Publications by authors named "Bernard Thorens"

141 Publications

Plasma triacylglycerols are biomarkers of β-cell function in mice and humans.

Mol Metab 2021 Oct 9;54:101355. Epub 2021 Oct 9.

Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland. Electronic address:

Objectives: To find plasma biomarkers prognostic of type 2 diabetes, which could also inform on pancreatic β-cell deregulations or defects in the function of insulin target tissues.

Methods: We conducted a systems biology approach to characterize the plasma lipidomes of C57Bl/6J, DBA/2J, and BALB/cJ mice under different nutritional conditions, as well as their pancreatic islet and liver transcriptomes. We searched for correlations between plasma lipids and tissue gene expression modules.

Results: We identified strong correlation between plasma triacylglycerols (TAGs) and islet gene modules that comprise key regulators of glucose- and lipid-regulated insulin secretion and of the insulin signaling pathway, the two top hits were Gck and Abhd6 for negative and positive correlations, respectively. Correlations were also found between sphingomyelins and islet gene modules that overlapped in part with the gene modules correlated with TAGs. In the liver, the gene module most strongly correlated with plasma TAGs was enriched in mRNAs encoding fatty acid and carnitine transporters as well as multiple enzymes of the β-oxidation pathway. In humans, plasma TAGs also correlated with the expression of several of the same key regulators of insulin secretion and the insulin signaling pathway identified in mice. This cross-species comparative analysis further led to the identification of PITPNC1 as a candidate regulator of glucose-stimulated insulin secretion.

Conclusion: TAGs emerge as biomarkers of a liver-to-β-cell axis that links hepatic β-oxidation to β-cell functional mass and insulin secretion.
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http://dx.doi.org/10.1016/j.molmet.2021.101355DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8602044PMC
October 2021

Glucokinase neurons of the paraventricular nucleus of the thalamus sense glucose and decrease food consumption.

iScience 2021 Oct 11;24(10):103122. Epub 2021 Sep 11.

Center for Integrative Genomics, University of Lausanne, Genopode Building, 1015 Lausanne, Switzerland.

The paraventricular nucleus of the thalamus (PVT) controls goal-oriented behavior through its connections to the nucleus accumbens (NAc). We previously characterized Glut2 neurons that are activated by hypoglycemia, and which increase sucrose seeking behavior through their glutamatergic projections to the NAc. Here, we identified glucokinase ()-expressing neurons of the PVT (Gck) and generated a mouse line expressing the Cre recombinase from the glucokinase locus ( mice). calcium imaging and whole-cell patch clamp recordings revealed that Gck neurons that project to the NAc were mostly activated by hyperglycemia. Their chemogenetic inhibition or optogenetic stimulation, respectively, enhanced food intake or decreased sucrose-seeking behavior. Collectively, our results describe a neuronal population of Gck-expressing neurons in the PVT, which has opposite glucose sensing properties and control over feeding behavior than the previously characterized Glut2 neurons. This study allows a better understanding of the complex regulation of feeding behavior by the PVT.
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http://dx.doi.org/10.1016/j.isci.2021.103122DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8481977PMC
October 2021

Mike Mueckler (1953-2021): the father of the mammalian SLC2 glucose transporter family.

Am J Physiol Endocrinol Metab 2021 10 23;321(4):E490-E492. Epub 2021 Aug 23.

Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.

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http://dx.doi.org/10.1152/ajpendo.00290.2021DOI Listing
October 2021

Distinct Molecular Signatures of Clinical Clusters in People With Type 2 Diabetes: An IMI-RHAPSODY Study.

Diabetes 2021 Nov 10;70(11):2683-2693. Epub 2021 Aug 10.

Genetic and Molecular Epidemiology Unit, Lund University Diabetes Centre, Department of Clinical Sciences, Clinical Research Centre, Lund University, SUS, Malmö, Sweden.

Type 2 diabetes is a multifactorial disease with multiple underlying aetiologies. To address this heterogeneity, investigators of a previous study clustered people with diabetes according to five diabetes subtypes. The aim of the current study is to investigate the etiology of these clusters by comparing their molecular signatures. In three independent cohorts, in total 15,940 individuals were clustered based on five clinical characteristics. In a subset, genetic ( = 12,828), metabolomic ( = 2,945), lipidomic ( = 2,593), and proteomic ( = 1,170) data were obtained in plasma. For each data type, each cluster was compared with the other four clusters as the reference. The insulin-resistant cluster showed the most distinct molecular signature, with higher branched-chain amino acid, diacylglycerol, and triacylglycerol levels and aberrant protein levels in plasma were enriched for proteins in the intracellular PI3K/Akt pathway. The obese cluster showed higher levels of cytokines. The mild diabetes cluster with high HDL showed the most beneficial molecular profile with effects opposite of those seen in the insulin-resistant cluster. This study shows that clustering people with type 2 diabetes can identify underlying molecular mechanisms related to pancreatic islets, liver, and adipose tissue metabolism. This provides novel biological insights into the diverse aetiological processes that would not be evident when type 2 diabetes is viewed as a homogeneous disease.
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http://dx.doi.org/10.2337/db20-1281DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8564413PMC
November 2021

Ablation of glucokinase-expressing tanycytes impacts energy balance and increases adiposity in mice.

Mol Metab 2021 Nov 26;53:101311. Epub 2021 Jul 26.

Center for Integrative Genomics, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland; Department of Biomedical Sciences, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland. Electronic address:

Objectives: Glucokinase (GCK) is critical for glucosensing. In rats, GCK is expressed in hypothalamic tanycytes and appears to play an essential role in feeding behavior. In this study, we investigated the distribution of GCK-expressing tanycytes in mice and their role in the regulation of energy balance.

Methods: In situ hybridization, reporter gene assay, and immunohistochemistry were used to assess GCK expression along the third ventricle in mice. To evaluate the impact of GCK-expressing tanycytes on arcuate neuron function and mouse physiology, Gck deletion along the ventricle was achieved using loxP/Cre recombinase technology in adult mice.

Results: GCK expression was low along the third ventricle, but detectable in tanycytes facing the ventromedial arcuate nucleus from bregma -1.5 to -2.2. Gck deletion induced the death of this tanycyte subgroup through the activation of the BAD signaling pathway. The ablation of GCK-expressing tanycytes affected different aspects of energy balance, leading to an increase in adiposity in mice. This phenotype was systematically associated with a defect in NPY neuron function. In contrast, the regulation of glucose homeostasis was mostly preserved, except for glucoprivic responses.

Conclusions: This study describes the role of GCK in tanycyte biology and highlights the impact of tanycyte loss on the regulation of energy balance.
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http://dx.doi.org/10.1016/j.molmet.2021.101311DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8379510PMC
November 2021

Multi-omics profiling of living human pancreatic islet donors reveals heterogeneous beta cell trajectories towards type 2 diabetes.

Nat Metab 2021 07 28;3(7):1017-1031. Epub 2021 Jun 28.

Department of Molecular Diabetology, University Hospital and Faculty of Medicine, Technische Universität Dresden, Dresden, Germany.

Most research on human pancreatic islets is conducted on samples obtained from normoglycaemic or diseased brain-dead donors and thus cannot accurately describe the molecular changes of pancreatic islet beta cells as they progress towards a state of deficient insulin secretion in type 2 diabetes (T2D). Here, we conduct a comprehensive multi-omics analysis of pancreatic islets obtained from metabolically profiled pancreatectomized living human donors stratified along the glycemic continuum, from normoglycemia to T2D. We find that islet pools isolated from surgical samples by laser-capture microdissection display remarkably more heterogeneous transcriptomic and proteomic profiles in patients with diabetes than in non-diabetic controls. The differential regulation of islet gene expression is already observed in prediabetic individuals with impaired glucose tolerance. Our findings demonstrate a progressive, but disharmonic, remodelling of mature beta cells, challenging current hypotheses of linear trajectories toward precursor or transdifferentiation stages in T2D. Furthermore, through integration of islet transcriptomics with preoperative blood plasma lipidomics, we define the relative importance of gene coexpression modules and lipids that are positively or negatively associated with HbA1c levels, pointing to potential prognostic markers.
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http://dx.doi.org/10.1038/s42255-021-00420-9DOI Listing
July 2021

Replication and cross-validation of type 2 diabetes subtypes based on clinical variables: an IMI-RHAPSODY study.

Diabetologia 2021 Sep 10;64(9):1982-1989. Epub 2021 Jun 10.

Section of Cell Biology and Functional Genomics, Division of Diabetes, Endocrinology and Metabolism, Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK.

Aims/hypothesis: Five clusters based on clinical characteristics have been suggested as diabetes subtypes: one autoimmune and four subtypes of type 2 diabetes. In the current study we replicate and cross-validate these type 2 diabetes clusters in three large cohorts using variables readily measured in the clinic.

Methods: In three independent cohorts, in total 15,940 individuals were clustered based on age, BMI, HbA, random or fasting C-peptide, and HDL-cholesterol. Clusters were cross-validated against the original clusters based on HOMA measures. In addition, between cohorts, clusters were cross-validated by re-assigning people based on each cohort's cluster centres. Finally, we compared the time to insulin requirement for each cluster.

Results: Five distinct type 2 diabetes clusters were identified and mapped back to the original four All New Diabetics in Scania (ANDIS) clusters. Using C-peptide and HDL-cholesterol instead of HOMA2-B and HOMA2-IR, three of the clusters mapped with high sensitivity (80.6-90.7%) to the previously identified severe insulin-deficient diabetes (SIDD), severe insulin-resistant diabetes (SIRD) and mild obesity-related diabetes (MOD) clusters. The previously described ANDIS mild age-related diabetes (MARD) cluster could be mapped to the two milder groups in our study: one characterised by high HDL-cholesterol (mild diabetes with high HDL-cholesterol [MDH] cluster), and the other not having any extreme characteristic (mild diabetes [MD]). When these two milder groups were combined, they mapped well to the previously labelled MARD cluster (sensitivity 79.1%). In the cross-validation between cohorts, particularly the SIDD and MDH clusters cross-validated well, with sensitivities ranging from 73.3% to 97.1%. SIRD and MD showed a lower sensitivity, ranging from 36.1% to 92.3%, where individuals shifted from SIRD to MD and vice versa. People belonging to the SIDD cluster showed the fastest progression towards insulin requirement, while the MDH cluster showed the slowest progression.

Conclusions/interpretation: Clusters based on C-peptide instead of HOMA2 measures resemble those based on HOMA2 measures, especially for SIDD, SIRD and MOD. By adding HDL-cholesterol, the MARD cluster based upon HOMA2 measures resulted in the current clustering into two clusters, with one cluster having high HDL levels. Cross-validation between cohorts showed generally a good resemblance between cohorts. Together, our results show that the clustering based on clinical variables readily measured in the clinic (age, HbA, HDL-cholesterol, BMI and C-peptide) results in informative clusters that are representative of the original ANDIS clusters and stable across cohorts. Adding HDL-cholesterol to the clustering resulted in the identification of a cluster with very slow glycaemic deterioration.
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http://dx.doi.org/10.1007/s00125-021-05490-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8382625PMC
September 2021

Fgf15 Neurons of the Dorsomedial Hypothalamus Control Glucagon Secretion and Hepatic Gluconeogenesis.

Diabetes 2021 07 21;70(7):1443-1457. Epub 2021 Apr 21.

Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland

The counterregulatory response to hypoglycemia is an essential survival function. It is controlled by an integrated network of glucose-responsive neurons, which trigger endogenous glucose production to restore normoglycemia. The complexity of this glucoregulatory network is, however, only partly characterized. In a genetic screen of a panel of recombinant inbred mice we previously identified expressed in neurons of the dorsomedial hypothalamus (DMH), as a negative regulator of glucagon secretion. Here, we report on the generation of mice and their use to further characterize these neurons. We show that they were glutamatergic and comprised glucose-inhibited and glucose-excited neurons. When activated by chemogenetics, Fgf15 neurons prevented the increase in vagal nerve firing and the secretion of glucagon normally triggered by insulin-induced hypoglycemia. On the other hand, they increased the activity of the sympathetic nerve in the basal state and prevented its silencing by glucose overload. Higher sympathetic tone increased hepatic Creb1 phosphorylation, mRNA expression, and hepatic glucose production leading to glucose intolerance. Thus, Fgf15 neurons of the DMH participate in the counterregulatory response to hypoglycemia by a direct adrenergic stimulation of hepatic glucose production while suppressing vagally induced glucagon secretion. This study provides new insights into the complex neuronal network that prevents the development of hypoglycemia.
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http://dx.doi.org/10.2337/db20-1121DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8336003PMC
July 2021

Cold-induced dishabituation in rodents exposed to recurrent hypoglycaemia.

Diabetologia 2021 06 17;64(6):1436-1441. Epub 2021 Mar 17.

Division of Systems Medicine, School of Medicine, University of Dundee, Dundee, UK.

Aims/hypothesis: Recurrent hypoglycaemia in people with diabetes leads to progressive suppression of counterregulatory hormonal responses to subsequent hypoglycaemia. Recently it has been proposed that the mechanism underpinning this is a form of adaptive memory referred to as habituation. To test this hypothesis, we use two different durations of cold exposure to examine whether rodents exposed to recurrent hypoglycaemia exhibit two characteristic features of habituation, namely stimulus generalisation and dishabituation.

Methods: In the first study (stimulus generalisation study), hyperinsulinaemic-hypoglycaemic (2.8 mmol/l) glucose clamps were performed in non-diabetic rodents exposed to prior moderate-duration cold (4°C for 3 h) or control conditions. In the second study (dishabituation study), rodents exposed to prior recurrent hypoglycaemia or saline (154 mmol/l NaCl) injections over 4 weeks underwent a longer-duration cold (4°C for 4.5 h) exposure followed 24 h later by a hyperinsulinaemic-hypoglycaemic (2.8 mmol/l) glucose clamp. Output measures were counterregulatory hormone responses during experimental hypoglycaemia.

Results: Moderate-duration cold exposure blunted the adrenaline (epinephrine) response (15,266 ± 1920 vs 7981 ± 1258 pmol/l, Control vs Cold; p < 0.05) to next day hypoglycaemia in healthy non-diabetic rodents. In contrast, the suppressed adrenaline response (Control 5912 ± 1417 vs recurrent hypoglycaemia 1836 ± 736 pmol/l; p < 0.05) that is associated with recurrent hypoglycaemia was restored following longer-duration cold exposure (recurrent hypoglycaemia + Cold 4756 ± 826 pmol/l; not significant vs Control).

Conclusions/interpretation: Non-diabetic rodents exhibit two cardinal features of habituation, namely stimulus generalisation and dishabituation. These findings provide further support for the hypothesis that suppressed counterregulatory responses following exposure to recurrent hypoglycaemia in diabetes result from habituation.
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http://dx.doi.org/10.1007/s00125-021-05425-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8099849PMC
June 2021

Persistent or Transient Human β Cell Dysfunction Induced by Metabolic Stress: Specific Signatures and Shared Gene Expression with Type 2 Diabetes.

Cell Rep 2020 12;33(9):108466

Janssen RDUS, Philadelphia, PA, USA.

Pancreatic β cell failure is key to type 2 diabetes (T2D) onset and progression. Here, we assess whether human β cell dysfunction induced by metabolic stress is reversible, evaluate the molecular pathways underlying persistent or transient damage, and explore the relationships with T2D islet traits. Twenty-six islet preparations are exposed to several lipotoxic/glucotoxic conditions, some of which impair insulin release, depending on stressor type, concentration, and combination. The reversal of dysfunction occurs after washout for some, although not all, of the lipoglucotoxic insults. Islet transcriptomes assessed by RNA sequencing and expression quantitative trait loci (eQTL) analysis identify specific pathways underlying β cell failure and recovery. Comparison of a large number of human T2D islet transcriptomes with those of persistent or reversible β cell lipoglucotoxicity show shared gene expression signatures. The identification of mechanisms associated with human β cell dysfunction and recovery and their overlap with T2D islet traits provide insights into T2D pathogenesis, fostering the development of improved β cell-targeted therapeutic strategies.
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http://dx.doi.org/10.1016/j.celrep.2020.108466DOI Listing
December 2020

EphrinB1 modulates glutamatergic inputs into POMC-expressing progenitors and controls glucose homeostasis.

PLoS Biol 2020 11 30;18(11):e3000680. Epub 2020 Nov 30.

Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

Proopiomelanocortin (POMC) neurons are major regulators of energy balance and glucose homeostasis. In addition to being regulated by hormones and nutrients, POMC neurons are controlled by glutamatergic input originating from multiple brain regions. However, the factors involved in the formation of glutamatergic inputs and how they contribute to bodily functions remain largely unknown. Here, we show that during the development of glutamatergic inputs, POMC neurons exhibit enriched expression of the Efnb1 (EphrinB1) and Efnb2 (EphrinB2) genes, which are known to control excitatory synapse formation. In vivo loss of Efnb1 in POMC-expressing progenitors decreases the amount of glutamatergic inputs, associated with a reduced number of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor subunits and excitability of these cells. We found that mice lacking Efnb1 in POMC-expressing progenitors display impaired glucose tolerance due to blunted vagus nerve activity and decreased insulin secretion. However, despite reduced excitatory inputs, mice lacking Efnb2 in POMC-expressing progenitors showed no deregulation of insulin secretion and only mild alterations in feeding behavior and gluconeogenesis. Collectively, our data demonstrate the role of ephrins in controlling excitatory input amount into POMC-expressing progenitors and show an isotype-specific role of ephrins on the regulation of glucose homeostasis and feeding.
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http://dx.doi.org/10.1371/journal.pbio.3000680DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7728393PMC
November 2020

Hypoglycemia-Sensing Neurons of the Ventromedial Hypothalamus Require AMPK-Induced Txn2 Expression but Are Dispensable for Physiological Counterregulation.

Diabetes 2020 11 24;69(11):2253-2266. Epub 2020 Aug 24.

Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland

The ventromedial nucleus of the hypothalamus (VMN) is involved in the counterregulatory response to hypoglycemia. VMN neurons activated by hypoglycemia (glucose-inhibited [GI] neurons) have been assumed to play a critical although untested role in this response. Here, we show that expression of a dominant negative form of AMPK or inactivation of AMPK and subunit genes in Sf1 neurons of the VMN selectively suppressed GI neuron activity. We found that , encoding a mitochondrial redox enzyme, was strongly downregulated in the absence of AMPK activity and that reexpression of in Sf1 neurons restored GI neuron activity. In cell lines, was required to limit glucopenia-induced reactive oxygen species production. In physiological studies, absence of GI neuron activity after AMPK suppression in the VMN had no impact on the counterregulatory hormone response to hypoglycemia or on feeding. Thus, AMPK is required for GI neuron activity by controlling the expression of the antioxidant enzyme Txn2. However, the glucose-sensing capacity of VMN GI neurons is not required for the normal counterregulatory response to hypoglycemia. Instead, it may represent a fail-safe system in case of impaired hypoglycemia sensing by peripherally located glucose detection systems that are connected to the VMN.
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http://dx.doi.org/10.2337/db20-0577DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7576557PMC
November 2020

The Constitutive Lack of α7 Nicotinic Receptor Leads to Metabolic Disorders in Mouse.

Biomolecules 2020 07 16;10(7). Epub 2020 Jul 16.

Biology and Pathology of the Endocrine Pancreas, Université de Paris, BFA, UMR 8251, CNRS, F-75013 Paris, France.

Objective: Type 2 diabetes (T2D) occurs by deterioration in pancreatic β-cell function and/or progressive loss of pancreatic β-cell mass under the context of insulin resistance. α7 nicotinic acetylcholine receptor (nAChR) may contribute to insulin sensitivity but its role in the pathogenesis of T2D remains undefined. We investigated whether the systemic lack of α7 nAChR was sufficient to impair glucose homeostasis.

Methods: We used an α7 nAChR knock-out (α7) mouse model fed a standard chow diet. The effects of the lack of α7 nAChR on islet mass, insulin secretion, glucose and insulin tolerance, body composition, and food behaviour were assessed in vivo and ex vivo experiments.

Results: Young α7 mice display a chronic mild high glycemia combined with an impaired glucose tolerance and a marked deficit in β-cell mass. In addition to these metabolic disorders, old mice developed adipose tissue inflammation, elevated plasma free fatty acid concentrations and presented glycolytic muscle insulin resistance in old mice. Finally, α7 mice, fed a chow diet, exhibited a late-onset excessive gain in body weight through increased fat mass associated with higher food intake.

Conclusion: Our work highlights the important role of α7 nAChR in glucose homeostasis. The constitutive lack of α7 nAChR suggests a novel pathway influencing the pathogenesis of T2D.
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http://dx.doi.org/10.3390/biom10071057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7408520PMC
July 2020

Hypothalamic CDK4 regulates thermogenesis by modulating sympathetic innervation of adipose tissues.

EMBO Rep 2020 09 12;21(9):e49807. Epub 2020 Jul 12.

Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

This study investigated the role of CDK4 in the oxidative metabolism of brown adipose tissue (BAT). BAT from Cdk4 mice exhibited fewer lipids and increased mitochondrial volume and expression of canonical thermogenic genes, rendering these mice more resistant to cold exposure. Interestingly, these effects were not BAT cell-autonomous but rather driven by increased sympathetic innervation. In particular, the ventromedial hypothalamus (VMH) is known to modulate BAT activation via the sympathetic nervous system. We thus examined the effects of VMH neuron-specific Cdk4 deletion. These mice display increased sympathetic innervation and enhanced cold tolerance, similar to Cdk4 mice, in addition to browning of scWAT. Overall, we provide evidence showing that CDK4 modulates thermogenesis by regulating sympathetic innervation of adipose tissue depots through hypothalamic nuclei, including the VMH. This demonstrates that CDK4 not only negatively regulates oxidative pathways, but also modulates the central regulation of metabolism through its action in the brain.
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http://dx.doi.org/10.15252/embr.201949807DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7507572PMC
September 2020

A genetic screen identifies Crat as a regulator of pancreatic beta-cell insulin secretion.

Mol Metab 2020 07 13;37:100993. Epub 2020 Apr 13.

Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland. Electronic address:

Objectives: Glucose-stimulated insulin secretion is a critical function in the regulation of glucose homeostasis, and its deregulation is associated with the development of type 2 diabetes. Here, we performed a genetic screen using islets isolated from the BXD panel of advanced recombinant inbred (RI) lines of mice to search for novel regulators of insulin production and secretion.

Methods: Pancreatic islets were isolated from 36 RI BXD lines and insulin secretion was measured following exposure to 2.8 or 16.7 mM glucose with or without exendin-4. Islets from the same RI lines were used for RNA extraction and transcript profiling. Quantitative trait loci (QTL) mapping was performed for each secretion condition and combined with transcriptome data to prioritize candidate regulatory genes within the identified QTL regions. Functional studies were performed by mRNA silencing or overexpression in MIN6B1 cells and by studying mice and islets with beta-cell-specific gene inactivation.

Results: Insulin secretion under the 16.7 mM glucose plus exendin-4 condition was mapped significantly to a chromosome 2 QTL. Within this QTL, RNA-Seq data prioritized Crat (carnitine O-acetyl transferase) as a strong candidate regulator of the insulin secretion trait. Silencing Crat expression in MIN6B1 cells reduced insulin content and insulin secretion by ∼30%. Conversely, Crat overexpression enhanced insulin content and secretion by ∼30%. When islets from mice with beta-cell-specific Crat inactivation were exposed to high glucose, they displayed a 30% reduction of insulin content as compared to control islets. We further showed that decreased Crat expression in both MIN6B1 cells and pancreatic islets reduced the oxygen consumption rate in a glucose concentration-dependent manner.

Conclusions: We identified Crat as a regulator of insulin secretion whose action is mediated by an effect on total cellular insulin content; this effect also depends on the genetic background of the RI mouse lines. These data also show that in the presence of the stimulatory conditions used the insulin secretion rate is directly related to the insulin content.
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http://dx.doi.org/10.1016/j.molmet.2020.100993DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225740PMC
July 2020

Klf6 protects β-cells against insulin resistance-induced dedifferentiation.

Mol Metab 2020 05 6;35:100958. Epub 2020 Feb 6.

Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland. Electronic address:

Objectives: In the pathogenesis of type 2 diabetes, development of insulin resistance triggers an increase in pancreatic β-cell insulin secretion capacity and β-cell number. Failure of this compensatory mechanism is caused by a dedifferentiation of β-cells, which leads to insufficient insulin secretion and diabetic hyperglycemia. The β-cell factors that normally protect against dedifferentiation remain poorly defined. Here, through a systems biology approach, we identify the transcription factor Klf6 as a regulator of β-cell adaptation to metabolic stress.

Methods: We used a β-cell specific Klf6 knockout mouse model to investigate whether Klf6 may be a potential regulator of β-cell adaptation to a metabolic stress.

Results: We show that inactivation of Klf6 in β-cells blunts their proliferation induced by the insulin resistance of pregnancy, high-fat high-sucrose feeding, and insulin receptor antagonism. Transcriptomic analysis showed that Klf6 controls the expression of β-cell proliferation genes and, in the presence of insulin resistance, it prevents the down-expression of genes controlling mature β-cell identity and the induction of disallowed genes that impair insulin secretion. Its expression also limits the transdifferentiation of β-cells into α-cells.

Conclusion: Our study identifies a new transcription factor that protects β-cells against dedifferentiation, and which may be targeted to prevent diabetes development.
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http://dx.doi.org/10.1016/j.molmet.2020.02.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7093812PMC
May 2020

GLP-1 receptor agonists synergize with DYRK1A inhibitors to potentiate functional human β cell regeneration.

Sci Transl Med 2020 02;12(530)

Diabetes, Obesity and Metabolism Institute and Department of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.

Glucagon-like peptide-1 receptor (GLP1R) agonists and dipeptidyl peptidase 4 inhibitors are widely prescribed diabetes drugs due to their ability to stimulate insulin secretion from remaining β cells and to reduce caloric intake. Unfortunately, they fail to increase human β cell proliferation. Small-molecule inhibitors of dual-specificity tyrosine-regulated kinase 1A (DYRK1A) are able to induce adult human β cell proliferation, but rates are modest (~2%), and their specificity to β cells is limited. Here, we provide evidence that combining any member of the GLP1R agonist class with any member of the DYRK1A inhibitor class induces a synergistic increase in human β cell replication (5 to 6%) accompanied by an actual increase in numbers of human β cells. GLP1R agonist-DYRK1A inhibitor synergy required combined inhibition of DYRK1A and an increase in cAMP and did not lead to β cell dedifferentiation. These beneficial effects on proliferation were seen in both normal human β cells and β cells derived from individuals with type 2 diabetes. The ability of the GLP1R agonist-DYRK1A inhibitor combination to enhance human β cell proliferation, human insulin secretion, and blood glucose control extended in vivo to studies of human islets transplanted into euglycemic and streptozotocin-diabetic immunodeficient mice. No adverse events were observed in the mouse studies during a 1-week period. Because of the relative β cell specificity of GLP1R agonists, the combination provides an improved, although not complete, degree of human β cell specificity.
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http://dx.doi.org/10.1126/scitranslmed.aaw9996DOI Listing
February 2020

Use of preclinical models to identify markers of type 2 diabetes susceptibility and novel regulators of insulin secretion - A step towards precision medicine.

Mol Metab 2019 09;27S:S147-S154

Unité de Biologie Fonctionnelle et Adaptative, Sorbonne Paris Cité, CNRS UMR8251, Université Paris Diderot, Paris, France.

Background: Progression from pre-diabetes to type 2 diabetes (T2D) and from T2D to insulin requirement proceeds at very heterogenous rates among patient populations, and the risk of developing different types of secondary complications is also different between patients. The diagnosis of pre-diabetes and T2D solely based on blood glucose measurements cannot capture this heterogeneity, thereby preventing proposition of therapeutic strategies adapted to individual needs and pathogenetic mechanisms. There is, thus, a need to identify novel means to stratify patient populations based on a molecular knowledge of the diverse underlying causes of the disease. Such knowledge would form the basis for a precision medicine approach to preventing and treating T2D according to the need of identified patient subgroups as well as allowing better follow up of pharmacological treatment.

Scope Of Review: Here, we review a systems biology approach that aims at identifying novel biomarkers for T2D susceptibility and identifying novel beta-cell and insulin target tissue genes that link the selected plasma biomarkers with insulin secretion and insulin action. This work was performed as part of two Innovative Medicine Initiative projects. The focus of the review will be on the use of preclinical models to find biomarker candidates for T2D prediction and novel regulators of beta-cell function. We will demonstrate that the study of mice with different genetic architecture and widely different adaptation to metabolic stress can be a powerful approach to identify biomarkers of T2D susceptibility in humans or for the identification of so far unrecognized genes controlling beta-cell function.

Major Conclusions: The examples developed in this review will highlight the power of the systems biology approach, in particular as it allowed the discovery of dihydroceramide as a T2D biomarker candidate in mice and humans and the identification and characterization of novel regulators of beta-cell function.
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http://dx.doi.org/10.1016/j.molmet.2019.06.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6768503PMC
September 2019

Laser capture microdissection of human pancreatic islets reveals novel eQTLs associated with type 2 diabetes.

Mol Metab 2019 06 18;24:98-107. Epub 2019 Mar 18.

Imperial College London, Department of Genomics of Common Disease, London, UK; University of Lille, CNRS, Institute Pasteur de Lille, UMR 8199 - EGID, F-59000, Lille, France. Electronic address:

Objective: Genome wide association studies (GWAS) for type 2 diabetes (T2D) have identified genetic loci that often localise in non-coding regions of the genome, suggesting gene regulation effects. We combined genetic and transcriptomic analysis from human islets obtained from brain-dead organ donors or surgical patients to detect expression quantitative trait loci (eQTLs) and shed light into the regulatory mechanisms of these genes.

Methods: Pancreatic islets were isolated either by laser capture microdissection (LCM) from surgical specimens of 103 metabolically phenotyped pancreatectomized patients (PPP) or by collagenase digestion of pancreas from 100 brain-dead organ donors (OD). Genotyping (> 8.7 million single nucleotide polymorphisms) and expression (> 47,000 transcripts and splice variants) analyses were combined to generate cis-eQTLs.

Results: After applying genome-wide false discovery rate significance thresholds, we identified 1,173 and 1,021 eQTLs in samples of OD and PPP, respectively. Among the strongest eQTLs shared between OD and PPP were CHURC1 (OD p-value=1.71 × 10; PPP p-value = 3.64 × 10) and PSPH (OD p-value = 3.92 × 10; PPP p-value = 3.64 × 10). We identified eQTLs in linkage-disequilibrium with GWAS loci T2D and associated traits, including TTLL6, MLX and KIF9 loci, which do not implicate the nearest gene. We found in the PPP datasets 11 eQTL genes, which were differentially expressed in T2D and two genes (CYP4V2 and TSEN2) associated with HbA1c but none in the OD samples.

Conclusions: eQTL analysis of LCM islets from PPP led us to identify novel genes which had not been previously linked to islet biology and T2D. The understanding gained from eQTL approaches, especially using surgical samples of living patients, provides a more accurate 3-dimensional representation than those from genetic studies alone.
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http://dx.doi.org/10.1016/j.molmet.2019.03.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6531807PMC
June 2019

Targeting the Brain to Cure Type 2 Diabetes.

Authors:
Bernard Thorens

Diabetes 2019 03;68(3):476-478

Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland

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http://dx.doi.org/10.2337/dbi18-0051DOI Listing
March 2019

Profound Perturbation of the Metabolome in Obesity Is Associated with Health Risk.

Cell Metab 2019 02 11;29(2):488-500.e2. Epub 2018 Oct 11.

The Scripps Research Institute, La Jolla, CA 92037, USA. Electronic address:

Obesity is a heterogeneous phenotype that is crudely measured by body mass index (BMI). There is a need for a more precise yet portable method of phenotyping and categorizing risk in large numbers of people with obesity to advance clinical care and drug development. Here, we used non-targeted metabolomics and whole-genome sequencing to identify metabolic and genetic signatures of obesity. We find that obesity results in profound perturbation of the metabolome; nearly a third of the assayed metabolites associated with changes in BMI. A metabolome signature identifies the healthy obese and lean individuals with abnormal metabolomes-these groups differ in health outcomes and underlying genetic risk. Specifically, an abnormal metabolome associated with a 2- to 5-fold increase in cardiovascular events when comparing individuals who were matched for BMI but had opposing metabolome signatures. Because metabolome profiling identifies clinically meaningful heterogeneity in obesity, this approach could help select patients for clinical trials.
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http://dx.doi.org/10.1016/j.cmet.2018.09.022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6370944PMC
February 2019

SLC2A9 (GLUT9) mediates urate reabsorption in the mouse kidney.

Pflugers Arch 2018 12 13;470(12):1739-1751. Epub 2018 Aug 13.

Department of Pharmacology and Toxicology, University of Lausanne, 27 rue du Bugnon, 1011, Lausanne, Switzerland.

Uric acid (UA) is a metabolite of purine degradation and is involved in gout flairs and kidney stones formation. GLUT9 (SLC2A9) was previously shown to be a urate transporter in vitro. In vivo, humans carrying GLUT9 loss-of-function mutations have familial renal hypouricemia type 2, a condition characterized by hypouricemia, UA renal wasting associated with kidney stones, and an increased propensity to acute renal failure during strenuous exercise. Mice carrying a deletion of GLUT9 in the whole body are hyperuricemic and display a severe nephropathy due to intratubular uric acid precipitation. However, the precise role of GLUT9 in the kidney remains poorly characterized. We developed a mouse model in which GLUT9 was deleted specifically along the whole nephron in a tetracycline-inducible manner (subsequently called kidney-inducible KO or kiKO). The urate/creatinine ratio was increased as early as 4 days after induction of the KO and no GLUT9 protein was visible on kidney extracts. kiKO mice are morphologically identical to their wild-type littermates and had no spontaneous kidney stones. Twenty-four-hour urine collection revealed a major increase of urate urinary excretion rate and of the fractional excretion of urate, with no difference in urate concentration in the plasma. Polyuria was observed, but kiKO mice were still able to concentrate urine after water restriction. KiKO mice displayed lower blood pressure accompanied by an increased heart rate. Overall, these results indicate that GLUT9 is a crucial player in renal handling of urate in vivo and a putative target for uricosuric drugs.
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http://dx.doi.org/10.1007/s00424-018-2190-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6224025PMC
December 2018

Protective role of the ELOVL2/docosahexaenoic acid axis in glucolipotoxicity-induced apoptosis in rodent beta cells and human islets.

Diabetologia 2018 08 12;61(8):1780-1793. Epub 2018 May 12.

Unité Biologie Fonctionnelle et Adaptative, CNRS UMR 8251, Équipe Régulation de la glycémie par le système nerveux central, Université Paris Diderot, 4 rue Marie-Andrée-Lagroua-Weill-Hallé, 75205, Paris CEDEX 13, France.

Aims/hypothesis: Dietary n-3 polyunsaturated fatty acids, especially docosahexaenoic acid (DHA), are known to influence glucose homeostasis. We recently showed that Elovl2 expression in beta cells, which regulates synthesis of endogenous DHA, was associated with glucose tolerance and played a key role in insulin secretion. The present study aimed to examine the role of the very long chain fatty acid elongase 2 (ELOVL2)/DHA axis on the adverse effects of palmitate with high glucose, a condition defined as glucolipotoxicity, on beta cells.

Methods: We detected ELOVL2 in INS-1 beta cells and mouse and human islets using quantitative PCR and western blotting. Downregulation and adenoviral overexpression of Elovl2 was carried out in beta cells. Ceramide and diacylglycerol levels were determined by radio-enzymatic assay and lipidomics. Apoptosis was quantified using caspase-3 assays and poly (ADP-ribose) polymerase cleavage. Palmitate oxidation and esterification were determined by [U-C]palmitate labelling.

Results: We found that glucolipotoxicity decreased ELOVL2 content in rodent and human beta cells. Downregulation of ELOVL2 drastically potentiated beta cell apoptosis induced by glucolipotoxicity, whereas adenoviral Elovl2 overexpression and supplementation with DHA partially inhibited glucolipotoxicity-induced cell death in rodent and human beta cells. Inhibition of beta cell apoptosis by the ELOVL2/DHA axis was associated with a decrease in ceramide accumulation. However, the ELOVL2/DHA axis was unable to directly alter ceramide synthesis or metabolism. By contrast, DHA increased palmitate oxidation but did not affect its esterification. Pharmacological inhibition of AMP-activated protein kinase and etomoxir, an inhibitor of carnitine palmitoyltransferase 1 (CPT1), the rate-limiting enzyme in fatty acid β-oxidation, attenuated the protective effect of the ELOVL2/DHA axis during glucolipotoxicity. Downregulation of CPT1 also counteracted the anti-apoptotic action of the ELOVL2/DHA axis. By contrast, a mutated active form of Cpt1 inhibited glucolipotoxicity-induced beta cell apoptosis when ELOVL2 was downregulated.

Conclusions/interpretation: Our results identify ELOVL2 as a critical pro-survival enzyme for preventing beta cell death and dysfunction induced by glucolipotoxicity, notably by favouring palmitate oxidation in mitochondria through a CPT1-dependent mechanism.
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http://dx.doi.org/10.1007/s00125-018-4629-8DOI Listing
August 2018

Glucose transporter 2 mediates the hypoglycemia-induced increase in cerebral blood flow.

J Cereb Blood Flow Metab 2019 09 21;39(9):1725-1736. Epub 2018 Mar 21.

3 Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.

Glucose transporter 2 ()-positive cells are sparsely distributed in brain and play an important role in the stimulation of glucagon secretion in response to hypoglycemia. We aimed to determine if -positive cells can influence another response to hypoglycemia, i.e. increased cerebral blood flow (CBF). CBF of adult male mice devoid of , either globally () or in the nervous system only (NG2KO), and their respective controls were studied under basal glycemia and insulin-induced hypoglycemia using quantitative perfusion magnetic resonance imaging at 9.4 T. The effect on CBF of optogenetic activation of hypoglycemia responsive -positive neurons of the paraventricular thalamic area was measured in mice expressing channelrhodopsin2 under the control of the promoter. We found that in both mice and NG2KO mice, CBF in basal conditions was higher than in their respective controls and not further activated by hypoglycemia, as measured in the hippocampus, hypothalamus and whole brain. Conversely, optogenetic activation of -positive cells in the paraventricular thalamic nucleus induced a local increase in CBF similar to that induced by hypoglycemia. Thus, expression in the nervous system is required for the control of CBF in response to changes in blood glucose concentrations.
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http://dx.doi.org/10.1177/0271678X18766743DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6727137PMC
September 2019

α-cell glucokinase suppresses glucose-regulated glucagon secretion.

Nat Commun 2018 02 7;9(1):546. Epub 2018 Feb 7.

Center for Integrative Genomics, University of Lausanne, 1015, Lausanne, Switzerland.

Glucagon secretion by pancreatic α-cells is triggered by hypoglycemia and suppressed by high glucose levels; impaired suppression of glucagon secretion is a hallmark of both type 1 and type 2 diabetes. Here, we show that α-cell glucokinase (Gck) plays a role in the control of glucagon secretion. Using mice with α-cell-specific inactivation of Gck (αGckKO mice), we find that glucokinase is required for the glucose-dependent increase in intracellular ATP/ADP ratio and the closure of K channels in α-cells and the suppression of glucagon secretion at euglycemic and hyperglycemic levels. αGckKO mice display hyperglucagonemia in the fed state, which is associated with increased hepatic gluconeogenic gene expression and hepatic glucose output capacity. In adult mice, fed hyperglucagonemia is further increased and glucose intolerance develops. Thus, glucokinase governs an α-cell metabolic pathway that suppresses secretion at or above normoglycemic levels; abnormal suppression of glucagon secretion deregulates hepatic glucose metabolism and, over time, induces a pre-diabetic phenotype.
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http://dx.doi.org/10.1038/s41467-018-03034-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5803227PMC
February 2018

GLUT2-Expressing Neurons as Glucose Sensors in the Brain: Electrophysiological Analysis.

Methods Mol Biol 2018 ;1713:255-267

Department of Medicine, University of Fribourg, Fribourg, 1700, Switzerland.

Brain glucose sensing plays an essential role in the regulation of energy homeostasis. Recent publications report that neurons expressing glucose transporter GLUT2 act as glucose sensors in different regions of the brain and contribute to the control of glucose homeostasis and feeding behavior. In this chapter we describe the methods used to explore glucose sensing in genetically tagged GLUT2-expressing neurons with slice electrophysiology.
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http://dx.doi.org/10.1007/978-1-4939-7507-5_19DOI Listing
July 2018

Systems biology of the IMIDIA biobank from organ donors and pancreatectomised patients defines a novel transcriptomic signature of islets from individuals with type 2 diabetes.

Diabetologia 2018 03 28;61(3):641-657. Epub 2017 Nov 28.

F. Hoffmann-La Roche Ltd, Roche Innovation Center Basel, Basel, Switzerland.

Aims/hypothesis: Pancreatic islet beta cell failure causes type 2 diabetes in humans. To identify transcriptomic changes in type 2 diabetic islets, the Innovative Medicines Initiative for Diabetes: Improving beta-cell function and identification of diagnostic biomarkers for treatment monitoring in Diabetes (IMIDIA) consortium ( www.imidia.org ) established a comprehensive, unique multicentre biobank of human islets and pancreas tissues from organ donors and metabolically phenotyped pancreatectomised patients (PPP).

Methods: Affymetrix microarrays were used to assess the islet transcriptome of islets isolated either by enzymatic digestion from 103 organ donors (OD), including 84 non-diabetic and 19 type 2 diabetic individuals, or by laser capture microdissection (LCM) from surgical specimens of 103 PPP, including 32 non-diabetic, 36 with type 2 diabetes, 15 with impaired glucose tolerance (IGT) and 20 with recent-onset diabetes (<1 year), conceivably secondary to the pancreatic disorder leading to surgery (type 3c diabetes). Bioinformatics tools were used to (1) compare the islet transcriptome of type 2 diabetic vs non-diabetic OD and PPP as well as vs IGT and type 3c diabetes within the PPP group; and (2) identify transcription factors driving gene co-expression modules correlated with insulin secretion ex vivo and glucose tolerance in vivo. Selected genes of interest were validated for their expression and function in beta cells.

Results: Comparative transcriptomic analysis identified 19 genes differentially expressed (false discovery rate ≤0.05, fold change ≥1.5) in type 2 diabetic vs non-diabetic islets from OD and PPP. Nine out of these 19 dysregulated genes were not previously reported to be dysregulated in type 2 diabetic islets. Signature genes included TMEM37, which inhibited Ca-influx and insulin secretion in beta cells, and ARG2 and PPP1R1A, which promoted insulin secretion. Systems biology approaches identified HNF1A, PDX1 and REST as drivers of gene co-expression modules correlated with impaired insulin secretion or glucose tolerance, and 14 out of 19 differentially expressed type 2 diabetic islet signature genes were enriched in these modules. None of these signature genes was significantly dysregulated in islets of PPP with impaired glucose tolerance or type 3c diabetes.

Conclusions/interpretation: These studies enabled the stringent definition of a novel transcriptomic signature of type 2 diabetic islets, regardless of islet source and isolation procedure. Lack of this signature in islets from PPP with IGT or type 3c diabetes indicates differences possibly due to peculiarities of these hyperglycaemic conditions and/or a role for duration and severity of hyperglycaemia. Alternatively, these transcriptomic changes capture, but may not precede, beta cell failure.
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http://dx.doi.org/10.1007/s00125-017-4500-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5803296PMC
March 2018

Alain Ktorza, PhD.

Diabetes Obes Metab 2017 09;19 Suppl 1

Department of Medicine, Endocrinology & Metabolism Service, Hadassah Medical Centre, Hebrew University of Jerusalem, Jerusalem, Israel.

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http://dx.doi.org/10.1111/dom.13036DOI Listing
September 2017
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