DHA inhibits ER Ca2+ release and ER stress in astrocytes following in vitro ischemia

Endoplasmic reticulum stress impedes regulated secretion by governing key exocytotic and granulogenic molecular switches

Dense core vesicles (DCVs) and synaptic vesicles are specialised secretory vesicles in neurons and neuroendocrine cells, and abnormal release of their cargo is associated with various pathophysiologies. Endoplasmic reticulum (ER) stress and inter-organellar communication are also associated with disease biology. To investigate the functional status of regulated exocytosis arising from the crosstalk of a stressed ER and DCVs, ER stress was modelled in PC12 neuroendocrine cells using thapsigargin. DCV exocytosis was severely compromised in ER-stressed PC12 cells and was reversed to varying magnitudes by ER stress attenuators. Experiments with tunicamycin, an independent ER stressor, yielded similar results. Concurrently, ER stress also caused impaired DCV exocytosis in insulin-secreting INS-1 cells. Molecular analysis revealed blunted SNAP25 expression, potentially attributed to augmented levels of ATF4, an inhibitor of CREB that binds to the CREB-binding site. The effects of loss of function of ATF4 in ER-stressed cells substantiated this attribution. Our studies revealed severe defects in DCV exocytosis in ER-stressed cells for the first time, mediated by reduced levels of key exocytotic and granulogenic switches regulated via the eIF2α (EIF2A)-ATF4 axis.

Cross-talk between bioactive lipid mediators and the unfolded protein response in ischemic stroke

Ischemic cerebral stroke is a severe medical condition that affects about 15 million people every year and is the second leading cause of death and disability globally. Ischemic stroke results in neuronal cell death and neurological impairment. Current therapies may not adequately address the deleterious metabolic changes and may increase neurological damage. Oxygen and nutrient depletion along with the tissue damage result in endoplasmic reticulum (ER) stress, including the Unfolded Protein Response (UPR), and neuroinflammation in the affected area and cause cell death in the lesion core. The spatio-temporal production of lipid mediators, either pro-inflammatory or pro-resolving, decides the course and outcome of stroke. The modulation of the UPR as well as the resolution of inflammation promotes post-stroke cellular viability and neuroprotection. However, studies about the interplay between the UPR and bioactive lipid mediators remain elusive and this review gives insights about the crosstalk between lipid mediators and the UPR in ischemic stroke. Overall, the treatment of ischemic stroke is often inadequate due to lack of effective drugs, thus, this review will provide novel therapeutical strategies that could promote the functional recovery from ischemic stroke.

Adverse effects of gestational ω-3 and ω-6 polyunsaturated fatty acid imbalance on the programming of fetal brain development

Obesity is a key medical challenge of our time. The increasing number of children born to overweight or obese women is alarming. During pregnancy, the circulation of the mother and her fetus interact to maintain the uninterrupted availability of essential nutrients for fetal organ development. In doing so, the mother's dietary preference determines the amount and composition of nutrients reaching the fetus. In particular, the availability of polyunsaturated fatty acids (PUFAs), chiefly their ω-3 and ω-6 subclasses, can change when pregnant women choose a specific diet. Here, we provide a succinct overview of PUFA biochemistry, including exchange routes between ω-3 and ω-6 PUFAs, the phenotypes, and probable neurodevelopmental disease associations of offspring born to mothers consuming specific PUFAs, and their mechanistic study in experimental models to typify signaling pathways, transcriptional, and epigenetic mechanisms by which PUFAs can imprint long-lasting modifications to brain structure and function. We emphasize that the ratio, rather than the amount of individual ω-3 or ω-6 PUFAs, might underpin physiologically correct cellular differentiation programs, be these for neurons or glia, during pregnancy. Thereupon, the PUFA-driven programming of the brain is contextualized for childhood obesity, metabolic, and endocrine illnesses.

SAFit2 ameliorates paclitaxel-induced neuropathic pain by reducing spinal gliosis and elevating pro-resolving lipid mediators

BACKGROUND

Chemotherapy-induced neuropathic pain (CIPN) describes a pathological pain state that occurs dose-dependently as a side effect and can limit or even impede an effective cancer therapy. Unfortunately, current treatment possibilities for CIPN are remarkably confined and mostly inadequate as CIPN therapeutics themselves consist of low effectiveness and may induce severe side effects, pointing out CIPN as pathological entity with an emerging need for novel treatment targets. Here, we investigated whether the novel and highly specific FKBP51 inhibitor SAFit2 reduces paclitaxel-induced neuropathic pain.

METHODS

In this study, we used a well-established multiple low-dose paclitaxel model to investigate analgesic and anti-inflammatory properties of SAFit2. For this purpose, the behavior of the mice was recorded over 14 days and the mouse tissue was then analyzed using biochemical methods.

RESULTS

Here, we show that SAFit2 is capable to reduce paclitaxel-induced mechanical hypersensitivity in mice. In addition, we detected that SAFit2 shifts lipid levels in nervous tissue toward an anti-inflammatory and pro-resolving lipid profile that counteracts peripheral sensitization after paclitaxel treatment. Furthermore, SAFit2 reduced the activation of astrocytes and microglia in the spinal cord as well as the levels of pain-mediating chemokines. Its treatment also increased anti-inflammatory cytokines levels in neuronal tissues, ultimately leading to a resolution of neuroinflammation.

CONCLUSIONS

In summary, SAFit2 shows antihyperalgesic properties as it ameliorates paclitaxel-induced neuropathic pain by reducing peripheral sensitization and resolving neuroinflammation. Therefore, we consider SAFit2 as a potential novel drug candidate for the treatment of paclitaxel-induced neuropathic pain.

EPA stronger than DHA increases the mitochondrial membrane potential and cardiolipin levels but does not change the ATP level in astrocytes

Astrocytes are highly energy-consuming glial cells critical for metabolic support to neurons. A growing body of evidence suggests that mitochondrial dysfunction in astrocytes is involved in age-related neurodegenerative disorders and that fish oil, rich in docosahexaenoic (DHA) and eicosapentaenoic (EPA) fatty acids, may alleviate cognition impairment in Parkinson's and Alzheimer's diseases. The present study examines the effect of DHA and EPA on mitochondrial membrane potential (MMP), apoptosis activation and ATP levels in astrocytes cultured in medium containing glucose or galactose, which limits oxidative phosphorylation (OXPHOS). MMP, expressed as the ratio of red to green JC-10 and MitoTracker fluorescence, increased in EPA-incubated cells in a dose dependent manner and was higher than in DHA-incubated astrocytes, also after uncoupling of OXPHOS by carbonyl cyanide 3-chlorophenylhydrazone (CCCP). In cells cultured in glucose and galactose medium mitochondrial hyperpolarization had no impact on intracellular ATP level. Furthermore, both EPA and DHA elevated mitochondrial cardiolipin content, however only EPA did so in a dose-dependent manner and reduced apoptosis which was analyzed by flow cytometry.

Heliox Preconditioning Exerts Neuroprotective Effects on Neonatal Ischemia/Hypoxia Injury by Inhibiting Necroptosis Induced by Ca2+ Elevation

Our previous studies have indicated that heliox preconditioning (HePC) may exert neuroprotective effects on neonatal hypoxic-ischemic encephalopathy (HIE). The present study was to investigate whether HePC alleviates neonatal HIE by inhibiting necroptosis and explore the potential mechanism. Seven-day-old rat pups were randomly divided into Sham group, HIE group, HIE + HePC group, HIE + Dantrolene (DAN) group, and HIE + Necrostatin-1 (Nec-1) group. HIE was induced by common carotid artery ligation and subsequent hypoxia exposure. The neurological function, brain injury, and molecular mechanism were evaluated by histological staining, neurobehavioral test, Western blotting, Ca²⁺, immunofluorescence staining, co-immunoprecipitation (Co-IP), and transmission electron microscopy (TEM). Results supported that the expression of necroptosis markers and p-RyR2 in the brain increased significantly after HIE. HePC, DAN, or Nec-1 was found to improve the neurological deficits after H/I and inhibit neuronal necroptosis. Interestingly, both HePC and DAN inhibited the increases in cytoplasmic Ca²⁺ and CaMK-II phosphorylation in the brain secondary to HIE, but Nec-1 failed to affect Ca²⁺. In conclusion, our results suggest HePC may alleviate cytoplasmic Ca²⁺ overload by regulating p-RyR2, which inhibits the necroptosis in the brain, exerting neuroprotective effects on HIE.

Plasmalogens Regulate Retinal Connexin 43 Expression and Müller Glial Cells Gap Junction Intercellular Communication and Migration

Plasmalogens are a specific glycerophospholipid subtype characterized by a vinyl-ether bound at their sn-1 moiety. Their biosynthesis is initiated in the peroxisome by dihydroxyacetone phosphate-acyltransferase (DHAPAT), which is encoded by the DAPAT gene. Previous studies have shown that plasmalogen-deficient mice exhibit major physiological dysfunctions including several eye defects, among which abnormal vascular development of the retina and a reactive activation of macroglial Müller cells. Interestingly, plasmalogen deficiency in mice is also associated with a reduced expression of brain connexin 43 (Cx43). Cx43 is the main connexin subtype of retinal glial cells and is involved in several cellular mechanisms such as calcium-based gap junction intercellular communication (GJIC) or cell migration. Thus, the aim of our work was 1) to confirm the alteration of Cx43 expression in the retina of plasmalogen-deficient DAPAT−/- mice and 2) to investigate whether plasmalogens are involved in crucial functions of Müller cells such as GJIC and cell migration. First, we found that plasmalogen deficiency was associated with a significant reduction of Cx43 expression in the retina of DAPAT−/- mice in vivo. Secondly, using a siRNA targeting DHAPAT in vitro, we found that a 50%-reduction of Müller cells content in plasmalogens was sufficient to significantly downregulate Cx43 expression, while increasing its phosphorylation. Furthermore, plasmalogen-depleted Müller cells exhibited several alterations in ATP-induced GJIC, such as calcium waves of higher amplitude that propagated slower to neighboring cells, including astrocytes. Finally, in vitro plasmalogen depletion was also associated with a significant downregulation of Müller cells migration. Taken together, these data confirm that plasmalogens are critical for the regulation of Cx43 expression and for characteristics of retinal Müller glial cells such as GJIC and cell migration.

Docosahexaenoic acid increased MeCP2 mediated mitochondrial respiratory complexes II and III enzyme activities in cortical astrocytes

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the methyl-CpG-binding protein 2 (MeCP2) in the neurons and glial cells of the central nervous system. Currently, therapeutics for RTT is aimed at restoring the loss-of-function by MeCP2 gene therapy, but that approach has multiple challenges. We have already reported impaired mitochondrial bioenergetics in MeCP2 deficient astrocytes. Docosahexaenoic acid (DHA), a polyunsaturated fatty acid, has been shown with health benefits, but its impact on mitochondrial functions in MeCP2 deficient astrocytes has never been paid much attention. The present study aimed to investigate the effects of DHA on mitochondrial respiratory chain regulation in MeCP2 knockdown astrocytes. We determined NADH dehydrogenase (ubiquinone) flavoprotein 2 (Ndufv2-complex-I), Ubiquinol cytochrome c reductase core protein (Uqcrc1-complex-III) genes expression, Ndufv2 protein expression, respiratory electron transport chain complex I, II, III, and IV enzyme activities, intracellular Ca⁺² , reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) in DHA pre-incubated MeCP2 knock-down rat primary cortical astrocytes. Our study demonstrates that 100 µM DHA increases MeCP2 gene and protein expression. Increases brain-derived neurotrophic factor (BDNF) and Uqcrc1 gene expression, Ndufv2 protein expression, but has no effect on glial fibrillary acidic protein (GFAP) gene expression. DHA treatment also increases mitochondrial respiratory Complexes II and III activities and reduces intracellular calcium levels. Taken together, the effects of DHA seem independent of MeCP2 deficiency in astrocytes. Hence, further studies are warranted to understand the complicated mechanisms of DHA and for its therapeutic significance in MeCP2-mediated mitochondrial dysfunction and in RTT disease.

Docosahexaenoic acid monoglyceride induces apoptosis and autophagy in breast cancer cells via lipid peroxidation-mediated endoplasmic reticulum stress

Epidemiologic and preclinical studieshave shown that marine n-3 polyunsaturated fatty acids (n-3 PUFAs) elicit promising chemoprevention against breast cancer. Docosahexaenoic acid monoglyceride (MAG-DHA), a docosahexaenoic acid sn-1-monoacylglycerol does not required pancreatic lipase to be absorbed, eliciting a better bioavailability when compared with other formulations such as DHA-free fatty acid, DHA-triglycerol, or DHA-ethyl ester. However, the anticancer actions and underlying mechanisms of MAG-DHA on breast cancer remain to be assessed. In this study, MAG-DHA induced significant growth inhibition in MCF-7 and MDA-MB-231 breast cancer cells in a dose-dependent manner. MAG-DHA treatment (80 µM) led to 83.8 and 94.3% growth inhibition between MCF-7 and MDA-MB-231 cells, respectively. MAG-DHA-induced growth inhibition was tightly associated with apoptosis, as evidenced by increased active forms of caspase-3, poly (ADP-ribose) polymerase (PARP) and caspase-12. In particular, MAG-DHA-induced apoptosis was triggered by oxidative stress-mediated endoplasmic reticulum (ER) stress, as evidenced by activation of the PERK-eIF2α pathway in ER. MAG-DHA treatment also strongly suppressed the growth of E0771 murine breast cancer xenografts, significant differences of tumor volume were found between MAG-DHA group (0.271 cm³ ) and control group (0.875 cm³ ) after 15 daily MAG-DHA treatments. The in vitro antibreast cancer mechanism of MAG-DHA was supported by the in vivo xenograft model. In addition, MAG-DHA-induced ER stress concomitantly triggered autophagy in these cancer cells, and the induction of autophagy suppressed its ability to induce apoptotic cell death. Our data suggested that MAG-DHA as dietary supplement, in combination with autophagy inhibitors may be a useful therapeutic strategy in treating breast cancer.

Fatty Acid Synthesis in Glial Cells of the CNS

Fatty acids (FAs) are of crucial importance for brain homeostasis and neural function. Glia cells support the high demand of FAs that the central nervous system (CNS) needs for its proper functioning. Additionally, FAs can modulate inflammation and direct CNS repair, thereby contributing to brain pathologies such Alzheimer’s disease or multiple sclerosis. Intervention strategies targeting FA synthesis in glia represents a potential therapeutic opportunity for several CNS diseases.

Supplemental N-3 Polyunsaturated Fatty Acids Limit A1-Specific Astrocyte Polarization via Attenuating Mitochondrial Dysfunction in Ischemic Stroke in Mice

Ischemic stroke is one of the leading causes of death and disability for adults, which lacks effective treatments. Dietary intake of n-3 polyunsaturated fatty acids (n-3 PUFAs) exerts beneficial effects on ischemic stroke by attenuating neuron death and inflammation induced by microglial activation. However, the impact and mechanism of n-3 PUFAs on astrocyte function during stroke have not yet been well investigated. Our current study found that dietary n-3 PUFAs decreased the infarction volume and improved the neurofunction in the mice model of transient middle cerebral artery occlusion (tMCAO). Notably, n-3 PUFAs reduced the stroke-induced A1 astrocyte polarization both in vivo and in vitro. We have demonstrated that exogenous n-3 PUFAs attenuated mitochondrial oxidative stress and increased the mitophagy of astrocytes in the condition of hypoxia. Furthermore, we provided evidence that treatment with the mitochondrial-derived antioxidant, mito-TEMPO, abrogated the n-3 PUFA-mediated regulation of A1 astrocyte polarization upon hypoxia treatment. Together, this study highlighted that n-3 PUFAs prevent mitochondrial dysfunction, thereby limiting A1-specific astrocyte polarization and subsequently improving the neurological outcomes of mice with ischemic stroke.

Schizochytrium limacinum Supplementation in a Low Fish-Meal Diet Improved Immune Response and Intestinal Health of Juvenile Penaeus monodon

The aim of the present experiment was to evaluate the effects of Schizochytrium limacinum supplementation on the immune response, gut microbiota, and health of Penaeus monodon fed a low fish-meal (FM) diet. A diet containing 25% FM was used as a control (Diet A), and three other diets were formulated to contain 15% FM and supplemented with 0, 0.75, and 1.5% S. limacinum (Diet B, C, and D, respectively). The experiment was carried out in quadruplicates (30 shrimp per replicate, average weight 1.01 ± 0.01 g), and the shrimps were fed the test diets to apparent satiation three times daily for 8 weeks. Shrimp fed diet B and D showed lower weight gain than those fed diet A. Supplementation of 0.75% S. limacinum enhanced expression of antioxidative genes (superoxide dismutase and catalase) and immune-response-related genes in hepatopancreas but could not affect the gene expression of immune deficiency in hepatopancreas and Tube in the intestine. A low FM diet induced endoplasmic reticulum swelling of the intestinal epithelial cells, which was alleviated by S. limacinum supplementation. Ultra-performance liquid chromatography coupled with quadrupole time of flight mass spectrometry was employed to analyze the changes of hemolymph metabolomics, 49 significantly different metabolites were identified, and lysoPCs, deoxyinosine, inosine, and highly unsaturated fatty acids were lower in fish fed with low FM diets. Intestinal microbial diversity was lower in shrimp fed Diet B than those fed the control diet. Dietary supplementation of 0.75% S. limacinum increased intestinal microbial diversity of shrimp and decreased the ratio of pathogenic bacterium (Thalassotalea and Tenacibaculum). These results indicated that supplementing S. limacinum into a low FM diet improves the growth performance, immune response, and intestinal health of P. monodon. The optimum inclusion level of seems to be 0.75% of diet.

Docosahexaenoic Acid: Outlining the Therapeutic Nutrient Potential to Combat the Prenatal Alcohol-Induced Insults on Brain Development

Brain development is markedly affected by prenatal alcohol exposure, leading to cognitive and behavioral problems in the children. Protecting neuronal damage from prenatal alcohol could improve neural connections and functioning of the brain. DHA, a n-3 (ω-3) long-chain PUFA, is involved in the development of neurons. Insufficient concentrations of DHA impair neuronal development and plasticity of synaptic junctions and affect neurotransmitter concentrations in the brain. Alcohol consumption during pregnancy decreases the maternal DHA status and reduces the placental transfer of DHA to the fetus, resulting in less DHA being available for brain development. It is important to know whether DHA could induce beneficial effects on various physiological functions that promote neuronal development. This review will discuss the current evidence for the beneficial role of DHA in protecting against neuronal damage and its potential in mitigating the teratogenic effects of alcohol.

Potential role of endoplasmic reticulum stress is involved in the protection of fish oil on neonatal rats with necrotizing enterocolitis

Neonatal necrotizing enterocolitis (NEC) is a serious gastrointestinal disease with high death rate in premature infants. Fish oil (FO) and its constituents have been shown to ameliorate intestinal inflammation and mucosal damage. However, the underlying mechanism of action is not known. In the present study, we divided Sprague-Dawley rats into three groups: control group, NEC model group, and FO pre-feeding+NEC model group. Briefly, one week before NEC modeling, in addition to being fed with milk, the FO pre-feeding+NEC modeling group was fed with FO, the NEC group was fed with saline, and the control group was only inserted a gastric-tube for 7 days. Subsequently, histological assay, Western blot, and ELISA were performed. Pretreatment with FO attenuated the NEC symptoms, alleviated intestinal pathological injury, and decreased the expressions of pro-inflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Furthermore, pretreatment with FO reduced the expressions of endoplasmic reticulum stress (ERS) related proteins, caspase-12, and glucose-regulated protein 78 (GRP78). In addition, intestinal histopathological scores showed a significant positive correlation with intestinal expressions of IL-6, TNF-α, and caspase-12. Collectively, these results indicate that ERS pathway might be involved in the effect of FO in alleviating intestinal mucosal inflammation and injury in rats with NEC.

Effect of Docosahexaenoic Acid on Ca2+ Signaling Pathways in Cerulein-Treated Pancreatic Acinar Cells, Determined by RNA-Sequencing Analysis

Intracellular Ca²⁺ homeostasis is commonly disrupted in acute pancreatitis. Sustained Ca²⁺ release from internal stores in pancreatic acinar cells (PACs), mediated by inositol triphosphate receptor (IP3R) and the ryanodine receptor (RyR), plays a key role in the initiation and propagation of acute pancreatitis. Pancreatitis induced by cerulein, an analogue of cholecystokinin, causes premature activation of digestive enzymes and enhanced accumulation of cytokines and Ca²⁺ in the pancreas and, as such, it is a good model of acute pancreatitis. High concentrations of the omega-3 fatty acid docosahexaenoic acid (DHA) inhibit inflammatory signaling pathways and cytokine expression in PACs treated with cerulein. In the present study, we determined the effect of DHA on key regulators of Ca²⁺ signaling in cerulein-treated pancreatic acinar AR42 J cells. The results of RNA-Sequencing (RNA-Seq) analysis showed that cerulein up-regulates the expression of IP3R1 and RyR2 genes, and that pretreatment with DHA blocks these effects. The results of real-time PCR confirmed that DHA inhibits cerulein-induced IP3R1 and RyR2 gene expression, and demonstrated that DHA pre-treatment decreases the expression of the Relb gene, which encodes a component of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) transcriptional activator complex, and the c-fos gene, which encodes a component of activator protein-1 (AP-1) transcriptional activator complex. Taken together, DHA inhibits mRNA expression of IP3R1, RyR2, Relb, and c-fos, which is related to Ca²⁺ network in cerulein-stimulated PACs.

G-Protein-Coupled Receptor 120 Mediates DHA-Induced Apoptosis by Regulating IP3R, ROS and, ER Stress Levels in Cisplatin-Resistant Cancer Cells

The omega-3 fatty acid docosahexaenoic acid (DHA) is known to induce apoptosis and cell cycle arrest via the induction of reactive oxygen species (ROS) production and endoplasmic reticulum (ER) stress in many types of cancers. However, the roles of DHA in drug-resistant cancer cells have not been elucidated. In this study, we investigated the effects of DHA in cisplatin-resistant gastric cancer SNU-601/cis2 cells. DHA was found to induce ROS-dependent apoptosis in these cells. The inositol 1,4,5-triphosphate receptor (IP3R) blocker 2-aminoethyl diphenylboninate (2-APB) reduced DHA-induced ROS production, consequently reducing apoptosis. We also found that G-protein-coupled receptor 120 (GPR120), a receptor of long-chain fatty acids, is expressed in SNU-601/cis2 cells, and the knockdown of GPR120 using specific shRNAs alleviated DHA-mediated ROS production and apoptosis. GPR120 knockdown reduced the expression of ER stress response genes, similar to the case for the pre-treatment of the cells with N-acetyl-L-cysteine (NAC), an ROS scavenger, or 2-APB. Indeed, the knockdown of C/EBP homologous protein (CHOP), a transcription factor that functions under ER stress conditions, markedly reduced DHA-mediated apoptosis, indicating that CHOP plays an essential role in the anti-cancer activity of DHA. These results suggest that GPR120 mediates DHA-induced apoptosis by regulating IP3R, ROS, and ER stress levels in cisplatin-resistant cancer cells, and that GPR120 is an effective chemotherapeutic target for cisplatin resistance.

Salubrinal offers neuroprotection through suppressing endoplasmic reticulum stress, autophagy and apoptosis in a mouse traumatic brain injury model

Traumatic brain injury (TBI) is a complex injury that can cause severe disabilities and even death. TBI can induce secondary injury cascades, including but not limited to endoplasmic reticulum (ER) stress, apoptosis and autophagy. Although the investigators has previously shown that salubrinal, the selective phosphatase inhibitor of p-eIF2α, ameliorated neurologic deficits in murine TBI model, the neuroprotective mechanisms of salubrinal need further research to warrant the preclinical value. This study was undertaken to characterize the effects of salubrinal on cell death and neurological outcomes following TBI in mice and the potential mechanisms. In the current study, ER stress-related proteins including p-eIF2α, GRP78 and CHOP showed peak expressions both in the cortex and hippocampus from day 2 to day 3 after TBI, indicating ER stress was activated in our TBI model. Immunofluorescence staining showed that CHOP co-located NeuN-positive neuron, GFAP-positive astrocyte, Iba-1-positive microglia, CD31-positive vascular endothelial cell and PDGFR-β-positive pericyte in the cortex on day 2 after TBI, and these cells mentioned above constitute the neurovascular unit (NVU). We also found TBI-induced plasmalemma permeability, motor dysfunction, spatial learning and memory deficits and brain lesion volume were alleviated by continuous intraperitoneal administration of salubrinal post TBI. To investigate the underlying mechanisms further, we determined that salubrinal suppressed the expression of ER stress, autophagy and apoptosis related proteins on day 2 after TBI. In addition, salubrinal administration decreased the number of CHOP+/TUNEL+ and CHOP+/LC3+ cells on day 2 after TBI, detected by immunofluorescence. In conclusion, these data imply that salubrinal treatment improves morphological and functional outcomes caused by TBI in mice and these neuroprotective effects may be associated with inhibiting apoptosis, at least in part by suppressing ER stress-autophagy pathway.

Bladder cancer extracellular vesicles drive tumorigenesis by inducing the unfolded protein response in endoplasmic reticulum of nonmalignant cells

The field cancerization effect has been proposed to explain bladder cancer's multifocal and recurrent nature, yet the mechanisms of this effect remain unknown. In this work, using cell biology, flow cytometry, and qPCR analyses, along with a xenograft mouse tumor model, we show that chronic exposure to tumor-derived extracellular vesicles (TEVs) results in the neoplastic transformation of nonmalignant human SV-HUC urothelial cells. Inhibition of EV uptake prevented this transformation. Transformed cells not only possessed several oncogenic properties, such as increased genome instability, loss of cell-cell contact inhibition, and invasiveness, but also displayed altered morphology and cell structures, such as an enlarged cytoplasm with disrupted endoplasmic reticulum (ER) alignment and the accumulation of smaller mitochondria. Exposure of SV-HUC cells to TEVs provoked the unfolded protein response in the endoplasmic reticulum (UPR^ER). Prolonged induction of UPR^ER signaling activated the survival branch of the UPR^ER pathway, in which cells had elevated expression of inositol-requiring enzyme 1 (IRE1), NF-κB, and the inflammatory cytokine leptin, and incurred loss of the pro-apoptotic protein C/EBP homologous protein (CHOP). More importantly, inhibition of ER stress by docosahexaenoic acid prevented TEV-induced transformation. We propose that TEVs promote malignant transformation of predisposed cells by inhibiting pro-apoptotic signals and activating tumor-promoting ER stress-induced unfolded protein response and inflammation. This study provides detailed insight into the mechanisms underlying the bladder cancer field effect and tumor recurrence.

Mitochondrial Neuroglobin Is Necessary for Protection Induced by Conditioned Medium from Human Adipose-Derived Mesenchymal Stem Cells in Astrocytic Cells Subjected to Scratch and Metabolic Injury

Astrocytes are specialized cells capable of regulating inflammatory responses in neurodegenerative diseases or traumatic brain injury. In addition to playing an important role in neuroinflammation, these cells regulate essential functions for the preservation of brain tissue. Therefore, the search for therapeutic alternatives to preserve these cells and maintain their functions contributes in some way to counteract the progress of the injury and maintain neuronal survival in various brain pathologies. Among these strategies, the conditioned medium from human adipose-derived mesenchymal stem cells (CM-hMSCA) has been reported with a potential beneficial effect against several neuropathologies. In this study, we evaluated the potential effect of CM-hMSCA in a model of human astrocytes (T98G cells) subjected to scratch injury. Our findings demonstrated that CM-hMSCA regulates the cytokines IL-2, IL-6, IL-8, IL-10, GM-CSF, and TNF-α, downregulates calcium at the cytoplasmic level, and regulates mitochondrial dynamics and the respiratory chain. These actions are accompanied by modulation of the expression of different proteins involved in signaling pathways such as AKT/pAKT and ERK1/2/pERK, and may mediate the localization of neuroglobin (Ngb) at the cellular level. We also confirmed that Ngb mediated the protective effects of CM-hMSCA through regulation of proteins involved in survival pathways and oxidative stress. In conclusion, regulation of brain inflammation combined with the recovery of fundamental cellular aspects in the face of injury makes CM-hMSCA a promising candidate for the protection of astrocytes in brain pathologies.

Docosahexaenoic Acid Reduces Palmitic Acid-Induced Endoplasmic Reticulum Stress in Pancreatic Β Cells

Endoplasmic reticulum (ER) stress leads to peripheral insulin resistance and the progression of pancreatic beta cell failure in type 2 diabetes. Although ER stress plays an important role in the pathogenesis of diabetes, it is indispensable for cellular activity. Therefore, when assessing the pathological significance of ER stress, it is important to monitor and quantify ER stress levels. Here, we have established a novel system to monitor ER stress levels quickly and sensitively, and using this method, we have clarified the effect of differences in glucose concentration and various fatty acids on the ER of pancreatic β cells. First, we developed a cell system that secretes Gaussia luciferase in culture medium depending on the activation of the GRP78 promoter. This system could sensitively monitor ER stress levels that could not be detected with real-time RT-PCR and immunoblotting. This system revealed that hyperglycemia does not induce unfolded protein response (UPR) in a short period of time in MIN6 cells, a mouse pancreatic β cell line. Physiological concentrations of palmitic acid, a saturated fatty acid, induced ER stress quickly, while physiological concentrations of oleic acid, an unsaturated fatty acid, did not. Docosahexaenoic acid, an n-3 unsaturated fatty acid, inhibited palmitic acid-induced ER stress. In this study, we have established a system that can sensitively detect ER stress levels of living cells in a short period of time. This system can be used to monitor the state of the ER in living cells and lead to the investigation of the significance of physiological or pathological ER stress levels.

Acetylpuerarin inhibits oxygen-glucose deprivation-induced neuroinflammation of rat primary astrocytes via the suppression of HIF-1 signaling

In the central nervous system (CNS), ischemic injury induced by inflammation associated with astrocytes serves an important role in physiological and pathological processes. Neuroinflammation leads to the release of pro-inflammatory cytokines, including tumor necrosis factor-α and interleukin-1β. The aim of the present study was to investigate whether acetylpuerarin attenuates oxygen-glucose deprivation (OGD)-induced astrocyte inflammation and secretion of pro-inflammatory cytokines via inhibiting hypoxia-inducible factor-1 (HIF-1) activation and suppressing downstream primary astrocyte signaling in rats. The results demonstrated that acetylpuerarin attenuates astrocyte viability and induces morphological changes following OGD stress. Furthermore, acetylpuerarin suppresses the stimulation of HIF-1α and nuclear factor (NF)-κB signaling pathways, while attenuating the expression and secretion of pro-inflammatory cytokines via HIF-1 suppression in OGD-induced astrocytes. These findings indicate that acetylpuerarin may attenuate OGD-induced astrocyte damage and inflammation in rat primary astrocytes via suppressing HIF-1 activation and NF-κB signaling. These results suggest that acetylpuerarin regulates inflammation associated with astrocytes and may represent a novel therapeutic agent for the treatment of neuroinflammation in the CNS.

Upregulation of glutamate metabolism by BYHWD in cultured astrocytes following oxygen-glucose deprivation/reoxygenation in part depends on the activation of p38 MAPK

Recent studies have demonstrated that Buyang Huanwu Decoction (BYHWD) decreased glutamate levels subsequent to cerebral ischemia. Glutamate transporter-1 (GLT-1) and glutamine synthetase (GS), which are located in astrocytes, mainly contribute to glutamate transportation, thus reducing glutamate concentration. BYHWD has previously been demonstrated to upregulate GLT-1 and GS following ischemia in vivo. However, whether BYHWD can directly influence astrocytic GLT-1/GS levels remains unknown. In the present study, the effect of BYHWD containing serum (BYHWD-CS) on GLT-1/GS levels in astrocytes following oxygen-glucose deprivation/reoxygenation (OGD/R) was investigated. The results revealed that BYHWD-CS enhanced the expression levels of GLT-1 and GS in cultured astrocytes, which reduced glutamate concentration in the culture medium. Meanwhile, increased p38 mitogen-activated protein kinase (p38 MAPK) was phosphorylated (activation form) by BYHWD-CS in cultured astrocytes, and the specific p38 inhibitor SB203580 blocked the increase of GLT-1/GS accompanied by decreased cell viability. Furthermore, SB203580 suppressed the effect of BYHWD-CS on the level of glial fibrillary acidic protein (an astrocytic marker), thus confirming that astrocytes are directly involved in the protective role of BYHWD after OGD/R. These findings suggest that BYHWD upregulates GLT-1 and GS via p38 MAPK activation, and protects cultured astrocytes from death caused by OGD/R (typical in vitro model), which complemented the role of astrocytes in the protective effect of BYHWD.

ER stress and impaired autophagy flux in neuronal degeneration and brain injury

Autophagy is a highly controlled lysosome-mediated function in eukaryotic cells to eliminate damaged or aged long-lived proteins and organelles. It is required for restoring cellular homeostasis in cell survival under multiple stresses. Autophagy is known to be a double-edged sword because too much activation or inhibition of autophagy can disrupt homeostatic degradation of protein and organelles within the brain and play a role in neuronal cell death. Many factors affect autophagy flux function in the brain, including endoplasmic reticulum (ER) stress, oxidative stress, and aging. Newly emerged research indicates that altered autophagy flux functionality is involved in neurodegeneration of the aged brain, chronic neurological diseases, and after traumatic and ischemic brain injuries. In search to identify neuroprotective agents that may reduce oxidative stress and stimulate autophagy, one particular neuroprotective agent docosahexaenoic acid (DHA) presents unique functions in reducing ER and oxidative stress and modulating autophagy. This review will summarize the recent findings on changes of autophagy in aging, neurodegenerative diseases, and brain injury after trauma or ischemic strokes. Discussion of DHA functions is focused on modulating ER stress and autophagy in regard to its neuroprotection and anti-tumor functions.

Reduced acute neuroinflammation and improved functional recovery after traumatic brain injury by α-linolenic acid supplementation in mice

BACKGROUND

Adequate consumption of polyunsaturated fatty acids (PUFA) is vital for normal development and functioning of the central nervous system. The long-chain n-3 PUFAs docosahexaenoic acid (DHA) and eicosapentaenoic acid are anti-inflammatory and neuroprotective in the models of central nervous system injury including traumatic brain injury (TBI). In the present study, we tested whether a higher brain DHA status in a mouse model on an adequate dietary α-linolenic acid (ALA) leads to reduced neuroinflammation and improved spontaneous recovery after TBI in comparison to a moderately lowered brain DHA status that can occur in humans.

METHODS

Mice reared on diets with differing ALA content were injured by a single cortical contusion impact. Change in the expression of inflammatory cytokines was measured, and cellular changes occurring after injury were analyzed by immunostaining for macrophage/microglia and astrocytes. Behavioral studies included rotarod and beam walk tests and contextual fear conditioning.

RESULTS

Marginal supply (0.04 %) of ALA as the sole dietary source of n-3 PUFA from early gestation produced reduction of brain DHA by 35 % in adult offspring mice in comparison to the mice on adequate ALA diet (3.1 %). The DHA-depleted group showed significantly increased TBI-induced expression of pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 in the brain as well as slower functional recovery from motor deficits compared to the adequate ALA group. Despite the reduction of pro-inflammatory cytokine expression, adequate ALA diet did not significantly alter either microglia/macrophage density around the contusion site or the relative M1/M2 phenotype. However, the glial fibrillary acidic protein immunoreactivity was reduced in the injured cerebral cortex of the mice on adequate ALA diet, indicating that astrocyte activation may have contributed to the observed differences in cellular and behavioral responses to TBI.

CONCLUSIONS

Increasing the brain DHA level even from a moderately DHA-depleted state can reduce neuroinflammation and improve functional recovery after TBI, suggesting possible improvement of functional outcome by increasing dietary n-3 PUFA in human TBI.

Mechanisms of DHA transport to the brain and potential therapy to neurodegenerative diseases

Docosahexaenoic acid (DHA; 22:6 ω-3) is highly enriched in the brain and is required for proper brain development and function. Its deficiency has been shown to be linked with the emergence of neurological diseases. Dietary ω-3 fatty acid supplements including DHA have been suggested to improve neuronal development and enhance cognitive functions. However, mechanisms of DHA incorporation in the brain remain to be fully understood. Findings suggested that DHA is better incorporated when esterified within lysophospholipid rather than under its non-esterified form. Furthermore, DHA has the potential to be converted into diverse oxylipins with potential neuroprotective effects. Since DHA is poorly synthesized de novo, targeting the brain with specific carriers of DHA might provide novel therapeutic approaches to neurodegenerative diseases.

Modeling Alzheimer's Disease with Induced Pluripotent Stem Cells: Current Challenges and Future Concerns

Alzheimer's disease (AD) is the most prevalent type of dementia and its pathology is characterized by deposition of extracellular β-amyloid plaques, intracellular neurofibrillary tangles, and extensive neuron loss. While only a few familial AD cases are due to mutations in three causative genes (APP, PSEN1, and PSEN2), the ultimate cause behind the rest of the cases, called sporadic AD, remains unknown. Current animal and cellular models of human AD, which are based on the Aβ and tau hypotheses only, partially resemble the familial AD. As a result, there is a pressing need for the development of new models providing insights into the pathological mechanisms of AD and for the discovery of ways to treat or delay the onset of the disease. Recent preclinical research suggests that stem cells can be used to model AD. Indeed, human induced pluripotent stem cells can be differentiated into disease-relevant cell types that recapitulate the unique genome of a sporadic AD patient or family member. In this review, we will first summarize the current research findings on the genetic and pathological mechanisms of AD. We will then highlight the existing induced pluripotent stem cell models of AD and, lastly, discuss the potential clinical applications in this field.

Role of docosahexaenoic acid in the modulation of glial cells in Alzheimer's disease

Docosahexaenoic acid (DHA) is an omega-3 (ω-3) long-chain polyunsaturated fatty acid (LCPUFA) relevant for brain function. It has largely been explored as a potential candidate to treat Alzheimer’s disease (AD). Clinical evidence favors a role for DHA in the improvement of cognition in very early stages of the AD. In response to stress or damage, DHA generates oxygenated derivatives called docosanoids that can activate the peroxisome proliferator-activated receptor γ (PPARγ). In conjunction with activated retinoid X receptors (RXR), PPARγ modulates inflammation, cell survival, and lipid metabolism. As an early event in AD, inflammation is associated with an excess of amyloid β peptide (Aβ) that contributes to neural insult. Glial cells are recognized to be actively involved during AD, and their dysfunction is associated with the early appearance of this pathology. These cells give support to neurons, remove amyloid β peptides from the brain, and modulate inflammation. Since DHA can modulate glial cell activity, the present work reviews the evidence about this modulation as well as the effect of docosanoids on neuroinflammation and in some AD models. The evidence supports PPARγ as a preferred target for gene modulation. The effective use of DHA and/or its derivatives in a subgroup of people at risk of developing AD is discussed.

Docosahexaenoic acid and palmitic acid reciprocally modulate monocyte activation in part through endoplasmic reticulum stress

Palmitic acid (C16:0) and TLR2 ligand induce, but docosahexaenoic acid (DHA) inhibits monocyte activation. C16:0 and TLR2 or TLR4 ligand induce certain ER stress markers; thus, we determined whether ER stress induced by these agonists is sufficient to induce monocyte activation, and whether the ER stress is inhibited by DHA which is known to inhibit C16:0- or ligand-induced TLR activation. Monocyte activation and ER stress were assessed by TLR/inflammasome-induced IL-1β production, and phosphorylation of IRE-1 and eIF2 and expression of CHOP, respectively in THP-1 cells. TLR2 ligand Pam3CSK4 induced phosphorylation of eIF2, but not phosphorylation of IRE-1 and CHOP expression. LPS also induced phosphorylation of both IRE-1 and eIF2 but not CHOP expression suggesting that TLR2 or TLR4 ligand, or C16:0 induces different ER stress responses. C16:0-, Pam3CSK4-, or LPS-induced IL-1β production was inhibited by 4-phenylbutyric acid, an inhibitor of ER stress suggesting that IL-1β production induced by these agonists is partly mediated through ER stress. Among two ER stress-inducing molecules, thapsigargin but not tunicamycin led to the expression of pro-IL-1β and secretion of IL-1β. Thus, not all types of ER stress are sufficient to induce inflammasome-mediated IL-1β secretion in monocytes. Although both C16:0 and thapsigargin-induced IL-1β secretion was inhibited by DHA, only C16:0-mediated ER stress was responsive to DHA. These findings suggest that the anti-inflammatory effects of DHA are at least in part mediated through modulating ER homeostasis and that the propensity of ER stress can be differentially modulated by the types of dietary fat we consume.

Protection against Oxygen-Glucose Deprivation/Reperfusion Injury in Cortical Neurons by Combining Omega-3 Polyunsaturated Acid with Lyciumbarbarum Polysaccharide

Ischemic stroke, characterized by the disturbance of the blood supply to the brain, is a severe worldwide health threat with high mortality and morbidity. However, there is no effective pharmacotherapy for ischemic injury. Currently, combined treatment is highly recommended for this devastating injury. In the present study, we investigated neuroprotective effects of the combination of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) and Lyciumbarbarum polysaccharide (LBP) on cortical neurons using an in vitro ischemic model. Our study demonstrated that treatment with docosahexaenoic acid (DHA), a major component of the ω-3 PUFAs family, significantly inhibited the increase of intracellular Ca²⁺ in cultured wild type (WT) cortical neurons subjected to oxygen-glucose deprivation/reperfusion (OGD/R) injury and promoted their survival compared with the vehicle-treated control. The protective effects were further confirmed in cultured neurons with high endogenous ω-3 PUFAs that were isolated from fat-1 mice, in that a higher survival rate was found in fat-1 neurons compared with wild-type neurons after OGD/R injury. Our study also found that treatment with LBP (50 mg/L) activated Trk-B signaling in cortical neurons and significantly attenuated OGD/R-induced cell apoptosis compared with the control. Notably, both combining LBP treatment with ω-3 PUFAs administration to WT neurons and adding LBP to fat-1 neurons showed enhanced effects on protecting cortical neurons against OGD/R injury via concurrently regulating the intracellular calcium overload and neurotrophic pathway. The results of the study suggest that ω-3 PUFAs and LBP are promising candidates for combined pharmacotherapy for ischemic stroke.

Inhibition of Eukaryotic Initiation Factor 2 Alpha Phosphatase Reduces Tissue Damage and Improves Learning and Memory after Experimental Traumatic Brain Injury

Patients who survive traumatic brain injury (TBI) are often faced with persistent memory deficits. The hippocampus, a structure critical for learning and memory, is vulnerable to TBI and its dysfunction has been linked to memory impairments. Protein kinase RNA-like ER kinase regulates protein synthesis (by phosphorylation of eukaryotic initiation factor 2 alpha [eIF2α]) in response to endoplasmic reticulum (ER) stressors, such as increases in calcium levels, oxidative damage, and energy/glucose depletion, all of which have been implicated in TBI pathophysiology. Exposure of cells to guanabenz has been shown to increase eIF2α phosphorylation and reduce ER stress. Using a rodent model of TBI, we present experimental results that indicate that postinjury administration of 5.0 mg/kg of guanabenz reduced cortical contusion volume and decreased hippocampal cell damage. Moreover, guanabenz treatment attenuated TBI-associated motor, vestibulomotor, recognition memory, and spatial learning and memory dysfunction. Interestingly, when the initiation of treatment was delayed by 24 h, or the dose reduced to 0.5 mg/kg, some of these beneficial effects were still observed. Taken together, these findings further support the involvement of ER stress signaling in TBI pathophysiology and indicate that guanabenz may have translational utility.

Regulation of mitophagy in ischemic brain injury

The selective degradation of damaged or excessive mitochondria by autophagy is termed mitophagy. Mitophagy is crucial for mitochondrial quality control and has been implicated in several neurodegenerative disorders as well as in ischemic brain injury. Emerging evidence suggested that the role of mitophagy in cerebral ischemia may depend on different pathological processes. In particular, a neuroprotective role of mitophagy has been proposed, and the regulation of mitophagy seems to be important in cell survival. For these reasons, extensive investigations aimed to profile the mitophagy process and its underlying molecular mechanisms have been executed in recent years. In this review, we summarize the current knowledge regarding the mitophagy process and its role in cerebral ischemia, and focus on the pathological events and molecules that regulate mitophagy in ischemic brain injury.

Purine receptors are required for DHA-mediated neuroprotection against oxygen and glucose deprivation in hippocampal slices

Docosahexaenoic acid (DHA) is important for central nervous system function during pathological states such as ischemia. DHA reduces neuronal injury in experimental brain ischemia; however, the underlying mechanisms are not well understood. In the present study, we investigated the effects of DHA on acute hippocampal slices subjected to experimental ischemia by transient oxygen and glucose deprivation (OGD) and re-oxygenation and the possible involvement of purinergic receptors as the mechanism underlying DHA-mediated neuroprotection. We observed that cellular viability reduction induced by experimental ischemia as well as cell damage and thiobarbituric acid reactive substances (TBARS) production induced by glutamate (10 mM) were prevented by hippocampal slices pretreated with DHA (5 μM). However, glutamate uptake reduction induced by OGD and re-oxygenation was not prevented by DHA. The beneficial effect of DHA against cellular viability reduction induced by OGD and re-oxygenation was blocked with PPADS (3 μM), a nonselective P2X1-5 receptor antagonist as well as with a combination of TNP-APT (100 nM) plus brilliant blue (100 nM), which blocked P2X1, P2X3, P2X2/3, and P2X7 receptors, respectively. Moreover, adenosine receptors blockade with A1 receptor antagonist DPCPX (100 nM) or with A2B receptor antagonist alloxazine (100 nM) inhibited DHA-mediated neuroprotection. The addition of an A2A receptor antagonist ZM241385 (50 nM), or A3 receptor antagonist VUF5574 (1 μM) was ineffective. Taken together, our results indicated that neuroprotective actions of DHA may depend on P2X, A1, and A2B purinergic receptors activation. Our results reinforce the notion that dietary DHA may act as a local purinergic modulator in order to prevent neurodegenerative diseases.

Docosahexaenoic acid reduces ER stress and abnormal protein accumulation and improves neuronal function following traumatic brain injury

In this study, we investigated the development of endoplasmic reticulum (ER) stress after traumatic brain injury (TBI) and the efficacy of post-TBI administration of docosahexaenoic acid (DHA) in reducing ER stress. TBI was induced by cortical contusion injury in Sprague-Dawley rats. Either DHA (16 mg/kg in DMSO) or vehicle DMSO (1 ml/kg) was administered intraperitoneally at 5 min after TBI, followed by a daily dose for 3-21 d. TBI triggered sustained expression of the ER stress marker proteins including phosphorylated eukaryotic initiation factor-2α, activating transcription factor 4, inositol requiring kinase 1, and C/EBP homologous protein in the ipsilateral cortex at 3-21 d after TBI. The prolonged ER stress was accompanied with an accumulation of abnormal ubiquitin aggregates and increased expression of amyloid precursor protein (APP) and phosphorylated tau (p-Tau) in the frontal cortex after TBI. The ER stress marker proteins were colocalized with APP accumulation in the soma. Interestingly, administration of DHA attenuated all ER stress marker proteins and reduced the accumulation of both ubiquitinated proteins and APP/p-Tau proteins. In addition, the DHA-treated animals exhibited early recovery of their sensorimotor function after TBI. In summary, our study demonstrated that TBI induces a prolonged ER stress, which is positively correlated with abnormal APP accumulation. The sustained ER stress may play a role in chronic neuronal damage after TBI. Our findings illustrate that post-TBI administration of DHA has therapeutic potentials in reducing ER stress, abnormal protein accumulation, and neurological deficits.

The dual face of connexin-based astroglial Ca(2+) communication: a key player in brain physiology and a prime target in pathology

For decades, studies have been focusing on the neuronal abnormalities that accompany neurodegenerative disorders. Yet, glial cells are emerging as important players in numerous neurological diseases. Astrocytes, the main type of glia in the central nervous system , form extensive networks that physically and functionally connect neuronal synapses with cerebral blood vessels. Normal brain functioning strictly depends on highly specialized cellular cross-talk between these different partners to which Ca(2+), as a signaling ion, largely contributes. Altered intracellular Ca(2+) levels are associated with neurodegenerative disorders and play a crucial role in the glial responses to injury. Intracellular Ca(2+) increases in single astrocytes can be propagated toward neighboring cells as intercellular Ca(2+) waves, thereby recruiting a larger group of cells. Intercellular Ca(2+) wave propagation depends on two, parallel, connexin (Cx) channel-based mechanisms: i) the diffusion of inositol 1,4,5-trisphosphate through gap junction channels that directly connect the cytoplasm of neighboring cells, and ii) the release of paracrine messengers such as glutamate and ATP through hemichannels ('half of a gap junction channel'). This review gives an overview of the current knowledge on Cx-mediated Ca(2+) communication among astrocytes as well as between astrocytes and other brain cell types in physiology and pathology, with a focus on the processes of neurodegeneration and reactive gliosis. Research on Cx-mediated astroglial Ca(2+) communication may ultimately shed light on the development of targeted therapies for neurodegenerative disorders in which astrocytes participate. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

Omega-3 fatty acids protect the brain against ischemic injury by activating Nrf2 and upregulating heme oxygenase 1

Ischemic stroke is a debilitating clinical disorder that affects millions of people, yet lacks effective neuroprotective treatments. Fish oil is known to exert beneficial effects against cerebral ischemia. However, the underlying protective mechanisms are not fully understood. The present study tests the hypothesis that omega-3 polyunsaturated fatty acids (n-3 PUFAs) attenuate ischemic neuronal injury by activating nuclear factor E2-related factor 2 (Nrf2) and upregulating heme oxygenase-1 (HO-1) in both in vitro and in vivo models. We observed that pretreatment of rat primary neurons with docosahexaenoic acid (DHA) significantly reduced neuronal death following oxygen-glucose deprivation. This protection was associated with increased Nrf2 activation and HO-1 upregulation. Inhibition of HO-1 activity with tin protoporphyrin IX attenuated the protective effects of DHA. Further studies showed that 4-hydroxy-2E-hexenal (4-HHE), an end-product of peroxidation of n-3 PUFAs, was a more potent Nrf2 inducer than 4-hydroxy-2E-nonenal derived from n-6 PUFAs. In an in vivo setting, transgenic mice overexpressing fatty acid metabolism-1, an enzyme that converts n-6 PUFAs to n-3 PUFAs, were remarkably resistant to focal cerebral ischemia compared with their wild-type littermates. Regular mice fed with a fish oil-enhanced diet also demonstrated significant resistance to ischemia compared with mice fed with a regular diet. As expected, the protection was associated with HO-1 upregulation, Nrf2 activation, and 4-HHE generation. Together, our data demonstrate that n-3 PUFAs are highly effective in protecting the brain, and that the protective mechanisms involve Nrf2 activation and HO-1 upregulation by 4-HHE. Further investigation of n-3 PUFA neuroprotective mechanisms may accelerate the development of stroke therapies.

ER stress and effects of DHA as an ER stress inhibitor

The endoplasmic reticulum (ER) functions in the synthesis, folding, modification, and transport of newly synthesized transmembrane and secretory proteins. The ER also has important roles in the storage of intracellular Ca(2+) and regulation of Ca(2+) homeostasis. The integrity of the Ca(2+) homeostasis in the ER lumen is vital for proper folding of proteins. Dysregulation of ER Ca(2+) could result in an increase in unfolded or misfolded proteins and ER stress. ER stress triggers activation of the unfolded protein response (UPR), which is a fundamentally adaptive cell response and functions as a cytoprotective mechanism by over-expression of relevant chaperones and the global shutdown of protein synthesis. UPR activation occurs when three key ER membrane-sensor proteins detect an accumulation of aberrant proteins. The UPR acts to alleviate ER stress, but if the stress is too severe or prolonged, apoptosis will be triggered. In this review, we focused on ER stress and the effects of docosahexaenoic acid (DHA) on ER stress. DHA and its bioactive compounds, such as protectins and resolvins, provide neuroprotection against oxidative stress and apoptosis and have the ability to resolve inflammation in neurological diseases. New studies reveal that DHA blocks inositol trisphosphate receptor (IP3R)-mediated ER Ca(2+) depletion and ER stress. The administration of DHA post-traumatic brain injury (TBI) reduces ER stress, aberrant protein accumulation, and neurological deficits. Therefore, DHA presents therapeutic potentials for TBI via its pleiotropic effects including inhibition of ER stress.

Mesencephalic astrocyte-derived neurotrophic factor inhibits oxygen-glucose deprivation-induced cell damage and inflammation by suppressing endoplasmic reticulum stress in rat primary astrocytes

Astrocyte inflammation plays important roles both in physiological and pathological processes in the central nervous system (CNS). Ischemic injury in the CNS causes damage to astrocytes and the release of proinflammatory cytokines, such as tumor necrosis factor-α, interleukin-1β, and interleukin-6. This current study investigates whether mesencephalic astrocyte-derived neurotrophic factor (MANF) inhibits oxygen-glucose deprivation (OGD)-induced cell damage and inflammatory cytokine secretion by suppressing endoplasmic reticulum stress in rat primary astrocytes. We found that MANF alleviated OGD-induced astrocyte damage and rescued the cell viability, and the upregulation of GRP78 (endoplasmic reticulum (ER) stress marker) and NF-κB p65 (one of the central mediators of proinflammatory pathways) induced by OGD were significantly reduced by preincubation of MANF. In addition, the increases of secretion and mRNA expression levels of the proinflammatory cytokines IL-1β, IL-6, and TNF-α in astrocytes induced by OGD were significantly suppressed by MANF. These findings demonstrate that MANF shows the potential to alleviate cell damage and inflammation in rat primary astrocytes by suppressing ER stress, indicating that MANF plays an important role in astrocyte inflammation and functioning and may suggest a promising strategy for neuroprotection in the CNS.

Overexpression of conserved dopamine neurotrophic factor (CDNF) in astrocytes alleviates endoplasmic reticulum stress-induced cell damage and inflammatory cytokine secretion

Astrocyte damage and the disorders of cytokine secretion induced by endoplasmic reticulum stress (ERS) are crucial pathological processes in ischemic injury of the central nervous system (CNS), (e.g., ischemic reperfusion injury of the brain and spinal cord). ERS stimulates damage to astrocytes and the release of pro-inflammatory cytokines, which deteriorates CNS injury. This current study investigates whether the overexpression of conserved dopamine neurotrophic factor (CDNF) alleviates ER stress-induced cell damage and inflammatory cytokine secretion. We found that primary astrocytes showed both a successful transduction and a significant overexpression of CDNF protein following lentivirus application. Our results show that the percentage of LDH released as a result of ER stress was significantly lower in astrocytes with an overexpression of CDNF than in the control groups without CDNF overexpression, indicating that CDNF alleviates ER stress-induced astrocyte damage. The secretion and mRNA expression levels of pro-inflammatory cytokines were increased by tunicamycin, and this stimulation was significantly suppressed by an overexpression of CDNF, demonstrating that CDNF plays an important role in astrocyte inflammation and functioning by resisting ER stress. These findings suggest that primary astrocytes can be efficiently transduced with CDNF lentiviral vectors and that the overexpression of CDNF in astrocytes shows the potential to alleviate cell damage and proinflammatory cytokine secretion, which may represent a promising strategy for neuroprotection in the CNS.

Modeling Alzheimer's disease with iPSCs reveals stress phenotypes associated with intracellular Aβ and differential drug responsiveness

Oligomeric forms of amyloid-β peptide (Aβ) are thought to play a pivotal role in the pathogenesis of Alzheimer's disease (AD), but the mechanism involved is still unclear. Here, we generated induced pluripotent stem cells (iPSCs) from familial and sporadic AD patients and differentiated them into neural cells. Aβ oligomers accumulated in iPSC-derived neurons and astrocytes in cells from patients with a familial amyloid precursor protein (APP)-E693Δ mutation and sporadic AD, leading to endoplasmic reticulum (ER) and oxidative stress. The accumulated Aβ oligomers were not proteolytically resistant, and docosahexaenoic acid (DHA) treatment alleviated the stress responses in the AD neural cells. Differential manifestation of ER stress and DHA responsiveness may help explain variable clinical results obtained with the use of DHA treatment and suggests that DHA may in fact be effective for a subset of patients. It also illustrates how patient-specific iPSCs can be useful for analyzing AD pathogenesis and evaluating drugs.

The unfolded protein response to endoplasmic reticulum stress in cultured astrocytes and rat brain during experimental diabetes

Oxidative-nitrosative stress and inflammatory responses are associated with endoplasmic reticulum (ER) stress in diabetic retinopathy, raising the possibility that disturbances in ER protein processing may contribute to CNS dysfunction in diabetics. Upregulation of the unfolded protein response (UPR) is a homeostatic response to accumulation of abnormal proteins in the ER, and the present study tested the hypothesis that the UPR is upregulated in two models for diabetes, cultured astrocytes grown in 25mmol/L glucose for up to 4weeks and brain of streptozotocin (STZ)-treated rats with diabetes for 1-7months. Markers associated with translational blockade (phospho-eIF2α and apoptosis (CHOP), inflammatory response (inducible nitric oxide synthase, iNOS), and nitrosative stress (nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase, GAPDH) were not detected in either model. Nrf2 was present in nuclei of low- and high-glucose cultures, consistent with oxidative stress. Astrocytic ATF4 expression was not altered by culture glucose concentration, whereas phospho-IRE and ATF6 levels were higher in low- compared with high-glucose cultures. The glucose-regulated chaperones, GRP78 and GRP94, were also expressed at higher levels in low- than high-glucose cultures, probably due to recurrent glucose depletion between feeding cycles. In STZ-rat cerebral cortex, ATF4 level was transiently reduced at 4months, and p-IRE levels were transiently elevated at 3months. However, GRP78 and GRP94 expression was not upregulated, and iNOS, amyloid-β, and nuclear accumulation of GAPDH were not evident in STZ-diabetic brain. High-glucose cultured astrocytes and STZ-diabetic brain are relatively resistant to diabetes-induced ER stress, in sharp contrast with cultured retinal Müller cells and diabetic rodent retina.