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Unconjugated bilirubin exposure impairs hippocampal long-term synaptic plasticity.

Chang FY, Lee CC, Huang CC, Hsu KS - PLoS ONE (2009)

Bottom Line: UCB treatment produced a significant decrease in the levels of NR1, NR2A and NR2B subunits of N-methyl-D-aspartate (NMDA) receptors through a calpain-mediated proteolytic cleavage mechanism.Pretreatment of the hippocampal slice cultures with NMDA receptor antagonist or calpain inhibitors effectively prevented the UCB-induced impairment of LTP and LTD.Our results indicate that the proteolytic cleavage of NMDA receptor subunits by calpain may play a critical role in mediating the UCB-induced impairment of long-term synaptic plasticity in the hippocampus.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.

ABSTRACT

Background: Jaundice is one of the most common problems encountered in newborn infants, due to immaturity of hepatic conjugation and transport processes for bilirubin. Although the majority of neonatal jaundice is benign, some neonates with severe hyperbilirubinemia develop bilirubin encephalopathy or kernicterus. Accumulation of unconjugated bilirubin (UCB) in selected brain regions may result in temporary or permanent impairments of auditory, motor, or cognitive function; however, the molecular mechanisms by which UCB elicits such neurotoxicity are still poorly understood. The present study is undertaken to investigate whether prolonged exposure of rat organotypic hippocampal slice cultures to UCB alters the induction of long-term synaptic plasticity.

Methodology/principal findings: Using electrophysiological recording techniques, we find that exposure of hippocampal slice cultures to clinically relevant concentrations of UCB for 24 or 48 h results in an impairment of CA1 long-term potentiation (LTP) and long-term depression (LTD) induction in a time- and concentration-dependent manner. Hippocampal slice cultures stimulated with UCB show no changes in the secretion profiles of the pro-inflammatory cytokines, interleukin-1beta and tumor necrosis factor-alpha, or the propidium ioide uptake. UCB treatment produced a significant decrease in the levels of NR1, NR2A and NR2B subunits of N-methyl-D-aspartate (NMDA) receptors through a calpain-mediated proteolytic cleavage mechanism. Pretreatment of the hippocampal slice cultures with NMDA receptor antagonist or calpain inhibitors effectively prevented the UCB-induced impairment of LTP and LTD.

Conclusion/significance: Our results indicate that the proteolytic cleavage of NMDA receptor subunits by calpain may play a critical role in mediating the UCB-induced impairment of long-term synaptic plasticity in the hippocampus. These observations provide new insights into the molecular mechanisms underlying UCB-induced impairment of hippocampal synaptic plasticity which, in turn, might provide opportunities for the development of novel therapeutic strategies that targets these pathways for treatment.

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Related in: MedlinePlus

Prolonged UCB exposure decreases the protein levels of NMDA NR1, NR2A and NR2B subunits in rat organotypic slice cultures.(A) Representative immunoblots showing 10 µM UCB treatment for 48 h decreases NR1, NR2A and NR2B subunit expression in the hippocampal CA1 homogenate fractions. (B–D) Corresponding densitometric analysis showing the relative levels of NR1 (B), NR2A (C), and NR2B (D) subunits similar to those shown in (A). Number of experiments is indicated in the parenthesis. Error bars indicate SEM. *p<0.05 as compared with the control group by unpaired Student's t-test.
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pone-0005876-g004: Prolonged UCB exposure decreases the protein levels of NMDA NR1, NR2A and NR2B subunits in rat organotypic slice cultures.(A) Representative immunoblots showing 10 µM UCB treatment for 48 h decreases NR1, NR2A and NR2B subunit expression in the hippocampal CA1 homogenate fractions. (B–D) Corresponding densitometric analysis showing the relative levels of NR1 (B), NR2A (C), and NR2B (D) subunits similar to those shown in (A). Number of experiments is indicated in the parenthesis. Error bars indicate SEM. *p<0.05 as compared with the control group by unpaired Student's t-test.

Mentions: We next identified the possible mechanisms underlying the reduction of NMDA receptor-mediated synaptic transmission by prolonged UCB exposure. A decrease in the NMDA receptor-mediated synaptic transmission could reflect a decrease in the number of NMDA receptors. To test this possibility, we compared the protein expression levels of NMDA receptor subunits in the CA1 region of control and UCB- treated slices by Western blot analysis. Using antibodies that selectively label NR1, NR2A, or NR2B subunits, we found that the protein levels of NR1, NR2A, and NR2B subunits were significantly decreased by 10 µM UCB treatment for 24 or 48 h (Figure 4). However, no change in the levels of NR1, NR2A, and NR2B subunits was observed in slices treated with 1 µM UCB for 24 h. Level of β-actin was not altered significantly by UCB.


Unconjugated bilirubin exposure impairs hippocampal long-term synaptic plasticity.

Chang FY, Lee CC, Huang CC, Hsu KS - PLoS ONE (2009)

Prolonged UCB exposure decreases the protein levels of NMDA NR1, NR2A and NR2B subunits in rat organotypic slice cultures.(A) Representative immunoblots showing 10 µM UCB treatment for 48 h decreases NR1, NR2A and NR2B subunit expression in the hippocampal CA1 homogenate fractions. (B–D) Corresponding densitometric analysis showing the relative levels of NR1 (B), NR2A (C), and NR2B (D) subunits similar to those shown in (A). Number of experiments is indicated in the parenthesis. Error bars indicate SEM. *p<0.05 as compared with the control group by unpaired Student's t-test.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2690688&req=5

pone-0005876-g004: Prolonged UCB exposure decreases the protein levels of NMDA NR1, NR2A and NR2B subunits in rat organotypic slice cultures.(A) Representative immunoblots showing 10 µM UCB treatment for 48 h decreases NR1, NR2A and NR2B subunit expression in the hippocampal CA1 homogenate fractions. (B–D) Corresponding densitometric analysis showing the relative levels of NR1 (B), NR2A (C), and NR2B (D) subunits similar to those shown in (A). Number of experiments is indicated in the parenthesis. Error bars indicate SEM. *p<0.05 as compared with the control group by unpaired Student's t-test.
Mentions: We next identified the possible mechanisms underlying the reduction of NMDA receptor-mediated synaptic transmission by prolonged UCB exposure. A decrease in the NMDA receptor-mediated synaptic transmission could reflect a decrease in the number of NMDA receptors. To test this possibility, we compared the protein expression levels of NMDA receptor subunits in the CA1 region of control and UCB- treated slices by Western blot analysis. Using antibodies that selectively label NR1, NR2A, or NR2B subunits, we found that the protein levels of NR1, NR2A, and NR2B subunits were significantly decreased by 10 µM UCB treatment for 24 or 48 h (Figure 4). However, no change in the levels of NR1, NR2A, and NR2B subunits was observed in slices treated with 1 µM UCB for 24 h. Level of β-actin was not altered significantly by UCB.

Bottom Line: UCB treatment produced a significant decrease in the levels of NR1, NR2A and NR2B subunits of N-methyl-D-aspartate (NMDA) receptors through a calpain-mediated proteolytic cleavage mechanism.Pretreatment of the hippocampal slice cultures with NMDA receptor antagonist or calpain inhibitors effectively prevented the UCB-induced impairment of LTP and LTD.Our results indicate that the proteolytic cleavage of NMDA receptor subunits by calpain may play a critical role in mediating the UCB-induced impairment of long-term synaptic plasticity in the hippocampus.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, College of Medicine, National Cheng Kung University, Tainan, Taiwan.

ABSTRACT

Background: Jaundice is one of the most common problems encountered in newborn infants, due to immaturity of hepatic conjugation and transport processes for bilirubin. Although the majority of neonatal jaundice is benign, some neonates with severe hyperbilirubinemia develop bilirubin encephalopathy or kernicterus. Accumulation of unconjugated bilirubin (UCB) in selected brain regions may result in temporary or permanent impairments of auditory, motor, or cognitive function; however, the molecular mechanisms by which UCB elicits such neurotoxicity are still poorly understood. The present study is undertaken to investigate whether prolonged exposure of rat organotypic hippocampal slice cultures to UCB alters the induction of long-term synaptic plasticity.

Methodology/principal findings: Using electrophysiological recording techniques, we find that exposure of hippocampal slice cultures to clinically relevant concentrations of UCB for 24 or 48 h results in an impairment of CA1 long-term potentiation (LTP) and long-term depression (LTD) induction in a time- and concentration-dependent manner. Hippocampal slice cultures stimulated with UCB show no changes in the secretion profiles of the pro-inflammatory cytokines, interleukin-1beta and tumor necrosis factor-alpha, or the propidium ioide uptake. UCB treatment produced a significant decrease in the levels of NR1, NR2A and NR2B subunits of N-methyl-D-aspartate (NMDA) receptors through a calpain-mediated proteolytic cleavage mechanism. Pretreatment of the hippocampal slice cultures with NMDA receptor antagonist or calpain inhibitors effectively prevented the UCB-induced impairment of LTP and LTD.

Conclusion/significance: Our results indicate that the proteolytic cleavage of NMDA receptor subunits by calpain may play a critical role in mediating the UCB-induced impairment of long-term synaptic plasticity in the hippocampus. These observations provide new insights into the molecular mechanisms underlying UCB-induced impairment of hippocampal synaptic plasticity which, in turn, might provide opportunities for the development of novel therapeutic strategies that targets these pathways for treatment.

Show MeSH
Related in: MedlinePlus