Cystic fibrosis-related diabetes (CFRD) is a common complication for patients with cystic fibrosis (CF), a disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). The cause of CFRD is unclear, but a commonly observed reduction in first-phase insulin secretion suggests defects at the beta cell level. Here we aimed to examine alpha and beta cell function in the Cftr tm1 EUR/F508del mouse model (C57BL/6J), which carries the most common human mutation in CFTR, the F508del mutation. CFTR expression, beta cell mass, insulin granule distribution, hormone secretion and single cell capacitance changes were evaluated using islets (or beta cells) from F508del mice and age-matched wild type (WT) mice aged 7–10 weeks. Granular pH was measured with DND-189 fluorescence. Serum glucose, insulin and glucagon levels were measured in vivo, and glucose tolerance was assessed using IPGTT. We show increased secretion of proinsulin and concomitant reduced secretion of C-peptide in islets from F508del mice compared to WT mice. Exocytosis and number of docked granules was reduced. We confirmed reduced granular pH by CFTR stimulation. We detected decreased pancreatic beta cell area, but unchanged beta cell number. Moreover, the F508del mutation caused failure to suppress glucagon secretion leading to hyperglucagonemia. In conclusion, F508del mice have beta cell defects resulting in (1) reduced number of docked insulin granules and reduced exocytosis and (2) potential defective proinsulin cleavage and secretion of immature insulin. These observations provide insight into the functional role of CFTR in pancreatic islets and contribute to increased understanding of the pathogenesis of CFRD.
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- Abstract: Diabetes x
- Abstract: Islets x
- Abstract: Insulin x
- Abstract: BetaCells x
- Abstract: Pancreas x
- Abstract: Glucose x
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- Abstract: Hypoglycemia x
- Abstract: Insulinoma x
- Abstract: Glucagon x
- Abstract: Type 1 x
- Abstract: Type 2 x
A Edlund, M Barghouth, M Hühn, M Abels, J S E Esguerra, I G Mollet, E Svedin, A Wendt, E Renström, E Zhang, N Wierup, B J Scholte, M Flodström-Tullberg and L Eliasson
Hans Eickhoff, Teresa Louro, Paulo Matafome, Raquel Seiça and Francisco Castro e Sousa
Excessive or inadequate glucagon secretion promoting hepatic gluconeogenesis and glycogenolysis is believed to contribute to hyperglycemia in patients with type 2 diabetes. Currently, metabolic surgery is an accepted treatment for obese patients with type 2 diabetes and has been shown to improve glycemic control in Goto-Kakizaki (GK) rats, a lean animal model for type 2 diabetes. However, the effects of surgery on glucagon secretion are not yet well established. In this study, we randomly assigned forty 12- to 14-week-old GK rats to four groups: control group (GKC), sham surgery (GKSS), sleeve gastrectomy (GKSG), and gastric bypass (GKGB). Ten age-matched Wistar rats served as a non-diabetic control group (WIC). Glycemic control was assessed before and 4 weeks after surgery. Fasting- and mixed-meal-induced plasma levels of insulin and glucagon were measured. Overall glycemic control improved in GKSG and GKGB rats. Fasting insulin levels in WIC rats were similar to those for GKC or GKSS rats. Fasting glucagon levels were highest in GKGB rats. Whereas WIC, GKC, and GKSS rats showed similar glucagon levels, without any significant meal-induced variation, a significant rise occurred in GKSG and GKGB rats, 30 min after a mixed meal, which was maintained at 60 min. Both GKSG and GKGB rats showed an elevated glucagon:insulin ratio at 60 min in comparison with all other groups. Surprisingly, the augmented post-procedural glucagon secretion was accompanied by an improved overall glucose metabolism in GKSG and GKGB rats. Understanding the role of glucagon in the pathophysiology of type 2 diabetes requires further research.
Junhong Chen, Jing Sun, Michelle E Doscas, Jin Ye, Ashley J Williamson, Yanchun Li, Yi Li, Richard A Prinz and Xiulong Xu
p70 S6 kinase (S6K1) is a serine/threonine kinase that phosphorylates the insulin receptor substrate-1 (IRS-1) at serine 1101 and desensitizes insulin receptor signaling. S6K1 hyperactivation due to overnutrition leads to hyperglycemia and type 2 diabetes. Our recent study showed that A77 1726, the active metabolite of the anti-rheumatoid arthritis (RA) drug leflunomide, is an inhibitor of S6K1. Whether leflunomide can control hyperglycemia and sensitize the insulin receptor has not been tested. Here we report that A77 1726 increased AKTS473/T308 and S6K1T389 phosphorylation but decreased S6S235/236 and IRS-1S1101 phosphorylation in 3T3-L1 adipocytes, C2C12 and L6 myotubes. A77 1726 increased insulin receptor tyrosine phosphorylation and binding of the p85 subunit of the PI-3 kinase to IRS-1. A77 1726 enhanced insulin-stimulated glucose uptake in L6 myotubes and 3T3-L1 adipocytes, and enhanced insulin-stimulated glucose transporter type 4 (GLUT4) translocation to the plasma membrane of L6 cells. Finally, we investigated the anti-hyperglycemic effect of leflunomide on ob/ob and high-fat diet (HFD)-induced diabetes mouse models. Leflunomide treatment normalized blood glucose levels and overcame insulin resistance in glucose and insulin tolerance tests in ob/ob and HFD-fed mice but had no effect on mice fed a normal chow diet (NCD). Leflunomide treatment increased AKTS473/T308 phosphorylation in the fat and muscle of ob/ob mice but not in normal mice. Our results suggest that leflunomide sensitizes the insulin receptor by inhibiting S6K1 activity in vitro, and that leflunomide could be potentially useful for treating patients with both RA and diabetes.
Andréa M Caricilli, Paula H Nascimento, José R Pauli, Daniela M L Tsukumo, Lício A Velloso, José B Carvalheira and Mário J A Saad
The aims of the present study were to investigate the expression of toll-like receptor 2 (TLR2) in muscle and white adipose tissue (WAT) of diet-induced obesity (DIO) mice, and also the effects of its inhibition, with the use of TLR2 antisense oligonucleotide (ASON), on insulin sensitivity and signaling. The expression of TLR2 was increased in muscle and WAT of DIO mice, compared with those that received standard chow. Inhibition of TLR2 in DIO mice, by TLR2 ASON, improved insulin sensitivity and signaling in muscle and WAT. In addition, data show that the inhibition of TLR2 expression prevents the activation of IKBKB, MAPK8, and serine phosphorylation of IRS1 in DIO mice, suggesting that TLR2 is a key modulator of the crosstalk between inflammatory and metabolic pathways. We, therefore, suggest that a selective interference with TLR2 presents an attractive opportunity for the treatment of insulin resistance in obesity and type 2 diabetes.
The incretin hormone glucagon-like peptide 1 (GLP-1) has many effects in the body. It is best known for the ‘incretin effect’, facilitating insulin release from the pancreas under hyperglycaemic conditions. Building on this, GLP-1 mimetics have been developed as a treatment for type 2 diabetes. In the course of monitoring of patients, it has become apparent that GLP-1 mimetics have a range of other physiological effects in the body. In preclinical trials, a substantial body of evidence has been built that these mimetics have neuroprotective and anti-inflammatory effects. GLP-1 also has very similar growth-factor-like properties to insulin, which is presumably the underlying basis of the neuroprotective effects. In preclinical studies of Alzheimer's disease (AD), Parkinson's disease (PD), stroke and other neurodegenerative disorders, it has been shown that most GLP-1 mimetics cross the blood–brain barrier and show impressive neuroprotective effects in numerous studies. In animal models of AD, GLP-1 mimetics such as exendin-4, liraglutide and lixisenatide have shown protective effects in the CNS by reducing β-amyloid plaques, preventing loss of synapses and memory impairments, and reducing oxidative stress and the chronic inflammatory response in the brain. In animal models of PD, exendin-4 showed protection of dopaminergic neurons in the substantia nigra and prevention of dopamine loss in the basal ganglia while preserving motor control. These encouraging findings have spawned several clinical trials, some of which have shown encouraging initial results. Therefore, GLP-1 mimetics show great promise as a novel treatment for neurodegenerative conditions.
Jae Woo Jung, Chihoon Ahn, Sun Young Shim, Peter C Gray, Witek Kwiatkowski and Senyon Choe
Activins and bone morphogenetic proteins (BMPs) share activin type 2 signaling receptors but utilize different type 1 receptors and Smads. We designed AB215, a potent BMP2-like Activin A/BMP2 chimera incorporating the high-affinity type 2 receptor-binding epitope of Activin A. In this study, we compare the signaling properties of AB215 and BMP2 in HEK293T cells and gonadotroph LβT2 cells in which Activin A and BMP2 synergistically induce FSHβ. In HEK293T cells, AB215 is more potent than BMP2 and competitively blocks Activin A signaling, while BMP2 has a partial blocking activity. Activin A signaling is insensitive to BMP pathway antagonism in HEK293T cells but is strongly inhibited by constitutively active (CA) BMP type 1 receptors. By contrast, the potencies of AB215 and BMP2 are indistinguishable in LβT2 cells and although AB215 blocks Activin A signaling, BMP2 has no inhibitory effect. Unlike HEK293T, Activin A signaling is strongly inhibited by BMP pathway antagonism in LβT2 cells but is largely unaffected by CA BMP type 1 receptors. BMP2 increases phospho-Smad3 levels in LβT2 cells, in both the absence and the presence of Activin A treatment, and augments Activin A-induced FSHβ. AB215 has the opposite effect and sharply decreases basal phospho-Smad3 levels and blocks Smad2 phosphorylation and FSHβ induction resulting from Activin A treatment. These findings together demonstrate that while AB215 activates the BMP pathway, it has opposing effects to those of BMP2 on FSHβ induction in LβT2 cells apparently due to its ability to block Activin A signaling.
M. Tepel, S. Bauer, S. Husseini, A. Raffelsiefer and W. Zidek
Cytosolic free sodium concentrations ([Na+]i) in intact platelets from 32 type 2 (non-insulin-dependent) diabetic patients and from 27 age- and sex-matched non-diabetic control subjects were measured with the novel sodium-sensitive fluorescent dye sodium-binding-benzofuran-isophthalate. [Na+]i was significantly higher in platelets from type 2 diabetic patients compared with control subjects (40·6 ± 2·4 vs 32·0 ± 2·0 mmol/l, means ± s.e.m., P<0·03). Both systolic and diastolic blood pressure were significantly elevated in diabetic patients compared with control subjects. Analysis of diabetic patients showed a significant association between [Na+]i and diastolic blood pressure (P =0·026). Stimulation of Na/H exchange by thrombin increased [Na+]i in both groups. After inhibition of Na/K/ATPase by ouabain (1 mmol/l), [Na+]i was significantly increased both in diabetic patients and non-diabetic subjects in a similar way (by 40·2 ± 7·3 and 31·7 ± 5·3 mmol/l respectively). It is concluded that increased [Na+]i in cells from type 2 diabetic patients may be related to hypertension.
Journal of Endocrinology (1993) 138, 565–572
J. M. H. M. Reul, F. R. van den Bosch and E. R. de Kloet
The rat brain contains two receptor systems for corticosterone: the type-I corticosterone-preferring receptor and the classical type-II glucocorticoid receptor. The two receptor populations can be distinguished in binding studies with the 'pure' synthetic glucocorticoid 11β,17β-dihydroxy-6-methyl-17α (1-propynyl)-androsta-1,4,6-trione-3-one (RU 28362). In-vitro autoradiography and quantitative image analysis showed that the type-I receptor was localized almost exclusively in the hippocampus, whereas the type-II receptor extended throughout the brain, with the highest levels in the nucleus paraventricularis, nucleus supraopticus and in the thalamic, amygdaloid, hippocampal and septal regions. Unoccupied type-I and type-II receptor sites, as measured in vitro by cytosol binding of 3H-labelled steroids, displayed a large difference in the rate of appearance after adrenalectomy. The availability of type-I receptors exhibited a marked increase, reaching maximal levels within 4–7 h, and then remained constant until 2 weeks after adrenalectomy. The availability of type-II receptors did not change considerably during the first 24 h after adrenalectomy, but displayed a large increase in capacity during the subsequent 2 weeks. After adrenocortical activation as a consequence of exposure to a novel environment, plasma concentrations of corticosterone increased to reach a peak of 811 nmol/l after 30 min and attained the basal concentration (43 nmol/l) after 240 min. During this time, occupation of type-I receptors increased from 77·8% at 0 min to 97% at 30–60 min and then declined to 84·8% after 240 min. Occupation of the type-II receptors was 28·1% at 0 min, 74·5% after 30 min and 32·8% after 240 min. Injection of dexamethasone (25 μg/100 g body wt) at 08.00 h resulted in suppression of basal plasma concentrations of corticosterone and prevented the circadian-driven rise in circulating corticosterone. Occupation of type-I receptors did not change considerably as a result of injection of dexamethasone, but occupation of type-II receptors was markedly increased till 16.00 h compared with that after injection of vehicle.
It was concluded that the type-I and type-II receptors are not only localized differently in the rat brain, but also exhibit a striking difference in occupation after manipulation of the pituitary-adrenocortical system. The data further support the concept of a type-I receptor-mediated tonic activating influence and a type-II receptor-mediated feedback action of corticosterone on brain function.
J. Endocr. (1987) 115, 459–467
Weixia Han, Chen Wang, Zhifen Yang, Lin Mu, Ming Wu, Nan Chen, Chunyang Du, Huijun Duan and Yonghong Shi
Renal fibrosis is the major pathological characteristic of diabetic nephropathy (DN). Reportedly, increased SIRT1 expression played a renal protective role in animal models of DN. This study was designed to elucidate the molecular mechanisms underlying the protective effects of SRT1720, an SIRT1 activator, against diabetes-induced renal fibrosis. Type 2 diabetic mice (db/db) were treated with SRT1720 (50 mg/kg/day) by gavage for 10 weeks. Renal proximal tubular epithelial cells (HK-2 cells) were treated with high glucose (HG, 30 mM) in the presence or absence of SRT1720 (2.5 µM) for 48 h. We observed that impaired SIRT1 expression and activity were restored by SRT1720 administration in db/db mice as well as in HG-treated HK-2 cells. Moreover, SRT1720 administration improved the renal function, attenuated glomerular hypertrophy, mesangial expansion, glomerulosclerosis and interstitial fibrosis and inhibited TGFB1 and CTGF expressions and nuclear factor κB (NF-KB) activation in db/db mice. Similarly, HG-induced epithelial-to-mesenchymal transformation (EMT) and collagen IV and fibronectin expressions were inhibited in SRT1720-treated HK-2 cells. Mechanistic studies demonstrated that SRT1720 suppressed HIF1A, GLUT1 and SNAIL expressions both in vivo and in vitro. Furthermore, HIF1A or GLUT1 knockdown effectively abrogated HG-induced EMT and collagen IV and fibronectin expressions in HK-2 cells. These findings suggest that SRT1720 prevented diabetes-induced renal fibrosis via the SIRT1/HIF1A/GLUT1/SNAIL pathway.
Jennifer H Stern, Gordon I Smith, Shiuwei Chen, Roger H Unger, Samuel Klein and Philipp E Scherer
Hyperglucagonemia, a hallmark in obesity and insulin resistance promotes hepatic glucose output, exacerbating hyperglycemia and thus predisposing to the development type 2 diabetes. As such, glucagon signaling is a key target for new therapeutics to manage insulin resistance. We evaluated glucagon homeostasis in lean and obese mice and people. In lean mice, fasting for 24 h caused a rise in glucagon. In contrast, a decrease in serum glucagon compared to baseline was observed in diet-induced obese mice between 8 and 24 h of fasting. Fasting decreased serum insulin in both lean and obese mice. Accordingly, the glucagon:insulin ratio was unaffected by fasting in obese mice but increased in lean mice. Re-feeding (2 h) restored hyperglucagonemia in obese mice. Pancreatic perfusion studies confirm that fasting (16 h) decreases pancreatic glucagon secretion in obese mice. Consistent with our findings in the mouse, a mixed meal increased serum glucagon and insulin concentrations in obese humans, both of which decreased with time after a meal. Consequently, fasting and re-feeding less robustly affected glucagon:insulin ratios in obese compared to lean participants. The glucoregulatory disturbance in obesity may be driven by inappropriate regulation of glucagon by fasting and a static glucagon:insulin ratio.