Showing papers by "Bart De Strooper published in 2012"
TL;DR: The evidence supporting toxic Aβ oligomers as drivers of neurodegeneration is reviewed and some suggestions that might facilitate progress are made to facilitate progress in this complex field.
Abstract: The 'toxic Aβ oligomer' hypothesis has attracted considerable attention among Alzheimer's disease researchers as a way of resolving the lack of correlation between deposited amyloid-β (Aβ) in amyloid plaques-in terms of both amount and location-and cognitive impairment or neurodegeneration. However, the lack of a common, agreed-upon experimental description of the toxic Aβ oligomer makes interpretation and direct comparison of data between different research groups impossible. Here we critically review the evidence supporting toxic Aβ oligomers as drivers of neurodegeneration and make some suggestions that might facilitate progress in this complex field.
1,722 citations
TL;DR: Overall, this work provides a coherent explanation for the effect of different FAD mutations, demonstrating the importance of qualitative rather than quantitative changes in the Aβ products, and suggest fundamental improvements for current drug development efforts.
Abstract: The mechanisms by which mutations in the presenilins (PSEN) or the amyloid precursor protein (APP) genes cause familial Alzheimer disease (FAD) are controversial. FAD mutations increase the release of amyloid β (Aβ)42 relative to Aβ40 by an unknown, possibly gain-of-toxic-function, mechanism. However, many PSEN mutations paradoxically impair γ-secretase and 'loss-of-function' mechanisms have also been postulated. Here, we use kinetic studies to demonstrate that FAD mutations affect Aβ generation via three different mechanisms, resulting in qualitative changes in the Aβ profiles, which are not limited to Aβ42. Loss of ɛ-cleavage function is not generally observed among FAD mutants. On the other hand, γ-secretase inhibitors used in the clinic appear to block the initial ɛ-cleavage step, but unexpectedly affect more selectively Notch than APP processing, while modulators act as activators of the carboxypeptidase-like (γ) activity. Overall, we provide a coherent explanation for the effect of different FAD mutations, demonstrating the importance of qualitative rather than quantitative changes in the Aβ products, and suggest fundamental improvements for current drug development efforts.
446 citations
TL;DR: Although γ-secretase is a top target for developing disease-modifying AD therapeutics, interference with Notch signaling should be avoided, and compounds that alter Aβ production byγ- secretase without affecting Notch proteolysis and signaling have been identified.
Abstract: Presenilins were first discovered as sites of missense mutations responsible for early-onset Alzheimer disease (AD). The encoded multipass membrane proteins were subsequently found to be the catalytic components of γ-secretases, membrane-embedded aspartyl protease complexes responsible for generating the carboxyl terminus of the amyloid β-protein (Aβ) from the amyloid protein precursor (APP). The protease complex also cleaves a variety of other type I integral membrane proteins, most notably the Notch receptor, signaling from which is involved in many cell differentiation events. Although γ-secretase is a top target for developing disease-modifying AD therapeutics, interference with Notch signaling should be avoided. Compounds that alter Aβ production by γ-secretase without affecting Notch proteolysis and signaling have been identified and are currently at various stages in the drug development pipeline.
410 citations
TL;DR: A model is proposed in which LRRK2 kinase activity is part of an EndoA phosphorylation cycle that facilitates efficient vesicle formation at synapses, and this work uncovers a regulatory mechanism that indicates that reduced L RRK2 Kinase activity facilitates EndOA membrane association, while increased kinases activity inhibits membrane association.
326 citations
TL;DR: Drosophila UBIAD1/Heix was identified as a modifier of pink1, a gene mutated in Parkinson’s disease that affects mitochondrial function, and it was found that vitamin K2 was necessary and sufficient to transfer electrons in DrosophILA mitochondria.
Abstract: Human UBIAD1 localizes to mitochondria and converts vitamin K(1) to vitamin K(2). Vitamin K(2) is best known as a cofactor in blood coagulation, but in bacteria it is a membrane-bound electron carrier. Whether vitamin K(2) exerts a similar carrier function in eukaryotic cells is unknown. We identified Drosophila UBIAD1/Heix as a modifier of pink1, a gene mutated in Parkinson's disease that affects mitochondrial function. We found that vitamin K(2) was necessary and sufficient to transfer electrons in Drosophila mitochondria. Heix mutants showed severe mitochondrial defects that were rescued by vitamin K(2), and, similar to ubiquinone, vitamin K(2) transferred electrons in Drosophila mitochondria, resulting in more efficient adenosine triphosphate (ATP) production. Thus, mitochondrial dysfunction was rescued by vitamin K(2) that serves as a mitochondrial electron carrier, helping to maintain normal ATP production.
297 citations
TL;DR: Advances in understanding of the function of ncRNAs in the CNS are discussed, with a focus on the potential involvement of specific species, such as microRNAs, endogenous small interfering RNAs, long intergenic non-coding RNas, and natural antisense transcripts, in various neurodegenerative disorders.
Abstract: The importance of various classes of regulatory non-protein-coding RNA molecules (ncRNAs) in the normal functioning of the CNS is becoming increasingly evident. ncRNAs are involved in neuronal cell specification and patterning during development, but also in higher cognitive processes, such as structural plasticity and memory formation in the adult brain. We discuss advances in understanding of the function of ncRNAs in the CNS, with a focus on the potential involvement of specific species, such as microRNAs, endogenous small interfering RNAs, long intergenic non-coding RNAs, and natural antisense transcripts, in various neurodegenerative disorders. This emerging field is anticipated to profoundly affect clinical research, diagnosis, and therapy in neurology.
233 citations
TL;DR: A novel mouse model provides evidence that small, soluble Aβ1–42 oligomers are able to induce extensive neuronal loss in vivo and initiate a cascade of events that mimic the key neuropathological hallmarks of AD.
Abstract: Neuronal and synaptic degeneration are the best pathological correlates for memory decline in Alzheimer's disease (AD). Although the accumulation of soluble low-molecular-weight amyloid-β (Aβ) oligomers has been suggested to trigger neurodegeneration in AD, animal models overexpressing or infused with Aβ lack neuronal loss at the onset of memory deficits. Using a novel in vivo approach, we found that repeated hippocampal injections of small soluble Aβ(1-42) oligomers in awake, freely moving mice were able to induce marked neuronal loss, tau hyperphosphorylation, and deficits in hippocampus-dependent memory. The neurotoxicity of small Aβ(1-42) species was observed in vivo as well as in vitro in association with increased caspase-3 activity and reduced levels of the NMDA receptor subunit NR2B. We found that the sequestering agent transthyretin is able to bind the toxic Aβ(1-42) species and attenuated the loss of neurons and memory deficits. Our novel mouse model provides evidence that small, soluble Aβ(1-42) oligomers are able to induce extensive neuronal loss in vivo and initiate a cascade of events that mimic the key neuropathological hallmarks of AD.
168 citations
TL;DR: It is shown that L1 and CHL1 are cleaved by BACE1 under physiological conditions, and this work will help to predict or interpret possible side effects of Bace1 inhibitor drugs in current clinical trials.
162 citations
TL;DR: It is found that the microRNA network dependent on the endoribonuclease Dicer, and specifically microRNA miR-29a, was critical for diminishing the sensitivity of the thymic epithelium to simulated infection signals, protecting the thcyus against inappropriate involution.
Abstract: Thymic output is a dynamic process, with high activity at birth punctuated by transient periods of involution during infection Interferon-α (IFN-α) is a critical molecular mediator of pathogen-induced thymic involution, yet despite the importance of thymic involution, relatively little is known about the molecular integrators that establish sensitivity Here we found that the microRNA network dependent on the endoribonuclease Dicer, and specifically microRNA miR-29a, was critical for diminishing the sensitivity of the thymic epithelium to simulated infection signals, protecting the thymus against inappropriate involution In the absence of Dicer or the miR-29a cluster in the thymic epithelium, expression of the IFN-α receptor by the thymic epithelium was higher, which allowed suboptimal signals to trigger rapid loss of thymic cellularity
160 citations
TL;DR: The data show that BACE1 plays a critical role in retinal homeostasis and that the use of BACE inhibitors for AD should be viewed with extreme caution as they could lead to retinal pathology and exacerbate conditions such as age‐related macular degeneration.
Abstract: β‐Secretase (BACE1) is a major drug target for combating Alzheimer9s disease (AD). Here we show that BACE1 −/− mice develop significant retinal pathology including retinal thinning, apoptosis, reduced retinal vascular density and an increase in the age pigment, lipofuscin. BACE1 expression is highest in the neural retina while BACE2 was greatest in the retinal pigment epithelium (RPE)/choroid. Pigment epithelial‐derived factor, a known regulator of γ‐secretase, inhibits vascular endothelial growth factor (VEGF)‐induced in vitro and in vivo angiogenesis and this is abolished by BACE1 inhibition. Moreover, intravitreal administration of BACE1 inhibitor or BACE1 small interfering RNA (siRNA) increases choroidal neovascularization in mice. BACE1 induces ectodomain shedding of vascular endothelial growth factor receptor 1 (VEGFR1) which is a prerequisite for γ‐secretase release of a 100 kDa intracellular domain. The increase in lipofuscin following BACE1 inhibition and RNAI knockdown is associated with lysosomal perturbations. Taken together, our data show that BACE1 plays a critical role in retinal homeostasis and that the use of BACE inhibitors for AD should be viewed with extreme caution as they could lead to retinal pathology and exacerbate conditions such as age‐related macular degeneration.
140 citations
TL;DR: A central role for Complex I dysfunction in pink1-associated defects is indicated, and genetic analyses with heterologous ETC enzymes suggest that Ndi1p-dependent NADH dehydrogenase activity largely acts downstream of, or in parallel to, Pink1 but upstream of Parkin and mitochondrial remodeling.
Abstract: Pink1 is a mitochondrial kinase involved in Parkinson's disease, and loss of Pink1 function affects mitochondrial morphology via a pathway involving Parkin and components of the mitochondrial remodeling machinery. Pink1 loss also affects the enzymatic activity of isolated Complex I of the electron transport chain (ETC); however, the primary defect in pink1 mutants is unclear. We tested the hypothesis that ETC deficiency is upstream of other pink1-associated phenotypes. We expressed Saccaromyces cerevisiae Ndi1p, an enzyme that bypasses ETC Complex I, or sea squirt Ciona intestinalis AOX, an enzyme that bypasses ETC Complex III and IV, in pink1 mutant Drosophila and find that expression of Ndi1p, but not of AOX, rescues pink1-associated defects. Likewise, loss of function of subunits that encode for Complex I–associated proteins displays many of the pink1-associated phenotypes, and these defects are rescued by Ndi1p expression. Conversely, expression of Ndi1p fails to rescue any of the parkin mutant phenotypes. Additionally, unlike pink1 mutants, fly parkin mutants do not show reduced enzymatic activity of Complex I, indicating that Ndi1p acts downstream or parallel to Pink1, but upstream or independent of Parkin. Furthermore, while increasing mitochondrial fission or decreasing mitochondrial fusion rescues mitochondrial morphological defects in pink1 mutants, these manipulations fail to significantly rescue the reduced enzymatic activity of Complex I, indicating that functional defects observed at the level of Complex I enzymatic activity in pink1 mutant mitochondria do not arise from morphological defects. Our data indicate a central role for Complex I dysfunction in pink1-associated defects, and our genetic analyses with heterologous ETC enzymes suggest that Ndi1p-dependent NADH dehydrogenase activity largely acts downstream of, or in parallel to, Pink1 but upstream of Parkin and mitochondrial remodeling.
TL;DR: It is demonstrated that the secretion of Aβ is enhanced in an in vitro model of neuronal ageing, correlating with an increase in γ‐secretase complex formation, and nitrosative stress is identified as a potential mechanistic link between ageing and AD.
Abstract: Inherited familial Alzheimer's disease (AD) is characterized by small increases in the ratio of Aβ42 versus Aβ40 peptide which is thought to drive the amyloid plaque formation in the brain of these patients. Little is known however whether ageing, the major risk factor for sporadic AD, affects amyloid beta-peptide (Aβ) generation as well. Here we demonstrate that the secretion of Aβ is enhanced in an in vitro model of neuronal ageing, correlating with an increase in γ-secretase complex formation. Moreover we found that peroxynitrite (ONOO(-)), produced by the reaction of superoxide anion with nitric oxide, promoted the nitrotyrosination of presenilin 1 (PS1), the catalytic subunit of γ-secretase. This was associated with an increased association of the two PS1 fragments, PS1-CTF and PS1-NTF, which constitute the active catalytic centre. Furthermore, we found that peroxynitrite shifted the production of Aβ towards Aβ(42) and increased the Aβ(42) /Aβ(40) ratio. Our work identifies nitrosative stress as a potential mechanistic link between ageing and AD.
TL;DR: Chronic treatment with EVP-0015962 was well tolerated in mice and lowered the production of Aβ42, attenuated memory deficits, and reduced Aβ plaque formation and inflammation in Tg2576 transgenic animals.
Abstract: A hallmark of Alzheimer’s disease is the presence of senile plaques in human brain primarily containing the amyloid peptides Aβ42 and Aβ40. Many drug discovery efforts have focused on decreasing the production of Aβ42 through γ-secretase inhibition. However, identification of γ-secretase inhibitors has also uncovered mechanism-based side effects. One approach to circumvent these side effects has been modulation of γ-secretase to shift Aβ production to favor shorter, less amyloidogenic peptides than Aβ42, without affecting the overall cleavage efficiency of the enzyme. This approach, frequently called γ-secretase modulation, appears more promising and has lead to the development of new therapeutic candidates for disease modification in Alzheimer’s disease. Here we describe EVP-0015962, a novel small molecule γ-secretase modulator. EVP-0015962 decreased Aβ42 in H4 cells (IC50 = 67 nM) and increased the shorter Aβ38 by 1.7 fold at the IC50 for lowering of Aβ42. AβTotal, as well as other carboxyl-terminal fragments of amyloid precursor protein, were not changed. EVP-0015962 did not cause the accumulation of other γ-secretase substrates, such as the Notch and ephrin A4 receptors, whereas a γ-secretase inhibitor reduced processing of both. A single oral dose of EVP-0015962 (30 mg/kg) decreased Aβ42 and did not alter AβTotal peptide levels in a dose-dependent manner in Tg2576 mouse brain at an age when overt Aβ deposition was not present. In Tg2576 mice, chronic treatment with EVP-0015962 (20 or 60 mg/kg/day in a food formulation) reduced Aβ aggregates, amyloid plaques, inflammatory markers, and cognitive deficits. EVP-0015962 is orally bioavailable, detected in brain, and a potent, selective γ-secretase modulator in vitro and in vivo. Chronic treatment with EVP-0015962 was well tolerated in mice and lowered the production of Aβ42, attenuated memory deficits, and reduced Aβ plaque formation and inflammation in Tg2576 transgenic animals. In summary, these data suggest that γ-secretase modulation with EVP-0015962 represents a viable therapeutic alternative for disease modification in Alzheimer’s disease.
TL;DR: The immunohistochemical localization of LRRK2 in adult mouse and early postnatal mouse brain development is demonstrated and a functional role for LRRk2 in striosomes is suggested, but this work does not suggest a specific requirement of L RRK2 for generation or maintenance of the striosome compartment.
TL;DR: It is shown that PS2 plays an important role in mediating essential Notch signaling in several peripheral organs during pharmacological inhibition of PS1 and provides preclinical in vivo proof of concept for PS2-sparing inhibition as a novel, tolerable and efficacious γ-secretase targeting strategy for AD.
Abstract: gamma-Secretase inhibition represents a major therapeutic strategy for lowering amyloid beta (A beta) peptide production in Alzheimers disease (AD). Progress toward clinical use of gamma-secretase inhibitors has, however, been hampered due to mechanism-based adverse events, primarily related to impairment of Notch signaling. The gamma-secretase inhibitor MRK-560 represents an exception as it is largely tolerable in vivo despite displaying only a small selectivity between A beta production and Notch signaling in vitro. In exploring the molecular basis for the observed tolerability, we show that MRK-560 displays a strong preference for the presenilin 1(PS1) over PS2 subclass of gamma-secretases and is tolerable in wild-type mice but causes dose-dependent Notch-related side effect in PS2-deficient mice at drug exposure levels resulting in a substantial decrease in brain A beta levels. This demonstrates that PS2 plays an important role in mediating essential Notch signaling in several peripheral organs during pharmacological inhibition of PS1 and provide preclinical in vivo proof of concept for PS2-sparing inhibition as a novel, tolerable and efficacious gamma-secretase targeting strategy for AD.
TL;DR: The results indicate that the complex in vivo Aβ peptide array and variations thereof is critical in Alzheimer disease, which can influence the selection of current and new therapeutic strategies.
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TL;DR: A novel type of lipid‐coated superparamagnetic nanoparticles are manufactured that allow for a rapid isolation of plasma membranes (PMs), enabling high‐resolution proteomic, glycomic and lipidomic analyses of the cell surface, finding that many proteins are selectively downregulated at thecell surface of presenilin knockout cells.
Abstract: We manufactured a novel type of lipid‐coated superparamagnetic nanoparticles that allow for a rapid isolation of plasma membranes (PMs), enabling high‐resolution proteomic, glycomic and lipidomic analyses of the cell surface. We used this technology to characterize the effects of presenilin knockout on the PM composition of mouse embryonic fibroblasts. We found that many proteins are selectively downregulated at the cell surface of presenilin knockout cells concomitant with lowered surface levels of cholesterol and certain sphingomyelin species, indicating defects in specific endosomal transport routes to and/or from the cell surface. Snapshots of N‐glycoproteomics and cell surface glycan profiling further underscored the power and versatility of this novel methodology. Since PM proteins provide many pathologically relevant biomarkers representing two‐thirds of the currently used drug targets, this novel technology has great potential for biomedical and pharmaceutical applications.
TL;DR: Reduced Abca2 levels in mammalian cells in vitro, in Drosophila melanogaster and in mice resulted in altered γ-secretase processing of APP, and thus Aβ generation, without affecting Notch cleavage.
TL;DR: The results suggest that modulation of the membrane‐soluble domains could be a valuable alternative to reduce excessive Aβ generation.
Abstract: Several studies suggest that the generation of Aβ is highly dependent on the levels of cholesterol within membranes' detergent-resistant microdomains (DRM). Indeed, the β-amyloid precursor protein (APP) cleaving machinery, namely β- and γ-secretases, has been shown to be present in DRM and its activity depends on membrane cholesterol levels. Counterintuitive to the localization of the cleavage machinery, the substrate, APP, localizes to membranes' detergent-soluble microdomains enriched in phospholipids (PL), indicating that Aβ generation is highly dependent on the capacity of enzyme and substrate to diffuse along the lateral plane of the membrane and therefore on the internal equilibrium of the different lipids of DRM and non-DRM domains. Here, we studied to which extent changes in the content of a main non-DRM lipid might affect the proteolytic processing of APP. As phosphatidylethanolamine (PE) accounts for the majority of PL, we focused on its impact on the regulation of APP proteolysis. In mammalian cells, siRNA-mediated knock-down of PE synthesis resulted in decreased Aβ owing to a dual effect: promoted α-secretase cleavage and decreased γ-secretase processing of APP. In vivo, in Drosophila melanogaster, genetic reduction in PL synthesis results in decreased γ-secretase-dependent cleavage of APP. These results suggest that modulation of the membrane-soluble domains could be a valuable alternative to reduce excessive Aβ generation.
TL;DR: It is shown that PS1 and PS2 are located at the interface between mitochondria and endoplasmic reticulum (ER), which emerges as a new potential determinant of AD pathogenesis.
Abstract: Alzheimer9s disease (AD) is characterized by the loss of hippocampal and cortical neurons as a consequence of the accumulation of amyloid‐β (Aβ). Aβ is produced from the amyloid precursor protein (APP) by the γ‐secretase complex components presenilin‐1 (PS1) and ‐2 (PS2), which are mutated in genetic forms of AD. In this issue, Schon and coworkers show that PS1 and PS2 are located at the interface between mitochondria and endoplasmic reticulum (ER). In models of familial and sporadic AD, these two organelles are juxtaposed closely, affecting shared lipid metabolic pathways. The interface between mitochondria and ER emerges as a new potential determinant of AD pathogenesis.
TL;DR: It is reported that APOE4 activates a matrix metalloproteinase pathway in cells forming the blood–brain barrier in mice, leading to its breakdown and the neuronal uptake of blood-derived neurotoxic proteins, and suggested that cyclophilin A (CypA), a component of the APOE 4-activated pathway, is a potential target for treating APoe4-mediated neuronal dysfunction.
Abstract: Alterations in brain blood vessels in mice precede the neural dysfunction associated with Alzheimer's disease. The finding highlights potential targets for drug development. See Letter p.512
There are known connections between the Alzheimer's-disease-linked APOE4 gene and cerebrovascular integrity. However, the mechanisms that drive known blood–brain-barrier dysfunction both in rodent models and in APOE4-associated neurological disorders are unknown. Here, Berislav Zlokovic and colleagues report that APOE4 activates a matrix metalloproteinase pathway in cells forming the blood–brain barrier in mice, leading to its breakdown and the neuronal uptake of blood-derived neurotoxic proteins. In turn, microvascular and cerebral blood flow are reduced; together, these deficits can initiate neurodegenerative changes in rodents. The authors suggest that cyclophilin A (CypA), a component of the APOE4-activated pathway, is a potential target for treating APOE4-mediated neuronal dysfunction. Treatment with the CypA inhibitor cyclosporine A restores the blood–brain barrier in APOE4 mice.
TL;DR: A rare gene variant has been found that decreases the peptide deposition seen in the brains of people with Alzheimer's disease, providing support for the hypothesis that reducing the beta-cleavage of APP may protect against Alzheimer's.
Abstract: A rare gene variant has been found that decreases the peptide deposition seen in the brains of people with Alzheimer's disease. The mutation may also slow the normal cognitive decline that occurs with age. See Letter p.96
Alzheimer's disease is characterized by the existence in the brain of amyloid plaques, which form as a consequence of proteolic cleavage of amyloid precursor protein (APP). By screening almost 2,000 genomes, Kari Stefansson and colleagues find a coding mutation in the APP gene that protects against Alzheimer's disease and cognitive decline in elderly people who lack symptoms of Alzheimer's disease. The mutation causes an approximately 40% reduction in the formation of amyloidogenic peptides in vitro. The strong protective effect of this mutation, which lies next to the aspartyl protease beta-site in APP, provides support for the hypothesis that reducing the beta-cleavage of APP may protect against Alzheimer's. The results also raise the possibility that Alzheimer's disease and cognitive decline in the elderly are mechanistically related.
TL;DR: In conclusion, the authors do not agree that conclusive evidence is presented by Shilling et al. (1) to refute the hypothesis that presenilins act as passive ER Ca2+ leak channels, but respectfully disagree with the interpretation of their data.
TL;DR: A peptide sequence that, when fused to a virally derived translocation peptide, significantly lowered Aβ production in cell‐free and cell‐based assays using APP‐carboxy terminal fragment as a direct γ‐secretase substrate.
Abstract: Presenilins (PSENs) form the catalytic component of the γ-secretase complex, responsible for intramembrane proteolysis of amyloid precursor protein (APP) and Notch, among many other membrane proteins Previously, we identified a PSEN1-binding domain in APP, encompassing half of the transmembrane domain following the amyloid β (Aβ) sequence Based on this, we designed peptides mimicking this interaction domain with the aim to selectively block APP processing and Aβ generation through interfering with enzyme-substrate binding We identified a peptide sequence that, when fused to a virally derived translocation peptide, significantly lowered Aβ production (IC50: 317 nM) in cell-free and cell-based assays using APP-carboxy terminal fragment as a direct γ-secretase substrate Being derived from the APP sequence, this inhibitory peptide did not affect NotchΔE γ-cleavage, illustrating specificity and potential therapeutic value In cell-based assays, the peptide strongly suppressed APP shedding, demonstrating th
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