ISSN:
0730-2312
Keywords:
CALC gene family
;
genomic organization
;
transcription regulation
;
biosynthesis
;
islet β-cell
;
insulin resistance
;
islet amyloid
;
type 2 diabetes mellitus
;
animal model
;
Life and Medical Sciences
;
Cell & Developmental Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Islet amyloid polypeptide (“amylin”) is the major protein component of amyloid deposits in pancreatic islets of type 2 (non-insulin-dependent) diabetic patients. Islet amyloid polypeptide consists of 37 amino acids, is co-produced and co-secreted with insulin from islet β-cells, can act as a hormone in regulation of carbohydrate metabolism, and is implicated in the pathogenesis of islet amyloid formation and of type 2 diabetes mellitus. Rat islet amyloid polypeptide differs from human islet amyloid polypeptide particularly in the region of amino acids 25-28, which is important for amyloid fibril formation. In rat and mouse, diabetes-associated islet amyloid does not develop. To study the genetic organization and biosynthesis of islet amyloid polypeptide, we have isolated and analyzed the human and rat islet amyloid polypeptide 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 amino- and carboxy-terminal flanking peptides in addition to the mature islet amyloid polypeptide. To understand regulation of islet amyloid polypeptide gene expression, we have identified several potential cis-acting transcriptional control elements that influence β-cell-specific islet amyloid polypeptide gene expression. Using antisera raised against synthetic human islet amyloid polypeptide we developed a specific and sensitive radioimmunoassay to measure levels of islet amyloid polypeptide in plasma and tissue extracts. Also antisera raised against the flanking peptides will be used in studying human islet amyloid polypeptide 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, we generated transgenic mice that overproduce either the amyloidogenic human islet amyloid polypeptide or the nonamyloidogenic rat islet amyloid polypeptide in their islet β-cells. Despite moderately to highly (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 “per se” does not cause insulin resistance. No islet amyloid deposits were detected in mice up to 63 weeks of age, but in every mouse producing human islet amyloid polypeptide (as in man), accumulation of islet amyloid polypeptide was observed in β-cell lysosomal bodies. This may represent an initial phase in intracellular amyloid fibril formation. The human islet amyloid polypeptide overproducing transgenic mice model offers a unique opportunity to study the biosynthesis, intracellular handling, secretion, and extracellular handling of human islet amyloid polypeptide in vivo. © 1994 Wiley-Liss, Inc.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jcb.240550006
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