The nuclear receptor peroxisome proliferator-activated receptor ␥ (PPAR-␥) is an important target in diabetes therapy, but its direct role, if any, in the restoration of islet function has remained controversial. To identify potential molecular mechanisms of PPAR-␥ in the islet, we treated diabetic or glucose-intolerant mice with the PPAR-␥ agonist pioglitazone or with a control. Treated mice exhibited significantly improved glycemic control, corresponding to increased serum insulin and enhanced glucose-stimulated insulin release and Ca 2؉ responses from isolated islets in vitro. This improved islet function was at least partially attributed to significant upregulation of the islet genes Irs1, SERCA, Ins1/2, and Glut2 in treated animals. The restoration of the Ins1/2 and Glut2 genes corresponded to a two-to threefold increase in the euchromatin marker histone H3 dimethyl-Lys4 at their respective promoters and was coincident with increased nuclear occupancy of the islet methyltransferase Set7/9. Analysis of diabetic islets in vitro suggested that these effects resulting from the presence of the PPAR-␥ agonist may be secondary to improvements in endoplasmic reticulum stress. Consistent with this possibility, incubation of thapsigargin-treated INS-1 ␤ cells with the PPAR-␥ agonist resulted in the reduction of endoplasmic reticulum stress and restoration of Pdx1 protein levels and Set7/9 nuclear occupancy. We conclude that PPAR-␥ agonists exert a direct effect in diabetic islets to reduce endoplasmic reticulum stress and enhance Pdx1 levels, leading to favorable alterations of the islet gene chromatin architecture.Type 2 diabetes mellitus results from a combination of insulin resistance and progressive islet dysfunction (46). In many individuals, ␤-cell failure may precede the clinical diagnosis of diabetes, and landmark studies such as the United Kingdom Prospective Diabetes Study have shown a continued decrement in ␤-cell function despite treatment intervention with sulfonylureas, metformin, and insulin (52). Thiazolidinediones are orally active agents used in the treatment of type 2 diabetes that act as agonists for the nuclear transcription factor peroxisome proliferator-activated receptor ␥ (PPAR-␥) (60). Although thiazolidinediones are classically thought to act as peripheral insulin sensitizers, there is growing evidence from studies of human and animal models that these agents may also act to preserve and/or enhance ␤-cell function in the setting of progressive type 2 diabetes and insulin resistance (3, 12). PPAR-␥ is known to be expressed in the pancreatic islet (8, 48), and PPAR-responsive elements have been identified in the promoters of genes involved in glucose-stimulated insulin secretion, including Glut2, Gck, and Pdx1 (16,21,26,27,33). Reports from studies of ␤-cell lines, rodent models of progressive type 2 diabetes, and humans at risk for type 2 diabetes suggest that PPAR-␥ agonist administration leads to preservation of islet mass and function (10,13,18,22,25,33,57,58).Whereas the studies noted ab...

Background & Aims-The mature pancreatic acinar cell is dedicated to the production of very large amounts of digestive enzymes. The early stages of pancreatic development require the Rbpjform of the trimeric transcription factor complex PTF1 (PTF1-J). As acinar development commences, Rbpjl gradually replaces Rbpj; in the mature pancreas, PTF1 contains Rbpjl (PTF1-L). We investigated whether PTF1-L controls the expression of genes that complete the final stage of acinar differentiation.

Maintenance of cell type identity is crucial for health, yet little is known of the regulation that sustains the long-term stability of differentiated phenotypes. To investigate the roles that key transcriptional regulators play in adult differentiated cells, we examined the effects of depletion of the developmental master regulator PTF1A on the specialized phenotype of the adult pancreatic acinar cell in vivo. Transcriptome sequencing and chromatin immunoprecipitation sequencing results showed that PTF1A maintains the expression of genes for all cellular processes dedicated to the production of the secretory digestive enzymes, a highly attuned surveillance of unfolded proteins, and a heightened unfolded protein response (UPR). Control by PTF1A is direct on target genes and indirect through a ten-member transcription factor network. Depletion of PTF1A causes an imbalance that overwhelms the UPR, induces cellular injury, and provokes acinar metaplasia. Compromised cellular identity occurs by derepression of characteristic stomach genes, some of which are also associated with pancreatic ductal cells. The loss of acinar cell homeostasis, differentiation, and identity is directly relevant to the pathologies of pancreatitis and pancreatic adenocarcinoma. Loss of cellular identity has long been associated with tissue injury and a first step in cancer progression (for examples, see references 1 and 2). Maintenance of a specific cellular phenotype depends on the continued transcription of cell-type-specific genes, largely through open chromatin architecture (3, 4) maintained by a small group of lineage-restricted DNA-binding transcription factors (TFs) (5, 6) that establish a unique transcriptional regulatory network (7). Many physiologic or pathophysiologic perturbations can affect the differentiated state of a cell quantitatively, but fewer affect the state of differentiation qualitatively. Qualitative changes involve the acquisition of characteristics of another cell type (or types), often defined by one or a few cell-specific markers, in addition to the diminution of the original phenotype. Despite progress with cellular reprogramming (for example, see reference 8), the molecular and genetic mechanisms that maintain cellular identity within the context of adult organs remain incompletely understood. In this report, we show that inactivation of the transcriptional regulatory gene Ptf1a in adult pancreatic acinar cells has pleiotropic effects on gene expression that cause quantitative and multigene qualitative changes of acinar differentiation.The acinar cell of the pancreas has been an informative model of terminal cellular differentiation (9). Common cellular processes are greatly exaggerated in support of the prodigious synthesis, processing, storage, and exocytosis of secretory proteins. The pancreatic acinar cell has the most ribosomes (10) and the highest rate of protein synthesis (11) of any mammalian somatic cell; it synthesizes, stores, and secretes its weight in protein daily. Specialized cellular functions ...

We have determined the cistrome and transcriptome for the nuclear receptor liver receptor homolog-1 (LRH-1) in exocrine pancreas. Chromatin immunoprecipitation (ChIP)-seq and RNA-seq analyses reveal that LRH-1 directly induces expression of genes encoding digestive enzymes and secretory and mitochondrial proteins. LRH-1 cooperates with the pancreas transcription factor 1-L complex (PTF1-L) in regulating exocrine pancreas-specific gene expression. Elimination of LRH-1 in adult mice reduced the concentration of several lipases and proteases in pancreatic fluid and impaired pancreatic fluid secretion in response to cholecystokinin. Thus, LRH-1 is a key regulator of the exocrine pancreas-specific transcriptional network required for the production and secretion of pancreatic fluid.

OBJECTIVE-The activation of ␤-cell genes, particularly of those encoding preproinsulin, requires an appropriate euchromatin (or "open") DNA template characterized by hypermethylation of Lys4 of histone H3. We hypothesized that this modification is maintained in islet ␤-cells by the action of the histone methyltransferase Set7/9. RESEARCH DESIGN AND METHODS-To identify the role of Set7/9, we characterized its expression pattern and gene regulation and studied its function using RNA interference in both cell lines and primary mouse islets.RESULTS-Within the pancreas, Set7/9 protein shows striking specificity for islet cells, including ␣-and ␤-cells, as well as occasional cells within ducts. Consistent with these findings, the Set7/9 gene promoter contained an islet-specific enhancer located between Ϫ5,768 and Ϫ6,030 base pairs (relative to the transcriptional start site) that exhibited Pdx1-responsive activation in ␤-cells. To study Set7/9 function, we depleted insulinoma cells and primary mouse islets of Set7/9 protein using siRNA. Following siRNA treatment, we observed striking repression of genes involved in glucose-stimulated insulin secretion, including Ins1/2, Glut2, and MafA. These changes in transcription were accompanied by loss of dimethylated H3 Lys4 and RNA polymerase II recruitment, particularly at the Ins1/2 and Glut2 genes. Consistent with these data, depletion of Set7/9 in islets led to defects in glucose-stimulated Ca 2ϩ mobilization and insulin secretion.CONCLUSIONS-We conclude that Set7/9 is required for normal ␤-cell function, likely through the maintenance of euchromatin structure at genes necessary for glucose-stimulated insulin secretion. Diabetes 58: [185][186][187][188][189][190][191][192][193] 2009