Cryptic receptors for insulin-like growth factor II in the plasma membrane of rat adipocytes — a possible link to cellular insulin resistance

AbstractTo further elucidate the mechanisms for short-term regulation of the receptor for insulin-like growth factor II (IGF-II), we investigated effects of insulin, cAMP and phosphatase inhibitors on cell surface 125I-IGF-II binding in rat adipocytes. Preincubation with the serine/threonine phosphatase inhibitor okadaic acid (OA, 1 μMM) or the non-hydrolysable cAMP analogue N6-mbcAMP (4 mM) markedly impaired insulin-stimulated 125I-IGF-II binding. Furthermore, addition of OA enhanced the inhibitory effect exerted by N6-mbcAMP. N6-mbcAMP also induced an insensitivity to insulin which was normalized by concomitant addition of the tyrosine phosphatase inhibitor vanadate (0.5 mM). In contrast, vanadate did not affect the impairment in maximal insulin-stimulated 25I-IGF-II binding produced by either OA or N6-mbcAMP. Phospholipase C (PLC), which cleaves phospholipids at the cell surface, markedly enhanced cell surface 125I-IGF-II binding in a concentration-dependent manner. Scatchard analysis demonstrated that the effect of PLC was due to an increased number of binding sites suggesting that ‘cryptic’ IGF-II receptors are associated with the plasma membrane (PM). PLC (5 U/ml) also reversed the N6-mbcAMP-induced decrease of 125I-IGF-II binding at a low insulin concentration (10 μU/ml). Taken together, these data indicate that CAMP, similar to its effects on the glucose transporter GLUT 4 and the insulin receptor, may increase the proportion of functionally cryptic IGF-II receptors in the PM through mechanisms involving serine phosphorylation, possibly of a docking or coupling protein. Tyrosine phosphorylation appears to exert an opposite effect promoting the full cell surface expression of receptors

Increased Urine IgM and IgG2 Levels, Indicating Decreased Glomerular Size Selectivity, Are Not Affected by Dalteparin Therapy in Patients with Type 2 Diabetes

Fifty-four type 2 diabetic patients with neuroischemic foot ulcers were randomised to treatment with 5000 IU of dalteparin, (n = 28), or physiological saline, (n = 26), once daily until ulcer healing or for a maximum of 6 months. Thirty-three patients had normo-, 15 micro-, and 6 macroalbuminuria. The urinary levels of IgM and IgG2 were elevated in 47 and 50 patients, respectively. Elevated urinary levels of IgM and IgG2 indicate decreased glomerular size selectivity. Urine IgM levels were associated with IGF-1/IGFBP-1 and IGFBP-1 levels. Dalteparin treatment increased urinary levels of glycosaminoglycans (P < 0.001) and serum IGFBP-1 (P < 0.05) while no significant effects were seen in any of the other studied parameters. In conclusion, dalteparin therapy in patients with type 2 diabetes had no effects on urinary levels of albumin, IgM, or IgG2 despite significantly increased glycosaminoglycans in urine. Elevated urinary levels of IgM and IgG2 might be more sensitive markers of renal disease than albuminuria in patients with type 2 diabetes and antihypertensive therapy

Effects of gastric bypass surgery on brain connectivity responses to hypoglycemia

INTRODUCTION: Roux-en-Y gastric bypass (RYGB) leads to beneficial effects on glucose homeostasis, and attenuated hormonal counterregulatory responses to hypoglycemia are likely to contribute. RYGB also induces alterations in neural activity of cortical and subcortical brain regions. We aimed to characterize RYGB-induced changes in resting-state connectivity of specific brain regions of interest for energy homeostasis and behavioral control during hypoglycemia. METHOD: Ten patients with BMI > 35 kg/m(2) were investigated with brain PET/MR imaging during a hyperinsulinemic normo- and hypoglycemic clamp, before and 4 months after RYGB. Hormonal levels were assessed throughout the clamp. Resting-state (RS) fMRI scans were acquired in the glucose-lowering phase of the clamp, and they were analyzed with a seed-to-voxel approach. RESULTS: RS connectivity during initiation of hypoglycemia was significantly altered after RYGB between nucleus accumbens, thalamus, caudate, hypothalamus and their crosstalk with cortical and subcortical regions. Connectivity between the nucleus accumbens and the frontal pole was increased after RYGB, and this was associated with a reduction of ACTH (r = −0.639, p = 0.047) and cortisol (r = −0.635, p = 0.048) responses. Instead, connectivity between the caudate and the frontal pole after RYGB was reduced and this was associated with less attenuation of glucagon response during the hypoglycemic clamp (r = −0.728, p = 0.017), smaller reduction in fasting glucose (r = −0.798, p = 0.007) and less excess weight loss (r = 0.753, p = 0.012). No other significant associations were found between post-RYGB changes in ROI-to-voxel regional connectivity hormonal responses and metabolic or anthropometric outcomes. CONCLUSION: RYGB alters brain connectivity during hypoglycemia of several neural pathways involved in reward, inhibitory control, and energy homeostasis. These changes are associated with altered hormonal responses to hypoglycemia and may be involved in the glucometabolic outcome of RYGB

Cyclosporine A and tacrolimus reduce the amount of GLUT4 at the cell-surface in human adipocytes: increased endocytosis as a potential mechanism for the diabetogenic effects of immunosuppressive agents

Context:Immunosuppressive agentes are associated with profound metabolic side effects including new-onset diabetes and dyslipidemia after organ transplantation. Objective: Toi nvestigated the effects of the cyclosporine A(CsA)or tacrolimus ong lucose uptake and insulin signalling in human adipocytes and their impact on the regulation of celular trafficking of the glucose transporter 4 (GLUT4). Design:Human isolated adipocytes were incubated with therapeutic concentrations of either CsA or tacrolimus, and glucose uptake and expression of insulin signaling proteins were assessed. Furthermore,we studied effects of CsA and tacrolimus on the regulation of celular trafficking of the GLUT4 in differentiated human pre-adipocytes and L6 cells. Results:CsA and tacrolimus had a concentration-dependent inhibitory effect on basal and insulin stimulated 14C-glucose uptake in adipocytes. Although phosphorylation at Tyr1146 of insulin receptor (IR) was inhibited by tacrolimus, the phosphorylation and/or protein levels of the insulin signalling proteinsIRS1/2,p85-PI3K,PKB,AS160 and mTORC1,as well as GLUT4 and GLUT1,were unchanged by CsA or tacrolimus. Furthermore, CsA and tacrolimus reduced the GLUT4 amount localized at the cell surfasse of differentiated human pre-adipocytes and L6 cells in the presence of insulin.This occurred by na increased rate of GLUT4 endocytosis,with no change in the exocytosis rate. Conclusions: These results suggest that therapeutic concentrations of CsA and tacrolimus can inhibit glucose uptake independente of insulin signalling by removing GLUT4 from the cell surface via na increased rate of endocytosis.Such mechanisms can contribute to the development of insulin resistance and diabetes associated with immunosuppressive therapy.In addition,they may provide novel pharmacological approaches for treatment of diabetes

A metabolomics based molecular pathway analysis for how the SGLT2-inhibitor dapagliflozin may slow kidney function decline in patients with diabetes

Aim: To investigate which metabolic pathways are targeted by the sodium-glucose co-transporter-2 inhibitor dapagliflozin to explore the molecular processes involved in its renal protective effects. Methods: An unbiased mass spectrometry plasma metabolomics assay was performed on baseline and follow-up (week 12) samples from the EFFECT II trial in patients with type 2 diabetes with non-alcoholic fatty liver disease receiving dapagliflozin 10 mg/day (n = 19) or placebo (n = 6). Transcriptomic signatures from tubular compartments were identified from kidney biopsies collected from patients with diabetic kidney disease (DKD) (n = 17) and healthy controls (n = 30) from the European Renal cDNA Biobank. Serum metabolites that significantly changed after 12 weeks of dapagliflozin were mapped to a metabolite-protein interaction network. These proteins were then linked with intra-renal transcripts that were associated with DKD or estimated glomerular filtration rate (eGFR). The impacted metabolites and their protein-coding transcripts were analysed for enriched pathways. Results: Of all measured (n = 812) metabolites, 108 changed (P &lt; 0.05) during dapagliflozin treatment and 74 could be linked to 367 unique proteins/genes. Intra-renal mRNA expression analysis of the genes encoding the metabolite-associated proteins using kidney biopsies resulted in 105 genes that were significantly associated with eGFR in patients with DKD, and 135 genes that were differentially expressed between patients with DKD and controls. The combination of metabolites and transcripts identified four enriched pathways that were affected by dapagliflozin and associated with eGFR: glycine degradation (mitochondrial function), TCA cycle II (energy metabolism), L-carnitine biosynthesis (energy metabolism) and superpathway of citrulline metabolism (nitric oxide synthase and endothelial function). Conclusion: The observed molecular pathways targeted by dapagliflozin and associated with DKD suggest that modifying molecular processes related to energy metabolism, mitochondrial function and endothelial function may contribute to its renal protective effect.</p

Altered glucose-dependent secretion of glucagon and ACTH is associated with insulin resistance, assessed by population analysis

This study aimed to characterize how the dysregulation of counter-regulatory hormones can contribute to insulin resistance and potentially to diabetes. Therefore, we investigated the association between insulin sensitivity and the glucose- and insulin-dependent secretion of glucagon, adrenocorticotropic hormone (ACTH), and cortisol in non-diabetic individuals using a population model analysis. Data, from hyperinsulinemic–hypoglycemic clamps, were pooled for analysis, including 52 individuals with a wide range of insulin resistance (reflected by glucose infusion rate 20–60 min; GIR 20–60min). Glucagon secretion was suppressed by glucose and, to a lesser extent, insulin. The GIR20–60min and BMI were identified as predictors of the insulin effect on glucagon. At no rmoglycemia (5 mmol/L), a 90% suppression of glucagon was achieved at insulin concentrations of 16.3 and 43.4 μU/mL in individuals belonging to the highest and lowest quanti les of insulin sensitivity, respectively. Insulin resistance of glucagon secretion explained the elevated fasting glucagon for individuals with a low GIR20–60min. ACTH secretion was suppressed by glucose and not affected by insulin. The GIR20–60min was superior to other measures as a predictor of glucose-dependent ACTH secretion, with 90% suppression of ACTH secretion by glucose at 3.1 and 3.5 mmol/L for insulin-sensitive and insulin-resista nt individuals, respectively. This difference may appear small but shifts the suppression rang e into normoglycemia for individuals with insulin resistance, thus, leading to earli er and greater ACTH/cortisol response when the glucose falls. Based on modeling of pooled glucose-clamp data, insulin resistance was associated with generally elevated glucagon and a potentiated cortisol-axis response to hypoglycemia, and over time both hormonal pathways may therefore contribute to dysglycemia and possibly type 2 diabetes

The interactive role of predation, competition and habitat conditions in structuring an intertidal bivalve population

Habitat characteristics, predation and competition are known to interactively drive population dynamics. Highly complex habitats, for example, may reduce predation and competition, allowing more individuals living together in a certain area. However, the strength and direction of such interactions can differ strongly and are context dependent. Furthermore, as habitat characteristics are rapidly changing due to anthropogenic impacts, it becomes increasingly important to understand such interactions. Here, we studied the interactive effects of predation and competition on common cockle (Cerastoderma edule) recruitment, growth and survival under different habitat characteristics in the Wadden Sea, one of the world's largest intertidal ecosystems. In a predator-exclosure experiment, we manipulated cockle densities (100 vs. 1000 individuals m-2) and shorebird predation at two sites differing in habitat characteristics, namely at the wake of a blue mussel bed (Mytilus edulis) and at an adjacent sandy site. We found that recruitment was higher in the mussel-modified habitat, most likely due to reduction of hydrodynamic stress. Although bird predation strongly reduced recruit density, the combined effects still yielded more recruitment at the vicinity of the mussel bed compared to the sandy area. Furthermore, we found that high cockle densities combined with high densities of other potential prey (i.e. mussels) at the mussel-modified site, mitigated predation effects for adult cockles. Apart from these positive effects on adults, mussel-modified habitat reduced cockle growth, most likely by reducing hydrodynamics in the wake of the mussel bed and by increasing inter-specific competition for food. Our study experimentally underpins the importance of habitat characteristics, competition and predation in interactively structuring intertidal communities

Modulation of hypothalamic AMPK phosphorylation by olanzapine controls energy balance and body weight

[Background]: Second-generation antipsychotics (SGAs) are a mainstay therapy for schizophrenia. SGA-treated patients present higher risk for weight gain, dyslipidemia and hyperglycemia. Herein, we evaluated the effects of olanzapine (OLA), widely prescribed SGA, in mice focusing on changes in body weight and energy balance. We further explored OLA effects in protein tyrosine phosphatase-1B deficient (PTP1B-KO) mice, a preclinical model of leptin hypersensitivity protected against obesity.[Methods]: Wild-type (WT) and PTP1B-KO mice were fed an OLA-supplemented diet (5 mg/kg/day, 7 months) or treated with OLA via intraperitoneal (i.p.) injection or by oral gavage (10 mg/kg/day, 8 weeks). Readouts of the crosstalk between hypothalamus and brown or subcutaneous white adipose tissue (BAT and iWAT, respectively) were assessed. The effects of intrahypothalamic administration of OLA with adenoviruses expressing constitutive active AMPKα1 in mice were also analyzed.[Results]: Both WT and PTP1B-KO mice receiving OLA-supplemented diet presented hyperphagia, but weight gain was enhanced only in WT mice. Unexpectedly, all mice receiving OLA via i.p. lost weight without changes in food intake, but with increased energy expenditure (EE). In these mice, reduced hypothalamic AMPK phosphorylation concurred with elevations in UCP-1 and temperature in BAT. These effects were also found by intrahypothalamic OLA injection and were abolished by constitutive activation of AMPK in the hypothalamus. Additionally, OLA i.p. treatment was associated with enhanced Tyrosine Hydroxylase (TH)-positive innervation and less sympathetic neuron-associated macrophages in iWAT. Both central and i.p. OLA injections increased UCP-1 and TH in iWAT, an effect also prevented by hypothalamic AMPK activation. By contrast, in mice fed an OLA-supplemented diet, BAT thermogenesis was only enhanced in those lacking PTP1B. Our results shed light for the first time that a threshold of OLA levels reaching the hypothalamus is required to activate the hypothalamus BAT/iWAT axis and, therefore, avoid weight gain.[Conclusion]: Our results have unraveled an unexpected metabolic rewiring controlled by hypothalamic AMPK that avoids weight gain in male mice treated i.p. with OLA by activating BAT thermogenesis and iWAT browning and a potential benefit of PTP1B inhibition against OLA-induced weight gain upon oral treatment.This work was funded by grants PID-2021-122766OB-100 (to AMV) and PID2019-104399RB-I00 (to GS) funded by Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación /10.13039/501100011033 and “ERDF A way of making Europe” by the European Union. We also acknowledge grants H2020 Marie Sklodowska-Curie ITN-TREATMENT (Grant Agreement 721236, European Commission), S2017/BMD-3684 (Comunidad de Madrid, Spain), Fundación Ramón Areces (Spain) and CIBERdem (ISCIII, Spain) to AMV. JWE was funded by the Swedish Diabetes Foundation and the Novo Nordisk Foundation (NNF20OC0063864). VF was a recipient of a contract from ITN-TREATMENT and is currently a PhD fellow from the Portuguese Foundation for Science and Technology (FCT, Portugal)/ERDF (2020.08388.BD). CF was awarded with Sara Borrell contract (CD19/00078, ISCIII, Spain)