Linking glycolysis with oxidative stress in neural cells: a regulatory role for nitric oxide

Redox Pathogenesis in Rheumatic Diseases

Despite being some of the most anecdotally well-known roads to pathogenesis, the mechanisms governing autoimmune rheumatic diseases are not yet fully understood. The overactivation of the cellular immune system and the characteristic development of autoantibodies have been linked to oxidative stress. Typical clinical manifestations, such as joint swelling and deformities and inflammation of the skin and internal organs, have also been connected directly or indirectly to redox mechanisms. The differences in generation and restraint of oxidative stress provide compelling evidence for the broad variety in pathology among rheumatic diseases and explain some of the common triggers and discordant manifestations in these diseases. Growing evidence of redox mechanisms in pathogenesis has provided a broad array of new potential therapeutic targets. Here, we explore the mechanisms by which oxidative stress is generated, explore its roles in autoimmunity and end-organ damage, and discuss how individual rheumatic diseases exhibit unique features that offer targets for therapeutic interventions.

Nitric Oxide Enhancing Resistance to PEG-Induced Water Deficiency is Associated with the Primary Photosynthesis Reaction in Triticum aestivum L

Photosynthesis is affected by water-deficiency (WD) stress, and nitric oxide (NO) is a free radical that participates in the photosynthesis process. Previous studies have suggested that NO regulates excitation-energy distribution of photosynthesis under WD stress. Here, quantitative phosphoproteomic profiling was conducted using iTRAQ. Differentially phosphorylated protein species (DEPs) were identified in leaves of NO- or polyethylene glycol (PEG)-treated wheat seedlings (D), and in control seedlings. From 1396 unique phosphoproteins, 2257 unique phosphorylated peptides and 2416 phosphorylation sites were identified. Of these, 96 DEPs displayed significant changes (≥1.50-fold, p < 0.01). These DEPs are involved in photosynthesis, signal transduction, etc. Furthermore, phosphorylation of several DEPs was upregulated by both D and NO treatments, but downregulated only in NO treatment. These differences affected the chlorophyll A–B binding protein, chloroplast post-illumination chlorophyll-fluorescence-increase protein, and SNT7, implying that NO indirectly regulated the absorption and transport of light energy in photosynthesis in response to WD stress. The significant difference of chlorophyll (Chl) content, Chl a fluorescence-transient, photosynthesis index, and trapping and transport of light energy further indicated that exogenous NO under D stress enhanced the primary photosynthesis reaction compared to D treatment. A putative pathway is proposed to elucidate NO regulation of the primary reaction of photosynthesis under WD.

Chrysophanol attenuates nitrosative/oxidative stress injury in a mouse model of focal cerebral ischemia/reperfusion

Nitrosative/oxidative stress plays an important role in neuronal death following cerebral ischemia/reperfusion (I/R). Chrysophanol (CHR) has been shown to afford significant neuroprotection on ischemic stroke, however, whether its mechanism is related to attenuating nitrosative/oxidative stress is not clear. In the present study, we investigated the effect of CHR on neuronal injury related to nitric oxide (NO) production by using mouse middle cerebral artery occlusion (MCAO) model. Our results revealed that nitrite plus nitrate (NO_x^-) and 3-nitrotyrosine (3-NT) levels increased in ischemic brain 14 days after reperfusion, and were subsequently attenuated by CHR treatment. Moreover, 3-NT is colocalized with NeuN and TUNEL, suggesting that neuronal apoptosis following I/R is associated with 3-NT and CHR suppresses NO-associated neuronal cell death. Accordingly, cleaved caspase-3 expression in ischemic brain was decreased by CHR treatment. I/R also decreased the activity of total superoxide dismutase (SOD) and manganese-dependent SOD (MnSOD), whilst increased reactive oxygen species (ROS) production significantly. Interestingly, CHR reversed this decrease in total SOD, and MnSOD activity, and inhibited ROS generation in the ischemic brain. Taken together, our results provide direct evidence suggesting that CHR attenuates nitrosative/oxidative stress injury induced by I/R, providing a novel therapeutic target in the treatment of acute ischemic stroke.

Cellular stress and apoptosis contribute to the pathogenesis of autism spectrum disorder

The molecular pathogenesis of autism spectrum disorder, a neurodevelopmental disorder, is still elusive. In this study, we investigated the possible roles of endoplasmic reticulum (ER) stress, oxidative stress, and apoptosis as molecular mechanisms underlying autism. This study compared the activation of ER stress signals (protein kinase R-like endoplasmic reticulum kinase [PERK], activating transcription factor 6 [ATF6], inositol-requiring enzyme 1 alpha [IRE1α]) in different brain regions (prefrontal cortex, hippocampus, cerebellum) in subjects with autism and in age-matched controls. Our data showed that the activation of three signals of ER stress varies in different regions of the autistic brain. IRE1α was activated in cerebellum and prefrontal cortex but ATF6 was activated in hippocampus. PERK was not activated in the three regions. Furthermore, the activation of ER stress was confirmed because the expression of C/EBP-homologous protein (CHOP), which is the common downstream indicators of ER stress signals, and most of ER chaperones were upregulated in the three regions. Consistent with the induction of ER stress, apoptosis was found in the three regions by detecting the cleavage of caspase 8 and poly(ADP-ribose) polymerase as well as using the transferase dUTP nick end labeling assay. Moreover, our data showed that oxidative stress was responsible for ER stress and apoptosis because the levels of 4-Hydroxynonenal and nitrotyrosine-modified proteins were significantly increased in the three regions. In conclusion, these data indicate that cellular stress and apoptosis may play important roles in the pathogenesis of autism. Autism Res 2018, 11: 1076-1090. © 2018 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

Autism results in significant morbidity and mortality in children. The functional and molecular changes in the autistic brains are unclear. The present study utilized autistic brain tissues from the National Institute of Child Health and Human Development's Brain Tissue Bank for the analysis of cellular and molecular changes in autistic brains. Three key brain regions, the hippocampus, the cerebellum, and the frontal cortex, in six cases of autistic brains and six cases of non-autistic brains from 6 to 16 years old deceased children, were analyzed. The current study investigated the possible roles of endoplasmic reticulum (ER) stress, oxidative stress, and apoptosis as molecular mechanisms underlying autism. The activation of three signals of ER stress (protein kinase R-like endoplasmic reticulum kinase, activating transcription factor 6, inositol-requiring enzyme 1 alpha) varies in different regions. The occurrence of ER stress leads to apoptosis in autistic brains. ER stress may result from oxidative stress because of elevated levels of the oxidative stress markers: 4-Hydroxynonenal and nitrotyrosine-modified proteins in autistic brains. These findings suggest that cellular stress and apoptosis may contribute to the autistic phenotype. Pharmaceuticals and/or dietary supplements, which can alleviate ER stress, oxidative stress and apoptosis, may be effective in ameliorating adverse phenotypes associated with autism.

Wnt5a Increases the Glycolytic Rate and the Activity of the Pentose Phosphate Pathway in Cortical Neurons

In the last few years, several reports have proposed that Wnt signaling is a general metabolic regulator, suggesting a role for this pathway in the control of metabolic flux. Wnt signaling is critical for several neuronal functions, but little is known about the correlation between this pathway and energy metabolism. The brain has a high demand for glucose, which is mainly used for energy production. Neurons use energy for highly specific processes that require a high energy level, such as maintaining the electrical potential and synthesizing neurotransmitters. Moreover, an important metabolic impairment has been described in all neurodegenerative disorders. Despite the key role of glucose metabolism in the brain, little is known about the cellular pathways involved in regulating this process. We report here that Wnt5a induces an increase in glucose uptake and glycolytic rate and an increase in the activity of the pentose phosphate pathway; the effects of Wnt5a require the intracellular generation of nitric oxide. Our data suggest that Wnt signaling stimulates neuronal glucose metabolism, an effect that could be important for the reported neuroprotective role of Wnt signaling in neurodegenerative disorders.

Overexpressed neuroglobin raises threshold for nitric oxide-induced impairment of mitochondrial respiratory activities and stress signaling in primary cortical neurons

Surges of nitric oxide compromise mitochondrial respiration primarily by competitive inhibition of oxygen binding to cytochrome c oxidase (complex IV) and are particularly injurious in neurons, which rely on oxidative phosphorylation for all their energy needs. Here, we show that transgenic overexpression of the neuronal globin protein, neuroglobin, helps diminish protein nitration, preserve mitochondrial function and sustain ATP content of primary cortical neurons challenged by extended nitric oxide exposure. Specifically, in transgenic neurons, elevated neuroglobin curtailed nitric oxide-induced alterations in mitochondrial oxygen consumption rates, including baseline oxygen consumption, consumption coupled with ATP synthesis, proton leak and spare respiratory capacity. Concomitantly, activation of genes involved in sensing and responding to oxidative/nitrosative stress, including the early-immediate c-Fos gene and the phase II antioxidant enzyme, heme oxygenase-1, was diminished in neuroglobin-overexpressing compared to wild-type neurons. Taken together, these differences reflect a lesser insult produced by similar concentrations of nitric oxide in neuroglobin-overexpressing compared to wild-type neurons, suggesting that abundant neuroglobin buffers nitric oxide and raises the threshold of nitric oxide-mediated injury in neurons.

A facile electrophoretic technique to monitor phosphoenolpyruvate-dependent kinases

Phosphoenolpyruvate (PEP)-dependent kinases are central to numerous metabolic processes and mediate the production of adenosine triphosphate (ATP) by substrate-level phosphorylation (SLP). While pyruvate kinase (PK, EC: 2.7.1.40), the final enzyme of the glycolytic pathway is critical in the anaerobic synthesis of ATP from ADP, pyruvate phosphate dikinase (PPDK, EC: 2.7.9.1), and phosphoenolpyruvate synthase (PEPS, EC: 2.7.9.2) help generate ATP from AMP coupled to PEP as a substrate. Here we demonstrate an inexpensive and effective electrophoretic technology to determine the activities of these enzymes by blue-native polyacrylamide gel electrophoresis (BN-PAGE). The generation of pyruvate is linked to exogenous lactate dehydrogenase (LDH), and the oxidation of reduced nicotinamide adenine dinucleotide (NADH) coupled to 2,6-dichloroindophenol (DCIP) and iodonitrotetrazolium chloride (INT) results in a formazan precipitate which is easily quantifiable. The selectivity of the enzymes is ensured by including either AMP or ADP and pyrophosphate (PP(i) ) or inorganic phosphate (P(i) ). Activity bands were readily obtained after incubation in the respective reaction mixtures for 20-30 min. Cell-free extract concentrations as low as 20 μg protein equivalent yielded activity bands and substrate levels were manipulated to optimize sensitivity of this analytical technique. High-pressure liquid chromatography (HPLC), two-dimensional (2-D) SDS-PAGE (where SDS is sodium dodecyl sulfate), and immunoblot studies of the excised activity band help further characterize these PEP-dependent kinases. Furthermore, these enzymes were readily identified on the same gel by incubating it sequentially in the respective reaction mixtures. This technique provides a facile method to elucidate these kinases in biological systems.

Evidence of oxidative damage and inflammation associated with low glutathione redox status in the autism brain

Despite increasing evidence of oxidative stress in the pathophysiology of autism, most studies have not evaluated biomarkers within specific brain regions, and the functional consequences of oxidative stress remain relatively understudied. We examined frozen samples from the cerebellum and temporal cortex (Brodmann area 22 (BA22)) from individuals with autism and unaffected controls (n=15 and n=12 per group, respectively). Biomarkers of oxidative stress, including reduced glutathione (GSH), oxidized glutathione (GSSG) and glutathione redox/antioxidant capacity (GSH/GSSG), were measured. Biomarkers of oxidative protein damage (3-nitrotyrosine; 3-NT) and oxidative DNA damage (8-oxo-deoxyguanosine; 8-oxo-dG) were also assessed. Functional indicators of oxidative stress included relative levels of 3-chlorotyrosine (3-CT), an established biomarker of a chronic inflammatory response, and aconitase activity, a biomarker of mitochondrial superoxide production. Consistent with previous studies on plasma and immune cells, GSH and GSH/GSSG were significantly decreased in both autism cerebellum (P<0.01) and BA22 (P<0.01). There was a significant increase in 3-NT in the autism cerebellum and BA22 (P<0.01). Similarly, 8-oxo-dG was significantly increased in autism cerebellum and BA22 (P<0.01 and P=0.01, respectively), and was inversely correlated with GSH/GSSG in the cerebellum (P<0.01). There was a significant increase in 3-CT levels in both brain regions (P<0.01), whereas aconitase activity was significantly decreased in autism cerebellum (P<0.01), and was negatively correlated with GSH/GSSG (P=0.01). Together, these results indicate that decreased GSH/GSSG redox/antioxidant capacity and increased oxidative stress in the autism brain may have functional consequence in terms of a chronic inflammatory response, increased mitochondrial superoxide production, and oxidative protein and DNA damage.

N-methyl-aspartate receptor and neuronal nitric oxide synthase activation mediate bilirubin-induced neurotoxicity

Hyperbilirubinemia may lead to neurotoxicity and neuronal death. Although the mechanisms of nerve cell damage by unconjugated bilirubin (UCB) appear to involve a disruption of the redox status and excitotoxicity, the contribution of nitric oxide (NO·) and of N-methyl-D-aspartate (NMDA) glutamate receptors is unclear. We investigated the role of NO· and NMDA glutamate receptors in the pathways of nerve cell demise by UCB. Neurons were incubated with 100 micromol/L UCB, in the presence of 100 micromol/L human serum albumin for 4 h at 37ºC, alone or in combination with N-ω-nitro-L-arginine methyl ester (L-NAME) (an inhibitor of neuronal nitric oxide synthase [nNOS]), hemoglobin (an NO· scavenger) or (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) (an NMDA-receptor antagonist). Exposure to UCB led to increased expression of nNOS and production of both NO· and cyclic guanosine 3',5'-monophosphate (cGMP), along with protein oxidation and depletion of glutathione. These events concurred for cell dysfunction and death and were counteracted by L-NAME. Moreover, the UCB-induced loss of neuronal viability was abolished by hemoglobin, whereas the activation of nNOS and production of both NO· and cGMP were counteracted by MK-801, resulting in significant protection from cell dysfunction and death. These results reinforce the involvement of oxidative stress by showing that nerve cell damage by UCB is mediated by NO· and therefore is counteracted by NO· inhibitors or scavengers. Our findings strongly suggest that the activation of nNOS and neurotoxicity occur through the engagement of NMDA receptors. These data reveal a role for overstimulation of glutamate receptors in mediating oxidative damage by UCB.

Human cerebral neuropathology of Type 2 diabetes mellitus

The cerebral neuropathology of Type 2 diabetes (CNDM2) has not been positively defined. This review includes a description of CNDM2 research from before the 'Pubmed Era'. Recent neuroimaging studies have focused on cerebrovascular and white matter pathology. These and prior studies about cerebrovascular histopathology in diabetes are reviewed. Evidence is also described for and against the link between CNDM2 and Alzheimer's disease pathogenesis. To study this matter directly, we evaluated data from University of Kentucky Alzheimer's Disease Center (UK ADC) patients recruited while non-demented and followed longitudinally. Of patients who had come to autopsy (N = 234), 139 met inclusion criteria. These patients provided the basis for comparing the prevalence of pathological and clinical indices between well-characterized cases with (N = 50) or without (N = 89) the premortem diagnosis of diabetes. In diabetics, cerebrovascular pathology was more frequent and Alzheimer-type pathology was less frequent than in non-diabetics. Finally, a series of photomicrographs demonstrates histopathological features (including clinical-radiographical correlation) observed in brains of persons that died after a history of diabetes. These preliminary, correlative, and descriptive studies may help develop new hypotheses about CNDM2. We conclude that more work should be performed on human material in the context of CNDM2.

Assessing the physiological concentration and targets of nitric oxide in brain tissue

Low nanomolar concentrations of nitric oxide activate guanylyl cyclase to produce cGMP, which has diverse physiological effects. Higher concentrations inhibit mitochondrial respiration at cytochrome c oxidase and this has been proposed to be important physiologically, increasing oxygen permeation into tissue (by reducing the oxygen use of cells near blood vessels), activating AMP kinase, and regulating the relationship between cerebral blood flow and oxygen use. It is unclear, however, whether nitric oxide can accumulate physiologically to concentrations at which inhibition of respiration occurs. In rat cerebellar slices, we activated nitric oxide production from each isoform of nitric oxide synthase. Only activation of inducible nitric oxide synthase, which is expressed pathologically, caused any significant inhibition of respiration. Modelling oxygen and nitric oxide concentrations predicted that, in vivo, physiological nitric oxide levels are too low to affect respiration. Even pathologically, the nitric oxide concentration may only rise to 2.5 nm, producing a 1.5% inhibition of respiration. Thus, under physiological conditions, nitric oxide signals do not inhibit respiration but are well-tuned to the dynamic range of guanylyl cyclase activation.