Function and pathophysiological role of a novel glucose transporter expressed in skeletal muscle

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Diabetes is a disorder of metabolism resulting from a combination of deficiency of insulin and defective action of the insulin that is present. The most prominent metabolic abnormality is high blood glucose, which is often not satisfactorily corrected by insulin treatment. One of the main reasons for the high blood glucose is reduced uptake of glucose by muscle tissue. The mechanism by which insulin enhances glucose entry into muscle cells involves mobilisation of a specific protein from the glucose transporter protein family, which has been designated GLUT4. Surprisingly, animals that have been genetically altered to eliminate orknockout GLUT4 production do not develop diabetes. This finding has led to the theory that there is a backup glucose transporter protein that can prevent diabetes when there is a problem with GLUT4 function. We have recently discovered a new member of the glucose transporter protein family that could potentially function as either a parallel or a backup system for GLUT4. This new glucose transporter, which we have called GLUT8, is present in human muscle tissue and studies in other cells have shown that it alters its distribution within the cell in reponse to insulin. We now want to study in more detail the role of this new glucose transporter in muscle tissue and how it functions compared with GLUT4. In particular, we think it is possible that Type 2 diabetes occurs when there is not only a problem with the mobilisation of GLUT4 but also a defect in the production or function of GLUT8. If this is the case, then increasing GLUT8 production might improve glucose transport into muscle tissue and so improve control of blood glucose levels in diabetes.