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Molecular characterization of insulin-mediated suppression of hepatic glucose production in vivo.

Ramnanan CJ, Edgerton DS, Rivera N, Irimia-Dominguez J, Farmer B, Neal DW, Lautz M, Donahue EP, Meyer CM, Roach PJ, Cherrington AD - Diabetes (2010)

Bottom Line: Insulin-mediated suppression of hepatic glucose production (HGP) is associated with sensitive intracellular signaling and molecular inhibition of gluconeogenic (GNG) enzyme mRNA expression.Net GNG flux was restored to basal by 4 h, despite a substantial reduction in PEPCK protein, as gluconeogenically-derived carbon was redirected from lactate efflux to glycogen deposition.In response to acute physiologic hyperinsulinemia, 1) HGP is suppressed primarily through modulation of glycogen metabolism; 2) a transient reduction in net GNG flux occurs and is explained by increased glycolysis resulting from increased F2,6P(2) and decreased fat oxidation; and 3) net GNG flux is not ultimately inhibited by the rise in insulin, despite eventual reduction in PEPCK protein, supporting the concept that PEPCK has poor control strength over the gluconeogenic pathway in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA. chris.ramnanan@vanderbilt.edu

ABSTRACT

Objective: Insulin-mediated suppression of hepatic glucose production (HGP) is associated with sensitive intracellular signaling and molecular inhibition of gluconeogenic (GNG) enzyme mRNA expression. We determined, for the first time, the time course and relevance (to metabolic flux) of these molecular events during physiological hyperinsulinemia in vivo in a large animal model.

Research design and methods: 24 h fasted dogs were infused with somatostatin, while insulin (basal or 8 x basal) and glucagon (basal) were replaced intraportally. Euglycemia was maintained and glucose metabolism was assessed using tracer, (2)H(2)O, and arterio-venous difference techniques. Studies were terminated at different time points to evaluate insulin signaling and enzyme regulation in the liver.

Results: Hyperinsulinemia reduced HGP due to a rapid transition from net glycogen breakdown to synthesis, which was associated with an increase in glycogen synthase and a decrease in glycogen phosphorylase activity. Thirty minutes of hyperinsulinemia resulted in an increase in phospho-FOXO1, a decrease in GNG enzyme mRNA expression, an increase in F2,6P(2), a decrease in fat oxidation, and a transient decrease in net GNG flux. Net GNG flux was restored to basal by 4 h, despite a substantial reduction in PEPCK protein, as gluconeogenically-derived carbon was redirected from lactate efflux to glycogen deposition.

Conclusions: In response to acute physiologic hyperinsulinemia, 1) HGP is suppressed primarily through modulation of glycogen metabolism; 2) a transient reduction in net GNG flux occurs and is explained by increased glycolysis resulting from increased F2,6P(2) and decreased fat oxidation; and 3) net GNG flux is not ultimately inhibited by the rise in insulin, despite eventual reduction in PEPCK protein, supporting the concept that PEPCK has poor control strength over the gluconeogenic pathway in vivo.

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Molecular regulation of glycogen metabolism in 24 h fasted conscious dogs after either CTR or 8X INS treatments. A: Akt and GSK3β phosphorylation, expressed relative to total Akt and GSK3β protein content, respectively. B: Phosphorylation of glycogen synthase, expressed relative to total glycogen synthase. C: Glycogen synthase activity ratio (independent versus total, measured using 0.1 vs. 10 mmol/l G6P, respectively). D: Glycogen phosphorylase activity ratio (independent versus total, measured in the absence versus presence [3 mmol/l] of AMP, respectively). Histograms depict mean values ± SEM. *Significantly different from the value for control (CTR), P < 0.05. 8X INS, 8× insulin.
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Figure 6: Molecular regulation of glycogen metabolism in 24 h fasted conscious dogs after either CTR or 8X INS treatments. A: Akt and GSK3β phosphorylation, expressed relative to total Akt and GSK3β protein content, respectively. B: Phosphorylation of glycogen synthase, expressed relative to total glycogen synthase. C: Glycogen synthase activity ratio (independent versus total, measured using 0.1 vs. 10 mmol/l G6P, respectively). D: Glycogen phosphorylase activity ratio (independent versus total, measured in the absence versus presence [3 mmol/l] of AMP, respectively). Histograms depict mean values ± SEM. *Significantly different from the value for control (CTR), P < 0.05. 8X INS, 8× insulin.

Mentions: The time course of intracellular insulin-regulated events was assessed in hepatic biopsies obtained from the hyperinsulinemic group and expressed relative to the data obtained from control animals. In response to hyperinsulinemia, Akt and GSK-3β phosphorylation increased approximately twofold and approximately threefold at 30 and 60 min, respectively, relative to the control group (Fig. 6A). The level of phosphorylated glycogen synthase tended to decrease (∼20%, NS) by 60 min and was maximally reduced (45%) for the last 120 min of the study (Fig. 6B). The glycogen synthase activity ratio was elevated twofold from 30 min on (Fig. 6C), whereas the glycogen phosphorylase activity ratio was decreased 40% (Fig. 6D).


Molecular characterization of insulin-mediated suppression of hepatic glucose production in vivo.

Ramnanan CJ, Edgerton DS, Rivera N, Irimia-Dominguez J, Farmer B, Neal DW, Lautz M, Donahue EP, Meyer CM, Roach PJ, Cherrington AD - Diabetes (2010)

Molecular regulation of glycogen metabolism in 24 h fasted conscious dogs after either CTR or 8X INS treatments. A: Akt and GSK3β phosphorylation, expressed relative to total Akt and GSK3β protein content, respectively. B: Phosphorylation of glycogen synthase, expressed relative to total glycogen synthase. C: Glycogen synthase activity ratio (independent versus total, measured using 0.1 vs. 10 mmol/l G6P, respectively). D: Glycogen phosphorylase activity ratio (independent versus total, measured in the absence versus presence [3 mmol/l] of AMP, respectively). Histograms depict mean values ± SEM. *Significantly different from the value for control (CTR), P < 0.05. 8X INS, 8× insulin.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2874690&req=5

Figure 6: Molecular regulation of glycogen metabolism in 24 h fasted conscious dogs after either CTR or 8X INS treatments. A: Akt and GSK3β phosphorylation, expressed relative to total Akt and GSK3β protein content, respectively. B: Phosphorylation of glycogen synthase, expressed relative to total glycogen synthase. C: Glycogen synthase activity ratio (independent versus total, measured using 0.1 vs. 10 mmol/l G6P, respectively). D: Glycogen phosphorylase activity ratio (independent versus total, measured in the absence versus presence [3 mmol/l] of AMP, respectively). Histograms depict mean values ± SEM. *Significantly different from the value for control (CTR), P < 0.05. 8X INS, 8× insulin.
Mentions: The time course of intracellular insulin-regulated events was assessed in hepatic biopsies obtained from the hyperinsulinemic group and expressed relative to the data obtained from control animals. In response to hyperinsulinemia, Akt and GSK-3β phosphorylation increased approximately twofold and approximately threefold at 30 and 60 min, respectively, relative to the control group (Fig. 6A). The level of phosphorylated glycogen synthase tended to decrease (∼20%, NS) by 60 min and was maximally reduced (45%) for the last 120 min of the study (Fig. 6B). The glycogen synthase activity ratio was elevated twofold from 30 min on (Fig. 6C), whereas the glycogen phosphorylase activity ratio was decreased 40% (Fig. 6D).

Bottom Line: Insulin-mediated suppression of hepatic glucose production (HGP) is associated with sensitive intracellular signaling and molecular inhibition of gluconeogenic (GNG) enzyme mRNA expression.Net GNG flux was restored to basal by 4 h, despite a substantial reduction in PEPCK protein, as gluconeogenically-derived carbon was redirected from lactate efflux to glycogen deposition.In response to acute physiologic hyperinsulinemia, 1) HGP is suppressed primarily through modulation of glycogen metabolism; 2) a transient reduction in net GNG flux occurs and is explained by increased glycolysis resulting from increased F2,6P(2) and decreased fat oxidation; and 3) net GNG flux is not ultimately inhibited by the rise in insulin, despite eventual reduction in PEPCK protein, supporting the concept that PEPCK has poor control strength over the gluconeogenic pathway in vivo.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA. chris.ramnanan@vanderbilt.edu

ABSTRACT

Objective: Insulin-mediated suppression of hepatic glucose production (HGP) is associated with sensitive intracellular signaling and molecular inhibition of gluconeogenic (GNG) enzyme mRNA expression. We determined, for the first time, the time course and relevance (to metabolic flux) of these molecular events during physiological hyperinsulinemia in vivo in a large animal model.

Research design and methods: 24 h fasted dogs were infused with somatostatin, while insulin (basal or 8 x basal) and glucagon (basal) were replaced intraportally. Euglycemia was maintained and glucose metabolism was assessed using tracer, (2)H(2)O, and arterio-venous difference techniques. Studies were terminated at different time points to evaluate insulin signaling and enzyme regulation in the liver.

Results: Hyperinsulinemia reduced HGP due to a rapid transition from net glycogen breakdown to synthesis, which was associated with an increase in glycogen synthase and a decrease in glycogen phosphorylase activity. Thirty minutes of hyperinsulinemia resulted in an increase in phospho-FOXO1, a decrease in GNG enzyme mRNA expression, an increase in F2,6P(2), a decrease in fat oxidation, and a transient decrease in net GNG flux. Net GNG flux was restored to basal by 4 h, despite a substantial reduction in PEPCK protein, as gluconeogenically-derived carbon was redirected from lactate efflux to glycogen deposition.

Conclusions: In response to acute physiologic hyperinsulinemia, 1) HGP is suppressed primarily through modulation of glycogen metabolism; 2) a transient reduction in net GNG flux occurs and is explained by increased glycolysis resulting from increased F2,6P(2) and decreased fat oxidation; and 3) net GNG flux is not ultimately inhibited by the rise in insulin, despite eventual reduction in PEPCK protein, supporting the concept that PEPCK has poor control strength over the gluconeogenic pathway in vivo.

Show MeSH
Related in: MedlinePlus