Excitotoxicity Revisited: Mitochondria on the Verge of a Nervous Breakdown

The roles and mechanisms of CDGSH iron-sulfur domain 1 in kainic acid-induced mitochondrial iron overload, dysfunction and neuronal damage

Maintaining mitochondrial function plays a crucial role in preventing and treating neurodegenerative diseases. CDGSH iron-sulfur domain 1 (CISD1), a NEET family protein localized on the mitochondrial outer membrane, regulates mitochondrial iron transport. However, the precise mechanism by which CISD1 modulates mitochondrial Fe2 + remains unclear. In this study, we examine the link between aberrant iron metabolism and mitochondrial dysfunction using in vivo and in vitro excitotoxicity models. Our study also clarifies how CISD1 modulates KA-mediated excitotoxic neuronal damage. Overexpression of CISD1 reverses KA-induced mitochondrial iron overload and dysfunction. KA significantly downregulate the mitochondrial protein deacetylase SIRT1. SRT1460 (SIRT1-specific agonist) mitigates mitochondrial iron overload and restore CISD1 expression levels. Altogether, CISD1 protects against excitotoxic injury by mitigating mitochondrial iron overload, thereby providing a potential therapeutic target for neurodegenerative diseases.

Metabolic reprogramming: a new option for the treatment of spinal cord injury

Spinal cord injuries impose a notably economic burden on society, mainly because of the severe after-effects they cause. Despite the ongoing development of various therapies for spinal cord injuries, their effectiveness remains unsatisfactory. However, a deeper understanding of metabolism has opened up a new therapeutic opportunity in the form of metabolic reprogramming. In this review, we explore the metabolic changes that occur during spinal cord injuries, their consequences, and the therapeutic tools available for metabolic reprogramming. Normal spinal cord metabolism is characterized by independent cellular metabolism and intercellular metabolic coupling. However, spinal cord injury results in metabolic disorders that include disturbances in glucose metabolism, lipid metabolism, and mitochondrial dysfunction. These metabolic disturbances lead to corresponding pathological changes, including the failure of axonal regeneration, the accumulation of scarring, and the activation of microglia. To rescue spinal cord injury at the metabolic level, potential metabolic reprogramming approaches have emerged, including replenishing metabolic substrates, reconstituting metabolic couplings, and targeting mitochondrial therapies to alter cell fate. The available evidence suggests that metabolic reprogramming holds great promise as a next-generation approach for the treatment of spinal cord injury. To further advance the metabolic treatment of the spinal cord injury, future efforts should focus on a deeper understanding of neurometabolism, the development of more advanced metabolomics technologies, and the design of highly effective metabolic interventions.

Mito-Apocynin Protects Against Kainic Acid-Induced Excitotoxicity by Ameliorating Mitochondrial Impairment

Neurodegenerative diseases represent significant global health challenges, with rising incidence rates. A substantial body of evidence indicates that excitotoxicity may be a critical target in the context of these diseases. However, effective pharmacological interventions aimed at mitigating excitotoxicity remain elusive. This study aimed to elucidate the neuroprotective effects and mechanisms of the mitochondrion-targeted NOX inhibitor, mito-apocynin, in the context of kainic acid (KA)-induced excitotoxicity. Our findings demonstrate that KA disrupts mitochondrial morphology, leading to impaired energy metabolism and mitochondrial dysfunction. Western blotting experiments revealed that KA compromises mitochondrial quality control. Additionally, Nissl staining and CCK8 assays indicated that mito-apocynin (administered at 75 μg/kg in vivo and 1 μM in vitro) significantly reduced neuronal death resulting from KA-induced excitotoxic damage in both in vivo and in vitro models. Furthermore, mito-apocynin improved neurobehavioral deficits induced by KA and mitigated mitochondrial dysfunction observed in vitro. Notably, mito-apocynin significantly reversed the KA-induced increase in NOX4 levels within the striatal mitochondria, reduced the ratio of phosphorylated DRP1 (Ser616) to total DRP1, and enhanced the expression of PGC-1α, PINK1, and Parkin proteins throughout the total striatum. In summary, mito-apocynin alleviates oxidative stress, preserves normal mitochondrial function and energy metabolism, and promotes mitochondrial quality control by modulating NOX expression in mitochondria, thereby reducing KA-induced excitotoxic damage.

Danhong Injection Inhibits Apoptosis in Ischemia/Reperfusion Injury Based on Network Pharmacology Analysis, Molecular Docking, and Experimental Verification

Danhong injection (DHI), a Chinese patent compound injection, is widely used in the treatment of cardiovascular diseases (CVD) in China. However, the underlying mechanisms have not been fully elucidated. This study investigated the therapeutic effect and the underlying mechanisms of DHI against ischemia-reperfusion (I/R) injury and endothelial dysfunction (ED). Network pharmacology analysis revealed that DHI had six core active compounds (Danshensu, salvianolic acid A, salvianolic acid B, rosmarinic acid, protocatechualdehyde, and caffeic acid) and 19 potential targets in treating I/R injury. Notably, the regulation of apoptosis was significantly enriched, as indicated by the results of the gene ontology (GO) enrichment analysis. Molecular docking studies confirmed that these targets had high affinity with the active compounds of DHI. Finally, experimental validation in vivo and in vitro demonstrated that DHI could mitigate I/R injury and ED, potentially by reducing oxidative damage through the inhibition of apoptosis via the PTEN/AKT pathway. These findings significantly advance our understanding of the molecular mechanisms in DHI treatment and contribute further to promoting the clinical application of CVD.

Mitochondrial Ca2+ uniporter b (MCUb) regulates neuronal Ca2+ dynamics and resistance to ischemic stroke

Mitochondrial Ca2+ transport regulates many neuronal functions including synaptic transmission, ATP production, gene expression and neuronal survival. The mitochondrial Ca2+ uniporter (MCU) is the core molecular component of the mitochondrial Ca2+ uptake complex in the inner mitochondrial membrane. MCUb is a paralog of MCU that negatively regulates mitochondrial Ca2+ uptake in the heart and the cells of the immune system. However, the function of MCUb in the brain is largely unknown. Here, we report that MCUb knockout (KO) led to enhanced mitochondrial Ca2+ uptake in cortical neurons. By simultaneously monitoring changes in cytosolic and mitochondrial Ca2+ concentrations, [Ca2+]cyt and [Ca2+]mt, respectively, we also found that MCUb KO reduced the [Ca2+]cyt threshold required to induce mitochondrial uptake in cortical neurons during electrical stimulation. Exposure of cortical neurons to toxic concentrations of glutamate led to a collapse of mitochondrial membrane potential (ΔΨmt) and [Ca2+]cyt deregulation, and MCUb deletion accelerated the development of both events. Furthermore, using the middle cerebral artery occlusion (MCAO) as a model of transient ischemic stroke in mice, we found that MCUb KO significantly increased MCAO-induced brain damage in male, but not female mice. These results suggest that MCUb regulates neuronal Ca2+ dynamics and excitotoxicity and reveal a sex-dependent role of MCUb in controlling resistance to brain damage following ischemic stroke.

TRP Channels in Excitotoxicity

Glutamate excitotoxicity is a central mechanism contributing to cellular dysfunction and death in various neurological disorders and diseases, such as stroke, traumatic brain injury, epilepsy, schizophrenia, addiction, mood disorders, Huntington's disease, Alzheimer's disease, Parkinson's disease, multiple sclerosis, pathologic pain, and even normal aging-related changes. This detrimental effect emerges from glutamate binding to glutamate receptors, including α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, N-methyl-d-aspartate receptors, kainate receptors, and GluD receptors. Thus, excitotoxicity could be prevented by targeting glutamate receptors and their downstream signaling pathways. However, almost all the glutamate receptor antagonists failed to attenuate excitotoxicity in human patients, mainly due to the limited understanding of the underlying mechanisms regulating excitotoxicity. Transient receptor potential (TRP) channels serve as ancient cellular sensors capable of detecting and responding to both external and internal stimuli. The study of human TRP channels has flourished in recent decades since the initial discovery of mammalian TRP in 1995. These channels have been found to play pivotal roles in numerous pathologic conditions, including excitotoxicity. In this review, our focus centers on exploring the intricate interactions between TRP channels and glutamate receptors in excitotoxicity.

Discovery of HZS60 as a Novel Brain Penetrant NMDAR/TRPM4 Interaction Interface Inhibitor with Improved Activity and Pharmacokinetic Properties for the Treatment of Cerebral Ischemia

The death signaling complex comprising extrasynaptic NMDAR and TRPM4 plays a pivotal role in the pathogenesis of ischemic stroke. Targeting the protein-protein interactions between NMDAR and TRPM4 represents a promising therapeutic strategy for ischemic stroke. Herein, we describe the discovery of a novel series of NMDAR/TRPM4 interaction interface inhibitors aimed at enhancing neuroprotective efficacy and optimizing pharmacokinetic profiles. The representative compound HZS60 displayed significant neuroprotective effects against both NMDA and oxygen-glucose deprivation/reoxygenation-induced ischemic injury in primary neurons. Notably, HZS60 exhibited a favorable pharmacokinetic profile and excellent brain permeability. Furthermore, HZS60 provided effective neuroprotection following brain ischemia and reperfusion injury in vivo. Collectively, these findings underscore the potential of HZS60 as a promising candidate for the development of novel therapeutic strategies for ischemic stroke.

Impact of Oxidative Stress and Neuroinflammation on Sarco/Endoplasmic Reticulum Ca2+-ATPase 2b Downregulation and Endoplasmic Reticulum Stress in Temporal Lobe Epilepsy

Epilepsy is one of the most common neurological disorders. Calcium dysregulation and neuroinflammation are essential and common mechanisms in epileptogenesis. Sarco/endoplasmic reticulum (ER) Ca2+-ATPase 2b (SERCA2b), a crucial calcium regulatory pump, plays pathological roles in various calcium dysregulation-related diseases. However, the link between SERCA2b and neuroinflammation in epilepsy remains undetermined. This study aimed to establish the relationship between SERCA2b, oxidative stress, and neuroinflammation in epilepsy to elucidate the underlying molecular mechanism in epileptogenesis. Neuroinflammation and oxidative stress were induced in N2a cells using lipopolysaccharide (LPS) and hydrogen peroxide (H2O2). However, experimental temporal lobe epilepsy (TLE) was induced in mice using pilocarpine. Further, effects of oxidative stress and neuroinflammation on SERCA2b and ER stress markers were assessed at protein and mRNA levels. Calcium imaging was employed to determine intracellular calcium levels. SERCA2b expression significantly decreased after LPS, H2O2, and pilocarpine exposure at both mRNA and protein levels, mediated by upregulating neuroinflammation. This downregulation of SERCA2b was associated with increased production of reactive oxygen species and elevated intracellular calcium levels, leading to elevated ER stress markers. Our findings highlight a link between oxidative stress, neuroinflammation and SERCA2b in TLE. The results suggest that targeting SERCA2b could restore calcium homeostasis and ER stress processes, potentially providing a therapeutic option for TLE. This study underscores the importance of SERCA2b in the pathophysiology of epilepsy and its potential as a therapeutic target.

Endoplasmic reticulum-mitochondria lockdown in Wolfram syndrome

Wolfram syndrome (WS) is an incurable autosomal recessive disorder originally described as a mitochondriopathy. In a recent work, Liiv and colleagues found that an impaired endoplasmic reticulum (ER)-to-mitochondria calcium shuttling underlies mitochondrial dysfunction in WS models.

Current potential pathogenic mechanisms of copper-zinc superoxide dismutase 1 (SOD1) in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare neurodegenerative disease which damages upper and lower motor neurons (UMN and LMN) innervating the muscles of the trunk, extremities, head, neck and face in cerebrum, brain stem and spinal cord, which results in the progressive weakness, atrophy and fasciculation of muscle innervated by the related UMN and LMN, accompanying with the pathological signs leaded by the cortical spinal lateral tract lesion. The pathogenesis about ALS is not fully understood, and no specific drugs are available to cure and prevent the progression of this disease at present. In this review, we reviewed the structure and associated functions of copper-zinc superoxide dismutase 1 (SOD1), discuss why SOD1 is crucial to the pathogenesis of ALS, and outline the pathogenic mechanisms of SOD1 in ALS that have been identified at recent years, including glutamate-related excitotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, oxidative stress, axonal transport disruption, prion-like propagation, and the non-cytologic toxicity of glial cells. This review will help us to deeply understand the current progression in this field of SOD1 pathogenic mechanisms in ALS.

Neuroprotective gap-junction-mediated bystander transformations in the adult zebrafish spinal cord after injury

The adult zebrafish spinal cord displays an impressive innate ability to regenerate after traumatic insults, yet the underlying adaptive cellular mechanisms remain elusive. Here, we show that while the cellular and tissue responses after injury are largely conserved among vertebrates, the large-size fast spinal zebrafish motoneurons are remarkably resilient by remaining viable and functional. We also reveal the dynamic changes in motoneuron glutamatergic input, excitability, and calcium signaling, and we underscore the critical role of calretinin (CR) in binding and buffering the intracellular calcium after injury. Importantly, we demonstrate the presence and the dynamics of a neuron-to-neuron bystander neuroprotective biochemical cooperation mediated through gap junction channels. Our findings support a model in which the intimate and dynamic interplay between glutamate signaling, calcium buffering, gap junction channels, and intercellular cooperation upholds cell survival and promotes the initiation of regeneration.

Management of the Brain: Essential Oils as Promising Neuroinflammation Modulator in Neurodegenerative Diseases

Neuroinflammation, a pivotal factor in the pathogenesis of various brain disorders, including neurodegenerative diseases, has become a focal point for therapeutic exploration. This review highlights neuroinflammatory mechanisms that hallmark neurodegenerative diseases and the potential benefits of essential oils in counteracting neuroinflammation and oxidative stress, thereby offering a novel strategy for managing and mitigating the impact of various brain disorders. Essential oils, derived from aromatic plants, have emerged as versatile compounds with a myriad of health benefits. Essential oils exhibit robust antioxidant activity, serving as scavengers of free radicals and contributing to cellular defense against oxidative stress. Furthermore, essential oils showcase anti-inflammatory properties, modulating immune responses and mitigating inflammatory processes implicated in various chronic diseases. The intricate mechanisms by which essential oils and phytomolecules exert their anti-inflammatory and antioxidant effects were explored, shedding light on their multifaceted properties. Notably, we discussed their ability to modulate diverse pathways crucial in maintaining oxidative homeostasis and suppressing inflammatory responses, and their capacity to rescue cognitive deficits observed in preclinical models of neurotoxicity and neurodegenerative diseases.

Recent Developments in Coumarin Derivatives as Neuroprotective Agents

BACKGROUND

Neurodegenerative diseases are among the diseases that cause the foremost burden on the health system of the world. The diseases are multifaceted and difficult to treat because of their complex pathophysiology, which includes protein aggregation, neurotransmitter breakdown, metal dysregulation, oxidative stress, neuroinflammation, excitotoxicity, etc. None of the currently available therapies has been found to be significant in producing desired responses without any major side effects; besides, they only give symptomatic relief otherwise indicated off-episode relief. Targeting various pathways, namely choline esterase, monoamine oxidase B, cannabinoid system, metal chelation, β-secretase, oxidative stress, etc., may lead to neurodegeneration. By substituting various functional moieties over the coumarin nucleus, researchers are trying to produce safer and more effective neuroprotective agents.

OBJECTIVES

This study aimed to review the current literature to produce compounds with lower side effects using coumarin as a pharmacophore.

METHODS

In this review, we have attempted to compile various synthetic strategies that have been used to produce coumarin and various substitutional strategies used to produce neuroprotective agents from the coumarin pharmacophore. Moreover, structure-activity relationships of substituting coumarin scaffold at various positions, which could be instrumental in designing new compounds, were also discussed.

RESULTS

The literature review suggested that coumarins and their derivatives can act as neuroprotective agents following various mechanisms.

CONCLUSION

Various studies have demonstrated the neuroprotective activity of coumarin due to an oxaheterocyclic loop, which allows binding with a broad array of proteins, thus motivating researchers to explore its potential as a lead against various neurodegenerative diseases.

From diabetic hyperglycemia to cerebrovascular Damage: A narrative review

Diabetes mellitus is a globally significant disease that can lead to systemic complications, particularly vascular damage, including cardiovascular and cerebrovascular diseases of relevance. The physiological changes resulting from the imbalance in blood glucose levels play a crucial role in initiating vascular endothelial damage. Elevated glucose levels can also penetrate the central nervous system, triggering diabetic encephalopathy characterized by oxidative damage to brain components and activation of alternative and neurotoxic pathways. This brain damage increases the risk of ischemic stroke, a leading cause of mortality worldwide and a major cause of disability among surviving patients. The aim of this review is to highlight important pathways related to hyperglycemic damage that extend to the brain and result in vascular dysfunction, ultimately leading to the occurrence of a stroke. Understanding how diabetes mellitus contributes to the development of ischemic stroke and its impact on patient outcomes is crucial for implementing therapeutic strategies that reduce the incidence of diabetes mellitus and its complications, ultimately decreasing morbidity and mortality associated with the disease.

Active shrinkage protects neurons following axonal transection

Trauma, vascular events, or neurodegenerative processes can lead to axonal injury and eventual transection (axotomy). Neurons can survive axotomy, yet the underlying mechanisms are not fully understood. Excessive water entry into injured neurons poses a particular risk due to swelling and subsequent death. Using in vitro and in vivo neurotrauma model systems based on laser transection and surgical nerve cut, we demonstrated that axotomy triggers actomyosin contraction coupled with calpain activity. As a consequence, neurons shrink acutely to force water out through aquaporin channels preventing swelling and bursting. Inhibiting shrinkage increased the probability of neuronal cell death by about 3-fold. These studies reveal a previously unrecognized cytoprotective response mechanism to neurotrauma and offer a fresh perspective on pathophysiological processes in the nervous system.

Inhibiting NLRP3 inflammasome signaling pathway promotes neurological recovery following hypoxic-ischemic brain damage by increasing p97-mediated surface GluA1-containing AMPA receptors

BACKGROUND

The nucleotide-binding oligomeric domain (NOD)-like receptor protein 3 (NLRP3) inflammasome is believed to be a key mediator of neuroinflammation and subsequent secondary brain injury induced by ischemic stroke. However, the role and underlying mechanism of the NLRP3 inflammasome in neonates with hypoxic-ischemic encephalopathy (HIE) are still unclear.

METHODS

The protein expressions of the NLRP3 inflammasome including NLRP3, cysteinyl aspartate specific proteinase-1 (caspase-1) and interleukin-1β (IL-1β), the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionicacid receptor (AMPAR) subunit, and the ATPase valosin-containing protein (VCP/p97), were determined by Western blotting. The interaction between p97 and AMPA glutamate receptor 1 (GluA1) was determined by co-immunoprecipitation. The histopathological level of hypoxic-ischemic brain damage (HIBD) was determined by triphenyltetrazolium chloride (TTC) staining. Polymerase chain reaction (PCR) and Western blotting were used to confirm the genotype of the knockout mice. Motor functions, including myodynamia and coordination, were evaluated by using grasping and rotarod tests. Hippocampus-dependent spatial cognitive function was measured by using the Morris-water maze (MWM).

RESULTS

We reported that the NLRP3 inflammasome signaling pathway, such as NLRP3, caspase-1 and IL-1β, was activated in rats with HIBD and oxygen-glucose deprivation (OGD)-treated cultured primary neurons. Further studies showed that the protein level of the AMPAR GluA1 subunit on the hippocampal postsynaptic membrane was significantly decreased in rats with HIBD, and it could be restored to control levels after treatment with the specific caspase-1 inhibitor AC-YVAD-CMK. Similarly, in vitro studies showed that OGD reduced GluA1 protein levels on the plasma membrane in cultured primary neurons, whereas AC-YVAD-CMK treatment restored this reduction. Importantly, we showed that OGD treatment obviously enhanced the interaction between p97 and GluA1, while AC-YVAD-CMK treatment promoted the dissociation of p97 from the GluA1 complex and consequently facilitated the localization of GluA1 on the plasma membrane of cultured primary neurons. Finally, we reported that the deficits in motor function, learning and memory in animals with HIBD, were ameliorated by pharmacological intervention or genetic ablation of caspase-1.

CONCLUSION

Inhibiting the NLRP3 inflammasome signaling pathway promotes neurological recovery in animals with HIBD by increasing p97-mediated surface GluA1 expression, thereby providing new insight into HIE therapy.

Mitochondrial Ca2+ signaling and Alzheimer's disease: Too much or too little?

Alzheimer's disease (AD) is a neurodegenerative disease, caused by poorly known pathogenic mechanisms and aggravated by delayed therapeutic intervention, that still lacks an effective cure. However, it is clear that some important neurophysiological processes are altered years before the onset of clinical symptoms, offering the possibility of identifying biological targets useful for implementation of new therapies. Of note, evidence has been provided suggesting that mitochondria, pivotal organelles in sustaining neuronal energy demand and modulating synaptic activity, are dysfunctional in AD samples. In particular, alterations in mitochondrial Ca²⁺ signaling have been proposed as causal events for neurodegeneration, although the exact outcomes and molecular mechanisms of these defects, as well as their longitudinal progression, are not always clear. Here, we discuss the importance of a correct mitochondrial Ca²⁺ handling for neuronal physiology and summarize the latest findings on dysfunctional mitochondrial Ca²⁺ pathways in AD, analysing possible consequences contributing to the neurodegeneration that characterizes the disease.

Mitochondrial SIRT3 Deficiency Results in Neuronal Network Hyperexcitability, Accelerates Age-Related Aβ Pathology, and Renders Neurons Vulnerable to Aβ Toxicity

Aging is the major risk factor for Alzheimer's disease (AD). Mitochondrial dysfunction and neuronal network hyperexcitability are two age-related alterations implicated in AD pathogenesis. We found that levels of the mitochondrial protein deacetylase sirtuin-3 (SIRT3) are significantly reduced, and consequently mitochondria protein acetylation is increased in brain cells during aging. SIRT3-deficient mice exhibit robust mitochondrial protein hyperacetylation and reduced mitochondrial mass during aging. Moreover, SIRT3-deficient mice exhibit epileptiform and burst-firing electroencephalogram activity indicating neuronal network hyperexcitability. Both aging and SIRT3 deficiency result in increased sensitivity to kainic acid-induced seizures. Exposure of cultured cerebral cortical neurons to amyloid β-peptide (Aβ) results in a reduction in SIRT3 levels and SIRT3-deficient neurons exhibit heightened sensitivity to Aβ toxicity. Finally, SIRT3 haploinsufficiency in middle-aged App/Ps1 double mutant transgenic mice results in a significant increase in Aβ load compared with App/Ps1 double mutant mice with normal SIRT3 levels. Collectively, our findings suggest that SIRT3 plays an important role in protecting neurons against Aβ pathology and excitotoxicity.

Mitochondrial calcium cycling in neuronal function and neurodegeneration

Mitochondria are essential for proper cellular function through their critical roles in ATP synthesis, reactive oxygen species production, calcium (Ca2+) buffering, and apoptotic signaling. In neurons, Ca2+ buffering is particularly important as it helps to shape Ca2+ signals and to regulate numerous Ca2+-dependent functions including neuronal excitability, synaptic transmission, gene expression, and neuronal toxicity. Over the past decade, identification of the mitochondrial Ca2+ uniporter (MCU) and other molecular components of mitochondrial Ca2+ transport has provided insight into the roles that mitochondrial Ca2+ regulation plays in neuronal function in health and disease. In this review, we discuss the many roles of mitochondrial Ca2+ uptake and release mechanisms in normal neuronal function and highlight new insights into the Ca2+-dependent mechanisms that drive mitochondrial dysfunction in neurologic diseases including epilepsy, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. We also consider how targeting Ca2+ uptake and release mechanisms could facilitate the development of novel therapeutic strategies for neurological diseases.

Physiological roles of organelles at the pre-synapse in neurons

Mitochondria, endoplasmic reticulum and lysosomes are involved in different pathways that can regulate pre-synaptic function. In particular, they could modulate ATP availability in response to rapid changes, could control synaptic protein levels and adjust Ca²⁺ signalling, which could all impact on neuronal activity. Organelles functions in these processes need to be considered alone when describing the impact of pre-synaptic organelles on neurotransmission. However, the interplay among organelles, which occurs either via signalling pathways or through physical membranous contacts, has to be considered. In this brief review, the physiological role of organelles localized at the pre-synapse in neuronal function is discussed.

CKII Control of Axonal Plasticity Is Mediated by Mitochondrial Ca2+ via Mitochondrial NCLX

Mitochondrial Ca²⁺ efflux by NCLX is a critical rate-limiting step in mitochondria signaling. We previously showed that NCLX is phosphorylated at a putative Casein Kinase 2 (CKII) site, the serine 271 (S271). Here, we asked if NCLX is regulated by CKII and interrogated the physiological implications of this control. We found that CKII inhibitors down-regulated NCLX-dependent Ca²⁺ transport activity in SH-SY5Y neuronal cells and primary hippocampal neurons. Furthermore, we show that the CKII phosphomimetic mutants on NCLX inhibited (S271A) and constitutively activated (S271D) NCLX transport, respectively, rendering it insensitive to CKII inhibition. These phosphomimetic NCLX mutations also control the allosteric regulation of NCLX by mitochondrial membrane potential (ΔΨm). Since the omnipresent CKII is necessary for modulating the plasticity of the axon initial segment (AIS), we interrogated, in hippocampal neurons, if NCLX is required for this process. Similarly to WT neurons, NCLX-KO neurons can exhibit homeostatic plasticity following M-channel block. However, while WT neurons utilize a CKII-sensitive distal relocation of AIS Na⁺ and Kv7 channels to decrease their intrinsic excitability, we did not observe such translocation in NCLX-KO neurons. Thus, our results indicate that NCLX is regulated by CKII and is a crucial link between CKII signaling and fast neuronal plasticity.

The Emerging Roles of E3 Ligases and DUBs in Neurodegenerative Diseases

Despite annual increases in the incidence and prevalence of neurodegenerative diseases, there is a lack of effective treatment strategies. An increasing number of E3 ubiquitin ligases (E3s) and deubiquitinating enzymes (DUBs) have been observed to participate in the pathogenesis mechanisms of neurodegenerative diseases, on the basis of which we conducted a systematic literature review of the studies. This review will help to explore promising therapeutic targets from highly dynamic ubiquitination modification processes.

Astaxanthin Protection against Neuronal Excitotoxicity via Glutamate Receptor Inhibition and Improvement of Mitochondrial Function

Excitotoxicity is known to associate with neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Amyotrophic lateral sclerosis and Huntington’s disease, as well as aging, stroke, trauma, ischemia and epilepsy. Excessive release of glutamate, overactivation of glutamate receptors, calcium overload, mitochondrial dysfunction and excessive reactive oxygen species (ROS) formation are a few of the suggested key mechanisms. Astaxanthin (AST), a carotenoid, is known to act as an antioxidant and protect neurons from excitotoxic injuries. However, the exact molecular mechanism of AST neuroprotection is not clear. Thus, in this study, we investigated the role of AST in neuroprotection in excitotoxicity. We utilized primary cortical neuronal culture and live cell fluorescence imaging for the study. Our results suggest that AST prevents neuronal death, reduces ROS formation and decreases the abnormal mitochondrial membrane depolarization induced by excitotoxic glutamate insult. Additionally, AST modulates intracellular calcium levels by inhibiting peak and irreversible secondary sustained calcium levels in neurons. Furthermore, AST regulates the ionotropic glutamate subtype receptors NMDA, AMPA, KA and mitochondrial calcium. Moreover, AST decreases NMDA and AMPA receptor protein expression levels, while KA remains unaffected. Overall, our results indicate that AST protects neurons from excitotoxic neuronal injury by regulating ionotropic glutamate receptors, cytosolic secondary calcium rise and mitochondrial calcium buffering. Hence, AST could be a promising therapeutic agent against excitotoxic insults in neurodegenerative diseases.

Glutamate-Induced Deregulation of Krebs Cycle in Mitochondrial Encephalopathy Lactic Acidosis Syndrome Stroke-Like Episodes (MELAS) Syndrome Is Alleviated by Ketone Body Exposure

(1) Background: The development of mitochondrial medicine has been severely impeded by a lack of effective therapies. (2) Methods: To better understand Mitochondrial Encephalopathy Lactic Acidosis Syndrome Stroke-like episodes (MELAS) syndrome, neuronal cybrid cells carrying different mutation loads of the m.3243A > G mitochondrial DNA variant were analysed using a multi-omic approach. (3) Results: Specific metabolomic signatures revealed that the glutamate pathway was significantly increased in MELAS cells with a direct correlation between glutamate concentration and the m.3243A > G heteroplasmy level. Transcriptomic analysis in mutant cells further revealed alterations in specific gene clusters, including those of the glutamate, gamma-aminobutyric acid pathways, and tricarboxylic acid (TCA) cycle. These results were supported by post-mortem brain tissue analysis from a MELAS patient, confirming the glutamate dysregulation. Exposure of MELAS cells to ketone bodies significantly reduced the glutamate level and improved mitochondrial functions, reducing the accumulation of several intermediate metabolites of the TCA cycle and alleviating the NADH-redox imbalance. (4) Conclusions: Thus, a multi-omic integrated approach to MELAS cells revealed glutamate as a promising disease biomarker, while also indicating that a ketogenic diet should be tested in MELAS patients.

Restoration of Sarco/Endoplasmic Reticulum Ca2+-ATPase Activity Functions as a Pivotal Therapeutic Target of Anti-Glutamate-Induced Excitotoxicity to Attenuate Endoplasmic Reticulum Ca2+ Depletion

Glutamate-induced excitotoxicity is a pathological basis of many acute/chronic neurodegenerative diseases. Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2b) is a membrane-embedded P-type ATPase pump that manages the translocation of calcium ions (Ca2+) from cytosol into the lumen of the endoplasmic reticulum (ER) calcium stores. It participates in a wide range of biological functions in the central nervous system (CNS). However, the role of SERCA2b in glutamate-induced excitotoxicity and its mechanism must be elucidated. Herein, we demonstrate that SERCA2b mutants exacerbate the excitotoxicity of hypo-glutamate stimulation on HT22 cells. In this study, SERCA2b mutants accelerated Ca2+ depletion through loss-of-function (reduced pumping capacity) or gain-of-function (acquired leakage), resulting in ER stress. In addition, the occurrence of ER Ca2+ depletion increased mitochondria-associated membrane formation, which led to mitochondrial Ca2+ overload and dysfunction. Moreover, the enhancement of SERCA2b pumping capacity or inhibition of Ca2+ leakage attenuated Ca2+ depletion and impeded excitotoxicity in response to hypo-glutamate stimulation. In conclusion, SERCA2b mutants exacerbate ER Ca2+-depletion-mediated excitotoxicity in glutamate-sensitive HT22 cells. The mechanism of disruption is mainly related to the heterogeneity of SERCA2b mutation sites. Stabilization of SRECA2b function is a critical therapeutic approach against glutamate-induced excitotoxicity. These data will expand understanding of organelle regulatory networks and facilitate the discovery and creation of drugs against excitatory/inhibitory imbalance in the CNS.

Uncontrolled mitochondrial calcium uptake underlies the pathogenesis of neurodegeneration in MICU1-deficient mice and patients

Dysregulation of mitochondrial Ca²⁺ homeostasis has been linked to neurodegenerative diseases. Mitochondrial Ca²⁺ uptake is mediated via the calcium uniporter complex that is primarily regulated by MICU1, a Ca²⁺-sensing gatekeeper. Recently, human patients with MICU1 loss-of-function mutations were diagnosed with neuromuscular and cognitive impairments. While studies in patient-derived cells revealed altered mitochondrial calcium signaling, the neuronal pathogenesis was difficult to study. To fill this void, we created a neuron-specific MICU1-KO mouse model. These animals show progressive, abnormal motor and cognitive phenotypes likely caused by the degeneration of motor neurons in the spinal cord and the cortex. We found increased susceptibility to mitochondrial Ca²⁺ overload-induced excitotoxic insults and cell death in MICU1-KO neurons and MICU1-deficient patient-derived cells, which can be blunted by inhibiting the mitochondrial permeability transition pore. Thus, our study identifies altered neuronal mitochondrial Ca²⁺ homeostasis as causative in the clinical symptoms of MICU1-deficient patients and highlights potential therapeutic targets.

Calcium Permeable-AMPA Receptors and Excitotoxicity in Neurological Disorders

Excitotoxicity is one of the primary mechanisms of cell loss in a variety of diseases of the central and peripheral nervous systems. Other than the previously established signaling pathways of excitotoxicity, which depend on the excessive release of glutamate from axon terminals or over-activation of NMDA receptors (NMDARs), Ca²⁺ influx-triggered excitotoxicity through Ca²⁺-permeable (CP)-AMPA receptors (AMPARs) is detected in multiple disease models. In this review, both acute brain insults (e.g., brain trauma or spinal cord injury, ischemia) and chronic neurological disorders, including Epilepsy/Seizures, Huntington’s disease (HD), Parkinson’s disease (PD), Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), chronic pain, and glaucoma, are discussed regarding the CP-AMPAR-mediated excitotoxicity. Considering the low expression or absence of CP-AMPARs in most cells, specific manipulation of the CP-AMPARs might be a more plausible strategy to delay the onset and progression of pathological alterations with fewer side effects than blocking NMDARs.

Effects of Mild Excitotoxic Stimulus on Mitochondria Ca2+ Handling in Hippocampal Cultures of a Mouse Model of Alzheimer's Disease

In Alzheimer’s disease (AD), the molecular mechanisms involved in the neurodegeneration are still incompletely defined, though this aspect is crucial for a better understanding of the malady and for devising effective therapies. Mitochondrial dysfunctions and altered Ca²⁺ signaling have long been implicated in AD, though it is debated whether these events occur early in the course of the pathology, or whether they develop at late stages of the disease and represent consequences of different alterations. Mitochondria are central to many aspects of cellular metabolism providing energy, lipids, reactive oxygen species, signaling molecules for cellular quality control, and actively shaping intracellular Ca²⁺ signaling, modulating the intensity and duration of the signal itself. Abnormalities in the ability of mitochondria to take up and subsequently release Ca²⁺ could lead to changes in the metabolism of the organelle, and of the cell as a whole, that eventually result in cell death. We sought to investigate the role of mitochondria and Ca²⁺ signaling in a model of Familial Alzheimer’s disease and found early alterations in mitochondria physiology under stressful condition, namely, reduced maximal respiration, decreased ability to sustain membrane potential, and a slower return to basal matrix Ca²⁺ levels after a mild excitotoxic stimulus. Treatment with an inhibitor of the permeability transition pore attenuated some of these mitochondrial disfunctions and may represent a promising tool to ameliorate mitochondria and cellular functioning in AD and prevent or slow down cell loss in the disease.