Mitochondrial Ca2+ overload underlies Abeta oligomers neurotoxicity providing an unexpected mechanism of neuroprotection by NSAIDs

Protective effects of 2,4-dinitrophenol in okadaic acid-induced cellular model of Alzheimer's disease

Alzheimer's disease (AD) research started several decades ago and despite the many efforts employed to develop new treatments or approaches to slow and/or revert disease progression, AD treatment remains an unsolved issue. Knowing that mitochondria loss of function is a central hub for many AD-associated pathophysiological processes, there has been renewed interest in exploring mitochondria as targets for intervention. In this perspective, the present study was aimed to investigate the possible beneficial effects of 2,4 dinitrophenol (DNP), a mitochondrial uncoupler agent, in an in vitro model of AD. Retinoic acid-induced differentiated SH-SY5Y cells were incubated with okadaic acid (OA), a neurotoxin often used as an AD experimental model, and/or with DNP. OA caused a decrease in neuronal cells viability, induced multiple mitochondrial anomalies including increased levels of reactive oxygen species, decreased bioenergetics and mitochondria content markers, and an altered mitochondria morphology. OA-treated cells also presented increased lipid peroxidation levels, and overactivation of tau related kinases (GSK3β, ERK1/2 and AMPK) alongside with a significant augment in tau protein phosphorylation levels. Interestingly, DNP co-treatment ameliorated and rescued OA-induced detrimental effects not only on mitochondria but also but also reinstated signaling pathways homeostasis and ameliorated tau pathology. Overall, our results show for the first time that DNP has the potential to preserve mitochondria homeostasis under a toxic insult, like OA exposure, as well as to reestablish cellular signaling homeostasis. These observations foster the idea that DNP, as a mitochondrial modulator, might represent a new avenue for treatment of AD.

Induction of mitochondrial toxicity by non-steroidal anti-inflammatory drugs (NSAIDs): The ultimate trade-off governing the therapeutic merits and demerits of these wonder drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) are most extensively used over-the-counter FDA-approved analgesic medicines for treating inflammation, musculoskeletal pain, arthritis, pyrexia and menstrual cramps. Moreover, aspirin is widely used against cardiovascular complications. Owing to their non-addictive nature, NSAIDs are also commissioned as safer opioid-sparing alternatives in acute trauma and post-surgical treatments. In fact, therapeutic spectrum of NSAIDs is expanding. These "wonder-drugs" are now repurposed against lung diseases, diabetes, neurodegenerative disorders, fungal infections and most notably cancer, due to their efficacy against chemoresistance, radio-resistance and cancer stem cells. However, prolonged NSAID treatment accompany several adverse effects. Mechanistically, apart from cyclooxygenase inhibition, NSAIDs directly target mitochondria to induce cell death. Interestingly, there are also incidences of dose-dependent effects where NSAIDs are found to improve mitochondrial health thereby suggesting plausible mitohormesis. While mitochondria-targeted effects of NSAIDs are discretely studied, a comprehensive account emphasizing the multiple dimensions in which NSAIDs affect mitochondrial structure-function integrity, leading to cell death, is lacking. This review discusses the current understanding of NSAID-mitochondria interactions in the pathophysiological background. This is essential for assessing the risk-benefit trade-offs of NSAIDs for judiciously strategizing NSAID-based approaches to manage pain and inflammation as well as formulating effective anti-cancer strategies. We also discuss recent developments constituting selective mitochondria-targeted NSAIDs including theranostics, mitocans, chimeric small molecules, prodrugs and nanomedicines that rationally optimize safer application of NSAIDs. Thus, we present a comprehensive understanding of therapeutic merits and demerits of NSAIDs with mitochondria at its cross roads. This would help in NSAID-based disease management research and drug development.

Drug repurposing for neurodegenerative diseases using Zebrafish behavioral profiles

Drug repurposing can accelerate drug development while reducing the cost and risk of toxicity typically associated with de novo drug design. Several disorders lacking pharmacological solutions and exhibiting poor results in clinical trials - such as Alzheimer's disease (AD) - could benefit from a cost-effective approach to finding new therapeutics. We previously developed a neural network model, Z-LaP Tracker, capable of quantifying behaviors in zebrafish larvae relevant to cognitive function, including activity, reactivity, swimming patterns, and optomotor response in the presence of visual and acoustic stimuli. Using this model, we performed a high-throughput screening of FDA-approved drugs to identify compounds that affect zebrafish larval behavior in a manner consistent with the distinct behavior induced by calcineurin inhibitors. Cyclosporine (CsA) and other calcineurin inhibitors have garnered interest for their potential role in the prevention of AD. We generated behavioral profiles suitable for cluster analysis, through which we identified 64 candidate therapeutics for neurodegenerative disorders.

NB-02 Protects Neurons and Astrocytes from Oligomeric Amyloid-β-Mediated Damage

Alzheimer's disease (AD) is a progressive neurodegenerative disease with limited therapeutic strategies. NB-02 is a novel botanical drug that has shown promise as a protective and therapeutic treatment for AD in an APP/PS1 preclinical mouse model. In this paper, we investigate the underlying mechanisms by which NB-02 provides these therapeutic advantages using in vitro neuron-astrocyte co-cultures. Pretreatment with NB-02 prevented pathological calcium elevations in neurons and astrocytes after application of toxic soluble amyloid-β (Aβ) oligomers. NB-02 also prevented cell death associated with the addition of soluble Aβ oligomers suggesting NB-02 is effective at protecting both neurons and astrocytes from Aβ-mediated damage.

Genetic ablation of neuronal mitochondrial calcium uptake halts Alzheimer's disease progression

Alzheimer's disease (AD) is characterized by the extracellular deposition of amyloid beta, intracellular neurofibrillary tangles, synaptic dysfunction, and neuronal cell death. These phenotypes correlate with and are linked to elevated neuronal intracellular calcium ( i Ca 2+ ) levels. Recently, our group reported that mitochondrial calcium ( m Ca 2+ ) overload, due to loss of m Ca 2+ efflux capacity, contributes to AD development and progression. We also noted proteomic remodeling of the mitochondrial calcium uniporter channel (mtCU) in sporadic AD brain samples, suggestive of altered m Ca 2+ uptake in AD. Since the mtCU is the primary mechanism for Ca 2+ uptake into the mitochondrial matrix, inhibition of the mtCU has the potential to reduce or prevent m Ca 2+ overload in AD. Here, we report that neuronal-specific loss of mtCU-dependent m Ca 2+ uptake in the 3xTg-AD mouse model of AD reduced Aβ and tau-pathology, synaptic dysfunction, and cognitive decline. Knockdown of Mcu in a cellular model of AD significantly decreased matrix Ca 2+ content, oxidative stress, and cell death. These results suggest that inhibition of neuronal m Ca 2+ uptake is a novel therapeutic target to impede AD progression.

Finding Drug Repurposing Candidates for Neurodegenerative Diseases using Zebrafish Behavioral Profiles

Drug repurposing can accelerate drug development while reducing the cost and risk of toxicity typically associated with de novo drug design. Several disorders lacking pharmacological solutions and exhibiting poor results in clinical trials - such as Alzheimer's disease (AD) - could benefit from a cost-effective approach to finding new therapeutics. We previously developed a neural network model, Z-LaP Tracker, capable of quantifying behaviors in zebrafish larvae relevant to cognitive function, including activity, reactivity, swimming patterns, and optomotor response in the presence of visual and acoustic stimuli. Using this model, we performed a high-throughput screening of FDA-approved drugs to identify compounds that affect zebrafish larval behavior in a manner consistent with the distinct behavior induced by calcineurin inhibitors. Cyclosporine (CsA) and other calcineurin inhibitors have garnered interest for their potential role in the prevention of AD. We generated behavioral profiles suitable for cluster analysis, through which we identified 64 candidate therapeutics for neurodegenerative disorders.

Therapeutic Potential of Heterocyclic Compounds Targeting Mitochondrial Calcium Homeostasis and Signaling in Alzheimer's Disease and Parkinson's Disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative diseases in the elderly. The key histopathological features of these diseases are the presence of abnormal protein aggregates and the progressive and irreversible loss of neurons in specific brain regions. The exact mechanisms underlying the etiopathogenesis of AD or PD remain unknown, but there is extensive evidence indicating that excessive generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS), along with a depleted antioxidant system, mitochondrial dysfunction, and intracellular Ca²⁺ dyshomeostasis, plays a vital role in the pathophysiology of these neurological disorders. Due to an improvement in life expectancy, the incidence of age-related neurodegenerative diseases has significantly increased. However, there is no effective protective treatment or therapy available but rather only very limited palliative treatment. Therefore, there is an urgent need for the development of preventive strategies and disease-modifying therapies to treat AD/PD. Because dysregulated Ca²⁺ metabolism drives oxidative damage and neuropathology in these diseases, the identification or development of compounds capable of restoring Ca²⁺ homeostasis and signaling may provide a neuroprotective avenue for the treatment of neurodegenerative diseases. In addition, a set of strategies to control mitochondrial Ca²⁺ homeostasis and signaling has been reported, including decreased Ca²⁺ uptake through voltage-operated Ca²⁺ channels (VOCCs). In this article, we review the modulatory effects of several heterocyclic compounds on Ca²⁺ homeostasis and trafficking, as well as their ability to regulate compromised mitochondrial function and associated free-radical production during the onset and progression of AD or PD. This comprehensive review also describes the chemical synthesis of the heterocycles and summarizes the clinical trial outcomes.

Insights from Drosophila on Aβ- and tau-induced mitochondrial dysfunction: mechanisms and tools

Alzheimer's disease (AD) is the most prevalent neurodegenerative dementia in older adults worldwide. Sadly, there are no disease-modifying therapies available for treatment due to the multifactorial complexity of the disease. AD is pathologically characterized by extracellular deposition of amyloid beta (Aβ) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau. Increasing evidence suggest that Aβ also accumulates intracellularly, which may contribute to the pathological mitochondrial dysfunction observed in AD. According with the mitochondrial cascade hypothesis, mitochondrial dysfunction precedes clinical decline and thus targeting mitochondria may result in new therapeutic strategies. Unfortunately, the precise mechanisms connecting mitochondrial dysfunction with AD are largely unknown. In this review, we will discuss how the fruit fly Drosophila melanogaster is contributing to answer mechanistic questions in the field, from mitochondrial oxidative stress and calcium dysregulation to mitophagy and mitochondrial fusion and fission. In particular, we will highlight specific mitochondrial insults caused by Aβ and tau in transgenic flies and will also discuss a variety of genetic tools and sensors available to study mitochondrial biology in this flexible organism. Areas of opportunity and future directions will be also considered.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.

Effect of β-amyloid on blood-brain barrier properties and function

The deposition of beta-amyloid (Aβ) aggregates in the brain, accompanied by impaired cognitive function, is a characteristic feature of Alzheimer's disease (AD). An important role in this process is played by vascular disorders, in particular, a disturbance of the blood-brain barrier (BBB). The BBB controls the entry of Aβ from plasma to the brain via the receptor for advanced glycation end products (RAGE) and the removal of brain-derived Aβ via the low-density lipoprotein receptor-related protein (LRP1). The balance between the input of Aβ to the brain from the periphery and its output is disturbed during AD. Aβ changes the redox-status of BBB cells, which in turn changes the functioning of mitochondria and disrupts the barrier function of endothelial cells by affecting tight junction proteins. Aβ oligomers have the greatest toxic effect on BBB cells, and oligomers are most rapidly transferred by transcytosis from the brain side of the BBB to the blood side. Both the cytotoxic effect of Aβ and the impairment of barrier function are partly due to the interaction of Aβ monomers and oligomers with membrane-bound RAGE. AD therapies based on the disruption of this interaction or the creation of decoys for Aβ are being developed. The question of the transfer of various Aβ isoforms through the BBB is important, since it can influence the development of AD. It is shown that the rate of input of Aβ40 and Aβ42 from the blood into the brain is different. The actual question of the transfer of pathogenic Aβ isoforms with post-translational modifications or mutations through the BBB still remains open.

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

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

A Recent Update on Pathophysiology and Therapeutic Interventions of Alzheimer's Disease

AIM

Alzheimer's disease (AD) has been identified as a progressive brain disorder associated with memory dysfunction and the accumulation of β-amyloid plaques and neurofibrillary tangles of τ protein. Mitochondria is crucial in maintaining cell survival, cell death, calcium regulation, and ATP synthesis. Mitochondrial dysfunction and linked calcium overload have been involved in the pathogenesis of AD. CRM2 (Collapsin response mediator protein-2) is involved in endosomal lysosomal trafficking as well as autophagy, and their reduced level is also a primary culprit in the progression of AD. In addition, Cholinergic neurotransmission and neuroinflammation are two other mechanisms implicated in AD onset and might be protective targets to attenuate disease progression. The microbiota-gut-brain axis (MGBA) is another crucial target for AD treatment. Crosstalk between gut microbiota and brain mutually benefitted each other, dysbiosis in gut microbiota affects the brain functions and leads to AD progression with increased AD-causing biomarkers. Despite the complexity of AD, treatment is only limited to symptomatic management. Therefore, there is an urgent demand for novel therapeutics that target associated pathways responsible for AD pathology. This review explores the role of different mechanisms involved in AD and possible therapeutic targets to protect against disease progression.

BACKGROUND

Amidst various age-related diseases, AD is the most deleterious neurodegenerative disorder that affects more than 24 million people globally. Every year, approximately 7.7 million new cases of dementia have been reported. However, to date, no novel disease-modifying therapies are available to treat AD.

OBJECTIVE

The aim of writing this review is to highlight the role of key biomarker proteins and possible therapeutic interventions that could play a crucial role in mitigating the ongoing prognosis of Alzheimer's disease.

MATERIALS AND METHODS

The available information about the disease was collected through multiple search engines, including PubMed, Science Direct, Clinical Trials, and Google Scholar.

RESULTS

Accumulated pieces of evidence reveal that extracellular aggregation of β-amyloid plaques and intracellular tangles of τ protein are peculiar features of perpetuated Alzheimer's disease (AD). Further, the significant role of mitochondria, calcium, and cholinergic pathways in the pathogenesis of AD makes the respiratory cell organelle a crucial therapeutic target in this neurodegenerative disease. All currently available drugs either delay the clinical damage to cells or temporarily attenuate some symptoms of Alzheimer's disease.

CONCLUSION

The pathological features of AD are extracellular deposition of β-amyloid, acetylcholinesterase deregulation, and intracellular tangles of τ protein. The multifactorial heterogeneity of disease demands more research work in this field to find new therapeutic biological targets.

Distinct Effects of Beta-Amyloid, Its Isomerized and Phosphorylated Forms on the Redox Status and Mitochondrial Functioning of the Blood-Brain Barrier Endothelium

The Alzheimer's disease (AD)-associated breakdown of the blood-brain barrier (BBB) promotes the accumulation of beta-amyloid peptide (Aβ) in the brain as the BBB cells provide Aβ transport from the brain parenchyma to the blood, and vice versa. The breakdown of the BBB during AD may be caused by the emergence of blood-borne Aβ pathogenic forms, such as structurally and chemically modified Aβ species; their effect on the BBB cells has not yet been studied. Here, we report that the effects of Aβ₄₂, Aβ₄₂, containing isomerized Asp7 residue (iso-Aβ₄₂) or phosphorylated Ser8 residue (p-Aβ₄₂) on the mitochondrial potential and respiration are closely related to the redox status changes in the mouse brain endothelial cells bEnd.3. Aβ₄₂ and iso-Aβ₄₂ cause a significant increase in nitric oxide, reactive oxygen species, glutathione, cytosolic calcium and the mitochondrial potential after 4 h of incubation. P-Aβ₄₂ either does not affect or its effect develops after 24 h of incubation. Aβ₄₂ and iso-Aβ₄₂ activate mitochondrial respiration compared to p-Aβ₄₂. The isomerized form promotes a greater cytotoxicity and mitochondrial dysfunction, causing maximum oxidative stress. Thus, Aβ₄₂, p-Aβ₄₂ and iso-Aβ₄₂ isoforms differently affect the BBBs' cell redox parameters, significantly modulating the functioning of the mitochondria. The changes in the level of modified Aβ forms can contribute to the BBBs' breakdown during AD.

Mitochondrial Ca2+ Signaling and Bioenergetics in Alzheimer's Disease

Alzheimer's disease (AD) is a hereditary and sporadic neurodegenerative illness defined by the gradual and cumulative loss of neurons in specific brain areas. The processes that cause AD are still under investigation and there are no available therapies to halt it. Current progress puts at the forefront the "calcium (Ca2+) hypothesis" as a key AD pathogenic pathway, impacting neuronal, astrocyte and microglial function. In this review, we focused on mitochondrial Ca2+ alterations in AD, their causes and bioenergetic consequences in neuronal and glial cells, summarizing the possible mechanisms linking detrimental mitochondrial Ca2+ signals to neuronal death in different experimental AD models.

The Effect of 40-Hz White LED Therapy on Structure-Function of Brain Mitochondrial ATP-Sensitive Ca-Activated Large-Conductance Potassium Channel in Amyloid Beta Toxicity

Photobiomodulation therapy has become the focus of medical research in many areas such as Alzheimer's disease (AD), because of its modulatory effect on cellular processes through light energy absorption via photoreceptors/chromophores located in the mitochondria. However, there are still many questions around the underlying mechanisms. This study was carried out to unravel whether the function-structure of ATP-sensitive mitoBK_Ca channels, as crucial components for maintenance of mitochondrial homeostasis, can be altered subsequent to light therapy in AD. Induction of Aβ neurotoxicity in male Wistar rats was done by intracerebroventricular injection of Aβ1-42. After a week, light-treated rats were exposed to 40-Hz white light LEDs, 15 min for 7 days. Electrophysiological properties of mitoBK_Ca channel were investigated using a channel incorporated into the bilayer lipid membrane, and mitoBK_Ca-β2 subunit expression was determined using western blot analysis in Aβ-induced toxicity and light-treated rats. Our results describe that conductance and open probability (Po) of mitoBK_Ca channel decreased significantly and was accompanied by a Po curve rightward shift in mitochondrial preparation in Aβ-induced toxicity rats. We also showed a significant reduction in expression of mitoBK_Ca-β2 subunit, which is partly responsible for a leftward shift in BK_Ca Po curve in low calcium status. Interestingly, we provided evidence of a significant improvement in channel conductance and Po after light therapy. We also found that light therapy improved mitoBK_Ca-β2 subunit expression, increasing it close to saline group. The current study explains a light therapy improvement in brain mitoBK_Ca channel function in the Aβ-induced neurotoxicity rat model, an effect that can be linked to increased expression of β2 subunit.

TRPV1 Modulator Ameliorates Alzheimer-Like Amyloid-β Neuropathology via Akt/Gsk3β-Mediated Nrf2 Activation in the Neuro-2a/APP Cell Model

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder for which there is no effective therapeutic strategy. PcActx peptide from the transcriptome of zoantharian Palythoa caribaeorum has recently been identified and verified as a novel antagonist of transient receptor potential cation channel subfamily V member 1 (TRPV1). In the present study, we further investigated the neuroprotective potential of PcActx peptide and its underlying mechanism of action, in an N2a/APP cell model of AD. Both Western blot and RT-PCR analysis revealed that PcActx peptide markedly inhibited the production of amyloid-related proteins and the expression of BACE1, PSEN1, and PSEN2. Moreover, PcActx peptide notably attenuated the capsaicin-stimulated calcium response and prevented the phosphorylation of CaMKII and CaMKIV (calcium-mediated proteins) in N2a/APP cells. Further investigation indicated that PcActx peptide significantly suppressed ROS generation through Nrf2 activation, followed by enhanced NQO1 and HO-1 levels. In addition, PcActx peptide remarkably improved Akt phosphorylation at Ser 473 (active) and Gsk3β phosphorylation at Ser 9 (inactive), while pharmacological inhibition of the Akt/Gsk3β pathway significantly attenuated PcActx-induced Nrf2 activation and amyloid downregulation. In conclusion, PcActx peptide functions as a TRPV1 modulator of intercellular calcium homeostasis, prevents AD-like amyloid neuropathology via Akt/Gsk3β-mediated Nrf2 activation, and shows promise as an alternative therapeutic agent for AD.

Mitochondrial behavior when things go wrong in the axon

Axonal homeostasis is maintained by processes that include cytoskeletal regulation, cargo transport, synaptic activity, ionic balance, and energy supply. Several of these processes involve mitochondria to varying degrees. As a transportable powerplant, the mitochondria deliver ATP and Ca²⁺-buffering capabilities and require fusion/fission to maintain proper functioning. Taking into consideration the long distances that need to be covered by mitochondria in the axons, their transport, distribution, fusion/fission, and health are of cardinal importance. However, axonal homeostasis is disrupted in several disorders of the nervous system, or by traumatic brain injury (TBI), where the external insult is translated into physical forces that damage nervous tissue including axons. The degree of damage varies and can disconnect the axon into two segments and/or generate axonal swellings in addition to cytoskeletal changes, membrane leakage, and changes in ionic composition. Cytoskeletal changes and increased intra-axonal Ca²⁺ levels are the main factors that challenge mitochondrial homeostasis. On the other hand, a proper function and distribution of mitochondria can determine the recovery or regeneration of the axonal physiological state. Here, we discuss the current knowledge regarding mitochondrial transport, fusion/fission, and Ca²⁺ regulation under axonal physiological or pathological conditions.

Effect of Tau Protein on Mitochondrial Functions

Alzheimer's disease is the most common age-related progressive neurodegenerative disorder of brain cortex and hippocampus leading to cognitive impairment. Accumulation of extracellular amyloid plaques and intraneuronal neurofibrillary tangles are believed to be the main hallmarks of the disease. Origin of Alzheimer's disease is not totally clear, multiple initiator factors are likely to exist. Intracellular impacts of Alzheimer's disease include mitochondrial dysfunction, oxidative stress, ER-stress, disruption of autophagy, severe metabolic challenges leading to massive neuronal apoptosis. Mitochondria are the key players in all these processes. This formed the basis for the so-called mitochondrial cascade hypothesis. This review provides current data on the molecular mechanisms of the development of Alzheimer's disease associated with mitochondria. Special attention was paid to the interaction between Tau protein and mitochondria, as well as to the promising therapeutic approaches aimed at preventing development of neurodegeneration.

Targeting mitochondria in the regulation of neurodegenerative diseases: A comprehensive review

Mitochondria are one of the essential cellular organelles. Apart from being considered as the powerhouse of the cell, mitochondria have been widely known to regulate redox reaction, inflammation, cell survival, cell death, metabolism, etc., and are implicated in the progression of numerous disease conditions including neurodegenerative diseases. Since brain is an energy-demanding organ, mitochondria and their functions are important for maintaining normal brain homeostasis. Alterations in mitochondrial gene expression, mutations, and epigenetic modification contribute to inflammation and neurodegeneration. Dysregulation of reactive oxygen species production by mitochondria and aggregation of proteins in neurons leads to alteration in mitochondria functions which further causes neuronal death and progression of neurodegeneration. Pharmacological studies have prioritized mitochondria as a possible drug target in the regulation of neurodegenerative diseases. Therefore, the present review article has been intended to provide a comprehensive understanding of mitochondrial role in the development and progression of neurodegenerative diseases mainly Alzheimer's, Parkinson's, multiple sclerosis, and amyotrophic lateral sclerosis followed by possible intervention and future treatment strategies to combat mitochondrial-mediated neurodegeneration.

ATP-sensitive potassium channels: A double-edged sword in neurodegenerative diseases

ATP-sensitive potassium channels (K_ATP channels), a group of vital channels that link the electrical activity of the cell membrane with cell metabolism, were discovered on the ventricular myocytes of guinea pigs by Noma using the patch-clamp technique in 1983. Subsequently, K_ATP channels have been found to be expressed in pancreatic β cells, cardiomyocytes, skeletal muscle cells, and nerve cells in the substantia nigra (SN), hippocampus, cortex, and basal ganglia. K_ATP channel openers (KCOs) diazoxide, nicorandil, minoxidil, and the K_ATP channel inhibitor glibenclamide have been shown to have anti-hypertensive, anti-myocardial ischemia, and insulin-releasing regulatory effects. Increasing evidence has suggested that K_ATP channels also play roles in Alzheimer's disease (AD), Parkinson's disease (PD), vascular dementia (VD), Huntington's disease (HD) and other neurodegenerative diseases. KCOs and K_ATP channel inhibitors protect neurons from injury by regulating neuronal excitability and neurotransmitter release, inhibiting abnormal protein aggregation and Ca²⁺ overload, reducing reactive oxygen species (ROS) production and microglia activation. However, K_ATP channels have dual effects in some cases. In this review, we focus on the roles of K_ATP channels and their related openers and inhibitors in neurodegenerative diseases. This will enable us to precisely take advantage of the K_ATP channels and provide new ideas for the treatment of neurodegenerative diseases.

Amyloid Beta Oligomers-Induced Ca2+ Entry Pathways: Role of Neuronal Networks, NMDA Receptors and Amyloid Channel Formation

The molecular basis of amyloid toxicity in Alzheimer’s disease (AD) remains controversial. Amyloid β (Aβ) oligomers promote Ca2+ influx, mitochondrial Ca2+ overload and apoptosis in hippocampal neurons in vivo and in vitro, but the primary Ca2+ entry pathways are unclear. We studied Ca2+ entry pathways induced by Aβ oligomers in rat hippocampal and cerebellar neurons. Aβ oligomers induce Ca2+ entry in neurons. Ca2+ responses to Aβ oligomers are large after synaptic networking and prevented by blockers of synaptic transmission. In contrast, in neurons devoid of synaptic connections, Ca2+ responses to Aβ oligomers are small and prevented only by blockers of amyloid channels (NA7) and NMDA receptors (MK801). A combination of NA7 and MK801 nearly abolished Ca2+ responses. Non-neuronal cells bearing NMDA receptors showed Ca2+ responses to oligomers, whereas cells without NMDA receptors did not exhibit Ca2+ responses. The expression of subunits of the NMDA receptor NR1/ NR2A and NR1/NR2B in HEK293 cells lacking endogenous NMDA receptors restored Ca2+ responses to NMDA but not to Aβ oligomers. We conclude that Aβ oligomers promote Ca2+ entry via amyloid channels and NMDA receptors. This may recruit distant neurons intertwisted by synaptic connections, spreading excitation and recruiting further NMDA receptors and voltage-gated Ca2+ channels, leading to excitotoxicity and neuron degeneration in AD.

Imaging mitochondrial calcium dynamics in the central nervous system

Mitochondrial calcium handling is a particularly active research area in the neuroscience field, as it plays key roles in the regulation of several functions of the central nervous system, such as synaptic transmission and plasticity, astrocyte calcium signaling, neuronal activity… In the last few decades, a panel of techniques have been developed to measure mitochondrial calcium dynamics, relying mostly on photonic microscopy, and including synthetic sensors, hybrid sensors and genetically encoded calcium sensors. The goal of this review is to endow the reader with a deep knowledge of the historical and latest tools to monitor mitochondrial calcium events in the brain, as well as a comprehensive overview of the current state of the art in brain mitochondrial calcium signaling. We will discuss the main calcium probes used in the field, their mitochondrial targeting strategies, their key properties and major drawbacks. In addition, we will detail the main roles of mitochondrial calcium handling in neuronal tissues through an extended report of the recent studies using mitochondrial targeted calcium sensors in neuronal and astroglial cells, in vitro and in vivo.

In utero exposure to methylmercury impairs cognitive function in adult offspring: Insights from proteomic modulation

Methylmercury (MeHg) is a hazardous substance that has unique neurodevelopmental toxic effects. However, its molecular alteration profile, sensitive response biomarkers, and mechanism of neuronal injury remain largely unknown. Here, the effects of intrauterine methylmercury chloride (low-, medium- and high-dose groups: 0.6 mg/kg/d, 1.2 mg/kg/d, 2.4 mg/ kg /d, respectively) exposure on learning and memory were assessed in offspring rats by behavioral tests, pathological analysis and hippocampal proteomic analysis. The results suggested that intrauterine MeHg exposure impairs spatial learning and memory and leads a significant reduction in the number and dispersion scattered arrangement in the hippocampus of offspring. Furthermore, in the tandem mass tag-based proteomics analysis, compared with the control group, a total of 74 differentially expressed proteins (DEPs) were found in the MeHg exposure groups; specifically, 32 down-regulated and 42 up-regulated proteins were identified. In addition, the pathways enrichment analysis indicated that these DEPs are implicated in several biological processes, such as synaptic plasticity and energy metabolism, as well as various molecular functional categories. Simultaneously, MeHg reduced the postsynaptic density, diminished the active zone, amplified the synaptic cleft and changed the synaptic interface of pyramidal cells. Western blot analysis further revealed that MeHg significantly reduced the levels of Forkhead box protein (FOXP2), Synaptophysin (SYP) and Postsynaptic density protein 95 (PSD-95), and down-regulated the N-methyl-D-aspartate receptor 1 (NMDAR1), N-methyl-D-aspartate receptor 2 A (NR2A) and N-methyl-D-aspartate receptor 2B (NR2B). In general, from a functional perspective, most overlapping proteins were related to NMDA receptor-mediated glutamatergic signaling, which is an excitotoxicity mechanism known to influence learning and memory. These discoveries contribute to our understanding of the relationship between MeHg and cognitive deficits and provide insight into the protein mediators of this relationship and possible prospective early biomarkers.

Excitotoxicity, calcium and mitochondria: a triad in synaptic neurodegeneration

Glutamate is the most commonly engaged neurotransmitter in the mammalian central nervous system, acting to mediate excitatory neurotransmission. However, high levels of glutamatergic input elicit excitotoxicity, contributing to neuronal cell death following acute brain injuries such as stroke and trauma. While excitotoxic cell death has also been implicated in some neurodegenerative disease models, the role of acute apoptotic cell death remains controversial in the setting of chronic neurodegeneration. Nevertheless, it is clear that excitatory synaptic dysregulation contributes to neurodegeneration, as evidenced by protective effects of partial N-methyl-D-aspartate receptor antagonists. Here, we review evidence for sublethal excitatory injuries in relation to neurodegeneration associated with Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis and Huntington's disease. In contrast to classic excitotoxicity, emerging evidence implicates dysregulation of mitochondrial calcium handling in excitatory post-synaptic neurodegeneration. We discuss mechanisms that regulate mitochondrial calcium uptake and release, the impact of LRRK2, PINK1, Parkin, beta-amyloid and glucocerebrosidase on mitochondrial calcium transporters, and the role of autophagic mitochondrial loss in axodendritic shrinkage. Finally, we discuss strategies for normalizing the flux of calcium into and out of the mitochondrial matrix, thereby preventing mitochondrial calcium toxicity and excitotoxic dendritic loss. While the mechanisms that underlie increased uptake or decreased release of mitochondrial calcium vary in different model systems, a common set of strategies to normalize mitochondrial calcium flux can prevent excitatory mitochondrial toxicity and may be neuroprotective in multiple disease contexts.

Functional Selectivity of Coumarin Derivates Acting via GPR55 in Neuroinflammation

Anti-neuroinflammatory treatment has gained importance in the search for pharmacological treatments of different neurological and psychiatric diseases, such as depression, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. Clinical studies demonstrate a reduction of the mentioned diseases’ symptoms after the administration of anti-inflammatory drugs. Novel coumarin derivates have been shown to elicit anti-neuroinflammatory effects via G-protein coupled receptor GPR55, with possibly reduced side-effects compared to the known anti-inflammatory drugs. In this study, we, therefore, evaluated the anti-inflammatory capacities of the two novel coumarin-based compounds, KIT C and KIT H, in human neuroblastoma cells and primary murine microglia. Both compounds reduced PGE₂-concentrations likely via the inhibition of COX-2 synthesis in SK-N-SH cells but only KIT C decreased PGE₂-levels in primary microglia. The examination of other pro- and anti-inflammatory parameters showed varying effects of both compounds. Therefore, the differences in the effects of KIT C and KIT H might be explained by functional selectivity as well as tissue- or cell-dependent expression and signal pathways coupled to GPR55. Understanding the role of chemical residues in functional selectivity and specific cell- and tissue-targeting might open new therapeutic options in pharmacological drug development and might improve the treatment of the mentioned diseases by intervening in an early step of their pathogenesis.

Naproxen as a potential candidate for promoting rivastigmine anti-Alzheimer activity against aluminum chloride-prompted Alzheimer's-like disease in rats; neurogenesis and apoptosis modulation as a possible underlying mechanism

BACKGROUND AND AIM

Alzheimer's disease (AD) is one of the leading causes of dependence and disability among the elderly worldwide. The traditional anti-Alzheimer medication, rivastigmine, one of the cholinesterase inhibitors (ChEIs), fails to achieve a definitive cure. We tested the hypothesis that naproxen administration to the rivastigmine-treated aluminum chloride (AlCl3) Alzheimer's rat model could provide an additive neuroprotective effect compared to rivastigmine alone.

MATERIALS AND METHODS

The studied groups were control (Cont), AlCl3 treated (Al), rivastigmine treated (RIVA), naproxen treated (Napro), and combined rivastigmine and naproxen treated (RIVA + Napro). Rats' memory, spatial learning, and cognitive behavior were assessed followed by evaluation of hippocampal acetylcholinesterase (AChE) activity. Hippocampal and cerebellar histopathology were thoroughly examined. Activated caspase-3 and the neuroepithelial stem cells marker; nestin expressions were immunohistochemically assayed.

RESULTS

AD rats displayed significantly impaired memory and cognitive function, augmented hippocampal AChE activity; massive neurodegeneration associated with enhanced astrogliosis, apoptosis, and impaired neurogenesis. Except for the enhancement of neurogenesis and suppression of apoptosis, the combination therapy had no additional neuroprotective benefit over rivastigmine-only therapy.

CONCLUSION

Naproxen's efficacy was established by its ability to function at the cellular level, improved neurogenesis, and decreased, apoptosis without having an additional mitigating impact on cognitive impairment in rivastigmine-treated AD rats.

Mitochondrial calcium exchange in physiology and disease

The uptake of calcium into and extrusion of calcium from the mitochondrial matrix is a fundamental biological process that has critical effects on cellular metabolism, signaling, and survival. Disruption of mitochondrial calcium (_mCa²⁺) cycling is implicated in numerous acquired diseases such as heart failure, stroke, neurodegeneration, diabetes, and cancer, and is genetically linked to several inherited neuromuscular disorders. Understanding the mechanisms responsible for _mCa²⁺ exchange therefore holds great promise for the treatment of these diseases. The past decade has seen the genetic identification of many of the key proteins that mediate mitochondrial calcium uptake and efflux. Here, we present an overview of the phenomenon of _mCa²⁺ transport, and a comprehensive examination of the molecular machinery that mediates calcium flux across the inner mitochondrial membrane: the mitochondrial uniporter complex (consisting of MCU, EMRE, MICU1, MICU2, MICU3, MCUB, and MCUR1), NCLX, LETM1, the mitochondrial ryanodine receptor, and the mitochondrial permeability transition pore. We then consider the physiological implications of _mCa²⁺ flux and evaluate how alterations in _mCa²⁺ homeostasis contribute to human disease. This review concludes by highlighting opportunities and challenges for therapeutic intervention in pathologies characterized by aberrant _mCa²⁺ handling and by summarizing critical unanswered questions regarding the biology of _mCa²⁺ flux.

Erinacine A-Enriched Hericium erinaceus Mycelium Delays Progression of Age-Related Cognitive Decline in Senescence Accelerated Mouse Prone 8 (SAMP8) Mice

There have been many reports on the neuroprotective effects of Hericium erinaceus mycelium, in which the most well-known active compounds found are diterpenoids, such as erinacine A. Previously, erinacine A-enriched Hericeum erinaceus mycelium (EAHEM) was shown to decrease amyloid plaque aggregation and improve cognitive disability in Alzheimer’s disease model APP/PS1 mice. However, its effects on brain aging have not yet been touched upon. Here, we used senescence accelerated mouse prone 8 (SAMP8) mice as a model to elucidate the mechanism by which EAHEM delays the aging of the brain. Three-month-old SAMP8 mice were divided into three EAHEM dosage groups, administered at 108, 215 and 431 mg/kg/BW/day, respectively. During the 12th week of EAHEM feeding, learning and memory of the mice were evaluated by single-trial passive avoidance and active avoidance test. After sacrifice, the amyloid plaques, induced nitric oxidase synthase (iNOS) activity, thiobarbituric acid-reactive substances (TBARS) and 8-OHdG levels were analyzed. We found that the lowest dose of 108 mg/kg/BW EAHEM was sufficient to significantly improve learning and memory in the passive and active avoidance tests. In all three EAHEM dose groups, iNOS, TBARS and 8-OHdG levels all decreased significantly and showed a dose-dependent response. The results indicate that EAHEM improved learning and memory and delayed degenerative aging in mice brains.

Alzheimer's Disease: A Molecular View of β-Amyloid Induced Morbific Events

Amyloid-β (Aβ) is a dynamic peptide of Alzheimer’s disease (AD) which accelerates the disease progression. At the cell membrane and cell compartments, the amyloid precursor protein (APP) undergoes amyloidogenic cleavage by β- and γ-secretases and engenders the Aβ. In addition, externally produced Aβ gets inside the cells by receptors mediated internalization. An elevated amount of Aβ yields spontaneous aggregation which causes organelles impairment. Aβ stimulates the hyperphosphorylation of tau protein via acceleration by several kinases. Aβ travels to the mitochondria and interacts with its functional complexes, which impairs the mitochondrial function leading to the activation of apoptotic signaling cascade. Aβ disrupts the Ca²⁺ and protein homeostasis of the endoplasmic reticulum (ER) and Golgi complex (GC) that promotes the organelle stress and inhibits its stress recovery machinery such as unfolded protein response (UPR) and ER-associated degradation (ERAD). At lysosome, Aβ precedes autophagy dysfunction upon interacting with autophagy molecules. Interestingly, Aβ act as a transcription regulator as well as inhibits telomerase activity. Both Aβ and p-tau interaction with neuronal and glial receptors elevate the inflammatory molecules and persuade inflammation. Here, we have expounded the Aβ mediated events in the cells and its cosmopolitan role on neurodegeneration, and the current clinical status of anti-amyloid therapy.

Mitochondrial Calcium Signaling as a Therapeutic Target for Alzheimer's Disease

Mitochondria absorb calcium (Ca2+) at the expense of the electrochemical gradient generated during respiration. The influx of Ca2+ into the mitochondrial matrix helps maintain metabolic function and results in increased cytosolic Ca2+ during intracellular Ca2+ signaling. Mitochondrial Ca2+ homeostasis is tightly regulated by proteins located in the inner and outer mitochondrial membranes and by the cross-talk with endoplasmic reticulum Ca2+ signals. Increasing evidence indicates that mitochondrial Ca2+ overload is a pathological phenotype associated with Alzheimer's Disease (AD). As intracellular Ca2+ dysregulation can be observed before the appearance of typical pathological hallmarks of AD, it is believed that mitochondrial Ca2+ overload may also play an important role in AD etiology. The high mitochondrial Ca2+ uptake can easily compromise neuronal functions and exacerbate AD progression by impairing mitochondrial respiration, increasing reactive oxygen species formation and inducing apoptosis. Additionally, mitochondrial Ca2+ overload can damage mitochondrial recycling via mitophagy. This review will discuss the molecular players involved in mitochondrial Ca2+ dysregulation and the pharmacotherapies that target this dysregulation. As most of the current AD therapeutics are based on amyloidopathy, tauopathy, and the cholinergic hypothesis, they achieve only symptomatic relief. Thus, determining how to reestablish mitochondrial Ca2+ homeostasis may aid in the development of novel AD therapeutic interventions.

Structural and Functional Alterations in Mitochondria-Associated Membranes (MAMs) and in Mitochondria Activate Stress Response Mechanisms in an In Vitro Model of Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the accumulation of extracellular plaques composed by amyloid-β (Aβ) and intracellular neurofibrillary tangles of hyperphosphorylated tau. AD-related neurodegenerative mechanisms involve early changes of mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) and impairment of cellular events modulated by these subcellular domains. In this study, we characterized the structural and functional alterations at MAM, mitochondria, and ER/microsomes in a mouse neuroblastoma cell line (N2A) overexpressing the human amyloid precursor protein (APP) with the familial Swedish mutation (APPswe). Proteins levels were determined by Western blot, ER-mitochondria contacts were quantified by transmission electron microscopy, and Ca²⁺ homeostasis and mitochondria function were analyzed using fluorescent probes and Seahorse assays. In this in vitro AD model, we found APP accumulated in MAM and mitochondria, and altered levels of proteins implicated in ER-mitochondria tethering, Ca²⁺ signaling, mitochondrial dynamics, biogenesis and protein import, as well as in the stress response. Moreover, we observed a decreased number of close ER-mitochondria contacts, activation of the ER unfolded protein response, reduced Ca²⁺ transfer from ER to mitochondria, and impaired mitochondrial function. Together, these results demonstrate that several subcellular alterations occur in AD-like neuronal cells, which supports that the defective ER-mitochondria crosstalk is an important player in AD physiopathology.

Selective Neuron Vulnerability in Common and Rare Diseases-Mitochondria in the Focus

Mitochondrial dysfunction is a central feature of neurodegeneration within the central and peripheral nervous system, highlighting a strong dependence on proper mitochondrial function of neurons with especially high energy consumptions. The fitness of mitochondria critically depends on preservation of distinct processes, including the maintenance of their own genome, mitochondrial dynamics, quality control, and Ca²⁺ handling. These processes appear to be differently affected in common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease, as well as in rare neurological disorders, including Huntington’s disease, Amyotrophic Lateral Sclerosis and peripheral neuropathies. Strikingly, particular neuron populations of different morphology and function perish in these diseases, suggesting that cell-type specific factors contribute to the vulnerability to distinct mitochondrial defects. Here we review the disruption of mitochondrial processes in common as well as in rare neurological disorders and its impact on selective neurodegeneration. Understanding discrepancies and commonalities regarding mitochondrial dysfunction as well as individual neuronal demands will help to design new targets and to make use of already established treatments in order to improve treatment of these diseases.

Akt / GSK3β / Nrf2 / HO-1 pathway activation by flurbiprofen protects the hippocampal neurons in a rat model of glutamate excitotoxicity

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates redox homeostasis of the cell through regulation of the antioxidant response element genes transcription. Nrf2 also regulates the antiapoptotic Bcl-2 gene. Nrf2 degradation and nuclear translocation is regulated by upstream kinases Akt and GSK3β. Glutamate excitotoxicity is a process of neuronal cells death due to excessive activation of glutamate receptors. Glutamate excitotoxicity participates in the pathophysiology of several acute and chronic neurological conditions. In addition, glutamate excitotoxicity interrupts the PI3K/Akt prosurvival pathway so GSK3β remains active. Active GSK3β increases Nrf2 degradation, decreases Nrf2 nuclear translocation and increases Nrf2 nuclear export which decreases the ARE genes transcription such as, SOD, GSH synthesis enzyme and HO-1. Also, Bcl-2 transcription decreases. Flurbiprofen is a COX inhibitor. Previous studies showed that it has a neuroprotective effect in neurodegeneration and in focal cerebral ischemia/reperfusion model. In our research we aimed to test the hypothesis that flurbiprofen may have a neuroprotective effect in a rat model of glutamate-induced excitotoxicity and this neuroprotection may occur through modulation of (Akt/GSK3β/Nrf2/HO-1) pathway. Rats were divided into 4 groups; control, MSG (2.5 g/Kg, i.p), low dose FB (5 mg/kg, i.p) and high dose FB (10 mg/kg, i.p). We found that low and high doses FB decreased COX-2, PGE₂, NO and MDA and increased SOD and GSH in brain compared to MSG group. High dose was more effective than low dose. Western blotting analysis in hippocampus tissue showed that high dose FB increased p-Akt, p-GSK3β, nuclear Nrf2 and HO-1 and decreased cytosolic Nrf2 level in comparison with MSG group. Immunohistochemical analysis in hippocampus and cerebral cortex showed that high dose FB increased Bcl-2 and decreased Bax compared to MSG group. In addition, FB increased the number of intact neurons in hippocampus areas and cerebral cortex neurons and showed an anxiolytic-like action in OF and EPM tests. These findings suggest that FB has a neuroprotective effect in glutamate-induced excitotoxicity model through reduction of the glutamate excitotoxicity damage and activation of the survival pathway. These may occur due to modulation the survival pathway (Akt/GSK3β/Nrf2/HO-1) and inhibition of COX-2.

Calcium Dyshomeostasis in Alzheimer's Disease Pathogenesis

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

In vivo brain imaging of mitochondrial Ca2+ in neurodegenerative diseases with multiphoton microscopy

Mitochondria are involved in a large number of essential roles related to neuronal function. Ca2+ handling by mitochondria is critical for many of these functions, including energy production and cellular fate. Conversely, mitochondrial Ca2+ mishandling has been related to a variety of neurodegenerative diseases. Investigating mitochondrial Ca2+ dynamics is essential for advancing our understanding of the role of intracellular mitochondrial Ca2+ signals in physiology and pathology. Improved Ca2+ indicators, and the ability to target them to different cells and compartments, have emerged as useful tools for analysis of Ca2+ signals in living organisms. Combined with state-of-the-art techniques such as multiphoton microscopy, they allow for the study of mitochondrial Ca2+ dynamics in vivo in mouse models of the disease. Here, we provide an overview of the Ca2+ transporters/ion channels in mitochondrial membranes, and the involvement of mitochondrial Ca2+ in neurodegenerative diseases followed by a summary of the main tools available to evaluate mitochondrial Ca2+ dynamics in vivo using the aforementioned technique.

Mitochondrial calcium at the synapse

Mitochondria are dynamic organelles, which serve various purposes, including but not limited to the production of ATP and various metabolites, buffering ions, acting as a signaling hub, etc. In recent years, mitochondria are being seen as the central regulators of cellular growth, development, and death. Since neurons are highly specialized cells with a heavy metabolic demand, it is not surprising that neurons are one of the most mitochondria-rich cells in an animal. At synapses, mitochondrial function and dynamics is tightly regulated by synaptic calcium. Calcium influx during synaptic activity causes increased mitochondrial calcium influx leading to an increased ATP production as well as buffering of synaptic calcium. While increased ATP production is required during synaptic transmission, calcium buffering by mitochondria is crucial to prevent faulty neurotransmission and excitotoxicity. Interestingly, mitochondrial calcium also regulates the mobility of mitochondria within synapses causing mitochondria to halt at the synapse during synaptic transmission. In this review, we summarize the various roles of mitochondrial calcium at the synapse.

Mitochondrial Dysfunction and Mitophagy Closely Cooperate in Neurological Deficits Associated with Alzheimer's Disease and Type 2 Diabetes

Alzheimer's disease (AD) and type 2 diabetes (T2D) are known to be correlated in terms of their epidemiology, histopathology, and molecular and biochemical characteristics. The prevalence of T2D leading to AD is approximately 50-70%. Moreover, AD is often considered type III diabetes because of the common risk factors. Uncontrolled T2D may affect the brain, leading to memory and learning deficits in patients. In addition, metabolic disorders and impaired oxidative phosphorylation in AD and T2D patients suggest that mitochondrial dysfunction is involved in both diseases. The dysregulation of pathways involved in maintaining mitochondrial dynamics, biogenesis and mitophagy are responsible for exacerbating the impact of hyperglycemia on the brain and neurodegeneration under T2D conditions. The first section of this review describes the recent views on mitochondrial dysfunction that connect these two disease conditions, as the pathways are observed to overlap. The second section of the review highlights the importance of different mitochondrial miRNAs (mitomiRs) involved in the regulation of mitochondrial dynamics and their association with the pathogenesis of T2D and AD. Therefore, targeting mitochondrial biogenesis and mitophagy pathways, along with the use of mitomiRs, could be a potent therapeutic strategy for T2D-related AD. The last section of the review highlights the known drugs targeting mitochondrial function for the treatment of both disease conditions.

Detection and monitoring of the neuroprotective behavior of curcumin micelles based on an AIEgen probe

In recent years, the role of mitochondrial injury in the pathogenesis of Alzheimer's disease (AD) has attracted extensive attention. Studies have shown that curcumin (Cur) can protect nerve cells from beta-amyloid (Aβ)-induced mitochondrial damage. However, natural Cur encounters limited application due to its poor biocompatibility and bioavailability. To improve the solubility and biocompatibility of natural Cur, we prepared water-soluble curcumin micelles (CurM). Furthermore, the mitochondria-specific aggregation-induced emission (AIE) probe (TPE-Ph-In) was employed to observe the protective effect of CurM on the damage of mitochondrial morphology, distribution, and membrane potential caused by Aβ. Results showed that CurM had higher solubility, stronger stability and retention effect, and better cellular uptake than that of natural Cur. Furthermore, the inhibitory effects of CurM on mitochondrial morphology, distribution, and membrane potential damage induced by Aβ25-35 were observed utilizing TPE-Ph-In as an indicator of mitochondrial morphology and membrane potential. Thus, this method provides a useful strategy for experimental research and clinical treatment of AD with mitochondrial damage as the pathogenic mechanism.

Mitochondrial Permeability Transition: A Pore Intertwines Brain Aging and Alzheimer's Disease

Advanced age is the greatest risk factor for aging-related brain disorders including Alzheimer's disease (AD). However, the detailed mechanisms that mechanistically link aging and AD remain elusive. In recent years, a mitochondrial hypothesis of brain aging and AD has been accentuated. Mitochondrial permeability transition pore (mPTP) is a mitochondrial response to intramitochondrial and intracellular stresses. mPTP overactivation has been implicated in mitochondrial dysfunction in aging and AD brains. This review summarizes the up-to-date progress in the study of mPTP in aging and AD and attempts to establish a link between brain aging and AD from a perspective of mPTP-mediated mitochondrial dysfunction.

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

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

Targeting the Mitochondrial Permeability Transition Pore to Prevent Age-Associated Cell Damage and Neurodegeneration

The aging process is associated with significant alterations in mitochondrial function. These changes in mitochondrial function are thought to involve increased production of reactive oxygen species (ROS), which over time contribute to cell death, senescence, tissue degeneration, and impaired tissue repair. The mitochondrial permeability transition pore (mPTP) is likely to play a critical role in these processes, as increased ROS activates mPTP opening, which further increases ROS production. Injury and inflammation are also thought to increase mPTP opening, and chronic, low-grade inflammation is a hallmark of aging. Nicotinamide adenine dinucleotide (NAD+) can suppress the frequency and duration of mPTP opening; however, NAD+ levels are known to decline with age, further stimulating mPTP opening and increasing ROS release. Research on neurodegenerative diseases, particularly on Parkinson's disease (PD) and Alzheimer's disease (AD), has uncovered significant findings regarding mPTP openings and aging. Parkinson's disease is associated with a reduction in mitochondrial complex I activity and increased oxidative damage of DNA, both of which are linked to mPTP opening and subsequent ROS release. Similarly, AD is associated with increased mPTP openings, as evidenced by amyloid-beta (Aβ) interaction with the pore regulator cyclophilin D (CypD). Targeted therapies that can reduce the frequency and duration of mPTP opening may therefore have the potential to prevent age-related declines in cell and tissue function in various systems including the central nervous system.

Mitochondria-associated membranes (MAMs): a potential therapeutic target for treating Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is a leading global health concern for individuals and society. However, the potential mechanisms underlying the pathogenesis of AD have not yet been elucidated. Currently, the most widely acknowledged hypothesis is amyloid cascade owing to the brain characteristics of AD patients, including great quantities of extracellular β-amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFTs). Nevertheless, the amyloid cascade hypothesis cannot address certain pathologies that precede Aβ deposition and NFTs formation in AD, such as aberrant calcium homeostasis, abnormal lipid metabolism, mitochondrial dysfunction and autophagy. Notably, these earlier pathologies are closely associated with mitochondria-associated membranes (MAMs), the physical structures connecting the endoplasmic reticulum (ER) and mitochondria, which mediate the communication between these two organelles. It is plausible that MAMs might be involved in a critical step in the cascade of earlier events, ultimately inducing neurodegeneration in AD. In this review, we focus on the role of MAMs in the regulation of AD pathologies and the potential molecular mechanisms related to MAM-mediated pathological changes in AD. An enhanced recognition of the preclinical pathogenesis in AD could provide new therapeutic strategies, shifting the modality from treatment to prevention.

Single Point Mutation from E22-to-K in Aβ Initiates Early-Onset Alzheimer's Disease by Binding with Catalase

Amyloid-beta (Aβ) is a critical etiological factor for late-onset familial Alzheimer's disease (AD). However, an early-onset AD has been found to be related with an Aβ mutation in glutamic acid 22-to-lysine (Italian type E22K). Why only one single point mutation at E22 residue induces AD remains unclear. Here, we report that a Chinese familial AD pedigree with E22K mutation was associated with higher levels of serum hydrogen peroxide (H₂O₂) and lower activity of catalase (a H₂O₂ degrading enzyme) than controls. Further, we found that E22K binding with catalase caused more severe H₂O₂ accumulation in the brains of E22K-injected rats than Aβ-injected rats. Unexpectedly, H₂O₂ bound with the mutation site 22K residue of E22K and elicited more rapid aggregation of E22K than Aβ in vitro. Moreover, H₂O₂ acted with E22K synergistically to induce higher cellular toxicity than with Aβ. Notably, intrahippocampal infusion of E22K led to more severe plaque deposition, neuron death, and more rapid memory decline than Aβ-injected rats. However, L-cysteine, a H₂O₂ scavenger, not only prevented self-aggregation of E22K but also reduced H₂O₂-promoted E22K assembly in vitro; subsequently, it alleviated Alzheimer-related phenotypes. Hence, E22K binding with catalase promotes the early onset of familial AD, and L-cys may reverse this disease.

Aging-Dependent Mitophagy Dysfunction in Alzheimer's Disease

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

Anti-Aβ Antibody Aducanumab Regulates the Proteome of Senile Plaques and Closely Surrounding Tissue in a Transgenic Mouse Model of Alzheimer’s Disease

Background: Alzheimer’s disease (AD) is characterized by accumulation of amyloid-β (Aβ) species and deposition of senile plaques (SPs). Clinical trials with the anti-Aβ antibody aducanumab have been completed recently. Objective: To characterize the proteomic profile of SPs and surrounding tissue in a mouse model of AD in 10-month-old tgAPPPS1-21 mice after chronic treatment with aducanumab for four months with weekly dosing (10 mg/kg). Methods: After observing significant reduction of SP numbers in hippocampi of aducanumab-treated mice, we applied a localized proteomic analysis by combining laser microdissection and liquid chromatography-tandem mass spectrometry (LC-MS/MS) of the remaining SPs in hippocampi. We microdissected three subregions, containing SPs, SP penumbra level 1, and an additional penumbra level 2 to follow the proteomic profile as gradient. Results: In the aducanumab-treated mice, we identified 17 significantly regulated proteins that were associated with 1) mitochondria and metabolism (ACAT2, ATP5J, ETFA, EXOG, HK1, NDUFA4, NDUFS7, PLCB1, PPP2R4), 2) cytoskeleton and axons (ADD1, CAPZB, DPYSL3, MAG), 3) stress response (HIST1H1C/HIST1H1D, HSPA12A), and 4) AβPP trafficking/processing (CD81, GDI2). These pathways and some of the identified proteins are implicated in AD pathogenesis. Proteins associated with mitochondria and metabolism were mainly upregulated while proteins associated with AβPP trafficking/processing and stress response pathways were mainly downregulated, suggesting that aducanumab could lead to a beneficial proteomic profile around SPs in tgAPPPS1-21 mice. Conclusion: We identified novel proteomic patterns of SPs and surrounding tissue indicating that chronic treatment with aducanumab could inhibit Aβ toxicity and increase phagocytosis and cell viability.

Regulation of neuronal bioenergetics as a therapeutic strategy in neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis are a heterogeneous group of debilitating disorders with multifactorial etiologies and pathogeneses that manifest distinct molecular mechanisms and clinical manifestations with abnormal protein dynamics and impaired bioenergetics. Mitochondrial dysfunction is emerging as an important feature in the etiopathogenesis of these age-related neurodegenerative diseases. The prevalence and incidence of these diseases is on the rise with the increasing global population and average lifespan. Although many therapeutic approaches have been tested, there are currently no effective treatment routes for the prevention or cure of these diseases. We present the current status of our knowledge and understanding of the involvement of mitochondrial dysfunction in these diseases and highlight recent advances in novel therapeutic strategies targeting neuronal bioenergetics as potential approach for treating these diseases.

Alterations in inter-organelle crosstalk and Ca2+ signaling through mitochondria during proteotoxic stresses

BACKGROUND

Biogenesis and function of mitochondria is profoundly dependent on cytosolic translation of mitochondrial pre-proteins and its subsequent translocation and folding inside the organelle. Continuous exposure of non-native precursor proteins, exposure to damaging by-products of oxidative phosphorylation, load of mis-targeted or misfolded proteins from neighbouring compartments and unremitting demand of communication between mitochondrial and nuclear genomes, continuously pose proteotoxic threats to the organelle. Our knowledge of cellular mechanisms to cope up with such impending threat of proteotoxicity to mitochondria, is currently evolving. In recent years, several unique response and survival pathways have been discovered shedding light on cellular strategies to cope with stressed and dysfunctional mitochondria. As mitochondria compulsorily communicate with nucleus, cytosol and endoplasmic reticulum (ER) for its own biogenesis and function and in turn maintain critical cellular processes for survival, any impairment in communication by stressed or dysfunctional mitochondria may end up with fatal consequences.

DISCUSSION AND IMPLICATION

In this review, we have discussed about possible sources of mitochondrial proteotoxicity and the recent developments regarding cellular strategies to counter such stress to overcome dysfunctions of the organelle. Mitochondrial communication with neighbouring subcellular compartments like ER and cytosol during proteotoxic stress have been explored. In the context of mitochondrial proteotoxicity, alterations of crucial inter-organelle connections like ER-mitochondria contact sites and its implication on mitochondrial signaling activity like Ca²⁺ signaling have been dissected. Furthermore, an overview of pathological conditions, mainly neurodegenerative disorders that are known to be associated with mitochondrial proteotoxicity and Ca²⁺ dysregulation has been presented.

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

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

The yin and yang of mitochondrial Ca2+ signaling in cell physiology and pathology

Mitochondria are autonomous and dynamic cellular organelles orchestrating a diverse range of cellular activities. Numerous cell-signaling pathways target these organelles and Ca²⁺ is one of the most significant. Mitochondria are able to rapidly and transiently take up Ca²⁺, thanks to the mitochondrial Ca²⁺ uniporter complex, as well as to extrude it through the Na⁺/Ca²⁺ and H⁺/Ca²⁺ exchangers. The transient accumulation of Ca²⁺ in the mitochondrial matrix impacts on mitochondrial functions and cell pathophysiology. Here we summarize the role of mitochondrial Ca²⁺ signaling in both physiological (yang) and pathological (yin) processes and the methods that can be used to investigate mitochondrial Ca²⁺ homeostasis. As an example of the pivotal role of mitochondria in pathology, we described the state of the art of mitochondrial Ca²⁺ alterations in different pathological conditions, with a special focus on Alzheimer's disease.

Therapeutic Strategies to Target Calcium Dysregulation in Alzheimer's Disease

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