PrP-grafted antibodies bind certain amyloid β-protein aggregates, but do not prevent toxicity

Abstract

Background The prion protein (PrP) is known to bind certain soluble aggregates of the amyloid β-protein (Aβ), and two regions of PrP, one centered around residues 19-33, and the other around 87-112, are thought to be particularly important for this interaction. When either of these sequences are grafted into a human IgG the resulting antibodies react with disease-associated PrP conformers, whereas the parental b12 IgG does not.Methods Human antibodies containing grafts of PrP 19-33 or 87-112 were prepared as before (Solforosi et al. 2007) and tested for their ability to recognize synthetic and Alzheimer's disease (AD) brain-derived Aβ. Since aqueous extracts of AD brain contain a complex mixture of active and inactive Aβ species, we also assessed whether PrP-grafted antibodies could protect against neuritotoxicity mediated by AD brain-derived Aβ. For these experiments, human iPSC-derived neurons were grown in 96-well plates at 5000 cells per well and on post-induction day 21, AD brain extracts were added +/-test antibodies.Neurons were imaged for 3 days using an IncuCyte live-cell imaging system, and neurite number and density quantified. ResultsGrafted antibodies bound a significant portion of aggregated Aβ in aqueous AD extracts, but when these antibodies were co-incubated with neurons treated with brain extracts they did not reduce toxicity. By contrast, PrP and the PrP fragment N1 did protect against Aβ. ConclusionsThese results further demonstrate that not all Aβ oligomers are toxic and suggest that PrP derivatives may allow development of agents that differentially recognize toxic and innocuous Aβ aggregates.

PrP is a central player in toxicity mediated by soluble aggregates of neurodegeneration-causing proteins

“…It will fall to future studies to purify soluble protein aggregates from diseased brain and to test their toxic activities. In this regard, our recent observation that recombinant PrP N1 can protect against the toxicity of brain-derived Aβ [62] suggests that PrP derivatives such as N1 may serve as affinity reagents to enable the isolation and molecular identification of SPAs. Similarly, in vivo studies will be required to further investigate the translational nature of our work.…”

“…Importantly, SPAs of tau and αSyn bound to PrP with high affinity, but (as with Aβ) monomers and end-stage fibrils displayed little or no binding. Moreover, anti-PrP antibodies to the putative Aβ binding Sites I and II [19,31,32,62] effectively displaced SPAs of αSyn and tau, and deletion of these sites substantially attenuated binding. Multielectrode recordings from hippocampal slices of PrP WT mice revealed that soluble aggregates (but not monomers) of Aβ, tau and αSyn impair LTP, and recordings from PrP null mice demonstrate that this impairment required expression of PrP.…”

“…Of these candidates, the cellular prion protein (PrP C ) has more supportive evidence than most [81]. All published studies on the Aβ-PrP interaction have concluded that binding is high affinity (sub-nanomolar) and oligomer-specific, and many have found that binding to PrP mediates a toxic response [19,31,32,53,62,66,73,84,91,93]. However, there have been reports of deleterious effects of Aβ that do not require PrP C expression [4,15,20,51].…”

Transgenic Overexpression of the Disordered Prion Protein N1 Fragment in Mice Does Not Protect Against Neurodegenerative Diseases Due to Impaired ER Translocation

“…In our experiments, cytoplasmic N1 did neither confer protection against prions nor against Aβinduced neurotoxicity. Since exogenously administered N1 reliably blocks Aβ-induced neurotoxicity [38,[64][65][66][67][68][69][70][71], our data rather support a model where Aβinduced neurotoxicity is mainly executed by events occurring at the plasma membrane of neurons. Fig.…”

“…As a soluble ligand, N1 acts beneficial in several ways as it reduces hypoxia-induced neuronal damage [61] and may be involved in myelin maintenance [62] and intercellular communication (reviewed in [63]). With regard to AD, numerous studies have shown that exogenously administered N1 and N1-like peptides are able to block toxic Aβ oligomers and interfere with their synaptic impairment and neurotoxicity [38,[64][65][66][67][68][69][70][71].…”