Definition: Islet or insulinoma amyloid polypeptide (IAPP) is a 37-amino acid monomeric polypeptide isolated from pancreatic amyloid. Such amyloid is commonly found in the islets of patients with diabetes mellitus type II (MIM.269200) and in insulinomas. A specific immunoreactivity with antibodies to IAPP is found in islet amyloid and in cells of the islets of Langerhans, where it colocalizes with insulin in islet B cells.
Amylin is co-synthesized, co-packaged within the Golgi apparatus, and co-secreted within the secretory granule by the islet beta cell in response to elevations of plasma glucose. Amylin may be referred to as insulin’s "fraternal twin" as it is constitutively expressed with insulin when exposed to non-glucose and glucose stimulation (nutrient stimuli).
The amylin gene is located on the short arm of chromosome 12 and transcribes an 89 amino acid precursor peptide.
Proprotein convertases (PC1, PC2, and PC3) are responsible for the processing of the prehormones to the active secreted hormones insulin and amylin.
It is primarily PC2 that is responsible for amylin processing within the secretory granule and is responsible for converting the prohormone (89 amino acid) to the actively secreted (37 amino acid) amylin.
Since amylin’s discovery in 1987 it is currently thought to be the third active pancreatic islet hormone important in glucose homeostasis. It potently inhibits gastric emptying and is important in controlling and delaying the rate of meal derived glucose.
It inhibits hepatic release and production of glucose in the postprandial period. In addition to the above amylin has been shown to inhibit glucagon secretion as well as somatostatin. Amylin’s synthesis and excretion parallels insulin in the beta cell.
Islet amyloid
Islet amyloid is a feature of spontaneous diabetes in domestic cats and macaques, as well as in humans.
References
Jaikaran, E. T. A. S.; Clark, A. : Islet amyloid and type 2 diabetes: from molecular misfolding to islet pathophysiology. Biochim. Biophys. Acta 1537: 179-203, 2001. PubMed ID : 11731221
Hoppener JW, Oosterwijk C, van Hulst KL, Verbeek JS, Capel PJ, de Koning EJ, Clark A, Jansz HS, Lips CJ. Molecular physiology of the islet amyloid polypeptide (IAPP)/amylin gene in man, rat, and transgenic mice. J Cell Biochem. 1994;55 Suppl:39-53. PMID: 7929617
Stridsberg M, Wilander E. Islet amyloid polypeptide (IAPP). A short review. Acta Oncol. 1991;30(4):451-6. PMID: 1854502
Johnson KH, O’Brien TD, Betsholtz C, Westermark P. Islet amyloid, islet-amyloid polypeptide, and diabetes mellitus. N Engl J Med. 1989 Aug 24;321(8):513-8. PMID: 2668761