Spexin Co‐localizes with Insulin in Pancreatic Islet Cells of Normal and Diabetic Rats

Abstract

Spexin is a newly discovered gastrointestinal tract (GIT) peptide. Preliminary biochemical analysis showed that spexin was localized to secretory granules in a transfected pancreatic cell line. Spexin was also expressed in the submucosal cells of the mouse stomach indicating that it is a resident peptide in the GIT and may thus influence pancreatic function. It has been suggested that spexin may play a role in the regulation of physiological homeostasis. Our aim was to determine whether spexin is present in the pancreas of normal and streptozotocin‐induced diabetic rats. We also wanted to know whether spexin co‐localizes with pancreatic hormones in the islet of Langerhans. Immunohistochemical, immunofluorescence and transmission electron microscopy (TEM) methods were used to determine the cellular localization of spexin in the endocrine pancreas of non‐diabetic and diabetic rats. Immunofluorescence study showed that a significant number of cells in the core of rat pancreatic islet contains spexin, where insulin‐positive cells are located. We used double labelling immunofluorescence method to determine whether spexin and insulin co‐localize together in the same cell. We observed that these spexin‐immunoreactive cells also contain insulin. There was no evidence of co‐localization of spexin with either somatostatin or pancreatic polypeptide. The number of spexin‐ and insulin‐immunopositive cells was significantly (p <0.05) reduced after the onset of diabetes mellitus. Moreover, TEM showed that the secretory granules of pancreatic beta cells contain spexin‐labelled immunogold particles. In conclusion, the presence of spexin in pancreatic beta cells suggests a role in the regulation of pancreatic endocrine function.