Effects of islet neogenesis-associated protein pentadecapeptide on cell mass and insulin secretion of pancreatic β-cells.

Objective: To explore the effects of islet neogenesis- associated protein pentadecapeptide (INGAP-PP) on proliferation and secretion function of β-cells.
Methods: Islets of adult Sprague Dawley rats were isolated by collagenase digestion and treated with 10 μg/ml INGAP-PP, after 12, 24, 48 h, glucose-stimulated insulin secretion (GSIS) and acridine orange/pro pidium iodide (AO/PI) staining were used to detect the secretion function and cell viability. The INS-1 cells were treated with 0, 1, 10, 25, 50, 100, 250, and 500 μg/ml INGAP-PP for 24 or 48 h, MTT cell proliferation assay was adopted to survey the dose-response relationship between INGAP-PP and cell proliferation. The mRNA expression of roliferating cell nuclear antigen (PCNA), Cyclin D1, Cdk4, P27, p38MAPK, and JNK in INS-1 cells were examined by RT-PCR, and the protein expression of PCNA was examined by Western blot. The statistical significance was determined by Student's t-test or one-way analysis of variance.
Results: The insulin secreted by islets and the cell viability were increased by INGAP-PP. MTT indicated a dose-response relationship between INGAP-PP and quantity of INS-1 cells, and treatment for 48 h had a stronger effect on cell proliferation than the 24 h. INGAP-PP up-regulated the mRNA expression of PCNA, Cyclin D1, Cdk4 and downregulated P27, p38MAPK, and JNK. Moreover, the protein expression of PCNA was up-regulated by 45% after INGAPPP exposure for 48 h.
Conclusions: INGAP-PP increased the insulin secretion, enhanced the proliferation and might reduce apop tosis of β-cells. The mechanism may contribute to the changed expression of some genes related to cell cycle.