Transcriptome comparison of mouse pancreatic islets cultured at low vs high ambient glucose
ABSTRACT: Islets are known to respond to changes in ambient glucose. To quantify the transcriptome-wide changes in ambient glucose, we compared transcriptome of islets exposed to low and high glucose. Isolated islets from wild type male mice. Islets from adult males were pooled, cultured overnight in RPMI containing 11 mM glucose. The next day, all islets were starved in RPMI containing 2.8 mM glucose for 2 hours before stimulation with 2.8 mM glucose or 16.8 mM glucose for 12 hours. Islets were lysed in Trizol for RNA isolation and library construction.
Project description:Islets are known to respond to changes in ambient glucose. To quantify the transcriptome-wide changes in ambient glucose, we compared transcriptome of islets exposed to low and high glucose. Isolated islets from wild type male mice. Islets from adult males were pooled, cultured overnight in RPMI containing 11 mM glucose. The next day, all islets were starved in RPMI containing 2.8 mM glucose for 2 hours before stimulation with 2.8 mM glucose or 16.8 mM glucose for 12 hours. Islets were lysed in Trizol for RNA isolation and library construction.
Project description:Mitochondria and NADPH oxidase are important sources of reactive oxygen species in particular the superoxide radical (ROS) in pancreatic islets. These molecules derived from molecular oxygen are involved in pancreatic ?-cells signaling and control of insulin secretion. We examined the involvement of ROS produced through NADPH oxidase in the leucine- and/or glucose-induced insulin secretion by pancreatic islets from fed or 48-hour fasted rats. Glucose-stimulated insulin secretion (GSIS) in isolated islets was evaluated at low (2.8 mM) or high (16.7 mM) glucose concentrations in the presence or absence of leucine (20 mM) and/or NADPH oxidase inhibitors (VAS2870-20 ?M or diphenylene iodonium-DPI-5 ?M). ROS production was determined in islets treated with dihydroethidium (DHE) or MitoSOX Red reagent for 20 min and dispersed for fluorescence measurement by flow cytometry. NADPH content variation was examined in INS-1E cells (an insulin secreting cell line) after incubation in the presence of glucose (2.8 or 16.7 mM) and leucine (20 mM). At 2.8 mM glucose, VAS2870 and DPI reduced net ROS production (by 30%) and increased GSIS (by 70%) in a negative correlation manner (r = -0.93). At 16.7 mM glucose or 20 mM leucine, both NADPH oxidase inhibitors did not alter insulin secretion neither net ROS production. Pentose phosphate pathway inhibition by treatment with DHEA (75 ?M) at low glucose led to an increase in net ROS production in pancreatic islets from fed rats (by 40%) and induced a marked increase (by 144%) in islets from 48-hour fasted rats. The NADPH/NADP+ ratio was increased when INS-1E cells were exposed to high glucose (by 4.3-fold) or leucine (by 3-fold). In conclusion, increased ROS production through NADPH oxidase prevents the occurrence of hypoglycemia in fasting conditions, however, in the presence of high glucose or high leucine levels, the increased production of NADPH and the consequent enhancement of the activity of the antioxidant defenses mitigate the excess of ROS production and allow the secretory process of insulin to take place.
Project description:Maternal low-protein diet increases the susceptibility of offspring to type 2 diabetes. An insult to the pancreas during development can have long-term consequences on ?-cell mass and function. Because nutrients and growth factors signaling converge on mTOR, we hypothesized that mTOR plays a central role in ?-cell programming during fetal development. In this study, we revealed that newborns of dams exposed to low-protein diet (LP0.5) throughout pregnancy exhibited decreased insulin levels, ?-cell fraction, and mTOR signaling. Adult LP0.5 offspring demonstrated enhanced insulin sensitivity but remained glucose intolerant due to an insulin secretory defect and not reduced ?-cell mass. The insulin secretory defect was distal to Ca2+ influx, at the level of proinsulin biosynthesis and insulin content. LP0.5 islets exhibited reduced mTOR protein and increased expression of specific microRNAs. The reductions in mTOR protein and insulin secretion in LP0.5 islets were restored to normal by blockade of microRNAs 199a-3p and 342. Finally, transient activation of mTORC1 signaling in ?-cells during the last week of pregnancy rescued the neonatal ?-cell fraction defect and metabolic abnormalities in LP0.5 mice. These findings identify a major role of microRNAs and mTOR in ?-cell programing by maternal low-protein diet. To investigate which microRNAs are altered in islets isolated from 2-3 months old male offspring of dams fed low-protein diet (LP0.5) or control diet throughout pregnancy Pancreatic islets were isolated from 2-3 months old male offspring of dams fed low-protein diet (LP0.5) or control diet throughout pregnancy. Islets were isolated by collagenase digestion. The pancreas was perfused via the common duct with 1 mg/ml collagenase XI (Sigma-Aldrich) in HBSS (Life Technologies). Pancreatic digestion was carried out at 37 °C for 15 min, after which cold HBSS with 2.5% FBS (Life Technologies) was added. The suspension was centrifuged at 1000 rpm for 30s, washed 3 times with HBSS with 2.5% FBS, resuspended in RPMI complete media (RPMI 1640 with 5 mM Glucose, 10% FBS,100 IU/ml penicillin, 100 g/ml streptomycin) and poured onto a 70 µm cell strainer (BD Falcon, BD Biosciences). Islets were rinsed and handpicked. Islets were allowed to recover overnight in RPMI complete media before RNA isolation using MirVana Kit (Life Technologies).
Project description:The precise role of AMP-activated protein kinase (AMPK), a target of metformin, in pancreatic ? cells remains controversial, even though metformin was recently shown to enhance the expression of incretin receptors (GLP-1 and GIP receptors) in pancreatic ? cells. In this study, we investigated the effect of AMPK in the regulation of incretin receptors expression in pancreatic islets. The phosphorylation of AMPK in the mouse islets was decreased by increasing glucose concentrations. We showed the expression of incretin receptors in bell-shaped response to glucose. Expression of the incretin receptors in the isolated islets showed higher levels under a medium glucose concentration (11.1 mM) than that under a low glucose concentration (2.8 mM), but was suppressed under a high glucose concentration (22.2 mM). Both treatment with an AMPK inhibitor and DN-AMPK expression produced a significant increase of the incretin receptors expression under a low glucose concentration. By contrast, in hyperglycemic db/db islets, the enhancing effect of the AMPK inhibitor on the expression of incretin receptors was diminished under a low glucose concentration. Taken together, AMPK is involved in the regulation of incretin receptors expression in pancreatic islets under a low glucose concentration.
Project description:OBJECTIVES:Glucose-stimulated insulin secretion is a critical function in the regulation of glucose homeostasis, and its deregulation is associated with the development of type 2 diabetes. Here, we performed a genetic screen using islets isolated from the BXD panel of advanced recombinant inbred (RI) lines of mice to search for novel regulators of insulin production and secretion. METHODS:Pancreatic islets were isolated from 36 RI BXD lines and insulin secretion was measured following exposure to 2.8 or 16.7 mM glucose with or without exendin-4. Islets from the same RI lines were used for RNA extraction and transcript profiling. Quantitative trait loci (QTL) mapping was performed for each secretion condition and combined with transcriptome data to prioritize candidate regulatory genes within the identified QTL regions. Functional studies were performed by mRNA silencing or overexpression in MIN6B1 cells and by studying mice and islets with beta-cell-specific gene inactivation. RESULTS:Insulin secretion under the 16.7 mM glucose plus exendin-4 condition was mapped significantly to a chromosome 2 QTL. Within this QTL, RNA-Seq data prioritized Crat (carnitine O-acetyl transferase) as a strong candidate regulator of the insulin secretion trait. Silencing Crat expression in MIN6B1 cells reduced insulin content and insulin secretion by ?30%. Conversely, Crat overexpression enhanced insulin content and secretion by ?30%. When islets from mice with beta-cell-specific Crat inactivation were exposed to high glucose, they displayed a 30% reduction of insulin content as compared to control islets. We further showed that decreased Crat expression in both MIN6B1 cells and pancreatic islets reduced the oxygen consumption rate in a glucose concentration-dependent manner. CONCLUSIONS:We identified Crat as a regulator of insulin secretion whose action is mediated by an effect on total cellular insulin content; this effect also depends on the genetic background of the RI mouse lines. These data also show that in the presence of the stimulatory conditions used the insulin secretion rate is directly related to the insulin content.
Project description:The influence of down-regulation of protein kinase C on glucose-induced insulin secretion was studied. A 22-24 h exposure of mouse pancreatic islets to the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA; 0.16 microM) in RPMI 1640 culture medium (8.3 mM-glucose, 0.43 mM-Ca2+) abolished TPA (0.16 microM)-induced insulin secretion and led to a potentiation of phase 1 and a decrease in phase 2 of glucose-induced insulin secretion. Thus, although the total insulin release during 40 min of perfusion with glucose (16.7 mM) (45-85 min) was unaffected, the percentage released during phase 1 (45-55 min) was increased from 12.9 +/- 1.5 (4)% in controls to 35.8 +/- 3.9 (4)% in TPA-treated islets (P less than 0.01), and the percentage released during phase 2 (65-85 min) was decreased from 63.2 +/- 3.9 (4)% to 35.3 +/- 1.4 (4)% (P less than 0.005). In contrast, TPA exposure in TCM 199 medium (5.5 mM-glucose, 1.26 mM-Ca2+) caused a total abolition of both phases 1 and 2 of glucose-induced secretion. However, inclusion of the alpha 2-adrenergic agonists adrenaline (10 microM) or clonidine (10 microM), or lowering of the Ca2+ concentration in TCM 199 during down-regulation, preserved and potentiated phase 1 of glucose-induced secretion. Furthermore, perifusion of islets in the presence of staurosporine (1 microM), an inhibitor of protein kinase C, potentiated phase 1 and inhibited phase 2 of glucose-induced secretion. In addition, down-regulation of protein kinase C potentiated phase 1 and inhibited phase 2 of carbamoylcholine (100 microM)-induced insulin secretion at 3.3 mM-glucose, and abolished the potentiating effect of carbamoylcholine (100 microM) at 16.7 mM-glucose. These results substantiate a role for protein kinase C in insulin secretion, and suggest that protein kinase C inhibits phase 1 and stimulates phase 2 of both glucose-induced and carbamoylcholine-induced insulin secretion.
Project description:We set out to identify differences in the transcriptome influenced by knockout of the transcription factor T-cell factor 7 (Tcf7) in mouse islets. Furthermore, we wanted to determine if metabolic stress (age,diet) influences these changes. Therefore, we compared the islet transcriptome from WT and Tcf7-/- mice both at a young age (8 weeks old) fed a low fat (10%) diet, versus WT and Tcf7-/- mice at an old age (20 weeks old) on a high-fat (45%) diet. Tcf7-/- mice and littermate wildtype mice were compared. Mice were placed on either a low-fat (10%) or high-fat (45%) diet at weeks of age. For the low fat group, islets from 8 week old mice were isolated and total RNA was extracted with Trizol. For the high fat group, islets from 20 week old mice were isolated and total RNA was extracted with Trizol.
Project description:Observing different kinetics of nutrient-induced insulin secretion in fresh and cultured islets under the same condition we compared parameters of stimulus secretion coupling in freshly isolated and 22-h-cultured NMRI mouse islets. Stimulation of fresh islets with 30 mM glucose after perifusion without nutrient gave a continuously ascending secretion rate. In 22-h-cultured islets the same protocol produced a brisk first phase followed by a moderately elevated plateau, a pattern regarded to be typical for mouse islets. This was also the response of cultured islets to the nutrient secretagogue alpha-ketoisocaproic acid, whereas the secretion of fresh islets increased similarly fast but remained strongly elevated. The responses of fresh and cultured islets to purely depolarizing stimuli (tolbutamide or KCl), however, were closely similar. Signs of apoptosis and necrosis were rare in both preparations. In cultured islets, the glucose-induced rise of the cytosolic Ca2+ concentration started from a lower value and was larger as was the increase of the ATP/ADP ratio. The prestimulatory level of mitochondrial reducing equivalents, expressed as the NAD(P)H/FAD fluorescence ratio, was lower in cultured islets, but increased more strongly than in fresh islets. When culture conditions were modified by replacing RPMI with Krebs-Ringer medium and FCS with BSA, the amount of released insulin varied widely, but the kinetics always showed a predominant first phase. In conclusion, the secretion kinetics of fresh mouse islets is more responsive to variations of nutrient stimulation than cultured islets. The more uniform kinetics of the latter may be caused by a different use of endogenous metabolites.
Project description:Murine islets were isolated from 8-week-old WT and βRapKO mice and initially recovered in 1640 RPMI supplemented with 10% serum, 11.1mM glucose overnight. Then islets were transfected with Lenti-GFP or Lenti-Dnmt3a for 24 hours, following cultured in 1640 RPMI medium for 48 hours.Islets were harvested and stored in -80°C for preparation for RNA sequencing. Overall design: Transcriptome of three groups: WT, βRapKO, βRapKO+LvDnmt3a
Project description:The metabolism of endogenous nutrients was examined in pancreatic islets of control and Goto-Kakizaki (GK) rats. At the ultrastructural level, no glycogen was found in the islet cells of GK rats, a situation similar to that prevailing in normal islets. Likewise, by measuring the output of L-lactate from islets first incubated at 16.7 mM D-glucose and then at 2.8 mM D-glucose, no evidence of glycogenolysis was found in the islets of GK rats. The production of NH4+ and that of 14CO2 from islets prelabelled with either L-[U-14C]glutamine or [U-14C]palmitate were higher, however, in GK than in control rats. The changes in NH4+ and 14CO2 production evoked by D-glucose, by a non-metabolized analogue of L-leucine (2-amino-bicyclo[2,2,1]heptane-2-carboxylic acid; BCH) and by 3-phenylpyruvate were qualitatively comparable in control and GK rats. The secretory response to these three secretagogues was severely decreased in the islets of GK rats. This coincided with an impaired enhancing action of D-glucose on the conversion of [2-3H]glycerol into 3HOH. It is concluded that the catabolism of endogenous amino and fatty acids in islets is greater in GK than in control rats, especially at low D-glucose concentration. This may account, in part at least, for the altered secretory response to BCH and 3-phenylpyruvate. For glucose-induced insulin release, however, an impaired acceleration of the glycerol phosphate shuttle apparently also participates in the secretory defect.