Role of mitochondrial Ca2+ regulation in neuronal and glial cell signalling

Astroglial S100B Secretion Is Mediated by Ca2+ Mobilization from Endoplasmic Reticulum: A Study Using Forskolin and DMSO as Secretagogues

S100B, a homodimeric Ca2+-binding protein, is produced and secreted by astrocytes, and its extracellular levels have been used as a glial marker in brain damage and neurodegenerative and psychiatric diseases; however, its mechanism of secretion is elusive. We used primary astrocyte cultures and calcium measurements from real-time fluorescence microscopy to investigate the role of intracellular calcium in S100B secretion. In addition, the dimethyl sulfoxide (DMSO) effect on S100B was investigated in vitro and in vivo using Wistar rats. We found that DMSO, a widely used vehicle in biological assays, is a powerful S100B secretagogue, which caused a biphasic response of Ca2+ mobilization. Our data show that astroglial S100B secretion is triggered by the increase in intracellular Ca2+ and indicate that this increase is due to Ca2+ mobilization from the endoplasmic reticulum. Also, blocking plasma membrane Ca2+ channels involved in the Ca2+ replenishment of internal stores decreased S100B secretion. The DMSO-induced S100B secretion was confirmed in vivo and in ex vivo hippocampal slices. Our data support a nonclassic vesicular export of S100B modulated by Ca2+, and the results might contribute to understanding the mechanism underlying the astroglial release of S100B.

Acrylamide treatment alters the level of Ca2+ and Ca2+-related protein kinase in spinal cords of rats

This study aimed to analyze the neurological changes induced by acrylamide (ACR) poisoning and their underlying mechanisms within the spinal cords of male adult Wistar rats. The rats were randomly divided into three groups (n = 9 rats per group). ACR was intraperitoneally injected to produce axonopathy according to the daily dosing schedules of 20 or 40 mg/kg/day of ACR for eight continuous weeks (three times per week). During the exposure period, body weights and gait scores were assessed, and the concentration of Ca²⁺ was calculated in 27 mice. Protein kinase A (PKA), protein kinase C (PKC), cyclin-dependent protein kinase 5 (CDK5), and P35 were assessed by electrophoretic resolution and Western blotting. The contents of 3'-cyclic adenosine monophosphate (cAMP) and calmodulin (CaM) were determined using ELISA kits, and the activities of calcium/calmodulin-dependent protein kinase II (CaMKII), PKA, and PKC were determined using the commercial Signa TECTPKAassay kits. Compared with control rats, treatment with 20 and 40 mg/kg of ACR decreased body weight and increased gait scores at 8 weeks. Intracellular Ca²⁺ levels increased significantly in treated rats; CaM, PKC, CDK5, and P35 levels were significantly decreased; and PKA and cAMP levels remained unchanged. CaMKII, PKA, and PKC activities increased significantly. The results indicated that ACR can damage neurofilaments by affecting the contents and activities of CaM, CaMKII, PKA, cAMP, PKC, CDK5, and P35, which could result in ACR toxic neuropathy.

Gliocrine System: Astroglia as Secretory Cells of the CNS

Astrocytes are secretory cells, actively participating in cell-to-cell communication in the central nervous system (CNS). They sense signaling molecules in the extracellular space, around the nearby synapses and also those released at much farther locations in the CNS, by their cell surface receptors, get excited to then release their own signaling molecules. This contributes to the brain information processing, based on diffusion within the extracellular space around the synapses and on convection when locales relatively far away from the release sites are involved. These functions resemble secretion from endocrine cells, therefore astrocytes were termed to be a part of the gliocrine system in 2015. An important mechanism, by which astrocytes release signaling molecules is the merger of the vesicle membrane with the plasmalemma, i.e., exocytosis. Signaling molecules stored in astroglial secretory vesicles can be discharged into the extracellular space after the vesicle membrane fuses with the plasma membrane. This leads to a fusion pore formation, a channel that must widen to allow the exit of the Vesiclal cargo. Upon complete vesicle membrane fusion, this process also integrates other proteins, such as receptors, transporters and channels into the plasma membrane, determining astroglial surface signaling landscape. Vesiclal cargo, together with the whole vesicle can also exit astrocytes by the fusion of multivesicular bodies with the plasma membrane (exosomes) or by budding of vesicles (ectosomes) from the plasma membrane into the extracellular space. These astroglia-derived extracellular vesicles can later interact with various target cells. Here, the characteristics of four types of astroglial secretory vesicles: synaptic-like microvesicles, dense-core vesicles, secretory lysosomes, and extracellular vesicles, are discussed. Then machinery for vesicle-based exocytosis, second messenger regulation and the kinetics of exocytotic vesicle content discharge or release of extracellular vesicles are considered. In comparison to rapidly responsive, electrically excitable neurons, the receptor-mediated cytosolic excitability-mediated astroglial exocytotic vesicle-based transmitter release is a relatively slow process.

Neurointegrity and neurophysiology: astrocyte, glutamate, and carbon monoxide interactions

Astrocyte contributions to brain function and prevention of neuropathologies are as extensive as that of neurons. Astroglial regulation of glutamate, a primary neurotransmitter, is through uptake, release through vesicular and non-vesicular pathways, and catabolism to intermediates. Homeostasis by astrocytes is considered to be of primary importance in determining normal central nervous system health and central nervous system physiology - glutamate is central to dynamic physiologic changes and central nervous system stability. Gasotransmitters may affect diverse glutamate interactions positively or negatively. The effect of carbon monoxide, an intrinsic central nervous system gasotransmitter, in the complex astrocyte homeostasis of glutamate may offer insights to normal brain development, protection, and its use as a neuromodulator and neurotherapeutic. In this article, we will review the effects of carbon monoxide on astrocyte homeostasis of glutamate.

Sonic hedgehog protects endometrial hyperplasial cells against oxidative stress via suppressing mitochondrial fission protein dynamin-like GTPase (Drp1)

Hh/Gli1 cascade as well as Gsk3β-Gli1 crosstalk play crucial role in estrogen-dependent progression of endometrial hyperplasia (EH). However, the underlying mechanisms involved in progression of disease still remain unclear. In the present study, we explored the role of Hh signaling in protection of endometrial hyperplasial cells against oxidative stress and the underlying mechanism involved therein. EH cells were found to be more resistant towards H₂O₂-induced oxidative stress (IC₅₀: ~ 3×) as compared with normal endometrial cells. Estrogen (E2) pre-treatment followed by cytotoxic dose of H₂O_2, almost rescued the EH cells from apoptosis and caused the increased expression of downstream Shh signaling molecules i.e., Smo, Ptch and Gli1. Whereas pretreatment with cyclopamine was not able to curtail H₂O₂-induced effects indicating that estrogen protects these cells via activation of Shh pathway. Further, H₂O₂-induced ROS and lipid peroxidation alongwith decreased activities of antioxidant enzymes glutathione peroxidase and superoxide dismutase were found to be reversed in EH cells pre-exposed to E2 or rShh. The rShh suppressed H₂O₂-induced cell death and caused attenuation of mitochondrial apoptotic mediators and prevented disruption in mitochondrial morphology and mitochondrial membrane potential in EH cells. The functional blockage of signaling by Shh siRNA or Gli1siRNA led to significantly increased expression of mitochondrial fission protein dynamin-like GTPase (Drp1). The H₂O₂-treated EH cells showed diminished Gli1 and increased Drp1 expression, concurrent with reduced p-Drp1-(serine637). Whereas rShh pre-treated EH cells presented normal mitochondrial dynamics with dense, long networks of mitochondria alongwith nuclear accumulation of Gli1 and the decreased expression of Drp1. Overall, our results implicated that Shh signaling modulates antioxidant defense system and stabilizes mitochondrial dynamics by suppressing Drp1 protein which maintains survival of EH cells against oxidative stress.

Biological rationale and potential clinical use of gabapentin and pregabalin in bipolar disorder, insomnia and anxiety: protocol for a systematic review and meta-analysis

INTRODUCTION

Gabapentin has been extensively prescribed off-label for psychiatric indications, with little established evidence of efficacy. Gabapentin and pregabalin, a very similar drug with the same mechanism of action, bind to a subunit of voltage-dependent calcium channels which are implicated in the aetiopathogenesis of bipolar disorder, anxiety and insomnia. This systematic review and meta-analysis aims to collect and critically appraise all the available evidence about the efficacy and tolerability of gabapentin and pregabalin in the treatment of bipolar disorder, insomnia and anxiety.

METHODS AND ANALYSIS

We will include all randomised controlled trials (RCTs) reported as double-blind and comparing gabapentin or pregabalin with placebo or any other active pharmacological treatment (any preparation, dose, frequency, route of delivery or setting) in patients with bipolar disorder, anxiety or insomnia. For consideration of adverse effects (tolerability), single-blind or open-label RCTs and non-randomised evidence will also be summarised. The main outcomes will be efficacy (measured as dichotomous and continuous outcome) and acceptability (proportion of patients who dropped out of the allocated treatment). Published and unpublished studies will be sought through relevant database searches, trial registries and websites; all reference selection and data extraction will be conducted by at least 2 independent reviewers. We will conduct a random-effects meta-analysis to synthesise all evidence for each outcome. Heterogeneity between studies will be investigated by the I² statistic. Data from included studies will be entered into a funnel plot for investigation of small-study effects. No subgroup analysis will be undertaken, but we will carry out sensitivity analyses about combination treatment, psychiatric comorbidity, use of rescue medications and fixed versus random-effects model.

ETHICS AND DISSEMINATION

This review does not require ethical approval. This protocol has been registered on PROSPERO (CRD42016041802). The results of the systematic review will be disseminated via publication in a peer-reviewed journal.

Astrocytic Pathological Calcium Homeostasis and Impaired Vesicle Trafficking in Neurodegeneration

Although the central nervous system (CNS) consists of highly heterogeneous populations of neurones and glial cells, clustered into diverse anatomical regions with specific functions, there are some conditions, including alertness, awareness and attention that require simultaneous, coordinated and spatially homogeneous activity within a large area of the brain. During such events, the brain, representing only about two percent of body mass, but consuming one fifth of body glucose at rest, needs additional energy to be produced. How simultaneous energy procurement in a relatively extended area of the brain takes place is poorly understood. This mechanism is likely to be impaired in neurodegeneration, for example in Alzheimer’s disease, the hallmark of which is brain hypometabolism. Astrocytes, the main neural cell type producing and storing glycogen, a form of energy in the brain, also hold the key to metabolic and homeostatic support in the central nervous system and are impaired in neurodegeneration, contributing to the slow decline of excitation-energy coupling in the brain. Many mechanisms are affected, including cell-to-cell signalling. An important question is how changes in cellular signalling, a process taking place in a rather short time domain, contribute to the neurodegeneration that develops over decades. In this review we focus initially on the slow dynamics of Alzheimer’s disease, and on the activity of locus coeruleus, a brainstem nucleus involved in arousal. Subsequently, we overview much faster processes of vesicle traffic and cytosolic calcium dynamics, both of which shape the signalling landscape of astrocyte-neurone communication in health and neurodegeneration.

Mitochondrial calcium homeostasis: Implications for neurovascular and neurometabolic coupling

Mitochondrial function is critical to maintain high rates of oxidative metabolism supporting energy demands of both spontaneous and evoked neuronal activity in the brain. Mitochondria not only regulate energy metabolism, but also influence neuronal signaling. Regulation of "energy metabolism" and "neuronal signaling" (i.e. neurometabolic coupling), which are coupled rather than independent can be understood through mitochondria's integrative functions of calcium ion (Ca²⁺) uptake and cycling. While mitochondrial Ca²⁺ do not affect hemodynamics directly, neuronal activity changes are mechanistically linked to functional hyperemic responses (i.e. neurovascular coupling). Early in vitro studies lay the foundation of mitochondrial Ca²⁺ homeostasis and its functional roles within cells. However, recent in vivo approaches indicate mitochondrial Ca²⁺ homeostasis as maintained by the role of mitochondrial Ca²⁺ uniporter (mCU) influences system-level brain activity as measured by a variety of techniques. Based on earlier evidence of subcellular cytoplasmic Ca²⁺ microdomains and cellular bioenergetic states, a mechanistic model of Ca²⁺ mobilization is presented to understand systems-level neurovascular and neurometabolic coupling. This integrated view from molecular and cellular to the systems level, where mCU plays a major role in mitochondrial and cellular Ca²⁺ homeostasis, may explain the wide range of activation-induced coupling across neuronal activity, hemodynamic, and metabolic responses.

Ethanol-Induced Alterations in Purkinje Neuron Dendrites in Adult and Aging Rats: a Review

Uncomplicated alcoholics suffer from discrete motor dysfunctions that become more pronounced with age. These deficits involve the structure and function of Purkinje neurons (PN), the sole output neurons from the cerebellar cortex. This review focuses on alterations to the PN dendritic arbor in the adult and aging Fischer 344 rat following lengthy alcohol consumption. It describes seminal studies using the Golgi-Cox method which proposed a model for ethanol-induced dendritic regression. Subsequent ultrastructural studies of PN dendrites showed dilation of the extensive smooth endoplasmic reticulum (SER) which preceded and accompanied dendritic regression. The component of the SER that was most affected by ethanol was the sarco/endoplasmic reticulum Ca(2+) ATPase pump (SERCA) responsible for resequestration of calcium into the SER. Ethanol-induced decreases in SERCA pump levels, similar to the finding of SER dilation, preceded and occurred concomitantly with dendritic regression. Discrete ethanol-induced deficits in balance also accompanied these decreases. Ethanol-induced ER stress within the SER of PN dendrites was proposed as an underlying cause of dendritic regression. It was recently shown that increased activation of caspase 12, inherent to the ER, occurred in PN of acute slices in ethanol-fed rats and was most pronounced following 40 weeks of ethanol treatment. These findings shed new light into alcohol-induced disruption in PN dendrites providing a new model for the discrete but critical changes in motor function in aging, adult alcoholics.

Role of mitochondrial calcium uptake homeostasis in resting state fMRI brain networks

Mitochondrial Ca(2+) uptake influences both brain energy metabolism and neural signaling. Given that brain mitochondrial organelles are distributed in relation to vascular density, which varies considerably across brain regions, we hypothesized different physiological impacts of mitochondrial Ca(2+) uptake across brain regions. We tested the hypothesis by monitoring brain "intrinsic activity" derived from the resting state functional MRI (fMRI) blood oxygen level dependent (BOLD) fluctuations in different functional networks spanning the somatosensory cortex, caudate putamen, hippocampus and thalamus, in normal and perturbed mitochondrial Ca(2+) uptake states. In anesthetized rats at 11.7 T, mitochondrial Ca(2+) uptake was inhibited or enhanced respectively by treatments with Ru360 or kaempferol. Surprisingly, mitochondrial Ca(2+) uptake inhibition by Ru360 and enhancement by kaempferol led to similar dose-dependent decreases in brain-wide intrinsic activities in both the frequency domain (spectral amplitude) and temporal domain (resting state functional connectivity; RSFC). The fact that there were similar dose-dependent decreases in the frequency and temporal domains of the resting state fMRI-BOLD fluctuations during mitochondrial Ca(2+) uptake inhibition or enhancement indicated that mitochondrial Ca(2+) uptake and its homeostasis may strongly influence the brain's functional organization at rest. Interestingly, the resting state fMRI-derived intrinsic activities in the caudate putamen and thalamic regions saturated much faster with increasing dosage of either drug treatment than the drug-induced trends observed in cortical and hippocampal regions. Regional differences in how the spectral amplitude and RSFC changed with treatment indicate distinct mitochondrion-mediated spontaneous neuronal activity coupling within the various RSFC networks determined by resting state fMRI.

Loose excitation-secretion coupling in astrocytes

Astrocytes play an important housekeeping role in the central nervous system. Additionally, as secretory cells, they actively participate in cell-to-cell communication, which can be mediated by membrane-bound vesicles. The gliosignaling molecules stored in these vesicles are discharged into the extracellular space after the vesicle membrane fuses with the plasma membrane. This process is termed exocytosis, regulated by SNARE proteins, and triggered by elevations in cytosolic calcium levels, which are necessary and sufficient for exocytosis in astrocytes. For astrocytic exocytosis, calcium is sourced from the intracellular endoplasmic reticulum store, although its entry from the extracellular space contributes to cytosolic calcium dynamics in astrocytes. Here, we discuss calcium management in astrocytic exocytosis and the properties of the membrane-bound vesicles that store gliosignaling molecules, including the vesicle fusion machinery and kinetics of vesicle content discharge. In astrocytes, the delay between the increase in cytosolic calcium activity and the discharge of secretions from the vesicular lumen is orders of magnitude longer than that in neurons. This relatively loose excitation-secretion coupling is likely tailored to the participation of astrocytes in modulating neural network processing.

Expression of glucose transporters in the prelaminar region of the optic-nerve head of the pig as determined by immunolabeling and tissue culture

Background

To develop the use of cultured tissue of the prelaminar optic nerve of the pig to explore possible alterations of the astrocyte-axon metabolic pathways in glaucoma, we map the distribution of the glucose transporters GLUT1 and GLUT3 in fresh and cultured tissue.

Methods

We monitor cell survival in cultures of the prelaminar optic-nerve tissue, measuring necrosis and apoptosis markers biochemically as well as morphologically, and establish the presence of the glucose transporters GLUT1 and GLUT3. We map the distribution of these transporters with immunolabeling in histological sections of the optic nerve using confocal and electronic transmission microscopy.

Results

We find that the main death type in prelaminar culture is apoptosis. Caspase 7 staining reveals an increment in apoptosis from day 1 to day 4 and a reduction from day 4 to day 8. Western blotting for GLUT1 shows stability with increased culture time. CLSM micrographs locate GLUT1 in the columnar astrocytes and in the area of axonal bundles. Anti-GLUT3 predominantly labels axonal bundles. TEM immunolabeling with colloidal gold displays a very specific distribution of GLUT-1 in the membranes of vascular endothelial cells and in periaxonal astrocyte expansions. The GLUT-3 isoform is observed with TEM only in axons in the axonal bundles.

Conclusions

Tissue culture is suitable for apoptosis-induction experiments. The results suggest that glucose is transported to the axonal cleft intracytoplasmically and delivered to the cleft by GLUT1 transporters. As monocarboxylate transporters have been reported in the prelaminar region of the optic-nerve head, this area is likely to use both lactate and glucose as energy sources.

Excitable Astrocytes: Ca(2+)- and cAMP-Regulated Exocytosis

During neural activity, neurotransmitters released at synapses reach neighbouring cells, such as astrocytes. These get excited via numerous mechanisms, including the G protein coupled receptors that regulate the cytosolic concentration of second messengers, such as Ca(2+) and cAMP. The stimulation of these pathways leads to feedback modulation of neuronal activity and the activity of other cells by the release of diverse substances, gliosignals that include classical neurotransmitters such as glutamate, ATP, or neuropeptides. Gliosignal molecules are released from astrocytes through several distinct molecular mechanisms, for example, by diffusion through membrane channels, by translocation via plasmalemmal transporters, or by vesicular exocytosis. Vesicular release regulated by a stimulus-mediated increase in cytosolic second messengers involves a SNARE-dependent merger of the vesicle membrane with the plasmalemma. The coupling between the stimulus and vesicular secretion of gliosignals in astrocytes is not as tight as in neurones. This is considered an adaptation to regulate homeostatic processes in a slow time domain as is the case in the endocrine system (slower than the nervous system), hence glial functions constitute the gliocrine system. This article provides an overview of the mechanisms of excitability, involving Ca(2+) and cAMP, where the former mediates phasic signalling and the latter tonic signalling. The molecular, anatomic, and physiologic properties of the vesicular apparatus mediating the release of gliosignals is presented.

Oxidative/nitrosative stress and antidepressants: targets for novel antidepressants

The brain is an organ predisposed to oxidative/nitrosative stress. This is especially true in the case of aging as well as several neurodegenerative diseases. Under such circumstances, a decline in the normal antioxidant defense mechanisms leads to an increase in the vulnerability of the brain to the deleterious effects of oxidative damage. Highly reactive oxygen/nitrogen species damage lipids, proteins, and mitochondrial and neuronal genes. Unless antioxidant defenses react appropriately to damage inflicted by radicals, neurons may experience microalteration, microdysfunction, and degeneration. We reviewed how oxidative and nitrosative stresses contribute to the pathogenesis of depressive disorders and reviewed the clinical implications of various antioxidants as future targets for antidepressant treatment.

Mitochondrial calcium uptake capacity modulates neocortical excitability

Local calcium (Ca(2+)) changes regulate central nervous system metabolism and communication integrated by subcellular processes including mitochondrial Ca(2+) uptake. Mitochondria take up Ca(2+) through the calcium uniporter (mCU) aided by cytoplasmic microdomains of high Ca(2+). Known only in vitro, the in vivo impact of mCU activity may reveal Ca(2+)-mediated roles of mitochondria in brain signaling and metabolism. From in vitro studies of mitochondrial Ca(2+) sequestration and cycling in various cell types of the central nervous system, we evaluated ranges of spontaneous and activity-induced Ca(2+) distributions in multiple subcellular compartments in vivo. We hypothesized that inhibiting (or enhancing) mCU activity would attenuate (or augment) cortical neuronal activity as well as activity-induced hemodynamic responses in an overall cytoplasmic and mitochondrial Ca(2+)-dependent manner. Spontaneous and sensory-evoked cortical activities were measured by extracellular electrophysiology complemented with dynamic mapping of blood oxygen level dependence and cerebral blood flow. Calcium uniporter activity was inhibited and enhanced pharmacologically, and its impact on the multimodal measures were analyzed in an integrated manner. Ru360, an mCU inhibitor, reduced all stimulus-evoked responses, whereas Kaempferol, an mCU enhancer, augmented all evoked responses. Collectively, the results confirm aforementioned hypotheses and support the Ca(2+) uptake-mediated integrative role of in vivo mitochondria on neocortical activity.

Mitochondrial functional state impacts spontaneous neocortical activity and resting state FMRI

Mitochondrial Ca²⁺ uptake, central to neural metabolism and function, is diminished in aging whereas enhanced after acute/sub-acute traumatic brain injury. To develop relevant translational models for these neuropathologies, we determined the impact of perturbed mitochondrial Ca²⁺ uptake capacities on intrinsic brain activity using clinically relevant markers. From a multi-compartment estimate of probable baseline Ca²⁺ ranges in the brain, we hypothesized that reduced or enhanced mitochondrial Ca²⁺ uptake capacity would decrease or increase spontaneous neuronal activity respectively. As resting state fMRI-BOLD fluctuations and stimulus-evoked BOLD responses have similar physiological origins [1] and stimulus-evoked neuronal and hemodynamic responses are modulated by mitochondrial Ca²⁺ uptake capacity [2], [3] respectively, we tested our hypothesis by measuring hemodynamic fluctuations and spontaneous neuronal activities during normal and altered mitochondrial functional states. Mitochondrial Ca²⁺ uptake capacity was perturbed by pharmacologically inhibiting or enhancing the mitochondrial Ca²⁺ uniporter (mCU) activity. Neuronal electrical activity and cerebral blood flow (CBF) fluctuations were measured simultaneously and integrated with fMRI-BOLD fluctuations at 11.7T. mCU inhibition reduced spontaneous neuronal activity and the resting state functional connectivity (RSFC), whereas mCU enhancement increased spontaneous neuronal activity but reduced RSFC. We conclude that increased or decreased mitochondrial Ca²⁺ uptake capacities lead to diminished resting state modes of brain functional connectivity.

Translating neurotrophic and cellular plasticity: from pathophysiology to improved therapeutics for bipolar disorder

OBJECTIVE

Bipolar disorder (BD) likely involves, at a molecular and cellular level, dysfunctions of critical neurotrophic, cellular plasticity and resilience pathways and neuroprotective processes. Therapeutic properties of mood stabilizers are presumed to result from a restoration of the function of these altered pathways and processes through a wide range of biochemical and molecular effects. We aimed to review the altered pathways and processes implicated in BD, such as neurotrophic factors, mitogen-activated protein kinases, Bcl-2, phosphoinositol signaling, intracellular calcium and glycogen synthase kinase-3.

METHODS

We undertook a literature search of recent relevant journal articles, book chapter and reviews on neurodegeneration and neuroprotection in BD. Search words entered were 'brain-derived neurotrophic factor,''Bcl-2,''mitogen-activated protein kinases,''neuroprotection,''calcium,''bipolar disorder,''mania,' and 'depression.'

RESULTS

The most consistent and replicated findings in the pathophysiology of BD may be classified as follows: i) calcium dysregulation, ii) mitochondrial/endoplasmic reticulum dysfunction, iii) glial and neuronal death/atrophy and iv) loss of neurotrophic/plasticity effects in brain areas critically involved in mood regulation. In addition, the evidence supports that treatment with mood stabilizers; in particular, lithium restores these pathophysiological changes.

CONCLUSION

Bipolar disorder is associated with impairments in neurotrophic, cellular plasticity and resilience pathways as well as in neuroprotective processes. The evidence supports that treatment with mood stabilizers, in particular lithium, restores these pathophysiological changes. Studies that attempt to prevent (intervene before the onset of the molecular and cellular changes), treat (minimize severity of these deficits over time), and rectify (reverse molecular and cellular deficits) are promising therapeutic strategies for developing improved treatments for bipolar disorder.

Disrupted axo-glial junctions result in accumulation of abnormal mitochondria at nodes of ranvier

Mitochondria and other membranous organelles are frequently enriched in the nodes and paranodes of peripheral myelinated axons, particularly those of large caliber. The physiologic role(s) of this organelle enrichment and the rheologic factors that regulate it are not well understood. Previous studies suggest that axonal transport of organelles across the nodal/paranodal region is locally regulated. In this study, we have examined the ultrastructure of myelinated axons in the sciatic nerves of mice deficient in the contactin-associated protein (Caspr), an integral junctional component. These mice, which lack the normal septate-like junctions that promote attachment of the glial (paranodal) loops to the axon, contain aberrant mitochondria in their nodal/paranodal regions. These mitochondria are typically large and swollen and occupy prominent varicosities of the nodal axolemma. In contrast, mitochondria located outside the nodal/paranodal regions of the myelinated axons appear normal. These findings suggest that paranodal junctions regulate mitochondrial transport and function in the axoplasm of the nodal/paranodal region of myelinated axons of peripheral nerves. They further implicate the paranodal junctions in playing a role, either directly or indirectly, in the local regulation of energy metabolism in the nodal region.

Calcium signalling in astroglia

Astroglia possess excitability based on movements of Ca(2+) ions between intracellular compartments and plasmalemmal Ca(2+) fluxes. This "Ca(2+) excitability" is controlled by several families of proteins located in the plasma membrane, within the cytosol and in the intracellular organelles, most notably in the endoplasmic reticulum (ER) and mitochondria. Accumulation of cytosolic Ca(2+) can be caused by the entry of Ca(2+) from the extracellular space through ionotropic receptors and store-operated channels expressed in astrocytes. Plasmalemmal Ca(2+) ATP-ase and sodium-calcium exchanger extrude cytosolic Ca(2+) to the extracellular space; the exchanger can also operate in reverse, depending of the intercellular Na(+) concentration, to deliver Ca(2+) to the cytosol. The ER internal store possesses inositol 1,4,5-trisphosphate receptors which can be activated upon stimulation of astrocytes through a multiple plasma membrane metabotropic G-protein coupled receptors. This leads to release of Ca(2+) from the ER and its elevation in the cytosol, the level of which can be modulated by mitochondria. The mitochondrial uniporter takes up Ca(2+) into the matrix, while free Ca(2+) exits the matrix through the mitochondrial Na(+)/Ca(2+) exchanger as well as via transient openings of the mitochondrial permeability transition pore. One of the prominent consequences of astroglial Ca(2+) excitability is gliotransmission, a release of transmitters from astroglia which can lead to signalling to adjacent neurones.

Effects of mood stabilizers on mitochondrial respiratory chain activity in brain of rats treated with d-amphetamine

Bipolar disorder (BD) is a devastating major mental illness associated with high rates of suicide and work loss. There is an emerging body of data suggesting that bipolar disorder is associated with mitochondrial dysfunction. In this context, the present study aims to investigate the effects of mood stabilizers lithium (Li) and valproate (VPT) on mitochondrial respiratory chain activity in brain of rats undergoing treatment with the pro-manic agent d-AMPH d-amphetamine (d-AMPH). In the reversal treatment, Wistar rats were first given d-AMPH or saline for 14 days, and then, between days 8 and 14, rats were treated with Li, VPA or saline (Sal). In the prevention treatment, rats were pretreated with Li, VPA or Sal. Locomotor behavior was assessed using the open-field task and mitochondrial chain activity complexes I, II, III and IV were measured in brain structures (hippocampus, striatum and prefrontal). Li and VPA reversed and prevented d-AMPH-induced hyperactivity. In both experiments, d-AMPH inhibited mitochondrial respiratory chain activity in all analyzed structures. In the reversal treatment, VPA reversed d-AMPH-induced dysfunction in all brain regions analyzed. In the prevention experiment, the effects of Li and VPA on d-AMPH-induced mitochondrial dysfunction were dependent on the brain region analyzed. These findings suggested that dopamine can be an important link for the mitochondrial dysfunction seen in BD and, Li and VPA exert protective effects against this d-AMPH-induced mitochondrial dysfunction, but this effect varies depending on the brain region and the treatment regimen.

GM1 and nerve growth factor modulate mitochondrial membrane potential and neurofilament light mRNA expression in cultured dorsal root ganglion and spinal cord neurons during excitotoxic glutamate exposure

Monosialoganglioside GM1 is a known neurotrophic factor. Nerve growth factor (NGF), a member of the neurotrophin family, is important for the survival, differentiation and maturation of neurons. The aim of this study was to test whether administration of GM1 and NGF can ameliorate glutamate (Glu) neurotoxicity in primary cultured embryonic rat dorsal root ganglia (DRG) and spinal cord neurons, and to investigate the mechanism underlying any effect. DRG and spinal cord neurons were exposed to the following treatments: Glu (2 mmol/L); Glu (2 mmol/L) plus GM1 (10mg/mL); Glu (2 mmol/l) plus NGF (10 ng/mL); Glu (2 mmol/L) plus GM1 (5mg/mL) and NGF (5 ng/mL). Cell viability was assessed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, ultrastructural alterations were examined using inverse phase contrast microscopy and electron microscopy, mitochondrial membrane potential was measured using rhodamine 123 labeling and flow cytometry, and neurofilament light (NF-L) mRNA expression was detected by reverse transcription-polymerase chain reaction. It was found that GM1 and NGF can increase the viability of neurons incubated with Glu, which, after GM1 and NGF treatment, were almost morphologically normal. The mitochondrial membrane potential of neurons was lowest for neurons treated with Glu alone, and that for neurons treated with Glu plus GM1 and NGF was higher than that for treatment with GM1 or NGF alone. The mRNA of NF-L was expressed at the highest level in neurons treated with Glu plus GM1 and NGF. Our findings indicate that NGF and GM1 act synergistically to protect DRG and spinal cord neurons from Glu cytotoxicity. NGF and GM1 may function by maintaining normal mitochondrial membrane potential or by promoting NF-L mRNA expression.

Regulated exocytosis in astrocytic signal integration

Astrocytes can be considered as signal integrators in central nervous system activity. These glial cells can respond to signals from the heterocellular milieu of the brain and subsequently release various molecules to signal to themselves and/or other neighboring neural cells. An important functional module that enables signal integration in astrocytes is exocytosis, a Ca(2+)-dependent process consisting of vesicular fusion to the plasma membrane. Astrocytes utilize regulated exocytosis to release various signaling molecules stored in the vesicular lumen. Here we review the properties of exocytotic release of three classes of gliotransmitters: (i) amino acids, (ii) nucleotides and (iii) peptides. Vesicles may carry not only lumenal cargo, but also membrane-associated molecules. Therefore, we also discuss exocytosis as a delivery mechanism for transporters and receptors to the plasma membrane, where these proteins are involved in astrocytic intercellular signaling.

Gliotransmission: Exocytotic release from astrocytes

Gliotransmitters are chemicals released from glial cells fulfilling a following set of criteria: (i) they are synthesized by and/or stored in glia; (ii) their regulated release is triggered by physiological and/or pathological stimuli; (iii) they activate rapid (milliseconds to seconds) responses in neighboring cells; and (iv) they play a role in (patho)physiological processes. Astrocytes can release a variety of gliotransmitters into the extracellular space using several different mechanisms. In this review, we focus on exocytotic mechanism(s) underlying the release of three classes of gliotransmitters: (i) amino acids, such as, glutamate and d-serine; (ii) nucleotides, like adenosine 5'-triphosphate; and (iii) peptides, such as, atrial natriuretic peptide and brain-derived neurotrophic factor. It is becoming clear that astrocytes are endowed with elements that qualify them as cells communicating with neurons and other cells within the central nervous system by employing regulated exocytosis.

The trinity of Ca2+ sources for the exocytotic glutamate release from astrocytes

Astrocytes can exocytotically release the transmitter glutamate. Increased cytosolic Ca(2+) concentration is necessary and sufficient in this process. The source of Ca(2+) for the Ca(2+)-dependent exocytotic release of glutamate from astrocytes predominately comes from endoplasmic reticulum (ER) stores with contributions from both inositol 1,4,5-trisphosphate- and ryanodine/caffeine-sensitive stores. An additional source of Ca(2+) comes from the extracellular space via store-operated Ca(2+) entry due to the depletion of ER stores. Here transient receptor potential canonical type 1 containing channels permit entry of Ca(2+) to the cytosol, which can then be transported by the store-specific Ca(2+)-ATPase to (re)fill ER. Mitochondria can modulate cytosolic Ca(2+) levels by affecting two aspects of the cytosolic Ca(2+) kinetics in astrocytes. They play a role in immediate sequestration of Ca(2+) during the cytosolic Ca(2+) increase in stimulated astrocytes as a result of Ca(2+) entry into the cytosol from ER stores and/or extracellular space. As cytosolic Ca(2+)declines due to activity of pumps, such as the smooth ER Ca(2+)-ATPase, free Ca(2+) is slowly released by mitochondria into cytosol. Taken together, the trinity of Ca(2+) sources, ER, extracellular space and mitochondria, can vary concentration of cytosolic Ca(2+) which in turn can modulate Ca(2+)-dependent vesicular glutamate release from astrocytes. An understanding of how these Ca(2+) sources contribute to glutamate release in (patho)physiology of astrocytes will provide information on astrocytic functions in health and disease and may also open opportunities for medical intervention.

PDGF receptor-{beta} modulates metanephric mesenchyme chemotaxis induced by PDGF AA

PDGF B chain or PDGF receptor (PDGFR)-beta-deficient (-/-) mice lack mesangial cells. To study responses of alpha- and beta-receptor activation to PDGF ligands, metanephric mesenchymal cells (MMCs) were established from embryonic day E11.5 wild-type (+/+) and -/- mouse embryos. PDGF BB stimulated cell migration in +/+ cells, whereas PDGF AA did not. Conversely, PDGF AA was chemotactic for -/- MMCs. The mechanism by which PDGFR-beta inhibited AA-induced migration was investigated. PDGF BB, but not PDGF AA, increased intracellular Ca(2+) and the production of reactive oxygen species (ROS) in +/+ cells. Transfection of -/- MMCs with the wild-type beta-receptor restored cell migration and ROS generation in response to PDGF BB and inhibited AA-induced migration. Inhibition of Ca(2+) signaling facilitated PDGF AA-induced chemotaxis in the wild-type cells. The antioxidant N-acetyl-l-cysteine (NAC) or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) abolished the BB-induced increase in intracellular Ca(2+) concentration, suggesting that ROS act as upstream mediators of Ca(2+) in suppressing PDGF AA-induced migration. These data indicate that ROS and Ca(2+) generated by active PDGFR-beta play an essential role in suppressing PDGF AA-induced migration in +/+ MMCs. During kidney development, PDGFR beta-mediated ROS generation and Ca(2+) influx suppress PDGF AA-induced chemotaxis in metanephric mesenchyme.

Ethanol-related increases in degenerating bodies in the Purkinje neuron dendrites of aging rats

Chronic ethanol consumption in aging rats results in regression of Purkinje neuron (PN) dendritic arbors ([Pentney, 1995 Measurements of dendritic pathlengths provide evidence that ethanol-induced lengthening of terminal dendritic segments may result from dendritic regression. Alcohol Alcohol. 30, 87-96]), loss of synapses (Dlugos and Pentney, 1997), dilation of the smooth endoplasmic reticulum (SER), and the formation of degenerating bodies within PN dendrites ([Dlugos, C.A., 2006a. Ethanol-Related Smooth Endoplasmic Reticulum Dilation in Purkinje Dendrites of Aging Rats. Alcohol., Clin. Exp. Res. 30, 883-891,Dlugos, C.A., 2006b. Smooth endoplasmic reticulum dilation and degeneration in Purkinje neuron dendrites of aging ethanol-fed female rats. Cerebellum. 5, 155-162]). Dilation of the SER and the formation of degenerating bodies may be a predictor of dendritic regression. Ethanol-induced effects on mitochondria may be involved as mitochondria cooperate with the SER to maintain calcium homeostasis. The purpose of this study was to determine whether degenerating body number and mitochondrial density and structure are altered by chronic ethanol treatment in PN dendrites. Male, Fischer 344 rats, 12 months of age, were fed an ethanol or pair-fed liquid diet, or rat chow for a period of 10, 20, or 40 weeks (15 rats/treatment; 45 rats/treatment duration). Ethanol-fed rats received 35% of their calories as ethanol. At the end of treatment, all animals were euthanized, perfused, and tissue prepared for electron microscopy. The densities of degenerating bodies and mitochondria, mitochondrial areas, and the distance between the SER and the mitochondria were measured. Results showed that there was an ethanol-related increase in degenerating bodies compared to controls at 40 weeks. Ethanol-induced alterations to mitochondria were absent. Correlation of the present results with those of previous studies suggest that degenerating bodies may be formed from membrane reabsorption during dendritic regression or from degenerating SER whose function has been compromised by dilation.

Pulses of extracellular K+ produce two cytosolic Ca2+ transients that display different temperature dependence and carbonyl cyanide m-chlorophenyl sensitivity in SH-SY5Y cells

In SH-SY5Y cells we have shown that stimulation with high extracellular K+ ([K+]e) evokes a transient increase in cytoplasmic Ca2+ ([Ca2+]cyt) (K+on) that is triggered by the opening of voltage-dependent Ca2+ channels and followed by Ca2+ -induced Ca2+ release from the endoplasmic reticulum (Xu, F., Zhang, J., Recio-Pinto, E. and Blanck, T.J., Halothane and isoflurane augment depolarization-induced cytosolic CA2+ transients and attenuate carbachol-stimulated CA2+ transients, Anesthesiology, 92 (2000) 1746-56). The removal of high-[K+]e results in a second transient increase in [Ca2+]cyt (K+off) that is independent of extracellular Ca2+ (Corrales, A., Montoya, G.J., Sutachan, J.J., Cornillez-Ty, G., Garavito-Aguilar, Z., Xu, F., Blanck, T.J. and Recio-Pinto, E., Transient increases in extracellular K+ produce two pharmacological distinct cytosolic Ca2+ transients, Brain Res., 1031 (2005) 174-184). In this study we further characterize the properties of K+off. We found that K+off was detectable at near physiological temperatures (34-36 degrees C) but, depending on the level of [K+]e, it was undetectable or highly diminished at room temperature. In contrast, K+on was increased by lowering the temperature. Extracellular Na+ -replacement with K+ did not affect K+off, indicating that K+off was not generated by osmolarity changes. Replacement of extracellular Na+ with choline+ did not affect K+off, indicating that K+off did not result from activity changes of the plasma membrane Na+/Ca2+ exchanger. Caffeine decreased K+on but not K+off. CCCP (carbonyl cyanide m-chlorophenyl), a protonophore uncoupler that decreases mitochondrial Ca2+ uptake, decreased K+on but not K+off. CGP37157, an inhibitor of the mitochondria Na+/Ca2+ exchanger, decreased K+off when added alone but not when added simultaneously with CCCP. Clonazepam had similar effects as CGP37157. These findings indicate that the generation of K+off is strongly temperature-dependent and its pharmacology is distinct from the [Ca2+]cyt changes observed previously at room temperature.

Mitochondrial dysfunction precedes neurodegeneration in mahogunin (Mgrn1) mutant mice

Oxidative stress, ubiquitination defects and mitochondrial dysfunction are commonly associated with neurodegeneration. Mice lacking mahogunin ring finger-1 (MGRN1) or attractin (ATRN) develop age-dependent spongiform neurodegeneration through an unknown mechanism. It has been suggested that they act in a common pathway. As MGRN1 is an E3 ubiquitin ligase, proteomic analysis of Mgrn1 mutant and control brains was performed to explore the hypothesis that loss of MGRN1 causes neurodegeneration via accumulation of its substrates. Many mitochondrial proteins were reduced in Mgrn1 mutants. Subsequent assays confirmed significantly reduced mitochondrial complex IV expression and activity as well as increased oxidative stress in mutant brains. Mitochondrial dysfunction was obvious many months before onset of vacuolation, implicating this as a causative factor. Compatible with the hypothesis that ATRN and MGRN1 act in the same pathway, mitochondrial dysfunction and increased oxidative stress were also observed in the brains of Atrn mutants. Our results suggest that the study of Mgrn1 and Atrn mutant mice will provide insight into a causative molecular mechanism common to many neurodegenerative disorders.

Resveratrol-induced mitochondrial dysfunction and apoptosis are associated with Ca2+ and mCICR-mediated MPT activation in HepG2 cells

Resveratrol, a natural polyphenolic antioxidant, has been reported to possess the cancer chemopreventive potential in wide range by means of triggering tumor cells apoptosis through various pathways. It induced apoptosis through the activation of the mitochondrial pathway in some kinds of cells. In the present reports, we showed that resveratrol-induced HepG2 cell apoptosis and mitochondrial dysfunction was dependent on the induction of the mitochondrial permeability transition (MPT), because resveratrol caused the collapse of the mitochondrial membrane potential (DeltaPsi(m)) with the concomitant release of cytochrome c (Cyt.c). In addition, resveratrol induced a rapid and sustained elevation of intracellular [Ca(2+)], which compromised the mitochondrial DeltaPsi(m) and triggered the process of HepG2 cell apoptosis. In permeabilized HepG2 cells, we further demonstrated that the effect of the resveratrol was indeed synergistic with that of Ca(2+) and Ca(2+) is necessary for resveratrol-induced MPT opening. Calcium-induced calcium release from mitochondria (mCICR) played a key role in mitochondrial dysfunction and cell apoptosis: (1) mCICR inhibitor, ruthenium red (RR), prevent MPT opening and Cyt.c release; and (2) RR attenuated resveratrol-induced HepG2 cell apoptotic death. Furthermore, resveratrol promotes MPT opening by lowering Ca(2+)-threshold. These data suggest modifying mCICR and Ca(2+) threshold to modulate MPT opening may be a potential target to control cell apoptosis induced by resveratrol.

Smooth endoplasmic reticulum dilation and degeneration in Purkinje neuron dendrites of aging ethanol‐fed female rats

The effects of chronic ethanol consumption on the extensive Purkinje neuron (PN) dendritic arbor of male rats include dilation of the smooth endoplasmic reticulum (SER) and dendritic regression. The purpose of the present study was to examine the molecular layer of female rats for the presence of ethanol-related SER dilation and evidence of degeneration within the PN dendritic arbor. Twenty-one 12-month-old Fischer 344 female rats (n = 7/treatment group) received a liquid ethanol, liquid control, or rat chow diet for a period of 40 weeks. Ethanol-fed rats received 35% of their dietary calories as ethanol. Pair-fed rats received a liquid control diet that was isocaloric to the ethanol diet. Chow-fed rats received standard laboratory rat chow ad libitum. At the end of treatment, tissues from the anterior and posterior lobes of the cerebellar vermis were viewed and photographed with the electron microscope. The diameters of SER profiles were measured and the density of degenerating bodies within the PN dendritic arbor was quantitated. In the posterior lobe, ethanol-related SER dilation was apparent. In the anterior lobe, the density of degenerating bodies within PN dendritic shafts was significantly increased but SER dilation in PN dendritic shafts was absent. These results confirm that SER dilation and dendritic degeneration in PN dendrites may precede and contribute to ethanol-related regression in female rats. In addition, comparison of these results with data obtained in male rats from a previous study suggests that PN dendrites in females may be more sensitive to the effects of ethanol.

Increased mitochondrial reactive oxygen species production in newborn brain during hypoglycemia

Hypoglycemia is associated with gray and white matter injury in immature brain, but the specific mechanisms responsible for hypoglycemic brain injury remain poorly defined. We postulated that mitochondrial electron transport chain function is altered during hypoglycemia due to the decreased availability of reducing equivalents, and that altered activity of the electron transport chain would increase mitochondrial production of free radicals and lead to mitochondrial oxidant injury. The present study tests the hypothesis that production of reactive oxygen species (ROS) by cerebral mitochondria is increased during acute hypoglycemia. Studies were performed in an awake, chronically catheterized newborn piglet model. Hypoglycemia (blood glucose 1 mmol/L for 2 h) was induced using a bolus of intravenous lispro insulin, 25 U/kg. Superoxide and hydrogen peroxide production by mitochondria isolated from cerebral cortex of normoglycemic and hypoglycemic newborn piglets was measured using lucigenin- and luminol-derived chemiluminescence. After 2 h of hypoglycemia, superoxide generation was 60% higher and hydrogen peroxide generation was two-fold higher in mitochondria from hypoglycemia animals than in controls (p < 0.005). These data confirm that the ability of the mitochondria to produce ROS is increased after hypoglycemia in immature brain, and are, to our knowledge, the first evidence that ROS may play a role in brain injury due to neonatal hypoglycemia. Increased mitochondrial ROS production could result in alterations in brain structure and function due to oxidant injury to mitochondrial proteins and DNA or changes in oxidant-sensitive signal transduction pathways in brain.

Transfer and Tunneling of Ca2+ from Sarcoplasmic Reticulum to Mitochondria in Skeletal Muscle

The role of mitochondrial Ca2+ transport in regulating intracellular Ca2+ signaling and mitochondrial enzymes involved in energy metabolism is widely recognized in many tissues. However, the ability of skeletal muscle mitochondria to sequester Ca2+ released from the sarcoplasmic reticulum (SR) during the muscle contraction-relaxation cycle is still disputed. To assess the functional cross-talk of Ca2+ between SR and mitochondria, we examined the mutual relationship connecting cytosolic and mitochondrial Ca2+ dynamics in permeabilized skeletal muscle fibers. Cytosolic and mitochondrial Ca2+ transients were recorded with digital photometry and confocal microscopy using fura-2 and mag-rhod-2, respectively. In the presence of 0.5 mM slow Ca2+ buffer (EGTA (ethylene glycolbis(2-aminoethylether)-N,N,N',N'-tetraacetic acid)), application of caffeine induced a synchronized increase in both cytosolic and mitochondrial [Ca2+]. 5 mM fast Ca2+ buffer (BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)) nearly eliminated caffeine-induced increases in [Ca2+]c but only partially decreased the amplitude of mitochondrial Ca2+ transients. Confocal imaging revealed that in EGTA, almost all mitochondria picked up Ca2+ released from the SR by caffeine, whereas only about 70% of mitochondria did so in BAPTA. Taken together, these results indicated that a subpopulation of mitochondria is in close functional and presumably structural proximity to the SR, giving rise to subcellular microdomains in which Ca2+ has preferential access to the juxtaposed organelles.

Molecular characterization of mitocalcin, a novel mitochondrial Ca2+-binding protein with EF-hand and coiled-coil domains

Here we have identified and characterized a novel mitochondrial Ca2+-binding protein, mitocalcin. Western blot analysis demonstrated that mitocalcin was widely expressed in mouse tissues. The expression in brain was increased during post-natal to adult development. Further analyses were carried out in newly established neural cell lines. The protein was expressed specifically in neurons but not in glial cells. Double-labeling studies revealed that mitocalcin was colocalized with mitochondria in neurons differentiated from 2Y-3t cells. In addition, mitocalcin was enriched in the mitochondrial fraction purified from the cells. Immunohistochemical studies on mouse cerebellum revealed that the expression pattern of mitocalcin in glomeruli of the internal granular and molecular layers was well overlapped by the distribution pattern of mitochondria. Immunogold electron microscopy showed that mitocalcin was associated with mitochondrial inner membrane. Overexpression of mitocalcin in 2Y-3t cells resulted in neurite extension. Inhibition of the expression in 2Y-3t cells caused suppression of neurite outgrowth and then cell death. These findings suggest that mitocalcin may play roles in neuronal differentiation and function through the control of mitochondrial function.

mCICR is required for As2O3-induced permeability transition pore opening and cytochrome c release from mitochondria

The permeability transition pore (PTP) is central for apoptosis by acting as a good candidate pathway for the release of Cyt. c and apoptosis induction factors (AIF). Arsenite induces apoptosis via a direct effect on PTP. To characterize the exact mechanism for arsenite induces PTP opening, the effect of Ca2+ on As2O3-induced PTP opening, the relationship between As2O3-induced PTP opening and Cyt. c release from mitochondria and calcium-induced calcium release from mitochondria (mCICR), and the effects of As2O3 on Ca2+-induced PTP opening were studied. The results showed As2O3 induces Cyt. c release by triggering PTP opening. Ca2+ is necessary for As2O3-induced PTP opening. As2O3-induced PTP opening and Cyt. c release depends on mCICR. As2O3 promotes PTP opening by lowering Ca2+-threshold. These results indicated As2O3 induce Cyt. c release from mitochondria by lowering Ca2+-threshold for PTP and triggering mCICR-dependent PTP opening. Suggesting that it is possible to control apoptosis by altering Ca2+ threshold and mCICR to modulate PTP opening and Cyt. c release.

Mitochondrial dysfunction in bipolar disorder: evidence from magnetic resonance spectroscopy research

Magnetic resonance spectroscopy (MRS) affords a noninvasive window on in vivo brain chemistry and, as such, provides a unique opportunity to gain insight into the biochemical pathology of bipolar disorder. Studies utilizing proton ((1)H) MRS have identified changes in cerebral concentrations of N-acetyl aspartate, glutamate/glutamine, choline-containing compounds, myo-inositol, and lactate in bipolar subjects compared to normal controls, while studies using phosphorus ((31)P) MRS have examined additional alterations in levels of phosphocreatine, phosphomonoesters, and intracellular pH. We hypothesize that the majority of MRS findings in bipolar subjects can be fit into a more cohesive bioenergetic and neurochemical model of bipolar illness that is both novel and yet in concordance with findings from complementary methodological approaches. In this review, we propose a hypothesis of mitochondrial dysfunction in bipolar disorder that involves impaired oxidative phosphorylation, a resultant shift toward glycolytic energy production, a decrease in total energy production and/or substrate availability, and altered phospholipid metabolism.

Modelling of calcium handling in airway myocytes

Airway myocytes are the primary effectors of airway reactivity which modulates airway resistance and hence ventilation. Stimulation of airway myocytes results in an increase in the cytosolic Ca(2+) concentration ([Ca(2+)](i)) and the subsequent activation of the contractile apparatus. Many contractile agonists, including acetylcholine, induce [Ca(2+)](i) increase via Ca(2+) release from the sarcoplasmic reticulum through InsP(3) receptors. Several models have been developed to explain the characteristics of InsP(3)-induced [Ca(2+)](i) responses, in particular Ca(2+) oscillations. The article reviews the modelling of the major structures implicated in intracellular Ca(2+) handling, i.e., InsP(3) receptors, SERCAs, mitochondria and Ca(2+)-binding cytosolic proteins. We developed theoretical models specifically dedicated to the airway myocyte which include the major mechanisms responsible for intracellular Ca(2+) handling identified in these cells. These biocomputations pointed out the importance of the relative proportion of InsP(3) receptor isoforms and the respective role of the different mechanisms responsible for cytosolic Ca(2+) clearance in the pattern of [Ca(2+)](i) variations. We have developed a theoretical model of membrane conductances that predicts the variations in membrane potential and extracellular Ca(2+) influx. Stimulation of this model by simulated increase in [Ca(2+)](i) predicts membrane depolarisation, but not great enough to trigger a significant opening of voltage-dependant Ca(2+) channels. This may explain why airway contraction induced by cholinergic stimulation does not greatly depend on extracellular calcium. The development of such models of airway myocytes is important for the understanding of the cellular mechanisms of airway reactivity and their possible modulation by pharmacological agents.

Reduced mitochondrial buffering of voltage-gated calcium influx in aged rat basal forebrain neurons

Alterations of neuronal Ca(2+) homeostatic mechanisms could be responsible for many of the cognitive deficits associated with aging in mammals. Mitochondrial participation in Ca(2+) signaling is now recognized as a prominent feature in neuronal physiology. We combined voltage-clamp electrophysiology with Ca(2+)-sensitive ratiometric microfluorimetry and laser scanning confocal microscopy to investigate the participation in Ca(2+) buffering of in situ mitochondria in acutely dissociated basal forebrain neurons from young and aged F344 rats. By pharmacologically blocking mitochondrial Ca(2+) uptake, we determined that mitochondria were not involved in rapid buffering of small Ca(2+) influx through voltage-gated Ca(2+) channels (VGCCs) in the somatic compartment. For larger Ca(2+) influx, aged mitochondria showed a significant buffering deficit. Evidence obtained with the potentiometric indicator, JC-1, suggests a significantly reduced mitochondrial membrane potential in aged neurons. These results support the interpretation that there is a fundamental difference in the way young and aged neurons buffer Ca(2+), and a corresponding difference in the quality of the Ca(2+) signal experienced by young and aged neurons for different intensities of cytoplasmic Ca(2+) influx.

Dopamine toxicity involves mitochondrial complex I inhibition: implications to dopamine-related neuropsychiatric disorders

Dopamine, which is suggested as a prominent etiological factor in several neuropsychiatric disorders such as Parkinson's disease and schizophrenia, demonstrates neurotoxic properties. In such dopamine-related diseases mitochondrial dysfunction has been reported. Dopamine oxidized metabolites were shown to inhibit the mitochondrial respiratory system both in vivo and in vitro. In the present study, we suggest an additional mechanism for dopamine toxicity, which involves mitochondrial complex I inhibition by dopamine. In human neuroblastoma SH-SY5Y cells dopamine induced a reduction in ATP concentrations, which was negatively correlated to intracellular dopamine levels (r = - 0.96, P = 0.012), and was already evident at non-toxic dopamine doses. In disrupted mitochondria dopamine inhibited complex I activity with IC50 = 11.87 +/- 1.45 microm or 8.12 +/- 0.75 microM in the presence of CoQ or ferricyanide, respectively, with no effect on complexes IV and V activities. The catechol moiety, but not the amine group, of dopamine is essential for complex I inhibition, as is indicated by comparing the inhibitory potential of functionally and structurally dopamine-related compounds. In line with the latter is the finding that chelatable FeCl2 prevented dopamine-induced inhibition of complex I. Monoamine oxidase A and B inhibitors, as well as the antioxidant butylated hydroxytoluene (BHT), did not prevent dopamine-induced inhibition, suggesting that dopamine oxidation was not involved in this process. The present study suggests that dopamine toxicity involves, or is initiated by, its interaction with the mitochondrial oxidative phosphorylation system. We further hypothesize that this interaction between dopamine and mitochondria is associated with mitochondrial dysfunction observed in dopamine-related neuropsychiatric disorders, such as schizophrenia and Parkinson's disease.

Mitochondrial calcium, oxidative stress and apoptosis in a neurodegenerative disease model induced by 3-nitropropionic acid

Intracellular calcium homeostasis is important for cell survival. However, increase in mitochondrial calcium (Ca2+m) induces opening of permeability transition pore (PTP), mitochondrial dysfunction and apoptosis. Since alterations of intracellular Ca2+ and reactive oxygen species (ROS) generation are involved in cell death, they might be involved in neurodegenerative processes such as Huntington's disease (HD). HD is characterized by the inhibition of complex II of respiratory chain and increase in ROS production. In this report, we studied the correlation between the inhibitor of the complex II, 3-nitropropionic acid (3NP), Ca2+ metabolism, apoptosis and behavioural alterations. We showed that 3NP (1 mm) is able to release Ca2+m, as neither Thapsigargin (TAP, 2 microm) nor free-calcium medium affected its effect. PTP inhibitors and antioxidants inhibited this process, suggesting an increase in ROS generation and PTP opening. In addition, 3NP (0.1 mm) also induces apoptotic cell death. Behavioural changes in animals treated with 3NP (20 mg/kg/day for 4 days) were also attenuated by pre- and co-treatment with vitamin E (VE, 20 mg/kg/day). Taken together, our results show that complex II inhibition could involve Ca2+m release, oxidative stress and cell death that may precede motor alterations in neurodegenerative processes such as HD.

Characterisation of a sphingosine 1-phosphate-activated Ca2+ signalling pathway in human neuroblastoma cells

Sphingosine 1-phosphate (S1P) has assumed great importance within neuroscience research because of putative links between S1P-sensitive Edg receptors and neuroregeneration, cell survival, and alterations in neurite outgrowth. In the present study, we examined the mechanisms by which the endogenous complement of S1P-sensitive human Edg receptors can elevate Ca(2+) in the human neuroblastoma cell line, SH-SY5Y. Reverse transcriptase-polymersase chain reaction (RT-PCR) confirmed the expression of mRNA for Edg 3, 5, and 8 subtypes of S1P-responsive Edg receptors in SH-SY5Y cells. Neither S1P nor the muscarinic agonist methacholine were able to cause a change in SH-SY5Y cell morphology, whereas retinoic acid caused a range of changes, including an increase in neurite outgrowth, under similar test conditions. Stimulation with S1P resulted in a slowly rising increase in cytosolic Ca(2+) levels. These responses were dependent upon inositol-1,4,5-trisphosphate receptors, thapsigargin-sensitive endoplasmic reticulum, and also intact functional mitochondria. S1P-evoked Ca(2+) responses were similar in mechanism to those of methacholine, which activated a much faster responding, larger amplitude Ca(2+) response. These studies indicate that in an endogenous human expression system, S1P appears to be an efficacious agonist of Edg receptors. Despite its slow time course of response, S1P appears to activate the same single Ca(2+) store in SH-SY5Y cells as is activated by methacholine and other G protein coupled receptors.

Evidence for interactions between intracellular calcium stores during methylmercury-induced intracellular calcium dysregulation in rat cerebellar granule neurons

Acute exposure to methylmercury (MeHg) causes severe disruption of intracellular Ca(2+) ([Ca(2+)](i)) regulation, which apparently contributes to neuronal death. Activation of the mitochondrial permeability transition pore (MTP) evidently contributes to this effect. We examined in more detail the contribution of mitochondrial Ca(2+) ([Ca(2+)](m)) to elevations of [Ca(2+)](i) caused by acute exposure to a low concentration of MeHg in primary cultures of rat cerebellar granule neurons. In particular, we sought to determine whether interactions occurred between Ca(2+)(i) pools in response to MeHg. Prior depletion of Ca(2+)(m) using carbonyl cyanide m-chlorophenylhydrazone (CCCP) and oligomycin significantly decreased the amplitude of [Ca(2+)](i) release from intracellular stores, and delayed the onset of whole-cell [Ca(2+)](i) elevations, caused by 0.5 microM MeHg. CCCP alone hastened the MeHg-induced release of Ca(2+) within the cell, whereas oligomycin alone delayed the MeHg-induced influx of extracellular Ca(2+). In granule cells loaded with rhod-2 acetoxymethylester to measure changes in [Ca(2+)](m), MeHg exposure caused a biphasic increase in fluorescence. The initial increase in fluorescence occurred in the absence of extracellular Ca(2+) and was abolished by mitochondrial depolarization. The secondary increase was associated with spreading of the dye from punctate staining to whole-cell distribution, and was delayed significantly by the MTP inhibitor cyclosporin A and the smooth endoplasmic reticulum Ca(2+) ATPase inhibitor thapsigargin. We conclude that MeHg causes release of Ca(2+) from the mitochondria through opening of the MTP, which contributes the bulk of the elevated [Ca(2+)](i) observed during MeHg neurotoxicity. Additionally, the Ca(2+) that enters the mitochondria seems to originate in the smooth endoplasmic reticulum, providing a mechanism for the observed mitochondrial Ca(2+) overload.

Mitochondrial dysfunction in schizophrenia: a possible linkage to dopamine

Mitochondria are not only the principal source of high energy intermediates, but play an important role in intracellular calcium buffering, are main producers of reactive oxygen species, and are the source of pro- and antiapoptotic key factors. Moreover, the mitochondria are of a ubiquitous nature and the respiratory chain has a dual genetic basis, i.e. the mitochondrial and the nuclear DNAs. Thus mitochondrial impairment could provide an explanation for the tremendous heterogeneity of clinical and pathological manifestations in schizophrenia. This article reviews several independent lines of evidence that suggest an involvement of mitochondrial dysfunction in schizophrenia. Among them are altered cerebral energy metabolism, mitochondrial hypoplasia, dysfunction of the oxidative phosphorylation system and altered mitochondrial related gene expression. In addition, the interaction between dopamine, a predominant etiological factor in schizophrenia, and mitochondrial respiration is considered as a possible mechanism underlying the hyper- and hypo-activity cycling in schizophrenia. Understanding the role of mitochondria in schizophrenia may encourage novel treatment approaches, the identification of candidate genes and new insights into the pathophysiology and etiology of the disorder.

Inhibition of lipopolysaccharide-induced cyclooxygenase-2, tumor necrosis factor-alpha and [Ca2+]i responses in human microglia by the peripheral benzodiazepine receptor ligand PK11195

The anti-inflammatory actions of the mitochondrial peripheral benzodiazepine receptor (PBR) agonist PK11195 [1-(2-chloro- phenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline-carboxamide] were investigated in human microglia. Application of the microglial inflammatory stimulus lipopolysaccharide (LPS, at 100 ng/mL for 3 h), induced enhancement of the expressions of the inducible enzyme, cyclooxygenase-2 (COX-2) and the pro-inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha). PK11195 (at 50 microm) significantly inhibited the LPS-induced up-regulation of both inflammatory factors; at a lower concentration of PK11195 (2 microm) expression of TNF-alpha, but not COX-2, was reduced. Production of both factors, using immunocytochemistry for COX-2 and ELISA for TNF-alpha, was markedly reduced with 50 microm of PK11195 added to LPS solution. Acute application of LPS induced a transient increase in intracellular Ca2+[Ca2+]i exhibiting both a slow development and recovery in kinetic behavior. This increase in [Ca2+]i consisted primarily of a Ca2+ influx component accompanied by a smaller mobilization from intracellular Ca2+ stores. In the presence of PK11195, the amplitude of the [Ca2+]i response induced by LPS was reduced by 54%. Another mitochondrial agent cyclosporin A (CsA), which also acts at the permeability transition pore (PTP) of mitochondrial membrane but at a site different from the PBR, was ineffective in reducing either the LPS-induced expression of COX-2 and TNF-alpha or the endotoxin increase in [Ca2+]i. These results indicate that the mitochondrial effector PK11195 is a specific and effective agent for inhibiting LPS-induced microglial expressions of COX-2 and TNF-alpha and that modulation of Ca2+-mediated signaling pathways could be involved in the anti-inflammatory actions.

Native and Recombinant Human Edg4 Receptor-Mediated Ca2+ Signalling

We have developed an assay system suitable for assessment of compound action on the Edg4 subtype of the widely expressed lysophosphatidic acid (LPA)-responsive Edg receptor family. Edg4 was stably overexpressed in the rat hepatoma cell line Rh 7777, and a Ca(2+)-based FLIPR assay developed for measurement of functional responses. In order to investigate the mechanisms linking Edg4 activation to cytosolic Ca(2+) elevation, we have also studied LPA signalling in a human neuroblastoma cell line that endogenously expresses Edg4. LPA responses displayed similar kinetics and potency in the two cell lines. The Ca(2+) signal generated by activation of LPA-sensitive receptors in these cells is mediated primarily by endoplasmic reticulum. However, there is a substantial inhibition of the LPA response by FCCP, indicating that mitochondria also play a key role in the LPA response. Partial inhibition of the response by cyclosporin A could indicate an active Ca(2+) release role for mitochondria in the LPA response. The inositol 1,4,5-triphosphate receptor antagonist 2-aminoethyl diphenyl borate markedly inhibits, but does not abolish, the Ca(2+) response to LPA, suggesting further complexity to the signalling pathways activated by Edg receptors. In comparing Edg signalling in recombinant and native cells, there is a striking overall similarity in receptor expression pattern, agonist potency, and the effect of modulators on the Ca(2+) response. This indicates that the Edg4-overexpressing Rh7777 cell line is a very useful model system for studying receptor pharmacology and signalling mechanisms, and for investigating the Edg4 receptor's downstream effects.