The role of polyamine metabolism in neuronal injury following cerebral ischemia

A Metabolomic Signature of Ischemic Stroke Showing Acute Oxidative and Energetic Stress

Metabolomics is a powerful data-driven tool for in-depth biological phenotyping that could help identify the specific metabolic profile of cryptogenic strokes, for which no precise cause has been identified. We performed a targeted quantitative metabolomics study in West African patients who had recently suffered an ischemic stroke, which was either cryptogenic (n = 40) or had a clearly identified cause (n = 39), compared to a healthy control group (n = 40). Four hundred fifty-six metabolites were accurately measured. Multivariate analyses failed to reveal any metabolic profile discriminating between cryptogenic ischemic strokes and those with an identified cause but did show superimposable metabolic profiles in both groups, which were clearly distinct from those of healthy controls. The blood concentrations of 234 metabolites were significantly affected in stroke patients compared to controls after the Benjamini-Hochberg correction. Increased methionine sulfoxide and homocysteine concentrations, as well as an overall increase in saturation of fatty acids, were indicative of acute oxidative stress. This signature also showed alterations in energetic metabolism, cell membrane integrity, monocarbon metabolism, and neurotransmission, with reduced concentrations of several metabolites known to be neuroprotective. Overall, our results show that cryptogenic strokes are not pathophysiologically distinct from ischemic strokes of established origin, and that stroke leads to intense metabolic remodeling with marked oxidative and energetic stresses.

Molecular mechanism of caloric restriction mimetics-mediated neuroprotection of age-related neurodegenerative diseases: an emerging therapeutic approach

Aging-induced neurodegenerative diseases (NDs) are significantly increasing health problem worldwide. It has been well documented that oxidative stress is one of the potential causes of aging and age-related NDs. There are no drugs for the treatment of NDs, therefore there is an immediate necessity for the development of strategies/treatments either to prevent or cure age-related NDs. Caloric restriction (CR) and intermittent fasting have been considered as effective strategies in increasing the healthspan and lifespan, but it is difficult to adhere to these routines strictly, which has led to the development of calorie restriction mimetics (CRMs). CRMs are natural compounds that provide similar molecular and biochemical effects of CR, and activate autophagy process. CRMs have been reported to regulate redox signaling by enhancing the antioxidant defense systems through activation of the Nrf2 pathway, and inhibiting ROS generation through attenuation of mitochondrial dysfunction. Moreover, CRMs also regulate redox-sensitive signaling pathways such as the PI3K/Akt and MAPK pathways to promote neuronal cell survival. Here, we discuss the neuroprotective effects of various CRMs at molecular and cellular levels during aging of the brain. The CRMs are envisaged to become a cornerstone of the pharmaceutical arsenal against aging and age-related pathologies.

Ramelteon Mitigates Free Fatty Acid (FFA)-Induced Attachment of Monocytes to Brain Vascular Endothelial Cells

Acute ischemic stroke is a challenging disease that threatens the life of older people. Dysfunction of brain endothelial cells is reported to be involved in the pathogenesis of acute ischemic stroke. Ramelteon is a novel agonist of melatonin receptor developed for the treatment of insomnia. Recently, the promising protective effect of Ramelteon on brain injury has been widely reported. The present study aims to investigate the protective effect of Ramelteon against free fatty acid (FFA)-induced damages in brain vascular endothelial cells and the underlying mechanism. Firstly, we discovered that Ramelteon administration remarkably reversed the decreased cell viability, increased LDH release, activated oxidative stress, and excessive released inflammatory factors caused by FFAs. Secondly, Ramelteon extensively suppressed the attachment of U937 monocytes to bEnd.3 brain endothelial cells induced by FFAs. In addition, the elevated expression of E-selectin and the reduced expression of KLF2 induced by FFAs were pronouncedly alleviated by Ramelteon. Lastly, silencing of KLF2 abolished the protective effects of Ramelteon against FFA-induced expression of E-selectin and the attachment of U937 monocytes to bEnd.3 brain endothelial cells. In conclusion, Ramelteon mitigated FFA-induced attachment of monocytes to brain vascular endothelial cells by increasing the expression of KLF2 and reducing the expression of E-selectin.

RNA-seq analysis and compound screening highlight multiple signalling pathways regulating secondary cell death after acute CNS injury in vivo

Understanding the molecular mechanisms that regulate secondary cell death after acute central nervous system (CNS) injury is critical for the development of effective neuroprotective drugs. Previous research has shown that neurotoxic processes including excitotoxicity, oxidative stress and neuroinflammation can cause secondary cell death. Nevertheless, clinical trials targeting these processes have been largely unsuccessful, suggesting that the signalling pathways underlying secondary cell death remain incompletely understood. Due to their suitability for live imaging and their amenability to genetic and pharmacological manipulation, larval zebrafish provide an ideal platform for studying the regulation of secondary cell death in vivo Here, we use RNA-seq gene expression profiling and compound screening to identify signalling pathways that regulate secondary cell death after acute neural injury in larval zebrafish. RNA-seq analysis of genes upregulated in cephalic mpeg1⁺ macrophage-lineage cells isolated from mpeg1:GFP transgenic larvae after neural injury suggested an involvement of cytokine and polyamine signalling in secondary cell death. Furthermore, screening a library of FDA approved compounds indicated roles for GABA, serotonin and dopamine signalling. Overall, our results highlight multiple signalling pathways that regulate secondary cell death in vivo, and thus provide a starting point for the development of novel neuroprotective treatments for patients with CNS injury.This article has an associated First Person interview with the two first authors of the paper.

Cerebral Microvascular Endothelial Cell Apoptosis after Ischemia: Role of Enolase-Phosphatase 1 Activation and Aci-Reductone Dioxygenase 1 Translocation

Enolase-phosphatase 1 (ENOPH1), a newly discovered enzyme of the methionine salvage pathway, is emerging as an important molecule regulating stress responses. In this study, we investigated the role of ENOPH1 in blood brain barrier (BBB) injury under ischemic conditions. Focal cerebral ischemia induced ENOPH1 mRNA and protein expression in ischemic hemispheric microvessels in rats. Exposure of cultured brain microvascular endothelial cells (bEND3 cells) to oxygen-glucose deprivation (OGD) also induced ENOPH1 upregulation, which was accompanied by increased cell death and apoptosis reflected by increased 3-(4, 5-Dimethylthiazol-2-yl)-2, 5- diphenyltetrazolium bromide formation, lactate dehydrogenase release and TUNEL staining. Knockdown of ENOPH1 expression with siRNA or overexpressing ENOPH1 with CRISPR-activated plasmids attenuated or potentiated OGD-induced endothelial cell death, respectively. Moreover, ENOPH1 knockdown or overexpression resulted in a significant reduction or augmentation of reactive oxygen species (ROS) generation, apoptosis-associated proteins (caspase-3, PARP, Bcl-2 and Bax) and Endoplasmic reticulum (ER) stress proteins (Ire-1, Calnexin, GRP78 and PERK) in OGD-treated endothelial cells. OGD upregulated the expression of ENOPH1’s downstream protein aci-reductone dioxygenase 1 (ADI1) and enhanced its interaction with ENOPH1. Interestingly, knockdown of ENOPH1 had no effect on OGD-induced ADI1 upregulation, while it potentiated OGD-induced ADI1 translocation from the nucleus to the cytoplasm. Lastly, knockdown of ENOPH1 significantly reduced OGD-induced endothelial monolayer permeability increase. In conclusion, our data demonstrate that ENOPH1 activation may contribute to OGD-induced endothelial cell death and BBB disruption through promoting ROS generation and the activation of apoptosis associated proteins, thus representing a new therapeutic target for ischemic stroke.

Amine oxidase copper-containing 1 (AOC1) is a downstream target gene of the Wilms tumor protein, WT1, during kidney development

Amine oxidase copper-containing 1 (AOC1; formerly known as amiloride-binding protein 1) is a secreted glycoprotein that catalyzes the degradation of putrescine and histamine. Polyamines and their diamine precursor putrescine are ubiquitous to all organisms and fulfill pivotal functions in cell growth and proliferation. Despite the importance of AOC1 in regulating polyamine breakdown, very little is known about the molecular mechanisms that control its expression. We report here that the Wilms tumor protein, WT1, which is necessary for normal kidney development, activates transcription of the AOC1 gene. Expression of a firefly luciferase reporter under control of the proximal AOC1 promoter was significantly enhanced by co-transfection of a WT1 expression construct. Binding of WT1 protein to a cis-regulatory element in the AOC1 promoter was confirmed by electrophoretic mobility shift assay and chromatin immunoprecipitation. Antisense inhibition of WT1 protein translation strongly reduced Aoc1 transcripts in cultured murine embryonic kidneys and gonads. Aoc1 mRNA levels correlated with WT1 protein in several cell lines. Double immunofluorescent staining revealed a co-expression of WT1 and AOC1 proteins in the developing genitourinary system of mice and rats. Strikingly, induced changes in polyamine homeostasis affected branching morphogenesis of cultured murine embryonic kidneys in a developmental stage-specific manner. These findings suggest that WT1-dependent control of polyamine breakdown, which is mediated by changes in AOC1 expression, has a role in kidney organogenesis.

Toxicity of polyamines and their metabolic products

Polyamines are ubiquitous and essential components of mammalian cells. They have multiple functions including critical roles in nucleic acid and protein synthesis, gene expression, protein function, protection from oxidative damage, the regulation of ion channels, and maintenance of the structure of cellular macromolecules. It is essential to maintain a correct level of polyamines, and this amount is tightly regulated at the levels of transport, synthesis, and degradation. Catabolic pathways generate reactive aldehydes including acrolein and hydrogen peroxide via a number of oxidases. These metabolites, particularly those from spermine, can cause significant toxicity with damage to proteins, DNA, and other cellular components. Their production can be increased as a result of infection or cell damage that releases free polyamines and activates the oxidative catabolic pathways. Since polyamines also have an important physiological role in protection from oxidative damage, the reduction in polyamine content may exacerbate the toxic potential of these agents. Increases in polyamine catabolism have been implicated in the development of diseases including stroke, other neurological diseases, renal failure, liver disease, and cancer. These results provide new opportunities for the early diagnosis, prevention, and treatment of disease.

N(1)-(quinolin-2-ylmethyl)butane-1,4-diamine, a polyamine analogue, attenuated injury in in vitro and in vivo models of cerebral ischemia

It has been widely recognized that glutamate (Glu)-induced cytotoxicity, intracellular calcium overload and excessive free radical production are the key players in the development and progression of ischemic brain injury. Since MK-801, an antagonist of N-methyl-d-aspartate (NMDA) receptor, showed many adverse reactions that hampered its clinical applications, development of safe and effective agent for the treatment of cerebral ischemia is eagerly required. This study was to investigate the effects of N(1)-(quinolin-2-ylmethyl)butane-1,4-diamine (QMA), a polyamine analogue, on the in vitro and in vivo models of cerebral ischemic damage. The results revealed that pretreatment with QMA could attenuate Glu, putrescine (Put) and oxygen-glucose deprivation (OGD)-induced cell death, lipid peroxidation as well as the elevation of reactive oxygen species (ROS) and intracellular [Ca(2+)](i) in pheochromocytoma (PC12) cells and in rat primary cortical neurons. The results also demonstrated that QMA could inhibit NMDA-mediated intracellular [Ca(2+)](i) accumulation in rat primary cortical neurons and reduce brain infarct volume in middle cerebral artery occlusion (MCAO) rats. The present report suggested that polyamines played a crucial role in the pathological processes of cerebral ischemic damage and that QMA or other novel polyamine analogues could be promising therapeutic candidates for stroke by virtue of their anti-hypoxia and antioxidation property.

Polyamine catabolism contributes to enterotoxigenic Bacteroides fragilis-induced colon tumorigenesis

It is estimated that the etiology of 20-30% of epithelial cancers is directly associated with inflammation, although the direct molecular events linking inflammation and carcinogenesis are poorly defined. In the context of gastrointestinal disease, the bacterium enterotoxigenic Bacteroides fragilis (ETBF) is a significant source of chronic inflammation and has been implicated as a risk factor for colorectal cancer. Spermine oxidase (SMO) is a polyamine catabolic enzyme that is highly inducible by inflammatory stimuli resulting in increased reactive oxygen species (ROS) and DNA damage. We now demonstrate that purified B. fragilis toxin (BFT) up-regulates SMO in HT29/c1 and T84 colonic epithelial cells, resulting in SMO-dependent generation of ROS and induction of γ-H2A.x, a marker of DNA damage. Further, ETBF-induced colitis in C57BL/6 mice is associated with increased SMO expression and treatment of mice with an inhibitor of polyamine catabolism, N(1),N(4)-bis(2,3-butandienyl)-1,4-butanediamine (MDL 72527), significantly reduces ETBF-induced chronic inflammation and proliferation. Most importantly, in the multiple intestinal neoplasia (Min) mouse model, treatment with MDL 72527 reduces ETBF-induced colon tumorigenesis by 69% (P < 0.001). The results of these studies indicate that SMO is a source of bacteria-induced ROS directly associated with tumorigenesis and could serve as a unique target for chemoprevention.

LPS-induced CCL2 expression and macrophage influx into the murine central nervous system is polyamine-dependent

Increased polyamine production is observed in a variety of chronic neuroinflammatory disorders, but in vitro and in vivo studies yield conflicting data on the immunomodulatory consequences of their production. Ornithine decarboxylase (ODC) is the rate-limiting enzyme in endogenous polyamine production. To identify the role of polyamine production in CNS-intrinsic inflammatory responses, we defined CNS sites of ODC expression and the consequences of inhibiting ODC in response to intracerebral injection of LPS±IFNγ. In situ hybridization analysis revealed that both neurons and non-neuronal cells rapidly respond to LPS±IFNγ by increasing ODC expression. Inhibiting ODC by co-injecting DFMO decreased LPS-induced CCL2 expression and macrophage influx into the CNS, without altering LPS-induced microglial or macrophage activation. Conversely, intracerebral injection of polyamines was sufficient to trigger macrophage influx into the CNS of wild-type but not CCL2KO mice, demonstrating the dependence of macrophage influx on CNS expression of CCL2. Consistent with these data, addition of putrescine and spermine to mixed glial cultures dramatically increased CCL2 expression and to a much lesser extent, TNF expression. Addition of all three polyamines to mixed glial cultures also decreased the numbers and percentages of oligodendrocytes present. However, in vivo, inhibiting the basal levels of polyamine production was sufficient to induce expression of apolipoprotein D, a marker of oxidative stress, within white matter tracts. Considered together, our data indicate that: (1) CNS-resident cells including neurons play active roles in recruiting pro-inflammatory TREM1-positive macrophages into the CNS via polyamine-dependent induction of CCL2 expression and (2) modulating polyamine production in vivo may be a difficult strategy to limit inflammation and promote repair due to the dual homeostatic and pro-inflammatory roles played by polyamines.

Selective vulnerability of hippocampal cornu ammonis 1 pyramidal cells to excitotoxic insult is associated with the expression of polyamine-sensitive N-methyl-D-asparate-type glutamate receptors

Excess glutamate release and stimulation of post-synaptic glutamatergic receptors have been implicated in the pathophysiology of many neurological diseases. The hippocampus, and the pyramidal cell layer of the cornu ammonus 1 (CA1) region in particular, has been noted for its selective sensitivity to excitotoxic insults. The current studies examined the role of N-methyl-D-aspartate (NMDA) receptor subunit composition and sensitivity to stimulatory effects of the polyamine spermidine, an allosteric modulator of NMDA NR2 subunit activity, in hippocampal CA1 region sensitivity to excitotoxic insult. Organotypic hippocampal slice cultures of 8 day-old neonatal rat were obtained and maintained in vitro for 5 days. At this time, immunohistochemical analysis of mature neuron density (NeuN); microtubule associated protein-2(a,b) density (MAP-2); and NMDA receptor NR1 and NR2B subunit density in the primary cell layers of the dentate gyrus (DG), CA3, and CA1 regions, was conducted. Further, autoradiographic analysis of NMDA receptor distribution and density (i.e. [(125)I]MK-801 binding) and spermidine (100 microM)-potentiated [(125)I]MK-801 binding in the primary cell layers of these regions was examined. A final series of studies examined effects of prolonged exposure to NMDA (0.1-10 microM) on neurodegeneration in the primary cell layers of the DG, CA3, and CA1 regions, in the absence and presence of spermidine (100 microM) or ifenprodil (100 microM), an allosteric inhibitor of NR2B polypeptide subunit activity. The pyramidal cell layer of the CA1 region demonstrated significantly greater density of mature neurons, MAP-2, NR1 and NR2B subunits, and [(125)I]MK-801 binding than the CA3 region or DG. Twenty-four hour NMDA (10 microM) exposure produced marked neurodegeneration (approximately 350% of control cultures) in the CA1 pyramidal cell region that was significantly reduced by co-exposure to ifenprodil or DL-2-Amino-5-phosphonopentanoic acid (APV). The addition of spermidine significantly potentiated [(125)I]MK-801 binding and neurodegeneration induced by exposure to a non-toxic concentration of NMDA, exclusively in the CA1 region. This neurodegeneration was markedly reduced with co-exposure to ifenprodil. These data suggest that selective sensitivity of the CA1 region to excitotoxic stimuli may be attributable to the density of mature neurons expressing polyamine-sensitive NR2B polypeptide subunits.