MOLECULAR PHYSIOLOGY OF THE ISLET AMYLOID POLYPEPTIDE (IAPP) AMYLIN GENE IN MAN, RAT, AND TRANSGENIC MICE/

Islet amyloid polypeptide (''amylin'') is the major protein component of amyloid deposits in pancreatic islets of type 2 (non-insulin-depend ent) diabetic patients. Islet amyloid polypeptide consists of 37 amino acids, is co-produced and co-secreted with insulin from islet beta-ce lls, can act as a hormone in regulation of carbohydrate metabolism, an d is implicated in the pathogenesis of islet amyloid formation and of type 2 diabetes mellitus. Rat islet amyloid polypeptide differs from h uman islet amyloid polypeptide particularly in the region of amino aci ds 25-28, which is important for amyloid fibril formation. In rat and mouse, diabetes-associated islet amyloid does not develop. To study th e genetic organization and biosynthesis of islet amyloid polypeptide, we have isolated and analyzed the human and rat islet amyloid polypept ide gene and corresponding cDNAs. Both genes contain 3 exons, encoding precursor proteins of 89 amino acids and 93 amino acids, respectively . Apart from a putative signal sequence, these precursors contain amin o- and carboxy-terminal flanking peptides in addition to the mature is let amyloid polypeptide. To understand regulation of islet amyloid pol ypeptide gene expression, we have identified several potential cis-act ing transcriptional control elements that influence beta-cell-specific islet amyloid polypeptide gene expression. Using antisera raised agai nst synthetic human islet amyloid polypeptide we developed a specific and sensitive radioimmunoassay to measure levels of islet amyloid poly peptide in plasma and tissue extracts. Also antisera raised against th e flanking peptides will be used in studying human islet amyloid polyp eptide biosynthesis. Elevated plasma islet amyloid polypeptide levels have been demonstrated in some diabetic, glucose-intolerant, and obese individuals, as well as in rodent models of diabetes and obesity. To examine the potential role of islet amyloid polypeptide overproduction in the pathogenesis of islet amyloid formation and type 2 diabetes, w e generated transgenic mice that overproduce either the amyloidogenic human islet amyloid polypeptide or the nonamyloidogenic rat islet amyl oid polypeptide in their islet beta-cells. Despite moderately to highl y (up to 15-fold) elevated plasma islet amyloid polypeptide levels, no marked hyperglycemia, hyperinsulinemia or obesity was observed. This suggests that chronic overproduction of islet amyloid polypeptide ''pe r se'' does not cause insulin resistance. No islet amyloid deposits we re detected in mice up to 63 weeks of age, but in every mouse producin g human islet amyloid polypeptide (as in man), accumulation of islet a myloid polypeptide was observed in beta-cell lysosomal bodies. This ma y represent an initial phase in intracellular amyloid fibril formation . The human islet amyloid polypeptide overproducing transgenic mice mo del offers a unique opportunity to study the biosynthesis, intracellul ar handling, secretion, and extracellular handling of human islet amyl oid polypeptide in vivo. (C) 1994 Wiley-Liss, Inc.