Defective mitophagy and the etiopathogenesis of Alzheimer's disease

Impact of diet and exercise on mitochondrial quality and mitophagy in Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder that affects millions of people worldwide. It is characterized by the accumulation of beta-amyloid and phosphorylated tau, synaptic damage, and mitochondrial abnormalities in the brain, leading to the progressive loss of cognitive function and memory. In AD, emerging research suggests that lifestyle factors such as a healthy diet and regular exercise may play a significant role in delaying the onset and progression of the disease. Mitochondria are often referred to as the powerhouse of the cell, as they are responsible for producing the energy to cells, including neurons to maintain cognitive function. Our article elaborates on how mitochondrial quality and function decline with age and AD, leading to an increase in oxidative stress and a decrease in ATP production. Decline in mitochondrial quality can impair cellular functions contributing to the development and progression of disease with the loss of neuronal functions in AD. This article also covered mitophagy, the process by which damaged or dysfunctional mitochondria are selectively removed from the cell to maintain cellular homeostasis. Impaired mitophagy has been implicated in the progression and pathogenesis of AD. We also discussed the impact of impaired mitophagy implicated in AD, as the accumulation of damaged mitochondria can lead to increased oxidative stress. We expounded how dietary interventions and exercise can help to improve mitochondrial quality, and mitochondrial function and enhance mitophagy in AD. A diet rich in antioxidants, polyphenols, and mitochondria-targeted small molecules has been shown to enhance mitochondrial function and protect against oxidative stress, particularly in neurons with aged and mild cognitively impaired subjects and AD patients. Promoting a healthy lifestyle, mainly balanced diet and regular exercise that support mitochondrial health, in an individual can potentially delay the onset and progression of AD. In conclusion, a healthy diet and regular exercise play a crucial role in maintaining mitochondrial quality and mitochondrial function, in turn, enhancing mitophagy and synaptic activities that delay AD in the elderly populations.

Mitochondria-targeting probes with large Stokes shift for detecting Amyloid-β and cellular viscosity changes

For effective in vivo applications, imaging probes must exhibit sufficient tissue penetration depth, high sensitivity, and specificity. Increasing evidence suggests that pathological accumulation of Aβ results in elevated mitochondrial viscosity. To achieve red-shifted absorption and emission characteristics of small-molecule theranostic agents and to enhance their mitochondrial targeting efficiency, a series of M-series probes (M13 ∼ M15) was rationally designed based on the previously reported Q-series compounds. Using compound Q16 as the parent structure, the M series probes retained the electron-donating dimethylamino group while replacing the benzene ring with a quinoline moiety. This modification was intended to enhance the intramolecular charge transfer (ICT) effect of the "D-π-A" system, thereby red-shifting the fluorescence emission wavelength and expanding the Stokes shift. The enhanced push-pull effect induced a redshift in the emission wavelength of probe M13 to 806 nm in DMSO, resulting in a Stokes shift of 266 nm. This large Stokes shift effectively minimizes the overlap between excitation and emission wavelengths, thereby reducing self-quenching effects. Building on this, the interactions between M-series probes and Aβ aggregates were further explored. The probes exhibited the expected fluorescence characteristics and displayed varying degrees of response upon binding with Aβ aggregates. To enable a more precise early diagnosis, M13, M14, and M15 were evaluated for their ability to monitor changes in mitochondrial viscosity and their mitochondrial targeting efficiency. The results demonstrated that the M-series fluorescent probes could effectively monitor variations in mitochondrial viscosity in cells. All three probes demonstrated strong mitochondrial targeting in HeLa cells, with M14 achieving a high colocalization coefficient of 0.89 when compared with a commercial mitochondrial dye. These findings highlight the potential application of M-series probes in the early diagnosis and treatment of Alzheimer's disease (AD).

A novel dual CCK/ GLP-1 receptor agonist ameliorates cognitive impairment in 5 × FAD mice by modulating mitophagy via the PINK1/Parkin pathway

To date, no therapeutic drugs available on the market can effectively reverse the progression of Alzheimer's disease (AD). Although Glucagon-like peptide-1 (GLP-1) receptor agonists (RAs) and Cholecystokinin (CCK) RAs have shown some promise in AD research, little is known about the neuroprotective effects of a novel dual CCK/GLP-1 RA in AD. This study sought to examine the effects of the novel dual CCK/GLP-1 RA on cognitive performance in an AD mouse model and to explore the associated mechanisms. Our findings indicate that dual CCK/GLP-1 RA improved cognitive deficits, reduced amyloid-beta (Aβ) accumulation, and alleviated mitochondrial damage in 5 × FAD mice by inducing mitophagy. In an in vitro model of AD cells induced by Aβ, CCK/GLP-1 RA could exert neuroprotective effects by regulating PINK1/Parkin-mediated mitophagy. These data reveal for the first time that the new CCK/GLP-1 RA modulates mitophagy via PINK1/Parkin pathway and enhances cognitive function in the 5 × FAD animal model. Moreover, the performance of the CCK/GLP-1 RA in certain indicators was superior to that of GLP-1 analogue liraglutide, suggesting that it may represent a more promising therapeutic option for AD.

Conjugation with the XJB peptide enhanced neuroprotective effect of honokiol via SIRT3 modulation

Mitochondria play a crucial role in cellular processes such as growth, differentiation, and energy conversion. Dysfunctional mitochondria have been implicated in Alzheimer's disease (AD), making mitochondrial improvement a promising therapeutic approach. SIRT3, a mitochondrial deacetylase, modulates mitochondrial function by deacetylating associated proteins. This study aimed to enhance the activity of honokiol, a natural SIRT3 modulator, and improve mitochondrial function for neuroprotective activity, using mitochondria targeting strategy. We synthesized mitochondrial targeting peptide conjugates using XJB as a carrier and found that honokiol conjugates exhibited lower toxicity and higher activity on neuronal injury models in vitro and in vivo (Zebrafish model) at lower concentrations compared to honokiol. The neuroprotective mechanism may involve the activation of cellular autophagy-related pathways, promotion of SIRT3 pathway activation, and up-regulation of mitochondrial fusion-associated protein Mfn-1 expression under damaged conditions. This study offers a promising approach for developing anti-Alzheimer's disease (AD) natural product derivatives based on SIRT3 regulation.

Comparative Analysis of Human Brain RNA-seq Reveals the Combined Effects of Ferroptosis and Autophagy on Alzheimer's Disease in Multiple Brain Regions

Ferroptosis and autophagy are closely associated with Alzheimer's disease (AD). Elevated ferric ion levels can induce oxidative stress and chronic inflammatory responses, resulting in brain tissue damage and further neurological cell damage. Autophagy in Alzheimer's has a dual role. On one hand, it protects neurons by removing β-amyloid and cellular damage products caused by oxidative stress and inflammation. On the other hand, abnormal autophagy is linked to neuronal apoptosis and neurodegeneration. However, the intricate interplay between ferroptosis and autophagy in AD remains insufficiently explored. This study focuses on the roles of ferroptosis and autophagy in AD and their interconnection through bioinformatics analysis, shedding light on the disease. Ferroptosis and autophagy significantly correlate with the development and course of AD. Using PPI network analysis and unsupervised consistency clustering analysis, we uncovered a complex network of interactions between ferroptosis and autophagy during disease progression, demonstrating a significant congruence in their modification patterns. Functional analyses further demonstrated that ferroptosis and autophagy together affect the immunological status and synaptic regulation in hippocampal regions in patients with AD, which significantly impacts the start and progression of the disease.

c-Triadem: A constrained, explainable deep learning model to identify novel biomarkers in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that requires early diagnosis for effective management. However, issues with currently available diagnostic biomarkers preclude early diagnosis, necessitating the development of alternative biomarkers and methods, such as blood-based diagnostics. We propose c-Triadem (constrained triple-input Alzheimer's disease model), a novel deep neural network to identify potential blood-based biomarkers for AD and predict mild cognitive impairment (MCI) and AD with high accuracy. The model utilizes genotyping data, gene expression data, and clinical information to predict the disease status of participants, i.e., cognitively normal (CN), MCI, or AD. The nodes of the neural network represent genes and their related pathways, and the edges represent known relationships among the genes and pathways. Simulated data validation further highlights the robustness of key features identified by SHapley Additive exPlanations (SHAP). We trained the model with blood genotyping data, microarray, and clinical features from the Alzheimer's Neuroimaging Disease Initiative (ADNI). We demonstrate that our model's performance is superior to previous models with an AUC of 97% and accuracy of 89%. We then identified the most influential genes and clinical features for prediction using SHapley Additive exPlanations (SHAP). Our SHAP analysis shows that CASP9, LCK, and SDC3 SNPs and PINK1, ATG5, and ubiquitin (UBB, UBC) expression have a higher impact on model performance. Our model has facilitated the identification of potential blood-based genetic markers of DNA damage response and mitophagy in affected regions of the brain. The model can be used for detection and biomarker identification in other related dementias.

Small molecule DDQ involvement of ERK-mediated signaling pathway with enhanced mitophagy in HT22 cells transfected with mTau

Tau hyperphosphorylation was the initial recognized pathogenic tau protein post-translational modification in Alzheimer's disease. In our present research, treatment of diethyl (3,4-dihydroxy phenethylamine) (quinolin-4-yl) methylphosphonate (DDQ) HT22 cells with mTau transfected HT22 cells decreased the phosphorylation of tau at Ser202, Thr205, p-ERK, and increased LC3B, and TOM20 as detected by Western blots. Moreover, DDQ p-tau and p-ERK inhibition of phosphorylation also contributed to significant mitochondrial protection in the presence of mTau. Taken together, for the first time, we found that DDQ is involved in phosphorylation inhibition to restore the mitophagy, which may relate to the Sirt3 activation of the ERK-CREB mediated pathway.

Mitochondrial quality control disorder in neurodegenerative disorders: Potential and advantages of traditional Chinese medicines

Neurodegenerative disorders (NDDs) are prevalent chronic conditions characterized by progressive synaptic loss and pathological protein alterations. Increasing evidence suggested that mitochondrial quality control (MQC) serves as the key cellular process responsible for clearing misfolded proteins and impaired mitochondria. Herein, we provided a comprehensive analysis of the mechanisms through which MQC mediates the onset and progression of NDDs, emphasizing mitochondrial dynamic stability, the clearance of damaged mitochondria, and the generation of new mitochondria. In addition, traditional Chinese medicines (TCMs) and their active monomers targeting MQC in NDD treatment have been demonstrated. Consequently, we compiled the TCMs that show great potential in the treatment of NDDs by targeting MQC, aiming to offer novel insights and a scientific foundation for the use of MQC stabilizers in NDD prevention and treatment.

BOK-engaged mitophagy alleviates neuropathology in Alzheimer's disease

Mitochondrial malfunction associated with impaired mitochondrial quality control and self-renewal machinery, known as mitophagy, is an under-appreciated mechanism precipitating synaptic loss and cognitive impairments in Alzheimer's disease. Promoting mitophagy has been shown to improve cognitive function in Alzheimer's disease animals. However, the regulatory mechanism was unclear, which formed the aim of this study. Here, we found that a neuron-specific loss of Bcl-2 family member BOK in patients with Alzheimer's disease and APPswe/PS1dE9 (APP/PS1) mice is closely associated with mitochondrial damage and mitophagy defects. We further revealed that BOK is the key to the Parkin-mediated mitophagy through competitive binding to the MCL1/Parkin complex, resulting in Parkin release and translocation to damaged mitochondria to initiate mitophagy. Furthermore, overexpressing bok in hippocampal neurons of APP/PS1 mice alleviated mitophagy and mitochondrial malfunction, resulting in improved cognitive function. Conversely, the knockdown of bok worsened the aforementioned Alzheimer's disease-related changes. Our findings uncover a novel mechanism of BOK signalling through regulating Parkin-mediated mitophagy to mitigate amyloid pathology, mitochondrial and synaptic malfunctions, and cognitive decline in Alzheimer's disease, thus representing a promising therapeutic target.

Recent advancements in the understanding of the alterations in mitochondrial biogenesis in Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease characterized by progressive memory loss and cognitive decline. The processes underlying the pathophysiology of AD are still not fully understood despite a great deal of research. Since mitochondrial dysfunction affects cellular energy metabolism, oxidative stress, and neuronal survival, it is becoming increasingly clear that it plays a major role in the development of AD. This review summarizes the recent developments of mitochondrial dysfunction in AD, emphasizing mitochondrial biogenesis, dynamics, axonal transport, interactions between endoplasmic reticulum and mitochondria, mitophagy, and mitochondrial proteostasis. It emphasizes how tau and amyloid-beta (Aβ) proteins worsen mitochondrial and synaptic dysfunction by impairing adenosine triphosphate (ATP) synthesis, causing oxidative stress, and upsetting equilibrium. Additionally, important processes controlling mitochondrial activity and their correlation to the brain health are also discussed. One of the promising therapeutic approaches to lessen neurodegeneration and cognitive decline in AD is to improve mitochondrial activity. This study highlights possible directions for creating focused therapies to impede the advancement of AD through incorporating knowledge of mitochondrial biogenesis and its related mechanisms.

Mitochondrial dysfunction in Alzheimer's disease: a key frontier for future targeted therapies

Alzheimer's disease (AD) is the most common neurodegenerative disorder, accounting for approximately 70% of dementia cases worldwide. Patients gradually exhibit cognitive decline, such as memory loss, aphasia, and changes in personality and behavior. Research has shown that mitochondrial dysfunction plays a critical role in the onset and progression of AD. Mitochondrial dysfunction primarily leads to increased oxidative stress, imbalances in mitochondrial dynamics, impaired mitophagy, and mitochondrial genome abnormalities. These mitochondrial abnormalities are closely associated with amyloid-beta and tau protein pathology, collectively accelerating the neurodegenerative process. This review summarizes the role of mitochondria in the development of AD, the latest research progress, and explores the potential of mitochondria-targeted therapeutic strategies for AD. Targeting mitochondria-related pathways may significantly improve the quality of life for AD patients in the future.

Tau phosphorylation suppresses oxidative stress-induced mitophagy via FKBP8 receptor modulation

Neurodegenerative diseases are often characterized by mitochondrial dysfunction. In Alzheimer's disease, abnormal tau phosphorylation disrupts mitophagy, a quality control process through which damaged organelles are selectively removed from the mitochondrial network. The precise mechanism through which this occurs remains unclear. Previously, we showed that tau which has been mutated at Thr-231 to glutamic acid to mimic an Alzheimer's-relevant phospho-epitope expressed early in disease selectively inhibits oxidative stress-induced mitophagy in Caenorhabditis elegans. Here, we use immortalized mouse hippocampal neuronal cell lines to extend that result into mammalian cells. Specifically, we show that phosphomimetic tau at Ser-396/404 (EC) or Thr-231/Ser-235 (EM) partly inhibits mitophagy induction by paraquat, a potent inducer of mitochondrial oxidative stress. Moreover, a combination of immunologic and biochemical approaches demonstrates that the levels of the mitophagy receptor FKBP8, significantly decrease in response to paraquat in cells expressing EC or EM tau mutants, but not in cells expressing wildtype tau. In contrast, paraquat treatment results in a decrease in the levels of the mitophagy receptors FUNDC1 and BNIP3 in the presence of both wildtype tau and the tau mutants. Interestingly, FKBP8 is normally trafficked to the endoplasmic reticulum during oxidative stress induced mitophagy, and our results support a model where this trafficking is impacted by disease-relevant tau, perhaps through a direct interaction. We provide new insights into the molecular mechanisms underlying tau pathology in Alzheimer's disease and highlight FKBP8 receptor as a potential target for mitigating mitochondrial dysfunction in neurodegenerative diseases.

Rlip76 in ageing and Alzheimer's disease: Focus on oxidative stress and mitochondrial mechanisms

RLIP76 (Rlip), a stress-responsive protein, plays a multifaceted role in cellular function. This protein acts primarily as a glutathione-electrophile conjugate (GS-E) transporter, crucial for detoxifying hazardous compounds and converting them into mercapturic acids. RLIP76 also modulates cytoskeletal motility and membrane plasticity through its role in the Ral-signaling pathway, interacting with RalA and RalB, key small GTPases involved in growth and metastasis. Beyond its ATP-dependent transport functions in various tissues, RLIP76 also demonstrates GTPase Activating Protein (GAP) activity towards Rac1 and Cdc42, with a preference for Ral-GTP over Ral-GDP. Its functions span critical physiological processes including membrane dynamics, oxidative stress response, and mitochondrial dynamics. The protein's widespread expression and evolutionary conservation underscore its significance. Our lab discovered that Rlip interacts with Alzheimer's disease (AD) proteins, amyloid beta and phosphorylated and induce oxidative stress, mitochondrial dysfnction and synaptic damage in AD. Our in vitro studies revealed that overexpression of Rlip reduces mitochondrial abnormalities. Further, our in vivo studies (Rlip+/- mice) revealed that a partial reduction of Rlip in mice (Rlip+/-), leads to mitochondrial abnormalities, elevated oxidative stress, and cognitive deficits resembling late-onset AD, emphasizing the protein's crucial role in neuronal health and disease. Finally, we discuss the experimental cross-breedings of overexpression of mice Rlip TG/TG or Rlip + /- mice with Alzheimer's disease models - earlyonset 5XFAD, late-onset APPKI and Tau transgenic mice, providing new insights into RLIP76's role in AD progression and development. This review summarizes RLIP76's structure, function, and cellular pathways, highlighting its implications in AD and its potential as a therapeutic target.

Tau proteins and senescent Cells: Targeting aging pathways in Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by abnormal accumulation of tau proteins and amyloid-β, leading to neuronal death and cognitive impairment. Recent studies have implicated aging pathways, including dysregulation of tau and cellular senescence in AD pathogenesis. In AD brains, tau protein, which normally stabilizes microtubules, becomes hyperphosphorylated and forms insoluble neurofibrillary tangles. These tau aggregates impair neuronal function and are propagated across the brain's neurocircuitry. Meanwhile, the number of senescent cells accumulating in the aging brain is rising, releasing a pro-inflammatory SASP responsible for neuroinflammation and neurodegeneration. This review explores potential therapeutic interventions for AD targeting tau protein and senescent cells, and tau -directed compounds, senolytics, eliminating senescent cells, and agents that modulate the SASP-senomodulators. Ultimately, a combined approach that incorporates tau-directed medications and targeted senescent cell-based therapies holds promise for reducing the harmful impact of AD's shared aging pathways.

c-Triadem: A constrained, explainable deep learning model to identify novel biomarkers in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that requires early diagnosis for effective management. However, issues with currently available diagnostic biomarkers preclude early diagnosis, necessitating the development of alternative biomarkers and methods, such as blood-based diagnostics. We propose c-Triadem (constrained triple-input Alzheimer's disease model), a novel deep neural network to identify potential blood-based biomarkers for AD and predict mild cognitive impairment (MCI) and AD with high accuracy. The model utilizes genotyping data, gene expression data, and clinical information to predict the disease status of participants, i.e., cognitively normal (CN), MCI, or AD. The nodes of the neural network represent genes and their related pathways, and the edges represent known relationships among the genes and pathways. We trained the model with blood genotyping data, microarray, and clinical features from the Alzheimer's Neuroimaging Disease Initiative (ADNI). We demonstrate that our model's performance is superior to previous models with an AUC of 97% and accuracy of 89%. We then identified the most influential genes and clinical features for prediction using SHapley Additive exPlanations (SHAP). Our SHAP analysis shows that CASP9, LCK, and SDC3 SNPs and PINK1, ATG5, and ubiquitin (UBB, UBC) expression have a higher impact on model performance. Our model has facilitated the identification of potential blood-based genetic markers of DNA damage response and mitophagy in affected regions of the brain. The model can be used for detection and biomarker identification in other related dementias.

Mitochondrial Quality Control in Alzheimer's Disease: Insights from Caenorhabditis elegans Models

Alzheimer's disease (AD) is a complex neurodegenerative disorder that is classically defined by the extracellular deposition of senile plaques rich in amyloid-beta (Aβ) protein and the intracellular accumulation of neurofibrillary tangles (NFTs) that are rich in aberrantly modified tau protein. In addition to aggregative and proteostatic abnormalities, neurons affected by AD also frequently possess dysfunctional mitochondria and disrupted mitochondrial maintenance, such as the inability to eliminate damaged mitochondria via mitophagy. Decades have been spent interrogating the etiopathogenesis of AD, and contributions from model organism research have aided in developing a more fundamental understanding of molecular dysfunction caused by Aβ and toxic tau aggregates. The soil nematode C. elegans is a genetic model organism that has been widely used for interrogating neurodegenerative mechanisms including AD. In this review, we discuss the advantages and limitations of the many C. elegans AD models, with a special focus and discussion on how mitochondrial quality control pathways (namely mitophagy) may contribute to AD development. We also summarize evidence on how targeting mitophagy has been therapeutically beneficial in AD. Lastly, we delineate possible mechanisms that can work alone or in concert to ultimately lead to mitophagy impairment in neurons and may contribute to AD etiopathology.

NRF2 Deficiency Promotes Ferroptosis of Astrocytes Mediated by Oxidative Stress in Alzheimer's Disease

Oxidative stress is involved in the pathogenesis of Alzheimer's disease (AD), which is linked to reactive oxygen species (ROS), lipid peroxidation, and neurotoxicity. Emerging evidence suggests a role of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a major source of antioxidant response elements in AD. The molecular mechanism of oxidative stress and ferroptosis in astrocytes in AD is not yet fully understood. Here, we aimed to investigate the mechanism by which Nrf2 regulates the ferroptosis of astrocytes in AD. We found decreased expression of Nrf2 and upregulated expression of the ROS marker NADPH oxidase 4 (NOX4) in the frontal cortex from patients with AD and in the cortex of 3×Tg mice compared to wildtype mice. We demonstrated that Nrf2 deficiency led to ferroptosis-dependent oxidative stress-induced ROS with downregulated heme oxygenase-1 and glutathione peroxidase 4 and upregulated cystine glutamate expression. Moreover, Nrf2 deficiency increased lipid peroxidation, DNA oxidation, and mitochondrial fragmentation in mouse astrocytes (mAS, M1800-57). In conclusion, these results suggest that Nrf2 deficiency promotes ferroptosis of astrocytes involving oxidative stress in AD.

Recent advances in Alzheimer's disease: Mechanisms, clinical trials and new drug development strategies

Alzheimer's disease (AD) stands as the predominant form of dementia, presenting significant and escalating global challenges. Its etiology is intricate and diverse, stemming from a combination of factors such as aging, genetics, and environment. Our current understanding of AD pathologies involves various hypotheses, such as the cholinergic, amyloid, tau protein, inflammatory, oxidative stress, metal ion, glutamate excitotoxicity, microbiota-gut-brain axis, and abnormal autophagy. Nonetheless, unraveling the interplay among these pathological aspects and pinpointing the primary initiators of AD require further elucidation and validation. In the past decades, most clinical drugs have been discontinued due to limited effectiveness or adverse effects. Presently, available drugs primarily offer symptomatic relief and often accompanied by undesirable side effects. However, recent approvals of aducanumab (1) and lecanemab (2) by the Food and Drug Administration (FDA) present the potential in disrease-modifying effects. Nevertheless, the long-term efficacy and safety of these drugs need further validation. Consequently, the quest for safer and more effective AD drugs persists as a formidable and pressing task. This review discusses the current understanding of AD pathogenesis, advances in diagnostic biomarkers, the latest updates of clinical trials, and emerging technologies for AD drug development. We highlight recent progress in the discovery of selective inhibitors, dual-target inhibitors, allosteric modulators, covalent inhibitors, proteolysis-targeting chimeras (PROTACs), and protein-protein interaction (PPI) modulators. Our goal is to provide insights into the prospective development and clinical application of novel AD drugs.

Tau phosphorylation suppresses oxidative stress-induced mitophagy via FKBP8 receptor modulation

Neurodegenerative diseases are often characterized by mitochondrial dysfunction. In Alzheimer's disease, abnormal tau phosphorylation disrupts mitophagy, a quality control process through which damaged organelles are selectively removed from the mitochondrial network. The precise mechanism through which this occurs remains unclear. Previously, we showed that tau which has been mutated at Thr-231 to glutamic acid to mimic an Alzheimer's-relevant phospho-epitope expressed early in disease selectively inhibits oxidative stress-induced mitophagy in C. elegans. Here, we use immortalized mouse hippocampal neuronal cell lines to extend that result into mammalian cells. Specifically, we show that phosphomimetic tau at Ser-396/404 (EC) or Thr-231/Ser-235 (EM) partly inhibits mitophagy induction by paraquat, a potent inducer of mitochondrial oxidative stress. Moreover, a combination of immunologic and biochemical approaches demonstrates that the levels of the mitophagy receptor FKBP8, significantly decrease in response to paraquat in cells expressing EC or EM tau mutants, but not in cells expressing wildtype tau. In contrast, paraquat treatment results in a decrease in the levels of the mitophagy receptors FUNDC1 and BNIP3 in the presence of both wildtype tau and the tau mutants. Interestingly, FKBP8 is normally trafficked to the endoplasmic reticulum during oxidative stress induced mitophagy, and our results support a model where this trafficking is impacted by disease-relevant tau, perhaps through a direct interaction. We provide new insights into the molecular mechanisms underlying tau pathology in Alzheimer's disease and highlight FKBP8 receptor as a potential target for mitigating mitochondrial dysfunction in neurodegenerative diseases.

Mitochondrial DNA Leakage and cGas/STING Pathway in Microglia: Crosstalk Between Neuroinflammation and Neurodegeneration

Neurodegenerative diseases, characterized by abnormal deposition of misfolded proteins, often present with progressive loss of neurons. Chronic neuroinflammation is a striking hallmark of neurodegeneration. Microglia, as the primary immune cells in the brain, is the main type of cells that participate in the formation of inflammatory microenvironment. Cytoplasmic free mitochondrial DNA (mtDNA), a common component of damage-associated molecular patterns (DAMPs), can activate the cGas/stimulator of interferon genes (STING) signalling, which subsequently produces type I interferon and proinflammatory cytokines. There are various sources of free mtDNA in microglial cytoplasm, but mitochondrial oxidative stress accumulation plays the vital role. The upregulation of cGas/STING pathway in microglia contributes to the abnormal and persistent microglial activation, accompanied by excessive secretion of neurotoxic inflammatory mediators such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), which exacerbates the damage of neurons and promotes the development of neurodegeneration. Currently, novel therapeutic approaches need to be found to delay the progression of neurodegenerative disorders, and regulation of the cGas/STING signaling in microglia may be a potential target.

Development of a P-tau217 Electrochemiluminescent Immunosensor Reinforced with Au-Cu Nanoparticles for Alzheimer's Disease Precaution

To simply and rapidly detect the highly phosphorylated tau protein at threonine 217 (p-tau217) as a precautionary measure against Alzheimer's disease and distinguish it from other neurodegenerative diseases, a novel immunosensor was prepared using luminol as the electrochemiluminescent (ECL) sensing probe reinforced by Au-Cu nanoparticles (Au-Cu NPs). The Au-Cu alloy NPs were prepared via a co-reduction reaction, exhibiting excellent conductivity and catalytic activity. These properties remarkably enhanced the ECL of luminol, providing a suitable background for the sensing response. After the Au-Cu NPs were decorated on the surface of indium tin oxide glass using 3-amino-propyl trimethoxysilane, the antibody of p-tau217 was immobilized via dominant Au-N bonding to enable the biological specificity of the immunosensor. When p-tau217 specifically interacted with an antibody to form an immune complex on the sensing interface, the ECL signal of the sensor was considerably inhibited by the resulting giant biomolecular complex. This complex prevented luminol diffusion to the electrode surface and electron transfer. The resulting immunosensor showed remarkable sensitivity to p-tau217, with a wide linear detection range from 5 to 600 pg/mL. A detection limit of 0.56 pg/mL was achieved, with recoveries in human serum ranging from 92.3 to 109%. This ECL immunosensor demonstrated high sensitivity and specificity toward p-tau217, along with good reproducibility and stability, providing a new approach for clinical research on Alzheimer's disease.

Ketogenic diet alleviates cognitive dysfunction and neuroinflammation in APP/PS1 mice via the Nrf2/HO-1 and NF-κB signaling pathways

Alzheimer's disease is a progressive neurological disorder characterized by cognitive decline and chronic inflammation within the brain. The ketogenic diet, a widely recognized therapeutic intervention for refractory epilepsy, has recently been proposed as a potential treatment for a variety of neurological diseases, including Alzheimer's disease. However, the efficacy of ketogenic diet in treating Alzheimer's disease and the underlying mechanism remains unclear. The current investigation aimed to explore the effect of ketogenic diet on cognitive function and the underlying biological mechanisms in a mouse model of Alzheimer's disease. Male amyloid precursor protein/presenilin 1 (APP/PS1) mice were randomly assigned to either a ketogenic diet or control diet group, and received their respective diets for a duration of 3 months. The findings show that ketogenic diet administration enhanced cognitive function, attenuated amyloid plaque formation and proinflammatory cytokine levels in APP/PS1 mice, and augmented the nuclear factor-erythroid 2-p45 derived factor 2/heme oxygenase-1 signaling pathway while suppressing the nuclear factor-kappa B pathway. Collectively, these data suggest that ketogenic diet may have a therapeutic potential in treating Alzheimer's disease by ameliorating the neurotoxicity associated with Aβ-induced inflammation. This study highlights the urgent need for further research into the use of ketogenic diet as a potential therapy for Alzheimer's disease.

Targeting autophagy in Alzheimer's disease: Animal models and mechanisms

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder that leads to cognitive impairment and memory loss. Emerging evidence suggests that autophagy plays an important role in the pathogenesis of AD through the regulation of amyloid-beta (Aβ) and tau metabolism, and that autophagy dysfunction exacerbates amyloidosis and tau pathology. Therefore, targeting autophagy may be an effective approach for the treatment of AD. Animal models are considered useful tools for investigating the pathogenic mechanisms and therapeutic strategies of diseases. This review aims to summarize the pathological alterations in autophagy in representative AD animal models and to present recent studies on newly discovered autophagy-stimulating interventions in animal AD models. Finally, the opportunities, difficulties, and future directions of autophagy targeting in AD therapy are discussed.

A circadian rhythm-restricted diet regulates autophagy to improve cognitive function and prolong lifespan

Diet and circadian rhythms have been found to have a profound impact on health, disease, and aging. Skipping breakfast, eating late, and overeating have adverse effects on the body's metabolism and increase the risk of cardiovascular and metabolic diseases. Disturbance of circadian rhythms has been associated with increased risk of atherosclerosis, Alzheimer's disease, Parkinson's disease, and other diseases. Abnormal deposition of amyloid β (Aβ) and tau proteins in the brain and impaired synaptic function are linked to cognitive dysfunction. A restrictive diet following the circadian rhythm can affect the metabolism of lipids, glucose, and amino acids such as branched chain amino acids and cysteine. These metabolic changes contribute to autophagy through molecular mechanisms such as adenosine monophosphate-activated protein kinase (AMPK), rapamycin (mTOR), D-β-hydroxybutyrate (D-BHB), and neuropeptide Y (NPY). Autophagy, in turn, promotes the removal of abnormally deposited proteins and damaged organelles and improves cognitive function, ultimately prolonging lifespan. In addition, a diet restricted to the circadian rhythm induces increased expression of brain-derived neurotrophic factor (BDNF) in the forebrain region, regulating autophagy and increasing synaptic plasticity, thus enhancing cognitive function. Consequently, circadian rhythm-restricted diets could serve as a promising non-pharmacological treatment for preventing and improving cognitive dysfunction and prolonging lifespan.

Human umbilical cord mesenchymal stem cell-derived exosome suppresses programmed cell death in traumatic brain injury via PINK1/Parkin-mediated mitophagy

AIMS

Recently, human umbilical cord mesenchymal stem cell (HucMSC)-derived exosome is a new focus of research in neurological diseases. The present study was aimed to investigate the protective effects of HucMSC-derived exosome in both in vivo and in vitro TBI models.

METHODS

We established both mouse and neuron TBI models in our study. After treatment with HucMSC-derived exosome, the neuroprotection of exosome was investigated by the neurologic severity score (NSS), grip test score, neurological score, brain water content, and cortical lesion volume. Moreover, we determined the biochemical and morphological changes associated with apoptosis, pyroptosis, and ferroptosis after TBI.

RESULTS

We revealed that treatment of exosome could improve neurological function, decrease cerebral edema, and attenuate brain lesion after TBI. Furthermore, administration of exosome suppressed TBI-induced cell death, apoptosis, pyroptosis, and ferroptosis. In addition, exosome-activated phosphatase and tensin homolog-induced putative kinase protein 1/Parkinson protein 2 E3 ubiquitin-protein ligase (PINK1/Parkin) pathway-mediated mitophagy after TBI. However, the neuroprotection of exosome was attenuated when mitophagy was inhibited, and PINK1 was knockdown. Importantly, exosome treatment also decreased neuron cell death, suppressed apoptosis, pyroptosis, and ferroptosis and activated the PINK1/Parkin pathway-mediated mitophagy after TBI in vitro.

CONCLUSION

Our results provided the first evidence that exosome treatment played a key role in neuroprotection after TBI through the PINK1/Parkin pathway-mediated mitophagy.

APOE ε4 allele, along with G206D-PSEN1 mutation, alters mitochondrial networks and their degradation in Alzheimer's disease

Introduction

Alzheimer's disease remains the most common neurodegenerative disorder, depicted mainly by memory loss and the presence in the brain of senile plaques and neurofibrillary tangles. This disease is related to several cellular alterations like the loss of synapses, neuronal death, disruption of lipid homeostasis, mitochondrial fragmentation, or raised oxidative stress. Notably, changes in the autophagic pathway have turned out to be a key factor in the early development of the disease. The aim of this research is to determine the impact of the APOE allele ε4 and G206D-PSEN1 on the underlying mechanisms of Alzheimer's disease.

Methods

Fibroblasts from Alzheimer's patients with APOE 3/4 + G206D-PSEN1 mutation and homozygous APOE ε4 were used to study the effects of APOE polymorphism and PSEN1 mutation on the autophagy pathway, mitochondrial network fragmentation, superoxide anion levels, lysosome clustering, and p62/SQSTM1 levels.

Results

We observed that the APOE allele ε4 in homozygosis induces mitochondrial network fragmentation that correlates with an increased colocalization with p62/SQSTM1, probably due to an inefficient autophagy. Moreover, G206D-PSEN1 mutation causes an impairment of the integrity of mitochondrial networks, triggering high superoxide anion levels and thus making APOE 3/4 + PSEN1 fibroblasts more vulnerable to cell death induced by oxidative stress. Of note, PSEN1 mutation induces accumulation and clustering of lysosomes that, along with an increase of global p62/SQSTM1, could compromise lysosomal function and, ultimately, its degradation.

Conclusion

The findings suggest that all these modifications could eventually contribute to the neuronal degeneration that underlies the pathogenesis of Alzheimer's disease. Further research in this area may help to develop targeted therapies for the treatment of Alzheimer's disease.

The Depletion of NAMPT Disturbs Mitochondrial Homeostasis and Causes Neuronal Degeneration in Mouse Hippocampus

Nicotinamide phosphoribosyltransferase (NAMPT) is the key enzyme in the salvaging synthesis pathway of the nicotinamide adenine dinucleotide (NAD). Both NAMPT and NAD progressively decline upon aging and neurodegenerative diseases. The depletion of NAMPT induces mitochondrial dysfunction in motor neurons and causes bioenergetic stress in neurons. However, the roles of NAMPT in hippocampus neurons need to be further studied. Using floxed Nampt (Nampt^flox/flox) mice, we knocked out Nampt specifically in the hippocampus CA1 neurons by injecting rAAV-hSyn-Cre-APRE-pA. The depletion of NAMPT in hippocampus neurons induced cognitive deficiency in mice. Nevertheless, no morphological change of hippocampus neurons was observed with immunofluorescent imaging. Under the transmission electron microscope, we observed mitochondrial swollen and mitochondrial number decreasing in the cell body and the neurites of hippocampus neurons. In addition, we found the intracellular Aβ (6E10) increased in the hippocampus CA1 region. The intensity of Aβ42 remained unchanged, but it tended to aggregate. The GFAP level, an astrocyte marker, and the Iba1 level, a microglia marker, significantly increased in the mouse hippocampus. In the primary cultured rat neurons, NAMPT inhibition by FK866 decreased the NAD level of neurons at > 10^-9 M. FK866 dropped the mitochondrial membrane potential in the cell body of neurons at > 10^-9 M and in the dendrite of neurons at > 10^-8 M. FK866 decreased the number and shortened the length of branches of neurons at > 10^-7 M. Together, likely due to the injury of mitochondria, the decline of NAMPT level can be a critical risk factor for neurodegeneration.

Co-occurring pathogenic variants in 6q27 associated with dementia spectrum disorders in a Peruvian family

Evidence suggests that there may be racial differences in risk factors associated with the development of Alzheimer's disease and related dementia (ADRD). We used whole-genome sequencing analysis and identified a novel combination of three pathogenic variants in the heterozygous state (UNC93A: rs7739897 and WDR27: rs61740334; rs3800544) in a Peruvian family with a strong clinical history of ADRD. Notably, the combination of these variants was present in two generations of affected individuals but absent in healthy members of the family. In silico and in vitro studies have provided insights into the pathogenicity of these variants. These studies predict that the loss of function of the mutant UNC93A and WDR27 proteins induced dramatic changes in the global transcriptomic signature of brain cells, including neurons, astrocytes, and especially pericytes and vascular smooth muscle cells, indicating that the combination of these three variants may affect the neurovascular unit. In addition, known key molecular pathways associated with dementia spectrum disorders were enriched in brain cells with low levels of UNC93A and WDR27. Our findings have thus identified a genetic risk factor for familial dementia in a Peruvian family with an Amerindian ancestral background.

Modifiable risk factors of dementia linked to excitation-inhibition imbalance

Recent evidence identifies 12 potentially modifiable risk factors for dementia to which 40% of dementia cases are attributed. While the recognition of these risk factors has paved the way for the development of new prevention measures, the link between these risk factors and the underlying pathophysiology of dementia is yet not well understood. A growing number of recent clinical and preclinical studies support a role of Excitation-Inhibition (E-I) imbalance in the pathophysiology of dementia. In this review, we aim to propose a conceptual model on the links between the modifiable risk factors and the E-I imbalance in dementia. This model, which aims to address the current gap in the literature, is based on 12 mediating common mechanisms: the hypothalamic-pituitary-adrenal (HPA) axis dysfunction, neuroinflammation, oxidative stress, mitochondrial dysfunction, cerebral hypo-perfusion, blood-brain barrier (BBB) dysfunction, beta-amyloid deposition, elevated homocysteine level, impaired neurogenesis, tau tangles, GABAergic dysfunction, and glutamatergic dysfunction. We believe this model serves as a framework for future studies in this field and facilitates future research on dementia prevention, discovery of new biomarkers, and developing new interventions.

Mitochondrial DNA Repair in Neurodegenerative Diseases and Ageing

Mitochondria are the only organelles, along with the nucleus, that have their own DNA. Mitochondrial DNA (mtDNA) is a double-stranded circular molecule of ~16.5 kbp that can exist in multiple copies within the organelle. Both strands are translated and encode for 22 tRNAs, 2 rRNAs, and 13 proteins. mtDNA molecules are anchored to the inner mitochondrial membrane and, in association with proteins, form a structure called nucleoid, which exerts a structural and protective function. Indeed, mitochondria have evolved mechanisms necessary to protect their DNA from chemical and physical lesions such as DNA repair pathways similar to those present in the nucleus. However, there are mitochondria-specific mechanisms such as rapid mtDNA turnover, fission, fusion, and mitophagy. Nevertheless, mtDNA mutations may be abundant in somatic tissue due mainly to the proximity of the mtDNA to the oxidative phosphorylation (OXPHOS) system and, consequently, to the reactive oxygen species (ROS) formed during ATP production. In this review, we summarise the most common types of mtDNA lesions and mitochondria repair mechanisms. The second part of the review focuses on the physiological role of mtDNA damage in ageing and the effect of mtDNA mutations in neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. Considering the central role of mitochondria in maintaining cellular homeostasis, the analysis of mitochondrial function is a central point for developing personalised medicine.