Overlapping profiles of Abeta peptides in the Alzheimer's disease and pathological aging brains

Abstract

IntroductionA hallmark of Alzheimer's disease (AD) is the presence of senile plaques composed of aggregated amyloid β (Aβ) peptides. Pathological aging (PA) is a postmortem classification that has been used to describe brains with plaque pathology similar in extent to AD, minimal cortical tau pathology, and no accompanying history of cognitive decline in the brain donor prior to death. PA may represent either a prodromal phase of AD, a benign form of Aβ accumulation, or inherent individual resistance to the toxic effects of Aβ accumulation. To attempt to distinguish between these possibilities we have systematically characterized Aβ peptides in a postmortem series of PA, AD and non-demented control (NDC) brains.MethodsAβ was sequentially extracted with tris buffered saline (TBS), radioimmunoprecipitation buffer (RIPA), 2% sodium dodecyl sulfate (SDS) and 70% formic acid (FA) from the pre-frontal cortex of 16 AD, eight PA, and six NDC patients. These extracts were analyzed by 1) a panel of Aβ sandwich ELISAs, 2) immunoprecipitation followed by mass spectrometry (IP/MS) and 3) western blotting. These studies enabled us to asses Aβ levels and solubility, peptide profiles and oligomeric assemblies.ResultsIn almost all extracts (TBS, RIPA, 2% SDS and 70% FA) the average levels of Aβ1-40, Aβ1-42, Aβ total, and Aβx-42 were greatest in AD. On average, levels were slightly lower in PA, and there was extensive overlap between Aβ levels in individual PA and AD cases. The profiles of Aβ peptides detected using IP/MS techniques also showed extensive similarity between the PA and AD brain extracts. In select AD brain extracts, we detected more amino-terminally truncated Aβ peptides compared to PA patients, but these peptides represented a minor portion of the Aβ observed. No consistent differences in the Aβ assemblies were observed by western blotting in the PA and AD groups.ConclusionsWe found extensive overlap with only subtle quantitative differences between Aβ levels, peptide profiles, solubility, and SDS-stable oligomeric assemblies in the PA and AD brains. These cross-sectional data indicate that Aβ accumulation in PA and AD is remarkably similar. Such data would be consistent with PA representing a prodromal stage of AD or a resistance to the toxic effects of Aβ.

Neuronal NLRP1 inflammasome activation of Caspase-1 coordinately regulates inflammatory interleukin-1-beta production and axonal degeneration-associated Caspase-6 activation

“…48 Indeed, Nlrp1 protein increased in 5-to 9-month-old PS1ΔE9/APP Sw mice and injection of Nlrp1 siRNAs in mice brains reduced apoptosis, Casp1, IL-1β production, amyloid plaques, and corrected memory deficits. Furthermore, Nlrp1 siRNAs reduced the susceptibility of primary rat cortical neurons to 5 μM Aβ 42 . Human primary neurons are not susceptible to Aβ-mediated toxicity, unless neurons are already vulnerable.…”

“…Activated NLRP1 recruits and activates Casp1, which converts pro-IL-1β into secreted IL-1β, thus activating a second phase of inflammation in astrocytes and microglia. 6 Simultaneously, Casp1 activates Casp6-mediated axonal degeneration 9,11,13 and increased production of Aβ 42 . 41 Aβ 42 becomes toxic to already vulnerable human neurons expressing FAD-associated mutant genes or submitted to agedependent insults, or very high Aβ 42 concentrations activate the Nlrp1 in rodent neurons as demonstrated by Tan. 48 Note that rodents express three paralogous Nlrp1 genes, whereas humans only express one NLRP1 gene.…”

“…6 Simultaneously, Casp1 activates Casp6-mediated axonal degeneration 9,11,13 and increased production of Aβ 42 . 41 Aβ 42 becomes toxic to already vulnerable human neurons expressing FAD-associated mutant genes or submitted to agedependent insults, or very high Aβ 42 concentrations activate the Nlrp1 in rodent neurons as demonstrated by Tan. 48 Note that rodents express three paralogous Nlrp1 genes, whereas humans only express one NLRP1 gene. 43 That the human Nlrp1 protein N-terminus contains a pyrin protein interacting domain, whereas the mouse Nlrp1 contains a NR100 domain of unknown function could explain variability between rodent and human Nlrp1 activation.…”

“…This was consistent with our previous experiments, 40,41 and previously published data showing an increase in Aβ 42 ratio in AD. 42 Neurons pre-treated with NLRP1, CASP1, or CASP6 siRNAs lost that statistically significant increase of Aβ 42 , indicating that the NLRP1-Casp1-Casp6 pathway increased the ratio of Aβ 42 peptides. NLRP1 siRNA in serum-deprived conditions did not significantly decrease Aβ 42, whereas both CASP1 and CASP6 siRNAs did, suggesting that NLRP1 may not the only inflammasome activating Casp1 in serum-deprived conditions.…”

Alternative Selection of β-Site APP-Cleaving Enzyme 1 (BACE1) Cleavage Sites in Amyloid β-Protein Precursor (APP) Harboring Protective and Pathogenic Mutations within the Aβ Sequence

“…8 and 40). Previous work showed that BACE1 also cleaves APP at the ␤Ј-site, but the biological significance of this reaction remained unclear because the ␤Ј-cleaved products of hAPP, CTF␤Ј/C89, and A␤(11-XX) are scarce relative to CTF␤/C99 and A␤(1-XX) (12,41). Along with previously reported data, our results confirm that mAPP is preferentially cleaved at the ␤Ј-site within the A␤ sequence and predominantly generates A␤(11-XX); by contrast, hAPP mostly generates A␤(1-XX) in vivo and in vitro (29 -31).…”