The long-term objective is to understand the mechanism of insulin resistance in NIDDM and obesity. The significance of this proposal is three fold: (i) A method to culture insulin responsive human adipocytes in serum-free medium has been developed; (ii) We have a well defined human model of NIDDM. Our institution performs over 100 gastric bypass procedures annually in morbidly obese subjects of whom 27% have NIDDM, 20% impaired, and the rest have normal glucose tolerance; and (iii) Following gastric bypass, these patients effectively loose weight and 75% of NIDDM patients are able to maintain euglycemia without therapy. First, we will determine insulin sensitivity and responsiveness of insulin actions in adipocytes from our patients. The decreased insulin binding in obesity and NIDDM is explained by insulin receptor turnover and mRNA levels. Then, the structure and function (in vitro and in vivo phosphorylation of B-subunit and endogenous substrate) of insulin receptor is analyzed to evaluate its role as a transducer of insulin action. Monoclonal antibodies are also used to probe the significance insulin receptor kinase in NIDDM and obesity. The mechanism of decreased glucose transport in obese and NIDDM patients is studied by determining the number, intracellular distribution, intrinsic activity and mRNA levels of glucose transporters. Primary cultures of adipocytes from control subjects will allow us to study the role of extracellular factors in inducing insulin resistance. For this purpose the effects of insulin, glucose and """"""""putative"""""""" serum factor(s) on various insulin actions will be determined. Finally, we will restudy insulin sensitivity and responsiveness in our patients eighteen months after surgery following weight loss and glycemic control and in age, weight and sex matched subjects with and without NIDDM. The significance of this proposal is enhanced by the recognition that these in vitro data from adipocytes will be correlated with those from muscle and liver and in vivo insulin sensitivity. It is hoped that this work will not only establish the cellular basis of insulin resistance in NIDDM and obesity but may help in dissecting the primary and secondary defects of NIDDM, and thus help to develop a more rational therapeutic approach to this major health problem.
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