Islet amyloid deposition occurs in approximately approximately 90% of subjects with type 2 diabetes and contributes to the progressive loss of islet beta-cell mass and function that characterize the disease. Understanding the mechanism(s) that underlie islet amyloid deposition will allow the development of approaches to prevent its formation and the resulting beta-cell loss and dysfunction. Islet amyloid comprises the beta-cell peptide islet amyloid polypeptide (IAPP, amylin) and the heparan sulfate proteoglycan perlecan. Perlecan may stimulate islet amyloid formation by binding amyloidogenic human IAPP (hIAPP) through its heparan sulfate glycosaminoglycan (HS GAG) side chains. We have recently shown that islet beta-cells express perlecan and that beta-cell perlecan binds hIAPP through its HS GAG chains. We have also shown that isolated islets, from mice expressing perlecan that lacks HS GAG chains, show a marked reduction in islet amyloid deposition in vitro. Thus, we hypothesize that perlecan HS GAGs are critical for islet amyloid deposition and its effects to cause beta-cell loss and dysfunction. The following studies will be performed to determine whether: 1. Perlecan HS GAGs are required for islet amyloid formation in vitro and in vivo. Mice expressing a mutant form of perlecan will be cross-bred with our hIAPP transgenic mouse model of islet amyloid formation. We expect expression of mutant perlecan to reduce islet amyloid formation and improve both insulin release and beta-cell volume in isolated islets cultured for seven days and in mice fed a high fat diet for 12 months. 2. Perlecan HS GAGs are required for the effect of amyloid to cause islet graft failure following transplantation. The mice described above will be used here as islet transplant donors and recipients. We have previously shown that transplantation of hIAPP transgenic islets results in islet amyloid formation, recurrence of hyperglycemia and reduced beta-cell volume in the transplanted islet graft. We expect that expression of mutant perlecan will prevent islet amyloid formation and improve islet graft survival. 3. The mechanism by which perlecan HS GAGs enhance amyloid formation. We will characterize the HS GAG composition of beta-cell perlecan and its ability to bind hIAPP and stimulate hIAPP fibril formation in vitro. Successful funding of this application will provide me with salary and protected research time in order to achieve my career goal of becoming an independent investigator in the field of type 2 diabetes.
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