Mechanisms of weight loss-induced remission in people with prediabetes: a post-hoc analysis of the randomised, controlled, multicentre Prediabetes Lifestyle Intervention Study (PLIS)

BACKGROUND

Remission of type 2 diabetes can occur as a result of weight loss and is characterised by liver fat and pancreas fat reduction and recovered insulin secretion. In this analysis, we aimed to investigate the mechanisms of weight loss- induced remission in people with prediabetes.

METHODS

In this prespecified post-hoc analysis, weight loss-induced resolution of prediabetes in the randomised, controlled, multicentre Prediabetes Lifestyle Intervention Study (PLIS) was assessed, and the results were validated against participants from the Diabetes Prevention Program (DPP) study. For PLIS, between March 1, 2012, and Aug 31, 2016, participants were recruited from eight clinical study centres (including seven university hospitals) in Germany and randomly assigned to receive either a control intervention, a standard lifestyle intervention (ie, DPP-based intervention), or an intensified lifestyle intervention for 12 months. For DPP, participants were recruited from 23 clinical study centres in the USA between July 31, 1996, and May 18, 1999, and randomly assigned to receive either a standard lifestyle intervention, metformin, or placebo. In both PLIS and DPP, only participants who were randomly assigned to receive lifestyle intervention or placebo and who lost at least 5% of their bodyweight were included in this analysis. Responders were defined as people who returned to normal fasting plasma glucose (FPG; <5·6 mmol/L), normal glucose tolerance (<7·8 mmol/L), and HbA1c less than 39 mmol/mol after 12 months of lifestyle intervention or placebo or control intervention. Non-responders were defined as people who had FPG, 2 h glucose, or HbA1c more than these thresholds. The main outcomes for this analysis were insulin sensitivity, insulin secretion, visceral adipose tissue (VAT), and intrahepatic lipid content (IHL) and were evaluated via linear mixed models.

FINDINGS

Of 1160 participants recruited to PLIS, 298 (25·7%) had weight loss of 5% or more of their bodyweight at baseline. 128 (43%) of 298 participants were responders and 170 (57%) were non-responders. Responders were younger than non-responders (mean age 55·6 years [SD 9·9] vs 60·4 years [8·6]; p<0·0001). The DPP validation cohort included 683 participants who lost at least 5% of their bodyweight at baseline. Of these, 132 (19%) were responders and 551 (81%) were non-responders. In PLIS, BMI reduction was similar between responders and non-responders (responders mean at baseline 32·4 kg/m2 [SD 5·6] to mean at 12 months 29·0 kg/m2 [4·9] vs non-responders 32·1 kg/m2 [5·9] to 29·2 kg/m2 [5·4]; p=0·86). However, whole-body insulin sensitivity increased more in responders than in non-responders (mean at baseline 291 mL/[min × m2], SD 60 to mean at 12 months 378 mL/[min × m2], 56 vs 278 mL/[min × m2], 62, to 323 mL/[min × m2], 66; p<0·0001), whereas insulin secretion did not differ within groups over time or between groups (responders mean at baseline 175 pmol/mmol [SD 64] to mean at 12 months 163·7 pmol/mmol [60·6] vs non-responders 158·0 pmol/mmol [55·6] to 154·1 pmol/mmol [56·2]; p=0·46). IHL decreased in both groups, without a difference between groups (responders mean at baseline 10·1% [SD 8·7] to mean at 12 months 3·5% [3·9] vs non-responders 10·3% [8·1] to 4·2% [4·2]; p=0·34); however, VAT decreased more in responders than in non-responders (mean at baseline 6·2 L [SD 2·9] to mean at 12 months 4·1 L [2·3] vs 5·7 L [2·3] to 4·5 L [2·2]; p=0·0003). Responders had a 73% lower risk of developing type 2 diabetes than non-responders in the 2 years after the intervention ended.

INTERPRETATION

By contrast to remission of type 2 diabetes, resolution of prediabetes was characterised by an improvement in insulin sensitivity and reduced VAT. Because return to normal glucose regulation (NGR) prevents development of type 2 diabetes, we propose the concept of remission of prediabetes in analogy to type 2 diabetes. We suggest that remission of prediabetes should be the primary therapeutic aim in individuals with prediabetes.

FUNDING

German Federal Ministry for Education and Research via the German Center for Diabetes Research; the Ministry of Science, Research and the Arts Baden-Württemberg; the Helmholtz Association and Helmholtz Munich; the Cluster of Excellence Controlling Microbes to Fight Infections; and the German Research Foundation.

Identification of MicroRNAs Associated with Prediabetic Status in Obese Women

MicroRNAs (miRNAs) recently emerged as means of communication between insulin-sensitive tissues to mediate diabetes development and progression, and as such they present a valuable proxy for epigenetic alterations associated with type 2 diabetes. In order to identify miRNA markers for the precursor of diabetes called prediabetes, we applied a translational approach encompassing analysis of human plasma samples, mouse tissues and an in vitro validation system. MiR-652-3p, miR-877-5p, miR-93-5p, miR-130a-3p, miR-152-3p and let-7i-5p were increased in plasma of women with impaired fasting glucose levels (IFG) compared to those with normal fasting glucose and normal glucose tolerance (NGT). Among these, let-7i-5p and miR-93-5p correlated with fasting blood glucose levels. Human data were then compared to miRNome data obtained from islets of Langerhans and adipose tissue of 10-week-old female New Zealand Obese mice, which differ in their degree of hyperglycemia and liver fat content. Similar to human plasma, let-7i-5p was increased in adipose tissue and islets of Langerhans of diabetes-prone mice. As predicted by the in silico analysis, overexpression of let-7i-5p in the rat β-cell line INS-1 832/12 resulted in downregulation of insulin signaling pathway components (Insr, Rictor, Prkcb, Clock, Sos1 and Kcnma1). Taken together, our integrated approach highlighted let-7i-5p as a potential regulator of whole-body insulin sensitivity and a novel marker of prediabetes in women.

Brain insulin action on peripheral insulin sensitivity in women depends on menstrual cycle phase

Insulin action in the human brain modulates eating behaviour, whole-body metabolism and body fat distribution1,2. In particular, brain insulin action increases whole-body insulin sensitivity, but these studies were mainly performed in lean men3,4. Here we investigate metabolic and hypothalamic effects of brain insulin action in women with a focus on the impact of menstrual cycle ( ClinicalTrials.gov registration: NCT03929419 ).Eleven women underwent four hyperinsulinemic-euglycemic clamps, two in the follicular phase and two in the luteal phase. Brain insulin action was introduced using nasal insulin spray5-7 and compared to placebo spray in a fourfold crossover design with change in glucose infusion rate as the primary endpoint. Here we show that during the follicular phase, more glucose has to be infused after administration of nasal insulin than after administration of placebo. This remains significant after adjustment for blood glucose and insulin. During the luteal phase, no significant influence of brain insulin action on glucose infusion rate is detected after adjustment for blood glucose and insulin (secondary endpoint). In 15 other women, hypothalamic insulin sensitivity was assessed in a within-subject design by functional magnetic resonance imaging with intranasal insulin administration8. Hypothalamus responsivity is influenced by insulin in the follicular phase but not the luteal phase.Our study therefore highlights that brain insulin action improves peripheral insulin sensitivity also in women but only during the follicular phase. Thus, brain insulin resistance could contribute to whole-body insulin resistance in the luteal phase of the menstrual cycle.

Acylated- and unacylated ghrelin during an oral glucose tolerance test in humans at risk for type 2 diabetes mellitus

BACKGROUND/OBJECTIVES

The orexigenic peptide hormone ghrelin has been implicated in the pathophysiology of obesity and type 2 diabetes mellitus through its effects on nutrient homeostasis. Ghrelin is subject to a unique post-translational acyl modification regulating its biochemical activity.

SUBJECTS/METHODS

In this study we aimed to investigate the relation of acylated (AcG) as well as unacylated ghrelin (UnG) with body weight and insulin resistance in the fasting (n = 545) and post-oral glucose tolerance test (oGTT) state (n = 245) in a metabolically well characterized cohort covering a broad range of BMI (17.95 kg/m²-76.25 kg/m²).

RESULTS

Fasting AcG (median 94.2 pg/ml) and UnG (median 175.3 pg/ml) were negatively and the AcG/UnG ratio was positively correlated with BMI (all p < 0.0001). Insulin sensitivity (ISI) correlated positively with AcG (p = 0.0014) and UnG (p = 0.0004) but not with the AcG/UnG ratio. In a multivariate analysis, including ISI and BMI, only BMI, but not ISI was independently associated with AcG and UnG concentrations. Significant changes of AcG and UnG concentrations were detectable after oGTT stimulation, with slight decreases after 30 min and increases after 90-120 min. Subject stratification into BMI-divergent groups revealed more pronounced AcG increases in the two groups with BMI < 40 kg/m².

CONCLUSION

Our data demonstrate lower concentrations for both AcG and UnG with increasing BMI as well as an increased proportion of the biologically active, acylated form of ghrelin giving point to pharmacologic intervention in ghrelin acylation and/or increase in UnG for treatment of obesity despite decreased absolute AcG levels.

Glucose-stimulated insulin secretion depends on FFA1 and Gq in neonatal mouse islets

AIMS/HYPOTHESIS

After birth, the neonatal islets gradually acquire glucose-responsive insulin secretion, a process that is subjected to maternal imprinting. Although NEFA are major components of breastmilk and insulin secretagogues, their role for functional maturation of neonatal beta cells is still unclear. NEFA are the endogenous ligands of fatty acid receptor 1 (FFA1, encoded by Ffar1 in mice), a Gq-coupled receptor with stimulatory effect on insulin secretion. This study investigates the role of FFA1 in neonatal beta cell function and in the adaptation of offspring beta cells to parental high-fat feeding.

METHODS

Wild-type (WT) and Ffar1-/- mice were fed high-fat (HFD) or chow diet (CD) for 8 weeks before mating, and during gestation and lactation. Blood variables, pancreas weight and insulin content were assessed in 1-, 6-, 11- and 26-day old (P1-P26) offspring. Beta cell mass and proliferation were determined in P1-P26 pancreatic tissue sections. FFA1/Gq dependence of insulin secretion was evaluated in isolated islets and INS-1E cells using pharmacological inhibitors and siRNA strategy. Transcriptome analysis was conducted in isolated islets.

RESULTS

Blood glucose levels were higher in CD-fed Ffar1-/- P6-offspring compared with CD-fed WT P6-offspring. Accordingly, glucose-stimulated insulin secretion (GSIS) and its potentiation by palmitate were impaired in CD Ffar1-/- P6-islets. In CD WT P6-islets, insulin secretion was stimulated four- to fivefold by glucose and five- and sixfold over GSIS by palmitate and exendin-4, respectively. Although parental HFD increased blood glucose in WT P6-offspring, it did not change insulin secretion from WT P6-islets. In contrast, parental HFD abolished glucose responsiveness (i.e. GSIS) in Ffar1-/- P6-islets. Inhibition of Gq by FR900359 or YM-254890 in WT P6-islets mimicked the effect of Ffar1 deletion, i.e. suppression of GSIS and of palmitate-augmented GSIS. The blockage of Gi/o by pertussis toxin (PTX) enhanced (100-fold) GSIS in WT P6-islets and rendered Ffar1-/- P6-islets glucose responsive, suggesting constitutive activation of Gi/o. In WT P6-islets, FR900359 cancelled 90% of PTX-mediated stimulation, while in Ffar1-/- P6-islets it completely abolished PTX-elevated GSIS. The secretory defect of Ffar1-/- P6-islets did not originate from insufficient beta cells, since beta cell mass increased with the offspring's age irrespective of genotype and diet. In spite of that, in the breastfed offspring (i.e. P1-P11) beta cell proliferation and pancreatic insulin content had a genotype- and diet-driven dynamic. Under CD, the highest proliferation rate was reached by the Ffar1-/- P6 offspring (3.95% vs 1.88% in WT P6), whose islets also showed increased mRNA levels of genes (e.g. Fos, Egr1, Jun) typically high in immature beta cells. Although parental HFD increased beta cell proliferation in both WT (4.48%) and Ffar1-/- (5.19%) P11 offspring, only the WT offspring significantly increased their pancreatic insulin content upon parental HFD (5.18 µg under CD to 16.93 µg under HFD).

CONCLUSIONS/INTERPRETATION

FFA1 promotes glucose-responsive insulin secretion and functional maturation of newborn islets and is required for adaptive offspring insulin secretion in the face of metabolic challenge, such as parental HFD.

Extracellular Matrix Expression in Human Pancreatic Fat Cells of Patients with Normal Glucose Regulation, Prediabetes and Type 2 Diabetes

Previously, we found that human pancreatic preadipocytes (PPAs) and islets influence each other and that the crosstalk with the fatty liver via the hepatokine fetuin-A/palmitate induces inflammatory responses. Here, we examined whether the mRNA-expression of pancreatic extracellular matrix (ECM)-forming and -degrading components differ in PPAs from individuals with normal glucose regulation (PPAs-NGR), prediabetes (PPAs-PD), and type 2 diabetes (PPAs-T2D), and whether fetuin-A/palmitate impacts ECM-formation/degradation and associated monocyte invasion. Human pancreatic resections were analyzed (immuno)histologically. PPAs were studied for mRNA expression by real-time PCR and protein secretion by Luminex analysis. Furthermore, co-cultures with human islets and monocyte migration assays in Transwell plates were conducted. We found that in comparison with NGR-PPAs, TIMP-2 mRNA levels were lower in PPAs-PD, and TGF-β1 mRNA levels were higher in PPAs-T2D. Fetuin-A/palmitate reduced fibronectin, decorin, TIMP-1/-2 and TGF-ß1 mRNA levels. Only fibronectin was strongly downregulated by fetuin-A/palmitate independently of the glycemic status. Co-culturing of PPAs with islets increased TIMP-1 mRNA expression in islets. Fetuin-A/palmitate increased MMP-1, usherin and dermatopontin mRNA-levels in co-cultured islets. A transmigration assay showed increased monocyte migration towards PPAs, which was enhanced by fetuin-A/palmitate. This was more pronounced in PPAs-T2D. The expression of distinct ECM components differs in PPAs-PD and PPAs-T2D compared to PPAs-NGR, suggesting that ECM alterations can occur even in mild hyperglycemia. Fetuin-A/palmitate impacts on ECM formation/degradation in PPAs and co-cultured islets. Fetuin-A/palmitate also enhances monocyte migration, a process which might impact on matrix turnover.

Brain insulin responsiveness is linked to age and peripheral insulin sensitivity

AIMS

Insulin action in the brain influences cognitive processes, peripheral metabolism and eating behavior. However, the influence of age and peripheral insulin sensitivity on brain insulin action remains unclear.

MATERIALS AND METHODS

We used intranasal administration of insulin and functional MRI in a randomized, placebo-controlled within-subject design in 110 participants (54 women, BMI 18-49 kg/m² , age 21-74 years). Cerebral blood flow was measured before and after nasal spray application to assess brain insulin action. Peripheral insulin sensitivity was assessed by a 5-point oral glucose tolerance test. Linear regressions were used to investigate associations between age and peripheral insulin sensitivity with brain insulin action in predefined region of interests (i.e., insulin-sensitive brain regions).

RESULTS

We found significant negative associations between age and insulin action in the hippocampus (β = -0.215; p = 0.017) and caudate nucleus (β = -0.184; p = 0.047); and between peripheral insulin sensitivity and insulin action in the amygdala (β = -0.190, p = 0.023). Insulin action in the insular cortex showed an interaction effect between age and peripheral insulin sensitivity (β = -0.219 p = 0.005). Furthermore, women showed the strongest negative association between age and hippocampal insulin action, while men showed the strongest associations with peripheral insulin sensitivity and age in reward-related brain regions.

CONCLUSION

We could show a region-specific relationship between brain insulin responsiveness, age and peripheral insulin sensitivity. Our findings underline the need to study brain insulin action in both men and women and further substantiate that brain insulin sensitivity is as a possible link between systemic metabolism and neurocognitive functions. This article is protected by copyright. All rights reserved.

Inceptor correlates with markers of prostate cancer progression and modulates insulin/IGF1 signaling and cancer cell migration

OBJECTIVE

The insulin/insulin-like growth factor 1 (IGF1) pathway is emerging as a crucial component of prostate cancer progression. Therefore, we investigated the role of the novel insulin/IGF1 signaling modulator inceptor in prostate cancer.

METHODS

We analyzed the expression of inceptor in human samples of benign prostate epithelium and prostate cancer. Further, we performed signaling and functional assays using prostate cancer cell lines.

RESULTS

We found that inceptor was expressed in human benign and malignant prostate tissue and its expression positively correlated with various genes of interest, including genes involved in androgen signaling. In vitro, total levels of inceptor were increased upon androgen deprivation and correlated with high levels of androgen receptor in the nucleus. Inceptor overexpression was associated with increased cell migration, altered IGF1R trafficking and higher IGF1R activation.

CONCLUSIONS

Our in vitro results showed that inceptor expression was associated with androgen status, increased migration, and IGF1R signaling. In human samples, inceptor expression was significantly correlated with markers of prostate cancer progression. Taken together, these data provide a basis for investigation of inceptor in the context of prostate cancer.

Lower Hepatic Fat Is Associated With Improved Insulin Secretion in a High-Risk Prediabetes Subphenotype During Lifestyle Intervention

The objective of this work was to investigate whether impaired insulin secretion can be restored by lifestyle intervention in specific subphenotypes of prediabetes. We assigned 1,045 participants from the Prediabetes Lifestyle Intervention Study (PLIS) to six recently established prediabetes clusters. Insulin secretion was assessed by a C-peptide-based index derived from oral glucose tolerance tests and modeled from three time points during a 1-year intervention. We also analyzed the change of glycemia, insulin sensitivity, and liver fat. All prediabetes high-risk clusters (cluster 3, 5, and 6) had improved glycemic traits during the lifestyle intervention, whereas insulin secretion only increased in clusters 3 and 5 (P < 0.001); however, high liver fat in cluster 5 was associated with a failure to improve insulin secretion (Pinteraction < 0.001). Thus, interventions to reduce liver fat have the potential to improve insulin secretion in a defined subgroup of prediabetes.

The role of hepatokines in NAFLD

Non-alcoholic fatty liver disease (NAFLD) is not only a consequence of insulin resistance, but it is also an important cause of insulin resistance and major non-communicable diseases (NCDs). The close relationship of NAFLD with visceral obesity obscures the role of fatty liver from visceral adiposity as the main pathomechanism of insulin resistance and NCDs. To overcome this limitation, in analogy to the concept of adipokines, in 2008 we introduced the term hepatokines to describe the role of fetuin-A in metabolism. Since then, several other hepatokines were tested for their effects on metabolism. Here we address the dysregulation of hepatokines in people with NAFLD. Then, we discuss pathophysiological mechanisms of cardiometabolic diseases specifically related to NAFLD by focusing on hepatokine-related organ crosstalk. Finally, we propose how the determination of major hepatokines and adipokines can be used for pathomechanism-based clustering of insulin resistance in NAFLD and visceral obesity to better implement precision medicine in clinical practice.

Diabetes and the Prostate: Elevated Fasting Glucose, Insulin Resistance and Higher Levels of Adrenal Steroids in Prostate Cancer

Although epidemiological studies suggest a lower prostate cancer incidence rate in patients with type 2 diabetes, cancer survival is markedly reduced. Underlying mechanisms that connect the two diseases are still unclear. Potential links between type 2 diabetes and prostate cancer are hallmarks of the metabolic syndrome, such as hyperglycemia and dyslipidemia. Therefore, we explored the systemic metabolism of 103 prostate cancer patients with newly diagnosed and yet untreated prostate cancer compared to 107 healthy controls, who were carefully matched for age and BMI. Here, we report that patients with prostate cancer display higher fasting blood glucose levels and insulin resistance, without changes in insulin secretion. With respect to lipid metabolism, serum triglyceride levels were lower in patients with prostate cancer. In addition, we report increased adrenal steroid biosynthesis in these patients. Our results indicate that higher fasting glucose levels in patients with prostate cancer may be explained at least in part by insulin resistance, due to the enhanced synthesis of adrenal steroids.

Interscapular fat is associated with impaired glucose tolerance and insulin resistance independent of visceral fat mass

OBJECTIVE

Dysregulated body fat distribution is a major determinant of various diseases. In particular, increased visceral fat mass and ectopic lipids in the liver are linked to metabolic disorders such as insulin resistance and type 2 diabetes. Furthermore, interscapular fat is considered to be a metabolically active fat compartment.

METHODS

This study measured interscapular fat mass and investigated its relationship with glucose metabolism in 822 individuals with a wide range of BMI values and different glucose tolerance statuses. Magnetic resonance imaging was used to quantify body fat depots, and an oral glucose tolerance test was performed to determine glucose metabolism.

RESULTS

Elevated interscapular fat mass was positively associated with age, BMI, and total body, visceral, and subcutaneous adipose tissue mass. High interscapular fat mass associated with elevated fasting glucose levels, glucose levels at 2 hours during the oral glucose tolerance test, glycated hemoglobin, and insulin resistance, independent of sex, age, and total body and visceral fat mass.

CONCLUSIONS

In conclusion, interscapular fat might be a highly specific fat compartment with a potential impact on glucose metabolism and the pathogenesis of diabetes mellitus.

Exercise restores brain insulin sensitivity in sedentary adults who are overweight and obese

BACKGROUNDInsulin resistance of the brain can unfavorably affect long-term weight maintenance and body fat distribution. Little is known if and how brain insulin sensitivity can be restored in humans. We aimed to evaluate the effects of an exercise intervention on insulin sensitivity of the brain and how this relates to exercise-induced changes in whole-body metabolism and behavior.METHODSIn this clinical trial, sedentary participants who were overweight and obese underwent an 8-week supervised aerobic training intervention. Brain insulin sensitivity was assessed in 21 participants (14 women, 7 men; age range 21-59 years; BMI range 27.5-45.5 kg/m2) using functional MRI, combined with intranasal administration of insulin, before and after the intervention.RESULTSThe exercise program resulted in enhanced brain insulin action to the level of a person of healthy weight, demonstrated by increased insulin-induced striatal activity and strengthened hippocampal functional connectivity. Improved brain insulin action correlated with increased mitochondrial respiration in skeletal muscle, reductions in visceral fat and hunger, as well as improved cognition. Mediation analyses suggest that improved brain insulin responsiveness helps mediate the peripheral exercise effects leading to healthier body fat distribution and reduced perception of hunger.CONCLUSIONOur study demonstrates that an 8-week exercise intervention in sedentary individuals can restore insulin action in the brain. Hence, the ameliorating benefits of exercise toward brain insulin resistance may provide an objective therapeutic target in humans in the challenge to reduce diabetes risk factors.TRIAL REGISTRATIONClinicalTrials.gov (NCT03151590).FUNDINGBMBF/DZD 01GI0925.

Sex differences in central insulin action: Effect of intranasal insulin on neural food cue reactivity in adults with normal weight and overweight

Background/Objectives

Central insulin action influences cognitive processes, peripheral metabolism, and eating behavior. However, the contribution of obesity and sex on central insulin-mediated neural food cue processing still remains unclear.

Subjects/Methods

In a randomized within-participant design, including two visits, 60 participants (30 women, BMI 18–32 kg/m², age 21–69 years) underwent a functional MRI task measuring blood oxygen level-dependent (BOLD) signal in response to visual food cues after intranasal insulin or placebo spray administration. Central insulin action was defined as the neural BOLD response to food cues after insulin compared to placebo administration. Afterwards, participants were asked to rate the food cues for desire to eat (i.e., wanting rating). For statistical analyses, participants were grouped according to BMI and sex.

Results

Food cue reactivity in the amygdala showed higher BOLD activation in response to central insulin compared to placebo. Furthermore, women with overweight and obesity and men of normal weight showed higher BOLD neural food cue responsivity to central insulin compared to placebo. Higher central insulin action in the insular cortex was associated with better peripheral insulin sensitivity and higher cognitive control. Moreover, central insulin action in the dorsolateral prefrontal cortex (DLPFC) revealed significant sex differences. In response to central insulin compared to placebo, men showed lower DLPFC BOLD activity, whereas women showed higher DLPFC activity in response to highly desired food cues. On behavioral level, central insulin action significantly reduced hunger, whereas the desire to eat, especially for low caloric food cues was significantly higher with central insulin than with placebo.

Conclusions

Obesity and sex influenced the central insulin-mediated neural BOLD activity to visual food cues in brain regions implicated in reward and cognitive control. These findings show that central insulin action regulates food response differentially in men and women, which may have consequences for metabolism and eating behavior.

Incretin Hypersecretion in Gestational Diabetes Mellitus

CONTEXT

Incretins are crucial stimulators of insulin secretion following food intake. Data on incretin secretion and action during pregnancy are sparse.

OBJECTIVE

The aim of the study was to investigate the incretin response during an oral glucose tolerance test (OGTT) in pregnant women with and without gestational diabetes mellitus (GDM).

DESIGN

We analyzed data from the ongoing observational PREG study (NCT04270578).

SETTING

The study was conducted at the University Hospital Tübingen.

PARTICIPANTS

We examined 167 women (33 with GDM) during gestational week 27 ± 2.2.

INTERVENTION

Subjects underwent 5-point OGTT with a 75-g glucose load.

MAIN OUTCOME MEASURES

We assessed insulin secretion and levels of total glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), glicentin, and glucagon during OGTT. Linear regression was used to analyze the relation of GLP-1 and glucose with insulin secretion and the association of incretin levels on birth outcome.

RESULTS

Insulin secretion was significantly lower in women with GDM (P < 0.001). Postload GLP-1 and GIP were ~20% higher in women with GDM (all P < 0.05) independent of age, body mass index, and gestational age. GLP-1 increase was associated with insulin secretion only in GDM, but not in normal glucose tolerance. Postprandial GLP-1 levels were negatively associated with birth weight.

CONCLUSIONS

The more pronounced GLP-1 increase in women with GDM could be part of a compensatory mechanism counteracting GLP-1 resistance. Higher GLP-1 levels might be protective against fetal overgrowth.

Bezafibrate Reduces Elevated Hepatic Fumarate in Insulin-Deficient Mice

Glucotoxic metabolites and pathways play a crucial role in diabetic complications, and new treatment options which improve glucotoxicity are highly warranted. In this study, we analyzed bezafibrate (BEZ) treated, streptozotocin (STZ) injected mice, which showed an improved glucose metabolism compared to untreated STZ animals. In order to identify key molecules and pathways which participate in the beneficial effects of BEZ, we studied plasma, skeletal muscle, white adipose tissue (WAT) and liver samples using non-targeted metabolomics (NMR spectroscopy), targeted metabolomics (mass spectrometry), microarrays and mitochondrial enzyme activity measurements, with a particular focus on the liver. The analysis of muscle and WAT demonstrated that STZ treatment elevated inflammatory pathways and reduced insulin signaling and lipid pathways, whereas BEZ decreased inflammatory pathways and increased insulin signaling and lipid pathways, which can partly explain the beneficial effects of BEZ on glucose metabolism. Furthermore, lysophosphatidylcholine levels were lower in the liver and skeletal muscle of STZ mice, which were reverted in BEZ-treated animals. BEZ also improved circulating and hepatic glucose levels as well as lipid profiles. In the liver, BEZ treatment reduced elevated fumarate levels in STZ mice, which was probably due to a decreased expression of urea cycle genes. Since fumarate has been shown to participate in glucotoxic pathways, our data suggests that BEZ treatment attenuates the urea cycle in the liver, decreases fumarate levels and, in turn, ameliorates glucotoxicity and reduces insulin resistance in STZ mice.

The German Gestational Diabetes Study (PREG), a prospective multicentre cohort study: rationale, methodology and design

INTRODUCTION

Even well-treated gestational diabetes mellitus (GDM) might still have impact on long-term health of the mother and her offspring, although this relationship has not yet been conclusively studied. Using in-depth phenotyping of the mother and her offspring, we aim to elucidate the relationship of maternal hyperglycaemia during pregnancy and adequate treatment, and its impact on the long-term health of both mother and child.

METHODS

The multicentre PREG study, a prospective cohort study, is designed to metabolically and phenotypically characterise women with a 75-g five-point oral glucose tolerance test (OGTT) during, and repeatedly after pregnancy. Outcome measures are maternal glycaemia during OGTTs, birth outcome and the health and growth development of the offspring. The children of the study participants are followed up until adulthood with developmental tests and metabolic and epigenetic phenotyping in the PREG Offspring study. A total of 800 women (600 with GDM, 200 controls) will be recruited.

ETHICS AND DISSEMINATION

The study protocol has been approved by all local ethics committees. Results will be disseminated via conference presentations and peer-reviewed publications.

TRIAL REGISTRATION NUMBER

The PREG study and the PREG Offspring study are registered with Clinical Trials (ClinicalTrials.gov identifiers: NCT04270578, NCT04722900).

Empagliflozin Improves Insulin Sensitivity of the Hypothalamus in Humans With Prediabetes: A Randomized, Double-Blind, Placebo-Controlled, Phase 2 Trial

OBJECTIVE

Insulin action in the human brain reduces food intake, improves whole-body insulin sensitivity, and modulates body fat mass and its distribution. Obesity and type 2 diabetes are often associated with brain insulin resistance, resulting in impaired brain-derived modulation of peripheral metabolism. So far, no pharmacological treatment for brain insulin resistance has been established. Since sodium-glucose cotransporter 2 (SGLT2) inhibitors lower glucose levels and modulate energy metabolism, we hypothesized that SGLT2 inhibition may be a pharmacological approach to reverse brain insulin resistance.

RESEARCH DESIGN AND METHODS

In this randomized, double-blind, placebo-controlled clinical trial, 40 patients (mean ± SD; age 60 ± 9 years; BMI 31.5 ± 3.8 kg/m2) with prediabetes were randomized to receive 25 mg empagliflozin every day or placebo. Before and after 8 weeks of treatment, brain insulin sensitivity was assessed by functional MRI combined with intranasal administration of insulin to the brain.

RESULTS

We identified a significant interaction between time and treatment in the hypothalamic response to insulin. Post hoc analyses revealed that only empagliflozin-treated patients experienced increased hypothalamic insulin responsiveness. Hypothalamic insulin action significantly mediated the empagliflozin-induced decrease in fasting glucose and liver fat.

CONCLUSIONS

Our results corroborate insulin resistance of the hypothalamus in humans with prediabetes. Treatment with empagliflozin for 8 weeks was able to restore hypothalamic insulin sensitivity, a favorable response that could contribute to the beneficial effects of SGLT2 inhibitors. Our findings position SGLT2 inhibition as the first pharmacological approach to reverse brain insulin resistance, with potential benefits for adiposity and whole-body metabolism.

Metabolic implications of pancreatic fat accumulation

Fat accumulation outside subcutaneous adipose tissue often has unfavourable effects on systemic metabolism. In addition to non-alcoholic fatty liver disease, which has received considerable attention, pancreatic fat has become an important area of research throughout the past 10 years. While a number of diagnostic approaches are available to quantify pancreatic fat, multi-echo Dixon MRI is currently the most developed method. Initial studies have shown associations between pancreatic fat and the metabolic syndrome, impaired glucose metabolism and type 2 diabetes mellitus. Pancreatic fat is linked to reduced insulin secretion, at least under specific circumstances such as prediabetes, low BMI and increased genetic risk of type 2 diabetes mellitus. This Review summarizes the possible causes and metabolic consequences of pancreatic fat accumulation. In addition, potential therapeutic approaches for addressing pancreatic fat accumulation are discussed.

Postprandial Dynamics of Proglucagon Cleavage Products and Their Relation to Metabolic Health

INTRODUCTION

While oral glucose ingestion typically leads to a decrease in circulating glucagon levels, a substantial number of persons display stable or rising glucagon concentrations when assessed by radioimmunoassay (RIA). However, these assays show cross-reactivity to other proglucagon cleavage products. Recently, more specific assays became available, therefore we systematically assessed glucagon and other proglucagon cleavage products and their relation to metabolic health.

RESEARCH DESIGN AND METHODS

We used samples from 52 oral glucose tolerance tests (OGTT) that were randomly selected from persons with different categories of glucose tolerance in an extensively phenotyped study cohort.

RESULTS

Glucagon concentrations quantified with RIA were non-suppressed at 2 hours of the OGTT in 36% of the samples. Non-suppressors showed lower fasting glucagon levels compared to suppressors (p=0.011). Similar to RIA measurements, ELISA-derived fasting glucagon was lower in non-suppressors (p<0.001). Glucagon 1-61 as well as glicentin and GLP-1 kinetics were significantly different between suppressors and non-suppressors (p=0.004, p=0.002, p=0.008 respectively) with higher concentrations of all three hormones in non-suppressors. Levels of insulin, C-peptide, and free fatty acids were comparable between groups. Non-suppressors were leaner and had lower plasma glucose concentrations (p=0.03 and p=0.047, respectively). Despite comparable liver fat content and insulin sensitivity (p≥0.3), they had lower 2-hour post-challenge glucose (p=0.01).

CONCLUSIONS

Glucagon 1-61, glicentin and GLP-1 partially account for RIA-derived glucagon measurements due to cross-reactivity of the assay. However, this contribution is small, since the investigated proglucagon cleavage products contribute less than 10% to the variation in RIA measured glucagon. Altered glucagon levels and higher post-challenge incretins are associated with a healthier metabolic phenotype.

Different Effects of Lifestyle Intervention in High- and Low-Risk Prediabetes: Results of the Randomized Controlled Prediabetes Lifestyle Intervention Study (PLIS)

Lifestyle intervention (LI) can prevent type 2 diabetes, but response to LI varies depending on risk subphenotypes. We tested whether individuals with prediabetes with low risk (LR) benefit from conventional LI and individuals with high risk (HR) benefit from an intensification of LI in a multicenter randomized controlled intervention over 12 months with 2 years' follow-up. A total of 1,105 individuals with prediabetes based on American Diabetes Association glucose criteria were stratified into an HR or LR phenotype based on previously described thresholds of insulin secretion, insulin sensitivity, and liver fat content. LR individuals were randomly assigned to conventional LI according to the Diabetes Prevention Program (DPP) protocol or control (1:1) and HR individuals to conventional or intensified LI with doubling of required exercise (1:1). A total of 908 (82%) participants completed the study. In HR individuals, the difference between conventional and intensified LI in postchallenge glucose change was -0.29 mmol/L [95% CI -0.54; -0.04], P = 0.025. Liver fat (-1.34 percentage points [95% CI -2.17; -0.50], P = 0.002) and cardiovascular risk (-1.82 percentage points [95% CI -3.13; -0.50], P = 0.007) underwent larger reductions with intensified than with conventional LI. During a follow-up of 3 years, intensified compared with conventional LI had a higher probability of normalizing glucose tolerance (P = 0.008). In conclusion, it is possible in HR individuals with prediabetes to improve glycemic and cardiometabolic outcomes by intensification of LI. Individualized, risk phenotype-based LI may be beneficial for the prevention of diabetes.

Elevated circulating follistatin associates with an increased risk of type 2 diabetes

The hepatokine follistatin is elevated in patients with type 2 diabetes (T2D) and promotes hyperglycemia in mice. Here we explore the relationship of plasma follistatin levels with incident T2D and mechanisms involved. Adjusted hazard ratio (HR) per standard deviation (SD) increase in follistatin levels for T2D is 1.24 (CI: 1.04–1.47, p < 0.05) during 19-year follow-up (n = 4060, Sweden); and 1.31 (CI: 1.09–1.58, p < 0.01) during 4-year follow-up (n = 883, Finland). High circulating follistatin associates with adipose tissue insulin resistance and non-alcoholic fatty liver disease (n = 210, Germany). In human adipocytes, follistatin dose-dependently increases free fatty acid release. In genome-wide association study (GWAS), variation in the glucokinase regulatory protein gene (GCKR) associates with plasma follistatin levels (n = 4239, Sweden; n = 885, UK, Italy and Sweden) and GCKR regulates follistatin secretion in hepatocytes in vitro. Our findings suggest that GCKR regulates follistatin secretion and that elevated circulating follistatin associates with an increased risk of T2D by inducing adipose tissue insulin resistance.

Follistatin promotes in type 2 diabetes (T2D) pathogenesis in model animals and is elevated in patients with T2D. Here the authors report that plasma follistatin associates with increased risk of incident T2D in two longitudinal cohorts, and show that follistatin regulates insulin-induced suppression lipolysis in cultured human adipocytes.

Detection of diabetes from whole-body MRI using deep learning

Obesity is one of the main drivers of type 2 diabetes, but it is not uniformly associated with the disease. The location of fat accumulation is critical for metabolic health. Specific patterns of body fat distribution, such as visceral fat, are closely related to insulin resistance. There might be further, hitherto unknown, features of body fat distribution that could additionally contribute to the disease. We used machine learning with dense convolutional neural networks to detect diabetes-related variables from 2371 T1-weighted whole-body MRI data sets. MRI was performed in participants undergoing metabolic screening with oral glucose tolerance tests. Models were trained for sex, age, BMI, insulin sensitivity, HbA1c, and prediabetes or incident diabetes. The results were compared with those of conventional models. The area under the receiver operating characteristic curve was 87% for the type 2 diabetes discrimination and 68% for prediabetes, both superior to conventional models. Mean absolute regression errors were comparable to those of conventional models. Heatmaps showed that lower visceral abdominal regions were critical in diabetes classification. Subphenotyping revealed a group with high future diabetes and microalbuminuria risk.Our results show that diabetes is detectable from whole-body MRI without additional data. Our technique of heatmap visualization identifies plausible anatomical regions and highlights the leading role of fat accumulation in the lower abdomen in diabetes pathogenesis.

Exercise prevents fatty liver by modifying the compensatory response of mitochondrial metabolism to excess substrate availability

Objective

Liver mitochondria adapt to high-calorie intake. We investigated how exercise alters the early compensatory response of mitochondria, thus preventing fatty liver disease as a long-term consequence of overnutrition.

Methods

We compared the effects of a steatogenic high-energy diet (HED) for six weeks on mitochondrial metabolism of sedentary and treadmill-trained C57BL/6N mice. We applied multi-OMICs analyses to study the alterations in the proteome, transcriptome, and lipids in isolated mitochondria of liver and skeletal muscle as well as in whole tissue and examined the functional consequences by high-resolution respirometry.

Results

HED increased the respiratory capacity of isolated liver mitochondria, both in sedentary and in trained mice. However, proteomics analysis of the mitochondria and transcriptomics indicated that training modified the adaptation of the hepatic metabolism to HED on the level of respiratory complex I, glucose oxidation, pyruvate and acetyl-CoA metabolism, and lipogenesis. Training also counteracted the HED-induced glucose intolerance, the increase in fasting insulin, and in liver fat by lowering diacylglycerol species and c-Jun N-terminal kinase (JNK) phosphorylation in the livers of trained HED-fed mice, two mechanisms that can reverse hepatic insulin resistance. In skeletal muscle, the combination of HED and training improved the oxidative capacity to a greater extent than training alone by increasing respiration of isolated mitochondria and total mitochondrial protein content.

Conclusion

We provide a comprehensive insight into the early adaptations of mitochondria in the liver and skeletal muscle to HED and endurance training. Our results suggest that exercise disconnects the HED-induced increase in mitochondrial substrate oxidation from pyruvate and acetyl-CoA-driven lipid synthesis. This could contribute to the prevention of deleterious long-term effects of high fat and sugar intake on hepatic mitochondrial function and insulin sensitivity.

•

High-energy diet promotes mitochondrial respiration in liver independent of training.

•

High-energy diet combined with training disconnects substrate oxidation from lipid synthesis.

•

High-energy diet combined with training reduces complex I formation in the liver.

•

Trained skeletal muscle unburdens the liver from substrate overload.

•

Comprehensive resource of mitochondrial adaptations to high-energy diet and training.

Central Insulin Modulates Dopamine Signaling in the Human Striatum

OBJECTIVE

Activity in the dopaminergic pathways of the brain is highly sensitive to body weight and metabolic states. Animal studies show that dopamine neurons are important targets for the metabolic hormone insulin with abolished effects in the insulin-resistant state, leading to increases in body weight and food intake. In humans, the influence of central acting insulin on dopamine and effects of their interplay are still elusive.

RESEARCH DESIGN AND METHODS

We investigated whether central administered insulin influences dopaminergic activity in striatal regions and whole-brain neural activity. Using a positron emission tomography (PET)/magnetic resonance imaging (MRI) hybrid scanner, we simultaneously performed [11C]-raclopride-PET and resting-state functional MRI in 10 healthy normal-weight men after application of intranasal insulin or placebo on 2 separate days in a randomized, placebo-controlled, blinded, crossover trial.

RESULTS

In response to central insulin compared with placebo administration, we observed greater [11C]-raclopride binding potential in the bilateral ventral and dorsal striatum. This suggests an insulin-induced reduction in synaptic dopamine levels. Resting-state striatal activity was lower 15 and 30 minutes after nasal insulin compared with placebo. Functional connectivity of the mesocorticolimbic circuitry associated with differences in dopamine levels: individuals with a stronger insulin-induced effect on dopamine levels showed a stronger increase in functional connectivity 45 minutes after intranasal insulin.

CONCLUSIONS

This study indicates that central insulin modulates dopaminergic tone in the striatum, which may affect regional brain activity and connectivity. Our results deepen the understanding of the insulin-dopamine interaction and the complex network that underlies the regulation of whole-body metabolism.

Comparison of the metabolome in urine prior and eight weeks after radical prostatectomy uncovers pathologic and molecular features of prostate cancer

Prostate cancer (PCa) is associated with cellular metabolism alterations leading to changes of the metabolome. So far, studies investigating these alterations mainly focused on comparisons of metabolite profiles of PCa patients and healthy controls. In the present study we compared for the first time metabolite profiles in a significant number of paired urine samples collected before and eight weeks after radical prostatectomy (rPX) in 34 patients with PCa. Our comprehensive non-targeted liquid chromatographic-mass spectrometric metabolomics approach covered > 3000 metabolite ion masses. We annotated 23 metabolites showing significant changes eight weeks after rPX. While the levels of uridine and six acylcarnitines in urine were increased before surgery, lower levels were detected for 16 metabolites, like e.g. citrate, phenyl-lactic acid, choline, myo-inositol, emphasizing a relevant pathophysiological role of these biomarkers and the associated metabolic pathways. These results have important implications for potential use of metabolome analyses for detection of prostate cancer and related pathologic and molecular features.

Lifestyle Intervention Improves Prothrombotic Coagulation Profile in Individuals at High Risk for Type 2 Diabetes

CONTEXT

Patients with obesity and insulin resistance are at higher risk for arterial and venous thrombosis due to a prothrombotic state.

OBJECTIVE

The present study addressed whether this is reversible by lifestyle intervention and elucidated potential underlying associations.

METHODS

A total of 100 individuals with impaired glucose tolerance or impaired fasting plasma glucose participated in a 1-year lifestyle intervention, including precise metabolic phenotyping and MRS-based determination of liver fat content as well as a comprehensive analysis of coagulation parameters before and after this intervention.

RESULTS

During the lifestyle intervention, significant reductions in coagulation factor activities (II, VII, VIII, IX, XI, and XII) were observed. Accordingly, prothrombin time (PT%) and activated partial thromboplastin time (aPTT) were slightly decreased and prolonged, respectively. Moreover, plasminogen activator inhibitor-1 (PAI-1), von Willebrand factor (vWF), and also protein C and protein S decreased. Fibrinogen, antithrombin, D-dimer, and FXIII remained unchanged. Searching for potential regulators, especially weight loss, but also liver fat reduction, improved insulin sensitivity, and decreased low-grade inflammation were linked to favorable changes in hemostasis parameters. Independent of weight loss, liver fat reduction (FII, protein C, protein S, PAI-1, vWF), improved insulin sensitivity (protein S, PAI-1), and reduced low-grade inflammation (PT%, aPTT, FVIII/IX/XI/XII, vWF) were identified as single potential regulators.

CONCLUSION

Lifestyle intervention is able to improve a prothrombotic state in individuals at high risk for type 2 diabetes. Besides body weight, liver fat content, insulin sensitivity, and systemic low-grade inflammation are potential mechanisms for improvements in hemostasis and could represent future therapeutic targets.

Liver-targeting drugs and their effect on blood glucose and hepatic lipids

The global epidemic of non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH) and the high prevalence among individuals with type 2 diabetes has attracted the attention of clinicians specialising in liver disorders. Many drugs are in the pipeline for the treatment of NAFLD/NASH, and several glucose-lowering drugs are now being tested specifically for the treatment of liver disease. Among these are nuclear hormone receptor agonists (e.g. peroxisome proliferator-activated receptor agonists, farnesoid X receptor agonists and liver X receptor agonists), fibroblast growth factor-19 and -21, single, dual or triple incretins, sodium-glucose cotransporter inhibitors, drugs that modulate lipid or other metabolic pathways (e.g. inhibitors of fatty acid synthase, diacylglycerol acyltransferase-1, acetyl-CoA carboxylase and 11β-hydroxysteroid dehydrogenase type-1) or drugs that target the mitochondrial pyruvate carrier. We have reviewed the metabolic effects of these drugs in relation to improvement of diabetic hyperglycaemia and fatty liver disease, as well as peripheral metabolism and insulin resistance.

Determinants of hepatic insulin clearance - Results from a Mendelian Randomization study

AIMS/HYPOTHESIS

Besides insulin resistance, type 2 diabetes associates with decreased hepatic insulin clearance (HIC). We now tested for causal relationship of HIC to liver fat accumulation or features of the metabolic syndrome.

METHODS

HIC was derived from oral glucose tolerance tests with the "Oral C-peptide and Insulin Minimal Models" (n = 3311). Liver fat was quantified by magnetic resonance spectroscopy (n = 1211). Mendelian Randomization was performed using established single nucleotide polymorphisms (SNPs; 115 for liver fat, 155 alanine-aminotransferase, 37 insulin sensitivity, 37 insulin secretion, 72 fasting insulin, 5285 BMI, 163 visceral fat, 270 waist circumference, 442 triglycerides, 620 HDL-Cholesterol, 193 C-reactive protein, 53 lipodystrophy-like phenotypes).

RESULTS

HIC associated inversely with liver fat (p < 0.003) and insulin sensitivity (p < 0.0001). Both liver fat and HIC were independently associated with insulin sensitivity (p < 0.0001). Neither liver fat nor alanine-aminotransferase were causally linked to HIC, as indicated by Mendelian Randomization (N_{liver fat} = 1054, N_HIC = 2254; N_{alanineaminotranferase} = 1985, N_HIC = 2251). BMI-related SNPs were causally associated with HIC (N_BMI = 2772, N_HIC = 2259, p < 0.001) but not waist circumference-SNPs (N_{SNPs-waist circumference} = 2751, N_HIC = 2280). Genetically determined insulin sensitivity was not causally related to HIC (N_{insulin sensitivity} = 2752, N_HIC = 2286). C-reactive protein and HDL were causally associated with HIC, with higher C-reactive protein and lower HDL leading to higher HIC (N_{C-reactive protein} = 2660, N_HIC = 2240; N_HDL = 2694, N_HIC = 2275).

CONCLUSIONS

This Mendelian Randomization analysis does not support a causal link between hepatic steatosis and HIC. Other components of the metabolic syndrome seem to compensate peripheral hyperinsulinemia by increasing hepatic insulin extraction.

The hepatokine fetuin-A disrupts functional maturation of pancreatic beta cells

AIMS/HYPOTHESIS

Neonatal beta cells carry out a programme of postnatal functional maturation to achieve full glucose responsiveness. A partial loss of the mature phenotype of adult beta cells may contribute to a reduction of functional beta cell mass and accelerate the onset of type 2 diabetes. We previously found that fetuin-A, a hepatokine increasingly secreted by the fatty liver and a determinant of type 2 diabetes, inhibits glucose-stimulated insulin secretion (GSIS) of human islets. Since fetuin-A is a ubiquitous fetal glycoprotein that declines peripartum, we examined here whether fetuin-A interferes with the functional maturity of beta cells.

METHODS

The effects of fetuin-A were assessed during in vitro maturation of porcine neonatal islet cell clusters (NICCs) and in adult human islets. Expression alterations were examined via microarray, RNA sequencing and reverse transcription quantitative real-time PCR (qRT-PCR), proteins were analysed by western blotting and immunostaining, and insulin secretion was quantified in static incubations.

RESULTS

NICC maturation was accompanied by the gain of glucose-responsive insulin secretion (twofold stimulation), backed up by mRNA upregulation of genes governing beta cell identity and function, such as NEUROD1, UCN3, ABCC8 and CASR (Log₂ fold change [Log₂FC] > 1.6). An active TGFβ receptor (TGFBR)-SMAD2/3 pathway facilitates NICC maturation, since the TGFBR inhibitor SB431542 counteracted the upregulation of aforementioned genes and de-repressed ALDOB, a gene disallowed in mature beta cells. In fetuin-A-treated NICCs, upregulation of beta cell markers and the onset of glucose responsiveness were suppressed. Concomitantly, SMAD2/3 phosphorylation was inhibited. Transcriptome analysis confirmed inhibitory effects of fetuin-A and SB431542 on TGFβ-1- and SMAD2/3-regulated transcription. However, contrary to SB431542 and regardless of cMYC upregulation, fetuin-A inhibited beta cell proliferation (0.27 ± 0.08% vs 1.0  ± 0.1% Ki67-positive cells in control NICCs). This effect was sustained by reduced expression (Log₂FC ≤ -2.4) of FOXM1, CENPA, CDK1 or TOP2A. In agreement, the number of insulin-positive cells was lower in fetuin-A-treated NICCs than in control NICCs (14.4 ± 1.2% and 22.3 ± 1.1%, respectively). In adult human islets fetuin-A abolished glucose responsiveness, i.e. 1.7- and 1.1-fold change over 2.8 mmol/l glucose in control- and fetuin-A-cultured islets, respectively. In addition, fetuin-A reduced SMAD2/3 phosphorylation and suppressed expression of proliferative genes. Of note, in non-diabetic humans, plasma fetuin-A was negatively correlated (p = 0.013) with islet beta cell area.

CONCLUSIONS/INTERPRETATION

Our results suggest that the perinatal decline of fetuin-A relieves TGFBR signalling in islets, a process that facilitates functional maturation of neonatal beta cells. Functional maturity remains revocable in later life, and the occurrence of a metabolically unhealthy milieu, such as liver steatosis and elevated plasma fetuin-A, can impair both function and adaptive proliferation of beta cells.

DATA AVAILABILITY

The RNAseq datasets and computer code produced in this study are available in the Gene Expression Omnibus (GEO): GSE144950; https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE144950.

Hemostatic alterations linked to body fat distribution, fatty liver, and insulin resistance

OBJECTIVE

Obesity, in particular visceral obesity, and insulin resistance emerged as major risk factors for severe coronavirus disease 2019 (COVID-19), which is strongly associated with hemostatic alterations. Because obesity and insulin resistance predispose to thrombotic diseases, we investigated the relationship between hemostatic alterations and body fat distribution in participants at risk for type 2 diabetes.

SUBJECTS

Body fat distribution (visceral and subcutaneous abdominal adipose tissue) and liver fat content of 150 participants - with impaired glucose tolerance and/or impaired fasting glucose - were determined using magnetic resonance imaging and spectroscopy. Participants underwent precise metabolic characterization and major hemostasis parameters were analyzed.

RESULTS

Procoagulant factors (FII, FVII, FVIII, and FIX) and anticoagulant proteins (antithrombin, protein C, and protein S) were significantly associated with body fat distribution. In patients with fatty liver, fibrinogen (298 mg/dl vs. 264 mg/dl, p = 0.0182), FVII (99% vs. 90%, p = 0.0049), FVIII (114% vs. 90%, p = 0.0098), protein C (124% vs. 111%, p = 0.0006), and protein S (109% vs. 89%, p < 0.0001) were higher than in controls. In contrast, antithrombin (97% vs. 102%, p = 0.0025) was higher in control patients. In multivariate analyses controlling for insulin sensitivity, body fat compartments, and genotype variants (PNPLA3^I148MM/MI/TM6SF2^E167kK/kE), only protein C and protein S remained significantly increased in fatty liver.

CONCLUSIONS

Body fat distribution is significantly associated with alterations of procoagulant and anticoagulant parameters. Liver fat plays a key role in the regulation of protein C and protein S, suggesting a potential counteracting mechanism to the prothrombotic state in subjects with prediabetes and fatty liver.

Low-Density Lipoprotein Cholesterol Is Associated With Insulin Secretion

CONTEXT

Pharmacological lowering of low-density lipoprotein (LDL) cholesterol potently reduces cardiovascular risk while concurrently increasing type 2 diabetes risk.

OBJECTIVE

The aim of this study was to investigate the relationship between LDL cholesterol concentrations and insulin secretion and glucagon levels.

METHODS

A total of 3039 individuals without cholesterol-lowering therapy, but with increased risk for diabetes, underwent routine blood tests and a 5-point oral glucose tolerance test (OGTT). Glucagon concentrations, insulin secretion, and insulin clearance indices were derived from the OGTT.

RESULTS

There was no association between LDL cholesterol and fasting glucagon (P = .7, β = -.01) or post-glucose load glucagon levels (P = .7, β = -.07), but we detected significant positive associations of LDL cholesterol and C-peptide-based indices of insulin secretion (area under the curve [AUC]C-Peptide(0-30min)/AUCGlucose(0-30min): P < .001, β = .06; AUCC-Peptide(0-120min) /AUCGlucose(0-120min): P < .001, β = -.08). In contrast, we found a negative association of insulin-based insulin secretion indices with LDL concentrations (insulinogenic index: P = .01, β = -.04; disposition index: P < .001, β = -.06). LDL cholesterol levels, however, were positively associated with insulin clearance assessed from C-peptide and insulin concentrations, both in the fasting state and post-glucose load (P < .001, β = .09 and P < .001, β = .06, respectively).

CONCLUSION

As C-peptide based indices reflect insulin secretion independent of hepatic clearance, our results indicate lower insulin secretion in case of lesser LDL cholesterol. This could explain deteriorating glycemic control in response to cholesterol-lowering drugs.

Pancreatic fat cells of humans with type 2 diabetes display reduced adipogenic and lipolytic activity

Obesity, especially visceral fat accumulation, increases the risk of type 2 diabetes (T2D). The purpose of this study was to investigate the impact of T2D on the pancreatic fat depot. Pancreatic fat pads from 17 partial pancreatectomized patients (PPP) were collected, pancreatic preadipocytes isolated, and in vitro differentiated. Patients were grouped using HbA1c into normal glucose tolerant (NGT), prediabetic (PD), and T2D. Transcriptome profiles of preadipocytes and adipocytes were assessed by RNAseq. Insulin sensitivity was estimated by quantifying AKT phosphorylation on Western blots. Lipogenic capacity was assessed with oil red O staining, lipolytic activity via fatty acid release. Secreted factors were measured using ELISA. Comparative transcriptome analysis of preadipocytes and adipocytes indicates defective upregulation of genes governing adipogenesis (NR1H3), lipogenesis (FASN, SCD, ELOVL6, and FADS1), and lipolysis (LIPE) during differentiation of cells from T2D-PPP. In addition, the ratio of leptin/adiponectin mRNA was higher in T2D than in NGT-PPP. Preadipocytes and adipocytes of NGT-PPP were more insulin sensitive than T2D-PPP cells in regard to AKT phosphorylation. Triglyceride accumulation was similar in NGT and T2D adipocytes. Despite a high expression of the receptors NPR1 and NPR2 in NGT and T2D adipocytes, lipolysis was stimulated by ANP 1.74-fold in NGT cells only. This stimulation was further increased by the PDE5 inhibitor dipyridamole (3.09-fold). Dipyridamole and forskolin increased lipolysis receptor independently 1.88-fold and 1.48-fold, respectively, solely in NGT cells. In conclusion, the metabolic status persistently affects differentiation and lipolysis of pancreatic adipocytes. These alterations could aggravate the development of T2D.

Type 2 diabetes risk gene Dusp8 regulates hypothalamic Jnk signaling and insulin sensitivity

Recent genome-wide association studies (GWAS) identified DUSP8, encoding a dual-specificity phosphatase targeting mitogen-activated protein kinases, as a type 2 diabetes (T2D) risk gene. Here, we reveal that Dusp8 is a gatekeeper in the hypothalamic control of glucose homeostasis in mice and humans. Male, but not female, Dusp8 loss-of-function mice, either with global or corticotropin-releasing hormone neuron-specific deletion, had impaired systemic glucose tolerance and insulin sensitivity when exposed to high-fat diet (HFD). Mechanistically, we found impaired hypothalamic-pituitary-adrenal axis feedback, blunted sympathetic responsiveness, and chronically elevated corticosterone levels driven by hypothalamic hyperactivation of Jnk signaling. Accordingly, global Jnk1 ablation, AAV-mediated Dusp8 overexpression in the mediobasal hypothalamus, or metyrapone-induced chemical adrenalectomy rescued the impaired glucose homeostasis of obese male Dusp8-KO mice, respectively. The sex-specific role of murine Dusp8 in governing hypothalamic Jnk signaling, insulin sensitivity, and systemic glucose tolerance was consistent with functional MRI data in human volunteers that revealed an association of the DUSP8 rs2334499 risk variant with hypothalamic insulin resistance in men. Further, expression of DUSP8 was increased in the infundibular nucleus of T2D humans. In summary, our findings suggest the GWAS-identified gene Dusp8 as a novel hypothalamic factor that plays a functional role in the etiology of T2D.

Elevated Circulating Glutamate Is Associated With Subclinical Atherosclerosis Independently of Established Risk Markers: A Cross-Sectional Study

OBJECTIVE

Elevated plasma glutamate levels are associated with an increased risk of cardiovascular disease (CVD). Because plasma glutamate levels are also strongly associated with visceral adiposity, nonalcoholic fatty liver disease, insulin resistance, and high circulating levels of branched-chain amino acids (BCAAs), it is unknown to what extent elevated circulating glutamate is an independent marker of an increased risk of atherosclerosis.

METHODS

Plasma levels of glutamate and BCAAs were measured in 102 individuals who were precisely phenotyped for body fat mass and distribution (magnetic resonance [MR] tomography), liver fat content (1H-MR spectroscopy), insulin sensitivity (oral glucose tolerance test and hyperinsulinemic, euglycemic clamp [N = 57]), and carotid intima media thickness (cIMT).

RESULTS

Plasma glutamate levels, adjusted for age, sex, body fat mass, and visceral fat mass, correlated positively with liver fat content and cIMT (all std β ≥ .22, all P ≤ .023) and negatively with insulin sensitivity (std β ≤ -.31, P ≤ .002). Glutamate levels also were associated with cIMT, independently of additional adjustment for liver fat content, insulin sensitivity and BCAAs levels (std β ≥ .24, P ≤ .02). Furthermore, an independent positive association of glutamate and interleukin-6 (IL-6) levels was observed (N = 50; std β = .39, P = .03). Although glutamate, adjusted for age, sex, body fat mass, and visceral fat mass, also correlated positively with cIMT in this subgroup (std β = .31, P = .02), after additional adjustment for the parameters liver fat content, insulin sensitivity, BCAAs, or IL-6 levels, adjustment for IL-6 most strongly attenuated this relationship (std β = .28, P = .05).

CONCLUSIONS

Elevated plasma glutamate levels are associated with increased cIMT, independently of established CVD risk factors, and this relationship may in part be explained by IL-6-associated subclinical inflammation.

Pathophysiology-based subphenotyping of individuals at elevated risk for type 2 diabetes

The state of intermediate hyperglycemia is indicative of elevated risk of developing type 2 diabetes1. However, the current definition of prediabetes neither reflects subphenotypes of pathophysiology of type 2 diabetes nor is predictive of future metabolic trajectories. We used partitioning on variables derived from oral glucose tolerance tests, MRI-measured body fat distribution, liver fat content and genetic risk in a cohort of extensively phenotyped individuals who are at increased risk for type 2 diabetes2,3 to identify six distinct clusters of subphenotypes. Three of the identified subphenotypes have increased glycemia (clusters 3, 5 and 6), but only individuals in clusters 5 and 3 have imminent diabetes risks. By contrast, those in cluster 6 have moderate risk of type 2 diabetes, but an increased risk of kidney disease and all-cause mortality. Findings were replicated in an independent cohort using simple anthropomorphic and glycemic constructs4. This proof-of-concept study demonstrates that pathophysiological heterogeneity exists before diagnosis of type 2 diabetes and highlights a group of individuals who have an increased risk of complications without rapid progression to overt type 2 diabetes.

Adolescent Nonalcoholic Fatty Liver Disease and Type 2 Diabetes in Young Adulthood

CONTEXT

The long-term risk of type 2 diabetes in adolescents with nonalcoholic fatty liver disease (NAFLD) is unclear.

OBJECTIVE

To assess type 2 diabetes risk among adolescents with NAFLD.

DESIGN AND SETTING

A nationwide, population-based study of Israeli adolescents who were examined before military service during 1997-2011 and were followed until December 31, 2016.

PARTICIPANTS

A total of 1 025 796 normoglycemic adolescents were included.

INTERVENTIONS

Biopsy or radiographic tests were prerequisite for NAFLD diagnosis. Data were linked to the Israeli National Diabetes Registry.

MAIN OUTCOME MEASURES

Type 2 diabetes incidence.

RESULTS

During a mean follow-up of 13.3 years, 12 of 633 adolescents with NAFLD (1.9%; all with high body mass index [BMI] at baseline) were diagnosed with type 2 diabetes compared with 2917 (0.3%) adolescents without NAFLD. The hazard ratio (HR) for type 2 diabetes was 2.59 (95% confidence interval [CI], 1.47-4.58) for the NAFLD vs. the non-NAFLD group after adjustment for BMI and sociodemographic confounders. The elevated risk persisted in several sensitivity analyses. These included an analysis of persons without other metabolic comorbidities (adjusted HR, 2.75 [95% CI, 1.48-5.14]) and of persons with high BMI; and an analysis whose outcome was type 2 diabetes by age 30 years (adjusted HR, 2.14 [95% CI, 1.02-4.52]). The results remained significant when a sex-, birth year-, and BMI-matched control group was the reference (adjusted HR, 2.98 [95% CI, 1.54-5.74]).

CONCLUSIONS

Among normoglycemic adolescents, NAFLD was associated with an increased adjusted risk for type 2 diabetes, which may be apparent before age 30 years.

Investigating obesity-associated brain inflammation using quantitative water content mapping

There is growing evidence that obesity is associated with inflammation in the brain, which could contribute to the pathogenesis of obesity. In humans, it is challenging to detect brain inflammation in vivo. Recently, quantitative magnetic resonance imaging (qMRI) has emerged as a tool for characterising pathophysiological processes in the brain with reliable and reproducible measures. Proton density imaging provides quantitative assessment of the brain water content, which is affected in different pathologies, including inflammation. We enrolled 115 normal weight, overweight and obese men and women (body mass index [BMI] range 20.1-39.7 kg m^-2 , age range 20-75 years, 60% men) to acquire cerebral water content mapping in vivo using MRI at 3 Tesla. We investigated potential associations between brain water content with anthropometric measures of obesity, body fat distribution and whole-body metabolism. No global changes in water content were associated with obesity. However, higher water content values in the cerebellum, limbic lobe and sub-lobular region were detected in participants with higher BMI, independent of age. More specifically, the dorsal striatum, hypothalamus, thalamus, fornix, anterior limb of the internal capsule and posterior thalamic radiation showed the strongest relationship with BMI, independent of age. In a subgroup with available measurements (n = 50), we identified visceral adipose tissue to be the strongest tested link between higher water content values and obesity. Individuals with metabolic syndrome had the highest water content values in the hypothalamus and the fornix. There is accumulating evidence that inflammation of the hypothalamus contributed to obesity-associated insulin resistance in that area. Whether brain inflammation is a cause or consequence of obesity in humans still needs to be investigated using a longitudinal study design. Using qMRI, we were able to detect marked water content changes in young and older obese adults, which is most likely the result of chronic low-grade inflammation.

No modulation of postprandial metabolism by transcutaneous auricular vagus nerve stimulation: a cross-over study in 15 healthy men

Experimental evidence suggests a crucial role of the autonomic nervous system in whole body metabolism with major regulatory effects of the parasympathetic branch in postprandial adaptation. However, the relative contribution of this mechanism is still not fully clear in humans. We therefore compared the effects of transcutaneous auricular vagus nerve stimulation (taVNS, Cerbomed Nemos) with sham stimulation during an oral glucose tolerance test in a randomized, single-blind, cross-over design in 15 healthy lean men. Stimulation was performed for 150 min, 30 min before and during the entire oral glucose tolerance test with stimulation cycles of 30 s of on-phase and 30 s of off-phase and a 25 Hz impulse. Heart rate variability and plasma catecholamine levels were assessed as proxies of autonomic tone in the periphery. Neither analyzed heart rate variability parameters nor plasma catecholamine levels were significantly different between the two conditions. Plasma glucose, insulin sensitivity and insulin secretion were also comparable between conditions. Thus, the applied taVNS device or protocol was unable to achieve significant effects on autonomic innervation in peripheral organs. Accordingly, glucose metabolism remained unaltered. Therefore, alternative approaches are necessary to investigate the importance of the autonomic nervous system in postprandial human metabolism.

Fully Automated and Standardized Segmentation of Adipose Tissue Compartments via Deep Learning in 3D Whole-Body MRI of Epidemiologic Cohort Studies

PURPOSE

To enable fast and reliable assessment of subcutaneous and visceral adipose tissue compartments derived from whole-body MRI.

MATERIALS AND METHODS

Quantification and localization of different adipose tissue compartments derived from whole-body MR images is of high interest in research concerning metabolic conditions. For correct identification and phenotyping of individuals at increased risk for metabolic diseases, a reliable automated segmentation of adipose tissue into subcutaneous and visceral adipose tissue is required. In this work, a three-dimensional (3D) densely connected convolutional neural network (DCNet) is proposed to provide robust and objective segmentation. In this retrospective study, 1000 cases (average age, 66 years ± 13 [standard deviation]; 523 women) from the Tuebingen Family Study database and the German Center for Diabetes research database and 300 cases (average age, 53 years ± 11; 152 women) from the German National Cohort (NAKO) database were collected for model training, validation, and testing, with transfer learning between the cohorts. These datasets included variable imaging sequences, imaging contrasts, receiver coil arrangements, scanners, and imaging field strengths. The proposed DCNet was compared to a similar 3D U-Net segmentation in terms of sensitivity, specificity, precision, accuracy, and Dice overlap.

RESULTS

Fast (range, 5-7 seconds) and reliable adipose tissue segmentation can be performed with high Dice overlap (0.94), sensitivity (96.6%), specificity (95.1%), precision (92.1%), and accuracy (98.4%) from 3D whole-body MRI datasets (field of view coverage, 450 × 450 × 2000 mm). Segmentation masks and adipose tissue profiles are automatically reported back to the referring physician.

CONCLUSION

Automated adipose tissue segmentation is feasible in 3D whole-body MRI datasets and is generalizable to different epidemiologic cohort studies with the proposed DCNet.Supplemental material is available for this article.© RSNA, 2020.

Pancreatic Steatosis Associates With Impaired Insulin Secretion in Genetically Predisposed Individuals

CONTEXT

Pancreatic steatosis leading to beta-cell failure might be involved in type 2 diabetes (T2D) pathogenesis.

OBJECTIVE

We hypothesized that the genetic background modulates the effect of pancreatic fat on beta-cell function and investigated genotype × pancreatic fat interactions on insulin secretion.

DESIGN

Two observational studies.

SETTING

University hospital.

PATIENTS OR PARTICIPANTS

A total of 360 nondiabetic individuals with elevated risk for T2D (Tuebingen Family Study [TUEF]), and 64 patients undergoing pancreatectomy (Pancreas Biobank [PB], HbA1c <9%, no insulin therapy).

MAIN OUTCOME MEASURES

Insulin secretion calculated from 5-point oral glucose tolerance test (TUEF) and fasting blood collection before surgery (PB). A genome-wide polygenic score for T2D was computed from 484,788 genotyped variants. The interaction of magnetic resonance imaging-measured and histologically quantified pancreatic fat with the polygenic score was investigated. Partitioned risk scores using genome-wide significant variants were also computed to gain insight into potential mechanisms.

RESULTS

Pancreatic steatosis interacted with genome-wide polygenic score on insulin secretion (P = 0.003), which was similar in the replication cohort with histological measurements (P = 0.03). There was a negative association between pancreatic fat and insulin secretion in participants with high genetic risk, whereas individuals with low genetic risk showed a positive correlation between pancreatic fat and insulin secretion. Consistent interactions were found with insulin resistance-specific and a liver/lipid-specific polygenic scores.

CONCLUSIONS

The associations suggest that pancreatic steatosis only impairs beta-cell function in subjects at high genetic risk for diabetes. Genetically determined insulin resistance specifically renders pancreatic fat deleterious for insulin secretion.

Response of Mitochondrial Respiration in Adipose Tissue and Muscle to 8 Weeks of Endurance Exercise in Obese Subjects

CONTEXT

Exercise training improves glycemic control and increases mitochondrial content and respiration capacity in skeletal muscle. Rodent studies suggest that training increases mitochondrial respiration in adipose tissue.

OBJECTIVE

To assess the effects of endurance training on respiratory capacities of human skeletal muscle and abdominal subcutaneous adipose tissue and to study the correlation with improvement in insulin sensitivity.

DESIGN

Using high-resolution respirometry, we analyzed biopsies from 25 sedentary (VO2 peak 25.1 ± 4.0 VO2 mL/[kg*min]) subjects (16 female, 9 male; 29.8 ± 8.4 years) with obesity (body mass index [BMI] 31.5 ± 4.3 kg/m2), who did not have diabetes. They performed a supervised endurance training over 8 weeks (3 × 1 hour/week at 80% VO2 peak).

RESULTS

Based on change in insulin sensitivity after intervention (using the Matsuda insulin sensitivity index [ISIMats]), subjects were grouped in subgroups as responders (>15% increase in ISIMats) and low-responders. The response in ISIMats was correlated to a reduction of subcutaneous and visceral adipose tissue volume. Both groups exhibited similar increases in fitness, respiratory capacity, and abundance of mitochondrial enzymes in skeletal muscle fibers. Respiratory capacities in subcutaneous adipose tissue were not altered by the intervention. Compared with muscle fibers, adipose tissue respiration showed a preference for β-oxidation and complex II substrates. Respiratory capacities were higher in adipose tissue from female participants.

CONCLUSION

Our data show that the improvement of peripheral insulin sensitivity after endurance training is not directly related to an increase in mitochondrial respiratory capacities in skeletal muscle and occurs without an increase in the respiratory capacity of subcutaneous adipose tissue.

Insulin sensitivity predicts cognitive decline in individuals with prediabetes

INTRODUCTION

Epidemiological studies indicate an association between type 2 diabetes and cognitive dysfunction that appear to start already in the prediabetic state. Although cross-sectional studies have linked insulin resistance to impaired cognition, the potential predictive value of insulin resistance has not yet been sufficiently studied longitudinally without confounding by overt diabetes (and its pharmacological treatment).

RESEARCH DESIGN AND METHODS

We investigated longitudinal data from participants of the 'Tübinger Evaluation of Risk Factors for Early Detection of Neurodegeneration' Study. Subjects underwent a neurocognitive assessment battery (CERAD Plus battery; Consortium to Establish a Registry for Alzheimer's Disease) at baseline and followed every 2 years (median follow-up 4.0 Q1-3: 2.2-4.3 years). Subjects within a pre-diabetic glycated hemoglobin range of 5.6%-6.5% underwent 5-point 75 g oral glucose tolerance tests (OGTTs) with assessment of insulin sensitivity and insulin secretion (n=175). Subjects with newly diagnosed diabetes mellitus or with major depressivity (Beck Depression Inventory >20) were excluded (n=15). Data were analyzed by mixed models using sex, age and glycemic trait as fixed effects. Subject and time since first measurement were used as random effects.

RESULTS

Insulin sensitivity was positively associated with the CERAD sum score (higher is better) in a time-dependent manner (p=0.0057). This result is mainly driven by a steeper decrease in the memory domain associated with lower insulin sensitivity (p=0.029). The interaction between age and insulin sensitivity was independent of glycemia (p=0.02). There was also no association between insulin secretion and cognition.

CONCLUSIONS

Insulin resistance rather than sole elevation of blood glucose predicts cognitive decline, specifically in the memory domain, in persons with prediabetes. Treatments of diabetes that improve insulin sensitivity might therefore have the potential to postpone or even prevent cognitive decline in patients with diabetes.

Characterization of Hormone-Dependent Pathways in Six Human Prostate-Cancer Cell Lines: A Gene-Expression Study

Prostate cancer (PCa), the most incident cancer in men, is tightly regulated by endocrine signals. A number of different PCa cell lines are commonly used for in vitro experiments, but these are of diverse origin, and have very different cell-proliferation rates and hormone-response capacities. By analyzing the gene-expression pattern of main hormone pathways, we systematically compared six PCa cell lines and parental primary cells. We compared these cell lines (i) with each other and (ii) with PCa tissue samples from 11 patients. We found major differences in the gene-expression levels of androgen, insulin, estrogen, and oxysterol signaling between PCa tissue and cell lines, and between different cell lines. Our systematic characterization gives researchers a solid basis to choose the appropriate PCa cell model for the hormone pathway of interest.

Lack of Gαi2 proteins in adipocytes attenuates diet-induced obesity

OBJECTIVES

Typically, obesity results from an inappropriate balance between energy uptake from nutrient consumption and burning of calories, which leads to a pathological increase in fat mass. Obesity is a major cause of insulin resistance and diabetes. Inhibitory G proteins (Gαi) form a subfamily that is involved in the regulation of adipose tissue function. Among the three Gαi members, i.e. Gαi1, Gαi2, Gαi3, the Gαi2, protein is predominantly expressed in adipose tissue. However, the functions of the Gαi2 isoform in adipose tissue and its impact on the development of obesity are poorly understood.

METHODS

By using AdipoqCreERT2 mice, we generated adipocyte-specific Gnai2-deficient mice to study Gαi2 function, specifically in white and brown adipocytes. These mice were fed either a control diet (CD) or a high fat diet (HFD). Mice were examined for obesity development, insulin resistance and glucose intolerance. We examined adipocyte morphology and the development of inflammation in the white adipose tissue. Finally, intracellular cAMP levels as an indicator of Gαi signaling and glycerol release as an indicator of lipolysis rates were measured to verify the impact of Gαi2 on the signaling pathway in brown and white adipocytes.

RESULTS

An adipocyte-specific deficiency of Gαi2 significantly reduced diet-induced obesity, leading to decreased fat masses, smaller adipocytes and decreased inflammation in the white adipose tissue relative to littermate controls. Concurrently, oxygen consumption of brown adipocytes and in vivo measured energy expenditure were significantly enhanced. In addition, glucose tolerance and insulin sensitivity of HFD-fed adipocyte-specific Gnai2-deficient mice were improved compared to the respective controls. In the absence of Gαi2, adrenergic stimulation of intracellular adipocyte cAMP levels was increased, which correlated with increased lipolysis and energy expenditure.

CONCLUSION

We conclude that adipocyte Gαi2 is a major regulator of adipocyte lipid content in diet-induced obesity by inhibiting adipocyte lipolysis in a cAMP-dependent manner resulting in increased energy expenditure.