Transmission of AA-amyloidosis: Similarities with Prion Disorders
Westermark, P Rudbeck laboratory, Department of Genetics and Pathology, Sweden
The systemic amyloidoses are characterized by widely spread amyloid deposits that can affect virtually every organ in the body. The precursor protein, which varies between different forms is produced at one or several locations, circulates with the plasma and is finally deposited as fibrils in the target organs by mechanisms yet to be determined. In one of the more common forms, systemic AA-amyloidosis, the substrate protein serum AA (SAA) is an acute phase reactant, with significant production only when certain proinflammatory signal substances are upregulated. A persistently high plasma concentration of SAA is a prerequisite for AA-amyloidosis to develop. AA-amyloidosis can easily be induced in many strains of mice by an inflammatory challenge, typically after a long lag phase. This phase is dramatically shortened by administration of amyloid fibrils extracted from an amyloidotic mouse, given intravenously, intra-nasally or given in the drinking water. The fibrillar extract is very potent, active down to pg of protein and facilitates amyloid formation even when given several months before an inflammation is induced. Also amyloid-like fibrils, produced in vitro from synthetic peptides have a clear effect, supporting the idea that the active principle is the misfolded and aggregated protein. AA-amyloidosis occurs in many avian and mammalian species. AA-fibrils from some, but not all species seed murine amyloidosis, showing a species barrier. AA-amyloidosis occurs in species, used as human food and may therefore be a risk factor. Consequently, AA-amyloidosis has similarity with prionoses, differing by the need of an upregulated production of the substrate SAA.
Cellular Prion Protein Regulates the ß-Secretase Cleavage of the Alzheimer’s Amyloid Precursor Protein
Hooper, NM1; Parkin, ET1; Watt, NT1; Baybutt, H2; Manson, J2; Hussain, I3; Turner, AJ1 1University of Leeds, Institute of Molecular and Cellular Biology, UK; 2Roslin Institute, Neuropathogenesis Unit, UK; 3GlaxoSmithKline, Neurodegeneration Research, UK
Background: The normal cellular function of the prion protein (PrP), the causative agent of the transmissible spongiform encephalopathies such as Creutzfeldt-Jakob disease (CJD) in humans, remains enigmatic. Several studies have reported combinations of Alzheimer’s Disease (AD) and CJD neuropathology and the Val/Met129 polymorphism in the PrP gene has been identified as a risk factor for early-onset AD, leading to speculation that there may be some pathogenic connection between these two neurodegenerative conditions. The amyloid ß (Aß) peptides that cause AD are derived from the amyloid precursor protein (APP) through sequential proteolytic cleavage by the ß-secretase (BACE1) and the g-secretase complex. Aim: As both APP and PrP are cleaved by zinc metalloproteases of the ADAM family, we investigated whether PrP alters the proteolytic processing of APP. Results: Here we show that expression of PrP in SH-SY5Y cells dramatically downregulated the cleavage of APP by BACE1 and reduced the secretion of Aß peptides into the conditioned medium by >92%. Conversely, siRNA reduction of endogenous PrP in N2a cells led to an increase in secreted Aß. Furthermore, levels of Aß were significantly increased in the brains of PrP null mice as compared with wild type mice. Two mutants of PrP, PG14 and A116V, that are associated with familial human prion diseases, did not inhibit the BACE1 cleavage of APP. To investigate whether the Val/Met129 polymorphism in human PrPC would alter the production of Aß, brains from mice with the human PrP gene with MM or VV 129 genotypes were analysed. In the MM mice there was a significant increase in Aß in the brains as compared with the VV mice. In the brains of two strains (79A and 87V) of scrapie-infected mice there was a significant increase in Aß peptides as compared to uninfected mice. Conclusions: Together these data reveal a novel function for PrP in regulating the processing of APP through inhibition of BACE1. The increase in APP processing in cells expressing disease-associated forms of PrP and in scrapie-infected brains raises the possibility that the increase in Aß may contribute to the neurodegeneration observed in prion diseases. Funded by the Medical Research Council of Great Britain.
Prion Protein Regulates the ß-Secretase Cleavage of the Alzheimer’s Amyloid Precursor Protein through Interaction with Glycosaminoglycans
Griffiths, HH; Parkin, ET; Watt, NT; Turner, AJ; Hooper, NM University of Leeds, Institute of Molecular and Cellular Biology, UK
Background: Proteolytic processing of the amyloid precursor protein (APP) by ßsecretase, BACE1, is the initial step in the production of the amyloid ß (Aß) peptide which is involved in the pathogenesis of Alzheimer’s disease. We have shown that the cellular prion protein (PrP) inhibits the cleavage of APP by BACE1 in cell and animal models. Aim: To investigate the mechanism by which PrP inhibits the action of BACE1. Results: Neither PrPdeltaGPI, which is not membrane attached, nor PrP-CTM, which is anchored by a transmembrane domain and is excluded from cholesterol-rich lipid rafts, reduced cleavage of APP, suggesting that to inhibit the BACE1 cleavage of APP PrP has to be localised to lipid rafts. Coimmunoprecipitation experiments demonstrated that PrP physically interacts with BACE1. However, PrP did not alter the activity of BACE1 towards a fluorogenic peptide substrate nor perturb the dimerisation of BACE1. Using constructs of PrP lacking either the octapeptide repeats or the 4 residues KKRP at the N-terminus of the mature protein (PrPdeltaN), we demonstrate that the KKRP sequence but not the octapeptide repeats, is essential for regulating the BACE1 cleavage of APP. As the KKRP sequence is known to participate in glycosaminoglycan (GAG) binding, we confirmed that PrPdeltaN did not bind to immobilised heparin. Addition of heparin to SH-SY5Y cells increased the amount of APP cleaved by BACE1 in a concentration-dependent manner and reduced the amount of BACE1 coimmunoprecipitated with PrP, suggesting that GAGs are required for PrP to interact with BACE1 and inhibit APP processing. Of a range of GAGs, including dextran sulphate, hyaluronic acid and chondroitin sulphate, investigated there was complete correlation between those that could restore BACE1 cleavage of APP in PrP expressing cells and those that bound PrP. Conclusion: These data suggest a possible mechanism by which PrP regulates the ßcleavage of APP is through the N-terminus of PrP interacting via GAGs with one or more of the heparin binding sites on BACE1 within a subset of cholesterol-rich lipid rafts, thereby restricting access of BACE1 to APP. Funded by the Medical Research Council of Great Britain.
Comparison of the Neuropsychological Profile of Patients with Sporadic Creutzfeldt-Jakob Disease and Patients with Alzheimer’s
Krzovska, M1; Cepek, L1; Ratzka, P2; Döhlinger, S3; Uttner, I1; Wolf, Stefanie4; Irle, Eva4; Mollenhauer, Brit5; Kretzschmar, Hans A.6; Riepe, Matthias7; v. Arnim, Christine1; Otto, Markus1 1University of Ulm, Germany; 2Department of Neurology, Germany; 3University of Goettingen, Germany; 4University of Goettingen, Germany; 5Elena Klinik, Germany; 6LMU, Germany; 7University of Berlin, Germany
Background:To evaluate the neuropsychological profile of sCJD we administered the cognitive subscale of the Alzheimer’s Disease Assessment Scale (ADAS-cog) in order to determine if and how the sCJD-Subgroups (Met/Met, Met/Val, Val/Val) have different results in the item analysis of the ADAS-cog. Furthermore, we studied how the scores differ from that of patients with Alzheimer’s disease (AD). Methods:33 sCJD patients (11 with definite CJD and 22 with probable CJD) underwent neuropsychological testing with the ADAS-cog and Mini Mental State Exam (MMSE). Of these 31 were genotyped at the Codon 129 (11 Val/Val, 18 Met/Val and 2 Met/Met). The patients were matched in regards to sex and total ADAS-cog score with AD patients. The scores of the 11 ADAS-cog items were compared between the sCJD and the AD groups as well as between the sCJD-subgroups Met/Val and Val/Val and the AD group. Results:The ADAS-cog total score of the sCJD and AD groups was 22.6+/- 6.5, respectively. Regarding the single Item scores of the sCJD patient group and the AD patient group, there were statistically significant differences in the Items Constructional praxis, Word-finding difficulty in spontaneous speech and Spoken language ability. When comparing the sCJD subtypes with each other no statistically significant difference was found in the items. Conclusion: In the speech domain and constructional praxis there is indication of greater impairment in sCJD patients in general when compared with AD patients. A disturbance of the speech appears to be an important characteristic of the Met/Val and Val/Val subtypes of sCJD, and should therefore be the focus of special attention in future neuropsychological studies.
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re-Association between Deposition of Beta-Amyloid and Pathological Prion Protein in Sporadic Creutzfeldt-Jakob Disease
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