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Enhanced energy expenditure, glucose utilization, and insulin sensitivity in VAMP8 mice.

Zong H, Wang CC, Vaitheesvaran B, Kurland IJ, Hong W, Pessin JE - Diabetes (2010)

Bottom Line: Insulin stimulated GLUT4 protein expressions on muscle cell surface were examined by immunofluorescence microscopy.Consistent with a role for VAMP8 in the endocytosis of the insulin-responsive GLUT4, sarcolemma GLUT4 protein levels were increased in both the basal and insulin-stimulated states without any significant change in the total amount of GLUT4 protein or related facilitative glucose transporters present in skeletal muscle, GLUT1, GLUT3, and GLUT11.These data demonstrate that, in the absence of VAMP8, the relative subcellular distribution of GLUT4 is altered, resulting in increased sarcolemma levels that can account for increased glucose clearance and insulin sensitivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine and Molecular Pharmacology, The Albert Einstein College of Medicine, Bronx, New York, USA.

ABSTRACT

Objective: Previous studies have demonstrated that the VAMP8 protein plays a complex role in the control of granule secretion, transport vesicle trafficking, phagocytosis, and endocytosis. The present study was aimed to investigate the role of VAMP8 in mediating GLUT4 trafficking and therefore insulin action in mice.

Research design and methods: Physiological parameters were measured using Oxymax indirect calorimetry system in 12-week-old VAMP8 mice. Dynamic analysis of glucose homeostasis was assessed using euglycemic-hyperinsulinemic clamp coupled with tracer radioactively labeled 2-deoxyglucose. Insulin stimulated GLUT4 protein expressions on muscle cell surface were examined by immunofluorescence microscopy.

Results: VAMP8 mice display reduced adiposity with increased energy expenditure despite normal food intake and reduced spontaneous locomotor activity. In parallel, the VAMP8 mice also had fasting hypoglycemia (84 ± 11 vs. 115 ± 4) and enhanced glucose tolerance with increased insulin sensitivity due to increases in both basal and insulin-stimulated glucose uptake in skeletal muscle (0.19 ± 0.04 vs. 0.09 ± 0.01 mmol/kg/min during basal, 0.6 ± 0.04 vs. 0.31 ± 0.06 mmol/kg/min during clamp in red-gastrocnemius muscle, P < 0.05). Consistent with a role for VAMP8 in the endocytosis of the insulin-responsive GLUT4, sarcolemma GLUT4 protein levels were increased in both the basal and insulin-stimulated states without any significant change in the total amount of GLUT4 protein or related facilitative glucose transporters present in skeletal muscle, GLUT1, GLUT3, and GLUT11.

Conclusions: These data demonstrate that, in the absence of VAMP8, the relative subcellular distribution of GLUT4 is altered, resulting in increased sarcolemma levels that can account for increased glucose clearance and insulin sensitivity.

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Related in: MedlinePlus

Determination of plasma glucose and insulin levels during euglycemic–hyperinsulinemic clamps. A: Plasma glucose and (B) plasma insulin level during basal and last 30 min of the euglycemic–hyperinsulinemic clamps (4 mU/kg/min insulin infusion with glucose level maintained at ∼90 mg/dl) for the WT (open boxes) and VAMP8 (filled boxes) mice. These data represent the mean ± SEM from 7–10 individual mice per group. *P < 0.05.
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Figure 5: Determination of plasma glucose and insulin levels during euglycemic–hyperinsulinemic clamps. A: Plasma glucose and (B) plasma insulin level during basal and last 30 min of the euglycemic–hyperinsulinemic clamps (4 mU/kg/min insulin infusion with glucose level maintained at ∼90 mg/dl) for the WT (open boxes) and VAMP8 (filled boxes) mice. These data represent the mean ± SEM from 7–10 individual mice per group. *P < 0.05.

Mentions: To specifically determine whether the VAMP8 mice display increased insulin sensitivity, we performed conscious nonstressed euglycemic–hyperinsulinemic clamps. As observed during the oral glucose tolerance test, in the basal or fasting level of plasma, glucose was reduced in the VAMP8 mice compared with wild-type control and was normalized to the same level (∼90 mg/dl) during the euglycemic–hyperinsulinemic clamp (Fig. 5A). Similarly, plasma insulin was normalized to the same hyperinsulinemic levels during the euglycemic–hyperinsulinemic clamp for both the wild-type and VAMP8 mice (Fig. 5B). Consistent with an increase in insulin sensitivity, the glucose infusion rate during the euglycemic–hyperinsulinemic clamp was greater in the VAMP8 mice along with increased whole-body glucose uptake (Fig. 6A and B). The overall rate of body glycogen/lipid synthesis was also increased with no statistically significantly change in total body glycolysis rate, although there was a consistent increased trend in the VAMP8 mice (Fig. 6C and D). Skeletal muscle accounts for the majority of glucose postprandial glucose uptake and was significantly increased in red type 1 skeletal muscle fibers (soleus and red gastrocnemius) in both the basal and insulin-stimulated states (Fig. 7A). In parallel, insulin induced a greater suppression of hepatic glucose output in the VAMP8 mice (Fig. 7B).


Enhanced energy expenditure, glucose utilization, and insulin sensitivity in VAMP8 mice.

Zong H, Wang CC, Vaitheesvaran B, Kurland IJ, Hong W, Pessin JE - Diabetes (2010)

Determination of plasma glucose and insulin levels during euglycemic–hyperinsulinemic clamps. A: Plasma glucose and (B) plasma insulin level during basal and last 30 min of the euglycemic–hyperinsulinemic clamps (4 mU/kg/min insulin infusion with glucose level maintained at ∼90 mg/dl) for the WT (open boxes) and VAMP8 (filled boxes) mice. These data represent the mean ± SEM from 7–10 individual mice per group. *P < 0.05.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3012186&req=5

Figure 5: Determination of plasma glucose and insulin levels during euglycemic–hyperinsulinemic clamps. A: Plasma glucose and (B) plasma insulin level during basal and last 30 min of the euglycemic–hyperinsulinemic clamps (4 mU/kg/min insulin infusion with glucose level maintained at ∼90 mg/dl) for the WT (open boxes) and VAMP8 (filled boxes) mice. These data represent the mean ± SEM from 7–10 individual mice per group. *P < 0.05.
Mentions: To specifically determine whether the VAMP8 mice display increased insulin sensitivity, we performed conscious nonstressed euglycemic–hyperinsulinemic clamps. As observed during the oral glucose tolerance test, in the basal or fasting level of plasma, glucose was reduced in the VAMP8 mice compared with wild-type control and was normalized to the same level (∼90 mg/dl) during the euglycemic–hyperinsulinemic clamp (Fig. 5A). Similarly, plasma insulin was normalized to the same hyperinsulinemic levels during the euglycemic–hyperinsulinemic clamp for both the wild-type and VAMP8 mice (Fig. 5B). Consistent with an increase in insulin sensitivity, the glucose infusion rate during the euglycemic–hyperinsulinemic clamp was greater in the VAMP8 mice along with increased whole-body glucose uptake (Fig. 6A and B). The overall rate of body glycogen/lipid synthesis was also increased with no statistically significantly change in total body glycolysis rate, although there was a consistent increased trend in the VAMP8 mice (Fig. 6C and D). Skeletal muscle accounts for the majority of glucose postprandial glucose uptake and was significantly increased in red type 1 skeletal muscle fibers (soleus and red gastrocnemius) in both the basal and insulin-stimulated states (Fig. 7A). In parallel, insulin induced a greater suppression of hepatic glucose output in the VAMP8 mice (Fig. 7B).

Bottom Line: Insulin stimulated GLUT4 protein expressions on muscle cell surface were examined by immunofluorescence microscopy.Consistent with a role for VAMP8 in the endocytosis of the insulin-responsive GLUT4, sarcolemma GLUT4 protein levels were increased in both the basal and insulin-stimulated states without any significant change in the total amount of GLUT4 protein or related facilitative glucose transporters present in skeletal muscle, GLUT1, GLUT3, and GLUT11.These data demonstrate that, in the absence of VAMP8, the relative subcellular distribution of GLUT4 is altered, resulting in increased sarcolemma levels that can account for increased glucose clearance and insulin sensitivity.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine and Molecular Pharmacology, The Albert Einstein College of Medicine, Bronx, New York, USA.

ABSTRACT

Objective: Previous studies have demonstrated that the VAMP8 protein plays a complex role in the control of granule secretion, transport vesicle trafficking, phagocytosis, and endocytosis. The present study was aimed to investigate the role of VAMP8 in mediating GLUT4 trafficking and therefore insulin action in mice.

Research design and methods: Physiological parameters were measured using Oxymax indirect calorimetry system in 12-week-old VAMP8 mice. Dynamic analysis of glucose homeostasis was assessed using euglycemic-hyperinsulinemic clamp coupled with tracer radioactively labeled 2-deoxyglucose. Insulin stimulated GLUT4 protein expressions on muscle cell surface were examined by immunofluorescence microscopy.

Results: VAMP8 mice display reduced adiposity with increased energy expenditure despite normal food intake and reduced spontaneous locomotor activity. In parallel, the VAMP8 mice also had fasting hypoglycemia (84 ± 11 vs. 115 ± 4) and enhanced glucose tolerance with increased insulin sensitivity due to increases in both basal and insulin-stimulated glucose uptake in skeletal muscle (0.19 ± 0.04 vs. 0.09 ± 0.01 mmol/kg/min during basal, 0.6 ± 0.04 vs. 0.31 ± 0.06 mmol/kg/min during clamp in red-gastrocnemius muscle, P < 0.05). Consistent with a role for VAMP8 in the endocytosis of the insulin-responsive GLUT4, sarcolemma GLUT4 protein levels were increased in both the basal and insulin-stimulated states without any significant change in the total amount of GLUT4 protein or related facilitative glucose transporters present in skeletal muscle, GLUT1, GLUT3, and GLUT11.

Conclusions: These data demonstrate that, in the absence of VAMP8, the relative subcellular distribution of GLUT4 is altered, resulting in increased sarcolemma levels that can account for increased glucose clearance and insulin sensitivity.

Show MeSH
Related in: MedlinePlus