High-fat feeding impairs insulin-stimulated GLUT4 recruitment via an early insulin-signaling defect.

Glucose transport in skeletal muscle can be mediated by two separate pathways, one stimulated by insulin and the other by muscle contraction. High-fat feeding impairs glucose transport in muscle, but the mechanism remains unclear. FVB mice (3 weeks old) were fed a high-fat diet (55% fat, 24% carbohydrate, 21% protein) or standard chow for 3-4 weeks or 8 weeks. Insulin-stimulated glucose transport, assessed with either 2-deoxyglucose or 3-O-methylglucose was decreased 35-45% (P < 0.001) in isolated soleus muscle, regardless of diet duration. Similarly, glucose transport stimulated by okadaic acid, a serine/threonine phosphatase inhibitor, was also 45% lower with high-fat feeding, but the glucose transport response to hypoxia or N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) (which are stimulators of the "contraction pathway") was intact. Hexokinase I, II, and total activity were normal in soleus muscle from high-fat-fed mice. GLUT4 expression in soleus muscle from the high-fat-fed mice was also normal, but the insulin-stimulated cell surface recruitment of GLUT4 assessed by exofacial photolabeling with [3H]-ATB bis-mannose was reduced by 50% (P < 0.001). Insulin-receptor substrate 1 (IRS-1) associated phosphatidylinositol (PI) 3-kinase activity stimulated by insulin was also reduced by 36% (P < 0.001), and expression of p85 and p110b subunits of PI 3-kinase was normal. In conclusion, high-fat feeding selectively impairs insulin-stimulated, but not contraction-pathway-mediated, glucose transport by reducing GLUT4 translocation to the plasma membrane. This appears to result from an acquired defect in insulin activation of PI 3-kinase. Since effects of okadaic acid on glucose transport are independent of PI 3-kinase, a second signaling defect may also be induced.