΔK280 mutation and two additional mutations (I277P, I308P) that oppose tau aggregation. [From Eckermann et al., 2007, Figure 4; licensed under Creative Commons BY 4.0.]

Validation

Despite the widespread use of this antibody, there is a dearth of validation data. Planel and colleagues (Petry et al., 2014) tested a series of tau antibodies in brain lysates from wild-type mice, tau knockout mice, and mice expected to have increased levels of  hyperphosphorylated tau—transgenic mice that express human amyloid precursor protein, presenilin-1, and tau with disease-linked mutations (3xTg) and hypothermic wild-type mice. The tau knockout mice were created by an in-frame insertion of EGFP (enhanced green fluorescent protein) into exon 1 of the mouse Mapt gene, and these mice express a chimeric protein consisting of the first 31 amino acids of tau fused to EGFP (Tucker et al., 2001). In western blots, MC-1 reacted strongly with a band at approximately 37 kDa in the tau knockouts, a band also detected by an antibody directed against EGFP. As suggested by Petry et al., the fusion of EGFP to the N terminal sequence of tau appeared to mimic the MC-1 epitope, at least under western-blotting conditions. These findings show that the discontinuous epitope defined in tau, described above, is not an absolute requirement for MC-1 reactivity.

MC-1 recognizes a prtoein in the brains of Mapt knockout mice.  MC-1 reacts strongly with an ~37-kDa protein in the brains of tau knockout (KO) mice but produces only weak signals in the brains of wild-type (WT) mice and mice expected to have increased levels of  hyperphosphorylated tau—transgenic mice that express human amyloid precursor protein, presenilin-1, and tau with disease-linked mutations (3xTg) and hypothermic wild-type mice (Hypo). Blot probed with MC-1 followed by a secondary antibody that recognizes non-denatured mouse IgG. [From Petry et al., 2014; Figure 3.A2. MC-1-TB, labels added; licensed under Creative Commons BY 4.0.]

Comments

No Available Comments

Make a Comment

To make a comment you must login or register.

References

Therapeutics Citations

1. Zagotenemab

Mutations Citations

1. MAPT P301L
2. MAPT K280del

Research Models Citations

1. TauΔK280 ("Proaggregation mutant")
2. rTg(tauP301L)4510
3. 3xTg

Paper Citations

1. Jicha GA, Bowser R, Kazam IG, Davies P. Alz-50 and MC-1, a new monoclonal antibody raised to paired helical filaments, recognize conformational epitopes on recombinant tau. J Neurosci Res. 1997 Apr 15;48(2):128-32. PubMed.
2. Jicha GA, Berenfeld B, Davies P. Sequence requirements for formation of conformational variants of tau similar to those found in Alzheimer's disease. J Neurosci Res. 1999 Mar 15;55(6):713-23. PubMed.
3. Jeganathan S, Hascher A, Chinnathambi S, Biernat J, Mandelkow EM, Mandelkow E. Proline-directed pseudo-phosphorylation at AT8 and PHF1 epitopes induces a compaction of the paperclip folding of Tau and generates a pathological (MC-1) conformation. J Biol Chem. 2008 Nov 14;283(46):32066-76. PubMed.
4. Rissman RA, Poon WW, Blurton-Jones M, Oddo S, Torp R, Vitek MP, Laferla FM, Rohn TT, Cotman CW. Caspase-cleavage of tau is an early event in Alzheimer disease tangle pathology. J Clin Invest. 2004 Jul;114(1):121-30. PubMed.
5. Koss DJ, Jones G, Cranston A, Gardner H, Kanaan NM, Platt B. Soluble pre-fibrillar tau and β-amyloid species emerge in early human Alzheimer's disease and track disease progression and cognitive decline. Acta Neuropathol. 2016 Dec;132(6):875-895. Epub 2016 Oct 21 PubMed.
6. Weaver CL, Espinoza M, Kress Y, Davies P. Conformational change as one of the earliest alterations of tau in Alzheimer's disease. Neurobiol Aging. 2000 Sep-Oct;21(5):719-27. PubMed.
7. Jicha GA, Lane E, Vincent I, Otvos L, Hoffmann R, Davies P. A conformation- and phosphorylation-dependent antibody recognizing the paired helical filaments of Alzheimer's disease. J Neurochem. 1997 Nov;69(5):2087-95. PubMed.
8. Petry FR, Pelletier J, Bretteville A, Morin F, Calon F, Hébert SS, Whittington RA, Planel E. Specificity of anti-tau antibodies when analyzing mice models of Alzheimer's disease: problems and solutions. PLoS One. 2014;9(5):e94251. Epub 2014 May 2 PubMed.
9. Götz J, Chen F, Barmettler R, Nitsch RM. Tau filament formation in transgenic mice expressing P301L tau. J Biol Chem. 2001 Jan 5;276(1):529-34. PubMed.
10. Ramsden M, Kotilinek L, Forster C, Paulson J, McGowan E, Santacruz K, Guimaraes A, Yue M, Lewis J, Carlson G, Hutton M, Ashe KH. Age-dependent neurofibrillary tangle formation, neuron loss, and memory impairment in a mouse model of human tauopathy (P301L). J Neurosci. 2005 Nov 16;25(46):10637-47. PubMed.
11. Eckermann K, Mocanu MM, Khlistunova I, Biernat J, Nissen A, Hofmann A, Schönig K, Bujard H, Haemisch A, Mandelkow E, Zhou L, Rune G, Mandelkow EM. The beta-propensity of Tau determines aggregation and synaptic loss in inducible mouse models of tauopathy. J Biol Chem. 2007 Oct 26;282(43):31755-65. Epub 2007 Aug 23 PubMed.
12. Tucker KL, Meyer M, Barde YA. Neurotrophins are required for nerve growth during development. Nat Neurosci. 2001 Jan;4(1):29-37. PubMed.

External Citations

1. licensed
2. Creative Commons BY 4.0
3. Neurobiology of Aging
4. Journal of Neuroscience
5. licensed
6. licensed
7. Creative Commons BY 4.0

Further Reading

No Available Further Reading