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Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice.

ABSTRACT: Endotoxemia correlates with the degree of liver failure and may participate in worsening of liver diseases. Lipopolysaccharide (LPS; synonymous with endotoxin) treatment in mice lowered the hepatic glutathione (GSH) level, which in turn is a variable that determines susceptibility to LPS-induced injury. We previously showed that LPS treatment in mice lowered hepatic expression of the rate-limiting enzyme in GSH synthesis, glutamate-cysteine ligase (GCL). The aim of our current work was to determine the molecular mechanism(s) responsible for these changes. Studies were done using RAW cells (murine macrophages), in vivo LPS-treated mice, and mouse hepatocytes. We found that LPS treatment lowered GCL catalytic and modifier (Gclc and Gclm) subunit expression at the transcriptional level, which was unrelated to alterations in nitric oxide production or induction of NF-?B/p65 subunit. The key mechanism was a decrease in sumoylation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and MafG, which is required for their heterodimerization and subsequent binding and trans-activation of the antioxidant-response element (ARE) present in the promoter region of these genes that is essential for their expression. LPS treatment lowered markedly the expression of ubiquitin-conjugating enzyme 9 (Ubc9), which is required for sumoylation. Similar findings also occurred in liver after in vivo LPS treatment and in LPS-treated mouse hepatocytes. Overexpression of Ubc9 protected against LPS-mediated inhibition of Gclc and Gclm expression in RAW cells and hepatocytes. In conclusion, LPS-mediated lowering of GCL expression in hepatocytes and macrophages is due to lowering of sumoylation of Nrf2 and MafG, leading to reduced heterodimerization, binding, and trans-activation of ARE.

SUBMITTER: Tomasi ML

PROVIDER: S-EPMC3943979 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice.

Tomasi Maria Lauda ML Ryoo Minjung M Yang Heping H Iglesias Ara Ainhoa A Ko Kwang Suk KS Lu Shelly C SC

Free radical biology & medicine 20131201

Endotoxemia correlates with the degree of liver failure and may participate in worsening of liver diseases. Lipopolysaccharide (LPS; synonymous with endotoxin) treatment in mice lowered the hepatic glutathione (GSH) level, which in turn is a variable that determines susceptibility to LPS-induced injury. We previously showed that LPS treatment in mice lowered hepatic expression of the rate-limiting enzyme in GSH synthesis, glutamate-cysteine ligase (GCL). The aim of our current work was to determ ...[more]

PMID: 24296246

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Project description:Sensorimotor gating refers to the ability to filter incoming sensory information in a stimulus-laden environment and disruption of this physiological process has been documented in psychiatric disorders characterized by cognitive aberrations. The effectiveness of current pharmacotherapies for treatment of sensorimotor gating deficits in the patient population still remains controversial. These challenges emphasize the need to better understand the biological underpinnings of sensorimotor gating which could lead to discovery of novel drug targets for therapeutic intervention. Notably, we recently reported a role for purinergic P2X4 receptors (P2X4Rs) in regulation of sensorimotor gating using prepulse inhibition (PPI) of acoustic startle reflex. P2X4Rs are ion channels gated by adenosine-5'-triphosphate (ATP). Ivermectin (IVM) induced PPI deficits in C57BL/6J mice in a P2X4R-specific manner. Furthermore, mice deficient in P2X4Rs [P2X4R knockout (KO)] exhibited PPI deficits that were alleviated by dopamine (DA) receptor antagonists demonstrating an interaction between P2X4Rs and DA receptors in PPI regulation. On the basis of these findings, we hypothesized that increased DA neurotransmission underlies IVM-mediated PPI deficits. To test this hypothesis, we measured the effects of D1 and D2 receptor antagonists, SCH 23390 and raclopride respectively and D1 agonist, SKF 82958 on IVM-mediated PPI deficits. To gain mechanistic insights, we investigated the interaction between IVM and dopaminergic drugs on signaling molecules linked to PPI regulation in the ventral striatum. SCH 23390 significantly attenuated the PPI disruptive effects of IVM to a much greater degree than that of raclopride. SKF 82958 failed to potentiate IVM-mediated PPI disruption. At the molecular level, modulation of D1 receptors altered IVM's effects on dopamine and cyclic-AMP regulated phosphoprotein of 32 kDa (DARPP-32) phosphorylation. Additionally, IVM interacted with the DA receptors antagonists and SKF 82958 in phosphorylation of Ca2+/calmodulin kinase II? (CaMKII?) and its downstream target, neuronal nitric oxide synthase (nNOS). Current findings suggest an involvement for D1 and D2 receptors in IVM-mediated PPI disruption via modulation of DARPP-32, CaMKII? and nNOS. Taken together, the findings suggest that stimulation of P2X4Rs can lead to DA hyperactivity and disruption of information processing, implicating P2X4Rs as a novel drug target for treatment of psychiatric disorders characterized by sensorimotor gating deficits.

Dataset Information

Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice.

Publications

Molecular mechanisms of lipopolysaccharide-mediated inhibition of glutathione synthesis in mice.

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