C Kaur

Singapore National Eye Centre, Tumasik, Singapore

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Publications (142)439.45 Total impact

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    ABSTRACT: This study was aimed at evaluating the role of increased iron accumulation in oligodendrocytes and its role in their apoptosis in the periventricular white matter damage (PWMD) following a hypoxic injury to the neonatal brain. In response to hypoxia, in the PWM, there was increased expression of proteins involved in iron acquisition, such as iron regulatory proteins (IRP1, IRP2) and transferrin receptor in oligodendrocytes. Consistent with this, following a hypoxic exposure, there was increased accumulation of iron in primary cultured oligodendrocytes. The increased concentration of iron within hypoxic oligodendrocytes was found to elicit ryanodine receptor (RyR) expression, and the expression of endoplasmic reticulum (ER) stress markers such as binding-immunoglobulin protein (BiP) and inositol-requiring enzyme (IRE)-1α. Associated with ER stress, there was reduced adenosine triphosphate (ATP) levels within hypoxic oligodendrocytes. However, treatment with deferoxamine reduced the increased expression of RyR, BiP, and IRE-1α and increased ATP levels in hypoxic oligodendrocytes. Parallel to ER stress there was enhanced reactive oxygen species production within mitochondria of hypoxic oligodendrocytes, which was attenuated when these cells were treated with deferoxamine. At the ultrastructural level, hypoxic oligodendrocytes frequently showed dilated ER and disrupted mitochondria, which became less evident in those treated with deferoxamine. Associated with these subcellular changes, the apoptosis of hypoxic oligodendrocytes was evident with an increase in p53 and caspase-3 expression, which was attenuated when these cells were treated with deferoxamine. Thus, the present study emphasizes that the excess iron accumulated within oligodendrocytes in hypoxic PWM could result in their death by eliciting ER stress and mitochondrial disruption.
    Molecular Neurobiology 08/2015; DOI:10.1007/s12035-015-9389-6 · 5.14 Impact Factor
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    Melatonin:Therapeutic Value and Neuroprotection, Edited by Venkatramanujan Srinivasan, Gabriella Gobbi, Samuel D. Shillcutt, Sibel Suzen, 01/2015: chapter 16: pages 189-202; CRC Press., ISBN: 9781482220094
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    ABSTRACT: This study was carried out to investigate the roles of tight junction proteins and other vascular factors in the increased permeability of the blood retinal barrier (BRB) affecting the immature neonatal retina following a hypoxic insult. The expression of endothelial tight junction proteins such as claudin-5, occludin and zonula occludens-1 (ZO-1) and endothelial cell specific molecule-1 (ESM-1), and associated structural changes in the blood vessels were analyzed in the retinas of 1-day-old wistar rats subjected to hypoxia for 2 h and subsequently sacrificed at different time points ranging from 3 h to 14 d. The mRNA and protein expression of claudin-5, occludin & ZO-1 was found to be reduced in the hypoxic retina, although, at the ultrastructural level, the tight junctions between the endothelial cells and retinal pigment epithelial cells appeared to be intact. Following a hypoxic insult vascular endothelial cells frequently showed presence of cytoplasmic vacuoles, vacuolated mitochondria and multivesicular aggregations projecting into the capillary lumen. The expression of ESM-1 in the immature retinas was found to be increased following hypoxic exposure. The structural and molecular changes in the hypoxic neonatal retinas were consistent with a hypoxia induced impairment of the BRB. Hypoxia reduced the expression of TJ proteins in the neonatal retina, but the role of increased ESM-1 expression in this process warrants further investigation. Copyright © 2014. Published by Elsevier Ltd.
    Experimental Eye Research 11/2014; 130. DOI:10.1016/j.exer.2014.11.011 · 2.71 Impact Factor
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    ABSTRACT: Purpose: Hypoxic insult to the developing retina results in apoptosis of retinal ganglion cells (RGCs) through production of inflammatory mediators, nitric oxide (NO), and free radicals. The present study was aimed at elucidating the pathway through which hypoxia results in overproduction of NO in the immature retina, and its role in causing apoptosis of RGCs. Methods: Wistar rats (1 day old) were exposed to hypoxia and their retinas were studied at 3 hours to 14 days after exposure. The protein expression of nuclear factor-κB (NF-κB) and neuronal nitric oxide synthase (nNOS) in the retina and primary cultures of RGCs was analyzed using Western blotting and double-immunofluorescence, whereas the concentration of NO was determined calorimetrically. In cultured RGCs, hypoxia-induced apoptosis was evaluated by caspase-3 immunolabeling. Results: Following hypoxic exposure, NF-κB-mediated expression of nNOS, which was localized to the RGCs, and subsequent NO production was significantly increased in the developing retina. In primary cultures of RGCs subjected to hypoxia, the upregulation of nNOS and NO was significantly suppressed when treated with 7-nitroindazole (7-NINA), an nNOS inhibitor or BAY, an NF-κB inhibitor. Hypoxia-induced apoptosis of RGCs, which was evident with caspase-3 labeling, also was suppressed when these cells were treated with 7-NINA or BAY. Conclusions: Our results suggest that in RGCs, hypoxic induction of nNOS is mediated by NF-κB and the resulting increased release of NO by RGCs causes their apoptosis through caspase-3 activation. It is speculated that targeting nNOS could be a potential neuroprotective strategy against hypoxia-induced RGCs death in the developing retina.
    Investigative Ophthalmology &amp Visual Science 08/2014; 55(9). DOI:10.1167/iovs.13-13718 · 3.40 Impact Factor
  • Gurugirijha Rathnasamy · Eng-Ang Ling · Charanjit Kaur ·
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    ABSTRACT: Cerebral edema/brain edema refers to the accumulation of fluid in the brain and is one of the fatal conditions that require immediate medical attention. Cerebral edema develops as a consequence of cerebral trauma, cerebral infarction, hemorrhages, abscess, tumor, hypoxia, and other toxic or metabolic factors. Based on the causative factors cerebral edema is differentiated into cytotoxic cerebral edema, vasogenic cerebral edema, osmotic and interstitial cerebral edema. Treatment of cerebral edema depends on timely diagnosis and medical assistance. Pragmatic treatment strategies such as antihypertensive medications, nonsteroidal anti-inflammatory drugs, barbiturates, steroids, glutamate and N-methyl-D-aspartate receptor antagonists and trometamol are used in clinical practice. Although the above mentioned treatment approaches are being used, owing to the complexity of the mechanisms involved in cerebral edema, a single therapeutic strategy which could ameliorate cerebral edema is yet to be identified. However, recent experimental studies have suggested that melatonin, a neurohormone produced by the pineal gland, could be an effective alternative for treating cerebral edema. In animal models of stroke, melatonin was not only shown to reduce cerebral edema but also preserved the blood brain barrier. Melatonin's beneficial effects were attributed to its properties, such as being a potent anti-oxidant, and its ability to cross the blood brain barrier within minutes after its administration. This review summarizes the beneficial effects of melatonin when used for treating cerebral edema.
    Histology and histopathology 05/2014; 29(12). · 2.10 Impact Factor
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    ABSTRACT: Although the etiology of Parkinson’s disease (PD) is not known, most patients with PD experience sleep-related problems like difficulty in initiating and maintaining sleep, excessive daytime sleepiness, sleep fragmentation, and reductions in non-REM or REM sleep. Since melatonin and its analogues have sleep-promoting and sleep-wake rhythm-regulating actions, interest has been focused on the role of melatonin in PD. Interestingly use of melatonin in animal models of PD has shown that melatonin has been useful in improving the neurotoxic effects of administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, or maneb and paraquat. Being an antioxidant melatonin counteracted the MPTP-induced lipid per oxidation. The finding of reduced expression of MT1 and MT2 melatonin receptors in amygdale and substantia nigra of patients with PD supports the involvement of melatonergic system in the possible etiology of PD. Use of melatonin or its analogues may be beneficial in treating patients with PD for improving the sleep quality and also for enhancing the neuroprotection against oxidative stress seen in PD.
    Melatonin and Melatonergic Drugs in Clinical Practice, Edited by Venkataramanujam Srinivasan, Amnon Brzezinski, Sukru Oter, Samuel D Shillcutt, 01/2014: chapter 17: pages 249-261; Springer India., ISBN: 978-81-322-0825-9
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    ABSTRACT: Alzheimer's disease (AD) is characterized by a progressive loss of memory and cognitive function as well as behavioral and sleep disturbances including insomnia. The pathophysiology of AD has been attributed to oxidative stress-induced amyloid β-protein (Aβ) deposition. Abnormal tau protein, mitochondrial dysfunction, and protein hyperphosphorylation have been demonstrated in neural tissues of AD patients. AD patients exhibit severe sleep-wake disturbances associated with rapid cognitive decline and memory impairment. Optimally effective management of AD patients requires a drug that can arrest Aβ-induced neurotoxic effects and restore the disturbed sleep-wake rhythm with improvement in sleep quality. In this context, the pineal hormone melatonin has been demonstrated to be an effective antioxidant that can prevent Aβ-induced neurotoxic effects through a variety of mechanisms. Sleep deprivation itself produces oxidative damage, impaired mitochondrial function, neurodegenerative inflammation, altered proteosomal processing, and abnormal activation of enzymes. Treating sleep disturbances is also necessary for preventing and arresting AD progression. Besides melatonin, use of melatonergic agonists such as ramelteon, agomelatine, and tasimelteon, which are now used clinically for treating insomnia and other sleep disorders, may also be beneficial in treating AD.
    Melatonin and Melatonergic Drugs in Clinical Practice, Edited by Venkataramanujam Srinivasan, Amnon Brzezinski, Sukru Oter, Samuel D. Shillcutt, 01/2014: chapter 16: pages 235-247; Springer India., ISBN: 978-81-322-0825-9
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    Linli Yao · Enci Mary Kan · Charanjit Kaur · S Thameem Dheen · Aijun Hao · Jia Lu · Eng-Ang Ling ·
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    ABSTRACT: Neuroinflammation mediated by the activated microglia is suggested to play a pivotal role in the pathogenesis of hypoxic brain injury; however, the underlying mechanism of microglia activation remains unclear. Here, we show that the canonical Notch signaling orchestrates microglia activation after hypoxic exposure which is closely associated with multiple pathological situations of the brain. Notch-1 and Delta-1 expression in primary microglia and BV-2 microglial cells was significantly elevated after hypoxia. Hypoxia-induced activation of Notch signaling was further confirmed by the concomitant increase in the expression and translocation of intracellular Notch receptor domain (NICD), together with RBP-Jκ and target gene Hes-1 expression. Chemical inhibition of Notch signaling with N-[N-(3,5-difluorophenacetyl)-1-alany1- S-phenyglycine t-butyl ester (DAPT), a γ-secretase inhibitor, effectively reduced hypoxia-induced upregulated expression of most inflammatory mediators. Notch inhibition also reduced NF-κB/p65 expression and translocation. Remarkably, Notch inhibition suppressed expression of TLR4/MyD88/TRAF6 pathways. In vivo, Notch signaling expression and activation in microglia were observed in the cerebrum of postnatal rats after hypoxic injury. Most interestingly, hypoxia-induced upregulation of NF-κB immunoexpression in microglia was prevented when the rats were given DAPT pretreatment underscoring the interrelationship between Notch signaling and NF-κB pathways. Taken together, we conclude that Notch signaling is involved in regulating microglia activation after hypoxia partly through the cross talk between TLR4/MyD88/TRAF6/NF-κB pathways. Therefore, Notch signaling may serve as a prospective target for inhibition of microglia activation known to be implicated in brain damage in the developing brain.
    PLoS ONE 11/2013; 8(11):e78439. DOI:10.1371/journal.pone.0078439 · 3.23 Impact Factor
  • Gurugirijha Rathnasamy · Eng-Ang Ling · Charanjit Kaur ·
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    ABSTRACT: Iron accumulation occurs in tissues such as periventricular white matter (PWM) in response to hypoxic injuries, and microglial cells sequester excess iron following hypoxic exposure. As hypoxia has a role in altering the expression of proteins involved in iron regulation, this study was aimed at examining the interaction between hypoxia inducible factor (HIF)-1α and proteins involved in iron transport in microglial cells, and evaluating the mechanistic action of deferoxamine and KC7F2 (a HIF-1α inhibitor) in iron mediated hypoxic injury. Treating the microglial cultures with KC7F2, led to decreased expression of transferrin receptor and divalent metal transporter-1. Administration of deferoxamine or KC7F2 to hypoxic microglial cells enhanced extracellular signal-regulated kinase (ERK) phosphorylation (p-ERK), but decreased the phosphorylation of p38 (p-p38). The increased p-ERK further phosphorylated the cAMP response element-binding protein (p-CREB) which in turn may have resulted in the increased mitogen activated protein kinase (MAPK) phosphatase 1 (MKP1), known to dephosphorylate MAPKs. Consistent with the decrease in p-p38, the production of pro-inflammatory cytokines TNF-α and IL-1β was reduced in hypoxic microglia treated with deferoxamine and SB 202190, an inhibitor for p38. This suggests that the anti-inflammatory effect exhibited by deferoxamine is by inhibition of p-p38 induced inflammation through the pERK-pCREB-MKP1 pathway, whereas that of KC7F2 requires further investigation. The present results suggest that HIF-1α may mediate iron accumulation in hypoxic microglia and KC7F2, similar to deferoxamine, might provide limited protection against iron induced PWMD.
    Neuropharmacology 10/2013; 77. DOI:10.1016/j.neuropharm.2013.10.024 · 5.11 Impact Factor
  • Linli Yao · Qiong Cao · Chunyun Wu · Charanjit Kaur · E A Ling ·
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    ABSTRACT: Notch signaling pathway is a major player in normal development in neurons, oligodendrocytes and astrocytes as well as neurological disorders of the central nervous system (CNS). Microglia, one of the major types of glial cells in the CNS, partakes in diverse roles within the CNS mainly related to normal brain development and inflammatory diseases, yet the involvement of Notch signaling pathway in microglia has remained elusive and has only recently been recognized suggesting its putative role in microglial maturation and activation. Notch ligands and receptors are constitutively expressed by microglia in developing brain. Notch signaling pathway is important for the maintenance of microglial population during early development as in other glial cells in normal development. Remarkably, Notch signaling pathway is also involved in microglial activation and inflammation process in neuroinflammatory diseases in both postnatal and adult rats. Targeting Notch signaling is therefore a promising strategy for prevention of neurodevelopmental diseases and development of future therapies for the treatment of neuroinflammatory disorders. This review highlights some recent findings of Notch signaling in microglia, both in normal development and pathological conditions.
    CNS & neurological disorders drug targets 09/2013; 12(6). DOI:10.2174/18715273113126660172 · 2.63 Impact Factor
  • Madhuvika Murugan · E A Ling · Charanjit Kaur ·
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    ABSTRACT: Expression of functional glutamate receptors (GluR) on glial cells in the developing and mature brain has been recently established. Over the last decade there has been physiological, molecular and biochemical evidence suggesting the presence of GluR on microglia. However, the significance of GluR activation in microglia remains largely unknown. In this review, we discuss the expression of GluR on microglia and the effect of GluR activation on microglial function. Microglia are the resident immune cells of the central nervous system, and activation of GluR in them has been shown to regulate their immunological response which may be either neuroprotective or neurotoxic. Microglial activation is known to initiate a myriad of molecular events such as nitric oxide production, free radicals generation, disruption of calcium regulation and release of proinflammatory cytokines, proteases, neurotransmitters, and excitatory amino acids, primarily glutamate. Since microglial activation has been implicated in several neuropathologies, an understanding of the pathway coupled to the various microglial GluR will help to develop therapeutic interventions for ameliorating microglia-mediated damage.
    CNS & neurological disorders drug targets 09/2013; DOI:10.2174/18715273113126660174 · 2.63 Impact Factor
  • Gurugirijha Rathnasamy · E A Ling · Charanjit Kaur ·
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    ABSTRACT: Iron is a vital element required by almost all cells for their normal functioning. The well-established role of iron in oxidative metabolism, myelination and synthesis of neurotransmitter makes it an indispensable nutrient required by the brain. Both iron deficiency and excess have been associated with numerous patho-physiologies of the brain, suggesting a need for iron homeostasis. Various studies have reported that the immune effector cells of the brain, the microglial cells, are involved in iron homeostasis in the brain. Microglial cells, which accumulate iron during the developmental period, have a role in myelination process. Along with the increased iron accumulation documented in neurodegenerative diseases, the striking finding is the presence of iron positive microglial cells at the foci of lesion. Though excess iron within activated microglia is demonstrated to enhance the release of pro-inflammatory cytokines and free radicals, a complete understanding of the role of iron in microglia is lacking. The present knowledge on iron mediated changes, in the functions of microglia is summarized in this review.
    CNS & neurological disorders drug targets 09/2013; 12(6). DOI:10.2174/18715273113126660169 · 2.63 Impact Factor
  • Charanjit Kaur · E A Ling ·

    CNS & neurological disorders drug targets 09/2013; 12(6). · 2.63 Impact Factor
  • Charanjit Kaur · Eng-Ang Ling ·

  • Madhuvika Murugan · Eng-Ang Ling · Charanjit Kaur ·
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    ABSTRACT: Excess glutamate mediates damage to oligodendroglia, resulting in myelination disturbances characteristic of hypoxic periventricular white matter (PWM) damage. We sought to examine if hypoxia altered the expression of astroglial excitatory amino acid transporters (EAAT1, EAAT2 and EAAT3) in the PWM, and, if so, whether it activated astroglial N-methyl D-aspartate receptors (NMDAR) leading to apoptosis of oligodendroglia. EAATs expression in the PWM of neonatal rats was measured at different time points after hypoxic exposure; it was attenuated at 7 and 14 d following hypoxia. Hypoxia prevented uptake of glutamate by astroglial EAATs causing increased levels of extracellular glutamate. Excess glutamate augmented the expression of functional astroglial NMDAR. Following hypoxia, an increase in gap junction proteins between astroglia and oligodendroglia aided in spreading of NMDAR-mediated excitotoxic calcium signals into the latter cell type triggering its apoptosis. Hence, dysregulated glutamate homeostasis is believed to contribute to hypoxia-induced death of oligodendroglia leading to neonatal PWM damage.
    Molecular and Cellular Neuroscience 07/2013; 56. DOI:10.1016/j.mcn.2013.07.005 · 3.84 Impact Factor
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    ABSTRACT: The pineal product melatonin has remarkable antioxidant properties. It is secreted during darkness and plays a key role in various physiological responses including regulation of circadian rhythms, sleep homeostasis, retinal neuromodulation, and vasomotor responses. It scavenges hydroxyl, carbonate, and various organic radicals as well as a number of reactive nitrogen species. Melatonin also enhances the antioxidant potential of the cell by stimulating the synthesis of antioxidant enzymes including superoxide dismutase, glutathione peroxidase, and glutathione reductase, and by augmenting glutathione levels. Melatonin preserves mitochondrial homeostasis, reduces free radical generation and protects mitochondrial ATP synthesis by stimulating Complexes I and IV activities. The decline in melatonin production in aged individuals has been suggested as one of the primary contributing factors for the development of age-associated neurodegenerative diseases. The efficacy of melatonin in preventing oxidative damage in either cultured neuronal cells or in the brains of animals treated with various neurotoxic agents, suggests that melatonin has a potential therapeutic value as a neuroprotective drug in treatment of Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), stroke, and brain trauma. Therapeutic trials with melatonin indicate that it has a potential therapeutic value as a neuroprotective drug in treatment of AD, ALS, and HD. In the case of other neurological conditions, like PD, the evidence is less compelling. Melatonin's efficacy in combating free radical damage in the brain suggests that it can be a valuable therapeutic agent in the treatment of cerebral edema following traumatic brain injury or stroke. Clinical trials employing melatonin doses in the range of 50-100 mg/day are warranted before its relative merits as a neuroprotective agent is definitively established.
    Neurotoxicity Research 06/2013; 23(3):267-300. DOI:10.1007/s12640-012-9337-4 · 3.54 Impact Factor
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    Linli Yao · Enci Mary Kan · Jia Lu · Aijun Hao · S Thameem Dheen · Charanjit Kaur · Eng-Ang Ling ·
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    ABSTRACT: Background Hypoxia induces microglial activation which causes damage to the developing brain. Microglia derived inflammatory mediators may contribute to this process. Toll-like receptor 4 (TLR4) has been reported to induce microglial activation and cytokines production in brain injuries; however, its role in hypoxic injury remains uncertain. We investigate here TLR4 expression and its roles in neuroinflammation in neonatal rats following hypoxic injury. Methods One day old Wistar rats were subjected to hypoxia for 2 h. Primary cultured microglia and BV-2 cells were subjected to hypoxia for different durations. TLR4 expression in microglia was determined by RT-PCR, western blot and immunofluorescence staining. Small interfering RNA (siRNA) transfection and antibody neutralization were employed to downregulate TLR4 in BV-2 and primary culture. mRNA and protein expression of tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) and inducible nitric oxide synthase (iNOS) was assessed. Reactive oxygen species (ROS), nitric oxide (NO) and NF-κB levels were determined by flow cytometry, colorimetric and ELISA assays respectively. Hypoxia-inducible factor-1 alpha (HIF-1α) mRNA and protein expression was quantified and where necessary, the protein expression was depleted by antibody neutralization. In vivo inhibition of TLR4 with CLI-095 injection was carried out followed by investigation of inflammatory mediators expression via double immunofluorescence staining. Results TLR4 immunofluorescence and protein expression in the corpus callosum and cerebellum in neonatal microglia were markedly enhanced post-hypoxia. In vitro, TLR4 protein expression was significantly increased in both primary microglia and BV-2 cells post-hypoxia. TLR4 neutralization in primary cultured microglia attenuated the hypoxia-induced expression of TNF-α, IL-1β and iNOS. siRNA knockdown of TLR4 reduced hypoxia-induced upregulation of TNF-α, IL-1β, iNOS, ROS and NO in BV-2 cells. TLR4 downregulation-mediated inhibition of inflammatory cytokines in primary microglia and BV-2 cells was accompanied by the suppression of NF-κB activation. Furthermore, HIF-1α antibody neutralization attenuated the increase of TLR4 expression in hypoxic BV-2 cells. TLR4 inhibition in vivo attenuated the immunoexpression of TNF-α, IL-1β and iNOS on microglia post-hypoxia. Conclusion Activated microglia TLR4 expression mediated neuroinflammation via a NF-κB signaling pathway in response to hypoxia. Hence, microglia TLR4 presents as a potential therapeutic target for neonatal hypoxia brain injuries.
    Journal of Neuroinflammation 02/2013; 10(1):23. DOI:10.1186/1742-2094-10-23 · 5.41 Impact Factor
  • V Sivakumar · W S Foulds · C D Luu · E.A. Ling · C Kaur ·
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    ABSTRACT: Hypoxia-induced glutamate accumulation in neural tissues results in damage to neurons through excitotoxic mechanisms via activation of glutamate receptors. Here we examine whether hypoxia in the developing retina would cause activation of the ionotropic α-amino-3-hydroxy-5-methylisoxazole-4-propioate (AMPA) glutamate receptors (GluRs) and increase in Ca(2+) influx into retinal ganglion cells (RGCs) that might ultimately lead to their death. Neonatal Wistar rats were subjected to hypoxia for 2 h and then sacrificed at various time points after the exposure together with normal age matched control rats. Primary cultures of RGCs were also prepared and subjected to hypoxia. Expression of AMPA glutamate receptor (GluR) 1-4 was examined in the retina. Additionally, expression of GluRs, intracellular Ca(2+) influx, reactive oxygen species (ROS) generation and cell death were investigated in cultured RGCs. GluR1-4 mRNA and protein expression showed a significant increase (P < 0.01) over control values after the hypoxic exposure both in vivo and in vitro. Cells expressing GluR1-4 in the retina were identified as RGCs by double immunofluorescence labeling with Thy1.1. Increased intracellular Ca(2+) in cultured RGCs following hypoxic exposure was reduced (P < 0.01) by 10 μM AMPA antagonist 6, 7-dinitroquinoxaline-2,3-dione (DNQX). Our results suggest that following a hypoxic insult, an increased amount of glutamate accumulates in the neonatal retina. This would then activate AMPA receptors which may damage RGCs through increased Ca(2+) accumulation and ROS generation. The involvement of AMPA receptors in damaging the RGCs is evidenced by suppression of intracellular Ca(2+) influx by DNQX which also decreases of ROS generation and cell death by 50%.
    Experimental Eye Research 01/2013; 109. DOI:10.1016/j.exer.2013.01.004 · 2.71 Impact Factor
  • Charanjit Kaur · Viswanathan Sivakumar · Zhirong Zou · Eng-Ang Ling ·
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    ABSTRACT: The developing cerebellum is extremely vulnerable to hypoxia which can damage the Purkinje neurons. We hypothesized that this might be mediated by tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) derived from activated microglia as in other brain areas. One-day-old rats were subjected to hypoxia following, which the expression changes of various proteins in the cerebellum including hypoxia inducible factor-1α, TNF-α, IL-1β, TNF-R(1) and IL-1R(1) were analyzed. Following hypoxic exposure, TNF-α and IL-1β immunoexpression in microglia was enhanced coupled by that of TNF-R(1) and IL-1R(1) in the Purkinje neurons. Along with this, hypoxic microglia in vitro showed enhanced release of TNF-α and IL-1β whose receptor expression was concomitantly increased in the Purkinje neurons. In addition, nitric oxide (NO) level was significantly increased in the cerebellum and cultured microglia subjected to hypoxic exposure. Moreover, cultured Purkinje neurons treated with conditioned medium derived from hypoxic microglia underwent apoptosis but the incidence was significantly reduced when the cells were treated with the same medium that was neutralized with TNF-α/IL-1β antibody. We conclude that hypoxic microglia in the neonatal cerebellum produce increased amounts of NO, TNF-α and IL-1β which when acting via their respective receptors could induce Purkinje neuron death.
    Brain Structure and Function 12/2012; 219(1). DOI:10.1007/s00429-012-0491-5 · 5.62 Impact Factor
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    ABSTRACT: The purpose of this study was to determine whether melatonin treatment would mitigate retinal ganglion cell (RGC) death in the developing retina following a hypoxic insult. Lipid peroxidation (LPO), glutathione (GSH), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) concentrations, expression of vascular endothelial growth factor receptors, Flt-1 and Flk-1, release of cytochrome c from mitochondria, and caspase-3 expression were examined in the retinas of 1-day-old rats at 3 hr to 14 days after a hypoxic exposure. The mRNA and protein expression of Flt-1 and Flk-1 and the tissue concentration of LPO, TNF-α, and IL-1β were upregulated significantly after the hypoxic exposure, whereas the content of GSH was decreased significantly. RGC cultures also showed increased LPO and decreased GSH levels after hypoxic exposure but these effects were reversed in cells treated with melatonin. TNF-α and IL-1β expression was specifically located on microglial cells, whereas Flt-1 and Flk-1 was limited to RGCs as confirmed by double immunofluorescence labeling. Cultures of hypoxic microglial cells treated with melatonin showed a significant reduction in the release of these cytokines as compared to untreated hypoxic cells. Hypoxia induced increase in the cytosolic cytochrome c and caspase-3 in RGCs was attenuated with melatonin treatment. The results suggest that, in hypoxic injuries, melatonin is neuroprotective to RGCs in the developing retina through its antioxidative, anti-inflammatory, and anti-apoptotic effects. Melatonin suppressed Flt-1 and Flk-1 expression in retinal blood vessels, which may result in reduced retinal vascular permeability and it also preserved mitochondrial function as shown by a reduction in cytochrome c leakage into the cytosol. The results may have therapeutic implications for the management of retinopathy of prematurity.
    Journal of Pineal Research 09/2012; 54(2). DOI:10.1111/jpi.12016 · 9.60 Impact Factor

Publication Stats

4k Citations
439.45 Total Impact Points


  • 2009-2014
    • Singapore National Eye Centre
      Tumasik, Singapore
    • Singapore Eye Research Institute
      Tumasik, Singapore
  • 1998-2013
    • National University of Singapore
      • Department of Anatomy
      Tumasik, Singapore
  • 2012
    • Royal Victorian Eye and Ear Hospital
      Melbourne, Victoria, Australia