Microglia, the immune cells of the brain, can have a beneficial effect in Alzheimer’s disease by phagocytosing amyloid-β. Two-photon in vivo imaging of neuron loss in the intact brain of living Alzheimer’s disease mice revealed an involvement of microglia in neuron elimination, indicated by locally increased number and migration velocity of microglia around lost neurons. Knockout of the microglial chemokine receptor Cx3cr1, which is critical in neuron-microglia communication, prevented neuron loss.

Alzheimer disease amyloid ␤-peptide (A␤) is generated via proteolytic processing of the ␤-amyloid precursor protein by ␤-and ␥-secretase. ␥-Secretase can be blocked by selective inhibitors but can also be modulated by a subset of non-steroidal antiinflammatory drugs, including sulindac sulfide. These drugs selectively reduce the generation of the aggregation-prone 42-amino acid A␤ 42 and concomitantly increase the levels of the rather benign A␤ 38 . Here we show that A␤ 42 and A␤ 38 generation occur independently from each other. The amount of A␤ 42 produced by cells expressing 10 different familial Alzheimer disease (FAD)-associated mutations in presenilin (PS) 1, the catalytic subunit of ␥-secretase, appeared to correlate with the respective age of onset in patients. However, A␤ 38 levels did not show a negative correlation with the age of onset. Modulation of ␥-secretase activity by sulindac sulfide reduced A␤ 42 in the case of wild type PS1 and two FAD-associated PS1 mutations (M146L and A285V). The remaining eight PS1 FAD mutants showed either no reduction of A␤ 42 or only rather subtle effects. Strikingly, even the mutations that showed no effect on A␤ 42 levels allowed a robust increase of A␤ 38 upon treatment with sulindac sulfide. Similar observations were made for fenofibrate, a compound known to increase A␤ 42 and to decrease A␤ 38 . For mutants that predominantly produce A␤ 42 , the ability of fenofibrate to further increase A␤ 42 levels became diminished, whereas A␤ 38 levels were altered to varying extents for all mutants analyzed. Thus, we conclude that A␤ 38 and A␤ 42 production do not depend on each other. Using an independent non-steroidal anti-inflammatory drug derivative, we obtained similar results for PS1 as well as for PS2. These in vitro results were confirmed by in vivo experiments in transgenic mice expressing the PS2 N141I FAD mutant. Our findings therefore have strong implications on the selection of transgenic mouse models used for screening of the A␤ 42 -lowering capacity of ␥-secretase modulators. Furthermore, human patients with certain PS mutations may not respond to ␥-secretase modulators.Alzheimer disease is the most abundant form of dementia, and increasing numbers of patients are to be expected in the near future. Amyloid ␤-peptide (A␤) 5 is a central player in the disease pathology. Originally it was purified as the building block of the disease-defining amyloid plaques. Now it is becoming clear that amyloid plaques are probably not the major neurotoxic entity in the disease rather this is an assembly of soluble oligomeric A␤ species (1). These assemblies initiate the so-called amyloid cascade and finally induce abnormal phosphorylation of tau and subsequent formation of paired helical filaments (2). A␤ is generated by proteolytic processing of the ␤-amyloid precursor protein (APP). Two proteases, ␤-secretase and ␥-secretase, perform the cleavages on the N and C termini of the A␤ domain, respectively (3). ␤-Secretase is a conventional aspartyl protease, whereas ␥-secretase i...

The mechanism by which aggregates of the β-amyloid peptide (Aβ) mediate their toxicity is uncertain. We show here that the expression of the 42-amino-acid isoform of Aβ (Aβ1–42) changes the expression of genes involved in oxidative stress in a Drosophila model of Alzheimer’s disease. A subsequent genetic screen confirmed the importance of oxidative stress and a molecular dissection of the steps in the cellular metabolism of reactive oxygen species revealed that the iron-binding protein ferritin and the H2O2 scavenger catalase are the most potent suppressors of the toxicity of wild-type and Arctic (E22G) Aβ1–42. Likewise, treatment with the iron-binding compound clioquinol increased the lifespan of flies expressing Arctic Aβ1–42. The effect of iron appears to be mediated by oxidative stress as ferritin heavy chain co-expression reduced carbonyl levels in Aβ1–42 flies by 65% and restored the survival and locomotion function to normal. This was achieved despite the presence of elevated levels of the Aβ1–42. Taken together, our data show that oxidative stress, probably mediated by the hydroxyl radical and generated by the Fenton reaction, is essential for Aβ1–42 toxicity in vivo and provide strong support for Alzheimer’s disease therapies based on metal chelation.

Pathogenic generation of the 42-amino acid variant of the amyloid ␤-peptide (A␤) by ␤-and ␥-secretase cleavage of the ␤-amyloid precursor protein (APP) is believed to be causative for Alzheimer disease (AD). Lowering of A␤ 42 production by ␥-secretase modulators (GSMs) is a hopeful approach toward AD treatment. The mechanism of GSM action is not fully understood. Moreover, whether GSMs target the A␤ domain is controversial. To further our understanding of the mode of action of GSMs and the cleavage mechanism of ␥-secretase, we analyzed mutations located at different positions of the APP transmembrane domain around or within the A␤ domain regarding their response to GSMs. We found that A␤ 42 -increasing familial AD mutations of the ␥-secretase cleavage site domain responded robustly to A␤ 42 -lowering GSMs, especially to the potent compound GSM-1, irrespective of the amount of A␤ 42 produced. We thus expect that familial AD patients carrying mutations at the ␥-secretase cleavage sites of APP should respond to GSM-based therapeutic approaches. Systematic phenylalanine-scanning mutagenesis of this region revealed a high permissiveness to GSM-1 and demonstrated a complex mechanism of GSM action as other A␤ species (A␤ 41 , A␤ 39 ) could also be lowered besides A␤ 42 . Moreover, certain mutations simultaneously increased A␤ 42 and the shorter peptide A␤ 38 , arguing that the proposed precursor-product relationship of these A␤ species is not general. Finally, mutations of residues in the proposed GSM-binding site implicated in A␤ 42 generation (Gly-29, Gly-33) and potentially in GSM-binding (Lys-28) were also responsive to GSMs, a finding that may question APP substrate targeting of GSMs.Alzheimer disease (AD) 3 is the most common neurodegenerative disorder worldwide. The ␤-amyloid precursor protein (APP), a type I membrane protein, plays a central role in the pathogenesis of the disease (1). Sequential cleavage of APP by ␤-and ␥-secretase generates the amyloid-␤ (A␤) peptide, which deposits as plaques in the brain of affected patients and represents one of the principal pathological hallmarks of the disease (1). ␥-Secretase is an intramembrane-cleaving protease complex, which cleaves the APP transmembrane domain (TMD) in a progressive, stepwise manner via cleavages at the ⑀-, -, and ␥-sites until it is sufficiently shortened to allow the release of A␤ from the membrane (2-4). A␤ peptides generated by ␥-secretase cleavage differ in their C termini. The major product released is A␤ 40 , whereas A␤ 38 and A␤ 42 represent minor species (1). The highly aggregation-prone, neurotoxic A␤ 42 is believed to be causative for AD by initiating a cascade of pathogenic events, which ultimately causes neurodegeneration and dementia (1). Increased production of A␤ 42 underlies the vast majority of mutations associated with familial AD (FAD), which manifests with a very early disease onset. The majority of FAD mutations have been found in PS1, the catalytic subunit of ␥-secretase (5), whereas only a few mutations were found in its h...

Highlights Estimates of players’ maturity status should be taken every 3–4 months during an annual season, with a focus on players approaching and during peak height velocity. Key stakeholders should be educated about maturation and peak height velocity, particularly in relation to the potential use of bio-banding strategies. Clear lines of communication should be established with key stakeholders in order to identify the volume of weekly physical activity each child is engaged in. The prediction error embroiled within each maturity-estimation equation should be considered, along with the implications of additional errors imposed by spurious anthropometric measurements (i.e., self-reported birth-parent stature). Key stakeholders should be aware of the increased risk of injuries owing to inappropriate training loads across peak height velocity.

Sequential processing of the ␤-amyloid precursor protein by ␤-and ␥-secretase generates the amyloid ␤-peptide (A␤), which is widely believed to play a causative role in Alzheimer disease. Selective lowering of the pathogenic 42-amino acid variant of A␤ by ␥-secretase modulators (GSMs) is a promising therapeutic strategy. Here we report that mutations in presenilin (PS), the catalytic subunit of ␥-secretase, display differential responses to non-steroidal anti-inflammatory drug (NSAID)-type GSMs and more potent second-generation compounds. Although many pathogenic PS mutations resisted lowering of A␤ 42 generation by the NSAID sulindac sulfide, the potent NSAID-like second-generation compound GSM-1 was capable of lowering A␤ 42 for many but not all mutants. We further found that mutations at homologous positions in PS1 and PS2 can elicit differential A␤ 42 responses to GSM-1, suggesting that a positive GSM-1 response depends on the spatial environment in ␥-secretase. The aggressive pathogenic PS1 L166P mutation was one of the few pathogenic mutations that resisted GSM-1, and Leu-166 was identified as a critical residue with respect to the A␤ 42 -lowering response of GSM-1. Finally, we found that GSM-1-responsive and -resistant PS mutants behave very similarly toward other potent second-generation compounds of different structural classes than GSM-1. Taken together, our data show that a positive A␤ 42 response for PS mutants depends both on the particular mutation and the GSM used and that attenuated A␤ 42 responses to low potency GSMs can be overcome for many PS mutants by second generation GSMs. The amyloid ␤-peptide (A␤)4 is a 37-43-amino acid secreted peptide and an invariant pathological hallmark of Alzheimer disease (AD). The 42-amino acid variant A␤ 42 has been suggested to be causative for the disease by triggering the amyloid cascade, a sequence of pathogenic events that ultimately leads to neurodegeneration and dementia in affected patients (1). The pathogenic peptide is generated by a sequential cleavage of the ␤-amyloid precursor protein (APP) by ␤-and ␥-secretase (2). After ␤-secretase cleavage, ␥-secretase cleaves the C-terminal fragment of APP that is left in the membrane by an intramembrane cleavage to release the various A␤ species (3-5). Although A␤ 42 is normally a minor species produced by this cleavage besides the major A␤ 40 species, its production is enhanced by familial AD (FAD) mutations in presenilin (PS) 1 and PS2, the catalytic component of ␥-secretase (6), as well as by a subset of FAD mutations in APP. Targeting ␤-and ␥-secretase by specific inhibitors is one of the current approaches toward an effective AD treatment (7). With respect to ␥-secretase, however, ␥-secretase inhibitors also block the cleavage of Notch1, a major physiological ␥-secretase substrate and, thus, the generation of the Notch1 intracellular domain (NICD), which is a crucial signaling molecule controlling cell differentiation (7). Interfering with the cleavage of this substrate accounts for adverse side effects in...

The two proteases ␤-secretase and ␥-secretase generate the amyloid ␤ peptide and are drug targets for Alzheimer's disease. Here we tested the possibility of targeting the cellular environment of ␤-secretase cleavage instead of the ␤-secretase enzyme itself. ␤-Secretase has an acidic pH optimum and cleaves the amyloid precursor protein in the acidic endosomes. We identified two drugs, bepridil and amiodarone, that are weak bases and are in clinical use as calcium antagonists. Independently of their calcium-blocking activity, both compounds mildly raised the membrane-proximal, endosomal pH and inhibited ␤-secretase cleavage at therapeutically achievable concentrations in cultured cells, in primary neurons, and in vivo in guinea pigs. This shows that an alkalinization of the cellular environment could be a novel therapeutic strategy to inhibit ␤-secretase. Surprisingly, bepridil and amiodarone also modulated ␥-secretase cleavage independently of endosomal alkalinization. Thus, both compounds act as dual modulators that simultaneously target ␤-and ␥-secretase through distinct molecular mechanisms. In addition to Alzheimer's disease, compounds with dual properties may also be useful for drug development targeting other membrane proteins.

Proteolytic cleavage of the amyloid precursor protein (APP) by the two proteases α- and β-secretases controls the generation of the amyloid β peptide (Aβ), a key player in Alzheimer’s disease pathogenesis. The α-secretase ADAM10 and the β-secretase BACE1 have opposite effects on Aβ generation and are assumed to compete for APP as a substrate, such that their cleavages are inversely coupled. This concept was mainly demonstrated in studies using activation or overexpression of α- and β-secretases. Here, we report that this inverse coupling is not seen to the same extent upon inhibition of the endogenous proteases. Genetic and pharmacological inhibition of ADAM10 and BACE1 revealed that the endogenous, constitutive α-secretase cleavage of APP is largely uncoupled from β-secretase cleavage and Aβ generation in neuroglioma H4 cells and in neuronally differentiated SH-SY5Y cells. In contrast, inverse coupling was observed in primary cortical neurons. However, this coupling was not bidirectional. Inhibition of BACE1 increased ADAM10 cleavage of APP, but a reduction of ADAM10 activity did not increase the BACE1 cleavage of APP in the neurons. Our analysis shows that the inverse coupling of the endogenous α- and β-secretase cleavages depends on the cellular model and suggests that a reduction of ADAM10 activity is unlikely to increase the AD risk through increased β-secretase cleavage.