Roman Vangoitsenhoven

The microRNA-29 Family Dictates the Balance Between Homeostatic and Pathological Glucose Handling in Diabetes and Obesity

The microRNA-29 (miR-29) family is among the most abundantly expressed microRNA in the pancreas and liver. Here, we investigated the function of miR-29 in glucose regulation using miR-29a/b-1 (miR-29a)-deficient mice and newly generated miR-29b-2/c (miR-29c)-deficient mice. We observed multiple independent functions of the miR-29 family, which can be segregated into a hierarchical physiologic regulation of glucose handling. miR-29a, and not miR-29c, was observed to be a positive regulator of insulin secretion in vivo, with dysregulation of the exocytotic machinery sensitizing β-cells to overt diabetes after unfolded protein stress. By contrast, in the liver both miR-29a and miR-29c were important negative regulators of insulin signaling via phosphatidylinositol 3-kinase regulation. Global or hepatic insufficiency of miR-29 potently inhibited obesity and prevented the onset of diet-induced insulin resistance. These results demonstrate strong regulatory functions for the miR-29 family in obesity and diabetes, culminating in a hierarchical and dose-dependent effect on premature lethality.

GLP1 and cancer: friend or foe?

The new incretin-based therapies, dipeptidyl peptidase-4 (DPP4) inhibitors and glucagon like peptide 1 (GLP1) receptor agonists are widely used for the treatment of type 2 diabetes because of their glucose-lowering capacity with low risk of hypoglycemia. As they are weight neutral or induce weight loss in this mostly overweight population, they are popular among clinicians and patients alike. Nonetheless, concerns have been raised about GLP1s trophic effects. While increased β cell mass observed in rodents sounds appealing for treatment of diabetes, there was also an increased incidence of medullary thyroid cancer (MTC) in some species. We reviewed literature available in the Medline database until March 2012. Safety signals have emerged for MTC and pancreatic carcinoma from adverse event databases in the United States and Europe. Considering the relatively short duration of these studies, it is more likely that premalignant lesions are stimulated in presence of GLP1, rather than new neoplasms induced. Moreover, interpreting results of animal studies is difficult because of species-specific differences in presence and density of GLP1 receptors. Furthermore, data are emerging suggesting beneficial effects of GLP1 on colon and breast cancer. In conclusion, presently, the benefits of using DPP4 inhibitors or GLP1 receptor agonists for treatment of type 2 diabetes outweigh the risks. Nonetheless, their safety profile should be monitored and their indications should be widened cautiously. At present they remain contra-indicated in patients with a personal or family history of MTC or multiple endocrine neoplasia type 2.

Foodborne cereulide causes Beta-cell dysfunction and apoptosis

Aims/Hypothesis To study the effects of cereulide, a food toxin often found at low concentrations in take-away meals, on beta-cell survival and function. Methods Cell death was quantified by Hoechst/Propidium Iodide in mouse (MIN6) and rat (INS-1E) beta-cell lines, whole mouse islets and control cell lines (HepG2 and COS-1). Beta-cell function was studied by glucose-stimulated insulin secretion (GSIS). Mechanisms of toxicity were evaluated in MIN6 cells by mRNA profiling, electron microscopy and mitochondrial function tests. Results 24 h exposure to 5 ng/ml cereulide rendered almost all MIN6, INS-1E and pancreatic islets apoptotic, whereas cell death did not increase in the control cell lines. In MIN6 cells and murine islets, GSIS capacity was lost following 24 h exposure to 0.5 ng/ml cereulide (P<0.05). Cereulide exposure induced markers of mitochondrial stress including Puma (p53 up-regulated modulator of apoptosis, P<0.05) and general pro-apoptotic signals as Chop (CCAAT/-enhancer-binding protein homologous protein). Mitochondria appeared swollen upon transmission electron microscopy, basal respiration rate was reduced by 52% (P<0.05) and reactive oxygen species increased by more than twofold (P<0.05) following 24 h exposure to 0.25 and 0.50 ng/ml cereulide, respectively. Conclusions/Interpretation Cereulide causes apoptotic beta-cell death at low concentrations and impairs beta-cell function at even lower concentrations, with mitochondrial dysfunction underlying these defects. Thus, exposure to cereulide even at concentrations too low to cause systemic effects appears deleterious to the beta-cell.

Changes in bone macro- and microstructure in diabetic obese mice revealed by high resolution microfocus X-ray computed tomography

High resolution microfocus X-ray computed tomography (HR-microCT) was employed to characterize the structural alterations of the cortical and trabecular bone in a mouse model of obesity-driven type 2 diabetes (T2DM). C57Bl/6J mice were randomly assigned for 14 weeks to either a control diet-fed (CTRL) or a high fat diet (HFD)-fed group developing obesity, hyperglycaemia and insulin resistance. The HFD group showed an increased trabecular thickness and a decreased trabecular number compared to CTRL animals. Midshaft tibia intracortical porosity was assessed at two spatial image resolutions. At 2 μm scale, no change was observed in the intracortical structure. At 1 μm scale, a decrease in the cortical vascular porosity of the HFD bone was evidenced. The study of a group of 8 week old animals corresponding to animals at the start of the diet challenge revealed that the decreased vascular porosity was T2DM-dependant and not related to the ageing process. Our results offer an unprecedented ultra-characterization of the T2DM compromised skeletal micro-architecture and highlight an unrevealed T2DM-related decrease in the cortical vascular porosity, potentially affecting the bone health and fragility. Additionally, it provides some insights into the technical challenge facing the assessment of the rodent bone structure using HR-microCT imaging.

Low cytochrome oxidase 4I1 links mitochondrial dysfunction to obesity and type 2 diabetes in humans and mice

Objectives:Cytochrome oxidase (COX) dysfunction is associated with mitochondrial oxidative stress. We determined the association between COX expression, obesity and type 2 diabetes.Subjects/methods:COX4I1 and COX10 genes were measured in monocytes of 24 lean controls, 31 glucose-tolerant and 67 diabetic obese patients, and 17 morbidly obese patients before and after bariatric surgery. We investigated the effect of caloric restriction and peroxisome proliferator-activated receptor (PPAR) agonist treatment on Cox in obese diabetic mice, and that of diet-induced insulin resistance in Streptozotocin-treated mice.Results:Low COX4I1 was associated with type 2 diabetes in obese patients, adjusting for age, gender, smoking, interleukin-6 and high-sensitivity C-reactive protein, all related to metabolic syndrome (MetS; odds ratio: 6.1, 95% confidence interval: 2.3–16). In contrast, COX10 was low in glucose-tolerant and diabetic obese patients. In morbidly obese patients, COX4I1 was lower in visceral adipose tissue collected at bariatric surgery. In their monocytes, COX4I1 decreased after bariatric surgery, and low COX4I1 at 4 months was associated with MetS at 7 years. In leptin-deficient obese diabetic mice, Cox4i1 was low in white visceral adipose tissue (n=13; P<0.001) compared with age-matched lean mice (n=10). PPARγ-agonist treatment (n=13), but not caloric restriction (n=11), increased Cox4i1 (P<0.001). Increase in Cox4i1 depended on the increase in glucose transporter 4 (Glut4) expression and insulin sensitivity, independent of the increase in blood adiponectin. In streptozotocin-treated mice (three groups of seven mice, diet-induced insulin resistance decreased Cox4i1 and Glut4 (P<0.001 for both).Conclusion:COX4I1 depression is related to insulin resistance and type 2 diabetes in obesity. In peripheral blood monocytes, it may be a diagnostically useful biomarker.

Cereulide food toxin, beta cell function and diabetes: Facts and hypotheses

The incidence of both type 1 and type 2 diabetes is increasing and although environmental pollutants are believed to be potential culprits, the extent to which they can be held responsible remains uncertain. Some bacterial strains of the Bacillus cereus produce a toxin, cereulide, which is frequently found in starchy meals and which is difficult to eradicate from the food chain as it is highly resistant to heat, acidity and proteolysis. While cereulide is well known to cause acute emetic toxicity when ingested at high doses, several in vitro studies have shown that also extremely low doses of cereulide can be toxic, with beta cells being particularly sensitive. Mechanistically, such low doses impair the mitochondrial activity of the beta cells thereby leading to hampered insulin secretion and cell death, both key traits in the pathophysiology of diabetes. In vivo studies of chronic or repeated low dose exposure to cereulide are currently lacking, but should be performed to further clarify the true relevance of cereulide as a potential environmental contributor to the ongoing diabetes epidemic.

Effect of a transcriptional inactive or absent vitamin D receptor on beta-cell function and glucose homeostasis in mice

Vitamin D deficiency is associated with beta-cell dysfunction and a higher risk of diabetes, but mice and humans with an absence of the vitamin D receptor (VDR) display normal glucose tolerance. Here, we investigated the direct effects of absence of VDR or absence of ligand activation of VDR on beta-cell function. For this purpose, we generated mice, with a mutation in the AF2 domain of Vdr (VDRΔAF2), preventing ligand-driven transcriptional activation of vitamin D responsive genes. VDRΔAF2 mice were compared to Vdr full knockout (VDR-/-) and wild type (WT) mice. In order to avoid hypocalcemia, which has a direct effect on beta-cell function, mice were fed a high calcium, high lactose diet yielding comparable serum calcium in all mice. While VDR-/- mice developed extensive alopecia by the age of 24 weeks, the fur of VDRΔAF2 remained normal. All VDRΔAF2 mice weighed significantly less than WT, while male but not female VDR-/- mice had a lower body weight than WT mice. Dual-energy X-ray absorptiometry showed that both VDRΔAF2 (17.2% (females) and 16.6% (males)) and VDR-/- (15.7% and 14.8%) mice have a lower percentage of body fat (vs 19.3% and 22.2% in WT). Serum 25(OH)D3 concentrations were lower for both VDRΔAF2 (-4.55 fold, P<0.001) and VDR-/- (-3.7 fold, P<0.001) as compared to 12 week old WT mice, while serum 1,25(OH)2D3 was increased for both strains 94.5 fold (P<0.01) and 92.8 fold (P<0.001) for VDRΔAF2 and VDR-/- vs WT, respectively). In vivo glucose tolerance tests performed at 12 and 24 weeks of age, as well as ex vivo glucose stimulated insulin secretion on freshly isolated islets, revealed no major differences between the three strains. Microarray analysis on freshly isolated islets showed only 1 differentially expressed gene, phosphodiesterase 10a (Pde10a), which was 2.16 and 1.75 fold up-regulated in VDRΔAF2 and VDR-/- islets as compared to WT islets, respectively (P≤0.001). We conclude that in the presence of normocalcemia, absence of VDR or its ligand-activated transcription of genes has no direct regulatory effect on murine glucose homeostasis or gene expression in islets of Langerhans.

Vhl deletion in osteoblasts boosts cellular glycolysis and improves global glucose metabolism

The skeleton has emerged as an important regulator of systemic glucose homeostasis, with osteocalcin and insulin representing prime mediators of the interplay between bone and energy metabolism. However, genetic evidence indicates that osteoblasts can influence global energy metabolism through additional, as yet unknown, mechanisms. Here, we report that constitutive or postnatally induced deletion of the hypoxia signaling pathway component von Hippel–Lindau (VHL) in skeletal osteolineage cells of mice led to high bone mass as well as hypoglycemia and increased glucose tolerance, not accounted for by osteocalcin or insulin. In vitro and in vivo data indicated that Vhl-deficient osteoblasts displayed massively increased glucose uptake and glycolysis associated with upregulated HIF-target gene expression, resembling the Warburg effect that typifies cancer cells. Overall, the glucose consumption by the skeleton was increased in the mutant mice, as revealed by 18F-FDG radioactive tracer experiments. Moreover, the glycemia levels correlated inversely with the level of skeletal glucose uptake, and pharmacological treatment with the glycolysis inhibitor dichloroacetate (DCA), which restored glucose metabolism in Vhl-deficient osteogenic cells in vitro, prevented the development of the systemic metabolic phenotype in the mutant mice. Altogether, these findings reveal a novel link between cellular glucose metabolism in osteoblasts and whole-body glucose homeostasis, controlled by local hypoxia signaling in the skeleton.

Long-term effects of gastric bypass surgery on psychosocial well-being and eating behavior: not all that glitters is gold

Objectives: The aim of this pilot study was to evaluate long-term effects of Roux-en-Y gastric bypass (RYGB) on physical and psychosocial health as well as eating behavior of obese patients. Methods: We compared 23 patients 7 years after RYGB to 23 body mass index (BMI), sex, and age matched obese control patients by means of self-reporting questionnaires: Hospital Anxiety and Depression Scale (HADS), Quality of Life Enjoyment and Satisfaction Questionnaire – Short Form (Q-LES-Q SF), Dutch Eating Behavior Questionnaire (DEBQ), and Alcohol Use Disorders Identification Test (AUDIT). Data are presented as median ± interquartile rage. Results: Physical health had improved and body image (80 ± 25% vs. 20 ± 49%, p < 0.001) was better in post-RYGB patients when compared to controls. HADS-depression score (4 ± 8 vs. 11 ± 9; p = 0.005) was lower post-RYGB. Satisfaction with physical health (2 ± 2 vs. 2 ± 1, p = 0.037), daily life functioning (4 ± 2 vs. 2 ± 2, p = 0.050), and hobbies (4 ± 1 vs. 2 ± 2, p = 0.011) was higher post-RYGB, but social relationships and sexual performance were not perceived as superior. In addition, post-RYGB patients were more prone to eat on external cues (13 ± 7 vs. 19 ± 13; p = 0.007). Conclusion: Seven years post-RYGB, patients reported a significant improvement of physical health and higher satisfaction with daily life, but not with social relationships or sexual performance. Eating behavior post-RYGB was more influenced by external cues.

Unraveling the compromised biomechanical performance of type 2 diabetes- and Roux-en-Y gastric bypass bone by linking mechanical-structural and physico-chemical properties

Type 2 diabetes mellitus (T2DM) is a metabolic disorder associated with obesity and hyperglycemia. Roux-en-Y gastric bypass (RYGB) surgery is a common treatment for severely obese patients and T2DM. Both RYGB and T2DM are linked to increased skeletal fragility, though the exact mechanisms are poorly understood. Our aim was to characterize the structural, mechanical and compositional properties of bones from diet-induced obese and RYGB-treated obese (bypass) mice to elucidate which the exact factors are contributing to the increased skeletal fragility. To achieve this, a combinatory approach including microfocus X-ray computed tomography, 3-point bending, finite element modeling and Raman spectroscopy, was used. Compared to aged-matched lean controls, the obese mice displayed decreased cortical thickness, trabecular bone loss, decreased stiffness and increased Young’s modulus. For the bypass mice, these alterations were even more pronounced, and additionally they showed low mineral-to-matrix ratio in the cortical endosteal area. Accumulation of the advanced glycation end-product (AGE) pentosidine was found in the cortex of obese and bypass groups and this accumulation was correlated with an increased Young’s modulus. In conclusion, we found that the increased fracture risk in T2DM- and post-RYGB bones is mainly driven by accumulation of AGEs and macro-structural alterations, generating biomechanical dysfunctionality.