Wirths O, Erck C, Martens H, Harmeier A, Geumann C, Jawhar S, Kumar S, Multhaup G, Walter J, Ingelsson M, Degerman-Gunnarsson M, Kalimo H, Huitinga I, Lannfelt L, Bayer TA. Identification of low molecular weight pyroglutamate A{beta} oligomers in Alzheimer disease: a novel tool for therapy and diagnosis. J Biol Chem. 2010 Dec 31;285(53):41517-24. PubMed.
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University of Gothenburg
The authors convincingly show that they have generated a specific antibody to one of the most AD-associated Aβ isoforms both with regard to neuropathology and cognitive deficits. They present data on the diagnostic and therapeutic potential of the antibody. I would love to see if the antibody could be used to monitor the possible acute emergence of AβpE3 peptides in CSF in response to successful passive or active anti-Aβ immunization.
Anhalt University of Applied Research
The Therapeutic and Diagnostic Potential of Anti AβpE3 Strategies
The article by the team led by Wirths and Bayer is a further step forward in clarifying the role of an abundant and apparently very toxic Aβ species in human brain deposits: N-pyroglutamyl Aβ (Wirths et al., 2010).
Especially oligomeric forms of Aβ were described as neurotoxic; however, the toxicity of Aβ peptides is still a matter of debate, since most of the generated APP-overexpressing mouse models show profound plaque deposition surprisingly in combination with a lack of neuron loss or robust cognitive impairment. Obviously, a crucial step or agent for the development of the disease must be underrepresented or lacking in most of the model systems (compare Maeda et al., 2007).
In contrast to the Aβ extracted from brains of AD mouse models, the majority of Aβ peptides deposited in human brain are N-terminally processed. Besides isomerization and racemization at positions 1 and 7 of the Aβ sequence, a substantial amount of Aβ peptides are N-terminally truncated and modified by a pyroglutamyl (pE) residue (Roher et al., 1993).
The modification renders Aβ peptides more hydrophobic due to the loss of N-terminal charges, and AβpE3 shows a substantially enhanced aggregation propensity compared to Aβ1-40/42. In addition, AβpE3 is more toxic to primary neuronal and glial cell cultures than Aβ1-42, and the pyroglutamated forms of Aβ have been shown to be poorly degraded by cultured astrocytes (Russo et al., 2002; Schilling et al., 2006).
Therefore, the formation of AβpE3 leads to further stabilization of a per se amyloidogenic peptide. Giving constant anabolic and catabolic processes leading to generation and clearance of Aβ peptides throughout life, the presence of such highly toxic and amyloidogenic Aβ species could represent a starting point for disease initiation (Gunn et al., 2010).
Since the discovery that AβpE3 and AβpE11 formation is catalyzed by the QCs (glutaminyl cyclases; see Schilling et al., 2004 and Cynis et al., 2006), four major routes of dealing with these peptide species are possible:
All these pathways are explored intensively (Schilling et al., 2008 and Gardberg et al., 2009), and some have now reached preclinical stage.
While vaccination is perhaps primarily targeting extracellular AβpE3, QC-inhibition can take place within the cell. pE-formation by QC occurs preferentially at acid pH-values, as they are found in the Golgi and/or within secretory vesicles (Cynis et al., 2006; Hartlage-Rübsamen et al., 2009). Where these peptides—intraneuronal or interstitial—unfold most of their toxicity remains to be seen. However, generating minute amounts of AβpE3 by directing an appropriate construct into the secretory apparatus of mice brains reveals extraordinary intraneuronal toxicity, neuron loss, and massive gliosis (Wirths et al., 2009). The neuron loss and glial stimulation dramatically exceeds that usually observed with hAPP-transgenic mouse models, which primarily produce full-length Aβ.
That AβpE3 generates—similar as pGlu-ABri or pGlu-ADan—rapidly degradation-resistant oligomers has been previously shown (Schlenzig et al., 2009). The extraordinary cytotoxicity of AβpE3 containing oligomers was demonstrated during the hot topic poster session of the 2010 ICAD meeting in Honolulu (Demuth et al., 2010), and further progress studying the tau-dependent mechanism was presented at SfN 2010 by Justin Nussbaum. That the new antibody 9D5 is capable to discriminate AD patients from non-demented age-matched controls is one of the major achievements described in the new paper by Wirths et al. (2010).
Also, the reduction of AβpE3 by passive immunization of tg mice is a striking result corroborated by the findings achieved by QC-inhibition (Schilling et al., 2008; Demuth et al., 2010), and which is paralleling the effective passive vaccination applying an AβpE3-specific monoclonal antibody raised against a monomeric epitope structure reported at the SFN 2010 Meeting by Jeff Frost and colleagues.
Considering the multiple structural forms misfolding peptides can adopt, it might be conceivable that antibodies raised against differently presented or synthesized epitopes recognize different monomeric or oligomeric species with different sensitivity and specificity. Using the monomer-specific antibody for immunohistochemistry in different laboratories, clear intraneuronal AβpE3 immunoreactivity partly colocalized with QC in mouse and human brain can be observed (Roßner et al.).
Intriguingly, while we did not find detectable amounts of AβpE3 in human plasma using our AβpE mAb, the AβpE3 oligomer-specific monoclonal antibody 9D5 recognizes the peptide in plasma of normal and healthy controls. Wirths et al. report in their paper a significant reduction by 46 percent as compared to healthy controls. If this result is supported by material and data of much greater patient populations, the antibody 9D5 may become a new breakthrough in AD-diagnostics and also may be an important new immunotherapy reagent.
See also:
Demuth HU, Bloom GS, Lemere CA. Pyroglutamated β-amyloid Is Toxic, Highly Abundant in Alzheimer's Brain, Amplifies Tau-dependent Beta-amyloid Cytotoxicity and can be Attenuated by Passive Immunization Or Inhibition Of Glutaminyl Cyclase. ICAD 2010, Hot Topic Poster: Control/Tracking Number: 10-HT-3507-ALZ.
Nussbaum J, Cynis H, Schilling S, Demuth HU, Bloom GS. Pyroglutamate-modified β-amyloid amplifies tau-dependent cytotoxicity of conventional β-amyloid. Program#/Poster#: 321.13, Monday, Nov 15, 2010, 11:00 AM -11:15 AM.
Frost JL, Liu B, Shi Q, Kleinschmidt M, Demuth HU, Schilling S, Lemere CA. Passive and active pyroglutamate-3 Aβ (AβN3pE) immunotherapy in AD-like transgenic mouse models. Program#/Poster#: 650.6/H38, Tuesday, Nov 16, 2010, 2:00 PM—3:00 PM.
References:
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