The role of Abeta-induced calcium dysregulation in the pathogenesis of Alzheimer's disease

Innovative pathological network-based multitarget approaches for Alzheimer's disease treatment

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease and is a major health threat globally. Its prevalence is forecasted to exponentially increase during the next 30 years due to the global aging population. Currently, approved drugs are merely symptomatic, being ineffective in delaying or blocking the relentless disease advance. Intensive AD research describes this disease as a highly complex multifactorial disease. Disclosure of novel pathological pathways and their interconnections has had a major impact on medicinal chemistry drug development for AD over the last two decades. The complex network of pathological events involved in the onset of the disease has prompted the development of multitarget drugs. These chemical entities combine pharmacological activities toward two or more drug targets of interest. These multitarget-directed ligands are proposed to modify different nodes in the pathological network aiming to delay or even stop disease progression. Here, we review the multitarget drug development strategy for AD during the last decade.

Design and Synthesis of Multi-Functional Ligands through Hantzsch Reaction: Targeting Ca2+ Channels, Activating Nrf2 and Possessing Cathepsin S Inhibitory, and Antioxidant Properties

This work relates to the design and synthesis of a series of novel multi-target directed ligands (MTDLs), i.e., compounds 4a-l, via a convenient one-pot three-component Hantzsch reaction. This approach targeted calcium channel antagonism, antioxidant capacity, cathepsin S inhibition, and interference with Nrf2 transcriptional activation. Of these MTDLs, 4i emerged as a promising compound, demonstrating robust antioxidant activity, the ability to activate Nrf2-ARE pathways, as well as calcium channel blockade and cathepsin S inhibition. Dihydropyridine 4i represents the first example of an MTDL that combines these biological activities.

Hyperactivity of medial prefrontal cortex pyramidal neurons occurs in a mouse model of early-stage Alzheimer's disease without β-amyloid accumulation

The normal function of the medial prefrontal cortex (mPFC) is essential for regulating neurocognition, but it is disrupted in the early stages of Alzheimer's disease (AD) before the accumulation of Aβ and the appearance of symptoms. Despite this, little is known about how the functional activity of medial prefrontal cortex pyramidal neurons changes as Alzheimer's disease progresses during aging. We used electrophysiological techniques (patch-clamping) to assess the functional activity of medial prefrontal cortex pyramidal neurons in the brain of 3xTg-Alzheimer's disease mice modeling early-stage Alzheimer's disease without Aβ accumulation. Our results indicate that firing rate and the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) were significantly increased in medial prefrontal cortex neurons from young Alzheimer's disease mice (4-5-month, equivalent of <30-year-old humans) compared to age-matched control mice. Blocking ionotropic glutamatergic NMDA receptors, which regulate neuronal excitability and Ca²⁺ homeostasis, abolished this neuronal hyperactivity. There were no changes in Ca²⁺ influx through the voltage-gated Ca²⁺ channels (VGCCs) or inhibitory postsynaptic activity in medial prefrontal cortex neurons from young Alzheimer's disease mice compared to controls. Additionally, acute exposure to Aβ42 potentiated medial prefrontal cortex neuronal hyperactivity in young Alzheimer's disease mice but had no effects on controls. These findings indicate that the hyperactivity of medial prefrontal cortex pyramidal neurons at early-stage Alzheimer's disease is induced by an abnormal increase in presynaptic glutamate release and postsynaptic NMDA receptor activity, which initiates neuronal Ca²⁺ dyshomeostasis. Additionally, because accumulated Aβ forms unconventional but functional Ca²⁺ channels in medial prefrontal cortex neurons in the late stage of Alzheimer's disease, our study also suggests an exacerbated Ca²⁺ dyshomeostasis in medial prefrontal cortex pyramidal neurons following overactivation of such VGCCs.

Tenuifolin in the prevention of Alzheimer's disease-like phenotypes: Investigation of the mechanisms from the perspectives of calpain system, ferroptosis, and apoptosis

Polygala tenuifolia was documented to calm the mind and promote wisdom. However, its underlying mechanisms are still unclear. This study aimed to investigate the mechanisms underlying the effects of tenuifolin (Ten) on Alzheimer's disease (AD)-like phenotypes. We first applied bioinformatics methods to screen the mechanisms of P. tenuifolia in the treatment of AD. Thereafter, the d-galactose combined with Aβ1-42 (GCA) was applied to model AD-like behaviors and investigate the action mechanisms of Ten, one active component of P. tenuifolia. The data showed that P. tenuifolia actioned through multi-targets and multi-pathways, including regulation of synaptic plasticity, apoptosis, and calcium signaling, and so forth. Furthermore, in vitro experiments demonstrated that Ten prevented intracellular calcium overload, abnormal calpain system, and down-regulation of BDNF/TrkB signaling induced by GCA. Moreover, Ten suppressed oxidative stress and ferroptosis in HT-22 cells induced by GCA. Calpeptin and ferroptosis inhibitor prevented the decrease of cell viability induced by GCA. Interestingly, calpeptin did not interrupt GCA-induced ferroptosis in HT-22 cells but blocked the apoptosis. Animal experiments further demonstrated that Ten prevented GCA-induced memory impairment in mice and increased synaptic protein expression while reducing m-calpain expression. Ten prevents AD-like phenotypes through multiple signaling by inhibiting oxidative stress and ferroptosis, maintaining the stability of calpain system, and suppressing neuronal apoptosis.

The Role of Caspases in Alzheimer's Disease: Pathophysiology Implications and Pharmacologic Modulation

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide. Although the main cause of the onset and development of AD is not known yet, neuronal death due to pathologic changes such as amyloid-β (Aβ) deposition, tau aggregation, neuroinflammation, oxidative stress, and calcium dyshomeostasis are considered to be the main cause. At the present, there is no cure for this insidious disorder. However, accurate identification of molecular changes in AD can help provide new therapeutic goals. Caspases are a group of proteases which are known because of their role in cellular apoptosis. In addition, different caspases are involved in other cellular responses to the environment, such as induction of inflammation. Emerging evidence suggest that these proteases play a central role in AD pathophysiology due to their role in the processing of amyloid-β protein precursor, tau cleavage, and neuroinflammation. Therefore, it seems that targeting caspases may be a suitable therapeutic option to slow the progression of AD. This review focuses on the role of caspases in AD pathophysiology and introduce results from studies targeted caspases in different models of AD.

Effects of Familial Alzheimer's Disease Mutations on the Assembly of a β-Hairpin Peptide Derived from Aβ16-36

Familial Alzheimer's disease (FAD) is associated with mutations in the β-amyloid peptide (Aβ) or the amyloid precursor protein (APP). FAD mutations of Aβ were incorporated into a macrocyclic peptide that mimics a β-hairpin to study FAD point mutations K16N, A21G, E22Δ, E22G, E22Q, E22K, and L34V and their effect on assembly, membrane destabilization, and cytotoxicity. The X-ray crystallographic structures of the four E22 mutant peptides reveal that the peptides assemble to form the same compact hexamer. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) experiments reveal that the mutant FAD peptides assemble as trimers or hexamers, with peptides that have greater positive charge assembling as more stable hexamers. Mutations that increase the positive charge also increase the cytotoxicity of the peptides and their propensity to destabilize lipid membranes.

Targeted Lipidomics of Mitochondria in a Cellular Alzheimer's Disease Model

Alzheimer’s disease (AD) is neuropathologically characterized by the accumulation of Amyloid-β (Aβ) in senile plaques derived from amyloidogenic processing of a precursor protein (APP). Recently, changes in mitochondrial function have become in the focus of the disease. Whereas a link between AD and lipid-homeostasis exists, little is known about potential alterations in the lipid composition of mitochondria. Here, we investigate potential changes in the main mitochondrial phospholipid classes phosphatidylcholine, phosphatidylethanolamine and the corresponding plasmalogens and lyso-phospholipids of a cellular AD-model (SH-SY5Y APPswedish transfected cells), comparing these results with changes in cell-homogenates. Targeted shotgun-lipidomics revealed lipid alterations to be specific for mitochondria and cannot be predicted from total cell analysis. In particular, lipids containing three and four times unsaturated fatty acids (FA X:4), such as arachidonic-acid, are increased, whereas FA X:6 or X:5, such as eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), are decreased. Additionally, PE plasmalogens are increased in contrast to homogenates. Results were confirmed in another cellular AD model, having a lower affinity to amyloidogenic APP processing. Besides several similarities, differences in particular in PE species exist, demonstrating that differences in APP processing might lead to specific changes in lipid homeostasis in mitochondria. Importantly, the observed lipid alterations are accompanied by changes in the carnitine carrier system, also suggesting an altered mitochondrial functionality.

Vascular Risk Factors and Alzheimer's Disease: Blood-Brain Barrier Disruption, Metabolic Syndromes, and Molecular Links

Alzheimer's disease (AD) is a neurodegenerative disorder, marked by cortical and hippocampal deposition of amyloid-β (Aβ) plaques and neurofibrillary tangles and cognitive impairment. Studies indicate a prominent link between cerebrovascular abnormalities and the onset and progression of AD, where blood-brain barrier (BBB) dysfunction and metabolic disorders play key risk factors. Pericyte degeneration, endothelial cell damage, astrocyte depolarization, diminished tight junction integrity, and basement membrane disarray trigger BBB damage. Subsequently, the altered expression of low-density lipoprotein receptor-related protein 1 and receptor for advanced glycation end products at the microvascular endothelial cells dysregulate Aβ transport across the BBB. White matter lesions and microhemorrhages, dyslipidemia, altered brain insulin signaling, and insulin resistance contribute to tau and Aβ pathogenesis, and oxidative stress, mitochondrial damage, inflammation, and hypoperfusion serve as mechanistic links between pathophysiological features of AD and ischemia. Deregulated calcium homeostasis, voltage gated calcium channel functioning, and protein kinase C signaling are also common mechanisms for both AD pathogenesis and cerebrovascular abnormalities. Additionally, APOE polymorphic alleles that characterize impaired cerebrovascular integrity function as primary genetic determinants of AD. Overall, the current review enlightens key vascular risk factors for AD and underscores pathophysiologic relationship between AD and vascular dysfunction.

Ca2+-permeable TRPV1 pain receptor knockout rescues memory deficits and reduces amyloid-β and tau in a mouse model of Alzheimer's disease

The transient receptor potential vanilloid 1 (TRPV1) protein is a pain receptor that elicits a hot sensation when an organism eats the capsaicin of red chili peppers. This calcium (Ca2+)-permeable cation channel is mostly expressed in the peripheral nervous system sensory neurons but also in the central nervous system (e.g. hippocampus and cortex). Preclinical studies found that TRPV1 mediates behaviors associated with anxiety and depression. Loss of TRPV1 functionality increases expression of genes related to synaptic plasticity and neurogenesis. Thus, we hypothesized that TRPV1 deficiency may modulate Alzheimer's disease (AD). We generated a triple-transgenic AD mouse model (3xTg-AD+/+) with wild-type (TRPV1+/+), hetero (TRPV1+/-) and knockout (TRPV1-/-) TRPV1 to investigate the role of TRPV1 in AD pathogenesis. We analyzed the animals' memory function, hippocampal Ca2+ levels and amyloid-β (Aβ) and tau pathologies when they were 12 months old. We found that compared with 3xTg-AD-/-/TRPV1+/+ mice, 3xTg-AD+/+/TRPV1+/+ mice had memory impairment and increased levels of hippocampal Ca2+, Aβ and total and phosphorylated tau. However, 3xTg-AD+/+/TRPV1-/- mice had better memory function and lower levels of hippocampal Ca2+, Aβ, tau and p-tau, compared with 3xTg-AD+/+/TRPV1+/+ mice. Examination of 3xTg-AD-derived primary neuronal cultures revealed that the intracellular Ca2+ chelator BAPTA/AM and the TRPV1 antagonist capsazepine decreased the production of Aβ, tau and p-tau. Taken together, these results suggested that TRPV1 deficiency had anti-AD effects and promoted resilience to memory loss. These findings suggest that drugs or food components that modulate TRPV1 could be exploited as therapeutics to prevent or treat AD.

A Novel Concept is Needed for Combating Alzheimer's Disease and NeuroHIV

Both Alzheimer’s disease (AD) and HIV-associated neurocognitive disorders (HAND) could progress to dementia, a severe consequence of neurodegenerative diseases. Cumulating evidence suggests that the β-amyloid (Aβ) theory, currently thought to be the predominant mechanism underlying AD and AD-related dementia (ADRD), needs re-evaluation, considering all treatments and new drug trials based upon this theory have been unsuccessful. Similar intention for treating HAND, including HIV-associated dementia (HAD), has also failed. Thus, novel theory, hypothesis, and therapeutic strategies are desperately needed for future study and effective treatments of AD/ADRD and HAND. There are numerous potential upstream mechanisms that may cause AD and/or HAND; but it is unrealistic to identify all of them. However, it is realistic and feasible to intervene the downstream mechanism of these two devastating neurodegenerative diseases by blocking the final common path to neurotoxicity mediated by overactivation of NMDA receptors (NMDARs) and voltage-gated calcium channels (VGCCs). Such a combined pharmacological intervention will likely ameliorate neuronal Ca²⁺ homeostasis by diminishing overactivated NMDAR and VGCC-mediated Ca²⁺ dysregulation (i.e., by reducing excessive Ca²⁺ influx and intracellular levels, [Ca²⁺]in)-induced hyperactivity, injury, and death of neurons in the critical brain regions that regulate neurocognition in the context of AD/ADRD or HAND, especially during aging. Here we present a novel theoretical concept, hypothesis, and working model for switching the battlefield from searching-and-fighting the original mechanism that may cause AD or HAND, to abolishing AD- and neuroHIV-induced neurotoxicity mediated by NMDAR and VGCC over activation, which may ultimately improve the therapeutic strategies for treating AD and HAND.

Design, Synthesis and Biological Evaluation of New Antioxidant and Neuroprotective Multitarget Directed Ligands Able to Block Calcium Channels

We report herein the design, synthesis and biological evaluation of new antioxidant and neuroprotective multitarget directed ligands (MTDLs) able to block Ca²⁺ channels. New dialkyl 2,6-dimethyl-4-(4-(prop-2-yn-1-yloxy)phenyl)-1,4-dihydropyridine-3,5-dicarboxylate MTDLs 3a–t, resulting from the juxtaposition of nimodipine, a Ca²⁺ channel antagonist, and rasagiline, a known MAO inhibitor, have been obtained from appropriate and commercially available precursors using a Hantzsch reaction. Pertinent biological analysis has prompted us to identify the MTDL 3,5-dimethyl-2,6–dimethyl–4-[4-(prop–2–yn–1-yloxy)phenyl]-1,4-dihydro- pyridine- 3,5-dicarboxylate (3a), as an attractive antioxidant (1.75 TE), Ca²⁺ channel antagonist (46.95% at 10 μM), showing significant neuroprotection (38%) against H₂O₂ at 10 μM, being considered thus a hit-compound for further investigation in our search for anti-Alzheimer’s disease agents.

Cyclical amyloid beta-astrocyte activity induces oxidative stress in Alzheimer's disease

Glial cell involvement in Alzheimer's disease (AD) is multi-faceted. The role of astrocytes in AD pathology, both as a causative agent of amyloid-beta (Aβ) production as well as a casualty of dysfunction resulting from the presence of Aβ has been well-delineated. In this review, we explore the influence of oxidative stress in astrocytes and the subsequent effect on Aβ levels in the brain from a perspective of intracellular calcium homeostasis and NADPH oxidase activity. The response of astrocytes to the presence of Aβ, as well astrocytic and microglial interaction and inflammatory cytokine release is also discussed, highlighting a cyclical behaviour of these cells in contributing to AD pathogenesis.

In vivo induction of membrane damage by β-amyloid peptide oligomers

Exposure to the β-amyloid peptide (Aβ) is toxic to neurons and other cell types, but the mechanism(s) involved are still unresolved. Synthetic Aβ oligomers can induce ion-permeable pores in synthetic membranes, but whether this ability to damage membranes plays a role in the ability of Aβ oligomers to induce tau hyperphosphorylation, or other disease-relevant pathological changes, is unclear. To examine the cellular responses to Aβ exposure independent of possible receptor interactions, we have developed an in vivo C. elegans model that allows us to visualize these cellular responses in living animals. We find that feeding C. elegans E. coli expressing human Aβ induces a membrane repair response similar to that induced by exposure to the CRY5B, a known pore-forming toxin produced by B. thuringensis. This repair response does not occur when C. elegans is exposed to an Aβ Gly37Leu variant, which we have previously shown to be incapable of inducing tau phosphorylation in hippocampal neurons. The repair response is also blocked by loss of calpain function, and is altered by loss-of-function mutations in the C. elegans orthologs of BIN1 and PICALM, well-established risk genes for late onset Alzheimer's disease. To investigate the role of membrane repair on tau phosphorylation directly, we exposed hippocampal neurons to streptolysin O (SLO), a pore-forming toxin that induces a well-characterized membrane repair response. We find that SLO induces tau hyperphosphorylation, which is blocked by calpain inhibition. Finally, we use a novel biarsenical dye-tagging approach to show that the Gly37Leu substitution interferes with Aβ multimerization and thus the formation of potentially pore-forming oligomers. We propose that Aβ-induced tau hyperphosphorylation may be a downstream consequence of induction of a membrane repair process.

Involvement of calpain in the neuropathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common (60% to 80%) age‐related disease associated with dementia and is characterized by a deterioration of behavioral and cognitive capacities leading to death in few years after diagnosis, mainly due to complications from chronic illness. The characteristic hallmarks of the disease are extracellular senile plaques (SPs) and intracellular neurofibrillary tangles (NFTs) with neuropil threads, which are a direct result of amyloid precursor protein (APP) processing to Aβ, and τ hyperphosphorylation. However, many indirect underlying processes play a role in this event. One of these underlying mechanisms leading to these histological hallmarks is the uncontrolled hyperactivation of a family of cysteine proteases called calpains. Under normal physiological condition calpains participate in many processes of cells’ life and their activation is tightly controlled. However, with an increase in age, increased oxidative stress and other excitotoxicity assaults, this regulatory system becomes impaired and result in increased activation of these proteases involving them in the pathogenesis of various diseases including neurodegeneration like AD. Reviewed here is a pool of data on the implication of calpains in the pathogenesis of AD, the underlying molecular mechanism, and the potential of targeting these enzymes for AD therapeutics.

Analyzing the Behavior of Neuronal Pathways in Alzheimer's Disease Using Petri Net Modeling Approach

Alzheimer's Disease (AD) is the most common neuro-degenerative disorder in the elderly that leads to dementia. The hallmark of AD is senile lesions made by abnormal aggregation of amyloid beta in extracellular space of brain. One of the challenges in AD treatment is to better understand the mechanism of action of key proteins and their related pathways involved in neuronal cell death in order to identify adequate therapeutic targets. This study focuses on the phenomenon of aggregation of amyloid beta into plaques by considering the signal transduction pathways of Calpain-Calpastatin (CAST) regulation system and Amyloid Precursor Protein (APP) processing pathways along with Ca2+ channels. These pathways are modeled and analyzed individually as well as collectively through Stochastic Petri Nets for comprehensive analysis and thorough understating of AD. The model predicts that the deregulation of Calpain activity, disruption of Calcium homeostasis, inhibition of CAST and elevation of abnormal APP processing are key cytotoxic events resulting in an early AD onset and progression. Interestingly, the model also reveals that plaques accumulation start early (at the age of 40) in life but symptoms appear late. These results suggest that the process of neuro-degeneration can be slowed down or paused by slowing down the degradation rate of Calpain-CAST Complex. In the light of this study, the suggestive therapeutic strategy might be the prevention of the degradation of Calpain-CAST complexes and the inhibition of Calpain for the treatment of neurodegenerative diseases such as AD.

Amyloid β1-42 (Aβ1-42) Induces the CDK2-Mediated Phosphorylation of Tau through the Activation of the mTORC1 Signaling Pathway While Promoting Neuronal Cell Death

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by cognitive impairment and memory loss. Amyloid β1-42 (Aβ) and hyper-phosphorylation of microtubule-associated protein tau have been considered as major histological features in AD. However, the mechanism of how Aβ induces the hyper-phosphorylation of tau remains to be clarified. In the present study, we investigated the underlying cellular mechanisms of Aβ with regard to the cell cycle regulatory protein-mediated phosphorylation of tau in promoting neuronal cell death. The oligomer Aβ (5 μM) significantly increased the level of caspase 3 cleavage and has the ability to induce cytotoxicity in human neuroblastoma SK-N-MC cells. Aβ induced the degree of extracellular calcium influx via the L-type channel to facilitate the production of reactive oxygen species (ROS). Aβ signaling through ROS production is uniquely mediated by the activation of PI3K/Akt, which is in turn required for mammalian target of rapamycin complex 1 (mTORC1) phosphorylation. mTORC1 activated by Aβ further increased the phosphorylation of eukaryotic translation initiation factor 4E (eIF4E), a binding protein (4E-BP1) and p70S6K1 to stimulate the HIF1α synthesis responsible for the induction of cyclinD₁/cyclin-dependent kinase 4 (CDK4) and cyclinE/CDK2, whereas it significantly attenuated the activation of autophagy. Aβ distinctively induced the CDK2-mediated phosphorylation of tau, which is responsible for microtubule destabilization in promoting neuronal apoptosis. In mouse hippocampal primary neurons, the apoptotic cell death induced by Aβ is highly susceptible to the mTORC1 signaling pathway. These results demonstrate that Aβ efficiently stimulates the mTORC1 signaling pathway to facilitate HIF1α synthesis and autophagy inhibition to promote the expression of cell cycle regulatory proteins, during which CDK2 uniquely stimulates tau phosphorylation for microtubule destabilization-mediated neuronal apoptosis.

A critical concentration of N-terminal pyroglutamylated amyloid beta drives the misfolding of Ab1-42 into more toxic aggregates

A wide consensus based on robust experimental evidence indicates pyroglutamylated amyloid-β isoform (AβpE3-42) as one of the most neurotoxic peptides involved in the onset of Alzheimer's disease. Furthermore, AβpE3-42 co-oligomerized with excess of Aβ1-42, produces oligomers and aggregates that are structurally distinct and far more cytotoxic than those made from Aβ1-42 alone. Here, we investigate quantitatively the influence of AβpE3-42 on biophysical properties and biological activity of Aβ1-42. We tested different ratios of AβpE3-42/Aβ1-42 mixtures finding a correlation between the biological activity and the structural conformation and morphology of the analyzed mixtures. We find that a mixture containing 5% AβpE3-42, induces the highest disruption of intracellular calcium homeostasis and the highest neuronal toxicity. These data correlate to an high content of relaxed antiparallel β-sheet structure and the coexistence of a population of big spheroidal aggregates together with short fibrils. Our experiments provide also evidence that AβpE3-42 causes template-induced misfolding of Aβ1-42 at ratios below 33%. This means that there exists a critical concentration required to have seeding on Aβ1-42 aggregation, above this threshold, the seed effect is not possible anymore and AβpE3-42 controls the total aggregation kinetics.

A 10-year follow-up study of the association between calcium channel blocker use and the risk of dementia in elderly hypertensive patients

Calcium channel blockers (CCBs) are widely used for reducing blood pressure of hypertensive patients. Recent reports document the beneficial effects of CCB for preventing dementia; however, the results are controversial. We aim to evaluate the risk of developing dementia among elderly hypertensive patients treated with CCB.We designed a retrospective population-based cohort study using the records of the National Health Insurance Research Database of Taiwan dated from 2000 to 2010. The study cohort comprised 82,107 hypertensive patients of more than 60 years of age, and 4004 propensity score (PS)-matched pairs were selected according to age, sex, year of hypertension diagnosis, and baseline comorbidities. We employed a robust Cox proportional hazard model to estimate the hazard ratio (HR) of developing dementia in the PS-matched cohort.The annual incidence of dementia in the CCB-exposure group was significantly lower than that in the comparator group (3.9 vs 6.9 per 1000 person-years, P < 0.01) during the follow-up period (4.4 ± 2.5 years). Based on the PS-matched cohort, the adjusted HR of dementia in the CCB-exposure group was significantly lower than that in comparator group (HR = 0.53, 95% confidence interval: 0.39-0.72, P < 0.01). Sensitivity and subgroup analyses also confirmed similar findings.Our results provided evidence for an association between CCB use and a lower risk of developing dementia among the elderly hypertensive patients. Further studies are required to explore the causal relationship between CCB use and dementia.

Amlodipine treatment of hypertension associates with a decreased dementia risk

Hypertension has been shown to be a risk factor for development of dementia. However, medical treatment of hypertension failed to reduce consistently the risk of dementia. Experimental study pointed to the possibility of difference between different calcium channel blockers (CCB) in their neuro-protective effect. The aim of our study was to evaluate the risk of dementia during treatment of hypertension with different CCBs. This is a retrospective cohort study based on electronic database of a large public health care organization. Study period was 11 years and it included patients aged 40-75 years old, having diagnosis of hypertension without diagnosis of dementia at the starting point, treated with either single specific CCB (study group) or with other than CCBs antihypertensive medications (control group) for at least 30 months during the study period. A total of 15,664 patients that satisfied these criteria were identified: 3,884 were treated with amlodipine, 2,062 were treated with nifedipine, 609 were treated with lercanidipine, and 9,109 never received CCBs. Dementia developed in 765 (4.9%) patients. Adjusted hazard ratio (HR) for dementia in patients treated with amlodipine, nifedipine, and lercanidipine was 0.60 (p < 0.001), 0.89 (NS), and 0.90 (NS). Decreased adjusted HR of dementia with amlodipine was demonstrated in the patients aged 60 or more (HR 0.61 [0.49-0.77], p < 0.001), but not in the patients aged less than 60 years old. This study shows that amlodipine therapy may be associated with a decreased dementia risk in hypertensive individuals older than 60 years, compared to those treated without CCBs.

Amyloid-β plaques disrupt axon initial segments

Amyloid-β (Aβ) plaques are one of the central pathologies of Alzheimer's disease (AD). Plaque formation in animal models of AD coincides with the appearance of synaptic abnormalities, aberrant neuronal excitability, and cognitive decline. Aβ plaques may disrupt neuronal excitability since they have been proposed to be synaptotoxic, to induce axonal varicosities and neurite breakage, and to significantly decrease spine density. Axon initial segments (AIS) also regulate neuronal excitability and help maintain neuronal polarity. Despite these essential functions, the effects of plaques on AIS structure have not been fully determined. Using a mouse AD model, we measured a significant decrease in the density of AIS up to 75μm away from the center of fibrillar, thioflavin-labeled plaques. The reduction was observed in animals with both moderate and severe plaque loads, and was associated with increased densities of microglia near the plaques. Furthermore, animals with severe plaque loads had significantly reduced AIS lengths adjacent to Aβ plaques. These results suggest the local environment surrounding Aβ plaques may be harmful to the AIS. We propose that AIS loss is a previously unappreciated consequence of AD that could significantly impact brain function.

SIGNIFICANCE STATEMENT

This paper demonstrates that neurons near Aβ plaques have disrupted axon initial segments. Loss or disruption of AIS is predicted to have detrimental consequences for brain function.

Loss of stability and hydrophobicity of presenilin 1 mutations causing Alzheimer's disease

Nearly 200 mutations in the gene coding for presenilin 1 (PSEN1) cause early-onset Alzheimer's disease, yet the molecular mechanism remains obscure. As a meta-analysis, we compiled available clinical and biochemical data for PSEN1 variants and correlated these to chemical properties of the mutants. We found statistically significant relationships between relative Aβ42 levels and clinical age of onset. We then computed chemical properties of the mutants from a variety of computational chemistry tools. Relative Aβ42 levels correlated significantly (95% confidence or more from p-values of linear regression) with loss of hydrophobicity for four different regression analyses (squared correlation coefficient of linear regression R(2) of 0.41-0.53) and with increased polarity (R(2) = 0.47, 0.59) and loss of protein stability (R(2) = 0.39, 0.63) for two independent data sets. Age of onset of patients carrying PSEN1 variants correlated with increased polarity (R(2) = 0.49, 0.40) and loss of stability (R(2) = 0.75, 0.44) of the protein for both data sets. These relations suggest that mutants impair the membrane-associated structural integrity of presenilin by reducing hydrophobic membrane association and overall protein stability. This explains why the many mutations that spread out across the protein and far from the catalytic aspartates can cause disease. The identified molecular determinants of clinical age of symptom onset may be relevant to future presenilin-modulating therapies specifically directed towards increasing the structural integrity and packing of the protein. Close to 200 mutations in presenilin 1 (PSEN1) cause Alzheimer's disease, but the biochemical relating these to disease remains debated. The chemical properties of PSEN1 variants were computed and correlated against clinical age of symptom onset. Loss of stability and hydrophobicity and gain of polarity relate to disease onset, suggesting that mutants impair the membrane structure of PSEN1 and that therapies should increase PSEN1 structural integrity.

The dynamic mechanism of presenilin-1 function: Sensitive gate dynamics and loop unplugging control protein access

There is no molecular explanation for the many presenilin 1 (PSEN1) mutations causing Alzheimer's disease, but both gain of function relating to amyloid production and loss of isolated PSEN1 function have been implied. We report here the first detailed dynamic all-atom model of mature PSEN1 from molecular dynamics in an explicit membrane with particular account of the as yet unexplored loop dynamics. We find that mature PSEN1 contains multiple distinct conformational states whereas non-mature PSEN1 is a typical one-state protein. We confirm a previously suggested gating mechanism, and find that the 106-131 loop acts as a "hinge" for the TM2 and TM6 "doors". More importantly, we identify an unplugging mechanism of the Exon 9 loop associated only with mature PSEN1. Proper opening of both the "gate" and "plug" in the membrane produces channel-like morphologies and access to the catalytic aspartates. Dynamically, these features seem linked. The long-range sensitivity of this gate-plug system to subtle conformational changes can explain why so many PSEN1 mutants cause disease. Reduced access and imprecise substrate cleavage associated with impaired gate-plug dynamics is directly illustrated by the effect of maturation in our work and could explain the overall reduction in Aβ levels upon PSEN1 mutation and the increase in the Aβ 42/40 ratio. Yet, our PSEN1-only dynamics are particularly insightful in revealing PSEN1-only dynamics relating to e.g. its role as membrane channel. Thus, our identified gate-plug mechanism is relevant for designing PSEN1 modulating therapies for treatment of Alzheimer's disease within both the amyloid/γ-secretase hypothesis and within the PSEN1 loss of function paradigm.

The Amyloid Precursor Protein-A Novel Player within the Molecular Array of Presynaptic Nanomachines

More than 20 years ago the amyloid precursor protein (APP) was identified as the precursor protein of the Aβ peptide, the main component of senile plaques in brains affected by Alzheimer’s disease (AD). The pathophysiology of AD, characterized by a massive loss of synapses, cognitive decline, and behavioral changes was in principle attributed to the accumulation of Aβ. Within the last decades, much effort has gone into understanding the molecular basis of the progression of AD. However, little is known about the actual physiological function of APPs. Allocating APP to the proteome of the structurally and functionally dynamic presynaptic active zone (PAZ) highlights APP as a hitherto unknown player within the setting of the presynapse. The molecular array of presynaptic nanomachines comprising the life cycle of synaptic vesicles, exo- and endocytosis, cytoskeletal rearrangements, and mitochondrial activity provides a balance between structural and functional maintenance and diversity. The generation of genetically designed mouse models further deciphered APP as an essential player in synapse formation and plasticity. Deletion of APP causes an age-dependent phenotype: while younger mice revealed almost no physiological impairments, this condition was changed in the elderly mice. Interestingly, the proteomic composition of neurotransmitter release sites already revealed substantial changes at young age. These changes point to a network that incorporates APP into a cluster of nanomachines. Currently, the underlying mechanism of how APP acts within these machines is still elusive. Within the scope of this review, we shall construct a network of APP interaction partners within the PAZ. Furthermore, we intend to outline how deletion of APP affects this network during space and time leading to impairments in learning and memory. These alterations may provide a molecular link to the pathogenesis of AD and the physiological function of APP in the central nervous system.

Metabolic methanol: molecular pathways and physiological roles

Methanol has been historically considered an exogenous product that leads only to pathological changes in the human body when consumed. However, in normal, healthy individuals, methanol and its short-lived oxidized product, formaldehyde, are naturally occurring compounds whose functions and origins have received limited attention. There are several sources of human physiological methanol. Fruits, vegetables, and alcoholic beverages are likely the main sources of exogenous methanol in the healthy human body. Metabolic methanol may occur as a result of fermentation by gut bacteria and metabolic processes involving S-adenosyl methionine. Regardless of its source, low levels of methanol in the body are maintained by physiological and metabolic clearance mechanisms. Although human blood contains small amounts of methanol and formaldehyde, the content of these molecules increases sharply after receiving even methanol-free ethanol, indicating an endogenous source of the metabolic methanol present at low levels in the blood regulated by a cluster of genes. Recent studies of the pathogenesis of neurological disorders indicate metabolic formaldehyde as a putative causative agent. The detection of increased formaldehyde content in the blood of both neurological patients and the elderly indicates the important role of genetic and biochemical mechanisms of maintaining low levels of methanol and formaldehyde.

Single-cell screening of cytosolic [Ca(2+)] reveals cell-selective action by the Alzheimer's Aβ peptide ion channel

Interaction of the Alzheimer's Aβ peptides with the plasma membrane of cells in culture results in chronic increases in cytosolic [Ca(2+)]. Such increases can cause a variety of secondary effects leading to impaired cell growth or cell degeneration. In this investigation, we made a comprehensive study of the changes in cytosolic [Ca(2+)] in single PC12 cells and human neurons stressed by continuous exposure to a medium containing Aβ42 for several days. The differential timing and magnitude of the Aβ42-induced increase in [Ca(2+)] reveal subpopulations of cells with differential sensitivity to Aβ42. These results suggest that the effect produced by Aβ on the level of cytosolic [Ca(2+)] depends on the type of cell being monitored. Moreover, the results obtained of using potent inhibitors of Aβ cation channels such as Zn(2+) and the small peptide NA7 add further proof to the suggestion that the long-term increases in cytosolic [Ca(2+)] in cells stressed by continuous exposure to Aβ is the result of Aβ ion channel activity.

Calcium channel blockers and dementia

Degenerative dementia is mainly caused by Alzheimer's disease and/or cerebrovascular abnormalities. Disturbance of the intracellular calcium homeostasis is central to the pathophysiology of neurodegeneration. In Alzheimer's disease, enhanced calcium load may be brought about by extracellular accumulation of amyloid-β. Recent studies suggest that soluble forms facilitate influx through calcium-conducting ion channels in the plasma membrane, leading to excitotoxic neurodegeneration. Calcium channel blockade attenuates amyloid-β-induced neuronal decline in vitro and is neuroprotective in animal models. Vascular dementia, on the other hand, is caused by cerebral hypoperfusion and may benefit from calcium channel blockade due to relaxation of the cerebral vasculature. Several calcium channel blockers have been tested in clinical trials of dementia and the outcome is heterogeneous. Nimodipine as well as nilvadipine prevent cognitive decline in some trials, whereas other calcium channel blockers failed. In trials with a positive outcome, BP reduction did not seem to play a role in preventing dementia, indicating a direct protecting effect on neurons. An optimization of calcium channel blockers for the treatment of dementia may involve an increase of selectivity for presynaptic calcium channels and an improvement of the affinity to the inactivated state. Novel low molecular weight compounds suitable for proof-of-concept studies are now available.

Discovery of candidate genes for muscle traits based on GWAS supported by eQTL-analysis

Biochemical and biophysical processes that take place in muscle under relaxed and stressed conditions depend on the abundance and activity of gene products of metabolic and structural pathways. In livestock at post-mortem, these muscle properties determine aspects of meat quality and are measurable. The conversion of muscle to meat mimics pathological processes associated with muscle ischemia, injury or damage in humans and it is an economic factor in pork production. Linkage, association, and expression analyses independently contributed to the identification of trait-associated molecular pathways and genes. We aim at providing multiple evidences for the role of specific genes in meat quality by integrating a genome-wide association study (GWAS) for meat quality traits and the detection of eQTL based on trait-correlated expressed genes and trait-associated markers. The GWAS revealed 51 and 200 SNPs significantly associated with meat quality in a crossbred Pietrain×(German Landrace×Large White) (Pi×(GL×LW)) and a purebred German Landrace (GL) population, respectively. Most significant SNPs in Pi×(GL×LW) were located on chromosomes (SSC) 4 and 6. The data of 47,836 eQTLs at a significance level of p<10^-5 were used to scale down the number candidate genes located in these regions. These SNPs on SSC4 showed association with expression levels of ZNF704, IMPA1, and OXSR1; SSC6 SNPs were associated with expression of SIGLEC10 and PIH1D1. Most significant SNPs in GL were located on SSC6 and associated with expression levels of PIH1D1, SIGLEC10, TBCB, LOC100518735, KIF1B, LOC100514845, and two unknown genes. The abundance of transcripts of these genes in muscle, in turn, is significantly correlated with meat quality traits. We identified several genes with evidence for their candidacy for meat quality arising from the integrative approach of a genome-wide association study and eQTL analysis.

Calcium channelopathies and Alzheimer's disease: insight into therapeutic success and failures

Calcium ions are versatile and universal biological signaling factors that regulate numerous cellular processes ranging from cell fertilization, to neuronal plasticity that underlies learning and memory, to cell death. For these functions to be properly executed, calcium signaling requires precise regulation, and failure of this regulation may tip the scales from a signal for life to a signal for death. Disruptions in calcium channel function can generate complex multi-system disorders collectively referred to as "calciumopathies" that can target essentially any cell type or organ. In this review, we focus on the multifaceted involvement of calcium signaling in the pathophysiology of Alzheimer's disease (AD), and summarize the various therapeutic options currently available to combat this disease. Detailing the series of disappointing AD clinical trial results on cognitive outcomes, we emphasize the urgency to design alternative therapeutic strategies if synaptic and memory functions are to be preserved. One such approach is to target early calcium channelopathies centrally linked to AD pathogenesis.

Monitoring of neuronal loss in the hippocampus of Aβ-injected rat: autophagy, mitophagy, and mitochondrial biogenesis stand against apoptosis

In the present study, we tried to answer the following questions: which kind of defense pathways are activated after Aβ insult? How defense systems react against noxious effects of Aβ and whether they are able to deal against apoptosis or not? So, we traced some molecular pathways including autophagy, mitophagy, and mitochondrial biogenesis before reaching to the endpoint of apoptosis. Besides, we measured the function of mitochondria after injection of Aβ (1-42) in CA1 area of hippocampus as a model of Alzheimer's disease (AD). Based on our data, autophagy markers reached to their maximum level and returned to the control level as apoptotic markers started to increase. As a specialized form of autophagy, mitophagy markers followed the trend of autophagy markers. Whereas mitochondrial dynamic processes shifted toward fission, mitochondrial biogenesis was severely affected by Aβ and significantly decreased. Alongside suppression of mitochondrial biogenesis, activity of specific enzymes involved in antioxidant defense system, electron transport chain, and tricarboxylic acid cycle (TCA) decreased in response to the Aβ. Activity of antioxidant enzymes increased at first and then decreased significantly compared to the control. TCA enzymes aconitase and malate dehydrogenase activities reduced immediately while citrate synthase and fumarase activities did not change. Based on our finding, monitoring of the master molecules of intracellular cascades and determining their trends before the destructive function of Aβ could be the target of therapeutic issues for AD.

Multiple effects of β-amyloid on single excitatory synaptic connections in the PFC

Prefrontal cortex (PFC) is recognized as an AD-vulnerable region responsible for defects in cognitive functioning. Pyramidal cell (PC) connections are typically facilitating (F) or depressing (D) in PFC. Excitatory post-synaptic potentials (EPSPs) were recorded using patch-clamp from single connections in PFC slices of rats and ferrets in the presence of β-amyloid (Aβ). Synaptic transmission was significantly enhanced or reduced depending on their intrinsic type (facilitating or depressing), Aβ species (Aβ 40 or Aβ 42) and concentration (1-200 nM vs. 0.3-1 μ M). Nanomolar Aβ 40 and Aβ 42 had opposite effects on F-connections, resulting in fewer or increased EPSP failure rates, strengthening or weakening EPSPs and enhancing or inhibiting short-term potentiation [STP: synaptic augmentation (SA) and post-tetanic potentiation (PTP)], respectively. High Aβ 40 concentrations induced inhibition regardless of synaptic type. D-connections were inhibited regardless of Aβ species or concentration. The inhibition induced with bath application was hard to recover by washout, but a complete recovery was obtained with brief local application and prompt washout. Our data suggests that Aβ 40 acts on the prefrontal neuronal network by modulating facilitating and depressing synapses. At higher levels, both Aβ 40 and Aβ 42 inhibit synaptic activity and cause irreversible toxicity once diffusely accumulated in the synaptic environment.

Two-step mechanism of membrane disruption by Aβ through membrane fragmentation and pore formation

Disruption of cell membranes by Aβ is believed to be one of the key components of Aβ toxicity. However, the mechanism by which this occurs is not fully understood. Here, we demonstrate that membrane disruption by Aβ occurs by a two-step process, with the initial formation of ion-selective pores followed by nonspecific fragmentation of the lipid membrane during amyloid fiber formation. Immediately after the addition of freshly dissolved Aβ(1-40), defects form on the membrane that share many of the properties of Aβ channels originally reported from single-channel electrical recording, such as cation selectivity and the ability to be blockaded by zinc. By contrast, subsequent amyloid fiber formation on the surface of the membrane fragments the membrane in a way that is not cation selective and cannot be stopped by zinc ions. Moreover, we observed that the presence of ganglioside enhances both the initial pore formation and the fiber-dependent membrane fragmentation process. Whereas pore formation by freshly dissolved Aβ(1-40) is weakly observed in the absence of gangliosides, fiber-dependent membrane fragmentation can only be observed in their presence. These results provide insights into the toxicity of Aβ and may aid in the design of specific compounds to alleviate the neurodegeneration of Alzheimer's disease.

BACE1 is at the crossroad of a toxic vicious cycle involving cellular stress and β-amyloid production in Alzheimer's disease

Alzheimer’s disease (AD) is a complex age-related pathology, the etiology of which has not been firmly delineated. Among various histological stigmata, AD-affected brains display several cellular dysfunctions reflecting enhanced oxidative stress, inflammation process and calcium homeostasis disturbance. Most of these alterations are directly or indirectly linked to amyloid β-peptides (Aβ), the production, molecular nature and biophysical properties of which likely conditions the degenerative process. It is particularly noticeable that, in a reverse control process, the above-described cellular dysfunctions alter Aβ peptides levels. β-secretase βAPP-cleaving enzyme 1 (BACE1) is a key molecular contributor of this cross-talk. This enzyme is responsible for the primary cleavage generating the N-terminus of “full length” Aβ peptides and is also transcriptionally induced by several cellular stresses. This review summarizes data linking brain insults to AD-like pathology and documents the key role of BACE1 at the cross-road of a vicious cycle contributing to Aβ production.

Mitochondria-specific accumulation of amyloid β induces mitochondrial dysfunction leading to apoptotic cell death

Mitochondria are best known as the essential intracellular organelles that host the homeostasis required for cellular survival, but they also have relevance in diverse disease-related conditions, including Alzheimer's disease (AD). Amyloid β (Aβ) peptide is the key molecule in AD pathogenesis, and has been highlighted in the implication of mitochondrial abnormality during the disease progress. Neuronal exposure to Aβ impairs mitochondrial dynamics and function. Furthermore, mitochondrial Aβ accumulation has been detected in the AD brain. However, the underlying mechanism of how Aβ affects mitochondrial function remains uncertain, and it is questionable whether mitochondrial Aβ accumulation followed by mitochondrial dysfunction leads directly to neuronal toxicity. This study demonstrated that an exogenous Aβ_1–42 treatment, when applied to the hippocampal cell line of mice (specifically HT22 cells), caused a deleterious alteration in mitochondria in both morphology and function. A clathrin-mediated endocytosis blocker rescued the exogenous Aβ_1–42-mediated mitochondrial dysfunction. Furthermore, the mitochondria-targeted accumulation of Aβ_1–42 in HT22 cells using Aβ_1–42 with a mitochondria-targeting sequence induced the identical morphological alteration of mitochondria as that observed in the APP/PS AD mouse model and exogenous Aβ_1–42-treated HT22 cells. In addition, subsequent mitochondrial dysfunctions were demonstrated in the mitochondria-specific Aβ_1–42 accumulation model, which proved indistinguishable from the mitochondrial impairment induced by exogenous Aβ_1–42-treated HT22 cells. Finally, cellular toxicity was directly induced by mitochondria-targeted Aβ_1–42 accumulation, which mimics the apoptosis process in exogenous Aβ_1–42-treated HT22 cells. Taken together, these results indicate that mitochondria-targeted Aβ_1–42 accumulation is the necessary and sufficient condition for Aβ-mediated mitochondria impairments, and leads directly to cellular death rather than along with other Aβ-mediated signaling alterations.

Should Alzheimer's disease be equated with human brain ageing? A maladaptive interaction between brain evolution and senescence

In this review Alzheimer's disease is seen as a maladaptive interaction between human brain evolution and senescence. It is predicted to occur in everyone although does not necessarily lead to dementia. The pathological process is initiated in relation to a senescence mediated functional down-regulation in the posteromedial cortex (Initiation Phase). This leads to a loss of glutamatergic excitatory input to layer II entorhinal cortex neurons. A human specific maladaptive neuroplastic response is initiated in these neurons leading to neuronal dysfunction, NFT formation and death. This leads to further loss of glutamatergic excitatory input and propagation of the maladaptive response along excitatory pathways linking evolutionary progressed vulnerable neurons (Propagation Phase). Eventually neurons are affected in many brain areas resulting in dementia. Possible therapeutic approaches include enhancing glutamatergic transmission. The theory may have implications with regards to how Alzheimer's disease is classified.

Effects of amyloid-β peptides on voltage-gated L-type Ca(V)1.2 and Ca(V)1.3 Ca(2+) channels

Overload of intracellular Ca(2+) has been implicated in the pathogenesis of neuronal disorders, such as Alzheimer's disease. Various mechanisms produce abnormalities in intracellular Ca(2+) homeostasis systems. L-type Ca(2+) channels have been known to be closely involved in the mechanisms underlying the neurodegenerative properties of amyloid-β (Aβ) peptides. However, most studies of L-type Ca(2+) channels in Aβ-related mechanisms have been limited to Ca(V)1.2, and surprisingly little is known about the involvement of Ca(V)1.3 in Aβ-induced neuronal toxicity. In the present study, we examined the expression patterns of Ca(V)1.3 after Aβ(25-35) exposure for 24 h and compared them with the expression patterns of Ca(V)1.2. The expression levels of Ca(V)1.3 were not significantly changed by Aβ(25-35) at both the mRNA levels and the total protein level in cultured hippocampal neurons. However, surface protein levels of Ca(V)1.3 were significantly increased by Aβ(25-35), but not by Aβ(35-25). We next found that acute treatment with Aβ(25-35) increased Ca(V)1.3 channel activities in HEK293 cells using whole-cell patch-clamp recordings. Furthermore, using GTP pulldown and co-immunoprecipitation assays in HEK293 cell lysates, we found that amyloid precursor protein interacts with β(3) subunits of Ca(2+) channels instead of Ca(V)1.2 or Ca(V)1.3 α(1) subunits. These results show that Aβ(25-35) chronically or acutely upregulates Ca(V)1.3 in the rat hippocampal and human kidney cells (HEK293). This suggests that Ca(V)1.3 has a potential role along with Ca(V)1.2 in the pathogenesis of Alzheimer's disease.

Neuregulin-1 prevents amyloid β-induced impairment of long-term potentiation in hippocampal slices via ErbB4

Neuregulin-1 (NRG1) participates in numerous neurodevelopmental processes and plasticity of the brain. Despite this, little is known about its role in Alzheimer's disease (AD). Amyloid β (Aβ) peptide is generally believed to play a critical role in the pathogenesis of AD. The present study examined the effect of synthetic Aβ₁₋₄₂ peptides on long-term potentiation (LTP) in the CA1 region of mice hippocampal slices, a cellular model of learning and memory. We found that application of a test dose of Aβ₁₋₄₂ (200 nM) significantly inhibited the development of LTP without affecting basal synaptic transmission. Pretreatment with NRG1 effectively prevented Aβ₁₋₄₂-induced impairment of LTP, an effect that was dose-dependent. This LTP-restoring action of NRG1 was almost completely abolished by blocking ErbB4, a key NRG1 receptor, suggesting that NRG1 acts through ErbB4 to exert its protective action on LTP. The present study thus provides the first demonstration that NRG1/ErbB4 protects against Aβ-induced hippocampal LTP impairment, suggesting that NRG1 may be a promising candidate for the treatment of early-stage AD.

Effect of Metal Chelators on γ-Secretase Indicates That Calcium and Magnesium Ions Facilitate Cleavage of Alzheimer Amyloid Precursor Substrate

Gamma-secretase is involved in the production of Aβ amyloid peptides. It cleaves the transmembrane domain of the amyloid precursor protein (APP) at alternative sites to produce Aβ and the APP intracellular domain (AICD). Metal ions play an important role in Aβ aggregation and metabolism, thus metal chelators and ligands represent potential therapeutic agents for AD treatment. A direct effect of metal chelators on γ-secretase has not yet been investigated. The authors used an in vitro  γ-secretase assay consisting of cleavage of APP C100-3XFLAG by endogenous γ-secretase from rodent brains and human neuroblastoma SH-SY5Y, and detected AICD production by western blotting. Adding metalloprotease inhibitors to the reaction showed that clioquinol, phosphoramidon, and zinc metalloprotease inhibitors had no significant effect on γ-secretase activity. In contrast, phenanthroline, EDTA, and EGTA markedly decreased γ-secretase activity that could be restored by adding back calcium and magnesium ions. Mg²⁺ stabilized a 1,000 kDa presenilin 1 complex through blue native gel electrophoresis and size-exclusion chromatography. Data suggest that Ca²⁺ and Mg²⁺ stabilize γ-secretase and enhance its activity.

Is BACE1 a suitable therapeutic target for the treatment of Alzheimer's disease? Current strategies and future directions

Alzheimer's disease (AD) is characterized by the extracellular deposition of the β-amyloid protein (Aβ). Aβ is a fragment of a much larger precursor protein, the amyloid precursor protein (APP). Sequential proteolytic cleavage of APP by β-secretase and γ-secretase liberates Aβ from APP. The aspartyl protease BACE1 (β-site APP-cleaving enzyme 1) catalyses the rate-limiting step in the production of Aβ, and as such it is considered to be a major target for drug development in Alzheimer's disease. However, the development of a BACE1 inhibitor therapy is problematic for two reasons. First, BACE1 has been found to have important physiological roles. Therefore, inhibition of the enzyme could have toxic consequences. Second, the active site of BACE1 is relatively large, and many of the bulky compounds that are needed to inhibit BACE1 activity are unlikely to cross the blood-brain barrier. This review focuses on the structure BACE1, current therapeutic strategies based on developing active-site inhibitors, and new approaches to therapy involving targeting the expression or post-translational regulation of BACE1.