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Islet Inflammation and Ductal Proliferation, a Link to Pancreattisin Type-2 Diabetes?

ABSTRACT: Pancreatitis is more frequent in type 2 diabetes (T2DM) although the underlying cause is unknown. We tested the hypothesis that ongoing beta-cell stress and apoptosis in T2DM induces ductal tree proliferation, particularly the pancreatic duct gland (PDG) compartment, and thus potentially obstructs exocrine outflow. PDG replication was increased two-fold in human pancreas from individuals with T2DM (P<0.01), and was associated with increased pancreatic intraepithelial neoplasia (PanINs) (P<0.05), lesions associated with pancreatic inflammation and with the potential to obstruct pancreatic outflow. Increased PDG replication (p<0.05) in the prediabetic HIP rat model of T2DM was concordant with increased beta-cell stress but preceding metabolic derangement. Moreover, the most abundantly expressed chemokines released by the islets in response to beta-cell stress in T2DM, CXCL1, 4 and 10, induced proliferation in human pancreatic ductal epithelium (p<0.05). Also, the diabetes medications that are reported as potential modifiers for the risk of pancreatitis in T2DM modulated PDG proliferation accordingly. We conclude that chronic stimulation and proliferation of the PDG compartment of the pancreas in response to islet inflammation in T2DM is a novel mechanism that serves as a link to the increased risk for pancreatitis in T2DM and may potentially be modified by currently available diabetes therapy.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE90779 | GEO | 2016/12/02

SECONDARY ACCESSION(S): PRJNA355882

REPOSITORIES: GEO

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Project description:Objective: Homozygous loss-of-function mutations in the gene coding for the homeobox transcription factor (TF) PDX1 leads to pancreatic agenesis, whereas heterozygous mutations can cause Maturity-Onset Diabetes of the Young 4 (MODY4). Although the function of Pdx1 is well studied in pre-clinical models during insulin-producing β-cell development and homeostasis, it remains elusive how this TF controls human pancreas development by regulating a downstream transcriptional program. Furthermore, many studies reported the association between single nucleotide polymorphisms (SNPs) and T2DM and it has been shown that islet enhancers are enriched in T2DM-associated SNPs. Whether regions, harboring T2DM-associated SNPs are PDX1 bound and active at the pancreatic progenitor stage has not been reported so far. Methods: In this study, we have generated a novel induced pluripotent stem cell (iPSC) line that efficiently differentiates into human pancreatic progenitors (PPs). Furthermore, PDX1 and H3K27ac chromatin immunoprecipitation sequencing (ChIP-seq) was used to identify PDX1 transcriptional targets and active enhancer and promoter regions. To address potential differences in the function of PDX1 during development and adulthood, we compared PDX1 binding profiles from PPs and adult islets. Moreover, combining ChIP-seq and GWAS meta-analysis data we identified T2DM-associated SNPs in PDX1 binding sites and active chromatin regions. Results: ChIP-seq for PDX1 revealed a total of 8088 PDX1-bound regions that map to 5664 genes in iPSC-derived PPs. The PDX1 target regions included important pancreatic TFs, such as PDX1 itself, RFX6, HNF1B and MEIS1, which were activated during the differentiation process as revealed by the active mono-acetylated chromatin mark H3K27ac and mRNA expression profiling, suggesting that auto-regulatory feedback regulation maintains PDX1 expression and initiates a pancreatic TF program. Remarkably, we identified several PDX1 target genes that have not been reported in human so far, including RFX3, required for ciliogenesis and endocrine differentiation in mouse, and the ligand for the Notch receptor, DLL1, which is important for endocrine induction and tip-trunk patterning. The comparison of PDX1 profiles from PPs and adult human islets identified sets of stage-specific target genes, associated with early pancreas development and adult β-cell function. Furthermore, we found an enrichment of T2DM-associated SNPs in active chromatin regions from iPSC-derived PPs. Two of these SNPs fall into PDX1 occupied sites that are located in the intronic regions of TCF7L2 and HNF1B. Both of these genes are key transcriptional regulators of endocrine induction and mutations in cis-regulatory regions predispose to diabetes. Conclusions: Our data provides stage-specific target genes of PDX1 during in vitro differentiation of stem cells into pancreatic progenitors that could be useful to identify pathways and molecular targets that predispose for diabetes. In addition, we show that T2DM-associated SNPs are enriched in active chromatin regions at the pancreatic progenitor stage, suggesting that the susceptibility to T2DM might originate from imperfect execution of a β-cell developmental program.

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Islet Inflammation and Ductal Proliferation, a Link to Pancreattisin Type-2 Diabetes?

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