Alpha-synuclein and beta-amyloid – different targets, same players: calcium, free radicals and mitochondria in the mechanism of neurodegeneration

Protective Contribution of Rosmarinic Acid in Rosemary Extract Against Copper-Induced Oxidative Stress

Rosemary extract (Rosmarinus officinalis) is a natural source of bioactive compounds with significant antioxidant properties. Among these, rosmarinic acid is celebrated for its potent antioxidant, anti-inflammatory, antimicrobial, and neuroprotective properties, making it a valuable component in both traditional medicine and modern therapeutic research. Neurodegenerative diseases like Alzheimer's and Parkinson's are closely linked to oxidative damage, and research indicates that rosmarinic acid may help protect neurons by mitigating this harmful process. Rosmarinic acid is able to bind cupric ions (Cu2+) and interfere with the production of reactive oxygen species (ROS) produced by copper through Fenton-like reactions. This study aims to further evaluate the contribution of rosmarinic acid within rosemary extract by comparing its activity to that of isolated rosmarinic acid. By using a detailed approach that includes chemical characterization, antioxidant capacity assessment, and neuroprotective activity testing, we have determined whether the combined components in rosemary extract enhance or differ from the effects of rosmarinic acid alone. This comparison is crucial for understanding whether the full extract offers added benefits beyond those of isolated rosmarinic acid in combating oxidative stress and Aβ-induced toxicity.

Interplay of mitochondrial calcium signalling and reactive oxygen species production in the brain

Intracellular communication and regulation in brain cells is controlled by the ubiquitous Ca2+ and by redox signalling. Both of these independent signalling systems regulate most of the processes in cells including the cell surviving mechanism or cell death. In physiology Ca2+ can regulate and trigger reactive oxygen species (ROS) production by various enzymes and in mitochondria but ROS could also transmit redox signal to calcium levels via modification of calcium channels or phospholipase activity. Changes in calcium or redox signalling could lead to severe pathology resulting in excitotoxicity or oxidative stress. Interaction of the calcium and ROS is essential to trigger opening of mitochondrial permeability transition pore - the initial step of apoptosis, Ca2+ and ROS-induced oxidative stress involved in necrosis and ferroptosis. Here we review the role of redox signalling and Ca2+ in cytosol and mitochondria in the physiology of brain cells - neurons and astrocytes and how this integration can lead to pathology, including ischaemia injury and neurodegeneration.

The relationship between hypoxia and Alzheimer's disease: an updated review

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases, and the most prevalent form of dementia. The main hallmarks for the diagnosis of AD are extracellular amyloid-beta (Aβ) plaque deposition and intracellular accumulation of highly hyperphosphorylated Tau protein as neurofibrillary tangles. The brain consumes more oxygen than any other organs, so it is more easily to be affected by hypoxia. Hypoxia has long been recognized as one of the possible causes of AD and other neurodegenerative diseases, but the exact mechanism has not been clarified. In this review, we will elucidate the connection between hypoxia-inducible factors-1α and AD, including its contribution to AD and its possible protective effects. Additionally, we will discuss the relationship between oxidative stress and AD as evidence show that oxidative stress acts on AD-related pathogenic factors such as mitochondrial dysfunction, Aβ deposition, inflammation, etc. Currently, there is no cure for AD. Given the close association between hypoxia, oxidative stress, and AD, along with current research on the protective effects of antioxidants against AD, we speculate that antioxidants could be a potential therapeutic approach for AD and worth further study.

Energy substrate supplementation increases ATP levels and is protective to PD neurons

Alteration of mitochondrial metabolism by various mutations or toxins leads to various neurological conditions. Age-related changes in energy metabolism could also play the role of a trigger for neurodegenerative disorders. Nonetheless, it is not clear if restoration of ATP production or supplementation of brain cells with substrates for energy production could be neuroprotective. Using primary neurons and astrocytes, and neurons with familial forms of neurodegenerative disorders we studied whether various substrates of energy metabolism could improve mitochondrial metabolism and stimulate ATP production, and whether increased ATP levels could protect cells against glutamate excitotoxicity and neurodegeneration. We found that supplementation of neurons with several substrates, or combination thereof, for the TCA cycle and cellular respiration, and oxidative phosphorylation resulted in an increase in mitochondrial NADH level and in mitochondrial membrane potential and led to an increased level of ATP in neurons and astrocytes. Subsequently, these cells were protected against energy deprivation during ischemia or glutamate excitotoxicity. Provision of substrates for energy metabolism to cells with familial forms of Parkinson's disease also prevented triggering of cell death. Thus, restoration of energy metabolism and increase of ATP production can play neuroprotective role in neurodegeneration. A combination of a succinate salt of choline and nicotinamide provided the best results.

Mitochondrial Permeability Transition, Cell Death and Neurodegeneration

Neurodegenerative diseases are chronic conditions occurring when neurons die in specific brain regions that lead to loss of movement or cognitive functions. Despite the progress in understanding the mechanisms of this pathology, currently no cure exists to treat these types of diseases: for some of them the only help is alleviating the associated symptoms. Mitochondrial dysfunction has been shown to be involved in the pathogenesis of most the neurodegenerative disorders. The fast and transient permeability of mitochondria (the mitochondrial permeability transition, mPT) has been shown to be an initial step in the mechanism of apoptotic and necrotic cell death, which acts as a regulator of tissue regeneration for postmitotic neurons as it leads to the irreparable loss of cells and cell function. In this study, we review the role of the mitochondrial permeability transition in neuronal death in major neurodegenerative diseases, covering the inductors of mPTP opening in neurons, including the major ones-free radicals and calcium-and we discuss perspectives and difficulties in the development of a neuroprotective strategy based on the inhibition of mPTP in neurodegenerative disorders.

Iron Overload in Brain: Transport Mismatches, Microbleeding Events, and How Nanochelating Therapies May Counteract Their Effects

Iron overload in many brain regions is a common feature of aging and most neurodegenerative diseases. In this review, the causes, mechanisms, mathematical models, and possible therapies are summarized. Indeed, physiological and pathological conditions can be investigated using compartmental models mimicking iron trafficking across the blood-brain barrier and the Cerebrospinal Fluid-Brain exchange membranes located in the choroid plexus. In silico models can investigate the alteration of iron homeostasis and simulate iron concentration in the brain environment, as well as the effects of intracerebral iron chelation, determining potential doses and timing to recover the physiological state. Novel formulations of non-toxic nanovectors with chelating capacity are already tested in organotypic brain models and could be available to move from in silico to in vivo experiments.

Mitochondria and Brain Disease: A Comprehensive Review of Pathological Mechanisms and Therapeutic Opportunities

Mitochondria play a vital role in maintaining cellular energy homeostasis, regulating apoptosis, and controlling redox signaling. Dysfunction of mitochondria has been implicated in the pathogenesis of various brain diseases, including neurodegenerative disorders, stroke, and psychiatric illnesses. This review paper provides a comprehensive overview of the intricate relationship between mitochondria and brain disease, focusing on the underlying pathological mechanisms and exploring potential therapeutic opportunities. The review covers key topics such as mitochondrial DNA mutations, impaired oxidative phosphorylation, mitochondrial dynamics, calcium dysregulation, and reactive oxygen species generation in the context of brain disease. Additionally, it discusses emerging strategies targeting mitochondrial dysfunction, including mitochondrial protective agents, metabolic modulators, and gene therapy approaches. By critically analysing the existing literature and recent advancements, this review aims to enhance our understanding of the multifaceted role of mitochondria in brain disease and shed light on novel therapeutic interventions.

Attenuation Aβ1-42-induced neurotoxicity in neuronal cell by 660nm and 810nm LED light irradiation

Oligomeric amyloid-β 1-42 (Aβ1-42) has a close correlation with neurodegenerative disorder especially Alzheimer's disease (AD). It induces oxidative stress and mitochondrial damage in neurons. Therefore, it is used to generate AD-like in vitro model for studying neurotoxicity and neuroprotection against amyloid-β. A low-level light therapy (LLLT) is a non-invasive method that has been used to treat several neurodegenerative disorders. In this study, the red wavelength (660nm) and near infrared wavelength (810nm) at energy densities of 1, 3, and 5 J/cm2 were used to modulate biochemical processes in the neural cells. The exposure of Aβ1-42 resulted in cell death, increased intracellular reactive oxygen species (ROS), and retracted neurite outgrowth. We showed that both of LLLT wavelengths could protect neurons form Aβ1-42-induced neurotoxicity in a biphasic manner. The treatment of LLLT at 3 J/cm2 potentially alleviated cell death and recovered neurite outgrowth. In addition, the treatment of LLLT following Aβ1-42 exposure could attenuate the intracellular ROS generation and Ca2+ influx. Interestingly, both wavelengths could induce minimal level of ROS generation. However, they did not affect cell viability. In addition, LLLT also stimulated Ca2+ influx, but not altered mitochondrial membrane potential. This finding indicated LLLT may protect neurons through the stimulation of secondary signaling messengers such as ROS and Ca2+. The increase of these secondary messengers was in a functional level and did not harmful to the cells. These results suggested the use of LLLT as a tool to modulate the neuronal toxicity following Aβ1-42 accumulation in AD's brain.

Natural Products as the Potential to Improve Alzheimer's and Parkinson's Disease

Alzheimer's disease and Parkinson's disease are the two most common neurodegenerative diseases in the world, and their incidence rates are increasing as our society ages. This creates a significant social and economic burden. Although the exact cause and treatment methods for these diseases are not yet known, research suggests that Alzheimer's disease is caused by amyloid precursor protein, while α-synuclein acts as a causative agent in Parkinson's disease. The accumulation of abnormal proteins such as these can lead to symptoms such as loss of protein homeostasis, mitochondrial dysfunction, and neuroinflammation, which ultimately result in the death of nerve cells and the progression of neurodegenerative diseases. The medications currently available for these diseases only delay their progression and have many adverse effects, which has led to increased interest in developing natural products with fewer adverse effects. In this study, we selected specific keywords and thesis content to investigate natural products that are effective in treating Alzheimer's and Parkinson's diseases. We reviewed 16 papers on natural products and found that they showed promising mechanisms of action such as antioxidant, anti-inflammatory, and mitochondrial function improvement. Other natural products with similar properties could also be considered potential treatments for neurodegenerative diseases, and they can be consumed as part of a healthy diet rather than as medicine.

Melatonin as a Chronobiotic/Cytoprotective Agent in REM Sleep Behavior Disorder

Dream-enactment behavior that emerges during episodes of rapid eye movement (REM) sleep without muscle atonia is a parasomnia known as REM sleep behavior disorder (RBD). RBD constitutes a prodromal marker of α-synucleinopathies and serves as one of the best biomarkers available to predict diseases such as Parkinson disease, multiple system atrophy and dementia with Lewy bodies. Most patients showing RBD will convert to an α-synucleinopathy about 10 years after diagnosis. The diagnostic advantage of RBD relies on the prolonged prodromal time, its predictive power and the absence of disease-related treatments that could act as confounders. Therefore, patients with RBD are candidates for neuroprotection trials that delay or prevent conversion to a pathology with abnormal α-synuclein metabolism. The administration of melatonin in doses exhibiting a chronobiotic/hypnotic effect (less than 10 mg daily) is commonly used as a first line treatment (together with clonazepam) of RBD. At a higher dose, melatonin may also be an effective cytoprotector to halt α-synucleinopathy progression. However, allometric conversion doses derived from animal studies (in the 100 mg/day range) are rarely employed clinically regardless of the demonstrated absence of toxicity of melatonin in phase 1 pharmacological studies with doses up to 100 mg in normal volunteers. This review discusses the application of melatonin in RBD: (a) as a symptomatic treatment in RBD; (b) as a possible disease-modifying treatment in α-synucleinopathies. To what degree melatonin has therapeutic efficacy in the prevention of α-synucleinopathies awaits further investigation, in particular multicenter double-blind trials.

Antioxidant Compounds from Edible Mushrooms as Potential Candidates for Treating Age-Related Neurodegenerative Diseases

The last century has seen an increase in our life expectancy. As a result, various age-related diseases, such as neurodegenerative diseases (NDs), have emerged, representing new challenges to society. Oxidative stress (OS), a condition of redox imbalance resulting from excessive production of reactive oxygen species, represents a common feature that characterizes the brains of elderly people, thus contributing to NDs. Consequently, antioxidant supplementation or dietary intake of antioxidant-containing foods could represent an effective preventive and therapeutic intervention to maintain the integrity and survival of neurons and to counteract the neurodegenerative pathologies associated with aging. Food contains numerous bioactive molecules with beneficial actions for human health. To this purpose, a wide range of edible mushrooms have been reported to produce different antioxidant compounds such as phenolics, flavonoids, polysaccharides, vitamins, carotenoids, ergothioneine, and others, which might be used for dietary supplementation to enhance antioxidant defenses and, consequently, the prevention of age-related neurological diseases. In this review, we summarized the role of oxidative stress in age-related NDs, focusing on the current knowledge of the antioxidant compounds present in edible mushrooms, and highlighting their potential to preserve healthy aging by counteracting age-associated NDs.

Upregulation of RIPK1 implicates in HEK 293T cell death upon transient transfection of A53T-α-synuclein

BACKGROUND

Alpha-synuclein (α-SN) is the central protein in synucleinopathies including Parkinson's disease. Nevertheless, the molecular mechanisms through which α-SN leads to neuronal death remain unclear.

METHODS

To elucidate the relationship between α-SN and apoptosis, some indicators of the intrinsic and extrinsic apoptotic cell death were assessed in normal and a stable HEK293T cell line expressing firefly luciferase after transfection with the wild-type (WT) and A53T mutant α-SN.

RESULTS

Opposite to WT-α-SN, overexpression of A53T-α-SN resulted in enhanced expression of almost two fold for RIPK1 (93.0 %), FADD (45 %), Caspase-8, and Casp-9 activity (52.0 %) in measured time. Transfection of both WT-α-SN and A53T-α-SN showed an increase in the Casp-3/Procasp-3 ratio (WT: 60.5 %; A53T: 41.0 %), Casp-3 activity (WT: 65.0 %; A53T: 20.5 %), and a decrease in luciferase activity (WT: 50 %; A53T: 34.8 %). Overexpression of A53T-α-SN brought about with more cell death percentage compared to WT-α-SN within 36 h. No significant alteration in cytochrome c and reactive oxygen species release into cytosol were observed for both WT-α-SN and A53T-α-SN.

CONCLUSION

Altogether, these findings highlight the link between disease related mutants of α-SN (like A53T-α-SN) in triggering of RIPK1-dependent extrinsic apoptotic pathway in cell death during neurodegeneration.

Cannabinoid CB2 Receptors in Neurodegenerative Proteinopathies: New Insights and Therapeutic Potential

Some of the most prevalent neurodegenerative disorders, including Alzheimer's and Parkinson's disease, are proteinopathies characterized by the accumulation of specific protein aggregates in the brain. Such misfolded protein aggregates can trigger modulation of the innate and adaptive immune systems and subsequently lead to chronic neuroinflammation that drives the onset and progression of neurodegenerative diseases. Since there is still no effective disease-modifying treatment, new therapeutic targets for neurodegenerative proteinopathies have been sought. The endocannabinoid system, and in particular the cannabinoid CB2 receptors, have been extensively studied, due to their important role in neuroinflammation, especially in microglial cells. Several studies have shown promising effects of CB2 receptor activation on reducing protein aggregation-based pathology as well as on attenuating inflammation and several dementia-related symptoms. In this review, we discuss the available data on the role of CB2 receptors in neuroinflammation and the potential benefits and limitations of specific agonists of these receptors in the therapy of neurodegenerative proteinopathies.

Cholesterol as a key player in amyloid β-mediated toxicity in Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder that is one of the most devastating and widespread diseases worldwide, mainly affecting the aging population. One of the key factors contributing to AD-related neurotoxicity is the production and aggregation of amyloid β (Aβ). Many studies have shown the ability of Aβ to bind to the cell membrane and disrupt its structure, leading to cell death. Because amyloid damage affects different parts of the brain differently, it seems likely that not only Aβ but also the nature of the membrane interface with which the amyloid interacts, helps determine the final neurotoxic effect. Because cholesterol is the dominant component of the plasma membrane, it plays an important role in Aβ-induced toxicity. Elevated cholesterol levels and their regulation by statins have been shown to be important factors influencing the progression of neurodegeneration. However, data from many studies have shown that cholesterol has both neuroprotective and aggravating effects in relation to the development of AD. In this review, we attempt to summarize recent findings on the role of cholesterol in Aβ toxicity mediated by membrane binding in the pathogenesis of AD and to consider it in the broader context of the lipid composition of cell membranes.

Retinitis Pigmentosa: Progress in Molecular Pathology and Biotherapeutical Strategies

Retinitis pigmentosa (RP) is genetically heterogeneous retinopathy caused by photoreceptor cell death and retinal pigment epithelial atrophy that eventually results in blindness in bilateral eyes. Various photoreceptor cell death types and pathological phenotypic changes that have been disclosed in RP demand in-depth research of its pathogenic mechanism that may account for inter-patient heterogeneous responses to mainstream drug treatment. As the primary method for studying the genetic characteristics of RP, molecular biology has been widely used in disease diagnosis and clinical trials. Current technology iterations, such as gene therapy, stem cell therapy, and optogenetics, are advancing towards precise diagnosis and clinical applications. Specifically, technologies, such as effective delivery vectors, CRISPR/Cas9 technology, and iPSC-based cell transplantation, hasten the pace of personalized precision medicine in RP. The combination of conventional therapy and state-of-the-art medication is promising in revolutionizing RP treatment strategies. This article provides an overview of the latest research on the pathogenesis, diagnosis, and treatment of retinitis pigmentosa, aiming for a convenient reference of what has been achieved so far.

Dietary Plant Polyphenols as the Potential Drugs in Neurodegenerative Diseases: Current Evidence, Advances, and Opportunities

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), are characterized by the progressive degeneration of neurons. Although the etiology and pathogenesis of neurodegenerative diseases have been studied intensively, the mechanism is still in its infancy. In general, most neurodegenerative diseases share common molecular mechanisms, and multiple risks interact and promote the pathologic process of neurogenerative diseases. At present, most of the approved drugs only alleviate the clinical symptoms but fail to cure neurodegenerative diseases. Numerous studies indicate that dietary plant polyphenols are safe and exhibit potent neuroprotective effects in various neurodegenerative diseases. However, low bioavailability is the biggest obstacle for polyphenol that largely limits its adoption from evidence into clinical practice. In this review, we summarized the widely recognized mechanisms associated with neurodegenerative diseases, such as misfolded proteins, mitochondrial dysfunction, oxidative damage, and neuroinflammatory responses. In addition, we summarized the research advances about the neuroprotective effect of the most widely reported dietary plant polyphenols. Moreover, we discussed the current clinical study and application of polyphenols and the factors that result in low bioavailability, such as poor stability and low permeability across the blood-brain barrier (BBB). In the future, the improvement of absorption and stability, modification of structure and formulation, and the combination therapy will provide more opportunities from the laboratory into the clinic for polyphenols. Lastly, we hope that the present review will encourage further researches on natural dietary polyphenols in the treatment of neurodegenerative diseases.

Beta-Amyloid Instigates Dysfunction of Mitochondria in Cardiac Cells

Alzheimer's disease (AD) includes the formation of extracellular deposits comprising aggregated β-amyloid (Aβ) fibers associated with oxidative stress, inflammation, mitochondrial abnormalities, and neuronal loss. There is an associative link between AD and cardiac diseases; however, the mechanisms underlying the potential role of AD, particularly Aβ in cardiac cells, remain unknown. Here, we investigated the role of mitochondria in mediating the effects of Aβ1-40 and Aβ1-42 in cultured cardiomyocytes and primary coronary endothelial cells. Our results demonstrated that Aβ1-40 and Aβ1-42 are differently accumulated in cardiomyocytes and coronary endothelial cells. Aβ1-42 had more adverse effects than Aβ1-40 on cell viability and mitochondrial function in both types of cells. Mitochondrial and cellular ROS were significantly increased, whereas mitochondrial membrane potential and calcium retention capacity decreased in both types of cells in response to Aβ1-42. Mitochondrial dysfunction induced by Aβ was associated with apoptosis of the cells. The effects of Aβ1-42 on mitochondria and cell death were more evident in coronary endothelial cells. In addition, Aβ1-40 and Aβ1-42 significantly increased Ca2+ -induced swelling in mitochondria isolated from the intact rat hearts. In conclusion, this study demonstrates the toxic effects of Aβ on cell survival and mitochondria function in cardiac cells.

Cerebral Microstructural Alterations in Patients With Early Parkinson's Disease Detected With Quantitative Magnetic Resonance Measurements

Objective: Parkinson’s disease (PD) is the second most common neurodegenerative disease in the elderly. In early stages of PD, patients typically display normal brain magnet resonance imaging (MRI) in routine screening. Advanced imaging approaches are necessary to discriminate early PD patients from healthy controls. In this study, microstructural changes in relevant brain regions of early PD patients were investigated by using quantitative MRI methods.

Methods: Cerebral MRI at 3T was performed on 20 PD patients in early stages and 20 age and sex matched healthy controls. Brain relative proton density, T1, T2, and T2′ relaxation times were measured in 14 regions of interest (ROIs) in each hemisphere and compared between patients and controls to estimate PD related alterations.

Results: In comparison to matched healthy controls, the PD patients revealed decreased relative proton density in contralateral prefrontal subcortical area, upper and lower pons, in ipsilateral globus pallidus, and bilaterally in splenium corporis callosi, caudate nucleus, putamen, thalamus, and mesencephalon. The T1 relaxation time was increased in contralateral prefrontal subcortical area and centrum semiovale, putamen, nucleus caudatus and mesencephalon, whereas T2 relaxation time was elevated in upper pons bilaterally and in centrum semiovale ipsilaterally. T2′ relaxation time did not show significant changes.

Conclusion: Early Parkinson’s disease is associated with a distinct profile of brain microstructural changes which may relate to clinical symptoms. The quantitative MR method used in this study may be useful in early diagnosis of Parkinson’s disease. Limitations of this study include a small sample size and manual selection of the ROIs. Atlas-based or statistical mapping methods would be an alternative for an objective evaluation. More studies are necessary to validate the measurement methods for clinical use in diagnostics of early Parkinson’s disease.

Sources and triggers of oxidative damage in neurodegeneration

Neurodegeneration describes a group of more than 300 neurological diseases, characterised by neuronal loss and intra- or extracellular protein depositions, as key neuropathological features. Multiple factors play role in the pathogenesis of these group of disorders: mitochondrial dysfunction, membrane damage, calcium dyshomeostasis, metallostasis, defect clearance and renewal mechanisms, to name a few. All these factors, without exceptions, have in common the involvement of immensely increased generation of free radicals and occurrence of oxidative stress, and as a result - exhaustion of the scavenging potency of the cellular redox defence mechanisms. Besides genetic predisposition and environmental exposure to toxins, the main risk factor for developing neurodegeneration is age. And although the "Free radical theory of ageing" was declared dead, it is undisputable that accumulation of damage occurs with age, especially in systems that are regulated by free radical messengers and those that oppose oxidative stress, protein oxidation and the accuracy in protein synthesis and degradation machinery has difficulties to be maintained. This brief review provides a comprehensive summary on the main sources of free radical damage, occurring in the setting of neurodegeneration.

Amyloid Prefibrillar Oligomers: The Surprising Commonalities in Their Structure and Activity

It has been proposed that a “common core” of pathologic pathways exists for the large family of amyloid-associated neurodegenerations, including Alzheimer’s, Parkinson’s, type II diabetes and Creutzfeldt–Jacob’s Disease. Aggregates of the involved proteins, independently from their primary sequence, induced neuron membrane permeabilization able to trigger an abnormal Ca²⁺ influx leading to synaptotoxicity, resulting in reduced expression of synaptic proteins and impaired synaptic transmission. Emerging evidence is now focusing on low-molecular-weight prefibrillar oligomers (PFOs), which mimic bacterial pore-forming toxins that form well-ordered oligomeric membrane-spanning pores. At the same time, the neuron membrane composition and its chemical microenvironment seem to play a pivotal role. In fact, the brain of AD patients contains increased fractions of anionic lipids able to favor cationic influx. However, up to now the existence of a specific “common structure” of the toxic aggregate, and a “common mechanism” by which it induces neuronal damage, synaptotoxicity and impaired synaptic transmission, is still an open hypothesis. In this review, we gathered information concerning this hypothesis, focusing on the proteins linked to several amyloid diseases. We noted commonalities in their structure and membrane activity, and their ability to induce Ca²⁺ influx, neurotoxicity, synaptotoxicity and impaired synaptic transmission.

Caffeine, a natural methylxanthine nutraceutical, exerts dopaminergic neuroprotection

Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects more than 10 million people worldwide. Oxidative stress and mitochondrial dysfunction play a significant role in altering the homeostasis of energy production and free radical generation. Current PD therapies are focused on reducing the cardinal symptoms rather than preventing disease progression in the patients. Adenosine A_2A receptor (A_2A R) antagonist (Istradephylline) combined with levodopa shows a promising therapy for PD. In animal studies, caffeine administration showed to improve motor functions and neuroprotective effect in the neurons. Caffeine is probably the most extensively used psychoactive substance. In this current study, we investigated the neuroprotective effect of caffeine against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurodegeneration. Here, we demonstrate that caffeine improves behavioral and neurotransmitter recovery against MPTP-induced toxicity. Caffeine restores endogenous antioxidant levels and suppresses neuroinflammation. Our finding suggests that the blockage of A_2AR is a promising disease-modifying therapy for PD. Target engagement strategies could be more beneficial in preventing disease progression rather than symptomatic reliefs in PD patients.

On the Role of Normal Aging Processes in the Onset and Pathogenesis of Diseases Associated with the Abnormal Accumulation of Protein Aggregates

Aging is a prime systemic cause of various age-related diseases, in particular, proteinopathies. In fact, most diseases associated with protein misfolding are sporadic, and their incidence increases with aging. This review examines the process of protein aggregate formation, the toxicity of such aggregates, the organization of cellular systems involved in proteostasis, and the impact of protein aggregates on important cellular processes leading to proteinopathies. We also analyze how manifestations of aging (mitochondrial dysfunction, dysfunction of signaling systems, changes in the genome and epigenome) facilitate pathogenesis of various proteinopathies either directly, by increasing the propensity of key proteins for aggregation, or indirectly, through dysregulation of stress responses. Such analysis might help in outlining approaches for treating proteinopathies and extending healthy longevity.

Amyloids: The History of Toxicity and Functionality

Proteins can perform their specific function due to their molecular structure. Partial or complete unfolding of the polypeptide chain may lead to the misfolding and aggregation of proteins in turn, resulting in the formation of different structures such as amyloid aggregates. Amyloids are rigid protein aggregates with the cross-β structure, resistant to most solvents and proteases. Because of their resistance to proteolysis, amyloid aggregates formed in the organism accumulate in tissues, promoting the development of various diseases called amyloidosis, for instance Alzheimer's diseases (AD). According to the main hypothesis, it is considered that the cause of AD is the formation and accumulation of amyloid plaques of Aβ. That is why Aβ-amyloid is the most studied representative of amyloids. Therefore, in this review, special attention is paid to the history of Aβ-amyloid toxicity. We note the main problems with anti-amyloid therapy and write about new views on amyloids that can play positive roles in the different organisms including humans.

The Diagnostic Potential of Amyloidogenic Proteins

Neurodegenerative disorders are a highly prevalent class of diseases, whose pathological mechanisms start before the appearance of any clear symptoms. This fact has prompted scientists to search for biomarkers that could aid early treatment. These currently incurable pathologies share the presence of aberrant aggregates called amyloids in the nervous system, which are composed of specific proteins. In this review, we discuss how these proteins, their conformations and modifications could be exploited as biomarkers for diagnostic purposes. We focus on proteins that are associated with the most prevalent neurodegenerative disorders, including Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and frontotemporal dementia. We also describe current challenges in detection, the most recent techniques with diagnostic potentials and possible future developments in diagnosis.

Regulation of Mitochondrial Dynamics in Parkinson's Disease-Is 2-Methoxyestradiol a Missing Piece?

Mitochondria, as "power house of the cell", are crucial players in cell pathophysiology. Beyond adenosine triphosphate (ATP) production, they take part in a generation of reactive oxygen species (ROS), regulation of cell signaling and cell death. Dysregulation of mitochondrial dynamics may lead to cancers and neurodegeneration; however, the fusion/fission cycle allows mitochondria to adapt to metabolic needs of the cell. There are multiple data suggesting that disturbed mitochondrial homeostasis can lead to Parkinson's disease (PD) development. 2-methoxyestradiol (2-ME), metabolite of 17β-estradiol (E2) and potential anticancer agent, was demonstrated to inhibit cell growth of hippocampal HT22 cells by means of nitric oxide synthase (NOS) production and oxidative stress at both pharmacologically and also physiologically relevant concentrations. Moreover, 2-ME was suggested to inhibit mitochondrial biogenesis and to be a dynamic regulator. This review is a comprehensive discussion, from both scientific and clinical point of view, about the influence of 2-ME on mitochondria and its plausible role as a modulator of neuron survival.

Is there a link between inorganic polyphosphate (polyP), mitochondria, and neurodegeneration?

Mitochondrial dysfunction - including increased apoptosis, calcium and protein dyshomeostasis within the organelle, and dysfunctional bioenergetics and oxidative status - is a common, early feature in all the major neurodegenerative diseases, including Alzheimer's Disease (AD) and Parkinson's Disease (PD). However, the exact molecular mechanisms that drive the organelle to dysfunction and ultimately to failure in these conditions are still not well described. Different authors have shown that inorganic polyphosphate (polyP), an ancient and well-conserved molecule, plays a key role in the regulation of mitochondrial physiology under basal conditions. PolyP, which is present in all studied organisms, is composed of chains of orthophosphates linked together by highly energetic phosphoanhydride bonds, similar to those found in ATP. This polymer shows a ubiquitous distribution, even if a high co-localization with mitochondria has been reported. It has been proposed that polyP might be an alternative to ATP for cellular energy storage in different organisms, as well as the implication of polyP in the regulation of many of the mitochondrial processes affected in AD and PD, including protein and calcium homeostasis. Here, we conduct a comprehensive review and discussion of the bibliography available regarding the role of polyP in the mitochondrial dysfunction present in AD and PD. Taking into account the data presented in this review, we postulate that polyP could be a valid, innovative and, plausible pharmacological target against mitochondrial dysfunction in AD and PD. However, further research should be conducted to better understand the exact role of polyP in neurodegeneration, as well as the metabolism of the polymer, and the effect of different lengths of polyP on cellular and mitochondrial physiology.

Mitochondrial Calcium Deregulation in the Mechanism of Beta-Amyloid and Tau Pathology

Aggregation and deposition of β-amyloid and/or tau protein are the key neuropathological features in neurodegenerative disorders such as Alzheimer's disease (AD) and other tauopathies including frontotemporal dementia (FTD). The interaction between oxidative stress, mitochondrial dysfunction and the impairment of calcium ions (Ca²⁺) homeostasis induced by misfolded tau and β-amyloid plays an important role in the progressive neuronal loss occurring in specific areas of the brain. In addition to the control of bioenergetics and ROS production, mitochondria are fine regulators of the cytosolic Ca²⁺ homeostasis that induce vital signalling mechanisms in excitable cells such as neurons. Impairment in the mitochondrial Ca²⁺ uptake through the mitochondrial Ca²⁺ uniporter (MCU) or release through the Na⁺/Ca²⁺ exchanger may lead to mitochondrial Ca²⁺ overload and opening of the permeability transition pore inducing neuronal death. Recent evidence suggests an important role for these mechanisms as the underlying causes for neuronal death in β-amyloid and tau pathology. The present review will focus on the mechanisms that lead to cytosolic and especially mitochondrial Ca²⁺ disturbances occurring in AD and tau-induced FTD, and propose possible therapeutic interventions for these disorders.

Interaction of Oxidative Stress and Misfolded Proteins in the Mechanism of Neurodegeneration

Aggregation of the misfolded proteins β-amyloid, tau, huntingtin, and α-synuclein is one of the most important steps in the pathology underlying a wide spectrum of neurodegenerative disorders, including the two most common ones—Alzheimer’s and Parkinson’s disease. Activity and toxicity of these proteins depends on the stage and form of aggregates. Excessive production of free radicals, including reactive oxygen species which lead to oxidative stress, is proven to be involved in the mechanism of pathology in most of neurodegenerative disorders. Both reactive oxygen species and misfolded proteins play a physiological role in the brain, and only deregulation in redox state and aggregation of the proteins leads to pathology. Here, we review the role of misfolded proteins in the activation of ROS production from various sources in neurons and glia. We discuss if free radicals can influence structural changes of the key toxic intermediates and describe the putative mechanisms by which oxidative stress and oligomers may cause neuronal death.

Insoluble tau aggregates induce neuronal death through modification of membrane ion conductance, activation of voltage-gated calcium channels and NADPH oxidase

Most neurodegenerative disorders are associated with aggregation and accumulation of misfolded proteins. One of these proteins, tau, is involved in a number of pathologies including Alzheimer's disease and frontotemporal dementia. Aggregation and phosphorylation of tau have been shown to be a trigger for abnormal signal transduction and disruption of cellular homeostasis. Here, we have studied the effect of extracellular tau at different stages of aggregation in cortical co-cultures of neurons and astrocytes, to understand how this process affects tau pathogenicity. We found that the species formed after prolonged in vitro aggregation of tau (longer than 1 day) are able to stimulate reactive oxygen species (ROS) production through the activation of NADPH oxidase without decreasing the level of the endogenous antioxidant glutathione. The same late insoluble aggregates of tau induced calcium signals in neurons and a gradual increase in the ionic current of artificial membranes. Both tau-induced calcium signals and ROS production in NADPH oxidase were reduced in the presence of the inhibitor of voltage-gated calcium channels (VGCC) nifedipine. This suggests that insoluble aggregates of tau incorporate into the membrane and modify ionic currents, changing plasma membrane potential and activating VGCCs, which induces a calcium influx that triggers ROS production in NADPH oxidase. The combination of all these effects likely leads to toxicity, as only the same insoluble tau aggregates which demonstrated membrane-active properties produced neuronal cell death.

Increased mitochondrial calcium levels associated with neuronal death in a mouse model of Alzheimer's disease

Mitochondria contribute to shape intraneuronal Ca2+ signals. Excessive Ca2+ taken up by mitochondria could lead to cell death. Amyloid beta (Aβ) causes cytosolic Ca2+ overload, but the effects of Aβ on mitochondrial Ca2+ levels in Alzheimer's disease (AD) remain unclear. Using a ratiometric Ca2+ indicator targeted to neuronal mitochondria and intravital multiphoton microscopy, we find increased mitochondrial Ca2+ levels associated with plaque deposition and neuronal death in a transgenic mouse model of cerebral β-amyloidosis. Naturally secreted soluble Aβ applied onto the healthy brain increases Ca2+ concentration in mitochondria, which is prevented by blockage of the mitochondrial calcium uniporter. RNA-sequencing from post-mortem AD human brains shows downregulation in the expression of mitochondrial influx Ca2+ transporter genes, but upregulation in the genes related to mitochondrial Ca2+ efflux pathways, suggesting a counteracting effect to avoid Ca2+ overload. We propose lowering neuronal mitochondrial Ca2+ by inhibiting the mitochondrial Ca2+ uniporter as a novel potential therapeutic target against AD.

Acetylation of Aβ42 at Lysine 16 Disrupts Amyloid Formation

The residue lysine 28 (K28) is known to form an important salt bridge that stabilizes the Aβ amyloid structure, and acetylation of lysine 28 (K28Ac) slows the Aβ42 fibrillization rate but does not affect fibril morphology. On the other hand, acetylation of lysine 16 (K16Ac) residue greatly diminishes the fibrillization property of Aβ42 peptide and also affects its toxicity. This is due to the fact that lysine 16 acetylated amyloid beta peptide forms amorphous aggregates instead of amyloid fibrils. This is likely a result of increased hydrophobicity of the K16-A21 region due to K16 acetylation, as confirmed by molecular dynamic simulation studies. The calculated results show that the hydrophobic patches of aggregates from acetylated peptides were different when compared to wild-type (WT) peptide. K16Ac and double acetylated (KKAc) peptide aggregates show significantly higher cytotoxicity compared to the WT or K28Ac peptide aggregates alone. However, the heterogeneous mixture of WT and acetylated Aβ42 peptide aggregates exhibited higher free radical formation as well as cytotoxicity, suggesting dynamic interactions between different species could be a critical contributor to Aβ pathology.

Oxidative Stress in Neurodegenerative Diseases: From a Mitochondrial Point of View

Age is the main risk factor for a number of human diseases, including neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, which increasing numbers of elderly individuals suffer. These pathological conditions are characterized by progressive loss of neuron cells, compromised motor or cognitive functions, and accumulation of abnormally aggregated proteins. Mitochondrial dysfunction is one of the main features of the aging process, particularly in organs requiring a high-energy source such as the heart, muscles, brain, or liver. Neurons rely almost exclusively on the mitochondria, which produce the energy required for most of the cellular processes, including synaptic plasticity and neurotransmitter synthesis. The brain is particularly vulnerable to oxidative stress and damage, because of its high oxygen consumption, low antioxidant defenses, and high content of polyunsaturated fats very prone to be oxidized. Thus, it is not surprising the importance of protecting systems, including antioxidant defenses, to maintain neuronal integrity and survival. Here, we review the role of mitochondrial oxidative stress in the aging process, with a specific focus on neurodegenerative diseases. Understanding the molecular mechanisms involving mitochondria and oxidative stress in the aging and neurodegeneration may help to identify new strategies for improving the health and extending lifespan.

The effects of GSK2981710, a medium-chain triglyceride, on cognitive function in healthy older participants: A randomised, placebo-controlled study

OBJECTIVE

This double-blind, randomised, placebo-controlled, two-part study assessed the impact of GSK2981710, a medium-chain triglyceride (MCT) that liberates ketone bodies, on cognitive function, safety, and tolerability in healthy older adults.

METHODS

Part 1 was a four-period dose-selection study (n = 8 complete). Part 2 was a two-period crossover study (n = 80 complete) assessing the acute (Day 1) and prolonged (Day 15) effects of GSK2981710 on cognition and memory-related neuronal activity. Safety and tolerability of MCT supplementation were monitored in both parts of the study.

RESULTS

The most common adverse event was diarrhoea (100% and 75% of participants in Parts 1 and 2, respectively). Most adverse events were mild to moderate, and 11% participants were withdrawn due to one or more adverse events. Although GSK2981710 (30 g/day) resulted in increased peak plasma β-hydroxybutyrate (BHB) concentrations, no significant improvements in cognitive function or memory-related neuronal activity were observed.

CONCLUSION

Over a duration of 14 days, increasing plasma BHB levels with daily administration of GSK2981710 had no effects on neuronal activity or cognitive function. This result indicates that modulating plasma ketone levels with GSK2981710 may be ineffective in improving cognitive function in healthy older adults, or the lack of observed effect could be related to several factors including study population, plasma BHB concentrations, MCT composition, or treatment duration.

Calcitonin native prefibrillar oligomers but not monomers induce membrane damage that triggers NMDA-mediated Ca2+-influx, LTP impairment and neurotoxicity

Amyloid protein misfolding results in a self-assembling aggregation process, characterized by the formation of typical aggregates. The attention is focused on pre-fibrillar oligomers (PFOs), formed in the early stages and supposed to be neurotoxic. PFOs structure may change due to their instability and different experimental protocols. Consequently, it is difficult to ascertain which aggregation species are actually neurotoxic. We used salmon Calcitonin (sCT) as an amyloid model whose slow aggregation rate allowed to prepare stable samples without photochemical cross-linking. Intracellular Ca²⁺ rise plays a fundamental role in amyloid protein-induced neurodegerations. Two paradigms have been explored: (i) the "membrane permeabilization" due to the formation of amyloid pores or other types of membrane damage; (ii) "receptor-mediated" modulation of Ca²⁺ channels. In the present paper, we tested the effects of native sCT PFOs- with respect to Monomer-enriched solutions in neurons characterized by an increasing degree of differentiation, in terms of -Ca²⁺-influx, cellular viability, -Long-Term Potentiation impairment, Post-Synaptic Densities and synaptophysin expression. Results indicated that PFOs-, but not Monomer-enriched solutions, induced abnormal -Ca²⁺-influx, which could only in part be ascribed to NMDAR activation. Thus, we propose an innovative neurotoxicity mechanism for amyloid proteins where "membrane permeabilization" and "receptor-mediated" paradigms coexist.

Switching on Endogenous Metal Binding Proteins in Parkinson's Disease

The formation of cytotoxic intracellular protein aggregates is a pathological signature of multiple neurodegenerative diseases. The principle aggregating protein in Parkinson’s disease (PD) and atypical Parkinson’s diseases is α-synuclein (α-syn), which occurs in neural cytoplasmic inclusions. Several factors have been found to trigger α-syn aggregation, including raised calcium, iron, and copper. Transcriptional inducers have been explored to upregulate expression of endogenous metal-binding proteins as a potential neuroprotective strategy. The vitamin-D analogue, calcipotriol, induced increased expression of the neuronal vitamin D-dependent calcium-binding protein, calbindin-D28k, and this significantly decreased the occurrence of α-syn aggregates in cells with transiently raised intracellular free Ca, thereby increasing viability. More recently, the induction of endogenous expression of the Zn and Cu binding protein, metallothionein, by the glucocorticoid analogue, dexamethasone, gave a specific reduction in Cu-dependent α-syn aggregates. Fe accumulation has long been associated with PD. Intracellularly, Fe is regulated by interactions between the Fe storage protein ferritin and Fe transporters, such as poly(C)-binding protein 1. Analysis of the transcriptional regulation of Fe binding proteins may reveal potential inducers that could modulate Fe homoeostasis in disease. The current review highlights recent studies that suggest that transcriptional inducers may have potential as novel mechanism-based drugs against metal overload in PD.

Noxious Iron-Calcium Connections in Neurodegeneration

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

Sigma-1 Receptor Agonists Induce Oxidative Stress in Mitochondria and Enhance Complex I Activity in Physiological Condition but Protect Against Pathological Oxidative Stress

The sigma1 receptor (σ1R) is a chaperone protein residing at mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs), where it modulates Ca2+ exchange between the ER and mitochondria by interacting with inositol-1,4,5 trisphosphate receptors (IP3Rs). The σ1R is highly expressed in the central nervous system and its activation stimulates neuromodulation and neuroprotection, for instance in Alzheimer's disease (AD) models in vitro and in vivo. σ1R effects on mitochondria pathophysiology and the downstream signaling are still not fully understood. We here evaluated the impacts of σ1R ligands in mouse mitochondria preparations on reactive oxygen species (ROS) production, mitochondrial respiration, and complex activities, in physiological condition and after direct application of amyloid Aβ1-42 peptide. σ1R agonists (2-(4-morpholinethyl)-1-phenylcyclohexanecarboxylate hydrochloride (PRE-084), tetrahydro-N,N-dimethyl-5,5-diphenyl-3-furanmethanamine (ANAVEX1-41, AN1-41), (S)-1-(2,8-dimethyl-1-thia-3,8-diazaspiro[4.5]dec-3-yl)-3-(1H-indol-3-yl)propan-1-one (ANAVEX3-71, AN3-71), dehydroepiandrosterone-3 sulfate (DHEA), donepezil) increased mitochondrial ROS in a σ1R antagonist-sensitive manner but decreased Aβ1-42-induced increase in ROS. σ1R ligands (agonists or antagonists) did not impact respiration but attenuated Aβ1-42-induced alteration. σ1R agonists (PRE-084, AN1-41, tetrahydro-N,N-dimethyl-2,2-diphenyl-3-furanmethanamine hydrochloride (ANAVEX2-73, AN2-73), AN3-71) increased complex I activity, in a Ca2+-dependent and σ1R antagonist-sensitive manner. σ1R ligands failed to affect complex II, III, and IV activities. The increase in complex I activity explain the σ1R-induced increase in ROS since ligands failed to affect other sources of ROS accumulation in mitochondria and homogenates, namely NADPH oxidase (NOX) and superoxide dismutase (SOD) activities. Furthermore, Aβ1-42 significantly decreased the activity of complexes I and IV and σ1R agonists attenuated the Aβ1-42-induced complex I and IV dysfunctions. σ1R activity in mitochondria therefore results in a Ying-Yang effect, by triggering moderate ROS increase acting as a physiological signal and promoting a marked anti-oxidant effect in pathological (Aβ) conditions.

Mitochondria and aging: A role for the mitochondrial transition pore?

The cellular mechanisms responsible for aging are poorly understood. Aging is considered as a degenerative process induced by the accumulation of cellular lesions leading progressively to organ dysfunction and death. The free radical theory of aging has long been considered the most relevant to explain the mechanisms of aging. As the mitochondrion is an important source of reactive oxygen species (ROS), this organelle is regarded as a key intracellular player in this process and a large amount of data supports the role of mitochondrial ROS production during aging. Thus, mitochondrial ROS, oxidative damage, aging, and aging-dependent diseases are strongly connected. However, other features of mitochondrial physiology and dysfunction have been recently implicated in the development of the aging process. Here, we examine the potential role of the mitochondrial permeability transition pore (mPTP) in normal aging and in aging-associated diseases.

The Role of Astaxanthin on Transcriptional Regulation of NMDA Receptors Voltage Sensitive Calcium Channels and Calcium Binding Proteins in Primary Cortical Neurons

Introduction

Calcium (Ca) is the phenomenon intracellular molecule that regulate many cellular process in neurons physiologically. Calcium dysregulation may occur in neurons due to excessive synaptic release of glutamate or other reasons related with neurodegeneration. Astaxanthin is a carotenoid that has antioxidant effect in cell. The purpose of this study was to investigate whether astaxanthin affects NMDA subunits, calcium binding proteins and L Type voltage sensitive Ca-channels (LVSCC) in primary cortical neuron cultures in order to see its role in calcium metabolism.

Methods

Primary cortical neurons were prepared from embryonic day 16-Sprague Dawley rat embryos. The cultures were treated with 10 nM and 20 nM astaxanthin on day 7. NMDA subunits, LVSCC-A1C and LVSCC-A1D, calbindinD28k and parvalbumin mRNA expression levels was determined by qRT-PCR at 4, 24 and 48 hours.

Results

Our findings indicate that astaxanthin could have direct or indirect outcome on calcium homeostasis by regulating mRNA expression levels of NMDA subunits, LVSCC-A1C and LVSCC-A1D, calbindinD28k and parvalbumin by a dose and time dependent manner.

Conclusion

Neuroprotective effects of astaxanthin as a Ca homeostasis regulator should be noted throughout neurodegenerative disorders, and neurosurgery applications.

Pharmacological Sequestration of Mitochondrial Calcium Uptake Protects Neurons Against Glutamate Excitotoxicity

Neuronal excitotoxicity which is induced by exposure to excessive extracellular glutamate is shown to be involved in neuronal cell death in acute brain injury and a number of neurological diseases. High concentration of glutamate induces calcium deregulation which results in mitochondrial calcium overload and mitochondrial depolarization that triggers the mechanism of cell death. Inhibition of mitochondrial calcium uptake could be potentially neuroprotective but complete inhibition of mitochondrial calcium uniporter could result in the loss of some physiological processes linked to Ca²⁺ in mitochondria. Here, we found that a novel compound, TG-2112x, can inhibit only the lower concentrations mitochondrial calcium uptake (induced by 100 nM-5 μM) but not the uptake induced by higher concentrations of calcium (10 μM and higher). This effect was not associated with changes in mitochondrial membrane potential and cellular respiration. However, a pre-treatment of neurons with TG-2112x protected the neurons against calcium overload upon application of toxic concentrations of glutamate. Thus, sequestration of mitochondrial calcium uptake protected the neurons against glutamate-induced mitochondrial depolarization and cell death. In our hands, TG-2112x was also protective against ionomycin-induced cell death. Hence, low rate mitochondrial calcium uptake plays an underestimated role in mitochondrial function, and its inhibition could protect neurons against calcium overload and cell death in glutamate excitotoxicity.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

Bioactivity-guided isolation of neuritogenic triterpenoids from the leaves of Ilex latifolia Thunb

Ilex latifolia Thunb is a traditional Chinese tea and herbal medicine. In this study, one new triterpene saponin (1) and six known triterpenoids (2-7) were isolated from the methanol extract of I. latifolia using a PC12 cell bioassay system. The structures and stereochemistry of these compounds were elucidated using spectroscopic methods and chemical derivatization. This new triterpene saponin (1) was characterized as an ursolic type acid with a 19α-hydroxyl and a trisaccharide moiety at C-3. Compound 1 significantly promoted the neurite outgrowth in PC12 cells by 52% at 10 μM, whereas compounds 2-7 showed less neuritogenic activity. Structure activity relationship studies indicated that introducing a trisaccharide moiety at C-3 is important for the neuritogenic activity, but the sugar group at C-28 decreased this activity. In addition, compound 1 increased the neurite outgrowth length in primary cortical neuron cells of mice and also exhibited a neuronal protection effect on H₂O₂-damaged PC12 cells at optimum concentrations.

The Role of Gene Editing in Neurodegenerative Diseases

Neurodegenerative diseases (NDs), at least including Alzheimer's, Huntington's, and Parkinson's diseases, have become the most dreaded maladies because there are no precise diagnostic tools or definite treatments for these debilitating diseases. The increased prevalence and a substantial impact on the social-economic and medical care of NDs propel governments to develop policies to counteract the impact. Although the etiologies of NDs are still unknown, growing evidence suggests that genetic, cellular, and circuit alternations may cause the generation of abnormal misfolded proteins, which uncontrolledly accumulate to damage and eventually overwhelm the protein-disposal mechanisms of these neurons, leading to a common pathological feature of NDs. If the functions and the connectivity can be restored, alterations and accumulated damages may improve. The gene-editing tools including zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats-associated nucleases (CRISPR/CAS) have emerged as a novel tool not only for generating specific ND animal models for interrogating the mechanisms and screening potential drugs against NDs but also for the editing sequence-specific genes to help patients with NDs to regain function and connectivity. This review introduces the clinical manifestations of three distinct NDs and the applications of the gene-editing technology on these debilitating diseases.

Role of mitochondrial ROS in the brain: from physiology to neurodegeneration

Mitochondria are key cell organelles in that they are responsible for energy production and control many processes from signalling to cell death. The function of the mitochondrial electron transport chain is coupled with the production of reactive oxygen species (ROS) in the form of superoxide anion or hydrogen peroxide. As a result of the constant production of ROS, mitochondria are protected by highly efficient antioxidant systems. The rapidly changing levels of ROS in mitochondria, coupled with multiple essential cellular functions, make ROS apt for physiological signalling. Thus, mutations, environmental toxins and chronic ischaemic conditions could affect the mitochondrial redox balance and lead to the development of pathology. In long-living and non-mitotic cells such as neurons, oxidative stress induced by overproduction of mitochondrial ROS or impairment of the antioxidant defence results in a dysfunction of mitochondria and initiation of the cell death cascade. Mitochondrial ROS overproduction and changes in mitochondrial redox homeostasis have been shown to be involved in both a number of neurological conditions and a majority of neurodegenerative diseases. Here, we summarise the involvement of mitochondrial ROS in the mechanism of neuronal loss of major neurodegenerative disorders.

Morphological analysis of mitochondria for evaluating the toxicity of α-synuclein in transgenic mice and isolated preparations by atomic force microscopy

A key molecular event in the pathogenesis of Parkinson's disease is mitochondrial damage caused by α-synuclein (α-syn). Mitochondria mediates both necrosis and apoptosis, which are associated with morphological changes. However, the mechanism by which α-syn alters mitochondrial morphology remains unclear. To address this issue, we investigated mitochondrial permeability transition pore (mPTP) opening and changes in cardiolipin (CL) levels in mitochondria isolated from the brain of Thy1α-syn mice. Cytoplasmic cytochrome C and cleaved caspase-3 protein levels were upregulated in the brain of transgenic mice. Morphological analysis by atomic force microscopy (AFM) suggested a correlation between mitochondrial morphology and function in these animals. Incubation of isolated mitochondria with recombinant human α-synuclein N terminus (α-syn/N) decreased mitochondrial CL content. An AFM analysis showed that α-syn/N induced mitochondrial swelling and the formation of pore-like structures, which was associated with decreased mitochondrial transmembrane potential and complex I activity. The observed mitochondrial dysfunction was abrogated by treatment with the mPTP inhibitor cyclosporin A, although there was no recovery of CL content. These results provide insight into the mechanism by which α-syn/N directly undermines mitochondrial structure and function via modulation of mPTP opening and CL levels, and suggests that morphological analysis of isolated mitochondria by AFM is a useful approach for evaluating mitochondrial injury.

Mitochondrial dysfunction in Parkinsonian mesenchymal stem cells impairs differentiation

Sporadic cases account for 90–95% of all patients with Parkinson's Disease (PD). Atypical Parkinsonism comprises approximately 20% of all patients with parkinsonism. Progressive Supranuclear Palsy (PSP) belongs to the atypical parkinsonian diseases and is histopathologically classified as a tauopathy. Here, we report that mesenchymal stem cells (MSCs) derived from the bone marrow of patients with PSP exhibit mitochondrial dysfunction in the form of decreased membrane potential and inhibited NADH-dependent respiration. Furthermore, mitochondrial dysfunction in PSP-MSCs led to a significant increase in mitochondrial ROS generation and oxidative stress, which resulted in decrease of major cellular antioxidant GSH. Additionally, higher basal rate of mitochondrial degradation and lower levels of biogenesis were found in PSP-MSCs, together leading to a reduction in mitochondrial mass. This phenotype was biologically relevant to MSC stemness properties, as it heavily impaired their differentiation into adipocytes, which mostly rely on mitochondrial metabolism for their bioenergetic demand. The defect in adipogenic differentiation was detected as a significant impairment of intracellular lipid droplet formation in PSP-MSCs. This result was corroborated at the transcriptional level by a significant reduction of PPARγ and FABP4 expression, two key genes involved in the adipogenic molecular network. Our findings in PSP-MSCs provide new insights into the etiology of ‘idiopathic’ parkinsonism, and confirm that mitochondrial dysfunction is important to the development of parkinsonism, independent of the type of the cell.

•

PSP pathology leads to inhibition of mitochondrial respiration and decrease mitochondrial membrane potential.

•

Mitochondrial dysfunction in PSP-MSCs induces ROS generation and oxidative stress.

•

Higher rate of mitophagy reduces mitochondrial mass in PSP-MSCs.

•

PSP impairs differentiation properties in MSCs.

Fifty-Hertz Magnetic Field Affects the Epigenetic Modulation of the miR-34b/c in Neuronal Cells

The exposure to extremely low-frequency magnetic fields (ELF-MFs) has been associated to increased risk of neurodegenerative diseases, although the underlying molecular mechanisms are still undefined. Since epigenetic modulation has been recently encountered among the key events leading to neuronal degeneration, we here aimed at assessing if the control of gene expression mediated by miRNAs, namely miRs-34, has any roles in driving neuronal cell response to 50-Hz (1 mT) magnetic field in vitro. We demonstrate that ELF-MFs drive an early reduction of the expression level of miR-34b and miR-34c in SH-SY5Y human neuroblastoma cells, as well as in mouse primary cortical neurons, by affecting the transcription of the common pri-miR-34. This modulation is not p53 dependent, but attributable to the hyper-methylation of the CpG island mapping within the miR-34b/c promoter. Incubation with N-acetyl-l-cysteine or glutathione ethyl-ester fails to restore miR-34b/c expression, suggesting that miRs-34 are not responsive to ELF-MF-induced oxidative stress. By contrast, we show that miRs-34 control reactive oxygen species production and affect mitochondrial oxidative stress triggered by ELF-MFs, likely by modulating mitochondria-related miR-34 targets identified by in silico analysis. We finally demonstrate that ELF-MFs alter the expression of the α-synuclein, which is specifically stimulated upon ELF-MFs exposure via both direct miR-34 targeting and oxidative stress. Altogether, our data highlight the potential of the ELF-MFs to tune redox homeostasis and epigenetic control of gene expression in vitro and shed light on the possible mechanism(s) producing detrimental effects and predisposing neurons to degeneration.