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Inactivation of NF- κ B p65 (RelA) in Liver Improves Insulin Sensitivity and Inhibits cAMP/PKA Pathway

View Article: PubMed Central - PubMed

ABSTRACT

The transcription factor nuclear factor-κB (NF-κB) mediates inflammation and stress signals in cells. To test NF-κB in the control of hepatic insulin sensitivity, we inactivated NF-κB in the livers of C57BL/6 mice through deletion of the p65 gene, which was achieved by crossing floxed-p65 and Alb-cre mice to generate L-p65-knockout (KO) mice. KO mice did not exhibit any alterations in growth, reproduction, and body weight while on a chow diet. However, the mice on a high-fat diet (HFD) exhibited an improvement in systemic insulin sensitivity. Hepatic insulin sensitivity was enhanced as indicated by increased pyruvate tolerance, Akt phosphorylation, and decreased gene expression in hepatic gluconeogenesis. In the liver, a decrease in intracellular cAMP was observed with decreased CREB phosphorylation. Cyclic nucleotide phosphodiesterase-3B (PDE3B), a cAMP-degrading enzyme, was increased in mRNA and protein as a result of the absence of NF-κB activity. NF-κB was found to inhibit PDE3B transcription through three DNA-binding sites in the gene promoter in response to tumor necrosis factor-α. Body composition, food intake, energy expenditure, and systemic and hepatic inflammation were not significantly altered in KO mice on HFD. These data suggest that NF-κB inhibits hepatic insulin sensitivity by upregulating cAMP through suppression of PDE3B gene transcription.

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Reduced cAMP content and signaling in liver of L-p65-KO mice. Livers were collected from mice on HFD for 16 weeks. A: pCREB. The phosphorylation was determined through Western blotting. B: cAMP levels in liver tissue. C: PDE3B protein in liver tissue. D: PDE3B mRNA expression in liver of HFD-fed mice (n = 5). Data are mean ± SEM. **P < 0.01.
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Figure 4: Reduced cAMP content and signaling in liver of L-p65-KO mice. Livers were collected from mice on HFD for 16 weeks. A: pCREB. The phosphorylation was determined through Western blotting. B: cAMP levels in liver tissue. C: PDE3B protein in liver tissue. D: PDE3B mRNA expression in liver of HFD-fed mice (n = 5). Data are mean ± SEM. **P < 0.01.

Mentions: Insulin action is antagonized by effects of glucagon in the control of hepatic gluconeogenesis. Glucagon activity depends on activation of the cAMP/PKA pathway. In the cAMP/PKA pathway, cAMP elevation leads to activation of serine kinase PKA, which phosphorylates the transcription factor CREB on S133. After phosphorylation, CREB promotes gluconeogenesis through the induction of PEPCK and G6pase transcription. CREB phosphorylation was examined in the livers of mice after overnight fasting. The phosphorylation signal was significantly reduced in KO liver (Fig. 4A), and this reduction was associated with a decrease in intracellular cAMP (Fig. 4B) and an increase in PDE3B expression (Fig. 4C and D). PDE3B is an intracellular enzyme that decreases cAMP levels in hepatocytes through catalyzing cAMP hydrolysis. Because cAMP concentrations are determined by relative rates of synthesis and degradation in cells, the increased expression of PDE3B is most likely responsible for the decreased cAMP content and cAMP/PKA signaling in liver tissue of KO mice.


Inactivation of NF- κ B p65 (RelA) in Liver Improves Insulin Sensitivity and Inhibits cAMP/PKA Pathway
Reduced cAMP content and signaling in liver of L-p65-KO mice. Livers were collected from mice on HFD for 16 weeks. A: pCREB. The phosphorylation was determined through Western blotting. B: cAMP levels in liver tissue. C: PDE3B protein in liver tissue. D: PDE3B mRNA expression in liver of HFD-fed mice (n = 5). Data are mean ± SEM. **P < 0.01.
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Related In: Results  -  Collection

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Figure 4: Reduced cAMP content and signaling in liver of L-p65-KO mice. Livers were collected from mice on HFD for 16 weeks. A: pCREB. The phosphorylation was determined through Western blotting. B: cAMP levels in liver tissue. C: PDE3B protein in liver tissue. D: PDE3B mRNA expression in liver of HFD-fed mice (n = 5). Data are mean ± SEM. **P < 0.01.
Mentions: Insulin action is antagonized by effects of glucagon in the control of hepatic gluconeogenesis. Glucagon activity depends on activation of the cAMP/PKA pathway. In the cAMP/PKA pathway, cAMP elevation leads to activation of serine kinase PKA, which phosphorylates the transcription factor CREB on S133. After phosphorylation, CREB promotes gluconeogenesis through the induction of PEPCK and G6pase transcription. CREB phosphorylation was examined in the livers of mice after overnight fasting. The phosphorylation signal was significantly reduced in KO liver (Fig. 4A), and this reduction was associated with a decrease in intracellular cAMP (Fig. 4B) and an increase in PDE3B expression (Fig. 4C and D). PDE3B is an intracellular enzyme that decreases cAMP levels in hepatocytes through catalyzing cAMP hydrolysis. Because cAMP concentrations are determined by relative rates of synthesis and degradation in cells, the increased expression of PDE3B is most likely responsible for the decreased cAMP content and cAMP/PKA signaling in liver tissue of KO mice.

View Article: PubMed Central - PubMed

ABSTRACT

The transcription factor nuclear factor-&kappa;B (NF-&kappa;B) mediates inflammation and stress signals in cells. To test NF-&kappa;B in the control of hepatic insulin sensitivity, we inactivated NF-&kappa;B in the livers of C57BL/6 mice through deletion of the p65 gene, which was achieved by crossing floxed-p65 and Alb-cre mice to generate L-p65-knockout (KO) mice. KO mice did not exhibit any alterations in growth, reproduction, and body weight while on a chow diet. However, the mice on a high-fat diet (HFD) exhibited an improvement in systemic insulin sensitivity. Hepatic insulin sensitivity was enhanced as indicated by increased pyruvate tolerance, Akt phosphorylation, and decreased gene expression in hepatic gluconeogenesis. In the liver, a decrease in intracellular cAMP was observed with decreased CREB phosphorylation. Cyclic nucleotide phosphodiesterase-3B (PDE3B), a cAMP-degrading enzyme, was increased in mRNA and protein as a result of the absence of NF-&kappa;B activity. NF-&kappa;B was found to inhibit PDE3B transcription through three DNA-binding sites in the gene promoter in response to tumor necrosis factor-&alpha;. Body composition, food intake, energy expenditure, and systemic and hepatic inflammation were not significantly altered in KO mice on HFD. These data suggest that NF-&kappa;B inhibits hepatic insulin sensitivity by upregulating cAMP through suppression of PDE3B gene transcription.

No MeSH data available.


Related in: MedlinePlus