Role of mitochondrial homeostasis and dynamics in Alzheimer's disease

New insights into the role of mitochondrial dynamics in oxidative stress-induced diseases

The accumulation of excess reactive oxygen species (ROS) can lead to oxidative stress (OS), which can induce gene mutations, protein denaturation, and lipid peroxidation directly or indirectly. The expression is reduced ATP level in cells, increased cytoplasmic Ca2+, inflammation, and so on. Consequently, ROS are recognized as significant risk factors for human aging and various diseases, including diabetes, cardiovascular diseases, and neurodegenerative diseases. Mitochondria are involved in the production of ROS through the respiratory chain. Abnormal mitochondrial characteristics, including mitochondrial OS, mitochondrial fission, mitochondrial fusion, and mitophagy, play an important role in various tissues. However, previous excellent reviews focused on OS-induced diseases. In this review, we focus on the latest progress of OS-induced mitochondrial dynamics, discuss OS-induced mitochondrial damage-related diseases, and summarize the OS-induced mitochondrial dynamics-related signaling pathways. Additionally, it elaborates on potential therapeutic methods aimed at preventing oxidative stress from further exacerbating mitochondrial disorders.

Pyrrole adducts mediated mitochondrial dysfunction activates SARM1-dependent axon degeneration in 2,5-hexanedione-induced neuropathy

2,5-hexanedione (HD) is the γ-diketone metabolite of industrial organic solvent n-hexane, primarily responsible for n-hexane neurotoxicity. Previous studies have shown that the formation of pyrrole adducts (PAs) is crucial for the toxic axonopathy induced by HD. However, the exact mechanism underlying PAs-induced axonal degeneration remains unclear. Recently, Sterile α and toll/interleukin 1 receptor motif-containing protein 1 (SARM1) has been identified as the central executor of axon degeneration. This study was designed to investigate the role of SARM1-mediated axon degeneration in rats exposed to HD. Furthermore, the causal relationship between PAs and SARM1-mediated axon degeneration was further explored using Sarm1 KO mice. Our findings suggest that HD causes axon degeneration and neuronal loss in animals. Mechanistic studies revealed that HD activates SARM1-dependent axonal degeneration machinery. In contrast, Sarm1 KO attenuates motor dysfunction and rescues neuron loss following HD exposure. Interestingly, the PAs formed by the binding of HD to proteins primarily accumulate on mitochondria, leading to mitochondrial dysfunction. This dysfunction serves as an upstream event in HD-induced nerve injuries. Our findings highlight the crucial role of PAs formation in the major pathological changes during n-hexane poisoning, providing a potential therapeutic target for n-hexane neuropathy.

Mitochondria-lysosome-extracellular vesicles axis and nanotheranostics in neurodegenerative diseases

The intricate functional interactions between mitochondria and lysosomes play a pivotal role in maintaining cellular homeostasis and proper cellular functions. This dynamic interplay involves the exchange of molecules and signaling, impacting cellular metabolism, mitophagy, organellar dynamics, and cellular responses to stress. Dysregulation of these processes has been implicated in various neurodegenerative diseases. Additionally, mitochondrial-lysosomal crosstalk regulates the exosome release in neurons and glial cells. Under stress conditions, neurons and glial cells exhibit mitochondrial dysfunction and a fragmented network, which further leads to lysosomal dysfunction, thereby inhibiting autophagic flux and enhancing exosome release. This comprehensive review synthesizes current knowledge on mitochondrial regulation of cell death, organelle dynamics, and vesicle trafficking, emphasizing their significant contributions to neurodegenerative diseases. Furthermore, we explore the emerging field of nanomedicine in the management of neurodegenerative diseases. The review provides readers with an insightful overview of nano strategies that are currently advancing the mitochondrial-lysosome-extracellular vesicle axis as a therapeutic approach for mitigating neurodegenerative diseases.

Highly-ordered assembled organic fluorescent materials for high-resolution bio-sensing: a review

Organic fluorescent materials (OFMs) play a crucial role in the development of biosensors, enabling the extraction of biochemical information within cells and organisms, extending to the human body. Concurrently, OFM biosensors contribute significantly to the progress of modern medical and biological research. However, the practical applications of OFM biosensors face challenges, including issues related to low resolution, dispersivity, and stability. To overcome these challenges, scientists have introduced interactive elements to enhance the order of OFMs. Highly-ordered assembled OFMs represent a novel material type applied to biosensors. In comparison to conventional fluorescent materials, highly-ordered assembled OFMs typically exhibit robust anti-diffusion properties, high imaging contrast, and excellent stability. This approach has emerged as a promising method for effectively tracking bio-signals, particularly in the non-invasive monitoring of chronic diseases. This review introduces several highly-ordered assembled OFMs used in biosensors and also discusses various interactions that are responsible for their assembly, such as hydrogen bonding, π-π interaction, dipole-dipole interaction, and ion electrostatic interaction. Furthermore, it delves into the various applications of these biosensors while addressing the drawbacks that currently limit their commercial application. This review aims to provide a theoretical foundation for designing high-performance, highly-ordered assembled OFM biosensors suitable for practical applications. Additionally, it sheds light on the evolving trends in OFM biosensors and their application fields, offering valuable insights into the future of this dynamic research area.

Personalized, Precision Medicine to Cure Alzheimer's Dementia: Approach #1

The goal of the treatment for Alzheimer's dementia (AD) is the cure of dementia. A literature review revealed 18 major elements causing AD and 29 separate medications that address them. For any individual with AD, one is unlikely to discern which major causal elements produced dementia. Thus, for personalized, precision medicine, all causal elements must be treated so that each individual patient will have her or his causal elements addressed. Twenty-nine drugs cannot concomitantly be administered, so triple combinations of drugs taken from that list are suggested, and each triple combination can be administered sequentially, in any order. Ten combinations given over 13 weeks require 2.5 years, or if given over 26 weeks, they require 5.0 years. Such sequential treatment addresses all 18 elements and should cure dementia. In addition, any comorbid risk factors for AD whose first presence or worsening was within ±1 year of when AD first appeared should receive appropriate, standard treatment together with the sequential combinations. The article outlines a randomized clinical trial that is necessary to assess the safety and efficacy of the proposed treatments; it includes a triple-drug Rx for equipoise. Clinical trials should have durations of both 2.5 and 5.0 years unless the data safety monitoring board (DSMB) determines earlier success or futility since it is uncertain whether three or six months of treatment will be curative in humans, although studies in animals suggest that the briefer duration of treatment might be effective and restore defective neural tracts.

Antioxidant Efficacy of Hwangryunhaedok-tang through Nrf2 and AMPK Signaling Pathway against Neurological Disorders In Vivo and In Vitro

Alzheimer's disease (AD) is a representative cause of dementia and is caused by neuronal loss, leading to the accumulation of aberrant neuritic plaques and the formation of neurofibrillary tangles. Oxidative stress is involved in the impaired clearance of amyloid beta (Aβ), and Aβ-induced oxidative stress causes AD by inducing the formation of neurofibrillary tangles. Hwangryunhaedok-tang (HHT, Kracie K-09®), a traditional herbal medicine prescription, has shown therapeutic effects on various diseases. However, the studies of HHT as a potential treatment for AD are insufficient. Therefore, our study identified the neurological effects and mechanisms of HHT and its key bioactive compounds against Alzheimer's disease in vivo and in vitro. In a 5xFAD mouse model, our study confirmed that HHT attenuated cognitive impairments in the Morris water maze (MWM) test and passive avoidance (PA) test. In addition, the prevention of neuron impairment, reduction in the protein levels of Aβ, and inhibition of cell apoptosis were confirmed with brain tissue staining. In HT-22 cells, HHT attenuates tBHP-induced cytotoxicity, ROS generation, and mitochondrial dysfunction. It was verified that HHT exerts a neuroprotective effect by activating signaling pathways interacting with Nrf2, such as MAPK/ERK, PI3K/Akt, and LKB1/AMPK. Among the components, baicalein, a bioavailable compound of HHT, exhibited neuroprotective properties and activated the Akt, AMPK, and Nrf2/HO-1 pathways. Our findings indicate a mechanism for HHT and its major bioavailable compounds to treat and prevent AD and suggest its potential.

Using Redox Proteomics to Gain New Insights into Neurodegenerative Disease and Protein Modification

Antioxidant defenses in biological systems ensure redox homeostasis, regulating baseline levels of reactive oxygen and nitrogen species (ROS and RNS). Oxidative stress (OS), characterized by a lack of antioxidant defenses or an elevation in ROS and RNS, may cause a modification of biomolecules, ROS being primarily absorbed by proteins. As a result of both genome and environment interactions, proteomics provides complete information about a cell's proteome, which changes continuously. Besides measuring protein expression levels, proteomics can also be used to identify protein modifications, localizations, the effects of added agents, and the interactions between proteins. Several oxidative processes are frequently used to modify proteins post-translationally, including carbonylation, oxidation of amino acid side chains, glycation, or lipid peroxidation, which produces highly reactive alkenals. Reactive alkenals, such as 4-hydroxy-2-nonenal, are added to cysteine (Cys), lysine (Lys), or histidine (His) residues by a Michael addition, and tyrosine (Tyr) residues are nitrated and Cys residues are nitrosylated by a Michael addition. Oxidative and nitrosative stress have been implicated in many neurodegenerative diseases as a result of oxidative damage to the brain, which may be especially vulnerable due to the large consumption of dioxygen. Therefore, the current methods applied for the detection, identification, and quantification in redox proteomics are of great interest. This review describes the main protein modifications classified as chemical reactions. Finally, we discuss the importance of redox proteomics to health and describe the analytical methods used in redox proteomics.

The Carnitine Palmitoyl-Transferase 2 Cascade Hypothesis for Alzheimer's Disease

Despite decades of intense research, the precise etiology of Alzheimer's disease (AD) remains unclear. In this hypothesis, we present a new perspective on this matter by identifying carnitine palmitoyl transferase-2 (CPT2) as a central target in AD. CPT2 is an enzyme situated within the inner mitochondrial membrane, playing a crucial role in beta-oxidation of fatty acids. It exhibits high sensitivity to hydrogen peroxide. This sensitivity holds relevance for the etiology of AD, as all major risk factors for the disease share a commonality in producing an excess of hydrogen peroxide right at this very mitochondrial membrane. We will explain the high sensitivity of CPT2 to hydrogen peroxide and elucidate how the resulting inhibition of CPT2 can lead to the characteristic phenotype of AD, thus clarifying its central role in the disease's etiology. This insight holds promise for the development of therapies for AD which can be implemented immediately.

O-GlcNAc regulates the mitochondrial integrated stress response by regulating ATF4

Background

Accumulation of mitochondrial dysfunctional is a hallmark of age-related neurodegeneration including Alzheimer's disease (AD). Impairment of mitochondrial quality control mechanisms leading to the accumulation of damaged mitochondria and increasing neuronal stress. Therefore, investigating the basic mechanisms of how mitochondrial homeostasis is regulated is essential. Herein, we investigate the role of O-GlcNAcylation, a single sugar post-translational modification, in controlling mitochondrial stress-induced transcription factor Activating Transcription Factor 4 (ATF4). Mitochondrial dysfunction triggers the integrated stress response (ISRmt), in which the phosphorylation of eukaryotic translation initiation factor 2α results in the translation of ATF4.

Methods

We used patient-derived induced pluripotent stem cells, a transgenic mouse model of AD, SH-SY5Y neuroblastoma and HeLa cell-lines to examine the effect of sustained O-GlcNAcase inhibition by Thiamet-G (TMG) on ISRmt using biochemical analyses.

Results

We show that TMG elevates ATF4 protein levels upon mitochondrial stress in SH-SY5Y neuroblastoma and HeLa cell-lines. An indirect downstream target of ATF4 mitochondrial chaperone glucose-regulated protein 75 (GRP75) is significantly elevated. Interestingly, knock-down of O-GlcNAc transferase (OGT), the enzyme that adds O-GlcNAc, in SH-SY5Y increases ATF4 protein and mRNA expression. Additionally, ATF4 target gene Activating Transcription Factor 5 (ATF5) is significantly elevated at both the protein and mRNA level. Brains isolated from TMG treated mice show elevated levels of ATF4 and GRP75. Importantly, ATF4 occupancy increases at the ATF5 promoter site in brains isolated from TMG treated mice suggesting that O-GlcNAc is regulating ATF4 targeted gene expression. Interestingly, ATF4 and GRP75 are not induced in TMG treated familial Alzheimer's Disease mice model. The same results are seen in a human in vitro model of AD.

Conclusion

Together, these results indicate that in healthy conditions, O-GlcNAc regulates the ISRmt through regulating ATF4, while manipulating O-GlcNAc in AD has no effect on ISRmt.

Mitochondrial dysfunction in neurodegenerative disorders: Potential therapeutic application of mitochondrial transfer to central nervous system-residing cells

Mitochondrial dysfunction is reiteratively involved in the pathogenesis of diverse neurodegenerative diseases. Current in vitro and in vivo approaches support that mitochondrial dysfunction is branded by several molecular and cellular defects, whose impact at different levels including the calcium and iron homeostasis, energetic balance and/or oxidative stress, makes it difficult to resolve them collectively given their multifactorial nature. Mitochondrial transfer offers an overall solution since it contains the replacement of damage mitochondria by healthy units. Therefore, this review provides an introducing view on the structure and energy-related functions of mitochondria as well as their dynamics. In turn, we summarize current knowledge on how these features are deregulated in different neurodegenerative diseases, including frontotemporal dementia, multiple sclerosis, amyotrophic lateral sclerosis, Friedreich ataxia, Alzheimer´s disease, Parkinson´s disease, and Huntington's disease. Finally, we analyzed current advances in mitochondrial transfer between diverse cell types that actively participate in neurodegenerative processes, and how they might be projected toward developing novel therapeutic strategies.

Exploring the therapeutic potential of the mitochondrial transfer-associated enzymatic machinery in brain degeneration

Mitochondrial dysfunction is a central event in the pathogenesis of several degenerative brain disorders. It entails fission and fusion dynamics disruption, progressive decline in mitochondrial clearance, and uncontrolled oxidative stress. Many therapeutic strategies have been formulated to reverse these alterations, including replacing damaged mitochondria with healthy ones. Spontaneous mitochondrial transfer is a naturally occurring process with different biological functions. It comprises mitochondrial donation from one cell to another, carried out through different pathways, such as the formation and stabilization of tunneling nanotubules and Gap junctions and the release of extracellular vesicles with mitochondrial cargoes. Even though many aspects of regulating these mechanisms still need to be discovered, some key enzymatic regulators have been identified. This review summarizes the current knowledge on mitochondrial dysfunction in different neurodegenerative disorders. Besides, we analyzed the usage of mitochondrial transfer as an endogenous revitalization tool, emphasizing the enzyme regulators that govern this mechanism. Going deeper into this matter would be helpful to take advantage of the therapeutic potential of mitochondrial transfer.

CRMP2 Participates in Regulating Mitochondrial Morphology and Motility in Alzheimer's Disease

Mitochondrial bioenergetics and dynamics (alterations in morphology and motility of mitochondria) play critical roles in neuronal reactions to varying energy requirements in health and disease. In Alzheimer's disease (AD), mitochondria undergo excessive fission and become less motile. The mechanisms leading to these alterations are not completely clear. Here, we show that collapsin response mediator protein 2 (CRMP2) is hyperphosphorylated in AD and that is accompanied by a decreased interaction of CRMP2 with Drp1, Miro 2, and Mitofusin 2, which are proteins involved in regulating mitochondrial morphology and motility. CRMP2 was hyperphosphorylated in postmortem brain tissues of AD patients, in brain lysates, and in cultured cortical neurons from the double transgenic APP/PS1 mice, an AD mouse model. CRMP2 hyperphosphorylation and dissociation from its binding partners correlated with increased Drp1 recruitment to mitochondria, augmented mitochondrial fragmentation, and reduced mitochondrial motility. (S)-lacosamide ((S)-LCM), a small molecule that binds to CRMP2, decreased its phosphorylation at Ser 522 and Thr 509/514, and restored CRMP2's interaction with Miro 2, Drp1, and Mitofusin 2. This was paralleled by decreased Drp1 recruitment to mitochondria, diminished mitochondrial fragmentation, and improved motility of the organelles. Additionally, (S)-LCM-protected cultured cortical AD neurons from cell death. Thus, our data suggest that CRMP2, in a phosphorylation-dependent manner, participates in the regulation of mitochondrial morphology and motility, and modulates neuronal survival in AD.

Meta-analysis of published cerebrospinal fluid proteomics data identifies and validates metabolic enzyme panel as Alzheimer's disease biomarkers

To develop therapies for Alzheimer's disease, we need accurate in vivo diagnostics. Multiple proteomic studies mapping biomarker candidates in cerebrospinal fluid (CSF) resulted in little overlap. To overcome this shortcoming, we apply the rarely used concept of proteomics meta-analysis to identify an effective biomarker panel. We combine ten independent datasets for biomarker identification: seven datasets from 150 patients/controls for discovery, one dataset with 20 patients/controls for down-selection, and two datasets with 494 patients/controls for validation. The discovery results in 21 biomarker candidates and down-selection in three, to be validated in the two additional large-scale proteomics datasets with 228 diseased and 266 control samples. This resulting 3-protein biomarker panel differentiates Alzheimer's disease (AD) from controls in the two validation cohorts with areas under the receiver operating characteristic curve (AUROCs) of 0.83 and 0.87, respectively. This study highlights the value of systematically re-analyzing previously published proteomics data and the need for more stringent data deposition.

GFP-based red-emissive fluorescent probes for dual imaging of β-amyloid plaques and mitochondrial viscosity

Alzheimer's disease (AD), with incurable neurodegenerative damage, has attracted growing interest in exploration of better AD biomarkers in its early diagnosis. Among various biomarkers, amyloid-β (Aβ) aggregates and mitochondrial viscosity are closely related to AD and their dual imaging might provide a potential and feasible strategy. In this work, five GFP-based red-emissive fluorescent probes were rationally designed and synthesized for selective detection of β-amyloid plaques and viscosity, among which C25e exhibited superior properties and could successfully image β-amyloid plaques and mitochondrial viscosity with different fluorescence wavelength signals "turn-on" at around 624 and 640 nm, respectively. Moreover, the staining of brain sections from a transgenic AD mouse showed that probe C25e showed higher selectivity and signal-to-noise ratio towards Aβ plaques than commercially-available Thio-S. In addition, the probe C25e was, for the first time, employed for monitoring amyloid-β induced mitochondrial viscosity changes. Therefore, this GFP-based red-emissive fluorescent probe C25e could serve as a dual-functional tool for imaging β-amyloid plaques and mitochondrial viscosity, which might provide a unique strategy for the early diagnosis of Alzheimer's disease.

Apolipoprotein E4 targets mitochondria and the mitochondria-associated membrane complex in neuropathology, including Alzheimer's disease

Apolipoprotein (apo) E4 sets the stage for neuropathology in Alzheimer's disease (AD) by causing mitochondrial dysfunction and altering mitochondria-associated membranes. Contact and apposition of mitochondrial-endoplasmic reticulum membranes are enhanced in brain cells in AD and associated with increases in tethering and spacing proteins that modulate many cellular processes. Contact site protein levels are higher in apoE4 cells. In apoE4 neurons, the NAD⁺/NADH ratio is lowered, reactive oxygen species are increased, and NAD/NADH pathway components and redox proteins are decreased. Oxidative phosphorylation is impaired and reserve ATP generation capacity is lacking. ApoE4 neurons have ∼50% fewer respiratory complex subunits (e.g., ATP synthase) and may increase translocase levels of the outer and inner mitochondrial membranes to facilitate delivery of nucleus-encoded complex subunits. Respiratory complex assembly relies on mitochondrial cristae organizing system subunits that are altered in apoE4 cells, and apoE4 increases mitochondrial proteases that control respiratory subunit composition for complex assembly.

Hesperidin methylchalcone (HMC) hinders amyloid-β induced Alzheimer's disease by attenuating cholinesterase activity, macromolecular damages, oxidative stress and apoptosis via regulating NF-κB and Nrf2/HO-1 pathways

Phytocompounds therapy has recently emerged as an effective strategy to treat Alzheimer's disease. Herein, the protective effect of hesperidin methylchalcone (HMC) was evaluated through Alzheimer's disease models of Neuro-2a cells and Wistar rats. The in vitro results showed that HMC possesses significant ability to inhibit the acetylcholinesterase enzyme and exhibiting anti-aggregation and disaggregation properties. Furthermore, HMC could protect the Neuro-2a cells against Aβ-induced neurotoxicity. Simultaneously, HMC treatment significantly improved the cognitive deficits caused by Aβ-peptide on spatial memory in Wistar rats. HMC significantly enhanced the cholinergic effects by inhibiting AChE, BuChE, β-secretase activity, caspase-3 activity, and attenuating macromolecular damages and apoptosis. Notably, HMC reduced the Aβ-induced oxidative stress by activating the antioxidative defence enzymes. In addition, the HMC treatment suppressed the expression of immunocytokines such as p-NF-κB p65, p-IκBα, induced by Aβ; whereas upregulating Nrf2, HO-1 in brain homogenate. These results suggest that HMC could attenuate Aβ-induced neuroinflammation in brain via suppressing NF-κB signalling pathway and activating the Nrf2/HO-1 pathway, thereby improving memory and cognitive impairments in Wistar rats. Overall, the present study reports that HMC can act as a potent candidate with multi-faceted neuroprotective potential against Aβ-induced memory dysfunction in Wistar rats for the treatment of Alzheimer's disease.

Insights into the promising prospect of medicinal chemistry studies against neurodegenerative disorders

Medicinal chemistry is an interdisciplinary field that incorporates organic chemistry, biochemistry, physical chemistry, pharmacology, informatics, molecular biology, structural biology, cell biology, and other disciplines. Additionally, it considers molecular factors such as the mode of action of the drugs, their chemical structure-activity relationship (SAR), and pharmacokinetic aspects like absorption, distribution, metabolism, elimination, and toxicity. Neurodegenerative disorders (NDs), which are defined by the breakdown of neurons over time, are affecting an increasing number of people. Oxidative stress, particularly the increased production of Reactive Oxygen Species (ROS), plays a crucial role in the growth of various disorders, as indicated by the identification of protein, lipid, and Deoxyribonucleic acid (DNA) oxidation products in vivo. Because of their inherent nature, most biological molecules are vulnerable to ROS, even if they play a role in metabolic parameters and cell signaling. Due to their high polyunsaturated fatty acid content, low antioxidant barrier, and high oxygen uptake, neurons are particularly vulnerable to oxidation by nature. As a result, excessive ROS generation in neurons looks especially harmful, and the mechanisms associated with biomolecule oxidative destruction are several and complex. This review focuses on the formation and management of ROS, as well as their chemical characteristics (both thermodynamic and kinetic), interactions, and implications in NDs.

The pathomimetic oAβ25–35 model of Alzheimer's disease: Potential for screening of new therapeutic agents

Alzheimer's disease (AD) is the most common form of dementia in the elderly, currently affecting more than 40 million people worldwide. The two main histopathological hallmarks of AD were identified in the 1980s: senile plaques (composed of aggregated amyloid-β (Aβ) peptides) and neurofibrillary tangles (composed of hyperphosphorylated tau protein). In the human brain, both Aβ and tau show aggregation into soluble and insoluble oligomers. Soluble oligomers of Aβ include their most predominant forms - Aβ_1-40 and Aβ_1-42 - as well as shorter peptides such as Aβ_25-35 or Aβ_25-35/40. Most animal models of AD have been developed using transgenesis, based on identified human mutations. However, these familial forms of AD represent less than 1% of AD cases. In this context, the idea emerged in the 1990s to directly inject the Aβ_25-35 fragment into the rodent brain to develop an acute model of AD that could mimic the disease's sporadic forms (99% of all cases). This review aims to: (1) summarize the biological activity of Aβ_25-35, focusing on its impact on the main structural and functional alterations observed in AD (cognitive deficits, APP misprocessing, tau system dysfunction, neuroinflammation, oxidative stress, cholinergic and glutamatergic alterations, HPA axis dysregulation, synaptic deficits and cell death); and (2) confirm the interest of this pathomimetic model in AD research, as it has helped identify and characterize many molecules (marketed, in clinical development, and in preclinical testing), and to the development of alternative approaches for AD prevention and therapy. Today, the Aβ_25-35 model appears as a first-intent choice model to rapidly screen the symptomatic or neuroprotective potencies of new compounds, chemical series, or innovative therapeutic strategies.

Defective proteostasis in Alzheimer's disease

The homeostasis of cellular proteins, or proteostasis, is critical for neuronal function and for brain processes, including learning and memory. Increasing evidence indicates that defective proteostasis contributes to the progression of neurodegenerative disorders, including Alzheimer's disease (AD), the most prevalent form of dementia in the elderly. Proteostasis comprises a set of cellular mechanisms that control protein synthesis, folding, post-translational modification and degradation, all of which are deregulated in AD. Importantly, deregulation of proteostasis plays a key role in synapse dysfunction and in memory impairment, the major clinical manifestation of AD. Here, we discuss molecular pathways involved in protein synthesis and degradation that are altered in AD, and possible pharmacological approaches to correct these defects.

Two polyphenols isolated from Corallodiscus flabellata B. L. Burtt ameliorate amyloid β-protein induced Alzheimer's disease neuronal injury by improving mitochondrial homeostasis

Corallodiscus flabellata B. L. Burtt (CF) is a Chinese folk herb with reported potential for the treatment of Alzheimer's disease (AD). 3,4-Dihydroxyphenylethanol-8-O-[4-O-trans-caffeoyl-β-D-apiofuranosyl-(1→3)-β-D-glucopyranosyl (1→6)][1]-β-D-glucopyranoside (SDC-1-8) and hydroxytyrosol (HT) are two polyphenolic compounds isolated from CF. The aim of this study was to investigate the protective effects of SDC-1-8 and HT on an Aβ_25-35-induced AD model and to study the underlying mechanism. The AD mouse model was established using a brain injection of amyloid β-protein 25-35 (Aβ_25-35, 200 μM), followed by continuous administration of SDC-1-8 and HT for 4 weeks, and found that they improved cognitive dysfunction; ameliorated neuronal damage and apoptosis; decreased oxidative stress, and mitochondrial fission protein levels; and increased mitochondrial fusion protein levels in AD mice. Moreover, SDC-1-8 and HT inhibited mitochondrial membrane depolarization, reduced intracellular stored Ca²⁺ levels, enhanced mitochondrial respiration, increased mitochondrial fusion, and decreased mitochondrial division in Aβ_25-35-induced PC12 cells even in the presence of mdivi-1. Furthermore, molecular docking simulations showed that SDC-1-8 and HT interacted with dynamin-related protein 1 with higher affinity than mitofusin 1. Thus, it is summarized that SDC-1-8 and HT may have neuroprotective effects by balancing the abnormalities of mitochondrial fission and fusion, and SDC-1-8 and HT are the components providing the therapeutic basis of CF.

Nanoparticles loaded with pharmacologically active plant-derived natural products: Biomedical applications and toxicity

Pharmacologically active natural products have played a significant role in the history of drug development. They have acted as sources of therapeutic drugs for various diseases such as cancer and infectious diseases. However, most natural products suffer from poor water solubility and low bioavailability, limiting their clinical applications. The rapid development of nanotechnology has opened up new directions for applying natural products and numerous studies have explored the biomedical applications of nanomaterials loaded with natural products. This review covers the recent research on applying plant-derived natural products (PDNPs) nanomaterials, including nanomedicines loaded with flavonoids, non-flavonoid polyphenols, alkaloids, and quinones, especially their use in treating various diseases. Furthermore, some drugs derived from natural products can be toxic to the body, so the toxicity of them is discussed. This comprehensive review includes fundamental discoveries and exploratory advances in natural product-loaded nanomaterials that may be helpful for future clinical development.

Cell-Membrane-Coated Nanoparticles for Targeted Drug Delivery to the Brain for the Treatment of Neurological Diseases

Neurological diseases (NDs) are a significant cause of disability and death in the global population. However, effective treatments still need to be improved for most NDs. In recent years, cell-membrane-coated nanoparticles (CMCNPs) as drug-targeting delivery systems have become a research hotspot. Such a membrane-derived, nano drug-delivery system not only contributes to avoiding immune clearance but also endows nanoparticles (NPs) with various cellular and functional mimicries. This review article first provides an overview of the function and mechanism of single/hybrid cell-membrane-derived NPs. Then, we highlight the application and safety of CMCNPs in NDs. Finally, we discuss the challenges and opportunities in the field.

Oxidative Stress and Aging as Risk Factors for Alzheimer's Disease and Parkinson's Disease: The Role of the Antioxidant Melatonin

Aging and neurodegenerative diseases share common hallmarks, including mitochondrial dysfunction and protein aggregation. Moreover, one of the major issues of the demographic crisis today is related to the progressive rise in costs for care and maintenance of the standard living condition of aged patients with neurodegenerative diseases. There is a divergence in the etiology of neurodegenerative diseases. Still, a disturbed endogenous pro-oxidants/antioxidants balance is considered the crucial detrimental factor that makes the brain vulnerable to aging and progressive neurodegeneration. The present review focuses on the complex relationships between oxidative stress, autophagy, and the two of the most frequent neurodegenerative diseases associated with aging, Alzheimer's disease (AD) and Parkinson's disease (PD). Most of the available data support the hypothesis that a disturbed antioxidant defense system is a prerequisite for developing pathogenesis and clinical symptoms of ADs and PD. Furthermore, the release of the endogenous hormone melatonin from the pineal gland progressively diminishes with aging, and people's susceptibility to these diseases increases with age. Elucidation of the underlying mechanisms involved in deleterious conditions predisposing to neurodegeneration in aging, including the diminished role of melatonin, is important for elaborating precise treatment strategies for the pathogenesis of AD and PD.

Insights into the Pathophysiology of Alzheimer's Disease and Potential Therapeutic Targets: A Current Perspective

The aging population increases steadily because of a healthy lifestyle and medical advancements in healthcare. However, Alzheimer's disease (AD) is becoming more common and problematic among older adults. AD-related cases show an increasing trend annually, and the younger age population may also be at risk of developing this disorder. AD constitutes a primary form of dementia, an irreversible and progressive brain disorder that steadily damages cognitive functions and the ability to perform daily tasks. Later in life, AD leads to death as a result of the degeneration of specific brain areas. Currently, the cause of AD is poorly understood, and there is no safe and effective therapeutic agent to cure or slow down its progression. The condition is entirely preventable, and no study has yet demonstrated encouraging findings in terms of treatment. Identifying this disease's pathophysiology can help researchers develop safe and efficient therapeutic strategies to treat this ailment. This review outlines and discusses the pathophysiology that resulted in the development of AD including amyloid-β plaques, tau neurofibrillary tangles, neuroinflammation, oxidative stress, cholinergic dysfunction, glutamate excitotoxicity, and changes in neurotrophins level may sound better based on the literature search from Scopus, PubMed, ScienceDirect, and Google Scholar. Potential therapeutic strategies are discussed to provide more insights into AD mechanisms by developing some possible pharmacological agents for its treatment.

The expression pattern of GDF15 in human brain changes during aging and in Alzheimer's disease

Introduction

Growth Differentiation Factor 15 (GDF15) is a mitochondrial-stress-responsive molecule whose expression strongly increases with aging and age-related diseases. However, its role in neurodegenerative diseases, including Alzheimer's disease (AD), is still debated.

Methods

We have characterized the expression of GDF15 in brain samples from AD patients and non-demented subjects (controls) of different ages.

Results

Although no difference in CSF levels of GDF15 was found between AD patients and controls, GDF15 was expressed in different brain areas and seems to be predominantly localized in neurons. The ratio between its mature and precursor form was higher in the frontal cortex of AD patients compared to age-matched controls (p < 0.05). Moreover, this ratio was even higher for centenarians (p < 0.01), indicating that aging also affects GDF15 expression and maturation. A lower expression of OXPHOS complexes I, III, and V in AD patients compared to controls was also noticed, and a positive correlation between GDF15 and IL-6 mRNA levels was observed. Finally, when GDF15 was silenced in vitro in dermal fibroblasts, a decrease in OXPHOS complexes transcript levels and an increase in IL-6 levels were observed.

Discussion

Although GDF15 seems not to be a reliable CSF marker for AD, it is highly expressed in aging and AD brains, likely as a part of stress response aimed at counteracting mitochondrial dysfunction and neuroinflammation.

Exercise and mitochondrial remodeling to prevent age-related neurodegeneration

Healthy brain activity requires precise ion and energy management creating a strong reliance on mitochondrial function. Age-related neurodegeneration leads to a decline in mitochondrial function and increased oxidative stress, with associated declines in mitochondrial mass, respiration capacity, and respiration efficiency. The interdependent processes of mitochondrial protein turnover and mitochondrial dynamics, known together as mitochondrial remodeling, play essential roles in mitochondrial health and therefore brain function. This mini-review describes the role of mitochondria in neurodegeneration and brain health, current practices for assessing both aspects of mitochondrial remodeling, and how exercise mitigates the adverse effects of aging in the brain. Exercise training elicits functional adaptations to improve brain health, and current literature strongly suggests that mitochondrial remodeling plays a vital role in these positive adaptations. Despite substantial implications that the two aspects of mitochondrial remodeling are interdependent, very few investigations have simultaneously measured mitochondrial dynamics and protein synthesis. An improved understanding of the partnership between mitochondrial protein turnover and mitochondrial dynamics will provide a better understanding of their role in both brain health and disease, as well as how they induce protection following exercise.

Ubiquitin-mediated mitochondrial regulation by MITOL/MARCHF5 at a glance

Mitochondria are involved in various cellular processes, such as energy production, inflammatory responses and cell death. Mitochondrial dysfunction is associated with many age-related diseases, including neurological disorders and heart failure. Mitochondrial quality is strictly maintained by mitochondrial dynamics linked to an adequate supply of phospholipids and other substances from the endoplasmic reticulum (ER). The outer mitochondrial membrane-localized E3 ubiquitin ligase MITOL/MARCHF5 is responsible for mitochondrial quality control through the regulation of mitochondrial dynamics, formation of mitochondria-ER contacts and mitophagy. MITOL deficiency has been shown to impair mitochondrial function, cause an excessive inflammatory response and increase vulnerability to stress, resulting in the exacerbation of the disease. In this study, we overview the ubiquitin-mediated regulation of mitochondrial function by MITOL and the relationship between MITOL and diseases.

Loss of Activity-Induced Mitochondrial ATP Production Underlies the Synaptic Defects in a Drosophila Model of ALS

Mutations in the gene encoding vesicle-associated membrane protein B (VAPB) cause a familial form of amyotrophic lateral sclerosis (ALS). Expression of an ALS-related variant of vapb (vapbP58S ) in Drosophila motor neurons results in morphologic changes at the larval neuromuscular junction (NMJ) characterized by the appearance of fewer, but larger, presynaptic boutons. Although diminished microtubule stability is known to underlie these morphologic changes, a mechanism for the loss of presynaptic microtubules has been lacking. By studying flies of both sexes, we demonstrate the suppression of vapbP58S -induced changes in NMJ morphology by either a loss of endoplasmic reticulum (ER) Ca2+ release channels or the inhibition Ca2+/calmodulin (CaM)-activated kinase II (CaMKII). These data suggest that decreased stability of presynaptic microtubules at vapbP58S NMJs results from hyperactivation of CaMKII because of elevated cytosolic [Ca2+]. We attribute the Ca2+ dyshomeostasis to delayed extrusion of cytosolic Ca2+ Suggesting that this defect in Ca2+ extrusion arose from an insufficient response to the bioenergetic demand of neural activity, depolarization-induced mitochondrial ATP production was diminished in vapbP58S neurons. These findings point to bioenergetic dysfunction as a potential cause for the synaptic defects in vapbP58S -expressing motor neurons.SIGNIFICANCE STATEMENT Whether the synchrony between the rates of ATP production and demand is lost in degenerating neurons remains poorly understood. We report that expression of a gene equivalent to an amyotrophic lateral sclerosis (ALS)-causing variant of vesicle-associated membrane protein B (VAPB) in fly neurons decouples mitochondrial ATP production from neuronal activity. Consequently, levels of ATP in mutant neurons are unable to keep up with the bioenergetic burden of neuronal activity. Reduced rate of Ca2+ extrusion, which could result from insufficient energy to power Ca2+ ATPases, results in the accumulation of residual Ca2+ in mutant neurons and leads to alterations in synaptic vesicle (SV) release and synapse development. These findings suggest that synaptic defects in a model of ALS arise from the loss of activity-induced ATP production.

Selenium Nanoparticles-Enriched Lactobacillus casei ATCC 393 Prevents Cognitive Dysfunction in Mice Through Modulating Microbiota-Gut-Brain Axis

Purpose

The bidirectional communication between the gut and the central nervous system mediated by gut microbiota is closely related to the occurrence and development of neurodegenerative diseases, including Alzheimer's disease (AD). Selenium (Se) has been identified as playing a role against AD. Probiotics have beneficial effects on host brain function and behavior by modulating the microbiota-gut-brain axis. Herein, we evaluated the protective effects of Lactobacillus casei ATCC 393 (L. casei ATCC 393) and selenium nanoparticles-enriched L. casei ATCC 393 (L. casei ATCC 393-SeNPs) against D-galactose/aluminum chloride-induced AD model mice.

Methods

The Morris Water Maze (MWM) test was used to assess cognitive function of mice. The morphology and histopathological changes, antioxidant capacity and immune responses in the brain and ileum were evaluated. The alterations in intestinal permeability of the mice were determined using FITC-dextran. Gut microbiota composition was assessed using 16s rRNA sequencing.

Results

Thirteen weeks intervention with L. casei ATCC 393 or L. casei ATCC 393-SeNPs significantly improved cognitive dysfunction, and minimized amyloid beta (Aβ) aggregation, hyperphosphorylation of TAU protein, and prevented neuronal death by modulating Akt/cAMP-response element binding protein (CREB)/brain-derived neurotrophic factor (BDNF) signaling pathway. Moreover, compared with L. casei ATCC 393, L. casei ATCC 393-SeNPs further effectively mitigated intestinal barrier dysfunction by improving antioxidant capacity, regulating immune response, restoring gut microbiota balance, and increasing the level of short-chain fatty acids and neurotransmitters, thereby inhibiting the activation of microglia and protecting brain neurons from neurotoxicity such as oxidative stress and neuroinflammation.

Conclusion

These findings indicated that targeting the microbiota-gut-brain axis with L. casei ATCC 393-SeNPs may have therapeutic potential for the deficits of cognitive function in the AD model mice. Thus, we anticipate that L. casei ATCC 393-SeNPs may be a promising and safe Se nutritional supplement for use as a food additive to prevent the neurodegenerative disease.

Mitochondria as the Essence of Yang Qi in the Human Body

The concept of Yang Qi in Traditional Chinese Medicine (TCM) has many similarities with mitochondria in modern medicine. Both are indispensable to human beings and closely related to life and death. This article discusses the similarities in various aspects between mitochondria and Yang Qi, including body temperature, aging, newborns, circadian rhythm, immunity, and meridian. It is well-known that Yang Qi is vital for human health. Interestingly, decreased mitochondrial function is thought to be key to the development of various diseases. Here, we further explain diseases induced by Yang Qi deficiency, such as cancer, chronic fatigue syndrome, sleep disorder, senile dementia, and metabolic diseases, from the perspective of mitochondrial function. We aim to establish similarities and connections between two important concepts, and hope our essay can stimulate further discussion and investigation on unifying important concepts in western medicine and alternative medicine, especially TCM, and provide unique holistic insights into understanding human health.

Salidroside Regulates Mitochondrial Homeostasis After Polarization of RAW264.7 Macrophages

ABSTRACT

Salidroside has anti-inflammatory and antiatherosclerotic effects, and mitochondrial homeostasis imbalance is closely related to cardiovascular disease. The aim of this study was to investigate the effect of salidroside on mitochondrial homeostasis after macrophage polarization and elucidate its possible mechanism against atherosclerosis. RAW264.7 cells were stimulated with 1 μg·mL -1 Lipopolysaccharide and 50 ng·mL -1 IFN-γ establish M1 polarization and were also pretreated with 400 μM salidroside. The relative expression of proinflammatory genes was detected by RT-PCR whereas that of mitochondrial homeostasis-related proteins and nuclear factor kappa-B (NF-κB) was detected by WB. Levels of intracellular reactive oxygen species (ROS), mitochondrial membrane potential, and mass were measured by chemifluorescence whereas that of NF-κB nuclear translocation was detected by immunofluorescence. Compared with the Mφ group, the M1 group demonstrated increased mRNA expression of interleukin-1β , inductible nitric oxide synthase (iNOS), and tumor necrosis factor-α ; increased protein expression of iNOS, NOD-like receptor protein 3, putative kinase 1 , and NF-κB p65 but decreased protein expression of MFN2, Tom20, and PGC-1α; decreased mitochondrial membrane potential and mass; and increased ROS levels and NF-κB p65 nuclear translocation. Salidroside intervention decreased mRNA expression of interleukin-1β and tumor necrosis factor-α compared with the M1 group but did not affect that of iNOS. Furthermore, salidroside intervention prevented the changes in protein expression, mitochondrial membrane potential and mass, ROS levels, and NF-κB p65 nuclear translocation observed in the M1 group. In summary, salidroside ultimately inhibits M1 macrophage polarization and maintains mitochondrial homeostasis after macrophage polarization by increasing mitochondrial membrane potential, decreasing ROS levels, inhibiting NF-κB activation, and in turn regulating the expression of proinflammatory factors and mitochondrial homeostasis-associated proteins.

Mechanisms of Acupuncture in Improving Alzheimer's Disease Caused by Mitochondrial Damage

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases among the elderly and it accounts for nearly 80% of all dementias. The pathogenesis of AD is complicated and enigmatic thus far. The mitochondrial cascade hypothesis assumes that mitochondrial damage may mediate, drive, or contribute to a variety of AD pathologies and may be the main factor in late-onset AD. Currently, there are no widely recognized drugs able to attenuate mitochondrial damage in AD. Notably, increasing evidence supports the efficacy of acupuncture for improving the mitochondrial structure and protecting mitochondrial functions in AD. This review reports the mechanisms by which acupuncture regulates mitochondrial dynamics, energy metabolism, calcium homeostasis and apoptosis. In conclusion, these findings suggest that AD mitochondrial dysfunction represents a reasonable therapeutic target and acupuncture could play a significant role in preventing and treating AD.

A tale of two systems: Lessons learned from female mid-life aging with implications for Alzheimer's prevention & treatment

Neurological aging is frequently viewed as a linear process of decline, whereas in reality, it is a dynamic non-linear process. The dynamic nature of neurological aging is exemplified during midlife in the female brain. To investigate fundamental mechanisms of midlife aging that underlie risk for development of Alzheimer's disease (AD) in late life, we investigated the brain at greatest risk for the disease, the aging female brain. Outcomes of our research indicate that mid-life aging in the female is characterized by the emergence of three phases: early chronological (pre-menopause), endocrinological (peri-menopause) and late chronological (post-menopause) aging. The endocrinological aging program is sandwiched between early and late chronological aging. Throughout the three stages of midlife aging, two systems of biology, metabolic and immune, are tightly integrated through a network of signaling cascades. The network of signaling between these two systems of biology underlie an orchestrated sequence of adaptative starvation responses that shift the brain from near exclusive dependence on a single fuel, glucose, to utilization of an auxiliary fuel derived from lipids, ketone bodies. The dismantling of the estrogen control of glucose metabolism during mid-life aging is a critical contributor to the shift in fuel systems and emergence of dynamic neuroimmune phenotype. The shift in fuel reliance, puts the largest reservoir of local fatty acids, white matter, at risk for catabolism as a source of lipids to generate ketone bodies through astrocytic beta oxidation. APOE4 genotype accelerates the tipping point for emergence of the bioenergetic crisis. While outcomes derived from research conducted in the female brain are not directly translatable to the male brain, the questions addressed in a female centric program of research are directly applicable to investigation of the male brain. Like females, males with AD exhibit deficits in the bioenergetic system of the brain, activation of the immune system and hallmark Alzheimer's pathologies. The drivers and trajectory of mechanisms underlying neurodegeneration in the male brain will undoubtedly share common aspects with the female in addition to factors unique to the male. Preclinical and clinical evidence indicate that midlife endocrine aging can also be a transitional bridge to autoimmune disorders. Collectively, the data indicate that endocrinological aging is a critical period "tipping point" in midlife which can initiate emergence of the prodromal stage of late-onset-Alzheimer's disease. Interventions that target both immune and metabolic shifts that occur during midlife aging have the potential to alter the trajectory of Alzheimer's risk in late life. Further, to achieve precision medicine for AD, chromosomal sex is a critical variable to consider along with APOE genotype, other genetic risk factors and stage of disease.

Mitochondria, energy, and metabolism in neuronal health and disease

Mitochondria are associated with various cellular activities critical to homeostasis, particularly in the nervous system. The plastic architecture of the mitochondrial network and its dynamic structure play crucial roles in ensuring that varying energetic demands are rapidly met to maintain neuronal and axonal energy homeostasis. Recent evidence associates ageing and neurodegeneration with anomalous neuronal metabolism, as age-dependent alterations of neuronal metabolism are now believed to occur prior to neurodegeneration. The brain has a high energy demand, which makes it particularly sensitive to mitochondrial dysfunction. Distinct cellular events causing oxidative stress or disruption of metabolism and mitochondrial homeostasis can trigger a neuropathology. This review explores the bioenergetic hypothesis for the neurodegenerative pathomechanisms, discussing factors leading to age-related brain hypometabolism and its contribution to cognitive decline. Recent research on the mitochondrial network in healthy nervous system cells, its response to stress and how it is affected by pathology, as well as current contributions to novel therapeutic approaches will be highlighted.

Morin attenuates memory deficits in a rat model of Alzheimer's disease by ameliorating oxidative stress and neuroinflammation

This study aimed to investigate the effect of flavonoid morin on oxidative/nitrosative stress, neuroinflammation, and histological, molecular, and behavioral changes caused by amyloid-beta (Aβ)_1-42 in male Wistar rats (Alzheimer's disease model). Rats received morin (20 mg/kg, oral gavage) for 14 consecutive days after intrahippocampal injection of Aβ_1-42. Morin decreased the levels of malondialdehyde and nitric oxide, increased glutathione content, and enhanced catalase activity in the hippocampus of animals receiving Aβ_1-42. It also reduced the expression of tumor necrosis factor-α, interleukin-1β, interleukin-6, nuclear factor-kappa B, and N-methyl-D-aspartate receptor subunits 2A and 2B and increased the expression of brain-derived neurotrophic factor and α7 nicotinic acetylcholine receptor in the hippocampus of Aβ_1-42-injected rats. Besides, morin modified neuronal loss and histological changes in the CA1 region of the hippocampus. Morin allowed Aβ_1-42-infused rats to swim more time in the target quadrant in the Morris water maze test. It is concluded that morin may be suitable for the prevention and treatment of Alzheimer's disease by strengthening the antioxidant system, inhibiting neuroinflammation, preventing neuronal death, and enhancing memory function.

Decrypting the potential role of α-lipoic acid in Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases with motor disturbances, cognitive decline, and behavioral impairment. It is characterized by the extracellular aggregation of amyloid-β plaques and the intracellular accumulation of tau protein. AD patients show a cognitive decline, which has been associated with oxidative stress, as well as mitochondrial dysfunction. Alpha-lipoic acid (α-LA), a natural antioxidant present in food and used as a dietary supplement, has been considered a promising agent for the prevention or treatment of neurodegenerative disorders. Despite multiple preclinical studies indicating beneficial effects of α-LA in memory functioning, and pointing to its neuroprotective effects, to date only a few studies have examined its effects in humans. Studies performed in animal models of memory loss associated with aging and AD have shown that α-LA improves memory in a variety of behavioral paradigms. Furthermore, molecular mechanisms underlying α-LA effects have also been investigated. Accordingly, α-LA shows antioxidant, antiapoptotic, anti-inflammatory, glioprotective, metal chelating properties in both in vivo and in vitro studies. In addition, it has been shown that α-LA reverses age-associated loss of neurotransmitters and their receptors. The review article aimed at summarizing and discussing the main studies investigating the neuroprotective effects of α-LA on cognition as well as its molecular effects, to improve the understanding of the therapeutic potential of α-LA in patients suffering from neurodegenerative disorders, supporting the development of clinical trials with α-LA.

Exercise-Induced Benefits for Alzheimer's Disease by Stimulating Mitophagy and Improving Mitochondrial Function

Neurons are highly specialized post-mitotic cells that are inherently dependent on mitochondria due to their higher bioenergetic demand. Mitochondrial dysfunction is closely associated with a variety of aging-related neurological disorders, such as Alzheimer’s disease (AD), and the accumulation of dysfunctional and superfluous mitochondria has been reported as an early stage that significantly facilitates the progression of AD. Mitochondrial damage causes bioenergetic deficiency, intracellular calcium imbalance and oxidative stress, thereby aggravating β-amyloid (Aβ) accumulation and Tau hyperphosphorylation, and further leading to cognitive decline and memory loss. Although there is an intricate parallel relationship between mitochondrial dysfunction and AD, their triggering factors, such as Aβ aggregation and hyperphosphorylated Tau protein and action time, are still unclear. Moreover, many studies have confirmed abnormal mitochondrial biosynthesis, dynamics and functions will present once the mitochondrial quality control is impaired, thus leading to aggravated AD pathological changes. Accumulating evidence shows beneficial effects of appropriate exercise on improved mitophagy and mitochondrial function to promote mitochondrial plasticity, reduce oxidative stress, enhance cognitive capacity and reduce the risks of cognitive impairment and dementia in later life. Therefore, stimulating mitophagy and optimizing mitochondrial function through exercise may forestall the neurodegenerative process of AD.

Alternative platelet activation pathways and their role in neurodegenerative diseases

PURPOSE OF THE REVIEW

The study of platelets in the context of neurodegenerative diseases is intensifying, and increasing evidence suggests that platelets may play an important role in the pathogenesis of neurodegenerative disorders. Therefore, we aim to provide a comprehensive overview of the role of platelets and their diverse activation pathways in the development of these diseases.

RECENT FINDINGS

Platelets participate in synaptic plasticity, learning, memory, and platelets activated by exercise promote neuronal differentiation in several brain regions. Platelets also contribute to the immune response by modulating their surface protein profile and releasing pro- and anti-inflammatory mediators. In Alzheimer's disease, increased levels of platelet amyloid precursor protein raise the production of amyloid-beta peptides promoting platelet activation, triggering at the same time amyloid-beta fibrillation. In Parkinson's disease, increased platelet α-synuclein is associated with elevated ROS production and mitochondrial dysfunction.

SUMMARY

In this review, we revise different platelet activation pathways, those classically involved in hemostasis and wound healing, and alternative activation pathways recently described in the context of neurodegenerative diseases, especially in Alzheimer's disease.

A multitude of signaling pathways associated with Alzheimer's disease and their roles in AD pathogenesis and therapy

The exact molecular mechanisms associated with Alzheimer's disease (AD) pathology continue to represent a mystery. In the past decades, comprehensive data were generated on the involvement of different signaling pathways in the AD pathogenesis. However, the utilization of signaling pathways as potential targets for the development of drugs against AD is rather limited due to the immense complexity of the brain and intricate molecular links between these pathways. Therefore, finding a correlation and cross-talk between these signaling pathways and establishing different therapeutic targets within and between those pathways are needed for better understanding of the biological events responsible for the AD-related neurodegeneration. For example, autophagy is a conservative cellular process that shows link with many other AD-related pathways and is crucial for maintenance of the correct cellular balance by degrading AD-associated pathogenic proteins. Considering the central role of autophagy in AD and its interplay with many other pathways, the finest therapeutic strategy to fight against AD is the use of autophagy as a target. As an essential step in this direction, this comprehensive review represents recent findings on the individual AD-related signaling pathways, describes key features of these pathways and their cross-talk with autophagy, represents current drug development, and introduces some of the multitarget beneficial approaches and strategies for the therapeutic intervention of AD.

Redox Homeostasis and Prospects for Therapeutic Targeting in Neurodegenerative Disorders

Reactive species, such as those of oxygen, nitrogen, and sulfur, are considered part of normal cellular metabolism and play significant roles that can impact several signaling processes in ways that lead to either cellular sustenance, protection, or damage. Cellular redox processes involve a balance in the production of reactive species (RS) and their removal because redox imbalance may facilitate oxidative damage. Physiologically, redox homeostasis is essential for the maintenance of many cellular processes. RS may serve as signaling molecules or cause oxidative cellular damage depending on the delicate equilibrium between RS production and their efficient removal through the use of enzymatic or nonenzymatic cellular mechanisms. Moreover, accumulating evidence suggests that redox imbalance plays a significant role in the progression of several neurodegenerative diseases. For example, studies have shown that redox imbalance in the brain mediates neurodegeneration and alters normal cytoprotective responses to stress. Therefore, this review describes redox homeostasis in neurodegenerative diseases with a focus on Alzheimer's and Parkinson's disease. A clearer understanding of the redox-regulated processes in neurodegenerative disorders may afford opportunities for newer therapeutic strategies.

Role of PITRM1 in Mitochondrial Dysfunction and Neurodegeneration

Mounting evidence shows a link between mitochondrial dysfunction and neurodegenerative disorders, including Alzheimer Disease. Increased oxidative stress, defective mitodynamics, and impaired oxidative phosphorylation leading to decreased ATP production, can determine synaptic dysfunction, apoptosis, and neurodegeneration. Furthermore, mitochondrial proteostasis and the protease-mediated quality control system, carrying out degradation of potentially toxic peptides and misfolded or damaged proteins inside mitochondria, are emerging as potential pathogenetic mechanisms. The enzyme pitrilysin metallopeptidase 1 (PITRM1) is a key player in these processes; it is responsible for degrading mitochondrial targeting sequences that are cleaved off from the imported precursor proteins and for digesting a mitochondrial fraction of amyloid beta (Aβ). In this review, we present current evidence obtained from patients with PITRM1 mutations, as well as the different cellular and animal models of PITRM1 deficiency, which points toward PITRM1 as a possible driving factor of several neurodegenerative conditions. Finally, we point out the prospect of new diagnostic and therapeutic approaches.

Immunization with Aβ3-10-KLH vaccine improves cognitive function and ameliorates mitochondrial dysfunction and reduces Alzheimer's disease-like pathology in Tg-APPswe/PSEN1dE9 mice

Alzheimer's disease is a common cause of dementia, for which no disease-modifying therapy is yet available. Aβ3-10-KLH, a vaccine for active immunization, has been shown to prevent pathological changes in young transgenic models of AD, but the effects of treatment with it and its effects on mitochondrial dysfunction remain unclear. We immunized 6-month-old Tg-APPswe/PSEN1dE9 mice with Aβ3-10-KLH to analyze whether it is capable of eliminating amyloid-β after its appearance. The vaccine effectively decreased amyloid-β deposits, improved cognitive function and ameliorated mitochondrial dysfunction. These results indicate the potential of Aβ3-10-KLH as a vaccine to treat AD.

Alzheimer's disease: An evolving understanding of noradrenergic involvement and the promising future of electroceutical therapies

Alzheimer's disease (AD) poses a significant global health concern over the next several decades. Multiple hypotheses have been put forth that attempt to explain the underlying pathophysiology of AD. Many of these are briefly reviewed here, but to-date no disease-altering therapy has been achieved. Despite this, recent work expanding on the role of noradrenergic system dysfunction in both the pathogenesis and symptomatic exacerbation of AD has shown promise. The role norepinephrine (NE) plays in AD remains complicated but pre-tangle tau has consistently been shown to arise in the locus coeruleus (LC) of patients with AD decades before symptom onset. The current research reviewed here indicates NE can facilitate neuroprotective and memory-enhancing effects through β adrenergic receptors, while α2A adrenergic receptors may exacerbate amyloid toxicity through a contribution to tau hyperphosphorylation. AD appears to involve a disruption in the balance between these two receptors and their various subtypes. There is also a poorly characterized interplay between the noradrenergic and cholinergic systems. LC deterioration leads to maladaptation in the remaining LC-NE system and subsequently inhibits cholinergic neuron function, eventually leading to the classic cholinergic disruption seen in AD. Understanding AD as a dysfunctional noradrenergic system, provides new avenues for the use of advanced neural stimulation techniques to both study and therapeutically target the earliest stages of neuropathology. Direct LC stimulation and non-invasive vagus nerve stimulation (VNS) have both demonstrated potential use as AD therapeutics. Significant work remains, though, to better understand the role of the noradrenergic system in AD and how electroceuticals can provide disease-altering treatments.

Identification of highest neurotoxic amyloid-β plaque type showing reduced contact with astrocytes

Amyloid-β (Aβ) plaques are strongly associated with the development of Alzheimer's disease (AD). However, it remains unclear how morphological differences in Aβ plaques determine the pathogenesis of Aβ. Here, we categorized Aβ plaques into four types based on the macroscopic features of the dense core, and found that the Aβ-plaque subtype containing a larger dense core showed the strongest association with neuritic dystrophy. Astrocytes dominantly accumulated toward these expanded/dense-core-containing Aβ plaques. Previously, we indicated that deletion of the mitochondrial ubiquitin ligase MITOL/MARCH5 triggers mitochondrial impairments and exacerbates cognitive decline in a mouse model with AD-related Aβ pathology. In this study, MITOL deficiency accelerated the formation of expanded/dense-core-containing Aβ plaques, which showed reduced contacts with astrocytes, but not microglia. Our findings suggest that expanded/dense-core-containing Aβ-plaque formation enhanced by the alteration of mitochondrial function robustly contributes to the exacerbation of Aβ neuropathology, at least in part, through the reduced contacts between Aβ plaques and astrocytes.

A transition to degeneration triggered by oxidative stress in degenerative disorders

Although the activities of many signaling pathways are dysregulated during the progression of neurodegenerative and muscle degeneration disorders, the precise sequence of cellular events leading to degeneration has not been fully elucidated. Two kinases of particular interest, the growth-promoting Tor kinase and the energy sensor AMPK, appear to show reciprocal changes in activity during degeneration, with increased Tor activity and decreased AMPK activity reported. These changes in activity have been predicted to cause degeneration by attenuating autophagy, leading to the accumulation of unfolded protein aggregates and dysfunctional mitochondria, the consequent increased production of reactive oxygen species (ROS), and ultimately oxidative damage. Here we propose that this increased ROS production not only causes oxidative damage but also ultimately induces an oxidative stress response that reactivates the redox-sensitive AMPK and activates the redox-sensitive stress kinase JNK. Activation of these kinases reactivates autophagy. Because at this late stage, cells have become filled with dysfunctional mitochondria and protein aggregates, which are autophagy targets, this autophagy reactivation induces degeneration. The mechanism proposed here emphasizes that the process of degeneration is dynamic, that dysregulated signaling pathways change over time and can transition from deleterious to beneficial and vice versa as degeneration progresses.

Mitochondrial Dysfunction and Oxidative Stress in Alzheimer's Disease

Mitochondria play a pivotal role in bioenergetics and respiratory functions, which are essential for the numerous biochemical processes underpinning cell viability. Mitochondrial morphology changes rapidly in response to external insults and changes in metabolic status via fission and fusion processes (so-called mitochondrial dynamics) that maintain mitochondrial quality and homeostasis. Damaged mitochondria are removed by a process known as mitophagy, which involves their degradation by a specific autophagosomal pathway. Over the last few years, remarkable efforts have been made to investigate the impact on the pathogenesis of Alzheimer’s disease (AD) of various forms of mitochondrial dysfunction, such as excessive reactive oxygen species (ROS) production, mitochondrial Ca²⁺ dyshomeostasis, loss of ATP, and defects in mitochondrial dynamics and transport, and mitophagy. Recent research suggests that restoration of mitochondrial function by physical exercise, an antioxidant diet, or therapeutic approaches can delay the onset and slow the progression of AD. In this review, we focus on recent progress that highlights the crucial role of alterations in mitochondrial function and oxidative stress in the pathogenesis of AD, emphasizing a framework of existing and potential therapeutic approaches.

Neuronal mitochondria-targeted therapy for Alzheimer's disease by systemic delivery of resveratrol using dual-modified novel biomimetic nanosystems

Reactive oxygen species (ROS)-induced neuronal mitochondrial dysfunction is a key pathologic factor in sporadic Alzheimer’s disease (AD). Neuronal mitochondria have been proposed to be a promising therapeutic target for AD, especially for the failures of phase III clinical trials on conventional amyloid-β (Aβ) targeted therapy. However, the efficient intravenous delivery of therapeutic agents to neuronal mitochondria in the brain remains a major challenge due to the complicated physiological environment. Recently, biomaterials-based nanomedicine has been widely investigated for the treatment of AD. Herein, we devised a strategy for functional antioxidant delivery to neuronal mitochondria by loading antioxidants into red blood cell (RBC) membrane-coated nanostructured lipid carriers (NLC) bearing rabies virus glycoprotein (RVG29) and triphenylphosphine cation (TPP) molecules attached to the RBC membrane surface (RVG/TPP NPs@RBCm). With the advantage of suitable physicochemical properties of NLC and unique biological functions of the RBC membrane, RVG/TPP NPs@RBCm are stabilized and enabled sustained drug release, providing improved biocompatibility and long-term circulation. Under the synergistic effects of RVG29 and TPP, RVG/TPP NPs@RBCm can not only penetrate the blood–brain barrier (BBB) but also target neuron cells and further localize in the mitochondria. After encapsulating Resveratrol (RSV) as the model antioxidant, the data demonstrated that RVG/TPP-RSV NPs@RBCm can relieve AD symptoms by mitigating Aβ-related mitochondrial oxidative stress both in vitro and in vivo. The memory impairment in APP/PS1 mice is significantly improved following the systemic administration of RVG/TPP-RSV NPs@RBCm. In conclusion, intravenous neuronal mitochondria-targeted dual-modified novel biomimetic nanosystems are a promising therapeutic candidate for ROS-induced mitochondrial dysfunction in AD.

Mitochondrial unfolded protein response: An emerging pathway in human diseases

Mitochondrial unfolded protein response (UPR^mt) is a mitochondria stress response, which the transcriptional activation programs of mitochondrial chaperone proteins and proteases are initiated to maintain proteostasis in mitochondria. Additionally, the activation of UPR^mt delays aging and extends lifespan by maintaining mitochondrial proteostasis. Growing evidences suggests that UPR^mt plays an important role in diverse human diseases, especially ageing-related diseases. Therefore, this review focuses on the role of UPR^mt in ageing and ageing-related neurodegenerative diseases such as Alzheimer's disease, Huntington's disease and Parkinson's disease. The activation of UPR^mt and the high expression of UPR^mt components contribute to longevity extension. The activation of UPR^mt may ameliorate Alzheimer's disease, Parkinson's disease and Huntington's disease. Besides, UPR^mt is also involved in the occurrence and development of cancers and heart diseases. UPR^mt contributes to the growth, invasive and metastasis of cancers. UPR^mt has paradoxical roles in heart diseases. UPR^mt not only protects against heart damage, but may sometimes aggravates the development of heart diseases. Considering the pleiotropic actions of UPR^mt system, targeting UPR^mt pathway may be a potent therapeutic avenue for neurodegenerative diseases, cancers and heart diseases.

Decreased mitochondrial electron transport proteins and increased complement mediators in plasma neural-derived exosomes of early psychosis

Potentially neurotoxic systems involved in traumatic and degenerative diseases of the brain were assessed in acute psychosis. Astrocyte-derived exosomes (ADEs) and neuron-derived exosomes (NDEs) were immunoprecipitated from plasma of ten untreated first-episode psychotics (FPs) and ten matched normal controls (Cs). Neural mitochondrial electron transport and complement proteins were extracted, quantified by ELISAs and normalized with levels of CD81 exosome marker. Levels of subunits 1 and 6 of NADH-ubiquinone oxidoreductase (complex I) and subunit 10 of cytochrome b-c1 oxidase (complex III), but not of subunit 1 of cytochrome C oxidase (complex IV) or superoxide dismutase 1 (SOD1) were significantly lower in ADEs and NDEs of FPs than Cs. This dysregulated pattern of electron transport proteins is associated with increased generation of reactive oxygen species. ADE glial fibrillary acidic protein levels were significantly higher in FPs than Cs, indicating a higher percentage of inflammatory astrocytes in FPs. ADE levels of C3b opsonin were significantly higher and those of C5b-9 attack complex was marginally higher in FPs than Cs. A significantly lower ADE level of the C3 convertase inhibitor CD55 may explain the higher levels of C3 convertase-generated C3b. ADE levels of the neuroprotective protein leukemia inhibitory factor (LIF) were significantly lower in FPs than Cs, whereas levels of IL-6 were no different. Plasma neural exosome levels of electron transport and complement proteins may be useful in predicting FP and guiding therapy. SOD mimetics, C3 convertase inhibitors and LIF receptor agonists also may have therapeutic benefits in FP.