Modes of Neuronal Calcium Entry and Homeostasis following Cerebral Ischemia

Role of Neuronal TRPC6 Channels in Synapse Development, Memory Formation and Animal Behavior

The transient receptor potential cation channel, subfamily C, member 6 (TRPC6), has been believed to adjust the formation of an excitatory synapse. The positive regulation of TRPC6 engenders synapse enlargement and improved learning and memory in animal models. TRPC6 is involved in different synaptoprotective signaling pathways, including antagonism of N-methyl-D-aspartate receptor (NMDAR), activation of brain-derived neurotrophic factor (BDNF) and postsynaptic store-operated calcium entry. Positive regulation of TRPC6 channels has been repeatedly shown to be good for memory formation and storage. TRPC6 is mainly expressed in the hippocampus, particularly in the dentate granule cells, cornu Ammonis 3 (CA3) pyramidal cells and gamma-aminobutyric acid (GABA)ergic interneurons. It has been observed that TRPC6 agonists have a great influence on animal behavior including memory formation and storage The purpose of this review is to collect the available information on the role of TRPC6 in memory formation in various parts of the brain to understand how TRPC6-specific pharmaceutical agents will affect memory in distinct parts of the central nervous system (CNS).

Brain Damage in Preterm and Full-Term Neonates: Serum Biomarkers for the Early Diagnosis and Intervention

The Brain is vulnerable to numerous insults that can act in the pre-, peri-, and post-natal period. There is growing evidence that demonstrate how oxidative stress (OS) could represent the final common pathway of all these insults. Fetuses and newborns are particularly vulnerable to OS due to their inability to active the antioxidant defenses. Specific molecules involved in OS could be measured in biologic fluids as early biomarkers of neonatal brain injury with an essential role in neuroprotection. Although S-100B seems to be the most studied biomarker, its use in clinical practice is limited by the complexity of brain damage etiopathogenesis and the time of blood sampling in relation to the brain injury. Reliable early specific serum markers are currently lacking in clinical practice. It is essential to determine if there are specific biomarkers that can help caregivers to monitor the progression of the disease in order to active an early neuroprotective strategy. We aimed to describe, in an educational review, the actual evidence on serum biomarkers for the early identification of newborns at a high risk of neurological diseases. To move the biomarkers from the bench to the bedside, the assays must be not only be of a high sensitivity but suitable for the very rapid processing and return of the results for the clinical practice to act on. For the best prognosis, more studies should focus on the association of these biomarkers to the type and severity of perinatal brain damage.

Changes in nanomechanical properties of single neuroblastoma cells as a model for oxygen and glucose deprivation (OGD)

Although complex, the biological processes underlying ischemic stroke are better known than those related to biomechanical alterations of single cells. Mechanisms of biomechanical changes and their relations to the molecular processes are crucial for understanding the function and dysfunction of the brain. In our study, we applied atomic force microscopy (AFM) to quantify the alterations in biomechanical properties in neuroblastoma SH-SY5Y cells subjected to oxygen and glucose deprivation (OGD) and reoxygenation (RO). Obtained results reveal several characteristics. Cell viability remained at the same level, regardless of the OGD and RO conditions, but, in parallel, the metabolic activity of cells decreased with OGD duration. 24 h RO did not recover the metabolic activity fully. Cells subjected to OGD appeared softer than control cells. Cell softening was strongly present in cells after 1 h of OGD and with longer OGD duration, and in RO conditions, cells recovered their mechanical properties. Changes in the nanomechanical properties of cells were attributed to the remodelling of actin filaments, which was related to cofilin-based regulation and impaired metabolic activity of cells. The presented study shows the importance of nanomechanics in research on ischemic-related pathological processes such as stroke.

Targeting CDK5 in Astrocytes Promotes Calcium Homeostasis Under Excitotoxic Conditions

Glutamate excitotoxicity triggers overactivation of CDK5 and increases calcium influx in neural cells, which promotes dendritic retraction, spine loss, increased mitochondrial calcium from the endoplasmic reticulum, and neuronal death. Our previous studies showed that CDK5 knockdown (KD) in astrocytes improves neurovascular integrity and cognitive functions and exerts neuroprotective effects. However, how CDK5-targeted astrocytes affect calcium regulation and whether this phenomenon is associated with changes in neuronal plasticity have not yet been analyzed. In this study, CDK5 KD astrocytes transplanted in CA3 remained at the injection site without proliferation, regulated calcium in the CA1 hippocampal region after excitotoxicity by glutamate in ex vivo hippocampal slices, improving synapsin and PSD95 clustering. These CDK5 KD astrocytes induced astrocyte stellation and neuroprotection after excitotoxicity induced by glutamate in vitro. Also, these effects were supported by CDK5 inhibition (CDK5i) in vitro through intracellular stabilization of calcium levels in astrocytes. Additionally, these cells in cocultures restored calcium homeostasis in neurons, redistributing calcium from somas to dendrites, accompanied by dendrite branching, higher dendritic spines and synapsin-PSD95 clustering. In summary, induction of calcium homeostasis at the CA1 hippocampal area by CDK5 KD astrocytes transplanted in the CA3 area highlights the role of astrocytes as a cell therapy target due to CDK5-KD astrocyte-mediated synaptic clustering, calcium spreading regulation between both areas, and recovery of the intracellular astrocyte-neuron calcium imbalance and plasticity impairment generated by glutamate excitotoxicity.

How cytosolic compartments play safeguard functions against neuroinflammation and cell death in cerebral ischemia

Ischemic stroke is the second leading cause of mortality and disability globally. Neuronal damage following ischemic stroke is rapid and irreversible, and eventually results in neuronal death. In addition to activation of cell death signaling, neuroinflammation is also considered as another pathogenesis that can occur within hours after cerebral ischemia. Under physiological conditions, subcellular organelles play a substantial role in neuronal functionality and viability. However, their functions can be remarkably perturbed under neurological disorders, particularly cerebral ischemia. Therefore, their biochemical and structural response has a determining role in the sequel of neuronal cells and the progression of disease. However, their effects on cell death and neuroinflammation, as major underlying mechanisms of ischemic stroke, are still not understood. This review aims to provide a comprehensive overview of the contribution of each organelle on these pathological processes after ischemic stroke.

Glial Cell-Based Vascular Mechanisms and Transplantation Therapies in Brain Vessel and Neurodegenerative Diseases

Neurodevelopmental and neurodegenerative diseases (NDDs) with severe neurological/psychiatric symptoms, such as cerebrovascular pathology in AD, CAA, and chronic stroke, have brought greater attention with their incidence and prevalence having markedly increased over the past few years. Causes of the significant neuropathologies, especially those observed in neurological diseases in the CNS, are commonly believed to involve multiple factors such as an age, a total environment, genetics, and an immunity contributing to their progression, neuronal, and vascular injuries. We primarily focused on the studies of glial involvement/dysfunction in part with the blood-brain barrier (BBB) and the neurovascular unit (NVU) changes, and the vascular mechanisms, which have been both suggested as critical roles in chronic stroke and many other NDDs. It has been noted that glial cells including astrocytes (which outnumber other cell types in the CNS) essentially contribute more to the BBB integrity, extracellular homeostasis, neurotransmitter release, regulation of neurogenic niches in response to neuroinflammatory stimulus, and synaptic plasticity. In a recent study for NDDs utilizing cellular and molecular biology and genetic and pharmacological tools, the role of reactive astrocytes (RACs) and gliosis was demonstrated, able to trigger pathophysiological/psychopathological detrimental changes during the disease progression. We speculate, in particular, the BBB, the NVU, and changes of the astrocytes (potentially different populations from the RACs) not only interfere with neuronal development and synaptogenesis, but also generate oxidative damages, contribute to beta-amyloid clearances and disrupted vasculature, as well as lead to neuroinflammatory disorders. During the past several decades, stem cell therapy has been investigated with a research focus to target related neuro-/vascular pathologies (cell replacement and repair) and neurological/psychiatric symptoms (paracrine protection and homeostasis). Evidence shows that transplantation of neurogenic or vasculogenic cells could be achieved to pursue differentiation and maturation within the diseased brains as expected. It would be hoped that, via regulating functions of astrocytes, astrocytic involvement, and modulation of the BBB, the NVU and astrocytes should be among major targets for therapeutics against NDDs pathogenesis by drug and cell-based therapies. The non-invasive strategies in combination with stem cell transplantation such as the well-tested intranasal deliveries for drug and stem cells by our and many other groups show great translational potentials in NDDs. Neuroimaging and clinically relevant analyzing tools need to be evaluated in various NDDs brains.

The Role of TRP Channels and PMCA in Brain Disorders: Intracellular Calcium and pH Homeostasis

Brain disorders include neurodegenerative diseases (NDs) with different conditions that primarily affect the neurons and glia in the brain. However, the risk factors and pathophysiological mechanisms of NDs have not been fully elucidated. Homeostasis of intracellular Ca²⁺ concentration and intracellular pH (pH_i) is crucial for cell function. The regulatory processes of these ionic mechanisms may be absent or excessive in pathological conditions, leading to a loss of cell death in distinct regions of ND patients. Herein, we review the potential involvement of transient receptor potential (TRP) channels in NDs, where disrupted Ca²⁺ homeostasis leads to cell death. The capability of TRP channels to restore or excite the cell through Ca²⁺ regulation depending on the level of plasma membrane Ca²⁺ ATPase (PMCA) activity is discussed in detail. As PMCA simultaneously affects intracellular Ca²⁺ regulation as well as pH_i, TRP channels and PMCA thus play vital roles in modulating ionic homeostasis in various cell types or specific regions of the brain where the TRP channels and PMCA are expressed. For this reason, the dysfunction of TRP channels and/or PMCA under pathological conditions disrupts neuronal homeostasis due to abnormal Ca²⁺ and pH levels in the brain, resulting in various NDs. This review addresses the function of TRP channels and PMCA in controlling intracellular Ca²⁺ and pH, which may provide novel targets for treating NDs.

Potential Drug Candidates to Treat TRPC6 Channel Deficiencies in the Pathophysiology of Alzheimer's Disease and Brain Ischemia

Alzheimer’s disease and cerebral ischemia are among the many causative neurodegenerative diseases that lead to disabilities in the middle-aged and elderly population. There are no effective disease-preventing therapies for these pathologies. Recent in vitro and in vivo studies have revealed the TRPC6 channel to be a promising molecular target for the development of neuroprotective agents. TRPC6 channel is a non-selective cation plasma membrane channel that is permeable to Ca²⁺. Its Ca²⁺-dependent pharmacological effect is associated with the stabilization and protection of excitatory synapses. Downregulation as well as upregulation of TRPC6 channel functions have been observed in Alzheimer’s disease and brain ischemia models. Thus, in order to protect neurons from Alzheimer’s disease and cerebral ischemia, proper TRPC6 channels modulators have to be used. TRPC6 channels modulators are an emerging research field. New chemical structures modulating the activity of TRPC6 channels are being currently discovered. The recent publication of the cryo-EM structure of TRPC6 channels should speed up the discovery process even more. This review summarizes the currently available information about potential drug candidates that may be used as basic structures to develop selective, highly potent TRPC6 channel modulators to treat neurodegenerative disorders, such as Alzheimer’s disease and cerebral ischemia.

Insights into the neuropathology of cerebral ischemia and its mechanisms

Cerebral ischemia is a result of insufficient blood flow to the brain. It leads to limited supply of oxygen and other nutrients to meet metabolic demands. These phenomena lead to brain damage. There are two types of cerebral ischemia: focal and global ischemia. This condition has significant impact on patient’s health and health care system requirements. Animal models such as transient occlusion of the middle cerebral artery and permanent occlusion of extracranial vessels have been established to mimic the conditions of the respective type of cerebral ischemia and to further understand pathophysiological mechanisms of these ischemic conditions. It is important to understand the pathophysiology of cerebral ischemia in order to identify therapeutic strategies for prevention and treatment. Here, we review the neuropathologies that are caused by cerebral ischemia and discuss the mechanisms that occur in cerebral ischemia such as reduction of cerebral blood flow, hippocampal damage, white matter lesions, neuronal cell death, cholinergic dysfunction, excitotoxicity, calcium overload, cytotoxic oedema, a decline in adenosine triphosphate (ATP), malfunctioning of Na+/K+-ATPase, and the blood-brain barrier breakdown. Altogether, the information provided can be used to guide therapeutic strategies for cerebral ischemia.

Memory and Learning Deficits Are Associated With Ca2+ Dyshomeostasis in Normal Aging

Neuronal intracellular Ca2+ homeostasis is critical to the normal physiological functions of neurons and neuronal Ca2+ dyshomeostasis has been associated with the age-related decline of cognitive functions. Accumulated evidence indicates that the underlying mechanism for this is that abnormal intracellular Ca2+ levels stimulate the dysregulation of intracellular signaling, which subsequently induces neuronal cell death. We examined intracellular Ca2+ homeostasis in cortical (in vivo) and hippocampal (in vitro) neurons from young (3-months), middle-age (12-months), and aged (24-months) wild type C57BL6J mice. We found a progressive age-related elevation of intracellular resting calcium ([Ca2+]r) in cortical (in vivo) and hippocampal (in vitro) neurons associated with increased hippocampal neuronal calpain activity and reduced cell viability. In vitro, removal of extracellular Ca2+ or treatment with SAR7334 or dantrolene reduced [Ca2+]r in all age groups and dantrolene treatment lowered calpain activity and increased cell viability. In vivo, both middle-aged and aged mice showed cognitive deficits compared to young mice, which improved after dantrolene treatment. These findings support the hypothesis that intracellular Ca2+ dyshomeostasis is a major mechanism underlying the cognitive deficits seen in both normal aging and degenerative neurologic diseases.

Micro RNA 181c-5p: A promising target for post-stroke recovery in socially isolated mice

Dysregulation of microRNAs (miRNAs) has been tied to several neurological disorders, including ischemic stroke. It has also been established that social environments can modulate miRNA profiles. We have previously shown that post-stroke social isolation (SI) is linked to poor stroke outcomes and that miR-181c-5p emerged as one of few lead miRNAs that was downregulated in both stroke and SI. Therefore, in this study we examined the potential role of miR-181c-5p mimic in reversing the detrimental effects of post-stroke SI. Two to three-month-old C57BL/6 male mice were pair-housed (PH) for at least two weeks. After two weeks, mice underwent stroke survival surgery using middle cerebral artery occlusion (MCAO) and were randomly assigned to one of two housing conditions: stroke isolation (ST-ISO) or stroke pair-housing with a healthy partner (ST-PH). ST-ISO mice were randomized to receive either miR-181c-5p mimic or a scrambled RNA (7 mg/kg i.v./day×drug) control at 24 h and 48 h after stroke. The effects of miR-181c-5p mimic treatment were evaluated at 1, 3, and 7 days after stroke at histological, behavioral, and biochemical levels. Target genes of miR-181c-5p were then analyzed by qPCR using an RT2 Profiler qPCR Array of pre-coated miR-181c gene targets. Temporal profile expression data suggested that miR-181c-5p was significantly downregulated (p < 0.05 vs ST-PH) up to 7 days after post-stroke SI. MiR-181c-5p mimic treatment significantly increased miR-181c-5p expression in brain tissue and showed partial swift recovery in sensorimotor deficit. Target gene analysis identified downregulation of several calcium signaling-related genes, e.g., Cpne2 and Gria 1 & 2 after miR-181c-5p mimic treatment. In summary, present data suggests that miR-181c-5p is a potential target for post-stroke SI. Data also suggests that genes related to calcium and glutamate signaling might be involved in the beneficial effect of the miR-181c-5p mimic.

Novel application of amino-acid buffered solution for neuroprotection against ischemia/reperfusion injury

Ischemic neuron loss contributes to brain dysfunction in patients with cardiac arrest (CA). Histidine–tryptophan–ketoglutarate (HTK) solution is a preservative used during organ transplantation. We tested the potential of HTK to protect neurons from severe hypoxia (SH) following CA. We isolated rat primary cortical neurons and induced SH with or without HTK. Changes in caspase-3, hypoxia-inducible factor 1-alpha (HIF-1α), and nicotinamide adenine dinucleotide phosphate oxidase-4 (NOX4) expression were evaluated at different time points up to 72 h. Using a rat asphyxia model, we induced CA-mediated brain damage and then completed resuscitation. HTK or sterile saline was administered into the left carotid artery. Neurological deficit scoring and mortality were evaluated for 3 days. Then the rats were sacrificed for evaluation of NOX4 and H₂O₂ levels in blood and brain. In the in vitro study, HTK attenuated SH- and H₂O₂-mediated cytotoxicity in a volume- and time-dependent manner, associated with persistent HIF-1α expression and reductions in procaspase-3 activation and NOX4 expression. The inhibition of HIF-1α abrogated HTK’s effect on NOX4. In the in vivo study, neurological scores were significantly improved by HTK. H₂O₂ level, NOX4 activity, and NOX4 gene expression were all decreased in the brain specimens of HTK-treated rats. Our results suggest that HTK acts as an effective neuroprotective solution by maintaining elevated HIF-1α level, which was associated with inhibited procaspase-3 activation and decreased NOX4 expression.

Multiomic Analysis of Zebrafish Models of Acute Organophosphorus Poisoning With Different Severity

Organophosphorus compounds are acetylcholinesterase inhibitors used as pesticides and chemical warfare nerve agents. Acute organophosphorus poisoning (acute OPP) affects 3 million people, with 300 000 deaths annually worldwide. Severe acute OPP effects include overstimulation of cholinergic neurons, seizures, status epilepticus, and finally, brain damage. In a previous study, we developed 3 different chemical models of acute OPP in zebrafish larvae. To elucidate the complex pathophysiological pathways related to acute OPP, we used integrative omics (proteomic, transcriptomics, and metabolomics) on these 3 animal models. Our results show that these stochastic, apparently disparate morphological phenotypes can result from almost linear concentration-response variations in molecular levels. Results from the multiomics analysis strongly suggest that endoplasmic reticulum stress might play a central role in the pathophysiology of severe acute OPP, emphasizing the urgent need of further research on this molecular pathway. Endoplasmic reticulum stress could be an important therapeutic target to be included in the treatment of patients with severe acute OPP.

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.

Mitochondria and neuroprotection in stroke: Cationic arginine-rich peptides (CARPs) as a novel class of mitochondria-targeted neuroprotective therapeutics

Stroke is the second leading cause of death globally and represents a major cause of devastating long-term disability. Despite sustained efforts to develop clinically effective neuroprotective therapies, presently there is no clinically available neuroprotective agent for stroke. As a central mediator of neurodamaging events in stroke, mitochondria are recognised as a critical neuroprotective target, and as such, provide a focus for developing mitochondrial-targeted therapeutics. In recent years, cationic arginine-rich peptides (CARPs) have been identified as a novel class of neuroprotective agent with several demonstrated mechanisms of action, including their ability to target mitochondria and exert positive effects on the organelle. This review provides an overview on neuronal mitochondrial dysfunction in ischaemic stroke pathophysiology and highlights the potential beneficial effects of CARPs on mitochondria in the ischaemic brain following stroke.

Contribution of Zinc-Dependent Delayed Calcium Influx via TRPC5 in Oxidative Neuronal Death and its Prevention by Novel TRPC Antagonist

Oxidative stress is a key mediator of neuronal death in acute brain injuries, such as epilepsy, trauma, and stroke. Although it is accompanied by diverse cellular changes, increases in levels of intracellular zinc ion (Zn²⁺) and calcium ion (Ca²⁺) may play a critical causative role in oxidative neuronal death. However, the mechanistic link between Zn²⁺ and Ca²⁺ dyshomeostasis in neurons during oxidative stress is not well-understood. Here, we show that the exposure of cortical neurons to H₂O₂ led to a zinc-triggered calcium influx, which resulted in neuronal death. The cyclin-dependent kinase inhibitor, NU6027, inhibited H₂O₂-induced Ca²⁺ increases and subsequent cell death in cortical neurons, without affecting the early increase in Zn²⁺. Therefore, we attempted to identify the zinc-regulated Ca²⁺ pathway that was inhibited by NU6027. The expression profile in cortical neurons identified transient receptor potential cation channel 5 (TRPC5) as a candidate that is known to involve in the generation of epileptiform burst firing and epileptic neuronal death (Phelan KD et al. 2012a; Phelan KD et al. 2013b). NU6027 inhibited basal and zinc-augmented TRPC5 currents in TRPC5-overexpressing HEK293 cells. Consistently, cortical neurons from TRPC5 knockout mice were highly resistant to H₂O₂-induced death. Moreover, NU6027 is neuroprotective in kainate-treated epileptic rats. Our results demonstrate that TRPC5 is a novel therapeutic target against oxidative neuronal injury in prolonged seizures and that NU6027 is a potent inhibitor of TRPC5.

Molecular mechanism of estrogen-mediated neuroprotection in the relief of brain ischemic injury

Background

This study aimed to explore the molecular mechanism of estrogen-mediated neuroprotection in the relief of cerebral ischemic injury. The gene expression profiles were downloaded from Gene Expression Omnibus database, and differentially expressed genes (DEGs) were identified using limma package in R software. Further, DEGs were subjected to Gene Ontology (GO) cluster analysis using online Gene Ontology Enrichment Analysis Software Toolkit and to GO functional enrichment analysis using DAVID software. Using the Gene Set Analysis Toolkit V2, enrichment analysis of Kyoto Encyclopedia of Genes and Genomes pathways was performed. In addition, protein-protein interaction (PPI) network was constructed using STRING database, and submodule analysis of PPI network. Lastly, the significant potential target sites of microRNAs (miRNAs) were predicted using Molecular Signatures Database, and the function analysis of targets of predicted miRNA was also performed using DAVID software.

Results

In total, 321 DEGs were screened in the estrogen-treated sample. The DEGs were mainly associated with intracellular signaling and metabolic pathways, such as calcium channel, calcineurin complex, insulin secretion, low-density lipoprotein reconstruction, and starch or sugar metabolism. In addition, GO enrichment analysis indicated an altered expression of the genes related to starch and sucrose metabolism, retinol metabolism, anti-apoptosis (eg., BDNF and ADAM17) and response to endogenous stimulus. The constructed PPI network comprised of 243 nodes and 590 interaction pairs, and four submodules were obtained from PPI network. Among the module d, four glutamate receptors as Gria4, Gria3, Grin3a and Grik4 were highlighted. Further, 5 novel potential regulatory miRNAs were also predicted. MIR-338 and MIR520D were closely associated with cell cycle, while the targets of MIR-376A and MIR-376B were only involved in cell soma.

Conclusions

The DEGs in estrogen-treated samples are closely associated with calcium channel, glutamate induced excitotoxicity and anti-apoptotic activity. In addition, some functionally significant DEGs such as BDNF, ADAM17, Gria4, Gria3, Grin3a, Grik4, Gys2 and Ugtla2, and new miRNAs like MIR-338 and MIR-376A were identified, which may serve as potential therapeutic targets for the effective treatment of cerebral ischemic injury.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0630-y) contains supplementary material, which is available to authorized users.

Non-linear actions of physiological agents: Finite disarrangements elicit fitness benefits

Finite disarrangements of important (vital) physiological agents and nutrients can induce plethora of beneficial effects, exceeding mere attenuation of the specific stress. Such response to disrupted homeostasis appears to be universally conserved among species. The underlying mechanism of improved fitness and longevity, when physiological agents act outside their normal range is similar to hormesis, a phenomenon whereby toxins elicit beneficial effects at low doses. Due to similarity with such non-linear response to toxins described with J-shaped curve, we have coined a new term “mirror J-shaped curves” for non-linear response to finite disarrangement of physiological agents. Examples from the clinical trials and basic research are provided, along with the unifying mechanisms that tie classical non-linear response to toxins with the non-linear response to physiological agents (glucose, oxygen, osmolarity, thermal energy, calcium, body mass, calorie intake and exercise). Reactive oxygen species and cytosolic calcium seem to be common triggers of signaling pathways that result in these beneficial effects. Awareness of such phenomena and exploring underlying mechanisms can help physicians in their everyday practice. It can also benefit researchers when designing studies and interpreting growing number of scientific data showing non-linear responses to physiological agents.

Electron transport chain in a thermotolerant yeast

Yeasts capable of growing and surviving at high temperatures are regarded as thermotolerant. For appropriate functioning of cellular processes and cell survival, the maintenance of an optimal redox state is critical of reducing and oxidizing species. We studied mitochondrial functions of the thermotolerant Kluyveromyces marxianus SLP1 and the mesophilic OFF1 yeasts, through the evaluation of its mitochondrial membrane potential (ΔΨ_m), ATPase activity, electron transport chain (ETC) activities, alternative oxidase activity, lipid peroxidation. Mitochondrial membrane potential and the cytoplasmic free Ca²⁺ ions (Ca²⁺ cyt) increased in the SLP1 yeast when exposed to high temperature, compared with the mesophilic yeast OFF1. ATPase activity in the mesophilic yeast diminished 80% when exposed to 40° while the thermotolerant SLP1 showed no change, despite an increase in the mitochondrial lipid peroxidation. The SLP1 thermotolerant yeast exposed to high temperature showed a diminution of 33% of the oxygen consumption in state 4. The uncoupled state 3 of oxygen consumption did not change in the mesophilic yeast when it had an increase of temperature, whereas in the thermotolerant SLP1 yeast resulted in an increase of 2.5 times when yeast were grown at 30^o, while a decrease of 51% was observed when it was exposed to high temperature. The activities of the ETC complexes were diminished in the SLP1 when exposed to high temperature, but also it was distinguished an alternative oxidase activity. Our results suggest that the mitochondria state, particularly ETC state, is an important characteristic of the thermotolerance of the SLP1 yeast strain.

Multimodal Imaging of Neurometabolic Pathology due to Traumatic Brain Injury

The impact of traumatic brain injury (TBI) involves a combination of complex biochemical processes beginning with the initial insult and lasting for days, months and even years post-trauma. These changes range from neuronal integrity losses to neurotransmitter imbalance and metabolite dysregulation, leading to the release of pro- or anti-apoptotic factors which mediate cell survival or death. Such dynamic processes affecting the brain's neurochemistry can be monitored using a variety of neuroimaging techniques, whose combined use can be particularly useful for understanding patient-specific clinical trajectories. Here, we describe how TBI changes the metabolism of essential neurochemical compounds, summarize how neuroimaging approaches facilitate the study of such alterations, and highlight promising ways in which neuroimaging can be used to investigate post-TBI changes in neurometabolism.

Aquaporin-4: A Potential Therapeutic Target for Cerebral Edema

Aquaporin-4 (AQP4) is a family member of water-channel proteins and is dominantly expressed in the foot process of glial cells surrounding capillaries. The predominant expression at the boundaries between cerebral parenchyma and major fluid compartments suggests the function of aquaporin-4 in water transfer into and out of the brain parenchyma. Accumulating evidences have suggested that the dysregulation of aquaporin-4 relates to the brain edema resulting from a variety of neuro-disorders, such as ischemic or hemorrhagic stroke, trauma, etc. During edema formation in the brain, aquaporin-4 has been shown to contribute to the astrocytic swelling, while in the resolution phase, it has been seen to facilitate the reabsorption of extracellular fluid. In addition, aquaporin-4-deficient mice are protected from cytotoxic edema produced by water intoxication and brain ischemia. However, aquaporin-4 deletion exacerbates vasogenic edema in the brain of different pathological disorders. Recently, our published data showed that the upregulation of aquaporin-4 in astrocytes probably contributes to the transition from cytotoxic edema to vasogenic edema. In this review, apart from the traditional knowledge, we also introduce our latest findings about the effects of mesenchymal stem cells (MSCs) and microRNA-29b on aquaporin-4, which could provide powerful intervention tools targeting aquaporin-4.

The Good and Bad Sides of NAAG

Why has such a small peptide been the source of controversy in neuroscience over the last 5 decades? Is N-acetyl-aspartyl-glutamate (NAAG) a neurotransmitter? Is NAAG located in neuronal tissue or in astrocytes? Is NAAG involved in neuropsychiatric and neurodegenerative disorders? Is NAAG therapeutically beneficial in the treatment of stroke or in initiating cascades of events leading to psychosis? After many years of intense research there is no clear consensus within the scientific community on how NAAG behaves in the brain. One of the major controversies about NAAG is its physiological action at N-methyl-d-aspartate (NMDA) receptors. While some researchers strongly argue that NAAG acts as a weak agonist at NMDA receptors, others have suggested that NAAG could behave as a potent antagonist. Published data from our laboratory demonstrate that the effect of NAAG on NMDA receptors could be influenced by a number of factors including the subcellular localization and subunit composition of NMDA receptors, as well as protons. In this chapter, we will summarize the knowledge of the literature on NAAG, however, we will place emphasis on our recently published data. More specifically, we have reported interesting findings on the effects of NAAG on NMDA receptors at synaptic and extrasynaptic sites using a pharmacological paradigm to distinguish the two populations of NMDA receptors. Additionally, we have evaluated the role of NAAG on GluN2A- and GluN2B-containing NMDA receptors using a HEK293 cell recombinant system. Finally, we have studied the effects of NAAG on GluN2A- and GluN2B-containing NMDA receptors in different extracellular pH conditions. We believe that our findings could potentially resolve some aspects of the debate regarding the role of NAAG at NMDA receptors.

TRPing on the pore phenomenon: what do we know about transient receptor potential ion channel-related pore dilation up to now?

Ion channels allow for rapid ion diffusion through the plasma membrane. In some conditions, ion channels induce changes in the critical plasma membrane permeability that permit 900-Da solutes to enter cells. This process is known as the pore phenomenon. Some transient receptor potential (TRP) channel subtypes have been highlighted such as the P2X7 receptor, plasma membrane VDAC-1 channel, and pannexin hemichannels. The TRP ion channels are considered multimodal transducers that respond to several kinds of stimuli. In addition, many TRP channel subtypes are involved in physiological and pathophysiological processes such as inflammation, pain, and cancer. The TRPA1, TRPM8, and TRPV1-4 subtypes have been shown to promote large-molecular-weight solute uptake, including impermeable fluorescent dyes, QX-314 hydrophilic lidocaine derivative, gabapentin, and antineoplastic drugs. This review discusses the current knowledge of TRP-associated pores and encourages scientists to study their features and explore them as novel therapeutic tools.

Antimicrobial peptides and complement in neonatal hypoxia-ischemia induced brain damage

Hypoxic-ischemic encephalopathy (HIE) is a clinical condition in the neonate, resulting from oxygen deprivation around the time of birth. HIE affects 1-5/1000 live births worldwide and is associated with the development of neurological deficits, including cerebral palsy, epilepsy, and cognitive disabilities. Even though the brain is considered as an immune-privileged site, it has innate and adaptive immune response and can produce complement (C) components and antimicrobial peptides (AMPs). Dysregulation of cerebral expression of AMPs and C can exacerbate or ameliorate the inflammatory response within the brain. Brain ischemia triggers a prolonged inflammatory response affecting the progression of injury and secondary energy failure and involves both innate and adaptive immune systems, including immune-competent and non-competent cells. Following injury to the central nervous system (CNS), including neonatal hypoxia-ischemia (HI), resident microglia, and astroglia are the main cells providing immune defense to the brain in a stimulus-dependent manner. They can express and secrete pro-inflammatory cytokines and therefore trigger prolonged inflammation, resulting in neurodegeneration. Microglial cells express and release a wide range of inflammation-associated molecules including several components of the complement system. Complement activation following neonatal HI injury has been reported to contribute to neurodegeneration. Astrocytes can significantly affect the immune response of the CNS under pathological conditions through production and release of pro-inflammatory cytokines and immunomodulatory AMPs. Astrocytes express β-defensins, which can chemoattract and promote maturation of dendritic cells (DC), and can also limit inflammation by controlling the viability of these same DC. This review will focus on the balance of complement components and AMPs within the CNS following neonatal HI injury and the effect of that balance on the subsequent brain damage.

Direct interactions of adaptor protein complexes 1 and 2 with the copper transporter ATP7A mediate its anterograde and retrograde trafficking

ATP7A is a P-type ATPase in which diverse mutations lead to X-linked recessive Menkes disease or occipital horn syndrome. Recently, two previously unknown ATP7A missense mutations, T994I and P1386S, were shown to cause an isolated distal motor neuropathy without clinical or biochemical features of other ATP7A disorders. These mutant alleles cause subtle defects in ATP7A intracellular trafficking, resulting in preferential plasma membrane localization compared with wild-type ATP7A. We reported previously that ATP7A(P1386S) causes unstable insertion of the eighth and final transmembrane segment, preventing proper position of the carboxyl-terminal tail in a proportion of mutant molecules. Here, we utilize this and other naturally occurring and engineered mutant ATP7A alleles to identify mechanisms of normal ATP7A trafficking. We show that adaptor protein (AP) complexes 1 and 2 physically interact with ATP7A and that binding is mediated in part by a carboxyl-terminal di-leucine motif. In contrast to other ATP7A missense mutations, ATP7A(P1386S) partially disturbs interactions with both APs, leading to abnormal axonal localization in transfected NSC-34 motor neurons and altered calcium-signaling following glutamate stimulation. Our results imply that AP-1 normally tethers ATP7A at the trans-Golgi network in the somatodendritic segments of motor neurons and that alterations affecting the ATP7A carboxyl-terminal tail induce release of the copper transporter to the axons or axonal membranes. The latter effects are intensified by diminished interaction with AP-2, impeding ATP7A retrograde trafficking. Taken together, these findings further illuminate the normal molecular mechanisms of ATP7A trafficking and suggest a pathophysiological basis for ATP7A-related distal motor neuropathy.

The major cholesterol metabolite cholestane-3β,5α,6β-triol functions as an endogenous neuroprotectant

Overstimulation of NMDA-type glutamate receptors is believed to be responsible for neuronal death of the CNS in various disorders, including cerebral and spinal cord ischemia. However, the intrinsic and physiological mechanisms of modulation of these receptors are essentially unknown. Here we report that cholestane-3β,5α,6β-triol (triol), a major metabolite of cholesterol, is an endogenous neuroprotectant and protects against neuronal injury both in vitro and in vivo via negative modulation of NMDA receptors. Treatment of cultured neurons with triol protects against glutamate-induced neurotoxicity, and administration of triol significantly decreases neuronal injury after spinal cord ischemia in rabbits and transient focal cerebral ischemia in rats. An inducible elevation of triol is associated with ischemic preconditioning and subsequent neuroprotection in the spinal cord of rabbits. This neuroprotection is effectively abolished by preadministration of a specific inhibitor of triol synthesis. Physiological concentrations of triol attenuate [Ca(2+)]i induced by glutamate and decrease inward NMDA-mediated currents in cultured cortical neurons and HEK-293 cells transiently transfected with NR1/NR2B NMDA receptors. Saturable binding of [(3)H]triol to cerebellar granule neurons and displacement of [(3)H]MK-801 binding to NMDA receptors by triol suggest that direct blockade of NMDA receptors may underlie the neuroprotective properties. Our findings suggest that the naturally occurring oxysterol, the major cholesterol metabolite triol, functions as an endogenous neuroprotectant in vivo, which may provide novel insights into understanding and developing potential therapeutics for disorders in the CNS.

Current status of hypothermia for hypoxemic ischemia of the newborn

This article reviews the pathophysiology of hypoxic-ischemic brain injury, and the impact of hypothermia as neuroprotection in the clinical setting. The results of trials performed in well resourced and mid and low resourced countries is presented. Infant and childhood outcome following hypothermia is provided. Biomarkers of outcome that are clinical, electrophysiological and imaging which will be helpful to clinicians are noted. Management of infants with encephalopathy, including safety of hypothermia is reviewed. The article concludes with knowledge gaps in neuroprotection and the future of hypothermia therapy.

Sodium-calcium exchangers (NCX): molecular hallmarks underlying the tissue-specific and systemic functions

NCX proteins explore the electrochemical gradient of Na(+) to mediate Ca(2+)-fluxes in exchange with Na(+) either in the Ca(2+)-efflux (forward) or Ca(2+)-influx (reverse) mode, whereas the directionality depends on ionic concentrations and membrane potential. Mammalian NCX variants (NCX1-3) and their splice variants are expressed in a tissue-specific manner to modulate the heartbeat rate and contractile force, the brain's long-term potentiation and learning, blood pressure, renal Ca(2+) reabsorption, the immune response, neurotransmitter and insulin secretion, apoptosis and proliferation, mitochondrial bioenergetics, etc. Although the forward mode of NCX represents a major physiological module, a transient reversal of NCX may contribute to EC-coupling, vascular constriction, and synaptic transmission. Notably, the reverse mode of NCX becomes predominant in pathological settings. Since the expression levels of NCX variants are disease-related, the selective pharmacological targeting of tissue-specific NCX variants could be beneficial, thereby representing a challenge. Recent structural and biophysical studies revealed a common module for decoding the Ca(2+)-induced allosteric signal in eukaryotic NCX variants, although the phenotype variances in response to regulatory Ca(2+) remain unclear. The breakthrough discovery of the archaebacterial NCX structure may serve as a template for eukaryotic NCX, although the turnover rates of the transport cycle may differ ~10(3)-fold among NCX variants to fulfill the physiological demands for the Ca(2+) flux rates. Further elucidation of ion-transport and regulatory mechanisms may lead to selective pharmacological targeting of NCX variants under disease conditions.

Calcium influx and calpain activation mediate preclinical retinal neurodegeneration in autoimmune optic neuritis

Optic neuritis is a common manifestation of multiple sclerosis, an inflammatory demyelinating disease of the CNS. Recently, the neurodegenerative component of multiple sclerosis has come under focus particularly because permanent disability in patients correlates well with neurodegeneration; and observations in both humans and multiple sclerosis animal models highlight neurodegeneration of retinal ganglion cells as an early event. After myelin oligodendrocyte glycoprotein immunization of Brown Norway rats, significant retinal ganglion cell loss precedes the onset of pathologically defined autoimmune optic neuritis. To study the role calcium and calpain activation may play in mediating early degeneration, manganese-enhanced magnetic resonance imaging was used to monitor preclinical calcium elevations in the retina and optic nerve of myelin oligodendrocyte glycoprotein-immunized Brown Norway rats. Calcium elevation correlated with an increase in calpain activation during the induction phase of optic neuritis, as revealed by increased calpain-specific cleavage of spectrin. The relevance of early calpain activation to neurodegeneration during disease induction was addressed by performing treatment studies with the calpain inhibitor calpeptin. Treatment not only reduced calpain activity but also protected retinal ganglion cells from preclinical degeneration. These data indicate that elevation of retinal calcium levels and calpain activation are early events in autoimmune optic neuritis, providing a potential therapeutic target for neuroprotection.

Neuroprotective therapies after perinatal hypoxic-ischemic brain injury

Hypoxic-ischemic (HI) brain injury is one of the main causes of disabilities in term-born infants. It is the result of a deprivation of oxygen and glucose in the neural tissue. As one of the most important causes of brain damage in the newborn period, the neonatal HI event is a devastating condition that can lead to long-term neurological deficits or even death. The pattern of this injury occurs in two phases, the first one is a primary energy failure related to the HI event and the second phase is an energy failure that takes place some hours later. Injuries that occur in response to these events are often manifested as severe cognitive and motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of HI injury, there is an increasing need to find effective therapies as new opportunities for the reduction of brain damage and its long term effects. Some of these therapies are focused on prevention of the production of reactive oxygen species, anti-inflammatory effects, anti-apoptotic interventions and in a later stage, the stimulation of neurotrophic properties in the neonatal brain which could be targeted to promote neuronal and oligodendrocyte regeneration.

Acute Hypoxia Activates an ENaC-like Channel in Rat Pheochromocytoma (PC12) Cells

Cells can resist and even recover from stress induced by acute hypoxia, whereas chronic hypoxia often leads to irreversible damage and eventually death. Although little is known about the response(s) to acute hypoxia in neuronal cells, alterations in ion channel activity could be preferential. This study aimed to elucidate which channel type is involved in the response to acute hypoxia in rat pheochromocytomal (PC12) cells as a neuronal cell model. Using perfusing solution saturated with 95% N(2) and 5% CO(2), induction of cell hypoxia was confirmed based on increased intracellular Ca(2+) with diminished oxygen content in the perfusate. During acute hypoxia, one channel type with a conductance of about 30 pS (2.5 pA at -80 mV) was activated within the first 2~3 min following onset of hypoxia and was long-lived for more than 300 ms with high open probability (P(o), up to 0.8). This channel was permeable to Na(+) ions, but not to K(+), Ca(+), and Cl(-) ions, and was sensitively blocked by amiloride (200 nM). These characteristics and behaviors were quite similar to those of epithelial sodium channel (ENaC). RT-PCR and Western blot analyses confirmed that ENaC channel was endogenously expressed in PC12 cells. Taken together, a 30-pS ENaC-like channel was activated in response to acute hypoxia in PC12 cells. This is the first evidence of an acute hypoxia-activated Na(+) channel that can contribute to depolarization of the cell.

Mitochondria in traumatic brain injury and mitochondrial-targeted multipotential therapeutic strategies

Traumatic brain injury (TBI) is a major health and socioeconomic problem throughout the world. It is a complicated pathological process that consists of primary insults and a secondary insult characterized by a set of biochemical cascades. The imbalance between a higher energy demand for repair of cell damage and decreased energy production led by mitochondrial dysfunction aggravates cell damage. At the cellular level, the main cause of the secondary deleterious cascades is cell damage that is centred in the mitochondria. Excitotoxicity, Ca(2+) overload, reactive oxygen species (ROS), Bcl-2 family, caspases and apoptosis inducing factor (AIF) are the main participants in mitochondria-centred cell damage following TBI. Some preclinical and clinical results of mitochondria-targeted therapy show promise. Mitochondria- targeted multipotential therapeutic strategies offer new hope for the successful treatment of TBI and other acute brain injuries.

The alterations of Ca2+/calmodulin/CaMKII/CaV1.2 signaling in experimental models of Alzheimer's disease and vascular dementia

The two critical forms of dementia are Alzheimer's disease (AD) and vascular dementia (VD). The alterations of Ca(2+)/calmodulin/CaMKII/CaV1.2 signaling in AD and VD have not been well elucidated. Here we have demonstrated changes in the levels of CaV1.2, calmodulin, p-CaMKII, p-CREB and BDNF proteins by Western blot analysis and the co-localization of p-CaMKII/CaV1.2 by double-labeling immunofluorescence in the hippocampus of APP/PS1 mice and VD gerbils. Additionally, expression of these proteins and intracellular calcium levels were examined in cultured neurons treated with Aβ1-42. The expression of CaV1.2 protein was increased in VD gerbils and in cultured neurons but decreased in APP/PS1 mice; the expression of calmodulin protein was increased in APP/PS1 mice and VD gerbils; levels of p-CaMKII, p-CREB and BDNF proteins were decreased in AD and VD models. The number of neurons in which p-CaMKII and CaV1.2 were co-localized, was decreased in the CA1 and CA3 regions in two models. Intracellular calcium was increased in the cultured neurons treated with Aβ1-42. Collectively, our results suggest that the alterations in CaV1.2, calmodulin, p-CaMKII, p-CREB and BDNF can be reflective of an involvement in the impairment in memory and cognition in AD and VD models.

Therapeutic hypothermia for neonatal encephalopathy

OPINION STATEMENT

Neonatal Hypoxic-ischemic encephalopathy in full term infants has been associated with a high risk for morbidity and mortality. The patho-physiology of brain injury following hypoxia-ischemia, noted in preclinical models, is a cascade of events resulting from excitotoxic and oxidative injury culminating in cell death. Hypothermia has been noted to be protective by inhibiting various events in the cascade of injury. Major randomized clinical trials in neonatal HIE have demonstrated reduction in death and disability and continued safety and efficacy of neuroprotection in childhood. There is now clinical and imaging evidence for hypothermia as neuroprotection. Hypothermia should be offered to term infants with either severe acidosis at birth or resuscitation needing continued ventilation and evidence of either moderate or severe encephalopathy within 6 hours of birth. The target temperature should be 33° to 34 °C and duration of cooling should be 72 hours, as per the published trials. Rewarming should be slow, at 0.5 °C per hour. Infants should have serial neurological examinations during and at the end of cooling and at discharge. Multiorgan function should be supported and hypocarbia should be avoided during ventilator therapy. If available, the amplitude integrated EEG should be obtained prior to cooling and following rewarming. All infants should have magnetic resonance brain imaging studies within 1 to 2 weeks of age. Information from the neurological examination, aEEG and MRI studies will be helpful in discussing prognosis with parents. All infants should be followed for a minimum of 18 months to evaluate growth parameters and neurodevelopment al outcome.

Treatment advances in neonatal neuroprotection and neurointensive care

Knowledge of the nature, prognosis, and ways to treat brain lesions in neonatal infants has increased remarkably. Neonatal hypoxic-ischaemic encephalopathy (HIE) in term infants, mirrors a progressive cascade of excito-oxidative events that unfold in the brain after an asphyxial insult. In the laboratory, this cascade can be blocked to protect brain tissue through the process of neuroprotection. However, proof of a clinical effect was lacking until the publication of three positive randomised controlled trials of moderate hypothermia for term infants with HIE. These results have greatly improved treatment prospects for babies with asphyxia and altered understanding of the theory of neuroprotection. The studies show that moderate hypothermia within 6 h of asphyxia improves survival without cerebral palsy or other disability by about 40% and reduces death or neurological disability by nearly 30%. The search is on to discover adjuvant treatments that can further enhance the effects of hypothermia.