O-50: A novel mechanism of cellular insulin resistance: Defective insulin-stimulated glucose transport due to malinsertion of glucose transporters into the plasma membrane of fibroblasts from a patient with an insulin resistance syndrome

Summary

The aim of this study was to examine the molecular defect responsible for the insulin resistance associated with defective insulin-stimulated glucose transport in cultured fibroblasts from a patient (VH) with clinical features of Werner syndrome. Thus, (i) insulin signalling from the insulin receptor to the glucose transport system, (ii) glucose transporter (GTer) translocation as well as (iii) insertion of GTers into the plasma membrane of fibroblasts derived from VH were determined. The results demonstrated that, when compared to control cells, in fibroblats of VH [1] the number and the affinity of the insulin receptor was normal, [2] insulin-stimulated phosphatidylinositol 3-kinase (PI 3-kinase) activity and protein level of the p85 alpha subunit of PI 3-kinase was normal, [3] GLUTI mRNA was increased by 4-5 fold, [4] in subcellular membranes GLUTI protein level were increased 5- and 8-fold in high-density microsomes and plasma membranes (PM) respectively; these results were supported by immunohistochemistry studies demonstrating an accumulation of GLUTI in the perinuclear region and in the plasma membrane, [5] the intrinsic activity of plasma membrane GLUTI was normal, [6] the entire GLUTI sequence was normal, [7] photoaffinity labeling of cell surface GLUTI revealed that only 14% of PM GTer were properly inserted into the PM, [8] protein level or rab4 were decreased in total cellular membranes and high-density microsomes by 70% and 58% respectively. In conclusion these data indicate, that the defective insulin-stimulated glucose transport in fibroblasts of VH is due to a malinsertion of GTer containing membrane vesicles into the PM. This new mechanism of cellular insulin resistance might also be involved in the pathogenesis of insulin resistance in more common diseases like NIDDM.