L-type channel antagonists are of therapeutic benefit in the treatment of hyperlipidaemia and insulin resistance. Our aim was to identify L-type voltage-gated Ca2+ channels in white fat adipocytes, and determine if they affect intracellular Ca2+, lipolysis and lipogenesis. We used a multidisciplinary approach of molecular biology, confocal microscopy, Ca2+ imaging and metabolic assays to explore this problem using adipocytes isolated from adult rat epididymal fat pads. CaV1.2, CaV1.3 and CaV1.1 alpha1, beta and alpha2delta subunits were detected at the gene expression level. The CaV1.2 and CaV1.3 alpha1 subunits were identified in the plasma membrane at the protein level. Confocal microscopy with fluorescent antibodies labelled CaV1.2 in the plasma membrane. Ca2+ imaging revealed that the intracellular Ca2+ concentration, [Ca2 +]i was reversibly decreased by removal of extracellular Ca2+, an effect mimicked by verapamil, nifedipine and Co2+, all blockers of L-type channels, whereas the Ca2+ channel agonist BAY-K8644 increased [Ca2+]i. The finding that the magnitude of these effects correlated with basal [Ca2+]i suggests that adipocyte [Ca2+]i is controlled by L-type Ca2+ channels that are constitutively active at the adipocyte depolarized membrane potential. Pharmacological manipulation of L-type channel activity modulated both basal and catecholamine-stimulated lipolysis but not insulin-induced glucose uptake or lipogenesis. We conclude that white adipocytes have constitutively active L-type Ca2+ channels which explains their sensitivity of lipolysis to Ca2+ channel modulators. Our data suggest CaV1.2 as a potential novel therapeutic target in the treatment of obesity.
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- Abstract: Diabetes x
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Olena A Fedorenko, Pawitra Pulbutr, Elin Banke, Nneoma E Akaniro-Ejim, Donna C Bentley, Charlotta S Olofsson, Sue Chan, and Paul A Smith
Yoko Yagishita, Akira Uruno, Dionysios V Chartoumpekis, Thomas W Kensler, and Masayuki Yamamoto
The transcription factor Nrf2 (NF-E2-related factor 2) plays a critical role in oxidative stress responses. Although activation of Nrf2 signaling is known to exert anti-inflammatory effects, the function of Nrf2 in inflammation-mediated autoimmune disorders, such as type 1 diabetes, is not well established. To address the roles of Nrf2 in protection against autoreactive T-cell-induced type 1 diabetes, we used non-obese diabetic (NOD) mice, which are a polygenic model of human type 1 diabetes, to generate a genetic model for assessment of the contribution of Nrf2 activation to prevention and/or treatment of type 1 diabetes. Because Keap1 (Kelch-like ECH-associated protein 1) negatively regulates Nrf2, we used Keap1 gene knockdown driven by either hypomorphic or knockout Keap1 alleles, which enhanced Nrf2 signaling to moderate or excess levels, respectively. Nrf2 activation in the NOD::Keap1 FA/ – mice inhibited T-cell infiltration within or near the islets, ameliorated impairment of insulin secretion and prevented the development of diabetes mellitus. Notably, Nrf2 activation decreased both the plasma interferon-γ (IFN-γ) levels and the IFN-γ-positive cell numbers in the pancreatic islets. The amelioration of diabetes was also observed in the NOD mice with two hypomorphic Keap1 alleles (Keap1 FA/FA) by intermediate activation of Nrf2. Both NOD::Keap1 FA/ – and NOD::Keap1 FA/FA mice had a decreased incidence of diabetes mellitus, demonstrating that activation of Nrf2 signaling prevented the onset of type 1 diabetes mellitus in NOD mice. Thus, Nrf2 appears to be a potential target for the prevention and treatment of type 1 diabetes.
Thomas H Claus, Clark Q Pan, Joanne M Buxton, Ling Yang, Jennifer C Reynolds, Nicole Barucci, Michael Burns, Astrid A Ortiz, Steve Roczniak, James N Livingston, Kevin B Clairmont, and James P Whelan
Type 2 diabetes is characterized by reduced insulin secretion from the pancreas and overproduction of glucose by the liver. Glucagon-like peptide-1 (GLP-1) promotes glucose-dependent insulin secretion from the pancreas, while glucagon promotes glucose output from the liver. Taking advantage of the homology between GLP-1 and glucagon, a GLP-1/glucagon hybrid peptide, dual-acting peptide for diabetes (DAPD), was identified with combined GLP-1 receptor agonist and glucagon receptor antagonist activity. To overcome its short plasma half-life DAPD was PEGylated, resulting in dramatically prolonged activity in vivo. PEGylated DAPD (PEG-DAPD) increases insulin and decreases glucose in a glucose tolerance test, evidence of GLP-1 receptor agonism. It also reduces blood glucose following a glucagon challenge and elevates fasting glucagon levels in mice, evidence of glucagon receptor antagonism. The PEG-DAPD effects on glucose tolerance are also observed in the presence of the GLP-1 antagonist peptide, exendin(9–39). An antidiabetic effect of PEG-DAPD is observed in db/db mice. Furthermore, PEGylation of DAPD eliminates the inhibition of gastrointestinal motility observed with GLP-1 and its analogues. Thus, PEG-DAPD has the potential to be developed as a novel dual-acting peptide to treat type 2 diabetes, with prolonged in vivo activity, and without the GI side-effects.
Xue Jiang, Jia Xiao, Mulan He, Ani Ma, and Anderson O L Wong
Type II suppressor of cytokine signaling (SOCS) serve as feedback repressors for cytokines and are known to inhibit growth hormone (GH) actions. However, direct evidence for SOCS modulation of GH-induced insulin-like growth factor 1 (Igf1) expression is lacking, and the post-receptor signaling for SOCS expression at the hepatic level is still unclear. To shed light on the comparative aspects of SOCS in GH functions, grass carp was used as a model to study the role of type II SOCS in GH-induced Igf1 expression. Structural identity of type II SOCS, Socs1–3 and cytokine-inducible SH2-containing protein (Cish), was established in grass carp by 5’/3’-RACE, and their expression at both transcript and protein levels were confirmed in the liver by RT-PCR and LC/MS/MS respectively. In carp hepatocytes, GH treatment induced rapid phosphorylation of JAK2, STATs, MAPK, PI3K, and protein kinase B (Akt) with parallel rises in socs1–3 and cish mRNA levels, and these stimulatory effects on type II SOCS were shown to occur before the gradual loss of igf1 gene expression caused by prolonged exposure of GH. Furthermore, GH-induced type II SOCS gene expression could be negated by inhibiting JAK2, STATs, MEK1/2, P38 MAPK, PI3K, and/or Akt respectively. In CHO cells transfected with carp GH receptor, over-expression of these newly cloned type II SOCS not only suppressed JAK2/STAT5 signaling with GH treatment but also inhibited GH-induced grass carp Igf1 promoter activity. These results, taken together, suggest that type II SOCS could be induced by GH in the carp liver via JAK2/STATs, MAPK, and PI3K/Akt cascades and serve as feedback repressors for GH signaling and induction of igf1 gene expression.
Yoko Fujiwara, Masami Hiroyama, Atsushi Sanbe, Junji Yamauchi, Gozoh Tsujimoto, and Akito Tanoue
[Arg8]-vasopressin (AVP) and oxytocin (OT) are neurohypophysial hormones which exert various actions, including the control of blood glucose, in some peripheral tissues. To investigate the type of receptors involved in AVP- and OT-induced glucagon secretion, we investigated the effect of these peptides on glucagon secretion in islets of wild-type (V1bR+/+) and vasopressin V1b receptor knockout (V1bR−/−) mice. AVP-induced glucagon secretion was significantly inhibited by the selective V1b receptor antagonist, SSR149415 (30%), and OT-induced glucagon secretion by the specific OT receptor antagonist, d(CH2)5[Tyr(Me)2, Thr4, Tyr-NH2 9]OVT (CL-14-26) (45%), in islets of V1bR+/+mice. AVP- and OT-induced glucagon secretions were not by the antagonist of each, but co-incubation with both 10−6 M SSR149415 and 10−6 M CL-14-26 further inhibited AVP- and OT-induced glucagon secretions in islets of V1bR+/+ mice (57 and 69% of the stimulation values respectively). In addition, both AVP and OT stimulated glucagon secretion with the same efficacy in V1bR−/− mice as in V1bR+/+ mice. AVP- and OT-induced glucagon secretion in V1bR−/− mice was significantly inhibited by CL-14-26. These results demonstrate that V1b receptors can mediate OT-induced glucagon secretion and OT receptors can mediate AVP-induced glucagon secretion in islets from V1bR+/+mice in the presence of a heterologous antagonist, while AVP and OT can stimulate glucagon secretion through the OT receptors in V1bR−/−mice, suggesting that the other receptor can compensate when one receptor is absent.
Gemma Llauradó, Victòria Ceperuelo-Mallafré, Carme Vilardell, Rafael Simó, Pilar Gil, Albert Cano, Joan Vendrell, and José-Miguel González-Clemente
The aim of this study was to investigate the relationship between advanced glycation end products (AGEs) and arterial stiffness (AS) in subjects with type 1 diabetes without clinical cardiovascular events. A set of 68 patients with type 1 diabetes and 68 age- and sex-matched healthy subjects were evaluated. AGEs were assessed using serum concentrations of N-carboxy-methyl-lysine (CML) and using skin autofluorescence. AS was assessed by aortic pulse wave velocity (aPWV), using applanation tonometry. Patients with type 1 diabetes had higher serum concentrations of CML (1.18 vs 0.96 μg/ml; P=0.008) and higher levels of skin autofluorescence (2.10 vs 1.70; P<0.001) compared with controls. These differences remained significant after adjustment for classical cardiovascular risk factors. Skin autofluorescence was positively associated with aPWV in type 1 diabetes (r=0.370; P=0.003). No association was found between CML and aPWV. Skin autofluorescence was independently and significantly associated with aPWV in subjects with type 1 diabetes (β=0.380; P<0.001) after adjustment for classical cardiovascular risk factors. Additional adjustments for HbA1c, disease duration, and low-grade inflammation did not change these results. In conclusion, skin accumulation of autofluorescent AGEs is associated with AS in subjects with type 1 diabetes and no previous cardiovascular events. These findings indicate that determination of tissue AGE accumulation may be a useful marker for AS in type 1 diabetes.
PM Jehle, DR Jehle, S Mohan, and BO Bohm
Osteopenia has been ascribed to diabetics without residual insulin secretion and high insulin requirement. However, it is not known if this is partially due to disturbances in the IGF system, which is a key regulator of bone cell function. To address this question, we performed a cross-sectional study measuring serum levels of IGF-I, IGF-binding protein-1 (IGFBP-1), IGFBP-3, IGFBP-4 and IGFBP-5 by specific immunoassays in 52 adults with Type 1 (n=27) and Type 2 (n=25) diabetes mellitus and 100 age- and sex-matched healthy blood donors. In the diabetic patients, we further determined serum levels of proinsulin, intact parathyroid hormone (PTH), 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3 and several biochemical bone markers, including osteocalcin (OSC), bone alkaline phosphatase (B-ALP), carboxy-terminal propeptide of type I procollagen (PICP), and type I collagen cross-linked carboxy-terminal telopeptide (ICTP). Urinary albumin excretion was ascertained as a marker of diabetic nephropathy. Bone mineral density (BMD) of hip and lumbar spine was determined by dual-energy X-ray absorptiometry. Data are presented as means+/-s.e.m. Differences between the experimental groups were determined by performing a one-way analysis of variance (ANOVA), followed by Newman-Keuls test. Correlations between variables were assessed using univariate linear regression analysis and partial correlation analysis. Type 1 diabetics showed significantly lower IGF-I (119+/-8 ng/ml) and IGFBP-3 (2590+/-104 ng/ml) but higher IGFBP-1 levels (38+/-10 ng/ml) compared with Type 2 patients (170+/-13, 2910+/-118, 11+/-3 respectively; P<0.05) or healthy controls (169+/-5, 4620+/-192, 3.5+/-0.4 respectively; P<0.01). IGFBP-5 levels were markedly lower in both diabetic groups (Type 1, 228+/-9; Type 2, 242+/-11 ng/ml) than in controls (460+/-7 ng/ml,P<0. 01), whereas IGFBP-4 levels were similar in diabetics and controls. IGF-I correlated positively with IGFBP-3 and IGFBP-5 and negatively with IGFBP-1 and IGFBP-4 in all subjects. Type 1 patients showed a lower BMD of hip (83+/-2 %, Z-score) and lumbar spine (93+/-2 %) than Type 2 diabetics (93+/-5 %, 101+/-5 % respectively), reaching significance in the female subgroups (P<0.05). In Type 1 patients, BMD of hip correlated negatively with IGFBP-1 (r=-0.34, P<0.05) and IGFBP-4 (r=-0.3, P<0.05) but positively with IGFBP-5 (r=0.37, P<0. 05), which was independent of age, diabetes duration, height, weight and body mass index, as assessed by partial correlation analysis. Furthermore, biochemical markers indicating bone loss (ICTP) and increased bone turnover (PTH, OSC) correlated positively with IGFBP-1 and IGFBP-4 but negatively with IGF-I, IGFBP-3 and IGFBP-5, while the opposite was observed with bone formation markers (PICP, B-ALP) and vitamin D3 metabolites. In 20 Type 2 patients in whom immunoreactive proinsulin could be detected, significant positive correlations were found between proinsulin and BMD of hip (r=0.63, P<0.005), IGF-I (r=0.59, P<0.01) as well as IGFBP-3 (r=0.49, P<0.05). Type 1 and Type 2 patients with macroalbuminuria showed a lower BMD of hip, lower IGFBP-5 but higher IGFBP-4 levels, suggesting that diabetic nephropathy may contribute to bone loss by a disturbed IGF system. In conclusion, the findings of this study support the hypothesis that the imbalance between individual IGF system components and the lack of endogenous proinsulin may contribute to the lower BMD in Type 1 diabetics.
Kanta Kon, Hiroshi Tsuneki, Hisakatsu Ito, Yoshinori Takemura, Kiyofumi Sato, Mitsuaki Yamazaki, Yoko Ishii, Masakiyo Sasahara, Assaf Rudich, Takahiro Maeda, Tsutomu Wada, and Toshiyasu Sasaoka
Disrupted sleep is associated with increased risk of type 2 diabetes. Central actions of orexin, mediated by orexin-1 and orexin-2 receptors, play a crucial role in the maintenance of wakefulness; accordingly, excessive activation of the orexin system causes insomnia. Resting-phase administration of dual orexin receptor antagonist (DORA) has been shown to improve sleep abnormalities and glucose intolerance in type 2 diabetic db/db mice, although the mechanism remains unknown. In the present study, to investigate the presence of functional link between sleep and glucose metabolism, the influences of orexin antagonists with or without sleep-promoting effects were compared on glucose metabolism in diabetic mice. In db/db mice, 2-SORA-MK1064 (an orexin-2 receptor antagonist) and DORA-12 (a DORA) acutely improved non-rapid eye movement sleep, whereas 1-SORA-1 (an orexin-1 receptor antagonist) had no effect. Chronic resting-phase administration of these drugs improved glucose intolerance, without affecting body weight, food intake, locomotor activity and energy expenditure calculated from O2 consumption and CO2 production. The expression levels of proinflammatory factors in the liver were reduced by 2-SORA-MK1064 and DORA-12, but not 1-SORA-1, whereas those in the white adipose tissue were reduced by 1-SORA-1 and DORA-12 more efficiently than 2-SORA-MK1064. When administered chronically at awake phase, these drugs caused no effect. In streptozotocin-induced type 1-like diabetic mice, neither abnormality in sleep–wake behavior nor improvement of glucose intolerance by these drugs were observed. These results suggest that both 1-SORA-type (sleep-independent) and 2-SORA-type (possibly sleep-dependent) mechanisms can provide chronotherapeutic effects against type 2 diabetes associated with sleep disturbances in db/db mice.
B. Lahlou, B. Fossat, J. Porthé-Nibelle, L. Bianchini, and M. Guibbolini
Cyclic AMP levels were measured in freshly isolated hepatocytes of the rainbow trout. Compared with basal values, the average levels were increased up to 60 times in a dose-dependent manner either by mammalian glucagon (concentration range 1 nmol– 1 μmol/l; dose giving half maximum response (EC50) 0· 18 μmol/l) or by forskolin (concentration range 0·1–100 μmol/l; EC50 about 10 μmol/l). These stimulatory effects were partially inhibited by fish or mammalian neurohypophysial hormones used at relatively high concentrations (1–5 μmol/l). It is suggested that these results are evidence for the presence of V1-type receptors in fish hepatocytes. Together with previous results obtained with gills on the hormonal inhibition of adenylate cyclase activity, they suggest that teleost fish may possess only V1-type receptors (or two V1-related types), while the V2 receptors have evolved (or have become functional) in higher vertebrates.
J. Endocr. (1988) 119, 439–445
Linda Ahlkvist, Bilal Omar, Anders Valeur, Keld Fosgerau, and Bo Ahrén
Stimulation of insulin secretion by short-term glucagon receptor (GCGR) activation is well characterized; however, the effect of long-term GCGR activation on β-cell function is not known, but of interest, since hyperglucagonemia occurs early during development of type 2 diabetes. Therefore, we examined whether chronic GCGR activation affects insulin secretion in glucose intolerant mice. To induce chronic GCGR activation, high-fat diet fed mice were continuously (2 weeks) infused with the stable glucagon analog ZP-GA-1 and challenged with oral glucose and intravenous glucose±glucagon-like peptide 1 (GLP1). Islets were isolated to evaluate the insulin secretory response to glucose±GLP1 and their pancreas were collected for immunohistochemical analysis. Two weeks of ZP-GA-1 infusion reduced insulin secretion both after oral and intravenous glucose challenges in vivo and in isolated islets. These inhibitory effects were corrected for by GLP1. Also, we observed increased β-cell area and islet size. We conclude that induction of chronic ZP-GA-1 levels in glucose intolerant mice markedly reduces insulin secretion, and thus, we suggest that chronic activation of the GCGR may contribute to the failure of β-cell function during development of type 2 diabetes.