Abstract
Hepatic encephalopathy (HE) is a major neurological complication in patients with severe liver failure. Elevated levels of ammonia have been strongly implicated as a factor in HE, and astrocytes appear to be the primary target of its neurotoxicity. Mechanisms mediating key aspects of ammonia-induced astrocyte dysfunction such as cell swelling and inhibition of glutamate uptake are not clear. We demonstrated previously that cultured astrocytes exposed to ammonia increase free radical production. We now show that treatment with antioxidants significantly prevents ammonia-induced astrocyte swelling as well as glutamate uptake inhibition. Because one consequence of oxidative stress is the phosphorylation of mitogen-activated protein kinases (MAPKs), we investigated whether phosphorylation of MAPKs may mediate astrocyte dysfunction. Primary cultured astrocytes exposed to 5 mM NH4Cl for different time periods (1-72 h) significantly increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38MAPK, and c-Jun N-terminal kinase (JNK) 1/2/3, which was inhibited by appropriate MAPK inhibitors 1, 4-diamino-2, 3-dicyano-1, 4-bis (2-aminophenylthio) butadiene (UO126; for ERK1/2), trans-1-(4-hydroxyclyclohexyl)-4-(4-fluorophenyl)-5-(2- methoxypyrimidin-4-yl)imidazole (SB 239063; for p38MAPK), and anthra[1,9-cd]pyrazol-6(2H)-one (SP600125; for JNK1/2/3), as well as by antioxidants. Kinase inhibitors partially or completely prevented astrocyte swelling. Although SB239063 and SP600125 significantly reversed glutamate uptake inhibition and ammonia-induced decline in glutamate-aspartate transporter protein levels, UO126 did not, indicating a differential effect of these kinases in ammonia-induced astrocyte swelling and glutamate transport impairment. These studies strongly suggest the involvement of oxidative stress and phosphorylation of MAPKs in the mechanism of ammonia-induced astrocyte dysfunction associated with ammonia neurotoxicity.
| Original language | English |
|---|---|
| Pages (from-to) | 4774-4784 |
| Number of pages | 11 |
| Journal | Journal of Neuroscience |
| Volume | 26 |
| Issue number | 18 |
| DOIs | |
| State | Published - Sep 7 2006 |
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Keywords
- Ammonia
- Astrocyte swelling
- Glutamate uptake
- Hepatic encephalopathy
- MAP kinases
- Oxidative stress
ASJC Scopus subject areas
- Neuroscience(all)
Cite this
Oxidative stress and mitogen-activated protein kinase phosphorylation mediate ammonia-induced cell swelling and glutamate uptake inhibition in cultured astrocytes. / Jayakumar, A. R.; Panickar, K. S.; Murthy, Ch R K; Norenberg, Michael D.
In: Journal of Neuroscience, Vol. 26, No. 18, 07.09.2006, p. 4774-4784.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Oxidative stress and mitogen-activated protein kinase phosphorylation mediate ammonia-induced cell swelling and glutamate uptake inhibition in cultured astrocytes
AU - Jayakumar, A. R.
AU - Panickar, K. S.
AU - Murthy, Ch R K
AU - Norenberg, Michael D
PY - 2006/9/7
Y1 - 2006/9/7
N2 - Hepatic encephalopathy (HE) is a major neurological complication in patients with severe liver failure. Elevated levels of ammonia have been strongly implicated as a factor in HE, and astrocytes appear to be the primary target of its neurotoxicity. Mechanisms mediating key aspects of ammonia-induced astrocyte dysfunction such as cell swelling and inhibition of glutamate uptake are not clear. We demonstrated previously that cultured astrocytes exposed to ammonia increase free radical production. We now show that treatment with antioxidants significantly prevents ammonia-induced astrocyte swelling as well as glutamate uptake inhibition. Because one consequence of oxidative stress is the phosphorylation of mitogen-activated protein kinases (MAPKs), we investigated whether phosphorylation of MAPKs may mediate astrocyte dysfunction. Primary cultured astrocytes exposed to 5 mM NH4Cl for different time periods (1-72 h) significantly increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38MAPK, and c-Jun N-terminal kinase (JNK) 1/2/3, which was inhibited by appropriate MAPK inhibitors 1, 4-diamino-2, 3-dicyano-1, 4-bis (2-aminophenylthio) butadiene (UO126; for ERK1/2), trans-1-(4-hydroxyclyclohexyl)-4-(4-fluorophenyl)-5-(2- methoxypyrimidin-4-yl)imidazole (SB 239063; for p38MAPK), and anthra[1,9-cd]pyrazol-6(2H)-one (SP600125; for JNK1/2/3), as well as by antioxidants. Kinase inhibitors partially or completely prevented astrocyte swelling. Although SB239063 and SP600125 significantly reversed glutamate uptake inhibition and ammonia-induced decline in glutamate-aspartate transporter protein levels, UO126 did not, indicating a differential effect of these kinases in ammonia-induced astrocyte swelling and glutamate transport impairment. These studies strongly suggest the involvement of oxidative stress and phosphorylation of MAPKs in the mechanism of ammonia-induced astrocyte dysfunction associated with ammonia neurotoxicity.
AB - Hepatic encephalopathy (HE) is a major neurological complication in patients with severe liver failure. Elevated levels of ammonia have been strongly implicated as a factor in HE, and astrocytes appear to be the primary target of its neurotoxicity. Mechanisms mediating key aspects of ammonia-induced astrocyte dysfunction such as cell swelling and inhibition of glutamate uptake are not clear. We demonstrated previously that cultured astrocytes exposed to ammonia increase free radical production. We now show that treatment with antioxidants significantly prevents ammonia-induced astrocyte swelling as well as glutamate uptake inhibition. Because one consequence of oxidative stress is the phosphorylation of mitogen-activated protein kinases (MAPKs), we investigated whether phosphorylation of MAPKs may mediate astrocyte dysfunction. Primary cultured astrocytes exposed to 5 mM NH4Cl for different time periods (1-72 h) significantly increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), p38MAPK, and c-Jun N-terminal kinase (JNK) 1/2/3, which was inhibited by appropriate MAPK inhibitors 1, 4-diamino-2, 3-dicyano-1, 4-bis (2-aminophenylthio) butadiene (UO126; for ERK1/2), trans-1-(4-hydroxyclyclohexyl)-4-(4-fluorophenyl)-5-(2- methoxypyrimidin-4-yl)imidazole (SB 239063; for p38MAPK), and anthra[1,9-cd]pyrazol-6(2H)-one (SP600125; for JNK1/2/3), as well as by antioxidants. Kinase inhibitors partially or completely prevented astrocyte swelling. Although SB239063 and SP600125 significantly reversed glutamate uptake inhibition and ammonia-induced decline in glutamate-aspartate transporter protein levels, UO126 did not, indicating a differential effect of these kinases in ammonia-induced astrocyte swelling and glutamate transport impairment. These studies strongly suggest the involvement of oxidative stress and phosphorylation of MAPKs in the mechanism of ammonia-induced astrocyte dysfunction associated with ammonia neurotoxicity.
KW - Ammonia
KW - Astrocyte swelling
KW - Glutamate uptake
KW - Hepatic encephalopathy
KW - MAP kinases
KW - Oxidative stress
UR - http://www.scopus.com/inward/record.url?scp=33646949200&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33646949200&partnerID=8YFLogxK
U2 - 10.1523/JNEUROSCI.0120-06.2006
DO - 10.1523/JNEUROSCI.0120-06.2006
M3 - Article
C2 - 16672650
AN - SCOPUS:33646949200
VL - 26
SP - 4774
EP - 4784
JO - Journal of Neuroscience
JF - Journal of Neuroscience
SN - 0270-6474
IS - 18
ER -