Interactions of Mitochondria/Metabolism and Calcium Regulation in Alzheimer's Disease: A Calcinist Point of View

Intranasal insulin administration affecting perioperative neurocognitive dysfunction by regulating calcium transport protein complex IP3R/GRP75/VDAC1 on MAMs

Perioperative neurocognitive disorders (PND) are common complications following surgery and anesthesia, especially in the elderly. These disorders are associated with disruptions in neuronal energy metabolism and mitochondrial function. This study explores the potential of intranasal insulin administration as a therapeutic strategy to prevent PND by targeting the calcium transport protein complex IP3R/GRP75/VDAC1 on mitochondria-associated endoplasmic reticulum membranes (MAMs).

METHODS

Male C57BL/6J mice underwent partial hepatectomy to induce PND and were subsequently treated with either intranasal insulin or saline. Cognitive function was evaluated using the Morris water maze test, and hippocampal tissue was analyzed for calcium transport protein complex IP3R/GRP75/VDAC1 expression and apoptosis markers. In vitro, HT22 and BV2 cell co-cultures were utilized to simulate surgical injury, with IP3R knockdown employed to assess its effects on oxidative stress and apoptosis.

RESULTS

Intranasal insulin effectively alleviated cognitive impairment as demonstrated by improved performance in the Morris water maze. It significantly reduced neuronal apoptosis and modulated the expression of the IP3R/GRP75/VDAC1 complex, enhancing mitochondrial ATP production and stabilizing MAMs. Furthermore, insulin administration also increased PI3K/AKT signaling, counteracting the impact of surgical stress. In vitro experiments confirmed that IP3R knockdown mitigated inflammation-induced oxidative stress and neuronal apoptosis, while insulin's beneficial effects were blocked by inhibition of the PI3K/AKT pathway.

CONCLUSION

Intranasal insulin mitigates PND by modulating the IP3R/GRP75/VDAC1 complex and enhancing mitochondrial function through the PI3K/AKT signaling pathway. This study supports the potential of intranasal insulin as a promising therapeutic strategy for preventing and managing PND, potentially leading to improved surgical outcomes for elderly patients.

The etiology and prevention of early-stage tau pathology in higher cortical circuits: Insights from aging rhesus macaques

Aging rhesus macaques provide a unique model for learning how age and inflammation drive early-stage pathology in sporadic Alzheimer's disease, and for testing potential therapeutics. Unlike mice, aging macaques have extensive association cortices and inflammatory signaling similar to humans, are apolipoprotein E ε4 homozygotes, and naturally develop tau and amyloid pathology with marked cognitive deficits. Importantly, monkeys provide the unique opportunity to study early-stage, soluble hyperphosphorylated tau (p-tau), including p-tau217. As soluble p-tau is rapidly dephosphorylated post mortem, it is not captured in human brains except with biopsy material. However, new macaque data show that soluble p-tau is toxic to neurons and capable of seeding across cortical circuits. Extensive evidence indicates that age-related inflammatory signaling contributes to calcium dysregulation, which drives tau hyperphosphorylation and amyloid beta generation. Pharmacological studies in aged macaques suggest that inhibiting inflammation and restoring calcium regulation can reduce tau hyperphosphorylation with minimal side effects, appropriate for potential preventive therapeutics. HIGHLIGHTS: Aging monkeys provide a unique window into early stage, soluble phosphorylated tau (p-tau). Inflammation with advancing age leads to calcium dysregulation, p-tau, and amyloid beta (Aβ). Macaque research shows p-tau undergoes transsynaptic seeding early in the cortex. p-tau traps amyloid precursor protein-containing endosomes, which may increase Aβ and drive vicious cycles. Restoring calcium regulation in cortex reduced p-tau217 levels in aged macaques.

Comparative outcomes of systemic diseases in people with type 2 diabetes, or obesity alone treated with and without GLP-1 receptor agonists: a retrospective cohort study from the Global Collaborative Network : Author list

BACKGROUND

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are increasingly used to manage type 2 diabetes (T2D) and obesity. Despite their recognized benefits in glycemic control and weight management, their impact on broader systemic has been less explored.

OBJECTIVE

This study aimed to evaluate the impact of GLP-1RAs on a variety of systemic diseases in people with T2D or obesity.

METHODS

We conducted a retrospective cohort study using data from the Global Collaborative Network, accessed through the TriNetX analytics platform. The study comprised two primary groups: individuals with T2D and those with obesity. Each group was further divided into subgroups based on whether they received GLP-1RA treatment or not. Data were analyzed over more than a 5-year follow-up period, comparing incidences of systemic diseases; systemic lupus erythematosus (SLE), systemic sclerosis (SS), rheumatoid arthritis (RA), ulcerative colitis (UC), crohn's disease (CD), alzheimer's disease (AD), parkinson's disease (PD), dementia, bronchial asthma (BA), osteoporosis, and several cancers.

RESULTS

In the T2D cohorts, GLP-1RA treatment was associated with significantly lower incidences of several systemic and metabolic conditions as compared to those without GLP-1RA, specifically, dementia (Risk Difference (RD): -0.010, p < 0.001), AD (RD: -0.003, p < 0.001), PD (RD: -0.002, p < 0.001), and pancreatic cancer (RD: -0.003, p < 0.001). SLE and SS also saw statistically significant reductions, though the differences were minor in magnitude (RD: -0.001 and - 0.000 respectively, p < 0.001 for both). Conversely, BA a showed a slight increase in risk (RD: 0.002, p < 0.001).

CONCLUSIONS

GLP-1RAs demonstrate potential benefits in reducing the risk of several systemic conditions in people with T2D or obesity. Further prospective studies are needed to confirm these effects fully and understand the mechanisms.

Interpretable machine learning-driven biomarker identification and validation for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by limited effective treatments, underscoring the critical need for early detection and diagnosis to improve intervention outcomes. This study integrates various bioinformatics methodologies with interpretable machine learning to identify reliable biomarkers for AD diagnosis and treatment. By leveraging differentially expressed genes (DEGs) analysis, weighted gene co-expression network analysis (WGCNA), and construction of Protein-Protein Interaction (PPI) Networks, we meticulously analyzed the AD dataset from the GEO database to pinpoint Hub genes. Subsequently, various machine learning algorithms were employed to construct diagnostic models, which were then elucidated using SHapley Additive exPlanations (SHAP). To visualize our findings, we generated an insightful bioinformatics map of 10 Hub genes. We then conducted experimental validation on less-studied Hub genes, revealing significant differential mRNA expression of MYH9 and RHOQ in an AD cell model. Finally, we explored the biological significance of these two genes at the single-cell transcriptome level. This study not only introduces interactive SHAP panels for precise decision-making in AD but also offers novel insights into the identification of AD biomarkers through interpretable machine learning diagnostic models. Particularly, MYH9 has emerged as a promising new potential biomarker, pointing the way towards enhanced diagnostic accuracy and personalized therapeutic strategies for AD. Although the mRNA expression patterns of RHOQ are opposite in AD cell models and human brain tissue samples, the role of RHOQ in AD remains worthy of further exploration due to the diversity and complexity of biological molecular regulation.

Progress in mitochondrial and omics studies in Alzheimer's disease research: from molecular mechanisms to therapeutic interventions

Alzheimer's disease (Alzheimer's disease, AD) is a progressive neurological disorder characterized by memory loss and cognitive impairment. It is characterized by the formation of tau protein neurofibrillary tangles and β-amyloid plaques. Recent studies have found that mitochondria in neuronal cells of AD patients exhibit various dysfunctions, including reduced numbers, ultrastructural changes, reduced enzyme activity, and abnormal kinetics. These abnormal mitochondria not only lead to the loss of normal neuronal cell function, but are also a major driver of AD progression. In this review, we will focus on the advances of mitochondria and their multi-omics in AD research, with particular emphasis on how mitochondrial dysfunction in AD drives disease progression. At the same time, we will focus on summarizing how mitochondrial genomics technologies have revealed specific details of these dysfunctions and how therapeutic strategies targeting mitochondria may provide new directions for future AD treatments. By delving into the key mechanisms of mitochondria in AD related to energy metabolism, altered kinetics, regulation of cell death, and dysregulation of calcium-ion homeostasis, and how mitochondrial multi-omics technologies can be utilized to provide us with a better understanding of these processes. In the future, mitochondria-centered therapeutic strategies will be a key idea in the treatment of AD.

A Molecular Framework for Delirium

Over 2.6 million adults over the age of 65 develop delirium each year in the United States (US). Delirium is associated with a significant increase in mortality and the US health care costs associated with delirium are estimated at over $164 billion annually. Despite the prevalence of the condition, the molecular pathophysiology of delirium remains unexplained, limiting the development of pharmacotherapies. Delirious patients can be identified by prominent impairments in attention and working memory (WM), two cognitive domains that localize to the dorsolateral prefrontal cortex (dlPFC). The dlPFC is also a key site for Alzheimer's disease (AD) pathology, and given the high risk of delirium in AD patients, suggests that efforts at understanding delirium might focus on the dlPFC as a final common endpoint for cognitive changes. Preclinical studies of the dlPFC reproduce many of the pharmacological observations made of delirious patients, including sensitivity to anticholinergics and an 'inverted U' pattern of dependence on monoaminergic input, with diminished performance outside a narrow range of signaling. Medications like guanfacine, which influence the dlPFC in the context of attention-deficit/hyperactivity disorder (ADHD), have emerged as therapies for delirium and motivate a detailed understanding of the influence of α-2 agonists on WM. In this review, I will discuss the neural circuitry and molecular mechanisms underlying WM and the function of the dlPFC. Localizing the cognitive deficits that are commonly seen in delirious patients may help identify new molecular targets for this highly prevalent disease.

Effects of Intranasal Dantrolene Nanoparticles on Brain Concentration and Behavior in PS19 Tau Transgenic Mice

Background

Repurposing dantrolene to treat Alzheimer's disease has been shown to be effective in amyloid transgenic mouse models but has not been examined in a model of tauopathy.

Objective

The effects of a nanoparticle intranasal formulation, the Eagle Research Formulation of Ryanodex (ERFR), in young adult and aged wild type and PS19 tau transgenic mice was investigated.

Methods

The bioavailability of intranasal ERFR was measured in 2 and 9-11-month-old C57BL/6J mice. Blood and brain samples were collected 20 minutes after a single ERFR dose, and the plasma and brain concentrations were analyzed. Baseline behavior was assessed in untreated PS19 tau transgenic mice at 6 and 9 months of age. PS19 mice were treated with intranasal ERFR, with or without acrolein (to potentiate cognitive dysfunction), for 3 months, beginning at 2 months of age. Animal behavior was examined, including cognition (cued and contextual fear conditioning, y-maze), motor function (rotarod), and olfaction (buried food test).

Results

The dantrolene concentration in the blood and brain decreased with age, with the decrease greater in the blood resulting in a higher brain to blood concentration ratio. The behavioral assays showed no significant changes in cognition, olfaction, or motor function in the PS19 mice compared to controls after chronic treatment with intranasal ERFR, even with acrolein.

Conclusions

Our studies suggest the intranasal administration of ERFR has higher concentrations in the brain than the blood in aged mice and has no serious systemic side effects with chronic use in PS19 mice.

Calcium Dyshomeostasis Drives Pathophysiology and Neuronal Demise in Age-Related Neurodegenerative Diseases

This review postulates that age-related neurodegeneration entails inappropriate activation of intrinsic pathways to enable brain plasticity through deregulated calcium (Ca2+) signalling. Ca2+ in the cytosol comprises a versatile signal controlling neuronal cell physiology to accommodate adaptive structural and functional changes of neuronal networks (neuronal plasticity) and, as such, is essential for brain function. Although disease risk factors selectively affect different neuronal cell types across age-related neurodegenerative diseases (NDDs), these appear to have in common the ability to impair the specificity of the Ca2+ signal. As a result, non-specific Ca2+ signalling facilitates the development of intraneuronal pathophysiology shared by age-related NDDs, including mitochondrial dysfunction, elevated reactive oxygen species (ROS) levels, impaired proteostasis, and decreased axonal transport, leading to even more Ca2+ dyshomeostasis. These core pathophysiological processes and elevated cytosolic Ca2+ levels comprise a self-enforcing feedforward cycle inevitably spiralling toward high levels of cytosolic Ca2+. The resultant elevated cytosolic Ca2+ levels ultimately gear otherwise physiological effector pathways underlying plasticity toward neuronal demise. Ageing impacts mitochondrial function indiscriminately of the neuronal cell type and, therefore, contributes to the feedforward cycle of pathophysiology development seen in all age-related NDDs. From this perspective, therapeutic interventions to safely restore Ca2+ homeostasis would mitigate the excessive activation of neuronal destruction pathways and, therefore, are expected to have promising neuroprotective potential.

Role of Calcium Modulation in the Pathophysiology and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the most frequent cause of progressive dementia in senior adults. It is characterized by memory loss and cognitive impairment secondary to cholinergic dysfunction and N-methyl-D-aspartate (NMDA)-mediated neurotoxicity. Intracellular neurofibrillary tangles, extracellular plaques composed of amyloid-β (Aβ), and selective neurodegeneration are the anatomopathological hallmarks of this disease. The dysregulation of calcium may be present in all the stages of AD, and it is associated with other pathophysiological mechanisms, such as mitochondrial failure, oxidative stress, and chronic neuroinflammation. Although the cytosolic calcium alterations in AD are not completely elucidated, some calcium-permeable channels, transporters, pumps, and receptors have been shown to be involved at the neuronal and glial levels. In particular, the relationship between glutamatergic NMDA receptor (NMDAR) activity and amyloidosis has been widely documented. Other pathophysiological mechanisms involved in calcium dyshomeostasis include the activation of L-type voltage-dependent calcium channels, transient receptor potential channels, and ryanodine receptors, among many others. This review aims to update the calcium-dysregulation mechanisms in AD and discuss targets and molecules with therapeutic potential based on their modulation.

The Role of Glucagon-Like Peptide-1 Receptor Agonists (GLP-1 RA) in Diabetes-Related Neurodegenerative Diseases

Recent clinical guidelines have emphasized the importance of screening for cognitive impairment in older adults with diabetes, however, there is still a lack of understanding about the drug therapy. Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) are widely used in the treatment of type 2 diabetes and potential applications may include the treatment of obesity as well as the adjunctive treatment of type 1 diabetes mellitus in combination with insulin. Growing evidence suggests that GLP-1 RA has the potential to treat neurodegenerative diseases, particularly in diabetes-related Alzheimer’s disease (AD) and Parkinson’s disease (PD). Here, we review the molecular mechanisms of the neuroprotective effects of GLP-1 RA in diabetes-related degenerative diseases, including AD and PD, and their potential effects.

Analysis and Identification Genetic Effect of SARS-CoV-2 Infections to Alzheimer's Disease Patients by Integrated Bioinformatics

BACKGROUND

COVID-19 pandemic is a global crisis which results in millions of deaths and causes long-term neurological sequelae, such as Alzheimer's disease (AD).

OBJECTIVE

We aimed to explore the interaction between COVID-19 and AD by integrating bioinformatics to find the biomarkers which lead to AD occurrence and development with COVID-19 and provide early intervention.

METHODS

The differential expressed genes (DEGs) were found by GSE147507 and GSE132903, respectively. The common genes between COVID-19 and AD were identified. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interactions (PPI) network analysis were carried out. Hub genes were found by cytoscape. A multivariate logistic regression model was constructed. NetworkAnalyst was used for the analysis of TF-gene interactions, TF-miRNA coregulatory network, and Protein-chemical Interactions.

RESULTS

Forty common DEGs for AD and COVID-19 were found. GO and KEGG analysis indicated that the DEGs were enriched in the calcium signal pathway and other pathways. A PPI network was constructed, and 5 hub genes were identified (ITPR1, ITPR3, ITPKB, RAPGEF3, MFGE8). Four hub genes (ITPR1, ITPR3, ITPKB, RAPGEF3) which were considered as important factors in the development of AD that were affected by COVID-19 were shown by nomogram. Utilizing NetworkAnalyst, the interaction network of 4 hub genes and TF, miRNA, common AD risk genes, and known compounds is displayed, respectively.

CONCLUSION

COVID-19 patients are at high risk of developing AD. Vaccination is required. Four hub genes can be considered as biomarkers for prediction and treatment of AD development caused by COVID-19. Compounds with neuroprotective effects can be used as adjuvant therapy for COVID-19 patients.

Studies of aging nonhuman primates illuminate the etiology of early-stage Alzheimer's-like neuropathology: An evolutionary perspective

Tau pathology in Alzheimer's disease (AD) preferentially afflicts the limbic and recently enlarged association cortices, causing a progression of mnemonic and cognitive deficits. Although genetic mouse models have helped reveal mechanisms underlying the rare, autosomal-dominant forms of AD, the etiology of the more common, sporadic form of AD remains unknown, and is challenging to study in mice due to their limited association cortex and lifespan. It is also difficult to study in human brains, as early-stage tau phosphorylation can degrade postmortem. In contrast, rhesus monkeys have extensive association cortices, are long-lived, and can undergo perfusion fixation to capture early-stage tau phosphorylation in situ. Most importantly, rhesus monkeys naturally develop amyloid plaques, neurofibrillary tangles comprised of hyperphosphorylated tau, synaptic loss, and cognitive deficits with advancing age, and thus can be used to identify the early molecular events that initiate and propel neuropathology in the aging association cortices. Studies to date suggest that the particular molecular signaling events needed for higher cognition-for example, high levels of calcium to maintain persistent neuronal firing- lead to tau phosphorylation and inflammation when dysregulated with advancing age. The expression of NMDAR-NR2B (GluN2B)-the subunit that fluxes high levels of calcium-increases over the cortical hierarchy and with the expansion of association cortex in primate evolution, consistent with patterns of tau pathology. In the rhesus monkey dorsolateral prefrontal cortex, spines contain NMDAR-NR2B and the molecular machinery to magnify internal calcium release near the synapse, as well as phosphodiesterases, mGluR3, and calbindin to regulate calcium signaling. Loss of regulation with inflammation and/or aging appears to be a key factor in initiating tau pathology. The vast expansion in the numbers of these synapses over primate evolution is consistent with the degree of tau pathology seen across species: marmoset < rhesus monkey < chimpanzee < human, culminating in the vast neurodegeneration seen in humans with AD.

The genie in the bottle-magnified calcium signaling in dorsolateral prefrontal cortex

Neurons in the association cortices are particularly vulnerable in cognitive disorders such as schizophrenia and Alzheimer's disease, while those in primary visual cortex remain relatively resilient. This review proposes that the special molecular mechanisms needed for higher cognitive operations confer vulnerability to dysfunction, atrophy, and neurodegeneration when regulation is lost due to genetic and/or environmental insults. Accumulating data suggest that higher cortical circuits rely on magnified levels of calcium (from NMDAR, calcium channels, and/or internal release from the smooth endoplasmic reticulum) near the postsynaptic density to promote the persistent firing needed to maintain, manipulate, and store information without "bottom-up" sensory stimulation. For example, dendritic spines in the primate dorsolateral prefrontal cortex (dlPFC) express the molecular machinery for feedforward, cAMP-PKA-calcium signaling. PKA can drive internal calcium release and promote calcium flow through NMDAR and calcium channels, while in turn, calcium activates adenylyl cyclases to produce more cAMP-PKA signaling. Excessive levels of cAMP-calcium signaling can have a number of detrimental effects: for example, opening nearby K+ channels to weaken synaptic efficacy and reduce neuronal firing, and over a longer timeframe, driving calcium overload of mitochondria to induce inflammation and dendritic atrophy. Thus, calcium-cAMP signaling must be tightly regulated, e.g., by agents that catabolize cAMP or inhibit its production (PDE4, mGluR3), and by proteins that bind calcium in the cytosol (calbindin). Many genetic or inflammatory insults early in life weaken the regulation of calcium-cAMP signaling and are associated with increased risk of schizophrenia (e.g., GRM3). Age-related loss of regulatory proteins which result in elevated calcium-cAMP signaling over a long lifespan can additionally drive tau phosphorylation, amyloid pathology, and neurodegeneration, especially when protective calcium binding proteins are lost from the cytosol. Thus, the "genie" we need for our remarkable cognitive abilities may make us vulnerable to cognitive disorders when we lose essential regulation.

A Review of the Relationship of the Cerebrospinal Fluid Changes During the Dysregulation of Parathyroid Hormone With Psychiatric or Neurological Manifestations

It is established that normal calcium and vitamin D concentrations are maintained in the body through parathyroid hormone (PTH), a signaling molecule secreted from parathyroid glands. A massive role is played by PTH in increasing calcium levels when they are extremely low in the body through different mechanisms. The dysregulation of this hormone is due to either over functioning of the gland (hyperparathyroidism) or compromised functioning in hypoparathyroidism. A detailed review was done to identify if any changes are happening in the cerebrospinal fluid (CSF) due to any pathology causing the parathormone to be dysregulated enough to, in turn, cause any further pathology in the nervous system. This may then lead to various disabling neuropsychiatric features. The calcium and vitamin D abnormalities are both directly and indirectly connected to psychiatric features like delusions, schizophrenia, disabled cognition, psychosis, coma, mania, and depression of all kinds.

Moreover, their irregularities are also linked to Alzheimer's. During these manifestations, the CSF is altered concentration-wise, where elevated calcium levels inside are observed during different studies. Despite PTH's indirect connection to the CSF modifications, their association hasn't been potently proven yet, considering more observational studies should be conducted in humans and for a more extended period, along with bigger and greater numbers of CSF samples. Suppose there is a possibility of the link of CSF alterations to PTH. In that case, we can consider a pronounced increase of CSF calcium or PTH as a risk factor for debilitating neuropsychiatric diseases. In this review, the possible correlation of CSF and PTH has been discussed.

Ca2+ Dyshomeostasis Disrupts Neuronal and Synaptic Function in Alzheimer's Disease

Ca²⁺ homeostasis is essential for multiple neuronal functions and thus, Ca²⁺ dyshomeostasis can lead to widespread impairment of cellular and synaptic signaling, subsequently contributing to dementia and Alzheimer's disease (AD). While numerous studies implicate Ca²⁺ mishandling in AD, the cellular basis for loss of cognitive function remains under investigation. The process of synaptic degradation and degeneration in AD is slow, and constitutes a series of maladaptive processes each contributing to a further destabilization of the Ca²⁺ homeostatic machinery. Ca²⁺ homeostasis involves precise maintenance of cytosolic Ca²⁺ levels, despite extracellular influx via multiple synaptic Ca²⁺ channels, and intracellular release via organelles such as the endoplasmic reticulum (ER) via ryanodine receptor (RyRs) and IP₃R, lysosomes via transient receptor potential mucolipin channel (TRPML) and two pore channel (TPC), and mitochondria via the permeability transition pore (PTP). Furthermore, functioning of these organelles relies upon regulated inter-organelle Ca²⁺ handling, with aberrant signaling resulting in synaptic dysfunction, protein mishandling, oxidative stress and defective bioenergetics, among other consequences consistent with AD. With few effective treatments currently available to mitigate AD, the past few years have seen a significant increase in the study of synaptic and cellular mechanisms as drivers of AD, including Ca²⁺ dyshomeostasis. Here, we detail some key findings and discuss implications for future AD treatments.

Genetic and non-genetic factors associated with the phenotype of exceptional longevity & normal cognition

In this study, we split 2156 individuals from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) data into two groups, establishing a phenotype of exceptional longevity & normal cognition versus cognitive impairment. We conducted a genome-wide association study (GWAS) to identify significant genetic variants and biological pathways that are associated with cognitive impairment and used these results to construct polygenic risk scores. We elucidated the important and robust factors, both genetic and non-genetic, in predicting the phenotype, using several machine learning models. The GWAS identified 28 significant SNPs at p-value [Formula: see text] significance level and we pinpointed four genes, ESR1, PHB, RYR3, GRIK2, that are associated with the phenotype though immunological systems, brain function, metabolic pathways, inflammation and diet in the CLHLS cohort. Using both genetic and non-genetic factors, four machine learning models have close prediction results for the phenotype measured in Area Under the Curve: random forest (0.782), XGBoost (0.781), support vector machine with linear kernel (0.780), and [Formula: see text] penalized logistic regression (0.780). The top four important and congruent features in predicting the phenotype identified by these four models are: polygenic risk score, sex, age, and education.

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.

In Vivo Chimeric Alzheimer's Disease Modeling of Apolipoprotein E4 Toxicity in Human Neurons

Despite its clear impact on Alzheimer's disease (AD) risk, apolipoprotein (apo) E4's contributions to AD etiology remain poorly understood. Progress in answering this and other questions in AD research has been limited by an inability to model human-specific phenotypes in an in vivo environment. Here we transplant human induced pluripotent stem cell (hiPSC)-derived neurons carrying normal apoE3 or pathogenic apoE4 into human apoE3 or apoE4 knockin mouse hippocampi, enabling us to disentangle the effects of apoE4 produced in human neurons and in the brain environment. Using single-nucleus RNA sequencing (snRNA-seq), we identify key transcriptional changes specific to human neuron subtypes in response to endogenous or exogenous apoE4. We also find that Aβ from transplanted human neurons forms plaque-like aggregates, with differences in localization and interaction with microglia depending on the transplant and host apoE genotype. These findings highlight the power of in vivo chimeric disease modeling for studying AD.

Mitochondrial calcium uniporter as a potential therapeutic strategy for Alzheimer's disease

Alzheimer's disease (AD), a neurodegenerative disorder, is the leading cause of dementia in the world whose aetiology is still unclear. AD was always related to ageing though there have been instances where people at an early age also succumb to this disease. With medical advancements, the mortality rate has significantly reduced which also makes people more prone to AD. AD is rare, yet the prominent disease has been widely studied with several hypotheses trying to understand the workings of its onset. The most recent and popular hypothesis in AD is the involvement of mitochondrial dysfunction and calcium homeostasis in the development of the disease though their exact roles are not known. With the sudden advent of the mitochondrial calcium uniporter (MCU), many previously known pathological hallmarks of AD may be better understood. Several studies have shown the effect of excess calcium in mitochondria and the influence of MCU complex in mitochondrial function. In this article, we discuss the possible involvement of MCU in AD by linking the uniporter to mitochondrial dysfunction, calcium homeostasis, reactive oxygen species, neurotransmitters and the hallmarks of AD - amyloid plaque formation and tau tangle formation.

Calcium Signaling During Brain Aging and Its Influence on the Hippocampal Synaptic Plasticity

Calcium (Ca²⁺) ions are highly versatile intracellular signaling molecules and are universal second messenger for regulating a variety of cellular and physiological functions including synaptic plasticity. Ca²⁺ homeostasis in the central nervous system endures subtle dysregulation with advancing age. Research has provided abundant evidence that brain aging is associated with altered neuronal Ca²⁺ regulation and synaptic plasticity mechanisms. Much of the work has focused on the hippocampus, a brain region critically involved in learning and memory, which is particularly susceptible to dysfunction during aging. The current chapter takes a specific perspective, assessing various Ca²⁺ sources and the influence of aging on Ca²⁺ sources and synaptic plasticity in the hippocampus. Integrating the knowledge of the complexity of age-related alterations in neuronal Ca²⁺ signaling and synaptic plasticity mechanisms will positively shape the development of highly effective therapeutics to treat brain disorders including cognitive impairment associated with aging and neurodegenerative disease.

Noxious Iron-Calcium Connections in Neurodegeneration

Iron and calcium share the common feature of being essential for normal neuronal function. Iron is required for mitochondrial function, synaptic plasticity, and the development of cognitive functions whereas cellular calcium signals mediate neurotransmitter exocytosis, axonal growth and synaptic plasticity, and control the expression of genes involved in learning and memory processes. Recent studies have revealed that cellular iron stimulates calcium signaling, leading to downstream activation of kinase cascades engaged in synaptic plasticity. The relationship between calcium and iron is Janus-faced, however. While under physiological conditions iron-mediated reactive oxygen species generation boosts normal calcium-dependent signaling pathways, excessive iron levels promote oxidative stress leading to the upsurge of unrestrained calcium signals that damage mitochondrial function, among other downstream targets. Similarly, increases in mitochondrial calcium to non-physiological levels result in mitochondrial dysfunction and a predicted loss of iron homeostasis. Hence, if uncontrolled, the iron/calcium self-feeding cycle becomes deleterious to neuronal function, leading eventually to neuronal death. Here, we review the multiple cell-damaging responses generated by the unregulated iron/calcium self-feeding cycle, such as excitotoxicity, free radical-mediated lipid peroxidation, and the oxidative modification of crucial components of iron and calcium homeostasis/signaling: the iron transporter DMT1, plasma membrane, and intracellular calcium channels and pumps. We discuss also how iron-induced dysregulation of mitochondrial calcium contributes to the generation of neurodegenerative conditions, including Alzheimer’s disease (AD) and Parkinson’s disease (PD).

Selection of Membrane RNA Aptamers to Amyloid Beta Peptide: Implications for Exosome-Based Antioxidant Strategies

The distribution of amyloid beta peptide 42 (Aβ42) between model exosomal membranes and a buffer solution was measured. The model membranes contained liquid-ordered regions or phosphatidylserine. Results demonstrated that up to ca. 20% of amyloid peptide, generated in the plasma (or intracellular) membrane as a result of proteolytic cleavage of amyloid precursor proteins by β- and γ-secretases, can stay within the membrane milieu. The selection of RNA aptamers that bind to Aβ42 incorporated into phosphatidylserine-containing liposomal membranes was performed using the selection-amplification (SELEX) method. After eight selection cycles, the pool of RNA aptamers was isolated and its binding to Aβ42-containing membranes was demonstrated using the gel filtration method. Since membranes can act as a catalytic surface for Aβ42 aggregation, these RNA aptamers may inhibit the formation of toxic amyloid aggregates that can permeabilize cellular membranes or disrupt membrane receptors. Strategies are proposed for using functional exosomes, loaded with RNA aptamers specific to membrane Aβ42, to reduce the oxidative stress in Alzheimer's disease and Down's syndrome.

Mitochondria, OxPhos, and neurodegeneration: cells are not just running out of gas

Mitochondrial respiratory deficiencies have been observed in numerous neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. For decades, these reductions in oxidative phosphorylation (OxPhos) have been presumed to trigger an overall bioenergetic crisis in the neuron, resulting in cell death. While the connection between respiratory defects and neuronal death has never been proven, this hypothesis has been supported by the detection of nonspecific mitochondrial DNA mutations in these disorders. These findings led to the notion that mitochondrial respiratory defects could be initiators of these common neurodegenerative disorders, instead of being consequences of a prior insult, a theory we believe to be misconstrued. Herein, we review the roots of this mitochondrial hypothesis and offer a new perspective wherein mitochondria are analyzed not only from the OxPhos point of view, but also as a complex organelle residing at the epicenter of many metabolic pathways.

Dantrolene : From Malignant Hyperthermia to Alzheimer's Disease

Dantrolene, a ryanodine receptor antagonist, is primarily known as the only clinically acceptable and effective treatment for Malignant Hyperthermia (MH). Inhibition of Ryanodine Receptor (RyR) by dantrolene decreases the abnormal calcium release from the Sarcoplasmic Reticulum (SR) or Endoplasmic Reticulum (ER), where RyR is located. Recently, emerging researches on dissociated cells, brains slices, live animal models and patients have demonstrated that altered RyR expression and function can also play a vital role in the pathogenesis of Alzheimer's Disease (AD). Therefore, dantrolene is now widely studied as a novel treatment for AD, targeting the blockade of RyR channels or another alternative pathway, such as the inhibitory effects of NMDA glutamate receptors and the effects of ER-mitochondria connection. However, the therapeutic effects are not consistent. In this review, we focus on the relationship between the altered RyR expression and function and the pathogenesis of AD, and the potential application of dantrolene as a novel treatment for the disease.

Aβ and the dementia syndrome: Simple versus complex perspectives

BACKGROUND

The amyloid cascade hypothesis (ACH) has dominated strategy in dementia research for decades despite evidence of its limitations including known heterogeneity of the dementia syndrome in the population and the narrow focus on a single molecule - the amyloid beta protein (Aβ) as causal for all Alzheimer-type dementia. Other hypotheses relevant to Aβ are the presenilin (PS) hypothesis (PSH) relating to the involvement of PS in the generation of Aβ, and the amyloid precursor protein (APP) matrix approach (AMA), relating to the complex and dynamic breakdown of APP, from which Aβ derives.

MATERIALS AND METHODS

In this article we explore perspectives relating to complex disorders occurring mainly in older populations through a detailed case study of the role of Aβ in AD.

RESULTS

Scrutiny of the evidence generated so far reveals and a lack of understanding of the wider APP proteolytic system and how narrow research into the dementia syndrome has been to date. Confounding factors add significant limitations to the understanding of the current evidence base.

CONCLUSIONS

A better characterisation of the entire APP proteolytic system in the human brain is urgently required to place Aβ in its complex physiological context. From a molecular perspective, a combination of the alternative hypotheses, the PSH and the AMA may better describe the complexity of the APP proteolytic system leading to new therapeutic approaches. The reductionist approach is widespread throughout biomedical research and this example highlights how neglect of complexity can undermine investigations of complex disorders, particularly those arising in the oldest in our populations.

Calcium Signaling Deficits in Glia and Autophagic Pathways Contributing to Neurodegenerative Disease

SIGNIFICANCE

Numerous cellular processes and signaling mechanisms have been identified that contribute to Alzheimer's disease (AD) pathology; however, a comprehensive or unifying pathway that binds together the major disease features remains elusive. As an upstream mechanism, altered calcium (Ca²⁺) signaling is a common driving force for many pathophysiological events that emerge during normal aging and development of neurodegenerative disease. Recent Advances: Over the previous three decades, accumulated evidence has validated the concept that intracellular Ca²⁺ dysregulation is centrally involved in AD pathogenesis, including the aggregation of pathogenic β-amyloid (Aβ) and phospho-τ species, synapse loss and dysfunction, cognitive impairment, and neurotoxicity.

CRITICAL ISSUES

Although neuronal Ca²⁺ signaling within the cytosol and endoplasmic reticulum (ER) has been well studied, other critical central nervous system-resident cell types affected by aberrant Ca²⁺ signaling, such as astrocytes and microglia, have not been considered as thoroughly. In addition, certain intracellular Ca²⁺-harboring organelles have been well studied, such as the ER and mitochondria; however other critical Ca²⁺-regulated organelles, such as lysosomes and autophagosomes, have only more recently been investigated. In this review, we examine Ca²⁺ dysregulation in microglia and astrocytes, as well as key intracellular organelles important for cellular maintenance and protein handling. Ca²⁺ dysregulation within these non-neuronal cells and organelles is hypothesized to disrupt the effective clearance of misaggregated proteins and cellular signaling pathways needed for memory networks.

FUTURE DIRECTIONS

Overall, we aim to explore how these disrupted mechanisms could be involved in AD pathology and consider their role as potential therapeutic targets. Antioxid. Redox Signal. 29, 1158-1175.

Ca2+, Astrocyte Activation and Calcineurin/NFAT Signaling in Age-Related Neurodegenerative Diseases

Mounting evidence supports a fundamental role for Ca²⁺ dysregulation in astrocyte activation. Though the activated astrocyte phenotype is complex, cell-type targeting approaches have revealed a number of detrimental roles of activated astrocytes involving neuroinflammation, release of synaptotoxic factors and loss of glutamate regulation. Work from our lab and others has suggested that the Ca²⁺/calmodulin dependent protein phosphatase, calcineurin (CN), provides a critical link between Ca²⁺ dysregulation and the activated astrocyte phenotype. A proteolyzed, hyperactivated form of CN appears at high levels in activated astrocytes in both human tissue and rodent tissue around regions of amyloid and vascular pathology. Similar upregulation of the CN-dependent transcription factor nuclear factor of activated T cells (NFAT4) also appears in activated astrocytes in mouse models of Alzheimer's disease (ADs) and traumatic brain injury (TBI). Major consequences of hyperactivated CN/NFAT4 signaling in astrocytes are neuroinflammation, synapse dysfunction and glutamate dysregulation/excitotoxicity, which will be covered in this review article.

Involvement of Insulin Signaling Disturbances in Bisphenol A-Induced Alzheimer's Disease-like Neurotoxicity

Bisphenol A (BPA), a member of the environmental endocrine disruptors (EDCs), has recently received increased attention because of its effects on brain insulin resistance. Available data have indicated that brain insulin resistance may contribute to neurodegenerative diseases. However, the associated mechanisms that underlie BPA-induced brain-related outcomes remain largely unknown. In the present study, we identified significant insulin signaling disturbances in the SH-SY5Y cell line that were mediated by BPA, including the inhibition of physiological p-IR Tyr1355 tyrosine, p-IRS1 tyrosine 896, p-AKT serine 473 and p-GSK3α/β serine 21/9 phosphorylation, as well as the enhancement of IRS1 Ser307 phosphorylation; these effects were clearly attenuated by insulin and rosiglitazone. Intriguingly, Alzheimer’s disease (AD)-associated pathological proteins, such as BACE-1, APP, β-CTF, α-CTF, Aβ _1–42 and phosphorylated tau proteins (S199, S396, T205, S214 and S404), were substantially increased after BPA exposure, and these effects were abrogated by insulin and rosiglitazone treatment; these findings underscore the specific roles of insulin signaling in BPA-mediated AD-like neurotoxicity. Thus, an understanding of the regulation of insulin signaling may provide novel insights into potential therapeutic targets for BPA-mediated AD-like neurotoxicity.