Objective: Impaired insulin-dependent glucose disposal in muscle and fat is a harbinger of type 2 diabetes, but murine models of selective insulin resistance at these two sites are conspicuous by their failure to cause hyperglycemia. A defining feature of muscle and fat vis-à-vis insulin signaling is that they both express the insulin-sensitive glucose transporter Glut4. We hypothesized that diabetes is the result of impaired insulin signaling in all Glut4-expressing tissues.
Research design and methods: To test the hypothesis, we generated mice lacking insulin receptors at these sites ("GIRKO" mice), including muscle, fat, and a subset of Glut4-positive neurons scattered throughout the central nervous system.
Results: GIRKO mice develop diabetes with high frequency because of reduced glucose uptake in peripheral organs, excessive hepatic glucose production, and β-cell failure.
Conclusions: The conceptual advance of the present findings lies in the identification of a tissue constellation that melds cell-autonomous mechanisms of insulin resistance (in muscle/fat) with cell-nonautonomous mechanisms (in liver and β-cell) to cause overt diabetes. The data are consistent with the identification of Glut4 neurons as a distinct neuroanatomic entity with a likely metabolic role.