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Alteration of de novo glucose production contributes to fasting hypoglycaemia in Fyn deficient mice.

Yang Y, Tarabra E, Yang GS, Vaitheesvaran B, Palacios G, Kurland IJ, Pessin JE, Bastie CC - PLoS ONE (2013)

Bottom Line: Impaired conversion of glycerol to glucose was observed in both glycerol tolerance test and determination of the conversion of (13)C-glycerol to glucose in the fasted state. α-glycerol phosphate levels were reduced but glycerol kinase protein expression levels were not changed.Fructose-bisphosphate aldolase (aldolase) mRNA or protein levels were normal in the Fyn-deficient livers, however, there was a large reduction in liver fructose-6-phosphate (30-fold) and fructose-1,6-bisphosphate (7-fold) levels as well as a reduction in glucose-6-phosphate (2-fold) levels.These data suggest a mechanistic defect in the allosteric regulation of aldolase activity.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Animal Fat Deposition and Muscle Development, College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, People's Republic of China ; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, United States of America.

ABSTRACT
Previous studies have demonstrated that glucose disposal is increased in the Fyn knockout (FynKO) mice due to increased insulin sensitivity. FynKO mice also display fasting hypoglycaemia despite decreased insulin levels, which suggested that hepatic glucose production was unable to compensate for the increased basal glucose utilization. The present study investigates the basis for the reduction in plasma glucose levels and the reduced ability for the liver to produce glucose in response to gluconeogenic substrates. FynKO mice had a 5-fold reduction in phosphoenolpyruvate carboxykinase (PEPCK) gene and protein expression and a marked reduction in pyruvate, pyruvate/lactate-stimulated glucose output. Remarkably, de novo glucose production was also blunted using gluconeogenic substrates that bypass the PEPCK step. Impaired conversion of glycerol to glucose was observed in both glycerol tolerance test and determination of the conversion of (13)C-glycerol to glucose in the fasted state. α-glycerol phosphate levels were reduced but glycerol kinase protein expression levels were not changed. Fructose-driven glucose production was also diminished without alteration of fructokinase expression levels. The normal levels of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate observed in the FynKO liver extracts suggested normal triose kinase function. Fructose-bisphosphate aldolase (aldolase) mRNA or protein levels were normal in the Fyn-deficient livers, however, there was a large reduction in liver fructose-6-phosphate (30-fold) and fructose-1,6-bisphosphate (7-fold) levels as well as a reduction in glucose-6-phosphate (2-fold) levels. These data suggest a mechanistic defect in the allosteric regulation of aldolase activity.

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Fructose-driven glucose production in 16-hour fasted wild type (WT) and FynKO mice (A) Fructose tolerance test in fasted wild type (WT, black circles) and FynKO (open circles) mice.*p<0.05. n= 5 WT, n=5 FynKO, experiments were repeated 4 times. (B) Hexose phosphate levels in liver of wild type (WT) and FynKO mice: glucose-6-phosphate (G-6-P), fructose-6-phosphate (F-6-P) and fructose-1,6- bisphosphate (F-1,6-P). *p<0.05, n=3 WT, n=3 FynKO. 
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pone-0081866-g005: Fructose-driven glucose production in 16-hour fasted wild type (WT) and FynKO mice (A) Fructose tolerance test in fasted wild type (WT, black circles) and FynKO (open circles) mice.*p<0.05. n= 5 WT, n=5 FynKO, experiments were repeated 4 times. (B) Hexose phosphate levels in liver of wild type (WT) and FynKO mice: glucose-6-phosphate (G-6-P), fructose-6-phosphate (F-6-P) and fructose-1,6- bisphosphate (F-1,6-P). *p<0.05, n=3 WT, n=3 FynKO. 

Mentions: Therefore, we next examined the ability of the liver to produce glucose using fructose as a gluconeogenic substrate. Similarly to the three-carbon substrates (i.e., pyruvate, lactate, glycerol), the FynKO mice were also refractory to glucose production from the six-carbon sugar fructose (Figure 5A), suggesting that fructose was not converted to glucose in the FynKO liver. Consistent with this hypothesis, metabolite analyses demonstrated an approximate 7-fold reduction in the levels of fructose-1,6-bisphosphate and a 30-fold reduction in fructose-6-phosphate levels, with a smaller reduction in glucose-6-phosphate in the liver of the FynKO mice compared to wild type mice (Figure 5B). Interestingly, despite the marked reduction in fructose-1,6-bisphosphate levels, we did not observe significant change in fructokinase gene expression (Figure 6A) or aldolase mRNA expression or aldolase protein levels (Figure 6B, C).


Alteration of de novo glucose production contributes to fasting hypoglycaemia in Fyn deficient mice.

Yang Y, Tarabra E, Yang GS, Vaitheesvaran B, Palacios G, Kurland IJ, Pessin JE, Bastie CC - PLoS ONE (2013)

Fructose-driven glucose production in 16-hour fasted wild type (WT) and FynKO mice (A) Fructose tolerance test in fasted wild type (WT, black circles) and FynKO (open circles) mice.*p<0.05. n= 5 WT, n=5 FynKO, experiments were repeated 4 times. (B) Hexose phosphate levels in liver of wild type (WT) and FynKO mice: glucose-6-phosphate (G-6-P), fructose-6-phosphate (F-6-P) and fructose-1,6- bisphosphate (F-1,6-P). *p<0.05, n=3 WT, n=3 FynKO. 
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3842980&req=5

pone-0081866-g005: Fructose-driven glucose production in 16-hour fasted wild type (WT) and FynKO mice (A) Fructose tolerance test in fasted wild type (WT, black circles) and FynKO (open circles) mice.*p<0.05. n= 5 WT, n=5 FynKO, experiments were repeated 4 times. (B) Hexose phosphate levels in liver of wild type (WT) and FynKO mice: glucose-6-phosphate (G-6-P), fructose-6-phosphate (F-6-P) and fructose-1,6- bisphosphate (F-1,6-P). *p<0.05, n=3 WT, n=3 FynKO. 
Mentions: Therefore, we next examined the ability of the liver to produce glucose using fructose as a gluconeogenic substrate. Similarly to the three-carbon substrates (i.e., pyruvate, lactate, glycerol), the FynKO mice were also refractory to glucose production from the six-carbon sugar fructose (Figure 5A), suggesting that fructose was not converted to glucose in the FynKO liver. Consistent with this hypothesis, metabolite analyses demonstrated an approximate 7-fold reduction in the levels of fructose-1,6-bisphosphate and a 30-fold reduction in fructose-6-phosphate levels, with a smaller reduction in glucose-6-phosphate in the liver of the FynKO mice compared to wild type mice (Figure 5B). Interestingly, despite the marked reduction in fructose-1,6-bisphosphate levels, we did not observe significant change in fructokinase gene expression (Figure 6A) or aldolase mRNA expression or aldolase protein levels (Figure 6B, C).

Bottom Line: Impaired conversion of glycerol to glucose was observed in both glycerol tolerance test and determination of the conversion of (13)C-glycerol to glucose in the fasted state. α-glycerol phosphate levels were reduced but glycerol kinase protein expression levels were not changed.Fructose-bisphosphate aldolase (aldolase) mRNA or protein levels were normal in the Fyn-deficient livers, however, there was a large reduction in liver fructose-6-phosphate (30-fold) and fructose-1,6-bisphosphate (7-fold) levels as well as a reduction in glucose-6-phosphate (2-fold) levels.These data suggest a mechanistic defect in the allosteric regulation of aldolase activity.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Animal Fat Deposition and Muscle Development, College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi, People's Republic of China ; Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, United States of America.

ABSTRACT
Previous studies have demonstrated that glucose disposal is increased in the Fyn knockout (FynKO) mice due to increased insulin sensitivity. FynKO mice also display fasting hypoglycaemia despite decreased insulin levels, which suggested that hepatic glucose production was unable to compensate for the increased basal glucose utilization. The present study investigates the basis for the reduction in plasma glucose levels and the reduced ability for the liver to produce glucose in response to gluconeogenic substrates. FynKO mice had a 5-fold reduction in phosphoenolpyruvate carboxykinase (PEPCK) gene and protein expression and a marked reduction in pyruvate, pyruvate/lactate-stimulated glucose output. Remarkably, de novo glucose production was also blunted using gluconeogenic substrates that bypass the PEPCK step. Impaired conversion of glycerol to glucose was observed in both glycerol tolerance test and determination of the conversion of (13)C-glycerol to glucose in the fasted state. α-glycerol phosphate levels were reduced but glycerol kinase protein expression levels were not changed. Fructose-driven glucose production was also diminished without alteration of fructokinase expression levels. The normal levels of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate observed in the FynKO liver extracts suggested normal triose kinase function. Fructose-bisphosphate aldolase (aldolase) mRNA or protein levels were normal in the Fyn-deficient livers, however, there was a large reduction in liver fructose-6-phosphate (30-fold) and fructose-1,6-bisphosphate (7-fold) levels as well as a reduction in glucose-6-phosphate (2-fold) levels. These data suggest a mechanistic defect in the allosteric regulation of aldolase activity.

Show MeSH
Related in: MedlinePlus