Calcium dyshomeostasis and intracellular signalling in Alzheimer's disease

Calcium signaling and endoplasmic reticulum stress

Cellular homeostasis is essential for healthy functioning of cells and tissues as well as proper organ development and maintenance. A disruption in cellular homeostasis triggers stress responses including the unfolded protein response (UPR), an endoplasmic reticulum (ER) stress coping response. There is increasing evidence that Ca²⁺ signaling plays a pivotal role in stress responses, as Ca²⁺ is involved many cellular activities. The ER is the main Ca²⁺ storage organelle and the source of Ca²⁺ for intracellular signaling. The ER is equipped with a variety of stress sensors and contains many Ca²⁺ handling proteins that support a role for Ca²⁺ in stress sensing and in coordinating strategies required to cope with cellular stress. Maintenance of ER Ca²⁺ homeostasis is therefore vital in sustaining cellular functions especially during times of cellular stress. Here we focus on selected aspects of ER Ca²⁺ homeostasis, its links to ER stress, and activation of the ER stress coping response.

The Relevance of Amyloid β-Calmodulin Complexation in Neurons and Brain Degeneration in Alzheimer's Disease

Intraneuronal amyloid β (Aβ) oligomer accumulation precedes the appearance of amyloid plaques or neurofibrillary tangles and is neurotoxic. In Alzheimer’s disease (AD)-affected brains, intraneuronal Aβ oligomers can derive from Aβ peptide production within the neuron and, also, from vicinal neurons or reactive glial cells. Calcium homeostasis dysregulation and neuronal excitability alterations are widely accepted to play a key role in Aβ neurotoxicity in AD. However, the identification of primary Aβ-target proteins, in which functional impairment initiating cytosolic calcium homeostasis dysregulation and the critical point of no return are still pending issues. The micromolar concentration of calmodulin (CaM) in neurons and its high affinity for neurotoxic Aβ peptides (dissociation constant ≈ 1 nM) highlight a novel function of CaM, i.e., the buffering of free Aβ concentrations in the low nanomolar range. In turn, the concentration of Aβ-CaM complexes within neurons will increase as a function of time after the induction of Aβ production, and free Aβ will rise sharply when accumulated Aβ exceeds all available CaM. Thus, Aβ-CaM complexation could also play a major role in neuronal calcium signaling mediated by calmodulin-binding proteins by Aβ; a point that has been overlooked until now. In this review, we address the implications of Aβ-CaM complexation in the formation of neurotoxic Aβ oligomers, in the alteration of intracellular calcium homeostasis induced by Aβ, and of dysregulation of the calcium-dependent neuronal activity and excitability induced by Aβ.

Calcium Dyshomeostasis in Alzheimer's Disease Pathogenesis

Alzheimer’s disease (AD) is the most common age-related neurodegenerative disorder that is characterized by amyloid β-protein deposition in senile plaques, neurofibrillary tangles consisting of abnormally phosphorylated tau protein, and neuronal loss leading to cognitive decline and dementia. Despite extensive research, the exact mechanisms underlying AD remain unknown and effective treatment is not available. Many hypotheses have been proposed to explain AD pathophysiology; however, there is general consensus that the abnormal aggregation of the amyloid β peptide (Aβ) is the initial event triggering a pathogenic cascade of degenerating events in cholinergic neurons. The dysregulation of calcium homeostasis has been studied considerably to clarify the mechanisms of neurodegeneration induced by Aβ. Intracellular calcium acts as a second messenger and plays a key role in the regulation of neuronal functions, such as neural growth and differentiation, action potential, and synaptic plasticity. The calcium hypothesis of AD posits that activation of the amyloidogenic pathway affects neuronal Ca²⁺ homeostasis and the mechanisms responsible for learning and memory. Aβ can disrupt Ca²⁺ signaling through several mechanisms, by increasing the influx of Ca²⁺ from the extracellular space and by activating its release from intracellular stores. Here, we review the different molecular mechanisms and receptors involved in calcium dysregulation in AD and possible therapeutic strategies for improving the treatment.

Lipocalin 2 regulates iron homeostasis, neuroinflammation, and insulin resistance in the brains of patients with dementia: Evidence from the current literature

Dementia accompanied by memory loss is considered one of the most common neurodegenerative diseases worldwide, and its prevalence is gradually increasing. Known risk factors for dementia include genetic background, certain lifestyle and dietary patterns, smoking, iron overload, insulin resistance, and impaired glucose metabolism in the brain. Here, we review recent evidence on the regulatory role of lipocalin 2 (LCN2) in dementia from various perspectives. LCN2 is a neutrophil gelatinase-associated protein that influences diverse cellular processes, including the immune system, iron homeostasis, lipid metabolism, and inflammatory responses. Although its functions within the peripheral system are most widely recognized, recent findings have revealed links between LCN2 and central nervous system diseases, as well as novel roles for LCN2 in neurons and glia. Furthermore, LCN2 may modulate diverse pathological mechanisms involved in dementia. Taken together, LCN2 is a promising therapeutic target with which to address the neuropathology of dementia.

Bridging heterogeneous mutation data to enhance disease gene discovery

Bridging heterogeneous mutation data fills in the gap between various data categories and propels discovery of disease-related genes. It is known that genome-wide association study (GWAS) infers significant mutation associations that link genotype and phenotype. However, due to the differences of size and quality between GWAS studies, not all de facto vital variations are able to pass the multiple testing. In the meantime, mutation events widely reported in literature unveil typical functional biological process, including mutation types like gain of function and loss of function. To bring together the heterogeneous mutation data, we propose a 'Gene-Disease Association prediction by Mutation Data Bridging (GDAMDB)' pipeline with a statistic generative model. The model learns the distribution parameters of mutation associations and mutation types and recovers false-negative GWAS mutations that fail to pass significant test but represent supportive evidences of functional biological process in literature. Eventually, we applied GDAMDB in Alzheimer's disease (AD) and predicted 79 AD-associated genes. Besides, 12 of them from the original GWAS, 60 of them are supported to be AD-related by other GWAS or literature report, and rest of them are newly predicted genes. Our model is capable of enhancing the GWAS-based gene association discovery by well combining text mining results. The positive result indicates that bridging the heterogeneous mutation data is contributory for the novel disease-related gene discovery.

Age-related calcium dysregulation linked with tau pathology and impaired cognition in non-human primates

Introduction

The etiology of sporadic Alzheimer's disease (AD) requires non‐genetically modified animal models.

Methods

The relationship of tau phosphorylation to calcium‐cyclic adenosine monophosphate (cAMP)‐protein kinase A (PKA) dysregulation was analyzed in aging rhesus macaque dorsolateral prefrontal cortex (dlPFC) and rat primary cortical neurons using biochemistry and immuno‐electron microscopy. The influence of calcium leak from ryanodine receptors (RyRs) on neuronal firing and cognitive performance was examined in aged macaques.

Results

Aged monkeys naturally develop hyperphosphorylated tau, including AD biomarkers (AT8 (pS202/pT205) and pT217) and early tau pathology markers (pS214 and pS356) that correlated with evidence of increased calcium leak (pS2808‐RyR2). Calcium also regulated early tau phosphorylation in vitro. Age‐related reductions in the calcium‐binding protein, calbindin, and in phosphodiesterase PDE4D were seen within dlPFC pyramidal cell dendrites. Blocking RyRs with S107 improved neuronal firing and cognitive performance in aged macaques.

Discussion

Dysregulated calcium signaling confers risk for tau pathology and provides a potential therapeutic target.

A comprehensive overview of the complex world of the endo- and sarcoplasmic reticulum Ca2+-leak channels

Inside cells, the endoplasmic reticulum (ER) forms the largest Ca²⁺ store. Ca²⁺ is actively pumped by the SERCA pumps in the ER, where intraluminal Ca²⁺-binding proteins enable the accumulation of large amount of Ca²⁺. IP₃ receptors and the ryanodine receptors mediate the release of Ca²⁺ in a controlled way, thereby evoking complex spatio-temporal signals in the cell. The steady state Ca²⁺ concentration in the ER of about 500 μM results from the balance between SERCA-mediated Ca²⁺ uptake and the passive leakage of Ca²⁺. The passive Ca²⁺ leak from the ER is often ignored, but can play an important physiological role, depending on the cellular context. Moreover, excessive Ca²⁺ leakage significantly lowers the amount of Ca²⁺ stored in the ER compared to normal conditions, thereby limiting the possibility to evoke Ca²⁺ signals and/or causing ER stress, leading to pathological consequences. The so-called Ca²⁺-leak channels responsible for Ca²⁺ leakage from the ER are however still not well understood, despite over 20 different proteins have been proposed to contribute to it. This review has the aim to critically evaluate the available evidence about the various channels potentially involved and to draw conclusions about their relative importance.

Genetic Variability in Molecular Pathways Implicated in Alzheimer's Disease: A Comprehensive Review

Alzheimer's disease (AD) is a complex neurodegenerative disease, affecting a significant part of the population. The majority of AD cases occur in the elderly with a typical age of onset of the disease above 65 years. AD presents a major burden for the healthcare system and since population is rapidly aging, the burden of the disease will increase in the future. However, no effective drug treatment for a full-blown disease has been developed to date. The genetic background of AD is extensively studied; numerous genome-wide association studies (GWAS) identified significant genes associated with increased risk of AD development. This review summarizes more than 100 risk loci. Many of them may serve as biomarkers of AD progression, even in the preclinical stage of the disease. Furthermore, we used GWAS data to identify key pathways of AD pathogenesis: cellular processes, metabolic processes, biological regulation, localization, transport, regulation of cellular processes, and neurological system processes. Gene clustering into molecular pathways can provide background for identification of novel molecular targets and may support the development of tailored and personalized treatment of AD.

Rosmarinic acid and ursolic acid alleviate deficits in cognition, synaptic regulation and adult hippocampal neurogenesis in an Aβ1-42-induced mouse model of Alzheimer's disease

BACKGROUND

Rosmarinus officinalis, commonly known as rosemary, is a medicinal herb that presents significant biological properties such as antimicrobial, antioxidant, anti-inflammatory, anti-diabetic and anti-depressant activities. Recent findings correlate impaired adult neurogenesis, which is crucial for the maintenance of synaptic plasticity and hippocampal functioning, synaptic regulation with the pathological hallmarks of Alzheimer's disease (AD). These observations call for the need to developing compounds that promote neurogenesis and alleviates deficits in cognition and synaptic regulation.

PURPOSE AND STUDY DESIGN

The present study was conducted to determine the proneurogenic effects of R. officinalis and its active compounds (ursolic acid and rosmarinic acid) in comparison to Donepezil in an Aβ1-42-induced mouse model of AD.

METHODS

BALB/c mice were divided into ten groups. Half were injected with Aβ1-42 in the hippocampus through stereotaxic surgery to generate the disease groups. The other half received control injections. Each set of five groups were administered orally with vehicle, an ethanolic extract of R. officinalis, ursolic acid, rosmarinic acid or donepezil. Behavior analysis included the Morris water maze test, the novel object recognition test and the Elevated plus maze. The mice were then sacrificed and the hippocampal tissue was processed for immunohistochemistry and gene expression analysis.

RESULTS

The results show a protective effect by rosmarinic acid and ursolic acid in reversing the deficits in spatial and recognition memory as well as changes in anxiety induced by Aβ1-42. The neuronal density and the expression levels of neurogenic (Ki67, NeuN and DCX) and synaptic (Syn I, II, III, Synaptophysin and PSD-95) markers were also normalized upon treatment with rosmarinic and ursolic acid.

CONCLUSION

Our findings indicate the potential of R. officinalis and its active compounds as therapeutic agents against Aβ1-42-induced neurotoxicity in AD.

Involvement of α7nAChR in the Protective Effects of Genistein Against β-Amyloid-Induced Oxidative Stress in Neurons via a PI3K/Akt/Nrf2 Pathway-Related Mechanism

Abnormal excessive production and deposition of β-amyloid (Aβ) peptides in selectively susceptible brain regions are thought to be a key pathogenic mechanism underlying Alzheimer's disease (AD), resulting in memory deficits and cognitive impairment. Genistein is a phytoestrogen with great promise for counteracting diverse Aβ-induced insults, including oxidative stress and mitochondrial dysfunction. However, the exact molecular mechanism or mechanisms underlying the neuroprotective effects of genistein against Aβ-induced insults are largely uncharacterized. To further elucidate the possible mechanism(s) underlying these protective effects, we investigated the neuroprotective effects of genistein against Aβ-induced oxidative stress mediated by orchestrating α7 nicotinic acetylcholine receptor (α7nAChR) signaling in rat primary hippocampal neurons. Genistein significantly increased cell viability, reduced the number of apoptotic cells, decreased accumulation of reactive oxygen species (ROS), decreased contents of malondialdehyde (MDA) and lactate dehydrogenase (LDH), upregulated BCL-2 expression, and suppressed Caspase-3 activity occurring after treatment with 25 μM Aβ25-35. Simultaneously, genistein markedly inhibited the decreases in α7nAChR mRNA and protein expression in cells treated with Aβ25-35. In addition, α7nAChR signaling was intimately involved in the genistein-mediated activation of phosphatidylinositol 3-kinase (PI3K)/Akt and Nrf2/keap1 signaling. Thus, α7nAChR activity together with the PI3K/Akt/Nrf2 signaling cascade likely orchestrates the molecular mechanism underlying the neuroprotective effects of genistein against Aβ-induced oxidative injury.

Mitochondria-associated endoplasmic reticulum membranes: At the crossroad between familiar and sporadic Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia and is incurable. The widely accepted amyloid hypothesis failed to produce efficient clinical therapies. In contrast, there is increasing evidence suggesting that the disruption of mitochondria-associated endoplasmic reticulum (ER) membranes (MAM) is a critical upstream event of AD pathogenesis. Here, we review MAM's role in some AD symptoms such as plaque formation, tau hyperphosphorylation, synaptic loss, aberrant lipid synthesis, disturbed calcium homeostasis, and abnormal autophagy. At last, we proposed that MAM plays a central role in familial AD (FAD) and sporadic AD (SAD).

Mitochondrial fission is a critical modulator of mutant APP-induced neural toxicity

Alterations in mitochondrial fission may contribute to the pathophysiology of several neurodegenerative diseases, including Alzheimer's disease (AD). However, we understand very little about the normal functions of fission or how fission disruption may interact with AD-associated proteins to modulate pathogenesis. Here we show that loss of the central mitochondrial fission protein dynamin-related protein 1 (Drp1) in CA1 and other forebrain neurons markedly worsens the learning and memory of mice expressing mutant human amyloid precursor protein (hAPP) in neurons. In cultured neurons, Drp1KO and hAPP converge to produce mitochondrial Ca²⁺ (mitoCa²⁺) overload, despite decreasing mitochondria-associated ER membranes (MAMs) and cytosolic Ca²⁺. This mitoCa²⁺ overload occurs independently of ATP levels. These findings reveal a potential mechanism by which mitochondrial fission protects against hAPP-driven pathology.

Compartmentalized Signaling in Aging and Neurodegeneration

The cyclic AMP (cAMP) signalling cascade is necessary for cell homeostasis and plays important roles in many processes. This is particularly relevant during ageing and age-related diseases, where drastic changes, generally decreases, in cAMP levels have been associated with the progressive decline in overall cell function and, eventually, the loss of cellular integrity. The functional relevance of reduced cAMP is clearly supported by the finding that increases in cAMP levels can reverse some of the effects of ageing. Nevertheless, despite these observations, the molecular mechanisms underlying the dysregulation of cAMP signalling in ageing are not well understood. Compartmentalization is widely accepted as the modality through which cAMP achieves its functional specificity; therefore, it is important to understand whether and how this mechanism is affected during ageing and to define which is its contribution to this process. Several animal models demonstrate the importance of specific cAMP signalling components in ageing, however, how age-related changes in each of these elements affect the compartmentalization of the cAMP pathway is largely unknown. In this review, we explore the connection of single components of the cAMP signalling cascade to ageing and age-related diseases whilst elaborating the literature in the context of cAMP signalling compartmentalization.

Binding of Amyloid β(1-42)-Calmodulin Complexes to Plasma Membrane Lipid Rafts in Cerebellar Granule Neurons Alters Resting Cytosolic Calcium Homeostasis

Lipid rafts are a primary target in studies of amyloid β (Aβ) cytotoxicity in neurons. Exogenous Aβ peptides bind to lipid rafts, which in turn play a key role in Aβ uptake, leading to the formation of neurotoxic intracellular Aβ aggregates. On the other hand, dysregulation of intracellular calcium homeostasis in neurons has been observed in Alzheimer's disease (AD). In a previous work, we showed that Aβ(1-42), the prevalent Aβ peptide found in the amyloid plaques of AD patients, binds with high affinity to purified calmodulin (CaM), with a dissociation constant ≈1 nM. In this work, to experimentally assess the Aβ(1-42) binding capacity to intracellular CaM, we used primary cultures of mature cerebellar granule neurons (CGN) as a neuronal model. Our results showed a large complexation of submicromolar concentrations of Aβ(1-42) dimers by CaM in CGN, up to 120 ± 13 picomoles of Aβ(1-42) /2.5 × 106 cells. Using fluorescence microscopy imaging, we showed an extensive co-localization of CaM and Aβ(1-42) in lipid rafts in CGN stained with up to 100 picomoles of Aβ(1-42)-HiLyteTM-Fluor555 monomers. Intracellular Aβ(1-42) concentration in this range was achieved by 2 h incubation of CGN with 2 μM Aβ(1-42), and this treatment lowered the resting cytosolic calcium of mature CGN in partially depolarizing 25 mM potassium medium. We conclude that the primary cause of the resting cytosolic calcium decrease is the inhibition of L-type calcium channels of CGN by Aβ(1-42) dimers, whose activity is inhibited by CaM:Aβ(1-42) complexes bound to lipid rafts.

Aberrant AZIN2 and polyamine metabolism precipitates tau neuropathology

Tauopathies display a spectrum of phenotypes from cognitive to affective behavioral impairments; however, mechanisms promoting tau pathology and how tau elicits behavioral impairment remain unclear. We report a unique interaction between polyamine metabolism, behavioral impairment, and tau fate. Polyamines are ubiquitous aliphatic molecules that support neuronal function, axonal integrity, and cognitive processing. Transient increases in polyamine metabolism hallmark the cell's response to various insults, known as the polyamine stress response (PSR). Dysregulation of gene transcripts associated with polyamine metabolism in Alzheimer's disease (AD) brains were observed, and we found that ornithine decarboxylase antizyme inhibitor 2 (AZIN2) increased to the greatest extent. We showed that sustained AZIN2 overexpression elicited a maladaptive PSR in mice with underlying tauopathy (MAPT P301S; PS19). AZIN2 also increased acetylpolyamines, augmented tau deposition, and promoted cognitive and affective behavioral impairments. Higher-order polyamines displaced microtubule-associated tau to facilitate polymerization but also decreased tau seeding and oligomerization. Conversely, acetylpolyamines promoted tau seeding and oligomers. These data suggest that tauopathies launch an altered enzymatic signature that endorses a feed-forward cycle of disease progression. Taken together, the tau-induced PSR affects behavior and disease continuance, but may also position the polyamine pathway as a potential entry point for plausible targets and treatments of tauopathy, including AD.

Cellular prion protein activates Caspase 3 for apoptotic defense mechanism in astrocytes

The cellular prion protein (PrP^C) is anchored in the plasma membrane of cells, and it is highly present in cells of brain tissue, exerting numerous cellular and cognitive functions. The present study proves the importance of PrP^C in the cellular defense mechanism and metal homeostasis in astrocytes cells. Through experimental studies using cell lines of immortalized mice astrocytes (wild type and knockout for PrP^C), we showed that PrPc is involved in the apoptosis cell death process by the activation of Caspase 3, downregulation of p53, and cell cycle maintenance. Metal homeostasis was determined by inductively coupled plasma mass spectrometry technique, indicating the crucial role of PrP^C to lower intracellular calcium. The lowered calcium concentration and the Caspase 3 downregulation in the PrP^C-null astrocytes resulted in a faster growth rate in cells, comparing with PrP^C wild-type one. The presence of PrP^C shows to be essential to cell death and healthy growth. In conclusion, our results show for the first time that astrocyte knockout cells for the cellular prion protein could modulate apoptosis-dependent cell death pathways.

Broad Kinase Inhibition Mitigates Early Neuronal Dysfunction in Tauopathy

Tauopathies are a group of more than twenty known disorders that involve progressive neurodegeneration, cognitive decline and pathological tau accumulation. Current therapeutic strategies provide only limited, late-stage symptomatic treatment. This is partly due to lack of understanding of the molecular mechanisms linking tau and cellular dysfunction, especially during the early stages of disease progression. In this study, we treated early stage tau transgenic mice with a multi-target kinase inhibitor to identify novel substrates that contribute to cognitive impairment and exhibit therapeutic potential. Drug treatment significantly ameliorated brain atrophy and cognitive function as determined by behavioral testing and a sensitive imaging technique called manganese-enhanced magnetic resonance imaging (MEMRI) with quantitative R1 mapping. Surprisingly, these benefits occurred despite unchanged hyperphosphorylated tau levels. To elucidate the mechanism behind these improved cognitive outcomes, we performed quantitative proteomics to determine the altered protein network during this early stage in tauopathy and compare this model with the human Alzheimer’s disease (AD) proteome. We identified a cluster of preserved pathways shared with human tauopathy with striking potential for broad multi-target kinase intervention. We further report high confidence candidate proteins as novel therapeutically relevant targets for the treatment of tauopathy. Proteomics data are available via ProteomeXchange with identifier PXD023562.

EDTA as a chelating agent in quantitative 1H-NMR of biologically important ions

Biologically important ions such as Ca, K, Mg, Fe, and Zn play major roles in numerous biological processes, and their homeostatic balance is necessary for the maintenance of cellular activities. Sudden and severe loss in homeostasis of just one biologically important ion can cause a cascade of negative effects. The ability to quickly, accurately, and reliably quantify biologically important ions in samples of human bio-fluids is something that has been sorely lacking within the field of metabolomics. ¹H-NMR spectra. The foundation of our investigation was the a-priori knowledge that free ethylenediaminetetraacetic acid (EDTA) produces two clear single peaks on ¹H-NMR spectra, and that EDTA chelated to different ions produces unique ¹H-NMR spectral patterns due to 3D conformational changes in the chemical structure of chelated-EDTA and varying degrees of electronegativity. The aim of this study was to develop and test a ¹H-NMR-based method, with application specifically to the field of metabolomics, to quantify biologically important ions within the physiological pH range of 6.50-7.50 using EDTA as a chelating agent. Our method produced linear, accurate, precise, and repeatable results for Ca, Mg, and Zn; however, K and Fe did not chelate with EDTA.

Aging-Dependent Mitophagy Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD) is the most common late-onset dementia characterized by the deposition of extracellular amyloid plaques and formation of intracellular neurofibrillary tangles, which eventually lead to neuronal loss and cognitive deficits. Multiple lines of evidence indicate that mitochondrial dysfunction is involved in the initiation and progression of AD. As essential machinery for mitochondrial quality control, mitophagy plays a housekeeping role in neuronal cells by eliminating dysfunctional or excessive mitochondria. At present, mounting evidence support that the activity of mitophagy markedly declines in human brains during aging. Impaired mitophagy and mitochondrial dysfunction were causally linked to bioenergetic deficiency, oxidative stress, microglial activation, and chronic inflammation, thereby aggravating the Aβ and tau pathologies and leading to neuron loss in AD. This review summarizes recent evidence for age-associated mitophagy decline during human aging and provides an overview of mitochondrial dysfunction involved in the process of AD. It also discusses the underlying mechanisms through which defective mitophagy leads to neuronal cell death in AD. Therapeutic interventions aiming to restore mitophagy functions can be used as a strategy for ameliorating AD pathogenesis.

Ginsenoside Rb1 protected PC12 cells from Aβ25-35-induced cytotoxicity via PPARγ activation and cholesterol reduction

Accumulating evidences suggest that amyloid β (Aβ)-peptide plays a key role in pathogenesis of Alzheimer's disease (AD) through aggregation and deposition into plaques in neuronal cells. Membrane components such as cholesterol and gangliosides not only enhance the production of amyloidogenic Aβ fragments, but also appear to strengthen Aβ-membrane interaction. Ginsenoside Rb1 (GRb1) is a major active component of Panax, which is widely used to improve learning and memory. In the present study, whether ginsenoside Rb1 could protect pheochromocytoma cells (PC12 cells) from Aβ_25-35-induced cytotoxicity including inhibiting cell growth, inducing apoptosis, producing reactive oxygen species (ROS), destroying the cytoskeleton and bringing about membrane toxicity was investigated. Our results indicated that ginsenoside Rb1 could serve as an agonist of peroxisom proliferator-activated receptor-γ (PPARγ) and reduce the level of cholesterol in AD model cells. Reduction of the Aβ_25-35-induced cytotoxicity by lowering cholesterol was evidenced by reduction of ROS production, lipid peroxidation, and protection of cytoskeleton and membrane surface rigidity. Most importantly, the viability of PC12 cells increased from 50.42 ± 5.51% for the AD group to 102.72 ± 4.34% for the 50 μM ginsenoside Rb1 group with cholesterol reduction. Our results suggested that ginsenoside Rb1 might function as an effective candidate to promote reverse cholesterol transport and lower ROS production, therefore providing a new insight into prevention and treatment of AD.

Enhanced Neuronal Activity and Asynchronous Calcium Transients Revealed in a 3D Organoid Model of Alzheimer's Disease

Advances in the development of three-dimensional (3D) brain organoids maintained in vitro have provided excellent opportunities to study brain development and neurodegenerative disorders, including Alzheimer's disease (AD). However, there remains a need to generate AD organoids bearing patient-specific genomic backgrounds that can functionally recapitulate the key features observed in the AD patient's brain. To address this need, we described a strategy to generate self-organizing 3D cerebral organoids which develop a functional neuronal network connectivity. This was achieved by neuroectoderm induction of human pluripotent stem cell (hPSCs) aggregates and subsequent differentiation into desired neuroepithelia and mature neurons in a 3D Matrigel matrix. Using this approach, we successfully generated AD cerebral organoids from human pluripotent stem cells (hPSCs) derived from a familial AD patient with a common mutation in presenilin 2 (PSEN2^N141I). An isogenic control with an identical genetic background but wild-type PSEN2 was generated using CRISPR/Cas9 technology. Both control and AD organoids were characterized by analyzing their morphology, the Aβ42/Aβ40 ratio, functional neuronal network activity, drug sensitivity, and the extent of neural apoptosis. The spontaneous activity of the network and its synchronization was measured in the organoids via calcium imaging. We found that compared with the mutation-corrected control organoids, AD organoids had a higher Aβ42/Aβ40 ratio, asynchronous calcium transients, and enhanced neuronal hyperactivity, successfully recapitulating an AD-like pathology at the molecular, cellular, and network level in a human genetic context. Moreover, two drugs which increase neuronal activity, 4-aminopyridine (4-AP) and bicuculline methochloride, induced high-frequency synchronized network bursting to a similar extent in both organoids. Therefore, our study presents a promising organoid-based biosystem for the study of the pathophysiology of AD and a platform for AD drug development.

Signaling Functions of Intramembrane Aspartyl-Proteases

Intramembrane proteolysis is more than a mechanism to "clean" the membranes from proteins no longer needed. By non-reversibly modifying transmembrane proteins, intramembrane cleaving proteases hold key roles in multiple signaling pathways and often distinguish physiological from pathological conditions. Signal peptide peptidase (SPP) and signal peptide peptidase-like proteases (SPPLs) recently have been associated with multiple functions in the field of signal transduction. SPP/SPPLs together with presenilins (PSs) are the only two families of intramembrane cleaving aspartyl proteases known in mammals. PS1 or PS2 comprise the catalytic center of the γ-secretase complex, which is well-studied in the context of Alzheimer's disease. The mammalian SPP/SPPL family of intramembrane cleaving proteases consists of five members: SPP and its homologous proteins SPPL2a, SPPL2b, SPPL2c, and SPPL3. Although these proteases were discovered due to their homology to PSs, it became evident in the past two decades that no physiological functions are shared between these two families. Based on studies in cell culture models various substrates of SPP/SPPL proteases have been identified in the past years and recently-developed mouse lines lacking individual members of this protease family, will help to further clarify the physiological functions of these proteases. In this review we concentrate on signaling roles of mammalian intramembrane cleaving aspartyl proteases. In particular, we will highlight the signaling roles of PS via its substrates NOTCH, VEGF, and others, mainly focusing on its involvement in vasculature. Delineating also signaling pathways that are affected and/or controlled by SPP/SPPL proteases. From SPP's participation in tumor progression and survival, to SPPL3's regulation of protein glycosylation and SPPL2c's control over cellular calcium stores, various crossovers between proteolytic activity of intramembrane proteases and cell signaling will be described.

The Role of Mitochondrial Calcium Homeostasis in Alzheimer's and Related Diseases

Calcium signaling is essential for neuronal function, and its dysregulation has been implicated across neurodegenerative diseases, including Alzheimer’s disease (AD). A close reciprocal relationship exists between calcium signaling and mitochondrial function. Growing evidence in a variety of AD models indicates that calcium dyshomeostasis drastically alters mitochondrial activity which, in turn, drives neurodegeneration. This review discusses the potential pathogenic mechanisms by which calcium impairs mitochondrial function in AD, focusing on the impact of calcium in endoplasmic reticulum (ER)–mitochondrial communication, mitochondrial transport, oxidative stress, and protein homeostasis. This review also summarizes recent data that highlight the need for exploring the mechanisms underlying calcium-mediated mitochondrial dysfunction while suggesting potential targets for modulating mitochondrial calcium levels to treat neurodegenerative diseases such as AD.

Alterations of the Endoplasmic Reticulum (ER) Calcium Signaling Molecular Components in Alzheimer's Disease

Sustained imbalance in intracellular calcium (Ca²⁺) entry and clearance alters cellular integrity, ultimately leading to cellular homeostasis disequilibrium and cell death. Alzheimer’s disease (AD) is the most common cause of dementia. Beside the major pathological features associated with AD-linked toxic amyloid beta (Aβ) and hyperphosphorylated tau (p-tau), several studies suggested the contribution of altered Ca²⁺ handling in AD development. These studies documented physical or functional interactions of Aβ with several Ca²⁺ handling proteins located either at the plasma membrane or in intracellular organelles including the endoplasmic reticulum (ER), considered the major intracellular Ca²⁺ pool. In this review, we describe the cellular components of ER Ca²⁺ dysregulations likely responsible for AD. These include alterations of the inositol 1,4,5-trisphosphate receptors’ (IP₃Rs) and ryanodine receptors’ (RyRs) expression and function, dysfunction of the sarco-endoplasmic reticulum Ca²⁺ ATPase (SERCA) activity and upregulation of its truncated isoform (S1T), as well as presenilin (PS1, PS2)-mediated ER Ca²⁺ leak/ER Ca²⁺ release potentiation. Finally, we highlight the functional consequences of alterations of these ER Ca²⁺ components in AD pathology and unravel the potential benefit of targeting ER Ca²⁺ homeostasis as a tool to alleviate AD pathogenesis.

Therapeutic Strategies to Target Calcium Dysregulation in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common form of dementia, affecting millions of people worldwide. Unfortunately, none of the current treatments are effective at improving cognitive function in AD patients and, therefore, there is an urgent need for the development of new therapies that target the early cause(s) of AD. Intracellular calcium (Ca²⁺) regulation is critical for proper cellular and neuronal function. It has been suggested that Ca²⁺ dyshomeostasis is an upstream factor of many neurodegenerative diseases, including AD. For this reason, chemical agents or small molecules aimed at targeting or correcting this Ca²⁺ dysregulation might serve as therapeutic strategies to prevent the development of AD. Moreover, neurons are not alone in exhibiting Ca²⁺ dyshomeostasis, since Ca²⁺ disruption is observed in other cell types in the brain in AD. In this review, we examine the distinct Ca²⁺ channels and compartments involved in the disease mechanisms that could be potential targets in AD.

Mathematical Modeling of Calcium Oscillatory Patterns in a Neuron

Calcium oscillations are an imperative mode of signaling phenomenon. These oscillations are due to the active interactions taking place between some of the parameters like voltage gated calcium channels (VGCC), sodium calcium exchanger (NCX), calcium binding buffers, endoplasmic reticulum (ER) and mitochondria. The present paper focuses on the problem of higher level of calcium concentration in neurons which may further result into Alzheimer's Disease (AD). For this, a three-dimensional mathematical model having a system of differential equations depicting the changes in cytosolic calcium (in presence of buffers, VGCC and NCX), ER calcium and mitochondrial calcium, is formulated. A three-dimensional neuronal structure is targeted as the domain which is further discussed and solved using finite element technique in Comsol Multiphysics 5.4. Apposite boundary conditions matching well with the in-situ conditions are assumed. The obtained results clearly show the significance of the lower amount of the buffer and higher calcium mediated activities of VGCC, NCX, ER and mitochondria on calcium profile. These changes may lead to AD. To transit from AD condition to normal, exogenous buffers are added to check their significance. The results thus show that the replenishment of buffer may balance the amount of cell calcium and hence can affect positively on Alzheimer's affected cells.

Differential Profile of Systemic Extracellular Vesicles From Sporadic and Familial Alzheimer's Disease Leads to Neuroglial and Endothelial Cell Degeneration

Evidence suggests that extracellular vesicles (EVs) act as mediators and biomarkers of neurodegenerative diseases. Two distinct forms of Alzheimer disease (AD) are known: a late-onset sporadic form (SAD) and an early-onset familial form (FAD). Recently, neurovascular dysfunction and altered systemic immunological components have been linked to AD neurodegeneration. Therefore, we characterized systemic-EVs from postmortem SAD and FAD patients and evaluated their effects on neuroglial and endothelial cells. We found increase CLN-5 spots with vesicular morphology in the abluminal portion of vessels from SAD patients. Both forms of AD were associated with larger and more numerous systemic EVs. Specifically, SAD patients showed an increase in endothelial- and leukocyte-derived EVs containing mitochondria; in contrast, FAD patients showed an increase in platelet-derived EVs. We detected a differential protein composition for SAD- and FAD-EVs associated with the coagulation cascade, inflammation, and lipid-carbohydrate metabolism. Using mono- and cocultures (endothelium-astrocytes-neurons) and human cortical organoids, we showed that AD-EVs induced cytotoxicity. Both forms of AD featured decreased neuronal branches area and astrocytic hyperreactivity, but SAD-EVs led to greater endothelial detrimental effects than FAD-EVs. In addition, FAD- and SAD-EVs affected calcium dynamics in a cortical organoid model. Our findings indicate that the phenotype of systemic AD-EVs is differentially defined by the etiopathology of the disease (SAD or FAD), which results in a differential alteration of the NVU cells implied in neurodegeneration.

Electrophysiological and Imaging Calcium Biomarkers of Aging in Male and Female 5×FAD Mice

BACKGROUND

In animal models and tissue preparations, calcium dyshomeostasis is a biomarker of aging and Alzheimer's disease that is associated with synaptic dysfunction, neuritic pruning, and dysregulated cellular processes. It is unclear, however, whether the onset of calcium dysregulation precedes, is concurrent with, or is the product of pathological cellular events (e.g., oxidation, amyloid-β production, and neuroinflammation). Further, neuronal calcium dysregulation is not always present in animal models of amyloidogenesis, questioning its reliability as a disease biomarker.

OBJECTIVE

Here, we directly tested for the presence of calcium dysregulation in dorsal hippocampal neurons in male and female 5×FAD mice on a C57BL/6 genetic background using sharp electrodes coupled with Oregon-green Bapta-1 imaging. We focused on three ages that coincide with the course of amyloid deposition: 1.5, 4, and 10 months old.

METHODS

Outcome variables included measures of the afterhyperpolarization, short-term synaptic plasticity, and calcium kinetics during synaptic activation. Quantitative analyses of spatial learning and memory were also conducted using the Morris water maze. Main effects of sex, age, and genotype were identified on measures of electrophysiology and calcium imaging.

RESULTS

Measures of resting Oregon-green Bapta-1 fluorescence showed significant reductions in the 5×FAD group compared to controls. Deficits in spatial memory, along with increases in Aβ load, were detectable at older ages, allowing us to test for temporal associations with the onset of calcium dysregulation.

CONCLUSION

Our results provide evidence that reduced, rather than elevated, neuronal calcium is identified in this 5×FAD model and suggests that this surprising result may be a novel biomarker of AD.

Genistein inhibits amyloid peptide 25-35-induced neuronal death by modulating estrogen receptors, choline acetyltransferase and glutamate receptors

PURPOSE

To explore genistein, the most active component of soy isoflavones, on viability, expression of estrogen receptor (ER) subtypes, choline acetyltransferase (ChAT), and glutamate receptor subunits in amyloid peptide 25-35-induced hippocampal neurons, providing valuable data and basic information for neuroprotective effect of genistein in Aβ_25-35-induced neuronal injury.

METHODS

We established an in vitro model of Alzheimer's disease by exposing primary hippocampal neurons of newborn rats to amyloid peptide 25-35 (20 μM) for 24 h and observing the effects of genistein (10 μM, 3 h) on viability, expression of ER subtypes, ChAT, NMDA receptor subunit NR2B and AMPA receptor subunit GluR2 in Aβ_25-35-induced hippocampal neurons.

RESULTS

We found that amyloid peptide 25-35 exposure reduced the viability of hippocampal neurons. Meanwhile, amyloid peptide 25-35 exposure decreased the expression of ER subtypes, ChAT and GluR2, and increased the expression of NR2B. Genistein at least partially reversed the effects of amyloid peptide 25-35 in hippocampal neurons.

CONCLUSION

Genistein could increase the expression of ChAT as a consequence of activating estrogen receptor subtypes, modulating the expression of NR2B and GluR2, and thereby ameliorating the status of hippocampal neurons and exerting neuroprotective effects against amyloid peptide 25-35. Our data suggest that genistein might represent a potential cell-targeted therapy which could be a promising approach to treating AD.

Protein Homeostasis Networks and the Use of Yeast to Guide Interventions in Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive multifactorial age-related neurodegenerative disorder that causes the majority of deaths due to dementia in the elderly. Although various risk factors have been found to be associated with AD progression, the cause of the disease is still unresolved. The loss of proteostasis is one of the major causes of AD: it is evident by aggregation of misfolded proteins, lipid homeostasis disruption, accumulation of autophagic vesicles, and oxidative damage during the disease progression. Different models have been developed to study AD, one of which is a yeast model. Yeasts are simple unicellular eukaryotic cells that have provided great insights into human cell biology. Various yeast models, including unmodified and genetically modified yeasts, have been established for studying AD and have provided significant amount of information on AD pathology and potential interventions. The conservation of various human biological processes, including signal transduction, energy metabolism, protein homeostasis, stress responses, oxidative phosphorylation, vesicle trafficking, apoptosis, endocytosis, and ageing, renders yeast a fascinating, powerful model for AD. In addition, the easy manipulation of the yeast genome and availability of methods to evaluate yeast cells rapidly in high throughput technological platforms strengthen the rationale of using yeast as a model. This review focuses on the description of the proteostasis network in yeast and its comparison with the human proteostasis network. It further elaborates on the AD-associated proteostasis failure and applications of the yeast proteostasis network to understand AD pathology and its potential to guide interventions against AD.

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.

Presenilin-2 and Calcium Handling: Molecules, Organelles, Cells and Brain Networks

Presenilin-2 (PS2) is one of the three proteins that are dominantly mutated in familial Alzheimer's disease (FAD). It forms the catalytic core of the γ-secretase complex-a function shared with its homolog presenilin-1 (PS1)-the enzyme ultimately responsible of amyloid-β (Aβ) formation. Besides its enzymatic activity, PS2 is a multifunctional protein, being specifically involved, independently of γ-secretase activity, in the modulation of several cellular processes, such as Ca2+ signalling, mitochondrial function, inter-organelle communication, and autophagy. As for the former, evidence has accumulated that supports the involvement of PS2 at different levels, ranging from organelle Ca2+ handling to Ca2+ entry through plasma membrane channels. Thus FAD-linked PS2 mutations impact on multiple aspects of cell and tissue physiology, including bioenergetics and brain network excitability. In this contribution, we summarize the main findings on PS2, primarily as a modulator of Ca2+ homeostasis, with particular emphasis on the role of its mutations in the pathogenesis of FAD. Identification of cell pathways and molecules that are specifically targeted by PS2 mutants, as well as of common targets shared with PS1 mutants, will be fundamental to disentangle the complexity of memory loss and brain degeneration that occurs in Alzheimer's disease (AD).

Synthesis of α-Ketoamide-Based Stereoselective Calpain-1 Inhibitors as Neuroprotective Agents

Calpain inhibitors have been proposed as drug candidates for neurodegenerative disorders, with ABT-957 entering clinical trials for Alzheimer's disease and mild cognitive impairment. The structure of ABT-957 was very recently disclosed, and trials were terminated owing to inadequate CNS concentrations to obtain a pharmacodynamic effect. The multistep synthesis of an α-ketoamide peptidomimetic inhibitor series potentially including ABT-957 was optimized to yield diastereomerically pure compounds that are potent and selective for calpain-1 over papain and cathepsins B and K. As the final oxidation step, with its optimized synthesis protocol, does not alter the configuration of the substrate, the synthesis of the diastereomeric pair (R)-1-benzyl-N-((S)-4-((4-fluorobenzyl)amino)-3,4-dioxo-1-phenylbutan-2-yl)-5-oxopyrrolidine-2-carboxamide (1 c) and (R)-1-benzyl-N-((R)-4-((4-fluorobenzyl)amino)-3,4-dioxo-1-phenylbutan-2-yl)-5-oxopyrrolidine-2-carboxamide (1 g) was feasible. This allowed the exploration of stereoselective inhibition of calpain-1, with 1 c (IC₅₀ =78 nM) being significantly more potent than 1 g. Moreover, inhibitor 1 c restored cognitive function in amnestic mice.

The Potential Influence of Bone-Derived Modulators on the Progression of Alzheimer's Disease

Bone, the major structural scaffold of the human body, has recently been demonstrated to interact with several other organ systems through the actions of bone-derived cells and bone-derived cell secretory proteins. Interestingly, the brain is one organ that appears to fall into this interconnected network. Furthermore, the fact that osteoporosis and Alzheimer's disease are two common age-related disorders raises the possibility that these two organ systems are interconnected in terms of disease pathogenesis. This review focuses on the latest evidence demonstrating the impact of bone-derived cells and bone-derived proteins on the central nervous system, and on how this may be relevant in the progression of Alzheimer's disease and for the identification of novel therapeutic approaches to treat this neurodegenerative disorder.

STIM1 Deficiency Leads to Specific Down-Regulation of ITPR3 in SH-SY5Y Cells

STIM1 is an endoplasmic reticulum (ER) protein that modulates the activity of a number of Ca²⁺ transport systems. By direct physical interaction with ORAI1, a plasma membrane Ca²⁺ channel, STIM1 activates the I_CRAC current, whereas the binding with the voltage-operated Ca²⁺ channel Ca_V1.2 inhibits the current through this latter channel. In this way, STIM1 is a key regulator of Ca²⁺ signaling in excitable and non-excitable cells, and altered STIM1 levels have been reported to underlie several pathologies, including immunodeficiency, neurodegenerative diseases, and cancer. In both sporadic and familial Alzheimer’s disease, a decrease of STIM1 protein levels accounts for the alteration of Ca²⁺ handling that compromises neuronal cell viability. Using SH-SY5Y cells edited by CRISPR/Cas9 to knockout STIM1 gene expression, this work evaluated the molecular mechanisms underlying the cell death triggered by the deficiency of STIM1, demonstrating that STIM1 is a positive regulator of ITPR3 gene expression. ITPR3 (or IP3R3) is a Ca²⁺ channel enriched at ER-mitochondria contact sites where it provides Ca²⁺ for transport into the mitochondria. Thus, STIM1 deficiency leads to a strong reduction of ITPR3 transcript and ITPR3 protein levels, a consequent decrease of the mitochondria free Ca²⁺ concentration ([Ca²⁺]_mit), reduction of mitochondrial oxygen consumption rate, and decrease in ATP synthesis rate. All these values were normalized by ectopic expression of ITPR3 in STIM1-KO cells, providing strong evidence for a new mode of regulation of [Ca²⁺]_mit mediated by the STIM1-ITPR3 axis.

Amyloid beta regulates ER exit sites formation through O-GlcNAcylation triggered by disrupted calcium homeostasis

BACKGROUND INFORMATION

Aberrant production of amyloid beta (Aβ) causes disruption of intracellular calcium homeostasis, a crucial factor in the pathogenesis of Alzheimer's disease. Calcium is required for the fusion and trafficking of vesicles. Previously, we demonstrated that Sec31A, a main component for coat protein complex II (COPII) vesicles at ER exit sites (ERES), is modulated by O-GlcNAcylation. O-GlcNAcylation, a unique and dynamic protein glycosylation process, modulates the formation of COPII vesicles.

RESULTS

In this study, we observed that disrupted calcium levels affected the formation of COPII vesicles in ERES through calcium-triggered O-GlcNAcylation of Sec31A. Additionally, we found that Aβ impaired ERES through Aβ-disturbed calcium homeostasis and O-GlcNAcylation of Sec31A in neuronal cells. Furthermore, we identified that Aβ disrupted the ribbon-like structure of Golgi. Golgi fragmentation by Aβ was rescued by up-regulation of O-GlcNAcylaion levels using Thiamet G (ThiG), an O-GlcNAcase inhibitor. Additionally, we observed that the Golgi reassembly stacking proteins having a function in Golgi stacking showed attenuation at COPII vesicles following Aβ treatment.

CONCLUSIONS

This study demonstrated that Aβ impaired Sec31A targeting to ERES through altered Sec31A O-GlcNAcylation triggered by disruption of intracellular calcium homeostasis.

SIGNIFICANCE

The findings of this study suggested that protection of ERES or Sec31 O-GlcNAcylation may offer a promising novel avenue for development of AD therapeutics.

Serum Calcium Levels and Parkinson's Disease: A Mendelian Randomization Study

BACKGROUND

Though increasing epidemiological studies have evaluated the correlation between serum calcium contents and Parkinson's disease (PD), the results are inconsistent. At present, whether there is a causal association between serum calcium content and PD remains undetermined.

OBJECTIVE AND METHODS

This study was designed to explore the relationship between increased serum calcium contents and PD risk. In this present study, a Mendelian randomization trial was carried out using a large-scale serum calcium genome-wide association study (GWAS) dataset (N = 61,079, Europeans) and a large-scale PD GWAS dataset (N = 8,477, Europeans including 4,238 PD patients and 4,239 controls). Here, a total of four Mendelian randomization methods comprising weighted median, inverse-variance weighted meta-analysis (IVW), MR-Egger, and MR-PRESSO were used.

RESULTS

Our data concluded that genetically higher serum calcium contents were not significantly related to PD.

CONCLUSION

In conclusion, we provided genetic evidence that there was no direct causal relationship between serum calcium contents and PD. Hence, calcium supplementation may not result in reduced PD risk.

NCX1 and EAAC1 transporters are involved in the protective action of glutamate in an in vitro Alzheimer's disease-like model

Increasing evidence suggests that metabolic dysfunctions are at the roots of neurodegenerative disorders such as Alzheimer's disease (AD). In particular, defects in cerebral glucose metabolism, which have been often noted even before the occurrence of clinical symptoms and histopathological lesions, are now regarded as critical contributors to the pathogenesis of AD. Hence, the stimulation of energy metabolism, by enhancing the availability of specific metabolites, might be an alternative way to improve ATP synthesis and to positively affect AD progression. For instance, glutamate may serve as an intermediary metabolite for ATP synthesis through the tricarboxylic acid (TCA) cycle and the oxidative phosphorylation. We have recently shown that two transporters are critical for the anaplerotic use of glutamate: the Na⁺-dependent Excitatory Amino Acids Carrier 1 (EAAC1) and the Na⁺-Ca²⁺ exchanger 1 (NCX1). Therefore, in the present study, we established an AD-like phenotype by perturbing glucose metabolism in both primary rat cortical neurons and retinoic acid (RA)-differentiated SH-SY5Y cells, and we explored the potential of glutamate to halt cell damage by monitoring neurotoxicity, AD markers, ATP synthesis, cytosolic Ca²⁺ levels and EAAC1/NCX1 functional activities. We found that glutamate significantly increased ATP production and cell survival, reduced the increase of AD biomarkers (amyloid β protein and the hyperphosphorylated form of tau protein), and recovered the increase of NCX reverse-mode activity. The RNA silencing of either EAAC1 or NCX1 caused the loss of the beneficial effects of glutamate, suggesting the requirement of a functional interplay between these transporters for glutamate-induced protection. Remarkably, our results indicate, as proof-of-principle, that facilitating the use of alternative fuels, like glutamate, may be an effective approach to overcome deficits in glucose utilization and significantly slow down neuronal degenerative process in AD.

Polyethylenimine-Assisted Generation of Optical Nanoprobes for Biosensing Applications

Detection of analytes in biological systems is pivotal to explore their physiological roles and provide diagnostic and treatment options for related diseases, which however remains a great challenge. Optical nanoprobes that exhibit absorption or fluorescence signal changes in response to the targets of interest have emerged as a versatile class of biosensors in the field. Polyethylenimine (PEI) with abundant amine groups plays indispensable roles in the construction of optical nanoprobes and mediating the sensing processes. After interaction with analytes, PEI-based optical nanoprobes can be induced to form aggregates, be disassembled or separated into individual units, or undergo structure/component alterations. As such, the optical properties of these nanoprobes have corresponding changes, allowing for sensitive and selective detection of a wide variety of analytes in biological environment. Up to now, detections of reactive oxygen species, pH, metal ions, biothiols, neurotransmitters, therapeutic agents, oxygen levels, enzyme activities, and virus/bacteria have been successfully demonstrated using PEI-based optical nanoprobes. Herein, we summarize the recent developments of PEI-based optical nanoprobes for biosensing applications and highlight the probe designs and sensing mechanisms. The existing challenges and prospects regarding biosensing applications of PEI-based optical nanoprobes are also briefly discussed.

Chemical Modulation of Mitochondria-Endoplasmic Reticulum Contact Sites

Contact sites between mitochondria and endoplasmic reticulum (ER) are points in which the two organelles are in close proximity. Due to their structural and functional complexity, their exploitation as pharmacological targets has never been considered so far. Notwithstanding, the number of compounds described to target proteins residing at these interfaces either directly or indirectly is rising. Here we provide original insight into mitochondria–ER contact sites (MERCs), with a comprehensive overview of the current MERCs pharmacology. Importantly, we discuss the considerable potential of MERCs to become a druggable target for the development of novel therapeutic strategies.

Feed-Forward and Feedback Control in Astrocytes for Ca 2+-Based Molecular Communications Nanonetworks

Synaptic plasticity depends on the gliotransmitters' concentration in the synaptic channel. And, an abnormal concentration of gliotransmitters is linked to neurodegenerative diseases, including Alzheimer's, Parkinson's, and epilepsy. In this paper, a theoretical investigation of the cause of the abnormal concentration of gliotransmitters and how to achieve its control is presented through a Ca ²⁺-signalling-based molecular communications framework. A feed-forward and feedback control technique is used to manipulate IP ₃ values to stabilize the concentration of Ca ²⁺ inside the astrocytes. The theoretical analysis of the given model aims i) to stabilize the Ca ²⁺ concentration around a particular desired level in order to prevent abnormal gliotransmitters' concentration (extremely high or low concentration can result in neurodegeneration), ii) to improve the molecular communication performance that utilizes Ca ²⁺ signalling, and maintain gliotransmitters' regulation remotely. It shows that the refractory periods from Ca ²⁺ can be maintained to lower the noise propagation resulting in smaller time-slots for bit transmission, which can also improve the delay and gain performances. The proposed approach can potentially lead to novel nanomedicine solutions for the treatment of neurodegenerative diseases, where a combination of nanotechnology and gene therapy approaches can be used to elicit the regulated Ca ²⁺ signalling in astrocytes, ultimately improving neuronal activity.

Calcium-Handling Defects and Neurodegenerative Disease

Calcium signaling is critical to neuronal function and regulates highly diverse processes such as gene transcription, energy production, protein handling, and synaptic structure and function. Because there are many common underlying calcium-mediated pathological features observed across several neurological conditions, it has been proposed that neurodegenerative diseases have an upstream underlying calcium basis in their pathogenesis. With certain diseases such as Alzheimer's, Parkinson's, and Huntington's, specific sources of calcium dysregulation originating from distinct neuronal compartments or channels have been shown to have defined roles in initiating or sustaining disease mechanisms. Herein, we will review the major hallmarks of these diseases, and how they relate to calcium dysregulation. We will then discuss neuronal calcium handling throughout the neuron, with special emphasis on channels involved in neurodegeneration.

Exploring the Role of PSEN Mutations in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia. Mutations of presenilin (PSEN) genes that encode presenilin proteins have been found as the vital causal factors for early-onset familial AD (FAD). AD pathological features such as memory loss, synaptic dysfunction, and formation of plaques have been successfully mimicked in the transgenic mouse models that coexpress FAD-related presenilin and amyloid precursor protein (APP) variants. γ-Secretase (GS) is an enzyme that plays roles in catalyzing intramembranous APP proteolysis to release pathogenic amyloid beta (Aβ). It has been found that presenilins can play a role as the GS's catalytic subunit. FAD-related mutations in presenilins can modify the site of GS cleavage in a way that can elevate the production of longer and highly fibrillogenic Aβ. Presenilins can interact with β-catenin to generate presenilin complexes. Aforesaid interactions have also been studied to observe the mutational and physiological activities in the catenin signal transduction pathway. Along with APP, GS can catalyze intramembrane proteolysis of various substrates that play a vital role in synaptic function. PSEN mutations can cause FAD with autosomal dominant inheritance and early onset of the disease. In this article, we have reviewed the current progress in the analysis of PSENs and the correlation of PSEN mutations and AD pathogenesis.

Annexin A5 prevents amyloid-β-induced toxicity in choroid plexus: implication for Alzheimer's disease

In Alzheimer’s disease (AD) amyloid-β (Aβ) deposits may cause impairments in choroid plexus, a specialised brain structure which forms the blood–cerebrospinal fluid (CSF) barrier. We previously carried out a mass proteomic-based study in choroid plexus from AD patients and we found several differentially regulated proteins compared with healthy subjects. One of these proteins, annexin A5, was previously demonstrated implicated in blocking Aβ-induced cytotoxicity in neuronal cell cultures. Here, we investigated the effects of annexin A5 on Aβ toxicity in choroid plexus. We used choroid plexus tissue samples and CSF from mild cognitive impairment (MCI) and AD patients to analyse Aβ accumulation, cell death and annexin A5 levels compared with control subjects. Choroid plexus cell cultures from rats were used to analyse annexin A5 effects on Aβ-induced cytotoxicity. AD choroid plexus exhibited progressive reduction of annexin A5 levels along with progressive increased Aβ accumulation and cell death as disease stage was higher. On the other hand, annexin A5 levels in CSF from patients were found progressively increased as the disease stage increased in severity. In choroid plexus primary cultures, Aβ administration reduced endogenous annexin A5 levels in a time-course dependent manner and simultaneously increased annexin A5 levels in extracellular medium. Annexin A5 addition to choroid plexus cell cultures restored the Aβ-induced impairments on autophagy flux and apoptosis in a calcium-dependent manner. We propose that annexin A5 would exert a protective role in choroid plexus and this protection is lost as Aβ accumulates with the disease progression. Then, brain protection against further toxic insults would be jeopardised.

Identification of Structural Calcium Binding Sites in Membrane-Bound Presenilin 1 and 2

Variants of presenilin (PS1 and PS2) are the main genetic risk factors of familial Alzheimer's disease and thus central to the disease etiology. Although mostly studied as catalytic units of γ-secretase controlling Aβ production, presenilins also affect calcium levels, which are disturbed in Alzheimer's disease. We investigated the interaction of calcium with both PS1 and PS2 using all-atom molecular dynamics (MD) simulations in realistic membrane models, with the specific aim to identify any Ca²⁺ sites. We did not observe any complete Ca²⁺ leak event, but we identified four persistent Ca²⁺ sites in membrane-bound PS1 and PS2: One in HL2 near the C-terminal of TM6, one in HL2 toward the N-terminal of TM7, a site at the catalytic aspartate on TM7, and a site at the PALP motif on TM9. The sites feature negatively charged glutamates and aspartates typical of calcium binding. Structural homology to diaspartate calcium transport proteins and mutation studies of calcium efflux support our identified calcium sites. Calcium consistently dampens HL2 motions in all comparisons (PS1, protonated PS1, PS2, protonated PS2). Due to their location in HL2 and the active site, we propose that the calcium sites control autoproteolytic maturation of presenilin by a pH-dependent conformational restriction of the HL2 recognition loop, which also regulates calcium transport proteins such as inositol 1,4,5-triphosphate receptor and ryanodine receptor. Our structural dynamics could provide a possible molecular basis for the need of both calcium and presenilin for lysosome proteolytic function, perhaps relevant also to other protein misfolding diseases.

Presynaptic failure in Alzheimer's disease

Synaptic loss is the best correlate of cognitive deficits in Alzheimer's disease (AD). Extensive experimental evidence also indicates alterations of synaptic properties at the early stages of disease progression, before synapse loss and neuronal degeneration. A majority of studies in mouse models of AD have focused on post-synaptic mechanisms, including impairment of long-term plasticity, spine structure and glutamate receptor-mediated transmission. Here we review the literature indicating that the synaptic pathology in AD includes a strong presynaptic component. We describe the evidence indicating presynaptic physiological functions of the major molecular players in AD. These include the amyloid precursor protein (APP) and the two presenilin (PS) paralogs PS1 or PS2, genetically linked to the early-onset form of AD, in addition to tau which accumulates in a pathological form in the AD brain. Three main mechanisms participating in presynaptic functions are highlighted. APP fragments bind to presynaptic receptors (e.g. nAChRs and GABA_B receptors), presenilins control Ca²⁺ homeostasis and Ca²⁺-sensors, and tau regulates the localization of presynaptic molecules and synaptic vesicles. We then discuss how impairment of these presynaptic physiological functions can explain or forecast the hallmarks of synaptic impairment and associated dysfunction of neuronal circuits in AD. Beyond the physiological roles of the AD-related proteins, studies in AD brains also support preferential presynaptic alteration. This review features presynaptic failure as a strong component of pathological mechanisms in AD.