Transmission of amyloid-ß protein pathology from cadaveric pituitary growth hormone.

We previously reported1 the presence of amyloid-ß protein (Aß) deposits in individuals with Creutzfeldt-Jakob disease (CJD) who had been treated during childhood with human cadaveric pituitary-derived growth hormone (c-hGH) contaminated with prions. The marked deposition of parenchymal and vascular Aß in these relatively young individuals with treatment-induced (iatrogenic) CJD (iCJD), in contrast to other prion-disease patients and population controls, allied with the ability of Alzheimer's disease brain homogenates to seed Aß deposition in laboratory animals, led us to argue that the implicated c-hGH batches might have been contaminated with Aß seeds as well as with prions. However, this was necessarily an association, and not an experimental, study in humans and causality could not be concluded. Given the public health importance of our hypothesis, we proceeded to identify and biochemically analyse archived vials of c-hGH. Here we show that certain c-hGH batches to which patients with iCJD and Aß pathology were exposed have substantial levels of Aß40, Aß42 and tau proteins, and that this material can seed the formation of Aß plaques and cerebral Aß-amyloid angiopathy in intracerebrally inoculated mice expressing a mutant, humanized amyloid precursor protein. These results confirm the presence of Aß seeds in archived c-hGH vials and are consistent with the hypothesized iatrogenic human transmission of Aß pathology. This experimental confirmation has implications for both the prevention and the treatment of Alzheimer's disease, and should prompt a review of the risk of iatrogenic transmission of Aß seeds by medical and surgical procedures long recognized to pose a risk of accidental prion transmission2,3.

Identification of a Compound That Disrupts Binding of Amyloid-ß to the Prion Protein Using a Novel Fluorescence-based Assay.

The prion protein (PrP) has been implicated both in prion diseases such as Creutzfeldt-Jakob disease, where its monomeric cellular isoform (PrP(C)) is recruited into pathogenic self-propagating polymers of misfolded protein, and in Alzheimer disease, where PrP(C) may act as a receptor for synaptotoxic oligomeric forms of amyloid-ß (Aß). There has been considerable interest in identification of compounds that bind to PrP(C), stabilizing its native fold and thereby acting as pharmacological chaperones to block prion propagation and pathogenesis. However, compounds binding PrP(C) could also inhibit the binding of toxic Aß species and may have a role in treating Alzheimer disease, a highly prevalent dementia for which there are currently no disease-modifying treatments. However, the absence of a unitary, readily measurable, physiological function of PrP makes screening for ligands challenging, and the highly heterogeneous nature of Aß oligomer preparations makes conventional competition binding assays difficult to interpret. We have therefore developed a high-throughput screen that utilizes site-specifically fluorescently labeled protein to identify compounds that bind to PrP and inhibit both Aß binding and prion propagation. Following a screen of 1,200 approved drugs, we identified Chicago Sky Blue 6B as the first small molecule PrP ligand capable of inhibiting Aß binding, demonstrating the feasibility of development of drugs to block this interaction. The interaction of Chicago Sky Blue 6B was characterized by isothermal titration calorimetry, and its ability to inhibit Aß binding and reduce prion levels was established in cell-based assays.

Soluble Aß aggregates can inhibit prion propagation.

Mammalian prions cause lethal neurodegenerative diseases such as Creutzfeldt-Jakob disease (CJD) and consist of multi-chain assemblies of misfolded cellular prion protein (PrPC). Ligands that bind to PrPC can inhibit prion propagation and neurotoxicity. Extensive prior work established that certain soluble assemblies of the Alzheimer's disease (AD)-associated amyloid ß-protein (Aß) can tightly bind to PrPC, and that this interaction may be relevant to their toxicity in AD. Here, we investigated whether such soluble Aß assemblies might, conversely, have an inhibitory effect on prion propagation. Using cellular models of prion infection and propagation and distinct Aß preparations, we found that the form of Aß assemblies which most avidly bound to PrP in vitro also inhibited prion infection and propagation. By contrast, forms of Aß which exhibit little or no binding to PrP were unable to attenuate prion propagation. These data suggest that soluble aggregates of Aß can compete with prions for binding to PrPC and emphasize the bidirectional nature of the interplay between Aß and PrPC in Alzheimer's and prion diseases. Such inhibitory effects of Aß on prion propagation may contribute to the apparent fall-off in the incidence of sporadic CJD at advanced age where cerebral Aß deposition is common.

Amyloid-ß nanotubes are associated with prion protein-dependent synaptotoxicity.

Growing evidence suggests water-soluble, non-fibrillar forms of amyloid-ß protein (Aß) have important roles in Alzheimer's disease with toxicities mimicked by synthetic Aß(1-42). However, no defined toxic structures acting via specific receptors have been identified and roles of proposed receptors, such as prion protein (PrP), remain controversial. Here we quantify binding to PrP of Aß(1-42) after different durations of aggregation. We show PrP-binding and PrP-dependent inhibition of long-term potentiation (LTP) correlate with the presence of protofibrils. Globular oligomers bind less avidly to PrP and do not inhibit LTP, whereas fibrils inhibit LTP in a PrP-independent manner. That only certain transient Aß assemblies cause PrP-dependent toxicity explains conflicting reports regarding the involvement of PrP in Aß-induced impairments. We show that these protofibrils contain a defined nanotubular structure with a previously unidentified triple helical conformation. Blocking the formation of Aß nanotubes or their interaction with PrP might have a role in treatment of Alzheimer's disease.

Interaction between prion protein and toxic amyloid ß assemblies can be therapeutically targeted at multiple sites.

A role for PrP in the toxic effect of oligomeric forms of Aß, implicated in Alzheimer's disease (AD), has been suggested but remains controversial. Here we show that PrP is required for the plasticity-impairing effects of ex vivo material from human AD brain and that standardized Aß-derived diffusible ligand (ADDL) preparations disrupt hippocampal synaptic plasticity in a PrP-dependent manner. We screened a panel of anti-PrP antibodies for their ability to disrupt the ADDL-PrP interaction. Antibodies directed to the principal PrP/Aß-binding site and to PrP helix-1, were able to block Aß binding to PrP suggesting that the toxic Aß species are of relatively high molecular mass and/or may bind multiple PrP molecules. Two representative and extensively characterized monoclonal antibodies directed to these regions, ICSM-35 and ICSM-18, were shown to block the Aß-mediated disruption of synaptic plasticity validating these antibodies as candidate therapeutics for AD either individually or in combination.