Adrenaline induces calcium signal in astrocytes and vasoconstriction via activation of monoamine oxidase

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

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

Exploring the potential of drug repurposing for treating depression

Researchers are interested in drug repurposing or drug repositioning of existing pharmaceuticals because of rising costs and slower rates of new medication development. Other investigations that authorized these treatments used data from experimental research and off-label drug use. More research into the causes of depression could lead to more effective pharmaceutical repurposing efforts. In addition to the loss of neurotransmitters like serotonin and adrenaline, inflammation, inadequate blood flow, and neurotoxins are now thought to be plausible mechanisms. Because of these other mechanisms, repurposing drugs has resulted for treatment-resistant depression. This chapter focuses on therapeutic alternatives and their effectiveness in drug repositioning. Atypical antipsychotics, central nervous system stimulants, and neurotransmitter antagonists have investigated for possible repurposing. Nonetheless, extensive research is required to ensure their formulation, effectiveness, and regulatory compliance.

RAGE induces physiological activation of NADPH oxidase in neurons and astrocytes and neuroprotection

The transmembrane receptor for advanced glycation end products (RAGE) is a signaling receptor for many damage- and pathogen-associated molecules. Activation of RAGE is associated with inflammation and an increase in reactive oxygen species (ROS) production. Although several sources of ROS have been previously suggested, how RAGE induces ROS production is still unclear, considering the multiple targets of pathogen-associated molecules. Here, using acute brain slices and primary co-culture of cortical neurons and astrocytes, we investigated the effects of a range of synthetic peptides corresponding to the fragments of the RAGE V-domain on redox signaling. We found that the synthetic fragment (60-76) of the RAGE V-domain induces activation of ROS production in astrocytes and neurons from the primary co-culture and acute brain slices. This effect occurred through activation of RAGE and could be blocked by a RAGE inhibitor. Activation of RAGE by the synthetic fragment stimulates ROS production in NADPH oxidase (NOX). This RAGE-induced NOX activation produced only minor decreases in glutathione levels and increased the rate of lipid peroxidation, although it also reduced basal and β-amyloid induced cell death in neurons and astrocytes. Thus, specific activation of RAGE induces redox signaling through NOX, which can be a part of a cell protective mechanism.

Major depressive disorder: hypothesis, mechanism, prevention and treatment

Worldwide, the incidence of major depressive disorder (MDD) is increasing annually, resulting in greater economic and social burdens. Moreover, the pathological mechanisms of MDD and the mechanisms underlying the effects of pharmacological treatments for MDD are complex and unclear, and additional diagnostic and therapeutic strategies for MDD still are needed. The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis, but these hypothesis cannot completely explain the pathological mechanism of MDD. Even it is still hard to adopt only one hypothesis to completely reveal the pathogenesis of MDD, thus in recent years, great progress has been made in elucidating the roles of multiple organ interactions in the pathogenesis MDD and identifying novel therapeutic approaches and multitarget modulatory strategies, further revealing the disease features of MDD. Furthermore, some newly discovered potential pharmacological targets and newly studied antidepressants have attracted widespread attention, some reagents have even been approved for clinical treatment and some novel therapeutic methods such as phototherapy and acupuncture have been discovered to have effective improvement for the depressive symptoms. In this work, we comprehensively summarize the latest research on the pathogenesis and diagnosis of MDD, preventive approaches and therapeutic medicines, as well as the related clinical trials.

High levels of FAD autofluorescence indicate pathology preceding cell death

Flavin adenine dinucleotide (FAD) autofluorescence from cells reports on the enzymatic activity which involves FAD as a cofactor. Most of the cellular FAD fluorescence comes from complex II of the electron transport chain in mitochondria and can be assessed with inhibitor analysis. The intensity of FAD autofluorescence is not homogeneous and vary between cells in tissue and in cell culture types. Using primary co-culture of neurons and astrocytes, and human skin fibroblasts we have found that very high FAD autofluorescence is a result of an overactivation of the mitochondrial complex II from ETC and from the activity of monoamine oxidases. Cells with high FAD autofluorescence were mostly intact and were not co-labelled with indicators for necrosis or apoptosis. However, cells with high FAD fluorescence showed activation of apoptosis and necrosis within 24 h after initial measurements. Thus, high level of FAD autofluorescence is an indicator of cell pathology and reveals an upcoming apoptosis and necrosis.

Role of astrocytes in sleep deprivation: accomplices, resisters, or bystanders?

Sleep plays an essential role in all studied animals with a nervous system. However, sleep deprivation leads to various pathological changes and neurobehavioral problems. Astrocytes are the most abundant cells in the brain and are involved in various important functions, including neurotransmitter and ion homeostasis, synaptic and neuronal modulation, and blood-brain barrier maintenance; furthermore, they are associated with numerous neurodegenerative diseases, pain, and mood disorders. Moreover, astrocytes are increasingly being recognized as vital contributors to the regulation of sleep-wake cycles, both locally and in specific neural circuits. In this review, we begin by describing the role of astrocytes in regulating sleep and circadian rhythms, focusing on: (i) neuronal activity; (ii) metabolism; (iii) the glymphatic system; (iv) neuroinflammation; and (v) astrocyte-microglia cross-talk. Moreover, we review the role of astrocytes in sleep deprivation comorbidities and sleep deprivation-related brain disorders. Finally, we discuss potential interventions targeting astrocytes to prevent or treat sleep deprivation-related brain disorders. Pursuing these questions would pave the way for a deeper understanding of the cellular and neural mechanisms underlying sleep deprivation-comorbid brain disorders.

In Vivo Laser-Induced Vasoactive Microenvironmental Setting via a Stimuli-Responsive Microstructured Depot

A stimuli-responsive polymeric three-dimensional microstructured film (PTMF) is a 3D structure with an array of sealed chambers on its external surface. In this work, we demonstrate the use of PTMF as a laser-triggered stimulus-response system for local in vivo targeted blood vessels stimulation by vasoactive substances. The native vascular networks of the mouse mesentery were used as model tissues. Epinephrine and KCl were used as vasoactive agents that were sealed into individual chambers upon precipitation in the amount of pictograms. We demonstrated the method for non-damaged one-by-one chamber activation using a focused 532 nm laser light passed through biological tissues. To avoid laser-induced photothermal damage to biological tissues, the PTMF was functionalized with Nile Red dye, which effectively absorbs laser light. Chemically stimulated blood vessel fluctuations were analyzed using digital image processing methods. Hemodynamics changes were measured and visualized using the particle image velocimetry approach.

Polycyclic aromatic hydrocarbons exposure was associated with microRNA differential expression and neurotransmitter changes: a cross-sectional study in coal miners

Exposure to polycyclic aromatic hydrocarbons (PAHs) may cause neurobehavioral changes. This study aimed to explore the underlying mechanism of PAH neurotoxicity in coal miners. Urinary PAH metabolites, neurotransmitters, and oxidative stress biomarkers of 652 coal miners were examined. Subjects were divided into high and low-exposure groups based on the median of total urinary PAH metabolites. Differentially expressed miRNAs were screened from 5 samples in the low-exposure group (≤ 4.88 μmol/mol Cr) and 5 samples in the high-exposure group (> 4.88 μmol/mol Cr) using microarray technology, followed by bioinformatics analysis of the potential molecular functions of miRNA target genes. Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) was used to validate differentially expressed miRNAs. Restricted cubic splines (RCS) were applied to assess the possible dose-response relationships. Compared to the low PAH exposure group, the high-exposure group had higher levels of 5-hydroxytryptamine (5-HT), epinephrine (E), and acetylcholine (ACh), and lower levels of acetylcholinesterase (AChE). 1-OHP had a dose-response relationship with malondialdehyde (MDA), dopamine (DA), 5-HT, and AChE (P for overall associations < 0.05). There were 19 differentially expressed microRNAs in microarray analysis, significantly enriched in the cell membrane, molecular binding to regulate transcription, and several signaling pathways such as PI3K-Akt. And in the validation stage, miR-885-5p, miR-20a-5p, and let-7i-3p showed differences in the low and high-exposure groups (P < 0.05). Changes in neurotransmitters and microRNA expression levels among the coal miners were associated with PAH exposure. Their biological functions are mainly related to the transcriptional regulation of nervous system diseases or signaling pathways of disorders. These findings provide new insights for future research of PAH neurotoxicity.

Novel Hydroxypyridine Compound Protects Brain Cells against Ischemic Damage In Vitro and In Vivo

A non-surgical pharmacological approach to control cellular vitality and functionality during ischemic and/or reperfusion-induced phases of strokes remains extremely important. The synthesis of 2-ethyl-6-methyl-3-hydroxypyridinium gammalactone-2,3-dehydro-L-gulonate (3-EA) was performed using a topochemical reaction. The cell-protective effects of 3-EA were studied on a model of glutamate excitotoxicity (GluTox) and glucose-oxygen deprivation (OGD) in a culture of NMRI mice cortical cells. Ca2+ dynamics was studied using fluorescent bioimaging and a Fura-2 probe, cell viability was assessed using cytochemical staining with propidium iodide, and gene expression was assessed by a real-time polymerase chain reaction. The compound anti-ischemic efficacy in vivo was evaluated on a model of irreversible middle cerebral artery (MCA) occlusion in Sprague-Dawley male rats. Brain morphological changes and antioxidant capacity were assessed one week after the pathology onset. The severity of neurological disorder was evaluated dynamically. 3-EA suppressed cortical cell death in a dose-dependent manner under the excitotoxic effect of glutamate and ischemia/reoxygenation. Pre-incubation of cerebral cortex cells with 10-100 µM 3-EA led to significant stagnation in Ca2+ concentration in a cytosol ([Ca2+]i) of neurons and astrocytes suffering GluTox and OGD. Decreasing intracellular Ca2+ and establishing a lower [Ca2+]i baseline inhibited necrotic cell death in an acute experiment. The mechanism of 3-EA cytoprotective action involved changes in the baseline and ischemia/reoxygenation-induced expression of genes encoding anti-apoptotic proteins and proteins of the oxidative status; this led to inhibition of the late irreversible stages of apoptosis. Incubation of brain cortex cells with 3-EA induced an overexpression of the anti-apoptotic genes BCL-2, STAT3, and SOCS3, whereas the expression of genes regulating necrosis and inflammation (TRAIL, MLKL, Cas-1, Cas-3, IL-1β and TNFa) were suppressed. 3-EA 18.0 mg/kg intravenous daily administration for 7 days following MCA occlusion preserved rats' cortex neuron population, decreased the severity of neurological deficit, and spared antioxidant capacity of damaged tissues. 3-EA demonstrated proven short-term anti-ischemic activity in vivo and in vitro, which can be associated with antioxidant activity and the ability to target necrotic and apoptotic death. The compound may be considered a potential neuroprotective molecule for further pre-clinical investigation.

Studies on the mechanism of energy metabolism via AMPK/PGC-1α signaling pathway induced by compatibility of Ligusticum chuanxiong Hort and Gastrodia

AMP-activated protein kinase (AMPK) regulates overall energy consumption and energy intake through cytokines. Ligusticum striatum DC (CX) combined with Gastrodia elata Blume (TM) has been used for migraine treatment for millennia. When used alone in clinical practice, CX causes symptoms of thirst, irritability, and yellow urine and has influenced the levels of cytokines such as AMP that activate the AMPK pathway of energy metabolism. However, relationships between this compatibility prescription, integral biological energy metabolism, and the AMPK pathway remain unclear. Studies were performed by treating normal rats with physiological saline, CX extract, CX coupled TM extract, and TM extracts separately for 4 weeks. Food intake, water intake, urine output, stool output, and body weight were monitored once a week by the metabolic cage method. Values of FBG, BUN, TP, TC and TG in blood samples were detected approaching the whole blood automatic detector from 1 to 4 weeks. Na+ -K+ -ATPase, Ca2+ -Mg2+ -ATPase, cAMP, and cGMP activity were determined by the enzyme-linked immunosorbent assay (ELISA); the biological samples that were obtained at 1, 2, 3, and 4 weeks after drug administration were tested by GC-TOF-MS. Then real-time PCR and Western Blot were applied to detect changes in expression of some substances involved in energy metabolism. The results demonstrated that administering CX alone increased energy input, mobility, and respiratory exchange ratio, accelerated energy consumption, and caused inflammatory infiltration in the liver. CX coupled with TM led to lower energy metabolism and liver damage in comparison with CX used alone. Moreover, CX-treated rats harbored higher levels of differential metabolites (including pyrophosphate, oxaloacetic acid, and galactinol). Glycerophospholipid metabolism and the citrate cycle are closely related to the differential metabolites above. In addition, CX-induced unbalanced energy metabolism depends on cAMP activation mediated by the AMPK/PGC-1α pathway in rats. Our findings suggest that CX-induced energy metabolism imbalance was corrected after coupling with TM by mediating the AMPK/PGC-1α pathway.

Laser-induced singlet oxygen selectively triggers oscillatory mitochondrial permeability transition and apoptosis in melanoma cell lines

Singlet oxygen (¹O₂) is an electronically excited state of triplet oxygen which is less stable than molecular oxygen in the electronic ground state and produced by photochemical, thermal, chemical, or enzymatic activation of O₂. Although the role of singlet oxygen in biology and medicine was intensively studied with photosensitisers, using of these compounds is limited due to toxicity and lack of selectivity. We generated singlet oxygen in the skin fibroblasts and melanoma cell lines by 1267 nm laser irradiation. It did not induce production of superoxide anion, hydrogen peroxide or activation of lipid peroxidation in these cells confirming high selectivity of 1267 nm laser to singlet oxygen. ¹O₂ did not change mitochondrial membrane potential (ΔΨm) in skin fibroblasts but induced fluctuation in ΔΨm and complete mitochondrial depolarisation due to opening permeability transition pore in B16 melanoma cells. 1267 nm irradiation did not change the percentage of fibroblasts with necrosis but significantly increased the number of B16 melanoma cells with apoptosis. Thus, singlet oxygen can induce apoptosis in cancer B16 melanoma cells by opening of mitochondrial permeability transition pore (PTP) but not in control fibroblasts.

Interaction of Mitochondrial Calcium and ROS in Neurodegeneration

Neurodegenerative disorders are currently incurable devastating diseases which are characterized by the slow and progressive loss of neurons in specific brain regions. Progress in the investigation of the mechanisms of these disorders helped to identify a number of genes associated with familial forms of these diseases and a number of toxins and risk factors which trigger sporadic and toxic forms of these diseases. Recently, some similarities in the mechanisms of neurodegenerative diseases were identified, including the involvement of mitochondria, oxidative stress, and the abnormality of Ca2+ signaling in neurons and astrocytes. Thus, mitochondria produce reactive oxygen species during metabolism which play a further role in redox signaling, but this may also act as an additional trigger for abnormal mitochondrial calcium handling, resulting in mitochondrial calcium overload. Combinations of these factors can be the trigger of neuronal cell death in some pathologies. Here, we review the latest literature on the crosstalk of reactive oxygen species and Ca2+ in brain mitochondria in physiology and beyond, considering how changes in mitochondrial metabolism or redox signaling can convert this interaction into a pathological event.

Brain region specificity in reactive oxygen species production and maintenance of redox balance

The brain produces various reactive oxygen species in enzymatic and non-enzymatic reactions as a by-product of metabolism and/or for redox signaling. Effective antioxidant system in the brain cells maintains redox balance. However, neurons and glia from some brain regions are more vulnerable to oxidative stress in ischemia/reperfusion, epilepsy, and neurodegenerative disorders than the rest of the brain. Using fluorescent indicators in live cell imaging and confocal microscopy, we have measured the rate of cytosolic and mitochondrial reactive oxygen species production, lipid peroxidation, and glutathione levels in cortex, hippocampus, midbrain, brain stem and cerebellum in acute slices of rat brain. We have found that the basal rate of ROS production is at its highest in brain stem and cerebellum, and that it is mainly generated by glial cells. Activation of neurons and glia by glutamate and ATP led to maximal rates of ROS production in the midbrain compared to the rest of the brain. Mitochondrial ROS had only minor implication to the total ROS production with maximal values in the cortex and minimal in the midbrain. The basal rate of lipid peroxidation was higher in the midbrain and hippocampus, while the GSH level was similar in most brain regions with the lowest level in the midbrain. Thus, the rate of ROS production, lipid peroxidation and the level of GSH vary across brain regions.

Metabolically induced intracellular pH changes activate mitophagy, autophagy, and cell protection in familial forms of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder induced by the loss of dopaminergic neurons in midbrain. The mechanism of neurodegeneration is associated with aggregation of misfolded proteins, oxidative stress, and mitochondrial dysfunction. Considering this, the process of removal of unwanted organelles or proteins by autophagy is vitally important in neurons, and activation of these processes could be protective in PD. Short-time acidification of the cytosol can activate mitophagy and autophagy. Here, we used sodium pyruvate and sodium lactate to induce changes in intracellular pH in human fibroblasts with PD mutations (Pink1, Pink1/Park2, α-synuclein triplication, A53T). We have found that both lactate and pyruvate in millimolar concentrations can induce a short-time acidification of the cytosol in these cells. This induced activation of mitophagy and autophagy in control and PD fibroblasts and protected against cell death. Importantly, application of lactate to acute brain slices of WT and Pink1 KO mice also induced a reduction of pH in neurons and astrocytes that increased the level of mitophagy. Thus, acidification of the cytosol by compounds, which play an important role in cell metabolism, can also activate mitophagy and autophagy and protect cells in the familial form of PD.

Sources and triggers of oxidative damage in neurodegeneration

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

Dopamine controls neuronal spontaneous calcium oscillations via astrocytic signal

Dopamine is a neuromodulator and neurotransmitter responsible for a number of physiological processes. Dysfunctions of the dopamine metabolism and signalling are associated with neurological and psychiatric diseases. Here we report that in primary co-culture of neurons and astrocytes dopamine-induces calcium signal in astrocytes and suppress spontaneous synchronous calcium oscillations (SSCO) in neurons. Effect of dopamine on SSCO in neurons was dependent on calcium signal in astrocytes and could be modified by inhibition of dopamine-induced calcium signal or by stimulation of astrocytic calcium rise with ATP. Ability of dopamine to suppress SSCO in neurons was independent on D1- or D2- like receptors but dependent on GABA and alpha-adrenoreceptors. Inhibitor of monoaminoxidase bifemelane blocked effect of dopamine on astrocytes but also inhibited the effect dopamine on SSCO in neurons. These findings suggest that dopamine-induced calcium signal may stimulate release of neuromodulators such as GABA and adrenaline and thus suppress spontaneous calcium oscillations in neurons.

Singlet oxygen stimulates mitochondrial bioenergetics in brain cells

Oxygen, in form of reactive oxygen species (ROS), has been shown to participate in oxidative stress, one of the major triggers for pathology, but also is a main contributor to physiological processes. Recently, it was found that 1267 nm irradiation can produce singlet oxygen without photosensitizers. We used this phenomenon to study the effect of laser-generated singlet oxygen on one of the major oxygen-dependent processes, mitochondrial energy metabolism. We have found that laser-induced generation of ¹O₂ in neurons and astrocytes led to the increase of mitochondrial membrane potential, activation of NADH- and FADH-dependent respiration, and importantly, increased the rate of maximal respiration in isolated mitochondria. The activation of mitochondrial respiration stimulated production of ATP in these cells. Thus, we found that the singlet oxygen generated by 1267 nm laser pulse works as an activator of mitochondrial respiration and ATP production in the brain.

Variability of mitochondrial energy balance across brain regions

Brain is not homogenous and neurons from various brain regions are known to have different vulnerabilities to mitochondrial mutations and mitochondrial toxins. However, it is not clear if this vulnerability is connected to different energy metabolism in specific brain regions. Here, using live-cell imaging, we compared mitochondrial membrane potential and nicotinamide adenine dinucleotide (NADH) redox balance in acute rat brain slices in different brain regions and further detailed the mitochondrial metabolism in primary neurons and astrocytes from rat cortex, midbrain and cerebellum. We have found that mitochondrial membrane potential is higher in brain slices from the hippocampus and brain stem. In primary co-cultures, mitochondrial membrane potential in astrocytes was lower than in neurons, whereas in midbrain cells it was higher than in cortex and cerebellum. The rate of NADH production and mitochondrial NADH pool were highest in acute slices from midbrain and midbrain primary neurons and astrocytes. Although the level of adenosine tri phosphate (ATP) was similar among primary neurons and astrocytes from cortex, midbrain and cerebellum, the rate of ATP consumption was highest in midbrain cells that lead to faster neuronal and astrocytic collapse in response to inhibitors of ATP production. Thus, midbrain neurons and astrocytes have a higher metabolic rate and ATP consumption that makes them more vulnerable to energy deprivation.