Glucose toxicity and the development of diabetes in mice with muscle-specific inactivation of GLUT4

Abstract

Using cre/loxP gene targeting, transgenic mice with muscle-specific inactivation of the GLUT4 gene (muscle GLUT4 KO) were generated and shown to develop a diabetes phenotype. To determine the mechanism, we examined insulin-stimulated glucose uptake and metabolism during hyperinsulinemic-euglycemic clamp in control and muscle GLUT4 KO mice before and after development of diabetes. Insulin-stimulated whole body glucose uptake was decreased by 55% in muscle GLUT4 KO mice, an effect that could be attributed to a 92% decrease in insulin-stimulated muscle glucose uptake. Surprisingly, insulin's ability to stimulate adipose tissue glucose uptake and suppress hepatic glucose production was significantly impaired in muscle GLUT4 KO mice. To address whether these latter changes were caused by glucose toxicity, we treated muscle GLUT4 KO mice with phloridzin to prevent hyperglycemia and found that insulin-stimulated whole body and skeletal muscle glucose uptake were decreased substantially, whereas insulin-stimulated glucose uptake in adipose tissue and suppression of hepatic glucose production were normal after phloridzin treatment. In conclusion, these findings demonstrate that a primary defect in muscle glucose transport can lead to secondary defects in insulin action in adipose tissue and liver due to glucose toxicity. These secondary defects contribute to insulin resistance and to the development of diabetes.

Figure 1

Whole body and skeletal muscle metabolic parameters during hyperinsulinemic-euglycemic clamps in awake mice at 20–21 weeks of age. (a) Basal plasma glucose concentration in the control (wild-type, lox/lox, and cre; open circles), muscle GLUT4 KO (MG4KO; filled circles), and PHZ-treated muscle GLUT4 KO (MG4KO + PHZ; open squares) mice. (b) Basal plasma insulin concentration in the control (open circles), muscle GLUT4 KO (filled circles), and PHZ-treated muscle GLUT4 KO (open squares) mice. (c) Insulin-stimulated whole body glucose uptake in vivo in control (open bar), heterozygous KO (Het KO; dark gray bar), muscle GLUT4 KO (black bar), and PHZ-treated muscle GLUT4 KO (MG4KO + PHZ; light gray bar) mice. (d) Insulin-stimulated glucose uptake in skeletal muscle (gastrocnemius) in vivo in control (open bar), heterozygous KO (dark gray bar), muscle GLUT4 KO (black bar), and PHZ-treated muscle GLUT4 KO (light gray bar) mice. Values are means plus or minus SE for 5–10 experiments. *P < 0.05 vs. control mice; ^#P < 0.05 for the PHZ-treated muscle GLUT4 KO mice vs. nontreated muscle GLUT4 KO mice.

Figure 2

Insulin-stimulated glucose metabolic flux in whole body and skeletal muscle (gastrocnemius) during hyperinsulinemic-euglycemic clamps in awake control (wild-type, lox/lox, and cre; open bar), heterozygous KO (dark gray bar), muscle GLUT4 KO (black bar), and PHZ-treated muscle GLUT4 KO (light gray bar) mice at 20–21 weeks of age. (a) Insulin-stimulated whole body glycolysis in vivo. (b) Insulin-stimulated whole body glycogen/lipid synthesis in vivo. (c) Insulin-stimulated skeletal muscle glycolysis in vivo. (d) Insulin-stimulated skeletal muscle glycogen synthesis in vivo. Values are means plus or minus SE for 5–10 experiments. *P < 0.05 vs. control mice; ^#P < 0.05 for the PHZ-treated muscle GLUT4 KO mice vs. nontreated muscle GLUT4 KO mice.

Figure 3

Insulin action in liver and adipose tissues during hyperinsulinemic-euglycemic clamps in awake control (wild-type, lox/lox, and cre; open bar), heterozygous KO (dark gray bar), muscle GLUT4 KO (black bar), and PHZ-treated muscle GLUT4 KO (light gray bar) mice at 20–21 weeks of age. (a) Percentage of suppression of basal hepatic glucose production. (b) Insulin-stimulated glucose uptake in epididymal white adipose tissue in vivo. (c) Insulin-stimulated glucose uptake in intrascapular brown adipose tissue in vivo. Values are means plus or minus SE for 5–10 experiments. *P < 0.05 vs. control mice. ^#P < 0.05 for the PHZ-treated muscle GLUT4 KO mice vs. nontreated muscle GLUT4 KO mice.

Figure 4

Insulin action in whole body and individual tissues during hyperinsulinemic-euglycemic clamps in awake young control (wild-type, lox/lox, and cre; open bar) and young muscle GLUT4 KO (MG4KO; filled bar) mice at approximately 10 weeks of age. (a) Insulin-stimulated whole body glucose uptake in vivo. (b) Insulin-stimulated glucose uptake in skeletal muscle (gastrocnemius) in vivo. (c) Basal and insulin-stimulated rates of hepatic glucose production. (d) Insulin-stimulated glucose uptake in epididymal white adipose tissue and intrascapular brown adipose tissue in vivo. Values are means plus or minus SE for 9–11 experiments. *P < 0.05 vs. young control mice.

Figure 5

Insulin-stimulated glucose metabolic flux in whole body and skeletal muscle (gastrocnemius) during hyperinsulinemic-euglycemic clamps in awake young control (wild-type, lox/lox, and cre; open bar) and young muscle GLUT4 KO (filled bar) mice at approximately 10 weeks of age. (a) Insulin-stimulated whole body glycolysis in vivo. (b) Insulin-stimulated whole body glycogen/lipid synthesis in vivo. (c) Insulin-stimulated skeletal muscle glycolysis in vivo. (d) Insulin-stimulated skeletal muscle glycogen synthesis in vivo. Values are means plus or minus SE for 9–11 experiments. *P < 0.05 vs. young control mice.