Biophysical Studies of Amyloid Formation by Polypeptide Hormones

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Amyloid formation has been implicated in more than thirty different human disorders. This application describes an interdisciplinary program designed to define the mechanism of amyloid formation by human islet amyloid polypeptide (IAPP, amylin), the causative agent of islet amyloidosis induced beta-cell toxicity in type-2 diabetes. IAPP is normally secreted as a soluble polypeptide hormone together with insulin from the pancreatic beta-cells and plays an adaptive role in glucose metabolism. However, IAPP is absent in type-1 diabetes, and forms pancreatic islet amyloid in type-2 diabetes. The process of islet amyloid formation is toxic to beta-cells and plays an important role in disease progression. Islet amyloid formation is also a major complicating factor in islet cell transplantation and aggregation of IAPP contributes to cardiovascular complications downstream of diabetes. Diabetes has reached epidemic proportions in the United States and there are no clinically approved inhibitors of islet amyloid formation or toxicity. IAPP is absent in type-1 diabetes and soluble analogs of human IAPP are of interest as adjuncts to insulin therapy and potentially for the treatment of obesity. An interdisciplinary combination of experimental protein biophysics, biochemistry, and cell biology will be used to elucidate the mechanism of amyloid formation by IAPP. Three specific aims will be carried out. The first aim will elucidate the role of the N-terminal region of IAPP in aggregation. The N-terminal region of IAPP is essential for the function of the hormone; understanding the role it plays in amyloid formation is critical for developing a full picture of IAPP amyloid formation and for developing soluble analogs of IAPP that can be used as adjuncts to insulin therapy. The second aim will critically examine the role early helical intermediates play in aggregation, an issue which is central to drug design. The third aim will characterize a recently discovered beta-sheet containing intermediate that appears to play a key role in IAPP amyloid formation and which may be the toxic entity responsible for beta-cell death. The work will offer insight into strategies for the treatment of type-2 diabetes and for the prevention of islet graft failure after transplantation and will aid efforts to design soluble analogs of IAPP. The general principles that will emerge from these studies and the methods which are being developed will be broadly applicable to other protein aggregation diseases.