19 research outputs found
Characterization of Ī±-gustducin
Aims/Introduction: Taste receptors, T1rs and T2rs, and the tasteāselective Gāprotein, Ī±āgustducin, are expressed outside the tasteāsensing system, such as enteroendocrine L cells. Here, we examined whether Ī±āgustducin also affects nutrition sensing and insulin secretion by pancreatic Ī²ācells.
Materials and Methods: The expression of Ī±āgustducin and taste receptors was evaluated in Ī²ācell lines, and in rat and mouse islets either by quantitative polymerase chain reaction or fluorescence immunostaining. The effects of Ī±āgustducin knockdown on insulin secretion and on cyclic adenosine monophosphate and intracellular Ca2+ levels in rat INSā1 cells were estimated. Sucralose (taste receptor agonist)āinduced insulin secretion was investigated in INSā1 cells with Ī±āgustducin suppression and in islets from mouse disease models.
Results: The expression of Tas1r3 and Ī±āgustducin was confirmed in Ī²ācell lines and pancreatic islets. Basal levels of cyclic adenosine monophosphate, intracellular calcium and insulin secretion were significantly enhanced with Ī±āgustducin knockdown in INSā1 cells. The expression of Ī±āgustducin was decreased in highāfat dietāfed mice and in diabetic db/db mice. Sucraloseāinduced insulin secretion was not attenuated in INSā1 cells with Ī±āgustducin knockdown or in mouse islets with decreased expression of Ī±āgustducin.
Conclusions: Ī±āGustducin is involved in the regulation of cyclic adenosine monophosphate, intracellular calcium levels and insulin secretion in pancreatic Ī²ācells in a manner independent of taste receptor signaling. Ī±āGustducin might play a novel role in Ī²ācell physiology and the development of type 2 diabetes
A map of open chromatin in human pancreatic islets
Tissue-specific transcriptional regulation is central to human disease(1). To identify regulatory DNA active in human pancreatic islets, we profiled chromatin by formaldehyde-assisted isolation of regulatory elements(2-4) coupled with high-throughput sequencing (FAIRE-seq). We identified similar to 80,000 open chromatin sites. Comparison of FAIRE-seq data from islets to that from five non-islet cell lines revealed similar to 3,300 physically linked clusters of islet-selective open chromatin sites, which typically encompassed single genes that have islet-specific expression. We mapped sequence variants to open chromatin sites and found that rs7903146, a TCF7L2 intronic variant strongly associated with type 2 diabetes(5), is located in islet-selective open chromatin. We found that human islet samples heterozygous for rs7903146 showed allelic imbalance in islet FAIRE signals and that the variant alters enhancer activity, indicating that genetic variation at this locus acts in cis with local chromatin and regulatory changes. These findings illuminate the tissue-specific organization of cis-regulatory elements and show that FAIRE-seq can guide the identification of regulatory variants underlying disease susceptibility
Glucocorticoid receptor-NECAB1 axis can negatively regulate insulin secretion in pancreatic Ī²-cells
Abstract The mechanisms of impaired glucose-induced insulin secretion from the pancreatic Ī²-cells in obesity have not yet been completely elucidated. Here, we aimed to assess the effects of adipocyte-derived factors on the functioning of pancreatic Ī²-cells. We prepared a conditioned medium using 3T3-L1 cell culture supernatant collected at day eight (D8CM) and then exposed the rat pancreatic Ī²-cell line, INS-1D. We found that D8CM suppressed insulin secretion in INS-1D cells due to reduced intracellular calcium levels. This was mediated by the induction of a negative regulator of insulin secretionāNECAB1. LCāMS/MS analysis results revealed that D8CM possessed steroid hormones (cortisol, corticosterone, and cortisone). INS-1D cell exposure to cortisol or corticosterone increased Necab1 mRNA expression and significantly reduced insulin secretion. The increased expression of Necab1 and reduced insulin secretion effects from exposure to these hormones were completely abolished by inhibition of the glucocorticoid receptor (GR). NECAB1 expression was also increased in the pancreatic islets of db/db mice. We demonstrated that the upregulation of NECAB1 was dependent on GR activation, and that binding of the GR to the upstream regions of Necab1 was essential for this effect. NECAB1 may play a novel role in the adipoinsular axis and could be potentially involved in the pathophysiology of obesity-related diabetes mellitus
Table_1_Lipid droplet accumulation in Ī² cells in patients with type 2 diabetes is associated with insulin resistance, hyperglycemia and Ī² cell dysfunction involving decreased insulin granules.docx
Background and objectivePancreatic fat is a form of ectopic fat. Lipid droplets (LDs) are also observed in Ī² cells; however, the pathophysiological significance, especially for Ī² cell function, has not been elucidated. Our aim was to assess LD accumulation in Ī² cells in various stages of glucose intolerance and to clarify its relationship with clinical and histological parameters.MethodsWe examined 42 Japanese patients who underwent pancreatectomy. The BODIPY493/503-positive (BODIPY-positive) area in Ī² cells was measured in pancreatic sections from 32 patients. The insulin granule numbers were counted in an additional 10 patients using electron microscopy.ResultsThe BODIPY-positive area in Ī² cells in preexisting type 2 diabetes patients was higher than that in normal glucose tolerance patients (p = 0.031). The BODIPY-positive area in Ī² cells was positively correlated with age (r = 0.45, p = 0.0097), HbA1c (r = 0.38, p = 0.0302), fasting plasma glucose (r = 0.37, p = 0.045), and homeostasis model assessment insulin resistance (r = 0.41, p = 0.049) and negatively correlated with an increase in the C-peptide immunoreactivity level by the glucagon test (r = -0.59, p = 0.018). The ratio of mature insulin granule number to total insulin granule number was reduced in the patients with rich LD accumulation in Ī² cells (p = 0.039).ConclusionsType 2 diabetes patients had high LD accumulation in Ī² cells, which was associated with insulin resistance, hyperglycemia, aging and Ī² cell dysfunction involving decreased mature insulin granules.</p
A map of open chromatin in human pancreatic islets
Tissue-specific transcriptional regulation is central to human disease(1). To identify regulatory DNA active in human pancreatic islets, we profiled chromatin by formaldehyde-assisted isolation of regulatory elements(2-4) coupled with high-throughput sequencing (FAIRE-seq). We identified similar to 80,000 open chromatin sites. Comparison of FAIRE-seq data from islets to that from five non-islet cell lines revealed similar to 3,300 physically linked clusters of islet-selective open chromatin sites, which typically encompassed single genes that have islet-specific expression. We mapped sequence variants to open chromatin sites and found that rs7903146, a TCF7L2 intronic variant strongly associated with type 2 diabetes(5), is located in islet-selective open chromatin. We found that human islet samples heterozygous for rs7903146 showed allelic imbalance in islet FAIRE signals and that the variant alters enhancer activity, indicating that genetic variation at this locus acts in cis with local chromatin and regulatory changes. These findings illuminate the tissue-specific organization of cis-regulatory elements and show that FAIRE-seq can guide the identification of regulatory variants underlying disease susceptibility
A map of open chromatin in human pancreatic islets
Tissue-specific transcriptional regulation is central to human disease(1). To identify regulatory DNA active in human pancreatic islets, we profiled chromatin by formaldehyde-assisted isolation of regulatory elements(2-4) coupled with high-throughput sequencing (FAIRE-seq). We identified similar to 80,000 open chromatin sites. Comparison of FAIRE-seq data from islets to that from five non-islet cell lines revealed similar to 3,300 physically linked clusters of islet-selective open chromatin sites, which typically encompassed single genes that have islet-specific expression. We mapped sequence variants to open chromatin sites and found that rs7903146, a TCF7L2 intronic variant strongly associated with type 2 diabetes(5), is located in islet-selective open chromatin. We found that human islet samples heterozygous for rs7903146 showed allelic imbalance in islet FAIRE signals and that the variant alters enhancer activity, indicating that genetic variation at this locus acts in cis with local chromatin and regulatory changes. These findings illuminate the tissue-specific organization of cis-regulatory elements and show that FAIRE-seq can guide the identification of regulatory variants underlying disease susceptibility
The HNF-1 target collectrin controls insulin exocytosis by SNARE complex formation
Defective glucose-stimulated insulin secretion is the main cause of hyperglycemia in type 2 diabetes mellitus. Mutations in HNF-1alpha cause a monogenic form of type 2 diabetes, maturity-onset diabetes of the young (MODY), characterized by impaired insulin secretion. Here we report that collectrin, a recently cloned kidney-specific gene of unknown function, is a target of HNF-1alpha in pancreatic beta cells. Expression of collectrin was decreased in the islets of HNF-1alpha (-/-) mice, but was increased in obese hyperglycemic mice. Overexpression of collectrin in rat insulinoma INS-1 cells or in the beta cells of transgenic mice enhanced glucose-stimulated insulin exocytosis, without affecting Ca(2+) influx. Conversely, suppression of collectrin attenuated insulin secretion. Collectrin bound to SNARE complexes by interacting with snapin, a SNAP-25 binding protein, and facilitated SNARE complex formation. Therefore, collectrin is a regulator of SNARE complex function, which thereby controls insulin exocytosis