Impacts Of Islet Neogenesis-associated Protein On Islet β-cell Function And Islet Neogenesis

ObjectiveExamine the effects of islet neogenesis-associated protein(INGAP) on isletβ-cell function in vitro and observe the impact of INGAP on islet neogenesis and blood glucose level in vivo with muscle injection.Methods1. Islets were isolated from male adult Wistar rats and were cultured in RPMI 1640 with or without INGAP (10ug/ml)for 24 hours.2. After 24 hours, cultured islets were collected to test glucose-stimulated insulin secretion, the expression of genes Bcl-2 and Akt-1 were detected by reverse transcription and polymerase chain reaction (RT-PCR) assay.3. Male adult Wistar rats were randomly divided into 2 groups. The control group received daily intramuscular injections of PBS for one week, the other group received daily injections of INGAP at dosage of 500ug for one week. After this period, pancreatic tissues were collected to examine the expression of Insulin, Ki67, CK19 and Nestin by immunocytochemical.4. C57BL/6 mice were rendered diabetic by intraperitoneal injection of streptozotocin(STZ). After confirmation that all mice were diabetic, they were randomized to receive daily injection of INGAP(500ug) or an equivalent volume of saline for 34 days. Blood glucose was determined every 2 days. The expression of gene Glut-2 and PDX-1 mRNA were tested by Realtime-PCR on day 34.Results1. INGAP cultured islets released more insulin in response to glucose at the concentrate of 16.7mM, the stimulating index of islets of INGAP group was higher than that of control group.2. Gene expression of Bcl-2 and Akt of INGAP group increased compared with that of control group.3. Image analysis of pancreatic issues showed that islets are larger and new islet cells stained positive for insulin are more in INGAP-treated mice than control group. In INGAP-treated animals, the expression of Nestin, CK19,Ki67 are significantly increased both in islets and among acinar cells.4. No significant difference in blood glucose levels was demonstrated between INGAP or PBS groups after 34 days treatment.5. Gene expression of Glut-2 and PDX-1 of INGAP-treated group increased compared with that of PBS group.Conclusions:1. INGAP improved the function of cultured islets, increased glucose-stimulated insulin secretion and decreasedβ-cell apoptosis.2. INGAP stimulated both duct and acinar-associated islet neogenesis, increasedβ-cell mass, but INGAP could not reverse STZ induced diabetes.