Following ectodomain shedding by β-secretase, successive proteolytic cleavages within the transmembrane sequence (TMS) of the amyloid precursor protein (APP) catalyzed by γ-secretase result in the release of amyloid-β (Aβ) peptides of variable length. Aβ peptides with 42 amino acids appear to be the key pathogenic species in Alzheimer's disease, as they are believed to initiate neuronal degeneration. Sulindac sulfide, which is known as a potent γ-secretase modulator (GSM), selectively reduces Aβ42 production in favor of shorter Aβ species, such as Aβ38. By studying APP-TMS dimerization we previously showed that an attenuated interaction similarly decreased Aβ42 levels and concomitantly increased Aβ38 levels. However, the precise molecular mechanism by which GSMs modulate Aβ production is still unclear. In this study, using a reporter gene-based dimerization assay, we found that APP-TMS dimers are destabilized by sulindac sulfide and related Aβ42-lowering compounds in a concentration-dependent manner. By surface plasmon resonance analysis and NMR spectroscopy, we show that sulindac sulfide and novel sulindac-derived compounds directly bind to the Aβ sequence. Strikingly, the attenuated APP-TMS interaction by GSMs correlated strongly with Aβ42-lowering activity and binding strength to the Aβ sequence. Molecular docking analyses suggest that certain GSMs bind to the GxxxG dimerization motif in the APP-TMS. We conclude that these GSMs decrease Aβ42 levels by modulating APP-TMS interactions. This effect specifically emphasizes the importance of the dimeric APP-TMS as a promising drug target in Alzheimer's disease.

Numerous studies have implicated the abnormal accumulation of intraneuronal amyloid-β (Aβ) as an important contributor to Alzheimer’s disease (AD) pathology, capable of triggering neuroinflammation, tau hyperphosphorylation and cognitive deficits. However, the occurrence and pathological relevance of intracellular Aβ remain a matter of controversial debate. In this study, we have used a multidimensional approach including high-magnification and super-resolution microscopy, cerebro-spinal fluid (CSF) mass spectrometry analysis and ELISA to investigate the Aβ pathology and its associated cognitive impairments, in a novel transgenic rat model overexpressing human APP. Our microscopy studies with quantitative co-localization analysis revealed the presence of intraneuronal Aβ in transgenic rats, with an immunological signal that was clearly distinguished from that of the amyloid precursor protein (APP) and its C-terminal fragments (CTFs). The early intraneuronal pathology was accompanied by a significant elevation of soluble Aβ42 peptides that paralleled the presence and progression of early cognitive deficits, several months prior to amyloid plaque deposition. Aβ38, Aβ39, Aβ40 and Aβ42 peptides were detected in the rat CSF by MALDI-MS analysis even at the plaque-free stages; suggesting that a combination of intracellular and soluble extracellular Aβ may be responsible for impairing cognition at early time points. Taken together, our results demonstrate that the intraneuronal development of AD-like amyloid pathology includes a mixture of molecular species (Aβ, APP and CTFs) of which a considerable component is Aβ; and that the early presence of these species within neurons has deleterious effects in the CNS, even before the development of full-blown AD-like pathology.Electronic supplementary materialThe online version of this article (doi:10.1186/2051-5960-2-61) contains supplementary material, which is available to authorized users.

The identification of hereditary familial Alzheimer disease (FAD) mutations in the amyloid precursor protein (APP) and presenilin-1 (PS1) corroborated the causative role of amyloid-␤ peptides with 42 amino acid residues (A␤42) in the pathogenesis of AD. Although most FAD mutations are known to increase A␤42 levels, mutations within the APP GxxxG motif are known to lower A␤42 levels by attenuating transmembrane sequence dimerization. Here, we show that aberrant A␤42 levels of FAD mutations can be rescued by GxxxG mutations. The combination of the APP-GxxxG mutation G33A with APP-FAD mutations yielded a constant 60% decrease of A␤42 levels and a concomitant 3-fold increase of A␤38 levels compared with the Gly 33 wild-type as determined by ELISA. In the presence of PS1-FAD mutations, the effects of G33A were attenuated, apparently attributable to a different mechanism of PS1-FAD mutants compared with APP-FAD mutants. Our results contribute to a general understanding of the mechanism how APP is processed by the ␥-secretase module and strongly emphasize the potential of the GxxxG motif in the prevention of sporadic AD as well as FAD. APP2 and APLPs were conventionally thought to exist and to act as monomers. However, biochemical and structural data have accumulated over the past few years, indicating that APP and APLPs exist as functional dimers or even are present in higher oligomeric units (1-6). Interactions of APP and APLPs were reported to promote cell adhesion in a homo-and heterotypic manner (7,8). Among other mechanisms, the varying strength of APP dimerization mediated through N-terminal sites (5) or by the transmembrane sequence (TMS) (9) has been reported to influence APP processing.APP is first cleaved by the ␤-site APP cleaving enzyme and is then sequentially processed by the ␥-secretase complex to generate A␤ peptides of varying length (10, 11). ␥-Secretase cleavage specificity is modulated by the GxxxG ("G-triple-x-G") dimerization motif of the APP-TMS, and we showed previously that APP can be cleaved as a homodimer by ␤-and ␥-secretases (9). APP, APLP1, and APLP2 share similar interaction motifs and can form APP-APLP1 and APP-APLP2 complexes (7). Cotransfections of APP with APLP1 or APLP2 influenced APP processing into A␤ leading to decreased A␤40 and A␤42 levels likely through an influence on ␥-secretase cleavages (7).According to the amyloid hypothesis, A␤ peptides represent the main culprit of Alzheimer disease (AD). Based on this assumption is the appealing prediction that reducing A␤ levels would ameliorate Alzheimer symptoms (12,13). In the current model of A␤ generation, the initial cut at the ⑀-site is executed by the presenilins of the ␥-secretase complex, leading to formation of the APP intracellular domain and A␤49 or A␤48 peptides (10, 14). The latter two likely remain bound to the active site and are successively cleaved every three to four residues at the -site and at the ␥-sites (11, 15). Most likely, two product lines exist. In the product line encompassing A␤40, A␤49 is trimmed to A␤4...

The amyloid-β (Aβ) peptide is contained within the C-terminal fragment (β-CTF) of the amyloid precursor protein (APP) and is intimately linked to Alzheimer's disease. In vivo, Aβ is generated by sequential cleavage of β-CTF within the γ-secretase module. To investigate γ-secretase function, in vitro assays are in widespread use which require a recombinant β-CTF substrate expressed in bacteria and purified from inclusion bodies, termed C100. So far, little is known about the conformation of C100 under different conditions of purification and refolding. Since C100 dimerization influences the efficiency and specificity of γ-secretase cleavage, it is also of great interest to determine the secondary structure and the oligomeric state of the synthetic substrate as well as the binding properties of small molecules named γ-secretase modulators (GSMs) which we could previously show to modulate APP transmembrane sequence interactions [Richter et al. (2010) Proc. Natl. Acad. Sci. U.S.A. 107, 14597-14602]. Here, we use circular dichroism and continuous-wave electron spin resonance measurements to show that C100 purified in a buffer containing SDS at micelle-forming concentrations adopts a highly stable α-helical conformation, in which it shows little tendency to aggregate or to form higher oligomers than dimers. By surface plasmon resonance analysis and molecular modeling we show that the GSM sulindac sulfide binds to C100 and has a preference for C100 dimers.

Financial toxicity is a side effect of cancer that results from the perceived financial distress an individual may experience in the course of the disease. The purpose of this paper is to analyse underlying factors related to subjective financial distress in high-income countries with universal healthcare coverage. A systematic literature review was conducted to identify qualitative and quantitative studies of cancer patient-reported subjective financial distress by performing a search in the databases of PubMed, PsycINFO and CINAHL up to December 2020. A qualitative synthesis was performed linking the time-dependent occurrence of risk factors to derived categories of risk factors. Out of 4321 identified records, 30 quantitative and 16 qualitative studies were eligible. Classification of risk factors resulted in eight categories with a total of 34 subcategories. Subjective financial distress is primarily determined by pre-diagnosis sociodemographic- factors as well as financial and work factors that might change during the course of the disease. The design of healthcare and social security systems shapes the country-specific degree of subjective financial distress. Further research should focus on evolving multidisciplinary intervention schemes and multidimensional instruments for subjective financial distress to account for identified risk factors in universal healthcare systems more precisely.

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A cationic iron complex has been found to catalyze the aminolysis of meso-N-aryl aziridines very efficiently furnishing valuable 1,2-diamines in typically excellent yields. This protocol is compatible with a range of functional groups both in the aziridine and amine components.

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