Ammonia-induced activation of p53 in cultured astrocytes: Role in cell swelling and glutamate uptake

K. S. Panickar, A. R. Jayakumar, K. V Rama Rao, Michael D Norenberg

Research output: Contribution to journalArticle

39 Citations (Scopus)

Abstract

Cytotoxic brain edema, due principally to astrocyte swelling, is a major neurological complication of the acute form of hepatic encephalopathy (HE) (acute liver failure, ALF), a condition likely caused by elevated levels of brain ammonia. Potential mediators of ammonia-induced astrocyte swelling include oxidative/nitrosative stress (ONS), the mitochondrial permeability transition (mPT), mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-κB), since blockade of these factors reduces the extent of astrocyte swelling. As p53, a tumor suppressor protein and transcription factor, is a downstream target of ONS and MAPKs, we examined its potential role in the mechanism of ammonia-induced astrocyte swelling. Astrocytes exposed to NH4Cl (5 mM) showed increased phosphorylation (activation) of p53(Ser392) at 1 h and such phosphorylation was significantly reduced by inhibitors of MAPKs (ERK1/2, JNK and p38-MAPK), antioxidants (vitamin E, catalase, PBN, desferoxamine, MnTBAP), as well as by L-NAME, an inhibitor of nitric oxide synthase, indicating a key role of oxidative/nitrosative stress and MAPKs in the ammonia-induced activation of p53. Since p53 is known to induce the mPT and to activate NF-κB (factors leading to ONS and implicated in ammonia-induced astrocyte swelling), we examined whether inhibition of p53 activation blocked mPT induction, NF-κB activation, as well as cell swelling. Pifithrin-α (PFT), an inhibitor of p53, blocked these processes. Impairment of astrocytic glutamate uptake is another important feature of HE and hyperammonemia. We therefore examined the potential role of p53 in the ammonia-induced inhibition of glutamate uptake and found that PFT also reversed the ammonia-induced inhibition of glutamate uptake. Our results indicate that a potentially important downstream target of ammonia neurotoxicity is p53, whose activation contributes to astrocyte swelling and glutamate uptake inhibition, processes likely a consequence of ONS derived from the mPT and activation of NF-κB.

Original languageEnglish
Pages (from-to)98-105
Number of pages8
JournalNeurochemistry International
Volume55
Issue number1-3
DOIs
StatePublished - Mar 6 2009

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Ammonia
Astrocytes
Glutamic Acid
Oxidative Stress
Permeability
Mitogen-Activated Protein Kinases
Hepatic Encephalopathy
p38 Mitogen-Activated Protein Kinases
Phosphorylation
Hyperammonemia
Tumor Suppressor Protein p53
Acute Liver Failure
JNK Mitogen-Activated Protein Kinases
Mitogen-Activated Protein Kinase 1
NG-Nitroarginine Methyl Ester
Brain Edema
Vitamin E
Nitric Oxide Synthase
Catalase
Transcription Factors

Keywords

  • Ammonia toxicity
  • Astrocytes
  • Cell swelling
  • Glutamate transport
  • Hepatic encephalopathy
  • MAP kinase
  • Mitochondrial permeability transition
  • NF-κB
  • Oxidative stress
  • p53

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience
  • Cell Biology

Cite this

Ammonia-induced activation of p53 in cultured astrocytes : Role in cell swelling and glutamate uptake. / Panickar, K. S.; Jayakumar, A. R.; Rao, K. V Rama; Norenberg, Michael D.

In: Neurochemistry International, Vol. 55, No. 1-3, 06.03.2009, p. 98-105.

Research output: Contribution to journalArticle

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AB - Cytotoxic brain edema, due principally to astrocyte swelling, is a major neurological complication of the acute form of hepatic encephalopathy (HE) (acute liver failure, ALF), a condition likely caused by elevated levels of brain ammonia. Potential mediators of ammonia-induced astrocyte swelling include oxidative/nitrosative stress (ONS), the mitochondrial permeability transition (mPT), mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-κB), since blockade of these factors reduces the extent of astrocyte swelling. As p53, a tumor suppressor protein and transcription factor, is a downstream target of ONS and MAPKs, we examined its potential role in the mechanism of ammonia-induced astrocyte swelling. Astrocytes exposed to NH4Cl (5 mM) showed increased phosphorylation (activation) of p53(Ser392) at 1 h and such phosphorylation was significantly reduced by inhibitors of MAPKs (ERK1/2, JNK and p38-MAPK), antioxidants (vitamin E, catalase, PBN, desferoxamine, MnTBAP), as well as by L-NAME, an inhibitor of nitric oxide synthase, indicating a key role of oxidative/nitrosative stress and MAPKs in the ammonia-induced activation of p53. Since p53 is known to induce the mPT and to activate NF-κB (factors leading to ONS and implicated in ammonia-induced astrocyte swelling), we examined whether inhibition of p53 activation blocked mPT induction, NF-κB activation, as well as cell swelling. Pifithrin-α (PFT), an inhibitor of p53, blocked these processes. Impairment of astrocytic glutamate uptake is another important feature of HE and hyperammonemia. We therefore examined the potential role of p53 in the ammonia-induced inhibition of glutamate uptake and found that PFT also reversed the ammonia-induced inhibition of glutamate uptake. Our results indicate that a potentially important downstream target of ammonia neurotoxicity is p53, whose activation contributes to astrocyte swelling and glutamate uptake inhibition, processes likely a consequence of ONS derived from the mPT and activation of NF-κB.

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