Gastrin Stimulates Gene Expression in Diabetic but Not in Normal Human Islets

Presentation Number: OR42-3
Date of Presentation: April 3rd, 2017

Ayelet Lenz*1, Kevin George Ferreri2 and Fouad R Kandeel1
1Diabetes & Metabolic Research Institute, Beckman Research Institute of City of Hope, Duarte, CA, 2City of Hope, Duarte, CA

Abstract

During embryonic development of the islets of Langerhans gastrin releasing G cells are differentiated from Neurog3+ cells but disappear shortly after birth [1]. In addition, gastrin is detected in a low percentage of delta cells and beta cells in islets isolated from donors with type 2 diabetes (T2D)but not in healthy adult islets [2]. These data indicate a role for gastrin during differentiation of islet cells in the pancreas. Furthermore, there have been many reports of a gastrin effect on adult beta cell mass through proliferation and/or differentiation of duct cells into insulin producing cells [3-9]. However, the reports have been inconsistent and the mechanism behind these observations remains poorly understood. To investigate a possible gastrin effect on human islets, the gastrin receptor, CCKBR, was first localized in adult human islets by immunofluorescence staining. Previous reports indicated that CCKBR is located on both delta and alpha cells, however we observed co-localization of CCKBR with somatostatin expressing cells in pancreas slices from 10 Donors (HbA1c 4.7-10.4), but did not detect any co-localization with glucagon, indicating that CCKBR is expressed only in delta cells. Next the effect of gastrin treatment on human islets was examined. Isolated human islets from 11 Donors (HbA1c 5.2-10.4) were treated with 0nM (untreated, UTR) or 100nM gastrin for 48 hours and gene expression was analyzed by qPCR. The results showed that the effect of gastrin was dependent on the HbA1c level of the islet donor, with HbA1c˃6.0 (n=5) showing a significant increase in insulin (2.0-fold over UTR, P<0.0001), somatostatin (1.8-fold over UTR, P<0.0001) and glucagon (1.4 fold over UTR, P<0.02) transcripts following treatment with 100nM gastrin, but no increase was detected in the HbA1c<6.0 group. In addition, there were significant increases in the transcripts of known beta and delta cell transcription factors MAFA, MNX1, NKX2.2, NKX6.1, PDX1 and HHEX only in the HbA1c˃6.0 group. To confirm that the gastrin response was mediated by CCKBR, islets from a human donor with HbA1c of 9.0 were treated with 100nM gastrin or 100nM gastrin+ 100nM of the CCKBR antagonist YM022. qPCR showed a 2.3-fold increase in insulin transcript levels compared to control islets while insulin transcript levels in islets treated with gastrin and the CCKBR antagonist decreased to 0.76. These data indicate that the gastrin confers its effect on transcription through CCKBR located on delta cells. We postulate that in patients with increased levels of HbA1c gastrin treatment may induce an increase in insulin levels either through transdifferentiation of delta cells into insulin expressing cells or in a manner of cross talk among different cell types. 

 

Nothing to Disclose: AL, KGF, FRK