Mitochondrial calcium handling during ischemia-induced cell death in neurons

The agreement between jugular bulb and cerebrospinal fluid lactate levels in patients with out-of-hospital cardiac arrest

We investigated the agreement between the jugular bulb (JB) and cerebrospinal fluid (CSF) lactate levels. The study was conducted from July 2021 to June 2023 as a prospective observational cohort study at a single center. The right jugular vein was accessed, and the placement of JB catheter tip was confirmed using lateral cervical spine X-ray. A lumbar catheter was inserted between the 3rd and 4th lumbar spine of the patient. Lactate levels were measured immediately, 24 h, 48 h, and 72 h after ROSC. In patients with a good neurological prognosis, kappa between JB and CSF lactate levels measured immediately, at 24 h, 48 h, and 72 h after ROSC were 0.08, 0.36, 0.14, - 0.05 (p = 0.65, 0.06, 0.48, and 0.75, respectively). However, in patients with a poor neurological prognosis, kappa between JB and CSF lactate levels measured immediately, at 24 h, 48 h, and 72 h after ROSC were 0.38, 0.21, 0.22, 0.12 (p = 0.001, 0.04, 0.04, and 0.27, respectively). This study demonstrated that JB lactate levels exhibited significant agreement with arterial lactate levels, compared to CSF lactate levels. Therefore, this should be considered when using JB lactate to monitor cerebral metabolism.

Research progress of mitophagy in chronic cerebral ischemia

Chronic cerebral ischemia (CCI), a condition that can result in headaches, dizziness, cognitive decline, and stroke, is caused by a sustained decrease in cerebral blood flow. Statistics show that 70% of patients with CCI are aged > 80 years and approximately 30% are 45-50 years. The incidence of CCI tends to be lower, and treatment for CCI is urgent. Studies have confirmed that CCI can activate the corresponding mechanisms that lead to mitochondrial dysfunction, which, in turn, can induce mitophagy to maintain mitochondrial homeostasis. Simultaneously, mitochondrial dysfunction can aggravate the insufficient energy supply to cells and various diseases caused by CCI. Regulation of mitophagy has become a promising therapeutic target for the treatment of CCI. This article reviews the latest progress in the important role of mitophagy in CCI and discusses the induction pathways of mitophagy in CCI, including ATP synthesis disorder, oxidative stress injury, induction of reactive oxygen species, and Ca2+ homeostasis disorder, as well as the role of drugs in CCI by regulating mitophagy.

Postoperative Delirium in Neurosurgical Patients: Recent Insights into the Pathogenesis

Postoperative delirium (POD) is a complication characterized by disturbances in attention, awareness, and cognitive function that occur shortly after surgery or emergence from anesthesia. Since it occurs prevalently in neurosurgical patients and poses great threats to the well-being of patients, much emphasis is placed on POD in neurosurgical units. However, there are intricate theories about its pathogenesis and limited pharmacological interventions for POD. In this study, we review the recent insights into its pathogenesis, mainly based on studies within five years, and the five dominant pathological theories that account for the development of POD, with the intention of furthering our understanding and boosting its clinical management.

Protective Effects of Nuciferine in Middle Cerebral Artery Occlusion Rats Based on Transcriptomics

Middle cerebral artery occlusion (MCAO), with the characteristics of high morbidity, high recurrence rate, high mortality, and disability rate, is a typical manifestation of ischemic stroke and has become a hot research topic in the clinical field. The protective effects of nuciferine on brain injury MCAO rats were investigated and its mechanisms of actions were revealed. The MCAO rats were established by the suture method. The pathological staining of the rat brain was processed and observed, the pharmacodynamics assay of nuciferine were studied, and the gene expression regulation by nuciferine was detected by transcriptome technology. The results showed that nuciferine significantly alleviated brain damage in MCAO rats, and the transcriptomic results suggested that nuciferine could exert therapeutic effects through the regulation of lipid metabolism, including arachidonic acid metabolism, sphingolipid metabolism, the PPAR signaling pathway and other related pathways. This finding provided new perspectives on the treatment of MCAO with nuciferine and facilitates the development of novel drugs for this disease.

Melatonin-Induced Postconditioning Suppresses NMDA Receptor through Opening of the Mitochondrial Permeability Transition Pore via Melatonin Receptor in Mouse Neurons

Mitochondrial membrane potential regulation through the mitochondrial permeability transition pore (mPTP) is reportedly involved in the ischemic postconditioning (PostC) phenomenon. Melatonin is an endogenous hormone that regulates circadian rhythms. Its neuroprotective effects via mitochondrial melatonin receptors (MTs) have recently attracted attention. However, details of the neuroprotective mechanisms associated with PostC have not been clarified. Using hippocampal CA1 pyramidal cells from C57BL mice, we studied the involvement of MTs and the mPTP in melatonin-induced PostC mechanisms similar to those of ischemic PostC. We measured changes in spontaneous excitatory postsynaptic currents (sEPSCs), intracellular calcium concentration, mitochondrial membrane potential, and N-methyl-D-aspartate receptor (NMDAR) currents after ischemic challenge, using the whole-cell patch-clamp technique. Melatonin significantly suppressed increases in sEPSCs and intracellular calcium concentrations. The NMDAR currents were significantly suppressed by melatonin and the MT agonist, ramelteon. However, this suppressive effect was abolished by the mPTP inhibitor, cyclosporine A, and the MT antagonist, luzindole. Furthermore, both melatonin and ramelteon potentiated depolarization of mitochondrial membrane potentials, and luzindole suppressed depolarization of mitochondrial membrane potentials. This study suggests that melatonin-induced PostC via MTs suppressed the NMDAR that was induced by partial depolarization of mitochondrial membrane potential by opening the mPTP, reducing excessive release of glutamate and inducing neuroprotection against ischemia-reperfusion injury.

Mitochondrial Calcium Signaling in Pancreatic β-Cell

Accumulation of calcium in energized mitochondria of pancreatic β-cells is emerging as a crucial process for pancreatic β-cell function. β-cell mitochondria sense and shape calcium signals, linking the metabolism of glucose and other secretagogues to the generation of signals that promote insulin secretion during nutrient stimulation. Here, we describe the role of mitochondrial calcium signaling in pancreatic β-cell function. We report the latest pharmacological and genetic findings, including the first mitochondrial calcium-targeted intervention strategies developed to modulate pancreatic β-cell function and their potential relevance in the context of diabetes.

Investigation of brain damage mechanism in middle cerebral artery occlusion/reperfusion rats based on i-TRAQ quantitative proteomics

The objective of this study is to analyze the differential protein expression profile in cerebral cortex of rats with middle cerebral ischemia/reperfusion (MCAO/R), explore the brain damage mechanism of MCAO/R at protein level, and provide experimental foundation for searching specific marker proteins of MCAO/R. Rat model of MCAO/R was established by modified suture-occluded method, and the model was evaluated by the results of brain 2,3,5-triphenyltetrazolium chloride (TTC) and hematoxylin-eosin (HE) staining. Cerebral cortex of rats from sham-operated group (Sham) and MCAO/R groups was used for FASP enzymatic hydrolysis, i-TRAQ quantitative labeling, and reverse-phase liquid chromatography purification and separation. Orbitrap Q Exactive mass spectrometry was used for qualitative and quantitative analyses of total differential protein expression profiles. MCAO/R rats had obvious cerebral infarction lesions, and the relative surface area of cerebral infarction was significantly different compared with sham rats, suggesting that MCAO/R rat model was successfully prepared. There were 199 significant difference proteins (MCAO/R vs Sham, p < 0.05, |fold change|> 1.2), including 104 up-regulated proteins and 95 down-regulated proteins. Gene ontology (GO) enrichment analysis showed that the up-regulated proteins were mainly concentrated in the biological processes of positive regulation of NF-κB transcription and I-κB kinase-NF-κB, etc. Down-regulated proteins were mainly concentrated in long-term synaptic potentiation, cellular response to DNA damage stimulus, etc. KEGG pathway analysis showed that the pathway involved in differential proteins includes oxidative phosphorylation, metabolic pathway, and Ras signaling pathway. Network analysis of differential proteins showed that Alb, ndufb5, ndufs7, ApoB, Cdc42, Ndufa3, Igf1r, P4hb, Mbp, Gc, Nme1, Akt2, and other proteins may play an important role in regulating oxidative stress, apoptosis, and inflammatory response in MCAO/R. Quantitative proteomics based on i-TRAQ labeling reveals the effect of inflammation and apoptosis in brain damage mechanism of MCAO/R. Besides, this research provide some experimental foundation for search and determination of potential therapeutic targets of MCAO/R.

Protection against acute cerebral ischemia/reperfusion injury by Leonuri Herba Total Alkali via modulation of BDNF-TrKB-PI3K/Akt signaling pathway in rats

OBJECTIVE

To observe the brain protective effect of Leonuri Herba Total Alkali (LHA) on cerebral ischemia reperfusion injury in rats, so as to provide basis for clinical research.

METHODS

Adult male SD rats were randomly assigned into sham group, middle cerebral artery occlusion/reperfusion (MCAO/R) group, and LHA + MCAO/R group (25 mg/kg, 50 mg/kg, and 100 mg/kg). Fourteen days before MCAO/R surgery, the rats in treatment groups were orally administered with LHA in ultrapure water once daily for 14 days, while rats in the sham and MCAO groups were given the same amount of saline in advance. After 1 h of administration on the 14th day, MCAO surgery was subjected. The neurological deficits, brain infarct volume, histopathology, immunofluorescence, inflammation indicators and the gene/protein expressions of BDNF-TrKB-PI3K/Akt signaling pathway in the rat brain tissue were evaluated 24 h after the MCAO/R-injury.

RESULTS

It was found that rats in LHA pre-administration group showed significantly reduced neurological deficit scores, infarction volume, the serum levels of NSE and S100β. Meanwhile, the content of Evans Blue (EB) in brain tissue from LHA group was decreased, as well as the levels of inflammatory cytokines and their gene levels. Moreover, LHA pre-administration inhibited the expression of CD44, GFAP, FOXO1 and promoted the expression of BDNF and NeuN. In addition, LHA pre-administration could up-regulate the protein expression of TrkB, p-PI3K, p-Akt, Bcl-2, and down-regulate the protein expression of Bax, and increase the level of Bcl-2/Bax.

CONCLUSIONS

The study demonstrated that LHA pre-administration could regulate the PI3K/Akt pathway by increasing BDNF levels, and play a neuroprotective role in cerebral ischemia-reperfusion injury.

Ischemic Stroke Risk Associated with Mitochondrial Haplogroup F in the Asian Population

Mitochondrial dysfunction is involved in the pathogenesis of atherosclerosis, the primary risk factor for ischemic stroke. This study aims to explore the role of mitochondrial genomic variations in ischemic stroke, and to uncover the nuclear genes involved in this relationship. Eight hundred and thirty Taiwanese patients with a history of ischemic stroke and 966 normal controls were genotyped for their mitochondrial haplogroup (Mthapg). Cytoplasmic hybrid cells (cybrids) harboring different Mthapgs were used to observe functional differences under hypoxia-ischemia. RNA sequencing (RNASeq) was conducted to identify the particularly elevated mRNA. The patient study identified an association between Mthapg F1 and risk of ischemic stroke (OR 1.72:1.27-2.34, p = 0.001). The cellular study further demonstrated an impeded induction of hypoxic inducible factor 1α in the Mthapg F1 cybrid after hypoxia-ischemia. Additionally, the study demonstrated that Mthapg F cybrids were associated with an altered mitochondrial function, including decreased oxygen consumption, higher mitochondrial ROS production, and lower mitochondrial membrane potential. Mthapg F cybrids were also noted to be prone to inflammation, with increased expression of several inflammatory cytokines and elevated matrix metalloproteinase 9. The RNASeq identified significantly elevated expressions of angiopoietin-like 4 in Mthapg F1 cybrids after hypoxia-ischemia. Our study demonstrates an association between Mthapg F and susceptibility to ischemic stroke.

Sex Differences in Ischemia/Reperfusion Injury: The Role of Mitochondrial Permeability Transition

Brain and heart ischemia are among the leading causes of death and disability in both men and women, but there are significant sex differences in the incidence and severity of these diseases. Ca²⁺ dysregulation in response to ischemia/reperfusion injury (I/RI) is a well-recognized pathogenic mechanism leading to the death of affected cells. Excess intracellular Ca²⁺ causes mitochondrial matrix Ca²⁺ overload that can result in mitochondrial permeability transition (MPT), which can have severe consequences for mitochondrial function and trigger cell death. Recent findings indicate that estrogens and their related receptors are involved in the regulation of MPT, suggesting that sex differences in I/RI could be linked to estrogen-dependent modulation of mitochondrial Ca²⁺. Here, we review the evidence supporting sex differences in I/RI and the role of estrogen and estrogen receptors in producing these differences, the involvement of mitochondrial Ca²⁺ overload in disease pathogenesis, and the estrogen-dependent modulation of MPT that may contribute to sex differences.

Calcium phosphate buffer formed in the mitochondrial matrix during preconditioning supports ΔpH formation and ischemic ATP production and prolongs cell survival -A hypothesis

Ischemic preconditioning makes cells less sensitive to oxygen deprivation. A similar effect can be achieved by increasing the calcium concentration and applying potassium channel openers. A hypothetical mechanism of preconditioning is presented. In the mitochondrial matrix, there is a calcium hydroxide buffer consisting of a few insoluble calcium phosphate minerals. During ischemia, calcium ions stored in the matrix buffer start to leak out, forming an electric potential difference, while hydroxyl ions remain in the matrix, maintaining its pH and the matrix volume. Preconditioning factors increase the matrix buffer capacity. Production of ATP during ischemia might be the relic of a pre-endosymbiotic past.

Resveratrol provides neuroprotection by regulating the JAK2/STAT3/PI3K/AKT/mTOR pathway after stroke in rats

Ischemic stroke is a common disease with high mortality and morbidity worldwide. One of the important pathophysiological effects of ischemic stroke is apoptosis. A neuroprotective effect is defined as the inhibition of neuronal apoptosis to rescue or delay the infarction in the surviving ischemic penumbra. Resveratrol is a natural polyphenol that reportedly prevents cerebral ischemia injury by regulating the expression of PI3K/AKT/mTOR. Therefore, this study aimed to elucidate the neuroprotective effect of resveratrol on cerebral ischemia/reperfusion injury and to investigate the signaling pathways and mechanisms through which resveratrol regulates apoptosis in the ischemic penumbra. Rats were subjected to middle cerebral artery occlusion for 2 h followed by 24 h reperfusion. Cerebral infarct volume was measured using 2% TTC staining. TUNEL staining was conducted to evaluate neuronal apoptosis. Western blotting and immunohistochemistry were used to detect the proteins involved in the JAK2/STAT3/PI3K/AKT/mTOR pathway. The results suggested that resveratrol significantly improved neurological function, reduced cerebral infarct volume, decreased neuronal damage, and markedly attenuated neuronal apoptosis; these effects were attenuated by the inhibition of PI3K/AKT with LY294002 and JAK2/STAT3 with AG490. We also found that resveratrol significantly upregulated the expression of p-JAK2, p-STAT3, p-AKT, p-mTOR, and BCL-2 and downregulated expression of cleaved caspase-3 and BAX, which was partially reversed by LY294002 and AG490. These results suggested that resveratrol provides a neuroprotective effect against cerebral ischemia/reperfusion injury, which is partially mediated by the activation of JAK2/STAT3 and PI3K/AKT/mTOR. Resveratrol may indirectly upregulate the PI3K/AKT/mTOR pathway by activating JAK2/STAT3.

Estrogen receptor beta modulates permeability transition in brain mitochondria

Recent evidence highlights a role for sex and hormonal status in regulating cellular responses to ischemic brain injury and neurodegeneration. A key pathological event in ischemic brain injury is the opening of a mitochondrial permeability transition pore (MPT) induced by excitotoxic calcium levels, which can trigger irreversible damage to mitochondria accompanied by the release of pro-apoptotic factors. However, sex differences in brain MPT modulation have not yet been explored. Here, we show that mitochondria isolated from female mouse forebrain have a lower calcium threshold for MPT than male mitochondria, and that this sex difference depends on the MPT regulator cyclophilin D (CypD). We also demonstrate that an estrogen receptor beta (ERβ) antagonist inhibits MPT and knockout of ERβ decreases the sensitivity of mitochondria to the CypD inhibitor, cyclosporine A. These results suggest a functional relationship between ERβ and CypD in modulating brain MPT. Moreover, co-immunoprecipitation studies identify several ERβ binding partners in mitochondria. Among these, we investigate the mitochondrial ATPase as a putative site of MPT regulation by ERβ. We find that previously described interaction between the oligomycin sensitivity-conferring subunit of ATPase (OSCP) and CypD is decreased by ERβ knockout, suggesting that ERβ modulates MPT by regulating CypD interaction with OSCP. Functionally, in primary neurons and hippocampal slice cultures, modulation of ERβ has protective effects against glutamate toxicity and oxygen glucose deprivation, respectively. Taken together, these results reveal a novel pathway of brain MPT regulation by ERβ that could contribute to sex differences in ischemic brain injury and neurodegeneration.

Imaging of Mitochondrial and Cytosolic Ca2+ Signals in Cultured Astrocytes

This unit provides a step-by-step protocol for constructing cell type- and mitochondria-targeted GCaMP genetically encoded Ca²⁺ indicators (GECIs) for mitochondrial Ca²⁺ imaging in astrocytes. Mitochondrial Ca²⁺ plays a critical role in controlling cytosolic Ca²⁺ buffering, energy metabolism, and cellular signal transduction. Mitochondrial Ca²⁺ overload contributes to various pathological conditions, including neurodegeneration and apoptotic cell death in neurological diseases. Live-cell mitochondrial Ca²⁺ imaging is an important approach to understand mitochondrial Ca²⁺ dynamics and thus cell physiology and pathology. We implement astrocyte-specific mitochondrial targeting of GCaMP5G/6s (mito-GCaMP5G/6s). By loading X-Rhod-1 into astrocytes, we can simultaneously image mitochondrial and cytosolic Ca²⁺ signals. This protocol provides a novel approach to image mitochondrial Ca²⁺ dynamics as well as Ca²⁺ interplay between the endoplasmic reticulum and mitochondria. © 2018 by John Wiley & Sons, Inc.

Tissue- and Condition-Specific Isoforms of Mammalian Cytochrome c Oxidase Subunits: From Function to Human Disease

Cytochrome c oxidase (COX) is the terminal enzyme of the electron transport chain and catalyzes the transfer of electrons from cytochrome c to oxygen. COX consists of 14 subunits, three and eleven encoded, respectively, by the mitochondrial and nuclear DNA. Tissue- and condition-specific isoforms have only been reported for COX but not for the other oxidative phosphorylation complexes, suggesting a fundamental requirement to fine-tune and regulate the essentially irreversible reaction catalyzed by COX. This article briefly discusses the assembly of COX in mammals and then reviews the functions of the six nuclear-encoded COX subunits that are expressed as isoforms in specialized tissues including those of the liver, heart and skeletal muscle, lung, and testes: COX IV-1, COX IV-2, NDUFA4, NDUFA4L2, COX VIaL, COX VIaH, COX VIb-1, COX VIb-2, COX VIIaH, COX VIIaL, COX VIIaR, COX VIIIH/L, and COX VIII-3. We propose a model in which the isoforms mediate the interconnected regulation of COX by (1) adjusting basal enzyme activity to mitochondrial capacity of a given tissue; (2) allosteric regulation to adjust energy production to need; (3) altering proton pumping efficiency under certain conditions, contributing to thermogenesis; (4) providing a platform for tissue-specific signaling; (5) stabilizing the COX dimer; and (6) modulating supercomplex formation.

Spatiotemporal expression of osteopontin in the striatum of rats subjected to the mitochondrial toxin 3-nitropropionic acid correlates with microcalcification

Our aim was to elucidate whether osteopontin (OPN) is involved in the onset of mineralisation and progression of extracellular calcification in striatal lesions due to mitochondrial toxin 3-nitropropionic acid exposure. OPN expression had two different patterns when observed using light microscopy. It was either localised to the Golgi complex in brain macrophages or had a small granular pattern scattered in the affected striatum. OPN labelling tended to increase in number and size over a 2-week period following the lesion. Ultrastructural investigations revealed that OPN is initially localised to degenerating mitochondria within distal dendrites, which were then progressively surrounded by profuse OPN on days 7–14. Electron probe microanalysis of OPN-positive and calcium-fixated neurites indicated that OPN accumulates selectively on the surfaces of degenerating calcifying dendrites, possibly via interactions between OPN and calcium. In addition, 3-dimensional reconstruction of OPN-positive neurites revealed that they are in direct contact with larger OPN-negative degenerating dendrites rather than with fragmented cell debris. Our overall results indicate that OPN expression is likely to correlate with the spatiotemporal progression of calcification in the affected striatum, and raise the possibility that OPN may play an important role in the initiation and progression of microcalcification in response to brain insults.

Quercetin ameliorates ischemia/reperfusion-induced cognitive deficits by inhibiting ASK1/JNK3/caspase-3 by enhancing the Akt signaling pathway

Cerebral ischemia/reperfusion (I/R) is a major cause of severe disability and death all worldwide. However, therapeutic options to minimize the detrimental effects of cerebral I/R injury are limited. Recent research has demonstrated that quercetin mediates neuroprotective effects associated with the activation of the Akt signaling pathway in the cerebral I/R brain. Therefore, the aim of this study was to further investigate the mechanisms of cognitive deficits induced by cerebral I/R injury and the effects of quercetin on these mechanisms. First, we assessed anxiety-like behavioral and cognitive impairment using the open field test and the Morris water maze test, respectively. Next, we examined the severity of apoptosis by staining hippocampal neurons by the Cresyl violet method. Third, we used western blot analysis to investigate the expression of total and phosphorylated Akt, ASK1, JNK3, c-Jun and caspase-3 after I/R injury. Our results revealed that mice subjected to bilateral common carotid occlusion exhibited severe anxiety-like behavior, learning and memory impairment, cell damage and apoptosis. These severe effects were attenuated by administration of quercetin. Further, western blot analysis revealed that quercetin increased p-Akt expression and decreased p-ASK1, p-JNK3 and cleaved caspase-3 expression after cerebral I/R injury and led to inhibition of neuronal apoptosis. Conversely, treatment with LY294002 (a selective inhibitor of Akt1) reversed the effects of quercetin. In conclusion, these findings highlight the important role of quercetin in protecting against cognitive deficits and inhibiting neuronal apoptosis via the Akt signaling pathway. We believe that quercetin might prove to be a useful therapeutic component in treating cerebral I/R diseases in the near future.

PI3K/Akt pathway contributes to neuroprotective effect of Tongxinluo against focal cerebral ischemia and reperfusion injury in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Tongxinluo (TXL), a compound prescription, is formulated according to the collateral disease doctrine of traditional Chinese medicine, and is widely used for the treatment of cardio-cerebrovascular diseases in China.

AIM OF THE STUDY

We aimed to investigate the neuroprotective effect of TXL on focal cerebral ischemia and reperfusion injury in rats by attenuating its brain damage and neuronal apoptosis, and to assess the potential role of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway in this protection.

MATERIALS AND METHODS

Adult Male Sprague-Dawley rats (n=120) were randomly divided into 5 groups: sham, cerebral ischemia and reperfusion (I/R), cerebral ischemia and reperfusion plus TXL (1.6g/kg/day) (TXL1.6), TXL1.6 plus LY294002 and dimethyl sulfoxide (DMSO) (TXL1.6+LY294002), TXL1.6 plus DMSO (TXL1.6+vehicle). Prior to the grouping, TXL1.6 was selected to be the optimal dose of TXL by evaluating the neurological deficits score of five group rats (Sham, I/R, TXL0.4, TXL0.8 and TXL1.6, n=30) at 0, 1, 3, 5, and 7 days after reperfusion. Rats, being subjected to middle cerebral artery occlusion (MCAO) for 90min followed by 24h reperfusion, were the cerebral ischemia/reperfusion models. At 24h after reperfusion, cerebral infarct area was measured via tetrazolium staining and neuronal damage was showed by Nissl staining. The double staining of Terminal deoxynucleotidyl transferase-mediated deoxyuridine 5-triphosphate nick end labeling (TUNEL) staining and immunofluorescence labeling with NeuN, was performed to evaluate neuronal apoptosis. Proteins involved in PI3K/Akt pathway were detected by Western blot.

RESULTS

The results showed that TXL markedly improved neurological function, reduced cerebral infarct area, decreased neuronal damage, and significantly attenuated neuronal apoptosis, while these effects were eliminated by inhibition of PI3K/Akt with LY294002. We also found that TXL up-regulated the expression levels of p-PDK1, p-Akt, p-c-Raf, p-BAD and down-regulated Cleaved caspase 3 expression notably, which were partially reversed by LY294002. Additionally, the increment of p-PTEN level on which LY294002 had little effect was also detected in response to TXL treatment.

CONCLUSIONS

These findings demonstrated that TXL provided neuroprotection against cerebral ischemia/reperfusion injury and neuronal apoptosis, and this effect was mediated partly by activation of the PI3K/Akt pathway.

Naoxintong Protects Primary Neurons from Oxygen-Glucose Deprivation/Reoxygenation Induced Injury through PI3K-Akt Signaling Pathway

Naoxintong capsule (NXT), developed from Buyang Huanwu Decoction, has shown the neuroprotective effects in cerebrovascular diseases, but the neuroprotection mechanisms of NXT on ischemia/reperfusion injured neurons have not yet been well known. In this study, we established the oxygen-glucose deprivation/reoxygenation (OGD/R) induced neurons injury model and treat the neurons with cerebrospinal fluid containing NXT (BNC) to investigate the effects of NXT on OGD/R induced neurons injury and potential mechanisms. BNC improved neuron viability and decreased apoptotic rate induced by OGD/R. BNC attenuated OGD/R induced cytosolic and mitochondrial Ca(2+) overload, ROS generation, intracellular NO levels and nNOS mRNA increase, and cytochrome-c release when compared with OGD/R group. BNC significantly inhibited both mPTP opening and ΔΨm depolarization. BNC increased Bcl-2 expression and decreased Bax expression, upregulated the Bcl-2/Bax ratio, downregulated caspase-3 mRNA and caspase-9 mRNA expression, and decreased cleaved caspase-3 expression and caspase-3 activity. BNC increased phosphorylation of Akt following OGD/R, while LY294002 attenuated BNC induced increase of phosphorylated Akt expression. Our study demonstrated that NXT protected primary neurons from OGD/R induced injury by inhibiting calcium overload and ROS generation, protecting mitochondria, and inhibiting mitochondrial apoptotic pathway which was mediated partially by PI3K-Akt signaling pathway activation.

Cofilin as a Promising Therapeutic Target for Ischemic and Hemorrhagic Stroke

Neurovascular unit (NVU) is considered as a conceptual framework for investigating the mechanisms as well as developing therapeutic targets for ischemic and hemorrhagic stroke. From a molecular perspective, oxidative stress, excitotoxicity, inflammation, and disruption of the blood brain barrier are broad pathophysiological frameworks on the basis on which potential therapeutic candidates for ischemic and hemorrhagic stroke could be discussed. Cofilin is a potent actin-binding protein that severs and depolymerizes actin filaments in order to generate the dynamics of the actin cytoskeleton. Although studies of the molecular mechanisms of cofilin-induced reorganization of the actin cytoskeleton have been ongoing for decades, the multicellular functions of cofilin and its regulation in different molecular pathways are expanding beyond its primary role in actin cytoskeleton. This review focuses on the role of cofilin in oxidative stress, excitotoxicity, inflammation, and disruption of the blood brain barrier in the context of NVU as well as how and why cofilin could be studied further as a potential target for ischemic and hemorrhagic stroke.

Modulation of the matrix redox signaling by mitochondrial Ca2+

Mitochondria sense, shape and integrate signals, and thus function as central players in cellular signal transduction. Ca²⁺ waves and redox reactions are two such intracellular signals modulated by mitochondria. Mitochondrial Ca²⁺ transport is of utmost physio-pathological relevance with a strong impact on metabolism and cell fate. Despite its importance, the molecular nature of the proteins involved in mitochondrial Ca²⁺ transport has been revealed only recently. Mitochondrial Ca²⁺ promotes energy metabolism through the activation of matrix dehydrogenases and down-stream stimulation of the respiratory chain. These changes also alter the mitochondrial NAD(P)H/NAD(P)⁺ ratio, but at the same time will increase reactive oxygen species (ROS) production. Reducing equivalents and ROS are having opposite effects on the mitochondrial redox state, which are hard to dissect. With the recent development of genetically encoded mitochondrial-targeted redox-sensitive sensors, real-time monitoring of matrix thiol redox dynamics has become possible. The discoveries of the molecular nature of mitochondrial transporters of Ca²⁺ combined with the utilization of the novel redox sensors is shedding light on the complex relation between mitochondrial Ca²⁺ and redox signals and their impact on cell function. In this review, we describe mitochondrial Ca²⁺ handling, focusing on a number of newly identified proteins involved in mitochondrial Ca²⁺ uptake and release. We further discuss our recent findings, revealing how mitochondrial Ca²⁺ influences the matrix redox state. As a result, mitochondrial Ca²⁺ is able to modulate the many mitochondrial redox-regulated processes linked to normal physiology and disease.

Pathophysiology and Treatments of Oxidative Injury in Ischemic Stroke: Focus on the Phagocytic NADPH Oxidase 2

SIGNIFICANCE

Phagocytes play a key role in promoting the oxidative stress after ischemic stroke occurrence. The phagocytic NADPH oxidase (NOX) 2 is a membrane-bound enzyme complex involved in the antimicrobial respiratory burst and free radical production in these cells.

RECENT ADVANCES

Different oxidants have been shown to induce opposite effects on neuronal homeostasis after a stroke. However, several experimental models support the detrimental effects of NOX activity (especially the phagocytic isoform) on brain recovery after stroke. Therapeutic strategies selectively targeting the neurotoxic ROS and increasing neuroprotective oxidants have recently produced promising results.

CRITICAL ISSUES

NOX2 might promote carotid plaque rupture and stroke occurrence. In addition, NOX2-derived reactive oxygen species (ROS) released by resident and recruited phagocytes enhance cerebral ischemic injury, activating the inflammatory apoptotic pathways. The aim of this review is to update evidence on phagocyte-related oxidative stress, focusing on the role of NOX2 as a potential therapeutic target to reduce ROS-related cerebral injury after stroke.

FUTURE DIRECTIONS

Radical scavenger compounds (such as Ebselen and Edaravone) are under clinical investigation as a therapeutic approach against stroke. On the other hand, NOX inhibition might represent a promising strategy to prevent the stroke-related injury. Although selective NOX inhibitors are not yet available, nonselective compounds (such as apocynin and fasudil) provided encouraging results in preclinical studies. Whereas additional studies are needed to better evaluate this therapeutic potential in human beings, the development of specific NOX inhibitors (such as monoclonal antibodies, small-molecule inhibitors, or aptamers) might further improve brain recovery after stroke.

Ultrastructural investigation of microcalcification and the role of oxygen-glucose deprivation in cultured rat hippocampal slices

Intracellular calcium accumulation is associated with cell death in several neuropathological disorders including brain ischemia, but the exact mechanisms of calcification need to be clarified. We used organotypic hippocampal slice culture - cultures subjected to oxygen-glucose deprivation (OGD) mimicking the in vivo situation to investigate the events underlying ectopic calcification. Alizarin red staining indicating calcium deposition was observed in the cornu ammonis (CA)1 and dentate gyrus regions in control hippocampal slices despite no specific labeling for cell death markers. Electron microscopy using the osmium/potassium dichromate method revealed scattered degenerated cells throughout the normally appearing CA1 region. They contained electron-dense precipitates within mitochondria, and electron probe microanalysis confirmed that they were calcifying mitochondria. Selective calcium deposition was noted within, but not beyond, mitochondria in these mineralized cells. They showed ultrastructural features of non-necrotic, non-apoptotic cell death and retained their compact ultrastructure, even after the majority of mitochondria were calcified. Unexpectedly, no intracellular calcification was noted in necrotic CA1 pyramidal cells after OGD, and there was no progression of calcification in OGD-lesioned slices. In addition, mineralized cells in both control and OGD-lesioned slices were closely associated with or completely engulfed by astrocytes but not microglia. These astrocytes were laden with heterogeneous cytoplasmic inclusions that appeared to be related with their phagocytic activity. These data demonstrate that microcalcification specifically associated with mitochondria might lead to a novel type of cell death and suggest that astrocytes may be involved in the phagocytosis of these mineralized cells and possibly in the regulation of ectopic calcification.

Hyperglycemia / hypoglycemia-induced mitochondrial dysfunction and cerebral ischemic damage in diabetics

Enhancement of ischemic brain damage is one of the most serious complications of diabetes. Studies from various in vivo and in vitro models of cerebral ischemia have led to an understanding of the role of mitochondria and complex interrelated mitochondrial biochemical pathways leading to the aggravation of ischemic neuronal damage. Advancements in the elucidation of the mechanisms of ischemic brain damage in diabetic subjects have revealed a number of key mitochondrial targets that have been hypothesized to participate in enhancement of brain damage. The present review initially discusses the neurobiology of ischemic neuronal injury, with special emphasis on the central role of mitochondria in mediating its pathogenesis and therapeutic targets. Later it further details the potential role of various biochemical mediators and second messengers causing widespread ischemic brain damage among diabetics via mitochondrial pathways. The present review discusses preclinical data which validates the significance of mitochondrial mechanisms in mediating the aggravation of ischemic cerebral injury in diabetes. Exploitation of these targets may provide effective therapeutic agents for the management of diabetes-related aggravation of ischemic neuronal damage.

The neuroprotective effect of a novel agent N2 on rat cerebral ischemia associated with the activation of PI3K/Akt signaling pathway

Ischemic stroke is the third leading cause of death and the main reason for severe disabilities in the world today. N2, 4 - (2 - (1H - imidazol - 1 - yl) ethoxy) - 3 - methoxybenzoic acid is considered as a novel potent agent for cerebral ischemia due to its effect in preventing neuronal cell death after ischemic stroke. In the present study, we investigated the post-ischemic neuroprotective effect of N2 and its underlying mechanisms. Using a MCAO rat model, we found that N2 reversed brain infarct size, reduced cerebral edema and decreased the neurological deficit score significantly. Moreover, N2 diminished TUNEL positive cells, down-regulated bax expression and up-regulated bcl-2 expression notably. In addition, we evaluated the oxygen glucose deprivation/reoxygenation (OGD/R) injury induced neuron cell death in rat primary cortical neuron and assessed the neuroprotective effect of our drug. N2 increased cell viability, ameliorated neuron cell injury by decreasing LDH activity, and inhibited cell apoptotic rate while suppressed apoptotic signaling via inhibiting the bax expression, and elevating the bcl-2 expression. Furthermore, the neuroprotective effect of N2 was associated with the PI3K/Akt pathway which was proved by the use of PI3K inhibitor LY294002. The combination of our findings disclosed that N2 can be used as an effective neuroprotective agent for ischemic stroke due to its significant effect on preventing neuronal cell death after cerebral ischemia both in vivo and in vitro and the effectiveness was dose dependent.

Studies on the Protective Effects of Scutellarein against Neuronal Injury by Ischemia through the Analysis of Endogenous Amino Acids and Ca2+Concentration Together with Ca2+-ATPase Activity

Scutellarin, which is extracted from the dried plant ofErigeron breviscapus, has been reported to protect the neural injury against excitotoxicity induced by ischemia. However, there are a few studies on the protective effects of scutellarein, which is the main metabolite of scutellarin in vivo. Thus, this study investigated the neuroprotective effects of scutellarein on cerebral ischemia/reperfusion in rats by bilateral common carotid artery occlusion (BCCAO) model, through the analysis of endogenous amino acids using HILIC-MS/MS, and evaluation of Ca2+concentration together with Ca2+-ATPase activity. The results showed that scutellarein having good protective effects on cerebral ischemia/reperfusion might by decreasing the excitatory amino acids, increasing the inhibitory amino acids, lowing intracellular Ca2+level, and improving Ca2+-ATPase activity, which suggested that scutellarein might be a promising potent agent for the therapy of ischemic cerebrovascular disease.

Imaging of mitochondrial Ca2+ dynamics in astrocytes using cell-specific mitochondria-targeted GCaMP5G/6s: mitochondrial Ca2+ uptake and cytosolic Ca2+ availability via the endoplasmic reticulum store

Mitochondrial Ca(2+) plays a critical physiological role in cellular energy metabolism and signaling, and its overload contributes to various pathological conditions including neuronal apoptotic death in neurological diseases. Live cell mitochondrial Ca(2+) imaging is an important approach to understand mitochondrial Ca(2+) dynamics. Recently developed GCaMP genetically-encoded Ca(2+) indicators provide unique opportunity for high sensitivity/resolution and cell type-specific mitochondrial Ca(2+) imaging. In the current study, we implemented cell-specific mitochondrial targeting of GCaMP5G/6s (mito-GCaMP5G/6s) and used two-photon microscopy to image astrocytic and neuronal mitochondrial Ca(2+) dynamics in culture, revealing Ca(2+) uptake mechanism by these organelles in response to cell stimulation. Using these mitochondrial Ca(2+) indicators, our results show that mitochondrial Ca(2+) uptake in individual mitochondria in cultured astrocytes and neurons can be seen after stimulations by ATP and glutamate, respectively. We further studied the dependence of mitochondrial Ca(2+) dynamics on cytosolic Ca(2+) changes following ATP stimulation in cultured astrocytes by simultaneously imaging mitochondrial and cytosolic Ca(2+) increase using mito-GCaMP5G and a synthetic organic Ca(2+) indicator, x-Rhod-1, respectively. Combined with molecular intervention in Ca(2+) signaling pathway, our results demonstrated that the mitochondrial Ca(2+) uptake is tightly coupled with inositol 1,4,5-trisphosphate receptor-mediated Ca(2+) release from the endoplasmic reticulum and the activation of G protein-coupled receptors. The current study provides a novel approach to image mitochondrial Ca(2+) dynamics as well as Ca(2+) interplay between the endoplasmic reticulum and mitochondria, which is relevant for neuronal and astrocytic functions in health and disease.

Mitochondria-targeted plastoquinone antioxidant SkQR1 decreases trauma-induced neurological deficit in rat

A protective effect of a mitochondria-targeted antioxidant, a cationic rhodamine derivative linked to a plastoquinone molecule (10-(6'-plastoquinonyl)decylrhodamine-19, SkQR1) was studied in the model of open focal trauma of rat brain sensorimotor cortex. It was found that daily intraperitoneal injections of SkQR1 (100 nmol/kg) for 4 days after the trauma improved performance in a test characterizing neurological deficit and decreased the volume of the damaged cortical area. Our results suggest that SkQR1 exhibits profound neuroprotective effect, which may be explained by its antioxidative activity.

NCLX protein, but not LETM1, mediates mitochondrial Ca2+ extrusion, thereby limiting Ca2+-induced NAD(P)H production and modulating matrix redox state

Mitochondria capture and subsequently release Ca(2+) ions, thereby sensing and shaping cellular Ca(2+) signals. The Ca(2+) uniporter MCU mediates Ca(2+) uptake, whereas NCLX (mitochondrial Na/Ca exchanger) and LETM1 (leucine zipper-EF-hand-containing transmembrane protein 1) were proposed to exchange Ca(2+) against Na(+) or H(+), respectively. Here we study the role of these ion exchangers in mitochondrial Ca(2+) extrusion and in Ca(2+)-metabolic coupling. Both NCLX and LETM1 proteins were expressed in HeLa cells mitochondria. The rate of mitochondrial Ca(2+) efflux, measured with a genetically encoded indicator during agonist stimulations, increased with the amplitude of mitochondrial Ca(2+) ([Ca(2+)]mt) elevations. NCLX overexpression enhanced the rates of Ca(2+) efflux, whereas increasing LETM1 levels had no impact on Ca(2+) extrusion. The fluorescence of the redox-sensitive probe roGFP increased during [Ca(2+)]mt elevations, indicating a net reduction of the matrix. This redox response was abolished by NCLX overexpression and restored by the Na(+)/Ca(2+) exchanger inhibitor CGP37157. The [Ca(2+)]mt elevations were associated with increases in the autofluorescence of NAD(P)H, whose amplitude was strongly reduced by NCLX overexpression, an effect reverted by Na(+)/Ca(2+) exchange inhibition. We conclude that NCLX, but not LETM1, mediates Ca(2+) extrusion from mitochondria. By controlling the duration of matrix Ca(2+) elevations, NCLX contributes to the regulation of NAD(P)H production and to the conversion of Ca(2+) signals into redox changes.

Mitochondrial channels: ion fluxes and more

The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.

Inhibition of cyclophilin D by cyclosporin A promotes retinal ganglion cell survival by preventing mitochondrial alteration in ischemic injury

Cyclosporin A (CsA) inhibits the opening of the mitochondrial permeability transition pore (MPTP) by interacting with cyclophilin D (CypD) and ameliorates neuronal cell death in the central nervous system against ischemic injury. However, the molecular mechanisms underlying CypD/MPTP opening-mediated cell death in ischemic retinal injury induced by acute intraocular pressure (IOP) elevation remain unknown. We observed the first direct evidence that acute IOP elevation significantly upregulated CypD protein expression in ischemic retina at 12 h. However, CsA prevented the upregulation of CypD protein expression and promoted retinal ganglion cell (RGC) survival against ischemic injury. Moreover, CsA blocked apoptotic cell death by decreasing cleaved caspase-3 protein expression in ischemic retina. Of interest, although the expression level of Bcl-xL protein did not show a significant change in ischemic retina treated with vehicle or CsA at 12 h, ischemic damage induced the reduction of Bcl-xL immunoreactivity in RGCs. More importantly, CsA preserved Bcl-xL immunoreactivity in RGCs of ischemic retina. In parallel, acute IOP elevation significantly increased phosphorylated Bad (pBad) at Ser112 protein expression in ischemic retina at 12 h. However, CsA significantly preserved pBad protein expression in ischemic retina. Finally, acute IOP elevation significantly increased mitochondrial transcription factor A (Tfam) protein expression in ischemic retina at 12 h. However, CsA significantly preserved Tfam protein expression in ischemic retina. Studies on mitochondrial DNA (mtDNA) content in ischemic retina showed that there were no statistically significant differences in mtDNA content among control and ischemic groups treated with vehicle or CsA. Therefore, these results provide evidence that the activation of CypD-mediated MPTP opening is associated with the apoptotic pathway and the mitochondrial alteration in RGC death of ischemic retinal injury. On the basis of these observations, our findings suggest that CsA-mediated CypD inhibition may provide a promising therapeutic potential for protecting RGCs against ischemic injury-mediated mitochondrial dysfunction.

Serine hydrolase inhibitors block necrotic cell death by preventing calcium overload of the mitochondria and permeability transition pore formation

Perturbation of calcium signaling that occurs during cell injury and disease, promotes cell death. In mouse lung fibroblasts A23187 triggered mitochondrial permeability transition pore (MPTP) formation, lactate dehydrogenase (LDH) release, and necrotic cell death that were blocked by cyclosporin A (CsA) and EGTA. LDH release temporally correlated with arachidonic acid release but did not involve cytosolic phospholipase A2α (cPLA2α) or calcium-independent PLA2. Surprisingly, release of arachidonic acid and LDH from cPLA2α-deficient fibroblasts was inhibited by the cPLA2α inhibitor pyrrophenone, and another serine hydrolase inhibitor KT195, by preventing mitochondrial calcium uptake. Inhibitors of calcium/calmodulin-dependent protein kinase II, a mitochondrial Ca(2+) uniporter (MCU) regulator, also prevented MPTP formation and arachidonic acid release induced by A23187 and H2O2. Pyrrophenone blocked MCU-mediated mitochondrial calcium uptake in permeabilized fibroblasts but not in isolated mitochondria. Unlike pyrrophenone, the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol and CsA blocked cell death and arachidonic acid release not by preventing mitochondrial calcium uptake but by inhibiting MPTP formation. In fibroblasts stimulated with thapsigargin, which induces MPTP formation by a direct effect on mitochondria, LDH and arachidonic acid release were blocked by CsA and 1-oleoyl-2-acetyl-sn-glycerol but not by pyrrophenone or EGTA. Therefore serine hydrolase inhibitors prevent necrotic cell death by blocking mitochondrial calcium uptake but not the enzyme releasing fatty acids that occurs by a novel pathway during MPTP formation. This work reveals the potential for development of small molecule cell-permeable serine hydrolase inhibitors that block MCU-mediated mitochondrial calcium overload, MPTP formation, and necrotic cell death.

Serum- and glucocorticoid-induced protein kinase 1 (SGK1) is regulated by store-operated Ca2+ entry and mediates cytoprotection against necrotic cell death

Serum and glucocorticoid-regulated kinase 1 (SGK1) encodes a phosphatidylinositol 3-kinase-dependent serine/threonine kinase that is rapidly induced in response to cellular stressors and is an important cell survival signal. Previous studies have suggested that an increase in cytoplasmic Ca(2+) concentration ([Ca(2+)]c) is required for increased SGK1 expression, but the subcellular source of Ca(2+) regulating SGK1 transcription remains uncertain. Activation of endoplasmic reticulum stress (ERS) with thapsigargin (TG) increased SGK1 mRNA and protein expression in MDA-MB-231 cells. Intracellular Ca(2+) imaging revealed that store-operated Ca(2+) entry played a prominent role in SGK1 induction by TG. Neither ERS nor release of Ca(2+) from the ER was sufficient to activate SGK1. Prolonged elevation of intracellular Ca(2+) levels, however, triggered cell death with a much greater proportion of the cells undergoing necrosis rather than apoptosis. A relative increase in the percentage of cells undergoing necrosis was observed in cells expressing a short hairpin RNA targeted to the SGK1 gene. Necrotic cell death evoked by cytoplasmic Ca(2+) overloading was associated with persistent hyperpolarization of the inner mitochondrial membrane and a modest increase in calpain activation, but did not involve detectable caspase 3 or caspase 7 activation. The effects of cytoplasmic Ca(2+) overloading on mitochondrial membrane potential were significantly reduced in cells expressing SGK1 compared with SGK1-depleted cells. Our findings indicate that store-operated Ca(2+) entry regulates SGK1 expression in epithelial cells and suggest that SGK1-dependent cytoprotective signaling involves effects on maintaining mitochondrial function.

microRNAs: innovative targets for cerebral ischemia and stroke

Stroke is one of the leading causes of death and disability worldwide. Because stroke is a multifactorial disease with a short therapeutic window many clinical stroke trials have failed and the only currently approved therapy is thrombolysis. MicroRNAs (miRNA) are endogenously expressed noncoding short single-stranded RNAs that play a role in the regulation of gene expression at the post-transcriptional level, via degradation or translational inhibition of their target mRNAs. The study of miRNAs is rapidly growing and recent studies have revealed a significant role of miRNAs in ischemic disease. miRNAs are especially important candidates for stroke therapeutics because of their ability to simultaneously regulate many target genes and since to date targeting single genes for therapeutic intervention has not yet succeeded in the clinic. Although there are already quite a few review articles about miRNA in ischemic heart disease, much less is currently known about miRNAs in cerebral ischemia. This review summarizes current knowledge about miRNAs and cerebral ischemia, focusing on the role of miRNAs in ischemia, both changes in expression and identification of potential targets, as well as the potential of miRNAs as biomarkers and therapeutic targets in cerebral ischemia.

Mitochondrial Ca2+ uptake from plasma membrane Cav3.2 protein channels contributes to ischemic toxicity in PC12 cells

T-type Ca(2+) channel inhibitors protect hippocampal CA1 neurons from delayed death after global ischemia in rats, suggesting that Cav3.1, Cav3.2, or Cav3.3 channels generate cytotoxic Ca(2+) elevations during anoxia. To test this hypothesis, we measured the Ca(2+) concentration changes evoked by oxygen and glucose deprivation (OGD) in the cytosol and in the mitochondria of PC12 cells. OGD evoked long-lasting cytosolic Ca(2+) elevations that were reduced by Cav3.2 inhibition (50 μm Ni(2+)) and Cav3.1/Cav3.2 silencing and potentiated by Cav3.2 overexpression. The kinetics of the sustained cytosolic Ca(2+) elevations occurring during OGD directly correlated to the extent of cell death measured 20 h after reoxygenation, which was decreased by Ni(2+) and Cav3.1/Cav3.2 silencing and increased by Cav3.2 overexpression. Ni(2+) and Cav3.1/Cav3.2 silencing delayed the decline of cellular ATP during OGD, consistent with a reduction in the Ca(2+) load actively extruded by plasma membrane Ca(2+) pumps. The cytosolic Ca(2+) elevations were paralleled by mitochondrial Ca(2+) elevations that were also increased by Cav3.2 overexpression and decreased by Ni(2+) but not by Cav3.1/Cav3.2 silencing. Overexpression and silencing of the mitochondrial Ca(2+) uniporter, the major mitochondrial Ca(2+) uptake protein, revealed that the cytotoxicity was correlated to the amplitude of the mitochondrial, rather than the cytosolic, Ca(2+) elevations. Selective activation of T-type Ca(2+) channels evoked both cytosolic and mitochondrial Ca(2+) elevations, but only the mitochondrial responses were reduced by Cav3.1/Cav3.2 silencing. We conclude that the opening of Cav3.2 channels during ischemia contribute to the entry of Ca(2+) ions that are transmitted to mitochondria, resulting in a deleterious mitochondrial Ca(2+) overload.

The bizarre pharmacology of the ATP release channel pannexin1

Pannexins were originally thought to represent a second and redundant family of gap junction proteins in addition to the well characterized connexins. However, it is now evident that pannexins function as unapposed membrane channels and the major role of Panx1 is that of an ATP release channel. Despite the contrasting functional roles, connexins, innexins and pannexins share pharmacological properties. Most gap junction blockers also attenuate the function of Panx1, including carbenoxolone, mefloquine and flufenamic acid. However, in contrast to connexin based gap junction channels, Panx1 channel activity can be attenuated by several groups of drugs hitherto considered very specific for other proteins. The drugs affecting Panx1 channels include several transport inhibitors, chloride channel blockers, mitochondrial inhibitors, P2X7 receptor ligands, inflammasome inhibitors and malaria drugs. These observations indicate that Panx1 may play an extended role in a wider spectrum of physiological functions. Alternatively, Panx1 may share structural domains with other proteins, not readily revealed by sequence alignments. This article is part of the Special Issue Section entitled 'Current Pharmacology of Gap Junction Channels and Hemichannels'.

Comparative analysis of cytosolic and mitochondrial ATP synthesis in embryonic and postnatal hippocampal neuronal cultures

ATP in neurons is commonly believed to be synthesized mostly by mitochondria via oxidative phosphorylation. Neuronal mitochondria have been studied primarily in culture, i.e., in neurons isolated either from embryos or from neonatal pups. Although it is generally assumed that both embryonic and postnatal cultured neurons derive their ATP from mitochondrial oxidative phosphorylation, this has never been tested experimentally. We expressed the FRET-based ATP sensor AT1.03 in cultured hippocampal neurons isolated either from E17 to E18 rat embryos or from P1 to P2 rat pups and monitored [ATP]c simultaneously with mitochondrial membrane potential (ΔΨm; TMRM) and NAD(P)H autofluorescence. In embryonic neurons, transient glucose deprivation induced a near-complete decrease in [ATP]c, which was partially reversible and was accelerated by inhibition of glycolysis with 2-deoxyglucose. In the absence of glucose, pyruvate did not cause any significant increase in [ATP]c in 84% of embryonic neurons, and inhibition of mitochondrial ATP synthase with oligomycin failed to decrease [ATP]c. Moreover, ΔΨm was significantly reduced by oligomycin, indicating that mitochondria acted as consumers rather than producers of ATP in embryonic neurons. In sharp contrast, in postnatal neurons pyruvate added during glucose deprivation significantly increased [ATP]c (by 54 ± 8%), whereas oligomycin induced a sharp decline in [ATP]c and increased ΔΨm. These signs of oxidative phosphorylation were observed in all tested P1-P2 neurons. Measurement of ΔΨm with the potential-sensitive probe JC-1 revealed that neuronal mitochondrial membrane potential was significantly reduced in embryonic cultures compared to the postnatal ones, possibly due to increased proton permeability of inner mitochondrial membrane. We conclude that, in embryonic, but not postnatal neuronal cultures, ATP synthesis is predominantly glycolytic and the oxidative phosphorylation-mediated synthesis of ATP by mitochondrial F1Fo-ATPase is insignificant.

Neuronal oxidative stress in acute ischemic stroke: sources and contribution to cell injury

Oxidative stress has emerged as a key deleterious factor in brain ischemia and reperfusion. Malfunction of the oxidative respiratory chain in mitochondria combines with the activation of cytoplasmic oxidases to generate a burst of reactive oxygen species that cannot be neutralised by the cell's antioxidant mechanisms. As a result, oxidative stress contributes directly to necrosis and apoptosis through a number of pathways in ischemic tissue. Pharmacological intervention with antioxidants or enhancers of endogenous antioxidant molecules is proving to be difficult due to the speed and scope of the oxidative impact. Additionally, the knowledge that neuronal fate in ischemic stroke is tightly linked to other brain cells like endothelial cells and astrocytes has shifted the focus of study from isolated neurons to the neurovascular unit. For this reason, recent efforts have been directed towards understanding the sources of oxidative stress in ischemic stroke and attempting to block the generation of oxygen radicals.

ER-Mitochondria Crosstalk during Cerebral Ischemia: Molecular Chaperones and ER-Mitochondrial Calcium Transfer

It is commonly believed that sustained elevations in the mitochondrial matrix Ca²⁺ concentration are a major feature of the intracellular cascade of lethal events during cerebral ischemia. The physical association between the endoplasmic reticulum (ER) and mitochondria, known as the mitochondria-associated ER membrane (MAM), enables highly efficient transmission of Ca²⁺ from the ER to mitochondria under both physiological and pathological conditions. Molecular chaperones are well known for their protective effects during cerebral ischemia. It has been demonstrated recently that many molecular chaperones coexist with MAM and regulate the MAM and thus Ca²⁺ concentration inside mitochondria. Here, we review recent research on cerebral ischemia and MAM, with a focus on molecular chaperones and ER-mitochondrial calcium transfer.

Regulation of pancreatic β-cell survival by nitric oxide: clinical relevance

The reduction of pancreatic β-cell mass is an important factor in the development of type 1 and type 2 diabetes. Understanding the mechanisms that regulate the maintenance of pancreatic β-cell mass as well as β-cell death is necessary for the establishment of therapeutic strategies. In this context, nitric oxide (NO) is a diatomic, gaseous, highly reactive molecule with biological activity that participates in the regulation of pancreatic β-cell mass. Two types of cellular responses can be distinguished depending on the level of NO production. First, pancreatic β-cells exposed to inflammatory cytokines, lipid stress or hyperglycaemia produce high concentrations of NO, mainly due to the activation of inducible NO synthase (iNOS), thus promoting cell death. Meanwhile, under homeostatic conditions, low concentrations of NO, constitutively produced by endothelial NO synthase (eNOS), promote cell survival. Here, we will discuss the current knowledge of the NO-dependent mechanisms activated during cellular responses, emphasizing those related to the regulation of cell survival.