Localisation of islet amyloid polypeptide and its carboxy terminal flanking peptide in islets of diabetic man and monkey

Abstract

Islet amyloid polypeptide is a normal constituent of islet Beta cells and is derived from a larger precursor by removal of flanking peptides at the carboxy (C) and amino (N) terminals. The role of these flanking peptides in the formation of amyloid in Type 2 (non-insulin-dependent) diabetes mellitus and in insulinomas is unknown. The C-terminal flanking peptide of islet amyloid polypeptide was localised by immunocytochemistry in human and monkey pancreatic islets from Type 2 diabetic and non-diabetic individuals by use of specific polyclonal antisera. Immunoreactivity for the C-terminal peptide was found in insulin-containing cells in both diabetic and non-diabetic tissue: no antibody binding was detected in islet amyloid of Type 2 diabetic man or of monkeys although a positive reaction occurred with antisera for islet amyloid polypeptide. The C-terminal peptide was localised by immunogold electron microscopy in the insulin granules in both diabetic and non-diabetic individuals but, unlike islet amyloid polypeptide, was not detected in lysosomes. The absence of immunoreactivity for the C-terminal peptide in amyloid suggests that incomplete cleavage of this flanking peptide from islet amyloid polypeptide is not a factor in the formation of islet amyloid.

Processing of pro‐islet amyloid polypeptide (proIAPP) by the prohormone convertase PC2

“…IAPP is colocalised with insulin in the secretory granules of islet fl-cells and co-secreted in response to fl-cell secretagogues [3,4]. IAPP has been identified in all species examined so far [5] and, in common with other secretory peptides, is synthesized as a larger precursor molecule.…”

“…Islet amyloid polypeptide (IAPP), 'amylin', is a component peptide of amyloid fibrils deposited in islets of type 2 diabetic patients [1,2]. IAPP is colocalised with insulin in the secretory granules of islet fl-cells and co-secreted in response to fl-cell secretagogues [3,4]. IAPP has been identified in all species examined so far [5] and, in common with other secretory peptides, is synthesized as a larger precursor molecule.…”

Pro Islet Amyloid Polypeptide (ProIAPP) Immunoreactivity in the Islets of Langerhans

“…However, we have earlier shown in an immunohistochemical study that the N-terminal fragment of IAPP can occur in islet amyloid [29]. Others have failed to find the Cterminal flanking peptide in islet amyloid [2]. Interestingly, however, it has also been shown that proIAPP can form amyloid like fibrils in vitro [7].…”