Insulin resistance at target tissue level is a characteristic feature of noninsulin-dependent (Type II) diabetes mellitus and obesity. The available evidence indicates that abnormalities both at the receptor binding level (receptor defects) and at steps distal to receptor binding (postreceptor defects) contribute to the overall insulin resistance in these disorders. However, the basic underlying cellular mechanisms responsible for the insulin resistance are not known. The overall goal of the proposed studies in this application is to further elucidate the cellular mechanisms by which insulin receptors and insulin action on glucose transport are regulated in human obesity and Type II diabetes mellitus and to determine which abnormalities in these processes contribute to the insulin resistance in these disease states. Specifically, we plan to: 1) characterize insulin receptors by in situ photoaffinity labeling on isolated adipocytes from obese and Type II diabetic subjects and then investigate the mechanism by which the receptors are internalized and processed (and possibly recycled) in these cells; 2) study the mechanisms and intracellular pathways of the processing of receptor bound insulin in these cells using a biologically active photoreactive insulin probe; 3) use primary cultures of adipocytes established from normal, obese and Type II diabetics for studies of the reversibility of the receptor defects of obsesity and Type II diabetes, and for comparative investigations of the mechanisms of insulin receptor biosynthesis, processing and membrane insertion; and 4) investigate the mechanism of the post-receptor defect in insulin-stimulated glucose transport activity in obesity and Type II diabetes by quantitating cellular glucose transport proteins and their distribution between intracellular and plasma membrane sites in response to insulin. It is hoped that the results of the studies proposed here will provide new information regarding the pathogenetic mechanisms of the cellular insulin resistance in obesity and Type II diabetes mellitus, which are major health problems that result in significant morbidity and mortality.
